JP2023000207A - ball screw device - Google Patents

Abstract

To provide a ball screw device capable of preventing breakage of a connection member even when shut-down torque is applied to a screw shaft.SOLUTION: A ball screw device includes: a housing; a nut; a screw shaft having a connected portion on a part in a longitudinal direction; a plurality of balls; an elastic body disposed at an outer peripheral side of the connected portion and extended in a circumferential direction; and a connection member having an annular connecting portion fitted to an outer peripheral side of the elastic body. When the nut is rotated in a first rotating direction, the screw shaft is moved in a first direction and a projection amount of the screw shaft from the nut is increased, and when the nut is rotated in a second rotating direction opposite to the first rotating direction, the screw shaft is moved in a second direction opposite to the first direction and the projection amount is decreased. An outer peripheral surface of the connected portion is provided with a projection for the screw shaft projecting to a radial outer side and kept into contact with the elastic body from the second rotating direction, and an inner peripheral surface of the connecting portion is provided with a projection for the connecting portion projecting to a radial inner side and kept into contact with the elastic body from the first rotating direction.SELECTED DRAWING: Figure 3

Description

The present invention relates to a ball screw device.

A brake booster includes a motor, a ball screw device, a piston, and a cylinder. When the brake pedal is stepped on, the motor of the brake booster is driven and the nut of the ball screw device is rotated. Also, the screw shaft of the ball screw device moves in the axial direction to press the piston. The piston pushes against the brake fluid in the cylinder, increasing the hydraulic pressure of the brake fluid. The increased hydraulic pressure is transmitted to the brake system located outside the brake boost. As a result, the disc brakes or drum brakes are actuated to slow down the vehicle. In this way, the ball screw device is sometimes mounted on the brake booster. In the brake booster, when the driver does not step on the brake pedal, the projection amount of the screw shaft of the ball screw device is the smallest.

In the following description, when the brake pedal is not stepped on, the initial position of the screw shaft (the state where the amount of protrusion of the screw shaft is the smallest) may be referred to as the origin. Further, in the moving direction of the screw shaft, moving in the direction of pushing the piston may be referred to as advancing, and moving in the direction opposite to the advancing may be referred to as retreating. Among the rotation directions of the nut, rotation in the direction of advancing the screw shaft may be referred to as forward rotation, and rotation in the direction of retracting the screw shaft may be referred to as reverse rotation.

Further, in the ball screw device disclosed in the following patent document, a protrusion is provided on one end surface of the nut (the end surface facing the piston). One end of the screw shaft (the end where the piston is located) is provided with a stopper that is non-rotatably fixed to the screw shaft. Then, when the screw shaft retreats and returns to the origin, the stopper comes into contact with the projection. As a result, when the brake pedal is not depressed, the screw shaft is positioned at the origin. Further, the stopper disclosed in the following patent document has an elastic body at a portion that contacts with the projection. This reduces the impact load received from the projection.

In addition, the screw shaft of the ball screw device is non-rotatably connected to a component such as an anti-rotation device. The anti-rotation is supported by a housing or the like so as to be non-rotatable and axially movable. Therefore, even if the nut rotates, the screw shaft moves axially without co-rotating with the nut.

Japanese Patent No. 6413555

By the way, in the brake booster, the hydraulic pressure of the brake fluid always acts on the piston. Further, the direction of hydraulic pressure acting on the piston is the direction in which the screw shaft retreats. Here, if a power failure occurs and the power supply to the motor stops, the rotor of the motor will idle. If a power failure occurs while the screw shaft is moving forward, the reaction force of the brake fluid causes the screw shaft to retreat. Along with this, the nut rotates in the reverse direction, and the rotor of the motor also rotates. Then, when the screw shaft returns to the origin, the stopper comes into contact with the protrusion of the nut, and the reverse rotation of the nut stops. However, the rotor of the motor continues to rotate due to inertia. Therefore, immediately after the screw shaft returns to the origin, the motor rotates in the reverse direction and applies a relatively large torque to the nut. Hereinafter, the torque applied to the nut by the motor due to inertia at the time of power failure will be referred to as shutdown torque.

Since the shutdown torque acts on the nut as described above, torque in the co-rotation direction (reverse rotation direction) acts on the screw shaft from the nut. In addition, there is a possibility that a relatively large torque associated with the shutdown torque will be input to a connecting portion of a connecting member such as an anti-rotation member or a stopper that is non-rotatably connected to the screw shaft, resulting in damage. In order to cope with this, it is conceivable to provide the screw shaft with a projection that prevents the connecting portion from rotating, and further provide the projection with an elastic body as in the above patent document. However, the protrusions have a short width in the circumferential direction. That is, even if an elastic body is provided on the projection, the length of the elastic body in the circumferential direction is limited to be short. Therefore, even if the structure of the above patent document is applied, there is a possibility that damage to the connecting portion of the connecting member cannot be avoided. In view of the above, there is a demand for development of a ball screw shaft device that can avoid breakage of the connecting member that connects to the screw shaft even if shutdown torque acts on the screw shaft.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a ball screw device that can avoid damage to a connecting member even if shutdown torque acts on a screw shaft.

To achieve the above object, a ball screw device according to one aspect of the present disclosure includes a housing, a screw shaft, a nut, a plurality of balls, an elastic body, and a connecting member. A nut is rotatably supported by the housing. The screw shaft has a part to be connected in a longitudinal direction and passes through the nut. A plurality of balls are arranged between the nut and the screw shaft. The elastic body is arranged on the outer peripheral side of the connected portion and extends in the circumferential direction. The connecting member has an annular connecting portion that fits on the outer peripheral side of the elastic body. When the nut rotates in the first rotation direction, the screw shaft moves in the first direction, and the amount by which the screw shaft protrudes from the nut increases. When the nut rotates in a second direction opposite to the first direction, the screw shaft moves in a second direction opposite to the first direction, thereby reducing the amount of protrusion. A projection for a screw shaft is provided on the outer peripheral surface of the connected portion so as to protrude radially outward and contact the elastic body from the second rotation direction. An inner peripheral surface of the connecting portion is provided with a connecting portion protrusion that protrudes radially inward and abuts against the elastic body from the first rotation direction.

