JPH11286278A - Control device for electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a motor and a control unit from overheating according to temperature by limiting the current control value by the larger limit value out of the current limit values outputted from a control unit overheat protecting means, a motor overheat protecting means and a motor low temperature demagnetization protecting means. SOLUTION: Temperature signals estimated by estimating means 50, 52, 54 are respectively inputted to a control unit overheat protecting means 51, a motor overheat protecting means 53 and a motor low temperature demagnetization protecting means 55, and the respective current limit values from the respective protecting means 51, 53, 55 are inputted to a steering auxiliary command value computing element 32 through a switching means 61. The predetermined control unit overheat protecting current limit value is read, and the motor overheat protecting current limit value and motor low temperature demagnetization protecting current limit value are read to judge the grades of the control unit overheat protecting current limit value and motor overheat protecting current limit value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device which applies a steering assist force by a motor to a steering system of an automobile or a vehicle. The present invention relates to a control device for an electric power steering device that realizes an overheat protection function of a control unit.

[0002]

2. Description of the Related Art An electric power steering apparatus for energizing a steering apparatus of an automobile or a vehicle with an auxiliary load by the rotational force of a motor uses a transmission mechanism such as a gear or a belt through a speed reducer to transmit the driving force of the motor to a steering shaft or the like. An auxiliary load is applied to the rack shaft. Such a conventional electric power steering apparatus performs feedback control of a motor current in order to accurately generate an assist torque (a steering assist torque). The feedback control adjusts the motor applied voltage so as to reduce the difference between the current control value and the motor current detection value. Generally, the adjustment of the motor applied voltage is performed by a PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

Here, a general configuration of an electric power steering apparatus will be described with reference to FIG.
Is connected to a tie rod 6 of a steered 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 for detecting a steering torque of the steering wheel 1. A motor 20 for assisting the steering force of the steering wheel 1 is coupled to the shaft 2 via a clutch 21 and a reduction gear 3. Have been. The control unit 30 for controlling the power steering device includes an ignition key 1 from the battery 14.
1 is supplied with power through the control unit 30
Calculates the steering assist command value I of the assist command based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12, and calculates the steering assist command value I based on the calculated steering assist command value I. The current supplied to the motor 20 is controlled. The clutch 21 is turned on / off by the control unit 30.
It is OFF controlled and is ON (coupled) in a normal operation state. Then, when the control unit 30 determines that the power steering device has failed, and when the ignition key 11 is used to supply power (voltage Vb) to the battery 14
Is off, the clutch 21 is turned off (disengaged).

The control unit 30 is mainly composed of a CP
FIG. 10 shows general functions executed by a program inside the CPU. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. Control unit 3
The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to enhance the stability of the steering system. It 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 determines a steering assist command value I which is a control target value of the current supplied to the motor 20 based on the input steering torque TA and the vehicle speed V. Is provided with a memory 33. The memory 33 stores a steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 32. Steering assist command value I
Is input to a subtractor 30A, and is also input to a feed-forward differential compensator 34 for increasing the response speed. The deviation (I-i) of the subtractor 30A is input to a proportional calculator 35, and the proportional output thereof is output. Is input to an adder 30B and also to an integration calculator 36 for improving the characteristics of the feedback system. Differential compensator 34 and integral compensator 3
6 is also input to the adder 30B, and 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 value i is input to the subtractor 30A and fed back.

A configuration example of the motor drive circuit 37 will be described with reference to FIG. 11. The motor drive circuit 37 is based on a current control value E from an adder 30B and has a field effect transistor (FET) FET1 as a motor drive element. FET gate drive circuit 371 for driving each gate of FET4, FET
H-bridge circuit consisting of 1 to FET4, FET1 and FE
It comprises a boost power supply 372 for driving the high side of T2. FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the motor 2
The magnitude of the current Ir flowing to 0 is controlled. In a region where the duty ratio D1 is small, the FET3 and the FET4 have a predetermined linear function formula (D2 = a · D1 + b where a and b are constants).
Is driven by the PWM signal having the duty ratio D2 defined by the following equation, and after the duty ratio D2 also reaches 100%, the PWM signal
It is turned on / off according to the rotation direction of the motor 20 determined by the sign of the signal.

