Steering system

A steering system includes: a steering shaft to which a steering member is coupled; a worm wheel attached to the steering shaft so as to be rotatable integrally with the steering shaft; a housing that houses the worm wheel; an output shaft that is coaxial with the steering shaft and rotatable relative to the steering shaft and coupled to a steering operation mechanism; and a clutch mechanism that enables and disables transmission of power between the steering shaft and the output shaft. The clutch mechanism is housed and disposed in an internal space in the housing. A solenoid in the clutch mechanism is disposed on the opposite side of the worm wheel in an axial direction from a mechanical portion of the clutch mechanism.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2015-121122 filed on Jun. 16, 2015 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a steering system.

2. Description of the Related Art

A steer-by-wire system has been proposed in which a steering member and a steering operation mechanism are not mechanically coupled together and in which a steering angle of a steering wheel is detected by an angle sensor so that a driving force exerted by a steering operation actuator controlled in accordance with a sensor output from the angle sensor is transmitted to the steering operation mechanism (see, for example, Japanese Patent Application Publication No. 2013-132950 (JP 2013-132950 A)). On the other hand, when the steer-by-wire system is mounted in a vehicle, an appropriate measure needs to be taken so that steered wheels can be steered even when the steering operation actuator or the like becomes defective.

Japanese Patent No. 4927608 and Japanese Patent No. 4347100 disclose, as a steering system for which the above-described measure has been taken, a configuration in which the steering member and the steering operation mechanism are coupled together via a clutch mechanism and in which the steering member and the steering operation mechanism are mechanically uncoupled from each other during a normal operation and are mechanically coupled together when an abnormality occurs.

When mounted in the steering system, a clutch mechanism may be, for example, interposed between an intermediate shaft and a steering column. However, in this case, the clutch mechanism may interfere with peripheral members. The steering system in which the clutch mechanism is mounted is desirably restrained from being increased in size.

SUMMARY OF THE INVENTION

An object of the invention is to provide a steering system in which a clutch mechanism can be mounted without interfering with peripheral members and which is restrained from being increased in size.

According to an aspect of the invention, a steering system includes: a steering shaft to which a steering member is coupled; a gear attached to the steering shaft so as to be rotatable integrally with the steering shaft; a housing that houses at least the gear; an output shaft that is rotatable relative to the steering shaft and coupled to a steering operation mechanism; and a clutch mechanism having a mechanical portion provided to enable the steering shaft and the output shaft to be coupled together and uncoupled from each other, and a driving force generating portion that generates a driving force allowing the mechanical portion to couple the steering shaft and the output shaft together and to uncouple the steering shaft and the output shaft from each other, the clutch mechanism enabling and disabling transmission of power between the steering shaft and the output shaft. The clutch mechanism is housed and disposed in an internal space in the housing. In the internal space, the diving force generating portion is disposed on the opposite side of the gear from the mechanical portion in an axial direction of the steering shaft.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the invention will be described below in detail with reference to the attached drawings.FIG. 1is a diagram depicting a general configuration of a steering system1according to an embodiment of the invention. The steering system1adopts what is called a steer-by-wire system in which a steering member3such as a steering wheel is mechanically uncoupled from a steering operation mechanism A allowing steering of steered wheels2.

In the steering system1, an operation of a steering operation actuator4is controlled according to a rotating operation of the steering member3. The operation is converted into linear motion of a steered shaft6in a vehicle width direction. The linear motion of the steered shaft6is converted into a steering motion of the right and left steered wheels2to be steered, thereby turning of the vehicle is achieved. Specifically, the steering operation actuator4includes a motor. A driving force of the motor is converted into linear motion in the axial direction of the steered shaft6by a motion conversion mechanism (a ball screw apparatus or the like) provided in connection with the steered shaft6. The linear motion of the steered shaft6is transmitted to tie rods7connected to respective opposite ends of the steered shaft6to cause respective knuckle arms8to pivot. Consequently, steering of the steered wheels2supported by the knuckle arms8is achieved. The steering operation mechanism A includes the steered shaft6, the tie rods7, and the knuckle arms8. A steered shaft housing9that supports the steered shaft6is fixed to a vehicle body B.

The steering member3is coupled to a steering shaft10. The steering shaft10is rotatably supported by a housing H of a steering column5fixed to the vehicle body B. The steering shaft10can rotate integrally with the steering member3. To the steering shaft10, a first motor11is attached, and a first speed reducer12is also attached which decelerates output rotation of the first motor11. The first speed reducer12includes a worm shaft13rotationally driven by the first motor11and a worm wheel (gear)14that meshes with the worm shaft13and that is fixed to the steering shaft10.

The steering shaft10is coupled to the steering operation mechanism A via the clutch mechanism15. Specifically, the steered shaft6of the steering operation mechanism A includes a rack shaft. To a pinion shaft18having, at a distal end thereof, a pinion19that engages with the rack shaft, an output shaft16is connected via an intermediate shaft17. The output shaft16is provided coaxially with the steering shaft10so as to be rotatable relative to the steering shaft10. The clutch mechanism15is interposed between the steering shaft10and the output shaft16.

In connection with the steering shaft10, the steering system1is provided with a steering angle sensor20that detects a steering angle of the steering member3. The steering shaft10is provided with a torque sensor21that detects a steering torque applied to the steering member3. The torque sensor21is housed in the housing H of the steering column5.

In connection with the steered wheels2, the steering system1is provided with a steered angle sensor22that to detects a steered angle of the steered wheels2, a vehicle speed sensor23that detects a vehicle speed, and the like. Detection signals from various sensors including the sensors20to23are input to a control apparatus24including an electronic control unit (ECU) including a microcomputer. The control apparatus24sets a target steered angle based on the steering angle detected by the steering angle sensor20and the vehicle speed detected by the vehicle speed sensor23. The control apparatus24controls and drives the steering operation actuator4based on a deviation between the target steered angle and the steered angle detected by the steered angle sensor22.

