JP2013216121A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device configured to apply engagement reaction of a driven gear fixed to an output shaft to a fitting part of an input shaft and the output shaft, to allow increase/decrease of the engagement reaction of the driven gear to increase/decrease loss torque based on friction of the shafts in the fitting part thereof.SOLUTION: In an electric power steering device, a bearing 16 is disposed around a fitting part K of an input shaft 13 and an output shaft 14 where engagement reaction of a worm wheel 32 fixed to the output shaft 14 is applied. The bearing 16 is supported in a gear housing 18.

Description

  The present invention relates to an electric power steering apparatus.

  As an electric power steering device, as described in Patent Document 1, an input shaft and an output shaft are supported on a gear housing and fitted to each other, and torque detecting means is provided between the input shaft and the output shaft. Some drive gears are driven by an electric motor controlled by a detection result, and a driven gear meshing with the drive gear is fixed to an output shaft.

  A steering wheel input torque (steering torque) based on the steering angle applied by the driver to the steering wheel is transmitted from the input shaft, the torsion bar, and the output shaft to the steering wheel via a steering device such as a rack and pinion type steering device.

  At this time, the above-mentioned handle input torque applied to the steering wheel by the driver is detected by the torque detection means, and the assist torque generated on the rotating shaft of the electric motor driven by this detection result is the engagement between the drive gear and the driven gear. It is transmitted to the output shaft via. The electric motor gives a desired assist torque to the output shaft by appropriately controlling the rotational force and the rotational direction.

JP2009-1240

  By the way, in Patent Document 1, an output shaft to which a driven gear is fixed is supported on a gear housing by two upper and lower bearings sandwiching the driven gear. In such an output shaft support structure, the meshing reaction force generated in the driven gear due to meshing with the drive gear is stably supported by the upper and lower bearings. For this reason, the meshing reaction force of the driven gear hardly reaches the fitting portion of the input shaft and the output shaft. Therefore, the increase or decrease of the loss torque generated based on the friction of both shafts at this fitting portion is small with respect to the increase or decrease of the meshing reaction force of the driven gear. This is a hysteresis characteristic as shown in FIG. 5 in which the horizontal axis represents the handle input torque Th (corresponding to the steering angle applied by the driver to the steering wheel) and the vertical axis represents the assist torque Tm of the electric motor. Means stabilization. As a result, in a turning state with a large steering wheel steering angle, the hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor is small, and the steering wheel input torque Th of the turning A and the turning back B during turning is reduced by a small steering angle. Even if it is only repeated, the assist torque Tm of the electric motor changes and the steering stability (feeling of sitting) is poor.

  In Patent Document 1, a fitting portion between the input shaft and the output shaft is disposed between the bearing that supports the output shaft on which the driven gear is fixed on the gear housing and the bearing that supports the input shaft on the gear housing. A support structure is also disclosed. In such a support structure for the input shaft and the output shaft, the input shaft and the output shaft are displaced so as to be bent with their fitting portions as the break points due to the meshing reaction force generated in the driven gear. For this reason, the meshing reaction force of the driven gear acting on the output shaft is not easily transmitted to the input shaft at the fitting portion with the input shaft. Therefore, also in this case, the increase or decrease of the loss torque generated based on the friction of both shafts at this fitting portion is small with respect to the increase or decrease of the meshing reaction force of the driven gear. As a result, the hysteresis characteristics of the steering wheel input torque Th and the assist torque Tm of the electric motor at this time are also the same as in FIG. 5, and as a result, the steering wheel with respect to the constant assist torque Tm of the electric motor in a turning state with a large steering angle. The hysteresis width w of the input torque Th is small, and the steering torque (Tm) of the electric motor is stabilized even if the steering input torque Th of the turning A and the turning back B during turning is repeated by a small steering angle. Feeling) is bad.

  The problem of the present invention is that in an electric power steering apparatus, the meshing reaction force of a driven gear fixed to an output shaft is exerted on the fitting portion of the input shaft and the output shaft, and the increase and decrease of the meshing reaction force of the driven gear is The purpose is to increase or decrease the loss torque based on the friction of both shafts in the fitting portion.

  According to the first aspect of the present invention, the input shaft and the output shaft are supported by the gear housing and fitted to each other, and torque detecting means is provided between the input shaft and the output shaft, and controlled by the detection result of the torque detecting means. In an electric power steering device in which a drive gear is driven by an electric motor and a driven gear meshing with the drive gear is fixed to the output shaft, the input shaft and output on which the meshing reaction force of the driven gear fixed to the output shaft acts A bearing is provided around the fitting portion of the shaft, and this bearing is supported by a gear housing.

