JP4427514B2 - Variable valve timing mechanism - Google Patents

Description

  The present invention relates to a variable valve timing mechanism capable of changing the opening / closing timing of an intake valve and an exhaust valve of an engine.

Various variable valve timing mechanisms (or variable valve timing lift mechanisms) have been developed and put into practical use so that the opening / closing timings and valve lift amounts of the intake and exhaust valves of the engine can be changed.
Various types of variable valve timing mechanisms (VVT mechanisms) are known, and one of them is a so-called vane type VVT mechanism (see Patent Document 1 below).

  In this vane type VVT mechanism, a cylindrical housing having a recess formed on the inner peripheral surface is fixed coaxially with the cam sprocket. The camshaft is provided with a rotor having vanes, and the rotor is accommodated in the housing so that the vane is positioned in the recess. With this configuration, the relative phase of the camshaft with respect to the cam sprocket can be changed within a range in which the vane can move in the recess.

In addition, a hydraulic chamber is formed in a space defined by the vane and the recess of the housing, and the phase of the camshaft with respect to the cam sprocket is advanced or controlled by controlling the supply and discharge state of the hydraulic oil to the hydraulic chamber. The valve can be retarded, thereby changing the opening / closing timing of the valve.
JP 2001-263107 A

By the way, as a method of controlling the supply state of hydraulic oil to the hydraulic chamber, a hydraulic circuit is interposed between the hydraulic chamber and the hydraulic source, and the supply of hydraulic oil to the hydraulic chamber is controlled in this hydraulic circuit. It is conceivable to provide a hydraulic control valve (oil control valve; OCV).
The opening of the hydraulic control valve is set to increase in accordance with a control signal (current value) from the controller, and when the target phase is the most retarded angle, the hydraulic control valve is set to maintain the most retarded position. In contrast, a holding current is supplied.

In this case, when the VVT mechanism is most retarded, the holding current must be supplied at all times, which is disadvantageous for the battery, fuel consumption, and the like.
In order to solve this problem, it is preferable that the most retarded angle can be maintained in the state in which the holding current is not supplied to the hydraulic control valve (control signal is off) during the most retarded angle control because wasteful current consumption does not occur.

However, even if the target phase becomes the most retarded by turning off the control signal, if the target phase leaves the most retarded time within a minute time (for example, about 200 msec) after the control signal is turned off, the actual current value may overshoot. There was a problem that the actual phase angle would overshoot.
This will be described with reference to FIG. 4. (a) is a diagram showing whether or not the VVT mechanism is in the minimum current value mode (control signal OFF), (b) is a diagram showing the target phase angle of the VVT mechanism, and (c). FIG. 4 is a diagram showing an actual phase angle of the VVT mechanism, and FIG. 4D is a diagram showing a target current value and an actual current value for the pressure regulating valve of the VVT mechanism.

As shown in FIG. 4B, when the target phase angle is set from the vicinity of the most retarded angle to the most retarded angle, the minimum current value mode is entered as shown in FIG. 4A. As a result, FIG. As shown in d), the target current value decreases to 0 with a slight delay, and the actual current also decreases. As a result, the actual phase angle also becomes the most retarded angle as shown in FIG.
However, after entering the minimum current value mode (ON), the actual current is not actually reduced to 0 as shown in FIG. 4 (d) within a very short time (here, 100 msec). A slight amount of current remains.

  In such a state, when the target phase angle is newly set to a value other than the most retarded angle as shown in FIG. 4B and the minimum current value mode is exited as shown in FIG. The current value output to the current value becomes larger than the target current value (overshoot), and as a result, the actual phase angle also overshoots. In particular, when the target phase repeatedly fluctuates in the vicinity of the most retarded angle during idling, there is a problem in that overshoot frequently occurs, causing shock and vibration.

  The present invention has been devised in view of such problems, and an object of the present invention is to provide a variable valve timing mechanism that can prevent overshoot of the target phase of the VVT mechanism without impairing drivability.

  The variable valve timing mechanism of the present invention includes a cam sprocket that is connected to an engine crankshaft and is rotationally driven by the crankshaft, a camshaft that is rotationally driven by a driving force from the cam sprocket, the cam sprocket, A phase change mechanism interposed between the cam shaft and the cam sprocket to change the phase of the cam shaft; and a control means for controlling the operation of the phase change mechanism. When the target phase angle of the camshaft is the most retarded angle, the control signal for the phase change mechanism is set to OFF, and after the control signal is set to OFF, the control signal is maintained OFF for a predetermined period. It is characterized (claim 1).

