JP2007196968A - Steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device for a vehicle having an electric power steering device capable of being constituted compact at high efficiency. <P>SOLUTION: An output shaft 20a of a reducer 20 is arranged in parallel to a rack bar 14. Further, a converter 30 is constituted such that it is provided with a worm shaft 31 coaxially connected to the output shaft 20a of the reducer 20 and rotated by rotation drive force outputted from the output shaft 20a; and a rack-like member 32 connected to the rack bar 14 and receiving the rotation drive force from the worm shaft 31 to be moved in an axis L direction. Since it has a constitution that the decelerator and the converter 30 are arranged in parallel to the rack bar 14 and the rack bar 14, the electric motor 15, the decelerator 20 and the converter 30 are arranged in parallel, it can be constituted compact. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a vehicle steering apparatus, and more particularly, to a rack assist type electric power steering apparatus that applies a steering assist force to a rack bar that is a drive shaft connected to wheels by an electric motor.

  2. Description of the Related Art Conventionally, a vehicle steering apparatus having a so-called power steering apparatus that assists in turning of steered wheels according to a steering operation of a steering wheel is known. Examples of the power steering device include a hydraulic power steering device that generates a steering assist force using a hydraulic actuator, and an electric power steering device (hereinafter also referred to as an EPS device) that generates a steering assist force using an electric actuator such as an electric motor. Are known. In particular, in recent years, EPS devices have attracted attention from the viewpoint of vehicle mountability and fuel efficiency.

  There are various types of EPS devices depending on where the steering assist force generated by the electric motor is applied. Among them, the rack assist type EPS device converts the rotational driving force output from the electric motor into a linear driving force, and transmits this linear driving force to the rack bar as an axial force. Therefore, as an element constituting the rack assist type EPS device, in addition to the electric motor, a conversion device that converts the rotational driving force from the electric motor into a linear driving force is required.

  As a conversion device used in a conventional rack assist type EPS device, a ball screw type conversion device is known. In this ball screw type conversion device, the rack bar is a ball screw shaft, and a ball screw nut is attached so as to surround the outer periphery of the rack bar to constitute the conversion device. Then, by rotating the ball screw nut, the rolling ball rolls on a rolling path formed by the spiral groove formed on the inner periphery of the ball screw nut and the spiral groove formed on the outer periphery of the rack bar. The rack bar is driven in the axial direction along with the rolling operation of the rolling ball.

In the conventional structure described above, the ball screw nut and the rack bar themselves constitute a ball screw mechanism, and the ball screw mechanism converts the rotational driving force into a linear driving force while reducing the rotational speed of the electric motor. However, with the above structure, it is difficult to increase the rotational output of the electric motor, and it is difficult to exert a high steering assist force with a slight rotational driving force of the electric motor. Therefore, as in the invention described in Patent Document 1, a gear type reduction gear having a small-diameter bevel gear and a large-diameter driven gear is provided between the electric motor and the rack bar. According to Patent Document 1, the rotation of the electric motor is decelerated by a gear-type reduction gear, and the decelerated rotation output is further decelerated by a ball screw mechanism and converted into a linear motion to give an axial force to the rack bar. It is. In this way, since the rotation of the electric motor is further decelerated by the gear-type decelerator before decelerating by the ball screw mechanism, it is possible to increase the output corresponding to the reduction ratio.
JP 2004-217046 A

  By the way, in the conventional conversion device that constitutes the ball screw mechanism by the ball screw nut and the rack bar, as described above, the spiral groove formed on the outer periphery of the rack bar and the spiral groove formed on the inner periphery of the ball screw nut. Rolling balls are arranged in the formed rolling path, and the rolling balls roll in the rolling path when the ball screw mechanism is operating. In order to repeat this rolling, a circulation path for circulating the ball is formed in the ball screw nut. However, when the ball enters the circulation path, there is a problem that abnormal noise such as a rolling sound of the ball is generated or a fluctuation of the handle torque occurs.

  In addition, in the steering device described in Patent Document 1, another reduction gear is attached before the deceleration by the ball screw mechanism to increase the output. However, the amount of attachment of the other reduction gear is increased in the radial direction of the rack bar. The structure is greatly swollen. For this reason, the enlargement of an apparatus will be caused. Further, there is a problem that the swelled portion in this way may interfere with other parts, and there is a problem that a great design restriction for avoiding the interference occurs.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a vehicle steering apparatus having an electric power steering apparatus that can be configured compactly with high output.

  In order to achieve the above object, the present invention relates to an electric motor that generates a steering assist force for assisting a steering operation of a steering wheel, and an output shaft of the electric motor. A reduction gear that decelerates, and a rotational driving force that is connected to the output shaft of the reduction gear and that is output from the output shaft is converted into a linear driving force, and the converted linear driving force is transmitted to the driving shaft connected to the wheels. In the vehicle steering apparatus comprising the conversion device, the output shaft of the speed reducer is disposed in parallel to the drive shaft, and the conversion device is coaxially connected to the output shaft of the speed reducer and A rotating member that rotates by a rotational driving force output from an output shaft, and a moving member that is connected to the driving shaft and moves in the axial direction of the rotating member by receiving the rotational driving force from the rotating member. age Configuration was.

  According to the steering device of the present invention configured as described above, since the reduction gear is interposed between the electric motor and the conversion device, the output speed of the electric motor is reduced by the reduction gear to increase the output. Can be achieved.

  Further, since the rotating member of the converter is coaxially connected to the output shaft of the speed reducer, the rotating member receives the rotational output of the speed reducer and rotates coaxially with the speed reducer. Furthermore, the rotational driving force of the rotating member is transmitted to the moving member of the conversion device, and the moving member moves in the axial direction of the rotating member. Since the moving member is connected to the drive shaft, the drive shaft also moves in the axial direction of the rotating member by the above movement. Here, the rotating member is provided coaxially with the output shaft of the speed reducer, and the output shaft of the speed reducer is disposed in parallel with the drive shaft. (Axial direction) coincides with the axial direction of the drive shaft. Therefore, the drive shaft is moved in the axial direction by the movement of the moving member. Thus, an axial force is applied to the drive shaft, and a steering operation is performed.

