Steering mechanism

Abstract

The electric power steering system (100) includes: a first pinion (16) disposed on a steering shaft (11) and rotating together with the steering shaft (11); a drive shaft (22) driven to rotate by an electric motor (21); a second pinion (23) disposed on the drive shaft (22) and rotating together with the drive shaft (22); a first force-applying mechanism (60) applying force to the rack shaft (12) toward the first pinion (16); and a second force-applying mechanism (70) applying force to the rack shaft (12) toward the second pinion (23). The first holding force applied by the first force-applying mechanism (60) to the rack shaft (12) to hold the first pinion (16) on the rack shaft (12) and the second holding force applied by the second force-applying mechanism (70) to the rack shaft (12) to hold the second pinion (23) on the rack shaft (12) are different.

Description

Technical Field

[0001] This invention relates to a steering device. Background Technology

[0002] Japanese Patent Application Publication No. JP2013-241051A describes a rack and pinion steering device including a preload mechanism for pressing the rack towards the pinion. The preload mechanism is constructed by sequentially inserting a rack guide, a preload spring, and an adjusting screw into the cylindrical portion of the housing. The preload spring applies force towards the rack guide, pressing the rack towards the pinion. This prevents backlash between the rack and pinion. Summary of the Invention

[0003] In the steering device described in Japanese Patent Application Publication No. JP2013-241051A, a holding force is generated by applying force to the rack through a preload mechanism, thereby holding the pinion to the rack. The preload mechanism described in Japanese Patent Application Publication No. JP2013-241051A is generally configured to increase the aforementioned holding force in order to prevent the generation of abnormal noise caused by backlash.

[0004] Here, the steering device described in Japanese Patent Application Publication No. JP2013-241051A is a so-called single-gear type. It is conceivable that the preload mechanism described in Japanese Patent Application Publication No. JP2013-241051A could also be applied to the two pinions of a double-gear steering device. In this case, when the holding force is increased to prevent abnormal noise caused by backlash, the reaction force borne by each pinion from the rack becomes too large, making it difficult for the rack to move. Consequently, the handling of the steering device may deteriorate. To address this, the holding force could be reduced; however, in this case, it might not be sufficient to prevent abnormal noise caused by backlash.

[0005] The purpose of this invention is to improve handling while preventing abnormal noise from a dual-gear steering system.

[0006] According to one aspect of the invention, a steering device comprises: a first shaft member that rotates according to the operation of a steering component performed by a driver; a first pinion disposed on the first shaft member and rotating together with the first shaft member; a second shaft member that is driven to rotate by a motor; a second pinion disposed on the second shaft member and rotating together with the second shaft member; a rack shaft having a rack gear meshing with the first pinion and the second pinion, and causing the wheels to change direction; a first force-applying mechanism that applies a force to the rack shaft toward the first pinion; and a second force-applying mechanism that applies a force to the rack shaft toward the second pinion, wherein a first holding force applied by the first force-applying mechanism to hold the first pinion on the rack shaft and a second holding force applied by the second force-applying mechanism to hold the second pinion on the rack shaft are different. Attached Figure Description

[0007] Figure 1 This is a structural diagram of the electric power steering device according to an embodiment of the present invention.

[0008] Figure 2 This is a partial sectional view of the rack shaft.

[0009] Figure 3 This is a partial cross-sectional view of the vicinity of the first force-applying mechanism.

[0010] Figure 4 This is a partial cross-sectional view of the vicinity of the second force-applying mechanism. Detailed Implementation

[0011] Referring to the accompanying drawings, an electric power steering device 100, which is a steering device according to an embodiment of the present invention, will be described.

[0012] like Figure 1 As shown, the electric power steering system 100 includes: a steering shaft 11 as a first shaft component, which rotates according to the control of a steering wheel 1 as a steering component performed by the driver; a first pinion 16 which is disposed on the steering shaft 11 and rotates together with the steering shaft 11; and a rack shaft 12 which has a rack gear 12a that meshes with the first pinion 16 and changes the direction of the wheels 2.

[0013] The steering shaft 11 consists of an input shaft 13 that rotates with the steering operation performed by the driver on the steering wheel 1, an output shaft 15 that displaces the rack shaft 12, and a torsion bar 14 that connects the input shaft 13 and the output shaft 15.

[0014] The rack and pinion shaft 12 is a shaft-shaped component that extends in the left-right direction of the vehicle and is connected to the wheel 2 via the ball joint 5 and the articulated arm 4.

