JP2010260469A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make over-heat protection of an electric motor 20 and a motor drive circuit 32 and prevention of rapid change of steering feeling. <P>SOLUTION: The number in which a vehicle becomes in the acceleration state is counted based on acceleration G detected by an acceleration sensor 70, and the number in which it does not become in the acceleration state from the count value for a constant time or longer is reduced. An upper limit current value of the electric motor 20 is reduced based on the added/reduced count value as the count value is large. Accordingly, since output restriction of the electric motor 20 can be gradually performed from before the electric motor 20 and the motor drive circuit 32 reach to the over-heat prevention temperature, inconvenience that the steering feeling is rapidly varied by sudden starting of the steering assist restriction as conventional is not generated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus including an electric motor for assisting a steering operation of a steering wheel by a driver.

  2. Description of the Related Art Conventionally, an 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.

  For example, the arithmetic circuit 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 the target current value and current corresponding to the target assist torque value are calculated. 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 sensor. Then, a PWM control signal corresponding to the voltage command value is output to the motor drive circuit. The motor drive circuit turns on / off the switching element according to the PWM control signal from the arithmetic circuit, and applies a voltage according 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.

  In such an electric power steering device, in order to prevent the electric motor and the motor drive circuit from being overheated and damaged, their temperatures are monitored, and the monitor temperature exceeds the set temperature for preventing overheating. The current flowing through the electric motor is limited. As an electric power steering device for preventing such overheating, for example, Patent Document 1 has been proposed.

JP2002-362393

  However, in the case of a system for overheat protection by monitoring the temperature, the current limit is performed after the monitor temperature actually reaches the overheat prevention temperature, and thus the steering assist limitation is suddenly started, and the steering wheel operation is suddenly started. It will be heavy.

  An object of the present invention is to address the above-described problems, and is to achieve both overheat protection of an electric motor and a motor drive circuit and prevention of sudden change in steering feeling.

In order to achieve the above object, the present invention is characterized by an electric motor that is provided in a steering mechanism and generates a steering assist torque, and a target that calculates a target current value that flows through the electric motor based on a steering operation by a driver. In an electric power steering apparatus comprising current value calculating means and motor drive control means for driving and controlling the electric motor according to the calculated target current value,
Information acquisition means for acquiring information representing the acceleration or deceleration of the vehicle, and based on the acquired information, the number of times the vehicle acceleration has exceeded the reference acceleration or the vehicle deceleration is the reference deceleration A counting means for counting the number of times the braking state is exceeded, and a value obtained by subtracting the number of times that the acceleration state has never been reached within a reference time from the number of times the acceleration state has been reached, or the braking state. Subtracting means for calculating a value obtained by subtracting the number of times that the braking state has never been reached within the reference time from the number of times, and the larger the value calculated by the subtracting means, the larger the upper limit of the target current value of the electric motor Current limiting means for lowering the value or setting a current limiting coefficient to be multiplied by the target current value of the electric motor to a small value.

  In the present invention, the target current value calculation means calculates the target current value that flows to the electric motor, and the motor drive control means controls the drive of the electric motor according to the calculated target current value. For example, the target current value calculating means detects a steering torque acting on the steering shaft, and calculates a target current value that increases as the steering torque increases. The motor drive control means controls the drive of the electric motor so that the current flowing through the electric motor becomes the target current value. When a large steering torque is frequently applied, such as when traveling on a mountain road, the electric motor tends to be overloaded. When the electric motor is overloaded, heat generation of the electric motor itself or the motor drive circuit increases, and it is necessary to protect them from overheating.

  Therefore, the present invention includes information acquisition means, counting means, and subtracting means, and detects in advance from acceleration or deceleration that the electric motor seems to be overloaded. The information acquisition means acquires information representing the acceleration or deceleration of the vehicle. The counting means counts the number of times that the acceleration of the vehicle is in an acceleration state that exceeds the reference acceleration, or the number of times that the vehicle is in a braking state in which the deceleration of the vehicle exceeds the reference deceleration. For example, the acceleration state or the braking state is determined by comparing the detected value of the acceleration sensor and the reference value, and the number of times the acceleration state or the braking state is reached is counted. Further, the reference acceleration and the reference deceleration are not limited to numerical values, and may represent a reference acceleration state or braking state. For example, the number of times that the traction control system is operated may be counted as the number of times that the vehicle has been accelerated, or the number of times that the antilock brake system has been operated is counted as the number of times that the vehicle has been braked. You may do it. The counting means counts a series of acceleration states (or braking states) as one acceleration state (or braking state).

