JP2013163485A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which is excellent in steering feeling even if a current detector goes wrong.SOLUTION: A current feedback means is so constituted that, when a current detector goes wrong, a real current value is not used for the current feedback means, which generates assist force, but a motor current value estimated from a rate of acceleration in the rotation angle of a motor is used. As a result, the load of a car body or sudden disturbance load is reflected on the rate of acceleration in the rotation angle of the motor, so that steering feeling can be improved.

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, an electric power steering device generates a current command value from a steering torque and a vehicle speed, and constitutes a current feedback control system that compensates proportionally, integrally, and differentially for deviation between the current command value and an actual current flowing through an assist motor. As a result, an assist force is generated.

  However, in the conventional current feedback control system, when the current detection unit that detects the actual current flowing through the motor fails, the current feedback control system does not function, and thus the generation of the assist force is stopped. As a result, the steering feeling may deteriorate rapidly.

  Therefore, for example, in the electric power steering device described in Patent Document 1, when the current detection unit fails, the current feedback control system is switched to an open loop system to prevent a sudden decrease in steering feeling. Yes.

Japanese Patent Laid-Open No. 10-167086

  However, if the current detection unit fails, simply switching the current feedback control system to an open loop system is sufficient when a heavy load is applied to the vehicle body or when a sudden disturbance load (for example, dredging) is applied. The assist power is not obtained. For this reason, there is a problem that the steering feeling cannot be sufficiently improved.

  An object of the present invention is to provide an electric power steering apparatus with good steering feeling even when a current detection unit fails.

In order to solve the above problems, the invention according to claim 1 is directed to a steering force assisting device (24) provided to apply an assist force for assisting a steering operation to a steering system using a motor (21) as a drive source. Steering torque detection means (26) for detecting steering torque, current detection means (34) for detecting the current of the motor (21), and failure detection means (29) for detecting a failure of the current detection means (34) ) And current feedback means (29) for driving the motor (21) in a feedback system according to the magnitude of the steering torque,
In the electric power steering apparatus (1) provided with control means (29) for controlling the operation of the steering force assisting device (24) through supply of driving power to the motor (21), the rotation of the motor (21) The motor rotation angular acceleration detection means (29) for detecting angular acceleration and the control means (29) are arranged such that when the failure detection means (29) detects a failure of the current detection means (34), the current The gist is to switch the feedback means (29) to be controlled by the motor rotation angular acceleration detected from the motor rotation angular acceleration detection means (29).

  In the electric power steering apparatus according to the present invention, when the current detecting means fails, the actual current value is not used for the current feedback means for generating the assist force, but the motor current value is calculated from the rotational angular acceleration of the motor. By estimating, the current feedback means is configured. That is, since the rotational angular acceleration of the motor reflects a load on the vehicle body or a sudden disturbance load, the feeling can be improved.

  According to the present invention, it is possible to provide an electric power steering apparatus with good steering feeling even when the current detection unit fails.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The flowchart which shows the process sequence of the switch part at the time of a motor current detection part being out of order (at the time of a non-failure). The flowchart which shows the process sequence of a motor rotation angular acceleration / current conversion part.

Hereinafter, an embodiment of the present invention embodied in a column-type electric power steering apparatus (hereinafter referred to as EPS) will be described with reference to the drawings.
As shown in FIG. 1, in the EPS 1 of the present embodiment, a steering shaft 3 to which a steering 2 is fixed is connected to a rack shaft 5 via a rack and pinion mechanism 4. The rotation of the steering shaft 3 accompanying the steering operation is converted into a reciprocating linear motion of the rack shaft 5 by the rack and pinion mechanism 4. The steering shaft 3 of this embodiment is formed by connecting a column shaft 8, an intermediate shaft 9, and a pinion shaft 10. The reciprocating linear motion of the rack shaft 5 accompanying the rotation of the steering shaft 3 is transmitted to a knuckle (not shown) via tie rods 11 connected to both ends of the rack shaft 5, whereby the steered angle of the steered wheels 12. Has been changed.

  The EPS 1 also includes an EPS actuator 24 as a steering force assisting device that applies an assist force for assisting a steering operation to the steering system using the motor 21 as a drive source, and an ECU 27 that controls the operation of the EPS actuator 24. Yes.

  The EPS actuator 24 of the present embodiment is a column type EPS actuator, and the motor 21 that is a drive source thereof is drivingly connected to the column shaft 8 via a speed reduction mechanism 23. The rotation of the motor 21 is decelerated by the speed reduction mechanism 23 and transmitted to the column shaft 8 so that the motor torque is applied to the steering system as an assist force.

  On the other hand, a vehicle speed sensor 25, a torque sensor 26, and a motor rotation angle sensor 22 are connected to the ECU 27. The ECU 27 is based on the output signals of these sensors, and the vehicle speed V, the steering torque τ, and the motor rotation angle. θm is detected.