According to the above configuration, when the power supply to the motor fails while the screw shaft is pressing the piston (moving in the first direction), shutdown torque in the second rotation direction is input to the nut. Further, torque in the second rotation direction acts on the screw shaft from the nut. Then, the screw shaft projection rotates in the second rotation direction and crushes the elastic body. Therefore, the load acting on the connection projection from the screw shaft projection is absorbed by the elastic body. Here, the elastic body is interposed between the screw shaft projection and the connecting projection, and has a relatively large length in the circumferential direction. That is, the load acting from the screw shaft projections to the connection projections is greatly reduced by the elastic body. As described above, damage to the connecting portion projection (connecting member) is avoided.

As a desirable aspect of the above-described ball screw device, the screw shaft projection abuts on the connecting portion projection from the first rotation direction.

The screw shaft projection is supported by the connecting portion projection from the first rotation direction. Therefore, the screw shaft is connected to the connecting member so as not to rotate in the first rotation direction.

As a desirable aspect of the above ball screw device, the nut has a nut projection projecting from a first end surface facing the first direction. The connecting member has a protruding portion that protrudes from the outer peripheral surface of the connecting portion. When the screw shaft is positioned at the origin, the nut protrusion contacts the protrusion from the second rotation direction.

According to the above configuration, when the screw shaft returns to the origin, the nut projection comes into contact with the projecting portion of the connecting member, and the rotation of the nut in the second rotation direction is restricted. Therefore, the initial position of the screw shaft is positioned at the origin.

As a desirable aspect of the above-described ball screw device, a plurality of the connecting portion projections, the screw shaft projections, and the elastic bodies are provided.

According to the above configuration, the load acting on the connecting member from the screw shaft is distributed to the plurality of connecting portion protrusions and the screw shaft protrusions. Therefore, the projection for the screw shaft and the projection for the connecting portion are less likely to be damaged.

As a desirable aspect of the above ball screw device, the elastic body is arranged between the screw shaft projection and the connecting portion projection in a circumferentially compressed state.

According to the above configuration, the elastic body is press-fitted between the screw shaft projection and the connecting portion projection. Therefore, the elastic body is less likely to be displaced in the axial direction from between the screw shaft projection and the connecting portion projection. Further, when the screw shaft projection abuts on the connection projection from the first rotation direction, the elastic body exerts an elastic deformation force that presses the screw shaft projection against the connection projection. For this reason, the abutment between the screw shaft projection and the connecting portion projection is less likely to be released, and contact noise between the screw shaft projection and the connecting portion projection is less likely to occur.

As a desirable aspect of the above ball screw device, at least a portion of the elastic body in the circumferential direction has a thickness in the radial direction smaller than the width from the inner peripheral surface of the connecting portion to the outer peripheral surface of the connected portion.

According to the above configuration, there is a gap in at least a part of the circumferential direction between the inner peripheral surface of the elastic body and the outer peripheral surface of the connected portion, or between the outer peripheral surface of the elastic body and the inner peripheral surface of the connecting portion. occur. If there is no gap, the elastic body deforms so as to protrude in the axial direction from between the screw shaft projection and the connecting portion projection. Then, there is a possibility that the elastic body presses and damages the cover member that prevents the elastic body from coming off. On the other hand, according to the present disclosure, when the elastic body is pressed by the screw shaft projection, it deforms so as to fill the gap. That is, there is a low possibility that the elastic body will protrude in the axial direction from between the screw shaft projection and the connecting portion projection.

The connecting member of the ball screw device may be an anti-rotation member that is movably supported in an axial direction parallel to the screw shaft and non-rotatably supported by the housing.

The connecting member of the ball screw device may be a stopper separated from the housing and not supported by the housing.

The above ball screw device may include a piston coupled to an end of the screw shaft in the first direction.

According to the ball screw device of the present disclosure, damage to the connecting member is avoided even if shutdown torque acts on the screw shaft.

FIG. 1 is a cross-sectional view of the brake booster of Embodiment 1, taken in the axial direction, with the screw shaft positioned at the origin. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 3 is a cross-sectional view taken along line III-III of FIG. 1. FIG. FIG. 4 is an enlarged view of the connected portion and its vicinity in FIG. 1 . 5 is a cross-sectional view taken along line VV in FIG. 2. FIG. FIG. 6 is a cross-sectional view when torque accompanying shutdown torque is input to the screw shaft. 7 is a cross-sectional view of an elastic body in a ball screw device of Modification 1. FIG. FIG. 8 is a side view of the ball screw device of Embodiment 2 as viewed from the first direction. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. FIG. 10 is a side view of the ball screw device of Embodiment 3 as viewed from the first direction. FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. 10. FIG. 12 is a side view of the ball screw device of Embodiment 4 as viewed from the first direction. FIG.

Hereinafter, the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, components in the following embodiments include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

(Embodiment 1)
FIG. 1 is a cross-sectional view of the brake booster of Embodiment 1, taken in the axial direction, with the screw shaft positioned at the origin. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 3 is a cross-sectional view taken along line III-III of FIG. 1. FIG. FIG. 4 is an enlarged view of the connected portion and its vicinity in FIG. 1 . 5 is a cross-sectional view taken along line VV in FIG. 2. FIG. FIG. 6 is a cross-sectional view when torque accompanying shutdown torque is input to the screw shaft.

The brake booster 100 is mounted on a vehicle and is a device for generating hydraulic pressure corresponding to the amount of depression of a brake pedal. As shown in FIG. 1 , the brake booster 100 of Embodiment 1 includes a motor 101 , a reduction gear 102 , a ball screw device 1 , a piston 110 and a housing 120 . For convenience of explanation, the direction parallel to the screw shaft 3 of the ball screw device 1 is called the axial direction. Further, among the axial directions, the direction in which the piston 110 is arranged as viewed from the nut 2 of the ball screw device 1 is called a first direction X1, and the direction opposite to the first direction is called a second direction X2.

The motor 101 includes a stator (not shown), a rotor (not shown), and an output shaft 101a. The motor 101 is powered by a power supply (not shown) to rotate the rotor and the output shaft 101a. Also, the motor 101 is supported by the housing 120 and the output shaft 101 a is parallel to the screw shaft 3 .

The speed reducer 102 includes a first gear 103 fitted to the output shaft 101 a of the motor 101 and a second gear 104 fitted to the outer peripheral side of the nut 2 of the ball screw device 1 . The second gear 104 is a gear with a larger diameter than the first gear 103 . Therefore, the reduction gear 102 reduces the speed of the rotational motion generated by the motor 101 and transmits it to the nut 2 .

