JP4258502B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and more particularly, to an electric power steering device that performs temperature protection control of a motor without providing a temperature sensor. The present invention relates to a control device.

  An electric power steering device for energizing an automobile or vehicle steering device with an auxiliary load by the rotational force of a motor is an auxiliary load applied to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It comes to be energized. In such an electric power steering device, when the end-locking state of the handle is held for a long time in a stationary state or a long garage operation is repeated, a large current continuously flows in the motor. However, there is a problem that it may cause an accident by generating heat, generating smoke, smelling, or even burning.

In order to prevent such heat generation due to excessive use of the motor or to protect the motor, a temperature sensor is conventionally attached to the motor, or a temperature sensor is attached to the radiator of the motor drive element to detect the temperature sensor. The winding temperature of the motor is estimated based on the temperature, and overheating of the motor is prevented according to the winding temperature. Further, as a motor protection device that does not use a temperature sensor, a method of limiting the maximum value of the motor current according to the magnitude of the average current of the motor current every predetermined time, as shown in Patent Document 1, is known. It has been.
Japanese Patent Laid-Open No. 1-186468 JP-A-8-67262

  The above-described method for protecting a motor by attaching a temperature sensor to the motor or the radiator of the driving element is not preferable because it requires a new temperature sensor to be added, resulting in an increase in cost. In addition, in the method of limiting the maximum value of the motor current according to the magnitude of the average current, the motor is driven in a state where there is a sufficient margin with respect to the energization capacity of the motor. Sometimes the maximum current limit works too quickly and the steering assist force is insufficient.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to estimate (detect) the motor winding temperature without newly providing a temperature sensor in the electric power steering apparatus, and to detect the motor temperature. It is an object of the present invention to provide a control device for an electric power steering apparatus that can be used while protecting and further making full use of a current-carrying capacity of a motor.

The present invention includes a torque sensor for detecting a steering torque of a steering wheel, a motor for biasing a steering shaft provided integrally with the steering wheel, and a control for driving the motor in accordance with the magnitude of the steering torque. The above-mentioned object of the present invention is to control the resistance between the motor terminals of the motor based on the detected voltage between the terminals and the detected motor current in the control unit. calculated values, the determined Me was motor terminal resistance value, the motor inter-terminal resistance value used in the mathematical model to determine the motor angular velocity, the winding temperature of the motor based on the motor inter-terminal resistance value determined estimated Back electromotive force constant based on the estimated winding temperature, the back electromotive force constant at a predetermined reference temperature, and the temperature coefficient of the back electromotive force constant. The force constant to temperature correction, the counter electromotive force constant which is temperature corrected, as one of the parameters used in the mathematical model, based on the mathematical model is accomplished by estimating the motor angular speed.

  According to the control device for the electric power steering apparatus of the present invention, the temperature of the motor winding can be estimated without newly providing a temperature sensor, and the temperature protection control of the motor can be performed based on the estimated temperature value. There are benefits that can be realized. Moreover, since the estimation of the motor winding temperature and the temperature protection control can be realized by software control of the control unit, it can be realized easily and economically. Furthermore, since the motor winding temperature is directly monitored, the motor can be reliably protected and the motor can be used up to the thermal performance limit. By correcting the constant used for the calculation of the motor angular velocity according to the estimated temperature value, the angular velocity can be detected more accurately, and stable steering performance independent of the motor temperature can be realized.

  In the present invention, when the rotation state of the motor of the electric power steering device is detected based on the motor back electromotive force and the non-rotation state, that is, the stop state of the motor is detected, the voltage between the motor terminals and the motor current detection value are detected. Thus, the motor winding temperature is estimated and the motor temperature protection is performed based on the winding temperature. Therefore, a new temperature sensor for detecting the motor temperature is not required, and the current is not limited. Therefore, the motor can be used by fully utilizing the current-carrying capacity of the motor. The temperature protection control according to the present invention can be easily handled only by changing the CPU program in the control unit.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the configuration of an electric power steering apparatus suitable for carrying out the present invention will be described with reference to FIG. A shaft 2 of the steering handle 1 is connected to a tie rod 6 of a steering wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1. A motor 20 that assists the steering force of the steering handle 1 is coupled to the shaft 2 via the clutch 21 and the reduction gear 3. Has been. Electric power is supplied from the battery 14 via the ignition key 11 to the control unit 30 that controls the power steering device. The control unit 30 detects 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 above, the steering assist command value I of the assist command is calculated, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I. The clutch 21 is ON / OFF controlled by the control unit 30 and is ON (coupled) in a normal operation state. The clutch 21 is turned off (disconnected) when the control unit 30 determines that the power steering apparatus is out of order and when the power of the battery 14 is turned off by the ignition key 11.

  The control unit 30 is mainly composed of a CPU, and FIG. 2 shows general functions executed by programs in the CPU. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. In addition, it is also possible to configure each functional element with independent hardware without configuring the control unit 30 with a CPU.

