JPH1146467A - Thrust actuator driven by motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make possible the large equivalent gear ratio of a thrust actuator driven by motor and generate its large thrust without making small the number of the teeth of its input gears, by configuring each of its reduction gears through the gear train comprising the combination of gears whose number is not smaller than a specific one. SOLUTION: A reduction gear is configured by the combination of three or more gears. Providing a front-side sun gear 1f at the left end of a rotor 1b and a rear-side sun gear 1g at the right end of the rotor 1b, one-portions of front-side and rear-side reduction gears 2, 3 are configured respectively. The front-side and rear-side reduction gears 2, 3 comprise respective two front-side and rear-side planetary gears 2b, 3b provided respectively around the front-side and rear-side sun gears 1f, 1g, and respective two front-side and rear-side internal gears 2a, 3a provided respectively on the outsides of the gears 2b, 3b and in an actuator housing 7. The respective two front-side and rear-side planetary gears 2b, 3b are all fastened rotatably to front-side and rear-side planet carriers 2d, 3d by axes 2c, 3c. As a result, changing the numbers of the teeth of the internal gears 2a, 3a and sun gears 1f, 1g one by one on the front and rear sides, the large equivalent gear ratio of a thrust actuator driven by motor can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric thrust actuator used for an electric brake or the like which converts a rotating operation of an electric motor into a straight running operation and presses a brake pad against a brake disk.

[0002]

2. Description of the Related Art As a conventional electric thrust actuator, there is, for example, an actuator for an electric brake disclosed by the present applicant in Japanese Patent Application Laid-Open No. Hei 6-327190.
This is called a first prior art). The electric brake actuator includes a set of planetary gear trains for reducing the rotation of the electric motor, a screw nut connected to the output side of the planetary gear train, a screw shaft fitted to the screw nut, and a screw shaft. It has a pressure member with a friction member attached to the tip of the shaft, and a one-way clutch connected to the screw shaft via a ball spline. Then, the rotation of the electric motor is reduced by the planetary gear train, the screw nut is rotated to move the screw shaft straight, and the friction member of the pressing member is pressed against the brake pad to make contact with the brake disk to apply a braking force. It has become. At this time, when the electric motor rotates in the direction in which the brake pad is pressed, the one-way clutch acts to suppress the rotation of the screw shaft, and the screw shaft is driven by the rotation of the screw nut to always perform a straight-ahead operation. On the other hand, when operating in the reverse direction, the one-way clutch does not work, but while the friction member is pressed against the brake pad, the rotation is suppressed by the frictional force and the operation is performed. Therefore, when the brake pad separates from the brake disc and the friction member simultaneously separates from the brake pad, the screw shaft also rotates with the rotation of the screw nut, and the movement of the screw shaft stops. As a result, the screw shaft can be stopped just before the brake pad is separated from the brake disc without the need for a brake pad position sensor, etc., and there is an advantage that there is no delay in the next pressing operation. I have.

Further, as a thrust actuator other than the one for the electric brake, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 3-48054 (hereinafter referred to as a second prior art). This thrust actuator has a first output gear formed on a screw shaft of a ball screw and a second output gear formed on a screw nut screwed to the screw shaft, while a first input gear is formed on an output shaft of the electric motor. And a second input gear, the first input gear meshes with the first output gear, and the second input gear meshes with the second output gear. A first gear ratio (first reduction ratio) between the first input gear and the first output gear is different from a second gear ratio (second reduction ratio) between the second input gear and the second output gear. . Then, the screw nut is rotated and moved forward in accordance with the difference in rotation angle between the first and second output gears, so that the torque of the electric motor is converted into thrust and output. At this time, if the second gear ratio and the first gear ratio are slightly different, the screw shaft and the screw nut rotate only slightly relative to one rotation of the electric motor. For example,
Assuming that the second gear ratio is reduced at a gear ratio of a: 1 and the first gear ratio is b: 1, the screw nut rotates 1 / a and the screw shaft rotates 1 / b with respect to one rotation of the electric motor. , The screw nut and the screw shaft rotate relatively (1 / a-1 / b).
Therefore, the electric motor needs to rotate 1 / (1 / a-1 / b) in order for the screw nut and the screw shaft to make one rotation relative to each other, and this value becomes an equivalent gear ratio. Therefore a
When b and b are close to each other, the same thrust can be obtained with two sets of gears as if a gear train with a large gear ratio was attached.

An actuator having a configuration similar to that of the second prior art is disclosed in Japanese Patent Application Laid-Open No. 8-28647 (hereinafter, referred to as a third prior art). In this actuator, a screw shaft of a ball screw to which a first gear is attached and a spline shaft to which a second gear is attached are installed in parallel, and the screw shaft and the spline shaft are connected to the first gear and the second gear.
They are connected by gear engagement. A screw nut having a third gear is mounted on the screw shaft, and a spline nut having a fourth gear is mounted on the spline shaft. The screw nut and the spline nut are connected by meshing a third gear and a fourth gear. Then, the screw shaft rotates A by the forward rotation of the motor, and the spline shaft is decelerated and rotates B through the first gear and the second gear.
This B rotation is transmitted to the screw nut via the third gear and the fourth gear, and the screw nut is decelerated and rotates C. This C
The screw nut rotates and moves forward in proportion to / A, and the motor torque is converted into thrust and output. The third prior art also discloses an example of an actuator using one stage of a planetary gear train, but the effect aimed at in each case is to obtain a large reduction ratio with a small number of gear stages. It is.