  Then, the value obtained by subtracting the number of times that the acceleration state has never been accelerated within the reference time from the number of times the acceleration state has entered the acceleration state (that is, each time the continuous time that has not become the acceleration state exceeds the reference time, Value obtained by subtracting 1 from the number of times the vehicle has entered the state), or a value obtained by subtracting the number of times that the vehicle has not entered the braking state within the reference time from the number of times the vehicle has entered the braking state (that is, the continuous time that has not entered the deceleration state) Every time the reference time is exceeded, a value obtained by subtracting 1 from the number of times of the deceleration state is calculated. The value calculated by the subtracting means represents the traveling state of the vehicle, and becomes a larger value in a traveling state in which an acceleration state or a braking state frequently occurs. Further, in such a running state, it is presumed that the heat generated by the electric motor and the motor drive circuit also increases.

  Therefore, the current limiting means lowers the upper limit value of the target current value of the electric motor or sets the current limiting coefficient multiplied by the target current value of the electric motor to a smaller value as the value calculated by the subtracting means is larger. Therefore, since the output of the electric motor can be gradually limited before the electric motor and the motor drive circuit reach the overheat prevention temperature, the steering feeling suddenly changes due to the sudden start of the steering assist restriction as in the past. It does not cause problems such as As a result, it is possible to achieve both overheat protection of the electric motor and motor drive circuit and prevention of sudden change in steering feeling.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a flowchart showing the steering assist control routine as 1st Embodiment. It is a graph showing an assist torque map. It is a flowchart showing the upper limit electric current value calculation routine as 1st Embodiment. It is a graph showing an upper limit electric current value map. It is a flowchart showing the 1st modification of an upper limit electric current value calculation routine. It is a flowchart showing the 2nd modification of an upper limit electric current value calculation routine. It is a flowchart showing the steering assist control routine as 2nd Embodiment. It is a flowchart showing the upper limit electric current value calculation routine as 2nd Embodiment. It is a graph showing the coefficient map for electric current limitation.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an electric power steering apparatus according to an embodiment of the present invention.

  The electric power steering apparatus for a vehicle includes a steering mechanism 10 that steers left and right front wheels FW1 and FW that are steered wheels by steering a steering handle 11, an electric motor 20 that is provided in the steering mechanism 10 and generates steering assist torque, An electronic control unit 30 (hereinafter referred to as an assist ECU 30) that drives and controls the electric motor 20 is provided.

  The steering mechanism 10 includes a steering shaft 12 connected to a steering handle 11 so as to rotate integrally with an upper end thereof, and a pinion gear 13 is connected to a 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 connected to both ends of the rack bar 14 via a tie rod and a knuckle arm (not shown) so as to be steerable. 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.

  A steering torque sensor 41 is provided on the steering shaft 12. The steering torque sensor 41 detects a steering torque that acts on the steering shaft 12 by a turning operation of the steering handle 11. Hereinafter, the torque value detected by the steering torque sensor 41 is referred to as a steering torque T. The steering torque T represents the direction in which the torque works (right direction, left direction) by its sign (positive or negative), and the magnitude of the torque by its absolute value.

  An electric motor 20 for steering assist (for example, a brushless motor) is assembled to the rack bar 14. The rotating shaft of the electric motor 20 is connected to the rack bar 14 via the ball screw mechanism 21 so as to be able to transmit power. By the rotation, the steering force is applied to the left and right front wheels FWL and FWR to assist the steering operation. The ball screw mechanism 21 functions as a speed reducer and a rotation-linear converter, and decelerates the rotation of the electric motor 20 and converts it into a linear motion and transmits it to the rack bar 14. In the present embodiment, the electric motor 20 is assembled to the rack bar 14, but instead, the rotation of the electric motor 20 is transmitted to the steering shaft 12 via the speed reducer so that the steering shaft 12 is driven around the axis. You may comprise.

  A rotation angle sensor 42 is incorporated in the electric motor 20. The rotation angle sensor 42 detects the rotation angle of the rotor of the electric motor 20. This rotation angle is used for energization control of the electric motor 20.

  The assist ECU 30 includes a microcomputer unit 31 including a microcomputer including a CPU, a ROM, a RAM, and the like as main parts, and a motor drive circuit 32. The motor drive circuit 32 is composed of, for example, a three-phase inverter circuit and inputs a PWM control signal from the microcomputer unit 31 to adjust the amount of current supplied to the electric motor 20 by controlling the duty ratio of the internal switching element. To do. The motor drive circuit 32 is provided with a current sensor 43 that detects a current flowing through the electric motor 20. A current value detected by the current sensor 43 is referred to as a motor current im.

