JP2002154449A - Motor-driven power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device of inexpensive constitution capable of making drive control of a motor in good performance. SOLUTION: A controller 6 is equipped with a steering angle calculation part 61 to determine the steering angle θ of a steering wheel 1 on the basis of the motor current i, etc., and an indicator voltage setting part 62 to set the voltage to be impressed on the motor 4, indicator voltage V*, on the basis of the obtained steering angle θ and the vehicle speed ν. The steering angle calculation part 61 calculates the steering angular velocity θ' on the basis of the indicator voltage V* and motor current i and determines the steering angle θby integrating the steering angular velocity θ'. The indicator voltage setting part 62 sets the indicator voltage V* to be impressed on the motor 4 on the basis of the obtained steering angle θ unless the vehicle speed ν is zero, and if ν is zero, the indicator voltage V* is set on the basis of the steering angular velocity θ'.

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 apparatus for assisting steering by using a driving force generated by an electric motor.

[0002]

2. Description of the Related Art In an electric power steering apparatus, an electric motor is used as a source of a steering assist force to be applied to a steering mechanism of a vehicle. The electric motor is generally driven and controlled based on an output signal of a torque sensor for detecting a steering torque applied to a steering wheel. However, the torque sensor is a relatively expensive sensor, and having such an expensive torque sensor is one of the causes of the high cost of the electric power steering device.

Therefore, a steering angle sensor which is less expensive than the torque sensor is provided in place of the torque sensor, and the drive control of the electric motor is controlled based on the steering angle (steering angle) of the steering wheel detected by the steering angle sensor. It is proposed to do. However, the steering angle sensor is inexpensive but generally expensive compared to the torque sensor, and the adoption of the configuration according to the above proposal does not provide a significant reduction in the cost of the electric power steering device. I can't.

On the other hand, as a technique for obtaining a steering angle of a steering wheel without using a steering angle sensor, a motor rotation speed is calculated based on a back electromotive force of an electric motor, and the calculated motor rotation speed is integrated. Has proposed a method for determining the steering angle of a steering wheel (see, for example, Japanese Patent No. 2781854). However, in the method according to this proposal, as the drive control of the electric motor progresses, integration errors accumulate, and the error between the steering angle obtained by calculation and the actual steering angle increases. Therefore, it is not possible to control the driving of the electric motor satisfactorily based on the steering angle obtained by the calculation.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned technical problems and to provide an inexpensive electric power steering apparatus capable of favorably controlling the driving of an electric motor. is there.

[0006]

According to the first aspect of the present invention, there is provided an electric motor (4) according to a position and an operation speed of an operation member (1).
And a motor current detecting means (7) for detecting a motor current flowing through the electric motor, the electric power steering apparatus comprising: Operating speed calculating means (6) for obtaining an operating speed (θ ') of the operating member based on the motor current detected by the motor current detecting means;
1, S3) and the operating speed of the operating member obtained by the operating speed calculating means are integrated to obtain the position (θ) of the operating member.
Operating position calculating means (61, S6) for obtaining the reference point; reference point detecting means (5) for outputting a detection signal in response to the position of the operating member reaching a predetermined reference point; When a detection signal is output, the result of integration by the operation position calculation means is set to a predetermined initial value (θ ₀ ).
An integration resetting means (S5) for resetting the vehicle speed, a vehicle speed detecting means (8) for detecting the vehicle speed, and when the vehicle speed is not zero, the electric motor is controlled in accordance with the position of the operating member. Control means (62, 63, S8, S9) for controlling the electric motor based on the operation speed of the operation member obtained by the operation speed calculation means.

[0007] Alphanumeric characters in parentheses indicate corresponding components in the embodiment described later. Hereinafter, the same applies in this section. According to this invention, the operation speed of the operation member is calculated based on the motor current, and the position of the operation member is obtained by integrating the operation speed. Then, the drive of the electric motor is controlled in accordance with the obtained position of the operation member. As a result, in controlling the electric motor,
Since a torque sensor for detecting a steering torque applied to an operating member such as a steering wheel and a sensor for detecting a position of the operating member (for example, a steering angle sensor for detecting a steering angle of a steering wheel) are not required, an electric motor is not required. The cost of the power steering device can be reduced as compared with the related art.

When the position of the operating member reaches a predetermined steering angle reference point, the result of integration by the operating position calculating means is reset to a predetermined initial value. As a result, accumulation of the integration error due to the progress of the drive control of the electric motor can be prevented, and good drive control of the electric motor based on the position of the operation member obtained by the integration operation can be realized. When the vehicle speed is zero, the electric motor may be controlled according to a linear combination of the position of the operation member and the operation speed.
This makes it possible to compensate for a steering resistance that increases as the steering angle increases.

