Rack and pinion mechanism

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

[Technical field]

[0001] The present invention relates to a rack and pinion mechanism. [Background technology]

[0002] The following Patent Document 1 describes a steering device in which a sliding rack guide is disposed at each of the positions where a second pinion, which rotates due to a manual steering force applied by a driver, meshes with a rack shaft, and where a first pinion, which rotates due to a steering assist force generated by an electric motor, meshes with the rack shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6120047 specification Summary of the Invention [Problem to be solved by the invention]

[0004] Since the sliding rack guide slides against the back surface of the rack bar and presses the rack teeth against the pinion gear, sliding friction occurs between the sliding rack guide and the rack bar. Therefore, if a sliding rack guide is provided at each of the positions where multiple pinions mesh with the rack bar, there is a problem in that the force required to drive the rack bar increases. The present invention has been made in consideration of such problems, and has an object to suppress an increase in friction force between a rack guide and a rack bar in a rack and pinion mechanism having multiple pinions. [Means for solving the problem]

[0005] In order to achieve the above-mentioned object, a rack and pinion mechanism according to one embodiment of the present invention comprises a first pinion having a first pinion gear and supported rotatably about 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 arranged at an axial position of the first pinion gear in the axial direction of the rack bar and pressing the rack teeth against the first pinion gear with a guide portion that slides against the back surface of the rack bar, a rolling rack guide arranged at an axial position of the second pinion gear in the axial direction and pressing the rack teeth against the second pinion gear with rollers that roll in contact with the back surface of the rack bar, and a pair of rack bushes provided on both axial sides of the rolling rack guide and supporting the rack bar so that it can slide freely in the axial direction. Effect of the Invention

[0006] According to the present invention, in a rack and pinion mechanism having multiple pinions, an increase in frictional force between the rack guide and the rack bar can be suppressed, wear at the sliding contact points between the rack guide and the rack bar can be reduced, and rigidity at the meshing points between the pinion gear and the rack teeth can be increased. [Brief description of the drawings]

[0007] [Figure 1] 1 is a configuration diagram illustrating an example of a steering mechanism including a rack-and-pinion mechanism according to an embodiment; [Diagram 2] FIG. 2 is a schematic cross-sectional view of an example of a sliding rack guide. [Diagram 3] FIG. 2 is a schematic cross-sectional view of an example of a rolling rack guide. [Figure 4] FIG. 1A is a conceptual diagram showing an example of change over time in steering torque applied by a driver, FIG. 1B is a conceptual diagram showing an example of change over time in assist torque corresponding to change over time in steering torque, and FIG. 1C is a conceptual diagram showing an example of change over time in friction force generated in a rack guide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the configuration, arrangement, etc. of the components to those described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims.

[0009] (First embodiment) (composition) 1 is a schematic diagram showing an example of a steering mechanism including a rack-and-pinion mechanism according to a first embodiment. The steering mechanism according to the first embodiment has an electric power steering device 1 that applies a 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 is connected to steered wheels 8L, 8R via universal joints 4a and 4b, a first pinion shaft 5, a first pinion gear 5a, a rack bar 6, and tie rods 7L, 7R.

[0010] On the other hand, the rotating shaft 21 which is the output shaft of the electric motor 20 is connected to the steered wheels 8L, 8R via the reduction mechanism 22, the second pinion shaft 23, the second pinion gear 23a, the rack bar 6, and the tie rods 7L, 7R, and transmits the steering assist torque generated by the electric motor 20 to the steered wheels 8L, 8R. The reduction mechanism 22 includes, for example, a drive gear 22a (e.g., a worm shaft or the like) connected to the rotating shaft 27, and a driven gear 22b (e.g., a worm wheel or the like) meshing with the drive gear 22a and connected to the second pinion shaft 23 so as to be rotatable together with it. The configuration for applying the rotational driving force to the second pinion shaft 23 and the second pinion gear 23a is not limited to the above configuration. The second pinion shaft 23 and the second pinion gear 23a can be rotationally driven by various actuators and various power transmission mechanisms other than the electric motor.

