JP2014046881A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device that gives a good steering feeling just after starting an engine by a simple method.SOLUTION: The electric power steering device, when temperature detected by temperature detection means is lower than a predetermined temperature, increases calorific power and decreases viscosity resistance by adding a predetermined d-axis current to a q-axis current for generating assist force. On the other hand, the device, when the temperature detected by the temperature detection means is higher than the predetermined temperature, does not add the d-axis current to the q-axis current for generating the assist force.

Description

  The present invention relates to an electric power steering apparatus.

  Conventionally, in an electric power steering apparatus that assists steering by an electric motor, the assist force is determined by the steering torque and the vehicle speed even immediately after the engine is started or after a sufficient time has elapsed after the engine is started. .

  However, in such a control method, immediately after the engine is started, the temperature of the electric power steering device is low, the viscosity resistance of the lubricant and the sliding resistance due to the sealing member are increased, and a good steering feeling is obtained. There was a possibility that it was difficult to obtain. Therefore, for example, in the electric power steering device described in Patent Document 1, by measuring the ambient temperature of the electric power steering device and changing the assist current correction coefficient according to the ambient temperature, the viscous resistance of the lubricant, In addition, the steering feeling is improved by setting the sliding resistance by the sealing member to an appropriate value.

JP 2002-308127 A

  However, in the method as described above, since the assist current, that is, the q-axis current command value is changed depending on the ambient temperature, there is a case where the steering torque varies and sufficient steering feeling cannot be obtained.

  An object of the present invention is to provide an electric power steering apparatus having a good steering feeling regardless of the ambient temperature by a simple method.

  In order to solve the above-described problems, the invention according to claim 1 is directed to a steering force assisting device provided to apply an assist force for assisting a steering operation to a steering system by a motor, and a steering torque detection for detecting a steering torque. Means for detecting the vehicle speed, temperature detecting means for detecting the temperature of the steering system, steering torque detected from the steering torque detecting means, and vehicle speed detected from the vehicle speed detecting means An assist force generating means that controls the operation of the steering force assisting device by supplying drive power to a motor that is a drive source of the steering force assisting device based on the assist force generating device; When the temperature detected from the temperature detection means is lower than a predetermined temperature, the control means includes the controller. A predetermined d-axis current is added to the q-axis current that generates the strike force. On the other hand, if the temperature detected by the temperature detection unit is higher than the predetermined temperature, the q-axis current that generates the assist force is The gist is not to add the d-axis current.

  In the electric power steering apparatus according to the present invention, when the temperature detected by the temperature detecting means is lower than the predetermined temperature, the predetermined d-axis current is added to the q-axis current that generates the assist force. On the other hand, when the temperature detected from the temperature detecting means is higher than a predetermined temperature, the d-axis current is not added to the q-axis current that generates the assist force.

  As a result, when the temperature detected by the temperature detecting means is lower than the predetermined temperature, the calorific value is increased and the viscous resistance is reduced by adding the predetermined d-axis current to the q-axis current that generates the assist force. As a result, the steering feeling can be improved. On the other hand, when the temperature detected by the temperature detection means is higher than the predetermined temperature, the d-axis current is not added to the q-axis current that generates the assist force, so that it is possible to prevent generation of useless heat generation.

  According to the present invention, it is possible to provide an electric power steering apparatus with good steering feeling immediately after the engine is started by a simple method.

The schematic block diagram of an electric power steering device (EPS). The control block diagram of EPS. The flowchart figure which shows the process sequence of an Id * electric current command value calculating part. Ambient temperature / Id * current command value map.

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 temperature sensor 20 (temperature detection means), a vehicle speed sensor 25 (vehicle speed detection means), a torque sensor 26 (steering torque detection means), and a motor rotation angle sensor 22 are connected to the ECU 27. Based on the output signal of each sensor, the ambient temperature th, the vehicle speed V, the steering torque τ, and the motor rotation angle θm are 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 supplies three-phase drive power to a motor 21 that is a drive source of the EPS actuator 24 based on a microcomputer 29 (control means) that outputs a motor control signal and the motor control signal. Drive circuit 40, and current sensors 30u, 30v, and 30w for detecting a U-phase current value Iu, a V-phase current value Iv, and a W-phase current value Iw that are supplied to the motor 21.

  The drive circuit 40 is a known PWM inverter (not shown) formed by connecting three arms corresponding to each phase 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 three-phase motor driving power based on the power supply voltage of the battery 28. The motor 21 is configured to output.

