Patent ID: 12228205

DESCRIPTION OF EMBODIMENTS

First Example of Embodiment

A first example of an embodiment of the present invention will be described usingFIGS.1to16. Note that in the present example, a case will be described in which a worm reducer according to an aspect of the present invention is applied to a pinion assist type electric power steering device. However, the worm reducer of the present invention is widely applicable to column assist type, dual pinion type electric power steering devices, and various mechanical devices other than electric power steering devices.

FIG.1shows a pinion assist type electric power steering device1incorporating a worm reducer of the present example. The electric power steering device1includes a steering wheel2, a steering shaft3, a steering column4, a pair of universal joints5aand5b, an intermediate shaft6, a steering gear unit7, and an electric assist device8.

The steering wheel2is supported and fixed to the rear end portion of the steering shaft3. The steering shaft3is rotatably supported inside the steering column4supported by a vehicle body. The front end portion of the steering shaft3is connected to a pinion shaft9of the steering gear unit7via the universal joint5aon the rear side, the intermediate shaft6, and the universal joint5bon the front side. Therefore, when the driver rotates the steering wheel2, the rotation of the steering wheel2is transmitted to the pinion shaft9via the steering shaft3, the pair of universal joints5aand5b, and the intermediate shaft6. The rotation of the pinion shaft9is converted into a linear motion of a rack shaft10of the steering gear unit7, which meshes with the pinion shaft9. As a result, a steering angle corresponding to the amount of rotational operation of the steering wheel2is applied to a pair of steered wheels. The electric assist device8applies auxiliary power generated using an electric motor15as a power source to the pinion shaft9. As a result, the force required for the driver to rotate the steering wheel2is reduced.

The steering gear unit7includes a housing11supported and fixed to the vehicle body, the rack shaft10, and the pinion shaft9. The housing11includes a rack accommodation portion12extending in the vehicle width direction, and a pinion accommodation portion13connected to one axial side portion (the right side portion inFIG.1) of the rack accommodation portion12. A central axis of the pinion accommodation portion13is present in a twisted position with respect to a central axis of the rack accommodation portion12. An inner space of the pinion accommodation portion13communicates with an inner space of the rack accommodation portion12. The rack shaft10is supported inside the rack accommodation portion12to be movable only in the axial direction (vehicle width direction). The pinion shaft9is supported inside the pinion accommodation portion13only to be rotatable. The pinion shaft9has pinion teeth on the outer circumferential surface of a front half portion (not shown) (the lower half portion inFIG.2) disposed inside the pinion accommodation portion13. A base end portion (the upper end portion inFIG.2) of the pinion shaft9protrudes to the outside of the housing11and is connected to the universal joint5bon the front side. The rack shaft10has rack teeth that mesh with the pinion teeth of the pinion shaft9at a circumferential part of the outer circumferential surface of one axial side portion (not shown) (the right side portion inFIG.1) disposed inside the rack accommodation portion12.

The electric assist device8includes a worm reducer14and the electric motor15. The electric assist device8is configured to reduce the rotation of the electric motor15using the worm reducer14and transmit the rotation to the pinion shaft9.

The worm reducer14includes a housing16, a worm wheel17, a worm18, a holder21, a support bearing19, a pad20, and an elastic member22.

The housing16includes a wheel accommodation portion23and a worm accommodation portion24disposed in a twisted position with respect to the wheel accommodation portion23and having an axially intermediate portion open to the wheel accommodation portion23.

That is, a central axis of the wheel accommodation portion23and a central axis of the worm accommodation portion24are disposed in twisted positions with respect to each other. The axially intermediate portion of the worm accommodation portion24is integrally connected to one location in the circumferential direction of the radially outer end portion of the wheel accommodation portion23, and through the connected part, an inner space of the worm accommodation portion24communicates with an inner space of the wheel accommodation portion23. In the present example, the worm accommodation portion24has a cylindrical shape with a bottom, and specifically, the tip end in the axial direction (the right end inFIG.3) is closed and the base end in the axial direction (the left end inFIG.3) is open.

In the present example, the wheel accommodation portion23is coaxially and integrally connected to an axially intermediate portion of the pinion accommodation portion13that configures the housing11of the steering gear unit7.

The inner space of the wheel accommodation portion23communicates with the inner space of the pinion accommodation portion13.

The worm wheel17has wheel teeth25on the outer circumferential surface thereof and is rotatably supported inside the wheel accommodation portion23. In the present example, the worm wheel17is externally fitted and fixed to an axially intermediate portion of the pinion shaft9.

The worm18has worm teeth26that meshes with the wheel teeth25at an axially intermediate portion on the outer circumferential surface, and is rotatably supported inside the worm accommodation portion24.

In the present example, the base end portion (the left end portion inFIG.3) of the worm18is supported with respect to the worm accommodation portion24to be able to swing slightly and be displaced, and is connected to an output shaft28of the electric motor15to be able to transmit torque.

Therefore, in the present example, the worm18has a female spline portion27on the inner circumferential surface of the base end portion. The electric motor15is coupled and fixed to the axial base end portion of the worm accommodation portion24with screw clamps while the output shaft28is disposed coaxially with the worm accommodation portion24. The female spline portion27of the worm18and a male spline portion29provided on the outer circumferential surface of the output shaft28of the electric motor15are spline-engaged. Thereby, the base end portion of the worm18and the output shaft28of the electric motor15are connected such that torque can be transmitted and the worm18can slightly swing and be displaced. The base end portion of the worm18is supported by a ball bearing30having a radial clearance with respect to the worm accommodation portion24to be able to swing slightly and be displaced.

