JPH05209552A - Engine control device - Google Patents

Abstract

PURPOSE:To provide an engine control device of high endurance reliability capable of switching the effective compression ratio of an engine into a compression ratio fit for lean-burn operation or normal operation at the time of performing the appropriate switching control of lean-burn operation and normal operation according to the operating state of the engine. CONSTITUTION:The operating state of an engine 2 is detected by various sensors 8, 16, 18, 20. In the case of being lean-burnable, an air-fuel ratio is set leaner than a stoichiometric air-fuel ratio, whereas in the case of being out of lean- burn, the air-fuel ratio is set in the vicinity of the stoichiometric air-fuel ratio, and the operation of a fuel injection valve 12 is controlled by an air-fuel ratio control unit 14. The operation of inlet cam switching mechanism 24 is controlled by a valve timing control unit 22, and at the lean control time, the valve opening timing of an intake valve is brought closer to the bottom dead center than the non-lean control time so as to heighten the effective compression ratio of the engine 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the operating state of an engine and controls the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio when a predetermined lean control execution condition is satisfied, while it is controlled when the lean control execution condition is not satisfied. This is related to the engine control device that controls the fuel ratio to rich in the vicinity of the stoichiometric air-fuel ratio, and in particular, to improve the emission performance during normal operation when the air-fuel ratio is controlled rich and to improve the combustion during lean burn operation that is controlled lean. The present invention relates to an engine control device that achieves both stability and improvement.

[0002]

2. Description of the Related Art Conventionally, the operating state of an engine is detected from the number of revolutions, the amount of intake air, etc., and when a predetermined condition enabling lean burn operation is satisfied, the air-fuel ratio of the air-fuel mixture to be supplied to the engine is theoretically calculated. While the fuel ratio is controlled to be leaner than the fuel ratio (A / F = 14.7) to improve the fuel consumption, the air-fuel ratio is controlled to be rich near the stoichiometric air-fuel ratio during normal operation when the above-mentioned predetermined condition is not satisfied. For example, Japanese Patent Application Laid-Open No. 59-208141 discloses a control technique of an engine that obtains sufficient output while ensuring exhaust purification performance by a three-way catalyst or the like.

Further, by varying the valve timing of the intake / exhaust valve in accordance with the operating state of the engine, the intake charge efficiency of the engine is improved from the low rotation range to the high rotation range of the engine to obtain a sufficient output. The engine control technology for securing the engine is already known.

[0004]

By the way, when the engine is operated in lean burn mode, the compression ratio of the air-fuel mixture is set to the air-fuel ratio in order to ensure sufficient combustion efficiency and combustion stability of the engine under lean burn operation. Is required to be set higher than in the normal operation in which the fuel is burned rich while being kept near the stoichiometric air-fuel ratio.

However, if the engine is set to a high compression ratio suitable for lean combustion, the combustion speed during normal operation becomes unnecessarily high, resulting in deterioration of NOx emissions and damage to the engine due to abnormal combustion. That problem will occur. For this reason, in the past, the air-fuel ratio under lean combustion could not be made lean enough to obtain sufficiently high effects in terms of combustion stability, thermal efficiency, and fuel consumption.

When the engine is set to a high compression ratio suitable for lean combustion, the ignition timing is delayed and the air-fuel mixture is made richer as a method for slowing the combustion speed during normal operation. There are two possible methods, but if the ignition timing is delayed to slow the combustion speed, the exhaust gas temperature rises and the exhaust system is liable to be damaged, and the mixture is made richer. If the combustion speed is slowed down and the exhaust gas temperature is lowered by doing so, adverse effects such as deterioration of fuel consumption and deterioration of HC emission will occur, and both cannot be effective measures.

That is, in order to achieve a higher degree of compatibility between the engine output performance and the fuel efficiency performance, the effective compression ratio of the engine is controlled when the lean burn operation and the normal operation are appropriately switched according to the operating condition of the engine. The control for switching between the compression ratio suitable for lean burn operation and the compression ratio suitable for normal operation may be performed at the same time.

As a mechanism for varying the effective compression ratio of the engine, there is known a mechanism for changing the relative position of the connecting portion between the connecting rod and the crankshaft or the connecting rod and the piston to increase or decrease the volume of the combustion chamber. However, since such a variable mechanism of the effective compression ratio is provided in a portion directly receiving the explosion pressure, there is a problem in terms of its durability and reliability at present. Yes, it is not practical.

