Steering device

Abstract

To provide a steering device capable of improving steering feeling and improving abrasion resistance of pinion teeth and rack teeth.SOLUTION: The steering device includes a first pinion shaft that has first pinion teeth on an outer periphery and is rotatable around a first rotation axis, a second pinion shaft that has second pinion teeth on an outer periphery and is rotatable around a second rotation axis, and a rack shaft that has first rack teeth that mesh with the first pinion teeth and second rack teeth that mesh with the second pinion teeth and extends in a longitudinal direction. An axial direction of the first rotation axis extends along a lateral direction of the rack shaft, and a total meshing ratio between the first pinion teeth and the first rack teeth is 1.8 or more.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a steering device including a rack shaft that extends in the longitudinal direction and has rack teeth, and a pinion shaft that has pinion teeth that mesh with the rack teeth and is rotatable around the axis of a rotary shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-99680 Summary of the Invention [Problem to be solved by the invention]

[0004] When the pinion shaft is rotated with the pinion teeth meshing with the rack teeth, if there is a large fluctuation in the operating torque acting on the pinion shaft, the steering feel felt by the driver may deteriorate.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a steering device that can improve steering feel and the wear resistance of pinion teeth and rack teeth. [Means for solving the problem]

[0006] In order to achieve the above object, a steering device according to one embodiment of the present disclosure includes a first pinion shaft having first pinion teeth on its outer periphery and rotatable around the axis of a first rotating shaft, a second pinion shaft having second pinion teeth on its outer periphery and rotatable around the axis of the second rotating shaft, and a rack shaft extending in the longitudinal direction and having first rack teeth that mesh with the first pinion teeth and second rack teeth that mesh with the second pinion teeth, wherein the axial direction of the first rotating shaft extends along the short direction of the rack shaft, and a total meshing ratio between the first pinion teeth and the first rack teeth is 1.8 or more.

[0007] As mentioned above, in the steering device described in Patent Document 1, when the pinion shaft is rotated with the pinion teeth meshing with the rack teeth, if there is a large fluctuation in the operating torque acting on the pinion shaft, the steering feeling felt by the driver may deteriorate.

[0008] In contrast, in the present disclosure, the total meshing ratio between the first pinion teeth and the first rack teeth is 1.8 or greater. When the total meshing ratio is 1.8 or greater, fluctuations in the operating torque acting on the first pinion shaft are smaller than when the total meshing ratio is 1.6 or less. It is generally known that steering feel improves when the fluctuations in operating torque are smaller, and therefore, in the present disclosure, the steering feel is improved. Furthermore, since an increase in the meshing ratio reduces the contact surface pressure between the teeth during meshing, in the present disclosure, the wear resistance of the pinion teeth and the rack teeth is improved.

[0009] In a preferred embodiment, the total meshing ratio between the first pinion teeth and the first rack teeth is 2.0 or more. Therefore, according to the present disclosure, as described above, the steering feel is further improved. Furthermore, since an increase in the meshing ratio reduces the contact surface pressure between the teeth during meshing, the present disclosure has the effect of further improving the wear resistance of the first pinion teeth and the first rack teeth.

[0010] In a preferred embodiment, the helix angle of the first rack teeth is 10 degrees or greater. This makes it possible to change the overall meshing ratio between the first pinion teeth and the first rack teeth by simply adjusting the helix angle of the first rack teeth.

[0011] A steering device according to one embodiment of the present disclosure includes a third pinion shaft having third pinion teeth on its outer periphery and rotatable around the axis of a third rotating shaft, and a rack shaft having third rack teeth that mesh with the third pinion teeth and extending in a longitudinal direction, wherein the axial direction of the third rotating shaft extends along the short direction of the rack shaft, and the overall meshing ratio between the third pinion teeth and the third rack teeth is 1.8 or greater.

