JPH0491310A - Valve system of four cycle engine - Google Patents

Abstract

PURPOSE:To improve engine output over a wide revolution range by means of selection of a cam through rotation of a rocker shaft by forming eccentric large diameter parts on the rocker shaft and by inserting a second and a third rocker arms into it. CONSTITUTION:When a rocker shaft 11 is rotated at a low revolution zone of an engine, each of thick top parts 12a and 13a of eccentric bushes 12 and 13 as eccentric large diameter parts are positioned diagonally front. Then, cam floor surfaces 8c and 9c of intermediate and high speed rocker arms 8 and 9 are moved downward in relation to a cam floor surface 7c of a low speed rocker arm 7 and set at almost the same position. However, as base circles 4X and 5X of intermediate and high speed cams 4 and 5 are formed at the diameter smaller than a base circle 3X of a low speed cam 3, a clearance is formed between the circumferential surfaces of the intermediate and high speed cams 4 and 5 and the cam floor surfaces 8c and 9c, and the intermediate and high speed cams 4 and 5 slip. When a cam shaft 6 is rotated, valves 1 and 2 are vertically moved based on a lift characteristic of the low speed cam 3.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention is a four-stroke engine that can change the lift amount and opening timing of intake and exhaust valves according to the operating conditions. The present invention relates to a valve train, and particularly to a valve train for a four-stroke engine that can reduce the weight of a rocker arm.

(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 has been made in consideration of the above-mentioned circumstances, and provides a valve train for a four-stroke engine that can improve output within a wide rotational speed range and can reduce the weight of a rocker arm. The purpose is to

[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. 1 rocker arm, second and third rocker arms disposed on both sides of the first rocker arm and fitted into the eccentric large diameter portion, and the first, second and third rocker arms, respectively. first, second, and third cams, the tips of the second and third rocker arms and the branched tips of the first rocker arm are vertically overlapped, and the second and third cams are vertically overlapped. and third
cams of the first cam are formed with the same cam profile, the cam profile of the first cam is formed differently from the cam profile, and the first cam drives the rocker arm disposed below the tip or the branch tip. The cam is characterized in that the base circle of the cam is formed to have a larger diameter than the base circles of other cams.

(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 surfaces of the second and 30th lever arms are rotated to the first position. 10 The position can be changed vertically relative to the cam floor surface of the arm.

At this time, when the cam floor surfaces of the second and 30th claw arms are moved downward relative to the cam floor surface of the 10th claw arm, the contact between the second and 30th claw arms and the second and third cams is released, The tenth lever arm and the first cam come into contact with each other, and the valves of the four-stroke engine are driven by the first cam.

Further, when the cam floor surfaces of the second and 30th lever arms are moved substantially upwardly or to the same position relative to the cam floor surface of the 10th lever arm, the contact between the 10th lever arm and the first cam is released, and the cam floor surface of the 10th lever arm is released. And the 30th hook arm and the second and third cams are in contact with each other, and the 4th
The valves of the cycle engine are actuated by the second and third cams. By rotating the rocker shaft and selecting a cam in this manner, engine output can be improved over a wide rotational speed range.

Furthermore, the rocker arm driven by a cam with a large base circle can have its cam floor surface set at a low position. As a result, the mass of the rocker arm whose tip or branched tip is located below can be reduced, so the inertial mass of the valve train can also be kept low, increasing the engine's limit speed in the low-speed or medium-high speed range. can be done.

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

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

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 low-speed cam 3 as a first cam, a medium-high speed cam 4 as a second cam, and a third cam disposed on one side and the other side of the low-speed cam 3, respectively. A camshaft 6 (FIG. 1 and FIG. 2) also has a cam 5 for medium and high speeds, a rocker arm 7 for low speeds as a tenth arm located below each of the cams 3, 4, and 5, and a rocker arm 20 for low speeds. A rocker arm 8 for medium and high speeds as a latch arm, a rocker arm 9 for medium and high speeds as a 30th latch arm, and these rocker arms 7
．． The rocker shaft 11 is fitted with the support parts 7a, 8a, and 9a of 8 and 9, and is rotatably supported by a bearing part (not shown).

The tip of the low-speed rocker arm 7 is branched into two directions, and both branched ends 7b are in contact with the stem heads of the valves 1 and 2, which open and close the combustion chambers of the engine (not shown), respectively. Further, 1. The support portion 7a of the low-speed rocker arm 7 is directly fitted onto the rocker shaft 11 and is 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 bushing 12 having a larger diameter than the rocker shaft 11. This eccentric bushing 12 has a fine P
, P' are eccentric from the center O of the rocker shaft 11, and are detachably fixed to the rocker shaft 11 by a retaining pin 10. Therefore, this eccentric bushing 1
2 functions as an eccentric large diameter portion in the rocker shaft 11.

