JP2006182166A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of accurately performing determination of abnormality by eliminating the influence of power generation by an electric motor. <P>SOLUTION: First and second relays 41, 42 are interposed on electricity feed lines 35, 36 between a motor drive circuit 27 and the electric motor M respectively. Pull-up resistance R1 and pull-down resistance R2 are connected to the electricity feed line 35 and give an abnormality detection voltage to the electricity feed line 35 when the motor drive circuit 27 is in the stopping state. Similarly, pull-up resistance R3 and pull-down resistance R4 are connected to the electricity feed line 36 and give the abnormality detection voltage to the electricity feed line 36 when the motor drive circuit 27 is in the stopping state. These abnormality detection voltages are monitored by an abnormality determination processing part 33. At the abnormality determination processing, at least one at the normal side of the first and second relays 41, 42 is made to the shutting off state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus configured to transmit power of an electric motor driven in accordance with an operation of an operation member for steering to a steering mechanism.

  2. Description of the Related Art Conventionally, an electric power steering device that assists steering by driving an electric motor in accordance with an operation of a steering wheel and transmitting the power of the electric motor to a steering mechanism is mounted on a vehicle and used. The electric power steering apparatus includes, for example, the electric motor and an electric power steering ECU (electronic control unit) that controls the electric motor.

The electric power steering ECU includes, for example, a motor drive circuit that supplies electric power from a battery to the electric motor, a PWM drive pulse generation circuit that supplies a PWM drive pulse to the motor drive circuit, and the PWM drive pulse generation circuit. And a microcomputer for providing a control signal representing the PWM duty.
FIG. 4 is an electric circuit diagram showing the basic configuration of the motor drive circuit. This motor drive circuit is configured by bridge-connecting four power transistors 1 to 4. That is, the series circuit of the transistors 1 and 2 and the series circuit of the transistors 3 and 4 are connected in parallel to each other between the power supply line on the power supply voltage Vb side from the battery and the ground. A connection point 5 between the transistors 1 and 2 and one terminal of the electric motor 10 are connected via the feed line 8, and a connection point 6 between the transistors 3 and 4 and the other terminal of the electric motor 10 are connected. Are connected via a fail-safe relay 7 and a power supply line 9. A pull-up resistor 11 is connected between the power supply line 8 and the power supply voltage Vb, and a pull-down resistor 12 is connected between the power supply line 9 and the ground. Reference numeral 13 denotes a motor current detection resistor.

The power transistors 1 to 4 are turned on / off in response to a drive signal from the PWM drive pulse generation circuit, whereby the power supply to the electric motor 10 is controlled.
The electric power steering ECU performs various types of abnormality detection processing. Among these, there is processing for detecting an abnormal drop in the terminal voltage of the electric motor 10. This abnormal decrease in terminal voltage is determined with reference to the potential at the connection points 5 and 6. The microcomputer in the electric power steering ECU detects a decrease in the potential at any one of the connection points 5 and 6 to determine abnormality, and further stops the generation of the PWM drive pulse from the PWM drive pulse generation circuit. Then, the motor driving circuit is stopped. In addition, the sum of the potentials at the connection points 5 and 6 is obtained. If this is the ground level, the abnormality determination is confirmed and the fail-safe relay 7 is shut off.

For example, as shown in FIG. 4, when the connection point 5 has a ground fault (specifically, a ground fault of the feed line 8), if the electric motor 10 is in a stopped state, the total potential of the connection points 5 and 6 Is at ground level.
JP-A-11-98888

  However, the situation is different when the electric motor 10 is in a rotating state and motor power generation is occurring. That is, the potential of the connection point 6 is increased by the motor power generation, and is increased to about the battery voltage Vb. In this case, even if the connection point 5 is grounded, the sum of the potentials at the connection points 5 and 6 does not substantially reach the ground level. Therefore, there is a possibility that it is determined that there is no ground fault and is normal.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering apparatus that can accurately determine an abnormality while eliminating the influence of power generation by an electric motor.

