JP2006096209A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent the situation that a joint center on a column output side is oscillated and torque fluctuation is caused. <P>SOLUTION: A hollow output shaft 20 formed to be hollow is fitted and fixed to a torque sensor shaft 3, and a core 12a of a worm wheel 12 of a worm deceleration mechanism is fitted and fixed to an outer peripheral surface of the hollow output shaft 20, and thereby a hollow shaft having no joint can be formed from a fitting part of the core 12a of the worm wheel 12 and the hollow output shaft 20 to a vehicle front end part of the hollow output shaft 20. That is, the long and integral output shaft for the electric power steering device can be provided without welding from the fitting part of the hollow output shaft 20 and the core 12a of the worm wheel 12 to the vehicle front end part of the hollow output shaft 20 on a rack and pinion side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus having an improved output shaft structure.

  In a steering system of an automobile, a so-called power steering device that performs steering assist using an external power source is widely adopted. Conventionally, vane type hydraulic pumps have been used as power sources for power steering devices, and many of these hydraulic pumps are driven by an engine. However, this type of power steering device has a large engine drive loss due to the constant drive of the hydraulic pump (several horsepower to about 10 horsepower at the maximum load), so it can be used in light vehicles with small displacement. It was difficult, and it was unavoidable that the fuel consumption of a car with a relatively large displacement was reduced to a level that could not be ignored.

  Therefore, in order to solve these problems, an electric power steering device (Electric Power Steering, hereinafter referred to as EPS) using an electric motor as a power source has attracted attention in recent years. The EPS uses an in-vehicle battery as a power source for the electric motor, so there is no direct engine drive loss, and since the electric motor is started only at the steering assist time, a decrease in driving fuel consumption is suppressed, and electronic control is performed. It has the feature that it can be done very easily.

  In EPS, auxiliary steering torque is generated from the electric motor in response to the steering torque applied to the steering wheel, and is decelerated by the power transmission mechanism (reduction gear) and transmitted to the output shaft of the steering mechanism. Yes.

  FIG. 8 is a longitudinal sectional view of a column assist type electric power steering apparatus according to a conventional example.

  In the column assist type electric power steering apparatus, a torque sensor shaft 3 is connected to the vehicle front side of a steering shaft 2 (input shaft) rotatably mounted in the steering column 1.

  A concave fitting portion 3a is formed at the vehicle front end portion of the torque sensor shaft 3, and the convex fitting portion 4a of the output shaft 4 is fitted and fixed to the concave fitting portion 3a. The concave fitting portion 3a and the convex fitting portion 4a are firmly fixed by welding. A rack and pinion type steering device (not shown) or the like is connected to the vehicle front side of the output shaft 4 via a universal joint (not shown) or the like.

  The base end of the torsion bar 5 is press-fitted and fixed to the front side of the steering shaft 2 (input shaft), and this torsion bar 5 extends inside the torque sensor shaft 3 formed in a hollow shape. The tip is fixed to the end of the torque sensor shaft 3 by a fixing pin 6.

  A torque sensor part TS is provided on the vehicle rear side of the torque sensor shaft 3. That is, a detection groove 7 of the torque sensor unit TS is formed on the rear side of the torque sensor shaft 3, and a sleeve 8 of the torque sensor unit TS is arranged on the outer side in the radial direction of these grooves 7. It is. The sleeve 8 has a vehicle rear side end fixed to a vehicle front side end of the steering shaft 2 (input shaft) by caulking or the like. A coil 9 and a substrate are provided outside the sleeve 8 in the radial direction.

  A worm wheel 12 meshed with a worm 11 of a worm reduction mechanism connected to a drive shaft of an electric motor (not shown) is attached to the torque sensor shaft 3. The worm wheel 12 includes a cored bar portion 12a fitted to the torque sensor shaft 3 and a resin gear portion 12b molded integrally with the cored bar portion 12a. Reference numeral WR indicates a warm chamber.

  The worm 11 and the worm wheel 12 are housed in a rear housing 13 and a front housing 14 (cover). That is, the rear housing 13 and the front housing 14 (cover) are assembled with an in-row fitting gap and are connected by the bolt 15.