Here, the axis P of the eccentric bushing 12 is the thick top portion 12a.
is the shaft center in the low engine speed range when the thick walled top part 12a is located diagonally forward (Fig. 2), and the shaft center P' is the shaft center in the engine medium to high speed range when the thick walled top portion 12a is located diagonally backward (Fig. 1). The details are meticulous.

Further, as shown in FIG. 4, the support portion 9a of the medium/high speed rocker shaft 9 is also supported via an eccentric bush 13 having the same shape as the eccentric bush 12 and eccentric in the same direction.
It is rotatably fitted into the rocker shaft 11. This eccentric bush 13 is also detachably fixed to the rocker shaft 11 by a retaining pin 10, and functions as an eccentric large diameter section.

Furthermore, as shown in FIGS. 1 and 2, shims 14a are attached to the lower surfaces of the respective tip portions 8a and 9a of the medium and high speed rocker arms 8 and 9 at one and the other branch tip portions 7b of the low speed rocker arm 7. are brought into contact with each other through the The points of contact between the branched tip 7b of the low speed rocker arm 7 and the tips 8b and 9b of the medium and high speed rocker arms 8 and 9 are set approximately on the axes of the valves 1 and 2;

Therefore, as shown in FIG.
When the cam floor surface 7C of the speed rocker arm 7 is pressed down to lower its respective tips 7b, the tips 8b and 9b of the rocker arms 8 and 9 follow the branched tips 7b and descend due to gravity. . On the other hand, as shown in FIG.
When the cam floor surfaces 8c and 9C of the rocker arms 8 and 9 are pressed down, the tips 8b and 9b of these rocker arms 8 and 9 press down the branch tips 7b of the low-speed rocker arm 7. is forced down.

The shim 14a is a T-shaped shim in longitudinal section, and is fitted into both branched tips 7b of the low-speed rocker arm 7 from above. Further, the valve stem heads of the valves 1 and 2 are covered with a shim 14b in the shape of a closed cylinder, and this shim 1
．． 4b, the lower surface of the branched end portion 7b of the low-speed rocker arm 7 abuts. These shims 14a and 14b are used to adjust the tappet clearances of valves 1 and 2.

Further, among the cams 3, 4 and 5, the medium/high speed cam 4
and 5 have the same cam profile, and the low speed cam 3 has a different cam profile from the cam profile of these medium and high speed cams 4 and 5. In other words,
The cam profile of the low-speed cam 3 is set so that a valve lift amount and valve opening/closing timing suitable for when the engine is operated in a low rotation speed range are obtained. Further, the cam profiles of the medium and high speed cams 4 and 5 are set so as to obtain a valve lift amount and valve opening/closing timing suitable for when the engine is operated in a medium and high speed range.

The above-mentioned valve lift amount is the stroke length of knobs 1 and 2, and corresponds to the cam lift amount. In FIG. 5, the cam profile of the low-speed cam 3 is shown by a solid line A (cam lift amount, Ca), and the cam profile of the medium-high speed cams 4 and 5 is shown by a broken line B (cam lift amount f!b). . As is clear from FIG. 5, the cam profiles of the medium and high speed cams 4 and 5 are set so that a larger valve lift amount can be obtained than that of the low speed cam 3.

In addition, the chain double-dashed line C in FIG. 5 indicates the middle and high speed cam when the rocker shaft 11 is rotated and the thick tops 12a and 13a of the eccentric bushings 12 and 13 are positioned diagonally forward (FIG. 2). 4 and 5 are shown.

Furthermore, among the cams 3.4 and 5, the base circle 3X of the low-speed rocker arm 3 that comes into contact with the cam floor surface 7c of the low-speed rocker arm 7 is different from the base circle 3X of the low-speed rocker arm 3, as shown in FIGS. The base circles 4X and 5X of the rocker arms 4 and 5 are formed to have a larger diameter.

Therefore, the cam floor surface 7c of the low-speed rocker arm 7
is at a lower position than the cam floor surface (indicated by the two-dot chain line in Figures 1 and 2) when the base circle 3X of the low-speed cam 3 is the same as the base circles 4X and 5X of the medium-high speed cams 4 and 5. Can be set. Therefore, the mass of the low-speed rocker arm 7 is reduced accordingly.

Incidentally, as shown in FIG. 3, 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. In addition, the hydraulic cylinder 15
is provided with a low-speed hydraulic boat 18 and a medium-high-speed hydraulic boat 19.
Hydraulic pressure from the engine is selectively guided to.

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, the pinion 17 is rotated in the direction of arrow M, and the eccentric bushes 12 and 13 are rotated as shown in FIG. As shown, the thick top portions 12a and 13a are rotated so as to be 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, the pinion 17 is rotated in the direction of arrow N, and the eccentric bush 12 and 13 is rotated so that its thick top portions 12a and 13a are positioned diagonally rearward, as shown in FIG.

