Electric power steering device

Abstract

To establish the configuration of an electric power steering device that can provide improved mountability to a vehicle.SOLUTION: A motor output shaft 52 of an electric motor 41 for applying assist drive force to a rack shaft 11 is connected via a power transmission device 42 to a worm shaft 46 constituting a worm reducer 40. Thus, the motor output shaft 52 can be arranged offset to the worm shaft 46.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electric power steering device. [Background technology]

[0002] Generally, a steering device for an automobile is configured to apply a steering angle to the steered wheels by transmitting the rotation of the steering wheel, which is rotated by the driver, to the steering-side pinion shaft of the steering gear unit via a steering shaft, an intermediate shaft, etc., and converting the rotational motion of the steering-side pinion shaft into linear motion of the rack shaft of the steering gear unit, which meshes with the steering-side pinion shaft.

[0003] In the field of steering devices, electric power steering devices that are configured to apply an assist drive force to the steering force transmission path to reduce the force required to turn the steering wheel are widely used. There are various types of electric power steering devices that differ in the position at which the assist drive force is applied.

[0004] For example, Japanese Patent Application Laid-Open Publication No. 2016-179760 (Patent Document 1) describes a dual-pinion electric power steering device in which an assist driving force is applied to a rack shaft by an assist side pinion shaft that is rotated and driven by an electric motor, separate from the steering side pinion shaft that is rotated and driven by the steering wheel.

[0005] A conventionally known dual-pinion electric power steering device includes a rack shaft, a steering-side pinion shaft, an assist-side pinion shaft, a worm reducer, and an electric motor.

[0006] The rack shaft has steering-side rack teeth on its outer peripheral surface at one axial side portion and assist-side rack teeth on its outer peripheral surface at the other axial side portion. The steering-side pinion shaft has steering-side pinion teeth on its outer peripheral surface that mesh with the steering-side rack teeth and is rotationally driven by rotating the steering wheel. The assist-side pinion shaft has assist-side pinion teeth on its outer peripheral surface that mesh with the assist-side rack teeth and is rotationally driven by an electric motor. The electric motor has a motor output shaft and rotates the assist-side pinion shaft via a worm reducer. The worm reducer has a worm wheel fixed to the assist-side pinion shaft so as not to rotate relative to the assist-side pinion shaft, and a worm shaft connected to the motor output shaft and meshed with the worm wheel. When the vehicle is being driven, an assist driving force is applied from the electric motor to the rack shaft via the worm reducer and the assist-side pinion shaft. This reduces the force required to rotate the steering wheel. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-179760 Summary of the Invention [Problem to be solved by the invention]

[0008] In a dual-pinion electric power steering device with a conventional structure, the worm shaft and the motor output shaft are coaxially arranged and connected to each other. This tends to increase the axial dimensions of the gear housing that houses the worm shaft and the electric motor. Therefore, when the electric power steering device is installed in an engine compartment, the gear housing that houses the worm shaft or the electric motor tends to interfere with surrounding components such as the engine mount and the engine, which may reduce the vehicle mountability of the electric power steering device.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide an electric power steering device that can be easily mounted on a vehicle. [Means for solving the problem]

[0010] An electric power steering device according to one aspect of the present invention includes a rack shaft, a steering-side pinion shaft, an assist-side pinion shaft, a worm wheel, a worm shaft, an electric motor, and a power transmission device. The rack shaft has steering-side rack teeth on a portion of the circumferential direction of the outer peripheral surface of one axial side portion, and has assist-side rack teeth on a portion of the circumferential direction of the outer peripheral surface of the other axial side portion. The steering-side pinion shaft has steering-side pinion teeth on its outer circumferential surface that mesh with the steering-side rack teeth, and is rotationally driven by operation of the steering wheel. The assist-side pinion shaft has assist-side pinion teeth on its outer circumferential surface that mesh with the assist-side rack teeth. The worm wheel is fixed to the assist-side pinion shaft so as not to be rotatable relative to the assist-side pinion shaft. The worm shaft is in mesh with the worm wheel. The electric motor is for driving the worm shaft to rotate, and has a motor output shaft. The power transmission device is disposed between the worm shaft and the motor output shaft, and transmits rotation of the motor output shaft to the worm shaft. In the electric power steering device according to one aspect of the present invention, the motor output shaft is offset with respect to the worm shaft, i.e., the motor output shaft and the worm shaft are arranged parallel to each other but not coaxially.

[0011] In the electric power steering device according to one aspect of the present invention, the power transmission device may be a belt-type power transmission device equipped with a belt. In this case, the worm shaft can be biased toward the worm wheel by utilizing the tension of the belt.

[0012] In the electric power steering device according to one aspect of the present invention, the power transmission device may be a gear-type power transmission device including a plurality of gears.