  Here, general functions and operations of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by the phase compensator 31 in order to enhance the stability of the steering system, and the phase-compensated steering torque TA is input to the steering assist command value calculator 32. Is done. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I that is a control target value of the current supplied to the motor 20 based on the input steering torque TA and vehicle speed V, and sends the steering assist command value calculator 32 to the steering assist command value calculator 32. Is provided with a memory 33. The memory 33 stores the steering assist command value I corresponding to the steering torque with the vehicle speed V as a parameter, and is used for the calculation of the steering assist command value I by the steering assist command value calculator 32. The steering assist command value I is input to the subtractor 30A, and is also input to the feedforward differential compensator 34 for increasing the response speed. The deviation (Ii) of the subtractor 30A is input to the proportional calculator 35. The proportional output is input to the adder 30B and to the integration calculator 36 for improving the characteristics of the feedback system. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.

In contrast to the general control unit 30 as described above, the present invention adopts a control unit configuration as shown in FIG. 4 in order to obtain the winding temperature of the motor 20. FIG. 4 is shown corresponding to FIG. The steering torque T from the torque sensor 10 is input to the phase compensator 31 and the steering wheel return controller 310, and the vehicle speed V from the vehicle speed sensor 12 is input to the steering wheel return controller 310 and the convergence controller 311, and steering assist A steering assist command value I, which is output from the command value calculator 320, is input to the adder / subtractor 321 as an assist command. Steering assist command value Iref, which is the output of the adder-subtracter 321 is input to the subtracter 30 A, the voltage Vb of the current control value E and the battery 14 from the adder 30 B is input to the terminal voltage estimator 340, between the terminals The terminal voltage estimation value Vm from the voltage estimator 340 is input to the angular velocity estimator 331 in the estimator 330. The motor current detection value i from the motor current detection circuit 38 is input to the subtracter 30A and also to the angular velocity estimator 331 in the estimator 330, and the estimated value PR1 estimated by the estimator 330 is the handle return control. The estimated value PR2 is input to the loss torque compensator 312, and the estimated value PR3 is input to the inertia compensator 313. Since the angular velocity ω estimated by the angular velocity estimator 331 in the estimator 330 is directly output as the estimated value PR1, the estimated value PR1 indicates the motor angular velocity ω. Also, since the angular velocity ω is input to the encoder 332 and its sign is determined, the estimated value PR2 indicates the motor rotation direction, and the estimated value PR3 obtained by differentiating the motor angular velocity ω by the approximate differentiator 333 indicates the motor angular acceleration. Show. The handle return signal HR output from the handle return controller 310 is added to the adder / subtractor 321, and the convergence signal AS output from the convergence controller 311 is subtracted into the adder / subtractor 321, from the loss torque compensator 312. The loss torque compensation signal LT and the inertia compensation signal IN from the inertia compensator 313 are added to the adder / subtractor 321, respectively.

  In contrast to the general control unit 30 as described above, the present invention adopts a control unit configuration as shown in FIG. 4 in order to obtain the winding temperature of the motor 20. FIG. 4 is shown corresponding to FIG. The steering torque T from the torque sensor 10 is input to the phase compensator 31 and the steering wheel return controller 310, and the vehicle speed V from the vehicle speed sensor 12 is input to the steering wheel return controller 310 and the convergence controller 311, and steering assist A steering assist command value I, which is output from the command value calculator 320, is input to the adder / subtractor 321 as an assist command. The steering assist command value Iref which is the output of the adder / subtractor 321 is input to the subtractor 30B, the current control value E from the adder 30A and the voltage Vb of the battery 14 are input to the terminal voltage estimator 340, and the terminal voltage estimation is performed. The terminal voltage estimation value Vm from the estimator 340 is input to the angular velocity estimator 331 in the estimator 330. The motor current detection value i from the motor current detection circuit 38 is input to the subtracter 30A and also to the angular velocity estimator 331 in the estimator 330, and the estimated value PR1 estimated by the estimator 330 is the handle return control. The estimated value PR2 is input to the loss torque compensator 312, and the estimated value PR3 is input to the inertia compensator 313. Since the angular velocity ω estimated by the angular velocity estimator 331 in the estimator 330 is directly output as the estimated value PR1, the estimated value PR1 indicates the motor angular velocity ω. Also, since the angular velocity ω is input to the encoder 332 and its sign is determined, the estimated value PR2 indicates the motor rotation direction, and the estimated value PR3 obtained by differentiating the motor angular velocity ω by the approximate differentiator 333 indicates the motor angular acceleration. Show. The handle return signal HR output from the handle return controller 310 is added to the adder / subtractor 321, and the convergence signal AS output from the convergence controller 311 is subtracted into the adder / subtractor 321. The loss torque compensation signal LT and the inertia compensation signal IN from the inertia compensator 313 are added to the adder / subtractor 321, respectively.

