Patent ID: 12252192

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of a steering device according to the present invention will be described below with reference to the drawings. In each of the following embodiments, an example in which the steering device is applied as an integral-type power steering device used for a large vehicle such as a truck is illustrated.

First Embodiment

(Configuration of Steering Device)

FIG.1is a first embodiment of a steering device according to the present invention, showing a longitudinal cross section of the steering device PS1cut along a rotation center of a steering shaft2.FIG.2shows a cross section of the steering device PS1cut along a plane A-A ofFIG.1. In the following description, a side where the steering shaft2is linked to a steering wheel (not shown) in a rotation axis X direction of the steering shaft2ofFIG.1is referred to as “one end side”, and a side where the steering shaft2is linked to a ball nut4is referred to as “the other end side”. Also, a side where a sector shaft3is linked to steered wheels (not shown) in a rotation axis Y direction of the sector shaft3ofFIG.2is referred to as “one end side”, and a side where the sector shaft3is linked to the ball nut4is referred to as “the other end side”.

As illustrated inFIGS.1and2, the steering device PS1is a well-known ball nut-type steering device, and has the steering shaft2linked to the steering wheel (not shown) and the sector shaft3linked to the steered wheels (not shown). These steering shaft2and sector shaft3are accommodated in a housing1. The ball nut4is interposed between the steering shaft2and the sector shaft3. Rotation of the steering shaft2is then converted to rotation of the sector shaft3through the ball nut4.

The housing1has a first housing11, a second housing12and a third housing13. The first housing11functions as a housing body that accommodates therein the steering shaft2, the sector shaft3and the ball nut4. That is, the first housing11has a substantially cylindrical steering shaft accommodation part111that extends in the rotation axis X direction and accommodates the steering shaft2and the ball nut4and a substantially cylindrical sector shaft accommodation part112that extends in the rotation axis Y direction orthogonal to the rotation axis X and accommodates the sector shaft3.

As illustrated inFIG.1, the steering shaft accommodation part111has a bottomed cylindrical shape in which one end side in the rotation axis X direction of the steering shaft accommodation part111is open to the outside through a first opening111a, and the other end side of the steering shaft accommodation part111is closed by an end wall111b. The first opening111ais closed by the second housing12that is fitted into the first opening111a.

The second housing12has a cylindrical shape whose outside diameter is reduced stepwise toward the other end side. The second housing12has a second housing body121that abuts on an end surface of the first opening111aand a second housing fitting portion122whose diameter is reduced stepwise with respect to the second housing body121and which is fitted into the first opening111a. A first seal member S1that can elastically abut on an inner circumferential surface of the first opening111ais attached to an outer circumferential side of the second housing fitting portion122. By this first seal member S1elastically abutting on the inner circumferential surface of the first opening111a, liquid tightness of an inside of the steering shaft accommodation part111is maintained.

Further, the second housing12has a steering shaft insertion hole123penetrating a middle portion of the second housing12. The steering shaft2is then inserted in the steering shaft accommodation part111from the outside through this steering shaft insertion hole123. The steering shaft insertion hole123is formed so that an inside diameter of the steering shaft insertion hole123is reduced stepwise from the one end side toward the other end side. The steering shaft insertion hole123has a large diameter hole portion123ahaving a relatively large diameter at the one end side and a small diameter hole portion123bhaving a relatively small diameter at the other end side. A steering shaft bearing113such as a ball bearing is accommodated in the large diameter hole portion123aof the steering shaft insertion hole123, and the steering shaft2is rotatably supported by this steering shaft bearing113.

The steering shaft bearing113has an inner race113aformed integrally with a second steering shaft22, an outer race113binserted into the large diameter hole portion123aand a plurality of ball members113cinterposed between the inner race113aand the outer race113b. The outer race113bis held in a state in which movement of the outer race113bin an axial direction is restricted by a lock nut114screwed into the large diameter hole portion123a.

As illustrated inFIG.2, the sector shaft accommodation part112is arranged substantially tangentially to the steering shaft accommodation part111. The sector shaft accommodation part112is formed so as to be able to communicate with the steering shaft accommodation part111by sharing a part in a circumferential direction of the sector shaft accommodation part112with the steering shaft accommodation part111. One end side in the rotation axis Y direction of the sector shaft accommodation part112is open to the outside through a second opening112a, and the other end side of the sector shaft accommodation part112is open to the outside through a third opening112b.

That is, at the sector shaft accommodation part112, one end portion of the sector shaft3inserted into the sector shaft accommodation part112through the third opening112bfaces the outside through the second opening112a, and is connected to a pitman arm (not shown) outside the housing1. On the other hand, the third opening112bis closed by the third housing13that is fitted into the third opening112bafter inserting the sector shaft3into the sector shaft accommodation part112through the third opening112b.

The third housing13has a cylindrical shape whose outside diameter is reduced stepwise toward the one end side. The third housing13has a third housing body131that abuts on an end surface of the third opening112band a third housing fitting portion132whose diameter is reduced stepwise with respect to the third housing body131and which is fitted into the third opening112b. A second seal member S2that can elastically abut on an inner circumferential surface of the third opening112bis attached to an outer circumferential side of the third housing fitting portion132. By this second seal member S2elastically abutting on the inner circumferential surface of the third opening112b, liquid tightness of an inside of the sector shaft accommodation part112is maintained.

