阅读说明：本技术 滚珠丝杠装置 (Ball screw device ) 是由 新本元东 于 2021-03-19 设计创作，主要内容包括：本发明涉及一种滚珠丝杠装置(17),包括：螺杆(18),该螺杆(18)具有外周上的第一螺旋沟(29)；螺母(19),该螺母(19)具有内周上的第二螺旋沟(30)；多个滚珠(20)；止动件(26),该止动件(26)设置在第二螺旋沟(30)的端部处；以及弹簧体(31),该弹簧体(31)置于最靠近止动件(26)的端部滚珠(20a)与止动件(26)之间。弹簧体(31)由沿着第一螺旋沟(29)和第二螺旋沟(30)排列的多个卷簧(32)构成。相邻的卷簧(32)每个都具有弹簧端部(34),该弹簧端部(34)的刚性大于弹簧中间部(33)的刚性。(The present invention relates to a ball screw device (17) including: a screw (18), the screw (18) having a first spiral groove (29) on the outer periphery; a nut (19), the nut (19) having a second spiral groove (30) on the inner periphery; a plurality of balls (20); a stopper (26), the stopper (26) being provided at an end of the second spiral groove (30); and a spring body (31), the spring body (31) being interposed between the end ball (20a) closest to the stopper (26) and the stopper (26). The spring body (31) is constituted by a plurality of coil springs (32) arranged along the first spiral groove (29) and the second spiral groove (30). Adjacent coil springs (32) each have a spring end portion (34), the spring end portion (34) being stiffer than the spring intermediate portion (33).)

1. A ball screw device (17), characterized by comprising:

a screw (18) having a first helical groove (29) on an outer periphery;

a nut (19) that is provided on an outer peripheral side of the screw (18) and has a second spiral groove (30) on an inner periphery;

a plurality of balls (20) disposed between the first helical groove (29) and the second helical groove (30);

a stopper (26) provided at an end of the second spiral groove (30); and

a spring body (31) interposed between an end ball (20a) of the plurality of balls (20) closest to the stopper (26) and the stopper (26), wherein

The spring body (31) is constituted by a plurality of coil springs (32) arranged along the first spiral groove (29) and the second spiral groove (30),

adjacent coil springs (32) are in contact with each other, and

the adjacent coil springs (32) each have a spring end portion (34) having a rigidity greater than that of a spring intermediate portion (33).

2. The ball screw device (17) according to claim 1, characterized in that since the pitch at the spring end portion (34) is narrower than the pitch at the spring intermediate portion (33), the spring end portion (34) is allowed to become compressed when the spring end portion (34) is compressed under a load at which the spring intermediate portion (33) exhibits elastic compression deformation.

3. The ball screw device (17) according to claim 1, wherein the spring end (34) is in a compressed state.

4. The ball screw device (17) according to claim 1, wherein the spring constant of the spring end portion (34) is high since the pitch at the spring end portion (34) is wider than the pitch at the spring intermediate portion (33).

5. The ball screw device (17) according to any one of claims 1 to 3, wherein the total dimension in the spring longitudinal direction of two of the adjacent spring ends (34) is smaller than the coil average diameter of the coil spring (32).

6. The ball screw device (17) according to any one of claims 1 to 4, wherein, of the coil springs (32) interposed between the end ball (20a) and the stopper (26), a spring constant of a coil spring (32c) at a side of the stopper (26) is smaller than a spring constant of a coil spring (32a) at a side of the end ball (20 a).

Technical Field

The present invention relates to a ball screw device.

Background

Japanese unexamined patent application publication No. 2016 (35289A) discloses a ball screw device suitable for a brake device of an automobile. The ball screw device includes: a screw having a spiral groove formed on an outer circumference; a nut having a spiral groove formed on an inner periphery; and a plurality of balls disposed between the helical groove of the screw and the helical groove of the nut. The nut is moved in the axial direction of the screw by rotation of the screw. The ball screw device disclosed in JP 2016-.