Therefore, in view of the above circumstances, the present applicant has noticed that the effective compression ratio can be varied by controlling the closing timing of the intake valve by utilizing the valve timing varying means of the intake / exhaust valve. Invented the present invention.

That is, an object of the present invention is to effectively switch the lean-burn operation and the normal operation in accordance with the operating state of the engine in order to achieve both the output of the engine and the fuel consumption. It is an object of the present invention to provide an engine control device capable of simultaneously performing control for switching between a compression ratio suitable for lean burn operation and a compression ratio suitable for normal operation, and having high durability and reliability.

[0011]

In order to achieve the above object, an engine control apparatus according to the present invention detects an operating state of an engine and sets an air-fuel ratio to a theoretical air-fuel ratio when a predetermined lean control execution condition is satisfied. While controlling by setting to a leaner side than the fuel ratio, when the lean control execution condition is not satisfied, the air-fuel ratio is set to rich in the vicinity of the stoichiometric air-fuel ratio and controlled, and the air-fuel ratio control means A valve timing variable that moves the closing timing of the intake valve closer to bottom dead center to increase the effective compression ratio of the engine during lean control, while moving the closing timing away from bottom dead center to reduce the effective compression ratio of the engine during non-lean control. And a control means.

The variable valve timing control means controls an intake cam switching mechanism that can switch the driving cam of the intake valve between the low compression ratio cam and the high compression ratio cam, and the operation of the switching mechanism. A valve timing control unit, the low compression ratio cam is provided with a valve lift characteristic for opening an intake valve before top dead center and closing it after bottom dead center, and at the same time, the high compression ratio cam is provided. Is provided with a valve lift characteristic in which the valve opening timing is closer to the top dead center and the valve closing timing is closer to the bottom dead center as compared with the low compression ratio cam, and the lean control is applied to the valve timing control unit. It is desirable to add a function to switch the drive cam of the intake valve to the high compression ratio cam at the same time, and to switch the drive cam to the low compression ratio cam during the non-lean control.

Alternatively, the variable valve timing control means comprises a phase angle changing mechanism capable of changing the phase angle of the camshaft, and a valve timing control unit for controlling the operation of the phase angle changing mechanism. In the control unit, the phase angle of the camshaft is advanced during the lean control to bring the closing timing of the intake valve close to the bottom dead center, while the phase angle is retarded during the non-lean control to decrease the closing timing. It is desirable to add the function of separating from the dead point.

[0014]

According to the present invention having the above-described structure, when the detected operating condition of the engine satisfies the predetermined lean control execution condition for the lean burn operation, the air-fuel ratio control means causes the air-fuel mixture to be supplied to the engine. The air-fuel ratio of is set to a leaner side than the theoretical air-fuel ratio to control the fuel supply amount, and the valve timing variable means makes the closing timing of the intake valve close to the bottom dead center to lengthen the effective compression stroke of the piston, Therefore, the effective compression ratio of the engine is increased. Further, when the lean control execution condition is not satisfied, the air-fuel ratio control means sets the air-fuel ratio of the air-fuel mixture supplied to the engine to rich in the vicinity of the theoretical air-fuel ratio and controls the fuel supply amount, The variable valve timing means separates the closing timing of the intake valve from the bottom dead center to shorten the effective compression stroke of the piston and thereby reduce the effective compression ratio of the engine.

Further, as a mechanism for changing the closing timing of the intake valve, a switching mechanism for the intake valve driving cam is adopted to bring the closing timing closer to the bottom dead center and increase the opening timing during lean control. When the dead point is approached, the overlap period with the exhaust valve can be shortened and the combustion stability can be improved by reducing the internal EGR.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a schematic structure of a DOHC engine equipped with an engine control device according to the present invention.
In the figure, reference numeral 2 designates an engine, and an intake passage 4 of the engine 2 has an air cleaner 6, an air flow meter 8, a throttle valve 10, a fuel injection valve 1 from the upstream side thereof.
2 are sequentially provided.

The fuel injection valve 12 is connected to the output side of an air-fuel ratio control unit 14 composed of a microcomputer, and its operation is controlled according to the operating state of the engine 2 according to a software program incorporated therein. On the input side of the air-fuel ratio control unit 14, various sensors for detecting the operating state of the engine 2, such as the air flow meter 8, the engine rotation sensor 16, the cooling water temperature sensor 18, the air-fuel ratio sensor 20, etc. Kind is connected. That is, the various sensors 8, 16, 18, 20, ..., The air-fuel ratio control unit 14, the fuel injection valve 12 and the like constitute an air-fuel ratio control means.