  At this time, as described above, the drive shaft and the output shaft of the speed reducer are parallel, and the output shaft of the speed reducer and the rotating member of the conversion device are coaxial, so the speed reducer and the conversion device are connected to the drive shaft. Are arranged in parallel. For this reason, it does not have a configuration in which the drive shaft (rack bar) is swollen in the radial direction by the speed reducer as in the invention described in Patent Document 1, and the vehicle steering device can be configured compactly.

  Any reduction gear may be used as long as it can reduce the output rotation speed from the output shaft of the electric motor at a predetermined reduction ratio. Examples of the reducer include a wave gear device type reducer, a planetary gear type reducer, a planetary roller type reducer, a pulley / belt type reducer, a gear type reducer, and a worm type reducer. Among these, the wave gear device type reduction device, the planetary gear type reduction device, and the planetary roller type reduction device have an advantage of being able to be made more compact. In addition, the pulley / belt type reduction gear and the gear type reduction gear have an advantage that the degree of freedom of arrangement of the electric motor can be increased because the input shaft and the output shaft are arranged in parallel. The worm type speed reducer has an advantage that a large speed reduction can be easily performed.

  The rotating member may be a worm shaft having a worm formed on the outer periphery, and the moving member may be a rack-shaped member having a tooth row that can mesh with the worm shaft. If it does in this way, a rotational drive force can be efficiently decelerated also in a converter by the same principle as a worm type reduction gear. Further, the configuration corresponding to the worm wheel in the worm type reduction gear is linearly configured as a rack-shaped member, so that the rotational driving force can be converted into the linear driving force.

  The rotating member may be a ball screw shaft having a spiral groove formed on an outer periphery thereof, and the moving member may be coaxially attached to the outer periphery of the drive shaft, and a parallel groove may be formed on the outer periphery, with respect to the drive shaft. Arranged in a space formed by a drive shaft side rotation member that is circumferentially rotatable, a spiral groove formed in the ball screw shaft and a parallel groove formed in the drive shaft side rotation member, It is good also as what has a ball which transmits the rotational drive force of a ball screw shaft to the drive shaft side rotation member.

  With this configuration, the rotation of the ball screw shaft as the rotating member is arranged in a space formed by the spiral groove formed on the outer periphery of the ball screw shaft and the parallel groove formed on the outer periphery of the drive shaft side rotating member. It is transmitted to the drive shaft side rotating member via the formed ball. At this time, the rotation of the ball causes the drive shaft side rotation member to rotate in the direction around the axis, and as the ball is fed in the axial direction of the ball screw shaft according to the lead of the spiral groove, the drive shaft side rotation member also moves to the ball screw shaft. Receives linear driving force in the axial direction. In this way, the rotational driving force from the ball screw shaft is decelerated and converted to a linear driving force.

  According to this configuration, the ball screw shaft in the ball screw mechanism is disposed coaxially with the output shaft of the speed reducer, while the drive side rotation member corresponding to the ball screw nut in the ball screw mechanism is coupled to the drive shaft. That is, the ball screw nut and the ball screw shaft are arranged in parallel, and a coaxial arrangement configuration (a configuration in which the ball screw nut is externally attached to the ball screw shaft) is not adopted as in a normal ball screw mechanism. With such a configuration, the rotational driving force can be converted into a linear driving force without requiring a circulation path for circulating the rolling balls as in the prior art. For this reason, there is no abnormal noise or steering torque fluctuation that occurs when the ball enters the circulation path. Further, since the driving force from the ball screw shaft is transmitted to the driving side rotating member by the rolling of the ball, there is little friction and the transmission efficiency can be improved.

  In this case, since the ball screw shaft and the drive shaft side rotating member are arranged in parallel with each other being circumscribed by the ball, it is necessary to always hold the ball at a position where the ball screw shaft and the drive shaft side rotating member face each other. There is. For this reason, it is good to further provide the ball holder for hold | maintaining a ball | bowl in the facing position of a ball screw shaft and a drive shaft side rotation member. This ball cage can be fixed to the drive shaft. And it can also move to the axial direction of a drive shaft, hold | maintaining a ball | bowl with the movement of a drive shaft.

  Further, in the above configuration, the moving member is configured by a roller bearing member in which a parallel groove is formed on the outer periphery and is rotatable in the axial direction of the drive shaft, instead of the drive shaft side rotating member. Also good. Even if such a roller bearing member is used, the drive from the ball screw shaft can be efficiently transmitted. Furthermore, since the roller bearing member can be compactly attached to the drive shaft, it can be made more compact.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall schematic diagram of a vehicle steering apparatus according to the present embodiment, which has an assist function for a steering operation by a driver.

  The vehicle steering apparatus includes a steering shaft 12 connected to a steering handle 11 so that an upper end thereof is integrally rotated, and a pinion gear 13 is connected to a lower end of the shaft 12 so as to be integrally rotated. The pinion gear 13 meshes with rack teeth 14r formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1 and FW2 are steerably connected to both ends of the rack bar 14, and the left and right front wheels FW1 and FW2 are left and right according to the axial displacement of the rack bar 14 as the steering shaft 12 rotates about the axis. Steered to.

  An electric motor 15 for assisting steering is assembled in the vicinity of the rack bar 14. The electric motor 15 generates a steering assist force for assisting the steering operation of the steering handle 11. The rotation of the electric motor 15 is decelerated by the speed reducer 20, and the rotation decelerated by the speed reducer 20 is further decelerated by the conversion device 30 and converted into a linear driving force. This linear driving force is applied to the rack bar 14 as an axial force to assist steering. Thus, in the present embodiment, the electric motor 15, the speed reducer 20, and the conversion device 30 constitute a rack assist type EPS device that applies a steering assist force to the rack bar 14 by an electric actuator (electric motor).

