JP2009250260A - Worm reduction gear and electric power steering device provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a worm reduction gear capable of effectively attenuating the vibration of a worm generated due to backlash without deteriorating fluctuation torque and operation torque at a meshing part of a worm wheel and a worm and an electric power steering device provided with the same. <P>SOLUTION: The worm reduction gear 9 is provided with the worm rotatably supported in a gear housing and the worm wheel meshing with the worm, and reducing the rotation of the worm by the worm wheel. Piezoelectric elements 20, 22 are put between the gear housing and a bearing rotatably supporting the worm at both ends on at least one side of which the dimension in a radial direction of the worm changes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a worm speed reducer that transmits and reduces the rotation of a worm rotatably supported in a gear housing to a worm wheel meshing with the worm, and an electric power steering apparatus including the worm speed reducer, More specifically, the present invention relates to a vibration damping structure that attenuates worm vibration generated in a worm reduction gear.

  Many of the vehicles in recent years are equipped with an electric power steering device (EPS) that assists the driver's steering by transmitting the driving force of the electric motor to the steering shaft via the speed reduction mechanism. Generally, in this type of electric power steering apparatus, a worm speed reducer is used as the speed reduction mechanism.

  FIG. 7 is a cross-sectional view of a main part showing a conventional worm speed reducer. In the figure, a worm speed reducer 100 includes a worm 102 rotatably supported in a gear housing 101 and a worm wheel 103 that meshes with the worm 102 so that the rotation of the worm 102 is decelerated by the worm wheel 103. It has become. The worm 102 is rotatably supported by the gear housing 101 via bearings 104 and 105 disposed at both ends, and a joint portion 102a formed at one end (right side in FIG. 7) of the worm 102 is connected to the gear housing 101. It is connected to a drive shaft of a drive source (such as an electric motor) attached to the motor attachment portion 101a. In addition, a main shaft (a steering shaft in the case of an electric power steering device) 106 to which power of a driving source is transmitted is fitted and fixed to the central portion of the worm wheel 103. With the worm speed reducer 100 having such a configuration, the power of the drive source is decelerated via the worm 102 and the worm wheel 103 and transmitted to the main shaft 106.

  By the way, in the worm speed reducer 100 having such a configuration, there is a possibility that backlash may occur at the meshing portion of the worm 102 and the worm wheel 103, and it is assembled with a predetermined processing accuracy so that this backlash does not occur. However, since wear occurs at the meshing portion of the worm 102 and the worm wheel 103, it is difficult to avoid backlash caused by this wear.

  In order to solve such a problem, for example, Patent Document 1 discloses that a worm is moved toward a worm wheel by a biasing means made of a coil spring, a screw, a metal or a synthetic resin elastic body, or the worm wheel. Is disclosed in which the backlash is favorably eliminated by moving the lens toward the worm.

JP 2000-43739 A

  However, in the structure disclosed in the above-mentioned Patent Document 1, in order to suppress the occurrence of a hitting sound (rattle sound) due to backlash, one member of the worm and the worm wheel is moved to the other member side with a certain degree of elastic force. Need to be energized. The larger the elastic force, the more the generation of a hitting sound can be suppressed. On the other hand, there is a problem that the operating torque and the fluctuation torque are deteriorated and the transmission efficiency of the driving force is lowered. There is a possibility that the gear life of the worm and the worm wheel may be shortened due to an increase in wear due to the force.

  Further, as described above, in the worm speed reducer that biases one member of the worm and the worm wheel to the other member side, the worm is likely to be shaken or tilted. There is also a problem that sound is generated, and a means capable of solving these problems has been demanded.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to effectively reduce worm vibration caused by backlash without deteriorating the operating torque and fluctuation torque at the meshing portion of the worm and the worm wheel. It is an object to provide a worm reduction gear that can be damped automatically and an electric power steering device including the same.