Disclosure of Invention

Fig. 9 is an explanatory diagram in which the screw groove of the screw and a part of the screw groove of the nut that the non-circulating type ball screw device has are viewed from the axial direction. A stopper (stopper ball) 92 is provided at an end of the spiral groove 90a of the nut 90. A coil spring 93 is provided between an end ball 99a closest to the stopper 92 among the plurality of balls 99 and the stopper 92.

When the nut 90 moves due to the rotation of the screw 94, the balls 99 move in the direction indicated by the arrow J along the spiral groove 94a of the screw 94 and the spiral groove 90a of the nut 90. Thus, the end ball 99a presses the coil spring 93, thereby compressing the coil spring 93. A portion 93a of the coil spring 93 at the side of the end ball 99a is easily compressed, and a portion 93b at the side of the stopper 92 is not easily compressed. This is because the force with which the end ball 99a presses the coil spring 93 is difficult to easily transmit further toward the stopper 92 side due to the frictional resistance between the coil spring 93 and the spiral grooves 90a and 94 a.

Thus, the coil spring 93 does not exhibit uniform compression deformation between the end ball 99a and the stopper 92 as a whole, and fatigue develops at a portion where the deformation is large (i.e., at the portion 93a on the end ball 99a side). As a result, the life of the coil spring 93 may be shortened as compared to when uniform compression deformation is exhibited as a whole. Further, by realizing the compression deformation of the coil spring 93 as a whole, the moving stroke of the nut 90 can be made large.

Thus, the present disclosure provides a ball screw device that can achieve compression deformation of a coil spring as a whole between an end ball and a stopper.

A ball screw device according to an aspect of the present disclosure includes: a screw having a first helical groove on an outer periphery; a nut provided on an outer peripheral side of the screw and having a second spiral groove on an inner periphery; a plurality of balls disposed between the first and second helical grooves; a stopper provided at an end of the second spiral groove; and a spring body interposed between an end ball of the plurality of balls that is closest to the stopper and the stopper. The spring body is comprised of a plurality of coil springs arranged along the first helical groove and the second helical groove.

According to the above ball screw device, the coil spring is divided into a plurality and arranged in a row between the end ball and the stopper. Thus, the coil springs can undergo compressive deformation between the end balls and the stoppers as a whole, for example, by changing the properties of each coil spring. As a result, the life of the coil spring can be extended.

In the ball screw device according to the above aspect, the adjacent coil springs are in contact with each other, and each of the adjacent coil springs has a spring end portion having a rigidity larger than that of the spring intermediate portion. When the coil spring is divided into a plurality, the spring ends come into contact with each other. When the outer shape of the spring end portion is the same as that of the spring intermediate portion, that is, when the rigidity of the spring end portion is low, there is a possibility that the centers of the spring end portions will be misaligned, for example, in a state in which the spring end portions are in contact with each other, resulting in unpredictable behavior. In such a case, the function of the ball screw device will deteriorate. However, according to the ball screw device of the present disclosure, the rigidity of the spring end portion is high. As a result, the orientation and behavior of the adjacent spring ends can be stabilized.

In the above aspect, since the pitch at the spring end portions is narrower than the pitch at the spring intermediate portion, when the spring end portions are compressed under a load at which the spring intermediate portion exhibits elastic compression deformation, the spring end portions can be allowed to become compressed. In such a case, when the coil spring is compressed, the spring intermediate portion exhibits elastic compression deformation, but the spring end portions are allowed to become compressed. By causing the coil spring to be compressed and become compressed at the spring coil portion, the rigidity of the spring end portion is higher than the rigidity of the spring intermediate portion.

Alternatively, in the aspect described above, the spring end may be in a compressed state. According to this configuration, the rigidity of the spring end portions is higher than the rigidity of the spring intermediate portion.

