Steering reaction force device

Abstract

To provide a steering reaction force device, the weight of which is further reduced and which is provided with a worm wheel.SOLUTION: A steering reaction force device includes a motor and a speed reduction mechanism. The speed reduction mechanism includes: a worm wheel attached to a steering shaft and including a plurality of wheel tooth portions on the outer circumference; and a worm shaft configured to be rotated by the motor. The worm wheel includes a metal core grid and the wheel tooth portions disposed on the outer circumference side of the core grid. The outer circumference of the core grid includes a cylindrical portion extending along the circumferential direction around the central axis and at least a protrusion protruding radially outward. The wheel tooth portions include first teeth that are disposed on the outer circumferential side of the cylindrical portion and composed of resin and second teeth that are composed of the protrusions and resin layers formed on the outer periphery of the protrusion.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] In a steer-by-wire steering system, the steering wheel and the steered wheels are mechanically disconnected. In this configuration, the steering reaction force is not transmitted from the steering mechanism including the steered wheels to the steering wheel. For this reason, a steering reaction force device is provided on the steering shaft connected to the steering wheel, and a reaction force in the opposite direction to the steering direction of the steering wheel is applied to the steering wheel, giving the driver a natural steering feel.

[0003] The steering reaction force device includes, for example, a motor and a reduction gear mechanism, and the steering reaction force generated by the motor is transmitted to the steering shaft via the reduction gear mechanism. The reduction gear mechanism includes, for example, a worm shaft and a worm wheel, and the rotation of the motor is transmitted to the worm wheel via the worm shaft by meshing the shaft teeth of the worm shaft with the wheel teeth of the worm wheel.

[0004] Here, while worm wheels have traditionally been made of metal, in recent years, a resin layer has sometimes been formed on the outer periphery of the wheel teeth of the worm wheel for purposes such as reducing rattle noise caused by backlash (see, for example, Patent Document 1). The worm wheel of Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, a plurality of protrusions that protrude radially outward are provided on the outer periphery of the core, the same number as the number of wheel teeth, over the entire circumference. The resin layer is formed on the outer periphery of all of the plurality of protrusions. In other words, all of the wheel teeth have a metal protrusion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-21980 Summary of the Invention [Problem to be solved by the invention]

[0006] It is desirable to further reduce the weight of a steering reaction force device that includes a worm wheel.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a steering reaction force device including a worm wheel that is lighter in weight. [Means for solving the problem]

[0008] In order to achieve the above object, a steering reaction force device according to one embodiment generates a steering reaction force to be applied to a steering wheel when steering is performed with the steering wheel that is mechanically uncoupled from a steering rack shaft, and includes a motor that serves as a source of the steering reaction force, and a speed reduction mechanism that is connected to the motor and transmits the output of the motor to the steering shaft of the steering wheel as a reaction torque, and the speed reduction mechanism is a worm wheel that is attached to the steering shaft, is rotatable around a central axis, and has a plurality of wheel teeth on its outer periphery. and a worm shaft having a shaft tooth portion that meshes with the wheel tooth portion and that is rotated by the motor, the worm wheel having a metal core and the wheel tooth portion provided on the outer periphery of the core, the outer periphery of the core having a cylindrical portion that extends circumferentially around the central axis and at least one protrusion that protrudes radially outward, the wheel tooth portion being provided on the outer periphery of the cylindrical portion and having a first tooth formed of resin and a second tooth formed of the protrusion and a resin layer formed on the outer periphery of the protrusion.

[0009] In a steer-by-wire steering system, a steering reaction force device is provided on a steering shaft connected to the steering wheel to apply a steering reaction force to the steering wheel in a direction opposite to the steering direction of the steering wheel. The steering reaction force device includes a motor and a reduction mechanism, and the reduction mechanism has a worm shaft and a worm wheel.

[0010] A steering system requires a stopper mechanism to notify the driver of the limit of the steering angle of the steered wheels. In vehicles where the steering wheel and steered wheels are mechanically connected, a stopper mechanism is provided on the steering rack shaft, for example. However, in vehicles equipped with a steer-by-wire steering system, a stopper mechanism must be provided on the steering reaction force device side. For example, the stopper mechanism uses the output of a motor. That is, the stopper mechanism stops the rotation of the motor of the steering reaction force device when the steering wheel reaches the limit of the steering angle, thereby preventing the steering wheel from rotating via the worm shaft, worm wheel, and steering shaft. The stopper mechanism is provided to prevent the steering wheel from rotating beyond a certain angle, for example, to notify the driver of the end stop position or to prevent the airbag harness connected to the steering wheel from breaking due to excessive rotation.

[0011] The shaft teeth of the worm shaft mesh with the wheel teeth of the worm wheel, and the rotation of the shaft teeth rotates the wheel teeth and the worm wheel. When the stopper mechanism is activated and the rotation of the worm wheel stops, a large load is input to the meshing portion of the wheel teeth that meshes with the shaft teeth.