[0011] As shown in the figure, 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 on both sides of the axial center C of the rack bar 6 (hereinafter sometimes simply referred to as the "axial direction"). In a range R1 of the rack bar 6 in the axial direction, first rack teeth 6a that mesh with the first pinion gear 5a are formed, and in a range R2 of the rack bar 6 in the axial direction, second rack teeth 6b that mesh with the second pinion gear 23a are formed. There are.

[0012] Furthermore, a sliding rack guide 10 is provided in the rack housing 9 that accommodates the rack bar 6 at an axial position of the first pinion gear 5a in the axial direction. The sliding rack guide 10 has a guide portion that slides against the back surface of the rack bar 6 to press the first rack teeth 6a against the first pinion gear 5a. On the other hand, a rolling rack guide 30 is provided in the rack housing 9 at an axial position of the second pinion gear 23a in the axial direction. The rolling rack guide 30 includes a roller that comes into rolling contact with the back surface of the rack bar 6 to press the second rack teeth 6b against the second pinion gear 23a.

[0013] The "rear surface" of the rack bar 6 refers to the surface of the outer circumferential surface of the rack bar 6 that is opposite to the first rack teeth 6a and the second rack teeth 6b in the radial direction of the rack bar 6. In the following description, the first pinion gear 5a and the second pinion gear 23a may be collectively referred to as "pinion gears," the first rack teeth 6a and the second rack teeth 6b may be collectively referred to as "rack teeth," and the sliding rack guide 10 and the rolling rack guide 30 may be collectively referred to as "rack guides."

[0014] Fig. 2 is a schematic cross-sectional view of an example of the sliding rack guide 10. 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 teeth 6a against the first pinion gear 5a, and the Y direction is the direction perpendicular to the X and Z directions. The 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 circumferential surface of the rack guide screw 12 meshes with a thread groove provided on the inner circumferential surface of the rack housing 9. The elastic member 15 is disposed 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 back surface of the rack bar 6, causing the guide portion 11 to come into sliding contact with the back surface of the rack bar 6 and press the first rack teeth 6a against the first pinion gear 5a. An engagement groove 16 is formed on the outer circumferential surface of the guide portion 11, and an elastic ring (e.g., an O-ring) 17 is engaged in the engagement groove 16. Providing such an elastic ring 17 prevents the guide portion 11 from rattling, and also prevents foreign matter such as muddy water from entering the inside of the sliding rack guide 10.

[0015] Fig. 3 is a schematic cross-sectional view of an example of the rolling rack guide 30. 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 teeth 6b against the second pinion gear 23a, and the Y direction is the direction perpendicular to the X direction and the Z direction. The rolling rack guide 30 includes a pin 31, a roller 32, and a substantially cylindrical holder 33. The rollers 32 that support the rack bar 6 are rotatably held on the pins 31 inserted into the pin insertion grooves 34 formed on the inner surface of a substantially cylindrical holder 33 via needle bearings 35. As a result, the rollers 32 roll and come into contact with the back surface of the rack bar 6, and the second rack teeth 6b are pressed against the second pinion gear 23a. A locking groove 36 is formed on the outer circumferential surface of the holder 33, and an elastic ring (e.g., an O-ring) 37 is locked in the locking groove 36. Providing such an elastic ring 37 prevents the holder 33 from rattling and also prevents foreign matter such as muddy water from entering the inside of the rolling rack guide 30.