[0005]

In the first prior art,
The thrust for pressing the brake pad is generated by the torque of the electric motor, but the stroke is very small but a very large thrust is required. Therefore, either a large torque is generated by a large electric motor or a small torque of a small electric motor is amplified with a large reduction ratio (for example, 100 or more) and used. If the planetary gear train has one stage as in the first prior art, the gear ratio (reduction ratio) is determined by the number of teeth of the internal gear and the number of teeth of the sun gear, and the reduction ratio is at most about 4 to 6. However, even a small light-duty passenger car requires a considerably large electric motor, and if there are multiple stages of reduction gears (planetary gear trains), three or more stages are required. Also, since this actuator is mounted in a small space called a brake caliper, it cannot be mounted when the electric motor is huge or when there are multiple stages of reduction gears. feeling·
There is a possibility that the steering performance may be deteriorated.

As one solution to this, there is a method of obtaining a large reduction ratio by using two sets of reduction gears as shown in the second prior art. However, in the second prior art, since the output shaft of the electric motor and the screw shaft of the ball screw are displaced, the device becomes larger in the direction perpendicular to the shaft, and the distance between the shafts of the two sets of reducers is the same. The total number of teeth of the input gear and the number of teeth of the output gear in both reduction gears must be the same. Therefore, for example, the first input gear 20 and the first output gear 4
When the number of gears is 0 (gear ratio 2), even if the gear ratios of the second input gear and the second output gear are closest and different values are selected, 21 second input gears and 39 second output gears (gear ratio 1) .85
7), and the equivalent gear ratio is 26 according to the above equation. This is smaller than a two-stage serial arrangement of an input gear having nine teeth and an output gear having 51 teeth (a total of 60 gears and a gear ratio of 5.67), and an extremely large gear ratio cannot be realized. Further, even if a planetary gear train is used as in the third related art, it is impossible to obtain a large gear ratio when the speed is reduced by one stage as in the related art. That is, there is a problem that the gear ratio and the size of the device required in the first related art cannot be realized by applying the second and third related arts. Further, in the first prior art, the friction member attached to the tip of the screw shaft has a structure in which the brake pad presses the brake pad from the back side. In general, the caliper is attached so as to sandwich the brake disk in a U-shape, When the brake is applied at high pressure, the tip deforms to open. Therefore, the friction member and the screw shaft need to be attached to a structure that is inclined but does not rotate with respect to each other, but such a structure is very difficult.

The present invention has been made in view of such a conventional problem. First, two sets of reduction gears realize a large equivalent gear ratio without reducing the number of teeth of an input gear. Secondly, a large thrust can be generated, and secondly, the size can be reduced and the cost can be reduced. Thirdly, when it is applied to an electric brake or the like, even if a screw shaft or the like tends to be deformed, it is impossible. It is an object of the present invention to provide an electric thrust actuator which operates properly without high stress and without any operation delay and has high reliability.

[0008]

In order to solve the above-mentioned problems, the present invention is directed to an electric motor, two sets of speed reducers driven by the electric motor and having different gear ratios, and two sets of speed reducers. A screw structure for taking out displacement in the straight traveling direction according to the difference in the number of rotations of the speed reducer, wherein the two sets of speed reducers are formed by a gear train composed of a combination of three or more gears. The gist is to constitute. With this configuration, by setting each of the two reduction gears to a combination of three or more gears, the gear ratio, that is, the reduction gear ratio is equal to the number of teeth of the input gear as in the case where the input gear and the output gear are directly meshed. Determined by the number of teeth of the output gear,
At this time, there is no restriction that the total number of teeth in both reduction gears must be the same. This makes it possible to set the gear ratio of both reduction gears arbitrarily.By setting the gear ratio of both reduction gears to a very close value, a large equivalent gear ratio is realized and a large thrust can be generated. Becomes

According to a second aspect of the present invention, in the electric thrust actuator according to the first aspect, one of the two sets of reduction gears is a first input gear attached to an output shaft of the electric motor, and the screw structure. A first output gear attached to the shaft of the motor and a first intermediate gear meshing with both the first input gear and the first output gear, and the other is a second input gear attached to the output shaft of the electric motor. The gist comprises a second output gear attached to the nut having the screw structure and a second intermediate gear meshing with both the second input gear and the second output gear. With this configuration, a combination of three or more gears is specifically realized by a combination of an input gear, an intermediate gear, and an output gear. The first output gear rotates the screw-structured shaft, and the second output gear rotates the screw-structured nut. The nut is driven in a straight line while rotating according to the difference between the number of rotations of the shaft and the nut. Is converted to thrust.

According to a third aspect of the present invention, in the electric thrust actuator according to the second aspect, the number of teeth of an input gear and an output gear of the two sets of reduction gears is the first output gear with respect to the first input gear. The gist is that the number of gears is increased by one, the first output gear and the second input gear are the same, and the number of the second output gear is increased by one with respect to the second input gear. With this configuration, the number of teeth of the input gear and the output gear is set to a value that is very close to the gear ratio of both reduction gears by a combination of the first input gear + 1 = the first output gear = the second input gear = the second output gear-1. , A large equivalent gear ratio is realized and an extremely large thrust can be generated.

