Power steering system

Abstract

To provide a power steering system whose performance has been upgraded.SOLUTION: A power steering system 10 includes an output shaft 160 having a cylindrical part 161 on one side of an axial direction, an electric motor 180 for steering assistance, and a worm decelerator 200 that decelerates the rotation of the electric motor 180 and transmits the resultant rotation to the output shaft 160. The worm decelerator 200 includes a worm shaft 210 and worm wheel 300. The worm wheel 300 is connected to the output shaft 160 and rotates together with the output shaft 160. The worm wheel 300 includes an annular teeth part 310 having plural teeth 311, which are annually arrayed, on the periphery, and a support body 320 secured on an internal circumference of the annular teeth part 310. The support body 320 includes a first shaft part 321 extending in an axial direction, and a second shaft part 324 which is coupled to the first shaft part 321 and to which the annular teeth part 310 is fixed. The first shaft part 321 is pressed and fitted into the inside (internal space 161a) of the cylindrical part 161.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a power steering device mounted on a vehicle. [Background technology]

[0002] The electric power steering device disclosed in Patent Document 1 includes an assist mechanism that assists the driver's steering operation. The assist mechanism includes an electric motor that applies assist torque to the column shaft and a reducer that transmits the rotation of the electric motor to the column shaft. The reducer includes a worm that is rotationally driven by the electric motor and a worm wheel that meshes with the worm. The worm wheel is connected to the output shaft of the column shaft so as to be rotatable together with the output shaft but so as to be immovable in the axial direction.

[0003] A backlash elimination mechanism is disclosed in Patent Document 2. The backlash elimination mechanism biases a bearing that supports one end of a worm shaft in a direction that reduces the center distance between the worm shaft and the worm wheel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-132080 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-36045 Summary of the Invention [Problem to be solved by the invention]

[0005] In the conventional electric power steering device described in Patent Document 1, the worm wheel and the output shaft are connected by press-fitting the outer periphery of the output shaft into the inner periphery of a metal annular support of the worm wheel. In this case, the annular support expands radially outward, resulting in an increase in the outer diameter of the worm wheel, i.e., the outer diameter of the annular teeth disposed on the outer periphery of the annular support. Because the amount of increase in the outer diameter varies, the axial distance between the worm and the worm wheel may be larger or smaller than the design value for each individual reducer. This can lead to an increase in rotational torque and / or the generation of rattle noise. Therefore, it is conceivable to incorporate a backlash elimination mechanism, such as that disclosed in Patent Document 2, into the reducer. However, the range of axial distances between the worm and the worm wheel that the backlash elimination mechanism can accommodate is limited. Therefore, the backlash elimination mechanism may not be able to fully resolve issues such as the generation of rattle noise caused by variations in the outer diameter of the worm wheel.

[0006] The present invention was made by the inventors of the present application by focusing on the above-mentioned problem, and has an object to provide a power steering device with improved performance. [Means for solving the problem]

[0007] A power steering device according to one embodiment of the present invention comprises an output shaft having a cylindrical portion on one side in the axial direction, an electric motor for steering assistance, and a worm reducer that reduces the rotation of the electric motor and transmits it to the output shaft, wherein the worm reducer comprises a worm shaft that is driven to rotate by the electric motor, and a worm wheel that meshes with the worm shaft, the worm wheel being connected to the output shaft and rotating integrally with the output shaft, wherein the worm wheel has an annular tooth portion having a plurality of teeth arranged in a ring shape on its outer periphery, and a support body fixed to the inner periphery of the annular tooth portion, and the support body includes a first shaft portion extending in the axial direction, and a second shaft portion connected to the first shaft portion and to which the annular tooth portion is fixed, and the first shaft portion is press-fitted inside the cylindrical portion. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a power steering device with improved performance. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a schematic overall configuration of a power steering device. [Figure 2] FIG. 2 is a first cross-sectional view showing the structure of the driving force applying mechanism according to the embodiment. [Figure 3] FIG. 3 is a second cross-sectional view showing the structure of the driving force applying mechanism according to the embodiment. [Figure 4] FIG. 4 is an enlarged cross-sectional view showing a connection portion between the support body and the cylindrical portion according to the embodiment. [Figure 5] FIG. 5 is a first diagram illustrating an example of an assembly process for the worm reducer according to the embodiment. [Figure 6] FIG. 6 is a second diagram illustrating an example of an assembly process for the worm reducer according to the embodiment. [Figure 7] FIG. 7 is a third diagram illustrating an example of an assembly process for the worm reducer according to the embodiment. [Figure 8] FIG. 8 is a fourth diagram illustrating an example of the assembly process of the worm reducer according to the embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing the structure of a driving force applying mechanism according to a modified example of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments and their variations described below all represent comprehensive or specific examples of the present invention. The numerical values, shapes, materials, components, component placement and connection configurations, steps, and step order shown in the following embodiments and variations are merely examples and are not intended to limit the present invention. Furthermore, among the components in the following embodiments and variations, components that are not recited in the independent claims that represent the highest concept are described as optional components. The drawings are schematic diagrams in which emphasis, omission, and proportion adjustments have been made as appropriate to illustrate the present invention, and may differ from the actual shapes, positional relationships, and proportions.