[0016] In the first embodiment, a sliding rack guide 10 is adopted as a rack guide (i.e., a rack guide that presses the first rack teeth 6a against the first pinion gear 5a; hereinafter, sometimes referred to as the "steering side rack guide") that is arranged in the axial position of the first pinion gear 5a that is connected to the steering wheel 2 and driven to rotate. In addition, a rolling rack guide 30 is disposed as a rack guide (i.e., a rack guide that presses the second rack teeth 6b against the second pinion gear 23a; hereinafter, this may be referred to as the "assist side rack guide") that is disposed in the axial position of the second pinion gear 23a that is connected to the electric motor 20 and driven to rotate. As a result, in a region where the rack bar 6 is moving and the steering assist torque from the electric motor 20 is relatively large, the frictional force generated between the rack bar 6 and the rack guide is reduced, and an increase in the force required to drive the rack bar can be suppressed. The reason for this will be explained below.

[0017] The friction 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 formula (1), F' is the kinetic friction force, μ' is the kinetic friction coefficient, and N is the normal force acting on the rack bar 6 in the rack guide axial direction (X direction).

[0018] Here, the relationship between the rotational torque generated in the pinion gear and the normal force will be described. In a rack and pinion mechanism, when a rotational torque is generated in the pinion gear, a force acts on the rack bar 6 in a direction away from the pinion gear. This 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.

[0019] Therefore, the greater the force transmitted from the pinion gear to the rack teeth, the greater the force moving the rack bar 6 away from the pinion gear. In other words, as the torque generated in the pinion gear increases, the force moving the rack bar 6 away from the pinion gear increases, and the normal force generated between the rack guide and the rack bar 6 also increases.

[0020] Here, in the region where the rack bar 6 is moving and the steering assist torque from the electric motor 20 is large, the rotational torque of the second pinion gear 23a, which is rotated and driven by the electric motor 20, is greater than the rotational torque of the first pinion gear 5a, which is rotated and driven by the steering wheel 2.

[0021] For this reason, 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. When the sliding friction between the rack guide and the rack bar becomes greater, the force required to drive the rack bar 6 increases. Therefore, by disposing the rolling-type rack guide 30, which has low 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. In addition, 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.

[0022] However, the rolling rack guide 30 tends to have a smaller holding force for holding the rack bar 6 in the Y direction perpendicular to the axial direction (Z direction) of the rack bar 6 and the rack guide axial direction (X direction) than the sliding rack guide 10. This is because the rolling rack guide 30 has a structure in which a pin 31 is inserted into an approximately cylindrical holder 33 and a roller 32 is arranged between the pin 31 and the rack bar 6, so there is a limit to the radial dimension of the roller 32 and the recess of the roller 32 formed on the surface facing the rack bar 6 is shallower than the recess of the guide portion 11 (Figure 2) of the sliding rack guide 10.

[0023] Therefore, in the rack and pinion mechanism of the first embodiment, a pair of rack bushes that slidably support the rack bar 6 are provided on both axial sides of the rolling rack guide 30. This makes it possible to increase the Y-direction holding force that holds the rack bar 6 at the arrangement position of the rolling rack guide 30. As a result, it is possible to increase the rigidity of the meshing portion between the second pinion gear 23a and the second rack teeth 6b.

[0024] 1 again, the rack housing 9 is provided with a pair of rack bushes 40, 41 on both axial sides of the rolling rack guide 30. The rack bushes 40, 41 support the rack bar 6 so that it is slidable in the axial direction. The rack bushings 40, 41 are cylindrical members that are inserted into the rack housing 9, and their relative axial movement with respect to the rack housing 9 is restricted by, for example, a configuration in which a flange on the outer peripheral surface of the cylindrical portion fits into a groove on the inner peripheral surface of the rack housing 9. The rack bar 6 is inserted into the rack bushes 40, 41, and the rack bushes 40, 41 are interposed in the gap between the rack housing 9 and the rack bar 6, whereby the rack bar 6 is supported so as to be slidable in the axial direction.

[0025] For example, one of the pair of rack bushes 40, 41 may be disposed between the sliding rack guide 10 and the rolling rack guide 30, and at a position closer to the rolling rack guide 30 than the axial center C of the rack bar 6. By arranging the rack bush 40 in 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 bushes 40, 41 may be provided near both axial sides of the rolling rack guide 30.