A ball screw device 1 includes a nut 2, a screw shaft 3, balls 4, an elastic body 5, and an anti-rotation 6 as a connecting member. Nut 2 is supported by two bearings 7 fitted to the inner peripheral surface of housing 120 . Thereby, the nut 2 is rotatable around the axis O of the screw shaft 3 .

Hereinafter, the rotation direction of the nut 2 is based on the rotation direction of the nut 2 when viewed from the first direction X. As shown in FIG. Specifically, as shown in FIG. 2, when the nut 2 rotates counterclockwise as viewed from the first direction X, the rotation direction is set to the first rotation direction L1 (see the arrow in FIG. 2). ). When the nut 2 rotates clockwise (clockwise) when viewed from the first direction X, the rotation direction is referred to as a second rotation direction L2 (see the arrow in FIG. 2).

As shown in FIG. 1, the inner peripheral surface of the nut 2 is provided with an inner peripheral raceway surface 2a. The inner raceway surface 2a and the outer raceway surface 3a are spiral raceway surfaces facing each other. The spiral direction of the inner circumferential raceway surface 2a moves in the second direction X2 toward the first rotation direction L1. Similarly, the spiral direction of the outer circumferential raceway surface 3a also moves in the first direction X1 toward the second rotation direction L2. A plurality of balls 4 are arranged between the inner raceway surface 2a and the outer raceway surface 3a. Therefore, when the nut 2 rotates in the first rotation direction L1, the screw shaft 3 moves in the first direction X1, and the amount of protrusion of the screw shaft 3 from the nut 2 increases. On the other hand, when the nut 2 rotates in the second rotation direction L2, the screw shaft 3 moves in the second direction X2, and the amount of protrusion of the screw shaft 3 from the nut 2 is reduced.

The nut 2 has a first end surface 20 facing the first direction X1. The first end surface 20 is provided with a nut protrusion 21 that protrudes in the first direction X1. As shown in FIG. 2 , the nut projection 21 has an arcuate shape around the axis O of the screw shaft 3 . Further, the nut projection 21 has a side surface 21a facing the second rotation direction L2.

As shown in FIG. 1, the screw shaft 3 passes through the nut 2. As shown in FIG. The screw shaft 3 includes a screw shaft main body 30 having an outer peripheral raceway surface 3a on its outer peripheral surface, a connected portion 31 arranged in the first direction X1 of the screw shaft main body 30, and a pressing portion 32 for pressing the piston 110. , provided.

The screw shaft body 30 is longer than the axial length of the nut 2 . The screw shaft main body 30 is arranged in a state in which the screw shaft 3 is located at the origin and protrudes greatly from the nut 2 in the second direction X2. In other words, the screw shaft 3 is supported by the nut 2 so as to be movable in the first direction X1 by rotating the nut 2 in the first rotation direction L1.

The connected portion 31 is a part of the screw shaft 3 in the longitudinal direction, and is a portion to which the anti-rotation 6 is fitted. The connected portion 31 of the first embodiment is adjacent to the screw shaft main body 30 in the first direction X1. That is, the connected portion 31 is arranged in the first direction X1 relative to the nut 2 in a state where the screw shaft 3 is at the origin.

As shown in FIG. 3, the outer peripheral surface 33 of the connected portion 31 has a circular shape when viewed from the axial direction. A screw shaft projection 34 projecting radially outward is provided on the outer peripheral surface 33 of the connected portion 31 . Two screw shaft projections 34 are provided at intervals of 180°. The screw shaft projection 34 has a substantially trapezoidal shape when viewed from the axial direction. Accordingly, the screw shaft projection 34 has a top surface 35 facing radially outward, a first side surface 36 facing in the first rotation direction L1, and a second side surface 37 facing in the second rotation direction L2.

As shown in FIG. 4 , the outer diameter r33 of the outer peripheral surface 33 of the connected portion 31 is smaller than the outer diameter of the screw shaft body 30 . Therefore, a stepped surface 38 facing the first direction X1 is provided at the boundary between the screw shaft body 30 and the connected portion 31 . The step surface 38 is in contact with the end surface 60a of the connecting portion 60 of the antirotation 6. As shown in FIG. Therefore, the screw shaft 3 is regulated so as not to move in the first direction X1 relative to the anti-rotation 6. As shown in FIG.

As shown in FIG. 1, the pressing portion 32 extends from the connected portion 31 in the first direction X1. The end of the pressing portion 32 in the first direction X1 is arranged inside the cylinder 121 of the housing 120 . An end portion of the pressing portion 32 in the first direction X1 is connected to the piston 110 . Therefore, the screw shaft 3 and the piston 110 move integrally in the axial direction.

The piston 110 is slidably fitted to the inner peripheral surface of the cylinder 121 . The inside of the cylinder 121 contains brake fluid (not shown). The cylinder 121 is provided with a through hole 121a. This through hole 121 a is a hole for transmitting the hydraulic pressure of the brake fluid to the outside of the brake booster 100 .

As shown in FIG. 2 , the anti-rotation 6 includes an annular connecting portion 60 fitted to the outer peripheral side of the elastic body 5 , first arm portions 61 extending radially outward from the outer peripheral surface of the connecting portion 60 , and first arm portions 61 and 61 . and two arms 62 .

An outer peripheral surface 63 of the connecting portion 60 has a circular shape when viewed from the axial direction. The first arm portion 61 and the second arm portion 62 are arranged on the outer peripheral surface 63 of the connecting portion 60 at an interval of 180°. For convenience of explanation, the arm extending leftward from the connecting portion 60 as viewed from the first direction X1 is referred to as a first arm portion 61, and the arm extending rightward from the connecting portion 60 is referred to as a second arm. referred to as section 62 .

The distal end portion 61 a of the first arm portion 61 and the distal end portion 62 a of the second arm portion 62 are each fitted in a guide groove 122 provided on the inner peripheral surface of the housing 120 . Therefore, even if a torque around the axis O acts on the anti-rotation 6, the first arm 61 and the second arm 62 are caught on the side surface of the guide groove 122, and the anti-rotation 6 does not rotate.

