Planetary roller screw drive assembly

Abstract

The invention provides a planetary roller screw transmission assembly. The planetary roller screw transmission assembly comprises a nut, a screw, a plurality of rollers, a retainer group and a friction elastic piece, the nut is provided with an axially penetrating inner hole, and the inner circumferential surface of the nut is provided with at least one annular groove section and at least one non-tooth-shaped section adjacent to the annular groove section. The screw rod is arranged in the inner hole in a penetrating mode and extends out of the nut. A plurality of rollers are arranged in an inner hole of the nut and arranged on the periphery of the screw in a surrounding mode, each roller is provided with at least one large-pitch-diameter section and at least one small-pitch-diameter section with a smooth face in the axial direction, the large-pitch-diameter sections are provided with annular teeth used for being meshed with the screw in a rolling mode, and the small-pitch-diameter sections are provided with annular teeth used for being meshed with the nut in a rolling mode. The retainer group is arranged at the axial end parts of the plurality of rollers. The friction elastic piece is arranged on the non-tooth-shaped section of the inner circumferential face of the nut and makes interference contact with the smooth face of the small-pitch-diameter section of the multiple pin rollers.

Description

Technical Field

[0001] The present invention relates to a transmission assembly, in particular to a planetary roller screw transmission assembly which can provide radial pre-pressure to rollers to improve rolling engagement stability. Background Art

[0002] Planetary roller screw drive assemblies offer high load-bearing capacity, high rigidity, excellent transmission efficiency, and positioning accuracy. They are widely used in precision machine tools, servo drive systems, aerospace control devices, robotics, and other fields that demand fast response and high dynamic performance. These assemblies utilize a plurality of rollers positioned within a nut and arranged around the outer circumference of the screw. Through rolling engagement between the rollers, the screw, and the nut, the screw's rotational motion is converted into linear motion relative to the nut, thereby driving an external load.

[0003] See also Figure 1A and Figure 1B As shown in FIG. 1 , a planetary roller screw transmission device comprises a screw 11, a nut 12, a plurality of rollers 13, and a retaining element assembly 14. The screw 11 has a threaded structure, and the nut 12 has an inner hole 120 for accommodating the plurality of rollers 13. Internal teeth 12t are provided on the inner circumference of the nut 12 for meshing with the external teeth of the rollers 13 to form rolling contact. The retaining element assembly 14 is disposed at both axial ends of the plurality of rollers 13 to position the plurality of rollers 13 between the screw 11 and the nut 12 and to maintain the circumferential spacing of the plurality of rollers 13.

[0004] Although the retaining member assembly 14 can provide spacing limitation and positioning functions for the rollers 13, it does not have a structural design that can provide friction or apply radial positive force to the rollers 13, nor can it effectively compensate for the radial engagement offset between the rollers 13 and the nut 12 and the screw 11 caused by manufacturing tolerances and assembly errors.

[0005] like Figure 1A and Figure 1B As shown, the rolling engagement between roller 13 and nut 12 relies primarily on the geometric fit of their tooth structures and the stable maintenance of the meshing contact position on the designed pitch circle. However, in practical applications, factors such as manufacturing tolerances, assembly errors, or variations in motion loads can cause the contact position to deviate from the ideal pitch circle, leading to unstable rolling contact and, consequently, slippage and idling. This disrupts the roller 13's intended pure rolling motion trajectory, compromising transmission efficiency.

[0006] On the other hand, the rolling contact between rollers 13 and screw 11 faces similar challenges. Because retainer assembly 14 only provides basic circumferential spacing and axial positioning for the multiple rollers 13, and lacks a mechanism for applying radial preload to the contact area between rollers 13 and the screw 11 thread structure, when screw 11 operates at high speeds or is subjected to variable loads, rollers 13 may experience radial displacement at the contact interface, causing the contact position to deviate from its designed pitch circle. Such displacement destabilizes the rolling contact, further causing slippage or idling, ultimately reducing the synchronization and transmission stability of the planetary motion.

