JP7721132B2 - Steering reaction force device - Google Patents

Description

This disclosure relates to a steering reaction force device.

In a steer-by-wire steering system, the steering wheel and steered wheels are mechanically disconnected. In this configuration, 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.

The steering reaction force device includes, for example, a motor and a reduction mechanism, and the steering reaction force generated by the motor is transmitted to the steering shaft via the reduction mechanism. The reduction 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 as the shaft teeth of the worm shaft mesh with the wheel teeth of the worm wheel.

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 in order to reduce rattle noise caused by backlash, etc. (See, for example, Patent Document 1). The worm wheel in Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, the outer periphery of the core has multiple protrusions that protrude radially outward, the same number as the wheel teeth, all around the circumference. The resin layer is formed on the outer periphery of all of the multiple protrusions. In other words, all of the wheel teeth have metal protrusions.

Japanese Patent Application Laid-Open No. 2002-21980

It is desirable to further reduce the weight of steering reaction force devices equipped with worm wheels.

The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a steering reaction force device equipped with a worm wheel that is lighter in weight.

To achieve the above-mentioned objective, one embodiment of the steering reaction force device 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 the steering rack shaft. The steering reaction force device includes a motor that serves as a source of the steering reaction force, and a reduction mechanism that is connected to the motor and transmits the motor's output as a reaction torque to the steering shaft of the steering wheel. The 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 that has shaft teeth that mesh with the wheel teeth and is rotated by the motor. The worm wheel has a metal core and the wheel teeth provided on the outer periphery of the core. The outer periphery of the core has a cylindrical portion that extends circumferentially around the central axis and at least one protrusion that protrudes radially outward. The wheel teeth are provided on the outer periphery of the cylindrical portion and have first teeth made of resin, and second teeth formed of the protrusions and a resin layer formed on the outer periphery of the protrusions.

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

Steering systems require a stopper mechanism to communicate the steering angle limit of the steered wheels to the driver. 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. For example, the stopper mechanism uses the output of a motor. That is, the stopper mechanism stops the rotation of the steering reaction force device motor at the steering angle limit of the steered wheels, preventing rotation of the steering wheel 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.

Here, the shaft teeth of the worm shaft mesh with the wheel teeth of the worm wheel, and the rotation of the shaft teeth causes the wheel teeth and worm wheel to rotate. Furthermore, when the stopper mechanism is activated and the rotation of the worm wheel stops, a large load is input to the portion of the wheel teeth that meshes with the shaft teeth.

As mentioned above, the worm wheel in Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, the core has multiple protrusions that protrude radially outward around the entire periphery, the same number as the number of wheel teeth, and the resin layer is formed on the outer periphery of all of the multiple protrusions. In other words, because all of the wheel teeth have metal protrusions, the worm wheel is heavy.

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, further reducing the weight of the worm wheel and steering reaction force device. 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.

In a preferred embodiment, the wheel tooth portion has a second tooth group in which multiple second teeth are adjacent to each other in the circumferential direction. This improves the rigidity of the wheel tooth portion compared to when there is only one second tooth, improving the meshing force between the wheel tooth portion and the shaft tooth portion, and ultimately enabling the stopper mechanism to more reliably prevent rotation of the steering wheel.

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 adjacent second tooth groups in the circumferential direction.

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

In a preferred embodiment, the device further includes 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.

When the stopper mechanism is activated at the limit of the steering angle of the steered wheels, the second set of teeth is positioned in the 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 installed in part of the housing, and under normal circumstances, this absolute angle sensor detects the absolute angle of the steering wheel. When the phase (rotation angle) of the steering wheel reaches a predetermined range, the second set of teeth is positioned in the meshing portion.

Here, the detection sensor detects the phase of the second tooth, which has a metal protrusion, and 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.

In a preferred embodiment, the detection sensor is a magnetically sensitive sensor having a Hall element, making it possible to detect the circumferential position of the second set of teeth with a simple structure.

In a preferred embodiment, the steering device is equipped with a stopper mechanism. For example, the stopper mechanism uses the output of the motor. That is, the stopper mechanism stops the rotation of the steering reaction force device motor at the limit of the steering angle of the steered wheels. This prevents the steering wheel from rotating via 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.

This disclosure makes it possible to provide a steering reaction force device equipped with a worm wheel that is lighter in weight.

