JPH0235848B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a centrifugal automatic pressure reducing device for a small internal combustion engine.

[Conventional technology and its issues]

Generally, when starting an internal combustion engine, it is necessary to apply rotational motion to the crankshaft from the outside by some means until fuel ignites in the combustion chamber. Therefore, the process of starting an engine involves the first stage in which the internal combustion engine's crankshaft is rotated by an external energy source until the first ignition begins, and the second stage in which the engine itself starts from the first ignition. This is thought to be the process of accelerating operation until the normal rotation speed is reached due to the explosive force of the engine.

By the way, in small internal combustion engines (5 to 6 PS or less), the former process is performed manually, ie, using a hand starter, rope starter, kick starter, etc. In order to facilitate this rotation, a pressure reducing device for reducing the pressure inside the cylinder is installed at an appropriate location in the valve train of the internal combustion engine.

For example, a collar is attached to the push rod and pressure is reduced by pushing the collar, a valve swing arm is pushed against a cam to reduce pressure, a valve swing arm shaft is rotated to reduce pressure, a valve tappet lifts type, and a hand-cranked valve. Various types of decompression devices are known, such as automatic decompression devices (centrifugal decompression devices) that return to their natural state at a certain period of time as they rotate. In any of these pressure reducing devices, one of the intake and exhaust valves is opened during the compression stroke of the engine, the crankshaft is rotated, the valve is returned to its original position after sufficient acceleration, and the rotating parts are The inertial force continues the rotation of the crankshaft, leading to ignition, and as mentioned above, it is natural to start the engine manually, but also when using other starting methods.
One of the pressure reducing devices is installed.

By the way, the present invention relates to a centrifugal automatic pressure reducing device among the speed reduction devices, and an example of such a centrifugal automatic pressure reducing device is an engine manufactured by Briggs Corporation in the United States, or the following device
41973) is known.

That is, as shown in Fig. 1, a cam shaft 3 having a protruding cam 2 that pushes up an intake valve or an exhaust valve 1 against a valve spring in a side valve type small gasoline engine is provided with a cam shaft 3 that extends through its diameter. A pin 4 is slidably provided, and one end of the pin 4 is brought into contact with the tappet 5 of the exhaust valve 1, and the other end is brought into contact with the bent portion 8 of a horseshoe-shaped weight cam 7 provided on the rib surface of the cam gear 6. are in contact. This bent portion 8 forms an arcuate cam. Therefore, the rotation of the crankshaft by human power does not generate much centrifugal force, so the weight cam 7 is not displaced, and the bent portion 8 moves the pin 4 from the base surface of the cam 2. The tappet 5 is pushed up against the valve spring to open the valve 1 and create a reduced pressure state.

However, in such a pressure reducing device, the spring force of the valve spring is controlled by other factors such as, for example, the intake valve to accurately open and close according to the movement of the cam against the intake pressure, and to overcome the inertia force of the valve mechanism. Since the pin 4 has a strong force that resists external force, the pin 4 works while resisting the spring force, so the severe spring force acts intensively on the support part of the weight cam 7 that pushes up the pin 4. . Therefore, if the engine is used for a long period of time, the support part (the spindle 9 in the illustrated example) will wear out and become damaged, causing play, which will eventually impair the stability of the decompression function. Become.

Therefore, proposals have been made to solve this problem. In other words, a centrifugal pin that penetrates the camshaft and has one end that can come into contact with the tappet of the valve, and the other end of which can come into contact with a weight cam that is supported by the rib surface of the cam gear and is displaced approximately linearly by centrifugal force. In the type automatic pressure reducing device, the weight cam is approximately L-shaped, and two elongated holes are provided on the base side of the weight cam so that the weight cam can move in a straight line. A proposal has been made for a centrifugal start-up decompression device in which fixed guide pins are loosely fitted into each other, and the base end of the weight cam is pulled by a spring to strengthen the support part (Utility Model Publication No. 137633/1983). (see official bulletin).