In this way, the rocker shaft 11 is connected to the hydraulic cylinder etc.
5, 16.17, the eccentric bushing 12.13
The thick top parts 12a and 13a of the rocker shaft 1 are always connected to the rocker shaft 1.
It is configured to rotate in the range from diagonally forward to diagonally backward on the upper half side of 1.

Next, the effect will be explained.

When the engine is in the low rotation speed range, the hydraulic cylinder 15
When the rocker shaft 11 is rotated in the direction of the arrow M by the operation, the thick top portions 12a and 13a of the eccentric bushes 12 and 13 are located diagonally forward (FIG. 2). As a result, the cam floor surfaces 8C and 9c of the medium and high speed rocker arms 8 and 9 move downward relative to the cam floor surface 7C of the low speed rocker arm 7, and are set at approximately the same position. However, since the base circles 4X and 5X of the medium and high speed cams 4 and 5 are formed to have a smaller diameter than the base circle 3X of the low speed cam 3, the circumferential surfaces of the medium and high speed cams 4 and 5 and the medium and high speed rocker arm 8 A gap is formed between the cam floor surfaces 8C and 9c of the cams 4 and 9 for medium and high speeds.
is idling.

At this time, since the low-speed rocker arm 7 is constantly pushed upward about the axis of the rocker shaft 11 by the biasing force of the valve spring 20, its cam floor surface 7C comes into contact with the circumferential 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 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 11 rotates in the direction of arrow N due to the operation of the hydraulic cylinder 15 when the engine is in a medium-high rotation range, the thick-walled top portions 12a and 13a of the eccentric bushings 12 and 13, respectively, are positioned diagonally rearward. (
Figure 1). As a result, the cam floor surfaces 8c and 9c of the medium-high speed rocker arms 8 and 9 move to an upper position relative to the cam floor surface 7c of the low-speed rocker arm 7, and the cam floor surfaces 8C and 9C respectively move to the upper position of the medium-high speed cam 4. and the peripheral surface of 5.

At this time, the cam floor surface 7d of the low-speed rocker arm 7 also comes into contact with the low-speed cam 3Q base circle 3X, but the fifth
As shown in the figure, the medium and high speed cams 4 and 5 are formed to have a larger cam lift than the low speed cam 3, so
When the camshaft 6 is rotated under the condition shown in FIG. 1, the low-speed cam 3 does not operate the low-speed rocker arm 7;
Medium and high speed cams 4 and 5 drive valves 1 and 2 via medium and high speed rocker arms 8 and 9, respectively, based on lift characteristic B shown in FIG. As a result, valves 1 and 2 open and close the combustion chamber while ensuring a valve lift amount suitable for the middle and high engine speed range.

According to the above embodiment, the low speed cam 3 has a cam profile suitable for the low engine speed range, and the medium and high speed cams 4 and 5 have cam profiles suitable for the medium and high engine speed range. Furthermore, the rocker arm 8 for medium and high speeds is attached to the eccentric bushes 12 and 13 of the rocker shaft 11.
and 9 are rotatably inserted into each other, and the low-speed rocker arm 7 is directly inserted into the rocker shaft 11. By the rotation of the rocker shaft 11, the low-speed rocker arm 7 is operated by the low-speed cam 3, and the low-speed rocker arm 7 is operated by the cam 3. Since the operation of the rocker arms 8 and 9 for medium and high speeds by the cams 4 and 5 can be selected, the valves 1 and 2 can be selectively driven by the cams 3 for low speeds or the cams 4 and 5 for medium and high speeds.

Therefore, the output of the four-stroke engine can be improved over a wide engine speed range from low engine speeds to medium and high engine speeds.

Also, since the selection of the low speed cam 3 and the medium and high speed cams 4 and 5 is performed by rotating the eccentric bushings 12 and 13, the cam 3. 4. 5. No large stress is caused to each part when selecting the parts. For this reason, cam 3. 4
．． 5 can be selected smoothly.

Further, the branched tip portion 7b of the rocker arm 7 for low speed is the tip portion 8b and 9b of the rocker arm 8 and 9 for medium and high speed.
The shims 14b are placed on the lower side of the valves 1 and 2.
The low speed cam 30 base circle 3X that drives the low speed rocker arm 7 contacts the base circles 4X and 5 of the medium and high speed cams 4 and 5 that drive the medium and high speed rocker arms 8 and 9. It is formed to have a larger diameter than 5X. Therefore, the cam floor surface 7C of the low-speed rocker arm 7 can be set at a low position, and the mass of the low-speed rocker arm 7 can be reduced accordingly. As a result, the inertial mass of the valve train can be suppressed to a low level, and the critical rotation speed of the engine in the low speed rotation range can be improved. At this time, the mass of the low-speed cam 3 increases, but the low-speed cam 3 rotates and the rocker arms 7, 8. reciprocate. 9
Therefore, even if the weight of the low-speed cam 3 increases, there is little effect on the inertial mass of the valve train.

