JPS61190118A - Control method of variable valve timing engine - Google Patents

Abstract

PURPOSE:To improve the warming performance of catalyst while to prevent overheating of catalyst under high temperature, in an engine associated with a mechanical supercharger, by relatively lagging the valve timing of exhaust valve under low engine temperature while leading under high engine temperature. CONSTITUTION:Catalyst is located in the exhaust system of engine associated with a mechanical supercharger 20 to be driven through a crank shaft 64 while an actuator 60 for controlling the open/close timing is arranged on the cam shaft 62 of an exhaust valve 18. The controller 50 is provided with various engine parameters to perform various controls including one where a valve timing actuator 60 is driven by an engine temperature signal 20 under low engine temperature to lag the timing relatively thus to discharge large amount of high temperature exhaust gas. Since the catalyst is overheated easily under high engine temperature, the valve timing is led relatively to suppress the high temperature exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of 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, the supercharger is effective! Considering during heavy load operation, it is necessary to reduce the compression ratio to prevent knocking from occurring due to excessive pressure in the combustion chamber, and also during light load operation when the supercharger is not effective. In this case, since the pressure inside the combustion chamber is low, thermal efficiency decreases and fuel efficiency worsens, 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 achieve the same effect as changing the compression ratio depending on the operating state of the supercharger (for example, -694
Publication No. 11, Publication of Utility Model Application No. 58-90338, Publication of Utility Model Application No. 58-90338, Publication No. 1989
No. 9-49742@).

[Problem that the invention seeks to solve]

In internal combustion engines such as those mentioned above, there is a problem in that when the engine is cold, the catalyst is difficult to activate due to the low catalyst temperature.
Another problem is that the temperature of the exhaust system rises too much during supercharging, which may cause heat damage to the catalyst. The present invention attempts to solve this problem by changing the valve timing of the exhaust valve.

[Means for solving problems]

In order to solve the above problems, the present invention makes the valve timing of the exhaust valve relatively late when the engine temperature is low, and relatively early the valve timing of the exhaust valve when the engine temperature is high. It is characterized by

〔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.

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 throat 16 are connected to an intake port 19 and an exhaust port 2, respectively.
0 is opened and closed, and the opening and closing drive is performed 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 port 19, a rotation speed detector 25 is provided in a distributor 24 attached to the cylinder head 16, and a rotation speed detector 25 is provided in the vicinity of the intake valve 17 of the engine body 10. A water temperature detector 70 is attached to each of the water coolers 7.

The air cleaner 26 is provided at the most upstream side of the intake passage 14, the air flow meter 27 is located at the downstream side, and further downstream, a throttle valve 28 is provided. 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 .

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

The switching valve 45 is controlled by an electronic control unit 50 equipped with a micro combinator to introduce atmospheric pressure or negative pressure to the actuator 40 . That is, when the load is light and supercharging by the supercharger 20 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 being driven, a portion of the discharged air is recirculated through the bypass passage 38 and returned to the inlet 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 cooling water temperature from the water temperature detector 70, and operates the supercharger as described above. 20 and the bypass valve 39, the variable valve timing mechanism 60 is controlled as follows to rotationally displace the cam 22 relative to the camshaft 62, thereby changing 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 pulley 63 is connected to the crankshaft 64 via an endless heald (not shown). The outer sleeve 602 and the inner sleeve 601 have slits 60 that are inclined to each other as shown in FIG.
2A and 601A, and a bearing 603 is placed within this slit. Shaft 6 carrying bearing 603
04 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. The slider 605 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 caused by the output shaft 608 and the nut 60.
6 is converted into a horizontal movement of the slider 605 in the direction of the camshaft 26.

Therefore, the inside of the inclined grooves 601A and 602A are inserted into the bearing 6.
03 moves in the direction of arrow X, causing relative rotational movement between the inner sleeve 601 and the outer sleeve 602. Therefore, the relative position between the camshaft 62 on the inner sleeve side and the timing boot IJ 63 on the outer sleeve side, in other words, the crankshaft 64 changes. This changes the timing at which the cam ridge on the cam 22 engages with the valve click attached to the valve stem, in other words, the valve timing. The control circuit 50 applies a signal to the variable valve timing mechanism 60, i.e., the step motor 607, to control such changes in valve timing. Change valve timing. For example, when the cooling water temperature Tw is lower than the predetermined value To, the valve timing of the exhaust valve 18 is made relatively early as shown in FIG. 5 (8), and conversely, when the cooling water temperature Tw is higher than the predetermined value To, As shown in FIG. 5(b), the valve timing of the exhaust valve 18 is relatively delayed.

