Steering device

Abstract

An electric power steering device (100) comprises: a first pinion gear (16) that is provided on a steering shaft (11) and rotates with the steering shaft (11); a drive shaft (22) that is rotationally driven by an electric motor (21); a second pinion gear (23) that is provided on the drive shaft (22) and rotates together with the drive shaft (22); a first biasing mechanism (60) that biases a rack shaft (12) toward the first pinion gear (16); and a second biasing mechanism (70) that biases the rack shaft (12) toward the second pinion gear (23). The first holding force by which the first pinion gear (16) is held on the rack shaft (12) by the rack shaft (12) being biased by the first biasing mechanism (60) and the second holding force by which the second pinion gear (23) is held on the rack shaft (12) by the rack shaft (12) being biased by the second biasing mechanism (70) are different.

Description

[Technical field]

[0001] The present invention relates to a steering device. [Background technology]

[0002] JP2013-241051A describes a rack-and-pinion steering device equipped with a preload mechanism that presses the rack against the pinion. The preload mechanism is configured by inserting a rack guide, a preload spring, and an adjustment screw, in that order, into a cylindrical portion of a housing, and the rack guide is biased toward the rack by the preload spring, thereby pressing the rack against the pinion. This prevents backlash from occurring between the rack and the pinion. Summary of the Invention

[0003] In the steering device described in JP2013-241051A, a preload mechanism biases the rack, generating a holding force that holds the pinion on the rack. Preload mechanisms such as those described in JP2013-241051A are generally configured to increase the holding force in order to prevent abnormal noise caused by backlash.

[0004] Here, the steering device described in JP2013-241051A is a so-called single pinion type, and it is considered that the preload mechanism described in JP2013-241051A is also applied to each of the two pinions of a dual pinion type steering device. In this case, if the holding force is increased to prevent abnormal noise due to backlash, the reaction force that each pinion receives from the rack becomes excessive, making it difficult for the rack to move. Therefore, there is a risk that the steerability of the steering device will deteriorate. In order to deal with this, it is also possible to reduce the holding force, but in this case, there is a risk that abnormal noise due to backlash cannot be sufficiently prevented.

[0005] An object of the present invention is to improve steering performance while preventing the generation of abnormal noise in a dual pinion steering device.

[0006] According to one aspect of the present invention, a steering device includes a first shaft member that rotates in response to steering of a steering member by a driver, a first pinion gear that is provided on the first shaft member and rotates together with the first shaft member, a second shaft member that is rotationally driven by a motor, a second pinion gear that is provided on the second shaft member and rotates together with the second shaft member, a rack shaft that has a rack gear that meshes with the first pinion gear and the second pinion gear and steers wheels, a first biasing mechanism that biases the rack shaft toward the first pinion gear, and a second biasing mechanism that biases the rack shaft toward the second pinion gear, wherein a first holding force is generated by which the first pinion gear is held on the rack shaft as a result of the rack shaft being biased by the first biasing mechanism. teeth, A second holding force that holds the second pinion gear on the rack shaft by the second biasing mechanism being biased by the second biasing mechanism Less than . [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a configuration diagram of an electric power steering device according to this embodiment. [Diagram 2] FIG. 2 is a partial cross-sectional view of the rack shaft. [Diagram 3] FIG. 3 is a partial cross-sectional view of the first biasing mechanism and its vicinity. [Figure 4] FIG. 4 is a partial cross-sectional view of the second biasing mechanism and its vicinity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An electric power steering device 100 as a steering device according to an embodiment of the present invention will be described with reference to the drawings.

[0009] As shown in FIG. 1, the electric power steering device 100 includes a steering shaft 11 as a first shaft member that rotates in response to steering of a steering wheel 1 as a steering member by a driver, a first pinion gear 16 that is provided on the steering shaft 11 and rotates together with the steering shaft 11, and a rack shaft 12 that has a rack gear 12a that meshes with the first pinion gear 16 and steers the wheels 2.

[0010] The steering shaft 11 is composed of an input shaft 13 that rotates in conjunction with the steering operation of the driver operating 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.

[0011] The rack shaft 12 is an axial member extending in the left-right direction of the vehicle, and is connected to the wheels 2 via tie rods 5 and knuckle arms 4 .

