JP4520804B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus provided with an electric motor and a speed reducer coaxially with a rack shaft.

  Conventionally, a so-called coaxial electric power steering device in which an electric motor and a speed reducer are arranged coaxially with a rack shaft is disclosed as shown in Patent Document 1 and Patent Document 2, respectively.

  This type of power steering device transmits the rotation of the steering wheel to the rack shaft via the input shaft and pinion shaft, and steers the left and right front wheels via tie rods connected to both ends of the rack shaft. The steering torque applied to the steering wheel is detected by a torque sensor, an electric motor arranged on the rack shaft is driven based on the detected torque, and the output torque of the electric motor is amplified by a speed reducer to The steering force is assisted by transmitting to the rack shaft via

By the way, the electric power steering device having a configuration in which an assisting electric motor and a speed reducer are arranged around the rack shaft is compactly arranged around the rack shaft, so that it can be easily mounted on a vehicle, and the motor is driven by the speed reducer. Since the output can be greatly amplified, an electric motor with a small capacity can be used, and the performance is excellent.
Japanese Patent Laid-Open No. 11-115779 JP 2003-137108 A

  However, the assist force required for a vehicle differs depending on the type of vehicle, for example, a sports car and a normal vehicle, or a normal vehicle and a light vehicle, and the required range is very wide. Accordingly, there has not yet been proposed a device that can maintain the basic output performance and satisfy the reliability and compactness at the same time.

  The electric power steering device shown in Patent Document 1 is configured to amplify the output of an electric motor using a flexure-meshing type reduction device, a so-called harmonic drive type reduction device as a reduction device, and is excellent in high output and compactness. ing. However, the speed reduction device described in Patent Document 1 has a problem in durability reliability because it is a flexure meshing type.

  That is, the speed reducer receives not only the force from the electric motor but also the reaction force from the wheels. For example, when riding on a curbstone, the reaction force is extremely large. Therefore, the flexible external gear, which is a basic component of the flexure meshing reduction gear, becomes a bottleneck against an excessive reaction force and has not yet been put into practical use.

  Further, the flexure-meshing type reduction gear is essentially a high reduction type, and is not suitable as a reduction gear with a medium / reduction speed ratio. In other words, in the flexure meshing reduction gear, the reduction gear ratio is determined by the difference in the number of teeth between the flexible external gear and the rigid internal gear meshing therewith. When the number difference is 1, the maximum reduction ratio is obtained. In order to reduce the reduction ratio, it is necessary to increase the difference in the number of teeth between the flexible external gear and the rigid internal gear. However, the short axis of the elliptical wave generator is reduced as the difference in the number of teeth is increased. Accordingly, the amount of flexure of the flexible external gear is increased and the durability becomes more severe.

  Therefore, the flexure-meshing type reduction gear shown in Patent Document 1 can provide a high reduction ratio, but the degree of freedom in setting the reduction ratio is narrow, and the durability of an electric power steering device in which a high load repeatedly acts is also high. Issues remain and reliability has not been established.

  Further, the power steering device disclosed in Patent Document 2 uses a planetary gear type reduction device as a reduction gear, fixes a sun gear to an input shaft that receives the output of an electric motor, and takes out the output from a carrier or ring gear that supports the pinion gear. It is configured as follows.

  In this system, the reduction ratio is basically governed by the ratio of the number of teeth between the sun gear and the ring gear, that is, the ratio of the pitch circle. In order to obtain a high reduction ratio, it is necessary to reduce the sun gear diameter and increase the ring gear diameter. When the diameter of the sun gear is reduced, it is necessary to reduce the shaft diameter of the input shaft, and it becomes difficult to insert the rack shaft radially inward. In order to insert the rack shaft, it is necessary to increase the diameter of the sun gear, and accordingly, the diameter of the ring gear also increases, and the compactness, which is the greatest advantage of the coaxial power steering device, is impaired, and the vehicle is limited. When laying out in an open space, great difficulty is involved. In order to ensure the compactness in the radial direction and the required high reduction ratio, it can be ensured by arranging a plurality of planetary gear mechanisms in the axial direction, but the structure becomes complicated and this is not practical.

