JPH08133107A - Control unit for motor-driven power steering and motor-driven power steering device using it - Google Patents

Abstract

PURPOSE: To provide the function of over-heating protection and at the same time realize cost reduction by limiting the maximum electric current value to be supplied to a motor according to the integration value or the average value of the inter-terminal voltage of the motor to generate steering wheel steering assist effort. CONSTITUTION: The detection signal of a steering torque sensor 5 and the vehicle speed signal of a vehicle speed sensor 9 are inputted into an electric current command operation portion 32 in a CPU 21, and the drive control of a motor drive circuit 22 is carried out by means of an electric current operation portion 35 according to an electric current command value from the electric current command operation portion 32 and a detected electric current from a motor electric current detection circuit 23a. Also, at this time, as the estimation of the relative temperature change of the motor is possible due to inter-terminal voltage, the temperature of the motor is estimated by inputting into a motor temperature estimating portion 37 the respective output signals of a motor inter-terminal voltage detecting portion 36 and the motor electric current detection circuit 23a, and a maximum electric current limit value is decided by means of a maximum electric current limiting means 38 according to this estimated temperature, and by outputting this value to the electric current command operation portion 32, it is used for the control of the motor 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control unit used in an electric power steering apparatus in which a steering force of a steering wheel is assisted by an output of a motor, and an electric power steering apparatus using the control unit.

[0002]

2. Description of the Related Art Conventionally, in an electric power steering device, in order to prevent a power element for driving a motor from failing due to overheating, a temperature sensor is provided in a heat radiation block to which the power element is attached, and the temperature of the power element is monitored. Then
Therefore, there is a device in which energization is controlled so that abnormal overheating does not occur. In addition, in order to protect the motor, there is one in which a temperature sensor is also provided in the motor to monitor the temperature of the motor and control the same. Further, there is one in which the temperature sensor of the heat radiation block is eliminated for the purpose of cost reduction, and the overheat protection of both is performed by the following method. That is, regarding each temperature rise characteristic of the motor and the power element, paying attention to the fact that the temperature rise of the motor is faster, and when the motor temperature becomes equal to or higher than a predetermined value, the power is reduced (the maximum current value is reduced), and
Power control is performed such that power is increased (the maximum current value is returned to the original value) when the value falls below a predetermined value. Then, in practice, the heat dissipation block is set to the extent that the power element is not destroyed by only this power control.

[0003]

However, in the recent demand for further cost reduction, when the temperature sensor is used,
Inevitably it becomes expensive, and the connector wiring / interface circuit between the temperature sensor and the control circuit is required.
These are obstacles to downsizing and cost reduction of the electric power steering device. There is also a method of limiting the maximum current value according to the average current detection value of the motor without providing a temperature sensor in the motor, but in this method, the motor current is not proportional to the heat loss of the motor,
There is a high possibility that the motor will be used above the rated temperature.
Also, when the ignition is repeatedly turned on and off in the full vehicle (maximum current) state in the actual vehicle, only the relative temperature rise of the motor can be known, and the absolute temperature is not known. Therefore, overheating may cause damage to the motor. It was

The present invention solves the above-mentioned problems. The structure of the motor is simplified by estimating the motor temperature from the voltage across the terminals of the motor without using a sensor for detecting the motor temperature and controlling the power based on this. It is an object of the present invention to provide a control unit used in an electric power steering apparatus that can realize an overheat protection function and reduce costs, and an electric power steering apparatus using the control unit.

[0005]

