Exhaust gas purifying apparatus for an internal combustion engine with a supercharger

Abstract

 An exhaust gas purifying apparatus for an internal combustion engine with a turbocharger is provided with an introduction port for EGR gas disposed upstream of a compressor and a throttle valve disposed upstream of the introduction port, and comprised of a fail safe means that the portion on the upstream side of the compressor does not have any excessive negative pressure even if a malfunction occurs in the throttle valve. The exhaust gas purifying apparatus for an internal combustion engine with a turbocharger is provided with a supercharger (6) having a turbine (6b) disposed in an exhaust passage (16) and a compressor (6a) disposed in an intake passage (3) and having an exhaust gas recirculation system (23,24 and 25) for connecting the exhaust passage (16) downstream of the turbine (6b) and the intake passage (3) with each other and for recirculating a part of exhaust gas back to an intake system of the internal combustion engine, wherein an introduction port for recirculating the part of the exhaust gas and a throttle valve (20) for opening/closing the intake passage (3) as desired are arranged in this order. A fail safe unit (21) for allowing a predetermined flow rate of intake air to flow to the compressor (6a) and giving a load, when the throttle valve (20) is fully closed, is provided in the intake passage (3) upstream of the compressor (6a).

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine with a supercharger, which is provided with the supercharger having a turbine disposed in an exhaust passage and a compressor disposed in an intake passage and an exhaust gas recirculation system for connecting the exhaust passage downstream of the turbine and the intake passage with each other and recirculating a part of exhaust gas to an intake system of the internal combustion engine.

Description of the Prior Art

[0002] In an exhaust system of some internal combustion engines, a particulate filter carrying catalyst (hereinafter simply referred to as a catalyst filter) or an exhaust gas recirculation system (hereinafter simply referred to as an EGR) is provided as a means for reducing an amount of NOx of exhaust gas.

[0003] Then, the catalyst filter is used for purifying the generated NOx before being discharged to the atmosphere by using a lean NOx catalyst such as a storage-reduction type NOx catalyst or a selective reduction type NOx catalyst.

[0004] Also, the EGR serves to return a part of the exhaust gas through an exhaust gas recirculation pipe (EGR pipe) back to an intake system to introduce inert gas to increase a heat capacitance of gas within a combustion chamber so as to lower a maximum combustion temperature, thereby reducing the generation of NOx. This is not a technology for purifying the NOx before being discharged to the atmosphere like a catalyst filter but a technology for suppressing the generation of NOx itself.

[0005] Also, in some cases, a turbocharger is disposed as a supercharger in the exhaust system of the internal combustion engine. In this turbocharger, the exhaust gas is introduced into a turbine of the turbocharger to drive the turbine. Then, a compressor coupled with this turbine is driven to pressurize the air introduced into the intake system of the internal combustion engine so as to increase the output.

[0006] By the way, in general, the EGR has a structure in which a start end of the EGR pipe is connected directly to an exhaust manifold. However, in this structure, a part of the exhaust gas to be introduced from the exhaust manifold to the turbine is returned back to the intake system through the EGR pipe and the exhaust gas flowing through the intake pipe is not fed to the side at which the turbine is driven. Accordingly, in some cases, it is impossible to obtain a sufficient driving force for the turbine and it is impossible to obtain the sufficient increase of the intake gas by the compressor.

[0007] Therefore, in some attempts, the start end of the EGR pipe is not connected directly to the exhaust manifold but is provided at the exhaust pipe on the downstream side of the turbine and an introduction port that is a terminal end of the EGR pipe is arranged on the upstream side of the compressor (see Japanese Patent Application Laid-open No. Hei 6-257518)

[0008] In these attempts, the start end of the EGR pipe is provided at the exhaust pipe on the downstream side of the turbine so that all the exhaust gas from the exhaust manifold is introduced into the turbine to make it possible to obtain the sufficient driving force for the turbine. Also, it is advantageous that the introduction port of the EGR pipe is disposed on the upstream side of the compressor, so that not only fresh air but also the exhaust gas to be re-introduced may be pressurized and fed into the intake system as the mixture gas by the rotation of the compressor.

[0009] However, according to the invention disclosed in Japanese Patent Application Laid-open No. Hei 6-257518, a flow rate of the exhaust gas recirculation introduced into the intake system is adjusted by an opening/closing control of an EGR valve but the fresh air is fed from the air cleaner side without any restriction. There is no attempt to adjust the flow rate of the fresh air. Namely, there is no attempt to suitably adjust a ratio of the mixture gas between the fresh air and the exhaust gas recirculation gas out of the intake gas to be introduced into the intake system in response to the operational condition.

[0010] Therefore, it is possible to propose a structure in which a throttle valve is provided between the introduction port of the EGR pipe and the side of the air cleaner into which the fresh air is to be introduced to thereby suitably adjust the mixture ratio of the intake gas to be introduced into the intake system in response to the operational condition.

[0011] However, if the throttle valve is provided in the intake passage on the upstream side of the compressor, in the case where the throttle valve is kept fully closed due to some malfunction, the following disadvantages are noticed. Namely, when the throttle valve on the upstream side of the compressor would be kept fully closed, the intake passage in the vicinity of the compressor would be kept under an excessive negative pressure condition (close to the real vacuum). Then, the turbine coupled with the compressor is rotated while receiving the exhaust gas pressure whereas the compressor is rotated without any resistance while not performing the pressurizing work. As a result, the turbocharger becomes too much rotated. For this reason, there is a possibility that the malfunction of the throttle valve would result in the damage of a bearing for the turbocharger.

STATEMENT OF THE INVENTION

[0012] The present invention has been made in view of the above, and an object of the present invention is therefore to provide an exhaust gas purifying apparatus for an internal combustion engine with a supercharger in which an introduction port for EGR gas is provided on the upstream side of a compressor and a throttle valve for adjusting a mixture ratio of the EGR gas and fresh air is disposed on the upstream side of the EGR gas introduction port, the exhaust gas purifying apparatus comprising a fail safe means in which, even if a malfunction occurs in the throttle valve, the portion on the upstream side of the compressor does not have any excessive negative pressure.