Further, the air-fuel ratio control unit 14 is connected to a valve timing variable control means for controlling the opening / closing timing of the intake / exhaust valves 2a, 2b of the engine 2 by receiving a signal from the air-fuel ratio control unit 14. The variable valve timing control means has a valve timing control unit 22 which is connected to the air-fuel ratio control unit 14 and receives signals from the air-fuel ratio control unit 14. The output side of the valve timing control unit 22 is operated by the control unit 22. The intake cam switching mechanism 24 for controlling the intake air, the intake camshaft phase angle changing mechanism 26, and the exhaust camshaft phase angle changing mechanism 28 are connected.

FIG. 2 shows a specific example of the intake cam switching mechanism 24. The intake cam switching mechanism 24 is fixed to the intake cam shaft 240 formed in a spline shape. High compression ratio cam 24
1 and a low compression ratio cam 2 which slides on the intake camshaft 240 and can move away from the high compression ratio cam 241 close to and away from each other.
42, a spring 243 that is provided on the high compression ratio cam 241 side and urges the low compression ratio cam 242 away from it, and a low compression ratio cam 242 against the biasing force of the spring 243. Of the hydraulic plunger 244 that moves the cam to the side of the high compression ratio cam 241 and abuts it, and the hydraulic plunger 244 that is formed by being drilled in the cam shaft 240.
A hydraulic oil supply passage 245 for supplying hydraulic oil to the oil supply passage and an oil pressure adjusting means (not shown) for driving and controlling the hydraulic oil supplied to the oil supply passage 245 under drive control by the valve timing control unit 22.

The high compression ratio cam 241 is fixedly arranged at a position in sliding contact with a hydraulic tappet 246 provided at the upper end of the intake valve 2a, and when the low compression ratio cam 242 comes close to the high compression ratio cam 241, the tappet described above is provided. When it comes into sliding contact with the 246 and is separated from it, it is separated from the tappet 246.

The cam profile of the high compression ratio cam 241 is such that the valve lift is started at the top dead center (TDC) of the piston and the valve lift is ended at the bottom dead center (BDC). The cam profile of the compression ratio cam 242 starts the valve lift before the top dead center and ends the valve lift after the bottom dead center, and the cam profile of the high compression ratio cam 241 is the low compression ratio cam. Two
The cam valve 242 has a shape to be included in the cam profile of the valve 42. When the low compression ratio cam 242 slides on the tappet 246, the intake valve 2a is opened and closed by the low compression ratio cam 242.

FIG. 3 shows a specific example of the phase angle changing mechanism 26 of the intake camshaft, and FIG. 4 shows a schematic configuration diagram of the phase angle changing mechanism 26. The phase angle changing mechanism 26 is arranged between a timing gear 312 that inputs crankshaft rotation via a timing belt (not shown) and an intake camshaft 240 that drives the intake valve 2a (not shown). An advancing plate 316 fitted to the inner circumference, a drum 318 screwed to the inner circumference of the advancing plate 316, a return spring 320 for biasing the drum 318 in a constant rotation direction, and a cam shaft 240 fixed to the cam shaft 240. And a hub 322 that operates.

A first member is provided on the inner circumference of the timing gear 312.
The claw member 312a is integrally provided so as to project, and a first engagement groove 316a is formed on the outer periphery of the advancing plate 316. The first claw member 31 is formed in the first engagement groove 316a.
The slidable engagement of 2a restricts the relative rotation of the timing gear 312 and the advancing plate 316 while allowing relative movement in the axial direction.

A female screw 316b is formed on the inner circumference of the advancing plate 316, and the drum 31
8 has a male screw 318a formed on the outer periphery thereof, and these female screw 31
6b and the male screw 318a are screwed together. Then, by rotating the advancing plate 316 and the drum 318 relatively, the female screw 316b and the male screw 318a are formed.
The advancing plate 316 through the drum 318
Move axially with respect to.

On the other hand, the return spring 320 is constructed as a spiral spring, the inner peripheral end 320a of which is locked to the drum 318 and the outer peripheral end 320b.
Of the return spring 3
20 urges the drum 318 in one direction of rotation.

