An oil lubrication structure for a motorcycle engine

Abstract

The present invention provides an oil lubrication structure for a motorcycle engine, belonging to the technical field of motorcycles. It solves the technical problem of insufficient stability of the oil delivery operation of the existing engine oil lubrication structure. For the oil lubrication structure of this motorcycle engine, the motorcycle includes a box body and an oil pump housing fixedly connected to each other. An internal oil passage is provided in the box body. The oil lubrication and delivery structure includes a pressure relief valve and an oil inlet chamber and an oil outlet chamber located in the oil pump housing. The oil outlet chamber is simultaneously communicated with the internal oil passage and the oil inlet end of the pressure relief valve. A return oil passage communicated with the oil inlet chamber is provided in the box body or the oil pump housing. The return oil passage is separated from the internal oil passage and the oil outlet end of the pressure relief valve is communicated with this return oil passage. The present invention can ensure the stable operation of oil delivery while reducing energy loss.

Description

Technical Field

[0001] The present invention belongs to the technical field of motorcycles and relates to an oil lubrication structure for a motorcycle engine. Background Art

[0002] During the running of a motorcycle, an oil pump on the motorcycle engine can rotate along with the operation of the engine. An internal structure with meshing inner and outer rotors is provided inside the oil pump to pressurize the oil, and then the oil is transported to various parts of the engine through an internal oil passage to achieve a lubrication effect. Most of the oil pumps of motorcycles are separately installed on the surface of the engine body.

[0003] For example, the patent with the authorization announcement number CN216198353U discloses an oil pump structure for a motorcycle engine, which includes an engine body and an oil pump housing. The oil pump housing is installed inside the engine body. One side of the oil pump housing is communicated with a pressure relief pipe. An oil passage is opened inside the engine body. The pressure relief pipe is inserted into the oil passage. The other end of the oil passage is communicated with an oil inlet pipe, and the oil inlet pipe is connected to the oil passage of the engine. A plurality of through holes are opened on the side wall of the pressure relief pipe. A pin is fixedly connected inside one end of the pressure relief pipe. A slider is movably connected inside the pressure relief pipe and on one side of the pin. A spring is installed inside the slider. A retaining piece is fixedly connected to the other end of the pressure relief pipe. The other end of the spring is in contact with the retaining piece.

[0004] The above structure directly sends the pressure-relieved oil into the internal oil passage of the engine body. Although it can reduce energy loss to a certain extent, when the oil pressure in the oil outlet cavity of the oil pump is relatively high, it often means that there is a temporary blockage in the internal oil passage. Sending the pressure-relieved oil into the internal oil passage will lead to a poor pressure relief effect and a continuous increase in oil pressure, affecting the transportation stability. Therefore, those of ordinary skill in the art are more likely to consider from the perspective of energy conservation: 1. Discharge the pressurized oil to an area far from the oil pump in the internal oil circuit; 2. Make the pressure relief position bypass the area where the internal oil passage is easily blocked. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides an oil lubrication structure for a motorcycle engine. The technical problem to be solved by the present invention is: how to reduce energy consumption loss and ensure the stable operation of oil transportation.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] An oil lubrication structure for a motorcycle engine. The motorcycle includes a box body and an oil pump housing fixedly connected to each other. An internal oil passage is provided in the box body. The oil lubrication and delivery structure includes a pressure relief valve and an oil inlet chamber and an oil outlet chamber located in the oil pump housing. The oil outlet chamber is simultaneously communicated with the internal oil passage and the oil inlet end of the pressure relief valve. It is characterized in that a return oil passage communicated with the oil inlet chamber is provided in the box body or the oil pump housing. The return oil passage is separated from the internal oil passage and the oil outlet end of the pressure relief valve is communicated with this return oil passage.

