Patent Application
20190085957
The present invention relates to an electric actuator.
In recent years, electrification of automobiles has been promoted for power saving and reduction in fuel consumption. For example, a system for operating an automatic transmission, a brake, and a steering wheel of ah automobile with use of power of an electric motor (motor) has been developed and brought to the market. As an electric actuator for use in such a system, there has been known an electric actuator employing a screw device (ball screw device) as a motion conversion mechanism configured to convert a rotary motion of a motor into a linear motion to output the motion (for example, see Patent Literature 1). In this case, a screw shaft of the ball screw device forms an output member of the electric actuator.
Patent Literature 1: JP 2015-104231 A
Incidentally, it is considered to mount the electric actuator to a device (system) such as a DCT, which is a type of the automatic transmission, in which two objects to be operated are coaxially arranged, or the electric actuator is actually mounted to such a device. However, when the electric actuators of Patent Literature 1 are mounted on such a device described above, the two actuators need to be independently arranged, and a form of coupling between the output member of each of the actuators and each of the objects to be operated needs to be devised, with the result that complexity and a size of the entire device may increase. Thus, for example, when an electric actuator having, two output members independently operable and coaxially arranged can be achieved, it is conceivable that the above-mentioned problem can be solved, as much as possible. However, even when, such an electric actuator can be achieved, low ease of assembly (productivity) and a problem in production cost resulting therefrom may cause difficulty in wide use of such an electric actuator.
The present invention, has been made in view of the above-mentioned, problem, and therefore has a main object to provide an electric actuator capable of independently operating a plurality of objects to be operated (in particular, objects to be operated that are coaxially arranged), and excellent in ease of assembly.
The present invention has been made in order to solve the above-mentioned problem, and according to one embodiment of the present invention, there is provided an electric actuator, comprising: a motor part configured to drive upon receiving supply of power; a motion conversion mechanism part configured to convert a rotary motion of the motor pan into a linear motion to output the linear motion; and a housing configured to accommodate the motor part and the motion conversion mechanism part, wherein the motion conversion mechanism part comprises; a screw shaft arranged coaxially with a rotation center of a rotor of the motor part; and a nut member rotatably fitted to an outer periphery of the screw shaft, wherein an operation part mounted to the screw shaft is configured to operate an object to be operated in an axial direction through a linear motion of the screw shaft in the axial direction along with a rotation of the nut member upon receiving a rotary motion of the rotor, wherein the housing comprises a plurality of members coupled to one another in the axial direction, wherein a terminal part configured to hold an electrical component comprises a tubular portion sandwiched by the members forming the housing from both sides in the axial direction, and has an opening portion formed in the tubular portion and configured to cause an inside and an outside of the housing to communicate with each other, and in which the screw shaft is formed into a hollow shape having a through hole extending in the axial direction. The “electrical component” mentioned in the present invention is a concept including, for example, a power supply circuit configured to supply drive power to the motor part and a rotation angle detection sensor used to control a rotation of the motor part.
With the above-mentioned configuration, the through hole formed in the screw shaft in the axial direction can be used as a portion that allows arrangement (insertion) of an operation part mounted to another screw shaft. Therefore, for example, in a case in which two actuator units each comprising the motor part, the motion conversion mechanism part, and the terminal part are arrayed in the axial direction and are coaxially arranged, an electric actuator, which is compact while having two output members (operation parts) independently operable and coaxially arranged, can be achieved through mounting the hollow operation part to the screw shaft of one actuator unit, and inserting the operation part mounted to the screw shaft of another actuator unit through the through hole of the screw shaft (and the operation part). An electric actuator in which three or more output members (operation parts) are independently operable and coaxially arranged can be achieved in the same manner.