[0013] In the electric power steering device according to one aspect of the present invention, the rack shaft and the motor output shaft can be disposed parallel to each other. [Effects of the Invention]

[0014] According to the present invention, an electric power steering device that can be easily mounted on a vehicle can be realized. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an electric power steering device according to a first example of an embodiment. [Figure 2] FIG. 2 is a front view of an electric power steering device according to a first example of the embodiment, with some components including a housing and an electric motor taken out, as viewed from the front side of the vehicle. [Figure 3] FIG. 3 is a bottom view of the electric power steering device according to the first embodiment, with some components including a housing and an electric motor taken out, as viewed from below the vehicle. [Figure 4] FIG. 4 is an exploded perspective view showing some parts including a housing and an electric motor taken out from an electric power steering device according to a first example of the embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line AO-OA in FIG. [Figure 6] FIG. 6 is a diagram corresponding to FIG. 2 and showing a second example of the embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view corresponding to FIG. 5, showing a third example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] [First example of embodiment] A first example of an embodiment will be described with reference to Figures 1 to 5. In the following description, the front-rear direction refers to the front-rear direction of the vehicle, the up-down direction refers to the up-down direction of the vehicle, and the left-right direction refers to the width direction of the vehicle. The left-right direction also corresponds to the axial direction of a rack shaft 11 and a rack housing unit 14, which will be described later. One side with respect to the axial direction of the rack shaft 11 and the rack housing unit 14 refers to the right side in Figures 1 to 4, and the other side with respect to the axial direction of the rack shaft 11 and the rack housing unit 14 refers to the left side in Figures 1 to 4.

[0017] [Overall configuration of electric power steering device] The electric power steering device 1 of this example is a dual pinion type electric power steering device that includes one rack shaft 11 and two pinion shafts, a steering-side pinion shaft 10 and an assist-side pinion shaft 13, and inputs a steering force from the steering-side pinion shaft 10 to the rack shaft 11, and inputs an assist driving force from the assist-side pinion shaft 13 to the rack shaft 11.

[0018] As shown in FIG. 1, the electric power steering device 1 includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a and 5b, an intermediate shaft 6, a housing 7 (omitted from FIG. 1, see FIG. 2), a steering mechanism 8, and an assist mechanism 9.

[0019] The steering shaft 3 is rotatably supported inside a steering column 4 supported on the vehicle body. A steering wheel 2, which is steered by the driver, is attached to the rear end of the steering shaft 3. The front end of the steering shaft 3 is connected to a steering-side pinion shaft 10, which constitutes a steering mechanism 8, via a universal joint 5a, an intermediate shaft 6, and another universal joint 5b. As a result, the rotational motion of the steering wheel 2 is transmitted to the steering-side pinion shaft 10. The rotational motion of the steering-side pinion shaft 10 is converted into axial linear motion of a rack shaft 11, which constitutes the steering mechanism 8. This imparts a steering angle to left and right steered wheels 12. In addition, the electric power steering device 1 imparts an assist driving force to the rack shaft 11 via an assist-side pinion shaft 13, which constitutes an assist mechanism 9, thereby reducing the steering force required for the driver to rotate the steering wheel 2.

[0020] <housing> The housing 7 is a die-cast product made from a light alloy such as an aluminum alloy, and is fixed to the vehicle body. When implementing the present invention, the housing can be configured by joining and fixing multiple parts together, as in the structure shown in the figure, or it can be configured as an integrated unit.

[0021] The housing 7 includes a rack accommodating portion 14, a steering side pinion accommodating portion 15, an assist side pinion accommodating portion 16, a steering side guide accommodating portion 17, an assist side guide accommodating portion 18, a gear housing portion 19, and a plurality of mounting portions 20a, 20b.

[0022] The rack housing 14 is a cylindrical member that extends in the left-right direction. The rack housing 14 is open at both axial ends. The axial middle portion of the rack shaft 11 that constitutes the steering mechanism 8 is housed inside the rack housing 14. The rack housing 14 is disposed substantially horizontally.

[0023] The steering side pinion accommodating portion 15 is a portion that accommodates the tip half of the steering side pinion shaft 10, and is arranged in a circumferential portion of one axial side portion of the rack accommodating portion 14. Specifically, the steering side pinion accommodating portion 15 is arranged in the front portion of one axial side portion of the rack accommodating portion 14 (the front side portion in Fig. 2, the upper side portion in Fig. 3). The steering side pinion accommodating portion 15 is arranged with its central axis facing up and down, and has a cylindrical shape with a bottom that is open only at the upper end. The steering side pinion accommodating portion 15 is arranged in a twisted positional relationship with respect to the rack accommodating portion 14. In other words, the central axis of the steering side pinion accommodating portion 15 and the central axis of the rack accommodating portion 14 are in a twisted positional relationship. In this example, the central axis of the steering side pinion accommodating portion 15 is not disposed in a direction perpendicular to the central axis of the rack accommodating portion 14 when viewed from the front-to-rear direction, which is a direction perpendicular to the central axis of the steering side pinion accommodating portion 15 and the central axis of the rack accommodating portion 14, but is inclined relative to the perpendicular direction. The internal space of the steering side pinion accommodating portion 15 communicates with the internal space of the rack accommodating portion 14.

