JP4513367B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus having a temperature estimation function for a heating element of a motor or a motor drive circuit.

  An electric power steering device that applies a steering assist force to a steering device of an automobile by the rotational force of a motor is a steering assist force applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. Is supposed to be granted. A simple configuration of such an electric power steering apparatus will be described with reference to FIG. A shaft 102 of the steering handle 101 is connected to a tie rod 106 of a steering wheel via a reduction gear 103, universal joints 104a and 104b, and a pinion rack mechanism 105. The shaft 102 is provided with a torque sensor 110 that detects the steering torque of the steering handle 101, and a motor 120 that assists the steering force of the steering handle 101 is connected to the shaft 102 via the reduction gear 103. . In the motor control of the electric power steering device, the control unit 130 controls the motor 120 using the torque value Tr detected by the torque sensor 110, the vehicle speed Vel detected from the vehicle speed sensor 112, and the like as input values. The control unit 130 is mainly composed of a CPU, and motor control is executed by a program. Note that power is supplied to the control unit 130 from the battery 114 via the ignition switch 16 and the contact 113.

  In such an electric power steering device, a heating element such as an FET or IGBT used in a motor 120 or a motor driving circuit (for example, an inverter) that drives the motor 120 generates heat and burns when current is applied. Therefore, the temperature of the motor, the FET, etc. is estimated and the current to be energized is limited or the power supply is shut off to protect them from burning out.

  Conventional techniques relating to such temperature estimation and protection will be described below using patent literature. In Patent Document 1, the ambient temperature detected by the temperature sensor is used as an initial value, and the temperature sensor cannot detect the temperature increase by adding the temperature rise of the motor or FET due to heat generated by the energization current to the initial value (ambient temperature). The absolute temperatures of the motor windings and FET junctions are estimated to protect them from burning. Generally, the temperature sensor is installed at a location away from the motor winding for temperature estimation. In the case of FET, it is often installed on the same substrate where the FET is installed. Since a cooling fin or the like is attached, there is a large temperature difference between the temperature detected by the temperature sensor and the estimated temperature unless a sufficient cooling time is allowed after energization.

  In other words, at the start of energization after a sufficient cooling time, the temperature of the temperature sensor and the estimated temperature of the motor or FET are the same, so the temperature detected by the temperature sensor is used as the initial value for temperature estimation. May be. Such temperature estimation can be expected to be correct if the temperature is continuously estimated, but cannot be expected to be correct in the following cases where temperature estimation cannot be continued.

  For example, if the steering wheel is repeatedly turned for a long time repeatedly when entering the garage, a large current is energized for a considerable period of time, so that the motor and FET generate heat violently and the temperature rises significantly. When the garage entry is completed, the ignition switch (hereinafter referred to as IGSW) is turned OFF, and as a result, the temperature estimation is also temporarily suspended. And after a short time, when the IGSW is turned on again and the steering wheel is switched to resume the operation, the temperature of the motor windings and FET junctions are not yet sufficiently cooled, Temperature estimation is started with the ambient temperature detected by the temperature sensor as an initial value. Since temperature estimation is basically performed by adding the temperature rise due to the energization current to the initial value, the ambient temperature, which is the temperature detected by the temperature sensor, is estimated as the initial value for estimating the temperature of the motor or FET. The estimated temperature is estimated to be lower than the actual motor or FET temperature. As a result, the motor or FET may be burned out.

  Therefore, in Patent Document 2, even if the power supply is temporarily shut down, the temperature is cooled until the estimated temperature becomes equal to or lower than the predetermined temperature, or the temperature difference between the estimated temperature and the temperature detected by the temperature sensor becomes equal to or lower than the predetermined value. The temperature estimation method is used to continue estimation. In the case of garage entry, the temperature estimation is continued until the motor and FET are sufficiently cooled, even if the IGSW operation is performed such that the power supply is temporarily shut off and the power supply is turned on again. .

