JP2700691B2 - Valve system for 4-cycle engine - Google Patents

Description

The present invention relates to a valve train for driving intake and exhaust valves of a four-stroke engine.

[Conventional technology]

In general, in a four-stroke engine mounted on 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 train includes a camshaft linked to the crankshaft of the engine, and the cam formed on the camshaft moves the intake and exhaust valves up and down at a predetermined timing.

[Problems to be solved by the invention]

By the way, it is desirable that the four-cycle engine be capable of obtaining a high output within a wide rotation speed range from a low rotation speed range to a middle / high rotation speed range, that is, a wide power band.

However, in the conventional valve train, since the valve opening / closing timing and the lift amount are fixed, only an output characteristic having a peak value can be obtained in a specific engine speed range.
Therefore, it is necessary to select whether to emphasize the output characteristics in the low rotation speed region or to emphasize the output characteristics in the middle and high rotation speed regions.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a valve device for a four-stroke engine capable of improving output within a wide rotation speed range up to a high rotation speed range.

[Means for solving the problem]

Therefore, according to the present invention, a first rocker arm directly abutting on a head of a valve provided in a combustion chamber of an engine, and a rotation support portion closer to the first rocker arm and closer to the rotation support portion than a cam follower surface A second rocker arm having a portion approaching to the upper surface of the first rocker arm, and respective rotation support portions of the first and second rocker arms rotatably supported are respectively fitted. Together with the first
A rocker shaft having an eccentric large-diameter portion having a diameter larger than that of the other portion in one of the inserted portions of the first and second rocker arms, and a cam for driving the first and second rocker arms. The above object has been achieved by providing a camshaft having first and second cams having different profiles.

[Action]

According to this valve operating device, the first cam or the second cam is based on a change in the vertical position of the rotation support portion of the first or second rocker arm caused by rotating the rocker shaft. Abuts on the rocker arm, whereby the valve is opened and closed by the first or second cam.

The rocker arm inserted into the eccentric large diameter portion and the vertical position are changed by rotating the rocker shaft, and accordingly, the valve opening / closing timing and the valve lift amount adapted to the engine speed range are set. .

〔Example〕

Hereinafter, an embodiment of a valve train according to the present invention will be described with reference to the drawings.

FIG. 1 conceptually shows a main part of a valve train 1 according to the present invention. Note that the valve gear 1 is disposed on the intake valve side and the exhaust valve side of one cylinder, respectively.

The valve gear 1 has a camshaft 4 in which two types of cams 2, 3 having different cam profiles are formed adjacent to each other.
A first rocker arm 5 and a second rocker arm 6 disposed below the cams 2 and 3, respectively;
Each of the support portions 5a, 6a of the rocker arms 5, 6 has a rocker shaft 7 fitted therein and rotatably supported by a bearing (not shown).

The tip of the first rocker arm 5 branches in two directions, and one and the other branch ends 5b are stem heads of a pair of valves 8 and 9 (for intake or exhaust) for opening and closing a combustion chamber of an engine (not shown). Each part is in contact.

Further, the first rocker arm 5 includes a contact plate 5c protruding toward the second rocker arm 6 as shown in FIG.

The support portion 6a of the second rocker arm 6 is inserted into the shaft 7 via an eccentric bush 11 having a larger diameter than the rocker shaft 7.

As shown in FIG. 3, the bush 11 has an axis eccentric from the axis of the rocker shaft 7, and is fixed to the rocker shaft 7 by a pin 12 (FIG. 2). The rocker arm 6 is rotatably fitted into the bush 11,
Therefore, the bush 11 functions as an eccentric large diameter portion of the camshaft 4.

On the other hand, the rocker arm 6 includes the rocker arm 5.
A projection as shown in FIG. 3 is formed on the lower surface located on the contact plate 5c.
6b is provided. The protrusion 6b is
, Specifically, a lower surface of a portion of the arm 6 closer to the support portion 6a than the cam follower surface 6c.

As shown in FIG. 3, the contact plate 5c of the rocker arm 5
, A shim 13 is provided at a position facing the protrusion 6b. The protrusion 6b is in contact with the shim 13 by the weight of the rocker arm 6, so that when the cam follower surface 5d of the rocker arm 5 is pressed, the rocker arm 6 rotates following the rocker arm 5. When the rocker arm 5 is pressed, the valves 8, 9 are naturally lifted.