  Next, the electric control device 50 that controls the operation of the electric motor 15 will be described. The electric control device 50 includes a steering torque sensor 51, a steering angle sensor 52, and a vehicle speed sensor 53. The steering torque sensor 51 is assembled to the steering shaft 12. Since the input torque inputted by the driver steering the steering handle 11 acts on the steering shaft 12, the torque acting on the steering shaft 12 is detected as the steering torque T. The steering angle sensor 52 is also assembled to the steering shaft 12 in the same manner as the steering torque sensor 51, and detects the steering angle θ of the steering handle 11 based on the rotation angle of the steering shaft 12 generated by the steering operation of the steering handle 11. The vehicle speed sensor 53 detects and outputs the vehicle speed V.

  The electric control device 50 includes an electronic control unit 54 connected to the steering torque sensor 51, the steering angle sensor 52, and the vehicle speed sensor 53. The electronic control unit 54 drives and controls the electric motor 15 via the drive circuit 55 by executing a control program for performing steering assistance, with a microcomputer including a CPU, ROM, RAM, and the like as main components. . The drive circuit 55 causes the drive current specified by the electronic control unit 54 to flow through the electric motor 15. In this way, the electric motor 15 is driven and controlled.

  FIG. 2 is a partial cross-sectional schematic diagram showing the configuration in the vicinity of the electric motor 15, the speed reducer 20, and the converter 30. As can be seen from the figure, the electric motor 15 has an output shaft 15 a, and the output shaft 15 a is arranged in parallel to the rack bar 14. The speed reducer 20 is connected to the output shaft 15 a of the electric motor 15. In the present embodiment, the speed reducer 20 is a planetary gear type speed reducer. Since the detailed structure of the planetary gear type reduction gear is well known, the description thereof is omitted. The speed reducer 20 has an output shaft 20 a, and the output shaft 20 a is arranged so as to be coaxial with the output shaft 15 a of the electric motor 15.

  The output shaft 20 a of the speed reducer 20 is connected to the conversion device 30 via an elastic joint 41. The conversion device 30 includes a worm shaft 31 and a rack-like member 32. As can be seen from the figure, both ends of the worm shaft 31 are supported by bearings 42a and 42b so as to be rotatable and immovable in the axial direction, and a worm 31a is formed on the outer periphery thereof. The worm shaft 31 is substantially coaxially connected to the output shaft 20 a of the speed reducer 20 via the elastic joint 41.

  Bearings 42a and 42b attached to both ends of the worm shaft 31 are connected to one ends of springs 43a and 43b, respectively. The other ends of the springs 43a and 43b are attached to the inner wall of a housing (not shown) that houses the electric motor 15, the speed reducer 20, the conversion device 30, and the rack bar 14. Therefore, the worm shaft 31 is elastically supported by the housing via the bearings 42a and 42b.

  The rack-like member 32 includes a rack-like tooth row 32a and a support portion 32b connected to the rack-like tooth row 32a. The rack-like tooth row 32a is formed by developing a worm wheel that can mesh with the worm 31a in the circumferential direction to form a tooth row in a straight line like rack teeth. It arrange | positions so that it may become an axial direction. The rack-like tooth row 32a faces the worm 31a and meshes with the worm 31a.

  The support portion 32b is connected to the back side (the upper side in the drawing) of the rack-like tooth row 32a. By fixing the support portion 32 b to the rack bar 14, the rack-like member 32 is connected to the rack bar 14. In the present embodiment, as shown in the figure, a recess 14a is provided in a part of the rack bar 14, and a support portion 32b is inserted and fixed in the recess 14a. If comprised in this way, the worm shaft 31 can be brought closer to the rack bar 14, and it can achieve more compact.

  As can be seen from FIG. 2 and the above description, the electric motor 15 is arranged side by side so that its output shaft 15 a is parallel to the rack bar 14, and the speed reducer 20 has its output shaft 20 a as the electric motor 15. Is arranged so as to be coaxial with the output shaft 15a. Further, the worm shaft 31 of the conversion device 30 is disposed so as to be substantially coaxial with the output shaft 20 a of the speed reducer 20 via the elastic joint 41. Therefore, the output shaft 15a of the electric motor 15, the output shaft 20a of the speed reducer 20, and the worm shaft 31 of the conversion device 30 are coaxially arranged along the axis L1. Therefore, in this embodiment, all the structures including the electric motor in the EPS apparatus are formed along one axis L1, and these can be configured in a compact manner.

  The axis L1 is parallel to the rack bar 14. Therefore, since the output shaft 15a of the electric motor 15, the output shaft 20a of the speed reducer 20, and the worm shaft 31 of the converter 30 are arranged in parallel along the rack bar 14, the rack bar 14 bulges outward in the radial direction. Can be suppressed as much as possible, and a very compact configuration can be obtained. For this reason, although it is an EPS device having the speed reducer 20 and the conversion device 30, the vehicle mountability is very good, and design restrictions when other components are mounted can be reduced.

  In the above configuration, when the electric motor 15 is driven, the output shaft 15a is rotationally driven. The rotational driving force of the output shaft 15a is transmitted to the speed reducer 20. The speed reducer 20 decelerates the output rotation speed from the electric motor 15 and outputs the rotational driving force from the output shaft 20a at the reduced rotation speed. The rotational driving force of the output shaft 20a is transmitted to the worm shaft 31 of the conversion device 30 via the elastic joint 41, and the worm shaft 31 rotates by the rotational driving force from the output shaft 20a. Along with this, the worm 31a formed on the outer periphery of the worm shaft 31 is rotationally driven.