[0008] The structural assembly combination shell of the oil pump housing and the box body on the box body forms an oil pump mechanism. The existing rotor assembly of the oil pump and the like are installed between the oil pump housing and the box body. An internal oil passage is provided in the box body to send the oil to various parts of the engine for lubrication. The oil inlet chamber and the oil outlet chamber respectively accommodate the oil before passing through the inner and outer rotor assemblies of the oil pump and the high-pressure oil after passing through the inner and outer rotor assemblies of the oil pump. The oil outlet chamber is communicated with the oil inlet end of the pressure relief valve. The pressure relief valve can be opened when the internal pressure in the oil outlet chamber is too high to discharge part of the high-pressure oil, so as to stabilize the output oil pressure and provide a protection function. By providing a return oil passage communicated with the oil inlet chamber in the box body or the oil pump housing, the return oil passage is separated from the internal oil passage and the oil outlet end of the pressure relief valve is arranged in the return oil passage. In this way, the pressurized oil discharged from the pressure relief valve can be buffered by the return oil passage after entering the return oil passage, so that the oil property is stable to ensure the lubrication effect. At the same time, the pressurized oil discharged from this part will directly enter the oil inlet chamber through the return oil passage, which can improve the pressure of the oil in the oil inlet chamber to a certain extent, and then improve the delivery flow of the oil pump, avoiding the energy of the pressure-relieved oil from dissipating and releasing in vain, and thus ensuring the stable operation of the oil delivery while reducing the energy loss.

[0009] In the above-mentioned oil lubrication structure of the motorcycle engine, an oil inlet passage communicated with the oil inlet chamber is provided in the box body. The return oil passage is arranged vertically and the upper end is closed. The oil inlet passage is communicated with the lower end of the return oil passage. An oil inlet is provided on the inner wall of the return oil passage and communicated with the oil inlet chamber. The oil outlet end is located above the oil inlet. The oil inlet passage can suck the oil in the oil sump. In this way, the return oil passage is arranged vertically and the upper end is closed, and the lower end of the return oil passage is communicated with the oil inlet passage. In this way, when the pressure at the upper end of the return oil passage is too low, an adsorption effect will be generated, and a small part of the oil stored in the return oil passage will enter the oil inlet along with the continuously flowing oil in the oil inlet passage. When the pressure relief valve is opened, the pressurized oil is mixed into the oil below, and the generated foam only floats on the surface of the oil in the return oil passage, and the oil located in the upper layer will not flow into the oil inlet, avoiding the foam from flowing into the oil pump, and the foam will gradually dissipate after the upper layer of oil is stationary, ensuring the quality of the oil at this place so that it can operate stably after entering the oil pump subsequently.

[0010] In the above-mentioned oil lubrication structure of the motorcycle engine, the oil outlet end is arranged at the upper end of the return oil passage, and the oil inlet is located at the lower end of the return oil passage. In this way, the distance between the pressure relief valve and the oil inlet is greater, which is conducive to reducing the influence of the oil flowing into the oil inlet from the oil inlet passage on the oil in the return oil passage, and further reducing the probability of the oil containing bubbles flowing into the oil inlet.

[0011] In the above-mentioned oil lubrication structure of the motorcycle engine, the pressure relief valve is columnar, and the oil outlet end of the pressure relief valve includes an oil discharge hole arranged in the middle section of the pressure relief valve, and the oil discharge hole is communicated with the return oil passage. The oil discharge hole on the pressure relief valve can make the oil discharged from the oil outlet cavity through the pressure relief valve spray out from the oil discharge hole, that is, the oil outlet end includes an oil discharge hole, and the arrangement of the oil discharge hole in the middle section of the pressure relief valve is conducive to reducing the interference of positioning and arranging the end of the pressure relief valve.

[0012] In the above-mentioned oil lubrication structure of the motorcycle engine, there are at least two oil discharge holes and they are spaced from each other, and the inner wall of the upper end of the return oil passage has an arc surface arranged around the periphery of the middle section of the pressure relief valve. In this way, the multiple oil discharge holes are conducive to discharging oil evenly and with a larger flow rate, and the arc surface can provide a certain guidance for the oil sprayed out from the oil discharge hole and at the same time avoid the side wall around the oil discharge hole from blocking the sprayed oil, making the oil flow smoothly.

[0013] In the above-mentioned oil lubrication structure of the motorcycle engine, an elastic washer is provided between the oil pump housing and the surface of the box body in a abutting manner. In this way, the elastic washer improves the sealing performance between the oil pump housing and the surface of the box body, and ensures that the pressurized oil will not flow out from the assembly gap of the oil pump housing.

[0014] In the above-mentioned oil lubrication structure of the motorcycle engine, part of the elastic washer is arranged circumferentially around the oil inlet end of the pressure relief valve, the inner wall of the oil pump housing has several pressing ridges, the return oil passage is located in the box body, and the pressing ridges are arranged circumferentially around the oil inlet end of the pressure relief valve and press the elastic washer at this place on the oil inlet end of the pressure relief valve. In this way, it is conducive to making part of the elastic washer fit tightly at the oil inlet end of the pressure relief valve, which is conducive to ensuring the restraint effect on the pressure relief valve, and at the same time avoiding the oil directly flushing into the fitting gap between the outer periphery of the pressure relief valve and the box body, so that the working effect of the pressure relief valve is not affected.

