Linear actuator having a wobble joint

Abstract

To solve problems with a joint in conventional screw-type linear actuators.SOLUTION: A screw-type linear actuator comprises a support structure, and a screw shaft that is axially stationary with respect to the support structure but rotatably drivable. A nut is mounted on the screw shaft, so that rotation of the screw shaft causes axial movement of the nut along the screw shaft. In addition, the screw shaft defines a first annular contact surface having a spherical profile with a first radius. A thrust flange is located on the screw shaft for rotation with the screw shaft, and has a second annular contact surface with a second radius, where the first annular contact surface engages the second annular contact surface.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 399,343, filed August 19, 2022, which is hereby incorporated by reference in its entirety for all purposes.

[0002] The present invention relates generally to linear actuators, and more particularly to threaded actuators such as ball screws. [Background technology]

[0003] A variety of applications utilize linear actuators, such as screw actuators. For example, a typical electromechanical braking system requires an actuator capable of providing a linear force. An example linear actuator is a ball screw assembly having a ball train interposed between a ball track formed in the outer surface of the ball screw shaft and a ball track formed in the inner surface of the ball screw nut. Recirculating ball and non-recirculating ball type ball screw assemblies are known.

[0004] Such linear actuators can have wobble joints with a spherical shape on the shaft and a conical contact on the flange that engages the spherical shape. An example of such an arrangement is shown in Figures 7A and 7B, where it can be seen that the wobble joint (A) has an annular surface (B) with a spherical shape formed on the shaft (C). The spherical shape engages a frusto-conical contact surface (D) formed on the flange (E). This arrangement has limited slippage reduction when subjected to larger axial loads, as friction often causes the joint to seize before full working load and deflection. [Prior art documents] [Patent documents]

[0005]

Patent Document 1

Summary of the Invention

[0006] The present invention recognizes and addresses considerations of prior art configurations and methods.

[0007] One embodiment of the present disclosure provides a screw-type linear actuator having a support structure and a screw shaft that is axially fixed relative to the support structure but rotatably drivable. A nut is installed on the screw shaft such that rotation of the screw shaft axially moves the nut along the screw shaft. Additionally, the screw shaft defines a first annular contact surface having a spherical profile with a first radius. A thrust flange is positioned on the screw shaft for rotation with the screw shaft, the thrust flange having a second annular contact surface with a second radius, and the first annular contact surface engaging the second annular contact surface.

[0008] According to some exemplary embodiments, the first radius has a first center point that coincides with the longitudinal central axis of the screw shaft. Additionally, the second radius can have a second center point that is offset from the longitudinal central axis of the screw shaft. The second radius can be larger than the first radius.

[0009] According to some exemplary embodiments, a thrust bearing can be positioned between the thrust flange and the support structure. Additionally, a bearing disk can be fixed to the support structure.

[0010] According to some exemplary embodiments, the linear actuator can have a ball screw assembly having a plurality of balls positioned between opposing ball tracks defined within the screw shaft and within the nut. For example, the ball screw assembly can have a non-recirculating ball screw assembly.

[0011] Another aspect of the present invention provides a screw-type linear actuator having a support structure and a screw shaft that is axially fixed to the support structure but rotatably drivable. A nut is disposed on the screw shaft such that rotation of the screw shaft axially moves the nut along the screw shaft. Additionally, the screw shaft defines a first annular contact surface having a spherical profile with a first radius. A thrust flange is positioned on the screw shaft for rotation therewith, the thrust flange having a second annular contact surface with a second radius, the first annular contact surface engaging the second annular contact surface. Additionally, a thrust bearing is positioned between the thrust flange and the support structure. The first radius has a first center point that coincides with the longitudinal central axis of the screw shaft, and the second radius has a second center point that is offset from the longitudinal central axis of the screw shaft.

[0012] Another aspect of the present invention provides a braking device having a brake caliper having a body with a brake cylinder. A piston is positioned within the brake cylinder. A first pad is fixed to an end of the piston, and a second pad is opposed to the first pad.

[0013] The braking device further comprises a screw-type linear actuator having a screw shaft that is axially fixed relative to the brake caliper but rotatably drivable. A nut is mounted on the screw shaft such that rotation of the screw shaft axially moves the nut along the screw shaft, and the nut is connected to the piston to axially move the piston. The screw shaft defines a first annular contact surface having a spherical profile with a first radius. A thrust flange is located on the screw shaft for rotation with the screw shaft, the thrust flange has a second annular contact surface with a second radius, and the first annular contact surface engages the second annular contact surface. A thrust bearing is located between the thrust flange and the brake caliper. The first radius has a first center point that coincides with the longitudinal central axis of the screw shaft, and the second radius has a second center point that is offset from the longitudinal central axis of the screw shaft.