[0011] (Embodiment) [1. Overview of the configuration of the power steering device 10] First, the overall configuration of a power steering device 10 according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram that schematically shows the overall configuration of the power steering device 10. As shown in Fig. 1, the power steering device 10 according to this embodiment is a device that steers steered wheels 500 in response to the operation of an operating member 110 such as a steering wheel.

[0012] More specifically, power steering device 10 includes a steering mechanism 100 that steers steerable wheels 500 in response to operation of an operating member 110, and a driving force applying mechanism 150 that applies a driving force for steering to steering mechanism 100. Steering mechanism 100 includes a steering shaft 130 that rotates in conjunction with rotation of operating member 110, a rack-and-pinion device 140a that converts the rotation of steering shaft 130 into reciprocating motion of a steered shaft 141, and a sensor device 120 that detects the steering torque applied by operating member 110. Steering shaft 130 is made up of three shafts: a column shaft 131, an intermediate shaft 132, and a pinion shaft 133.

[0013] Driving force applying mechanism 150 includes electric motor 180, and applies a driving force (assist torque) for steering to rack and pinion device 140b using electric motor 180 as a drive source. Electric motor 180 is controlled by an ECU (Electronic Control Unit), not shown. The ECU controls electric motor 180 based on, for example, the detection results of sensor device 120. This allows the assist torque provided by driving force applying mechanism 150 to be appropriately adjusted. More specifically, driving force applying mechanism 150 includes worm reduction gear 200, and the driving force generated by electric motor 180 is transmitted to output shaft 160 via worm reduction gear 200. In this embodiment, output shaft 160 is a pinion shaft. Rack and pinion device 140b converts the rotation of output shaft 160, which is a pinion shaft, into reciprocating motion of steered shaft 141. Rack and pinion device 140b is disposed at a position different from rack and pinion device 140a in the axial direction of steered shaft 141. In other words, power steering device 10 according to this embodiment is, for example, a power steering device called a dual pinion type (or double pinion type).

[0014] Although the sensor device 120 is disposed near the operating member 110 in FIG. 1, the sensor device 120 may be disposed on, for example, the pinion shaft 133 that is the input shaft for the rack and pinion device 140a.

[0015] The system of the power steering device 10 does not have to be a dual pinion system. The system of the power steering device 10 may be, for example, a column assist system in which an assist torque is applied to the column shaft 131, or a pinion assist system in which an assist torque is applied to the pinion shaft 133. In other words, the driving force applying mechanism 150 may apply an assist torque to the column shaft 131, or may apply an assist torque to the pinion shaft 133. The position where the driving force applying mechanism 150 is disposed may be determined appropriately depending on the position of the torque output destination.

[0016] 2. Configuration of driving force imparting mechanism 150 Next, the configuration and operation of the driving force applying mechanism 150 according to this embodiment will be described with reference to FIGS.

[0017] [2-1. Overall configuration of driving force imparting mechanism 150] FIG. 2 is a first cross-sectional view showing the structure of the driving force imparting mechanism 150 according to the embodiment. FIG. 2 simply illustrates a cross-section of the driving force imparting mechanism 150, the cross-section passing through the rotation axis Ra of the worm shaft 210 and perpendicular to the rotation axis Rb of the worm wheel 300 and the output shaft 160. FIG. 3 is a second cross-sectional view showing the structure of the driving force imparting mechanism 150 according to the embodiment. FIG. 3 simply illustrates a cross-section taken along line III-III in FIG. 2. FIG. 4 is an enlarged cross-sectional view showing a connection portion between the support 320 and the cylindrical portion 161 according to the embodiment.

[0018] The driving force imparting mechanism 150 includes an electric motor 180 and a worm reducer 200 that reduces the rotation speed of the electric motor 180 and transmits the reduced speed to the output shaft 160. The worm reducer 200 includes a worm shaft 210, a worm wheel 300 that meshes with the worm shaft 210, a housing 153, a first bearing 191, a second bearing 192, and a biasing member 159. The worm shaft 210 includes a worm teeth portion 211 having a plurality of worm teeth on its outer periphery. The worm teeth portion 211 of the worm shaft 210 meshes with the annular teeth portion 310 of the worm wheel 300, whereby the torque of the worm shaft 210 is transmitted to the worm wheel 300.

[0019] The housing 153 is a box-shaped structural member that houses the worm shaft 210 and the worm wheel 300. The housing 153 includes a housing main body 153a that houses the worm wheel 300 and other components therein, and a lid 153b that closes the opening of the housing main body 153a. The worm shaft 210 is rotatably supported at both ends within the housing 153 by a first bearing 191 and a second bearing 192. The worm shaft 210 is tiltably supported with respect to a rotation axis Ra and is pressed against the worm wheel 300 via the first bearing 191 by the biasing force of a biasing member 159. The rotation axis Ra is a virtual axis that serves as the rotation center of the output rotation shaft 181 of the electric motor 180. In this embodiment, the worm shaft 210 is connected to the electric motor 180 and repeatedly rotates, stops, and rotates in the reverse direction around its axis.