A second pawl member 32 is provided on the outer periphery of the hub 322.
2a integrally projecting, a second engaging groove 316c is formed on the outer periphery of the advancing plate 316, and the second claw member 322a slidably engages with the second engaging groove 316c. As a result, the relative rotation of the advancing plate 316 and the hub 322 is restricted while allowing relative movement in the axial direction.

A friction drum 324 is press-fitted and fixed to the inner circumference of the drum 318, and the friction drum 324 is also attached.
A pair of brake shoes 326 and 326a are arranged to face each other on the inner circumference of the. And these brake shoes 326, 326
a is interlocked with the solenoid actuator 330 via the links 328 and 328a, so that the friction brake 324, the brake shoes 326 and 326a, and the solenoid actuator 330 cause the electromagnetic brake 33.
Make up 2.

In this embodiment, as shown in FIG. 4, the first claw member 312a is inclined with respect to the axial direction to have a helical angle .theta.1 and the second claw member 322a is provided. Is similarly tilted in the axial direction to have a helical angle θ2. Incidentally, these helical angles θ1 and θ2 are set in an inverse relationship to each other with respect to the axial direction.

In the above phase angle changing mechanism 26, by applying a voltage (ON signal input) to the solenoid actuator 330 of the electromagnetic brake 332 to excite it,
The brake shoes 326 and 326a are brought into pressure contact with the inner circumference of the friction drum 24 to be in a braking state. Meanwhile, the voltage applied to the solenoid actuator 330 is cut off (OFF signal input).
Then, the brake shoes 326, 32 are demagnetized.
6a separates from the friction drum 324 and enters a non-braking state.

When the electromagnetic brake 332 is in a braking state, the drum 318 integrated with the friction drum 324 causes a rotation delay with respect to the advancing plate 316. Then, the advancing plate 316 moves in the axial direction (rightward in FIG. 1) via the female screw 316b and the male screw 318a. At this time, the first claw member 312a and the second claw member 322a are both tilted and the helical angle is increased. θ1
And .theta.2 are set, the advancing plate 316 and the hub 322 respectively advance relative to the timing gear 312 by rotating in the same direction. At this time, the hub 322 becomes the return spring 320.
Rotates against the urging force of.

Therefore, the timing gear 312 and the hub 32
2 means that the relative rotation amount is a sum of the relative rotation amount determined by the helical angle θ1 of the first claw member 312a and the relative rotation amount determined by the helical angle θ2 of the second claw member 322a. Become. Therefore, during transmission of the crankshaft rotation input to the timing gear 312 to the camshaft 240, the timing gear 31
2 and the relative rotation amount between the hub 322 are transmitted as they are as the rotational displacement amount of the cam shaft 240, and the intake valve 2a
The valve timing of can be changed.

On the other hand, when the electromagnetic brake 332 is in the non-braking state, the drum 318 causes the return spring 320 to move.
The advancing plate 316 is moved in the left direction in FIG. 3 by the biasing force of to move the advancing plate 316 to the left in FIG. Therefore, this advancing plate 316
The timing gear 312 and the hub 32
Relative rotation in the direction opposite to 2 causes the phase of the camshaft 240 to be set to the initial state.

The phase angle changing mechanism 2 for the exhaust camshaft
8 is also constructed in exactly the same manner as the phase angle changing mechanism 26 of the intake camshaft.

By the way, the air-fuel ratio control unit 14 detects the operating state of the engine 2 based on the information signals input from the various sensors 8, 16, 18, 20 and the operating state meets a predetermined lean control execution condition. If satisfied, the air-fuel ratio of the air-fuel mixture supplied to the engine 2 is set to be leaner than the stoichiometric air-fuel ratio to control the operation of the fuel injection valve 12, while the lean control execution condition is not satisfied, The fuel injection valve 12 is set by setting the air-fuel ratio rich near the stoichiometric air-fuel ratio.
Control the operation of.

Further, the valve timing control unit 22
Receives a signal from the air-fuel ratio control unit 14 to increase the effective compression ratio of the engine 2 when executing lean control,
Further, when the non-lean control is executed, the intake cam switching mechanism 24, the intake camshaft phase angle changing mechanism 26, and the exhaust camshaft phase angle changing mechanism 28 are arranged to reduce the effective compression ratio.
Control the operation of.

