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(11) | EP 2 275 661 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
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| (54) | INTERNAL COMBUSTION ENGINE FUEL INJECTION PRESSURE CONTROLLER |
| (57) In a common-rail diesel engine, a fuel pressure setting map is prepared, which allocates
a region of equal fuel injection pressure to an equal output region of the engine
output determined from engine revolution and engine torque. Thus, it becomes possible
to let changes of the heat generation rate approach an ideal state across the entire
engine operation region. Moreover, a systematic procedure for controlling the fuel
pressure can be implemented that is common to a number of engine types, so that it
becomes possible to simplify the preparation of the fuel pressure setting map for
setting the suitable fuel injection pressure in accordance with the operation state
of the engine. |
[Technical Field]
[0001] The present invention relates to a fuel injection pressure control apparatus for an internal combustion engine typified by a diesel engine. In particular, the present invention relates to strategies for optimizing the combustion state of air-fuel mixtures.
[Background Art]
[0002] As is conventionally known, in a diesel engine used as an automobile engine or the like, fuel injection control is performed that adjusts periods and amounts of fuel injection from a fuel injection valve (also referred to below as "injector") according to engine revolution, amount of accelerator operation, coolant temperature, intake air temperature, and the like (e.g., see Patent Literature 1 listed below).
[0003] Diesel engine combustion is achieved by premixed combustion and diffusion combustion. When fuel injection from a fuel injection valve begins, first a combustible mixture is produced by the vaporization and diffusion of fuel (ignition delay period). Next, this combustible mixture self-ignites at about the same time at numerous places in a combustion chamber, and combustion rapidly progresses (premixed combustion). Further, fuel is injected into the combustion chamber, so that combustion is continuously performed (diffusion combustion). Thereafter, unburned fuel is present even after fuel injection has ended, so heat continues to be produced for some period of time (afterburning period).
[0004] In diesel engines, as the vaporization of fuel in the cylinder grows more intense, flame propagation speed after ignition rises. When this flame propagation speed becomes high, the amount of fuel that burns at once becomes too great, pressure inside the cylinder drastically increases, thus generating vibration or noise. This phenomenon is called diesel knocking, and often occurs particularly when operating at a low load. Also, in this sort of situation, a drastic elevation in combustion temperature is accompanied by an increase in the amount of nitrogen oxide (referred to below as "NOx") produced, and thus exhaust emissions become worse.
[0005] In order to overcome these problems, the fuel pressure (may also be referred to as "fuel injection pressure" below) is adjusted as disclosed in the Patent Literatures 2 to 4 listed below. Ordinarily, the fuel pressure is set high in order to increase the combustion speed within the cylinder, or conversely, the fuel pressure is set low in order to control the generation of vibration or noise.
[Citation List]
[Patent Literature]
[Summary of Invention]
[Technical Problem]
[0007] However, in today's diesel engines, as a procedure for setting the fuel pressure in accordance with the operation state, the fuel pressure is adapted to each of the engine operation states of engine revolution and engine torque (corresponding to the engine load). That is to say, an adapted value of the fuel pressure is determined experimentally by trial and error for each engine operation state, and the adapted values of the fuel pressure corresponding to a large number of individual engine operation states are turned into a map, thus preparing a fuel pressure setting map. Then, by following this fuel pressure setting map, a target fuel pressure is set that is appropriate for the current engine operation state, and for example a high pressure fuel pump is controlled accordingly.
[0008] The following is an explanation of an example of a procedure for preparing a fuel pressure setting map that has been used up to now. In this procedure for preparing a fuel pressure setting map, first, a fuel pressure setting map as shown in Fig. 9(a) is prepared, and this fuel pressure setting map is changed as shown in Fig. 9(b) and Fig. 9(c) in that order, by determining experimentally by trial and error adapted values for the fuel pressure.
[0009] First, Fig. 9(a) is a fuel pressure setting map in which the fuel pressure gradually becomes higher, over the entire operation region, as the engine revolution increases. In this fuel pressure setting map, the lines of equal fuel pressure (the straight lines indicated as broken lines in the figure) are parallel to the vertical axis (engine torque axis) in the figure, so that they coincide with the lines of equal revolution. With this fuel pressure setting map, a favorable drivability is realized and even in a region of low revolution, the fuel pressure is quickly increased in accordance with an increase in engine revolution, so that delays in increasing the fuel pressure can be prevented.
[0010] However, with the fuel pressure setting map shown in Fig. 9(a), problems with regard to the quietness of the engine remain. Accordingly, a low fuel pressure region in a low torque region is enlarged towards the high revolution side compared to the fuel pressure setting map shown in Fig. 9(a), and thus the map is changed to the fuel pressure setting map shown in Fig. 9(b), in which a favorable quietness of the engine is attained in this operation region. The amount of change for this is determined experimentally by trial and error.
[0011] However, with the fuel pressure setting map shown in Fig. 9(b), problems with regard to exhaust emissions of the engine remain. Accordingly, a high fuel pressure region in an intermediate torque region is enlarged towards the low revolution side compared to the fuel pressure setting map shown in Fig. 9(b), and thus the atomization of the fuel in this operation region (in particular in the operation region enclosed by the dash-dotted line in Fig. 9(c)) is enhanced, so that the map is changed to a fuel pressure setting map as shown in Fig. 9(c), in which an improvement of the exhaust emissions is attained. The amount of change for this is determined experimentally by trial and error. In the fuel pressure setting map shown in Fig. 9(c), the low fuel pressure region near the maximum torque line is enlarged towards the high revolution side, and thus also a suppression of oil dilution is attained.
[0012] Since the above-described preparation procedure was used, the preparation of the fuel pressure setting map required a considerable effort. And what is more, since an adapted value for the fuel pressure had to be determined experimentally by trial and error for each engine operation state individually, there was also no guarantee that appropriate fuel pressures are set across the entire engine operation region. That is to say, there were cases in which, even though a reduction of combustion noise and a reduction of the generated amount of NOx may be achieved in a given operation region, the combustion efficiency worsens and a sufficient engine torque cannot be attained, and there were cases in which, conversely, even though a sufficiently high engine torque is attained, there is a tendency that the combustion noise increases and the generated amount of NOx increases.
[0013] Thus, conventionally, since the adapted values of the fuel pressure were decided through trial and error, the adaptation tended to be complicated, it was impossible to implement a systematic procedure for setting the fuel pressure that is common to a number of engine types, and an optimization of the fuel pressure could not be said to be accomplished across the entire engine operation region, so that there was still room for improvement.
[0014] The present invention was conceived in view of these problems, and it is an object thereof to provide a fuel injection pressure control apparatus with which it is possible to carry out fuel injection with a fuel injection pressure that is set by a systematic procedure for setting the fuel injection pressure, when setting a fuel injection pressure that is suitable for the operation state of the internal combustion engine.
[Solution to Problem]
- Principle by which the Problem is Solved -
[0015] The solving principle by which the present invention attains the above-noted object is to provide an unambiguous correlation between requested output (requested power) of the internal combustion engine and fuel injection pressure (for example the target fuel pressure within the common rail). Moreover, in a situation in which the output of the internal combustion engine changes due to a change in at least one of the revolution and torque of the internal combustion engine, a fuel injection with a correspondingly suitable fuel pressure can be carried out, whereas conversely in a situation in which the output of the internal combustion engine does not change even though the revolution or the torque of the internal combustion engine changes, the fuel pressure is not changed from the suitable value that was set so far. Thus, it becomes possible to let the change of the heat generation rate approach an ideal state during combustion of the air-fuel mixture.
- Means for Solving the Problem -
[0016] More specifically, the present invention is based on a fuel injection pressure control apparatus for an internal combustion engine of the compression ignition type that controls the pressure of fuel that is injected into a cylinder of the internal combustion engine. The fuel injection pressure is adjusted in accordance with the output requested by the internal combustion engine by allocating in advance a region of equal fuel injection pressure to a region of equal power requested by the internal combustion engine, across substantially the entire region in which the internal combustion engine can be operated.
