JP2015000594A - Steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering device which can suppress a malfunction resulting from an inclination of a nut of a ball screw mechanism.SOLUTION: An electric power steering device 1 comprises a ball screw mechanism 40 and a reduction mechanism 50. The ball screw mechanism 40 has a nut 41 which is screwed via a plurality of balls 42 at an external peripheral face of a rack shaft 16. The reduction mechanism 50 has a drive pulley 51 which is integrally assembled to an output shaft 21a of a motor 21, a driven pulley 52 which is integrally assembled to the nut 41, and a belt 53 which is wound to the pulleys 51, 52. The other side of the nut 41 is rotatably supported by a ball bearing 44 which is fit to an internal peripheral face of a cylindrical housing 30. A center axis of the internal peripheral face of the housing 30 to which the ball bearing 44 is fit is inclined to a direction in which the center axis is separated from the drive pulley 51 as progressing toward one side from the other side of the nut 41 with respect to a center axis of the rack shaft 16.

Description

  The present invention relates to a vehicle steering apparatus.

  As this type of steering device, a so-called rack parallel type electric power steering device in which an output shaft of a motor is arranged in parallel to a central axis of a rack shaft of a vehicle is known (see, for example, Patent Document 1). The electric power steering device includes a ball screw mechanism attached to the outer peripheral surface of the rack shaft, a speed reducing mechanism that reduces the rotation of the output shaft of the motor and transmits the rotation to the ball screw mechanism, and covers the periphery of the ball screw mechanism and the speed reducing mechanism. A cylindrical housing is provided.

  The ball screw mechanism includes a cylindrical nut that is screwed into a thread groove formed on the outer peripheral surface of the rack shaft via a plurality of balls. One side of the nut in the axial direction is rotatably supported by a ball bearing fitted to the inner peripheral surface of the housing. The ball screw mechanism applies an axial force to the rack shaft as the nut rotates relative to the rack shaft.

  The speed reduction mechanism includes a driven pulley that is integrally assembled to the other side opposite to one side in the axial direction of the nut, a driven pulley that is integrally assembled to the output shaft of the motor, and a pulley that is wound around each pulley. Equipped belt. The speed reduction mechanism decelerates the rotation of the output shaft of the motor via each pulley and belt, transmits the rotation to the nut of the ball screw mechanism, and rotates the nut.

  According to such a configuration, when the output shaft of the motor rotates, the nut of the ball screw mechanism rotates via the speed reduction mechanism, so that an axial force is applied to the rack shaft. The axial force applied to the rack shaft becomes an assist force to assist the driver's steering operation.

JP 2012-144202 A

  By the way, in such an electric power steering device, the inner diameter of the cylindrical portion of the housing into which the ball bearing is fitted is slightly smaller than the outer diameter of the ball bearing in order to absorb shape errors of the housing and the bearing. It is set to a large value. That is, a minute clearance (gap) is provided between the outer peripheral surface of the ball bearing and the inner peripheral surface of the housing. One side of the nut is cantilevered by a ball bearing. Therefore, when belt tension is applied via the driven pulley on the other side of the nut, the nut is inclined slightly according to the clearance between the ball bearing and the housing. If the ball passage from the ball circulation path such as a deflector to the rolling path is narrowed by the inclination of the nut, the sliding resistance of the ball increases, so that the operation noise may increase. When the nut is tilted, this ball passage is narrowed on the other side and widened on the one side, so that the sliding acting on the ball depends on the rotation direction of the nut relative to the rack shaft. Resistance can change. This becomes a factor of the left-right difference with respect to the preload, which may give the driver a feeling of strangeness. The preload is a steering torque required to rotate the steering wheel in a state where the assist force from the motor is not applied to the rack shaft.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a steering device that can suppress problems caused by the inclination of the nut of the ball screw mechanism.