  According to a second aspect of the present invention, in the first aspect of the present invention, the input shaft and the output shaft are fitted through a bush.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the output shaft further includes a bearing provided around a fitting portion with the input shaft, and a bearing provided at a lower portion of the fixed portion of the driven gear. It is made to be supported by the gear housing via.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the hysteresis characteristic between the handle input torque applied to the input shaft and the assist torque of the electric motor is such that the meshing reaction force of the driven gear. Accordingly, the torque is set by the loss torque generated in the fitting portion between the input shaft and the output shaft.

  In the invention according to claim 5, in the invention according to claim 4, the hysteresis width of the handle input torque with respect to the constant assist torque of the electric motor is set to be small in the vicinity of the neutral where the handle steering angle is small. In a large turning state, it is set to be large.

(Claims 1, 4, 5)
(a) A bearing is provided around the fitting portion between the input shaft and the output shaft on which the meshing reaction force of the driven gear fixed to the output shaft acts, and this bearing is supported by the gear housing. As a result, the input shaft to which the meshing reaction force of the driven gear has exerted from the output shaft is received and supported by the bearings around the fitting portion of both shafts. Therefore, the increase / decrease in the loss torque generated based on the friction of the two shafts at the fitting portion increases with respect to the increase / decrease in the meshing reaction force of the driven gear. This is because the hysteresis characteristic as shown in FIG. 5 is obtained by taking the steering wheel input torque Th (corresponding to the steering wheel steering angle applied by the driver to the steering wheel) on the horizontal axis and the assist torque Tm of the electric motor on the vertical axis. This means that the torque changes greatly as the handle input torque increases or decreases.

  Thus, near the neutral position where the steering wheel steering angle is small, the hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor is set small, and the steering response near the neutral steering angle can be maintained well.

  On the other hand, in a turning state where the steering wheel steering angle is large, the hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor is set to be large, and the steering wheel input torque Th of the turning A and the turning back B during turning is slightly steered. It is possible to stabilize the assist torque Ta of the electric motor when the corner is repeated, and to improve the feeling of sitting of the handle.

(Claim 2)
(b) When the input shaft and the output shaft are fitted through the bush, the meshing reaction force of the driven gear is applied to the input shaft from the output shaft through the bush. Can be stably received and supported by the bearings around.

(Claim 3)
(c) The output shaft is supported by the gear housing via a bearing provided around the fitting portion with the input shaft and a bearing provided below the fixed portion of the driven gear. Thereby, the above-mentioned (b) can be realized while the driven gear fixed to the output shaft is pivotally supported by the upper and lower bearings.

FIG. 1 is a sectional view showing an electric power steering apparatus. FIG. 2 is an enlarged cross-sectional view showing a main part of the electric power steering apparatus. FIG. 3 is a flowchart showing a steering procedure according to the present invention. FIG. 4 is a diagram showing hysteresis characteristics. FIG. 5 is a diagram showing conventional hysteresis characteristics.

  FIGS. 1 and 2 show a column assist type electric power steering apparatus 10 in which an upper column tube 11A and a lower column tube 11B constituting a column tube 11 are slidably fitted. A steering shaft 12 and an input shaft 13 that are spline-fitted are pivotally supported in both column tubes 11A and 11B.

  One end of a torsion bar 21 constituting the torque detecting means 20 is press-fitted and fixed to the inner diameter portion of the lower end of the input shaft 13. The torsion bar 21 extends in the hollow portion of the output shaft 14, and the tip thereof is fixed to the output shaft 14 by a pin 21A.

  As shown in FIG. 2, the input shaft 13 and the output shaft 14 are connected via a bush 15 at a fitting portion K in which the lower end enlarged inner peripheral portion of the input shaft 13 and the upper reduced diameter outer peripheral portion of the output shaft 14 are fitted to each other. And are supported by the gear housing 18 by bearings 16 and 17 as will be described later. The gear housing 18 is formed by connecting first and second gear housings 18A and 18B with bolts 18C, and supports the bearing 16 on the first gear housing 18A and supports the bearing 17 on the second gear housing 18B.

  The torque detection means 20 holds the magnet 22 in a magnet holding portion 22A fixed to the outer periphery of the input shaft 13, and holds a set of yokes 23 in a yoke holding portion 23A fixed to the outer periphery of the output shaft 14. . The yoke 23 is disposed around the magnet 22, and a magnetic sensor (torque sensor) 24 including a Hall IC or the like for detecting the magnetic flux density generated between the pair of yokes 23 is provided in the gear housing 18. When the handle input torque is applied to the input shaft 13 and the torsion bar 21 is twisted, the magnetic sensor 24 detects the magnetic flux density generated between the pair of yokes 23 due to the twist of the torsion bar 21. The handle input torque is detected by the detection signal of the magnetic sensor 24.

