JPH03286112A - Valve system of four-cycle engine - Google Patents

Abstract

PURPOSE:To prevent generation of hammering noises which may occur between a rocker arm and a cam by operating all rocker arms in both cases of a low speed operation and a medium/high speed operation of an engine. CONSTITUTION:One side branched end part 7b of a low speed rocker arm 7 is superposed on the end part 8b of a medium/high speed rocker arm 8, for driving a valve 1. The other branched end part 7b of the rocker arm 7 drives a valve 2. A rocker shaft 11 is then rotated and the rocker arm 8 is relatively displaced in a vertical direction through an eccentric bush 12, so that the rocker arm 8 is driven by a medium/high speed cam 4 and also the rocker arm 7 is driven by a low speed cam 3 during a medium/high speed operation of an engine. The rocker arm 8 is forcibly operated by the rocker arm 7 during a low speed operation of the engine. In both cases, accordingly, generation of hammering noises, which may occur between the rocker arm and the cam, can be prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention provides a four-stroke engine that can change the lift amount, valve opening timing, etc. of intake and exhaust valves according to operating conditions. The present invention relates to a valve train for a four-cycle engine, and more particularly to a valve train for a four-stroke engine that can prevent the occurrence of hammering noise that may occur between a floating rocker arm and a cam.

(Prior Art) Generally, in a four-stroke engine installed in a vehicle such as an automobile or a motorcycle, intake and exhaust valves are disposed above a combustion chamber, and these valves are driven by a valve train. That is, the valve operating device includes a camshaft that is interlocked with the crankshaft of the engine, and uses a cam formed on the camshaft to move the intake and exhaust valves up and down at predetermined timing.

(Problem to be Solved by the Invention) By the way, the above-mentioned 4-cycle engine has the ability to obtain high output within a wide rotational speed range from low rotational speed to medium and high rotational speed, that is, has a wide power band. is desirable.

However, in conventional valve train systems, the valve opening/closing timing and lift amount are fixed, so output characteristics that only have a peak value in a specific engine speed range can be obtained, and therefore the output characteristics in the low engine speed range cannot be obtained. You are forced to choose whether to focus on the engine or the output characteristics in the medium and high rotation speed range.

This invention was made in consideration of the above-mentioned circumstances, and is capable of improving output within a wide range of rotation speeds, and also reliably prevents the occurrence of hitting sounds that may occur between the cam and the rocker arm. The purpose of the present invention is to provide a valve train for a four-stroke engine that can be used in a four-stroke engine.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a rocker shaft that is rotatably supported and has an eccentric large diameter portion, and a rocker shaft that is directly inserted into the rocker shaft and has a branched tip portion. a second rocker arm that is fitted into the eccentric large diameter portion and arranged in parallel with the first rocker arm; and first and second cams that drive the first and second rocker arms, respectively. , wherein the first and second cams have different cam profiles, and one of the branched tips of the first rocker arm is overlapped with the tip of the second rocker arm. In addition, the other of the branched tips of the first rocker arm and the tip of the second rocker arm are configured to be able to come into contact with the valve.

(Function) Therefore, according to the valve operating system for a four-cycle engine according to the present invention, by rotating the rocker shaft by a predetermined angle and rotating the eccentric large diameter portion, the cam floor surface of the second rocker arm is moved to the first position. Change the position of the rocker arm relative to the cam floor surface in the vertical direction.

When the cam floor surface of the second rocker arm is positioned downward relative to the cam floor surface of the first rocker arm, the second
The contact between the rocker arm and the second cam is released, the first rocker arm and the first cam are brought into contact, and the valves of the four-cycle engine are driven by the first cam.

At this time, one of the branched tips of the first rocker arm is connected to the second rocker arm.
Since it is superimposed on the tip of the rocker arm, the second
The rocker arm is forcibly actuated by the first rocker arm. As a result, even if the second rocker arm is not driven by the second cam, it will not be in a floating state, and no hitting sound will be generated between the second cam and the second rocker arm.

Furthermore, when the cam floor surface of the second rocker arm is moved toward the road or at the same position relative to the cam floor surface of the first rocker arm, the second rocker arm and the second cam come into contact, and at the same time, the first rocker arm also moves toward the first rocker arm. Contact with the cam. As a result, among the valves of a 4-stroke engine,
The valve in contact with the tip of the second rocker arm is driven by the second cam, and the valve in contact with the other branched tip of the first rocker arm is driven by the first cam.

At this time, the first and second rocker arms are both driven by the first cam and the second cam, so
There is no floating state, and therefore, there is no possibility of any hitting noise that may occur between the cam and the rocker arm.