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

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 a person skilled in the art would easily imagine and those that are substantially identical. Furthermore, the components described below can be combined as appropriate. Furthermore, parts with the same structure are given the same reference numerals and explanations will be omitted. In three-dimensional coordinates, the X direction indicates the fore-and-aft direction of the vehicle body, the Y direction indicates the width direction of the vehicle, and the Z direction indicates the up-and-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.

[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 V-V in Fig. 3.

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.

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

As shown in Figures 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.

As shown in Figure 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 14.

As shown in FIG. 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 with the X1-side end 12a of the second shaft 12. The main body 11b of the first shaft 11 connects the end 11a and end 11c.

As shown in FIG. 4, a fitting hole 12e is provided in the X2-side end 12d of the second shaft 12. The X1-side end 14c of the torsion bar 14 fits into the fitting hole 12e. The main body 12c of the second shaft 12 connects the end 12a and end 12d.

As shown in FIG. 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 14a of the torsion bar 14 is fitted into the X2-side end 13c of the third shaft 13. The main body 13b of the third shaft 13 connects the end 13a and end 13c. The main body 14b of the torsion bar 14 connects the X1-side end 14c and the X2-side end 14a.

As shown in FIG. 4 , the first shaft 11 is rotatably supported in 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 in the third housing 23 via the bearing 16, and in the fourth housing 24 via the bearing 17. As described above, the steering shaft 1 is rotatably supported in the housing 2, which will be described later.

As shown in FIG. 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.

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.

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.

As shown in Figure 5, the worm wheel accommodating portion 243 protrudes toward the Z1 side and has 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.

The worm shaft accommodating portion 244 extends in 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. The worm shaft accommodating portion 244 is provided with a flange portion 24f that protrudes toward the Z2 side.

The Y1-side end 242 of the worm shaft accommodating portion 244 is open on the Y1 side, and the fitting member 24b is fitted into this 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.

A fitting member 24d is fitted inside 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 Figures 2 and 3, the lid portion 24e is fastened with two bolts BL.

Next, the steering reaction force device 110 will be described. As shown in FIG. 5, the steering reaction force device 110 includes a motor 27 and a reduction mechanism 3, which includes a worm wheel 300 and a worm shaft 32. The steering reaction force is expected to be, for example, a torque of 100 Nm or more.

The motor 27 generates a steering reaction force. That is, the output of the motor 27 becomes a reaction torque, which is transmitted to the steering shaft 1 of the steering wheel 10 via the reduction mechanism 3. As shown in FIG. 5, the front surface 27a of the motor 27 fits into a recess 245a provided 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.

As shown in FIG. 5, the worm shaft 32 includes a shaft tooth portion 32b, shaft portions 32a and 32d, an enlarged diameter portion 32c, and a protrusion 32e.

As shown in FIG. 5, the shaft tooth portion 32b has multiple teeth aligned in 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 on the Y2 side of the fitting member 24b, and a protrusion 32e is disposed inside the recess 24c.

As shown in FIG. 5, the 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 partially cross-sectional perspective view 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 the core metal included in the worm wheel of the first embodiment. FIG. 11 is a front view of FIG. 10.

As shown in Figures 6 to 9, the worm wheel 300 includes a core metal 310 and a wheel tooth portion 340. The worm wheel 300 is a circular member extending in an annular shape in the circumferential direction around the 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, for example, by punching multiple low-carbon steel plates. Note that the inner peripheral portion 320 and the outer peripheral portion 330 may be integral.

As shown in Figures 8 and 9, the inner periphery 320 has an inner periphery 321, an outer periphery 322, and side surfaces 323 and 324. The third shaft 13 is fitted onto the inner periphery 321. The side surface 323 is provided on the X2 side of the inner periphery 320, and the side surface 324 is provided on the X1 side of the inner periphery 320. The side surface 323 has a protruding portion 325 that is convex on the X2 side, and the side surface 324 has a protruding portion 326 that is convex on the X1 side. The outer periphery 322 and the inner periphery 321 extend in an annular shape in the circumferential direction around the central axis AX.

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

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

As shown in Figures 10 and 11, the cylindrical portion 332a extends circumferentially 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.

