Variable valve lift structure of motorcycle engine

Abstract

The invention relates to the technical field of motorcycle engines, and discloses a variable valve lift structure of a motorcycle engine, which comprises a cam mandrel, a switching sleeve, an air inlet cam, an exhaust cam, an electromagnetic valve, a timing driven chain wheel, a spring and a steel ball, the spring and the steel ball are arranged in a blind hole of the cam mandrel, the electromagnetic valve is in contact with the switching sleeve, the switching sleeve, the low-lift air inlet cam and the high-lift air inlet cam are respectively fixed on the cam mandrel and rotate along with the cam mandrel, a first axial sliding rail is arranged on the cam mandrel, a cam sleeve is in clearance fit with the first axial sliding rail, and a second axial sliding rail is arranged on the second axial sliding rail. A timing driven chain wheel is fixedly connected to the cam sleeve, the cam mandrel moves in the axis direction relative to the axially static cam sleeve, and the cam mandrel is limited in a low-lift groove or a high-lift groove in the cam sleeve through a spring and a steel ball. The device is small in size, low in machining precision and high in reliability.

Description

Technical Field

[0001] This invention relates to the field of motorcycle engine technology, and more specifically to a variable valve lift structure for a motorcycle engine. Background Technology

[0002] Variable valve lift (VVL) is a technology that automatically adjusts the valve opening degree during engine operation. Traditional gasoline engines have a fixed valve lift, meaning the camshaft has only one cam profile, which results in poor engine response at both high and low speeds. Variable valve lift technology, on the other hand, allows the engine to achieve optimal performance under different operating conditions, thereby improving engine efficiency and torque.

[0003] Chinese patent document CN103032121B discloses an internal combustion engine and a valve drive device for the internal combustion engine, including a rotatably supported camshaft for operating the scavenging valves of multiple cylinders in a cylinder bank. A sliding cam capable of axial sliding is arranged on the camshaft for each cylinder. A common actuator is provided for these sliding cams to allow the sliding cams, which are axially slidably supported on the corresponding camshaft, to slide axially. The document also proposes a valve drive device for an internal combustion engine, having at least one rotatably supported camshaft for operating the scavenging valves of multiple cylinders in a cylinder bank. A sliding cam capable of axial sliding is arranged on the camshaft for each cylinder. A common actuator is provided for these sliding cams to allow the sliding cams, which are axially slidably supported on the corresponding camshaft, to slide axially.

[0004] Chinese patent document CN111335977A discloses a variable valve lift camshaft structure, including a spindle and multiple cam sleeves sequentially sleeved on the spindle. Each cam sleeve includes a journal and two cam groups located on both sides of the journal. Each cam group includes a low-speed cam and a high-speed cam. The low-speed cam and the high-speed cam of the two cam groups are arranged in the same order. A stop is provided on the outer side of both the low-speed cam and the high-speed cam that are far from the journal. The cam sleeve makes linear displacement on the spindle and is limited by a limiting member. The cam sleeve makes circular motion as the spindle rotates. The principle of switching between high-speed and low-speed camshafts: A solenoid valve is installed on the cam sleeve. When the solenoid valve receives a signal indicating high-speed or low-speed operation, it drives the cam sleeve to make linear left-right displacements on the spindle. The toothed grooves and toothed protrusions engage to ensure the straightness of the cam sleeve and spindle during displacement. When the engine is at high speed, the steel ball is placed in the high-speed groove, causing the valve to contact the high-speed cam. The valve experiences a larger lift as the high-speed cam rotates. When the engine is at low speed, the steel ball moves through the inclined guide surface to the low-speed groove. At this time, the valve contacts the low-speed cam, and the valve experiences a lower lift as the low-speed cam rotates. This achieves the switching between high-speed and low-speed operating states, reducing valve throttling losses, improving charging efficiency, increasing engine power output at high speeds and heavy loads, and reducing fuel consumption.