On the other hand, when the cam follower surface 6c of the rocker arm 6 is pressed, the protrusion 6b presses the upper surface of the shim 13, so that the rocker arm 5 is forcibly rotated, and accordingly, the valve 8,
9 is lifted.

The profile of the cam 2 is set so as to obtain a valve working angle range and a valve lift that are appropriate when the engine is operated in a low speed range. The profile is set so that a valve working angle range and a valve lift that are appropriate when operating in the range are obtained.

The valve working angle range is the angle range of the cams 2 and 3 for opening the valves 8, 9 and FIG.
And 3 are respectively θa and θb
Is exemplified. As is clear from the drawing, the profile of the cam 3 is set so that a larger valve operating angle range than that of the cam 2 can be obtained. FIG. 5 also suggests the opening and closing timing of the valves by the cams 2 and 3.
As is apparent from FIG. 3, the cam 3 opens the valve faster than the cam 2 and closes the valve later.

The valve lift is the stroke length of the valves 8 and 9 when the valves 8 and 9 are driven by the rotation power of the cam 2 or the cam 3, and the valve lifts based on the driving of the cams 2 and 3 are shown in FIG. It is illustrated by l _a and l _b.

As is clear from the figure, the profile of the cam 3 is set so as to obtain a larger valve lift than the cam 2.

In FIG. 1, reference numeral 14 denotes a screw portion for adjusting a valve clearance, and reference numeral 15 denotes a valve spring.

 Hereinafter, the operation of this embodiment will be described.

Now, the rocker shaft 7 shown in FIG. 1 is rotated in the direction of the arrow, and the top 11a of the eccentric bush 11 (the part farthest from the axis of the rocker shaft 7) is positioned upward as shown in FIG. Then, the support 6a of the rocker arm 6 is moved upward with respect to the support 5a of the rocker arm 5.

When the support portion 6a of the rocker arm 6 moves upward, the rocker arm 6 swings around the projection 6b as a fulcrum, and the cam follower surface 6c descends. As a result, a gap t is formed between the peripheral surface of the cam 3 and the cam follower surface 6c, so that the contact between them is released, and the cam 3 rotates in an idle swing state.

On the other hand, since the rocker arm 5 is constantly pushed upward about the axis of the rocker shaft 7 by the urging force of the valve spring 15 shown in FIG. 1, its cam follower surface 5d contacts the peripheral surface of the cam 2. Touch Therefore, when the camshaft 4 rotates, the valves 8, 9 move up and down with the lift characteristic A illustrated in FIG. That is, valve 8,
No. 9 opens and closes the combustion chamber in a low rotational speed range while ensuring a suitable valve opening / closing timing and valve lift.

Next, the rocker shaft 7 is turned to move the top of the eccentric bush 11 as shown in FIGS.
The case where 11a is positioned below will be described.

In this case, the support 6a of the rocker arm 6 moves relatively downward with respect to the support 5a of the rocker arm 5.

At this time, since the protrusion 6b of the rocker arm 6 is in contact with the shim 13, the cam follower surface 6c of the arm 6 rises, thereby causing the cam follower surface 6c to move as shown in FIG.
6c contacts the peripheral surface of the cam 3.

As shown in FIG. 5, the cam 3 is formed so that the cam lift is larger than that of the cam 2, and the protrusion 6b formed on the rocker arm 6 has a protrusion 6b formed by the elasticity of the valve spring 15. Shim 13 is in contact.

Therefore, when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. 4, the cam 2 rotates in an idle swing state, while the cam 3 rotates with the rocker arm 6 and the projection 6b.
And the rocker arm 5 is driven via the shim 13.

As a result, the valves 8, 9 open and close the combustion chamber in accordance with the lift characteristic B shown in FIG. 5, that is, while securing a suitable opening / closing timing and lift amount at medium / high speed rotation.

By the way, at the time of the idle rotation operation of the cam 3 shown in FIG. 3, since the rocker arm 6 is in the free state,
There is a possibility that the projection 6b collides with the shim 13 that moves up and down, thereby generating noise. In order to prevent such an inconvenience, the rocker arm 6 may be biased counterclockwise in FIG. 3 with respect to the rocker arm 5 using a suitable spring means. In this way, the protrusion 6b is forcibly brought into contact with the shim 13, so that the rocker arm 6 can be synchronized with the movement of the rocker arm 5, and as a result, the generation of noise due to the rocking of the rocker arm 6 is prevented.