According to a fourth aspect of the present invention, in the electric thrust actuator according to the first aspect, the electric motor has a rotor having a hollow structure, and the two sets of speed reducers are first and second planetary gear trains. Wherein the first planetary gear train includes a first sun gear formed at one end of a rotor of the electric motor;
It comprises a first planetary gear, a first internal gear, and a first planet carrier rotatably supporting the first planetary gear, and the second planetary gear train is formed at the other end of the rotor of the electric motor. A second sun gear, a second planetary gear, a second internal gear, and a second planet carrier rotatably supporting the second planetary gear, are penetrated through a hollow portion of a rotor of the electric motor, and are rotatable and shaftable. A screw nut which is not movable in the direction and is supported on one end side of the screw shaft so as to be rotatable and movable in the axial direction. The screw nut to which the first planet carrier is connected and the thrust working end is attached is attached. The other end of the screw shaft is provided with a screw structure connected to the second planet carrier. With this configuration, a combination of three or more gears is specifically realized by a planetary gear train having sun gears, planetary gears, and internal gears. A second planetary gear train rotates a screw shaft that penetrates through the hollow portion of the motor rotor, and a first planetary gear train rotates a screw nut with a thrust acting end attached thereto, and the first and second planetary gear trains The torque of the electric motor is converted into a thrust according to the different gear ratios in the row and output.

[0012] The fifth aspect of the present invention is the first aspect of the present invention.
In the electric thrust actuator according to 2, 3, or 4,
The gist of the present invention is that the screw structure is a ball screw.
With this configuration, the shaft of the screw structure and the nut rotate relatively with low friction, and the mechanical loss is extremely reduced.

[0013] The invention according to claim 6 is the invention according to claim 1,
In the electric thrust actuator according to 2, 3, or 4,
The gist of the present invention is that the screw structure is a sliding screw. With this configuration, the screw structure can be configured at very low cost.

[0014] The invention according to claim 7 is the invention according to claims 4 and 5.
Or the electric thrust actuator according to 6, wherein the number of teeth of the second sun gear is one more or less than the number of teeth of the first sun gear, and the number of teeth of the second internal gear is the number of teeth of the first internal gear. The gist should be one more or less than the number. With this configuration, when the two sets of reduction gears are the first and second planetary gear trains, the number of teeth of the sun gear and the internal gear is set to 1 between the first and second gears.
By setting the number of teeth different for each sheet, the gear ratios of the two reduction gears are set to very close values, a large equivalent gear ratio is realized, and an extremely large thrust can be generated.

[0015] The invention of claim 8 provides the above-mentioned claim 4,
In the electric thrust actuator according to 5, 6, or 7,
The connecting portion between the screw shaft and the second planet carrier includes a friction member that generates a frictional force when the screw shaft and the second planet carrier are pressed against each other, and a screw nut in a direction in which the thrust acts. The screw shaft and the second planet carrier are fixed so that they cannot rotate relative to each other only when the electric motor is rotated in the moving direction, and when the electric motor rotates in the reverse direction, the screw shaft and the second planet carrier are fixed. The point is that the carrier and the one-way clutch that can rotate relatively freely are constituted. With this configuration, when applied to an electric brake or the like and a thrust is generated, even if the screw shaft or the like tends to be deformed, it is possible to operate the screw shaft without applying excessive stress due to the presence of the friction material. Become. When the electric motor rotates in the reverse direction and the thrust acting end separates from the brake pad, etc., when the thrust is lost, the frictional force due to the friction material disappears and the clutch operation of the one-way clutch is released, the screw shaft and the screw nut rotate together and the screw The nut, the thrust end, will not retract any further. Therefore, the initial position when the electric motor rotates forward and the thrust acting end acts next is reliably determined to the predetermined position.

According to a ninth aspect of the present invention, in the electric thrust actuator according to any one of the fourth to eighth aspects,
The gist of the present invention is that an aligning bearing is provided between the thrust acting end and the screw nut so that both can rotate smoothly even if the central axes of both are bent. With this configuration, when applied to an electric brake or the like and a thrust is generated, even if the thrust acting end and the central axis of both the screw shaft are displaced, the axial displacement is corrected, and an excessive stress is applied to the screw shaft. It works without such.

According to a tenth aspect of the present invention, in the electric thrust actuator according to any one of the fourth to ninth aspects, the second planet carrier supports a bearing that is rotatable and cannot move in the axial direction. The gist is that a load sensor for detecting an axial load applied to the bearing is provided between the bearing and a housing supporting the bearing. With this configuration, when a thrust is generated and acting on a brake pad or the like, a load corresponding to the total thrust is applied to the second planet carrier, so that the generated total thrust is detected.

[0018]

According to the first aspect of the present invention, since the two sets of reduction gears are each constituted by a gear train composed of a combination of three or more gears, the total number of teeth in both reduction gears must be the same. This eliminates the restriction that the gear ratio must be set, and allows the gear ratio of both reduction gears to be set arbitrarily.
By setting the gear ratios of both reduction gears to very close values, a large equivalent gear ratio can be realized with two sets of reduction gears without reducing the number of teeth of the input gear, and a large thrust can be generated. Since it is not necessary to reduce the number of teeth of the input gear, the meshing ratio of the gear train is improved, and no abnormal noise occurs during operation.