[0005] The prior art has the following shortcomings: In the prior art, the cam sleeve is axially displaced on the spindle, causing the cam sleeve, high-speed cam, low-speed cam and other structures to move at the same time, resulting in a non-compact motorcycle engine structure, a more complex overall structure and difficulty in reducing its size. Summary of the Invention

[0006] This invention provides a miniaturized and simple variable valve lift structure for a motorcycle engine, comprising a camshaft, a switching sleeve, an intake cam, an exhaust cam, a solenoid valve, a timing driven sprocket, a spring, and a steel ball. The intake cam includes a low-lift intake cam and a high-lift intake cam. The spring and steel ball are disposed within a blind hole in the camshaft. The solenoid valve contacts the switching sleeve. The key feature is that the switching sleeve, the low-lift intake cam, and the high-lift intake cam are respectively fixed to the camshaft and rotate with it. The camshaft has an axial slide rail, on which a cam sleeve is fitted with a clearance fit. The timing driven sprocket is fixedly connected to the cam sleeve. The camshaft moves axially relative to the axially stationary cam sleeve. The camshaft is confined in a low-lift or high-lift groove on the cam sleeve by the spring and steel ball. The solenoid valve, through the switching sleeve, causes the camshaft to move axially on the cam sleeve, thereby driving the low-lift and high-lift intake cams to move axially to achieve valve change.

[0007] To facilitate the reciprocating switching between the low-lift and high-lift intake cams, the surfaces at both ends of the switching sleeve are provided with two symmetrically raised helical profiles, Helical Profile 1 and Helical Profile 2, along the radial centerline. The helical heights of Helical Profile 1 and Helical Profile 2 are equal, and the helical height is equal to the distance between the centers of the low-lift and high-lift grooves. The endpoints of the helical lines of Helical Profile 1 and Helical Profile 2 are helical points, and the helical height determines the axial movement distance of the camshaft.

[0008] To facilitate the axial movement of the cam spindle, the connecting journals at both ends of the cam spindle are used to support the cylinder head. The inner ring of the cam sleeve is provided with an inner slide rail corresponding to the axial slide rail 1. The cross-section of the axial slide rail 1 and the inner slide rail of the cam sleeve 4 is a polygon with an even number of sides, where the even number is ≥4, and the adjacent sides are rounded.

[0009] To facilitate the installation of the switching sleeve and achieve precise positioning of the switching sleeve, the cam spindle is also provided with an axial slide rail two. The cross-section of the axial slide rail one is larger than that of the axial slide rail two. A shoulder is formed on the axial slide rail one. The switching sleeve is fixed on the axial slide rail two, and one side of the switching sleeve is positioned by the shoulder.

[0010] Preferably, the inner ring of the switching sleeve is provided with an inner slide rail corresponding to the second axial slide rail. The cross-section of the second axial slide rail and the inner slide rail is a polygon with an even number of sides, where the even number is ≥4. The adjacent sides are rounded. The switching sleeve is clearance-fitted with the second axial slide rail. The second axial slide rail is provided with a bushing and a bearing. The axial movement of the switching sleeve is restricted by the shoulder, bushing, and bearing. There is no relative sliding between the switching sleeve and the cam spindle.

[0011] To reduce the overall axial dimension of the variable valve lift structure, the exhaust cam is mounted on one end of the cam sleeve, and the other end has two cam sleeve journals. A signal wheel and a timing driven sprocket are clearance-fitted onto cam sleeve journal one, with the timing driven sprocket having cup-shaped teeth. A flange is interference-fitted onto cam sleeve journal two, and the concave cavity of the cup-shaped teeth accommodates the flange. The signal wheel and the cup-shaped teeth are fixed to the flange. The cam sleeve, timing driven sprocket, and signal wheel rotate under the drive of the timing chain, and the cam spindle rotates synchronously under the drive of the cam sleeve. By using cup-shaped teeth, the axial dimension of the camshaft assembly can be reduced, allowing the engine timing chain to be positioned closer to the cylinder center, resulting in a more compact engine structure and smaller engine size. This avoids the need for redeveloping the crankcase, crankshaft, and cylinder block due to the increased distance between the timing chain and the cylinder center; only the cylinder head needs to be developed, allowing existing conventional engine products to be quickly upgraded to variable valve products, thus reducing development costs.

[0012] To facilitate support of the cam sleeve, two limiting discs are provided in the middle of the cam sleeve, and the cam sleeve journal three is located between the limiting discs. The cam sleeve journal three is used to install bearings to connect to the cylinder head or to be directly connected to the cylinder head.

[0013] Preferably, the switching sleeve is split into two switching sleeves, each of which has only one raised spiral profile. The split switching sleeves are set in different positions and driven by different solenoid valves. One switching sleeve is used to switch from low lift to high lift, and the other switching sleeve is used to switch from high lift to low lift.