[0012] When the total contact ratio is 1.8 or more, fluctuations in the operating torque acting on the third pinion shaft are smaller than when the total contact ratio is 1.6 or less. Therefore, as described above, according to the present disclosure, steering feel is further improved. Furthermore, since an increase in the contact ratio reduces the contact surface pressure between the teeth during meshing, according to the present disclosure, the wear resistance of the third pinion teeth and the third rack teeth is further improved.

[0013] In a desirable embodiment, the total meshing ratio between the third pinion teeth and the third rack teeth is equal to or greater than 2.0. Therefore, according to the present disclosure, the steering feel is further improved, and the wear resistance of the third pinion teeth and the third rack teeth is further improved.

[0014] In a preferred embodiment, the helix angle of the third rack teeth is 10 degrees or greater. This makes it possible to change the overall meshing ratio between the third pinion teeth and the third rack teeth by simply adjusting the helix angle of the third rack teeth.

[0015] In a preferred embodiment, the first pinion shaft is provided on an assist side that transmits an assist steering torque to the rack shaft, and the second pinion shaft is provided on a manual side that transmits a steering force to the rack shaft. This provides the effects of improving the steering feel and further improving wear resistance in both single pinion and dual pinion systems. [Effects of the Invention]

[0016] According to the steering device of the present disclosure, it is possible to provide a steering device that can improve the steering feel and the wear resistance of the pinion teeth and rack teeth. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a steering device according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing a part of the steering device according to the embodiment. [Figure 3] FIG. 3 is a front view showing a part of the steering device according to the embodiment. [Figure 4] FIG. 4 is a rear view showing a part of the steering device according to the embodiment. [Figure 5] FIG. 5 is a side view showing a part of the steering device according to the embodiment. [Figure 6] FIG. 6 is a front view of the device shown in FIG. 3 with the rack housing removed. [Figure 7] FIG. 7 is a perspective view of the rack shaft according to the embodiment. [Figure 8] FIG. 8 is a schematic diagram of the first rack teeth, showing the state in which the meshing traces of the first pinion teeth remain. [Figure 9] FIG. 9 is a graph showing the total engagement ratio on the horizontal axis and the adjacent torque fluctuation of the operating torque on the vertical axis. [Figure 10A] FIG. 10A is a schematic graph showing the operating torque according to the first embodiment with a total contact ratio of 1.45. [Figure 10B]FIG. 10B is a schematic graph showing the operating torque according to the fourth embodiment with a total contact ratio of 2.16. [Figure 11] FIG. 11 is a schematic diagram showing a part of a steering device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0019] [Embodiment] First, an embodiment will be described. Fig. 1 is a schematic diagram of a steering device according to the embodiment.

[0020] 1, steering device 80 includes, in the order in which force applied by an operator is transmitted, a steering wheel 81, a steering shaft 82, a universal joint 84, an intermediate shaft 85, a universal joint 86, a stub shaft 87, a steering gear 100, and a tie rod 89. Steering device 80 also includes a control device (hereinafter referred to as an ECU (Electronic Control Unit)) 99, a torque sensor 10, and an electric motor 102. A vehicle speed sensor 101 is provided in the vehicle and outputs a vehicle speed signal V to ECU 99 via CAN (Controller Area Network) communication.

[0021] The steering shaft 82 is connected at one end to the steering wheel 81 and at the other end to a universal joint 84. The intermediate shaft 85 is connected at one end to the universal joint 84 and at the other end to a universal joint 86. The stub shaft 87 is connected at one end to the universal joint 86 and at the other end to the second pinion shaft 4. The torque sensor 10 is attached to the stub shaft 87.

[0022] The torque sensor 10 detects the rotational torque transmitted between the stub shaft 87 and the second pinion shaft 4 .

[0023] The steering gear 100 includes a first pinion shaft 2, a rack shaft 3, and a second pinion shaft 4. The second pinion shaft 4 is connected to a stub shaft 87 via a torsion bar. The rack shaft 3 meshes with the first pinion shaft 2 and the second pinion shaft 4.