[0017] Due to these characterizing features, when the output requested by the internal combustion engine has changed during operation of the internal combustion engine, the fuel injection pressure (target fuel injection pressure) is set such that it becomes the fuel injection pressure that has been allocated in advance in correspondence with the requested output of the internal combustion engine. Moreover, the fuel injection pressure is obtained by allocating a region of equal fuel injection pressure to a region of equal output, so that a systematic procedure for setting the fuel pressure can be implemented that is common to a number of engine types, and the preparation of the fuel setting map for setting a fuel injection pressure that is suitable for the operation state of the internal combustion engine can be simplified.
[0018] By adjusting the fuel injection pressure, for example, it is possible to let the change of the heat generation rate during combustion of the air-fuel mixture approach an ideal state. More specifically, if the fuel injection pressure is set to be high, the amount by which the heat generation rate increases per unit time during the initial period of the combustion can be made large (the slope angle of the waveform of the heat generation rate can be made large), and the injection period over which the same injection amount is attained can be made short, so that the combustion period can be shortened (the lowering of the heat generation rate can be set to an earlier timing). That is to say, the phase of the heat generation rate waveform with respect to the advancement of the crank angle can be made short (the timing at which the heat generation rate is lowered can be shifted in the advance direction of the crank angle). Moreover, also the peak of the heat generation rate (local maximum of the heat generation rate waveform) can be increased. Conversely, if the fuel injection pressure is set to be low, the slope angle of the heat generation rate waveform during the initial period of the combustion can be made small, the phase of the heat generation rate waveform with respect to the advancement of the crank angle can be made large, and moreover, the local maximum (peak) of the heat generation rate waveform can be lowered. Thus, the change of the heat generation rate waveform can be changed by adjusting the fuel injection pressure, and it becomes possible to let this heat generation rate waveform approach an ideal waveform. Accordingly, it becomes possible to satisfy several requirements at the same time, namely to improve the exhaust emissions by reducing the amount of NOx generated, to reduce combustion noise during the combustion stroke, and to ensure a sufficient engine torque. Furthermore, it becomes possible to simplify the preparation of the fuel pressure setting map for obtaining this ideal combustion waveform.
[0019] As a way to allocate the region of equal fuel injection pressure to the region of equal output of the internal combustion engine, it is possible to allocate a region of equal fuel injection pressure to the region of equal power of the internal combustion engine, such that the fuel injection pressure does not change if the output that is determined from a revolution and a torque of the internal combustion engine does not change even though the revolution and the torque of the internal combustion engine has changed.
[0020] Thus, it is possible to change the fuel injection pressure only when the requested output of the internal combustion engine changes, and to set a suitable fuel injection pressure unambiguously with respect to the requested output of the internal combustion engine. For example, if the revolution of the internal combustion engine rises but there is no change of the requested output due to a lowering of the torque, or conversely, if the torque of the internal combustion engine rises but there is no change of the requested output due to a lowering of the revolution, then the fuel injection pressure is not changed, and the suitable value that has been set up to then is maintained.
[0021] As a way to allocate the fuel injection pressure region, it is possible to allocate a fuel injection pressure that is higher the higher the output requested by the internal combustion engine is. That is to say, in a high-torque operation state or in a high-revolution state of the internal combustion engine, the requested output is attained by increasing the heat generation rate within the cylinder.
[0022] As a way to allocate the fuel injection pressure region, it is possible to set a fuel injection pressure region where the fuel injection pressure increases in any of the cases that both the revolution and the torque of the internal combustion engine increase, that the torque increases at constant revolution of the internal combustion engine, and that the revolution increases at constant torque of the internal combustion engine. That is to say, the fuel injection pressure can be adjusted such that the fuel injection pressure increases only in situations in which the requested output of the internal combustion engine rises.
[0023] Moreover, a proportion of a change of the fuel injection pressure with respect to a change of the output requested by the internal combustion engine can be set to become smaller the lower the revolution of the internal combustion engine becomes. That is to say, in a region of low revolutions of the internal combustion engine, the change of the fuel injection pressure can be made smooth, and a sharp increase of the combustion pressure within the cylinder is avoided in this operation state, so that the generation of vibrations or noise accompanying the combustion can be suppressed. Conversely, in a region of high revolutions of the internal combustion engine, the fuel injection pressure changes considerably with an increase of the torque, for example, and the requested output is attained quickly, so that the responsiveness of the internal combustion engine becomes favorable.
[0024] Furthermore, the fuel pressure setting map that is looked up in order to adjust the fuel injection pressure is as follows: Lines of equal output and lines of equal fuel injection pressure drawn within a map where a horizontal axis denotes revolution of the internal combustion engine and a vertical axis denotes torque of the internal combustion engine substantially match across substantially the entire region in which the internal combustion engine can be operated.
[0025] The following example can be given for a specific procedure for deciding the fuel injection pressure in accordance with the output requested by the internal combustion engine: The fuel injection pressure can be made proportional, with a predetermined proportionality constant, to the output requested by the internal combustion engine, and the fuel injection pressure can be determined by adding a predetermined pressure offset to a provisional fuel injection pressure obtained by multiplying this requested output with the proportionality constant.
[0026] In this case, the pressure offset can be set such that a heat generation rate reaches a local maximum at a time when a crank angle has reached about 10° after compression top dead center, if the fuel of a main injection that is injected by a fuel injection valve starts to combust at a time when a piston of the internal combustion engine has reached compression top dead center.
[0027] Thus, it becomes possible to specifically decide the fuel injection pressure in accordance with the output requested by the internal combustion engine. Moreover, if the fuel injection is carried out at the thusly decided fuel injection pressure, then 50% of the air-fuel mixture within the cylinder will be completely combusted at the time of 10° after compression top dead center of the piston (ATDC 10°). That is to say, about 50% of the total amount of generated heat in the expansion stroke is generated until ATDC 10°, and it becomes possible to operate the internal combustion engine with high thermal efficiency.
[0028] The following example can be given for a specific procedure for deciding the fuel injection pressure in an output region where combustion noise is addressed, which is an output region where the output requested by the internal combustion engine is relatively low: The fuel injection pressure at the output region where combustion noise is addressed may be determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure that is determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
[0029] In this case, the fuel injection pressure may be determined by setting the amount by which the reference pressure is correctively decreased in the output region where combustion noise is addressed to become larger the smaller the output requested by the internal combustion engine becomes.
[0030] If the pressure offset is set in this manner, it is possible to suppress combustion noise in the combustion chamber and to improve the quietness of the internal combustion engine in situations in which the output of the internal combustion engine is relatively low.
[0031] The following example can be given for a specific procedure for deciding the fuel injection pressure in an output region where NOx is addressed, which is an output region where the output requested by the internal combustion engine is relatively high: The fuel injection pressure at an output region where NOx is addressed may be determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
[0032] In this case, the fuel injection pressure may be determined by setting the amount by which the reference pressure is correctively decreased in the output region where NOx is addressed to become larger the larger the output requested by the internal combustion engine becomes.
[0033] If the pressure offset is set in this manner, then it is possible to suppress the combustion speed within the combustion chamber to a low level and to considerably reduce the amount of NOx generated in the course of combustion within the cylinder in situations in which the output of the internal combustion engine is relatively high
[0034] The following example can be given for a specific procedure for deciding the fuel injection pressure in an output region where smoke is addressed, which is an output region where the output requested by the internal combustion engine is substantially intermediate: The fuel injection pressure at an output region where smoke is addressed may be determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively increasing this reference pressure.
[0035] If the pressure offset is set in this manner, then even if the main injection is implemented by a plurality of partial injections, the injection amount per unit time can be increased, a shortening of the injection period can be accomplished, and a deterioration of the efficiency accompanying a lengthening of the injection period can be overcome.