[0014] Preferably, the intake cam abuts against the intake rocker arm, and the exhaust cam abuts against the exhaust rocker arm. When the engine is not started and is operating at low speed, the intake rocker arm abuts against the low-lift intake cam, and the opening of the intake valve lift is controlled by the low-lift intake cam. When the engine speed increases from low to critical switching speed, the solenoid valve extends its pin, and the pin contacts the spiral contour of the rotating switching sleeve. The switching sleeve and the cam spindle move together in the axial direction relative to the cam sleeve which is stationary in the axial direction, causing the high-lift intake cam on the cam spindle to move towards the low-lift intake cam. The displacement distance is the spiral height of a preset spiral line. When the displacement action stops, the cam spindle is positioned in the high-lift groove of the cam sleeve by the spring and the steel ball, the pin of the solenoid valve retracts, the high-lift intake cam contacts the intake rocker arm, and the intake valve lift is controlled by the high-lift intake cam.

[0015] To accommodate multi-cylinder engines, the camshaft is provided with several cam sleeves, switching sleeves, intake cams, and exhaust cams. Each of the switching sleeves is provided with a low-lift groove or a high-lift groove. A limiting spring and a steel ball are provided at the corresponding positions on the camshaft.

[0016] The present invention has the following beneficial effects: 1. This structure is located on the engine cylinder head. The valve lift switching action is as follows: the journals at both ends of the camshaft and the shaft diameter on the cam sleeve are supported in the cylinder head mounting hole. The cam sleeve limit plate on the cam sleeve cooperates with the cylinder head to restrict the axial movement of the cam sleeve. The cam sleeve and the timing driven sprocket and signal wheel mounted on the cam sleeve can rotate under the drive of the timing chain. The camshaft rotates synchronously under the drive of the cam sleeve. At low speed, the low lift intake cam on the camshaft contacts the intake rocker arm to meet the engine's low lift requirement. When the engine speed reaches the preset valve lift switching speed range, the solenoid valve will extend its pin. The solenoid valve is fixed on the cylinder head. The rotating switching sleeve contacts one pin of the solenoid valve. Under the guidance of the preset spiral contour contact line of the switching sleeve, the switching sleeve and the camshaft move axially together. The high lift intake cam moves towards the low lift intake cam and contacts the intake rocker arm, completing the low lift to high lift switching. Conversely, when the engine speed is lower than the switching speed, the other pin of the solenoid valve contacts the spiral contour on the switching sleeve, completing the switch from high lift to low lift. The camshaft of this invention not only has a short axial dimension, but also eliminates the need for movement of the cam sleeve, cup-shaped gear, and signal wheel. Only the camshaft and intake cam shaft need to move axially, thus eliminating the space required for movement of the cam sleeve, cup-shaped gear, and signal wheel within the cylinder head. This results in a more compact engine structure and smaller engine size. With fewer moving parts, the required precision of the cylinder head, gears, and camshaft is lower, leading to improved overall reliability and easier component processing.

[0017] 2. In this invention, the crankcase, crankshaft, cylinder block, etc., do not need to be redeveloped due to the increased distance between the timing chain and the cylinder head. Only the cylinder head needs to be developed to quickly upgrade existing conventional engine products to variable valve products, thus reducing development costs.

[0018] 3. This invention occupies less internal space within the cylinder head, reserving space for spark plug installation. The spark plug on the engine cylinder head is positioned on the outer side of the camshaft journal, defined as the side opposite the timing driven sprocket. This allows the spark plug to be closer to the center of the cylinder head, enabling faster combustion and thrust generation, thereby improving engine power performance. It also improves fuel economy, reduces fuel consumption, and minimizes unburned fuel and exhaust emissions, making it more environmentally friendly.

[0019] 4. Applicable to single-cylinder and multi-cylinder motorcycle engines. In multi-cylinder engines, only one cam sleeve needs to be limited, making the overall structure simpler. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an embodiment of a variable valve lift structure for a motorcycle engine. Figure 2This is a schematic diagram of the cam spindle structure; Figure 3 This is a side view of the cam spindle; Figure 4 This is a schematic diagram of the cam sleeve; Figure 5 This is a sectional view of the cam sleeve. Figure 6 This is a schematic diagram of the switching sleeve; Figure 7 This is a front view of the switch sleeve; Figure 8 This is a schematic diagram of a bowl-shaped tooth; Figure 9 This is a cross-sectional view of the variable valve lift structure of a motorcycle engine. Detailed Implementation

