JP2009168096A - Ball screw device - Google Patents

Abstract

A ball screw device suitable for use in a form in which a screw shaft linearly moves in an axial direction without rotating.
A ball screw nut 4 and a rotor 11 of a motor 5 are coupled via a clutch mechanism 7. The clutch mechanism 7 includes a friction plate 14 interposed between the ball screw nut 4 and the motor rotor 11, and a diaphragm spring 15 that urges the ball screw nut 4 and the motor rotor 11 toward each other. When the screw shaft 3 pushes the diaphragm spring 15 in the direction opposite to the urging direction, the connection between the ball screw nut 4 and the motor rotor 11 is disconnected.
[Selection] Figure 1

Description

  The present invention relates to a ball screw device, and more particularly to a ball screw device used in a form in which a screw shaft moves linearly in an axial direction without rotating.

A ball screw device including a screw shaft and a ball screw nut screwed to the screw shaft is often used for an electric actuator or a shock absorber. For example, Patent Document 1 discloses a motor for a ball screw nut and a motor. It is disclosed that a ball screw device in which a rotor is connected and a screw shaft is linearly moved is applied to a shock absorber. This type of shock absorber is usually provided with a stopper in order to prevent the screw shaft from moving beyond a predetermined amount when receiving a strong force from the outside.
JP 2005-264992 A

  In the ball screw device used in Patent Document 1 described above, the screw shaft moves at a high speed and the ball screw nut rotates at a high speed immediately before the screw shaft is stopped by the stopper. A large rotational inertia force is generated in the ball screw nut, and an indentation may occur in the raceway portion of the ball screw due to the rotational inertia force. In order to prevent the indentation of the ball screw raceway, it is sufficient to increase the strength by enlarging the entire ball screw device, but this is not preferable because the moment of inertia increases.

  An object of the present invention is to provide a ball screw device suitable for use in a form in which a screw shaft moves linearly in the axial direction without rotating.

  The ball screw device according to the present invention includes a screw shaft that linearly moves in the axial direction, a ball screw nut that is screwed to the screw shaft via a ball and rotates in accordance with the linear movement of the screw shaft, and a rotation of the ball screw nut. A ball screw device in which the limit position in the forward direction of the screw shaft is defined by a stopper, and the ball screw nut and the motor rotor are coupled via a clutch mechanism. The coupling of the motor rotor is characterized in that it is disconnected before the screw shaft advances and reaches the extreme position.

  The ball screw device according to the present invention may be used as an actuator (a configuration in which a ball screw nut is rotated by a motor, whereby the screw shaft moves linearly), and a shock absorber (the screw shaft is driven by an external force). In some cases, the ball screw nut is rotated linearly, whereby the electromagnetic force generated by the motor becomes a damping force.

  In any case, the screw shaft reciprocates linearly and is usually in a predetermined direction (referred to as “advance direction” in this specification. The “advance direction” means the movement direction that collides with the stopper, and is specific. Is provided with a stopper for preventing movement of a predetermined amount or more in any of the vertical direction, front-rear direction, left-right direction, and other directions. The stopper can be formed, for example, by providing the screw shaft with a flange portion that contacts the housing when the screw shaft moves by a predetermined amount or more, and the stopper is formed on a member that moves linearly integrally with the screw shaft. Alternatively, it may be provided on a member that does not move linearly (a housing or a hollow shaft). Since the limit position in the forward direction of the screw shaft is defined by the stopper, the screw shaft is forcibly stopped when the limit position is reached. If the moving speed of the screw shaft at this time is fast, an indentation may occur on the ball screw raceway because the rotational inertia force of the nut at the time of sudden stop of the screw shaft is large.

  In particular, in the conventional one, since the ball screw nut and the motor rotor are rigidly coupled, when the movement of the screw shaft is forcibly stopped, the inertia force of the motor rotor also acts on the ball screw nut, and the indentation Is likely to occur.

