JP5131435B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, many of electric power steering devices (EPS) have an abnormality when at least an abnormality related to the supply of driving power to a motor that is a driving source has occurred, such as a disconnection of a power supply line or a contact failure of a driving circuit. An abnormality detecting means capable of detecting the occurrence of this is provided. And when generation | occurrence | production of the said abnormality is detected, the structure which stops motor control rapidly and aims at fail safe is common (for example, refer patent document 1).

  However, when the motor control is stopped as described above, the steering characteristic changes greatly. Further, since a large steering force is required for the steering operation, there is a problem that the burden on the driver increases.

In consideration of this point, for example, in the EPS described in Patent Document 2, the detected abnormality is an energization failure for only one of the three-phase (U, V, W) motor coils. The motor control is continued with the two phases other than the current-carrying failure occurrence phase as current-carrying phases. As a result, the application of assist force to the steering system is continued to avoid an increase in the driver's burden associated with fail-safe control.
JP 2000-177610 A JP 200326020 A

  However, in the above-described conventional configuration, since it is an essential requirement to specify a poorly energized phase, the abnormality detection process that constitutes the fail-safe control becomes extremely complicated. For this reason, the information processing apparatus (microcomputer) constituting the control means is required to have a high degree of arithmetic processing capability, and as a result, there is a problem that the manufacturing cost increases. In addition, when the current detection that is the basis of the abnormality detection is not correct, that is, due to the failure of the current sensor, even if the assist force is applied as described above, the appropriate assist force cannot be applied. There was a possibility, and in this respect, there was still room for improvement.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an electric power steering apparatus that can avoid an increase in the burden on the driver due to fail-safe control with a simple configuration. It is to provide.

  In order to solve the above-described problems, the invention according to claim 1 is directed to a steering force assisting device that applies an assisting force for assisting a steering operation to a steering system using a motor as a driving source, and a driving power for the motor. Control means for controlling the operation of the steering force assisting device through supply, and at least an abnormality detection means capable of detecting an abnormality related to the supply of the driving power to the motor, and the control means, when detecting the abnormality, The electric power steering device that performs the control to stop applying the assist force to the steering system, wherein the control means supplies the drive power by performing open control without performing current detection, and The gist is to continue applying the assist force when the vehicle speed is equal to or lower than a predetermined speed even at the time of detection.

  According to the above configuration, even when an abnormality is detected, in a situation where a large steering force is required, the assist force can be continuously applied to avoid an increase in the driver's burden associated with fail-safe control. . Further, since complicated determination processing is not performed in fail-safe control, the calculation load is extremely small. Therefore, it is possible to avoid an increase in cost due to the adoption of an electronic control device (microcomputer) having a high arithmetic processing capability. In addition, since power is supplied based on the execution of open control, it is possible to avoid erroneous detection due to failure of the current sensor, and to realize stable assist force application even after abnormality detection. .

  According to a second aspect of the present invention, the driving power is supplied via a driving circuit formed by connecting a plurality of switching elements, and the control means is configured to stop the application of the assist force. The gist is to control all the switching elements to be in an open state.

  The invention according to claim 3 includes a shut-off device capable of physically shutting off the power supply to the motor, and the control means shuts off the power supply by the shut-off device when the assist force application is stopped. The gist is to control as much as possible.

  That is, in the configuration in which the driving power is supplied based on the open control, the power supply does not necessarily stop even if the current command value is set to “0”. However, according to each said structure, supply of drive electric power can be stopped reliably and fail safe can be aimed at promptly.

  ADVANTAGE OF THE INVENTION According to this invention, the electric power steering apparatus which can avoid the driver | operator's burden increase accompanying fail safe control with a simple structure can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of the EPS 1 of the present embodiment. As shown in the figure, a steering shaft 3 to which a steering wheel (steering) 2 is fixed is connected to a rack 5 via a rack and pinion mechanism 4. It is converted into a reciprocating linear motion of the rack 5 by the and pinion mechanism 4. The rudder angle of the steered wheels 6 is changed by the reciprocating linear motion of the rack 5.

  Further, the EPS 1 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 11 as a control unit that controls the operation of the EPS actuator 10. .

  The EPS actuator 10 of the present embodiment is a so-called rack-type EPS actuator in which a motor 12 that is a driving source thereof is arranged coaxially with the rack 5, and an assist torque generated by the motor 12 is a ball screw mechanism (not shown). Is transmitted to the rack 5 via. In addition, the motor 12 of this embodiment is a brushless motor, and rotates by receiving supply of three-phase (U, V, W) driving power from the ECU 11. And ECU11 as a motor control apparatus controls the assist force given to a steering system by controlling the assist torque which this motor 12 generate | occur | produces (power assist control).