[Advantageous Effects of Invention]
[0036] In the present invention, a fuel injection pressure of an internal combustion engine of the compression ignition type is set in such a manner that a region of equal fuel injection pressure is allocated to an equal output region across substantially the entire region in which the internal combustion engine can be operated. Thus, it becomes possible to implement a systematic procedure for setting the fuel pressure that is common to a number of engine types.
[Brief Description of Drawings]
[0037]
[FIG. 1]
Fig. 1 is a conceptual diagram of an engine according to an embodiment and its control
system.
[FIG. 2]
Fig. 2 is a cross-sectional view showing a combustion chamber of a diesel engine and
its surroundings.
[FIG. 3]
Fig. 3 is a block diagram showing the configuration of a control system, such as an
ECU.
[FIG. 4]
Fig. 4 is a waveform diagram illustrating the change of the heat generation ratio
at an expansion stroke.
[FIG. 5]
Fig. 5 is a diagram showing the relation between the requested engine output and the
target fuel pressure set in accordance with this requested output, in a first embodiment.
[FIG. 6]
Fig. 6 is a diagram showing a fuel setting map that is looked up when deciding the
target fuel pressure in the first embodiment.
[FIG. 7]
Fig. 7 is a diagram showing a fuel setting map that is looked up when deciding the
target fuel pressure in the second embodiment.
[FIG. 8]
Fig. 8 is a diagram showing the relation between the requested engine output and the
target fuel pressure set in accordance with this requested output, in a third embodiment.
[FIG. 9]
Fig. 9 is a diagram illustrating an example of a conventional method for preparing
a fuel pressure setting map.
[Description of Embodiments]
[0038] The following is a description of an embodiment of the present invention based on the drawings. In the present embodiment, a case is described in which the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, inline four-cylinder) diesel engine (compression ignition internal combustion engine) mounted in an automobile.
- Engine configuration -
[0039] First, the overall configuration of a diesel engine (referred to below as simply "engine") according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and a control system for the same according to the present embodiment. FIG. 2 is a cross-sectional view that shows a combustion chamber 3 of the diesel engine and parts in the vicinity of the combustion chamber 3.
[0040] As shown in FIG. 1, the engine 1 according to the present embodiment is configured as a diesel engine system whose main portions are a fuel supply system 2, combustion chambers 3, an intake system 6, an exhaust system 7, and the like.
[0041] The fuel supply system 2 is provided with a supply pump 21, a common rail 22, injectors (fuel injection valves) 23, a cutoff valve 24, a fuel addition valve 26, an engine fuel path 27, an added fuel path 28, and the like.
[0042] The supply pump 21 draws fuel from a fuel tank, and after putting the drawn fuel under high pressure, supplies that fuel to the common rail 22 via the engine fuel path 27. The common rail 22 functions as an accumulation chamber where high pressure fuel supplied from the supply pump 21 is held (accumulated) at a predetermined pressure, and this accumulated fuel is distributed to each injector 23. The injectors 23 are configured from piezo injectors within which a piezoelectric element (piezo element) is provided, and which supply fuel by injection into the combustion chambers 3 by opening a valve as suitable. The details of the control of fuel injection from the injectors 23 will be described later.
[0043] Also, the supply pump 21 supplies part of the fuel drawn from the fuel tank to the fuel addition valve 26 via the added fuel path 28. In the added fuel path 28, the aforementioned cutoff valve 24 is provided in order to stop fuel addition by cutting off the added fuel path 28 during an emergency.
[0044] The fuel addition valve 26 is configured from an electronically controlled opening/closing valve whose valve opening period is controlled with an addition control operation by an ECU 100 described later such that the amount of fuel added to the exhaust system 7 becomes a target addition amount (an addition amount such that the exhaust A/F becomes a target A/F), or such that a fuel addition timing becomes a predetermined timing. That is, a desired amount of fuel from the fuel addition valve 26 is supplied by injection to the exhaust system 7 (to an exhaust manifold 72 from exhaust ports 71) at an appropriate timing.
[0045] The intake system 6 is provided with an intake manifold 63 connected to an intake port 15a formed in a cylinder head 15 (see FIG. 2), and an intake tube 64 that constitutes an intake path is connected to the intake manifold 63. Also, in this intake path, an air cleaner 65, an airflow meter 43, and a throttle valve 62 are disposed in that order from the upstream side. The airflow meter 43 outputs an electrical signal corresponding to the amount of air that flows into the intake path via the air cleaner 65.
[0046] The exhaust system 7 is provided with the exhaust manifold 72 connected to the exhaust ports 71 formed in the cylinder head 15, and exhaust tubes 73 and 74 that constitute an exhaust path are connected to the exhaust manifold 72. Also, in this exhaust path, a maniverter (exhaust purification apparatus) 77 is disposed that is provided with a NOx storage catalyst (NSR catalyst: NOx storage reduction catalyst) 75 and a DPNR catalyst (diesel particulate-NOx reduction catalyst) 76, which are described later. The following is a description of the NSR catalyst 75 and the DPNR catalyst 76.
[0047] The NSR catalyst 75 is an NOx storage and reduction catalyst, and is configured using, for example, alumina (Al2O3) as a support, with, for example, an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), an alkaline earth element such as barium (Ba) or calcium (Ca), a rare earth element such as lanthanum (La) or Yttrium (Y), and a precious metal such as platinum (Pt) supported on this support.
[0048] In a state in which a large amount of oxygen is present in the exhaust, the NSR catalyst 75 stores NOx, and in a state in which the oxygen concentration in the exhaust is low and a large amount of a reduction component (for example, an unburned component (HC) of fuel) is present, the NSR catalyst 75 reduces NOx to NO2 or NO and releases the resulting NO2 or NO. NOx that has been released as NO2 or NO is further reduced due to quickly reacting with HC or CO in the exhaust and becomes N2. Also, by reducing NO2 or NO, HC and CO themselves are oxidized and thus become H2O and CO2. In other words, by appropriately adjusting the oxygen concentration or the HC component in the exhaust introduced to the NSR catalyst 75, it is possible to purify HC, CO, and NOx in the exhaust. In the configuration of the present embodiment, adjustment of the oxygen concentration or the HC component in the exhaust can be performed with an operation to add fuel from the aforementioned fuel addition valve 26.
[0049] On the other hand, in the DPNR catalyst 76, an NOx storage and reduction catalyst is supported on a porous ceramic structure, for example, and PM in exhaust gas is captured when passing through a porous wall. When the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage and reduction catalyst, and when the air-fuel ratio is rich, the stored NOx is reduced and released. Furthermore, a catalyst that oxidizes/burns the captured PM (for example, an oxidization catalyst whose main component is a precious metal such as platinum) is supported on the DPNR catalyst 76.
[0050] Here, the configuration of the combustion chamber 3 of the diesel engine and parts in the vicinity of the combustion chamber 3 will be described. The following description makes reference to FIG. 2. As shown in FIG. 2, in a cylinder block 11 that constitutes part of the main body of the engine, a cylindrical cylinder bore 12 is formed in each cylinder (each of four cylinders), and a piston 13 is housed within each cylinder bore 12 such that the piston 13 can slide in the vertical direction.
[0051] The aforementioned combustion chamber 3 is formed on the top side of a top face 13a of the piston 13. More specifically, the combustion chamber 3 is defined by a lower face of the cylinder head 15 installed on top of the cylinder block 11 via a gasket 14, an inner wall face of the cylinder bore 12, and the top face 13a of the piston 13. Cavities 13b are concavely provided in approximately the center of the top face 13a of the piston 13, and these cavities 13b also constitute part of the combustion chamber 3.
