TW201905319A - Engine with decompression device - Google Patents

Abstract

The present invention relates to an engine with a decompression device, including a cylinder head, a cam shaft assembly, a centrifugal weight, a sliding bar, an elastic member and a decompression shaft. The centrifugal weight is provided with a hook part, and located between a first support bearing and a valve cam. Elastic force provided by the elastic member abuts against a cam shaft and the sliding bar. The sliding bar connected with the centrifugal weight is inserted into a radial hole of the cam shaft, so that the centrifugal weight can slide between a closed position and an opened position depending on the resultant force of centrifugal force, gravity force and elastic force. The decompression shaft comprises a cam part and a combining part engaged with the hook part, so that the decompression shaft can rotate correspondingly with the displacement of the centrifugal weight. As such, the centrifugal weight of the present invention not only has lighter mass, but the center of mass is far away the center of the cam shaft. Therefore, the ratio between elastic force of the elastic member and gravity force of the centrifugal weight will become larger, which overcomes the problem that the engine is hard to ignite in prior art.

Description

Engine with pressure reducing device

The invention relates to an engine with a pressure reducing device, in particular to an engine with a pressure reducing device suitable for various vehicles.

When the engine is turned off, the crankshaft is rotated by the inertia of the rotating system, so that the engine will continue to rotate a certain number of turns. During this process, many impedances will cause the number of revolutions to gradually slow down and finally stop running. The largest impedance is the compression pressure of the compression stroke, so the engine is often subjected to the compression pressure to cause the normal rotation to stop and then reverse, and then stop.

When the engine is to be restarted, the piston in the cylinder moves toward the combustion chamber. At this time, since both the intake valve and the exhaust valve system are closed, the piston must overcome the pressure of the compressed gas in the cylinder to complete the movement. The movement of the rest. That is, whether starting with an electric motor or manually applying a force, it is necessary to provide a torque sufficient to overcome the gas pressure in the aforementioned cylinder. Otherwise, if the electric motor is started, the electric motor must be designed to have a large torque and cannot be small. If it is started by manual force, for example, when the engine needs to be driven by pedaling or hand-drawn, it will cause difficulty in exerting force and increase the burden on the user.

In response to the above pressure problems, some engines are currently equipped with so-called pressure reducing devices to reduce the pressure of the engine at the start-up and to avoid the above problems. As is known, the decompression device installed in some engines is a centrifugal decompression device, which is controlled by the centrifugal force generated by the centrifugal weight when the camshaft rotates to control the decompression device at a set speed. Function, and if the speed is set above this, the decompression effect is lost.

Please refer to FIG. 9 to FIG. 11 , which are respectively an exploded view of a conventional pressure reducing device, a perspective view of a conventional pressure reducing device in a closed position, a perspective view of a conventional pressure reducing device in an open position, and a conventional pressure reducing device in a closed position. A schematic view of the axis. As shown in the figure, the Republic of China Patent No. M404273 discloses a pressure reducing device comprising a cam shaft 931 having a radial through hole 930 and a centrifugal weight 94 having a first tooth portion 941. The self-centrifugal weight 94 extends outwardly through a sliding rod 95 of the radial through hole 930, an elastic member 96 that abuts against the sliding rod 95, and includes a cam portion 971 and a second tooth portion 972. Pressure bar 97. The cam shaft 931 is fixed with a valve cam 932 on the outer circumference. The second tooth portion 972 of the pressure reducing lever 97 is engaged with the first tooth portion 941 of the centrifugal weight 94, and the cam portion 932 is rotated to be higher or lower than the valve cam 932 with the sliding of the centrifugal weight 94. Thereby, the centrifugal weight 94 is slidably driven by the rack and pinion transmission mode to drive the pressure reducing lever 97 to selectively exert a pressure reducing function.

