JP2008195246A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To take full advantage of a steering function of an electric motor, such as a steering assist function, by reducing frequency of use of temporary estimated temperature data. <P>SOLUTION: A microcomputer stores the motor's estimated temperature data when an assist control is complete in an EEPROM, and uses the data as a default of operation of motor estimated temperature by reading the data when the next assist control is started. The microcomputer writes the temporary estimated temperature data in the EEPROM during the assist control to be prepared for reset due to reduction in supply voltage. The temporary estimated temperature data are not written in the EEPROM in such a situation that the electric motor is not high in temperature since the temporary estimated temperature data are supposed to be written when a current Ix flowing through the electric motor becomes larger than a set current value Ith. Accordingly, it is possible to take full advantage of the steering function of the electric motor while maintaining an overheat prevention function. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steering apparatus such as an electric power steering apparatus that generates a steering torque by an electric motor.

  Conventionally, for example, an electric power steering device is known as this type of steering device. The electric power steering apparatus includes an electric motor that generates a steering assist torque in response to a steering operation of a steering wheel, and an electronic control unit that controls energization of the electric motor. The electronic control unit includes an arithmetic circuit whose main part is composed of a microcomputer and calculates a target energization control amount of the electric motor, and a motor drive circuit that energizes the electric motor in response to a command signal from the arithmetic circuit.

  The arithmetic circuit, for example, calculates a target assist torque value based on the steering torque acting on the steering wheel detected by the steering torque sensor and the vehicle speed detected by the vehicle speed sensor, and a target current value corresponding to the target assist torque value; A voltage command value to be applied to the electric motor is calculated according to the deviation from the actual current value actually flowing through the electric motor detected by the current sensor, and is output to the motor drive circuit. The motor drive circuit turns on / off the switching circuit at a duty ratio corresponding to the voltage command value from the arithmetic circuit, and applies a voltage corresponding to the voltage command value to the electric motor.

The direction of the steered wheels is changed by the sum of the steering assist torque generated by the electric motor and the steering torque applied to the steering wheel by the driver.
Hereinafter, the control performed by such an electronic control unit is referred to as assist control.

  In such an electric power steering device, the temperature of the electric motor or the motor drive circuit is monitored in order to prevent the electric motor or the motor drive circuit from being damaged due to heat generation, and the monitor temperature exceeds the set temperature for preventing overheating. Restricts the current flowing to the electric motor. In this case, the temperature of the electric motor (e.g., the temperature of the brush portion at a high temperature) is difficult to directly measure with a temperature sensor, and is estimated by calculation based on the energized state. Such temperature estimation techniques for electric motors are proposed in Patent Documents 1 to 4.

This temperature estimation process is repeatedly performed during assist control. When the assist control ends, estimated temperature data corresponding to the estimated temperature at that time is stored in the nonvolatile memory. The estimated temperature data stored in the non-volatile memory is used as the initial estimated temperature when the next assist control is started. In other words, since the estimated temperature of the electric motor is obtained by adding the heat generated by energization to the estimated temperature at the start of assist (initial estimated temperature), the estimated calculation requires the initial estimated temperature at the start of assist. Therefore, data representing the estimated temperature at the end of the assist control is stored in the nonvolatile memory, and when the next assist control is started, the estimated temperature data stored in the nonvolatile memory is read and used as the initial estimated temperature. Used for estimation calculation.
JP 2002-212425 A JP 2001-138929 A JP-A-2005-319822 JP 2005-12888

  By the way, since the arithmetic circuit of the electronic control unit that performs such assist control is constituted by a microcomputer, it is reset when the output voltage of the in-vehicle battery falls below the minimum operating voltage of the microcomputer. For example, when the engine is restarted after engine control is started after the assist control is started, the microcomputer is reset due to a temporary voltage drop of the battery, particularly when the battery is deteriorated. As a result, the assist control cannot be completed normally. Therefore, the estimated temperature data at that time cannot be written in the nonvolatile memory.

  Therefore, in the conventional electric power steering apparatus, in preparation for such a situation that the estimated temperature information is lost due to the resetting of the microcomputer, the temporary estimated temperature data (fixed value) is stored in the nonvolatile memory immediately after the start of the assist control. I try to overwrite it. Therefore, even if the microcomputer is reset during the assist control, the temporary estimated temperature data is read from the non-volatile memory at the start of the next assist control, and the temporary estimated temperature represented by the temporary estimated temperature data is set. The temperature estimation calculation can be performed with the initial estimated temperature.

  The temporary estimated temperature is set high so that the overheating of the electric motor can be prevented regardless of the situation in which the assist control is started. The timing for storing (overwriting) the temporary estimated temperature data in the nonvolatile memory is performed after a very short time has elapsed since the start of the assist control. Therefore, in the case where the microcomputer is reset after the assist control is once started and then the assist control is resumed, the electric motor current is limited by the estimated temperature calculated based on the temporary estimated temperature data. . For this reason, even if the electric motor is not actually overheated, the current limitation of the electric motor works excessively and the handle operation becomes heavy. In such a situation, the driver is misunderstood as having a malfunction.

  The present invention has been made to cope with the above-described problem, and an object thereof is to make full use of a steering function by an electric motor such as a steering assist function while maintaining an overheat prevention function.

  In order to achieve the above object, the present invention is characterized in that an electric motor for generating a steering torque, a temperature estimating means for estimating the temperature of the electric motor by sequential calculation, and a steering detecting means for detecting the steering state of the steering wheel. And calculating a target energization control amount of the electric motor based on the detected steering state of the steering wheel while applying a current limit based on the estimated temperature, and according to the calculated target energization control amount Motor control means for driving and controlling the electric motor, non-volatile storage means for storing estimated temperature data relating to the estimated temperature of the electric motor, and estimated by the temperature estimating means at the end of drive control of the electric motor The estimated temperature data relating to the estimated temperature of the electric motor is written in the nonvolatile storage means, and the next drive of the electric motor is performed. Data read / write means for reading estimated temperature data stored in the nonvolatile storage means at the start of control, and estimated temperature data stored in the nonvolatile storage means after the drive control of the electric motor is started, Temporary estimated temperature data overwriting means for rewriting the preset temporary estimated temperature data, and the temperature estimating means uses the estimated temperature data read by the data read / write means at the start of drive control of the electric motor. In the steering device that estimates the temperature of the electric motor by sequential calculation, the temporary estimated temperature data overwriting means is configured such that the energization current value to the electric motor is preset after the drive control of the electric motor is started. When it is determined that the set current value is exceeded, the estimated temperature data stored in the non-volatile storage means is In rewriting the estimated temperature data.