[0012] The output shaft 15 and the rack shaft 12 are connected to each other via a rack-and-pinion mechanism consisting of a first pinion gear 16 provided at the end of the output shaft 15 and a rack gear 12a provided on the rack shaft 12. The torque of the output shaft 15 is converted into an axial load of the rack shaft 12 via the first pinion gear 16 and the rack gear 12a, which mesh with each other, and is transmitted to the rack shaft 12. As a result, the rack shaft 12 is displaced in the axial direction by the transmitted torque, and steers the wheels 2 via the tie rods 5.

[0013] The electric power steering device 100 also includes an electric motor 21 as a motor that is a power source for the steering assist torque, a drive shaft 22 as a second shaft member that is rotationally driven by the electric motor 21, a second pinion gear 23 that is provided on the drive shaft 22 and rotates together with the drive shaft 22, and a reduction gear section 50 that reduces the rotation of the electric motor 21 and transmits it to the drive shaft 22.

[0014] The speed reducer 50 is a worm gear mechanism including a worm shaft 51 driven by the electric motor 21 and a worm wheel 52 provided 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 gear 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 gear 23 and the rack gear 12a.

[0015] In addition, the electric power steering device 100 further includes a torque sensor 40 that detects the torque acting on the torsion bar 14 , and a controller 30 that controls the driving of the electric motor 21 in accordance with the detection value of the torque sensor 40 .

[0016] The controller 30 is configured with a microcomputer including a CPU (Central Processing Unit) that performs arithmetic processing, a ROM (Read-Only Memory) that stores control programs executed by the CPU, and a RAM (Random Access Memory) that stores the CPU's arithmetic results, etc. The controller 30 may be configured with a single microcomputer or may be configured with a plurality of microcomputers.

[0017] The torque sensor 40 detects the steering torque applied to the input shaft 13 in accordance with the steering operation by the driver, and outputs a voltage signal corresponding to the detected steering torque to the controller 30. The controller 30 calculates the torque to be output by the electric motor 21 based on the voltage signal from the torque sensor 40, and controls the driving of the electric motor 21 so as to generate the calculated torque.

[0018] In this way, in the electric power steering device 100 configured as described above, the steering torque applied to the input shaft 13 is detected by the torque sensor 40, and the driving of the electric motor 21 is controlled by the controller 30 based on the detection result, thereby making it possible to assist the steering operation of the driver. As described above, the electric power steering device 100 is a dual pinion type steering device in which the steering torque by the driver and the steering assist torque by the electric motor 21 are input to the rack shaft 12 independently.

[0019] As shown in FIG. 2, the electric power steering device 100 includes a rack housing 17 as a case member that accommodates the rack shaft 12, a shaft housing 18 that accommodates the steering shaft 11, and a worm housing 53 that accommodates the reduction gear unit 50 and the drive shaft 22.

[0020] The rack housing 17 has an accommodating hole 17a that is formed to penetrate in the axial direction and accommodates the rack shaft 12, and a first insertion hole 17b and a second insertion hole 17c that are formed on the outer circumferential surface and have one end open so as to intersect with the accommodating hole 17a. The shaft housing 18 is connected to the rack housing 17 via a bolt (not shown) such that the output shaft 15 is inserted into the first insertion hole 17b. The worm housing 53 is connected to the rack housing 17 via a bolt (not shown) such that the drive shaft 22 is inserted into the second insertion hole 17c.

[0021] 3, the electric power steering device 100 includes a first biasing mechanism 60 that biases the rack shaft 12 toward the first pinion gear 16. The first biasing mechanism 60 is accommodated in a first accommodating portion 17d provided in the rack housing 17. In other words, the rack housing 17 has a first accommodating portion 17d that accommodates the first biasing mechanism 60. The first accommodating portion 17d extends perpendicular to the rack shaft 12 and the output shaft 15, and is a through hole that opens into the inner circumferential surface of the accommodating hole 17a and the outer circumferential surface of the rack housing 17.

[0022] The first biasing mechanism 60 has a first yoke 61 as a first abutment portion that abuts against the rack shaft 12, a first spring 62 as a first biasing member that biases the first yoke 61 toward the rack shaft 12, a first cover 63 that covers the opening of the first accommodating portion 17d of the rack housing 17, and an O-ring 64 as an elastic member provided on the outer peripheral surface of the first yoke 61.

[0023] The first yoke 61 is slidably housed in the first housing portion 17d. The first yoke 61 is provided with an abutment surface 61a that fits along the outer circumferential surface of the rack shaft 12, and the rack shaft 12 is housed in contact with the abutment surface 61a. An O-ring 64 is provided between the outer circumferential surface of the first yoke 61 and the inner circumferential surface of the first housing portion 17d to seal the gap therebetween.

