Crankshaft transmission mechanism for an engine

Abstract

The application discloses a crankshaft transmission mechanism for an engine, which comprises a crankshaft and a connecting rod, a crank arm and a balance weight are integrally formed and are connected through a smooth transition of a concave arc surface; a first boss in a ring shape is arranged on the outer side surface of the crank arm near the two ends of the crankshaft, and the radial outer contour of the first boss extends to be tangent to the concave arc surface; the end surface of the one end of the crank arm where a connecting rod journal is located is a circular arc surface, is concentric with the connecting rod journal, and has a diameter smaller than the outer diameter of the axial end surface of the big end of the connecting rod. The radial size of the first boss is enlarged to increase the contact area with the inner wall of the shell to reduce the surface pressure, meanwhile, the big end of the connecting rod is exposed to the axial end surface to form a lubrication exposed area through the circular arc surface, so that forced lubrication and cooling are realized; and through the structure that the end surface of the driving gear is integrated into a contact surface, the semi-ring second boss surface is axially positioned, the connecting rod journal is thickened, and the eccentric mass block of the balance shaft is recessed to avoid, the wear resistance, the lubrication and heat dissipation performance, the structural strength and the running stability of the crankshaft transmission mechanism are simultaneously improved under the compact layout.

Description

Technical Field

[0001] This invention relates to the technical field of motorcycle engine transmission, and more particularly to a crankshaft transmission mechanism for an engine. Background Technology

[0002] In the crankshaft connecting rod mechanism of a motorcycle engine, the main journals at both ends of the crankshaft are supported on the inner wall of the engine housing by bearings or bushings. To reduce the overhang length of the crankshaft and improve the support rigidity, the main journals at both ends are usually located close to the crank arms. To withstand axial forces and achieve axial positioning of the crankshaft, an annular boss is usually integrally formed on the outer surface of the crank arms near both ends, surrounding the main journal. The annular boss contacts and engages with the inner wall of the engine housing. In traditional designs, the radial dimension of this annular boss is small, resulting in a small contact area with the inner wall of the engine housing. During engine operation, excessive surface pressure can easily cause abnormal wear on the inner wall of the housing, affecting engine life and reliability. To address this issue, existing improvements involve adding a copper gasket between the annular boss and the inner wall of the engine housing to increase the contact area and reduce surface pressure. However, this solution requires an additional gasket as a separate component, and grooves or steps for mounting and positioning the gasket must be machined on the crankshaft. This not only increases the number of parts and material costs but also increases processing complexity and assembly steps, which is detrimental to overall weight reduction and cost control.

[0003] Meanwhile, in the crankshaft connecting rod mechanism, the big end of the connecting rod is fitted onto the connecting rod journal and needs to be axially contacted and positioned with the crank arm. In the traditional structure, the crank arm has an annular boss surface coaxial with the connecting rod journal on the side facing the connecting rod. The radial inner contour of this annular boss surface is connected to the connecting rod journal, and the radial outer contour extends to match the outer diameter of the annular axial end face on the big end of the connecting rod, so that the crank arm and the axial end face of the connecting rod are in full contact. While this traditional structure provides a large axial contact area, the axial end face of the connecting rod is completely covered by the annular boss surface, i.e., blocked by the crank arm. This means that the lubricating oil splashed in the crankcase can only enter radially between the crank arm and the big end of the connecting rod. The lubricating oil in the contact area is limited and the turnover is slow, resulting in weak lubrication and heat dissipation. Especially for crankcases with a left-right hinge structure, the middle of the crankshaft lacks support. Insufficient lubrication and heat dissipation not only aggravate the friction and wear between the crank arm and the big end of the connecting rod, but also subject the crankshaft to a large connecting rod load, posing a severe test to the structural strength and wear resistance of the crankshaft, and easily leading to crankshaft wear or even breakage.