  In the present embodiment, a torque sensor 14 and a vehicle speed sensor 15 are connected to the ECU 11. Then, the ECU 11 executes the operation of the EPS actuator 10, that is, power assist control, based on the steering torque τ and the vehicle speed V detected by the torque sensor 14 and the vehicle speed sensor 15, respectively.

Next, the electrical configuration of the EPS of this embodiment will be described.
FIG. 2 is a control block diagram of the EPS of this embodiment. As shown in the figure, the ECU 11 supplies three-phase drive power to the motor 12 based on the microcomputer 17 serving as motor control signal output means for outputting a motor control signal and the motor control signal output from the microcomputer 17. And a drive circuit 18.

  The drive circuit 18 of the present embodiment is formed by connecting a plurality of switching elements (FETs) 18a to 18f. Specifically, the drive circuit 18 includes FETs 18a and 18d, FETs 18b and 18e, and FETs 18c and 18f connected in series. 19u, 19v, and 19w are connected to the motor coils 12u, 12v, and 12w of the motor 12, respectively.

  That is, the drive circuit 18 of the present embodiment is a well-known PWM inverter in which three arms corresponding to each phase are connected in parallel with a pair of switching elements connected in series as a basic unit (arm). The motor control signal output by 17 defines the on-duty ratio of each of the FETs 18 a to 18 f constituting the drive circuit 18. A motor control signal is applied to the gate terminals of the FETs 18a to 18f, and the FETs 18a to 18f are turned on / off in response to the motor control signals, so that the DC voltage of the in-vehicle power supply is changed to three phases (U, V, W). ) And is supplied to the motor 12.

  More specifically, the microcomputer 17 of this embodiment is calculated by a current command value calculation unit 22 that calculates a current command value Iq * as a control target amount of assist force applied to the steering system, and a current command value calculation unit 22. And a motor control signal generator 24 for generating a motor control signal based on the current command value.

  In the present embodiment, the steering torque τ and the vehicle speed V detected by the torque sensor 14 and the vehicle speed sensor 15 are input to the current command value calculation unit 22. The current command value calculation unit 22 calculates a current command value Iq * corresponding to a larger target assist force as the steering torque τ increases and the vehicle speed V decreases.

  A motor rotation angle θ detected by a rotation angle sensor 25 provided in the motor 12 is input to the motor control signal generation unit 24 together with the current command value Iq * calculated by the current command value calculation unit 22. Then, the motor control signal generator 24 generates a motor control signal based on the input current command value Iq * and the motor rotation angle θ (rotation angular velocity ω). That is, in the microcomputer 17 of the present embodiment, the motor control signal generation unit 24 generates a motor control signal by performing open control without performing current detection.

  Specifically, the current command value Iq * input to the motor control signal generation unit 24 is combined with the rotation angular velocity ω obtained by differentiating the motor rotation angle θ as the q-axis current command value, and the open control calculation unit 26. Is input. Then, the open control calculation unit 26 calculates the d-axis voltage command value Vd * and the q-axis voltage command value Vq * by solving the following equations (1) and (2) based on these state quantities.

Vd * = − L × Iq * × ω (1)
Vq * = R × Iq * + K × ω (2)
(K: Motor back electromotive force constant, R: Phase resistance, L: Phase inductance)
The above equations (1) and (2) are obtained by substituting “Id * = 0” as the d-axis current command value Id * into the general equation of the motor voltage equation shown in the following equations (3) and (4). It is obtained.

Vd * = (R + Ls) × Id * −L × Iq * × ω (3)
Vq * = (R + Ls) × Iq * + L × Id * × ω + K × ω (4)
These d-axis voltage command value Vd * and q-axis voltage command value Vq * calculated by the open control calculation unit 26 are converted into three-phase voltage command values Vu *, Vv *, Vw in the 2-phase / 3-phase conversion unit 27. Is converted to * and output to the PWM control calculation unit 28. In the PWM control calculation unit 28, a duty command value corresponding to each of the voltage command values Vu *, Vv *, Vw * is generated, so that a motor having an on-duty ratio indicated by each of the duty command values. A control signal is generated.