  The worm 31a meshes with the rack-like tooth row 32a of the rack-like member 32. Therefore, when the worm 31a rotates, the rack-like tooth row 32a is sent under the rotational driving force of the worm 31a, and the rack-like member 32 moves in the direction of the axis L1 that is the axial direction of the worm shaft 31. Thereby, the rotational driving force from the output shaft 20a of the speed reducer 20 is decelerated and converted into a linear driving force in the direction of the axis L1. Further, since the rack-shaped member 32 is fixed to the rack bar 14, the rack bar 14 also moves in the direction of the axis L 1, that is, the axial direction of the rack bar 14 by the movement of the rack-shaped member 32. Thus, the axial moving force is transmitted to the rack bar 14, the rack bar 14 is moved in the axial direction, and the vehicle is steered.

  Thus, according to this embodiment, since the rotation of the electric motor 15 is decelerated by the speed reducer 20, a high output can be achieved. Further, the output shaft 20a of the speed reducer 20 is disposed in parallel with the rack bar 14, and the converter 30 is coaxially connected to the output shaft 20a of the speed reducer 20 and output from the output shaft 20a. The speed reducer 20 includes a worm shaft 31 that rotates with a driving force, and a rack-like member 32 that is connected to the rack bar 14 and moves in the direction of the axis L1 in response to the rotational driving force from the worm shaft 31. And the conversion device 30 are arranged in parallel to the rack bar 14. Therefore, the EPS device is arranged along the axis of the rack bar and can be configured compactly.

  The worm shaft 31 is rotatably supported by bearings 42a and 42b attached to both ends thereof, and the bearings 42a and 42b are fixed to the housing by springs 43a and 43b. Therefore, the worm shaft 31 is elastically supported by these springs 43a and 43b, and the upper side in FIG. 2, that is, the worm 31a approaches the rack-like tooth row 32a by the urging force of the springs 43a and 43b. Biased in the direction. For this reason, the backlash at the time of mesh | engagement with the worm | warm 31a and the rack-shaped tooth row | line | column 32a can be eliminated, and generation | occurrence | production of the noise at the time of meshing can be prevented effectively. At this time, the worm shaft 31 may slightly deviate from the axis L1 due to the urging force of the springs 43a and 43b. In this case, the driving force from the speed reducer 20 is applied while absorbing the displacement by the elastic joint 41. Transmission to the worm shaft 31 is possible.

(Modification 1)
FIG. 3 is a diagram showing a modification of the present embodiment. The modification shown in FIG. 3 is an example in which a pulley / belt type speed reducer is used as the speed reducer. That is, in the figure, the speed reducer 20 includes an input shaft 21, a drive pulley 22, a driven pulley 23, an output shaft 20 a, and a belt 24. The input shaft 21 is coaxially connected to the output shaft 15 a of the electric motor 15. A drive pulley 22 is attached to the input shaft 21 so as to rotate coaxially and integrally. On the other hand, the output shaft 20 a is attached to the worm shaft 31 of the conversion device 30 via an elastic joint 41 so as to be coaxial. A driven pulley 23 is attached to the output shaft 20a so as to rotate coaxially and integrally.

  Further, as can be seen from the figure, the belt 24 is wound around the driving pulley 22 and the driven pulley 23 so that the rotational driving force from the driving pulley 22 is transmitted to the driven pulley 23 via the belt 24. It has become. Further, since the diameter of the drive pulley 22 is smaller than the diameter of the driven pulley 23, when the rotational driving force is transmitted to the driven pulley 23 via the belt 24, it is proportional to the ratio of the diameters of both pulleys. The rotational speed is reduced by the reduction ratio. In this way, the output rotation speed from the electric motor is reduced by the pulley / belt type reduction gear as the reduction gear 20. In addition, since the other structure is the same as said 1st embodiment, the same code | symbol is attached | subjected to the same part and the description is abbreviate | omitted.

  Also in this example, since the output shaft 20a of the speed reducer 20 (pulley / belt type speed reducer) and the worm shaft 31 of the conversion device 30 are arranged in parallel along the rack bar 14, the electric motor, the speed reduction mechanism, the conversion An EPS apparatus having a mechanism can be configured compactly. Further, the input shaft 21 and the output shaft 20a of the speed reducer 20 are not coaxial but are arranged in parallel. For this reason, the electric motor 15 may be arranged as shown by the solid line in the figure, or may be arranged from the opposite side to the arrangement by the solid line as shown by the dotted line in the figure. Therefore, the degree of freedom of the mounting position of the electric motor 15 can be increased.

(Modification 2)
FIG. 4 is a diagram showing another modification of the present embodiment. The modification shown in FIG. 4 is an example in which a gear reducer with meshing gears is used as the reducer. That is, in the figure, the speed reducer 20 includes an input shaft 25, a drive gear 26, a driven gear 27, and an output shaft 20a. The input shaft 25 is coaxially connected to the output shaft 15 a of the electric motor 15. A drive gear 26 having teeth (helical teeth in this example) formed on the outer periphery is attached to the input shaft 25 so as to rotate coaxially and integrally. On the other hand, the output shaft 20 a is attached to the worm shaft 31 of the conversion device 30 via an elastic joint 41 so as to be coaxial. A driven gear 27 having teeth (helical teeth in this example) formed on the outer periphery is attached to the output shaft 20a so as to rotate coaxially and integrally. The drive gear 26 and the driven gear 27 are arranged in mesh with each other.

  Further, as can be seen from the figure, the diameter of the drive gear 26 is made smaller than the diameter of the driven gear 27, and the number of teeth of the drive gear 26 is made smaller than the number of teeth of the driven gear 27. For this reason, when the rotational driving force is transmitted from the driving gear 26 to the driven gear 27, the rotational speed is reduced at a reduction ratio proportional to the gear ratio of both gears. In this way, the output rotation speed from the electric motor 15 is reduced by the gear type reduction gear as the reduction gear 20. In addition, since the other structure is the same as said 1st embodiment, the same code | symbol is attached | subjected about the same part and the description is abbreviate | omitted.