Moreover, with the above-mentioned configuration, the motor part can be brought into an operable state through coupling the members forming the housing to one another in the axial direction so as to assemble the housing. In particular, when an opening portion configured to cause an inside and an outside of the housing to communicate with each other is formed in a tubular portion of the terminal part, electric wires connected to the electric components can be drawn out to a radially outer side of the housing through the opening portion. In this case, a routing operation of the electric wires can be completed under a state in which the terminal part exists alone. Thus, the complex routing operation of the electric wires does not need to be earned out in an assembly stage of the electric actuator. Therefore, even in an electric actuator in which two or more output members are independently operable and coaxialty arranged, the ease of assembly and the productivity can be increased, and the cost thereof can thus be reduced.
At least a part of a stator of the motor part may be fitted to the tubular portion of the terminal part. With such a configuration, the stator of the motor part can be assembled to the inner periphery of the housing simultaneously with the assembly of the housing, and the ease of assembly of the electric actuator can further be increased.
The rotor of the motor may comprise a hollow rotary shaft, which has the nut member arranged on an inner periphery thereof, and is supported rotatably by rolling bearings arranged at two positions apart from each other in the axial direction. In this ease, the hollow rotary shaft may comprise an inner raceway surface of one of the two rolling bearings. With such a configuration, the hollow rotary shaft and the housing can be downsized in the axial direction. As a result, an electric actuator downsized is the axial direction, and excellent in mountability with respect to a device to be used can be achieved.
In a case in which the inner raceway surface is formed on the hollow rotary shaft, when the inner raceway surface is arranged within an axial width of the nut member, the electric actuator can be further downsized in the axial direction.
The motion conversion mechanism part may comprise a speed reducer configured to reduce a speed of the rotation of the rotor, and transmit the rotation to the nut member. With such a configuration, a small motor can be employed, and the weight and the size of the electric actuator can thus be reduced. A planetary gear speed reducer can be employed as the speed reducer. When the planetary gear speed reducer is employed, a speed reduction ratio can easily be adjusted through, for example, changing specifications of the gears or changing the number of stages of the installed planetary gears. Further, there is also an advantage in that, even when the planetary gears are installed in a large number of stages, an increase in sizes of the speed reducer and the electric actuator can be avoided.
As described above, according to the present invention, there can be achieved an electric actuator capable of independently operating a plurality of objects to be operated, and excellent in ease of assembly.
Now, description is made of embodiments of the present invention with reference to the drawings.
The housing 2 is formed of a plurality of members coupled in the axial direction under a state in which the members are coaxially arranged. The housing 2 of this embodiment is formed of a coupled body comprising a casing 20, a cover 29, an intermediate casing 80, and the terminal parts D (terminal main bodies 50). The casing 20 is arranged on one side in the axial direction (right side of the drawing sheer in
As illustrated in an enlarged form in
As illustrated in
As illustrated in
Description is now made of detailed structures of the motor part A, the motion conversion mechanism part B, and the terminal part D. The first and second actuator units 3 and 4 have basically the same structures in the motor part A, the motion conversion mechanism part B, and the terminal part D except that output members are different from each other in configuration. Therefore, hereinafter, the motor part A and the like forming the first actuator unit 3 are is described in detail, and detailed description of the motor part A and the like forming the second actuator unit 4 is basically omitted.
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The ball screw device 31 comprises a screw shaft 33, a nut member 32, and deflectors 35. The screw shall 33 is arranged coaxially with a rotation center of the rotor 24. The nut member 32 is rotatably fitted to an outer periphery of the screw shaft 33 through intermediation of a plurality of balls 34, and is arranged on an inner periphery of the rotor inner 26. The deflectors 35 serve as circulation members. The screw shaft 33 is formed into a hollow shape having a through hole 33b opened in both end surfaces in the axial direction. Between a spiral groove 32a formed in an inner peripheral surface, of the nut member 32 and a spiral groove 33a formed in an outer peripheral surface of the screw shaft 33, the plurality of balls 34 are loaded, and the deflectors 35 are incorporated. With such a configuration, when the screw shaft 33 performs a linear motion in the axial direction along with the rotation of the nut member 32, the balls 34 circulate between the spiral grooves 32a and 33a.