  In this invention, the temperature estimation means estimates the temperature of the electric motor by sequential calculation, and the motor control means applies a current limit based on this estimated temperature while applying the target current control amount of the electric motor based on the steering state of the steering wheel. And the electric motor is driven and controlled according to the target energization control amount. Thus, steering torque is generated by the drive control of the electric motor. At this time, the electric motor is prevented from being overheated by current limitation based on the estimated temperature.

  The data read / write means writes the estimated temperature data of the electric motor estimated at the end of the drive control of the electric motor to the nonvolatile storage means, and the estimated temperature data stored in the nonvolatile storage means at the next drive control of the electric motor Is read. The read estimated temperature data is used for temperature estimation of the electric motor.

  If a power supply abnormality occurs during drive control of the electric motor, the drive control of the electric motor cannot be terminated normally by resetting the microcomputer, and the estimated temperature data relating to the estimated temperature that has been sequentially calculated by the temperature estimation means is non-volatile. It becomes impossible to overwrite the sex memory means. In preparation for such a situation, the temporary estimated temperature data overwriting means rewrites the estimated temperature data stored in the nonvolatile storage means to preset temporary estimated temperature data after the drive control of the electric motor is started. This temporary estimated temperature is a temperature set higher in consideration of overheating prevention, that is, a set temperature for overheating prevention.

  If the drive control of the electric motor is normally completed without causing a power supply abnormality or the like, the estimated temperature data at that time is overwritten in the nonvolatile storage means. Therefore, the temporary estimated temperature data stored in the nonvolatile storage means is rewritten to estimated temperature data related to the estimated temperature at the end of the electric motor drive control. In this case, at the start of the next electric motor drive control, the estimated temperature data at the end of the previous electric motor drive control is read from the nonvolatile storage means.

  On the other hand, if a power supply abnormality occurs during the drive control of the electric motor, the drive control of the electric motor cannot be terminated normally, and the estimated temperature data relating to the estimated temperature sequentially calculated by the temperature estimating means is non-volatile. The sex memory cannot be overwritten. Therefore, the temporary estimated temperature data remains as it is in the nonvolatile storage means, and is used for temperature estimation calculation at the next drive control of the electric motor. In this case, the temperature estimating means sequentially calculates the temperature of the electric motor based on the high estimated temperature set for preventing overheating. For this reason, even if the temperature of the electric motor is actually low, the current limit is applied according to the higher estimated temperature.

  In order to maintain the overheat prevention function of the electric motor, the temporary estimated temperature cannot be lowered. Therefore, the temporary estimated temperature data overwriting means sets the timing for writing the temporary estimated temperature data to the non-volatile storage means in which the energization current value to the electric motor is set in advance after the drive control of the electric motor is started. This is performed when it is determined that the current value has been exceeded, so that temporary estimated temperature data is not written at an earlier stage than necessary. In other words, the temporary estimated temperature data is not written immediately after the drive control of the electric motor is started, but is written when it is determined that a current equal to or greater than the set current value has actually flowed into the electric motor.

  In general, power supply abnormality to the steering device (decrease in power supply voltage) frequently occurs when the engine is started. Therefore, if the engine is restarted after the electric motor drive control is started, the microcomputer may be reset due to a temporary drop in the power supply voltage.

  Even in such a case, according to the present invention, temporary estimated temperature data is written in the non-volatile storage means as long as a current equal to or higher than the set current value does not flow through the electric motor before resetting. Absent. For this reason, when the drive control of the first electric motor after the reset is started, the temporary estimated temperature data is not read, but the estimated temperature data at the end of the motor drive control before the reset occurs is read. Become. Therefore, excessive current limitation does not work, and the steering function by the electric motor can be used effectively.

On the other hand, if a current equal to or greater than the set current value flows in the electric motor before resetting, temporary estimated temperature data is written to the nonvolatile storage means at that stage, so the first electric motor of the first electric motor after the reset is reset. At the time of drive control, the motor temperature is calculated based on the temporary estimated temperature data, so that overheating can be reliably prevented.
Therefore, according to the present invention, it is possible to make full use of the steering function by the electric motor by maintaining the overheat prevention function and reducing the frequency at which the temporary estimated temperature data is used more than necessary.

  The estimated temperature data relating to the estimated temperature in the present invention includes not only data representing the estimated temperature itself but also data from which the estimated temperature can be derived.

  The steering detection means of the present invention detects the steering state of the steering handle. For example, the steering torque detection means for detecting the steering torque applied to the steering handle, and the steering angle for detecting the steering angle of the steering handle. Examples include detection means, steering angular velocity detection means for detecting the steering angular velocity of the steering wheel, and the like, as long as at least one of them is provided.

  The temperature estimation means of the present invention sequentially calculates the temperature of the electric motor based on, for example, the estimated temperature data read from the nonvolatile storage means by the data read / write means and the current value energized to the electric motor. Can be estimated.

  Further, the steering torque generated by the electric motor in the present invention includes a steering assist torque that works in a direction that assists the steering operation of the steering wheel, a steering reaction torque that works in a direction that hinders the steering operation of the steering wheel, and the steering operation of the driver It means torque required for steering control, such as steering torque for steering steered wheels without using force. Therefore, the steering device of the present invention can be applied to an electric power steering device, a steering-by-wire steering device, and the like.

  Another feature of the present invention is that whether or not the current value supplied to the electric motor is equal to or greater than a preset current value is detected by detecting the current flowing through the electric motor or by the motor control means. Is performed based on the target energization control amount calculated by.

  According to the present invention, the current value actually flowing to the electric motor or the current value supplied to the electric motor based on the target current control amount calculated by the motor control means becomes equal to or greater than a preset current value. Therefore, it is possible to make an accurate determination.

  Another feature of the present invention is that the set current value is set to a value at which the electric motor does not exceed a predetermined reference temperature for overheating prevention even if the current of the set current value is continuously supplied to the electric motor. It is in.

  Even after the drive control of the electric motor is started, the motor temperature is suppressed to a temperature lower than the overheat prevention reference temperature in a period in which the motor current does not exceed the set current value. That is, overheating can be prevented without writing temporary estimated temperature data in the nonvolatile storage means during this period. Therefore, according to the present invention, it is possible to write temporary estimated temperature data to the nonvolatile storage means at an appropriate timing, and it is possible to satisfactorily achieve both a reduction in the frequency with which the temporary estimated temperature data is used and an overheat prevention function. I can.

  Another feature of the present invention is that the determination as to whether or not the energization current value to the electric motor is equal to or greater than a preset current value is based on the steering torque acting on the steering wheel, the steering angle of the steering wheel, The estimation is performed based on the steering angular velocity of the steering wheel.

