JP2000018361A - Motor-driven linear actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide at low cost a structure for preventing sudden displacement of an output shaft when balls are damaged. SOLUTION: A stopper ring 60 is provided between a ball nut 7b to which the rear end portion of an axially freely displaceable output shaft 8 is secured and a ball screw portion 6 provided on a part of a rotating shaft 2. The stopper ring 60 comprises a circular-cross-section wire formed into a spiral shape as a whole, half of its outer periphery being fitted in place inside a ball nut groove 22b formed in the inner peripheral surface of the ball nut 7b. Also, half of its inner periphery is made to advance into a part of a ball screw groove 21 formed in the outer peripheral surface of the ball screw part 6, with a gap intervening therebetween.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION An electric linear actuator according to the present invention includes, for example, a nursing bed, an elevating table,
It is used in a state of being incorporated in various mechanical devices such as a T scanner, a truck cabin tilt device, and a lifter.

[0002]

2. Description of the Related Art For example, electric linear actuators are incorporated in electric beds for nursing care, elevating tables, CT scanners, truck cabin tilt devices, lifters, and the like.
By using an electric motor as a drive source, angle adjustment, position adjustment, and the like of these various mechanical devices can be freely performed. Conventionally, such an electric linear actuator has been disclosed in Japanese Patent Application Laid-Open No. 8-322.
Nos. 189, 9-303514 and the like are known. FIG. 9 shows Japanese Patent Application Laid-Open No.
1 shows an electric linear actuator described in JP-A-322189.

The electric linear actuator includes a housing 1, a rotating shaft 2 as a shaft member, an electric motor (not shown), a speed reducer 5, a ball screw portion 6, and a ball nut 7, for example. Such as a backrest angle adjustment device used in an electric bed for a vehicle, to which a thrust load in the compression direction is applied during use. Inside the housing 1, the base end (the left end in FIG. 9) of the rotary shaft 2 is supported by a pair of ball bearings 3a and 3b so as to rotate only freely. The electric motor is fixed to a mounting flange 4 provided on a part of the housing 1 so that a drive shaft (not shown) can freely rotate forward and reverse. The speed reducer 5 including a worm 10 and a worm wheel 11 is provided between the drive shaft of the electric motor and the rotary shaft 2, and the torque of the drive shaft is increased by the speed reducer 5 to increase the rotational speed. It can be transmitted to the shaft 2 freely.

On the other hand, a portion of the rotary shaft 2 other than the base end portion has a helical ball screw groove 21 having an arc-shaped cross section on the outer peripheral surface.
Are formed as the ball screw portion 6 described above. And
The ball nut 7 is screwed around the ball screw portion 6 via a plurality of balls 12. Therefore, a helical ball nut groove 22 having a circular cross section is formed on the inner peripheral surface of the ball nut 7. Then, the base end of the cylindrical output shaft 8 is screwed and fixed to a thread portion formed on a part of the outer peripheral surface of the ball nut 7, and the periphery of the ball nut 7 and the output shaft 8 is formed into a tapered cylindrical shape. Cover 13. In a state where the electric linear actuator is assembled, the output shaft 8 is supported by the axial displacement with respect to the housing 1 only by connecting the distal end to a predetermined portion.

A one-way clutch is provided between the housing 1 and the rotating shaft 2 between the installation portion of the worm wheel 11 and the base end of the ball screw portion 6 in order from the outer diameter side. Are provided with a roller clutch 14 which is a kind of the above, an intermediate cylinder 15 which can freely rotate with respect to the rotary shaft 2, and a sliding bearing 16. A friction plate 18 is sandwiched between the spacer 17 that rotates together with the rotation shaft 2 and the end surface of the cylinder 15. The thrust load applied to the intermediate cylinder 15 from the output shaft 8 via the rotary shaft 2, the spacer 17, and the friction plate 18 in the compression direction is the right one of the pair of ball bearings 3a and 3b in FIG. Ball bearing 3b. When the rotating shaft 2 tends to rotate based on the thrust load, the roller clutch 14 is locked, and conversely, when the output shaft 2 is displaced against the thrust load, the roller clutch 14 is locked. Clutch 1
4 is not locked. Also, even when the end surface of the intermediate cylinder 15 slides on one surface of the friction plate 18, the other surface of the friction plate 18 and one surface of the spacer 17 are not relatively displaced.

The electric linear actuator constructed as described above has a fixed mounting portion 19 formed at the base end (left end in FIG. 9) of the housing 1 and a distal end of the output shaft 8. The displacement-side mounting portions 20 formed at the right end of FIG. 9 are pivotally supported on displacement axes. In this assembled state, the electric linear actuator operates the output shaft 8 based on the rotation direction of the drive shaft of the electric motor.
Is displaced in the axial direction, and when the drive shaft is stopped, the output shaft 8 is prevented from being displaced based on the thrust load. Further, in a state where the drive shaft is reversed, a torque transmitted from the drive shaft via the speed reducer 5 is applied to the rotating shaft 2 in addition to a torque applied based on the thrust load, and Cylinder 15
The rotating shaft 2 is rotated against the frictional force between the end face of the shaft and the friction plate 18. At this time, since the frictional force becomes a resistance to the rotation of the drive shaft, it is possible to prevent the drive shaft from being rapidly rotated. Therefore, if the friction coefficient between one surface of the friction plate 18 and the end surface of the intermediate cylinder 15 and the driving torque of the electric motor are set to appropriate values,
The expansion and contraction of the electric linear actuator can be smoothly performed with a small electric motor.