[0024] The assist side pinion accommodating portion 16 is a portion that accommodates the assist side pinion shaft 13, and is arranged in a circumferential portion of the other axial side portion of the rack accommodating portion 14. Specifically, the assist side pinion accommodating portion 16 is arranged in the upper portion of the other axial side portion of the rack accommodating portion 14 (the upper portion in FIG. 2, the rear portion in FIG. 3). The assist side pinion accommodating portion 16 is arranged with its central axis facing the front-rear direction, and has a cylindrical shape with both front-rear direction ends open. The rear end opening of the assist side pinion accommodating portion 16 is closed by a cap 21a. The internal space of the assist side pinion accommodating portion 16 is in communication with the internal space of the rack accommodating portion 14. The assist side pinion accommodating portion 16 is arranged in a twisted positional relationship with respect to the rack accommodating portion 14. In this example, the central axis of the assist side pinion accommodating portion 16 is arranged in a direction perpendicular to the central axis of the assist side pinion accommodating portion 16 and the central axis of the rack accommodating portion 14 when viewed from the up-down direction, which is a direction perpendicular to the central axis of the assist side pinion accommodating portion 16 and the central axis of the rack accommodating portion 14. However, when implementing the present invention, the central axis of the assist side pinion accommodating portion can also be arranged in a direction oblique to the central axis of the assist side pinion accommodating portion and the central axis of the rack accommodating portion when viewed from the direction perpendicular to the central axis of the assist side pinion accommodating portion and the central axis of the rack accommodating portion.

[0025] The steering side guide accommodating portion 17 is a portion that accommodates a steering side rack guide (not shown), and is arranged in a portion of the rack accommodating portion 14 that is diametrically opposite to the steering side pinion accommodating portion 15. In other words, the steering side guide accommodating portion 17 is arranged in the rear portion of the rack accommodating portion 14 at the same axial position as the steering side pinion accommodating portion 15. The steering side guide accommodating portion 17 has a cylindrical shape and extends in radial directions about the central axis of the rack accommodating portion 14. The steering side guide accommodating portion 17 in this example extends in the front-to-rear direction. An end opening on the rear side of the steering side guide accommodating portion 17 is closed by a cap 21b. The internal space of the steering side guide accommodating portion 17 also communicates with the internal space of the rack accommodating portion 14.

[0026] The assist-side guide accommodating portion 18 is a portion that accommodates an assist-side rack guide (not shown), and is disposed in a portion of the rack accommodating portion 14 that is diametrically opposite the assist-side pinion accommodating portion 16. That is, the assist-side guide accommodating portion 18 is disposed in a lower portion of the rack accommodating portion 14 at the same axial position as the assist-side pinion accommodating portion 16. The assist-side guide accommodating portion 18 has a cylindrical shape and extends in radial directions about the central axis of the rack accommodating portion 14. In this example, the assist-side guide accommodating portion 18 extends in the vertical direction. An opening at the lower end of the assist-side guide accommodating portion 18 is closed by a cap 21c. The internal space of the assist-side guide accommodating portion 18 also communicates with the internal space of the rack accommodating portion 14.

[0027] The gear housing portion 19 is a portion that houses a worm reducer 40 and a power transmission device 42 (to be described later) that constitute the assist mechanism portion 9, and includes a wheel housing portion 22, a worm housing portion 23, and a power transmission device housing portion 24. The gear housing portion 19 can also be formed separately from other portions of the housing 7 and fixed to those portions with bolts or the like.

[0028] The wheel accommodating portion 22 is a portion that accommodates the worm wheel 45 that constitutes the worm reducer 40, and is disposed adjacent to the assist-side pinion accommodating portion 16 in the axial direction. Specifically, the wheel accommodating portion 22 is disposed on the front side of the assist-side pinion accommodating portion 16. The wheel accommodating portion 22 has a substantially cylindrical shape, and is disposed coaxially with the assist-side pinion accommodating portion 16. An end opening on the front side of the wheel accommodating portion 22 is closed by a circular lid portion 25.

[0029] The worm accommodating section 23 is a section that accommodates the worm shaft 46 that constitutes the worm reducer 40, and is arranged at a portion of the wheel accommodating section 22 in the circumferential direction. Specifically, the worm accommodating section 23 is arranged at an upper side of the wheel accommodating section 22. Furthermore, the central axis of the worm accommodating section 23 is arranged at a twisted position with respect to the central axis of the wheel accommodating section 22 and parallel to the central axis of the rack accommodating section 14. The worm accommodating section 23 has a cylindrical shape with a bottom, and has an opening at one end on the axial side of the rack accommodating section 14. The internal space of the worm accommodating section 23 and the internal space of the wheel accommodating section 22 are in communication with each other.

