Exhaust pulsation control system for an internal combustion engine

Abstract

 An exhaust pulsation control system for an internal combustion engine having at least one cylinder communicating with an intake passage via an intake port and with an exhaust passage via an exhaust port, comprises engine operating condition detecting means and exhaust gas temperature detecting means. Further, there is provided a memory storing target values of exhaust gas temperature related to predetermined engine operating conditions and a control means connected to said memory and adapted to control an air/fuel ratio of an air/fuel mixture to be supplied to said engine so as to approach said detected exhaust gas temperature to said target exhaust gas temperature corresponding to the engine operating conditions detected.

Description

[0001] This invention relates to an exhaust pulsation control system and to a method for controlling an exhaust pulsation for an internal combustion engine.

[0002] Devices for controlling the exhaust pulsation of engine have been proposed to effectively utilize the exhaust pulsation to improve the engine performances such as fuel consumption. Practically, the engine performance is improved by making the timing at which the reflection wave of the exhaust gas reaches the exhaust port (to be referred to as "reaching timing" hereinafter) appropriate, by which fresh air is prevented from blowing by the combustion chamber while the draft of burnt gas out of the combustion chamber into the exhaust pipe is promoted.

[0003] In the case above, when the engine circumference is changed by rain, snow, or the like, the exhaust temperture in the exhaust pipe is also changed, and the reflection wave "reaching timing" above is also changed by the sound speed change accompanying the exhaust temperature change above.

[0004] Therefore, a device for controlling the exhaust pulsation has been proposed by which, even if the engine circumference is changed, a desired "reaching timing" is obtained by making the exhaust temperature a predetermined one corresponding to the current engine operating state, and one of such devices has been disclosed by Japanese Unexamined Patent Publication Sho58-74826.

[0005] According to the publication above, the exhaust pipe is provided with a water jacket, and this water jacket is supplied with high temperature cooling water used for cooling the engine. By this water supply, the exhaust is kept at a predetermined temperature corresponding to the engine operating state, and the desired "reaching timing" is obtained.

[0006] However, the conventional exhaust pulsation control system above has a problem that it may become bulky, heavy and expensive due to the water jacket installed on the exhaust pipe and the weight of cooling water supplied to the water jacket.

[0007] Accordingly, it is an objective of the present invention to provide an improved exhaust pulsation control system for an internal combustion engine which is capable to always ensure a reliable control of an exhaust gas temperature for controlling the exhaust gas pulsation with simple technical means and which simultaneously is easy to handle and producable with low costs.

[0008] According to the invention, this objective is solved by an exhaust pulsation control system for an internal combustion engine having at least one cylinder communicating with an intake passage via an intake port and with an exhaust passage via an exhaust port, comprising engine operating condition detecting means and exhaust gas temperature detecting means, wherein a memory storing target values of exhaust gas temperature related to predetermined engine operating conditions is provided together with a control means connected to said memory and adapted to control an air/fuel ratio of an air/fuel mixture to be supplied to said engine so as to approach said detected exhaust gas temperature to said target exhaust gas temperature corresponding to the engine operating conditions detected.

[0009] It is a further objective of the present invention to provide a method of controlling an exhaust pulsation for an internal combustion engine which always ensures a reliable control of the exhaust temperature for controlling the exhaust gas pulsation under all environment conditions.

[0010] According to the invention, this further objective is solved by a method of controlling an exhaust pulsation for an internal combustion engine having at least one cylinder communicating with an intake passage via an intake port and with an exhaust passage via an exhaust port, comprising the steps of detecting an engine operating condition with an engine operating condition detecting means, detecting an exhaust gas temperature with an exhaust gas temperature detecting means and maintaining said detected exhaust gas temperature at a level at least close to a predetermined temperature corresponding to the detected engine operating condition, further comprising the steps of storing and outputting target exhaust temperature data into or from, respectively, a memory, said target exhaust temperature data corresponding to said detected engine operating state, comparing the detected exhaust gas temperature with said target exhaust temperature and increasing or decreasing, respectively, an air/fuel ratio to approach the detected exhaust gas temperature to said target exhaust gas temperature.