[0012] As described above, the worm wheel of Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, the core has a plurality of radially outwardly protruding protrusions on the entire periphery, the number of which is the same as the number of wheel teeth, and the resin layer is formed on the outer periphery of all of the protrusions. In other words, because all of the wheel teeth have metal protrusions, the worm wheel is heavy.

[0013] In contrast, in the wheel tooth portion according to the present disclosure, some of the teeth are second teeth with metal protrusions, and the rest are first teeth made of resin. The second teeth are lighter in weight than the first teeth. Therefore, if the phase (circumferential position) at which the worm wheel stops rotating when the stopper mechanism is activated is predetermined, by arranging the second teeth at the meshing portion of the wheel tooth portion that meshes with the shaft tooth portion, the number of metal protrusions can be reduced, and the weight of the worm wheel and steering reaction force device can be further reduced. The worm wheel according to the present disclosure can achieve a weight reduction of, for example, 10% to 20% compared to the worm wheel of Patent Document 1.

[0014] In a preferred embodiment, the wheel tooth portion has a second tooth group in which a plurality of the second teeth are adjacent to each other in the circumferential direction. Therefore, compared to a case in which there is only one second tooth, the rigidity of the wheel tooth portion is improved, and the meshing force between the wheel tooth portion and the shaft tooth portion is improved, thereby more reliably preventing rotation of the steering wheel by the stopper mechanism.

[0015] In a preferred embodiment, a plurality of the second tooth groups are provided, the plurality of second tooth groups are spaced apart along the circumferential direction, and at least one first tooth is provided between two of the second tooth groups adjacent to each other in the circumferential direction.

[0016] This makes it possible to accommodate multiple phases (circumferential positions) at which the worm wheel stops rotating when the stopper mechanism is activated, which means that it is possible to accommodate needs such as changing the phase (circumferential position) at which the worm wheel stops rotating from an initially set phase to another phase, or installing worm wheels of the same configuration on vehicles of different models.

[0017] In a preferred embodiment, the gear mechanism further comprises a detection sensor attached to a housing that houses the worm wheel at a position facing the outer periphery of the wheel tooth portion, and that detects the circumferential position of the second tooth.

[0018] When the stopper mechanism is activated in a limit range of the steering angle of the steered wheels, the second set of teeth is positioned in a meshing portion that meshes with the shaft teeth of the worm shaft. To achieve this, for example, an absolute angle sensor that detects the rotation angle of the steering shaft is provided in a part of the housing, and under normal circumstances, the absolute angle sensor detects the absolute angle of the steering wheel, and when the phase (rotation angle) of the steering wheel reaches a predetermined range, the second set of teeth is positioned in the meshing portion.

[0019] Here, the detection sensor detects the phase of the second tooth having a metal protrusion, and by adjusting (calibrating) the absolute angle sensor and the phase (circumferential position) of the second tooth in advance, even if the absolute angle sensor fails, the detection sensor can estimate the rotation angle of the steering wheel from the rotation speed of the worm wheel.

[0020] In a preferred embodiment, the detection sensor is a magnetically sensitive sensor having a Hall element, so that the circumferential position of the second set of teeth can be detected with a simple structure.

[0021] In a preferred embodiment, the steering device includes a stopper mechanism. For example, the stopper mechanism uses the output of a motor. That is, the stopper mechanism stops the rotation of the motor of the steering reaction force device at the limit of the steering angle of the steered wheels. This prevents the steering wheel from rotating through the worm shaft, worm wheel, and steering shaft. The stopper mechanism prevents the steering wheel from rotating beyond a certain angle, for example, to notify the driver of the end stop position or to prevent the airbag harness connected to the steering wheel from breaking due to excessive rotation. [Effects of the Invention]

[0022] According to the present disclosure, it is possible to provide a steering reaction force device including a worm wheel that is lighter in weight. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram of the overall configuration of an electric power steering device according to a first embodiment. [Figure 2] FIG. 2 is a perspective view that schematically shows the steering unit of the first embodiment. [Figure 3] FIG. 3 is a side view of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a perspective view schematically showing the worm wheel of the first embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8] FIG. 8 is a perspective view, partly in cross section, schematically showing the worm wheel of the first embodiment. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 10 is a perspective view schematically showing a core metal included in the worm wheel of the first embodiment. [Figure 11] FIG. 11 is a front view of FIG. [Figure 12] FIG. 12 is a front view schematically showing a core metal included in the worm wheel of the second embodiment. [Figure 13] FIG. 13 is a cross-sectional view schematically showing a worm wheel according to the second embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view of a steering reaction force device of the third embodiment, and corresponds to FIG. 5 of the first embodiment. [Figure 15] FIG. 15 is an enlarged view of a part of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0024] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the components described below can be combined as appropriate. Furthermore, parts with the same structure are given the same reference numerals and their description will be omitted. In three-dimensional coordinates, the X direction indicates the front-to-rear direction of the vehicle body, the Y direction indicates the width direction of the vehicle, and the Z direction indicates the up-down direction. Furthermore, the X1 side indicates the input shaft side of the first steering shaft, and the X2 side indicates the output shaft side. The Y1 side indicates the right side in the width direction of the vehicle, and the Y2 side indicates the left side. The Z1 side indicates the upper side, and the Z2 side indicates the lower side.