Further, the third housing13has, at an inner circumferential side of the third housing fitting portion132, a bottomed cylindrical shaft supporting portion133for rotatably supporting the other end portion of the sector shaft3. The shaft supporting portion133has a third housing cylindrical portion134being open to the one end side and a third housing end wall135closing the other end side of the third housing cylindrical portion134.

As illustrated inFIG.1, the steering shaft2has a first steering shaft21whose one end side is connected to the steering wheel (not shown) and the second steering shaft22which is connected to the other end side of the first steering shaft21so as to be able to relatively rotate through a torsion bar23with a part of the second steering shaft22overlapping the first steering shaft21in a radial direction. The first steering shaft21is connected to the torsion bar23through a first pin member241that penetrates the other end portion of the first steering shaft21in the radial direction. Likewise, the second steering shaft22is connected to the torsion bar23through a second pin member242that penetrates the other end portion of the second steering shaft22in the radial direction.

It is noted that the steering shaft2could be mechanically connected to the steering wheel (not shown), or may be electrically connected to the steering wheel (not shown) by well-known steer-by-wire, although these drawings are omitted in the present embodiment. Further, the steering shaft2can be applied to not only a case where the steering shaft2is connected to the steering wheel (not shown) and a steering torque is input to the steering shaft2through the steering wheel by manual drive, but also a case where the steering shaft2is connected to a motor (not shown) and a steering torque is input to the steering shaft2through the motor by automatic drive. The case of the manual drive includes a case where a steering torque is input to the steering shaft2from the steering wheel (not shown) and also a steering assist torque is input to the steering shaft2from a motor (not shown).

As illustrated inFIG.2, the sector shaft3has a sector shaft portion31extending along the rotation axis Y direction that crosses the rotation axis X of the steering shaft2at a substantially right angle and a sector gear32arranged at the other end portion of the sector shaft portion31so as to face the ball nut4. The sector shaft portion31and the sector gear32are formed integrally with each other, and when the sector gear32rotates, the sector shaft portion31also rotates integrally with the sector gear32.

One end side of the sector shaft portion31with respect to the sector gear32is formed as a large diameter shaft portion311having a relatively large diameter, and the other end side with respect to the sector gear32is formed as a small diameter shaft portion312having a relatively small diameter. One end side of the large diameter shaft portion311is connected to the pitman arm (not shown), and the other end side of the large diameter shaft portion311is rotatably supported by a large diameter bearing331that is accommodated at an inner circumferential side of the second opening112a. That is, since the large diameter shaft portion311provides large torque to the steered wheels (not shown) through the pitman arm (not shown) connected to the one end portion of the large diameter shaft portion311, the diameter of the large diameter shaft portion311is formed relatively large in order to ensure rigidity that can resist the large torque exerted on the large diameter shaft portion311.

Further, a large diameter seal member341that can liquid-tightly seal a gap between an outer circumferential surface of the large diameter shaft portion311and an inner circumferential surface of the second opening112ais provided at one end side of the large diameter bearing331. With this, an outflow of hydraulic fluid filling an inside of the housing1(the sector shaft accommodation part112) to the outside through the second opening112ais suppressed.

On the other hand, the small diameter shaft portion312is rotatably supported by a small diameter bearing332that is accommodated at an inner circumferential side of the third housing cylindrical portion134. That is, the small diameter shaft portion312is a portion that rotatably supports the other end side of the sector shaft3, and since large torque like the large torque exerted on the large diameter shaft portion311is not exerted on the small diameter shaft portion312and there is no need to ensure high rigidity that can resist the large torque, the diameter of the small diameter shaft portion312is formed relatively small.

Further, a small diameter seal member342that can liquid-tightly seal a gap between an outer circumferential surface of the small diameter shaft portion312and an inner circumferential surface of the third housing cylindrical portion134is provided at the other end side of the small diameter bearing332. With this, an outflow of the hydraulic fluid filling the inside of the housing1(the sector shaft accommodation part112) to the outside through an after-described female screw hole136is suppressed.

As illustrated inFIGS.1and2, the sector gear32has a connection base portion320that is provided between the large diameter shaft portion311and the small diameter shaft portion312and connected to the large diameter shaft portion311and the small diameter shaft portion312, a first sector tooth321, a second sector tooth322and a third sector tooth323that are provided at a side portion of the connection base portion320so as to face rack teeth42of the ball nut4. The first sector tooth321protrudes along a Z-axis direction orthogonal to the rotation axis X and the rotation axis Y in a neutral state of the sector gear32. The second sector tooth322protrudes in a right oblique direction of the first sector tooth321toward the one end side of the rotation axis X. The third sector tooth323protrudes in a left oblique direction of the first sector tooth321toward the other end side of the rotation axis X.

The sector gear32is formed as a so-called tapered gear. That is, as depicted inFIG.2, a first tooth bottom325positioned between the first sector tooth321and the second sector tooth322and a second tooth bottom326positioned between the first sector tooth321and the third sector tooth323are formed so as to have such tapered surfaces that tooth heights T of the first to third sector teeth321to323gradually increase toward the one end side of the sector shaft3.

With the configuration of the tapered gear, the female screw hole136penetrating the third housing end wall135along the rotation axis Y is formed at the third housing end wall135, and an adjustment screw5is screwed into this female screw hole136from the other end side of the third housing13(from the outside). This adjustment screw5is screwed with the adjustment screw being in contact with the other end portion (the small diameter shaft portion312) of the sector shaft3, then the adjustment screw5moves forward to the one end side and forces the sector shaft3to the one end side. That is, by screwing the adjustment screw5and moving the sector shaft3to the one end side, gaps between the first and second tooth bottoms325and326and second and third rack teeth422and423are reduced (become narrow), thereby reducing backlash of the sector gear32with respect to the rack teeth42.