During a normal operation of the vehicle, the control apparatus24keeps the clutch mechanism15in a disengaged state to mechanically disconnect the steering member3and the steering operation mechanism A from each other. In this state, based on the detection signals output by the steering angle sensor20, the torque sensor21, and the like, the control apparatus24controls and drives the first motor11so as to apply, to the steering member3, an appropriate reaction force acting in a direction opposite to a direction in which the steering member3is steered. Output rotation of the first motor11is decelerated (amplified) by the first speed reducer12, and the resultant rotation is transmitted to the steering member3via the steering shaft10. That is, during a normal operation of the vehicle, the first motor11and the first speed reducer12function as a reaction force generating mechanism.

On the other hand, when, for example, in the event of abnormal conditions such as when an ignition of the vehicle is off and the steer-by-wire system is malfunctioning, the control apparatus24brings the clutch mechanism15into an engaged state to mechanically couple the steering member3and the steering operation mechanism A together. This enables the steering operation mechanism A to be directly operated using the steering member3. A configuration is adopted in which the steering shaft10and the steering operation mechanism A can be mechanically coupled together via the clutch mechanism15. This makes the steer-by-wire system mechanically fail-safe.

For example, when one of the steering operation actuator4and the first motor11malfunctions, the control apparatus24controls and drives the other of the steering operation actuator4and the first motor11so as to apply a steering assist force to the steering operation mechanism A based on the detection signals output by the steering angle sensor20, the torque sensor21, and the like. Output rotation of the first motor11is decelerated by the first speed reducer12, and the resultant rotation is transmitted to the steering operation mechanism A via the output shaft16, the intermediate shaft17, and the pinion shaft18. Output rotation of the steering operation actuator4is transmitted to the steering operation mechanism A by the motion conversion mechanism. That is, if an abnormality occurs, the first motor11and the first speed reducer12or the steering operation actuator4and the motion conversion mechanism function as a steering assist mechanism.

In particular, when the steering operation actuator4is malfunctioning, the first motor11and the first speed reducer12can be used as a steering assist mechanism when an abnormality occurs and also as a reaction force generating mechanism during a normal operation. This configuration enables a reduction in costs as compared to a configuration in which the steering assist mechanism and the reaction force generating mechanism are separately provided. The reaction force generating mechanism has not only the first motor11but also the first speed reducer12, which amplifies the output from the first motor11. Thus, a high rotary torque can be generated as a reaction force. Consequently, a reaction force of a desired magnitude can be applied to the steering member3.

The steering column5has the housing H in which at least the first speed reducer12is housed. The clutch mechanism15is housed in an internal space S (seeFIG. 2) in the housing H.FIG. 2is a sectional view of the housing H. The sectional view inFIG. 2is taken along the section line II-II inFIG. 3described below.

The steering shaft10includes a middle shaft27, an input shaft28, an inner shaft29, and a torsion bar30. The middle shaft27is connected to the steering member3(seeFIG. 1). The input shaft28is coaxially fixed to the middle shaft27. The torsion bar30couples the input shaft28and the inner shaft29together in line. When a steering torque is input to the input shaft28via the middle shaft27, torsion bar30is elastically torsionally deformed. Consequently, the input shaft28and the inner shaft29rotate relative to each other. The steering torque is detected by the torque sensor21based on a rate of relative rotation between the input shaft28and the inner shaft29.

The steering column5, which supports the steering shaft10, has a cylindrical jacket J, a sensor housing26, and a speed reducer housing25. The jacket J houses at least a part of the middle shaft27. The sensor housing26is disposed below the steering shaft10with respect to the jacket J in the axial direction (on an steering operation mechanism A side) to house at least a part of the torque sensor21and to hold the torque sensor21. The speed reducer housing25is disposed below the steering shaft10with respect to the sensor housing26in the axial direction to house the first speed reducer12. The sensor housing26and the speed reducer housing25are included in the housing H.

The steering column5is attached to a predetermined portion72of a vehicle body B by use of an upper attachment structure71disposed on a rear side of the vehicle and to a predetermined portion74of the vehicle body B by use of a lower attachment structure73disposed on a front side of the vehicle. The jacket J is supported by the upper attachment structure71, and the speed reducer housing25is supported by the lower attachment structure73. In this state, the steering shaft10is supported in an oblique orientation (the oblique orientation in which the steering member3(seeFIG. 1) is positioned above) with respect to a front-rear direction of the vehicle.

The steering column5is supported so as to be able to swing around a tilt center shaft75. The upper attachment structure71and the lower attachment structure73perform a tilt adjusting function to adjust a height position of the steering member3(seeFIG. 1) by swinging and tilting the steering column5around the tilt center shaft75. The lower attachment structure73functions as a tilt hinge mechanism.

The torque sensor21is shaped like a ring that surrounds the steering shaft10and is fitted on and supported by an inner periphery26aof the sensor housing26. The sensor housing26is fixed to the speed reducer housing25. The sensor housing26includes an outer tube38, an inner tube39, and an annular wall40. The outer tube38is in abutting contact with an upper end of the speed reducer housing25. The inner tube39supports an outer ring50aof a first bearing50on an inner periphery39aof the inner tube39. The annular wall40connects the outer tube38and the inner tube39together.

The torque sensor21detects a steering torque based on a magnetic flux generated in a magnetic-circuit forming mechanism44provided in connection with the input shaft28and the inner shaft29. The magnetic-circuit forming mechanism44includes a multipolar magnet45and a pair of magnetic yokes46to form a magnetic circuit. The multipolar magnet45is coupled to one of the input shaft28and the inner shaft29so as to be rotatable integrally therewith. The magnetic yokes46are disposed in a magnetic field of the multipolar magnet45and coupled to the other of the input shaft28and the inner shaft29so as to be rotatable integrally therewith.

