JP2004203236A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new technological means for determining friction of a steering system, for preventing reduction in steering feeling and properly coping with disturbance. <P>SOLUTION: This electric power steering device assists steering by using torque of an electric motor 6, and determines upper side and lower side frictions Fi and Fo so as to satisfy the following inequality Fo ≤ Fi when the upper side friction applied to a steering system A between a steering member 1 and a torque detecting mechanism B is set to Fi, and the lower side friction applied to the steering system A between the torque detecting mechanism B and a steered wheel is set to Fo. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric power steering device used for a vehicle such as an automobile and assisting a driver's steering operation using an electric motor.
[0002]
[Prior art]
For example, in an electric power steering device for an automobile, a torque detecting mechanism for detecting a steering torque applied to a steering member by a driver is provided in a steering system from the steering member to a steered wheel. In this detection mechanism, a rotating body with a target is provided on each of an input side and an output side of a torsion bar connected to a steering member, and the amount of torsion of the torsion bar, that is, the input of the torsion bar is detected by a sensor arranged opposite to the target. The amount of relative rotation between the output side and the output side is detected, and the steering torque is detected based on this. In the electric power steering device, a command value to the electric motor is determined according to the detected torque, and the motor rotational force is transmitted to the steering system via the speed reduction mechanism, thereby applying a steering assist force to the steering system. It assists the driver's steering operation (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP 2002-116095 A (Page 4, FIG. 1)
[0004]
[Problems to be solved by the invention]
By the way, in the steering system of the above-described conventional apparatus, there are many components that apply friction to the steering system in accordance with a driver's steering operation, a road surface resistance accompanying a vehicle running, and the like. Specifically, a rack-and-pinion type transmission having a pinion shaft connected below the torsion bar and a rack shaft connected to the pinion shaft and having both ends connected to the left and right steering wheels, respectively. A mechanism is included in the steering system, and friction is generated at a connection portion between the pinion shaft and the rack shaft.
[0005]
However, in the conventional device, an appropriate guideline regarding the friction generated by the friction element as described above has not been established, and depending on the magnitude of the generated friction, the steering feeling of the driver may be reduced, or the torque detection mechanism may be reduced on the road surface. In some cases, the disturbance cannot be quickly and accurately detected, and the disturbance cannot be properly compensated. In addition, from the viewpoint of improving the detection accuracy of the road surface condition and the steering characteristics such as a sense of unity of the steering operation and the vehicle behavior to be felt by the driver (and, consequently, a steering feeling such as a wobble of the steering member), the friction of the steering system is considered. Is preferably reduced as much as possible, but merely reducing the friction makes the entire steering system a simple vibration system including the torsion bar, and conversely causes a reduction in steering feeling and a reduction in disturbance compensation accuracy.
[0006]
Accordingly, the present invention has been made in consideration of the above-described conventional problems, and can prevent a decrease in steering feeling and determine a friction of a steering system capable of appropriately responding to disturbance. The purpose is to provide new technical means for doing so.
[0007]
[Means for Solving the Problems]
The present invention relates to an electric power steering that applies a torque from an electric motor to the steering system based on torque detected by a torque detection mechanism provided in a steering system from a steering member to a steered wheel to assist steering. A device,
In the steering system, when the friction between the steering member and the torque detection mechanism is Fi and the friction between the torque detection mechanism and the steered wheels is Fo, the following inequality (1) is obtained. To be satisfied
Fo ≦ Fi --- (1)
The frictions Fi and Fo are determined.
[0008]
In the steering system of the electric power steering apparatus configured as described above, by setting the upper friction Fi to be equal to or higher than the lower friction Fo, the inventor of the present application can reduce the steering feeling. It has been found that it is possible to appropriately cope with disturbances from the road surface, as well as to prevent disturbances. That is, the inventor of the present application first divides the friction applied to the steering system into an upper side and a lower side with the torque detection mechanism as a boundary, and further makes the upper side friction Fi relatively large so that the driver can feel the wobble of the steering member. It was noted that it was possible to prevent the steering feeling from being reduced by suppressing the sensing of the steering wheel. In addition, by selecting the lower friction Fo that is equal to or lower than the upper friction Fi, the steering device can quickly and accurately detect the disturbance by the torque detection mechanism and appropriately compensate for the disturbance, and can also adjust the steering feeling. It has been found that the ring can be prevented from lowering.
