JPH0621579B2 - Variable valve timing engine control method - Google Patents

Description

The present invention relates to a control method for an internal combustion engine including a mechanical supercharger and a variable valve timing mechanism.

[Conventional technology]

There is an internal combustion engine provided with a supercharger to improve the output of the engine. In such an internal combustion engine, considering the high load operation in which the supercharger works, it is necessary to reduce the compression ratio in order to prevent the pressure in the combustion chamber from becoming excessive and knocking to occur. In addition, considering the light load operation in which the supercharger is not working, since the pressure in the combustion chamber is low, the thermal efficiency is reduced and the fuel efficiency is deteriorated. Therefore, it is necessary to increase the compression ratio. However, conventionally, there is known an internal combustion engine that changes the opening / closing timing of an intake valve in order to obtain the same effect as changing the compression ratio according to the operating state of the supercharger (for example, Japanese Patent Laid-Open No. 56- 69411, JP 58-90338, JP 59-49742).

[Problems to be solved by the invention]

If the so-called overlap period from the start of opening the intake valve to the end of closing the exhaust valve is always kept constant while the supercharger is driven, then changes in operating conditions such as changes in supercharging pressure will occur. Therefore, the scavenging of the residual gas in the combustion chamber may not always be in a good state. Further, if the fuel injection is performed before the exhaust valve is closed, unburned fuel is discharged from the exhaust port, resulting in not only insufficient output but also poor fuel efficiency.

[Means for solving problems]

When the supercharger is not driven, the present invention sets the overlap period from the start of opening the intake valve to the end of closing the exhaust valve to be smaller than when the supercharger is driven, and the supercharger is driven. The overlap period is set to be relatively large when the engine supercharging pressure is low, and becomes smaller as the engine supercharging pressure becomes higher according to the engine operating state, and the fuel injection is performed after the exhaust valve is closed. It is characterized by controlling to perform.

〔Example〕

 The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an internal combustion engine to which an embodiment of the present invention is applied.
In the figure, a piston 12 is slidably supported in a cylinder bore 11 formed in an engine body 10, and a combustion chamber 13 is formed above the piston 12. An intake passage 14 and an exhaust passage 15 communicate with the combustion chamber 13. The intake valve 17 and the exhaust valve 18 supported by the cylinder head 16 include an intake port 19 and an exhaust port 20, respectively.
Is opened and closed, and its opening and closing drive is performed by the cams 21 and 22. These cams 21 and 22 are respectively connected to the cam shafts 61 and 61 by a variable valve timing mechanism 60 as described later.
It is relatively rotationally displaced with respect to 62, and changes the opening / closing timing of the intake valve 17 and the exhaust valve 18. A fuel injection valve 23 is provided near the intake valve 17 of the intake port 19, and a rotation speed detector 25 is provided at a distributor 24 attached to the cylinder head 16.

The air cleaner 26 is provided on the most upstream side of the intake passage 14, the air flow meter 27 is located on the downstream side thereof, and further, the throttle valve 28 is disposed on the downstream side thereof. The throttle valve 28 changes the flow passage area in the intake passage 14 in conjunction with the accelerator pedal 29. A surge tank 30 is formed in the intake passage 14 downstream of the supercharger 20, and a pressure detector 70 is attached to the surge tank 30.

The drive shaft 34 of the supercharger 20 is connected to a pulley 35 having an electromagnetic clutch, and this pulley 35 is connected to a crank pulley 36 provided on the engine body 10 by an endless belt 37. Therefore, when the electromagnetic clutch is in the connected state, the supercharger 20
It is driven via the crank pulley 36. Intake passage 14
An upstream side and a downstream side of the supercharger 20 are connected by a bypass passage 38, and a bypass valve 39 for opening and closing the bypass passage 38 is provided in the middle of the bypass passage 38. The actuator 40 that opens and closes the bypass valve 39 includes a shell 41
A diaphragm 42 is formed inside to form a negative pressure chamber 43, and a spring 44 is provided in the negative pressure chamber 43. The diaphragm 42 is connected to the bypass valve 39. Atmospheric pressure or negative pressure is selectively introduced into the negative pressure chamber 43 via the switching valve 45. The atmospheric pressure is introduced from the opening 46 of the air cleaner 16, and the negative pressure is provided downstream of the throttle valve 28. It is led from the negative pressure port 47 on the side.