[0030] The power transmission device accommodating section 24 is a section that accommodates a power transmission device 42 such as a pulley device or a gear device, and is arranged adjacent to the opening side of the worm accommodating section 23. Specifically, the power transmission device accommodating section 24 is arranged adjacent to one side of the worm accommodating section 23 in the axial direction of the rack accommodating section 14. The power transmission device accommodating section 24 has an oval (egg-shaped, elliptical, or oval) cylindrical shape. The internal space of the power transmission device accommodating section 24 and the internal space of the worm accommodating section 23 are in communication with each other.

[0031] The power transmission device accommodating section 24 is disposed offset relative to the worm accommodating section 23. In this example, the power transmission device accommodating section 24 is disposed offset downward relative to the worm accommodating section 23. Therefore, the lower half of the power transmission device accommodating section 24 protrudes downward more than the worm accommodating section 23 and faces the wheel accommodating section 22 in the axial direction of the rack accommodating section 14.

[0032] The power transmission device housing 24 has an opening at one end in the axial direction of the rack housing 14 and a bottom plate 26 at the other end in the axial direction of the rack housing 14. The opening of the power transmission device housing 24 is closed by an oval-shaped cover plate 27. Specifically, a plurality of bolts 30 are inserted through insertion holes 29 in a first flange 28 provided on the outer peripheral edge of the cover plate 27 and threadedly engaged with female threaded holes 32 in a second flange 31 provided on the outer peripheral surface of the power transmission device housing 24, thereby closing the opening of the power transmission device housing 24 with the cover plate 27. The cover plate 27 is provided with a cover-side through-hole 33 through which a tip end of a motor output shaft 52 of an electric motor 41 (described later) is inserted. On the other hand, the bottom plate 26 is provided with a bottom-side through-hole 34 at a portion facing the opening of the worm housing 23, through which a mounting shaft 59 of a driven pulley 57 (described later) is inserted.

[0033] The multiple mounting portions 20a, 20b are used to secure the housing 7 to the vehicle body. In this example, two mounting portions 20a, 20b are provided on each end of the rack accommodating portion 14 in the axial direction. The housing 7 is secured to the vehicle body using fastening members such as bolts or studs that are inserted through the mounting portions 20a, 20b, respectively.

[0034] <Steering mechanism> The steering mechanism 8 has a steering-side pinion shaft 10, a rack shaft 11, and a steering-side rack guide (not shown), and converts the rotational movement of the steering wheel 2 into linear movement in the axial direction of the rack shaft 11.

[0035] The steering side pinion shaft 10 has steering side pinion teeth 35 on the outer peripheral surface of its tip half. The steering side pinion shaft 10 is rotatably supported inside the steering side pinion accommodating portion 15 using a plurality of bearings. The central axis of the steering side pinion shaft 10 is arranged coaxially with the central axis of the steering side pinion accommodating portion 15. The steering side pinion shaft 10 is connected to the steering wheel 2 via universal joints 5a, 5b and an intermediate shaft 6, and rotates in response to the steering operation of the steering wheel 2. The rotation of the steering side pinion shaft 10 is converted into linear motion of the rack shaft 11, which pushes and pulls tie rods 36 connected to both axial ends of the rack shaft 11. This imparts a steering angle to the left and right steered wheels 12.

[0036] The rack shaft 11 is a rod-shaped member made of metal such as carbon steel. The rack shaft 11 is disposed with its axial direction (longitudinal direction) oriented in the left-right direction. The rack shaft 11 has steering-side rack teeth 37 that mesh with steering-side pinion teeth 35 provided on the outer peripheral surface of the steering-side pinion shaft 10 on a circumferential portion of the outer peripheral surface of one axial side portion, and has assist-side rack teeth 38 that mesh with assist-side pinion teeth 44 provided on the outer peripheral surface of the assist-side pinion shaft 13 on a circumferential portion of the outer peripheral surface of the other axial side portion. In this example, the rack shaft 11 has the steering-side rack teeth 37 on a front side surface of the one axial side portion, and the assist-side rack teeth 38 on an upper side surface of the other axial side portion.

[0037] The rack shaft 11 is supported inside the rack housing 14 so as to be able to move back and forth in the axial direction, with its axial direction facing the left-right direction and both axial ends protruding from both left-right openings of the rack housing 14. Both axial ends of the rack shaft 11 are connected to tie rods 36 via spherical joints 39.

[0038] The steering side rack guide presses the rack shaft 11 toward the steering side pinion shaft 10 and is disposed inside the steering side guide housing portion 17. As a result, the steering side rack guide is disposed so that the rack shaft 11 is sandwiched between the steering side rack guide and the steering side pinion shaft 10. As the steering side rack guide, for example, a sliding type rack guide including a pad and an elastic member can be used. By pressing the rack shaft 11 toward the steering side pinion shaft 10, the steering side rack guide reduces backlash at the meshing portion between the steering side pinion teeth 35 and the steering side rack teeth 37. This prevents abnormal noise from being generated at the meshing portion between the steering side pinion teeth 35 and the steering side rack teeth 37.

