JP3779475B2 - Variable valve timing device for engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a variable valve timing apparatus for an engine, and more particularly to a valve timing control technique for improving engine startability.
[0002]
[Prior art]
Conventionally, in a vehicle engine, a variable valve timing mechanism is known in which the opening / closing timing of an intake valve and / or an exhaust valve is advanced or delayed by changing the rotational phase of a camshaft by hydraulic pressure (Japanese Patent Application Laid-Open No. 7-101). No. 233713, JP-A-8-246820, etc.).
[0003]
[Problems to be solved by the invention]
By the way, in the variable valve timing mechanism, at the time of low load and low rotation such as idling, the valve timing is normally controlled to the minimum valve overlap, and the valve overlap is controlled to the minimum even at the start. .
On the other hand, in order to improve the startability of the engine, it is known that it is effective to accelerate the rise of the rotational speed from the start of the start. However, it is attempted to accelerate the rise response by increasing the torque of the starter motor. Then, a large-sized starter motor is required, and there is a problem that the cost is increased and the installation space for the starter motor is increased.
[0004]
The present invention has been made in view of the above circumstances, and in an engine equipped with a variable valve timing mechanism, it is possible to speed up the start-up response of the rotation at the start by changing the valve timing, leading to an increase in cost and the like. The purpose is to improve the startability.
[0005]
[Means for Solving the Problems]
Therefore, the invention according to claim 1 detects the start of the engine and outputs a hydraulic control signal corresponding to the maximum valve overlap amount, while the actual valve timing exceeds the allowable valve overlap amount at the start. Then, the valve timing is changed in the direction of expanding the valve overlap with respect to the valve timing at the time of normal low load and low rotation when the engine is started , by returning to the hydraulic control signal corresponding to the normal overlap amount .
[0010]
According to such a configuration, in a configuration in which the valve timing is changed by controlling the hydraulic pressure, when the start is started, a hydraulic control signal corresponding to the maximum valve overlap amount is output, and the valve timing is set to the maximum valve overlap. It will be changed toward the position. Here, since the actual valve overlap changes with a delay with respect to the control signal due to a delay in the response of the hydraulic pressure, the actual valve timing after that is monitored, and an allowable overlap amount smaller than the maximum overlap amount is monitored. Return to normal valve timing when it exceeds. That is, the valve overlap is expanded after the hydraulic control signal corresponding to the maximum valve overlap amount is output until the actual overlap amount reaches the allowable overlap amount. As a result, even when the setting is such that the overlap amount is controlled to a minimum during low load and low rotation, at the time of start-up, for example, the opening timing of the intake valve is advanced to increase the overlap.
[0011]
【The invention's effect】
According to the first aspect of the invention, the valve timing can be changed in a responsive manner in the direction in which the overlap amount increases, and it is possible to prevent the overlap amount from being excessively increased and the combustibility from being greatly deteriorated. effective.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a system configuration of an engine provided with a variable valve timing mechanism in the embodiment.
In FIG. 1, the air measured by the throttle valve 2 is supplied to the engine 1 through the intake valve 3 into the cylinder, and the combustion exhaust is discharged through the exhaust valve 4. The intake valve 3 and the exhaust valve 4 are opened and closed by cams provided on the intake side cam shaft and the exhaust side cam shaft, respectively.
[0014]
The intake-side camshaft 5 is provided with a variable valve timing mechanism 6 that continuously increases or decreases the opening / closing timing of the intake valve 3 with a constant opening / closing angle by changing the rotational phase of the camshaft with respect to the crankshaft. It has been.
The variable valve timing mechanism 6 is a hydraulic mechanism that continuously changes the rotational phase by the hydraulic pressure supplied by the hydraulic pump driven by the engine, and the hydraulic pressure acting in the advance direction of the rotational phase and the retarded direction. The hydraulic pressure acting on the camshaft is respectively controlled to control the rotational phase of the camshaft to the target rotational phase, and the hydraulic pressure is adjusted by a hydraulic pressure control signal from the control unit 7.
[0015]
Further, the variable valve timing mechanism 6 is provided with mechanical stoppers for restricting the change of the rotational phase in both the retarded direction and the advanced direction of the rotational phase. The position and the most retarded angle position are defined. Furthermore, a return spring that biases toward the most retarded position is provided.
[0016]
Note that the retarding direction of the rotational phase of the intake camshaft 5 is a direction in which the opening timing of the intake valve 3 is delayed and the overlap amount between the exhaust valve and the intake valve decreases, and the advance direction is the intake angle. The opening timing of the valve 3 is advanced and the overlap amount between the exhaust valve and the intake valve is increased.
As shown in FIG. 2, the variable valve timing mechanism 6 is attached to a cam sprocket 21 of the intake side camshaft 5, and a phase adjusting mechanism 22 for changing the phase between the crankshaft and the intake side camshaft 5, And a control valve 23 for controlling the supply of operating hydraulic pressure to the adjusting mechanism 22.