As described above, in the present embodiment, a backlash adjustment mechanism which is configured by the sector gear32formed by the tapered gear and the adjustment screw5forcing the sector shaft3and which can adjust the backlash between the sector gear32and the rack teeth42by manual operation of rotation (screwing) of the adjustment screw5is provided. With this backlash adjustment mechanism, when maintaining or servicing a vehicle, it is possible to adjust the backlash between the sector gear32and the rack teeth42which increases due to wear etc. of the sector gear32and the rack teeth42.

As illustrated inFIGS.1and2, the ball nut4is cylindrical in shape, and a shaft hole41is formed at the ball nut4along the rotation axis X direction. That is, the ball nut4is provided so as to be able to move forward and backward (or upward and downward) in the rotation axis X direction through a plurality of balls43interposed between a shaft-side ball groove401that is provided at an outer circumferential side of the second steering shaft22accommodated in the steering shaft accommodation part111and a nut-side ball groove402that is provided at an inner circumferential side (in the shaft hole41) of the ball nut4. At an outside portion of the ball nut4in the rotation axis X direction, the rack teeth42(after-described first to fourth rack teeth421to424) that are engaged with the sector gear32are formed in a predetermined range facing the sector gear32. Further, at the outside portion of the ball nut4in the rotation axis X direction, a cylindrical tube member44connecting one end side and the other end side of the nut-side ball groove402for circulating the plurality of balls43is arranged on a back surface side of the rack teeth42, i.e. on an opposite side to the rack teeth42with respect to the rotation axis X.

As illustrated inFIG.1, the rack teeth42has the first rack tooth421, the second rack tooth422, the third rack tooth423and the fourth rack tooth424that are arranged parallel to each other along the rotation axis X direction at the side portion of the ball nut4which faces the sector gear32. Between the second rack tooth422and the third rack tooth423, a first rack tooth bottom425which is a specific tooth bottom facing the first sector tooth321which is a central tooth is formed. Between the first rack tooth421and the second rack tooth422, a second rack tooth bottom426which faces the second sector tooth322is formed. Between the third rack tooth423and the fourth rack tooth424, a third rack tooth bottom427which faces the third sector tooth323is formed.

The ball nut4functions as a piston of a power cylinder operated by hydraulic pressure of hydraulic fluid filling an inside of the steering shaft accommodation part111, and is slidably provided in the steering shaft accommodation part111. That is, at the inside of the steering shaft accommodation part111, two hydraulic chambers, i.e. a first hydraulic chamber P1and a second hydraulic chamber P2which face each other in the rotation axis X direction with respect to the ball nut4, are defined by the ball nut4. The second hydraulic chamber P2is formed so as to be able to communicate with the sector shaft accommodation part112via a communication hole115provided at the first housing11. The hydraulic fluid in the second hydraulic chamber P2is introduced into the sector shaft accommodation part112, thereby lubricating the sector gear32and the rack teeth42(the gaps between the sector gear32and the rack teeth42).

Further, a well-known rotary valve RV as a control valve that can selectively provide the hydraulic fluid, which is supplied by a hydraulic pressure source (e.g. a pump) (not shown) according to a relative rotation of the first steering shaft21and the second steering shaft22, to the first hydraulic chamber P1or the second hydraulic chamber P2of the power cylinder is configured at an inside of the second housing12. The rotary valve RV has a rotor210formed integrally with the other end portion of the first steering shaft21and a sleeve220provided at an outer circumferential side of the rotor210and formed integrally with one end portion of the second steering shaft22.

At an inner circumferential side of the second housing12, an introduction port124a, a supply port124band a discharge port124cas circumferential direction grooves extending along a circumferential direction of the rotation axis X are arranged parallel to each other in the rotation axis X direction. Further, an introduction passage124dconnecting an introduction pipe (not shown) and the introduction port124aand a discharge passage124econnecting the discharge port124cand a discharge pipe (not shown) are provided at the inside of the second housing12. Also, at the insides of the first housing11and the second housing12, a supply passage L connecting the supply port124band the first hydraulic chamber P1is formed so as to span the first housing11and the second housing12. More specifically, the supply passage L is configured by a first housing supply passage116provided at the inside of the first housing11and a second housing supply passage126provided at the inside of the second housing12and connecting the supply port124band the first housing supply passage116. The introduction port124ais connected to the hydraulic pressure source (not shown) via the introduction passage124dand the introduction pipe (not shown). The supply port124bis connected to the first hydraulic chamber P1via the supply passage L. The discharge port124cis connected to a reservoir tank (not shown) via the discharge passage124eand the discharge pipe (not shown).