  A motor rotation angle sensor 22 for detecting the motor rotation angle θm of the motor 21 is connected to the ECU 27. Then, the microcomputer 29 adjusts the phase current values Iu, Iv, Iw and the motor rotation angle θm of the motor 21 detected based on the output signals of these sensors, the ambient temperature th, the steering torque τ, and the vehicle speed V. Based on this, a motor control signal is output to the drive circuit 40.

  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 an Iq * current command value calculation unit 31 that calculates a q-axis current command value Iq * for controlling the motor 21, and an Id * current command that calculates a d-axis current command value Id *. The value calculating part 32 and the motor control signal generation part 44 which produces | generates the motor control signal which controls the drive circuit 40 are provided.

  The microcomputer 29 performs current feedback control in the d / q coordinate system by mapping the phase current values Iu, Iv, and Iw to the d / q coordinate system (d / q conversion). Then, the PWM output unit 39 generates a DUTY command value for determining the on / off timing of the FET constituting the drive circuit 40, and outputs a gate on / off signal based on the DUTY command value.

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 Iq * current command value calculation unit 31 (assist force generation means). Based on the steering torque τ and the vehicle speed V, the Iq * current command value calculation unit 31 determines the q-axis current command value Iq *, which is a control target for the assist torque, from the steering torque / q-axis current command value map.
The steering torque / q-axis current command value map is configured to determine a larger q-axis current command value Iq * as the vehicle speed V is smaller for the same steering torque.

  The ambient temperature th detected by the temperature sensor 20 is input to the Id * current command value calculation unit 32. The Id * current command value calculation unit 32 determines the d-axis current command value Id * using the ambient temperature / Id * current command value map based on the magnitude of the ambient temperature th. When the ambient temperature th is smaller than the predetermined ambient temperature value, the d-axis current command value Id * based on the ambient temperature / Id * current command value map is output. By doing so, the atmospheric temperature th rises, the viscosity resistance of the lubricant and the sliding resistance due to the sealing member are reduced, and the steering feeling is improved.

  The motor control signal generation unit 44 includes a d / q conversion calculation unit 33, a q-axis current control calculation unit 34, a q-axis PID control unit 35, a d-axis current control calculation unit 36, a d-axis PID control unit 37, and a d / q reverse A conversion calculation unit 38 and a PWM output unit 39 are included.

  The U-phase current value Iu, the V-phase current value Iv, and the W-phase current value Iw input to the d / q conversion calculation unit 33 are d / q-converted to obtain a q-axis current value Iq and a d-axis current value Id. Become. The q-axis current value Iq is input to the subtractor 34J. The subtractor 34J inputs the q-axis deviation current value ΔIq obtained by subtracting the q-axis current value Iq from the q-axis current command value Iq * output from the Iq * current command value calculation unit 31 to the q-axis PID control unit 35. . The q-axis voltage command value Vq * calculated by the q-axis PID control unit 35 is input to the d / q inverse conversion calculation unit 38.

  On the other hand, the d-axis current value Id converted by the d / q conversion calculation unit 33 is input to the subtractor 35J. The subtractor 35J inputs a d-axis deviation current value ΔId obtained by subtracting the d-axis current value Id from the d-axis current command value Id * output from the Id * current command value calculation unit 32 to the d-axis PID control unit 37. . The d-axis voltage command value Vd * calculated by the d-axis PID control unit 37 is input to the d / q inverse conversion calculation unit 38.

  The q-axis voltage command value Vq * and the d-axis voltage command value Vd * input to the d / q reverse conversion calculation unit 38 are converted by the d / q reverse conversion calculation unit 38 into the U-phase voltage command value Vu * and V-phase. The voltage command value Vv * and the W-phase voltage command value Vw * are converted and input to the PWM output unit 39.

Next, the processing procedure of the Id * current command value calculation unit by the microcomputer 29 of this embodiment will be described with reference to FIG.
That is, the microcomputer 29 first reads the ambient temperature th (step S101). Subsequently, the microcomputer 29 determines whether or not the ambient temperature th is equal to or higher than the ambient temperature predetermined value th0 (step S102). The microcomputer 29 sets the d-axis current command value Id * to zero (Id * = 0, step) when the atmospheric temperature th is equal to or higher than the predetermined atmospheric temperature value th0 (th ≧ th0, step S102: YES). S103). Then, the microcomputer 29 outputs the d-axis current command value Id * to the d-axis current control calculation unit 36 (step S104), and the process ends.