In the present example, the outer circumferential surface of the tip end portion of the worm18is configured with a stepped cylindrical surface. That is, the outer circumferential surface of the tip end portion of the worm18has a small diameter cylindrical surface portion31configuring the tip end side portion and a large diameter cylindrical surface portion32configuring the base end side portion having a larger diameter than the small diameter cylindrical surface portion31.

In the worm reducer14of the present example, a central axis O17of the worm wheel17and a central axis (the central axis of the output shaft28of the electric motor15) O18of the worm18are orthogonal to each other when viewed in a first direction (the up-down direction inFIGS.3and4) which will be described later. However, the present invention can also be applied to an oblique intersection type worm reducer in which the central axis O17of the worm wheel17and the central axis (the central axis of the output shaft28of the electric motor15) O18of the worm18obliquely intersect each other, that is, an acute angle is formed, when viewed in the first direction.

In the worm reducer14of the present example, as shown inFIGS.3to6, the holder21, the support bearing19, the pad20, and the elastic member22are disposed between the outer circumferential surface of the tip end portion of the worm18and the inner circumferential surface of the tip end portion of the worm accommodation portion24.

Specifically, the holder21is configured in an annular shape, the tip end portion of the worm18is inserted therethrough radially inward, and the holder21is internally fitted and fixed to the worm accommodation portion24. The support bearing19is a rolling bearing having an inner ring33and an outer ring34, and is disposed between the outer circumferential surface of the tip end portion of the worm18and the inner circumferential surface of the holder21while a clearance in the radial direction is interposed between the inner circumferential surface of the inner ring33and the outer circumferential surface of the tip end portion of the worm18. The pad20is disposed around the tip end portion of the worm18at a location adjacent to the support bearing19in the axial direction, and is used to press the tip end portion of the worm18in a direction toward the worm wheel. The elastic member22is assembled to the holder21and elastically urges the tip end portion of the worm18toward the worm wheel17(the lower side inFIGS.3and4) via the pad20. Accordingly, backlash at the meshing portion between the wheel teeth25and the worm teeth26is reduced.

Note that, when implementing the present invention, the positional relationship between the support bearing and the pad in a second direction (the left-right direction inFIGS.3and4) can be reversed from that in the present example. For example, a configuration can also be adopted in which an assembly of the holder21, the support bearing19, the pad20, and the elastic member22is disposed in the opposite direction to that in the present example in the second direction between the outer circumferential surface of the tip end portion of the worm18and the inner circumferential surface of the tip end portion of the worm accommodation portion24. Note that, when such a configuration is adopted, one side in the second direction is the left side inFIGS.3and4.

The holder21has two holder inclined surfaces45(refer toFIGS.8,12,14A to14D, and the like), which are two holder engagement portions at a position where the pad20is sandwiched from both sides in a third direction (the front-back direction inFIGS.3and4) orthogonal to both the first direction (the up-down direction inFIGS.3and4) that is the urging direction of the elastic member22and the second direction (the left-right direction inFIGS.3and4) that is the axial direction of the worm accommodation portion24. The two holder inclined surfaces45each extend in the first direction, and are inclined in a direction toward each other toward one side (in the present example, the right side inFIGS.3and4) in the second direction. When implementing the present invention, the direction of inclination of the two holder inclined surfaces in the second direction can also be made to be the opposite direction to that of the present example. Then, one side in the second direction is the left side inFIGS.3and4. Note that the holder21is preferably made of a material having sufficient strength and rigidity, such as a metal material.

More specifically, in the present example, as shown inFIGS.4,8, and14A to14D, the holder21includes a cylindrical tubular portion37, an annular side plate portion38extending radially inward from the end portion on one side in the second direction of the tubular portion37, and a substantially U-shaped protrusion portion39extending from the radially inner end portion of the side plate portion38toward one side in the second direction.

The tubular portion37is a part which is internally fitted to the inner circumferential surface of the worm accommodation portion24and on which the support bearing19is disposed on the radially inner side. In the present example, the tubular portion37has a bearing holding surface40at the end portion on the other side (the left side inFIGS.3and4) in the second direction and on the inner circumferential surface of the intermediate portion. The tubular portion37has a fitting surface42formed by arranging protrusions41having triangular cross-sections at a plurality of locations in the circumferential direction on the outer circumferential surface. In the present example, to internally fit and fix the holder21to the inner circumferential surface of the worm accommodation portion24, the fitting surface42of the tubular portion37is internally fitted to the inner circumferential surface of the worm accommodation portion24by a tight fit.

In the present example, the inner circumferential surface61of the side plate portion38has recess portions62recessed toward both sides in the third direction on both side parts in the third direction, as shown inFIG.14D. The bottom surface of the recess portion62is configured by a plane orthogonal to the third direction. A part of the inner circumferential surface61of the side plate portion38that is removed from the two recess portions62, that is, both side parts in the first direction, is configured with a cylindrical surface centered on the central axis of the holder21.

In the present example, the protrusion portion39protrudes toward one side in the second direction from the part excluding the end portion of the radially inner end portion of the side plate portion38on the side far from the worm wheel17in the first direction. The protrusion portion39includes two guide portions43and a connection portion44. The two guide portions43configure the end portions of the protrusion portion39on both sides in the third direction. That is, as shown inFIGS.8,14A, and14D, the two guide portions43extend toward one side in the second direction from two locations of the radially inner end portion of the side plate portion38spaced apart in the third direction, specifically, the same circumferential locations as the two recess portions62. The two guide portions43have a shape extending in the first direction. The connection portion44configures an end portion of the protrusion portion39on the side close to the worm wheel17in the first direction. That is, the connection portion44extends from the end portion of the radially inner end portion of the side plate portion38on the side close to the worm wheel17in the first direction toward one side in the second direction, and connects the end portion of the two guide portions43on the side close to the worm wheel17in the first direction. The connection portion44has a partially cylindrical shape centered on the central axis of the holder21. Note that, when the holder has sufficient strength to prevent deformation of the two guide portions, the connection portion can be omitted.

