JPS61187530A - Control method of variable valve timing engine - Google Patents

Abstract

PURPOSE:To improve fuel consumption and output by relatively delaying the valve timing of an exhaust valve when the intake pressure is relatively high, thus lowering the exhaust temperature and avoiding the need of making the mixed gas rich, in an engine equipped with a mechanical supercharger. CONSTITUTION:A selector valve 45 is controlled by an electronic control part 50 so that the atmospheric pressure is introduced into an actuator 40 in high loading. Then, the inside of a negative pressure chamber 43 becomes equal to the atmosphere, and a bypass valve 39 is urged by a spring 44 to close a bypass passage 38, and a supercharger 20 performs supercharge. In this case, into the electronic control part 50, each signal of an air flow meter 70, revolution speed detector 25, and a pressure sensor 70 in a surge tank 30 is input, and a variable valve timing mechanism 60 is controlled to relatively revolution- shifts a cam 22 with respect to a cam shaft 62, and the opening and closing timing of an exhaust valve 18 is varied. Therefore, when the engine load is larger than the prescribed value, the opening timing for the exhaust valve 18 is relatively delayed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling an internal combustion engine equipped with a mechanical supercharger and a variable valve timing mechanism.

[Conventional technology]

Some internal combustion engines are equipped with a supercharger to improve the engine's output. In such an internal combustion engine, when operating under high load when the supercharger is active, it is necessary to reduce the compression ratio to prevent knocking from occurring due to excessive pressure in the combustion chamber. Also, considering light load operation when the supercharger is not working, the pressure in the combustion chamber is low, which lowers thermal efficiency and worsens fuel efficiency, so it is necessary to increase the compression ratio. Conventionally, internal combustion engines have been known that change the opening and closing timing of the intake valve in order to obtain the same effect as changing the compression ratio depending on the operating state of the supercharger (for example, 6941
Publication No. 1, Publication of Utility Model Application No. 58-90338, Publication of Utility Model Application No. 1983
-49742).

[Problem that the invention seeks to solve]

In a variable valve timing engine equipped with a supercharger, since the intake air temperature and intake pressure are high during supercharging, the combustion temperature becomes high, which causes the exhaust temperature to rise. However, the temperature of the exhaust system cannot be raised above a certain value due to the action of the catalyst, etc., and conventionally, the combustion temperature has been lowered by setting the air-fuel mixture at a level higher than the output air-fuel ratio.

For this reason, there has been a problem in that there are certain limits to improving fuel efficiency and output performance.

[Means for solving problems]

In order to solve the above problems, the present invention is characterized in that when the intake pressure is relatively high, the valve timing of the exhaust valve is relatively delayed.

〔Example〕

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

FIG. 2 shows an internal combustion engine to which an embodiment of the present invention is applied.

shows. 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. An intake valve 17 and an exhaust valve 18 supported by the cylinder head 16 open and close an intake boat 19 and an exhaust port 20, respectively, and are driven to open and close by cams 21 and 22. The cams 22 are rotationally displaced relative to the camshaft 62 by a variable valve timing mechanism 60, as will be described later, to change the opening/closing timing of the exhaust valve 18. A fuel injection valve 23 is provided near the intake valve 17 of the intake boat 19, and a rotation speed detector 25 is provided on the distributor 24 attached to the cylinder 16.

The air cleaner 26 is provided at the most upstream side of the intake passage 14, the air flow meter 27 is located downstream thereof, and the throttle valve 28 is further provided downstream thereof. The throttle valve 28 operates in conjunction with the accelerator pedal 29 to open the intake passage 1.
4. Change the flow path area in 4. A surge tank 30 is formed downstream of the supercharger 20 in the intake passage 14, and a pressure detector 70 is attached to the surge tank 30.

A 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 crankboo IJ36. Intake passage 1
The upstream and downstream sides of the No. 4 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 is connected to the shell 4
1 is partitioned by a diaphragm 42 to form a negative pressure chamber 43, and a spring 44 is provided within this negative pressure chamber 43. The diaphragm 42 is connected to a bypass valve 39. Atmospheric pressure or negative pressure is selectively introduced into the negative pressure chamber 43 via a switching valve 45. Atmospheric pressure is introduced from the opening 46 of the air cleaner 16, and negative pressure is introduced downstream of the throttle valve 28. It is guided from a negative pressure boat 47 on the side.