[0020] The electric motor 180 has a motor body 185 having a stator, a rotor, etc. inside, and an output rotating shaft 181 protruding from the motor body 185. The output rotating shaft 181 of the electric motor 180 and the worm shaft 210 are connected by a connecting member 190.

[0021] The worm wheel 300 is rotatably held within the housing 153. In this embodiment, the worm wheel 300 is connected to the output shaft 160, which is a pinion shaft, and rotates integrally with the output shaft 160. As a result, the worm wheel 300 amplifies the torque input from the worm shaft 210 and applies an assist torque to the output shaft 160. As shown in FIG. 2 , the worm wheel 300 and the output shaft 160 rotate about a rotation axis Rb (a virtual axis). Specifically, the output shaft 160 is rotatably supported by an output bearing 170, and when the worm wheel 300 rotates due to the torque input from the worm shaft 210, the worm wheel 300 and the output shaft 160 rotate about the rotation axis Rb.

[0022] The output shaft 160 is provided with a cylindrical portion 161 connected to the worm wheel 300 at one end in the axial direction of the output shaft 160 (a direction parallel to the rotation axis Rb), and a pinion tooth portion 165 that meshes with a rack of the steered shaft 141 at the other end closer to the cylindrical portion 161 in the axial direction. As a result, the torque of the output shaft 160 that rotates due to the assist torque acts on the steered shaft 141 as an external force for moving the steered shaft 141 in the left-right direction. In this embodiment, the axial direction of the output shaft 160 is parallel to the X-axis direction. In this specification and the like, the simple term "axial direction" refers to the axial direction of the output shaft 160. The axial direction of the output shaft 160 coincides with the axial directions of the worm wheel 300, the first shaft portion 321, and the second shaft portion 324.

[0023] More specifically, as shown in FIGS. 2 and 3 , a worm wheel 300 according to this embodiment includes an annular toothed portion 310 having a plurality of annularly arranged teeth 311 on its outer periphery, and a support 320 fixed to the inner periphery of the annular toothed portion 310. The support 320 includes a first shaft portion 321 extending in the axial direction and a second shaft portion 324 connected to the first shaft portion 321 and to which the annular toothed portion 310 is fixed. In this embodiment, the metal support 320 is fixed to the inner periphery of the resin annular toothed portion 310 via a resin intermediate portion 330. In other words, the resin annular toothed portion 310 is fixed to the metal support 320 via the resin intermediate portion 330. The intermediate portion 330 is integrated with the metal support 320 by, for example, insert molding.

[0024] In the present embodiment, in support body 320, first shaft portion 321 and second shaft portion 324 are spaced apart in the radial direction of first shaft portion 321, and one end portion in the axial direction (the end portion in the negative Y-axis direction in FIG. 3) is connected by connecting portion 326. In other words, second shaft portion 324 is a cylindrical portion, and is arranged so as to surround first shaft portion 321.

[0025] The worm wheel 300 and the output shaft 160 are connected by fitting the cylindrical portion 161 of the output shaft 160 into the support body 320 having the above structure. Specifically, the first shaft portion 321 is press-fitted into the interior (internal space 161a) of the cylindrical portion 161. This connects the worm wheel 300 and the output shaft 160. In other words, the outer peripheral surface 322 of the first shaft portion 321 and the inner peripheral surface 162 of the cylindrical portion 161 press against each other in the radial direction, and as a result, the output shaft 160 is fixed to the worm wheel 300. Therefore, unlike when the outer periphery of the output shaft is press-fitted into the inner periphery of the worm wheel support body, the outer diameter of the worm wheel 300 is not increased by connecting the worm wheel 300 and the output shaft 160.

[0026] More specifically, in this embodiment, the cylindrical portion 161 of the output shaft 160 has an increased outer diameter due to the first shaft portion 321 being press-fitted into the internal space 161a, and the second shaft portion 324 of the support body 320 is present on the radially outer side. Therefore, it is conceivable that an increase in the outer diameter of the cylindrical portion 161 will affect the outer diameter of the worm wheel 300. However, in the worm reducer 200 according to this embodiment, as shown in FIGS. 2 to 4, a gap (first gap S1) exists between the outer peripheral surface 163 of the cylindrical portion 161 and the inner peripheral surface 325 of the second shaft portion 324. In other words, the sizes and shapes of the support body 320 and the cylindrical portion 161 are designed in anticipation of the maximum increase in the outer diameter of the cylindrical portion 161 due to the first shaft portion 321 being press-fitted into the internal space 161a. Therefore, even if there is variation in the amount of increase in the outer diameter of the cylindrical portion 161 among individual worm reducers 200, the first gap S1 exists between the outer peripheral surface 163 of the cylindrical portion 161 and the inner peripheral surface 325 of the second shaft portion 324. This more reliably suppresses an increase in the outer diameter of the worm wheel 300 due to the connection between the worm wheel 300 and the output shaft 160.