[0024] An electric motor 102 is connected to the first pinion shaft 2 via a worm reduction gear. The first pinion shaft 2 rotates by a driving force transmitted from the electric motor 102. The electric motor 102 rotates the first pinion shaft 2 via the worm reduction gear. The electric motor 102 is, for example, a brushless motor, but may also be a motor equipped with brushes (sliders) and a commutator (commutator).

[0025] The steering gear 100 converts the rotational motion transmitted to the first pinion shaft 2 and the second pinion shaft 4 into linear motion by the rack shaft 3. The steering device 80 according to this embodiment is of a dual pinion assist type in which the rack shaft 3 performs linear motion by the rotational motion transmitted from the first pinion shaft 2 and the second pinion shaft 4. A tie rod 89 is connected to the rack shaft 3. In other words, the steering device 80 is a rack-and-pinion type electric power steering device.

[0026] The torque sensor 10 detects the steering force of the driver transmitted to the steering shaft 82 via the steering wheel 81 as a steering torque. The vehicle speed sensor 101 detects the traveling speed (vehicle speed) of the vehicle on which the steering device 80 is mounted. The electric motor 102, the torque sensor 10, and the vehicle speed sensor 101 are electrically connected to the ECU 99.

[0027] The ECU 99 controls the operation of the electric motor 102. The ECU 99 also acquires signals from the torque sensor 10 and the vehicle speed sensor 101. That is, the ECU 99 acquires the steering torque T from the torque sensor 10 and the vehicle speed signal V from the vehicle speed sensor 101. When the ignition switch 103 is in the on state, the ECU 99 is supplied with power from a power supply device (for example, an on-board battery) 104. The ECU 99 calculates an assist steering command value of the assist command based on the steering torque T and the vehicle speed signal V. Then, the ECU 99 adjusts the power value S to be supplied to the electric motor 102 based on the calculated assist steering command value. The ECU 99 acquires, as operation information R, information on the induced voltage from the electric motor 102 or information output from a rotation detection device such as a resolver provided in the electric motor 102.

[0028] The steering force of the operator (driver) input to the steering wheel 81 is transmitted to the second pinion shaft 4. The steering force transmitted to the second pinion shaft 4 is transmitted to the tie rod 89 via the steering gear 100, displacing the wheels.

[0029] Furthermore, the steering force input by the operator to the steering wheel 81 is transmitted to a torque sensor 10 arranged in a steering force transmission path from the steering wheel 81 to the second pinion shaft 4. At this time, the ECU 99 acquires the steering torque T from the torque sensor 10 and acquires a vehicle speed signal V from a vehicle speed sensor 101. Then, the ECU 99 controls the operation of the electric motor 102. The auxiliary steering torque generated by the electric motor 102 is transmitted to the first pinion shaft 2.

[0030] The auxiliary steering torque transmitted to the first pinion shaft 2 is transmitted to the tie rod 89 via the steering gear 100, displacing the wheels. That is, the steering device 80 displaces the wheels using not only the steering force of the operator transmitted to the rack shaft 3 via the second pinion shaft 4, but also the auxiliary steering torque of the electric motor 102 transmitted to the rack shaft 3 via the first pinion shaft 2.

[0031] 1, steering device 80 is of a dual pinion type having both a manual side that transmits steering force to rack shaft 3 via second pinion shaft 4 and an assist side that transmits assistive steering torque of electric motor 102 to rack shaft 3 via first pinion shaft 2, but is not limited to this. Steering device 80 may be, for example, a column assist type electric power steering device in which assist force is applied to steering shaft 82, or a single pinion assist type electric power steering device in which assist force is applied to second pinion shaft 4. Steering device 80 may also be a rack assist type electric power steering device in which assist force is applied to rack shaft 3 without going through a pinion, such as a ball screw type electric power steering device in which assist force is applied to rack shaft 3 by a ball screw.

