JP2022108908A - Rack-and-pinion mechanism - Google Patents

Abstract

To suppress an increase in friction force between a rack guide and a rack bar in a rack-and-pinion mechanism including a plurality of pinions.SOLUTION: A rack-and-pinion mechanism includes: a rack guide 10 disposed on an axial position of a first pinion gear 5a and configured to press a rack tooth 6a against the first pinion gear 5a by a guide portion 11 slidable on a back surface of a rack bar 6; a rolling rack guide 30 disposed on an axial position of a second pinion gear 23a in an axial direction and configured to press a rack tooth 6b against the second pinion gear 23a by a roller 32 coming into rolling-contact with the back surface of the rack bar 6; and a pair of rack bushes 40, 41 disposed on both sides in an axial direction of the rolling rack guide 30 and supporting the rack bar 6 such that the rack bar is axially slidable.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rack and pinion mechanism.

Patent Document 1 below discloses a position where a second pinion rotated by a manual steering force applied by a driver meshes with a rack shaft, and a position where a first pinion rotated by a steering assist force generated by an electric motor meshes with a rack shaft. Each describes a steering device with a sliding rack guide.

Patent No. 6120047

Since the sliding rack guide slides against the rear surface of the rack bar and presses the rack teeth against the pinion gear, sliding friction is generated between the sliding rack guide and the rack bar. Therefore, if a sliding rack guide is arranged at each position where a plurality of pinions mesh with the rack bar, there is a problem that the force required to drive the rack bar increases.
The present invention has been made in view of such problems, and an object of the present invention is to suppress an increase in frictional force between a rack guide and a rack bar in a rack and pinion mechanism having a plurality of pinions. do.

To achieve the above object, a rack and pinion mechanism according to one aspect of the present invention includes a first pinion that has a first pinion gear and is rotatably supported around an axis, and a second pinion gear that rotates around an axis. a rack bar having a second pinion supported thereon and rack teeth meshing with the first pinion gear and the second pinion gear; A sliding rack guide that presses the rack teeth against the first pinion gear at a guide part that slides on the . A rolling type rack guide that presses against the second pinion gear, and a pair of rack bushings that are provided on both sides in the axial direction of the rolling type rack guide and support the rack bar so as to be slidable in the axial direction.

ADVANTAGE OF THE INVENTION According to this invention, in the rack-and-pinion mechanism which has a several pinion, it can suppress that the frictional force between a rack guide and a rack bar increases. In addition, it is possible to reduce the abrasion of the sliding contact portion between the rack guide and the rack bar, and increase the rigidity of the meshing portion between the pinion gear and the rack teeth.

1 is a configuration diagram showing an overview of an example of a steering mechanism including a rack and pinion mechanism according to an embodiment; FIG. 1 is a schematic cross-sectional view of an example of a sliding rack guide; FIG. 1 is a schematic cross-sectional view of an example of a rolling rack guide; FIG. (a) is a conceptual diagram showing an example of temporal changes in steering torque applied by a driver, (b) is a conceptual diagram showing an example of temporal changes in assist torque in response to temporal changes in steering torque, (c) is a conceptual diagram showing an example of temporal change in frictional force generated in the rack guide.

Embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the embodiments of the present invention shown below are examples of apparatuses and methods for embodying the technical idea of the present invention. are not specific to the following: Various modifications can be made to the technical idea of the present invention within the technical scope defined by the claims.

(First embodiment)
(Constitution)
FIG. 1 is a configuration diagram showing an outline of an example of a steering mechanism provided with a rack and pinion mechanism according to the first embodiment. The steering mechanism of the first embodiment has an electric power steering device 1 that applies steering assist torque to a steering system of a vehicle by an actuator (for example, an electric motor).
In the electric power steering device 1, a steering shaft (steering shaft, handle shaft) 3 of a steering wheel (steering handle) 2 includes universal joints 4a and 4b, a first pinion shaft 5, a first pinion gear 5a, a rack bar 6, and a tie rod. It is connected to steerable wheels 8L, 8R via 7L, 7R.

