Self-locking planetary roller lead screw transmission mechanism for rear wheel steering

Abstract

The invention relates to a transmission structure. A self-locking planetary roller lead screw transmission mechanism for rear wheel steering comprises a nut, a lead screw and a roller are installed in the nut, the roller and the lead screw are in threaded connection to form a first transmission pair, and the roller and the nut are also in threaded connection to form a second transmission pair. And one group of the first transmission pair and the second transmission pair is a point transmission pair, and the other group of the first transmission pair and the second transmission pair is a surface transmission pair. According to the self-locking type planetary roller lead screw transmission mechanism for rear wheel steering, self-locking is effectively achieved, meanwhile, the transmission efficiency is high, all rollers are well standardized, the rollers can be directly assembled without classification, and assembling is convenient. The technical problems that in the prior art, a planetary roller lead screw transmission structure is either complex in self-locking structure or low in transmission efficiency, and the requirement for all rollers is high in the assembling process are solved.

Description

Technical Field

[0001] The invention relates to a transmission structure, in particular to a self-locking planetary roller screw transmission mechanism for rear wheel steering. Background Art

[0002] At present, rear-wheel steering is mainly achieved in two ways, one is through mechanical structure, and the other is through motor or hydraulic force. When a planetary roller screw structure is adopted in the mechanical structure, it includes a screw, which mainly includes two types: trapezoidal nut screw and planetary roller screw. The trapezoidal nut screw structure is relatively simple, but it has the defect of low transmission efficiency, and the transmission efficiency is only about 25%. The transmission efficiency of the planetary roller screw is relatively high, usually above 60%. However, the problem brought by high efficiency is that mechanical self-locking cannot be achieved. It is usually necessary to add a preload device or a differential planetary roller screw structure to achieve it. The differential planetary roller screw needs to classify the rollers due to structural limitations, and the cost is relatively high. The existing additional preload device greatly increases the structural complexity of the planetary roller screw solution, making it have defects such as high cost, insufficient load-bearing capacity, and easy damage under large load impact. Summary of the invention

[0003] The present invention provides a self-locking planetary roller screw transmission mechanism for rear wheel steering which can effectively realize self-locking, has high transmission efficiency, has standardized rollers, can be directly assembled without classification, and is easy to assemble; the present invention solves the technical problems in the prior art that the planetary roller screw transmission structure either has a complex self-locking structure or has low transmission efficiency and has high requirements for each roller during assembly.

[0004] The above technical problems of the present invention are solved by the following technical solutions: a self-locking planetary roller screw transmission mechanism for rear wheel steering, comprising a nut, a screw and a roller are installed in the nut, the roller and the screw are connected by threads to form a first transmission pair, and the roller and the nut are also connected by threads to form a second transmission pair; among the first transmission pair and the second transmission pair, one group is a point transmission pair and the other group is a surface transmission pair. The surface transmission pair realizes the self-locking function, which solves the problem that the prior art needs a cumbersome self-locking structure to achieve it. The point transmission pair solves the problem that the trapezoidal nut screw structure used in the prior art can be self-locking, but the transmission efficiency is low, and the friction is reduced by a group of point transmission pair structures to improve the transmission efficiency. The surface transmission pair can be on the contact surface between the nut and the roller, or on the contact surface between the screw and the roller. The screw and the nut are generally multi-start threads, and the roller is a single-start thread, and the three have the same tooth angle. Design appropriate thread parameters according to the requirements of the transmission pair, and ensure high transmission efficiency under the premise of self-locking performance.

[0005] Preferably, a left retainer and a right retainer are installed at both ends of the roller, and at the same time, the two ends of the roller are connected with a left gear ring and a right gear ring through meshing teeth. A left limiting structure and a right limiting structure are provided at both ends of the roller, and the limiting structure includes a pressure plate and a gasket, and the gasket is in contact with the roller. The pressure plate is fixed to the nut by threaded connection, interference connection or riveting. The difficult problem that the processing state of all rollers needs to be consistent is solved by adjusting the axial position of the roller during the assembly process of the screw pair, thereby reducing the difficulty of roller processing. At the same time, a limiting structure is designed on the retainers at both ends of the mechanism. The limiting structure can not only avoid the occurrence of axial movement problems caused by axial position deviation of each roller, but also provide pre-tightening force to the planetary roller screw pair, avoid obvious slippage at the thread meshing point, ensure the stability of the transmission ratio and improve the transmission efficiency.