[0032] Fig. 2 is a perspective view showing a part of the steering device according to the embodiment. Fig. 3 is a front view showing a part of the steering device according to the embodiment. Fig. 4 is a rear view showing a part of the steering device according to the embodiment. Fig. 5 is a side view showing a part of the steering device according to the embodiment.

[0033] As shown in Figures 2 to 5, the rack shaft 3 and the rack housing 30 extend along the longitudinal direction X of the rack shaft 3. The longitudinal direction X of the rack shaft 3 coincides with the axial direction of the center axis AX4. One side of the longitudinal direction X is the X1 side, and the other side is the X2 side. The X1 side is, for example, the left side of the vehicle, and the X2 side is, for example, the right side of the vehicle.

[0034] As shown in Figures 2 to 5, the rack housing 30 is cylindrical, and the rack shaft 3 is inserted inside the rack housing 30. The rack shaft 3 and the rack housing 30 extend in the axial direction of the central axis AX4 of the rack shaft. An electric motor 102 is attached to the end of the rack housing 30 on the X1 side. A worm shaft 35 is provided on the output shaft of the electric motor 102. The electric motor 102 and the worm shaft 35 extend in the axial direction of the motor central axis AX3. The worm shaft 35 meshes with a worm wheel 34.

[0035] A first housing 36 is attached to a portion of the rack housing 30 on the X1 side, and a second housing 44 is attached to a portion of the rack housing 30 on the X2 side. The first pinion shaft 2 and the worm wheel 34 are housed inside the first housing 36. The second pinion shaft 4 is housed inside the second housing 44. The central axis AX4 of the rack shaft 3 is approximately parallel to the motor central axis AX3.

[0036] Fig. 6 is a front view of Fig. 3 with the rack housing removed. Fig. 7 is a perspective view of the rack shaft according to the embodiment. As shown in Fig. 6, a steering device 80 according to the embodiment includes a first pinion shaft 2, a second pinion shaft 4, and a rack shaft 3.

[0037] As shown in Fig. 7, the rack shaft 3 has a large diameter portion 3a and a small diameter portion 3b. The large diameter portion 3a is located on the X1 side of the axial center of the rack shaft 3. The small diameter portion 3b is located on the X2 side of the axial center of the rack shaft 3. The small diameter portion 3b has a smaller diameter than the large diameter portion 3a. The rack shaft 3 extends in the X direction, which is its longitudinal direction.

[0038] As shown in FIGS. 6 and 7 , first rack teeth 31 are formed on the large diameter portion 3a. The first rack teeth 31 include multiple teeth arranged at equal intervals in the X direction. The first rack teeth 31 have a twist angle θ1 with respect to a line L1 perpendicular to a central axis AX4 of the rack shaft 3. That is, the angle of intersection between a line L2 along the first rack teeth 31 and the line L1 is the twist angle θ1. The first pinion shaft 2 has a shaft 23 having first pinion teeth 21 formed on its outer periphery. The first pinion shaft 2 has a first rotation axis AX1. The first pinion teeth 21 mesh with the first rack teeth 31. An end 23a of the shaft 23 is connected to a worm wheel 34. The first pinion shaft 2 and the worm wheel 34 are rotatable about the first rotation axis AX1. The first rotation axis AX1 and the central axis AX4 of the rack shaft 3 are substantially perpendicular to each other. In other words, the axial direction of the first rotation axis AX1 extends along the short direction of the rack shaft 3. That is, the intersection angle α between the first rotation axis AX1 and the central axis AX4 is approximately 90 degrees. A pad 22 is disposed on the opposite side of the rack shaft 3 from the first pinion shaft 2. The pad 22 supports the back surface of the rack shaft 3.

