JP4792820B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device in which a steering assist force by a motor is applied to a steering system of a vehicle, and in particular, monitors an outside air temperature and a temperature of a control unit, and a current command value for overheat protection. The present invention relates to a control device for an electric power steering device that controls a motor by changing a gain.

  A control device for an electric power steering device that applies a steering assist force by a motor to a vehicle steering system is applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. A steering assist force is applied.

  First, a general configuration of the electric power steering apparatus will be described with reference to FIG.

  A shaft 2 of the steering handle 1 is connected to a tie rod 6 of a steering wheel via a reduction gear 3, universal joints 4A and 4B, and a pinion rack mechanism 5. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the shaft 2 via the reduction gear 3. . The control unit 30 that controls the electric power steering apparatus is supplied with electric power from the battery 14 and is also supplied with an ignition key signal via the ignition key 11. The control unit 30 detects the steering torque T detected by the torque sensor 10. Then, the steering assist command value I of the assist command is calculated based on the vehicle speed V detected by the vehicle speed sensor 12, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.

  In such a control device for an electric power steering device, if frequent steering is repeated for a long time, a large current continuously flows to the motor, the motor overheats and emits smoke, gives off a smell, Furthermore, there was a possibility of occurrence of problems such as burning.

  In order to prevent such heat generation due to excessive use of the motor or to protect the motor, it is easy to arrange a temperature sensor in the motor and perform temperature protection control. In the control device of the steering device, there are many restrictions on the installation location and the like, and it was difficult to easily attach the temperature sensor to the motor.

  Therefore, in the control device described in Japanese Patent Laid-Open No. 2003-284375 (Patent Document 1), it is possible to accurately detect the motor temperature of the motor housing, stator, coil, etc. without incorporating a temperature sensor in the motor. A motor control device is provided that provides a motor temperature estimation device, limits the current flowing through the motor in accordance with the motor coil temperature estimated by the temperature estimation device, and accurately suppresses the temperature rise of the motor coil. .

  In addition, in the control device for an electric power steering device described in Japanese Patent Application Laid-Open No. 2004-82757 (Patent Document 2), a temperature sensor and a motor current detection unit are provided in the control unit of the electric power steering device, and detection is performed by the motor current detection unit. The temperature of the control unit is estimated from the motor current, the target current of the motor current flowing to the motor of the electric power steering device is limited based on the estimated temperature of the control unit and the temperature detected by the temperature sensor, and the estimated temperature is Only when the temperature rises, a failure of the temperature sensor is detected by comparing the estimated temperature with the detected value of the temperature sensor. For this reason, the number of sensors can be reduced. In addition, since the temperature is directly estimated from the motor current detected by the motor current detection unit, there is no possibility of a discrepancy between the temperature of the control unit and the temperature detected by the temperature sensor.

  Furthermore, in the electric power steering apparatus described in Japanese Patent Application Laid-Open No. 2004-268671 (Patent Document 3), the temperature of the electric power steering apparatus is estimated by detecting the current flowing through the motor, and the estimated temperature and the temperature sensor Since the motor output is limited based on the higher of the virtual temperatures obtained from the detected temperature, overheating of the heating elements such as the drive circuit in the electric power steering device is prevented, and the overheating of the heating elements such as the drive circuit is ensured. Can be protected.

Furthermore, in the electric power steering device described in Japanese Patent Laid-Open No. 2002-59859 (Patent Document 4), the motor rotation speed estimation unit of the motor control device detects the drive current detected by the current sensor and the drive detected by the voltage sensor. The rotational speed of the motor is estimated based on the voltage and the specific resistance value of the motor, the motor temperature detecting means detects the motor temperature directly or indirectly, and the resistance value temperature correcting unit is detected by the motor temperature detecting means. The specific resistance value of the motor is corrected for temperature according to the motor temperature. As a result, the motor rotation speed estimation unit accurately estimates the rotation speed of the motor based on the specific resistance value of the motor whose temperature is corrected by the resistance value temperature correction unit.
JP 2003-284375 A JP 2004-82757 A JP 2004-268671 A JP 2002-59859 A

  However, in the prior art, the temperature of the motor and the temperature of the switching element are detected by a temperature sensor or temperature estimation means, and are not in close contact with each electronic component or motor. For this reason, the temperature change caused by Joule heat generated by the current flowing through each electronic component or motor is transferred by heat conduction from the current flowing part to the position of the temperature sensor. There is a problem that the detection of the temperature of the component or the motor is delayed, and there is a discrepancy between the actual temperature of each actual electronic component or motor and the temperature detected or estimated by the temperature sensor.

