JP2016161086A - Electric linear actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To return an actuator to a returned state by compensating driving force when the driving force for driving the actuator fails.SOLUTION: An electric actuator includes a housing 10, a motor 20, a driving force transmission mechanism 30 for transmitting driving force of rotation by the motor 20, a driving shaft 40 disposed axially movable forward and backward, a ball screw mechanism 50 converting the driving force of the rotation from the driving force transmission mechanism 30 into linear driving force, to axially drive the driving shaft 40, and energization means 60 for energizing the driving shaft 40 in the axial direction. The ball screw mechanism 50 includes a screw shaft 51 coaxially connected to the driving shaft 40 and having a threaded groove on an outer peripheral face, a nut 52 disposed coaxially with the screw shaft 51 and having a threaded groove on a position corresponding to the threaded groove formed on the screw shaft 51, on an inner peripheral face, a ball disposed on both thread grooves, and a co-rotation prevention mechanism 53 for preventing co-rotation of the screw shaft 51 and the nut 52.SELECTED DRAWING: Figure 1

Description

  The present invention is an electric linear actuator that employs a ball screw mainly used in an automobile, and particularly includes an operation assist mechanism that assists the driving force when the driving force that drives the actuator fails. About things.

  The electric linear actuator is a function that transmits the rotational force of the motor to the ball screw via a reduction mechanism using a gear such as a spur gear and converts the rotation of the nut of the ball screw into a linear motion in the axial direction of the drive shaft. And is widely used in driving parts of automobiles and the like. For example, as shown in FIG. 1 of Patent Document 1, the electric linear actuator includes a housing, an electric motor attached to the housing, a speed reduction mechanism that transmits the rotational force of the motor shaft of the electric motor, and the rotational force as the shaft of the drive shaft. The ball screw mechanism that converts to linear motion in the direction is the main component.

  The ball screw mechanism is provided coaxially with the drive shaft, and a screw groove is formed at a position corresponding to a nut formed with a screw groove on the inner peripheral surface and a screw groove formed coaxially with the drive shaft. And a plurality of balls provided in a thread groove formed in the nut and the screw shaft. A bag hole is formed in the cylindrical housing, and a sleeve in which a concave groove extending in the axial direction is formed on the inner peripheral side is fitted into the bag hole. Further, a locking pin is provided on the screw shaft so as to protrude outward in the radial direction, and the locking pin is guided in the axial direction of the screw shaft by a concave groove. Thus, the locking pin is guided by the concave groove to prevent the nut and the screw shaft from rotating together, and the screw shaft (drive shaft) linearly moves in the axial direction as the nut rotates. It has become.

  For example, as shown in FIG. 2 of Patent Document 2, this type of electric linear actuator is also employed in a brake system for a by-wire type automobile.

JP 2014-80995 A JP 2012-210879 A

  The electric linear actuator described in Patent Document 1 is assumed to be used under various environments. For example, when used in a cold region, problems such as the battery for driving the motor running up tend to occur, and the actuator drive shaft protrudes from the housing when it is housed in the housing. It is also assumed that the state will remain. As described above, when the drive shaft remains in an operating state, there is a problem in that, for example, problems such as the brake being unable to be released occur.

  Accordingly, an object of the present invention is to return the actuator to a return state by compensating for the driving force when the driving force for driving the actuator is lost.

  In order to solve this problem, in the present invention, a housing, a motor provided in the housing, a driving force transmission mechanism for transmitting a driving force of rotation by the motor, and an axially movable back and forth are provided. A drive shaft, a ball screw mechanism that converts the rotational drive force from the drive force transmission mechanism into a linear drive force and drives the drive shaft in the axial direction, and biases the drive shaft in the axial direction Biasing means, and the ball screw mechanism is provided coaxially with the drive shaft and has a screw shaft having a screw groove formed on the outer peripheral surface thereof, and is provided coaxially with the screw shaft on the inner peripheral surface. A nut having a thread groove formed at a position corresponding to a thread groove formed in the screw shaft, a ball provided in the thread groove formed in each of the screw shaft and the nut, and the screw shaft To rotate with the nut A corotation prevention mechanism for stopping, to constitute a electric linear actuator with a.

  In this way, by providing the drive shaft with the biasing means, for example, in a cold region, when the control of the motor is lost due to troubles on the control system or battery exhaustion, the drive shaft remains in operation. The drive shaft can be returned to the return state by the urging force of the urging means. For this reason, it is possible to avoid troubles such as the brake being unable to be released because the drive shaft remains in operation.

  In the configuration, the co-rotation preventing mechanism is a guide projection provided on the screw shaft and a guide that is not rotatable about the shaft relative to the housing and guides the guide projection in the axial direction of the screw shaft. It is preferable to have a configuration including a groove. Thus, by guiding the guide projection by the guide groove, the screw shaft is prevented from rotating together with the nut, and the drive shaft connected coaxially with the screw shaft is reliably advanced and retracted in the axial direction. Can do.

