JPH0333412A - Variable valve timing device of single cylinder engine - Google Patents

Abstract

PURPOSE:To prevent structural components from the reduction of their mechanical lives and the occurrence of breakages by engaging a freely projecting and retreating cam follower with the side cam of a end journal section to shift axially a cam shaft. CONSTITUTION:In a variable valve timing device 1, a cam shaft 2 is formed over the whole periphery of the end journal section 2a with side cams 8, 9 respectively for high and low speed change-over. Piston pins 14a, 15a acting as cam followers treating projecting from and retreating in and a bearing section 7 for supporting an end journal section 2a are provided. Piston pins 14a, 15a operated by hydraulic cylinder mechanisms 14, 15 are engaged with side cams 8, 9 to move axially the cam shaft 2. Thus, during one rotation of the cam shaft 2, the cam shaft 2 can be instantly and largely moved. Then, the occurrence of excessive contact surface pressure between valve opening and closing cams 3H, 3L, 4H and 4L and rocker arms 19, 20 can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a variable valve timing device.

[Traditional M technique]

Some modern engines are equipped with variable valve timing devices that change valve timing and valve lift in accordance with engine load conditions in order to improve output and reduce fuel consumption.

FIG. 6 shows the variable valve timing VTL! f)′
-Illustrative examples.

In this IIfA, a low-speed valve opening/closing cam C having a low-speed cam profile and a high-speed valve opening/closing cam D having a high-speed cam profile are integrally arranged in parallel on the camshaft B. is supported by the cylinder head E so as to be rotatable and movable in the axial direction.

The camshaft B is linked with a camshaft moving means F composed of, for example, a hydraulic cylinder actuator, and this moving means ``moves the camshaft B along the axial direction based on the engine speed. As a result, the low-speed cam C or the high-speed cam D on the camshaft B will selectively occupy the position directly above the valve G depending on the engine speed and open and close the valve G. The engine operates efficiently.

Note that the reference symbol in the figure is a rocker arm in a 5OHC type engine.

(Problem to be Solved by the Invention) By the way, as shown in FIGS. 7(a) and 7(b), the low-speed cam C and the high-speed cam D have the same pace circle diameters Cr and D. On the other hand, the valve lift member is set larger for high-speed cam D than for low-speed cam C. Therefore, in order to switch the cam that operates valve G from cam C to cam D, When the shaft B is moved, when the valve G is lifted by the cam C, the side surface DJ of the lift part of the cam D (Fig. 7) comes into contact with the rocker arm, as shown by the gl line in Fig. 6. Then, when the base circle peripheral surface cb of the cam C is located on the slipper surface of the rocker arm, in other words, the lift portion of the cam D is located in the side area of the rocker arm. Side Di
Camshaft B can be moved to position cam D on the slipper surface of the rocker arm only during periods when the rocker arm is not facing.

However, as the engine speed becomes higher, the time during which the cam D can be moved to position it on the slipper surface of the rocker arm during one rotation of the camshaft B becomes shorter, and therefore, the above-mentioned hydraulic cylinder The camshaft moving means F, such as the actuator F, can only move the camshaft B a small amount per revolution of the camshaft B.

Therefore, at the initial point in time when the cam D is transferred to the slipper surface of the rocker arm H, as the camshaft B rotates, the cam D and the slipper surface of the rocker arm come into contact with each other over a small area. For this reason, the contact surface pressure between them becomes extremely large, causing significant wear on the cam D and rocker arm, shortening their lifespan, or causing damage in the case of I & Wrong. there were.

In view of the above-mentioned circumstances, an object of the present invention is to provide a variable valve timing device for a single-cylinder engine that can prevent a reduction in mechanical life and occurrence of damage to components such as valve opening/closing cams and rocker arms. shall be.

[Means to solve the problem]

Therefore, in the present invention, a side cam is formed over the entire circumference of the end journal part of the camshaft, and a cam follower that can freely protrude and retract is provided in the bearing that supports the end journal part, and the cam follower and the side surface cam are provided with a retractable cam follower. The above object was achieved by configuring the camshaft to move in the axial direction by engaging with the cam.

[Effect]

According to the above configuration, it is possible to instantly move the camshaft by a large amount during one rotation of the camshaft, thereby suppressing the generation of excessive contact surface pressure between the valve opening/closing cam and the rocker arm. I can do it.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, the specific structure of this invention is demonstrated in detail based on drawing which shows one Example.

1 to 5 show examples in which the variable valve timing device for a single-cylinder engine according to the present invention is applied to a single-cylinder engine that employs a 5OL (C-type valve type).

The camshaft 2 of the variable valve timing device 1 has a high-speed exhaust valve opening/closing cam 3 having a high-speed cam profile and a low-speed exhaust valve opening/closing cam 3L having a low-speed cam profile. are formed close together. Further, the cam 3 is attached to the camshaft 2.
8.3L, a high-speed intake valve opening/closing cam 4H and a low-speed intake valve opening/closing cam 4L are formed close to each other.

