JP2010126081A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for properly correcting assist characteristics corresponding to a state when the overheat protection of the electric power steering device is required, and preventing the degradation of steering feeling due to rapid change of steering assist force. <P>SOLUTION: In this electric power steering device provided with a control unit that computes a steering assist command value based on steering torque and vehicle speed, and drives a motor with a current command value that is the steering assist command value of which the maximum value is limited through a driving control part, and applying assist torque to a vehicle steering mechanism by driving the motor, a function for detecting the temperature of the control unit every predetermined time, correcting the limit value of the maximum value based on the detected temperature gap between the first detection temperature and the second detection temperature, and correcting the steering assist command value is provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a steering assist force to a steering system, and in particular, an electric power steering apparatus that corrects assist characteristics of the electric power steering apparatus based on a detected temperature difference before and after a predetermined time elapses. Relates to the device.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the detected motor current is small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  The general configuration of the electric power steering apparatus will be described with reference to FIG. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering wheel 1, and a motor 20 that assists the steering force of the steering wheel 1 is connected to the column shaft 2 via the reduction gear 3. . Electric power is supplied from the battery 13 to the control unit 30 that controls the electric power steering device, and an ignition key signal is input through the ignition key 11. The control unit 30 calculates a steering assist command value (current command value) I of an assist (steering assist) command based on the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12. Based on the calculated steering assist command value I, the current supplied to the motor 20 is controlled.

  The control unit 30 is mainly composed of a CPU (or MPU or MCU). FIG. 7 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 7. The steering torque T detected and input by the torque sensor 10 and the vehicle speed V from the vehicle speed sensor 12 are input to the steering assist command value calculation unit 31. Thus, the steering assist command value Iref1 is calculated. The calculated steering assist command value Iref1 is phase compensated by the phase compensator 32 for enhancing the stability of the steering system, and the phase compensated steering assist command value Iref2 is input to the adder 33. Further, the steering torque T is input to a feedforward differential compensation unit 35 for increasing the response speed, and the differentially compensated steering torque TA is input to an addition unit 33, which adds the steering assist command value Iref2 and the steering. Add torque TA. The steering assist command value Iref3 as the addition result is input to the current limiting unit 36, and the current limiting unit 36 performs steering when the steering assist command value Iref3 is larger than the maximum current value Imax set in the current limiting unit 36. The auxiliary command value Iref3 is limited to the maximum current value Imax. Then, the current command value Iref4 that is the output of the current limiting unit 34 is input to the subtracting unit 34.

  The subtractor 34 obtains a deviation Iref5 = (Iref4-i) between the current command value Iref4 and the motor current i fed back, and the deviation Iref5 is PI-controlled by the PI controller 37 and further input to the PWM controller 38. The duty is calculated, and the motor 20 is PWM driven via the inverter 39. The motor current value i of the motor 20 is detected by a motor current detecting means (not shown), and is input to the subtracting unit 34 and fed back.

  Such a conventional electric power steering apparatus has a function of limiting the motor current and performing overheat protection in order to prevent overheating of the motor and the drive element due to the continued high output state of the motor.

  Japanese Patent No. 3055777 (Patent Document 1) discloses an electric power steering device that prevents a decrease in steering feeling due to a sudden decrease in steering assist force for overheat protection. In this electric power steering apparatus, the heat generation amount Ch is calculated from the motor current value, and this heat generation amount Ch is compared with the first heat generation amount signal Cf and the second heat generation amount signal Cm. The first calorific value signal Cf is a calorific value signal that is estimated that the temperature of the motor driving means for driving the motor becomes the first predetermined value, and the second calorific value signal Cm is the second value of the electric motor driving means that is the second temperature value. It is a calorific value signal estimated to be a predetermined value. When the heat generation amount Ch exceeds the first heat generation amount signal Cf, in order to limit the maximum value of the steering assist force, the maximum value of the motor current is limited so that the heat generation amount Ch is greater than the first heat generation amount signal Cf. Is greater than the second second calorific value signal Cm, the steering assist force is corrected to decrease.