  In order to solve the above-mentioned problem, a cylindrical nut screwed into a thread groove formed on the outer peripheral surface of a turning shaft of a vehicle via a plurality of balls is provided, and the rolling nut is rotated based on the rotation of the nut. A ball screw mechanism that applies axial force to the rudder shaft; a drive pulley that is integrally assembled to the output shaft of the motor; a driven pulley that is integrally assembled to one side of the nut in the axial direction; Deceleration having an endless belt wound around the drive pulley and the driven pulley, and decelerating the rotation of the output shaft of the motor via the drive pulley, the belt, and the driven pulley and transmitting it to the nut Fitting mechanism to the inner peripheral surface of a cylindrical housing that covers the periphery of the ball screw mechanism and the speed reduction mechanism, and rotatably supports the other side opposite to the one side in the axial direction of the nut Bearings to In the steering device that applies a force from the motor to the steered shaft via the speed reduction mechanism and the ball screw mechanism, the center axis of the inner peripheral surface of the housing, into which the bearing is fitted, is It was made to incline in the direction which leaves | separates from the said drive pulley toward the said one side part from the said other side part of the said nut with respect to the center axis | shaft of a shaft.

  According to this configuration, when the bearing is fitted to the inner peripheral surface of the housing, the center axis of the bearing is inclined with respect to the center axis of the steered shaft. Thereby, the central axis of the nut supported by the bearing is also inclined with respect to the central axis of the steered shaft. More specifically, the central axis of each of the bearing and the nut is inclined with respect to the central axis of the steered shaft in a direction away from the drive pulley toward the one side from the other side of the nut. In this state, if belt tension is applied to one side of the nut, the central axes of the bearing and the nut are inclined toward the drive pulley. As a result, the central axis of the nut and the central axis of the steered shaft Can be matched. Therefore, the malfunction resulting from the inclination of the nut can be suppressed.

  The steering device as described above is preferably applied to a steering device in which the output shaft of the motor is arranged in parallel with the central axis of the steered shaft, that is, a rack parallel type steering device. Since the steering device having such a configuration tends to cause the inclination of the nut due to the tension of the belt, it is particularly effective to have a configuration for suppressing the inclination of the nut as described above.

  According to this steering device, it is possible to suppress problems caused by the inclination of the nut of the ball screw mechanism.

Sectional drawing which shows the cross-sectional structure about one Embodiment of an electric power steering device. Sectional drawing which shows the cross-sectional structure of the assist mechanism periphery about the electric power steering apparatus of embodiment. Sectional drawing which shows the cross-sectional structure of the ball bearing periphery which supports the nut of the ball screw mechanism about the assist mechanism of embodiment. Sectional drawing which shows the partial cross section structure of the 1st housing about the electric power steering apparatus of embodiment. Sectional drawing which shows the cross-sectional structure in the state in which the tension | tensile_strength of the belt is not provided to the nut about the electric power steering apparatus of embodiment. Sectional drawing which shows the cross-sectional structure in the state by which the tension | tensile_strength of the belt was provided to the nut about the electric power steering apparatus of embodiment.

Hereinafter, an embodiment of an electric power steering apparatus will be described with reference to FIGS.
As shown in FIG. 1, the electric power steering apparatus 1 includes a steering mechanism 10 for turning the steered wheels 3 based on an operation of the driver's steering wheel 2 and an assist mechanism 20 for assisting the driver's steering operation. ing.

  The steering mechanism 10 includes a steering shaft 11 that serves as a rotating shaft of the steering wheel 2. The steering shaft 11 includes a column shaft 12 connected to the steering wheel 2, an intermediate shaft 13 connected to the lower end portion of the column shaft 12, and a pinion shaft 14 connected to the lower end portion of the intermediate shaft 13. A lower end portion of the pinion shaft 14 is connected to a rack shaft 16 that is a steered shaft via a rack and pinion mechanism 15. In the steering mechanism 10, the column shaft 12, the intermediate shaft 13, and the pinion shaft 14 rotate integrally as the driver operates the steering wheel 2. Then, the rotational motion of the pinion shaft 14 is converted into a reciprocating linear motion in the axial direction of the rack shaft 16 via the rack and pinion mechanism 15. The reciprocating linear motion of the rack shaft 16 is transmitted to the tie rod 18 through ball joints 17 connected to both ends thereof, and the tie rod 18 operates. Based on the operation of the tie rod 18, the turning angle of the steered wheels 3 changes.