As shown in Figures 10 and 11, side surfaces 41a and 41b are provided on one and the other circumferential sides of protrusion 41. Top surface 41c circumferentially connects the radially outer ends of side surfaces 41a and 41b. Side surfaces 42a and 42b are provided on one and the other circumferential sides of protrusion 42. Top surface 42c circumferentially connects the radially outer ends of side surfaces 42a and 42b.

As shown in Figures 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 Figures 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 Figures 10 and 11. Therefore, the second tooth 342A is formed by the protrusion 41 and the resin layer 40 on the outer periphery of the protrusion 41. Similarly, the second tooth 342B is formed by the protrusion 42 and the resin layer 40 on the outer periphery of the protrusion 42. 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 set of teeth 342 of the worm wheel are composed of the metal protrusions 41, 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 flank (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.

As shown in Figures 6 and 7, the wheel tooth portion 340 also 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.

As shown in FIG. 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.

In addition, 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 of the steering angle of the steered wheels. This prevents the steering wheel 10 from rotating beyond a certain angle, for example, to let the driver know the end stop position or to prevent the airbag harness connected to the steering wheel 10 from breaking due to excessive rotation.

As described above, the steering reaction force device 110 according to this embodiment generates a steering reaction force that is applied to the steering wheel 10 when steering is performed with the steering wheel 10 that is mechanically uncoupled from the steering rack shaft. The steering reaction force device 110 includes a motor 27 that serves as a source of steering reaction force, and a reduction mechanism 3 that is connected to the motor 27 and transmits the output of the motor 27 as reaction torque to the steering shaft 1 of the steering wheel 10. The reduction mechanism 3 includes a worm wheel 300 that is attached to the steering shaft 1, is rotatable around the central axis AX, and has a plurality of wheel teeth 340 on its outer periphery, and a worm shaft 32 that has shaft teeth 32b that mesh with the wheel teeth 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 "at least one protrusion" in the above description and claims refers to the presence of at least one protrusion (either protrusion 41 or protrusion 42). In this embodiment, this refers to the presence of two protrusions.

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

A stopper mechanism must be provided 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 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 of the steering angle of the steered wheels, thereby preventing rotation of the steering wheel 10 via the worm shaft 32, worm wheel 300, and 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.

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 causes the wheel teeth 340 and the worm wheel 300 to rotate. 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.

As mentioned above, the worm wheel in Patent Document 1 has a metal core and a resin layer formed on the entire outer periphery of the core. Specifically, the core has multiple protrusions that protrude radially outward around the entire periphery, the same number as the number of wheel teeth, and the resin layer is formed on the outer periphery of all of the multiple protrusions. In other words, because all of the wheel teeth have metal protrusions, the worm wheel is heavy.

In contrast, in the wheel tooth portion 340 according to this embodiment, some of the teeth are second teeth 342A, 342B with metal protrusions 41, 42, and the rest are first teeth 341 made of resin. The second teeth 342A, 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, 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.

The wheel tooth portion 340 also has a second tooth group 342 in which multiple 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, thereby more reliably preventing rotation of the steering wheel 10 by the stopper mechanism.

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

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.

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

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 multiple second teeth adjacent to each other in the circumferential direction. In this embodiment, of the multiple teeth 347 that make up the wheel tooth portion 340, the second tooth group 343 is formed by second tooth 343A and second tooth 343B. The second tooth 343A and 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. Furthermore, the first tooth 341 is provided between the two second tooth groups (second tooth group 342 and second tooth group 343).

As described above, two (plural) second tooth groups 342, 343 are provided, the two (plural) second tooth groups 342, 343 are spaced apart in the circumferential direction, and at least one first tooth 341 is provided between two circumferentially adjacent second tooth groups 342.

This allows for multiple phases (circumferential positions) at which the worm wheel stops rotating when the stopper mechanism is activated. This makes it possible to accommodate needs such as changing the phase (circumferential position) at which the worm wheel stops rotating from the initially set phase to another phase, or installing worm wheels of the same configuration on different vehicles. In the first embodiment, by setting the second tooth group 342 to one, the rotation angle (phase) at which the steering wheel 10 is prevented from rotating due to the motor 27 stopping becomes, for example, a multiple of 360 degrees. In contrast, in the second embodiment, there are two second tooth groups (second tooth group 342 and second tooth group 343). This allows for rotation angles (phases) at which the steering wheel 10 is prevented from rotating due to the motor 27 stopping that are not, for example, a multiple of 360 degrees.