[0015] The output shaft 15 and the rack shaft 12 are connected to each other via a rack and pinion mechanism, which consists of a first pinion 16 located at the end of the output shaft 15 and a rack gear 12a located on the rack shaft 12. The torque of the output shaft 15 is converted into a load in the axial direction of the rack shaft 12 via the meshing first pinion 16 and rack gear 12a, and is transmitted to the rack shaft 12. Thereby, the rack shaft 12 is displaced in the axial direction by the transmitted torque, and the wheel 2 is redirected via the ball joint 5.

[0016] In addition, the electric power steering device 100 includes: an electric motor 21, which serves as a power source for controlling auxiliary torque; a drive shaft 22, which serves as a second shaft component and is driven to rotate by the electric motor 21; a second pinion 23, which is disposed on the drive shaft 22 and rotates together with the drive shaft 22; and a reduction unit 50, which reduces the rotation of the electric motor 21 and transmits it to the drive shaft 22.

[0017] The reduction unit 50 is a worm gear mechanism consisting of a worm shaft 51 driven by an electric motor 21 and a worm wheel 52 disposed on the drive shaft 22. The worm shaft 51 and the worm wheel 52 mesh with each other, and the torque of the electric motor 21 is transmitted to the drive shaft 22 via the worm shaft 51 and the worm wheel 52. In addition, the second pinion 23 and the rack gear 12a mesh with each other, and the torque transmitted from the electric motor 21 to the drive shaft 22 is further transmitted to the rack shaft 12 via the second pinion 23 and the rack gear 12a.

[0018] In addition, the electric power steering system 100 also includes: a torque sensor 40, which detects the torque acting on the torsion bar 14; and a controller 30, which controls the drive of the electric motor 21 based on the detection value of the torque sensor 40.

[0019] The controller 30 is composed of a microcomputer, which includes: a CPU (Central Processing Unit) for performing calculations; ROM (Read-Only Memory) for storing control programs executed by the CPU; and RAM (Random Access Memory) for storing the results of the CPU's calculations. The controller 30 can be composed of a single microcomputer or multiple microcomputers.

[0020] The torque sensor 40 detects the control torque applied to the input shaft 13 during steering operations performed by the driver and outputs a voltage signal corresponding to the detected control torque to the controller 30. The controller 30 calculates the torque output by the electric motor 21 based on the voltage signal from the torque sensor 40 and controls the drive of the electric motor 21 in the manner in which the torque is generated.

[0021] Thus, in the electric power steering system 100 with the above-described structure, the torque sensor 40 can detect the control torque applied to the input shaft 13, and the controller 30 can control the drive of the electric motor 21 based on the detection result, thereby assisting the driver's steering operation. As described above, the electric power steering system 100 is a bi-gear type steering system in which the control torque applied by the driver and the control assistance torque applied by the electric motor 21 are independently input to the rack shaft 12.

[0022] like Figure 2 As shown, the electric power steering system 100 includes: a rack housing 17, which serves as a housing component and houses the rack shaft 12; a shaft housing 18, which houses the steering shaft 11; and a worm housing 53, which houses the reduction gear 50 and the drive shaft 22.

[0023] The rack housing 17 has: a receiving hole 17a formed through the rack shaft 12 in an axially extending manner; a first through hole 17b and a second through hole 17c, one end of which is open on the outer peripheral surface and formed intersecting the receiving hole 17a. The shaft housing 18 is connected to the rack housing 17 by bolts (not shown) such that the output shaft 15 is inserted into the first through hole 17b. The worm housing 53 is connected to the rack housing 17 by bolts (not shown) such that the drive shaft 22 is inserted into the second through hole 17c.

[0024] like Figure 3 As shown, the electric power steering system 100 includes a first force-applying mechanism 60 that applies force to the rack shaft 12 toward the first pinion 16. The first force-applying mechanism 60 is housed in a first receiving portion 17d provided on the rack housing 17. In other words, the rack housing 17 has a first receiving portion 17d that houses the first force-applying mechanism 60. The first receiving portion 17d is a through hole that extends perpendicularly to the rack shaft 12 and the output shaft 15 and opens on the inner peripheral surface of the receiving hole 17a and the outer peripheral surface of the rack housing 17.

[0025] The first force-applying mechanism 60 includes: a first yoke 61 as a first abutting part, which abuts against the rack shaft 12; a first spring 62 as a first force-applying member, which applies force to the first yoke 61 toward the rack shaft 12; a first cover 63, which blocks the opening of the first receiving part 17d of the rack housing 17; and an O-ring 64 as an elastic member, which is disposed on the outer peripheral surface of the first yoke 61.

