JP2019206221A - Electric power steering device - Google Patents

Abstract

To provide an electric power steering device capable of suppressing wear in a housing.SOLUTION: The electric power steering device includes: a housing; a ball screw having a nut arranged at the housing, a screw shaft penetrating through the nut and a rolling element arranged between the nut and the screw shaft; a bearing for supporting the nut so that the nut can rotate against the housing; and a cushioning member arranged between an end face of the bearing and the housing. The material of the housing includes light metal. The cushioning member includes an annular part of an annular shape and in contact with the housing and a plurality of claw parts arranged at regular intervals in the peripheral direction of the annular part and in contact with the bearing.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an electric power steering apparatus.

  2. Description of the Related Art A rack assist type electric power steering device in which power of an electric motor is transmitted to a rack is known. A ball screw is used in the rack assist type electric power steering apparatus. Conventionally, vibration generated around the ball screw has been a problem. For example, Patent Document 1 describes an example of an electric power steering device intended to suppress vibration. The electric power steering device of Patent Document 1 includes a support member disposed between a bearing that supports a nut and a housing. The support member includes a main body formed in an annular shape and a support protrusion protruding from the main body.

US Patent Application Publication No. 2018/0009464

  By the way, for the purpose of reducing the weight of the ball screw or improving the vibration absorption of the ball screw, a light metal may be used for the ball screw housing. However, in the electric power steering device of Patent Document 1, the housing may be worn by the support protrusion.

  The present disclosure has been made in view of the above-described problems, and an object thereof is to provide an electric power steering device that can suppress wear of a housing.

  In order to achieve the above object, an electric power steering apparatus according to an aspect of the present disclosure includes a housing, a nut disposed in the housing, a screw shaft that passes through the nut, and between the nut and the screw shaft. A ball screw including rolling elements disposed on the bearing, a bearing that supports the nut so that the nut can rotate with respect to the housing, and a buffer member disposed between an end surface of the bearing and the housing; The material of the housing includes a light metal, and the buffer member is annular and has an annular portion that contacts the housing, and a plurality of annular members that are arranged at intervals in the circumferential direction of the annular portion and that are in contact with the bearing A claw portion.

  Thereby, the vibration around the ball screw is suppressed by the deformation of the claw portion. As a result, vibration transmitted to the operator is reduced. Further, since the annular portion is in contact with the housing while the claw portion is in contact with the bearing, the force applied to the housing from the buffer member is easily dispersed. That is, the pressure applied to the housing by the buffer member is reduced. Therefore, the electric power steering apparatus can suppress the wear of the housing.

  As a desirable aspect of the electric power steering apparatus, at least a part of the annular portion is parallel to a surface of the housing that contacts the annular portion.

  Thereby, a contact area with the annular part of a housing tends to become large. The pressure applied to the housing by the buffer member becomes smaller. Therefore, the electric power steering device can further suppress the wear of the housing.

  As a desirable aspect of the electric power steering apparatus, the claw portion is disposed on the bearing side with respect to the bent portion, a root portion disposed between the bent portion and the annular portion, and the bent portion. An angle formed by the surface of the tip portion facing the bearing with respect to the end surface of the bearing is such that the surface of the root portion facing the bearing is with respect to the end surface of the bearing. It is smaller than the angle formed.

  Thereby, while being able to maintain the deformation | transformation capability of a nail | claw part, a contact area with the nail | claw part of a bearing tends to become large. The pressure applied to the bearing is reduced by the buffer member. Therefore, the electric power steering apparatus can suppress the wear of the bearing.

  As a desirable mode of the above-mentioned electric power steering device, the buffer member is deformed by being sandwiched between the bearing and the housing.

  Thereby, even when the bearing moves in the axial direction, the state where the claw portion is in contact with the bearing is maintained. That is, the state in which vibration is absorbed by the claw portion is maintained. Therefore, the electric power steering apparatus can further suppress vibration around the ball screw.

  As a desirable aspect of the electric power steering device, the housing includes a main body that covers the ball screw, and a plate that is disposed between the main body and the annular portion.

  Thus, the dimensions can be adjusted by the plate without improving the processing accuracy of the main body. For this reason, the dimension adjustment for positioning a bearing appropriately becomes easy. Therefore, the electric power steering apparatus can be easily assembled.

  As a desirable aspect of the electric power steering apparatus, the housing includes a displacement restricting portion that is disposed so as to face an end surface of the bearing and restricts the displacement of the claw portion in the axial direction of the screw shaft.

  Thereby, the excessive deformation | transformation of a nail | claw part is suppressed. Therefore, the electric power steering apparatus can suppress damage to the buffer member.

  As a desirable mode of the above electric power steering device, the plate includes a displacement restricting portion that is disposed so as to face an end face of the bearing and restricts the displacement of the claw portion in the axial direction of the screw shaft.

  Thereby, the excessive deformation | transformation of a nail | claw part is suppressed. Therefore, the electric power steering apparatus can suppress damage to the buffer member.