[0007] Therefore, how to improve the contact stability between the roller and the nut, strengthen the rolling engagement effect between the roller and the screw, and effectively suppress sliding and idling without significantly increasing the complexity and cost of the components, thereby ensuring the stability of the overall planetary rolling motion, is a technical problem that needs to be urgently solved in this field. Summary of the Invention

[0008] To solve the above problems, the present invention aims to provide a planetary roller screw transmission assembly.

[0009] The present invention provides a planetary roller screw transmission assembly, characterized by comprising:

[0010] A nut having an axially extending inner hole, wherein the inner circumference of the nut is provided with at least one annular groove section and at least one non-toothed section adjacent to the annular groove section;

[0011] a screw rod passing through the inner hole of the nut and extending to the outside of the nut, wherein the outer peripheral surface of the screw rod is provided with a thread structure;

[0012] a plurality of rollers disposed in the inner hole of the nut and arranged on the outer periphery of the screw, the outer periphery of each roller being provided with a plurality of annular teeth, and each roller being provided with at least one large pitch diameter section and at least one small pitch diameter section having a smooth surface along the axial direction, the large pitch diameter section being provided with annular teeth for forming rolling engagement with the screw, and the small pitch diameter section being provided with annular teeth for forming rolling engagement with the nut;

[0013] a retaining member assembly disposed at the axial ends of the plurality of rollers for maintaining the circumferential spacing of the plurality of rollers; and

[0014] At least one friction elastic member is disposed on the non-toothed section of the inner circumference of the nut and forms interference contact with the smooth surface of the small pitch diameter section of the plurality of rollers.

[0015] In the planetary roller screw transmission assembly, the inner circumference of the nut is further provided with at least one retreat groove section, and the retreat groove section is arranged at a position corresponding to the large pitch diameter section of the plurality of rollers.

[0016] In the planetary roller screw transmission assembly, the inner circumferential surface of the nut is provided with a first groove in the non-toothed section, and the friction elastic member is embedded in the first groove.

[0017] The planetary roller screw transmission assembly, wherein the radial distance from the contact point where the friction elastic member forms interference contact with the smooth surface of the small pitch diameter section of the roller to the geometric center of the nut is equivalent to the radial distance from the contact point where the annular groove section of the nut forms rolling contact with the small pitch diameter section of the roller to the geometric center of the nut.

[0018] The planetary roller screw transmission assembly described above, wherein the screw has a pitch circle radius Rs, which refers to the radial distance from the contact point where the screw's thread structure forms rolling contact with the large pitch diameter section of the roller to the geometric center of the screw; the large pitch diameter section of the roller has a pitch circle radius Rps, which refers to the radial distance from the contact point where the annular teeth of the large pitch diameter section form rolling contact with the screw's thread structure to the geometric center of the roller; the small pitch diameter section of the roller has a pitch circle radius Rpr, which refers to the radial distance from the contact point where the annular teeth of the small pitch diameter section form rolling contact with the annular groove section of the nut to the geometric center of the roller; the nut has a pitch circle radius Rr, which refers to the radial distance from the contact point where the annular groove section of the nut forms rolling contact with the small pitch diameter section of the roller to the geometric center of the nut; the above-mentioned pitch circle radii satisfy the following relationship: Rr=Rs+Rpr+Rps.

[0019] The planetary roller screw transmission assembly, wherein the retaining member group includes two annular components, which are sleeved on the screw and respectively arranged at the axial ends of the multiple rollers to jointly maintain the circumferential spacing configuration of the multiple rollers.

[0020] In the planetary roller screw transmission assembly, the annular component is provided with a plurality of positioning grooves, each positioning groove is used to accommodate the axial end of a corresponding roller to maintain the spacing arrangement of the plurality of rollers in the circumferential direction.

[0021] The planetary roller screw transmission assembly further comprises at least one fixing member which is arranged in the inner hole of the nut and abuts against the side of the annular member away from the plurality of rollers to limit the axial displacement of the retaining member group in the nut.