However, in the proposed centrifugal automatic pressure reducing device, the L-shaped weight cam is supported at its base side, and the weighted tip of the weight cam is a swingable free end. Although the base end of the weight cam is pulled by a spring, it is supported in a cantilevered manner, and furthermore,
Although it is supported by two guide pins, in addition to the strong force of the valve spring mentioned above, the impactful centrifugal force of the weight cam swinging is frequently applied to the support part, so it becomes unbalanced. This tends to cause wear and play, and in engines that are used for a long period of time, there is a risk that linear movement of the weight cam (movement to bring the pin into contact with an inclined surface from a horizontal surface) may be hindered.

In other words, in this proposal, when the weight cam is moved horizontally by the centrifugal force generated in the weight cam, a weight is attached to the free end of the weight cam and only the base side of the weight cam is supported. There was a problem in that even though it was supported by two guide pins, a severe load was applied to the part.

[Means to solve the problem]

Therefore, the present invention was created in an attempt to solve the disadvantages of the prior art, and its gist is to provide a pin that passes through the camshaft and has one end that can come into contact with the tappet of the intake or exhaust valve. In a centrifugal automatic pressure reducing device whose end can come into contact with a weight cam that is supported by a rib surface of a cam gear and is displaced approximately linearly by centrifugal force, the weight cam is connected to an upper piece surrounding a cam shaft and a connecting piece. A weight is attached to the connecting piece, and the free ends of the upper piece and the lower piece are each biased by a spring so as to be pulled in the opposite direction to the centrifugal force caused by the weight. The upper piece, the connecting piece, and the lower piece are each provided with long holes through which the weight cam can move in a straight line, and guide pins protruding from and fixed to the rib surface are loosely fitted into these long holes. A centrifugal automatic pressure reducing device for a small internal combustion engine.

〔Example〕

The structure and operation of the present invention will be explained in detail based on the embodiments shown in FIGS. 2 and 3.

FIG. 2 is a partially sectional front view of an embodiment of the present invention, and FIG. 3 is a sectional view taken along line A--A in FIG. The same parts as in the prior art shown in FIG. 1 are denoted by the same reference numerals used in these figures, and the explanation thereof will be omitted.

The internal combustion engine of this embodiment is a general-purpose small gasoline engine (eg, 100 to 200 c.c.) of a side valve type and is started by a rope starter.

The weight cam 7 is formed to surround the cam shaft 3 in a substantially U-shape. That is, a weight plate 11 is attached to a U-shaped board (connection piece) 10 made of sheet metal,
Elongated holes 12, 12 parallel to each other are formed in the upper and lower pieces of the substrate 10, respectively. Further, on the outside of the weight plate 11 (on the right side in FIG. 3), a long hole-shaped cutout groove 13 parallel to these long holes 12 is bored. These long holes 12, 12 and notched grooves 13
Guide pins 15, 15 and 16 fixed and protruding from the rib surface 14 of the cam gear 6 are loosely fitted into the cam gear 6, respectively. Springs 18 and 18 that are engaged with protrusions 17 provided on the rib surface 14 of the cam gear 6 are respectively engaged at the upper and lower ends of the base plate 10, so that the U-shaped base plate 10 and the weight plate 11 are always kept on the protrusion 17 side. It's trying to attract you. Therefore, the two springs 18, 18 cause the U-shaped substrate 10 to
and the long hole 12,
12 and notch grooves 13 are bored in the same direction, so when centrifugal force acts on the weight plate 11, the U-shaped base plate 10 and the weight plate 11
slides and is displaced linearly.