[0052] A small end 18a of a connecting rod 18 is linked to the piston 13 by a piston pin 13c, and a large end of the connecting rod 18 is linked to a crankshaft serving as an engine output shaft. Thus, back and forth movement of the piston 13 within the cylinder bore 12 is transmitted to the crankshaft via the connecting rod 18, and engine output is obtained due to rotation of this crankshaft. Also, a glow plug 19 is disposed facing the combustion chamber 3. The glow plug 19 glows due to the flow of electrical current immediately before the engine 1 is started, and functions as a starting assistance apparatus whereby ignition and combustion are promoted due to part of a fuel spray being blown onto the glow plug.
[0053] In the cylinder head 15, the intake port 15a that introduces air to the combustion chamber 3 and the exhaust port 71 that discharges exhaust gas from the combustion chamber 3 are respectively formed, and an intake valve 16 that opens/closes the intake port 15a and an exhaust valve 17 that opens/closes the exhaust port 71 are disposed. The intake valve 16 and the exhaust valve 17 are disposed facing each other on either side of a cylinder center line P. That is, the engine 1 is configured as a cross flow-type engine. Also, the injector 23 that injects fuel directly into the combustion chamber 3 is installed in the cylinder head 15. The injector 23 is disposed approximately at the center above the combustion chamber 3, in an erect orientation along the cylinder center line P, and injects fuel introduced from the common rail 22 toward the combustion chamber 3 at a predetermined timing.
[0054] Furthermore, as shown in FIG. 1, the engine 1 is provided with a turbocharger 5. This turbocharger 5 is provided with a turbine wheel 5B and a compressor wheel 5C that are linked via a turbine shaft 5A. The compressor wheel 5C is disposed facing the inside of the intake tube 64, and the turbine wheel 5B is disposed facing the inside of the exhaust tube 73. Thus the turbocharger 5 uses exhaust flow (exhaust pressure) received by the turbine wheel 5B to rotate the compressor wheel 5C, thereby performing a so-called turbocharging operation that increases the intake pressure. In the present embodiment, the turbocharger 5 is a variable nozzle-type turbocharger, in which a variable nozzle vane mechanism (not shown) is provided on the turbine wheel 5B side, and by adjusting the opening degree of this variable nozzle vane mechanism it is possible to adjust the turbocharging pressure of the engine 1.
[0055] An intercooler 61 for forcibly cooling intake air heated due to supercharging with the turbocharger 5 is provided in the intake tube 64 of the intake system 6. The throttle valve 62 provided on the downstream side from the intercooler 61 is an electronically controlled opening/closing valve whose opening degree is capable of stepless adjustment, and functions to constrict the area of the path of intake air under predetermined conditions, and thus adjust (reduce) the supplied amount of intake air.
[0056] Also, the engine 1 is provided with an exhaust gas recirculation path (EGR path) 8 that connects the intake system 6 and the exhaust system 7. The EGR path 8 decreases the combustion temperature by appropriately recirculating part of the exhaust to the intake system 6 and resupplying that exhaust to the combustion chamber 3, thus reducing the amount of NOx produced. Also, provided in the EGR path 8 are an EGR valve 81 that by being opened/closed steplessly under electronic control is capable of freely adjusting the amount of exhaust flow that flows through the EGR path 8, and an EGR cooler 82 for cooling exhaust that passes through (recirculates through) the EGR path 8.
- Sensors -
[0057] Various sensors are installed at respective sites in the engine 1, and these sensors output signals related to environmental conditions at the respective sites and the operating state of the engine 1.
[0058] For example, the above airflow meter 43 outputs a detection signal corresponding to an intake air flow amount (intake air amount) on the upstream side of the throttle valve 62 within the intake system 6. An intake temperature sensor 49 is disposed in the intake manifold 63, and outputs a detection signal corresponding to the temperature of intake air. An intake pressure sensor 48 is disposed in the intake manifold 63, and outputs a detection signal corresponding to the intake air pressure. An A/F (air-fuel ratio) sensor 44 outputs a detection signal that continuously changes according to the oxygen concentration in the exhaust on the downstream side of the maniverter 77 of the exhaust system 7. An exhaust temperature sensor 45 likewise outputs a detection signal corresponding to the temperature of the exhaust gas (exhaust temperature) on the downstream side of the maniverter 77 of the exhaust system 7. A rail pressure sensor 41 outputs a detection signal corresponding to the pressure of fuel accumulated in the common rail 22. A throttle opening degree sensor 42 detects the opening degree of the throttle valve 62.
-ECU-
[0059] As shown in FIG. 3, the ECU 100 is provided with a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. In the ROM 102, various control programs, maps that are referred to when executing those various control programs, and the like are stored. The CPU 101 executes various computational processes based on the various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores data resulting from computations with the CPU 101 or data that has been input from the respective sensors, and the backup RAM 104, for example, is a nonvolatile memory that stores that data or the like to be saved when the engine 1 is stopped.
[0060] The CPU 101, the ROM 102, the RAM 103, and the backup RAM 104 are connected to each other via a bus 107, and are connected to an input interface 105 and an output interface 106 via the bus 107.
[0061] The rail pressure sensor 41, the throttle opening degree sensor 42, the airflow meter 43, the A/F sensor 44, the exhaust temperature sensor 45, the intake pressure sensor 48, and the intake temperature sensor 49 are connected to the input interface 105. Further, a water temperature sensor 46 that outputs a detection signal corresponding to the coolant temperature of the engine 1, an accelerator opening degree sensor 47 that outputs a detection signal corresponding to the amount that an accelerator pedal is depressed, a crank position sensor 40 that outputs a detection signal (pulse) each time that the output shaft (crankshaft) of the engine 1 rotates a fixed angle, and the like are connected to the input interface 105. On the other hand, the aforementioned injectors 23, fuel addition valve 26, throttle valve 62, EGR valve 81, and the like are connected to the output interface 106.
[0062] The ECU 100 executes various controls of the engine 1 based on the output of the various sensors described above. Furthermore, the ECU 100 executes pilot injection, pre-injection, main injection, after-injection, and post injection, as control of fuel injection of the injectors 23.
[0063] The fuel injection pressure when executing these fuel injections is determined by the internal pressure of the common rail 22. As the common rail internal pressure, ordinarily, the target value of the fuel pressure supplied from the common rail 22 to the injectors 23 (i.e., the target rail pressure) is set to increase as the engine load increases, and as the engine revolution increases. That is, when the engine load is high, a large amount of air is drawn into the combustion chamber 3, so it is necessary to inject a large amount of fuel into the combustion chamber 3 from the injectors 23, and therefore it is necessary to set a high injection pressure from the injectors 23. Also, when the engine revolution is high, the period during which injection is possible is short, so it is necessary to inject a larger amount of fuel per unit time, and therefore it is necessary to set a high injection pressure from the injectors 23. In this way, the target rail pressure is ordinarily set based on the engine load and the engine revolution. As one of the features of the present invention, a specific method for setting the target value of the fuel pressure is explained later.
[0064] The optimum values of fuel injection parameters for fuel injection such as the above pilot injection, main injection, and the like differ depending on temperature conditions of the engine, intake air, and the like.
[0065] For example, the ECU 100 adjusts the amount of fuel discharged by the supply pump 21 such that the common rail pressure becomes the same as the target rail pressure set based on the engine operating state, i.e., such that the fuel injection pressure matches the target injection pressure. Also, the ECU 100 determines the fuel injection amount and the form of fuel injection based on the engine operating state. Specifically, the ECU 100 calculates an engine revolution speed based on the value detected by the crank position sensor 40 and obtains an amount of accelerator pedal depression (accelerator opening degree) based on the value detected by the accelerator opening degree sensor 47, and determines the total fuel injection amount (the sum of the injection amount in pre-injection and the injection amount in main injection) based on the engine revolution speed and the accelerator opening degree.
- Setting of Target Fuel Pressure -
[0066] The following is an explanation of a procedure for setting the target fuel pressure and of a fuel pressure setting map, which are characteristic for the present embodiment. First, the technical idea behind setting the target fuel pressure in the present embodiment is explained.
