JP2756812B2 - Linear actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a direct-acting actuator provided with a planetary ball type traction drive mechanism, and relates to an actuator used for, for example, a drum brake device of an automobile.

<Prior Art> Conventionally, there is a direct-acting actuator provided with a planetary gear type reduction mechanism using an electric motor as a prime mover, and is used, for example, in a drum brake device of an automobile. In this drum brake device, when the brake is operated, the brake shoe is moved to the side where the brake shoe is pressed against the inner peripheral surface of the brake drum by protruding the output shaft of the direct acting actuator in one axial direction.

<Problems to be Solved by the Invention> In the above-described conventional linear-acting actuator, power is transmitted by meshing of gears. Therefore, for example, the linear-acting actuator is driven by a reaction force when a brake shoe is pressed against a brake drum. In the planetary gear type reduction mechanism of the actuator, the mutual gear galling noise is likely to occur, and in severe cases, the gear may be damaged.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a highly reliable direct acting actuator that does not generate noise or damage internal components even when an excessive load is applied to an output shaft.

<Means for Solving the Problems> The present invention has the following configuration to achieve such an object.

The direct-acting actuator of the present invention is screwed into a prime mover, a planetary ball type traction drive mechanism having a rotation axis of the prime mover as a sun axis, and a driven body of the planetary ball type traction drive mechanism. And the planetary ball type traction drive mechanism, wherein the planetary ball is made of ceramic, and the planetary ball contacts the sun shaft, the fixed wheel, and the driven body, respectively. It is configured to be.

In the linear motion actuator, the driven body of the planetary ball traction drive mechanism may be provided with clutch means for switching between a state where power is transmitted from the driven body to the output shaft or a state where power transmission is interrupted. You may.

<Operation> In the above configuration, since power transmission is performed by friction, an excessive load is applied to the output shaft, for example, when the movement of the output shaft is prevented despite the rotation shaft of the prime mover continuing to rotate. In this case, the planetary ball slips with respect to the sun shaft, the moving body, and the fixed wheel that come into contact with the planetary ball, and the power transmission between the rotating shaft and the output shaft is interrupted.

Moreover, since the planetary ball is made of ceramic, even if the planetary ball slips more than necessary, wear and damage to the rolling surface are suppressed. Further, if the driven body is provided with the clutch means, similarly to the above, when an excessive load is applied to the output shaft, the clutch means switches the power transmission between the driven body and the output shaft to be cut off.
In this case, the planet ball does not slip more than necessary.

<Example> Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

1 and 2 show a first embodiment of the present invention. The direct-acting actuator 1 in the illustrated example is configured to include an electric motor 2 as a prime mover, a planetary ball type traction drive mechanism 3, and an output shaft 4.

The electric motor 2 includes a bottomed cylindrical case 21 and this case.
A rotating shaft 24 having one end supported by a case 21 via a rolling bearing 23; and a rotor 25 fixed to the outer circumferential surface of the rotating shaft 24. .

The planetary ball type traction drive mechanism 3 includes a sun shaft 31 integrally formed at the other end of the rotation shaft 24 of the electric motor 2,
A fixed wheel 32 attached to the open end of the case 21 of the electric motor 2, a plurality of ceramic planetary balls 34 held at equal circumferential intervals by a retainer 33, and a rolling bearing on the inner peripheral surface of the fixed wheel 32. And a cylindrical follower 36, one end face of which is pressed through on the peripheral surface of the planetary ball 34. In this configuration, the planetary ball 34 is in two-point contact with the raceway groove of the sun shaft 31, and is also in contact with the raceway surface 32A of the fixed wheel 32 and one end surface of the driven body 36, respectively.

In the output shaft 4, a screw groove 41 formed on the outer peripheral surface is screwed into a screw hole 37 formed at the center of the driven body 36, and a portion having the screw groove 41 is located at the center of the sun shaft 31. It is designed to enter and exit the formed recess 38 without contact.

