JP2013159165A - Electric power steering device - Google Patents

Abstract

Provided is an electric power steering apparatus capable of continuing assist without lowering a steering feeling during backup control even if an abnormality occurs in one of two systems.
During normal operation, a current value ½ of a current command value I * is output to each of the two drive circuits (step S507). In the case of indicating the detection of an energization failure (step S501), the system where the energization failure has occurred is determined (step S502). Then, power supply in the system in which the energization failure has occurred is stopped (steps S503 and 505), and control signals Smc for the remaining normal system drive circuits are output (steps S504 and 506). When the current command value I * is less than the current gain K times the maximum current limit value I * max, the normal system current command value I * _a or I * _b is set to I *, and the current command value I * is the maximum. When it is larger than the current gain K times the current limit value I * max, it is set to I * max × K.
[Selection] Figure 4

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, there is an electric power steering device (EPS) using a motor as a drive source as a power steering device for a vehicle. Usually, such an electric power steering apparatus detects a steering torque by a torque sensor, and electrically controls an assist force applied to the steering system based on the detected steering torque, vehicle speed, and the like. For example, when a failure is detected, such as when an abnormality is detected in the torque sensor, the motor that is the drive source is stopped and promptly fail-safe (for example, , See Patent Document 1). In addition, it has two redundant systems, and controls the motors of both systems at the same time under normal conditions. If there is any failure in one of them, the motor is stopped and continuously driven by the remaining system motor. An electric power steering device has been proposed (see, for example, Patent Document 2).

JP 2003-182608 A JP 2004-10024 A

  In the electric power steering apparatus having the two systems as described above, the motors of both systems are simultaneously driven and controlled with a half output torque at the time of normal operation. For this reason, when an abnormality occurs in any of the systems and the assist is stopped, the assist control can be continued with the remaining motors on the system side. However, the output torque at this time is half the normal output torque, and even if the driver tries to continue the steering operation, the steering wheel is heavy and the steering feeling is lowered.

  The present invention has been made to solve the above-described problems, and its purpose is to continue assisting without lowering the steering feeling during backup control even if an abnormality occurs in one of the two systems. An object of the present invention is to provide an electric power steering device that can be used.

  In order to solve the above-mentioned problem, the invention according to claim 1 is provided with two systems of a motor for applying an assist force corresponding to a steering torque to a steering system and two motor coils of the motor. And a control means for driving the motor to control driving of the motor. The control means is a power target value for generating a motor torque corresponding to the assist force. Current command value calculation means for calculating a current command value, control signal output means for outputting two systems of control signals based on the current command value, and corresponding two systems of motor coils based on the control signals Two systems of motor drive means for outputting driving power, respectively, and when one of the systems fails, the control signal output means Calorific value is summarized in that changing the system-based current instruction value which is the target value of the driving power to be equal to or less than the amount of heat generated during normal.

  According to the above configuration, the control means of the present embodiment outputs two systems of motor drive means provided corresponding to the two systems of motor coils and outputs control signals to these motor drive means, respectively. And a control signal output means. If a failure occurs in one of the two systems, the current command value, which is the target value of the drive power, is set so that it is equal to or less than the normal amount of heat generation for the remaining other systems. Adjust and continue motor drive. As a result, the motor drive current during the backup control can be limited to suppress the motor output, so that the heat generation of the motor is suppressed and the assist can be continued without lowering the steering feeling.

  According to the present invention, it is possible to provide an electric power steering apparatus that can continue assist without lowering the steering feeling during backup control even if an abnormality occurs in one of the two systems.

The schematic block diagram of an electric power steering apparatus. The control block diagram of an electric power steering device. The control block diagram of an electric power steering device. The flowchart which shows the process sequence of control of the electric power steering apparatus in embodiment of this invention. Current command value pattern during steering. The schematic block diagram of the electric power steering apparatus in other embodiment of this invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a vehicle steering apparatus. As shown in FIG. 1, the vehicle steering apparatus 1 according to the present embodiment is provided with an electric power steering apparatus (EPS) 20. In the electric power steering apparatus 20 of the present embodiment, the steering shaft 3 to which the steering wheel 2 is fixed is connected to the rack shaft 5 via the rack and pinion mechanism 4, and the rotation of the steering shaft 3 accompanying the steering operation is performed. The rack and pinion mechanism 4 converts the rack shaft 5 into a reciprocating linear motion. Note that the steering shaft 3 of the present embodiment is formed by connecting a column shaft 3a, an intermediate shaft 3b, and a pinion shaft 3c. The linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to the knuckle (not shown) via the tie rods 6 connected to both ends of the rack shaft 5, whereby the steered wheels (wheels) 7 are steered. The corner, that is, the traveling direction of the vehicle is changed.