The torque sensor21includes a pair of magnetic force collecting rings47, a magnetic-flux detecting element (not depicted in the drawings) such as a Hall IC, and an annular main body48formed of a resin and holding the magnetic force collecting rings47a. The magnetic force collecting rings47are magnetically coupled to the respective magnetic yokes46. The magnetic-flux detecting element such as a Hall IC detects a magnetic flux between magnetic force collecting portions (not depicted in the drawings) of the magnetic force collecting rings47. The annular main body48is formed of a resin and holds the magnetic-flux detecting element and the magnetic force collecting rings47. A wire49extends outward from the main body48of the torque sensor21in a radial direction. The sensor housing26supports the inner shaft29so that the inner shaft29is rotatable via the first bearing50. The inner ring50bof the first bearing50is fitted over the inner shaft29so as to be rotatable integrally with the inner shaft29.

The speed reducer housing25is formed by a tubular worm shaft housing portion34and a worm wheel housing portion35that are formed of a single material and that cross each other. The worm shaft housing portion34houses and holds a worm shaft13. The worm wheel housing portion35houses and holds a worm wheel14. The worm wheel housing portion35is fixed to the sensor housing26. The worm wheel14is coupled to an upper end of the inner shaft29in the axial direction so as to be rotatable integrally with the inner shaft29and to be immovable in the axial direction. The worm wheel14includes an annular core metal portion31and a synthetic resin member32. The core metal portion31is bound to the inner shaft29so as to be rotatable integrally with the inner shaft29. The synthetic resin member32surrounds the core metal portion31to form teeth32aon an outer peripheral surface of the core metal portion31. The core metal portion31is inserted into a mold when, for example, a resin is molded into the synthetic resin member32. The core metal portion31and the synthetic resin member32are bound together so as to be rotatable integrally with each other.

The core metal portion31has one or more (in this embodiment, for example, three) insertion holes33penetrating the core metal portion31in a thickness direction thereof. When a plurality of the insertion holes33is formed, the insertion holes33are disposed at the same distance from a rotation center of the inner shaft29. The insertion holes33are disposed at regular intervals in a circumferential direction of the worm wheel. The output shaft16protrudes downward (toward the steered shaft6) from the worm wheel housing portion35in the axial direction. The output shaft16is disposed coaxially with the inner shaft29so as to surround an outer periphery of the inner shaft29. A very small clearance is formed between an inner periphery of the output shaft16and the outer periphery of the inner shaft29. The output shaft16is supported coaxially with the inner shaft29so as to be rotatable relative to the inner shaft29, by a second bearing36provided such that the output shaft16is interposed between the second bearing36and the outer periphery of the inner shaft29. As the second bearing36, a plain bearing as depicted inFIG. 2may be adopted or a rolling bearing may be adopted. The output shaft16is connected to the steering operation mechanism A (seeFIG. 1) via the intermediate shaft17(seeFIG. 1) and the like.

The worm wheel housing portion35supports the output shaft16via a third bearing37so that the output shaft16is rotatable. The third bearing37is disposed below the worm wheel14in the axial direction of the steering shaft10. The output shaft16supports the inner shaft29via the third bearing37so that the inner shaft29is rotatable. An inner ring37aof the third bearing37is fitted over the output shaft16so as to be rotatable integrally with the output shaft16.

The internal space S in the housing H is partitioned into a first space Sa and a second space Sb by the worm wheel14. The first space Sa is provided on a lower side with respect to the worm wheel14in the axial direction of the steering shaft10. The second space Sb is provided on an upper side with respect to the worm wheel14in the axial direction of the steering shaft10.

The clutch mechanism15includes a mechanical portion51and a driving portion52. The mechanical portion51includes a two-way clutch106described below. In the present embodiment, the driving portion52includes an annular solenoid54and an actuating member55. The solenoid54is a driving force generating portion53. The actuating member55receives an electromagnetic force (driving force) from the driving force generating portion53to actuate the mechanical portion51.

The mechanical portion51is housed and disposed in the first space Sa, which is a lower portion of the internal space S in the housing H. The solenoid54is housed and disposed in the second space Sb, which is an upper portion of the internal space S in the housing H. That is, the solenoid54is disposed on the opposite side of the worm wheel14from the mechanical portion51in the axial direction of the steering shaft10. The solenoid54is fixed to an inner side surface40aof the annular wall40of the sensor housing26. The solenoid54has a coil56athat is a wound copper wire or the like and a core56bdisposed in proximity to the coil56a. An inner peripheral portion of the solenoid54functions as a push-out portion that pushes out an armature of the actuating member55.

FIG. 3is a sectional view taken along the section line III-III inFIG. 2.FIG. 4is a perspective view of the two-way clutch106depicted inFIG. 3.FIG. 4depicts the two-way clutch106from which an outer ring105has been removed. With reference toFIGS. 2 to 4, the two-way clutch106will be described. The axial direction of the steering shaft10is hereinafter referred to as the axial direction X. The axial direction of an inner ring104and the axial direction of the outer ring105coincide with the axial direction X. Of the axial direction X, an axial direction toward a rear side of the vehicle is referred to as a first axial direction X1. Of the axial direction X, an axial direction toward a front side of the vehicle is referred to as a second axial direction X2.

A direction along a rotating direction of the steering shaft10is referred to as a circumferential direction Y. A circumferential direction of the inner ring104, a circumferential direction of the outer ring105, and the circumferential direction of the worm wheel14coincide with the circumferential direction Y. Of the circumferential direction Y, a circumferential direction that is a clockwise direction as viewed from a second axial direction X2side is referred to as a first circumferential direction Y1. Of the circumferential direction Y, a circumferential direction that is a counterclockwise direction as viewed from the second axial direction X2side is referred to as a second circumferential direction Y2. The direction of a turning radius of the steering shaft10is referred to as a radial direction Z. A radial direction of the inner ring104, a radial direction of the outer ring105, and a radial direction of the worm wheel14coincide with the radial direction Z.

