JP2007255524A - Worm reduction gear and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase rigidity and suppress occurrence of vibration and noise caused by vibration without increasing weight. <P>SOLUTION: A worm wheel of a worm reduction gear is composed of a metallic core unit 10 fixed to an output shaft and a gear part 20 made of synthetic resin, fixed to an outer peripheral part of the core unit 10, and having a gear tooth face. The core unit 10 is composed of a boss part 11 and a rim part 12 and is molded by, for example, cold forging. A radial rib 13 extending toward the outer periphery from the boss part 11 is provided in the rim part 12 of the core unit 10. This rib 13 is molded in a cold forging process for molding the core unit 10. As a result, rigidity of the core unit 10 can be increased and vibration and noise can be suppressed without increasing weight. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention detects a steering torque applied to a worm reducer and a steering wheel by a torque sensor, generates an auxiliary steering torque from an electric motor corresponding to the detected steering torque, and decelerates by the worm reducer. The present invention relates to an electric power steering apparatus that transmits to an output shaft of a steering mechanism, and more particularly to an apparatus that can suppress vibration and noise of a worm reducer.

  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.

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

  In EPS using a worm reducer as the power transmission mechanism (reduction gear), a worm wheel meshes with a worm on the drive shaft side of the electric motor, and this worm wheel is connected to the output shaft (for example, the steering mechanism) It is fitted to the pinion shaft and column shaft).

  By the way, the worm wheel of the worm reduction gear is shown in Patent Document 1 (pages 1 to 4, FIG. 2, and FIG. 3) and Patent Document 2 (page 4, FIG. 4, FIG. 6, and FIG. 8). In some cases, a synthetic resin gear portion is fixed to the outer periphery of a cored bar formed by press-molding a relatively thin steel plate or the like.

  That is, in Patent Document 1, in a worm wheel used in an electric power steering apparatus that applies assisting force by a motor to a steering mechanism, a core metal member that fixes the worm wheel to an output shaft of the electric power steering apparatus; It is composed of a resin toothed member that meshes with a worm that is rotated by a motor, and the cored bar member is formed so that its cross-sectional shape is substantially U-shaped, on the outer periphery of the cored bar member, A shoulder portion on which the resin constituting the toothed member is placed and a plurality of grooves into which the resin enters are provided.

Further, in Patent Document 2, a worm wheel having a metal fitting portion fitted to a steering shaft and a synthetic resin tooth portion integrated with an outer peripheral portion of the fitting portion and meshed with a worm. The fitting part is formed by press molding of a metal material. Moreover, the fitting part is provided with the several hole for filling a part of synthetic resin of a tooth | gear part. Furthermore, the fitting part is provided with a plurality of grooves in a direction substantially parallel to the rotating shaft on the outer peripheral part thereof to prevent sliding of the fitting part and the tooth part in the rotation direction.
JP-A-11-301501 JP 2001-206230 A (P2001-206230A)

  However, if the axial thickness of the rim part of the core metal is reduced for the purpose of reducing the weight and cost, the core metal is likely to be seized due to the reduction in rigidity and the gearing or sliding of the reduction gear part. (A decrease in the eigenvalue), and a sound due to vibration may occur.

  The present invention has been made in view of the circumstances as described above, and can improve the rigidity without increasing the weight, and can suppress the vibration and the sound generated by the vibration. An object is to provide an electric power steering apparatus.

In order to achieve the above object, a worm reduction gear according to the present invention has a worm meshed with a worm wheel,
The worm wheel is
A metal core fixed to the output shaft;
A synthetic resin gear portion fixed to the outer peripheral portion of the metal core and having a gear tooth surface;
Radial ribs are provided on the rim portion of the metal cored bar.

  Preferably, the rib extends to the inside of the synthetic resin gear portion.

  Preferably, the ribs increase the vibration rigidity of the worm wheel, and the natural frequency of the worm wheel is about 8 kHz or more.

  The electric power steering device according to the present invention detects a steering torque applied to a steering wheel by a torque sensor, and generates an auxiliary steering torque from the electric motor in response to the detected steering torque. 3. The vehicle is decelerated by the worm reducer according to any one of 3 and transmitted to the output shaft of the steering mechanism.

  According to the present invention, the rigidity can be increased without increasing the weight, and the vibration and the sound generated by the vibration can be suppressed.