  The electric power steering device according to the present invention assists steering by transmitting the power of the electric motor (M) controlled in accordance with the operation of the operating member (21) to the steering mechanism (22). ) To control the power supply to the electric motor to drive the electric motor, and is connected between the motor driving circuit and the first terminal (m1) of the electric motor. First switching means (41), second switching means (42) connected between the motor drive circuit and the second terminal (m2) of the electric motor, the first switching means, A pull-up resistor (R1, R3) is connected between the second switching means and the motor drive circuit, and generates a predetermined abnormality detection voltage when the motor drive circuit is stopped. It is characterized in that it comprises a pull-down resistor (R2, R4). The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.

According to this configuration, if at least the normal-side switching means in which no abnormality has occurred among the first and second switching means is set in the cut-off state, the first and second switching means and the motor drive circuit By monitoring this potential, it is possible to perform accurate abnormality determination processing without being affected by power generation by the electric motor.
For example, when a ground fault occurs in the power supply line on the first switching means side, a pull-up resistor or a motor drive circuit is provided between the second switching means and the motor drive circuit if the second switching means is turned off. The abnormality detection voltage generated by the pull-down resistor appears and is not affected by the power generation from the electric motor. Thereby, an accurate abnormality determination process can be performed. In this case, only the second switching means may be in the cutoff state, or both the first and second switching means may be in the cutoff state.

  In one embodiment of the present invention, a pull-up resistor (R1) is connected between the first power supply line (35) between the first switching means and the motor drive circuit and the power supply line (46). The pull-down resistor (R2) is connected to the ground. Similarly, a pull-up resistor (R3) is connected between the second power supply line (36) between the second switching means and the motor drive circuit, and between the power supply line and the ground. A pull-down resistor (R4) is connected. Thereby, when the motor drive circuit is in a stopped state, if there is no failure, an abnormality detection voltage due to the voltage division of the pull-up resistor and the pull-down resistor appears in the first and second power supply lines. At this time, for example, if the first and second switching means are in the cut-off state, the abnormality detection voltage can be monitored by eliminating the influence of power generation by the electric motor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram for explaining a configuration example of an electric power steering apparatus according to an embodiment of the present invention. This electric power steering apparatus is used by being mounted on a vehicle, and drives an electric motor M in response to an operation of a steering wheel 21 as an operation member for steering, and the power generated by the electric motor M is used as a steering mechanism 22. Steering assistance is performed by mechanically transmitting to.

  The electric power steering apparatus includes a torque sensor 23 that detects a steering torque applied to the steering wheel 21 and an electric power steering ECU (electronic control unit) 25 as a controller. The ECU 25 is provided with an output signal from a vehicle speed sensor 24 that detects the speed (vehicle speed) of the vehicle. The ECU 25 controls the drive of the electric motor M based on signals from the torque sensor 23 and the vehicle speed sensor 24.

  The ECU 25 includes a microcomputer 30, a PWM (pulse width modulation) pulse generation circuit 26, a motor drive circuit 27, and a current detection circuit 28. The microcomputer 30 generates a control signal for controlling the electric motor M based on the steering torque, the vehicle speed, and the current flowing through the electric motor M, and supplies the control signal to the PWM pulse generation circuit 26. The PWM pulse generation circuit 26 generates a PWM pulse having a duty corresponding to the given control signal and inputs the PWM pulse to the motor drive circuit 27. The motor drive circuit 27 includes a plurality of switching elements (power transistors) that are turned on / off based on the PWM pulse supplied from the PWM pulse generation circuit 26, and supplies a current corresponding to the control signal to the electric motor M. The current actually flowing through the electric motor M is detected by the current detection circuit 28, and the detection result is fed back to the microcomputer 30.

