Electric power steering device

Abstract

In this electric power steering device, a ball bearing (7) is held by a holding member (8), the movement of which in the axial direction is restricted by a second housing (12). That is, the holding member (8) is not screwed into the housing, so that bite and loosening due to thermal expansion do not occur. Moreover, when thermal expansion occurs in the holding member (8), the amount of thermal expansion is absorbed by the first elastic member (91) or the second elastic member (92), and thus there is no risk that the holding ability of the holding member (8) to the ball bearing (7) is reduced due to the thermal expansion.

Description

Technical Field

[0001] The invention relates to an electric power steering device. Background Art

[0002] As conventional electric power steering devices, for example, those described in the following patent documents are known.

[0003] In the electric power steering device of the patent document, the rotating portion (pulley) of the ball screw mechanism is supported on the outer peripheral side of the rack bar via a bearing so as to be rotatable relative to the housing, and the bearing is fastened to the housing via a lock nut screwed into the housing.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: (Japanese) Patent Publication No. 2018-039391 Summary of the invention

[0007] Technical problem to be solved by the invention

[0008] However, the conventional electric power steering device has a structure in which the bearing is fastened to the housing by the lock nut. Therefore, there is a risk of the lock nut biting the housing. In addition, when the lock nut is made of a material different from that of the housing, there is a risk of the lock nut loosening due to heat, and there is room for improvement in this regard.

[0009] The present invention has been made in view of the above technical problems, and provides an electric power steering device capable of appropriately and continuously holding a bearing.

[0010] Technical solutions for solving technical problems

[0011] According to one aspect of the present invention, the bearing housed and supported in the first housing is held by a holding member, and the axial movement of the holding member is restricted by a second housing disposed axially opposed to the first housing.

[0012] Effects of the Invention

[0013] According to the present invention, the bearing can be appropriately and continuously held. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a front view of the steering device of the present invention.

[0015] Figure 2 yes Figure 1 A cross-sectional view near the transmission mechanism shown.

[0016] Figure 3 yes Figure 2 An enlarged view of the main part.

[0017] Figure 4 yes Figure 2 An enlarged view of the retaining component is shown. DETAILED DESCRIPTION

[0018] The following is based on Figures 1 to 4 The embodiments of the electric power steering device of the present invention are described. It should be noted that in the following embodiments, the electric power steering device of the present invention is applied to a steering device of an automobile in the same manner as in the past. Figures 1 to 4 In the description, for convenience, the following Figure 2 The description will be made with the direction of the central axis X of the rack bar 3 being the “axial direction”, the direction orthogonal to the central axis X of the rack bar 3 being the “radial direction”, and the direction around the central axis X of the rack bar 3 being the “circumferential direction”.

[0019] (Structure of electric power steering device)

[0020] Figure 1 FIG. 1 shows the appearance of the electric power steering device according to the present embodiment and is a front view of the electric power steering device.

[0021] like Figure 1 As shown, the electric power steering device includes a steering mechanism SM for steering based on the driver's operation and a steering assist mechanism AM for assisting the driver's steering operation. Furthermore, the electric power steering device is suspended on the vehicle body via a bracket BKT, and the bracket BKT is attached to a first housing 11 and a second housing 12 that accommodate the steering mechanism SM and the steering assist mechanism AM.

[0022] The steering mechanism SM includes a steering shaft 2 connected to a steering wheel (not shown) and a rack shaft (i.e., a rack bar 3) connected to a steering wheel (not shown). The steering shaft 2 and the rack bar 3 are connected via a conversion mechanism (not shown). The conversion mechanism is a so-called rack-and-pinion mechanism composed of pinion teeth (not shown) formed on the steering shaft 2 (output shaft 22 described later) and rack teeth (not shown) formed on the rack bar 3.

[0023] The steering shaft 2 is formed by connecting an input shaft 21 that rotates integrally with a steering wheel (not shown) and an output shaft 22 connected to the rack bar 3 using a torsion bar (not shown). Figure 1 The upper end side of the output shaft 22 is connected to a steering wheel (not shown), and the other end side is connected to a torsion bar (not shown). Figure 1The output shaft 22 is connected to a torsion bar (not shown) at one end thereof, and the other end thereof is connected to the rack bar 3. That is, a pinion tooth (not shown) is formed on the outer periphery of the other end of the output shaft 22, and the pinion tooth meshes with the rack tooth (not shown) of the rack bar 3, thereby being able to convert the rotation of the output shaft 22 into the axial movement of the rack bar 3 and transmit it. In addition, a torque sensor TS for detecting the steering torque input to the steering shaft 2 by the driver is arranged on the outer periphery of the steering shaft 2. The torque sensor TS detects the steering torque based on the displacement amount of the relative rotation between the input shaft 21 and the output shaft 22.

[0024] The rack bar 3 has both ends connected to the left and right steering wheels (not shown) via the tie rods and knuckle arms (not shown). That is, the rack bar 3 moves in the axial direction and pulls the knuckle arms (not shown) via the tie rods (not shown), thereby changing the direction of the steering wheels (not shown).

[0025] Furthermore, the rack bar 3 is housed in a rack bar housing 10 formed in a through state inside a substantially cylindrical rack housing 1 so as to be movably axially with both ends exposed to the outside. The rack housing 1 is formed by being divided into two parts in the axial direction by casting, and is composed of a first housing 11 that houses one axial end side of the rack bar 3 and a second housing 12 that houses the other end side of the rack bar 3. The first housing 11 and the second housing 12 are fastened by a plurality of first screws SW1. It should be noted that the rack bar housing 10 is composed of a first rack bar housing 110 that axially passes through the interior of the first housing 11, and a second rack bar housing 120 that is connected to the first rack bar housing 110 and axially passes through the interior of the second housing 12 (see Figure 2 ).

[0026] The steering assist mechanism AM includes a motor 4 that generates a steering assist force, a control device 5 that drives and controls the motor 4, and a transmission mechanism 6 that transmits the driving force of the motor 4 to the rack bar 3. That is, the steering assist mechanism AM assists the axial movement of the rack bar 3 by using the driving force of the motor 4 that is driven and controlled by the control device 5 based on the detection results of various sensors such as the torque sensor TS and the vehicle speed sensor (not shown). It should be noted that the torque sensor TS is connected to the control device 5 by wire via a wire harness WH provided along the rack housing 1.

[0027] Figure 2 A partial cross-sectional view of the electric power steering system is shown in which the vicinity of the transmission mechanism 6 is enlarged and illustrated.

[0028] like Figure 2As shown, the first housing 11 is integrally formed of a metal material, such as an aluminum alloy material. Specifically, the first housing 11 integrally comprises: a cylindrical first rack bar receiving portion 110, which receives one axial end of the rack bar 3; a bearing receiving portion 111, which is formed in a stepped manner with respect to the first rack bar receiving portion 110, and receives a ball bearing 7 that supports the rotation of a ball nut 641 described later; and a motor supporting portion 112, which is radially outward ( Figure 2 The upper side of the housing 1 extends to support the motor 4.

[0029] The first rack bar housing portion 110 is formed to extend in the axial direction on the first end side of the first housing 11. The bearing housing portion 111 is formed by expanding the diameter in a stepped manner via an end wall 114 on the second housing 12 side of the first rack bar housing portion 110, and has an inner diameter capable of inserting the outer ring portion 71 of the ball bearing 7 in a non-pressed state.

[0030] The motor 4 is fastened and fixed to the first housing 11 via a plurality of second screws SW2 at the first end of the motor support 112, i.e., the end on the opposite side to the second housing 12. In addition, the motor support 112 has a motor receiving hole 112a that penetrates substantially parallel to the first rack bar receiving portion 110, and receives the front end side bearing portion 40 of the motor 4 in a loose fitting state via the motor receiving hole 112a.

[0031] The second housing 12 is formed integrally with the first housing 11 by the same metal material as the first housing 11, such as an aluminum alloy material, and is connected to the second end of the first housing 11 via a plurality of first screws SW1 (see FIG. Figure 1 Specifically, the second housing 12 integrally comprises: a cylindrical second rack bar housing portion 120 which houses the other axial end of the rack bar 3; and a transmission mechanism housing portion 121 which is formed in a stepped manner with respect to the second rack bar housing portion 120 and houses the transmission mechanism 6.

[0032] The second rack bar storage section 120 is formed in an axially extending manner on the second end side of the second housing 12. The transmission mechanism storage section 121 is formed in an elliptical cylindrical shape with a bottom that is open to the first housing 11 side that is opposite in the axial direction, and is formed in a stepped and expanded manner at the end (first end) on the first housing 11 side of the second rack bar storage section 120. That is, the transmission mechanism storage section 121 has: a first pulley storage section 122 that stores the input side pulley 61 described later; a second pulley storage section 123 that stores the output side pulley 62 described later; and a belt storage section (not shown) that is arranged across the first pulley storage section 122 and the second pulley storage section 123 and stores the belt component 63 described later.

[0033] The transmission mechanism 6 includes: an input pulley 61 and an output pulley 62 as a pair of pulleys; a belt member 63 wound between the input pulley 61 and the output pulley 62; and a ball screw mechanism 64 as a speed reduction mechanism, which converts the rotation of the output pulley 62 into the axial movement of the rack bar 3 while reducing the speed. It should be noted that the transmission mechanism 6 can be any combination of a pair of sprockets and a chain wound between the two sprockets, in addition to the combination of the pair of pulleys 61, 62 and the belt member 63 wound between the two pulleys 61, 62 illustrated in the present embodiment, and can be arbitrarily changed according to the specifications of the electric power steering device to which it is applied.

[0034] The input side pulley 61 is formed of a metal material into a cylindrical shape having a smaller diameter than the output side pulley 62, and is fixed to the outer peripheral side of the front end portion of the output shaft 41 of the motor 4 by press-fitting through a through hole 620 that penetrates the inner peripheral side in the axial direction. That is, the input side pulley 61 rotates integrally with the output shaft 41 around the second reference axis A2, which is the rotation axis of the output shaft 41 of the motor 4.

[0035] The output side pulley 62 is arranged on the outer peripheral side of the rack bar 3, and is connected to the rack bar 3 via the ball screw mechanism 64. Specifically, the output side pulley 62 is made of the same metal material as the input side pulley 61, and is formed into a bottomed cylindrical shape with a larger diameter than the input side pulley 61, and is fixed to the outer periphery of the ball nut 641 described later, and rotates integrally with the ball nut 641 described later, with the first reference axis A1 corresponding to the central axis of the rack bar 3 as the center.

[0036] The belt member 63 is an endless V-belt having glass fiber, steel wire or the like buried therein as a core material, and transmits the rotational force of the input pulley 61 to the output pulley 62 by connecting the input pulley 61 and the output pulley 62 and rotating them synchronously.

[0037] The ball screw mechanism 64 includes: a cylindrical ball nut 641, which is arranged on the outer peripheral side of the rack rod 3; a series of ball circulation grooves 642, which are formed between the ball nut 641 and the rack rod 3; a plurality of balls 643, which are interposed in the ball circulation grooves 642 in a rollable manner; and a cylindrical tube 644, which connects the two ends of the ball circulation grooves 642 to circulate the above-mentioned balls 643.

[0038] The ball nut 641 is formed of a metal material into a cylindrical shape surrounding the rack bar 3, and is rotatably supported by the first housing 11 via the ball bearing 7, and is relatively rotatably arranged relative to the rack bar 3. The ball circulation groove 642 is composed of a shaft-side ball screw groove 642a provided on the outer circumference of the rack bar 3 and having a spiral groove shape, and a nut-side ball screw groove 642b provided on the inner circumference of the ball nut 641 and having a spiral groove shape corresponding to the shaft-side ball screw groove 642a.

[0039] The ball bearing 7 includes: an outer ring portion 71, which is held in the bearing housing portion 111 of the first housing 11 via a holding member 8; an inner ring portion 72, which is arranged opposite to the inner circumference of the outer ring portion 71 and is formed integrally with the ball nut 641; and a plurality of balls 73, which are rolled and housed between the outer ring portion 71 and the inner ring portion 72. It should be noted that in the present embodiment, the inner ring portion 72 is shown as being formed integrally with the ball nut 641, but the inner ring portion 72 is not limited to being formed integrally with the ball nut 641, and may be formed separately from the ball nut 641 and fixed to the ball nut 641, for example.

[0040] Figure 3 Indicates that Figure 2 FIG. 1 is an enlarged view of the main parts of the electric power steering device, showing the vicinity of the main part, namely the ball bearing 7, enlargedly shown. Figure 4 It is expressed as a monomer Figure 2 The figure of the holding member 8 shown in FIG. 1 is an enlarged cross-sectional view of the holding member 8 showing the cross section of the holding member 8. It should be noted that, in the following description of each part, for convenience, Figure 3 , Figure 4 The right end of is set as the first end, Figure 3 , Figure 4 The left end portion is set as the second end portion.

[0041] like Figure 3 As shown, the first housing 11 has: a bearing receiving portion 111, which receives the ball bearing 7 at the axial end (second end) opposite to the second housing 12; and a first retaining member receiving portion 113, which is formed with a stepped diameter expansion toward the second end relative to the bearing receiving portion 111, and receives the first end side of the retaining member 8 (the convex portion 82 described later). The first end of the bearing receiving portion 111 is formed with a first rack bar receiving portion 110 (see Figure 2 ) An end wall 114 extending radially outward. Also, a first step portion 115 extending radially outward from the first holding member housing portion 113 is formed between the bearing housing portion 111 and the first holding member housing portion 113.

[0042] The second housing 12 has a second holding member receiving portion 124 for receiving and holding a second end side (a base portion 81 to be described later) of the holding member 8 at an axial end portion (a first end portion) opposed to the first housing 11. Furthermore, a second step portion 125 extending radially outward from the second holding member receiving portion 124 is formed between the transmission mechanism receiving portion 121 and the second holding member receiving portion 124.

[0043] Here, the first holding member storage portion 113 and the second holding member storage portion 124 have the same inner diameter R, and the peripheral wall 113a of the first holding member storage portion 113 and the peripheral wall 124a of the second holding member storage portion 124 together constitute the engaged surface 13 that enables the holding member 8 to be engaged. That is, the engaged surface 13 has an inner diameter R that is slightly smaller than the outer diameter Dx of the holding member 8, so that the holding member 8 can be engaged. In other words, by the so-called embedded structure in which the holding member 8 is engaged with the engaged surface 13 constituted by the peripheral wall 113a of the first holding member storage portion 113 and the peripheral wall 124a of the second holding member storage portion 124, it is possible to achieve centering that makes the center of the first housing 11 (first rack bar storage portion 110) coincide with the center of the second housing 12 (second rack bar storage portion 120).

[0044] Furthermore, the axial distance between the first holding member receiving portion 113 and the second holding member receiving portion 124, that is, the axial distance L between the first step portion 115 and the second step portion 125 is set to be slightly larger than the axial length W of the holding member 8 received between the first holding member receiving portion 113 and the second holding member receiving portion 124, including the base portion 81 and the convex portion 82. In other words, the axial distance L from the first step portion 115 to the second step portion 125 is set to a length that can form an axial gap Cx between the convex portion 82 and the first step portion 115 in a state where the base portion 81 and the second step portion 125 are in contact with each other.

[0045] The ball bearing 7 comprises: an outer ring portion 71, which is held in the bearing receiving portion 111 of the first housing 11 via the holding member 8; an inner ring portion 72, which is arranged radially opposite to the inner circumference of the outer ring portion 71; and a plurality of balls 73, which are held in a rollable manner between the outer ring portion 71 and the inner ring portion 72. The outer ring portion 71 is inserted into the bearing receiving portion 111 of the first housing 11 from the second end side, and the axial movement of the first end side is restricted by the end wall 114 of the first housing 11, and the axial movement of the second end side is restricted by the holding member 8.

[0046] Furthermore, the first elastic member 91 exists between the outer ring portion 71 and the end wall 114 in a state of exerting elastic force (a state of being given preload), and the second elastic member 92 exists between the outer ring portion 71 and the retaining member 8 (the base portion 81 described later) in a state of exerting elastic force (a state of being given preload). In addition, the first elastic member 91 and the second elastic member 92 are the same elastic members composed of, for example, wave washers, disc springs, etc., and have an outer diameter D slightly smaller than the outer diameter D of the outer ring portion 71, and have an inner diameter larger than the outer ring portion 71. That is, the first elastic member 91 and the second elastic member 92 are configured to be able to abut against each axial end face of the outer ring portion 71 as a whole.

[0047] like Figure 3 , Figure 4 As shown, the retaining member 8 is integrally formed of a metal material into a substantially annular shape having an L-shaped cross section, and has a substantially disc-shaped base 81 arranged axially opposite to the outer ring portion 71, and a substantially cylindrical convex portion 82 extending axially from the end surface of the first end side of the base 81. Moreover, when the retaining member 8 is in a state where the first housing 11 and the second housing 12 are engaged, the base 81 is urged toward the second end side based on the elastic force of the first elastic member 91 and the second elastic member 92 (mainly the second elastic member 92). That is, the retaining member 8 is urged toward the second end side based on the elastic force of the second elastic member 92, and the base 81 is pressed against the second step portion 125 of the second housing 12. On the other hand, for the retaining member 8, the base 81 is urged toward the second end side based on the elastic force of the second elastic member 92, so that the front end (first end) of the convex portion 82 is separated from the first step portion 115.

[0048] It should be noted that the holding member 8 is preferably formed of a metal material (e.g., an aluminum alloy material) having the same linear expansion coefficient as the first shell 11 and the second shell 12, but the first shell 11 and the second shell 12 may also be formed of a metal material having a different linear expansion coefficient. In this way, when the first shell 11 and the second shell 12 and the holding member 8 are formed of metal materials having different linear expansion coefficients, the expansion difference caused by the difference in linear expansion coefficients between the first shell 11 and the second shell 12 and the holding member 8 is mainly absorbed by the elastic force of the second elastic member 92.

[0049] like Figure 3 , Figure 4 As shown, the base 81 is in the shape of a disk with a substantially uniform thickness (axial width), and has a through hole 810 in the center for the ball nut 641 formed integrally with the inner ring portion 72 to pass through. The through hole 810 is set to have an inner diameter that is sufficiently larger than the outer diameter of the ball nut 641. Figure 4As shown, a groove 811 is provided at a corner formed at the boundary between the base 81 and the convex portion 82, which is recessed in the axial direction toward the side (the second end side) opposite to the second elastic member 92. The groove 811 opens toward the second elastic member 92 side (the first end side) in the outer peripheral region of the second elastic member 92, and is formed into a continuous ring along the circumferential direction. In other words, the fillet portion (not shown) formed at the boundary between the base 81 and the convex portion 82 during the manufacturing process is removed by the groove 811. It should be noted that the second elastic member 92 is configured to abut against a flat surface 812 on the inner peripheral side than the groove 811.

[0050] And, if Figure 4 As shown, the base 81 has a protrusion 813 formed by slightly protruding the area opposite to the second step portion 125 on the end surface on the side (second end side) opposite to the second step portion 125. The protrusion 813 slightly protrudes toward the second end side relative to the general portion 814 on the inner circumferential side that does not abut against the second shell 12, and is formed into a continuous ring along the circumferential direction, and abuts against the second step portion 125 as a whole. It should be noted that the protrusion 813 does not necessarily need to be formed into a ring, and a plurality of protrusions may be provided intermittently in the circumferential direction. In addition, the abutting surface 813a of the protrusion 813 and the second step portion 125 is different from the unprocessed general portion 814, and is precisely finished by machining or the like. In other words, in this embodiment, only the abutting surface 813a of the protrusion 813 abutting against the second step portion 125 is precisely finished by machining or the like.

[0051] And, if Figure 4 As shown, the base 81 has a base-side tapered portion 815 formed by gradually reducing the outer diameter Dx toward the second end side on the outer peripheral side of the second end portion inserted into the second holding member receiving portion 124. Therefore, when the base 81 is inserted into the second holding member receiving portion 124, the base-side tapered portion 815 guides the second holding member receiving portion 124 to fit relative to the base 81, thereby ensuring smooth assembly of the second housing 12 relative to the first housing 11.

[0052] like Figure 3 As shown, the convex portion 82 is formed in a cylindrical shape along the circumferential direction at the outer peripheral edge portion of the base portion 81, and has an axial length Wx (see FIG. 1 ) that can surround the outer peripheral side of the outer ring portion 71 and the second elastic member 92 in a manner overlapping with the outer ring portion 71 and the second elastic member 92 when viewed from the radial direction. Figure 4 ). It should be noted that, with this structure, when assembling the second elastic member 92, the second elastic member 92 can be integrally assembled with the holding member 8 by covering the outer ring portion 71 of the ball bearing 7 while the second elastic member 92 is held in the holding member 8. In addition, the convex portion 82 has an inner diameter Rx slightly larger than the outer diameter D of the outer ring portion 71, and a radial gap Cr can be formed between the convex portion 82 and the outer ring portion 71.

[0053] And, if Figure 3 As shown, the convex portion 82 is formed to be continuous with the base portion 81 without a step on the outer peripheral side, and the retaining member 8 has a continuous flat fitting surface 80 spanning the base portion 81 and the convex portion 82. The outer diameter Dx of the fitting surface 80 is set to an arbitrary outer diameter that can be fitted with the fitting surface 13 spanning the first shell 11 and the second shell 12. It should be noted that in this embodiment, the outer diameter Dx of the fitting surface 80 is set to an outer diameter that can be loosely matched with the fitting surface 13 of the first shell 11 and the second shell 12.

[0054] And, if Figure 4 As shown, the base 82 has a first convex portion side tapered portion 821 formed by gradually reducing the outer diameter Dx toward the first end portion side on the outer peripheral side of the first end portion inserted into the first holding member receiving portion 113. Therefore, when the convex portion 82 is inserted into the first holding member receiving portion 113, the first convex portion side tapered portion 821 guides the convex portion 82 to fit with the first holding member receiving portion 113, thereby ensuring smooth assembly of the holding member 8 with respect to the first housing 11.

[0055] In addition, if Figure 4 As shown, the convex portion 82 has a second convex portion side tapered portion 822 formed by gradually expanding the inner diameter Rx toward the first end side on the inner circumferential side surrounding the first end portion of the outer ring portion 71. Therefore, when the convex portion 82 is inserted into the first holding member storage portion 113, the insertion of the convex portion 82 relative to the outer ring portion 71 is guided by the second convex portion side tapered portion 822, thereby ensuring smooth assembly of the holding member 8 relative to the first housing 11.

[0056] (Effects of this embodiment)

[0057] In the above-mentioned conventional electric power steering device, the ball bearing 7 is fastened to the housing 1 by a lock nut. Therefore, there is a risk that the lock nut will bite the housing 1. In addition, when the lock nut is formed of a material different from that of the housing 1, there is a risk that the lock nut will loosen due to heat, and there is room for improvement in this regard.

[0058] On the other hand, the electric power steering device according to the present embodiment can solve the technical problems of the conventional electric power steering device described above by achieving the following effects.

[0059] That is, the electric power steering device of the present embodiment includes: a rack bar 3 connected to the steering shaft 2; a transmission mechanism 6 that transmits the steering assist force generated by the motor 4 to the rack bar 3; a first housing 11 that accommodates the rack bar 3; a second housing 12 that is coupled to the first housing 11 in a manner opposed to the rack bar 3 in the axial direction and accommodates the transmission mechanism 6; a ball screw mechanism 64 that is provided on the outer peripheral side of the rack bar 3; a ball bearing 7 that supports a rotating portion (ball nut 641) of the ball screw mechanism 64 so as to be rotatable relative to the first housing 11; a retaining member 8 whose axial end surface on the opposite side to the ball bearing 7 abuts against the second housing 12 and holds the ball bearing 7 between the first housing 11; and an elastic member (a first elastic member 91 or a second elastic member 92) that is arranged in the axial direction of the rack bar 3 between the ball bearing 7 and the retaining member 8 or between the ball bearing 7 and the first housing 11 on at least one of the two sides.

[0060] Thus, in the present embodiment, the ball bearing 7 is held by the holding member 8 whose axial movement is limited by the second housing 12. That is, the holding member 8 is not screwed into the housing, so there is no bite or looseness caused by thermal expansion. Furthermore, in the case where the holding member 8 undergoes thermal expansion, the thermal expansion is absorbed by the first elastic member 91 or the second elastic member 92, so there is no risk of the holding member 8 reducing the holding performance of the ball bearing 7 due to the thermal expansion.

[0061] Furthermore, in the present embodiment, the elastic member is disposed both between the ball bearing 7 and the holding member 8 and between the ball bearing 7 and the first housing 11 in the axial direction of the rack bar 3 .

[0062] Thus, in the present embodiment, the first elastic member 91 is arranged between the ball bearing 7 and the first housing 11, and the second elastic member 92 is arranged between the ball bearing 7 and the retaining member 8, and the elastic members are provided on both axial sides of the ball bearing 7 (outer ring portion 71). According to this structure, the outer ring portion 71 of the ball bearing 7 is in a state where force is applied from both axial sides, and the left-right difference in steering feeling during steering can be reduced.

[0063] Furthermore, in the present embodiment, the holding member 8 is positioned relative to the second housing 12 on the outer peripheral side of the ball bearing 7 .

[0064] When the holding member 8 is positioned by using the axial end of the ball bearing 7, there is a risk of interference between the holding member 8 and the transmission mechanism 6. In order to avoid this interference, there is a risk of increasing the size of the housing 1 in the axial direction. In contrast, in this embodiment, the holding member 8 is positioned relative to the second housing 12 on the outer peripheral side of the ball bearing 7. Therefore, it is possible to avoid interference between the holding member 8 and the transmission mechanism 6, and to achieve miniaturization of the housing 1 in the axial direction.

[0065] Furthermore, in the present embodiment, the elastic member (second elastic member 92) is arranged between the ball bearing 7 and the retaining member 8 in the axial direction of the rack bar 3, and the retaining member 8 has a convex portion 82 that protrudes toward the ball bearing 7 in the axial direction of the rack bar 3 and surrounds the elastic member (second elastic member 92).

[0066] Thus, in the present embodiment, the holding member 8 has a convex portion 82 that protrudes toward the ball bearing 7 in the axial direction of the rack bar 3 and can surround the second elastic member 92. Thus, the convex portion 82 of the holding member 8 can be used to restrict the second elastic member 92 from falling off. It should be noted that the convex portion 82 is effective not only after the second elastic member 92 is assembled, but also during the assembly of the second elastic member 92.

[0067] Furthermore, in the present embodiment, the holding member 8 has a groove 811 formed at a corner formed at the boundary with the convex portion 82 , the groove 811 being recessed toward the side opposite to the elastic member (the second elastic member 92 ) in the axial direction of the rack bar 3 .

[0068] Thus, in the present embodiment, a groove 811 is provided at a corner formed at the boundary portion of the holding member 8 and the convex portion 82, which is recessed toward the opposite side of the second elastic member 92 in the axial direction of the rack bar 3. In other words, the rounded corner portion (not shown) formed at the boundary portion of the base portion 81 and the convex portion 82 during the manufacturing process is removed by the groove 811. Therefore, the groove 811 can prevent the second elastic member 92 from slipping to the boundary portion of the base portion 81 and the convex portion 82 in the holding member 8, that is, the rounded corner portion, and being separated, and the second elastic member 92 can be appropriately arranged.

[0069] It should be noted that, as a method of preventing the second elastic member 92 from sliding onto the rounded corner, it is also conceivable to form the groove 811 so as to be recessed from the inner side of the protrusion 82 toward the radial outer side of the rack bar 3. In this case, when the second elastic member 92 moves in the radial direction, the second elastic member 92 is embedded in the groove 811, and the second elastic member 92 cannot exert its proper elastic function, which is not appropriate.

[0070] Furthermore, in the present embodiment, the outer peripheral surface of the holding member 8 is fitted into at least one of the first housing 11 and the second housing 12 .

[0071] Thus, in the present embodiment, the outer peripheral surface (fitting surface 80) of the holding member 8 is fitted with at least one of the first housing 11 (the peripheral wall 113a of the first holding member storage portion 113) and the second housing 12 (the peripheral wall 124a of the second holding member storage portion 124). Therefore, the first housing 11 and the second housing 12 can be centered by the holding member 8 fitted with the first housing 11 or the second housing 12. Thus, the electric power steering device can be appropriately mounted on the vehicle body via the vehicle body suspension portion (bracket BKT) provided on each of the housings 11 and 12.

[0072] Furthermore, in the present embodiment, the holding member 8 includes the convex portion 82 that faces the ball bearing 7 in the radial direction of the rack bar 3 , and the inner diameter Rx of the convex portion 82 is larger than the outer diameter D of the ball bearing 7 .

[0073] According to the present invention, the inner diameter Rx of the convex portion 82 is formed larger than the outer diameter D of the outer ring portion 71 of the ball bearing 7, and a radial gap Cr is formed between the convex portion 82 and the ball bearing 7. Therefore, when the ball bearing 7 moves in the axial direction of the rack bar 3 during steering, the movement of the ball bearing 7 is not hindered by the retaining member 8. This helps to ensure smooth steering and a good steering feel.

[0074] Furthermore, in the present embodiment, the retaining member 8 has a convex portion 82 opposed to the ball bearing 7 in the radial direction of the rack bar 3 , and the convex portion 82 has a tapered portion (first convex portion side tapered portion 821 ) at the axial end portion of the rack bar 3 whose outer diameter Dx gradually decreases toward the axial end portion.

[0075] Thus, in the present embodiment, the convex portion 82 of the holding member 8 has a first convex portion side tapered portion 821 whose outer diameter Dx gradually decreases toward the end side at the axial end portion (first end portion) of the rack bar 3. The first convex portion side tapered portion 821 can guide the introduction of the holding member 8 relative to the first holding member storage portion 113 when assembling the holding member 8, thereby improving the assemblability of the holding member 8.

[0076] Furthermore, in the present embodiment, the portion of the holding member 8 that comes into contact with the second housing 12 protrudes toward the second housing 12 .

[0077] In order to properly join the first housing 11 and the second housing 12, it is necessary to precisely finish the abutting surface of the holding member 8 with the second housing 12 (the second step portion 125). Therefore, in the case where the opposing surface of the holding member 8 with the second housing (the second step portion 125) is formed as a flat shape as a whole, it is necessary to precisely finish the entire opposing surface. In contrast, in the present embodiment, by partially protruding only the protruding portion 813 formed by the portion of the holding member 8 that abuts against the second housing (the second step portion 125), only the end surface of the protruding portion 813 is precisely finished, thereby achieving improved productivity and reduced manufacturing costs of the electric power steering device.

[0078] Furthermore, in the present embodiment, the holding member 8 abuts against the second housing 12 and does not abut against the first housing 11 in a state where the first housing 11 and the second housing 12 are coupled together.

[0079] Thus, in this embodiment, in the state where the first housing 11 and the second housing 12 are combined, the holding member 8 is in contact with the second housing 12 and is not in contact with the first housing 11. Therefore, there is no risk of floating (gap) between the first housing 11 and the second housing 12 due to the accuracy (manufacturing error, etc.) of the holding member 8 interposed between the first housing 11 and the second housing 12. Thus, it is possible to suppress the intrusion of foreign matter into the housing 1 through the gap between the first housing 11 and the second housing 12.

[0080] The present invention is not limited to the configuration described in the above embodiment, and can be freely changed according to the specifications of the electric power steering device to which it is applied, as long as the configuration can achieve the effects of the present invention.

[0081] In particular, for the retaining component 8, the protrusion 82 is not a necessary structure, and although the specific illustration is omitted, the protrusion 82 can also be arranged on the axial end sides of the above-mentioned first end side and the above-mentioned second end side as a structure so as to abut against the second shell (the second step portion 125).

[0082] Furthermore, the first elastic member 91 and the second elastic member 92 corresponding to the elastic members of the present invention do not necessarily need to be arranged at both axial ends of the outer ring portion 71 of the ball bearing 7, and can be configured to be arranged at either side to bias the retaining member 8 toward the second housing (second step portion 125).

[0083] Furthermore, the bearing of the present invention is not limited to the ball bearing 7 disclosed in the present embodiment, and any bearing may be used as long as it can rotatably support the ball nut 641 , and can be arbitrarily changed according to the specifications of the electric power steering device to which it is applied.

Claims

1. An electric power steering device, characterized in that: have: a rack shaft connected to the steering shaft; a transmission mechanism that transmits the steering assist force generated by the electric motor to the rack shaft; A first housing, which accommodates the rack shaft; a second housing which is coupled to the first housing in an opposed manner in the axial direction of the rack shaft and accommodates the transmission mechanism; A ball screw mechanism, which is arranged on the outer peripheral side of the rack shaft; a bearing that supports a rotating portion of the ball screw mechanism so as to be rotatable relative to the first housing; a retaining member, the axial end surface of which is on the opposite side to the bearing abuts against the second housing, and sandwiches and retains the bearing between the first housing and the second housing; An elastic member is disposed in at least one of between the bearing and the holding member or between the bearing and the first housing in the axial direction of the rack shaft.

2. The electric power steering device according to claim 1, characterized in that: The elastic member is arranged both between the bearing and the holding member and between the bearing and the first housing in the axial direction of the rack shaft.

3. The electric power steering device according to claim 1, characterized in that: The holding member is configured to perform positioning relative to the second housing on the outer peripheral side of the bearing.

4. The electric power steering device according to claim 2, characterized in that: The elastic member is arranged between the bearing and the holding member in the axial direction of the rack shaft. The holding member has a convex portion that protrudes toward the bearing in the axial direction of the rack shaft and surrounds the elastic member.

5. The electric power steering device according to claim 4, characterized in that: The holding member has a groove formed at a corner portion formed at a boundary with the convex portion and recessed toward a side opposite to the elastic member in the axial direction of the rack shaft.

6. The electric power steering device according to claim 1, characterized in that: The outer peripheral surface of the holding member is fitted with at least one of the first housing and the second housing.

7. The electric power steering device according to claim 1, characterized in that: The holding member has a convex portion facing the bearing in the radial direction of the rack shaft. The inner diameter of the protrusion is larger than the outer diameter of the bearing.

8. The electric power steering device according to claim 1, characterized in that: The holding member has a convex portion facing the bearing in the radial direction of the rack shaft. The convex portion has a tapered portion at an axial end portion of the rack shaft, the outer diameter of which gradually decreases toward the axial end portion.

9. The electric power steering device according to claim 1, characterized in that: A portion of the holding member that comes into contact with the second housing protrudes toward the second housing.

10. The electric power steering device according to claim 1, characterized in that: The holding member is in contact with the second housing and does not contact with the first housing when the first housing and the second housing are connected.

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