[0039] Second rack teeth 32 are formed on the small diameter portion 3b. The second rack teeth 32 have multiple teeth arranged at equal intervals in the X direction. The second pinion shaft 4 has a shaft 42 with second pinion teeth 41 formed on its outer periphery. The second pinion teeth 41 mesh with the second rack teeth 32. The second pinion shaft 4 is rotatable around the second rotation axis AX2. The intersection angle β between the second rotation axis AX2 and the central axis AX4 of the rack shaft is, for example, 90 degrees or less. A pad 43 is arranged on the opposite side of the rack shaft 3 from the second pinion shaft 4. The pad 43 supports the back surface of the rack shaft 3.

[0040] FIG. 8 is a schematic diagram of the first rack teeth, showing a state in which meshing traces of the first pinion teeth remain. FIG. 8 shows a state in which three teeth are meshed. Specifically, meshing traces P1, P2, and P3 of the first pinion teeth 21 remain on the first rack teeth 31 from the X1 side to the X2 side. Each of the meshing traces P1, P2, and P3 extends along a direction intersecting the central axis AX4. As shown in FIG. 8, the first rack teeth 31 have a tooth tip 310 and a tooth flank 311. The tooth flank 311 rises from a tooth bottom 312. In FIG. 8, the meshing traces P1, P2, and P3 are formed on the tooth flank 311.

[0041] 8, when the first pinion shaft 2 rotates one revolution around the first rotation axis AX1 (i.e., the rotation angle around the axis is 360 degrees), the number of teeth of the first pinion teeth 21 that mesh with the first rack teeth 31 changes depending on the rotation angle. Here, in the present application, the total meshing ratio C is defined as "the sum of values ​​obtained by multiplying A by B when a state in which the number of teeth of the first pinion teeth 21 that mesh with the first rack teeth 31 is A teeth when the first pinion shaft 2 rotates one revolution around the first rotation axis AX1 (i.e., the rotation angle around the axis is 360 degrees), and this state occurs at a ratio B." In other words, when a plurality of A teeth and a plurality of ratios B corresponding to A teeth occur depending on the rotation angle, the total meshing ratio C is the sum of these multiple values.

[0042] For example, when the first pinion shaft 2 rotates once, if the state in which two of the first pinion teeth 21 mesh with the first rack teeth 31 occurs 50% of the time, and the state in which three of the first pinion teeth 21 mesh with the first rack teeth 31 occurs 50% of the time, the total meshing ratio is (2×0.5)+(3×0.5)=2.5.

[0043] Fig. 9 is a graph showing the adjacent torque variation of the operating torque on the vertical axis and the total contact ratio on the horizontal axis. Fig. 10A is a schematic graph showing the operating torque according to Mode 1 where the total contact ratio is 1.45. Fig. 10B is a schematic graph showing the operating torque according to Mode 4 where the total contact ratio is 2.16. Table 1 is a table listing the helix angle of the first pinion shaft, the total contact ratio between the first pinion teeth and the first rack teeth, etc.

[0044] The relationship between the total contact ratio and the average adjacent fluctuation of operating torque will be described with reference to FIG. 9 and Table 1. Note that hereinafter, "adjacent fluctuation of operating torque" will also be referred to as "adjacent torque fluctuation." The adjacent torque fluctuation Tr will be briefly described. As shown in FIG. 10A , when the first pinion shaft 2 is rotated with the first pinion teeth 21 meshed with the first rack teeth 31, the operating torque that rotates the first pinion shaft 2 changes in a wave-like manner according to the rotation angle of the first pinion shaft 2. Here, for one adjacent operating torque, for example, operating torque T1, in terms of the rotation angle, the difference between the peak and trough of operating torque T1 is referred to as adjacent torque fluctuation Tr. In other words, the torque fluctuation over one pinion tooth cycle is referred to as adjacent torque fluctuation Tr. In other words, adjacent torque fluctuation Tr is the difference between the peak and trough of one wave. The total contact ratio is changed by changing the helix angle θ1 of the first rack teeth 31 (see FIG. 6). As described with reference to FIG. 6, the axial direction of the first rotation shaft AX1 extends along the short side direction of the rack shaft 3. [Table 1]