[0011] According to an embodiment of the invention, the air/fuel ratio is controllable via a fuel supply system which may comprise a fuel tank communicating with a fuel injection valve located in the intake passage, a fuel pump for pressurizing fuel, a regulator for regulating the fuel pressure and an actuator for actuating said fuel injection valve. However, it is also possible that said fuel supply system comprises a fuel tank communicating with a carburetor located in said intake passage and controllable by said control means.

[0012] In order to detect said engine operating condition, it is advantageous when said engine operating condition detecting means comprise an engine speed detecting sensor and a throttle opening detecting sensor which are both connected to said control means.

[0013] According to an advantageous embodiment of the invention, said memory of the exhaust pulsation control system comprises a first map containing specific fuel supply amounts to be supplied when said detected engine speed exceeds a first predetermined value and/or when said detected throttle opening exceeds a second predetermined value, and a second map containing said target exhaust gas temperature data.

[0014] According to another embodiment of the invention, the exhaust gas temperature detecting means is adapted to detect the temperature of the wall of an exhaust pipe enclosing said exhaust passage. This allows the use of cheaper temperature sensors because they must not withstand the aggressive exhaust gases.

[0015] This inventive exhaust pulsation control system is not only applicable to 4-cycle stroke type engines but also to 2-cycle stroke engines.

[0016] Other preferred embodiments of the present invention are laid down in further dependent claims.

[0017] The function according to this invention is as follows:

It is widely known that, if the value of the air-fuel ratio (A/F) of the fuel 16 to be supplied to the engine 2 is changed while the engine 2 is operating, the temperature of the exhaust gas 26 after combustion of the fuel 16 changes accordingly.

[0018] Therefore, if the controller or control means 25 compares the actual exhaust temperature T detected by the exhaust temperature detecting means 38 with the target exhaust temperature T_o corresponding to the engine operating condition detected by the operating condition detecting means 33, and decides that the actual exhaust temperature T is lower (or higher) than the target exhaust temperature T_o, it increases (or decrease) the air-fuel ratio value R so that the actual exhaust temperature may come closer to the target exhaust temperature T_o.

[0012]

[0019] By that, the temperature of the exhaust 29 can be brought closer to the predetermined temperature corresponding to the current engine operating state, by which desired "reaching timing" is obtained in spite of the engine circumferernce changes described above, exhaust pulsation is effectively utilized and the engine performance is improved.

[0013]

[0020] In addition, since the effective utilization of the exhaust pulsation described above is achieved by an exhaust pulsation control system 32 comprising electronic components such as operating condition detecting means 33, memory 37, exhaust temperature detecting means 38 and controller 25, the conventional bulky and heavy water jacket is no more required.

[0021] In the following, the present invention is explained in greater detail with respect to several embodiments thereof in conjunction with the accompanying drawings, wherein:

Figure 1 is an overall schematic illustration for the embodiment 1;

Figure 2 is a flow chart for the controller of the embodiment 1;

Figure 3 is a flow chart for the sub-program of the controller of the embodiment 1;

Figure 4 is a map diagram related to engine speed and fuel supply of the embodiment 1;

Figure 5 is a map diagram related to engine speed and target exhaust temperature of the embodiment 1;

Figure 6 is a graph showing general relationship between the air/fuel ratio value and the detected exhaust temperature;

Figure 7 is an illustration for embodiment 2 corresponding to figure 1; and

Figure 8 is a sectional view of a carburetor for embodiment 2.

[0022] Embodiments of this invention are described hereafter referring to appended drawings.

[0023] Although the embodiments will be described with respect to 2-cycle stroke internal combustion engines, the present invention is also applicable to 4-cycle stroke internal combustion engines.

[0024] Figures 1 through 6 show embodiment 1.