In the above embodiment, the lift characteristics A and B shown in FIG. 5 are obtained by the cams 2 and 3, but the lift profile as illustrated in FIGS. Properties can be obtained.

FIG. 8 shows a means for rotating the rocker shaft 7.

As shown in the figure, a pinion 7a is formed at an end of the rocker shaft 7, and a rack 16 is engaged with the pinion 7a. A cylinder 18 to which hydraulic pressure or pneumatic pressure is applied via a solenoid valve 17 is connected to the rack 16.

The engine speed sensor 19 detects the engine speed (not shown) and applies a signal corresponding to the engine speed to the solenoid valve drive circuit 20.

Solenoid valve drive circuit 20, based on the output signal of the sensor 19,
When the engine speed indicates a value in the low speed range and the values in the middle and high speed ranges, the cylinder 18 is extended and retracted, respectively.

Therefore, for example, when the engine speed changes from a value in the medium or high speed range to a value in the low speed range,
The extension operation of 18 causes the rocker shaft 7 to rotate until the bush 11 is in the state shown in FIG.
As a result, the valves 8 and 9 perform opening and closing operations (operations shown by the characteristic A in FIG. 5) suitable for the low rotation speed range by the cam 2.

On the other hand, when the engine speed changes from the value in the low speed range to the value in the middle or high speed range, the cylinder 18 is contracted and the bush 11 is brought into the state shown in FIG. The rocker shaft 7 is rotated up to this point. As a result, the valves 8 and 9 perform opening and closing operations (operations indicated by the characteristic B in FIG. 5) suitable for the middle and high rotation speed ranges by the cam 3.

Note that it is naturally possible to use an electric motor such as a servomotor as a rotating means of the rocker shaft 7.

FIG. 9 shows another embodiment of the present invention. In addition,
In the figure, in order to show the correspondence between the elements shown in FIG. 2, the reference numerals of the elements having the same functions as those elements are indicated by dashes.

In this embodiment, the support portion 5a 'of the rocker arm 5' is inserted into the rocker shaft 7 'via the eccentric bush 11', and the support portion 6a 'of the rocker arm 6' is directly connected to the rocker shaft 7 '. It is inserted in.

Therefore, by rotating the rocker shaft 7 ', the support portion 5a' of the rocker arm 5 'moves up and down relatively to the support portion 6a' of the rocker arm 6 '(in FIG. 9, the support portion 5a' is perpendicular to the plane of the drawing). Direction).

Now, the rocker shaft 7 'is rotated, and the support 5a' of the rocker arm 5 'is moved to the support 6 of the rocker arm 6'.
When moved downward relative to a ', the cam follower surface 6c' of the rocker arm 6 'lowers relative to the cam follower surface 5d' of the rocker arm 5 '. As a result, the cam comes into contact only with the rocker arm 5 ', and the rotation of the cam causes the valve to open and close via the rocker arm 5'.

On the other hand, the rocker shaft 7 'is rotated so that the support 5a' of the rocker arm 5 'is
When moved upward relative to a ', the cam follower surface 5d' of the rocker arm 5 'is moved to the rocker arm 6'.
Of the cam follower surface 6c '. As a result, the cam comes into contact only with the rocker arm 6 ', and this cam opens and closes the valve via the rocker arm 6', the projection 6b ', and the rocker arm 5'.

〔The invention's effect〕

The valve gear according to the present invention includes two types of valve driving cams having different profiles from each other, and by rotating the rocker shaft by a predetermined angle, it is possible to select which of the cams to use. Therefore, if one of the cams has a profile suitable for driving in the low rotation speed range and the other has a profile suitable for driving in the middle or high rotation speed range, the cam starts from the low rotation speed range. During·
The output of the four-stroke engine can be improved within a wide rotation speed range up to a high rotation speed range.

Further, in the valve gear of the present invention, the cam is selected by rotating the eccentric large-diameter portion, so that a large stress is not applied to each part when the cam is selected, so that the cam can be smoothly selected. .

Further, since the base end of the second rocker arm is in contact with the upper surface of the first rocker arm, the length of the second rocker arm is made as short as possible to reduce its equivalent inertial mass. Can be.

