JPH0244006Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a pressure reducing device for an internal combustion engine that opens and closes an intake valve or an exhaust valve during a compression stroke by operating an auxiliary cam provided on a camshaft during startup.

(Prior Art) For example, there is a pressure reducing device disclosed in Japanese Utility Model Application Publication No. 56-127806, which improves the startability of the engine by reducing the compression pressure in the cylinder when starting the engine. This is a structure in which the intake or exhaust valves are opened for a certain period of time during the compression stroke at startup, in addition to the regular opening and closing operations by normal cams, and the valves are not opened or closed once a predetermined rotational speed is reached. .

(Problem that the invention aims to solve) However, with this device, if the valve closing timing is set later, the starting pulling force when starting the engine becomes lighter, but the problem is that the compression pressure is insufficient and ignition becomes difficult. It was hot. Further, if the valve closing timing is set earlier, the ignitability improves, but there is a problem in that the starting tensile force suddenly increases near the maximum engine rotational speed at the beginning of engine starting.

In view of these points, the present invention has a simple structure and reliable operation, reduces the pressure at the start of the engine to reduce the rope pulling force at the time of starting, and also reduces the pressure during the transition from the start of the engine to normal operation. It is an object of the present invention to provide a pressure reducing device for an internal combustion engine, in which good ignition is performed during the period, and overall startability is improved without impairing drivability during normal operation.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention is provided on a camshaft, and on one side thereof a guide slope is formed which is inclined with respect to a plane orthogonal to the axis of the camshaft. The main cam is provided with a main cam whose outer cam surface contacts a cam force transmitting part that transmits cam force to the intake valve or exhaust valve to open and close the intake valve or exhaust valve in a regular stroke, and the main cam is attached to the camshaft. The cam is rotatably and slidably fitted opposite the guide slope of the cam, and the side surface facing the guide slope is inclined with respect to a plane perpendicular to the axis of the camshaft and slides into contact with the guide slope. The auxiliary cam is provided with a sliding slope and a cam surface on the outer periphery that contacts the cam force transmitting portion to open and close the intake valve or the exhaust valve during the compression stroke. The auxiliary cam also includes a spring that presses the auxiliary cam so that its sliding slope comes into contact with a guide slope of the main cam, and a support that is provided on the camshaft and rotates together with the camshaft. Furthermore, it is rotatably supported by the support body, and has a lever portion that engages with the auxiliary cam on one end side of the pivot point, and a lever portion that engages with the auxiliary cam on the other end side from the center of rotation of the camshaft due to the centrifugal force accompanying the rotation of the camshaft. The auxiliary cam has a weight part that rotates in a direction that moves away, and rotates the auxiliary cam in a direction that accelerates the closing timing of the intake valve or exhaust valve by the auxiliary cam as the rotation of the camshaft increases during startup. A centrifugal arm is provided which is moved in a direction away from the main cam by rotationally sliding contact of the sliding slope with the guide slope so as to release the contact with the cam force transmitting part. Further, the centrifugal arm is provided with a spring that urges the weight portion of the centrifugal arm in a direction toward the center of rotation of the camshaft.

(Function) As a result, in the present invention, at the time of starting, the closing timing of the intake valve or exhaust valve by the auxiliary cam is advanced in proportion to the increase in centrifugal force accompanying the increase in engine speed, and the timing of closing the intake valve or exhaust valve by the auxiliary cam is advanced in proportion to the increase in centrifugal force accompanying the increase in engine rotation. The pressure inside the cylinder is increased in proportion to the increase in engine speed caused by the starter. During normal operation after startup, the auxiliary cam is released from contact with the cam force transmission section, and the auxiliary cam reliably opens and closes the valve.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show a pressure reducing device for a four-stroke engine that opens and closes an intake valve or an exhaust valve during a compression stroke by operating an auxiliary cam provided on a camshaft. Although the engine is not shown,
It is started by a recoil starter.

In FIG. 1, 1 is a tappet connected to an intake valve 2 (FIG. 2) and serves as a cam force transmitting part that transmits cam force to the intake valve 2, 3 is a camshaft, and 4 is a tapered part provided on the camshaft 3 and connected to the intake valve 2. The main cam 5 is a gear provided on the camshaft 3 for opening and closing the main cam 5 during the regular intake stroke, and the main cam 4 and the gear 5 are rotated together with the camshaft 3.

Camshaft 3 between the main cam 4 and gear 5
An auxiliary cam 6 is rotatably and slidably fitted in the auxiliary cam 6, and a spring 7 is inserted between the auxiliary cam and the gear 5.
(Fig. 2) is interposed.

