JP2009056849A - Control device of electric power steering apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply, cheaply, and accurately protect power system electronic components and signal system electronic components constituting an ECU from being overheated. <P>SOLUTION: A temperature of the power system electronic component is detected by a thermistor 132 and a temperature detection circuit block 14 provided in the vicinity of an FET 131 of a motor drive circuit 13. A temperature of the signal system electronic component is estimated from a change in internal resistance accompanied by a temperature of an anomaly detection circuit 121 normally included in an FET drive circuit 12. A microcomputer 11 changes a current command value so as to limit a current fed from the motor drive circuit 13 to a motor 2 when either of the temperatures exceeds set thresholds, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device that applies a steering assist force by a motor to a steering mechanism of a vehicle such as an automobile, and more particularly to a temperature protection function of an electronic component mounted on the control device.

  2. Description of the Related Art In vehicles such as automobiles, an electric power steering device that assists the steering of the steering wheel by applying an assisting force to the steering mechanism by the assist torque of the motor during steering by the steering is widely used.

  Such an electric power steering apparatus includes a control device (hereinafter also referred to as an ECU) for controlling a current supplied to the motor so that the motor generates a desired auxiliary torque, and is generated with the controlled current. The steering torque is urged to the steering mechanism by transmitting the motor torque to the steering shaft and the rack shaft directly connected to the steering handle via a reduction gear and a transmission mechanism such as a gear or a belt.

  FIG. 4 is a block diagram showing a configuration of a conventional electric power steering apparatus. The electric power steering device includes an ECU 5 that is a control device, a motor 6 that is a brush motor, a battery 7 that supplies power to the ECU 5, and an ignition switch 8.

  The ECU 5 generates a control value of the current supplied to the motor 6 based on the steering torque generated in the steering handle and the vehicle speed detected by a sensor (not shown), and a microcomputer (microcomputer) as control means 51, an FET drive circuit unit 52 that supplies a voltage to the gate of an FET (drive element) 531 based on a generated current control value, and an electric current that is supplied to the motor 6 by forming an H-bridge circuit with four FETs 531 And a power supply circuit unit 55 that generates a voltage for reducing the power supply voltage of the battery 7 and supplying it to the microcomputer 51.

  In addition, regarding such a conventional electric power steering apparatus, the motor drive circuit unit 53 is further provided with temperature detection means including a temperature sensor 532 such as a thermistor and a temperature detection circuit block 54, and the temperature of the FET 531 is estimated from the detected temperature. Overheat protection means for limiting current, motor overheat protection means for limiting current based on motor brush temperature estimated based on temperature detected at startup, and temperature of motor magnetic body estimated based on temperature detected at startup And a motor low-temperature demagnetization protection means for limiting the current by the above, and the one that limits the current with any one of the larger limits and performs overheat protection of the electronic components mounted inside the ECU 5 is known ( For example, see Patent Document 1).

JP-A-11-286278

  However, in such a conventional electric power steering apparatus, since the temperature detection means is provided in the vicinity of the FET (power system electronic component) 531 whose temperature is increased by the current supplied to the motor 6, the microcomputer It was not possible to sufficiently grasp the temperature rise of the signal-system electronic components that input / output weak signals such as 51 and the FET drive circuit section 52. For this reason, overheat protection has been implemented mainly for power electronic components, and there has been a disagreement that the overheat protection of signal electronic components is not fully demonstrated.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an electric motor that can easily and inexpensively implement overheat protection in consideration of both power electronic components and signal electronic components. It is to provide a control device for a power steering device.

  The object of the present invention described above is achieved by the following configuration.

