JPH08277729A - Valve timing control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a valve timing control device for an internal combustion engine, and an object thereof is to reliably prevent engine stall even when the engine speed is drastically reduced at the start of the vehicle. To do. A variable valve timing mechanism capable of steplessly changing the opening / closing timing of at least one of an intake valve and an exhaust valve, and a variable valve timing mechanism for realizing a target valve overlap period determined by an engine operating state. A variable valve timing mechanism control means (steps 103 and 110) for controlling the engine speed, and a target valve overlap period reduction means (step 109) that reduces the target valve overlap period determined by the engine operating state when the vehicle starts. To have.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve timing control device for an internal combustion engine.

[0002]

2. Description of the Related Art A valve overlap in which an intake valve and an exhaust valve are opened at the same time has a long period, so that pumping loss is considerably reduced and a relatively large amount of exhaust gas is internally recirculated. The exhaust emission is considerably improved.

However, since exhaust gas recirculation is accompanied by some deterioration of combustion, it is necessary to prevent the engine stall by reducing the internal exhaust gas recirculation amount at low engine speed and low load where combustion is unstable. JP-A-4-19433
No. 1 public information is equipped with a variable valve timing mechanism that can change the opening / closing timing of at least one of the intake valve and the exhaust valve, and shortens the valve overlap period to reduce the internal exhaust gas recirculation amount when the engine speed is low and the load is low. A valve timing controller is described.

[0004]

Normally, when the vehicle is started, the clutch is engaged after the accelerator pedal is depressed to raise the rotational speed to some extent. However, depending on how the clutch is connected, the engine rotational speed may increase rapidly. It may decrease. In such a case, the above-mentioned prior art valve timing control device will lengthen the valve overlap period as the accelerator pedal is depressed, and then shorten the valve overlap period as the engine speed drops sharply. However, a general hydraulic or electromagnetic variable valve timing mechanism cannot follow such a momentary change in the engine speed, and the engine speed is reduced. A relatively large amount of internal exhaust gas recirculation is maintained, and there is a possibility of engine stall due to deterioration of combustion.

Accordingly, an object of the present invention is to provide a valve timing control device for an internal combustion engine, which effectively utilizes internal exhaust gas recirculation by changing the valve overlap period in accordance with the engine operating state, so that the engine rotation is performed when the vehicle starts. This is to ensure that engine stall can be prevented even if the number drops sharply.

[0006]

According to a first aspect of the present invention, there is provided a valve timing control device for an internal combustion engine, comprising a variable valve timing mechanism capable of continuously changing the opening / closing timing of at least one of an intake valve and an exhaust valve. Variable valve timing mechanism control means for controlling the variable valve timing mechanism so that the target valve overlap period determined by the engine operating state is realized, and the target valve determined by the engine operating state when the vehicle starts. Target valve overlap period reducing means for reducing the overlap period.

A valve timing control device for an internal combustion engine according to a second aspect of the present invention is used in an internal combustion engine having a manual transmission, and the valve timing control device for an internal combustion engine according to the first aspect is used. The target valve overlap period reducing means greatly reduces the target valve overlap period as the vehicle speed at the start of the vehicle is lower.

A valve timing control device for an internal combustion engine according to a third aspect of the present invention is used in an internal combustion engine having a manual transmission, and the valve timing control device for an internal combustion engine according to the first aspect is used. The target valve overlap period reducing means largely reduces the target valve overlap period as the engine output is lower when the vehicle starts.

[0009]

In the valve timing control device for an internal combustion engine according to claim 1, the variable valve timing mechanism control means includes a variable valve timing mechanism capable of continuously changing the opening / closing timing of at least one of the intake valve and the exhaust valve, The target valve overlap period determined by the engine operating state is controlled so that the target valve overlap period reducing means reduces the target valve overlap period determined by the engine operating state when the vehicle starts. Therefore, the valve overlap period at this time is shortened as compared with the same engine operating state when the vehicle is traveling.

The valve timing control device for an internal combustion engine according to claim 2 is used in an internal combustion engine having a manual transmission, and the target valve overlap period reducing means is arranged so that the vehicle speed is low when the vehicle starts. In order to greatly reduce the target valve overlap period, the internal exhaust gas recirculation is reduced as the vehicle speed is low and a large load is applied to the internal combustion engine when the clutch is engaged.