[0021] The following detailed description illustrates the specific implementation method: 1. The reference numerals in the accompanying drawings of the instruction manual include: camshaft 1, low-lift intake cam 1-1, high-lift intake cam 1-2, intake rocker arm 2, exhaust rocker arm 3, cam sleeve 4, exhaust cam 4-1, cam sleeve journal three 4-2, right limit plate 4-3, left limit plate 4-4, high-lift groove 4-5, low-lift groove 4-6, cam sleeve journal two 4-7, cam sleeve journal one 4-8, timing driven sprocket 5, signal wheel 6, switching sleeve 7, spiral profile one 7-1, spiral profile two 7-2, spiral line dot 7-3, groove 7-4, radial center line 7-5, bearing one 8, bushing 9, flange 10, bolt 11, spring 12, steel ball 13, VVL solenoid valve 14, connecting journal one a, axial slide rail two b, axial slide rail one c, blind hole d, connecting journal two e, shoulder f. Example

[0022] like Figures 1-9As shown, a variable valve lift structure for a motorcycle engine includes a camshaft 1, an intake rocker arm 2, an exhaust rocker arm 3, a switching sleeve 7, an intake cam, a VVL solenoid valve 14, a timing driven sprocket 5, a signal wheel 6, a bearing 8, a spring 12, and a steel ball 13. The intake cam includes a low-lift intake cam 1-1 and a high-lift intake cam 1-2. The spring 12 and the steel ball 13 are disposed in a blind hole d in the camshaft 1, the axis of which is perpendicular to the axis of the camshaft 1. The VVL solenoid valve 14 is fixed to the cylinder head and contacts the switching sleeve 7. The switching sleeve 7, the low-lift intake cam 1-1, and the high-lift intake cam 1-2 are respectively fixed on the camshaft 1. When shaft 1 rotates, an axial slide rail c is provided on the cam spindle 1. A cam sleeve 4 is fitted on the axial slide rail c with clearance. The cam sleeve 4 is provided with an exhaust cam 4-1, a flange 10, a timing driven sprocket 5, and a signal wheel 6. The cam spindle 1 moves in the axial direction relative to the axially stationary cam sleeve 4. The cam spindle 1 is limited in the low-lift groove 4-6 or high-lift groove 4-5 on the cam sleeve 4 by the spring 12 and the steel ball 13. The center distance in the low-lift groove 4-6 or high-lift groove 4-5 is the axial sliding distance of the cam spindle 1. The steel ball 13 cooperates with the low-lift groove 4-6 or high-lift groove 4-5 on the inner side of the cam sleeve 4 to axially position the relative position of the cam spindle 1 and the cam sleeve 4.

[0023] The surfaces at both ends of the switching sleeve 7 are provided with symmetrical raised spiral contours 7-1 and 7-2 along the radial centerline 7-5. The spiral heights of spiral contours 7-1 and 7-2 are equal, and the spiral height is equal to the distance between the centers of the low-lift groove 4-6 and the high-lift groove 4-5. Spiral contour 7-1 corresponds to the position of the low-lift intake cam 1-1 and the low-lift groove 4-6, and spiral contour 7-2 corresponds to the position of the high-lift intake cam 1-2 and the high-lift groove 4-5. The spiral height determines the axial movement distance of the cam spindle 1. The endpoint of the spirals of spiral contours 7-1 and 7-2 is spiral point 7-3. When the pin of the VVL solenoid valve 14 moves to spiral point 7-3, it retracts to avoid interfering with the rotation of the switching sleeve 7. A weight-reducing groove 7-4 is also provided between spiral contours 7-1 and 7-2.

[0024] Of course, the switching sleeve 7 can be split into two switching sleeves along the radial center line 7-5. Each switching sleeve is provided with only one raised spiral profile. The spiral profiles on the two switching sleeves are spiral profile one 7-1 and spiral profile two 7-2, respectively. The split switching sleeves are set in different positions and driven by different VVL solenoid valves 14. One switching sleeve is used to switch from low lift to high lift, and the other switching sleeve is used to switch from high lift to low lift.