Further, in Patent Document 3, if the temperature estimation is continued after the power supply is shut off, the battery power supply is consumed. Therefore, the nonvolatile storage means (for example, capable of holding data without supplying the power without supplying the power) , EEPROM) and the power supply is cut off later to interrupt the temperature estimation. When the power is turned on again, the temperature estimation is resumed by reading out the estimated temperature at the time of power-off from the EEPROM as the initial value of the temperature estimation from the EEPROM. Estimated.
JP-A-11-286278 JP 2002-362393 A JP 2001-138828 A

  If it is known in advance to shut off the power supply as described above, the temperature can be estimated by using the power shutdown signal or continuing the temperature estimation or recording the estimated temperature in a nonvolatile storage means such as an EEPROM. It is possible to prevent false estimation. However, when cranking after engine stall (hereinafter referred to as engine stall) occurs, if the amount of power stored in the battery is small, a large current flows at the start of the cell motor, and the voltage of the battery power supply is greatly reduced for a moment. Reset due to momentary voltage drop. As a result, the estimated temperature is reset and the battery voltage is restored immediately after cranking, but the reference temperature is required for the temperature estimation to resume after the restoration. By the way, when an engine stall occurs, it is not always necessary to turn off the power and turn on the power again (an operation to turn on after turning off the IGSW). Therefore, if cranking occurs without turning off the power, it is stored in the EEPROM. The estimated temperature is reset to the reference temperature, and the estimated temperature as the reference temperature is lost. Therefore, if the reference temperature is set to the detected temperature of the temperature sensor, the temperature of the motor or FET has increased due to the operation of the steering wheel before the engine stall, etc. If the temperature is estimated using the low temperature detected by the reference temperature as a reference temperature, there is a problem that the motor and FET are burned out by miscalculating that there is a margin in temperature.

  The present invention has been made for the above-mentioned circumstances, and the object of the present invention is to set the reference temperature to a safe temperature that can prevent burning or the like even when the power supply voltage is reduced in the case of cranking. Thus, an object of the present invention is to provide an electric power steering device capable of temperature estimation capable of preventing the motor and the motor driving circuit from being burned out.

The present invention relates to an electric power steering apparatus including a motor that applies a steering assist force to a steering system of a vehicle, and temperature estimation means that calculates an estimated temperature Ts of a heating element of the motor or a motor drive circuit. The above object of the invention is to provide a non-volatile storage means capable of storing without power supply, an engine speed detection means for detecting an engine speed N of the vehicle and outputting a trigger signal; and a temperature sensor for detecting the ambient temperature Ta of the motor or the heating element, the engine speed detecting means, the Te vehicle engine starting after smell, while the ignition switch is turned on, before SL engine The trigger signal is generated when the rotational speed N becomes equal to or lower than a predetermined rotational speed Ns, and the ambient temperature Ta and the nonvolatile storage means store the trigger signal. The higher one of the estimated temperatures is input to the temperature estimation means as an initial value Ti for calculating the estimated temperature, and the estimated temperature Ts estimated by the temperature estimation means is calculated based on the trigger signal. This is achieved by recording in the sex storage means. Further, the above object of the present invention is to provide a non-volatile storage means capable of storing without power supply, and voltage detection for detecting a power supply voltage value V of the electric power steering device and outputting a trigger signal. and means, and a temperature sensor for detecting the ambient temperature Ta of the motor or the heating element, in a state where the ignition switch is turned on, before Symbol voltage detector was set the power supply voltage V in advance An initial value for generating the trigger signal when the voltage falls below a predetermined constant voltage value Vs and calculating the estimated temperature of the higher of the ambient temperature Ta and the estimated temperature stored in the nonvolatile storage means By inputting Ti to the temperature estimating means and recording the estimated temperature Ts estimated by the temperature estimating means in the nonvolatile storage means based on the trigger signal It is made. The above-mentioned object of the present invention is achieved by recording the estimated temperature Ts when the temperature estimating means ends the estimation in the nonvolatile memory means.