In the electric linear actuator described in the above-mentioned publication, which is constructed and operates as described above, the balls 12, 12 constituting the ball screw are excessively large so as to exceed the expected use of the electric linear actuator. If the output shaft 8 is broken by an impact load or the like, the output shaft 8 may be rapidly displaced based on the thrust load. In order to prevent the output shaft 8 from being suddenly displaced in this way, the ball 12,
Increasing the diameter of the motor 12 or increasing the number of the balls 12, 12 may increase the safety factor of the electric linear actuator. , Undesirable,
Also, without using a ball for the electric linear actuator,
Although it is possible to eliminate the above-mentioned inconvenience by adopting a structure using the screwing between the square screws, the efficiency of the electric linear actuator is reduced. If the size of the electric motor is increased to compensate for the decrease in performance of the electric linear actuator due to the decrease in efficiency, the size of the entire electric linear actuator also increases.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the present invention, the inventor of the present invention has found that the output shaft can be rapidly displaced in the axial direction even in the unlikely event that a ball is broken without increasing the size of the entire electric linear actuator. The following invention was made in order to prevent the problem. FIGS. 10 to 11 show an example of the electric linear actuator invented prior to the present invention in such circumstances.

In the electric linear actuator according to the prior invention, the ball nut 7a is screwed around the ball screw portion 6 of the rotary shaft 2 through the plurality of balls 12, 12.
Is configured as follows. That is, this ball nut 7a
Has a thin cylindrical portion 24 having a larger inner diameter and a smaller outer diameter in the first half (the right half in FIG. 10) than the base half (the left half in FIG. 10). A ball nut groove 22a having an arc-shaped cross section and a spiral shape as a whole is formed on the inner peripheral surface of the base half of the ball nut 7a. The portion where the ball nut groove 22a is formed and the inner peripheral surface of the cylindrical portion 24 are connected by a step 25. Further, the thin-walled tube portion 24 has a first half whose outer diameter is smaller than that of a base half of the thin-walled cylinder 24, and a thread portion 26 formed on the outer peripheral surface of the first half. The proximal end of the cylindrical output shaft 8 (see FIG. 9) is screwed and fixed to the screw portion 26.
Also, the output shaft 8 and the ball nut 7a are prevented from rotating by connecting the distal end of the output shaft 8 to a predetermined portion, similarly to the aforementioned conventional structure. Therefore, in a state where the electric linear actuator is assembled, the ball nut 7 a is supported around the rotary shaft 2 so as to be freely displaceable only in the axial direction of the rotary shaft 2.

A ball tube 28 for circulating the balls 12, 12 is embedded in the base half of the ball nut 7a. In the illustrated example, a tube band 29 is provided around the ball tube 28 to prevent the ball tube 28 from coming off.
However, the ball tube 28 may be prevented from coming off by another method such as caulking a part of the ball nut 7a. In the illustrated example, the balls 12, 12 provided in a continuous state between the ball screw groove 21 and the ball nut groove 22a are helically arranged with 1.5 turns.

A substantially cylindrical stopper member 30 made of heat-treated steel or high-strength non-ferrous metal or the like is fixed inside a portion of the ball nut 7a deviated from the ball nut groove 22a. are doing. The stopper member 30 has a helical projection 31 having a semicircular cross section on the inner peripheral surface, while the outer peripheral surface is a simple cylindrical surface. Then, the stopper member 30 is fitted inside the ball nut 7a in such a manner that the stopper member 30 abuts against a step 25 formed on the inner peripheral surface of the ball nut 7a. In this state, the stopper member 30 is connected to the step portion 25 and the thin cylindrical portion 2.
The stopper member 30 is prevented from moving in the axial direction by being sandwiched between a retaining ring 32 fixed to the inner peripheral surface of the stopper member 4.

The screw hole 3 formed in the thin cylindrical portion 24
3 is screwed to the stopper member 3
The stopper member 30 is prevented from rotating with respect to the ball nut 7a by abutting against the outer peripheral surface of the ball nut 7a. At this time, the helical projection 31 formed on the inner peripheral surface of the stopper member 30 has a predetermined minute gap between the inner surface of the ball screw groove 21 and a part of the inside of the ball screw groove 21. Let go in the state that was made. The width c of the gap is, for example,
The diameter d of each of the balls 12, 12 is 3.969 mm,
When the width B of the spiral projection 31 is 3.5 mm,
0.23 mm. Therefore, such that the spiral protrusion 31 is located on the extension of the spiral of the ball nut groove 22a,
The pitch and phase of the spiral projection 31 are regulated.

According to the electric linear actuator of the present invention constructed as described above, the output shaft 8 fixed to the ball nut 7a is prevented from suddenly displacing irrespective of the possibility of the balls 12 being damaged. You can do it. That is, when a part of the balls 12, 12 is broken and the output shaft 8 tends to be displaced based on a thrust load in the compression direction, a part of the inner surface of the ball screw groove 21 is formed.
Spiral projection 31 provided on the inner peripheral surface of the stopper member 30
Abuts in the axial direction. Thereby, the stopper member 30 prevents the ball nut 7a from being displaced in the axial direction based on the thrust load,
The output shaft 8 is prevented from being suddenly displaced. Further, since such a stopper member 30 is provided inside the ball nut 7a, it is not necessary to increase the diameter of the balls 12, 12 or to increase the number of the balls 12, 12. The size of the entire actuator is not increased.

