JPH0721845Y2 - Decompression device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a decompression device used when starting an internal combustion engine.

[Conventional technology]

As an example of the prior art, the decompression device described in Japanese Utility Model Application No. 63-153474 is shown in FIGS. 5 and 6. FIG. 5 is a front view of a longitudinal cross section of the main part around the cam. FIG. 6 shows a flyweight, a decompression pin, and an actuating spring when the ZZ section of FIG. 5 is viewed from right to left (viewed from the arrow).

In FIG. 5, reference numeral 1 is a crankshaft, and a gear 6 is attached to the shaft 1.
Is fixed. 2 is a cam shaft, and 2 cams 4 are provided on this shaft 2.
It is composed as a unit. The cam 4 is for opening and closing the intake valve and the exhaust valve, and the tapette 3 is located in the middle thereof to transmit the reciprocating motion to the intake / exhaust valve in accordance with the intake / exhaust timing. A cam gear 5 is mounted on the cam shaft 2.
Is fixed. Further, the cam shaft 2 has a hole 7 that obliquely penetrates it.
The pin 8 is inserted into the hole 7 and has a gap that can move in the penetrating direction of the hole 7. 5 is a cam gear, which meshes with the gear 6 (meshing ratio is 1/2 reduction).

A pin 11 is fixed to the gear 5 as shown in FIG.
A flyweight 13 is supported so as to be able to rotate around the pin 11, and the amount of movement of the flyweight 13 is limited by a pin 14 also fixed to the gear 5. This flyweight
13 is the same flyweight as the pin 16 fixed to the gear 5.
A tension spring 15 is stretched between the two to pull the flyweight 13 against the centrifugal force generated when the shaft 2 rotates. Decompression pin 8 is attached to the free end of this flyweight 13.
When the spring 15 is effective, the decompression pin 8 is pushed out to the decompression position, and when the centrifugal force exceeds the spring force, the pin 8 retracts and acts so as to lose the decompression function.

The position of the flyweight 13 is at the position shown by the solid line in FIG. 6 when the internal combustion engine is stopped and when the centrifugal force of the flyweight 13 is smaller than the tension of the tension spring 15 due to low rotation of the internal combustion engine. At this time, the decompression pin 8 is supported by the surface 9 of the flyweight 13, and at this position, the decompression pin 8 plays the role of a cam that pushes up the taper of the intake valve or the exhaust valve, and the pressure of the combustion chamber in the compression stroke of the internal combustion engine. Depressurize.

When the rotation of the internal combustion engine, that is, the rotation of the crankshaft 1 and the camshaft 2 is increased, the centrifugal force of the flyweight 13 causes the tension spring 15 to rotate.
6, the flyweight 13 in FIG. 6 moves to the position indicated by the chain double-dashed line, and the head of the decompression pin 8 moves to position 12 at the end of the flyweight 13. At this time, the decompression pin 8 loses the role of the decompression cam with respect to the retractable tapette 3. Therefore, the tapette 3 enters the normal reciprocating motion by the cam 4, and the internal combustion engine can continue the normal operation.

With such a function, the torque required at the time of starting the internal combustion engine becomes small and the starting becomes easy.

[Problems to be solved by the device]

 The above-mentioned conventional technique has the following problems.

(1) Since the fine hole 7 through which the decompression pin 8 penetrates is diagonally processed with high accuracy on the cam shaft 2, the processing cost is high.

(2) The decompression pin 8 has an elongated shape due to its structure. Especially, the tapette side is thin and the contact surface with the tapette is small, and the tapette contact surface has a high surface pressure, and the tapette is easily damaged.

(3) The stability of the lift amount of the decompression pin 8 is lacking. That is, the factors that determine the lift amount, (a) the cam R of the flyweight 13, (b) the flyweight 13 and the crimp pin 11
Mating clearance, (C) Pin 8 length, (D) Cam 4
It is necessary to finish each of the base circle diameters of with high precision.

(4) Since the profile setting of the decompression is determined only by the lift amount of the decompression pin 8, it is impossible to set the profile such that the decompression period is lengthened and the decompression lift is reduced.

[Means for Solving the Problems]

A decompression pin is not used, but a cylinder whose coaxial axis is the rotation axis is fitted to the camshaft, and a decompression cam is provided on the cylinder so that the decompression function is activated when the internal combustion engine is started.

Further, a gear driven by a pinion or an internal gear (hereinafter referred to as a pinion) is provided at the end of the cylinder, and a rack or an internal gear intermittent gear (hereinafter referred to as a rack) provided on the side surface of the cam gear is operated by centrifugal force. By giving rotation to the pinion by, the phase of the decompression cam is shifted,
Decompression function can be deleted.

[Action]

(1) The cylinder provided with the decompression cam and the pinion can be easily processed by sintering or the like. The cam shaft does not need to be drilled, and racks with weights can be easily drilled.

Therefore, the processing cost is significantly reduced.

(2) The decompression cam can have any shape, and the decompression timing can be adjusted. Moreover, since the contact surface with the tapette is large and the contact surface pressure can be reduced, the durability is improved.

〔Example〕

Figure 1 shows an example of this implementation. 2 and 3 are sectional views taken along the line X-X of FIG. Fig. 2 shows the state of decompression, and Fig. 3 shows that the rotation of the camshaft rises,
Centrifugal force acts on the rack, and the decompression cam enters the valve cam profile and decompression is no longer effective. FIG. 4 shows the stroke of the piston of the 4-cycle internal combustion engine and the working timings of the intake / exhaust valve cam and the decompression cam by the rotation angles of the crankshaft and the camshaft.

