JP2013079875A - Steering torque detection method and electric power steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering apparatus that can detect steering torque with a simpler configuration than before.SOLUTION: An electric power steering apparatus in which steering torque generated by operation of a steering wheel 3 by a driver is assisted by an electric motor 7 so as to be transmitted to wheels 15a and 15b via a steering device 6, comprises two gyro sensors 2a and 2b provided between the steering wheel 3 and the steering device 6 with a torsion bar 12 provided between the sensors. The apparatus calculates an integral value of a difference between angular velocities ω1 and ω2 detected by the two gyro sensors 2a and 2b to calculate the steering torque by using a predetermined formula on the basis of the integral value.

Description

  The present invention relates to an electric power steering device that assists the movement of a steering rack and steering operation by a motor in accordance with the operation of a steering wheel by a driver. About things.

This type of conventional device electronically controls the motors in the steering column and steering rack based on the steering torque of the steering wheel detected by the torque sensor and the steering angle of the steering wheel detected by the steering angle sensor. Various electric power steering devices that assist the steering wheel operation of the driver by assisting the movement of the steering column and the steering rack have been proposed and put into practical use (see, for example, Patent Document 1).
In such an electric power steering apparatus, as a torque sensor for detecting the steering force of the steering wheel, for example, a sensor configured to detect a torsion amount of a so-called torsion bar as a magnetostriction signal or a magnetic flux change signal. Various proposals and practical applications have been made (see, for example, Patent Document 2).

JP-A-62-71756 (second page, FIG. 1 to FIG. 2) JP 2011-80870 A (page 6-13, FIGS. 1 to 9)

However, the conventional torque sensor as described above is composed of a large number of mechanical parts and is mainly fitted to an appropriate part of the torsion bar. Therefore, it takes time to install and high cost. There is a problem that the apparatus configuration is complicated.
In addition, in a vehicle, it is desirable that the space required for mounting the components is as small as possible. However, the conventional torque sensor as described above requires a relatively large mounting space because of its structure. There is also a problem that further space reduction is desired.

  The present invention has been made in view of the above circumstances, and provides a steering torque detection method and an electric power steering device that enable detection of steering torque with a simpler configuration than conventional ones.

In order to achieve the above object of the present invention, a steering torque detection method according to the present invention comprises:
A method for detecting the steering torque in an electric power steering device configured to assist a steering torque by an operation of a steering wheel of a driver by an electric motor and transmit the steering torque to a wheel via a steering device,
Two gyro sensors are provided across a torsion burn provided between the steering wheel and the steering device,
An integral value of a difference between angular velocities detected by the two gyro sensors is calculated, and the steering torque is calculated by a predetermined arithmetic expression based on the integral value.
In order to achieve the above object of the present invention, an electric power steering apparatus according to the present invention includes:
An electric power steering device configured to assist a steering torque by an operation of a driver's steering wheel by an electric motor and to be transmitted to a wheel via a steering device,
Two gyro sensors are provided across a torsion burn provided between the steering wheel and the steering device,
An integrated value of the difference between the angular velocities detected by the two gyro sensors is calculated, the steering torque is calculated by a predetermined calculation formula based on the integrated value, and the calculated calculation torque is used for controlling the electric motor. It is configured to be provided.

According to the present invention, the gyro sensor only needs to be attached to the front and back of the torsion bar, so that the configuration is simpler than the configuration in which the conventional torque sensor is provided, and not only the number of parts can be reduced, but also the conventional configuration. Since the adjustment work at the time of proper attachment is not required, further cost reduction of the apparatus can be realized.
In addition, since two gyro sensors are provided and the steering torque is obtained by calculation based on the output signals of these two gyro sensors, if one fails, the failure can be detected by comparing the two signals. Instead, the emergency steering torque can be obtained by using, for example, a predetermined alternative value such as an estimated value instead of the output of the failed sensor, and the safety of the automobile specified by ISO (International Organization for Standardization) As a result, it is possible to satisfy the ASIL (Automotive Safety Integrity Level) highest level (ASIL-D), which is a standard for safety. In particular, in the case of using a MEMS gyro sensor as a gyro sensor, the above-described effect can be further ensured.

It is a lineblock diagram showing a schematic structure of an electric power steering device in an embodiment of the invention. It is the functional block diagram which represented the function of the electronic control unit which performs the steering torque calculation process in embodiment of this invention with the functional block. It is a functional block diagram showing the function of the electronic control unit which performs the other example of the steering torque calculation process in embodiment of this invention with the functional block. It is a functional block diagram of the electronic control unit explaining a rudder angle calculation process at the time of using a MEMS gyro sensor as a rudder angle sensor.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3.
The members and arrangements described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
First, a configuration example of the electric power steering apparatus according to the embodiment of the present invention will be described with reference to FIG.
The electric power steering apparatus according to the embodiment of the present invention includes a steering wheel 3 based on outputs of two gyro sensors 2a and 2b attached to the steering column 1 and two gyro sensors 2a and 2b as will be described later. The steering control calculation processing (details will be described later) of the electronic control unit (indicated as “ECU” in FIG. 1) 4 and the power steering based on the steering torque obtained by the electronic control unit 4 The electronic power steering control unit (indicated as “EPS” in FIG. 1) 5 that executes control is roughly divided into components.