[0025] In Fig.1, the numeral 1 shows a driving system for a motorcycle. This driving system 1 has a 2-cycle stroke internal combustion engine 2, one end of an intake pipe 3 is connected to the intake port formed through the crankcase of this engine 2, an air cleaner 4 is connected to the other end of the intake pipe 3, and the interiors of the intake pipe 3 and the air cleaner 4 constitute an intake passage 5 for making the exterior of the engine 2 communicate with the intake port of the engine 2.

[0026] The intake pipe 3 is provided with a throttle valve 6 for closing and opening the intake passage longitudinally midway thereof, and this throttle valve 6 is operatively linked with throttle operating means 7, a throttle operating grip 8, through a wire 9.

[0027] The cylinder of the engine 2 has one end of the exhaust pipe 12 connected to the exhaust port formed therethrough, a silencer 13 is connected to the other end of the exhaust pipe 12, and the interiors of the exhaust pipe 12 and the silencer 13 constitute an exhaust passage 14 making the exhaust port of the engine 2 communicate with the exterior of this engine 2.

[0028] A fuel supply system 17 is provided for supplying fuel 16 into the intake passage 5. The fuel supply system 17 comprises a fuel tank 18 for reserving fuel 16, a fuel injection vave 19 for injecting fuel 16 into the intake passage 5 between the engine 2 and the throttle valve 6, a fuel pump 20 for pressurizing the fuel 16 of the fuel tank 18 and supplying it to the fuel injection valve 19 and a regulator 21 for regulating the pressure of the fuel 16 to be supplied to the fuel injection valve 19 upto a specified pressure, while the fuel injection valve 19 is opened/closed by an actuator 22, which is a solenoid valve.

[0029] The engine 2 is provided with an ignition system 24, and the discharging electrode of the ignition plug for this ignition system 24 faces into the combustion chamber of this engine 2. A controller 25 is provided for controlling the engine 2 electronically, while the actuator 22 and the ignition system 24 are electrically connected to this controller 25.

[0030] When the engine 2 is started, the air 27 for the engine 2 is, after filtration by the air cleaner 4, suctioned first into the intake passage 5 by the negative pressure in the crankcase of the engine 2. On the other hand, the fuel injection valve 19 is opened at a predetermined timing for a predetermined length of time by the action of the actuator 22 under the control of the controller 25, and, while the fuel injection valve 19 is thus opened, fuel 16 is injected from the fuel injection valve 19 into the air 27 in the intake passage 5, which produces fuel-air mixture 28. The mixture 28 is, after precompression in the crankcase, sent into the combustion chamber, and is ignited at a predetermined timing by the ignition system 24 under the control of the controller 25 and is combusted.

[0031] The heat energy caused by this combustion is converted into motive power, which is outputted through the crankshaft of the engine 2 and makes the motorcycle travel along.

[0032] The gas produced by the combustion above is discharged, as exhaust gas 29, out of the engine 2 through the exhaust passage 14.

[0033] The driving system 1 constructed as described above is further provided with an exhaust pulsation control system 32 to cotrol the pulsation of the exhaust gas 29 and effectively utilize it for improving the engine performance.

[0034] The exhaust pulsation control system 32 has engine operating state detecting means 33 for detecting the operating state of the engine 2. The means 33 is provided with a speed detecting sensor 34 for detecting the number N of rotation per unit time of the crankshaft of the engine 2, and a throttle opening detecting sensor 35 for detecting the opening of the intake passage 5 to be varied by the throttle valve 6, that is, the throttle opening θ, and these sensors 34 and 35 are also connected to the controller 25 electrically.

[0035] A memory 37 storing the data of the target exhaust temperature T_o corresponding to the engine operating state detected by the speed detecting sensor 34 and the throttle opening detecting sensor 35, that is, the target exhaust temperature T_o desirable for effectively utilizing the exhaust pulsation (the Map 2 in Fig.5 to be described later) is also provided, and this memory 37 also is electrically connected to the controller 25.

