JP3938472B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering apparatus that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and in particular, when an abnormality or failure occurs in a temperature sensor in a function of overheating protection of a control unit and a motor. The present invention relates to an electric power steering apparatus having a function related to alternative control.
[0002]
[Prior art]
An electric power steering device that applies an auxiliary steering force to a steering device of an automobile or a vehicle with the rotational force of a motor transmits the driving force of the motor to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. It is designed to be applied. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.
[0003]
Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 6. 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 coupled to the shaft 2 via the reduction gear 3. . The control unit 30 that controls the power steering device is supplied with electric power from the battery 14 via the ignition key 11 and the relay 13, and the control unit 30 is detected by the steering torque T detected by the torque sensor 10 and the vehicle speed sensor 12. The steering assist command value I of the assist command is calculated based on the vehicle speed V, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 8 shows general functions executed by a program inside the CPU.
[0005]
The function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to improve the stability of the steering system, and the phase-compensated steering torque. TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 refers to a characteristic map (lookup table) 33 based on the input steering torque TA and vehicle speed V, and a steering assist command value that is a control target value of the current supplied to the motor 20. I is determined.
[0006]
The steering assist command value I is input to the subtractor 30A and is also input to the feedforward differential compensator 34 for increasing the response speed. The deviation (I-i) obtained by the subtractor 30A is a proportional calculator 35. The proportional output is input to the adder 30B and to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integration calculator 36 are also added to the adder 30B, and the current command value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current detection value i is input to the subtractor 30A and fed back.
[0007]
Here, in general, a temperature sensor is appropriately disposed to prevent the motor 20 and the control unit 30 from being overheated. Then, the initial temperature is the temperature of the control unit when the ignition switch is turned on, and the initial temperature of the motor is set, and the estimated temperature is obtained by adding the increased temperature calculated based on the motor current to this initial temperature. The motor current is limited based on
[0008]
On the other hand, when the temperature sensor fails, the motor output is prohibited, and the motor output prohibition is held until the ignition switch is turned off. Alternatively, the initial temperature is set to a relatively high temperature such as the maximum operating temperature, and a motor estimated temperature is obtained by adding a rising temperature calculated based on the motor current to the initial temperature, and the motor current is calculated based on the estimated motor temperature. Restricted.
[0009]
[Problems to be solved by the invention]
In the conventional method, although the motor drive system can operate normally, the assist is prohibited and the steering after the temperature sensor failure is performed without assist. Also, when the initial temperature is set to the maximum operating temperature and the motor temperature is limited by estimating the motor temperature based on the motor current, the ignition switch is turned off immediately after repeated stationary steering with a large motor current, and the ignition is turned on again. The motor temperature is estimated when the same steering is repeated with the switch turned on, or when steering is performed to maintain a large region of motor current output by continuously steering the stationary at parking or at low speed. The difference between the value and the actual motor temperature may increase and the motor may overheat.
[0010]
The control unit stops the protection operation because the temperature of the motor drive unit cannot be measured when the temperature sensor fails. Therefore, until the overheat protection of the motor by the alternative control is activated, the current is output without being protected, and the motor drive unit of the control unit may be overheated like the motor.
[0011]
The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a function relating to alternative control when a temperature sensor fails, and even if the temperature sensor fails, the continuous rating of the motor or control unit is provided. An object of the present invention is to provide an electric power steering apparatus in which the assist is not prohibited by setting the current to the maximum output current value.
[0012]
[Means for Solving the Problems]
The present invention provides a function for limiting the motor current based on a temperature sensor attached to the motor drive unit of the control unit, and the temperature of the control unit when the ignition switch is turned on as the initial temperature of the motor. The present invention relates to an electric power steering apparatus having a function of adding a rising temperature calculated based on the motor current to obtain a motor estimated temperature and limiting the motor current based on the estimated motor temperature. The object is to detect a temperature sensor abnormality detecting means for detecting an abnormality or failure of the temperature sensor, a control unit overheat protection means for performing an overheat protection operation based on the temperature sensor, and the motor current based on the control unit overheat protection means. A current command limit value generating means for limiting the motor current; A fault current command limit value generating means, and a switching means for switching the current command limit value generating means or the current command limit value generating means at the time of failure based on the output of the temperature sensor abnormality detecting means, When the temperature sensor abnormality detecting means determines that the temperature sensor is abnormal or faulty , the switching means switches from the current command limit value generating means to the current command limit value generating means at the time of failure, and the control unit or motor This is achieved by outputting a current to the motor based on an assist characteristic at the time of occurrence of an abnormality or failure with the smaller continuous rated current being the maximum value.
[0013]
The assist characteristic when a failure occurs may be realized by multiplying the characteristic map by a gain. Alternatively, the above object can be achieved by limiting the motor current command value by setting the smaller of the continuous rated currents of the control unit or the motor as the maximum output current limit value.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Both motors and control units have continuous rated currents that can be damaged even when current is continuously applied. Therefore, when the temperature sensor fails, the maximum output current value is switched to the assist characteristic set to the lower of the continuous rated temperatures of the motor or control unit (or the characteristic map is gained). Assisting continuously after failure of the temperature sensor.
[0015]
As a result, the assist is turned off when the conventional temperature sensor fails. However, the assist can be continued at the continuous rated current without the necessity. Therefore, even if the assist is continued, there is no possibility of burning the motor or the control unit.
[0016]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
FIG. 1 is a block diagram showing a first embodiment of the present invention corresponding to FIG. 8, and a temperature sensor 300 is provided in the vicinity of the motor drive circuit 37 (or the motor 20). The temperature sensor 300 is composed of a thermistor, and has characteristics as shown in FIG. 2. The solid line is a normal region, and the upper and lower hatched portions are abnormal regions. The detection signal TS of the temperature sensor 300 is input to the control unit overheat protection means 301 and also input to the temperature sensor abnormality detection means 302. The abnormality detection signal AS of the temperature sensor abnormality detection unit 302 switches the switching unit 303, and the output of the switching unit 303 is added to the adder 304. The adder 304 is disposed between the steering assist command value calculator 32 and the subtractor 30A. The switching unit 303 includes a current command limit value generating unit 310 and a current command limit value generating unit 311 at the time of failure. Output is being input.
[0018]
The temperature sensor 300 has the characteristics shown in FIG. 2. In normal operation, the thermistor voltage operates like a solid line (about 0.4 V to 4.7 V). In this region, the control unit overheat protection means 301 Current control is performed by an overheat protection operation (characteristic A1 in FIG. 3) based on the operation. That is, the output of the current command limit value generating means 310 controlled by the control unit overheat protection means 301 is applied to the adder 304 via the contact point a of the switching means 303.
[0019]
Further, when the thermistor voltage becomes 0.1V or less in the shaded region or 4.9V or more, this is detected by the temperature sensor abnormality detection means 302, and the switching means 303 is switched from the contact point a to the contact point b by the abnormality detection signal AS. . By switching from the contact point a to the contact point b, the signal applied to the adder 304 is switched from the output of the current command limit value generating unit 310 to the output of the current command limit value generating unit 311 at the time of failure. B1. It should be noted that Icont in FIG. 3 indicates the continuous rated current (whichever is lower) of the motor 20 or the control unit 30, and if this output current Icont is used, the motor 20 and The control unit 30 is not overheated.
[0020]
FIG. 4 is a flowchart showing an example of the operation of the present invention. In normal operation, the switching means 303 is connected to the contact a, and the output of the current command limit value generating means 310 controlled by the control unit overheat protection means 301 is added to the adder. The steering command value from the steering assist command value calculator 32 is current-controlled. Then, the temperature sensor abnormality detection means 302 always reads the detection signal TS of the temperature sensor 300 (step S1), and whether the input value is in the normal range, that is, whether the thermistor voltage is in the solid line range of FIG. (Step S2), if it is in the normal range, the control unit overheat protection means 301 calculates the temperature from the detection signal TS of the temperature sensor 300 (Step S3). In accordance with the temperature calculated value (detected temperature) from the control unit overheat protection means 301, the current command limit value generating means 310 limits the current command value from the steering assist command value calculator 32 according to the detected temperature (step S4). That is, when the output of the current command limit value generating means 310 is applied to the adder 304 through the switching means 303, the relationship between the input torque and the output current becomes the characteristic A1 in FIG. Thereafter, the count of the measurement time is cleared (step S5), and the process returns to step S1.
[0021]
On the other hand, if it is determined in step S2 that the input value is not normal, it is determined whether or not the predetermined time has continued (step S1). If the predetermined time has not elapsed, the measurement time is counted. Count up (step S7) and return to step S1.
[0022]
In step S6, when the predetermined time has elapsed, the temperature sensor detection means 302 outputs an abnormality detection signal AS, switches the switching means 303 from the contact point a to the contact point b, and generates a current command limit value generation means at the time of failure. The output of 311 is applied to the adder 304 (step S8). Thereby, the relationship between the input torque and the output current becomes the characteristic B1 in FIG. 3, and the output current is limited to a constant continuous rated current Itont in a region where the input torque is large.
[0023]
FIG. 5 shows a second embodiment of the present invention corresponding to FIG. 1. In this embodiment, the output of the current command limit value generating means 310 is applied to the adder 304 as it is. In addition, a normal characteristic map 331 and a temperature sensor abnormal characteristic map 332 are provided as maps, and are supplied to the steering assist command value calculator 32 via the switching means 303. The switching means 303 detects the temperature sensor abnormality. The contacts a and b are switched by the detection means 302. The normal characteristic map 331 holds a normal characteristic such as the characteristic A2 in FIG. 6 as a map, and the temperature sensor abnormal characteristic map 332 holds the abnormal characteristic as a characteristic B2 in FIG. Yes.
[0024]
In such a configuration, the switching means 303 is connected to the contact a at the normal time, and the steering assist command value calculator 32 generates a current command value according to the normal characteristic map 331. Further, the current command limit value generation means 310 limits the current command value from the steering assist command value calculator 32 according to the control unit overheat protection means 301. On the other hand, when the abnormality of the temperature sensor 300 is detected by the temperature sensor abnormality detection unit 302, the contact point a of the switching unit 303 is switched to the contact point b by the abnormality detection signal AS, and the characteristic B2 of the temperature sensor abnormality time characteristic map 332 is steered. This is supplied to the command value calculator 32. The steering assist command value calculator 32 generates a current command value according to the characteristic B2 from the temperature sensor abnormality characteristic map 332. Thereby, the relationship between the input torque and the output current becomes the characteristic B2 in FIG. 6, and the output current is limited to a constant continuous rated current Itont in a region where the input torque is large.
[0025]
The present invention can be applied not only to column type and pinion type electric power steering apparatuses, but also to rack assist type electric power steering apparatuses.
[0026]
【The invention's effect】
In the present invention, when it is determined that the temperature sensor is in failure, current output to the motor is performed based on the assist characteristic at the time of occurrence of failure with the smaller continuous rated current of the control unit or motor as the maximum value. Alternatively, the motor current command value is limited with the smaller of the continuous rated currents of the control unit or motor as the maximum output current limit value. For this reason, it is not necessary to prohibit the assist even if the temperature sensor breaks down, and overheating of the control unit and the motor can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.
FIG. 2 is a diagram showing a characteristic example of a temperature sensor used in the present invention.
FIG. 3 is a diagram for explaining the operation of the present invention.
FIG. 4 is a flowchart showing an operation example of the present invention.
FIG. 5 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.
FIG. 6 is a diagram for explaining the operation of the present invention.
FIG. 7 is a structural diagram showing a schematic configuration of an electric power steering apparatus.
FIG. 8 is a block configuration diagram showing an example of a control device of the electric power steering device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 31 Phase compensator 32 Steering assistance command value calculator 33 Characteristic map 37 Motor drive circuit 38 Motor current detection circuit 301 Control unit overheat protection means 302 Temperature Sensor abnormality detecting means 303 Switching means 310 Current command limit value generating means 311 Current command limit value generating means at the time of failure

Claims (3)

A function for limiting the motor current based on a temperature sensor attached to the motor drive unit of the control unit, and the temperature of the control unit when the ignition switch is turned on as the initial temperature of the motor. In the electric power steering apparatus having the function of limiting the motor current based on the estimated motor temperature by adding the rising temperature calculated on the basis of the estimated temperature, an abnormality or failure of the temperature sensor is detected. Temperature sensor abnormality detection means, control unit overheat protection means for performing overheat protection operation based on the temperature sensor, current command limit value generation means for limiting the motor current based on the control unit overheat protection means, and the motor current limiting the abnormal or current command limit value of failure Generating means and switching means for switching the current command limit value generating means or the current command limit value generating means at the time of failure based on the output of the temperature sensor abnormality detecting means, and the temperature sensor abnormality detecting means When the temperature sensor is determined to be abnormal or faulty , the switching means switches from the current command limit value generating means to the current command limit value generating means at the time of the fault, and the smaller of the continuous rated currents of the control unit or motor is selected. An electric power steering apparatus characterized in that current output to the motor is performed based on an assist characteristic at the time of occurrence of abnormality or failure with a maximum value. The electric power steering apparatus according to claim 1, wherein the temperature sensor is a thermistor. A function for limiting the motor current based on a temperature sensor attached to the motor drive unit of the control unit, and the temperature of the control unit when the ignition switch is turned on as the initial temperature of the motor. In the electric power steering apparatus having the function of limiting the motor current based on the estimated motor temperature by adding the rising temperature calculated on the basis of the estimated temperature, an abnormality or failure of the temperature sensor is detected. Temperature sensor abnormality detection means, control unit overheat protection means for performing overheat protection operation based on the temperature sensor, current command limit value generation means for limiting the motor current based on the control unit overheat protection means, and the motor current Special map for steering assist command value calculator A normal characteristic map and a temperature sensor abnormal characteristic map, and switching means for switching the normal characteristic map or the temperature sensor abnormal characteristic map based on the output of the temperature sensor abnormality detecting means, When the temperature sensor abnormality detecting means determines that the temperature sensor is abnormal or faulty , the switching means switches from the normal characteristic map to the temperature sensor abnormal characteristic map, and the continuous rated current of the control unit or motor is small. An electric power steering apparatus characterized in that the motor current command value is limited with the direction as the limit value of the maximum output current.

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