The outer peripheral surfaces of the case 21 of the electric motor 2 and the fixed wheel 32 of the planetary ball type traction drive mechanism 3 are formed substantially flush with each other. Shaft end 42 is projected. Further, a seal member 5 is attached to an open end of the fixed wheel 32, and an inner peripheral lip portion of the seal member 5 is brought into contact with an outer peripheral surface of the output shaft 4.

Next, the operation will be described. When the case 21 of the electric motor 2, the fixed wheel 32 of the planetary ball type traction drive mechanism 3, and the main power shaft 4 are not allowed to rotate, and the rotation shaft 24 of the electric motor 2 is rotated, the sun shaft integrated with the rotation shaft 24 is formed. Due to the speed difference between 31 and fixed wheel 32, planetary ball 34
Revolves around the sun axis 31, and the planetary ball 34 rotates about this dashed line P in FIG. Due to the rotation of the planetary ball 34, the driven body 36 is rotated at a lower speed than the rotational speed of the planetary ball 34. As described above, the reduction ratio of the planetary ball traction drive mechanism 3 is, for example, about 1/20 to 1/100, and can be set to be larger than the reduction ratio of a general planetary roller traction drive mechanism. When the driven body 36 is rotated, the output shaft 4 screwed with the driven body 36 is moved in one of the axial directions by the same principle as that of the feed screw mechanism.

In other words, according to the structure of this embodiment, the rotation speed of the electric motor 2 can be greatly reduced by the planetary ball type traction drive mechanism 3 and the driven body 36 can be slightly rotated. Does not need to be performed finely, and a small amount of movement control of the output shaft 4 can be performed.

As described above, the direct acting actuator 1 of the present embodiment
Since the structure is such that power is transmitted by friction, for example, when the movement of the output shaft 4 in the axial direction is forcibly stopped despite the operation of the electric motor 2, the rotation of the driven body 36 is stopped. Stopped and planetary ball 34
Is stopped. Therefore, the planetary ball 34 slips on the follower 36, the sun shaft 31, and the fixed wheel 32, and the impact caused by the stop of the output shaft 4 is absorbed by the slip.

By the way, when the planetary ball 34 is made of the same steel material as the sun shaft 31, the fixed wheel 32, and the driven body 36, if unnecessary slip occurs due to the same kind of metal, an adhesion phenomenon occurs between the contact members, and the planetary ball 34 However, if the planetary ball 34 is made of ceramic as in this embodiment, abnormal wear of the planetary ball 34 due to slip is suppressed, and contact with the planetary ball 34 is prevented. The rolling surface of the other member is less likely to be damaged.

Next, FIGS. 3 and 4 show a second embodiment of the present invention. In this figure, the same components as those shown in FIGS. 1 and 2 of the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

The second embodiment is different from the first embodiment in that the driven body 36 is provided with a clutch means 6 for switching between a state in which power is transmitted from the driven body 36 to the output shaft 4 and a state in which power transmission is interrupted. That is.

Specifically, the driven member 36 is divided into a driven member main body 80 and a nut member 81 having a screw hole at the center, and the clutch means 6 is provided with an end face of the driven member main body 80 and a radially outer portion provided on the nut member 81. It is interposed between the flange 82 of the orientation. The driven body 80 of the driven body 36 is attached to the shaft end of the sun shaft 31 via a rolling bearing 35.

The clutch means 6 includes a disc spring 61 disposed on the flange 82 side of the nut member 81, a ring body 62 urged toward the end face of the driven body 80 by the spring force of the disc spring 61, 62
And a plurality of balls 64 sandwiched between grooves 63 and 83 having a V-shaped cross section formed corresponding to several locations on the circumference of one surface and the end face of the driven body 80, respectively, and holding the plurality of balls 64 vessel
Consists of 65. The ring body 62 is spline-fitted to the nut member 81, while the driven body 80 is attached to the nut member 81 so as to be relatively rotatable.