[0036] Exhaust temperature detecting means 38 for indirectly detecting the temperature of the exhaust gas 29 by detecting the temperature of the pipe wall of the exhaust pipe 12 is provided, and this exhaust temperature detecting means 38 is also connected to the controller electrically.

[0037] The air/fuel ratio (A/F) of the mixture 28 is so determined by the control of the controller 25 that the detected exhaust temperature T detected by the exhaust temperature detecting means 38 while detecting the engine operating state may come closer to the target exhaust temperature T_o corresponding to the engine operating state, that is, the engine speed N and the throttle opening θ detected by the speed detecting sensor 34 and the throttle opening sensor 35 of operating state detecting means 33.

[0038] Here, the controller 25 for the exhaust pulsation control system 32 is described in further detail referring to Figs.2 through 6. Figs.2 and 3 show flow charts for the controller 25 for the exhaust pulsation control system 32, and (P-1) through (P-25) in these charts show individual steps of these programs.

[0039] When the engine is started at (P-1), the engine speed N detected by the speed detecting sensor 34 and the throttle opening θ detected by the throttle opening detecting sensor 35 are first inputted at (P-2).

[0040] Next at (P-3), it is decided whether the engine 2 is being rapidly accelerated (decelera ted) or not by comparing the engine speed N_o and the throttle opening θ_o which has been s tored in the memory in the previous cycle with the engine speed N and the throttle opening θ detected anew.

[0041] In practice, at (P-3), |(N-N_o)/N_o| is calculated, and, if this value (engine speed changing rate) exceeds a predetermined value a₁, it is decided that the engine speed is being rapidly increased or decreased, that is, the engine 2 is being rapidly accelerated or decelerated, and (P-4) is executed.

[0042] Similarly, at (P-3), |(θ-θ_o)/θ_o| is calculated, and, if this value (throttle opening changing rate) exceeds a predetermined value a₂, it is decided that the throttle valve is being rapidly opened or closed, that is, the engine 2 is being rapidly accelerated or decelerated, and (P-4) is executed.

[0043] If it is decided that the engine 2 is being rapidly accelerated or decelerated at (P-3) as described above, the fuel supply amount Q (cc/cycle) to be supplied to the engine 2 per each cycle is obtained from the Map 1 shown in Fig.4 at (P-4). That is, the injection period of the actuator 22 for the fuel injection valve 19 is determined, and the fuel as much as the fuel supply amount Q is supplied to the engine 2 by fuel injection in this period at (P-5).

[0044] Next at (P-6), the flow is returned to (P-2) with the current engine speed N and the current throttle opening θ taken as N_o and θ_o for the previous cycle, and these values N_o and θ_o are used at (P-3).

[0045] At (P-3) above, if the changing rate of the engine speed N is not larger than a predetermined value a₁ and the changing rate of the throttle opening θ is not larger than a predetermined value a₂, it is decided that the engine 2 is being neither accelerated nor decelerated rapidly, that is, the engine 2 is in an ordinary operating state, the steps (P-7) and (P-8) having the same contents as the steps (P-4) and (P-5), respectively, are executed, the initial operation of the engine 2 is continued, and then (P-9) is executed.

[0046] The memory 37 is constituted of Map 2 shown in Fig.5. At (P-9) above, a target exhaust temperature T_o is obtained on the basis of the engine speed N and the throttle opening θ inputted at (P-2). Next at (P-10), the detected exhaust temperature T detected by the exhaust temperature detecting means 38 is inputted. Further, a sub-program is executed at (P-11).

[0047] The sub-program above has steps (P-12)∼(P-25) shown in Fig.3.

[0048] When the sub-program above is started at (P-12), dT/dR is calculated at (P-13), where R is the value of the air-fuel ratio, and, in principle, there is a relation shown in Fig.6 between the air-fuel ratio value R and the detected exhaust temperature T.