  The object of the present invention is to provide a worm speed reducer comprising a worm rotatably supported in a gear housing and a worm wheel meshing with the worm, wherein the worm reduces the rotation of the worm by the worm wheel. , At least one of which is rotatably supported by the gear housing via bearings disposed at both ends thereof, and which changes in the radial direction of the worm between each of the bearings and the gear housing. This is achieved by interposing a piezoelectric element.

  Moreover, the said objective is achieved effectively by the said piezoelectric element being distribute | arranged between each said bearing and the said gear housing on the side facing the said worm wheel.

  Moreover, the said objective is effectively achieved by the said piezoelectric element being distribute | arranged between each said bearing by the side of the said worm wheel, and the said gear housing.

  Moreover, the said objective is effectively achieved by providing the electric power regeneration means for regenerating the electrical energy which arises in the said piezoelectric element.

  Further, the object is to provide a vibration actuator comprising the piezoelectric element disposed between the bearing on the side facing the worm wheel and the gear housing, the bearing on the side facing the vibration actuator, and the An acceleration sensor that is arranged between the gear housing and that detects vibration acceleration of the worm; and is electrically connected to the excitation actuator and the acceleration sensor; and based on a detection value of the acceleration sensor, vibration of the worm By virtue of the vibration control means for controlling the vibration of the vibration actuator so as to cancel the vibration, it is effectively achieved.

  Further, the above object is provided between the bearing on the side facing the worm wheel and the gear housing, and detects an acceleration sensor for detecting vibration acceleration of the worm, and the bearing on the side facing the acceleration sensor. A vibration actuator composed of the piezoelectric element disposed between the gear housing and the vibration actuator and the acceleration sensor are electrically connected, and the vibration of the worm is controlled based on a detection value of the acceleration sensor. This is achieved effectively by including the vibration control means for controlling the vibration of the vibration actuator so as to cancel.

  The above-mentioned object is effectively achieved by the fact that the acceleration sensor is a piezoelectric element capable of detecting electric energy corresponding to the vibration acceleration of the worm by the piezoelectric effect.

  Further, the above object is effectively achieved by the vibration control means operating the vibration actuator only when the vibration acceleration of the worm detected by the acceleration sensor is equal to or greater than a predetermined value. .

  Further, the object is to provide an electric motor having the worm reducer, a steering shaft connected to the worm wheel of the worm reducer, a drive shaft connected to the worm of the worm reducer, and the electric motor. And a control unit for controlling the driving of the motor.

  The object is further provided with a vehicle speed sensor that is electrically connected to the vibration control means and detects the speed of the vehicle, and the vibration control means detects the speed of the vehicle detected by the vehicle speed sensor. This is effectively achieved by operating the excitation actuator and the acceleration sensor only when the speed becomes a predetermined value or more.

  Moreover, the said objective is achieved effectively by the said electric power regeneration means being provided in the said control unit.

  Furthermore, the object is effectively achieved by providing the vibration control means in the control unit.

  According to the worm speed reducer and the electric power steering apparatus including the worm speed reducer according to the present invention, the piezoelectric element whose dimensions change in the radial direction of the worm between the bearings and the gear housing that rotatably support both ends of the worm. By interposing, the vibration of the worm can be damped by the electrical conversion action due to the dimensional change of the piezoelectric element. In particular, by placing this piezoelectric element between each bearing on the side facing the worm wheel and the gear housing, or between each bearing on the worm wheel side and the gear housing, a rattling sound (rattle sound) ) In the radial direction at the meshing portion of the worm can be effectively damped. Thereby, it is possible to reduce the hitting sound at the meshing portion between the worm and the worm wheel without deteriorating the operating torque and the fluctuation torque of the worm reducer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a mechanism diagram showing a schematic configuration of an electric power steering apparatus according to an embodiment of the present invention. In the figure, the steering mechanism of the electric power steering apparatus 1 includes a steering shaft 3 that rotates in response to a steering operation of a steering wheel 2 attached to a tip portion, and a universal joint 4 on the other end side of the steering shaft 3. 5 and a rack and pinion mechanism 6 that converts the rotational motion of the steering shaft 3 into a linear motion of the rack shaft, and a tie rod 7 that transmits the motion of the rack shaft of the rack and pinion mechanism 6 to the steering wheel. It is composed of