  The electric power steering apparatus 10 includes an electric motor 30 fixed to a gear housing 18. A worm gear (drive gear) 31 connected to the rotating shaft of the electric motor 30 is pivotally supported by the gear housing 18, and a worm wheel (driven gear) 32 that meshes with the worm gear 31 is fixed to the outer periphery of the intermediate portion of the output shaft 14. ing. The electric motor 30 is controlled by a detection signal of the magnetic sensor 24 constituting the torque detection means 20 by an ECU (not shown), and drives the worm gear 31.

  Therefore, the electric power steering apparatus 10 operates as shown in steps 1 to 5 of FIG. That is, the steering wheel input torque Th (steering torque) based on the steering angle applied by the driver to the steering wheel is transmitted from the input shaft 13, the torsion bar 21, and the output shaft 14 via a steering device such as a rack and pinion type steering device. It is transmitted to the steering wheel. At this time, the above-mentioned handle input torque applied to the steering wheel by the driver is detected by the torque detection means 20, and the assist torque Tm generated on the rotating shaft of the electric motor 30 driven by this detection result is the worm gear 31 and the worm wheel. 32 is transmitted to the output shaft 14 through the meshing. The electric motor 30 gives a desired assist torque to the output shaft 14 by appropriately controlling the rotational force and the rotational direction by the ECU.

  However, in the electric power steering apparatus 10, in step 5 of FIG. 3, the electric motor 30 applies the assist torque Tm to the worm gear 31, the worm wheel 32, and the output shaft 14, and the meshing reaction force caused by the meshing with the worm gear 31. Is generated in the worm wheel 32 (step 6), the increase / decrease in the meshing reaction force of the worm wheel 32 increases / decreases the loss torque based on the friction of the shafts 13, 14 at the fitting portion K of the input shaft 13 and the output shaft 14. As obtained (step 7), the following configuration is provided.

  That is, the bearing 16 is provided around the fitting portion K between the input shaft 13 and the output shaft 14 where the meshing reaction force of the worm wheel 32 fixed to the output shaft 14 acts, and the bearing 16 is supported by the gear housing 18.

  In this embodiment, the input shaft 13 and the output shaft 14 are fitted via the bush 15. In the present invention, in the axial direction of the input shaft 13, the output shaft 14, and the bearing 16, at least a part of the fitting portion K (bush 15) of the input shaft 13 and the output shaft 14 is located within the bearing width of the bearing 16. Anything is fine. Most preferably, the fitting portion K (bush 15) of the input shaft 13 and the output shaft 14 is located in the entire bearing width of the bearing 16.

  In the present embodiment, the output shaft 14 includes a bearing 16 provided around the fitting portion K with the input shaft 13 and a worm wheel 32 that is inserted and fixed to the outer periphery of the intermediate portion of the output shaft 14. The boss (fixed portion) 32A was supported by the gear housing 18 via a bearing 17 provided at the lower outer periphery. The bearing 16 and the bearing 17 are ball bearings. The outer ring of the bearing 16 is loaded into the step hole of the first gear housing 18 </ b> A, and the inner ring is loaded and held on the outer periphery of the input shaft 13. The bearing 17 has an outer ring sandwiched between a step hole of the second gear housing 18B and a retaining ring 17A fixed to the gear housing 18, and an inner ring having a step shoulder of the boss 32A of the worm wheel 32 and the output shaft 14. The nut 17B is screwed to the nut 17B and fixed.

Thereby, in the electric power steering apparatus 10, as will be described in detail later,
(1) The hysteresis characteristic between the handle input torque Th applied to the input shaft 13 and the assist torque Tm of the electric motor 30 is such that the input shaft 13 and the output shaft according to the meshing reaction force of the worm wheel 32 as shown in FIG. 14 is set by the loss torque generated in the fitting portion K,
(2) The hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor 30 is set small in the vicinity of the neutral where the steering wheel steering angle is small, and large in the turning state where the steering wheel steering angle is large.