As shown in FIG. 1, the right end journal portion 2a of the camshaft 2 is supported by a bearing portion 7 consisting of a cylinder head 5a and a cam housing 6 so as to be rotatable and movable along the axial direction. . Further, the end journal 2a is provided with a high-speed switching side cam 8 and a low-speed switching side cam 9, which will be described in detail later.

On the other hand, the left end portion 2b of the camshaft 2 is spline-coupled to a camshaft sprocket 10 rotatably supported by the cylinder head 5b so as to be movable in the axial direction. Also, a stopper protrusion 2C is provided on the left end portion 2b.
Further, a return spring 12 is interposed between the wall plate 11 fixed to the cylinder head 5 and the camshaft 2.

The cam housing 6 is formed with a chamber 13 that accommodates the end journal portion 2a of the camshaft 2, and the right end portion of the chamber 13 in FIG. 1 is provided with the end journal portion 2a.
An oil chamber 13a is defined by the end surface 2d. The cam housing 6 also includes the end journal portion 2.
A high-speed switching hydraulic cylinder mechanism 14 and a low-speed switching hydraulic cylinder mechanism 15 are provided in the upper region of a.

The high-speed switching hydraulic cylinder mechanism 14 can freely move back and forth in a direction perpendicular to the axis of the camshaft 2 and can freely move in and out of the chamber 13! It is composed of a piston pin 14a as a cam follower which is rotated 1QW1, an oil chamber 14b and a return spring 14C.

On the other hand, the low-speed switching hydraulic cylinder mechanism 15 is movable in a direction perpendicular to the axis of the camshaft 2 and
It is composed of a piston pin 15a as a cam follower installed in the cam follower 3 so as to be freely retractable, an oil chamber 15b, and a return spring 15c.

The oil chamber 14b and the oil chamber 15b in both cylinder mechanisms 14.15 are communicated with each other via an oil passage 16, and the oil chambers 14b, 15b and the oil chamber 13a mentioned above are connected to a hydraulic oil passage 17, respectively. is communicated with.

The hydraulic oil passage 17 is connected to a hydraulic oil supply source (not shown), and a valve 18 is interposed in the passage 17. The valve 18 is a general flow control valve that includes a valve body 18a, a solenoid 18C1 for operating the spool 18b1, a hydraulic oil supply passage 18d, and a hydraulic oil discharge passage 18e.

As shown in FIG. 2, the high-speed switching side cam 8 and the low-speed switching side cam 9 have protrusions 8a and 9a that protrude only within the central angle range θ. Here, as shown in Fig. 3, the exhaust valve opening/closing cam 38.31
Although the valve lift timings of the intake valve opening/closing cams 4H and 3H are 90" apart, their base circles overlap over the center angle range θ, and the side cam 8
Angular range θ in which the protrusions 8a and 9a are formed at °9
corresponds to the central angle range θ over which the base circle of the cams 38, 31, and 4L overlaps.

Further, the protrusions 8a and 9a are the cam 3H.

When the base circles of 3L, 4H, and 4L are in contact with the rocker arm, the above-mentioned hydraulic cylinder mechanism 14.1
It is formed at a position opposite to 5.

When the engine is currently being operated in a low rotational speed range, as shown in FIG. 1, each oil chamber 13a, 14b.

15b are respectively connected to valves 18 via hydraulic oil passages 17.
The camshaft 2 is forced to the right by the return spring 12, and is in communication with the hydraulic oil discharge passage 18e.
The right end surface 2d is located at the right limit position where it abuts against the stopper step 13b of the chamber 13. This allows the exhaust valve (
The exhaust side rocker arm 19 linked to the exhaust valve (not shown) and the intake rocker arm 20 linked to the intake valve (not shown) are opened and closed by a low speed exhaust valve opening/closing cam 3L and a low speed intake valve opening/closing cam 4L, respectively. There is. Further, the piston pin 14a in the high-speed switching hydraulic cylinder mechanism 14 is urged upward by the return spring 14C and is at the maximum raised position, while the piston pin 15a in the low-speed switching hydraulic cylinder mechanism 15 is pushed upward by the return spring 14C. It is urged downward by the spring 15G and is at the maximum lowered position.

When the operating speed of the engine increases and exceeds a preset threshold value, the spool 18b of the valve 18 moves to the right, and hydraulic oil is supplied to each of the oil chambers 13a, 14b, and 15blC. As a result, the camshaft 2 starts moving to the left against the return spring 12, and the piston pins 14a and 15a in both cylinder mechanisms 14 and 15 begin to descend and rise, respectively, against the return spring 14C215c. .

FIG. 4 shows a state in which the camshaft 2 is moved slightly to the left. At this point, the piston pin 15a is already at the maximum raised position where it does not protrude into the chamber 13. on the other hand,
Although the piston pin 14a has started to descend, it comes into contact with the circumferential surface 8b of the high-speed switching side cam 8 and is prevented from descending.

When the camshaft 2 moves slightly to the left from the state shown in FIG. descend instantly. At this point,
The side surface of the tip end of the piston pin 14a is in contact with the flat portion 8C on the cam surface of the high speed switching side cam 8.