One side of the main cam 4 facing the auxiliary cam 6 is formed into a guide slope 4a slightly inclined with respect to a plane perpendicular to the axis of the camshaft 3; is formed on a sliding slope 6a that is slightly inclined with respect to a plane perpendicular to the axis of the camshaft 3. The sliding slope 6a of the auxiliary cam 6 is in sliding contact with the guide slope 4a of the main cam 4. Further, the auxiliary cam 6 is provided so as to be movable back and forth in the axial direction of the camshaft 3, so that the auxiliary cam 6 can be withdrawn from below the tappet 1, that is, the contact with the tappet 1 can be released. Furthermore, the relative positions of the auxiliary cam 6 and the main cam 4 are arranged such that when the engine is stopped, the auxiliary cam 6 is delayed in phase by about 90 degrees with respect to the main cam 4, as shown in FIG. There is.

The centrifugal arm 10 is formed into a substantially dogleg shape with a lever portion 10a and a weight portion 10b, and a bent portion is pivotally supported on the side surface 5a of the gear 5 by a support shaft 8. The lever portion 10a projects in the axial direction of the camshaft 3, and its tip portion 10c is inserted into and engaged with an engagement recess 6b provided on the circumference of the auxiliary cam 6. The weight portion 10b is formed in an arc shape along the outer periphery of the gear 5. Further, a spring 12 is provided between the lever portion 10a of the centrifugal arm 10 and the locking shaft 11 provided on the side surface 5a of the gear 5.
is installed. The weight portion 10b of the centrifugal arm 10 is always urged toward the center of the camshaft 3 by the spring 12.

Note that the lever portion 10a of the centrifugal arm 10 is connected to the regulating pins 13a, 1 provided on the side surface 5a of the gear 5.
The rotation range is restricted by 3b. Symbol R in the diagram
is the rotation direction of the camshaft 3, symbol t is the main cam 4
The clearance between the tappet 1 and the tappet 1, symbol L is the base circle of the main cam 4 that includes this clearance t.

Next, the operation of the pressure reducing device having the above configuration will be explained with reference to FIG. Note that FIG. 3 shows the relationship between compression pressure and engine rotation speed.

Engine rotation speed at the start of engine startup (3rd
In range A) in the figure, the biasing force of the spring 12 overcomes the centrifugal force acting on the weight part 10b of the centrifugal arm 10, and the auxiliary cam 6 is at a position where the phase is delayed by about 90 degrees with respect to the main cam 4 (as shown in FIG. positional relationship)
It is rotated together with the main cam 4 while maintaining the main cam 4. Therefore, during the compression stroke, the action of the auxiliary cam 6 pushes up the intake valve 2 near the bottom dead center (compression start point) of the piston (not shown), and the intake valve 2 is pushed up near the bottom dead center (compression completion point) of the piston (not shown).
The intake valve 2 will be closed in the vicinity. While the piston moves from the bottom dead center to the top dead center, a considerable amount of the mixed gas in the syringe 14 (Fig. 2) escapes from the intake valve 2, so the compression pressure decreases and the recoil starter at the start of engine startup. The starting pulling force becomes lighter.

When the engine speed increases at the start of engine startup (range B in Figure 3), centrifugal arm 1
The centrifugal force acting on the weight portion 10b of the centrifugal arm 10 overcomes the biasing force of the spring 12, and the weight portion 10b of the centrifugal arm 10 begins to move away from the center of the camshaft 3. Along with this movement of the centrifugal arm 10, the auxiliary cam 6 is displaced in the direction Q (Fig. 1) in which the phase delay is reduced relative to the main cam 4. Therefore, during the compression stroke, the auxiliary cam 6 is The timing at which the intake valve 2 closes due to the action of the cam 6 is shifted from near the top dead center of the piston (not shown) to the bottom dead center. Therefore, the amount of mixed gas that escapes from the intake valve during the compression stroke decreases, and as the engine speed increases, the compression pressure within the cylinder 14 increases, increasing the compression pressure required for ignition (range C in Figure 3). approach. During this time, the starting resistance of the recoil starter gradually increases, but since the starting rope has momentum when pulled, even if the compression pressure increases, it will not be a burden to the operator.

At near the maximum engine rotation speed at the start of engine startup or at engine rotation speed during idling (range D in FIG. 3), the auxiliary cam 6
Furthermore, it is displaced in the direction Q (Fig. 1) in which the phase delay is reduced relative to the main cam 4, and the clearance t between the main cam 4 and the tappet 1 (Fig. 1).
Base circle L of main cam 4 including minutes (Fig. 1)
The auxiliary cam 6 is housed inside. Furthermore, the auxiliary cam 6 is also moved in the axial direction P of the camshaft 3 (in the direction away from the main cam 4) by the rotational sliding contact of the sliding slope 6a with the guide slope 4a.
The auxiliary cam 6 is withdrawn from below the tapepet 1.
Therefore, the mixed gas in the ricinder 14 is compressed to a normal compression pressure, and the engine is started.