[0015] In the above-mentioned oil lubrication structure of the motorcycle engine, the side wall of the upper end of the return oil passage has a positioning blind hole, and one end of the pressure relief valve far from the oil inlet end is inserted into the positioning blind hole in a positioning manner. In this way, both ends of the pressure relief valve are supported by the positioning blind hole and the side wall between the oil outlet cavity and the return oil passage respectively, which is conducive to improving the stability of the position and state of the pressure relief valve and ensuring its working effect.

[0016] In the above-mentioned oil lubrication structure of the motorcycle engine, an elastic sealing ring that seals against the box body is sleeved on the outer periphery of the pressure relief valve. This can improve the sealing performance between the outer peripheral surface of the pressure relief valve and the box body, prevent the pressurized oil in the oil outlet cavity from flowing into the oil return channel without passing through the pressure relief valve, and make the oil delivery structure work more reliably.

[0017] In the above-mentioned oil lubrication structure of the motorcycle engine, the pressure relief valve includes a cylinder body and a valve core that is slidably connected inside the cylinder body and can reciprocate axially along the cylinder body. The valve core is columnar, and an elastic member is provided between the valve core and the bottom of one end of the cylinder body in a butting manner. The valve core is columnar, and the outer peripheral surface of the valve core is in sealing cooperation with the inner wall of the cylinder body. The oil discharge hole is located on the outer peripheral surface of the middle section of the cylinder body. The other end of the cylinder body is open and communicates with the oil outlet cavity. When the valve core moves towards one end of the cylinder body, the oil outlet cavity can be communicated with the oil return channel through the oil discharge hole. There is also a balance hole on the outer peripheral surface near one end of the cylinder body that is always communicated with the inner cavity of the cylinder body. The open end of the cylinder body at the other end is the oil inlet end of the pressure relief valve. In this way, the balance hole can allow a small amount of surrounding oil to enter the inner cavity of the cylinder body to lubricate the components, prevent the valve core from failing due to excessive resistance when it has not been working for a long time, and ensure the stable operation of the pressure relief work.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] In the oil lubrication structure of the present motorcycle engine, the pressurized oil discharged from the pressure relief valve can be buffered by the oil return channel after entering the oil return channel, making the oil properties stable and ensuring the lubrication effect. At the same time, the pressurized oil discharged from this part will directly enter the oil inlet cavity through the oil return channel, which can improve the pressure of the oil in the oil inlet cavity to a certain extent, and then increase the delivery flow rate of the oil pump, avoiding the waste of energy of the pressure relief oil, and ensuring the stable operation of the oil delivery while reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the three-dimensional structure schematic diagram of this embodiment.

[0021] Figure 2 is the top view structure schematic diagram of this embodiment.

[0022] Figure 3 is Figure 2 the schematic diagram of the A-A cross-section in

[0023] Figure 4 is Figure 3 the enlarged view of part D in

[0024] Figure 5 is Figure 2 the schematic diagram of the B-B cross-section in

[0025] Figure 6 isFigure 5 Enlarged view of part E in

[0026] Figure 7 is Figure 2 Schematic diagram of C-C section in

[0027] Figure 8 is the schematic diagram of the partial exploded three-dimensional structure of this embodiment.

[0028] Figure 9 is Figure 8 Enlarged view of part F in

[0029] In the figure, 1 is the box body; 11 is the internal oil passage; 12 is the oil inlet passage;

[0030] 2 is the oil pump housing; 21 is the pressing edge;

[0031] 3 is the oil inlet cavity; 4 is the oil outlet cavity;

[0032] 5 is the pressure relief valve; 51 is the oil inlet end; 52 is the oil outlet end; 53 is the oil drain hole; 54 is the cylinder body; 55 is the valve core; 56 is the elastic member; 57 is the balance hole;

[0033] 6 is the return oil passage; 61 is the oil inlet; 62 is the arc surface; 63 is the positioning blind hole;

[0034] 7 is the elastic washer; 8 is the elastic sealing ring. Specific embodiments

[0035] The following are specific embodiments of the present invention and in combination with the attached drawings, the technical solutions of the present invention are further described, but the present invention is not limited to these embodiments.

