JP2007112188A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimum electric current limiting method to protect a part being used from breakage and deterioration due to heat on an electric power steering device. <P>SOLUTION: This electric power steering device to assist steering of a steering system by controlling an electrified electric current to a motor 6 in accordance with steering information by providing the motor 6 to give steering assisting force to the steering system is constituted by furnishing a temperature assumption apparatus 7 to compute temperature of each portion of the electric power steering device from a calorific value 71 of the heating portion of the electric power steering device and a mathematic model 72 concerning heat movement of the electric power steering device and an upper limit electric current computer 8 to compute an upper limit value of the electrified electric current to the motor in accordance with the temperature computed by the temperature assumption apparatus 7. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus, and more particularly to an electric power steering apparatus that limits an energization current in order to protect a component being used from destruction or deterioration due to heat.

  A conventional electric power steering apparatus detects steering torque from a torque sensor attached to a steering shaft, and controls a current that flows to a motor in accordance with the steering torque to assist steering in a steering system. The current is controlled by a semiconductor power element provided in the power circuit of the control system by switching the energized current and performing pulse width modulation.

  However, in such an electric power steering device, since the energization current of the motor is large, parts such as semiconductor power elements through which the energization current flows and the heat generation amount of the motor are large, and the power circuit and the motor may become high temperature. There is a risk that the parts being damaged will be destroyed or deteriorated by heat.

  For this reason, as a method of preventing overheating of the parts used in the electric power steering apparatus, at least one of the temperature sensor for detecting the temperature of the motor installed in the vicinity of the motor and the temperature sensor for detecting the temperature of the power circuit is used. By controlling so as to reduce the maximum current limit value that can be passed through the semiconductor power element, the semiconductor power element is prevented from being overheated even when a large motor current continues to flow. (For example, refer to Patent Document 1).

In addition, a motor ambient temperature detector is installed near the motor, and a power circuit ambient temperature detector is installed near the power circuit. The amount of heat generated by the motor and power circuit is calculated based on the current flowing through the motor. By predicting the temperature rise of the motor and power circuit from the amount, if there is a possibility of overheating, current limitation was performed to prevent overheating.
(For example, refer to Patent Document 2).

JP-A-2-92781 Japanese Patent Laid-Open No. 11-59444

  However, since the method disclosed in Patent Document 1 does not take into account heat escaping from the power circuit and the motor to the outside, it is necessary to perform current limiting on the assumption that the ambient temperature is high, and the ambient temperature is low. However, there is a problem that current limitation is performed even though there is a margin in heat resistance.

  In addition, in the method disclosed in Patent Document 2, since the detection temperature depends only on the temperature of the power circuit and the motor, depending on the installation form of the power circuit and the motor, the fluctuation of the ambient temperature affects the temperature rise. In some cases, heat generation of the power circuit and the motor may affect each other. In such a case, it is difficult to predict the temperature rise with sufficient accuracy only by detecting the temperature of the power circuit or the motor.

  Furthermore, since the detection temperature depends only on the temperature of the power circuit and the motor, the temperature is directly affected by the temperature detection noise, so that there are many errors in the temperature. Thus, since the temperature rise is estimated from the temperature including the error, there is a problem that the accuracy of the estimated temperature information is lowered. When the accuracy of the estimated temperature is low, it is necessary to provide a margin for the current limiting temperature in order to prevent overheating of the power circuit and the motor.

  As described above, in the conventional method, the current limit is performed at a temperature that allows sufficient heat resistance of the parts. However, if the current limit is applied to the motor energization current, the output torque of the motor becomes insufficient, and steering is performed. Since the assistance of the vehicle becomes weak, there is a problem that the steering feeling is adversely affected.

  Further, in the conventional method, in order to protect both the power circuit and the motor, it is necessary to install a temperature detector in the vicinity of the power circuit and the motor, respectively, but the installation of a plurality of temperature detectors causes an increase in cost. There is a problem. Furthermore, since the temperature detector needs to be installed in the vicinity of the power circuit and the motor, there is a problem that the installation position of the temperature detector is less flexible, and circuit design and structural design are restricted.