However, the above-described operation of the decompression device has the following disadvantages: First, the centrifugal weight 94 and the pressure reducing lever 97 are driven by the tooth shape, so that the centrifugal weight 94 and the pressure reducing rod 97 are complicated to manufacture. Second, when the engine is started, the centrifugal weight 94 has become open, or when the engine stops, the centrifugal weight 94 cannot be quickly closed to maintain the open state, so that the compression pressure cannot be normally reduced when the next engine is started. There is a problem of poor startability, and the reason is that the gravity ratio of the elastic force of the elastic member 96 and the centrifugal weight 94 is not large enough, and the centrifugal weight 94 is not normally closed or opened at an appropriate speed, but if only The elastic force is likely to cause the set pressure reduction On/Off action speed (ie, the set speed) to increase, resulting in abnormal sound in the pressure reducing device. (1) As shown in FIG. 11, the centrifugal weight 94 is in the closed state, first The opening angle formed by the end portion 942 and the second end portion 943 and the center of the cam shaft 931 is greater than 180 degrees. (2) As shown in FIG. 10, when the centrifugal weight 94 is in the closed position and the open position, the cam shaft 931 is axially oriented. The observations are all within the outer diameter of the support bearing 933. The above factors (1)(2) will cause the center of mass to be closer to the center of the camshaft 931, resulting in less centrifugal force of the centrifugal weight 94 at the set rotational speed and reducing the elastic force requirement. Caused a reduction in the bomb Gravity and the centrifugal weight ratio of 94, and thus a problem centrifugal weights 94 not to open or normally closed speed relevance, especially when the centrifugal weights 94 of the opening direction consistent with the direction of gravity.

Because of this, in the spirit of active invention, we have thought of "an engine with a decompression device" that can solve the above problems, and finally completed the present invention after several research experiments.

The main object of the present invention is to provide an engine with a pressure reducing device, which is configured by fitting a centrifugal weight and a pressure reducing rod in a manner of fitting a convex hook portion and a groove-like joint portion. In addition to reducing the manufacturing difficulty of the component, if the centroid of the centrifugal weight is further changed away from the center of the camshaft, the weight ratio of the spring force to the centrifugal weight can be increased, and the opening direction and the gravity direction of the centrifugal weight are improved. When consistent, the problem caused by poor engine start-up.

To achieve the above object, an engine with a pressure reducing device of the present invention includes a cylinder head, a camshaft assembly, a centrifugal weight, a sliding rod, an elastic member, and a pressure reducing rod. The camshaft assembly is disposed in the cylinder head, and includes a camshaft having a radial through hole, a valve moving cam, a first support bearing and a second support bearing, so that the camshaft has the first support bearing and the first The two support bearings are supported in the cylinder head and can be rotated. The centrifugal weight includes a staking portion, and the pressure reducing rod is rotated by the centrifugal force to achieve a decompression effect below the set speed, thereby helping the engine to start again, wherein the centrifugal weight is located at the first support bearing and the valve Between the moving cams. The elastic member is sleeved on the sliding rod for abutting the cam shaft and the sliding rod, and can apply an elastic force in a direction parallel to the sliding of the centrifugal weight. The sliding rod is connected to the centrifugal weight and is disposed in the radial through hole, so that the centrifugal weight can be slid between a closed position and an open position according to the combined force of the centrifugal force, the gravity and the elastic force of the rotating speed. The pressure reducing rod includes a cam portion and a joint portion interlocking with the hooking portion, and the pressure reducing rod correspondingly generates a rotation change accompanying the sliding displacement of the centrifugal weight.

Wherein, in the axial direction of the camshaft, when the centrifugal weight is in the closed position, the cam portion is higher than the valve cam outer contour, and the outer edge of the centrifugal weight is located within the outer diameter of the first support bearing; When the centrifugal weight is in the open position, the cam portion is lower than the valve cam profile and the outer edge of the centrifugal weight exceeds the outer diameter of the first support bearing. With the above design, the centrifugal weight of the present invention has the characteristics of being easily assembled in the cylinder head and having a small mass and a center of mass farther away from the center of the camshaft, so that the ratio of the elastic force of the elastic member to the gravity of the centrifugal weight is It has become bigger and effectively improves the problem of poor engine start-up in conventional technology.

The centrifugal weight may further include a first end and a second end, viewed in the axial direction of the cam shaft, and the centrifugal weight is in a closed state, the first end, the second end and the camshaft center The resulting opening angle is less than 180 degrees. Thereby, through the design of the centrifugal weight, the centroid of the centrifugal weight can be effectively moved toward the outer diameter direction, and the center of the camshaft is away from the center of the camshaft to produce a better weighting effect.

The interlocking of the centrifugal weight and the pressure reducing rod can simplify the structure of the tooth portion of the centrifugal weight in the prior art by fitting the convex hook portion and the groove-like joint portion, which can help The center of mass of the centrifugal weight is moved toward the outer diameter and away from the center of the camshaft.