FIG. 6 is a flow chart showing the outline of the control contents executed by the air-fuel ratio control unit 14 and the valve timing control unit 22. As shown in the figure, first, various sensors 8, 16, 18, 20 ,. Is read to detect the operating state of the engine and (S
10) Calculate the intake charge ratio CE from the intake air flow rate Qa and the engine speed (S20), and determine the basic drive signal Tm of the fuel injection valve 12 required to control the intake charge ratio CE to the stoichiometric air-fuel ratio. Calculate (S30).

Next, it is judged whether or not the load condition for executing the lean control is satisfied (S40). This load condition is whether or not both the calculated intake charge ratio CE and the detected engine speed are included in a predetermined lean control execution region defined by the relationship between the intake charge ratio CE and the engine speed. The lean control execution area is stored in advance in the air-fuel ratio control unit 14 as a map.

If the load condition is satisfied (S40, Y
es), next, it is determined whether or not the water temperature condition of the lean control execution condition, that is, the cooling water temperature is equal to or higher than a predetermined value THWL (S50).

If the determination in step S50 is NO, and if the determination in step S40 is NO, the routine proceeds to step S110, where the basic air-fuel ratio is made rich in the vicinity of the theoretical air-fuel ratio. After the drive signal Tm is multiplied by the correction coefficient C during normal operation to calculate the actual drive signal Ti (= Tm * C) at the time of rich, the intake cam switching mechanism 2
A low compression ratio valve timing signal is output to the actuator (hydraulic pressure adjusting means) of No. 4, the solenoid actuator of the intake camshaft phase angle changing mechanism 26, and the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28 (S120). The actual drive signal Ti (= Tm * C) is output to the fuel injection valve 12 (S130).

When a low compression ratio valve timing signal is input to the actuator (hydraulic pressure adjusting means) of the intake cam switching mechanism 24, the actuator (hydraulic pressure adjusting means) switches the hydraulic pressure supplied to the working oil to the high pressure side. , The plunger 244 is extended to engage the low compression ratio cam 242 with the hydraulic tappet of the intake valve 2a.
Is opened and closed by the low compression ratio cam 242. Also,
When a low compression ratio valve timing signal (voltage ON) is input to the solenoid actuator 330 of the intake camshaft phase angle changing means 26, the intake camshaft 240
Is set to the advance side. Furthermore, when a low compression ratio valve timing signal (voltage OFF) is input to the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28, the exhaust camshaft is set to the retard side.

That is, the valve lift characteristic of the intake valve 2a at this time is such that the valve starts to open before the top dead center and closes after the bottom dead center as shown by the broken line A in FIG. The effective compression stroke Sa of the piston is shortened by the amount of the delayed closing, and the effective compression ratio of the engine is lowered. On the other hand, the valve lift characteristic of the exhaust valve 2b starts to open before the bottom dead center and closes after the top dead center as shown by the broken line B in the figure, and the intake valve 2a and the exhaust valve 2b are not lean. A predetermined overlap period suitable for normal operation during control is set.

On the other hand, the determination in step S50 is Yes.
If the cooling water temperature is equal to or higher than the predetermined value THWL in s, the lean control of the air-fuel ratio is performed, but before that, in the next step S60, the engine speed is set to a high speed region higher than the predetermined speed Nc. Determine if there is. Then, if this determination is No and the engine speed is in the low speed region, the routine proceeds to step S70, where the correction coefficient C and the lean coefficient in the normal operation are added to the basic drive signal Tm so that the air-fuel ratio becomes leaner than the theoretical air-fuel ratio. After calculating the lean actual drive signal Ti (= Tm * C * CLEAN) by multiplying by the correction coefficient CLEAN, the actuator (hydraulic pressure adjusting means) of the intake cam switching mechanism 24 and the solenoid of the intake camshaft phase angle changing mechanism 26. A low rotation and high compression ratio valve timing signal is output to the actuator and the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28 (S
80) together with the actual drive signal Ti (= T) to the fuel injection valve 12.
m * C * CLEAN) is output (S130).