  The torque sensor shaft 3 is rotatably supported by a bearing 16 on the vehicle rear side of the worm wheel 12 and a bearing 17 on the vehicle front side of the worm wheel 12, and the bearing 17 has a tapered snap ring. 18 is fixed.

  Therefore, the steering force generated when the driver steers the steering wheel (not shown) is transmitted through the steering shaft 2 (input shaft), the torsion bar 5, the torque sensor shaft 3, and the rack and pinion type steering device. And transmitted to a steered wheel (not shown).

Further, the rotational force of the electric motor (not shown) is transmitted to the torque sensor shaft 3 via the worm 11 and the worm wheel 12, and the rotational force and the rotational direction of the electric motor (not shown) are determined. Appropriate steering assist torque can be applied to the torque sensor shaft 3 by appropriate control.
JP 2004-155225 A JP-A-8-240491

  By the way, in the electric power steering apparatus shown in FIG. 8, the cored bar portion 12 a of the worm wheel 12 is fitted and fixed on the torque sensor shaft 3.

  Moreover, the torque sensor shaft 3 and the output shaft 4 are integrally formed. That is, a concave fitting portion 3a is formed at the vehicle front end portion of the torque sensor shaft 3, and the convex fitting portion 4a of the output shaft 4 is fitted and fixed to the concave fitting portion 3a. The concave fitting portion 3a and the convex fitting portion 4a are firmly fixed by welding.

  However, the output shaft 4 to which the conventional welding has been applied may be bent very rarely in the welded portions (uneven fitting portions 3a and 4a). As a result, the joint center on the column output side is There is a problem that torque fluctuation occurs due to vibration.

  The present invention has been made in view of the circumstances as described above, and provides an electric power steering device that can reliably prevent the occurrence of torque fluctuation due to the joint center on the column output side being shaken. For the purpose.

In order to achieve the above object, an electric power steering apparatus according to claim 1 of the present invention generates an auxiliary steering torque from an electric motor in accordance with a steering torque applied to a steering wheel, and decelerates the worm reduction mechanism. In the electric power steering device that transmits to the output shaft of the steering mechanism
A hollow output shaft formed in a hollow shape is fitted and fixed to a torque sensor shaft that is connected to the input shaft of the steering shaft via a torsion bar and has a detection groove for the torque sensor formed on the outer peripheral surface. And
A worm wheel of the worm reduction mechanism is fitted and fixed to the outer peripheral surface of the hollow output shaft,
At least one bearing is interposed between the hollow output shaft and the housing.

  According to the present invention, the hollow output shaft formed in a hollow shape is fitted and fixed to the torque sensor shaft, and the worm wheel of the worm speed reduction mechanism is fitted and fixed to the outer peripheral surface of the hollow output shaft. Therefore, it is possible to form a hollow shaft without a joint from the fitting portion between the worm wheel and the hollow output shaft to the tip of the hollow output shaft. That is, to provide a long integrated output shaft for an electric power steering device without welding from the fitting portion of the hollow output shaft and the worm wheel to the end of the hollow exit shaft on the rack and pinion side. Can do. Accordingly, it is possible to reliably prevent the torque fluctuation from occurring due to the joint center on the column output side being shaken.

  Moreover, since the hollow output shaft formed in the hollow shape is used as an output shaft, weight reduction can be achieved.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a longitudinal sectional view of a column assist type electric power steering apparatus according to a first embodiment of the present invention.

  2A is a cross-sectional view of a main part of the electric power steering apparatus shown in FIG. 1, FIG. 2B is a cross-sectional view of a fitting portion of the worm wheel, and FIG. It is an expanded sectional view of the part surrounded by a circle.

  In the column assist type electric power steering apparatus, a torque sensor shaft 3 is connected to the vehicle front side of a steering shaft 2 (input shaft) rotatably mounted in the steering column 1.

  The base end of the torsion bar 5 is press-fitted and fixed to the front side of the steering shaft 2 (input shaft), and this torsion bar 5 extends inside the torque sensor shaft 3 formed in a hollow shape. The tip is fixed to the end of the torque sensor shaft 3 by a fixing pin 6.