In the first actuator unit 3, the output member thereof comprises the screw shaft 33, a hollow inner member 36, and an actuator head 39. The inner member 36 is accommodated in the through hole 33b of the screw shaft 33. The actuator head 39 serving as the operation part C is formed into a hollow shape having a through hole in the axial direction, and is removably fixed to an end portion of the screw shaft 33 on the one side in the axial direction.
As illustrated in
The small-diameter shaft portion 91b is arranged on inner peripheries of the hollow screw shaft 33 (inner member 36) and the actuator head 39 forming the first actuator unit 3. As illustrated in
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When the planetary gear carrier 43 and the nut member 32 are coupled to each other in a torque transmittable manner through the press-fitting of the inner peripheral surface of the cylindrical portion 43 a to the outer peripheral surface 32b of the nut member 32 in this way, ease of coupling operation at the lime of assembly is excellent, and stable torque transmission can be performed with respect to high torque after reduction in speed. Moreover, the rotor inner 26 and the sun gear 41 are coupled to each other in a torque transmittable manner through the press-fitting of the sun gear 41 to the step-portion inner peripheral surface 26c of the rotor inner 26. Thus, the ease of coupling operation at the time of assembly is excellent also in terms of this point. Even when such a coupling structure is employed, the sun gear 41 is only required to rotate together with the rotor inner 26 before reduction in speed, and hence the torque transmission performance required between the sun gear 41 and the rotor inner 26 can be sufficiently secured. Further, the rotor inner 26 and the son gear 41 are coupled to each other at a position directly below the rolling bearing 27 configured to support the rotor inner 26. Thus, the rotation accuracy of the sun gear 41 is also excellent.
With the planetary gear speed reducer 10 having the configuration described above, the rotary motion of the rotor 24 (rotor inner 26) of the motor 25 is reduced in speed and transmitted to the nut member 32. With this action, rotation torque can be increased. Thus, the motor 25 having a small size can be employed.
As illustrated in
Next, with reference to
As illustrated in
The terminal part D (terminal main body 50) holds an electrical component such as a power supply circuit for supplying drive power to the motor 25. The power supply circuit is formed by connecting the coil 23c of the stator 23 to terminals 51a of the bus bar 51 for respective phases of a U-phase, a V-phase, and a W-phase as illustrated in
As illustrated in
A procedure of assembling the electric actuator 1 having the above-mentioned configuration is briefly described. First, the ring gear 40 of the first actuator unit 3 is assembled to the casing 20 (see
Then, a subassembly (see
After that, of a subassembly (see
In the electric actuator 1 (respective actuator units 3 and 4) described above, the screw shafts 33 of the ball screw devices 31 forming the output members are formed into the hollow shapes having the through holes 33b extending in the axial direction. With such a configuration, the through hole 33b formed in the screw shaft 33 can be used as the portion that allows insertion of the operation part C mounted to the another screw shaft. Therefore, as in the electric actuator 1, in a case in which the first and second actuator units 3 and 4 each comprising the motor part A, the motion conversion mechanism part B, and the terminal part D are arrayed in the axial direction and are coaxially arranged, the electric actuator 1, which is compact while having the two output members independently operable and coaxially arranged, can be achieved through mounting the hollow operation part D (actuator head 39) to the screw shaft 33 of the first actuator unit 3, and inserting the operation part D (small-diameter shaft portion 91b of the flanged shaft member 91) mounted to the screw shaft 33 of the second actuator unit 4 through the through hole of the screw shaft 33 (and the actuator head 39).