  The present invention has been made to cope with these problems, and maintains the amount of current supplied to the motor as much as possible while protecting the components used in the electric power steering apparatus from destruction and deterioration due to heat. An object of the present invention is to provide an electric power steering apparatus capable of performing the above.

  An electric power steering apparatus according to the present invention is provided with a motor that gives a steering assisting force to a steering system, and controls an energization current to the motor in accordance with steering information to assist steering of the steering system. A temperature estimator for calculating a temperature of each part of the electric power steering device from a calorific value of the heat generating part of the electric power steering device and a mathematical model relating to heat transfer of the electric power steering device, and the temperature estimator And an upper limit current calculator for calculating an upper limit value of the current flowing to the motor based on the temperature calculated by the above.

  The electric power steering apparatus according to the present invention is configured as described above, and calculates the temperature of each part based on a mathematical model related to heat transfer. Therefore, by using a highly accurate model, the error of the calculated temperature of each part. Can be reduced. In addition, in order to calculate the upper limit value of the current flowing to the motor based on the temperature with less error, the amount of current supplied to the motor as much as possible while protecting the parts used in the electric power steering device from thermal destruction and deterioration Can be maintained.

  Furthermore, according to the present invention, a temperature detector is unnecessary, and the components can be protected from thermal destruction and deterioration at low cost. In the temperature estimator, an error between a temperature detected by a temperature detector installed at an arbitrary position of the electric power steering apparatus and a temperature calculated by the temperature estimator may be fed back to the temperature estimator. Since it is possible, the error of the temperature calculated by the temperature estimator can be further reduced.

  Furthermore, since the temperature detector only needs to be installed at an arbitrary location, the degree of freedom in circuit design and structural design can be increased, and the temperature detector need only be installed at a minimum location, so that the cost can be reduced. You can build a system.

  Further, the temperature estimator can calculate not only the temperature of each part of the electric power steering but also the ambient temperature by a mathematical model relating to heat transfer. Normally, when the ambient temperature fluctuates, the amount of heat that moves outside the electric power steering device also fluctuates, but when the ambient temperature is calculated by the temperature estimator, the amount of heat that moves outside the electric power steering device is accurately calculated. Therefore, the accuracy of the temperature calculated by the temperature estimator can be increased.

  In addition, according to the present invention, by installing the temperature detection device in the vicinity of a component in which the heat resistance performance of the electric power steering device is a problem, the temperature detected by the temperature detection device and the arbitrarily set upper limit temperature It is possible to provide an electric power steering apparatus having an upper limit current calculator that calculates a function of the difference as an upper limit value of an energization current to the motor.

  In addition, when the temperature in the vicinity of a component where heat resistance performance is a problem reaches an arbitrarily set upper limit temperature, the current value is a constant value. At this time, the component where heat resistance performance is a problem is in thermal equilibrium. Or, by setting the function so that it is cooled, the temperature of the part where the heat resistance performance is a problem can be set below the upper limit temperature, and the temperature near the part where the heat resistance performance is a problem is arbitrarily set If the temperature is lower than the temperature, an arbitrary amount of current can be set as an upper limit value by selecting a function, so that the amount of current supplied to the motor can be maintained as much as possible.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the electric power steering apparatus according to the first embodiment. As shown in FIG. 1, based on the torque signal 20 detected by the torque detector 1, the assist amount required by the motor target current calculator 2 is calculated, and the current required for the motor to output the assist amount. The value 21 is calculated.

  In the current value comparator 3, the current value signal 21 calculated by the motor target current calculator 2 is compared with an upper limit current value signal 25 calculated by the method described later, and a smaller value is used as the current value signal 22. Output to the drive controller 5. In the motor drive controller 5, the current value signal 22 output from the current value comparator 3 is supplied with power from the power supply 4 and is output as a current 23 supplied to the motor 6 to drive the motor 6.

  The temperature estimator 7 includes a calorific value calculator 71 and a mathematical model 72 of heat transfer in the electric power steering apparatus. This mathematical model 72 can be constructed, for example, by dividing the electric power steering into any number of parts and calculating the heat transfer between each part and the atmosphere. In such a mathematical model, it is possible to calculate the current temperature of each part by setting the initial temperature at the start of the electric power steering device and sequentially inputting the heat generation amount calculated by the heat generation amount calculator 71 It becomes.