[0006] As a preferred method, the gear modulus of the left and right gear rings is selected to be the smallest under the premise of ensuring the strength of the gear. The range of the axial position adjustment amount L of the roller is: 0≤L≤p / (2z), where p is the roller pitch and z is the number of teeth of the gear ring. From the formula, it can be concluded that when the roller pitch is determined, the more teeth the gear ring has, the smaller the maximum axial position adjustment amount of the roller is. Therefore, under the premise of ensuring the strength of the gear, the smaller the gear modulus is, the better.

[0007] As a preference, the gasket is a rigid gasket.

[0008] As another preferred embodiment, the gasket is an elastic gasket, which can be a disc spring, and the elastic gasket is convenient for adjusting the preload force.

[0009] Preferably, the helix angle between the roller and the nut is βrn, the helix angle between the roller and the screw is βrs, the equivalent friction angle is fv, βrn<fv or βrs<fv, the thread center diameter angle and lead are calculated by the helix angle, wherein βrn=atan[Ln / (πdn)], wherein Ln is the lead of the nut, and dn is the center diameter of the nut; βrs=atan[Ls / (πds)], wherein Ls is the lead of the screw, and ds is the center diameter of the screw, and fv=atan[f / cos(α / 2)], wherein f is the friction coefficient of the thread surface, and α is the thread tooth angle, when the contact form of the thread surface is point contact, f is usually taken between 0.003 and 0.01, and when the contact form of the thread surface is surface contact, f is usually taken between 0.1 and 0.2.

[0010] Preferably, the outer circumferential surface of the nut is provided with a gear matching the motor transmission system, and the outer circumferential surface of the nut on both sides of the gear is provided with a bearing mounting surface. A number of rollers are evenly distributed around the lead screw, and are respectively meshed with the lead screw and the nut through threads, and are meshed with the inner gear ring through involute gears at both ends. The nut is installed on the steering gear housing through the centripetal thrust bearings at both ends, and the interfaces connected with the steering rod are processed at both ends of the lead screw. The motor drives the nut to realize the linear motion of the lead screw through the threaded meshing transmission, and then drives the movement of the steering rod, and then the purpose of steering the rear wheels of the vehicle is achieved through the steering rod. In order to avoid deformation of the meshing contact surface between the nut and the roller due to the press-fitting of the motor transmission gear, a gear matching the motor transmission system is processed on the nut. The motor drives the nut to rotate through the gear transmission mechanism. When the motor characteristic is low speed and high torque, the nut and the motor can be integrated to optimize the overall structure and save the installation space of the steering gear.

[0011] Preferably, both ends of the lead screw are provided with threaded holes for connecting to the rear wheel steering rod.

[0012] Preferably, the contact surface of the nut or the contact surface of the lead screw forming the point transmission pair is an arc surface. The meshing surfaces forming the point transmission pair are the nut and the roller, or the roller and the lead screw. The shape of the roller is fixed, and the contact surface on the nut or the lead screw is changed to form a point transmission pair. Therefore, the arc surface is designed on the nut, and it can also be on the lead screw. The arc-shaped contact surface allows the two surfaces forming the transmission pair to contact each other, thereby forming a point transmission pair, reducing friction and improving transmission efficiency.

