Ball screw

Abstract

The present invention provides a ball screw that preferably restricts the rotation of the nut. [Solution] The outer surface (11B) of the ball screw nut (11) has a restricting groove (113) that extends in the axial direction of the screw shaft to prevent the nut (11) from rotating together with the screw shaft. The connecting path (112) that connects the end point and the start point of the rolling path (131) demarcated by the male screw groove (101) of the screw shaft and the female screw groove of the nut (11) is formed so as to avoid the restricting groove (113) in the circumferential direction of the nut (11).

Description

Technical Field

[0001] The present disclosure relates to a ball screw.

Background Art

[0002] Patent Document 1 discloses a deflector-type ball screw that circulates balls in a circulation path formed by a rolling path defined by a female screw groove formed on the inner peripheral surface of a nut and a male screw groove formed on the outer peripheral surface of a screw shaft, and a connection path that connects one end and the other end in the longitudinal direction of the rolling path.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Ball screws are known to be used as mechanical elements for linear motion conversion that converts rotational motion into linear motion. When converting the rotational motion of a screw shaft into the linear motion of a nut, the rotation of the nut is restricted to prevent the nut from rotating together with the screw shaft, in order to improve conversion efficiency. For example, a technique is known that physically restricts the rotation of the nut by fitting a part of a non-rotating object into a groove of the nut. However, there is room for improvement in the rotation restriction of the nut of a ball screw. An aspect of the present disclosure aims to provide a ball screw in which the rotation of the nut is suitably restricted.

Means for Solving the Problems

[0005] To solve the above problems, a ball screw according to one aspect of the present disclosure comprises a screw shaft having a male screw groove formed on its outer circumference, a nut having a female screw groove formed on its inner circumference and moving in a straight line with the rotation of the screw shaft, and a plurality of balls arranged in a rolling path partitioned by the female screw groove and the male screw groove facing it, which transmit torque between the nut and the screw shaft, wherein a connecting path is formed in the nut connecting the end point and the start point of the rolling path, and the balls circulate between the rolling path and the connecting path, wherein a regulating groove is formed on the outer circumference of the nut to prevent the nut from rotating together with the screw shaft and extends in the axial direction of the screw shaft, and the connecting path is formed so as to avoid the regulating groove in the circumferential direction of the nut. [Effects of the Invention]

[0006] According to one aspect of this disclosure, the rotation of the ball screw nut can be suitably restricted. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram showing one example of the configuration of a ball screw according to one embodiment of the present disclosure. [Figure 2] A perspective view showing an example of a nut according to one embodiment of this disclosure. [Figure 3] This figure shows an example of the arrangement of balls in a nut according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0008] Figure 1 is a schematic diagram showing an example configuration of a ball screw according to one embodiment of the present disclosure. The ball screw 1 shown in Figure 1 comprises a screw shaft 10 with a male screw groove 101 formed on its outer circumference and a cylindrical nut 11 with a female screw groove 111 formed on its inner circumference 11A. The male screw groove 101 is positioned opposite the female screw groove 111. A rolling path 131 is defined between the male screw groove 101 and the female screw groove 111. Multiple balls 120 are arranged in the rolling path 131. In the ball screw 1, torque is transmitted between the screw shaft 10 and the nut 11 via the balls 120.

[0009] In Figure 1, the ball screw 1 is mounted on the electric braking device 20 as a linear motion conversion mechanism. The electric braking device 20 includes the ball screw 1, a cylinder 21, a piston 22, and a friction member 23. In the electric braking device 20, rotational motion, such as that of an electric motor, is transmitted to the screw shaft 10 via a reduction mechanism or the like.

[0010] The piston 22 is fitted with the nut 11 of the ball screw 1. When the nut 11 moves linearly in the axial direction of the screw shaft 10 due to the torque transmitted from the screw shaft 10 via the ball 120, the piston 22 slides inside the cylinder 21 in the axial direction of the screw shaft 10. In the electric braking device 20, the piston 22 comes into contact with the friction member 23, and by pressing the friction member 23 against a rotating member that rotates with the vehicle's wheel, braking force is applied to the wheel.