[0013] In order to attain this and other objects, the exhaust gas purifying apparatus for an internal combustion engine with a supercharger has the following features:

[0014] According to the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine with a supercharger, comprising a supercharger having a turbine disposed in an exhaust passage and a compressor disposed in an intake passage and an exhaust gas recirculation system for connecting the exhaust passage downstream of the turbine and the intake passage with each other and for recirculating a part of exhaust gas back to an intake system of the internal combustion engine, in which an introduction port for recirculating the part of the exhaust gas and a throttle valve for opening/closing the intake passage as desired are arranged in this order in the intake passage upstream of the compressor, wherein, a fail safe means for allowing a predetermined flow rate of intake air to flow to the compressor and giving a negative pressure when the throttle valve is fully closed is provided in the intake passage upstream of the compressor.

[0015] With such a structure, the throttle valve is provided between the side of the air cleaner into which fresh air is to be introduced and the introduction port for recirculating the part of the exhaust gas and the throttle valve is controlled to be opened by means of electronic controlling unit (ECU) for controlling an engine whereby the mixture ratio of the suction mixture gas to be introduced into the intake system may be suitably adjusted in response to the operational condition. Also, even if the throttle valve is fully closed due to the malfunction, the fail safe means allows the predetermined flow rate of intake air to flow to the compressor and gives the negative pressure to avoid the excessive negative pressure of the intake passage. It is therefore possible to avoid the non-resistance rotation of the compressor and the excessive rotation of the supercharger.

[0016] The "excessive negative pressure condition" referred here means the condition that the compressor is rotated without any resistance not to be pressurized. In this case, the turbine coupled with the compressor becomes excessively rotated by receiving only the exhaust gas pressure so as to lead to the defects such as sticking of bearings. The condition of "allowing the predetermined flow rate of intake air to flow to the compressor and giving the negative pressure" means the condition of giving the intake resistance to ensure an number of engine rotation such an extent that the supercharger is not broken out, to the intake passage upstream of the compressor the intake.

[0017] Also, in the exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to the present invention, it is possible to exemplify the case where the fail safe means is an opening degree regulating means for regulating an opening/closing angle of the throttle valve upon fully closed operation to a predetermined opening angle. In this case, even in the fully closed condition, the throttle valve is regulated to the condition that the valve is opened at the predetermined opening angle by the opening degree regulating means. A minimum flow rate of intake air is introduced through the opening portion to ensure the intake air resistance to an extent that the supercharger is not broken down, and to prevent the excessive rotation of the supercharger.

[0018] The "opening degree regulating means" referred here means a means for keeping a minimum opening limiter of the throttle valve in the condition of a minimum opening degree (predetermined angle) such that the supercharger is not excessively rotated and is adapted to give the intake air flow The "minimum opening degree" means a valve opening degree such that the intake air resistance is given to the compressor so that the abnormality such as sticking of the supercharger would not occur and the intake air for keeping the allowed number of engine rotation may be introduced.

[0019] Furthermore, in the exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to the present invention, it is possible to take the structure in which a control valve that is controlled to be fully closed in starting or stopping of the internal combustion engine is provided in the intake passage downstream of the compressor. Incidentally, the "fully closed control" means a control of, when a diesel engine having a high compression ratio is started or stopped, throttling the control valve to reduce the air to be introduced into the combustion chamber so as to reduce the compression ratio of the internal combustion engine to facilitate the rotation to suppress the vibration. Namely, if the control valve is closed, the pressure within the combustion chamber in the initial stage of the compression is decreased so that the compression pressure is decreased. When the compression pressure is reduced, the compression work by the piston is reduced resulting in the reduction in vibration of the internal combustion engine. Accordingly, with such a structure with the control valve, it is possible to suppress the-vibration and noise in addition to the fail safe effect to keep the intake air on the upstream side of the compressor.

[0020] Moreover, in the exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to the present invention, it is possible to take the structure in which the opening/closing operations of the throttle valve and the control valve are kept in the same operational mode. Since the opening/closing timing of the throttle valve and the control valve are operated in relation to a demanded load (acceleration step-in amount) of the internal combustion engine, with the structure in the same operational mode of the opening/closing operation, it is possible to commonly use a control command signal of the opening/closing operation outputted from the electronic controlling unit (ECU) for controlling an engine and to commonly use an operating actuator for opening/closing the throttle valve and the control valve on the basis of the control command signal.

[0021] Furthermore, in the exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to the present invention, it is possible to exemplify the case in which the fail safe means comprises a bypass passage for allowing the predetermined flow rate of intake air to flow bypassing the throttle valve. In this case, a minimum flow rate of intake air is introduced through the bypass passage to ensure the intake air resistance to an extent that the supercharger is not broken down, and to prevent the excessive rotation of the supercharger.

DESCRIPTION OF THE DRAWINGS

[0022] The object and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic view showing an internal combustion engine in accordance with a first embodiment to which an exhaust gas purifying apparatus for an internal combustion engine with a supercharger, according to the present invention, is applied;

Fig. 2 is an enlarged view of a throttle valve and an opening degree regulating means;

Fig. 3 is a graph showing a relationship among an open condition of the throttle valve, an EGR rate, generation amounts of NOx and the like;

Fig. 4 is a graph showing a relationship between a fuel injection amount and a mixture gas amount;

Figs. 5A and 5B are views showing maps of target opening degrees of the throttle valve and an EGR valve, Fig. 5A being directed to the map representative of the target opening degree of the throttle valve and Fig. 5B being directed to the map representative of the target opening degree of the EGR valve;

Fig. 6 is a graph showing a relationship between the opening conditions of the throttle valve, the EGR valve, the generation amounts of NOx and the like;

Fig. 7 is a schematic view showing an internal combustion engine in accordance with a second embodiment to which an exhaust gas purifying apparatus for an internal combustion engine with a supercharger, according to the present invention, is applied;

Fig. 8 is an enlarged view of a control valve;

Fig. 9 is a schematic view showing an internal combustion engine in accordance with a third embodiment to which an exhaust gas purifying apparatus for an internal combustion engine with a supercharger, according to the present invention, is applied; and

Fig. 10 is an enlarged view of a throttle valve and a fail safe means in accordance with a fourth embodiment.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0023] An exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Incidentally, the embodiments that will be described are examples where the present invention is applied to a diesel engine for driving an automotive vehicle as an internal combustion engine.