[0022] Through this interference contact, a radial pre-pressure can be applied to the plurality of rollers, thereby achieving the following two technical effects: First, the tangential component of the radial pre-pressure on the contact surface between the friction elastic member and the roller forms a static friction force. This static friction force can be used to stabilize the revolution behavior of the roller in the circumferential direction, guide it to move along the designed pitch circle trajectory, and thus effectively avoid the phenomenon of slippage or idling of the roller relative to the nut; Second, the radial pre-pressure will also generate a normal force through the geometric contact structure of the roller, further enhancing the contact pressure and meshing force between the roller and the screw, enabling the roller, the screw, and the nut to maintain stable rolling contact, and thereby improving the overall transmission efficiency. Description of the Drawings

[0023] Figure 1A It is a schematic structural diagram of an existing planetary roller screw drive device.

[0024] Figure 1B is Figure 1A a schematic diagram of the meshing contact relationship between the roller and the nut in

[0025] Figure 2 It is a schematic exploded view of the main components of the planetary roller screw drive assembly according to the first embodiment of the present invention.

[0026] Figure 3A It is a schematic cross-sectional view of the planetary roller screw drive assembly according to the first embodiment of the present invention.

[0027] Figure 3B It is an enlarged schematic diagram of the tooth profile matching relationship between the roller and the nut in the first embodiment of the present invention.

[0028] Figure 3C It is a schematic cross-sectional view of the planetary roller screw drive assembly according to the second embodiment of the present invention.

[0029] Figure 4 It is a schematic diagram of the structure and configuration of the positioning assembly in the first embodiment of the present invention.

[0030] Figure 5 It is a schematic diagram of applying a radial pre-pressure to the roller by setting a friction elastic member in the first embodiment of the present invention.

[0031] Figure 6A It is a schematic diagram of the roller being positioned at the pitch circle position after the friction elastic member of the planetary roller screw drive assembly in the first embodiment of the present invention is interfered.

[0032] Figure 6B corresponding to Figure 6A is a schematic diagram of the pitch circle composition and planetary motion relationship of the planetary roller screw drive assembly.

[0033] Description of reference numerals: Planetary roller screw drive assembly 1; nuts 10, 12; internal teeth 12t; internal holes 100, 120; flange portion 101; annular groove section 102; annular teeth 102t; annular groove 102g; non-toothed section 103; first groove 104; relief groove section 105; second groove 106; screws 11, 20; thread structure 201; rollers 13, 30; annular teeth 30t; annular groove 30g; large pitch diameter section 301; small pitch diameter section 302; smooth surface 302S; friction elastic member 40; retaining member groups 14, 50; annular member 50r; through hole 500; protruding structure 501; positioning groove 502; fixing member 60; interference contact position P1 between the friction elastic member and the roller; position P2 where the nut and the roller form a rolling contact; radial distance D1 from the interference contact position between the friction elastic member and the roller to the geometric center of the nut; radial distance D2 from the position where the nut and the roller form a rolling contact to the geometric center of the nut; pitch circle radius Rs of the screw; pitch circle radius Rps of the large pitch diameter section of the roller; pitch circle radius Rpr of the small pitch diameter section of the roller; pitch circle radius Rr of the nut; radial pre-pressure F; static friction force F1; normal force F2. Detailed implementation manners

[0034] The structural and functional characteristics of the planetary roller screw drive assembly provided by the present invention will be described based on the preferred embodiments shown in the accompanying drawings.

[0035] Please refer to Figure 2 , Figure 3A and Figure 3B as shown.

[0036] The first embodiment of the present invention provides a planetary roller screw drive assembly 1, including: a nut 10, a screw 20, a plurality of rollers 30, a retaining member group 50, at least one fixing member 60, and at least one friction elastic member 40.