Alternatively, in the aspect described above, since the pitch at the spring end portions is wider than the pitch at the spring intermediate portion, the spring constant of the spring end portions may be high. In the coil spring, according to the above configuration, enlarging the pitch of the coil spring wire and reducing the number of coils increases the spring constant, and thus the rigidity of the spring end portion is higher than the rigidity of the spring intermediate portion. In addition, with this configuration, the spring end portion can also exhibit elastic compression deformation, and thus, the effective length of the spring body constituted by the coil spring interposed between the end ball and the stopper is longer. Thus, the movement stroke of the nut can be made even larger.

In addition, in the aspect described above, the total dimension in the spring longitudinal direction of two of the adjacent spring ends may be smaller than the coil average diameter of the coil spring. In arrangements in which spacer balls are interposed between the wrap springs, the diameter of the spacer balls is approximately the same as the average diameter of the coils of the wrap springs. Thus, according to the above configuration, the spring end is short, and the effective length of the coil spring can be made longer than when the spacer balls are employed.

When the nut moves in the axial direction of the screw due to the rotation of the screw, the balls also move along the first and second spiral grooves. The coil spring compressed by the movement of the end ball included in the balls is easily compressed at the end ball side, but is not easily compressed at the stopper side. Thus, in the above aspect, in the coil spring interposed between the end ball and the stopper, the spring constant of the coil spring at the stopper side may be smaller than the spring constant of the coil spring at the end ball side. According to the above configuration, it is easy to cause the coil spring at the stopper side to exhibit compressive deformation. Thus, the spring body constituted by the coil spring as a whole can be easily made to exhibit compressive deformation. As a result, the moving stroke of the nut can be increased.

According to the present disclosure, compression deformation of the coil spring as a whole can be achieved between the end ball and the stopper.

Drawings

Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like reference numerals denote like elements, and in which:

fig. 1 is a sectional view showing an example of a brake device provided with a ball screw device;

fig. 2 is an exploded perspective view of the ball screw device;

fig. 3 is a sectional view of the ball screw device;

fig. 4 is an explanatory view showing the first spiral groove and the second spiral groove in a developed state on a plane;

fig. 5 is an explanatory view in which the first spring body is viewed from the axial direction of the ball screw device;

fig. 6 is an explanatory view of spring ends (first arrangement) of adjacent coil springs;

fig. 7 is an explanatory view of spring ends (second arrangement) of adjacent coil springs;

fig. 8 is an explanatory view of spring ends (third arrangement) of adjacent coil springs; and

fig. 9 is an explanatory diagram in which a screw groove of a screw and a part of a nut (prior art) of a non-circulating type ball screw device are viewed from an axial direction.

Detailed Description

Fig. 1 is a sectional view showing an example of a brake device provided with a ball screw device. The ball screw device 17 shown in fig. 1 is used in the brake device 5 in a vehicle (automobile), for example. The brake device 5 applies a braking force from friction to a brake disc 6, and the brake disc 6 rotates integrally with a wheel of an automobile. The brake device 5 is provided with a ball screw device 17 to generate such braking force. The braking device 5 is in the unbraked state in fig. 1.

The brake device 5 is provided with a floating caliper 7 supported by a knuckle or the like, not shown, and a pair of brake pads 8 sandwiching the brake disc 6. The caliper 7 is provided with a first body 9 and a second body 10, the second body 10 being provided integrally with the first body 9.

One (right side in fig. 1) brake shoe 8 is attached to a housing 21 described below with which the ball screw device 17 has, via a first backup brake plate 12. The other (left side in fig. 1) brake shoe 8 is attached to the second body 10 via a second spare brake plate 13.

The first body 9 has a cylindrical shape (a cylindrical shape with a bottom) including a cylindrical body portion 14 and a bottom brake plate portion 15, and opens toward the brake disk 6 side. A ball screw device 17 is provided on the inside of the cylindrical body portion 14. The ball screw device 17 is provided with a screw 18, a nut 19 provided on the outer peripheral side of the screw 18, and a plurality of balls 20. The housing 21 is attached to the nut 19. The center line C of the screw 18 is the center line of the ball screw device 17. In the present disclosure, a direction parallel to the center line C will be referred to as an "axial direction".

