JP2006044437A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device capable of sufficiently feeding the assist force while protecting a heating element from overheat even when a temperature sensor of the heater is failed. <P>SOLUTION: The electric power steering device comprises a temperature estimation and operation means to estimate the temperature of a heating element, and a temperature sensor trouble detection means to detect a trouble of a temperature sensor. When the temperature sensor is failed, the motor current is limited based on the estimated temperature in place of the detected temperature. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric power steering apparatus, and more particularly, to an electric power steering apparatus with improved temperature protection when a temperature sensor fails.

  An electric power steering device that urges an assisting force (assist torque) with a rotational force of a motor in an automobile or a vehicle is provided by a transmission mechanism such as a gear or a belt via a speed reducer. Auxiliary force is applied to the rack shaft. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.

  Here, a general configuration of the electric power steering apparatus will be described with reference to FIG. 5. A shaft 102 of the steering handle 101 is connected to a tie rod of a steering wheel via a reduction gear 103, universal joints 104 a and 104 b, and a pinion rack mechanism 105. 106. A torque sensor 107 that detects the steering torque of the steering handle 101 is provided on the shaft 102, and a motor 108 that assists the steering force of the steering handle 101 is coupled to the shaft 102 via the reduction gear 103. . The control unit 130 that controls the power steering device is supplied with electric power from the battery 114 via the ignition key 111 and the power relay 113, and the control unit 130 detects the steering torque T detected by the torque sensor 107 and the vehicle speed sensor 112. The assist command current command value Iref is calculated based on the calculated vehicle speed V, and the current supplied to the motor 108 is controlled based on the calculated current command value Iref.

  The control unit 130 is mainly composed of a CPU, and FIG. 6 shows general functions executed by programs in the CPU. For example, the current command value calculation unit 204 does not indicate a current command value calculator as independent hardware, but indicates a current command value calculation function executed by the CPU.

  The function and operation of the control unit 130 will be described below. The torque value T detected by the torque sensor 107 and the vehicle speed V detected by the vehicle speed sensor 112 are input to the current command value calculation unit 204, the current command value Iref is output, and the current command value Iref is input to the subtraction unit 207. Entered. On the other hand, the motor current Im detected by the current detector 205 is also fed back to the subtraction unit 207, and the subtraction unit 207 calculates a deviation ΔI = (Iref−Im). The deviation is input to the proportional-plus-integral control unit (PI control unit) 208, and the voltage command value Vref is output from the PI control unit 208. In this example, as an example of the current control unit, an example of feedback control in which a deviation between the current command value Iref and the motor current Im is input to the proportional integral control is shown.

  Next, the voltage command value Vref is input to a limiter 209 described later, and the voltage command value Vreflim subjected to the limitation is output. Based on the voltage command value Vreflim, the PWM control unit 210 outputs a PWM signal to the inverter circuit 211. The inverter circuit 211 is PWM-controlled based on the PWM signal and supplies the motor current Im to the motor 108.

  Here, the function of the limiter 209 will be described with reference to FIG. The limiter 209 is an example of a heating element in components constituting the electric power steering apparatus, for example, a motor 108 (strictly speaking, a winding of the motor) or a drive circuit that supplies a motor current to the motor 108. This is provided to protect switching elements such as FETs used in the inverter circuit 211 from overheating.

  An electric power steering device does not normally use a large current close to its maximum output continuously for a long time, and steering with steering on a road is sufficient with a small assist, and a large motor current Im does not flow. . On the other hand, when parking in a confined space, the steering wheel operation increases and assists near the maximum output, so a large motor current Im flows and the above-mentioned heating element violently overheats, requiring overheat protection. However, such an assist period ends in a short time.

  Therefore, the maximum limit current Imax at the time of a stationary operation that is completed in a short time becomes a value larger than the continuous energization maximum current Icon that can energize the heating element continuously for a long time. For example, as an example, if the maximum limit current Imax is 100 A (100%), the continuous energization maximum current is 50 A (50%). However, if the installation operation is continued for a relatively long time, the heating element to be overheated is overheated. Therefore, when the temperature of the heating element reaches the protection start temperature Tst, the energizable motor current Im is gradually reduced. Then, a limiter 209 having a protection characteristic that prevents energization at the maximum limit temperature Tmax limits the motor current Im to provide overheat protection. Specifically, as an example, the temperature sensor 230 is installed in the motor 108, and information on the detected temperature Ts detected by the temperature sensor 230 is transmitted to the limiter 209. The limiter 209 has the protection characteristics shown in FIG. The protection characteristic sets a limit value of the motor current Im with respect to the temperature of the heating element, and the motor 108 can be protected from overheating by limiting the motor current by a limiter based on the protection characteristic. The protection characteristic shown in FIG. 7 for setting the limit value of the motor current Im for the detected temperature Ts detected by the temperature sensor is referred to as a detected temperature protection characteristic A.