  The assist mechanism 20 is provided on the rack shaft 16. The assist mechanism 20 includes a motor 21 and a power transmission mechanism 22. The output shaft 21 a of the motor 21 is disposed in parallel with the central axis of the rack shaft 16. That is, the electric power steering device 1 is a rack parallel type electric power steering device. The power transmission mechanism 22 converts the rotational force of the output shaft 21 a of the motor 21 into the axial force of the rack shaft 16 and applies it to the rack shaft 16. The assist mechanism 20 assists the driver's steering operation using the force applied from the motor 21 to the rack shaft 16 via the power transmission mechanism 22 as an assist force.

  The outer periphery of the rack shaft 16 is covered with a housing 30 made of a metal material. The housing 30 includes a first housing 31 and a second housing 32, and is configured by connecting them together. The housing 30 accommodates the pinion shaft 14, the rack shaft 16, and the power transmission mechanism 22 therein. A recess 33 is formed at the bottom of the housing 30 that houses the power transmission mechanism 22 so as to protrude downward in the vertical direction. The motor 21 is fixed to the side wall 33 a of the recess 33. A through hole 34 is formed in the side wall 33 a of the recess 33. The output shaft 21 a of the motor 21 is inserted into the housing 30 through the through hole 34 and is connected to the power transmission mechanism 22.

Next, the configuration of the power transmission mechanism 22 will be described.
As shown in FIG. 2, the power transmission mechanism 22 includes a ball screw mechanism 40 attached around the rack shaft 16 and a speed reduction mechanism 50 that decelerates the rotation of the output shaft 21 a of the motor 21 and transmits the rotation to the ball screw mechanism 40. It has.

  The ball screw mechanism 40 includes a cylindrical nut 41 that is screwed into a thread groove 16 a formed on the outer peripheral surface of the rack shaft 16 via a plurality of balls 42. A thread groove 41 a is formed on the inner peripheral surface of the nut 41. A spiral rolling path L1 is formed by a space surrounded by the screw groove 41a of the nut 41 and the screw groove 16a of the rack shaft 16. The nut 41 is formed with a recess 41b that opens to the outer peripheral surface side. Through holes 41c and 41d communicating with the thread groove 41a are formed on the bottom surfaces of both ends of the recess 41b in the axial direction of the nut 41, respectively. A circulation member (deflector) 43 is fitted into the recess 41b. The circulation member 43 forms the circulation path L2 which short-circuits between two places of the rolling path L1 with the inner wall surface of the recessed part 41b. The rolling path L1 and the circulation path L2 serve as paths through which the balls 42 roll.

  On the other hand, an annular flange portion 41e is formed on one side of the nut 41 in the axial direction. A driven pulley 52 is fitted to the outer peripheral surface of the nut 41 so as to engage with the flange portion 41 e in the axial direction, and a single row ball bearing 44 is fitted adjacent to the driven pulley 52. . A male screw portion 41 f is formed on the other side of the nut 41 in the axial direction. A lock nut 45 is screwed onto the male screw portion 41f. The driven pulley 52 and the ball bearing 44 are sandwiched between the lock nut 45 and the flange portion 41 e, whereby the driven pulley 52 and the inner ring 44 a of the ball bearing 44 are integrally assembled to the nut 41. The outer ring 44 b of the ball bearing 44 is fitted on the inner peripheral surface of the first housing 31. That is, the nut 41 is rotatably supported by the ball bearing 44. In the drawing, the direction from the male thread portion 41f of the nut 41 toward the flange portion 41e, that is, the direction from the other side portion of the nut 41 toward the one side portion is indicated by an arrow a.