In the illustrated example, the shaft member is connected to the housing 1.
And a ball nut 7a that freely supports only a displacement in the axial direction with respect to the rotary shaft 2 so that the output shaft 8 can freely displace in the axial direction. An example of such a structure is shown. However, in the electric linear actuator, the shaft member itself is used as an output shaft that freely supports only displacement in the axial direction with respect to the housing, and the ball nut is supported only inside the housing so as to freely rotate only, so that the electric motor has an electric motor. In some cases, the torque may be transmitted to the ball nut via a speed reducer. In this case,
The predetermined portion is displaced by connecting the tip of a shaft member which is displaceable in the axial direction with respect to the ball nut to a predetermined portion. The stopper member 30 can also be used for an electric linear actuator having such a structure.

[0015]

In the case of the electric linear actuator of the prior invention, which is constructed and operates as described above, the stopper member 30 for constituting the safety device has a helical projection provided on the inner peripheral surface thereof. Since it is required to process the shape and dimensions of the 31 with high precision, the manufacturing operation is troublesome. Further, since such a stopper member 30 is fixed to the ball nut 7a, the number of parts increases. Further, the operation of adjusting the phases of the spiral protrusion 31 of the stopper member 30 and the ball screw groove 21 is troublesome. As a result, it is inevitable that the manufacturing cost of the entire electric linear actuator increases. In view of the above-described circumstances, the present invention does not increase the size of the entire electric linear actuator, and suddenly displaces the output shaft or the shaft member that can be displaced in the axial direction due to breakage of the ball. This is intended to realize a structure for preventing the inexpensive problem.

[0016]

The electric linear actuator of the present invention, like the above-mentioned electric linear actuator of the above-mentioned invention, has a housing and a housing in which only rotation or only displacement in the axial direction is provided inside the housing. A shaft member freely supported, a forward-reverse rotating electric motor fixed to the housing, and a part of the shaft member;
A ball screw portion having an arc-shaped cross section on the outer peripheral surface and having a helical ball screw groove as a whole, and an inner peripheral surface provided around the ball screw portion so as to be free only for displacement or rotation only in the axial direction. A ball nut groove having an arc-shaped cross section and having a spiral shape as a whole, and a ball nut screwed into the ball screw groove through a plurality of balls, and a drive shaft of the electric motor and the shaft member. Or a speed reducer provided between the drive shaft and the ball nut to increase the torque of the drive shaft and transmit the torque to the shaft member or the ball nut; and, if the ball is broken, the ball nut And a safety device for preventing the shaft member from being relatively displaced in the axial direction.

In particular, the electric linear actuator of the present invention includes a stopper ring formed by spirally forming a wire having a circular cross section, and the outer peripheral half of the stopper ring is formed in the ball nut groove. The safety device is inserted into and fixed to a part of the ball screw groove, and the inner half of the ball is inserted into a part of the ball screw groove with a gap interposed between the ball screw groove surface. Make up.

[0018]

With the electric linear actuator of the present invention constructed as described above, the output shaft or shaft member connected to the ball nut is displaced in the axial direction in accordance with the rotation direction of the drive shaft of the electric motor. This is the same as the above-described conventional electric linear actuator. Further, the safety device prevents the output shaft or the shaft member from being suddenly displaced due to the breakage of the ball without increasing the size of the entire electric linear actuator. This is similar to the case of the linear actuator. In particular, in the case of the electric linear actuator of the present invention, in order to constitute the above-mentioned safety device, a stopper ring formed by spirally forming a wire having a circular cross section is provided. And
The outer peripheral half of the stopper ring is internally fitted and fixed in a part of the ball nut groove. Similarly, the inner peripheral half is partially in the ball screw groove, and a gap is formed between the stopper ring and the ball screw groove surface. The above-described safety device is configured by entering the vehicle with the vehicle interposed therebetween. To form such a stopper ring, it is only necessary to cut a wire having a predetermined diameter by a predetermined length and form it into a spiral shape, and high-precision processing is not required. Further, fixing the stopper ring to the ball nut does not increase the number of parts. Therefore, the manufacturing cost of the entire electric linear actuator does not increase. As a result, according to the present invention, it is possible to prevent the output shaft or the shaft member that can be displaced in the axial direction from being suddenly displaced due to the breakage of the ball without increasing the size of the entire electric linear actuator. Can be realized at low cost.

[0019]

1 to 5 show a first embodiment of the present invention. The electric linear actuator of the present invention comprises a housing 1 and a rotating shaft 2 as a shaft member, similarly to the electric linear actuator invented earlier.
, An electric motor 9, a speed reducer 5, a ball screw portion 6,
It has a ball nut 7b and a safety device, and is attached to a portion where a thrust load in the compression direction is applied during use. The housing 1 is manufactured by, for example, die-casting an aluminum alloy. Inside the housing 1, the base end (the left end in FIG. 1) of the rotary shaft 2 is supported by a pair of ball bearings 3a and 3b each of which is a deep groove type so as to be rotatable only. These pair of ball bearings 3a, 3b
Among them, the ball bearing 3a on the left side in FIG. 1 mainly supports a radial load. On the other hand, the ball bearing 3b on the right side of FIG.
Supports not only the radial load but also the thrust load in the compression direction. For this reason, one axial end surface (the left end surface in FIG. 1) of the outer ring 35 constituting the right ball bearing 3 b abuts against a retaining ring 36 fixed to the inner peripheral surface of the housing 1.