[0004] Therefore, how to reduce crankshaft wear on the engine housing wall, improve lubrication and heat dissipation between the crank arm and the big end of the connecting rod, and take into account a compact layout space, without increasing the number of parts and costs, is an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the existing technology, the purpose of this invention is to solve the technical problem of excessive friction between the crankshaft and the inner wall of the engine housing and the connecting rod, and to provide a crankshaft transmission mechanism for an engine that can improve the reliability and durability of the crankshaft transmission mechanism.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A crankshaft transmission mechanism for an engine includes a crankshaft and a connecting rod. The crankshaft includes a main journal, a connecting rod journal, a crank arm, and a counterweight. The crank arm is perpendicularly connected to the main journal and the connecting rod journal on both sides along its thickness direction. The length direction of the crank arm corresponds to the direction of the center line connecting the eccentrically distributed main journal and the connecting rod journal. The main journal and the connecting rod journal are located near the two ends of the crank arm. The width of the crank arm gradually narrows from the end where the main journal is located to the end where the connecting rod journal is located. The large end of the connecting rod is fitted onto the connecting rod journal, and the small end is used to connect to the piston. The counterweight is located on the crank arm at the end where the main journal is located and is integrally formed with the crank arm. The crankshaft has a structure in which the counterweight is smoothly connected to both sides of the crank arm in the width direction via a concave arc surface. Each of the two crank arms near the crankshaft ends has a first boss on its side facing the adjacent crankshaft end. The first boss is annular and coaxial with the main journal. The end face of the first boss is used for contact and positioning with the inner wall of the engine housing. The radial inner contour of the first boss connects to the main journal, and the radial outer contour extends to be tangent to the concave arc surface. The end face of the connecting rod journal on the crank arm is an arc surface, smoothly connected to both sides of the crank arm in the width direction. The arc surface is concentric with the connecting rod journal, and its diameter is smaller than the outer diameter of the axial end face of the connecting rod big end.

[0008] Furthermore, one of the two first bosses has a mounting portion protruding from its end face. The mounting portion is annular and coaxial with the main journal. The radial inner contour of the mounting portion is connected to the main journal. The crankshaft is provided with a drive gear for driving the engine balance shaft. The drive gear is fitted on the outer peripheral surface of the mounting portion. The end face of the drive gear is flush with the end face of the mounting portion and forms a contact surface. The contact surface is used to replace the end face of the first boss on the same side in contacting the inner wall of the engine housing.

[0009] Furthermore, the main journal has a bearing mounting position, and in the axial direction, the mounting part and the drive gear are located on the side of the bearing mounting position near the crank arm.

[0010] Furthermore, there are at least four crank arms, and among the crank arms furthest from the drive gear, at least one is a thickened crank arm, with the thickness of the thickened crank arm being greater than the thickness of the crank arm closest to the drive gear.

[0011] Furthermore, the counterweight integrated with the thickened crank arm is a thickened counterweight, and the thickness of the thickened counterweight is greater than the thickness of the counterweight near the drive gear.

[0012] Furthermore, the crankshaft includes at least two connecting rod journals, and at least three main journals are distributed alternately along the axial direction with each connecting rod journal. The crank arm is connected to the connecting rod journal and the main journal on both sides respectively. The thickened crank arm and the thickened counterweight are thickened axially towards the side where the main journal is located.

[0013] Furthermore, the crank arm has a second boss on the side facing the connecting rod in the thickness direction, which is used to contact and position with the axial end face of the big end of the connecting rod; the second boss is a semi-circular shape concentric with the connecting rod journal, and the radial inner contour of the second boss is connected to the connecting rod journal, and the radial outer contour matches the outer diameter of the axial end face of the big end of the connecting rod.

[0014] Furthermore, the diameter of the arc surface is larger than the inner diameter of the axial end face of the connecting rod big end, and there is an arc chamfer at the junction of the connecting rod journal and the crank arm.

[0015] Furthermore, the main journal and the connecting rod journal are radially intersected.

