JPH0891234A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE: To provide a motor driven power steering device which is assured of its necessary stiffness and assembling performance, and equipped with a torque detection means high in detection accuracy. CONSTITUTION: There is provided a motor driven power steering device which is made up of an output shaft 112 transmitting steering force for steering each wheel, an input shaft 102 connecting a steering wheel with the output shaft, a detection means 120 detecting steering force transmitted to the input shaft, a motor 111 which is driven in response to the result of detection by the detection means, and generates auxiliary steering force, and of a power transmission mechanism transmitting the auxiliary steering force of the motor to the output shaft. Therefore, the torque detection shaft section 108 of a magneto-striction type torque sensor 120 is larger in outer diameter that the input shaft 102, and moreover made hollow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device mounted on a vehicle or the like for assisting steering operation and reducing force required for steering.

[0002]

2. Description of the Related Art As an electric power steering device for a vehicle or the like, the rotational output of an electric motor, which is an auxiliary steering torque, is reduced by a gear device and transmitted to an output shaft of a steering mechanism to assist the steering force applied to a steering wheel. Then, there is known one configured to steer the wheels.
In such an electric power steering device,
A detection device for detecting the steering force transmitted to the input shaft is provided, and the electric motor is driven according to the detection result of the detection device to generate an auxiliary steering force.

In such an electric power steering device, a torque detecting device includes a housing, a sensor coil provided on the inner surface of the housing, and a torque detecting shaft portion which is inserted into the housing so as to face the sensor coil. It consists of Especially, in the magnetostrictive torque sensor,
In order to secure the detection accuracy, the distance between the sensor coil and the torque detection shaft portion is set to a predetermined minute gap.

[0004]

[Problems to be solved] By the way, a member used for a steering lock portion which is an input shaft is generally φ in order to secure strength.
Requires an outer diameter of 20 or more. Further, the steering lock portion needs to pass through the inner diameter of the sensor coil in order to assemble the device. Therefore, the inner diameter of the sensor coil must be larger than the steering lock portion. In a torque sensor (for example, disclosed in Japanese Patent Laid-Open No. 63-252487) that detects torque by utilizing the inverse effect of magnetostriction, an output is obtained according to the magnitude of the twist stress of the detection shaft.
Further, it is necessary to increase the torsional stress generated in the detection shaft in order to secure the detection accuracy.

However, if the inner diameter of the sensor coil is increased so that the steering lock portion can pass while reducing the outer diameter of the detection shaft in order to increase the torsional stress, the gap between the detection shaft and the sensor coil becomes large, which is sufficient. Excitation may be difficult and the required detection output may not be obtained. Further, if the outer diameter of the detection shaft is made too large in accordance with the steering lock portion, the torsional stress of the detection shaft decreases, and as a result, the necessary detection output cannot be obtained.

It is an object of the present invention to provide an electric power steering device that achieves both required rigidity and detection accuracy (sensitivity).

[0007]

In order to achieve the above object, an electric power steering apparatus according to the present invention is provided with an output shaft for transmitting a steering force for steering a wheel, and an input for connecting a steering wheel and the output shaft. Shaft, a detection device that detects the steering force transmitted to the input shaft, a motor that is driven according to the detection result of the detection device to generate an auxiliary steering force, and an auxiliary steering force of the motor that is output from the output shaft. In the electric power steering device including a power transmission mechanism that transmits the torque, the detection device is a magnetostrictive torque sensor, and the torque detection shaft portion of the torque sensor has an outer diameter larger than the outer diameter of the input shaft. It is characterized by being hollow and hollow.

[0007]

According to the electric power steering apparatus of the present invention, the outer diameter of the detection shaft portion is made larger than the outer diameter of the steering lock portion in order to obtain sufficient detection output while ensuring the assemblability. The gap between the inner diameter of the sensor coil and the inner diameter of the sensor coil can be minimized. Further, since the detection shaft portion is hollow, the torsional stress generated in the detection shaft portion can be increased, and a sufficient detection output can be obtained.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a partial axial cross-sectional view of an electric power steering apparatus 100 that is an embodiment of the present invention.

In FIG. 1, an electric power steering apparatus 100 includes a cylindrical upper column 103, a cylindrical lower column 107 fitted to one axial end of the upper column 103, and one axial end of the lower column 107. The combined torque detection device 120. An upper tube 104 having an upper shaft 102 fitted to one end thereof is inserted and attached to the upper column 103. Further, the lower column 10 is attached to the other end of the upper tube 104.
The lower shaft 106, which is attached to the No. 7, is fitted. The lower shaft 106 is fixed to the upper tube 104 by a fixing member 113 such as resin. Since the upper column 103 is fixed to a part of the vehicle body (not shown) by the bracket 101, the electric power steering device 100 is also fixed to the vehicle body. Further, the upper shaft 102 is connected to a steering wheel (not shown) via a mechanism (not shown), and the steering force of the steering wheel is transmitted. Upper column 103
A steering lock portion (key lock) 105 is provided on the upper tube 104.

The electric power steering device 100 is provided with a magnetostrictive torque sensor 120 as a detection device for detecting the torque of the shaft according to the steering force. The torque sensor 120 includes a housing 110, a sensor coil 109 provided on the inner peripheral surface of the housing 110, and a housing 11.
It is composed of a torque detection shaft portion 108 provided in the zero position. The outer peripheral surface of the torque detection shaft portion 108 faces the sensor coil 109 via a predetermined minute gap. Further, the torque detection shaft portion 108 is integrated with the output shaft 112 connected to the wheels via a link mechanism or the like (not shown). The torque detection shaft portion 108 has a hollow structure, and the lower shaft 106 is fitted to one end that is open.