[0067] In the diesel engine 1, it is important to satisfy several requirements at the same time, namely to improve the exhaust emissions by reducing the amount of NOx generated, to reduce combustion noise during the combustion stroke, and to ensure a sufficient engine torque. The inventors of the present invention recognized that, as a way to satisfy these requirements at the same time, it is effective to suitably control the change of the heat generation rate within the cylinder during the combustion stroke (the change represented by the waveform of the heat generation rate), and, as a way to control this change of the heat generation rate, found the procedure of setting the target fuel pressure described in the following.
[0068] The solid line in Fig. 4 indicates the ideal waveform of the heat generation rate for the combustion of fuel injected at the main injection, where the horizontal axis denotes the crank angle and the vertical axis denotes the heat generation rate. TDC in the drawing indicates the crank angle position corresponding to the compression top dead center of the piston 13. As this heat generation rate waveform, the combustion of the fuel injected at the main injection commences from the compression top dead center (TDC) of the piston 13, the heat generation rate reaches its local maximum (peak) at a predetermined piston position after compression top dead center (for example at the time of 10° after compression top dead center (ATDC 10°)), and the combustion of the fuel injected at the main injection is finished at a further predetermined piston position after compression top dead center (for example at the time of 25° after compression top dead center (ATDC 25°). If the combustion of the air-fuel mixture is carried out with such a change of the heat generation ratio, then for example 50% of the air-fuel mixture within the cylinder will be completely combusted at the time of 10° after compression top dead center (ATDC 10°). That is to say, about 50% of the total amount of heat generated in the expansion stroke is generated until ATDC 10°, and it becomes possible to operate the engine 1 with high thermal efficiency.
[0069] The waveform denoted by the dash-dotted line in Fig. 4 denotes the waveform of the heat generation rate for the combustion of fuel that is injected at the pre-injection. Thus, a stable diffusion combustion of the fuel injected at the main injection is realized. For example, a heat amount of 10[J] is generated by the combustion of the fuel injected at this pre-injection. There is no limitation to this value. For example, it may be set as appropriate in accordance with the total amount of the fuel injection. Furthermore, while not shown in the drawings, also a pilot injection is carried out prior to the pre-injection, sufficiently raising the temperature inside the cylinder, so that favorable ignition characteristics of the fuel injected at the main injection can be maintained.
[0070] Thus, in the present embodiment, sufficient pre-warming inside the cylinder is carried out by the pilot injection and the pre-injection. Due to this pre-warming, when the main injection, which is explained later, begins, the fuel injected at this main injection is immediately exposed to a temperature environment of at least its own self-ignition temperature, so that thermal decomposition advances, and the combustion begins immediately after the injection.
[0071] More specifically, there are physical delays and chemical delays as fuel ignition delays in diesel engines. A physical delay is the time required for the vaporization and mixing of the fuel drops, which depends on the gas temperature of the combustion space. On the other hand, a chemical delay is the time required for the chemical breakdown of compounds of the fuel vapor and for the heat generation by oxidation. The physical delay can be suppressed to a minimum in situations in which there is pre-heating within the cylinder, as described above, and as a result, also the ignition delay can be suppressed to a minimum.
[0072] Consequently, as a combustion form of fuel injected by the main injection, almost no pre-mixing combustion takes place. As a result, controlling the fuel injection timing becomes almost the same as controlling the combustion timing, and the controllability of the combustion can be greatly improved. That is to say, up to now, this premixing combustion took up a large proportion of the combustion in diesel engines, but in the present embodiment, the proportion of this premixing combustion is suppressed to a minimum, making it possible to largely improve the controllability of the combustion by controlling the waveform of the heat generation rate (ignition period and heat generation amount) through control of the fuel injection timing and fuel injection amount (control of the injection rate waveform). In the present embodiment, this new form of combustion is referred to as "successive combustion (combustion that begins immediately after the fuel has been injected)" or "controlled combustion (combustion that is actively controlled through the fuel injection timing and the fuel injection amount)".
[0073] The waveform of the dash-dot-dot line a in Fig. 4 shows waveform of the heat generation rate for the case that the fuel injection pressure is set to be higher than an appropriate value, leading to a state where the combustion speed and the peak value are both too high, and there is the concern that the combustion noise becomes large and there is an increased amount of NOx generated. On the other hand, the waveform of the dash-dot-dot line β in Fig. 4 shows the heat generation rate waveform for the case that the fuel injection pressure is set to be lower than an appropriate value, leading to a state where the combustion speed is low and the timing of the peak is shifted considerably towards later angles, so that there is the concern that a sufficient engine torque cannot be ensured.
[0074] As explained above, the procedure for setting the target fuel pressure in accordance with the present embodiment is based on the technical idea of achieving increased combustion efficiency by optimizing the change of the heat generation rate (optimizing the heat generation rate waveform). In order to realize this, the target fuel pressure is set as described below. In the following, several embodiments of procedures for setting the target fuel pressure are described.
First Embodiment
[0076] The solid line in Fig. 5 shows the relation between the required output (required power) of the engine 1 according to the present embodiment and the target fuel pressure set in accordance with this required output. Thus, the required output and the target fuel pressure are proportional to each other, and the target fuel pressure can be determined unambiguously from the required output. In other words, a target fuel pressure is allocated in advance to each requested output.
[0077] Referring to Fig. 5, the following is a more specific explanation of the procedure for setting the target fuel pressure in accordance with the requested output.
[0078] First, a provisional fuel pressure line as indicated by the broken line in Fig. 5 is set. This provisional fuel pressure line is set such that when the requested output is "0", also the target fuel pressure becomes "0", as a straight line passing through the origin in the graph of Fig. 5 and having a predetermined slope.
[0079] The slope of this provisional fuel pressure line is determined for example by the exhaust amount of the engine 1. That is to say, the larger the exhaust amount of the engine 1 is, the smaller the slope of the provisional fuel pressure line is set, for example. The target fuel pressures on this provisional fuel pressure line correspond to the provisional fuel injection pressures of the present invention, and these provisional fuel injection pressures are determined through the proportional relation with the requested output, which is given by a predetermined proportionality constant (corresponding to the slope of the provisional fuel pressure line). That is to say, the provisional fuel injection pressures can be determined by multiplying the requested output with the predetermined proportionality constant, and the set of these provisional fuel injection pressures constitutes the provisional fuel pressure line.
[0080] Then, the provisional fuel pressure line is shifted parallel towards the high fuel pressure side (upwards in Fig. 5) by a predetermined pressure offset with respect to a power centroid (the point of 40 kW requested output in the graph shown in Fig. 5) on the provisional fuel pressure line, whereby the fuel pressure line shown by the solid line in the figure is set. It should be noted that there is no limitation to the above-noted value as the power centroid.
[0081] Here, the power centroid is set as the value corresponding to that output that is used with the highest frequency among the outputs of the engine 1.
[0082] Furthermore, the pressure offset amount is set such that the heat generation rate within the cylinder reaches its local maximum (peak) at a predetermined piston position after compression top dead center (at the time of 10° after compression top dead center (ATDC 10°), if the fuel of the main injection injected by the injector 23 begins its combustion at the compression top dead center (TDC) of the piston 13. That is to say, the pressure offset amount is set such that at the power centroid the ideal heat generation rate waveform shown by the solid line in Fig. 4 is attained. It should be noted that this pressure offset amount depends on the exhaust amount and the number of cylinders of the engine 1, and is set individually for each type of engine 1 through advance experimentation or simulation. Moreover, the fuel supply system 2 of the engine 1 according to the present embodiment is set to 200 MPa as an upper limit of the target fuel pressure (maximum rail pressure).
[0083] Fig. 6 is a fuel pressure setting map that is looked up when deciding the target fuel pressure. This fuel pressure setting map is prepared in accordance with the fuel pressure line shown by the solid line in Fig. 5, and is stored for example in the ROM 102. In this fuel pressure setting map, the horizontal axis denotes engine revolution and the vertical axis denotes engine torque. Tmax in Fig. 6 denotes the maximum torque line.
