JP2005012888A - Temperature estimating device and electric power steering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature estimating device capable of precisely estimating the temperature of a current flowing unit. <P>SOLUTION: The current flowing unit is modeled to be a heating part which heats with a current and a heat radiating part which radiates heat from the periphery of the unit. The square of a current value flowing the unit is outputted through a low pass filter having a first time constant to provide a heating part estimated temperature. The square of a current value flowing the unit is outputted through a low pass filter having a second time constant which is higher than the first time constant to provide a heat radiating part estimated temperature. The sum of the heating part estimated temperature and the heat radiating part estimated temperature is the estimated temperature of the unit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for estimating the temperature of a unit through which a current flows, and more particularly to a technique for estimating the temperature of an electric motor provided in an electric power steering apparatus.
[0002]
[Prior art]
Conventionally, a technique disclosed in Patent Document 1 is known as a technique for estimating the temperature of an electric motor. In this publication, the temperature of the motor is estimated using the current value detected by the motor current detecting means and the voltage value between the terminals.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-10093 (see FIG. 8).
[0004]
[Problems to be solved by the invention]
However, in the electric power steering apparatus described in Patent Document 1, high estimated accuracy cannot be expected since the estimated temperature does not take into account the temperature change for the heat radiation. In particular, if the motor current suddenly increases at the time of lock end abutment, the estimation error is large, so a logic to calculate the current limit value for lock end abutment is required separately from the current limit value based on the estimated temperature. There is a problem that the current limit control becomes complicated.
[0005]
The present invention has been made paying attention to the above-described problems, and an object thereof is to provide a temperature estimation device capable of accurately estimating the temperature of a unit through which a current flows.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, in the temperature estimation device for a unit through which a current flows, the unit is modeled into a heat generating part that generates heat by current and a heat dissipating part that dissipates heat from the periphery of the unit. The square of the current value flowing through the unit is output through a low-pass filter having a first time constant to obtain the heat generating portion estimated temperature, and the square of the current value flowing through the unit is set to a second time constant larger than the first time constant. The estimated temperature of the heat radiating part was obtained by outputting through a low-pass filter, and the estimated temperature of the unit was the sum of the estimated temperature of the heat generating part and the estimated temperature of the heat radiating part.
[0007]
Therefore, it is possible to accurately achieve modeling regarding the heat generation of the unit, and the temperature can be estimated with high accuracy.
[0008]
Further, in the second aspect of the invention, the temperature estimation device according to the first aspect is applied to the temperature estimation of the electric motor of the electric power steering device, so that the motor temperature can be estimated with high accuracy.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a diagram in which a unit through which a current flows is modeled as a heat generating portion and a heat radiating portion. At this time, in the temperature estimation of the heat generating portion, the square of the current value is extracted by a low-pass filter having a short time constant τ1, and the heat generating portion temperature based on the heat generation amount is estimated. Furthermore, in the temperature estimation of the heat radiation part, the square of the current value is extracted by a low-pass filter having a long time constant τ2, and the heat radiation part temperature based on the heat radiation amount is estimated. Next, the sum of the estimated heat generating portion temperature and the heat radiating portion temperature is set as the estimated temperature of the unit.
[0010]
FIG. 2 is a diagram showing a temperature change when a certain current value is passed through the unit. As shown in FIG. 2, the estimated unit temperature obtained by adding the estimated temperature of the heat generating part and the estimated temperature of the heat radiating part is almost the same as the actually measured unit measured temperature. As described above, by appropriately setting the time constants τ1 and τ2 according to the unit, it is possible to provide a temperature estimation device with extremely high estimation accuracy (corresponding to claim 1).
[0011]
(First embodiment)
Next, a first embodiment to which the logic of the above-described temperature estimation device is applied will be described. In the first embodiment, the logic of the temperature estimation device is applied to a power steering device.
[0012]
FIG. 3 is a system diagram showing the overall configuration of the electric power steering apparatus. First, the configuration will be described. The steering wheel 1 is provided with a universal joint 3, an intermediate shaft 4, and a universal joint 5 via a column shaft 2. In this universal joint 5, the tie rod 11 is operated by a steering mechanism including a pinion shaft 9 and a rack shaft 10 connected to the input shaft 6, and the steering direction of the steered wheels 17L and 17R is determined.
[0013]
The input shaft 6 is provided with a torque sensor 7 that detects the steering torque of the driver and a speed reducer 8 that applies a steering assist force. The speed reducer 8 is driven by an electric motor 12 to assist the driver's steering force.
[0014]
The control unit 13 inputs a vehicle speed signal from the vehicle speed sensor 14 and a torque signal from the torque sensor 7, and supplies current to the electric motor 12 using the battery 16 as a power source. When the driver operates the steering wheel 1, the rotation direction of the electric motor 12 is switched according to the operation direction, and assists the driver's steering force.
[0015]
FIG. 4 is a block diagram showing the configuration inside the control unit 13.
The vehicle speed calculation means 201 converts the signal from the vehicle speed sensor 14 into the vehicle speed V.
The steering torque calculation means 202 converts the signal from the torque sensor 7 into torque T.