[0037] The nut 10 is a hollow cylindrical member, having an internal hole 100 penetrating through both ends along its axial direction. One end portion thereof may be provided with a radially outwardly expanded flange portion 101, which is used as a positioning reference or a stop structure when the nut 10 is assembled, and can be used to fix the nut 10 to an external member of the mechanism. At least one annular groove section 102 is provided on the inner peripheral surface of the nut 10. In this embodiment, two annular groove sections 102 are provided as an example.

[0038] As Figure 3A and Figure 3B shown, the annular groove section 102 of the nut 10 has a plurality of annular grooves 102g and annular teeth 102t distributed circumferentially.

[0039] The inner circumferential surface of the nut 10 is provided with at least one non-toothed section 103 at a position adjacent to the annular groove section 102. The non-toothed section 103 refers to the section of the inner circumferential surface of the nut 10 where no tooth-shaped structure is provided, and this section has a relatively smooth surface. As Figure 3A shown, a first groove 104 and a second groove 106 may be provided in the non-toothed section 103.

[0040] The inner circumferential surface of the nut 10 is further provided with at least one relief groove section 105. The relief groove section 105 is, for example, provided between two annular groove sections 102, and the relief groove section 105 has an inner diameter larger than that of the annular groove section 102 in the radial direction.

[0041] The screw rod 20 is a long rod-shaped member, for example, a long cylindrical shaft body, which is axially inserted into the inner hole 100 of the nut 10 along the axis of the nut 10 and extends outside the nut 10 to facilitate connection to a driving device or other external mechanisms. The outer circumferential surface of the screw rod 20 is provided with a thread structure 201 (which can also be called a helical groove or helical teeth). In actual operation, the screw rod 20 can be driven to rotate by an external power source (not shown in the figure).

[0042] A plurality of rollers 30 are arranged in the inner hole 100 of the nut 10 and are arranged around the outer circumference of the screw rod 20, spaced apart circumferentially.

[0043] In the first embodiment of the present invention, a plurality of rollers 30 are respectively arranged at different circumferential positions on the outer circumference of the screw rod 20 and form rolling engagement with the thread structures 201 corresponding to each position. Although the rollers 30 are generally similar in appearance, they are all independent components with individual identifiability, corresponding to the thread geometric features of the screw rod 20 in different circumferential sections respectively, so as to achieve multi-point independent and precise rolling fit and further improve the meshing stability.

[0044] As Figure 3A and Figure 3B shown, the outer circumferential surface of each roller 30 is provided with a plurality of annular teeth 30t and corresponding annular grooves 30g. The annular teeth 30t of the roller 30 may be provided with a curved surface profile, and this tooth profile design can improve the point contact stability between the roller 30 and the tooth surfaces of the nut 10 or the screw rod 20 during the planetary rolling motion of the roller 30.

[0045] Each roller 30 is provided with at least one large pitch diameter section 301 and at least one small pitch diameter section 302 along its axial direction. The pitch diameter of the large pitch diameter section 301 is greater than that of the small pitch diameter section 302. The large pitch diameter section 301 is provided with an annular tooth for forming rolling engagement with the thread structure 201 of the screw 20, and the small pitch diameter section 302 is provided with an annular tooth for forming rolling engagement with the annular groove section 102 of the nut 10. The large pitch diameter section 301 is disposed at a position corresponding to the relief groove section 105, so that the large pitch diameter section 301 of the roller 30 does not come into contact with or interfere with the inner peripheral surface of the nut 10. The small pitch diameter section 302 is disposed at a position corresponding to the annular groove section 102 of the nut 10, so that the annular tooth on its outer periphery can form rolling engagement with the annular groove section 102. In this embodiment, each roller 30 is provided with one large pitch diameter section 301 and two small pitch diameter sections 302 located on both sides thereof, as Figure 2 and Figure 3A shown. The small pitch diameter sections 302 located at both axial ends of each roller 30 are provided with smooth surfaces 302S, and no tooth-shaped structure is provided on their outer peripheral surfaces.