In the above-described electric power steering apparatus, since a large current (30 A to 60 A, and sometimes 100 A) flows through the motor, it is necessary to take measures to protect the motor from the viewpoint of vehicle safety. Conventionally, 6-5
As described in Japanese Patent No. 1474 and Japanese Patent No. 2528119, based on a motor current detection value, an average value in a predetermined time is obtained from the current value to limit the current, or the average current is not less than a predetermined value. In some cases, the motor is protected from overheating by taking measures to limit the current at predetermined time intervals.

FIG. 12 shows an example of a conventional apparatus. The motor temperature estimating means 40 estimates the motor temperature based on the motor current value i from the motor current detecting circuit 38, and the motor temperature estimating means 40 estimates the motor temperature. Motor overheat protection means 41 for limiting the steering assist command value I (or the current control value E) based on the estimated temperature value is provided. As described above, conventionally, the motor current is limited by the concept of time and current to protect the motor from overheating, but no protection is provided against the magnetic demagnetization of the motor when the current flows at low temperatures. Had not been.

[0008]

In the above-mentioned conventional method, the amount of heat generation is estimated from the motor current to calculate and limit the motor current. However, since this method does not take the absolute temperature into consideration, the position of the vehicle is limited. In some cases, the estimated temperature deviates from the actual temperature due to the outside air temperature, and the motor and the motor drive circuit of the control unit cannot be sufficiently protected. In addition, if the temperature (threshold) of the overheat protection is set assuming a high temperature, the protection function is activated quickly at a normal temperature or a low temperature, and the time during which a large current can be output during a stationary operation is reduced.

Further, in the conventional method, the motor current is limited by measuring only the temperature of the radiator of the control unit, or the motor current is limited by estimating the motor temperature. However, since the thermal time constant of the radiator of the control unit and the thermal time constant of the motor are different, for example, if only the radiator of the control unit is measured and the motor current is limited to perform overheat protection, the motor temperature will not decrease. It is conceivable that the restriction on the motor current may be released and the motor may be damaged.

Furthermore, in the conventional method, since the location of the component that needs to be overheat-protected has not been clearly determined, it is clear which component should fail to cause a serious failure. I didn't. For this reason, a situation has occurred in which the control unit cannot accurately recognize the heat generated by the output current. Conventionally, the motor is protected at a high temperature. However, when a large current flows through the motor at a low temperature, there is a phenomenon that a magnetic material used in the motor is demagnetized. In such a case, even if a large current is supplied to the motor for a short time, the motor is demagnetized, and there is a possibility that a normal output cannot be obtained after that even though the rated current is supplied.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to detect the temperature of a motor of an electric power steering apparatus and a control unit thereof, so that the motor and the control unit are controlled in accordance with the temperature. It is an object of the present invention to provide a control device for an electric power steering device which is designed to protect the vehicle from overheating.

[0012]

SUMMARY OF THE INVENTION The present invention provides a steering mechanism for steering a steering mechanism based on a steering assist command value calculated based on a steering torque generated in a steering shaft and a current control value calculated from a current value of a motor. The present invention relates to a control device for an electric power steering device adapted to control the motor for providing an assisting force, and the object of the present invention is to provide a temperature detection means provided in a motor drive circuit of a control unit, Means for estimating the motor drive element temperature based on the temperature obtained by the means, and a control unit overheat protection means for limiting the current control value by the estimated temperature; and The reference value is corrected by adding the reference value and the temperature estimation value from the motor brush temperature estimation means value. A motor overheat protection means for limiting the current control value by a motor brush temperature estimation value, and a temperature from the temperature detection means at the time of startup as a reference value of the motor magnetic body temperature, and A motor low-temperature demagnetization protection unit for correcting the current control value by the corrected motor magnetic body temperature estimation value by adding and correcting the temperature estimation value, and a current limit value output from the control unit overheat protection unit. This is achieved by limiting the current control value to the larger of the current limit value output from the motor overheat protection means and the current limit value output from the motor low temperature demagnetization protection means.