[0025] The cam sleeve 4 is an active rotation mechanism that drives the cam spindle 1 to rotate. When the speed is within the preset valve lift switching speed range, the VVL solenoid valve 14 is controlled by the electronic control system to extend its pin in a timely manner according to the cam angle position signal provided by the signal wheel 6. The signal wheel 6 provides the signal because the valve lift switching action must be completed at the base circle of the low-lift intake cam 1-1 and the high-lift intake cam 1-2; otherwise, switching cannot be achieved. Therefore, the vehicle's electronic control system must know the real-time position of the cams. Thus, the signal wheel 6 installed on the cam sleeve 4 can provide the signal of the cam base circle position. The specific signal calculation involves the VVL solenoid valve. The solenoid valve, VVL solenoid valve, is a mature existing technology and will not be elaborated here. When the cam spindle 1 drives the switching sleeve 7 to rotate, the spiral profile 7-1 or spiral profile 7-2 on the switching sleeve 7 contacts a pin of the VVL solenoid valve 14. Since the VVL solenoid valve 14 is fixed to the cylinder head and will not move, the cam spindle 1 and the switching sleeve 7 will generate axial displacement under the interaction force of the switching sleeve 7 and the pin, thereby enabling the high or low lift intake cams 1-1 and 1-2 to contact the intake rocker arm 2 to achieve different valve lift requirements. The structure of the VVL solenoid valve 14 is a mature existing technology and its principle will not be elaborated here.

[0026] The cam spindle 1 has connecting journal a and connecting journal e at both ends. Connecting journal a is located near the end of the switching sleeve 7, and connecting journal e is located near the end of the intake cam. Connecting journal a and connecting journal e can be used to install bearing 8 simultaneously or one of them can be used to install bearing 8 and support it on the cylinder head. The inner ring of the cam sleeve 4 has an inner slide rail corresponding to the axial slide rail c. The cam spindle 1 also has an axial slide rail b. The cross section of the axial slide rail c is larger than the cross section of the axial slide rail b. A shoulder f is formed on the axial slide rail c. The switching sleeve 7 is fixed on the axial slide rail b. One side of the switching sleeve 7 is positioned by the shoulder f.

[0027] The inner ring of the switching sleeve 7 is provided with an inner slide rail corresponding to the second axial slide rail b. The cross-sections of the first axial slide rail c, the second axial slide rail b, the inner slide rail of the cam sleeve 4, and the inner slide rail of the switching sleeve 7 are polygons with an even number of sides, where the even number is 4. Adjacent sides are rounded. The cam sleeve 4 is clearance-fitted with the first axial slide rail c, and the switching sleeve 7 is clearance-fitted with the second axial slide rail b. The second axial slide rail b is provided with a bushing 9 and a bearing 8. The axial movement of the switching sleeve 7 is restricted by the shoulder f, the bushing 9, and the bearing 8. On one hand, the cam spindle 1 and the cam sleeve 4 are clearance-fitted, allowing the cam spindle 1 to move along the axial direction relative to the axially stationary cam sleeve 4, thus providing a guiding function. On the other hand, due to the cross-sectional shape of the two slide rails, the first axial slide rail c on the surface of the cam spindle 1 meshes with the inner slide rail of the cam sleeve 4, causing the cam spindle 1 to rotate with the cam sleeve 4, thus providing a transmission function.

[0028] The exhaust cam 4-1 is provided at one end of the cam sleeve 4, and the exhaust cam 4-1 and the cam sleeve 4 are integral. The other end of the cam sleeve 4 is provided with a cam sleeve journal 4-8 and a cam sleeve journal 4-7. A signal wheel 6 and a timing driven sprocket 5 are fitted on the cam sleeve journal 4-8 with clearance. The timing driven sprocket 5 has cup-shaped teeth and two through holes. A flange 10 is interference-fitted on the cam sleeve journal 4-7. The concave cavity of the cup-shaped teeth accommodates the flange 10. The signal wheel 6 and the cup-shaped teeth are connected by bolts 11. Fixed on the flange 10, the cam sleeve 4, timing driven sprocket 5, and signal wheel 6 rotate under the drive of the timing chain. The cam spindle 1 rotates synchronously under the drive of the cam sleeve 4. Reducing the axial dimension of the camshaft assembly allows the engine timing chain to be closer to the cylinder center, resulting in a more compact engine structure and smaller engine size. It avoids the need to redevelop crankcase, crankshaft, cylinder block, etc. due to the increased distance between the timing chain and the cylinder center. Only the cylinder head needs to be developed to quickly upgrade existing conventional engine products to variable valve products.