At an outer circumferential side of the rotor210, supply recessed portions210aand discharge recessed portions (not shown) each extending in a vertical groove shape along the rotation axis X direction are alternately arranged parallel to each other in the circumferential direction. Likewise, at an inner circumferential side of the sleeve220, right steering recessed portions220aand left steering recessed portions (not shown) each extending in a vertical groove shape along the rotation axis X direction are alternately arranged parallel to each other in the circumferential direction. The sleeve220is provided with a first communication passage221, a second communication passage222, a supply communication passage223and a discharge communication passage224so that these passages communicate with an inner circumference and an outer circumference of the sleeve220. The first communication passage221is open to the right steering recessed portions220a. The second communication passage222is open to the left steering recessed portions (not shown). The supply communication passage223or the discharge communication passage224is open to protruding portions (not shown) arranged between the right steering recessed portions220aand the left steering recessed portions (not shown) in the circumferential direction, and these supply communication passage223and discharge communication passage224are alternately arranged in the circumferential direction.

As illustrated inFIGS.1and2, a preload applying mechanism6that adjusts engagement between the sector gear32and the rack teeth42in the vicinity of a neutral position (a position shown inFIG.1) of the sector shaft3which corresponds to a straight-ahead steering state is provided between the sector gear32and the rack teeth42. In the present embodiment, as depicted inFIGS.1and2, a case where the preload applying mechanism6is disposed at the ball nut4side will be described. Particularly as depicted inFIG.2, the preload applying mechanism6according to the present embodiment is provided at a position of one end side in a tooth width direction of the first rack tooth bottom425as the specific tooth bottom engaged with the first sector tooth321as the central tooth and at a position of a side facing one end side of the first sector tooth321close to the large diameter shaft portion311.

(Configuration of Preload Applying Mechanism)

FIG.3shows an enlarged view of the preload applying mechanism6, which is a main part ofFIG.1, and its vicinity.

As illustrated inFIG.3, the preload applying mechanism6has a plunger receiving hole60formed at the first rack tooth bottom425, a plunger61accommodated in the plunger receiving hole60so as to be able to move forward and backward and a forcing member62interposed between a bottom of the plunger receiving hole60and a bottom of the plunger61and forcing the plunger61toward the first sector tooth321.

The plunger receiving hole60has a substantially circular cross section. One end of the plunger receiving hole60is open to the first rack tooth bottom425, and the other end is closed by a bottom wall600. The plunger receiving hole60is a round hole (or a circular hole) having a constant inside diameter in an axial direction. A ring-shaped annular member63is press-fitted into the plunger receiving hole60from the opening side.

Therefore, the plunger receiving hole60is formed into a tapered stepped diameter shape. That is, the plunger receiving hole60has a large diameter hole portion601provided at the bottom wall600side and having a relatively large diameter and a small diameter hole portion602provided at the opening side and formed at an inner circumferential side of the annular member63and having a relatively small diameter. Between the large diameter hole portion601and the small diameter hole portion602, a stopper630that restricts a forward-moving amount of the plunger61, i.e. a protruding amount of the plunger61protruding from the small diameter hole portion602, by coming into contact with a large diameter portion611of the plunger61is formed by the annular member63.

In a state in which a rotation phase of the sector shaft3is in the vicinity of the neutral position, the stopper630does not come into contact with the plunger large diameter portion611(does not abut on the plunger large diameter portion611), and allows contact of the plunger61with the first sector tooth321(allows the plunger61to abut on the first sector tooth321) (seeFIG.4A). On the other hand, in a state in which the rotation phase of the sector shaft3exceeds the vicinity of the neutral position, the stopper630comes into contact with the plunger large diameter portion611, and restricts the contact of the plunger61with the first sector tooth321(seeFIG.4C).

The plunger61is formed as a single-piece member with resin material, and formed into a tapered shape whose outside diameter is reduced stepwise toward its top end. More specifically, the plunger61has the plunger large diameter portion611received and accommodated in the large diameter hole portion601of the plunger receiving hole60and a plunger small diameter portion612slidably provided in the small diameter hole portion602of the plunger receiving hole60. The plunger large diameter portion611faces the bottom wall600of the plunger receiving hole60, and functions as a seating surface of the forcing member62. On the other hand, the plunger small diameter portion612protrudes from the small diameter hole portion602of the plunger receiving hole60and faces the outside, and faces the first sector tooth321. A top end portion of the plunger small diameter portion612has a gentle curved surface, and when the sector shaft3rotates, the top end portion of the plunger small diameter portion612can smoothly come into sliding-contract with a tooth surface of the first sector tooth321.

One end portion of the forcing member62is seated on the bottom wall600of the plunger receiving hole60, and the other end is seated on the plunger large diameter portion611, then the forcing member62is accommodated between the bottom wall600of the plunger receiving hole60and the plunger large diameter portion611with a predetermined pressurization given to the forcing member62. That is, the forcing member62is given the predetermined pressurization so that even when the plunger large diameter portion611abuts on the stopper630, a forcing force of the forcing member62acts on the plunger61. The forcing member62then constantly applies the forcing force to the plunger61. In the present embodiment, the forcing member62is configured by stacking a plurality of well-known disc springs in series. It is noted that the forcing member62is not limited to the plurality of stacked disc springs like the present embodiment. As long as a forcing member such as a coil spring can continuously force the plunger61, its material and shape or form can be arbitrarily changed.

(Description of Working of Preload Applying Mechanism)

FIGS.4A to4Care drawings showing change of the protruding amount of the plunger61according to a steering state.FIG.4Ais the neutral state in which a steering angle is 0 degree.FIG.4Bis a steering state in which the steering angle 12 degrees.FIG.4Cis a steering state in which the steering angle 25 degrees.