[0045] Table 1 summarizes the relationship between adjacent torque fluctuation and total contact ratio in Figure 9. Specifically, Table 1 lists the total contact ratios of 1.45, 1.63, 1.81, and 2.16. Figure 9 also lists the adjacent torque fluctuation corresponding to each of these total contact ratios. Also, in Figure 9, circles indicate the average adjacent torque fluctuation, while crosses indicate individual values ​​(individual variations) of adjacent torque fluctuation. The experimental data shown in Figure 9 and Table 1 are examples of measurements of the assist and manual sides of a dual pinion, not experimental data for the assist side alone. To minimize the influence of the manual side, the manual side was used as the same sample under each condition. Pinion samples with tooth space runout of 30 μm or less and minimal variation in tooth profile and tooth trace shape were selected. The pinion was connected to the operating torque tester via a joint, and the pinion rotation angle and torque were measured. As a lubricant, 12 g of grease (Molywhite LSG) was applied to the pinion tooth grooves, rack tooth grooves, and rack back surface. The measurement speed was 10 rpm, and the measurement range was ±490 degrees (98% of the full stroke). As described above, the total contact ratio was changed by changing the helix angle θ1 of the first rack teeth 31 (see FIG. 6 ). More specifically, the total contact ratio was determined by the combination of the helix angle and the intersecting angle. In all of the examples 1 to 4 in Table 1, the intersecting angle was 0 degrees. As shown in FIG. 9 and Table 1, there is a large difference between the average adjacent torque fluctuation when the total contact ratio is 1.6 and the average adjacent torque fluctuation when the total contact ratio is 1.8. That is, in Example 1, the helix angle θ1 of the first pinion teeth 21 is 5 degrees, the total contact ratio is 1.45, and the average adjacent torque fluctuation is 0.47 Nm. In mode 2, the helix angle θ1 of the first pinion tooth 21 is 7.5 degrees, the total contact ratio is 1.63, and the average adjacent torque fluctuation is 0.49 Nm. As such, there is not much difference between mode 1 and mode 2, with the average adjacent torque fluctuation being 0.47 Nm (total contact ratio 1.45) and the average adjacent torque fluctuation being 0.49 Nm (total contact ratio 1.63).

[0046] In Example 3, the helix angle θ1 of the first pinion teeth 21 is 10 degrees, the total contact ratio is 1.81, and the average adjacent torque fluctuation is 0.30 Nm. In Example 4, the helix angle θ1 of the first pinion teeth 21 is 15 degrees, the total contact ratio is 2.16, and the average adjacent torque fluctuation is 0.22 Nm. As such, there is not much difference between Example 3 and Example 4, with the average adjacent torque fluctuation being 0.30 Nm (total contact ratio of 1.81) and the average adjacent torque fluctuation being 0.22 Nm (total contact ratio of 2.16). Furthermore, the average adjacent torque fluctuation of 0.22 Nm when the total contact ratio is 2.16 is smaller than the average adjacent torque fluctuation of 0.30 Nm when the total contact ratio is 1.81.

[0047] However, there is a large difference in the average adjacent torque fluctuation and the torsion angle θ1 between Mode 2 and Mode 3. Specifically, the average adjacent torque fluctuation is 0.49 Nm in Mode 2, and 0.3 Nm in Mode 3. The torsion angle θ1 is 7.5 degrees in Mode 2, and 10 degrees in Mode 3.

[0048] Next, the relationship between the total contact ratio and the variation in adjacent torque fluctuation will be explained. As shown in Table 1, the standard deviation σ of adjacent torque fluctuation is 0.143, 0.163, 0.128, and 0.069 in modes 1 to 4. There is also a difference in the variation in adjacent torque fluctuation between modes 2 and 3. Note that in Figures 10A and 10B, the vertical axis represents the rotation angle of the first pinion shaft, and the horizontal axis represents the operating torque.