[0039] <Assist mechanism> The assist mechanism 9 applies an assist driving force to the rack shaft 11, thereby reducing the steering force required for the driver to operate the steering wheel 2. The assist mechanism 9 includes an assist side pinion shaft 13, an assist side rack guide (not shown), a worm reducer 40, an electric motor 41, a power transmission device 42, and a torque sensor 43.

[0040] The assist side pinion shaft 13 has assist side pinion teeth 44 on the outer peripheral surface of its tip half that mesh with the assist side rack teeth 38 of the rack shaft 11. The assist side pinion shaft 13 is rotatably supported inside the assist side pinion accommodating portion 16 using a plurality of bearings (not shown). The central axis of the assist side pinion shaft 13 is arranged coaxially with the central axis of the assist side pinion accommodating portion 16. The assist side pinion shaft 13 is rotationally driven by an electric motor 41 via a worm reducer 40 and a power transmission device 42.

[0041] The assist-side rack guide presses the rack shaft 11 toward the assist-side pinion shaft 13 and is disposed inside the assist-side guide accommodating portion 18. As a result, the assist-side rack guide is disposed so that the rack shaft 11 is sandwiched between the assist-side rack guide and the assist-side pinion shaft 13. As the assist-side rack guide, for example, a roller-type rack guide including a roller, a holder, and an elastic member can be used. The assist-side rack guide presses the rack shaft 11 toward the assist-side pinion shaft 13, thereby reducing backlash at the meshing portion between the assist-side pinion teeth 44 and the assist-side rack teeth 38. This prevents abnormal noise from being generated at the meshing portion between the assist-side pinion teeth 44 and the assist-side rack teeth 38.

[0042] The worm reducer 40 includes a worm wheel 45 and a worm shaft 46 and reduces the rotation of the electric motor 41 , that is, increases the drive torque of the electric motor 41 , and transmits it to the assist-side pinion shaft 13 .

[0043] The worm wheel 45 has wheel teeth 47 on its outer circumferential surface and is disposed inside the wheel accommodating portion 22. The worm wheel 45 is fitted and fixed to the base end (front end) of the assist-side pinion shaft 13 so as not to rotate relative to it.

[0044] The worm shaft 46 has worm teeth 48 that mesh with the wheel teeth 47 at the axially intermediate portion of its outer circumferential surface, and is rotatably supported inside the worm accommodating portion 23 by a pair of rolling bearings 49a, 49b. Specifically, the tip end of the worm shaft 46 is rotatably supported by the rolling bearing 49a, and the base end of the worm shaft 46 is rotatably supported by the rolling bearing 49b. As a result, in this example, the worm shaft 46 is disposed above the worm wheel 45. Also, the central axis O of the worm shaft 46 is 46 is the central axis O of the rack shaft 11. 11The worm shaft 46 in this example is supported to be able to oscillate slightly around a rolling bearing 49a disposed at the tip end of the worm shaft 46. The worm shaft 46 has a mounting hole 50 in the center of the base end side (one side in the axial direction of the rack shaft 11), which extends in the axial direction and opens to the end face on the base end side.

[0045] The electric motor 41 is for applying an assist driving force to the rack shaft 11 via the power transmission device 42, the worm reducer 40, and the assist side pinion shaft 13, and has a motor body 51 and a motor output shaft 52.

[0046] The motor main body 51 is configured by accommodating coils, cores, and the like (not shown) inside a substantially cylindrical motor housing 53. The motor output shaft 52 is rotatably supported inside the motor housing 53 using a plurality of bearings (not shown). The tip of the motor output shaft 52 protrudes axially from the motor housing 53 and is inserted into the internal space of the power transmission device accommodating section 24 through a lid-side through-hole 33 in a lid plate portion 27 that covers the opening of the power transmission device accommodating section 24.

[0047] The electric motor 41 is supported and fixed to the power transmission device accommodating portion 24 using bolts 30 for fixing the cover plate portion 27. Specifically, the bolts 30 are inserted in order through insertion holes 55 of a motor-side flange portion 54 provided on the outer circumferential surface of the motor housing 53 and through insertion holes 29 of a first flange portion 28 provided on the cover plate portion 27, and then screwed into female threaded holes 32 of a second flange portion 31 provided on the power transmission device accommodating portion 24, thereby fixing (co-fastening) the electric motor 41 and the cover plate portion 27 to the power transmission device accommodating portion 24 with the bolts 30.

