JP2568856B2 - Engine valve gear - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a valve train for an engine in which a valve timing is switched according to an operating state of the engine.

(Prior Art) Various attempts have been made to improve the charging efficiency and the combustion state in a wide rotation range from a low speed to a high speed by switching a valve timing and a lift characteristic according to an operation state of an engine. As a variable valve timing mechanism for this purpose, usually, there are many mechanisms in which the camshaft is made slidable, and conversely, the rocker arm is made slidable, thereby switching between the low-speed cam and the high-speed cam. Further, if the camshaft or the rocker arm is made to be slidable or moved up and down, the structure becomes complicated and lacks quickness. For example, as described in Japanese Utility Model Application Laid-Open No. 58605/1986. Hydraulic locking means for providing two types of swing arm type rocker arms for low speed and high speed with respect to a camshaft having two types of cams for low speed and high speed, and removably connecting these two rocker arms. There has also been proposed a device in which both rocker arms are interlocked or non-interlocked by using a switch to selectively switch between valve operation using a high-speed cam and valve operation using a low-speed cam.

By the way, in the conventional variable valve timing type valve actuation device in which the low-speed rocker arm and the high-speed rocker arm are detachably connected as described above, the low-speed rocker arm and the high-speed rocker arm are supported by a single rocker shaft. Because the clearance of the shaft support has a double effect as an engagement error, and the rocker shaft also becomes longer,
There is a problem that the positioning accuracy of the lock portions of both rocker arms is hardly obtained. Therefore, in the conventional valve train as described above, the responsiveness of the cam switching control is not very good. In addition, from the viewpoint of maintenance-free operation, there is a demand for mounting a hydraulic lash adjuster (so-called hydro-lash adjuster, abbreviated as HLA) in the valve device. In a valve device, it is difficult to mount a mechanical lash adjuster on a valve follower formed on a low-speed rocker arm, and mounting an HLA is difficult as a practical problem. Further, in such a valve operating device, since one long rocker shaft usually passes in the cylinder row direction, there is also a problem that the assemblability of the valve operating device is not good.

Instead of a mechanism that supports both the low-speed and high-speed rocker arms with a long rocker shaft, for example, a rocker mechanism with an HLA-type end pivot is adopted, and one rocker arm is held by the other rocker arm. If the valve train can be constituted by the above, a variable valve timing type valve train with good assemblability and small engagement displacement of the lock portion can be obtained, and the above-mentioned problems of the conventional device can be solved. However, when one of the rocker arms is supported by the end pivot and the other rocker arm is held by the rocker arm, the valve center position and the end pivot position of the valve follower portion provided on the low-speed rocker arm are set. For the connecting balance axis,
Since the cam follower sensor of at least one of the rocker arms is offset, there is a problem that the rocker arm is inclined. In particular, if the cam follower center of the high-speed rocker arm is largely offset with respect to the balance axis, the inclination of the rocker arm becomes too large during high-speed operation under severe load conditions,
There is a possibility that the reliability of the valve train may be significantly deteriorated.

(Object of the Invention) The present invention has been made in view of the above problems,
Utilizing a rocker mechanism with an end pivot that can take advantage of the HLA, the lock between the low-speed rocker arm and the high-speed rocker arm is less disengaged, the assembly is good, and the rocker arm at high speeds It is an object of the present invention to obtain an engine valve train capable of sufficiently suppressing the inclination of the engine.

(Structure of the Invention) The present invention realizes accurate positioning of the low-speed rocker arm and the high-speed rocker arm while utilizing the features of the end pivot type, which is easy to mount the HLA and has excellent assemblability,
At the same time, the inclination of the rocker arm at high speed can be suppressed, and the configuration is as follows. That is, the valve train of the engine according to the present invention includes a low-speed cam and a high-speed cam, a low-speed rocker arm and a high-speed rocker arm that are in contact with these cams, and an engagement / disengagement mechanism that removably connects the two rocker arms. In the variable valve timing type valve actuating device provided, a valve follower portion is provided on the low-speed rocker arm, and the adjacent high-speed rocker arm is supported by an end pivot, and a rocker shaft portion integrated with the high-speed rocker arm is provided. The low-speed rocker arm is swingably supported.