On the other hand, the rotary shaft 21, which is the output shaft of the electric motor 20, is connected to the steerable wheels 8L, 8R via the speed reduction mechanism 22, the second pinion shaft 23, the second pinion gear 23a, the rack bar 6, the tie rods 7L, 7R. , the steering assist torque generated by the electric motor 20 is transmitted to the steered wheels 8L, 8R. The speed reduction mechanism 22 includes, for example, a drive gear 22a (eg, a worm shaft) connected to a rotating shaft 27, and a driven gear 22b (eg, a worm wheel) that meshes with the drive gear 22a and is connected to the second pinion shaft 23 so as to rotate integrally therewith. etc.).
In addition, the structure which provides a rotational driving force to the 2nd pinion shaft 23 and the 2nd pinion gear 23a is not restricted to said structure. The second pinion shaft 23 and the second pinion gear 23a can be rotationally driven by various actuators other than the electric motor and various power transmission mechanisms.

As shown, the first pinion shaft 5 and the first pinion gear 5a, and the second pinion shaft 23 and the second pinion gear 23a are arranged in the axial direction of the rack bar 6 (hereinafter sometimes simply referred to as "axial direction"). are arranged on both sides in the axial direction across the center C of the .
A first rack tooth 6a that meshes with the first pinion gear 5a is formed in a range R1 of the rack bar 6 in the axial direction, and a second rack tooth 6a that meshes with the second pinion gear 23a is formed in a range R2 of the rack bar 6 in the axial direction. Two rack teeth 6b are formed.
there is

A rack housing 9 that houses the rack bar 6 is provided with a sliding rack guide 10 at an axial position of the first pinion gear 5a in the axial direction. The sliding rack guide 10 has a guide portion that presses the first rack tooth 6a against the first pinion gear 5a by slidingly contacting the rear surface of the rack bar 6. As shown in FIG.
On the other hand, the rack housing 9 is provided with a rolling rack guide 30 at the axial position of the second pinion gear 23a in the axial direction. The rolling rack guide 30 has a roller that presses the second rack tooth 6b against the second pinion gear 23a by rolling contact with the rear surface of the rack bar 6. As shown in FIG.

The “back surface” of the rack bar 6 refers to the surface of the outer peripheral surface of the rack bar 6 that is opposite to the first rack tooth 6a and the second rack tooth 6b in the radial direction of the rack bar 6. As shown in FIG.
In the following description, the first pinion gear 5a and the second pinion gear 23a are collectively referred to as "pinion gear", the first rack teeth 6a and the second rack teeth 6b are collectively referred to as "rack teeth", The sliding rack guide 10 and the rolling rack guide 30 may be collectively referred to as "rack guide".

FIG. 2 is a schematic cross-sectional view of an example of the sliding rack guide 10. As shown in FIG. In FIG. 2, the Z direction is the axial direction of the rack bar 6, the X direction is the rack guide axial direction in which the sliding rack guide 10 presses the first rack tooth 6a against the first pinion gear 5a, and the Y direction is the X direction. and a direction perpendicular to the Z direction.
A rack guide screw 12 of the sliding rack guide 10 is attached to the rack housing 9 . For example, a thread groove provided on the outer peripheral surface of the rack guide screw 12 meshes with a thread groove provided on the inner peripheral surface of the rack housing 9 . The elastic member 15 is arranged between the rack guide screw 12 and the guide portion 11 . The elastic member 15 is, for example, a coil spring.
The elastic member 15 presses the guide portion 11 against the rear surface of the rack bar 6 so that the guide portion 11 slides against the rear surface of the rack bar 6 and presses the first rack tooth 6a against the first pinion gear 5a.
A locking groove 16 is formed in the outer peripheral surface of the guide portion 11 , and an elastic ring (for example, an O-ring) 17 is locked in the locking groove 16 . By providing such an elastic ring 17, it is possible to prevent the guide portion 11 from rattling and to prevent foreign matter such as muddy water from entering the inside of the sliding rack guide 10. - 特許庁

FIG. 3 is a schematic cross-sectional view of an example of the rolling rack guide 30. As shown in FIG. In FIG. 3, the Z direction is the axial direction of the rack bar 6, the X direction is the rack guide axial direction in which the rolling rack guide 30 presses the second rack tooth 6b against the second pinion gear 23a, and the Y direction is the X direction. and a direction perpendicular to the Z direction.
The rolling rack guide 30 includes pins 31 , rollers 32 and a substantially cylindrical holder 33 .
A roller 32 supporting the rack bar 6 is rotatably held via a needle bearing 35 on a pin 31 inserted into a pin insertion groove 34 formed on the inner surface of a substantially cylindrical holder 33 . As a result, the roller 32 is brought into rolling contact with the rear surface of the rack bar 6, and the second rack tooth 6b is pressed against the second pinion gear 23a.
A locking groove 36 is formed on the outer peripheral surface of the holder 33 , and an elastic ring (for example, an O-ring) 37 is locked in the locking groove 36 . By providing such an elastic ring 37, it is possible to prevent the holder 33 from rattling and to prevent foreign matter such as muddy water from entering the inside of the rolling rack guide 30. FIG.