Embodiment 1

[0024] An exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with a first embodiment will now be described with reference to Figs. 1 to 6.

[0025] An engine 1 is a linear four-cylinder diesel engine as shown in the overall view of Fig. 1. Intake air is introduced through an intake manifold 2 and an intake pipe 3 into a combustion chamber of each cylinder. An air cleaner 4 is provided at a start end of the intake pipe 3. Disposed in the midway of the intake pipe 3 are an air flow meter 5, a throttle valve 20, a compressor 6a of a turbocharger (supercharger) 6 and an inter cooler 7.

[0026] The air flow meter 5 outputs an output signal in correspondence with the air amount of fresh air, which is to be introduced through the air cleaner 4 to the intake pipe 3, to an electronic controlling unit for controlling engine(ECU) 9. The ECU 9 calculates the flow rate of the mixture gas to be introduced into an intake system on the basis of the output signal of the air flow meter 5.

[0027] The inter cooler 7 is a device disposed around the intake pipe 3 between the intake manifold 2 and the turbocharger 6 for cooling down the mixture gas flowing through the intake pipe 3. The running air blow is introduced to the inter cooler 7. The mixture gas is cooled down by means of the running air blow.

[0028] Further, fuel (light oil) is injected from a fuel injection valve 10 into the combustion chamber of each cylinder of the engine 1. The fuel is pumped up from a fuel tank(not shown) by means of a fuel pump 12 and fed to the fuel injection valve 10 through a common rail 11. Incidentally, the fuel pump 12 is driven by means of a crankshaft (not shown) of the engine 1. A valve opening timing and a valve opening period of each fuel injection valve 10 are controlled in response to the operational condition of the engine to be described later by means of the ECU 9.

[0029] Further, the exhaust gas generated in the combustion chamber of each cylinder of the engine 1 is discharged from an exhaust port 13 of each cylinder to an exhaust manifold 14. The exhaust manifold 14 is connected to an exhaust gas gathering pipe 15 for introducing the exhaust gas to a turbine 6b of the turbocharger 6. The turbine 6b is driven by the exhaust gas to drive the compressor 6a coupled with the turbine 6b so as to pressurize the intake air.

[0030] The exhaust gas is discharged from the turbine 6b to an exhaust pipe 16 and discharged through a muffler (not shown) to the atmosphere. A casing 18 having a particulate filter (hereinafter referred to as a catalyst filter) 17 carrying catalyst is provided in the midway of the exhaust pipe 16.

[0031] The catalyst filter 17 is used for purifying the generated NOx before being discharged to the atmosphere by means of a lean NOx catalyst such as an storage-reduction type NOx catalyst or a selective reduction type NOx catalyst.

[0032] In this catalyst filter 17, for example, an alumina (Al₂O₃) is used as a carrier, and at least one selected from, for example, alkaline metal such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earth such as barium Ba and calcium Ca, and rare-earth such as lanthanum La and yttrium Y is carried on the carrier and noble metal such as platinum Pt is also carried on the carrier.

[0033] The catalyst filter 17 absorbs NOx when an air/fuel ratio of the flowing-in exhaust gas (hereinafter simply referred to as an exhaust gas air/fuel ratio) is leaner than a stoichiometric air/fuel ratio, and effects the absorption discharging effect of NOx for discharging the absorbed NOx in the form of NO₂ or NO when the exhaust gas air/fuel ratio is equal to or richer than the stoichiometric air/fuel ratio to decrease the oxygen concentration in the flowing-in exhaust gas. Then, the NOx (NO₂ or NO) discharged from the catalyst filter 17 immediately reacts with unburned HC or CO in the exhaust gas to be reduced to N₂. Accordingly, it is possible to purify HC, CO and NOx contained in the exhaust gas if the exhaust gas air/fuel ratio is suitably controlled.

[0034] Incidentally, the exhaust gas air/fuel ratio means a ratio of the sum of the fuel (hydrocarbon) amount to the sum of the air amount fed to the exhaust passage on the upstream side of the catalyst filter 17, the engine combustion chambers, the intake passage and the like, respectively. Accordingly, in the case where the fuel or air is not fed into the exhaust passage upstream of the catalyst filter 17, the exhaust gas air/fuel ratio is identified with the air/fuel ratio of the mixture gas to be fed into the engine combustion chambers.

[0035] One end of an exhaust gas recirculation pipe (hereafter simply referred to as an EGR pipe) 23 for returning a part of the exhaust gas back to the intake system is connected to the exhaust pipe 16 downstream of the catalyst filter 17. The other end of the EGR pipe 23 (EGR introduction port 23a) is connected to the intake pipe 3 upstream of the compressor 6a. An EGR cooler 24 and an EGR valve 25 are provided in the midway of the EGR pipe 23. Thus, the exhaust gas recirculation system (EGR) is constituted of the EGR pipe 23, the EGR cooler 24 and the EGR valve 25.

[0036] This EGR is adapted to reduce the generation of NOx by returning the part of the exhaust gas through the EGR pipe 23 back to the intake system, introducing the inert gas to thereby increase the heat capacitance of the combustion chamber gas and lowering the maximum combustion temperature. This is the technology that is not to purify the NOx before being discharged to the atmosphere like the catalyst filter 17 but to control the generation of the NOx per se.

[0037] Then, the EGR cooler 24 is a device disposed around the EGR pipe 23 for cooling EGR gas (exhaust gas) flowing through the EGR pipe 23. The engine cooling water is led to the EGR cooler 24 to cool the exhaust gas down.