[0009]
In the electric power steering device, the torque detection mechanism may include a torsion bar having an upper end connected to the steering member and a lower end connected to the steered wheels.
In this case, the upper and lower frictions of the elastic body composed of the torsion bar are appropriately determined in the steering system, and a device excellent in steering feeling and disturbance compensation can be configured.
[0010]
Further, in the electric power steering device described above, the sum of the frictions Fi and Fo may be 2.0 (N) or less.
In this case, the lower friction Fo is limited to 1.0 (N) or less, and the disturbance can be quickly and accurately detected by the torque detection mechanism, so that appropriate disturbance compensation can be performed more reliably.
[0011]
The electric power steering device further includes a bearing that rotatably supports a member provided on the steering member side of the torque detection mechanism,
It is preferable to support the member in a state where a preload is applied to the bearing so that the friction Fi is equal to or higher than the friction Fo.
In this case, the upper friction Fi can be reliably set to be equal to or greater than the lower friction Fo by the bearing, and a device excellent in steering feeling and disturbance compensation can be more reliably configured.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of an electric power steering device of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a main configuration of an electric power steering apparatus according to an embodiment of the present invention. In the figure, the device is mounted on, for example, an automobile and includes a steering shaft 2 (not shown) that changes the direction of steered wheels according to a steering operation of a driver applied to a steering member (steering wheel) 1. The steering shaft 2 includes a cylindrical mounting shaft 21 to which the steering member 1 is mounted on an upper end, a cylindrical input shaft 22 connected to the mounting shaft 21 so as to be integrally rotatable, and a torsion bar 23. A cylindrical output shaft 24 is provided coaxially connected to the input shaft 22. The left and right output shafts 24 are connected to the output shaft 24 via a known rack and pinion type transmission mechanism (not shown). The steering operation is performed by the steered wheels.
[0013]
The mounting shaft 21 is fixed to the vehicle body while being housed in the steering column 25, and the lower end of the mounting shaft 21 is provided with an upper end of the input shaft 22 in which one end of the torsion bar 23 is fixed. Are connected by The other end of the torsion bar 23 is internally fixed to the lower end of the output shaft 24 by a pin 27.
The input shaft 22 and the output shaft 24 are fixed to the vehicle body side, and are rotatable via needle bearings 31 and ball bearings 32, 33 inside upper and lower housings H1, H2 separable up and down in the drawing. Attached to. The needle bearing 31 supports the input shaft 22 in a state where a predetermined load (preload) is applied in the radial direction, and has a function as a friction applying unit that increases an upper friction Fi described later.
The output shaft 24 has a worm 41 and a reduction mechanism 4 having a worm wheel 42 meshing with the worm 41. The worm 41 is attached to the output shaft so as to be integrally rotatable, and is controlled by a control unit (ECU) 5. The auxiliary electric motor 6 is connected. The deceleration mechanism 4 and the electric motor 6 constitute a steering assist unit that applies a steering assist force by a motor rotational force to a steering system A from the steering member 1 to the steered wheels.
[0014]
In the steering system A, a torque detection mechanism B is incorporated at a position on the way. The torque detecting mechanism B detects a steering torque input from the steering member 1 to the steering system A in accordance with the steering operation of the driver, and drives the electric motor 6 based on the detected steering torque to drive the steering assist force. To assist the driver's steering operation. Further, the torque detection mechanism B is configured to perform steering due to a disturbance that is reversely input from the steered wheels to the steering system A, for example, friction (steering resistance) between the steered wheels and the road surface due to running of the vehicle. The force acting on the system A (that is, the rotational torque acting on the output shaft 24 from the steered wheels to rotate the output shaft 24 in one direction) is also detected. Then, the torque detection mechanism B drives the electric motor 6 so as to reduce the detected disturbance and compensates for the disturbance. The disturbance includes a self-aligning torque as a restoring torque acting on the steering system A in reaction to the steering operation by the driver, which is determined by the structure of the individual vehicle such as a support structure that supports the steered wheels. I have. Further, by performing such disturbance compensation, it is possible to prevent the influence of the disturbance from being transmitted to the driver via the steering member 1 and prevent the steering feeling from deteriorating.