[0025] [First embodiment] A first embodiment will be described below. Fig. 1 is a schematic diagram of the overall configuration of an electric power steering device of the first embodiment. Fig. 2 is a perspective view showing a steering unit of the first embodiment. Fig. 3 is a side view of Fig. 2. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 2. Fig. 5 is a cross-sectional view taken along line VV in Fig. 3.

[0026] As shown in FIG. 1, the electric power steering device 100 includes a steering unit 7, a control device (ECU) 70, and a steering unit 80.

[0027] Steering unit 7 is provided with a steering reaction force device 110 for applying a steering reaction force to steering wheel 10 in a direction opposite to the steering direction of steering wheel 10 when steering wheel 10 is steered. Control device (ECU) 70 calculates a reaction torque according to the vehicle's running state based on operation information, adjusts the power value supplied to motor 27 of steering reaction force device 110 based on the reaction torque, and operates motor 27 according to the power value, thereby transmitting the steering reaction force of steering wheel 10 to the operator. Control device (ECU) 70 also calculates a current command value based on the operation information and controls the current supplied to steering motor 81 of steering unit 80. In steering unit 80, steered wheels 82 are steered via various gears connected to steering motor 81. Each component of electric power steering device 100 will be described in detail below.

[0028] As shown in FIGS. 1 to 4, the steering unit 7 includes a steering wheel 10, a steering shaft 1, a housing 2, and a steering reaction force device 110.

[0029] 4, the steering shaft 1 extends in the X direction (axial direction). The steering shaft 1 has a first shaft 11, a second shaft 12, a third shaft 13, and a torsion bar .

[0030] 4, the steering wheel 10 is rotatably connected to the X1-side end 11a of the first shaft 11. The X2-side end 11c of the first shaft 11 is spline-fitted to the X1-side end 12a of the second shaft 12. The main body 11b of the first shaft 11 connects the end 11a and the end 11c.

[0031] 4, a fitting hole 12e is provided in the end 12d on the X2 side of the second shaft 12. The end 14c on the X1 side of the torsion bar 14 is fitted into the fitting hole 12e. The main body 12c of the second shaft 12 connects the end 12a and the end 12d.

[0032] 4, the X2-side tip 12f of the second shaft 12 is fitted into the X1-side end 13a of the third shaft 13. The X2-side end 13c of the third shaft 13 is fitted into the X2-side end 14a of the torsion bar 14. The main body 13b of the third shaft 13 connects the end 13a and the end 13c. The main body 14b of the torsion bar 14 connects the X1-side end 14c and the X2-side end 14a.

[0033] 4, the first shaft 11 is rotatably supported by the first housing 21 via a bearing 15. A bearing 16 is provided between the outer periphery of the X1-side end 13a of the third shaft 13 and the inner periphery of the third housing 23. A bearing 17 is provided between the outer periphery of the main body 13b of the third shaft 13 and the inner periphery of the X2-side end of the fourth housing 24. Therefore, the third shaft 13 is rotatably supported by the third housing 23 via the bearing 16, and is rotatably supported by the fourth housing 24 via the bearing 17. In this way, the steering shaft 1 is rotatably supported by the housing 2, which will be described later.

[0034] 4, the housing 2 includes a first housing 21, a second housing 22, a third housing 23, and a fourth housing 24. The first housing 21, the second housing 22, the third housing 23, and the fourth housing 24 are arranged in this order from the X1 side to the X2 side.

[0035] As shown in FIG. 4 , the first housing 21 is disposed on the outer periphery of the first shaft 11 and the second shaft 12. A flange 21a is provided at the end of the first housing 21 on the X2 side. Through holes penetrating in the X direction are provided in the flange 21a, the second housing 22, the third housing 23, and the fourth housing 24, and a bolt BL is inserted into the through hole. A male thread portion BLa is formed at the end of the bolt BL, and a female thread portion is formed in the fourth housing 24. The male thread portion BLa of the bolt BL engages with the female thread portion of the fourth housing 24, thereby fastening the bolt BL to the flange 21a, the second housing 22, the third housing 23, and the fourth housing 24.

[0036] As shown in FIG. 5, the fourth housing 24 includes a worm wheel accommodating portion 243 , a worm shaft accommodating portion 244 , and a flange portion 245 .

[0037] 5, the worm wheel accommodating portion 243 is formed to protrude toward the Z1 side and to have an arc-shaped cross section. The worm wheel 300 is accommodated inside the worm wheel accommodating portion 243. Flange portions 24g and 24h protrude radially outward from the outer periphery of the worm wheel accommodating portion 243.

