JPH0244007Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to an automatic pressure reduction device for an engine that automatically reduces compression pressure at the time of starting and reduces the power required for starting.

Conventional technology Conventionally, in an engine having a valve mechanism,
In order to reduce the power required for starting, the engine is equipped with an automatic pressure reducing device that automatically reduces the compression pressure at the time of starting. A typical automatic pressure reducing device is one that utilizes the difference between the centrifugal force of a weight and the biasing force of a spring. That is, during startup when centrifugal force is small, a protrusion is projected from the outer circumferential surface of the cam by the biasing force of the spring, and the protrusion is brought into contact with the raceway surface of a valve operating member such as a tappet, thereby reducing the pressure during the compression stroke. At this time, the valve is opened to reduce the compression pressure, and at high speeds, the protrusion is retracted into the outer peripheral surface of the cam by the centrifugal force of the weight against the biasing force of the spring.

In addition, as other automatic decompression devices,
As described in Publication No. 171911, the thrust of a helical gear is used to slide the camshaft in the axial direction, and at low starting speeds, a pressure reducing cam integrally formed on the camshaft is brought into contact with the raceway surface of the tappet. Some tappets make contact with each other to reduce the compression pressure, and at high speeds the pressure reducing cam is separated from the tappet raceway surface.

Problems that the invention aims to solve: In a device that uses the difference between the centrifugal force of the weight and the biasing force of the spring to make protrusions appear and retract from the outer circumferential surface of the cam, the force of the valve spring is applied directly to the weight via the tappet. In order to prevent this from occurring, a fulcrum shaft is provided separately from the fulcrum shaft of the weight, and various link mechanisms are used to change the operating direction of the protrusion relative to the direction in which the force of the valve spring is applied. Therefore, the number of parts has increased, the structure has become more complex, and manufacturing costs have increased. Furthermore, a large space is required to install the link mechanism, which increases the size and weight of the entire engine. Furthermore, a large centrifugal force is required to move a link mechanism with a complex structure, and with the generation of this large centrifugal force, a large force acts on the fulcrum shaft, which can easily wear out and cause failure. There are drawbacks such as:

Furthermore, although the automatic pressure reducing device described in Japanese Utility Model Application Publication No. 171911/1983 has a simple structure, the thrust of the helical gear changes depending on the force applied to the tooth surface, and changes with the engine speed. There is no exact proportional relationship. For this reason, the pressure may not be reduced at the time of starting, or the reduced pressure state may not be released even after starting, resulting in a decrease in engine output.

This invention has been made in view of the above points, and the object thereof is to provide an automatic engine pressure reduction device that can reliably perform automatic pressure reduction of compression pressure at the time of startup with a simple structure.

Means for Solving the Problem A pressure reducing cam protruding from the outer circumferential surface of the cam by a predetermined distance is provided close to the cam shaft having a cam that comes into contact with the raceway surface of the valve operating member, and the cam shaft is connected to the pressure reducing cam. The cam is slidably provided at a position where the cam contacts the raceway surface of the valve operating member and a position where it separates from the raceway surface of the valve operating member, and the cam is provided at a position where the pressure reducing cam contacts the raceway surface of the valve operating member. A biasing body for sliding the shaft is provided, a plurality of grooves are formed radially in the central part of the camshaft and the depth becomes shallower toward the outer end, and a steel plate is provided in which the grooves are in contact with the thrust receiving part. The balls were stored in a movable manner.

Effect When the engine starts, the centrifugal force is small, so
The camshaft is slid by the biasing force of the biasing body, and the pressure-reducing cam comes into contact with the raceway surface of the valve operating member, whereby the valve operating member is pushed up by a predetermined amount compared to when the cam is in contact with the valve operating member. During the compression stroke, the valve is opened and the compression pressure is reduced.
After starting, as the rotation speed increases and the centrifugal force increases, the camshaft is slid by the actuating body,
The pressure reducing cam separates from the raceway surface of the valve operating member, and only the cam comes into contact with the raceway surface of the valve operating member, and the valve is no longer opened during the compression stroke, allowing a sufficiently high compression pressure to be obtained. The steel ball that slides the camshaft is installed in a groove formed radially in the center of the camshaft, so the camshaft slides smoothly and is precisely proportional to the engine speed. This is something that can be made to perform certain movements.