  On the other hand, when the ambient temperature th is lower than the ambient temperature predetermined value th0 (th <th0, step S102: NO), the microcomputer 29 sets the d-axis current command value Id * from the ambient temperature / Id * current command value map. Read (step S105). Then, the microcomputer 29 outputs the d-axis current command value Id * to the d-axis current control calculation unit 36 (step S104), and the process ends.

Next, an atmosphere temperature / Id * current command value map by the microcomputer 29 of this embodiment will be described with reference to FIG.
The ambient temperature / Id * current command value map is a map in which the horizontal axis represents the ambient temperature and the vertical axis represents the Id * current command value. When the ambient temperature is equal to or higher than the predetermined ambient temperature th0, it is determined that the ambient temperature is sufficiently high, the viscous resistance of the lubricant and the sliding resistance due to the sealing member are reduced, and the steering feeling is improved. Then, the Id * current command value is set to zero.
On the other hand, as the ambient temperature becomes lower than the ambient temperature predetermined value th0, it is determined that the viscous resistance of the lubricant and the sliding resistance due to the sealing member are large, and the steering feeling is not improved. * The current command value flows (curve L1).

Next, the operation and effect of the EPS 1 of the present embodiment configured as described above will be described.
When the temperature detected from the temperature detecting means is lower than the predetermined temperature, the predetermined d-axis current is added to the q-axis current that generates the assist force. On the other hand, when the temperature detected from the temperature detecting means is higher than a predetermined temperature, the d-axis current is not added to the q-axis current that generates the assist force.

  As a result, when the temperature detected by the temperature detecting means is lower than the predetermined temperature, the calorific value is increased and the viscous resistance is reduced by adding the predetermined d-axis current to the q-axis current that generates the assist force. As a result, the steering feeling can be improved. On the other hand, when the temperature detected by the temperature detection means is higher than the predetermined temperature, the d-axis current is not added to the q-axis current that generates the assist force, so that it is possible to prevent generation of useless heat generation.

In addition, you may change this embodiment as follows.
In the present embodiment, when the ambient temperature is lower than the ambient temperature predetermined value th0, for example, the Id * current command value is flowed in the positive direction, but the Id * current command value is flowed in the negative direction. Alternatively, the Id * current command value may flow alternately in the plus and minus directions.

In this embodiment, the magnitude of the PID gain of the d-axis current control calculation unit is constant, but when it is determined that the Id * current command value is larger than the ambient temperature / Id * current command value map, the PID gain It is good also as a structure which enlarges the magnitude | size.

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, 20: temperature sensor (temperature detection means)
21: Motor, 22: Motor rotation angle sensor, 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 (control means),
30u, 30v, 30w: current sensor (current detection means),
31: Iq * current command value calculation unit (assist force generation means),
32: Id * current command value calculation unit, 33: d / q conversion calculation unit,
34: q-axis current control calculation unit, 35: q-axis PID control unit,
36: d-axis current control calculation unit, 37: d-axis PID control unit,
38: d / q inverse conversion calculation unit, 39: PWM output unit,
40: drive circuit, 44: motor control signal generator,
34J, 35J: subtractor,
V: vehicle speed, τ: steering torque, θm: motor rotation angle,
th: ambient temperature, th0: ambient temperature predetermined value,
Iu, Iv, Iw: current value of each phase,
Iq *: q-axis current command value, Iq: q-axis current value, ΔIq: q-axis deviation current value,
Id *: d-axis current command value, Id: d-axis current value, ΔId: d-axis deviation current value,
Vq *: q-axis voltage command value, Vd *: d-axis voltage command value,
Vu *, Vv *, Vw *: Voltage command value for each phase

Claims (1)

A steering force assisting device provided to apply an assisting force to assist the steering operation to the steering system by the motor;
Steering torque detection means for detecting steering torque;
Vehicle speed detection means for detecting the vehicle speed;
Temperature detecting means for detecting the temperature of the steering system;
An assist force generating means for generating an assist force from the steering torque detected from the steering torque detecting means and the vehicle speed detected from the vehicle speed detecting means;
An electric power steering apparatus comprising: control means for controlling the operation of the steering force assisting device by supplying driving power to a motor that is a drive source of the steering force assisting device based on the assist force generating device. In
The control means adds a predetermined d-axis current to the q-axis current for generating the assist force when the temperature detected from the temperature detection means is lower than a predetermined temperature, while the temperature detection means When the detected temperature is higher than a predetermined temperature, do not add the d-axis current to the q-axis current that generates the assist force;
An electric power steering device.

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