  In the configuration in which the guide groove is formed, it is preferable to further include a bag hole formed in the housing and a sleeve in which the guide groove is formed and fitted in the bag hole. Thus, if the guide groove is formed in the sleeve, it can be easily processed as compared with the case where the guide groove is directly formed in the housing, and the shape of the guide groove can be easily changed. .

  Moreover, in the structure which forms a guide groove, it is preferable that the said biasing means is set as the structure provided in the said guide groove. As described above, by providing the biasing means in the guide groove, even if a twisting or bending force is applied in the axial direction of the biasing means, the twisting or bending is prevented by contact with the inner wall of the guide groove. The rigidity of the urging means can be ensured. For this reason, the drive shaft (screw shaft) can be reliably urged in the axial direction by the urging means.

  Furthermore, in the configuration for forming the guide groove, the biasing means is a rectangular spring having a rectangular cross section, and is arranged so that one side of the rectangular portion is along the inner wall surface of the guide groove. A configuration is preferable. Thus, by adopting the rectangular spring, it is possible to ensure a large contact area with the inner wall surface as compared with the case of a circular cross section. For this reason, the rigidity of the urging means increases, and when a force of twisting or bending acts on the urging means, the twisting or bending is prevented and the drive shaft (screw shaft) is more reliably applied in the axial direction. In addition, the durability of the urging means can be improved.

  In this invention, the structure which provided the urging means which urges | biases this drive shaft to the axial direction was employ | adopted for the drive shaft of the electric linear actuator. By providing the urging means, for example, when the motor control is lost in a cold region and the drive shaft remains in operation, the urging force of the urging means returns the drive shaft to the return state. be able to. For this reason, for example, it is possible to avoid troubles such as the brake still being operated by the drive shaft in the operating state.

The electric linear actuator which concerns on this invention WHEREIN: The longitudinal cross-sectional view which shows the state (state which the drive shaft protruded from the housing) which the actuator act | operated In the electric linear actuator shown in FIG. 1, a longitudinal sectional view showing a state in which the actuator is returned (a state in which the drive shaft is retracted into the housing) FIG. 2 is a side view (partially sectional view) showing biasing means (coil spring) used in the electric actuator shown in FIG. 1, wherein (a) is a rectangular spring having a rectangular cross section, and (b) is a circular spring having a circular cross section.

  1 and 2 show an embodiment of an electric linear actuator according to the present invention. FIG. 1 shows a state where the actuator is operated (a state where the drive shaft protrudes from the housing), and FIG. 2 shows a state where the actuator is returned (a state where the drive shaft is retracted into the housing). The state shown in FIG. 2 is the initial position of the electric linear actuator. This electric linear actuator is used, for example, for automobile brake control.

  The electric linear actuator includes a housing 10, a motor 20, a driving force transmission mechanism 30, a driving shaft 40, a ball screw mechanism 50, and an urging means 60 as main components.

  The housing 10 is configured by combining two of a first divided housing 11 and a second divided housing 12 that are divided into two in the axial direction. Both divided housings 11 and 12 are integrated by a bolt 13. A through hole 11a penetrating in the axial direction of the drive shaft 40 is formed inside the first divided housing 11, and a receiving part for attaching a connecting device connected to the electric linear actuator to the opening of the through hole 11a. 11b is formed, and a recess 11c for attaching the motor 20 is formed. A bottomed bag hole 12 a is formed in the second divided housing 12 on the same extension line as the through hole 11 a formed in the first divided housing 11. Furthermore, both the split housings 11 and 12 are formed with recesses in accordance with the shapes of the parts constituting the driving force transmission mechanism 30 and the like. When the split housings 11 and 12 are integrated, the housing 10 A space for storing the driving force transmission mechanism 30 and the like is secured inside.

  The motor 20 is attached to a recess 11 c formed in the first divided housing 11, and an output shaft 21 of the motor 20 passes through the first divided housing 11, and its tip is formed in the second divided housing 12. The recessed portion is fitted through a bearing 22 so as to be rotatable around an axis.

  The driving force transmission mechanism 30 includes a first gear 31, a second gear 32, and a third gear 33 that are spur gears, and the gears 31, 32, and 33 are sequentially meshed with each other. The drive force transmission mechanism 30 acts as a speed reduction mechanism that reduces the rotation of the output shaft 21 of the motor 20 and transmits it to the drive shaft 40 side. The first gear 31 is fitted coaxially to the output shaft 21 of the motor 20. Further, the second gear 32 is rotatably provided by a shaft body 34 provided across both the divided housings 11 and 12 and a bearing 35 provided coaxially with the shaft body 34 so as to mesh with the first gear 31. Is arranged. Further, the third gear 33 is disposed on the outer peripheral side of the nut 52 of the ball screw mechanism 50 described later so as to be engaged with the nut 52 and the second gear 32 via the key member 36.