  In addition, a column portion of the electric power steering apparatus 1 includes a torque sensor 8 that detects a steering torque input to the steering shaft 3 via the steering wheel 2 and a steering shaft 3 via a speed reduction mechanism (worm reducer) 9. And an electric motor 10 for assisting steering connected to the motor.

  Driving of the electric motor 10 is controlled by a control unit (ECU) 11 equipped with a control circuit and the like. The control unit 11 is supplied with electric power from a battery (power source) 12 and receives an ignition key signal from an ignition key 13. The control unit 11 calculates the steering assist command value I based on the steering torque value T detected by the torque sensor 8 and the vehicle speed V detected by the vehicle speed sensor 14, and the calculated steering assist command value is calculated. The drive current supplied to the electric motor 10 is controlled according to I.

[First Embodiment]
FIG. 2 is a cross-sectional view of the main part showing the worm speed reducer according to the first embodiment of the present invention, and FIG. It is explanatory drawing.

  In FIG. 2, the worm speed reducer 9 includes a worm 16 rotatably supported in a gear housing 15 and a worm wheel 17 that meshes with the worm 16 and has the steering shaft 3 fitted and fixed at the center. The rotation of the worm 16 is decelerated by the worm wheel 17 and transmitted to the steering shaft 3.

  The worm 16 is disposed so as to be orthogonal to the steering shaft 3 and is rotatable through a first bearing 18 disposed on one end shaft portion 16a of the worm 16 and a second bearing 19 disposed on the other end shaft portion 16b. The first bearing 18 and the second bearing 19 are held by a bearing holding portion in the gear housing 15. A motor mounting portion 15a is formed at the other end portion of the gear housing 15 in accordance with the shape of the flange portion of the electric motor 10, and the drive shaft of the electric motor 10 fixed to the motor mounting portion 15a is a worm 16. The other end shaft portion 16b is spline-fitted through a joint portion 16c formed at the tip of the other end shaft portion 16b and is coupled to the worm 16 so as to be integrally rotatable. That is, in the electric power steering apparatus 1 according to the present embodiment, the driving force of the electric motor 10 is transmitted to the steering shaft 3 via the worm 16 and the worm wheel 17, so that the steering assist force is applied. Yes.

  Each bearing 18, 19 includes inner rings 18a, 19a having raceways on the outer peripheral surface, outer rings 18b, 19b having raceways on the inner peripheral surface, and between the raceways of the inner rings 18a, 19a and the outer rings 18b, 19b. The rolling elements 18c and 19c are provided so as to be freely rollable.

  The radial direction of the worm 16 is between the bearings 18 and 19 on the side facing the worm wheel 17 and the gear housing 15 and between the bearings 18 and 19 on the worm wheel 17 side and the gear housing 15. The piezoelectric elements 20 to 23 whose dimensions change are respectively interposed. These piezoelectric elements 20 to 23 respond to vibration of the worm 17 transmitted through the bearings 18 and 19 (particularly, vibration in the radial direction (arrow X1-X2 direction in FIG. 2) at the meshing portion of the worm 17). The dimensions change. By the electrical conversion action due to the dimensional change of the piezoelectric elements 20 to 23, the vibration of the worm 17 that causes the hitting sound (rattle sound) at the meshing portion is converted into electrical energy and attenuated.

  Further, as shown in FIG. 3, each of the piezoelectric elements 20 to 23 is electrically connected to power regeneration means 24 provided in the control unit 11. The power regeneration means 24 stores electrical energy generated by dimensional changes of the piezoelectric elements 20 to 23 in a power storage unit made of a capacitor or the like, and regenerates the stored electrical energy as power for the control unit 11.