Furthermore, in the above embodiment, the branching tip 7b of the rocker arm 7 for low speed is in contact with the valves 1 and 2 via the shim 14b, but as shown in FIG. The present invention can also be applied to a valve train in which the tip ends 8b and 9b of the rocker arms 8 and 9 abut against the valves 1 and 2 via shims 14b.

That is, in the valve operating system shown in FIG. The stem head of No. 2 is brought into contact with the stem head of No. 2 via a shim 14b. Then, each branch tip 7b' of the low-speed rocker arm 7' serving as the tenth lever arm comes into contact with the upper surface of the tip 8b' and 9' of the medium-high speed rocker arm 8' and 9' via the shim 14a. be done.

In this case, the base circle of the medium-high speed cam that comes into contact with the cam floor surface 80′ of the medium-high speed rocker arm 8′,
The base circle of the medium/high speed cam that contacts the cam floor surface 9c of the medium/high speed rocker arm 9' is formed to have a larger diameter than the base circle of the low speed cam 3 that contacts the cam floor surface 7c' of the low speed rocker arm 7'. Ru. Therefore, in this case as well, cam floor surfaces 8c' and 90'
The rocker arm 8' for medium and high speeds can be set in a fixed position.
and 9' can be reduced in weight, and the engine's limit rotational speed in the medium and high rotational speed range can be improved.

In both of the above embodiments, the cam profiles of the medium and high speed cams 4 and 5 are as shown by the broken line B in FIG. 5, but the cam profiles of the medium and high speed cams 4 and 5 are Dashed line B' in the figure or dashed line B'' in Figure 7
The lifts of valves 1 and 2 during medium and high engine speeds may be changed as shown in FIG.

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-cycle engine according to the present invention, the eccentric large diameter portion is formed in the rotatably supported rocker shaft, and the second and third
Since the 0th lever arm was fitted into this eccentric large diameter portion, and the 10th lever arm was placed between the 2nd and 30th lever arms and directly fitted into the rocker shaft, the rotation of the cam due to the rotation of the rocker shaft was Depending on the selection, engine output can be improved over a wide rotational speed range.

In addition, the base circle of the cam that drives the rocker arm located below the tip or the branch tip is formed to have a larger diameter than the base circles of other cams. The weight of the rocker arm driven by the cam can be reduced.

[Brief explanation of drawings]

1 and 2 are side views showing the operating state of the valve train shown in FIG. 3, FIG. 3 is a perspective view showing an embodiment of the valve train for a four-stroke engine according to the present invention, and FIG. 5 is a plan view showing the valve train shown in FIG. 3, FIG. 5 is a view showing the cam profile of the cam shown in FIG. 3, and FIGS. 6 and 7 are modifications of the cam profile shown in FIG. Figure 8
The figure is a plan view showing a rocker arm portion in another embodiment of a valve train for a four-stroke engine. 1.2...Valve, 3...Low speed cam, 3X...
Base circle of low-speed cam, 4, 5...Medium-high speed cam, 4X, 5X...Base circle of medium-high speed cam,
7...Low speed rocker arm, 7a...Low speed rocker arm support part, 7b...Low speed rocker arm branch tip, 7c...Low speed rocker arm cam floor surface, 8, 9...Mid-high speed Rocker arm for 8a, 9a...
・Supporting part of the rocker arm for medium and high speeds, 8b, 9b... Tip of the rocker arm for medium and high speeds, 11... Rocker shaft, 12.13... Eccentric bushing, A... Cam profile of the cam for low speeds, B...Cam profile for medium and high speed cam. Applicant's agent Hisashi Hatano 8(S 8σ(9a) 8c(5 8(" 8b (9b),

Claims (1)

[Claims] A rocker shaft that is rotatably supported and is formed with an eccentric large diameter portion; a first rocker arm that is directly fitted onto the rocker shaft and has a branched tip; second and third rocker arms arranged and fitted into the eccentric large diameter portion; first, second and third cams that drive the first, second and third rocker arms, respectively; the tip portions of the second and third rocker arms and the branched tip portions of the first rocker arm are vertically overlapped, and the second and third cams are formed to have the same cam profile; The cam profile of the first cam is formed differently from the cam profile, and the base circle of the cam that drives the rocker arm disposed below the tip or the branch tip is different from that of the other cam. A valve train for a four-stroke engine that is characterized by having a diameter larger than the base circle.