A through hole 16 is formed in the bottom stopper plate portion 15 of the first body 9. A bearing 22 is attached to the through hole 16. The screw 18 is rotatably supported by a bearing 22. A key 24 is provided between the housing 21 and the cylindrical body portion 14. The housing 21 is arranged to be reciprocally movable in the axial direction with respect to the cylindrical body portion 14, but not rotatable in the circumferential direction about the center line C.

The nut 19 is integral with the housing 21. When the screw 18 rotates (rotates forward) in one direction about the center line C, the nut 19 and the housing 21 move along the screw 18 from one side (right side in fig. 1) in the axial direction toward the other side (left side in fig. 1) in the axial direction. In contrast, when the screw 18 is rotated (reversely rotated) in the other direction about the center line C, the nut 19 and the housing 21 are moved along the screw 18 from the other side in the axial direction toward the one side in the axial direction.

A motor (electric motor) 51 and a speed reducer 23 are provided outside the cylindrical body portion 14. Command signals from the control unit 52 are input to the motor 51, and the output shaft of the motor 51 performs forward rotation, reverse rotation, and stop based on these command signals. The speed reducer 23 is composed of, for example, a plurality of gears, and reduces the rotation of an output shaft from the motor 51 to rotate the screw 18. Thus, when the motor 51 rotates, the nut 19 and the housing 21 move in the axial direction. That is, the rotational motion of the screw 18 transmitted from the motor 51 via the speed reducer 23 is converted into the linear motion of the nut 19 and the housing 21 in the axial direction by the ball screw device 17. Thus, the brake pads 8 clamp the brake disc 6, thereby generating braking force.

Fig. 2 is an exploded perspective view of the ball screw device 17. Fig. 3 is a sectional view of the ball screw device 17. A first spiral groove 29 is formed on the outer periphery of the screw 18. The second spiral groove 30 is formed on the inner periphery of the nut 19. A ball row 25 of balls 20 is provided between the first helical groove 29 and the second helical groove 30.

Fig. 4 is an explanatory diagram showing the first spiral groove 29 and the second spiral groove 30 in a state of being developed on a plane. All the balls 20 (ball rows 25) are in a state of being accommodated at the inner peripheral side of the nut 19. The ball screw device 17 is further provided with stoppers 26 and 27, and the stoppers 26 and 27 are provided at respective ends of the second spiral groove 30. The stoppers 26 and 27 are provided on respective sides in the axial direction on the inner peripheral side (second spiral groove 30) of the nut 19. The first stopper 26 on one side is constituted by a wall portion at an end portion on one side of the second spiral groove 30. The wall is part of the nut 19. The second stopper 27 on the other side is constituted by a wall portion at the end portion on the other side of the second spiral groove 30. It should be noted that one or both of the first stopper 26 and the second stopper 27 may be constituted by, for example, balls provided to the nut 19 in an immovable manner, or by a pin member fixed to the nut 19.

Of the balls 20 included in the ball row 25, the ball 20 closest to the first stopper 26, i.e., the ball 20 at the rightmost side in fig. 4, will be referred to as "first end ball 20 a". A first spring body 31 composed of a coil spring is provided between the first end ball 20a and the first stopper 26. The first spring body 31 is in a compressed state.

Among the balls 20 included in the ball row 25, the ball 20 closest to the second stopper 27, i.e., the ball 20 at the leftmost side in fig. 4, will be referred to as "second end ball 20 b". A second spring body 37 composed of a coil spring is provided between the second end ball 20b and the second stopper 27. The second spring body 37 is in compression.

The ball screw device 17 having the above-described configuration is a non-circulating ball screw device in which, when the nut 19 is moved in the axial direction of the screw 18, the balls 20 roll while being retained in the second spiral groove 30. The nut 19 moves through a predetermined stroke from the state of the initial position. When the nut 19 is moved from the initial position, the moving direction of the ball row 25 is a direction toward the first stopper 26. That is, when the nut 19 is moved from the initial position, the moving direction of the ball row 25 is a direction in which the first spring body 31 is further compressed.