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0015] A complete and enabling disclosure of the invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in this specification with reference to the accompanying drawings.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7A

Figure 7B

Best Mode for Carrying Out the Invention

[0017] The repeated use of reference numerals in this specification and the drawings is intended to represent equal or similar features or elements of the present invention according to this disclosure.

[0018] Next, reference will be made in detail to presently preferred embodiments of the present invention. One or more examples of presently preferred embodiments of the present invention are shown in the accompanying drawings. Each example is presented non-limitingly by way of explanation of the present invention. It will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope and spirit of the present invention. For example, features shown and described as part of one embodiment can also be used in another embodiment to produce still another embodiment. Accordingly, the present invention is intended to embrace such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0019] Aspects of the present invention are particularly applicable to various screw actuators, where an axially movable part moves linearly relative to an axially fixed part. For example, the axially movable part may be in the form of a nut that moves back and forth along a screw shaft in accordance with the rotational direction of the screw shaft. Various screw actuators, including ball screws (recirculating ball screws and non-recirculating ball screws), lead screws (including planetary lead screws), and roller screws, can utilize the teachings of the present invention.

[0020] In this regard, FIG. 1 shows an exemplary application where the principles of the present invention can be employed. As shown, a brake assembly 1 has a linear actuator in the form of a ball screw assembly 100. The brake assembly 1 selectively applies a frictional braking force to a disk 2 that rotates integrally with a wheel, such as in an automobile. The brake device 1 has a caliper 3, a first backup plate 4 and a second backup plate 5, and a first pad 6 and a second pad 7. The caliper 3 is movably supported by a knuckle joint (not shown), and the first backup plate 4 and the second backup plate 5 are disposed on the caliper 3, thereby sandwiching the brake disk 2 therebetween. The first pad 6 and the second pad 7 are respectively fixed to the first backup plate 4 and the second backup plate 5 and can press against respective side surfaces of the disk 2.

[0021] The caliper 3 has a first body 8, a second body 9, and a cover 10. The first body 8 and the second body 9 are integrally fixed. The cover 10 is fixed to the second body 9. The first body 8 has a body portion 11 and an arm portion 12. One end of the second body 9 is fixed to the body portion 11. The arm portion 12 is coupled to the body portion 11 at a right angle. The second backup plate 5 is fixed to the arm portion 12. The second body 9 has a brake cylinder 13 and an extension plate 14. The cylinder 13 is fixed to the body portion 11 of the first body 8. The extension plate 14 extends from the cylinder 13.

[0022] The cylinder 13 has a first end 41 and a second end 42 that are axially opposite each other. The cylinder 13 has a cylindrical portion 15 that opens at the first end 41 and an end face plate 16 that is coupled to the second end 42 of the cylindrical portion 15. A piston 17 that is movable in the axial direction ST is accommodated in the cylinder 13. An end 73 of the piston 17 projects toward the disk 2 through an opening at an end of the cylinder 13 (corresponding to the first end 41 of the cylindrical portion 15). The first backup plate 4 is fixed to the end 73 of the piston 17.

[0023] A seal member 18 is inserted between the cylindrical outer surface 67 of the piston 17 and the inner surface of the cylinder 13 (corresponding to the inner surface 69 of the cylindrical portion 15), thereby closing the gap between the outer surface 67 and the inner surface 69. The seal member 18 may be an O-ring accommodated in an accommodation groove formed in the inner surface 69 of the cylinder 13. The outer surface 67 of the piston 17 and the inner surface 69 of the cylinder 13 are integrally coupled via a key 19 provided in key grooves formed in the outer surface 67 and the inner surface 69. By key coupling using the key 19, the movement of the piston 17 in the axial direction ST can be induced, and rotation of the piston 17 with respect to the cylinder 13 becomes impossible.

[0024] The caliper 3 functions to press both the pads 6 and 7 against the disk 2, thereby generating a braking force. For this purpose, the brake assembly 1 has a linear actuator that functions to move the piston 17 in the axial direction. In this case, the linear actuator is in the form of a screw actuator, i.e., a non-recirculating ball screw assembly 100. For this purpose, the caliper 3 further has an electric motor 20 and a reduction device 21. The reduction device 21 reduces the rotational speed of the electric motor 20. The ball screw assembly 100 converts the rotational motion from the electric motor 20 into a linear motion of the piston 17 in the axial direction ST via the reduction device 21.