The predetermined period is preferably a period until the target phase reaches a predetermined value or more on the advance side of the most retarded angle (Claim 2).
Further, the phase change mechanism includes a hydraulic chamber provided between the cam sprocket and the camshaft and a pressure regulating valve for adjusting the amount of hydraulic oil supplied to the hydraulic chamber, and when the control signal is turned off. Preferably, the pressure regulating valve is closed and the hydraulic oil in the hydraulic chamber is drained (Claim 3).

  According to the variable valve timing mechanism of the present invention, after the control signal is set to be off, the control signal is kept off for a predetermined period, so that control overshoot can be reliably prevented. This also prevents shock and vibration.

Hereinafter, a variable valve timing mechanism according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration, and FIG. 2 shows a rotation direction of a cam shaft of an engine to which the present invention is applied. FIG. 3 is a schematic diagram showing an example of the configuration of the main part.
In FIG. 1, reference numeral 3 denotes an engine, and an intake system of the engine 3 is provided with an intake pipe 6, a surge tank 7, an intake manifold 8, and the like. An intake port 11 is formed at the downstream end of the intake manifold 8, and the intake port 4 and the combustion chamber 10 in the cylinder 9 communicate with each other when the intake valve 4 is opened. . The intake system includes a throttle valve 12 that adjusts the amount of intake air flowing into the combustion chamber 10 in accordance with the accelerator opening, a throttle opening sensor 13 that detects the opening of the throttle valve 12, and an intake air amount. An air flow sensor AFS for detection is provided.

  On the other hand, an exhaust port 14 is formed at the upstream end of the exhaust manifold 22 in the exhaust system of the engine 3, and the exhaust port 14 and the combustion chamber 10 communicate with each other by opening the exhaust valve 5. Yes. Further, an exhaust gas purification catalyst (not shown) is provided downstream of the exhaust manifold 22. The engine 3 includes a piston 15, a spark plug 16, an injector 17 and the like in addition to the intake system and the exhaust system described above.

  Reference numeral 2 denotes a variable valve timing mechanism (VVT mechanism) that can change the opening and closing timing of the intake valve and the exhaust valve. In this embodiment, the VVT mechanism 2 is an exhaust side valve that changes the valve timing of the exhaust valve 5. A VVT mechanism (exhaust VVT) 2a and an intake-side VVT mechanism (intake VVT) 2b for changing the valve timing of the intake valve 4 are configured. Note that the VVT mechanism applied in this embodiment advances the valve lift characteristic as a whole without changing the valve opening period by changing the valve opening timing and the valve closing timing of the intake valve and the exhaust valve. Or retarded.

  As shown in FIG. 2, the exhaust VVT 2a mainly includes a sprocket (cam sprocket) 31, an exhaust camshaft 25, and a phase change mechanism 23a that changes the phase of the cam sprocket 31 and the exhaust camshaft 25. It is configured. Similarly, the intake VVT 2 b is mainly composed of a sprocket 32, an intake camshaft 27, and a phase changing mechanism 23 b that changes the phases of the sprocket 32 and the intake camshaft 27.

Further, the exhaust-side sprocket 31 and the intake-side sprocket 32 are connected to the crankshaft 18 of the engine 3 via the timing belt 19, and both the sprockets 32, 31 is driven at a timing synchronized with the crankshaft 18 in the same direction (see arrows C ₂ and C ₁ ). The timing belt 19 is adapted to hold an appropriate tension by a tensioner 33.

The exhaust valve is changed by independently changing the relative phase between the exhaust-side sprocket 31 and the exhaust camshaft 25 and the relative phase between the intake-side sprocket 32 and the intake camshaft 27 by the phase changing mechanisms 23a and 23b. 5 and the opening / closing timing of the intake valve 4 can be changed / adjusted with respect to the phase of the crankshaft 18.
Note that the phase change in the traveling direction of the timing belt 19, that is, the phase change in the directions indicated by the arrows D ₁ and D ₂ in FIG. That is, the phase change in the direction indicated by the arrows E ₁ and E ₂ is the phase change to the retard side.

Hereinafter, the detailed mechanism of the VVT mechanism 2 will be described with reference to FIGS. In the following, the intake VVT 2b will be described, but the exhaust VVT 2a is similarly configured.
As shown in FIGS. 3A and 3B, the intake camshaft 27 and the cam sprocket 32 are disposed coaxially. Further, the phase changing mechanism 23 b is interposed between the sprocket 32 and the camshaft 27. The phase changing mechanism 23b is mainly configured by including a hydraulic chamber 40 and a pressure regulating valve (oil control valve; OCV) 21 to be described later, and the operation to be supplied to and discharged from the hydraulic chamber 40 by the pressure regulating valve 21. By changing the flow rate of oil, the phase of the camshaft 27 with respect to the sprocket 32 is changed.