(1) A control unit that generates a control value of a current supplied to the motor to apply a steering assist force to the steering mechanism, a motor driving unit that drives the motor by a driving element, and a semiconductor element, A drive element control means for controlling the drive element based on a control value;
further,
Temperature detecting means for detecting the temperature inside the control device;
Internal resistance detection means for detecting the internal resistance of the semiconductor element;
And the control means comprises
Based on the internal resistance detected by the internal resistance detection means, the temperature inside the control device is estimated,
When at least one of the estimated temperature or the temperature detected by the temperature detecting means exceeds a threshold value set individually,
The control device for an electric power steering apparatus, wherein the control value is changed so as to limit a current supplied to the motor.
(2) The temperature detecting means includes
The control device for an electric power steering device according to (1) above, wherein the control device is disposed at a position where a temperature correlated with the temperature of the drive element can be detected.
(3) The control means includes:
The control apparatus for an electric power steering apparatus according to the above (1) or (2), characterized in that the control apparatus is constituted by a microcomputer.

According to the control device for the electric power steering apparatus described in (1) above, power system electrons such as a power FET that supplies current to the motor by the temperature detection means inside the control device and the internal resistance detection means of the semiconductor element. The temperature of each component and signal system electronic component such as a gate driver IC can be grasped, and a threshold value is individually set for each of these detected temperatures, and any one of the detected temperatures sets the threshold value. Since the control value is changed so as to limit the current supplied to the motor when it exceeds, overheat protection that considers both power system electronic components and signal system electronic components can be implemented easily and inexpensively with high accuracy. it can.
Further, according to the configuration described in (2) above, the temperature detecting means is disposed in the vicinity of the power electronic component (FET or the like) that is a driving element of the motor, for example. Overheat protection can be performed with high accuracy.
According to the configuration described in (3) above, the control means is configured by a microcomputer, so that overheating protection of each of the power electronic component and the signal electronic component can be performed easily, inexpensively, and with high accuracy. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus of the electric power steering apparatus which can implement the overheat protection which considered both the power system electronic component and the signal system electronic component simply and cheaply accurately can be provided.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of the electric power steering apparatus according to the present embodiment.

  As shown in FIG. 1, the electric power steering apparatus of the present embodiment is configured so that a brushless motor (hereinafter simply referred to as a motor) 2 that applies a steering assist force to the steering mechanism and the motor 2 generate a desired torque. ECU 1 for controlling the current supplied to the motor 2, a battery 3 for supplying power to the ECU 1, and an ignition switch 4 for turning on the power to the ECU 1.

  The ECU 1 includes a microcomputer (microcomputer) 11 that generates a current command value that is a control target value of a current supplied to the motor 2 based on a steering torque and a vehicle speed detected by a sensor (not shown), and a signal system electronic component. The FET driver circuit unit 12 is configured by a gate driver IC (semiconductor element) and drives a gate of a power FET (power system electronic component) 131, which will be described later, based on a current command value, and a current supplied to the motor 2 A temperature detection circuit for detecting the temperature of the power FET 131 based on the output of a motor drive circuit unit 13 having six power FETs (field effect transistors) 131 constituting an H-bridge circuit for control and a thermistor 132 described later. The block 14 and the voltage for reducing the power supply voltage of the battery 3 and supplying it to the microcomputer 11 are generated. A power supply circuit unit 15 which is configured with a.

In the motor drive circuit unit 13, a power FET 131 that configures an H bridge circuit and supplies power for driving the motor 2 is mounted on a heat sink such as aluminum, and the temperature of the power FET 131 is accurately detected. A thermistor 132 for detecting the temperature is installed on the position where the temperature correlated with the temperature of the power FET 131 can be detected, more specifically, on the same heat sink.
The thermistor 132 is an element having a characteristic that the resistance value changes with temperature, and the temperature can be detected using this characteristic.

  In addition to the function of supplying a voltage to the gate of the FET 131, the gate driver IC constituting the FET drive circuit unit 12 normally has an abnormality in the energization path in the H-bridge circuit based on the output signal of the FET drive circuit unit 12. And an abnormality detection circuit 121 that detects the occurrence of an abnormality when the abnormality is detected.

The abnormality detection circuit 121 is configured by an open drain MOSFET 122, and is normally in an on state and outputs a binary signal “0”.
Note that the output terminal of the abnormality detection circuit 121 in this embodiment is connected to the microcomputer 11 via the pull-up resistor 16.

