JPH055430A - Valve timing regulating device for internal combustion engine - Google Patents

Abstract

PURPOSE:To achieve improvement of output and a fuel consumption for a valve timing regulating device by reducing a pumping loss at the time of low rotation speed with a light load and contriving optimum valve timing in a wide range of operation. CONSTITUTION:A device 5 varying a phase of a cam shaft 3 of an intake valve relative to a crankshaft is provided, the cam shaft 3 is provided with a cam 1 and cam 2 which are changed over by moving a rocker arm 14 with a hydraulic cylinder 60. The cam 2 of which valve opening period is shorter than that of the cam 1 has a cam profile of a large valve lift. Intake valve closing timing is delayed by using the cam 1 to reduce a pumping loss at the time of low revolution speed with a light load. The valve closing timing is advanced with increase of the load, but in the case that the revolution speed is lower than a specific value, a changeover from the cam 1 to the cam 2 is made to lessen valve overlap when the valve closing timing is lead-angled from a fixed value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve timing adjusting device for an internal combustion engine, and more particularly to reducing pumping loss at low load and low rotation and optimizing valve timing under wide operating conditions. The present invention relates to a valve timing adjusting device for an internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine having a throttle valve in its intake pipe, the throttle valve is substantially fully closed when the engine load is low, and the pressure on the downstream side of the throttle valve becomes a large negative pressure. Therefore, in the intake stroke of the cylinder, the piston operates against this negative pressure, resulting in extra output loss, so-called pumping loss, which is one of the causes of deterioration of fuel consumption.

In order to reduce this pumping loss,
A means for varying the closing timing of the intake valve is provided, and the throttle valve opening is kept large during low engine load and low rotation,
A method of delaying the closing timing of the intake valve by a time larger than the piston bottom dead center in the intake stroke is effective. That is, by performing the intake valve closing delay, the air once sucked into the cylinder is discharged into the intake pipe as the piston rises, and the intake air amount can be increased or decreased by changing the intake valve closing timing. .. In this case, the throttle valve opening is kept large, and the suction and discharge are performed at about atmospheric pressure, so that the piston operating resistance is reduced and pumping loss is reduced.

When the intake valve closing delay is performed, the amount of fresh air remaining in the cylinder increases as the intake valve is closed earlier in the piston ascending stroke after the bottom dead center of the intake stroke. Therefore, the engine load can be controlled by changing the intake valve closing timing instead of controlling the engine load by the throttle opening.

An example of this type of valve timing adjusting device is disclosed in Japanese Patent Application Laid-Open No. 61-145310. In the device of the publication, a cylindrical phase control member is attached to one end of a camshaft for driving an intake valve via a helical spline, and further, a helical spline having a twist in the opposite direction to the above is provided outside the phase control member. The timing pulley is attached. When the timing pulley is driven from the crankshaft by a belt, a chain or the like, the camshaft is rotated in synchronization with the crankshaft due to the meshing of the timing pulley and the phase control member and the helical spline between the phase control member and the camshaft. Further, when the phase control member is moved in the axial direction of the camshaft, the camshaft and the timing pulley are opposite to each other with respect to the slip phase control member along their teeth while being engaged with the helical splines between the phase control member and the phase control member. Rotate in the direction. Therefore, the valve timing of the intake valve can be changed during operation, and the closing timing of the intake valve can be arbitrarily set during low load and low rotation.

When the phase of the camshaft is changed to control the closing timing of the intake valve as described above, the opening period of the intake valve itself does not change. Therefore, if the intake valve closing timing is advanced with increasing load, the intake valve opening timing is also advanced. Therefore, if the lead angle is advanced beyond a certain angle, there arises a problem that the valve overlap between the intake valve and the exhaust valve increases. When the valve overlap increases at low speed, the intake volume efficiency decreases due to blowback of exhaust gas,
The internal EGR will increase, causing problems such as a reduction in output and deterioration of the combustion state.

In the device disclosed in Japanese Patent Laid-Open No. 61-145310, this problem is solved by changing the opening period of the intake valve. That is, in the device of the above publication, the rocker arm is used to push the intake valve from the camshaft so that the curved back surface of the rocker arm is brought into fulcrum contact with the lever provided freely swingable. By swinging the lever, the contact position between the lever and the rocker arm changes, and the fulcrum position of the rocker arm changes, so the valve opening period of the intake valve can be changed. When the intake valve closing timing is advanced, the above-mentioned device is used to shorten the intake valve opening period, thereby preventing excessive valve overlap.