  As a desirable aspect of the electric power steering apparatus, the displacement restricting portion is disposed between the two claw portions.

  Thereby, a nail | claw part and a displacement control part do not overlap in a radial direction. For this reason, it becomes possible to enlarge a nail | claw part to radial direction. As a result, the claw portion is more easily deformed, so that the vibration absorbing ability of the buffer member is improved. Therefore, the electric power steering apparatus can further suppress vibration around the ball screw. Further, the claw portion and the displacement restricting portion do not overlap in the axial direction. For this reason, the length of the axial direction of the space which a buffer member and a displacement control part occupy becomes small. As a result, the housing can be downsized in the axial direction. Further, since the claw portion is not sandwiched between the displacement restricting portion and the bearing, unintended stress is hardly generated in the claw portion. Accordingly, since the plastic deformation and the like of the claw portion is suppressed, the vibration absorbing ability of the buffer member is easily maintained.

  As a desirable mode of the above-mentioned electric power steering device, the claw portion is disposed radially inside with respect to the annular portion.

  Thereby, since an annular part is arrange | positioned on the outer side of radial direction rather than a nail | claw part, it is easy to enlarge an annular part. For this reason, a contact area with the annular part of a housing becomes larger. Therefore, wear of the housing is further suppressed.

  According to the electric power steering device of the present disclosure, wear of the housing can be suppressed.

FIG. 1 is a schematic diagram of a steering apparatus according to the present embodiment. FIG. 2 is a front view of the periphery of the rack according to the present embodiment. FIG. 3 is a cross-sectional view around the ball screw of the present embodiment. FIG. 4 is an enlarged view of FIG. FIG. 5 is an enlarged view of FIG. 6 is a cross-sectional view of the periphery of the ball screw taken along a plane different from that in FIG. FIG. 7 is an enlarged view of FIG. FIG. 8 is a perspective view of the buffer member of the present embodiment. FIG. 9 is a perspective view of the buffer member and the displacement restricting portion of the present embodiment. FIG. 10 is a cross-sectional view around the bearing of the first modification. FIG. 11 is a cross-sectional view of the periphery of the bearing of the first modified example taken along a plane different from that in FIG. FIG. 12 is a cross-sectional view around the bearing of the second modification. FIG. 13 is a cross-sectional view of the periphery of the bearing of the second modified example taken along a plane different from FIG. FIG. 14 is a perspective view of a buffer member according to a third modification. FIG. 15 is a perspective view of a part of the buffer member of the fourth modified example. FIG. 16 is a perspective view of a part of the buffer member of the fifth modified example. FIG. 17 is a perspective view of a buffer member according to a sixth modification.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, constituent elements 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 in a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be appropriately combined.

(Embodiment)
FIG. 1 is a schematic diagram of a steering apparatus according to the present embodiment. FIG. 2 is a front view of the periphery of the rack according to the present embodiment. As shown in FIG. 1, the electric power steering apparatus 80 includes a steering wheel 81, a steering shaft 82, a universal joint 84, a lower shaft 85, a universal joint 86, a pinion shaft 87, a pinion 88a, and a rack 88b. And comprising.

  As shown in FIG. 1, the steering wheel 81 is connected to the steering shaft 82. One end of the steering shaft 82 is connected to the steering wheel 81. The other end of the steering shaft 82 is connected to the universal joint 84. One end of the lower shaft 85 is connected to the steering shaft 82 via the universal joint 84. The other end of the lower shaft 85 is connected to the pinion shaft 87 via the universal joint 86. The pinion shaft 87 is connected to the pinion 88a. The pinion 88a meshes with the rack 88b. When the pinion 88a rotates, the rack 88b moves in the vehicle width direction of the vehicle. The pinion 88a and the rack 88b convert the rotational motion transmitted to the pinion shaft 87 into a straight motion. The rack 88 b is connected to the tie rod 89. The angle of the wheels changes as the rack 88b moves. The operation of the steering wheel 81 may be converted into an electric signal, and the wheel angle may be changed by the electric signal. That is, a steer-by-wire system may be applied to the electric power steering apparatus 80.

  As shown in FIG. 1, the electric power steering device 80 includes an electric motor 93, a torque sensor 94, a vehicle speed sensor 95, and an ECU (Electronic Control Unit) 90. The electric motor 93, the torque sensor 94, and the vehicle speed sensor 95 are electrically connected to the ECU 90. The electric motor 93 is, for example, a brushless motor, but may be a motor including a brush (slider) and a commutator (commutator). The electric motor 93 is disposed in the housing 7 described later. The torque sensor 94 is attached to the pinion 88a, for example. The torque sensor 94 outputs the steering torque transmitted to the pinion 88a to the ECU 90 by CAN (Controller Area Network) communication. The vehicle speed sensor 95 detects the traveling speed (vehicle speed) of the vehicle body on which the electric power steering device 80 is mounted. The vehicle speed sensor 95 is provided in the vehicle body and outputs the vehicle speed to the ECU 90 by CAN communication.