  The microcomputer 17 according to the present embodiment outputs the motor control signal generated by executing the open control in this way to each switching element (the gate terminal thereof) constituting the drive circuit 18, thereby driving the same. The operation of the circuit 18, that is, the supply of driving power to the motor 12 is controlled.

  In addition, the microcomputer 17 of the present embodiment has an abnormality detection means for detecting the occurrence of an abnormality in the EPS 1 such as a mechanical failure of the EPS actuator 10 or occurrence of disconnection or overcurrent. The abnormality determination unit 30 is provided. Specifically, the abnormality determination unit 30 includes a rotational angular velocity ω of the motor 12, a current command value Iq * that is a control target amount of assist force, a vehicle speed V, a steering torque τ, a power supply voltage Vb, and a drive circuit 18. A terminal voltage Vp is input. And the abnormality determination part 30 of this embodiment becomes a structure which can detect the abnormality regarding supply of drive electric power to the motor 12 at least based on each of these input state quantities.

  In the present embodiment, when any abnormality is detected by the abnormality determination, the abnormality determination unit 30 outputs an abnormality detection signal Sd indicating that fact. In this embodiment, the abnormality detection signal Sd is input to the PWM control calculation unit 28. The PWM control calculation unit 28 is driven when the abnormality detection signal Sd is input. A motor control signal indicating that all switching elements constituting the circuit 18, that is, all of the FETs 18a to 18f should be opened, is generated. The microcomputer 17 outputs the motor control signal to the drive circuit 18 so that the operation of the motor 12 is stopped.

  That is, in the present embodiment, the ECU 11 controls the operation of the EPS actuator 10 to stop applying the assist force to the steering system when an abnormality occurs. And thereby, it is comprised so that a fail safe can be aimed at promptly.

  Furthermore, in the present embodiment, each power line connecting the drive circuit 18 and each phase motor coil 12u, 12v, 12w has a phase as a cutoff device that can physically cut off the power supply to the motor 12, respectively. Open relays 31u, 31v, 31w are provided. Further, the ECU 11 is provided with a phase open relay drive circuit 32 for driving the phase open relays 31u, 31v, 31w, and the abnormality detection signal Sd output from the abnormality determination unit 30 is the phase open relay drive circuit. 32 is also input. Then, based on the input of the abnormality detection signal Sd, the phase open relay drive circuit 32 drives the phase open relays 31u, 31v, 31w so that the phase open relays 31u, 31v, 31w are opened. .

  That is, the ECU 11 according to the present embodiment supplies the electric power together with the stop of the motor control by opening these phase release relays 31u, 31v, 31w when the assist force is stopped. Cut off. As a result, the supply of drive power is reliably stopped.

  Here, the ECU 11 according to the present embodiment allows the vehicle speed V to increase when the steering reaction force at the time of the steering operation becomes large, that is, when the assist force is stopped, even if the abnormality determination unit 30 detects an abnormality. If the load is less than or equal to the predetermined speed V1, the power assist control is continued. Specifically, even if any abnormality is detected by the abnormality determination, the abnormality determination unit 30 performs the PWM control calculation of the abnormality detection signal Sd when the vehicle speed V is equal to or lower than the predetermined speed V1. The output to the unit 28 and the phase open relay drive circuit 32 is not executed.

  Thus, the EPS 1 of the present embodiment allows the assist force to be continuously applied in a situation where a large steering force is required even when an abnormality is detected, thereby increasing the driver's burden associated with fail-safe control. It is the composition which avoids.

Next, the processing procedure of the failsafe control will be described.
As shown in the flowchart of FIG. 3, when the microcomputer 17 determines that some abnormality has occurred (step 102: YES) by executing the abnormality determination (step 101), the vehicle speed V is set to a predetermined value. It is determined whether or not the speed V1 is exceeded (step 103). When it is determined that the vehicle speed V exceeds the predetermined speed V1 (V> V1, step 103: YES), the power assist control is stopped (step 104), and the vehicle speed V is equal to or lower than the predetermined speed V1. If it is determined (V ≦ V1, step 103: NO), the power assist control is continued (step 105).

  When it is determined in step 102 that no abnormality has occurred (step 102: NO), the power assist control is naturally continued without executing the processing of steps 103 and 104.

As described above, according to the present embodiment, the following operations and effects can be obtained.
(1) The ECU 11 controls the operation of the EPS actuator 10 through the supply of drive power based on the execution of the open control. Further, the ECU 11 (microcomputer 17) executes an abnormality determination process (step 101). When an abnormality occurs (step 102: YES), the operation of the EPS actuator 10 is basically stopped, that is, the power assist control is stopped. (Step 104). Even when the abnormality occurs, when the vehicle speed V is equal to or lower than the predetermined speed V1 (V ≦ V1, step 103: NO), the power assist control is continued (step 105).