[0015]
Specifically, the torque detecting mechanism B includes the torsion bar 23 provided between the input / output shafts 22 and 24 and the outer periphery of the lower end of a cylindrical rotating body 71 attached to the input shaft 22 so as to be integrally rotatable. And targets 72a and 72b formed on the outer periphery of the upper end of a cylindrical rotating body 72 attached to the output shaft 24 so as to be integrally rotatable. The targets 71a, 72a, and 72b are formed, for example, by forming irregularities made of a magnetic material in a gear shape at a constant pitch in the circumferential direction, and causing a periodic magnetic change around the target by rotation. One of the targets 72a and 72b and The other is used for relative angle detection and absolute angle detection, respectively.
Further, the torque detecting mechanism B is disposed inside the sensor housing 8 so as to face the targets 71a, 72a and 72b, and converts a magnetic change of a magnetoresistive element (MR element) into an electric signal. The output signals from these sensors are sequentially output to the arithmetic unit 51 of the ECU 5. Then, the calculation unit 51 detects the relative angle (the relative rotation amount) between the input and output shafts 22 and 24 based on the output signal, and calculates the torque input to the steering system A according to the driver's steering operation or disturbance by calculation. The drive control unit 52 generates a drive signal for driving the electric motor 6 according to the torque obtained by the calculation unit 51, and drives the motor 6 to perform steering assist and disturbance compensation.
[0016]
Referring to FIG. 2, the steering system A includes a component (friction) that generates friction in accordance with a driver's steering operation, road surface resistance associated with driving of the vehicle, and the like. The upper friction Fi applied to the steering system A between the steering member 1 and the torque detection mechanism B, and the lower friction Fo applied to the steering system A between the torque detection mechanism B and the steered wheels. Determines the values of the upper friction Fi and the lower friction Fo so as to satisfy the following inequality, Fi ≦ Fo. Further, the frictional force of the entire steering system A obtained from the sum of the upper friction Fi and the lower friction Fo is 1.5 to 2.0 (N) (preferably 2.0 (N)). The preferred range of the upper friction Fi is 1.2 to 1.3 (N), and the preferred range of the lower friction Fo is 0.7 to 0.8 (N).
[0017]
More specifically, the above-described needle bearing 31 is included in a friction element that applies the upper friction Fi to the steering system A above the torsion bar 23 and the steering member 1. The needle bearing 31 is mounted such that the preload in the radial direction is larger than that of the conventional example so that the upper friction Fi is equal to or higher than the lower friction Fo. ) Is installed between the input shaft 22 and the housing H1. When the steering member 1 is rotated by the driver, the bearing 31 attenuates the rotational (input) torque Th from the steering member 1 in accordance with the driver's rotation operation by rolling contact with the input shaft 22 to perform steering. The torque Ti is transmitted to the torsion bar 23. Then, the torque detecting mechanism B detects the steering torque Ti based on the amount of twist of the torsion bar 23, and causes the electric motor 6 to apply the motor torque Ta corresponding to the steering torque Ti to the steering system A.
[0018]
On the other hand, the friction element that applies the lower friction Fo to the steering system A below the torsion bar 23 and between the steering wheel 60 is connected to the meshing portion between the worm 41 and the worm wheel 42 and the output shaft 24 side. The material is selected so that the lower friction Fo is 0.8 (N) or less for the entire friction element, and the element is configured. ing. The sliding portion has a pinion shaft connected to the output shaft 24, and a rack having a rack tooth portion meshing with the pin-on of the pinion shaft, and a rack shaft connected to the left and right steering wheels 60. In the pinion-type transmission mechanism, a meshing portion between the pin-on and the rack tooth portion, a support yoke for pressing the rack shaft toward the pinion shaft and a sliding surface between the rack shaft, and the rack shaft in the vicinity of each steering wheel 60. There is a rack guide for guiding and a sliding surface for the rack shaft. For example, when the vehicle travels on a curve in response to the driver's steering operation, cornering power (CP) acts on the steered wheels 60 from the road surface, and a self-aligning torque (S.A.) corresponding to the cornering power is applied. .T) is input to the steering system A, attenuated by the lower friction Fo, and transmitted to the torsion bar 23. Then, the torque detecting mechanism B detects the self-aligning torque based on the amount of twist of the torsion bar 23, and applies the motor rotational force Ta to the steering system A so as to reduce the torque.