In this way, by rotating the rocker shaft and selecting a cam, it is possible to improve engine output over a wide rotation speed range, and at the same time, the first and second rocker arms are in a floating state when the valve train is operated. Therefore, it is possible to reliably prevent the occurrence of hitting sounds that may occur between the rocker arm and the cam.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a perspective view showing an embodiment of the valve train for a four-stroke engine according to the present invention, FIG. 2 is a plan view of the valve train shown in FIG. 1, and FIGS. FIG. 3 is a side view of the operating state of the valve train shown in FIG.

This valve train is disposed on the intake side and the exhaust side of one cylinder of the engine, respectively. Therefore, the first
The valves 1 and 2 shown in FIGS. 1 to 4 are arranged for intake or exhaust.

This embodiment includes a camshaft 6 having a low-speed cam 3 as a first cam and a medium-high speed cam 4 as a second cam disposed on one side of the low-speed cam 3,
A low-speed rocker arm 7 as a first rocker arm and a medium-high speed rocker arm 8 as a second rocker arm are positioned below each of the cams 3 and 4, and these rocker arms 7 and 8 support parts 7a and 8a are fitted, The rocker shaft 11 is rotatably supported by a rocker shaft bearing portion (not shown).

The tip of the rocker arm 7 for low speeds is branched into two directions, and one of the two branched tips 7b and 7b' is in contact with the upper surface of the tip 8b of the rocker arm 8 for medium and high speeds via a shim 14a. Ru. The other branch tip 7b' extends downward and comes into contact with the stem head of the valve 2 via a shim 14b.

Further, the support portion 7a of this low-speed rocker arm 7 has a second
As shown in the figure, it is inserted directly into the rocker shaft 11,
Rotatably provided.

The support portion 8a of the medium/high speed rocker arm 8 is rotatably fitted onto the rocker shaft 11 via an eccentric bush 12 having a larger diameter than the rocker shaft 11. As shown in FIG. 3, this eccentric bushing 12 has an axis eccentric from the center of the rocker shaft 11, and is detachably fixed to the rocker shaft 11 by a pin 10. Therefore, this eccentric bushing 12 functions as an eccentric large diameter portion of the camshaft 11.

As shown in FIG. 1, the lower surface of the tip 8b of the medium/high speed rocker arm 8 is brought into contact with the stem head of the valve 1 that opens and closes the fuel chamber of the engine via a shim 14b. One branched tip 7b of the low speed rocker arm 7 is superimposed on the tip 8b of the medium/high speed rocker arm 8, and the contact point between the branched tip 7b and the tip 8bb is set approximately on the axis of the valve 1. be done.

Therefore, as shown in FIG. 3, when the low-speed cam 3 pushes down the cam floor surface 7C of the low-speed rocker arm 7 and lowers each branch tip 7b and 7b', one of the branch tips 7b Tip part 8 of rocker arm 8 for medium and high speeds
Since b is pressed down, the medium/high speed rocker arm 8 is forcibly lowered.

On the other hand, when the medium-high speed cam 4 presses down the cam floor surface 8C of the medium-high speed rocker arm 8 as shown in FIG.
Since the cam floor surface 7C of the low-speed rocker arm 7 also contacts the low-speed cam 3 at the same time, the low-speed rocker arm 7 is driven by the low-speed cam 3 and is not in a floating state.

Here, the shims 14a and 14b are both used for tappet clearance adjustment. The shim 14a has a T-shaped longitudinal section and is similar to the tip 8b of the medium-high speed rocker arm 8.
is fitted from above. Further, the shim 14b has a closed cylindrical shape and covers the stem heads of the valves 1 and 2.

The cam profiles of the cams 3 and 4 are different for the low-speed cam 3 and the medium-high speed cam 4. In other words, low speed cam 3
The cam profile is set to obtain the appropriate valve lift amount and valve opening/closing timing when the engine is operated in a low rotation speed range. Further, the cam profile of the medium/high speed cam 4 is set so that a valve lift amount and valve opening/closing timing suitable for when the engine is operated in a medium/high speed range are obtained.

The above-mentioned valve lift amount is the stroke length of valves 1 and 2, and coincides with the cam lift amount. In Fig. 5, the cam profile of the low-speed cam 3 is shown as a solid line A (cam lift amount 1
1a), and the cam profile of the medium/high speed cam 4 is shown by a broken line B (cam lift amount 1b). This fifth
As is clear from the figure, the cam profile of the medium-high speed cam 4 is set so that a larger valve lift amount can be obtained than that of the low-speed cam 3.