In the first embodiment, a rack guide (that is, a rack guide that presses the first rack tooth 6a against the first pinion gear 5a, A sliding rack guide 10 is employed as a "steering-side rack guide" below.
A rack guide (that is, a rack guide that presses the second rack tooth 6b against the second pinion gear 23a, hereinafter referred to as an "assist side A rolling rack guide 30 is arranged as a rack guide.
As a result, in a region where the rack bar 6 is moving and the steering assist torque by the electric motor 20 is relatively large, the frictional force generated between the rack bar 6 and the rack guide is reduced, and the force required to drive the rack bar is increased. can be suppressed. The reason is explained below.

The frictional force generated between the rack guide and the rack bar 6 while the rack bar 6 is moving is calculated by the following formula (1).
F'=μ'N (1)
In equation (1), F′ is dynamic friction force, μ′ is dynamic friction coefficient, and N is normal force acting on rack bar 6 in the rack guide axial direction (X direction).

Here, the relationship between the rotational torque generated in the pinion gear and the normal force will be described.
In the rack and pinion mechanism, when rotational torque is generated in the pinion gear, force acts on the rack bar 6 in a direction away from the pinion gear.
The force in the direction away from the pinion gear is a component force generated in the rack guide axial direction of the force transmitted from the pinion gear to the rack teeth.

Therefore, as the force transmitted from the pinion gear to the rack teeth increases, the force separating the rack bar 6 from the pinion gear increases. In other words, when the torque generated in the pinion gear increases, the force with which the rack bar 6 separates from the pinion gear increases, and the vertical force generated between the rack guide and the rack bar 6 also increases.

Here, in a region where the rack bar 6 is moving and the steering assist torque by the electric motor 20 is large, the rotational torque of the first pinion gear 5a rotationally driven by the steering wheel 2 is greater than the rotational torque of the second pinion gear 5a rotationally driven by the electric motor 20. The rotational torque of the pinion gear 23a is greater.

Therefore, the frictional force between the assist-side rack guide and the rack bar 6 tends to be greater than the frictional force between the steering-side rack guide and the rack bar 6 . As the sliding friction between the rack guide and the rack bar increases, the force required to drive the rack bar 6 increases.
Therefore, by arranging the rolling rack guide 30 having a small sliding resistance as the assist side rack guide and reducing the frictional force generated in the assist side rack guide, the friction generated in the entire rack bar 6 can be effectively reduced. can.
Also, the wear resistance of the sliding contact portion between the rack guide provided on the assist side rack guide and the rack bar 6 can be improved.

However, in the rolling rack guide 30, the holding force for holding the rack bar 6 in the Y direction orthogonal to the axial direction (Z direction) of the rack bar 6 and the axial direction (X direction) of the rack guide is It tends to be smaller than the rack guide 10.
This is because the rolling rack guide 30 has a structure in which a pin 31 is placed in a substantially cylindrical holder 33 and a roller 32 is arranged between the pin 31 and the rack bar 6, so the radial dimension of the roller 32 is This is because the concave portion of the roller 32 formed on the surface facing the rack bar 6 is shallower than the concave portion of the guide portion 11 (FIG. 2) of the sliding rack guide 10.

Therefore, in the rack and pinion mechanism of the first embodiment, a pair of rack bushings for slidably supporting the rack bar 6 are provided on both axial sides of the rolling rack guide 30 .
Thereby, the holding force in the Y direction for holding the rack bar 6 at the arrangement position of the rolling rack guide 30 can be increased. As a result, the rigidity of the meshing portion between the second pinion gear 23a and the second rack tooth 6b can be increased.

Refer to FIG. 1 again. The rack housing 9 is provided with a pair of rack bushes 40 and 41 on both axial sides of the rolling rack guide 30 . The rack bushes 40 and 41 support the rack bar 6 so as to be slidable in the axial direction.
The rack bushings 40 and 41 are cylindrical members to be inserted into the rack housing 9 . relative movement in the axial direction with respect to is restricted.
By inserting the rack bar 6 into the rack bushes 40 and 41 and interposing the rack bushes 40 and 41 in the gap between the rack housing 9 and the rack bar 6, the rack bar 6 is axially slidably supported.