  Also in this example, since the output shaft 20a of the speed reducer 20 (pulley / belt type speed reducer) and the worm shaft 31 of the conversion device 30 are arranged in parallel along the rack bar 14, the electric motor, the speed reduction mechanism, and the conversion An EPS apparatus having a mechanism can be configured compactly. Further, the input shaft 25 and the output shaft 20a of the speed reducer 20 are not coaxial but are arranged in parallel. For this reason, the freedom degree of the attachment position of the electric motor 15 can be enlarged similarly to the modification shown in FIG.

(Second embodiment)
Next, a second embodiment of the present invention will be described. This embodiment uses a ball screw shaft and a bearing as a configuration of the conversion device, and transmits the drive in a state where the ball screw shaft and the bearing are circumscribed via the ball. Therefore, the present invention is characterized in that deceleration and conversion into linear driving force are performed, and the other points are substantially the same as those in the first embodiment. Note that, in the following embodiments, the same points as those of the above-described embodiments will be denoted by the same reference numerals, detailed description thereof will be omitted, and different portions will be mainly described.

  FIG. 5 is a partial cross-sectional schematic diagram showing the vicinity of the electric motor, the speed reducer, and the conversion device used in the EPS device in the vehicle steering system showing the present embodiment. As shown in the figure, the output shaft 15a of the electric motor 15 and the output shaft 20a of the speed reducer 20 (a planetary gear type speed reducer in this embodiment) are arranged so as to be coaxial. Further, the output shaft 20 a of the speed reducer 20 is connected to the conversion device 30 via an elastic joint 41. In the present embodiment, the conversion device 30 includes a ball screw shaft 33, a bearing 34, and a ball 35.

  The ball screw shaft 33 is connected to the output shaft 20a of the speed reducer 20 via an elastic joint 41 on the right end side in the drawing. As can be seen from the figure, the ball screw shaft 33 and the output shaft 20a of the speed reducer 20 are arranged coaxially and both have an axis L1. The axis L1 is parallel to the rack bar 14 in the axial direction. Further, bearings 42a and 42b are attached to both ends of the ball screw shaft 33, and the ball screw shaft 33 is supported by these bearings 42a and 42b so as to be rotatable and not movable in the axial direction. The bearings 42a and 42b are fixed to a housing (not shown) via springs 43a and 43b as in the first embodiment. Therefore, the ball screw shaft 33 is elastically supported by the housing through the intervention of these springs 43a and 43b. Furthermore, the ball screw shaft 33 has a portion in which a spiral groove 33a is formed on the outer periphery thereof. The spiral groove 33 a has an arc shape with a concave cross section, and is formed with a predetermined lead so as to advance in a spiral around the axis of the ball screw shaft 33.

  The bearing 34 is a ball bearing member having an outer ring 34a, an inner ring 34b, a ball 34c, and a cage (not shown). The bearing 34 of the present embodiment shown in FIG. 5 has a double-row angular ball bearing structure, and can receive an axial load and a radial load from both directions simultaneously.

  The bearing 34 is attached to the outer periphery of the rack bar 14. As shown in the figure, the rack bar 14 has a small diameter portion 14b having the smallest outer diameter, a medium diameter portion 14c having a larger outer diameter than the small diameter portion 14b, and a large diameter having a larger outer diameter than the medium diameter portion 14c. A small-diameter portion 14b, a medium-diameter portion 14c, and a large-diameter portion 14d are formed substantially coaxially in this order from the left side to the right side in the drawing. Therefore, the rack bar 14 is formed so that the outer diameter gradually increases from the left side to the right side in the drawing. The axial length of the bearing 34 is the same as the axial length of the medium diameter portion 14c of the rack bar 14, and the inner diameter of the inner ring 34b of the bearing 34 is substantially the same as the outer diameter of the medium diameter portion 14c. ing.

  Therefore, in order to assemble the bearing 34 to the rack bar 14, first, the bearing 34 is inserted from the small diameter portion 14b side of the rack bar 14 and is slid to the medium diameter portion 14c. Since the inner diameter of the inner ring 34b of the bearing 34 is smaller than the outer diameter of the large diameter portion 14d of the rack bar 14, one end surface side (the right end surface side in the drawing) of the bearing 34 is the large diameter portion 14d and the medium diameter portion 14c of the rack bar 14. Is in contact with a step 14e formed at the boundary. On the other hand, the illustrated left end face side of the bearing 34 is in contact with a stopper 14f attached to the boundary between the medium diameter portion 14c and the small diameter portion 14b of the rack bar 14.

In this manner, the bearing 34 is attached so as not to move in the axial direction of the rack bar 14 by the step 14e and the stopper 14f. The inner ring 34b of the bearing 34 is non-rotatably attached to the rack bar 14 by a known means such as a keyway, press-fitting or joining. Therefore, the inner ring 34 b of the bearing 34 is fixed to the rack bar 14, and the outer ring 34 a is rotatable in the circumferential direction with respect to the rack bar 14 by rolling of the balls 34 c that are rolling wheels. In the present embodiment, the outer ring 34a of the bearing 34 corresponds to the drive shaft side rotation member in the present invention.

  FIG. 6 is a front view of the outer ring 34 a of the bearing 34. As shown in FIG. 6, a plurality of parallel grooves 34 d are formed on the outer periphery of the outer ring 34 a of the bearing 34 in the circumferential direction. The parallel groove 34d is an annular groove formed along the direction around the axis with respect to the axis L2 of the outer ring 34a, and the cross section thereof has a concave arc shape. A plurality (seven in this embodiment) are formed at equal intervals in the axial direction of the outer ring 34a. The width of the parallel groove 34d is substantially the same as the width of the spiral groove 33a formed in the ball screw shaft 33. Further, the groove interval of the parallel grooves 34d is made equal to the lead of the spiral groove 33a.