In order to achieve the above object, the invention of claim 1 is, in a control unit used in an electric power steering apparatus having a motor for generating a steering wheel assisting force, between terminals of the motor. A maximum current limiting means for limiting the maximum current value supplied to the motor according to the average value or integrated value of the voltage is provided.
According to a second aspect of the present invention, in a control unit used in an electric power steering apparatus having a motor that generates a steering wheel assisting force, an average value or an integrated value of values obtained by multiplying a terminal voltage of the motor by a motor current. According to the above, the maximum current limiting means for limiting the maximum current value supplied to the motor is provided. The invention of claim 3 is
In the electric power steering control unit according to claim 1 or 2, when the steering torque or the motor current is a predetermined value or more, according to an average value or an integrated value of values obtained by dividing the terminal voltage of the motor by the motor current, A maximum current control correction means for correcting the control of the maximum current value supplied to the motor is provided. According to the invention of claim 4, a steering torque sensor for detecting a steering torque of the steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a signal from the steering torque sensor are controlled. In the electric power steering apparatus including the control unit, the control unit includes maximum current limiting means for limiting the maximum current value supplied to the motor according to the average value or integrated value of the voltage across the terminals of the motor. Is. According to the invention of claim 5, a steering torque sensor for detecting steering torque of the steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a signal from the steering torque sensor are controlled. In the electric power steering apparatus equipped with a control unit that controls the maximum current value supplied to the motor, the control unit limits the maximum current value supplied to the motor according to an average value or an integrated value of values obtained by multiplying the motor terminal voltage by the motor current. It is provided with a current limiting means. According to the invention of claim 6, in the electric power steering apparatus according to claim 4 or 5, the control unit divides the terminal voltage of the motor by the motor current when the steering torque or the motor current is equal to or more than a predetermined value. A maximum current control correction means for correcting the control of the maximum current value supplied to the motor in accordance with the average value or integrated value of the values is provided.

[0006]

In the electric power steering control unit according to the first aspect of the present invention, the maximum current limiting means is configured to change the average or integrated value of the voltage across the terminals of the motor.
Limit the maximum current value supplied to the motor. This allows
Since there is a phenomenon that the armature resistance of the motor rises as the temperature rises, it is possible to estimate the relative temperature change of the motor from the voltage across the terminals without using a sensor that detects the motor temperature. Control becomes possible. Further, in the electric power steering control unit according to claim 2, the maximum current limiting means sets the maximum current value to be supplied to the motor in accordance with an average value or an integrated value of values obtained by multiplying the motor terminal voltage by the motor current. Restrict. As a result, the relative temperature change of the motor can be estimated based on the integral value of the power loss of the motor, and the power control for heating protection can be performed. Further, in the electric power steering control unit according to claim 3, the maximum current control correction means, when the steering torque or the motor current is equal to or greater than a predetermined value, an average value or an integral of values obtained by dividing the terminal voltage of the motor by the motor current. Since the control of the maximum current value supplied to the motor is corrected according to the value, in addition to the above operation, it is possible to estimate a value close to the absolute temperature of the motor from the calculated value of the motor armature resistance, and more accurate heating protection. It becomes possible to control the power. Further, in the electric power steering device according to claim 4, the maximum current limiting means of the control unit limits the maximum current value supplied to the motor according to the average value or the integrated value of the voltage across the terminals of the motor. An effect equivalent to is obtained. Further, in the electric power steering apparatus according to claim 5, the maximum current limiting means of the control unit sets the maximum current value to be supplied to the motor in accordance with an average value or an integrated value of values obtained by multiplying the terminal voltage of the motor by the motor current. Because it is limited, claim 2
An effect equivalent to is obtained. Further, in the electric power steering apparatus according to claim 6, the maximum current control correction means of the control unit is an average value of values obtained by dividing the terminal voltage of the motor by the motor current when the steering torque or the motor current is a predetermined value or more, or Since the control of the maximum current value supplied to the motor is corrected according to the integrated value, the same effect as in claim 3 can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an electric power steering device. The electric power steering device is
The driver includes a steering wheel 1 which applies a steering torque, and the steering wheel 1 is connected to a pinion gear 2 and a rack shaft 3 via a steering shaft 1a.
The steering wheel 4 is connected to the steering wheel 4. Further, the electric power steering apparatus includes a steering torque sensor 5 that detects a steering torque applied to the steering wheel 1, a motor 6 that generates an auxiliary driving force necessary for steering the steering wheel 1, and the motor 6
An auxiliary drive mechanism 7 for applying the auxiliary drive force of the above to the rack shaft 3,
It has a control device 8 (control unit) that receives the steering torque detected by the steering torque sensor 5 and controls the amount of electricity supplied to the motor 6. A vehicle speed signal from a vehicle speed sensor 9 is also input to the control device 8, and power is supplied from a battery 10.