[0036] Such as Figures 1-7As shown in the figure, in the oil lubrication structure of the motorcycle engine, the motorcycle includes a box body 1 and an oil pump housing 2 fixedly connected to each other. The box body 1 has an internal oil passage 11. The oil delivery structure includes a pressure relief valve and an oil inlet chamber 3 and an oil outlet chamber 4 located in the oil pump housing 2. The oil outlet chamber 4 is communicated with the internal oil passage 11, and the oil outlet chamber 4 is also communicated with the oil inlet end 51 of the pressure relief valve 5. There is a return oil passage 6 in the box body 1 that is communicated with the oil inlet chamber 3. The return oil passage 6 is separated from the internal oil passage 11, and the oil outlet end 52 of the pressure relief valve 5 is communicated with the return oil passage 6. In this embodiment, the internal and external rotor structure in the oil pump housing 2 is not shown as it is prior art. The assembly combination of the structures on the oil pump housing 2 and the box body 1 can form an oil pump mechanism. The existing internal and external rotor components of the oil pump are installed between the oil pump housing 2 and the box body 1. The internal oil passage 11 is provided in the box body 1 to send the oil to various parts of the engine for lubrication. The oil inlet chamber 3 and the oil outlet chamber 4 respectively accommodate the oil before passing through the internal and external rotor components of the oil pump and the high-pressure oil after passing through the internal and external rotor components of the oil pump. The oil outlet chamber 4 is communicated with the oil inlet end 51 of the pressure relief valve 5 inserted into the box body 1. The pressure relief valve 5 can be opened when the internal pressure in the oil outlet chamber 4 is too high to discharge part of the high-pressure oil, so as to stabilize the output oil pressure and provide a protection function. By providing a return oil passage 6 in the box body 1 that is communicated with the oil inlet chamber 3, separating the return oil passage 6 from the internal oil passage 11 and arranging the oil outlet end 52 of the pressure relief valve 5 to be communicated with the return oil passage 6, the pressurized oil discharged from the pressure relief valve 5 can be buffered by the return oil passage 6 after entering the return oil passage 6, so that the oil property is stable to ensure the lubrication effect. At the same time, the pressurized oil discharged from this part will directly enter the oil inlet chamber 3 through the return oil passage 6, which can improve the pressure of the oil in the oil inlet chamber 3 to a certain extent, and then increase the delivery flow rate of the oil pump, avoiding the waste of the energy of the pressure relief oil and ensuring the stable operation of the oil delivery while reducing the energy loss. Specifically, there is an oil inlet passage 12 in the box body 1 that is communicated with the oil inlet chamber 3. The return oil passage 6 is arranged vertically with the upper end closed. The oil inlet passage 12 is communicated with the lower end of the return oil passage 6. There is an oil inlet 61 on the inner wall of the return oil passage 6 that is communicated with the oil inlet chamber 3. The oil outlet end 52 of the pressure relief valve 5 is located above the oil inlet 61. The oil inlet passage 12 can suck the oil in the oil sump. In this way, the return oil passage 6 is arranged vertically with the upper end closed, and the lower end of the return oil passage 6 is communicated with the oil inlet passage 12. When the pressure at the upper end of the return oil passage 6 is too low, an adsorption effect will be generated, and a small part of the oil stored in the return oil passage 6 will enter the oil inlet 61 along with the continuously flowing oil in the oil inlet passage 12. When the pressure relief valve 5 is opened, the pressurized oil is mixed with the oil below, and the generated foam only floats on the surface of the oil in the return oil passage 6, and the oil in the upper layer will not flow into the oil inlet 61, avoiding the foam from flowing into the oil pump. The foam will gradually dissipate after the upper layer of oil is stationary, ensuring the quality of the oil at this place so that it can operate stably after entering the oil pump subsequently. The oil outlet end 52 of the pressure relief valve 5 is arranged at the upper end of the return oil passage 6, and the oil inlet 61 is located at the lower end of the return oil passage 6.In this way, the distance between the pressure relief valve 5 and the oil inlet 61 is greater, which is conducive to reducing the influence of the engine oil flowing into the oil inlet 61 from the oil inlet passage 12 on the engine oil in the return oil passage 6, thereby reducing the probability of the engine oil containing bubbles flowing into the oil inlet 61. The pressure relief valve 5 is columnar, and the oil outlet end 52 of the pressure relief valve 5 includes an oil discharge hole 53 located in the middle section of the pressure relief valve 5, and the oil discharge hole 53 communicates with the return oil passage 6. The oil discharge hole 53 on the pressure relief valve 5 can cause the engine oil discharged from the oil outlet cavity 4 through the pressure relief valve 5 to spray out from the oil discharge hole 53. That is, the oil discharge hole 53 belongs to the oil outlet end 52 of the pressure relief valve 5, and the arrangement of the oil discharge hole 53 in the middle section of the pressure relief valve 5 is conducive to reducing the interference with the positioning arrangement of the end of the pressure relief valve 5. There are four oil discharge holes 53 and they are arranged at equal intervals in a ring shape. The inner wall at the upper end of the return oil passage 6 has an arc surface 62 arranged around the periphery of the middle section of the pressure relief valve 5. In this way, the four oil discharge holes 53 are conducive to discharging oil evenly and with a larger flow rate. The arc surface 62 can provide a certain guiding effect on the engine oil sprayed out from the oil discharge hole 53 and at the same time prevent the side wall around the oil discharge hole 53 from blocking the sprayed oil, making the engine oil flow smoothly. The side wall at the upper end of the return oil passage 6 has a positioning blind hole 63, and one end of the pressure relief valve 5 far from the oil inlet end 51 is inserted into the positioning blind hole 63 for positioning. In this way, both ends of the pressure relief valve 5 are supported by the positioning blind hole 63 and the side wall between the oil outlet cavity 4 and the return oil passage 6, which is conducive to improving the stability of the position and state of the pressure relief valve 5 and ensuring its working effect. An elastic sealing ring 8 is sleeved on the outer periphery of the pressure relief valve 5 and is in sealed contact with the box body 1. In this way, the sealing performance between the outer peripheral surface of the pressure relief valve 5 and the box body 1 can be improved, preventing the pressurized engine oil in the oil outlet cavity 4 from flowing into the return oil passage 6 without passing through the pressure relief valve 5, making the engine oil conveying structure work more reliably.