The two-way clutch106includes the inner ring104, the outer ring105, roller pairs123each include a first roller123aand a second roller123b, and a first pressing member131and a second pressing member132. The inner ring104is coaxially coupled to the output shaft16(seeFIG. 2). The outer ring105is coaxially coupled to the inner shaft29(seeFIG. 2) and is rotatable relative to the inner ring104. The roller pairs123each include the first roller123aand the second roller123bare disposed in the circumferential direction Y such that each roller pair123is provided in a corresponding one of one or more (in this embodiment, for example, three) wedge spaces129formed by an outer periphery of the inner ring104and an inner periphery of the outer ring105. The first and second pressing members131and132are disposed so as to be rotatable relative to each other around the steering shaft10. The first pressing member131moves in the second circumferential direction Y2to press and move the first rollers123aof the roller pairs123in the second circumferential direction Y2. The second pressing member132moves in the first circumferential direction Y1. Consequently, the second rollers123bof the roller pairs123are pressed and moved in the first circumferential direction Y1.

As depicted inFIG. 2, the outer ring105is fixedly fitted in an annular groove41formed in a lower surface of the core metal portion31of the worm wheel14that is located on the second axial direction X2side of the core metal portion31. Fixing the outer ring105to the core metal portion31allows the outer ring105to be coupled to the steering shaft10with a simple configuration. The outer ring105is formed of a metal material such as steel. The outer ring105is fixed by being press-fitted in the annular groove41in the core metal portion31. In the present embodiment, the core metal portion31and the outer ring105are separate members due to a difference in demanded hardness between the core metal portion31and the outer ring105. However, a configuration may be adopted in which the outer ring105is integrated with the core metal portion31of the worm wheel14.

The inner ring104is integrated with the output shaft16as depicted inFIG. 2. That is, an output shaft member57integrally including the inner ring104and the output shaft16is provided. The output shaft member57is formed of a metal material, for example, steel. The inner ring104and the output shaft16may be provided using different members. As depicted inFIG. 3, each of the wedge spaces129is defined by a cylindrical surface121and a cam surface122. The cylindrical surface121is formed around the inner periphery of the outer ring105. The cam surface122is formed around the outer periphery of the inner ring104and faces the cylindrical surface121in the radial direction Z. Each wedge space129is narrower toward opposite ends thereof in the circumferential direction Y. In each wedge space129, an elastic member124is disposed which elastically presses the first and second rollers123aand123bin the circumferential direction Y in which the first and second rollers123aand123bmove away from each other. The elastic member124may be, for example, a coil spring. The cam surfaces122each include a pair of inclined surfaces127aand127band a flat spring support surface128. The inclined surfaces127aand127bincline in opposite directions in the circumferential direction Y. The spring support surface128is provided between the inclined surfaces127aand127bto connect the inclined surfaces127aand127btogether.

Each roller pair includes the first roller123aon a first circumferential direction Y1side of the roller pair and the second roller123bon the second circumferential direction Y2side of the roller pair. The first pressing member131includes pillar-like first pressing portions135and an annular first support portion136(seeFIG. 2). The first support portion136collectively supports first ends of the respective first pressing portions135. The first support portion136, for example, supports a plurality of the first pressing portions135from inside in the radial direction Z. The first pressing member131is provided such that the first support portion136is coaxial with the inner ring104and the outer ring105and is rotatable relative to the inner ring104and the outer ring105. The first pressing portions135are identical in number (in the present embodiment, three) to the roller pairs123and are shaped like pillars extending in the axial direction X and disposed at regular intervals in the circumferential direction Y. The first pressing portions135and the first support portion136may be integrally formed using a synthetic resin material or a metal material. The first pressing member131may function as a cage that holds the roller pairs123and the elastic members124.

The second pressing member132includes pillar-shaped second pressing portions140and an annular second support portion141(seeFIG. 4). The second support portion141collectively supports the second pressing portions140. The second support portion141, for example, supports a plurality of the second pressing portions140from outside in the radial direction Z. The second pressing member132is provided such that the second support portion141is coaxial with the inner ring104and the outer ring105and is rotatable relative to the inner ring104and the outer ring105. The second pressing portions140are identical in number (in the present embodiment, three) to the roller pairs123and are shaped like pillars extending in the axial direction X and disposed at regular intervals in the circumferential direction Y. The second pressing portions140and the second support portion141may be integrally formed using a synthetic resin material or a metal material. The second pressing member132may function as a cage that holds the roller pairs123and the elastic members124.

As depicted inFIG. 3andFIG. 4, the first pressing member131and the second pressing member132are combined together such that the first pressing portions135and the second pressing portions140are alternately aligned in the circumferential direction Y. As depicted inFIG. 3andFIG. 4, between each first pressing portion135and a corresponding one of the second pressing portions140(hereinafter referred to as the “second pressing portion140for the adjacent roller pair123”), one actuating portion155is disposed. The first pressing portion135can press a first roller123aincluded in a corresponding one of the roller pairs123. The second pressing portion140can press a second roller123bincluded in another roller pair123that is adjacent to the corresponding roller pair123on the first circumferential direction Y1side. At the second circumferential direction Y2side of the first pressing portion135, another second pressing portion140is disposed via the corresponding roller pair123. That other second pressing portion140presses a second roller123bpaired with the first roller123athat can be pressed by the first pressing portion135. At the first circumferential direction Y1side of the first pressing portion135, the second pressing portion140for the adjacent roller pair123is disposed via the corresponding actuating portion155.

As depicted inFIG. 3andFIG. 4, on a surface of each first pressing portion135located on the second circumferential direction Y2side thereof, a first pressing surface137is formed which is configured to press the first roller123aof the corresponding roller pair123. The first pressing surface137includes, for example, a flat surface. The first pressing surface137is not limited to the one including a flat surface but may come into surface contact, line contact, or point contact with the first roller123a.