  The ECU 90 controls the operation of the electric motor 93. The ECU 90 acquires signals from each of the torque sensor 94 and the vehicle speed sensor 95. The ECU 90 is supplied with electric power from a power supply device 99 (for example, an in-vehicle battery) in a state where the ignition switch 98 is on. The ECU 90 calculates an auxiliary steering command value based on the steering torque and the vehicle speed. The ECU 90 adjusts the power value supplied to the electric motor 93 based on the auxiliary steering command value. The ECU 90 acquires information on the induced voltage from the electric motor 93 or information output from a resolver or the like provided in the electric motor 93.

  FIG. 3 is a cross-sectional view around the ball screw of the present embodiment. FIG. 4 is an enlarged view of FIG. FIG. 5 is an enlarged view of FIG. 6 is a cross-sectional view of the periphery of the ball screw taken along a plane different from that in FIG. FIG. 7 is an enlarged view of FIG. FIG. 8 is a perspective view of the buffer member of the present embodiment. FIG. 9 is a perspective view of the buffer member and the displacement restricting portion of the present embodiment. As shown in FIG. 3, the electric power steering apparatus 80 includes a housing 7, a ball screw 1, a transmission mechanism 2, a bearing 3, a first buffer member 5a, and a second buffer member 5b.

  The housing 7 includes a light metal. For example, the housing 7 is made of an aluminum alloy or a magnesium alloy. As shown in FIGS. 2 to 3, the housing 7 includes a first main body 71, a second main body 73, a third main body 75, a first plate 77, a second plate 78, a third plate 79, Is provided.

  The first main body 71 supports the bearing 3. The first body 71 is substantially cylindrical and covers the bearing 3 and the ball screw 1. The second main body 73 is disposed between the first main body 71 and the third main body 75. The second main body 73 is connected to the first main body 71 and the third main body 75 by bolts or the like. The third main body 75 supports the electric motor 93. The third body 75 is substantially cylindrical and covers the electric motor 93.

  The first plate 77 is disposed inside the first main body 71. The first plate 77 is annular, and is disposed between the bottom surface 719 of the first main body 71 and the buffer member 5 as shown in FIG. 4. The second plate 78 is disposed inside the first main body 71. The second plate 78 is annular, and is disposed between the third plate 79 and the buffer member 5 as shown in FIG. The third plate 79 is disposed between the first main body 71 and the second main body 73. The third plate 79 is annular. The third plate 79 is pressed against the second plate 78 by the second main body 73.

  As shown in FIG. 3, the ball screw 1 includes a nut 13, a screw shaft 11, and a plurality of rolling elements 15. The nut 13 is disposed inside the first main body 71 of the housing 7. The nut 13 includes a thread groove on the inner peripheral surface. The screw shaft 11 passes through the nut 13. The screw shaft 11 includes a thread groove on the outer peripheral surface. The screw shaft 11 is a part of the rack 88b. That is, the screw shaft 11 is integral with the rack 88b. The rolling element 15 is disposed between the nut 13 and the screw shaft 11. The rolling element 15 is a ball. The rolling element 15 circulates infinitely on a rolling path formed by the thread groove of the nut 13 and the thread groove of the screw shaft 11. When the nut 13 rotates, the screw shaft 11 (rack 88b) moves in the vehicle width direction. The ball screw 1 converts rotational motion into straight motion.

  The transmission mechanism 2 transmits the power of the electric motor 93 to the nut 13. As shown in FIG. 3, the transmission mechanism 2 includes a first pulley 21, a second pulley 23, and a power transmission member 25. The first pulley 21 is fixed to the shaft of the electric motor 93. The first pulley 21 rotates integrally with the shaft of the electric motor 93. The second pulley 23 is fixed to the nut 13. The second pulley 23 rotates integrally with the nut 13. The power transmission member 25 is wound around the first pulley 21 and the second pulley 23. The power transmission member 25 transmits from the first pulley 21 to the second pulley 23. The power transmission member 25 is, for example, a belt.

  The bearing 3 supports the nut 13 so that the nut 13 can rotate with respect to the housing 7. The bearing 3 is formed of steel such as bearing steel. As shown in FIG. 3, the bearing 3 includes an outer ring 31, an inner ring 33, and a plurality of rolling elements 35. The outer ring 31 is fitted to the inner peripheral surface of the first main body 71. The outer ring 31 is positioned in the axial direction of the rack 88b (hereinafter simply referred to as the axial direction) by the housing 7 and the buffer member 5. The inner ring 33 is fitted to the outer peripheral surface of the nut 13. The nut 13 is fixed to the inner ring 33 by a lock nut 37. The inner ring 33 rotates together with the nut 13. The rolling element 35 is disposed between the outer ring 31 and the inner ring 33. The rolling element 35 is a ball. The bearing 3 may be a double row bearing. Further, the inner ring 33 may be integrated with the nut 13 of the ball screw 1. That is, the inner ring 33 may be a part of the nut 13.