The valve timing control device for an internal combustion engine according to claim 3 is used in an internal combustion engine having a manual transmission, and the target valve overlap period reducing means has a low engine output when the vehicle starts and an engine rotation speed. The target valve overlap period is greatly reduced and the internal exhaust gas recirculation is reduced as the engine stalls more easily due to the decrease in the number.

[0012]

1 is a schematic diagram showing the structure of a valve timing control system for an internal combustion engine according to the present invention. In the figure, 1 is a combustion chamber and 2 is a piston. In the combustion chamber 1,
An exhaust passage 4 communicates with the exhaust valve 3, and an intake passage 6 communicates with the intake valve 5. A fuel injection valve 7 is arranged downstream of the surge tank 6a in the intake passage 6, and a throttle valve 8 is arranged upstream of the surge tank 6a.

The camshaft 11 for the intake valve 5 is connected to the crankshaft via a belt or the like by a pulley 11a provided at the end thereof, and the end of the camshaft 12 for the exhaust valve 3 and the pulley 11a. The pulley 12a provided in the above is connected via a belt or the like. As a result, both camshafts 11,
12 is rotationally driven so that the intake valve 5 and the exhaust valve 3 are opened and closed at a set crank angle.

In particular, the camshaft 11 for the intake valve 5 is provided with a generally known variable valve timing mechanism. This is the camshaft 11 and the pulley 11
a is rotated relative to each other, for example, by connecting the two via an intermediate gear having helical teeth as external teeth and moving the intermediate gear in the axial direction using hydraulic pressure or electromagnetic force. The above-mentioned relative rotation is realized, whereby the intake valve 5 near the exhaust top dead center is achieved.
Also, the period of valve overlap in which both the exhaust valve 3 and the exhaust valve 3 are opened can be changed steplessly.

A control unit 2 which controls the valve overlap period via the variable valve timing mechanism.
0 is provided, and the control device 20 includes a water temperature sensor 21 for detecting the engine cooling water temperature, an air flow meter 22 for detecting the intake air amount, a rotation sensor 23 for detecting the engine speed, and a throttle valve. A throttle valve opening sensor 24 for detecting the opening of No. 8, a speed sensor 25 for detecting the vehicle speed, a clutch pedal sensor 26 for issuing an ON signal when the clutch pedal for the manual transmission is depressed, and the like are connected. ing.

FIG. 2 is a first flowchart showing the control of the variable valve timing mechanism by the controller 20.
First, in step 101, the engine speed NE is detected by the rotation sensor 23, and in step 102,
The intake air amount GN is detected by the air flow meter 22. Next, at step 103, the target valve overlap period VP is determined from the map shown in FIG. 3 based on the engine speed NE and the intake air amount GN. The valve overlap reduces pumping loss during that period, and in the intake stroke during that period, a part of the exhaust gas is introduced from the intake passage 6 into the combustion chamber 1 depending on the opening timing of the exhaust passage 4 and / or the intake valve 3. It is possible to cause internal exhaust gas recirculation that causes a reverse flow, and lower the combustion temperature and NOx due to the large heat capacity of the inert gas that is the main component of the exhaust gas. However, since exhaust gas recirculation involves some deterioration of combustion, the map shown in FIG. 3 is based on the assumption that required engine output and sufficiently stable combustion are realized for each engine operating state. The longest valve overlap period is set as the target value. Of course, since the combustion stability changes depending on the engine temperature, a map as shown in FIG. 3 is provided for each cooling water temperature, and the map used in step 103 is set based on the current cooling water temperature measured by the water temperature sensor 21. You may make it select.

Next, at step 104, it is judged if the ON signal is issued from the clutch pedal sensor 26, and if this judgment is affirmative, step 1
05, the vehicle speed SP is detected by the speed sensor 25, and in step 106, the vehicle speed SP is 5
When it is determined whether the vehicle speed is less than km / h and both of these determinations are affirmative, it is determined that the vehicle is starting, and the routine proceeds to step 109, where the above-mentioned target valve overlap period VP is halved and new. The target valve overlap period VP is set to a different value, and in step 110, the variable valve timing mechanism is controlled so that the target valve overlap period VP is realized. On the other hand, if the determination in step 104 is negative, it means that the vehicle is traveling with the clutch pedal already released, and if the determination in step 106 is negative, it means that the vehicle is undergoing a shift change. Since neither is starting the vehicle, the process directly proceeds to step 110, and the variable valve timing mechanism is controlled so that the target valve overlap period VP determined in step 103 is realized.