  The present invention has been made in view of such points, and in a coaxial electric power steering device in which an electric motor and a speed reducer are coaxially arranged with respect to a rack shaft, radial and axial compactness can be secured, An object of the present invention is to obtain an electric power steering device that is excellent in mountability to a vehicle, has a wide degree of freedom in setting a reduction ratio, and is excellent in durability against a high reaction force from a wheel accompanying kickback.

The means according to claim 1 of the present invention for solving the above problems is an electric power steering apparatus comprising an electric motor coaxially around a rack shaft and a speed reducer for reducing the rotation of the electric motor. And
The speed reducer includes an input shaft driven by the electric motor, a rotating body rotatably supported at an inclined portion formed on the outer periphery or inner periphery of the input shaft, and a feed screw mechanism with respect to the rack shaft. A second output gear having a number of teeth n2 meshing with a first gear having a number of teeth n1 fixed to the housing, and the number of teeth formed on the output shaft. A third gear with n3 teeth meshing with the fourth gear of n4 is formed, and is configured as an oscillating speed reducer that changes the meshing position between the gears while the rotor rotates by the rotation of the input shaft. ,
The speed reducer and the electric motor are arranged coaxially with a rack shaft, and are arranged so as to overlap in the radial direction .

In the present invention, a so-called oscillating speed reducer that decelerates by a oscillating motion of a rotating body supported on an inclined portion of an input shaft is arranged coaxially with a rack shaft. By utilizing the unique features organically, it is possible to ensure compactness as a feature of the coaxial electric power steering device and also to ensure high durability against high reaction force from the wheel side. Moreover, since the degree of freedom in setting the reduction ratio can be increased without impairing the compactness in the radial direction and the axial direction, it can be applied to various vehicles having different steering characteristics and is highly useful .

Moreover, the above-mentioned reduction gear and the electric motor arranged rack shaft coaxially with, yet so arranged so as to overlap both radially without compromising unnecessarily the radial compactness, the axial compactness Greatly contributes to

According to a second aspect of the present invention , in the first aspect , the input shaft of the speed reducer is linked with the rotor of the electric motor on the outer periphery, and rotatably supports the rotating body at an inclined portion formed on the inner peripheral side. It is comprised as follows. According to this configuration, in addition to contributing to the downsizing in the axial direction, the linkage structure with respect to the rack shaft can be greatly simplified. That is, according to the above configuration, since a large-diameter through space can be secured on the inner peripheral side of the rotating body without being restricted by the input shaft, the required diameter of the through space may be limited by the input shaft. In addition, the output shaft and the large-diameter rack shaft can be arranged, and the cooperation structure can be simplified.

  Since the electric power steering device of the present invention is configured as described above, it is possible to ensure compactness as a feature of the coaxial electric power steering device and also to ensure high durability against high reaction force from the wheel side. . Moreover, since the degree of freedom in setting the reduction ratio can be increased without impairing the compactness in the radial direction and the axial direction, it can be applied to various vehicles having different steering characteristics and is highly useful.

First, a reference example having a configuration similar to that of the embodiment of the present invention will be described with reference to FIGS. 1 and 2, and then the examples will be described . In the reference example shown in FIGS. 1 and 2, reference numeral 10 denotes a housing, and rack shafts 11 that are linked to tie rods (not shown) that are linked to wheels at both ends of the housing 10 are disposed therethrough. The rack shaft 11 is linked with a pinion shaft 12 that transmits an operation torque of a steering handle (not shown) at a predetermined angle. In the housing 10, an electric motor 13 and a speed reducer 14 are arranged coaxially with respect to the rack shaft 11.

