JP2009051255A - Control device of electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of carrying out the overheat protection of an electronic component in a control device even if a temperature detection means normally used such as a thermistor fails. <P>SOLUTION: Normally, the overheat protection is carried out by detecting the temperature of a power FET 131 by the temperature detection means composed of a thermistor 132 arranged in a motor driving circuit section 13 and a temperature detection circuit block 14. When the temperature detection means fails, a temperature of a gate driver IC is estimated from the internal resistance of an abnormality detection circuit 121 that an FET driving circuit section 12 normally has. When the estimated temperature exceeds a threshold which is previously set, a current command value is changed to limit a current fed to a motor 2, thereby protecting the component constituting an ECU1 from overheat. <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, 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 the generated current control value, and an electric current that is supplied to the motor 6 by forming an H-bridge circuit with six FETs 531 And a power supply circuit section 55 that generates a voltage for stepping down the power supply voltage of the battery 7 and supplying it to the control circuit section 51.

  In the electric power steering apparatus configured as described above, the electronic components constituting the ECU 5, for example, the elements constituting the microcomputer 51, the FET drive circuit unit 52, the motor drive circuit unit 53, etc., generate heat by the applied current, For this reason, when the temperature rises and becomes overheated, the electronic component may be burned out.

Therefore, in order to prevent parts from being burned out due to this overheating, a general control device controls the temperature of the motor drive circuit unit 53 with temperature detection means comprising a temperature sensor 532 such as a thermistor and a temperature detection circuit block 54. The detected temperature is fed back to the control circuit 51.
That is, the microcomputer 51 changes the control value so as to limit the current supplied to the motor 6 when the detected temperature exceeds a set threshold value. As a result, the current supplied to the motor 6 is reduced, the temperature is lowered, and the electronic parts constituting the ECU 5 can be prevented from being burned out due to overheating (see, for example, Patent Document 1).

JP 2001-130432 A

  However, in such a conventional electric power steering apparatus, if either the temperature sensor 532 or the temperature detection circuit block 54 fails, the temperature cannot be detected. For example, until the warning lamp is turned on and the vehicle is stopped. Therefore, there is a possibility that the temperature of the parts constituting the ECU 5 further rises and cannot be protected from overheating.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to carry out overheat protection of electronic components inside a control device even when a commonly used temperature detecting means such as a thermistor fails. An object of the present invention is to provide an electric power steering device capable of performing the above.

  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,
First temperature detecting means for detecting the temperature inside the control device;
Second temperature detecting means for estimating the temperature inside the control device;
And the control means comprises
In a normal state, when the temperature value output based on the first temperature detecting means exceeds the first threshold value,
Changing the control value to limit the current supplied to the motor;
In a state in which the first temperature detection unit has failed, when the temperature value output based on the second temperature detection unit exceeds a second threshold value,
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 first temperature detection 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 second temperature detection means includes:
The abnormality detection means normally provided in the drive element control means includes an internal resistance detection means for detecting an internal resistance of the semiconductor element, and the control means
The control device for an electric power steering device according to (1) or (2), wherein the temperature inside the control device is estimated based on the detected internal resistance.
(4) The control means includes:
The control apparatus for an electric power steering apparatus according to any one of (1) to (3), wherein the control apparatus is configured by a microcomputer.

According to the configuration described in (1) above, even if the first temperature detection unit that is normally used for overheating protection of the electronic components in the control device is in a state of failure, the control is performed by the second temperature detection unit. It is possible to perform overheat protection of electronic components constituting the control device by estimating the temperature inside the device.
In addition, according to the configuration described in (2) above, the first temperature detecting means that is normally used for overheating protection of the electronic components inside the control device is, for example, a motor driving element that is the main cause of heat generation. Therefore, overheat protection can be performed with high accuracy in a normal state.
Furthermore, according to the configuration described in the above (3), even if the first temperature detection means that is normally used for changing the control value and overheating protection of the electronic components inside the control device is in failure, The second temperature detection means can detect the internal resistance of the semiconductor element by using the abnormality detection means that is normally provided in the drive element control means, and can estimate the temperature inside the control device. Thus, overheating protection of electronic components can be performed easily and inexpensively.
According to the configuration described in (4) above, the control means is configured by a microcomputer, so that overheat protection of the electronic components inside the control device can be performed easily, inexpensively and with higher accuracy.

  According to the present invention, it is possible to provide an electric power steering device capable of implementing overheat protection of electronic components inside a control device even when a normally used temperature detecting means such as a thermistor fails.

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 according to the present embodiment controls a motor 2 that applies a steering assist force to the steering mechanism and a current supplied to the motor 2 so that the motor 2 generates a desired torque. The ECU 1 includes an ECU 1, a battery 3 that supplies power to the ECU 1, and an ignition switch 4 that supplies power to the ECU 1.

The ECU 1 is a control unit that generates a current command value that is a control target value of the current supplied to the motor 2 based on the steering torque generated in the steering handle and the vehicle speed detected by a sensor (not shown). Microcomputer (microcomputer) 11 and a signal system electronic component, which is composed of a gate driver IC (semiconductor element) and drives a gate of a power FET (power system electronic component) 131 described later based on a current command value. An FET drive circuit section 12 that performs the above operation, a motor drive circuit section 13 that includes six power FETs (field effect transistors) 131 that form an H-bridge circuit for controlling the current supplied to the motor 2, and a thermistor 132 that will be described later. Based on the output, the temperature detection circuit block 14 for detecting the temperature of the power FET 131 and the power source of the battery 3 Configured to include a power supply circuit portion 15 which steps down the pressure to produce a voltage to be supplied to the microcomputer 11.
In addition, in order to comprise such a circuit part, ECU1 has many electronic components, such as power FET13, a resistance element, a capacitor element, in the inside.

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 power that is a main cause of heat generation in the ECU 1. In order to accurately detect the temperature of the FET 131, a thermistor 132 is disposed at a position where a 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 its 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, and when this is transmitted to the microcomputer 11 and processed, the microcomputer 11 causes the temperature of the gate driver IC constituting the FET drive circuit unit 12, that is, the internal temperature of the ECU 1. 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 normal overheat protection operation will be described. FIG. 2 is a schematic diagram for explaining an overheat protection operation in a normal state.

  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 a temperature signal is sent to the microcomputer 11 via the temperature detection circuit block 14. Thereby, the temperature of the power system electronic component which is the main cause of heat generation is detected.

  In FIG. 2A, the temperature of the power FET 131 detected in this way gradually increases with time as shown by the solid line. When the microcomputer 11 determines that the detected temperature exceeds a preset threshold value T1, the current supplied from the motor drive circuit unit 13 to the motor 2 is changed from I1 to I2 as shown in FIG. The current command value is changed to limit to

  As a result, the temperature of the power FET 131 gradually decreases as shown in FIG. 2A, so that the ECU 1 can be protected from overheating.

  Next, an overheat protection operation when the thermistor 132 or the temperature detection circuit block 14 fails will be described. FIG. 3 is a schematic diagram for explaining the overheat protection operation when the thermistor 132 or the temperature detection circuit block 14 fails.

  In FIG. 3A, the temperature A of the power FET 131 detected by the thermistor 132 and the temperature detection circuit block 14 (the curve indicated by the solid line in FIG. 3A) increases with time, but at time t0. If the thermistor 132 or the temperature detection circuit block 14 fails at that time, the temperature value exceeds a certain value. Therefore, in order to detect this failure, a threshold value T0 larger than the threshold value T1 is set, and this threshold value T0 is set. If exceeded, it is judged as a failure.

If it is determined that there is a failure, the microcomputer 11 inputs a signal output from the abnormality detection circuit 121 of the FET drive circuit unit 12, and continues the temperature detection operation of the ECU 1 and the overheat protection operation of the electronic component.
Hereinafter, a temperature detection operation and an overheat protection operation based on a signal transmitted from the abnormality detection circuit 121 will be described.

  In FIG. 3A, when the temperature B of the gate driver IC (the curve indicated by the one-dot chain line in FIG. 3A) tries to exceed the threshold value T2 set for the temperature of the gate driver IC at time t2. The microcomputer 11 estimates that the internal temperature of the ECU 1 is reaching an overheated state, and sets the current command value to limit the current supplied to the motor 2 from I1 to I2, as shown in FIG. change.

As a result, the temperature of the gate driver IC of the FET drive circuit section 12 gradually decreases as shown in FIG. 3A, and the electronic components inside the ECU 1 such as the power FET 131 are protected from overheating.
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 present embodiment, in the normal state, the temperature detection means including the thermistor 132 and the temperature detection circuit block 14 installed in the motor drive circuit unit 13 detects the temperature of the power FET 131 to protect against overheating. However, if this temperature detection means fails, the microcomputer 11 estimates the temperature of the gate driver IC from the internal resistance of the abnormality detection circuit 121 that is normally provided in the FET drive circuit unit 12, and sets the preset threshold value. If exceeded, the ECU 1 is presumed to be in an overheated state, the current command value is changed to limit the current supplied to the motor 2, and the components constituting the ECU 1 are protected from overheating.

  As a result, even if the temperature detecting means such as the thermistor fails, the internal temperature of the ECU 1 can be grasped, so that the electronic components constituting the ECU 1 can be protected from overheating.

  Further, according to the present embodiment, when the temperature detection means including the thermistor 132 and the temperature detection circuit block 14 fails, the microcomputer 11 determines the gate driver IC from the internal resistance of the abnormality detection circuit 121 normally provided in the FET drive circuit unit 12. If the temperature of the ECU 1 exceeds a preset threshold, it is estimated that the ECU 1 is in an overheated state, so that existing means can be used as it is, and overheating protection of the electronic components inside the ECU 1 can be performed easily and inexpensively. 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 above-described threshold values T0, T1, and T2 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 determined appropriately by various methods such as whether to be determined through experimentation or not.

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 the power type electronic component in overheat protection operation, (b) is a figure which shows typically the change of the motor current in overheat protection operation. (A) is a figure which shows typically the change of the detection temperature of the electronic component in overheat protection operation when temperature detection means, such as a thermistor, fails, (b), the temperature detection means, such as a thermistor, has failed. It is a figure which shows typically the change of the motor current in a case. 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 (Drive element)
132 Thermistor

Claims (4)

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,
First temperature detecting means for detecting the temperature inside the control device;
Second temperature detecting means for estimating the temperature inside the control device;
And the control means comprises
In a normal state, when the temperature value output based on the first temperature detecting means exceeds the first threshold value,
Changing the control value to limit the current supplied to the motor;
In a state in which the first temperature detection unit has failed, when the temperature value output based on the second temperature detection unit exceeds a second threshold value,
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 first 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 second temperature detecting means includes
The abnormality detection means normally provided in the drive element control means includes an internal resistance detection means for detecting the internal resistance of the semiconductor element, and the control means includes:
3. The control device for an electric power steering apparatus according to claim 1, wherein an internal temperature of the control device is estimated based on the detected internal resistance. 4. The control means includes
The control apparatus for an electric power steering apparatus according to any one of claims 1 to 3, wherein the control apparatus comprises a microcomputer.

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