Here, when a signal of low rotation / high compression ratio valve timing is input to the actuator (hydraulic pressure adjusting means) of the intake cam switching mechanism 24, this actuator (hydraulic pressure adjusting means) changes the hydraulic pressure of the working oil supplied to the low pressure side. Then, the plunger 244 is pushed back by the spring 243 to disengage the low compression ratio cam 242 from the hydraulic tappet of the intake valve 2a, and the intake valve 2a is opened and closed by the high compression ratio cam 241. Further, the intake camshaft phase angle changing means 2
When a signal of low rotation and high compression ratio valve timing (voltage ON) is input to the solenoid actuator 330 of No. 6,
The intake camshaft 240 is set to the advance side. Furthermore, when a low rotation / high compression ratio valve timing signal (voltage ON) is input to the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28, the exhaust camshaft is set to the advance side.

That is, the valve lift characteristic of the intake valve 2a at this time is such that the valve starts to open from substantially top dead center and closes substantially at bottom dead center as shown by the solid line C in FIG. The stroke Sc becomes longer and the effective compression ratio of the engine becomes higher. On the other hand, the valve lift characteristic of the exhaust valve 2b is advanced as shown by the solid line D in the figure, starts to open before the bottom dead center and closes at the top dead center, so that the intake valve 2a and the exhaust valve 2b are closed. There is almost no overlap period between and, and combustion is stabilized by reducing the internal EGR.

Further, the judgment in step S60 is Yes.
If the engine speed is in the high speed range in step s, step S9
0 (same as S70), the basic drive signal Tm is multiplied by the correction coefficient C during normal operation and the lean correction coefficient CLEAN so that the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio, and the actual drive signal during lean is obtained. Ti (= Tm * C * CLEA
After calculating N), a high rotation height is obtained with respect to the actuator (hydraulic pressure adjusting means) of the intake cam switching mechanism 24, the solenoid actuator of the intake camshaft phase angle changing mechanism 26, and the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28. The signal of the compression ratio valve timing is output (S100), and the actual drive signal Ti (= Tm * C * CLEAN) is output to the fuel injection valve 12 (S13).
0).

Here, when a signal of high rotation / high compression ratio valve timing is input to the actuator (hydraulic pressure adjusting means) of the intake cam switching mechanism 24, this actuator (hydraulic pressure adjusting means) operates as in the case of low rotation / high compression ratio. Similarly, the supply hydraulic pressure of the hydraulic oil is switched to the low pressure side, and the intake valve 2a is opened / closed by the high compression ratio cam 241. Further, the solenoid actuator 33 of the intake camshaft phase angle changing means 26.
Signal of high rotation and high compression ratio valve timing to 0 (voltage OF
When F) is input, the intake camshaft 240 is set to the retard side. When a high rotation / high compression ratio valve timing signal (voltage ON) is input to the solenoid actuator of the exhaust camshaft phase angle changing mechanism 28, the exhaust camshaft is advanced toward the advance side as in the case of the low rotation / high compression ratio. Is set.

In other words, in the case of high rotation and high compression ratio, FIG.
As indicated by the alternate long and short dash line E, the valve lift characteristic of the intake valve 2a is slightly retarded from that at the time of the low rotation and high compression ratio, so that the inertial supercharging action of the intake at the time of high rotation is utilized. Improve filling efficiency. Further, even if the closing timing of the intake valve 2a is slightly delayed in this way, the effective compression stroke Se of the piston hardly changes, so that the effective compression ratio of the engine 2 can be kept high.

In the embodiment described above, the effective compression ratio of the engine is changed by using the intake cam switching mechanism capable of switching the intake valve driving cam to the low compression ratio cam and the high compression ratio cam. However, in the present invention, basically, the effective compression ratio may be increased by bringing the closing timing of the intake valve during lean control of the air-fuel ratio closer to the bottom dead center than during non-lean control. The effective compression ratio may be changed by attaching a phase angle changing mechanism and making the valve closing timing closer to the bottom dead center in lean control than in non-lean control.

The present invention is not limited to the DOHC engine of the above embodiment, but can be applied to a SOHC engine. Also in this case, the phase angle changing mechanism is attached to the single camshaft that drives the intake valve and the exhaust valve,
The intake valve closing timing may be brought close to the bottom dead center during lean control, or two intake valve driving cams for the low compression ratio and the high compression ratio may be provided on the camshaft and these may be appropriately set. You may make it switch. The cam switching mechanism may be a mechanism that moves the cam itself or a mechanism that moves the rocker arm side. Furthermore, both the phase angle changing mechanism and the intake cam switching mechanism are provided to change the compression ratio by switching the cams, and the phase angle changing mechanism advances the valve timing of the exhaust valve to eliminate the overlap. You may do it.
Further, a differential planetary gear mechanism or the like may be adopted as the phase angle changing mechanism.