  In the conventional overheat protection, for example, according to Patent Document 1, when the temperature sensor is normal, the limiter of the detected temperature protection characteristic A is allowed based on the temperature detected by the temperature sensor when steering the steering wheel. The motor current can be applied up to the maximum limit current Imax. However, if the temperature sensor fails, the motor temperature cannot be detected correctly. Therefore, for the sake of safety so that the motor does not burn out, the limit of the motor current is not limited to the maximum limit current Imax but the maximum continuous current Icon. It is small and strictly limited.

JP 2002-2111425 A

  However, the above-described conventional overheat protection significantly limits the output of the electric power steering device due to the failure of a temperature sensor, which is not a major component of the electric power steering device, and provides sufficient assist power during stationary steering. There is a problem that cannot be provided. Therefore, in order to avoid the problem that the temperature sensor cannot be sufficiently assisted due to the failure of the temperature sensor, it is conceivable to perform overheat protection by estimating the temperature without using the temperature sensor. However, since the general usage environment of automobiles cannot be broadly specified from low temperature to high temperature, it is difficult to realize temperature estimation that safely realizes overheat protection in an environment with such a wide temperature change. As a result, there is a problem that the CPU is forced to take a heavy burden on a non-main function of the electric power steering apparatus such as the temperature estimation function, so that it cannot be practically adopted.

  The present invention has been made under the circumstances as described above, and the object of the present invention is to provide an assist force while protecting the heating element from overheating even when a temperature sensor for detecting the temperature of the heating element fails. An object of the present invention is to provide an electric power steering apparatus that can output sufficiently.

The present invention relates to a motor that applies a steering assist force to a steering system of a vehicle and a current command value that is determined based on an output value of a torque sensor that detects a steering force acting on a steering wheel. The present invention relates to an electric power steering apparatus comprising current control means for controlling current and a temperature sensor for detecting the temperature of the heating element, and controlled to limit the current of the motor based on the detected temperature of the heating element. And the object of the present invention is provided with a temperature estimation calculation means for estimating and calculating the temperature of the heating element, and a temperature sensor failure detection means for detecting that the temperature sensor has failed, and the temperature sensor has failed. This is achieved by limiting the motor current based on the estimated temperature instead of the detected temperature.
Further, the object includes a detected temperature protection characteristic for limiting the motor current based on the detected temperature and an estimated temperature protection characteristic for limiting the motor current based on the estimated temperature, and the temperature sensor has failed. In this case, it is more effectively achieved by limiting the motor current based on the estimated temperature protection characteristic instead of the detected temperature protection characteristic.
Further, the object is that the detected temperature protection characteristic and the estimated temperature protection characteristic are at least the maximum current limit of the motor current, the protection start temperature of the heating element, the maximum limitation temperature of the heating element, or the detection. It is more effectively achieved by using the temperature or the reduction rate of the motor current with respect to the estimated temperature as a constituent element.

Further, the above object is more effectively achieved by making the maximum limit current of the estimated temperature protection characteristic smaller than the maximum limit current of the detected temperature protection characteristic.
Further, the above object is more effectively achieved by the fact that the protection start temperature of the estimated temperature protection characteristic is lower than the protection start temperature of the detected temperature protection characteristic.
Further, the above object is more effectively achieved by the fact that the maximum limit temperature of the estimated temperature protection characteristic is lower than the maximum limit temperature of the detection temperature protection characteristic.
Further, the above object is more effective when the rate of decrease in the motor current with respect to an increase in the estimated temperature of the estimated temperature protection characteristic is greater than the rate of decrease in the motor current with respect to an increase in the detected temperature of the detected temperature protection characteristic Achieved.