[0038] The worm shaft accommodating portion 244 extends along the Y direction. A through hole 24a is provided in the worm shaft accommodating portion 244, and the worm shaft 32 is accommodated inside the worm shaft accommodating portion 244. A flange portion 24f that protrudes toward the Z2 side is provided in the worm shaft accommodating portion 244.

[0039] The end 242 on the Y1 side of the worm shaft accommodating portion 244 is open on the Y1 side, and the fitting member 24b is fitted into the opening. A bearing 26 is disposed on the Y2 side of the fitting member 24b. The bearing 26 is, for example, a rolling bearing. A flange portion 245 is disposed on the Y1 side of the end 242 of the worm shaft accommodating portion 244.

[0040] A fitting member 24d is fitted into the inside of the Y2-side end 241 of the worm shaft accommodating portion 244. A bearing 25 is provided on the inner periphery of the fitting member 24d. The bearing 25 is, for example, a plain bearing. The Y2-side end 241 of the worm shaft accommodating portion 244 is open on the Y2 side, and a lid portion 24e is fitted into this opening. As shown in FIGS. 2 and 3, the lid portion 24e is fastened with two bolts BL.

[0041] Next, a description will be given of the steering reaction force device 110. As shown in Fig. 5, the steering reaction force device 110 includes a motor 27 and a speed reduction mechanism 3, and the speed reduction mechanism 3 has a worm wheel 300 and a worm shaft 32. The steering reaction force is assumed to be, for example, a torque of 100 Nm or more.

[0042] The motor 27 serves as a source of steering reaction force. That is, the output of the motor 27 becomes reaction torque, and the reaction torque is transmitted to the steering shaft 1 of the steering wheel 10 via the speed reducer 3. As shown in FIG. 5, a front surface 27a of the motor 27 fits into a recess 245a formed in the flange portion 245 of the fourth housing 24. The motor 27 is provided with an output shaft (not shown), which is connected to the protrusion 32e of the worm shaft 32.

[0043] As shown in FIG. 5, the worm shaft 32 includes a shaft tooth portion 32b, shaft portions 32a and 32d, an expanded diameter portion 32c, and a protruding portion 32e.

[0044] As shown in FIG. 5, the shaft tooth portion 32b has multiple teeth arranged along the Y direction. The shaft tooth portion 32b meshes with the wheel tooth portion 340 of the worm wheel 300. The shaft portion 32a is provided on the Y2 side of the shaft tooth portion 32b. The shaft portion 32a is rotatably supported by the fitting member 24d via a bearing 25. The expanded diameter portion 32c is provided adjacent to the Y1 side of the shaft tooth portion 32b. The outer peripheral surface of the expanded diameter portion 32c is an inclined surface whose diameter increases toward the Y1 side. The shaft portion 32d is provided on the Y1 side of the expanded diameter portion 32c. The shaft portion 32d is rotatably supported by the end portion 242 via a bearing 26. A recess 24c is formed in the fitting member 24b on the Y2 side, and a protrusion 32e is disposed inside the recess 24c.

[0045] As shown in Fig. 5, a third shaft 13 is fitted onto the inner periphery of the worm wheel 300. The configuration of the worm wheel 300 will be described below. Fig. 6 is a perspective view schematically showing the worm wheel of the first embodiment. Fig. 7 is a cross-sectional view taken along line VII-VII in Fig. 6. Fig. 8 is a perspective view, partly in cross section, schematically showing the worm wheel of the first embodiment. Fig. 9 is a cross-sectional view taken along line IX-IX in Fig. 7. Fig. 10 is a perspective view schematically showing a core metal included in the worm wheel of the first embodiment. Fig. 11 is a front view of Fig. 10.

[0046] As shown in FIGS. 6 to 9 , the worm wheel 300 includes a core metal 310 and a wheel tooth portion 340. The worm wheel 300 is an annular member extending in an annular shape in the circumferential direction around a central axis AX. The core metal 310 is made of metal. The core metal 310 has an inner peripheral portion 320 and an outer peripheral portion 330. The inner peripheral portion 320 and the outer peripheral portion 330 are each formed by punching a plurality of low-carbon steel plates, for example. The inner peripheral portion 320 and the outer peripheral portion 330 may be integral with each other.

[0047] 8 and 9, inner circumferential portion 320 has inner periphery 321, outer periphery 322, and side surfaces 323 and 324. Third shaft 13 is fitted onto inner periphery 321. Side surface 323 is provided on the X2 side of inner periphery portion 320, and side surface 324 is provided on the X1 side of inner periphery portion 320. Side surface 323 is formed with protruding portion 325 that is convex toward the X2 side, and side surface 324 is formed with protruding portion 326 that is convex toward the X1 side. Outer periphery 322 and inner periphery 321 extend in an annular shape along the circumferential direction around central axis AX.