  The electric power steering device 20 includes an EPS actuator 10 as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system, and an ECU (control) that controls the operation of the EPS actuator 10. Means) 11.

  The EPS actuator 10 of the present embodiment is configured as a so-called column type EPS actuator in which a motor 12 as a driving source is drivingly connected to a column shaft 3 a via a speed reduction mechanism 13. In the present embodiment, a brushless motor is adopted as the motor 12. The EPS actuator 10 is configured to apply motor torque as an assist force to the steering system by decelerating the rotation of the motor 12 and transmitting it to the column shaft 3a.

  On the other hand, a torque sensor 14 and a vehicle speed sensor 15 are connected to the ECU 11. Then, the ECU 11 detects the steering torque τ and the vehicle speed V based on the output signals of the sensors.

  In the present embodiment, the torsion bar 17 is provided in the middle of the column shaft 3a, more specifically, on the steering wheel 2 side with respect to the speed reduction mechanism 13 constituting the EPS actuator 10. The torque sensor 14 of the present embodiment includes sensor elements 14a and 14b that output sensor signals Sa and Sb that can calculate the steering torque τ transmitted through the steering shaft 3 based on the twist of the torsion bar 17. It is prepared for.

  In the present embodiment, the ECU 11 as the torque calculation means detects the steering torque τ based on the sensor signals Sa and Sb output from the sensor elements 14a and 14b as output elements of the torque sensor 14. The ECU 11 calculates a target assist force based on the steering torque τ and the vehicle speed V detected by the vehicle speed sensor 15, and drives the motor 12 as a drive source to generate the target assist force in the EPS actuator 10. By supplying power, the assist force applied to the steering system is controlled.

Next, the electrical configuration of the EPS (electric power steering device) of the present embodiment will be described. 2 and 3 are control block diagrams of the electric power steering apparatus.
As shown in FIG. 2, the motor 12 of this embodiment has a stator and a rotor that are common to the two motor coils 21A and 21B, and the rotor is a motor coil 21A wound around each tooth. 21B rotates based on the magnetomotive force generated. And ECU11 of this embodiment is the structure which controls the motor torque by supplying drive electric power to each of these motor coils 21A and 21B each independently.

  The ECU 11 according to the present embodiment has two drive circuits (motor drive means) 26A and 26B provided independently for the motor coils 21A and 21B, and the drive circuits 26A and 26B, respectively. And a microcomputer (hereinafter referred to as CPU) 27 that independently outputs control signals Smc_a and Smc_b.

  Specifically, the drive circuit 26A is connected to the first system motor coil 21A via a power line, and the drive circuit 26B is connected to the second system motor coil 21B via a power line. The control signal Smc_a output from the CPU 27 is input to the drive circuit 26A, and the other control signal Smc_b is input to the drive circuit 26B. In the present embodiment, each of the drive circuits 26A and 26B employs a known PWM inverter in which three arms corresponding to each phase are connected in parallel with a switching element pair connected in series as a basic unit (arm). The control signals Smc_a and Smc_b output from the CPU 27 define the on-duty ratio of each phase arm. The ECU 11 is configured to supply the drive power output from the drive circuits 26A and 26B to the corresponding motor coils 21A and 21B independently of each other based on the control signals Smc_a and Smc_b.

  More specifically, as shown in FIG. 3, the CPU 27 of the present embodiment generates an electric power supply current command value I * for the motor 12 in order to generate a motor torque corresponding to the target assist force (current (Command value calculation means) 30 and a control signal output section (control signal output means) 31 for executing the output of the two systems of control signals Smc_a and Smc_b based on the current command value I *.

  In the present embodiment, the assist control unit 30 serving as command means is a current command value corresponding to the target assist force based on the steering torque τ detected by the torque sensor 14 and the vehicle speed V detected by the vehicle speed sensor 15. Calculate I *. Specifically, the current command value I * is calculated such that the greater the steering torque τ and the slower the vehicle speed V, the larger assist force is generated. The assist control unit 30 is configured to output the current command value I * based on the steering torque τ and the vehicle speed V to the control signal output unit 31 as a current command value for power supply to the motor 12.