FIG. 2 is a specific configuration diagram of the electric power steering apparatus. The control device 8 includes a CPU 21 that controls the entire electric power steering device, and a C21.
A motor drive circuit 22 that is controlled by the PU 21 to drive and control the motor 6, and a CPU that detects the motor current / voltage.
21, a motor current / voltage detection circuit 23 to be input to 21, a fail-safe circuit 24 that limits the current value when the motor current exceeds a predetermined allowable value, and a power supply to the motor drive circuit 22 for fail-safe A relay circuit 25 and a relay contact 26 for controlling cutoff are provided. CPU2
In addition to the detection signals from the steering torque sensor 5 and the vehicle speed sensor 9, an engine speed signal 27 is input to the steering wheel 1. Further, when the ignition key switch 28 is turned on, the relay circuit 25 operates and power is supplied to the motor drive circuit 22. The CPU 21 performs pulse width modulation (PWM) on the motor drive circuit 22 in accordance with the steering torque detected by the steering torque sensor 5 to generate an auxiliary force of the force required for steering.
Energization control.

FIG. 3 is a circuit diagram showing a specific configuration of the motor drive circuit 22 and the motor current / voltage detection circuit 23 shown in FIG. The motor drive circuit 22 is composed of an FET drive circuit 22a and field effect transistors FET1 to FET4 (hereinafter referred to as FETs) which are bridge-connected power elements, and the terminal of the motor 6 is connected between the midpoints of the bridges. ing. The FET drive circuit 22a is additionally provided with a prohibition circuit that prohibits energization when overcurrent is detected. Further, the motor current / voltage detection circuit 23 is the current detection circuit 23.
a and a terminal voltage detection circuit 23b (ground fault detection). The current detection circuit 23a obtains a signal from both ends of the shunt resistor RS through which the motor current flows. The terminal voltage detection circuit 23b detects the voltages at both terminals A and B of the motor 6. The interface 25a corresponds to the relay circuit 25. The booster circuit 29 is driven by a pulse from the CPU 21, and applies a boosted voltage to the FET drive circuit 22a.

FIG. 4 is a relationship diagram between the steering torque sensor detection value and the motor drive current (steering assist torque). As shown in the figure, the motor drive current is limited to the maximum current in consideration of the heat resistance of the motor, and moreover, the steering operation is the same at high vehicle speed as compared to stationary steering and low vehicle speed. The motor drive current is reduced with respect to the torque. In addition,
+ And-correspond to the left and right directions of steering.

FIG. 5 is a block diagram of a motor control function executed by the CPU 21. The steering torque detection signal from the steering torque sensor 5 is transmitted via the torque sensor input unit 31, and the vehicle speed signal from the vehicle speed sensor 9 is transmitted via the vehicle speed sensor input unit 33, the vehicle speed coefficient calculation unit 34, and the current command calculation unit 32. Entered in. The current control unit 35 uses the current command value from the current command calculation unit 32 and the motor current detection circuit 23a.
The motor drive circuit 22 is driven and controlled according to the detected current from In addition, the motor terminal (right and left) voltage detection circuit 23b
The detected voltage from is input to the motor temperature estimation unit 37 via the motor terminal voltage detection unit 36. The motor temperature estimation unit 37 estimates the motor temperature from the detected motor terminal voltage and the detected current from the motor current detection circuit 23a.
The maximum current limiting means 38 determines the maximum current limiting value according to the estimated motor temperature, and outputs it to the current command computing unit 32. Further, the output of the torque differential value calculation unit 39 is also input to the current command calculation unit 32.

The operation of the electric power steering apparatus constructed as described above, particularly the motor current control, will be described with reference to the flowchart of FIG. The ignition key switch 28 of the electric power steering device is turned on.
Then, power is supplied to the control device 8 and CP
U21 is a steering torque detection signal from the steering torque sensor 5, a motor current from the motor current detection circuit 23a, and a terminal voltage detection circuit 23 according to a main flowchart (not shown).
The voltage between the motor terminals is read from b, and the motor current is controlled by the current command calculator 32, the current controller 35, the maximum current limiter 38, and the like. From the main flow chart, the subroutine of FIG. 6 is entered at a predetermined interval.