  The electric motor 13 includes a stator 15 and a rotor 16. The stator 15 is fixed to the inner periphery of the housing 10. The rotor 16 is a hollow motor output shaft that is rotatably supported by the housing 10 via a bearing as a bearing member. It is fixed to 17 integrally.

  The speed reducer 14 includes an input shaft 18, a rotating body 19, and an output shaft 20. The input shaft 18 is configured as a part of the motor output shaft 17 and transmits the output torque of the electric motor 13 to the rotating body 19. Further, on the outer periphery of the input shaft 18, an inclined portion 21 of an axis Y that is inclined by a predetermined angle with respect to the axis X of the input shaft 18 is formed. It is supported rotatably via.

  The rotating body 19 includes an inner ring 23 and an outer ring 24, and a ball 22 is interposed therebetween. The inner ring 23 is fixed to the outer periphery of the inclined portion 21 of the input shaft 18. A second gear A2 that meshes with the first gear A1 fixed to the housing 10 on one side is formed on the axial end surface of the outer ring 24, and a third gear that meshes with the fourth gear A4 fixed to the output shaft 20 on the other side. A gear A3 is formed. These first to fourth gears A1 to A4 are formed as bevel gears, and a roller 26 is interposed between the meshing portion of the first gear A1 and the second gear A2 and the meshing portion of the third gear A3 and the fourth gear A4. Has been. The tooth profile of each gear is formed in a concave shape that fits the roller 26. The roller 26 is disposed on the first gear A1 and the fourth gear A4 side, the first and fourth gears are formed as convex teeth with the roller 26 located in the recess, and the second and third gears are It is configured as a concave tooth that meshes with the convex tooth.

  The output shaft 20 includes a large-diameter portion 27 in which a fourth gear A4 is formed on the end surface, and a small-diameter portion 28 that is rotatably supported on the gear housing 10 via a bearing as a bearing member. A feed nut 29 is formed on the inner periphery of the small diameter portion 28, and the feed nut 29 is engaged with the feed screw portion 31 of the rack shaft 11 via a ball 30. The feed nut 29, the ball 30 and the feed screw portion 31 of the rack shaft constitute a ball screw mechanism, and the rotary motion of the output shaft 20 is converted into a linear motion by this ball screw mechanism.

  32 is an encoder as a rotation sensor that detects the rotation angle of the input shaft 18, 33 and 34 are thrust sensors as stress sensors that detect the thrust of the left and right wheels, and 35 is a torque sensor provided on the pinion shaft. It is a handle sensor. A control device 36 controls the electric power steering device, and includes an interface 37 that performs signal processing from each of the sensors, a CPU 38 that performs various calculations in response to the control signals, and a driver 39. The control device 36 is configured to control the output of the electric motor, that is, the assist force based on the torque of the handle sensor 35, the difference between the left and right thrusts, and the like.

Is configured electrostatic power steering apparatus having the above operates as follows.

  When the driver operates the steering handle, the operation torque is transmitted to the wheels via the pinion shaft 12, the rack shaft 11, and the tie rod. At this time, when the operation torque is detected by the handle sensor 35 provided on the pinion shaft 12, the detection signal is output to the control device 36, and the electric motor 13 is operated by a command from the CPU 38 of the control device 36. The electric motor 13 operates at a predetermined current value, and its output is transmitted to the input shaft 18 of the speed reducer 14, and the motor output is greatly amplified by the speed reducing action of the speed reducer 14, that is, the torque amplifying action. It is transmitted to the rack shaft 11. Therefore, the rack shaft 11 is given a predetermined assist force from the electric power steering device, and the driver can give a necessary operation angle with a light operation force. In this case, since the output of the electric motor 13 is greatly amplified by the speed reducing action of the speed reducer 14, a small capacity electric motor may be used.