[0049] From the viewpoint of reducing the average adjacent torque fluctuation and the variation in adjacent torque fluctuation, the total meshing ratio between the first pinion teeth 21 and the first rack teeth 31 is preferably 1.8 or more. The total meshing ratio between the first pinion teeth 21 and the first rack teeth 31 is more preferably 2 or more. When the total meshing ratio between the first pinion teeth 21 and the first rack teeth 31 is 2 or more, for example, two teeth are always in mesh with each other, which reduces the contact surface pressure between the teeth during meshing, thereby providing the effect of increasing the wear resistance of the first pinion teeth 21 and the first rack teeth 31.

[0050] As described above, the steering device 80 includes the first pinion shaft 2 having the first pinion teeth 21 on its outer periphery, the second pinion shaft 4 having the second pinion teeth 41 on its outer periphery, and the rack shaft 3 having the first rack teeth 31 meshing with the first pinion teeth 21 and the second rack teeth 32 meshing with the second pinion teeth, and extending in the longitudinal direction X. The axial direction of the first rotation shaft AX1 extends along the short direction of the rack shaft 3, and the total meshing ratio between the first pinion teeth 21 and the first rack teeth 31 is 1.8 or more.

[0051] As mentioned above, in the steering device described in Patent Document 1, when the pinion shaft is rotated with the pinion teeth meshing with the rack teeth, if there is a large fluctuation in the operating torque acting on the pinion shaft, the steering feeling felt by the driver may deteriorate.

[0052] In contrast, in the present disclosure, the total meshing ratio between the first pinion teeth and the first rack teeth is 1.8 or greater. When the total meshing ratio is 1.8 or greater, fluctuations in the operating torque acting on the first pinion shaft are smaller than when the total meshing ratio is 1.6 or less. It is generally known that steering feel improves when the fluctuations in operating torque are smaller, and therefore, according to this embodiment, the steering feel is improved. Furthermore, since an increase in the meshing ratio reduces the contact surface pressure between the teeth during meshing, according to this embodiment, the wear resistance of the first pinion teeth 21 or the first rack teeth 31 is improved.

[0053] The total meshing ratio between the first pinion teeth 21 and the first rack teeth 31 is 2.0 or more. Therefore, according to this embodiment, the steering feel is further improved, and the wear resistance of the first pinion teeth 21 or the first rack teeth 31 is further improved.

[0054] The helix angle of the first rack teeth 31 is 10 degrees or more. This makes it possible to change the overall meshing ratio between the first pinion teeth 21 and the first rack teeth 31 by simply adjusting the helix angle θ1 of the first rack teeth 31.

[0055] The central axis AX4 of the rack shaft 3 is substantially parallel to the central axis AX3 of the motor. Therefore, the rack shaft 3 and the electric motor 102 can be arranged substantially parallel to each other, which allows the steering device 80 to be made smaller and allows for more space to mount components in the vehicle.

[0056] [Variation] Next, a modified example will be described. Fig. 11 is a schematic diagram showing a part of a steering device according to a modified example.

[0057] The rack shaft 3A according to the modified example is applied to a single-pinion steering device 80A. The rack shaft 3A has third rack teeth 32A. The third rack teeth 32A have a helix angle θ1. The third pinion shaft 4A includes a shaft 42, on the outer periphery of which third pinion teeth 41A are provided. The third pinion shaft 4A rotates about a third rotation axis AX2A. The intersection angle α between the third rotation axis AX2A and the central axis AX4 is approximately 90 degrees. Even in the modified example, the total meshing ratio between the third pinion teeth 41A and the third rack teeth 32A is preferably 1.8 or greater, and more preferably 2 or greater. Note that while FIG. 9 and Table 1 described above show an example of a dual pinion, FIG. 9 and Table 1 can also be applied to a single pinion. In other words, the total meshing ratio is determined by the combination of the helix angle and the intersecting angle, and the meshing ratio can be improved to reduce adjacent fluctuations, so this idea applies to both single pinions and dual pinions.