For example, one rack bushing 40 of the pair of rack bushings 40 and 41 may be positioned between the sliding rack guide 10 and the rolling rack guide 30 and closer to the rolling rack guide 30 than the axial center C of the rack bar 6. It can be placed in close proximity.
By arranging the rack bushing 40 at a position close to the rolling rack guide 30, the holding force of the rack bar 6 in the Y direction at the arrangement position of the rolling rack guide 30 can be further increased.
For example, the pair of rack bushings 40 and 41 may be provided near both sides of the rolling rack guide 30 in the axial direction.

Further, for example, one of the pair of rack bushings 40 and 41, which is arranged between the sliding rack guide 10 and the rolling rack guide 30, may be placed between the rack bar 6 and the rack bar 6 when the rack bar 6 is in the neutral position. 6 may be arranged so as to support the range R2 in which the second rack teeth 6b are formed.
By arranging the rack bushing 40 at a position close to the rolling rack guide 30 in this way, the holding force of the rack bar 6 in the Y direction at the position where the rolling rack guide 30 is arranged can be further increased.
When the rack bar 6 is in the neutral position means when the steering mechanism is in the neutral position or when the steering wheel 2 is in the neutral position.

In the example of FIG. 1, the pair of rack bushings are provided only on both sides of the rolling rack guide 30 in the axial direction of the sliding rack guide 10 and the rolling rack guide 30. Not provided on both sides. This is because the holding force for the sliding rack guide 10 to hold the rack bar 6 in the Y direction can be easily increased compared to the case of the rolling rack guide 30 . However, as a modification, a pair of rack bushes may be provided on both sides of the sliding rack guide 10 in the axial direction.

(Effect of the first embodiment)
(1) The rack and pinion mechanism includes a first pinion shaft 5 having a first pinion gear 5a and supported rotatably around an axis, and a second pinion shaft 5 having a second pinion gear 23a and supported rotatably around an axis. A rack bar 6 having a pinion shaft 23, a first rack tooth 6a and a second rack tooth 6b meshing with the first pinion gear 5a and the second pinion gear 23a, and an axial direction of the first pinion gear 5a in the axial direction of the rack bar 6. A slide type rack guide 10 that presses the first rack tooth 6a against the first pinion gear 5a with a guide portion 11 that is disposed at a position and is in sliding contact with the rear surface of the rack bar 6, and a second pinion gear 23a in the axial direction. A rolling rack guide 30 that presses the second rack tooth 6b against the second pinion gear 23a with a roller 32 that is arranged and is in rolling contact with the rear surface of the rack bar 6; A pair of rack bushings 40 and 41 that support the bar 6 so as to be slidable in the axial direction are provided.

As a result, one of the rack guide that presses the first rack tooth 6a against the first pinion gear 5a and the rack guide that presses the second rack tooth 6b against the second pinion gear 23a is replaced with the rolling rack guide 30 with low sliding resistance. By doing so, it is possible to suppress an increase in the force required to drive the rack bar 6 due to friction between the rack guide and the rack bar 6 .
In addition, it is possible to reduce wear of the sliding contact portion between the rack guide provided at the axial position of the second pinion gear 23a and the rack bar 6. As shown in FIG.

By providing a pair of rack bushes 40 and 41 on both sides of the rolling rack guide 30 in the axial direction, the rack bar 6 is held at the position where the rolling rack guide 30 is arranged. The holding force in the direction perpendicular to the guide shaft direction) can be increased, and the rigidity of the meshing portion between the second pinion gear 23a and the second rack tooth 6b can be increased.

(2) The rack guide on the assist side may be the rolling rack guide 30, and the rack guide on the steering side may be the sliding rack guide 10.
In a region where the steering assist torque by the actuator is large, the rotational torque of the pinion gear on the assist side rotationally driven by the actuator is larger than that of the pinion gear on the steering side rotationally driven by the steering wheel 2 . Therefore, the frictional force between the assist-side rack guide and the rack bar 6 tends to increase.
By using the rolling type rack guide 30 as the assist side rack guide, the friction generated in the entire rack bar 6 can be effectively reduced.