Further, the sensor shaft portion 108 and the output shaft 112.
Are rotatably supported by bearings 113 and 114. An electric motor 111 is provided in the housing 110. The rotation of the electric motor 111 is transmitted through the gear device 115 such as a worm gear to the torque detection shaft unit 10.
8 is transmitted to the output shaft 112. The torque sensor 120 and the electric motor 114 are connected to a control device (not shown).

In the electric power steering apparatus 100 of the present invention having the above-described structure, the torque sensor 12
0 operates as follows. The steering force of a steering wheel (not shown) is applied to the upper shaft 10 which constitutes an input shaft.
2, transmitted to the torque detection shaft 108 of the torque sensor 120 as rotation through the upper tube 104 and the lower shaft 106. At this time, a torsion stress is generated in the torque detection shaft portion 108.

The torsional stress generated in the torque detecting shaft portion 108 is detected by a sensor coil 109 arranged so as to face the outer peripheral surface of the torque detecting shaft portion 108 through a minute gap, and the detection result is not shown. It is input to the control device in the form of an electrical signal. The drive signal from the controller is the electric motor 1
11, the electric motor 111 is driven to apply a necessary auxiliary steering force to the output shaft 112.

Here, the relationship between the outer diameters of the torque detecting shaft portion and the input shaft and the fact that the torque detecting shaft portion has a hollow structure will be considered in comparison with the conventional structure.
The principal stress τ ₀ generated by the torque T is Z _p , where the polar section coefficient is

[Equation 1] Therefore, the polar section coefficient Z _p is as follows for the hollow shaft and the solid shaft. Incidentally, d is the outer diameter of the solid shaft, d ₁ is the outer diameter of the hollow shaft, and nd ₁ is the inner diameter of the hollow shaft. However, 1>n> 0
Is.

[Equation 2] When the outer diameter necessary and sufficient for obtaining the necessary sensitivity on the solid axis is d ₀ , and the outer diameter required by the layout is d ₁ (d ₀ <d ₁ ), Z _p0 = Z _p1 So that n
The main stress τ ₀ due to the torque T can be made the same by adjusting

Further, the torsional rigidity and bending rigidity of the solid shaft and the hollow shaft are shown as follows: Torsional rigidity: G · I _po ··· For solid shaft G · I _p1 ···・ ・ ・ Hollow shaft Bending stiffness: E ・ I _Xo・ ・ ・ ・ ・ ・_Solid shaft (circular cross section) E ・ I _X1・ ・ ・ ・ ・ Hollow shaft Here, G is the lateral elastic modulus , E is the longitudinal elastic modulus, I _po , I _p1
Is the second polar moment of area, and I _Xo and I _X1 are the second moments of area. Furthermore, the second polar moment of area is

[Equation 3] The second moment of area is

[Equation 4] Therefore, if the pole section coefficient Z _p is the same, it can be said that the larger the shaft outer diameter, the higher the rigidity. Further, since bending stress harmful to torque detection is inversely proportional to bending rigidity, according to the configuration of the present invention, it is possible to reduce bending stress that is high in rigidity and harmful to detection while maintaining an effective stress state due to torque. it can.

In consideration of the above points, in the electric power steering system of the present invention, as shown in FIG.
No. 0 sensor coil 109 inner diameter D, torque detection shaft portion 10
8, the outer diameter d ₁ of the steering lock portion 105 that is a part of the output shaft, that is, the outer diameter d _{2 of the} upper tube 104.
Have the following relationships. D> d ₁ > d ₂ That is, the sensor coil 109 and the torque detection shaft 108
While maintaining a minute gap to the extent that they do not contact slightly larger than the outer diameter d ₁ of the inner diameter D of the torque detection shank 108 of the sensor coil 109 between the outer diameter d ₁ of the torque detection shank 108 Is larger than the outer diameter d ₂ of the steering lock portion 105, that is, the upper tube 104.

[0017]

As described above, according to the electric power steering device of the present invention, the detection device is a magnetostrictive torque sensor, and the torque detection shaft portion of the torque sensor is larger than the outer diameter of the input shaft. Since it has an outer diameter and is hollow,
Sufficient detection accuracy can be obtained without sacrificing the required rigidity while ensuring the assemblability.

[Brief description of drawings]

FIG. 1 is a partial axial cross-sectional view of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is an exploded view of the electric power steering device of FIG. 1 before assembly, showing the relationship of the diameter of each part.

[Explanation of symbols]

 102, 104, 106 ... Input shaft 112 ... Output shaft 120 ... Detection device 111 ... Electric motor

Claims (1)

[Claims] 1. An output shaft for transmitting a steering force for steering a wheel, an input shaft for connecting a steering wheel to the output shaft, and a detection device for detecting the steering force transmitted to the input shaft. An electric power steering device comprising: a motor that is driven according to a detection result of the detection device to generate an auxiliary steering force; and a power transmission mechanism that transmits the auxiliary steering force of the motor to the output shaft. Is a magnetostrictive torque sensor, and the torque detection shaft portion of the torque sensor has an outer diameter larger than the outer diameter of the input shaft and is hollow.