[0051]

As described in detail in the above embodiments, the engine control device according to the present invention exhibits the following excellent effects.

(1) When the operating state of the engine is detected, and when the state allows lean combustion, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to be leaner than the theoretical air-fuel ratio. When lean combustion is not possible, when controlling the air-fuel ratio rich near the stoichiometric air-fuel ratio, the effective compression ratio of the engine is increased during lean control compared to during non-lean control, so the air-fuel ratio under lean combustion is burned. Not only can it be made lean until a sufficiently high effect is obtained in terms of stability, thermal efficiency and fuel efficiency, but it also prevents the deterioration of emulation and the occurrence of abnormal combustion during non-lean controlled normal operation as much as possible. it can.

(2) As a mechanism for changing the effective compression ratio of the engine, without using a mechanism for changing the relative position of the connecting portion between the connecting rod and the crankshaft or the connecting rod and the piston to increase or decrease the volume of the combustion chamber. Since the effective compression ratio of the engine is changed by changing the closing timing of the intake valve, the explosion pressure of the engine does not act on the mechanism for changing the compression ratio, which is excellent in terms of reliability and durability. ..

(3) If the intake cam is switched to change the valve timing of the intake valve, not only the closing timing of the intake valve can approach the bottom dead center during lean combustion, but also the opening timing of the intake valve tops. Since it is close to the point, the overlap period between the intake valve and the exhaust valve can be shortened to reduce the internal EGR, and combustion stability can be improved as much as possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an engine control device according to the present invention.

FIG. 2 is a view showing an example of an intake cam switching mechanism shown in FIG.

3 is a diagram showing an example of an intake camshaft phase angle changing mechanism shown in FIG.

FIG. 4 is a schematic configuration diagram showing a main part of FIG.

FIG. 5 is a diagram illustrating an operation by control of the engine according to the present invention.

FIG. 6 is a flowchart schematically showing an example of control contents by the engine control device according to the present invention.

[Explanation of symbols]

 2 engine 2a intake valve 8 air flow meter 12 fuel injection valve 14 air-fuel ratio control unit 16 engine rotation sensor 18 water temperature sensor 20 air-fuel ratio sensor 22 valve timing control unit 24 intake cam switching mechanism 26 (intake) camshaft phase angle changing mechanism 240 ( Intake) Camshaft 241 High compression ratio cam 242 Low compression ratio cam

Claims (3)

[Claims] 1. A lean control means for detecting an operating state of an engine to set the air-fuel ratio to a leaner side than a stoichiometric air-fuel ratio when a predetermined lean control execution condition is satisfied, and an air-fuel ratio when the lean control execution condition is not satisfied. The air-fuel ratio control means having a non-lean control means for setting rich to near the stoichiometric air-fuel ratio, and the intake valve closing timing to increase the effective compression ratio of the engine during lean control of the air-fuel ratio by the air-fuel ratio control means. And a valve timing variable control means for separating the valve closing timing from the bottom dead center in order to lower the effective compression ratio of the engine during non-lean control, while controlling the valve timing to a bottom dead center. 2. The variable valve timing control means controls an intake cam switching mechanism capable of switching a driving cam of an intake valve between a low compression ratio cam and a high compression ratio cam, and controls the operation of the switching mechanism. And a valve timing control unit, wherein the low compression ratio cam has a valve lift characteristic of opening the intake valve before top dead center and closing it after bottom dead center, and the high compression ratio cam includes The valve timing control unit has a valve lift characteristic in which the valve opening timing is closer to the top dead center and the valve closing timing is closer to the bottom dead center as compared with the low compression ratio cam. The engine control device according to claim 1, further comprising a function of switching the drive cam to a high compression ratio cam and switching the drive cam to a low compression ratio cam during non-lean control. 3. The valve timing variable control means comprises a phase angle changing mechanism capable of changing the phase angle of the camshaft, and a valve timing control unit controlling the operation of the phase angle changing mechanism. The control unit advances the phase angle of the camshaft during lean operation to bring the intake valve closing timing closer to the bottom dead center, while delaying the phase angle during non-lean control to reduce the valve closing timing. The engine control device according to claim 1, having a function of separating from a dead point.