Moreover, the said objective is achieved more effectively by making the detected temperature memorize | stored immediately before the said temperature sensor failure into an initial value at the time of the said estimation calculation when the said temperature sensor fails.
Moreover, the said objective is achieved more effectively by performing the said temperature estimation calculation after the said temperature sensor fails.
Moreover, the said objective is achieved more effectively by the said heat generating body being the switching element of the drive circuit which supplies the said motor or the said motor electric current.

According to the electric power steering apparatus of the present invention, even when the temperature sensor fails, the heating element is protected from overheating based on the estimated temperature estimated by the temperature estimation calculation means. It is possible to provide an electric power steering apparatus that can output a sufficient assist force without excessively limiting the current.
In addition, it has a detected temperature protection characteristic based on the detected temperature detected by the temperature sensor and an estimated temperature protection characteristic based on the estimated temperature estimated by calculation of the temperature of the heating element. Even if the sensor fails, an electric power steering device can be provided that can sufficiently output the assist force without excessively limiting the motor current while protecting the heating element from overheating by the estimated temperature protection characteristic.
The detected temperature protection characteristic and the estimated temperature protection characteristic include at least the maximum current limit of the motor current, the protection start temperature of the heating element, the maximum limit temperature of the heating element, the detection temperature, or the estimated temperature. The component of the estimated temperature protection characteristic is set on the safe side as overheat protection with respect to the component of the detected temperature protection characteristic. Thus, it is possible to provide an electric power steering device that can protect the heating element from overheating without excessively limiting the above.
Moreover, since the detected temperature immediately before the failure of the temperature sensor is used as the initial value for temperature estimation, an effect of improving the accuracy of the estimated temperature can be expected.
Further, since the temperature estimation is executed only when the temperature sensor fails, there is an effect that can be realized without imposing a burden on the CPU or the like.

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

FIG. 1 shows a preferred embodiment of the present invention in which a limiter having a detected temperature protection characteristic and an estimated temperature protection characteristic is provided for a voltage command value. In FIG. 1, the same numbers as those used in the description of the prior art have the same functions.

  In FIG. 1, a switch 14-1 is arranged after the PI control 208 that outputs the voltage command value Vref, and the voltage command value Vref is connected to the limiter 209 having the detected temperature protection characteristic A via the switch 14-1. It is configured to be sent to one of the limiters 16 having the estimated temperature protection characteristic B. Further, it is disposed after the limiter 209 and the limiter 16 in the switch 14-2 so that either the limiter 209 or the output of the limiter 16 is selected and the voltage command value Vreflim is sent to the PWM control unit 210.

  The switches 14-1 and 14-2 are switches that are controlled based on the output of the temperature sensor failure detection means 12. When the temperature sensor 230 is normal, the temperature sensor failure detection means 12 inputs the output of the temperature sensor 230 to detect the normality of the temperature sensor 230, and the switch 14-1 switches between the PI control unit 208 and the limiter 209. The switch 14-2 connects the limiter 209 and the PWM control unit 210. On the other hand, if the temperature sensor 230 fails, the temperature sensor failure detection means 12 detects a failure of the temperature sensor 230 and outputs a failure signal (Error), and the switch 14-1 detects the PI controller 208 and the limiter 16. The switch 14-2 connects the limiter 16 and the PWM control unit 210.

  The limiter 209 sets a limit value such as a motor current Imax that is limited by the detected temperature retention characteristic A based on the detected temperature Ts of the motor 108 that is an example of the heating element detected by the temperature sensor 230. On the other hand, the limiter 16 is a motor that is limited by the estimated temperature protection characteristic B based on the estimated temperature Te estimated by the temperature estimation calculation unit 10 based on the motor current Im detected by the current detector 205. Limit values such as current Iemax are set.

  Here, the temperature estimation calculation unit 10 that estimates the temperature of the motor will be described. The motor winding has a winding resistance. When the motor current is energized, the winding resistance generates heat, and the motor winding is overheated. . The motor has a structure that cools the generated heat, and the temperature of the motor is determined by the cooling capacity, the energization current, the ambient temperature, and the like, and the motor temperature can be estimated based on the relationship. it can. The technique for estimating the temperature of the motor is disclosed in, for example, Japanese Patent Document (Japanese Patent Laid-Open No. 10-10093).