As illustrated inFIG.4A, in the neutral state in which the steering angle is 0 degree, the plunger61is in a retracted state, the plunger large diameter portion611separates from the stopper630, and a top end surface of the plunger small diameter portion612elastically abuts on a tooth tip of the first sector tooth321by the forcing force of the forcing member62. In this state, by a reaction force generated by the elastic abutting of the plunger61on the tooth tip of the first sector tooth321, the ball nut4is forced to one side in the rotation direction of the ball nut4. As a result, at the other end side of the sector gear32, a gap C between the first sector tooth321and the first rack tooth bottom425is reduced. With this, engagement (or mesh) between the first sector tooth321and the second and third rack teeth422,423becomes deeper, then backlash between the first sector tooth321and the second and third rack teeth422,423is reduced.

As illustrated inFIG.4B, in the steering state in which the steering angle 12 degrees, the plunger61is in a forward-moving state, the plunger large diameter portion611is in a state immediately before coming into contact with the stopper630, and the top end (a tip) of the plunger small diameter portion612elastically abuts on the tooth tip of the first sector tooth321by the forcing force of the forcing member62. In this state, as compared with the neutral state, a relatively small forcing force due to extension of the forcing member62by the forward-movement of the plunger61acts on the plunger61. That is, by a reaction force generated by elastic abutting of the plunger61on the tooth tip of the first sector tooth321by the forcing force that is smaller than that of the neutral state, the ball nut4is forced to the one side in the rotation direction of the ball nut4. As a result, at the other end side of the sector gear32, the gap C between the first sector tooth321and the first rack tooth bottom425is reduced, then backlash between the first sector tooth321and the second and third rack teeth422,423is reduced.

As illustrated inFIG.4C, in the steering state in which the steering angle 25 degrees, the plunger61is in the most forward-moving state, the plunger large diameter portion611abuts on the stopper630and the forward-movement of the plunger61is restricted, and the top end of the plunger small diameter portion612separates from the tooth tip of the first sector tooth321. In this state, since the forcing force does not act on the ball nut4, the gap C between the first sector tooth321and the first rack tooth bottom425does not change, and backlash between the first sector tooth321and the second and third rack teeth422,423is not adjusted.

Working and Effect of the Present Embodiment

In the conventional steering device, the plunger provided at the inside of the ball nut so as to be able to be forced toward the sector gear elastically abuts on the plunger sliding-contact portion provided adjacent to the sector gear and having the predetermined cam profile, and by the reaction force from the plunger sliding-contact portion generated by this elastic contact (elastic abutment), the ball nut is forced to the one side in the rotation direction, then the preload applying mechanism reduces backlash between the rack teeth and the sector gear in the vicinity of the neutral position of the sector shaft. However, in the case of the conventional steering device, it is necessary to provide the plunger sliding-contact portion separately from the sector gear. Because of this, there is still room for improvement in that a size of the sector shaft in the axial direction is increased by a size of the plunger sliding-contact portion.

In contrast to this, the steering device PS1according to the present embodiment has: the rack teeth42formed at the outer side of the ball nut4screwed onto the steering shaft2(the second steering shaft22) linked to the steering wheel (not shown); the sector gear32provided at the sector shaft3linked to the steered wheels (not shown) and having the plurality of sector teeth (the first sector tooth321, the second sector tooth322and the third sector tooth323) including the central tooth (the first sector tooth321) most deeply engaged (or meshed) with the rack teeth42in the neutral position state of the sector shaft3which corresponds to the straight-ahead steering state, which are provided in the circumferential direction of the sector shaft3and which are engaged (or meshed) with the rack teeth42(the sector gear32is engaged with the rack teeth42by the plurality of sector teeth (321,322and323) including the central tooth (321)); and the preload applying mechanism6adjusting engagement between the rack teeth42and the sector gear32in the vicinity of the neutral position of the sector shaft3. The preload applying mechanism6is provided at the one end portion in the tooth width direction of the specific tooth bottom (the first rack tooth bottom425) of the rack teeth42, which faces the tooth tip of the central tooth (the first sector tooth321) when the sector shaft3is in the vicinity of the neutral position. The preload applying mechanism6forces the ball nut4to the one side in the rotation direction of the ball nut4by the reaction force generated by the elastic contact of the preload applying mechanism6with the tooth tip of the central tooth (the first sector tooth321).

As described above, the present embodiment is configured to provide a rotation torque to the one side in the rotation direction of the ball nut4by the reaction force generated by the elastic contact (elastic abutment) of the plunger61with (on) the tooth tip of the first sector tooth321of the sector gear32. Therefore, in the present embodiment, unlike the conventional steering device, there is no need to provide a pressed portion to be pressed by the plunger61separately from the sector gear32. Increase in size of the sector shaft3due to formation of the pressed portion can therefore be suppressed.

Further, in the present embodiment, the preload applying mechanism6has the plunger receiving hole60formed at the specific tooth bottom (the first rack tooth bottom425), the plunger61which is accommodated in the plunger receiving hole60so as to be able to move forward and backward and whose top end side can protrude from the opening, which faces the sector gear32, of the plunger receiving hole60, and the forcing member62interposed between the bottom (the bottom wall600) of the plunger receiving hole60and the plunger61and forcing the plunger61toward the central tooth (the first sector tooth321).

That is, in the present embodiment, the preload applying mechanism6is configured by only the plunger receiving hole60formed at the ball nut4, the forcing member62and the plunger61both accommodated in the plunger receiving hole60. Then, by pressing the tooth tip of the first sector tooth321of the sector gear32by the plunger61, the rotation torque to the ball nut4is generated.