  As shown in FIG. 5, the bearing 34 and the ball screw shaft 33 are arranged so that their axes are parallel to each other. Further, both are arranged in a state where the groove forming surface of the parallel groove 34 d formed on the bearing 34 faces the groove forming surface of the spiral groove 33 a formed on the ball screw shaft 33. A ball 35 is disposed in a facing space having a substantially circular cross section formed by both grooves facing each other.

  As shown in the drawing, a plurality of the facing spaces are formed along the axial direction of the ball screw shaft 33 and the bearing 34. And the ball | bowl 35 is arrange | positioned by aligning an axial direction position so that it may be settled in the facing space formed in multiple numbers along an axial direction. Although it is not necessary to store the balls 35 in all the facing spaces, it is preferable to store the balls in a plurality of facing spaces in order to disperse the driving force received by each ball 35.

  Further, as shown in the figure, the position of each ball 35 contained in the facing space cannot be freely moved by the ball holder 36. FIG. 7 is a front view of the ball cage 36. As shown in the drawing, the ball cage 36 is formed in a flat plate shape, and a circular hole 36 a having a size corresponding to the ball 35 or slightly larger than the ball 35 is formed from the front surface to the back surface. A plurality of circular holes 36 a are formed in the longitudinal direction at the same interval as the interval of the parallel grooves 34 d of the bearing 34. The ball holder 36 shown in FIG. 7 is formed of a first piece 36b and a second piece 36c that are divided into two in the longitudinal direction, and a circular hole 36a is formed in a state where both pieces are abutted and fixed. However, it may be integrally formed.

  Such a ball holder 36 is fixed to the rack bar 14 by a fixing bracket 37 as shown in FIG. 5 in a state where the ball 35 is accommodated in each circular hole 36a. The ball 35 accommodated in each circular hole 36a of the ball holder 36 and held in the facing space is in contact with a spiral groove 33a formed on the outer periphery of the ball screw shaft 33 on one side and the outer periphery of the bearing 34 on the other side. Are in contact with the parallel grooves 34d formed on the surface. Therefore, the ball screw shaft 33 and the bearing 34 are circumscribed via the ball 35. At this time, the ball 35 cannot be moved by the ball holder 36 but can rotate on the spot. In addition, since it is the same as said 1st embodiment about another structure, the same code | symbol is attached | subjected about the same part and the description is abbreviate | omitted.

  In the above configuration, when the electric motor 15 is driven, the output shaft 15a is rotationally driven. The rotational driving force of the output shaft 15a is transmitted to the speed reducer 20. In the speed reducer 20, the output rotational speed from the output shaft 15a is decelerated, and the rotational driving force is output from the output shaft 20a at the reduced rotational speed. The rotational driving force of the output shaft 20 a of the speed reducer 20 is transmitted to the ball screw shaft 33 of the conversion device 30 via the elastic joint 41. Thereby, the ball screw shaft 33 is rotationally driven.

  In the spiral groove 33 a formed on the outer periphery of the ball screw shaft 33, the balls 35 are arranged in a line in the axial direction while being held by the ball holder 36. When the ball screw shaft 33 rotates in this state, the ball 35 rotates on the spiral groove 33a. Here, since the position of the ball 35 is restricted so that it cannot be moved by the ball holder 36, the ball 35 rotates on the spot. Further, the ball 35 is in contact with the spiral groove 33 a and at the same time, is in contact with a parallel groove 34 d formed on the outer periphery of the bearing 34. For this reason, the outer ring 34 a of the bearing 34 in which the parallel groove 34 d is formed is rotated by the rotation of the ball 35, and rotates around the axis with respect to the rack bar 14.

  At this time, the ball 35 rotates on the spot and rolls in the spiral groove 33a, and is sent in the direction of the axis L1 that is the axial direction of the ball screw shaft 33 according to the lead of the spiral groove 33a. As the ball 35 is fed, the bearing 34 receives a linear driving force in the direction of the axis L1. This linear driving force is further transmitted to the rack bar 14 which fixes the bearing 34 so as not to move in the axial direction. In this way, the rotational driving force from the output shaft 20a of the speed reducer 20 is decelerated and converted into a linear driving force, transmitted to the rack bar 14, and the rack bar 14 moves in the axial direction. At this time, the ball holder 36 fixed to the rack bar 14 with the fixing bracket 37 also moves simultaneously with the ball 35. Thus, an axial force is applied to the rack bar 14 and the vehicle is steered.

  According to the present embodiment, as in the first embodiment, the output shaft 20a of the speed reducer 20 and the conversion device 30 can be achieved even though the EPS device can achieve high output using the speed reducer 20. Since the ball screw shaft 33 is arranged in parallel with the axial direction of the rack bar 14, it can be made compact. Further, according to the configuration of the conversion device 30 of the present embodiment, unlike a normal ball screw, the ball screw shaft 33 and the bearing 34 are circumscribed to transmit the driving force, and the ball that mediates the transmission of the driving force is used. 35 only rotates on the spot by the ball holder 36. Therefore, it is not necessary to circulate the ball 35 interposed between the both 33 and 34, and there is no abnormal noise or handle torque fluctuation that occurs when the ball enters the circulation path.

  Further, since the parallel groove 34d is formed in the bearing 34, the rotational driving force in the direction around the axis of the driving force transmitted from the ball screw shaft 33 is transmitted by the ball 35 rolling on the parallel groove 34d. Is done. As described above, since the driving force in the direction around the axis is transmitted by rolling, the generation of friction due to slipping can be reduced. Therefore, the transmission efficiency can be improved.

  The ball screw shaft 33 is rotatably supported by bearings 42a and 42b attached to both ends thereof, and the bearings 42a and 42b are fixed to the housing by springs 43a and 43b. Therefore, the ball screw shaft 33 is elastically supported by the springs 43a and 43b, and the ball 35 is pressed by the spiral groove 33a of the ball screw shaft 33 and the parallel groove 34d of the bearing 34 by the urging force of the springs 43a and 43b. It is done. By this pressing force, the ball 35 can be reliably rolled in each groove, and drive transmission can be performed reliably.

