JP2013180736A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device configured to reduce disturbance torque or torque variation due to a change in motor torque constant, to obtain good steering feeling.SOLUTION: An actual motor current value estimation part 33 estimates an actual motor current value on the basis of a motor rotation angular acceleration αm detected by a motor rotation angular acceleration sensor 22. An estimated motor current value Isui estimated by the actual motor current value estimation part 33 is fed back to a current feedback means. The motor rotation angular acceleration αm is detected as a result including a motor torque constant Kt or a disturbance torque τ1. The value is fed back to current feedback control, to obtain assist power corresponding to a target steering torque τ. The disturbance torque τ1 or the torque variation due to a change in motor torque constant Kt, thereby improving steering feeling.

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, an electric power steering apparatus generates a motor current command value I * from a steering torque τ and a vehicle speed V, and obtains a current deviation value ΔI between the motor current command value I * and a motor actual current value Im flowing through an assist motor. An assist force is generated by configuring a current feedback control system that performs PID control (proportional / integral / differential compensation).

  However, in the conventional current feedback control system, there are cases where the assist force corresponding to the target steering torque τ cannot be obtained. Details thereof will be described with reference to FIG. FIG. 4 shows a main block diagram of the ECU 27 and the motor 21. The ECU 27 includes a current command value calculation unit 30 (details will be described later), a motor current command value I * generated from the current command value calculation unit 30, and a motor actual current value Im detected from the motor current detection unit 53. The current feedback control unit is configured to compensate the current deviation value ΔI subtracted by the subtractor 36 by a known PID controller 31.

  The current deviation value ΔI is compensated by the PID controller 31 and then output to the PWM output unit 32 at the subsequent stage. The PWM signal output from the PWM output unit 32 is output to a subsequent motor drive circuit (commonly called an inverter device) 40. The output voltage Vm output from the motor drive circuit 40 is applied to the motor 21.

  Here, assuming that the resistance of the motor winding is R and the inductance of the motor winding is L, the model of the motor winding is (R + L · S) (S is a Laplace operator). A motor actual current value Im obtained by dividing the output voltage Vm output from the motor drive circuit 40 by the motor winding model (R + L · S) flows through the motor winding. In the conventional current feedback control, the motor actual current value Im detected by the motor current detection unit 53 is input to the subtractor 36.

  However, as can be seen from FIG. 4, the motor torque Tm output from the shaft 21 of the motor 21 by the motor 21 is a value obtained by multiplying the motor actual current value Im by the motor torque constant Kt. The motor torque Tm is subtracted by the disturbance torque τ1 applied to the shaft axis of the motor 21, and the final torque T output from the shaft axis of the motor 21 is T = Tm−τ, which is the initial target steering torque. The assist force does not correspond to τ.

  Further, the motor torque constant Kt described above is not a constant value, but is a constant that changes according to a temperature change or a secular change. On the other hand, the disturbance torque τ1 also varies greatly depending on the vehicle state and the vehicle condition. Therefore, the conventional current feedback control type electric power steering apparatus has an assist force different from the assist force corresponding to the initial target steering torque τ. As a result, the steering feeling is reduced.

  Therefore, for example, in the electric power steering apparatus described in Patent Document 1, the inertial force considered as the disturbance torque τ1 is calculated and added to the motor current command value I *, thereby preventing the steering feeling from being lowered. .

JP 2008-92633 A

  However, as described above, there are many factors that can be considered as the disturbance torque τ1, and it is difficult to add them all to the motor current command value I * to compensate. Further, since the motor torque constant Kt also changes, the assist force corresponding to the target steering torque τ cannot be obtained. As a result, the steering feeling may not be sufficiently improved.

  An object of the present invention is to provide an electric power steering apparatus that suppresses torque fluctuation due to a change in disturbance torque τ1 and a motor torque constant Kt and has a good steering feeling.

  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, vehicle speed detection means (25) for detecting vehicle speed, steering torque detected from the steering torque detection means (26) and detection from the vehicle speed detection means (25) Current command value calculation means (29) for generating a motor current command value from the vehicle speed thus obtained, and the motor (21) is fed back according to the motor current command value generated from the current command value calculation means (29). And a control means for controlling the operation of the steering force assisting device (24) through the supply of driving power to the motor (21). 29), the motor rotational angular acceleration detecting means (22) for detecting the rotational angular acceleration of the motor (21) and the motor rotational angular acceleration detecting means (22). The motor actual current value estimating means (29) for estimating the motor actual current value from the motor rotational angular acceleration, and the control means (29) are configured to calculate the estimated motor current value estimated from the motor actual current value estimating means (29). The gist is to feed back to the current feedback means (29).

  The electric power steering apparatus according to the present invention constitutes motor actual current value estimation means for estimating the motor actual current value from the motor rotation angular acceleration detected from the motor rotation angular acceleration detection means. The motor estimated current value estimated from the motor actual current value estimating means is fed back to the current feedback means. As apparent from FIG. 4, since the motor rotational angular acceleration is detected as a result including the motor torque constant Kt and the disturbance torque τ1 described above, the target steering is obtained by feeding back the value to the current feedback means. An assist force corresponding to the torque τ is obtained.