  The microcomputer 30 substantially has a plurality of function processing units realized by a CPU (not shown) executing a predetermined program stored in an internal memory (not shown). The plurality of function processing units include a target current value calculation unit 31 that calculates a target current value to be supplied to the electric motor M based on the steering torque detected by the torque sensor 23 and the vehicle speed detected by the vehicle speed sensor 24, and A current control unit 32 for generating a control signal to be given to the PWM pulse generation circuit 26 in order to match the target current value calculated by the target current value calculation unit 31 with the motor current detected by the current detection circuit 28; An abnormality determination processing unit 33 that determines whether there is an abnormality in the electric power steering apparatus is included.

  With such a configuration, the electric motor M is feedback-controlled so that the target current value corresponding to the steering torque and the vehicle speed is achieved, and accordingly, the electric motor M is appropriately controlled according to the steering torque and the vehicle speed applied to the steering wheel 21. A steering assist force is applied to the steering mechanism 22. On the other hand, when any abnormality occurs in the electric power steering apparatus by the abnormality determination processing by the abnormality determination processing unit 33, fail-safe processing for stopping the electric motor M for applying the steering assist force to the steering mechanism 22 is performed. It has come to be.

  More specifically, the pair of power supply lines 35 and 36 that connect the ECU 25 and the electric motor M are connected to the first terminal m1 and the second terminal m2 of the electric motor M, respectively. A first relay 41 as a first switching means and a second relay 42 as a second switching means are interposed between the power supply lines 35 and 36 and the ECU 25, respectively. The abnormality determination processing unit 33 performs a fail-safe process for stopping power supply to the electric motor M by setting one or both of the first and second relays 41 and 42 to a cut-off state when any abnormality occurs. Execute.

  In the power supply lines 35 and 36, the motor drive circuit 27 is connected to the ECU 25 side with respect to the first and second relays 41 and 42. The motor drive circuit 27 is supplied with power from the in-vehicle battery 45. A motor current detection resistor 29 is connected between the motor drive circuit 27 and the ground. When the voltage between the terminals of the motor current detection resistor 29 is detected by the current detection circuit 28, the current detection circuit 28 inputs a current detection signal corresponding to the motor current to the microcomputer 30.

  The power feed line 35 between the motor drive circuit 27 and the first relay 41 is connected to the power supply line 46 and connected to the ground (between the motor current detection resistor 29 and the ground). May be connected to the pull-down resistor R2. The potential of the connection point 51 of these resistors R1 and R2 (that is, the power supply line 35 between the motor drive circuit 27 and the first relay 41) is monitored by the abnormality determination processing unit 33 in the microcomputer 30. It has become.

  On the other hand, the power supply line 36 between the motor drive circuit 27 and the second relay 42 is connected to a power supply line 46, and is connected to the ground (between the motor current detection resistor 29 and the ground). The pull-down resistor R4 may be connected to. The potential of the connection point 52 of the resistors R3 and R4 (that is, the potential of the power supply line 36 between the motor drive circuit 27 and the second relay 42) is monitored by the abnormality determination processing unit 33 in the microcomputer 30. It has become.

  FIG. 2 is an electric circuit diagram for explaining a specific configuration of the motor drive circuit 27. The motor drive circuit 27 is constituted by a bridge circuit of four power transistors (switching elements) Q1, Q2, Q3, Q4 connected between the power supply line 46 and the motor current detection resistor 29. More specifically, motor drive circuit 27 connects a series circuit of power transistors Q1 and Q2 and a series circuit of power transistors Q3 and Q4 in parallel between power supply line 46 and motor current detection resistor 29. In addition, the power supply line 35 is connected to the connection point 61 of the transistors Q1 and Q2, and the power supply line 36 is connected to the connection point 62 of the transistors Q3 and Q4.