As depicted inFIG. 3andFIG. 4, a first mating sliding contact surface138is formed on a surface of each first pressing portion135located on the first circumferential direction Y1side thereof. A first sliding contact surface153is formed on a surface of each actuating portion155located on the second circumferential direction Y2side thereof. The first sliding contact surface153and the first mating sliding contact surface138are shaped to come into line contact with each other. Specifically, in the present embodiment, the first mating sliding contact surface138includes a curved surface C that is curved so as to be recessed in the second circumferential direction Y2. The first sliding contact surface153includes a curved surface D that is curved so as to protrude in the second circumferential direction Y2. The curved surface C has a radius of curvature set smaller than the radius of curvature of the curved surface D. The curved surface C and the curved surface D are in line contact with each other. In other words, the first sliding contact surface153and the first mating sliding contact surface138are in line contact with each other. A position on the curved surface C where the curved surface C contacts the curved surface D moves on the curved surface C in conjunction with movement of the actuating member55in the axial direction X. In a normal state, the position is prevented from deviating from the curved surface C.

As depicted inFIG. 3andFIG. 4, on a surface of each second pressing portion140located on the first circumferential direction Y1side thereof, a second pressing surface142is formed which presses the second roller123bof the corresponding roller pair123. The second pressing surface142includes, for example, a flat surface. The second pressing surface142is not limited to the one including a flat surface but may come into surface contact, line contact, or point contact with the second roller123b.

As depicted inFIG. 3andFIG. 4, a second mating sliding contact surface143is formed on a surface of each second pressing portion140located on the second circumferential direction Y2side thereof. A second sliding contact surface154is formed on a surface of each actuating portion155located on the second circumferential direction Y2side thereof. The second sliding contact surface154and the second mating sliding contact surface143are shaped to come into line contact with each other. Specifically, in the present embodiment, the second mating sliding contact surface143includes a curved surface E that is curved so as to be recessed in the first circumferential direction Y1. The second sliding contact surface154includes a curved surface F that is curved so as to protrude in the first circumferential direction Y1. The curved surface E has a radius of curvature set smaller than the radius of curvature of the curved surface F. The curved surface E and the curved surface F are in line contact with each other. In other words, the second sliding contact surface154and the second mating sliding contact surface143are in line contact with each other. A position on the curved surface E where the curved surface E contacts the curved surface F moves on the curved surface E in conjunction with movement of the actuating member55in the axial direction X. In the normal state, the position is prevented from deviating from the curved surface E.

FIG. 5is an exploded perspective view of the actuating member55. The actuating member55includes a first circular-ring member58and a second circular-ring member59. The first and second circular-ring members58,59are provided coaxially with the steering shaft10(seeFIG. 2or any other relevant figure) and have a first facing surface58aand a second facing surface59a, respectively, that face each other. On a first opposite surface58bopposite to the first facing surface58aof the first circular-ring member58, wedge members (first members)126are fixed each of which engages with the corresponding first pressing portion135and the corresponding second pressing portion140(seeFIG. 3or any other relevant figure). The wedge members126extend in the axial direction X and are identical in number to the roller pairs123. As depicted inFIG. 5, the wedge members126may be disposed at regular intervals in the circumferential direction Y. The first circular-ring member58and the wedge members126may be formed of a resin material or a metal material.

On a second opposite surface59bopposite to the second facing surface59aof the second circular-ring member59, insertion pins (extension portions or second members)61are fixed which are inserted through the respective insertion holes33in the worm wheel14. The insertion pins61extend along the axial direction X. In the present embodiment, the insertion pins61are identical in number to the insertion holes33. Each of the insertion pins61is shaped, in a section thereof orthogonal to the axis thereof, like, for example, a rectangle. InFIG. 5, the number of the insertion pins61is the same as the number of the wedge members126, but this is only illustrative, and another number may be adopted.

The second circular-ring member59and the insertion pins61are formed of a metal material such as steel. The second circular-ring member59and the insertion pins61function as an armature. Distal ends61aof the insertion pins61are inserted through the respective insertion holes33and disposed so as to face an inner periphery of the solenoid54(seeFIG. 2or any other relevant figure). When a current is conducted through the solenoid54to excite the coil56a, the insertion pins61are pushed out. The actuating member55, subjected to this push-out, moves in the second axial direction X2.

Only the insertion pins61may function as an armature. The whole actuating member55may function as an armature. The first and second circular-ring members58,59are provided to be movable integrally with each other in the axial direction X and to be rotatable relative to each other around the steering shaft10. In other words, the insertion pins61and the wedge members126are provided to be movable integrally with one another in the axial direction X and so as to be rotatable relative to one another around the steering shaft10. For example, the first and second circular-ring members58,59may be fitted together with a fitting member (not depicted in the drawings), so as to be rotatable relative to each other around the steering shaft10. In this case, the first facing surface58aand the second facing surface59amay contact each other, and the first and second circular-ring members58,59may be slidable relative to each other in the circumferential direction Y.

While the steer-by-wire system is in operation, the output shaft16rotates in conjunction with steering by the steering operation mechanism A (seeFIG. 1). At this time, in conjunction with rotation of the output shaft16, the first and second pressing members131,132(seeFIG. 2or any other relevant figure) included in the two-way clutch106(seeFIG. 2or any other relevant figure) rotate. In this state, the two-way clutch106is released, and thus, the worm wheel14(seeFIG. 2or any other relevant figure) is prevented from rotating in conjunction with rotation of the output shaft16. Thus, rotation of the output shaft16is accompanied by a variation in the relative rotating orientation between each of the first and second pressing members131,132and the worm wheel14. The actuating member55includes the insertion pins61and the wedge members126, which are movable integrally with one another in the axial direction X and to be rotatable relative to one another around the steering shaft10. Consequently, regardless of a variation in relative rotating orientation between each of the first and second pressing members131,132and the worm wheel14, the first and second pressing members131,132can be appropriately operated using an electromagnetic force from the driving force generating portion53(solenoid54).