The switching valve 45 is controlled by an electronic control unit 50 equipped with a microcomputer to guide the actuator 40 to atmospheric pressure or negative pressure. That is, at the time of a light load that does not require supercharging by the supercharger 20, the switching valve 45 is controlled so as to guide the negative pressure on the downstream side of the throttle valve 28 to the actuator 40. When the negative pressure is equal to or higher than the predetermined value, the diaphragm 42 moves down against the spring 44, and the bypass valve 39 opens the bypass passage 38. As a result, even if the supercharger 20 is driven, a part of the discharged air flows back through the bypass passage 38 and returns to the inlet side of the supercharger 20, and the supercharger 20 does not substantially perform supercharging. On the other hand, the switching valve 45 is controlled so as to guide the atmospheric pressure to the actuator 40 at the time of high load that requires supercharging by the supercharger 20. Then, the negative pressure chamber 43 becomes the atmospheric pressure, and the bypass valve 39 is biased by the spring 44 to close the bypass passage 38, whereby the supercharger 20 supercharges.

The electronic control unit 50 outputs a signal indicating the intake air amount from the air flow meter 27, a signal indicating the engine speed from the rotation speed detector 25, and a signal indicating the pressure in the surge tank 30 from the pressure detector 70, that is, the boost pressure P _E. Is input to control the supercharger 20 and the bypass valve 39 as described above, and the variable valve timing mechanism 6 is operated as follows.
0 to control the cams 21 and 22 to the cam shafts 61 and 6 respectively.
The rotational opening and closing timings of the intake valve 17 and the exhaust valve 18 are changed by performing relative rotational displacement with respect to 2.

The variable valve timing mechanism 60 is, as shown in FIG. 3, fixed to the inner sleeve 601 fixed to one end of the cam shafts 61 and 62, rotatably fitted to the inner sleeve 601, and fixed to the timing pulley 63. Outer sleeve 602. The timing pulley 63 is connected to the crankshaft 64 via an endless belt (not shown). The outer sleeve 602 and the inner sleeve 601 have slits 602A and 601A which are inclined with respect to each other as shown in FIG. 4, and a bearing 603 is arranged in this slit. The shaft 604 carrying the bearing 603 is a cam shaft 61, 62.
It is attached to a slider 605 which has an axis line orthogonal to the axis line of and slides left and right in the inner sleeve 601. Slider 6
05 is connected to the output shaft 608 of the step motor 607 via the nut 606. The rotary motion of the step motor 607 is the output shaft 608.
By the screw fitting of the nut 606 with the nut 606, the slider 605 is converted into horizontal movement in the direction of the cam shaft 26. Therefore, the inclined groove 601
The bearing 603 moves in the A and 602A as shown by the arrow X, and causes relative rotation between the inner sleeve 601 and the outer sleeve 602. Therefore, the camshaft 6 on the inner sleeve side
1, 62 and a timing pulley 63 on the outer sleeve side,
In other words, the relative position to the crankshaft 64 changes. As a result, the timing at which the cam crests on the cam shafts 21 and 22 engage with the valve lifter attached to the valve stem, in other words, the valve timing changes. The control circuit 50 provides a signal for controlling such changes in valve timing to the variable valve timing mechanism 60, i.e. the step motor.
Apply to 607.

The electronic control unit 50 controls the intake valve 1 according to the magnitude of the period load.
7 and the opening / closing timing of the exhaust valve 18 are changed. For example, when the engine load is smaller than a predetermined value, the supercharger 2
When 0 is stopped, the opening timing of the intake valve 17 is relatively delayed and the opening timing of the exhaust valve 18 is relatively advanced, as indicated by the broken line in FIG.
That is, near the piston top dead center (TDC), as shown in FIG. 5 (a), the so-called overlap period θ ₁ from the start of opening the intake valve 17 to the completion of closing the exhaust valve 18 is relatively large. Short. After the exhaust valve 18 is closed, the fuel injection valve 23 injects fuel as shown by the broken line in FIG.