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

  In the present embodiment, generally, a shape in which radial ribs are provided on the rim portion of the core metal is employed. The rib can increase the rigidity of the core metal without increasing the weight. Further, the rib can be formed in a cold forging process for forming the cored bar or in a press process. Therefore, by providing the rib on the rim portion of the cored bar, the rigidity can be increased without increasing the weight, and the vibration and the sound generated by the vibration can be suppressed. With this rib, it is possible to increase the natural frequency of the worm wheel to 8 kHz or more, which is difficult to be felt by human hearing. Further, by extending the rib to the inside of the synthetic resin gear portion, it is possible to provide a circumferential detent function between the cored bar and the synthetic resin gear portion.

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

  In the column assist type electric power steering apparatus, for example, an upper column (not shown) is slidably fitted to a lower column 2 (column tube) of a steering column so as to be telescopically slidable. A solid lower shaft 4 (input shaft) is rotatably supported in the lower column 2 (column tube).

  An output shaft 5 is connected to the vehicle front side of the lower shaft 4 (input shaft). An intermediate shaft (not shown) is connected to the front side of the output shaft 5 via, for example, a universal joint (not shown).

  A base end of a torsion bar 6 is press-fitted and fixed on the vehicle front side of the lower shaft 4 (input shaft). The torsion bar 6 extends inside a hollow output shaft 5 and has a distal end. Is fixed to the end of the output shaft 5 by a fixing pin 5a.

  A torque sensor part TS is provided on the vehicle rear side of the output shaft 5. That is, a detection groove 7 of the torque sensor unit TS is formed on the vehicle rear side of the output shaft 5, and a sleeve 8 of the torque sensor unit TS is disposed outside the groove 7 in the radial direction. is there. The sleeve 8 has a vehicle rear side end fixed to a vehicle front side end of the lower shaft 4 (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 22 meshing with a worm 21 of a worm reduction gear connected to a drive shaft of an electric motor (not shown) is attached to the output shaft 5.

  The worm 21 and the worm wheel 22 are housed in a rear housing 23 (gear housing) and a front housing 24 (cover).

  The output shaft 5 is rotatably supported by bearings 25 and 26 in the rear housing 23 (gear housing) and the front housing 24 (cover). Further, the lower shaft 4 (input shaft) is sealed by a seal member 17 provided in the rear housing 23 (gear housing).

  Therefore, the steering force generated when the driver steers the steering wheel (not shown) is applied to the steered wheels (not shown) via the input shaft 4, the torsion bar 6, the output shaft 5, and the rack and pinion type steering device. Communicated. Further, the rotational force of the electric motor (not shown) is transmitted to the output shaft 5 via the worm 21 and the worm wheel 22, and the rotational force and the rotational direction of the electric motor (not shown) are appropriately set. By controlling, an appropriate steering assist torque can be applied to the output shaft 5.

  FIG. 2A is a side view of the worm wheel of the worm speed reducer according to the first embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line bb in FIG. (C) is sectional drawing along the cc line of (a), (d) is a side view of the core metal of a worm wheel, (e) is the ee line of (d). FIG.

  The worm wheel 22 of the worm reducer includes a metal core 10 fixed to the output shaft, and a synthetic resin gear 20 fixed to the outer periphery of the core 10 and having a gear tooth surface.

  The cored bar 10 is composed of a boss part 11 and a rim part 12, and in this embodiment is formed by cold forging.

  In the present embodiment, radial ribs 13 extending from the boss portion 11 toward the outer periphery are provided on the rim portion 12 of the core metal 10.

  The rib 13 is formed in a cold forging process for forming the cored bar 10. Without increasing the weight, the rigidity of the cored bar 10 can be increased, and vibration and noise can be suppressed. With the rib 13, the natural frequency of the worm wheel 22 can be increased to 8 kHz or more which is difficult to be felt by human hearing.

(Second Embodiment)
FIG. 3A is a side view of the worm wheel of the worm speed reducer according to the second embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along line bb in FIG. (C) is sectional drawing along the cc line of (a), (d) is a side view of the core metal of a worm wheel, (e) is the ee line of (d). FIG.

  The present embodiment is substantially the same in configuration, operation, and effect as the first embodiment described above, and the differences will be described.

  The cored bar 10 is composed of a boss part 11 and a rim part 12, and is also formed by cold forging in the present embodiment.

  In the present embodiment, radial ribs 13 extending from the boss portion 11 to the outer periphery are provided on the rim portion 12 of the core metal 10, and the ribs 13 are formed in a cold forging process for forming the core metal 10. However, the rib 13 extends to the inside of the synthetic resin gear portion 20 (that is, the rib 13 extends to the outer periphery of the core metal 10). Thereby, it is also possible to provide a circumferential detent function between the cored bar 10 and the synthetic resin gear part 20. Other operations and effects are the same as those of the above-described embodiment.

