JP6777360B2 - Power steering device - Google Patents

Description

The present invention relates to a power steering device.

Patent Document 1 discloses a power steering device that transmits a driving force of an electric motor to a ball screw mechanism via an input pulley, a belt, and an output pulley and converts it into an axial thrust of a rack shaft. The output pulley is fastened to the nut of the ball screw mechanism by a screw.

Japanese Unexamined Patent Publication No. 2014-184739

In the above-mentioned conventional power steering device, since there is a portion of the output pulley where the axial cross-sectional area suddenly changes from the head of the screw to the axial force of the screw, stress concentration occurs in the portion and the maximum generated stress is increased. There was a problem of getting bigger.
One of the objects of the present invention is to provide a power steering device capable of reducing the maximum generated stress of the output pulley.

In the power steering device according to the embodiment of the present invention, the output pulley has a thin wall portion provided in a predetermined region on the radial outer side of the screw insertion hole, and is adjacent to the thin wall portion in the circumferential direction and has a larger wall thickness than the thin wall portion. It has a thick portion and a centering portion that comes into contact with the outer peripheral surface of the nut.

Therefore, in the present invention, the maximum generated stress of the output pulley can be reduced.
Further, since the centering portion comes into contact with the outer peripheral surface of the nut, the rotation axis of the output pulley can be brought closer to the rotation axis of the nut, so that workability at the time of assembly can be improved.

It is sectional drawing in the axial direction of the power steering apparatus 1 of Embodiment 1. FIG. It is a cross-sectional view of S1-S1 in FIG. It is sectional drawing in the axial direction of the ball screw mechanism 4 passing through the rotation axis of a nut 11. It is a front view of the output pulley 12. It is a rear view of the output pulley 12. It is sectional drawing in the axial direction of the output pulley 12 passing through the rotation axis of a nut 11. It is sectional drawing in the axial direction of the main part of the ball screw mechanism 4 which shows the state which the X-axis positive direction end part of the nut 11 is press-fitted inside each centering part 41. It is an enlarged view of the main part of FIG. It is an enlarged view of the main part of FIG.

[Embodiment 1]
FIG. 1 is an axial sectional view of the power steering device 1 of the first embodiment, and FIG. 2 is a sectional view taken along the line S1-S1 of FIG.
The power steering device 1 is mounted on a vehicle powered by an engine. The power steering device 1 includes a steering mechanism 2, an electric motor 3, a ball screw mechanism 4, and a housing 5.
The steering mechanism 2 steers the front wheels, which are the steering wheels. The steering mechanism 2 has a rack bar (steering shaft) 6 extending in the vehicle body width direction. The rack bar 6 is formed by using an iron-based metal material such as a steel material. The rack bar 6 moves in the vehicle body width direction according to the rotation of the steering shaft connected to the steering wheel (not shown). The ends of a pair of tie rods 7 and 7 are connected to both ends of the rack bar 6. The front wheels are connected to the pair of tie rods 7 and 7.
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 a motor control unit (not shown) according to the steering torque of the driver and the vehicle speed input to the steering wheel (not shown). An input pulley 9 is attached to the motor shaft 8 of the electric motor 3. One end side of the belt (transmission member) 10 is wound around the outer circumference of the input pulley 9.

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 the propulsive force of the steering mechanism 2. The ball screw mechanism 4 has a nut 11. The nut 11 is formed in a substantially cylindrical shape surrounding the rack bar 6. An output pulley 12 is fixed to the outer circumference of the nut 11. The rotation axis of the output pulley 12 coincides with the rotation axis of the nut 11. The rotation axes of the nut 11 and the output pulley 12 are arranged offset in the radial direction of the input pulley 9 with respect to the rotation axis of the input pulley 9. The outer diameter of the output pulley 12 is larger than the outer diameter of the input pulley 9. The other end of the belt 10 is wound around the outer circumference of the output pulley 12. The nut 11 is supported with respect to the housing 5 so as to be rotatable and not movable in the axial direction. A ball circulation groove 13 is formed on the inner circumference of the nut 11 and the outer circumference of the rack bar 6. A plurality of balls 14 are arranged in the ball circulation groove 13. Each ball 14 moves to one end side or the other end side of the ball circulation groove 13 according to the rotation of the nut 11. The ball 14 that has reached 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 via the tube (see FIG. 3) 4a which is a circulation mechanism.

The housing 5 is formed by die casting using an aluminum alloy. The housing 5 includes a steering mechanism housing 15, a motor housing 16, and a ball screw mechanism housing 17. The steering mechanism housing 15 houses a part of the steering mechanism 2 (a part of the steering shaft, a rack bar 6, etc.) inside. The inner ends of the dust boots 18 in the vehicle width direction are fixed to both ends of the steering mechanism housing 15 in the vehicle width direction. The dust boot 18 is formed in a bellows ring using rubber or the like. The outer end of the dust boot 18 in the vehicle width direction is fixed to the tie rod 7. The motor housing 16 houses the electric motor 3 inside. The ball screw mechanism housing 17 houses the ball screw mechanism 4 inside.

Next, the nut 11 and the output pulley 12 of the first embodiment will be described in detail. In FIG. 1, the X-axis is set in the axial direction of the rack bar 6, the direction from the steering mechanism 2 side to the ball screw mechanism 4 side is the X-axis positive direction, the X-axis orthogonal direction is the radial direction, and the X-axis. The surrounding direction is defined as the circumferential direction.
FIG. 3 is an axial cross-sectional view of the ball screw mechanism 4 passing through the rotation axis of the nut 11.
The central portion of the nut 11 in the X-axis direction is formed to have a smaller diameter than both ends in the X-axis direction. In the nut 11, a spiral nut-side ball screw groove 19 is formed on the inner circumference of the central portion in the X-axis direction. On the other hand, a spiral rack bar side ball screw groove (steering shaft side ball screw groove) 20 is formed on the outer periphery of the rack bar 6. The nut-side ball screw groove 19 and the rack bar-side ball screw groove 20 form the ball circulation groove 13. The inner race 21a of the ball bearing 21 is integrally formed at the X-axis negative end of the nut 11. The ball bearing 21 rotatably supports the nut 11 with respect to the ball screw mechanism housing 17. The ball bearing 21 has an inner race 21a, an outer race 21b and a ball 21c. The outer race 21b is fixed to the ball screw mechanism housing 17. The ball 21c intervenes between the inner race 21a and the outer race 21b. Four female threaded portions 22 are formed at the X-axis positive end of the nut 11. The female thread portion 22 extends along the X-axis direction. The female screw portions 22 are arranged at 90 ° intervals in the circumferential direction.

FIG. 4 is a front view of the output pulley 12, FIG. 5 is a rear view of the output pulley 12, and FIG. 6 is an axial sectional view of the output pulley 12 passing through the rotation axis of the nut 11.
The output pulley 12 is formed in a bottomed cup shape by injection molding using a resin material. In the first embodiment, a disc gate (diaphragm gate) type is adopted as a gate at the time of injection molding. The output pulley 12 has a hub portion 23 and a winding portion 24. The hub portion 23 is located at the X-axis positive end of the output pulley 12. The hub portion 23 is formed in a substantially annular disk shape. Four screw insertion holes 23c penetrate the hub portion 23 in the X-axis direction. The screw insertion holes 23c are arranged at 90 ° intervals in the circumferential direction. A screw 25 is inserted into each screw insertion hole 23c from the positive direction side of the X-axis. The screw 25 fastens the output pulley 12 and the nut 11. The screw 25 has a head portion 26 and a shaft portion 27. The outer shape of the head 26 is substantially circular when viewed from the X-axis direction. A male threaded portion (male threaded groove) 27a is formed on the shaft portion 27. The male threaded portion 27a is fitted into the female threaded portion 22 of the nut 11 by a screwing action. A washer 28 is interposed between the screw 25 and the outer surface (X-axis positive side surface) 23a of the hub portion 23. The washer 28 is formed in an annular disk shape. The outer diameter of the washer 28 is larger than the outer diameter of the head 26. The hub portion 23 has a rack bar insertion hole (steering shaft insertion hole) 29 at the center thereof in the radial direction. The rack bar 6 penetrates through the rack bar insertion hole 29.

The winding portion 24 extends in the negative direction of the X-axis from the outer circumference of the hub portion 23. The winding portion 24 has an outer cylinder portion 30, an inner cylinder portion 31, and 16 bridge portions 32. The outer cylinder portion 30 is formed in a cylindrical shape. A belt 10 is wound around the outer cylinder portion 30. The inner cylinder portion 31 is located inside the outer cylinder portion 30 in the radial direction. The inner cylinder portion 31 is formed in a cylindrical shape having a diameter smaller than that of the outer cylinder portion 30. The X-axis positive end of the outer cylinder 30 is connected to the inner cylinder 31. The bridge portion 32 extends radially between the outer cylinder portion 30 and the inner cylinder portion 31 and connects the outer cylinder portion 30 and the inner cylinder portion 31. The bridge portions 32 are arranged at intervals of 22.5 ° in the circumferential direction.
The winding portion 24 and the hub portion 23 are smoothly connected by the connecting portion 33. In the axial cross section of the output pulley 12 passing through the rotation axis of the nut 11, the connecting portion 33 is formed in an arc shape. Here, in FIG. 6, the inferior angle of the angle (relative angle) formed by the tangent line La of the inner side surface 33a of the connecting portion 33 and the rotation axis Lb of the nut 11 gradually increases from the rotation axis Lb toward the outside in the radial direction. The portion that becomes smaller and becomes 45 ° is defined as the boundary portion 34 between the hub portion 23 and the winding portion 24. Further, the region around the screw insertion hole 23c of the hub portion 23, which overlaps the head portion 26 of the screw 25 in the radial direction, is defined as the fastened portion 35. The fastened portion 35 is a portion that receives the axial force of the screw 25 from the head 26 of the screw 25 when the output pulley 12 and the nut 11 are fastened by the screw 25. The fastened portion 35 is located radially inside the boundary portion 34. The outer peripheral edge of the washer 28 radially overlaps the boundary portion 34.

The hub portion 23 of the output pulley 12 has a protruding portion 36 on its inner side surface (X-axis negative direction side surface) 23b. The protruding portion 36 projects from the inner side surface 23b in the negative direction of the X-axis by a predetermined length. The protrusion 36 has four radial protrusions 37 and an annular protrusion 38. The radial protrusions 37 are arranged at 90 ° intervals in the circumferential direction in accordance with the position of the screw insertion hole 23c. Each radial protrusion 37 abuts substantially flush with the X-axis positive end of the nut 11. The radial protrusion 37 extends in the radial direction and has a shape including the entire projected area of the fastened portion 35 when viewed from the X-axis direction. The annular protrusion 38 is arranged at the opening edge of the rack bar insertion hole 29. The annular protrusion 38 connects to the radial medial end of each radial protrusion 37.
The hub portion 23 has four thin-walled portions 39 and eight thick-walled portions 40 on its inner side surface 23b. The thin portion 39 is a predetermined region portion radially outside the screw insertion hole 23c of the radial protrusion 37. The width (circumferential length) of the thin portion 39 is wider than the width of the radial protrusion 37. The thick portion 40 is arranged at the same radial position as the thin portion 39. The thick portion 40 is adjacent to the thin portion 39 in the circumferential direction. The thick portion 40 projects by a predetermined length in the negative direction of the X axis from the thin portion 39, that is, the radial protrusion 37. That is, when the material thickness of the hub portion 23 in the X-axis direction is taken as the wall thickness, the wall thickness of the thick portion 40 is formed to be larger than that of the thin portion 39 (radial protrusion 37).
Each thick portion 40 has a centering portion 41 inside in the radial direction. The centering portion 41 has an arc shape that is convex inward in the radial direction. As shown in FIG. 7, each centering portion 41 is in pressure contact with the outer peripheral surface 11a of the X-axis positive end portion of the nut 11. That is, the X-axis positive end of the nut 11 is press-fitted inside the centering portion 41.

Next, the operation and effect of the power steering device 1 of the first embodiment will be described.
8 is an enlarged view of a main part of FIG. 5, and FIG. 9 is an enlarged view of a main part of FIG.
When the nut 11 and the output pulley 12 are fastened with the screw 25, if the tightening torque of the screw 25 is increased, the parts of the output pulley 12 to be fastened 35 that come into contact with the nut 11 (head 26 and nut). The portion sandwiched between the 11s) is compressively deformed, and the portion not in contact with the nut 11 (the portion not sandwiched between the head 26 and the nut 11) is bent and deformed in the negative X-axis direction. In the conventional output pulley, the boundary portion connecting the hub portion and the winding portion overlaps the fastened portion in the radial direction. The boundary portion is a portion where the axial cross-sectional area of the output pulley changes abruptly, that is, a portion where the rigidity suddenly changes. Therefore, in the conventional output pulley, stress concentration occurs in the fastened portion, and the maximum generated stress in the fastened portion increases. Here, the output pulley 12 of the first embodiment is made of a resin material for the purpose of weight reduction and cost reduction. Since the output pulley made of resin has a lower allowable stress (fatigue strength) than the output pulley made of metal, if the maximum generated stress is large, a disadvantage in strength (damage due to cracks or a decrease in durability) is likely to occur.
On the other hand, in the output pulley 12 of the first embodiment, the fastened portion 35 is arranged radially inside the boundary portion 34. That is, the boundary portion 34 whose axial cross-sectional area suddenly changes is missed radially outward from the fastened portion 35 that receives the axial force from the head 26 of the screw 25. Therefore, since there is no portion of the fastened portion 35 where the axial cross-sectional area changes suddenly, the stress generated by the axial force of the screw 25 can be dispersed and the stress concentration can be relaxed. As a result, the maximum stress generated at the fastened portion 35 can be reduced.
In the output pulley 12 of the first embodiment, the predetermined region on the radial outer side of the screw insertion hole 23c is the thin-walled portion 39, and the axial cross-sectional area of the thin-walled portion 39 is the thick-walled portion 40 adjacent to the thin-walled portion 39 in the circumferential direction. It was made smaller than the axial cross-sectional area. As a result, changes in the axial cross-sectional area can be suppressed in the region around the screw insertion hole 23c, which receives a large axial force of the screw 25. Therefore, the stress generated by the axial force of the screw 25 can be dispersed, and the stress concentration can be relaxed. As a result, the maximum stress generated at the fastened portion 35 can be reduced.

A washer 28 is provided between the fastened portion 35 and the head 26 of the screw 25. As a result, it is possible to prevent the fastened portion 35 made of the resin material from being damaged by contact with the head 26.
The outer peripheral edge of the washer 28 overlaps the boundary portion 34 in the radial direction of the screw 25. By increasing the contact area of the washer 28 with respect to the hub portion 23, the axial force (surface pressure) per unit area acting on the hub portion 23 from the washer 28 can be reduced, and the deformation of the hub portion 23 can be suppressed.
The output pulley 12 is located inside the winding portion 24 in the radial direction, and has a centering portion 41 that abuts on the outer peripheral surface 11a of the nut 11. When the nut 11 and the output pulley 12 are fastened with the screw 25, the centering portion 41 comes into contact with the outer peripheral surface 11a of the nut 11 so that the rotation axis of the output pulley 12 can be brought closer to the rotation axis of the nut 11 (alignment). Action). As a result, the workability at the time of assembly can be improved, such as facilitating the radial alignment of the screw insertion hole 23c and the female thread portion 22.
The centering portion 41 has an arc shape that is convex inward in the radial direction of the output pulley 12. When the apex of the arc comes into contact with the outer peripheral surface 11a of the nut 11, the contact portion between the two approaches the line tangent line, so that the influence of the molding accuracy of the contact surface can be suppressed. Further, since the contact area when the nut 11 is press-fitted into each centering portion 41 can be minimized, the press-fitting load can be reduced and the workability at the time of assembly can be improved.
The fastened portion 35 has a protruding portion 36 on the inner side surface 23b of the hub portion 23 that protrudes in the negative direction of the X-axis from a portion adjacent to each fastened portion 35. Here, the molding accuracy of the output pulley 12 affects the assembly accuracy on the contact surface with the nut 11, but each fastened portion 35 projects toward the nut 11 side from the other adjacent portions (inner side surface 23b). Therefore, it is possible to suppress the molding accuracy of other parts from affecting the contact surface with the nut 11. That is, since the assembly accuracy depends only on the molding accuracy of the protruding portion 36, for example, when the output pulley 12 is removed from the mold after injection molding, even if the other part is pressed and a pressing mark remains, the assembly accuracy is improved. Has no effect. Therefore, both ease of manufacture and assembly accuracy can be improved.

The output pulley 12 has an annular protrusion 38 that surrounds the rack bar insertion hole 29 into which the rack bar 6 is inserted. Since the annular protrusion 38 makes the axial cross-sectional area around the rack bar insertion hole 29 uniform, the degree of cooling shrinkage around the rack bar insertion hole 29 is adjusted in the cooling shrinkage process after injection molding of the output pulley 12. Can be homogenized.
The winding portion 24 extends in the radial direction of the outer cylinder portion 30 formed in a tubular shape and around which the belt 10 is wound, the inner cylinder portion 31 formed in a tubular shape and provided inside the outer cylinder portion 30, and the nut 11. It has a bridge portion 32 that connects the outer cylinder portion 30 and the inner cylinder portion 31. It is desirable that the winding portion 24 has a higher cylindricity from the viewpoint of suppressing abnormal noise and suppressing vibration when the output pulley 12 rotates. Here, if the winding portion has a solid structure, when the output pulley is removed from the mold after injection molding, the end portion of the winding portion opposite to the hub portion cools and shrinks, and bends inward in the radial direction. There is a risk of swelling. On the other hand, in the winding portion 24 of the first embodiment, the cooling shrinkage of the outer cylinder portion 40 can be suppressed by the bridge portion 32. Therefore, the cylindricity of the outer cylinder portion 30 can be improved as compared with the case where the winding portion has a solid structure.
In the output pulley 12, a region (connecting portion 33) between the hub portion 23 and the winding portion 24 in the axial cross section of the output pulley 12 passing through the rotation axis of the nut 11 is formed in an arc shape. That is, by smoothly connecting the hub portion 23 and the winding portion 24 by the arc-shaped connecting portion 33, the change in the axial cross-sectional area becomes gentle, so that the stress concentration between the hub portion 23 and the winding portion 24 Can be relaxed.
The output pulley 12 is formed by disc gate type injection molding. In the pingate type, since a weld line (hot water boundary) is formed, there is a concern that the composition may be lowered due to the decrease in the adhesion strength at the interface. On the other hand, since the disc gate type is less likely to generate a weld line, the rigidity of the output pulley 12 can be improved as compared with other methods such as a pin gate.

[Other Embodiments]
Although the embodiments for carrying out the present invention have been described above, the specific configuration of the present invention is not limited to the configurations of the embodiments, and there are design changes and the like within a range that does not deviate from the gist of the invention. Is also included in the present invention.
The transmission member may be a chain or the like.
It is not necessary to provide a washer between the fastened portion and the head of the screw.
The centering portion may be provided separately from the thick portion.

1 Power steering device
3 Electric motor
4 ball screw mechanism
4a tube (circulation mechanism)
6 Rack bar (rudder shaft)
9 Input pulley
10 Belt (transmission member)
11 nut
12 Output pulley
13 ball circulation groove
14 balls
19 Nut side ball screw groove
20 Rack bar side ball screw groove (steering shaft side ball screw groove)
23 Hub
23c Screw insertion hole
24 Winding part
25 screw
26 head
27 Shaft
27a Male thread (male thread groove)
28 washer
29 Rack bar insertion hole (rudder shaft insertion hole)
30 Outer cylinder
31 Inner cylinder
32 Bridge
35 Fastened part
36 Overhang
38 annular protrusion
39 thin wall
40 thick part
41 Centering section

Claims (8)

A steering shaft that steers the steering wheel by moving in the axial direction as the steering wheel rotates,
A nut provided in an annular shape so as to surround the steering shaft,
A ball screw mechanism for moving the steering shaft with respect to the nut in the direction of the rotation axis of the nut, which is provided on the outer peripheral side of the steering shaft and has a spiral groove shape. A nut-side ball screw groove, which is provided on the inner peripheral side of the nut and has a spiral groove shape and constitutes a ball circulation groove together with the steering shaft-side ball screw groove, and a ball circulation groove provided in the ball circulation groove. A ball screw mechanism having a plurality of balls and a circulation mechanism for circulating the plurality of balls from one end side to the other end side of the ball circulation groove.
A hub portion provided so as to face one end surface of the nut in the direction of the rotation axis of the nut and formed of a resin material, and a winding formed integrally with the hub portion and formed in a tubular shape made of a resin material. An output pulley having a hanging portion and a screw insertion hole provided in the hub portion and penetrating in the direction of the rotation axis of the nut.
A screw that is inserted into the screw insertion hole, has a head portion, and a shaft portion in which a thread groove of a male screw is formed, and fastens the nut and the output pulley.
When the material thickness of the output pulley in the direction of the rotation axis of the nut is taken as the wall thickness of the output pulley,
A thin portion provided on the output pulley and provided in a predetermined region outside the screw insertion hole in the radial direction on the rotation axis of the nut, and a radial dimension which is a distance from the rotation axis of the nut is the thin portion. A thick portion that is the same and is provided in a region adjacent to the thin portion in the direction around the rotation axis of the nut, and the wall thickness of the thin portion is larger than that of the thick portion. The thin and thick parts that are formed small,
A centering portion provided inside the output pulley and in contact with the outer peripheral surface of the nut,
An input pulley arranged so as to be offset in the radial direction with respect to the rotation axis of the nut,
A transmission member provided so as to straddle the output pulley and the input pulley and transmit the rotation of the input pulley to the output pulley.
An electric motor that rotationally drives the input pulley and
Power steering device with. In the power steering device according to claim 1,
The centering portion is a power steering device having an arc shape that is convex inward in the radial direction along the rotation axis of the output pulley. In the power steering device according to claim 1,
The output pulley is provided with a fastened portion in a region that overlaps the head of the screw in the radial direction on the rotation axis of the screw.
A power steering device having a washer provided between the fastened portion and the head of the screw. In the power steering device according to claim 3,
The fastened portion is a power steering device having a protruding portion on the side of the hub portion facing the nut, which protrudes toward the nut in the direction of the rotation axis of the nut from a portion adjacent to the fastened portion. In the power steering device according to claim 4,
The output pulley includes a steering shaft insertion hole provided in the hub portion and into which the steering shaft is inserted.
The protrusion is a power steering device having an annular protrusion formed in an annular shape so as to surround the steering shaft insertion hole. In the power steering device according to claim 1,
The winding portion has an outer cylinder portion formed in a tubular shape and around which the transmission member is wound, an inner cylinder portion formed in a tubular shape and provided inside the outer cylinder portion, and a radial direction of the rotation axis of the nut. A power steering device having a bridge portion formed so as to extend to the outer cylinder portion and connecting the outer cylinder portion and the inner cylinder portion. In the power steering device according to claim 1,
The output pulley is a power steering device in which a region between the hub portion and the winding portion in the axial cross section of the output pulley passing through the rotation axis of the nut is formed in an arc shape. In the power steering device according to claim 1,
The output pulley is a power steering device formed by disc gate type injection molding.

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