Further, in the electric power steering apparatus disclosed in Japanese Patent No. 3198834 (Patent Document 2), as a countermeasure against the heat generation of the motor, the maximum assist current characteristic is not limited but the steering assist force characteristic with respect to the steering torque is changed. In this way, the feeling during steering is made to have a uniform weight. In this electric power steering device, when the average value of the drive current of the motor exceeds a specified value, the slope of the steering torque-motor current characteristic is changed, and the motor current value is changed from before the change with respect to the same steering torque. Also try to decrease.
Japanese Patent No. 3055777 Japanese Patent No. 3198834

  In recent years, electric power steering devices have been installed in large vehicles with displacements exceeding 2000 CC. In such a large vehicle, since it is necessary to apply a large steering assist force, the motor rating of the electric power steering device and the current supplied to the motor increase, and the amount of heat generation tends to increase. In addition, if the motor current is limited for overheat protection, the motor of the electric power steering device mounted on the large vehicle has a larger torque constant than the motor of the electric power steering device mounted on the small vehicle. Even when the current is limited to the same level, the reduction in the steering assist force is larger in a large vehicle than in a small vehicle. For this reason, there is a strong demand for an electric power steering apparatus that can more appropriately limit the motor current for overheat protection.

  In the electric power steering device described in Patent Document 1 described above, when the amount of heat generation exceeds a predetermined value, a certain correction is made to the steering assist force in accordance with the amount of heat generation. In other words, the steering assist force is corrected at a constant temperature, and the speed of temperature rise is not taken into account when correcting the steering assist force. For this reason, the correction amount of the steering assist force may be excessive or insufficient, and there is a problem that appropriate correction is difficult.

  Further, in the electric power steering device described in Patent Document 2 described above, since the inclination of the steering torque-motor current characteristic is changed, when the average value of the motor drive current exceeds a specified value, the steering torque is reduced. Even if it is small, there is a problem that the motor current is limited and the steering assist force is limited. In particular, in stationary steering such as garage storage that requires steering assistance, the steering assistance force is restricted from the stage where the restriction of the steering assistance force is not necessary, and the driver's burden may increase.

  The present invention has been made for the above-described circumstances, and an object of the present invention is to appropriately correct assist characteristics according to the situation when there is a need for overheating protection of an electric power steering device, and to steer the vehicle. An object of the present invention is to provide an electric power steering apparatus that can prevent a decrease in steering feeling due to a sudden change in auxiliary force.

  The present invention comprises a control unit that calculates a steering assist command value based on the steering torque and the vehicle speed, and drives the motor via a drive control unit with a current command value that limits the maximum value of the steering assist command value. The present invention relates to an electric power steering device that applies an assist torque to a steering mechanism of a vehicle by driving the motor, and the object of the present invention is to detect the temperature of the control unit every predetermined time, The gain 1 for correcting the limit value of the maximum value is detected by providing the function of correcting the limit value of the maximum value based on the detected temperature difference between the two detected temperatures and correcting the steering assist command value. The gain 2 for correcting the steering assist command value is based on the detected temperature difference because it changes based on the temperature difference. Is achieved by which is so varied.

  The present invention also provides a steering assist command value calculation unit that calculates a steering assist command value based on a steering torque and a vehicle speed, a current limiting unit that limits a maximum value of the steering assist command value, and a current from the current limiting unit. An electric power steering apparatus having a control unit including a drive control unit for driving a motor with a command value, and applying an assist torque to a steering mechanism of a vehicle by driving the motor. A temperature detection unit that detects the temperature of the unit; and an assist characteristic correction unit that instructs the current limiting unit and the steering assist command value calculation unit to correct the assist characteristic based on the temperature detected by the temperature detection unit; When the first detected temperature detected by the temperature detection unit is greater than a predetermined temperature, the assist characteristic correction unit, The second detection temperature detected by the temperature detection unit after a predetermined time has elapsed since the detection of the first detection temperature is input, and the detection temperature difference between the second detection temperature and the first detection temperature is input based on the detected temperature difference. A correction value for correcting the assist characteristic is obtained, and the current limiting unit and the steering assist command value calculation unit correct the assist characteristic based on the correction value, or the assist characteristic correction unit includes: When the detected temperature difference is greater than or equal to a first predetermined value, by correcting the assist characteristic by limiting the maximum value of the steering assist command value according to the magnitude of the detected temperature difference, or the assist characteristic The correction unit reduces the gain of the steering assist command value according to the magnitude of the detected temperature difference when the detected temperature difference is greater than or equal to a second predetermined value that is greater than the first predetermined value. The assist characteristic correction unit calculates the detected temperature difference at every temperature sample interval while the first detected temperature is higher than the predetermined temperature. Or when the assist characteristic correction unit determines that the first detected temperature is equal to or lower than the predetermined temperature and the steering torque determination unit determines that the steering torque is smaller than a predetermined torque value. When the correction unit corrects the assist characteristic, the assist characteristic correction unit cancels the correction of the assist characteristic, or when the first detected temperature is equal to or lower than the predetermined temperature, the assist characteristic correction The unit is effectively achieved by inputting the first detected temperature detected by the temperature detecting unit every predetermined time. The