  According to the above configuration, even when an abnormality is detected, in a situation where a large steering force is required, the assist force can be continuously applied to avoid an increase in the driver's burden associated with fail-safe control. . Moreover, since complicated determination processing is not performed in the fail-safe control, the calculation load is extremely small. Therefore, it is possible to avoid an increase in cost due to the adoption of a microcomputer having a high arithmetic processing capability. In addition, since power is supplied based on the execution of open control, it is possible to avoid erroneous detection due to failure of the current sensor, and to realize stable assist force application even after abnormality detection. .

  (2) Supply of drive power to the motor 12 that is a drive source of the EPS actuator 10 is performed via a drive circuit 18 formed by connecting a plurality of switching elements (FETs) 18a to 18f. The supply of driving power to the motor 12 is controlled by turning on / off the FETs 18a to 18f by the output of the control signal. When the power assist control is stopped, the microcomputer 17 outputs a motor control signal indicating that all the FETs 18a to 18f constituting the drive circuit 18 should be opened.

  (3) Each power line connecting the drive circuit 18 and each phase motor coil 12u, 12v, 12w has a phase open relay 31u as a cutoff device that can physically cut off the power supply to the motor 12, respectively. 31v and 31w are provided. The ECU 11 controls the phase open relays 31u, 31v, 31w so that the phase open relays 31u, 31v, 31w are in an open state (open) when the assist force application is stopped.

  That is, in the configuration in which the driving power is supplied based on the open control, even if the current command value Iq * is set to “0”, the power supply does not necessarily stop. However, if the configurations (2) and (3) are adopted, the supply of drive power can be reliably stopped and fail-safe can be achieved promptly.

In addition, you may change this embodiment as follows.
In the present embodiment, when the power assist control is stopped, both the FETs 18a to 18f constituting the drive circuit 18 are fully opened and the phase open relays 31u, 31v, 31w are fully opened. However, the present invention is not limited to this, and any one of them may be configured.

  In the present embodiment, the microcomputer 17 is provided with the abnormality determination unit 30, and the abnormality determination unit 30 includes the rotational angular velocity ω of the motor 12, the current command value Iq * that is the control target amount of the assist force, the vehicle speed V, and the steering torque τ. The abnormality determination is performed based on the power supply voltage Vb and the terminal voltage Vp of the drive circuit 18. However, the present invention is not limited to this, and the abnormality determination unit 30 may be configured to be provided outside the microcomputer 17 and eventually the ECU 11, and the form of the abnormality determination is not limited to this.

The schematic block diagram of an electric power steering device (EPS). The block diagram which shows the electric constitution of EPS. The flowchart which shows the process sequence of fail safe control.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus (EPS), 10 ... EPS actuator, 11 ... ECU, 12 ... Motor, 17 ... Microcomputer, 18 ... Drive circuit, 18a-18f ... Switching element (FET), 22 ... Current command value calculating part, 24: motor control signal generation unit, 26: open control calculation unit, 30: abnormality determination unit, 31u, 31v, 31w: each phase open relay, 32: phase open relay drive circuit, V: vehicle speed, V1: speed.

Claims (3)

A steering force assisting device for applying an assist force for assisting a steering operation to a steering system using a motor as a drive source, a control means for controlling the operation of the steering force assisting device through supply of drive power to the motor, and at least the An abnormality detecting means capable of detecting an abnormality relating to the supply of the driving power to the motor, and the control means performs the control to stop the application of assist force to the steering system when the abnormality is detected. Because
The control means supplies the driving power by executing open control without performing current detection, and when the vehicle speed is equal to or lower than a predetermined speed even when the abnormality is detected, An electric power steering device characterized by continuing the application. The electric power steering apparatus according to claim 1, wherein
The supply of the drive power is performed via a drive circuit formed by connecting a plurality of switching elements,
The electric power steering apparatus, wherein the control means controls all the switching elements to be in an open state when the assist force application is stopped. In the electric power steering device according to claim 1 or 2,
Comprising a shut-off device capable of physically shutting off the power supply to the motor;
The electric power steering apparatus according to claim 1, wherein the control means controls the power supply to be shut off by the shut-off device when the assist force application is stopped.

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