  Here, the internal resistance during conduction of a semiconductor such as a gate driver IC generally has a characteristic of increasing or decreasing linearly with a temperature change. The gate driver IC that constitutes the FET drive circuit unit 12 rises in temperature as the motor 2 is driven. At this time, the MOSFET 122 of the abnormality detection circuit 121 also has an internal resistance (resistance between the drain and source) when conducting. Changes.

  As the internal resistance of the MOSFET 122 changes with temperature, the current flowing through the pull-up resistor 14 also changes. That is, along with this, the drain voltage changes. When this is transmitted to the microcomputer 11 and processed, the microcomputer 11 detects the temperature of the gate driver IC constituting the FET drive circuit unit 12, that is, the signal system electronic component. Temperature can be estimated.

  Further, in the electric power steering apparatus configured as described above, the microcomputer 11 of the ECU 1 generates and outputs a pulse width modulation (PWM) signal based on the generated current command value, and the FET drive circuit unit 12 A voltage is supplied to the gate terminal of the power FET 131 of the motor drive circuit unit 13 in accordance with the PWM signal. Thereby, each power FET 131 of the motor drive circuit unit 13 is turned on, the motor 2 is rotated, and steering assist control is realized.

  Next, the overheat protection operation of the ECU 1 according to the embodiment of the present invention will be described. First, a temperature detection operation for implementing overheat protection will be described.

  The temperature of the power FET 131 mounted on the heat sink is detected by a thermistor 132 installed on the same heat sink, and the detected temperature is output to the microcomputer 11 via the temperature detection circuit block 14. As a result, the temperature of the power system electronic component is detected.

  On the other hand, the microcomputer 11 inputs a signal output from the abnormality detection circuit 121 of the FET drive circuit unit 12 and estimates the temperature of the gate driver IC, that is, the temperature of the signal system electronic component.

  When either one of the temperature of the signal system electronic component obtained by this estimation and the detected temperature of the power system electronic component exceeds a threshold value set individually, the microcomputer 11 The current command value is changed so as to limit the current supplied from the unit 13 to the motor 2, and the ECU 1 is overheat protected.

Hereinafter, the overheat protection operation of the ECU 1 will be specifically described with reference to the drawings.
2 is a schematic diagram for explaining the overheat protection operation when the detected temperature of the power electronic component exceeds the threshold value first, and FIG. 3 is a diagram illustrating the temperature of the signal electronic component obtained by the estimation. It is a schematic diagram for demonstrating the overheat protection operation | movement when a threshold value is exceeded previously.

As shown in FIG. 2A, the temperature A of the power system electronic component detected by the thermistor 132 and the temperature detection circuit block 14 (the curve indicated by the solid line in FIG. 2A) is the power system at time t1. The threshold value T1 set for the temperature of the electronic component is exceeded.
At this time, the temperature B of the signal system electronic component estimated based on the output signal of the abnormality detection circuit 121 (the curve indicated by the one-dot chain line in FIG. 2A) is set with respect to the temperature of the signal system electronic component. Does not exceed the set threshold T2.

  As described above, when the temperature A of the power electronic component exceeds the threshold value T1, the microcomputer 11 restricts the current supplied to the motor 2 from I1 to I2, as shown in FIG. Change the value.

  As a result, the temperatures of the power system electronic component and the signal system electronic component both gradually decrease as shown in FIG. 2A, so that both the power system electronic component and the signal system electronic component can be accurately overheated. Can be protected.

On the other hand, as shown in FIG. 3A, the temperature B ′ of the signal system electronic component such as the gate driver IC (the curve indicated by the alternate long and short dash line in FIG. 3A) becomes the temperature of the signal system electronic component at time t2. The threshold value T2 set for the threshold value T2 is exceeded.
At this time, the temperature A ′ of the power system electronic component (the curve indicated by the solid line in FIG. 3A) does not exceed the threshold value T1 set for the temperature of the power system electronic component.

  As described above, when the temperature B ′ of the signal system electronic component exceeds the threshold value first, the microcomputer 11 restricts the current supplied to the motor 2 from I1 to I2, as shown in FIG. 3B. Change the value.