[0013] Therefore, the self-locking planetary roller screw transmission mechanism for rear-wheel steering of the present invention has the following advantages: the three components of the screw, the ball and the nut form two transmission pairs, one of which is a surface transmission pair, so that the planetary roller screw structure can achieve self-locking, and the other transmission pair is a point transmission pair, which has high transmission efficiency while achieving self-locking. The end clearance is adjusted by the limit structure to reduce the difficulty of roller installation, avoid obvious slippage at the threaded engagement, and ensure the transmission ratio. The planetary roller screw structure is applied to the rear-wheel steering, which realizes the steering function well, ensures the stability of the rear-wheel steering, and saves the installation space of the steering gear. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A cross-sectional view of a self-locking planetary roller screw drive mechanism for rear wheel steering.

[0015] Figure 2 This is an enlarged view of point A in Example 1.

[0016] Figure 3 It is a schematic diagram of the rigid limit structure.

[0017] Figure 4 It is a schematic diagram of the flexible limiting structure.

[0018] Figure 5 It is a three-dimensional diagram of the nut.

[0019] Figure 6 It is a stereogram applied to rear wheel steering.

[0020] Figure 7 This is an enlarged view of point A in Example 2. DETAILED DESCRIPTION

[0021] The technical solution of the invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0022] Embodiment 1: like Figure 1 and 2 As shown, a self-locking planetary roller screw transmission mechanism for rear wheel steering includes a screw 1 located in the center, and threaded holes 4 are processed at both ends of the screw 1 for connecting with the left tie rod 17 and the right tie rod 22 of the rear wheel steering. The outer circumferential surface of the screw 1 is processed with multiple threads. A plurality of rollers 2 that are threaded with the screw are evenly distributed around the screw 1, and a nut 3 is sleeved outside the roller 2, and a thread is processed inside the nut 3. The threaded surface of the inner wall of the nut 3 and the threaded surface of the roller form a point transmission pair 11, and the threaded surface formed on the inner wall of the nut 3 is an arc surface. The screw 1 and the roller 2 form a surface transmission pair 12. The helical parameters of roller 2, screw 1 and nut 3 can be designed according to the following method: the helix angle of roller 2 and nut 3 is βrn, the helix angle of roller 2 and screw 1 is βrs, the equivalent friction angle is fv, βrn<fv or βrs<fv, the thread pitch diameter angle and lead are calculated by the helix angle, where βrn=atan[Ln / (πdn)], where Ln is the lead of the nut and dn is the mid-diameter of the nut; βrs=atan[Ls / (πds)], where Ls is the lead of the screw and ds is the mid-diameter of the screw, fv=atan[f / cos(α / 2)], where f is the friction coefficient of the thread surface and α is the thread pitch angle. When the contact form of the thread surface is point contact, f is usually taken between 0.003 and 0.01, and when the contact form of the thread surface is surface contact, f is usually taken between 0.1 and 0.2.

[0023] The left retainer 7 and the right retainer 10 are installed at both ends of the roller 2, and the left gear ring 8 and the right gear ring 9 are fixed at both ends of the inner surface of the nut 3. The left gear ring 8 and the right gear ring 9 are welded to the inner circumferential surface of the nut 3, and the left gear ring 8 and the right gear ring 9 are meshed with the roller 2 for transmission. The left limit structure is installed on the left side of the left retainer 7, and the right limit structure is installed on the right side of the right retainer 10. The left limit structure is the same as the right limit structure. The limit mechanism is located in the gear ring, and the limit structure includes a pressure plate 5 and a gasket 6.

[0024] like Figure 3 As shown, the pressure plate 5 can be fixed to the gear ring by threaded connection, interference connection or riveting. The gasket is a rigid gasket 13, which abuts on the retaining frame. The pressure plate 5 presses the rigid gasket on the end face of the roller to avoid axial movement caused by different axial positions of the roller after the screw pair is assembled, avoid obvious slippage at the threaded meshing point, ensure the stability of the transmission ratio and improve the transmission efficiency. The range of the axial position adjustment amount L of the roller is: 0≤L≤p / (2z), where p is the roller pitch and z is the number of teeth of the gear ring. It can be concluded from the formula that when the roller pitch is determined, the more teeth the gear ring has, the smaller the maximum axial position adjustment amount of the roller. Therefore, under the premise of ensuring the strength of the gear, the gear module should be as small as possible.

