JP3850180B2 - Rack and pinion type electric power steering system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rack and pinion type electric power steering apparatus that applies a steering assist force by a motor.
[0002]
[Prior art]
An input shaft that rotates by steering, a pinion that is connected to the input shaft via an intermediate shaft, a rack that meshes with the pinion, a motor for generating a steering assist force, and a deceleration that decelerates the output shaft rotation speed of the motor 2. Description of the Related Art Conventionally, an electric power steering device that includes a mechanism, transmits rotation of an input shaft by steering to a pinion via an intermediate shaft, and changes a steering angle of a vehicle by moving a rack has been used.
[0003]
[Problems to be solved by the invention]
Since the rotation of the output shaft of the steering assist force generating motor is transmitted to the intermediate shaft, if the motor output is increased to obtain a large steering assist force, the strength of the pinion is reduced.
[0004]
An object of the present invention is to provide a rack and pinion type electric power steering apparatus that can solve the above-described problems.
[0005]
[Means for Solving the Problems]
In the rack and pinion type electric power steering apparatus of the present invention, an input shaft that is rotated by steering, an intermediate shaft that is connected to the input shaft via a speed increasing mechanism, a pinion that is connected to the intermediate shaft, and the pinion , A motor for generating a steering assist force, and a speed reduction mechanism for reducing the output shaft rotation speed of the motor, and the output shaft rotation of the motor is transmitted from the speed reduction mechanism via the speed increase mechanism. is transmitted to the intermediate shaft, the intermediate shaft rotation is transmitted to the pinion steering angle of the vehicle by the rack to move you change.
According to the configuration of the present invention, since the rotational speed of the input shaft is increased by the speed increasing mechanism, a constant steering angle change is performed with a constant steering amount as compared with the case where such a speed increasing mechanism does not exist. The number of pinion teeth necessary for obtaining can be reduced. Thereby, since it can design so that the intensity | strength of a pinion can improve, it becomes possible to enlarge the output of a motor and to obtain sufficient steering assistance force. Further, the torque applied to the intermediate shaft can be reduced by connecting the output shaft of the motor to the input side of the speed increasing mechanism.
[0006]
In rack and pinion type electric power steering apparatus of the present invention, the speed increasing mechanism includes a coupling shaft that is elastically relatively rotatably coupled to the input shaft, the connecting shaft and the input shaft is a coaxial The rotation of the output shaft of the motor is transmitted to the connecting shaft via the speed reduction mechanism, and a torque sensor is provided for detecting a steering torque in accordance with the relative rotation of the input shaft and the connecting shaft. A first shaft portion disposed coaxially with the connecting shaft; and a second shaft portion connected to the first shaft portion via a universal joint, the second shaft portion being connected to the first shaft portion via a universal joint. coupled to the pinion, generating steering assist force of the motor in accordance with the detected torque by the torque sensor that are controlled.
Thereby, since the input shaft, the connecting shaft, and the first shaft portion of the intermediate shaft can be arranged coaxially, the apparatus can be made compact.
[0007]
In the rack and pinion type electric power steering apparatus according to the present invention, the speed reduction mechanism includes a first gear provided coaxially with the connecting shaft, and a second gear meshed with the first gear. second gear is driven by the motor, the speed increasing mechanism, Ru is disposed radially inward of the first gear.
Thereby, the device can be made more compact by disposing the speed increasing mechanism in the radially inward region of the first gear.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A rack and pinion type electric power steering apparatus 1 shown in FIGS. 1 to 3 includes an input shaft 3 that is rotated by steering by a steering wheel 2, an intermediate shaft 5 that is coupled to the input shaft 3 via a speed increasing mechanism 4, A pinion 6 connected to the intermediate shaft 5, a rack 7 meshing with the pinion 6, and an electric motor 8 for generating a steering assist force are provided. Wheels are connected to the rack 7 via tie rods, knuckle arms, or the like. Thereby, the rotation of the input shaft 3 by steering is transmitted to the intermediate shaft 5, and the rotation of the intermediate shaft 5 is transmitted to the pinion 6 so that the rack 7 moves, thereby changing the steering angle of the vehicle.
[0009]
The speed increasing mechanism 4 has a connecting shaft 11 that is elastically connected to the input shaft 3 in a relatively rotatable manner. The input shaft 3 and the connecting shaft 11 are arranged coaxially. The input shaft 3 is supported by the inner periphery of a recess formed at one end of the connecting shaft 11 so as to be relatively rotatable via a bush 25. A torsion bar 23 is inserted into the input shaft 3 and the connecting shaft 11 as an elastic member. One end of the torsion bar 23 is connected to the input shaft 3 by a pin 22, and the other end is connected to the connection shaft 11 by a serration 24. As a result, the input shaft 3 and the connecting shaft 11 are elastically rotatable relative to the steering torque.