Thereafter, as the camshaft 2 rotates, the cam 8d of the protrusion 8a of the side cam 8 comes into sliding contact with the side surface of the tip end of the piston pin 1't a, and the pin 14a pushes the side cam 8 away. As a result, the camshaft 2 is instantaneously and forcibly moved to the position shown in Fig. gM5. At this time, as described above, the protrusions 8a on the side cam 8
When the base circle of the cam is in contact with the rocker arms 19 and 20, the hydraulic cylinder mechanism 14, specifically the piston pin 14a, is provided at a position facing the cam. can be moved smoothly. Further, the overhang dimension WH of the protruding portion 8a of the side cam 8 shown in FIG. The dimensions are set so that the camshaft can be moved into contact.

By continuing to supply hydraulic oil to the oil chamber 13a, the camshaft 2 moves further to the left from the position shown in FIG. . When the camshaft 2 is located at the left limit position shown in FIG.
and 20 are opened and closed by high-speed cams 30 and 4, respectively.

When the operating speed of the engine decreases and falls below the threshold value, the spool 18b of the valve 18 moves to the left, and each oil chamber 13a, 1
4b and 15b each communicate with the hydraulic oil discharge passage 18e. As a result, the camshaft 2 starts moving to the right due to the elastic return force of the return spring 12, and both cylinder mechanisms 14.
The piston pins 14a and 15a at 15 begin to rise and fall due to the elastic return forces of return springs 14c and 15c, respectively.

Thereafter, in the same way as the above-mentioned cooperation between the side cam 8 and the piston pin 14a, the low speed switching side cam 9 and the piston pin 15a in the low speed switching hydraulic cylinder mechanism 15 work together. , the camshaft 2 instantly moves to the right, and the cams 3L, 4L partially wrap around the rocker arms 19,20. Note that the protrusion dimension WL of the protrusion 9a of the side cam 9 is similar to the protrusion dimension Wl+ of the protrusion 8a of the side cam 8 described above, so that when the cam moves on the rocker arm, the rocker arm and the cam are sufficiently connected. Of course, the dimensions are set such that the camshafts can be moved so as to come into contact with each other over a wide area.

Then, as the camshaft 2 is pushed to the right eye-field position by the return spring 12, the rocker arms 19 and 20 are opened and closed by the low-speed cams 3L and 4L, respectively.

〔Effect of the invention〕

As described above in detail, according to the variable valve timing ViW1 for a small cylinder engine according to the present invention, a side cam is formed over the entire circumference of the end journal portion of the camshaft, while supporting the end journal portion. The bearing is provided with a cam follower that can freely move in and out, and the cam follower and the side cam are engaged to move the camshaft in the axial direction. It became possible to move it significantly. As a result, when the camshaft is moved to change the valve opening/closing cam that operates the valve, the valve opening/closing cam and the slipper surface of the rocker arm can come into contact over a wide area during one rotation of the camshaft. In this way, it is possible to prevent a decrease in the mechanical life of the component or damage due to an increase in contact surface pressure.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional side view of the main parts around the camshaft showing a variable valve timing device according to the present invention, Fig. 2 is a developed view of a side cam formed in the end journal portion of the camshaft, and Fig. 3 1 is a cross-sectional view taken along the line l-111 in FIG. 1, FIGS. 4, 5, and 6 are conceptual cross-sectional side views showing operating modes of the variable valve timing device according to the present invention, and FIG. 8(a) and (b) are main part sectional side views showing a conventional variable valve timing device.
are the cross-sectional views of ■a-■am and ■b- in Fig. 7, respectively.
■It is a sectional view of bllA. DESCRIPTION OF SYMBOLS 1... Variable valve timing device, 2... Camshaft, 2a... End journal part,
3H...Exhaust valve opening/closing cam for high speed, 3L...Exhaust valve opening/closing cam for low speed, 40...Intake valve opening/closing cam for high speed, 4L...Intake valve opening/closing cam for low speed, 8...
- Side cam for high-speed switching, 9... Side cam for low-speed switching, 14... Hydraulic cylinder mechanism for high-speed switching, 14a...
Piston pin, 15... Hydraulic cylinder mechanism for low speed switching, 15a...
Piston pin, 19.20...rocker arm. Figure 5 Figure 6 Figure 7 (Q) (b) Figure 8 Procedural amendment (voluntary)

Claims (1)

[Scope of Claims] By moving a camshaft in which a plurality of valve opening/closing cams having different cam profiles are arranged in parallel in close proximity to each other in the axial direction of the camshaft, a selection can be made from among the plurality of valve opening/closing cams. A variable valve timing device for a single-cylinder engine in which a valve is operated by a single valve opening/closing cam, comprising: a side cam formed over the entire circumference of an end journal portion of the camshaft; A bearing part that supports the end journal part of the camshaft is provided with a bearing part that can move forward and backward in a direction perpendicular to the axis of the camshaft in order to engage and disengage from the cam surface of the side cam, but cannot move in the axial direction of the camshaft. and a cam follower provided so that the side cam can move, and when the cam follower and the side cam are engaged, the camshaft is moved in the axial direction of the camshaft by the cooperative action of the two. Variable valve timing device for single-cylinder engines.