The control unit overheat protection means includes a temperature T1 that does not require a current limit and a temperature T2 that requires a limit to a current value at which the control unit can continuously supply current according to the estimated motor drive element temperature.
The current control value may be calculated based on the motor drive element temperature T3 at which the motor current needs to be interrupted, and the current control value may be limited. Further, the motor overheat protection means cuts off the motor current based on the estimated motor brush temperature, a temperature T1 that does not require a current limit, a temperature T2 that requires a limit to a current value at which the motor can be continuously supplied, and a motor current. A current limit value is calculated based on the required motor brush temperature T3, and the current control value is limited. The motor low-temperature demagnetization protection means uses the motor magnetic material temperature estimated value to calculate the magnetic material of the motor. If the temperature is equal to or higher than the temperature T1 at which demagnetization does not occur, the current limit is not performed. If the temperature is equal to or lower than the temperature T1 at which demagnetization of the magnetic body of the motor occurs, the current limit value is set so that the current value has no influence of demagnetization. May be calculated to limit the current control value.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a temperature detecting means such as a thermistor is provided on a printed circuit board near a heat radiator or an FET of a motor drive circuit of a control unit to measure an actual temperature. To detect. The detected temperature is corrected by a previously determined thermal resistance or heat capacity from the temperature detecting means to the FET junction to calculate the junction temperature of the FET. Since the temperature obtained from the temperature detection means of the control unit at the time of starting can be said to be substantially equivalent to the ambient temperature in the vehicle compartment, the temperature can be said to be the temperature at the time of starting the motor. Therefore, the motor temperature is determined by using the temperature in the control unit at the time of starting as a reference temperature, and after starting, estimating a relative motor temperature from, for example, a motor current, and correcting the reference temperature to obtain a motor estimated temperature. And At this time, the estimated motor temperature is corrected so as to estimate the temperature of the motor brush. Similarly, using the temperature in the control unit at the time of starting as a reference temperature of the motor magnetic body, after starting, for example, a relative motor temperature is estimated from a motor current or the like, and the reference temperature of the motor magnetic body temperature at the time of starting and this reference temperature. The reference temperature value and the temperature estimated value obtained from the motor magnetic body temperature estimating means are added and corrected, and this is used as a corrected motor magnetic body temperature estimated value. The relative temperature of the motor is estimated by calculating the motor resistance from the voltage between the motor terminals and the motor current when the angular velocity of the motor is ω = 0, and calculating the relative temperature of the brush or the magnetic body of the motor from the motor resistance. It may be estimated.

In the present invention, the motor current limit value is calculated by the control unit overheat protection means from the estimated junction temperature of the FET obtained by the above method, and the motor current limit value is calculated by the motor overheat protection means from the estimated brush temperature of the motor. Calculate and calculate the motor current limit value in the motor low-temperature demagnetization protection means from the motor magnetic body temperature,
The current control value is limited to the larger one of the current limit values.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, a configuration example of the present invention is shown in FIG. 1 corresponding to FIG. In the present invention, the control unit 30
A motor driving circuit temperature detecting means 60 is provided in the motor driving circuit 37 in A, and the detected temperature T is inputted to the FET junction temperature estimating means 50, the motor brush temperature estimating means 52 and the motor magnetic body temperature estimating means 54. The temperature signals estimated by the estimating means 50, 52, 54 are input to a control unit (ECU) overheat protection means 51, a motor overheat protection means 53, and a motor low temperature demagnetization protection means 55, respectively. Each current limit value from 55 is input to the steering assist command value calculator 32 via the switching means 61. Further, the FET junction temperature estimating means 5
0, the motor current value i from the motor current detection circuit 38 is input to the motor brush temperature estimating means 52 and the motor magnetic body temperature estimating means 54, and the respective contacts of the switching means 61 are sequentially switched. I have.

Control unit overheat protection means 51
Are divided into three states as shown in FIG. 2 based on the estimated junction temperature of the FET. That is, a range of the temperature T1 or lower where the maximum current output is possible and the current is not limited,
It is considered that there are a range of temperatures T1 and T2 where the control unit 30A gradually limits the current value to a current value that can be continuously supplied, and a range of temperatures T2 and T3 where the motor current needs to be cut off at the maximum junction temperature of the FET. The temperature T1 is a junction temperature at which a maximum current output is possible, the temperature T2 is a junction temperature at which a continuous rated output is possible, and the temperature T
3 is the maximum temperature of the FET junction. Further, the motor overheat protection means 53 is considered by dividing into three states as shown in FIG. That is, the temperature T at which the maximum current can be output and the current limit is not required.
It is considered to be a range of 1 or less, a range of temperatures T1 and T2 that need to be limited to a current value at which the motor can be continuously energized, and a range of motor brush temperatures T2 and T3 that need to cut off the motor current. Temperature T1 is a brush temperature at which a maximum current output is possible, temperature T2 is a brush temperature at which a continuous rated output is possible, and temperature T3 is a motor heat-resistant limit temperature. Further, as shown in FIG. 4, the motor low-temperature demagnetization protection means 55 does not limit the current when the temperature of the magnetic body of the motor is equal to or higher than T1 as shown in FIG. When the temperature is equal to or lower than the temperature T1 at which demagnetization of the body occurs, the current limit value is calculated so that the current value does not have the effect of demagnetization, and the current control value is limited.

Among the motor current limit values calculated from the three protection means of the control unit overheat protection means 51, the motor overheat protection means 53, and the motor low temperature demagnetization protection means 55, a value having a large current limit is adopted. To limit the current control value.

FIG. 5 shows an operation example of the present invention. First, a predetermined control unit overheat protection current limit value Lecu is read (step S1), and the motor overheat protection current limit value Lmot (step S2) and the motor are sequentially read. The low temperature demagnetization protection current limit value Lmag is read (step S
3), control unit overheat protection current limit value Lec
The magnitude of u and the motor overheat protection current limit value Lmot is determined (step S4). In step S4, Lecu
If> Lmot, it is further determined whether the control unit overheat protection current limit value Lecu and the motor low temperature demagnetization protection current limit value Lmag are large or small (step S5).
If Lecu> Lmag in 5, the current control value is limited by the current limit value Lecu by the control unit overheat protection (step S10). If Lecu ≦ Lmot in step S4, the motor low-temperature demagnetization protection current limit value Lmag and the motor overheat protection current limit value Lmo are set.
The magnitude of t is determined (step S6), and Lmag> Lmo
In the case of t and if Lecu ≦ Lmag in step S5, the current control value is limited by the current limit value Lmag by the motor low-temperature demagnetization protection (step S20), and Lmag ≦ L
If it is mot, the current limit value Lmo due to motor overheat protection
The current control value is limited by t (step S30).

FIG. 6 shows an operation example of the control unit overheat protection in step S10 in FIG. 5. First, an estimated junction temperature Tfet of the FET is read (step S11), and a predetermined temperature T1 (see FIG. 2) is read. The magnitude is determined (step S12A), and if Tfet <T1, the current limit value is set to “0” and the maximum current is output (step S13). In the above step S12A, Tfet ≦ T
If it is 1, the magnitude of the predetermined temperature T2 is further determined (step S12B). If Tfet <T2, the current limit value Lecu is calculated from the junction temperature Tfet of the FET (step S14), and the current limit value is set to Lecu. (Step S15). Also, Tfe is determined in step S12B.
If t ≧ T2, it is determined whether the temperature is still different from another predetermined temperature T3 (step S12C).
u-max is determined (step S16), and the current limit value is set to Lecu-max (step S17). And
In step S12C, if Tfet ≧ T3, the current limit value Lecu− that turns off the motor current.
is determined (step S18), and the current limit value is set to Le.
cu-off (step S19).

The details of step S20 in FIG. 5 are described in FIG.
First, the motor magnetic body temperature estimated value Tf
el is read (step S21), and a predetermined temperature T1 (FIG. 4)
(See step S22), and Tfel
If> T1, the current limit value is set to "0" and the maximum current output is made (step S23). Tf in the above step S22
If el ≦ T, a current limit value Lfel is calculated from the motor magnetic body temperature Tfel (step S24), and the current limit value is set to Lfel (step S25).

FIG. 8 shows an operation example of the motor overheat protection in step S30 in FIG. 5. First, an estimated motor brush temperature value Tbrsh is read (step S3).
1) The magnitude of the predetermined temperature T1 (see FIG. 3) is determined (step S32A). If Tbrsh <T1, the current limit value is set to "0" and the maximum current is output (step S3).
3). If Tbrsh ≧ T1 in step S32A, the magnitude of the predetermined temperature T2 is further determined (step S32).
B), if Tbrsh <T2, the motor brush temperature Tb
The current limit value Lbrsh is calculated from rsh (step S
34), the current limit value is set to Lbrsh (step S3)
5).

In step S32B, Tbrsh
If ≧ T2, the magnitude with respect to another predetermined temperature T3 is determined (step S32C), and if Tbrsh <T3, a current limit value Lbr that limits the motor to the continuous rated current.
sh-max is determined (step S36), and the current limit value is set to Lbrsh-max (step S37). In step S32C, Tbrsh ≧ T3
If so, the current limit area Lb that turns off the motor current
rsh-off is determined (step S38), and the current limit value is set to Lbrsh-off (step S39).

[0025]

According to the present invention, the motor drive circuit or the control unit is provided with temperature detecting means, and the limiting current of the control unit, the limiting current of the motor overheat protection and the limiting current of the motor low temperature demagnetization protection are determined. Since the corresponding limiting current is instructed, efficient and economical motor protection can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of the present invention.

FIG. 2 is a diagram for explaining overheat protection of a control unit according to the present invention.

FIG. 3 is a diagram for explaining motor overheat protection according to the present invention.

FIG. 4 is a diagram illustrating motor low temperature demagnetization protection according to the present invention.

FIG. 5 is a flowchart showing a current limit value selecting operation according to the present invention.

FIG. 6 is a flowchart showing an operation example of overheat protection of the control unit according to the present invention.

FIG. 7 is a flowchart showing an operation example of motor low-temperature demagnetization protection according to the present invention.

FIG. 8 is a flowchart showing an operation example of motor overheat protection according to the present invention.

FIG. 9 is a block diagram showing an example of an electric power steering device.

FIG. 10 is a block diagram showing a general internal configuration of a control unit.

FIG. 11 is a connection diagram illustrating an example of a motor drive circuit.

FIG. 12 is a block diagram illustrating an example of a conventional motor protection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30, 30A control unit 50 FET junction temperature estimating means 52 Motor brush temperature estimating means 54 Motor magnetic body temperature estimating means 60 Motor drive circuit temperature detecting means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuya Mori Omron Co., Ltd. 10 Hanazono Todocho, Ukyo-ku, Kyoto-shi, Kyoto

Claims (4)

[Claims] 1. A motor for applying a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated based on a steering torque generated on a steering shaft and a current value of the motor. In the control device of the electric power steering device, the temperature of the motor driving element is estimated based on the temperature detected by the temperature detecting means provided in the motor driving circuit of the control unit. A control unit overheat protection means for limiting the current control value according to the estimated temperature, and a temperature from the temperature detection means as a reference value of the motor brush temperature at the time of startup, and a temperature estimation from the reference value and the motor brush temperature estimation means. The current control value is limited by the corrected motor brush temperature estimated value. The motor overheat protection means and the temperature from the temperature detection means at startup are used as a reference value of the motor magnetic body temperature, and the reference value and the temperature estimation value from the motor magnetic body temperature estimation means are added and corrected. Motor low temperature demagnetization protection means for limiting the current control value according to the motor magnetic material temperature estimated value, the current limit value output from the control unit overheat protection means, the current limit output from the motor overheat protection means A control device for an electric power steering apparatus, wherein the current control value is limited to a larger one of a current limit value and a current limit value output from the motor low-temperature demagnetization protection means. 2. The control unit overheat protection means includes a temperature T1 that does not require a current limit according to the estimated motor drive element temperature and a temperature T2 that requires a limit to a current value at which the control unit can continuously supply current.
The control of the electric power steering apparatus according to claim 1, wherein the current control value is calculated based on a temperature T3 of the motor drive element that needs to cut off the motor current, and the current control value is limited. apparatus. 3. The motor overheat protection means includes: a temperature T1 that does not require a current limit, a temperature T2 that needs a limit to a current value at which the motor can be continuously energized, and a motor current based on the motor brush temperature estimated value. 2. The control device for an electric power steering device according to claim 1, wherein the current control value is limited by calculating a current limit value based on a motor brush temperature T3 which needs to cut off the current control value. 4. The motor low-temperature demagnetization protection means does not limit the current when the temperature of the magnetic body of the motor is equal to or higher than T1 based on the estimated temperature of the magnetic body of the motor. 2. The current control value according to claim 1, wherein when the temperature is equal to or lower than a temperature T1 at which demagnetization of the body occurs, a current limit value is calculated so as to be a current value having no influence of demagnetization, and the current control value is limited. Control device for electric power steering device.