As described above, in the present embodiment, the preload applying mechanism6has a simple configuration formed by only the plunger61, the forcing member62and the plunger receiving hole60accommodating therein these plunger61and forcing member62. Therefore, in the present embodiment, unlike the conventional steering device, there is no need to process (machine) or form the pressed portion of the plunger61. The preload applying mechanism6can therefore be configured at a relatively low cost, thereby reducing a manufacturing cost of the steering device PS1.

Also, in the present embodiment, the plunger61has the large diameter portion (the plunger large diameter portion611) sliding in the plunger receiving hole60, and the small diameter portion (the plunger small diameter portion612) whose diameter is reduced stepwise with respect to the large diameter portion (the plunger large diameter portion611) and which can protrude from the opening of the plunger receiving hole60. The plunger receiving hole60has the stopper630which is formed by reducing an inside diameter of the opening to be smaller than the outside diameter of the large diameter portion (the plunger large diameter portion611) and which restricts the protruding amount of the small diameter portion (the plunger small diameter portion612) by coming into contact with the large diameter portion (the plunger large diameter portion611). In the state in which the rotation phase of the sector shaft3is in the vicinity of the neutral position, the large diameter portion (the plunger large diameter portion611) does not come into contact with the stopper630, and contact of the plunger61with the central tooth (the first sector tooth321) is allowed. On the other hand, in the state in which the rotation phase of the sector shaft3exceeds the vicinity of the neutral position, the large diameter portion (the plunger large diameter portion611) comes into contact with the stopper630, and the contact of the plunger61with the central tooth (the first sector tooth321) is restricted.

That is, the present embodiment is configured so that when the rotation phase of the sector shaft3is in the vicinity of the neutral position of the steering, the contact of the plunger61with the first sector tooth321is allowed, whereas when the rotation phase of the sector shaft3exceeds the vicinity of the neutral position, the contact of the plunger61with the first sector tooth321is restricted by the stopper630.

As described above, in the present embodiment, by restricting the protruding amount of the plunger61by the stopper630, only in the vicinity of the neutral position of the sector shaft3which requires rigidity, the engagement between the rack teeth42and the sector gear32can be adjusted. In other words, except when the sector shaft3is in the vicinity of the neutral position which does not particularly require the rigidity, by restricting the contact of the plunger61with the first sector tooth321, deterioration of steering feeling, such as so-called grinding feeling caused by sliding-contact of the plunger61with the first sector tooth321, can be suppressed.

In the present embodiment, the stopper630is structured only by narrowing the opening of the plunger receiving hole60by the annular member63. Therefore, in the present embodiment, unlike the conventional steering device, it is possible to restrict the protruding amount of the plunger61by the relatively simple structure without forming the complicated or sophisticate cam profile, which can contribute to reduction in the manufacturing cost of the steering device PS1.

Further, in the present embodiment, the tooth bottom (the first tooth bottom325and the second tooth bottom326) of the sector gear32has such tapered surface that the tooth height T of the sector gear32gradually increases toward the one end side in the axial direction of the sector shaft3. The sector shaft3is configured to be movable to the one end side in the axial direction of the sector shaft3by the adjustment screw5screwed from the other end side in the axial direction of the sector shaft3through the female screw hole136formed at the end wall (the third housing13) of the housing1(the first housing11) accommodating therein the sector shaft3.

As described above, in the present embodiment, the sector gear32has the tapered gear shape in which the first tooth bottom325and the second tooth bottom326of the sector gear32are the tapered surfaces, and by moving the sector shaft3to the one end side in the axial direction by the adjustment screw5, the engagement between the rack teeth42and the sector gear32can be adjusted. With this, not only in the vicinity of the neutral position of the sector shaft3, but also in the entire rotation range of the sector shaft3, proper engagement between the rack teeth42and the sector gear32can be ensured.

Modified Example

FIG.5is a modified example of the first embodiment of the present invention. In this modified example, arrangement of the preload applying mechanism6of the first embodiment is changed, but the other configuration is the same as that of the first embodiment. Therefore, the same structure or configuration as that of the first embodiment is denoted by the same reference sign, and its detailed description is omitted here.

FIG.5is a steering device PS1′ according to the modified example of the first embodiment of the present invention, showing a cross section of the steering device PS1′, which corresponds to the sectional view taken along the plane A-A ofFIG.1.

As illustrated inFIG.5, in the steering device PS1′ according to the modified example, the plunger receiving hole60is provided at a position of the other end side in the tooth width direction of the first rack tooth bottom425, and the plunger61is provided at a position of a side facing the other end side of the first sector tooth321close to the small diameter shaft portion312.

With this configuration, in the preload applying mechanism6of the steering device PS1′ according to the modified example, in the vicinity of the neutral position of the sector shaft3, the plunger61arranged at the other end side in the tooth width direction of the first rack tooth bottom425elastically abuts on the tooth tip of the first sector tooth321of the sector gear32by the forcing force of the forcing member62. In this state, by a reaction force generated by the elastic abutting of the plunger61on the first sector tooth321by the forcing force of the forcing member62, the ball nut4is forced to the other side in the rotation direction of the ball nut4. As a result, at the one end side of the sector gear32, a gap C between the first sector tooth321and the first rack tooth bottom425is reduced, then backlash between the first sector tooth321and the second and third rack teeth422,423is reduced.