  When the electric motor 93 is driven, the power generated by the electric motor 93 is transmitted to the nut 13 via the transmission mechanism 2. Thereby, the nut 13 supported by the bearing 3 rotates. When the nut 13 rotates, an axial force acts on the rack 88b (screw shaft 11). This reduces the force required to move the rack 88b. That is, the electric power steering device 80 is a rack assist type.

  As shown in FIG. 4, the first buffer member 5 a is disposed between the bearing 3 and the first plate 77 of the housing 7. The second buffer member 5 b is disposed between the bearing 3 and the second plate 78 of the housing 7. In the following description, when it is not necessary to distinguish between the first buffer member 5a and the second buffer member 5b, the buffer member 5 is described. The buffer member 5 is formed of a material harder than the material of the housing 7. The Young's modulus of the material of the buffer member 5 is larger than the Young's modulus of the material of the housing 7. For example, the buffer member 5 is made of steel. As shown in FIG. 8, the buffer member 5 includes an annular portion 51 and a plurality of claw portions 53.

  The annular portion 51 has an annular plate shape and contacts the housing 7. As shown in FIG. 4, the annular portion 51 of the first buffer member 5 a is in contact with the first plate 77. At least a part of the annular portion 51 of the first buffer member 5 a is parallel to the surface of the housing 7 (the surface of the first plate 77) in contact with the annular portion 51. The annular portion 51 of the second buffer member 5 b is in contact with the second plate 78. At least a part of the annular portion 51 of the second buffer member 5 b is parallel to the surface of the housing 7 (the surface of the second plate 78) in contact with the annular portion 51.

  As shown in FIG. 8, the claw portion 53 protrudes outward in the radial direction from the annular portion 51 and contacts the bearing 3. The radial direction is a direction along a straight line passing through the center of the annular portion 51 and parallel to the annular portion 51, and is used in the same meaning in the following description. The plurality of claw portions 53 are arranged at equal intervals in the circumferential direction. The circumferential direction is a direction along the circumference centered on a straight line passing through the center of the annular portion 51 and orthogonal to the annular portion 51, and is used in the same meaning in the following description.

  As shown in FIG. 4, the claw portion 53 contacts the outer ring 31 of the bearing 3. As shown in FIG. 5, the claw portion 53 includes a bent portion 531, a root portion 533, and a tip portion 535. The claw portion 53 is bent at the bent portion 531. The root portion 533 has a plate shape and is disposed between the bent portion 531 and the annular portion 51. The front end portion 535 is plate-shaped and is disposed on the bearing 3 side with respect to the bent portion 531 and contacts the outer ring 31. The angle θ1 formed by the surface 5351 of the front end portion 535 facing the bearing 3 with respect to the end surface 311 of the outer ring 31 is larger than the angle θ2 formed by the surface 5331 of the root portion 533 facing the bearing 3 with respect to the end surface 311 of the outer ring 31. small. For example, at least part of the surface 5351 and the surface 5331 is planar. More specifically, the angle θ1 is an angle formed by the planar portion of the surface 5351 and the end surface 311. The angle θ2 is an angle formed by the planar portion of the surface 5331 and the end surface 311.

  A preload is applied to the buffer member 5. In the buffer member 5, the deformed state is maintained by being sandwiched between the bearing 3 and the housing 7. In the buffer member 5, a state in which the ball screw 1 is deformed while no external force is applied is maintained. The claw portion 53 is deformed by a reaction force received from the outer ring 31 of the bearing 3. For this reason, even when the bearing 3 moves in the axial direction, the state where the claw portion 53 is in contact with the outer ring 31 is maintained.

When the vehicle is traveling, the load received by the wheel from the road surface is transmitted to the rack 88b via the tie rod 89. The tie rod 89 is arranged so as to form an angle with respect to the rack 88b. For this reason, not only the load in the axial direction but also loads in various directions are applied to the rack 88b. A load applied to the rack 88 b is transmitted to the bearing 3 through the nut 13. Further, a load due to the tension of the power transmission member 25 (belt) is transmitted to the bearing 3 through the nut 13.
Therefore, not only the load in the axial direction but also loads in various directions are applied to the bearing 3. A moment load is applied to the bearing 3.

  In the present embodiment, the shock-absorbing member 5 includes a plurality of claw portions 53 arranged at intervals in the circumferential direction. Thereby, the some nail | claw part 53 can deform | transform independently. For this reason, even when the bearing 3 receives loads in various directions, the buffer member 5 can absorb vibration by appropriately changing the deformation amounts of the plurality of claw portions 53. In addition, the assembly error (misalignment) is absorbed by the deformation of the plurality of claw portions 53. As a result, vibration around the ball screw 1 is suppressed and so-called rattle noise is reduced. In addition, when a disc spring is used as the buffer member, for example, the spring constant of the elastically deformed portion of the disc spring increases to some extent. On the other hand, in the buffer member 5 of the present embodiment, since the plurality of claw parts 53 that are elastically deformed portions are arranged at intervals in the circumferential direction, the spring constant of the elastically deformable portion can be reduced. It is. For this reason, according to the buffer member 5, the vibration absorption performance can be easily adjusted.