  FIG. 1 shows only components necessary for obtaining a steering torque required for power steering control executed in the electronic power steering control unit 5 in order to simplify the illustration and facilitate understanding of the invention. The portions relating to the supply of other signals required by the electronic power steering control unit 5 are not shown.

First, each of the electronic control unit 4 and the electronic power steering control unit 5 includes, for example, a memory element (not shown) such as a RAM or ROM, mainly a microcomputer having a known and well-known configuration, An external interface circuit (not shown) and the like are configured as main components.
The electronic control unit 4 executes a steering torque calculation process (details will be described later).
On the other hand, the electronic power steering control unit 5 is provided in the steering device 6 based on data such as the steering torque obtained by the electronic control unit 4 and the steering angle obtained by a steering angle sensor (not shown). Further, by driving a steering rack (not shown) by a motor 7 (see FIG. 2), power assist for steering torque is performed.

On the other hand, the steering column 1 is roughly divided into an input shaft 11 to which a steering wheel 3 is fixed, a torsion bar 12, and an output shaft 13. The input shaft 11 and the output shaft 13 are connected via the torsion bar 12. Connected. The output shaft 13 is connected to the steering device 6 through a shaft (not shown).
The steering device 6 is, for example, of a rack and pinion type, and the rotation of the steering wheel 3 is transmitted to a pinion (not shown) of the steering device 6 and a rack (not shown) meshing with the pinion. ing. The movement of the rack (not shown) is converted into a change in the steering angle of the wheels 15a and 15b attached to the end portions via the tie rods 14a and 14b.

  The rack (not shown) of the steering device 6 described above is provided with the rotational force of a motor 7 (see FIG. 2) provided in the device 6 and controlled in operation by the electronic power steering control unit 5. The power assist for the steering torque generated by the operation of the steering wheel 3 is performed.

As the gyro sensors 2a and 2b in the embodiment of the present invention, a so-called MEMS (micro electro mechanical systems) gyro sensor (angular velocity) using Si (silicon) micromachining technology is used, and the MEMS gyro sensor itself is It is not unique to the present invention, and has a well-known and publicly known configuration.
Conventionally, one such gyro sensor has been used as a yaw rate sensor in a vehicle. However, in an embodiment of the present invention, a gyro sensor that has been conventionally used as a yaw rate sensor, particularly a MEMS gyro sensor. By providing two, the function of a conventional torque sensor for detecting the steering torque of the steering wheel 3 can be achieved as will be described later.

  The MEMS gyro sensor has various forms such as a sensing part only, and a sensing part and an electronic circuit that performs signal amplification, etc. In the embodiment of the present invention, only the sensing part is provided. The thing of composition is used. This eliminates the need for a power supply line between the gyro sensors 2a and 2b and the electronic control unit 4 and minimizes the wiring between the electronic control unit 4 and a configuration including an electronic circuit. This is because it can.

As shown in FIG. 1, the gyro sensors 2 a and 2 b are attached at two arbitrary positions with the torsion bar 12 sandwiched in the axial direction of the steering column 1.
That is, in the embodiment of the present invention, one gyro sensor 2a is attached to an arbitrary location on the input shaft 11, and the other gyro sensor 2b is attached to an arbitrary location on the output shaft 13. It has become.

The attachment location of the gyro sensors 2a and 2b need not be limited to the above-described example, and may be any location where the movement according to the steering angle of the steering wheel 3 can be detected at two locations across the torsion bar 12. good.
Accordingly, one gyro sensor 2a is disposed at an arbitrary position between the steering wheel 3 and the torsion bar 12, and the other gyro sensor 2b is connected to the steering shaft 6 from the connection portion with the output shaft 13 of the torsion bar 12. It is preferable to attach to any place between the two.

Next, the calculation processing of the steering torque of the steering wheel 3 based on the detection signals of the two gyro sensors 2a and 2b performed in the electronic control unit 4 will be described with reference to FIG.
FIG. 2 is a functional block diagram showing a calculation process of the steering torque of the steering wheel 3 based on the detection signals of the two gyro sensors 2a and 2b executed in the electronic control unit 4.

The angular velocity signals ω1 and ω2 obtained by the two gyro sensors 2a and 2b are converted into digital signals after being subjected to necessary amplification and signal shaping in the electronic control unit 4, and integrated by digital calculation, respectively. Thus, the angles α1 and α2 are calculated (see symbols a and b in FIG. 2).
Here, the angles α1 and α2 are rotation angles generated in the member to which the gyro sensors 2a and 2b are attached, for example, the output shaft 13, and the magnitude thereof corresponds to the steering torque.

Next, the difference (α1−α2) = α between the two angles α1 and α2 is calculated (see symbol c in FIG. 2).
Then, a steering torque X (mN) with respect to the angle difference α at this time is calculated by a steering torque calculation function f (α) set in advance as a function of the angle difference α (see symbol d in FIG. 2). As in the case of using the sensor, the electronic power steering control unit 5 is used for driving control of the motor 7.