[0016] Furthermore, the crankshaft transmission mechanism also includes a balance shaft, which is arranged parallel to the main journal of the crankshaft. A driven gear is coaxially fixedly connected to the balance shaft, and the driven gear meshes with the driving gear. An eccentric mass block is connected to or integrally formed on the balance shaft, and the eccentric mass block corresponds to the position of the connecting rod on the crankshaft. The back of the eccentric mass block is recessed to form a recessed portion, which is used to avoid the connecting rod on the crankshaft.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention extends the radial outer contour of the first boss on the outer surface of the crank arm to be tangent to the concave arc surface, thereby achieving the maximum permissible radial dimension within a limited structural space. This increases the contact area with the inner wall of the engine housing, effectively reducing the pressure per unit area and alleviating abnormal wear on the inner wall of the housing. Simultaneously, the end face of the connecting rod journal on the crank arm is constructed as an arc surface with a diameter smaller than the outer diameter of the axial end face of the connecting rod big end. This exposes a portion of the axial end face of the connecting rod big end, forming a lubrication exposure area. Splashed lubricating oil can directly adhere axially and be continuously carried into the contact surfaces as the crankshaft rotates, forming forced lubrication and cooling. This reduces the coefficient of friction and operating temperature, thus achieving the dual technical effects of external wear prevention and internal friction reduction on a single crankshaft structure without the need for additional parts, thus achieving both lightweight and cost control.

[0019] 2. This invention forms a mounting portion by protruding on the end face of a first boss, and mounts the drive gear onto the mounting portion, making its end face flush with the end face of the mounting portion to form a contact surface. This integrates the end face of the existing drive gear into part of the contact surface, expanding the bearing area on this side without adding any parts. At the same time, a second boss surface, which is semi-annular and whose outer contour matches the axial end face size of the big end of the connecting rod, is retained on the side of the crank arm facing the connecting rod. This is used for axial contact positioning of the big end of the connecting rod. While introducing an axial lubrication exposure area, it maintains the axial limiting function of the connecting rod, effectively constraining the axial movement of the connecting rod and ensuring piston alignment. Thus, a good balance is achieved between expanding the bearing area and strengthening lubrication, and between axial positioning and friction reduction and heat dissipation.

[0020] 3. This invention shortens the axial overhang length of the crankshaft at that end by placing the drive gear and mounting part on the side of the bearing mounting position close to the crank arm. Furthermore, by using a thickened counterweight at the end furthest from the drive gear, the imbalance in mass distribution caused by the built-in drive gear is compensated, ensuring smooth crankshaft operation. Simultaneously, by thickening the connecting rod journal to create a radial interlacing with the main journal, the bending section modulus of the connecting rod journal is increased, enhancing the overall structural rigidity of the crankshaft and enabling better adaptation to crankcase structures with left and right gearboxes and a lack of main journal support in the middle. Additionally, a recessed portion is provided on the back of the eccentric mass block of the balance shaft to avoid the connecting rod, allowing the balance shaft to be closer to the crankshaft for a more compact arrangement and improved gear meshing rigidity. Thus, the entire crankshaft transmission mechanism is comprehensively optimized in terms of wear resistance, high lubrication, compact structure, and smooth operation. Attached Figure Description

[0021] To make the purpose, technical solution, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings:

[0022] Figure 1 This is a partial perspective view of the crankshaft transmission mechanism described in the embodiment;

[0023] Figure 2 This is a partial perspective view of the crankshaft described in the embodiment;

[0024] Figure 3 This is a partial perspective view of the crankshaft described in the embodiment;

[0025] Figure 4 This is a partial perspective view of the connecting rod described in the embodiment;

[0026] Figure 5 This is a front view of the crankshaft described in the embodiment;

[0027] Among them, the main journal 1, crank arm 2, counterweight 3, concave arc surface 4, first boss 5, mounting part 6, driving gear 7, bearing mounting position 8, thickened crank arm 9, thickened counterweight 10, connecting rod journal 11, connecting rod 12, connecting rod big end 13, arc surface 14, axial end face 15, second boss surface 16, arc chamfer 17, balance shaft 18, driven gear 19, eccentric mass block 20, and recess 21. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product is in use. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. In addition, the terms "horizontal," "vertical," etc., do not indicate that the component is required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0031] Example:

[0032] Please see Figure 1 , Figure 2 and Figure 3A crankshaft transmission mechanism for an engine includes a crankshaft and a connecting rod 12. The crankshaft includes a main journal 1, a connecting rod journal 11, a crank arm 2, and a counterweight 3. The crank arm 2 is perpendicularly connected to the main journal 1 and the connecting rod journal 11 on both sides in its thickness direction. The length direction of the crank arm 2 corresponds to the direction of the center line connecting the eccentrically distributed main journal 1 and the connecting rod journal 11. The main journal 1 and the connecting rod journal 11 are located near the two ends of the crank arm 2. The width of the crank arm 2 gradually narrows from the end where the main journal 1 is located to the end where the connecting rod journal 11 is located. The large end of the connecting rod 12 is fitted onto the connecting rod journal 11, and the small end is used to connect to the piston. The counterweight 3 is located on the crank arm 2 at the end where the main journal 1 is located and is integrally formed with the crank arm 2. The structure features a counterweight 3 that smoothly connects to both sides of the crank arm 2 in the width direction via a concave arc surface 4. Each of the two crank arms 2 near the crankshaft ends has a first boss 5 on its side facing the adjacent crankshaft end. The first boss 5 is annular and coaxial with the main journal 1. The end face of the first boss 5 is used for contact and positioning with the inner wall of the engine housing. The radial inner contour of the first boss 5 connects to the main journal 1, and the radial outer contour extends to be tangent to the concave arc surface 4, i.e., both connected and tangent. The end face of the connecting rod journal 11 on the crank arm 2 is an arc surface 14, which smoothly connects to both sides of the crank arm 2 in the width direction. The arc surface 14 is concentric with the connecting rod journal 11, and its diameter is smaller than the outer diameter of the axial end face 15 of the connecting rod big end 13.

[0033] The crankshaft transmission mechanism of this invention features a first boss 5 on the outer surface of the crank arm 2, surrounding the main journal 1. Its radial outer contour extends to be tangent to a concave arc surface 4. The concave arc surface 4 is the innermost radial boundary formed by the connection between the crank arm 2 and the counterweight 3. The fact that the first boss 5 extends to be tangent to this boundary indicates that the area occupied by the first boss 5 on the outer surface of the crank arm 2 has reached the maximum radial dimension allowed by the structural space. Compared to the first boss 5 with its limited radial dimension in traditional crankshafts, this solution increases the effective contact area between the first boss 5 and the inner wall of the engine housing without adding components or changing the overall crankshaft layout. When the engine is running, the axial force on the crankshaft is transmitted to the inner wall of the housing through the larger end face of the first boss 5, reducing the pressure per unit area and effectively mitigating wear in the contact area of ​​the inner wall of the housing, thus extending the engine's service life. Simultaneously, it eliminates the need for additional copper gaskets and their mounting and positioning structures, avoiding the problems of increased parts quantity, processing complexity, and assembly procedures, while also achieving both lightweighting and cost control. Secondly, by defining the end face of the connecting rod journal 11 on the crank arm 2 as an arc surface 14, concentric with the connecting rod journal 11, and with its diameter smaller than the outer diameter of the axial end face 15 of the connecting rod big end 13, a portion of the axial end face 15 of the connecting rod big end 13 is exposed axially, forming a lubrication exposure area not obscured by the crank arm 2. During the working cycle, the splashed lubricating oil can not only penetrate radially between the crank arm 2 and the connecting rod big end 13, but also directly splash axially and adhere to the exposed axial end face 15 of the connecting rod big end 13, and be further lubricated as the two rotate relative to each other. The lubrication is inserted between the crank arm 2 and the big end 13 of the connecting rod, thereby achieving continuous and forced lubrication and cooling, reducing the friction coefficient and operating temperature of the kinematic pair. This solves the defect in the traditional structure where the axial end face 15 of the big end 13 of the connecting rod is completely covered and can only rely on radial oil inlet, thus reducing friction and wear. For engine conditions with left and right gearboxes and a lack of support in the middle of the crankshaft, this effectively reduces the additional crankshaft load caused by friction, prevents premature fatigue or fracture of the crankshaft under thermo-mechanical coupling, and improves the reliability and durability of the crankshaft connecting rod 12 mechanism under harsh conditions.