  As shown in FIG. 7, the first plate 77 includes a base 771 and a plurality of displacement restricting portions 773. The base portion 771 has an annular plate shape and contacts the first main body 71. The plurality of displacement restricting portions 773 are arranged at equal intervals in the circumferential direction. The displacement restricting portion 773 protrudes in the axial direction from the base portion 771 and faces the end surface 311 of the outer ring 31. A gap is provided between the displacement restricting portion 773 and the end surface 311. When the bearing 3 moves in the axial direction by a predetermined amount, the displacement restricting portion 773 comes into contact with the outer ring 31 to restrict the movement of the bearing 3. The displacement restricting portion 773 restricts the displacement of the claw portion 53 in the axial direction.

  As shown in FIG. 9, the displacement restricting portion 773 is disposed between the two claw portions 53. For example, the number of displacement restricting portions 773 is equal to the number of claw portions 53 provided in one buffer member 5. That is, the displacement restricting portions 773 and the claw portions 53 are alternately arranged over the entire circumference.

  As shown in FIG. 7, the second plate 78 includes a base portion 781 and a displacement restricting portion 783. The base portion 781 has an annular plate shape and contacts the third plate 79. The plurality of displacement restricting portions 783 are arranged at equal intervals in the circumferential direction. The displacement restricting portion 783 protrudes in the axial direction from the base portion 781 and faces the end surface 311 of the outer ring 31. A gap is provided between the displacement regulating portion 783 and the end surface 311. When the bearing 3 moves in the axial direction by a predetermined amount, the displacement restricting portion 783 comes into contact with the outer ring 31 to restrict the movement of the bearing 3. The displacement restricting portion 783 restricts the displacement of the claw portion 53 in the axial direction.

  The displacement restricting portion 783 is disposed between the two claw portions 53. For example, the number of displacement restricting portions 783 is equal to the number of claw portions 53 provided in one buffer member 5. That is, the displacement restricting portions 783 and the claw portions 53 are alternately arranged over the entire circumference. The relative positional relationship between the displacement restricting portion 783 and the claw portion 53 is the same as the relative positional relationship between the displacement restricting portion 773 and the claw portion 53 shown in FIG.

  For example, when the steering wheel 81 is largely operated while the vehicle is stopped, a load larger than the load transmitted from the road surface may be input to the bearing 3. In such a case, if all loads are received by the claw portion 53, the claw portion 53 may be plastically deformed and damaged. On the other hand, in this embodiment, the displacement restricting portion 773 and the displacement restricting portion 783 restrict the movement of the bearing 3 before an excessive load is applied to the claw portion 53. Thereby, since the deformation amount of the nail | claw part 53 is maintained below a predetermined amount, damage to the nail | claw part 53 is suppressed.

  Note that the displacement restricting portion 773 and the displacement restricting portion 783 are not necessarily arranged as described above. For example, the displacement restriction part 773 and the displacement restriction part 783 may be provided over the entire circumference. In this case, the displacement restricting portion 773 and the displacement restricting portion 783 are disposed, for example, on the outer side in the radial direction with respect to the buffer member 5. Or the displacement control part 773 and the displacement control part 783 may be arrange | positioned so that it may overlap with the nail | claw part 53 in an axial direction. That is, the displacement restricting portion 773 may be disposed between the base portion 771 and the claw portion 53. The displacement restricting portion 783 may be disposed between the base portion 781 and the claw portion 53.

  The buffer member 5 does not necessarily have the shape as described above. The nail | claw part 53 does not necessarily need to be arrange | positioned on the outer side in the radial direction with respect to the annular part 51. The number of the claw parts 53 is not limited to the number shown in FIG. 8, and may be at least two. The claw portion 53 does not necessarily need to contact the outer ring 31 of the bearing 3 and may contact the inner ring 33. The buffer member 5 only needs to include at least an annular portion 51 that contacts the housing 7 and a member that is supported by the annular portion 51 and contacts the bearing 3.

  The housing 7 does not necessarily have to include the first plate 77, the second plate 78, and the third plate 79. For example, the first plate 77 may not be provided, and the first main body 71 may be in contact with the first buffer member 5a. That is, the first plate 77 may be integrated with the first main body 71. For example, the second plate 78 and the third plate 79 may not be provided, and the second main body 73 may be in contact with the second buffer member 5b. That is, the second plate 78 and the third plate 79 may be integrated with the second main body 73.