[0010]
A torque sensor 20 that detects a steering torque according to the relative rotation of the input shaft 3 and the connecting shaft 11 is provided. The torque sensor 20 includes a housing 21 attached to the vehicle body, first and second detection coils 33 and 34 held by the housing 21, and a first detection made of a magnetic material fixed to the outer periphery of the input shaft 3. It has the ring 36 and the 2nd detection ring 37 made from a magnetic material fixed to the outer periphery of the connecting shaft 11. The input shaft 3 is supported by the housing 21 via bearings 26 and 27. The one end surface of the first detection ring 36 and the one end surface of the second detection ring 37 are arranged so as to face each other, and teeth 36a, 37a are provided along the circumferential direction on the opposite end surfaces of the detection rings 36, 37, respectively. A plurality are provided. The other end side of the first detection ring 36 is a small diameter portion 36b having a smaller outer diameter than the one end side. The first detection coil 33 is disposed so as to cover the space between the first detection ring 36 and the second detection ring 37 facing each other. The second detection coil 34 is disposed so as to cover the first detection ring 36. Each of the detection coils 33 and 34 is connected to a printed circuit board 41 attached to the housing 21 by wiring.
A signal processing circuit shown in FIG. 4 is formed on the printed circuit board 41. That is, the first detection coil 33 is connected to the oscillator 46 through the resistor 45, the second detection coil 34 is connected to the oscillator 46 through the resistor 47, and each of the detection coils 33 and 34 is connected to the differential amplifier circuit 48. Is done. Thereby, when the torsion bar 23 is twisted according to the steering torque and the first detection ring 36 and the second detection ring 37 are relatively rotated, the opposing areas of the teeth 36a and 37a of the detection rings 36 and 37 change. Due to the change in area, the magnetic resistance to the magnetic flux generated by the first detection coil 33 between the teeth 36a and 37a is changed. The output of the first detection coil 33 changes according to the change in the magnetic resistance, and the transmission torque corresponding to the output is detected. The second detection coil 34 faces the small diameter portion 36 b of the first detection ring 36. The outer diameter of the small-diameter portion 36b is set so that the magnetic resistance with respect to the magnetic flux generated by the second detection coil 34 and the magnetic resistance with respect to the magnetic flux generated by the first detection coil 33 are equal in a state where the steering resistance is not acting. ing. Thereby, the output fluctuation of the first detection coil 33 due to the temperature fluctuation is equal to the output fluctuation of the second detection coil 34 due to the temperature fluctuation, so that it is canceled out by the differential amplifier circuit 48, and the fluctuation of the detected value of the transmission torque due to the temperature. Compensated.
[0011]
The intermediate shaft 5 has a first shaft portion 5 a disposed coaxially with the connection shaft 11, and a second shaft portion 5 b connected to the first shaft portion 5 a via a universal joint 12. The first shaft portion 5 a is rotatably supported via bearings 13 and 14 by the inner periphery of a recess formed at the other end of the connecting shaft 11. The second shaft portion 5 b is connected to the pinion 6 via the universal joint 15.
[0012]
The speed increasing mechanism 4 is constituted by a traction drive mechanism in the present embodiment. That is, a plurality of planetary rollers 16 are arranged between the inner periphery of the connecting shaft 11 and the outer periphery of the first shaft portion 5 a of the intermediate shaft 5. Each planetary roller 16 is rotatably supported by the connecting shaft 11. Thereby, the planetary roller 16 revolves around the first shaft portion 5a of the intermediate shaft 5 by the rotation of the connecting shaft 11, and the planetary roller 16 is caused by friction between the planetary roller 16, the connecting shaft 11, and the first shaft portion 5a. And the intermediate shaft 5 rotate, the rotation of the connecting shaft 11 is increased and transmitted to the intermediate shaft 5.