[0038] The EGR valve 25 is a device for adjusting the recirculation amount of the exhaust gas to be fed back to the intake system. The EGR valve opening degree is controlled in response to the operational condition of the engine 1 by means of the ECU 9 to be described later.

[0039] The throttle valve 20 is provided in the intake pipe 3 on the upstream side of the compressor 6a, and more specifically, is provided in the intake pipe 3 between the air cleaner 4 and the EGR introduction port 23a. This throttle valve 20 is connected to the ECU 9 through a vacuum regulated valve (VRV; negative pressure regulative valve). The throttle valve 20 is adapted to adjust a ratio of the mixture gas between the intake amount of fresh air and the exhaust gas recirculation flow rate while the opening degree of the throttle valve is being controlled by the ECU 9 in response to the operational condition of the engine 1 as will be described later. The VRV 28 perform the duty control of the vacuum value set in the throttle valve 20 by means of the negative pressure generated by a vacuum pump separately provided. It is thus possible to change the negative pressure for operating the throttle valve 20 as desired, thereby controlling the opening degree of the throttle valve 20 on the basis of the command of the ECU 9.

[0040] As shown in Fig. 2, the throttle valve 20 is regulated such that the opening/closing angle is opened at a predetermined angle α upon the fully closed operation by means of an opening degree regulating means 21. In other words, this opening regulating means 21 means a minimum opening degree limiter for regulating the opening/closing angle of the throttle valve 20 at the minimum opening degree (predetermined angle α) even if the throttle valve 20 is kept in the fully closed condition.

[0041] Namely, the opening degree regulating means 21 includes a slant hole 3a obliquely formed in the intake pipe 3, a nut portion 21a fixed to the outside of the intake pipe 3 coaxially with the slant hole 3a, and a screw rod 21b threadedly engaged with the nut portion 21a and inserted into the slant hole 3a with its top portion being projecting inwardly from the inner wall of the intake pipe 3. Then, the valve is retained at the top portion of the screw rod 21b even if the throttle valve 20 is kept in the fully closed condition. The throttle valve 20 is regulated so as to be open at the predetermined angle α. Incidentally, a length of the projection of the top portion of the screw rod 21b from the inner wall of the intake pipe 3 is adjustable in consideration of the threaded relation with the nut portion 21a. Also, the space between the slant hole 3a and the nut portion 21a and the screw rod 21b is sealed so that the gas within the intake pipe 3 is not leaked to the outside of the opening degree regulating means 21.

[0042] The predetermined angle α means the minimum opening degree at which the intake air may be always introduced to the side of the compressor 6a. The introduction of the intake air imparts the load to the compressor 6a (that is, obtaining the more positive pressure imparts the work to the compressor 6a) so as to ensure the number of engine rotation that the abnormality such as sticking of bearings of the turbocharger 6 may be prevented. This predetermined angle α is determined on the basis of the experimental results. The projecting/retracting position of the top portion of the screw rod 21b is adjusted such that the angle of the valve upon the fully closed condition is at the predetermined angle α.

[0043] The ECU 9 consists of a digital computer and is provided a ROM (read only memory), a RAM (random access memory), a CPU (central processing unit), an input port and an output port that are connected to each other through bidirectional bus for controlling the opening degrees of the EGR valve 25 and the throttle valve 20 and the basic control such as a fuel injection amount control of the engine 1.

I. Fuel Infection Amount Control

[0044] For the fuel injection amount control, an input signal from an acceleration opening degree sensor 26, an input signal from a crank angle sensor 27 and an input signal from the air flow meter 5 are inputted into the input port of the ECU 9.

[0045] The acceleration opening degree sensor 26 outputs an output voltage in proportion to the opening degree of the throttle valve 20 to the ECU 9. The ECU 9 calculates the engine load on the basis of the input signal of the acceleration opening degree sensor 26. Also, the crank angle sensor 27 outputs the output pulse to the ECU 9 whenever the crankshaft rotates at a predetermined angle. The ECU 9 calculates the number of engine rotation on the basis of the output pulse. Then, the engine condition is determined according to these engine load and the number of engine rotation. The ECU 9 controls the valve opening timing and valve opening period of the fuel injection valve 10 in response to the engine condition.

[0046] For instance, in the fuel injection valve control, the ECU 9 determines the fuel amount to be injected from the fuel injection valve 10 and subsequently determines the timing when the fuel is injected from the fuel injection valve 10. In the case where the fuel injection amount is to be determined, the ECU 9 reads out the output signal (acceleration opening degree) of the acceleration opening degree sensor 26 and the number of engine rotation stored in the RAM. For example, the ECU 9 accesses a map for controlling the fuel injection amount and calculates the basic fuel injection amount (basic fuel injection period) in correspondence with the acceleration opening degree and the number of engine rotation. The ECU 9 compensates for the basic fuel injection period on the basis of data such as an intake temperature or an output signal value of the air flow meter 5 and determines the final fuel injection period.

[0047] When the fuel injection period and the fuel injection timing are determined, for instance, the ECU 9 compares the fuel injection timing with the output signal of the crank angle sensor 27 and starts the application of the driving power to the fuel injection valve 10 at the time the output signal of the crank angle sensor 27 is identified with the fuel injection timing. The ECU 9 stops the application of the driving power to the fuel injection valve 10 at a point in time when the lapse from the time of the start of the application of the driving power to the fuel injection valve 10 reaches the fuel injection period.

[0048] Subsequently, in the fuel pump control, the ECU 9 reads out the acceleration opening degree and the number of engine rotation stored in, for example, the RAM. The ECU 9 accesses the map for controlling the common rail pressure and calculates the target pressure corresponding to the opening degree and the number of engine rotation. Subsequently, the ECU 9 accesses the map for controlling the fuel outlet pressure, calculates the outlet pressure of the fuel pump 12 in correspondence with the target pressure and controls the fuel pump 12 to obtain the outlet pressure.

II. Opening Degree Control of Throttle Valve 20 and EGR Valve 25

[0049] How a discharge amounts of NOx, CO, HC and smoke and an output torque change in response to a change of the air/fuel ratio A/F (abscissa in Fig. 3),when the opening degree of the throttle valve 20 and the EGR valve 25 are controlled, will now be described with reference to the experimental example upon the engine low load operation shown in Fig. 3.