According to the electric power steering apparatus of the present invention, in the case of an engine stall or the like, the engine speed is reduced. Even if the cranking that often occurs after the engine stall occurs and the CPU is reset, the reference value for temperature estimation is higher than the detected temperature instead of the detected temperature of the temperature sensor. Since the estimated temperature recorded in the storage means can be read and the temperature estimation can be continued, the heating element of the motor and the motor drive circuit can be protected from burning . In addition, the motor torque constant can be corrected by the estimated temperature, so that an optimum assist torque can be provided.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a control block diagram according to the present invention, and the inside of the control unit 130 is mainly illustrated. First, basic control of the electric power steering apparatus will be described first, and then temperature estimation, which is a main part of the present invention, will be described.

  The torque value Tr detected by the torque sensor 110 and the vehicle speed Vel detected by the vehicle speed sensor 112 are input to the current command value calculation unit 200, and the current command value Iref is calculated. On the other hand, the motor current Im is detected by the motor current detection circuit 210, and the subtraction unit 202 calculates the deviation ΔI between the current command value Iref and the motor current Im and inputs the deviation ΔI to the proportional integration unit 204. The voltage command value Vref (duty ratio) output from the proportional integration unit 204 is input to the PWM control unit 206, and a PWM signal is output. As the motor drive circuit 208, for example, an inverter composed of switching elements such as FETs is used. The inverter is PWM-controlled based on the PWM signal, the motor current Im is supplied to the motor 120 from the motor drive circuit 208, and the steering assist force desired by the operation handle 101 is applied by the motor 120. Note that power is supplied from the battery 114 to the control unit 130 via the contact 113, and is also a power source for the motor drive circuit 208 and a control power source for the control unit. The above is the basic control of the electric power steering apparatus.

  However, as described above, the winding of the motor 120, the core magnetic body, the FET of the motor drive circuit, and the like change their characteristics or burn out due to overheating, so it is necessary to estimate the temperature and protect it from overheating. As an example of overheat protection, an overheat protection means 224 is provided. The overheat protection means 224 receives the estimated temperature Ts output from the temperature estimation means 10 and outputs a current output from the current command value calculation unit 200 according to the estimated temperature Ts. Overheat protection such as imposing a limit on the command value Iref is implemented. In order to perform overheat protection, the temperature sensor 12 is mounted on a substrate on which an FET constituting an inverter serving as the motor drive circuit 208 is mounted, and is detected as the ambient temperature Ta of the control unit 130.

  In this embodiment, a case where the temperature is estimated by assuming that the ambient temperature of the motor 120 is the same as the ambient temperature Ta detected by the temperature sensor 12 will be described. However, in order to detect the ambient temperature of the motor 120 separately, a temperature sensor is used for the motor 120. For example, if a temperature sensor is separately installed inside the motor 120 and the temperature of the motor 120 is estimated using the detected temperature of the temperature sensor as the ambient temperature of the motor 120, the temperature of the motor is more accurate than in this embodiment. Can be estimated.

  First, an embodiment will be described in which vehicle state detection means for detecting a vehicle state and outputting a trigger signal detects the engine speed, determines whether the engine speed is slower than a predetermined speed, and outputs a trigger signal.

  The engine speed N detected by the engine speed detecting means 14 and the IG signal indicating whether the ignition switch (hereinafter referred to as IGSW) 16 is turned on or off from the ignition switch (IGSW) 16 and the ambient temperature Ta detected by the temperature sensor 12 are the temperature. The temperature is input to the temperature estimation unit 10 that is an estimation means. In addition, an EEPROM 18 as a non-volatile storage means that can be stored without power supply is arranged in the control unit 130, and the estimated temperature Ts estimated by the temperature estimation unit 10 is written to or written in the EEPROM 18. The estimated temperature Ts is read from the EEPROM 18.

  The operation of the embodiment configured as described above will be described with reference to the flowcharts of FIGS.