[0049] As shown in Fig.6, while the air-fuel ratio value R is gradually increased from a small value, the temperature of the exhaust gas 29, i.e., the detected exhaust temperature T, once becomes higher (range A in Fig.6), and favorable engine performance is obtained in this range A. If the air-fuel ratio value R further increases (if the mixture 28 becomes further leaner), the detected exhaust temperature begins to drop (range B in Fig.6), and the engine performance tends to drop accordingly.

[0050] The relation between the air-fuel ratio value R and the detected exhaust temperature T is shown as an upwardly convex arcuate curve when the air-fuel ratio value R is taken on the abcissa and the detected exhaust temperature T is taken on the ordinate as shown in Fig.6. The apex C of this arcuate curve indicates the highest value of the exhaust temperature T, and it is positioned on the boundary of the ranges A and B described above. Therefore, the value dT/dR calculated at (P-13) shows the inclination of the curve above at a value of the air-fuel ratio R

[0051] When the inclination |dT/dR| is not smaller than a predetermined value a₃ at (P-14), it is decided that this inclination is large and that the air-fuel ratio value R at this instance is apart from that corresponding to the highest value C, that is, it is decided that the air-fuel ratio value R is in the range A(a) or B(a) shown in Fig.6. It is comprehended from Fig.6 that, in this case, the detected exhaust temperature T changes remarkably when the air-fuel ratio value R is varied. Therefore, (P-15) is executed.

[0052] When it is decided at (P-15) that dT/dR>0, that is, the inclination of the curve of Fig.6 has a positive value at an air-fuel ratio value R, the air-fuel ratio value R at this instance is in the range A(a) shown in Fig.6, and the air fuel ratio value R in this case is decided to be in a range appropriate for the engine performance, and (P-16) is executed.

[0053] When it is decided at (P-16) that the value |T-T_o| is not smaller than a predetermined value a₄, i.e., that the difference between the detected exhaust temperature T and the target exhaust temperature T_o is large, (P-17) is executed.

[0054] When it is decided at (P-17) that the detected exhaust temperature T is lower than the target exhaust temperature T_o, the injection period at the fuel injection valve 19 is shortened at (P-18) so that the fuel supply Q to the engine 2 is decreased. Thereupon, since the air-fuel ratio value R in the range A(a) above in Fig.6 becomes greater, the detected exhaust temperature T is raised, that is, the temperature of the exhaust 29 is brought closer to the target exhaust temperature T_o.

[0055] Next at (P-19), the fuel supplys Q's at the previous and present cycles are stored, and also the detected exhaust temperature T of the present cycle is stored. Then the process is returned to (P-6) in Fig.2 at (P-20).

[0056] When it is decided at (P-17) that the detected exhaust temperature T is not lower than the target exhaust temperature T_o, the injection period at the fuel injection valve 19 is lengthened at (P-21) so that the fuel supply Q to the engine 2 is increased. Thereupon, since the air-fuel ratio value R in the range A(a) above in Fig.6 becomes smaller, the detected exhaust temperature T is lowered, that is, the temperature of the exhaust 29 is brought closer to the target exhaust temperature T_o. Then, the steps (P-19) and (P-20) are executed in order.

[0057] When it is decided at (P-15) that dT/dR<0, that is, the inclination of the curve of Fig.6 has a negative value at an air-fuel ratio value R, the air-fuel ratio value R at this instance is in the range B(a) shown in Fig.6, and is decided to be too large to be in a range appropriate for engine performance, and (P-22) is executed. At (P-22), the injection period at the fuel injection valve 19 is lengthened so that the fuel supply Q to the engine 2 is increased, by which the air-fuel ratio value R is decreased and shifted into the range A in Fig.6 until the value R becomes appropriate for the engine performance. Then, (P-19) and (P-20) are executed in order.

[0058] When the value |dT/dR| showing the inclination in Fig.6 is smaller than a predetermined value a₃ at (P-14) above, it is decided that this inclination is small, and that the air-fuel ratio value R in this instance is positioned near that for the highest value C in Fig.6, that is, in the ranges A(b) and B(b) of Fig.6. It is comprehended from Fig.6 that, in this case, the detected exhaust temperature T will not vary much even if the air-fuel ratio value R is varied somewhat. Then (P-23) is executed.