The cam shaft may further be provided with a positioning flange having a flange hole through which the pressure reducing rod passes. Moreover, through the positioning flange, the axial direction gap between the centrifugal weight and the positioning flange is smaller than the axial direction gap between the centrifugal weight and the first support bearing, thereby being used to restrain the rotation of the centrifugal weight and The centrifugal weight is not in contact with the first support bearing, and further, the positioning flange may be smaller than the outer diameter of the first support bearing when viewed in the axial direction of the cam shaft to facilitate assembly of the camshaft assembly.

The valve cam can open a receiving groove, and the cam portion of the pressure reducing rod can be partially accommodated in the receiving groove.

The centrifugal weight can be recessed with a socket, and the sliding rod can be inserted into the socket and interlocked with the centrifugal weight. Thereby, the sliding rod of the present invention and the centrifugal weight can be interlocked. As the centrifugal weight is subjected to different centrifugal forces, the sliding rod will have different displacement changes in the radial direction.

The centrifugal weight may further include a positioning portion for conforming the cam shaft to the cam shaft when the centrifugal weight is in the closed position. The sliding rod may further include a stopping portion for abutting against the cam shaft, and the centrifugal weight is slidably positioned in the open position to restrain the rotation angle of the pressure reducing rod.

The elastic member may be a compression spring. The centrifugal weight is reduced below the set speed due to the centrifugal force, and the elastic force of the compression spring can return the centrifugal weight to the closed position. The centrifugal weight increases above the set speed due to the centrifugal force and resists compression. The spring force moves to the open position.

The above summary and the following detailed description are exemplary in order to further illustrate the scope of the invention. Other objects and advantages of the present invention will be described in the following description and drawings.

Please refer to FIG. 1, FIG. 2A and FIG. 2B, which are respectively a cross-sectional view of an engine with a pressure reducing device, a front view of a cylinder head, and a cross-sectional view of a camshaft assembly according to a first embodiment of the present invention. The figure shows an engine structure. The engine 1 mainly includes a cylinder head 2, a cylinder block 21 and a crankcase 22 connected in sequence. In the present embodiment, a camshaft assembly 3 is disposed inside the cylinder head 2, a piston rod set 211 is disposed inside the cylinder block 21, a crank mechanism 221 is disposed inside the crankcase 22, and a crank mechanism 221 is coupled to the The transmission mechanism (not shown) transmits the rotational power. The cylinder head 2 further includes two rocker arms 23, 24 and two valves 231, 241 corresponding to the two rocker arms 23, 24 respectively, so when the two rocker arms 23, 24 are respectively subjected to the valve cams 30, 32 or the pressure reducing device When the force is applied, the force can be transmitted to the valves 231 and 241 correspondingly, and the valves 231 and 241 are sequentially driven to a lift.

3 and FIG. 4 are respectively a perspective view and an exploded view of a pressure reducing device according to a first embodiment of the present invention. As shown in the figure, a camshaft assembly 3 is disposed in the cylinder head 2, which mainly includes a camshaft 31 having a radial through hole 310, a valve cam 32 having a receiving groove 320, and another A valve cam 30, a first support bearing 33 and a second support bearing 34. Thereby, the cam shaft 31 is rotatably supported by the first support bearing 33 and the second support bearing 34 in the cylinder head 2, so that the valve cams 30, 32 can collectively produce the effect of synchronous rotation.

On the other hand, as described in the prior art, in order to prevent the piston rod set 211 from being difficult to overcome the pressure of the pressed gas in the cylinder block 21 when the engine 1 is ready to be restarted, a so-called engine decompression is developed. Device. In the present embodiment, the pressure reducing device 10 is a centrifugal pressure reducing device including a centrifugal weight 4, a sliding rod 5, an elastic member 6, and a pressure reducing rod 7. The centrifugal weight 4 includes a hooking portion 41, a socket 44 and a positioning portion 45. The centrifugal weight 4 is located between the first support bearing 33 and the valve moving cam 32, and the sliding rod 5 is inserted. In the above-mentioned insertion hole 44, the sliding rod 5 and the centrifugal weight 4 are interlocked, and the sliding rod 5 is bored in the radial through hole 310, so that the centrifugal weight 4 receives centrifugal force due to the rotation speed of the cam shaft 31. The difference in size can be slid between a closed position and an open position, causing the slide bar 5 to produce different displacement changes in the radial direction. The positioning portion 45 can abut against the cam shaft 31 in the closed position, and the centrifugal weight 4 and the cam shaft 31 are held in a fitting state for limiting the rotation angle of the pressure reducing lever 7 in the closed position.