[0084] As a feature of this fuel pressure setting map the lines of equal fuel injection pressures (regions of equal fuel injection pressures) denoted by A - I in the figure are allocated to equal power lines (regions of equal output) of the requested output (requested power) of the engine 1 that is determined based on, for example, the amount by which the accelerator pedal is pressed down. That is to say, this fuel pressure setting map is set such that the lines of equal power and the lines of equal fuel injection pressure substantially match.
[0085] More specifically, the curve A in Fig. 6 is the line where the requested engine output is 10 kW, and the line of a fuel injection pressure of 66 MPa is allocated to this line. Similarly, the curve B is the line where the requested engine output is 20 kW, and the line of a fuel injection pressure of 83 MPa is allocated to this line. The curve C is the line where the requested engine output is 30 kW, and the line of a fuel injection pressure of 100 MPa is allocated to this line. The curve D is the line where the requested engine output is 40 kW, and the line of a fuel injection pressure of 116 MPa is allocated to this line. The curve E is the line where the requested engine output is 50 kW, and the line of a fuel injection pressure of 133 MPa is allocated to this line. The curve F is the line where the requested engine output is 60 kW, and the line of a fuel injection pressure of 150 MPa is allocated to this line. The curve G is the line where the requested engine output is 70 kW, and the line of a fuel injection pressure of 166 MPa is allocated to this line. The curve H is the line where the requested engine output is 80 kW, and the line of a fuel injection pressure of 183 MPa is allocated to this line. The curve I is the line where the requested engine output is 90 kW, and the line of a fuel injection pressure of 200 MPa is allocated to this line. There is no limitation to these values, and they can be set as appropriate in view of the performance characteristics of the engine 1.
[0086] Moreover, in these lines A - I, the proportion of change of the fuel injection pressure with respect to a change in the requested engine output is set to be substantially equivalent.
[0087] Accordingly, a fuel injection pressure control apparatus in accordance with the present invention is constituted by the ROM 102 in which this fuel pressure setting map is stored, the supply pump 21, and the CPU 101.
[0088] Thus, the target fuel pressure that is appropriate for the requested output of the engine 1 is set in accordance with the fuel pressure setting map prepared in this manner, and the supply pump 21 is controlled accordingly, for example.
[0089] Moreover, the fuel injection pressure increases when the engine revolution and the engine torque increase simultaneously (see arrow I in Fig. 6), when the engine torque increases at constant engine revolution (see arrow II in Fig. 6), or when the engine revolution increases at constant engine torque (see arrow III in Fig. 6). Thus, when the engine torque (engine load) is high, a fuel injection amount that is suitable for the intake air amount can be ensured, and when the engine revolution is high, the necessary fuel injection amount can be ensured within a short period of time by increasing the fuel injection amount per unit time. Therefore, it is possible to consistently realize a combustion form of the ideal heat generation rate waveform shown by the solid line in Fig. 4, regardless of the engine output and the engine revolution, and it becomes possible to satisfy the requirements of improving the exhaust emissions by reducing the amount of NOx generated, reducing combustion noise during the combustion stroke, and ensuring a sufficient engine torque.
[0090] On the other hand, if the engine output does not change following a change in the engine revolution and the engine torque (corresponding to the arrow IV in Fig. 6), the optimal value of the fuel injection pressure that was set until then is maintained without changing the fuel injection pressure. That is to say, the fuel injection pressure is not changed due to the change of the engine operation following this line of equal fuel injection pressure (coinciding with the line of equal power), and the combustion form of the above-noted ideal heat generation rate waveform is continued. In this case, it becomes possible to continuously satisfy the requirements of improving the exhaust emissions by reducing the amount of NOx generated, reducing combustion noise during the combustion stroke, and ensuring a sufficient engine torque.
[0091] As noted above, in the present embodiment, an unambiguous correlation is maintained between the requested output (requested power) of the engine 1 and the fuel injection pressure (common rail pressure), and in a situation in which the engine output changes due to a change in at least one of the engine revolution and engine torque, a fuel injection with a correspondingly suitable fuel pressure can be carried out, whereas conversely in a situation in which the engine output does not change even though the engine revolution or the engine torque changes, the fuel pressure is not changed from the suitable value that was set so far. Thus, it becomes possible to let the change of the heat generation rate approach an ideal state across the entire engine operation region. Moreover, in the present embodiment, a systematic procedure for setting the fuel pressure is implemented that is common to a number of engine types, so that it is possible to simplify the preparation of the fuel pressure setting map for setting the suitable fuel injection pressure in accordance with the operation state of the engine 1.
Second Embodiment
[0092] The following is an explanation of a second embodiment. In this embodiment, a modified example of the fuel pressure setting map is used, whereas the remaining configuration and control method are the same as in the first embodiment. Accordingly, only the fuel pressure setting map is explained.
[0093] Fig. 7 shows a fuel pressure setting map that is referenced when deciding the target fuel pressure in the present embodiment. This fuel pressure setting map is stored for example in the above-mentioned ROM 102.
[0094] As in the above-described first embodiment, a feature of this fuel pressure setting map is that the lines of equal fuel injection pressure (regions of equal fuel injection pressure), which are indicated by A - L in the figure, are allocated to lines of equal power (regions of equal power) of the requested output (requested power) for the engine 1 that is determined based on the amount by which the accelerator pedal is pressed down. That is to say, also in this fuel pressure setting map, the lines of equal power and the lines of equal fuel injection pressure are set to substantially match each other.
[0095] More specifically, the curve A in Fig. 7 is the line where the requested engine output is 10 kW, and the line of a fuel injection pressure of 30 MPa is allocated to this line. Similarly, the curve B is the line where the requested engine output is 20 kW, and the line of a fuel injection pressure of 45 MPa is allocated to this line. The curve C is the line where the requested engine output is 30 kW, and the line of a fuel injection pressure of 60 MPa is allocated to this line. The curve D is the line where the requested engine output is 40 kW, and the line of a fuel injection pressure of 75 MPa is allocated to this line. The curve E is the line where the requested engine output is 50 kW, and the line of a fuel injection pressure of 90 MPa is allocated to this line. The curve F is the line where the requested engine output is 60 kW, and the line of a fuel injection pressure of 105 MPa is allocated to this line. The curve G is the line where the requested engine output is 70 kW, and the line of a fuel injection pressure of 120 MPa is allocated to this line. The curve H is the line where the requested engine output is 80 kW, and the line of a fuel injection pressure of 135 MPa is allocated to this line. The curve I is the line where the requested engine output is 90 kW, and the line of a fuel injection pressure of 150 MPa is allocated to this line. The curve J is the line where the requested engine output is 100 kW, and the line of a fuel injection pressure of 165 MPa is allocated to this line. The curve K is the line where the requested engine output is 110 kW, and the line of a fuel injection pressure of 180 MPa is allocated to this line. The curve L is the line where the requested engine output is 120 kW, and the line of a fuel injection pressure of 200 MPa is allocated to this line. There is no limitation to these values, and they can be set as appropriate in view of the performance characteristics of the engine 1.
[0096] Moreover, in these lines A - L, the proportion of change of the fuel injection pressure with respect to a change in the requested engine output is set to become smaller as the engine revolution becomes lower. That is to say, the distance between the lines is set to be wider in the region of small revolutions than in the region of high revolutions.
[0097] Thus, the target fuel pressure that is appropriate for the requested output of the engine 1 is set in accordance with the fuel pressure setting map prepared in this manner, and the supply pump 21 is controlled accordingly, for example.