More specifically, as shown in FIG. 3, a housing 34 is fastened to the sprocket 32 by a plurality of bolts 35, and the housing 34 has recesses 34a formed at four locations in the same phase. .
Further, a rotor 36 is fastened to the cam shaft 27 by a center bolt 44, and the rotor 36 is fixed so as not to rotate relative to the cam shaft 27. Further, four vanes 39 are fixed radially to the rotor 36 outwardly.

As shown in FIG. 3A, the rotor 36 is housed in the housing 34, and the vanes 39 are arranged in the respective recesses 34a. A space defined by the sprocket 32, the vane 39, and the housing 34 functions as the hydraulic chamber 40.
Further, as shown in FIG. 3B, a torsion spring 41 is interposed between the rotor 36 and the housing 34, and the rotor 36 is counterclockwise (that is, retarded) in FIG. Side). Therefore, when the hydraulic pressure in the hydraulic chamber 40 decreases, the rotor 36 is rotated to the retard side by the urging force of the torsion spring 41.

Further, a hydraulic circuit 51 as shown in FIG. 1 is connected to the VVT mechanism 2, and a hydraulic pump 50 driven by the engine 3 is connected to the hydraulic circuit 51.
The hydraulic circuit 51 is provided with a pressure regulating valve (OCV) 21 that adjusts the supply amount of hydraulic oil pressurized by the hydraulic pump 50 to the hydraulic chamber 40 of the phase change mechanism 23. For example, By opening the pressure regulating valve 21, hydraulic oil is supplied from the hydraulic pump 50 to the hydraulic chamber 40 via the hydraulic circuit 51. On the other hand, when the pressure regulating valve (OCV) 21 is closed, the hydraulic oil in the hydraulic chamber 40 is drained.

The pressure regulating valve 21 includes an exhaust side pressure regulating valve 21a and an intake side exhaust side pressure regulating valve 21b. Hereinafter, the reference numeral 21 is simply used when there is no particular distinction between the exhaust side and the intake side. Similarly, for the VVT mechanism and the phase change mechanism, reference numerals 2 and 23 are simply used when there is no particular distinction between the exhaust side and the intake side.
When the pressure regulating valve 21 is opened and hydraulic oil is supplied to the hydraulic chamber 40, the vane 39 disposed in the hydraulic chamber 40 receives the hydraulic pressure, and the rotor 36 is indicated by an arrow D2 in FIG. As a result, the camshaft 27 is also rotated in the direction of the arrow D2, and the relative phase between the sprocket 32 and the camshaft 27 is changed to the advance direction.

  Further, by closing the pressure regulating valve 21, the hydraulic pressure in the hydraulic chamber 40 decreases, and due to the difference between the driving force of the sprockets 31, 32 and the rotational inertial force of the camshafts 25, 27, and the urging force of the torsion spring 41. The rotor 36 and the camshaft are rotated in the direction opposite to the arrow D2, and the relative phases of the sprockets 31 and 32 and the camshafts 25 and 27 are changed in the retard direction.

  By the way, as shown in FIG. 1, the engine 3 is provided with a control means (referred to as a controller or ECU) for controlling the operation of various devices such as the VVT mechanism 2, the injector 17 and the spark plug 16. The operation of the pressure regulating valve 21 is controlled based on a control signal from the ECU 1. Further, the pressure regulating valve 21 includes a solenoid coil (not shown), and the opening of the pressure regulating valve is adjusted according to the current value supplied to the solenoid coil. The current value is set. Specifically, the opening degree of the pressure regulating valve 21 is increased as the current value output from the ECU 1 to the pressure regulating valve 21 is increased. Moreover, the opening degree of the pressure regulation valve 21 becomes small, so that an electric current value becomes small.

Therefore, by setting the control signal (current value) output from the ECU 1 to the pressure regulating valve 21 to the maximum value, the valve opening / closing timing of the VVT mechanism 2 can be advanced most, and the above current value is set to the minimum value. By setting, the valve opening / closing timing can be retarded most.
Incidentally, in addition to the throttle opening sensor 13 and the air flow sensor AFS, the ECU 1 detects a pressure sensor (mani pressure sensor) that detects an intake manifold pressure (mani pressure) as an engine load and an engine speed. Various sensors such as an engine speed sensor (all not shown) are connected.