  Further, the ball 35 is always rotated at the same position by the ball holder 36. For this reason, the ball 35 can be rotated stably, and the ball 35 can be prevented from being detached from between the ball screw shaft 33 and the bearing 34.

  Moreover, according to the structure in this embodiment, when manufacturing the ball screw shaft 33, the part in which the spiral groove 33a is formed can be shape | molded by a rolling process. At this time, for example, a spiral groove is formed in the axial direction by rolling on a single shaft, and the spiral groove 33a of the ball screw shaft 33 is formed by cutting it by a necessary length. Can be used. When the portion in which the spiral groove 33a is formed in this way is formed, the accuracy of the rolling process becomes uniform, so that the accuracy of the spiral groove can be improved, and the difference in the rolling of the ball 35 can be improved. Sound can be reduced. Note that the ball screw shaft 33 may be manufactured by other processing methods, such as grinding, if it is not necessary to consider the accuracy or cost as described above.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In this embodiment, a ball screw shaft and a roller bearing are used as a configuration of the conversion device, and the drive transmission is performed in a state where the ball screw shaft and the roller bearing are circumscribed via the ball. Thus, the rotational driving force is converted into a linear driving force, and the other points are substantially the same as those in the second embodiment.

  FIG. 8 is a partial cross-sectional schematic diagram showing the vicinity of the electric motor, the reduction gear, and the conversion device used in the EPS device in the vehicle steering system showing the present embodiment. As shown in the figure, the output shaft 15a of the electric motor 15 and the output shaft 20a of the speed reducer 20 (a planetary gear type speed reducer in this embodiment) are arranged so as to be coaxial. Further, the output shaft 20 a of the speed reducer 20 is connected to the conversion device 30 via an elastic joint 41. In the present embodiment, the conversion device 30 includes a ball screw shaft 33, a roller bearing 38, and a ball 35. Since the configurations of the ball screw shaft 33 and the ball 35 are the same as those in the second embodiment, description thereof is omitted.

  As shown in FIG. 8, the roller bearing 38 is attached to the concave portion 14 a cut out in the axial direction of the rack bar 14. FIG. 9 is a front view of the roller bearing 38. As shown in FIG. 9, the roller bearing 38 includes a shaft portion 38a and a roller portion 38b. The shaft portion 38a is a portion that supports the roller portion 38b and is formed in a long shape. A roller portion 38b is provided on the shaft portion 38a so as to be coaxial and integrally rotatable. A parallel groove 38c is formed on the outer periphery of the roller portion 38b. The parallel groove 38c is formed in an annular shape in the circumferential direction of the roller portion 38b, and its cross-sectional shape is a concave arc shape. A plurality of parallel grooves 38c are formed continuously in the axial direction, and the width and interval of each groove are substantially equal to the width and lead of the spiral groove 33a formed on the outer periphery of the ball screw shaft 33.

  As shown in FIG. 8, bearings 45 a and 45 b are embedded in the wall surface of the recess 14 a of the rack bar 14 so as to face each other in the axial direction. The shaft portion 38a of the roller bearing 38 is supported by these bearings 45a and 45b. Therefore, the roller bearing 38 is pivotally supported by the bearings 45a and 45b so as to be rotatable around the axis of the rack bar 14.

  The roller bearing 38 and the ball screw shaft 33 are arranged so that their axes are parallel to each other. Further, both are arranged in a state where the groove forming surface of the parallel groove 38 c formed on the roller bearing 38 faces the groove forming surface of the spiral groove 33 a formed on the ball screw shaft 33. A ball 35 is disposed in a facing space having a substantially circular cross section formed by both grooves facing each other.

  The balls 35 are arranged with their axial positions aligned so as to be within a facing space formed along the axial direction of the roller bearings 38 and the ball screw shafts 33, and each ball 35 is positioned by a ball holder 36. It cannot be moved freely. Since the structure of the ball holder 36 and other structures are the same as those described in the first embodiment or the second embodiment, the description thereof is omitted.

  In the above configuration, when the electric motor 15 is driven, the output shaft 15a is rotationally driven. The rotational driving force of the output shaft 15a is transmitted to the speed reducer 20. In the speed reducer 20, the output rotational speed from the output shaft 15a is decelerated, and the rotational driving force is output from the output shaft 20a at the reduced rotational speed. The rotational driving force of the output shaft 20 a of the speed reducer 20 is transmitted to the ball screw shaft 33 of the conversion device 30 via the elastic joint 41. Thereby, the ball screw shaft 33 is rotationally driven.

  In the spiral groove 33 a formed on the outer periphery of the ball screw shaft 33, the balls 35 are arranged in a line in the axial direction while being held by the ball holder 36. When the ball screw shaft 33 rotates in this state, the ball 35 rotates in the spiral groove 33a. Here, since the position of the ball 35 is restricted so that it cannot be moved by the ball holder 36, the ball 35 rotates on the spot. Further, the ball 35 is in contact with the spiral groove 33 a and at the same time, is in contact with a parallel groove 38 c formed on the outer periphery of the roller bearing 38. For this reason, the roller bearing 38 in which the parallel groove 38 c is formed is rotated by the rotation of the ball 35, and the roller bearing 38 rotates in the direction around the axis of the rack bar 14.

  At this time, the ball 35 rotates on the spot and rolls in the spiral groove 33a, and is sent in the direction of the axis L1 according to the lead of the spiral groove 33a. Accordingly, the roller bearing 38 receives a linear driving force in the direction of the axis L 1, and this linear driving force is further transmitted to the rack bar 14 that fixes the roller bearing 38. In this way, the rotational driving force from the output shaft 20a of the speed reducer 20 is decelerated by the conversion device 30 and is converted into a linear driving force and transmitted to the rack bar 14, and the rack bar 14 moves in the axial direction. Thus, an axial force is applied to the rack bar 14 and the vehicle is steered.