  The microcomputer unit 31 is connected to a CAN (Controller Area Network) communication system via a communication interface (not shown). Connected to the CAN communication system are vehicle control devices such as a skid ECU 50 and an engine ECU 60, and sensors such as an acceleration sensor 70, a vehicle speed sensor 71, a steering angle sensor 72, and a yaw rate sensor 73. The acceleration sensor 70 outputs an acceleration signal representing the acceleration G in the horizontal direction of the vehicle. For the acceleration G, acceleration at which the forward speed of the vehicle increases is represented by a positive value, and deceleration at which the forward speed of the vehicle decreases is represented by a negative value. The vehicle speed sensor 71 outputs a vehicle speed signal representing the vehicle speed V. The steering angle sensor 72 is provided on the steering shaft 12 and outputs a steering angle signal representing the steering angle θ with respect to the neutral position of the steering handle 11. The yaw rate sensor 73 outputs a yaw rate signal representing the yaw rate γ of the vehicle body. The steering angle θ and the yaw rate γ are represented by their absolute values, and the left-right direction is identified by a sign (positive or negative). Each sensor 70-73 transmits the detection signal to a CAN communication system.

  The skid ECU 50 connects sensors such as a wheel speed sensor and a brake pedal sensor (not shown) and a brake actuator, and based on the detection signals of these sensors and the sensor detection signal sent from the CAN communication system, the wheel at the time of sudden braking Anti-lock brake control to prevent locking, traction control to prevent slipping of drive wheels during sudden start and acceleration, and behavior stabilization control to ensure stability in the turning direction of the vehicle. Moreover, the control signal showing the control state which concerns on antilock brake control, traction control, and behavior stability control is output to a CAN communication system.

  Next, steering assist control performed by the microcomputer unit 31 will be described. In order to describe two embodiments of the steering assist control, the steering assist control described first is referred to as the steering assist control of the first embodiment. FIG. 2 shows a steering assist control routine executed by the microcomputer unit 31. The steering assist control routine is stored as a control program in the ROM of the microcomputer unit 31, and is started after an ignition switch (not shown) is turned on and the initial diagnosis is completed, and is repeated at a predetermined short cycle.

  When this control routine is started, the microcomputer unit 31 first reads the vehicle speed V detected by the vehicle speed sensor 71 and the steering torque T detected by the steering torque sensor 41 in step S11.

  Subsequently, in step S12, with reference to the assist torque map shown in FIG. 3, a basic assist torque Tas set according to the input vehicle speed V and steering torque T is calculated. The assist torque map is stored in the ROM of the microcomputer unit 31, and is set so that the basic assist torque Tas increases as the steering torque T increases, and increases as the vehicle speed V decreases. The assist torque map shown in FIG. 3 represents the characteristic of the basic assist torque Tas with respect to the steering torque T in the right direction. The left direction characteristic is the same when viewed in absolute value only in the opposite direction.

  Subsequently, in step S13, the microcomputer unit 31 calculates the target command torque T * by adding the compensation torque to the basic assist torque Tas. This compensation torque is a return torque corresponding to a return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θ and a resistance force that opposes the rotation of the steering shaft 12 that increases in proportion to the steering speed ω. Is calculated as the sum of In this calculation, the steering angle θ is obtained from the steering angle information transmitted to the CAN communication system, and the steering speed ω is calculated by differentiating the steering angle θ with time. The steering angle θ may be detected from the motor rotation angle detected by the rotation angle sensor 42.

  Next, in step S14, the microcomputer unit 31 calculates a target current value ias * that is a current value corresponding to the target command torque T *. The target current value ias * is obtained by dividing the target command torque T * by the torque constant.

  Subsequently, in step S <b> 15, the microcomputer unit 31 calculates an upper limit current value ilim that is an upper limit value that can flow to the electric motor 20. The upper limit current value ilim is set for overcurrent protection of the electric motor 20 and the motor drive circuit 32. The calculation process of the upper limit current value ilim will be described later using a subroutine shown in FIG.

  Subsequently, in step S16, the microcomputer unit 31 determines whether or not the target current value ias * calculated in the previous step S14 is larger than the upper limit current value ilim set in step S15. If the target current value ias * is larger than the upper limit current value ilim (S16: Yes), the target current value ias * is set to the upper limit current value ilim in step S17. On the other hand, if the target current value ias * is equal to or less than the upper limit current value ilim, the target current value ias * is not changed.

  Subsequently, the microcomputer unit 31 reads the motor current im flowing through the electric motor 20 from the current sensor 43 in step S18. Subsequently, in step S19, a deviation Δi between the motor current im and the previously calculated target current value ias * is calculated, and a target command voltage v * is calculated by PI control (proportional integral control) based on the deviation Δi. . In calculating the target command voltage v *, the three-phase motor current is converted into a two-phase current (d-axis current, q-axis current) in the dq coordinate system, and the two-phase target current value ias * (d A deviation from an axis target current value and a q-axis target current value) is calculated. Then, a three-phase target command voltage v * corresponding to the two-phase current deviation is calculated by two-phase / three-phase conversion.