Note that the guide groove 122 extends in the axial direction (see FIG. 1). Further, the tip portion 61a of the first arm portion 61 and the tip portion 62a of the second arm portion 62 are fitted in the guide grooves 122 so as to be slidable in the axial direction. Therefore, the anti-rotation 6 is axially movable along the guide groove 122 .

As shown in FIG. 5 , the axial length of the second arm portion 62 is longer than the axial length of the first arm portion 61 . Therefore, the back surface 62c of the second arm portion 62 is located in the second direction X2 relative to the back surface 61c of the first arm portion 61. As shown in FIG. With the screw shaft 3 at the origin, the rear surface 62c of the second arm 62 is located in the second direction X2 relative to the end surface 21b of the protrusion 21 in the first direction X1. On the other hand, the rear surface 61c of the first arm portion 61 is located in the first direction X1 relative to the end surface 21b of the protrusion 21. As shown in FIG. Therefore, when the screw shaft 3 is at the origin, the projection 21 can come into contact with the second arm 62 in the circumferential direction. It's becoming

Further, as shown in FIG. 2, the second arm portion 62 has a first side surface 62b facing the first rotation direction L1. The first side surface 62b of the second arm portion 62 is in contact with the side surface 21a of the nut projection 21 of the nut 2 when the screw shaft 3 is at the origin. That is, the second arm portion 62 contacts the nut projection 21 from the second rotation direction L2. Therefore, the screw shaft 3 is restricted from moving further in the second direction X2 than the origin (the nut 2 is prevented from rotating in the second rotation direction L2) due to the hydraulic pressure of the brake fluid.

As shown in FIG. 3, the inner peripheral surface 64 of the connecting portion 60 has a circular shape when viewed from the axial direction. The top surface 35 of the screw shaft projection 34 faces the inner peripheral surface 64 of the connecting portion 60 . Here, the outer diameter (distance from the axis O to the top surface 35 ) r34 of the screw shaft projection 34 is slightly smaller than the inner diameter r64 of the inner peripheral surface 64 of the connecting portion 60 . Therefore, a minute gap (not shown) is provided between the inner peripheral surface 64 of the connecting portion 60 and the top surface 35 of the screw shaft projection 34 .

An inner peripheral surface 64 of the connecting portion 60 is provided with a connecting portion protrusion 65 that protrudes radially inward. Two connection projections 65 are provided at intervals of 180°. The connecting portion projection 65 has a substantially trapezoidal shape when viewed from the axial direction. Thus, the connection projection 65 has a top surface 66 facing radially inward, a first side surface 67 facing in the first rotation direction L1, and a second side surface 68 facing in the second rotation direction L2.

A top surface 66 of the connecting portion projection 65 faces the outer peripheral surface 33 of the connected portion 31 . An inner diameter (distance from the axis O to the top surface 66 ) r65 of the connecting portion projection 65 is slightly larger than an outer diameter r33 of the outer peripheral surface 33 of the connected portion 31 . Therefore, a minute gap (not shown) is provided between the outer peripheral surface 33 of the connecting portion 31 and the top surface 66 of the connecting portion projection 65 . As described above, the screw shaft 3 and the anti-rotation 6 are relatively rotatable.

As shown in FIG. 3 , the second side surface 68 of the coupling projection 65 is in contact with the first side surface 36 of the screw shaft projection 34 . That is, the connecting portion projection 65 abuts against the screw shaft projection 34 in the first rotation direction L1. Therefore, the screw shaft projection 34 (screw shaft 3) is supported by the connecting portion projection 65 from the first rotation direction L1.

On the other hand, the first side surface 67 of the coupling projection 65 is separated from the second side surface 37 of the screw shaft projection 34 . That is, it is between the first side surface 67 of the connecting portion projection 65 and the second side surface 37 of the screw shaft projection 34, and between the inner peripheral surface 64 of the connecting portion 60 and the outer peripheral surface of the connected portion 31. is provided with an accommodation space Q. Moreover, the length of the housing space Q in the circumferential direction is M. As shown in FIG. In addition, the circumferential length M of the housing space Q is greater than the circumferential widths of the screw shaft projection 34 and the connecting portion projection 65 .

The elastic body 5 is made of an elastically deformable material such as rubber or resin. Two elastic bodies 5 are provided. In other words, the screw shaft projections 34 and the connecting portion projections 65 have the same number of elastic bodies 5 . The elastic body 5 has an arc shape when viewed from the axial direction. The elastic body 5 is arranged in the housing space Q. As shown in FIG. The inner peripheral surface 50 of the elastic body 5 is in contact with the outer peripheral surface 33 of the connected portion 31 . The length of the elastic body 5 in the circumferential direction is the same as the length M of the housing space Q in the circumferential direction. In other words, the elastic body 5 is longer than the circumferential width of the screw shaft projection 34 and the connecting portion projection 65 . One end 51 of the elastic body 5 in the first rotation direction L1 is in contact with the second side surface 37 of the screw shaft projection 34 . The other end 52 of the elastic body 5 in the second rotation direction L2 is in contact with the first side surface 67 of the connecting projection 65 . As described above, the screw shaft projection 34 (screw shaft 3) is supported by the connecting portion projection 65 (anti-rotation 6) via the elastic body 5 from the second rotation direction L2.

Moreover, the circumferential length of the elastic body 5 before being attached to the ball screw device 1 is longer than the circumferential length M of the housing space Q. As shown in FIG. That is, the elastic body 5 is arranged in the accommodation space Q in a state of being compressed in the circumferential direction. Therefore, the elastic body 5 exerts an elastic deformation force that separates the screw shaft projection 34 and the connecting portion projection 65 that are in contact with each other in the circumferential direction. As a result, the elastic body 5 has a high frictional force with the screw shaft projection 34 and the connecting portion projection 65 that are in contact with each other. Therefore, it is difficult for the elastic body 5 to move in the axial direction and fall out of the accommodation space Q. The second direction X2 of the housing space Q is blocked by the step surface 38. As shown in FIG. Therefore, the elastic body 5 does not move from the housing space Q in the second direction X2.

Due to the elastic deformation force of the elastic body 5, the frictional force between the first side surface 36 of the screw shaft projection 34 and the second side surface 68 of the connecting portion projection 65 is extremely high. In addition, as described above, the elastic body 5 has a high frictional force with the screw shaft projection 34 and the connecting portion projection 65 that come into contact therewith. That is, the screw shaft projection 34 and the connecting portion projection 65 are relatively difficult to move in the axial direction. Thereby, the anti-rotation 6 and the screw shaft 3 are axially inseparably connected.

