JP2004306858A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device which performs electric current feedback control and can detect an open abnormality. <P>SOLUTION: The electric power steering device has an electric motor generating an assist force to a turning operation of a steering wheel, a torque sensor detecting torque by the turning operation, an electric current feedback control means determining an indication current value to the electric motor from a target current determined based on the torque detected by the torque sensor and an actual current flowing in the electric motor, and a current-carrying control means controlling current-carrying to the electric motor according to an indication current value. The current feedback control means determines that the open abnormality occurs in a circuit composing the current-carrying means when an actual current is zero and the duty ratio of the indication current value is 100 %. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to an electric power steering device that performs current feedback control, and more particularly to an electric power steering device that can detect that an open abnormality has occurred in a current supply circuit to a motor.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electric power steering device that determines that a short circuit abnormality has occurred in a current supply circuit to a motor when an actual current value flowing through the motor exceeds a command current value to the motor determined according to a vehicle speed by a predetermined value or more. Is known (for example, refer to Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Publication No. 6-29031
[Problems to be solved by the invention]
However, the above-described conventional electric power steering apparatus detects a short circuit abnormality (for example, page 6, left column, lines 6 to 15 and page 3, right column, 14 to 18 of Patent Document 1). Line, etc.), an open failure such as opening of a switching element or disconnection of a motor harness is not detected.
[0005]
In addition, the conventional electric power steering apparatus does not control the actual current to approach the target current (for example, page 24, right column, lines 24 to 36 of Patent Document 1 and FIG. 5). S6 to S9, etc.), so-called feedback control is not assumed.
[0006]
The present invention has been made to solve such a problem, and has as its main object to provide an electric power steering device capable of performing current feedback control and detecting an open abnormality.
[0007]
[Means for Solving the Problems]
One embodiment of the present invention for achieving the above object is an electric motor that generates an assist force for a turning operation of a steering wheel, a torque sensor that detects a torque due to the turning operation, and a torque sensor that detects the torque. Current feedback control means for determining a command current value to the electric motor from a target current determined based on the torque and an actual current flowing to the electric motor; and energizing the electric motor according to the command current value. And an energization control unit for controlling the energization control unit, wherein the current feedback control unit is configured to control the energization control unit when the actual current is zero and the duty ratio of the indicated current value is 100%. An electric power steering apparatus characterized in that it is determined that an open abnormality has occurred in a circuit constituting the power steering apparatus.
[0008]
In this aspect, the energization control means includes, for example, a circuit having a plurality of switching elements and controlling the energization current and energization direction of the electric motor by PWM control.
[0009]
Further, in this aspect, the open abnormality refers to a state in which current does not flow through the motor due to an open failure of a switching element for energizing a battery power supply to the motor generating the steering assist force or a disconnection of the motor harness. Shall point to.
[0010]
According to this aspect, when an open abnormality occurs in the electric power steering device that performs the current feedback control, the duty ratio of the current value specified by the current feedback control becomes 100%, but the actual current flowing through the motor is zero. , The open abnormality can be easily and reliably detected.
[0011]
In this embodiment, when an open abnormality is detected, all the switching elements of the energization control means are opened, and a relay provided on the motor harness is turned off. It is preferable to take measures such as avoiding the state.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0013]
First, a schematic configuration of the electric power steering device according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram partially showing an electric power steering device 100 according to the present embodiment.
[0014]
The torque sensor 101 is a sensor that detects a steering torque input by a driver through a steering handle (not shown), and the sensor type or detection method may be any.
[0015]
The microcomputer 102 is a control unit that causes the motor 109 to generate a steering assist force according to the torque detected by the torque sensor 101, and includes an analog / digital (A / D) converter 103, a target current calculation unit 104, a current feedback It has a controller 105 and a PWM duty control unit 106. In the present embodiment, these components 103 to 106 of the microcomputer 102 are realized as software or a program.
[0016]
The target current calculator 104 calculates a target current i ^* based on the torque sensor output value A / D converted by the A / D converter 103. Here, the target current is basically determined so as to increase as the steering torque increases, but the specific determination method may be an arbitrary method. Also, other parameters such as vehicle speed may be considered in addition to the steering torque.
[0017]
Current feedback controller 105, based on a value obtained by subtracting the actual current i flowing through the motor 109 measured by the current sensor 112 from the target current ^{i * (i} * -i), matching the actual current i to the target current ^{i *} The current flowing through the motor 109, specifically, the duty ratio of the current is determined.
[0018]
The PWM duty control unit 106 controls the opening and closing of the switching elements Tr1 to Tr4 so that the duty ratio instructed by the current feedback controller 105 is realized, and the current flowing from the battery 107 to the motor 109 and the current flowing direction. Adjust / switch.