  The torque sensor 26 is a twin resolver type torque sensor. The ECU 27 calculates a steering torque τ based on output signals from a pair of resolvers provided at both ends of a torsion bar (not shown). Further, the ECU 27 calculates a target assist force based on each of the detected state quantities, and assists the operation of the EPS actuator 24 through the supply of drive power to the motor 21 that is the drive source, that is, the assist that is given to the steering system. Control the power.

Next, an electrical configuration in the EPS 1 of the present embodiment will be described.
FIG. 2 is a control block diagram of the EPS 1 of the present embodiment. As shown in the figure, the ECU 27 includes a microcomputer 29 that outputs a motor control signal, a motor drive circuit 40 that supplies drive power to the motor 21 that is a drive source of the EPS actuator 24 based on the motor control signal, and And a motor current detection unit 34 for detecting a motor actual current value Im supplied to the motor 21.

  The motor drive circuit 40 is a known H bridge circuit (not shown) formed by connecting two arms in parallel with a pair of switching elements connected in series as a basic unit (arm). Further, the motor control signal output from the microcomputer 29 defines the on-duty ratio of each switching element constituting the motor drive circuit 40. A motor control signal is applied to the gate terminal of each switching element, and in response to the motor control signal, each switching element is turned on / off to generate motor driving power based on the power supply voltage of the battery 28, and the motor 21. It is configured to output to.

  A motor rotation angle sensor 22 for detecting the motor rotation angle θm of the motor 21 is connected to the ECU 27. The microcomputer 29 controls the motor drive circuit 40 based on the motor actual current value Im and the motor rotation angle θm detected based on the output signals of these sensors, the steering torque τ, and the vehicle speed V. Output a signal.

  Each control block shown below is realized by a computer program executed by the microcomputer 29. The microcomputer 29 detects each state quantity at a predetermined sampling period, and generates a motor control signal by executing each arithmetic processing shown in the following control blocks every predetermined period.

  As shown in FIG. 2, the microcomputer 29 includes a current command value calculation unit 30 that calculates a current command value I * that controls the motor 21 and a motor control signal that generates a motor control signal E that controls the motor drive circuit 40. And a generation unit 44.

The steering torque τ detected by the torque sensor 26 and the vehicle speed V detected by the vehicle speed sensor 25 are input to the current command value calculation unit 30. The current command value calculation unit 30 is a map (not shown) configured with the steering torque τ on the horizontal axis and the current command value I * on the vertical axis.
In the above map, when the vehicle speed V is a parameter and the steering torque τ is the same, the current command value I * increases as the vehicle speed V decreases.

  The motor control signal generation unit 44 detects failures in the subtractor 36, the proportional / integral / differential compensator 31, the motor rotation angular acceleration / current conversion unit 33, the switching unit 35, and the motor current detection unit, which constitute current feedback means. And a failure detection unit 32 for detection.

  When the failure detection unit 32 detects a failure in the motor current detection unit, the failure detection unit 32 sets a switching flag FLG1 for switching the switching unit 35 (FLG1 = "1"). Further, when the motor current detection unit is normal, the failure detection unit 32 resets the switching flag FLG1 for switching the switching unit 35 (FLG1 = “0”). In addition, since the detection method of a failure detection part is the same as the failure detection method described in Patent Document 1, description thereof is omitted.

  When the switching flag FLG1 output from the failure detection unit 32 is “0”, the switching unit 35 determines that the motor current detection unit 34 is normal, and connects the contact 35c and the contact 35b. By doing so, the actual current value Imo after passing through the motor current detector detected from the motor current detector 34 is fed back to the current feedback means.

  On the other hand, when the switching flag FLG1 output from the failure detection unit 32 is “1”, the switching unit 35 determines that the motor current detection unit 34 is in failure and connects the contact 35c and the contact 35a. By doing so, the estimated motor current value Imsui detected from the motor rotation angular acceleration / current conversion unit 33 is fed back to the current feedback means.

  The motor rotation angular acceleration / current conversion unit 33 calculates the motor rotation angular acceleration from the motor rotation angle θm, and calculates the motor estimated current value from the motor shaft equivalent inertia (nominal value) Jn and the motor torque constant (nominal value) Ktn. Imsui is obtained and output to the contact point 35a of the switching unit 35.

  The current command value I * output from the current command value calculation unit 30 and the feedback current value I output from the switching unit 35 are input to the subtractor 36 to generate a current deviation ΔI. The current deviation ΔI is input to the proportional / integral / derivative compensator 31, and after the gain and phase are compensated, it becomes the motor control signal E and is output to the motor drive circuit 40.

Next, a processing procedure of the switching unit 35 when the motor current detection unit by the microcomputer 29 of the present embodiment is in failure (non-failure) will be described with reference to FIG.
The microcomputer 29 determines whether or not the switching flag FLG1 output from the failure detection unit 32 is “1” (step S101). When the switching flag FLG1 output from the failure detection unit 32 is “1” (FLG1 = “1”, step S101: YES), the microcomputer 29 connects the contact point 35c and the contact point 35a of the switching unit 35 ( Step S102), and the process ends.

