JPH0228687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a valve timing changing device for internal combustion engines, particularly diesel engines, and more specifically,
A valve timing change device that automatically changes the opening timing of the intake valve in response to high-load and low-load operation of a highly supercharged diesel engine, and maintains the diesel engine in the best operating condition at all times. It is related to.

Conventional technology The timing of opening and closing of the intake and exhaust valves installed in a diesel engine is normally set to the optimal state within a certain range according to the engine's output and rotation speed, but as the engine output increases, As supercharging increases, it is necessary to increase the period during which the intake and exhaust valves are open at the same time, that is, the overlap period, in order to increase the scavenging effect and suppress the heat load during high-load operation.

For this reason, during low-load operation close to non-supercharging, due to the excessive overlap period, exhaust gas blows back into the combustion chamber and intake system, resulting in fouling, and exhaust color due to a drop in compression temperature and piston temperature due to a drop in supply air pressure. Problems such as defects and startup failures occur.

Therefore, it is desirable to shorten the overlap period when the load is low in order to maintain the best operating condition of the engine.

For example, when the load is high, the intake valve opens at position A, approximately 80 degrees before the piston top dead center [TDC], as shown by the solid line in Figure 4a, and closes to the bottom dead center [BDC].
The exhaust valve closes at position B, approximately 45 degrees after piston, opens at position C, approximately 50 degrees before piston bottom dead center [BDC], and closes at position D, approximately 60 degrees after top dead center [TDC], as shown by the broken line. When the load is low, the overlap period can be shortened by setting the intake valve to open at position A', approximately 20 degrees before top dead center (TDC), as shown in FIG. 4b.

As mentioned above, as a device for automatically changing valve timing during high load and low load, there is a device disclosed in Japanese Utility Model Application No. 50-59808, and this device is driven by an engine. The hydraulic pressure generated by the fluid pump is supplied to the valve opening device of the intake/exhaust valve through the switching valve, and the switching of the switching valve is performed by the switching valve operating device using the timing cam as the driving source. The actuator incorporates a valve opening/closing timing adjustment mechanism.

Another example is the British patent no.
The specification of No. 1224168 consists of a pump having a piston that reciprocates in the axial direction in cooperation with a cam, and a plunger that is operated by hydraulic pressure generated by this pump to drive a valve, and rotates the piston. This disclosure discloses a valve timing changing device that is capable of changing valve timing.

Problems to be Solved by the Invention By the way, the former valve timing changing device [Utility Model Application Publication No. 59808/1983] requires a fluid pump to constantly generate high pressure, resulting in large energy loss. The use of fluid pumps, switching valves, etc. makes the entire device complicated and expensive.Furthermore, since both valves open and close during the cam lift upward stroke, the cam lift upward curve has to be gradual. Therefore, the valve opens slowly, and there is a drawback that a sufficient valve opening area cannot be secured, so that the valve is not yet sufficient.

Furthermore, the latter valve timing changing device [British Patent No. 1224168] has only one hydraulic control hole, and control notches are provided at both axial ends of one land of the piston. Therefore, the lower notch opens the hydraulic control hole and releases the hydraulic pressure acting on the plunger before the end of the piston's upward stroke. Even though the piston is moved up and down by the cam, the opening and closing of the valve is controlled only by the cam in the upward stroke of the piston.
This has the disadvantage that not only is it difficult to increase the valve opening area due to a lot of unnecessary movement of the piston, but it is also difficult to accurately set the valve closing timing.

That is, in the above two examples, since the valves are controlled to open and close only during the upward stroke of the cam lift, it is unreasonable and causes a large energy loss, and furthermore, the device itself inevitably becomes larger and more complicated. Also, in diesel engines,
By increasing the overlap period, it is possible to clean the residual gas in the combustion chamber, increase the amount of intake air, and cool the inside of the combustion chamber. Therefore, during high-load operation,
Since the engine can be operated in the best possible condition by advancing the opening timing of the intake valve, there is a need for a simple and inexpensive valve timing changing device that changes the opening timing of only the intake valve.

Means for Solving the Problems The present invention includes a drive piston built into a drive cylinder and reciprocating in the axial direction in cooperation with a tappet;
The actuating piston is built in the actuating cylinder and is actuated by hydraulic pressure generated by the driving piston to drive the intake valve, and the valve timing can be changed by changing the stroke of the driving piston. The valve timing changing device is provided with a control piston for changing the stroke of the driving piston between the tappet and the driving piston, and the working cylinder is supplied with excess pressure oil from the working cylinder chamber. An oil relief groove is formed for the oil to escape to the oil outlet, and the control piston is controlled by supplying hydraulic oil to the control hydraulic chamber defined by the control piston or by discharging the hydraulic oil from the control hydraulic chamber. This is a valve timing changing device for a diesel engine, which changes the stroke amount of the driving piston by moving it, and changes the valve timing of an intake valve according to the load of the diesel engine.