  In the present invention, the energization amount of the electric motor is controlled by the motor control means based on the steering state of the steering wheel. Therefore, the motor current value can be estimated to some extent from the steering state of the steering wheel without detecting the motor current. Therefore, in the present invention, the energization state of the electric motor is estimated based on the steering torque, the steering angle, or the steering angular velocity, that is, the steering state of the steering handle.

  In this case, for example, when the steering torque detecting means for detecting the steering torque acting on the steering handle is provided as the steering detecting means, the temporary estimated temperature data overwriting means performs the steering after the drive control of the electric motor is started. When it is determined that the torque is equal to or higher than a preset torque, the estimated temperature data stored in the nonvolatile storage means is rewritten with temporary estimated temperature data.

  Further, for example, when the steering angle detecting means for detecting the steering angle of the steering wheel is provided as the steering detecting means, the temporary estimated temperature data overwriting means has the steering angle after the drive control of the electric motor is started. When it is determined that the steering angle is equal to or larger than a preset steering angle, the estimated temperature data stored in the non-volatile storage means is rewritten to temporary estimated temperature data.

Further, for example, when the steering angular velocity detecting means for detecting the steering angular velocity of the steering wheel is provided as the steering detecting means, the temporary estimated temperature data overwriting means has the steering angular velocity after the drive control of the electric motor is started. When it is determined that the steering angular velocity is higher than the preset steering angular velocity, the estimated temperature data stored in the nonvolatile storage means is rewritten to temporary estimated temperature data.
In addition, the comparison judgment with the set values of the energization current, the steering torque, the steering angle, and the steering angular velocity described above is performed with a magnitude (absolute value) that is not related to the steering direction.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows an electric power steering device for a vehicle as an embodiment of a steering device of the present invention, and FIG. 2 schematically shows a control system and a power supply system in the electric power steering device.

  The electric power steering apparatus 1 for a vehicle can be broadly divided into a steering mechanism 10 that steers steered wheels by steering a steering handle 11, an electric motor 15 that is assembled to the steering mechanism 10 and generates a steering assist torque, and a steering handle 11. The electronic control unit 30 controls the operation of the electric motor 15 in accordance with the steering state.

  The steering mechanism 10 is a mechanism for steering the left and right front wheels FW1 and FW2 by a rotating operation of the steering handle 11, and includes a steering shaft 12 connected so as to rotate integrally with the upper end of the steering handle 11. A pinion gear 13 is connected to the lower end of the steering shaft 12 so as to rotate integrally. The pinion gear 13 meshes with rack teeth formed on the rack bar 14 to constitute a rack and pinion mechanism. Left and right front wheels FW1, FW2 are steerably connected to both ends of the rack bar 14 via tie rods and knuckle arms (not shown). The left and right front wheels FW1 and FW2 are steered left and right in accordance with the axial displacement of the rack bar 14 accompanying the rotation of the steering shaft 12 around the axis. Accordingly, the steering mechanism 10 is constituted by the steering handle 11, the steering shaft 12, the rack and pinion mechanisms 13, 14, the tie rod, the knuckle arm, and the like.

  An electric motor 15 for steering assist is assembled to the rack bar 14. In the present embodiment, a single-phase brush motor is used. The rotating shaft of the electric motor 15 is connected to the rack bar 14 via the ball screw mechanism 16 so that power can be transmitted, and assists the steering of the left and right front wheels FW1, FW2 by the rotation. The ball screw mechanism 16 functions as a speed reducer and a rotation-linear converter. The ball screw mechanism 16 decelerates the rotation of the electric motor 15 and converts it into a linear motion and transmits it to the rack bar 14. Further, instead of assembling the electric motor 15 to the rack bar 14, the electric motor 15 is assembled to the steering shaft 12, and the rotation of the electric motor 15 is transmitted to the steering shaft 12 via the speed reducer so that the shaft 12 is axially connected. You may comprise so that it may drive around.

  A steering torque sensor 21 is provided on the steering shaft 12. The steering torque sensor 21 outputs a signal corresponding to the steering torque that acts on the steering shaft 12 by the turning operation of the steering handle 11. Hereinafter, the value of the steering torque detected by the signal output from the steering torque sensor 21 is referred to as steering torque Th. As for the steering torque Th, the operation direction of the steering wheel 11 is identified by a positive or negative value. In the present embodiment, the steering torque Th when the steering handle 11 is steered in the right direction is indicated by a positive value, and the steering torque Th when the steering handle 11 is steered in the left direction is indicated by a negative value. Therefore, the magnitude of the steering torque Th is the magnitude of its absolute value.

  The electric motor 15 is provided with a rotation angle sensor 23. The rotation angle sensor 23 is incorporated in the electric motor 15 and outputs a detection signal corresponding to the rotation angle position of the rotor of the electric motor 15. The detection signal of the rotation angle sensor 23 is used to calculate the rotation angle and rotation angular velocity of the electric motor 15. On the other hand, since the rotation angle of the electric motor 15 is proportional to the steering angle of the steering handle 11, it is commonly used as the steering angle of the steering handle 11. Further, the rotational angular velocity obtained by differentiating the rotational angle of the electric motor 15 with respect to time is proportional to the steering angular velocity of the steering handle 11, and thus is commonly used as the steering angular velocity of the steering handle 11.

Hereinafter, the value of the steering angle of the steering wheel 11 detected by the output signal of the rotation angle sensor 23 is referred to as a steering angle θ, and the value of the steering angular velocity obtained by time differentiation of the steering angle θ is referred to as a steering angular velocity ω. Note that the steering angle θ and the steering angular velocity ω are calculated by the microcomputer 41 of the electronic control circuit 40 described later.
The steering angle θ represents the steering angle in the right direction and the left direction with respect to the neutral position of the steering handle 11 by using positive and negative values. In the present embodiment, the neutral position of the steering handle 11 is set to “0”, the steering angle in the right direction with respect to the neutral position is indicated by a positive value, and the steering angle in the left direction with respect to the neutral position is indicated by a negative value.

Next, the electronic control unit 30 will be described with reference to FIG.
The electronic control unit 30 (hereinafter referred to as ECU 30) calculates a target energization control amount of the electric motor 15, and drives the electric motor 15 with the calculated target energization control amount, and an electronic control circuit And a motor drive circuit 32 that drives the electric motor 15 in accordance with a control command from 40.
The electronic control circuit 40 includes a microcomputer 41 (hereinafter referred to as a microcomputer 41) composed of a CPU, ROM, RAM, and the like, an input interface 42, an output interface 43, and an EEPROM (Electric Erasable PROM) 44. The ROM in the microcomputer 41 stores a control program, various data, and the like, which will be described later.