In addition, in the present disclosure, the connection between the anti-rotation 6 and the screw shaft 3 is not limited to the above example. For example, the outer diameter r34 of the screw shaft projection 34 is slightly larger than the inner diameter r64 of the inner peripheral surface 64 of the connecting portion 60, and the screw shaft projection 34 has an interference on the inner peripheral surface 64 of the connecting portion 60. You may do so. According to this, the connected portion 31 is press-fitted (lightly press-fitted) into the interior of the connecting portion 60, and the anti-rotation 6 and the screw shaft 3 are connected. Alternatively, the inner diameter r65 of the connecting portion projection 65 is made slightly smaller than the outer diameter r33 of the outer peripheral surface 33 of the connected portion 31 so that the connecting portion projection 65 has an interference with the outer peripheral surface 33 of the connected portion 31. You may have Furthermore, both the screw shaft projection 34 and the connecting portion projection 65 may have interference. However, in order to enable relative rotation between the anti-rotation 6 and the screw shaft 3, it is necessary to set the interference of the screw shaft projection 34 or the connecting portion projection 65 to be very small.

A radial thickness N of the elastic body 5 is smaller than a radial width P of the accommodation space Q. As shown in FIG. Therefore, an arcuate gap S is formed between the outer peripheral surface 54 of the elastic body 5 and the inner peripheral surface 64 of the connecting portion 60 .

Next, an operation example of the brake booster 100 of Embodiment 1 will be described. In the brake booster 100, the hydraulic pressure of the brake fluid (the load in the second direction X2) always acts on the screw shaft 3 via the piston 110. As shown in FIG. The load acting on the screw shaft 3 in the second direction X2 receives a reaction force from the balls 4 contacting the outer circumferential raceway surface 3a, and is converted into torque in the first rotation direction L1. As a result, torque in the first rotation direction L<b>1 acts on the screw shaft 3 from the balls 4 . As described above, the torque in the first rotation direction L1 acts on the screw shaft 3 regardless of its position in the axial direction.

On the other hand, the screw shaft 3 is supported by the anti-rotation 6 so as not to rotate in the first rotation direction L1. Therefore, the screw shaft 3 is prevented from rotating by the hydraulic pressure of the brake fluid. Note that when the screw shaft 3 moves in the first direction X1, the hydraulic pressure of the brake fluid increases, and the torque in the first rotation direction L1 received from the balls 4 also increases. On the other hand, when the screw shaft 3 moves in the second direction X2, the hydraulic pressure of the brake fluid decreases and the torque in the first rotation direction L1 received from the balls 4 also decreases.

Further, when the brake pedal (not shown) is not stepped on, the motor 101 is not driven. Therefore, as shown in FIG. 1, the screw shaft 3 is positioned at the origin. The nut projection 21 of the nut 2 abuts on the second arm portion 62 of the antirotation 6 (see FIG. 2).

When a brake pedal (not shown) is stepped on, the motor 101 is driven. Rotational motion generated by the motor 101 is reduced by the reduction gear 102 and transmitted to the nut 2 . The nut 2 rotates in the first rotation direction L1. The screw shaft 3 is supported by the anti-rotation 6 so as not to rotate in the first rotation direction L1. Therefore, the screw shaft 3 moves in the first direction X<b>1 without rotating together with the nut 2 . Piston 110 then pushes the brake fluid. This increases hydraulic pressure and activates the brake system.

When the stepped state of the brake pedal (not shown) is released, the rotor (not shown) of the motor 101 rotates in the reverse direction, and the nut 2 rotates in the second rotation direction L2. On the other hand, the screw shaft 3 receives torque in the first rotation direction L1 from the balls 4 due to the hydraulic pressure of the brake fluid. Therefore, only torque in the first rotation direction L<b>1 acts on the screw shaft 3 . Further, the screw shaft 3 is supported by the anti-rotation 6 so as not to rotate in the first rotation direction L1. Therefore, the screw shaft 3 moves in the second direction X2 without rotating together with the nut 2 .

Then, when the screw shaft 3 returns to the origin, the driving of the motor 101 is stopped. Whether or not the screw shaft 3 has returned to the origin is detected by a rotation sensor (not shown). Also, the nut protrusion 21 of the nut 2 contacts the second arm portion 62 of the antirotation 6, and the screw shaft 3 is positioned at the origin.

Further, when the power supply to the motor 101 fails while the screw shaft 3 is moving from the origin in the first direction X1, the stator (not shown) of the motor 101 does not generate a rotating magnetic field and the rotor (not shown) does not generate a rotating magnetic field. shown) becomes idle. Since the load acting on the screw shaft 3 is only the hydraulic pressure of the brake fluid, the screw shaft 3 moves in the second direction X2. Accordingly, the nut 2 rotates in the second rotation direction L2, and the reduction gear 102 and the rotor (not shown) also rotate.

When the screw shaft 3 returns to the origin, the nut projection 21 of the nut 2 contacts the second arm portion 62 of the antirotation 6 . As a result, the nut 2 temporarily stops rotating in the second rotation direction L2. Also, the rotational motion of the reduction gear 102 is stopped. On the other hand, the rotor (not shown) continues to rotate due to inertia. As a result, the shutdown torque in the second rotation direction L2 acts on the nut 2 immediately after the screw shaft 3 returns to the origin. Also, the torque associated with the shutdown torque is transmitted from the nut 2 to the screw shaft 3 .

As shown in FIG. 6 , the screw shaft projection 34 of the screw shaft 3 moves in the second rotation direction L2 and presses the elastic body 5 . Thereby, the elastic body 5 is deformed so as to be compressed in the circumferential direction. Therefore, the torque (load) acting on the connecting projection 65 from the screw shaft projection 34 is absorbed by the elastic body 5 . In addition, since the elastic body 5 is long in the circumferential direction, the torque (load) acting on the connecting projection 65 from the screw shaft projection 34 is greatly reduced.