(Operation) The high-speed rocker arm is driven by the high-speed cam,
Swing with the end pivot part as a fulcrum. The low-speed rocker arm is driven by a low-speed cam, and swings while being supported by a rocker shaft integrated with the high-speed rocker arm. The engagement / disengagement mechanism sets the two rocker arms in a non-interlocked state when the engine is rotating at a low speed, and sets the two rocker arms in an interlocked state when the engine is rotating at a high speed. Therefore, at low speed, only the low-speed cam acts on the low-speed rocker arm to drive the valve. At high speed, the high-speed cam acts on the low-speed rocker arm via the high-speed rocker arm, giving priority to the low-speed cam. Drive.

Since the rocker shaft portion that supports the low-speed rocker arm is formed integrally with the high-speed rocker arm, engagement displacement between the two rocker arms can be suppressed to a small value. Therefore, the operation of the engaging and disengaging mechanism is performed smoothly. Further, the valve gear can be assembled as a unit for each cylinder. In addition, each end pivot supporting the high-speed rocker arm has an HLA
The automatic adjustment of the valve gap becomes possible only by adopting. The cam follower sensor of the low-speed rocker arm and the high-speed rocker arm is offset to the left and right with respect to the balance axis connecting the valve center and the end pivot position, but the offset amount of the valve follower of the high-speed rocker arm where the load condition is particularly severe is the end pivot Is smaller than that provided on the low-speed rocker arm side, and the inclination of the rocker arm can be suppressed to an allowable range. Also, the offset amount on the low-speed rocker arm side is of such a degree that does not actually cause a problem.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention applied to a 4-valve double overhead cam type (abbreviated as DOHC) engine.

In this embodiment, an intake camshaft 2 is supported on the right and left sides of the top of the cylinder head 1 and an exhaust camshaft 2 is supported on the left side in FIG. A combustion chamber recess 4 is formed at the bottom of the cylinder head 1, and intake ports 5 a and 5 b and exhaust ports 6 opening to the combustion chamber recess 4 are formed.
a, 6b extend to the left and right end surfaces of the cylinder head 1. The intake valves 7a, 7b and the exhaust valves 8a, 8b are mounted in a V-shape with the exhaust valves 8a, 8b being more inclined with respect to the longitudinal center line of the cylinder head 1, and these valves 7a, 7b, 8a HLA parallel to 8b
An end pivot 9a, 9b, 10a, 10b of the type is provided.
The intake rocker arm includes low-speed rocker arms 11a and 11b and high-speed rocker arms 12a and 12b, and the high-speed rocker arms 12a and 12b are supported by end pivots 9a and 9b. The high-speed rocker arms 12a, 12b are provided at one end with engagement surfaces 13a, 13b for engaging with the spherical heads of the end pivots 9a, 9b, and at the other end, slippers contacting the high-speed cam surface of the intake camshaft 2. Parts 14a and 14b are provided. Rollers 15a, which roll in contact with the low-speed cam surface of the intake camshaft 2 at an intermediate portion, are provided at one end side of the high-speed rocker arms 12a, 12b.
15b, and low-speed rocker arms 12a, 12b each having an alve-follower portion 16a, 16b at its tip end. Rollers 17 are provided on the exhaust end pivots 10a and 10b.
a, 17b, and comes into contact with the cam surface of the exhaust camshaft 3, and swings about the end pivots 10a, 10b as fulcrums.
Swing arm type rocker arm 18a that drives 8b,
18b is installed.

As shown in detail in FIG. 3, the intake end pivot 9
Rocker shaft portions 19a and 19b that support the low-speed rocker arms 11a and 11b toward the inside of each cylinder are integrally formed with the high-speed rocker arms 12a and 12b that are supported by the a and 9b.
FIG. 3 shows a cross section of one rocker arm portion on the intake valve 7a side, but the rocker arm portion on the other intake valve 7b is completely the same as the cross section in the opposite direction. The low-speed rocker arms 11a and 11b are provided with rocker shaft portions 19a and 1b from the sliding contact surface side with the high-speed rocker arms 12a and 12b.
Plunger holes 20a and 20b are formed in parallel with the 9b axis, and the back of the inserted plungers 21a and 21b is
a, 22b. On the other hand, high-speed rocker arms 12a and 12b
The rocker arms 11a, 11b, 12a for low speed and high speed
The plunger holes 20a, 2b of the high-speed rocker arms 12a, 12b with both
0b are formed with fitting holes 23a, 23b which are perfectly aligned with the springs 24a, 24b.
The sleeve bodies 25a and 25b urged by are inserted. Air vent holes 26a, 26b are provided at the bottoms of the fitting holes 23a, 23b.