  As described above, the electric power steering device 80 includes the housing 7, the ball screw 1, the bearing 3, and the buffer member 5. The ball screw 1 includes a nut 13 disposed in the housing 7, a screw shaft 11 passing through the nut 13, and a rolling element 15 disposed between the nut 13 and the screw shaft 11. The bearing 3 supports the nut 13 so that the nut 13 can rotate with respect to the housing 7. The buffer member 5 is disposed between the end surface 311 of the bearing 3 and the housing 7. The material of the housing 7 includes a light metal. The buffer member 5 includes an annular part 51 that is annular and in contact with the housing 7, and a plurality of claw parts 53 that are arranged at intervals in the circumferential direction of the annular part 51 and that are in contact with the bearing 3.

  Thereby, the vibration around the ball screw 1 is suppressed by the deformation of the claw portion 53. As a result, vibration transmitted to the operator is reduced. Further, since the annular portion 51 is in contact with the housing 7 while the claw portion 53 is in contact with the bearing 3, the force applied from the buffer member 5 to the housing 7 is easily dispersed. That is, the pressure applied to the housing 7 by the buffer member 5 is reduced. Therefore, the electric power steering device 80 can suppress the wear of the housing 7.

  In the electric power steering apparatus 80, at least a part of the annular portion 51 is parallel to the surface of the housing 7 that is in contact with the annular portion 51.

  Thereby, the contact area with the annular portion 51 of the housing 7 tends to be large. The pressure applied to the housing 7 by the buffer member 5 becomes smaller. Therefore, the electric power steering device 80 can further suppress the wear of the housing 7.

  In the electric power steering apparatus 80, the claw portion 53 is disposed on the bearing 3 side with respect to the bending portion 531, a root portion 533 disposed between the bending portion 531 and the annular portion 51, and the bending portion 531. A tip portion 535 in contact with the. The angle θ1 formed by the surface 5351 of the tip 535 facing the bearing 3 with respect to the end surface 311 of the bearing 3 is larger than the angle θ2 formed by the surface 5331 of the root portion 533 facing the bearing 3 with respect to the end surface 311 of the bearing 3. small.

  Thereby, while being able to maintain the deformation | transformation capability of the nail | claw part 53, the contact area with the claw part 53 of the bearing 3 tends to become large. The pressure applied to the bearing 3 by the buffer member 5 is reduced. Therefore, the electric power steering device 80 can suppress the wear of the bearing 3.

  In the electric power steering apparatus 80, the buffer member 5 is deformed by being sandwiched between the bearing 3 and the housing 7.

  Thereby, even when the bearing 3 moves in the axial direction, the state where the claw portion 53 is in contact with the bearing is maintained. That is, the state in which vibration is absorbed by the claw portion 53 is maintained. Therefore, the electric power steering device 80 can further suppress vibration around the ball screw 1.

  In the electric power steering apparatus 80, the housing 7 includes a main body (first main body 71 or second main body 73) that covers the ball screw 1 and a plate (first plate 77 or first plate) disposed between the main body and the annular portion 51. 2 plates 78).

  Accordingly, the dimensions can be adjusted by the plate (the first plate 77 or the second plate 78) without improving the processing accuracy of the main body (the first main body 71 or the second main body 73). For this reason, the dimension adjustment for positioning the bearing 3 appropriately becomes easy. Therefore, the electric power steering device 80 can be easily assembled.

  In the electric power steering device 80, the housing 7 is disposed so as to face the end surface 311 of the bearing 3, and a displacement restricting portion 773 (or a displacement restricting portion 783) that restricts the displacement of the claw portion 53 in the axial direction of the screw shaft 11. Is provided.

  Thereby, the excessive deformation | transformation of the nail | claw part 53 is suppressed. Therefore, the electric power steering device 80 can suppress damage to the buffer member 5.

  In the electric power steering device 80, the plate (the first plate 77 or the second plate 78) is disposed so as to face the end surface 311 of the bearing 3 and is a displacement that regulates the displacement of the claw portion 53 in the axial direction of the screw shaft 11. A restriction portion 773 (or a displacement restriction portion 783) is provided.

  Thereby, the excessive deformation | transformation of the nail | claw part 53 is suppressed. Therefore, the electric power steering device 80 can suppress damage to the buffer member 5.

  In the electric power steering device 80, the displacement restricting portion 773 (or the displacement restricting portion 783) is disposed between the two claw portions 53.

  Thereby, the nail | claw part 53 and the displacement control part 773 (or displacement control part 783) do not overlap in a radial direction. For this reason, it becomes possible to enlarge the nail | claw part 53 to radial direction. As a result, the claw portion 53 is more easily deformed, so that the vibration absorbing ability of the buffer member 5 is improved. Therefore, the electric power steering device 80 can further suppress vibration around the ball screw 1. Further, the claw portion 53 and the displacement restricting portion 773 (or the displacement restricting portion 783) do not overlap in the axial direction. For this reason, the axial length of the space occupied by the buffer member 5 and the displacement restricting portion 773 (or the displacement restricting portion 783) is reduced. As a result, the housing 7 can be reduced in size in the axial direction. Further, since the claw portion 53 is not sandwiched between the displacement restricting portion 773 (or the displacement restricting portion 783) and the bearing 3, unintended stress is hardly generated in the claw portion 53. Accordingly, since the plastic deformation and the like of the claw portion 53 are suppressed, the vibration absorbing ability of the buffer member 5 is easily maintained.