By the control of the variable valve timing mechanism according to this flow chart, the optimum valve overlap period is achieved in each engine operating state while the vehicle is traveling, and low fuel consumption and good combustion of exhaust emission are realized. When the vehicle starts, a large load may momentarily act on the engine depending on how the clutch is connected, and the engine speed may drop sharply. In this case, the general variable valve timing mechanism described above cannot follow such a rapid change in the engine speed, and the valve overlap period before the decrease in rotation is maintained. However, in this flowchart, when the vehicle starts, the engine speed rapidly increases because the valve overlap period is halved compared to the engine operating state with the same engine speed and intake air amount when the vehicle is running. Even if the valve overlap period is reduced and the valve overlap period before that is maintained, the internal exhaust gas recirculation amount is too large at this time and engine stall is not caused due to deterioration of combustion.

FIG. 4 is a second flowchart showing the control of the variable valve timing mechanism by the controller 20.
Only the differences from the above-described first flowchart will be described below. In this flowchart, when the determinations at steps 204 and 206 are both affirmative, it is determined that the vehicle is starting, and the process proceeds to step 207, where the throttle valve opening sensor 24 detects the throttle valve opening TA.
Next, at step 208, it is judged if the throttle valve opening TA is less than 30 °. When this judgment is denied, a relatively large engine output is generated, and even if a large load momentarily acts on the engine when the vehicle starts, a significant decrease in engine speed is unlikely to occur.
The routine proceeds to step 210 without halving the target valve overlap period in step 209.

According to this flow chart, the target valve overlap period is not reduced when the engine is running without engine stall even when the vehicle starts.
To that extent, compared to the control of the variable valve timing mechanism according to the first flowchart, it is possible to reduce fuel consumption,
Also, exhaust emission can be improved.

FIG. 5 is a third flowchart showing the control of the variable valve timing mechanism by the controller 20.
Only the differences from the above-mentioned second flowchart will be described below. In this flowchart, when the determinations in steps 304 and 306 are both affirmative, it is determined that the vehicle is starting, the process proceeds to step 307, the throttle valve opening sensor 24 detects the throttle valve opening TA, and then the process proceeds to step 308. Then, based on the throttle valve opening TA, the first correction coefficient k1 is determined from the map shown in FIG. 6, and in step 309, the target valve overlap period VP determined in step 303 is multiplied by this first correction coefficient k1. Then, a new target valve overlap period VP is calculated.

In the map shown in FIG. 6, the first correction coefficient k1 becomes 1 when the throttle valve opening TA becomes maximum (90 °), and the larger the throttle valve opening θ becomes,
It is set to approach 1. As a result, the new target valve overlap period VP calculated in step 309 is such that as the engine output increases with the throttle valve opening degree TA, the decrease range of the engine speed at the start of the vehicle decreases and the engine speed decreases. Considering that the engine stall is less likely to occur even if the previous valve overlap period is maintained, the target valve overlap period VP during traveling of the vehicle can be approached.

Therefore, according to this flowchart, so to speak, when the vehicle is started, the optimum valve overlap period for each engine operating state is set in consideration of the range of decrease in engine speed that may occur when the clutch is engaged. In order to achieve this, compared to the control of the variable valve timing mechanism according to the second flowchart, it is possible to prevent the engine stall more reliably, and to set the valve overlap period for each engine operating state when the vehicle starts. By making it as long as possible, it becomes possible to further improve fuel economy and exhaust emission.

FIG. 7 is a fourth flowchart showing the control of the variable valve timing mechanism by the controller 20.
Only the differences from the above-mentioned third flowchart will be described below. In this flowchart, when the determinations at steps 404 and 406 are both affirmative, it is determined that the vehicle is starting, and the process proceeds to step 408 and step 401.
The second correction coefficient k2 is determined from the map shown in FIG. 8 on the basis of the engine speed NE detected in step 409.
In, the target valve overlap period VP determined in step 403 is multiplied by the second correction coefficient k2 to calculate a new target valve overlap period VP.