In this subroutine, sensorless
In order to protect the motor 6 and the power element from overheating, it is checked whether the average value of the steering torque input or the average value of the motor current is larger than a predetermined value (S1). ), The average value of the steering torque or the motor current is smaller than the specified value (S).
If NO in 1), the process proceeds to S2 to calculate a unit time integral value of the product of the motor current and the voltage between the motor terminals (motor loss power),
Let this be PM. It is checked whether PM is larger than the specified value 1 which is the maximum allowable value defined from the viewpoint of overheat protection (S3). If it is not larger than the specified value 1 (N in S3
O), then, it is checked whether PM is smaller than a prescribed value 2 which is smaller than the prescribed value 1 (S5). If it is not smaller than the prescribed value 2 (NO in S5), the maximum motor current value is limited. If you do not need to do this, exit this subroutine. S
3, when PM becomes larger than the specified value 1 (S
If YES in step 3, the maximum current value ILIMn is calculated to limit the maximum motor current value, and the maximum motor value is reduced based on the calculated maximum current value ILIMn (S4). By performing the above operation, the maximum current value limitation is performed by estimating the relative temperature change of the motor based on the integral value of the motor loss power. Also,
In S5, when PM becomes smaller than the specified value 2 (YES in S5), the maximum current value ILIMn is calculated in order to release the limitation of the maximum motor current value, and the maximum motor value is restored based on this (S6). .

Further, when the torque or the motor current average value becomes larger than the specified value in the full assist state, S
It becomes YES in 1 and proceeds to S7, which is 1 in this driving.
If it is the first time (YES in S7), the motor terminal voltage is divided by the motor current to calculate the armature resistance value RM (S).
8). The maximum current limit value ILIM0 for performing the motor maximum current limit value correction is obtained from this armature resistance value RM (S
9) Next, it is checked whether the maximum current limit value ILIM0 is smaller than the current maximum current value ILIMn (S10). If it is smaller (YES in S10), the safe side is taken and the maximum current limit value ILIM0 is set to the current maximum. The current value ILIMn is set (S11), and if it is not small (NO in S10), no correction is performed and the current maximum current value ILIMn is kept (S12). In addition, 1 in S7
If not, go to S2. By performing the above operation, it is possible to estimate a value close to the absolute temperature of the motor from the armature resistance calculated values when the torque is large and the current is large. As a result, further, the maximum current value limit obtained in S4 is calculated. Can be corrected and the ignition is turned on in the fully assisted state.
Even in situations such as repeated / OFF, power down can be handled at an early timing.

FIG. 7 shows changes in the motor temperature when the maximum current is limited during normal operation in the full assist state. This operation is the same in the conventional and the present embodiment. Ignition ON in full assist state /
FIG. 8 shows changes in the motor temperature when the maximum current is limited by the conventional method in a situation where the current is repeatedly turned off, and FIG. 9 shows changes in the motor temperature when the maximum current is limited by the present embodiment. . In the conventional case of FIG. 8, the motor temperature rises abnormally and the motor is damaged.
In the case of the present embodiment of FIG. 9, the motor temperature does not rise abnormally and the motor is not damaged. In this way, overheat protection of the motor and the like can be performed at low cost without using the motor temperature sensor and its interface circuit.

The reason why a value close to the absolute temperature of the motor can be estimated without a sensor from the calculated armature resistance value will be described below. Since the motor terminal voltage value E includes a reverse voltage when the motor is rotating (ω) as described below, the value obtained by dividing the motor terminal voltage value E by the motor current value I is not necessarily the armature resistance value R. Don't

[Equation 1] E / I = (R · I + KE · ω) / I = R + KE · ω / IKE: Back electromotive force constant However, the brush voltage drop is ignored.

However, when the steering torque value or the motor current value continues to be large to some extent, it can be assumed that the motor is hardly in a rotating state. Therefore, KE.omega./I
E / I = R can be regarded as = 0. The motor armature resistance value increases as the temperature rises, as shown in FIG.
10A, 10B, and 10C, the motor temperature is -30 ° C.
The motor current waveform when a voltage of 5 V step is applied between the motor terminals at 25 ° C. and 158 ° C. is shown.

Although the above flowchart does not show the control in response to the vehicle speed from the vehicle speed sensor 9 shown in FIG. 2 and the control processing using the engine speed signal 27, these vehicle speed response and engine speed are not shown. Even number detection,
If the motor current is limited in consideration of the value of the steering torque, more accurate control becomes possible. Also,
As a method of reducing the motor current, in addition to limiting the maximum value of the motor current as described above, a method of limiting the average value of the motor current can be considered. Further, when the maximum current value or the like is obtained, the method of obtaining the maximum value of the current has been described in the above flowchart, but a method of using a table may be used instead of the calculation.