  On the other hand, the control signal output unit 31 constituting the control signal output means includes the phase current values Iu_a, Iv_a, Iw_a and Iu_b, Iv_b, Iw_b and the rotation angle of the motor 12 which are supplied to the motor coils 21A, 21B of each system. θ is input. In the present embodiment, the phase current values Iu_a, Iv_a, Iw_a and Iu_b, Iv_b, Iw_b are respectively represented by current sensors 32ua, 32va, 32wa provided in the power lines of the respective systems with reference to FIG. On the other hand, the rotation angle θ of the motor 12 is detected by a common rotation angle sensor 33 while being detected independently by 32 ub, 32 vb and 32 wb. The control signals Smc_a and Smc_b corresponding to the control signal drive circuits 26A and 26B of the present embodiment are output.

  More specifically, the control signal output unit 31 of the present embodiment includes a current control unit 35A and a PWM conversion unit 36A corresponding to the first system (system including the drive circuit 26A, the motor coil 21A, and the power line shown in FIG. 2). And a current control unit 35B and a PWM conversion unit 36B corresponding to the second system (system including the drive circuit 26B, the motor coil 21B, and the power line shown in FIG. 2).

  The control signal output unit 31 uses the current command value I * input from the assist control unit 30 as the first current command value I * _a and the second current command value (system-specific current command value) I * _b. An output command arbitration unit 37 is provided. Each of the current control units 35A and 35B is configured to independently execute current feedback control based on the input first and second current command values I * _a and I * _b.

  Specifically, each current control unit 35A, 35B uses the phase current values Iu_a, Iv_a, Iw_a and Iu_b, Iv_b, Iw_b of the corresponding system as d in the d / q coordinate system according to the rotation angle θ of the motor 12. Conversion into an axial current value and a q-axis current value (d / q conversion). The current command value I * is input as a q-axis current command value (d-axis current command value is “0”). Each current command unit 35A, 35B maps the d-axis voltage command value and the q-axis voltage command value obtained by executing the current feedback control in the d / q coordinate system on the three-phase AC coordinate system. (D / q reverse conversion), the respective phase voltage command values Vu * _a, Vv * _a, Vw * _a and Vu * _b, Vv * _b, Vw * _b of the corresponding system are calculated.

  The PWM converters 36A and 36B respectively receive the phase voltage command values Vu * _a, Vv * _a, Vw * _a and Vu * _b, Vv * input from the corresponding current controllers 35A and 35B, respectively. Based on _b and Vw * _b, the control signals Smc_a and Smc_b are output to the corresponding drive circuits 26A and 26B.

  Next, a control method of the electric power steering device (EPS) in this embodiment will be described. FIG. 4 is a flowchart showing a control processing procedure of the electric power steering apparatus according to the embodiment of the present invention, and FIG. 5 is a current command value pattern during steering.

  ECU11 (refer FIG. 2) of this embodiment has a function as a detection means which detects abnormality of the electric power steering apparatus 20. FIG. If any abnormality (for example, the motor 12, the ECU 11, the torque sensor 14, etc.) is detected by the abnormality detection determination, the operation of the electric power steering device 20 is stopped in order to make the fail safe. As shown in FIG. 3, the CPU 27 of the present embodiment is provided with an abnormality detection unit 38 that can detect the occurrence of energization failure that has occurred in the power supply paths of the systems corresponding to the motor coils 21A and 21B. ing.

  Specifically, the abnormality detection unit 38 of the present embodiment includes respective phase current values Iu_a, Iv_a, Iw_a and Iu_b, Iv_b, Iw_b, and control signals Smc_a, which are supplied to the motor coils 21A, 21B of each system. Duty signals Sduty_a and Sduty_b indicating the on duty of each phase defined by Smc_b and the rotational angular velocity ω of the motor 12 are input. And the abnormality detection part 38 as a detection means becomes a structure which detects generation | occurrence | production of the conduction failure in each system | strain for every phase based on each of these state quantities.

  That is, when any of the phases indicates that the duty signals Sduty_b and Sduty_b are in a state of being energized, the phase current value is a value indicating a non-energized state. It can be determined that an energization failure has occurred. Then, the abnormality detection unit 38 of the present embodiment further adds a speed condition based on the rotational angular speed ω of the motor, and eliminates the high-speed rotation in which the influence of the counter electromotive voltage becomes obvious, thereby accurately It is the structure which can detect generation | occurrence | production of the electricity supply failure.