[0011] Figure 2 is a perspective view showing an example of a nut according to one embodiment of the present disclosure. The inner circumferential surface 11A of the nut 11 shown in Figure 2 is provided with five female screw grooves 111 that define the rolling path 131. Between the start and end points of each female screw groove 111 (between the start and end points of the rolling path 131), there is one connecting passage 112. The balls 120 that have reached the end point of the rolling path 131 are returned to the start point of the rolling path 131 via these connecting passages 112. The balls 120 circulate between the rolling path 131 and the connecting passages 112 connected to it. The connecting passages 112 connected to each of the five female screw grooves 111 are formed so as to avoid each other in the circumferential direction of the nut 11 and in the axial direction of the screw shaft 10. The outer circumferential surface 11B of the nut 11 is provided with five fitting grooves 113 that engage with the piston 22. The fitting grooves 113 are an example of regulating grooves. The fitting grooves 113 extend in the axial direction of the screw shaft 10.

[0012] Figure 3 shows an example of ball arrangement in a nut according to one embodiment of the present disclosure. As shown in Figure 3, the five fitting grooves 113 are arranged at equal intervals along the circumferential direction of the outer surface 11B of the nut 11 in a plan view when the nut 11 is viewed from the axial direction. The five connecting passages 112 are arranged at equal intervals along the circumferential direction of the inner surface 11A of the nut 11 in a plan view when the nut 11 is viewed from the axial direction. In other words, the angles formed by the perpendiculars drawn from the bottom surface of each fitting groove 113 to the central axis of the nut 11 are approximately equal angles in a plan view of the nut 11. The angles formed by the perpendiculars drawn from the center of each connecting passage 112 to the central axis of the nut 11 are approximately equal angles in a plan view of the nut 11. Each connecting passage 112 is arranged so as to avoid the fitting grooves 113 in the circumferential direction of the nut 11. More specifically, one connecting passage 112 is arranged in each portion 11C between the fitting grooves 113 that are aligned in the circumferential direction on the outer surface 11B.

[0013] In each connecting passage 112, the path for guiding the ball 120 from the end point to the starting point of the rolling passage 131 is located radially outward of the nut 11 compared to the rolling passage 131. If the connecting passage 112 were arranged radially alongside the fitting groove 113 and the nut 11, the thickness of the nut 11 would increase. In this disclosure, each connecting passage 112 has the fitting groove 113 positioned to avoid the circumferential direction of the nut 11, so the thickness of the nut 11 does not increase, and thus does not hinder the miniaturization of the ball screw 1.

[0014] A fitting projection 22A of the piston 22 fits into each fitting groove 113. The fitting projection 22A protrudes radially inward from, for example, the portion of the inner circumferential surface of the piston 22 that faces the outer circumferential surface 11B of the nut 11. The fitting projection 22A illustrated in Figure 3 extends in the axial direction of the screw shaft 10. The ball screw 1 is housed inside the piston 22 by sliding the ball screw 1 in the axial direction while engaging each fitting groove 113 with the fitting projection 22A.

[0015] The piston 22 is prevented from rotating with the screw shaft 10 by the frictional force between it and the inner circumferential wall of the cylinder 21 and the friction member 23. The nut 11 is prevented from rotating with the screw shaft 10 because its fitting groove 113 is fitted into the fitting projection 22A. Since the rotation of the nut 11 around the screw shaft 10 is prevented, the ball screw 1 can efficiently convert the rotation of the screw shaft 10 into the linear motion of the nut 11.

[0016] [Variation] In the above embodiment, the rotation of the nut 11 of the ball screw 1 is restricted around the screw shaft 10 by the fitting groove 113 fitting into the fitting projection 22A of the piston 22. However, the means for restricting the rotation of the nut 11 around the screw shaft 10 is not limited to the fitting of the fitting groove 113 and the fitting projection 22A. For example, the rotation of the nut 11 around the screw shaft 10 may be restricted by inserting a guide pin, which is inserted and fixed through the piston 22 or cylinder 21, into the fitting groove 113. If the rotation of the nut 11 around the screw shaft 10 is restricted by a guide pin fixed to the cylinder 21, the piston 22 may be fixed to the nut 11 to restrict the rotation of the piston 22 around the screw shaft 10.

[0017] In the above embodiment, the nut 11 is provided with five connection paths 112 and five fitting grooves 113 each. However, the number of connection paths 112 and fitting grooves 113 provided in the nut 11 is not limited to five. Further, the number of connection paths 112 provided in the nut 11 may be larger than the number of fitting grooves 113. For example, the number of connection paths 112 provided in the nut 11 may be a positive integer multiple of the number of fitting grooves 113 provided in the nut 11. It is preferable that the connection paths 112 provided more than the fitting grooves 113 are distributed substantially evenly to each portion 11C. By distributing the connection paths 112 substantially evenly, a decrease in the rigidity of the nut 11 can be suppressed.