Japanese Patent Laid-Open No. 1-134013 discloses another valve timing adjusting device. In the device of the same publication, the rotational phase of the timing pulley and the cam shaft is changed by using the same means as in the above-mentioned JP-A-61-145310, but the opening period of the intake valve is adjusted by different methods. ..
That is, in the device disclosed in the publication, the intake valve driving piston is pressed by the cam of the cam shaft without using the rocker arm. The piston is provided at one end of the hydraulic chamber, and the piston for pushing the intake valve is provided at the other end of the hydraulic chamber. When the driving piston is pushed by the cam, the piston at the other end is also pushed through the oil filled in the hydraulic chamber, and the intake valve opens. In the device of the publication, a relief valve for releasing the pressure in the hydraulic chamber is provided, and the valve opening period of the intake valve is adjusted by controlling the timing for releasing the hydraulic pressure.
That is, the opening period of the intake valve is shortened as the relief valve is opened earlier after the start of pushing the intake valve. As a result, it becomes possible to reduce the valve overlap at the time of low speed rotation as in the device disclosed in the above-mentioned Japanese Patent Laid-Open No. 61-145310.

[0009]

However, in any of the above-mentioned prior arts, there arises a problem that the valve opening period of the intake valve is shortened and at the same time the valve lift is reduced. That is, the device disclosed in JP-A-61-145310 is also disclosed in JP-A-1-13401.
In the device of Publication No. 3 as well, the cam profile of the camshaft is constant, and the valve opening period is shortened by using only part of the cam profile to perform the valve opening operation. It will decrease.

However, since the opening period of the intake valve is shortened as the load increases, originally, the valve lift must be increased by the shortened opening period to secure the intake air amount. In contrast to this, the above-mentioned conventional technique results in a decrease in both the valve opening period and the valve lift. Therefore, in the above-mentioned conventional technique, there is a possibility that the amount of intake air is reduced at the time of high load and a sufficient output cannot be obtained. SUMMARY OF THE INVENTION It is an object of the present invention to provide a valve timing adjusting device for an internal combustion engine which solves the above problems and can both reduce pumping loss under low load and ensure output under high load.

[0011]

According to the present invention, a means for changing the closing timing of the intake valve is provided, and the intake valve closing timing is retarded at the time of low engine load to reduce the pumping loss of the cylinder. In a valve timing adjusting device for an internal combustion engine, which advances the intake valve closing timing with an increase in load to improve the intake volume efficiency of a cylinder, the intake valve valve lift is maintained at least equal to or more than that of the intake valve. A means for shortening the valve opening period is provided so that the engine speed is lower than a predetermined value.
Further, there is provided a valve timing adjusting device for an internal combustion engine, wherein the intake valve opening period is shortened under the condition that the intake valve closing timing is earlier than a predetermined timing.

[0012]

When the engine speed is low and the load is low, the intake valve closing timing is significantly delayed from the bottom dead center position of the intake stroke to reduce pumping loss. The intake valve closing timing is advanced as the load increases, and the amount of intake air taken into the cylinder increases. However, the intake valve opening timing is advanced due to the advance of the intake valve opening / closing timing, and the valve overlap with the exhaust valve is increased, so that the intake volume efficiency is reduced when the engine speed is low.

In order to prevent this, when the engine speed is below a predetermined value (low speed) and the advance angle is above a predetermined value, the intake valve opening period is shortened to reduce the overlap. However,
At this time, the valve lift is maintained so as to be equal to or more than that, thereby preventing a decrease in intake air amount due to a shortened valve opening period.
Further, in high-rotation and high-load operation, there is an exhausting effect due to exhaust pulsation, and the larger the valve overlap, the higher the volume efficiency. Therefore, the intake valve opening period is not shortened when the engine speed is equal to or higher than a predetermined value.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the construction of an embodiment of a valve timing adjusting device of the present invention. In this embodiment, a device similar to that disclosed in Japanese Patent Application Laid-Open No. 61-279713 is used as the intake valve retarding control device 5, and the phase between the timing pulley 12 and the camshaft 3 is changed. It is like this.

Further, since only the opening period of the intake valve is changed without changing the valve lift, the camshaft 3 is used in this embodiment.
Is equipped with two types of cams 1 and 2 for each intake valve,
The rocker arm 14 is moved in parallel to the cam shaft 3 and engaged with the cam 1 or the cam 2, so that the opening period of the intake valve is changed. This type of cam switching mechanism is disclosed in JP-A-57-179314. In this embodiment, the cam 1 has a cam profile that lengthens the intake valve opening period, and the cam 2 has a profile that shortens the valve opening period.