On the other hand, when the engine load is larger than the predetermined value, the electronic control unit 50 drives the supercharger 20 and determines the overlap period according to the operating state of the engine. Increase the overlap period. The electronic control unit 50 is, for example, the sixth
As indicated by the solid line in the figure, the opening timing of the intake valve 17 is relatively advanced, the opening timing of the exhaust valve 18 is relatively delayed, and after the exhaust valve 18 is closed, Inject. Then, near the top dead center,
As shown in FIG. 6B, the overlap period θ ₂ is relatively long, and the absolute values of the crank angle at the opening start timing of the intake valve 17 and the crank angle at the closing completion timing of the exhaust valve 18 are mutually equal. Is approximately equal to. That is, the intake valve 17 is started from just before the piston 12 reaches the top dead center (1 / 2θ ₂ crank angle before the top dead center).
Is opened and the piston slightly exceeds top dead center (after top dead center
At 1 / 2θ ₂ crank angle), the exhaust valve 18 closes.
As described above, the lift amount of the exhaust valve 18 is relatively large before the top dead center, and the residual gas in the combustion chamber 13 remains in the piston 1
2 is scavenged from the exhaust port 20 by the compression action, and the lift amount of the intake valve 17 is relatively large after top dead center,
The residual gas in the combustion chamber 13 is scavenged from the exhaust port 20 by the introduction of fresh air from the intake port 19 as the piston 12 descends.

Now, in the present embodiment, when the supercharger 20 is driven, the overlap period is determined again according to the operating state of the engine, that is, the change in supercharging pressure. That is, when the supercharging pressure detected by the pressure detector 70 provided in the surge tank 30 is higher than a predetermined value, the fuel chamber 1
Since the residual gas in 3 is sufficiently scavenged, the overlap period is shortened. Conversely, when the supercharging pressure is lower than a predetermined value, the residual gas is not sufficiently scavenged by this supercharging pressure.
Set the overlap period to be long.

FIG. 1, FIG. 7 and FIG. 8 show flowcharts of control performed by the electronic control unit 50. In the main routine that calls the subroutine shown in this flowchart, the flag f is initialized to 1 in advance when the ignition key switch of the engine is turned on. Step 10
At 1, the intake air amount Q is the engine speed N surplus value Q / N
Corresponds to the load, it is determined whether or not this Q / N is larger than a predetermined value Q ₁ . Initially, the load is smaller than the predetermined value Q ₁ , so the routine proceeds to step 102. In step 102, it is determined whether the flag f is 0. Since f = 1 is set in the main routine as described above, a negative determination is made when step 102 is executed for the first time, and the process proceeds to step 103, where the electromagnetic clutch of supercharger 20 is turned off.
Then, step 104 is executed to delay the valve opening timing of the intake valve 17.

In step 104, a subroutine is executed according to the flowchart shown in FIG. 7, the step motor 607 (FIG. 3) is rotationally driven, and the angular position of the cam 21 with respect to the cam shaft 61 is changed. That is, first, at step 201, the set value of the step motor 607, that is, the target angular position I is read. The target angular position I is determined by the valve opening timing of the intake valve 17. Next, at step 202, the actual angular position J of the step motor 607 is read, and at step 203
Then, it is determined whether the actual angular position J is substantially equal to the target angular position I. Step motor 607 if equal
This subroutine ends to stop the driving of
If they are equal, step 204 is executed and step motor 607
Is rotated by one pulse. In this case, the rotation direction of the motor 607 differs depending on whether the actual angular position J is larger or smaller than the target angular position I. Then, step 202 is executed again, and the loop of steps 204, 202 and 203 is repeated until J = I in step 203.

When the opening timing of the intake valve 17 is changed, step 105 is then executed to advance the opening timing of the intake valve 18. Also in this case, the step motor 607 is controlled by the subroutine of FIG. 7, and the angular position of the cam 22 corresponding to the exhaust valve 18 with respect to the cam shaft 62 is changed. Then, in step 106, the flag f is set to 0, and step 107 is executed to determine whether or not the exhaust valve 18 is closed. Since the exhaust valve 18 is not yet closed at the beginning, this routine ends, and when it is later determined that the exhaust valve 18 is closed, step 108 is executed to start the fuel injection. That is, when this routine is executed for the second time, when step 101 transfers to step 102, since f = 0 in this case, step 107 is executed and this routine ends, but when the exhaust valve 18 closes soon, The routine proceeds from step 107 to step 108, fuel injection is performed, and this routine ends.

When it is determined in step 101 that the load is larger than the predetermined value, steps 110 and thereafter are executed in the same manner as described above. First, in step 110, it is judged whether or not the flag f is 1, but since f = 0 before that, a negative judgment is made here and the routine proceeds to step 111. Then, in step 111, the electromagnetic clutch is turned on to start the supercharger 20, and in step 112 the flag f is set to 1.