Hereinafter, the basic operation of the rocking type reduction gear 13 that involved in the present invention (basic principle) will be described in detail.
When the input shaft 18 rotates, the inclined portion 21 swings, that is, swings around the head, and the rotating body 19 pivotally supported by the tilting portion 21 swings as if just before stopping. The rotating body 19 swings to mesh the second gear A2 with the first gear A1 and the third gear A3 in the week direction of the fourth gear A4. Then, the second gear A2 rotates with respect to the first gear A1 by an amount corresponding to the difference in the number of teeth from the first gear A1 per one cycle of swinging motion (one rotation of the input shaft 1). That is, one-stage deceleration is performed between the first gear A1 and the second gear A2.

  Consider the case where the number of teeth of the first gear A1 is 99 and the number of teeth of the second gear A2 is 100. When the input shaft 1 rotates forward once, the second gear A2 rotates forward by 1/100 with respect to the first gear A1. The movement of the second gear A2 is directly transmitted to the third gear A3, and the same meshing is performed between the third gear A3 and the fourth gear A4. In this case, assuming that the number of teeth of the third gear A3 is 101 and the number of teeth of the fourth gear A4 is 100, the fourth gear A4 rotates reversely by 1/100 with respect to the third gear A3. Therefore, one-stage deceleration is also performed between the third gear A3 and the fourth gear A4. That is, when the rotational motion of the input shaft 18 is transmitted to the output shaft 20, two-stage deceleration is performed between the first and second gears A1 and A2 and between the third and fourth gears A3 and A4. Will be affected.

R = 1− (n1 × n3) / (n2 × n4) (i) where R is the reduction ratio of the oscillating speed reducer and R is the number of rotations of the output shaft 20 when the input shaft 18 makes one rotation. )
Where n1 is the number of teeth of the first gear A1, n2 is the number of teeth of the second gear A2, n3 is the number of teeth of the third gear A3, and n4 is the number of teeth of the fourth gear A4. If n1 = 999, n2 = 1000, n3 = 1001, and n4 = 1000, the reduction ratio R = 1 / 1,000,000 (forward rotation).

  Further, when the second gear A2 and the third gear A3 are engaged with the first gear A1 and the fourth gear A4 while oscillating, the sliding surface is slid on the meshing surface as long as the meshing between the fixed teeth. Is produced. In order to prevent seizure due to noise, vibration and heat generated by the sliding, the roller 26 is interposed in the meshing portion of each gear as described above. Therefore, as shown in FIG. 4, when the rotating body 19 swings in the circumferential direction, the meshing position of the first gear A1 and the second gear A2 (meshing position of the third gear A3 and the fourth gear) is It moves in the direction and meshes each concave tooth and convex tooth. The sliding that occurs between the concave teeth and the convex teeth is absorbed by the rotation of the rollers 26. Therefore, not only the setting of the backlash is unnecessary, but also a precise engagement can be performed by applying a preload between the gears.

  As described above, when the difference between the number of teeth of the first gear A1 and the number of teeth of the second gear A2 is 1, when the oscillating motion advances by one cycle, the distance between the first gear A1 and the second gear A2 Thus, the teeth that mesh are shifted by one. Further, when the difference in the number of teeth is 2, when the oscillating motion advances by one period, the meshing teeth are shifted by two between the first gear A1 and the second gear A2. Similarly, when the difference in the number of teeth is n, the meshing teeth are shifted by n. This also applies to the relationship between the third and fourth gears A3 and A4 (in addition, the details of this type of reduction gear are described in Japanese Patent Publication No. 7-56324 by the inventor of the present invention. ing).

  As described above, the oscillating speed reducer 14 according to the present invention can transmit a large torque for its size, and the setting of the reduction ratio is not limited to the high reduction ratio, and Since it is possible to arbitrarily set from high reduction ratio to reduction speed ratio by changing the number of teeth and changing the module without changing the outer diameter, the assist characteristics without impairing the mountability of the electric power steering device on the vehicle The freedom of setting is greatly expanded. Since this oscillating speed reducer is composed of four rigid gears, it is highly durable against high reaction forces from the wheels, and the reliability as an electric power steering device can be greatly enhanced. In addition, since the shaft portion of the rotating body 19 can secure a large-diameter through hole radially inward without being directly affected by the reduction ratio, a rack shaft or the like directly linked to the input / output shaft and the output shaft can be secured. The degree of freedom in designing related parts is greatly improved.