  In the present embodiment, the piezoelectric elements 20 and 22 are disposed between the bearings 18 and 19 on the side facing the worm wheel 17 and the gear housing 15, and the bearings 18 and 19 on the worm wheel 17 side. The piezoelectric elements 21 and 23 are also arranged between the gear housing 15 and the gear housing 15, but the present invention is not limited to this, and the piezoelectric elements (for example, only the piezoelectric elements 20 and 22 only) are provided on either side. ) May be arranged, or three (three) or more piezoelectric elements may be interposed between the bearings 18 and 19 and the gear housing 15.

  As described above, according to the worm speed reducer 9 according to the present embodiment, the piezoelectric elements 20 to 23 whose dimensions change in the radial direction of the worm 16 are interposed between the bearings 18 and 19 and the gear housing 15. . Thereby, the vibration of the worm 16 is converted into electric energy and attenuated by the electric conversion action due to the dimensional change of the piezoelectric elements 20 to 23. In particular, in the present embodiment, since the piezoelectric elements 20 to 23 are disposed between the bearings 18 and 19 on the worm wheel 17 side and the worm wheel 17 side and the gear housing 15, the worm speed reduction is performed. The vibration in the radial direction at the meshing portion of the worm 16 that causes the occurrence of the beating sound of the machine 9 can be effectively damped. As a result, it is possible to reduce the hitting sound caused by backlash between the worm 16 and the worm wheel 17 without deteriorating the operating torque and the fluctuation torque of the worm speed reducer 9.

  Further, the worm speed reducer 9 according to the present embodiment does not have a structure in which one member of the worm 16 and the worm wheel 17 is urged toward the other member as in the prior art. Therefore, it is possible to reduce the operating vibration and operating noise of the reduction gear.

  Further, in the worm speed reducer 9 according to the present embodiment, the power regeneration means 24 for regenerating the electrical energy generated in each of the piezoelectric elements 20 to 23 is provided in the control unit 11, and the power regeneration means 24 and each piezoelectric element 20. By electrically connecting ˜23, the electric energy can be stored and regenerated as electric power required for the operation of the control unit 11 and the electric motor 10. As a result, it is possible to save energy of the electric power steering apparatus 1 and contribute to energy saving.

[Second Embodiment]
FIG. 4 is a cross-sectional view of a main part showing a worm speed reducer according to a second embodiment of the present invention, and FIG. 5 shows a cross section and a schematic configuration of the worm speed reducer along the line V-V in FIG. It is explanatory drawing. In the present embodiment, the same members as those in the first embodiment described above are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 4, in the worm speed reducer 9 </ b> A according to this embodiment, the piezoelectric element 20 described in the first embodiment is interposed between the bearings 18 and 19 on the side facing the worm wheel 17 and the gear housing 15. To 23, vibration actuators 25 and 26 made of piezoelectric elements whose dimensions change in the radial direction of the worm 17 are provided, and bearings on the side facing the vibration actuators 25 and 26, that is, the bearings on the worm wheel 17 side. Acceleration sensors 27 and 28 for detecting the vibration acceleration of the worm 17 are disposed between the gear housing 15 and the gear housing 15. As shown in FIG. 5, the vibration actuators 25 and 26 and the acceleration sensors 27 and 28 are electrically connected to a vibration control means 29 provided in the control unit 11A.

  The acceleration sensors 27 and 28 detect the vibration acceleration in the radial direction at the meshing portion of the worm 17 in real time and output the detection signal to the vibration control means 29. For example, a moving magnet type vibration detection sensor Alternatively, a piezoelectric vibration sensor made of a piezoelectric element capable of detecting electrical energy corresponding to the vibration acceleration of the worm 17 by the piezoelectric effect is preferable. The vibration acceleration detection signals detected by the acceleration sensors 27 and 28 are output to the vibration control means 29 in the control unit 11A.