Furthermore, the sliding rod 5 is sleeved with an elastic member 6. The elastic member 6 is a compression spring in the embodiment, and a stopper portion 51 is disposed at one end of the sliding rod 5, so that the elastic member 6 can be respectively separated. The top cam shaft 31 and the stopper portion 51 of the slide bar 5 are applied with an elastic force in a direction parallel to the sliding of the centrifugal weight 4 to help the centrifugal weight 4 to smoothly switch between the open position and the closed position. The stopper portion 51 abuts against the cam shaft 31 in the open position, restricting the slip distance of the slide bar 5, and thus further restricts the angle of rotation of the pressure reducing lever 7 in the open position.

In addition, the cam shaft 31 is further provided with a positioning flange 311 having a flange hole 312 for limiting the rotation angle of the centrifugal weight 4, and the pressure reducing rod 7 is inserted into the flange hole 312 to make the pressure reducing rod 7 can be positioned in the accommodating groove 320. At this time, if viewed in the axial direction of the cam shaft 31, the positioning flange 311 is smaller than the outer diameter of the first support bearing 33 to facilitate assembly of the camshaft assembly 3. . In addition, the pressure reducing rod 7 includes a cam portion 71 and a joint portion 72. In the embodiment, the joint portion 72 is a groove having a shape for fitting the hook portion 41 to Can produce a linkage effect. The cam portion 71 is accommodated in the accommodating groove 320. With the sliding change of the centrifugal weight 4, the cam portion 71 can be rotated to be higher or lower than the outer periphery of the valve cam 32, and the decompression operation of the engine can be selectively adjusted.

Furthermore, referring to FIG. 2B, the centrifugal weight 4 and the positioning flange 311 have an axial gap D1, the centrifugal weight 4 and the first support bearing 33 have an axial gap D2, and the axial direction gap D1 is smaller than the axial clearance. D2, if the centrifugal weight 4 is rotated, the centrifugal weight 4 will abut against the positioning flange 311 to limit the rotation angle, and the centrifugal weight 4 will not contact the first support bearing 33. In addition, the positioning flange 311 of the embodiment is designed integrally with the cam shaft 31, but may be assembled separately for two separate parts.

Please refer to FIG. 5A to FIG. 5C , which are respectively a perspective view, an axial schematic view and an actuation diagram of the pressure reducing device according to the first embodiment of the present invention in a closed position. As shown, when the engine is restarted or is lower than the set speed, the centrifugal weight 4 is in the closed position. At this time, the cam portion 71 is higher than the outer contour of the valve cam 32, and can push the rocker arm 23 upward. The valve 231 opens a lift and does achieve the effect of decompression. The decompression device of the present invention is characterized in that the first end portion 42 of the centrifugal weight 4, a second end portion 43, and the center of the cam shaft 31 are formed under the axial direction of the cam shaft 31. The angle of the opening is less than 180 degrees. Thereby, through the above arrangement, in addition to effectively reducing the mass of the selected centrifugal weight 4, the center of mass can be further away from the center of the camshaft 31, so that the centrifugal weight 4 is prone to change in the radial direction and is improved. The sensitivity of the closed position to the open position transition.

Please refer to FIG. 6A to FIG. 6C , which are respectively a perspective view, an axial schematic view and an actuation diagram of the pressure reducing device according to the first embodiment of the present invention in an open position. As shown in the figure, when the engine is operated above a set speed, the sliding rod 5 and the centrifugal weight 4 are subjected to centrifugal force sufficient to resist the elastic force of the elastic member 6 to slide in the opposite direction to the above, the sliding rod The slip limit of 5 is a position at which the stopper portion 51 abuts against the cam shaft 31. At this time, the retracting rod 7 is pivoted by the engaging portion 41 and the joint portion 72. The cam portion 71 is built in the accommodating groove 320; that is, when the centrifugal weight 4 is in the open position, the cam portion 71 is lower than the outer contour of the valve cam 32, and the cam portion 71 is not The rocker arm 32 is topped, so there is no decompression action.

With the above design, the centrifugal weight 4 of the pressure reducing device of the present invention is coupled with the pressure reducing rod 5 in such a manner that the convex hook portion 41 is fitted into the groove-like joint portion 72, which is different from the conventional teeth. The type of meshing method can simplify the manufacturing process of the above parts and effectively reduce the cost. Furthermore, compared with the prior art, in the embodiment, the joint of the protruding hook portion 41 and the groove-shaped joint portion 72 can reduce the structure of the first end portion 42 and can make the centrifugal weight block. 4 The center of mass moves toward the outer diameter and away from the center of the camshaft 31, which can increase the gravity ratio between the elastic force and the centrifugal weight 4 to improve the engine startability.