  Then, in step S20, the microcomputer unit 31 outputs a PWM control signal corresponding to the target command voltage v * to the motor drive circuit 32, and once ends this control routine. This control routine is repeatedly executed at a predetermined fast cycle. Therefore, by executing this control routine, the duty ratio of the switching element of the motor drive circuit 32 is controlled, and a desired assist torque corresponding to the driver's steering operation is obtained.

  Next, the upper limit current value calculation process in step S15 will be described. FIG. 4 shows an upper limit current value calculation routine executed by the microcomputer unit 31. The upper limit current value calculation routine is incorporated as step S15 of the steering assist control routine and is repeated at a predetermined short cycle.

  When the upper limit current value calculation routine is activated, the microcomputer unit 31 reads the acceleration G detected by the acceleration sensor 70 via CAN communication in step S21. Subsequently, in step S22, it is determined whether or not the flag F is “0”. As will be understood from the processing described later, this flag F indicates whether or not the current running state of the vehicle is in a predetermined acceleration state, and is “0” (non-acceleration state) at the start of this routine. ) Is set. Accordingly, the microcomputer unit 31 advances the process to step S23 when judging that F = 0.

  In step S23, the microcomputer unit 31 determines whether or not the acceleration G exceeds a preset reference acceleration Ga1. If the acceleration G is equal to or less than the reference acceleration Ga1 (S23: No), it is determined in a subsequent step S24 whether or not the timer value t has reached the set time ta. The timer value t represents a continuous time during which the vehicle is not in a predetermined acceleration state, and is set to t = 0 when this routine is started. Therefore, the microcomputer unit 31 determines “No” here, and increments the timer value t by the value “1” in the subsequent step S25.

  Subsequently, in step S26, the microcomputer unit 31 calculates the upper limit current value ilim with reference to the upper limit current value map shown in FIG. The upper limit current value map associates a relationship between a count value N and an upper limit current value ilim, which will be described later, and sets an upper limit current value ilim that decreases as the count value N increases. The count value N is set to “0” (N = 0) when this routine is started. Therefore, here, the upper limit current value ilim is set to ilim1 which is the maximum value.

  When the microcomputer unit 31 calculates the upper limit current value ilim, the microcomputer 31 once exits from this routine and proceeds to step S16 of the main routine (steering assist control in FIG. 3). The upper limit current value calculation routine is repeated at a predetermined short cycle. Accordingly, the timer value t is added while the acceleration G is equal to or less than the reference acceleration Ga1. If the acceleration G exceeds the reference acceleration Ga1 before the timer value t reaches ta (S23: Yes), the microcomputer unit 31 advances the process to step S27.

  The microcomputer unit 31 increments the count value N by the value “1” in step S27, and sets the flag F to “1” in the subsequent step S28. Subsequently, in step S26, the microcomputer unit 31 calculates the upper limit current value ilim with reference to the upper limit current value map based on the count value N (= 1). The upper limit current value map sets an upper limit current value ilim to the maximum ilim1 while the count value N is 0 to N1, and when the count value N becomes larger than N1, the upper limit decreases as the count value N increases. Sets the current value ilim. When the count value N is larger than N2, the upper limit current value ilim is set to a fixed ilim2 that is the minimum. Therefore, here, since the count value N is still small (N <N1), the upper limit current value ilim is set to ilim1 which is the maximum value. In the present embodiment, a configuration is used in which the upper limit current value ilim is calculated using the upper limit current value map. However, a function representing the relationship between the count value N and the upper limit current value ilim is a storage element such as a ROM. The upper limit current value ilim may be calculated from the count value N using this function.

  The microcomputer unit 31 once exits this routine when it calculates the upper limit current value ilim in step S26. From the next time, since the flag F is set to “1”, the determination in step S22 becomes “No”, and the acceleration state end determination process from step S29 is started.

  After determining that the vehicle has accelerated (S23: Yes), the microcomputer unit 31 repeatedly determines whether or not the acceleration G has fallen below the reference acceleration Ga2 in step S29. The reference acceleration Ga2 is a determination value that is set to a value smaller than the reference acceleration Ga1 and determines the end of the acceleration state. While the acceleration G does not fall below the reference acceleration Ga2 (S29: No), the process proceeds to the calculation process of the upper limit current value ilim in step S26. In this case, since the count value N is not changed, the upper limit current value ilim is not changed.

  The microcomputer unit 31 repeats such processing, and when detecting that the acceleration G is lower than the reference acceleration Ga2 (S29: Yes), the flag F is reset to “0” in step S30, assuming that the acceleration state has ended. In step S31, the timer value is cleared to zero. Therefore, from the next time, since the flag F is reset to “0”, the determination in step S22 is “Yes”, and the acceleration state start determination process from step S23 is started.