The two holder inclined surfaces45configuring the holder21are provided on an inner surface46of the two guide portions43, which are side surfaces facing each other in the third direction. In the present example, each of the inner surfaces46of the two guide portions43has a crank shape having a stepped surface (holder inclined surface45) at the intermediate portion in the second direction, as shown inFIG.14C, when viewed in the first direction. That is, the two holder inclined surfaces45are provided at an intermediate portion of the inner surface46of the two guide portions43in the second direction, more specifically, at one side part of the intermediate portion in the second direction. The two holder inclined surfaces45are inclined toward each other toward one side in the second direction. On the inner surfaces46of the two guide portions43, each of the part positioned on one side of the two holder inclined surfaces45in the second direction, and the part positioned on the other side of the two holder inclined surfaces45in the second direction is configured with a plane orthogonal to the third direction. Therefore, the interval between the inner surfaces46of the two guide portions43is narrower than the part positioned on one side of the two holder inclined surfaces45in the second direction and the part positioned on the other side of the two holder inclined surfaces45in the second direction.

When implementing the present invention, an inclination angle θ of the holder inclined surface45with respect to the second direction can be set to any value in the range of 0°<θ<90° but is set to, preferably, 200 or more and 800 or less, and more preferably, 30° or more and 700 or less. In the present example, the inclination angle θ is 70°.

Each of the two guide portions43has a holder pressed surface47on a tip end surface that is an end surface on one side in the second direction. That is, the two holder pressed surfaces47face one side in the second direction. In the present example, the two holder pressed surfaces47and the tip end surface, which is an end surface of the connection portion44on one side in the second direction, are continuous with each other and are on the same virtual plane orthogonal to the second direction.

In the present example, the support bearing19is configured with a ball bearing. That is, the support bearing19includes the inner ring33having an inner ring raceway on the outer circumferential surface thereof, an outer ring34having an outer ring raceway on the inner circumferential surface thereof, and a plurality of balls35, each of which is a rolling element disposed between the inner ring raceway and the outer ring raceway. However, when implementing the present invention, a rolling bearing such as a cylindrical roller bearing of which rolling elements are cylindrical rollers, or a tapered roller bearing of which rolling elements are tapered rollers, can also be used as the support bearing.

In the present example, a radial clearance is interposed between the inner circumferential surface of the inner ring33and the outer circumferential surface of the tip end portion of the worm18. In the present example, a cylindrical bush36is disposed between the inner circumferential surface of the inner ring33and the outer circumferential surface of the tip end portion of the worm18. Specifically, the inner ring33is externally fitted to the outer circumferential surface of the bush36by a tight fit, and the bush36is externally fitted to the large diameter cylindrical surface portion32of the worm18by a clearance fit. Note that the bush36is a member for ensuring slidability and/or cushioning performance with respect to the outer circumferential surface of the tip end portion of the worm18. Preferably, the bush36is made of synthetic resin, a light alloy such as an aluminum alloy, or the like, which are materials that have a small coefficient of friction with respect to the metal material that configures the worm18.

In the present example, the outer ring34is internally fitted to the bearing holding surface40of the holder21with a clearance fit. That is, the outer ring34is internally fitted and fixed to the holder21.

In the present example, the tip end portion of the worm18can be displaced in the first direction (the up-down direction inFIGS.3and4) that is the urging direction of the elastic member22, based on the radial clearance that is present between the inner circumferential surface of the inner ring33and the outer circumferential surface of the tip end portion of the worm18, specifically, and the annular clearance that is present between the inner circumferential surface of the bush36and the large diameter cylindrical surface portion32.

When implementing the present invention, the inner ring of the support bearing can be externally fitted and fixed to the tip end portion of the worm, and the radial clearance can be interposed between the outer circumferential surface of the outer ring of the support bearing and the inner circumferential surface of the holder, that is, the tip end portion of the worm can also be displaced in the first direction based on the radial clearance. Here, a cylindrical bush can be disposed between the outer circumferential surface of the outer ring and the inner circumferential surface of the holder, specifically, for example, the outer ring can be internally fitted to the inner circumferential surface of the bush by a tight fit, and the outer circumferential surface of the bush can also be internally fitted to the inner circumferential surface of the holder with a clearance fit. Here, the bush is used as a member for ensuring slidability and/or cushioning performance with respect to the inner circumferential surface of the holder. However, when implementing the present invention, the bush can be omitted.

As shown inFIGS.8,12,13,15A to15D, and16, the pad20has two pad inclined surfaces48which are two pad engagement portions that come into contact with the two holder inclined surfaces45at both side portions in the third direction, and a pad elastic pressing portion49that applies a preload to the contact portion between the holder inclined surface45and the pad inclined surface48by elastically pressing a part of the holder21toward the other side in the second direction. In the present example, the two pad inclined surfaces48are in surface contact with the two holder inclined surfaces45, specifically, the two pad inclined surfaces48are inclined in the same direction and at the same angle as the two holder inclined surfaces45(refer toFIG.13). In the present example, the parts of the holder21that are elastically pressed toward the other side in the second direction by the pad elastic pressing portion49are the two holder pressed surfaces47.