  In addition, a map (target phase setting means) 20 in which target phases of the intake valve 4 and the exhaust valve 5 are stored using the manifold pressure (engine load) and the engine speed as parameters is provided in the ECU 1. Here, the target phase setting map 20 sets a target valve opening timing (IO) of the intake valve 4 and a target valve closing timing (EC) of the exhaust valve 5, and can be set by the VVT mechanism 2. The target phase corresponding to the manifold pressure and the engine speed is stored for each predetermined phase (for example, every 0.05 degrees) with the most retarded angle as a reference (that is, the most retarded angle = 0 °).

As described above, when the target phase is the most retarded angle, the current value for the pressure regulating valve 21 is set to the minimum value. For this reason, the case where the target phase is the most retarded angle, that is, the case where the current value for the pressure regulating valve 21 becomes the minimum value is hereinafter referred to as the minimum current value mode.
Here, the minimum current value is set to current value = 0 (control signal off), and the pressure regulating valve 21 is closed when the control signal is off. With this configuration, a simple control logic that cuts off the current supply when the target phase is the most retarded angle can be realized, and the current consumption can be reduced.

However, when the target phase becomes the most retarded angle in this way, the target phase becomes the most retarded with a time other than the most retarded angle within a short time (for example, about 200 msec) after entering the minimum current value mode (after turning off the current). When the angular mode is released, an overshoot occurs in the actual current value, and the actual phase angle may overshoot. Even if the target phase once reaches the most retarded angle (current value = 0), current may remain in the solenoid coil for a very short time. Under such circumstances, the current value corresponding to the new target phase This is because a current larger than the originally required current flows through the pressure regulating valve 21 and the actual current value overshoots. (See Figure 4)
Therefore, in this apparatus, after the target phase is set to the most retarded angle (for example, 0 °), when the target phase is less than a predetermined value (for example, 1.25 °) more advanced than the most retarded angle. While the control signal is kept off (current value = 0), the control signal corresponding to the target phase is set only when the target phase is not less than the predetermined value (predetermined period) on the advance side. ing. That is, once the minimum current value mode is entered, the minimum current value mode is maintained unless the target phase exceeds the predetermined value.

Thereby, for example, when the target phase frequently fluctuates in the vicinity of the most retarded angle, hunting between entering and leaving the minimum current value mode can be prevented, and overshooting of the actual current value with respect to the pressure regulating valve 21 can be prevented. be able to. Further, overshoot of the actual phase angle of the VVT mechanism 2 can be prevented, and stable control can be realized.
Note that when the target phase of a predetermined value or more is set on the advance side, the minimum current value mode is naturally left out. Therefore, an actual current overshoot occurs within a minute time from the entry of the minimum current value mode. However, when a relatively large target phase is set on such an advance angle side, it is considered that the driver intends to accelerate by depressing the accelerator pedal relatively, so there is a slight overshoot of the phase angle. There is no loss of drivability.

Since the variable valve timing mechanism according to the embodiment of the present invention is configured as described above, the following operations and effects are achieved. First, during operation of the engine 3, the pressure (manifold pressure) of the intake manifold 8 is detected by a pressure sensor (not shown), and the engine speed is also detected by an engine speed sensor (not shown).
On the other hand, the ECU 1 reads the target phase of the opening / closing timing of the intake valve 4 and the exhaust valve 5 from the target phase setting map 20 based on the engine speed and the manifold pressure (load), and performs control corresponding to the target phase. A signal (current value) is set.

Then, by outputting this control signal to the pressure regulating valve 21, the opening degree of the pressure regulating valve 21 is adjusted, and the amount of oil supplied to the oil chamber 40 provided in the phase changing mechanism 23 of the VVT mechanism 2 is reduced. Adjusted. Thereby, the camshafts 25 and 27 are advanced or retarded with respect to the cam sprockets 31 and 32, and the opening / closing timings of the intake valve 4 and the exhaust valve 5 are changed.
When the target phase is set to the most retarded angle, the mode shifts to the minimum current value mode and the current value is set to zero. As a result, the supply of the hydraulic oil to the hydraulic chamber 40 is stopped, the hydraulic oil that has already been supplied is drained, and the phases of the camshafts 25 and 27 are the most retarded with respect to the sprockets 31 and 32. Become.

Further, when the target phase is set to the most retarded angle in this way, even if the target phase angle is subsequently changed, the minimum current value mode is set when the target phase angle is less than a predetermined value (that is, for a predetermined period) The current value corresponding to the target phase is set only when the target phase is equal to or greater than the predetermined value (that is, after the predetermined period has elapsed).
Therefore, even when the target phase is changed from the most retarded angle to the minute advance angle phase, the minimum current value mode is maintained, and the departure from the minimum current value mode can be prevented. Thereby, the overshoot of the actual current value with respect to the pressure regulating valve 21 and the overshoot of the actual phase angle of the VVT mechanism 2 can be prevented.