[0098] Moreover, the fuel injection pressure increases when the engine revolution and the engine torque increase simultaneously (see arrow I in Fig. 7), when the engine torque increases at constant engine revolution (see arrow II in Fig. 7), or when the engine revolution increases at constant engine torque (see arrow III in Fig. 7). Thus, when the engine torque (engine load) is high, a fuel injection amount that is suitable for the intake air amount can be ensured, and when the engine revolution is high, the necessary fuel injection amount can be ensured within a short period of time by increasing the fuel injection amount per unit time. Therefore, it is possible to consistently realize a combustion form of the ideal heat generation rate waveform shown by the solid line in Fig. 4, regardless of the engine output and the engine revolution, and it becomes possible to satisfy the requirements of improving the exhaust emissions by reducing the amount of NOx generated, reducing combustion noise during the combustion stroke, and ensuring a sufficient engine torque.
[0099] On the other hand, if the engine output does not change following a change in the engine revolution and the engine torque (corresponding to the arrow IV in Fig. 7), the suitable value of the fuel injection pressure that was set until then is maintained without changing the fuel injection pressure. That is to say, the fuel injection pressure is not changed due to the change of the engine operation following this line of equal fuel injection pressure (coinciding with the line of equal power), and the combustion form of the above-noted ideal heat generation rate waveform is continued. In this case, it becomes possible to continuously satisfy the requirements of improving the exhaust emissions by reducing the amount of NOx generated, reducing combustion noise during the combustion stroke, and ensuring a sufficient engine torque.
[0100] As noted above, in the present embodiment, an unambiguous correlation is maintained between the requested output (requested power) of the engine 1 and the fuel injection pressure (common rail pressure). Thus, it becomes possible to let the change of the heat generation rate approach an ideal state across the entire engine operation region. Moreover, in the present embodiment, a systematic procedure for setting the fuel pressure is implemented that is common to a number of engine types, so that it is possible to simplify the preparation of the fuel pressure setting map for setting the suitable fuel injection pressure in accordance with the operation state of the engine 1.
[0101] And as noted above, with the fuel pressure setting map of the present embodiment, the proportion of the change amount of the fuel injection pressure with respect to change of the engine output is set to become smaller as the engine revolution becomes lower. Therefore, changes in the fuel injection pressure in the region of lower revolutions of the engine 1 become smooth, so that a sudden increase of the combustion pressure within the cylinder can be avoided in this operation state, and the generation of oscillations and noise accompanying combustion can be suppressed. On the other hand, in the region of high revolutions of the engine 1, there is a large change of the fuel injection pressure as the torque increases, for example, so that the requested output can be quickly attained and a favorable responsiveness of the engine 1 is achieved.
Third Embodiment
[0102] The following is an explanation of a third embodiment. In the above-described first embodiment, the fuel pressure line (see Fig. 5) was set such that the target fuel pressure was proportional to the requested output of the engine 1. Instead, in the present embodiment, an optimization of the fuel pressure line is attained through a corrective decrease or a corrective increase of the target fuel pressure with respect to the fuel pressure line shown in Fig. 5 (in the present embodiment, this fuel pressure line is a second provisional fuel pressure line, explained below, for determining the provisional fuel injection pressure of the present invention). This is explained in detail in the following.
[0103] The solid line in Fig. 8 denotes the relation between the requested output (requested power) of the engine 1 according to the present embodiment and the target fuel pressure that is set in accordance with this requested output. As shown, the requested output power and the target fuel pressure are not proportional to each other, but the target fuel pressure can be decided unambiguously from the requested power. In other words, the target fuel pressures are allocated in advance to the requested outputs.
[0104] Referring to Fig. 8, the following is a more specific explanation of a procedure for setting the target fuel pressure in accordance with the requested output.
[0105] First, as in the case of the above-described first embodiment, a first provisional fuel pressure line (provisional fuel pressure line of the first embodiment) as indicated by the dash-dotted line in Fig. 8 is set. This first provisional fuel pressure line is set such that when the requested output is "0", also the target fuel pressure becomes "0", as a line passing through the origin in the graph of Fig. 8 and having a predetermined slope.
[0106] As in the case of the above-described first embodiment, the slope of this first provisional fuel pressure line is determined for example by the exhaust amount of the engine 1. The target fuel pressures on this first provisional fuel pressure line correspond to the provisional fuel injection pressures of the present invention, and these provision fuel injection pressures are determined by the proportional relation with the requested output, which is given by a predetermined proportionality constant (corresponding to the slope of the first provisional fuel pressure line). That is to say, the provisional fuel injection pressures can be determined by multiplying the requested output with the predetermined proportionality constant, and the set of these provisional fuel injection pressures constitute the first provisional fuel pressure line.
[0107] Then, the first provisional fuel pressure line is shifted parallel towards the high fuel pressure side (upwards in Fig. 8) by a predetermined pressure offset (a pressure basic offset according to the present invention) with respect to a power centroid on the first provisional fuel pressure line (the point where the requested output is 40 kW in the graph shown in Fig. 8), whereby a second provisional fuel pressure line shown by the broken line in the figure is set.
It should be noted that there is no limitation to the above-noted value as the power centroid.
[0108] The power centroid and the pressure offset amount are determined in the same manner as in the case of the above-described first embodiment, so that further explanations are omitted here.
[0109] The final fuel pressure line is set by subjecting the second provisional pressure line that has been set in this manner to a corrective decrease or a corrective increase of the target fuel pressure, as explained below.
[0110] First, the fuel injection pressure in the output region where combustion noise is addressed, which is a region where the output requested by the engine 1 is relatively low, is determined by correctively decreasing the fuel pressure on the second provisional fuel pressure line (the reference pressure in the present invention). The amount by which the reference pressure on the second provisional fuel pressure line is correctively reduced is set such that it becomes larger the smaller the output requested by the engine 1 is. That is to say, the smaller the output requested by the engine 1 is, the more the reference pressure on the second provisional pressure line is reduced, and the lower the target fuel pressure is set.
[0111] The fuel injection pressure at the output region where NOx is addressed, which is a region where the output requested by the engine 1 is relatively high, is determined by correctively decreasing the reference pressure on the second provisional fuel pressure line. The amount by which the reference pressure on the second provisional fuel pressure line is correctively reduced is set to become larger the larger the output requested by the engine 1 is. That is to say, the larger the output requested by the engine 1 is, the more the reference pressure on the second provisional fuel pressure line is reduced, and the lower the target fuel pressure is set.
[0112] Furthermore, the fuel injection pressure at the output region where smoke is addressed, which is roughly an output region, of the possible output regions of the internal combustion engine 1, where the output requested by the engine 1 is intermediate, is determined by correctively increasing the reference pressure on the second provisional fuel pressure line. The amount by which the reference pressure on the second provisional fuel pressure line is correctively increased is set to become smaller towards the output region where the combustion noise is addressed and towards the output region where the NOx is addressed, so that continuity of the fuel pressure line (continuity between the output region where combustion noise is addressed and the output region where smoke is addressed, and continuity between the output region where NOx is addressed and the output region where smoke is addressed) can be ensured.
[0113] The following effects can be achieved by setting the fuel pressure line in this manner and setting the target fuel pressure accordingly.
[0114] Since the fuel injection pressure is correctively decreased in the output region where combustion noise is addressed, the combustion noise in the combustion chamber 3 can be suppressed to a low level in situations where the output of the engine 1 is relatively low, and the quietness of the engine 1 can be improved.
[0115] Moreover, since the fuel injection pressure is correctively decreased in the output region where NOx is addressed, the combustion speed in the combustion chamber 3 can be suppressed to a low level in situations where the output of the engine 1 is relatively high, and the amount of NOx generated with the combustion in the cylinder can be reduced considerably. Also, the requested output reaching the upper limit of the target fuel pressure (maximum rail pressure) can be shifted towards the high output side.
[0116] Moreover, since the fuel injection pressure is correctively increased in the output region where smoke is addressed, the fuel injection amount per unit time can be increased, even when the main injection is implemented by a plurality of partial injections, for example accompanying an increase in EGR, and a shortening of the injection period can be accomplished, so that it is possible to overcome the deterioration of efficiency that accompanies a lengthening of the injection period.