  The flowchart of FIG. 2 is a basic flowchart of temperature estimation. First, when the IGSW 16 is turned on, an IG ON signal is read (S11), and the CPU is initialized (S12). Next, the temperature estimation calculation is initialized (S13). The temperature estimation initialization process for initializing the temperature estimation calculation will be described in detail later with reference to FIG. Next, assist control of the electric power steering device is executed (S14). Next, a temperature estimation calculation for estimating the temperature and calculating the estimated temperature Ts is executed (S15). This temperature estimation calculation process will be described later in detail with reference to FIG.

  Next, overheat protection processing is executed based on the calculated estimated temperature Ts (S16). As an example of the overheat protection method, it is determined whether or not the estimated temperature Ts is higher than the protection temperature for overheat protection, for example, 180 ° C. If the estimated temperature Ts is higher than the protection temperature 180 ° C., the current command value Iref There are also methods of limiting the current flowing to the motor and FET, or shutting off the current to the motor by turning off all FETs.

  Next, it is determined whether the IGSW 16 is OFF (S17). If IGSW is ON, the process returns to before the assist control (S16), and steps S14, S15, and S16 are repeated. If the IGSW 16 is OFF, a temperature estimation end process is executed (S18).

  First, the temperature estimation initialization process described above will be described with reference to FIG. The ambient temperature Ta detected by the temperature sensor 12 is read (S131). The recording temperature Tep stored in the next EEPROM 18 is read (S132). It is determined which of the ambient temperature Ta and the recording temperature Tep of the EEPROM 18 is higher (S133). If the ambient temperature Ta is higher than the recording temperature Tep, the ambient temperature Ta is used as the initial value Ti for temperature estimation (S134). If the recording temperature Tep is higher than the ambient temperature Ta, the recording temperature Tep is used as the initial value Ti for temperature estimation (S135). Thus, by using the higher one of the ambient temperatures Ta as the initial value of the recording temperature Tep, it is possible to prevent the motor and FET from being burned by the principle of temperature estimation described later.

  The temperature estimation calculation process will be described with reference to FIG. First, an estimated temperature value Ts is calculated (S151). As an example of this temperature estimation method, the absolute temperature of the motor or FET is estimated by adding a temperature increase ΔT generated by the energizing current to the initial value with the initial value Ti as a reference. There are various calculation methods for adding the temperature rise ΔT to the initial value Ti, which are disclosed in, for example, a patent document (Japanese Patent Laid-Open No. 10-10093).

  Next, the engine speed N detected by the engine speed detecting means 14 is read (S152). Next, it is determined whether the engine speed N has reached a predetermined speed Ns set in advance, for example, 500 rpm or less (determines whether the engine speed N has crossed 500 rpm from the high speed side to the low speed side). (S153). When the engine speed N is higher than the predetermined speed Ns, the temperature estimation calculation process is terminated as it is. However, if the engine speed Ns is lower than the predetermined speed Ns, the estimated temperature Ts is written in the EEPROM 18 as the recording temperature Tep, assuming that the trigger signal of the vehicle state detecting means is output (S154).

  It is an important point of the present invention to write the estimated temperature Ts in the EEPROM when the engine speed is lower than the predetermined speed. That is, even if the power supply voltage drop due to cranking after the engine stall occurs, the estimated temperature Ts is already written in the EEPROM as the recording temperature Tep. Therefore, even if the CPU is reset due to the power supply voltage drop, the estimated temperature Ts is lost. It will never be. Further, even if the IGSW is turned on again and the temperature estimation is restarted before the motor or FET is sufficiently cooled, if the recording temperature Tep is higher than the ambient temperature Ta, the high temperature recording temperature Tep is used as the initial value Ti for temperature estimation. Therefore, the temperature of the motor or FET can be correctly estimated, and the motor or FET can be protected from burning.