  According to the electric power steering device of the present invention, when there is a need for overheat protection, the assist characteristic is appropriately corrected according to the situation, so that the steering feeling is reduced due to a sudden change in the steering assist force. Can be prevented.

  In addition, since the motor current for overheat protection can be more appropriately limited, the motor current can be suitably used even in a large vehicle that may place a heavy burden on the driver due to the excessive limitation of the motor current.

  In the electric power steering apparatus according to the present invention, when the first detected temperature detected by the control unit of the electric power steering apparatus exceeds a predetermined value, the second detection is performed after a predetermined time from the time when the first detected temperature is detected. The temperature is detected, and the assist characteristic is corrected based on the difference between the second detected temperature and the first detected temperature. Since the assist characteristic is corrected by correcting the maximum current value and the steering assist command value, it is possible to correct the assist characteristic appropriately according to the situation when overheat protection is necessary. Become.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram showing the overheat protection means of the electric power steering apparatus according to the present invention corresponding to FIG. The overheat protection means 100 is provided in the control unit 30 and has a temperature detection unit 101 for detecting the temperature of the control unit 30 (for example, the inverter 39) and an assist characteristic based on the temperature detected by the temperature detection unit 101. An assist characteristic correcting unit 102 that instructs the steering assist command value calculating unit 31 and the current limiting unit 36 to correct, and a steering torque determining unit 103 that determines whether or not the steering torque T is equal to or less than a predetermined value _Tth. It has.

  An example of the operation of the overheat protection means 100 will be described with reference to the flowchart of FIG.

When the first detection temperature theta ₁ of the control unit 30 by the temperature detection unit 101 is detected (step S1), the greater than a predetermined temperature theta _d that first detected temperature theta ₁ is assist characteristic correcting unit 102 is set in advance It is determined whether or not (step S2). If the first detected temperature theta ₁ is greater than the predetermined temperature theta _d, assist characteristic correction unit 102 sets the assist correction flag (step S3), and the second detection temperature theta detected by the temperature detection unit 101 after the predetermined time T _{md 2} is input (step S4). Then, the assist characteristic correcting unit 102 calculates the detected temperature difference Δθ = θ ₂ −θ ₁ from the first detected temperature θ ₁ and the second detected temperature θ ₂ (step S5), and whether the detected temperature difference Δθ is greater than 0. It is determined whether or not (step S6).

  In step S6, when the detected temperature difference Δθ is 0 or less, the process returns to step S1.

On the other hand, if the detected temperature difference [Delta] [theta] is greater than 0, corrects _{G lim} upper limit of the maximum motor current ([Delta] [theta]) (step S7), and performs further assist map gain correction _{G map} the ([Delta] [theta]) (step S8 ). The upper limit value of the motor maximum current is corrected by setting a value obtained by multiplying the maximum current value Imax before correction by a coefficient G _lim (Δθ) as a correction value for the maximum current value. Further, the assist characteristic correction unit 102 inputs the correction value G _lim (Δθ) · Imax of the maximum current value to the current limiting unit 36, and the current limiting unit 36 inputs the correction value G _lim (Δθ of the input maximum current value). ) · Imax is set as a new maximum current value to limit the maximum value of the steering assist command value Iref3.