The input interface 42 is connected to the microcomputer 41 via a bus, and is connected to the steering torque sensor 21, the vehicle speed sensor 22, the rotation angle sensor 23, the current sensor 24, and the temperature sensor 25. A detection signal is supplied. The input interface 42 includes an A / D converter (not shown) that generates a digital signal corresponding to the power supply voltage from the power supply supplied to the electronic control circuit 40 and supplies the digital signal to the microcomputer 41. Therefore, this A / D converter also has a function as a power supply voltage detection sensor.
The vehicle speed sensor 22 outputs a vehicle speed signal that represents the traveling speed vx of the vehicle.

  The output interface 43 is connected to the microcomputer 41 via a bus, and is connected to the motor drive circuit 32 and a normally open type power supply relay 57, and these conductions are based on a command from the microcomputer 41. A signal for changing the state is transmitted. The EEPROM 44 is a non-volatile storage unit that stores and holds data even when the power supply from the power supply device 50 is not received, and is connected to the microcomputer 41 via a bus.

  The motor drive circuit 32 includes four switching elements Tr1 to Tr4 made of MOSFETs each having a gate connected to the output interface 43, and two resistors R1 and R2. One end of the resistor R1 is connected to the power supply line 55 of the power supply device 50, and the other end of the resistor R1 is connected to the sources of the switching elements Tr1 and Tr2. The drains of the switching elements Tr1 and Tr2 are connected to the sources of the switching elements Tr3 and Tr4, respectively, and the drains of the switching elements Tr3 and Tr4 are grounded via a resistor R2. The switching elements Tr1 and Tr3 are connected to one pole of the electric motor 15, and the switching elements Tr2 and Tr4 are connected to the other pole of the electric motor 15. A current sensor 24 is provided between the resistor R <b> 2 and the switching elements Tr <b> 3 and Tr <b> 4 and outputs a detection signal representing a current value Ix flowing through the electric motor 15 to the input interface 42.

  In the motor drive circuit 32, when the switching elements Tr1 and Tr4 are selectively turned on (on state) in a state where power is supplied, a current in a predetermined direction flows through the electric motor 15 and the motor 15 When the motor rotates clockwise and the switching elements Tr2 and Tr3 are selectively turned on, a current in the direction opposite to the predetermined direction flows through the electric motor 15 and the motor 15 rotates counterclockwise.

  Further, the motor drive circuit 32 is provided with a temperature sensor 25 constituted by a thermistor or the like for detecting the temperature of the circuit board on which the switching elements Tr1 to Tr4 are provided. The temperature sensor 25 outputs a signal representing the substrate temperature Tb. The motor drive circuit 32 is generally disposed at a position farther from the engine (not shown) than the electric motor 15 because of the heat resistance strength. This particularly means that the influence of the heat generation of the engine on the temperature rise of the motor drive circuit 32 is smaller than the influence of the heat generation of the engine on the temperature rise of the electric motor 15.

Next, a power supply circuit configuration to the electronic control circuit 40 and the motor drive circuit 32 will be described with reference to FIG.
The ECU 30 is supplied with power from a power supply device 50 including a battery 51 and an alternator 52 that generates electric power by rotating the engine. As the battery 51, a general in-vehicle battery having a rated output voltage of 12V is used.

  The power supply device 50 commonly supplies power not only to the electric power steering device 1 but also to other in-vehicle electric loads including an engine starter and the like. An ignition switch 60 is connected to the power supply source line 53 connected to the power supply terminal (+ terminal) of the battery 51. The ECU 30 includes a control power supply line 54 that supplies power to the electronic control circuit 40 from the secondary side of the ignition switch 60, and a drive power supply that supplies power mainly to the motor drive circuit 32 from the primary side (power side) of the ignition switch 60. And a supply line 55.

  The control power supply line 54 is provided with a diode 56. The diode 56 is a backflow prevention element that is provided with the cathode facing the electronic control circuit 40 and the anode facing the power supply device 50 and can be energized only in the power supply direction. The drive power supply line 55 is provided with a power relay 57 in the middle thereof. The power supply relay 57 is turned on by a control signal from the electronic control circuit 40 to form a power supply circuit to the electric motor 15.

  The drive power supply line 55 is connected to the control power supply line 54 via a connecting line 58 on the load side of the power relay 57. The connection line 58 is connected between the diode 56 and the electronic control circuit 40 in the control power supply line 54. A diode 59 is connected to the connecting line 58. The diode 59 is provided with a cathode facing the control power supply line 54 side and an anode facing the drive power supply line 55 side, and a backflow prevention element capable of energizing only from the drive power supply line 55 to the control power supply line 54. It is. In the power supply system configured as described above, when the power relay 57 is turned on, power is supplied to the electronic control circuit 40 and the motor drive circuit 32 regardless of the state of the ignition switch 60. ing.

Next, processing performed by the ECU 30 will be described.
The ECU 30 includes an assist control process for applying an appropriate assist torque to the steering wheel operation by the driver, a motor temperature estimation process for estimating and calculating the motor temperature in order to prevent overheating of the electric motor 15 during the assist control, An estimated temperature data read / write control process for reading / writing the EEPROM 44 as an initial value necessary for calculating the estimated temperature is performed.

  First, assist control processing executed by the ECU 30 will be described. FIG. 3 shows an assist control routine performed by the microcomputer 41. The assist control routine is stored in the ROM of the microcomputer 41 as a control program and repeatedly executed in a short cycle. This control routine is started when the ignition switch 60 is turned on and a predetermined initial diagnosis is completed, and is executed in parallel with a motor temperature estimation routine described later.

  When this control routine is activated, the microcomputer 41 first reads the vehicle speed vx detected by the vehicle speed sensor 22 and the steering torque Th detected by the steering torque sensor 21 in step S11.

  Subsequently, with reference to the assist torque table shown in FIG. 4, a basic assist torque Tas set according to the input vehicle speed vx and steering torque Th is calculated (S12). The assist torque table is stored in the ROM of the microcomputer 41, and is set so that the basic assist torque Tas increases as the steering torque Th increases, and increases as the vehicle speed vx decreases.

The characteristic graph of FIG. 4 shows only the relationship between the positive region, that is, the steering torque Th in the right direction and the basic assist torque Tas, but the negative region, that is, the left direction steering torque Th and the basic assist torque Tas, 4 is moved to a point-symmetrical position around the origin. In the present embodiment, the basic assist torque Tas is calculated using the assist torque table, but a function that defines the basic assist torque Tas that changes according to the steering torque Th and the vehicle speed vx instead of the assist torque table. May be prepared, and the basic assist torque Tas may be calculated using the function.
Further, the calculation of the basic assist torque Tas is not necessarily calculated from the combination of the vehicle speed vx and the steering torque Th, and may be performed based on at least a detection signal corresponding to the steering state.