In the map shown in FIG. 8, the second correction coefficient k2 is set to 1 when the engine speed NE is equal to or higher than the predetermined engine speed NE1, and is set to be closer to 1 when the engine speed NE is higher than the predetermined engine speed NE1. As a result, the new target valve overlap period V calculated in step 409 is obtained.
As for the engine speed P, as the engine speed increases and approaches the predetermined engine speed NE1, a certain decrease in engine speed is brought about when the clutch is engaged. Even if combustion deteriorates due to a long valve overlap period before that, engine stall occurs. In consideration of the difficulty of occurrence, the target valve overlap period VP during traveling of the vehicle can be approached.

Therefore, according to the control of the variable valve timing mechanism according to this flowchart, when the vehicle is started, the target valve overlap period is compared with that when the vehicle is running in the engine operating state in which the possibility of engine stall is high when the clutch is engaged. By shortening it, as in the case of the third flow chart, engine stall can be reliably prevented, and the valve overlap period for each engine operating state at the time of vehicle start is made as long as possible,
It is possible to improve fuel efficiency and exhaust emission.

FIG. 9 is a fifth flowchart showing the control of the variable valve timing mechanism by the controller 20.
Only the differences from the above-mentioned third flowchart will be described below. In this flowchart, when the determinations in steps 504 and 506 are both affirmative, it is determined that the vehicle is starting, and the process proceeds to step 508 to determine the third correction coefficient k3 from the map shown in FIG. 10 based on the vehicle speed SP. In step 509, the target valve overlap period VP determined in step 503 is multiplied by the third correction coefficient k3 to calculate a new target valve overlap period VP.

In the map shown in FIG. 10, the third correction coefficient k3 indicates that the vehicle speed SP is a predetermined speed (for example, 5 km /
It is set so that it becomes 1 when it is equal to or more than h) and approaches 1 as the vehicle speed SP becomes higher when it is less than that. Accordingly, the new target valve overlap period VP calculated in step 509 is the vehicle speed S
As P approaches the predetermined speed, the load acting on the engine when the clutch is engaged becomes smaller and the decrease range of the engine speed becomes smaller. Therefore, engine stall occurs even if the valve overlap period before the decrease in speed is maintained. In consideration of the difficulty, the target valve overlap period VP when the vehicle is traveling can be approached.

Therefore, according to the control of the variable valve timing mechanism according to the present flow chart, when the vehicle starts, the vehicle speed state in which the possibility of engine stall is high when the clutch is engaged, the target valve overlap period is the same when the vehicle is running. Shorten compared to the operating state,
As a result, when the vehicle starts, it is possible to reliably prevent the engine stall, and, for example, when the vehicle speed increases due to the use of the downhill and the engine stall hardly occurs, the third and third engine stalls are performed. Compared with the four flowchart, the valve overlap period for each engine operating state at the time of starting the vehicle can be lengthened, and fuel consumption and exhaust emission can be further improved.

In the case where the internal combustion engine is provided with an automatic transmission, for example, immediately after the accelerator pedal is depressed to start the vehicle, the accelerator pedal is opened for some reason and the throttle valve is fully closed. In this case, the engine speed drops sharply, and as in the case where the internal transmission is equipped with a manual transmission, the valve overlap period before the decrease in the engine speed is maintained and there is a possibility of engine stall. is there.

The present invention is also effective in preventing engine stall of an internal combustion engine having such an automatic transmission, and in the first flowchart shown in FIG. 2, since the clutch pedal is not provided, the vehicle is started. It is only necessary to omit step 104 from the above judgment. Further, as shown in the fourth flow chart shown in FIG. 7, when the target valve overlap period is reduced based on the engine speed when the vehicle starts, contrary to the case of the internal combustion engine having the manual transmission,
It is preferable that the target valve overlap period is greatly reduced as the engine speed increases when the vehicle starts. This is because the higher the engine speed, the longer the target valve overlap period when the vehicle is running and the larger amount of internal exhaust gas recirculation is being executed. This is because the engine stall is likely to occur when the exhaust gas recirculation amount is maintained.