[0017]
The phase adjusting mechanism 22 is provided with a front side hydraulic passage 25 that supplies hydraulic pressure to the front side of the plunger 24 built in the cam sprocket 21 and a rear side hydraulic passage 26 that supplies hydraulic pressure to the rear side of the plunger 24. ing.
The plunger 24 meshes with the cam sprocket 21 and the intake side camshaft 5 by a helical gear 27, and the plunger 24 rotates while being rotated by the camshaft by the balance between the hydraulic pressure supplied to the front side and the hydraulic pressure supplied to the rear side. 5 along the axial direction. At this time, since the cam sprocket 21 is fixed by a timing chain (or timing belt) (not shown), the cam shaft 5 side rotates with the plunger 24, and the phase position between the cam sprocket 21 and the cam shaft 5 changes. In this embodiment, when the plunger 24 is moved in the direction approaching the cam shaft 5 (the right direction in FIG. 2), the rotational phase of the cam shaft 5 changes in the advance direction, and conversely, the plunger 24 is moved to the cam shaft 5. When moving in a direction away from (leftward in FIG. 2), the rotational phase of the camshaft 5 changes in the retarding direction.
[0018]
Further, a return spring 28 is provided to urge the plunger 24 in a direction away from the camshaft. When the hydraulic pressure on the front side of the plunger 24 is smaller than the urging force of the return spring 28, the return spring 28 is provided. The plunger 24 is moved to the most retarded position away from the cam shaft 5 by the urging force.
[0019]
The control valve 23 for controlling the hydraulic pressure supplied to the front side and the rear side of the plunger 24 includes a linear solenoid 29 and a spool valve 30. By changing the position of the spool valve 30 by the linear solenoid 29, the front side hydraulic passage The hydraulic pressure supplied to the front side of the plunger 24 via 25 and the hydraulic pressure supplied to the rear side of the plunger 24 via the rear hydraulic passage 26 are controlled.
[0020]
The linear solenoid 29 is duty-controlled by the control unit 7 to turn on / off the current. When the duty ratio (ON time ratio) is 0%, the hydraulic pressure is exclusively applied to the rear side of the plunger 24. The camshaft 5 is controlled to the most retarded position (minimum overlap position). On the other hand, when the duty ratio is 100%, the hydraulic pressure is supplied exclusively to the front side of the plunger 24, and the camshaft 5 is the most advanced angle. The position (maximum overlap position) is controlled.
[0021]
In FIG. 2, 31 is a hydraulic pressure source (hydraulic pump driven by the engine), and 32 is a drain passage from the spool valve 30.
Further, as shown in FIG. 2, a cam sensor 9 that outputs a detection signal at a predetermined angular position of the cam shaft 5 is provided.
Further, a crank angle sensor 8 for outputting a detection signal at a predetermined angular position of the crankshaft is provided, and the control unit 7 is configured to detect the camshaft relative to the crankshaft based on the detection signals from the crank angle sensor 8 and the cam sensor 9. 5 is detected, so that the opening / closing timing of the intake valve 3 is detected, and the rotational speed Ne of the engine 1 is calculated based on the detection signal from the crank angle sensor 8.
[0022]
The control unit 7 includes detection signals from the crank angle sensor 8 and the cam sensor 9, an air flow meter 10 for detecting the intake air amount of the engine 1, a water temperature sensor 11 for detecting the cooling water temperature Tw of the engine 1, and the like. The detection signal is input.
Then, the control unit 7 determines a target advance value of the phase of the camshaft 5 based on information such as the engine load, the engine speed Ne, the coolant temperature Tw, and the duty of the duty corresponding to the target advance value. A hydraulic control signal is output to the linear solenoid 29.
[0023]
Here, in a predetermined low rotation and low load region including at least idle, the target advance value is set to 0 °, so that a hydraulic control signal with a duty of 0% is output to the linear solenoid 29, and the camshaft 5 is controlled to the most retarded angle side (minimum overlap amount).
However, in the present embodiment, at the time of start-up, even if the rotation speed is low and the load is low, the valve overlap amount is normally increased by controlling to the more advanced angle side rather than controlling to the most retarded angle side. The state of opening / closing timing control of the intake valve 3 at the time of starting will be described in detail with reference to the flowchart of FIG.
[0024]
In the flowchart of FIG. 3, in S1, it is determined whether the start switch is ON or OFF.
Then, if the start switch is OFF, the process proceeds to S6, and in accordance with normal control for setting the target advance value to 0 ° (corresponding to the minimum overlap amount) in a predetermined low rotation and low load region including at least idle. The opening / closing timing of the intake valve 3 is controlled.
[0025]
On the other hand, at the time of start-up when the start switch is ON, the process proceeds to S2, where it is determined whether or not the elapsed time after the start switch is turned on is equal to or longer than a predetermined time.
In S3, it is determined whether or not the engine rotational speed Ne is equal to or lower than a reference rotational speed Ns (for example, 800 rpm) that is recognized as a complete explosion state, and if it is equal to or lower than the reference rotational speed Ns, the process proceeds to S4.