Function The valve timing changing device for a diesel engine according to the present invention supplies hydraulic oil into the control hydraulic chamber or discharges hydraulic oil from the control hydraulic chamber depending on low load or high load. The control piston is moved to adjust the stroke of the drive piston, thereby changing the timing at which the actuating piston starts to rise, thereby changing the opening timing of the intake valve.

Embodiment FIGS. 1 to 3 are drawings showing an embodiment of a valve timing changing device for a diesel engine according to the present invention.

In the drawings, 1 is a camshaft, 2 is a timing cam integrally formed with the camshaft 1,
3 is a tappet that moves up and down by a timing cam 2; 4 is a device body installed upright on a cylinder block 5; a tappet guide 6 integrally formed at the bottom of the device body 4 is fitted and fixed to the cylinder block 5; The tappet 3 slides within this tappet guide 6. Inside the device main body 4, a drive cylinder 7 is provided along the axial direction, and an operating cylinder 8 that interlocks with the drive cylinder 7 is provided at the top. A refueling section 9 is provided. Reference numeral 10 denotes a drive piston that is slidably fitted into the drive cylinder 7, and the upper end surface of the drive piston defines a hydraulic pressure generation chamber A within the drive cylinder 7. 11 is a push rod interposed on the same axis between the tappet 3 and the drive cylinder 10; 12 is the drive piston 10;
A spring 12' is compressed and interposed between the lower flange 10a and the drive cylinder 8, and a spring 12' is compressed and interposed between the upper surface of the tappet 3 and the main body 4 of the device. The driving piston 10 and the tappet 3 are pushed up in conjunction with the tappet 3 via the springs 12 and 12', respectively. Reference numeral 13 denotes a control piston that is housed in the device main body 4 so as to be slidable in the axial direction and comes into contact with the lower end of the drive piston 10.
The push rod 11 is slidably inserted through the center of the holder. A control hydraulic chamber B is defined on the lower surface of the control piston 13 in the apparatus main body 4, and on the lower side of the apparatus main body 4,
An oil supply section 14 for supplying hydraulic oil to the control hydraulic chamber B is provided. Reference numeral 15 denotes a check valve disposed between the oil supply section 14 and the control hydraulic chamber B, which allows the hydraulic oil supplied into the control hydraulic chamber B to reach the drive piston 10.
The high pressure generated in the control hydraulic chamber B due to the pressing force during the downward movement prevents backflow. Reference numeral 16 denotes a control piston that pushes open the check valve 15 by the elastic restoring force of a spring 17 when there is no pressure oil in the oil supply part 14, and discharges the hydraulic oil in the control hydraulic chamber B from the oil supply part 14. It is for. A solenoid valve 18 switches and controls the supply of hydraulic oil to the oil supply section 14 and the discharge of hydraulic oil from the oil supply section 14 . Reference numeral 19 denotes an oil supply hole for supplying hydraulic oil to the drive cylinder 7, which supplies oil to the upper part of the drive cylinder 7 through a check valve 20, and closes the check valve 20 as the drive piston 10 rises. Oil passage 21, 2
2 to the working cylinder 8. 23 is
The working piston is slidably fitted into the working cylinder 8 and supports the spherical end of the push rod 24, and rises in accordance with the amount of oil supplied from the oil passage 22 as the driving piston 10 rises. 25 is a rocker arm that is swung by the shaft rod 24, 26 is an intake valve that is opened and closed by the rocker arm 25, and 27 is a valve spring.
Reference numeral 28 denotes an oil relief groove provided in the working cylinder 8. When the working piston 23 rises by a predetermined amount, the working oil supplied to the working cylinder 8 is released, and the oil passage 2
9, the air is discharged to the outside via the pressure regulating valve 30 to regulate the amount of rise of the operating piston 23, and the intake valve 26 is actuated in a constant stroke. As will be described later, the pressure regulating valve 30 regulates the pressure of the hydraulic oil from the oil passage 29 of the working cylinder 8 to a constant pressure, prevents a sudden drop in the hydraulic oil pressure in the oil passage 22, and prevents the hydraulic oil pressure from the working piston 23. This is to prevent hunting in the valve drive system up to the intake valve 26. 31 is a stopper for the actuating piston 23.