[0059] When it is decided at (P-23) that the value |T-T_o| is smaller than a predetermined value a₄, that is, The difference between the detected exhaust temperature T and the target exhaust temperature T_o is small, since the air-fuel ratio value R is not required to be changed much, the engine 2 is continued to be supplied with fuel of the same amount Q as that for the previous cycle at (P-24), and (P-19) above is executed thereafter.

[0060] When it is decided at (P-23) that the value |T-T_o| is not smaller than a predetermined value a₄, that is, the difference between the detected exhaust temperature T and the target exhaust temperature T_o is large, (P-25) is executed.

[0061] When it is decided at (P-25) that the detected exhaust temperature T is lower than the target exhaust temperature T_o, since the air-fuel ratio value R in this instance is near that for the highest value C in Fig.6 and the detected exhaust temperature T will not vary much even if the air-fuel ratio R is varied, (P-24) above is executed. For example, when the outside air temperature is very low because of snow or the like, the difference between the detected exhaust temperature T and the target exhaust temperature T_o is large (P-23) and T is fairly lower than T_o (P-25), and, therefore, the detected exhaust temperature T is not expected to rise even if the air-fuel ratio value R is changed, this detected exhaust temperature T is maintained as is.

[0062] When it is decided at (P-25) that the detected exhaust temperature T is higher than the target exhaust temperature T_o, (P-21) is executed, the air-fuel ratio R is made smaller so that the detected exhaust temperature T is lowered.

[0063] When it is decided at (P-16) that the value of |T-T_o| is smalller than a predetermined value a₄, that is, that the difference between the detected exhaust temperature T and the target exhaust temperature is small, since the temperature of the exhaust 29 may be left as is, (P-24) above is executed.

[0064] By controlling the air-fuel ratio of the mixture 28 as described above, the detected exhaust temperature T is brought closer to the target exhaust temperature T_o, the "reaching timing" is made appropriate, and the engine performance is improved.

[0065] The throttle operating means 7 for opening/closing the throttle valve 6 may be, instead of the throttle operating grip 8, a motor-driven actuator 40 to be driven by an electric servomotor as shown in Fig.1 in dash-and-single-dotted lines.

[0066] Figs.7 and 8 show Embodiment 2.

[0067] This embodiment is provided with a carburetor 42 in place of the throttle valve 6 and the fuel injection valve 19 in the fuel supply system 17 for the Embodiment 1.

[0068] The carburetor 42 has a casing 43, the interior of which constitutes an intake passage 5. A float chamber 44 is formed in the lower section of the casing 43, and fuel 16 from the fuel tank is supplied into this float chamber 44.

[0069] A piston type throttle valve 6 is inserted vertically slidably through the upper wall of the intake passage 5 in the casing 43, and a venturi portion 45 is formed between the inner surface of the intake passage 5 and the lower end of the throttle valve 6. Through the lower wall of the intake passage 5 at this venturi portion 45 are formed a main nozzle 46 and a pilot nozzle 47 both in communication with the float chamber 44. The throttle valve 6 has a needle 48 projected from the lower end thereof, and the projecting end of this needle 48 is slidably fitted in the main nozzle 46.

[0070] The throttle valve 6 is connected with the throttle control grip 8 of the throttle control means 7 through a wire 9, and the throttle valve 6 is raised or lowered through a wire 9 by operating the throttle control grip 8. By raising the throttle valve 6, the needle 48 being raised together with the throttle valve 6 gradually enlarges the opening of the main nozzle 46.

[0071] The float chamber 44 communicates with the intake passage 5 in the casing 43 through a first passage 50 provided with a first control valve 51, a solenoid valve for opening/ closing this first passage 50. The middle of the main nozzle 46 communicates with the exterior of the casing 43 through a second passage 52 provided with a second control valve 53, a solenoid valve for opening/closing this second passage 52. Further, the exterior of the casing 43 communicates with the middle of the pilot nozzle 47 through a third passage 54 provided with a third control valve 55, a solenoid valve for opening/ closing this third passage 54.

