JP2006029341A - Control device for 4-stroke engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cause self-ignition in a 4-stroke engine. <P>SOLUTION: In a predetermined load range from low load to medium load in an engine, an exhaust valve is closed before an intake top dead center TDC, and as demand load L is reduced, valve closing timing EC for the exhaust valve is advanced. An intake valve is opened after the intake top dead center TDC, and as the demand load L is reduced, valve opening timing IO of the intake valve is delayed. The intake valve is closed after an intake bottom dead center BDC, and as the demand load L is increased, valve closing timing IC for the intake valve is gradually delayed, and then it is gradually advanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for a four-stroke engine.

  In a 4-stroke engine, the engine output is normally controlled by a throttle valve disposed in the engine intake passage. However, when the engine output is controlled in this way, a large pumping loss occurs when the throttle valve opening is small. Therefore, an internal combustion engine in which the engine output is controlled by removing the throttle valve in order to prevent the occurrence of such a pumping loss and changing the closing timing of the intake valve is known (Patent Document 1). reference).

  On the other hand, when a large amount of burned gas remains in the combustion chamber in a two-stroke engine, fresh fuel supplied into the combustion chamber is thermally decomposed by the high-temperature burned gas, and as a result, radicals are generated. When radicals are generated in this way, the fuel self-ignites regardless of the spark plug. Since this self-ignition occurs simultaneously at multiple points in the entire combustion chamber, if such self-ignition occurs, the air-fuel mixture in the entire combustion chamber can be burned well. As a result, the thermal efficiency is improved, and thus the fuel consumption rate is improved. In addition, since this self-ignition occurs at multiple points in the entire combustion chamber at the same time, the combustion temperature in the combustion chamber does not increase locally, and therefore generation of NOx can be suppressed.

In view of this, a crank chamber compression type two-stroke engine is known in which self-ignition is caused by controlling the opening area of the exhaust port in accordance with the engine speed and the throttle opening (see Patent Document 2). .
JP-A-55-128610 JP 7-71279 A

  By the way, since the two-stroke engine employs a combustion method in which a large amount of burned gas remains essentially, self-ignition can be caused relatively easily. However, since a 4-stroke engine inherently employs a combustion method that leaves as much burned gas as possible, it is not as easy to cause self-ignition in a 4-stroke engine as in a 2-stroke engine.

Further, if self-ignition is caused, the fuel consumption rate can be improved as described above. However, if a pumping loss occurs at this time, the merit of improving the fuel consumption rate by self-ignition is also halved. Therefore, it is important to cause self-ignition without causing a pumping loss.
By the way, if the engine output is controlled by changing the closing timing of the intake valve as described above, the generation of pumping loss can be prevented. However, it is difficult to cause self-ignition only by controlling the closing timing of the intake valve in this way.

  An object of the present invention is to provide a control device capable of causing self-ignition while preventing generation of pumping loss in a four-stroke engine.

  In order to achieve the above object, according to the present invention, in a four-stroke engine equipped with a spark plug, when the engine load is within a predetermined load range from low load to medium load, it is supplied into the combustion chamber. The intake valve on / off valve timing and the exhaust valve on / off valve timing are controlled so that the intake air temperature rises to a temperature at which self-ignition can occur. In some cases, it is ignited by a spark plug.

  In a four-stroke engine, when the engine load is in a predetermined load range from low load to medium load, self-ignition can be caused. When the engine load is outside this load range, normal combustion is performed by the spark plug.

  Referring to FIG. 1, 1 is a 4-stroke engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is a spark plug, 7 is an intake valve, 8 is an intake valve drive actuator, Reference numeral 9 denotes an intake port, 10 denotes an exhaust valve, 11 denotes an exhaust valve driving actuator, and 12 denotes an exhaust port. The intake port 9 is connected to a surge tank 14 via a corresponding intake branch pipe 13, and a fuel injection valve 15 is attached to each intake branch pipe 13. The surge tank 14 is connected to an air cleaner 17 via an intake duct 16, and a throttle valve 19 driven by an electric motor 18 is disposed in the intake duct 16. On the other hand, the exhaust port 12 is connected to an exhaust manifold 20, and an air-fuel ratio sensor 21 is disposed in the exhaust manifold 20.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. The output signal of the air-fuel ratio sensor 21 is input to the input port 35 via the corresponding AD converter 37. A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. . Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. On the other hand, the output port 36 is connected to the spark plug 6, the actuators 8 and 11, the fuel injection valve 15, and the electric motor 18 through a corresponding drive circuit 38.