According to the second aspect of the present invention, one of the two sets of reduction gears has a first input gear attached to an output shaft of the electric motor, and a first output gear attached to a shaft having the screw structure. A gear and a first intermediate gear meshing with both the first input gear and the first output gear; the other is mounted on a second input gear mounted on an output shaft of the electric motor, and mounted on a nut having the screw structure. The second input gear and the second intermediate gear meshing with both the second input gear and the second output gear, the second input gear and the second output gear correspond to the number of teeth of the first input gear and the first output gear. By setting such that the number of teeth of the output gear is increased by, for example, one by one, a large equivalent gear ratio is realized by two sets of reduction gears composed of a combination of an input gear, an intermediate gear, and an output gear, and a large thrust can be generated. .

According to the third aspect of the present invention, the number of teeth of the input and output gears of the two sets of reduction gears is increased by one for the first output gear relative to the first input gear. One output gear and the second input gear are the same, and the number of the second output gear is increased by one with respect to the second input gear. Specifically, the number of teeth of the input gear and the output gear is changed to the first input gear. +1
= 1st output gear = 2nd input gear = 2nd output gear-1, the gear ratio of both reduction gears is set to a very close value, a large equivalent gear ratio is realized, and an extremely large thrust is achieved. Can be generated.

According to the fourth aspect of the present invention, the electric motor has a rotor having a hollow structure, and the two sets of reduction gears are first and second planetary gear trains, and the first planetary gear train is provided. The gear train includes a first sun gear formed at one end of a rotor of the electric motor, a first planetary gear, a first internal gear, and a first planet carrier rotatably supporting the first planetary gear. The second planetary gear train includes a second sun gear, a second planetary gear, a second internal gear, and a second planet carrier rotatably supporting the second planetary gear formed at the other end of the rotor of the electric motor. Then, penetrated through the hollow portion of the rotor of the electric motor, a screw shaft that is rotatable but cannot move in the axial direction and is supported on one end side of the screw shaft so that both rotation and axial movement are possible. The said Has a screw nut which thrust action end is attached with the planet carrier is connected, for the other end of the screw shaft which is disposed an attached screw structure to the second planet carrier, the first sun gear,
By setting the number of teeth of the second sun gear and the number of teeth of the second internal gear to be increased by, for example, one by one with respect to the number of teeth of the first internal gear, a large equivalent gear ratio is realized with two sets of reduction gears including a planetary gear train. Large thrust can be generated. Further, since the electric motor, the screw structure, and the first and second planetary gear trains are arranged coaxially, the size can be reduced.

According to the fifth aspect of the present invention, since the screw structure is a ball screw, mechanical loss is extremely reduced, and a large thrust can be generated effectively.

According to the sixth aspect of the present invention, since the screw structure is a sliding screw, there is an effect that the screw structure can be formed at a low cost.

According to the present invention, the number of teeth of the second sun gear is one more or less than the number of teeth of the first sun gear, and the number of teeth of the second internal gear is the first number of teeth. Since the number of teeth is one more or less than the number of teeth of the internal gear, when the two sets of reduction gears are the first and second planetary gear trains, the number of teeth of the sun gear and the internal gear is specifically set to the first number. By setting the number of teeth different between the first and second gears, the gear ratios of the two reduction gears are set to very close values, a large equivalent gear ratio is realized, and an extremely large thrust can be generated. At this time, the first and second
The planetary gears can be used as common parts with the same number of teeth, and cost can be reduced.

According to the eighth aspect of the present invention, the connecting portion between the screw shaft and the second planet carrier generates a frictional force when the screw shaft and the second planet carrier are pressed against each other. The screw shaft and the second planet carrier are fixed so that they cannot rotate relative to each other only when the friction material and the electric motor are rotated in a direction in which the screw nut moves in the direction of action of the thrust. In the case of rotation, since the screw shaft and the second planet carrier are constituted by a one-way clutch which can relatively freely rotate, the present invention is applied to an electric brake or the like, and when a thrust is generated, the screw shaft tends to deform. Can be operated without applying excessive stress to the screw shaft due to the interposition of the friction material. Also, when the electric motor rotates in the reverse direction and the thrust action end is separated from the brake pad or the like, the clutch operation of the one-way clutch is released, so the retraction of the thrust action end stops, and then the electric motor rotates forward and the thrust action The initial position when the end works is reliably determined to the predetermined position, and no operation delay occurs.

According to the ninth aspect of the present invention, an aligning bearing is provided between the thrust acting end and the screw nut so that the two can rotate smoothly even if the center axes of both are bent. When a thrust is applied, even if the thrust acting end and the central axis of both the screw shafts are displaced, the axial displacements are corrected and the screw shafts can be operated without excessive stress. .