According to a second aspect of the present invention, the electric power steering device further includes an operation acceleration calculating means for differentiating an operation speed obtained by the operation speed calculation means to obtain an operation acceleration, and the control means When the vehicle speed is not zero, the electric motor is controlled according to a linear combination of the position of the operation member, the operation speed of the operation member calculated by the operation speed calculation means, and the operation acceleration calculated by the operation acceleration calculation means. Preferably, it is controlled. This makes it possible to compensate for the viscosity and inertia of the steering mechanism and the electric motor.

According to a third aspect of the present invention, the position of the operating member obtained by the operating position calculating means increases from a value lower than a lower limit value of a predetermined range including the predetermined reference point and falls within the predetermined range. By further increasing, while being larger than the upper limit of the predetermined range and deviating from the predetermined range, or while the position of the operating member is reduced from a value larger than the upper limit of the predetermined range and within the predetermined range, When the detection signal is output from the reference point detecting means while the value is smaller than the lower limit value of the predetermined range and deviates from the predetermined range by further decreasing, the reference point detecting means If it is determined that the signal is normal and no detection signal is output from the reference point detection means, an abnormality determination means for determining that the reference point detection means has an abnormality ( 3 is an electric power steering apparatus according to claim 1, wherein further comprising a T 1 -T 10).

According to the present invention, it is possible to detect whether or not an abnormality has occurred in the reference point detecting means. Therefore,
For example, if it is determined that an abnormality has occurred in the reference point detecting means, the operation is shifted to the fail-safe mode so that the driving of the electric motor is stopped. By not resetting to a value, inappropriate steering assist due to an accumulated integration error can be prevented.

[0012]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an electric configuration of an electric power steering apparatus according to one embodiment of the present invention. A steering torque applied to a steering wheel 1 as an operation member is mechanically transmitted to a steering mechanism 3 via a steering shaft 2. The driving force generated from the electric motor 4 is transmitted to the steering mechanism 3 as a steering assist force via a driving force transmission mechanism such as a gear mechanism or a ball screw mechanism.

In relation to the steering shaft 2, the position of the steering wheel 1 is determined in advance by a steering angle reference point (for example, the steering wheel 1 when the vehicle is traveling straight ahead).
Is provided, a reference point sensor 5 is provided which outputs a detection signal when the steering angle reaches the middle point of the steering angle. The reference point sensor 5 is, for example, a proximity sensor including a magnet attached to the steering shaft 2 and a detector that detects the magnet when the position of the steering wheel 1 reaches the steering angle reference point and outputs a detection signal. Can be configured. The detection signal of the reference point sensor 5 is input to the controller 6.

The controller 6 includes a motor current sensor 7 for detecting a current i flowing through the electric motor 4 and a vehicle speed sensor 8 for detecting a traveling speed (vehicle speed) ν of the vehicle, in addition to the detection signal of the reference point sensor 5. Is input.
The controller 6 controls the electric motor 4 based on the detection signals input from the reference point sensor 5, the motor current sensor 7, and the vehicle speed sensor 8 so that a steering assist force corresponding to the steering of the steering wheel 1 is given to the steering mechanism 3.
Drive control.

The controller 6 obtains a steering angle θ (the rotation angle of the steering wheel 1 with respect to the steering angle midpoint) based on the motor current i and the like by a program processing by a microcomputer provided therein. A calculation unit 61; a command voltage setting unit 62 for setting a voltage (command voltage) V ^* to be applied to the electric motor 4 based on the steering angle θ and the vehicle speed ν obtained by the steering angle calculation unit 61; Each function of the abnormality detection unit 63 that detects an abnormality of the reference point sensor 5 based on the detection signal of No. 5 and the steering angle θ obtained by the steering angle calculation unit 61 is realized. Further, the controller 6 includes a motor driver 64 that applies a voltage corresponding to the command voltage V ^* set by the command voltage setting unit 62 to the electric motor 4.

FIG. 2 is a flowchart for explaining the drive control of the electric motor 4. When the IG (ignition) switch of the vehicle is turned on (step S
1 and YES), first, the steering angle θ output by the steering angle calculation unit 61.
The command voltage V ^* output from the command voltage setting unit 62 is initialized to an initial value “0” (step S2). Next, the steering angle calculator 61 calculates the initial value “0” of the command voltage V ^* and the motor current i detected by the motor current sensor 7.
, The steering angle speed θ ′, which is the time rate of change of the steering angle θ of the steering wheel 1, is calculated (step S3).
Specifically, the steering angle calculator 61 calculates the steering angular velocity θ ′ according to the following equation (1).