Further, the tips of the rocker shaft portions 19a and 19b extending from the high-speed rocker arms 12a and 12b are inserted and supported by a partition wall 28 of the cylinder head 1 on which a cam bearing portion 27 is formed. Drilled holes 30a and 30b communicating with an oil passage 29 formed in the partition wall 28 of the cylinder head 1 are formed in the portion. These drill holes 30a, 30b
Communicates with the hydraulic chambers 22a and 22b through the communication passages 31a and 31b.
The oil passage 29 on the partition wall 28 side communicates with a bolt hole 32 for a cam cap mounting bolt of the cylinder head 1. The high-pressure oil for operating the plungers 21a and 21b is sent using the bolt holes 32, and the oil passage 29, the drill holes 30
a, 30b, and are supplied to the hydraulic chambers 22a, 22b via the communication passages 31a, 31b.

The insertion portions of the rocker shaft portions 19a and 19b are loosely supported by seal members 33a and 33b, and the low-speed rocker arms 11a and 11b are positioned by snap rings 34a and 34b.

The high-speed rocker arms 12a and 12b are also connected to the springs 3 via the receivers 35a and 35b as shown in FIGS.
It is urged toward the cam at 6a and 36b. Thus, rattling in a state where the low-speed rocker arms 11a and 11b are separated from each other is suppressed.

Low-speed rocker arms 11a and 11b and high-speed rocker arms 12
When high hydraulic pressure acts on the back of plungers 21a and 21b while both a and 12b are on the base circle of the cam,
Plungers 21a and 21b are fitted with springs 24a of fitting holes 23a and 23b.
Pressing the sleeve bodies 25a, 25b against 24b, and fitting holes 23a, 23b
Rush inside. In this state, the low-speed rocker arm 11a,
11b and the high-speed rocker arms 12a, 12b are locked and move together. Therefore, the high-speed cam takes priority, and the two intake valves 7a and 7b are operated with the high-speed lift characteristics. When the high oil pressure is released, the springs 24a, 24b push the plungers 21a, 21b back to release the low-speed rocker arms 11a, 1b.
Only the low-speed cam functions to separate the high-speed rocker arms 12a and 12b from the high-speed rocker arms 12a and 12b, and the intake valves 7a and 7b are operated with the low-speed lift characteristics.

Using such a mechanism, switching is performed such that the valve timing and lift determined by the high-speed cam are selected when the engine speed is high, and the valve timing and lift determined by the low-speed cam are selected when the engine speed is low. I do.

Although the above embodiment has been described with reference to the case where the present invention is applied to a four-valve DOHC engine, the present invention is not limited thereto.
Can be applied to C engine.

Also, the end pivot need not necessarily be HLA-style.

(Effects of the Invention) Since the present invention is configured as described above, it is possible to reduce the engagement displacement between the low-speed rocker arm and the high-speed rocker arm while taking advantage of the advantage of the HLA and the excellent assemblability of the end pivot type, In addition, the inclination of the rocker arm can be kept small even on the high-speed side where the load condition is severe.

[Brief description of the drawings]

FIG. 1 is a front view of an engine valve gear according to an embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is III-III in FIG.
It is principal part sectional drawing of the same valve apparatus seen in the direction. 2: Intake camshaft, 7a, 7b: intake valve, 9a, 9b: end pivot for intake, 11a, 11b: rocker arm for low speed, 12a, 12b: rocker arm for high speed, 16a, 16b: valve follower, 19a, 19
b: Rocker shaft, 20a, 20b: Plunger holes, 21a, 21
b: plunger, 22a, 22b: hydraulic chamber, 23a, 23b: fitting hole, 25
a, 25b: Sleeve body.

Claims (1)

(57) [Claims] 1. A variable valve timing type engine comprising a low speed cam and a high speed cam, a low speed rocker arm and a high speed rocker arm abutting on these cams, and an engagement / disengagement mechanism for removably connecting the two rocker arms. In the valve gear, the low-speed rocker arm is provided with a valve follower portion, and the adjacent high-speed rocker arm is supported by an end pivot, and the low-speed rocker arm is swingable by a rocker shaft portion integrated with the high-speed rocker arm. A valve train for an engine, wherein the valve train is supported.