[0026] The first yoke 61 is slidably housed within the first receiving portion 17d. An abutting surface 61a is provided on the first yoke 61 along the outer circumferential surface of the rack shaft 12, and the rack shaft 12 is abutted and housed on the abutting surface 61a. An O-ring 64 is disposed between the outer circumferential surface of the first yoke 61 and the inner circumferential surface of the first receiving portion 17d, sealing the gap between them.

[0027] The first spring 62 is arranged with its central axis orthogonal to the central axis of the rack shaft 12. Furthermore, the first cover 63 is screwed into the rack housing 17 via a female thread (not shown) provided in the first receiving portion 17d. The first spring 62 is positioned in a compressed state between the first yoke 61 and the first cover 63. Thus, the first spring 62 applies force to the rack shaft 12 towards the first pinion 16 via the first yoke 61.

[0028] like Figure 4 As shown, the electric power steering system 100 includes a second force-applying mechanism 70 that applies force to the rack shaft 12 toward the second pinion 23. The second force-applying mechanism 70 is housed in a second receiving portion 17e provided on the rack housing 17. In other words, the rack housing 17 has a second receiving portion 17e that houses the second force-applying mechanism 70. The second receiving portion 17e is a through hole that extends perpendicularly to the rack shaft 12 and the drive shaft 22 and opens on the inner peripheral surface of the receiving hole 17a and the outer peripheral surface of the rack housing 17.

[0029] The second force-applying mechanism 70 includes: a second yoke 71 serving as a second abutment portion, which abuts against the rack shaft 12; a second spring 72 serving as a second force-applying component, which applies force to the second yoke 71 toward the rack shaft 12; a second cover 73, which blocks the opening of the second receiving portion 17e of the rack housing 17; and an O-ring 74 serving as an elastic component, which is disposed on the outer peripheral surface of the second yoke 71. Since the basic structure of the second force-applying mechanism 70 is the same as that of the first force-applying mechanism 60, detailed descriptions are omitted. Furthermore, the differences between the first force-applying mechanism 60 and the second force-applying mechanism 70 will be described later.

[0030] In the electric power steering device 100 with the above-described structure, a holding force is generated that applies force to the rack shaft 12 via the first force-applying mechanism 60 and the second force-applying mechanism 70, thereby holding the first pinion 16 and the second pinion 23 to the rack shaft 12. Specifically, in this embodiment, the holding force refers to the force acting on the first pinion 16 and the second pinion 23 via the rack shaft 12. Forces act on the first pinion 16 and the second pinion 23 from the first force-applying mechanism 60 and the second force-applying mechanism 70 via the rack shaft 12. Furthermore, forces act on the first pinion 16 and the second pinion 23 from the rack shaft 12 as reaction forces to the forces input from themselves to the rack shaft 12. In this embodiment, the holding force is a force formed by combining the above two forces.

[0031] Generally, the force-applying mechanism that applies force to the rack shaft towards the pinion is configured to increase the holding force of the pinion on the rack shaft to prevent abnormal noise caused by backlash. In a dual-gear steering system, increasing the holding force of each pinion on the rack increases the reaction force from each pinion to the rack, making it difficult to move the rack shaft using input from each pinion. This can worsen the handling of the electric power steering system. To counteract this, reducing the holding force of each pinion on the rack shaft is also an option; however, in this case, it may not be sufficient to prevent abnormal noise caused by backlash.

[0032] In contrast, the electric power steering device 100 in this embodiment is configured such that the first holding force applied to the rack shaft 12 by the first force application mechanism 60 to hold the first pinion 16 on the rack shaft 12 is different from the second holding force applied to the rack shaft 12 by the second force application mechanism 70 to hold the second pinion 23 on the rack shaft 12.

[0033] The first holding force can be adjusted, for example, by changing the load setting of the first spring 62. This is because the force of the first spring 62 changes, thus changing the force acting on the first pinion 16 via the rack shaft 12. When the load setting of the first spring 62 is increased, the force of the first spring 62 increases, and the force acting on the first pinion 16 via the rack shaft 12 increases. Therefore, the first holding force increases. Conversely, when the load setting of the first spring 62 is decreased, the force of the first spring 62 decreases, and the force acting on the first pinion 16 via the rack shaft 12 decreases. Therefore, the first holding force decreases. Similarly, the second holding force can be adjusted by changing the load setting of the second spring 72. Thus, the electric power steering system 100 can independently set and optimize the first and second holding forces through the components constituting the first force application mechanism 60 and the second force application mechanism 70.