Fig. 5 is an explanatory diagram in which the first spring body 31 is viewed from the axial direction of the ball screw device 17. As described previously, the first spring body 31 is disposed between the first end ball 20a and the first stopper 26. The first spring body 31 includes a plurality of coil springs 32. The coil springs 32 are arranged in series along the first helical groove 29 and the second helical groove 30. Adjacent coil springs 32 are in direct contact with each other at their ends. In the present disclosure, three coil springs 32a, 32b, and 32c are included in the first spring body 31. It should be noted that the number of the coil springs 32 included in the first spring body 31 may be freely changed according to the model of the ball screw device 17 and the like.

The coil springs 32 each have a middle portion, and end portions on both sides of the middle portion. In the present disclosure, the intermediate portion is referred to as "spring intermediate portion 33", and the end portions are referred to as "spring end portions 34". The spring ends 34 of the adjacent coil springs 32 are in a state of contacting each other. With the present disclosure, the spring end 34a-2 of the first coil spring 32a and the one spring end 34b-1 of the second coil spring 32b are in a state of contact, and the other spring end 34b-2 of the second coil spring 32b and the spring end 34c-1 of the third coil spring 32c are in a state of contact.

In the first spring body 31, the properties (spring constants) of the coil springs 32a, 32b, and 32c are different from each other. The third coil spring 32c at the side of the first stopper 26 has a smaller spring constant than the second coil spring 32b, and the second coil spring 32b has a smaller spring constant than the first coil spring 32a at the side of the end ball 20 a. Note that the spring constant referred to here is a value at the spring intermediate portion 33. That is, in the first spring body 31, the spring constant of the spring intermediate portion 33 of the coil spring 32 at the first stopper 26 side is smaller than the spring constant of the spring intermediate portion 33 of the coil spring 32 at the end ball 20a side. It should be noted that the coil average diameter D (see fig. 6) is the same for each of the coil springs 32a, 32b, and 32 c. The wire (coil spring wire) of the coil springs 32a, 32b and 32c may be the same or may be different in diameter. The length of each coil spring 32a, 32b, and 32c may be the same or may be different.

The first coil spring 32a in direct contact with the end ball 20a will be described. One spring end 34a-1 of the first coil spring 32a contacts the end ball 20 a. The spring end portion 34a-1 has the same properties (the same rigidity) as the spring intermediate portion 33 a. The other spring end portion 34a-2 of the first coil spring 32a has a configuration in which its rigidity is higher than the spring intermediate portion 33a of the first coil spring 32 a. In the present disclosure, spring end 34a-2 is crimped, as shown in FIG. 6. That is, the spacing between the helical spring wires that make up the coil spring 32a is zero at the spring end 34 a-2. It should be noted that other configurations may be made to increase the rigidity, as will be described below. The boundary between the first coil spring 32a and the second coil spring 32b is indicated by a long-dashed line in fig. 6.

Description will be made with respect to the second coil spring 32b adjacent to the first coil spring 32 a. One spring end 34b-1 of the second coil spring 32b contacts the spring end 34a-2 of the first coil spring 32 a. The one spring end portion 34b-1 of the second coil spring 32b has a configuration in which the rigidity thereof is higher than that of the spring intermediate portion 33b of the second coil spring 32 b. In the present disclosure, spring end 34b-1 is crimped, as shown in FIG. 6. The other spring end 34b-2 (see fig. 5) of the second coil spring 32b contacts the spring end 34c-1 of the third coil spring 32 c. The other spring end portion 34b-2 of the second coil spring 32b has a configuration in which the rigidity thereof is higher than that of the spring intermediate portion 33b of the second coil spring 32 b. In the present disclosure, spring end 34b-2 is crimped.