[0048] In this example, with the electric motor 41 supported and fixed to the power transmission device housing 24, the motor output shaft 52 is not arranged coaxially with the worm shaft 46 that constitutes the worm reducer 40, but is arranged offset. Specifically, in this example, the motor output shaft 52 is arranged offset downward from the worm shaft 46. Therefore, the central axis O of the motor output shaft 52 is 52 is the central axis O of the worm shaft 46 46 and the central axis O of the worm shaft 46. 46 In this specification, "offset" refers to a state of being shifted in parallel. When implementing the present invention, the offset direction of the motor output shaft relative to the worm shaft can be changed as appropriate depending on the relationship with the members housed in the engine compartment.

[0049] Furthermore, the motor output shaft 52 is disposed parallel to the rack shaft 11. In this example, when the electric power steering device 1 is mounted on a vehicle, the central axis O of the motor output shaft 52 is 52 is the central axis O of the rack shaft 11. 11 As a result, the electric motor 41 (motor body 51) is disposed in front of the rack housing portion 14 that houses the rack shaft 11. In this example, the central axis O of the motor output shaft 52 52 The vertical position of the rack shaft 11 is 11 In other words, the vertical position of the central axis O of the motor output shaft 52 when viewed from the front-rear direction is approximately the same as that of the 52 and the central axis O of the rack shaft 11 11 are located on substantially the same straight line. In the electric power steering device 1 of this example, the electric motor 41 is disposed near the center in the left-right direction of the housing 7. However, when implementing the present invention, the electric motor 41 can also be disposed at one of the left-right ends of the housing 7.

[0050] The power transmission device 42 is a belt-type power transmission device including a drive pulley 56, a driven pulley 57, and a belt 58, and is a so-called pulley device. The power transmission device 42 is disposed inside the power transmission device housing 24, and transmits the rotation of the electric motor 41 to the worm shaft 46 that constitutes the worm reducer 40, either at a constant speed or after reducing or increasing the speed. In this example, the power transmission device 42 reduces the speed of the rotation of the electric motor 41 before transmitting it to the worm shaft 46. This allows for the miniaturization of the worm reducer 40 and / or the miniaturization of the electric motor 41.

[0051] The drive pulley 56 has external teeth on its outer circumferential surface, and is fitted and fixed to the tip of the motor output shaft 52 of the electric motor 41 so as not to rotate relative to the shaft.

[0052] The driven pulley 57 has external teeth on its outer circumferential surface and is fixed to the base end of the worm shaft 46 so as to be non-rotatable relative to the worm shaft 46. For this reason, in this example, a mounting shaft portion 59 arranged coaxially with the worm shaft 46 is fitted (inserted) into a mounting hole 50 provided at the base end of the worm shaft 46 so as to be non-rotatable relative to the worm shaft 46. The driven pulley 57 is externally fitted and fixed to a portion of the mounting shaft portion 59 arranged inside the power transmission device housing portion 24 through the bottom-side through-hole 34 of the bottom plate portion 26 so as to be non-rotatable relative to the worm shaft 46. When implementing the present invention, the worm shaft and the mounting shaft portion can also be configured as one unit. In other words, the driven pulley can be directly fixed to a portion of the worm shaft so as to be non-rotatable relative to the worm shaft.

[0053] The belt 58 has internal teeth on its inner peripheral surface and is stretched over the drive pulley 56 and the driven pulley 57. A tension is applied to the belt 58 to generate a frictional force between the belt 58 and the drive pulley 56 and between the belt 58 and the driven pulley 57.

[0054] In this example, as described above, the worm shaft 46 constituting the worm reducer 40 and the motor output shaft 52 constituting the electric motor 41 are not directly connected but are connected via a belt-type power transmission device 42, making it possible to position the motor output shaft 52 offset from the worm shaft 46.

[0055] In this example, the tension of the belt 58 is used to apply a force to the driven pulley 57 in a direction that moves it closer to the drive pulley 56, i.e., a forward force. This urges the worm shaft 46, to whose base end the driven pulley 57 is fixed, toward the worm wheel 45 (the lower side in FIG. 5 ). As a result, the worm shaft 46 is caused to swing about the rolling bearing 49a on the tip side, and the worm teeth 48 provided on the outer peripheral surface of the worm shaft 46 are pressed against the wheel teeth 47 provided on the outer peripheral surface of the worm wheel 45. This reduces backlash at the meshing portion between the worm teeth 48 and the wheel teeth 47, preventing abnormal noise from occurring at the meshing portion between the worm teeth 48 and the wheel teeth 47.

[0056] The torque sensor 43 is disposed around the steering side pinion shaft 10 and detects the magnitude and direction of the torque input to the steering side pinion shaft 10. As a result, the torque sensor 43 outputs a signal corresponding to the torque input to the steering side pinion shaft 10 to the electronic control unit of the electric motor 41. As the torque sensor 43, various types of torque sensors can be used, such as a non-contact torque sensor that utilizes the magnetostrictive effect.

[0057] The assist mechanism 9 controls the driving of the electric motor 41 based on the output signal of the torque sensor 43. As a result, the driving torque generated by the electric motor 41 is transmitted as an assist driving force to the rack shaft 11 via the power transmission device 42, the worm reduction gear 40, and the assist-side pinion shaft 13. As a result, the steering force required for the driver to operate the steering wheel 2 is reduced.