The electric motor 9 which can rotate forward and reverse is mounted on a mounting flange 4 formed on the outer surface of the housing 1.
Is fixed. The drive shaft 3 of the electric motor 9
7 is inserted into the housing 1. The speed reducer 5 is provided between the drive shaft 37 and the rotary shaft 2 so that the torque of the drive shaft 37 is increased so that the torque can be transmitted to the rotary shaft 2. In the illustrated case, a worm speed reducer is used as the speed reducer 5. For this reason, the worm wheel 11 is externally fitted to one end of the rotating shaft 2 and further fixed by a nut 61 to be fixed. By forming flat surfaces that engage with each other on a part of the outer peripheral surface of the rotating shaft 2 and a part of the inner peripheral surface of the worm wheel 11, rotation of the worm wheel 11 with respect to the rotating shaft 2 is prevented. I'm trying.

A worm 10 is provided in the housing 1.
Is rotated by the pair of ball bearings 38a and 38b.
The worm 10 and the worm wheel 11 are meshed with each other so as to be rotatable only in the torsional direction. Outer ring 3 forming one ball bearing 38a of a deep groove type
9, a preload is applied to the worm 10 and the pair of ball bearings 38a, 38b by abutting an outer peripheral edge of a leaf spring 40. Therefore, there is no play in the meshing portion.
Further, the end of a stud 41 screwed into a screw hole formed in the wall of the housing 1 is brought into contact with the center of the leaf spring 40 to adjust the preload freely. 42 is a lock nut. A protruding piece 43 extending in the diametric direction is provided on the base end surface (the right end surface in FIG. 2) of the worm 10, and a notch 44 extending in the diametric direction is provided on the distal end surface of the drive shaft 37.
Each is formed. The rotation of the drive shaft 37 can be transmitted to the worm 10 by engaging the projections 43 with the notches 44.

On the other hand, a portion of the rotary shaft 2 excluding the base end portion has a helical ball screw groove 21 having an arc-shaped cross section on its outer peripheral surface.
Is formed, and the ball screw portion 6 is formed. And
Around the ball screw portion 6, the ball nut 7b is
The plurality of balls 12 are screwed together. As shown in detail in FIG. 3, the ball nut 7b has a base half (left half in FIGS. 1 and 3) as a large-diameter cylindrical portion 45 and a distal end (FIGS. 1 to 3).
2 has a smaller outer diameter than the large-diameter cylindrical portion 45,
Further, a small-diameter cylindrical portion 47 having a screw portion 46 formed on the outer peripheral surface is provided. The cylindrical output shaft 8 is connected to the screw portion 46.
Is screwed and fixed.

A spiral ball nut groove 22b having an arc-shaped cross section is formed on the inner peripheral surface of the ball nut 7b over the entire length in the axial direction. And this ball nut groove 2
2b and the ball screw groove 21 between the large-diameter cylindrical portion 45
A plurality of balls 12, 12 are interposed in an axially intermediate portion of the ball in a state in which adjacent balls 12, 12 are brought close to or in contact with each other. In the case of this example, the plurality of balls 12, 12 are provided in a spiral shape with a winding number of 2.5. In order to circulate the balls 12, 12, a ball tube 49 is provided in a part of the large-diameter cylindrical portion 45. For this reason, the tube clamp 52 is inserted into the concave portion 50 formed in a part of the outer peripheral surface of the large-diameter cylindrical portion 45 and the set screw 5
1 and 51, and the ball tube 49 is fixed to the ball nut 7b by the tube clamp 52.
It is fixed against.

The large-diameter cylindrical portion 45 of the ball nut 7b
Is covered with a cover 53 formed by combining a pair of elements each having a semi-cylindrical shape. or,
The periphery of the ball nut 7b and the output shaft 8 is covered by a tapered cylindrical cover 13. The output shaft 8
The rotation of the ball nut 7b is prevented by connecting the distal end of the output shaft 8 to a driven portion (not shown) with the installation of the electric linear actuator. Therefore, in the assembled state of the electric linear actuator, the ball nut 7b is supported around the rotary shaft 2 so as to be freely displaceable only in the axial direction of the rotary shaft 2.

Further, limit switches 23a and 23b (see FIG. 8) are provided at the base end and the front end of the cover 13, respectively. Then, one of the limit switches 23a and 23b is turned ON and OFF while the ball nut 7b is moved to the end in the moving direction. That is, the limit switch 23a provided at the base end is turned on when the ball nut 7b is moved to the base end of the ball screw portion 6 and the electric linear actuator is fully contracted.
N, turn OFF. On the other hand, the limit switch 23b provided at the distal end is turned on and off when the ball nut 7b moves to the distal end of the ball screw section 6 and the electric linear actuator is fully extended. The electric motor 9
The energization to these limit switches 23a, 23b
Is controlled based on the detection signal. That is, it is possible to prevent the electric linear actuator from being energized in the direction of further contraction from the fully contracted state, or prevented from being energized in the direction of further extension from the fully extended state. The cover 13 is made of a synthetic resin or a metal, and the protrusions 54 formed on the inner peripheral surface of the base end are engaged with the concave grooves 55 formed on the outer peripheral surface of the housing 1. By fastening with the band 56, it is fixedly connected to the housing 1.