Description will be made with respect to the third coil spring 32c that is brought into direct contact with the first stopper 26. One spring end 34c-1 of the third coil spring 32c contacts the spring end 34b-2 of the second coil spring 32 b. The one spring end portion 34c-1 of the third coil spring 32c has a configuration in which the rigidity thereof is higher than that of the spring intermediate portion 33c of the third coil spring 32 c. In the present disclosure, spring end 34c-1 is crimped. The other spring end 34c-2 of the third coil spring 32c contacts the first stopper 26. The spring end portion 34a-2 has the same properties (the same rigidity) as the spring intermediate portion 33 c.

As described above, the adjacent first and second coil springs 32a and 32b have spring end portions 34a-2 and 34b-1, respectively, which are stiffer than the spring intermediate portions 33a and 33 b. The adjacent second and third coil springs 32b and 32c have spring end portions 34b-2 and 34c-1, respectively, which are stiffer than the spring intermediate portions 33b and 33 c.

Construction for improving rigidity of spring end 34 (first arrangement)

As described above, the spring end portions 34 are in a compressed state so that the rigidity of the spring end portions 34 is higher than the rigidity of the spring intermediate portion 33. According to this configuration, the orientation and behavior of each of the adjacent spring ends 34 can be stabilized. Further, the wire of the adjacent coil spring 32 is not easily displaced into the spring end 34. For example, in FIG. 6, the wire of the spring end 34b-1 of the second wrap spring 32b that is in contact with the spring end 34a-2 of the first wrap spring 32a is not easily displaced into the spring end 34a-2 because the spring end 34a-2 is crimped. Likewise, in the same manner, the wire of the spring end 34a-2 of the first coil spring 32a that is in contact with the spring end 34b-1 of the second coil spring 32b is not easily displaced into the spring end 34b-1 because the spring end 34b-1 is crimped.

As described above, the coil average diameters D of the three coil springs 32 are the same. One spring end 34a-2 is in contact with the other spring end 34 b-1. The one spring end 34a-2 has a dimension L1 in the spring longitudinal direction, and the other spring end 34b-1 has a dimension L2 in the spring longitudinal direction. It should be noted that the spring longitudinal direction is a length in a direction along the center line of the coil spring 32. In the arrangement shown in fig. 6, the dimensions L1 and L2 are the dimensions of the pressed portion in the longitudinal direction of the spring, respectively. The sum (L1+ L2) of the dimension L1 of the one spring end 34a-2 in the spring longitudinal direction and the dimension L2 of the other spring end 34b-1 in the spring longitudinal direction is smaller than the coil average diameter D of the coil spring 32 in the present disclosure, i.e., (L1+ L2 < D).

In addition, the spring end 34b-2 of the second coil spring 32b and the spring end 34c-1 of the third coil spring 32c (see FIG. 5) have the same configuration. That is, the sum of the dimension of the one spring end 34b-2 in the spring longitudinal direction and the dimension of the other spring end 34c-1 in the spring longitudinal direction is smaller than the coil average diameter of the coil springs 32b and 32 c.

As described above (see FIG. 6), the overall dimension in the longitudinal direction of the spring (L1+ L2) of the two adjacent spring ends 34a-2, 34b-1 is smaller than the coil average diameter D of the coil springs 32a, 32b, i.e., (L1+ L2 < D).

In fig. 6, assuming that spacer balls 38 (indicated by the two-dot chain lines) are inserted between the first coil spring 32a and the second coil spring 32b, the diameter D of the spacer balls 38 will be substantially the same as the coil average diameter D of the coil springs 32a (32b) (D ═ D). Thus, according to the above-described configuration of L1+ L2 < D, the spring ends 34a-2 and 34b-1 are shorter in the spring longitudinal direction, enabling the effective length of the coil springs 32a, 32b to be longer than when the spacer balls 38 are employed. In addition, the spacer balls 38 are not required in the ball screw device 17 according to the present disclosure, and the number of parts of the ball screw device 17 can be reduced.