However, when implementing the present invention, some of the holders can be selected freely. For example, an end surface on one side in the second direction of the side plate portion configuring the holder is set as a part of the holder (holder pressed surface), and the part of the holder can also be elastically pressed toward the other side in the second direction by the pad elastic pressing portion provided at the base portion of the pad. Note that, preferably, the pad20is made of synthetic resin, a light alloy such as an aluminum alloy, or the like, which are materials that have a small coefficient of friction with respect to the metal material that configures the worm18.

In the present example, the pad elastic pressing portion49is positioned farther on one side in the second direction than the two pad inclined surfaces48, and are configured with two pad elastic pressing plates50each extending from the center portion of the pad20in the third direction toward sides away from each other in the third direction.

More specifically, in the present example, the pad20includes a base portion51disposed between the two guide portions43, and a through-hole53which penetrates the base portion51in the second direction and into which the tip end portion of the worm18is inserted, two pad inclined surfaces48are provided at both side portions of the base portion51in the third direction, and a flat plate portion52including the two pad elastic pressing plates50is connected to a part of the base portion51that protrudes from between the two guide portions43to one side in the second direction.

The base portion51includes abase main body54and two base projection portions55.

The base main body54extends in the first direction and has a substantially rectangular end surface shape. The through-hole53has a circular opening shape, and penetrates, in the second direction, a half portion of the base main body54on the side close to the worm wheel17in the first direction. The base main body54has two pressed portions56at both end portions in the third direction of a part on the other side in the second direction, at the end portion far from the worm wheel17in the first direction. Each of the two pressed portions56is configured with a partial cylindrical surface centered on the central axis of the through-hole53. The base main body54has a flange portion57that projects toward a side farther from the worm wheel17than the two pressed portions56in the first direction on one side part in the second direction, at the end portion far from the worm wheel17in the first direction.

The two base projection portions55protrude toward the sides away from each other in the third direction from a part of the base main body54on the side close to the worm wheel17in the first direction in the half portion on the other side in the second direction. Each of the two base projection portions55extends in the first direction.

In the present example, the two pad inclined surfaces48configuring the pad20are provided on a side surface of the two base projection portions55on one side in the second direction. The two pad inclined surfaces48are inclined toward each other toward one side in the second direction. The inclination angle θ of the pad inclined surface48with respect to the second direction is the same as the inclination angle θ of the holder inclined surface45with respect to the second direction.

The flat plate portion52is integrally connected to an end portion of the base main body54on one side in the second direction, and has a circular outer circumferential shape when viewed from one side in the second direction. The through-hole53penetrates the radially center portion of the flat plate portion52in the second direction. Therefore, the flat plate portion52has a circular flat plate shape centered on the central axis of the through-hole53. The outer diameter dimension of the flat plate portion52is larger than the width dimension of the base main body54in the third direction. The end portions of the flat plate portion52on both sides in the third direction project toward both sides in the third direction from the base main body54. The end portion of the flat plate portion52close to the worm wheel17in the first direction projects toward a side closer to the worm wheel17than the base main body54in the first direction. The end portion of the base main body54far from the worm wheel17in the first direction projects toward a side farther from the worm wheel17than the flat plate portion52in the first direction.

In the present example, the two pad elastic pressing plates50configuring the pad20are connected to a part that protrudes toward one side in the second direction from between the two guide portions43in the base portion51. Specifically, the two pad elastic pressing plates50are configured with the end portions of the flat plate portion52on both sides in the third direction.

In the present example, each of the two pad elastic pressing plates50has protrusions58aand58bextending in the first direction on the side surface on the other side in the second direction, as shown inFIGS.12,13,15A to15D, and16. In the present example, each of the two pad elastic pressing plates50includes two protrusions58aand58b. The two protrusions58aand58bare disposed to be spaced apart from each other in the third direction. When implementing the present invention, the number of protrusions can also be one or three or more. In the present example, each of the two pad elastic pressing plates50has a slit59that penetrates in the second direction and extends in the first direction at the base end portion which is the end portion on the center side of the pad20in the third direction. In the present example, based on appropriate regulation of the width and length of the slit59and the plate thickness of the pad elastic pressing plate50, the bending rigidity in the second direction of the base end portion of the pad elastic pressing plate50at the parts adjacent to each other on both sides in the length direction of the slit59is adjusted. However, when implementing the present invention, the slit can be omitted.

In the present example, the inner circumferential surface of the through-hole53has a fitting surface60configured as a cylindrical surface at an axially intermediate portion. The fitting surface60has an inner diameter slightly larger than the outer diameter of the small diameter cylindrical surface portion31at the tip end portion of the worm18.

As shown inFIGS.4,6,11, and12, the pad20is assembled to the protrusion portion39of the holder21and is externally fitted to the tip end portion of the worm18.

Specifically, while a part of the base portion51of the pad20on the side close to the worm wheel17in the first direction is disposed between the two guide portions43that configure the protrusion portion39of the holder21, the two pad inclined surfaces48are in surface contact with the two holder inclined surfaces45. The tip end portions of the protrusions58aand58bof the two pad elastic pressing plates50elastically press the two holder pressed surfaces47toward the other side in the second direction. Thereby, a preload is applied to the contact portion between the two holder inclined surfaces45and the two pad inclined surfaces48.

The small diameter cylindrical surface portion31at the tip end portion of the worm18is internally fitted to the fitting surface60of the through-hole53of the pad20to be relatively rotatable without rattling in the radial direction.

Here, as shown inFIG.6, a clearance in the first direction is present between the side surface of the base portion51of the pad20on the side close to the worm wheel17in the first direction, and the side surface of the connection portion44that configures the protrusion portion39of the holder21on the side far from the worm wheel17in the first direction. In the present example, the pad20can be displaced in the first direction with respect to the holder21based on the clearance in the first direction.