  A torque sensor part TS is provided on the vehicle rear side of the torque sensor shaft 3. That is, a detection groove 7 of the torque sensor portion TS is formed on the vehicle rear side of the torque sensor shaft 3, and a sleeve 8 of the torque sensor portion TS is disposed outside the groove 7 in the radial direction. It is. The sleeve 8 has a vehicle rear side end fixed to a vehicle front side end of the steering shaft 2 (input shaft) by caulking or the like. A coil 9 and a substrate are provided outside the sleeve 8 in the radial direction.

  In the present embodiment, a hollow output shaft 20 formed in a hollow shape is fitted and fixed to the vehicle front side of the torque sensor shaft 3. A rack and pinion type steering device (not shown) and the like are connected to the front side of the hollow output shaft 20 via a universal joint (not shown) and the like.

  A worm wheel 12 meshing with a worm 11 of a worm reduction mechanism connected to a drive shaft of an electric motor (not shown) is attached to the outer peripheral surface of the hollow output shaft 20. The worm wheel 12 includes a cored bar portion 12a fitted to the hollow output shaft 20, and a resin gear portion 12b molded integrally with the cored bar portion 12a. Reference numeral WR indicates a warm chamber.

  The worm 11 and the worm wheel 12 are housed in a rear housing 13 and a front housing 14 (cover). That is, the rear housing 13 and the front housing 14 (cover) are assembled with an in-row fitting gap and are connected by the bolt 15.

  The torque sensor shaft 3 is rotatably supported by a bearing 16 on the vehicle rear side of the worm wheel 12 and between the rear housing 13 and the hollow output shaft 20 is supported by the worm wheel 12. The bearing 17 is rotatably supported by a bearing 17 interposed between the front housing 14 and the front housing 14. The bearing 17 is fixed by a tapered retaining ring 18.

  Therefore, the steering force generated when the driver steers the steering wheel (not shown) is the steering shaft 2 (input shaft), the torsion bar 5, the torque sensor shaft 3, the hollow output shaft 20, and the rack and pinion. Is transmitted to a steered wheel (not shown) via a steering device.

  The rotational force of the electric motor (not shown) is transmitted to the torque sensor shaft 3 and the hollow output shaft 20 via the worm 11 and the worm wheel 12, and the rotation of the electric motor (not shown). An appropriate steering assist torque can be applied to the torque sensor shaft 3 and the hollow output shaft 20 by appropriately controlling the force and the rotation direction.

  As shown in detail in FIG. 2, the outer surface of the torque sensor shaft 3 to which the hollow output shaft 20 is fitted is subjected to a flat low red process, and a flat knurled portion 21 is formed. The hollow output shaft 20 and the torque sensor shaft 3 are press-fitted and fixed by the flat knurled portion 21.

  The outer surface of the hollow output shaft 20 into which the cored bar portion 12a of the worm wheel 12 is fitted is subjected to a flat knurling process, and a flat knurled portion 22 is formed. By this flat knurled portion 22, the core metal portion 12 a of the worm wheel 12 and the hollow output shaft 20 are press-fitted and fixed.

  Further, the fixing pin 6 for fixing the torsion bar 5 prevents the hollow output shaft 20 and the torque sensor shaft 3 from coming off in the axial direction.

  Since it is configured as described above, according to the present embodiment, the hollow output shaft 20 formed in a hollow shape is fitted and fixed to the torque sensor shaft 3, and the outer peripheral surface of the hollow output shaft 20 is Since the cored bar part 12a of the worm wheel 12 of the worm reduction mechanism is fitted and fixed, the front part of the hollow output shaft 20 from the fitting part of the cored bar part 12a of the worm wheel 12 and the hollow output shaft 20 To the end, it can be constituted by a hollow shaft without a joint.

  That is, a long integrated electric power without welding from the fitting portion between the hollow output shaft 20 and the core metal portion 12a of the worm wheel 12 to the front end portion of the hollow shaft 20 on the rack and pinion side. An output shaft for a steering device can be provided.

  Accordingly, it is possible to reliably prevent the torque fluctuation from occurring due to the joint center on the column output side being shaken.

  Moreover, since the hollow output shaft 20 formed in a hollow shape is used as the output shaft, the weight can be reduced.

  FIG. 3A is a cross-sectional view of the main part of the electric power steering apparatus according to the first modification of the first embodiment, and FIG. 3B is a cross-sectional view of the fitting part of the worm wheel.