[0029] like Figure 9 As shown, the spark plug position on the engine cylinder head can be arranged on the outside of the connecting journal 2e of the camshaft 1. The outside refers to the side opposite to the switching sleeve 7, with the timing driven sprocket 5 as the boundary. The switching sleeve 7 and bearing 8 are mounted on the left side of the cup-shaped tooth. The left side of the switching sleeve 7 is axially positioned by the bushing 9 and bearing 8. The bearing 8 is limited by the step or retaining ring provided on the cylinder head.

[0030] The cam sleeve journal 4-8 is designed to assemble the cup-shaped tooth and signal wheel 6. The center hole of the cup-shaped tooth and signal wheel 6 is clearance-fitted with the journal, allowing the cup-shaped tooth and signal wheel 6 to be assembled onto the cam sleeve journal 4-8. This makes it easier to attach the timing chain to the cup-shaped tooth. The cup-shaped tooth and signal wheel 6 are fixed to the flange 10 by bolts 11. The engine timing chain will drive the cup-shaped tooth and signal wheel 6 to rotate around the axis of the cam sleeve 4.

[0031] like Figure 5 As shown, when the cam sleeve 4 does not need to be equipped with a bearing: the cam sleeve 4 is provided with two limiting discs in the middle, namely the left limiting disc 4-4 and the right limiting disc 4-3. The cam sleeve journal 3 4-2 is located between the left limiting disc 4-4 and the right limiting disc 4-3. The cam sleeve journal 3 4-2 is supported in the cylinder head mounting hole. The left limiting disc 4-4 limits the flange 10.

[0032] When a bearing needs to be installed on the cam sleeve 4: the cam sleeve 4 is provided with only a right limiting plate 4-3 in the middle for positioning the right side of the bearing. The flange 10 is pressed on the cam sleeve journal 4-7 and is axially limited by the bearing. The bearing is axially positioned by the stepped hole and pressure plate on the cylinder head. The flange 10 is interference-fitted with the cam sleeve 4.

[0033] The intake cam abuts against the intake rocker arm 2, and the exhaust cam 4-1 abuts against the exhaust rocker arm 3. When the engine is not started and is operating at low speed, the intake rocker arm 2 abuts against the low-lift intake cam 1-1, and the opening of the intake valve lift is controlled by the low-lift intake cam 1-1. When the engine speed increases from low to the critical switching speed, the VVL solenoid valve extends its pin, and the pin contacts the spiral contour of the rotating switching sleeve 7. The switching sleeve 7 and the cam spindle 1 are axially related. The stationary cam sleeve 4 moves along the axial direction, causing the high-lift intake cam 1-2 on the cam spindle 1 to move towards the low-lift intake cam 1-1. The displacement distance is the helix height of the preset helix. When the displacement action stops, the cam spindle 1 is positioned in the high-lift groove 4-5 of the cam sleeve 4 by the spring 12 and the steel ball 13. The pin of the VVL solenoid valve retracts, and the high-lift intake cam 1-2 contacts the intake rocker arm 2. The intake valve lift is controlled by the high-lift intake cam 1-2.

[0034] Depending on whether the engine is single-cylinder or multi-cylinder, the camshaft 1 is provided with a corresponding number of cam sleeves 4, switching sleeves 7, intake cams, and exhaust cams 4-1. Each of the cam sleeves 4 is provided with a low-lift groove 4-6 or a high-lift groove 4-5. A limiting spring 12 and a steel ball 13 are provided at the corresponding positions on the camshaft 1. The cam sleeve 4 may not use a flange 10 to fix the cup-shaped teeth, or a conventional timing driven sprocket 5 may be directly press-fitted on.

[0035] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A variable valve lift structure of a motorcycle engine, comprising a cam core, a switching sleeve, an intake cam, an exhaust cam, a solenoid valve, a timing driven sprocket, a spring and a steel ball, the intake cam comprising a low lift intake cam and a high lift intake cam, the spring and the steel ball being disposed in a blind hole of the cam core, the solenoid valve being in contact with the switching sleeve, characterized in that, The switching sleeve, low-lift intake cam and high-lift intake cam are fixed on the cam core shaft and rotate with the cam core shaft, the cam core shaft is provided with an axial slide rail one, the cam sleeve is clearance fitted on the axial slide rail one, the cam sleeve is fixedly connected with a timing driven sprocket, the cam core shaft moves in the axial direction relative to the axially stationary cam sleeve, the cam core shaft is limited in the low-lift groove or high-lift groove on the cam sleeve by the spring and steel ball.