Next, based on FIG. 3, it described real施例of the present invention. Parts that are the same as or equivalent to those in the reference example described above are given the same reference numerals, and detailed descriptions thereof are omitted.
The electric power steering device of the actual施例has a feature that the two are disposed so as to overlap in the radial direction together with the electric motor 13 and speed reducer 14 are coaxially arranged with respect to the rack shaft 11 To do.

  Specifically, the speed reducer 14 includes an input shaft 18 supported via a bearing with respect to the inner peripheral surface of the housing 10, a rotating body 19 supported on the inner periphery of the input shaft 18, and an output shaft 20. With.

  The input shaft 18 is configured as a hollow shaft, is supported concentrically with the rack shaft 11, and an inclined portion having an axial center Y inclined at a predetermined angle with respect to the axial center X of the input shaft 18 on the inner peripheral surface thereof 21. A rotating body 19 is rotatably supported on the inclined portion 21 of the input shaft 18 via balls 22 and 22 as bearing members.

Similar to the reference example, the rotating body 19 includes an inner ring 23 and an outer ring 24, and is the same in that a ball 22 is interposed therebetween, but the outer ring 24 is fixed to the inner peripheral surface of the input shaft 18, The difference is that second and third gears are formed on the end face on the inner ring side. Therefore, the rotating body 19 performs a swinging motion, that is, a swing motion, inward of the input shaft 18 in the radial direction. Further, a second gear A2 and a third gear A3 are formed on the end surface of the rotating body 19 in the axial direction. The second gear A2 meshes with the first gear A1 formed on the axial end surface of the sleeve 40 that is integrally fixed to the end wall of the housing 10 with a bolt, and the third gear A3 is integrated with the output shaft 20. Is configured to mesh with a fourth gear A4 formed on the axial end surface of the sleeve 41 fixed to the sleeve 41. A roller 26 is interposed in each meshing portion. In addition, a large-diameter through hole 42 penetrating in the axial direction is formed inward of the rotary body 19 in the radial direction and inward of the second and third gears A2, A3.

  The output shaft 20 is disposed through the through hole 42 of the rotating body 19 and is supported on the housing 10 via the bearing 43 at the end on the first gear side, and the bearing on the fourth gear side. And a large-diameter portion 46 supported by the housing 10 via 45. The small-diameter portion 44 and the large-diameter portion 46 are formed as separate members, and both are fixed to the inner peripheral end face of the sleeve 41 with bolts at the end flange portion on the fourth gear side of the small-diameter portion 44. Thus, they are joined together. Moreover, the continuous through-hole penetrated to an axial direction in the axial center part is formed in both. A feed nut 29 is formed in the through hole on the large-diameter portion side and meshes with the feed screw portion 31 of the rack shaft 11 via the ball 30, and the torque of the output shaft 20 is applied to the rack shaft 11 via this ball screw mechanism as an assist force. Is configured to communicate as. An encoder 47 as a rotation sensor that detects the rotation angle of the output shaft 20 is attached to the outer periphery of the small-diameter portion of the output shaft 20.

  The electric motor 13 that transmits the drive torque to the speed reducer 14 configured as described above is arranged so as to be coaxial with the rack shaft 11 and to be superimposed on the outside of the speed reducer 14 in the radial direction. The electric motor 13 is configured as a coreless motor, and includes a stator 15 and a rotor 16. The rotor 16 is press-fitted to the input shaft 18 of the speed reducer 14. Accordingly, the drive torque of the electric motor 13 is efficiently transmitted from the radially outer side to the inner side via the input shaft 18, the rotating body 19, and the output shaft 20 to the rack shaft 11.