  The temperature estimation end process will be described with reference to FIG. When the temperature estimation is finished immediately after the IGSW 16 is turned off, the initial value Ti is the ambient temperature detected by the temperature sensor when the IGSW 16 is turned on and the temperature estimation is resumed after the IGSW 16 is turned off before the motor or FET is sufficiently cooled. This is because there is a risk of burning the motor and FET using Ta. After the IGSW 16 is turned off (S17), for example, the temperature difference between the estimated temperature Ts and the ambient temperature Ta detected by the temperature sensor is 10 ° C. (denoted as ΔT10) or less as a determination condition that can end the temperature estimation continuation. Continue temperature estimation until

  Therefore, the temperature estimated value is calculated (S191). It is determined whether the temperature difference between the estimated temperature Ts and the ambient temperature Ta detected by the temperature sensor is ΔT10 or less (S192). If the temperature difference ΔT is equal to or greater than ΔT10 (YES), the temperature estimation is continued. On the other hand, if the temperature difference ΔT is equal to or smaller than ΔT10, the temperature estimation is finished and a predetermined initial temperature used as an initial value of the temperature estimation calculation, for example, −40 ° C. (the lowest temperature that can be detected by the temperature sensor. (Denoted as (−40)) is written as the recording temperature Tep in the EEPROM (S193), and the process ends. This step is to use the ambient temperature Ta detected by the temperature sensor as the initial value Ti as the initial value of the temperature estimation in step S133 in the normal temperature estimation in which the IGSW is turned on after the motor and FET are sufficiently cooled. It is a treatment.

  If the temperature estimation end processing is performed in this manner, the motor or FET can be protected from burning even if the IGSW is turned on before the motor or FET is sufficiently cooled after the IGSW is turned off.

  Next, an embodiment will be described in which vehicle state detecting means for detecting a vehicle state and outputting a trigger signal detects a power supply voltage value, determines whether or not the voltage is lower than a predetermined voltage value, and outputs a trigger signal.

  A voltage detection unit 20 that receives the voltage of the battery 114 is provided, and the voltage detection unit 20 inputs the detected power supply voltage value V to the temperature estimation unit 10.

  FIG. 6 shows a flowchart of the temperature estimation calculation when the vehicle state is detected and the power supply voltage value V is used as a trigger signal. Also in the second embodiment, the temperature estimation basic shown in FIG. 2, the temperature estimation initialization flow shown in FIG. 3, and the temperature estimation end processing flow shown in FIG. 5 are the same as those in the first embodiment. That is, instead of the temperature estimation calculation when the engine speed of FIG. 4 of the first embodiment is used, the temperature estimation calculation when the power supply voltage value shown in FIG. 6 is used is executed.

  First, the estimated temperature Ts is calculated by performing the temperature estimation calculation (S151A). Next, the power supply voltage value V detected by the voltage detection means 20 is compared with a predetermined voltage value Vs set in advance, for example, 7 V (S153A). If the power supply voltage value V is higher than 7V, the temperature estimation calculation process is terminated. However, if the power supply voltage value V is lower than 7V, the estimated temperature Ts is written as the recording temperature Tep in the EEPROM, assuming that the trigger signal of the vehicle state detection means is output (S154A).

  As described above, if the estimated temperature Ts is recorded in the EEPROM, the estimated temperature Ts can be recorded in the EEPROM before the CPU is reset even when the CPU is reset due to a decrease in power supply voltage due to cranking. Even if IGSW is turned on immediately after cranking, the temperature of the motor or FET that is not sufficiently cooled can be detected correctly and the motor or FET can be prevented from being burned out.

  When the estimated temperature is written to the EEPROM due to the power supply voltage drop, the predetermined voltage value Vs is set sufficiently high so that the writing can be completed normally before the CPU is reset, or the CPU and EEPROM are written. It goes without saying that the power supply should be strengthened as much as possible.

  As described above, according to the present invention, even if a CPU reset occurs due to a power supply voltage drop due to cranking after engine stall, if the engine speed is detected and the engine falls below a predetermined speed, If the voltage falls below a predetermined voltage value, the estimated temperature Ts that has been estimated is recorded in an EEPROM that can be stored even when power is not supplied, and the temperature read from the EEPROM when the IGSW 16 is turned on again. Since the higher temperature is used as the initial value of the temperature estimation calculation with the ambient temperature Ta detected by the temperature sensor and the temperature sensor, it is safe that the motor and FET are not miscalculated as low temperatures and burned out. An electric power steering device can be provided. In particular, even if the IGSW 16 is not turned off after the engine stall, in the present invention, the engine speed is detected or the power supply voltage value is detected and the EEPROM is written, so that the estimated temperature Ts being calculated is recorded reliably. There is an effect that can be done.

