JPH04298617A - Decompression device - Google Patents

Abstract

PURPOSE:To provide a decompressor device for an engine capable of presenting the decompression function without increasing the kind of parts at the time of start-up and reverse rotation of the engine CONSTITUTION:Two decompression units are composed of same parts group. Each unit serves to control the rotation of a decompression shaft 37 arranged in parallel with a cam shaft 7 to rotate freely together with the shaft 7 as one body and prejecting and retreating a decompression cam 47 from cam base faces 25, 26 of intake and exhaust cams 15, 16, by means of a centrifugal lever 39 extending in the centrifugal direction with centrifugal force while rotating together with the cam shaft 7 as one body. These decompression units are arranged in the axial direction of the cam shaft 7 in a face-to-face relation therewith as decompression units for start-up and reverse rotation 32, 33.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine decompression device.

0003

[Prior Art] For example, when starting a four-cycle gasoline engine for a motorcycle, the crankshaft is rotated in run-up by external power such as a starter motor or kick starter until the engine starts rotating on its own, and the mixture is sucked and compressed. , ignition, and exhaust strokes.

However, the reaction force of the crankshaft during the compression stroke is strong, and a small starter motor installed in the limited space of a motorcycle or a human-powered kick starter is ineffective, so depending on the type of motorcycle, the reaction force of the crankshaft is strong. Some engines are difficult to start because the shaft cannot be rotated fast enough.

[0005] This tendency becomes more pronounced as the engine displacement per cylinder becomes larger, and the engine has a larger displacement and fewer cylinders. Therefore, such engines are often equipped with a starting decompression device.

Most starting decompression devices are mounted on the camshaft, and during the run-up rotation of the crankshaft when starting the engine, the decompression cam is protruded onto the cam base surface of the camshaft, and the valves that should normally be closed are slightly opened. It is something that can be done.

[0007] As a result, the air-fuel mixture leaks out of the cylinder during the compression stroke, the compression pressure is lowered, and the reaction force of the crankshaft is reduced. Therefore, the load on the external power for starting the engine is reduced, making it easier to start the engine.

When the engine starts and the rotational speed of the camshaft increases, the starting decompression device uses centrifugal force to immerse the decompression cam under the cam base surface of the camshaft to stop the leakage of the intake air-fuel mixture. It is designed to restore proper compression pressure to the engine.

[0009]

[Problems to be Solved by the Invention] A starting decompression device is effective for improving engine startability, but when the engine suddenly rotates in reverse due to abnormal combustion etc. during low speed rotation after starting, a similar decompression device is required. It does not function to prevent engine damage.

[0010] To compensate for this, a decompression device for reversing has been developed, but the conventional decompression device for reversing has a greatly different structure from that of a decompression device for starting. The number of types of parts increased, which led to an increase in costs.

The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an engine decompression device that can perform a decompression function both when starting the engine and when reversing the engine without increasing the number of types of parts. With the goal. [Structure of the invention]

0012

[Means for Solving the Problems] In order to achieve the above object, an engine decompression device according to the present invention is provided parallel to a camshaft so as to be able to rotate integrally with the camshaft, and the cam base of the intake and exhaust cams is rotated by rotational displacement. Two decompression devices are constructed from the same group of parts, each having a decompression shaft that causes a decompression cam to move in and out of the surface, and a centrifugal lever that rotates together with the camshaft and controls the rotation of the decompression shaft using centrifugal force. One of the two decompression devices is a starting decompression device and the other is a reversing decompression device, which are installed opposite each other in the axial direction of the camshaft.

[0013]

[Operation] By configuring the engine decompression device in this manner, the parts of the decompression device for starting and reversing are made common, reducing the number of types of parts and contributing to cost reduction.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a left side view of a motorcycle equipped with an engine decompression device according to the present invention.

This motorcycle 1 has a single-cylinder engine 3 mounted near the front of a body frame 2, and a chain 4.
The rear wheels 5 are driven by the rear wheels 5.

FIG. 2 is a longitudinal sectional view of the engine 3 shown in FIG. This engine 3 is of an overhead cam type in which an intake valve 8 and an exhaust valve 9 are opened and closed by a camshaft 7 rotatably supported within a cylinder head 6.

The intake and exhaust valves 8 and 9 are biased by strong double coiled valve springs 10 and 11 in a direction that always closes the intake and exhaust ports 12 and 13, thereby sealing the combustion chamber 14. .