FIG. 6 is a block diagram showing an excitation control circuit according to this embodiment. In the figure, the vibration control means 29 controls the vibration force of the vibration actuators 25 and 26 using a program or the like stored in advance in an arithmetic circuit or a storage unit. Based on this detection signal, an excitation force for canceling the vibration of the worm 17 is calculated, and the excitation signal is output to each of the excitation actuators 25 and 26. For example, when the piezoelectric vibration sensor described above is applied as the acceleration sensors 27 and 28, and the voltage corresponding to the vibration acceleration detected by the piezoelectric vibration sensor is V ₊ , the vibration control means 29 will determine the vibration acceleration V A voltage V ₋ = αV ₊ (α: arbitrary proportionality coefficient) that changes the size of the piezoelectric element in the direction of canceling ₊ is applied to each of the vibration actuators 25 and 26 for vibration. In other words, in this embodiment, the vibration control means 29 reverses the phase of the vibration acceleration input to the worm 17 and vibrates the vibration actuator, thereby canceling the input vibration.

  The vibration control means 29 operates the vibration actuators 25 and 26 only when the vibration acceleration of the worm 17 detected by the acceleration sensors 27 and 28 is equal to or greater than a predetermined value stored in the storage unit or the like. The operation of the vibration actuators 25 and 26 when the vibration acceleration of 17 is below a predetermined value is limited. Further, the vibration control means 29 takes in the detection signal of the vehicle speed sensor 14 electrically connected to the control unit 11A, and the detected vehicle speed is greater than or equal to a predetermined value stored in the storage unit or the like in advance. Only when the vibration actuators 25 and 26 and the acceleration sensors 27 and 28 are operated, the operations of the vibration actuators 25 and 26 and the acceleration sensors 27 and 28 when the vehicle speed is lower than a predetermined value are limited. .

  As described above, according to the worm speed reducer 9 </ b> A according to the present embodiment, the excitation actuators 25 and 26 made of piezoelectric elements are provided between the bearings 18 and 19 on the side facing the worm wheel 17 and the gear housing 15. In addition, acceleration sensors 27 and 28 for detecting the vibration acceleration of the worm 17 are arranged between the bearings 18 and 19 on the worm wheel 17 side and the gear housing 15, and an additional sensor provided in the control unit 11A. The vibration control means 29 controls the vibration of the vibration actuators 25 and 26 based on the detection values of the acceleration sensors 27 and 28 to cancel the vibration of the worm 16. Thereby, the vibration in the radial direction at the meshing portion of the worm 16 that causes the squealing sound of the worm speed reducer 9 can be effectively attenuated, and the same effect as in the first embodiment described above can be obtained. it can.

  In the present embodiment, the vibration control means 29 restricts the vibration actuators 25 and 26 and / or the acceleration sensors 27 and 28 from operating unless the vibration of the worm 16 and the vehicle speed exceed the predetermined values. Yes. Therefore, wasteful energy consumption can be avoided in situations where the anti-vibration measures for the worm reducer 9A are unnecessary, such as when the vehicle is in a low speed state or when the vibration of the worm 16 is small.

  In the worm speed reducer 9A according to the present embodiment, the vibration actuators 25 and 26 are disposed between the bearings 18 and 19 on the side facing the worm wheel 17 and the gear housing 15, and the worm wheel 17 side. Although the acceleration sensors 27 and 28 are disposed between the bearings 18 and 19 and the gear housing 15, the present invention is not limited to this. For example, the bearings 18 and 19 on the side facing the worm wheel 17 The acceleration sensors 27 and 28 are disposed between the gear housing 15 and the vibration actuators 25 and 26 are disposed between the bearings 18 and 19 on the worm wheel 17 side and the gear housing 15. Also, the same effects as in the present embodiment can be obtained.

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to this, In the range which does not deviate from the meaning, it can change suitably.