[0027] Furthermore, a second gap S2 also exists between the cylindrical portion 161 and the support body 320 in the axial direction. Specifically, as shown in Figures 3 and 4, the second gap S2 is formed between an inner bottom surface 327, which is the surface on the other axial side (positive direction of the Y axis) of the connecting portion 326, and an end surface 164 on one axial side (negative direction of the Y axis) of the cylindrical portion 161. This structure is obtained by controlling the distance of press-fitting when press-fitting the first shaft portion 321 into the internal space 161a of the cylindrical portion 161.

[0028] That is, in this embodiment, the cylindrical portion 161 of the output shaft 160 and the support 320 of the worm wheel 300 are configured such that the outer peripheral surface 322 of the first shaft portion 321 contacts the inner peripheral surface 162 of the cylindrical portion 161, but do not contact each other at other locations. Therefore, for example, the magnitude of the slip torque of the cylindrical portion 161 relative to the support 320 (the torque at which the cylindrical portion 161 begins to rotate while slipping relative to the support 320) depends on the size of the contact area between the outer peripheral surface 322 of the first shaft portion 321 and the inner peripheral surface 162 of the cylindrical portion 161. Therefore, for example, contact between the end face 164 of the cylindrical portion 161 and the connecting portion 326 of the support 320 prevents the slip torque from becoming excessive. As a result, for example, when a reverse input from the output shaft 160 to the worm wheel 300 occurs during driving on a rough road, the cylindrical portion 161 can be designed to slide relative to the first shaft portion 321. In other words, when a reverse input occurs, the sliding torque of the cylindrical portion 161 relative to the support 320 is excessive, i.e., the cylindrical portion 161 does not slide relative to the support 320, thereby preventing problems such as damage to the annular tooth portion 310.

[0029] The metal support body 320 having the above structure is produced by, for example, forging. Therefore, unlike when a support body having a through hole into which the output shaft is press-fitted is produced by forging, no waste material is generated by punching out the metal body during the forging process.

[0030] In this embodiment, housing 153 is provided with hole 154 penetrating housing 153 and mounting portion 156 disposed on the outside of hole 154. Biasing member 159 such as a coil spring is disposed in hole 154. Preload member 155 that pressurizes biasing member 159 is attached to mounting portion 156.

[0031] Hole 154 is a through-hole that penetrates from the outside to the inside of housing 153 in the radial direction of first bearing 191. Mounting portion 156 is a cylindrical portion that is provided coaxially with hole 154, and has a female thread on its inner circumferential surface. Preload member 155 has a male thread on its outer periphery that screws into mounting portion 156 of housing 153, and is a member that is fixed by screwing into mounting portion 156 and pressurizes biasing member 159.

[0032] The first bearing 191 holds one end of the worm shaft 210 inside the housing 153 (the end in the negative X-axis direction in FIG. 2). The first bearing 191 is held reciprocally relative to the housing 153 in a direction toward the worm wheel 300 and a direction away from the worm wheel 300 (the Z-axis direction in FIG. 2). That is, the first bearing 191 is disposed so as to allow the worm shaft 210 to tilt with respect to the rotation axis Ra. The second bearing 192 has a structure that allows the worm shaft 210 to tilt. In this structure, the first bearing 191 is biased in the negative Z-axis direction by the biasing member 159, as shown in FIG. 2. That is, in the driving force imparting mechanism 150 according to this embodiment, the worm shaft 210 is pressed against the worm wheel 300 by the biasing force of the biasing member 159, thereby suppressing an increase in backlash. This constitutes a so-called anti-backlash system (ABLS).

[0033] For example, an external force in the Z-axis direction acts on the worm wheel 300, attempting to change the distance between the rotation axis Rb and the rotation axis Ra, due to impact or vibration that the vehicle equipped with the power steering device 10 receives from the road surface. Even in this case, in the present embodiment, the biasing force of the biasing member 159 acts on the worm shaft 210 so as to press the worm shaft 210 against the worm wheel 300. That is, the biasing force of the biasing member 159 acts so as not to increase backlash between the worm shaft 210 and the worm wheel 300. In other words, in the worm reducer 200 according to the present embodiment, individual differences (variations) in the outer diameter of the worm wheel 300 are suppressed, and an increase in backlash between the worm shaft 210 and the worm wheel 300 is suppressed. As a result, the worm wheel 300 and the worm shaft 210 can be meshed more satisfactorily, and this state can be maintained.

[0034] [2-2. Example of assembly process for worm reducer 200] 5 to 8 are first to fourth diagrams showing an example of an assembly process for the worm reducer 200 according to the embodiment. Specifically, in Fig. 5 to Fig. 8, the assembly process for a structure made up of the worm reducer 200 and the output shaft 160 is shown in simplified cross-sectional views. The positions of the cross sections in Fig. 5 to Fig. 8 correspond to the positions of the cross sections in Fig. 3.