The basic assist torque calculation means 203 calculates the basic assist torque from the vehicle speed V and torque T using a map or the like.
The torque differential correction torque calculation means 204 differentiates the torque T. Then, an inertia compensation current value for compensating the inertial force of the electric motor 12 with respect to the driver's steering is calculated based on the steering torque differential value and the vehicle speed V.
The damping torque calculation means 205 calculates a damping current value that acts in the direction opposite to the steering angular speed estimated by the steering angular speed estimation means 212 in order to compensate for applying resistance to the steering operation.
[0016]
The command current calculation means 206 adds or subtracts the current value calculated by each calculation means to calculate a motor current command value. This calculated motor current command value limits the motor current command value in the current limiting means 207 by the operating state of the electric power steering device, the temperature estimating means 215, and the like. This limited motor current command value is output to the current feedback control means 208 as a final command value.
The power element driving unit 209 outputs a current command value to the drive circuit 210, and current is supplied from the drive circuit 210 to the electric motor 12.
[0017]
The electric motor terminal voltage detection means 211 detects the terminal voltage of the electric motor 12 and outputs it to the steering angular speed estimation means 212.
The motor current detection means 214 detects the current value supplied from the battery 16 to the drive circuit 210 and outputs it to the steering angular speed estimation means 212 and also to the current feedback control means 208.
The temperature estimation unit 215 estimates the motor temperature from the detected motor current value, and outputs a current limit value corresponding to the temperature to the current limit unit 207.
[0018]
FIG. 5 is a block diagram showing the configuration of the temperature estimating means 215. The calorific value conversion unit 301 squares the detected motor current value I. That is, the calorific value is approximately proportional to I ² R [R is a resistance value], and thus the square of the current value is a parameter proportional to the calorific value.
[0019]
The first low-pass filter 302 outputs the square of the current value through a low-pass filter having a time constant τ1 (for example, 8 to 9 s), and outputs a value Temp1 proportional to the estimated heat generation temperature of the electric motor 12. Here, the low pass filter is represented by the following equation.
Yn = T (X−Yn−1) / τ1 + Yn−1
Yn: Current square value after low-pass filter (for current control cycle)
Yn-1: current square value after low-pass filter (for previous control cycle)
X: Current square value (before filter)
T: The control cycle.
[0020]
The second low-pass filter 303 outputs the square of the current value via a low-pass filter having a time constant τ2 (for example, several hundred s), and outputs a value Temp2 that is proportional to the estimated heat radiation portion temperature of the electric motor 12.
[0021]
The first gain multiplication unit 304 outputs the heat generation portion estimated temperature Temp1 ′ by multiplying the output value Temp1 of the first low-pass filter 302 by the first gain K1.
[0022]
The second gain multiplication unit 305 outputs the heat radiation unit estimated temperature Temp2 ′ by multiplying the output value Temp2 of the second low-pass filter 303 by the second gain K2.
[0023]
Adder 306 adds the heat generating portion estimated temperature and the heat radiating portion estimated temperature and outputs the result as motor estimated temperature Te.
[0024]
FIG. 6 is a map showing the relationship between the estimated temperature and the limit current value. As shown in FIG. 6, when the temperature rises, the current limit value is set to 0 in a high temperature state so that the current limit value is gradually set small in order to prevent seizure due to excessive heat generation. Shall be.
[0025]
Here, the current limiting means 207 in FIG. 4 outputs a current limiting value from the map shown in FIG. 6 based on the estimated temperature. In the electric power steering apparatus according to the first embodiment, since temperature estimation is achieved with high accuracy, only the current limit value logic based on the temperature estimation value needs to be provided. It is possible to simplify the control without requiring any special logic in the case of a sudden rise (corresponding to claim 2).
[0026]
FIG. 7 is a flowchart showing the process of calculating the estimated motor temperature value.
In step 401, the heat generating part current square value Temp1 is calculated, and the process proceeds to step 402.
[0027]
In step 402, the heat sink current square value Temp2 and the heat generating current square value Temp1 are set to the same value, and the process proceeds to step 403.
[0028]
From step 403 to step 406, the current primary delay value of the heat generating portion is calculated, and the process proceeds to step 407. Steps 403 to 406 correspond to the low-pass filter equation described in the following.
[0029]
In step 407, an estimated temperature Temp1 ′ of the heat generating part is calculated by taking into consideration the element of the temperature correction constant in the calculated current primary delay value of the heat generating part (that is, a value proportional to the heat generation amount), and the process proceeds to step 408.
[0030]
From step 408 to step 411, the current primary delay value of the heat radiating section is calculated, and the routine proceeds to step 412. Steps 408 to 411 correspond to the low-pass filter equation described in the following.
[0031]
In step 412, an estimated temperature Temp 2 ′ of the heat radiating part is calculated by taking into consideration the element of the temperature correction constant in the calculated current primary delay value of the heat radiating part (that is, a value proportional to the heat generation amount), and the process proceeds to step 413.
[0032]
In step 413, the estimated temperature Te is calculated from the sum of the heat generating portion estimated temperature and the heat radiating portion estimated temperature, and this control flow ends.