Embodiment An embodiment of this invention will be described based on the drawings. A camshaft 5 is provided so as to be rotatable around its axis, with one end inserted into a bearing hole 2 formed in a crankcase 1 and the other end inserted into a bearing hole 4 formed in a crankcase cover 3. The camshaft 5
A cam 8 is integrally formed on the cam 8, which abuts against a raceway surface 7 of a tappet 6, which is a valve operating member that slides back and forth in conjunction with the opening and closing of a valve (not shown). Further, a pressure reducing cam 9 is integrally formed on the camshaft 5 at a position close to the cam 8, and the outer peripheral surface of the pressure reducing cam 9 is larger than the outer peripheral surface of the cam 8 by a predetermined dimension α.
It is set prominently.

The camshaft 5 is provided so as to be slidable within a predetermined dimension β in the axial direction, and an air vent hole 10 is formed in the bearing holes 2 and 4 to allow the camshaft 5 to slide smoothly. ing. One end of the camshaft 5 is marked with an arrow A.
A spring 11, which is a biasing body that biases in the direction, is attached. A cam gear 12 is integrally formed at the other end of the camshaft 5, and a plurality of grooves 13 are formed radially in the center of the cam gear 12.
is formed. A steel ball 14 as an actuating body is movably housed in each groove 13, and the crankcase cover 3 has a thrust receiver that acts as a thrust receiver to prevent the steel ball 14 from slipping out of the groove 13. A plate 15 is fixed. Further, the depth of the groove 13 is set to become shallower toward the outer end. The cam gear 12 meshes with a timing gear 17 that is integrally formed with a crankshaft 16 that rotates with an axis parallel to the camshaft 5.

In such a configuration, FIG. 1 shows the state before the engine is started, and the camshaft 5 slides in the direction of arrow A by the urging force of the spring 11.
The pressure reducing cam 9 is attached to the raceway surface 7 of the tappet 6 by a predetermined dimension γ.
are in contact. Note that this predetermined dimension γ is the camshaft 5.
is set smaller than a predetermined slideable dimension β. Further, the steel ball 14 is located at the innermost end of the groove 13.

When the engine is started, the rotational speed of the camshaft 5 is low and the centrifugal force acting on the steel balls 14 is also small, so the steel balls 14 are maintained approximately at the position shown in FIG. 1. Therefore, at the time of starting at a low rotational speed, the pressure reducing cam 9 comes into contact with the raceway surface 7 of the tappet 6 at a predetermined timing and pushes the tappet 6 up by a predetermined distance α. Due to this pushing up, the valve is opened with a predetermined gap in the middle of the compression stroke, and the compression pressure is reduced. Therefore, the power required for starting is reduced, and especially in an engine that is started by manually rotating the crankshaft 16, starting can be easily performed.

Next, as the rotational speed of the camshaft 5 increases after starting, the centrifugal force acting on the steel ball 14 also gradually increases, and the steel ball 14 moves toward the outer end of the groove 13. The depth of the groove 13 becomes shallower toward the outer end, and one side of the steel ball 14 is in contact with the thrust plate 15, so that the steel ball 1
4 moves toward the outer end of the groove 13, the camshaft 5 slides in the direction of arrow B against the biasing force of the spring 11. Then, when the rotational speed of the camshaft 5 reaches a predetermined rotational speed and the centrifugal force acting on the steel ball 14 exceeds a predetermined value, the sliding dimension of the camshaft 5 in the direction of arrow B becomes a predetermined dimension γ or more, and the pressure is reduced. The cam 9 separates from the raceway surface 7 of the tappet 6, and the pressure reducing operation by the pressure reducing cam 9 is released. Therefore, the valve is not opened during the compression stroke during high-speed operation, and a sufficiently high compression pressure is ensured during high-speed operation, so that the output performance of the engine is not impaired. In addition, steel ball 14
Since there is a proportional relationship between the centrifugal force acting on the camshaft 5 and the number of revolutions of the camshaft 5, the number of revolutions of the camshaft 5 and the sliding dimension of the camshaft 5 in the direction of arrow B are proportional, and the decompression operation is set to be released. Can be performed accurately at rotational speed.

