JP4221564B2 - Electric actuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes, for example, a power window of an automobile, a wire winding mechanism of an electric parking brake device, a caliper propulsion mechanism of an electric disc brake device, an automatic clutch release driving mechanism, a VVT driving device, a 2WD 4WD switching mechanism, and general industrial use. The present invention relates to an electric actuator used for a winch, a hoist, a crane, various positioning devices, and the like.
[0002]
[Prior art]
For example, an electric actuator is incorporated in a power window of an automobile, and the window can be freely opened and closed using an electric motor as a drive source. For such an electric actuator, the rotational movement of the electric motor is converted into the axial movement of the output shaft. And a function to prevent the output shaft from rotating when the electric motor is stopped.
[0003]
As an electric actuator having both of these functions, for example, a ball screw in which a nut is screwed to a screw shaft via a number of rolling elements to make the screw shaft a rotating portion and an output portion in which the nut moves in the axial direction. An electric motor that transmits a rotational force to the screw shaft of the ball screw, a rotating body with a one-way clutch that is rotatable only in the forward rotation direction of the screw shaft and is substantially concentric with the screw shaft, and a one-way clutch When the torque in the reverse rotation direction acts on the screw shaft from the driven side via the nut when the screw shaft is stopped, the one-way clutch rotates in the reverse rotation direction. Some include a friction material that cooperates with the lock function and generates a braking torque by a frictional force against a reverse rotation direction torque from the driven side of the screw shaft (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 8-322189
[Problems to be solved by the invention]
However, in the electric actuator described in Patent Document 1, since the reverse rotation direction torque from the driven side is held only by the braking torque by the friction material, the conditions required for the friction material (selection of the friction coefficient, There is a problem that the accuracy and the like are strict and the cost is high.
[0006]
Accordingly, an object of the present invention is to solve the above-described problems, and to provide an electric actuator capable of holding the reverse rotation direction torque from the driven side at low cost.
[0007]
[Means for Solving the Problems]
The above object of the present invention is to provide a housing and a ball screw in which a nut is screwed to a screw shaft through a number of rolling elements, and one of the screw shaft and the nut is a rotating portion and the other is an output portion. And a sleeve fixed to the rotating part, an electric motor that transmits the rotational force to the rotating part of the ball screw, and a housing supported by a thrust bearing, and can be rotated only in the normal rotation direction of the rotating part. The rotating body with a one-way clutch disposed substantially concentrically with the part, and the rotating body with a one-way clutch and the sleeve are interposed between the rotating part and the output part from the driven side with respect to the rotating part when the rotating part is stopped. A friction material that generates a braking torque by a frictional force with respect to the reverse rotation direction torque from the driven side in cooperation with the reverse rotation direction lock function of the one-way clutch when the reverse rotation direction torque acts. Equipped with friction material Some are held between the axial sleeve and with the one-way clutch rotating body, the frictional force proportional to the load by being given a pinching force by the load occurs, the electric actuator, from the driven side the braking torque by the friction material The reverse rotation direction torque is maintained by the braking force obtained by combining the friction torque of the electric motor obtained by combining the friction torque of the electric motor with the friction torque of the electric motor, which is smaller than the reverse rotation direction torque. This is achieved by an electric actuator characterized in that.
[0008]
According to the above arrangement, since holding the reverse rotation direction torque from the driven side by the torque obtained by combining the unfavorable action torque braking torque and the electric motor by the friction material, it is possible to lower the friction coefficient of the friction material, The conditions required for the friction material are relaxed, and the cost can be reduced.
[0009]
By using a polyacetal resin or a tetrafluoroethylene resin as the friction material, it is inexpensive and excellent in wear resistance, and a stable friction coefficient can be obtained whether dry or grease or oil lubrication.
[0010]
In addition, if the torque, which is the sum of the braking torque generated by the friction material and the starting torque or friction torque of the electric motor, falls below the reverse rotation direction torque from the driven side, the electric motor is de-energized when the rotating part stops. By short-circuiting the lead wire of the electric motor, the friction torque of the electric motor can be increased to cope with it, and when the rotating part stops, the electric motor is supplied with a current lower than that at the time of driving. It can also respond.
In the latter case, since a certain amount of braking force is obtained by the friction material, the current value for the electric motor can be low, and the power loss can be kept low.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electric actuator according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 1 is a cross-sectional view of an electric actuator according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line XX of FIG. 1, and FIG. 3 is a cross-sectional view taken along line YY of FIG.