  In this modified example, uneven fitting parts 23 and 24 are used instead of the flat knurled parts 21 and 22.

  That is, the concave / convex fitting portion 23 is formed on the hollow output shaft 20 and the torque sensor shaft 3. The hollow output shaft 20 and the torque sensor shaft 3 are press-fitted and fixed by the uneven fitting portion 23.

  An uneven fitting portion 24 is formed on the cored bar portion 12 a of the worm wheel 12 and the hollow output shaft 20. By the uneven fitting portion 24, the core metal portion 12a of the worm wheel 12 and the hollow output shaft 20 are press-fitted and fixed.

  Other configurations, operations, and effects are the same as those in the first embodiment described above.

  FIG. 4 is a cross-sectional view of a main part of an electric power steering device according to a second modification of the first embodiment.

  In this modification, the hollow output shaft 20 is on the vehicle front side of the worm wheel 12 and on the vehicle front side of the worm wheel 12 and the bearing 16 interposed between the front housing 14 and the front side. It is rotatably supported by two bearings including a bearing 17 interposed between the housing 14 and the housing 14.

  The inner ring of the bearing 17 is fixed by a lock nut 19 or the like.

  Other configurations, operations, and effects are the same as those in the first embodiment described above. In FIG. 4, reference numeral 10 indicates an electric motor.

  Further, the fitting method between the cored bar portion 12a of the worm wheel 12 and the hollow output shaft 20 is not limited to the flat knurling and the concave-convex fitting, and a tightening fit or other methods may be used. The same applies to the following embodiments.

(Second Embodiment)
FIG. 5 is a longitudinal sectional view of a column assist type electric power steering apparatus according to the second embodiment of the present invention.

  The basic structure of this embodiment is the same as that of the first embodiment described above, and only differences will be described.

  In the present embodiment, a solid second output shaft 30 is fitted and connected to the vehicle front side of the hollow output shaft 20.

  A female spline portion 31 is formed on the vehicle front side of the hollow output shaft 20, and a male spline portion 32 is formed on the vehicle rear side of the second output shaft 30. By these female / male spline portions 31, 32, the hollow output shaft 20 and the second output shaft 30 are telescopic sliding structures.

  Other configurations, operations, and effects are the same as those in the first embodiment described above. That is, according to the present embodiment, the hollow output shaft 20 formed in a hollow shape is fitted and fixed to the torque sensor shaft 3, and the worm wheel 12 of the worm reduction mechanism is attached to the outer peripheral surface of the hollow output shaft 20. Since the core metal part 12a is fitted and fixed, the front end of the hollow output shaft 20 and the second output shaft 30 from the fitting part between the core metal part 12a of the worm wheel 12 and the hollow output shaft 20 Up to the part, it can be constituted by a hollow shaft without a joint.

  That is, without welding from the fitting portion between the hollow output shaft 20 and the core metal portion 12a of the worm wheel 12 to the hollow output shaft 20 on the rack and pinion side and the vehicle front end portion of the second output shaft 30. An output shaft for a long integrated electric power steering device can be provided.

  Accordingly, it is possible to reliably prevent the torque fluctuation from occurring due to the joint center on the column output side being shaken. Further, since the hollow output shaft 20 formed in a hollow shape is used as the output shaft, the weight can be reduced.

  FIG. 6 is a longitudinal sectional view of a column assist type electric power steering apparatus according to a first modification of the second embodiment of the present invention.

  In this modification, a solid second output shaft 30 is fitted and connected to the vehicle front side of the hollow output shaft 20.

  A female spline portion 31 is formed on the vehicle front side of the hollow output shaft 20, and a male spline portion 32 is formed on the vehicle rear side of the second output shaft 30. By these female / male spline portions 31, 32, the hollow output shaft 20 and the second output shaft 30 are telescopic sliding structures.

  Moreover, the second output shaft 30 is formed with a concave portion 33 having a substantially arc-shaped cross section in the circumferential direction, and synthetic resin is injected (injected) into the concave portion 33 through the through hole 34 of the hollow output shaft 20. Molded. Thereby, the resin injection part 35 is formed in the recessed part 33.

  The resin injection portion 35 provides a collapsible structure that can collapse the hollow output shaft 20 and the second output shaft 30 in an emergency such as a secondary collision.