[0058] According to the electric power steering device 1 of this embodiment as described above, it is possible to improve the ease of mounting on a vehicle. That is, in this example, the worm shaft 46 of the worm reducer 40 and the motor output shaft 52 of the electric motor 41 are connected via the belt-type power transmission device 42, so that the motor output shaft 52 is disposed offset from the worm shaft 46. Therefore, the motor main body 51 (motor housing 53) of the electric motor 41 can be disposed offset from the worm accommodating portion 23 of the gear housing portion 19 that accommodates the worm shaft 46. This makes it possible to dispose the worm accommodating portion 23 and / or the motor main body 51 so as to avoid interference with peripheral components when the electric power steering device 1 is disposed in an engine compartment, thereby improving the mountability of the electric power steering device 1 on a vehicle.

[0059] Furthermore, in this example, the motor output shaft 52 is arranged parallel to the rack shaft 11. Therefore, the amount of vertical protrusion of the electric motor 41 (motor body 51) from the rack housing portion 14 can be made smaller than when the rack shaft and the output shaft of the electric motor are arranged non-parallel. Therefore, also from this point of view, the electric power steering device 1 of this example can be easily installed in the engine room.

[0060] In this example, the rotation of the electric motor 41 is reduced in speed and transmitted to the worm shaft 46 by the belt-type power transmission device 42. This allows the worm reducer 40 (and the gear housing 19 that houses the worm reducer 40) to be made smaller in size and / or the electric motor 41 to be made smaller in size.

[0061] Furthermore, in this example, the tension of the belt 58 that constitutes the power transmission device 42 is used to urge the worm shaft 46 toward the worm wheel 45, thereby pressing the worm teeth 48 against the wheel teeth 47. Therefore, backlash at the meshing portion between the worm teeth 48 and the wheel teeth 47 can be reduced without providing a dedicated urging device for reducing backlash.

[0062] [Second example of embodiment] A second example of the embodiment will be described with reference to FIG.

[0063] In this example, the assist side pinion shaft 13 (see Figure 1) is positioned above the rack shaft 11, similar to the structure of the first example embodiment, but the mounting phase of the worm shaft 46 relative to the worm wheel 45 is changed from the structure of the first example embodiment.

[0064] That is, in this example, the worm shaft 46 is disposed below the worm wheel 45. In addition, the central axis O of the worm shaft 46 46 the central axis O of the rack shaft 11 11 As a result, the central axis O of the worm shaft 46 is 46 and the central axis O of the rack shaft 11 11 The distance (vertical distance) L2 between the center axis O of the worm shaft 46 in the structure of the first example of the embodiment is 46 and the central axis O of the rack shaft 11 11 The distance between the <L1)。

[0065] Also in this example, the worm shaft 46 and the motor output shaft 52 (see FIG. 5) of the electric motor 41 are connected via the pulley-type power transmission device 42.

[0066] In this example, the central axis O of the worm shaft 46 46 and the central axis O of the rack shaft 11 11 The distance L2 between the first and second electrodes can be made smaller than in the structure of the first example embodiment, which makes it possible to reduce the size of the electric power steering device 1. This allows for space saving, which further improves the ease of installation in a vehicle. The other configurations and effects are the same as those of the first embodiment.

[0067] [Third example of embodiment] A third example of the embodiment will be described with reference to FIG.

[0068] In this example, the worm shaft 46 constituting the worm reducer 40 and the motor output shaft 52 constituting the electric motor 41 are connected via a gear-type power transmission device 42a having a plurality of gears.

[0069] The power transmission device 42a is a gear-type power transmission device, or so-called gear device, that includes a drive gear 60, a driven gear 61, and a transmission gear 62. The power transmission device 42a transmits the rotation of the electric motor 41 to the worm shaft 46 that constitutes the worm reducer 40, either at a constant speed or after reducing or increasing the speed. In this example, the power transmission device 42a also reduces the speed of the rotation of the electric motor 41 before transmitting it to the worm shaft 46.

[0070] The drive gear 60 has external teeth on its outer circumferential surface, and is fitted and fixed to the tip of the motor output shaft 52 of the electric motor 41 so as not to rotate relative to the shaft 52.

[0071] The driven gear 61 has external teeth on its outer circumferential surface, and is fixed to the base end of the worm shaft 46 so as to be non-rotatable relative to the worm shaft 46. For this reason, in the present example as well, the mounting shaft portion 59, which is arranged coaxially with the worm shaft 46, is fitted (inserted) into the mounting hole 50 provided at the base end of the worm shaft 46 so as to be non-rotatable relative to the worm shaft 46. The driven gear 61 is externally fitted and fixed to the portion of the mounting shaft portion 59 that is arranged inside the power transmission device housing portion 24 through the cover-side through-hole 33 of the cover plate portion 27 so as to be non-rotatable relative to the worm shaft 46.