The types of the electric motor 13 include a normal type in which a winding is wound around an iron core serving as a core, and a coreless motor in which the winding is solidified with resin and the core is omitted . In actual施例, it is configured to control the spread radial dimension of the electric power steering system by using a coreless motor. That is, the core of the coreless motor is literally omitted from the core of the stator, and the occupied space in the radial direction as the electric motor is compressed accordingly.

  Reference numeral 48 denotes a resolver as a rotation sensor that detects the rotation angle of the input shaft 18.

Above configured real施例of the electric power steering apparatus as is characterized as follows.

First, since the electric motor 13 and the speed reducer 14 are arranged coaxially with respect to the rack shaft 11 and at the same time arranged so as to overlap in the radial direction, the electric motor 13 as in the reference example. Compared to the case where the reduction gear 14 and the rack shaft 11 are provided in the axial direction, the dimension in the axial direction can be greatly shortened without unnecessarily increasing the dimension in the radial direction.

  In addition, since the input shaft 18 is positioned radially outward of the rotating body 19, the large-diameter through space of the rotating body 19 can be used as a dedicated space for the output shaft 20. In setting, the required diameter can be secured without being restricted by the input shaft 18, and the rack shaft 11 of the required diameter can be inserted and inserted into the shaft center portion, and the degree of freedom in designing peripheral related parts is increased. improves.

  Particularly, since the output shaft 20 can be disposed through the through hole 42 of the rotating body 19 and can be supported by the housing 10 at both ends thereof, the support rigidity of the output shaft 20 is improved.

(Other embodiments)
The present invention is not limited to the above reference examples and examples , and various modifications can be made without departing from the gist of the present invention.

In the above reference examples and examples, the deceleration action by the reduction gear has been described for the example of two-stage deceleration, but the first to fourth gears are set by the number of teeth, the inclination angle between the inclined portion and the input shaft is set to the first Also, it can be limited to a one-stage deceleration action between the second gears, and can be arbitrarily set as required.

In the above reference examples and examples, but the rotating member is constituted by an inner ring and an outer ring, omit the inner ring (in reference example) or an outer ring which is fixed at the input shaft side (in the case of real施例) It is also possible to configure so that the ball is directly supported by the inclined portion.

Sectional drawing of the electric power steering apparatus concerning the reference example of this invention. FIG. 2 is an enlarged view of a main part of the electric power steering device shown in FIG. Main portion sectional view of an electric power steering apparatus according to the actual施例of the present invention. Explanatory drawing which shows the meshing part of the gear of the said reference example and an Example.

11 Rack axis
13 Electric motor
14 Reducer
18 Input shaft
19 Rotating body
20 Output shaft
21 Inclined part
29 Feed nut
31 Lead screw shaft
A1 1st gear
A2 Second gear
A3 3rd gear
A4 4th gear

Claims (2)

An electric power steering device comprising an electric motor and a reduction gear that decelerates rotation of the electric motor coaxially around the rack shaft,
The speed reducer includes an input shaft driven by the electric motor, a rotating body rotatably supported at an inclined portion formed on the outer periphery or inner periphery of the input shaft, and a feed screw mechanism with respect to the rack shaft. A second output gear having a number of teeth n2 meshing with a first gear having a number of teeth n1 fixed to the housing, and the number of teeth formed on the output shaft. A third gear with n3 teeth meshing with the fourth gear of n4 is formed, and is configured as an oscillating speed reducer that changes the meshing position between the gears while the rotor rotates by the rotation of the input shaft. ,
An electric power steering apparatus, wherein the speed reducer and the electric motor are arranged coaxially with a rack shaft and are arranged so as to overlap in the radial direction . The input shaft of the speed reducer is linked with the rotor of the electric motor at the outer periphery, and is configured to rotatably support the rotating body at an inclined portion formed on the inner periphery side. The electric power steering apparatus according to 1 .

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