[0035] 5 and 6, when assembling the worm reducer 200, the output shaft 160 to which the output bearing 170 is attached is attached to the housing main body 153a. Specifically, the output bearing 170 is press-fitted into an output-side opening 153c provided on the output side (positive direction of the Y axis) of the housing main body 153a, whereby the output shaft 160 is held in a rotatable state relative to the housing main body 153a.

[0036] Next, as shown in FIGS. 6 and 7, the support 320 of the worm wheel 300 is fitted to the cylindrical portion 161 of the output shaft 160. Specifically, the worm wheel 300 is brought closer to the output shaft 160 from the direction in which the cylindrical portion 161 of the output shaft 160 faces (the negative Y-axis direction). At this time, as shown in FIG. 7, before the fitting of the support 320 to the cylindrical portion 161 begins, that is, before the first shaft portion 321 begins to be press-fitted into the cylindrical portion 161, the annular teeth portion 310 of the worm wheel 300 and the worm teeth portion 211 of the worm shaft 210 begin to mesh together. Therefore, the first shaft portion 321 can be press-fitted into the internal space 161a of the cylindrical portion 161 with the rotational position of the worm wheel 300 about the rotation axis Rb (see FIG. 3) set to a rotational position that allows the worm wheel 300 and the worm shaft 210 to be properly meshed together. In other words, with the phases of the worm wheel 300 and the worm shaft 210 adjusted, the first shaft portion 321 can be press-fitted into the internal space 161a of the cylindrical portion 161. Thereafter, as shown in Fig. 8, the cover 153b is positioned to close the opening of the housing main body 153a in the negative Y-axis direction. As a result, the worm reducer 200 having the structure shown in Fig. 3 is obtained.

[0037] Here, assume that a through-hole is provided in the center of the support body 320, and one end of the output shaft 160 is press-fitted into the through-hole to connect the worm wheel 300 and the output shaft 160. In this case, for example, to ensure a sufficient sliding torque between the worm wheel 300 and the output shaft 160, it is conceivable to make the length of the press-fit portion of the output shaft 160 equal to or greater than the axial length of the through-hole. That is, it is conceivable to press-fit one end of the output shaft 160 into and pass through the through-hole. In this case, when the worm wheel 300 is brought closer to the output shaft 160 to press-fit the one end of the output shaft 160 into the through-hole of the support body 320, the following situation occurs. That is, after the one end of the output shaft 160 starts to be press-fitted into the through-hole, the annular teeth portion 310 of the worm wheel 300 and the worm teeth portion 211 of the worm shaft 210 start to mesh with each other. In other words, the press-fitting of one end of the output shaft 160 into the through-hole of the support body 320 begins before the appropriate rotational position of the worm wheel 300 has been determined. This can cause a problem in that the worm wheel 300 and the worm shaft 210 cannot be properly meshed. Alternatively, equipment for changing the rotational position of the worm shaft 210 is required at the assembly site of the worm reducer 200 in order to properly mesh the worm wheel 300 and the worm shaft 210. Alternatively, it can become necessary to strictly control the rotational positions of the worm wheel 300 and the worm shaft 210 before the press-fitting.

[0038] To address the above problem, the power steering device 10 according to this embodiment employs a structure in which the first shaft portion 321, which protrudes from an inner bottom surface 327 (see FIG. 4 ) inside the second shaft portion 324 of the support body 320, is press-fitted into the internal space 161a of the cylindrical portion 161 of the output shaft 160. Therefore, in the assembly process of the worm reducer 200, it is easy to start meshing between the annular teeth portion 310 of the worm wheel 300 and the worm teeth portion 211 of the worm shaft 210 before the first shaft portion 321 starts to be press-fitted into the cylindrical portion 161. Furthermore, even if the outer diameter of the first shaft portion 321 is increased to increase the slip torque between the worm wheel 300 and the output shaft 160, the resulting increase in the outer diameter of the cylindrical portion 161 is unlikely to affect the outer diameter of the worm wheel 300. Therefore, the power steering device 10 according to this embodiment has a structure in which the variation in the outer diameter of the worm wheel 300 is suppressed and the worm wheel 300 and the worm shaft 210 are properly meshed with each other. Moreover, the power steering device 10 having this structure can be efficiently manufactured.

[0039] [3. Summary of the embodiment] The technical features of the power steering device 10 according to the present embodiment described above can be explained as follows, for example, in (1) to (3).

[0040] (1) A power steering device 10 according to this embodiment includes an output shaft 160 having a cylindrical portion 161 on one side in the axial direction, an electric motor 180 for steering assistance, and a worm reducer 200 that reduces the rotation of the electric motor 180 and transmits the reduced rotation to the output shaft 160. The worm reducer 200 includes a worm shaft 210 that is driven to rotate by the electric motor 180, and a worm wheel 300 that meshes with the worm shaft 210. The worm wheel 300 is connected to the output shaft 160 and rotates integrally with the output shaft 160. The worm wheel 300 includes an annular toothed portion 310 that has a plurality of teeth 311 arranged annularly on its outer periphery, and a support body 320 that is fixed to the inner periphery of the annular toothed portion 310. The support body 320 includes a first shaft portion 321 extending in the axial direction, and a second shaft portion 324 connected to the first shaft portion 321 and having the annular teeth portion 310 fixed thereto. The first shaft portion 321 is press-fitted into the interior (internal space 161a) of the cylindrical portion 161.