  As shown in FIG. 3, a circumferential groove 35 is formed on the inner circumferential surface of the first housing 31 to which the outer ring 44 b of the ball bearing 44 is fitted. An O-ring 46 is inserted into the circumferential groove 35 while being compressed by the outer ring 44 b of the ball bearing 44. Due to the elastic deformation of the O-ring 46, it is possible to ensure smooth rotation of the nut 41 even when an axial deviation exists between the rack shaft 16 and the nut 41 due to, for example, an assembly error. .

  In the ball screw mechanism 40 having such a structure, when the nut 41 rotates relative to the rack shaft 16, the ball 42 receives a load (frictional force) from the nut 41 and the rack shaft 16 and rolls in the rolling path L1. Move. When the ball 42 rolling in the rolling path L1 reaches one of the connection points of the rolling path L1 and the circulation path L2, it is guided into the circulation path L2. The ball 42 introduced into the circulation path L2 is discharged to the rolling path L1 through the other connection point of the rolling path L1 and the circulation path L2. That is, the ball 42 circulates infinitely in the rolling path L1 through the circulation path L2. The ball screw mechanism 40 transmits the torque of the nut 41 to the rack shaft 16 by such infinite circulation of the balls 42, and moves the rack shaft 16 in the axial direction with respect to the nut 41. That is, the ball screw mechanism 40 applies an axial force to the rack shaft 16 based on the rotation of the nut 41.

  As shown in FIG. 2, the speed reduction mechanism 50 is wound around the drive pulley 51 that is integrally assembled with the output shaft 21 a of the motor 21, the driven pulley 52 that is integrally assembled with the nut 41, and the pulleys 51 and 52. An endless belt 53 is provided. In the speed reduction mechanism 50, the rotation of the drive pulley 51 is decelerated via the belt 53 and the driven pulley 52 and transmitted to the nut 41.

  In the assist mechanism 20 having such a configuration, when the output shaft 21 a of the motor 21 is rotated based on energization of the motor 21, the drive pulley 51 rotates integrally with the output shaft 21 a of the motor 21. As a result, the drive pulley 51 integrally rotates the driven pulley 52 and the nut 41 via the belt 53. As the nut 41 rotates, an axial force is applied to the rack shaft 16.

  Next, the shape of the fitting portion of the ball bearing 44 in the first housing 31 will be described with reference to FIG. In FIG. 4, the center axis of the rack shaft 16 is indicated by “m1”.

  As shown in FIG. 4, the portion of the first housing 31 where the outer ring 44b of the ball bearing 44 fits is a cylindrical portion 31a having one end opened. The inner diameter of the cylindrical portion 31 a is set to a value slightly larger than the outer diameter of the outer ring 44 b of the ball bearing 44. The central axis m2 of the inner peripheral surface of the cylindrical portion 31a is inclined with respect to the central axis m1 of the rack shaft 16 by a predetermined angle θ in a direction away from the drive pulley 51 as it goes in the direction indicated by the arrow a. In addition, the direction shown by the arrow a shows the direction which goes to the flange part 41e from the external thread part 41f of the nut 41 as demonstrated in FIG. Further, in the figure, for reference, the position of the inner peripheral surface of the cylindrical portion 31a when the central axis m2 of the cylindrical portion 31a coincides with the central axis m1 of the rack shaft 16 is indicated by a two-dot chain line. .

Next, with reference to FIG.5 and FIG.6, the effect | action of the electric power steering apparatus 1 of this embodiment is demonstrated.
As shown in FIG. 5, when the electric power steering apparatus 1 is manufactured, the ball bearing 44 and the driven pulley 52 are integrally assembled with the nut 41, and then the nut 41 is opened from the opening portion of the first housing 31 to the inside thereof. Insert into. Then, the ball bearing 44 is fitted to the inner peripheral surface of the cylindrical portion 31a. At this time, the central axis of the ball bearing 44, in other words, the central axis m3 of the nut 41 substantially coincides with the central axis m2 of the cylindrical portion 31a.