Further, in the current control, when the temperature of the thermistor as a temperature sensor exceeds 85 ° C., the assist force is drastically decreased due to the control of the overheat protection, which may affect the steering feeling. In addition, since the current overheat protection control requires a long time to return to the vicinity of the maximum current value, once the overheat protection control is applied, the assist force cannot be returned smoothly. is there. In addition, overheat protection is activated more than necessary to guarantee a wide temperature range, and when the control unit is in the vehicle compartment and the motor is in the engine room, the There is also a problem that a temperature difference occurs.

  The present invention has been made for the above-described circumstances, and an object of the present invention is to control the current in advance in consideration of normal usage by monitoring the outside air temperature and the temperature sensor temperature of the control unit. To provide a control device for an electric power steering device that prevents a sudden drop in assist force and efficiently prevents overheating protection of a motor by applying a current limit in advance when the outside air temperature is high It is in.

The present invention includes a motor for applying a steering assist force to a steering system of a vehicle, a current control unit for the motors controlled on the basis of the current command value thus computed with the output value of the torque sensor for detecting a steering force of the steering wheel The above-described object of the present invention is to provide a temperature sensor mounted on the control unit, an outside air temperature sensor installed in an engine room, and estimation by the temperature sensor. A gain calculation unit that calculates a gain of overheat protection based on an added value of temperature and the temperature of the outside air temperature sensor, and controls the motor by multiplying the current command value by the gain from the gain calculation unit Is achieved.

The above-described object of the present invention is more to the gain calculation unit calculates the gain with temperature motor map is more effectively achieved.

  According to the control device for an electric power steering device according to the present invention, the current is limited or controlled in advance by monitoring the outside air temperature and the temperature sensor temperature, so that a sudden decrease in assist force can be prevented. it can.

  Further, according to the control device for the electric power steering apparatus according to the present invention, the motor current is limited by the temperature monitor, so that the overheating protection of the motor can be surely and efficiently prevented.

  In the present invention, the current (current command value) is controlled in advance by monitoring the outside air temperature and the temperature of the temperature sensor provided in the control unit. Protection can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an embodiment of the present invention, and shows the configuration of a control unit (controller) that controls a motor 20 that applies assist force.

  The function and operation of the control unit will be described with reference to FIG. 1. A steering torque value T detected by a torque sensor (not shown) and a vehicle speed V detected by a vehicle speed sensor (not shown) are expressed as a current command value. The current command value calculation unit 31 that calculates Im is input. The current command value calculation unit 31 determines a current command value Im, which is a control target value of the current supplied to the motor 20, using an assist map or the like based on the input steering torque value T and vehicle speed V. The current command value Im is input to the current limiting unit 36, the current command value with the maximum current limited is input to the subtractor 39, and a deviation E (Im-Iout) from the fed back motor current value Iout is calculated. Due to the deviation E, the motor 20 is PWM driven via the motor drive circuit 37 for improving and driving the characteristics of the steering operation. The current value Iout of the motor 20 is detected by the motor current detection circuit 38 and fed back to the subtractor 39. The motor drive circuit 37 uses an FET as a drive element, and is configured by an H bridge circuit of the FET.

  A temperature sensor (for example, a thermistor) 32 is attached to the control unit, and a temperature signal Th 1 from the temperature sensor 32 is input to the ECU temperature estimation means 33. The ECU temperature estimation means 33 receives the temperature signal Th1 from the temperature sensor 32, estimates the temperature of the control unit and diagnoses the failure of the temperature sensor 32, and inputs the estimated temperature signal Th2 to the gain calculation unit 35. An outside air temperature sensor 34 for measuring the outside air temperature is provided, and an outside air temperature signal Th 3 measured by the outside air temperature sensor 34 is input to the gain calculation unit 35. Further, the current limiting unit 36 receives the gain signal Gout from the gain calculating unit 35, limits the current command value Im, and inputs it to the subtractor 39.

  In such a configuration, the operation will be described with reference to the flowchart of FIG.

  First, the gain calculation unit 35 determines whether or not the total temperature of the estimated temperature signal Th2 from the temperature sensor 32 and the outside temperature signal Th3 from the outside temperature sensor 34 is equal to or higher than a threshold value a (step S10), and the estimated temperature from the temperature sensor 32 is determined. When the total temperature of the signal Th2 and the outside air temperature signal Th3 from the outside air temperature sensor 34 is less than the threshold value a, the gain signal Gout output from the gain calculator 35 is constant (step S11). If the total temperature of the estimated temperature signal Th2 from the temperature sensor 32 and the outside air temperature signal Th3 from the outside air temperature sensor 34 is equal to or higher than the threshold value a in step S10, Gout = a / (outside air temperature + temperature sensor estimated value). ), The decrease rate of the gain signal Gout is obtained from the rate of increase of the denominator (outside air temperature + temperature sensor estimated value) (step S12). The set value assumed here is that when a thermistor is used as the temperature sensor 32, the temperature related to the overheat protection of the control unit is 85 ° C., and therefore, a value obtained by taking −5 ° C. into consideration as a margin = 80. However, in practice, there is no problem even if the threshold value a is variable.

  Step S12 may be calculated using a temperature motor map prepared in advance. The current limiter 36 limits the current command value Im by the gain signal Gout output from the gain calculator 35.

  Next, the operation when the current command value Im is corrected by multiplying by the gain Gout from the gain calculator 35 will be described with reference to the flowchart of FIG.

  First, a control unit such as a CPU determines whether or not each temperature exceeds half of each guaranteed temperature (step S20). That is, it is determined whether or not the temperature sensor estimated value (Th2) / control unit operation guaranteed temperature> 0.5, or whether the outside air temperature (engine room temperature; Th3) / rack guaranteed temperature> 0.5. To do. The control unit operation guarantee temperature and the rack guarantee temperature are set in advance. If none of the expressions exceeds half (0.5) as a result of the determination, it is determined that the temperature is normal, and a normal assist operation is performed (step S21). In this example, the determination is made at half (0.5) of the set guaranteed temperature, but the value can be changed as appropriate.

  In step S20, when one or both of the temperatures exceed half of the guaranteed temperature, a coefficient m for gain reduction (correction) is calculated (step S22). In the present invention, the increment of the total temperature of the rack guaranteed temperature, the temperature sensor estimated value, and the outside air temperature (engine room temperature) is observed with respect to the value related to the overheat protection, and the rack guaranteed temperature, the temperature sensor estimated value, and the outside air temperature are A value obtained by dividing the total temperature by the threshold value a that shifts to the overheat protection of the control unit is calculated as a coefficient m corresponding to the decreasing rate. After that, the current command value Iout after changing the value obtained by multiplying the current command value Im, which is the original value calculated by the assist map or the like, by a factor of (10−m) / 10 is a current command value Iout. And input to the subtractor 39 (step S23).

  In the present invention, the current command value Im is corrected as described above, and as a result, the motor current characteristic decreases as shown in FIG. In FIG. 4, the horizontal axis indicates the input torque, the vertical axis indicates the motor current, the characteristic A is a normal current characteristic, and the current characteristic is indicated by B by correcting the current command value Im of the present invention. To about 80%.

  In addition, this invention is applied also to the motor mounted in various apparatuses other than a vehicle. The present invention is not limited to the above-described embodiments and modifications, and various modifications can be employed within the scope of the present invention.

It is a block block diagram which shows the Example of this invention. It is a flowchart which shows the operation example of this invention. It is a flowchart which shows the operation example of this invention. It is a figure which shows the example of a characteristic of the input torque vs. motor current of this invention. It is a figure showing an example of composition of a general electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 2 Shaft 3 Reduction gear 4A, 4B Universal joint 5 Pinion rack mechanism 6 Tie rod 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 14 Battery 20 Motor 30 Control unit 31 Current command value calculating part 32 Temperature sensor (thermistor)
33 ECU temperature estimating means 34 outside air temperature sensor 35 gain calculation unit 36 current limiting unit 37 motor drive circuit 38 motor current detection circuit 39 subtractor

Claims (2)

A control unit having a motor for applying a steering assist force to a steering system of a vehicle and controlling the motor based on a current command value calculated from an output value of a torque sensor for detecting a steering force of the steering wheel In the control device of the electric power steering device provided,
A temperature sensor mounted on the control unit; an outside temperature sensor installed in the engine room;
A gain calculation unit for calculating a gain of overheat protection based on an added value of the estimated temperature by the temperature sensor and the temperature of the outside air temperature sensor, and multiplying the current command value by the gain from the gain calculation unit A control device for an electric power steering device, wherein the motor is controlled. The control device for an electric power steering apparatus according to claim 1, wherein the gain calculation unit calculates the gain from a temperature motor map.

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