[0026]
In S4, the actual advance value (actual valve overlap amount) of the camshaft 5 detected based on the detection signals from the crank angle sensor 8 and the cam sensor 9 is an allowable maximum advance value (allowable) at the time of start. It is determined whether or not the valve overlap amount is less than or equal to. The allowable maximum advance value is a maximum value of an advance angle range in which combustion can be normally performed at the time of starting, and is set to a value equal to or less than the maximum advance value in the variable valve timing mechanism 6.
[0027]
If it is determined in S4 that the actual advance value of the camshaft 5 is less than or equal to the allowable maximum advance value, the process proceeds to S5 and a signal with a duty of 100% (corresponding to the maximum overlap amount) as the hydraulic control signal. Is output to the linear solenoid 29.
Therefore, at the same time when the start switch is turned on, a signal with a duty of 100% is output to the linear solenoid 29 as the hydraulic control signal, and a duty of 100% corresponding to this most advanced position (maximum overlap amount) By outputting a hydraulic pressure control signal, the rotation phase of the intake camshaft 5 is changed to the advance side with the maximum response.
[0028]
When the start switch is turned on, a hydraulic pressure control signal with a duty of 100% is continuously output. When the start switch is turned off, when the predetermined time or more has elapsed since the start switch is turned on, the engine rotational speed Ne is set to the reference rotational speed Ns. If the actual advance value of the camshaft 5 exceeds the allowable maximum advance value, the process proceeds to S6 to return to normal control, so that the cam phase that has been advanced up to that point is changed. The normal maximum retard position (minimum overlap amount) is controlled.
[0029]
Here, as described above, even if a hydraulic control signal with a duty of 100% is output to the linear solenoid 29 simultaneously with the start of the start, there is a delay in the response of the hydraulic pressure. Since it may be missing, as shown in FIG. 4, the actual valve timing starts to change in the advance direction with a delay from the output of the hydraulic control signal with a duty of 100%.
[0030]
In the time chart of FIG. 4, since the output of the hydraulic control signal with a duty of 100% is started at the same time as the start switch is turned on, the engine rotational speed Ne exceeds the reference rotational speed Ns. An example in the case of returning to a duty 0%) corresponding to the minimum overlap amount) is shown.
According to the above configuration, the opening / closing timing of the intake valve is advanced more than usual at the start, and the amount of overlap between the intake valve 3 and the exhaust valve 4 is increased, so the intake / exhaust load is reduced. The rise response of rotation (cranking speed) is improved, and startability is improved.
[0031]
In addition, when the start switch is turned off, when a predetermined time has elapsed, when the speed exceeds the reference speed, or when the advance value exceeds the allowable maximum advance value, the normal advance value (maximum (Retard angle position, minimum overlap position), it is possible to prevent the startability from being deteriorated by excessive advance angle control.
Further, by outputting a hydraulic pressure control signal with a duty of 100% simultaneously with turning on the start switch, the rotation phase of the intake camshaft 5 can be changed to the advance side with the maximum response.
[0032]
In the above-described embodiment, the overlap amount is increased by advancing the opening / closing timing of the intake valve 3. However, the opening / closing timing of the exhaust valve 4 is delayed together with or in place of the intake valve 3. The overlap amount may be increased.
In addition, it is not limited to a mechanism that changes the valve timing while keeping the opening / closing angle constant by changing the phase of the camshaft with respect to the crankshaft, but a variable valve configured to increase the overlap amount as the opening / closing angle increases. A timing mechanism may be used.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of an engine in an embodiment.
FIG. 2 is a partial cross-sectional view showing a variable valve timing mechanism in the embodiment.
FIG. 3 is a flowchart showing a state of valve timing control at start-up in the embodiment.
FIG. 4 is a time chart showing characteristics of valve timing control at the start in the embodiment.
[Explanation of symbols]
1 Engine 2 Throttle valve 3 Intake valve 4 Exhaust valve 5 Intake side camshaft 6 Variable valve timing mechanism 7 Control unit 8 Crank angle sensor 9 Cam sensor
10 Air flow meter
11 Water temperature sensor
21 Cam sprocket
22 Phase adjustment mechanism
23 Control valve
24 Plunger
25 Front side hydraulic passage
26 Rear hydraulic passage
27 Helical gear
28 Return spring
29 Linear solenoid
30 Spool valve

Claims (1)

An engine variable valve timing device that changes valve timing by hydraulic pressure,
Detects engine start and outputs a hydraulic pressure control signal corresponding to the maximum valve overlap amount. On the other hand, when the actual valve timing exceeds the allowable valve overlap amount at the start, the hydraulic pressure corresponding to the normal overlap amount Return to the control signal,
A variable valve timing apparatus for an engine characterized by changing the valve timing in a direction in which the valve overlap is expanded with respect to the valve timing at the time of normal low load and low rotation when the engine is started.

Images