  By supplying the PWM pulses from the PWM pulse generation circuit 26 to the power transistors Q1 to Q4, power is supplied to the electric motor M via the first and second relays 41 and 42. For example, when the electric motor M is rotated in the first direction, the PWM pulse generation circuit 26 holds the transistors Q2 and Q3 in the off state, holds the transistor Q4 in the on state, and applies a duty to the transistor Q1. Supply a controlled PWM pulse. Thereby, the electric current which passes the power transistor Q1, the 1st relay 41, the electric motor M, the 2nd relay 42, and the power transistor Q4 in order from the vehicle-mounted battery 45 flows. On the other hand, when the electric motor M is rotated in the second direction opposite to the first direction, for example, the PWM pulse generation circuit 26 holds the power transistors Q1 and Q4 in the off state and the power transistor Q2 in the on state. At the same time, a duty-controlled PWM pulse is applied to the power transistor Q3. As a result, the current from the in-vehicle battery 45 flows through the transistor Q3, the second relay 42, the electric motor M, the first relay 41, and the power transistor Q2 in this order.

  The pull-up resistor R1 and the pull-down resistor R2 are configured to reduce the potential at the connection point 61 (that is, the potential of the power supply line 35) when the transistors Q1 and Q2 are both off (when the motor drive circuit 27 is stopped). A predetermined potential (abnormal detection voltage) corresponding to the voltage division ratio of R1 and R2 is used. Specifically, for example, the resistance values of the resistors R1 and R2 are determined to be equal. As a result, when both of the power transistors Q1 and Q2 are in the off state, the potential at the connection point 61 is a half of the battery voltage Vb. Vb / 2 appears.

  Similarly, the pull-up resistor R3 and the pull-down resistor R4 are connected to the connection point 62 (that is, the power supply line 36) when the power transistors Q3 and Q4 are both off (when the motor drive circuit 27 is stopped). This is for generating a predetermined abnormality detection voltage corresponding to the voltage division ratio of R3 and R4. Specifically, if the resistance values of the resistors R3 and R4 are set equal, the battery voltage Vb is applied to the connection point 62 (that is, the power supply line 36) when both of the power transistors Q3 and Q4 are off. One half of the potential Vb / 2 appears.

  In the configuration of FIG. 2, since the pull-down resistors R2 and R4 are connected to the motor current detection resistor 29, when the resistance values of the resistors R1 and R2 are actually equal and the resistance values of the resistors R3 and R4 are equal, Although the potential of the connection points 61 and 62 when the motor drive circuit 27 is stopped is not exactly Vb / 2, the resistance value of the motor current detection resistor 29 is compared with the resistance values of the resistors R1, R2, R3, and R4. If it is sufficiently small, the potential at the connection points 61 and 62 is approximately Vb / 2.

  For example, when a ground fault occurs at the connection point 61 (that is, the power supply line 35), the potential at the connection point 61 (equal to the potential at the connection point 51) becomes the ground level. At this time, the abnormality determination processing unit 33 (see FIG. 1) of the microcomputer 30 adds the potentials of the connection points 51 and 52 to obtain the determination value Vmadd. The abnormality determination processing unit 33 determines that a ground fault has occurred based on the fact that this determination value Vmadd is clearly less than a predetermined determination reference value (for example, battery voltage Vb). Based on this abnormality determination, the abnormality determination processing unit 33 interrupts at least one of the first and second relays 41 and 42 and stops the supply of current to the electric motor M.

  When a ground fault occurs at the connection point 61 side, if the electric motor M is in a rotating state, the electric potential of the connection point 62 may rise to almost the battery voltage Vb due to the electric power generation of the electric motor M. As a result, the abnormality determination process may not be performed accurately. Therefore, in this embodiment, when a ground fault occurs on the connection point 61 side, the abnormality determination processing unit 33 opens (turns off) at least the second relay 42 on the normal side, The potential of 36 is monitored and added to obtain a determination value Vmadd. Thereby, the abnormality determination process can be performed without being affected by the power generation of the electric motor M.

  FIG. 3 is a flowchart for explaining the abnormality determination processing by the abnormality determination processing unit 33. The abnormality determination processing unit 33 constantly monitors the potentials of the connection points 51 and 52 (that is, the potentials of the power supply lines 35 and 36) during the operation of the electric power steering apparatus. When a voltage drop in one of the power supply lines 35 and 36 (that is, a voltage drop in the terminals m1 and m2 of the electric motor M) is detected (step S1), the power supply on the normal side that is not the abnormal side where the voltage drop is detected is detected. The relay 41 or 42 inserted in the line is turned off (OFF) (step S2). At this time, both the first and second relays 41 and 42 may be cut off.