[0024] The first spring 62 is disposed so that its central axis is perpendicular to the central axis of the rack shaft 12. The first cover 63 is attached to the rack housing 17 by being screwed into a female thread (not shown) provided in the first accommodation portion 17d. The first spring 62 is provided in a compressed state between the first yoke 61 and the first cover 63. As a result, the first spring 62 biases the rack shaft 12 toward the first pinion gear 16 via the first yoke 61.

[0025] 4, the electric power steering device 100 includes a second biasing mechanism 70 that biases the rack shaft 12 toward the second pinion gear 23. The second biasing mechanism 70 is accommodated in a second accommodating portion 17e provided in the rack housing 17. In other words, the rack housing 17 has a second accommodating portion 17e that accommodates the second biasing mechanism 70. The second accommodating portion 17e is a through hole that extends perpendicular to the rack shaft 12 and the drive shaft 22 and opens to the inner circumferential surface of the accommodating hole 17a and the outer circumferential surface of the rack housing 17.

[0026] The second biasing mechanism 70 has a second yoke 71 as a second abutment portion that abuts against the rack shaft 12, a second spring 72 as a second biasing member that biases the second yoke 71 toward the rack shaft 12, a second cover 73 that closes the opening of the second accommodation portion 17e of the rack housing 17, and an O-ring 74 as an elastic member provided on the outer circumferential surface of the second yoke 71. The second biasing mechanism 70 has the same basic configuration as the first biasing mechanism 60, and therefore a detailed description thereof will be omitted. Note that the differences between the first biasing mechanism 60 and the second biasing mechanism 70 will be described later.

[0027] In the electric power steering device 100 having the above configuration, the rack shaft 12 is biased by the first biasing mechanism 60 and the second biasing mechanism 70, thereby generating a holding force that holds the first pinion gear 16 and the second pinion gear 23 on the rack shaft 12. Specifically, the holding force in this embodiment refers to a force acting on the first pinion gear 16 and the second pinion gear 23 through the rack shaft 12. A force is applied to the first pinion gear 16 and the second pinion gear 23 from the first biasing mechanism 60 and the second biasing mechanism 70 through the rack shaft 12. Furthermore, a force is applied to the first pinion gear 16 and the second pinion gear 23 from the rack shaft 12 as a reaction force to a force input from the first pinion gear 16 and the second pinion gear 23 to the rack shaft 12. The holding force in this embodiment is a combination of the above two forces.

[0028] Generally, a biasing mechanism that biases the rack shaft toward the pinion gear is configured to increase the force with which the pinion gear is held by the rack shaft in order to prevent the generation of abnormal noise due to backlash. In a dual-pinion steering device, if the force with which each pinion is held by the rack is increased, the reaction force that each pinion receives from the rack increases, making it difficult for the rack shaft to move due to input from each pinion gear. This may result in a deterioration in the steerability of the electric power steering device. To address this, it may be possible to reduce the force with which each pinion gear is held by the rack shaft, but in this case, there is a risk that abnormal noise due to backlash cannot be sufficiently prevented.

[0029] In contrast, the electric power steering device 100 in this embodiment is configured so that a first holding force, where the first pinion gear 16 is held on the rack shaft 12 by the first biasing mechanism 60 biasing the rack shaft 12, is different from a second holding force, where the second pinion gear 23 is held on the rack shaft 12 by the second biasing mechanism 70 biasing the rack shaft 12.

[0030] The first holding force can be adjusted, for example, by changing the set load of the first spring 62. This is because the force acting on the first pinion gear 16 through the rack shaft 12 changes as the biasing force of the first spring 62 changes. When the set load of the first spring 62 is increased, the biasing force of the first spring 62 increases, and the force acting on the first pinion gear 16 through the rack shaft 12 increases. Therefore, the first holding force increases. Conversely, when the set load of the first spring 62 is decreased, the biasing force of the first spring 62 decreases, and the force acting on the first pinion gear 16 through the rack shaft 12 decreases. Therefore, the first holding force decreases. Similarly, the second holding force can be adjusted by changing the set load of the second spring 72. In this way, the electric power steering device 100 can individually set and optimize the first holding force and the second holding force by the members constituting the first biasing mechanism 60 and the second biasing mechanism 70.