[0041] As described above, in this embodiment, the output shaft 160 and the worm wheel 300 are connected by press-fitting the first shaft portion 321 of the worm wheel 300 into the cylindrical portion 161 of the output shaft 160. Therefore, unlike when the end of the output shaft 160 is press-fitted into a through-hole or the like provided inside the annular tooth portion 310 of the worm wheel 300, radial expansion of the annular tooth portion 310 (i.e., an increase in the outer diameter) is unlikely to occur. This makes it possible to suppress variations (individual differences) in the outer diameter of the worm wheel 300 caused by connecting the output shaft 160 and the worm wheel 300. As a result, an increase in the torque (also referred to as "rotational torque") required to rotate the worm shaft 210 and the worm wheel 300 and / or the generation of rattle noise due to variations in the outer diameter are suppressed. Therefore, the power steering device 10 according to this embodiment is a power steering device with improved performance.

[0042] (2) In the power steering device 10 described in (1) above, the support 320 further includes a connecting portion 326. The second shaft portion 324 is a cylindrical portion arranged to surround the radial outside of the first shaft portion 321, and has the annular teeth portion 310 fixed to its outer peripheral surface. In this embodiment, the annular teeth portion 310 is fixed to the outer peripheral surface of the second shaft portion 324 via an intermediate portion 330. The connecting portion 326 connects an end portion of the first shaft portion 321 on one axial side (the negative Y-axis direction) to an end portion of the second shaft portion 324 on one axial side (the negative Y-axis direction) while separating them radially. A first gap S1 is formed between an inner peripheral surface 325 of the second shaft portion 324 and an outer peripheral surface 163 of the cylindrical portion 161 of the output shaft 160 (see FIGS. 3 and 4).

[0043] According to this configuration, even if the cylindrical portion 161 bulges radially outward due to the first shaft portion 321 being press-fitted into the inside of the cylindrical portion 161, a first gap S1 exists between the inner circumferential surface 325 of the second shaft portion 324 and the outer circumferential surface 163 of the cylindrical portion 161 of the output shaft 160. Therefore, an increase in the radial direction of the annular toothed portion 310 caused by the connection between the output shaft 160 and the worm wheel 300 is more reliably suppressed.

[0044] Furthermore, because the first shaft portion 321 is disposed on the inner periphery of the cylindrical second shaft portion 324, the axial length of the support body 320 including the first shaft portion 321 and the second shaft portion 324 can be made relatively short. This makes it possible to make relatively short, for example, the axial distance between the pinion teeth portion 165 (see FIG. 3) of the output shaft 160 and the worm wheel 300. As a result, the torque output by the worm reducer 200 can be efficiently transmitted to the steered shaft 141 (see FIG. 1). Also, the driving force imparting mechanism 150 can be made more compact.

[0045] 5 to 8, when assembling the worm reducer 200, it is easy to start meshing between the annular teeth portion 310 and the worm teeth portion 211 before starting to press-fit the first shaft portion 321 into the cylindrical portion 161. This contributes to improving the efficiency of manufacturing the power steering device 10.

[0046] (3) In the power steering device 10 described in (1) or (2) above, a second gap S2 is formed between the support body 320 and the end face 164 of the cylindrical portion 161 on one side in the axial direction (see FIGS. 3 and 4). Specifically, the second gap S2 is formed between the end face 164 of the cylindrical portion 161 and an inner bottom surface 327, which is the surface on the other side in the axial direction of the connecting portion 326.

[0047] According to this configuration, for example, contact between the end face 164 of the cylindrical portion 161 and the connecting portion 326 of the support body 320 prevents the sliding torque of the cylindrical portion 161 relative to the support body 320 from becoming excessive. As a result, when a reverse input from the output shaft 160 to the worm wheel 300 occurs, the cylindrical portion 161 does not slip relative to the support body 320, which prevents problems such as damage to the annular tooth portion 310.

[0048] The power steering device 10 according to the embodiment has been described above, focusing on the configuration and operation of the driving force imparting mechanism 150. However, the configuration of the driving force imparting mechanism 150 provided in the power steering device 10 may be different from the configuration shown in Figures 2 to 8. Therefore, modifications of the driving force imparting mechanism 150 will be described below, focusing on the differences from the above embodiment.