It is a mechanism figure showing a schematic structure of an electric power steering device concerning an embodiment of the present invention. It is principal part sectional drawing which shows the worm reduction gear which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows the cross section and schematic structure of a worm gear reducer along the III-III line | wire in FIG. It is principal part sectional drawing which shows the worm speed reducer which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the cross section and schematic structure of a worm gear reducer along the VV line | wire in FIG. It is a block diagram which shows the vibration control circuit which concerns on 2nd Embodiment of this invention. It is principal part sectional drawing which shows the conventional worm reduction gear.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device 3 ... Steering shaft 9, 9A ... Worm speed reducer (deceleration mechanism)
10: Electric motor 11, 11A: Control unit (ECU)
14 ... Vehicle speed sensor 15 ... Gear housing 16 ... Worm 16a, 16b ... Worm shaft 17 ... Worm wheel 18 ... First bearing 19 ... Second bearing 20-23 ..Piezoelectric element 24 ... Power regeneration means 25, 26 ... Excitation actuator (piezoelectric element)
27, 28 ... Acceleration sensor 29 ... Excitation control means

Claims (12)

A worm reducer comprising a worm rotatably supported in a gear housing and a worm wheel meshing with the worm, wherein the worm wheel decelerates rotation of the worm,
The worm is rotatably supported by the gear housing via bearings disposed at both ends thereof, and
A worm speed reducer characterized in that at least one piezoelectric element having a dimensional change in the radial direction of the worm is interposed between each bearing and the gear housing.   The worm reduction gear according to claim 1, wherein the piezoelectric element is disposed between the bearings on the side facing the worm wheel and the gear housing.   3. The worm speed reducer according to claim 1, wherein the piezoelectric element is disposed between the bearings on the worm wheel side and the gear housing. 4.   The worm speed reducer according to any one of claims 1 to 3, further comprising power regeneration means for regenerating electrical energy generated in the piezoelectric element. An excitation actuator comprising the piezoelectric element disposed between the bearing on the side facing the worm wheel and the gear housing;
An acceleration sensor that is arranged between the bearing on the side facing the excitation actuator and the gear housing and detects vibration acceleration of the worm;
Vibration control means electrically connected to the vibration actuator and the acceleration sensor, and controlling vibration of the vibration actuator so as to cancel vibration of the worm based on a detection value of the acceleration sensor; The worm speed reducer according to claim 1 provided. An acceleration sensor disposed between the bearing on the side facing the worm wheel and the gear housing, and detecting vibration acceleration of the worm;
An excitation actuator comprising the piezoelectric element disposed between the bearing on the side facing the acceleration sensor and the gear housing;
Vibration control means electrically connected to the vibration actuator and the acceleration sensor, and controlling vibration of the vibration actuator so as to cancel vibration of the worm based on a detection value of the acceleration sensor; The worm speed reducer according to claim 1 provided.   The worm speed reducer according to claim 5 or 6, wherein the acceleration sensor is a piezoelectric element capable of detecting electrical energy corresponding to vibration acceleration of the worm by a piezoelectric effect.   The worm speed reducer according to any one of claims 5 to 7, wherein the vibration control means operates the vibration actuator only when the vibration acceleration of the worm detected by the acceleration sensor is equal to or greater than a predetermined value. A worm reducer according to any one of claims 1 to 8,
A steering shaft coupled to the worm wheel of the worm reducer;
An electric motor having a drive shaft coupled to the worm of the worm reducer;
An electric power steering apparatus comprising: a control unit that controls driving of the electric motor. A vehicle speed sensor that is electrically connected to the vibration control means and detects the speed of the vehicle;
10. The electric power steering apparatus according to claim 9, wherein the vibration control unit activates the vibration actuator and the acceleration sensor only when a speed of the vehicle detected by the vehicle speed sensor exceeds a predetermined value. .   The electric power steering apparatus according to claim 9 or 10, wherein the power regeneration means is provided in the control unit.   The electric power steering apparatus according to any one of claims 9 to 11, wherein the vibration control means is provided in the control unit.

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