Θ ′ = {(V ^* −iR) −L · di / dt} / Ke (1) where R: internal resistance of electric motor 4 L: inductance of electric motor 4 Ke: Back electromotive force constant The steering angle calculation unit 61 further determines whether or not a detection signal indicating that a steering angle reference point has been detected is input from the reference point sensor 5 (step S4). If the detection signal is input from the reference point sensor 5, the steering angle θ of the steering wheel 1 is reset to a predetermined steering angle initial value θ ₀ (step S5), and the steering wheel after this reset is reset. The steering angle θ (= θ ₀ ) of 1 and the steering angular velocity θ ′ calculated according to the above equation (1) are given to the command voltage setting unit 62 and the abnormality detection unit 63. On the other hand, when the detection signal is not input from the reference point sensor 5, the steering angle θ is obtained by integrating the steering angular velocity θ ′ calculated according to the above equation (1) (step S6), and the obtained steering angle θ is obtained. And the steering angular velocity θ ′ are given to the command voltage setting unit 62 and the abnormality detection unit 63.

The steering angle initial value θ ₀ is set to the steering angle when the steering wheel 1 is at the steering angle reference point.
For example, when the steering angle reference point is set at the steering angle midpoint, the steering angle initial value θ ₀ is set to the steering angle “0” when the steering wheel 1 is at the steering angle midpoint. The instruction voltage setting unit 62 determines whether the vehicle speed ν detected by the vehicle speed sensor 8 is zero (Step S7). If the vehicle speed ν is not zero, the road surface reaction force returns even in the steering-holding state (the steering angular velocity is zero), so the command voltage setting unit 62 calculates the steering angle θ based on the steering angle θ obtained by the steering angle calculation unit 61. An instruction voltage V ^* which is an instruction value of a voltage to be applied to the electric motor 4 is set (steering angle sensitive assist control). That is, when the vehicle speed ν is not zero, the command voltage V ^* is set according to the following equation (2) (step S8).

V ^* = K _θ (ν) · θ (2) K _θ (ν): steering angle assist coefficient (function of vehicle speed ν) On the other hand, when vehicle speed ν is zero, steering is stopped. Unless this happens, the road reaction force will not return. In the configuration in which the command voltage is set based on the steering angle, the electric motor 4 is driven if the steering angle θ is present even when no steering force is applied to the steering wheel 1, so the command voltage setting unit 62 Sets an instruction voltage V ^* , which is an instruction value of a voltage to be applied to the electric motor 4, based on the steering angle speed θ ′ obtained by the steering angle calculation unit 61, instead of the steering angle θ (steering angle speed sensitive assist). control).
That is, when the vehicle speed ν is zero, the command voltage V ^* is set according to the following equation (3) (step S9).

V ^* = K _{θ ′} · θ ′ (3) K _{θ ′} : steering angular velocity assist coefficient (constant) When the indicated voltage V ^* is set in this way, the indicated voltage V ^*
, The motor driver 64 is controlled, and a driving voltage is applied from the motor driver 64 to the electric motor 4. It is determined whether the IG switch of the vehicle has been turned off (step S10). While the IG switch is on, the process returns from step S10 to step S3, and the processes of steps S3 to S10 described above are repeatedly performed. If the IG switch is turned off while the processing of steps S3 to S10 is repeatedly performed, step S1 is performed.
When it is determined that the IG switch is off at 0, it is affirmed, and the process for drive control of the electric motor 4 ends.

As described above, according to this embodiment, the steering angular velocity θ 'is calculated based on the command voltage V ^* and the motor current i, and the steering angle θ is obtained by integrating the steering angular velocity θ'. . If the vehicle speed ν is not zero, the command voltage V ^* to be applied to the electric motor 4 is set based on the obtained steering angle θ. If the vehicle speed ν is zero, the command voltage V ^* is set based on the steering angular speed θ ′. Thus, the command voltage V ^* is set. Thereby, the steering wheel 1 is used for controlling the electric motor 4.
Since a torque sensor for detecting the steering torque applied to the steering wheel and a steering angle sensor for detecting the steering angle of the steering wheel 1 are not required, the cost of the electric power steering apparatus can be reduced as compared with the related art.