The cut AG 45 is controlled by an electronic control unit 50 equipped with a microcomputer to introduce atmospheric pressure or negative pressure to the actuator 40 . That is, supercharger 20
When the load is light and supercharging is not required, the switching valve 45 is controlled to guide the negative pressure downstream of the throttle valve 28 to the actuator 40. When the negative pressure is greater than a predetermined value, the diaphragm 42 moves downward 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 portion of the discharged air recirculates through the bypass passage 38 and returns to the population side of the supercharger 20, so that the supercharger 20 does not substantially perform supercharging. On the other hand, when the load is high and requires supercharging by the supercharger 20, the switching valve 45 is controlled to introduce atmospheric pressure to the actuator 40.

Therefore, the inside of the negative pressure chamber 43 becomes atmospheric pressure, and the bypass valve 39
is biased by the spring 44 to close the bypass passage 38, thereby causing the supercharger 20 to perform supercharging.

The electronic control unit 50 receives a signal indicating the intake air amount from the air flow meter 27, a signal indicating the engine rotation speed from the rotation speed detector 25, and a signal indicating the pressure in the surge tank 30, that is, the supercharging pressure Pg from the pressure detector 70. In addition to controlling the supercharger 20 and bypass valve 39 as described above, the variable valve timing mechanism 6
0 to rotate the cam 22 relative to the camshaft 62 and change the opening/closing timing of the exhaust valve 18.

As shown in FIG. 3, the variable valve timing mechanism 60 includes an inner sleeve 60 fixed to one end of a camshaft 62.
1, and an outer sleeve 602 rotatably fitted into the inner sleeve 601 and fixed to the timing pulley 63.

The timing boot IJ63 is connected to the crankshaft 64 via an endless belt (not shown). The outer sleeve 602 and the inner sleeve 601 have mutually inclined slits 602A and 601A, as shown in FIG. 4, and a bearing 603 is disposed within these slits. A shaft 604 carrying a bearing 603 has an axis perpendicular to the axis of the camshaft 62, and is attached to a slider 605 that slides left and right inside the inner sleeve 601. slider 6
05 is connected to an output shaft 608 of a step motor 607 via a nut 606. The rotational movement of the step motor 607 is converted into a horizontal movement of the slider 605 in the direction of the camshaft 26 by threading the output shaft 608 and the nut 606. Therefore, the inclined groove 601A.

A bearing 603 moves within 602A in the direction of arrow X, causing relative rotational movement between inner sleeve 601 and outer sleeve 602. Therefore, the camshaft 62 on the inner sleeve side and the timing pulley 63 on the outer sleeve side
In other words, the relative position with respect to the crankshaft 64 changes.

This changes the timing at which the cam ridge on the camshaft 22 engages with the valve lifter attached to the valve stem, in other words, the valve timing. A control circuit 50 provides signals for controlling such changes in valve timing to a variable valve timing mechanism 60, ie, a stepper motor 60.
7.

The electronic control unit 50 controls the exhaust valve 1 according to the magnitude of the engine load.
Change the valve timing of 8. For example, when the engine load is smaller than a predetermined value, the supercharger 20 is stopped and the exhaust valve 1 is stopped as shown in FIG. 5(a).
The valve opening timing of No. 8 is made relatively early. On the other hand,
When the engine load is greater than a predetermined value, the electronic control unit 50 drives the supercharger 20 and operates as shown in FIG.
), the opening timing of the exhaust valve 18 is relatively delayed.

1 and 7 show flowcharts of control performed by the electronic control section 50. FIG. In the main routine that calls the subroutine shown in this flowchart, when the engine ignition key switch is turned on, the flag r
is initialized to 1. In step 101, assuming that the value Q/N obtained by multiplying the intake air amount Q by the engine speed N corresponds to the load, it is determined whether this Q/N is larger than a predetermined value Q or not. Initially, the load is smaller than the predetermined value Q1, so the process moves to step 102. In step 102, it is determined whether the flag f is O or not. Since r=t is set in the main routine as described above, when step 102 is executed for the first time, a negative determination is made, and the process moves to step 103, where the electromagnetic clutch of the supercharger 20 is turned off. Then, step 104 is executed to advance the valve timing of the exhaust valve 18.

In step 104, a subroutine is executed according to the flowchart shown in FIG.
(FIG. 3) is rotationally driven to change the angular position of the cam 22 with respect to the camshaft 62.

That is, first in step 201, the step motor 607
The setting value, that is, the target angular position ■ is read. This target angular position I is determined by the opening timing of the exhaust valve 18. Next, in step 202, the step motor 607
The actual angular position J is read, and in step 203 it is determined whether the actual angular position J is substantially equal to the target angular position (2).

If they are equal, the step motor 607 is stopped and the subroutine ends, but if not equal, step 204 is executed and the 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. Step 202 is then executed again, and the loop of steps 204, 202 and 203 is repeated until J=I in step 203.

When the valve timing of the exhaust valve 18 is changed,
Next, step 105 is executed, flag f is set to 0, and this routine ends. Immediately after that, this routine is started again and step 102 is executed, but since f=o, steps 103 to 105 are not executed.