According to the tenth aspect of the present invention, the second
The planet carrier is provided with a bearing that supports rotatable and cannot move in the axial direction, and a load sensor that detects an axial load applied to the bearing is provided between the bearing and a housing that supports the bearing. When a thrust is generated and acting on a brake pad or the like, a load corresponding to the total thrust is applied to the second planet carrier, so that the generated total thrust can be reliably detected. Therefore, if the current supplied to the electric motor is controlled based on this detection signal, an arbitrary thrust = braking force can be generated. By providing a load sensor between the bearing and the housing, the load sensor does not rotate, move, etc., so there is no risk of disconnection of the sensor harness, etc.
Durable and highly reliable sensor mounting can be performed.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a first embodiment of the present invention. FIG. 1 shows an example of a brake caliper incorporating the present embodiment. Reference numeral 1 denotes an electric motor to which a brushless motor is applied. Rotor position sensor 1
c, the position of the rotor 1b is detected, and the rotor 1b having a hollow structure is rotated by sequentially applying a current to the plurality of windings 1a.
The rotor position sensor 1c is a rotary encoder that rotates a disk having a slit at a predetermined angle and detects the position of the rotor 1b by counting the intermittent light passing through the slit. 1d and 1e are ball bearings, and the rotor 1
b is rotatably supported. A front (first) sun gear 1f is provided at the left end of the rotor 1b in the figure, and a rear (second) sun gear 1g is provided at the right end, and front and rear (first and second).
Of the planetary gear trains (reducers) 2 and 3 of FIG.
1h is a motor yoke, 1i and 1j are motor caps. Reference numeral 2 denotes a front planetary gear train, which includes four front planetary gears 2b arranged around a front sun gear 1f and a front internal gear 2a provided on an actuator housing 7 outside the front sun gear 1b. Each gear of the front planetary gear 2b is rotatably fixed to the front planet carrier 2d by a shaft 2c, and the front planet carrier 2d is integrally formed as a flange portion of a screw nut 4a of the ball screw 4 having a screw structure. ing. The front sun gear 1f and the front internal gear 2a
Has a longer tooth width, and the front planetary gear 2b can move in the axial direction. Here, the number of teeth of the front internal gear 2a is set to 40 in order to match the example described above, and the number of teeth of the front sun gear 1f is set to 20. The number of teeth of the front planetary gear 2b is 10 because it is half the difference between the two. Reference numeral 3 denotes a rear planetary gear train, which includes four rear planetary gears 3b arranged around a rear sun gear 1g, and a rear internal gear 3a provided in an actuator housing 7 outside the rear sun gear 1g.
The rear planetary gears 3b are all rotatably fixed to the rear planet carrier 3d by shafts 3c. Here, the number of teeth of the rear internal gear 3a was 41, and the number of teeth of the rear sun gear 1g was 21. The number of teeth was increased by one each for the front internal gear 2a and the sun gear 1f. The number of teeth of the rear planetary gear 3b is the same as that of the front one
It is zero. The rear planet carrier 3d is fixed by a ball bearing 3e so as to be rotatable and immovable to the left in the drawing. The clearance between the ball bearing 3e and the actuator housing 7 is adjusted so that the ball bearing 3e can freely move to the right. The rear planet carrier 3d has a one-way clutch 3f on the right side of the center. The one-way clutch 3f can realize a structure in which the shaft inserted therein rotates freely in one direction but does not rotate in the other direction. Here, when viewed from the direction of the arrow A, when the rear planet carrier 3d relatively rotates counterclockwise relative to the center axis, the clutch operates to rotate integrally. Shall be installed so that it can rotate freely. Reference numeral 4 denotes a ball screw, which includes a screw nut 4a, a screw shaft 4b, and a ball 4c. The ball 4c is housed between a spiral groove formed on the screw shaft 4b at the left third in the drawing and a spiral groove formed at the same pitch on the screw nut 4a. At one end through a ball passage formed inside the nut to the opposite end. Therefore, when the screw nut 4a and the screw shaft 4b rotate relatively, they relatively move in the axial direction. At this time, the force is transmitted by the ball 4c rolling in an infinite passage formed by the groove and the passage, so that a low friction operation is possible. A friction material 4d is attached to the right side of the screw shaft 4b in the drawing, and when pressed against the rear planet carrier 3d, a frictional force acts so that the rotation between the screw shaft 4b and the rear planet carrier 3d stops. Further, the right side of the screw shaft 4b is inserted into a one-way clutch 3f mounted on the rear planet carrier 3d. A load sensor 5 detects a load applied to the ball bearing 3e in the right direction in the figure. The load applied to the ball bearing 3e is a rightward load applied to the rear planet carrier 3d, and this load is the thrust itself generated by the actuator applied through the screw shaft 4b. Therefore, by detecting the load here, the thrust generated by the actuator can be detected. The configuration of the load sensor 5 is 2
A piezo element is sandwiched between two electrodes, and a voltage generated between both electrodes due to a load is detected. 6
Is a piston acting as a thrust acting end, the left end face abuts against the back surface of the brake pad 8, and the right end face is a self-aligning bearing 6a.
And is connected to the screw nut 4a through the nut. The self-aligning bearing 6a is attached to the screw nut 4a by a coupling member 6b, and holds the shaft so that even if the shafts of the outer ring and the inner ring of the bearing are bent, they can rotate relatively smoothly. Reference numeral 7 denotes an actuator housing, which houses the front and rear planetary gear trains 2 and 3, the electric motor 1, and the like. The left side of the figure is attached to the housing 10, and the right side is closed by an end cap 7a. Reference numeral 8 denotes a brake pad, which is a brake disk 9 provided inside by the piston 6.
To suppress the rotation of the brake disc 9. Reference numeral 10 denotes a housing, which accommodates the entire apparatus, is attached to a carrier 11 via pins 10a, and is fixed to an axle (not shown) by the carrier 11. A piston seal 10b and a rotary linear bush 10c are attached to the inside of the housing 10. The piston seal 10b supports the piston 6 so as to be movable in the left and right directions in FIG. Prevents foreign matter from entering the actuator from the side. In addition, the rotary / linear motion bush 10
c supports the screw nut 4a so that it can move in the left-right direction in the figure while rotating.