Subsequently, in step S13, the microcomputer 41 calculates the target torque T * by adding the compensation torque to the basic assist torque Tas. Although this compensation torque is not necessarily required, for example, it opposes the return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θ and the rotation of the steering shaft 12 that increases in proportion to the steering angular velocity ω. It is calculated as the sum of the return torque corresponding to the resistance force. In this calculation, the rotation angle θ of the electric motor 15 detected by the rotation angle sensor 23 and the angular velocity ω of the electric motor 15 (corresponding to the steering angular velocity ω obtained by differentiating the steering angle θ of the steering handle 11 with respect to time) are input. calculate.
Next, in step S14, the microcomputer 41 calculates a necessary current I * necessary for generating the target torque T *. The required current I * is obtained by dividing the target torque T * by the torque constant.

  Subsequently, in step S15, the microcomputer 41 reads the latest estimated motor temperature Tm calculated in a motor temperature estimation routine described later. Next, in step S16, an upper limit current value Imax for energizing the electric motor 15 from the estimated motor temperature Tm is set. The upper limit current value Imax is obtained with reference to the upper limit current value map shown in FIG. This upper limit current value map is stored in the ROM of the microcomputer 41, and the upper limit current value Imax is set to a smaller value as the estimated motor temperature Tm is higher. The upper limit current value Imax represents an absolute value that is not related to the magnitude, that is, the direction in which the current flows.

  Subsequently, the microcomputer 41 proceeds to step S17, and obtains a final target current I ** from the necessary current I * calculated in step S14 and the upper limit current value Imax calculated in step S16. If the magnitude (absolute value) of the required current I * is equal to or less than the upper limit current value Imax, the target current I ** is set to the same value as the required current I *, and the magnitude of the required current I * is equal to the upper limit current value Imax. If it is larger, the target current I ** is set to the same magnitude as the upper limit current value Imax.

Subsequently, the microcomputer 41 advances the process to step S18, calculates a deviation ΔI between the target current I ** and the actual current Ix, and performs a target command voltage V * by PI control (proportional integral control) based on the deviation ΔI. Calculate The actual current Ix used for the calculations in steps S15 and S18 is a current value flowing through the electric motor 15 detected by the current sensor 24.
The target command voltage V * is calculated by the following formula, for example.
V * = Kp · ΔI + Ki · ∫ΔI dt
Here, Kp is a control gain of a proportional term in PI control, and Ki is a control gain of an integral term in PI control.

  In step S19, the microcomputer 41 outputs a PWM control voltage signal corresponding to the target command voltage V * to the motor drive circuit 32, and temporarily ends the assist control routine. This control routine is repeatedly executed at a predetermined short cycle. Therefore, by executing this control routine, the duty ratio of the switching elements Tr1 to Tr4 of the motor drive circuit 32 is controlled by the PWM control, and a steering assist torque corresponding to the driver's steering operation is obtained. Further, in this assist control, a current limit corresponding to the estimated motor temperature Tm is added, so that overheating damage of the electric motor 15 and the motor drive circuit 32 can be prevented.

  Next, the motor temperature estimation process will be described. FIG. 6 shows a motor temperature estimation routine performed by the microcomputer 41, which is stored as a control program in the ROM of the microcomputer 41 and repeatedly executed in a short cycle. This routine starts when the ignition switch 60 is turned on and a predetermined initial diagnosis is completed, and ends when the estimated temperature data read / write control process described later ends.

  When the motor temperature estimation routine is started, the microcomputer 41 first reads the substrate temperature Tb detected by the temperature sensor 25 in step S41. Subsequently, in step S42, the offset temperature Toff is calculated by adding the ambient temperature difference α to the substrate temperature Tb (Toff = Tb + α).

  Here, the atmospheric temperature difference α for calculating the offset temperature Toff will be described. Since the electric motor 15 is located closer to the engine than the motor driving circuit 32, the atmospheric temperature difference α is higher than the atmospheric temperature of the motor driving circuit 32 because the electric motor 15 is located closer to the engine. It represents. Regarding the determination of the ambient temperature difference α, the ambient temperature at which the electric motor 15 and the motor drive circuit 32 are located is measured under various vehicle environments, and data representing the difference between these measured temperatures is collected. For example, the maximum value of the difference in measured temperature is α.

After the process of step S42, the microcomputer 41 calculates the current motor temperature fluctuation dTm of the electric motor 15 by executing the calculation of the following formula (1) in step S43.
dTm = a · dTm−1 + β · (1−a) · Ix ² (1)
In the equation (1), Ix is a current value flowing through the electric motor 15 detected by the current sensor 24. This motor temperature estimation routine is repeatedly executed at an early cycle. The current motor temperature fluctuation dTm calculated in step S43 is the temperature of the electric motor calculated by the motor temperature estimation routine executed in the current control cycle. Represents fluctuation.

  DTm-1 represents the temperature fluctuation of the electric motor 15 calculated by the previous execution of the motor temperature estimation routine (one control period before). Hereinafter, this dTm-1 is referred to as the previous motor temperature fluctuation dTm-1. At the start of this control routine, the data D read from the EEPROM 44 in step S22 of the estimated temperature data read / write control process described later is used as the initial value of the previous motor temperature fluctuation dTm-1. That is, the current motor temperature fluctuation dTm is calculated by substituting the data D read from the EEPROM 44 into the previous motor temperature fluctuation dTm−1 of the equation (1). The data D will be described in detail later.

In equation (1), the value a is a predetermined constant larger than “0” and smaller than “1”. The value β is a predetermined temperature conversion coefficient. Further, the first term a · dTm−1 in the equation (1) increases as the previous motor temperature fluctuation dTm−1 increases, and decreases as the previous motor temperature fluctuation dTm−1 decreases. This is a term representing the influence of the previous motor temperature fluctuation dTm-1 on the current motor temperature fluctuation dTm in consideration of the natural heat dissipation of the electric motor 15 into the outside air. Further, the second term β · (1−a) · Ix ² in the expression (1) is a term representing the amount of heat generated by flowing the motor current Ix through the electric motor 15.

After the processing in step S43, the microcomputer 41 calculates the current estimated motor temperature Tm in step S44 by adding the offset temperature Toff and the current motor temperature fluctuation dTm as shown in the following equation (2). .
Tm = dTm + Toff (2)
The estimated motor temperature Tm represents the current temperature of the electric motor 15 that changes with time due to heat dissipation and heat generation.

  That is, the estimated motor temperature Tm is calculated by adding the current motor temperature fluctuation dTm due to energization of the electric motor 15 to the offset temperature Toff obtained by adding the ambient temperature difference α to the substrate temperature Tb. The current motor temperature fluctuation dTm is calculated by taking into account the previous motor temperature fluctuation dTm-1. Therefore, in calculating the estimated motor temperature Tm, the previous motor temperature fluctuation dTm-1 is required, and the data D read from the EEPROM 44 is used as the initial value of the previous motor temperature fluctuation dTm-1.