[0048] As shown in Figures 8 and 9, outer peripheral portion 330 is provided on the outer peripheral side of inner peripheral portion 320. Outer peripheral portion 330 is fixed to inner peripheral portion 320. Outer peripheral portion 330 has inner periphery 331, outer periphery 332, and side surfaces 333 and 334. Inner periphery 331 contacts outer periphery 322 of inner peripheral portion 320. Inner periphery 331 is fixed to outer periphery 322 of inner peripheral portion 320. Side surface 333 is flush with side surface 323. Side surface 334 is flush with side surface 324.

[0049] As shown in FIGS. 10 and 11, the outer periphery 332 of the outer periphery portion 330 has a cylindrical portion 332a and a protrusion 4.

[0050] As shown in Figures 10 and 11, the cylindrical portion 332a extends in the circumferential direction around the central axis AX. The cylindrical portion 332a has a smooth cylindrical surface. The protrusion 4 has two protrusions 41 and 42. The protrusion 41 has side surfaces 41a and 41b, a top surface 41c, and a bottom surface 41d. The protrusion 42 has side surfaces 42a and 42b and a top surface 42c.

[0051] 10 and 11, side surfaces 41a, 41b are provided on one and the other circumferential sides of protrusion 41. Top surface 41c connects radially outer ends of side surfaces 41a, 41b to each other in the circumferential direction. Side surfaces 42a, 42b are provided on one and the other circumferential sides of protrusion 42. Top surface 42c connects radially outer ends of side surfaces 42a, 42b to each other in the circumferential direction.

[0052] As shown in FIGS. 7 and 8, the wheel tooth portion 340 includes a first tooth 341 and a second set of teeth 342. The first tooth 341 is provided on the outer periphery of the cylindrical portion 332a. The first tooth 341 is formed of resin. The second set of teeth 342 includes a second tooth 342A and a second tooth 342B. Each of the second tooth 342A and the second tooth 342B is formed by a protrusion 4 and a resin layer 40 provided on the outer periphery of the protrusion 4. That is, the resin layer 40 shown in FIGS. 6 to 8 is formed on the outer periphery of the side surfaces 41a, 41b, top surface 41c, and bottom surface 41d of the protrusion 41 described in FIGS. 10 and 11. Therefore, the protrusion 41 and the resin layer 40 on the outer periphery of the protrusion 41 form the second tooth 342A. Similarly, the protrusion 42 and the resin layer 40 on the outer periphery of the protrusion 42 form the second tooth 342B. In other words, the radially outer sides of the protrusions 41 and 42 are covered with the resin layer 40, and the tooth tips of the second tooth group 342 of the worm wheel are formed by the metal protrusions 41 and 42 and the resin layer 40. As shown in FIG. 7, each tooth 347 in the wheel tooth portion 340 has a tooth tip 344, a tooth surface (tooth side surface) 345, and a tooth bottom 346. The tooth tip 344 has end portions 344a, 344b and a central portion 344c. The end portions 344a, 344b are provided at both axial ends of the tooth tip 344, and the central portion 344c is provided between the end portions 344a and 344b.

[0053] 6 and 7, the wheel tooth portion 340 has a second tooth group 342. The second tooth group 342 is formed by a plurality of second teeth adjacent to each other in the circumferential direction. In this embodiment, of the plurality of teeth 347 that make up the wheel tooth portion 340, the second tooth group 342 is formed by second tooth 342A and second tooth 342B.

[0054] 8, the wheel tooth portion 340 has side surfaces 348 and 349. The side surface 348 is flush with the side surface 333 of the core metal 310. The side surface 349 is flush with the side surface 334 of the core metal 310. The wheel tooth portion 340 is a helical gear.

[0055] Furthermore, in a vehicle equipped with the steer-by-wire steering system according to this embodiment, a stopper mechanism is provided in the steering reaction force device 110. For example, the stopper mechanism uses the output of the motor 27. That is, the stopper mechanism stops the rotation of the motor 27 of the steering reaction force device 110 at the limit range of the steering angle of the steered wheels. This prevents the rotation of the steering wheel 10 via the worm shaft 32, the worm wheel 300, and the steering shaft 1. The stopper mechanism prevents the steering wheel 10 from rotating beyond a certain angle, for example, to notify the driver of the end stop position or to prevent the airbag harness connected to the steering wheel 10 from breaking due to excessive rotation.