In other words, when the engine is cold, the exhaust valve timing is advanced to open the exhaust valve 18 at a position θ crank angle ahead of bottom dead center.This reduces the expansion ratio, increases the exhaust pressure and temperature, and Improves warm-up performance.

1 and 7 show flowcharts of control performed by the electronic control section 50. FIG. In step 301, the electronic control unit 5
The data of the cooling water temperature Tl1l stored in the memory of 0 is read. This data is input to the electronic control unit 50 by A/D converting the water temperature signal detected by the water temperature detector 70. In step 302, it is determined whether the cooling water temperature Tw is higher than a predetermined value To. If the cooling water temperature Tw is higher than the predetermined value TO, step 303 is executed to make settings for delaying the valve timing of the exhaust valve 18. That is, the target angular position of the step motor 607 (FIG. 3) of the variable valve timing mechanism 60 is determined so that the exhaust valve 18 begins to open a crank angle θ2 (FIG. 5(b)) ahead of the bottom dead center. . On the other hand, if the cooling water temperature Tw is lower than the predetermined value T9, the process moves to step 304, where settings are made to advance the valve timing of the exhaust valve 18,
The exhaust valve 18 moves from the bottom dead center to the crank angle θ1 (Fig. 5(a)
)) The target angular position of the step motor 607 (FIG. 3) is determined so that the valve begins to open at the front. In addition,
The exhaust valve timing does not need to be changed stepwise according to the cooling water temperature Tw, but may be changed linearly according to the cooling water temperature Tw.

Next, in step 305, it is determined whether the currently set exhaust valve timing is substantially equal to the exhaust valve timing determined in steps 303 and 304. If they are equal, the routine ends, but if not, the routine moves to step 306 to change the exhaust valve timing.

This change in exhaust valve timing is performed according to the flowchart of FIG. 7, which will be described below.

In FIG. 7, first, in step 201, the setting value of the step motor 607, that is, the target angular position (2) is read.

This target angular position I is determined by the valve timing of the exhaust valve 18. Next, in step 202, the actual angular position J of the step motor 607 is read, and in step 203, it is determined whether the actual angular displacement 1iJ 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 rotational direction of the motor 607 differs depending on whether the actual angular position J is larger or smaller than the target angular position (2). Step 202 is then executed again, and the loop of steps 204, 202, and 203 is repeated until J-T is reached in step 203.

As described above, in this embodiment, it is determined whether or not it is a cold time based on the cooling water temperature, and the exhaust valve timing is advanced when the engine is cold. Therefore, the expansion ratio of the combustion gas becomes smaller, and as shown in Fig. 6, the cylinder pressure decreases in a stepwise manner in front of the bottom dead center by a crank angle θ1, but after that it remains at a nearly constant value. (indicated by a solid line in the figure), and as a result, the exhaust valve timing becomes larger near the bottom dead center compared to when the exhaust valve timing is relatively late (indicated by a broken line in the figure). That is, the combustion gas does not expand much, the exhaust gas temperature increases, the catalyst warms up better, and the exhaust gas emissions are improved. On the other hand, during normal operation, the exhaust valve timing is delayed and the over-ramp period during which both the intake valve 17 and the exhaust valve 18 are open becomes longer, thereby increasing the scavenging effect of the residual gas in the combustion chamber 13 and increasing the output. and improved fuel efficiency. Furthermore, since the expansion ratio of the combustion gas is increased, the exhaust temperature can be kept low, and heat damage to the catalyst can be prevented.

Note that the above-described control may be performed using engine oil temperature or catalyst temperature instead of cooling water temperature Tw.

FIG. 8 shows a flowchart of the second embodiment.