  The microcomputer unit 31 increments the timer value t by a value “1” while determining that the acceleration G is equal to or less than the reference acceleration Ga1 in step S23. That is, the continuous time during which acceleration is not achieved is measured. If the acceleration G exceeds the reference acceleration Ga1 before the timer value t reaches the set time ta (S23: Yes), the count value N is incremented by the value “1” in step S27 as described above. In step S28, the flag F is set to “1”. Therefore, when acceleration traveling is frequently performed, the count value N gradually increases.

  On the other hand, when the timer value t representing the continuous time in the non-accelerated state reaches the set time ta, the count value N is decremented by the value “1” in step S32, and the timer value t is cleared to zero in step S33. To do. Therefore, during a gentle travel where acceleration travel is not performed much, the count value N decreases by “1” every time the set time ta elapses. The microcomputer unit 31 sets the count value N to “0” when the count value N subtracted in step S32 becomes minus (−1).

  Therefore, the count value N is an index that represents the frequency at which the vehicle is accelerated. In other words, it can be said that the greater the count value N, the higher the frequency of the acceleration state. The microcomputer unit 31 calculates the upper limit current value ilim from the upper limit current value map based on the latest count value N set in this way.

  When traveling on a winding road such as a mountain road, the steering operation is repeated, and the electric motor 20 is likely to be overloaded. When the electric motor 20 enters an overload state, the electric motor 20 and the motor drive circuit 32 (hereinafter collectively referred to as a motor circuit) generate a large amount of heat. Accordingly, it is necessary to prevent damage due to overheating of the motor circuit, that is, to protect against overheating. Conventionally, the temperature of the motor circuit is detected, and when the detected temperature reaches the overheat prevention temperature, the electric motor 20 is detected. As a result, the steering assist restriction suddenly started, and the steering wheel operation suddenly became heavy.

  While the vehicle is traveling such that the steering operation is repeated, there are many cases where the vehicle repeats acceleration and deceleration alternately. Therefore, in the present embodiment, a traveling state in which the electric motor 20 is likely to be overloaded is detected based on the count value N representing the frequency at which the vehicle is accelerated, and the upper limit current is gradually increased as the count value N increases. The value ilim is reduced. Therefore, before the temperature of the motor circuit rises, the output limitation of the electric motor 20 can be gradually started to prevent overheating. For this reason, it is possible to achieve both overheating protection of the motor circuit and prevention of sudden change of the steering feeling.

  Next, a first modification example related to the upper limit current value calculation routine will be described. In the embodiment described above, the traveling state in which the electric motor 20 is likely to be overloaded is estimated from the frequency at which the vehicle is in the accelerated state. However, the traveling state in which the electric motor 20 is likely to be in the overloaded state is It can also be estimated from the frequency of the state. Therefore, in the first modification, the count value N is set based on the deceleration.

  FIG. 6 is a flowchart showing an upper limit current value calculation routine as a first modification. The upper limit current value calculation routine of the first modification performs the determination process of step S231 and step S291 instead of the determination process of step S23 and step S29 in the upper limit current value calculation routine of the first embodiment described above. Yes, the other processes are the same as those in the first embodiment. Therefore, the same processing as that of the first embodiment is denoted by the same step number in the drawing and description thereof is omitted.

  When starting the upper limit current value calculation routine of the first modification, the microcomputer unit 31 reads the acceleration G detected by the acceleration sensor 70 (S21), and when the flag F is “0” (S22: Yes), In step S231, it is determined whether or not the acceleration G is smaller than a preset reference deceleration −Gb1. The acceleration sensor 70 outputs an acceleration G (= deceleration) indicating a negative value when the vehicle is decelerating. The reference deceleration -Gb1 is a negative value. Therefore, in this step S231, whether or not the vehicle is in a braking state in which the vehicle decelerates at a deceleration greater than the reference deceleration -Gb1 (a braking state in which the acceleration G is a negative value and the absolute value is greater than Gb1). Determine whether.

  If the acceleration G detected by the acceleration sensor 70 is greater than or equal to the reference deceleration −Gb1, the microcomputer unit 31 determines “No” in step S231 and advances the process to step S24. On the other hand, when the acceleration G is less than the reference deceleration −Gb1, the microcomputer unit 31 determines “Yes” in step S231 and advances the process to step S27. That is, when it is determined that the vehicle is in a braking state in which the vehicle decelerates at a deceleration greater than the reference deceleration −Gb1 (S231: Yes), the count value N is incremented by “1” and is not in such a braking state. That is, when it is determined that the vehicle is in the non-braking state (S231: No), the duration of the non-braking state is measured and the count value N is decremented by “1” when the timer value t reaches the set time ta. To do.

