Electric power steering device

Abstract

To provide a housing for an electric power steering device that can ensure uniform tightening axial force.SOLUTION: A housing for an electric power steering device includes: a first housing including a mechanism housing part that has a first end portion covering a portion of a rack bar and a second end portion housing at least a portion of a speed reduction mechanism; and a second housing having a first end portion with a closing portion that closes the mechanism housing part and a second end portion covering a portion of the rack bar. The first housing includes: a rack bar insertion hole through which the rack bar passes in the longitudinal direction; and a cylindrical electric motor shaft insertion hole which is disposed outward in a radial direction of the rack bar insertion hole and through which an electric motor shaft extending from an electric motor passes. The rack bar insertion hole includes an annular tightening portion which is overlapped with an inner circumferential surface of the electric motor shaft insertion hole in the longitudinal direction of the rack bar when the longitudinal axis line of the rack bar is viewed from the outer side in the radial direction and by which a ball screw mechanism is fixed into the rack bar insertion hole.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an electric power steering device. in a position

Background Art

[0002] Patent Document 1 discloses a housing for an electric power steering device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the structure of the housing for the electric power steering device described in Patent Document 1, there is a problem that when under a high load, due to deformation caused by uneven wall thickness on the outer periphery of the screw, the balance of the fastening axial force is disrupted, which may cause the lock nut to loosen. One object of the present invention is to provide an electric power steering device capable of ensuring a uniform fastening axial force. having a housing electric power steering device the position

Means for Solving the Problems

[0005] An electric power steering device according to an embodiment of the present invention includes an electric motor, a speed reduction mechanism that reduces the output of the electric motor, a ball screw mechanism that converts the rotational motion transmitted from the speed reduction mechanism into a linear motion, and a rack bar connected to the ball screw mechanism, and is an electric power steering device comprising a first housing having a first end portion covering a part of the rack bar and a second end portion having a mechanism accommodating portion that accommodates at least a part of the speed reduction mechanism and the ball screw mechanism. wherein an electric motor is fixed having and a second housing that closes the mechanism accommodating portion of the first housing, first ​​​The housing has a rack bar insertion hole portion through which a rack bar is inserted in the longitudinal direction and has an annular fastening portion for fixing a ball screw mechanism. The electric motor shaft insertion portion is arranged to overlap with the fastening portion in the longitudinal direction of the rack bar and has an intermediate portion with a continuous shape formed between the fastening portion and the electric motor shaft insertion hole portion.

Advantages of the Invention

[0006] Therefore, in the electric power steering apparatus of the present invention, one reduction in the strength of the housing is suppressed, The combined deformation during high load caused by the electric motor and the reduction mechanism in the electric power steering apparatus cannot occur, and one and a uniform fastening axial force can be ensured for the housing. can suppress the loosening of the lock nut from occurring

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0008] Hereinafter, modes for carrying out the present invention will be described with reference to the drawings. ​[Embodiment 1] FIG. 1 is an overall configuration diagram of the electric power steering apparatus according to Embodiment 1, and FIG. 2 is an axial sectional view of a ball screw mechanism and a speed reduction mechanism passing through the longitudinal axis of the rack bar according to Embodiment 1.

[0009] (Overall Configuration of Electric Power Steering Apparatus) The electric power steering apparatus 1 according to Embodiment 1 is mounted on a vehicle having an engine as a power source. The electric power steering apparatus 1 includes a steering mechanism 2, an electric motor 3, a ball screw mechanism 4, a speed reduction mechanism 7, and a housing 5. The steering mechanism 2 steers the front wheels which are steering wheels. The steering mechanism 2 includes a rack bar 6. The rack bar 6 is a steering shaft extending in the vehicle body width direction (the left - right direction in the drawing), and is formed using an iron - based metal material such as steel. The rack bar 6 has a main body portion 6a extending in the vehicle body width direction. The rack bar 6 moves in the vehicle body width direction in response to the rotation of a steering shaft 2a connected to a steering wheel (not shown). Front wheels are connected to both ends of the rack bar 6 via tie rods (not shown). The electric motor 3 applies a steering force to the steering mechanism 2. The electric motor 3 is, for example, a three - phase brushless motor. The output of the electric motor 3 is controlled by an electric motor control unit (not shown) according to the steering torque of the driver input to the steering wheel (not shown) and the vehicle speed. An electric motor pulley 9 is attached to an electric motor shaft 8 of the electric motor 3. One end side of an endless belt 10 is wound around the outer periphery of the electric motor pulley 9.

