JP2004229337A - Linear actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear actuator capable of realizing cost reduction, high reliability, and highly accurate driving. <P>SOLUTION: This linear actuator has an electric motor 11, a thread shaft 13 connected with a rotating shaft 11a of the electric motor 11, a nut member 16 disposed around the thread shaft 13, and a ball rolling in a radial groove formed between the thread shaft 13 and the nut member 16. With this constitution, the rotating shaft 11a and the thread shaft 13 are connected by engaging a recessed portion 13d having a non-circle cross section formed on one side of the rotating shaft 11a of the electric motor 11 and the thread shaft 13 with a protruding portion 11a formed on the other side. The rotational shaft 11a and the thread shaft 13 are connected with each other. Therefore, power can be transmitted more efficiently than the case which uses a warm system is used, the number of components can be reduced more than in the case which uses a key connection, and its constitution can be provided with less effort and at a lower cost than in the case which uses a serration connection. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a linear actuator, for example, a power window of an automobile, a wire winding mechanism of an electric parking brake device, a caliper pushing mechanism of an electric disc brake device, a cam phase conversion mechanism in a variable valve timing device of an engine, and other industrial winches. The present invention relates to a linear actuator using an electric motor as a power source, which can be used for hoists, cranes, various positioning devices, and the like.
[0002]
[Prior art]
For example, there is known an electric parking brake driving device that operates a parking brake of a vehicle by using the power of an electric motor to reduce a burden on a driver. As such an electric parking brake driving device, a device has been proposed in which a pulley is rotated by an electric motor to wind up a wire to operate a parking brake, and a wire is rewound to release the parking brake (Patent Document 1).
[Patent Document 1]
JP 2001-106060 A
[Problems to be solved by the invention]
The electric parking brake driving device disclosed in the above-mentioned publication uses a worm gear and a worm hole to reduce the power from the electric motor and transmit the power to the parking brake. When power is transmitted by using the worm gear and the worm wheel, the reduction ratio can be increased, and the power from the parking brake can be prevented from being transmitted to the electric motor by appropriately designing the helical angle of the worm. There is.
[0004]
However, if the above advantages are reversed, worm gears and worm holes have the disadvantage of low transmission efficiency, and therefore the power of the electric motor must be increased in order to operate the parking brake, thereby increasing the power of the electric motor. However, there is a problem that the size becomes large and power cannot be saved. One measure to solve such a problem is to use a ball screw mechanism that can convert the rotational force of the electric motor in the axial direction. The ball screw mechanism can convert a rotational force into an axial force with low friction and high efficiency by a ball rolling in a spiral groove formed between a screw shaft and a nut member.
[0005]
Here, one problem in such a configuration is how to connect the rotation shaft and the screw shaft of the electric motor such that they cannot rotate relative to each other. For example, Patent Document 2 discloses a configuration in which a ball screw and a rotating shaft of a motor are connected by a key. However, according to such a connection method, a key is required in addition to forming key grooves on both the ball screw and the rotating shaft, and the number of parts is increased. On the other hand, it is conceivable that the screw shaft and the rotation shaft are serrated, but there is also a problem that the serration processing is troublesome.
[Patent Document 2]
JP-A-9-303519
The present invention has been made in view of the problems of the related art, and has as its object to provide a linear actuator that can drive accurately with low cost while maintaining reliability.
[0007]
[Means for Solving the Problems]
The linear actuator of the present invention
An electric motor,
A screw shaft connected to a rotation shaft of the electric motor,
A nut member arranged around the screw shaft;
A ball that rolls in a spiral groove formed between the screw shaft and the nut member,
By engaging a non-circular concave portion with a non-circular concave portion formed on one of the rotary shaft and the screw shaft of the electric motor and the convex portion having a shape corresponding to the concave portion formed on the other side, The rotary shaft and the screw shaft are integrally rotatably connected to each other.
[0008]
[Action]
The linear actuator according to the present invention includes an electric motor, a screw shaft connected to a rotation shaft of the electric motor, a nut member arranged around the screw shaft, and a nut member formed between the screw shaft and the nut member. A ball that rolls in the formed spiral groove, wherein a cross section orthogonal to the axis formed on one of the rotating shaft and the screw shaft of the electric motor is formed in a non-circular concave portion and the other side. By engaging the convex portion having a shape corresponding to the concave portion, the rotation shaft and the screw shaft are integrally rotatably connected, as compared with a case where a worm mechanism is used. Power can be transmitted efficiently, and the number of parts is smaller than when keyed connection is used. There is an advantage that Do configuration is provided.
[0009]
Furthermore, when the recess is formed by forging, the amount of material to be cut is smaller than in the case where machining is performed alone, and machining time and tools can be saved. It is preferable to use both forging and machining (finishing) because the dimensional accuracy is further improved.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front view of the linear actuator according to the first embodiment, and FIG. 2 is a diagram illustrating an end of a screw shaft. In FIG. 1, the electric motor and the screw shaft are shown in a separated state.
[0011]