Reference numeral 1 is a crank shaft, and a gear 6 is fixed to the shaft 1. The gear 6 meshes with the cam gear 23 and drives the cam shaft 21.
Reference numeral 3 is a tapette which is pushed up by the cam 22 to push open the intake / exhaust valve. Reference numeral 21 denotes a cam shaft, which is made of a finished steel rod with high dimensional accuracy by drawing or the like, and the cam 22 for the intake / exhaust valve is fixed at a fixed position and at a fixed phase angle, for example, laser Beam welded and fixed. A decompression cam 24 is rotatably fitted on the cam shaft 21. Further, a cam gear 23 is fitted on the cam shaft 21, and this is also fixed by, for example, laser beam welding.

Reference numeral 23 denotes a cam gear, which supports a rack arm 26 provided with an internal gear 29 (hereinafter referred to as a rack) such as a rack or an intermittent toothed gear on the side surface of the gear 23 so as to freely rotate around a pin 27. . Fix the pin 28 on the same side of the cam gear 23,
This limits the range of movement of this arm 26. Pin 32 is also a cam gear
Fixed to the same side of 23 and tension spring 25
And pulls the arm 26 counterclockwise.

A rack arm 26 has an internal gear 29. This internal gear 29 meshes with the pinion 30 of the decompression cam 24,
The rotation of 26 rotates the decompression cam 24. Arm 26
A weight 31 is attached to a part of the arm, and a large centrifugal force is generated when the cam shaft rotates to push the arm 26 in the clockwise direction in the figure.

A decompression cam 24 is manufactured by precision casting or sintering and has a structure in which a pinion 30 that engages with the rack arm 26 and a decompression cam portion 33 are provided in a cylindrical body. The pinion 30 may be driven by the internal gear 29.

In such a device, when the internal combustion engine is started, the crankshaft 1 rotates, and at the same time, the gear 6 and the cam gear 23 work to rotate the camshaft 21. When the rotation speed is lower than the predetermined rotation speed, the rack arm 26 is rotated by the pulling force of the spring 25 urged by the weight 31 to the position shown in FIG.
The cam part 33 of the comes out to the position shown in the figure, and every time it rotates,
Push up. The time to push up this tapette is the 4th
The position of the decompression cam Y in the figure, that is, during the compression stroke of the internal combustion engine, the pressure in the compression chamber of the internal combustion engine is reduced or decompressed. When the rotation speed of the internal combustion engine increases, the centrifugal force of the weight 31 of the arm 26 exceeds the tensile force of the tension spring 25, the arm 26 moves to the position shown in FIG. 3, and the decompression cam 24
The cam portion 33 of the is inserted into the profile of the valve cam 22. That is, the position of the decompression cam Y'in FIG. 4 is reached, and the internal combustion engine starts normal operation at this position.

As described above, when the internal combustion engine is started, the torque of the crankshaft can be reduced, the rotation speed can be increased, and the start can be facilitated.

[Effect of device]

As described above, according to the present invention, the side surface of the gear fixed to the camshaft is provided with a rack arm which is oscillated by centrifugal force at the time of rotation and whose swing range is restricted by a pin. The pinion meshes with the rack, and when starting, when the internal combustion engine speed is below the predetermined speed, it abuts the tapet and pushes up the tapet to reduce the pressure in the cylinder chamber during the compression stroke, and the speed rises above the predetermined speed. Then, a decompression cam integrally formed with a cam that rotates due to the swing of the rack arm and enters the profile of the valve cam provided on the cam shaft is provided on the cam shaft between the gear and the valve cam. The pinion that meshes with the rack of the rack arm and the cam that enters into the profile of the valve cam are integrally formed because they are fitted so that they can rotate and cannot move in the axial direction. The decompression cam is fitted on the cam shaft to facilitate its processing and mounting, and the contact width between the decompression cam and tapette can be widened to reduce the contact surface pressure, improve the durability and mesh with the decompression cam. Since the rack arm is attached to the side surface of the gear fixed to the cam shaft with its swing range restricted by the pin, the decompression can be set easily and accurately.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part according to an embodiment of the present invention, FIGS. 2 and 3 are views taken along the line XX in FIG. 1, and FIG. 2 shows a state in which a decompression cam operates. Figure 3 shows the decompression cam hidden by the valve cam due to the action of centrifugal force. Fourth
FIG. 5 is an explanatory view of the stroke of the piston of the internal combustion engine and the timings of the supply / exhaust valve cam and the decompression cam, FIG. 5 is a sectional view showing a prior art example, and FIG. 3 ... Tapette, 21 ... Cam shaft 22 ... Cam, 23 ... Cam gear 24 ... Decompression cam, 26 ... Rack arm 29 ... Internal gear (luck), 30 ... Pinion

Claims (1)

[Scope of utility model registration request] 1. A decompression device for an internal combustion engine, which raises and lowers a tapet according to the number of revolutions of the internal combustion engine at the time of starting to reduce the compression pressure, and applies a centrifugal force during rotation to a side surface of a gear fixed to a cam shaft. A rack arm that receives and swings and its swing range is regulated by a pin is provided, and a pinion that meshes with a rack formed on the rack arm and a tappet when the internal combustion engine speed is equal to or lower than a predetermined speed at start-up. When the abutment is pushed up and the tapet is pushed up to reduce the pressure in the cylinder chamber during the compression stroke, and the rotation speed rises above a predetermined rotation speed, the rack arm swings to rotate and the profile of the valve cam provided on the cam shaft A decompression cam integrally formed with a cam that goes inside is fitted on the cam shaft between the gear and the valve cam so as to be rotatable and immovable in the axial direction. Decompression device for internal combustion engine.