Here, the coefficient G _lim (Δθ) changes as shown in FIG. 3, for example, according to the detected temperature difference Δθ. That is, when the detected temperature difference Δθ is smaller than the predetermined value a1, it is “1.0”. When the detected temperature difference Δθ reaches the predetermined value a1, the value Ga1 is smaller than “1.0”, and the detected temperature difference Δθ is the predetermined value. When it becomes larger than a1, it gradually decreases linearly, and when the detected temperature difference Δθ becomes equal to or larger than the predetermined value b1, the constant value Gb1 is held. The gain decrease when the detected temperature difference Δθ is between the predetermined value a1 and the predetermined value b1 may be nonlinear.

The correction of the gain of the assist map, that is, the correction of the gain of the motor current is performed by setting a value obtained by multiplying the gain G before correction by a coefficient G _map (Δθ) as a gain correction value G · G _map (Δθ). The assist characteristic correction unit 102 inputs the gain correction value G · G _map (Δθ) to the steering assist command value calculation unit 31, and the steering assist command value calculation unit 31 inputs the gain correction value G · G _map (Δθ). As a new gain, the assist map gain is corrected.

Here, the coefficient G _map (Δθ) changes as shown in FIG. 4, for example, according to the detected temperature difference Δθ. That is, when the detected temperature difference Δθ is smaller than the predetermined value a2 (> a1), it is “1.0”, and when the detected temperature difference Δθ reaches the predetermined value a2, the value Ga2 is smaller than “1.0”. When Δθ becomes larger than the predetermined value a2, it gradually decreases linearly, and when the detected temperature difference Δθ becomes equal to or larger than the predetermined value b2, the constant value Gb2 is held. The gain decrease when the detected temperature difference Δθ is between the predetermined value a2 and the predetermined value b2 may be nonlinear.

On the other hand, if the first detected temperature theta ₁ in step S2 is determined to be equal to or less than the predetermined temperature theta _d, assist characteristic correcting unit 102 determines whether the assist correction flag is set (step S9). When it is determined that the assist correction flag is set, the steering torque determination unit 103 determines whether or not the steering torque T is equal to or less than a predetermined value _Tth (step S10). When it is determined that the steering torque T is equal to or less than the predetermined value _Tth , the assist characteristic correction unit 102 cancels the assist correction flag (step S11), corrects the upper limit value of the motor maximum current, and sets the assist map gain. The correction is canceled, and the process returns to step S1 to repeat the above operation.

If it is determined in step S9 that the assist correction flag is not set, or if it is determined in step S10 that the steering torque T is greater than the predetermined value _Tth , the process returns to step S1. Repeat the above operation.

Incidentally, the assist characteristic correction unit 102 calculates the detected temperature difference Δθ for each temperature sample interval T _s while the first detected temperature θ ₁ is higher than the predetermined temperature θ _d . For example, as shown in FIG. 5, when the first detected temperature θ ₁ (1) exceeds the predetermined temperature θ _d at the time t (1), the second time at the time t (1) + T _md after the predetermined time T _md . When the detected temperature θ ₂ (1) is detected, and the detected temperature difference Δθ (1) = θ ₂ (1) −θ ₁ (1) is larger than 0, the assist characteristic depends on the value of the detected temperature difference Δθ (1). Is corrected. In parallel with this, the first detected temperature θ ₁ (2) is detected at the time t (2) = t (1) + T _{s after} the temperature sample interval T _{s of} the time t (1). When the first detection temperature θ ₁ (2) exceeds the predetermined temperature θ _d , the second detection temperature θ ₂ (2) is detected at the time point t (2) + T _md . When the detected temperature difference Δθ (2) = θ ₂ (2) −θ ₁ (2) is larger than 0, the assist characteristic is corrected according to the value of the detected temperature difference Δθ (2). Next, in order to calculate the third detected temperature difference Δθ (3) = θ ₂ (3) −θ ₁ (3) at time t (3) = t (2) + T _s , the first detected temperature θ ₁ (3) is detected. In this way, the detection temperature difference Δθ is calculated every temperature sample interval T _s until the first detection temperature θ ₁ becomes equal to or lower than the predetermined temperature θ _d .

While the first detected temperature θ ₁ is equal to or lower than the predetermined temperature θ _d , the assist characteristic correcting unit 102 inputs the first detected temperature θ ₁ detected by the temperature detecting unit 101 every predetermined time T ₀ .

  As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to this, In the range which does not deviate from the meaning, it can change suitably.