That is, according to the present embodiment, the following effects are obtained.
(a) A bearing 16 is provided around the fitting portion K between the input shaft 13 and the output shaft 14 on which the meshing reaction force of the worm wheel 32 fixed to the output shaft 14 acts, and the bearing 16 is supported by the gear housing 18. . Accordingly, the input shaft 13 to which the meshing reaction force of the worm wheel 32 exerts from the output shaft 14 is received and supported by the bearing 16 around the fitting portion K of the shafts 13 and 14. Therefore, as the mesh reaction force of the worm wheel 32 increases / decreases, the loss torque generated based on the friction between the shafts 13 and 14 at the fitting portion K increases. This is a hysteresis characteristic as shown in FIG. 5 in which the horizontal axis represents the handle input torque Th (corresponding to the steering angle applied by the driver to the steering wheel) and the vertical axis represents the assist torque Tm of the electric motor 30. However, it means that it greatly changes with the increase / decrease of the handle input torque.

  As a result, in the vicinity of the neutral where the steering wheel steering angle is small, the hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor 30 is set small, and the steering response near the neutral steering angle can be maintained well.

  On the other hand, in a turning state with a large steering wheel steering angle, the hysteresis width w of the steering wheel input torque Th with respect to the constant assist torque Tm of the electric motor 30 is set large, and the steering wheel input torque Th of the cutting A and the turning back B during turning is very small. It is possible to stabilize the assist torque Ta of the electric motor 30 when the steering angle is repeated, and to improve the steering feeling of the steering wheel.

  (b) When the input shaft 13 and the output shaft 14 are fitted through the bush 15, the meshing reaction force of the worm wheel 32 is applied to the input shaft 13 exerted from the output shaft 14 through the bush 15. The bearings 16 around the fitting portions K of the shafts 13 and 14 can be stably received and supported.

  (c) The output shaft 14 is connected to a gear 16 via a bearing 16 provided around the fitting portion K with the input shaft 13 and a bearing 17 provided at the lower outer periphery of a boss (fixed portion) 32A of the worm wheel 32. It is supported by the housing 18. Thereby, the above-mentioned (b) can be realized while the worm wheel 32 fixed to the output shaft 14 is pivotally supported by the upper and lower bearings 16 and 17 stably.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and even if there is a design change or the like without departing from the gist of the present invention. It is included in the present invention. For example, in the electric power steering apparatus to which the present invention is applied, the drive gear and the driven gear are not limited to those constituting the worm reduction gear, and are composed of other gears such as a helical gear and a bevel gear. Also good.

  In the present invention, the input shaft and the output shaft are supported by the gear housing, fitted to each other, and provided with a torque detection means between the input shaft and the output shaft, and driven by an electric motor controlled by the detection result of the torque detection means. In an electric power steering apparatus in which a driven gear meshing with a drive gear is fixed to an output shaft while driving the gear, the engagement between the input shaft and the output shaft on which the meshing reaction force of the driven gear fixed to the output shaft acts A bearing was provided around the portion, and this bearing was supported by the gear housing. Thus, in the electric power steering apparatus, the meshing reaction force of the driven gear fixed to the output shaft is exerted on the fitting portion of the input shaft and the output shaft, and the increase and decrease of the meshing reaction force of the driven gear is increased by the fitting portion of both shafts. The loss torque based on the friction of both axes in can be increased or decreased.

DESCRIPTION OF SYMBOLS 10 Electric power steering apparatus 13 Input shaft 14 Output shaft 15 Bushing 16, 17 Bearing 18 Gear housing 20 Torque detection means 30 Electric motor 31 Worm gear (drive gear)
32 Worm wheel (driven gear)
K mating part

Claims (5)

The input shaft and the output shaft are supported by the gear housing and fitted with each other, and a torque detection means is provided between the input shaft and the output shaft
In the electric power steering device in which the driving gear is driven by the electric motor controlled by the detection result of the torque detecting means, and the driven gear meshing with the driving gear is fixed to the output shaft.
An electric power steering apparatus characterized in that a bearing is provided around a fitting portion between an input shaft and an output shaft on which a meshing reaction force of a driven gear fixed to the output shaft acts, and the bearing is supported by a gear housing.   The electric power steering apparatus according to claim 1, wherein the input shaft and the output shaft are fitted via a bush.   The said output shaft is supported by the gear housing via the bearing provided in the circumference | surroundings of the fitting part with an input shaft, and the bearing provided in the lower part of the fixing | fixed part of the driven gear. Electric power steering device.   The hysteresis characteristic between the handle input torque applied to the input shaft and the assist torque of the electric motor is set by a loss torque generated in a fitting portion between the input shaft and the output shaft in accordance with the meshing reaction force of the driven gear. The electric power steering device according to any one of 1 to 3. The hysteresis width of the handle input torque with respect to the constant assist torque of the electric motor is
It is set to be small near the neutral position where the steering angle is small.
The electric power steering apparatus according to claim 4, wherein the electric power steering apparatus is set to be large in a turning state with a large steering angle.

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