  On the other hand, if the microcomputer unit 31 determines that the vehicle is in the braking state, it sets the flag F to “1” (S28), and thereafter starts the braking state end determination process in step S291. In this step S291, it is determined whether or not the acceleration G exceeds the reference deceleration −Gb2. The reference deceleration -Gb2 is a determination value that is set to a negative value that is larger (absolute value is smaller) than the reference deceleration -Gb1 and determines the end of the braking state. While the acceleration G does not exceed the reference deceleration −Gb2 (S291: No), the process proceeds to the calculation process of the upper limit current value ilim in step S26. In this case, since the count value N is not changed, the upper limit current value ilim is not changed.

  When the microcomputer unit 31 repeats such processing and detects that the acceleration G exceeds the reference deceleration −Gb2 (S291: Yes), the flag F is reset to “0” in step S30, assuming that the braking state has ended. In step S31, the timer value t is cleared to zero. Accordingly, from the next time, since the flag F is reset to “0”, the determination in step S22 is “Yes”, and the brake state start determination process from step S231 is started.

  Thus, in the first modification, the count value N is incremented by “1” each time a braking state in which the acceleration G is less than the reference deceleration −Gb1 (that is, a braking state in which the deceleration exceeds the reference deceleration) is detected. The count value N is incremented and decremented by “1” each time the set time ta elapses when the braking state is not detected. Therefore, the count value N is an index representing the frequency with which the vehicle is in a braking state. In other words, it can be said that the greater the count value N, the more frequently the vehicle is in a braking state. The microcomputer unit 31 calculates the upper limit current value ilim from the upper limit current value map based on the latest count value N set in this way.

  While the vehicle is traveling such that the steering operation is repeated, there are many cases where the vehicle repeats acceleration and deceleration alternately. Therefore, in the first modified example, a traveling state in which the electric motor 20 is likely to be overloaded is detected based on the count value N representing the frequency at which the vehicle is in a braking state, and the upper limit is gradually increased as the count value N increases. The current value ilim is reduced. Therefore, before the temperature of the motor circuit rises, the output limitation of the electric motor 20 can be gradually started to prevent overheating. For this reason, it is possible to achieve both overheating protection of the motor circuit and prevention of sudden change of the steering feeling.

  Next, a second modification example related to the upper limit current value calculation routine will be described. This second modification is a combination of the first embodiment described above and the first modification, and calculates the upper limit current value ilim from the frequency at which the vehicle enters the acceleration state and the braking state.

  FIG. 7 is a flowchart showing an upper limit current value calculation routine as a second modification. The upper limit current value calculation routine of the second modification performs the determination process of step S232 and step S292 instead of the determination process of step S23 and step S29 in the upper limit current value calculation routine of the first embodiment described above. Yes, the other processes are the same as those in the first embodiment. Therefore, the same processing as that of the first embodiment is denoted by the same step number in the drawing and description thereof is omitted.

  When starting the upper limit current value calculation routine of the second modification, the microcomputer unit 31 reads the acceleration G detected by the acceleration sensor 70 (S21), and when the flag F is “0” (S22: Yes), In step S232, it is determined whether or not the acceleration G is within a reference acceleration Ga1 from a preset reference deceleration -Gb1. That is, it is determined whether or not the vehicle is in an acceleration state in which the acceleration G is greater than the reference acceleration Ga1, or in a braking state in which the acceleration G is less than the reference deceleration −Gb1 (increases as an absolute value).

  If the acceleration G does not fall between the reference acceleration −Gb1 and the reference acceleration Ga1 (S232: No), the microcomputer 31 advances the process to step S27, and conversely, the acceleration G becomes the reference deceleration− If it falls within the range from Gb1 to the reference acceleration Ga1, (S232: Yes), the process proceeds to step S24. That is, when it is determined that the vehicle is in an accelerating state or a braking state, the count value N is incremented by “1”, and when it is determined that the vehicle is not in such a state, the duration time of the state is set. When the timer value t reaches the set time ta after measurement, the count value N is decremented by “1”.

  If the microcomputer unit 31 determines that the vehicle is in the acceleration state or the braking state, the microcomputer 31 sets the flag F to "1" (S28). Thereafter, in step S292, the microcomputer 31 determines whether to end the acceleration state or the braking state. Start processing. In step S292, it is determined whether or not the acceleration G is within the reference acceleration Ga2 from a preset reference deceleration -Gb2. While the acceleration G does not fall between the reference deceleration -Gb2 and the reference acceleration Ga2 (S292: No), the process proceeds to the calculation process of the upper limit current value ilim in step S26. In this case, since the count value N is not changed, the upper limit current value ilim is not changed.