An intake cam 15 and an exhaust cam 16 are integrally provided on the camshaft 7 at a predetermined angle, and rocker arms 17 and 18 are mounted on the intake and exhaust cams 15 and 16. Shaft 19, 20
It is pivoted so that it can swing freely using the fulcrum.

Both ends of the rocker arms 17 and 18 rest on the upper ends of the intake and exhaust cams 15 and 16 and the intake and exhaust valves 8 and 9, respectively, and as shown in FIG.
The portions where 7 and 18 contact the intake and exhaust cams 15 and 16 form smooth rocker floor surfaces 21 and 22.

On the other hand, the other end sides of the rocker arms 17 and 18 are tappet parts 23 and 24, and by adjusting these parts with screws, the rocker floor surfaces 21 and 22 can be adjusted to the cam base surfaces 25 and 25 of the intake and exhaust cams 15 and 16, respectively. 26 (the surface on which the ridges 27 and 28 of the intake and exhaust cams 15 and 16 are not raised) is provided with a small gap (about 0.1 to 0.2 mm).

The camshaft 7 is rotated in conjunction with the crankshaft 29 in FIG. 2 by a transmission means such as a chain (not shown), and rotates forward (rotates to the left in the figure) at half the rotation speed of the crankshaft 29.

When the camshaft 7 rotates, the peaks 27 and 28 of the suction and exhaust cams 15 and 16 move toward the rocker arms 17 and 16, respectively.
18, the tappet parts 23 and 24 of the rocker arms 17 and 18 descend to push down the intake and exhaust valves 8 and 9, and the combustion chamber 14 is opened.

[0024] When the intake valve 8 is opened in this way,
The crank is configured so that as the piston 30 descends, the air-fuel mixture flows into the cylinder 31 from the intake port 12, and when the exhaust valve 9 opens, the exhaust gas in the cylinder 31 is discharged to the exhaust port 13 as the piston 30 rises. Shaft 29 and camshaft 7 are timed.

FIG. 4 is a view of the camshaft 7 shown in FIG. 3 in the direction of arrow A, and FIG. 5(a) is a sectional view taken along line BB in FIG.
FIG. 5(b) is a sectional view taken along line CC in FIG. still,
The intake cam 15 and intake cam 16 shown in FIG. 4 are oriented in the same direction for clarity of drawing.

This camshaft 7 has a camshaft 7
Two decompression devices 32 and 33, which rotate integrally with each other and are constructed from the same group of parts, are installed facing each other in the axial direction of the camshaft 7. One of the decompression devices is used as a starting decompression device 32, and the other is a reversing decompression device 33.
It is established as

The starting decompression device 32 is installed, for example, on the inner surface of a cam driven gear (or sprocket) 34 that rotates the camshaft 7 in conjunction with the crankshaft 29, and faces the exhaust cam 16. On the other hand, the reverse rotation decompression device 33 is installed on the inner surface of a mount plate 35 fixed to the camshaft 7 and faces the intake cam 15. In accordance with the rotational direction D of the camshaft 7, the starting decompression device 32 rotates, for example, to the left, and the reversing decompression device 33 rotates, for example, to the right, as shown in FIGS. 5(a) and 5(b).

The starting decompression device 32 and the reversing decompression device 33 each include a decompression bracket 36, a decompression shaft 37, a pin 38, a centrifugal lever 39, a return spring 40, etc. (FIG. 4)
, the return spring 40 is omitted).

The decompression bracket 36 is manufactured by pressing sheet metal, for example, and is formed by bending a U-shaped retainer portion 41 and two stoppers 42, 43 inward, and further includes an arm 44. ing. The decompression bracket 36 is caulked and fixed to the cam driven gear 34 and the mount plate 35 by, for example, two rivets 45 (the rivets 45 are omitted in FIG. 4 for clarity of drawing).

The decompression shaft 37 is in the shape of a round bar as shown in FIG.
6 is processed, and a decompression cam 47 is formed.

The camshaft 7 includes intake and exhaust cams 15,
16 cam base surfaces 25, 26 are partially cut out,
A recessed surface 48 parallel to the axis is formed, and the decompression shaft 37 is placed on this recessed surface 48 with its decompression cam 47 side facing toward the exhaust cams 15 and 16. The decompression shaft 37 is connected to the retainer portion 41 of the decompression bracket 36 and the cam driven gear 3.
The cam base surface 25 of the intake and exhaust cams 15 and 16 is provided parallel to the camshaft 7 and rotatable together with the camshaft 7 by being inserted into a bearing hole 49 bored in the camshaft 4 and the mount plate 35. Decompression cam 4 on 26
7 appears. Here, the decompression cam 47 overlaps the intake and exhaust cams 15 and 16 by an amount F out of the thickness E thereof.

The pin 38 is provided to protrude perpendicularly to the axis of the decompression shaft 37, and comes into contact with the stoppers 42, 43 of the decompression bracket 36 as the decompression shaft 36 rotates, thereby regulating the rotation range of the decompression shaft 37. There is.

The centrifugal lever 39 has a crescent shape,
The base end portion thereof is caulked to the cam driven gear 34 or the mount plate 35 by, for example, a rivet 50, and is locked so as to be swingable in the centrifugal direction. Further, a hook-shaped hook 51 is formed on the free end side of the centrifugal lever 39.
The pin 38 is clamped.

The centrifugal lever 39 rotates together with the camshaft 7 to expand in the centrifugal direction, and controls the rotation of the decompression shaft 37 as described below.

First, when the camshaft 7 is stopped or rotating at a very low speed, the centrifugal lever 39 is pulled toward the camshaft 7 by the return spring 40 suspended between the arm 44 of the decompression bracket 36. , the pin 38 held by the hook 51 is brought into contact with the stopper 42. Therefore, the flat surface 46 of the decompression cam 47 stands upright, and the cam base surfaces 25, 2 of the intake/exhaust cams 15, 16
6, the decompression cam 47 protrudes by G and H, and the rocker arms 17 and 18 that slide on the cam base surfaces 25 and 26 are pushed up by that amount (however, the rocker arms 17 are pushed up when the camshaft 7 is reversed). ,
The rocker arm 18 is pushed up when the camshaft 7 rotates normally).

Further, when the rotation of the camshaft 7 becomes faster, the starting decompression device 32 and the reversing decompression device 3
A centrifugal force is applied to the pin 3 held by the hook 51, and the centrifugal lever 39 opens in the centrifugal direction against the force of the return spring 40, as shown in FIGS.
8 is brought into contact with the stopper 43 side. Therefore, the decompression shaft 37 is rotationally displaced, and the decompression cam 47 is sunk below the cam base surfaces 25 and 26 of the intake and exhaust cams 15 and 16. Therefore, the rocker arms 17 and 18 are connected to the intake and exhaust cams 15.
, 16 slides on the cam base surfaces 25, 26 without being pushed up.

The starting decompression device 32 and the reversing decompression device 33 operate as follows depending on the operating condition of the engine 3.

First, when starting the engine 3, the camshaft 7 starts rotating at a very low speed in conjunction with the crankshaft 29 rotated by a kick starter or the like. The decompression cam 47 remains protruding from the cam base surface 26 of the exhaust cam 16, and the rocker arm 18 rides on the decompression cam 47 every time the exhaust cam 16 rotates and is pushed up by H. Therefore, the exhaust valve 9 shown in FIG. 2 opens slightly into the combustion chamber 14, and a portion of the compressed air-fuel mixture leaks into the exhaust port 13, so that the reaction force of the crankshaft 29 is significantly reduced. Therefore, the crankshaft 29 can be given a sufficiently fast run-up rotation even by a kick starter or a small starter motor, making it very easy to start the engine 3.

Then, when the engine 3 starts and the rotational speed of the camshaft 7 increases, the starting decompression device 32
When centrifugal force is applied to the pin 38, the pin 38 is pulled by the hook 51 of the centrifugal lever 39 and comes into contact with the stopper 43 as shown in FIG. to die in Therefore, rocker arm 18
slides along the natural cam profile of the exhaust cam 16 and provides the engine 3 with the appropriate compression pressure.

Next, when the engine 3 is started, the reversing decompression device 33 has a decompression cam 47 projected above the cam base surface 25 of the intake cam 15 as shown in FIG. , since the rotation direction is opposite to that of the starting decompression device 32, the decompression cam 47
The flat part 46 is pushed back by the rocker arm 17,
It rotates and sinks below the cam base surface 25. Therefore, the rocker arm 17 does not rise above the original cam profile of the intake cam 15.

After the engine 3 is started, the rotational speed of the camshaft 7 increases, so the reversing decompression device 33
Centrifugal force is applied to the pin 38 as shown in Figure 10(b).
is pulled by the hook 51 of the centrifugal lever 39 and comes into contact with the stopper 43, and the decompression cam 47 sinks below the cam base surface 25 of the intake cam 15.

Furthermore, if the engine 3 suddenly rotates in reverse at low speed, for example, the centrifugal lever 39, which had expanded in the centrifugal direction as shown in FIGS. 8(a) and 8(b), immediately returns to the camshaft 7 side due to inertia. Release the pin 38 held by the hook 51 from the stopper 43 as shown in FIG.
2. Therefore, the decompression cam 47 protrudes above the cam base surface 25 of the intake cam 15, and the rocker arm 17 rides on it and is pushed up by G. For this reason,
The intake valve 8 shown in FIG. 2 opens into the combustion chamber 14 and allows the expanded gas to escape to the intake port 12, so that the engine 3 immediately stops. This prevents the engine 3 from rotating in reverse and being damaged.

In the engine decompression device constructed in this manner, the starting decompression device 32 and the reversing decompression device 33 are constructed from the same group of parts, so the number of types of parts can be reduced, resulting in low cost. It can be implemented in

[0044] The engine 3 is then easily started, and the engine 3 is protected by reliably preventing reverse rotation.

[0045]

As explained above, the engine decompression device according to the present invention is provided parallel to the camshaft so as to be able to rotate integrally therewith, and the decompression cam is moved in and out of the cam base surface of the intake and exhaust cams by rotational displacement. Two decompression devices each having a decompression shaft and a centrifugal lever that rotates together with a camshaft and controls the rotation of the decompression shaft by centrifugal force are constructed from the same group of parts,
One of the two decompression devices mentioned above is a starting decompression device and the other is a reversing decompression device, and they are installed facing each other in the axial direction of the camshaft, so they can have both starting and reversing functions at low cost without increasing the number of parts. It is possible to provide an engine decompression device comprising:

[Brief explanation of drawings]

FIG. 1 is a left side view of a motorcycle equipped with an engine decompression device according to the present invention.

FIG. 2 is a longitudinal sectional view of the engine shown in FIG. 1.

FIG. 3 is an enlarged view of the camshaft, intake and exhaust valves, and rocker arm shown in FIG. 2;

FIG. 4 is a view taken along arrow A of the camshaft shown in FIG. 3, and is a front view showing an embodiment of the engine decompression device according to the present invention.

5(a) is a view taken along line B-B in FIG. 4, and (b) is a view taken along line C-C in FIG. 4. FIG.

FIG. 6 is a perspective view showing detailed shapes of a decompression shaft, a camshaft, a decompression bracket, etc.

FIG. 7 is a front view showing the operating state of the engine decompression device according to the present invention.

8(a) is a view taken along the line II in FIG. 7, and (b) is a view taken along the line JJ in FIG. 7. FIG.

[Fig. 9] (a) shows K- in Fig. 4 at the time of starting the engine.
A sectional view taken along line K, and (b) a sectional view taken along line LL in FIG. 7 after starting the engine.

[Fig. 10] (a) shows M in Fig. 4 at the time of starting the engine.
- A sectional view taken along the line M, (b) a sectional view taken along the line NN in FIG. 7 after the engine is started, and (c) a sectional view taken along the line MM in FIG. 4 when the engine is reversed.

[Explanation of symbols]

7 Camshaft 15 Intake cam 16 Exhaust cam 17,18 Rocker arm 25, 26 Cam base surface 32　Starting decompression device 33　Reverse decompression device 34 Cam driven gear 35 Mount plate 36 Decompression bracket 37 Decompression shaft 38 pin 39 Centrifugal lever 40 Return spring 41 Retainer part 42, 43 Stopper 44 Arm 47 Decomp cam 51 Hook

Claims (1)

[Claims] Claim 1: A decompression shaft that is provided parallel to and rotatable together with the camshaft, and that causes a decompression cam to move in and out of the cam base surface of the suction and exhaust cams by rotational displacement; Two decompression devices each having a centrifugal lever that controls the rotation of the decompression shaft are constructed from the same group of parts. An engine decompression device characterized by being installed facing each other in the axial direction.