FIG. 6AandFIG. 6Bare perspective views depicting a configuration of each of the wedge members126of the actuating member55. InFIG. 6AandFIG. 6B, the wedge member126is viewed in two different directions. Each wedge member126includes a wedge portion152located in the middle of the wedge member126in the axial direction X thereof and spreading in the opposite directions of the circumferential direction Y. The wedge portion152includes the first sliding contact surface153formed on the second circumferential direction Y2side of the wedge portion152and the second sliding contact surface154formed on the first circumferential direction Y1side of the wedge portion152. The wedge portion152comes into sliding contact with the first and second pressing members131,132from a first axial direction X1side. The first sliding contact surface153and the second sliding contact surface154are shaped as described above.

FIG. 7is a diagram illustrating a positional relation between the actuating member55and both the first and second pressing members131,132observed while the two-way clutch106is engaged.FIG. 8is a sectional view of the two-way clutch106in a released state.FIG. 9is a diagram illustrating a positional relation between the actuating member55and both the first and second pressing members131,132observed while the two-way clutch106is released.

With reference toFIG. 2,FIG. 3, andFIGS. 7 to 9, engagement and disengagement of the clutch mechanism15will be described.

To allow the clutch mechanism15to be engaged, power feeding to the solenoid54is turned off. In this state, the insertion pins61are not pushed out in the second axial direction X2by the solenoid54. Therefore, the elastic members124press the first pressing members131in the first circumferential direction Y1via the respective first rollers123a, while pressing the second pressing members132in the second circumferential direction Y2via the respective second rollers123b. The directions of the pressing forces and the inclinations of the first sliding contact surfaces153and the second sliding contact surfaces154act to allow the wedge members126to be pushed back in the first axial direction X1, while allowing the insertion pins61to be pushed back via the circular-ring members58,59. Thus, the actuating member55is placed in a first position (the position depicted inFIG. 7) in the axial direction X. With the actuating member55placed in the first position, the two-way clutch106is engaged. In this engaged state, as depicted inFIG. 3, each elastic member124elastically presses the corresponding first roller123atoward a first engagement position129aat an end of the corresponding wedge space129located on the first circumferential direction Y1side thereof. Thus, the first rollers123aare engaged with the outer periphery of the inner ring104and the inner periphery of the outer ring105. Each elastic member124elastically presses the corresponding second roller123btoward a second engagement position129bat an end of the corresponding wedge space129located on the second circumferential direction Y2side thereof. Thus, the second rollers123bare engaged with the outer periphery of the inner ring104and the inner periphery of the outer ring105. As a result, the engaged two-way clutch106couples the inner shaft29and the output shaft16together, in turn mechanically coupling the steering member3(seeFIG. 1) and the steering operation mechanism A (seeFIG. 1) together.

On the other hand, to allow the clutch mechanism15to be disengaged, the power feeding to the solenoid54is turned on. When the power feeding to the solenoid54is switched on, a force exerted by the solenoid54to push out the insertion pins61overcomes a force exerted by the elastic members124to push back the insertion pins61while the clutch is engaged as described above. As depicted inFIG. 9, the insertion pins61are pushed out by the solenoid54. As a result, the first circular-ring member58is pushed out via the second circular-ring member59. Consequently, the actuating member55is pushed out in the second axial direction X2to move in the second axial direction X2(for example, approximately 1 to 2 mm). Thus, the actuating member55is placed in a second position (the position depicted inFIG. 9) located on the second axial direction X2side with respect to the first position (the position depicted inFIG. 7).

As described above, each first sliding contact surface153includes the curved surface D shaped so as to protrude in the second circumferential direction Y2and is in line contact with the corresponding first mating sliding contact surface138. The second sliding contact surface154includes the curved surface F shaped so as to protrude in the first circumferential direction Y1and is in line contact with the corresponding second mating sliding contact surface143. In other words, the first sliding contact surface153and the second sliding contact surface154include respective portions configured such that the portions protrude in the opposite first and second circumferential directions Y1, Y2as they extend in the first axial direction X1. The first sliding contact surface153and the second sliding contact surface154are configured to come into line contact with the mating sliding contact surfaces138,148, respectively. Therefore, in conjunction with movement of the actuating member55toward the second position on the second axial direction X2side, the first mating sliding contact surfaces138, that is, the first pressing portions135move in the second circumferential direction Y2, whereas the second mating sliding contact surfaces143, that is, the second pressing portions140move in the first circumferential direction Y1.

Consequently, the first pressing portions135(first pressing surfaces137) press and move the respective first rollers123ain the second circumferential direction Y2against the elastic pressing forces of the respective elastic members124. Consequently, each first roller123aleaves the first engagement position129a(seeFIG. 3). As depicted inFIG. 8, a clearance S1is formed between each first roller123aand the inner periphery of the outer ring105. That is, each first roller123ais disengaged from the outer periphery of the inner ring104and from the inner periphery of the outer ring105.

The second pressing portions140(second pressing surfaces142) are moved in the first circumferential direction Y1to press and move the respective second rollers123bin the first circumferential direction Y1against the elastic pressing forces of the respective elastic members124. Consequently, each second roller123bleaves the second engagement position129b(seeFIG. 3). As depicted inFIG. 8, a clearance S2is formed between each second roller123band the inner periphery of the outer ring105. That is, each second roller123bis disengaged from the outer periphery of the inner ring104and from the inner periphery of the outer ring105.

With the actuating member55placed at the second position, the two-way clutch106is released. In this released state, the rollers123aand123bare disengaged from the inner ring104and from the outer ring105. The released two-way clutch106allows mechanical coupling between the inner shaft29and the output shaft16to be released. Consequently, the steering member3(seeFIG. 1) and the steering operation mechanism A (seeFIG. 1) are uncoupled from each other.