When the engine is stopped, the centrifugal arm 10 returns to the position when the engine is stopped (Fig. 1) by the action of the spring 12, and the auxiliary cam 6 linked to the centrifugal arm 12 is also moved to the position when the engine is stopped (Fig. 1). and Fig. 2).

In addition, the straight line shown by the broken line in FIG. 3 shows an example in which the compression pressure increases almost at the same time as the engine starts rotating. In this way, at what stage of the engine rotation speed the compression pressure starts to increase can be determined by arbitrarily setting the biasing force of the spring 12 or the weight of the weight portion 10b.

Further, FIG. 4 shows the phase relationship between the cam (main cam) and the auxiliary cam, and the case where the phase curve of the auxiliary cam with respect to the phase curve of the cam is at position E corresponds to range A in FIG. The period during which the phase curve of the auxiliary cam relative to the phase curve of the cam is displaced in the S direction corresponds to range B in FIG. The case where the phase curve of the auxiliary cam with respect to the phase curve of the cam is at position F corresponds to range D in FIG.

By the way, in the above explanation of the operation, the auxiliary cam 6
It is actually difficult to adjust the timing and cam profile so that the main cam 4 falls within the base circle L of the main cam 4. For this reason, the structure is such that the auxiliary cam 6 is withdrawn from below the tappet 1 at the engine speed mentioned above.

In addition, in the above embodiment, an example was explained in which the intake valve 2 is opened and closed using the auxiliary cam 6, but the auxiliary cam 6
may be provided on a camshaft on the exhaust valve (not shown) side to open and close the exhaust valve. In this case, the auxiliary cam is arranged to be about 180 degrees behind the main cam.

Further, in addition to the gear 5 described above, the centrifugal arm may be pivoted to a support body separately fixed to the camshaft.

(Effects of the invention) As explained above, the pressure reducing device for an internal combustion engine of the invention rotates and displaces the auxiliary cam and moves it away from the main cam by the rotational action of the centrifugal arm. Since the compression pressure can be increased in proportion to the increase in engine speed due to the starter, the starting pulling force can be reduced and good ignition can be achieved. Furthermore, after the engine is started, the compression pressure in the cylinder can be reliably maintained at the normal pressure to ensure good ignitability and drivability. Therefore, the overall startability of the engine can be improved from the start of engine startup to the transition period to normal operation. Note that this pressure reducing device can also be applied to engines using an electric starter starting method.

[Brief explanation of the drawing]

The drawings illustrate an embodiment of the present invention, and FIG. 1 is a front view of the pressure reducing device, FIG. 2 is a side view of the same pressure reducing device, and FIG. 3 is an explanatory diagram showing the relationship between compression pressure and engine rotation speed. FIG. 4 is a curve diagram showing changes in the phase of the auxiliary cam with respect to the cam phase. 1... Tappet, 2... Intake valve, 3... Camshaft, 4... Main cam, 4a... Guide slope, 5...
...Gear, 6...Auxiliary cam, 6a...Sliding slope, 7
... Spring, 8 ... Support shaft, 10 ... Centrifugal arm, 10a ... Lever section, 10b ... Weight section, 12 ... Spring.

Claims (1)

[Claims for Utility Model Registration] A guide slope is provided on the camshaft and is inclined on one side with respect to a plane perpendicular to the axis of the camshaft, and the cam surface on the outer periphery applies cam force to the intake valve or exhaust valve. a main cam that opens and closes the intake valve or exhaust valve in a regular stroke by coming into contact with a cam force transmitting part that transmits a A sliding slope is formed on the side surface facing the guide slope and is inclined with respect to a plane perpendicular to the axis of the camshaft and slides in sliding contact with the guide slope, and the cam surface on the outer periphery is connected to the cam force transmitting portion. an auxiliary cam that contacts the camshaft to open and close the intake valve or exhaust valve during a compression stroke; a spring that presses the auxiliary cam so that its sliding slope contacts the guide slope of the main cam; a support that rotates integrally with the camshaft; a lever that is rotatably supported on the support and that engages with the auxiliary cam at one end of the pivot point; and a lever that engages with the auxiliary cam at the other end; The auxiliary cam has a weight part that rotates in a direction away from the center of rotation of the camshaft due to centrifugal force, and as the rotation of the camshaft increases during startup, the auxiliary cam closes the intake valve or the exhaust valve earlier. a centrifugal arm that rotates the auxiliary cam in a direction and moves the auxiliary cam in a direction away from the main cam by rotating and sliding in contact with the guide slope of the sliding slope so that the auxiliary cam is released from contact with the cam force transmission part; A pressure reducing device for an internal combustion engine, comprising: a spring that biases a weight portion of the weight portion in a direction toward a rotation center of a camshaft;