  When the motor estimated temperature Tm is calculated in step S44, the current motor temperature fluctuation dTm calculated this time is set as the previous motor temperature fluctuation dTm-1 in step S45. This process is performed for the next calculation process in step S43. After performing the process of step S45, the microcomputer 41 once ends the motor temperature estimation routine. Since this routine is repeatedly executed at a predetermined short cycle, the estimated motor temperature Tm is sequentially calculated every predetermined time.

The latest estimated motor temperature Tm sequentially calculated in this way is used to determine the motor upper limit current value Imax in the assist control (S16).
In calculating the estimated motor temperature Tm, it is not possible to estimate only the amount of heat generated by the electric motor 15 from the start of the assist control, but the heat remaining in the electric motor 15 at the start of the assist control must also be taken into consideration. For example, when the assist control is resumed without much time elapse from the end of the assist control, the electric motor 15 may be in a high temperature state. Therefore, in the present embodiment, the current motor temperature fluctuation dTm related to the heat generation amount of the electric motor 15 at the end of the assist control is written as data D in the EEPROM 44, and when the next assist control is started, the EEPROM 44 By reading the data D (= dTm) written in (1) and using it as the previous motor temperature fluctuation dTm-1 in the equation (1), an appropriate motor estimated temperature Tm can be calculated.
Therefore, this data D is data related to the estimated motor temperature Tm and corresponds to the estimated temperature data of the present invention. Hereinafter, this data is referred to as estimated temperature data D.

  By the way, when assist control is being performed, if the power supply voltage decreases and the microcomputer 41 is reset, the assist control described above cannot be continued. Such a phenomenon occurs mainly when the engine is restarted. In other words, when the engine is stalled after the engine is started, if the engine restart operation is performed from there, the power generated by the alternator 52 is not obtained, and the power supply voltage temporarily decreases greatly. In such a case, the microcomputer 41 is reset in a situation where the assist control has already been started. After reset, the microcomputer 41 resumes assist control when the power supply voltage is restored and a predetermined condition is satisfied. However, since the previous assist control is interrupted, the current motor temperature fluctuation dTm at the end of the assist control is not written in the EEPROM 44 as the estimated temperature data D. Therefore, when the assist control is resumed, an appropriate motor estimated temperature Tm cannot be calculated.

  Therefore, in preparation for such a situation, the microcomputer 41 stores temporary estimated temperature data dTt representing the temporary motor temperature fluctuation corresponding to the current motor temperature fluctuation dTm in the ROM, and from the ROM during the assist control. Temporary estimated temperature data dTt is read out, and this temporary estimated temperature data dTt is stored in the EEPROM 44 as estimated temperature data D. The provisional estimated temperature data dTt is data that is calculated to a high motor estimated temperature Tm from the viewpoint of preventing overheating damage. That is, when the estimated motor temperature Tm is calculated by substituting the temporary estimated temperature data dTt into the previous motor temperature fluctuation dTm−1 in the equation (1), the estimated motor temperature Tm becomes the highest temperature that the electric motor 15 can take. It is preset so that This is a safety measure because the heat generation state of the electric motor 15 is not known when the microcomputer 41 is reset and the assist control is interrupted.

  Therefore, in the assist control after resetting the microcomputer 41, the estimated motor temperature Tm is calculated based on the temporary estimated temperature data dTt. Therefore, even if the motor temperature is actually low at the start of the assist control. It is estimated that the temperature is high, and the current limit works. Therefore, in the present embodiment, the timing for writing the temporary estimated temperature data dTt to the EEPROM 44 as the estimated temperature data D is not performed immediately after the start of the assist control as in the prior art, but as follows.

  FIG. 7 shows a read / write control routine for estimated temperature data executed by the microcomputer 41. This routine is stored as a control program in the ROM of the microcomputer 41 and is activated when the ignition switch 60 is turned on. FIG. 8 is a timing chart showing the processing in time series.

  When the ignition switch 60 is switched from the off state to the on state, power is supplied from the power supply device 50 to the ECU 30. When receiving the power supply, the microcomputer 41 starts this control routine (time t0), and first performs an initial diagnosis in step S21. That is, in-system diagnosis and initial setting in the electric power steering apparatus 1 are performed. During this initial diagnosis, the estimated temperature data D stored in the EEPROM 44 is read (step S22, time t1).

  When the initial diagnosis is completed, the microcomputer 41 starts the assist control described above in step S23 (time t2). At the start of the assist control, the power relay 57 is turned on to form a power supply circuit to the electric motor 15. At this time, motor temperature estimation processing is also started in parallel with the assist control. In the initial calculation of the estimated motor temperature Tm, as described above, the estimated temperature data D read in step S22 (time t1) is used as the previous motor temperature fluctuation dTm-1 in the equation (1). . The estimated motor temperature Tm is repeatedly calculated at a predetermined cycle. In the second and subsequent cycles, the current motor temperature fluctuation dTm of the immediately previous time (one control cycle before) is replaced with the previous motor temperature fluctuation dTm-1. To calculate.

  When the assist control is started, the microcomputer 41 first determines in step S24 whether or not the flag F is “1”. This flag F is set to F = 0 when this control routine is started, and is set to F = 1 when temporary estimated temperature data dTt is stored in the EEPROM 44. Immediately after the assist control is started, since F = 0 is set, the determination in step S24 is “NO”, and the microcomputer 41 advances the process to step S25.

  In step S25, it is determined whether the magnitude (| Ix |) of the energization current value Ix to the electric motor 15 is equal to or greater than a preset set current value Ith. The energization current value Ix to the electric motor 15 is not limited to the actual current value detected by the current sensor 24, and may be the target current value I ** calculated in step S17. This is because the target current value I ** and the actual current value Ix become almost the same value by feedback control based on the current deviation ΔI. In addition, the set current value Ith is set to a value that does not exceed a predetermined overheat prevention reference temperature (for example, 150 ° C.) even if the current of the set current value Ith is continuously supplied to the electric motor 15.

  While no electric current larger than the set current value Ith flows through the electric motor 15, the process proceeds to step S28 to determine whether or not the ignition switch 60 is turned off. While the ignition switch 60 remains on, the process returns to step S24 and the above-described processing is repeated. That is, the comparison determination of whether or not the magnitude | Ix |

  During the assist control, the energization amount of the electric motor 15 is controlled according to the steering torque Th and the vehicle speed vx as described above. When the energization current value Ix of the electric motor 15 increases and reaches the set current value Ith, the determination in step S25 is switched to “YES”. The microcomputer 41 proceeds with the process to step S26 based on this determination.