[0058] As described above, the rack shaft 3A according to the modified example includes the third pinion shaft 4A having the third pinion teeth 41A on its outer periphery and rotatable about the third rotation shaft AX2A, and the rack shaft 3A extending in the longitudinal direction and having the third rack teeth 32A meshing with the third pinion teeth 41A. The axial direction of the third rotation shaft AX2A extends along the short direction of the rack shaft 3A, and the total meshing ratio between the third pinion teeth 41A and the third rack teeth 32A is 1.8 or greater.

[0059] As in the above-described embodiment, when the total contact ratio is 1.8 or more, the average value and variation of the adjacent torque fluctuation Tr are smaller than when the total contact ratio is 1.6 or less, as shown in Fig. 9. Therefore, this modification also improves the steering feel and the wear resistance of the third pinion teeth 41A or the third rack teeth 32A.

[0060] The total meshing ratio between the third pinion teeth 41A and the third rack teeth 32A is 2.0 or more. Therefore, this modification also further improves the steering feel and the wear resistance of the third pinion teeth 41A or the third rack teeth 32A. [Explanation of symbols]

[0061] 10 Torque sensor 2. First pinion shaft 21 First pinion tooth 22 pads 23 Shaft 23a End 3, 3A rack axis 3a Large diameter part 3b Small diameter section 30 rack housing 31 First rack tooth 310 Tooth tip 311 Tooth surface 312 Root of tooth 32 Second rack tooth 32A 3rd rack tooth 34 Worm Wheel 35 worm shaft 36 First Housing 4 Second pinion shaft 4A 3rd pinion shaft 41 Second pinion tooth 41A 3rd pinion tooth 42 Shaft 43 Pad 44 Second Housing 80, 80A steering device 81 Steering wheel 82 Steering shaft 84 Universal joint 85 Intermediate shaft 86 Universal joint 87 Stub shaft (first shaft) 89 tie rod 99 ECU 100 steering gear 101 Vehicle speed sensor 102 electric motor 103 Ignition switch 104 Power supply AX1 First rotation axis AX2 Second rotation axis AX2A 3rd rotation axis AX3 motor central shaft AX4 rack axis center L1, L2 straight line Tr Adjacent torque fluctuation T1 operating torque P1 Engagement marks P2 Engagement marks P3 Engagement marks X Longitudinal direction α, β intersection angle θ1 Twist angle

Claims

1. a first pinion shaft having first pinion teeth on its outer periphery and rotatable around the axis of the first rotary shaft; a second pinion shaft having second pinion teeth on its outer periphery and rotatable around the axis of the second rotary shaft; a rack shaft extending in a longitudinal direction and having first rack teeth meshing with the first pinion teeth and second rack teeth meshing with the second pinion teeth; Equipped with an axial direction of the first rotating shaft extends along a short direction of the rack shaft, a total meshing ratio between the first pinion teeth and the first rack teeth is 1.8 or more; Steering device.

2. a total meshing ratio between the first pinion teeth and the first rack teeth is 2.0 or more; The steering device according to claim 1 .

3. the helix angle of the first rack tooth is 10 degrees or greater; 3. A steering device according to claim 1 or 2.

4. a third pinion shaft having third pinion teeth on its outer periphery and rotatable around the axis of the third rotation shaft; a rack shaft extending in the longitudinal direction and having third rack teeth that mesh with the third pinion teeth; Equipped with an axial direction of the third rotation shaft extends along a short direction of the rack shaft, a total meshing ratio between the third pinion teeth and the third rack teeth is 1.8 or more; Steering device.

5. a total meshing ratio between the third pinion teeth and the third rack teeth is 2.0 or more; The steering device according to claim 4.

6. the helix angle of the third rack tooth is 10 degrees or greater; The steering device according to claim 5.

7. the first pinion shaft is provided on an assist side that transmits an assist steering torque to the rack shaft, The second pinion shaft is provided on a manual side that transmits steering force to the rack shaft. The steering device according to claim 1 .

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