In step 311, data on the exhaust temperature TEX and catalyst temperature TCCIIO stored in the memory of the electronic control unit 50 is read. Exhaust temperature T. is the exhaust temperature detector 7 installed on the exhaust pipe.
1 (shown by imaginary lines in Figure 2), and the catalyst temperature 'rcc'+to is detected by the catalyst temperature detector 7 attached to the catalyst.
2 (shown in phantom lines in FIG. 2). In step 312, the exhaust temperature T is determined. is the predetermined value T.

It is determined whether or not the exhaust valve timing is higher, and if it is higher, the process moves to step 313, where settings are made to delay the exhaust valve timing. Further, in step 312, the exhaust temperature TEX is set to a predetermined value T.
If it is determined that the catalyst temperature TCCIIO is lower than the predetermined value T2, the process moves to step 314, and it is determined whether the catalyst temperature TCCIIO is higher than the predetermined value T2.
15 to make settings for advancing the exhaust valve timing. When advancing the exhaust valve timing θ (the crank angle measured forward from the bottom dead center when the exhaust valve 1B starts to open) in step 315, the engine speed N and the engine load Q are determined as shown in FIG. /N(
Based on the map created as a relationship between Q: intake air amount and N: engine speed, the higher the engine speed N is, the higher the engine speed is, and the larger the engine load Q/N is, the higher the speed is. In other words, the exhaust valve timing can be obtained in accordance with the operating conditions of the engine, resulting in good output and fuel efficiency.

Next, step 316 determines whether the currently set exhaust valve timing is substantially equal to that set in steps 313 and 315. If they are equal, this routine ends, but if not, the routine moves to step 317, and the exhaust valve timing is changed according to the flowchart in FIG. □ As described above, in the second embodiment, the exhaust valve timing is changed depending on the exhaust system temperature.

That is, when the exhaust system temperature is high, the exhaust valve timing is delayed to increase the expansion ratio of combustion gas, thereby lowering the exhaust temperature and preventing heat damage to the catalyst. Furthermore, when the exhaust system temperature is low, the exhaust valve timing is determined by the engine speed and load, so that the output, fuel efficiency, and stability of driving conditions are good.

〔Effect of the invention〕

As described above, since the present invention changes the exhaust valve timing according to the engine temperature, it is possible to improve the warm-up of the catalyst and hasten its activation, and also prevent heat damage to the catalyst. You can get the effect that you can.

[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 present invention is applied, FIG. 3 is a sectional view showing a variable pulp timing mechanism, and FIG. Arrow view of the slit shape seen from the ■ direction in Figure 3, No. 5
Figure fat is a graph showing the exhaust valve timing when the engine is at low temperature, Figure 5 is a graph showing the exhaust valve timing when the engine is at high temperature, Figure 6 is a graph showing the exhaust valve timing when the engine is at high temperature, and Figure 6 is the change in cylinder pressure with changes in crank angle. FIG. 7 is a flowchart showing control of the step motor, FIG. 8 is a flowchart showing control in the second embodiment, and FIG. 9 is a graph showing exhaust valve timing that changes depending on engine speed and load. 18... Exhaust valve, 70... Water temperature detector, 71... Exhaust temperature detector, 72... Catalyst temperature detector. Fig. 5 (a) (b) Top dead center Below top dead center dead center
Bottom dead center Figure 6 Crank angle Figure 7

Claims (5)

[Claims] 1. A control method for a variable valve timing engine equipped with a mechanical supercharger, in which the valve timing of the exhaust valve is relatively delayed when the engine temperature is low, and when the engine temperature is high,
A control method for a variable valve timing engine characterized by making the valve timing of an exhaust valve relatively early. 2. The control method according to claim 1, characterized in that the valve timing of the exhaust valve is changed in accordance with the cooling water temperature. 3. The control method according to claim 1, characterized in that the valve timing of the exhaust valve is changed in accordance with the exhaust gas temperature. 4. The control method according to claim 1, characterized in that the valve timing of the exhaust valve is changed in accordance with the catalyst temperature. 5. 2. The control method according to claim 1, wherein the valve timing of the exhaust valve is changed in accordance with engine oil temperature.