  According to the present embodiment, as in the first embodiment, the output shaft 20a of the speed reducer 20 and the conversion device 30 can be achieved even though the EPS device can achieve high output using the speed reducer 20. Since the ball screw shaft 33 is arranged in parallel with the axial direction of the rack bar 14, it can be made compact. Furthermore, according to the configuration of the conversion device 30 of the present embodiment, since the circulation path of the ball 35 is not necessary, there is no abnormal noise or handle torque fluctuation that occurs when the ball enters the circulation path.

  Further, since the parallel groove 38c is formed on the outer periphery of the roller portion 38b of the roller bearing 38, the rotational driving force in the direction around the axis of the driving force transmitted from the ball screw shaft 33 is generated by the ball 35 in the parallel groove 38c. Is transmitted by rolling. As described above, since the driving force in the direction around the axis is transmitted by rolling, the generation of friction due to slipping can be reduced. Therefore, the transmission efficiency can be improved.

  Further, since the bearing 34 used in the second embodiment is attached to the outer periphery of the rack bar 14, it slightly swells in the radial direction of the rack bar 14. In this embodiment, the roller bearing 38 is connected to the ball screw shaft 33 and the rack bar. Since it is only necessary to provide between the two, the size can be further reduced.

1 is an overall schematic diagram of a vehicle steering apparatus having an assist function with respect to a steering operation by a driver according to an embodiment of the present invention. It is a partial section schematic diagram showing the details near the electric motor and reduction gear in the first embodiment of the present invention. It is a partial section schematic diagram showing the details near an electric motor and a reduction gear in the modification of a first embodiment. It is a partial section schematic diagram showing details of an electric motor and reduction gear neighborhood in other modifications of a first embodiment. It is a partial section schematic diagram showing the details near the electric motor and reduction gear in the second embodiment of the present invention. It is a front view of the outer ring | wheel of the bearing in 2nd embodiment. It is a front view of a ball cage in a second embodiment. It is a partial section schematic diagram showing the details near an electric motor and a reduction gear in a third embodiment of the present invention. It is a front view of the roller bearing in 3rd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Steering handle, 12 ... Steering shaft, 13 ... Pinion gear, 14 ... Rack bar (drive shaft), 14a ... Recessed part, 14b ... Small diameter part, 14c ... Medium diameter part, 14d ... Large diameter part, 14e ... Step difference, 14f ... Stopper, 14r ... rack teeth, 15 ... electric motor, 15a ... output shaft, 20 ... reduction gear, 20a ... output shaft, 21 ... input shaft, 22 ... drive pulley, 23 ... driven pulley, 24 ... belt, 25 ... input shaft , 26 ... drive gear, 27 ... driven gear, 30 ... converter, 31 ... worm shaft (rotating member), 31a ... worm, 32 ... rack-like member (moving member), 32a ... rack-like tooth row, 32b ... support part 33 ... Ball screw shaft (rotating member), 33a ... Spiral groove, 34 ... Bearing, 34a ... Outer ring (moving member, drive shaft side rotating member), 34b ... Inner ring, 34c ... Bo 34d ... Parallel grooves, 35 ... Ball (moving member), 36 ... Ball cage, 36a ... Circular hole, 36b ... First piece, 36c ... Second piece, 37 ... Fixed bracket, 38 ... Roller bearing (roller bearing member) ), 38a ... shaft portion, 38b ... roller portion, 38c ... parallel groove, 41 ... elastic joint, 42a, 42b ... bearing, 43a, 43b ... spring, 45a, 45b ... bearing, 50 ... electric control device, 51 ... steering torque Sensor 52 ... Steering angle sensor 53 ... Vehicle speed sensor 54 ... Electronic control unit 55 ... Drive circuit

Claims (4)

An electric motor that generates a steering assist force for assisting a steering operation of the steering handle; a speed reducer connected to the output shaft of the electric motor and decelerating an output rotation speed of the electric motor; and an output shaft of the speed reducer And a converter for converting the rotational driving force output from the output shaft into a linear driving force and transmitting the converted linear driving force to the driving shaft connected to the wheels. ,
The output shaft of the speed reducer is disposed in parallel with the drive shaft,
The converter is coaxially connected to the output shaft of the speed reducer and is rotated by a rotational driving force output from the output shaft, and is connected to the drive shaft and rotated from the rotating member. A vehicle steering apparatus comprising: a moving member that receives a driving force and moves in an axial direction of the rotating member. The vehicle steering apparatus according to claim 1,
The rotating member is a worm shaft having a worm formed on the outer periphery,
The vehicle steering apparatus according to claim 1, wherein the moving member is a rack-like member in which a tooth row that can mesh with the worm shaft is linearly formed. The vehicle steering apparatus according to claim 1,
The rotating member is a ball screw shaft having a spiral groove formed on the outer periphery,
The moving member is coaxially and rotatably attached to the outer periphery of the drive shaft and has a parallel groove formed on the outer periphery, and a spiral groove formed on the ball screw shaft. And a ball that is disposed in a space formed by parallel grooves formed in the drive shaft-side rotating member, and that transmits a rotational driving force of the ball screw shaft to the drive shaft-side rotating member. Vehicle steering device. The vehicle steering apparatus according to claim 1,
The rotating member is a ball screw shaft having a spiral groove formed on the outer periphery,
The moving member has a roller bearing member formed with a parallel groove on the outer periphery and rotatable in the axial direction of the drive shaft, a spiral groove formed on the ball screw shaft, and a parallel groove formed on the roller bearing member. A vehicle steering apparatus comprising: a ball disposed in a space formed by a groove and transmitting a rotational driving force of the ball screw shaft to the roller bearing member.

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