(3) One rack bushing 41 of the pair of rack bushings 40 and 41 is positioned between the sliding rack guide 10 and the rolling rack guide 30 and further than the center C of the rack bar 6 in the axial direction. can be placed close to
By arranging the rack bushing 40 at a position close to the rolling rack guide 30 in this way, the holding force of the rack bar 6 in the Y direction at the position where the rolling rack guide 30 is arranged can be further increased.

(4) Of the pair of rack bushes 40 and 41, one of the rack bushes 40 arranged between the sliding rack guide 10 and the rolling rack guide 30 is moved to the rack bar 6 when the rack bar 6 is in the neutral position. 6 may be arranged so as to support the range R2 in which the second rack teeth 6b are formed.
By arranging the rack bushing 40 at a position close to the rolling rack guide 30 in this way, the holding force of the rack bar 6 in the Y direction at the position where the rolling rack guide 30 is arranged can be further increased.

(5) Of the sliding rack guide 10 and the rolling rack guide 30, the pair of rack bushes 40 and 41 may be provided only on both sides of the rolling rack guide 30 in the axial direction.
As a result, the holding force of the rack bar 6 in the Y direction at the position where the rolling rack guide 30 is arranged can be further increased.

(Second embodiment)
In the rack-and-pinion mechanism of the second embodiment, the rolling rack guide 30 is used as the steering-side rack guide, and the sliding rack guide 10 is used as the assist-side rack guide.
A pair of rack bushes 40 and 41 are provided on both sides in the axial direction of the rolling rack guide 30, which is the steering side rack guide.

As a result, the steering operation characteristics can be improved in a region where the steering assist torque by the electric motor 20 is relatively small, compared to the case where sliding rack guides are used for both the assist side rack guide and the steering side rack guide.
A specific example of the region where the assist torque is low is the region from when the driver starts steering until immediately after the electric motor 20 generates the steering assist torque (so-called start-up region).

In this movement area, the driver tends to feel a so-called clinging feeling. The clinging feeling is a feeling experienced by the driver when the amount of movement of the rack bar 6 that matches the steering torque applied by the driver cannot be obtained.
Normally, when the driver applies a relatively large steering torque, the driver expects the rack bar 6 to move greatly. I feel like

Typically, when the rack bar 6 is moved in the axial direction, the greater the frictional force generated in the direction opposite to the direction of movement, the greater the feeling of clinging to the driver.
When the rolling rack guide 30 is used as the steering-side rack guide and the sliding rack guide 10 is used as the assist-side rack guide, compared to the case where the sliding rack guides are used as both the assist-side rack guide and the steering-side rack guide, , the frictional force generated in the rack bar 6 can be effectively reduced in a region where the steering assist torque by the electric motor 20 is low, so that the clinging feeling can be reduced.

FIGS. 4(a) to 4(c) show the steering torque Tm and the electric motor 20 when the driver starts applying the steering torque Tm at time t1 and holds the steering torque Tm at a predetermined value at t4. FIG. 5 is a conceptual diagram showing temporal changes in assist torque (steering assist torque) Ta and frictional force generated in each rack guide.
As shown in FIG. 4(a), the steering torque Tm increases from time t1 and is maintained at a predetermined value at time t4. Further, as shown in FIG. 4B, the assist torque Ta starts increasing at time t2, which is slightly later than time t1, and is maintained at a predetermined value at time t5, which is slightly later than time t4.

Such a delay in the time change of the assist torque with respect to the time change of the steering torque is caused by the control calculation in the controller.
FIG. 4(c) is a diagram showing changes over time in the frictional force generated between each rack guide and the rack bar 6 when both the steering-side rack guide and the assist-side rack guide are sliding rack guides. is.

A solid line indicates the friction force generated in the assist side rack guide, which is a sliding rack guide, and a dashed line indicates the friction force generated in the steering side rack guide, which is a sliding rack guide.
As described above, the greater the rotational torque generated in the pinion, the greater the frictional force generated between the rack guide and rack bar 6 .

Therefore, the frictional force (broken line) generated in the steering-side rack guide increases at the same timing as the steering torque Tm increases from time t1 to time t4.
Further, the frictional force generated in the assist-side rack guide increases at the same timing as the assist torque Ta increases from time t2 to time t5.