[0072] The first, second and third control valves 51, 53 and 55 are all connected electrically with the controller 25, and are controlled by this controller 25 so that predetermined openings may be arbitrarily selected.

[0073] When the first control valve 51 is opened under the control of the controller 25, the fuel 16 in the float chamber 44 is supplied into the intake passage 45 by the negative pressure of the intake air in the intake passage 45 of the casing 43, by which the air-fuel ratio value R is made smaller. On the contrary, when the first control valve 51 is closed, the supply of the fuel 16 into the intake passage decreases, by which the air-fuel ratio value R is made smaller.

[0074] When the second or third control valve 53 or 55 is opened under the control of the controller 25, the main nozzle 46 or the pilot nozzle 47 is supplied with external air, the supply of the fuel 16 to the intake passage 5 through these nozzles is decreased as less as the external air supply increase above, and the air-fuel ratio value R becomes greater. On the contrary, when the second or third control valve 53 or 55 is closed, the supply of the fuel 16 into the intake passage 5 through the main nozzle 46 or the pilot nozzle 47 increases as much as the air supply through these nozzles decreases, and the air-fuel ratio value R becomes smaller.

[0075] Thus, the detected exhaust temperature T detected by the exhaust temperature detecting means is brought closer to the target exhaust temperature T_o corresponding to the engine operating state detected by the operating state detecting means 33 by adjusting the air-fuel ratio value R through the adjustment of the air-fuel ratio R by the first, second and third control valve 51, 52 and 53.

[0076] Since other structures and functions of the second embodiment are similar to those of the first embodiment, their description is omitted by assigning commom reference symbols on the drawings.

[0077] Since the exhaust pulsation control system according to this invention comprises operating state detecting means for detecting the operating state of engine, memory for storing the target exhaust temperature data corresponding to the engine operating state detected by the operating state detecting means, exhaust temperature detecting means for detecting the exhaust temperature of engine, and further a controller for controlling the air-fuel ratio of the mixture to be supplied to the engine so that the exhaust temperature detected by the exhaust temperature detecting means may come closer to the target exhaust temperture corresponding to the engine operating state detected by the engine operating state detecting means, it has folllowing effects:

[0078] It is well-known that, if the air-fuel ratio of the fuel to be supplied to the engine is varied while the engine is operating, the temperature of the exhaust gas after the combustion of the fuel above changes.

[0079] Therefore, the detected exhaust temperature detected by the exhaust temperature detecting means is compared with the target exhaust temperature corresponding to the engine operating state detected by the engine operating state detecting means in the controller, and, if it is decided, from this comparison, that the detected exhaust temperature is lower (or higher) than the target exhaust temperature, the air-fuel ratio value is made larger (or smaller) so that the detected exhaust temperature may be brought closer to the target exhaust temperature.

[0080] Thereupon, the exhaust temperature can be brought closer to the predetermined temperature corresponding to the current engine operating state even if the engine circumference changes, by which desired "reaching timing" is obtained, the exhaust pulsation is effectively utilized and the engine performance is improved inspite of the change of the engine circumference.

[0081] Further, the effective utilization of the exhaust pulsation above is achieved by constructing the exhaust pulsation control system with electronic components such as engine operating state detecting means, memories, exhaust temperature detecting means, and controller, and the exhaust pulsation control system becomes smaller, lighter and less expensive as less as the conventional bulky and heavy water jacket can be disused.

Claims

1. Exhaust pulsation control system for an internal combustion engine having at least one cylinder communicating with an intake passage via an intake port and with an exhaust passage via an exhaust port, comprising engine operating condition detecting means and exhaust gas temperature detecting means, wherein a memory (37) storing target values of exhaust gas temperature (To) related to predetermined engine operating conditions is provided together with a control means (25) connected to said memory (37) and adapted to control an air/fuel ratio (R) of an air/fuel mixture (28) to be supplied to said engine (2) so as to approach said detected exhaust gas temperature (T) to said target exhaust gas temperature (To) corresponding to the engine operating conditions detected.