Here, as shown inFIGS.12and13, a clearance in the third direction is present between the base portion51of the pad20and each of the part positioned on one side of the two holder inclined surfaces45in the second direction and the part positioned on the other side of the two holder inclined surfaces45in the second direction on the inner surfaces46of the two guide portions43. In the present example, the pad20can be displaced in the third direction with respect to the holder21based on the clearance in the third direction.

In the present example, the elastic member22is configured with a plate spring. More specifically, in the present example, the elastic member22is configured with a C-shaped cylindrical plate spring having a discontinuous portion at one location in the circumferential direction, as shown inFIGS.6and8. However, when implementing the present invention, the shape of the plate spring configuring the elastic member22can also be made into a shape other than the C-shaped cylindrical shape. The elastic member can also be configured with a torsion coil spring.

The elastic member22is assembled to the holder21to be externally fitted to the base portion51of the pad20and the two guide portions43. In the present example, while the base portion51of the pad20and the protrusion portion39of the holder21are inserted into the radially inner side of the elastic member22, the inner circumferential surface of the circumferential center portion of the elastic member22is elastically pressed against the two pressed portions56of the pad20, and the inner circumferential surface of both end portions of the elastic member22in the circumferential direction is elastically pressed against the side surface of the connection portion44configuring the protrusion portion39of the holder21on the side close to the worm wheel17in the first direction. Thereby, the tip end portion of the worm18is elastically urged via the pad20toward the worm wheel17side, that is, toward the side close to the worm wheel17in the first direction. Accordingly, the backlash at the meshing portion between the wheel teeth25and the worm teeth26is reduced.

According to the worm reducer14of the present example, the following effects can be achieved.

The two pad inclined surfaces48configuring the pad20are in surface contact with two holder inclined surfaces45configuring the holder21. The tip end portions of the protrusions58aand58bof the two pad elastic pressing plates50configuring the pad20elastically press the two holder pressed surfaces47configuring the holder21toward the other side in the second direction. Thereby, a preload is applied to the contact portion between the two holder inclined surfaces45and the two pad inclined surfaces48. Therefore, based on the contact between the two holder inclined surfaces45and the two pad inclined surfaces48, displacement of the pad20in the third direction with respect to the holder21is regulated, and the pad20can prevent rattling without resistance in the third direction with respect to the holder21.

Specifically, in the present example, as shown inFIGS.12and13, based on the fact that the tip end portions of the protrusions58aand58bof the pad elastic pressing plate50elastically press the holder pressed surface47toward the other side in the second direction, an elastic force (preload force) Fp toward one side in the second direction acts from the pad inclined surface48to the holder inclined surface45. Then, the elastic force Fp is converted into an elastic force (preload force) Fx acting from the pad inclined surface48to the holder inclined surface45and facing outward in the third direction. In the structure of the present example, based on the elastic force Fx, it is possible to prevent the pad20from rattling without resistance in the third direction with respect to the holder21.

Therefore, even when the rotation direction of the worm18changes, and the direction of the component in the third direction of the reaction force applied from the wheel teeth25to the worm teeth26changes, the tip end portion of the worm18becomes difficult to displace in the third direction. As a result, it is possible to prevent abnormal noises such as rattling noise from occurring at the meshing portion between the wheel teeth25and the worm teeth26, and abnormal noises such as collision noises from occurring between the pad20and the holder21.

When implementing the present invention, based on the fact that the width and the length of the slit59, the plate thickness of the pad elastic pressing plate50, the height of the protrusions58aand58bin the second direction, and the like are changed, the bending rigidity in the second direction at a part of the base end portion of the pad elastic pressing plate50adjacent to both sides of the slit59in the length direction can be changed. Accordingly, the magnitude of the force with which the tip end portions of the protrusions58aand58bof the pad elastic pressing plate50elastically press the holder pressed surface47toward the other side in the second direction can be changed. Accordingly, the magnitude of the elastic force Fp can be changed freely.

The pad elastic pressing plate50locally presses the holder pressed surface47with the tip end portions of the protrusions58aand58b. Therefore, the pressing force can be stabilized compared to the case where the pad elastic pressing plate presses the holder pressed surface over a wide range.

The relational expression “Fx=Fp/tan θ” is established between the elastic force Fx and the elastic force Fp. In the present example, since the inclination angle θ=70°. Fx=Fp/tan 70°=0.4 Fp. That is, the elastic force Fx becomes smaller than the elastic force Fp. When implementing the present invention, the magnitude of the elastic force Fx can be changed freely by changing not only the magnitude of Fp but also the magnitude of the inclination angle θ. For example, when θ=45°, Fx=Fp can be satisfied, when 45°<θ<90°, Fx<Fp can be satisfied, and when 0°<θ<45°, Fx>Fp can be satisfied. The magnitude of the elastic force Fx can be adjusted by changing the inclination angle θ without changing the material of the pad20(the elastic force based on the material). Therefore, the magnitude of the elastic force Fx can be easily adjusted at the design stage.

Note that, when implementing the present invention, the inclination angle of the holder inclined surface45in the second direction and the inclination angle of the pad inclined surface48in the second direction do not need to be strictly the same, and may be changed within the manufacturing error range. The inclination angle of the holder inclined surface45in the second direction can also be made smaller than the inclination angle of the pad inclined surface48in the second direction. For example, the inclination angle of the holder inclined surface45in the second direction can be made smaller than the inclination angle of the pad inclined surface48in the second direction by approximately 0.5°. Accordingly, at the contact portion between the holder inclined surface45and the pad inclined surface48, the tip end portion of the pad inclined surface48(the right end portion in the third direction inFIG.13, the other end portion in the second direction inFIG.13) comes into particularly strong surface contact with the holder inclined surface45. As a result, the posture of the pad20with respect to the holder21becomes stable.