(Third embodiment)
FIG. 4A is a side view of a worm wheel of a worm reduction gear according to a third embodiment of the present invention, and FIG. 4B is a cross-sectional view taken along line bb in FIG. (C) is sectional drawing along the cc line of (a), (d) is a side view of the core metal of a worm wheel, (e) is the ee line of (d). FIG.

  This embodiment is substantially the same in configuration, operation, and effect as the first and second embodiments described above, and the differences will be described.

  The cored bar 10 includes a boss part 11 and a rim part 12, and in the present embodiment, is formed by press molding.

  Also in the present embodiment, the rim portion 12 of the core metal 10 is provided with radial ribs 13 extending from the boss portion 11 toward the outer periphery. The rib 13 is formed by a pressing process for forming the cored bar 10. Other operations and effects are the same as those of the above-described embodiment.

(Fourth embodiment)
FIG. 5A is a side view of a worm wheel of a worm reduction gear according to a fourth embodiment of the present invention, and FIG. 5B is a cross-sectional view taken along line bb in FIG. (C) is sectional drawing along the cc line of (a), (d) is a side view of the core metal of a worm wheel, (e) is the ee line of (d). FIG.

  This embodiment is substantially the same in configuration, operation, and effect as the first, second, and third embodiments described above, and the differences will be described.

  The cored bar 10 includes a boss part 11 and a rim part 12, and in the present embodiment, is formed by press molding.

  Also in the present embodiment, the rim portion 12 of the core metal 10 is provided with radial ribs 13 extending from the boss portion 11 toward the outer periphery. The rib 13 is formed by a pressing process for forming the cored bar 10.

  The rib 13 extends to the inside of the gear portion 20 made of synthetic resin (that is, the rib 13 extends to the outer periphery of the core metal 10). Thereby, it is also possible to provide a circumferential detent function between the cored bar 10 and the synthetic resin gear part 20. Other operations and effects are the same as those of the above-described embodiment.

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

1 is a longitudinal sectional view of an electric power steering device according to a first embodiment of the present invention. (A) is a side view of the worm wheel of the worm reduction gear according to the first embodiment of the present invention, (b) is a cross-sectional view taken along line bb of (a), (c) ) Is a cross-sectional view taken along the line cc of (a), (d) is a side view of the core of the worm wheel, and (e) is taken along the line ee of (d). FIG. (A) is a side view of the worm wheel of the worm speed reducer which concerns on 2nd Embodiment of this invention, (b) is sectional drawing along the bb line of (a), (c) ) Is a cross-sectional view taken along the line cc of (a), (d) is a side view of the core of the worm wheel, and (e) is taken along the line ee of (d). FIG. (A) is a side view of the worm wheel of the worm reduction gear which concerns on 3rd Embodiment of this invention, (b) is sectional drawing along the bb line of (a), (c) ) Is a cross-sectional view taken along the line cc of (a), (d) is a side view of the core of the worm wheel, and (e) is taken along the line ee of (d). FIG. (A) is a side view of the worm wheel of the worm reducer which concerns on 4th Embodiment of this invention, (b) is sectional drawing along the bb line of (a), (c) ) Is a cross-sectional view taken along the line cc of (a), (d) is a side view of the core of the worm wheel, and (e) is taken along the line ee of (d). FIG.

Explanation of symbols

2 Lower column (column tube)
4 Lower shaft (input shaft)
DESCRIPTION OF SYMBOLS 5 Output shaft 5a Fixing pin 6 Torsion bar 7 Detection groove 8 Sleeve 9 Coil 10 Metal core 11 Boss part 12 Rim part 13 Radial rib 20 Synthetic resin gear part 21 Worm 22 Worm wheel 23 Rear housing ( Gear housing)
24 Front housing (cover)
25, 26 Bearing 27 Seal member TS Torque sensor part

Claims (4)

In the worm speed reducer in which the worm is engaged with the worm wheel,
The worm wheel is
A metal core fixed to the output shaft;
A synthetic resin gear portion fixed to the outer peripheral portion of the metal core and having a gear tooth surface;
A worm speed reducer characterized in that radial ribs are provided on a rim portion of the metal cored bar.   The worm gear reducer according to claim 1, wherein the rib extends to the inside of the synthetic resin gear portion.   3. The worm speed reducer according to claim 1, wherein a vibration rigidity of the worm wheel is increased by the rib, and a natural frequency of the worm wheel is about 8 kHz or more.   The worm reduction gear according to any one of claims 1 to 3, wherein a steering torque applied to the steering wheel is detected by a torque sensor, and an auxiliary steering torque is generated from the electric motor in response to the detected steering torque. The electric power steering apparatus is characterized in that the electric power steering apparatus decelerates and transmits to the output shaft of the steering mechanism.

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