Here, the illustrated time t3 is the time at which the frictional force generated in the steering-side rack guide and the frictional force generated in the assist-side rack guide coincide.
That is, from time t1 to t3, the frictional force generated in the steering-side rack guide is greater than the frictional force generated in the assist-side rack guide. Therefore, from time t1 to t3, the friction generated in the entire rack bar 6 can be effectively reduced by reducing the frictional force generated in the steering-side rack guide.

The dashed line in FIG. 4(c) is a diagram showing the change over time of the frictional force generated in the steering-side rack guide when a rolling rack guide is used as the steering-side rack guide. Since the rolling rack guide has a smaller coefficient of dynamic friction μ' than the sliding rack guide, the generated frictional force is smaller than when the sliding rack guide is used (dotted line).

(Effect of Second Embodiment)
In the rack and pinion mechanism of the second embodiment, the rolling rack guide 30 is used as the steering rack guide, and the sliding rack guide 10 is used as the assist rack guide.
As a result, it is possible to effectively reduce the frictional force generated in the rack bar 6 in a region in which the steering assist torque by the electric motor 20 is low, thereby reducing the clinging feeling experienced by the driver.

(Modification)
Also, in the above description, the case where the rack and pinion mechanism of the embodiment is applied to an electric power steering apparatus that applies steering assist torque to a steering system of a vehicle by means of an actuator has been described. However, the present invention is not limited to this, and is widely applicable to rack and pinion mechanisms having rack bars that mesh with at least two pinion gears. For example, it may be applied to a steer-by-wire (SBW) type steering system in which a steering wheel and steerable wheels are mechanically separated. In this case, one pinion gear may be connected to the steering wheel via a clutch, and an actuator that generates a steering force may be connected to the other pinion gear.

REFERENCE SIGNS LIST 1 electric power steering device 2 steering wheel 3 steering shaft 4a, 4b universal joint 5 first pinion shaft 5a first pinion gear 6 rack bar 6a first rack tooth 6b Second rack tooth 7L, 7R Tie rod 8L, 8R Steering wheel 9 Rack housing 10 Sliding rack guide 11 Guide part 12 Rack guide screw 15 Elastic member 20 Electric motor 21 Rotating shaft 22 Reduction mechanism 22a Drive gear 22b Driven gear 23 Second pinion shaft 23a Second pinion gear 30 Rolling rack guide 31 Pin 32 Roller , 33...holder, 34...pin insertion groove, 35...needle bearing, 40, 41...rack bush

Claims (6)

a first pinion that has a first pinion gear and is rotatably supported around an axis;
a second pinion having a second pinion gear and supported rotatably about an axis;
a rack bar having rack teeth meshing with the first pinion gear and the second pinion gear;
a sliding rack guide that is arranged at a position in the axial direction of the first pinion gear in the axial direction of the rack bar and that presses the rack teeth against the first pinion gear with a guide portion that is in sliding contact with the rear surface of the rack bar;
a rolling rack guide that is arranged in the axial direction of the second pinion gear in the axial direction and presses the rack teeth against the second pinion gear with a roller that is in rolling contact with the rear surface of the rack bar;
a pair of rack bushings provided on both sides of the rolling rack guide in the axial direction and supporting the rack bar so as to be slidable in the axial direction;
A rack and pinion mechanism comprising: 2. A rack and pinion mechanism according to claim 1, wherein said first pinion is connected to a steering wheel and driven to rotate, and said second pinion is connected to an actuator and driven to rotate. 2. A rack and pinion mechanism according to claim 1, wherein said first pinion is connected to an actuator and driven to rotate, and said second pinion is connected to a steering wheel and driven to rotate. One rack bushing of the pair of rack bushings is arranged between the sliding rack guide and the rolling rack guide and at a position closer to the rolling rack guide than the center of the rack bar in the axial direction. The rack and pinion mechanism according to any one of claims 1 to 3, characterized in that: The rack teeth have first rack teeth that mesh with the first pinion gear and second rack teeth that mesh with the second pinion gear,
One rack bushing of the pair of rack bushings is arranged between the sliding rack guide and the rolling rack guide, and when the rack bar is in a neutral position, the second rack bushing is attached to the rack bar. support where the teeth are formed,
The rack and pinion mechanism according to claim 2 or 3, characterized in that: 6. The pair of rack bushings according to any one of claims 1 to 5, wherein, of the sliding rack guide and the rolling rack guide, the pair of rack bushings are provided only on both sides of the rolling rack guide in the axial direction. The rack and pinion mechanism described in .

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