Moreover, the housing 2 of the electric actuator 1 comprises the plurality of members coupled in the axial direction, and the terminal parts D holding the electrical components such as the power supply circuits are sandwiched by the members forming the housing 2 from both sides in the axial direction. That is, the electric actuator 1 of this embodiment employs such a sandwich, structure that the terminal main body 50 holding the electrical components for the first actuator unit 3 is sandwiched in the axial direction, by the casing 29 and the intermediate casing 80, and the terminal main body 50 holding the electrical components for the second actuator unit 4 is sandwiched in the axial direction by the intermediate casing 80 and the cover 29. With such a configuration, the motor part A can be brought into an operable state through coupling the members forming the housing 2 to one another hi the axial direction so as to assemble the housing 2.
In particular, when the opening portion 50c configured to cause the inside and the outside of the housing 2 to communicate with each other is formed in the tubular portion 50A of the terminal main body 50, the electric wires such as the lead line connected to the power supply circuit, and the signal line connected to the rotation angle detection sensor 53 can be drawn out to the radially outer side of the housing 2 through the opening portion 50c. In this case, a routing operation of the electric wires can be completed under a state in which the terminal part D exists alone. Thus, the complex routing operation of the electric wires does not need to be carried out in an assembly stage of the electric actuator 1 (housing 2). Therefore, even in the electric actuator 1 as that of this embodiment in which two output members are independently operable and coaxially arranged, the ease of assembly and the productivity can be increased, and the cost thereof can thus be reduced.
Moreover, in this embodiment, as illustrated in
Moreover, when the routing operation of the electric wires can be completed under the state in which the terminal main body 50 exists alone as described above, even when specifications of, for example, the motor 25 and the planetary gear speed reducer 10 are changed, the terminal main body 50 can be standardized as long as shapes of coupled, portions of members (the casing 20 and the intermediate casing 80) to be coupled to the terminal main body 50 remain the same. With this, series production of various types of the electric actuator 1 with standardized components can easily be achieved.
Moreover, through a combination of the downsizing of the motor part A (motor 25) achieved by providing the planetary gear speed reducer 10 in the motion conversion mechanism pan B and the overlap structure in the radial direction of the rotor inner 26, the cylindrical portion 43a of the planetary gear carrier 43, and the nut member 32, a radial dimension M (see
Moreover, the rotor inner 26 serving as the hollow rotary shaft comprises the inner raceway surface 27a of the rolling bearing 27 arranged adjacent to the end portion of the rotor core 24a on the one side in the axial direction, and the end portion on the one side in the axial direction is supported by the rolling bearing 27 so as to be rotatable. With such a structure, the rotor inner 26 can be downsized in the axial direction. In addition, in combination with the structure in which the rolling bearing 27 is arranged within the axial width of the nut member 32, both the actuator units 3 and 4, and the electric actuator 1 can be further downsized in the axial direction. With such a configuration, there can be achieved the electric actuator 1 that is excellent in mountability with respect to a device to be used, and can also contribute to downsizing of the device to be used.
Further, as long as the rotation of the rotor 24 is balanced, it is only required that the rolling bearings 27 and 30 configured to support the rotor inner 26 be capable of supporting a radial load as small as the own weight of the rotor 24. In this case, it is not required that the rotor inner 26 integrally having the inner raceway surface 27a of the rolling bearing 27 be made of a material having a high strength. A required strength can be secured even when the rotor inner 26 is made of, for example, an inexpensive soft steel material for which thermal treatment such as quenching and tempering is omitted. In particular, in the electric actuator 1 (each of the actuator units 3 and 4) of this embodiment, the rotary motion of the motor 25 is transmitted to the nut member 32 through the planetary gear speed reducer 10. Thus, the radial load is not generated. Moreover, the reaction force (thrust load) generated along with the linear motion of the screw shaft 33 is directly supported by the needle roller bearing 47 arranged adjacent to the nut member 32 on the another side in the axial direction. Thus, it is only required that the rolling bearing 27 have a function of positioning in the radial direction, and hence the above-mentioned material specification is sufficient for the rotor inner 26 integrally having the inner raceway surface 27a of the rolling bearing 27. With this configuration, the electric actuator 1 can be reduced in cost.