[0050] In Fig. 3, when the EGR rate is about 40% and the air/fuel ratio A/F is about 30, the smoke starts to generate. In this case, when the EGR rate is increased and the air/fuel ratio A/F is decreased, the smoke is rapidly decreased. Then, when the EGR rate is equal to or more than 65% and the air/fuel ratio A/F is close to 15.0, the smoke becomes substantially zero. That is, particulate is hardly generated. In this case, the output torque of the engine is somewhat lowered, and the amount of the generated NOx is rather low. In contrast, the generation amounts of HC and CO start to increase.

[0051] Accordingly, from the experimental result of Fig. 3, it is safe to say the following. Namely, first of all, when the air/fuel ratio A/F is equal to or less than 15.0 and the generation amount of the smoke is kept substantially at zero, the generation amount of NOx is rather lowered. The fact that the generation amount of the NOx is lowered means the decrease of the temperature within the combustion chamber. Accordingly, it is safe to say that the temperature of the combustion chamber is lowered when almost no fine particulate is generated.

[0052] Secondly, when the generation amount of the smoke, i.e., when the generation amount of particulate is substantially zero, as shown in Fig. 3, the discharge amounts of HC and CO are increased. This means that the hydrocarbon HC does not grow up to be particulate but is discharged.

[0053] Summing up these analyses on the basis of the experimental results, when the temperature within the combustion chamber is low, the generation rate of particulate is substantially zero and at this time, the hydrocarbon is discharged from the combustion chamber.

[0054] Namely, in the case where fuel is present in the mixture gas of the large amount of inert gas and the small amount of air, a evaporated fuel is diffused to the ambient and reacts with oxygen mixed in the inert gas to be burnt. In this case, since the combustion heat is absorbed to the ambient inert gas, the combustion temperature is not so elevated. Namely, it is possible to suppress the combustion temperature to a lower level.

[0055] In this case, in order to keep the combustion temperature and the gas temperature lower than the temperature at which the particulate is generated, it is necessary to provide the inert gas to be absorbable a sufficient heat capacitance. Accordingly, if the fuel amount is increased, the amount of necessary inert gas is also increased in accordance therewith. Incidentally, in this case, the larger a specific heat of the inert gas, the stronger a heat absorption effect will become. It is therefore preferable to use the inert gas having a large specific heat. In this connection, since CO₂ or EGR gas has a relatively large specific heat, it is safe to say that CO₂ or EGR gas is preferably used as the inert gas.

[0056] In the case the EGR gas is used as the inert gas, the amount of the mixture gas of the EGR gas and the air needed for keeping the temperature of the fuel upon combustion and the ambient gas thereof lower than the temperature at which the particulate is generated, the ratio of the air in the mixture gas, and the ratio of the EGR gas contained in the mixture gas will now be described with reference to Fig. 4.

[0057] Incidentally, in Fig. 4, the ordinate shows the entire intake gas amount sucked in the combustion chamber, and the one-dot-and-dash line Y indicates an entire intake gas amount that may enter the combustion chamber when no supercharge is effected. Also, the abscissa shows the demanded load, and Z1 indicates the low load operational region. Furthermore, the ratio of air (air amount in the mixture gas) shows the necessary air amount for the complete combustion of the injected fuel. Namely, the ratio between the air amount and the fuel injection amount becomes a stoichiometric air/fuel ratio. Moreover, the ratio of the EGR gas (EGR gas amount in the mixture gas) shows the necessary and minimum EGR gas amount for keeping the temperature of the fuel and the ambient gas lower than the temperature at which the particulate is generated when the injected fuel is burnt. The EGR gas amount is expressed as substantially 70% or more in terms of the EGR rate.

[0058] Namely, assuming that the entire intake gas amount sucked into the combustion chamber is expressed by the solid line X in Fig. 4 and the ratio between the EGR gas amount and the air amount in the entire intake gas amount X is one as shown in Fig. 4, the temperature of the fuel and the ambient gas temperature are lower than the temperature at which the fine particulate is generated. No particulate is generated at all. Also, at this time, the generation amount NOx is about 10 p.p.m. or less. Accordingly, the NOx generation amount is very small.

[0059] If the fuel injection amount is increased, the heat capacitance when the fuel is burnt is increased. Accordingly, in order to keep the temperature of the fuel and the ambient gas lower than the temperature at which the particulate is generated, it is necessary to increase the heat absorption amount by means of the EGR gas. Accordingly, as the fuel injection amount is increased, the EGR gas amount must be increased. Namely, as the demanded load is increased, the EGR gas amount must be increased.

[0060] On the other hand, in a load region Z2 in Fig. 4, the necessary entire intake gas amount X for preventing the generation of particulate exceeds the entire intake gas amount Y that may be sucked. Accordingly, in this case, in order to feed into the combustion chamber the necessary entire intake gas amount X for preventing the generation of particulate, it is necessary to supercharge and/or pressurize both the intake air and the EGR gas or only the EGR gas. In the case where the EGR gas or the like is neither supercharged nor pressurized, in the load region Z2, the entire intake gas amount X is identified with the entire intake gas amount Y that may be sucked. Accordingly, in this case, in order to prevent the particulate from generating, the air amount is somewhat decreased so as to increase the EGR gas amount and at the same time, the fuel is burnt at a rich air/fuel ratio.

[0061] Fig. 4 shows a case where the combustion is attained at the stoichiometric air/fuel ratio. Even if in the low load operational region Z1, the air amount is smaller than that shown in Fig. 4, i.e., the air/fuel ratio is kept rich, it is possible to reduce the generation amount of NOx to about 10 p.p.m. or less while preventing the generation of the particulate. Also, even if the air amount is increased more than that shown in Fig. 4, i.e., the average of the air/fuel ratio is kept lean at 17 to 18, it is possible to reduce the generation amount of NOx to about 10 p.p.m. or less while preventing the generation of the particulate.