In FIG. 1, a rotating shaft 11a of an electric motor 11 attached to a housing (not shown) has a tip formed as a hexagonal column-shaped projection centered on the rotating axis. On the other hand, the end of the screw shaft 13 in which the cylindrical shaft portions 13a and 13b at both ends are rotatably supported by the bearings 12 and 14 with respect to the housing (not shown) corresponds to the shape of the rotation shaft 11a. A recess 13d having a hexagonal cross section centered at the center is formed. By engaging the convex portion 11a with the concave portion 13d, the rotating shaft 11a and the screw shaft 13 are integrally rotatably connected.
[0012]
A screw groove 13c (only part of which is shown) is formed on the outer peripheral surface of the screw shaft 13 except for the cylindrical portions 13a and 13b, while a screw groove 13c is formed on the inner peripheral surface of the nut member 16 disposed on the outer periphery thereof. A screw groove (not shown) is formed opposite to the screw groove 13c, and a number of balls (not shown) are rotatably arranged in a spiral space formed by both screw grooves 13c (one not shown). ing. Further, on the outer periphery of the nut member 16, a tube 16b for returning the ball from one end of the nut member 16 to the other end is provided. The nut member 16, the screw shaft 13, and a ball (not shown) constitute a ball screw mechanism BS.
[0013]
The operation of the present embodiment will be described. In FIG. 1, when power is supplied from a power source (not shown) and the screw shaft 13 rotates in one direction together with the rotating shaft 11a of the electric motor 11, the nut member 16 receives a force to move rightward in the drawing. Thus, a control shaft (not shown) for driving, for example, a valve timing mechanism of the internal combustion engine is driven to rotate in one direction via a link member or the like (not shown) connected to the nut member 16. On the other hand, when power having an inverse characteristic is supplied from a power supply (not shown) and the screw shaft 13 rotates in the other direction together with the rotating shaft 11a of the electric motor 11, the nut member 16 receives a force to move leftward in the drawing. . Thereby, for example, the above-described control shaft (not shown) is driven to rotate in the opposite direction via a link member or the like (not shown) connected to the nut member 16. Therefore, if the linear actuator according to the present embodiment is used, the valve timing mechanism and the like can be arbitrarily controlled.
[0014]
According to the present embodiment, by engaging concave portion 13d having a non-circular cross section formed on one of rotary shaft 11a and screw shaft 13 of electric motor 11, with convex portion 11a formed on the other side, Since the rotary shaft 11a and the screw shaft 13 are connected, power can be transmitted more efficiently than when a worm mechanism is used, and the number of parts is smaller than when a key combination is used. In addition, as compared with the case where the serration coupling is used, there is an advantage that a processing cost is reduced and a low-cost configuration is provided.
[0015]
FIG. 3 is a front view of the linear actuator according to the second embodiment, and FIG. 4 is a diagram illustrating an end of a screw shaft. Note that FIG. 3 also shows the electric motor and the screw shaft in a separated state. This embodiment is different from the embodiment shown in FIGS. 1 and 2 only in the shape of the convex portion and the concave portion.
[0016]
In FIG. 3, the rotating shaft 11 a ′ of the electric motor 11 has, as a projection, a so-called two-sided width shape obtained by shaving the outer peripheral surface with two surfaces parallel to the axis with respect to the cylindrical shape. On the other hand, the end of the screw shaft 13 has a concave portion 13d 'having a shape shown in FIG. 4 corresponding to the shape of the rotating shaft 11a. By engaging the convex portion 11a 'with the concave portion 13d', the rotating shaft 11a and the screw shaft 13 are integrally rotatably connected.
[0017]
In the embodiment described above, the recesses 13d and 13d 'can be formed quickly without any trouble by forming them by machining after forging. However, the recesses 13d and 13d 'may be formed only by forging if accuracy is secured, or the protrusions 11a and 11a' may be formed by forging or forging and machining.
[0018]
As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above embodiments, and it is needless to say that modifications and improvements can be made as appropriate. For example, the shapes of the convex portions and the concave portions are not limited to hexagons and dihedral widths, and may be employed as long as the cross-section orthogonal to the axis is non-circular, such as a quadrangle. It goes without saying that a concave portion may be formed on the rotating shaft and a corresponding convex portion may be formed on the screw shaft.
[0019]
【The invention's effect】
The linear actuator according to the present invention includes an electric motor, a screw shaft connected to a rotating shaft of the electric motor, a nut member disposed around the screw shaft, and a nut member formed between the screw shaft and the nut member. And a ball that rolls in the spiral groove formed in the linear groove. By engaging the convex portion having a shape corresponding to the concave portion, the rotating shaft and the screw shaft are integrally rotatably connected, so as compared with a case where a worm mechanism is used. Power can be transmitted efficiently, and the number of parts is smaller than when keyed connection is used. There is an advantage that Do configuration is provided.
[Brief description of the drawings]
FIG. 1 is a front view of a linear actuator according to a first embodiment.
FIG. 2 is a diagram illustrating an end of a screw shaft according to the first embodiment.
FIG. 3 is a front view of a linear actuator according to a second embodiment.
FIG. 4 is a diagram illustrating an end of a screw shaft according to a second embodiment.
[Explanation of symbols]
11 electric motor 11a, 11a 'convex part 13 screw shaft 13d, 13d' concave part 16 nut member

Claims (2)

An electric motor,
A screw shaft connected to a rotation shaft of the electric motor,
A nut member arranged around the screw shaft;
A ball that rolls in a spiral groove formed between the screw shaft and the nut member,
By engaging a non-circular concave portion with a non-circular concave portion formed on one of the rotary shaft and the screw shaft of the electric motor and the convex portion having a shape corresponding to the concave portion formed on the other side, A linear actuator, wherein the rotary shaft and the screw shaft are integrally rotatably connected. 2. The linear actuator according to claim 1, wherein the recess is formed by forging.

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