Next, the operation and effects of the electric thrust actuator configured as described above will be described. Generally, in a planetary gear train, the number of teeth of a sun gear is set to Hs, and the number of teeth of an internal gear is set to Hi. When an input is given to the sun gear and an output is taken out from the planet carrier as in this configuration, the rotation of the planet carrier with respect to the sun gear becomes , Reduction ratio Hs /
It is decelerated at (Hi + Hs). Therefore, when the number of teeth is determined as described above, each gear ratio is as follows: front planetary gear train: 3 rear planetary gear train: 2.95238. Therefore, when a current is applied to the electric motor 1 to rotate the rotor 1b counterclockwise as viewed from the direction of the arrow A in the figure, the rotation of the electric motor 1 per one rotation

## EQU1 ## Front planet carrier 2d: 1/3 turn counterclockwise Rear planet carrier 3d: 1 / 2.9 counterclockwise
It rotates 5238 times. Since the front planet carrier 2d is integral with the screw nut 4a, this is equivalent to the rotation of the screw nut 4a. The screw shaft 4b is dragged by the screw nut 4a by the frictional force between the screw nut 4a and attempts to rotate in the same manner. However, since the rotation of the rear planet carrier 3d is larger than the rotation angle of the screw nut 4a, The one-way clutch 3f works, and the screw shaft 4b is connected to the rear planet carrier 3d.
Rotate the same as. Therefore, the screw shaft 4b and the screw nut 4a both rotate counterclockwise, but the screw shaft 4b
Has a larger rotation angle, so that the operation is the same as stopping the screw nut 4a and turning only the screw shaft 4b counterclockwise, and the screw nut 4a moves leftward in the figure. At the same time, the front planetary gear 2b moves with the screw nut 4a in the range of the tooth width of the internal gear 2a and the sun gear 1f. At this time, the relative rotation of the screw shaft 4b and the screw nut 4a corresponds to one rotation of the electric motor 1,

## EQU2 ## The rotation becomes 1 / 2.95238-／ = 0.00537634. Since the reciprocal is 186, when the electric motor 1 rotates 186 times, the screw shaft 4b and the screw nut 4
a rotates one rotation relatively, and the operation is the same as when only the screw nut 4a is turned at the gear ratio 186. Therefore, if the motor generates a certain torque, the torque is multiplied by 186 to drive the ball screw 4. If the lead of the ball screw 4 is set to L, the thrust of torque × 2π / L is applied to the centering bearing. 6a · Brake pad 8 via piston 6
To act on. For example, lead 10mm, torque 0.5
If Nm and efficiency are 80%, a power of 4.7 ton can be generated. The ratio of the effective diameter of the brake disc 9 to the tire diameter is 1: 3, and the friction coefficient of the brake pad 8 is 0.1.
Even with 3, the braking force of one wheel is 953 kgf, and a sufficient braking force for a passenger car can be obtained. If this gear ratio 186 is to be realized by simply connecting the planetary gear train in series, for example, even if the gear ratio 6 is realized by setting the number of teeth of the sun gear to 8, three stages are required, and the number of gear teeth is set to 8, for example. If the value is set to a small value, the meshing rate becomes poor, and there is a disadvantage that sound is generated during operation. However, in this embodiment, the planetary gear trains 2 and 3 can be realized in two stages.
Moreover, the number of teeth of the sun gear is 20 and 19, and the number of planetary gears is 10, and a gear having a small number of teeth such as 8 is not required. Further, by changing the number of teeth of the internal gear and the sun gear one by one as in this embodiment, a large equivalent gear ratio is realized, and the front and rear planetary gears 2b, 3b can be used as common parts. Yes, it is advantageous in terms of cost. When a thrust is generated, the housing 10 is deformed so that the rear end of the electric motor 1 moves to the upper side of the figure with the upper side of the figure as a center.
Both central axes are bent not in a straight line but in a downwardly convex shape. In the prior art, the piston part was composed of a friction material and a ball screw shaft, and it was necessary to adopt a structure in which the friction material was pressed and the shaft did not rotate, so the shaft and the friction material bend in any direction, but the rotation was It was necessary to attach it with a structure that does not do it, and it was not practically feasible. On the other hand, in this embodiment, the friction material 4d is provided between the rear planet carrier 3d and the screw shaft 4b, and the piston 6 and the screw nut 4a, which are affected by the deformation, are connected by the self-aligning bearing 6a. Therefore, the ball screw 4 can be operated with a realistic structure without applying excessive stress. Further, the self-aligning bearing 6a receives a large load in the upper part of the figure when deformed. However, since the nut rotates and the pad gradually decreases, a large load is applied. The receiving rollers are sequentially changed, and the contact positions of the inner and outer rings also change. Therefore, since points receiving a large load are dispersed, the durability of the roller is improved. Since the generated thrust pushes the rear planet carrier 3d via the friction material 4d, this force pushes the end cap 7a via the ball bearing 3e.
Therefore, the end cap 7a and the ball bearing 3
By providing the load sensor 5 during the period e, it is possible to detect the thrust force generated by the actuator and acting on the brake pad 8. Therefore, if the current supplied to the electric motor 1 is adjusted using this signal, Any thrust = braking force can be generated. Further, since the load sensor 5 attached to this portion does not rotate or move, there is no fear of disconnection of the sensor harness and the like, and highly durable and highly reliable sensor mounting is possible.