Further, when a target phase equal to or greater than a predetermined value is set, a current value corresponding to the target phase is set. At this time, an overshoot of the actual current may occur, but in this case, since the driver is requesting acceleration, the drivability is improved by giving priority to the driver's intention and leaving the minimum current value mode. Secured.
While the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the case where the VVT mechanism 2 is provided on both the intake side and the exhaust side has been described. However, the VVT mechanism may be provided only on either the intake side or the exhaust side.

  Further, the phase changing means 23 of the VVT mechanism 2 is not limited to that shown in FIG. 3, and various changes can be made to the shapes of the rotor, vanes, and housing. Further, as the phase changing means 23 of the VVT mechanism 2, a motor (for example, a stepper motor) is provided between the camshaft and the cam sprocket other than the one that changes the phase by hydraulic pressure, and the current to the motor is changed. The phase may be set to be changed by controlling the value, and the phase may be set to the most retarded angle by turning off the current value to the motor.

In the above description, the load of the engine 3 is obtained from the manifold pressure. However, the engine load may be obtained from the throttle opening or the intake air amount.
In the above description, the period until the target phase becomes equal to or greater than the predetermined value is set as the predetermined period. However, after the target phase is set to the most retarded angle, the control signal is turned off (current value = 0) for the predetermined time. A timer may be set to maintain. In this case, for example, when a relatively large target phase is set on the advance side, the responsiveness is delayed for a predetermined time, but hunting and overshooting can be prevented with simple control.

It is a mimetic diagram showing the whole variable valve timing mechanism composition concerning one embodiment of the present invention. It is a schematic diagram which shows the rotation direction of the cam shaft of the engine to which this invention is applied. It is a schematic diagram shown about an example of the principal part structure of the variable valve timing mechanism which concerns on one Embodiment of this invention, (a) is the front view, (b) is sectional drawing in the side surface. It is a figure explaining the subject of this invention, (a) is a figure which shows whether a VVT mechanism is the minimum electric current value mode (control signal OFF), (b) is a figure which shows the target phase angle of a VVT mechanism, (c) is a figure which shows the actual phase angle of a VVT mechanism, (d) is a figure which shows the target electric current value and actual electric current value with respect to the pressure regulation valve of a VVT mechanism.

Explanation of symbols

1 Control means (controller or ECU)
2, 2a, 2b Variable valve timing mechanism (VVT mechanism)
3 Engine 4 Intake Valve 5 Exhaust Valve 6 Intake Pipe 7 Surge Tank 8 Intake Manifold 9 Cylinder 10 Combustion Chamber 11 Intake Port 12 Throttle Valve 13 Throttle Opening Sensor 14 Exhaust Port 15 Piston 16 Spark Plug 17 Injector 18 Crankshaft 19 Timing Belt 20 Map (target phase setting means)
21, 21a, 21b Pressure regulating valve (oil control valve; OCV)
22 Exhaust manifold 25, 27 Camshaft 23, 23a, 23b Phase change mechanism 31, 32 Sprocket (cam sprocket)
33 Tensioner 34 Housing 36 Rotor 39 Vane 40 Hydraulic chamber 50 Hydraulic pump 51 Hydraulic circuit

Claims (3)

A cam sprocket connected to the crankshaft of the engine and driven to rotate by the crankshaft;
A camshaft that is rotationally driven by a driving force from the cam sprocket;
A phase change mechanism that is interposed between the cam sprocket and the cam shaft and changes the phase of the cam shaft with respect to the cam sprocket;
Control means for controlling the operation of the phase change mechanism;
The control means sets the control signal for the phase change mechanism to OFF when the target phase angle of the camshaft is the most retarded angle,
A variable valve timing mechanism, wherein the control signal is kept off for a predetermined period after the control signal is set off.   The variable valve timing mechanism according to claim 1, wherein the predetermined period is a period until the target phase becomes a predetermined value or more on an advance side of the most retarded angle. The phase change mechanism is
A hydraulic chamber provided between the cam sprocket and the camshaft;
A pressure regulating valve for adjusting the amount of hydraulic oil supplied to the hydraulic chamber;
The variable valve timing mechanism according to claim 1 or 2, wherein when the control signal is turned off, the pressure regulating valve is closed and the hydraulic oil in the hydraulic chamber is drained.

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