Moreover, there is a gap S on the outer peripheral side of the elastic body 5, and a space is provided in which the elastic body 5 can be deformed. Therefore, the elastic body 5 pressed by the screw shaft projection 34 deforms so as to increase in thickness. That is, the thickness N1 of the elastic body 5 after deformation is greater than the thickness N (see FIG. 4) before being pressed by the screw shaft projection 34 . Note that if the gap S is not provided, the elastic body 5 may be deformed so as to protrude from the housing space Q in the axial direction. in short. The elastic body 5 may press the step surface 38 to move in the first direction X<b>1 and fall out of the accommodation space Q. Therefore, in Embodiment 1, the possibility that the elastic body 5 will drop out of the housing space Q is low.

After the torque acting on the screw shaft 3 disappears, the elastic body 5 presses the screw shaft protrusion 34 in the first rotation direction L1. As a result, the screw shaft projection 34 rotates in the first rotation direction L<b>1 and comes into contact with the connecting portion projection 65 .

As described above, even if the screw shaft 3 is subjected to torque associated with the shutdown torque, the connection projection 65 (anti-rotation 6) is less likely to be damaged. Further, the screw shaft projection 34 receives the elastic deformation force of the elastic body 5 and is pressed in the first rotation direction L1. Therefore, the contact with the connection projection 65 is maintained. Therefore, contact noise between the screw shaft projection 34 and the connecting portion projection 65 is less likely to occur.

As described above, the ball screw device 1 of Embodiment 1 includes the housing 120, the nut 2, the screw shaft 3, the plurality of balls 4, the elastic body 5, and the connecting member. Nut 2 is rotatably supported by housing 120 . The screw shaft 3 has a connected portion 31 at a portion in the longitudinal direction and passes through the nut 2 . A plurality of balls 4 are arranged between the nut 2 and the screw shaft 3 . The elastic body 5 is arranged on the outer peripheral side of the connected portion 31 and extends in the circumferential direction. The connecting member has an annular connecting portion 60 fitted to the outer peripheral side of the elastic body 5 . When the nut 2 rotates in the first rotation direction L1, the screw shaft 3 moves in the first direction X1, and the amount of protrusion of the screw shaft 3 from the nut 2 increases. When the nut 2 rotates in the second rotation direction L2 opposite to the first rotation direction L1, the screw shaft 3 moves in the second direction X2 opposite to the first direction X1, thereby reducing the protrusion amount. An outer peripheral surface 33 of the connected portion 31 is provided with a screw shaft protrusion 34 that protrudes radially outward and contacts the elastic body 5 in the second rotation direction L2. An inner peripheral surface 64 of the connecting portion 60 is provided with a connecting portion protrusion 65 that protrudes radially inward and contacts the elastic body 5 in the first rotation direction L1. Further, the connecting member of the first embodiment is the anti-rotation 6 supported by the housing 120 so as to be movable in the axial direction parallel to the screw shaft 3 and unrotatable.

According to the ball screw device 1 of Embodiment 1 described above, when the torque associated with the shutdown torque acts on the screw shaft 3 , it is absorbed by the elastic body 5 . Therefore, the load acting on the connection projection 65 is small, and damage to the connection projection 65 (connection portion 60) is avoided.

Further, the screw shaft projection 34 of the ball screw device 1 of Embodiment 1 is in contact with the connecting portion projection 65 from the first rotation direction L1.

According to the configuration described above, the screw shaft 3 does not rotate in the first rotation direction L1. Therefore, the screw shaft 3 moves in the axial direction without rotating together with the nut 2 .

Further, the nut 2 of Embodiment 1 has a nut protrusion 21 that protrudes from the first end surface 20 facing the first direction X1. The connecting member (anti-rotation 6 ) has a projecting portion (second arm portion 62 ) projecting from the outer peripheral surface 63 of the connecting portion 60 . When the screw shaft 3 is positioned at the origin, the nut protrusion 21 contacts the protrusion (the second arm 62) in the second rotation direction L2.

According to the configuration described above, when the screw shaft 3 returns to the origin, the nut projection 21 abuts on the projecting portion (second arm portion 62) of the connecting member. Therefore, the initial position of the screw shaft 3 is positioned at the origin.

Further, a plurality of screw shaft projections 34, connecting portion projections 65, and elastic bodies 5 of Embodiment 1 are provided.

According to the above configuration, the torque acting on the connecting member (anti-rotation 6) from the screw shaft 3 is distributed to the plurality of screw shaft protrusions 34 and the connecting portion protrusions 65. As shown in FIG. Therefore, the screw shaft projection 34 and the connecting portion projection 65 are less likely to be damaged.

The elastic body 5 of Embodiment 1 is arranged between the screw shaft projection 34 and the connecting portion projection 65 in a circumferentially compressed state.

According to the configuration described above, the elastic body 5 is press-fitted between the screw shaft projection 34 and the connecting portion projection 65 . Therefore, the elastic body 5 is less likely to be displaced in the axial direction from between the screw shaft projection 34 and the connecting portion projection 65 . Further, since the screw shaft projection 34 is pressed by the elastic body 5, it is difficult to move in the second rotation direction L2. Therefore, contact noise between the screw shaft projection 34 and the connecting portion projection 65 is less likely to occur.

At least a portion of the elastic body 5 in the first embodiment in the circumferential direction has a radial thickness N smaller than the width P from the inner peripheral surface 64 of the connecting portion 60 to the outer peripheral surface 33 of the connected portion 31 .

According to the ball screw device 1 of Embodiment 1, the elastic body 5 is deformed so as to enter the gap S, so the possibility of the elastic body 5 axially protruding from between the connecting portion 60 and the connected portion 31 is low. .

Although the first embodiment has been described above, the present disclosure is not limited to the first embodiment. Next, Modified Example 1 in which the shape of the elastic body 5 is modified will be described.

(Modification 1)
7 is a cross-sectional view of an elastic body in a ball screw device of Modification 1. FIG. As shown in FIG. 7, the ball screw device 1A of Modification 1 is different from the ball screw device 1 of Embodiment 1 in that instead of the elastic body 5, an elastic body 5A is provided. The following description focuses on the differences.

The elastic body 5A has an arc shape. 5 A of elastic bodies are arrange|positioned in the accommodation space Q in the state compressed in the circumferential direction like the elastic body 5 of Embodiment 1. As shown in FIG. Moreover, the radial thickness of the elastic body 5A is larger than the radial width P of the accommodation space Q before being attached to the ball screw device 1 . Therefore, the elastic body 5A is arranged in the housing space Q while being compressed not only in the circumferential direction but also in the radial direction.