[0037] As Figures 3-9 shown, an elastic gasket 7 is provided between the oil pump housing 2 and the surface of the box body 1 in a contacting manner. In this way, the elastic gasket 7 improves the sealing performance between the oil pump housing 2 and the surface of the box body 1, ensuring that the pressurized engine oil does not flow out from the assembly gap of the oil pump housing 2. Part of the elastic gasket 7 is arranged circumferentially around the oil inlet end 51 of the pressure relief valve 5. The inner wall of the oil pump housing 2 has several pressing ridges 21. The return oil passage 6 is located in the box body 1. The pressing ridges 21 are arranged circumferentially around the oil inlet end 51 of the pressure relief valve 5 and press the elastic gasket 7 at this position on the oil inlet end 51 of the pressure relief valve 5. In this way, it is conducive to making part of the elastic gasket 7 tightly attached to the oil inlet end 51 of the pressure relief valve 5, which is conducive to ensuring the restraint effect on the pressure relief valve 5. At the same time, it also prevents the engine oil from directly flushing into the fitting gap between the outer periphery of the pressure relief valve 5 and the box body 1, so that the working effect of the pressure relief valve 5 is not affected.

[0038] As Figure 5 、 Figure 6 、 Figure 8 、 Figure 9As shown in the figure, the pressure relief valve 5 includes a cylinder body 54 and a valve core 55 that is slidably connected within the cylinder body 54 and can reciprocate axially along the cylinder body 54. The valve core 55 is columnar, and an elastic member 56 is provided between the valve core 55 and the bottom of one end of the cylinder body 54 in a top-contact manner. The valve core 55 is columnar, and the outer peripheral surface of the valve core 55 is in sealing cooperation with the inner wall of the cylinder body 54. The oil drain hole 53 is located on the outer peripheral surface of the middle section of the cylinder body 54. The other end of the cylinder body 54 is open and communicates with the oil outlet cavity 4. When the valve core 55 moves towards one end of the cylinder body 54, it can cause the oil outlet cavity 4 to communicate with the oil return passage 6 through the oil drain hole 53. The outer peripheral surface near one end of the cylinder body 54 also has a balance hole 57 that is always in communication with the inner cavity of the cylinder body 54. The open end of the other end of the cylinder body 54 is the oil inlet end 51 of the pressure relief valve 5. In this way, the balance hole 57 can allow a small amount of surrounding engine oil to enter the inner cavity of the cylinder body 54 to lubricate the components, avoiding excessive resistance and failure of the valve core 55 due to long-term inactivity, and ensuring stable pressure relief operation.