Next, the operation when the electric motor 1 is rotated in the reverse direction (clockwise as viewed from A). The already generated thrust is transmitted through the screw shaft 4b and presses the friction material 4d against the rear planet carrier 3d. Therefore, the friction material 4d
The screw shaft 4b and the rear planet carrier 3d rotate clockwise together due to the frictional force generated in the above. At the same time, the screw nut 4a also rotates clockwise, whereby the screw nut 4a is retracted by an operation reverse to the above operation. When fully retracted, the brake pad 8 separates from the brake disk 9 and at the same time the piston 6 separates from the brake pad 8, so that no thrust is generated. Then, the friction material 4d pressed by the thrust and the rear planet carrier 3d
There is no friction between them. At this time, the screw shaft 4b is dragged by the rotation of the screw nut 4a and tries to rotate together, and the rotation angle of the screw nut 4a and the rotation angle of the rear planet carrier 3d are, as described above, that of the rear planet carrier 3d. Because it is large, the rear planet carrier 3d rotates to rotate clockwise relative to the screw shaft 4b, and the one-way clutch 3f does not work. Therefore, when the thrust is lost, the screw shaft 4b and the screw nut 4a rotate together, and the screw nut 4a does not recede any more. Therefore, the screw nut 4a is always located at a position just before the brake pad 8 and the brake disk 9 hit. Stop at As a result, even if the brake pad 8 gradually decreases, no operation delay occurs when the electric motor 1 is rotated forward to apply the brake next time.

Although the electric motor 1 used here is a brushless motor, other motors such as a DC motor with a brush used in the first prior art or a reluctance motor may be used. Any motor can be used as long as it can have a hollow structure. Further, the number of gear teeth is not limited to this, and any number of physically achievable teeth may be used.
As described above, in the case of a combination of 20 sheets and 40 sheets, if the maximum gear ratio is to be obtained by increasing one by one,
It was 86, but when it was increased one by one to 19 and 39, it becomes 174. Therefore, a desired equivalent gear ratio may be set by adjusting both the total value and distribution of the number of teeth of the sun gear and the number of teeth of the internal gear. The screw structure is not limited to a ball screw, and may be a sliding screw. The same applies to the load sensor, and another method such as a method in which the axial strain of the material sandwiched between the portions is detected by a strain gauge or the like may be used.

FIGS. 2 and 3 show a second embodiment of the present invention. In this embodiment, an electric motor and a ball screw are separately arranged, and driven by two sets of reduction gears using spur gears. First, the configuration will be described. Electric motor 20
The first input gear 21a and the second input gear 22a
Is attached. Screw shaft 23a of ball screw 23
The first output gear 21b is attached to the
A spline shaft 24a cut in the axial direction is attached to 3b. The spline shaft 24a is connected via a ball 24c to a rotating shaft 25 integrally formed with a spline nut 24b, whereby the rotating shaft 25 can be moved relative to the spline shaft 24a and the ball screw nut 23b in the axial direction. However, relative rotation is impossible. A second output gear 22b is formed at the right end of the rotating shaft 25. A thrust acting end 26 is attached to the left end of the spline shaft 24a via a thrust bearing. The configuration up to this point is almost the same as that of the second prior art (Japanese Patent Application Laid-Open No. 3-48054), except that the first input gear 21a and the first output gear 2
1b, the second input gear 22a and the second output gear 22b do not directly mesh with each other.
The first input gear 21a and the first output gear 21b are in
As seen from the direction of the arrow, they mesh with each other via a first intermediate gear 21c as shown in FIG. Second input gear 22
a and the second output gear 22b are also meshed via the second intermediate gear 22c.

Next, the operation and effects of the second embodiment configured as described above will be described. In the case of this reduction gear configuration, the gear ratio is the number of intermediate gear teeth / number of input gear teeth from the input gear to the intermediate gear, and the output gear number / intermediate gear number of teeth from the intermediate gear to the output gear. The product from the gear to the output gear is the product of the two, and eventually becomes the number of output gear teeth / the number of input gear teeth, and the number of teeth of the intermediate gear does not affect the gear ratio. Therefore, the gear ratio of the two reduction gears may be determined by the number of teeth of the input gear and the number of teeth of the output gear as in the case of direct meshing. At that time, since they are not directly engaged,
There is no restriction that the total number of teeth of both gears must be the same as in the second prior art. Therefore, as described in the first embodiment, it is also possible to set such that each of them is increased by one, for example, as in the first embodiment, 20 sheets / 40 sheets and 21 sheets / 41 sheets Then, the equivalent gear ratio is 82. Also, if the values are set to be close to 40 sheets / 41 sheets and 41 sheets / 42 sheets, 1722
Therefore, it is possible to obtain a maximum gear ratio which is considered impossible in the first embodiment. After determining the number of teeth of the input gear and the output gear, the two can be engaged without affecting the set gear ratio by adjusting the number of teeth or the position of the intermediate gear.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of an electric thrust actuator according to the present invention.