[0019]

As described above, according to the control unit for electric power steering or the electric power steering apparatus of the invention of claim 1 or 4, the motor is controlled in accordance with the average value or the integral value of the terminal voltage of the motor. By limiting the maximum current value to be supplied, overheat protection of the motor can be performed without using the motor temperature sensor and the interface circuit, and the cost and size can be reduced. According to the control unit for electric power steering or the electric power steering apparatus according to the invention of claim 2 or 5, the voltage is supplied to the motor in accordance with the average value or integrated value of the values obtained by multiplying the terminal voltage of the motor by the motor current. By limiting the maximum current value, it is possible to limit the maximum current value by estimating the relative temperature change of the motor based on the integral value of the motor loss power, and it is possible to accurately protect the motor from overheating, and to reduce cost and size. It will be possible. According to the control unit for electric power steering or the electric power steering device of the invention of claim 3 or 6, the voltage is supplied to the motor in accordance with the average value or integrated value of the values obtained by dividing the voltage between the terminals of the motor by the motor current. In addition to the above effects, it is possible to estimate a value close to the absolute temperature of the motor because the control of the maximum current value is corrected.
Even in a situation where N / OFF is repeated, power down can be dealt with early.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a specific configuration diagram of an electric power steering device.

FIG. 3 is a circuit diagram showing a specific configuration of a motor drive circuit portion in the electric power steering device.

FIG. 4 is a relationship diagram between a steering torque sensor detection value and a motor drive current.

FIG. 5 is a block diagram of a motor control function executed by a CPU in the electric power steering device.

FIG. 6 is a flowchart showing a motor current control operation in the electric power steering device.

FIG. 7 is a diagram showing a change in motor temperature when a maximum current limit in a normal state is performed in a full assist state.

FIG. 8 is a diagram showing a change in motor temperature when a maximum current is limited by a conventional method in a full assist state.

FIG. 9 is a diagram showing a change in motor temperature when maximum current limitation is performed by the method of the present embodiment.

FIG. 10 is a diagram showing motor current waveforms when a voltage is applied between motor terminals in various temperature states.

[Explanation of symbols]

 1 Handle 5 Steering Torque Sensor 6 Motor 8 Control Device 21 CPU 22 Motor Drive Circuit 23 Motor Current / Voltage Detection Circuit 32 Current Command Calculation Unit 37 Motor Temperature Estimator 38 Maximum Current Limiting Means

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Claims (6)

[Claims] 1. A control unit used in an electric power steering apparatus having a motor for generating an assisting force for steering a steering wheel according to an average value or an integrated value of a terminal voltage of the motor,
A control unit for electric power steering, comprising maximum current limiting means for limiting a maximum current value supplied to the motor. 2. A control unit used in an electric power steering apparatus having a motor for generating an assisting force for steering a steering wheel according to an average value or an integrated value of values obtained by multiplying a voltage between terminals of the motor by the motor current. And a control unit for electric power steering, comprising maximum current limiting means for limiting a maximum current value supplied to the motor. 3. A maximum current value supplied to the motor according to an average value or an integrated value of values obtained by dividing a voltage across terminals of the motor by the motor current when the steering torque or the motor current is a predetermined value or more. The control unit for electric power steering according to claim 1 or 2, further comprising a maximum current control correction means for correcting the control. 4. A steering torque sensor for detecting steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a signal from the steering torque sensor. In the electric power steering apparatus including a control unit, the control unit includes a maximum current limiting unit that limits a maximum current value supplied to the motor according to an average value or an integrated value of the voltage across the motor. An electric power steering device characterized in that 5. A steering torque sensor for detecting a steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor in response to a signal from the steering torque sensor. In an electric power steering apparatus including a control unit, the control unit sets a maximum current value to be supplied to the motor according to an average value or an integrated value of values obtained by multiplying a voltage between terminals of the motor by the motor current. An electric power steering apparatus comprising a maximum current limiting means for limiting. 6. The control unit supplies the motor according to an average value or an integrated value of a value obtained by dividing a voltage between terminals of the motor by a motor current when the steering torque or the motor current is a predetermined value or more. The electric power steering apparatus according to claim 4, further comprising a maximum current control correction means for correcting the control of the maximum current value.