  As a method for setting the initial temperature, for example, it is assumed that the temperature in the electric power steering device in the initial stage is uniform, information on the ambient temperature is obtained from the outside of the electric power steering device, and this value is used as the initial temperature of all parts. And it is sufficient. Further, assuming that the environmental temperature becomes maximum, the value may be set as the initial temperature of all the parts.

  The motor upper limit current calculator 8 is a current for preventing the temperature of a part that may be thermally destroyed from exceeding a certain level based on the temperature signal 24 of each part of the electric power steering device obtained by the temperature estimator 7. Calculate the value. This current value is set as the upper limit value of the current flowing through the motor, and is sent to the current value comparator 3 as an upper limit current value signal 25. In the current value comparator 3, the current value signal 21 calculated by the motor target current calculator 2 is compared with the upper limit current value 25, and a smaller value is output as the current value signal 22 to the motor drive controller 5. .

According to the above configuration, based on the temperature obtained by the temperature estimator 7, the current value for preventing the temperature of the part that may be thermally destroyed from exceeding a certain value is obtained as the upper limit current, Since no current is supplied, the temperature of a portion where there is a possibility of thermal destruction can be prevented from exceeding a certain level, and components can be prevented from being destroyed or deteriorated due to heat.
Moreover, since the temperature detector is not required in the above configuration, the components used can be protected from thermal destruction and deterioration at low cost.

  When there are a plurality of heat generating components in the electric power steering device, for example, in the electric power steering device in which the motor and the power circuit portion are integrated, the motor and the power circuit component generate heat. In such a case, a mathematical model having two heat generating parts, that is, a motor and a power circuit component, may be used.

  Further, when the housing is divided into two or more, a plurality of mathematical models may be provided. For example, when the motor and the power circuit part are completely separated, a mathematical model for heat transfer of the motor part and a mathematical model for heat transfer of the power circuit part may be provided.

  In the above example, the temperature estimator 7 estimates the temperature of each part based on the mathematical model 72 and determines the upper limit current based on this temperature. The current may be limited based on the time derivative of this temperature.

  In the above example, the temperature estimator 7 calculates the calorific value from the current value signal 22 sent to the motor drive controller 5, but the current that is actually energized to the motor is measured and the measurement is performed. It is good also as a structure which calculates the emitted-heat amount based on a value. The temperature observer 7 may be configured to calculate the amount of heat generation based on the torque signal 20 detected from the torque detector 1.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the electric power steering apparatus according to the second embodiment. In this figure, the same or corresponding parts as in FIG.

  The difference from FIG. 1 is that at least one temperature detector 9 is provided at an arbitrary location of the electric power steering apparatus, and an error between the temperature detected by the temperature detector 9 and the temperature calculated by the temperature estimator 7 is calculated. The error calculator 73 calculates the error and feeds back the error as a temperature error signal 74 to the mathematical model 72 of the temperature estimator 7 to reduce the error in the temperature estimator 7.

In addition, although the temperature of the site | part which has provided the temperature detector 9 may be calculated by the temperature estimation device 7, the temperature detected by the temperature detector 9 may be used as it is.
Further, the portion for detecting the temperature by the temperature detector 9 may be an arbitrary portion of the electric power steering apparatus. Furthermore, the temperature of one part may be detected by a plurality of temperature detectors 9, and an error between the average of the detected temperatures and the temperature calculated by the temperature estimator 7 may be fed back to the temperature estimator 7.

Furthermore, when there is a possibility that noise is included in the temperature detected by the temperature detector 9, a noise filter such as a low-pass filter may be applied to the detected temperature signal to remove the noise from the detected temperature. .
Moreover, it is good also as a structure which detects the temperature of several site | parts and feeds back the error of the detected temperature in each site | part, and the temperature calculated in the temperature estimator 7. FIG.
If it is determined that the temperature detector 9 has failed, the error feedback may be canceled and the control according to the first embodiment may be performed.

Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described.
In the first or second embodiment described above, the temperature calculated in the temperature estimator 7 may include not only the temperature of each part of the electric power steering apparatus but also the ambient temperature.
In the third embodiment, by calculating the atmospheric temperature as well, even when the atmospheric temperature fluctuates, the heat transferred to the outside can be accurately calculated, and the temperature of each part of the electric power steering device can be calculated more accurately. It can be calculated accurately.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing the configuration of the electric power steering apparatus according to the fourth embodiment. As shown in FIG. 3, based on the torque signal 20 detected by the torque detector 1, the assist amount required by the motor target current calculator 2 is calculated, and the current required for the motor to output the assist amount. The value 21 is calculated.

On the other hand, a temperature detector 9 is provided in the vicinity of a component that causes a problem in heat resistance performance, and temperature information 24 detected by the temperature detector 9 is sent to the upper limit current calculator 8. The upper limit current calculator 8 calculates the upper limit value of the current that can be supplied to the motor as a function of the difference between the arbitrarily set upper limit temperature and the temperature detected by the temperature detection device. For example, if the upper limit temperature is Tmax and the temperature detected by the temperature detector 9 is T, the upper limit current is A × (Tmax−T) ² .

  In the current value comparator 3, the current value signal 21 calculated by the motor target current calculator 2 is compared with the upper limit current value signal 25 calculated by the upper limit current calculator 8, and a smaller value is set as the current signal 22. Output to the motor drive controller 5. In the motor drive controller 5, the current signal 22 output from the current value comparator 3 is output as an energization current 23 to the motor 6 to drive the motor 6.

  With this configuration, as the difference between the arbitrarily set upper limit temperature and the temperature detected by the temperature detector 9 becomes smaller, the upper limit value of the current that can be supplied to the motor 6 can be reduced. it can. In particular, when the difference between the arbitrarily set upper limit temperature and the temperature detected by the temperature detector 9 is 0, the amount of current that can be supplied to the motor 6 is also 0, and no heat is generated. For this reason, it is possible to prevent components that are problematic in heat resistance from being destroyed or deteriorated by heat.

  In the above example, the upper limit current is proportional to the square of the difference between the upper limit temperature arbitrarily set and the temperature detected by the temperature detector 9, but the upper limit temperature arbitrarily set and the temperature detector 9 is set. Any function of the difference between the arbitrarily set upper limit temperature and the temperature detected by the temperature detector 9 may be used, such as being proportional to the difference with the detected temperature. In the above example, when the difference between the arbitrarily set upper limit temperature and the temperature detected by the temperature detector 9 is 0, the amount of current that can be supplied to the motor 6 is also 0, but the heat that escapes to the outside If the detected temperature does not exceed the upper limit temperature due to the influence of the above, the amount of current that can be energized at this time may be 0 or more.

  In addition, as a component that is a problem in heat resistance performance, a temperature detector 9 that detects the temperature of each component may be placed near a plurality of components, and the upper limit temperature may be set to a different value depending on each component, Different functions may be provided for each part. In this case, the lowest current value among the plurality of upper limit current values may be set as the upper limit current.

  If there is a possibility that noise is included in the temperature detected by the temperature detector 9, a noise filter such as a low-pass filter may be applied to the detected temperature signal to remove the noise from the detected temperature.

Embodiment 5. FIG.
Next, a fifth embodiment of the present invention will be described.
In the third embodiment described above, the upper limit current calculator 8 calculates a current for maintaining the temperature detected by the temperature detector 9 at an arbitrarily set upper limit temperature, and outputs it as the upper limit current value signal 25. It is also good. For example, if the upper limit temperature is Tmax, the temperature detected by the temperature detector 9 is T, and the heat capacity of a component that is a problem in heat resistance performance is C, the temperature detected by the temperature detector 9 after time τ is arbitrarily set The amount of heat Q required to maintain the upper limit temperature can be expressed as Q = C × (Tmax−T) / τ. The upper limit current calculator 8 may be configured to calculate a current value at which the heat generation amount of the heat generating component becomes Q from the temperature detected by the temperature detector 9 and output it as the upper limit current value signal 25.