Note that, when viewed in the first direction, as shown inFIGS.12and13, the case is considered in which the pad20is displaced on either side of the holder21in the third direction, for example, on the right side inFIGS.12and13, from the neutral state where the central axis of the holder21and the central axis of the pad20are aligned with each other. Here, along with the sliding displacement of the right pad inclined surface48along the right holder inclined surface45, the base portion51of the pad20is displaced toward the other side in the second direction, and at the same time, the right pad elastic pressing plate50is elastically deformed to fall to one side in the second direction. Then, as the elastic pressing force acting from the right pad elastic pressing plate50to the right holder pressed surface47increases according to the amount of the elastic deformation, the elastic forces Fp and Fx increase. As a result, the pad20becomes more difficult to displace toward the right side. The same applies to the case where the pad20is displaced from the neutral state to the left side inFIGS.12and13with respect to the holder21.

The inner circumferential surface of the circumferentially center portion of the elastic member22is elastically pressed against the two pressed portions56provided at both end portions of the base main body54configuring the pad20in the third direction. Therefore, force having not only a component in a direction approaching the worm wheel17in the first direction but also a component in opposite directions in the third direction is applied to the two pressed portions56. From such point of view, when the rotation direction of the worm18changes, the tip end portion of the worm18becomes difficult to displace in the third direction.

Second Example of Embodiment

A second example of the embodiment of the present invention will be described usingFIGS.17to20.

In the structure of the present example, the inclination angle θ of the holder inclined surface45aand the pad inclined surface48awith respect to the second direction is 30°. Therefore, the elastic force Fx acting from the pad inclined surface48ato the holder inclined surface45aand facing outward in the third direction is Fx=Fp/tan 30°=1.7 Fp. In other words, the elastic force Fx is larger than the elastic force Fp acting from the pad inclined surface48ato the holder inclined surface45aand facing one side in the second direction. Therefore, when the rotation direction of the worm18(refer toFIGS.3and4) changes, the tip end portion of the worm18can be made more difficult to displace in the third direction.

Other configurations and effects are the same as in the first example of the embodiment.

Third Example of Embodiment

A third example of the embodiment of the present invention will be described usingFIGS.21A to22C. In the present embodiment, the configuration of the elastic member22is different from each of the above-described embodiments. The other configurations and effects are the same as those of the first and second examples of the embodiment, and thus the description thereof will be omitted.

FIGS.21A to21Dare diagrams showing the elastic member according to the present embodiment, withFIG.21Ashowing a view from one side in the third direction,FIG.21Bshowing a view in the second direction,FIG.21Cshowing a view from the other side in the third direction, andFIG.21Dshowing a view in the first direction.FIGS.22A to22Care diagrams showing a stacked state of the elastic members, withFIG.22Ashowing a perspective view,FIG.22Bshowing a view in the first direction, andFIG.22Cshowing a view from one side in the third direction.

As described above, the elastic member22is assembled to the holder21and elastically urges the tip end portion of the worm18toward the worm wheel17(the lower side inFIGS.3and4) via the pad20. As shown inFIGS.21A to21D, the elastic member22is configured with an approximately C-shaped cylindrical plate spring having a discontinuous portion71at one location in the circumferential direction, and by increasing the set load of the plate spring, it is possible to prevent the occurrence of backlash at the meshing portion between the wheel teeth25and the worm teeth26, and to prevent the occurrence of abnormal noise. However, when the set load is increased, a trade-off arises in that the friction at the meshing portion between the wheel teeth25and the worm teeth26increases.

Therefore, the set load by the elastic member22needs to be moderate in friction while preventing the occurrence of abnormal noise at the meshing portion between the wheel teeth25and the worm teeth26, and thus a plurality of elastic members22with different set loads are required.

Here, as a method of changing the set load of the elastic member22, there are three methods such as a method of changing the dimension of the discontinuous portion71at one location in the circumferential direction of the elastic member22, a method of changing the plate thickness (radial thickness) of the elastic member22, and a method of changing the plate width (width in the second direction) of the elastic member22.

As shown inFIG.21B, the elastic member22has the discontinuous portion71having a substantially C-shaped shape when viewed in the second direction, and thus, when paying no attention to the packing form, the plurality of elastic members22may become entangled with each other, causing problems in workability. Therefore, it is preferable to perform stack packing in which the plurality of elastic members22are stacked and packed.

The present inventors have invented a new shape that enables stack packing in which the elastic members22do not become entangled with each other when selecting the method of changing the plate width (the width in the second direction) of the elastic members22among the above three methods of changing the set load. The specific configuration of the elastic member22will be described below.

As shown inFIGS.21A to21D, the elastic member22has a base portion73extending toward both sides in the third direction on one side in the first direction (the upper side inFIG.21B), a pair of arm portions75A and75B extending in a substantially semi-cylindrical shape from both end portions of the base portion73in the third direction toward the other side in the first direction (the lower side inFIG.21B), and projection portions74and74that are bent from the tip end portions of the pair of the pair of arm portions75A and75B and protrude toward the other side in the first direction (the lower side inFIG.21B). As shown inFIG.21B, the plate thickness (radial thickness) of the elastic member22is constant throughout the base portion73, the pair of arm portions75A and75B, and the projection portions74and74.