[0056] As described above, the steering reaction force device 110 according to this embodiment generates a steering reaction force to be applied to the steering wheel 10 when steering is performed with the steering wheel 10 that is mechanically disconnected from the steering rack shaft. The steering reaction force device 110 includes the motor 27 that serves as a source of generating a steering reaction force, and the speed reduction mechanism 3 that is connected to the motor 27 and transmits the output of the motor 27 as a reaction torque to the steering shaft 1 of the steering wheel 10. The speed reduction mechanism 3 includes a worm wheel 300 that is attached to the steering shaft 1, is rotatable about the central axis AX, and has a plurality of wheel tooth portions 340 on its outer periphery, and a worm shaft 32 that has shaft tooth portions 32b that mesh with the wheel tooth portions 340 and is rotated by the motor 27. The worm wheel 300 includes a metal core 310 and a wheel tooth portion 340 provided on the outer periphery of the core 310. The outer periphery of the core 310 includes a cylindrical portion 332a extending circumferentially around the central axis AX and at least one protrusion 41, 42 protruding radially outward. The wheel tooth portion 340 includes a first tooth 341 provided on the outer periphery of the cylindrical portion 332a and formed of resin, and second teeth 342A, 342B formed by the protrusions 41, 42 and a resin layer 40 formed on the outer periphery of the protrusions 41, 42. Note that the phrase "at least one protrusion" in the above description and claims refers to the presence of one or more protrusions (either the protrusion 41 or the protrusion 42). In this embodiment, this refers to the presence of two protrusions.

[0057] In a steer-by-wire steering device, a steering reaction force device 110 is provided on the steering shaft 1 connected to the steering wheel 10 in order to apply a steering reaction force to the steering wheel 10 in a direction opposite to the steering direction of the steering wheel 10. The steering reaction force device 110 includes a motor 27 and a speed reduction mechanism 3, and the speed reduction mechanism 3 has a worm shaft 32 and a worm wheel 300.

[0058] A stopper mechanism must be provided to notify the driver of the limit of the steering angle of the steered wheels. In vehicles in which the steering wheel and steered wheels are mechanically coupled, a stopper mechanism is provided, for example, on the steering rack shaft. However, in vehicles equipped with a steer-by-wire steering system, a stopper mechanism must be provided on the steering reaction force device 110. For example, the stopper mechanism uses the output of the motor 27. That is, the stopper mechanism stops the rotation of the motor 27 of the steering reaction force device 110 when the stopper mechanism reaches the limit of the steering angle of the steered wheels, thereby preventing rotation of the steering wheel 10 via the worm shaft 32, the worm wheel 300, and the steering shaft 1. The stopper mechanism is provided to prevent rotation of the steering wheel 10 beyond a certain angle, for example, to notify the driver of the end stop position or to prevent the airbag harness connected to the steering wheel 10 from breaking due to excessive rotation.

[0059] Here, the shaft teeth 32b of the worm shaft 32 mesh with the wheel teeth 340 of the worm wheel 300, and the rotation of the shaft teeth 32b rotates the wheel teeth 340 and the worm wheel 300. Furthermore, when the rotation of the worm wheel 300 stops due to the operation of the stopper mechanism, a large load is input to the meshing portion of the wheel teeth 340 that meshes with the shaft teeth 32b.

[0060] As described above, the worm wheel of Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, the core has a plurality of radially outwardly protruding protrusions on the entire periphery, the number of which is the same as the number of wheel teeth, and the resin layer is formed on the outer periphery of all of the protrusions. In other words, because all of the wheel teeth have metal protrusions, the worm wheel is heavy.

[0061] In contrast, in the wheel tooth portion 340 according to this embodiment, some of the teeth are second teeth 342A and 342B having metal protrusions 41 and 42, and the rest are first teeth 341 made of resin. The second teeth 342A and 342B are lighter in weight than the first teeth 341. Therefore, if the phase (circumferential position) at which the rotation of the worm wheel 300 stops when the stopper mechanism is activated is predetermined, the weight of the worm wheel 300 and the steering reaction force device 110 can be further reduced by arranging the second teeth 342A and 342B at the meshing portion of the wheel tooth portion 340 that meshes with the shaft tooth portion 32b. The worm wheel 300 according to this embodiment can achieve a weight reduction of, for example, 10% to 20% compared to the worm wheel of Patent Document 1.

[0062] The wheel tooth portion 340 also has a second tooth group 342 in which a plurality of second teeth 342A, 342B are adjacent to each other in the circumferential direction. Therefore, compared to when there is only one second tooth, the rigidity of the wheel tooth portion 340 is improved, and the meshing force between the wheel tooth portion 340 and the shaft tooth portion 32b is improved, which in turn makes it possible for the stopper mechanism to more reliably prevent the steering wheel 10 from rotating.

[0063] In the first embodiment, by setting the second tooth group 342 to one, the rotation angle (phase) at which the rotation of the steering wheel 10 is prevented due to the stopping of the motor 27 becomes, for example, a multiple of 360 degrees.

[0064] [Second embodiment] Next, a second embodiment will be described. Fig. 12 is a front view schematically showing a core metal included in a worm wheel of the second embodiment. Fig. 13 is a cross-sectional view schematically showing the worm wheel of the second embodiment. The second embodiment differs from the first embodiment in that a plurality of second tooth groups are provided. This will be described in detail below.