  In the illustrated example, a collapsible structure with the resin injection portion 35 is used, but instead of this, a caulking connection or an elliptical fitting may be used.

  Other configurations, operations, and effects are the same as those in the first embodiment described above.

  FIG. 7 is a longitudinal sectional view of a column assist type electric power steering apparatus according to a second modification of the second embodiment of the present invention.

  In this modification, the hollow second output shaft 30 is fitted and connected to the vehicle front side of the hollow output shaft 20.

  A female spline portion 31 is formed on the vehicle front side of the hollow output shaft 20, and a male spline portion 32 is formed on the vehicle rear side of the second output shaft 30. By these female / male spline portions 31, 32, the hollow output shaft 20 and the second output shaft 30 are telescopic sliding structures. For smooth sliding, the female / male spline portions 31 and 32 may be coated with resin.

  Moreover, a yoke 36 constituting a universal joint is integrally formed at the vehicle front end portion of the hollow second output shaft 30. In this case, the second output shaft 30 may be configured to be solid.

  Further, the hollow output shaft 20 and the second output shaft 30 are formed with caulking portions 37 and 38, respectively.

  Thereby, the collapsible structure which can collapse the hollow output shaft 20 and the 2nd output shaft 30 at the time of emergency, such as at the time of a secondary collision, is provided. In the illustrated example, a collapsible structure by caulking is used, but instead of this, the above-described resin injection or elliptical fitting may be used.

  In addition, this invention is not limited to embodiment mentioned above, A various deformation | transformation is possible.

1 is a longitudinal sectional view of a column assist type electric power steering device according to a first embodiment of the present invention. (A) is sectional drawing of the principal part of the electric power steering apparatus shown in FIG. 1, (b) is a cross-sectional view of the fitting part of a worm wheel, (c) is (b) It is an expanded sectional view of the part surrounded by a circle. (A) is sectional drawing of the principal part of the electric power steering apparatus which concerns on the 1st modification of 1st Embodiment, (b) is a cross-sectional view of the fitting part of a worm wheel. It is sectional drawing of the principal part of the electric power steering apparatus which concerns on the 2nd modification of 1st Embodiment. It is a longitudinal cross-sectional view of the column-assist type electric power steering device concerning a 2nd embodiment of the present invention. It is a longitudinal cross-sectional view of the column-assist type electric power steering device concerning the 1st modification of a 2nd embodiment of the present invention. It is a longitudinal cross-sectional view of the column-assist type electric power steering device concerning the 2nd modification of a 2nd embodiment of the present invention. It is a longitudinal cross-sectional view of the column assist type electric power steering device according to the conventional example.

Explanation of symbols

1 Steering column 2 Steering shaft (input shaft)
DESCRIPTION OF SYMBOLS 3 Torque sensor shaft 3a Concave fitting part 4 Output shaft 4a Convex fitting part 5 Torsion bar 6 Fixing pin 7 Detection groove 8 Sleeve 9 Coil TS Torque sensor part 10 Electric motor 10a Drive shaft 11 Worm 12 Worm wheel 12a Metal core Part 12b Resin gear part 13 Rear housing 14 Front housing (cover)
15 bolt 13 rear housing 14 front housing (cover)
15 Bolt 16, 17 Bearing 18 Tapered retaining ring 19 Lock nut 20 Hollow output shaft 21, 22 Flat knurled portion 23, 24 Concave / concave fitting portion 30 Second output shaft 31 Female spline portion 32 Male spline portion 33 Recessed portion 34 Through hole 35 Resin Injection part 36 Yoke 37, 38 Clamping part WR Warm chamber

Claims (1)

In an electric power steering device that generates an auxiliary steering torque from an electric motor according to a steering torque applied to a steering wheel, decelerates it by a worm deceleration mechanism, and transmits it to an output shaft of the steering mechanism.
A hollow output shaft formed in a hollow shape is fitted and fixed to a torque sensor shaft that is connected to the input shaft of the steering shaft via a torsion bar and has a detection groove for the torque sensor formed on the outer peripheral surface. And
A worm wheel of the worm reduction mechanism is fitted and fixed to the outer peripheral surface of the hollow output shaft,
An electric power steering apparatus, wherein at least one bearing is interposed between the hollow output shaft and the housing.

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