In addition, the two-dot chain line C in FIG. 5 shows the cam profile of the medium-high speed cam 4 when the rocker shaft 11 is rotated and the top portion 12a of the eccentric bushing 12 is positioned diagonally forward (FIG. 3). .

Incidentally, as shown in FIG. 1, the rocker shaft 11 is rotated by a hydraulic cylinder 15 operated by oil pressure from the engine. A rack 16 is connected to a piston (not shown) of the hydraulic cylinder 15, and the rack 16 is engaged with a pinion 17 formed at one end of the rocker shaft 11. The hydraulic cylinder 15 also includes a low-speed hydraulic boat 18 and a high-speed hydraulic boat 19.
are provided, respectively, and hydraulic pressure from the engine is selectively guided to each boat 18, 19.

When the engine speed is in the low speed range, hydraulic pressure is supplied to the low-speed hydraulic boat 18, the rack 16 is pulled back, and the pinion 17 is rotated in the direction of arrow M in FIG.
The eccentric bushing 12 has its top 12 as shown in FIG.
Rotate so that a is positioned diagonally forward. Further, when the engine speed is in the medium/high speed range, hydraulic pressure is supplied to the medium/high speed hydraulic boat 19, the rack 16 is pushed out, and the pinion 17 is rotated in the direction of arrow N in FIG. As shown in FIG. 4, the eccentric bushing 12 has a top portion 12a.
Rotate so that it is positioned diagonally to the rear.

Next, the effects will be explained.

When the engine is in the low rotation speed range, the hydraulic cylinder 15
When the rocker shaft 11 rotates in the direction of the arrow M in FIG. 1 due to the operation, the top portion 12a of the eccentric bushing 12 is positioned diagonally forward (FIG. 3).

As a result, the cam floor surface 8 of the rocker arm 8 for medium and high speeds
c moves downward relative to the cam floor surface 7C of the low-speed rocker arm 7. Therefore, a gap is formed between the circumferential surface of the medium and high speed cam 4 and the cam floor surfaces 8c and 9c of the medium and high speed rocker arms 8 and 9,
As a result, the medium and high speed cams 4 and 5 idle.

Also, at this time, the low-speed rocker arm 7 receives the urging force of the valve spring 20 indirectly via the tip 8b of the medium-high speed rocker arm 8, or directly by the other branched tip 7b', and the rocker shaft 11 receives the urging force of the valve spring 20. Since the cam floor surface 7c is constantly pushed upward about the axis of the cam 3, the cam floor surface 7c comes into contact with the surface of the low speed cam 3. Therefore, when the camshaft 6 rotates, the valves 1 and 2 move up and down based on the lift characteristic A of the low-speed cam 3 shown in FIG. In other words, valves 1 and 2 ensure a valve lift amount suitable for the low engine speed range, while
Open and close the combustion chamber.

At this time, one branch end 7 of the low speed rocker arm 7
b is superimposed on the tip 8b of the medium/high speed rocker arm 8, so the medium/high speed rocker arm 8 is forcibly operated by the movement of the low speed rocker arm 7. As a result,
Even if the medium/high speed rocker arm 8 is not driven by the medium/high speed cam 4, the medium/high speed rocker arm 8 is not in a floating state, and no hitting sound is generated between the medium/high speed rocker arm 8 and the medium/high speed cam 4.

On the other hand, when the rocker shaft 11 rotates in the direction of the arrow N in FIG. Figure 4). As a result, the cam floor surface 8C of the medium/high speed rocker arm 8 moves toward the road or to the same position relative to the cam floor surface 7c of the low speed rocker arm 7, and this cam floor surface 8
C comes into contact with the circumferential surface of the medium/high speed cam 4. At the same time, the cam floor surface 7c of the low-speed rocker arm 7 also comes into contact with the peripheral surface of the low-speed cam 3.

Therefore, when the camshaft 6 is rotated under the condition shown in FIG. 4, the medium-high speed cam 4 drives the valve 1 via the medium-high speed rocker arm 8 based on the lift characteristic B shown in FIG. Further, the low speed cam 3 drives the valve 2 via the low speed rocker arm 7 based on the lift characteristic A shown in FIG. As a result, valve 1 opens and closes the combustion chamber while ensuring a valve lift amount suitable for the engine's medium and high speed range, and valve 2 performs combustion with a valve lift amount suitable for the engine's low speed range. Open and close the room.

At this time, both the low-speed rocker arm 7 and the medium-high speed rocker arm 8 are driven by the low-speed cam 3 and the medium-high speed cam 4, respectively, so that neither of them is in a floating state. Therefore, no tapping noise is generated between the low speed cam 3 and the low speed rocker arm 7 and the medium and high speed cam 4 and the medium and high speed rocker arm 8.