As described above, in the steering device PS1′ according to the modified example, one end side in the axial direction of the sector shaft3with respect to the sector gear32, which is the side connected to the pitman arm (not shown), is formed so as to have a relatively large diameter, and the other end side in the axial direction of the sector shaft3with respect to the sector gear32is formed so as to have a relatively small diameter as compared with that of the one end side in the axial direction of the sector shaft3. The plunger receiving hole60is provided at one of the both end portions in the tooth width direction of the specific tooth bottom (the first rack tooth bottom425), which corresponds to the other end side in the axial direction of the sector shaft3.

That is, in the present modified example, the plunger receiving hole60forming the preload applying mechanism6is arranged at the small diameter shaft portion312side where the diameter of the sector shaft3is relatively small. Therefore, a space in which the preload applying mechanism6can be arranged is expanded by a space equivalent to the reduction in diameter of the sector shaft portion31like the small diameter shaft portion312, and the preload applying mechanism6can be arranged at a position farther away from a rotation center of the ball nut4. With this, a greater rotation torque can be provided to the ball nut4, thereby adjusting the engagement between the first sector tooth321and the second and third rack teeth422,423more effectively.

Second Embodiment

FIGS.6to8show a second embodiment of the steering device according to the present invention. In the present embodiment, arrangement of the preload applying mechanism6of the first embodiment is changed, but the other configuration is the same as that of the first embodiment. Therefore, the same structure or configuration as that of the first embodiment is denoted by the same reference sign, and its detailed description is omitted here.

FIG.6is the second embodiment of the steering device according to the present invention, showing a longitudinal cross section of the steering device PS2cut along the rotation center of the steering shaft2.FIG.7shows a cross section of the steering device PS2cut along a plane A-A ofFIG.6.FIG.8shows an enlarged view of the preload applying mechanism6, which is a main part ofFIG.6, and its vicinity.

As illustrated inFIGS.6to8, in the steering device PS2according to the present embodiment, the preload applying mechanism6is provided not on the rack teeth42side like the first embodiment, but on the sector gear32side. More specifically, the plunger receiving hole60of the preload applying mechanism6according to the present embodiment is provided at the tooth tip of one end portion (an end portion close to the large diameter shaft portion311) in a tooth width direction of the first sector tooth321as the central tooth. The preload applying mechanism6is then configured so that in the vicinity of the neutral position of the sector shaft3, the plunger61forced by the forcing force of the forcing member62can elastically abut on the one end side in the tooth width direction of the first rack tooth bottom425.

With such configuration, in the preload applying mechanism6of the steering device PS2according to the present embodiment, in the vicinity of the neutral position of the sector shaft3, the plunger61arranged at the one end side in the tooth width direction of the first sector tooth321elastically abuts on the first rack tooth bottom425by the forcing force of the forcing member62. In this state, by a forcing force generated by the elastic abutting of the plunger61on the first rack tooth bottom425by the forcing force of the forcing member62, the ball nut4is forced to the one side in the rotation direction of the ball nut4. As a result, at the other end side of the sector gear32, a gap C between the first sector tooth321and the first rack tooth bottom425is reduced, then backlash between the first sector tooth321and the second and third rack teeth422,423is reduced.

As described above, in the steering device PS2according to the present embodiment, in particular, the preload applying mechanism6is provided at the one end portion in the tooth width direction of the central tooth (the first sector tooth321), and by the forcing force generated by the elastic abutment on (the elastic contact with) the specific tooth bottom (the first rack tooth bottom425) of the rack teeth42which faces the tooth tip of the central tooth (the first sector tooth321) in the vicinity of the neutral position of the sector shaft3, the ball nut4is forced to the one side in the rotation direction of the ball nut4.

Therefore, also in the present embodiment, in the same manner as the first embodiment, a rotation torque can be provided to the one side in the rotation direction of the ball nut4by the forcing force generated by the elastic contact (elastic abutment) of the plunger61with (on) the first rack tooth bottom425. Thus, unlike the conventional steering device, there is no need to provide a pressed portion to be pressed by the plunger61separately from the sector gear32. As a result, increase in size of the sector shaft3due to formation of the pressed portion can be suppressed.

Modified Example

FIG.9is a modified example of the second embodiment of the present invention. In this modified example, arrangement of the preload applying mechanism6of the second embodiment is changed, but the other configuration is the same as that of the second embodiment. Therefore, the same structure or configuration as that of the second embodiment is denoted by the same reference sign, and its detailed description is omitted here.

FIG.9is a steering device PS2′ according to the modified example of the second embodiment of the present invention, showing a cross section of the steering device PS2′, which corresponds to the sectional view taken along the plane A-A ofFIG.6.

As illustrated inFIG.9, in the steering device PS2′ according to the modified example, the plunger receiving hole60is provided at a position of the other end side in the tooth width direction of the first sector tooth321, and the preload applying mechanism6is provided at a position of a side facing the other end side of the first rack tooth bottom425close to the small diameter shaft portion312.

With such configuration, in the preload applying mechanism6of the steering device PS2′ according to the present embodiment, in the vicinity of the neutral position of the sector shaft3, the plunger61arranged at the other end side in the tooth width direction of the first sector tooth321elastically abuts on the first rack tooth bottom425by the forcing force of the forcing member62. In this state, by a forcing force generated by the elastic abutting of the plunger61on the first rack tooth bottom425by the forcing force of the forcing member62, the ball nut4is forced to the other side in the rotation direction of the ball nut4. As a result, at the one end side of the sector gear32, a gap C between the first sector tooth321and the first rack tooth bottom425is reduced, then backlash between the first sector tooth321and the second and third rack teeth422,423is reduced.