As shown inFIG.21B, the base portion73has a planar radially outer surface73aand a radially inner surface73bextending in the third direction. Therefore, the base portion73has a substantially flat plate shape extending in the third direction. The elastic member22is assembled to the holder21to be externally fitted to the base portion51of the pad20and the two guide portions43(refer toFIG.11and the like), but since the base portion73is flat, it is possible to easily determine the phase with respect to the holder21using the base portion73as a reference.

As shown inFIG.21D, the base portion73has a constricted portion76of which the plate width in the second direction is L1. The plate width L1of the constricted portion76of the base portion73is smaller than plate widths L2and L3of a base portion side wide portion77and a tip end portion side wide portion78of the arm portions75A and75B (L1<L2=L3), which will be described later. As described above, since the base portion73has the constricted portion76and has a partially constricted shape, when the elastic member22is assembled to the holder21, the phase can be easily determined with respect to the holder21using the constricted portion76as a reference. Note that the constricted portion76of the base portion73does not contribute to adjusting the set load of the elastic member22, unlike narrow portions79and79of the pair of arm portions75A and75B, which will be described later.

Note that the method for determining the phase between the elastic member22and the holder21is not limited to the above-described method using the flat shape of the base portion73as a reference or the method using the constricted portion76as a reference, but any method such as imprinting a mark may be used. Therefore, as long as the phase can be determined, the base portion73does not necessarily have to have a substantially flat plate shape extending in the third direction, and may have a curved shape. When the phase can be determined, the base portion73does not necessarily have to include the constricted portion76having the plate width L1, and may have the same plate width as the plate widths L2and L3of the base portion side wide portion77and the tip end portion side wide portion78of the arm portions75A and75B, which will be described later.

The pair of arm portions75A and75B include a radially outer surface75cand a radially inner surface75dthat are connected to the radially outer surface73aand the radially inner surface73bof the base portion73, respectively. The radially outer surface75cand the radially inner surface75dare each formed of a single curved surface having the same radius of curvature.

The pair of arm portions75A and75B include the base portion side wide portion77connected to the base portion73and having a plate width of L2in the second direction, a narrow portion79connected to the base portion side wide portion77and having a plate width of L4in the second direction, and the tip end portion side wide portion78connected to the narrow portion79and having a plate width of L3in the second direction. Note that the base portion side wide portion77is disposed on one side in the first direction (the upper side inFIG.21B) from the center O of the elastic member22, the narrow portion79is disposed to overlap the center O of the elastic member in the first direction, and the tip end portion side wide portion78is disposed on the other side in the first direction (the lower side inFIG.21B) from the center O of the elastic member22. Here, the plate width L2of the base portion side wide portion77and the plate width L3of the tip end portion side wide portion78are the same (L2=L3). The plate width L4of the narrow portion79is smaller than the plate widths L2and L3of the base portion side wide portion77and the tip end portion side wide portion78(L4<L2=L3).

The plate width in the second direction of the projection portion74that is continuous with the tip end portion side wide portion78is equal to the plate width L3of the tip end portion side wide portion78. Note that the projection portion74does not necessarily have to be provided.

As such, in the elastic member22of the present embodiment, the narrow portion79, having the plate width L4smaller than those of the base portion side wide portion77and the tip end portion side wide portion78on both sides in the circumferential direction, is provided at the circumferentially intermediate portion of the pair of arm portions75A and75B, and the set load of the elastic member22is appropriately set by the narrow portion79. That is, by providing the narrow portion79, the set load of the elastic member22is reduced, and the friction at the meshing portion between the wheel teeth25and the worm teeth26is reduced.

The base portion side wide portion77and the tip end portion side wide portion78having the plate widths L2and L3equal to each other are provided on both side portions of the pair of arm portions75A and75B in the circumferential direction. Therefore, as shown inFIGS.22A to22C, when performing stack packing in which the plurality of elastic members22are stacked in the second direction, by causing the entire circumferential areas of the base portion side wide portion77and the tip end portion side wide portion78of the upper and lower elastic members22to abut against each other, the postures of the plurality of elastic members22can be maintained appropriately without being tilted with respect to the direction of gravity. Note that the projection portion74provided integrally with the tip end portion side wide portion78and having the plate width L3also abuts against the projection portion74of the upper and lower elastic members22.

In the present embodiment, to stack and pack the plurality of elastic members22, the plate widths L2and L3are set to be the same at four locations including the tip end portion side wide portions78and78(and the projection portions74and74provided integrally with the tip end portion side wide portions78and78) provided on the tip end portion sides of the pair of arm portions75A and75B, respectively, and the base portion side wide portions77and77provided on the base portion sides of the pair of arm portions75A and75B, respectively, and the elastic members22are supported at the four locations.

However, the present invention is not limited thereto, and to stack and pack the plurality of elastic members22, the plate widths of at least three locations needs to be the same. For example, by not providing the constricted portion76in the base portion73and making the plate width of the base portion73the same as the plate width L2of the base portion side wide portions77and77, the base portion side wide portions77and77of the pair of arm portions75A and75B and the base portion73may be integrally formed with the plate width of L2. Here, the plate widths L2and L3are set to be the same at the three locations including the two locations of the tip end portion side wide portions78and78of the pair of arm portions75A and75B, and one location of the base portion side wide portions77and77and the base portion73of the pair of integrally formed arm portions75A and75B, and the elastic members22stacked at the three locations are appropriately supported without tilting each other.

Comparative Example

FIGS.23A to23Dare diagrams showing the elastic member according to a comparative example, withFIG.23Ashowing a view from one side in the third direction,FIG.23Bshowing a view in the second direction,FIG.23Cshowing a view from the other side in the third direction, andFIG.23Dshowing a view in the first direction.FIGS.24A to24Care diagrams showing a stacked state of the elastic members according to the comparative example, withFIG.24Ashowing a perspective view,FIG.24Bshowing a view in the first direction, andFIG.24Cshowing a view in the third direction.