2. The variable valve lift structure of a motorcycle engine according to claim 1, characterized by: The surfaces of the two ends of the switching sleeve are provided with radially central line-symmetrical convex spiral profiles one and two, the spiral lines of the spiral profiles one and two are equal in height, and the spiral line height is equal to the distance between the centers of the low-lift groove and high-lift groove.

3. The variable valve lift mechanism of a motorcycle engine according to claim 2, characterized by: The connecting journal of the two ends of the cam core shaft 1 is used for supporting on the cylinder head, the inner ring of the cam sleeve 4 is provided with an inner slide rail corresponding to the axial slide rail one c, the cross sections of the axial slide rail one c and the inner slide rail of the cam sleeve 4 are corresponding polygons with an even number of sides, and the even number is greater than or equal to 4, and the two adjacent sides are circularly arc transitioned.

4. The variable valve lift mechanism of a motorcycle engine according to any one of claims 1 to 3, characterized by: The cam core shaft is further provided with an axial slide rail two, the cross section of the axial slide rail one is greater than that of the axial slide rail two, an axial shoulder is formed on the axial slide rail one, the switching sleeve is fixed on the axial slide rail two, and one side of the switching sleeve is positioned by the axial shoulder.

5. The variable valve lift mechanism of a motorcycle engine according to claim 4, characterized by: The inner ring of the switching sleeve is provided with an inner slide rail corresponding to the axial slide rail two, the cross sections of the axial slide rail two and the inner slide rail are corresponding polygons with an even number of sides, and the even number is greater than or equal to 4, and the two adjacent sides are circularly arc transitioned, the switching sleeve is clearance fitted with the axial slide rail two, the axial slide rail two is provided with a bushing and a bearing one, and the switching sleeve is limited in axial movement by the axial shoulder, the bushing and the bearing one.

6. The variable valve lift mechanism structure of a motorcycle engine according to claim 5, characterized by: The cam sleeve is provided with the exhaust cam at one end and cam sleeve journal one and cam sleeve journal two at the other end, the signal wheel and the timing driven sprocket are clearance fitted on the cam sleeve journal one, the timing driven sprocket is a bowl-shaped tooth, the flange plate is interference fitted on the cam sleeve journal two, the bowl-shaped tooth recess contains the flange plate, the signal wheel and the bowl-shaped tooth are fixed on the flange plate, the cam sleeve, the timing driven sprocket and the signal wheel rotate under the driving of the timing chain, and the cam core shaft rotates synchronously under the driving of the cam sleeve.

7. The variable valve lift mechanism of a motorcycle engine according to claim 6, characterized by: The cam sleeve is provided with two limiting discs in the middle part, and the cam sleeve journal three is between the limiting discs.

8. The variable valve lift mechanism structure of a motorcycle engine according to claim 1, characterized by: The switching sleeve is split into two switching sleeves, only one convex spiral profile is arranged on each switching sleeve, the split switching sleeves are arranged at different positions and driven by different electromagnetic valves, one switching sleeve is used for switching from low lift to high lift, and the other switching sleeve is used for switching from high lift to low lift.

9. The variable valve lift mechanism of a motorcycle engine according to claim 6 or 7, characterized by: The intake cam is in abutment with the intake rocker arm, and the exhaust cam is in abutment with the exhaust rocker arm. When the engine is not started and works at low speed, the intake rocker arm is in abutment with the low-lift intake cam, and the opening of the intake valve lift is controlled by the low-lift intake cam. When the engine speed is increased from low speed to a critical switching speed, the solenoid valve extends the pin head, the pin head is in contact with the helical contour of the rotating switching sleeve, the switching sleeve and the cam core shaft are axially displaced together relative to the axially stationary cam sleeve, the high-lift intake cam on the cam core shaft is moved to the low-lift intake cam direction, the displacement distance is the helical height of the preset helix, and when the displacement is stopped, the cam core shaft is positioned in the high-lift groove of the cam sleeve by the spring and the steel ball, the pin head of the solenoid valve is retracted, the high-lift intake cam is in contact with the intake rocker arm, and the intake valve lift is controlled by the high-lift intake cam.

10. The variable valve lift mechanism of a motorcycle engine according to claim 9, characterized by: The cam core shaft is provided with a plurality of cam sleeves, switching sleeves, intake cams and exhaust cams, and any one of the switching sleeves is provided with a low-lift groove or a high-lift groove.

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