[0010] The ball screw mechanism 4 is provided between the steering mechanism 2 and the electric motor 3. The ball screw mechanism 4 converts the rotational force of the electric motor 3 into a propulsive force of the steering mechanism 2. The ball screw mechanism 4 includes a nut 11. The nut 11 has a substantially cylindrical tubular main body portion 11a surrounding the rack bar 6. A nut pulley 12 is disposed on the outer periphery of the nut 11. The nut pulley 12 rotates integrally with the nut 11. The rotation axis of the nut pulley 12 coincides with the rotation axis of the nut 11 (the longitudinal axis P of the rack bar 6). The rotation axes of the nut 11 and the nut pulley 12 are arranged offset in the radial direction of the electric motor pulley 9 with respect to the rotation axis of the electric motor pulley 9. The diameter of the nut pulley 12 is larger than the diameter of the electric motor pulley 9. The other end side of the endless belt 10 is wound around the outer periphery of the nut pulley 12. The nut pulley 12, the electric motor pulley 9 smaller than the diameter of the nut pulley 12, and the endless belt 10 wound around both pulleys constitute a speed reduction mechanism 7. The nut 11 is supported by the housing 5 so as to be rotatable and non-axially movable. Ball circulation grooves 13 are formed on the inner periphery of the nut 11 and the outer periphery of the rack bar 6. A plurality of balls 14 are arranged in the ball circulation grooves 13. Each ball 14 moves to one end side or the other end side of the ball circulation groove 13 in accordance with the rotation of the nut 11. The ball 14 that reaches one end or the other end of the ball circulation groove 13 due to the rotation of the nut 11 is returned to the other end or one end of the ball circulation groove 13 through the tube 4a which is a circulation mechanism.

[0011] The housing 5 is formed by die casting using an aluminum alloy. The housing 5 includes a first housing 16 having a first end portion 16a covering a part of the rack bar 6 and a mechanism accommodating portion 162 in which the second end portion 16b accommodates at least a part of the ball screw mechanism 4 and the speed reduction mechanism 7, and a first end portion 17a having a mechanism accommodating portion 171 in which at least a part of the ball screw mechanism 4 and the speed reduction mechanism 7 are accommodated, and a closing portion 172 closing the mechanism accommodating portion 162 of the first housing 16, and a second end portion 17b covering a part of the rack bar 6, and a second housing 17. Further, the first housing 16 has a rack bar insertion hole portion 161 through which the rack bar 6 is inserted in the longitudinal direction, a cylindrical electric motor shaft insertion hole portion 167 through which an electric motor shaft 8 supported by the electric motor housing 31 and extending from the electric motor 3 is inserted outside the radial direction of the rack bar insertion hole portion 161, and when the longitudinal axis P of the rack bar 6 is viewed from the outside in the radial direction, an annular female screw portion (fastening portion) 164 with which a lock nut 40 that overlaps the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 in the longitudinal direction of the rack bar 6 is screwed to fix the ball screw mechanism 4 to the rack bar insertion hole portion 167. Thus, since the female screw portion 164 is annularly connected, it is possible to suppress the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed. In addition, since the inner peripheral surface of the cylindrical electric motor shaft insertion hole portion 167 is also annularly connected, it has a structure that resists the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed, and the diameter expansion deformation of the female screw portion 164 can be further suppressed.

[0012] The first housing 16 and the second housing 17 are joined at the second end portion 16b side of the mechanism accommodating portion 162 of the first housing 16 and the first end portion 17a side of the closing portion 172 of the second housing 17, and have a joint surface 110 fixed by a plurality of bolts (not shown). The joint surface 110 is provided via an extension portion 163 formed on the second end portion 16b side of the first housing 16 rather than the female screw portion 164. Thus, by providing the extension portion 163 where the fastening load when the lock nut 40 is screwed into the female screw portion 164 does not directly act, the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed can be further suppressed.

[0013] The electric motor shaft 8 of the electric motor 3 is disposed at a position offset in the radial direction with respect to the rotation axis (longitudinal axis P of the rack bar 6) of the nut 11. The electric motor shaft 8 is supported by a ball bearing 18 fixed in an electric motor housing 31 fixed to the first housing 16. The motor pulley 9 is formed in a cylindrical shape using a metal material. The motor pulley 9 has a spline hole 9a at its radial center. The spline hole 9a is fitted with a spline 8a formed at the tip of the electric motor shaft 8.

[0014] The nut 11 is rotatably provided in the mechanism housing portion 162 of the first housing 16 and the mechanism housing portion 171 of the second housing 17. In the cylindrical main body portion 11a of the nut 11, the central portion in the longitudinal axis P direction of the rack bar 6 is formed with a smaller diameter than both end portions in the longitudinal axis P direction of the rack bar 6. On the inner circumference of the central portion in the longitudinal axis P direction of the rack bar 6 in the cylindrical main body portion 11a, a spiral nut-side ball screw groove 19 is formed. On the other hand, on the outer circumference of the main body portion 6a of the rack bar 6, a spiral rack-bar-side ball screw groove 20 is formed. The nut-side ball screw groove 19 and the rack-bar-side ball screw groove 20 constitute the ball circulation groove 13. On the right end in the longitudinal axis P direction of the rack bar 6 of the nut 11, an inner race 21a of the ball bearing 21 is integrally formed. The ball bearing 21 supports the nut 11 so as to be rotatable in the circumferential direction with respect to the first housing 16. The ball bearing 21 has an inner race 21a, an outer race 21b, and balls 21c. The outer race 21b is fixed to the annular female screw portion 164 of the first housing 16 by a lock nut 40. The balls 21c are interposed between the inner race 21a and the outer race 21b.

[0015] The nut pulley 12 is formed in a bottomed cup shape using a metal material. The nut pulley 12 has a hub portion 23 and a winding portion 24. The hub portion 23 is located at the left end in the longitudinal axis P direction of the rack bar 6 of the nut pulley 12 as shown in the figure. The hub portion 23 is formed in a substantially annular disk shape. The hub portion 23 is fastened to the nut 11 by four screws 28. The hub portion 23 has a rack bar insertion hole 29 at its radial center. The rack bar 6 passes through the rack bar insertion hole 29. The winding portion 24 extends from the outer periphery of the hub portion 23 in the rightward direction in the drawing along the longitudinal axis P of the rack bar 6. The winding portion 24 is formed in a cylindrical shape. An endless belt 10 is wound around the winding portion 24.

[0016] FIG. 3 is a plan view of the first housing of Embodiment 1 as viewed from the second end side, FIG. 4 is a cross-sectional view taken along the line D-D of FIG. 3, FIG. 5 is a cross-sectional view taken along the line E-E of FIG. 3, and FIG. 6 is a cross-sectional view taken along the line F-F of FIG. 3.

[0017] (Detailed Structure of the First Housing) On the first end portion 16a side of the first housing 16 of the extension portion 163, an intermediate portion 165 that is continuously formed with the extension portion 163 is formed between the female screw portion 164 and the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167. In the intermediate portion 165, a pair of recesses 166 having bottoms are formed toward the first end portion 16a side of the first housing 16. In this way, by providing the pair of recesses 166, the weight of the first housing 16 can be reduced and the generation of voids can be suppressed. Further, since the pair of recesses 166 have bottoms and do not penetrate, when the motor housing 31 is fastened to the first housing 16, the first housing 16 can be used as a seat surface for sealing. Also, the pair of recesses 166 are formed in the circumferential direction of the electric motor shaft insertion hole portion 167 along the electric motor shaft insertion hole portion 167, respectively. Furthermore, the circumferential length e of the recess 166 in the circumferential direction of the motor shaft insertion hole portion 167 is formed to be larger than the radial length d of the recess 166 in the electric motor shaft insertion hole portion 167. Therefore, if the radial length d of the electric motor shaft insertion hole portion 167 of the recess 166 becomes too large, the portion away from the electric motor shaft insertion hole portion 167 of the recess 166 will taper, and the durability of the mold for molding the recess 166 will decrease. However, since the radial length d of the electric motor shaft insertion hole portion 167 of the recess 166 is formed to be smaller than the circumferential length e of the motor shaft insertion hole portion 167 of the recess 166, it is possible to suppress a decrease in the durability of the mold for molding the recess 166.

[0018] FIG. 7 is an enlarged view of the portion taken along arrow C in FIG. 3.

[0019] The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is taken from the radially outer side (see FIG. 4). The length b of the second proximity portion 101 where the rack bar insertion hole portion 161 on the second end portion 16b side and the recess 166 on the second end portion 16b side are closest is formed to be longer than the length a of the first proximity portion 100 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side are closest. Thereby, the first proximity portion 100 can be supported in an arch shape by the electric motor shaft insertion hole portion 167. Since the strength of the second proximity portion 101 is reduced due to the presence of the recess 166, by forming the length b of the second proximity portion 101 to be longer than the length a of the first proximity portion 100, it is possible to suppress a decrease in the strength of the second proximity portion 101.

[0020] Further, the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is taken from the radially outer side (see FIG. 5). The length a of the first proximity portion 100 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side are closest to each other is shorter than the length c of the third proximity portion 103 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side, which are located on the concave portion 166 side in the circumferential direction of the longitudinal axis P of the rack bar 6, are close to each other. Therefore, by forming it so as to gradually increase in thickness from the first proximity portion 100 toward the third proximity portion 103, stress concentration on the first proximity portion 100 can be alleviated.

[0021] FIG. 8 is an enlarged cross-sectional view of the portion viewed in the direction of arrow G in FIG. 4, FIG. 9 is an enlarged cross-sectional view of the portion viewed in the direction of arrow H in FIG. 5, and FIG. 10 is an enlarged cross-sectional view of the portion viewed in the direction of arrow I in FIG. 6.

[0022] As shown in FIG. 8, the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is viewed from the radially outer side. The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 is formed to be inclined by an angle α toward the first end portion 16a in the longitudinal axis P direction of the rack bar 6. The length a of the first proximity portion 100 on the second end portion 16b side between the rack bar insertion hole portion 161 and the electric motor shaft insertion hole portion 167 is formed to gradually increase toward the length a1 of the first proximity portion 100 on the first end portion 16a side in the longitudinal axis P direction of the rack bar 6 (a1 > a). Therefore, since the first proximity portion 100 is formed to gradually increase from the second end portion side to the first end portion 16a side in the longitudinal axis P direction of the rack bar 6, it becomes less likely to bend, and the internal stress on the first end portion 16a side of the first proximity portion 100 in the longitudinal axis P direction of the rack bar 6 can be alleviated. Also, as shown in FIG. 9, the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 is formed to be inclined by an angle γ toward the first end portion 16a side in the longitudinal axis P direction of the rack bar 6, and the length c of the third proximity portion 102 on the second end portion 16b side between the rack bar insertion hole portion 161 and the electric motor shaft insertion hole portion 167 is formed to gradually increase toward the length c1 of the third proximity portion 102 on the first end portion 16a side in the longitudinal axis P direction of the rack bar 6 (c1 > c), and the internal stress on the first end portion 16a side of the third proximity portion 102 in the longitudinal axis P direction of the rack bar 6 can be relaxed.

[0023] Furthermore, as shown in FIG. 10, the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 and the inner peripheral surface 166a of the concave portion 166 extend to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is viewed from the radially outward side, and the inner peripheral surface 166a of the concave portion 166 is formed to be inclined by an angle β toward the first end portion 16a side in the longitudinal axis P direction of the rack bar 6, and the length b of the second proximity portion 101 on the second end portion 16b side between the rack bar insertion hole portion 161 and the concave portion 166 is formed to gradually increase toward the length b1 of the second proximity portion 101 on the first end portion 16a side in the longitudinal axis P direction of the rack bar 6 (b1 > b). Therefore, since the length of the second proximity portion 101 between the rack bar insertion hole portion 161 and the concave portion 166 on the second end portion 16b side is gradually increased toward the first end portion 16a side in the longitudinal axis P direction of the rack bar 6, it becomes difficult to bend, and the internal stress on the first end portion 16a side of the second proximity portion 101 between the rack bar insertion hole portion 161 and the concave portion 166 in the longitudinal axis P direction of the rack bar 6 can be relaxed.

[0024] Next, the operation and effect will be described. The operation and effect of the steering load control device 1 of Embodiment 1 are listed below. (1) The first housing 16 has a rack bar insertion hole portion 161 through which the rack bar 6 is inserted in the longitudinal direction, and a cylindrical electric motor shaft insertion hole portion 167 that is supported by the electric motor housing 31 and through which the electric motor shaft 8 extending from the electric motor 3 is inserted radially outward of the rack bar insertion hole portion 161. In the rack bar insertion hole portion 167, when the longitudinal axis P of the rack bar 6 is viewed from the radially outward side, it overlaps with the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 in the longitudinal direction of the rack bar 6, and an annular female screw portion (fastening portion) 164 is provided with which a lock nut 40 for fixing the ball screw mechanism 4 to the rack bar insertion hole portion 167 is screwed. Therefore, since the female screw portion 164 is annularly connected, it is possible to suppress the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed. Also, since the inner peripheral surface of the cylindrical electric motor shaft insertion hole portion 167 is also annularly connected, it has a structure that resists the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed, and the diameter expansion deformation of the female screw portion 164 can be further suppressed.

[0025] (2) The first housing 16 and the second housing 17 are joined at the second end portion 16b side of the mechanism accommodating portion 162 of the first housing 16 and the first end portion 17a side of the closing portion 172 of the second housing 17, and have a joint surface 110 fixed by a plurality of bolts (not shown). The joint surface 110 is provided via an extension portion 163 formed on the second end portion 16b side of the first housing 16 rather than the female screw portion 164. Therefore, by providing the extension portion 163 where the fastening load when the lock nut 40 is screwed into the female screw portion 164 does not directly act, the diameter expansion deformation of the female screw portion 164 due to the fastening load when the lock nut 40 is screwed can be further suppressed.

[0026] (3) On the first end portion 16a side of the first housing 16 of the extension portion 163, an intermediate portion 165 that is continuously formed with the extension portion 163 is formed between the female screw portion 164 and the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167. In the intermediate portion 165, a pair of recesses 166 having bottoms are formed toward the first end portion 16a side of the first housing 16. Therefore, by providing the pair of recesses 166, it is possible to reduce the weight of the first housing 16 and suppress the generation of nests.

[0027] (4) The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is viewed from the radially outer side. The length b of the second proximity portion 101 where the rack bar insertion hole portion 161 on the second end portion 16b side and the recess 166 on the second end portion 16b side are closest to each other is formed to be longer than the length a of the first proximity portion 100 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side are closest to each other. Therefore, the first proximity portion 100 can be supported in an arch shape by the electric motor shaft insertion hole portion 167. Since the strength of the second proximity portion 101 is reduced due to the presence of the recess 166, by forming the length b of the second proximity portion 101 to be longer than the length a of the first proximity portion 100, the reduction in the strength of the second proximity portion 101 can be suppressed.

[0028] (5) The pair of recesses 166 are configured to have bottoms. Therefore, since the recess 166 does not penetrate, when the motor housing 31 is fastened to the first housing 16, the first housing 16 can be used as a sealing seat surface.

[0029] (6) The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is viewed from the radially outer side. The length a of the first proximity portion 100 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side are closest is shorter than the length c of the third proximity portion 103 where the rack bar insertion hole portion 161 on the second end portion 16b side and the electric motor shaft insertion hole portion 167 on the second end portion 16b side are close to each other and located on the concave portion 166 side in the circumferential direction of the longitudinal axis P of the rack bar 6, starting from the first proximity portion 100 where they are closest. Therefore, by forming it so that the thickness gradually increases from the first proximity portion 100 toward the third proximity portion 103, stress concentration on the first proximity portion 100 can be alleviated.

[0030] (7) The circumferential length e of the motor shaft insertion hole portion 167 of the concave portion 166 is formed to be larger than the radial length d of the motor shaft insertion hole portion 167 of the concave portion 166. Therefore, if the radial length d of the motor shaft insertion hole portion 167 of the concave portion 166 becomes too large, the portion away from the motor shaft insertion hole portion 167 of the concave portion 166 becomes tapered, and the durability of the molding die for molding the concave portion 166 decreases. However, since the radial length d of the motor shaft insertion hole portion 167 of the concave portion 166 is formed to be smaller than the circumferential length e of the motor shaft insertion hole portion 167 of the concave portion 166, it is possible to suppress a decrease in the durability of the molding die for molding the concave portion 166.

[0031] (8) When the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 is viewed from the radially outward direction of the longitudinal axis P of the rack bar 6, it extends to a position facing the female screw portion 164. The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 is formed to be inclined by an angle α toward the first end portion 16a in the longitudinal axis P direction of the rack bar 6. The length a of the first proximity portion 100 on the second end portion 16b side between the rack bar insertion hole portion 161 and the electric motor shaft insertion hole portion 167 is formed to gradually increase toward the length a1 of the first proximity portion 100 on the first end portion 16a side in the longitudinal axis P direction of the rack bar 6 (a1 > a). Therefore, since the first proximity portion 100 is gradually formed larger toward the first end portion 16a in the longitudinal axis P direction of the rack bar 6, it becomes less likely to bend, and the internal stress on the first end portion 16a side of the rack bar 6 in the longitudinal axis P direction of the first proximity portion 100 can be relieved.

[0032] (9) When the inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 is viewed from the radially outward direction of the longitudinal axis P of the rack bar 6, it is formed to be inclined by an angle γ toward the first end portion 16a in the longitudinal axis P direction of the rack bar 6. The length c of the third proximity portion 102 on the second end portion 16b side between the rack bar insertion hole portion 161 and the electric motor shaft insertion hole portion 167 is formed to gradually increase toward the length c1 of the third proximity portion 102 on the first end portion 16a side in the longitudinal axis P direction of the rack bar 6 (c1 > c). Therefore, the internal stress on the first end portion 16a side of the rack bar 6 in the longitudinal axis P direction of the third proximity portion 102 can be relieved.

[0033] The inner peripheral surface 167a of the electric motor shaft insertion hole portion 167 extends to a position facing the female screw portion 164 when the longitudinal axis P of the rack bar 6 is viewed from the radially outer side. The inner peripheral surface 166a of the recess 166 is formed to be inclined by an angle β toward the first end portion 16a side in the direction of the longitudinal axis P of the rack bar 6. The length b of the second end portion 16b side of the second proximity portion 101 between the rack bar insertion hole portion 161 and the recess 166 is formed to gradually increase toward the length b1 of the first end portion 16a side of the second proximity portion 101 in the direction of the longitudinal axis P of the rack bar 6 (b1 > b). Therefore, since the length of the second end portion 16b side of the second proximity portion 101 between the rack bar insertion hole portion 161 and the recess 166 is gradually increased toward the first end portion 16a in the direction of the longitudinal axis P of the rack bar 6, it becomes difficult to bend, and the internal stress on the first end portion 16a side in the direction of the longitudinal axis P of the rack bar 6 of the second proximity portion 101 between the rack bar insertion hole portion 161 and the recess 166 can be relieved.

[0034] 〔Other Embodiments〕 As described above, the embodiments for carrying out the present invention have been described. However, the specific configuration of the present invention is not limited to the configuration of the embodiments, and design changes and the like within the scope not departing from the gist of the invention are also included in the present invention.

[0035] The technical idea that can be grasped from the embodiments described above will be described below. In one aspect, the housing for an electric power steering apparatus, the electric power steering apparatus includes an electric motor, a speed reduction mechanism that reduces the output of the electric motor, a ball screw mechanism that converts the rotational motion transmitted from the speed reduction mechanism into a linear motion, and a rack bar connected to the ball screw mechanism. The housing includes a first housing having a first end portion that covers a part of the rack bar and a second end portion that has a mechanism accommodating portion for accommodating at least a part of the speed reduction mechanism and the ball screw mechanism, and a second housing having a first end portion that has a closing portion for closing the mechanism accommodating portion and a second end portion that covers a part of the rack bar. The first housing has a rack bar insertion hole portion through which the rack bar is inserted in the longitudinal direction, and a cylindrical electric motor shaft insertion hole portion through which an electric motor shaft extending from the electric motor is inserted radially outward of the rack bar insertion hole portion. In the rack bar insertion hole portion, when the longitudinal axis of the rack bar is viewed from the radially outward, an annular fastening portion that overlaps the inner peripheral surface of the electric motor shaft insertion hole portion in the longitudinal direction of the rack bar and fixes the ball screw mechanism to the rack bar insertion hole portion is provided. In a more preferable aspect, in the above aspect, the first housing and the second housing have a joint surface that joins at the second end portion side of the mechanism accommodating portion of the first housing and the first end portion side of the closing portion of the second housing, and the joint surface is provided via an extension portion formed on the second end portion side of the first housing rather than the fastening portion. In a more preferable aspect, in the above aspect, on the first end portion side of the extension portion, there is an intermediate portion that is continuously formed between the fastening portion and the inner peripheral surface of the electric motor shaft insertion hole portion, and the intermediate portion is provided with a recess formed toward the first end portion side of the first housing.

[0036] In a more preferred embodiment, in the above-described embodiment, the inner peripheral surface of the electric motor shaft insertion hole portion extends to a position facing the fastening portion when the longitudinal axis of the rack bar is viewed from the radially outer side, and the length of the second proximity portion where the rack bar insertion hole portion on the second end side of the first housing and the recess on the second end side of the first housing are closest to each other is longer than the length of the first proximity portion where the rack bar insertion hole portion on the second end side of the first housing and the electric motor shaft insertion hole portion on the second end side of the first housing are closest to each other. In yet another preferred embodiment, in any of the above embodiments, a bottom portion is formed in the recess. In yet another preferred embodiment, in any of the above embodiments, the inner peripheral surface of the electric motor shaft insertion hole portion extends to a position facing the fastening portion when the longitudinal axis of the rack bar is viewed from the radially outer side, and the length of the first proximity portion where the rack bar insertion hole portion on the second end side of the first housing and the electric motor shaft insertion hole portion on the second end side of the first housing are closest to each other is shorter than the length of the third proximity portion where the rack bar insertion hole portion and the electric motor shaft insertion hole portion located on the recess side in the circumferential direction of the longitudinal axis of the rack bar from the first proximity portion are close to each other.

[0037] In yet another preferred embodiment, in any of the above embodiments, the recess is formed in the circumferential direction of the electric motor shaft insertion hole portion along the electric motor shaft insertion hole portion, and the circumferential length of the recess in the electric motor shaft insertion hole portion is formed to be longer than the radial length of the motor shaft insertion hole portion of the recess. In yet another preferred embodiment, in any of the above embodiments, when the longitudinal axis of the rack bar is viewed from the radially outer side, the inner peripheral surface of the electric motor shaft insertion hole portion extends to a position facing the fastening portion, and the length of the first proximity portion or the third proximity portion between the rack bar insertion hole portion and the electric motor shaft insertion hole portion gradually increases from the second end side to the first end side of the first housing. In yet another preferred embodiment, in any of the above embodiments, the inner peripheral surface of the electric motor shaft insertion hole portion and the inner peripheral surface of the concave portion extend to a position facing the fastening portion when the longitudinal axis of the rack bar is viewed from the radially outer side, and the length of the second proximity portion between the electric motor shaft insertion hole portion and the concave portion gradually increases from the second end side to the first end side of the first housing.

Explanation of Signs

[0038] 1 Electric power steering device 3 Electric motor 3a Electric motor shaft 4 Ball screw mechanism 5 Housing 6 Rack bar 7 Reduction mechanism 16 First housing 16a First end 16b Second end 161 Rack bar insertion hole portion 162 Mechanism accommodation portion 163 Extension portion 164 Female screw portion (fastening portion) 165 Intermediate portion 166 Concave portion 167 Electric motor shaft insertion hole portion 167a Inner peripheral surface 17 Second housing 17a First end 17b Second end 172 Closing portion 100 First proximity portion 101 Second proximity portion 102 Third proximity portion 110 Joint surface a Length of the first proximity part on the second end side of the first housing a1 Length of the first proximity part on the first end side of the first housing b Length of the second proximity part on the second end side of the first housing b1 Length of the second proximity part on the first end side of the first housing c Length of the third proximity part on the second end side of the first housing c1 Length of the third proximity part on the second end side of the first housing d Radial length of the electric motor shaft insertion hole part of the recess e Circumferential length of the electric motor shaft insertion hole part of the recess P Longitudinal axis of the rack bar

Claims

1. An electric power steering apparatus comprising: an electric motor; a speed reduction mechanism for reducing the output of the electric motor; a ball screw mechanism for converting the rotational motion transmitted from the speed reduction mechanism into a linear motion; and a rack bar connected to the ball screw mechanism, a first housing having a first end portion covering a part of the rack bar and a second end portion having a mechanism accommodating portion for accommodating at least a part of the speed reduction mechanism and the ball screw mechanism, and the electric motor being fixed thereto; and a second housing closing the mechanism accommodating portion of the first housing, The first housing, has a rack bar insertion hole portion through which the rack bar is inserted in the longitudinal direction and having an annular fastening portion for fixing the ball screw mechanism, and an annular electric motor shaft insertion hole portion through which an electric motor shaft extending from the electric motor is inserted, outside the radial direction of the rack bar insertion hole portion, and has, the electric motor shaft insertion hole portion is arranged to overlap with the fastening portion in the longitudinal direction of the rack bar, and has an intermediate portion formed between the fastening portion and the electric motor shaft insertion hole portion and having a continuous shape, The electric power steering apparatus is characterized by this.

2. The electric power steering apparatus according to claim 1, wherein a recess is provided in the intermediate portion and formed toward the first end portion side. The electric power steering apparatus is characterized by this.

3. The electric power steering apparatus according to claim 2, wherein the recess has a bottom and is formed along the circumferential direction in the electric motor shaft insertion hole portion. The electric power steering apparatus is characterized by this.

4. The electric power steering apparatus according to claim 2, The concave portion is formed such that the circumferential length in the electric motor shaft insertion hole portion is larger than the radial length in the electric motor shaft insertion hole portion. An electric power steering apparatus characterized by the above.

5. The electric power steering apparatus according to claim 2, The inner peripheral surface of the electric motor shaft insertion hole portion extends to a position facing the fastening portion when the longitudinal axis of the rack bar is viewed from the radially outer side. Regarding the rack bar insertion hole portion and the electric motor shaft insertion hole portion on the second end side, the length of the first proximity portion where the rack bar insertion hole portion and the electric motor shaft insertion hole portion are closest is shorter than the length of the third proximity portion where the rack bar insertion hole portion and the electric motor shaft insertion hole portion located on the concave portion side in the circumferential direction of the longitudinal axis of the rack bar are close to each other, among the rack bar insertion hole portion and the electric motor shaft insertion hole portion on the second end side. An electric power steering apparatus characterized by the above.

6. The electric power steering apparatus according to claim 1, The intermediate portion has a continuous arch shape. An electric power steering apparatus characterized by the above.

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