If it is determined in step 101 that the load is larger than the predetermined value, steps 110 and subsequent steps are executed in exactly the same manner as described above. First, in step 110, the flag f
It is determined whether -IJ<1, but since f=o before that, a negative determination is made here and the process moves to step 111. Then, in step 111, the electromagnetic clutch is turned on to start the supercharger 20, and in step 112
In this step, the valve timing of the exhaust valve 18 is delayed by the subroutine shown in FIG. Then, in step 113, the flag f is set to 1, and this routine ends. When this routine is subsequently activated and step 110 is executed, steps 111 to 113 are not executed because "=1."

As described above, in this embodiment, the valve timing of the exhaust valve 18 is delayed as shown in FIG. 5(b) when the supercharger 20 is activated.

Therefore, the expansion ratio of the combustion gas increases, and the cylinder pressure decreases in a stepwise manner forward of the bottom dead center by the crank angle θ2, as shown in FIG.
In the case where the valve timing of the exhaust valve 18 is relatively early (indicated by a solid line in the figure), the timing becomes smaller near the bottom dead center. That is, the combustion gas is sufficiently expanded to lower the exhaust temperature, thereby making it possible to make the mixer lean. At this time, the valve timing of the exhaust valve 18 is delayed, so the overramp period during which both the intake valve 17 and the exhaust valve 18 are opened becomes longer, and the scavenging effect of the residual gas in the combustion chamber 13 is enhanced, resulting in output will improve. On the other hand, when the supercharger 20 is stopped, the valve timing of the exhaust valve 18 is advanced as shown in FIG. It can be prevented.

In addition, the supercharger 20 determines whether or not it is during supercharging.
Instead of using the electromagnetic clutch, the control may be performed using the opening degree of the throttle valve 28 or the control signal of the bypass valve 39.

FIG. 8 shows a second embodiment. In this second embodiment, the supercharging pressure P
[The valve timing of the exhaust valve 18 is controlled to be delayed as l becomes higher.

In this flowchart, in step 301, data on the boost pressure PII stored in the memory of the electronic control unit 50 is read. This data is inputted to the electronic control section 50 by A/D converting the signal detected by the pressure detection gas 70. In step 302, the supercharging pressure P is increased.

Find the exhaust valve timing θ according to . As shown in FIG. 9, the exhaust valve timing θ is determined to decrease linearly as the supercharging pressure pH increases, and PIl=
When 0, θ=θI (maximum value), P, = P, (maximum value)
When θ=02 (minimum value). In step 303, it is determined whether the currently set exhaust valve timing is substantially equal to the exhaust valve timing determined in step 302. If they are equal, the routine ends; if not, step 304
Move on to change the exhaust valve timing.

This change in exhaust valve timing is performed according to the flowchart shown in FIG.

As described above, in the second embodiment, the higher the supercharging pressure P8, the later the exhaust valve timing is delayed, so that the expansion ratio of the combustion gas increases, the exhaust pressure decreases, and the exhaust temperature decreases. That is, the second embodiment also provides the same effects as the first embodiment.

〔Effect of the invention〕

As described above, according to the present invention, the exhaust gas temperature can be lowered, so there is no need to lynch the air-fuel mixture as in the past, and fuel efficiency and output can be improved.

[Brief explanation of drawings]

Fig. 1 is a flowchart showing control of an embodiment of the present invention, Fig. 2 is a system diagram showing an internal combustion engine to which the invention is applied, Fig. 3 is a sectional view showing a variable valve timing mechanism, and Fig. 4 is a flowchart showing control of an embodiment of the present invention. Arrow view of the slit shape seen from the ■ direction in Figure 3, No. 5
Figure (a) is a graph showing valve timing under light load.
FIG. 5(b) is a graph showing valve timing under high load, FIG. 6 is a graph showing changes in cylinder pressure due to changes in crank angle, FIG. 7 is a flowchart showing step motor control, FIG. 8 is a flowchart showing control in the second embodiment, and FIG. 9 is a graph showing the relationship between boost pressure and exhaust valve timing. 18...Exhaust valve, 20...Supercharger. Figure 5 (a) (b) Figure 6 Crank angle

Claims (3)

[Claims] 1. A control method for a variable valve timing engine equipped with a mechanical supercharger, the control method for a variable valve timing engine comprising relatively slowing the valve timing of an exhaust valve when the intake pressure is relatively high. Method. 2. 2. The control method according to claim 1, wherein the valve timing of the exhaust valve is relatively delayed when the supercharger is being driven. 3. 2. The control method according to claim 1, wherein the higher the supercharging pressure, the slower the valve timing of the exhaust valve.