As described above, according to the ball screw device 1</b>A of Modification 1, the inner peripheral surface 50 of the elastic body 5</b>A is in contact with the outer peripheral surface 33 of the connected portion 31 . Further, the outer peripheral surface 54 of the elastic body 5A is in contact with the inner peripheral surface 64 of the connecting portion 60 . Further, the elastic body 5A exerts an elastic deformation force such that the outer peripheral surface 33 of the connected portion 31 and the inner peripheral surface 64 of the connecting portion 60 are separated from each other in the radial direction. Therefore, the elastic body 5</b>A has a high frictional force with respect to the outer peripheral surface 33 of the connected portion 31 and the inner peripheral surface 64 of the connecting portion 60 . Therefore, the elastic body 5A of the modified example 1 is more difficult to move in the axial direction than the elastic body 5 of the first embodiment. As a result, the elastic body 5A is prevented from falling out of the accommodation space Q.

The elastic body 5A of Modification 1 is radially sandwiched between the outer peripheral surface 33 of the connected portion 31 and the inner peripheral surface 64 of the connecting portion 60, and is difficult to move (hardly deform) in the circumferential direction. In other words, when the screw shaft projection 34 rotates in the second rotation direction L2 and presses the one end portion 51 of the elastic body 5A, only the one end portion 51 of the elastic body 5A is elastically deformed, and the remaining portion is not elastically deformed. There is a risk. Therefore, the torque absorbed by the elastic body 5A may be lower than that of the elastic body 5 of the first embodiment. Therefore, in the present disclosure, the elastic body 5 of Embodiment 1, in which the gap S is provided on the outer peripheral side, can absorb the torque received from the screw shaft projection 34 in the entire circumferential direction. This is a more preferred form than 5A.

Although Embodiment 1 and Modification 1 have been described above, the elastic body of the present disclosure is not limited to the elastic bodies 5 and 5A of Embodiment 1 and Modification. For example, in the ball screw device 1 of Embodiment 1, the gap S is provided on the outer peripheral side of the elastic body 5 , but in the present disclosure, the gap S may be provided on the inner peripheral side of the elastic body 5 . Moreover, the radial thickness of the elastic body 5 may be the same as the radial width P of the accommodation space Q before being attached to the ball screw device 1 . That is, the elastic body 5 may be arranged in the accommodation space Q without being compressed in the radial direction. Since such an elastic body is not radially sandwiched between the outer peripheral surface 33 of the connected portion 31 and the inner peripheral surface 64 of the connecting portion 60, the entire elastic body 5 is deformed in the circumferential direction. Also, the length of the elastic body 5 in the circumferential direction may be the same as the length M of the accommodation space Q in the circumferential direction. Moreover, the cross-sectional shape of the elastic body 5 is not limited to an arc shape. For example, the elastic body 5 may have a wavy cross-sectional shape. Such a corrugated shape is easily deformed when receiving torque from the screw shaft projection 34 .

Moreover, although the elastic bodies 5 and 5A of Embodiment 1 and Modification 1 are fixed between the screw shaft 3 and the anti-rotation 6 by press fitting, the ball screw device of the present disclosure is not limited to this. Ball screw devices 1B and 1C of Embodiments 2 and 3 according to other fixing methods will be described below.

(Embodiment 2)
FIG. 8 is a side view of the ball screw device of Embodiment 2 as viewed from the first direction. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. FIG. As shown in FIGS. 8 and 9, a ball screw device 1B of the second embodiment differs from the ball screw device 1 of the first embodiment in that it includes a cover member 70 and a clip 71. FIG.

As shown in FIG. 9, the cover member 70 is a component that closes the accommodation space Q from the first direction X1. The accommodation space Q in the second direction X2 is blocked by the step surface 38, as in the first embodiment. A through hole 72 is provided in the central portion of the cover member 70 . The pressing portion 32 of the screw shaft is inserted into the through hole 72 . The outer diameter of the cover member 70 is larger than the inner peripheral surface 64 of the connecting portion 60 . Therefore, it is in contact with the end face 60b of the connecting portion 60 in the first direction.

The clip 71 is a retaining ring having a C shape when viewed from the axial direction. As shown in FIG. 9, the clip 71 is fitted into a groove 32a provided on the outer peripheral surface of the pressing portion 32. As shown in FIG. As a result, the clip 71 contacts the cover member 70 in the first direction X1, and the cover member 70 is restricted from moving in the first direction.

As described above, according to the ball screw device 1B of the second embodiment, the housing space Q is closed by the cover member 70 . Therefore, the elastic body 5 is regulated so as not to drop out of the accommodation space Q. As shown in FIG. As a result, the elastic body 5 does not need to be press-fitted into the accommodation space Q, and the flexibility of the shape of the elastic body 5 is increased. Furthermore, since the cover member 70 abuts against the anti-rotation 6 in the first direction X1, it is not displaced in the first direction X1.

(Embodiment 3)
10 is a side view of the ball screw device of Embodiment 3 as viewed from the first direction. FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. 10. FIG. As shown in FIGS. 10 and 11, the ball screw device 1C of the third embodiment differs from the ball screw device 1B of the second embodiment in that a nut 74 is provided instead of the clip 71. FIG.

As shown in FIG. 11, a screw groove 32b is provided on the outer peripheral surface of the pressing portion 32 of the screw shaft 3. As shown in FIG. Therefore, the pressing portion 32 is a male thread portion. The nut 74 is screwed into the thread groove 32b and tightens the cover member 70 in the second direction X2. As a result, the housing space Q is closed without the cover member 70 moving in the first direction X1. Therefore, the elastic body 5 does not drop out of the accommodation space Q. Also, the anti-rotation 6 is not displaced in the first direction X1.