  The drive shaft 40 is disposed coaxially with the through hole 11 a in the through hole 11 a formed in the first divided housing 11, and can be advanced and retracted in the axial direction by the ball screw mechanism 50. When the actuator is operated, the drive shaft 40 protrudes from the housing 10, and when the actuator is returned, the drive shaft 40 is retracted into the housing 10.

  The ball screw mechanism 50 includes a screw shaft 51 provided coaxially with the drive shaft 40, a nut 52 provided coaxially with the screw shaft 51, a plurality of balls, and a common rotation prevention mechanism 53. A screw groove is formed in a spiral shape on the outer peripheral surface of the screw shaft 51. A spiral thread groove is formed on the inner peripheral surface of the nut 52 at a position corresponding to the thread groove formed on the screw shaft 51. In FIG. 1 and FIG. 2, the description of the balls and the thread grooves formed in the threaded shaft 51 and the nut 52 is omitted.

  A third gear 33 is fitted on the outer peripheral surface of the nut 52 via the key member 36, and the nut 52 rotates around the axis of the screw shaft together with the third gear 33. Further, bearings 37 and 37 are provided on the outer peripheral surfaces of both end portions in the axial direction of the nut 52, and the nut 52 is configured to smoothly rotate around the shaft relative to the housing 10 by the bearings 37 and 37. ing. The balls are provided in thread grooves formed in the screw shaft 51 and the nut 52, respectively.

  The co-rotation preventing mechanism 53 is formed at the rear end portion of the screw shaft 51 (the end portion opposite to the side where the drive shaft 40 is continuously provided) standing up radially outward from the axis of the screw shaft 51. And two guide grooves 55 and 55 for respectively guiding the guide protrusions 54 and 54 in the axial direction of the screw shaft 51. The guide protrusion 54 is formed with a locking hole (not shown) for hooking a hook of a coil spring (biasing means 60) described later. The two guide grooves 55, 55 are formed at positions facing each other on the inner peripheral surface of the cylindrical sleeve 56 that is non-rotatably fitted in the bag hole 12 a formed in the second divided housing 12. An end cap 57 is fitted into the end portion of the sleeve 56 (the bottom side of the bag hole 12a). Thus, by forming a plurality of guide protrusions 54, the screw shaft 51 can be reliably prevented from co-rotating with the nut 52, and the drive shaft 40 can be smoothly advanced and retracted in the axial direction. It is possible to improve the durability by increasing the rigidity.

  The formation positions and number of the guide protrusions 54 and the guide grooves 55 are not limited to the embodiment shown in FIGS. 1 and 2, and the material constituting the common rotation prevention mechanism 53 as long as the drive shaft 40 can be smoothly advanced and retracted. It can be appropriately changed in consideration of the rotational force to be applied. The guide protrusion 54 may be configured integrally with the screw shaft 51 or may be configured such that another member is inserted from the peripheral surface side of the screw shaft 51.

  The urging means 60 is a coil spring, and hooks are formed at both ends thereof. The hook on one end side is locked in a locking hole formed in the guide projection 54, and the hook on the other end side is locked in a fitting portion between the end portion of the sleeve 56 and the end cap 57. The urging means 60 urges the drive shaft 40 (screw shaft 51) to be retracted into the housing 10. This urging means 60 is provided in the guide groove 55. By providing the urging means 60 in the guide groove 55, it is not necessary to provide a separate space for providing the urging means 60, and the co-rotation preventing mechanism 53 can be made compact.

  When a coil spring is employed as the urging means 60, as shown in FIGS. 3 (a) and 3 (b), a rectangular spring 60a (see FIG. 3 (a)) whose cross-sectional shape is rectangular or a circular cross-sectional shape is circular. Any of the circular springs 60b (see this figure (b)) can be employed. In addition, illustration of the hook part of a coil spring is abbreviate | omitted in this figure.

  When the rectangular spring 60a is employed, the rectangular spring 60a is preferably arranged so that one side of the rectangular portion is along the inner wall surface of the guide groove. When arranged in this way, the contact area associated with the contact with the inner wall surface increases as compared to the case of a circular cross section. For this reason, the rigidity of the rectangular spring 60a increases, and when a twisting or bending force is applied to the rectangular spring 60a, the twisting or bending is prevented, and the drive shaft 40 (screw shaft 51) is moved by the rectangular spring 60a. Further, it is possible to urge the shaft spring more reliably in the axial direction, and it is possible to improve the durability of the rectangular spring 60a.