In this embodiment, when the steering wheel 1 reaches a predetermined steering angle reference point (eg, a steering angle midpoint), the steering angle θ obtained by the integral calculation is changed to a predetermined steering angle initial value. Reset to θ ₀ . As a result, it is possible to prevent accumulation of integration errors due to the progress of the drive control of the electric motor 4, and to realize good drive control of the electric motor 4 based on the steering angle θ obtained by the integral calculation. However, if an abnormality occurs in the reference point sensor 5 that detects that the steering wheel 1 has reached a predetermined steering angle reference point, the steering angle θ is not reset at the correct timing. An error between the required steering angle θ and the actual steering angle of the steering wheel 1 increases, which may adversely affect the drive control of the electric motor 4. Therefore, as described above, the controller 6
An abnormality detection unit 63 for detecting an abnormality of the reference point sensor 5 is provided. When the abnormality detection unit 63 detects an abnormality of the reference point sensor 5, for example, a transition is made to a fail-safe mode, and Driving is stopped.

FIG. 3 is a flowchart for explaining the abnormality detection processing executed by the abnormality detection section 63.
This abnormality detection process is, for example, an interrupt process performed at predetermined time intervals when the vehicle is running. The abnormality detection unit 63 first determines that the steering angle θ calculated by the steering angle calculation unit 61 is within a predetermined angle range (for example, a range of ± 10 degrees from the steering angle θ ₀ when the steering wheel 1 is at the steering angle reference point). Inside: θ ₀ −10 degrees ≦ θ ≦ θ ₀ +10 degrees) is determined (step T1). If the steering angle θ is not within the predetermined angle range, the abnormality detection processing is immediately returned, and the processing described below is not performed.

If the steering angle θ is within the above-mentioned predetermined angle range, the abnormality detecting section 63 sets “1” to a reference point detection flag indicating whether or not the steering angle reference point has been detected (step T).
2). Then, it is determined whether or not a detection signal indicating that the steering wheel 1 has reached the steering angle reference point is input from the reference point sensor 5 (step T3).
When the detection signal is input from the reference point sensor 5, the reference point detection flag is reset to “0” (step T).
4) Then, it is determined whether or not the steering angle θ calculated by the steering angle calculation unit 61 is out of the predetermined angle range (for example, θ <θ ₀ −10 degrees or θ ₀ +10 degrees <θ). (Step T5). On the other hand, when the detection signal is not input from the reference point sensor 5, the reference point detection flag is “1”.
It is determined whether or not the steering angle θ calculated by the steering angle calculation unit 61 is out of the predetermined angle range (step T5). While the steering angle θ is within the predetermined angle range, the determination as to whether the steering angle θ is out of the predetermined angle range is denied, and whether the detection signal is input from the reference point sensor 5 is determined. Can be checked repeatedly.

When the steering angle θ is out of the predetermined angle range, the abnormality detecting section 63 increases the steering angle θ from a value smaller than the lower limit of the predetermined angle range (for example, θ <θ ₀ -10 degrees). Then, it is determined whether or not the angle is within the predetermined angle range, further increases and becomes larger than the upper limit value of the predetermined angle range (for example, θ ₀ +10 degrees) and deviates from the predetermined angle range (step T6). Further, the steering angle θ decreases from a value larger than the upper limit value of the predetermined angle range, enters the predetermined angle range, further decreases and becomes smaller than the lower limit value of the predetermined angle range, and It is determined whether the deviation has occurred (step T7).

If one of the determinations in steps T6 and T7 is affirmative, the abnormality detecting section 63 sets the reference point detection flag to "1".
It is determined whether or not is set (step T8).
If the reference point detection flag is still set to “1”, the detection signal is not output from the reference point sensor 5 even though the steering wheel 1 has passed the steering angle reference point. The abnormality detection unit 63
Determines that an abnormality has occurred in the reference point sensor 5 (step T9). On the other hand, if the reference point detection flag has been reset to "0", the abnormality detection unit 63 determines that the reference point sensor 5 is operating normally (step T1).
0). Then, the abnormality detection processing is returned.

If both of the determinations in steps T6 and T7 are negative (NO in step T7), that is, the steering angle θ increases from a value smaller than the lower limit value of the predetermined angle range to increase the steering angle θ in the predetermined angle range. When the steering angle θ falls below the lower limit of the predetermined angle range and deviates from the predetermined angle range, or the steering angle θ decreases from a value larger than the upper limit of the predetermined angle range. The steering wheel 1 does not pass through the steering angle reference point when the steering wheel 1 is within the predetermined angle range and thereafter increases and exceeds the upper limit value of the predetermined angle range to deviate from the predetermined angle range. Since there is a possibility that it is not possible to accurately determine whether or not an abnormality has occurred in the reference point sensor 5, this abnormality detection processing is returned.