[0046] Through this structure, the roller 30 can establish bilateral rolling contact with both the screw 20 and the nut 10 at the same time, and realize its stable two-way meshing function during the planetary motion. In addition, by means of the surrounding guiding and restricting functions provided by the annular groove section 102 of the nut 10, the plurality of rollers 30 can be stably arranged on the inner peripheral surface of the nut 10, and at the same time, the plurality of rollers 30 can be prevented from coming out in the axial direction.

[0047] During actual operation, when the screw 20 is driven to rotate by an external power source, the plurality of rollers 30 can synchronously perform planetary rolling contact between the outer periphery of the screw 20 and the inner peripheral surface of the nut 10, and are accompanied by a compound motion of self-rotation and revolution. By forming rolling engagement between the thread structure 201 of the screw 20 and the large pitch diameter section 301 of the roller 30, the roller 30 can realize planetary motion between the screw 20 and the nut 10, and further convert the rotational motion of the screw 20 into its axial linear movement relative to the nut 10. Through this motion mechanism, each roller 30 can also share the original axial load applied to the screw 20, thereby improving the durability and stability of the overall transmission structure.

[0048] Please refer to Figure 3A and Figure 4As shown, the retaining member group 50 may include two integrally formed ring-shaped members 50r, which are respectively disposed at the axially opposite ends of the plurality of rollers 30, sleeved on the outer periphery of the screw 20, and cooperate with the non-toothed section 103 of the nut 10. Each ring-shaped member 50r is provided with a through hole 500 at its center to allow the screw 20 to pass through. In actual operation, the two ring-shaped members 50r can rotate synchronously with the revolution of the rollers 30, and the two side ends of the corresponding rollers 30 are received in the positioning grooves 502 provided thereon to maintain the circumferential spacing configuration of each roller 30.

[0049] As Figure 4 shown, a plurality of convex structures 501 arranged at intervals are provided on the periphery of the retaining member group 50 along its circumferential direction, and the convex structures 501 are spaced from each other to define a corresponding number of positioning grooves 502. The groove profile of each positioning groove 502 corresponds to the outer shape of the axial end of the roller 30 to receive the ends of the plurality of rollers 30 and stably position them at a specific circumferential position. With this structure, the retaining member group 50 can arrange the plurality of rollers 30 at intervals between the screw 20 and the nut 10 to ensure their circumferential arrangement during planetary rolling motion.

[0050] Please refer again to Figure 2 and Figure 3A shown, the fixing member 60 is disposed in the inner hole 100 of the nut 10 and abuts against the side of the ring-shaped member 50r facing away from the plurality of rollers 30. The fixing member 60 can be an annular elastic fastener disposed in the second groove 106 provided on the inner circumferential surface of the nut 10 to form a locking fit with the ring-shaped member 50r. The fixing member 60 is not an essential component in the present invention, and its setting can further enhance the positioning stability of the retaining member group 50 in the nut 10, prevent the retaining member group 50 from axially shifting in the inner hole 100 of the nut 10 during long-term operation or under external force, and further improve the structural stability of the overall transmission assembly. Whether to set the fixing member 60 can be flexibly adjusted according to the actual use situation and structural requirements.

[0051] The friction elastic member 40 is, for example, an annular member, which can be made of a material having elasticity and wear resistance, such as rubber, engineering plastic or elastic metal. Its outer shape is generally a circular ring structure with a specific thickness to achieve a radial interference fit with the outer periphery of the roller and maintain a stable contact state during operation.

[0052] The friction elastic member 40 is disposed on the non-toothed section 103 of the inner peripheral surface of the nut 10 and forms an interference contact with the smooth surface 302S provided on the small-diameter section 302 of the roller 30. Specifically, in the first embodiment of the present invention, the inner peripheral surface of the nut 10 is provided with a non-toothed section 103 without a tooth-shaped structure adjacent to the annular groove section 102. Each roller 30 is provided with a smooth surface 302S on the outer peripheral surface of the axial end of the small-diameter section 302 as a contact corresponding surface for the friction elastic member 40. The non-toothed section 103 corresponds to the smooth surface 302S. By surrounding the friction elastic member 40 between the non-toothed section 103 and the smooth surfaces 302S and forming a stable interference contact with each roller 30, a radial pre-pressure can be applied to each roller 30. To ensure the reliability of the installation and positioning of the friction elastic member 40, a first groove 104 may be provided in the non-toothed section 103 of the nut 10 for the friction elastic member 40 to be embedded therein.