The operating procedure of the valve timing changing device having the above configuration will be explained below.

First, in the state shown in FIG.
Therefore, the stroke distance of the drive piston 10 is set to be the same as that of the tappet 3, and the valve timing is set at high load. .

In this state, when the tappet 3 is pushed up by the timing cam 2, the drive piston 10 is pushed up via the push rod 11, and in order to increase the hydraulic oil pressure in the oil pressure generation chamber A, the check valve 2
0 is closed and the hydraulic oil in the oil pressure generation chamber A flows into the oil path 2.
1 and 22, and flows into the working cylinder chamber of the working cylinder 8. Due to the inflow of this hydraulic oil, the working piston 23 rises within the working cylinder 8, and this upward movement of the working piston 23 causes the push rod 2 to rise.
4 and the rocker arm 25 to open the intake valve 26. When the working piston 23 rises to a predetermined position and opens the oil relief groove 28, the hydraulic oil supplied from the oil passage 22 is discharged from the oil relief groove 28 to the oil passage 29 to the outside of the system. Therefore, the working piston 23 does not rise any further and maintains this position, so that the opening degree of the intake valve 26 is kept constant.

Note that at this time, the pressure of the hydraulic oil discharged from the oil passage 29 is regulated to a constant pressure by the pressure regulating valve 30, so that the operating piston 23 of the valve drive system
Hunting in the system from the to the intake valve 26 is prevented. In other words, if the pressure regulating valve 30 is not provided, when the working piston 23 rises to a predetermined position and the working oil flows toward the oil relief groove 28, the working oil pressure in the oil passage 22 will be 0 kg. /cm ² , the operating piston 23 is pushed back by the elastic restoring force of the valve spring 27 until it closes the oil relief groove 28 and the oil pressure returns to the predetermined pressure. This causes the intake valve 26 to sag. Therefore, if the pressure regulating valve 30 is provided as described above, the hydraulic oil pressure in the oil passages 22, 29 and the working cylinder 8 is maintained at a predetermined pressure by the pressure regulating valve 30, so that the working piston 23 The elastic restoring force of the valve spring 27 keeps it at a constant position without being pushed back, and therefore the intake valve 26 does not swing.

In addition, in the above operation process, the operating piston 2
The upper limit position of No. 3 is limited by a stopper 31.

After the drive piston 10 rises to the position shown by the dashed line in FIG. 1 due to the rotation of the timing cam 2, the elastic restoring force of the springs 12 and 12' causes The drive piston 10 and tappet 3 are pushed down and begin to descend. Then, the working piston 23
The hydraulic pressure acting on the valve spring 27 is no longer applied, and the actuating piston 23 is pushed down by the elastic restoring force of the valve spring 27 in accordance with the amount of descent of the driving piston 10, and the intake valve 26 is closed.

FIG. 3 shows the operating characteristics of the drive piston 10 and the operating piston 23 under the above-mentioned high load conditions. As shown, it rises following the drive piston 10, stops rising at a predetermined position and stands still, and also descends following the drive piston 10 when descending.

Next, the operation at low load will be explained.

In this case, as shown in FIG. 2, first operate the solenoid valve 18 to supply hydraulic oil to the oil supply section 14,
The hydraulic pressure of the hydraulic oil moves the control piston 16 to the right against the elastic restoring force of the spring 17 and pushes the check valve 15 open.
Hydraulic oil is caused to flow into the control hydraulic chamber B and the control piston 13 is pushed up. This upward movement of the control piston 13 causes the drive piston 10 to move towards the spring 1.
The drive piston 10 is pushed up against the elastic restoring force of the push rod 11, and the drive piston 10 is separated from the upper end of the push rod 11, thereby setting the valve timing at low load.
Note that the hydraulic oil supplied to the control hydraulic chamber B is prevented from flowing backward by the check valve 15, so that the control piston 13 resists the elastic restoring force of the spring 12 acting via the drive piston 10. to maintain the above-mentioned raised position.

When the tappet 3 is pushed up by the timing cam 2 in this state, the push rod 11 is also pushed up by the tappet 3, and after the tappet 3 and the push rod 11 have been raised by a predetermined amount, the upper end of the push rod 11 is raised. It comes into contact with the lower surface of the drive piston 10 and pushes up the drive piston 10. Therefore, the drive piston 10 starts to rise after a predetermined time delay from the tappet 3 and pumps hydraulic oil to the working cylinder 8, so that the working piston 23
starts to rise after a predetermined period of time, and the push rod 2
4 and the intake valve 2 via the Rocker arm 25.
6 is opened.