As depicted inFIG. 2, a ring-like seal member80is disposed which creates a seal between a lower surface of the outer ring105of the two-way clutch106in the axial direction (the surface closer to the steering operation mechanism A) and a lower surface of the inner ring104of the two-way clutch106in the axial direction (the surface closer to the steering operation mechanism A). The seal member80includes a contact seal. The wedge spaces129are filled with a clutch lubricant that lubricates a frictional surface of the two-way clutch106. The clutch lubricant exhibits a very high viscosity unlike a lubricant that is contained in the worm wheel housing portion35and lubricates meshing portions of the worm shaft13and the worm wheel14. Thus, when the clutch lubricant leaks from any of the wedge spaces129and reaches the meshing portions of the worm shaft13and the worm wheel14, the lubrication of the meshing portions may be adversely affected. Thus, the seal member80is used to prevent the lubricant from flowing out from the wedge spaces129.

The clutch mechanism15is assumed to be disposed between the intermediate shaft and the steering column instead of being housed and disposed in the internal space S (seeFIG. 2) in the housing H (seeFIG. 2). Specifically, a driving force transmission mechanism described in Japanese Patent Application Publication No. 2013-92191 (JP 2013-92191 A) is assumed to be interposed between the intermediate shaft17(seeFIG. 1) and the steering column5(seeFIG. 1or any other relevant figure). In this case, the driving force transmission mechanism is a large apparatus. Thus, a housing of the driving force transmission mechanism may interfere with the lower attachment structure73of the steering column5. The intermediate shaft17needs to be displaced downward by a distance equal to the dimension of the housing of the driving force transmission mechanism. This may cause a fluctuation in torque (angle transmission errors) due to a bend angle of a joint portion of the intermediate shaft17.

As described above, in an embodiment of the invention, the clutch mechanism15is housed and disposed in the internal space S in the housing H. The clutch mechanism15is housed and disposed inside the housing H, which houses the first speed reducer12and the torque sensor21. This makes it possible to avoid interference of the clutch mechanism15with peripheral members (for example, the lower attachment structure73). Inside the housing H, the driving force generating portion53is disposed on the opposite side of the worm wheel14from the mechanical portion51in the axial direction X. That is, the clutch mechanism15is divided into the portions between which the worm wheel14is sandwiched. Thus, the internal space S in the housing H can be effectively utilized to dispose the clutch mechanism15therein. This suppresses an increase in the size of the steering system1.

Therefore, the steering system1can be provided which allows the clutch mechanism15to be mounted in the vehicle without interfering with the peripheral members and which is restrained from being increased in size. The actuating member55extends to the mechanical portion51through the insertion holes33in the worm wheel14. The actuating member55receives a driving force from the driving force generating portion53to operate the mechanical portion51. Consequently, the mechanical portion51can be appropriately operated using an electromagnetic force from the driving force generating portion53(solenoid54) disposed the opposite side of the worm wheel14from the mechanical portion51.

The two-way clutch106is engaged when the roller pairs123engage both with the inner ring104and with the outer ring105. In this engaged state, the first pressing member131is moved in the second circumferential direction Y2, and the second pressing member132is moved in the first circumferential direction Y1. Consequently, (since the first pressing member131and the second pressing member132are moved in the opposite predetermined directions) the roller pairs123each can be pressed and moved in the directions in which the first and second rollers123a,123bapproach one another. Thus, the roller pairs123are disengaged from the inner ring104and from the outer ring105, allowing the two-way clutch106to be released. This allows the two-way clutch106to provide the mechanical portion51that couples the steering shaft10and the output shaft16together and that releases the coupling between the steering shaft10and the output shaft16.

The first and second sliding contact surfaces153,154of each of the wedge portions152include the respective portions that protrude in the opposite first and second circumferential directions Y1, Y2as they extend in the first axial direction X1. Thus, the actuating member55is moved in the first axial direction X1to allow the first pressing member131to move in the second circumferential direction Y2, while allowing the second pressing member132to move in the first circumferential direction Y1. Consequently, the roller pairs123each can be pressed and moved in the directions in which the first and second rollers123a,123bapproach one another. Therefore, the two-way clutch106can be appropriately switched between the engaged state and the released state.

In a steering system with no clutch mechanism mounted therein, the inner shaft29and the intermediate shaft17are connected together. In contrast, in the steering system1, the output shaft16provided coaxially with the inner shaft29so as to be rotatable relative to the inner shaft29is connected to the intermediate shaft17. This allows the coordinates of the intermediate shaft17in the steering system1(the position of the intermediate shaft17in the vehicle) to be made equivalent to the coordinates of the intermediate shaft in the steering system with no clutch mechanism mounted therein. This makes it possible to avoid a fluctuation in torque (angle transmission errors) caused by the bend angle of the joint portion of the intermediate shaft.

The embodiment of the invention has been described. The invention may be implemented in any other embodiment. For example, in the above-described embodiment, each of the wedge portions152is provided in the middle of the corresponding wedge member126in the axial direction X. However, the wedge portion152may be provided at an end of the wedge member126in the axial direction X as depicted inFIG. 14andFIG. 15. In this case, manufacturing is facilitated because the wedge member126may be processed at the end thereof.

In the above-described embodiment, the first sliding contact surface153, the second sliding contact surface154, the first mating sliding contact surface138, and the second mating sliding contact surface143are each formed by a surface including a curved portion. However, these surfaces may each be formed by a surface including a flat (inclined) portion. In other words, the above-described surfaces may each be formed by a combination of a flat (inclined) surface and a curved surface or exclusively by a flat (inclined) surface. One of the sliding contact surface (153,154) and the mating sliding contact surface (138,143) may be formed by a curved surface, and the other may be formed by a flat (inclined) surface. Alternatively, both the sliding contact surface (153,154) and the mating sliding contact surface (138,143) may be formed exclusively by curved surfaces or flat (inclined) surfaces.