  According to the present invention, it is possible to provide an electric power steering apparatus that suppresses torque fluctuation due to a change in the disturbance torque τ1 and the motor torque constant Kt and has a good steering feeling.

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 a motor actual electric current value estimation means. The block diagram of the conventional current feedback control.

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 angular acceleration 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. The angular acceleration αm 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, and 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. I have.

  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.

  The ECU 27 is connected to a motor rotation angular acceleration sensor 22 for detecting the motor rotation angular acceleration αm of the motor 21. The microcomputer 29 outputs a motor control signal to the motor drive circuit 40 based on the motor rotation angular acceleration αm of the motor 21 detected based on the output signals of these sensors, the steering torque τ, and the vehicle speed V.

  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 motor current command value I * for controlling the motor 21, and a motor control signal that generates a motor control signal for controlling 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 motor 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 motor current command value I * increases as the vehicle speed V decreases.

  The motor control signal generation unit 44 includes a subtractor 36, a PID controller (proportional / integral / derivative compensation) 31, a PWM output unit 32, and a motor actual current value estimation unit (motor actual current value estimation means) 33. Configure feedback means.

  The motor actual current value estimation unit 33 uses the motor rotation angular acceleration αm detected from the motor rotation angular acceleration sensor 22 as an input signal. Then, the motor rotational angular acceleration αm is multiplied by the motor shaft equivalent inertia Jn (nominal value), and the value obtained by the multiplication is divided by the motor torque constant Ktn (nominal value) to obtain the estimated motor current value Isui. . Next, the current feedback control is configured by inputting the estimated motor current value Isui to the subtractor 36.

Next, the processing procedure of the motor actual current value estimation means by the microcomputer 29 of this embodiment will be described with reference to FIG.
First, the microcomputer 29 determines whether or not an IG (ignition switch) is on (step S101). Next, when the IG is on (step S101: YES), the microcomputer 29 reads the motor shaft equivalent inertia Jn (nominal value) (step S102). Then, the microcomputer 29 reads the motor torque constant Ktn (nominal value) (step S103).

Further, the microcomputer 29 reads the motor rotation angular acceleration αm (step S104). Then, the microcomputer 29 calculates the motor estimated current value Isui from the equation (1) (step S105).
Isui = αm × Jn × 1 / Ktn (1)

Next, the microcomputer 29 outputs the estimated motor current value Isui (step S106).
Then, the microcomputer 29 determines whether or not IG is off (step S107). And the microcomputer 29 complete | finishes a process, when IG is OFF (step S107: YES). On the other hand, when the IG is not OFF (step S107: NO), the microcomputer 29 proceeds to step S104. In addition, when the IG is not first turned on (step S101: NO), the microcomputer 29 ends the process without doing anything.

Next, the operation and effect of the EPS 1 of the present embodiment configured as described above will be described.
A motor actual current value estimation unit is configured to estimate the motor actual current value from the motor rotation angular acceleration detected from the motor rotation angular acceleration sensor. The motor estimated current value estimated from the motor actual current value estimating unit is fed back to the current feedback means. As apparent from FIG. 4, since the motor rotation angular acceleration is detected as a result including the motor torque constant Kt and the disturbance torque τ1 described above, the value is fed back to the current feedback control to obtain the target steering. An assist force corresponding to the torque τ is obtained. As a result, it is possible to suppress the torque fluctuation due to the change in the disturbance torque τ1 and the motor torque constant Kt and improve the steering feeling.

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

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 angular acceleration sensor (motor rotation angular acceleration detection means),
23: Deceleration mechanism, 24: EPS actuator (steering force assist device),
25: Vehicle speed sensor (vehicle speed detection means), 26: Torque sensor (steering torque detection means),
27: ECU, 28: battery,
29: Microcomputer (current command value calculation means, current feedback means, control means, motor actual current value estimation means),
30: Current command value calculation unit, 31: PID controller (proportional / integral / derivative compensation),
32: PWM output unit, 33: Motor actual current value estimation unit, 36: Subtractor,
40: motor drive circuit, 44: motor control signal generator, 53: motor current detector,
V: vehicle speed, τ: steering torque, αm: motor rotation angular acceleration,
IG: Ignition switch,
I *: Motor current command value, Im: Motor actual current value, ΔI: Current deviation value,
Isui: Motor estimated current value, Vm: Output voltage,
Jn: Motor shaft equivalent inertia (nominal value),
Ktn: Motor torque constant (nominal value), Kt: Motor torque constant,
R: motor winding resistance, L: motor winding inductance,
Tm: Motor torque, T: Final torque, τ1: Disturbance torque

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;
Vehicle speed detection means for detecting the vehicle speed;
Current command value calculation means for generating a motor current command value from the steering torque detected from the steering torque detection means and the vehicle speed detected from the vehicle speed detection means;
Current feedback means for driving the motor in a feedback system in accordance with the motor current command value generated from the current command value calculation means;
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;
Motor actual current value estimation means for estimating a motor actual current value from the motor rotation angular acceleration detected from the motor rotation angular acceleration detection means;
The control means feeds back the motor estimated current value estimated from the motor actual current value estimating means to the current feedback means;
Electric power steering device characterized by

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