[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.

In the steering reaction force device 110A shown in Figures 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.

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 set of teeth 342, 343 with the metal protrusion 41. The signal value is transmitted to the control unit (ECU) 70 (see FIG. 1) via wiring 63. The control unit (ECU) 70 detects the phase of the second tooth with 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 steering wheel rotation angle from the rotation speed of the worm wheel 300. While the detection sensor 6 has been described as including a Hall IC (Hall element), other magnetically sensitive sensors may also be used.

As described above, the fourth housing (casing) 24, which houses the worm wheel 300, is further equipped 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 position of the second teeth 342A, 342B.

When the stopper mechanism is activated at the limit of the steering angle of the steered wheels, the second set of teeth 342, 343 are positioned at the meshing portion that meshes with the shaft teeth 32b of the worm shaft 32. To achieve this, an absolute angle sensor that detects the rotation angle of the steering shaft 1 is provided, for example, in a part of the housing 2, and under normal circumstances, this absolute angle sensor detects the absolute angle of the steering wheel 10. In other words, the absolute angle sensor detects the absolute angle of the steering wheel 10, and rotation of the steering wheel 10 is prevented at a rotation angle that corresponds to the limit of the steering angle of the steered wheels.

According to the third embodiment, the detection sensor 6 detects the phase of the second teeth 342A, 342B, which have metal protrusions 41, 42, and by pre-adjusting (calibrating) the absolute angle sensor and the phase (circumferential position) of the second teeth 342A, 342B, the detection sensor 6 can re-detect the absolute angle of the steering wheel 10 even if the absolute angle sensor fails.

In addition, because the detection sensor 6 is a magnetically sensitive sensor with a Hall element, it can detect the circumferential position of the second tooth groups 342, 343 with a simple structure.

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, but 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 turning mechanism are mechanically connected (such as column types in which the assist mechanism is provided on the steering mechanism side, or pinion and rack types in which the assist mechanism is provided on the turning mechanism side). In this case, the protrusion is provided at the rack end phase, which is the limit range of the turning angle of the steered wheels.

REFERENCE SIGNS LIST 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 bearing 16 bearing 17 bearing 21 first housing 21a flange 22 second housing 23 third housing 24 fourth housing (housing)
24a Through hole 24b Fitting member 24c Recess 24d Fitting member 24e Cover portion 24f, 24g, 24h Flange portion 25, 26 Bearing 27 Motor 27a Front surface 32 Worm shaft 32a Shaft portion 32b Shaft teeth portion 32c Expanded diameter portion 32d Shaft portion 32e Projection portion 41 Projection portion 41a Side surface 41b Side surface 41c Top surface 41d Bottom portion 42 Projection portion 42a Side surface 42b Side surface 42c Top surface 51 Projection portion 51a Side surface 51b Side surface 51c Top surface 51d Bottom portion 52 Projection portion 52a Side surface 52b Side surface 52c Top surface 61 Detection portion 62 Magnet 63 Wiring 70 Control device (ECU)
80 Turning unit 81 Steering motor 82 Steering wheel 100 Electric power steering device 110, 110A Steering reaction force device 241, 242 End 243 Worm wheel accommodating portion 244 Worm shaft accommodating portion 245 Flange portion 245a Recess 300, 300A Worm wheel 310, 310A Core metal 320 Inner periphery 321 Inner periphery 322 Outer periphery 323 Side surface 324 Side surface 325 Protrusion 326 Protrusion 330 Outer periphery 331 Inner periphery 332 Outer periphery 332a Cylindrical portion 333 Side surface 334 Side surface 340, 340A Wheel tooth portion 341 First tooth 342 Second tooth group 342A, 342B Second tooth 343 Second tooth group 343A, 343B Second tooth 344 Tooth tips 344a, 344b End portion 344c Center portion 345 Tooth surface (tooth side surface)
346 Tooth bottom 347 Teeth 348, 349 Side surface AX Center axis BL Bolt BLa Male thread portion

Claims (6)

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. 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. 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. 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. The detection sensor is a magnetic sensor having a Hall element.
5. A steering reaction force device according to claim 4. Equipped with a stopper mechanism,
A steering reaction force device according to any one of claims 1 to 5.