Note that the reference point detection flag is reset to "0" upon return from the abnormality detection processing. As described above, in this embodiment, the abnormality detection unit 63 realized by the program processing by the microcomputer provided in the controller 6 detects whether the reference point sensor 5 has an abnormality. Here, a configuration is conceivable in which the same sensor as the reference point sensor 5 is added as a sensor for fail detection, and the outputs of these two sensors are compared to detect an abnormality of the reference point sensor 5. Inevitably increases the cost of the electric power steering device.
On the other hand, according to the configuration according to this embodiment, no new sensor or the like is required, so that the cost of the electric power steering device does not increase.

Although the embodiment of the present invention has been described above, the present invention can be embodied in other forms. For example, as shown in step S80 of FIG.
When the vehicle speed ν is not zero, the command voltage V ^* is set based on a linear combination of the operation position θ, the steering angular velocity θ ′, and the steering angular acceleration θ ″ obtained by further differentiating the steering angular velocity θ ′. That is, when the vehicle speed ν is not zero, the command voltage V ^* is set according to the following equation (4).

V ^* = K _θ (ν) · θ + K _{θ ′} · θ ′ + K _{θ ”} · θ” (4) K _{θ ”} : steering angle acceleration assist coefficient (constant) In FIG. Steps having the same contents as the respective steps in Fig. 2 are denoted by the same reference numerals as those in Fig. 2. In the above-described embodiment, the steering wheel 1 is used as the operation member. The operation member has been described above, but the operating member may be a lever or the like that moves linearly.

In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric configuration of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining an example of drive control of an electric motor.

FIG. 3 is a flowchart illustrating an abnormality detection process.

FIG. 4 is a flowchart for explaining another example of drive control of the electric motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steering wheel 3 Steering mechanism 4 Electric motor 5 Reference point sensor 6 Controller 7 Motor current sensor 61 Steering angle calculation part 62 Instruction voltage setting part 63 Abnormality detection part 64 Motor driver i Motor current V ^* Instruction voltage θ 'Steering angular velocity θ Steering angle θ ₀ steering angle initial value

Claims (3)

[Claims] 1. An electric power steering apparatus for controlling an electric motor according to a position and an operation speed of an operation member and applying a driving force from the electric motor to a steering mechanism to assist in steering, wherein a motor flowing to the electric motor is provided. Motor current detecting means for detecting a current; operating speed calculating means for obtaining an operating speed of the operating member based on the motor current detected by the motor current detecting means; and operation of the operating member obtained by the operating speed calculating means Operating position calculating means for calculating the position of the operating member by integrating the speed; reference point detecting means for outputting a detection signal in response to the position of the operating member reaching a predetermined reference point; When a detection signal is output from
Integral resetting means for resetting the result of integration by the operating position calculating means to a predetermined initial value, vehicle speed detecting means for detecting vehicle speed, and when the vehicle speed is not zero, controlling the electric motor according to the position of the operating member, An electric power steering apparatus, comprising: control means for controlling the electric motor based on the operation speed of the operation member obtained by the operation speed calculation means when the vehicle speed is zero. 2. An operation acceleration calculating means for differentiating an operation speed obtained by the operation speed calculation means to obtain an operation acceleration, wherein the control means determines a position of the operation member when the vehicle speed is not zero. 2. The electric motor according to claim 1, wherein the electric motor is controlled in accordance with a linear combination value of the operation speed of the operation member obtained by the operation speed calculation means and the operation acceleration obtained by the operation acceleration calculation means. Power steering device. 3. The method according to claim 1, wherein the position of the operating member determined by the operating position calculating means increases from a value smaller than a lower limit value of a predetermined range including the predetermined reference point, enters the predetermined range, and further increases. While the value exceeds the upper limit of the predetermined range and deviates from the predetermined range, or the position of the operation member decreases from a value larger than the upper limit of the predetermined range, enters the predetermined range, and further decreases. Accordingly, if the detection signal is output from the reference point detecting means while the value is smaller than the lower limit value of the predetermined range and deviates from the predetermined range, it is determined that the reference point detecting means is normal. The apparatus further includes abnormality presence / absence determination means for determining that an abnormality has occurred in the reference point detection means when a detection signal is not output from the reference point detection means. Electric power steering apparatus according to claim 1 or 2, wherein that.