  In the present embodiment, the result of abnormality detection by the abnormality detection unit 38 is input to the control signal output unit 31 as the abnormality detection signal S_tr. Then, the control signal output unit 31 of the present embodiment drives the other system when the occurrence of an energization failure is detected in one of the two systems corresponding to the motor coils 21A and 21B. The configuration is such that priority is given to the output of a control signal to the circuit.

  More specifically, as shown in the flowchart of FIG. 4, in the control signal output unit 31 of the present embodiment, the command arbitration unit 37 determines that the input abnormality detection signal S_tr indicates the detection of an energization failure (step S501). : YES), it is subsequently determined whether or not the current-carrying failure has occurred in the first system (step S502). Then, if the occurrence of the energization failure is in the first system (step S502: YES), the power supply in the first system is stopped (step S503, I * _a = 0), and the other second system Priority is given to the output of the control signal Smc_b to the drive circuit 26B (step S504). At this time, if the current command value I * is equal to or less than the current gain K times the maximum current limit value I * max, which is the maximum allowable current of the drive circuit, the second current command value I * _b is set to I *, When the current command value I * is larger than the current gain K times the maximum current limit value I * max, the second current command value I * _b is set to I * max × K.

  If the command arbitration unit 37 determines in step S502 that the failure of energization occurs in the second system (step S502: NO), it stops power supply in the second system (steps S505, I * _b = 0), priority is given to the output of the control signal Smc_a to the drive circuit 26A of the first system (step S506). At this time, if the current command value I * is equal to or less than the current gain K times the maximum current limit value I * max, which is the maximum allowable current of the drive circuit, the first current command value I * _a is set to I *, When the current command value I * is larger than the current gain K times the maximum current limit value I * max, the first current command value I * _a is set to I * max × K. In the present embodiment, when it is determined in step S501 that the abnormality detection signal S_tr does not indicate the occurrence of an energization failure (step S501: NO), in step S507, the corresponding drive circuit 26A, The control signals Smc_a and Smc_b are output to 26B. At this time, the first current command value I * _a and the second current command value I * _b are both set to current values that are ½ times the current command value I * (I * _a = I * / 2). I * _b = I * / 2).

  Here, the current gain K is set so that when one of the systems fails, the heat generation amount of the remaining other system is equal to the heat generation amount at the normal time. That is, as shown in FIG. 5, a calorific value that is 1/2 of the total calorific value indicated by the alternate long and short dash line is calculated as a calorific value of each system from an arbitrary steering current pattern at normal time. When the system fails, the current gain K is calculated so that the heat generation amount of the remaining normal systems is equal. The failure current pattern shown by the solid line in FIG. 5 shows the current command values I * _a or I * _b when the first half is in the motor rotation state and the second half is when the steering wheel is in the locked state (motor non-rotation state). Show. For example, the steering wheel (steering wheel) operation is heavy when the current value at the time of failure is larger than the normal current value, and the steering wheel operation is light when the current value is small.

  Furthermore, each current control unit 35A, 35B provided in the control signal output unit 31 of the present embodiment generates the three-phase drive power as described above at the normal time when the occurrence of a conduction failure in each system is not detected. Each phase voltage command value Vu *, Vv *, Vw * is calculated for supply. The phase voltage command values Vu *, Vv *, Vw * calculated in the current control unit 35 are input to the PWM conversion unit 36. That is, in the control signal output unit 31 of the present embodiment, when the input abnormality detection signal S_tr indicates that “the occurrence of a failure in energization in the corresponding system has not been detected”, the drive circuit of the corresponding system Control signals Smc_a and Smc_b for 26A and 26B are output. (Normal control)

  Next, another embodiment embodying the present invention will be described. FIG. 6 is a schematic configuration diagram of an electric power steering apparatus according to another embodiment of the present invention. As shown in FIG. 6, the electric power steering device 40 is configured by integrating a speed reduction mechanism 47, a motor 46, and an ECU 41. The ECU 41 includes a control board 45 and two large and small motor drive circuits 42A and 42B having different outputs. The motor drive circuits 42A and 42B are provided with a power board 43 and heat sinks 44A and 44B corresponding to the outputs. . The output torque when the motor 46 is operating is the sum of the output torques generated by the motor drive circuits 42A and 42B. The two motor drive circuits 42 have different motor outputs that can be driven, and the motor 46 is driven by the motor drive circuit 42B having a larger output during normal steering, and the other output is small during a high load such as stationary driving. The output is increased by simultaneously driving the motor drive circuit 42A. In the present embodiment, an example in which two systems of control boards 45 that are control circuit units of the ECU 41 are independently arranged is shown. The motor drive circuit 42A with a small amount of heat generation on the low output side sandwiches the motor 46. The reduction mechanism 47 is disposed at a position away from the gear housing 48. Thus, when one of the systems fails, the assist is continued in a state where the current command value is limited by the remaining other system.