  Thereafter, as shown in FIG. 6, when the tension F of the belt 53 is applied to the driven pulley 52 of the nut 41, the nut 41 cantilevered by the ball bearing 44 is inclined toward the drive pulley 51 by the tension F of the belt 53. . That is, the central axis m3 of the nut 41 is inclined toward the drive pulley 51. Therefore, the central axis m3 of the nut 41 can be made to coincide with the central axis m1 of the rack shaft 16. That is, the inclination of the nut 41 can be suppressed. Thereby, the increase in the operation sound resulting from the inclination of the nut 41 and the left-right difference with respect to the preload can be suppressed.

As described above, according to the electric power steering apparatus 1 of the present embodiment, the following effects can be obtained.
(1) The central axis m2 of the inner peripheral surface of the cylindrical portion 31a of the first housing 31 to which the ball bearing 44 is fitted is set to one side portion from the other side portion of the nut 41 with respect to the central axis m2 of the rack shaft 16. Inclination is made in a direction away from the drive pulley 51 as it goes to. As a result, when the tension F of the belt 53 is applied to the other side portion of the nut 41, the central axis m3 of the nut 41 and the central axis m1 of the rack shaft 16 can be made to coincide with each other. Problems can be suppressed.

In addition, the said embodiment can also be implemented with the following forms.
In the above embodiment, the single row ball bearing 44 is used as a bearing for supporting the nut 41. However, the bearing is not limited to this, and an appropriate bearing such as a double row ball bearing can be used.

  In the above embodiment, as an example of the steering device, the electric power steering device 1 that assists the operation of the rack shaft 16 that linearly moves in conjunction with the operation of the steering wheel 2 by using the rotational force of the motor 21 is described. For example, a steer-by-wire (SBW) type steering device may be employed. The steer-by-wire is a steering device that does not have a mechanical connection between the steering wheel and the steered wheel, and transmits the operation of the steering wheel to the steered actuator with an electric signal. The steered actuator includes a power transmission mechanism that converts the rotational force of the output shaft of the motor into the axial force of the steered shaft and transmits the force to the steered shaft. As the power transmission mechanism, for example, a ball screw mechanism and a speed reduction mechanism can be employed as in the above embodiment. The steer-by-wire type steering device can be embodied not only as a front wheel steering device but also as a rear wheel steering device or a four wheel steering device (4WS).

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 16 ... Rack shaft, 16a ... Screw groove, 21 ... Motor, 21a ... Output shaft, 30 ... Housing, 40 ... Ball screw mechanism, 41 ... Nut, 42 ... Ball, 44 ... Ball bearing (bearing ), 50... Deceleration mechanism, 51... Driving pulley, 52.

Claims (2)

A cylindrical nut is screwed through a plurality of balls into a thread groove formed on the outer peripheral surface of a turning shaft of a vehicle, and axial force is applied to the turning shaft based on rotation of the nut. A ball screw mechanism to be applied;
A drive pulley integrally assembled to the output shaft of the motor, a driven pulley integrally assembled to one axial side of the nut, and an endless belt wound around the drive pulley and the driven pulley A reduction mechanism that reduces the rotation of the output shaft of the motor via the drive pulley, the belt, and the driven pulley and transmits the rotation to the nut;
A bearing that is fitted to an inner peripheral surface of a cylindrical housing that covers the periphery of the ball screw mechanism and the speed reduction mechanism, and that rotatably supports the other side opposite to the one side in the axial direction of the nut; With
In the steering device that applies force to the steered shaft from the motor via the speed reduction mechanism and the ball screw mechanism,
The central axis of the inner peripheral surface of the housing to which the bearing is fitted is separated from the drive pulley toward the one side from the other side of the nut with respect to the central axis of the steered shaft. A steering device that is inclined in a direction. The steering apparatus according to claim 1, wherein
An output shaft of the motor is arranged in parallel with a central axis of the steered shaft.