[0025] The electric motor 20 has a motor housing 23 and an output shaft 24. The motor housing 23 is fixed to an extension plate 14 of the second body 9. The reduction gear 21 has a drive gear 25, a floating gear 26, and a driven gear 27. The drive gear 25 is attached to one end of the output shaft 24 of the electric motor 20 and thus rotates together with the output shaft 24. The floating gear 26 meshes with the drive gear 25. The driven gear 27 meshes with the floating gear 26. The floating gear 26 is pivotally supported by the second body 9 and is thus rotatable. A cover 10 is fixed to the second body 9 so as to cover the reduction gear 21.

[0026] The ball screw assembly 100 has a ball screw shaft 110 and a ball nut 130. The ball screw shaft 110 is an input member. The ball nut 130 is an output member that is screwed onto the ball screw shaft 110 via a plurality of main balls 140. As shown, the ball screw shaft 110 extends through the ball nut 130. The ball screw shaft 110 is supported by the second body 9 so as to be non-movable axially but rotatable. The ball nut 130 is supported by the piston 17 so as to be movable axially when the ball screw shaft 110 rotates, but the ball nut 130 is non-rotatable.

[0027] As can be seen, the end of the screw shaft 10 extends through a hole 31 formed in the end face plate 16 of the body 9. A bearing 32 assists the rotation between the screw shaft 110 and the cylinder 13. The bearing 32 is shown as a simple ball bearing in this schematic view, but various needle bearings and / or thrust bearings are often used as will be shown later. The passive gear 27 is coupled to the end 112 of the ball screw shaft 110 and thus rotates with the ball screw shaft 110. As shown, the ball nut 130 has a cylindrical outer surface 132 and an inner surface 134. A ball track 136 is formed within the inner surface 134. The ball screw shaft 110 has a cylindrical outer surface 114, and a ball track 116 is formed within the cylindrical outer surface 114. The main balls 140 forming the ball train are disposed within a ball race 150 (FIG. 4) defined between the ball track 116 and the ball track 136.

[0028] The outer surface 132 of the ball nut 130 is fitted within the cylindrical inner surface portion of the piston 17. Preferably, those skilled in the art will recognize that a structure (key, spline, etc.) is provided so as not to rotate the ball nut 130 relative to the piston 17. (The piston 17 and the nut 130 are shown here as separate pieces, but embodiments in which the nut 130 and the piston 17 are formed as a single piece are also contemplated.) The ball nut 130 has a first end 137 near the disk 2 and a second end 139 opposite the first end 137 in the axial direction X of the ball nut. In the embodiment shown, a retaining ring (coronary member) 40 fitted within an annular groove formed within the inner surface 77 of the piston 17 is engaged with the end face of the second end 139 of the ball nut 130. However, embodiments that do not utilize such a retaining ring 40 are also contemplated.

[0029] When the rotation of the output shaft 24 of the electric motor 20 is transmitted via the speed reducer 21 to the ball screw shaft 110 to thereby rotate the ball screw shaft 110, the ball nut 130 moves in the axial direction X (axial direction ST) of the ball nut. At this time, the piston 17 is guided by the key 19 and moves together with the ball nut 130 in the axial direction ST.

[0030] Figures 2 - 4 show certain perspectives of an exemplary ball screw assembly 100 that may be used in various embodiments of the present invention. In this case, the ball screw assembly 100 is formed as a non - recirculating ball screw that is similar in some respects to that disclosed in U.S. Patent No. 11,536,335, which is hereby incorporated by reference in its entirety for all purposes. As shown, a plurality of main balls 140 are held within the ball race 150, thereby forming a ball train 160. The ball train 160 has a first end 162 (Figure 4) and a second end 164. One or more link springs 197 may be disposed between adjacent main balls 140 of the ball train 160. The ball screw assembly 100 has a main coil spring assembly 170 and a return coil spring 180 disposed on both sides of the ball train 160 in the race 150.

[0031] As best seen in FIGS. 3 and 4, the main coil spring assembly 170 has a first end 170a and a second end 170b. The first end 170a is engaged with the main ball 140a at the first end 162 of the ball train 160. The second end 170b of the main spring assembly 170 is engaged with a stopper pin 190 received within a recess 193 formed within the ball nut 130, such that the stopper pin 190 extends into the ball race 150. The return coil spring 180 has a first end 180a and a second end 180b. The first end 180a is engaged with the main ball 140b at the second end 164 of the ball train 160. The second end 180b of the return spring 180 is engaged with a stopper pin 195 received within a recess (not shown) formed within the ball nut 130, such that the stopper pin 195 extends into the ball race 150. It should be noted that in an alternative embodiment, the ball screw apparatus 100 can have a pair of stopper balls (not shown) held within the recessed portion of the ball nut 130 instead of the stopper pins. Typically, the stopper balls have a diameter larger than the diameter of the main ball 140 and thus do not fit entirely within the ball race. However, depending on the configuration of the corresponding recess and the ball race 150, the diameter of the stopper balls can be equal to or smaller than the diameter of the main ball 140.