[0062] Namely, when the air/fuel ratio is enriched, the fuel would be excessive but the combustion temperature is suppressed to a lower temperature. Thus, the excessive fuel does not grow to be the particulate and the particulate is not generated. Also, in this case, the amount of NOx generation is very small. On the other hand, even if the average air/fuel ratio is lean, or the air/fuel ratio is at the stoichiometric air/fuel ratio, if the combustion temperature is elevated, the small amount of the particulate is generated but the particulate is not generated at all because the combustion temperature is suppressed to a lower temperature. Furthermore, only a small amount of NOx is generated. Thus, in the engine low load operational region Z1, irrespective of the air/fuel ratio, i.e., even if the air/fuel ratio is rich or at the stoichiometric air/fuel ratio, or the average air/fuel ratio is lean, the particulate is not generated and a very small amount of NOx is generated. Accordingly, it is safe to say that it is preferable to lean the average air/fuel ratio in consideration of the enhancement of the fuel consumption rate.

[0063] By the way, the possibility that the temperature of the fuel upon the combustion and the ambient gas temperature may be controlled to be lower than a temperature at which the growth of the hydrocarbon is stopped on the way in the combustion chamber is limited to the case where the engine load is relatively low and the heat capacitance due to the combustion is small. Accordingly, when the engine load is relatively low in the first embodiment, the temperature of the fuel upon the combustion and the ambient gas temperature are suppressed down to the temperature or lower at which the growth of the hydrocarbon is stopped on the way to perform a first combustion, i.e., the low temperature combustion and when the engine load is relatively high, a second combustion, i.e., the combustion that has been conventionally performed in general is performed. Incidentally, the first combustion (low temperature combustion) means combustion in which the inert gas amount within the combustion chamber is larger than the worst inert gas amount at which the maximum amount of particulate is generated and particulate hardly generate, and the second combustion (ordinary combustion) means combustion in which the inert gas amount within the combustion chamber is smaller than the worst inert gas amount at which the maximum amount of particulate is generated.

[0064] In the diesel engine in this first embodiment, the first combustion (low temperature combustion) and the second combustion (ordinary combustion) are switched over on the basis of the number of engine rotation N and the step-in amount of the acceleration pedal (demanded load L) . In each combustion mode, the opening degree control of the throttle valve 20 and the EGR valve 25 is executed on the basis of the number of engine rotation N and the step-in amount of the acceleration pedal (demanded load L). Incidentally, the target opening degree ST of the throttle valve 20 needed for keeping the air/fuel ratio at the target air/fuel ratio is stored in advance in the ROM in the form of a map, which is a function of the number of engine rotation N and the demanded load L as shown in Fig. 5A. Also, the target opening degree SE of the EGR valve 25 needed for keeping the air/fuel ratio at the target air/fuel ratio is stored in advance in the ROM in the form of a map, which is a function of the number of engine rotation N and the demanded load L as shown in Fig. 5B.

[0065] Then, the ECU 9 executes the opening degree control of the throttle valve 20 and the EGR valve 25 on the basis of the map in response to the demanded load L.

[0066] Then, in the first operational region I where the demanded load L is low, as shown in Fig. 6, the opening degree of the throttle valve 20 gradually increases from the extent close to the fully closed condition to the semi-opened condition as the demanded load L is higher, and the opening degree of the EGR valve 25 gradually increases from the extent close to the fully closed condition to the semi-opened condition as the demanded load L is higher. Incidentally, at this time, in the first operational region I, the EGR rate is kept substantially at 70%, and the air/fuel ratio is kept at a lean air/fuel ratio that is somewhat lean.

[0067] In other words, at this time, in the first operational region I, the opening degree of the throttle valve 20 and the opening degree of the EGR valve 25 are controlled so that the EGR rate is kept substantially at 70% and the air/fuel ratio is kept at the lean air/fuel ratio that is somewhat lean. Incidentally, at this time, the opening degree of the EGR valve 25 is corrected on the basis of the output signal of the air/fuel ratio sensor or the like so that the air/fuel ratio is controlled to be the target lean air/fuel ratio. Also, in the first operational region I, the fuel injection is effected before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the demanded load L is higher, and the injection completion timing θE is also delayed as the injection start timing θS is delayed.

[0068] On the other hand, when the operational region of the engine is changed from the first operational region I to the second operational region II, the opening degree of the throttle valve 20 is increased stepwise from the semi-opened condition to a fully opened condition. In this case, in the example shown in the drawing, the EGR rate is decreased stepwise from about 70% to 40% or less, and the air/fuel ratio is increased stepwise. Namely, since the EGR rate jumps over the EGR rate range where the large amount of smoke is generated, there is no possibility of the generation of the large amount of smoke when the operational region of the engine is changed from the first operational region I to the second operational region II.

[0069] In the second operational region II, the conventionally performed combustion is performed. In this combustion method, a small amount of fine particulate and NOx is generated but the thermal efficiency is high in comparison with the low temperature combustion. Accordingly, when the operational region of the engine is changed from the first operational region I to the second operational region II, the injection amount may be reduced stepwise.

[0070] In the second operational region II, the throttle valve 20 is kept under the fully opened condition except for a part and the opening degree of the EGR valve 25 is gradually decreased as the demanded load L is higher. In this operational region II, the higher the demanded load L, the lower the EGR rate will become, and the higher the demanded load L, the lower the air/fuel ratio will become. However, even if the demanded load L is high, the air/fuel ratio is the lean air/fuel ratio. Also, the injection start timing θS is close to the compression top dead center TDC in the second operational region II.

[0071] In the first operational region I, the lower the demanded load L, the leaner the air/fuel ratio A/F will become. Namely, the lower the demanded load L, the smaller the combustion amount due to the combustion. Accordingly, the low temperature combustion may be performed even if the EGR rate is lowered such that the demanded load L is lower. When the EGR rate is lowered, the air/fuel ratio is increased. As the demanded load L is lowered, the air/fuel ratio A/F is increased. The larger the air/fuel ratio A/F, the more the fuel consumption rate will become. Accordingly, to lean the air/fuel ratio as much as possible, the air/fuel ratio A/F is increased as the demanded load L is lowered.