[0034] Please see Figure 1 , Figure 2 and Figure 3 Of the two first bosses 5, one of the first bosses 5 has a mounting portion 6 protruding from its end face. The mounting portion 6 is annular and coaxial with the main journal 1. The radial inner contour of the mounting portion 6 is connected to the main journal 1. The crankshaft is provided with a drive gear 7 for driving the engine balance shaft 18. The drive gear 7 is fitted on the outer peripheral surface of the mounting portion 6. The end face of the drive gear 7 is flush with the end face of the mounting portion 6 and forms a contact surface. The contact surface is used to replace the end face of the first boss 5 on the same side in contacting the inner wall of the engine housing.

[0035] Thus, a mounting portion 6 is formed by a coaxial protrusion on the end face of the first boss 5 at one end of the crankshaft. The drive gear 7 is fitted onto the outer circumferential surface of the mounting portion 6, and the end face of the drive gear 7 is flush with the end face of the mounting portion 6. Together, they form a continuous contact surface, which replaces the end face of the first boss 5 on this side and is used to contact the inner wall of the engine housing. Since the drive gear 7 itself is an existing part required to drive the balance shaft 18, integrating its end face into part of the contact surface is equivalent to expanding the effective contact area on this side by utilizing the end face area of ​​the drive gear 7 itself without adding any additional parts. This can also reduce surface pressure and reduce wear on the inner wall of the housing. At the same time, the mounting portion 6 provides reliable radial positioning support for the drive gear 7, and the structure in which the end face of the drive gear 7 is flush with the end face of the mounting portion 6 ensures the flatness and integrity of the contact surface.

[0036] Please see Figure 1 , Figure 2 and Figure 3 The main journal 1 has a bearing mounting position 8. In the axial direction, the mounting part 6 and the drive gear 7 are located on the side of the bearing mounting position 8 near the crank arm 2.

[0037] In this way, the mounting part 6 and the drive gear 7 mounted on it are located axially on the side of the bearing mounting position 8 near the crank arm 2. That is, the drive gear 7 is arranged as a whole on the inner side of the bearing or bearing of the main journal 1. This makes the drive gear 7 different from the traditional structure in which it is suspended outside the bearing or bearing, shortening the axial overhang length of the crankshaft at this end. This is beneficial to reducing the space occupied by the crankshaft in the engine housing and is conducive to the miniaturization and compact design of the overall engine layout.

[0038] Please see Figure 1 , Figure 2 and Figure 3 There are at least four crank arms 2. Among the crank arms 2 that are far away from the drive gear 7, at least one is a thickened crank arm 9. The thickness of the thickened crank arm 9 is greater than the thickness of the crank arm 2 that is close to the drive gear 7.

[0039] In this way, as the drive gear 7 moves inward toward the bearing, the weight in the area between the bearing bushes at both ends increases. By increasing the thickness of the crank arm 2 at the end away from the drive gear 7, the imbalance in the overall mass distribution of the crankshaft caused by the change in the position of the drive gear 7 can be effectively compensated, so that the imbalance of the crankshaft during rotation can be effectively controlled and the vibration during engine operation can be reduced.

[0040] Please see Figure 1 , Figure 2 and Figure 3 The counterweight 3 integrated with the thickened crank arm 9 is a thickened counterweight 10, and the thickness of the thickened counterweight 10 is greater than the thickness of the counterweight 3 near the drive gear 7.