  When the microcomputer unit 31 repeats such processing and detects that the acceleration G falls within the reference acceleration −Gb2 to the reference acceleration Ga2 (S292: Yes), it is determined in step S30 that the acceleration state or the braking state has ended. , The flag F is reset to “0”, and the timer value t is cleared to zero in step S31. Therefore, from the next time, since the flag F is reset to “0”, the determination in step S22 is “Yes”, and the determination process from step S232 is started.

  Thus, in the second modified example, every time the vehicle enters the acceleration state or the braking state, the count value N is incremented by “1”, and the continuous time during which the vehicle does not enter the acceleration state or the braking state is the set time. Each time ta passes, the count value N is decremented by "1". Therefore, the count value N is an index that represents the frequency with which the vehicle enters the acceleration state and the braking state. A running state in which the electric motor 20 is likely to be overloaded is detected from the count value N, and the upper limit current value ilim is reduced as the count value N increases. Therefore, before the temperature of the motor circuit rises, the output limitation of the electric motor 20 can be gradually started to prevent overheating. As a result, it is possible to achieve both overheating protection of the motor circuit and prevention of sudden change of the steering feeling. Note that the reference accelerations Ga1 and Ga2 and the reference decelerations Gb1 and Gb2 used in the second modification may be set to the same values as those used in the first embodiment and the first modification.

  Next, an electric power steering apparatus according to a second embodiment will be described. In the first embodiment and its modifications 1 and 2 described above, the upper limit current value ilim is used to prevent overheating of the motor circuit. In the second embodiment, the current limiting coefficient is added to the target current value ias *. Multiplication by α (0 ≦ α ≦ 1) prevents overheating of the motor circuit. Hereinafter, although 2nd Embodiment is described, since 2nd Embodiment only differs in the process of the microcomputer part 31 with respect to 1st Embodiment, it will limit only description about a difference here.

  FIG. 8 is a flowchart showing a steering assist control routine according to the second embodiment. The steering assist control routine of the second embodiment performs the processes of steps S50 and S51 instead of the processes of steps S15 to S17 in the steering assist control routine of the first embodiment described above. Is the same as the processing of the first embodiment. FIG. 9 is a flowchart showing a current limiting coefficient calculation routine which is the process of step S50. This current limiting coefficient calculation routine performs the process of step S261 instead of the process of step S26 of the upper limit current value calculation routine of the first embodiment, and the other processes are the same as those of the first embodiment. Are the same. Therefore, in FIG. 8, FIG. 9, about the process same as 1st Embodiment, the same step number is attached | subjected to drawing and description is abbreviate | omitted.

  When the steering assist control routine is activated, the microcomputer unit 31 calculates a target current value ias * based on various parameters (T, V, θ, ω) (S11 to S14). Subsequently, in step S50, a calculation process of the current limiting coefficient α is executed. The process of step S50 will be described later. After calculating the current limiting coefficient α in step S50, the microcomputer unit 31 obtains a value (α · ias *) obtained by multiplying the target current value ias * by the current limiting coefficient α in step S51. Set as a new target current value ias *. The microcomputer unit 31 calculates the target command voltage v * based on the deviation Δi between the target current value ias * and the motor current im, and outputs a PWM control signal corresponding to the target command voltage v * to the motor drive circuit 32. The electric motor 20 is driven and controlled (S18 to S20).

  The microcomputer unit 31 executes a current limiting coefficient calculation routine shown in FIG. 9 in calculating the current limiting coefficient α in step S50. In this current limiting coefficient calculation routine, the current limiting coefficient α is calculated in step S261 using the count value N added or subtracted according to the running state. The current limiting coefficient α is calculated with reference to the current limiting coefficient map shown in FIG. The current limiting coefficient map associates the relationship between the count value N and the current limiting coefficient α, and sets the current limiting coefficient α that decreases as the count value N increases. In this example, while the count value N is 0 to N1, a current limiting coefficient α that is a constant value “1” is set (α = 1), and when the count value N becomes larger than N1, the count value N Is set to a current limiting coefficient α that decreases with increasing. When the count value N is greater than N2, the current limiting coefficient α is set to a constant value αmin that is minimized. In the present embodiment, a configuration is used in which the current limiting coefficient α is calculated using the current limiting coefficient map, but a function representing the relationship between the count value N and the current limiting coefficient α is a ROM or the like. The current limiting coefficient α may be calculated from the count value N using this function.