[0013]
The rotation of the output shaft of the motor 8 for generating the steering assist force is transmitted to the intermediate shaft 5 through the speed increasing mechanism 4 from the speed reduction mechanism 9 that decelerates the output shaft rotation speed of the motor 8. That is, the speed reduction mechanism 9 has a worm wheel (first gear) 9a provided coaxially with the connecting shaft 11 and a worm (second gear) 9b meshed with the worm wheel 9a. The worm wheel 9a is fixed, for example, by being press-fitted into the outer periphery of the connecting shaft 11, and the speed increasing mechanism 4 is disposed radially inward of the worm wheel 9a. The worm 9 b is supported by the housing 21 via bearings 28 and 29, and is connected to the output shaft 8 a of the motor 8 via the coupling 30. As a result, the worm 9 b is rotationally driven by the motor 8, the output shaft rotation of the motor 8 is transmitted to the connecting shaft 11 via the speed reduction mechanism 9, and the steering assist force generated by the motor 8 is transmitted via the intermediate shaft 5. To the rack 7.
[0014]
The generated steering assist force of the motor 8 is controlled according to the torque detected by the torque sensor 20. That is, a signal corresponding to the steering torque output from the differential amplifier circuit 48 is sent to a control device outside the figure, and the motor 8 is controlled by the control device.
[0015]
According to the above configuration, the rotational speed of the input shaft 3 is increased by the speed increasing mechanism 4, and therefore, a constant steering angle change with a constant steering amount compared to the case where such a speed increasing mechanism 4 does not exist. The number of teeth of the pinion 6 necessary for obtaining Thereby, since it can design so that the intensity | strength of the pinion 6 may improve, it becomes possible to enlarge the output of the motor 8 and to obtain sufficient steering assistance force. Further, the torque applied to the intermediate shaft 5 can be reduced by connecting the output shaft of the motor 8 to the input side of the speed increasing mechanism 4. Moreover, since the input shaft 3, the connecting shaft 11, and the first shaft portion 5a of the intermediate shaft 5 can be arranged coaxially, the device 1 can be made compact. Furthermore, by arranging the speed increasing mechanism 4 in the radially inner region of the worm wheel 9a of the speed reducing mechanism 9, the device 1 can be made more compact.
[0016]
The present invention is not limited to the above embodiment. For example, the speed increasing mechanism 4 only needs to increase the rotational speed of the input shaft 3 and transmit it to the intermediate shaft 5, and a planetary gear mechanism or the like may be employed instead of the traction drive mechanism. Further, instead of the worm and the worm wheel, for example, another gear such as a bevel gear or a hypoid gear may be employed as the speed reduction mechanism 9.
[0017]
【The invention's effect】
According to the present invention, it is possible to provide a rack and pinion type electric power steering apparatus capable of achieving a high output of a steering assist force generating motor with a compact structure.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of an electric power steering apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 4 is an explanatory diagram of a circuit configuration of a torque sensor of the electric power steering apparatus according to the embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Rack and pinion type electric power steering device 3 Input shaft 4 Speed increasing mechanism 5 Intermediate shaft 5a First shaft portion 5b Second shaft portion 6 Pinion 7 Rack 8 Motor 9a Worm wheel (first gear)
9b Worm (second gear)
11 Connection shaft 12, 15 Universal joint 20 Torque sensor

Claims (1)

An input shaft that rotates by steering;
An intermediate shaft coupled to the input shaft via a speed increasing mechanism;
A pinion connected to the intermediate shaft;
A rack meshing with the pinion,
A motor for generating steering assist force;
A reduction mechanism that decelerates the output shaft rotation speed of the motor,
The output shaft rotation of the motor is transmitted from the deceleration mechanism to the intermediate shaft via the speed increasing mechanism,
A rack and pinion type electric power steering device in which the rotation angle of the intermediate shaft is transmitted to the pinion and the rudder angle of the vehicle changes as the rack moves ,
The speed increasing mechanism has a connecting shaft that is elastically connected to the input shaft in a relatively rotatable manner,
The input shaft and the connecting shaft are coaxial.
The output shaft rotation of the motor is transmitted to the connecting shaft through the speed reduction mechanism,
A torque sensor for detecting a steering torque according to the relative rotation of the input shaft and the connecting shaft;
The intermediate shaft has a first shaft portion arranged coaxially with the connecting shaft, and a second shaft portion connected to the first shaft portion via a universal joint, and the second shaft portion is Connected to the pinion through a universal joint,
The generated steering assist force of the motor is controlled according to the torque detected by the torque sensor,
The speed reduction mechanism has a first gear provided coaxially with the connecting shaft, and a second gear meshed with the first gear, and the second gear is driven by the motor,
The rack and pinion type electric power steering apparatus is characterized in that the speed increasing mechanism is disposed radially inward of the first gear .

Images