[0041] In this way, by further increasing the thickness of the corresponding counterweight 3 on the basis of thickening the crank arm 2, the overall mass on the side away from the drive gear 7 can be better compensated, making the mass distribution of the crankshaft more balanced relative to the center of rotation, improving the dynamic balance quality, and reducing vibration and noise during high-speed operation.

[0042] Please see Figure 1 , Figure 2 and Figure 3 The crankshaft includes at least two connecting rod journals 11, and the main journal 1 has at least three sections that are alternately distributed along the axial direction with each connecting rod journal 11. The crank arm 2 is connected to the connecting rod journal 11 and the main journal 1 on both sides respectively. The thickened crank arm 9 and the thickened counterweight 10 are thickened in the axial direction toward the side where the main journal 1 is located.

[0043] In this way, while increasing the mass to achieve balance compensation, it will not encroach on the axial space where the connecting rod journal 11 is located, avoid interference with the big end of the connecting rod 12, and ensure that the normal installation and flexible rotation of the connecting rod 12 are not affected. The balance problem is solved while taking into account the rationality of the structure and the feasibility of assembly.

[0044] Please see Figure 1 , Figure 2 and Figure 3 In this embodiment, the wear-resistant crankshaft includes three main journals 1, two connecting rod journals 11, four crank arms 2, and four counterweights 3. The main journals 1 and connecting rod journals 11 are alternately distributed along the axial direction, and the crank arms 2 are distributed at intervals along the axial direction and connected between adjacent main journals 1 and connecting rod journals 11. The counterweights 3 correspond one-to-one with the crank arms 2. The wear-resistant crankshaft is an integrally formed structure.

[0045] Please see Figure 1 , Figure 2 and Figure 4 The crank arm 2 has a second boss surface 16 on the side facing the connecting rod 12 in the thickness direction, which is used to contact and position with the axial end face 15 of the big end 13 of the connecting rod; the second boss surface 16 is a semi-annular shape concentric with the connecting rod journal 11, and the radial inner contour of the second boss surface 16 is connected to the connecting rod journal 11, and the radial outer contour is matched with the outer diameter of the axial end face 15 of the big end 13 of the connecting rod.

[0046] Thus, based on the aforementioned large-area lubrication and heat dissipation effect, the crank arm 2 is further limited to the side facing the connecting rod 12 in the thickness direction, while still retaining a second boss surface 16 for contacting and positioning with the axial end face 15 of the connecting rod big end 13; this ensures that while introducing an axial lubrication exposure area and reducing the coverage area of ​​the crank arm 2 body, the axial limiting function of the connecting rod 12 during operation is not sacrificed; the second boss surface 16 is optimized into a semi-annular shape concentric with the connecting rod journal 11, and its radial dimension is consistent with the axis of the connecting rod big end 13. The second boss surface 16 is aligned with the axial end face 15 of the connecting rod big end 13 on the side of the connecting rod journal 11 near the counterweight 3. It provides the largest contact support area within the size range of the crank arm 2, ensuring stable axial support and uniform stress distribution between the connecting rod big end 13 and the crank arm 2 during high-load power strokes. This avoids excessive local pressure and abnormal wear caused by insufficient contact area, thereby improving lubrication performance while ensuring the reliability of axial contact positioning.

[0047] Please see Figure 1 , Figure 2 and Figure 4 The diameter of the arc surface 14 is larger than the inner diameter of the axial end face 15 of the connecting rod big end 13, and there is an arc chamfer 17 at the junction of the connecting rod journal 11 and the crank arm 2.

[0048] In this way, the crank arm 2 can completely cover and extend beyond the end face area of ​​the shaft hole of the connecting rod big end 13 in the radial direction, so that the crank arm 2 forms an effective axial enclosure against the inner edge of the shaft hole of the connecting rod big end 13. This prevents the lubricating oil that enters the mating clearance between the connecting rod big end 13 and the connecting rod journal 11 under the action of centrifugal force from being easily thrown out and leaked from the axial opening. This helps to maintain a stable and full lubricating oil film between the shaft hole of the connecting rod big end 13 and the connecting rod journal 11, thereby reliably preventing lubrication failure. At the same time, the connection between the connecting rod journal 11 and the crank arm 2 has a rounded chamfer 17, which effectively reduces the stress concentration factor of this connection part. When the crankshaft is subjected to alternating bending loads, it can prevent fatigue cracks from starting from the root, thereby improving the fatigue strength and overall structural life of the crankshaft.