As a result, as shown in FIG. 3A, the temperatures of the power system electronic component and the signal system electronic component are both gradually lowered, so that both the power system electronic component and the signal system electronic component can be accurately overheated. Can be protected.
Here, since the gate driver IC is a signal system electronic component to which a weak signal is input / output, the threshold value T2 is set to a value smaller than the threshold value T1 for the power FET 131 of the power system electronic component.

  As described above, according to the control device of the electric power steering apparatus according to the embodiment of the present invention, the power system is configured by the thermistor 132 and the temperature detection circuit block 14 installed in the vicinity of the FET 131 of the motor drive circuit unit 13. While detecting the temperature of an electronic component, the temperature of a signal type | system | group electronic component is estimated from the change of internal resistance with the temperature of the abnormality detection circuit 121 with which the FET drive circuit unit 12 is normally equipped.

  Then, the microcomputer 11 changes the current command value so as to limit the current supplied from the motor drive circuit unit 13 to the motor 2 when any one of the temperatures exceeds the individually set threshold value.

  As a result, the motor current is reduced and the temperatures of both the power electronic component and the signal electronic component are lowered. Therefore, both the power electronic component and the signal electronic component can be protected easily and inexpensively from overheating with high accuracy. can do.

  The description of the specific embodiments is finished above, but the aspect of the present invention is not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, the thermistor has been described as the first temperature detection unit, but the present invention is not limited to this, and various temperature sensors can be employed.

  Further, the values of the threshold values T1 and T2 described above are values that can be appropriately changed, for example, held in a nonvolatile memory, and the values are determined based on a predetermined relationship or empirical rule. It is appropriately determined by various methods such as whether to determine through experiments.

  Moreover, although the said embodiment demonstrated what employ | adopted the brushless motor as a motor, this invention is applicable not only to this but a brush motor etc.

It is a block diagram which shows schematic structure of the control apparatus of the electric power steering apparatus which concerns on embodiment of this invention. (A) is a figure which shows typically the change of the detection temperature of a power type electronic component and the estimated temperature of a signal type electronic component in case the temperature of a power type electronic component exceeds a threshold value first, (b) FIG. 5 is a diagram schematically showing a change in motor current in the overheat protection operation of the power system electronic component and the signal system electronic component when the temperature of the power system electronic component first exceeds the threshold value. (A) is a figure which shows typically the change of the detection temperature of a power type electronic component and the estimated temperature of a signal type electronic component in case the temperature of a signal type electronic component exceeds a threshold value first, (b) FIG. 6 is a diagram schematically showing a change in motor current in the overheat protection operation of the power system electronic component and the signal system electronic component when the temperature of the signal system electronic component first exceeds the threshold value. It is a block diagram which shows schematic structure of the conventional electric power steering apparatus.

Explanation of symbols

1 ECU (control device for electric power steering device)
2 Motor 11 Microcomputer (control means)
12 FET drive circuit (drive element control means)
13 Motor drive circuit (motor drive means)
14 Temperature detection circuit block 121 Abnormality detection circuit 122 MOSFET
131 Power FET
132 Thermistor

Claims (3)

In order to apply a steering assist force to the steering mechanism, a control unit that generates a control value of a current supplied to the motor, a motor driving unit that drives the motor by a driving element, and a semiconductor element, the control value is A drive element control means for controlling the drive element based on the control device of the electric power steering apparatus,
further,
Temperature detecting means for detecting the temperature inside the control device;
Internal resistance detection means for detecting the internal resistance of the semiconductor element;
And the control means comprises
Based on the internal resistance detected by the internal resistance detection means, the temperature inside the control device is estimated,
When at least one of the estimated temperature or the temperature detected by the temperature detecting means exceeds a threshold value set individually,
The control device for an electric power steering apparatus, wherein the control value is changed so as to limit a current supplied to the motor. The temperature detecting means includes
2. The control device for an electric power steering apparatus according to claim 1, wherein the control device is disposed at a position where a temperature correlated with a temperature of the drive element can be detected. The control means includes
3. The control device for an electric power steering device according to claim 1, wherein the control device is constituted by a microcomputer.

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