A step 57 having a large diameter on the ball screw portion 6 side is formed at a base end portion of the ball screw portion 6 in a part of the rotary shaft 2. And this step 57
One side (the right side surface in FIG. 1) of the thick, ring-shaped spacer 17 is abutted against the inner periphery. Therefore, a thrust load in the compression direction applied to the rotating shaft 2 in the leftward direction in FIG. 1 is transmitted to the spacer 17. The inner peripheral edge of the spacer 17 is fitted to the outer peripheral surface of the rotating shaft 2 by interference fit or is fitted to the non-circular peripheral surfaces. Therefore, the spacer 17 rotates together with the rotation shaft 2.

Further, in order to constitute a mechanism for preventing the rotation of the rotating shaft 2 from rotating, a part of the rotating shaft 2 is provided between the installation portion of the worm wheel 11 and the base end of the ball screw portion 6. Supports a thick cylindrical intermediate cylinder 15 rotatably via a slide bearing 16. A roller clutch 14, which is a kind of one-way clutch, is provided between the outer peripheral surface of the intermediate tube 15 and the inner peripheral surface of the housing 1. That is, the outer ring 58 having the inner peripheral surface as a cam surface is
, So that the outer ring 58 does not rotate with respect to the housing 1. A plurality of rollers 59 are provided between the inner peripheral surface of the outer ring 58 and the outer peripheral surface of the intermediate cylinder 15.
59 are provided. As is well known, each of these rollers 59, 5
9 is elastically pressed in one circumferential direction by a spring provided between the holder and a non-rotating retainer (not shown). Therefore, when the intermediate cylinder 15 rotates in a predetermined direction, the rollers 59, 59 do not bite into the cam surface, and the rotation of the intermediate cylinder 15 is allowed. On the other hand, when the intermediate cylinder 15 rotates in the opposite direction, the rollers 59, 59 bite into the cam surface, and the intermediate cylinder 15 stops rotating inside the housing 1.

Further, one end surface of the intermediate tube 15 in the axial direction (FIG. 1)
Between the spacer 17 and the spacer 17.
8 is pinched. The friction plate 18 has at least both side surfaces made of a material having a large friction coefficient, and frictionally engages with one surface of the spacer 17 and the end surface of the spacer 15 which are mating surfaces. However, in order to keep the frictional engagement state constant, when the spacer 17 and the intermediate cylinder 15 are relatively rotated, one of the frictional engagement surfaces slides (relative displacement) and the other frictional engagement surface moves. Is preferably not displaced relative to each other. Therefore, one opposing surface (for example, one surface of the spacer 17 and one surface of the friction plate 18) may be bonded.

In particular, in the case of the electric linear actuator of the present invention, the safety device for preventing the output shaft 8 from being suddenly displaced due to the breakage of the balls 12, 12 must be configured as shown in FIG. 4, a stopper ring 60 is provided inside the ball nut 7b.
The stopper ring 60 is formed by cutting a wire (steel wire) having a predetermined diameter and having a circular cross section by a predetermined length, and then bending the wire so as to form a spiral as a whole. The radius of curvature of the cross section of the wire constituting the stopper ring 60 is
The radius of curvature of the cross section of the ball screw groove 21 and the ball nut groove 22b is slightly smaller. In the case of this example, the stopper ring 60 is formed in a spiral shape with 1.5 turns. And this stopper ring 6
The outer half of the ball nut 7 is internally fitted and fixed to a part of the ball nut groove 22b which deviates from the part where the balls 12, 12 are provided (in FIGS. 1 and 3, a part near the right end of the ball nut 7b). ing. On the other hand, the inner peripheral half portion of the stopper ring 60 is made to enter a part of the inside of the ball screw groove 21 with a minute gap interposed between the stopper ring 60 and the surface of the ball screw groove 21. The width c of this gap is, for example, 0.2
About 0.3 mm.

The electric linear actuator of the present invention constructed as described above has a fixed mounting portion 19 formed at the base end (the left end in FIG. 1) of the housing 1, for example, with the output shaft 8 as the fixed shaft. 1 are pivotally supported on a displacement axis with a displacement-side mounting portion 20 formed at the tip (the right end in FIG. 1). Since the displacement shaft tends to be displaced in a direction approaching the fixed shaft, the electric linear actuator is used in a state where a thrust load in the compression direction is applied to the output shaft 8. In this assembled state, the electric linear actuator operates as follows to displace the output shaft 8 in the axial direction based on the rotation direction of the drive shaft 37 of the electric motor 9. .

First, the operation of extending the electric actuator by rotating the drive shaft 37 of the electric motor 9 forward and displacing the output shaft 8 against the thrust load will be described. In this case, the rotating shaft 2 rotates in a predetermined direction via the speed reducer 5, and the intermediate cylinder 15 is rotatable with respect to the housing 1 without locking the roller clutch 14. Therefore, in this state, the intermediate cylinder 15, the friction plate 18, and the spacer 17 rotate together with the rotary shaft 2, and the presence of these members 15, 18, 17 does not cause resistance to the rotation of the rotary shaft 2. Absent. Further, the roller clutch 14 acts like a roller bearing, and permits the rotation of the intermediate cylinder 15. Therefore, the roller clutch 14 which is a one-way clutch
Does not become a resistance to the rotation of the rotating shaft 2.