[0019]
As described above, in the electric power steering apparatus according to the present embodiment, the friction applied to the steering system A mutually affects the upper friction Fi, which relatively easily affects the driver's steering feeling, and the disturbance. These frictions Fi and Fo are determined so that the upper friction Fi is equal to or higher than the lower friction Fo. As a result, the steering feeling can be prevented from lowering, and the disturbance can be promptly and accurately detected by the torque detection mechanism B, and the compensation can be appropriately performed. That is, by making the upper friction Fi relatively large, it is possible to suppress the driver from feeling the wobble of the steering member 1. Further, by making the lower friction Fo relatively small, the fluctuation of the reverse input (disturbance) from the steered wheels can be transmitted to the torque detection mechanism B as soon as possible and detected accurately, and the disturbance can be detected quickly. It is possible to compensate. Further, since the disturbance compensation can be improved in this manner, the disturbance can be prevented from being transmitted to the driver via the steering system A, and the steering feeling of the driver can be prevented from being deteriorated by the influence of the disturbance. be able to.
[0020]
In the present embodiment, the value of the sum of the upper friction Fi and the lower friction Fo is limited to 2.0 (N) or less, so the lower friction Fo is limited to 1.0 (N) or less. The disturbance can be quickly and accurately detected by the torque detection mechanism B, and appropriate disturbance compensation can be performed more reliably.
On the other hand, in the above conventional example, the friction of the entire steering system was about 2.0 (N), but the upper and lower frictions were, for example, 0.5 (N) and 1.5 (N). ) And the lower friction are set to three times or more, and it is difficult for the torque detection mechanism to quickly and accurately detect the disturbance.
[0021]
In the above description, the case where the needle bearing 31 that supports the input shaft 22 in a state where a preload is applied in the radial direction is used as the friction applying means, but the friction applying means of the present invention uses the upper friction Fi. There is no particular limitation as long as the size is increased, and a member that causes friction such as a wound bush may be attached to the input shaft 22. However, when the upper friction Fi is increased by using a member originally included in the steering device like the needle bearing 31, it is preferable in that the device can be configured at a low cost by suppressing an increase in the number of parts.
[0022]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, while compensating for the disturbance accompanying a vehicle driving | running can be performed appropriately, the electric power steering device excellent in the vehicle operation feeling which a driver | operator can experience can be comprised.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a main part of an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a diagram schematically illustrating forces (torque and friction) applied to a steering system of the electric power steering device.
[Explanation of symbols]
1 steering member 22 input shaft (member provided on the steering member side)
23 Torsion bar 31 Needle bearing A Steering system B Torque detection mechanism

Claims (4)

An electric power steering device that applies a rotational force from an electric motor to the steering system based on a torque detected by a torque detection mechanism provided in a steering system from a steering member to a steered wheel to assist steering. ,
In the steering system, when the friction between the steering member and the torque detection mechanism is Fi and the friction between the torque detection mechanism and the steered wheels is Fo, the following inequality (1) is obtained. To be satisfied
Fo ≦ Fi --- (1)
An electric power steering device wherein the frictions Fi and Fo are determined. The electric power according to claim 1, wherein the torque detecting mechanism includes a torsion bar having an upper end connected to the steering member and a lower end connected to the steered wheels. Steering device. 3. The electric power steering apparatus according to claim 1, wherein the sum of the frictions Fi and Fo is 2.0 (N) or less. A bearing that rotatably supports a member provided on the steering member side of the torque detection mechanism,
The electric power steering apparatus according to any one of claims 1 to 3, wherein the member is supported in a state where a preload is applied to the bearing so that the friction Fi is equal to or higher than the friction Fo.

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