JPH08246826A - Valve system for four-cycle engine - Google Patents

Abstract

PURPOSE: To improve follow-up performance of valve action in an engine medium and high speed rotation areas by providing second and third cams having the same cam profiles, and differentiating a cam profile of a first cam from those of the second and third cams. CONSTITUTION: Medium and high speed rocker arms 21, 22 are superposed on leading ends 19b, 20b of low speed rocker arms 21, 22. Support parts 19a, 20a of the low speed rocker arms 19, 20 are directly fitted to a rocker shaft 23. The low speed rocker arms 19, 20 are driven by means of a low speed cam 15 which is a first cam. The medium and high speed cams 16, 17 which are second and third cams. The medium and high speed cams 16 and 17 have the same cam profile. The low speed cam 15 has the different cam profile therefrom. Follow-up performance of valve action is improved in medium and high speed rotation areas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve operating mechanism for a four-cycle engine, and more particularly to a valve operating mechanism for a four-cycle engine which changes the valve opening / closing timing and lift according to the engine speed.

[0002]

2. Description of the Related Art Generally, in engines mounted on vehicles such as automobiles and motorcycles, intake / exhaust valves are disposed above a combustion chamber, and these valves are driven by a valve operating mechanism. The valve operating mechanism includes a cam shaft that interlocks with the crankshaft of the engine, and a cam formed on the cam shaft moves the intake / exhaust valve up and down at a predetermined timing.

By the way, it is desirable for a four-cycle engine to obtain a high output in a wide rotational speed range from a low rotational speed range to a medium / high rotational speed range. However, in the conventional valve operating mechanism, since the valve opening / closing timing and the lift amount are fixed, only the output characteristic having the peak value in the specific engine speed range can be obtained, and therefore the output characteristic in the low speed range is obtained. They were forced to choose between focusing on or focusing on the mid-high rpm range.

Therefore, in recent years, for example, Japanese Unexamined Patent Publication No. 5-6581.
As disclosed in Japanese Patent Publication No. 5, a low speed cam and a middle and high speed cam are arranged side by side on a cam shaft, and a low speed rocker arm and a middle and high speed rocker arm are arranged side by side, and a control device is used. A valve mechanism was devised in which the operation of these cams and rocker arms was switched according to the engine speed.

As shown in FIGS. 6 and 7, this valve mechanism is provided with a low speed rocker arm 1 having a bifurcated tip and a branch tip 1a, and is arranged on both sides of the low speed rocker arm 1, respectively. , The tip portions 2a and 3a are coaxially provided with the medium and high speed rocker arms 2 and 3 which are superposed on the branch tip portion 1a of the low speed rocker arm 1, and the low speed cam 4 is provided in the low engine speed range. Through the low speed rocker arm 1 and through the medium and high speed cams 5 and 6 through the medium and high speed rocker arms 2 and 3 in the middle and high rpm range of the engine. Are simultaneously moved up and down at a predetermined timing. Reference numeral 9 is a bubble spring.

[0006]

However, the valves are driven by one medium / high speed rocker arm per valve in the medium / high speed range of the engine, but the tip of the medium / high speed rocker arm is for low speed. Since it is superposed on the tip of the branch of the rocker arm, one medium-high speed rocker arm receives the loads of two valves, two valve springs, and the low-speed rocker arm.

Considering the followability of the valve behavior in the middle and high rpm range of the engine, if the inertial weight of the valve train is large, jumping of the valve occurs and the cam lift curve as designed cannot be reproduced. It is desirable that the load applied to one rocker arm is small.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a valve operating mechanism for a four-cycle engine, which is capable of improving the followability of valve behavior in the middle / high engine speed range of the engine. To aim.

[0009]

In order to solve the above-mentioned problems, a valve operating mechanism for a four-cycle engine according to the present invention has, as described in claim 1, a first and a second valves each provided with a tip portion. A second rocker arm and third and fourth rocker arms which are arranged on both sides of the first and second rocker arms and whose tip portions are superposed above the respective tip portions of the first and second rocker arms. And eccentric large-diameter portion is formed while being rotatably supported, and the support portions of the third and fourth rocker arms are fitted and inserted into the eccentric large-diameter portion,
A rocker shaft into which the supporting portions of the first and second rocker arms are directly fitted, a first cam that drives the first and second rocker arms, and second and third rockers that drive the third and fourth rocker arms. 3 cams, the second and third cams are formed in the same cam profile, and the cam profile of the first cam is formed differently from the cam profiles of the second and third cams. .