Construction for improving rigidity of spring end 34 (second arrangement)

In order to make the rigidity of the spring end portion 34 higher than that of the spring intermediate portion 33, the spring end portion 34 may be configured as follows. That is, by making the pitch at the spring end portion 34a-2 of the first coil spring 32a narrower than the pitch at the spring intermediate portion 33a in fig. 7 (P2 < P1 in fig. 7), it is allowed to become compressed when the spring end portion 34a-2 is compressed under a load at which the spring intermediate portion 33a exhibits elastic compression deformation. In the same manner, by making the pitch at the spring end portion 34b-1 of the second coil spring 32b narrower than the pitch at the spring intermediate portion 33b, it is allowed to become compressed when the spring end portion 34b-1 is compressed under a load at which the spring intermediate portion 33b exhibits elastic compression deformation.

According to the configuration shown in fig. 7, when the coil springs 32a and 32b are compressed, the spring intermediate portions 33a and 33b exhibit elastic compression deformation, but the spring end portions 34a-2 and 34b-1 are allowed to become compressed. By compressing the coil springs 32a and 32b and each of the spring end portions 34a-2 and 34b-1 becomes compressed, the rigidity of each of the spring end portions 34a-2 and 34b-1 becomes higher than the rigidity of the spring intermediate portions 33a and 33 b. Thus, the orientation and behavior of each of the adjacent spring ends 34a-2 and 34b-1 may be stabilized. In addition, in the same manner as in fig. 6, the wire of the coil spring 32b (32a) is not easily displaced into the spring end 34a-2(34b-1) because the spring end 34a-2(34b-1) becomes compressed.

The spring end 34b-2 and the spring end 34c-1 have the same configuration as that shown in fig. 7, wherein the spring end 34b-2 and the spring end 34c-1 form a contact portion in which the second coil spring 32b and the third coil spring 32c are in contact. Thus, the orientation and behavior of adjacent spring ends 34b-2 and 34c-1 may be stabilized.

When the two adjacent spring ends 34a-2 and 34b-1(34b-2 and 34c-1) become compressed, as in the arrangement of fig. 6, the overall dimension of these spring ends 34a-2 and 34b-1(34b-2 and 34c-1) in the longitudinal direction of the spring is also preferably smaller than the average coil diameter of the coil springs 32a and 32b in the arrangement of fig. 7.

Construction for improving rigidity of spring end 34 (third arrangement)

In order to make the rigidity of the spring end portions 34 higher than the rigidity of the spring intermediate portion 33, the spring end portions 34 have a high spring constant because the pitch of the spring end portions 34 is wider than the pitch of the spring intermediate portion 33. To describe this in detail, in the first coil spring 32a, the pitch at the spring end portion 34a-2 is wider than the pitch at the spring intermediate portion 33a, as shown in fig. 8 (in fig. 8, P2> P1). Needless to say, in the coil spring, widening the pitch of the coil spring wire (wire) and reducing the number of coils increases the spring constant. Thus, according to this configuration, the rigidity of the spring end portion 34a-2 is higher than the rigidity of the spring intermediate portion 33a in the first coil spring 32 a.

In the second coil spring 32b, the pitch at the spring end portion 34b-1 is wider than the pitch at the spring intermediate portion 33 b. According to this configuration, the rigidity of the spring end portion 34b-1 is higher than the rigidity of the spring intermediate portion 33b in the second coil spring 32 b.

In addition, according to this configuration (third arrangement), the spring end 34a-2 and the spring end 34b-1 can also exhibit elastic compression deformation. Thus, the effective length of the first spring body 31 is longer, and the moving stroke of the nut 19 can be made larger.