[0034] Specifically, the load on the first spring 62 of the electric power steering system 100 is less than the load on the second spring 72. In other words, the first holding force is less than the second holding force. That is, the reaction force on the first pinion 16 from the rack shaft 12 is less than the reaction force on the second pinion 23 from the rack shaft 12. Therefore, the rack shaft 12 is more easily moved by the input from the steering shaft 11 compared to the input from the drive shaft 22. This improves the handling of the electric power steering system 100. In addition, since the second holding force is higher than the first holding force, backlash between the rack shaft 12 and the second pinion 23 can be prevented. Thus, the electric power steering system 100 can simultaneously achieve the prevention of abnormal noise and the improvement of handling.

[0035] Furthermore, the electric power steering system 100 is not limited to a structure where the first holding force is less than the second holding force; it can be any structure where at least the first holding force and the second holding force are different. With such a structure, by making the first holding force of the first pinion 16 held on the rack shaft 12 different from the second holding force of the second pinion 23 held on the rack shaft 12, the force transmitted to the rack shaft 12 can be optimized overall. In addition, not only can the magnitude of the force transmitted to the rack shaft 12 be optimized, but also the method of force transmission from the first force application mechanism 60 and the second force application mechanism 70 to the rack shaft 12 can be optimized. This allows for the simultaneous prevention of abnormal noise from the electric power steering system 100 and the improvement of its handling.

[0036] According to the above implementation method, the following effects are achieved.

[0037] The electric power steering system 100 optimizes the force transmitted to the rack shaft 12 as a whole by differentiating the first holding force that holds the first pinion 16 to the rack shaft 12 and the second holding force that holds the second pinion 23 to the rack shaft 12. This allows for the simultaneous prevention of abnormal noise from the electric power steering system 100 and improved handling.

[0038] Specifically, in the electric power steering system 100, the first holding force is less than the second holding force. Therefore, the reaction force borne by the first pinion 16 from the rack shaft 12 is less than the reaction force borne by the second pinion 23 from the rack shaft 12. Thus, the rack shaft 12 is more easily moved by the input from the steering shaft 11 compared to the input from the drive shaft 22. This improves the maneuverability of the electric power steering system 100. Furthermore, since the second holding force is higher than the first holding force, backlash between the rack shaft 12 and the second pinion 23 can be prevented. In this way, the electric power steering system 100 simultaneously achieves prevention of abnormal noise and improved maneuverability.

[0039] Next, variations of this embodiment will be described.

[0040] <Variation Example 1>

[0041] The electric power steering device 100 of the above embodiment is a structure in which the first holding force is less than the second holding force because the load on the first spring 62 is less than the load on the second spring 72. The structure of the electric power steering device 100 is not limited to this; other methods may also be used to make the first holding force less than the second holding force.

[0042] For example, a structure in which the coefficient of friction of the first yoke 61 is less than that of the second yoke 71 can also be used. Specifically, a structure can be adopted in which the coefficient of friction of the first yoke 61 against the rack shaft 12 is less than that of the second yoke 71 by forming the first yoke 61 and the second yoke 71 with different materials, or by coating the contact surfaces 61a and 71a with different materials. When the coefficient of friction of the first yoke 61 is smaller, the frictional force generated between the contact surface 61a of the first yoke 61 and the rack shaft 12 is reduced. As a result, the reaction force borne by the first pinion 16 from the rack shaft 12 is less than the reaction force borne by the second pinion 23 from the rack shaft 12. Thus, the first holding force is less than the second holding force, achieving the same effect as the above-described embodiment.

[0043] <Variation Example 2>

[0044] The electric power steering device 100 of the above embodiment has a structure where the first holding force is less than the second holding force. As mentioned above, the structure of the electric power steering device 100 is not limited to this; any structure where the first holding force and the second holding force are different is acceptable. For example, it could be a structure where the load on the first spring 62 is different from the load on the second spring 72. Alternatively, it could be a structure where the friction system of the first yoke 61 and the friction coefficient of the second yoke 71 are different. In the above structures, the first holding force and the second holding force can be independently set and optimized using the first spring 62 and the second spring 72, or the first yoke 61 and the second yoke 71.

[0045] The structure, function, and effects of the embodiments of the present invention as described above are summarized and explained.