[0010]

In the present invention having the above-mentioned structure, the first and second rocker arms each having a tip portion,
The third and fourth rocker arms, which are arranged on both sides of the first and second rocker arms and have their respective tip portions superposed above the respective tip portions of the first and second rocker arms, are rotatable with each other. The eccentric large diameter portion is formed while being supported, the support portions of the third and fourth rocker arms are fitted into the eccentric large diameter portion, and the support portions of the first and second rocker arms are directly fitted. A rocker shaft, a first cam that drives the first and second rocker arms, and second and third cams that drive the third and fourth rocker arms, wherein the second and third cams are The third cam has the same cam profile, and the cam profile of the first cam is different from that of the second and third cams. Preload applied to the fourth rocker arm is improved followability of the valve behavior during middle and high speed range of the engine becomes smaller than before.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an example of a valve operating mechanism of a 4-cycle engine to which the present invention is applied. 2 is a plan view of the valve mechanism, and FIG. 3 is a front view of the valve mechanism. Further, FIG. 4 and FIG. 5 are side views of the operating state showing the operation of the valve mechanism.

The valve mechanism 11 is arranged on each of the intake side and the exhaust side of one cylinder of the engine, and two valves are provided on each of the intake side and the exhaust side. There is something. Therefore,
The valves 12 and 13 shown in FIGS. 1 to 5 are arranged to perform intake or exhaust. In addition, each valve 12, 1
3 is urged by valve springs 14 and 14 so as to always come into close contact with an intake hole or an exhaust hole of a combustion chamber of an engine (not shown).

This embodiment has a low speed cam 15 as a first cam and a pair of middle and high speed cams 16 and 17 as second and third cams arranged on both sides of the low speed cam 15, respectively. A pair of low-speed rocker arms 19 and 20 as first and second rocker arms and a third and fourth rocker arms located below the camshaft 18 and the low-speed cam 15 and the medium- and high-speed cams 16 and 17, respectively. A pair of medium and high speed rocker arms 21,
22 and these rocker arms 19, 20, 21, 22
Rocker shaft 23 into which the support portions 19a to 22a of the above are fitted and rotatably supported by a bearing portion (not shown).
And is configured.

The tip portions 19b and 20b of both low speed rocker arms 19 and 20 are stem head portions 12a and 13 of valves 12 and 13 for opening and closing a combustion chamber of an engine (not shown).
Contact a. Also, both low speed rocker arms 19,
The respective support portions 19a and 20a of 20 are directly fitted into the rocker shaft 23 and are rotatably provided.

On the other hand, both middle and high speed rocker arms 21,
Each of the support portions 21a and 22a of the 22 is a rocker shaft 23.
The rocker shaft 23 is rotatably fitted into the rocker shaft 23 via eccentric bushes 24, 25 each having a larger diameter. As shown in FIGS. 4 and 5, the eccentric bushes 24, 25 have their axes eccentric from the center of the rocker shaft 23.
The retaining pin 26 is detachably fixed to the rocker shaft 23. Therefore, these eccentric bushes 2
4, 25 function as eccentric large-diameter portions of the rocker shaft 23.

The middle and high speed rocker arm tips 21b and 22
The lower surface of b is the tip of each low-speed rocker arm 19b, 20.
b, respectively, through shims 27a. These shims 27a have a T-shaped vertical cross section, and are fitted into the low-speed rocker arm tips 19b and 20b from above. In addition, the stem head 12a of each valve 12, 13
13a is capped with a shim 27b having a cylindrical shape, and the tips 19 of the low-speed rocker arms are attached to these shims 27b.
b and 20b contact. These shims 27a, 27b
Is used for adjusting the tappet clearance of the valves 12 and 13. Then, each low-speed rocker arm tip portion 19
b, 20b and the rocker arm tips 21b for medium and high speeds,
22b are vertically overlapped with each other, and these tip portions 19b are
The contact points 22b to 22b are set substantially on the axes of the valves 12 and 13.