  In step S26, the microcomputer 41 reads the temporary estimated temperature data dTt from the ROM and writes it as the estimated temperature data D in the EEPROM 44 (time t3). Therefore, the estimated temperature data D stored in the EEPROM 44, that is, the estimated temperature data D representing the current motor temperature fluctuation dTm at the end of the previous assist control is rewritten to the temporary estimated temperature data dTt (overwriting). The rewriting of the estimated temperature data D is a process performed in preparation for a situation where the estimated temperature information disappears due to the microcomputer 41 being reset during the assist control. Therefore, the temporary estimated temperature data dTt is not used for the assist control performed at the present time.

  The microcomputer 41 sets the flag F to F = 1 when the provisional estimated temperature data dTt is completely written to the EEPROM 44 in step S26. Accordingly, after that, the determination in step S24 is “YES”, and the determination of the OFF state of the ignition switch 60 in step S28 is continued.

  When the ignition switch 60 is operated and an off state is detected (time t4), the assist control is terminated in step S29. Therefore, thereafter, the electric motor 15 is not driven and controlled. Subsequently, in step S30, the microcomputer 41 writes the current motor temperature fluctuation dTm at the end of the assist control as the estimated temperature data D in the EEPROM 44.

The estimated motor temperature Tm is obtained by adding the offset temperature Toff and the current motor temperature fluctuation dTm, as can be seen from the equation (2). Therefore, the estimated temperature data D (= dTm) written in the EEPROM 44 in step S30 represents the temperature rise due to motor energization at the end of assist control.
Thus, the temporary estimated temperature data dTt stored in the EEPROM 44 in the previous step S26 is rewritten with the estimated temperature data (current motor temperature fluctuation dTm) at the end of the assist control.

  Subsequently, the microcomputer 41 starts a timer in step S31, and determines whether a predetermined time (for example, 10 minutes) has elapsed in step S32. When the assist control is finished and the elapse of a predetermined time is confirmed (S32: YES), the microcomputer 41 writes the current motor temperature fluctuation dTm at that time in the EEPROM 44 as the estimated temperature data D in step S33 ( Time t5). The microcomputer 41 calculates the estimated temperature of the electric motor 15 by the motor temperature estimation routine even after the end of the assist control. In this case, since no current flows through the electric motor 15 for a predetermined time or more, the current motor temperature fluctuation dTm calculated by the equation (1) is a small value.

  Thus, the current motor temperature fluctuation dTm stored in the EEPROM 44 as the estimated temperature data D in the previous step S30 is finally rewritten to the current motor temperature fluctuation dTm after the predetermined time has elapsed. This estimated temperature data D is read in step S22 when the next ignition switch 60 is turned on, and is used as an initial value of the previous motor temperature variation dTm-1 in the equation (1) of the motor temperature estimation calculation process. .

When the writing of the estimated temperature data D (= dTm) to the EEPROM 44 is completed in step S33, the microcomputer 41 turns off the power supply relay 57 in step S34 and ends all the processes.
When the ignition switch 60 is turned on during a predetermined time waiting (time t4 to t5), the microcomputer 41 does not write the final estimated temperature data D (= dTm) as described above. The process from the initial diagnosis (S21) is started. In this case, in the motor temperature estimation calculation process at the start of the assist control, the estimated temperature data D (= dTm) stored at the end of the previous assist control (time t4) is the previous motor temperature fluctuation amount dTm of the equation (1). Used as an initial value of -1.

  According to the electric power steering apparatus 1 of the present embodiment described above, the temperature of the electric motor 15 is estimated, and the upper limit current value that can be passed to the electric motor 15 is set based on the estimated temperature Tm. The overheat damage of the electric motor 15 and the motor drive circuit 32 can be prevented. When estimating the temperature of the electric motor 15, the estimated temperature data D at the end of the previous assist control is stored in the EEPROM 44, and the estimated temperature data D is read out at the start of the next assist control to calculate the estimated motor temperature Tm. Therefore, the calculated estimated motor temperature Tm is highly reliable. In addition, the provisional estimated temperature data dTt is written in the EEPROM 44 in preparation for a situation where the estimated temperature information is lost due to the reset of the microcomputer 41 during the assist control, so that the overheat damage prevention function is high.

  In the present embodiment, the provisional estimated temperature data dTt is written to the EEPROM 44 when it is determined that a current equal to or greater than the set current value Ith flows through the electric motor 15, so that it is faster than necessary. It is prevented that the temporary estimated temperature data dTt is written at the timing. That is, the temporary estimated temperature data dTt is not written in a usage situation where a large temperature increase of the electric motor 15 is not expected.

  The reset of the microcomputer 41 during the assist control is likely to occur immediately after the engine is started. For example, after the engine is started by a starter (not shown), the assist control is started when the engine stops due to a start failure (engine stall). If the engine is restarted at this time, the microcomputer 41 may be reset due to a temporary drop in the power supply voltage.

  Even in such a case, according to the present embodiment, the provisional estimated temperature data dTt is stored in the EEPROM 44 as long as the steering operation is performed before the microcomputer 41 is reset and a current equal to or greater than the set current value Ith does not flow through the electric motor 15. Is not written to. For this reason, at the time of the first assist control after reset, the frequency at which the temporary estimated temperature data dTt set higher is read is reduced. Therefore, it is possible to reduce the situation where the current assist is more than necessary and the steering assist function cannot be obtained satisfactorily. In addition, the number of cases where the driver misunderstands that the steering wheel operation becomes heavy due to a failure is reduced.

  On the other hand, if a current greater than or equal to the set current value Ith flows through the electric motor 15 before the microcomputer 41 is reset, the temporary estimated temperature data dTt is written in the EEPROM 44 at that stage, so the first assist after the reset At the time of control, the estimated motor temperature Tm is calculated on the basis of the provisional estimated temperature data dTt, so that it is possible to prevent overheating of the electric motor 15 when assist is resumed. In addition, since the set current value Ith is set to a value that does not exceed the predetermined overheat prevention reference temperature (for example, 150 ° C.) even if the set current value Ith continues to flow through the electric motor 15, the temporary estimated temperature data dTt The writing timing to the EEPROM 44 is not delayed, and a high overheat prevention capability can be maintained. As a result, according to the present embodiment, the steering function by the electric motor 15 can be fully utilized by reducing the frequency of use of the temporary estimated temperature data dTt while maintaining the overheat prevention function.

The electric power steering apparatus according to the present embodiment has been described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.
For example, in this embodiment, the timing for writing the temporary estimated temperature data dTt to the EEPROM 44 is determined based on the current value (actual current value Ix or target current value I **) flowing through the electric motor 15. In place of the current value, the steering torque Th, the steering angle θ, and the steering angular velocity ω may be used. The energization amount of the electric motor 15 is controlled by the microcomputer 41 according to the steering torque Th acting on the steering handle 11. Therefore, the motor current value can be estimated from the steering torque Th without directly detecting the motor current. Further, since the steering angle θ and the steering angular velocity ω are also related to the steering torque Th, the motor current value can be estimated from these.