[0053] The friction coefficient of the friction elastic member 40 can be designed and adjusted through parameters such as its material, contact area, thickness, or modulus of elasticity to appropriately control the rolling friction characteristics between the roller 30 and the nut 10 and further optimize the overall transmission performance.

[0054] Please refer to Figure 3C As shown, the present invention further discloses a planetary roller screw drive assembly of a second embodiment, the main difference of which is that the installation position of the friction elastic member 40 is slightly different from that of the first embodiment, which is an example of another configuration method.

[0055] In this embodiment, the friction elastic member 40 is still disposed on the non-toothed section 103 of the inner peripheral surface of the nut 10 and forms an interference contact with the smooth surface 302S of the small-diameter section 302 of the roller 30. Different from the first embodiment in which the friction elastic member 40 is disposed at the corresponding position of the axial end of the roller 30, in this embodiment, a non-toothed section 103 is added at a position adjacent to the relief groove section 105, so that the friction elastic member 40 is turned closer to the middle section of the roller 30. This setting method makes the friction elastic member 40 closer to the geometric center position of the roller 30, and different force application direction characteristics can be shown when applying radial pre-pressure, and it provides another design reference in practical applications, which helps technicians to make elastic adjustments according to system requirements.

[0056] Please refer to Figure 5 and Figure 6B As shown. As Figure 5 shown, the friction elastic member 40 is disposed on the non-toothed section 103 of the inner peripheral surface of the nut 10 and forms a radial interference contact with the smooth surface 302S provided on the small-diameter section 302 of the roller 30, whereby a stable radial pre-pressure F can be applied to the roller 30.

[0057] The radial pre-pressure F generated by the interference contact can further achieve the following two technical effects:

[0058] First, as shown in Figure 5 and Figure 6B the tangential component of the radial pre-pressure F on the contact surface between the friction elastic member 40 and the roller 30 forms a static friction force F1. The static friction force F1 provides circumferential positioning for the roller 30, enabling its rotation and revolution to be always controlled by the designed pitch circle, avoiding slip or idling, and contributing to maintaining the rolling contact stability between the roller 30 and the nut 10. It is worth noting that although the friction elastic member 40 is disposed between the roller 30 and the nut 10 and does not directly press the roller 30 against the tooth surface of the nut 10, the static friction force F1 generated by it is sufficient to guide the roller 30 to maintain a pure rolling contact state, preventing the roller 30 from sliding or idling due to unstable movement or offset of the contact position. Thereby, it can further ensure that the rotational movement of the screw 20 can be stably converted into an axial linear movement relative to the nut 10.

[0059] Secondly, as shown in Figure 5 the radial pre-pressure F will also be transmitted to its contact interface with the screw 20 through the geometric configuration of the roller 30, and then a component force in the normal direction, i.e., the positive force F2, is generated at the contact point between the roller 30 and the screw 20. This positive force F2 can stably press the roller 30 against the tooth surface of the thread structure of the screw 20, compensating for the possible radial offset caused by load variation or high-speed operation, further increasing the contact pressure and meshing stability, and contributing to improving the accuracy and reliability of the overall transmission system.

[0060] Please refer to Figure 6A As shown, to ensure that the friction elastic member 40 can accurately apply a radial pre-pressure to the plurality of rollers 30 and establish a stable and consistent rolling contact relationship between the rollers 30 and the nut 10, the first embodiment of the present invention particularly performs geometric optimization design on the installation position of the friction elastic member 40 and its corresponding pitch circle diameter with interference.