[0031] Specifically, in the electric power steering device 100, the set load of the first spring 62 is smaller than the set load of the second spring 72. In other words, the first holding force is smaller than the second holding force. That is, the reaction force that the first pinion gear 16 receives from the rack shaft 12 is smaller than the reaction force that the second pinion gear 23 receives from the rack shaft 12, so that the rack shaft 12 is more likely to move due to the input from the steering shaft 11 than the input from the drive shaft 22. This can improve the steerability of the electric power steering device 100. In addition, since the second holding force is higher than the first holding force, it is possible to prevent backlash occurring between the rack shaft 12 and the second pinion gear 23. In this way, the electric power steering device 100 can achieve both prevention of abnormal noise and improvement of steerability.

[0032] The electric power steering device 100 is not limited to a configuration in which the first holding force is smaller than the second holding force, but may be configured such that at least the first holding force and the second holding force are different. With this configuration, the force transmitted to the rack shaft 12 can be optimized as a whole by making the first holding force with which the first pinion gear 16 is held on the rack shaft 12 different from the second holding force with which the second pinion gear 23 is held on the rack shaft 12. In addition to the magnitude of the force transmitted to the rack shaft 12, the manner in which the force is transmitted from the first biasing mechanism 60 and the second biasing mechanism 70 to the rack shaft 12 can also be optimized. This makes it possible to prevent the electric power steering device 100 from generating abnormal noise and improve the steering performance at the same time.

[0033] According to the present embodiment described above, the following advantageous effects are obtained.

[0034] In the electric power steering device 100, the first holding force with which the first pinion gear 16 is held on the rack shaft 12 is different from the second holding force with which the second pinion gear 23 is held on the rack shaft 12, thereby optimizing the force transmitted to the rack shaft 12 as a whole. This makes it possible to prevent the electric power steering device 100 from generating abnormal noise while improving steering performance.

[0035] In particular, in the electric power steering device 100, since the first holding force is smaller than the second holding force, the reaction force that the first pinion gear 16 receives from the rack shaft 12 is smaller than the reaction force that the second pinion gear 23 receives from the rack shaft 12. Therefore, the rack shaft 12 is more likely to move due to the input from the steering shaft 11 than the input from the drive shaft 22. This can improve the steerability of the electric power steering device 100. In addition, since the second holding force is higher than the first holding force, it can prevent backlash that occurs between the rack shaft 12 and the second pinion gear 23. In this way, the electric power steering device 100 can achieve both prevention of abnormal noise and improvement of steerability.

[0036] Next, a modification of this embodiment will be described.

[0037] <Variation 1> In the electric power steering device 100 of the above embodiment, the set load of the first spring 62 is smaller than the set load of the second spring 72, so that the first holding force is smaller than the second holding force. The configuration of the electric power steering device 100 is not limited to this, and the first holding force may be smaller than the second holding force by another method.

[0038] For example, the first yoke 61 may have a smaller friction coefficient than the second yoke 71. Specifically, the first yoke 61 and the second yoke 71 may be formed of different materials, or the abutment surface 61a and the abutment surface 71a may be formed by coating with different materials, so that the friction coefficient of the first yoke 61 with respect to the rack shaft 12 may be smaller than the friction coefficient of the second yoke 71. If the friction coefficient of the first yoke 61 is small, the friction force generated between the abutment surface 61a of the first yoke 61 and the rack shaft 12 becomes small. As a result, the reaction force that the first pinion gear 16 receives from the rack shaft 12 becomes smaller than the reaction force that the second pinion gear 23 receives from the rack shaft 12. Therefore, the first holding force becomes smaller than the second holding force, and the same effect as that of the above embodiment is achieved.

[0039] <Variation 2> The electric power steering device 100 of the above embodiment is configured such that the first holding force is smaller than the second holding force. As described above, the configuration of the electric power steering device 100 is not limited to this, and may be configured such that the first holding force and the second holding force are different. For example, the set load of the first spring 62 and the set load of the second spring 72 may be configured differently. Also, the friction coefficient of the first yoke 61 and the friction coefficient of the second yoke 71 may be configured differently. In these configurations, the first holding force and the second holding force can be individually set and optimized by the first spring 62 and the second spring 72, or the first yoke 61 and the second yoke 71.

[0040] The configuration, operation, and effects of the embodiment of the present invention configured as above will be described below.