2. Exhaust pulsation control system according to claim 1, characterized in that said air/fuel ratio (R) is controllable via a fuel supply system (17).

3. Exhaust pulsation control system according to claim 2, characterized in that said fuel supply system (17) comprises a fuel tank (18) communicating with a fuel injection valve (19) located in the intake passage (5), a fuel pump (20) for pressurizing fuel (16), a regulator (21) for regulating the fuel pressure and an actuator (22) for actuating said fuel injection valve (19).

4. Exhaust pulsation control system according to claim 2, characterized in that said fuel supply system (17) comprises a fuel tank (18) communicating with a carburettor (42) located in said intake passage (5) and controllable by said control means (25).

5. Exhaust pulsation control system according to at least one of claims 2 to 4, characterized in that said engine operating condition detecting means (33) comprise an engine speed detecting sensor (34) and a throttle opening detecting sensor (35) both connected to said control means (25).

6. Exhaust pulsation control system according to claim 5, characterized in that said memory (37) comprises a first map (Map 1) containing specific fuel supply amounts (Q) to be supplied when said detected engine speed (N) exceeds a first predetermined value (a₁) and/or when said detected throttle opening exceeds a second predetermined value (a₂), and a second map (Map 2) containing said target exhaust temperature data (To).

7. Exhaust pulsation control system according to at least one of claims 1 to 6, characterized in that said exhaust gas temperature detecting means (38) is adapted to detect the temperature of the wall of an exhaust pipe (12) enclosing said exhaust passage (14).

8. Exhaust pulsation control system according to at least one of claims 4 to 7, characterized in that said carburettor (42) comprises a casing (43) the interior of which constituting said intake passage, a float chamber (44), a venturi portion (45) having a main nozzle (46) and a pilot nozzle (47) both communicating with said float chamber (44) and a needle (48) the projecting end of which is slidably fitted in said main nozzle (46), whereby said float chamber (44) communicates with said intake passage (5) through a first passage (50), the main nozzle (46) communicates with the exterior of the casing (43) through a second passage (52) and the pilot nozzle (47) communicates with the exterior of said casing (43) through a third passage (54) whereby each of said three passages comprises a respective control valve (51, 53, 55) being controllable by said control means (25).

9. Exhaust pulsation control system according to at least one of claims 1 to 8, characterized in that said internal combustion engine (2) is of the 4-cycle stroke type or of the 2-cycle stroke type.

10. Method of controlling an exhaust pulsation for an internal combustion engine having at least one cylinder communicating with an intake passage via an intake port and with an exhaust passage via an exhaust port, comprising the steps of detecting an engine operating condition with an engine operating condition detecting means, detecting an exhaust gas temperature with an exhaust gas temperature detecting means and maintaining said detected exhaust gas temperature at a level at least close to a predetermined temperature corresponding to the detected engine operating state, characterized by storing and outputting target exhaust temperature data into or from, respectively, a memory, said target exhaust gas temperature data corresponding to said detected engine operating condition, comparing the detected exhaust gas temperature with said target exhaust gas temperature and increasing or decreasing, respectively, an air/fuel ratio to approach the detected exhaust gas temperature to said target exhaust gas temperature.

11. Method according to claim 10, characterized in that said air/fuel ratio is controlled by controlling a fuel supply system.

12. A method according to claim 10 or 11, characterized in that said engine operating state is detected by detecting the engine speed (N) and the throttle opening of a throttle operating means located within said intake passage.

13. A method according to claim 12, characterized in that said memory comprises a first map containing specific fuel supply amounts to be supplied when said detected engine speed (N) exceeds a first predetermined value and/or when said detected throttle opening exceeds a second predetermined value, and a second map (Map 2) containing said target exhaust temperature data.

Drawing