Moreover, as described above, when the needle roller bearing 47 is configured to directly support the thrust load acting on the nut member 32, the action of the moment load on the ball screw device 31 (motion conversion mechanism part B) and on the rotor 24 of the motor 25 can be suppressed effectively. In particular, when the needle roller bearing 47 is arranged within the range in the axial direction between the rolling bearings 27 and 30 as in this embodiment, the effect of suppressing the moment load can be enhanced. When the moment load can be suppressed in this way, operation accuracy and durability life of the output member of the electric actuator 1 can be improved as well as the needle roller bearing 47 having a smaller size can be used.
The needle roller bearing 47 is arranged near a center portion in the axial direction between both of the rolling bearings 27 and 30 in this embodiment; and the effect of suppressing the moment load can thus be farther enhanced in this ease. Therefore, the downsizing of the needle roller bearing 47 can be further promoted. As a result, for example, the needle roller bearing 47 and the thrust receiving ring 46 having extremely small sixes can be employed. Consequently, the dimension in the axial direction of the electric actuator 1 can be prevented from increasing as much as possible.
Finally, of the electric actuator 1 having the above-mentioned configuration, an operation mode of the first actuator unit 3 is briefly described with reference to
First, for example, when an operation amount is input to an ECU provided at an upper position of the vehicle (not shown), the ECU calculates a requested pressure command value based on the operation amount. The pressure command value is transmitted to the controller 81 of the control device 80, and the controller 81 calculates a control signal of a motor rotation angle required in accordance with the pressure command value, and transmits the control signal to the motor 25.
When, the rotor 24 rotates based on the control signal transmitted from the controller 81, the rotary motion is transmitted to the motion conversion mechanism part B. Specifically, when the rotor 24 rotates, the sun gear 41 of the planetary gear speed reducer 10 coupled to the rotor inner 26 rotates. Along with this rotation, the planetary gears 42 revolve, and the planetary gear carrier 43 rotates. With this, the rotary motion of the rotor 24 is transmitted to the nut member 32 coupled to the cylindrical portion 43a of the planetary gear carrier 43. At this time, the revolving motion of the planetary gears 42 reduces the rotation number of the rotor 24, thereby increasing rotation torque transmitted to the not member 32.
When the nut member 32 rotates upon receiving the rotary motion of the rotor 24, the screw shaft 33 performs the linear motion in the axial direction (advances toward the one side in the axial direction) while being stopped in rotation. At this time, the screw shaft 33 advances to a position based on the control signal of the controller 81, and the actuator head 39 feed to the end portion of the screw shaft 33 on the one side in the axial direction operates an object to be operated (not shown).
An operation pressure of the screw shaft 33 (actuator head 39) is detected by the pressure sensor 83 installed outside, and a detection signal thereof is transmitted to a comparison portion 82 of the control device 80. Then, the comparison portion 82 calculates a difference between a detection, value detected by the pressure sensor 83 and the pressure command value, and the controller 81 transmits a control signal to the motor 25 based on the calculated value and the signal, transmitted from the rotation angle detection sensor 53. In such a manner, a position of the screw shaft 33 (actuator head 39) in the axial direction is subjected to feedback control. The power for driving the motor 25 and the sensor 53 is supplied from an external power supply (not shown), such as a battery provided on the vehicle, to the motor 25 through the control device 80 and the power supply circuit, held by the terminal portion D.
In the above, description is made of the electric actuator 1 (actuator units 3 and 4) according to one embodiment of the present invention. However, the present invention is not limited to the embodiment described above.
For example, in the above-mentioned embodiment, the ball screw device 31 is employed for the motion conversion mechanism part B, but the present invention can be applied to fee electric actuator employing a screw device in which the balls 34 and the deflectors 35 are omitted for the motion conversion mechanism part B. However, in consideration of operability and the like of the screw shaft 33, it is preferred that the ball screw device 31 be employed for the motion conversion mechanism part B.