[0032] Continuing to refer to FIGS. 3 and 4, the main spring assembly 170 can be formed by a plurality of coil spring portions having various spring constants, thereby assisting in stabilizing spring compression over the length of the main spring assembly 170. As shown, the main spring assembly 170 in this embodiment has a first spring portion 172 having a first spring constant (k1), a second spring portion 174 having a second spring constant (k2), and a third spring portion 178 having a third spring constant (k3). The first spring portion 172 is disposed adjacent to the first end 162 of the ball train 160 and is separated from the second spring portion 174 by the first link ball 191a. The third spring portion 178 is disposed adjacent to the stopper pin 190 and is separated from the second spring portion by the second link ball 191b. The link balls 191a and 191b assist the motion of the spring portions 172, 174, and 178 within the race while reducing deformation.

[0033] FIGS. 5A and 5B show a preferred embodiment of a wobble joint 200 according to the present invention. As can be seen, the wobble joint 200 is formed between a ball screw shaft 110 and a thrust flange 220 that supports the axial load of the ball screw assembly 100. Preferably, the wobble joint 200 is a mating spherical joint between the annular contact surface 202 of the ball screw shaft 110 and the annular contact surface 222 of the thrust flange 220. Preferably, the thrust flange 220 is splined to the shaft 110 such that the thrust flange 220 and the shaft 110 rotate integrally, but can swing relative to the shaft 110. A thrust bearing 230 having a plurality of rollers 232 assists rotation between the thrust flange 220 and a fixed surface such as the bearing disk 218. The bearing disk 218 may be an integral part of the end face plate 16 or a separate piece fixed to the end face plate 16.

[0034] Referring now further to FIG. 6, both of the contact surfaces 202 and 222 preferably have a spherical profile (i.e., their surface shapes conform to a portion of a larger virtual sphere). In this regard, the contact surfaces 202 and 222 can have respective radii R1 and R2. Often, it is desirable for R2 to be slightly larger than R1. Additionally, the radius R1 is preferably disposed at the center of the longitudinal central axis 204 of the shaft 110. In contrast, as shown, the center point 240 of the radius of curvature of the annular contact surface 222 of the thrust flange 220 is preferably offset by an offset distance D from the longitudinal central axis 204 of the shaft. The offset radius of curvature of the annular contact surface 222 is often referred to as a Gothic arch. This contact geometry allows for movement to facilitate controlling misalignment between the shaft 110, the flange 220, the thrust bearing 230, and the system. For example, the thrust flange 220 can deform in cooperation with the support wall to apply a more uniform load to the thrust bearing rollers 232. This results in reduced contact stress compared to the prior art, enabling easier movement under large loads.

[0035] While one or more preferred embodiments of the invention have been described above, it will be recognized by those skilled in the art that various modifications and variations can be made to the invention without departing from the scope and spirit of the invention. The invention is intended to embrace such modifications and variations as fall within the scope of the appended claims and the spirit and their equivalents.

Explanation of Reference Numerals

[0036] 1 Brake device 2 Disk 3 Caliper 4 First backup plate 5 Second backup plate 6 First pad 7 Second pad 8 First body 9 Second body 10 Cover 11 Body part 12 Arm part 13 Brake cylinder 14 Extension plate 15 Cylindrical part 16 End face plate 17 Piston 18 Seal member 19 Key 20 Electric motor 21 Reduction gear 23 Motor housing 24 Output shaft 25 Driving gear 26 Idler gear 27 Driven gear 32 Rolling bearing 41 First end of the cylindrical part 42 Second end of the cylindrical part 67 Cylindrical outer surface of the piston 69 Inner surface of the cylindrical part 73 End of the piston 77 Inner surface of the piston 100 Ball screw assembly 100a Ball screw assembly 110 Ball screw shaft 112 End of the ball screw shaft 130 Ball nut 132 Cylindrical outer surface of the ball nut 134 Inner surface of the ball track 136 Ball track 137 First end of the ball nut 139 Second end of the ball nut 140 Main ball 140a Main ball 140b Main ball 150 Ball race 160 Ball train 162 First end of the ball train The second end of the 164 ball train 170 Coil spring assembly 170a The first end of the coil spring assembly 170b The second end of the coil spring assembly 172 The first spring part 174 The second spring part 178 The third spring part 180 Return coil spring 180a The first end of the return coil spring 180b The second end of the return coil spring 190 Stopper pin 191a The first link ball 191b The second link ball 195 Stopper pin 193 Recess 197 Link spring k1 The first spring constant k2 The second spring constant k3 The third spring constant ST Axial direction X Axial direction