[0065] 12, two protrusions (protrusion 4 and protrusion 5) are arranged circumferentially spaced apart on the core bar 310A. That is, the protrusion 5 according to the second embodiment has protrusions 51 and 52. The protrusion 51 has side surfaces 51a and 51b, a top surface 51c, and a bottom surface 51d. The protrusion 52 has side surfaces 52a and 52b and a top surface 52c.

[0066] In the worm wheel 300A shown in FIG. 13, the wheel tooth portion 340A has two second tooth groups (second tooth group 342 and second tooth group 343). The second tooth group 343 is formed by a plurality of second teeth adjacent to each other in the circumferential direction. In this embodiment, among the plurality of teeth 347 constituting the wheel tooth portion 340, the second tooth group 343 is formed by the second tooth 343A and the second tooth 343B. The second tooth 343A and the second tooth 343B are adjacent to each other in the circumferential direction. The second tooth 342A is formed by the protrusion 51 and the resin layer 40 on the outer circumferential side of the protrusion 51. Similarly, the second tooth 343B is formed by the protrusion 52 and the resin layer 40 on the outer circumferential side of the protrusion 52. In addition, the first tooth 341 is provided between the two second tooth groups (second tooth group 342 and second tooth group 343).

[0067] As described above, two (plural) second tooth groups 342, 343 are provided, the two (plural) second tooth groups 342, 343 are arranged at a distance along the circumferential direction, and at least one first tooth 341 is provided between two circumferentially adjacent second tooth groups 342.

[0068] This allows for multiple phases (circumferential positions) at which the worm wheel stops rotating when the stopper mechanism is activated. For example, this allows for changing the phase (circumferential position) at which the worm wheel stops rotating from an initially set phase to another phase, or for installing worm wheels of the same configuration on different vehicles. In the first embodiment, the number of second tooth groups 342 is set to one, so that the rotation angle (phase) at which the steering wheel 10 is prevented from rotating due to the motor 27 being stopped is, for example, a multiple of 360 degrees. In contrast, the second embodiment provides two second tooth groups (the second tooth groups 342 and 343). This allows for a rotation angle (phase) at which the steering wheel 10 is prevented from rotating due to the motor 27 being stopped that is not, for example, a multiple of 360 degrees.

[0069] [Third embodiment] Next, a third embodiment will be described. Fig. 14 is a schematic cross-sectional view of a steering reaction force device of the third embodiment, and corresponds to Fig. 5 of the first embodiment. Fig. 15 is an enlarged view of a part of Fig. 14.

[0070] In the steering reaction force device 110A shown in FIGS. 14 and 15, a detection sensor 6 is provided in the worm wheel accommodating portion 243 of the fourth housing (casing) 24. Specifically, the detection sensor 6 is attached to a portion of the worm wheel accommodating portion 243 that faces the outer periphery of the wheel tooth portion 340. The detection sensor 6 is, for example, a magnetically sensitive sensor that has a Hall IC (Hall element). The detection sensor 6 has a detection portion 61, a magnet 62, and wiring 63.

[0071] The detection unit 61 includes, for example, a Hall IC. The Hall IC detects the magnetic field of the magnet 62 and outputs a signal. When the worm wheel 300 rotates, the signal value differs depending on whether the detection unit 61 faces the resin first tooth 341 or the second tooth group 342, 343 having the metal protrusion 41. The signal value is transmitted to the control unit (ECU) 70 (see FIG. 1) via a wiring 63. The control unit (ECU) 70 detects the phase of the second tooth having the metal protrusion based on the output signal of the Hall IC. By pre-adjusting (calibrating) the absolute angle sensor and the phase (circumferential position) of the second tooth, even if the absolute angle sensor fails, the detection sensor can estimate the rotation angle of the steering wheel from the rotation speed of the worm wheel 300. Note that although the detection sensor 6 has been described as including a Hall IC (Hall element), other magnetically sensitive sensors may also be used.

[0072] As described above, the fourth housing (casing) 24 that houses the worm wheel 300 is further provided with a detection sensor 6 that is attached to a position facing the outer periphery of the wheel tooth portion 340 and detects the circumferential positions of the second teeth 342A, 342B.

[0073] When the stopper mechanism is activated in the limit range of the steering angle of the steered wheels, the second tooth groups 342, 343 are arranged in an engagement portion that engages with the shaft tooth portion 32b of the worm shaft 32. For this purpose, for example, an absolute angle sensor that detects the rotation angle of the steering shaft 1 is provided in a part of the housing 2, and under normal circumstances, the absolute angle sensor detects the absolute angle of the steering wheel 10. In other words, the absolute angle of the steering wheel 10 is detected by the absolute angle sensor, and rotation of the steering wheel 10 is prevented at a rotation angle that corresponds to the limit range of the steering angle of the steered wheels.

[0074] According to the third embodiment, the detection sensor 6 detects the phase of the second teeth 342A, 342B having the metal protrusions 41, 42, and the absolute angle sensor and the phase (circumferential position) of the second teeth 342A, 342B are adjusted (calibrated) in advance, so that even if the absolute angle sensor fails, the detection sensor 6 can re-detect the absolute angle of the steering wheel 10.