  The estimated temperature Ts of the motor can be used not only for overheat protection but also for correction of the torque constant (Kt), thereby enabling generation of optimal assist torque. Specifically, in FIG. 1, the estimated temperature Ts estimated by the temperature estimating means 10 is input to the torque constant (Kt) correcting means 226 of the motor 120, and the torque constant is calculated by the estimated temperature Ts in the torque constant correcting means 226. The corrected torque constant is input to the current command value calculation unit 200. As a result, the current command value Iref for generating the optimum assist torque is calculated by the current command value calculation unit 200. As described above, the optimum assist torque can be provided by correcting the torque constant using the estimated temperature Ts of the motor.

  In the above embodiment, the FET has been described as an example of the heating element of the motor drive circuit. However, it may be an IGBT instead of an FET, and if there are parts or parts that are hotter than the switching element. Needless to say, the parts and parts are to be protected.

It is a control block diagram concerning the present invention. It is a basic flowchart concerning the present invention. It is a flowchart of temperature estimation initialization. It is a flowchart of the temperature estimation calculation at the time of using an engine speed. It is a flowchart of a temperature estimation end process. It is a flowchart of the temperature estimation calculation at the time of using a power supply voltage value. It is a block diagram of an electric power steering device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Temperature estimation means 12 Temperature sensor 14 Engine speed detection means 16 Ignition switch 18 EEPROM
20 Voltage detection means 224 Overheat protection means 226 Torque constant correction means

Claims (4)

An electric power steering apparatus comprising: a motor that applies a steering assist force to a steering system of a vehicle; and a temperature estimation unit that calculates an estimated temperature Ts of a heating element of the motor or a motor drive circuit.
Non-volatile storage means capable of storing without power supply, engine speed detection means for detecting the engine speed N of the vehicle and outputting a trigger signal, and the motor or the heating element A temperature sensor for detecting the ambient temperature Ta,
The engine speed detecting means, the Te vehicle engine starting after smell, while the ignition switch is on, the trigger signal when the front SL engine rotational speed N is equal to or less than a preset predetermined rotation speed Ns The higher one of the ambient temperature Ta and the estimated temperature stored in the nonvolatile storage means is input to the temperature estimation means as an initial value Ti for calculating the estimated temperature, and the temperature estimation The estimated temperature Ts estimated by the means is recorded in the nonvolatile storage means based on the trigger signal. 2. The electric power steering apparatus according to claim 1, wherein the temperature estimation means records the estimated temperature Ts when the estimation is completed in the nonvolatile storage means. An electric power steering apparatus comprising: a motor that applies a steering assist force to a steering system of a vehicle; and a temperature estimation unit that calculates an estimated temperature Ts of a heating element of the motor or a motor drive circuit.
Non-volatile storage means capable of storing without power supply, voltage detection means for detecting a power supply voltage value V of the electric power steering device and outputting a trigger signal, the motor or the heating element and a temperature sensor for detecting the ambient temperature Ta of,
In a state where the ignition switch is turned on, before Symbol voltage detecting means to said trigger signal is generated when the power supply voltage value V becomes equal to or less than a preset predetermined constant voltage value Vs, the non and the ambient temperature Ta The higher one of the estimated temperatures stored in the sex storage means is input to the temperature estimating means as the initial value Ti for calculating the estimated temperature, and the estimated temperature Ts estimated by the temperature estimating means is used as the initial temperature Ti. An electric power steering apparatus characterized in that recording is performed in the nonvolatile storage means based on a trigger signal. The electric power steering apparatus according to claim 3, wherein the estimated temperature Ts when the temperature estimation means ends the estimation is recorded in the nonvolatile storage means.

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