  In the temperature estimation calculation, the detected temperature detected by the temperature sensor is generally used as the initial value (or reference temperature) of the calculation. However, when the temperature sensor fails, the detected temperature of the failed temperature sensor cannot be used as the initial value. Therefore, as a countermeasure, the detected temperature is stored in a certain cycle, and when the temperature sensor fails, the detected temperature stored immediately before the failure can be used as the initial value of the estimation calculation. With such a configuration, accurate temperature estimation can be realized with a simple configuration.

  Specifically, in FIG. 1, the storage unit 18 is installed, and the detected temperature Ts from the temperature sensor 230 and the failure signal (Error) from the temperature sensor failure detection means 12 are input as its input signals, and the estimation calculation is performed. The initial value Tso is output and input to the temperature estimation calculation unit 10. In the operation, the storage unit 18 stores and updates the detected temperature Ts detected by the temperature sensor 230 at a certain cycle. When the temperature sensor 230 fails, the storage unit 18 stops storing and updating the detected temperature Ts based on the failure signal (Error). Therefore, when the temperature sensor 230 fails, the detected temperature Ts immediately before the failure of the temperature sensor 230 is input to the temperature estimation calculation unit 10 as the initial value Tso. On the other hand, when the failure signal (Error) is input, the temperature estimation calculation unit 10 receives the initial value Tso that is the detected temperature Ts immediately before the failure of the temperature sensor 230 and the motor current Im, and estimates the estimated temperature Te. To do.

  Here, the detected temperature protection characteristic A and the estimated temperature protection characteristic B, which are important elements of the present invention, will be described with reference to FIG. The detected temperature protection characteristic A and the estimated temperature protection characteristic B are at least the maximum current limit of the motor current, the protection start temperature of the motor that is a heating element, the maximum limit temperature of the motor, or the rise of the detected temperature or the estimated temperature. The reduction rate of the motor current is a component.

  First, the detected temperature protection characteristic A is a protection characteristic of the limiter 209 that is used when the temperature sensor 230 is normal. The protection characteristic is that the motor current is limited based on the detected temperature Ts of the motor. When the motor temperature is equal to or lower than the protection start temperature Tst (for example, 100 degrees), the motor current Im is the maximum limit current Imax (for example, the motor current is 100%). , 100A) or less, and when the motor temperature becomes equal to or higher than the protection start temperature Tst (100 degrees), the limit value of the motor current is set to gradually decrease to the maximum limit temperature Tmax (for example, 200 degrees). Yes.

  On the other hand, the detected temperature protection characteristic B is a protection characteristic of the limiter 16 that is used when the temperature sensor 230 fails. The protection characteristic is that the motor current is limited based on the estimated temperature Te of the motor. When the motor temperature is equal to or lower than the protection start temperature Test (for example, 80 degrees), the motor current Im is the maximum limit current Iemax (for example, the motor current is 80%). 80A), the motor current limit value is set to gradually decrease up to the maximum limit temperature Temax (for example, 150 degrees) when the motor temperature is equal to or higher than the protection start temperature Test (80 degrees). Yes.

  Here, when each component of the detected temperature protection characteristic A and the estimated temperature protection characteristic B is compared, with respect to the maximum limit current, Iemax (80 A) is a smaller current value than Imax (100 A), and protection starts. Regarding temperature, Test is lower than Tst, and regarding maximum limit temperature, Tmax (200 degrees) is lower than Temax (150 degrees). That is, the motor current is severely limited in the case of overheat protection based on the estimated temperature Te than in the case of overheat protection based on the detected temperature Ts. However, even in the case of overheating protection based on the estimated temperature Te, the motor current can be greatly increased with Iemax (80 A) as compared with the continuous energization maximum current Icon (50 A). Instead of defining the maximum current limit, the rate of decrease of the current limit in the section above the protection start temperature and below the maximum temperature limit may be used. In this case, the rate of decrease of the estimated temperature protection characteristic B is the detected temperature. If it is made to decrease more greatly than the decrease rate of the protection characteristic A, overheat protection can be performed safely even at the estimated temperature.

  Since the motor current Im can be controlled by the voltage command value Vref, if the voltage command value Vref is limited so as to be the motor current Im on the vertical axis of the protection characteristics of FIG. 2, the actual motor current Im is converted to the motor of FIG. It can be limited like current.

The operation of the first embodiment configured as described above will be described with reference to FIGS.
The torque value T detected by the torque sensor 107 and the vehicle speed V detected by the vehicle speed sensor 112 are input to the current command value calculation unit 204, the current command value Iref is output, and the current command value Iref is input to the subtraction unit 207. Entered. On the other hand, the motor current Im detected by the current detector 205 is also fed back to the subtraction unit 207, and the subtraction unit 207 calculates a deviation ΔI = (Iref−Im). The deviation is input to the proportional-plus-integral control unit (PI control unit) 208, and the voltage command value Vref is output from the PI control unit 208.

  Here, when the temperature sensor 230 is normal, the temperature sensor failure detection means 12 detects normality of the temperature sensor 230 based on the output signal of the temperature sensor 230, and the switch 14-1 detects PI based on the normal signal. The control unit 208 and the limiter 209 having the detected temperature protection characteristic A are connected, and the switch 14-2 connects the limiter 209 and the PWM control unit 210. Therefore, the voltage command value Vref passes through the limiter 209 and is sent to the PWM control unit 210 as the voltage command value Vreflim, and the inverter circuit 211 supplies the motor current Im to the motor 108 based on the PWM control signal.

  That is, during stationary steering, the voltage command value Vref is limited by the limiter 209 by the detected temperature Ts and the detected temperature protection characteristic A, but the motor current is, for example, at the protection start temperature Tst or lower. The maximum limit current Imax (100 A), which is larger than the continuous energization maximum current Icon (50 A), can be supplied, and a sufficient assist force can be supplied while protecting the motor from overheating.

  Next, when the temperature sensor 230 fails, the temperature sensor failure detection means 12 that has received the signal from the temperature sensor 230 detects the failure of the temperature sensor 230 and outputs a failure signal (Error). Based on the failure signal (Error), the storage unit 18 stops updating the detected temperature Ts of the temperature sensor 230. On the other hand, the temperature estimation calculation unit 10 inputs the detected temperature Ts stored immediately before the temperature sensor failure from the storage unit 18 as the initial value Tso and also inputs the motor current Im, and performs the estimation calculation to calculate the estimated temperature Te. To the limiter 16.

  On the other hand, based on the failure signal (Error) of the temperature sensor failure detection means 12, the switch 14-1 connects the PI control unit 208 and the limiter 16 having the estimated temperature protection characteristic B, and the switch 14-2 connects the limiter 16 and the PWM. The control unit 210 is connected. Therefore, at the time of stationary steering, the voltage command value Vref is limited by the limiter 16 by the estimated temperature Te and the detected temperature protection characteristic B. For example, at the protection start temperature Test or lower temperature, the maximum limit current Iemax (80A) can flow, and unlike conventional devices, even if the temperature sensor is faulty, a current larger than the continuous energization maximum current Icon (50A) can be passed, and sufficient assistance is provided while protecting the motor from overheating. Can supply power.

  FIG. 3 is a flowchart when the present embodiment is realized by software. First, the torque value T detected by the torque sensor 107 and the vehicle speed V detected by the vehicle speed sensor 112 are read (S11). Next, the motor current Im detected by the current detector 205 is read (S12). A voltage command value Vref is calculated based on the torque value T, the vehicle speed V, and the motor current Im (S13). A signal from the temperature sensor is read (S14). It is determined whether or not the temperature sensor is malfunctioning (S15).

  If the temperature sensor is normal, first, the detected temperature Ts as the initial value Tso of the motor temperature estimation calculation is updated and stored (S16A). Next, the detected temperature Ts is set as the motor temperature (S17A). The limiter is set with the detected temperature protection characteristic A (S18A).

  On the other hand, if the temperature sensor is faulty, a temperature estimation calculation is performed using the initial value Tso, which is the detected temperature Ts stored immediately before the temperature sensor failure, and the motor current Im in step 16A to calculate the estimated temperature Te. (S16B). Next, the estimated temperature Te is set as the motor temperature (S17B). Next, a limiter is set with the estimated temperature protection characteristic B (S18B).

  It is checked whether the motor is overheated and the limiter is limited (S21). If the motor is not overheated, the voltage command value Vreflim is determined without being limited to the limiter (S23). However, if the motor is overheated, the voltage command value Vref is limited by the limiter. In this case, if the temperature sensor is normal, the limiter limited by the detected temperature protection characteristic A and the detected temperature Ts set in step 18A is limited by the maximum limited current Imax. On the other hand, if the temperature sensor is out of order, the temperature sensor is limited by the maximum limit current Iemax limited by the estimated temperature protection characteristic B and the estimated temperature Te set in step 18B (S22). Then, the voltage command value Vreflim limited by the limiter set by the detected temperature protection characteristic A or the estimated temperature protection characteristic B is determined (S23).

  As described above, if the present embodiment is used, the motor current can be supplied with the maximum limited current Iemax (80 A) larger than the continuous energization maximum current Icon (50 A) of the conventional device even when the temperature sensor fails. It is possible to provide an electric power steering apparatus capable of supplying a sufficiently large assist force while protecting the motor from overheating.

  In the following embodiment, the limiter is applied to the current command value Iref instead of the voltage command value Vref described above. This embodiment will be described with reference to FIG. A limiter 209-1 and a limiter 16-1 that limit the current command value Iref are connected to the current command value calculation unit 204 via the switch 14-1. Further, the limiter 209-1 and the limiter 16-1 are connected to the subtraction unit 207 via the switch 14-2. Here, the limiter 209-1 is a limiter that limits the current command value Iref when the temperature sensor 230 is normal, and the limiter 16-1 is a limiter that limits the current command value Iref when the temperature sensor 230 fails. It is. The detected temperature protection characteristic of the limiter 209-1 and the estimated temperature protection characteristic of the limiter 16-1 are basically the same as the detected temperature protection characteristic A and the estimated temperature protection characteristic B shown in FIG. It becomes the current command value Iref.

  The operation of the embodiment configured as described above is as follows. First, when the temperature sensor 230 is normal, the temperature sensor failure detection means 12 detects the normality of the temperature sensor 230, and the switch 14-1 causes the current command value calculation unit 204, the limiter 209-1, The switch 14-2 connects the limiter 209-1 and the subtracting unit 207. Therefore, the current command value Iref is limited via the limiter 209-1 determined by the detected temperature Ts and the detected temperature protection characteristic A, and is sent to the subtracting unit 207 as the current command value Ireflim. Therefore, at the time of stationary steering, the current command value Ireflim is not the continuous energization maximum current Icon (50 A) but the maximum limit current Imax (100 A) at, for example, the protection start temperature Tst or lower, and the motor is protected from overheating. In addition, sufficient assist power can be supplied.

  Next, when the temperature sensor 230 fails, the temperature sensor failure detection means 12 detects the failure of the temperature sensor 230, and the switch 14-1 causes the current command value calculation unit 204 and the limiter 16-1 based on the output signal. The switch 14-2 connects the limiter 16-1 and the subtracting unit 207. Therefore, the current command value Iref is limited via the limiter 16-1 determined by the estimated temperature Te and the estimated temperature protection characteristic B, and is sent to the subtracting unit 207 as the current command value Ireflim. Therefore, even during stationary steering, the current command value Ireflim is, for example, the maximum limit current Iemax (80 A) larger than the conventional continuous energization maximum current (50 A) at the protection start temperature Test or lower, and the motor is overheated. Sufficient assist power can be supplied while protecting from the above.

  As described above, if the present invention is used as a limiter for a current command value, it is possible to provide an electric power steering device that can sufficiently supply assist force while protecting the motor from overheating even when the temperature sensor fails.

  In addition, if the temperature estimation calculation is used only for limiting the motor current when the temperature sensor fails, the estimation accuracy is not required so much, so that the effect can be realized with a simple hardware configuration or a configuration that does not impose a burden on the CPU. is there.

  In the above description, the heating element has been described as a motor (strictly speaking, a motor winding). However, the heating element is not limited to a motor winding, but a motor such as an FET that is a switching element of an inverter circuit. The present invention can be applied to a heating element that generates heat by current.

  In FIG. 2, the maximum current limit of the motor current, which is a component of the estimated temperature protection characteristic B, the protection start temperature of the heating element, the maximum limit temperature of the heating element, the detected temperature, or the rise of the estimated temperature The reduction rate of the motor current with respect to the detected temperature protection characteristic A was set to the safe side in all the corresponding components, but some components were set to the safe side and other components were It may be the same. For example, the maximum limit current of the estimated temperature protection characteristic B may be set to Iemax (80 A) and the safe side, and the protection start temperature may be the same Tst (100 degrees) as the detected temperature protection characteristic A. How to set the estimated temperature protection characteristic B in comparison with the detected temperature protection characteristic A may be determined by various combinations of components depending on the protection target and protection concept.

  Further, in the above-described embodiment, when the initial value that is the reference for the temperature estimation calculation is the temperature sensor detection temperature in the temperature estimation of the heating element, the initial value of the temperature estimation after the failure of the temperature sensor is immediately before the failure. However, if the detected temperature of a temperature sensor different from the temperature sensor attached to the protection target of the present invention is used as an initial value, the present invention can be achieved without using storage means. realizable.

  Further, the present invention can also be realized by using hardware such as EPROM as storage means for recording the detected temperature for the initial value.

As described above, according to the present invention, there is an effect that it is possible to provide an electric power steering device that can sufficiently supply assist force while protecting the heating element from overheating even if the temperature sensor of the heating element fails.

1 is a block diagram of overheat protection of Example 1. FIG. It is a figure which shows a detection temperature protection characteristic and an estimated temperature protection characteristic. FIG. 3 is a flowchart of the first embodiment. FIG. 3 is a block diagram of overheat protection of Example 2. It is a block diagram of an electric power steering device. It is a conventional overheat protection block diagram. It is a figure which shows a detection temperature protection characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Temperature estimation calculating part 12 Temperature sensor failure detection part 14-1, 14-2 Switch 18 Memory | storage part 209 Limiter (Detection temperature protection characteristic A)
16 Limiter (Estimated temperature protection characteristic B)

Claims (10)

The current of the motor is controlled based on a current command value determined based on an output value of a torque sensor that detects a steering force acting on a steering wheel and a motor that applies a steering assist force to a vehicle steering system. In the electric power steering apparatus comprising a current control means and a temperature sensor for detecting the temperature of the heating element, and controlled to limit the current of the motor based on the detected temperature of the heating element,
A temperature estimation calculation means for estimating and calculating the temperature of the heating element; and a temperature sensor failure detection means for detecting that the temperature sensor has failed. When the temperature sensor fails, the estimation is performed instead of the detected temperature. An electric power steering device, wherein the motor current is limited based on temperature. A detection temperature protection characteristic for limiting the motor current based on the detected temperature; and an estimated temperature protection characteristic for limiting the motor current based on the estimated temperature, and the detected temperature protection when the temperature sensor fails. The electric power steering apparatus according to claim 1, wherein the motor current is limited based on the estimated temperature protection characteristic instead of the characteristic. The detected temperature protection characteristic and the estimated temperature protection characteristic are at least the maximum limit current of the motor current, the protection start temperature of the heating element, the maximum limitation temperature of the heating element, the detection temperature, or the estimated temperature. The electric power steering apparatus according to claim 2, wherein a reduction rate of the motor current with respect to an increase of the motor power is a component. The electric power steering apparatus according to claim 3, wherein a maximum limit current of the estimated temperature protection characteristic is smaller than a maximum limit current of the detected temperature protection characteristic. The electric power steering apparatus according to claim 3, wherein a protection start temperature of the estimated temperature protection characteristic is lower than a protection start temperature of the detected temperature protection characteristic. The electric power steering apparatus according to claim 3, wherein a maximum limit temperature of the estimated temperature protection characteristic is lower than a maximum limit temperature of the detected temperature protection characteristic. The electric power steering apparatus according to claim 3, wherein a decrease rate of the motor current with respect to an increase in the estimated temperature of the estimated temperature protection characteristic is larger than a decrease rate of the motor current with respect to an increase in the detected temperature of the detected temperature protection characteristic. The electric power steering apparatus according to any one of claims 1 to 7, wherein when the temperature sensor fails, a detected temperature stored immediately before the temperature sensor fails is set as an initial value at the time of the estimation calculation. The electric power steering apparatus according to any one of claims 1 to 8, wherein the temperature estimation calculation is executed after the temperature sensor has failed. The electric power steering apparatus according to any one of claims 1 to 9, wherein the heating element is a switching element of a drive circuit that supplies the motor or the motor current.

Images