(First modification)
FIG. 10 is a cross-sectional view around the bearing of the first modification. FIG. 11 is a cross-sectional view of the periphery of the bearing of the first modified example taken along a plane different from that in FIG. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIGS. 10 and 11, the housing 7 </ b> A of the first modified example does not include the first plate 77 described above. The housing 7A includes a first main body 71A. As shown in FIG. 10, the annular portion 51 of the first buffer member 5a is in contact with the bottom surface 719A of the first main body 71A. At least a part of the annular portion 51 of the first buffer member 5a is parallel to the surface (bottom surface 719A) of the housing 7A in contact with the annular portion 51.

  As shown in FIG. 11, the first main body 71A includes a displacement restricting portion 711A. The first main body 71A includes a plurality of displacement restricting portions 711A arranged at equal intervals in the circumferential direction, like the first plate 77 described above. The displacement restricting portion 711 </ b> A protrudes in the axial direction from the bottom surface 719 </ b> A and faces the end surface 311 of the outer ring 31. A gap is provided between the displacement restricting portion 711A and the end surface 311. The displacement restricting portion 711A is disposed between the two claw portions 53. The displacement restricting portions 711A and the claw portions 53 are alternately arranged over the entire circumference.

  Compared to the embodiment described above, in the first modification, the electric power steering device 80 can reduce the number of parts by providing the first main body 71A of the housing 7A with the displacement restricting portion 711A.

(Second modification)
FIG. 12 is a cross-sectional view around the bearing of the second modification. FIG. 13 is a cross-sectional view of the periphery of the bearing of the second modified example taken along a plane different from that of FIG. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIGS. 12 and 13, the housing 7 </ b> B of the second modified example does not include the second plate 78 and the third plate 79 described above. The housing 7B includes a second main body 73B. As shown in FIG. 12, the annular portion 51 of the first buffer member 5a is in contact with the surface 739B of the second main body 73B. At least a part of the annular portion 51 of the first buffer member 5a is parallel to the surface (surface 739B) of the housing 7B in contact with the annular portion 51.

  As shown in FIG. 13, the second main body 73B includes a displacement restricting portion 731B. Similar to the second plate 78 described above, the second main body 73B includes a plurality of displacement restricting portions 731B arranged at equal intervals in the circumferential direction. The displacement restricting portion 731B protrudes in the axial direction from the surface 739B and faces the end surface 311 of the outer ring 31. A gap is provided between the displacement restricting portion 731B and the end surface 311. The displacement restricting portion 731B is disposed between the two claw portions 53. The displacement restricting portions 731B and the claw portions 53 are alternately arranged over the entire circumference.

  In the second modification, the second main body 73B is combined with the first main body 71A of the first modification, but the second main body 73B is combined with the first main body 71 and the first plate 77 of the embodiment. May be.

  Compared to the embodiment described above, in the second modification, the electric power steering device 80 can reduce the number of parts by providing the second main body 73B of the housing 7B with the displacement restricting portion 731B.

(Third Modification)
FIG. 14 is a perspective view of a buffer member according to a third modification. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 14, the buffer member 5 </ b> C of the third modified example includes a plurality of projecting portions 54 and a plurality of claw portions 55. The protruding portion 54 protrudes radially outward from the annular portion 51. The plurality of protrusions 54 are arranged at equal intervals in the circumferential direction. The claw portion 55 protrudes from the protruding portion 54 in the circumferential direction. Two claw portions 55 are provided for one protrusion 54. One of the two claw portions 55 protrudes from the protruding portion 54 to one side in the circumferential direction. The other of the two claw portions 55 protrudes from the protruding portion 54 to the other side in the circumferential direction. The claw portion 55 is in contact with the outer ring 31 of the bearing 3.

(Fourth modification)
FIG. 15 is a perspective view of a part of the buffer member of the fourth modified example. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 15, the buffer member 5 </ b> D of the fourth modified example includes a plurality of claw portions 56. The claw portion 56 protrudes radially inward from the annular portion 51 and contacts the bearing 3. The plurality of claw portions 56 are arranged at equal intervals in the circumferential direction. The claw portion 56 contacts the inner ring 33 of the bearing 3. The claw part 56 has a symmetrical shape with respect to the claw part 53 described above. That is, the claw part 56 includes a configuration corresponding to the bent part 531, the root part 533, and the tip part 535 of the claw part 53.

  As described above, in the fourth modified example, the claw portion 56 is disposed on the radially inner side with respect to the annular portion 51.

  Thereby, since the annular part 51 is arrange | positioned in the radial direction outer side rather than the nail | claw part 56, it is easy to enlarge the annular part 51. FIG. For this reason, a contact area with the annular part 51 of the housing 7 becomes larger. Therefore, wear of the housing 7 is further suppressed.