Although the second and third embodiments have been described above, the second and third embodiments are examples, and the present disclosure restricts the elastic body 5 from coming off in the first direction X1 by another fixing method. good too. In the first embodiment, the screw shaft protrusion 34 and the connecting portion protrusion 65 have a small interference so that the anti-rotation 6 is not displaced in the first direction X1 with respect to the screw shaft 3. When the cover member 70 restricts the positional deviation of the anti-rotation 6 in the first direction X1 as shown in the second and third embodiments, the screw shaft projection 34 and the connecting portion projection 65 have interference. It doesn't have to be. That is, in the present disclosure, the outer diameter r34 of the screw shaft projection 34 may be the same as the inner diameter r63 of the connecting portion 60 (see FIG. 3). Similarly, the inner diameter r65 of the connecting portion projection 65 may be the same as the outer diameter r33 of the connected portion 31 (see FIG. 3). Further, according to such a modification, the sliding resistance of the screw shaft projection 34 and the connecting portion projection 65 is reduced. Therefore, when the torque associated with the shutdown torque acts on the screw shaft 3, the screw shaft 3 rotates smoothly and the amount of deformation of the elastic body 5 increases. That is, the load absorbed by the elastic body 5 is increased, and the connecting projection 65 is less likely to break.

Further, in the above-described embodiment and modification, an example in which the connection member is applied to the anti-rotation 6 has been described, but in the present disclosure, the connection member may be applied to a stopper. Hereinafter, in Embodiment 4, an example applied to a stopper will be described.

(Embodiment 4)
12 is a side view of the ball screw device of Embodiment 4 as viewed from the first direction. FIG. As shown in FIG. 12, the ball screw device 1C of the fourth embodiment differs from the ball screw device 1 of the first embodiment in that a stopper 8 is provided in place of the anti-rotation 6. As shown in FIG. Although not shown, the screw shaft 3 is non-rotatably and axially movably supported by the housing 120 by other parts.

The stopper 8 includes a connecting portion 80 to which the elastic body 5 is fitted from the outer peripheral side, and a restricting portion 81 protruding radially outward from the connecting portion 80 . The connecting portion 80 has the same shape as the connecting portion 60 of the anti-rotation 6 of the first embodiment. That is, the connecting portion 80 has two connecting portion projections 83 protruding radially inward from the inner peripheral surface 82 . A top surface 84 of the connecting portion projection 83 is in contact with the outer peripheral surface 33 of the connected portion 31 . A first side surface 85 of the coupling projection 83 facing in the first rotation direction L<b>1 abuts the other end 52 of the elastic body 5 . A second side surface 86 of the coupling projection 83 facing the second rotation direction L2 abuts the first side surface 36 of the screw shaft projection 34 .

According to the ball screw device 1D of Embodiment 4, when the screw shaft 3 returns to the origin, the nut protrusion 21 of the nut 2 contacts the restricting portion 81 of the stopper 8 from the second rotation direction L2. Therefore, the stopper 8 receives torque in the second rotation direction L2. However, the coupling projection 83 of the stopper 8 contacts the screw shaft projection 34, and the stopper 8 does not rotate in the second rotation direction L2.

Further, immediately after the screw shaft 3 returns to the origin, a shutdown torque is input to the nut 2, and a torque acts on the screw shaft 3 in the second rotation direction L2. Then, the screw shaft projection 34 rotates in the second rotation direction L2. One end 51 of the elastic body 5 is pressed against the screw shaft projection 34 and deformed so as to be compressed in the circumferential direction. As a result, the load acting on the connection projection 83 from the screw shaft projection 34 is reduced, and damage to the connection projection 83 is avoided.

Each of the embodiments and modifications has been described above. There may be one, or three or more, and there is no particular limitation in the present disclosure. Also, the present disclosure may include both anti-rotation 6 and stopper 8 . When the anti-rotation 6 and the stopper 8 are provided, the configurations shown in the embodiments and modified examples are applied to each in order to avoid damage to the connecting portion (projection for connecting portion) between the anti-rotation 6 and the stopper 8. good too.

1, 1A, 1B, 1C, 1D ball screw device 2 nut 3 screw shaft 4 ball 5, 5A elastic body 6 anti-rotation (connecting member)
8 stopper (connecting member)
21 nut projection 30 screw shaft body 31 connected portion 34 screw shaft projection 60 connecting portion 61 first arm 62 second arm (protruding portion)
65 Connecting part projection 70 Cover member 71 Clip 74 Nut 81 Regulating part (protruding part)
83 Projection for connecting part 100 Brake booster 101 Motor 102 Reduction gear 110 Piston 120 Housing 121 Cylinder

Claims (9)

a housing;
a nut rotatably supported by the housing;
a screw shaft having a connected portion in a part of the longitudinal direction and penetrating the nut;
a plurality of balls arranged between the nut and the screw shaft;
an elastic body arranged on the outer peripheral side of the connected portion and extending in the circumferential direction;
a connecting member having an annular connecting portion fitted to the outer peripheral side of the elastic body;
with
When the nut rotates in the first rotation direction, the screw shaft moves in the first direction, and the amount of protrusion of the screw shaft from the nut increases,
When the nut rotates in a second direction opposite to the first direction, the screw shaft moves in a second direction opposite to the first direction, thereby reducing the amount of protrusion,
The outer peripheral surface of the connected portion is provided with a projection for a screw shaft that protrudes radially outward and abuts against the elastic body from the second rotation direction,
A ball screw device, wherein a protrusion for a connecting portion is provided on an inner peripheral surface of the connecting portion, protruding radially inward and coming into contact with the elastic body from the first rotation direction. The ball screw device according to claim 1, wherein the screw shaft projection abuts on the connecting portion projection from the first rotation direction. The nut has a nut protrusion protruding from a first end face facing the first direction,
The connecting member has a protruding portion that protrudes from the outer peripheral surface of the connecting portion,
3. The ball screw device according to claim 1, wherein when the screw shaft is positioned at the origin, the nut projection abuts against the projection from the second rotation direction. 4. The ball screw device according to any one of claims 1 to 3, wherein a plurality of said connecting portion projections, said screw shaft projections and said elastic bodies are provided. The ball screw device according to any one of claims 1 to 4, wherein the elastic body is arranged between the screw shaft projection and the connecting portion projection in a state of being compressed in the circumferential direction. . 6. The radial thickness of at least a part of the elastic body in the circumferential direction is smaller than the width from the inner peripheral surface of the connecting portion to the outer peripheral surface of the connected portion. The ball screw device according to . The ball screw device according to any one of claims 1 to 6, wherein the connecting member is an anti-rotation member that is non-rotatably supported by the housing while being movable in an axial direction parallel to the screw shaft. The ball screw device according to any one of claims 1 to 6, wherein the connecting member is a stopper separated from the housing and not supported by the housing. The ball screw device according to any one of claims 1 to 8, further comprising a piston connected to the end of the screw shaft in the first direction.

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