  According to the ball screw device of the present invention, since the ball screw nut and the motor rotor are coupled via the clutch mechanism, and the coupling is disconnected before colliding with the stopper, the movement of the screw shaft is forcibly stopped. Then, the motor rotor idles, thereby reducing the rotational inertia force and reducing the impact load acting on the ball screw. As a result, indentation is prevented from occurring on the ball screw track.

  The clutch mechanism includes, for example, a friction plate interposed between the ball screw nut and the motor rotor, and an elastic member (for example) a diaphragm spring that urges the ball screw nut and the motor rotor toward each other. When the screw shaft pushes the elastic member in the direction opposite to the biasing direction, the coupling between the ball screw nut and the motor rotor is disconnected.

  A spline for guiding the linear movement of the screw shaft may be provided integrally with the screw shaft. The spline in this case may be a ball spline, for example, a fitting spline such as an involute spline.

  According to the ball screw device of the present invention, since the ball screw nut and the rotor of the motor are separated before the screw shaft is forcibly stopped, the impact load acting on the ball screw can be reduced. Indentation can be prevented from occurring on the track. As a result, the problem of an increase in the moment of inertia when the whole is increased to ensure the strength is solved, and the ball screw device can be reduced in size and weight.

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, “upper and lower” refers to the upper and lower sides of the figure, and “upward” is the forward direction.

  FIG. 1 shows an embodiment of a ball screw device according to the present invention.

  The ball screw device (1) includes a vertical cylindrical housing (2), a steel screw shaft (3) extending vertically in the housing (2), and a ball on the upper end of the screw shaft (3). A ball screw nut (4) screwed together, a motor (5) disposed in a motor housing (6) provided at the upper end of the housing (2), a ball screw nut (4) and a motor (5 And a clutch mechanism (7) for coupling with the rotor (11).

  This ball screw device (1) is used in such a manner that the screw shaft (3) moves up and down (linear motion), and the ball screw nut (4) rotates accordingly. For example, the screw shaft (3) The bracket (B) connected to the vehicle axle side is provided at the lower end of the vehicle), and the motor accommodating portion (6) of the housing (2) is attached to the vehicle body so that it can be used as an electromagnetic shock absorber.

  The motor housing portion (6) includes a bottom wall portion (8) provided with an insertion hole (8a) for the screw shaft (3), and an outer cylinder portion (upper portion) erected along the outer periphery of the bottom wall portion (8). 9) and an inner cylinder portion (10) erected along the screw insertion hole (8a) of the bottom wall portion (8).

  The motor (5) includes a motor rotor (11) that is rotatably supported by the inner cylinder portion (10) via a bearing (13) and rotates with the rotation of the ball screw nut (4), and a motor rotor (11). The stator (12) is fixed to the inner periphery of the outer tube portion (10) so as to face each other. The motor rotor (11) is disposed below the ball screw nut (4), and the outer diameter thereof is larger than the outer diameter of the ball screw nut (4).

  The clutch mechanism (7) is provided on the friction plate (14) interposed between the lower surface of the ball screw nut (4) and the upper surface of the central portion of the motor rotor (11), and on the upper surface of the outer peripheral portion of the motor rotor (11). A diaphragm spring (15) having a downward biasing force, and a pressing plate (16) provided on the upper surface of the ball screw nut (4) to transmit the downward biasing force of the diaphragm spring (15) to the ball screw nut (4). Consists of. Thereby, the ball screw nut (4) and the motor rotor (11) are not rigidly coupled but coupled by elastic force and frictional force.

  The diaphragm spring (15) includes an annular portion (15a) and a plurality of lever portions (15b) extending from the annular portion (15a) toward the center.

  The diameter of the circle (15c) formed by the tip surfaces of the plurality of lever portions (15b) (the inner diameter of the diaphragm spring (15)) is smaller than the diameter of the screw shaft (3). The upper end surface (tip surface) of 3) faces the circle (15c) formed by the tip surfaces of the plurality of lever portions (15b) from below. The upper limit position (extreme position) of the screw shaft (3) is defined by a stopper (not shown), and the upper limit position of the upper end surface of the screw shaft (3) is a plurality of lever portions as indicated by a two-dot chain line. It is set above the circle (15c) formed by the tip surface of (15b).