  On the other hand, when the switching flag FLG1 output from the failure detection unit 32 is “0” (FLG1 = “0”, step S101: NO), the microcomputer 29 connects the contact 35c and the contact 35b of the switching unit 35 ( Step S103), and the process ends.

Next, a processing procedure of the motor rotation angular acceleration / current conversion unit 33 by the microcomputer 29 of this embodiment will be described with reference to FIG.
The microcomputer 29 determines whether or not the switching flag FLG1 output from the failure detection unit 32 is “1” (step S201). When the switching flag FLG1 output from the failure detection unit 32 is “1” (FLG1 = “1”, step S201: YES), the microcomputer 29 reads the motor shaft equivalent inertia (nominal value) Jn ( Step S202). Next, the microcomputer 29 reads a motor torque constant (nominal value) Ktn (step S203). Further, the microcomputer 29 reads the motor rotation angle θm (step S204).

  Next, the microcomputer 29 calculates motor rotation angular acceleration d / dt (dθm / dt) from the motor rotation angle θm (step S205). Then, the microcomputer 29 calculates the motor estimated torque (Tmsui) from the calculated motor rotation angular acceleration (Tmsui = Jn × d / dt (dθm / dt), step S206). Further, the microcomputer 29 calculates a motor estimated current value (Imsui) from the calculated motor estimated torque (Tmsui) (Imsui = 1 / Ktn × Tmsui, step S207).

  Next, the microcomputer 29 outputs the calculated motor estimated current (Imsui) to the contact point 35a of the switching unit 35 (step S208). Then, the microcomputer 29 determines whether or not the IG (ignition switch) is off (step S209). And the microcomputer 29 returns to step 204, when IG is not OFF (step S209: NO). On the other hand, the microcomputer 29 ends the process when the IG is off (step S209: YES). Further, when the switching flag FLG1 output from the failure detection unit 32 is “0” (FLG1 = “0”, step S201: NO), the microcomputer 29 ends this process without doing anything.

Next, the operation and effect of the EPS 1 of the present embodiment configured as described above will be described.
If the current detection means fails, the current feedback means is configured by estimating the motor current value from the rotational angular acceleration of the motor instead of using the actual current value for the current feedback means for generating the assist force. It was decided to. That is, the load on the vehicle body or a sudden disturbance load is reflected in the rotational angular acceleration of the motor. As a result, the steering feeling can be further improved.

In addition, you may change this embodiment as follows.
In this embodiment, the rotational angular acceleration of the motor is obtained by calculation from the motor rotational angle sensor, but an acceleration sensor may be attached to the motor shaft and the output value may be used.

In the present embodiment, the motor is described as a DC motor, but the motor may be a brushless DC motor.

In the present embodiment, the present invention is embodied in the column assist EPS, but the present invention may be applied to a rack assist EPS or a pinion assist EPS.

1: Electric power steering device (EPS), 2: Steering,
3: Steering shaft, 4: Rack and pinion mechanism, 5: Rack shaft,
8: column shaft, 9: intermediate shaft, 10: pinion shaft, 11: tie rod, 12: steered wheel, 21: motor, 22: motor rotation angle sensor,
23: Deceleration mechanism, 24: EPS actuator (steering force assist device),
25: Vehicle speed sensor, 26: Torque sensor (steering torque detection means),
27: ECU, 28: battery,
29: microcomputer (failure detection means, current feedback means, control means, acceleration detection means),
30: Current command value calculation unit, 31: Proportional / integral / differential compensator, 32: Failure detection unit,
33: Motor rotation angular acceleration / current conversion unit 34: Motor current detection unit (current detection means),
35: switching unit, 35a, 35b, 35c: contact point, 36: subtractor,
40: Motor drive circuit, 44: Motor control signal generator,
V: vehicle speed, τ: steering torque, θm: motor rotation angle,
I *: current command value, I: feedback current value, ΔI: current deviation,
Im: actual motor current value, Imo: actual current value after passing through the motor current detector,
Imsui: Motor estimated current value, E: Motor control signal,
Jn: Motor shaft equivalent inertia (nominal value),
Ktn: Motor torque constant (nominal value),
Tmsui: Estimated motor torque, FLG1: Switch flag

Claims (1)

A steering force assisting device provided to apply an assisting force for assisting a steering operation to a steering system using a motor as a drive source;
Steering torque detection means for detecting steering torque;
Current detecting means for detecting the current of the motor;
A failure detection means for detecting a failure of the current detection means;
Current feedback means for driving the motor in a feedback system according to the magnitude of the steering torque;
In an electric power steering apparatus comprising a control means for controlling the operation of the steering force assisting device through supply of driving power to the motor,
Motor rotational angular acceleration detecting means for detecting rotational angular acceleration of the motor;
The control means, when the failure detection means detects a failure of the current detection means, to switch the current feedback means to be controlled by the motor rotation angular acceleration detected from the motor rotation angular acceleration detection means;
Electric power steering device characterized by

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