Claims

1. A support structure, a screw shaft that is axially fixed to the support structure but rotatably drivable, a nut attached to the screw shaft, whereby rotation of the screw shaft causes axial movement of the nut along the screw shaft, the screw shaft defining a first annular contact surface having a spherical profile with a first radius, a thrust flange positioned on the screw shaft for rotation therewith, the thrust flange having a second annular contact surface with a second radius, the first annular contact surface engaging the second annular contact surface, a screw linear actuator having, the screw linear actuator, wherein the second radius is greater than the first radius.

2. The screw linear actuator according to claim 1, wherein the first radius has a first center point that coincides with the longitudinal central axis of the screw shaft.

3. The screw linear actuator according to claim 2, wherein the second radius has a second center point that is offset from the longitudinal central axis of the screw shaft.

4. The screw actuator according to claim 1, further comprising a thrust bearing positioned between the thrust flange and the support structure.

5. The screw actuator according to claim 4, further comprising a bearing disk fixed to the support structure.

6. The screw linear actuator according to claim 1, wherein the linear actuator has a ball screw assembly, the ball screw assembly having a plurality of balls positioned between opposing ball tracks defined within the screw shaft and within the nut.

7. The screw actuator according to claim 6, wherein the ball screw assembly has a non-recirculating ball screw assembly.

8. The screw linear actuator according to claim 1, further comprising a brake piston axially movable by the nut.

9. A support structure, a screw shaft that is axially fixed to the support structure but rotatably drivable, a nut attached to the screw shaft, whereby rotation of the screw shaft causes axial movement of the nut along the screw shaft, The screw shaft defining a first annular contact surface having a spherical profile with a first radius, A thrust flange positioned on the screw shaft for rotation with the screw shaft, the thrust flange having a second annular contact surface with a second radius, the first annular contact surface engaging the second annular contact surface, a thrust flange; A thrust bearing positioned between the thrust flange and the support structure A screw linear actuator having, The first radius has a first center point that coincides with the longitudinal central axis of the screw shaft, and the second radius has a second center point offset from the longitudinal central axis of the screw shaft, a screw linear actuator.

10. The screw linear actuator according to claim 9, wherein the second radius is greater than the first radius.

11. The screw actuator according to claim 10, further comprising a bearing disk fixed to the support structure.

12. The screw linear actuator according to claim 9, wherein the linear actuator has a ball screw assembly, and the ball screw assembly has a plurality of balls positioned between opposing ball tracks defined within the screw shaft and within the nut.

13. The screw actuator according to claim 12, wherein the ball screw assembly has a non-recirculating ball screw assembly.

14. A brake caliper having a body with a brake cylinder, A piston positioned within the brake cylinder, A first pad fixed to an end of the piston, A second pad opposing the first pad, And a screw linear actuator A brake device having, The screw linear actuator is A screw shaft that is axially fixed to the brake caliper but rotatably drivable, A nut attached to the screw shaft, whereby rotation of the screw shaft causes axial movement of the nut along the screw shaft, and the nut is connected to the piston so as to cause axial movement of the piston, a nut, The screw shaft defining a first annular contact surface having a spherical profile with a first radius, A thrust flange positioned on the screw shaft for rotation with the screw shaft, the thrust flange having a second annular contact surface with a second radius, the first annular contact surface engaging the second annular contact surface, the thrust flange; A thrust bearing positioned between the thrust flange and the brake caliper; A brake device, wherein the first radius has a first center point that coincides with the longitudinal central axis of the screw shaft, and the second radius has a second center point that is offset from the longitudinal central axis of the screw shaft. **Claim 15** The brake device according to claim 14, wherein the first radius has a first center point that coincides with the longitudinal central axis of the screw shaft, and the second radius has a second center point that is offset from the longitudinal central axis of the screw shaft. **Claim 16** The brake device according to claim 15, wherein the second radius is larger than the first radius. **Claim 17** The brake device according to claim 14, further comprising a bearing disk fixed to the brake caliper. **Claim 18** The brake device according to claim 14, wherein the linear actuator has a ball screw assembly having a plurality of balls positioned in opposing ball tracks defined within the screw shaft and within the nut.

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