As shown in FIGS. 1 to 3, the electric actuator 10 according to one embodiment of the present invention is configured such that a nut 13 is screwed onto a screw shaft 11 via a large number of rolling elements 12, and the nut 13 serves as a rotating portion. And a tube circulation type ball screw 14 which is an output part in which the screw shaft 11 moves in the axial direction, an electric motor 15 which transmits a rotational force to the nut 13 of the ball screw 14, and a rotation of the nut 13 only in the normal rotation direction. A thrust sleeve (rotary body) 17 with a one-way clutch 16 that is arranged substantially concentrically with the nut 13, and is interposed between the thrust sleeve 17 with a one-way clutch 17 and the nut 13 to stop the nut 13. Sometimes, when a torque in the reverse rotation direction acts on the nut 13 from the driven side via the screw shaft 11, the nut 13 follows the lock function of the reverse rotation direction of the one-way clutch 16. And a friction member 18 to generate a braking torque by the friction force with respect to the reverse rotational direction torque from the side.
[0012]
The electric motor 15 includes a stator 20 that is fixed to the inner peripheral surface of the housing H, and a rotor 21 that is disposed radially opposite to the inner diameter surface of the stator 20 in the housing H, and the rotating shaft 22 of the rotor 21. Both end portions are rotatably supported by ball bearings 23 and 24, respectively. A screw shaft 11 of the ball screw 14 is inserted into the rotary shaft 22 so as to be movable in the axial direction, and an output shaft 25 is concentrically arranged in the axial direction at the end of the screw shaft 11 on the side away from the electric motor 15. It is extended.
[0013]
A main sleeve 26 is externally fitted and fixed to the nut 13 screwed to the screw shaft 11 via the rolling element 12, and the main sleeve 26 is connected to the rotary shaft 22 by a key coupling 27 or the like. Thereby, the rotational force of the electric motor 15 is transmitted to the nut 13.
[0014]
The main sleeve 26 includes a large-diameter cylindrical portion 28 that is externally fitted and fixed to the nut 13, and a small-diameter cylindrical portion 29 that is provided at the end of the large-diameter cylindrical portion 28 that is separated from the electric motor 15. The end of the small diameter cylindrical portion 29 is rotatably supported by a needle bearing 30 or the like, and the output shaft 25 is inserted into the small diameter cylindrical portion 29.
[0015]
A thrust sleeve 17 with a one-way clutch 16 is externally fitted to a small-diameter cylindrical portion 29 of the main sleeve 26 via a friction material 18.
The friction material 18 includes a cylindrical portion 31 that is externally inserted into the small-diameter cylindrical portion 29 in a state of being fitted and fixed to the inner peripheral portion of the thrust sleeve 17 by press-fitting or the like, and an end facing the large-diameter cylindrical portion 28 side of the cylindrical portion 31. And a flange portion 32 that is sandwiched between the end surfaces of the large-diameter cylindrical portion 28 and the thrust sleeve 17. A frictional force corresponding to the clamping force of the flange portion 32 is used as a braking torque. The nut is provided to the nut 13 via 26.
The clamping force here is given by the load, where the magnitude corresponds to the load. If the friction coefficient is constant, the generated friction force is proportional to the load. Therefore, it is convenient to obtain a braking force corresponding to the reverse rotation torque.
[0016]
The end of the thrust sleeve 17 on the side away from the large-diameter cylindrical portion 28 is rotatably supported by a thrust bearing 33, and the thrust sleeve 17 has an outer peripheral surface only in the positive rotation direction of the nut 13 of the thrust sleeve 17. A one-way clutch 16 is provided that allows the rotation of the one-way clutch 16.
[0017]
The one-way clutch 16 is constituted by a roller clutch or the like, and an outer ring 34 whose inner peripheral surface is a cam surface 34 a is fitted and fixed to the housing H.
A plurality of rollers 35 are disposed in the circumferential direction between the inner peripheral surface of the outer ring 34 and the outer peripheral surface of the thrust sleeve 17, and each roller 35 is a spring provided between the non-rotating cage 36. (Not shown) is elastically pressed in one circumferential direction.
[0018]
Therefore, when the thrust sleeve 17 rotates in the forward rotation direction of the nut 13, the rollers 35 are not rotated into the cam surface 34a, and the thrust sleeve 17 is allowed to rotate in the same direction.
On the other hand, when the thrust sleeve 17 tries to rotate in the reverse rotation direction of the nut 13, each roller 35 bites into the cam surface 34 a and is locked, and rotation in the same direction is restricted.
[0019]
When the electric actuator 10 having the above configuration is incorporated in a power window of an automobile, for example, when the switch is turned on, the electric motor 15 is driven, and the rotational force is transmitted to the nut 13 via the rotary shaft 22 and the main sleeve 26. As the nut 13 rotates, the screw shaft 11 moves in the axial direction through the rolling of the rolling element 12, and the window opens and closes. When the switch is turned off, the driving of the electric motor 15 is stopped, the rotation of the nut 13 is stopped, and the opening / closing operation of the window is interrupted.