  Next, the abnormality determination processing unit 33 adds the potentials of the connection points 51 and 52 (the potentials of the power supply lines 35 and 36 between the motor drive circuit and the first and second relays 41 and 42) and adds up the sum of them. The determination value Vmadd is obtained (step S3). Further, the abnormality determination processing unit 33 determines whether or not the obtained determination value Vmadd is substantially equal to the battery voltage Vb as the determination reference value (step S4). If the determination value Vmadd is substantially equal to the battery voltage Vb, it is determined that no abnormality has occurred, that is, it is normal (step S5), and the relays 41 and 42 that have been disconnected are closed (turned on) (step S6). Then, the power supply to the electric motor M is continued.

On the other hand, when the determination value Vmadd is clearly smaller than the battery voltage Vb (NO in step S4), the abnormality determination processing unit 33 determines that an abnormality (in this case, a ground fault) has occurred. (Step S7), the relays 41 and 42 are kept in the cut-off state, and power supply to the electric motor M is prohibited.
The abnormality determination processing unit 33 may perform initial abnormality determination processing before starting control of the electric motor M, in addition to the above-described abnormality determination processing that is always performed during the operation of the electric power steering apparatus. This initial abnormality determination process can be performed in the same manner as steps S2 to S7 shown in FIG. However, in this case, it is preferable that both the first and second relays 41 and 42 are in the cut-off state, the sum of the potentials of the power supply lines 35 and 36 is obtained as the determination value Vmadd, and the abnormality determination is performed based on this.

  As described above, according to this embodiment, the first and second relays 41 and 42 are respectively inserted in the power supply lines 35 and 36 connected to the first and second terminals m1 and m2 of the electric motor M, respectively. At the same time, the abnormality determination process can be accurately performed in a state where the electric motor M is disconnected by the configuration in which the abnormality detection voltage is generated by the pull-up resistors R1 and R3 and the pull-down resistors R2 and R4. As a result, accurate abnormality determination is possible without being affected by the power generation of the electric motor M.

  As mentioned above, although one Embodiment of this invention was described, this invention can also be implemented with another form. For example, in the above-described embodiment, the abnormality determination process is performed using the total potential appearing in the power supply lines 35 and 36 when the motor drive circuit 27 is stopped as the determination value Vmadd. The abnormality appearing process may be performed by individually comparing the potential appearing at と with a predetermined judgment reference value (for example, Vb / 2).

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

It is a block diagram for demonstrating the structural example of the electric power steering apparatus which concerns on one Embodiment of this invention. It is an electric circuit diagram for demonstrating the specific structure of a motor drive circuit. It is a flowchart for demonstrating the abnormality determination process by an abnormality determination process part. It is an electric circuit diagram which shows the basic composition of a motor drive circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Steering wheel, 25 ... Electric power steering ECU, 30 ... Microcomputer, 35, 36 ... Feed line, 41 ... First relay, 42 ... Second relay, 45 ... In-vehicle battery, 46 ... Power supply line, m1, m2 ... Terminal, M ... Electric motor, R1, R3 ... Pull-up resistor, R2, R4 ... Pull-down resistor

Claims (1)

An electric power steering device for assisting steering by transmitting power of an electric motor controlled according to an operation of an operation member to a steering mechanism,
A motor drive circuit for controlling power feeding from a power source to the electric motor to drive the electric motor;
First switching means connected between the motor drive circuit and the first terminal of the electric motor;
Second switching means connected between the motor drive circuit and a second terminal of the electric motor;
A pull-up resistor or a pull-down resistor that is connected between the first switching means and the second switching means and the motor drive circuit and generates a predetermined abnormality detection voltage when the motor drive circuit is in a stopped state. And an electric power steering device.

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