[0072] The operation of the exhaust gas purifying apparatus for the internal combustion engine with the supercharger in accordance with the first embodiment of the present invention will now be described.

[0073] In the case where the throttle valve 20 is fully closed due to the malfunction, the throttle valve 20 is regulated to the condition (see Fig.2) in which the fully closed opening degree is regulated to the predetermined angle α by the opening degree regulating means 21. Then, the intake air is always fed on the side of the compressor 6a by means of the opening portion. Then, it is possible to impart the load to the compressor 6a by the introduction of the intake air. Due to this load, there is no possibility that the compressor 6a is rotated without any resistance. It is possible to ensure such an the number of engine rotation that the abnormality such as sticking of the bearings of the turbocharger 6 may be avoided. Accordingly, even if the throttle valve 20 is fully closed due to the malfunction, there is no possibility that the turbocharger 6 is excessively rotated.

Embodiment 2

[0074] An exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with a second embodiment will now be described with reference to Figs. 7 and 8. Incidentally, in this second embodiment, the exhaust gas purifying apparatus in accordance with the above-described first embodiment is further developed for the purpose of preventing the generation of noise and vibration of a diesel engine having a high compression ratio.

[0075] The exhaust gas purifying apparatus for the internal combustion engine with the supercharger in accordance with the second embodiment is characterized in that a control valve 8 is provided in the intake pipe 3 on the downstream side of the compressor 6a for the purpose of preventing the generation of noise and vibration of the engine 1. The difference from the structure of the first embodiment is only that the control valve 8 is provided in the intake pipe 3 downstream of the compressor 6a and the control valve 8 is controlled on the fully closed upon starting or stopping. Accordingly, in Fig. 7, the same reference numerals are used to indicate the like components of the first embodiment shown in Fig. 1 and the detailed explanation therefor will be omitted because the function thereof is the same.

[0076] As shown in Fig. 7, the control valve 8 is a throttle valve that is provided in the intake pipe 3 between the inter cooler 7 and the intake manifold 2 for opening/closing the intake pipe 3. This control valve 8 is connected to the ECU 9 through a VRV₂ 29. Also, the opening degree of the control valve 8 is controlled in response to the operational condition of the engine 1 by means of the ECU 9. The control of the opening degree of this control valve 8 is substantially the same as the throttle valve 20. The VRV₂ 29 is a load regulation valve for duty control of the load valve applied to an operating actuator of the control valve 8 and adjusts the intake amount of the intake pipe 3 by adjusting the opening degree of the control valve 8 on the basis of the command of the ECU 9.

[0077] Namely, the ECU 9 calculates the engine load on the basis of the input signal from the acceleration opening degree sensor 26. Also, the ECU calculates the number of engine rotation on the basis of the output pulse outputted from the crank angle sensor 27. Then, the engine condition is determined in accordance with the engine load and the number of engine rotation. The ECU 9 controls the opening valve timing of the fuel injection valve 10 and the opening period thereof in response to the engine condition and also controls the respective opening degrees of the control valve 8 and the throttle valve 20.

[0078] By the way, in starting, stopping or idling operation, the ECU 9 controls the control valve 8 and the throttle valve 20 to be fully closed. At this time, the EGR valve 25 is also fully closed. Incidentally, the "fully closing closed control" means a control that the control valve 8 is temporarily fully closed in starting, stopping and idling operation of the diesel engine having a high compression ratio to thereby reduce the air introduced into the combustion chamber and the compression ratio within the combustion chamber is reduced to facilitate the rotation so as to suppress the vibration or noise.

[0079] Then, when the control valve 8 is closed approximately the fully closed condition, the amount of air to be introduced into the combustion chamber is decreased and the pressure within the combustion chamber in the initial stage of the compression is lowered so as to reduce the compression pressure. When the compression pressure is decreased, the compression work by the piston is reduced. Accordingly, the rotation of the piston is easy and the vibration of the engine body is reduced. Namely, upon starting, stopping or the idling operation, it is possible to suppress the vibration or the noise caused by the vibration of the engine body.

[0080] Incidentally, upon fully closing control, the throttle valve 20 is regulated by the opening degree regulating means 21 to the condition (see Fig. 2) that the fully closed opening degree is opened at the predetermined angle α. Then, the intake air is always led on the side of the compressor 6a through the opening portion.

Embodiment 3

[0081] An exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with a third embodiment will now be described with reference to Fig. 9. Incidentally, in the above-described second embodiment, the case where the control valve 8 and the throttle valve 20 control. the negative pressure values to be led to the control valve 8 and the throttle valve 20 by the separate negative pressure regulation valves (VRV, VRV₂) 28 and 29, respectively, has been described. Since the opening/closing operations of the control valve 8 and the throttle valve 20 are substantially the same, in the third embodiment, the exhaust gas purifying apparatus according to the above-described second embodiment is further developed so that the opening/closing operations of the control valve 8 and the throttle valve 20 take the same operational mode. Also, in Fig. 9, the same reference numerals are used to indicate the like components of the first or second embodiment shown in Fig. 1 or 7 and the detailed explanation therefor will be omitted because the function thereof is the same.

[0082] In the exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with the third embodiment, as shown in Fig. 9, the control valve 8 and the throttle valve 20 are connected to the VRV 28a and connected through this VRV 28a to the ECU 9. This VRV 28a is a load regulation valve for duty control of the load value to be applied to the operating actuator of the control valve 8 and the throttle valve 20 and adjusts the opening degrees of the control valve 8 and the throttle valve 20 in accordance with commands of the ECU 9 to adjust the suction amount of the intake pipe 3.

[0083] Namely, the ECU 9 calculates the engine load on the basis of the input signal from the acceleration opening degree sensor 26. Further, the ECU 9 calculates the number of engine rotation on the basis of the output pulse outputted from the crank angle sensor 27. Then, the engine condition is determined in accordance with these engine load and the number of engine rotation. The ECU 9 controls the valve opening timing and valve opening period of the fuel injection valve 10 in response to the engine condition and controls the opening degrees of the control valve 8 and the throttle valve 20 in the same operational mode through the VRV 28a.