Referring to FIGS. 5B and 6B, another feature of the present invention is that, when viewed in the axial direction of the camshaft 31, when the centrifugal weight 4 is in the closed position, the outer edge 40 of the centrifugal weight 4 is located at the first support bearing 33. Within the outer diameter; when the centrifugal weight 4 is in the open position, the outer edge 40 of the centrifugal weight 4 extends beyond the outer diameter of the first support bearing 33. By this design, in addition to facilitating the assembly of the camshaft 31 to the cylinder head 2, the centroid of the centrifugal weight 4 can be moved toward the outer diameter direction and away from the center of the camshaft 31.

In addition, please refer to FIG. 7, FIG. 8A and FIG. 8B, which are respectively an exploded view of the pressure reducing device according to a second embodiment of the present invention, a perspective view in a closed position, and a perspective view in an open position. In the present embodiment, the basic structure of the camshaft assembly 3a and the pressure reducing device 10a are the same as those of the first embodiment, and will not be described herein, except that the valve cam 32a of the present embodiment is different. The accommodating groove 320 described in the first embodiment is not provided. Therefore, if the joint portion 72a is not changed, the length of the pressure reducing rod 7a must be relatively short, so that it passes through the flange hole 312 only Projecting to the side of the valve cam 32a without affecting the rotation of the valve cam 32a, as shown in Figs. 8A and 8B, the position of the pressure reducing lever 7a is shown in the closed position and the open position. And its rotation state, as shown in the figure, the cam portion 71a of the pressure reducing lever 7a can push the rocker arm 23 at the closed position, but only the different positions of the rocker arm 23 can be pushed up, and the pressure reducing effect can also be achieved.

The above-mentioned embodiments are merely examples for convenience of description, and the scope of the claims is intended to be limited to the above embodiments.

1‧‧‧ engine

10,10a‧‧‧Reducing device

2‧‧‧ cylinder head

21‧‧‧Cylinder block

211‧‧‧Piston connecting rod set

22‧‧‧ crankcase

221‧‧‧ crank mechanism

23,24‧‧‧ rocker arm

231,241‧‧‧ Valves

3,3a‧‧‧Camshaft assembly

30,32,32a‧‧‧valve cam

31‧‧‧Camshaft

310‧‧‧radial through hole

311‧‧‧ positioning flange

312‧‧‧Flange hole

320‧‧‧ accommodating slots

33‧‧‧First support bearing

34‧‧‧Second support bearing

4‧‧‧ Centrifugal weights

40‧‧‧ outer edge

41‧‧‧Hunting Department

42‧‧‧First end

43‧‧‧second end

44‧‧‧ jack

45‧‧‧ Positioning Department

5‧‧‧Sliding rod

51‧‧‧Departure

6‧‧‧Flexible parts

7,7a‧‧‧Relief rod

71, 71a‧‧‧Cam Department

72,72a‧‧‧Combination

930‧‧‧radial through holes

931‧‧‧Camshaft

932‧‧‧ valve cam

933‧‧‧Support bearing

94‧‧‧ centrifugal weights

941‧‧‧First tooth

942‧‧‧ first end

943‧‧‧second end

95‧‧‧Sliding rod

96‧‧‧Flexible parts

97‧‧‧Relief rod

971‧‧‧Cam Department

972‧‧‧second tooth

D1, D2‧‧‧ axial clearance

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing an engine with a pressure reducing device according to a first embodiment of the present invention. Fig. 2A is a front elevational view showing a cylinder head of an engine having a pressure reducing device according to a first embodiment of the present invention. 2B is a cross-sectional view showing a camshaft assembly of an engine having a pressure reducing device according to a first embodiment of the present invention. Figure 3 is a perspective view of a pressure reducing device according to a first embodiment of the present invention. Figure 4 is an exploded view of the pressure reducing device of a first embodiment of the present invention. Figure 5A is a perspective view of the pressure reducing device of the first embodiment of the present invention in a closed position. Figure 5B is a schematic axial view of the pressure reducing device of the first embodiment of the present invention in a closed position. Figure 5C is a schematic view showing the operation of the pressure reducing device of the first embodiment of the present invention in the closed position. Figure 6A is a perspective view of the pressure reducing device of the first embodiment of the present invention in an open position. Figure 6B is a schematic axial view of the pressure reducing device of the first embodiment of the present invention in an open position. Figure 6C is a schematic view showing the operation of the pressure reducing device of the first embodiment of the present invention in an open position. Figure 7 is an exploded view of a pressure reducing device according to a second embodiment of the present invention. Figure 8A is a perspective view of the pressure reducing device of the second embodiment of the present invention in a closed position. Figure 8B is a perspective view of the pressure reducing device of the second embodiment of the present invention in an open position. Figure 9 is an exploded view of a conventional pressure reducing device. Figure 10A is a perspective view of a conventional pressure reducing device in a closed position. Figure 10B is a perspective view of a conventional pressure reducing device in an open position. Figure 11 is a schematic axial view of a conventional pressure reducing device in a closed position.