[0041] The electric power steering device 100 as a steering device includes a steering shaft 11 as a first shaft member that rotates in response to steering of a steering wheel 1 as a steering member by a driver, a first pinion gear 16 that is provided on the steering shaft 11 and rotates together with the steering shaft 11, a drive shaft 22 as a second shaft member that is rotationally driven by an electric motor 21 as a motor, and a second pinion gear 23 that is provided on the drive shaft 22 and rotates together with the drive shaft 22. The vehicle comprises a rack shaft 12 having a rack gear 12a that meshes with a first pinion gear 16 and a second pinion gear 23 and steers the wheels 2, a first biasing mechanism 60 that biases the rack shaft 12 toward the first pinion gear 16, and a second biasing mechanism 70 that biases the rack shaft 12 toward the second pinion gear 23, and a first holding force that holds the first pinion gear 16 on the rack shaft 12 by biasing the rack shaft 12 by the first biasing mechanism 60 is different from a second holding force that holds the second pinion gear 23 on the rack shaft 12 by biasing the rack shaft 12 by the second biasing mechanism 70.

[0042] In this configuration, by making the first holding force with which the first pinion gear 16 is held on the rack shaft 12 different from the second holding force with which the second pinion gear 23 is held on the rack shaft 12, it is possible to optimize the force transmitted to the rack shaft 12 as a whole. This makes it possible to prevent the occurrence of abnormal noise in the electric power steering device 100 and improve steering performance at the same time.

[0043] The electric power steering device 100 further includes a rack housing 17 as a case member that accommodates the rack shaft 12, and the rack housing 17 has a first accommodating portion 17d that accommodates the first biasing mechanism 60 and a second accommodating portion 17e that accommodates the second biasing mechanism 70. The first biasing mechanism 60 has a first yoke 61 as a first abutment portion that abuts against the rack shaft 12 and a first spring 62 as a first biasing member that biases the first yoke 61 toward the rack shaft 12. The second biasing mechanism 70 has a second yoke 71 as a second abutment portion that abuts against the rack shaft 12 and a second spring 72 as a second biasing member that biases the second yoke 71 toward the rack shaft 12.

[0044] In addition, in the electric power steering device 100, the set load of the first spring 62 and the set load of the second spring 72 are different.

[0045] In these configurations, the first and second retention forces can be individually set and optimized by the first and second springs 62, 72.

[0046] In addition, in the electric power steering device 100, the friction coefficient of the first yoke 61 and the friction coefficient of the second yoke 71 are different from each other.

[0047] In this configuration, the first holding force and the second holding force can be individually set and optimized by the first yoke 61 and the second yoke 71.

[0048] Moreover, in the electric power steering device 100, the first holding force is smaller than the second holding force.

[0049] In this configuration, the rack shaft 12 is more likely to move with input from the steering shaft 11 than with input from the drive shaft 22. This improves the steering performance of the electric power steering device 100. In addition, since the second holding force is higher than the first holding force, backlash occurring between the rack shaft 12 and the second pinion gear 23 can be prevented.

[0050] Although the embodiments of the present invention have been described above, the above-mentioned embodiments merely show some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above-mentioned embodiments.

[0051] The steering device may be of a so-called two-assist type having a mechanism for assisting steering operation also on the steering shaft side.

[0052] This application claims priority based on 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: a first shaft member that rotates in response to steering of a steering member by a driver; a first pinion gear provided on the first shaft member and rotating together with the first shaft member; A second shaft member that is rotationally driven by a motor; a second pinion gear provided 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 gear and the second pinion gear to steer wheels; a first biasing mechanism that biases the rack shaft toward the first pinion gear; a second biasing mechanism that biases the rack shaft toward the second pinion gear, a first retaining force by which the first pinion gear is held on the rack shaft as a result of the rack shaft being biased by the first biasing mechanism is smaller than a second retaining force by which the second pinion gear is held on the rack shaft as a result of the rack shaft being biased by the second biasing mechanism.

2. 2. The steering device according to claim 1, A case member that houses the rack shaft is further provided. The case member is a first housing portion that houses the first biasing mechanism; a second housing portion that houses the second biasing mechanism, the first biasing mechanism includes a first contact portion that contacts the rack shaft and a first biasing member that biases the first contact portion toward the rack shaft, The second biasing mechanism is a steering device having a second abutment portion that abuts against the rack shaft and a second biasing member that biases the second abutment portion toward the rack shaft.

3. 3. The steering device according to claim 2, A steering device in which a set load of the first urging member and a set load of the second urging member are different from each other.

4. 3. The steering device according to claim 2, A steering device, wherein a friction coefficient of the first contact portion and a friction coefficient of the second contact portion are different.

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