[0026] Also, for example, of the pair of rack bushes 40, 41, one of the rack bushes 40 arranged between the sliding rack guide 10 and the rolling rack guide 30 may be arranged so as to support the range R2 in which the second rack teeth 6b are formed on the rack bar 6 when the rack bar 6 is in the neutral position. In this way, by arranging the rack bush 40 in 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. Incidentally, when the rack bar 6 is in the neutral position, it means when the steering mechanism is in the neutral position or when the steering wheel 2 is in the neutral position.

[0027] 1, a pair of rack bushes are provided only on both axial sides of the rolling rack guide 30 out of the sliding rack guide 10 and the rolling rack guide 30, and are not provided on both axial sides of the sliding rack guide 10. This is because the holding force for the sliding rack guide 10 to hold the rack bar 6 in the Y direction can be made larger than that of the rolling rack guide 30. However, as a modified example, a pair of rack bushes may be provided on both axial sides of the sliding rack guide 10.

[0028] (Effects 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 about an axis, a second pinion shaft 23 having a second pinion gear 23a and supported rotatably about an axis, a rack bar 6 having first rack teeth 6a and second rack teeth 6b meshing with the first pinion gear 5a and the second pinion gear 23a, and a gear 21 disposed at an axial position of the first pinion gear 5a in the axial direction of the rack bar 6 and in sliding contact with the back surface of the rack bar 6. The rack bar 6 is provided with a sliding rack guide 10 that presses the first rack teeth 6a against the first pinion gear 5a with a guide portion 11 that presses the first rack teeth 6a against the first pinion gear 5a, a rolling rack guide 30 that is arranged at an axial position of the second pinion gear 23a in the axial direction and presses the second rack teeth 6b against the second pinion gear 23a with rollers 32 that roll in contact with the back surface of the rack bar 6, and a pair of rack bushes 40, 41 that are provided on both axial sides of the rolling rack guide 30 and support the rack bar 6 so that it can slide freely in the axial direction.

[0029] As a result, by using the rolling-type rack guide 30 with low sliding resistance as one of the rack guides pressing the first rack teeth 6a against the first pinion gear 5a and the rack guide pressing the second rack teeth 6b against the second pinion gear 23a, 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. Furthermore, wear at the sliding contact points between the rack bar 6 and a rack guide provided in the axial direction of the second pinion gear 23a can be reduced.

[0030] Furthermore, by providing a pair of rack bushings 40, 41 on both axial sides of the rolling rack guide 30, the holding force in the Y direction (a direction perpendicular to the axial direction of the rack bar 6 and the rack guide axial direction) that holds the rack bar 6 at the arrangement position of the rolling rack guide 30 is increased, and the rigidity of the meshing points between the second pinion gear 23a and the second rack teeth 6b can be increased.

[0031] (2) The assist side rack guide may be a rolling type rack guide 30, and the steering side rack guide may be a sliding type rack guide 10. In a region where the steering assist torque by the actuator is large, the rotational torque of the assist side pinion gear rotated and driven by the actuator is larger than that of the steering side pinion gear rotated and driven by the steering wheel 2. For this reason, the frictional force between the assist side rack guide and the rack bar 6 tends to become large. 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.

[0032] (3) One of the pair of rack bushes 40, 41, the rack bush 41, may be disposed between the sliding rack guide 10 and the rolling rack guide 30, and at a position closer to the rolling rack guide 30 than the axial center C of the rack bar 6. In this way, by arranging the rack bush 40 in 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.

[0033] (4) Of the pair of rack bushes 40, 41, one of the rack bushes 40 disposed between the sliding rack guide 10 and the rolling rack guide 30 may be disposed so as to support the range R2 in which the second rack teeth 6b are formed on the rack bar 6 when the rack bar 6 is in the neutral position. In this way, by arranging the rack bush 40 in 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.