[0033]
FIG. 8 is a diagram showing the difference in current limit value associated with the relationship between the estimated temperature and the actual temperature between the present invention and the conventional example.
FIG. 8A shows the relationship between the estimated temperature and the current limit value in this embodiment. FIG. 8B shows the relationship between the estimated temperature and the current limit value when the actual temperature is higher than the estimated temperature in the conventional example. FIG. 8C shows the relationship between the estimated temperature and the current limit value when the actual temperature is lower than the estimated temperature in the conventional example.
[0034]
In the conventional example, as shown in FIG. 8B, when the estimated temperature is lower than the actual temperature, the current limit value is not easily limited. Therefore, there is a possibility that the temperature further rises and motor burn-in occurs.
[0035]
Further, as shown in FIG. 8C, when the estimated temperature is higher than the actual temperature, the current value is limited although the motor temperature does not actually increase so much. Therefore, there is a problem that a desired steering assist torque cannot be obtained and the driver feels uncomfortable.
[0036]
8A and 8C, the estimated temperature takes an appropriate value in FIG. 8A in the present invention. Therefore, since a current limit value corresponding to the temperature is added, the current value is not excessively limited, and motor burn-in due to temperature rise can be prevented.
[0037]
As described above, in the electric power steering apparatus according to the first embodiment, the heat generation amount of the motor heat generating portion is estimated by the square of the current value extracted through the low-pass filter having a short time constant, and is long. The heat generation amount of the motor heat radiating section is estimated by the square of the current value extracted through the low-pass filter having a time constant, and the sum of the heat generating section estimated temperature and the heat radiating section estimated temperature is determined as the motor estimated temperature. As a result, the estimated motor temperature becomes a temperature close to the actual temperature, so that accurate motor temperature estimation can be performed.
Further, due to deterioration in accuracy of the estimated temperature, it is possible to prevent steering assist shortage due to excessive current limitation and burn-in of the electric motor 12 due to no current limitation being applied.
In addition, since high estimation accuracy can be obtained, it is possible to set the current limit value using only the estimated motor temperature regardless of the lock end abutment condition, and omit the calculation of the current limit for the lock end abutment Thus, the control can be simplified (corresponding to claim 2).
[0038]
In the first embodiment, the present invention is applied to the temperature estimation for the electric motor of the electric power steering apparatus. However, the present invention is not limited to this configuration. For example, the temperature estimation of the drive circuit may be used. In addition to the electric power steering device, the part that generates heat according to the current value is not particularly limited to the application part as long as the time constants of the heat generating part and the heat radiating part are appropriately set.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a temperature estimation configuration of a unit through which a current flows in the first embodiment.
FIG. 2 is a diagram illustrating a relationship between an estimated temperature and an actually measured temperature in the first embodiment.
FIG. 3 is a system diagram showing the overall configuration of the electric power steering apparatus in the first embodiment.
FIG. 4 is a block diagram showing a configuration within a control unit in the first embodiment.
FIG. 5 is a block diagram showing a configuration of temperature estimation means in the first embodiment.
FIG. 6 is a map showing the relationship between temperature and current limit value in the first embodiment.
FIG. 7 is a flowchart showing a process of calculating an estimated motor temperature value in the first embodiment.
FIG. 8 is a diagram illustrating a relationship between an estimated temperature and a current limit value for each temperature estimation accuracy between the present invention and a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Column shaft 3 Universal joint 4 Intermediate shaft 5 Universal joint 6 Input shaft 7 Torque sensor 8 Reducer 9 Pinion shaft 10 Rack shaft 11 Tie rod 12 Electric motor 13 Control unit 14 Vehicle speed sensor 15 Ignition switch 16 Battery 17 Steering wheel

Claims (2)

In the temperature estimation device of the unit through which current flows,
The unit is modeled as a heat generating part that generates heat by current and a heat dissipating part that dissipates heat from the periphery of the unit.
By outputting the square of the current value flowing through the unit through a low-pass filter having a first time constant, the heat generation part estimated temperature is obtained.
By outputting the square of the current value flowing through the unit through a low-pass filter having a second time constant larger than the first time constant, the heat radiation part estimated temperature is obtained.
The estimated temperature of the unit is a sum of the estimated heat generation temperature and the estimated heat dissipation temperature. Motor current detection means for detecting current by an electric motor;
Temperature estimating means for estimating the temperature of the electric motor based on the current value detected by the motor current detecting means;
Current limit value calculating means for calculating a current limit value based on the temperature estimated by the temperature estimating means;
In the electric power steering apparatus with
The electric motor is modeled into a heat generating part that generates heat by current and a heat releasing part that dissipates heat from the periphery of the electric motor,
By outputting the square of the current value flowing through the electric motor through a low-pass filter having a first time constant, the heat generation part estimated temperature is obtained.
By outputting the square of the current value flowing through the electric motor through a low-pass filter having a second time constant larger than the first time constant, it is set as a heat radiation portion estimated temperature,
The electric power steering apparatus according to claim 1, wherein the estimated temperature of the electric motor is a sum of the heat generating portion estimated temperature and the heat radiating portion estimated temperature.

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