[0046] The electric power steering system 100, as a steering device, includes: a steering shaft 11 as a first shaft component, which rotates according to the operation of a steering wheel 1, which is a steering component, performed by a driver; a first pinion 16, which is disposed on the steering shaft 11 and rotates together with the steering shaft 11; a drive shaft 22 as a second shaft component, which is driven to rotate by an electric motor 21, which is a motor; a second pinion 23, which is disposed on the drive shaft 22 and rotates together with the drive shaft 22; and a rack shaft 12, which has a pinion gear 16 that rotates with the first pinion 16. The rack and pinion 12a meshes with the second pinion 23, causing the wheel 2 to change direction; the first force-applying mechanism 60 applies force to the rack shaft 12 towards the first pinion 16; the second force-applying mechanism 70 applies force to the rack shaft 12 towards the second pinion 23. The first holding force applied by the first force-applying mechanism 60 to the rack shaft 12, thereby holding the first pinion 16 on the rack shaft 12, and the second holding force applied by the second force-applying mechanism 70 to the rack shaft 12, thereby holding the second pinion 23 on the rack shaft 12, are different.

[0047] In this structure, by making the first holding force holding the first pinion 16 to the rack shaft 12 different from the second holding force holding the second pinion 23 to the rack shaft 12, the force transmitted to the rack shaft 12 as a whole can be optimized. This allows for the simultaneous prevention of abnormal noise from the electric power steering system 100 and improved handling.

[0048] In addition, the electric power steering system 100 also includes a rack housing 17 as a housing component that houses the rack shaft 12. The rack housing 17 has: a first housing portion 17d that houses the first force-applying mechanism 60; and a second housing portion 17e that houses the second force-applying mechanism 70. The first force-applying mechanism 60 has: a first yoke portion 61 as a first abutting portion that abuts against the rack shaft 12; and a first spring 62 as a first force-applying component that applies force to the first yoke portion 61 toward the rack shaft 12. The second force-applying mechanism 70 has: a second yoke portion 71 as a second abutting portion that abuts against the rack shaft 12; and a second spring 72 as a second force-applying component that applies force to the second yoke portion 71 toward the rack shaft 12.

[0049] In addition, the load setting of the first spring 62 and the load setting of the second spring 72 of the electric power steering device 100 are different.

[0050] In the above structure, the first holding force and the second holding force can be set independently and optimized by the first spring 62 and the second spring 72.

[0051] In addition, the friction coefficients of the first yoke 61 and the second yoke 71 of the electric power steering device 100 are different.

[0052] In this structure, the first holding force and the second holding force can be set and optimized independently through the first yoke 61 and the second yoke 71.

[0053] In addition, the first holding force of the electric power steering 100 is less than the second holding force.

[0054] In this structure, the rack shaft 12 is more easily moved by the input from the steering shaft 11 compared to the input from the drive shaft 22. This improves the maneuverability of the electric power steering system 100. Furthermore, since the second holding force is higher than the first holding force, backlash between the rack shaft 12 and the second pinion 23 can be prevented.

[0055] The embodiments of the present invention have been described above. However, the above embodiments are merely some examples of the application of the present invention and are not intended to limit the technical scope of the present invention to the specific structures of the above embodiments.

[0056] The steering system can also be a so-called dual-assistance steering system, which has a mechanism on the steering axle side that assists in steering operation.

[0057] This application claims priority based on Japanese Patent Application No. 2021-060897 filed with the Japan Patent Office on March 31, 2021, the entire contents of which are incorporated herein by reference.

Claims

1. A steering device comprising: The first axle component rotates according to the steering component operated by the driver; A first pinion is disposed on the first shaft component and rotates together with the first shaft component; The second shaft component is driven by a motor. The second pinion is disposed on the second shaft component and rotates together with the second shaft component; A rack shaft having a rack gear that meshes with the first pinion and the second pinion, and causing the wheel to change direction; The first force-applying mechanism applies force to the rack shaft toward the first pinion; The second force-applying mechanism applies force to the rack shaft towards the second pinion. The first holding force, which applies force to the rack shaft through the first force-applying mechanism to keep the first pinion on the rack shaft, and the second holding force, which applies force to the rack shaft through the second force-applying mechanism to keep the second pinion on the rack shaft, are different. The first holding force is less than the second holding force.

2. The steering device as claimed in claim 1, wherein, It also includes a housing component for accommodating the rack shaft. The housing component has: The first containment unit contains the first force-applying mechanism; The second containment unit contains the second force-applying mechanism. The first force-applying mechanism has: The first abutting part abuts against the rack shaft; The first force-applying component applies force to the first abutment portion toward the rack shaft. The second force-applying mechanism has: The second abutting part abuts against the rack shaft; The second force-applying component applies force to the second abutment portion toward the rack shaft.

3. The steering device as claimed in claim 2, wherein, The load on the first force-applying component is different from the load on the second force-applying component.

4. The steering device as claimed in claim 2, wherein, The coefficient of friction of the first contact part is different from that of the second contact part.

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