  FIG. 2 shows an enlarged view of the intake valve driving actuator 8. Referring to FIG. 2, 50 is a disc-shaped iron piece attached to the top of the intake valve 7, 51 and 52 are solenoids arranged on both sides of the iron piece 50, and 53 and 54 are compression springs arranged on both sides of the iron piece 50. Respectively. When the solenoid 51 is energized, the iron piece 50 is raised and the intake valve 7 is closed. On the other hand, when the solenoid 52 is energized, the iron piece 50 is lowered and the intake valve 7 is opened. Therefore, by controlling the urging timing of the solenoids 51 and 52, the intake valve 7 can be opened and closed at an arbitrary timing. The exhaust valve drive actuator 11 also has the same structure as the intake valve drive actuator 8 shown in FIG. 2, and therefore the exhaust valve 10 can be opened and closed at any time.

  FIG. 3 shows the opening timing IO of the intake valve 7, the closing timing IC of the intake valve 7, the opening timing EO of the exhaust valve 10, the closing timing EC of the exhaust valve 10, and the opening θ of the throttle valve 19. . In FIG. 3, the horizontal axis represents the amount of depression L of the accelerator pedal 40, that is, the required load. The embodiment according to the present invention is intended to cause self-ignition in a predetermined load range from low engine load to medium load, and this load range is shown as a self-ignition region in FIG.

  As shown in FIG. 3, the valve opening timing EO of the exhaust valve 10 is fixed to a crank angle slightly before the compression bottom dead center BDC regardless of the required load L. On the other hand, in the self-ignition region, the closing timing EC of the exhaust valve 10 is set slightly before the intake top dead center TDC, and the closing timing EC of the exhaust valve 10 is advanced as the required load L becomes lower. . When the closing timing EC of the exhaust valve 10 is advanced, the burnt gas remaining in the combustion chamber 5 increases, and when the burnt gas remaining in the combustion chamber 5 increases, it is supplied into the combustion chamber 5 during the intake stroke. Intake air volume decreases. That is, the intake air amount decreases as the required load L decreases.

  On the other hand, as shown in FIG. 3, the throttle valve 19 is maintained in the fully open state over almost the entire self-ignition region. Therefore, the control of the intake air amount with respect to the required load L is performed by setting the closing timing of the exhaust valve 10. This is done by changing, that is, by changing the amount of residual burnt gas. Therefore, the engine output can be controlled according to the required load L without causing a pumping loss.

  As shown in FIG. 3, in the self-ignition region, the valve opening timing IO of the intake valve 7 is set when the intake top dead center TDC is slightly exceeded, and the valve opening timing IO of the intake valve 7 is the required load. The lower the L, the slower. When the opening timing IO of the intake valve 7 is delayed, the intake air amount decreases. Therefore, the control of the valve opening timing IO of the intake valve 7 also serves to control the engine output in accordance with the required load L.

  On the other hand, it has been found that self-ignition occurs when the intake air temperature supplied into the combustion chamber 5 reaches approximately 1000 ° K. Since the intake air is heated by the burned gas and the temperature rises, whether or not the temperature of the intake air supplied into the combustion chamber 5 can be raised to about 1000 ° K remains in the combustion chamber 5. It depends on the heat energy of the gas. As shown in FIG. 3, when the required load L decreases, the valve closing timing EC of the exhaust valve 10 is advanced, so the amount of residual burned gas increases. From this point of view, the thermal energy of the burned gas is determined by the required load L. The lower it is, the higher it will be. On the other hand, the lower the required load L, the lower the combustion temperature. From this point of view, the thermal energy of the burned gas decreases as the required load L decreases. Overall, the thermal energy of the burned gas decreases as the required load L decreases.

  On the other hand, when the required load L increases, the amount of residual burned gas decreases, but the burnt gas temperature increases because the combustion temperature increases. In this case, when viewed comprehensively, the thermal energy of the burned gas decreases as the required load L increases. That is, when the required load L is neither low nor high, the amount of residual burned gas is relatively large, and the residual burned gas temperature is also relatively high. At this time, the thermal energy of the burned gas becomes the highest. That is, the thermal energy of the residual burned gas changes as shown in FIG.