  Under normal conditions, the screw shaft (3) moves up and down as long as the upper end surface thereof does not contact the lever portion (15b) of the diaphragm spring (15). In this case, since the ball screw nut (4) and the motor rotor (11) are coupled via the friction plate (14), they can rotate together to obtain an electromotive force due to the rotation of the motor rotor (11). it can.

  When a strong upward force is applied to the screw shaft (3), the screw shaft (3) reaches the upper limit position and is forcibly stopped. At this point, since the ball screw nut (4) has a rotational inertia force, the ball screw nut (4) tries to continue to rotate and rotates between the screw shaft (3) and the ball screw nut (4) via the ball. Inertial force acts.

  When the ball screw nut (4) and the motor rotor (11) are rigidly connected (conventional), the rotational inertia force of the motor rotor (11) is added to the rotational inertia force of the ball screw nut (4), so the screw shaft (3) A large force acts between the nut and the ball screw nut (4).

  In contrast, in the ball screw device (1) according to the present invention, before the screw shaft (3) reaches the upper limit position, the upper end surface of the screw shaft (3) faces the lever portion (15b) of the diaphragm spring (15) upward. As a result, the coupling between the ball screw nut (4) and the motor rotor (11) is disconnected, and the motor rotor (11) is idled. Therefore, the impact load acting between the screw shaft (3) and the ball screw nut (4) is only due to the rotational inertia force of the ball screw nut (4).

  This ball screw device (1) is suitable for use as, for example, an electromagnetic shock absorber for an automobile. The electromagnetic shock absorber converts the axial motion transmitted from the tire into rotational motion by a ball screw mechanism, takes this rotational motion into the motor (10), and uses the electromagnetic force generated by the motor (10) as a damping force. During suspension overstroke, such as over a protrusion, the bump stopper provided at the linear movement part collides with the housing (2) (for example, a motor flange), so that the motor (5) rotating at high speed suddenly There is a case where an excessive axial force is applied to the ball screw portions (3) and (4) due to the inertia torque of the motor (5), and protection of the ball screw mechanism in this case is a problem.

  According to the above ball screw device (1), the connection between the ball screw nut (4) and the motor rotor (11) is disconnected by the movement of the screw shaft (3) before the stopper collides with the housing (2). Because the clutch mechanism (7) is released by this, when the stopper hits the housing (2), the impact load acting on the screw shaft (3) is only due to the rotational inertia force of the ball screw nut (4). . Therefore, the ball screw mechanism is protected and problems such as the generation of indentations are prevented.

FIG. 1 is a longitudinal sectional view showing an embodiment of the ball screw device of the present invention.

Explanation of symbols

(1) Ball screw device
(3) Screw shaft
(4) Ball screw nut
(5) Motor
(7) Clutch mechanism
(11) Motor rotor
(14) Friction plate
(15) Diaphragm spring

Claims (2)

A screw shaft that linearly moves in the axial direction, a ball screw nut that is screwed to the screw shaft via a ball and rotates along with the linear movement of the screw shaft, and a motor rotor that rotates as the ball screw nut rotates. In the ball screw device in which the extreme position in the forward direction of the screw shaft is defined by the stopper,
The ball screw nut and the motor rotor are connected via a clutch mechanism, and the ball screw nut and the motor rotor are connected to each other before the screw shaft advances and reaches the extreme position. And ball screw device.   The clutch mechanism has a friction plate interposed between the ball screw nut and the motor rotor, and a diaphragm spring that urges the ball screw nut and the motor rotor toward each other, and the screw shaft is attached with the diaphragm spring. 2. The ball screw device according to claim 1, wherein the ball screw nut and the motor rotor are disconnected by being pushed in the direction opposite to the biasing direction.

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