[0020]
At this time, torque in the reverse rotation direction acts from the driven side of the nut 13 through the screw shaft 11, and the flange portion 32 of the friction material 18 locks the reverse rotation direction of the one-way clutch 16 against the torque in the reverse rotation direction. Cooperate with the function to generate braking torque by frictional force.
The one-way clutch is locked in the reverse operation rotation direction due to the load in the direction in which the window is lowered by its own weight, and braking force is generated. Therefore, the window does not move even after the switch is turned off, and battery consumption can be suppressed.
[0021]
Here, in this embodiment, the braking torque by the friction material 18 is made smaller than the reverse rotation direction torque from the driven side, and the torque obtained by combining the braking torque by the friction material 18 with the starting torque, friction torque, etc. of the electric motor 15 is used. The reverse rotation direction torque from the driven side is maintained. Thereby, the friction coefficient of the friction material 18 can be lowered, and as a result, the conditions required for the friction material 18 are relaxed, and the cost can be reduced.
[0022]
When the torque obtained by combining the braking torque by the friction material 18 and the starting torque or friction torque of the electric motor 15 is lower than the reverse rotation direction torque from the driven side, the electric motor 15 is energized when the nut 13 is stopped. Is cut off and the lead wire of the electric motor 15 is short-circuited, so that the friction torque of the electric motor 15 can be increased and the reverse rotation direction torque from the driven side can be maintained. The reverse rotation direction torque from the driven side can also be maintained by energizing the motor 15 with a current having a value lower than that during driving.
[0023]
The electric actuator according to the present invention is not limited to the above-described embodiment, and can take various forms based on the gist of the present invention.
For example, in the above-described embodiment, the ball screw 14 in which the nut 13 is a rotating portion and the screw shaft 11 is an output portion that moves in the axial direction is taken as an example. However, the present invention is not limited thereto, and the screw shaft 11 rotates. Of course, the present invention can be applied to an electric actuator including a ball screw which is a part and an output part in which the nut 13 moves in the axial direction.
[0024]
Moreover, in the said embodiment, although the nut 13 and the main sleeve 26 are made into a different body, both are good also as an integral structure.
Further, in the above embodiment, the main sleeve 26 is connected to the rotary shaft 22 by the key coupling 27 or the like, but instead, the main sleeve 26 and the rotary shaft 22 may be connected by serration coupling.
[0025]
【The invention's effect】
As described above, according to the electric actuator of the present invention described above, the braking torque by the friction material is made smaller than the reverse rotation direction torque from the driven side, and the braking torque by the friction material and the starting torque, friction torque, etc. of the electric motor are combined. Since the torque in the reverse rotation direction from the driven side is maintained by the torque, the friction coefficient of the friction material can be lowered, and as a result, the conditions required for the friction material are eased and the cost can be reduced. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an electric actuator according to an embodiment of the present invention.
2 is a cross-sectional view taken along line XX of FIG.
3 is a cross-sectional view taken along line YY in FIG.
[Explanation of symbols]
10 Electric actuator 11 Screw shaft (output part)
12 Rolling elements 13 Nut (rotating part)
14 Ball screw 15 Electric motor 16 One-way clutch 17 Thrust sleeve (rotating body)
18 Friction material

Claims (3)

A housing, a ball screw in which a nut is screwed to a screw shaft via a number of rolling elements, and one of the screw shaft and the nut is a rotating portion and the other is an output portion, and the rotating portion A sleeve fixed to the motor, an electric motor for transmitting a rotational force to the rotating part of the ball screw, and supported by the housing via a thrust bearing, and can be rotated only in the positive rotation direction of the rotating part. A rotating body with a one-way clutch arranged substantially concentrically with the rotating part, and interposed between the rotating body with the one-way clutch and the sleeve, and when the rotating part stops, from the driven side to the rotating part When a torque in the reverse rotation direction is applied via the output unit, the frictional force against the reverse rotation direction torque from the driven side is applied to the rotation unit in cooperation with the reverse rotation direction lock function of the one-way clutch. And a friction member for generating a dynamic torque, the portion of the friction material is held between the sleeve in the axial direction the one-way clutch with the rotary body, the frictional force proportional to the load by being given a pinching force by the load In an electric actuator where
The braking torque by the friction material is smaller than the reverse rotation direction torque from the driven side,
The reverse rotation direction torque is maintained by the braking force obtained by combining the friction torque of the electric motor obtained when the power supply to the electric motor is cut off and the braking torque of the friction material. Electric actuator.   2. The electric actuator according to claim 1, wherein when the rotating portion is stopped, the energization of the electric motor is interrupted to short-circuit the lead wire of the electric motor.   The electric actuator according to claim 1, wherein a current having a lower value is supplied to the electric motor when the rotating unit is stopped.

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