As the timing cam 2 rotates, the drive piston 10 rises to the position shown by the dashed line in FIG. 10 and tappet 3 are pushed down and begin to descend. Then, the hydraulic pressure acting on the working piston 23 disappears, and this working piston 2
3 is pushed down by the elastic restoring force of the valve spring 27 in accordance with the amount of descent of the drive piston 10, and the intake valve 26 is closed.

By the way, the downward movement of the drive piston 10 ends when it comes into contact with the upper end of the control piston 13, but the tappet 3 and push rod 11
is further lowered by the rotation of timing cam 2,
The upper end of the push rod 11 is the drive piston 1.
0 until it is separated by the predetermined distance.

When the drive piston 10 comes into contact with the control piston 13, a downward force is applied to the control piston 13 due to the elastic restoring force of the spring 12 as described above, but the check valve 15 operates and the control hydraulic chamber is closed. Since the hydraulic oil in B is not discharged to the outside, the control piston 13 maintains a predetermined raised position.

As described above, when the load is low, by limiting the upward stroke of the drive piston 10 to a smaller value by the control piston 13, the start of the upward movement of the drive piston 10 is delayed, and the supply of hydraulic oil to the working cylinder 8 is delayed. Accordingly, the timing at which the actuating piston 23 starts to rise can be delayed.

FIG. 3 shows the operating characteristics of the driving piston 10 and the working piston 23 at low loads. The operating characteristics shown by the two-dot chain line are shown, and the operating piston 2
No. 3 exhibits the same operating characteristics as the drive piston 10 described above, as shown by the chain line.

Effects of the Invention As explained above, the valve timing changing device for a diesel engine according to the present invention moves the control piston by supplying hydraulic oil into the control hydraulic chamber or discharging hydraulic oil from the control hydraulic chamber. to adjust the stroke of the drive piston, thereby
Since the opening timing of the intake valve is changed by changing the timing at which the working piston starts to rise, the opening timing of the intake valve can be changed as appropriate and the intake valve can be opened at either high load or low load. By adjusting the overlap period of the exhaust valve, it is possible to always operate the engine in the best condition.In addition, the operating hydraulic pressure for the intake valve is generated by the drive cylinder itself functioning as a hydraulic pump, so it is possible to operate the engine in the best condition at all times. No hydraulic pump is required, making the device simple and inexpensive.

Furthermore, the valve timing changing device for a diesel engine according to the present invention generates the hydraulic pressure for the intake valve intermittently only when the intake valve is operated, so there is little energy loss, which is extremely rational, and saves the engine itself. Fuel efficiency can also be achieved.

[Brief explanation of drawings]

1 to 3 are drawings showing an embodiment of the valve timing changing device for a diesel engine according to the present invention, in which FIG. 1 is a vertical cross-sectional side view showing the operating state under high load, and FIG. FIG. 3, a longitudinal side view showing the operating state under low load, shows a diagram showing the operating characteristics of the drive piston and the working piston. Figure 4 a, b
1 is a diagram showing an example of valve timing suitable for high-load operation and low-load operation of a typical diesel engine. 3... Tappet, 7... Drive cylinder, 8...
Working cylinder, 10... Drive piston, 13...
Control piston, 19... Oil supply hole, 23... Operating piston, 26... Intake valve, 28... Oil relief groove, A... Hydraulic pressure generation chamber, B... Control hydraulic pressure chamber.

Claims (1)

[Claims] 1. A driving piston built in the driving cylinder and reciprocating in the axial direction in cooperation with a tapepet; and an operating piston built in the working cylinder and actuated by hydraulic pressure generated by the driving piston to drive the intake valve. A valve timing changing device capable of changing valve timing by changing the stroke amount of the drive piston, the valve timing changing device comprising: a valve timing changing device configured to change the valve timing by changing the stroke amount of the drive piston, the valve timing changing device changing the stroke amount of the drive piston between the tappet and the drive piston; an oil relief groove is formed in the working cylinder to release excess pressure oil from the working cylinder chamber to the oil outlet; By supplying hydraulic oil or discharging hydraulic oil from the control hydraulic chamber, the control piston is moved to change the stroke amount of the drive piston, and the valve timing of the intake valve is adjusted according to the load of the diesel engine. A valve timing changing device for a diesel engine, characterized in that the valve timing is changed.