  For example, in the case where the timing for writing the temporary estimated temperature data dTt is set based on the steering torque Th instead of the detection of the motor current, step S25a in FIG. 9 is performed instead of step S25 in FIG. To do. That is, in step S25a, it is determined whether or not the magnitude (| Th |) of the steering torque Th is equal to or greater than the set torque Th0, and it is determined that the magnitude (| Th |) of the steering torque Th is equal to or greater than the set torque Th0. The temporary estimated temperature data dTt is written in the EEPROM 44.

  Further, for example, when the write timing of the temporary estimated temperature data dTt is set based on the steering angle θ instead of detecting the motor current, step S25b in FIG. 10 is performed instead of step S25 in FIG. Like that. That is, in step S25b, it is determined whether or not the magnitude of the steering angle θ (| θ |) is equal to or larger than the set steering angle θ0, and the magnitude of the steering angle θ (| θ |) is equal to or larger than the set steering angle θ0. When the determination is made, temporary estimated temperature data dTt is written in the EEPROM 44.

  Further, for example, when the write timing of the temporary estimated temperature data dTt is set based on the steering angular velocity ω instead of detecting the motor current, step S25c in FIG. 11 is performed instead of step S25 in FIG. Like that. That is, in step S25c, it is determined whether or not the magnitude (| ω |) of the steering angular velocity ω is equal to or larger than the set steering angular velocity ω0. When the determination is made, temporary estimated temperature data dTt is written in the EEPROM 44.

  Further, in the present embodiment, the estimated temperature data D is stored in the EEPROM 44, but the present invention is not limited to this, and may be stored in another nonvolatile memory. The electric motor is not limited to a brush motor but may be a brushless motor, or may be a three-phase motor without being limited to a single-phase motor. Further, the part of the electric motor that is to be overheat protected is not limited to the brush but may be a coil part or the like.

  In this embodiment, the electric power steering device that assists the steering operation has been described. However, the present invention can also be applied to a steering-by-wire steering device in which the steering handle and the steered wheels are mechanically separated. That is, at least one of an electric motor that generates a steering reaction torque for a steering operation of the driver and an electric motor that generates a steering torque for steering the steered wheels is provided, and the temperature of at least one of the electric motors is adjusted. It is possible to estimate and to prevent overheating damage by adding a current limit based on the estimated temperature.

The microcomputer 41 in the present embodiment constitutes the temperature estimation means, motor control means, data read / write means, and temporary estimated temperature data overwrite means of the present invention. In particular, the processing of the motor temperature estimation routine of the present embodiment is performed. The functional unit to perform corresponds to the temperature estimation unit of the present invention, the functional unit to perform the assist control routine processing of the present embodiment corresponds to the motor control unit of the present invention, in the read / write control routine of the estimated temperature data of the present embodiment The functional unit that performs the processes of steps S22, S30, and S33 corresponds to the data read / write unit of the present invention, and the functional unit that performs the processes of steps S25 and S26 in the read / write control routine of the estimated temperature data of the present embodiment is the temporary of the present invention. This corresponds to estimated temperature data overwrite means.

1 is an overall configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a schematic circuit block diagram showing the control system and power supply system in an electric power steering device. It is a flowchart showing an assist control routine. It is a characteristic view showing an assist torque map. It is a characteristic view showing an upper limit electric current value map. It is a flowchart showing a motor temperature estimation routine. It is a flowchart showing the reading / writing control routine of estimated temperature data. It is a timing chart which shows the reading / writing timing of estimated temperature data. It is a partial modification in the reading / writing control routine of estimated temperature data. It is a partial modification in the reading / writing control routine of estimated temperature data. It is a partial modification in the reading / writing control routine of estimated temperature data.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 15 ... Electric motor, 21 ... Steering torque sensor, 22 ... Vehicle speed sensor, 23 ... Rotation angle sensor, 24 ... Current sensor, 25 DESCRIPTION OF SYMBOLS ... Temperature sensor, 30 ... Electronic control unit (ECU), 32 ... Motor drive circuit, 40 ... Electronic control circuit, 41 ... Microcomputer, 42 ... Input interface, 43 ... Output interface, 44 ... EEPROM, 50 ... Power supply device, 51 ... Battery, 60 ... ignition switch, FW1, FW2 ... left and right front wheels (steering wheels).

Claims (4)

An electric motor that generates steering torque;
Temperature estimating means for estimating the temperature of the electric motor by sequential calculation;
Steering detection means for detecting the steering state of the steering wheel;
While applying a current limit based on the estimated temperature, the target energization control amount of the electric motor is calculated based on the detected steering state of the steering wheel, and the electric motor is controlled according to the calculated target energization control amount. Motor control means for driving and controlling the motor;
Nonvolatile storage means for storing estimated temperature data relating to the estimated temperature of the electric motor;
The estimated temperature data related to the estimated temperature of the electric motor estimated by the temperature estimating means at the end of the drive control of the electric motor is written in the nonvolatile storage means, and the nonvolatile data is started at the next start of the drive control of the electric motor. Data read / write means for reading estimated temperature data stored in the storage means;
A temporary estimated temperature data overwriting means for rewriting the estimated temperature data stored in the nonvolatile storage means to preset temporary estimated temperature data after the drive control of the electric motor is started;
In the steering apparatus that estimates the temperature of the electric motor by sequential calculation using the estimated temperature data read by the data read / write means at the start of drive control of the electric motor,
The temporary estimated temperature data overwriting means, when the drive control of the electric motor is started, determines that the energization current value to the electric motor is equal to or higher than a preset current value, and then stores the non-volatile memory. A steering apparatus, wherein the estimated temperature data stored in the means is rewritten to the temporary estimated temperature data.   The determination as to whether or not the energization current value to the electric motor is equal to or greater than a preset set current value is based on detection of the current flowing in the electric motor or a target energization control amount calculated by the motor control means. The steering apparatus according to claim 1, wherein the steering apparatus is performed based on the following.   3. The set current value is set to a value at which the electric motor does not exceed a predetermined reference temperature for preventing overheating even if the current of the set current value is continuously supplied to the electric motor. Steering device.   The determination as to whether or not the current value supplied to the electric motor is equal to or greater than a preset current value is based on the steering torque acting on the steering wheel, the steering angle of the steering wheel, or the steering angular velocity of the steering wheel. The steering apparatus according to claim 1, wherein the steering apparatus is performed by estimation.

Images