[0032]

As described above, according to the valve timing control device for the internal combustion engine of the first aspect, the variable valve timing mechanism control means continuously changes the opening / closing timing of at least one of the intake valve and the exhaust valve. The possible variable valve timing mechanism is controlled so that the target valve overlap period determined by the engine operating state is realized,
The target valve overlap period reducing means reduces the target valve overlap period determined by the engine operating state when the vehicle starts, so that the valve overlap period at this time is the same as the engine operating state when the vehicle is running. It is shortened compared with time, and even if the engine speed drops sharply at the start of the vehicle and the valve overlap period is maintained before the decrease in rotation, the internal exhaust gas recirculation amount is relatively small and combustion deteriorates. The occurrence of engine stall is prevented.

According to the valve timing control device for an internal combustion engine according to a second aspect of the invention, the target valve overlap period reducing means is used in an internal combustion engine having a manual transmission, and the vehicle speed is low when the vehicle starts. In order to greatly reduce the target valve overlap period over time, the internal exhaust gas recirculation is considered to be small when the vehicle speed is low and a large load may be exerted on the internal combustion engine when the clutch is engaged, and the engine speed is actually reduced. Even if the number rapidly decreases and the valve overlap period before the rotation decrease is maintained at this time, engine stall is prevented from occurring due to deterioration of combustion. In addition, in order to reduce the target valve overlap period as necessary to prevent engine stall according to the vehicle speed, the valve overlap period is set as long as possible even when the vehicle starts, and the pumping loss is correspondingly increased. Further, the internal exhaust gas recirculation amount is reduced, and the fuel consumption and exhaust emission are improved.

According to the valve timing control device for an internal combustion engine according to a third aspect of the present invention, the target valve overlap period reducing means is used for an internal combustion engine having a manual transmission, and the engine output is low when the vehicle starts. As time goes by, the target valve overlap period is greatly reduced, and the internal exhaust gas recirculation is reduced to a small amount, and the engine speed actually drops sharply. At this time, even if the valve overlap period before the rotation decrease is maintained, Engine stall is prevented from occurring due to deterioration of combustion. Also, in order to reduce the target valve overlap period as necessary to prevent engine stall according to the engine output, the valve overlap period is set as long as possible even when the vehicle starts, and the pumping loss is correspondingly increased. Further, the internal exhaust gas recirculation amount is reduced, and the fuel consumption and exhaust emission are improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an internal combustion engine provided with a valve timing control device according to the present invention.

FIG. 2 is a first for controlling a variable valve timing mechanism.
It is a flowchart.

FIG. 3 is a map for determining a target valve overlap period according to an engine operating state.

FIG. 4 is a second for controlling the variable valve timing mechanism.
It is a flowchart.

FIG. 5 is a third part for controlling the variable valve timing mechanism.
It is a flowchart.

FIG. 6 is a map for determining a first correction coefficient according to a throttle valve opening.

FIG. 7 is a fourth view for controlling the variable valve timing mechanism.
It is a flowchart.

FIG. 8 is a map for determining a second correction coefficient according to the engine speed.

FIG. 9 is a fifth part for controlling the variable valve timing mechanism.
It is a flowchart.

FIG. 10 is a map for determining a third correction coefficient according to the vehicle speed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Combustion chamber 2 ... Piston 3 ... Exhaust valve 4 ... Exhaust passage 5 ... Intake valve 6 ... Intake passage 8 ... Throttle valve 11 ... Intake valve camshaft 12 ... Exhaust valve camshaft 20 ... Control device 21 ... Water temperature sensor 24 ... Throttle valve opening sensor

Claims (3)

[Claims] 1. A variable valve timing mechanism capable of continuously changing the opening / closing timing of at least one of an intake valve and an exhaust valve, and the variable valve timing mechanism for realizing a target valve overlap period determined by an engine operating state. Variable valve timing mechanism control means for controlling the valve timing mechanism, and target valve overlap period reduction means for reducing the target valve overlap period determined by the engine operating state when the vehicle starts. Valve timing control device for internal combustion engine. 2. The target valve overlap period reduction means used in an internal combustion engine having a manual transmission, wherein the target valve overlap period reduction means largely reduces the target valve overlap period as the vehicle speed at the start of the vehicle is lower. The valve timing control device for an internal combustion engine according to claim 1. 3. The internal combustion engine having a manual transmission, wherein the target valve overlap period reduction means largely reduces the target valve overlap period as the engine output is lower when the vehicle starts. The valve timing control device for an internal combustion engine according to claim 1.