[0049] Please see Figure 2 and Figure 5 The main journal 1 and the connecting rod journal 11 are radially intersected, and the intersecting is achieved by increasing the diameter of the connecting rod journal 11; that is, the radial dimension of the connecting rod journal 11 is configured such that the axial projection of the connecting rod journal 11 overlaps with the axial projection of the main journal 1.

[0050] This increases the cross-sectional area of ​​the connecting rod journal 11, improving its bending section modulus and torsional stiffness. In the above improvements, although some material was reduced at one end of the crank arm 2 to create axial clearance, the thickened connecting rod journal 11, as the core structure connecting the crank arm 2, effectively compensates for and strengthens the overall structural strength of the crankshaft. This allows the solution to better adapt to the application scenario of a left-right crankcase without intermediate main journal 1 support, effectively suppressing the bending deformation of the crankshaft under high speed and high load, ensuring the coaxiality and rotational smoothness of the main journal 1 and connecting rod journal 11, and ensuring the reliable and durable power output of the engine under harsh conditions.

[0051] Please see Figure 1 The crankshaft transmission mechanism also includes a balance shaft 18, which is set parallel to the main journal 1 of the crankshaft. A driven gear 19 is coaxially fixedly connected to the balance shaft 18, and the driven gear 19 meshes with the driving gear 7. An eccentric mass block 20 is connected to or integrally formed on the balance shaft 18, and the eccentric mass block 20 corresponds to the position of the connecting rod 12 on the crankshaft. A recessed portion 21 is formed on the back of the eccentric mass block 20, which is used to avoid the connecting rod 12 on the crankshaft.

[0052] Thus, by recessing the back of the eccentric mass block 20 of the balance shaft 18 to form a recess 21, the recess 21 provides effective clearance space for the connecting rod 12 on the crankshaft during installation, allowing the balance shaft 18 to be positioned closer to the crankshaft in the radial direction. This structural improvement achieves a compact arrangement of the crankshaft and balance shaft 18 without increasing the overall lateral dimension of the engine, significantly improving the space utilization of the entire crankshaft transmission mechanism. Combined with the structure in the claim where the drive gear 7 is fitted onto the outer circumferential surface of the mounting portion 6 and its end face is flush with the end face of the mounting portion 6 to form a contact surface, the drive gear 7 is located on the side of the bearing mounting position 8 near the crank arm 2, shortening the axial overhang length of that end of the crankshaft. Furthermore, after the balance shaft 18 is further moved closer to the crankshaft via the recess 21, the meshing arrangement of the driven gear 19 on the balance shaft 18 and the drive gear 7 on the crankshaft is more compact, reducing the support span of the transmission gears and improving gear meshing stiffness and transmission smoothness. Meanwhile, while maintaining sufficient inertial mass to effectively counteract the inertial force and vibration at the location of the connecting rod 12 on the crankshaft, the eccentric mass block 20 removes some non-load-bearing material through the recess 21, which helps to reduce the overall weight of the balance shaft 18 and reduce the moment of inertia, thereby reducing mechanical losses during engine operation and improving the engine's power response and fuel economy.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A crankshaft transmission mechanism for an engine, comprising a crankshaft and a connecting rod, the crankshaft including a main journal, a connecting rod journal, a crank arm, and a counterweight, the crank arm being perpendicularly connected to the main journal and the connecting rod journal on both sides in its thickness direction, the length direction of the crank arm corresponding to the direction of the center line connecting the eccentrically distributed main journal and connecting rod journal, the main journal and the connecting rod journal being close to both ends of the crank arm, the width of the crank arm gradually narrowing from the end where the main journal is located to the end where the connecting rod journal is located; the large end of the connecting rod is fitted onto the connecting rod journal, and the small end is used to connect to the piston; the counterweight is located on the crank arm at the end where the main journal is located, and is integrally formed with the crank arm, the counterweight being smoothly connected to both sides of the crank arm in the width direction through concave arc surfaces; each of the two crank arms near the two ends of the crankshaft has a first boss on its side facing the adjacent crankshaft end, the first boss being annular and coaxial with the main journal, the end face of the first boss being used for contact and positioning with the inner wall of the engine housing; characterized in that: The radial inner contour of the first boss is connected to the main journal, and the radial outer contour extends to be tangent to the concave arc surface; the end face of the connecting rod journal on the crank arm is an arc surface, and is smoothly connected to both sides in the width direction of the crank arm. The arc surface is concentric with the connecting rod journal, and its diameter is smaller than the outer diameter of the axial end face of the big end of the connecting rod.