With respect to the ball screw device 17 according to the present disclosure

As described above, the ball screw device 17 (see fig. 5) according to the present disclosure is provided with: a screw 18; a nut 19; a ball 20, the ball 20 being disposed between a first spiral groove 29 of the screw 18 and a second spiral groove 30 of the nut 19; a first stopper 26, the first stopper 26 being provided at an end of the second spiral groove 30; and a first spring body 31, the first spring body 31 being disposed between the end ball 20a and the first stopper 26. The first spring body 31 is composed of coil springs 32(32a, 32b, 32c) arranged in a row along the first spiral groove 29 and the second spiral groove 30.

According to the ball screw device 17 having the above-described configuration, the coil spring 32(32a, 32b, 32c) is divided into a plurality and arranged in a row between the end ball 20a and the first stopper 26. Thus, the first spring body 31, i.e., the coil springs 32(32a, 32b, 32c), can undergo compression deformation between the end ball 20a and the first stopper 26 as a whole by changing the property (spring constant) of each coil spring 32(32a, 32b, 32 c). As a result, the life of the coil spring 32 can be extended against fatigue. Further, by setting the properties (spring constants) of the coil springs 32(32a, 32b, 32c) to exhibit compression deformation uniformly to the maximum extent as a whole, it is possible to further increase the movement stroke of the nut 19, which will be described later.

In addition, in the ball screw device 17 according to the present disclosure, the adjacent coil springs 32 contact each other at the spring end 34. The adjacent first and second coil springs 32a and 32b each have spring end portions 34a-2 and 34b-1, and the spring end portions 34a-2 and 34b-1 are stiffer than the spring intermediate portions 33a and 33 b. The adjacent second coil spring 32b and third coil spring 32c each have spring end portions 34b-2 and 34c-1, and the spring end portions 34b-2 and 34c-1 are stiffer than the spring intermediate portions 33b and 33 c.

As described above, when the coil spring 32(32a, 32b, 32c) is divided into a plurality, the spring ends 34 are brought into contact with each other. When the outer shape of the spring end portion 34 is the same as the outer shape of the spring intermediate portion 33, that is, when the rigidity of the spring end portion 34 is low, there is a possibility that the centers of the spring end portions 34 will be misaligned, for example, in a state in which the spring end portions 34 are in contact with each other, resulting in unpredictable behavior. In such a case, the function of the ball screw device 17 will deteriorate. However, according to the ball screw device 17 of the present disclosure, the rigidity of the spring end portion 34 is high. As a result, the orientation and behavior of the adjacent spring ends 34 can be stabilized.

In the ball screw device 17, the nut 19 moves in the axial direction of the screw 18 due to the rotation of the screw 18, and the balls 20 also move along the first and second spiral grooves 29 and 30. When the nut 19 moves through a predetermined stroke from the state of the initial position, the moving direction is the direction indicated by the arrow J in fig. 4 and 5. The movement of the end ball 20a included in the ball 20 compresses the coil springs 32a, 32b, and 32 c. The coil springs 32a, 32b, and 32c compressed in this way are easily compressed at the end ball 20a side, but are not easily compressed at the first stopper 26 side.

Thus, in the present disclosure, in the first spring body 31, as described above, the spring constant of the coil spring 32 (spring intermediate portion 33) on the side toward the first stopper 26 is set smaller than the spring constant of the coil spring 32 (spring intermediate portion 33) on the side toward the end ball 20 a. According to this configuration, it is easier to cause the coil spring 32 at the first stopper 26 side to exhibit compressive deformation than the coil spring 32 at the end ball 20a side. Thus, the first spring body 31 composed of the coil springs 32a, 32b, and 32c as a whole can be easily made to exhibit compression deformation uniformly to the maximum extent. As a result, the movement stroke of the nut 19 can be increased even further.

In addition, the rigidity of the spring end portion 34 contacting the adjacent coil spring 32 is higher than the rigidity of the spring intermediate portion 33, and thus, the spring is better seated at both the adjacent spring end portions 34. That is, the centers of the spring ends 34 are easily aligned, and the first spring body 31 can be made to behave like a single coil spring 32.

The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is not limited to the above-described embodiments, and includes all modifications made within a scope equivalent to the configuration set forth in the claims.