Therefore, as shown in FIG. 4, when the low speed cam 15 pushes down the respective cam floor surfaces 19c, 20c of both low speed rocker arms 19, 20 to lower their respective tip portions 19b, 20b. The rocker arm tips 21b and 22b for medium and high speeds descend by following the rocker arm tips 19b and 20b for low speed due to gravity. On the other hand, as shown in FIG. 5, both the middle and high speed cams 16 and 17 are provided.
When the floor surfaces 21c and 22c of both the medium and high speed rocker arms 21 and 22 are pressed, the medium and high speed rocker arm tips 21b and 22b press the low speed rocker arm tips 21b and 22b, respectively. Therefore, the low speed rocker arm tips 19b and 20b are forcibly lowered.

Of the above-mentioned cams 15 to 17, both the middle and high speed cams 16 and 17 have the same cam profile (the cross-sectional shape of the cam), and the low speed cam 15 is the middle and high speed cam 16. , 17 different cam profiles. That is, the low speed cam 15
The cam profile is set so that an appropriate valve lift amount and opening / closing valve timing can be obtained when the engine is operating in a low engine speed range. Also, the cam 1 for medium and high speed
The cam profiles of Nos. 6 and 17 are set so that an appropriate valve lift amount and opening / closing valve timing can be obtained when the engine is operating in the medium / high speed range.

By the way, as shown in FIG. 1, the rocker shaft 23 is rotated by a hydraulic cylinder 28 which is operated by hydraulic pressure from the engine. A rack 29 is connected to a piston (not shown) in the hydraulic cylinder 28, and the rack 29 is meshed with a pinion gear 30 formed at one end of the rocker shaft 23. Further, the hydraulic cylinder 28 is provided with a low speed hydraulic port 31 and a medium and high speed hydraulic port 32, respectively, and the hydraulic pressure from the engine is selectively guided to the respective hydraulic ports 31, 32.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low speed hydraulic port 31, and the rack 2
9 is pulled back, the pinion gear 30 is rotated in the direction of the arrow O, and both eccentric bushes 24, 25 are turned so that their respective thick tops 24a, 25a are located diagonally forward as shown in FIG. Move. Also, the engine speed is medium
When in the high rpm range, hydraulic pressure is supplied to the medium / high speed hydraulic port 32, the rack 29 is pushed out, the pinion gear 30 is rotated in the direction of arrow P, and both eccentric bushes 2 are moved.
4, 25, as shown in FIG.
4a and 25a are rotated so that they are located diagonally rearward.

Next, the operation of this embodiment will be described.

When the rocker shaft 23 rotates in the direction of the arrow O by the operation of the hydraulic cylinder 28 while the engine is in the low speed range, as shown in FIG. 4, the wall thicknesses of both eccentric bushes 24, 25 are increased. The tops 24a and 25a are located diagonally forward. As a result, each medium and high speed rocker arm 2
The cam floor surfaces 21c and 22c of the wheels 1 and 22 move downward relative to the cam floor surfaces 19c and 20c of the low speed rocker arms 19 and 20, respectively. Therefore, the peripheral surfaces of the cams 16 and 17 for medium and high speed and the rocker arms 21 and 2 for medium and high speed are provided.
A gap is formed between the second cam floor surfaces 21c and 22c, and as a result, the middle and high speed cams 16 and 17 are formed.
Spins idle.

At this time, both the low speed rocker arms 19 and 20 are constantly pushed upward by the urging force of the valve springs 14 and 14 about the axial center of the rocker shaft 23.
c and 20 cc contact the peripheral surface of the low speed cam 15. Therefore, when the cam shaft 18 rotates, both valves 12 and 13 move up and down based on the lift characteristic of the low speed cam 15. That is, both valves 12 and 13 open and close the combustion chamber while ensuring a valve lift amount suitable for a low engine speed range.

On the other hand, when the rocker shaft 23 rotates in the direction of arrow P by the operation of the hydraulic cylinder 28 while the engine is in the medium / high speed range, as shown in FIG. Each thick top 24a, 25 of
a is located diagonally rearward. As a result, the cam floor surfaces 21c and 22c of the medium- and high-speed rocker arms 21 and 22 become the cam floor surfaces 19c and 19c of the low-speed rocker arms 19 and 20, respectively.
20c relatively moved to the substantially upper position or the same position,
Cam floor surface 21 of each medium and high speed rocker arm 21, 22
c and 22c contact the peripheral surfaces of the middle and high speed cams 16 and 17, respectively.