Further, as the thrust bearing to be arranged adjacent to the nut member 32 on another side in the axial direction, a rolling bearing other than the needle roller bearing 47, for example, a cylindrical roller bearing can be employed. However, in consideration of ability to support the thrust load and the axial dimension of the bearing, the needle roller bearing 47 is preferred.
Moreover, although the planetary gear speed reducer 10 is provided in the motion conversion mechanism, part B in the above-mentioned embodiment, a speed reducer other than the planetary gear speed reducer 10 may be employed as the speed reducer.
Moreover, the speed reducer such as the planetary gear speed reducer 10 does not always need to be provided, and may be omitted when the speed reducer is not necessary. When the planetary gear speed reducer 10 is omitted, the rotor 24 (rotor inner 26) of the motor 25 and the nut member 32 of the ball screw device 31 may directly be coupled to each other in a torque transmittable manner. However, with such a configuration, it is necessary to employ members having different shapes for at least one of the rotor inner 26 and the nut member 32. Therefore, when the planetary gear speed reducer 10 is omitted, it is preferred that an intermediate member in a cylindrical shape be arranged between the inner peripheral surface 26d of the rotor inner 26 and the outer peripheral surface 32b of the nut member 32, and that an outer peripheral surface and an inner peripheral surface of the intermediate member be coupled respectively to the inner peripheral surface 26d of the rotor inner 26 and the outer peripheral surface 32b of the nut member 32 in a torque transmittable manner (not shown). As a result, even when the planetary gear speed reducer 10 is omitted, at least one of the motor part A (motor 25) and the ball screw device 31 can be a standardized component, and an increase in cost can thus be suppressed.
Moreover, for example, as illustrated in
With such a configuration, the screw shad 33 can always be urged toward the another side (original point side) in the axial direction by a spring force of the compression coil spring 48 under a state in which the motion conversion mechanism part B is accommodated in the inner periphery of the housing 2. In this case, there is an advantage in that, for example, when drive power is not appropriately supplied to tire motor 25, the screw shaft 33 can automatically be returned to the original point, thereby being capable of reducing a risk of adverse effect exerted to the operation of an object to be operated (not shown) as much as possible. Moreover, when the compression coil spring 48 is provided in the above-mentioned mode, a preload can be applied to the nut member 32 in the axial direction. As a result, a response lag caused by an operating internal clearance generally formed between the nut member 32 and the screw shaft 33 can be eliminated, thereby being capable of increasing the operability of the screw shaft 33.
Moreover, although the above-mentioned electric actuator 1 is formed through arraying in the axial direction and coaxially arranging the first and second actuator units 3 and 4 having the same configurations/structures in the motor part A, the motion conversion mechanism part B, and the terminal part D. However, both the actuator units 3 and 4 may have different configurations/structures in the motor part A and the like without departing from the spirit of the present invention.
Further, the present invention may be applied to a case in which three or more actuator units each comprising the motor part A, the motion conversion mechanism part B, and the terminal part D are arrayed in the axial direction and arranged coaxially.
The present invention is not limited to the above-mentioned embodiments. As a matter of course, the present invention may be carried out in various modes without departing from the spirit of the present invention. The scope of the present invention is defined in claims, and encompasses equivalents described in claims and all changes within the scope of claims.
1 electric actuator
2 housing
3 first actuator unit
4 second actuator unit
10 planetary gear speed, reducer (speed, reducer)
20 casing
23 stator
24 rotor
25 motor
26 rotor inner (hollow rotary shaft)
29 cover
31 ball screw device
32 nut member
33 screw shaft
33
b through hole
34 ball
39 actuator head (operation part)
47 needle roller bearing (thrust bearing)
50 terminal main body
50A tubular portion
50B disc-shaped portion
50c opening portion
80 intermediate casing
91 flanged shaft member (operation part)
A motor part
B motion conversion mechanism part
C operation part.
D terminal part
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-061626 | Mar 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/009524 | 3/9/2017 | WO | 00 |