In the above-described embodiment, the solenoid54is displaced from the torque sensor21in the axial direction X. However, the solenoid54and the torque sensor21may at least partly overlap in the axial direction X. In this case, the solenoid54is disposed so as to surround an outer periphery of the torque sensor21. The solenoid54is housed in the sensor housing26. In the above-described embodiment, the driving force generating portion53(seeFIG. 2) drives the mechanical portion51using an electromagnetic force resulting from conduction of a current through the coil56a(seeFIG. 2). However, as depicted inFIG. 10, the driving force generating portion53may generate a driving force using oil pressure.

In a first variation depicted inFIG. 10, the driving force generating portion53includes an oil pressure generating portion201. In the oil pressure generating portion201, a part of the housing H (for example, the sensor housing26) is sealed in a liquid tight manner to define an oil chamber202. The driving force generating portion53further includes an oil pressure control circuit203that controls the oil pressure in the oil chamber202. In this case, an actuating member55A is a member extending in the axial direction X and movable in the axial direction X. The actuating member55A and the housing H (for example, the sensor housing26) are slidable relative to each other. An end55Aa of the actuating member55A located on the first axial direction X1side thereof is fitted in the oil chamber202. A circular-ring-shaped seal204creates a seal between a peripheral surface202aof the oil chamber202and the actuating member55A.

The oil pressure generating portion201is housed and disposed in a second space Sb that is an upper portion of the internal space S in the housing H. That is, the oil pressure generating portion201is disposed on the opposite side of the worm wheel14(seeFIG. 2) from the mechanical portion51(seeFIG. 2) in the axial direction X. Control by the oil pressure control circuit203allows oil pressure to be applied to the actuating member55A via the oil chamber202. The applied pressure allows the actuating member55A to move in the axial direction X. Movement of the actuating member55A in the axial direction X switches the clutch mechanism15(seeFIG. 2or any other relevant figure) between the engaged state and the released state.

Although not depicted inFIG. 10, the actuating member55A includes, on the second axial direction X2side thereof, a first circular-ring member (corresponding to the first circular-ring member58) and a second circular-ring member (corresponding to the second circular-ring member59) as is the case with the above-described embodiment. The first circular-ring member is movable integrally with the second circular-ring member in the axial direction X and rotatable relative to the second circular-ring member around the steering shaft10. In the first variation, the oil pressure generating portion201is used as the driving force generating portion53. As compared to a configuration in which the solenoid54(seeFIG. 2) is adopted as the driving force generating portion53, the configuration in the first variation allows avoiding the adverse effect of electromagnetic fields on the torque sensor21and the first bearing50.

As depicted inFIG. 11, the driving force generating portion53may generate a driving force using an output from a motor. In a second variation depicted inFIG. 11, the driving force generating portion53includes an electric driving portion301. An actuating member55B is a member extending in the axial direction X and movable in the axial direction X. The electric driving portion301includes a second motor302and a second speed reducer303that decelerates output rotation of the second motor302. The second speed reducer303includes a drive gear304and a driven gear305. The drive gear304is formed on an output shaft302aof the second motor302. The driven gear305is formed on the actuating member55B so as to be rotatable integrally with the actuating member55B and meshes with the drive gear304. The second motor302is provided on the core metal portion31of the worm wheel14via a base306so as to be rotatable integrally with the core metal portion31.

The second speed reducer303amplifies the output rotation of the second motor302and converts the output rotation into a driving force of the actuating member55B in the axial direction X. The drive gear304may be, for example, pinion teeth. The driven gear305may be, for example, rack teeth aligned along the axial direction X. The electric driving portion301is housed and disposed in the second space Sb that is an upper portion of the internal space S in the housing H. That is, the electric driving portion301is disposed on the opposite side of the worm wheel14from the mechanical portion51(seeFIG. 2) in the axial direction X.

Rotational driving performed by the second motor302moves the actuating member55B in the axial direction X. Movement of the actuating member55B in the axial direction X switches the clutch mechanism15(seeFIG. 2or any other relevant figure) between the engaged state and the released state. In the second variation, the electric driving portion301is used as the driving force generating portion53. Thus, as compared to a configuration in which the solenoid54(seeFIG. 2or any other relevant figure) is adopted as the driving force generating portion53, the configuration in the second variation allows avoiding the adverse effect of electromagnetic fields on the torque sensor21and the first bearing50.

While the power feeding to the second motor302is stopped, the output shaft302adoes not rotate. Consequently, the clutch mechanism15(seeFIG. 2or any other relevant figure) can be kept engaged or released without using energy (electric power). As described above, the mechanical portion51is the two-way clutch106(seeFIG. 3or any other relevant figure). However, the mechanical portion51may be configured to include a friction clutch402as depicted inFIG. 12. AlthoughFIG. 12illustrates that a single disc clutch is used as the friction clutch402, any other clutch such as a multi-disc clutch may be adopted.

The mechanical portion51may be configured to include a positive clutch403as depicted inFIG. 13.

As described above, the inner ring104is coupled to the output shaft16, and the outer ring105is coupled to the inner shaft29(steering shaft10). However, the inner ring104may be coupled to the inner shaft29(steering shaft10), and the outer ring105may be coupled to the output shaft16.

As described above, the sensor housing26and the speed reducer housing25are included in the housing H. However, the housing H may be optionally configured so long as the housing H includes at least the speed reducer housing25. That is, the housing H need not house the torque sensor21so long as the housing H houses the first speed reducer12. Therefore, the invention is applicable to a steering system with no torque sensor.

By way of example, the worm wheel14is used as the gear that is attached to the steering shaft10so as to be rotatable integrally with the steering shaft10. However, as this gear, any other type of gear may be adopted.

Various other modifications may be made to the invention within the scope of the claims.