FIG. 3 shows another configuration example of the calculation process of the steering torque of the steering wheel 3 based on the detection signals of the two gyro sensors 2a and 2b, which will be described below with reference to FIG.
In this example, the angular velocity signals ω1 and ω2 obtained by the two gyro sensors 2a and 2b are subjected to necessary amplification, signal shaping, and the like in the electronic control unit 4 and then converted into digital signals. A difference (ω1−ω2) between the angular velocities ω1 and ω2 is calculated by digital calculation (see symbol e in FIG. 3).

Next, integration is performed on the angular velocity difference (ω1−ω2) obtained as described above, and an angle α corresponding to the angular velocity difference (ω1−ω2) is calculated (see symbol f in FIG. 3).
The steering torque X (mN) with respect to the obtained angle α is calculated by the steering torque calculation function f (α) in the same manner as described with reference to FIG. 2 (see symbol d in FIG. 2). In FIG. 2, illustration of such processing is omitted.

  As described above, in the electric power steering apparatus according to the embodiment of the present invention, since the two MEMS gyro sensors 2a and 2b are used, if one of them fails, for example, the failure is detected by comparing two signals. It is possible to obtain emergency steering torque by using a predicted value instead of the output of a failed sensor, and is a standard related to vehicle safety defined by ISO (International Organization for Standardization). It is possible to satisfy the highest level (ASIL-D) of a certain ASIL (Automotive Safety Integrity Level).

Next, a configuration example for detecting a steering angle using a gyro sensor will be described with reference to FIG. For convenience of explanation, FIG. 1 is also referred to as appropriate.
In this example, a MEMS gyro sensor 8 as a steering angle sensor is provided, and as described below, the steering angle of the steering wheel 3 is obtained by arithmetic processing based on the output signal, and provided to the electronic power steering control unit 5. It is made to be able to.
First, the MEMS gyro sensor 8 as a steering angle sensor is attached to a place where the steering angle of the steering wheel 3 can be detected, like the conventional angle sensor, and is attached to an appropriate position of the steering column 1, for example.

  Further, in this configuration example, a MEMS gyro sensor 9 as a reference sensor is provided for acquiring a reference value. The MEMS gyro sensor 9 as such a reference sensor is for acquiring the movement of the vehicle (not shown) as reference data, and therefore needs to be fixed to the vehicle chassis (not shown).

Next, the steering angle calculation process in the electronic control unit 4 will be described.
In the electronic control unit 4, the output value of the MEMS gyro sensor 9 as the reference sensor is subtracted from the output value of the MEMS gyro sensor 8 as the rudder angle sensor (see symbol g in FIG. 4). By this subtraction, the rolling component around the X-axis direction (the vehicle front-rear direction) and the tilt component around the Y-axis direction (the vehicle lateral direction perpendicular to the X-axis) are removed.
Then, the above-mentioned subtraction result is integrated (see symbol h in FIG. 4), and the integration result is used as a steering angle of the steering wheel 3 for driving control of the motor 7 by the electronic power steering control unit 5. It will be.
The MEMS gyro sensor 9 as the reference sensor in this configuration example need not be limited to the case where the reference sensor is provided independently as in this configuration example, as long as it is fixed to the chassis of the vehicle. For example, the gyro sensor used for detecting the yaw rate of the vehicle in the ESC (side skid prevention device) may be shared as the reference sensor in the present configuration example, or in the control unit in the occupant protection device such as an airbag. A gyro sensor that is attached to and used for control may be shared as a reference sensor, and various modifications are possible.

  This is suitable for an electric power steering apparatus in which a steering torque detection mechanism with a simpler configuration is desired.

DESCRIPTION OF SYMBOLS 1 ... Steering column 2a, 2b ... Gyro sensor 3 ... Steering wheel 4 ... Electronic control unit 5 ... Electronic power steering control unit 6 ... Steering device

Claims (4)

The steering torque detection method in an electric power steering device configured to assist a steering torque by an operation of a driver's steering wheel by an electric motor and to be transmitted to a wheel via a steering device,
Two gyro sensors are provided across a torsion burn provided between the steering wheel and the steering device,
A steering torque detection method, wherein an integral value of a difference between angular velocities detected by the two gyro sensors is calculated, and the steering torque is calculated by a predetermined arithmetic expression based on the integral value.   The steering torque detection method according to claim 1, wherein the gyro sensor is a MEMS gyro sensor. An electric power steering device configured to assist a steering torque by an operation of a driver's steering wheel by an electric motor and to be transmitted to a wheel via a steering device,
Two gyro sensors are provided across a torsion burn provided between the steering wheel and the steering device,
An integrated value of the difference between the angular velocities detected by the two gyro sensors is calculated, the steering torque is calculated by a predetermined calculation formula based on the integrated value, and the calculated calculation torque is used for controlling the electric motor. An electric power steering apparatus characterized by being configured to be provided.   4. The electric power steering apparatus according to claim 3, wherein the gyro sensor is a MEMS gyro sensor.

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