  When the residual burned gas has a high thermal energy, the intake air temperature will reach about 1000 ° K even if the compression ratio is low, and when the residual burned gas has a low thermal energy, the compression ratio must be increased to raise the intake air temperature. The intake air temperature does not reach nearly 1000 ° K. On the other hand, if the valve closing timing IC of the intake valve 7 is delayed after the intake bottom dead center BDC, the compression ratio becomes lower as it is delayed. Accordingly, the closing timing IC of the intake valve 7 is gradually delayed with an increase in the required load L as shown in FIG. 3 so that the compression ratio becomes the smallest when the residual burned gas has the highest thermal energy. It is done. By controlling the opening timing IO and the closing timing IC of the intake valve 7 and the closing timing EC of the exhaust valve 10 in the self-ignition region as shown in FIG. 3, self-ignition is performed in the self-ignition region shown in FIG. Can be generated.

  As shown in FIG. 3, when the required load L is lower than the self-ignition region, self-ignition does not occur, and at this time, normal combustion by the spark plug 6 is performed. At this time, the engine output is controlled by controlling the opening degree of the throttle valve 19 in accordance with the required load L. Further, when the required load L is higher than the self-ignition region, self-ignition does not occur, and normal combustion by the spark plug 6 is also performed at this time. However, at this time, the engine output is controlled by changing the valve opening period of the intake valve 7 and the valve opening period of the exhaust valve 10 according to the required load.

  In an embodiment according to the present invention, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio in order to cause self-ignition over a wide range of operating conditions. The basic injection time TP necessary for setting the air-fuel ratio to the stoichiometric air-fuel ratio is stored in advance in the ROM 32 as a function of the engine speed N and the required load L in the form of a map shown in FIG. Is corrected based on the output signal of the air-fuel ratio sensor 21, so that the air-fuel ratio is maintained at the stoichiometric air-fuel ratio.

  FIG. 6 shows an engine operation control routine. Referring to FIG. 6, first, at step 60, the valve opening timing IO and the valve closing timing IC of the intake valve 7 corresponding to the required load L shown in FIG. 3 are calculated, and then at step 61, the required load shown in FIG. The valve opening timing EO and the valve closing timing EC of the exhaust valve 10 corresponding to L are calculated. Next, at step 62, the opening degree θ of the throttle valve 19 corresponding to the required load L shown in FIG. 3 is calculated. Next, at step 63, the basic injection time TP is calculated from the map shown in FIG. 5, and then at step 64, the basic injection time TP is corrected based on the output signal of the air-fuel ratio sensor 21 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. An injection time TAU is calculated.

1 is an overall view of a 4-stroke engine. It is an expanded side sectional view of the actuator for intake valve driving. It is a figure which shows the on-off valve timing etc. of an intake valve and an exhaust valve. It is a figure which shows the thermal energy of residual burned gas. It is a figure which shows the map of basic injection time. It is a flowchart for performing operation control of an engine.

Explanation of symbols

7 Intake valve 10 Exhaust valve 15 Fuel injection valve

Claims (8)

  In a four-stroke engine equipped with a spark plug, when the engine load is within a predetermined load range from low load to medium load, the intake air temperature supplied into the combustion chamber rises to a temperature at which self-ignition is possible. A four-stroke engine that controls the intake valve on / off valve timing and exhaust valve on / off valve timing to cause self-ignition that does not depend on the spark plug, and that is ignited by the spark plug when the engine load is outside the load range. Control device.   The control apparatus for a four-stroke engine according to claim 1, wherein the temperature at which the self-ignition is possible is approximately 1000 ° K.   The four-stroke engine according to claim 1, wherein when the engine load is within the load range, the exhaust valve is closed before the intake top dead center, and the closing timing of the exhaust valve is advanced as the required load decreases. Control device.   2. The four-stroke engine according to claim 1, wherein when the engine load is within the load range, the intake valve is opened after intake top dead center, and the opening timing of the intake valve is delayed as the required load decreases. Control device.   2. The engine according to claim 1, wherein when the engine load is within the load range, the intake valve is closed after the intake bottom dead center, and the closing timing of the intake valve is gradually delayed as the required load increases and then gradually advanced. 4. A control device for a 4-stroke engine.   2. The control apparatus for a four-stroke engine according to claim 1, wherein a throttle valve is disposed in the engine intake passage, and the throttle valve is held in a fully open state in substantially the entire load range.   When the engine load is within the above load range, the engine output is controlled by changing either or both of the exhaust valve closing timing and the intake valve opening timing according to the required load, and the engine load is 7. The control device for a four-stroke engine according to claim 6, wherein when the pressure is lower than the range, the engine output is controlled by controlling the opening of the throttle valve.   The control apparatus for a four-stroke engine according to claim 1, wherein the air-fuel ratio is made the stoichiometric air-fuel ratio when the engine load is within the load range.

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