2. The crankshaft transmission mechanism for an engine according to claim 1, characterized in that: Of the two first bosses, one of the first bosses has a mounting portion protruding from its end face. The mounting portion is annular and coaxial with the main journal. The radial inner contour of the mounting portion is connected to the main journal. The crankshaft is provided with a drive gear for driving the engine balance shaft. The drive gear is fitted on the outer circumferential surface of the mounting portion. The end face of the drive gear is flush with the end face of the mounting portion and forms a contact surface. The contact surface is used to replace the end face of the first boss on the same side in contacting the inner wall of the engine housing.

3. The crankshaft transmission mechanism for an engine according to claim 2, characterized in that: The main journal has a bearing mounting position, and in the axial direction, the mounting part and the drive gear are located on the side of the bearing mounting position near the crank arm.

4. The crankshaft transmission mechanism for an engine according to claim 3, characterized in that: There are at least four crank arms. Among the crank arms furthest from the drive gear, at least one is a thickened crank arm, and the thickness of the thickened crank arm is greater than the thickness of the crank arm closest to the drive gear.

5. The crankshaft transmission mechanism for an engine according to claim 4, characterized in that: The counterweight integrated with the thickened crank arm is a thickened counterweight, and the thickness of the thickened counterweight is greater than the thickness of the counterweight near the drive gear.

6. The crankshaft transmission mechanism for an engine according to claim 5, characterized in that: The crankshaft includes at least two connecting rod journals, and at least three main journals are distributed alternately along the axial direction with each connecting rod journal. The crank arm is connected to the connecting rod journal and the main journal on both sides respectively. The thickened crank arm and the thickened counterweight are thickened axially towards the side where the main journal is located.

7. The crankshaft transmission mechanism for an engine according to claim 1, characterized in that: The crank arm has a second boss on the side facing the connecting rod in the thickness direction, which is used to contact and position with the axial end face of the big end of the connecting rod; the second boss is a semi-circular shape concentric with the connecting rod journal, and the radial inner contour of the second boss is connected to the connecting rod journal, and the radial outer contour matches the outer diameter of the axial end face of the big end of the connecting rod.

8. The crankshaft transmission mechanism for an engine according to claim 1, characterized in that: The diameter of the arc surface is larger than the inner diameter of the axial end face of the connecting rod big end, and there is an arc chamfer at the junction of the connecting rod journal and the crank arm.

9. The crankshaft transmission mechanism for an engine according to claim 1, characterized in that: The main journal and the connecting rod journal are intersected radially.

10. The crankshaft transmission mechanism for an engine according to claim 1, characterized in that: The crankshaft transmission mechanism also includes a balance shaft, which is set parallel to the main journal of the crankshaft. A driven gear is coaxially fixedly connected to the balance shaft, and the driven gear meshes with the driving gear. An eccentric mass block is connected to or integrally formed on the balance shaft, and the eccentric mass block corresponds to the position of the connecting rod on the crankshaft. The back of the eccentric mass block is recessed to form a recessed part, which is used to avoid the connecting rod on the crankshaft.

Images