In the elastic member22A according to the comparative example, the pair of arm portions75A and75B has the base portion side wide portion77connected to the base portion73and having a plate width of L2in the second direction, and the narrow portion79connected to the base portion side wide portion77and having a plate width of L4in the second direction. That is, the pair of arm portions75A and75B is not provided with the tip end portion side wide portion78connected to the narrow portion79and having a plate width of L3in the second direction, as in the third embodiment described above. Here, the projection portion74is continuous with the narrow portion79, and the plate width of the projection portion74in the second direction is equal to the plate width L4of the narrow portion79.

In the elastic member22A of the comparative example, the narrow portion79having the plate width L4smaller than the plate width L2of the base portion side wide portion77is provided at a part other than the base portion side wide portion77, and a set load of the elastic member22is set by the narrow portion79. That is, by providing the narrow portion79, the set load of the elastic member22is reduced, and the friction at the meshing portion between the wheel teeth25and the worm teeth26is reduced.

As described above, the elastic member22A of the comparative example is excellent in that the set load can be adjusted, but has a problem in that the elastic member22A cannot be stacked and packed. As shown inFIGS.24A to24C, when stack packing is performed by stacking the plurality of elastic members22A in the second direction, the base portion side wide portions77and77of the upper and lower elastic members22come into contact with each other, and at the same time, the tip end portions (the projection portions74and74) of the narrow portions79and79come into contact with each other. Here, since the plate width L4of the narrow portions79and79(projection portions74and74) is smaller than the plate width L2of the base portion side wide portions77and77, as the elastic members22A are stacked, the elastic members22A are tilted toward the narrow portions79and79(the projection portions74and74). Therefore, the elastic member22A of the comparative example is not suitable for stack packing.

In each of the embodiments described above, the holder has two holder inclined surfaces (holder engagement portions) at positions sandwiching the pad from both sides in the third direction, the pad has two pad engagement portions (pad inclined surfaces) that come into contact with the two holder engagement portions on both side portions in the third direction, and the displacement of the pad in the third direction with respect to the holder is regulated based on the contact between the two holder engagement portions and the two pad engagement portions. However, at least one holder inclined surface (holder engagement portion) and one pad engagement portion (pad inclined surface) needs to be provided. That is, a structure may be adopted in which the holder may have a holder engagement portion in at least one of the positions sandwiching the pad from both sides in the third direction orthogonal to both the first direction that is an urging direction of the elastic member and the second direction that is the axial direction of the worm accommodation portion, the pad may have a pad engagement portion that comes into contact with the holder engagement portion in at least a part of both side portions in the third direction, and displacement of the pad in the third direction with respect to the holder is regulated based on the contact between the holder engagement portion and the pad engagement portion.

In each of the embodiments described above, a structure is adopted in which the two holder engagement portions are configured by two holder inclined surfaces, and the two pad engagement portions are configured by two pad inclined surfaces that are in surface contact with the two holder inclined surfaces. However, when implementing the present invention, when it is possible to regulate (reduce or prevent) displacement of the pad in the third direction with respect to the holder based on the contact between the two holder engagement portions and the two pad engagement portions, the holder engagement portion and the pad engagement portion are not limited to the holder inclined surface and the pad inclined surface, and may have any shape. When adopting a holder inclined surface and a pad inclined surface, the inclined surfaces are not limited to an inclined flat surface, but an inclined curved surface can also be adopted.

Although various embodiments were described with reference to the drawings, it is needless to say that the present invention is not limited to such examples. It is obvious that those skilled in the art can come up with various examples of changes or modifications within the scope of the claims, which are also naturally understood that the examples of changes or modifications belong to the technical scope of the present invention. Each configuration element in the above-described embodiment may be combined in any manner within the range that does not depart from the gist of the invention.

REFERENCE SIGNS LIST

1Electric power steering device2Steering wheel3Steering shaft4Steering column5a,5bUniversal joint6Intermediate shaft7Steering gear unit8Electric assist device9Pinion shaft10Rack shaft11Housing12Rack accommodation portion13Pinion accommodation portion14Worm reducer15Electric motor16Housing17Worm wheel18Worm19Support bearing20Pad21Holder22Elastic member23Wheel accommodation portion24Worm accommodation portion25Wheel teeth26Worm teeth27Female spline portion28Output shaft29Male spline portion30Ball bearing31Small diameter cylindrical surface portion32Large diameter cylindrical surface portion33Inner ring34Outer ring35Ball36Bush37Tubular portion38Side plate portion39Protrusion portion40Bearing holding surface41Protrusion42Fitting surface43Guide portion44Connection portion45,45aHolder inclined surface (holder engagement portion)46Inner surface47Holder pressed surface48,48aPad inclined surface (pad engagement portion)49Pad elastic pressing portion50Pad elastic pressing plate51Base portion52Flat plate portion53Through-hole54Base main body55Base projection portion56Pressed portion57Flange portion58a.58bProtrusion59Slit60Fitting surface61Inner circumferential surface62Recess portion71Discontinuous portion73Base portion73aRadially outer surface73bRadially inner surface74Projection portion75A,75B Arm portion75cRadially outer surface75dRadially inner surface76Constricted portion77Base portion side wide portion78Tip end portion side wide portion79Narrow portion100Worm reducer101Housing102Worm wheel103Worm104Wheel accommodation portion105Worm accommodation portion106Wheel teeth107Rotary shaft108Worm teeth109a,109bBall bearing110Holder111Large diameter portion112Bush113Electric motor114Pad115Torsion coil spring