When the engine is stopped, the rotational speed of the camshaft 5 decreases, and the centrifugal force acting on the steel balls 14 also decreases, causing the steel balls 14 to move toward the inner end of the groove 13. That is, since the steel ball 14 moves to a deeper position in the groove, the camshaft 5 slides in the direction of arrow A by the biasing force of the spring 11. When the engine is stopped, the pressure reducing cam 9 returns to the state in which it contacts the raceway surface 7 of the tappet 6, as shown in FIG. Therefore, even at the time of restarting, the compression pressure is reduced by the pressure reducing cam 9, and restarting can be easily performed. Note that when the camshaft 5 is sliding, the air and lubricating oil in the bearing holes 2 and 4 are released from the air vent hole 10, so that the camshaft 5 can slide smoothly.

In this example, a steel ball 1 is used as the actuating body.
4 was used, but the centrifugal force is converted into thrust and the camshaft 5 is
It may be any mechanism that slides, and may be a weight type or other mechanism.

Effects of the invention As described above, this invention provides a camshaft having a cam that comes into contact with the raceway surface of a valve operating member, and a pressure-reducing cam protruding from the outer peripheral surface of the cam by a predetermined distance close to the cam. is provided so as to be slidable between a position where the pressure reducing cam contacts the raceway surface of the valve operating member and a position where it separates from the raceway surface of the valve operating member,
A biasing body for sliding the camshaft is provided at a position where the pressure reducing cam comes into contact with the raceway surface of the valve operating member, and a plurality of biasing bodies are provided in the center of the camshaft and the depth becomes shallower toward the outer end. The grooves are formed radially, and the steel balls that contact the thrust receiver are movably housed in these grooves, so when the engine is started, the camshaft is moved by the biasing force of the biasing body because the centrifugal force is small. As the pressure reducing cam slides, it comes into contact with the raceway surface of the valve train member, and as a result, the valve train member is pushed up a predetermined distance compared to when the cam is in contact with it, and the valve is opened in the middle of the compression stroke, causing compression. When the pressure is reduced and the centrifugal force increases as the rotation speed increases after startup, the camshaft is slid by the actuating body, and the pressure reducing cam is separated from the raceway surface of the valve train member, leaving only the cam on the raceway surface of the valve train member. contact, the valve does not open during the compression stroke, and a sufficiently high compression pressure is obtained.Moreover, the steel balls that slide the camshaft fit into the grooves radially formed in the center of the camshaft. Because of this provision, the sliding movement of the camshaft can be performed smoothly, and furthermore, it has the effect of being able to perform a movement that is accurately proportional to the rotational speed of the engine.

[Brief explanation of the drawing]

The drawing shows one embodiment of this invention.
The figure is a vertical side view, FIG. 2 is a front view of the cam gear, and FIG. 3 is a sectional view taken along line CC in FIG. 1. 5... Camshaft, 6... Tappet (valve train member),
7... Raceway surface, 8... Cam, 9... Decompression cam, 1
1... Spring (biasing body), 14... Steel ball (operating body).

Claims (1)

[Scope of utility model registration request] A camshaft having a cam that contacts the raceway surface of the valve operating member is provided with a pressure reducing cam protruding by a predetermined distance from the outer circumferential surface of the cam in close proximity to the cam, an urging body that is slidably provided in a position where it contacts the raceway surface of the valve operating member and a position where it separates from the raceway surface of the valve operating member, and slides the camshaft to a position where the pressure reducing cam contacts the raceway surface of the valve operating member; A plurality of grooves are formed radially in the center of the camshaft and the depth becomes shallower toward the outer end, and a steel ball that contacts the thrust receiving portion is movably housed in these grooves. An automatic engine decompression device featuring: