JPH04191408A - Automatic decompression device for four-cycle engine - Google Patents

Abstract

PURPOSE:To carry out operation with normal compressive pressure by projecting a decompression cam at the time of starting an engine, releasing the compressive pressure, cranking a crank shaft with a light force, and lowering the decompression cam by means of a centrifugal weight in accordance with increasing of rotational number of a cam shaft. CONSTITUTION:An intake cam 4, for instance, is provided on a cam shaft 2, while the intake cam 4 presses up an intake rocker arm 6 to open an intake valve. A decompression cam 4 formed with a long hole 12 is provided, and the cam shaft 2 is inserted into the long hole 12 such that the decompression cam 13, arranged adjacently to the intake cam 4, abuts against the intake rocker arm 6. The decompression cam 13 is fixed rotatably within the range of the long hole 12 by means of a pin 14 projected to an outer periphery of the cam shaft 2. A spring 15 is inserted into a hole of the cam shaft 2 so as to energize the decompression cam 13 in one direction in the long hole 12 and project it from a profile of the intake cam 4. An outward-projecting centrifugal weight 16 is integrated with the decompression cam 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an auto-decompression device for a four-stroke engine.

[Conventional technology]

A four-cycle engine operates by opening and closing intake and exhaust valves in conjunction with the reciprocating motion of a piston, using an intake and exhaust cam on a camshaft that is linked to the crankshaft. When starting an engine, it is difficult to start if the compression pressure is high from the beginning, so a decompression device is installed to reduce the pressure and allow the crankshaft to rotate easily.
Once the engine has gained inertia during cranking, the decompression device is stopped, allowing the engine to start and run.

An automatic decompression device that uses centrifugal force is convenient. For example, see JP-A-60-40715 and JP-A-62-261610.

[Problem to be solved by the invention]

The auto decompression device works automatically at startup and is convenient because there are no operating points. However, it uses a governor, has a double-track structure, has many parts, and is expensive. Furthermore, in the case where the pin of the camshaft is placed on the decompression cam to perform decompression, the contact area of the pin is increased and the surface pressure is increased, which poses a problem in terms of durability when used repeatedly.

In view of the above, an object of the present invention is to provide an autodecompression device for a four-cycle engine that has a small number of parts, is low cost, has high durability, and is reliable.

[Means to solve the problem]

In order to achieve the above object, the auto decompression device for a four-cycle engine of the present invention has the long hole of the decompression cam inserted into the camshaft in line with the intake cam of the camshaft so as to hit the intake port/tsuka arm. It is fixed with a pin in one place so that it can be rotated, and the elongated hole is biased to one side by a spring so that the decompression cam protrudes.A centrifugal weight is provided on the decompression cam, and when the rotation of the camshaft increases, the centrifugal weight moves the elongated hole into a spring. The reason is that the decombination cam is lowered by rotating it in the other direction.

[Effect]

When starting the engine, the decombination cam is biased by a spring toward one side of the elongated hole, and while the decombination cam protrudes and the intake rocker arm is pushed up, the intake valve is opened extra. The compression pressure is released and the crankshaft can crank easily. Then, when the crankshaft starts rotating and the camshaft rotation increases,
The centrifugal force of the centrifugal weight of the decompression cam increases, and the decompression cam is rotated to the other side of the long hole by centrifugal force against the spring, lowering the decompression cam, so that the decompression cam no longer works, and the start operation can be started at normal pressure. .

〔Example〕

Hereinafter, the present invention will be explained with reference to embodiments shown in the drawings.

A camshaft 2 is mounted on a cylinder head 1 of a four-cycle engine, and is linked to a crankshaft by a chain or timing belt 3. The camshaft 2 is provided with an intake cam 4 and an exhaust cam 5, and the intake cam 4 pushes up an intake port/lock arm 6 to open an intake valve 8 of an intake hole 7. Further, the exhaust cam 5 pushes up the exhaust rocker arm 9 and opens the exhaust valve 11 of the exhaust hole 10.

On the other hand, the present invention provides a decompression cam 13 having a long hole 12, and inserts the long hole 12 into the camshaft 2 so that the decompression cam 13 or the intake rocker arm 6 is aligned with the intake cam 4. A pin 14 protruding from the outer periphery of the camshaft 2 is fixed so that the decompression cam 13 can rotate within the range of the elongated hole 12. A spring 15 is inserted into the hole of the camshaft 2, and the spring 15 urges the decombination cam 13 toward one side of the elongated hole 12, causing the decombination cam 13 to protrude from the profile of the intake cam 4.

(See Figure 1) At this time, the intake rocker arm 6 is
In addition to being pushed up by intake cam 4, decompression cam 1
3 is also pushed up, releasing the compression pressure and allowing the crankshaft to crank lightly. The decompression cam 13 is integrally provided with a centrifugal weight 16 that projects outward.

When the crankshaft rotates and the rotation of the camshaft 2 increases, the centrifugal force of the centrifugal weight 16 increases, causing the decompression cam 13 to rotate toward the other side of the elongated hole 12 against the spring 15. Lower it to within the profile of 4. (See FIG. 2) In this way, the intake rocker arm 6 is pushed up only by the intake cam 4, a normal compression pressure is obtained, and operation is started.

〔Effect of the invention〕

As explained above, since the present invention is configured as described above, the decompression cam protrudes when the engine is started, the compression pressure is released, and the crankshaft can be cranked with a light force. Then, when inertia is built up due to cranking and the rotation of the camshaft increases, the decompression cam is rotated and lowered by the centrifugal weight, the decompression cam stops working, and operation can be shifted to normal compression pressure.

The decombination cam uses a spring and a centrifugal weight to move from one side of the long hole to the other, and is highly durable because there are no pins or other places where strong force is applied. Furthermore, the centrifugal weight can be integrally provided with the decompression cam, reducing the number of parts and making it possible to produce the product at low cost.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention. Fig. 1 is a side view of the main part when the decompression cam is in operation, Fig. 2 is a side view of the main part when the decompression cam is not in operation, and Fig. 3 is the decompression cam alone. FIG. 4 is a vertical sectional side view, and FIG. 5 is a front view taken along line A-A in FIG. 4. 2...Camshaft, 4...Intake cam, 6...Intake rocker arm, 12...Elongated hole, 13...Decombination cam, 14...Bin, 15...Spring, 16...・
Centrifugal weight. Applicant's agent Hiroshi Fujimoto Tip rod Figure 4 Figure 5

Claims (1)

[Claims] Align the decompression cam with the intake cam of the camshaft so that it hits the intake rocker arm, insert the long hole of the decompression cam into the camshaft, fix it with a pin so that it can rotate freely, and push the long hole to one side so that the decompression cam protrudes with a spring. A four-cycle engine is provided with a centrifugal weight on the decompression cam, and when the rotation of the camshaft increases, the centrifugal weight rotates a long hole in the other direction against a spring to lower the decompression cam. auto decompression device.