FIG. 2 shows the valve opening characteristics of the intake valves by the respective cams 1 and 2, I shows the characteristics by the cam 1, and II shows the characteristics by the cam 2. The cam 1 and the cam 2 are arranged so that the closing timings of the intake valves coincide with each other, and the cam profile is set so that the valve lift by the cam 2 is larger than that by the cam 1. 1 is a crank angle sensor for detecting the crank phase, and 7 is a cam angle sensor for detecting the cam shaft phase.

In this embodiment, a crankshaft-driven lubricating oil pump 13 is provided to supply lubricating oil to each part of the engine and to control the intake valve retard angle control device 5 via the hydraulic pressure switching valves (OSV) 9-11. Further, pressure oil is supplied to the hydraulic cylinder 60 of the moving mechanism of the rocker arm 14.

Reference numeral 8 denotes an electronic control unit (ECU) which performs basic control such as engine fuel injection and ignition timing control. The ECU 8 is composed of a digital computer,
In addition to the basic control of the engine, the valve timing control of the present invention is performed. For this purpose, the outputs of the crank angle sensor 6 and the cam angle sensor 7 are input to the ECU 8,
Parameters required for basic control such as the intake air amount of the engine and the cooling water temperature are input from various sensors (not shown). The ECU 8 is connected to the actuators of OSV9 to 11 via a drive circuit (not shown) and controls switching of OSV9 to OSV11.

FIG. 3 shows the above-mentioned Japanese Unexamined Patent Publication No. SHO 61 used in this embodiment.
2 is a cross-sectional view showing the structure of an intake valve retard control device 5 of Japanese Patent Publication No. 279713. In the figure, 21 is a sleeve that is concentrically fixed to the camshaft 3 and rotates integrally, and 23 is the timing pulley 1.
Reference numeral 25 denotes a cylindrical housing that rotates integrally with 2, and 25 denotes a cylindrical piston. The piston 25 has helical splines 27a and 29a formed on its outer peripheral surface and inner peripheral surface, respectively. The helical spline 27a is a helical spline 27b formed on the inner peripheral surface of the housing 23, and the helical spline 29a is the outer peripheral surface of the sleeve 21. And the helical splines 29b formed in each of the above. Therefore, the rotation of the timing pulley 12 is caused by the housing 23 and the spline.
It is transmitted to the camshaft 3 via 27b and 27a, the piston 25, the splines 29a and 29b, and the sleeve 21, and the timing pulley 12 and the camshaft 3 rotate integrally.

An annular hydraulic chamber 31 is formed between the shaft-side end surface of the cylindrical piston 25 and the housing 23. The hydraulic chamber 31 is formed through a hydraulic passage 33 formed in the camshaft. It is connected to the hydraulic switching valves OSV9 and OSV10. OSV9 is from oil pump 13 to hydraulic chamber 31
The OSV 10 controls the oil supply from the hydraulic chamber 31 to the drain. Reference numeral 35 in FIG. 3 is a compression spring for pressing and urging the piston 25 toward the hydraulic chamber 31.

OSV9 is opened (ON) and OSV10 is closed (OFF)
Then, the pressure oil from the pump 13 is supplied to the hydraulic chamber 31 via the OSV 9 and the hydraulic passage 33, and the piston 25 moves to the right in the figure while compressing the spring 35. When the piston 25 moves in the axial direction, the housing 23 and the sleeve 2
1 is a helical spline for each piston 25
The phases of the pulley 12 and the camshaft 3 change because they rotate relative to each other along the tooth traces of 27a, b and 29a, b. When both OSV9 and OSV10 are turned off in this state, the position of the piston 25 is held constant, so that a predetermined phase is maintained. Also, with OSV9 turned off, OSV10 turned on
In this case, the piston 25 is pushed by the compression spring 35 and moves leftward in the figure, and the oil in the hydraulic chamber 31 is discharged through the OSV 10. Therefore, the desired intake valve closing timing can be obtained by switching control of OSV9 and OSV10 based on the outputs of the crank angle sensor 6 and the cam angle sensor 7 by the ECU 8.