  With such a configuration, when a large current is calculated by the motor target current calculator 2 so that the ambient temperature of the component where heat resistance is a problem exceeds the upper limit temperature, it is calculated by the upper limit current calculator 8. Since the current value is a current for maintaining the arbitrarily set upper limit temperature, the current value calculated by the upper limit current calculator 8 is lower than the current value calculated by the motor target current calculator 2. . Therefore, since the current value actually energized to the motor is the current value calculated by the upper limit current calculator 8, the ambient temperature of the component where heat resistance is a problem does not exceed the upper limit temperature, and the heat resistance performance is improved. The problem parts can be prevented from being destroyed or deteriorated by heat.

  In the above example, the upper limit current value is calculated from an amount proportional to the deviation between the upper limit temperature and the current temperature, but the upper limit current value is an upper limit temperature that is set arbitrarily by the temperature detected by the temperature detector 9. Any current value can be used as long as the current value can be maintained. For example, the upper limit current value may be changed in proportion to the integral and derivative of the deviation between the upper limit temperature and the current temperature.

  If there is a possibility that noise is included in the temperature detected by the temperature detector 9, a noise filter such as a low-pass filter may be applied to the detected temperature signal to remove the noise from the detected temperature.

  In the first to fifth embodiments described above, as a method for controlling the energization current, a case where the present invention is applied to an electric power steering device has been described. However, in a device driven using a motor by a device other than the electric power steering device. It can also be applied as an output limiting method.

1 is a block diagram showing a configuration of an electric power steering device according to Embodiment 1 of the present invention. FIG. It is a block diagram which shows the structure of the electric power steering apparatus by Embodiment 2 of this invention. It is a block diagram which shows the structure of the electric power steering apparatus by Embodiment 4 of this invention.

Explanation of symbols

1 Torque detector, 2 Motor target current calculator, 3 Current value comparator,
4 power supply, 5 motor drive controller, 6 motor, 7 temperature estimator,
8 Motor upper limit current calculator, 9 Temperature detector, 20 Torque signal,
21 target current value signal, 22 motor current value signal, 23 current value,
24 temperature signal, 25 upper limit current value signal, 71 calorific value calculator,
72 mathematical model of heat transfer, 73 error calculator, 74 temperature error signal.

Claims (5)

In the electric power steering apparatus that provides a steering assisting power to the steering system, and assists the steering of the steering system by controlling the energization current to the motor according to the steering information,
A temperature estimator for calculating a temperature of each part of the electric power steering device from a calorific value of the heat generating part of the electric power steering device and a mathematical model relating to heat transfer of the electric power steering device;
An electric power steering apparatus comprising: an upper limit current calculator for calculating an upper limit value of a current flowing to the motor based on the temperature calculated by the temperature estimator.   The electric power steering apparatus is provided with at least one temperature detector at an arbitrary location, and feeds back an error between the temperature detected by the temperature detector and the temperature calculated by the temperature estimator to the temperature estimator. The electric power steering apparatus according to claim 1, wherein an error in temperature calculated by the temperature estimator is reduced. In the electric power steering apparatus that provides a steering assisting power to the steering system, and assists the steering of the steering system by controlling the energization current to the motor according to the steering information,
A temperature estimator that calculates the temperature of each part of the electric power steering device and the atmosphere from a calorific value of the heat generating part of the electric power steering device and a mathematical model relating to heat transfer of the electric power steering device;
An electric power steering apparatus comprising: an upper limit current calculator for calculating an upper limit value of a current flowing to the motor based on the temperature calculated by the temperature estimator. In the electric power steering apparatus that provides a steering assisting power to the steering system, and assists the steering of the steering system by controlling the energization current to the motor according to the steering information,
A temperature detection device installed in the vicinity of a component in which the heat resistance performance of the electric power steering device is a problem;
An electric power steering comprising: an upper limit current calculator for calculating a function of a difference between an arbitrarily set upper limit temperature and a temperature detected by the temperature detection device as an upper limit value of a current flowing to the motor. apparatus.   The upper limit current calculator calculates a current value for maintaining the temperature detected by the temperature detection device at an arbitrarily set upper limit temperature as an upper limit value of the energization current to the motor. The electric power steering apparatus according to claim 4.

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