A bent part 8 is formed on the inside of the lower part of the U-shaped substrate 10, and this bent part 8 consists of a plane 19 parallel to the tappet 5 and an inclined plane 20 (inclination of about 25 to 30 degrees) in FIG. It consists of Therefore, when the engine is stopped, the weight cam 7 is connected to the spring 18,
18, the pin 4 is brought into contact with the flat surface 19 of the bent portion 8 against the valve spring 21, and the exhaust valve 1 is lifted to its maximum opening. then,
Since the pin 4 is in contact with this plane 19, the direction of the strong force of the valve spring is not resolved but is shared in the same direction by the guide pins 15, 15, 16, so that the U-shaped board 10 is not twisted, and the U-shaped board 10 is not distorted. The substrate 10 is not deformed. When the engine is started, the centrifugal force is not so large and the weight cam 7 remains as it is, so the exhaust valve 1 is still lifted. In other words, it becomes a decombination state. Next, when the engine starts operating, centrifugal force acts on the weight cam 7, causing it to move linearly to the right in FIG. has no effect on

The pin 4 passes through the center of the camshaft 3 as shown in FIG. It abuts on the bent portion 8 at a position l apart from the outer periphery of the holder. Therefore, when the camshaft 3 rotates, one end of the pin 4 that is in contact with the bent portion 8 is
Even if this one end rotates toward the tappet 5, it will not come into contact with it. In other words, since one end protrudes from the outer shape of the cam 2, it is not restricted by the cam profile.

In the above embodiment, the guide pin 15 is provided, but instead of the guide pin 15, a projection piece 21 may be provided protruding from the rib 14 of the cam gear 6, and the weight cam 7 may be slid by this. However, these are collectively referred to as guide pins. code 22
indicates a washia.

〔Effect of the invention〕

Originally, in addition to the enormous force of the valve springs, centrifugal force frequently and impactfully acts on the weight cam when starting the engine or changing gears during operation, so the support part is subject to severe loads. Moreover, since the weight cam is restricted to move in a straight line by this centrifugal force, the support part tends to be strained, and uneven wear is likely to occur as in the one described in the above-mentioned Japanese Utility Model Publication No. 137633/1983. Therefore, backlash is likely to occur.
Conversely, in engines that are used for a long period of time, it is difficult to move the weight cam in a straight line, but according to the present invention,
Such backlash can be prevented and such difficulties can be overcome.

That is, according to the present invention, the upper and lower pieces of the substantially U-shaped weight cam are each supported (that is, supported at both ends), and the connecting piece to which the weight is attached is also supported, so that the entire body is firmly supported and guided. The free ends of the upper and lower pieces are each pulled in the opposite direction to the centrifugal force by the weights (in other words, they are pulled symmetrically to the centrifugal force). (The weight cam has a square shape), so the weight cam can move smoothly in a straight line without being complicated.

Further, since the spring force that biases the weight cam also acts on both ends of the weight cam, the bias is equally divided, and it is possible to prevent the linear movement of the weight cam from becoming distorted.

In addition, since the weight cam is supported at both ends and in the middle, centrifugal force is equally distributed to each support part, and uneven wear does not occur in each support part. Therefore, even an engine that has been used for a long time can be started in one go.

[Brief explanation of drawings]

Fig. 1 is a front view of the main part of the conventional example, Fig. 2 is a partially cutaway front view of the embodiment of the present invention, and Fig. 3 is A to A of Fig. 2.
It is an A sectional view. 1...Intake or exhaust valve, 2...Cam, 3...
Camshaft, 4... Pin, 5... Tappet, 6... Cam gear, 7... Weight cam, 12... Long hole, 1
3... Notch groove, 15, 16... Guide pin.

Claims (1)

[Claims] 1. The pin passes through the camshaft and has one end that can come into contact with the tappet of an intake or exhaust valve.The other end of the pin is supported by the rib surface of the cam gear and is displaced approximately linearly by centrifugal force. In a centrifugal automatic pressure reducing device that can come into contact with a weight cam, the weight cam has a substantially U-shaped structure consisting of an upper piece surrounding the cam shaft, a connecting piece, and a lower piece, and the weight is attached to the connecting piece. The free ends of the upper piece and the lower piece are each biased by a spring so as to be pulled in a direction opposite to the centrifugal force caused by the weight, and the weight cam can be moved linearly to the upper piece, the connecting piece, and the lower piece, respectively. A centrifugal automatic pressure reducing device for a small internal combustion engine, characterized in that long holes are provided, and guide pins protruding from and fixed to a rib surface are loosely fitted into these long holes.