[0019]
The motor harness 110 is provided with a fail-safe relay 108. Further, a bridge circuit including the switching elements Tr1 to Tr4 is grounded via the shunt resistor 111.
[0020]
Next, the operation of the electric power steering apparatus according to the present embodiment, particularly when an open abnormality is detected, will be described with reference to FIG. FIG. 2 is a flowchart partially showing the operation of the electric power steering device 100 according to the present embodiment.
[0021]
First, in S201, the target current calculation unit 104 calculates a target current i ^* according to the steering torque.
[0022]
Next, in S202, the actual current i flowing through the motor 109 is measured by the current sensor 112.
[0023]
Next, in S203, the PWM duty is calculated by the current feedback controller 105.
[0024]
Next, in S204, the current feedback controller 105 determines whether the duty ratio calculated in S203 is 100%.
[0025]
If the duty ratio is not 100% ("NO" in S204), it is determined that the open abnormality has not occurred, the energization control of the motor 109 is performed according to the duty ratio, and the process returns to S201.
[0026]
If the duty ratio is 100% ("YES" in S204), then in S205, current feedback controller 105 determines whether or not actual current i is zero (zero amperes (0A)).
[0027]
If it is not 0A ("NO" in S205), it is determined that the current is within the range of the normal current feedback control, the energization control to the motor 109 is performed according to the duty ratio, and the process returns to S201.
[0028]
By the way, as shown in an example in FIG. 3, in the electric power steering apparatus 100 according to the present embodiment, the current feedback control by the current feedback controller 105 controls the duty ratio so that the actual current i approaches the target current i ^*. Have been. When an open failure such as an open failure of the switching elements Tr1 to Tr4 or a disconnection of the motor harness 110 occurs, no current flows to the motor 109, and the actual current i measured by the current sensor 112 is 0A. Therefore, when the open abnormality occurs, if the target current i ^* is not zero, the duty ratio is set to 100% by the current feedback control to make the actual current i (= 0 A) approach the target current i ^*. become.
[0029]
In a normal state, even if there is a difference between the target current i ^* and the actual current i, the difference should be reduced by controlling the duty ratio and flowing the current to the motor 109. In particular, when a current flows through the motor 109 at a duty ratio of 100% in a normal state, the measured value of the actual current i does not become 0 A for a predetermined time or more.
[0030]
Therefore, the electric power steering apparatus according to the present embodiment utilizes the characteristics of the current feedback control as described above, and when the actual current i is 0 A for a predetermined time or more despite the duty ratio being 100% ( (“YES” in S205), it is determined that the current is not flowing through the motor 109, that is, that the open abnormality has occurred.
[0031]
When an open abnormality has occurred, although the battery power is not supplied to the motor 109, a regenerative current flows in a direction opposite to the original energizing direction due to self-generation of the motor 109, and the steering brake state (reverse assist state) is changed. Can occur.
[0032]
Therefore, when it is determined that the open abnormality has occurred, the electric power steering apparatus according to the present embodiment turns off the switching elements Tr1 to Tr4 and the relay 108 to cut off the regenerative current (S206 and S207).
[0033]
As described above, according to the present embodiment, in the electric power steering device that performs the current feedback control, the open abnormality can be easily and reliably detected by using the characteristics of the current feedback control.
[0034]
In the above embodiment, when the state where the duty ratio is 100% and the actual current is 0 A continues for a predetermined period of time, it is determined that an open abnormality has occurred. The length of the predetermined time can be arbitrarily set. For example, it may be set in consideration of the time required for lock-to-lock rotation of the steering wheel. Similarly, when implementing the above-described embodiment, it is apparent that the numerical values of 100% of the duty ratio and 0 A of the actual current need not be strict, but can have an allowable width.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an electric power steering apparatus capable of performing current feedback control and detecting an open abnormality.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram partially showing an electric power steering device according to an embodiment of the present invention.
FIG. 2 is a flowchart partially showing an operation of the electric power steering device according to the embodiment of the present invention.
FIG. 3 is a graph showing an example of a change in an actual current and a duty ratio when an open abnormality occurs during current feedback control.
[Explanation of symbols]
REFERENCE SIGNS LIST 100 Electric power steering device 101 Torque sensor 102 Microcomputer 103 A / D converter 104 Target current calculation unit 105 Current feedback controller 106 PWM duty control unit 107 Battery 108 Relay 109 Motor 110 Motor harness 111 Shunt resistor 112 Current sensors Tr1 to Tr4 Switching elements

Claims (1)

An electric motor that generates an assist force for the turning operation of the steering wheel, a torque sensor that detects a torque due to the turning operation, a target current determined based on the torque detected by the torque sensor, and the electric motor. An electric power steering device comprising: a current feedback control unit that determines an instruction current value to the electric motor from an actual current flowing; and an energization control unit that controls energization to the electric motor according to the instruction current value. So,
When the actual current is zero and the duty ratio of the command current value is 100%, the current feedback control means determines that an open abnormality has occurred in a circuit constituting the conduction control means. An electric power steering device characterized by the above-mentioned.

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