- Other Embodiments -
[0117] The above-described embodiments were explained for the case that the present invention is applied to an inline four-cylinder diesel engine mounted in an automobile. However, the present invention is not limited to use in automobiles, and can also be applied to engines utilized for other uses. Moreover, there is no particular limitation concerning the number of cylinders or the engine type (in-line engine, V-type engine, etc.)
[0118] Moreover, in the above-described embodiments, an NSR catalyst 75 and a DPNR catalyst 76 were provided as the maniverter 77, but it is also possible to provide an NSR catalyst 75 and a DPF (diesel particulate fitter).
[0119] Moreover, in the above-described embodiments, the lines of equal fuel injection pressure are allocated to the lines of equal power across the entire engine operation region. However, the present invention is not limited to this, and it is also possible to provide a region where the lines of equal fuel injection pressure do not match the lines of equal power, in a portion of the engine operation region (for example near the maximum torque line Tmax).
[0120] Moreover, in the above-described embodiments, the provisional fuel pressure line (the broken line in Fig. 5) and the first provisional fuel pressure line (the dash-dotted line in Fig. 8) are straight lines, and the requested outputs and the target fuel pressures are proportional on this line, but it is also possible to set the provisional fuel pressure line and the first provisional fuel pressure line as curves (quadratic curves), as shown by the dash-dot-dot lines in Fig. 5 and Fig. 8. However, also in this case, it is necessary that the target fuel pressure can be decided unambiguously from the requested output.
[Industrial Applicability]
[0121] The present invention can be applied to the control of the fuel injection pressure in common-rail in-cylinder direct injection multi-cylinder diesel engines mounted in automobiles.
[Reference Signs List]
1. A fuel injection pressure control apparatus for an internal combustion engine, which
controls a pressure of fuel that is injected into a cylinder of an internal combustion
engine of the compression ignition type,
wherein a fuel injection pressure is adjusted in accordance with an output requested by the internal combustion engine by allocating in advance, across substantially the entire region in which the internal combustion engine can be operated, a region of equal fuel injection pressure to a region of equal power requested by the internal combustion engine.
wherein a fuel injection pressure is adjusted in accordance with an output requested by the internal combustion engine by allocating in advance, across substantially the entire region in which the internal combustion engine can be operated, a region of equal fuel injection pressure to a region of equal power requested by the internal combustion engine.
2. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 1,
wherein the region of equal fuel injection pressure is allocated to the region of equal power of the internal combustion engine, such that the fuel injection pressure does not change if an output that is determined from a revolution and a torque of the internal combustion engine does not change even though the revolution and the torque of the internal combustion engine have changed.
wherein the region of equal fuel injection pressure is allocated to the region of equal power of the internal combustion engine, such that the fuel injection pressure does not change if an output that is determined from a revolution and a torque of the internal combustion engine does not change even though the revolution and the torque of the internal combustion engine have changed.
3. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 1 or 2,
wherein the fuel injection pressure that is allocated is higher the higher the output requested by the internal combustion engine is.
wherein the fuel injection pressure that is allocated is higher the higher the output requested by the internal combustion engine is.
4. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 1, 2 or 3,
wherein a fuel injection pressure region is set where the fuel injection pressure increases in any of the cases that both revolution and torque of the internal combustion engine increase, that torque increases at constant revolution of the internal combustion engine, and that revolution increases at constant torque of the internal combustion engine.
wherein a fuel injection pressure region is set where the fuel injection pressure increases in any of the cases that both revolution and torque of the internal combustion engine increase, that torque increases at constant revolution of the internal combustion engine, and that revolution increases at constant torque of the internal combustion engine.
5. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 4,
wherein a proportion of a change of the fuel injection pressure with respect to a change of the output requested by the internal combustion engine is set to become smaller the lower the revolution of the internal combustion engine becomes.
wherein a proportion of a change of the fuel injection pressure with respect to a change of the output requested by the internal combustion engine is set to become smaller the lower the revolution of the internal combustion engine becomes.
6. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 5,
wherein the fuel injection pressure is adjusted in accordance with a fuel pressure setting map where lines of equal output and lines of equal fuel injection pressure drawn within a map where a horizontal axis denotes revolution of the internal combustion engine and a vertical axis denotes torque of the internal combustion engine substantially match across substantially the entire region in which the internal combustion engine can be operated.
wherein the fuel injection pressure is adjusted in accordance with a fuel pressure setting map where lines of equal output and lines of equal fuel injection pressure drawn within a map where a horizontal axis denotes revolution of the internal combustion engine and a vertical axis denotes torque of the internal combustion engine substantially match across substantially the entire region in which the internal combustion engine can be operated.
7. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 6,
wherein the fuel injection pressure is proportional, with a predetermined proportionality constant, to the output requested by the internal combustion engine, and the fuel injection pressure is determined by adding a predetermined pressure offset to a provisional fuel injection pressure obtained by multiplying this requested output with the proportionality constant.
wherein the fuel injection pressure is proportional, with a predetermined proportionality constant, to the output requested by the internal combustion engine, and the fuel injection pressure is determined by adding a predetermined pressure offset to a provisional fuel injection pressure obtained by multiplying this requested output with the proportionality constant.
8. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 7,
wherein the pressure offset is set such that a heat generation rate reaches a local maximum at a time when a crank angle has reached about 10° after compression top dead center, if the fuel of a main injection that is injected by a fuel injection valve starts to combust at a time when a piston of the internal combustion engine has reached compression top dead center.
wherein the pressure offset is set such that a heat generation rate reaches a local maximum at a time when a crank angle has reached about 10° after compression top dead center, if the fuel of a main injection that is injected by a fuel injection valve starts to combust at a time when a piston of the internal combustion engine has reached compression top dead center.
9. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 6,
wherein a fuel injection pressure at an output region where combustion noise is addressed, which is an output region where the output requested by the internal combustion engine is relatively low, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
wherein a fuel injection pressure at an output region where combustion noise is addressed, which is an output region where the output requested by the internal combustion engine is relatively low, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
10. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 9,
wherein the fuel injection pressure is determined by setting the amount by which the reference pressure is correctively decreased in the output region where combustion noise is addressed to become larger the smaller the output requested by the internal combustion engine becomes.
wherein the fuel injection pressure is determined by setting the amount by which the reference pressure is correctively decreased in the output region where combustion noise is addressed to become larger the smaller the output requested by the internal combustion engine becomes.
11. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 6,
wherein a fuel injection pressure at an output region where NOx is addressed, which is an output region where the output requested by the internal combustion engine is relatively high, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
wherein a fuel injection pressure at an output region where NOx is addressed, which is an output region where the output requested by the internal combustion engine is relatively high, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively decreasing this reference pressure.
12. The fuel injection pressure control apparatus for an internal combustion engine according
to claim 11,
wherein the fuel injection pressure is determined by setting the amount by which the reference pressure is correctively decreased in the output region where NOx is addressed to become larger the larger the output requested by the internal combustion engine becomes.
wherein the fuel injection pressure is determined by setting the amount by which the reference pressure is correctively decreased in the output region where NOx is addressed to become larger the larger the output requested by the internal combustion engine becomes.
13. The fuel injection pressure control apparatus for an internal combustion engine according
to any of claims 1 to 6,
wherein a fuel injection pressure at an output region where smoke is addressed, which is an output region, of the possible output regions of the internal combustion engine, where the output requested by the internal combustion engine is substantially intermediate, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively increasing this reference pressure.
wherein a fuel injection pressure at an output region where smoke is addressed, which is an output region, of the possible output regions of the internal combustion engine, where the output requested by the internal combustion engine is substantially intermediate, is determined by determining a reference pressure by adding a predetermined pressure basic offset to a provisional fuel injection pressure determined by multiplying a predetermined proportionality constant to the output requested by the internal combustion engine, and then correctively increasing this reference pressure.
REFERENCES CITED IN THE DESCRIPTION
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.
Patent documents cited in the description