FIG. 2 is a longitudinal sectional view showing a second embodiment of the present invention.

3 is a diagram showing a meshing relationship among a first (second) input gear, a first (second) intermediate gear, and a first (second) output gear as viewed from the B side in FIG. 2;

[Explanation of symbols]

 1,20 Electric motor 1b Rotor 1f Front (first) sun gear 1g Rear (second) sun gear 2 Front (first) planetary gear train (reduction gear) 2a Front (first) internal gear 2b Front (first) planetary Gear 2d Front (first) planet carrier 3 Rear (second) planetary gear train (reducer) 3a Rear (second) internal gear 3b Rear (second) planetary gear 3d Rear (second) planet carrier 3e Ball bearing 3f One-way clutch 4,23 Ball screw (screw structure) 4a, 23b Screw nut 4b, 23a Screw shaft 4d Friction material 5 Load sensor 6 Piston (thrust action end) 6a Self-aligning bearing 8 Brake pad 9 Brake disk 20a Motor shaft 21a First input gear 21b First output gear 21c First intermediate gear 22a Second input gear 22b Second output gear 22c Second intermediate gear 26 Thrust working end

Claims (10)

[Claims] An electric motor, two sets of speed reducers driven by the electric motor having different gear ratios, and a screw structure for taking out a displacement in a straight traveling direction in accordance with a difference in rotation speed between the two sets of speed reducers. Wherein the two sets of speed reducers are each configured by a gear train composed of a combination of three or more gears. 2. One of the two sets of speed reducers includes a first input gear mounted on an output shaft of the electric motor, a first output gear mounted on a shaft having the screw structure, and the first input gear. A first intermediate gear meshes with both of the first output gears, and the other is a second input gear attached to an output shaft of the electric motor, a second output gear attached to a nut having the screw structure, and the second output gear. 2. The electric thrust actuator according to claim 1, comprising a second intermediate gear meshing with both the two-input gear and the second output gear. 3. The number of teeth of an input gear and an output gear of the two sets of reduction gears is such that the number of teeth of the first output gear is increased by one with respect to the number of the first input gear, and the number of teeth of the first output gear and the number of teeth of the second input gear are increased. The electric thrust actuator according to claim 2, wherein the gears are the same, and the number of the second output gear is increased by one with respect to the second input gear. 4. The electric motor has a rotor having a hollow structure, and the two sets of speed reducers are first and second planetary gear trains, and the first planetary gear train is a motor of the electric motor. A first sun gear, a first planetary gear formed at one end of the rotor,
The first planetary gear train comprises a first internal gear and a first planetary gear rotatably supporting the first planetary gear, and the second planetary gear train includes a second sun gear formed at the other end of a rotor of the electric motor, It comprises a 2 planetary gear, a second internal gear, and a second planet carrier rotatably supporting the second planetary gear. The second planetary gear is penetrated by a hollow portion of a rotor of the electric motor, and can rotate and move in the axial direction. A screw nut which is rotatably and axially movable on one end of the screw shaft and one end of the screw shaft, has a screw nut to which the first planet carrier is connected and to which a thrust acting end is attached; 2. The electric thrust actuator according to claim 1, wherein a screw structure connected to the second planet carrier is provided on the other end of the thrust actuator. 5. The electric thrust actuator according to claim 1, wherein said screw structure is a ball screw. 6. The electric thrust actuator according to claim 1, wherein said screw structure is a sliding screw. 7. The number of teeth of the second sun gear is one more or less than the number of teeth of the first sun gear, and the number of teeth of the second internal gear is one more than the number of teeth of the first internal gear. 7. The electric thrust actuator according to claim 4, 5 or 6, wherein the number is large or small. 8. The connecting portion between the screw shaft and the second planet carrier includes a friction member that generates a frictional force when the screw shaft and the second planet carrier are pressed against each other, and the screw nut. The screw shaft and the second planet carrier are fixed so that they cannot rotate relative to each other only when the electric motor is rotated in the direction in which the thrust acts, and when the electric motor rotates in the reverse direction, the screw shaft is fixed. 8. The electric thrust actuator according to claim 4, further comprising a one-way clutch capable of relatively freely rotating the second planet carrier and the second planet carrier. 9. Between the thrust acting end and the screw nut,
9. An aligning bearing which allows both of them to rotate smoothly even if their central axes are bent.
The electric thrust actuator according to any one of the above. 10. The second planet carrier includes a bearing that supports rotatable and non-movable in the axial direction, and applies an axial load applied to the bearing between the bearing and a housing that supports the bearing. The load sensor for detecting is provided.
An electric thrust actuator according to any one of claims 1 to 9.