[0075] Furthermore, since the detection sensor 6 is a magnetically sensitive sensor having a Hall element, it is possible to detect the circumferential positions of the second tooth groups 342, 343 with a simple structure.

[0076] Although the above-described embodiment is applied to the worm wheels 300, 300A of the reduction mechanism 3 in the steering reaction force devices 110, 110A, it may also be applied to the worm wheels of the reduction mechanism in various electric power steering devices in which the steering mechanism and the turning mechanism are mechanically connected (such as a column type in which the assist mechanism is provided on the steering mechanism side, or a pinion type or rack type in which the assist mechanism is provided on the turning mechanism side). In this case, the protrusion is provided at the phase of the rack end, which is the limit range of the turning angle of the steered wheels. [Explanation of symbols]

[0077] 1 Steering shaft 2. Housing 3 Reduction mechanism 4 Protrusion 5 Protrusion 6 detection sensor 7 Steering unit 10. Steering wheel 11 First Shaft 11a End 11b Main body 11c end 12 Second shaft 12a end 12c Main body 12d end 12e fitting hole 12f tip 13 Third Shaft 13a End 13b Main body 13c end 14 Torsion bar 14a End 14b Main body 14c end 15 Bearings 16 Bearings 17 Bearings 21 First Housing 21a flange 22 Second Housing 23 Third Housing 24 4th housing (chassis) 24a through hole 24b Fitting member 24c recess 24d Fittings 24e Lid 24f, 24g, 24h flange 25, 26 Bearings 27 Motor 27a Front part 32 worm shaft 32a Shaft 32b Shaft tooth 32c Expanded diameter part 32d shaft 32e protrusion 41 Protrusion 41a side 41b Side 41c top surface 41d bottom 42 Protrusion 42a side 42b Side 42c top surface 51 Protrusion 51a side 51b Side 51c top surface 51d bottom 52 Protrusion 52a Side 52b Side 52c top surface 61 Detector 62 Magnet 63 Wiring 70 Control Unit (ECU) 80 Serpent Unit 81 Steering motor 82 Steering wheel 100 Electric power steering device 110, 110A Steering reaction device 241, 242 End 243 Worm wheel housing 244 Worm shaft housing 245 Flange 245a Recess 300, 300A worm wheel 310, 310A core metal 320 Inner circumference 321 Inner circumference 322 Outer circumference 323 Side 324 Side 325 Protruding part 326 Protruding part 330 Outer periphery 331 Inner circumference 332 Outer circumference 332a Cylindrical part 333 Side 334 Side 340, 340A Wheel teeth 341 First tooth 342 Second set of teeth 342A, 342B 2nd tooth 343 Second set of teeth 343A, 343B 2nd tooth 344 Tooth tip 344a, 344b end 344c central part 345 Tooth surface (side of tooth) 346 Tooth bottom 347 teeth 348, 349 Side AX center axis BL Bolt BLa male thread

Claims

1. A steering reaction force device that generates a steering reaction force to be applied to a steering wheel when steering is performed with the steering wheel that is mechanically uncoupled from a steering rack shaft, a motor that serves as a source of the steering reaction force; a reduction mechanism connected to the motor and transmitting an output of the motor to a steering shaft of the steering wheel as a reaction torque, The reduction mechanism is a worm wheel attached to the steering shaft, rotatable around a central axis, and having a plurality of wheel teeth on an outer periphery; a worm shaft having shaft teeth that mesh with the wheel teeth and that is rotated by the motor; the worm wheel has a metal core and the wheel teeth portion provided on an outer circumferential side of the metal core, The outer periphery of the core metal is a cylindrical portion extending in a circumferential direction around the central axis; At least one protrusion protruding radially outward, The wheel tooth portion is a first tooth provided on an outer circumferential side of the cylindrical portion and made of resin; a second tooth formed by the protrusion and a resin layer formed on the outer periphery of the protrusion; Steering reaction device.

2. The wheel tooth portion is the plurality of second teeth include a group of second teeth adjacent to each other in the circumferential direction; 2. The steering reaction force device according to claim 1.

3. The second group of teeth is provided in plurality, the plurality of second tooth groups are arranged at intervals along the circumferential direction, and at least one first tooth is provided between two second tooth groups adjacent to each other in the circumferential direction; 3. The steering reaction force device according to claim 2.

4. a detection sensor attached to a housing that accommodates the worm wheel at a position facing an outer periphery of the wheel tooth portion and configured to detect a circumferential position of the second tooth; A steering reaction force device according to any one of claims 1 to 3.

5. The detection sensor is a magnetic sensor having a Hall element.

5. A steering reaction force device according to claim 4.

6. Equipped with a stopper mechanism, A steering reaction force device according to any one of claims 1 to 5.

Images