Next, FIG. 4 shows a cam switching mechanism of this embodiment. This mechanism has a structure similar to that described in Japanese Patent Application Laid-Open No. 57-179314, and 41 in the drawing is a hollow rocker shaft extending in parallel with the camshaft 3. The rocker arm 14 is attached to the rocker shaft 41 via a bush 43. The bush 43 is attached to the rocker shaft 41 so as to be rotatable and slidable in the axial direction. The rocker arm 14 is provided with a cam follower 45 that is in sliding contact with the cam 1 or 2. The rocker arm 14 swings around the rocker shaft 41 as the cams 1 and 2 rotate and presses the valve lifter 16 of the intake valve at the other end to open and close the intake valve.

A shaft 49 slidable in the axial direction is inserted in the rocker shaft 41. A pin 51 is fixed to the bush 43, and the tip of the pin 51 is in contact with the peripheral surface of the shaft 49 and is slidable in the axial direction.
Further, compression springs 55a and 55b are mounted on both sides of the pin 51 of the shaft 49 between the pins 53 and the rings 53a and 53b fixed to the shaft 49, respectively. That is, when the shaft 49 moves in the left-right direction in the drawing, the movement is transmitted to the pin 51 via the compression spring 55a or 55b,
The bush 43 is moved along the axis of the rocker shaft 41.

Reference numeral 57 in the drawing denotes a ratchet device for positioning the bush 43. A spring provided inside the bush presses a steel ball against the outer peripheral surface of the rocker shaft 41, and the ratchet device is provided at a predetermined position on the outer peripheral surface. The structure is such that it fits into the circumferential groove and is positioned. Ratchet 57
The positioning circumferential grooves are provided at two positions, that is, a position where the cam follower 45 is in sliding contact with the cam 1 and a position where it is in sliding contact with the cam 2. A hydraulic cylinder 60 is provided at one end of the shaft 49.
Is provided, and the shaft 49 is moved by introducing pressure oil into the hydraulic chambers 60a, 60b on both sides of the piston 61 connected to the shaft 49. Hydraulic chambers 60a and 60b are O
It is connected to SV11 and the hydraulic pressure is changed to 60 by switching OSV11.
It can be installed by switching to a or 60b.

Now, when the shaft 49 is switched to one side by switching from the OSV 11, the bush 43 does not move for a while after the start of the movement, because the ratchet 57 positions it. Therefore, the spring 55a or 55b is compressed between the pin 51 and the ring 53a or 53b. When the shaft 49 continues to move and the pressing force of the compression spring becomes larger than the holding force of the ratchet 57, the steel ball of the ratchet 57 is disengaged from one circumferential groove, and the bush 43 is pushed by the force of the spring and the other ratchet circles are pushed. It moves rapidly to the circumferential groove position. Therefore, the rocker arm 14 instantly moves from one of the cams 1 and 2 to the other, and the cam switching is immediately completed. (Note that a safety mechanism (not shown) is provided to prevent the rocker arm 14 from moving only on the common base circle of the cams 1 and 2 even if the ratchet 57 is removed.

Next, the valve timing setting of this embodiment will be described with reference to FIG. FIG. 5 shows the valve lift (vertical axis) and valve timing of the exhaust valve (EX) and the intake valve (IN). Curve A in FIG. 5 shows the valve timing of the intake valve when the load is low. When the load is low, the rocker arm 14 (FIG. 4) is engaged with the cam 1 and the retard angle adjusting device 5 (FIG. 1) delays the opening / closing timing of the intake valve. Therefore, the intake valve opens from the middle of the intake stroke, The valve closes in the latter half of the compression stroke after the dead center (BDC).

FIG. 5Ta shows the intake valve closing timing (crank angle) at this time. Therefore, in this state, during the stroke from BDC to Ta (section I in Fig. 5), the intake air once sucked into the cylinder is made to flow back into the intake pipe, but this adjusts the intake air amount without performing intake throttling. Therefore, pumping loss is reduced. Next, a curve B in FIG. 5 shows a state in which the load is increased from this state and the intake valve closing timing is advanced to Tc.

As a result of advancing the valve closing timing, the amount of air flowing back into the intake pipe (section II in FIG. 5) decreases, so the amount of intake air remaining in the cylinder increases and the output increases. However, in this state, the overlap area with the exhaust valve has expanded due to the advance of the intake valve (Fig. 5, Section III), and in the case of low speed operation, combustion instability and output due to increase of internal EGR Occurs. Therefore, in the present embodiment, when the engine speed is equal to or lower than the predetermined value and the intake valve closing timing is advanced from the predetermined value Tc, the cam 1 is switched to the cam 2 and the intake valve opening of the curve C is performed. Change to characteristics. By switching to the characteristic of curve C, the intake valve opening period can be shortened and the valve overlap can be reduced (FIG. 5, section IV). As a result, it is possible to improve output and ensure combustion stability during low-speed operation. It should be noted that under the condition of high rotation and high load, it is preferable that the valve overlap is large, and therefore switching to the cam 2 is not performed.