[0084] In the case of this third embodiment, only one operating actuator suffices, and the operation command signal outputted from the ECU 9 may be commonly used to simplify the system. Incidentally, in the case of the structure for driving the control valve 8 and the throttle valve 20 by means of an electric motor, the ECU 9 controls the electric motor such that the opening degree characteristics of the control valve 8 and the throttle valve 20 are kept in the same operational mode.

Embodiment 4

[0085] An exhaust gas purifying apparatus for an internal combustion engine with a supercharger in accordance with a fourth embodiment will now be described with reference to Fig. 10. Incidentally, in the fourth embodiment, the opening degree regulating means 21 is not used as the fail safe means as in the first to third embodiments but a bypass pipe 21c straddling a throttle valve 20a is provided on the outer wall of the intake pipe 3 to form the fail safe means. Accordingly, the difference between the fourth embodiment and the first to third embodiments is only in the fail safe means. Accordingly, in the fourth embodiment, only the fail safe means will be described only the fail safe means and omitted the other detailed description.

[0086] Namely, as shown in Fig. 10, the fail safe means according to the fourth embodiment is the bypass pipe 21c provided on the outer wall of the intake pipe 3 so as to bypass the throttle valve 20a. This bypass pipe 21c bypass the throttle valve 20a to allow the intake air to always enter on the side of the compressor 6a. Incidentally, the intake flow rate introduced through the bypass pipe 21c may secure such the number of engine rotation that the intake air introduced impose the compressor 6a on the load to prevent the abnormality such as sticking of the bearings of the turbocharger 6 from generating in the case that the throttle valve 20a is fully closed.

[0087] In the case of the fourth embodiment, the throttle valve 20a controls the intake pipe 3 to be fully closed by the control of the ECU 9. Then, even if the throttle valve 20a is fully closed, the intake air may always be introduced on to the side of the compressor 6a from the bypass pipe 21c. It is therefore possible to avoid the excessive negative pressure of the intake pipe 3 between the throttle valve 20 and the compressor 6a.

[0088] According to the present invention, even if the throttle valve is fully closed due to the malfunction, the excessive negative pressure of the intake passage may be prevented by the fail safe means. It is therefore possible to prevent the non-resistance rotation of the compressor and the excessive rotation thereof. Accordingly, since the excessive rotation of the supercharger may be prevented, it does not generated the defects such as sticking of the bearings.

[0089] An exhaust gas purifying apparatus for an internal combustion engine with a turbocharger is provided with an introduction port for EGR gas disposed upstream of a compressor and a throttle valve disposed upstream of the introduction port, and comprised of a fail safe means that the portion on the upstream side of the compressor does not have any excessive negative pressure even if a malfunction occurs in the throttle valve. The exhaust gas purifying apparatus for an internal combustion engine with a turbocharger is provided with a supercharger (6) having a turbine (6b) disposed in an exhaust passage (16) and a compressor (6a) disposed in an intake passage (3) and having an exhaust gas recirculation system (23,24 and 25) for connecting the exhaust passage (16) downstream of the turbine (6b) and the intake passage (3) with each other and for recirculating a part of exhaust gas back to an intake system of the internal combustion engine, wherein an introduction port for recirculating the part of the exhaust gas and a throttle valve (20) for opening/closing the intake passage (3) as desired are arranged in this order. A fail safe unit (21) for allowing a predetermined flow rate of intake air to flow to the compressor (6a) and giving a load, when the throttle valve (20) is fully closed, is provided in the intake passage (3) upstream of the compressor (6a).

Claims

1. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger, comprising a supercharger having a turbine disposed in an exhaust passage and a compressor disposed in an intake passage and an exhaust gas recirculation system for connecting the exhaust passage downstream of the turbine and the intake passage with each other and for recirculating a part of exhaust gas back to an intake system of the internal combustion engine, in which an introduction port for recirculating the part of the exhaust gas and a throttle valve for opening/closing the intake passage as desired are arranged in this order in the intake passage upstream of the compressor,
   wherein a fail safe means for allowing a predetermined flow rate of intake air to flow to the compressor and giving a negative pressure, when the throttle valve is fully closed, is provided in the intake passage upstream of the compressor.

2. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 1, wherein the fail safe means is an opening degree regulating means for regulating an opening/closing angle of the throttle valve to a predetermined opening angle upon fully closed operation.

3. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 2, wherein the opening degree regulating means keeps a minimum opening limiter of the throttle valve open at the minimum opening degree such that the supercharger is not excessively rotated and supplies the intake air flow rate to the intake passage upstream of the compressor.

4. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 3, wherein the opening degree regulating means is disposed to project into the intake passage upstream of the compressor to make it possible to prevent the fully closed condition of the throttle valve and keep the minimum opening degree.

5. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 4, wherein the opening degree regulating means includes a slant hole formed obliquely in the intake passage, a nut portion fixed on the outside of the intake passage coaxially with the slant hole and a screw rod screwed into the nut portion, inserted into the slant hole with a top portion thereof projecting from an inner wall of the intake passage to inward and touched the throttle valve.

6. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 5, wherein the opening/closing angle of the throttle valve is changed by regulating a length of the top portion of the screw rod projecting inwardly from the inner wall of the intake passage in screwed relation with the nut portion.

7. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to any preceding claim, wherein a control valve that is controlled to be a fully closed condition, when the internal combustion engine is started or stopped, is provided in the intake passage downstream of the compressor.

8. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 7, wherein the opening/closing operations of the throttle valve and the control valve are kept in the same operational mode.

9. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to any preceding claim, wherein the fail safe means comprises a bypass passage for allowing the predetermined flow rate of intake air to flow bypassing the throttle valve.

10. An exhaust gas purifying apparatus for an internal combustion engine with a supercharger according to claim 9, wherein the bypass passage is provided on an outer wall of the intake passage so as to bypass the throttle valve.

Drawing