As a result, the rotation shaft 2 rotates smoothly in a predetermined direction with the forward rotation of the drive shaft 37. And
The ball nut 7b screwed into the ball screw portion 6 of the rotating shaft 2 is displaced in the axial direction (to the right in FIGS. 1 and 3), and displaces the output shaft 8 against the thrust load. At this time, as described above, the presence of the intermediate cylinder 15, the friction plate 18, the spacer 17, and the roller clutch 14, which constitute the reverse rotation preventing mechanism, does not become a resistance against displacing the output shaft 8.
Therefore, the driving force of the electric motor 9 is effectively used for displacing the output shaft 8. As a result, the electric motor 9
Therefore, the electric linear actuator can be sufficiently extended without using a particularly large one or increasing the reduction ratio (torque increase ratio) of the speed reducer 5.
At this time, since a gap having a width of c is interposed between the inner peripheral portion of the stopper ring 60 and the surface of the ball screw groove 21, the stopper ring 60 and the ball screw groove 21 However, there is no rubbing with the rotation of the rotating shaft 2. Therefore, the presence of the stopper ring 60 determines whether the ball nut 7
There is no hindrance when b is displaced in the axial direction.

Next, in a state where the drive shaft 37 is stopped, a force applied to the ball screw portion 6 from the output shaft 8 via the ball nut 7b and the plurality of balls 12 based on the thrust load is obtained. The rotating shaft 2 tends to rotate in a direction opposite to the predetermined direction. At the same time, the intermediate cylinder 15 tends to rotate in the same direction as the rotating shaft 2.
As a result, the roller clutch 14 is locked, and the intermediate cylinder 15 does not rotate with respect to the housing 1. In this state, in order to rotate the rotating shaft 2, it is necessary to slide the side surface of the friction plate 18 and the end surface of the intermediate cylinder 15 which is the mating surface. Therefore, these friction plates 1
By restricting the coefficient of friction between the side surface of the shaft 8 and the end surface of the intermediate cylinder 15 to a desired value determined in design, the rotation shaft 2 is prevented from rotating based on the thrust load, and the output shaft is prevented. 8 can be prevented from being displaced in the axial direction.

Further, when the output shaft 8 is displaced in the direction in which the thrust load acts, the drive shaft 37 of the electric motor is reversed. When the drive shaft 37 is rotated in the reverse direction, the torque transmitted from the drive shaft 37 via the speed reducer 5 is applied to the rotating shaft 2 in addition to the torque applied based on the thrust load. Join in the opposite direction. Therefore, the drive shaft 37 and the rotary shaft 2 rotate against the frictional force acting between the side surface of the friction plate 18 and the end surface of the intermediate cylinder 15. At this time, since the frictional force becomes a resistance to the rotation of the drive shaft 37 and the rotation shaft 2, the rotation of the drive shaft 37 and the rotation shaft 2 is prevented from being rapidly performed. Therefore, the friction plate 18
If the friction coefficient between the side surface of the inner cylinder and the end surface of the intermediate cylinder 15 and the driving torque of the electric motor 9 are set to appropriate values, the small-sized electric motor 9 can smoothly perform not only the extension but also the contraction of the electric linear actuator. Can do things.

In particular, in the case of the electric linear actuator of the present invention, a safety device is provided for preventing the output shaft 8 from being suddenly displaced based on the thrust load due to the breakage of the balls 12 and 12. A stopper ring 6 formed by spirally forming a wire having a circular cross section as a whole.
0 is provided. Then, the outer peripheral half of the stopper ring 60 is internally fitted and fixed to a part of the ball nut groove 22 b, and the inner peripheral half is also partially inside the ball screw groove 21. The above-described safety device is configured by entering the vehicle with a gap interposed between the surface and the surface. That is, if all or a part of the balls 12, 12 is broken by any chance and the output shaft 8 tends to be displaced based on the thrust load in the compression direction,
A partial surface of the ball screw groove 21 and an inner peripheral half of the stopper ring 60 abut in the axial direction. The stopper ring 60 does not rotate due to a large frictional force acting between the ball nut groove 22b and the inner surface of the ball nut groove 22b, and is engaged with the ball nut groove 22b and the ball screw groove 21 in a meshing state. Therefore, even if the balls 12, 12 are damaged, the ball nut 7b is prevented from being displaced in the axial direction based on the thrust load, and the output shaft 8 is prevented from being rapidly displaced. it can.

Since the stopper ring 60 is provided inside the ball nut 7b, it is not necessary to increase the diameter of the balls 12, 12 or to increase the number of the balls 12, 12. The whole is not enlarged. Further, in order to form such a stopper ring 60, it is only necessary to cut a wire having a predetermined diameter by a predetermined length and form a spiral shape, and a high-precision processing operation is not required. Further, in the operation of fixing the stopper ring 60 to the ball nut 7b, a part of the ball nut groove 22b has a diameter slightly larger than the diameter of the ball nut groove 22b (the vertical dimension in FIG. 1). It is only necessary to push the stopper ring 60 while elastically reducing its diameter, and the number of parts does not increase. Moreover,
When the stopper ring 60 is pushed into the ball nut groove 22b, the phase of the stopper ring 60 and the phase of the ball screw groove 21 are automatically adjusted, and the stopper ring 60 does not move based on the elasticity of the stopper ring 60 itself. Therefore, it is possible to prevent the manufacturing cost of the entire electric linear actuator from increasing. As a result, according to the electric linear actuator of the present invention, the ball can be broken by any chance without increasing the size of the entire electric linear actuator.
A structure for preventing sudden displacement of the output shaft can be realized at low cost.