Next, FIG. 6 shows a flow chart of an embodiment of the valve timing control operation of the present invention by the ECU 8. This routine is executed as a repetitive routine at regular time intervals (for example, every 16 milliseconds). When the routine starts in FIG. 6, in step 100, the engine speed N, the engine load, and the current intake valve closing timing (crank angle) T are calculated. Here, the engine speed N is calculated from the output of the crank angle sensor 6, and the valve closing timing T is calculated from the outputs of the crank angle sensor 6 and the cam angle sensor 7. The intake air amount Q / N per engine revolution is used as a parameter representing the engine load.

Next, at step 105, the engine load Q / N
From the above, the target valve closing timing To of the intake valve is calculated using the relationship of FIG. Referring to FIG. 7, the target valve closing timing To is set at a delay when the load is extremely low (the crank angle To is large), and the advance angle is set (the To is small) as the load increases. Next, at step 110, it is judged if the current engine speed is lower than a predetermined value Nc, and if the engine speed is high (N ≧ N
In step c), the process proceeds to step 125, the OSV 11 is switched and the cam 1 is selected, and the valve opening timing is not shortened. This is because if the engine is running at high speed, the output will not decrease even if the load increases and the overlap increases. Engine speed N is Nc
If it is lower, then in step 115, it is judged whether or not the current valve closing timing T is less than or equal to a predetermined value Tc (advancing from Tc).
If it is on the retard side from c, proceed to step 125 to select cam 1, and if it is on the advance side from Tc, proceed to step 120 and OSV1
Switch 1 to select cam 2. Next, steps 130 to 140 are executed, and in step 105, OSV9 and OSV10 are operated so that the target valve closing timing is reached, and the routine is ended.

In this embodiment, one example of the retard control device for the intake valve and the mechanism for shortening the opening period of the intake valve is shown. However, these devices and mechanisms are limited to those shown in this embodiment. It is not done. In particular, as a mechanism for shortening the valve opening period, various types can be changed as long as they do not reduce the valve lift. For example, by using two intake valves whose valve opening timings are slightly shifted, It is possible to employ a mechanism that provides a mechanism for stopping or operating the valve and shortens the valve opening period without reducing the valve lift as a whole.

[0032]

According to the present invention, in an engine that delays the intake valve closing timing during low rotation and low load operation, the intake valve opening period can be shortened without reducing the valve lift at low rotation and high load. By doing so, it is possible to prevent the output from decreasing and to improve the fuel efficiency and the output in a wide driving range.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a valve timing adjusting device of the present invention.

FIG. 2 is a diagram illustrating an intake valve opening characteristic of the embodiment of FIG.

FIG. 3 is a cross-sectional view showing an intake valve retard angle control device used in the embodiment of FIG.

FIG. 4 is a schematic sectional view showing a cam switching mechanism used in the embodiment of FIG.

5 is a diagram illustrating valve timing control of the embodiment of FIG.

FIG. 6 is a flowchart showing an example of a control operation of the valve timing adjusting device of the present invention.

FIG. 7 is a diagram showing a relationship between engine load and intake valve closing timing in the embodiment of FIG.

[Explanation of symbols]

 1, 2 ... Cam 3 ... Cam shaft 5 ... Intake valve retard angle control device 6 ... Crank angle sensor 7 ... Cam angle sensor 8 ... Electronic control unit (ECU) 9, 10, 11 ... Hydraulic switching valve (OSV) 12 ... Timing Pulley 13 ... Oil pump 14 ... Rocker arm 16 ... Valve lifter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location F02D 13/02 H 7367-3G

Claims (1)

Claim: What is claimed is: 1. A means for changing the closing timing of an intake valve, wherein the intake valve closing timing is retarded when the engine load is low to reduce the pumping loss of the cylinder and to increase the load. In a valve timing control device for an internal combustion engine, which advances the intake valve closing timing to improve the intake volume efficiency of a cylinder,
A means for shortening the opening period of the intake valve while maintaining the valve lift of the intake valve at least equal or more is provided, and intake is performed under the condition that the engine speed is lower than a predetermined value and the intake valve closing timing is earlier than the predetermined time. A valve timing adjusting device for an internal combustion engine, characterized in that a valve opening period is shortened.