  When the urging means 60 itself has sufficient rigidity against torsion and deflection, a plurality of the urging means 60 are arranged in parallel and between the screw shaft 51 and the end of the sleeve 56 on the end cap 57 side. By interposing, it can also be set as the structure which does not form the guide protrusion 54 and the guide groove 55. FIG. This is because by arranging a plurality of the urging members 60 in parallel, the rotation of the screw shaft 51 is suppressed, and the effect of preventing the screw shaft 51 and the nut 52 from rotating together is exhibited.

  In the initial state of the electric linear actuator, as described above, the drive shaft 40 is retracted into the housing 10 (see FIG. 2). From this initial state, when the motor 20 is actuated to rotate the output shaft 21 in one direction, the drive shaft transmits the drive shaft against the biasing force of the biasing member 60 by the action of the driving force transmission mechanism 30 and the common rotation prevention mechanism 53. 40 becomes the state which protruded from the housing 10 (refer FIG. 1). In this state, when the output shaft 21 is rotated in the reverse direction, the drive shaft 40 is again housed in the housing 10 (see FIG. 2).

  When the drive shaft 40 protrudes from the housing 10 and the motor 20 fails for some reason, the drive shaft 40 cannot be returned to the initial position by the operation of the motor 20. In this case, by pulling the screw shaft 51 to the biasing means 60 side by the biasing force of the biasing means 60, the driving force transmission mechanism 30 that transmits the rotational force to the screw shaft 51 is forcibly reversely rotated. The drive shaft 40 can be returned to the state where the drive shaft 40 is retracted into the housing 10 (see FIG. 2).

  Thus, by providing the urging means 60, the electric linear actuator can be returned to the initial state even when an unexpected trouble such as a failure of the motor 20 occurs. The shaft 40 can avoid troubles such as the brake still being operated. Further, for example, even when the control of the motor 20 fails at a high temperature and the drive shaft 40 tries to return to the initial state vigorously, the components of the electric linear actuator are damaged by the buffering action of the biasing means 60. It is also possible to prevent troubles such as

  The electric linear actuator according to each of the embodiments described above is merely an example, and when the driving force for driving the actuator is lost, the problem of the present invention in which the driving force is compensated to return the actuator to the return state is solved. As long as it is obtained, it is allowed to appropriately change the shape and arrangement of each member.

DESCRIPTION OF SYMBOLS 10 Housing 11 1st division | segmentation housing 11a Through-hole 11b Receiving part 11c Recess 12 2nd division | segmentation housing 12a Bag hole 20 Motor 21 Output shaft 22 Bearing 30 Driving force transmission mechanism 31 First gear 32 Second gear 33 Third gear 34 Shaft 35 Bearing 36 Key member 40 Drive shaft 50 Ball screw mechanism 51 Screw shaft 52 Nut 53 Co-rotation prevention mechanism 54 Guide protrusion 55 Guide groove 56 Sleeve 57 End cap 60 Energizing means 60a Rectangular spring 60b Circular spring

Claims (5)

A housing (10);
A motor (20) provided in the housing (10);
A driving force transmission mechanism (30) for transmitting the rotational driving force of the motor (20);
A drive shaft (40) provided to be movable back and forth in the axial direction;
A ball screw mechanism (50) that converts the rotational driving force from the driving force transmission mechanism (30) into a linear driving force to drive the driving shaft (40) in the axial direction;
Biasing means (60) for biasing the drive shaft (40) in the axial direction thereof;
The ball screw mechanism (50) is provided coaxially with the drive shaft (40), and has a screw shaft (51) having a screw groove formed on the outer peripheral surface thereof, and is coaxial with the screw shaft (51). A nut (52) provided with a thread groove at a position corresponding to a thread groove formed in the screw shaft (51) on the inner peripheral surface, and formed on the screw shaft (51) and the nut (52), respectively. A ball provided in the thread groove, and a co-rotation prevention mechanism (53) for preventing the screw shaft (51) from co-rotating with the nut (52);
Electric linear actuator with   The co-rotation prevention mechanism (53) is not rotatable about the guide projection (54) provided on the screw shaft (51) and the housing (10), and the guide projection (54) The electric linear actuator of Claim 1 provided with the guide groove (55) guided to the axial direction of the said screw shaft (51).   The bag hole (12a) formed in the housing (10), and a sleeve (56) in which the guide groove (55) is formed and fitted in the bag hole (12a). The electric linear actuator described in 1.   The electric linear actuator according to claim 2 or 3, wherein the biasing means (60) is provided in the guide groove (55).   The biasing means (60) is a rectangular spring (60a) having a rectangular cross section, and is arranged so that one side of the rectangular portion is along the inner wall surface of the guide groove (55). Item 5. The electric linear actuator according to Item 4.

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