Since the cam lift amounts of the middle and high speed cams 16 and 17 are larger than that of the low speed cam 15, when the cam shaft 18 is rotated under the condition shown in FIG. While idling, both of the middle and high speed cams 16 and 17 are driven by the middle and high speed rocker arms 21 and 21, respectively.
Both valves 12 and 13 are driven via 22 based on the lift characteristics of the middle and high speed cams 16 and 17. As a result, both valves 12 and 13 open and close the combustion chamber while ensuring a valve lift amount suitable for the medium / high engine speed range of the engine.

According to the above embodiment, the low-speed rocker arms 19 and 20 are divided into a pair of divided low-speed rocker arms 19 and 20 instead of the conventional one having a bifurcated front end and a branched tip. As a result, each of the medium- and high-speed rocker arms 21 and 22 has one valve, one valve spring, and the low-speed rocker arm 1 that is about half the weight of the conventional engine when the engine is operating in the medium-high speed range.
Only receives a load of 9,20. If the inertial weight of the valve train is small, jumping of the valves 12 and 13 is suppressed, and the cam lift curve as designed can be reproduced, so the load on one rocket arm for medium and high speeds will be less than that of the conventional engine. It is possible to improve the followability of the valve behavior in the middle / high speed range.

When the present invention is applied to a conventional model,
Since only the low speed rocker arms 19 and 20 need to be changed,
The cost increase due to the change is low. Further, since the valve mechanism 11 itself does not change, the number of steps for assembling and the maintenance method do not change significantly.

[0029]

As described above, according to the valve operating mechanism of the four-cycle engine according to the present invention, the first and second rocker arms each having a tip portion and the first and second rocker arms are provided. Third and fourth rocker arms, which are arranged on both sides of the first and second rocker arms and are superposed above the respective tip parts of the first and second rocker arms, and are rotatably supported and have an eccentric large-diameter portion. Is formed, and the support portions of the third and fourth rocker arms are fitted and inserted into the eccentric large-diameter portion, and the support portions of the first and second rocker arms are directly inserted and the first and second rocker shafts. A first cam that drives the second rocker arm, and second and third cams that drive the third and fourth rocker arms,
Since the second and third cams have the same cam profile and the cam profile of the first cam is different from that of the second and third cams, the load applied to the third and fourth rocker arms is increased. Compared with conventional models, the followability of valve behavior in the middle and high engine speed range is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a valve mechanism for a 4-cycle engine according to the present invention.

FIG. 2 is a plan view of a valve mechanism.

FIG. 3 is a front view of a valve mechanism.

FIG. 4 is a side view of the operating state showing the operation of the valve mechanism.

FIG. 5 is a side view of an operating state showing the operation of the valve mechanism.

FIG. 6 is a plan view of a conventional valve mechanism.

FIG. 7 is a front view of a conventional valve mechanism.

[Explanation of symbols]

11 valve mechanism 12,13 valve 15 low speed cam (first cam) 16,17 medium and high speed cam (second and third cam) 18 camshaft 19,20 low speed rocker arm (first and second cam) Rocker arm) 19a, 20a Low-speed rocker arm support 19b, 20b Low-speed rocker arm tip 19c, 20c Low-speed rocker arm floor surface 21,22 Medium-high speed rocker arm (3rd and 4th rocker arm) 21a, 22a Medium-high speed Rocker arm support 21b, 22b Tip of middle and high speed rocker arm 21c, 22c Floor surface of medium and high speed rocker arm 23 Rocker shaft 24, 25 Eccentric bush 24a, 25a Thick top of eccentric bush

Claims (1)

[Claims] 1. A first rocker arm and a second rocker arm, each of which has a tip portion, and both side portions of the first and second rocker arms, the tip portions of which are the first and second rocker arms, respectively.
And third and fourth rocker arms that are superposed above the respective tip end portions of the second rocker arm, and rotatably supported and an eccentric large-diameter portion is formed, and the support portions of the third and fourth rocker arms are formed. The first and second eccentric large-diameter parts are fitted and inserted into the first and second eccentric large-diameter parts.
A rocker shaft having a rocker arm supporting portion directly inserted therein, a first cam for driving the first and second rocker arms, and second and third cams for driving the third and fourth rocker arms are provided. However, the second and third cams are formed in the same cam profile, and the cam profile of the first cam is formed differently from the cam profiles of the second and third cams. Valve mechanism.