[0034] (5) Of the sliding rack guide 10 and the rolling rack guide 30, a pair of rack bushes 40, 41 may be provided only on both axial sides of the rolling rack guide 30. This makes it possible to further increase the holding force of the rack bar 6 in the Y direction at the arrangement position of the rolling rack guide 30.

[0035] Second embodiment In the rack and pinion mechanism of the second embodiment, the steering side rack guide is a rolling type rack guide 30, and the assist side rack guide is a sliding type rack guide 10. A pair of rack bushes 40, 41 are provided on both axial sides of the rolling rack guide 30, which is the steering-side rack guide.

[0036] As a result, compared to when sliding rack guides are used for both the assist side rack guide and the steering side rack guide, the steering operation characteristics can be improved in a range where the steering assist torque from the electric motor 20 is relatively small. A specific example of a region where the assist torque is low is a region from when the driver starts steering until immediately after the electric motor 20 generates the steering assist torque (a so-called start-of-motion region).

[0037] In this start-of-motion region, the driver is likely to feel a so-called sticking sensation. The sticking sensation is a sensation that the driver feels when the amount of movement of the rack bar 6 does not correspond to the steering torque applied by the driver. Usually, when a driver applies a relatively large steering torque, the driver expects the rack bar 6 to move a large amount, but if the amount of movement of the rack bar 6 is small, the driver feels as if the rack bar 6 is stuck in its current position.

[0038] Typically, when the rack bar 6 is moved in the axial direction, the greater the frictional force that occurs in the direction opposite to the direction of movement, the greater the sticking sensation felt by the driver. When the rolling type rack guide 30 is used as the steering side rack guide and the sliding type rack guide 10 is used as the assist side rack guide, the friction force generated in the rack bar 6 can be effectively reduced in the range where the steering assist torque by the electric motor 20 is low, compared to when sliding type rack guides are used for both the assist side rack guide and the steering side rack guide, and therefore the feeling of sticking can be reduced.

[0039] Figures 4(a) to 4(c) are conceptual diagrams showing the changes over time in steering torque Tm, assist torque (steering assist torque) Ta by electric motor 20, and frictional force generated in each rack guide when the driver begins to apply steering torque Tm at time t1 and maintains steering torque Tm at a predetermined value at t4. As shown in Fig. 4(a), the steering torque Tm starts to increase from time t1 and is maintained at a predetermined value at time t4. As shown in Fig. 4(b), the assist torque Ta starts to increase from time t2, which is slightly delayed from time t1, and is maintained at a predetermined value at time t5, which is slightly delayed from time t4.

[0040] Such a delay in the time change of the assist torque relative to the time change of the steering torque occurs due to control calculations in the controller, etc. FIG. 4(c) is a diagram showing the change over time of 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.

[0041] The solid line indicates the friction force generated in the assist-side rack guide, which is a sliding type rack guide, and the dashed line indicates the friction force generated in the steering-side rack guide, which is also a sliding type 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 the rack bar 6.

[0042] For this reason, the friction force (dashed 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. Furthermore, as the assist torque Ta increases from time t2 to time t5, the frictional force generated in the assist side rack guide increases at the same timing.

[0043] Here, time t3 shown in the figure is the time when the frictional force generated in the steering side rack guide and the frictional force generated in the assist side rack guide match. That is, from time t1 to time t3, the frictional force generated in the steering side rack guide is larger than the frictional force generated in the assist side rack guide. Therefore, from time t1 to time t3, by reducing the frictional force generated in the steering side rack guide, it is possible to effectively reduce the friction generated in the entire rack bar 6.

[0044] The dashed-dotted line in Figure 4(c) shows the change over time in friction force generated in the steering-side rack guide when a rolling rack guide is used as the steering-side rack guide. Because the rolling rack guide has a smaller dynamic friction coefficient μ' than a sliding rack guide, the friction force generated is smaller than when a sliding rack guide is used (dotted line).