Next, an example of calculating the actual strength (shear strength) of the stopper ring 60 used in the electric linear actuator of the present invention will be described in comparison with the case of the balls 12 and 12. For these balls 12, 12, for example, the diameter d was 3.969 mm, the pitch diameter d _p was 20.5 mm, and the number of turns was 2.5.
In this case, the static rated load for permanently deforming each of the balls 12, 12 by 0.01% is 2150 kgf. And
Breakage load F that damages each of these balls 12, 12
₁₂ is 5 times this static rated load, about 10750 kg
f.

On the other hand, the strength F _{60 of the} stopper ring ₆₀
Is represented by the following equation. F ₆₀ = π × d _p × D × N × τ (1) For example, when the stopper ring 60 has a shear stress τ of 10
When a spiral wire having a winding number N of 1.5 is formed from a steel wire (piano wire) having a sectional diameter D of 3.5 mm made of a material having a weight of 0 kgf / mm ² , the above (1) By substituting the above numerical values into the equation, the intensity F ₆₀ is 3380
It becomes 0 kgf.

From these results, the strength F ₆₀ (≒ 33800) of the spiral stopper ring 60 with the number of windings set to 1.5 is obtained.
kgf) is a helical ball 12, 1 having 2.5 turns.
3 times or more of the failure load F ₁₉ (≒ 10750 kgf)
₆₀ > 3 · F ₁₉ ). Therefore, in order to obtain the same strength as the stopper ring 60 by using only the balls 12 and 12 instead of using the spiral stopper ring 60 having the number of turns of 1.5, the number of turns is reduced. It is necessary to provide the balls 12, 12 which are at least 4.5 times, which is at least three times the number of turns (1.5) of the stopper ring 60. On the other hand, in the case of the present invention, since the stopper ring 60 is used, the number of turns is smaller (1.5 turns) than when only the balls 12 are used.
And the overall length of the ball nut 7b can be reduced.

FIGS. 6 and 7 show a second embodiment of the present invention. In the case of this example, the roller clutch 1 provided in the case of the above-described first example, for preventing the rotation shaft 2 from rotating in the reverse direction based on the thrust load in the compression direction.
4, the spacer 17, the spacer 15, and the friction plate 18 (see FIGS. 1 and 9) are omitted. Instead, in the case of this example, a motor having a built-in brake mechanism is used as the electric motor 9a, and the drive shaft 37a of the electric motor 9a is used.
When the rotation is stopped, the rotation shaft 2 is prevented from rotating based on the thrust load. Electric motors with such a built-in brake mechanism have been known for a long time.
A detailed description of this electric motor will be omitted. still,
In the case of the illustrated example, a notch 62 long in the diameter direction provided on the base end surface (the left end surface in FIG. 7) of the worm 10 and a protrusion 63 long in the diameter direction provided on the front end surface of the drive shaft 37a. Is engaged, the rotation of the drive shaft 37a can be transmitted to the worm 10.

One end is provided between a step 64 provided on a part of the inner peripheral surface of the housing 1a and a step 57 provided at a base end of the ball screw 6 on a part of the rotary shaft 2. Flange 65
Are provided in series in the axial direction with each other, and a thrust load in the compression direction applied to the rotary shaft 2 can be supported by these members 66 and 67. Therefore, in the case of this example, a pair of ball bearings 3a provided on both axial sides of the worm wheel 11,
3a supports only a radial load.

Further, in the case of the present embodiment, the outer peripheral surface of the ball nut 7c is simply a cylindrical surface, and the ball nut 7c
A plurality of concave holes 68 are provided at a plurality of positions in the circumferential direction on the outer peripheral surface of c. Then, the distal ends of a plurality of bolts 70, 70 in which screw holes 69, 69 formed in the base end of the cylindrical output shaft 8 a are screwed from the outer diameter side to the inner diameter side are connected to the respective concave holes 68, 70.
68, the ball nut 7c and the output shaft 8a are connected and fixed. Other configurations and operations are the same as those of the above-described first example. Therefore, the same components are denoted by the same reference numerals, and overlapping description and illustration are omitted.

When the drive shaft 37a of the electric motor 9a is stopped, the lead angle of the worm 10 constituting the speed reducer is set to prevent the rotation shaft 2 from rotating in the reverse direction based on the thrust load in the compression direction. By making it smaller, it is possible to make it difficult for the drive shaft 37a to rotate in the reverse direction (rotate based on the thrust load).

In each of the above-described examples, the structure in which the thrust load in the compression direction acts when the electric linear actuator is used has been described. However, in the present invention, the thrust load in the tension direction acts in use. It can also be implemented with a structure. In this case, the stopper ring 60 prevents the output shafts 8 and 8a from being suddenly displaced due to the breakage of the balls 12 and 12, so that the total length of the electric linear actuator is suddenly extended.

Also, in each of the above-described examples, the rotating member 2 is a rotating member that supports the shaft member only inside the housings 1 and 1a so as to freely rotate.
And the ball nuts 7b and 7c are freely supported only in the axial direction with respect to the rotary shaft 2, and the output shafts 8 and 8a
The case where the present invention is applied to a structure in which the displacement in the axial direction can be freely described has been described. However, as shown in FIG. 8 as a third embodiment of the present invention, the shaft member is an output shaft 71 that freely supports only the displacement in the axial direction with respect to the housing 1b, and the ball nut 7d is Housing 1b
Only the rotation is freely supported inside the electric motors 9 and 9a.
The present invention can also be implemented with a structure in which the output of (see FIGS. 2 and 7) is transmitted to the ball nut 7d via the reduction gear 5a. In this case, by connecting a mating member to the tip (the right end in FIG. 8) of the output shaft 71 which can be displaced in the axial direction with respect to the ball nut 7d, the rotation of the electric motors 9 and 9a is reduced. The above-mentioned partner member can be displaced based on this. A stopper ring 60 is provided on a part of the ball nut groove 22b provided on the inner peripheral surface of the ball nut 7d.
The stopper ring 60 prevents the output shaft 71 from being suddenly displaced due to breakage of the balls 12 and 12.