Claims (11)

An engine with a pressure reducing device includes: a cylinder head; a camshaft assembly disposed in the cylinder head, including a cam shaft having a radial through hole, a valve moving cam, and a first support a bearing and a second supporting bearing; a centrifugal weight comprising a staking portion, the centrifugal weight is located between the first supporting bearing and the valve moving cam; a sliding rod connecting the centrifugal weight and Inserted in the radial through hole, the centrifugal weight can be slid between a closed position and an open position; an elastic member is sleeved on the sliding rod to abut the cam shaft and the sliding rod And a pressure reducing rod comprising a cam portion and a joint portion with the hooking portion, wherein the pressure reducing rod correspondingly generates a rotation change along with a sliding displacement of the centrifugal weight; wherein, the axis of the cam shaft Observing, when the centrifugal weight is in the closed position, the cam portion is higher than the valve cam outer contour, and the outer edge of the centrifugal weight is located within the outer diameter of the first support bearing; When the centrifugal weight is in the open position The cam portion below the outside contour of the valve cam, and the outside edge of the centrifugal weights beyond the outer diameter of the first bearing support. An engine with a pressure reducing device includes: a cylinder head; a camshaft assembly disposed in the cylinder head, including a cam shaft having a radial through hole, a valve moving cam, and a first support a bearing and a second supporting bearing; a centrifugal weight comprising a staking portion, the centrifugal weight is located between the first supporting bearing and the valve moving cam; a sliding rod connecting the centrifugal weight and Inserted in the radial through hole, the centrifugal weight can be slid between a closed position and an open position; an elastic member is sleeved on the sliding rod to abut the cam shaft and the sliding rod And a pressure reducing rod comprising a cam portion and a joint portion interlocking with the hooking portion, wherein the pressure reducing rod correspondingly generates a rotation change along with a sliding displacement of the centrifugal weighting block; wherein the centrifugal weighting block is further The first end portion and the second end portion are formed. The centrifugal weight is formed in the closed state, and the first end portion, the second end portion and the center of the cam shaft are formed in the closed state. The opening angle is less than 180 degrees. The engine with a pressure reducing device according to the first aspect of the invention, wherein the centrifugal weight further comprises a first end portion and a second end portion, the centrifugal fitting is viewed in an axial direction of the cam shaft When the weight is in the closed state, the first end portion, the second end portion and the center of the cam shaft form an opening angle of less than 180 degrees. An engine having a pressure reducing device according to the first or second aspect of the invention, wherein the cam shaft is further provided with a positioning flange having a flange hole through which the pressure reducing rod passes. The engine with a pressure reducing device according to the fourth aspect of the invention, wherein the axial weight gap between the centrifugal weight and the positioning flange is smaller than the axial direction gap between the centrifugal weight and the first support bearing. The engine with a pressure reducing device according to claim 4, wherein the positioning flange is located in an outer diameter of the first support bearing when viewed in the axial direction of the cam shaft. An engine having a pressure reducing device according to the first or second aspect of the invention, wherein the centrifugal weight is recessed with a socket, and the sliding rod is inserted into the socket and separated from the socket Heart weights are linked. The engine of claim 1 or 2, wherein the centrifugal weight further comprises a positioning portion for fitting the centrifugal weight in the closed position. The camshaft. The engine of claim 1 or 2, wherein the sliding rod further comprises a stopping portion for abutting the centrifugal weight in the open position against the cam axis. The engine of the pressure reducing device according to the first or the second aspect of the invention, wherein the valve cam has a receiving groove, and the cam portion is partially accommodated in the receiving groove. The engine of claim 1 or 2, wherein the elastic member is a compression spring.