As described above, according to the present embodiment, the following operations and effects can be obtained.
According to the above-described configuration, the ECU 11 of the present embodiment has two motor drive circuits 26A and 26B provided independently corresponding to the motor coils 21A and 21B, and the drive circuits 26A and 26B. The control signal output unit 31 outputs the control signals Smc_a and Smc_b independently of each other. If a failure occurs in one of the systems, the motor current command value is limited by adjusting the current gain K so that the remaining heat generation system is equal to or less than the normal heat generation. Continue motor drive. As a result, the motor drive current during the backup control can be limited to suppress the motor output, so that the heat generation of the motor is suppressed and the assist can be continued without lowering the steering feeling.
Also, by providing two systems of motor drive circuits 42 with large and small outputs, the drive circuit 42A on the low output side is simultaneously driven during a high load during normal control to increase the motor output. Thereby, since the heat sink 44A on the low output side can be reduced, the ECU 41 having two systems can be downsized.

  As described above, it is possible to provide an electric power steering apparatus that can continue the assist without lowering the steering feeling during the backup control even if an abnormality occurs in one of the two systems.

In addition, you may change each said embodiment as follows.
In the above embodiment, the method of limiting each current command value by the current gain so that the amount of heat generated at the time of failure is equal to or less than that at the normal time is shown. A method of detecting and protecting using estimation may be applied.

  In the above embodiment, when one of the systems fails, the current gain is set so that the heat generation amount of the remaining other system is equal to or less than the heat generation amount at the normal time. However, the present invention is not limited to this, and a lower value may be set so that the driver can recognize the failure state when assisting continues.

  In the above embodiment, the brushless motor is used as the motor that is the drive source of the EPS actuator. However, the present invention is not limited to this, and may be embodied in an electric power steering device that uses a brushed DC motor as the drive source. .

  In the above embodiment, the present invention is embodied in a so-called column type electric power steering apparatus. However, the present invention may be applied to a pinion type or rack assist type electric power steering apparatus.

1: Steering device for vehicle, 2: Steering wheel, 3: Steering shaft, 3a: Column shaft, 3b: Intermediate shaft, 3c: Pinion shaft, 4: Rack and pinion mechanism, 5: Rack shaft, 6: Tie rod, 7 : Steered wheel, 10: EPS actuator (steering force assist device), 11, 41: ECU (control means), 12, 46: motor, 13, 47: deceleration mechanism, 14: torque sensor, 14a, 14b: sensor element, 15: Vehicle speed sensor, 16: Steering sensor, 17: Torsion bar, 18: Rotor, 19: Sensor element, 20, 40: Electric power steering device (EPS), 21: Motor coil, 26, 42: Drive circuit (motor Drive means), 27: CPU (microcomputer), 30: Assist control unit (current command value calculation hand) ), 31: control signal output unit (control signal output means), 32: current sensor, 33: rotation angle sensor, 35: current control unit, 36: PWM conversion unit, 37: command arbitration unit, 38: abnormality detection unit, 43: Power board, 44: Heat sink, 45: Control board, 48: Gear housing,
I *: current command value, I * max: maximum current limit value, I * _a, I * _b: first and second current command values (system-specific current command values), Iu, Iv, Iw: actual current values, Smc: motor control signal, S_tr: abnormality detection signal, Vu *, Vv *, Vw *: voltage command value, Sduty: duty signal, τ: steering torque, V: vehicle speed, θ: motor rotation angle, ω: motor rotation angular velocity , Sa, Sb: sensor signal, K: current gain

Claims (1)

A motor for applying an assist force according to the steering torque to the steering system;
In the electric power steering apparatus comprising: two motor coils of the motor; and a control unit that outputs driving power to each of the two motor coils and controls driving of the motor.
The control means calculates a current command value calculating means for calculating a current command value that is a target value of electric power to generate a motor torque corresponding to the assist force;
Control signal output means for outputting two systems of control signals based on the current command value;
Two systems of motor driving means for outputting the driving power to the corresponding two systems of motor coils based on the control signal, respectively,
The control signal output means is the target value of the drive power that is the target value of the drive power so that when one of the systems fails, the heat generation amount of the remaining other system is equal to or less than the heat generation amount at normal time An electric power steering device characterized by changing a current command value.

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