In step 300, as described above, a longer overlap period is set as compared with the case where the supercharger 20 is not driven. In this case, in order to determine the intake valve timing and the exhaust valve timing according to the operating state of the engine, step 300 calls a subroutine executed according to the flowchart shown in FIG. In this subroutine, first, in step 301, the supercharging pressure P ₃ is read, and in step 302, the overlap amount θ corresponding to the supercharging pressure P _B is obtained. As shown in FIG. 9, the overlap amount θ is determined so as to directly decrease as the supercharging pressure P _B increases. When the supercharging pressure P _B = 0, the maximum value θ ₂ and the supercharging pressure P _{B are set.} = P _1, the minimum value θ ₁ is taken, and if P ₁ or more, the minimum value θ ₁ is taken. In step 303, the amount of change in intake valve timing is calculated based on the overlap amount θ obtained in step 302, and similarly, in step 304, the amount of change in exhaust valve timing is calculated. That is, the next steps 305, 306
In order to rotate the step motor 607 at, the target angular position I of the step motor 607 is calculated. In this embodiment, the amount of change in the intake and exhaust valve timings is the same, and the crank angle and exhaust gas of the intake valve 17 at the opening start are the same as those shown in FIGS. 5 (a) and 5 (b). The absolute values of the closing angle of the valve 18 and the crank angle are equal to each other. Then, in step 305, the intake valve timing is changed, and in step 306, the intake valve timing is changed. These valve timing changes are made in accordance with the flow chart shown in FIG. 7 as in steps 104 and 105 of FIG.

As described above, according to the present embodiment, the overlap amount can be changed according to the supercharging pressure P _B, and the residual gas in the combustion chamber 13 can always be effectively scavenged. It is only possible to improve the output performance under high load while ensuring the performance.

〔The invention's effect〕

As described above, according to the present invention, the valve overlap period is set to be smaller when the supercharger is not operating than when the supercharger is operating,
When the supercharger is operating, the overlap period is set to be relatively large when the supercharging pressure is small and decreases as the supercharging pressure increases, according to the engine operating state, and fuel injection is performed after the exhaust valve is closed. Therefore, the residual gas in the combustion chamber can always be scavenged satisfactorily, and the engine output and fuel consumption can be improved under high load while maintaining good combustion under light load.

[Brief description of drawings]

FIG. 1 is a flow chart showing the control of one embodiment of the present invention, FIG. 2 is a system diagram showing an internal combustion engine to which the present invention is applied,
FIG. 3 is a sectional view showing a variable valve timing mechanism, and FIG.
Fig. 5 is a view of the slit shape seen from the IV direction in Fig. 3, and Fig. 5 (a) is a graph showing the valve timing at light load.
FIG. 5 (b) is a graph showing valve timing at high load, FIG. 6 is a timing chart showing operation timings of the intake valve, the exhaust valve and the fuel injection valve, FIG. 7 is a flowchart showing control of the step motor, FIG. 8 is a flowchart showing the control in the first embodiment, and FIG. 9 is a graph showing the relationship between the supercharging pressure and the overlap amount. 17 ... Intake valve, 18 ... Exhaust valve, 20 ... Supercharger (supercharger), 23 ... Fuel injection valve, 25 ... Rotation speed detector, 70,71 ... Pressure detector, 72 ... Exhaust temperature detector, 73 ... Catalyst temperature detector.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location F02D 41/34 F 8011-3G (56) Reference JP-A-58-20934 (JP, A) Special features Open Sho 58-28588 (JP, A) Actual Open Sho 59-49742 (JP, U) Japanese Patent Sho 56-10445 (JP, B2)

Claims (1)

[Claims] 1. A method of controlling a variable valve timing engine having a mechanical supercharger, wherein the supercharger is not driven.
The overlap period from the start of opening the intake valve to the end of closing the exhaust valve is set to be smaller than when the supercharger is driven, and when the supercharger is driven, the overlap period is set to the engine supercharge. A variable valve timing characterized in that it is controlled so that it is relatively large when the pressure is low and decreases as the engine supercharging pressure becomes high, according to the engine operating state, and that fuel injection is performed after the exhaust valve is closed. Engine control method.