[0061] Specifically, the friction elastic member 40 forms an interference contact with the smooth surface 302S of the small diameter section 302 of the roller 30, and through specific geometric design and machining accuracy control, the radial distance D1 from the interference contact position P1 to the geometric center of the nut 10 is substantially equal to the radial distance D2 from the position P2 where the annular groove section 102 of the nut 10 and the small diameter section 302 of the roller 30 are in rolling contact to the geometric center of the nut 10. With this design, it can be ensured that the radial pre-pressure applied by the friction elastic member 40 accurately corresponds to the meshing pitch circle position of the roller 30 and the nut 10, avoiding the offset of the contact point, and thus maintaining the stability of the rolling contact.

[0062] Please refer to Figure 6A and Figure 6BAs shown, in the first embodiment of the present invention, to ensure precise and stable rolling meshing between the roller 30 and the screw 20 and the nut 10, a geometric structure design is specifically carried out for the pitch circle radius relationship corresponding to each meshing section, so that when the roller 30 makes rolling contact with the screw 20 and the nut 10, each contact point corresponds to a consistent designed pitch circle position, thereby establishing a continuous and synchronous rolling contact state, further ensuring the meshing stability and planetary motion consistency of the roller 30 during operation.

[0063] As Figure 6A and Figure 6B shown, the screw 20 is provided with a thread structure 201. The radial distance from the contact point where the thread structure 201 makes rolling contact with the annular teeth (or annular grooves) of the large pitch diameter section 301 of the roller 30 to the geometric center of the screw 20 is defined as the pitch circle radius Rs of the screw; the radial distance from the contact point where the annular teeth (or annular grooves) of the large pitch diameter section 301 of the roller 30 make rolling contact with the thread structure 201 of the screw to the geometric center of the roller is defined as the pitch circle radius Rps of the large pitch diameter section of the roller; the radial distance from the contact point where the annular teeth (or annular grooves) of the small pitch diameter section 302 of the roller 30 make rolling contact with the annular groove section 102 on the inner peripheral surface of the nut 10 to the geometric center of the roller is defined as the pitch circle radius Rpr of the small pitch diameter section of the roller; the radial distance from the contact point where the annular groove section 102 on the inner peripheral surface of the nut 10 makes rolling contact with the small pitch diameter section 302 of the roller 30 to the geometric center of the nut is defined as the pitch circle radius Rr of the nut. In the first embodiment of the present invention, the above pitch circle radii are specifically made to satisfy the following relational expression: Rr = Rs + Rps + Rpr, so as to ensure that when the roller 30 performs planetary motion composed of self-rotation and revolution, it can make rolling contact with the screw 20 and the nut 10 at consistent designed pitch circle positions respectively. Through this geometric correspondence relationship, problems such as sliding or unstable contact caused by contact errors or assembly deviations can be effectively avoided, and the overall transmission stability can be further improved.

[0064] To sum up, for the planetary roller screw drive assembly provided by the present invention, by arranging a friction elastic member in the non-toothed section of the nut to form interference contact with the smooth surface of the small pitch diameter section of the roller to apply a radial pre-pressure to the roller, a stable static friction force is generated. During the planetary motion in which the roller performs self-rotation and revolution, this structure can provide an effective circumferential stability mechanism, which helps to suppress the slippage or swinging phenomenon of the roller during the movement process, and further ensures that the roller and the nut maintain a pure rolling contact state. In addition, this radial pre-pressure can also generate a positive force towards the screw direction, so that the contact force between the roller and the screw can be increased, thereby enhancing the rolling meshing stability on both sides of the roller and the nut and the screw, effectively suppressing unstable phenomena such as sliding or idling, and further improving the overall transmission accuracy and reliability.

[0065] Furthermore, through the geometric optimization design based on the installation position of the friction elastic member and its corresponding interference pitch circle radius, the radial pre-pressure can act precisely on the pitch circle position where the roller meshes with the nut. In addition, by virtue of the mutual geometric relationship of the pitch circle radii corresponding to the roller, the screw and the nut, all the rolling contact points are uniformly positioned on the designed pitch circle, effectively improving the rolling meshing accuracy and transmission efficiency.