  Also in the second embodiment, similarly to the first embodiment, before the temperature of the motor circuit rises, the output limitation of the electric motor 20 can be gradually started to prevent overheating. For this reason, it is possible to achieve both overheating protection of the motor circuit and prevention of sudden change of the steering feeling. The current limiting coefficient calculation routine shown in FIG. 9 shows an example of a configuration in which the count value N is added or subtracted based on the frequency at which the vehicle is accelerated. The present invention can also be applied to a configuration in which the count value N is calculated based on the frequency of the braking state or the frequency of the acceleration state and the braking state, as in FIG.

  The electric power steering apparatus according to the present embodiment has been described above, but 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 acceleration state or braking state of the vehicle is determined based on the acceleration G detected by the acceleration sensor 70, but the operation of the traction control or antilock brake control executed by the skid ECU 50 is performed. A control signal representing the state can be read via the CAN communication system, and the acceleration state or the braking state can be detected based on the control signal.

  The skid ECU 50 outputs a traction control signal to the engine ECU 60 and a brake actuator (not shown) to reduce the engine output so that the drive wheels do not slip when a sudden start / acceleration of the vehicle is detected. Or brake braking. Therefore, when this traction control signal is output, it can be considered that the acceleration of the vehicle exceeds the reference acceleration. Further, the skid ECU 50 outputs an anti-lock brake control signal to the brake actuator to reduce the brake braking force so that the wheel is not locked when the sudden braking is detected. Therefore, when this antilock brake control signal is output, it can be considered that the vehicle is in a braking state in which the deceleration of the vehicle exceeds the reference deceleration. Therefore, instead of the acceleration G, the count value N may be added or subtracted based on a control signal representing the control state of the skid ECU 50.

  In this case, for example, in the upper limit current value calculation routine shown in FIG. 4, a control signal indicating the control state of the skid ECU 50 is read in step S21, and it is determined whether or not a traction control signal is output in step S23. do it. In step S29, it may be determined whether or not the output of the traction control signal is stopped.

  Similarly, in the upper limit current value calculation routine shown in FIG. 6, in step S231, a control signal indicating the control state of the skid ECU 50 is read, and in step S23, it is determined whether or not an antilock brake control signal is output. do it. In step S291, it may be determined whether the output of the antilock brake control signal has been stopped.

  In the upper limit current value calculation routine shown in FIG. 7, a control signal indicating the control state of the skid ECU 50 is read in step S232, and whether or not an antilock brake control signal or a traction control signal is output in step S23. You just have to judge. In step S292, it may be determined whether the output of the detected control signal is stopped.

  Further, the configuration for detecting the acceleration state or the braking state of the vehicle by the control signal of the skid ECU 50 can be similarly applied to the second embodiment.

  Further, instead of the skid ECU 50, the control state information of the engine ECU 60 may be acquired to detect the acceleration state of the vehicle. For example, accelerator information is acquired from the engine ECU 60, and when the acceleration speed of the accelerator opening exceeds the reference speed, it can be considered that the acceleration of the vehicle exceeds the reference acceleration. In this case, for example, in the upper limit current value calculation routine shown in FIG. 4, in step S21, a signal indicating the control state of the engine ECU 60 is read, and in step S23, whether or not the increase speed of the accelerator opening exceeds the reference speed. You just have to judge. Further, in step S29, it may be determined whether or not the increase in accelerator opening is stopped. Note that the configuration for determining the acceleration state of the vehicle based on the control state information of the engine ECU 60 can be similarly applied to the second embodiment.

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Electric motor, 30 ... Assist ECU, 31 ... Microcomputer part, 32 ... Motor drive circuit, 41 ... Steering torque sensor, 50 ... Skid ECU, 60 ... Engine ECU, 70 ... acceleration sensor, 71 ... vehicle speed sensor, 72 ... steering angle sensor, 73 ... yaw rate sensor.

Claims (1)

An electric motor provided in the steering mechanism for generating steering assist torque;
Target current value calculation means for calculating a target current value to be passed through the electric motor based on a driver's steering operation;
An electric power steering apparatus comprising: motor drive control means for driving and controlling the electric motor according to the calculated target current value;
Information acquisition means for acquiring information representing acceleration or deceleration of the vehicle;
Based on the acquired information, a counting means for counting the number of times the acceleration of the vehicle is in an acceleration state exceeding the reference acceleration, or the number of times the vehicle deceleration is in a braking state exceeding the reference deceleration;
A value obtained by subtracting the number of times that the acceleration state has never been reached within the reference time from the number of times that the acceleration state has been reached, or if the braking state has never been within the reference time from the number of times that the braking state has been reached. Subtracting means for calculating a value obtained by subtracting the number of times that there has not been,
Current limiting means for lowering the upper limit value of the target current value of the electric motor or reducing the current limiting coefficient multiplied by the target current value of the electric motor as the value calculated by the subtracting means increases. An electric power steering apparatus comprising:

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