In the illustrated example, the ball nut 7d
Is rotatably supported inside the housing 1b by a ball bearing 73a. When the electric linear actuator is used, a thrust load in the compression direction is applied to the output shaft 71 in the leftward direction in FIG.
A worm wheel 1 for constituting the reduction gear 5a
1a is externally fitted and fixed to the outer peripheral surface of the ball nut 7d by interference fit, and further, if necessary, cannot be rotated with respect to the ball nut 7d by a key or the like. The distal end (right end in FIG. 8) of the sleeve 15a is rotatably supported via a slide bearing 72 around the base end (left end in FIG. 8) of the ball nut 7d. Further, a roller clutch 14 and a ball bearing 73b are provided at portions axially separated between the intermediate cylinder 15a and the housing 1b, and a flange formed at a tip end of the intermediate cylinder 15a. A spacer 17 and a friction plate 18 are provided between one side of the ball nut 75 and a step 74 formed on the outer peripheral surface of the intermediate portion of the ball nut 7b. With this configuration, the drive shafts 37, 37a of the electric motors 9, 9a (FIGS. 2, 7)
(See FIG. 3), a reverse rotation preventing mechanism for preventing reverse rotation of the ball nut 7b based on the thrust load.

[0047]

Since the present invention is constructed and operates as described above, the output shaft or shaft member may be damaged due to the breakage of the ball without increasing the size of the entire electric linear actuator or complicating the assembly operation. A structure for preventing sudden displacement can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a first example of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an enlarged view of a part B of FIG.

FIG. 4 is a perspective view showing a stopper ring used in the first example.

FIG. 5 is an enlarged view of a portion C in FIG. 3;

FIG. 6 is a view similar to FIG. 1, showing a second example of the embodiment of the present invention.

FIG. 7 is a sectional view taken along line DD of FIG. 6;

FIG. 8 is a sectional view showing a third example of the embodiment of the present invention.

FIG. 9 is a sectional view showing an example of a conventional structure.

FIG. 10 is an enlarged cross-sectional view corresponding to a portion E in FIG. 9, showing an example of the invention prior to the present invention with a part thereof omitted;

FIG. 11 is an enlarged view of a portion F in FIG. 10;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a, 1b Housing 2 Rotating shaft 3a, 3b Ball bearing 4 Mounting flange 5, 5a Reduction gear 6 Ball screw part 7, 7a, 7b, 7c, 7d Ball nut 8, 8a Output shaft 9, 9a Electric motor 10 Worm 11 , 11a Worm wheel 12 Ball 13 Cover 14 Roller clutch 15, 15a Inter tube 16 Slide bearing 17 Spacer 18 Friction plate 19 Fixed side mounting portion 20 Displacement side mounting portion 21 Ball screw groove 22, 22a, 22b Ball nut groove 23a, 23b Limit switch 24 Thin wall section 25 Step section 26 Screw section 28 Ball tube 29 Tube band 30 Stopper member 31 Spiral projection 32 Retaining ring 33 Screw hole 34 Set screw 35 Outer ring 36 Retaining ring 37, 37a Drive shaft 38a, 38b Ball Bearing 39 Outer ring 40 Leaf spring 41 Star Head 42 Lock nut 43 Protrusion 44 Notch 45 Large diameter cylinder 46 Screw 47 Small diameter cylinder 49 Ball tube 50 Recess 51 Set screw 52 Tube clamp 53 Cover 54 Protrusion 55 Recessed groove 56 Band 57 Step 57 Outer ring 59 Roller 60 Stopper ring 61 Nut 62 Notch 63 Projection 64 Step 65 Flange 66 Intermediate tube 67 Thrust ball bearing 68 Concave hole 69 Screw hole 70 Bolt 71 Output shaft 72 Slide bearing 73a, 73b Ball bearing 74 Step

Claims (1)

[Claims] 1. A housing, a shaft member supported inside the housing so as to freely rotate or only displace in an axial direction, an electric motor fixed to the housing and capable of normal rotation and reverse rotation, and the shaft. A ball screw portion provided on a part of the member and having an arc-shaped cross section on the outer peripheral surface and having a helical ball screw groove as a whole, and only displacement or rotation only in the axial direction around the ball screw portion. A ball nut groove, which is freely provided, has an arc-shaped cross section on the inner peripheral surface and is entirely helical, and is screwed with the ball screw groove via a plurality of balls; and A speed reducer provided between the drive shaft and the shaft member, or between the drive shaft and the ball nut, for increasing the torque of the drive shaft and transmitting the torque to the shaft member or the ball nut; If the An electric linear actuator having a safety nut for preventing relative displacement between the nut and the shaft member in the axial direction, wherein a stopper having a wire having a circular cross section formed entirely in a spiral shape. The stopper ring has an outer peripheral half portion fixedly fitted in a part of the ball nut groove, and an inner peripheral half portion partially inside the ball screw groove, and a ball screw groove surface. An electric linear actuator, characterized in that the above-mentioned safety device is constituted by entering with a gap interposed therebetween.