[0025] Of course, the limiting structure can also adopt the structure shown in Figure 4, where the gasket adopts a disc spring 14, which can not only realize the function of a rigid gasket but also adjust the preload force.

[0026] like Figure 5 and 6 As shown, a gear 15 matching the motor transmission system is integrally formed on the outer circumferential surface of the nut 2, and a bearing mounting surface 16 is provided on the outer circumferential surface of the nut on both sides of the gear. The planetary roller screw structure is installed between the left housing 19 and the right housing 21 of the rear wheel steering through a radial thrust bearing. A left pull rod 17 is arranged in the left housing 19, and a right pull rod 22 is arranged in the right housing 21. When in use, the motor 20 of the steering gear drives the nut to rotate through the gear transmission mechanism, and the planetary roller screw structure converts the rotation of the nut into the linear motion of the screw through the spiral transmission, and then achieves the purpose of steering the rear wheels of the vehicle through the left pull rod 17 and the right pull rod 22. When the motor characteristic is low speed and high torque, the nut and the motor can be integrated to optimize the overall structure and save the installation space of the steering gear.

[0027] Embodiment 2: like Figure 7 As shown, the difference from the first embodiment is that the threaded surface of the screw 1 and the threaded surface of the roller 2 form a point transmission pair 11, the threaded surface of the screw is an arc surface, and the threaded surface of the inner wall of the nut 3 and the roller 2 form a surface transmission pair 12.

[0028] The specific embodiments described herein are merely examples of the concept of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A self-locking planetary roller screw transmission mechanism for rear wheel steering, comprising a nut, a screw and a roller installed in the nut, characterized in that: The roller and the lead screw are threadedly connected to form a first transmission pair, and the roller and the nut are also threadedly connected to form a second transmission pair; among the first transmission pair and the second transmission pair, one group is a point transmission pair and the other group is a surface transmission pair.

2. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to claim 1, characterized in that: A left retainer and a right retainer are installed at both ends of the roller respectively. At the same time, the two ends of the roller are connected with a left gear ring and a right gear ring through meshing teeth. A left limiting structure and a right limiting structure are provided at both ends of the roller. The limiting structure includes a pressure plate and a gasket, and the gasket is in contact with the roller.

3. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to claim 2, characterized in that: The gear module of the left and right ring gears is selected to be the smallest while ensuring the strength of the gears.

4. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to claim 2, characterized in that: The gasket is a rigid gasket.

5. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to claim 2, characterized in that: The gasket is an elastic gasket.

6. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to any one of claims 1 to 5, characterized in that: Preferably, the helix angle between the roller and the nut is βrn, the helix angle between the roller and the screw is βrs, the equivalent friction angle is fv, βrn<fv or βrs<fv, the thread pitch angle and lead are calculated by the helix angle, wherein βrn=atan[Ln / (πdn)], where Ln is the lead of the nut and dn is the middle diameter of the nut; βrs=atan[Ls / (πds)], where Ls is the lead of the screw and ds is the middle diameter of the screw, fv=atan[f / cos(α / 2)], where f is the friction coefficient of the thread surface, α is the thread pitch angle, when the contact form of the thread surface is point contact, f is usually taken between 0.003 and 0.01, and when the contact form of the thread surface is surface contact, f is usually taken between 0.1 and 0.

2.

7. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to any one of claims 1 to 5, characterized in that: The outer circumferential surface of the nut is provided with a gear matching the motor transmission system, and the outer circumferential surfaces of the nut on both sides of the gear are provided with bearing mounting surfaces.

8. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to any one of claims 1 to 5, characterized in that: Both ends of the lead screw are provided with threaded holes for connecting to the rear wheel steering rod.

9. A self-locking planetary roller screw transmission mechanism for rear wheel steering according to any one of claims 1 to 5, characterized in that: The contact surface of the nut or the contact surface of the lead screw forming the point transmission pair is an arc surface.

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