[0072] The transmission gear 62 has external teeth on its outer circumferential surface, and meshes with the external teeth of the drive gear 60 and the driven gear 61. The transmission gear 62 is rotatably supported by a transmission shaft 63 that is arranged parallel to both the worm shaft 46 and the motor output shaft 52. Although the illustrated example includes only one transmission gear 62, when implementing the present invention, multiple transmission gears may be provided, or the transmission gear may be omitted and the drive gear and driven gear may be directly meshed with each other.

[0073] In the case of the present example as described above, by connecting the worm shaft 46 of the worm reducer 40 and the motor output shaft 52 of the electric motor 41 via a gear-type power transmission device 42a, the motor output shaft 52 can be disposed offset from the worm shaft 46. Therefore, when the electric power steering device 1 is disposed in an engine room, the worm housing portion 23 and / or the motor main body 51 can be disposed so as to avoid interference with surrounding components. As a result, the mountability of the electric power steering device 1 on a vehicle can be improved. The other configurations and effects are the same as those of the first embodiment.

[0074] Although the embodiments of the present invention have been described above, the present invention is not limited to these and can be modified as appropriate within the scope of the technical concept of the invention. Furthermore, the structures of the examples of the embodiments can be combined as appropriate as long as no contradiction occurs.

[0075] When implementing the present invention, the offset direction of the motor output shaft relative to the worm shaft is not limited to the directions described in each example of the embodiment, and can be determined appropriately in relation to the components stored in the engine compartment.

[0076] When implementing the present invention, the structure of the power transmission device is not limited to the belt type or gear type described in the embodiment, but power transmission devices of other structures such as a chain type can also be used.

[0077] Furthermore, when implementing the present invention, the respective formation positions (phases) of the steering-side rack teeth and the assist-side rack teeth provided on the rack shaft are not limited to the positions shown in the examples of the embodiments, and can be changed as appropriate. [Explanation of symbols]

[0078] 1 Electric power steering device 2 steering wheels 3 Steering shaft 4 Steering column 5a, 5b universal joint 6 Intermediate shaft 7. Housing 8 Steering mechanism 9 Assist mechanism 10 Steering side pinion shaft 11 Rack axis 12 steering wheel 13 Assist side pinion shaft 14 Rack storage area 15 Steering side pinion housing 16 Assist side pinion housing 17 Steering side guide housing 18 Assist side guide housing 19 Gear housing 20a, 20b Mounting parts 21a, 21b, 21c Caps 22 Wheel housing 23 Worm housing 24 Power transmission device housing 25 Lid 26 Bottom plate part 27 Lid plate part 28 First flange 29 Insertion hole 30 volts 31 Second flange 32 female threaded hole 33 Lid side hole 34 Bottom side hole 35 Steering side pinion teeth 36 tie rod 37 Steering side rack teeth 38 Assist side rack teeth 39 Spherical joint 40 Worm reducer 41 Electric motor 42, 42a Power transmission device 43 Torque sensor 44 Assist side pinion teeth 45 worm wheel 46 Worm shaft 47 Wheel Teeth 48 worm teeth 49a, 49b Rolling bearings 50 mounting holes 51 Motor body 52 Motor output shaft 53 Motor housing 54 Motor side flange 55 Insertion hole 56 Drive pulley 57 Driven pulley 58 Belt 59 Mounting shaft 60 Drive gear 61 Driven gear 62 Transmission gear 63 Transmission shaft

Claims

1. a rack shaft having steering-side rack teeth on a portion of an outer circumferential surface of one axial side portion and assist-side rack teeth on a portion of an outer circumferential surface of the other axial side portion; a steering side pinion shaft having steering side pinion teeth on its outer circumferential surface that mesh with the steering side rack teeth, and that is rotationally driven by operation of a steering wheel; an assist-side pinion shaft having assist-side pinion teeth on its outer circumferential surface that mesh with the assist-side rack teeth; a worm wheel fixed to the assist-side pinion shaft so as not to be rotatable relative to the assist-side pinion shaft; a worm shaft meshed with the worm wheel; an electric motor having a motor output shaft for rotationally driving the worm shaft; a power transmission device disposed between the worm shaft and the motor output shaft, for transmitting rotation of the motor output shaft to the worm shaft, The motor output shaft is offset relative to the worm shaft. Electric power steering device.

2. 2. The electric power steering device according to claim 1, wherein the power transmission device is a belt-type power transmission device having a belt.

3. 3. The electric power steering apparatus according to claim 2, wherein the worm shaft is biased toward the worm wheel by utilizing the tension of the belt.

4. 2. The electric power steering device according to claim 1, wherein the power transmission device is a gear-type power transmission device having a plurality of gears.

5. 5. The electric power steering device according to claim 1, wherein the rack shaft and the motor output shaft are disposed parallel to each other.

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