According to the above embodiment, the low speed cam 3 is formed with a cam profile suitable for the low engine speed range, the medium and high speed cam 4 is formed with a cam profile suitable for the medium and high engine speed range, Furthermore, the rocker arm 8 for medium and high speeds is rotatably fitted into the eccentric bush 12 of the rocker shaft 11, and the rocker arm 7 for low speeds is directly fitted and inserted into the rocker shaft 11. Since the valve 1 can be selectively driven by the low speed cam 3 or the medium and high speed cam 4.5, the valve 1 can be selectively driven by the low speed cam 3 or the medium and high speed cam 4.5. be able to. (Note that the valve 2 is always driven by the low-speed cam 3.) Therefore, it is possible to improve the output of the 4-cycle engine over a wide engine speed range from low engine speeds to medium and high engine speeds. can.

In addition, since the selection of the low-speed cam 3 and the medium-high speed cam 4 is performed by rotating the eccentric bushing 12, the cam 3
, 4, no large stress is generated in each part. Therefore, the cams 3 and 4 can be selected smoothly.

When the engine rotates at medium and high speeds, the medium and high speed rocker arm 8 is driven by the medium and high speed cam 4, and at the same time, the low speed rocker arm 7 is driven by the low speed cam 3, so the low speed rocker arm 7 is never in a floating state. do not have. Of course, even at low engine speeds, the medium-high speed rocker arm 8 is forcibly operated by the low-speed rocker arm 7 driven by the low-speed cam 3, so it does not become floating.

Therefore, whether the engine is rotating at a low speed or when the engine is rotating at a medium or high speed, it is possible to prevent the occurrence of a hammering sound that may occur between the cam and the rocker arm.

In the above embodiment, the cam profile of the medium-high speed cam 4 is as shown by the broken line B in FIG. 5, but the cam profile of the medium-high speed cam 4 is shown in the broken line B' in FIG. Alternatively, as shown by the broken line B' in FIG. 7, the lift of the valve 1 during medium and high engine speeds may be changed.

Further, in the above embodiment, a case has been described in which the hydraulic cylinder 15 is used as a rotational drive source for the rocker shaft 11, but a motor is used as the rotational drive source, and the rocker shaft 11 is rotationally driven by a power transmission means such as a pulley and a belt. You may also do so.

〔Effect of the invention〕

As described above, according to the valve train for a four-stroke engine according to the present invention, the eccentric large diameter portion is formed in the rotatably supported rocker shaft, and the second rocker arm is fitted into the eccentric large diameter portion. Along with being
A first rocker arm is directly fitted onto the rocker shaft, one of the branched tips of the first rocker arm is superimposed on the tip of the second rocker arm, and the other of the branched tips of the first rocker arm and the second rocker arm are overlapped. Since the tip of the cam is configured so that it can come into contact with the valve, by rotating the rocker shaft and selecting the first and second cams,
It is possible to improve the engine output over a wide range of rotation speeds, and at the same time, it is possible to reliably prevent the occurrence of hitting noises that may occur between the cam and the rocker arm.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the valve train for a four-cycle engine according to the present invention, FIG. 2 is a plan view of the valve train shown in FIG. 1, and FIGS. 3 and 4 are the views shown in FIG. FIG. 5 is a diagram showing the cam profile of the cam in FIG. 1, and FIGS. 6 and 7 are modifications of the cam profile shown in FIG. 5. It is a diagram. 1.2... Valve, 3... Cam for low speed, 4... Cam for medium/high speed, 7... Rocker arm for low speed, 7b...
One branch end of the low speed rocker arm, 7b'...
Other branch tip of rocker arm for low speed, 8... Rocker arm for medium and high speed, 8b... Tip of rocker arm for medium and high speed, 11... Rocker shaft, 12... Eccentric bush, A... Low speed Cam profile of the cam for B.
...Cam profile for medium and high speed cams.

Claims (1)

[Claims] a rocker shaft rotatably supported and formed with an eccentric large diameter section; a first rocker arm that is directly fitted onto the rocker shaft and has a branched tip; and a first rocker arm that is fitted onto the eccentric large diameter section. a second rocker arm arranged parallel to the first rocker arm, and first and second cams that respectively drive the first and second rocker arms; The cam profiles of the cams are formed differently, and one of the branched tips of the first rocker arm is overlapped with the tip of the second rocker arm, and the other of the branched tips of the first rocker arm is overlapped with the tip of the second rocker arm. A valve operating system for a four-stroke engine, wherein the and the tip of the second rocker arm are configured to be able to come into contact with a valve.