[0039] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute them, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. An oil lubrication structure for a motorcycle engine. The motorcycle includes a box body (1) and an oil pump housing (2) fixedly connected to each other. An internal oil passage (11) is provided in the box body (1). The oil lubrication structure includes a pressure relief valve (5), an oil inlet chamber (3) and an oil outlet chamber (4) located in the oil pump housing (2). The oil outlet chamber (4) is simultaneously communicated with the internal oil passage (11) and the oil inlet end (51) of the pressure relief valve (5). It is characterized in that, Inside the box body (1) or inside the oil pump housing (2), there is a return oil passage (6) communicating with the oil inlet chamber (3). The return oil passage (6) is separated from the internal oil passage (11), and the oil outlet end (52) of the pressure relief valve (5) is communicated with this return oil passage (6). Inside the box body (1), there is an oil inlet passage (12) communicating with the oil inlet chamber (3). The return oil passage (6) is arranged vertically with the upper end closed. The oil inlet passage (12) is communicated with the lower end of the return oil passage (6). On the inner wall of the return oil passage (6), there is an oil inlet (61) communicating with the oil inlet chamber (3). The oil outlet end (52) is located above the oil inlet (61). The oil outlet end (52) is arranged at the upper end of the return oil passage (6), and the oil inlet (61) is located at the lower end of the return oil passage (6). The pressure relief valve (5) is columnar. The oil outlet end (52) of the pressure relief valve (5) includes an oil discharge hole (53) arranged in the middle section of the pressure relief valve (5). The oil discharge hole (53) is communicated with the return oil passage (6). There are at least two oil discharge holes (53) which are spaced from each other. The inner wall at the upper end of the return oil passage (6) has an arc surface (62) arranged around the periphery of the middle section of the pressure relief valve (5).

2. The oil lubrication structure of the motorcycle engine according to claim 1, wherein, An elastic gasket (7) is provided in a pressing manner between the surface of the oil pump housing (2) and the box body (1).

3. The oil lubrication structure of the motorcycle engine according to claim 2, characterized in that, Part of the elastic gasket (7) is arranged circumferentially around the oil inlet end (51) of the pressure relief valve (5). The inner wall of the oil pump housing (2) has several pressing ribs (21). The return oil passage (6) is located inside the box body (1). The pressing ribs (21) are arranged circumferentially around the oil inlet end (51) of the pressure relief valve (5) and press the elastic gasket (7) at this position onto the oil inlet end (51) of the pressure relief valve (5).

4. The oil lubrication structure of the motorcycle engine according to claim 1, characterized in that, On the inner wall at the upper end of the return oil passage (6), there is a positioning blind hole (63). The end of the pressure relief valve (5) far from the oil inlet end (51) is inserted into the positioning blind hole (63) for positioning.

5. The oil lubrication structure of a motorcycle engine according to claim 1 or 2 or 3, characterized in that, An elastic sealing ring (8) which is in sealed contact with the box body (1) is sleeved on the outer periphery of the pressure relief valve (5).

6. The oil lubrication structure of the motorcycle engine according to claim 1, characterized in that, The pressure relief valve (5) includes a cylinder body (54) and a valve core (55) which is slidably connected inside the cylinder body (54) and can reciprocate axially along the cylinder body (54). The valve core (55) is columnar, and an elastic member (56) is provided in a top-contact manner between the valve core (55) and the bottom of one end of the cylinder body (54). The valve core (55) is columnar, and the outer peripheral surface of the valve core (55) is in sealed cooperation with the inner wall of the cylinder body (54). The oil discharge hole (53) is located on the outer peripheral surface of the middle section of the cylinder body (54). The other end of the cylinder body (54) is open and communicated with the oil outlet chamber (4). When the valve core (55) moves towards one end of the cylinder body (54), the oil outlet chamber (4) can be communicated with the return oil passage (6) through the oil discharge hole (53). There is also a balance hole (57) on the outer peripheral surface near one end of the cylinder body (54) which is always communicated with the inner cavity of the cylinder body (54).

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