[0018] In the above embodiment, the ball screw 1 is applied to the electric brake device 20 that applies a braking force to the vehicle wheel by bringing the piston 22 into contact with the friction member 23 and pressing the friction member 23 against a rotating member that rotates together with the vehicle wheel. However, the ball screw 1 may be applied as a linear motion conversion device to an electric brake device that adjusts the hydraulic pressure in a wheel cylinder by causing the piston in the cylinder to move forward based on the rotational motion of an electric motor, thereby discharging brake fluid in a hydraulic chamber defined by the cylinder and the piston to the outside of the hydraulic chamber.

[0019] [Summary] A ball screw according to one aspect of the present disclosure includes: a screw shaft having a male screw groove formed on an outer peripheral surface thereof; a nut having a female screw groove formed on an inner peripheral surface thereof and configured to linearly move as the screw shaft rotates; and a plurality of balls arranged in a rolling path defined by the female screw groove and the male screw groove facing the female screw groove, and configured to transmit torque between the nut and the screw shaft, wherein a connection path connecting an end point and a start point of the rolling path is formed in the nut, and in the ball screw in which the balls are circulated through the rolling path and the connection path, a restriction groove that prevents the nut from rotating together with the screw shaft and extends in an axial direction of the screw shaft is formed on an outer peripheral surface of the nut, and the connection path is formed so as to avoid the restriction groove in a circumferential direction of the nut. According to the above configuration, the connection path is formed to avoid the restriction groove in the circumferential direction of the nut, and the connection path and the restriction groove do not overlap in the radial direction of the nut, so the wall thickness of the nut can be reduced while ensuring the strength of the nut. Therefore, the ball screw with restricted nut rotation can be miniaturized in the axial direction of the screw shaft. An electric brake device or a hydraulic pressure generating device using the above ball screw as a linear motion conversion mechanism can be reduced in size in the radial direction of the ball screw by miniaturizing the ball screw in the axial direction of the screw shaft.

[0020] In the ball screw according to one aspect of the present disclosure, in the above aspect, the nut has a plurality of the connection paths, and the plurality of connection paths are formed so as to avoid each other in the axial direction of the screw shaft. According to the above configuration, the connection paths are formed so as to avoid each other in the axial direction of the screw shaft, thereby avoiding interference caused by adjacent connection paths and preventing the axial length of the nut from increasing.

[0021] In the ball screw according to one aspect of the present disclosure, in the above aspect, the nut has a plurality of the connection paths and a plurality of the restriction grooves, and the plurality of restriction grooves and the plurality of connection paths are arranged at equal intervals along the circumferential direction of the nut in a plan view of the nut viewed from the axial direction. According to the above configuration, the center of gravity of the nut can be suppressed from being displaced from the central axis of the nut. In an electric brake device or a hydraulic pressure generating device using the above ball screw as a linear motion conversion mechanism, an eccentric load is less likely to be applied to the nut when the nut moves linearly together with the piston.

[0022] In the ball screw according to one aspect of the present disclosure, in the above aspect, the nut has the same number of the connection paths as the restriction grooves. According to the above configuration, since one connection path can be arranged between every two adjacent restriction grooves, it is easy to suppress the center of gravity of the nut from being displaced from the central axis of the nut.

[0023] [Additional Notes] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. [Explanation of Symbols]

[0024] 1 Ball screw 10 Screw shaft 11 nuts 101 Male thread groove 111 Female thread groove 112 Connections 113 Fitting groove (regulating groove) 120 balls 131 Turning track

Claims

1. A ball screw comprising: a screw shaft with a male screw groove formed on its outer circumference; a nut with a female screw groove formed on its inner circumference and which moves in a straight line with the rotation of the screw shaft; and a plurality of balls arranged in a rolling path partitioned by the female screw groove and the male screw groove opposite it, which transmit torque between the nut and the screw shaft, wherein a connecting path is formed in the nut connecting the end point and the start point of the rolling path, and the balls are circulated between the rolling path and the connecting path, The outer surface of the nut is provided with a regulating groove that extends in the axial direction of the screw shaft, preventing the nut from rotating together with the screw shaft. The connecting path is a ball screw formed so as to avoid the restricting groove in the circumferential direction of the nut.

2. The nut has multiple rolling paths and connecting paths, The ball screw according to claim 1, wherein the plurality of connection paths are formed so as to avoid each other in the axial direction of the screw shaft.

3. The nut has multiple connection paths and regulating grooves, The ball screw according to claim 1, wherein the plurality of regulating grooves and the plurality of connecting passages are arranged at equal intervals along the circumferential direction of the nut in a plan view of the nut from the axial direction.

Images