It is a block block diagram which shows the structural example of the electric power steering apparatus which mounts the overheat protection means which concerns on this invention. It is a flowchart which shows the operation example of this invention. It is a figure which shows the relationship between coefficient _Glim for correcting the motor maximum electric current upper limit, and detected temperature difference (DELTA) (theta). It is a figure which shows the relationship between coefficient _Gmap for correcting the gain of an assist map, and detected temperature difference (DELTA) (theta). The temperature sample interval T _s to calculate the detected temperature difference [Delta] [theta], is a diagram illustrating the relationship between the detected temperature and time. It is a figure showing an example of composition of a general electric power steering device. It is a block diagram which shows the structural example of a control unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering wheel 2 Column shaft 4a, 4b Universal joint 5 Pinion rack mechanism 6 Tie rod 10 Torque sensor 11 Ignition key 12 Vehicle speed sensor 13 Battery 20 Motor 30 Control unit 31 Steering assistance command value calculating part 32 Phase compensation part 35 Differential compensation part 36 Current Limiting unit 37 PI control unit 38 PWM drive unit 39 Inverter 100 Overheat protection means 101 Temperature detection unit 102 Assist characteristic correction unit 103 Steering torque determination unit

Claims (9)

A control unit that calculates a steering assist command value based on the steering torque and the vehicle speed, and drives the motor via a drive control unit with a current command value that limits a maximum value of the steering assist command value; In the electric power steering apparatus that applies assist torque to the steering mechanism of the vehicle by detecting the temperature of the control unit every predetermined time, and based on the detected temperature difference between the first detected temperature and the second detected temperature An electric power steering apparatus comprising a function of correcting a limit value of a maximum value and correcting the steering assist command value. The electric power steering apparatus according to claim 1, wherein a gain 1 for correcting the limit value of the maximum value is changed based on the detected temperature difference. The electric power steering apparatus according to claim 1 or 2, wherein a gain 2 for correcting the steering assist command value is changed based on the detected temperature difference. A steering assist command value calculation unit that calculates a steering assist command value based on the steering torque and the vehicle speed, a current limiting unit that limits the maximum value of the steering assist command value, and a current command value from the current limiting unit An electric power steering apparatus that provides an assist torque to a steering mechanism of a vehicle by driving the motor, and a temperature detection unit that detects a temperature of the control unit; An assist characteristic correction unit that instructs the current limiting unit and the steering assist command value calculation unit to correct the assist characteristic based on the temperature detected by the temperature detection unit, and the assist characteristic correction unit includes the temperature When the first detected temperature detected by the detection unit is higher than a predetermined temperature, the predetermined temperature is detected after the first detected temperature is detected. A correction for inputting a second detection temperature detected by the temperature detection unit after a lapse of time and correcting the assist characteristic based on a detected temperature difference between the second detection temperature and the first detection temperature The electric power steering apparatus is characterized in that the current limiting unit and the steering assist command value calculation unit correct the assist characteristic based on the correction value. The assist characteristic correction unit corrects the assist characteristic by limiting a maximum value of the steering assist command value according to a magnitude of the detected temperature difference when the detected temperature difference is equal to or greater than a first predetermined value. The electric power steering apparatus according to claim 4. The assist characteristic correction unit reduces the gain of the steering assist command value according to the magnitude of the detected temperature difference when the detected temperature difference is greater than or equal to a second predetermined value that is greater than the first predetermined value. The electric power steering apparatus according to claim 5, wherein the assist characteristic is corrected. The electric assist according to any one of claims 4 to 6, wherein the assist characteristic correcting unit calculates the detected temperature difference at each temperature sample interval while the first detected temperature is higher than the predetermined temperature. Power steering device. When the assist characteristic correcting unit determines that the first detected temperature is equal to or lower than the predetermined temperature and the steering torque determining unit determines that the steering torque is smaller than a predetermined torque value, the assist characteristic correcting unit The electric power steering apparatus according to any one of claims 4 to 7, wherein when the characteristic is corrected, the assist characteristic correction unit cancels the correction of the assist characteristic. 9. The assist characteristic correction unit inputs the first detection temperature detected by the temperature detection unit every predetermined time when the first detection temperature is equal to or lower than the predetermined temperature. Electric power steering device.

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