[0049] [4. Modifications] FIG. 9 is a cross-sectional view showing the structure of a driving force imparting mechanism 150 according to a modified example of the embodiment. The position of the cross section in FIG. 9 corresponds to the position of the cross section in FIG. 3. The driving force imparting mechanism 150 according to this modified example includes a worm reducer 200a. The worm reducer 200a includes a worm shaft 210 and a worm wheel 300a that meshes with the worm shaft 210. The worm wheel 300a has an annular toothed portion 310 and a support body 320a. The support body 320a includes a first shaft portion 321a extending in the axial direction and a second shaft portion 324a that is connected to the first shaft portion 321a and has the annular toothed portion 310 fixed thereto. More specifically, the first shaft portion 321a and the second shaft portion 324a are connected by a connecting portion 326a. The first shaft portion 321a is press-fitted into the cylindrical portion 161 of the output shaft 160. These configurations are common to the worm reducer 200 according to the embodiment.

[0050] In this modified example, the end of the first shaft portion 321a on one axial side (negative Y-axis direction) and the end of the second shaft portion 324a on the other axial side (positive Y-axis direction) are connected by connecting portion 326a, and in this respect, it differs from the worm reducer 200 of the embodiment.

[0051] That is, in this modification, the first shaft portion 321a and the second shaft portion 324a are arranged side by side in the axial direction. Even in this case, the radial expansion of the cylindrical portion 161 caused by press-fitting the first shaft portion 321a of the worm wheel 300a into the cylindrical portion 161 of the output shaft 160 is unlikely to affect the outer diameter of the worm wheel 300a. Therefore, variations (individual differences) in the outer diameter of the worm wheel 300a due to the connection between the output shaft 160 and the worm wheel 300a can be suppressed. As a result, an increase in rotational torque and / or the generation of rattle noise during operation of the power steering device 10 is suppressed.

[0052] In this modification, as shown in FIG. 9, a gap (corresponding to the second gap S2 (see FIG. 4) in the embodiment) exists between the cylindrical portion 161 and the support body 320a in the axial direction. This prevents the sliding torque of the cylindrical portion 161 relative to the support body 320a from becoming excessive. As a result, when a reverse input is applied from the output shaft 160 to the worm wheel 300a, the cylindrical portion 161 does not slip relative to the support body 320a, which prevents problems such as damage to the annular tooth portion 310.

[0053] In the worm reducer 200a according to this modification, the first shaft portion 321a is disposed outside (on the positive side of the Y-axis) the second shaft portion 324a of the support body 320a. As a result, as shown in Fig. 9, the output bearing 170 that rotatably supports the output shaft 160 is disposed at a position relatively far from the worm wheel 300a. Therefore, from the viewpoint of, for example, more stable rotation of the worm wheel 300a and / or further miniaturization of the driving force imparting mechanism 150, a configuration in which the first shaft portion 321a is disposed radially inside the second shaft portion 324, as in the worm reducer 200 according to the embodiment (see Fig. 3), is preferable.

[0054] [5. Other Modifications] The power steering device according to the present invention has been described above based on the embodiment and its modifications. However, the present invention is not limited to the above embodiment and modifications. As long as they do not deviate from the spirit of the present invention, various modifications that a person skilled in the art can make to the above embodiment or modifications, or configurations constructed by combining multiple components described above, are also included within the scope of the present invention.

[0055] For example, the output shaft 160 connected to the support 320 of the worm wheel 300 does not have to be a pinion shaft. As described above, the driving force imparting mechanism 150 may be arranged to impart assist torque to, for example, the column shaft 131 (see FIG. 1). In this case, for example, the column shaft 131 may be connected to the first shaft portion 321 of the support 320 as the output shaft 160, and a shaft connected to the operating member 110 may be connected to the end of the support 320 in the negative Y-axis direction. The driving force imparting mechanism 150 may be arranged to impart assist torque to, for example, the pinion shaft 133 (see FIG. 1). In this case, for example, the pinion shaft 133 may be connected to the first shaft portion 321 of the support 320 as the output shaft 160, and a shaft connected to the intermediate shaft 132 may be connected to the end of the support 320 in the negative Y-axis direction.

[0056] It is not essential that the first gap S1 exists between the cylindrical portion 161 and the support 320. For example, at least a portion of the inner circumferential surface 325 of the second shaft portion 324 may be in contact with at least a portion of the outer circumferential surface 163 of the cylindrical portion 161 of the output shaft 160. Even in this case, if the force with which the cylindrical portion 161 presses the second shaft portion 324 radially outward is relatively small and the contact between the cylindrical portion 161 and the second shaft portion 324 does not substantially affect the outer diameter of the worm wheel 300, the contact may be permitted. However, from the viewpoint of more reliably suppressing an increase in the outer diameter of the worm wheel 300, it is preferable that the inner circumferential surface 325 of the second shaft portion 324 does not come into contact with the outer circumferential surface 163 of the cylindrical portion 161, that is, that the first gap S1 exists between the cylindrical portion 161 and the support 320.

[0057] It is not essential that there be a second gap S2 between the cylindrical portion 161 and the support 320. For example, at least a portion of the inner bottom surface 327 of the support 320 may be in contact with at least a portion of the end surface 164 of the cylindrical portion 161. Even in this case, if the force with which one of the inner bottom surface 327 and the end surface 164 presses the other is relatively small and the contact between the inner bottom surface 327 and the end surface 164 does not substantially affect the sliding torque of the cylindrical portion 161 relative to the support 320, the contact may be permitted. However, from the perspective of more strictly controlling the sliding torque of the cylindrical portion 161 relative to the support 320, it is preferable that there be no contact between the inner bottom surface 327 of the support 320 and the end surface 164 of the cylindrical portion 161, that is, that there be a second gap S2 between the cylindrical portion 161 and the support 320.