[0066] The above has described the present invention in detail. However, what has been described above is only the preferred embodiment of the present invention, and it should not be used to limit the scope of implementation of the present invention. That is, all equivalent changes and modifications made according to the technical concept of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A planetary roller screw drive assembly, characterized in that, include: A nut having an axially extending inner hole, wherein the inner circumference of the nut is provided with at least one annular groove section and at least one non-toothed section adjacent to the annular groove section; a screw rod passing through the inner hole of the nut and extending to the outside of the nut, wherein the outer peripheral surface of the screw rod is provided with a thread structure; a plurality of rollers disposed in the inner hole of the nut and arranged on the outer periphery of the screw, the outer periphery of each roller being provided with a plurality of annular teeth, and each roller being provided with at least one large pitch diameter section and at least one small pitch diameter section having a smooth surface along the axial direction, the large pitch diameter section being provided with annular teeth for forming rolling engagement with the screw, and the small pitch diameter section being provided with annular teeth for forming rolling engagement with the nut; a retaining member assembly disposed at the axial ends of the plurality of rollers for maintaining the circumferential spacing of the plurality of rollers; and At least one friction elastic member is disposed on the non-toothed section of the inner circumference of the nut and forms interference contact with the smooth surface of the small pitch diameter section of the plurality of rollers.

2. The planetary roller screw drive assembly according to claim 1, wherein, The inner circumference of the nut is further provided with at least one retreat groove section, and the retreat groove section is arranged corresponding to the position corresponding to the large pitch diameter section of the plurality of rollers.

3. The planetary roller screw drive assembly according to claim 1, characterized in that, The inner circumference of the nut is provided with a first groove in the non-tooth section, and the friction elastic member is embedded in the first groove.

4. The planetary roller screw drive assembly according to claim 1, wherein, The radial distance from the contact point where the friction elastic member forms interference contact with the smooth surface of the small pitch diameter section of the roller to the geometric center of the nut is equivalent to the radial distance from the contact point where the annular groove section of the nut forms rolling contact with the small pitch diameter section of the roller to the geometric center of the nut.

5. The planetary roller screw drive assembly according to claim 1, characterized in that, The screw has a pitch circle radius Rs, which refers to the radial distance from the contact point where the thread structure of the screw forms rolling contact with the large pitch diameter section of the roller to the geometric center of the screw; the large pitch diameter section of the roller has a pitch circle radius Rps, which refers to the radial distance from the contact point where the annular teeth of the large pitch diameter section form rolling contact with the thread structure of the screw to the geometric center of the roller; the small pitch diameter section of the roller has a pitch circle radius Rpr, which refers to the radial distance from the contact point where the annular teeth of the small pitch diameter section form rolling contact with the annular groove section of the nut to the geometric center of the roller; the nut has a pitch circle radius Rr, which refers to the radial distance from the contact point where the annular groove section of the nut forms rolling contact with the small pitch diameter section of the roller to the geometric center of the nut; the above-mentioned pitch circle radii satisfy the following relationship: Rr=Rs+Rpr+Rps.

6. The planetary roller screw drive assembly according to claim 1, characterized in that, The retaining component assembly includes two annular components, which are sleeved on the screw and respectively arranged at two axial ends of the plurality of rollers to jointly maintain the spacing arrangement of the plurality of rollers in the circumferential direction.

7. The planetary roller screw drive assembly according to claim 6, characterized in that, The annular component is provided with a plurality of positioning grooves, each positioning groove is used to accommodate the axial end portion of a corresponding roller to maintain the spacing arrangement of the plurality of rollers in the circumferential direction.

8. The planetary roller screw drive assembly according to claim 7, characterized in that: The invention also comprises at least one fixing member, which is arranged in the inner hole of the nut and stops at a side of the annular component away from the plurality of rollers to limit the axial displacement of the retaining member assembly in the nut.

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