[0045] (Effects of the second embodiment) In the rack and pinion mechanism of the second embodiment, the steering side rack guide is a rolling type rack guide 30, and the assist side rack guide is a sliding type rack guide 10. This makes it possible to effectively reduce the frictional force generated in the rack bar 6 in a region where the steering assist torque by the electric motor 20 is low, thereby reducing the sticky feeling felt by the driver.

[0046] (Modification) In the above description, the rack and pinion mechanism of the embodiment is applied to an electric power steering device that applies steering assist torque to a steering system of a vehicle by an actuator. However, the present invention is not limited to this, and can be widely applied to a rack and pinion mechanism having a rack bar that meshes with at least two pinion gears. For example, the present invention may be applied to a steer-by-wire (SBW) type steering device in which the steering wheel and the steered 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. [Explanation of symbols]

[0047] 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 portion, 12...rack guide screw, 15...elastic member, 20...electric motor, 21...rotating shaft, 22...reduction mechanism, 22a...driving 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

1. a first pinion having a first pinion gear and supported rotatably about 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 disposed at an axial position 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 a back surface of the rack bar; a rolling rack guide that is disposed at an axial position of the second pinion gear in the axial direction and that presses the rack teeth against the second pinion gear by a roller that rolls and contacts a back surface of the rack bar; a pair of rack bushes provided on both axial sides of the rolling rack guide and supporting the rack bar slidably in the axial direction; the rack teeth include first rack teeth meshing with the first pinion gear and second rack teeth meshing with the second pinion gear, one of the pair of rack bushes is disposed between the sliding rack guide and the rolling rack guide, and supports a portion of the rack bar where the second rack teeth are formed when the rack bar is in a neutral position; A rack and pinion mechanism.

2. 2. The rack and pinion mechanism according to claim 1, wherein the first pinion is connected to a steering wheel and is rotatably driven, and the second pinion is connected to an actuator and is rotatably driven.

3. 2. The rack and pinion mechanism according to claim 1, wherein the first pinion is connected to an actuator and is rotatably driven, and the second pinion is connected to a steering wheel and is rotatably driven.

4. 2. The rack and pinion mechanism according to claim 1, wherein one of the pair of rack bushes is disposed between the sliding rack guide and the rolling rack guide and at a position closer to the rolling rack guide than the axial center of the rack bar.

5. The rack and pinion mechanism according to any one of claims 1 to 4, characterized in that the pair of rack bushes are provided only on both axial sides of the rolling type rack guide, out of the sliding type rack guide and the rolling type rack guide.

6. A first pinion having a first pinion gear and supported rotatably 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 disposed at an axial position 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 a back surface of the rack bar; a rolling rack guide that is disposed at an axial position of the second pinion gear in the axial direction and that presses the rack teeth against the second pinion gear by a roller that rolls and contacts a back surface of the rack bar; a rack bush that is disposed between the sliding rack guide and the rolling rack guide and that supports, when the rack bar is in a neutral position, a portion of the rack bar where rack teeth that mesh with the second pinion gear are formed, so as to be slidable in the axial direction; Equipped with The first pinion is connected to an actuator and is rotatably driven, and the second pinion is connected to a steering wheel and is rotatably driven. A rack and pinion mechanism.

7. A first pinion having a first pinion gear and supported rotatably 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 disposed at an axial position 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 a back surface of the rack bar; a rolling rack guide that is disposed at an axial position of the second pinion gear in the axial direction and that presses the rack teeth against the second pinion gear by a roller that rolls and contacts a back surface of the rack bar; Equipped with the first pinion is connected to an actuator and is rotatably driven, and the second pinion is connected to a steering wheel and is rotatably driven, a pair of rack bushings that support the rack bar slidably in the axial direction are provided only on both axial sides of the rolling rack guide out of the sliding rack guide and the rolling rack guide.

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