[0058] If the thickness (width in the Y-axis direction) of the worm wheel 300 is relatively small, the contact area between the outer circumferential surface 322 of the first shaft portion 321 and the inner circumferential surface 162 of the cylindrical portion 161 may not be sufficient for the required sliding torque. In this case, in order to increase the sliding torque of the cylindrical portion 161 relative to the support body 320, at least a part of the inner bottom surface 327 of the support body 320 may be brought into contact with at least a part of the end surface 164 of the cylindrical portion 161.

[0059] The worm wheel 300 does not necessarily have to include the intermediate portion 330. For example, if the outer diameter of the worm wheel 300 is relatively small, the support body 320 and the annular teeth portion 310 may be directly connected. That is, the annular teeth portion 310 may be fixed directly to the outer circumferential surface of the second shaft portion 324. In this case, the worm wheel 300 having the metal support body 320 and the resin annular teeth portion 310 integrally formed therewith may be produced by insert molding.

[0060] There is no particular limitation on the type of biasing member 159 included in the power steering device 10. The biasing member 159 may be a spring such as a coil spring, a leaf spring, or a spiral spring, or may be an elastic body such as a block of rubber. The power steering device 10 does not necessarily have to include the biasing member 159. Even if the power steering device 10 does not include the biasing member 159, the outer diameter of the worm wheel 300 is within the design range by including the configuration shown in FIG. 3 etc. Therefore, an increase in rotational torque and / or the generation of rattle noise caused by the outer diameter of the worm wheel 300 being too large or too small is suppressed.

[0061] The supplementary points regarding the power steering device 10 according to the embodiment described above may also be applied to the power steering device 10 according to the modified example of the embodiment. Configurations constructed by arbitrarily combining the components included in the above embodiment and the modified example thereof are also included within the scope of the present invention. [Industrial Applicability]

[0062] The power steering device according to the present invention is useful as a power steering device that steers steered wheels in response to the operation of an operating member, and can be employed, for example, as a power steering device for vehicles such as automobiles, agricultural machinery, or construction machinery. [Explanation of symbols]

[0063] 10: power steering device, 100: steering mechanism, 110: operating member, 120: sensor device, 130: steering shaft, 131: column shaft, 132: intermediate shaft, 133: pinion shaft, 140a, 140b: rack and pinion device, 141: steered shaft, 150: driving force imparting mechanism, 153: housing, 153a: housing main body, 153b: cover body, 153c: output side opening, 154: hole portion, 155: preload member, 156: mounting portion, 159: biasing member, 160: output shaft, 161: cylindrical portion, 161a: internal space, 162, 325: inner peripheral surface, 163, 322: outer peripheral surface, 164: end face, 165: pinion tooth portion, 170: output bearing, 180: electric motor, 181: output rotating shaft, 185: motor body, 190: connecting member, 191: first bearing, 192: second bearing, 200, 200a: worm reducer, 210: worm shaft, 211: worm tooth portion, 300, 300a: worm wheel, 310: annular tooth portion, 311: tooth, 320, 320a: support, 321, 321a: first shaft portion, 324, 324a: second shaft portion, 326, 326a: connecting portion, 327: inner bottom surface, 330: intermediate portion, 500: steered wheel, S1: first gap, S2: second gap

Claims

1. an output shaft having a cylindrical portion on one side in the axial direction; an electric motor for steering assistance; a worm reducer that reduces the rotation of the electric motor and transmits the reduced rotation to the output shaft, The worm reducer is a worm shaft that is rotationally driven by the electric motor; a worm wheel that meshes with the worm shaft, is connected to the output shaft, and rotates integrally with the output shaft; The worm wheel is an annular tooth portion having a plurality of teeth arranged annularly on an outer periphery; a support member fixed to the inner periphery of the annular teeth portion, The support is a first shaft portion extending in the axial direction; a second shaft portion connected to the first shaft portion and having the annular teeth portion fixed thereto; The first shaft portion is press-fitted into the cylindrical portion. Power steering device.

2. The support further has a connecting portion; the second shaft portion is a cylindrical portion arranged to surround the radial outside of the first shaft portion, and the annular teeth portion is fixed to an outer peripheral surface thereof, the connecting portion connects the end portion of the first shaft portion on the one side in the axial direction and the end portion of the second shaft portion on the one side in the axial direction in a state where they are spaced apart in the radial direction, A first gap is formed between an inner peripheral surface of the second shaft portion and an outer peripheral surface of the cylindrical portion of the output shaft.

2. The power steering device according to claim 1.

3. a second gap is formed between the support body and the end surface of the cylindrical portion on the one side in the axial direction; 3. The power steering device according to claim 1 or 2.

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