As described above, in the steering device PS2′ according to the modified example, one end side in the axial direction of the sector shaft3with respect to the sector gear32, which is the side connected to the pitman arm (not shown), is formed so as to have a relatively large diameter, whereas the other end side in the axial direction of the sector shaft3with respect to the sector gear32is formed so as to have a relatively small diameter as compared with that of the one end side in the axial direction of the sector shaft3. The plunger receiving hole60is provided at one of the both end portions in the tooth width direction of the central tooth (the first sector tooth321), which corresponds to the other end side in the axial direction of the sector shaft3.

That is, in the present modified example, the plunger receiving hole60forming the preload applying mechanism6is arranged at the small diameter shaft portion312side where the diameter of the sector shaft3is relatively small. Therefore, a space in which the preload applying mechanism6can be arranged is expanded by a space equivalent to the reduction in diameter of the sector shaft portion31like the small diameter shaft portion312, and the preload applying mechanism6can be arranged at a position farther away from a rotation center of the ball nut4. With this, a greater rotation torque can be provided to the ball nut4, thereby adjusting the engagement between the first sector tooth321and the second and third rack teeth422,423more effectively.

Third Embodiment

FIG.10shows a third embodiment of the steering device according to the present invention. In the present embodiment, a shape of the sector gear32of the modified example of the first embodiment is changed, but the other configuration is the same as that of the first embodiment. Therefore, the same structure or configuration as that of the first embodiment is denoted by the same reference sign, and its detailed description is omitted here.

FIG.10is the third embodiment of the steering device according to the present invention, showing a cross section of the steering device PS3, which corresponds to the sectional view taken along the plane A-A ofFIG.1.

As illustrated inFIG.10, in the steering device PS3according to the present embodiment, the backlash adjustment mechanism is removed, and the tooth bottom of the sector gear32is formed as a flat surface parallel to the rotation axis Y of the sector shaft3so that the tooth height T of the sector gear32is substantially constant.

As described above, in the present embodiment, the tooth bottom of the sector gear32has a straight shape parallel to the rotation axis Y of the sector shaft3. That is, the present embodiment is configured so that unlike the first embodiment, without forming the tooth bottom of the sector gear32into the tapered shape and without providing the mechanism (the backlash adjustment mechanism) adjusting the engagement between the rack teeth42and the sector gear32other than the preload applying mechanism6, the engagement between the rack teeth42and the sector gear32is adjusted by only the preload applying mechanism6. Therefore, the structure or configuration of the steering device PS3is simplified, thereby contributing to improvement in productivity of the steering device PS3and reduction in the manufacturing cost of the steering device PS3.

Further, in the present embodiment, by the removal of the backlash adjustment mechanism, the female screw hole136of the third housing13can be removed. As a result, a problem of leaking the hydraulic fluid filling the inside of the sector shaft accommodation part112to the outside through the female screw hole136can be suppressed.

Fourth Embodiment

FIG.11shows a fourth embodiment of the steering device according to the present invention. In the present embodiment, a shape of the sector gear32of the modified example of the second embodiment is changed, but the other configuration is the same as that of the second embodiment. Therefore, the same structure or configuration as that of the second embodiment is denoted by the same reference sign, and its detailed description is omitted here.

FIG.11is the fourth embodiment of the steering device according to the present invention, showing a cross section of the steering device PS4, which corresponds to the sectional view taken along the plane A-A ofFIG.6.

As illustrated inFIG.11, in the steering device PS4according to the present embodiment, the backlash adjustment mechanism is removed, and the tooth bottom of the sector gear32is formed as a flat surface parallel to the rotation axis Y of the sector shaft3so that the tooth height T of the sector gear32is substantially constant.

As described above, also in the present embodiment, in the same manner as the third embodiment, the tooth bottom of the sector gear32has a straight shape parallel to the rotation axis Y of the sector shaft3. Then, the present embodiment is configured so that the engagement between the rack teeth42and the sector gear32is adjusted by only the preload applying mechanism6without providing the mechanism (the backlash adjustment mechanism) adjusting the engagement between the rack teeth42and the sector gear32other than the preload applying mechanism6. Therefore, the structure or configuration of the steering device PS4is simplified, thereby contributing to improvement in the productivity of the steering device PS4and reduction in the manufacturing cost of the steering device PS4.

Further, in the same manner as the third embodiment, by the removal of the backlash adjustment mechanism, the female screw hole136of the third housing13can be removed. Therefore, a problem of leaking the hydraulic fluid filling the inside of the sector shaft accommodation part112to the outside through the female screw hole136can be suppressed.

The present invention is not limited to the structure or configuration of the above embodiments and modified examples. Not only detail of structure or configuration of the steering device, which is not directly related to the structure or configuration of the present invention, such as structure or configuration of the steering shaft2, an input configuration to the steering shaft2and shapes of the sector gear32and the rack teeth42, but also structure or configuration of the preload applying mechanism6, which is directly related to the structure or configuration of the present invention, such as shape, structure or configuration of the plunger61and the forcing member62, can be freely changed according to a steering device to which the present invention is applied and specification of the vehicle without departing from the scope of the present invention.