Therefore, the response of the second rocker arm when the engine is operated in the high rotation speed range is improved,
Smooth opening and closing of the valve can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view conceptually showing one embodiment of a valve train according to the present invention, FIG. 2 is a plan view of the valve train of this embodiment, and FIGS. FIGS. 5, 5, 6 and 7 which show the operation of this embodiment, respectively.
8 is a conceptual diagram illustrating a means for rotating a rocker shaft, and FIG. 9 is a plan view illustrating another embodiment of the present invention. 1. Valve operating device, 2, 3 ... Cam, 4 ... Cam shaft,
5,6,5 ', 6' ... rocker arm, 5c ... abutment plate, 5d, 6
c, 5d ', 6c': Cam follower surface, 6b: Projection, 7 ...
Rocker shaft, 7a …… Pinion, 8,9 …… Valve, 1
1,11 '… Eccentric bush, 13… Sim, 16
... Rack, 18 ... Cylinder, 19 ... Engine rotation sensor.

Claims (2)

(57) [Claims] A first rocker arm which is directly in contact with a head of a valve provided in a combustion chamber of an engine; a first rocker arm disposed adjacent to the first rocker arm; A second rocker arm in contact with an upper surface of the rocker arm; a second rocker arm rotatably supported; each of the support portions of the first and second rocker arms is fitted and inserted; A rocker shaft having an eccentric large-diameter portion whose diameter is larger than that of the other portion and whose axis is eccentric from the axis of the other portion, and the first and second rocker arms; A camshaft having first and second cams having different profiles from each other for driving the eccentric large-diameter portion by rotating the rocker shaft by a predetermined angle. By rotation, the second
The support portion of the rocker arm is moved downward relative to the support portion of the first rocker arm, so that the base end of the second rocker arm abutting on the upper surface of the first rocker arm is moved. The cam follower surface of the second rocker arm is moved upward as a fulcrum, thereby releasing the contact of the first rocker arm with the first cam, and contacting the second rocker arm with the second cam. The valve is actuated by the second cam through the base end of the second rocker arm that is in contact with the upper surface of the first rocker arm, and the rocker shaft is rotated by a predetermined angle. Due to the rotation of the eccentric large diameter portion, the second
By moving the support portion of the first rocker arm upward relative to the support portion of the first rocker arm, the base end of the second rocker arm abutting on the upper surface of the first rocker arm is moved. The cam follower surface of the second rocker arm is lowered as a fulcrum, thereby releasing the contact of the second rocker arm with the second cam, and bringing the first rocker arm into contact with the first cam. A valve operating device for a four-stroke engine, wherein the valve is operated by the first cam. 2. A first rocker arm which is directly in contact with a head of a valve provided in a combustion chamber, and is disposed adjacent to the first rocker arm, and has a base end having the first rocker arm. A second rocker arm that is in contact with the upper surface of the first rocker arm, the first rocker arm support portion is rotatably supported, and each of the support portions of the first and second rocker arms is inserted. A rocker shaft having an eccentric large-diameter portion having a diameter larger than that of the other portion and having an axis eccentric from the axis of the other portion, and driving the first and second rocker arms; A camshaft having first and second cams having different profiles from each other for rotation of the eccentric large diameter portion by rotating the rocker shaft by a predetermined angle. The supporting portion of the first rocker arm by moving upwardly relative supporting portion of the second rocker arm,
The cam follower surface of the second rocker arm is moved upward relative to the cam follower surface of the first rocker arm with the base end of the second rocker arm abutting on the upper surface of the first rocker arm as a fulcrum. With this, the contact of the first rocker arm with the first cam is released, and the second rocker arm is brought into contact with the second cam, so as to contact the upper surface of the first rocker arm. The valve is actuated by the second cam through the base end of the second rocker arm that is in contact with the second rocker arm, and the first rocker arm is rotated by rotating the eccentric large diameter portion by rotating the rocker shaft by a predetermined angle. By moving the support portion of the second rocker arm downward relative to the support portion of the second rocker arm,
Lowering the cam follower surface of the second rocker arm relative to the cam follower surface of the first rocker arm with the base end of the second rocker arm abutting on the upper surface of the first rocker arm as a fulcrum. This releases the contact of the second rocker arm with the second cam and causes the first rocker arm to contact the first cam so that the valve is actuated by the first cam. A valve train for a four-stroke engine, characterized in that: