JP5136297B2 - Electric power steering device - Google Patents

Description

  The present invention relates to a steering apparatus, and more particularly to an electric power steering apparatus that drives an electric motor to apply a required steering assist force to a steering gear.

  As shown in Patent Document 1, an electric power steering device drives an electric motor to rotate a worm wheel that meshes with a worm with a required steering assist force, and rotates an output shaft having the worm wheel so that a steering gear is used. The direction of the steering wheel is changed by moving the connected tie rods.

  6 and 7 show such a conventional electric power steering apparatus. FIG. 6 is a longitudinal sectional view of a main part of a conventional electric power steering apparatus, and FIG. 7 is a view taken in the direction of arrow P in FIG. As shown in FIGS. 6 and 7, an inner shaft (input shaft) 12 </ b> B and an output shaft 23 are arranged on the same central axis in the gear housing 21 of the assist device 20 of the electric power steering apparatus, and the output shaft 23 is A bearing (deep groove radial ball bearing) 41 is rotatably supported by the cover 22.

  The cover 22 covers the left open end of the gear housing 21. The inner shaft 12B and the output shaft 23 are connected by a torsion bar 24. The rotation of the output shaft 23 is transmitted to a steering gear (not shown) via the universal joint 15 and the intermediate shaft 16, and the direction of the steered wheels is changed via a tie rod connected to the steering gear.

  A disc-shaped cored bar 52 is press-fitted into an intermediate portion of the output shaft 23, and a worm wheel 51 that meshes with the worm 53 is press-fitted into the outer periphery of the cored bar 52. The worm 53 is driven by the electric motor 25 (see FIG. 7). The right end surface 521 of the cored bar 52 is in contact with the stepped portion 231 of the output shaft 23 to restrict the cored bar 52 from moving to the right side (rear side of the vehicle body) with respect to the output shaft 23. The output shaft 23 is rotatably supported on the cover 22 of the gear housing 21 by a bearing 41 that abuts on the left end surface 522 of the core metal 52.

  The nut 26 screwed into the output shaft 23 sandwiches the inner ring of the bearing 41 with the left end surface 522 of the core metal 52. Further, the outer ring of the bearing 41 is press-fitted into the bearing hole 221 formed in the cover 22 with an interference fit, and is fixed to the cover 22 by a retaining ring 27 inserted into the ring groove of the bearing hole 221. By press-fitting the outer ring of the bearing 41 into the bearing hole 221 with an interference fit, the internal clearance of the bearing 41 is set to a negative value.

  The output shaft 23 is rotatably supported on the gear housing 21 by a bearing (deep groove radial ball bearing) 42 on the outer periphery on the right side of the step portion 231. The outer ring of the bearing 42 is press-fitted into a bearing hole 211 formed in the gear housing 21, and the left end surface of the inner ring of the bearing 42 is in contact with the right end surface 521 of the cored bar 52.

  The torsion bar 24 whose right end (end on the rear side of the vehicle body) is press-fitted into the inner shaft 12B is connected to the left end of the output shaft 23 by a pin (not shown) at the left end (end on the front side of the vehicle body). An intermediate portion of the torsion bar 24 is pivotally supported by a bush 29 at the right end of the output shaft 23.

  A torque sensor 61 that detects torque acting on the torsion bar 24 includes a sensor shaft portion 62, detection coils 63 and 64, and a cylindrical member 65. The sensor shaft portion 62 is formed integrally with the right end (the vehicle body rear side end portion) of the output shaft 23, and detection coils 63 and 64 are disposed on a yoke 66 press-fitted inside the gear housing 21. The cylindrical member 65 is disposed in a gap between the outer periphery of the sensor shaft portion 62 and the inner periphery of the detection coils 63 and 64.

  The cylindrical member 65 is fixed to the left end (the vehicle body front side end) of the inner shaft 12B, and the sensor shaft portion 62 is formed with a plurality of ridges extending in the axial direction at equal intervals in the circumferential direction. The cylindrical member 65 is formed with a plurality of rectangular windows at equal intervals in the circumferential direction at positions facing the detection coils 63 and 64.

  When the inner shaft 12 </ b> B rotates by operating a steering wheel (not shown), the rotational force is transmitted to the output shaft 23 via the torsion bar 24. At this time, the torsion bar 24 that connects the inner shaft 12B and the output shaft 23 is twisted due to the resistance on the steering wheel side, and relative rotation occurs between the protrusion on the surface of the sensor shaft portion 62 and the window of the cylindrical member 65. .

  With this relative rotation, the magnetic flux generated in the sensor shaft portion 62 increases and decreases, and the increase and decrease of the magnetic flux is detected by the detection coils 63 and 64 as a change in inductance. From this detection result, torque acting on the torsion bar 24 is detected, and the electric motor 25 is driven to rotate the worm 53 with a required steering assist force. The rotation of the worm 53 is transmitted to the steering gear via the worm wheel 51, the output shaft 23, the universal joint 15, and the intermediate shaft 16, and changes the direction of the steered wheel via a tie rod connected to the steering gear.

  As shown in FIG. 6, the universal joint 15 intersects at a joint angle β (generally 20 degrees to 50 degrees). Therefore, when the intermediate shaft 16 receives a rotational torque, the secondary coupling 15 is generated in the universal joint 15. Due to the force, a large moment load acts on the output shaft 23. This moment load M is expressed by M = T cos θ · tan β.

  Here, T is the rotational torque of the intermediate shaft 16, β is the joint angle, and θ is the phase angle of the yoke of the universal joint 15. This moment load M has the largest value when the phase angle of the yoke is 0 degree (the phase of the yoke of the universal joint 15 is the state shown in FIGS. 6 and 7).

  As shown in FIGS. 6 and 7, the moment load M becomes a rotational force around the Z axis passing through the center of the cross shaft 151 of the universal joint 15. Therefore, a large load is applied to the output shaft 23 in the Y-axis direction of FIG. 7 (perpendicular to the plane passing through the axis of the output shaft 23 and the axis of the intermediate shaft 16).

  Therefore, a large load acts on the bearing 41 that supports the output shaft 23 in the Y-axis direction. As a result, of the balls of the bearing 41, the surface pressure of the balls in the Y-axis direction becomes excessive, the wear of the bearing 41 increases, the durability decreases, and riding noise occurs and a noise is generated. The driver could be uncomfortable.

JP 2002-19626 A

  An object of the present invention is to provide an electric power steering device that improves the durability of a bearing that supports an output shaft and prevents the generation of abnormal noise so as not to cause discomfort to the driver. And

  The above problem is solved by the following means. That is, the first invention is a gear housing, an input shaft that is inserted through the gear housing and to which the rotation of the steering wheel is transmitted, an output shaft that is coupled to the input shaft, and is coupled to the output shaft via a universal joint. An intermediate shaft that transmits the rotation of the output shaft to the wheel side, a torque sensor that detects torque acting on the input shaft, and an electric motor that applies a predetermined steering assist force to the output shaft in accordance with a detection value of the torque sensor The output shaft is inserted between the cover that covers the gear housing and the output shaft, the outer ring is fitted into the cover with an interference fit, and the output shaft is rotatably supported with a negative internal clearance. The cover includes a bearing, and the cover is formed so that rigidity in a direction perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft is smaller than rigidity in other directions. An electric power steering apparatus according to.

  A second aspect of the invention is the electric power steering apparatus according to the first aspect of the invention, wherein the cover has an axial thickness perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft. Is an electric power steering device characterized in that a thin portion thinner than the thickness in the other direction is formed.

  A third invention is the electric power steering apparatus according to the first invention, wherein the cover has ribs formed radially from the axis of the cover, and the axis of the output shaft and the axis of the intermediate shaft The electric power steering apparatus is characterized in that ribs in the direction perpendicular to the plane passing through the line are omitted.

  According to a fourth aspect of the invention, in the electric power steering apparatus of the first aspect, the thickness of the rib formed radially from the axis of the cover is a plane passing through the axis of the output shaft and the axis of the intermediate shaft. The electric power steering apparatus is characterized in that the rib in the vertical direction is formed thinner than the rib in the other direction.

  In the electric power steering apparatus of the present invention, the outer ring is inserted between the cover that covers the gear housing and the output shaft, the outer ring is fitted into the cover with an interference fit, the internal clearance is a negative value, and the output shaft is The cover is provided with a rotatably supported bearing, and the cover is formed so that the rigidity in the direction perpendicular to the plane passing through the axis of the output shaft and the axis of the intermediate shaft is smaller than the rigidity in the other direction.

  Therefore, the outer ring of the bearing has an elliptical shape whose major axis is perpendicular to the plane passing through the axis of the output shaft and the axis of the intermediate shaft. For this reason, the surface pressure of the balls in the major axis direction of the outer ring is smaller than the surface pressure of the other balls. Therefore, even when a large load is applied in the major axis direction of the outer ring, the surface pressure of the balls in the major axis direction of the outer ring does not become excessive, and the durability of the bearing is improved and the generation of abnormal noise is prevented. Does not cause any discomfort.

  Embodiments 1 to 3 of the present invention will be described below with reference to the drawings.

  FIG. 1 is an overall front view showing a whole of an electric power steering apparatus according to a first embodiment of the present invention, with a part thereof cut. 2 is a longitudinal sectional view of the main part of FIG. 1, and FIG. 3 is a front view of the cover of FIG.

  As shown in FIGS. 1 to 3, the electric power steering apparatus of the present invention includes a steering shaft 12 on which a steering wheel 11 can be mounted on the rear side of the vehicle body (the right side in FIGS. 1 and 2), and the steering shaft 12. A steering column 13 inserted through, an assist device 20 for applying auxiliary torque to the steering shaft 12, and a rack / pinion mechanism (not shown) are provided on the front side of the vehicle body of the steering shaft 12 (left side in FIGS. 1 and 2). And a steering gear 30 connected to each other.

  In the steering shaft 12, an outer shaft 12A and an inner shaft (input shaft) 12B are combined by spline engagement so that rotational force can be transmitted and relative displacement in the axial direction can be achieved. Therefore, when the outer shaft 12A and the inner shaft 12B collide, the spline engaging portion slides relative to each other so that the entire length can be shortened.

  Further, the cylindrical steering column 13 inserted through the steering shaft 12 combines the outer column 13A and the inner column 13B so that they can be telescopically moved. It has a so-called collapsible structure in which the entire length is shortened while absorbing water.

  The vehicle body front side end portion of the inner column 13B is press-fitted and fixed to the vehicle body rear side end portion of the gear housing 21 of the assist device 20. Further, the vehicle body front side end portion of the inner shaft (input shaft) 12B is passed through the inside of the gear housing 21, and is coupled to the vehicle body rear side end portion of the output shaft (female shaft) 23 of the assist device 20.

  The steering column 13 is supported by a support bracket 14 at a middle portion thereof on a part of the vehicle body 18 such as a lower surface of the dashboard. Further, a locking portion (not shown) is provided between the support bracket 14 and the vehicle body 18, and when an impact in a direction toward the front side of the vehicle body is applied to the support bracket 14, the support bracket 14 is locked to the locking bracket 14. It moves away from the vehicle and moves to the front side of the vehicle.

  The upper end portion of the gear housing 21 is also pivotally supported on a part of the vehicle body 18. In this embodiment, the height position of the steering wheel 11 and the longitudinal position of the vehicle body can be freely adjusted by providing a tilt mechanism and a telescopic mechanism. Such a tilt mechanism and a telescopic mechanism are well known in the art and are not characteristic features of the present invention, and thus detailed description thereof is omitted.

  The output shaft 23 protruding from the end face on the front side of the vehicle body of the gear housing 21 is connected to the rear end portion of the intermediate shaft 16 via the universal joint 15. Further, the input shaft 31 of the steering gear 30 is connected to the front end portion of the intermediate shaft 16 via another universal joint 17. A pinion (not shown) is formed at the vehicle body front side end portion of the input shaft 31. A rack (not shown) meshes with the pinion, and the rotation of the steering wheel 11 moves the tie rod 32 to steer a wheel (not shown).

  2 and 3, an inner shaft (input shaft) 12B and an output shaft 23 are arranged on the same central axis in the gear housing 21 of the assist device 20, and the output shaft 23 is a bearing (groove-shaped radial). A ball bearing 41 is rotatably supported on the cover 22. The cover 22 covers the left open end of the gear housing 21. The inner shaft 12B and the output shaft 23 are connected by a torsion bar 24.

  A disc-shaped cored bar 52 is press-fitted into an intermediate portion of the output shaft 23, and a worm wheel 51 that meshes with the worm 53 is press-fitted into the outer periphery of the cored bar 52. As shown in FIG. 1, a case 251 of the electric motor 25 is fixed to the gear housing 21, and a worm 53 is connected to an output shaft of the electric motor 25.

  The right end surface 521 of the cored bar 52 is in contact with the stepped portion 231 of the output shaft 23 to restrict the cored bar 52 from moving to the right side (rear side of the vehicle body) with respect to the output shaft 23. The output shaft 23 is rotatably supported on the cover 22 of the gear housing 21 by a bearing (deep groove radial ball bearing) 41 that contacts the left end surface 522 of the core metal 52.

  The nut 26 screwed into the output shaft 23 sandwiches the inner ring of the bearing 41 with the left end surface 522 of the core metal 52. Further, the outer ring of the bearing 41 is press-fitted into the bearing hole 221 formed in the cover 22 with an interference fit, and is fixed to the cover 22 by a retaining ring 27 inserted into the ring groove of the bearing hole 221. By press-fitting the outer ring of the bearing 41 into the bearing hole 221 with an interference fit, the internal clearance of the bearing 41 is set to a negative value.

  As shown in FIGS. 2 and 3, the cover 22 is formed with meat stealing portions 222 and 222. The meat stealing portions 222 and 222 are formed on both sides in the Y-axis direction of FIG. 3 (perpendicular to a plane passing through the axis of the output shaft 23 and the axis of the intermediate shaft 16) with the bearing hole 221 of the cover 22 in between. ing.

Accordingly, since the thin portion is formed in the Y-axis direction of the cover 22 so that the axial thickness is thinner than the thickness in the other direction, the rigidity of the cover 22 in the Y-axis direction is the same as the rigidity in the other direction. It is formed smaller than. Therefore, when the outer ring of the bearing 41 is press-fitted into the bearing hole 221 with an interference fit, the outer ring of the bearing 41 becomes an elliptical shape having a major axis in the Y-axis direction and a minor axis in the Z-axis direction. Therefore, the bearing 41
The surface pressure of the balls in the Y-axis direction is smaller than the surface pressure of the balls in the other directions.

  The output shaft 23 is rotatably supported on the gear housing 21 by a bearing (deep groove radial ball bearing) 42 on the outer periphery on the right side of the step portion 231. The outer ring of the bearing 42 is press-fitted into a bearing hole 211 formed in the gear housing 21, and the left end surface of the inner ring of the bearing 42 is in contact with the right end surface 521 of the cored bar 52.

  The torsion bar 24 whose right end (end on the rear side of the vehicle body) is press-fitted into the inner shaft 12B is connected to the left end of the output shaft 23 by a pin (not shown) at the left end (end on the front side of the vehicle body). An intermediate portion of the torsion bar 24 is pivotally supported by a bush 29 at the right end of the output shaft 23.

  A torque sensor 61 that detects torque acting on the torsion bar 24 includes a sensor shaft portion 62, detection coils 63 and 64, and a cylindrical member 65. The sensor shaft portion 62 is formed integrally with the right end (the vehicle body rear side end portion) of the output shaft 23, and detection coils 63 and 64 are disposed on a yoke 66 press-fitted inside the gear housing 21. The cylindrical member 65 is disposed in a gap between the outer periphery of the sensor shaft portion 62 and the inner periphery of the detection coils 63 and 64.

  The cylindrical member 65 is fixed to the left end (the vehicle body front side end) of the inner shaft 12B, and the sensor shaft portion 62 is formed with a plurality of ridges extending in the axial direction at equal intervals in the circumferential direction. The cylindrical member 65 is formed with a plurality of rectangular windows at equal intervals in the circumferential direction at positions facing the detection coils 63 and 64.

  When the inner shaft 12 </ b> B rotates by operating the steering wheel 11, the rotational force is transmitted to the output shaft 23 via the torsion bar 24. At this time, the torsion bar 24 that connects the inner shaft 12B and the output shaft 23 is twisted due to the resistance on the steering wheel side, and relative rotation occurs between the protrusion on the surface of the sensor shaft portion 62 and the window of the cylindrical member 65. .

  With this relative rotation, the magnetic flux generated in the sensor shaft portion 62 increases and decreases, and the increase and decrease of the magnetic flux is detected by the detection coils 63 and 64 as a change in inductance. From this detection result, torque acting on the torsion bar 24 is detected, and the electric motor 25 is driven to rotate the worm 53 with a required steering assist force. The rotation of the worm 53 is transmitted to the steering gear 30 via the worm wheel 51, the output shaft 23, the universal joint 15, and the intermediate shaft 16, and changes the direction of the steered wheel via the tie rod 32 connected to the steering gear 30.

  In the first embodiment of the present invention, when the moment load M acts on the output shaft 23 due to the secondary couple generated in the universal joint 15 as in the conventional example, the output shaft 23 has a Y-axis direction (output) in FIG. A large load is applied in the direction perpendicular to the plane passing through the axis of the shaft 23 and the axis of the intermediate shaft 16.

  In the first embodiment of the present invention, the outer ring of the bearing 41 is press-fitted in an elliptical shape having a major axis in the Y-axis direction and a minor axis in the Z-axis direction. However, it is smaller than the surface pressure of the ball in the other direction. Therefore, even when a large load is applied in the Y-axis direction, the surface pressure of the balls in the Y-axis direction does not become excessive, and the durability of the bearing is improved and the generation of abnormal noise is prevented. Does not give pleasure.

  Next, a second embodiment of the present invention will be described. FIG. 4 is a rear view of the cover showing the second embodiment of the present invention. In the following description, only structural portions and operations different from those of the first embodiment will be described, and overlapping descriptions will be omitted. Further, the same parts will be described with the same numbers.

  The second embodiment is an example in which the rigidity of the cover 22 in the Y-axis direction is made smaller than the rigidity in other directions by arranging the ribs of the cover 22. That is, as shown in FIG. 4, six ribs 223 are formed radially from the axis of the cover 22 on the back surface of the cover 22, but the ribs in the Y-axis direction are omitted. Therefore, the rigidity of the cover 22 in the Y-axis direction is smaller than the rigidity in other directions.

  Therefore, when the outer ring of the bearing 41 is press-fitted into the bearing hole 221 with an interference fit, the outer ring of the bearing 41 becomes an elliptical shape having a major axis in the Y-axis direction and a minor axis in the Z-axis direction, and a ball in the Y-axis direction of the bearing 41. Is smaller than the surface pressure of the balls in other directions. For this reason, even if a large load is applied in the Y-axis direction, the surface pressure of the balls in the Y-axis direction does not become excessive, and the durability of the bearing is improved. Does not give pleasure.

  Next, a third embodiment of the present invention will be described. FIG. 5 is a rear view of the cover showing the third embodiment of the present invention. In the following description, only structural portions and operations different from the above embodiment will be described, and redundant description will be omitted. Further, the same parts will be described with the same numbers.

  The third embodiment is an example in which the rigidity of the cover 22 in the Y-axis direction is made smaller than the rigidity in other directions by changing the thickness of the ribs of the cover 22. That is, as shown in FIG. 5, eight ribs are formed on the back surface of the cover 22 at intervals of 45 degrees radially from the axis of the cover 22, but the two ribs 225 in the Y-axis direction, The wall thickness T1 of 225 is formed thinner than the wall thickness T2 of the six ribs 224 in the other direction. Therefore, the rigidity of the cover 22 in the Y-axis direction is smaller than the rigidity in other directions.

  Therefore, when the outer ring of the bearing 41 is press-fitted into the bearing hole 221 with an interference fit, the outer ring of the bearing 41 becomes an elliptical shape having a major axis in the Y-axis direction and a minor axis in the Z-axis direction, and a ball in the Y-axis direction of the bearing 41. Is smaller than the surface pressure of the balls in other directions. For this reason, even if a large load is applied in the Y-axis direction, the surface pressure of the balls in the Y-axis direction does not become excessive, and the durability of the bearing is improved. Does not give pleasure.

It is the whole electric power steering device of Example 1 of the present invention, and is the whole front view which cut a part. It is a longitudinal cross-sectional view of the principal part of FIG. It is a front view of the cover of FIG. It is a rear view of the cover which shows Example 2 of this invention. It is a rear view of the cover which shows Example 3 of this invention. It is a longitudinal cross-sectional view of the principal part of the conventional electric power steering device. It is a P arrow view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Steering shaft 12A Outer shaft 12B Inner shaft 13 Steering column 13A Outer column 13B Inner column 14 Support bracket 15 Universal joint 151 Cross shaft 16 Intermediate shaft 17 Universal joint 18 Car body 20 Assist device 21 Gear housing 211 Bearing hole 22 Cover 221 Bearing hole 222 Stealing portion 223, 224, 225 Rib 23 Output shaft 231 Step portion 24 Torsion bar 25 Electric motor 251 Case 26 Nut 27 Retaining ring 29 Bush 30 Steering gear 31 Input shaft 32 Tie rod 41 Bearing (Deep groove radial ball bearing )
42 Bearing (Deep groove radial ball bearing)
51 Worm wheel 52 Core metal 521 Right end surface 522 Left end surface 53 Worm 61 Torque sensor 62 Sensor shaft portion 63, 64 Detection coil 65 Cylindrical member 66 York

Claims (4)

Gear housing,
An input shaft that is inserted into the gear housing and transmits the rotation of the steering wheel;
An output shaft connected to the input shaft,
An intermediate shaft connected to the output shaft via a universal joint and transmitting the rotation of the output shaft to the wheel side;
A torque sensor for detecting torque acting on the input shaft;
An electric motor that applies a predetermined steering assist force to the output shaft in accordance with a detection value of the torque sensor;
A bearing that is inserted between a cover that covers the gear housing and the output shaft, whose outer ring is fitted into the cover with an interference fit, and whose internal clearance is a negative value and rotatably supports the output shaft With
The electric power steering apparatus according to claim 1, wherein the cover is formed so that rigidity in a direction perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft is smaller than rigidity in other directions. In the electric power steering apparatus according to claim 1,
The cover above
An electric power characterized in that a thin-walled portion is formed in a direction perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft, and the thickness in the axial direction is thinner than the thickness in the other direction. Steering device. In the electric power steering apparatus according to claim 1,
The above cover
Having ribs formed radially from the axis of the cover;
An electric power steering apparatus characterized in that a rib perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft is omitted. In the electric power steering apparatus according to claim 1,
The thickness of the ribs formed radially from the axis of the cover is as follows:
An electric power steering apparatus, wherein a rib in a direction perpendicular to a plane passing through the axis of the output shaft and the axis of the intermediate shaft is formed thinner than a rib in another direction.

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