(5th modification)
FIG. 16 is a perspective view of a part of the buffer member of the fifth modified example. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 16, the buffer member 5 </ b> E of the fifth modification includes a plurality of protrusions 57 and a plurality of claw portions 58. The protruding portion 57 protrudes radially inward from the annular portion 51. The plurality of protrusions 57 are arranged at equal intervals in the circumferential direction. The claw portion 58 protrudes from the protruding portion 57 in the circumferential direction. Two claws 58 are provided for one protrusion 57. One of the two claw portions 58 protrudes from the protruding portion 57 to one side in the circumferential direction. The other of the two claw portions 58 protrudes from the protruding portion 57 to the other side in the circumferential direction. The claw portion 58 contacts the outer ring 31 of the bearing 3.

  As described above, in the fifth modification, the claw portion 58 is disposed on the radially inner side with respect to the annular portion 51.

  Thereby, since the annular portion 51 is disposed on the outer side in the radial direction than the claw portion 58, the annular portion 51 can be easily enlarged. For this reason, a contact area with the annular part 51 of the housing 7 becomes larger. Therefore, wear of the housing 7 is further suppressed.

(Sixth Modification)
FIG. 17 is a perspective view of a buffer member according to a sixth modification. Note that the same components as those described in the above-described embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 17, the buffer member 5 </ b> F of the sixth modified example includes two claw portions 53. The two claw portions 53 are arranged at equal intervals in the circumferential direction. One claw portion 53 is disposed on the opposite side to the other claw portion 53. Thus, the number of the claw parts 53 is not particularly limited.

DESCRIPTION OF SYMBOLS 1 Ball screw 11 Screw shaft 13 Nut 15 Rolling element 2 Transmission mechanism 21 1st pulley 23 2nd pulley 25 Power transmission member 3 Bearing 31 Outer ring 311 End surface 33 Inner ring 35 Rolling element 37 Lock nut 5, 5C, 5D, 5E, 5F Buffer Member 5a first buffer member 5b second buffer member 51 annular portion 53, 55, 56, 58 claw portion 531 bent portion 533 root portion 5331 surface 535 tip portion 5351 surface 54, 57 projecting portion 7, 7A, 7B housing 71 first Main body 711A Displacement restricting portions 719, 719A Bottom surface 73 Second main body 731B Displacement restricting portion 739B Surface 75 Third main body 77 First plate 771 Base 773 Displacement restricting portion 78 Second plate 781 Base 783 Displacement restricting portion 79 Third plate 80 Electric power Steering device 81 Steering wheel 82 Steering shaft 84 Universal joint 85 Lower shaft 86 Universal joint 87 Pinion shaft 88a Pinion 88b Rack 89 Tie rod 90 ECU
93 Electric motor 94 Torque sensor 95 Vehicle speed sensor 98 Ignition switch 99 Power supply

Claims (9)

A housing;
A ball screw including a nut disposed in the housing, a screw shaft penetrating the nut, and a rolling element disposed between the nut and the screw shaft;
A bearing that supports the nut so that the nut can rotate relative to the housing;
A buffer member disposed between an end face of the bearing and the housing;
With
The housing material comprises a light metal,
The shock-absorbing member includes an annular portion that is annular and in contact with the housing, and a plurality of claw portions that are arranged at intervals in the circumferential direction of the annular portion and that are in contact with the bearing. The electric power steering apparatus according to claim 1, wherein at least a part of the annular portion is parallel to a surface of the housing that contacts the annular portion. The claw portion includes a bent portion, a root portion disposed between the bent portion and the annular portion, and a tip portion disposed on the bearing side with respect to the bent portion and in contact with the bearing,
The angle which the surface of the said front-end | tip part which faces the said bearing makes with respect to the end surface of the said bearing is smaller than the angle which the surface of the said base part which faces the said bearing makes with respect to the end surface of the said bearing. The electric power steering device described in 1. The electric power steering apparatus according to any one of claims 1 to 3, wherein the buffer member is deformed by being sandwiched between the bearing and the housing. The electric power steering device according to any one of claims 1 to 4, wherein the housing includes a main body that covers the ball screw, and a plate that is disposed between the main body and the annular portion. 5. The electric motor according to claim 1, wherein the housing includes a displacement restricting portion that is disposed so as to face an end surface of the bearing and restricts displacement of the claw portion in an axial direction of the screw shaft. Power steering device. The electric power steering apparatus according to claim 5, wherein the plate includes a displacement restricting portion that is disposed so as to face an end surface of the bearing and restricts displacement of the claw portion in an axial direction of the screw shaft. The electric power steering apparatus according to claim 6 or 7, wherein the displacement restricting portion is disposed between the two claw portions. The electric power steering apparatus according to any one of claims 1 to 8, wherein the claw portion is disposed radially inward of the annular portion.