Direct-acting actuator 1 having this clutch means 6
Will be described. In the state shown in the figure, since the driven body 80 and the nut member 81 are integrally held via the clutch means 6, if the electric motor 2 is operated, the planetary ball type traction drive mechanism 3 is used. The output shaft 4 will be moved to the left side of the figure. At this time, even if the axial movement of the output shaft 4 is prevented, the electric motor 2
As the driven body 80 continues to be rotated by the driving force from the motor, as shown in FIG.
The disc spring 61 is compressed and deformed while the ball 64 remaining in the groove 62 of the ring body 62 comes out of the ring body 62, and when the ball 64 comes out of the groove 83 completely, the nut member 81 does not rotate and the driven body 80 Power is not transmitted to the output shaft 4.

In the direct-acting actuator 1 of this embodiment, when an excessive load is applied to the output shaft 4, the power transmission between the driven body 80 and the output shaft 4 is cut off by the clutch means 6, so that the planetary ball 34 hardly slips.

The clutch means 6 is not limited to the one having the illustrated configuration.

The direct acting actuator 1 of the first and second embodiments described above can be used in a drum brake device 7, for example, as shown in FIG. That is, one brake shoe 71 is engaged with the bottom wall of the case 21 of the direct acting actuator 1, and the other brake shoe 72 is engaged with the protruding end 42 of the output shaft 4. In this case, the case 21 and the output shaft 4 of the electric motor 2 are
2, the output shaft 4 is sent out in the axial direction when the electric motor 2 is operated, and both brake shoes 71 and 72 are pressed against the inner peripheral surface of the brake drum 73. When this is pressed, the output shaft 4
Is stopped, and the internal components are protected depending on whether the planetary ball 34 is slipped or the power transmission is interrupted by the clutch means 6 as described above.

Of course, it goes without saying that the direct acting actuator 1 of the present invention can be used for other than the drum brake device 7.

<Effects of the Invention> As described above, in the present invention, power is transmitted by friction using the planetary ball type traction drive mechanism. Therefore, when an excessive load acts on the output shaft, the planetary ball slips. As a result, the power transmission between the rotating shaft and the output shaft can be cut off, thereby preventing the conventional components from being damaged or generating noise.

Moreover, since the planetary ball is made of ceramic, it is effective to prevent abnormal wear of the planetary ball and damage to the rolling portion of the planetary ball even if the slip occurs more than necessary, and the life of the linear motion type actuator is reduced. You can contribute to improvement.

In addition, in the case of an overload acting on the output shaft of the direct acting actuator, each component is protected by cutting off the power transmission by the clutch means without causing the planetary ball to slip more than necessary. Is also good. In this case, since the planetary ball does not slip more than necessary, it is possible to prevent wear of the planetary ball and damage to the rolling surface from occurring.

[Brief description of the drawings]

1 and 2 relate to a first embodiment of the present invention, and FIG. 1 is a longitudinal sectional side view showing a configuration of a direct acting actuator;
FIG. 2 is a sectional view taken along the line II-II of FIG. 3 and 4 relate to a second embodiment of the present invention. FIG. 3 is a diagram corresponding to FIG. 1, and FIG. 4 is a diagram used for explaining the operation of the clutch means. FIG. 5 is a partial front view showing a structure in which the direct acting actuator according to the first or second embodiment is used for a drum brake device of an automobile. 2 ... Electric motor, 24 ... Rotary shaft, 3 ... Planetary ball type traction drive mechanism, 31 ... Sun shaft, 32 ... Fixed wheel, 34 ... Planetary ball, 36 ... Follower, 4 ... Output Shaft, 6 ... clutch means.

Claims (2)

(57) [Claims] A motor, a planetary ball type traction drive mechanism having a rotation axis of the motor as a sun axis, and a driven body of the planetary ball type traction drive mechanism, which is axially driven by rotation of the driven body. An output shaft to be moved, and the planetary ball type traction drive mechanism comprises:
A direct-acting actuator, wherein the planetary ball is made of ceramic, and the planetary ball is configured to contact the sun shaft, the fixed wheel, and the driven body. 2. The direct-acting actuator according to claim 1, wherein a state where power is transmitted from the driven body to an output shaft or a power transmission is interrupted to a driven body of the planetary ball traction drive mechanism. A direct-acting actuator, characterized in that a clutch means for switching to a state is provided.