  The steering assist command value calculator 320 calculates and outputs a steering assist command value I as an assist command from the steering torque T and the vehicle speed V based on the assist characteristics shown in FIG. The controller 310 assists in the direction in which the steering wheel returns by outputting the steering wheel return signal HR in the steering wheel return state in order to improve the steering wheel return characteristic at medium and low speeds. The convergence controller 311 applies a brake to the operation of the steering wheel swinging in order to improve the yaw convergence of the vehicle. Therefore, the vehicle speed V from the vehicle speed sensor 12 is input to the handle return controller 310 and the convergence controller 311. In order to cancel the influence of the loss torque of the motor 20, the loss torque compensator 312 outputs a loss torque compensation signal LT and performs assist corresponding to the loss torque in the direction in which the loss torque of the motor 20 is generated, that is, the rotation direction of the motor 20. . The inertia compensator 313 assists the force equivalent to the force generated by the inertia of the motor 20, and outputs an inertia compensation signal IN to prevent deterioration of the sense of inertia or control responsiveness. Therefore, the estimated value PR2 input to the loss torque compensator 312 indicates the motor rotation direction, and the estimated value PR3 input to the inertia compensator 313 indicates the motor angular acceleration.

By the way, as shown in Patent Document 2, for example, the motor angular velocity ω can be obtained from the estimated value of the motor back electromotive force. In other words, the estimated value K _T · ω of the motor back electromotive force is obtained from the motor terminal voltage Vm and the motor current detection value i, with the resistance between the motor terminals as R, by the following equation (1). However, the frequency component of the angular velocity ω of the motor is assumed to be sufficiently lower than the electrical response characteristics of the motor.

(Equation 1)
K _T · ω = Vm−R · i
K _T : Back electromotive force constant The angular velocity ω of the motor 20 can be obtained from the above equation 1, but the resistance R between the motor terminals and the back electromotive force constant K _T vary under the influence of the temperature t. When there is a difference between the actual electric characteristics of the motor and the electric characteristics defined by the mathematical model, the estimated value ω of the motor angular velocity causes an estimation error e with respect to the direction having the offset. In an actual motor, the motor inductance L affects, but the characteristic when the inductance L is ignored is a mathematical model, and is expressed as Vm = R · i. When this offset error e is used, when the correction signal is generated using the estimated value, for example, it is erroneously determined that the motor 20 is rotating regardless of the steered state, and thus an incorrect correction signal is output. . Actually, since the electrical characteristics of the motor 20 are affected by variations in manufacturing and temperature fluctuations, the occurrence of the offset error e is inevitable. In order to solve such a problem, as shown in FIG. 6, it is conceivable to set a fixed dead zone DZ for the estimated value K _T · ω of the motor back electromotive force. There is a problem that the electromotive force cannot be estimated.

(Equation 2)
R = Rm + ΔRt + ΔRp
Rm: resistance value of model, ΔRt: resistance value variation due to temperature,
ΔRp: Due to the resistance value variation due to manufacturing variations, the actual motor terminal voltage Vm is calculated by substituting Equation 2 into Equation 1 (Equation 3).
Vm = (Rm + ΔRt + ΔRp) · i + K _T · ω
On the other hand, in a mathematical model that does not take into account variations during manufacturing and temperature changes, the following equation 4 is obtained.

(Equation 2)
R = Rm + ΔRt + ΔRp
Rm: resistance value of model, ΔRt: resistance value variation due to temperature,
ΔRp: Due to resistance variation due to manufacturing variations, the actual motor terminal voltage Vm is calculated by substituting Equation 3 into Equation 1 above.

(Equation 3)
Vm = (Rm + ΔRt + ΔRp) · i + K _T · ω
On the other hand, in a mathematical model that does not take into account variations during manufacturing and temperature changes, the following equation 4 is obtained.

(Equation 4)
Vm = Rm · i + K _T · ω ′
Therefore, the estimation error e of the back electromotive force is obtained from the above equations 3 and 4.

(Equation 5)
e = K _T · ω′−K _T · ω
= Vm-Rm.i- {Vm- (Rm + .DELTA.Rt + .DELTA.Rp) .i}
= (ΔRt + ΔRp) · i
Thus, an offset error e proportional to the current i is generated. Therefore, for example, by performing the dead band process proportional to the current i in the relationship shown in FIG. 7, the offset value is small when the current i is small, and the dead band width DZ = K · i is accordingly reduced. The motor back electromotive force can be estimated even in a region where the angular velocity ω is small.

  By the way, when the angular velocity ω is estimated from the current control value E that is a PWM output and the motor current value i, the dead zone width DZ is assumed to be proportional to the motor current value i. That is, DZ = K · i is established with K as a constant. In this case, the value K equal to or greater than the maximum value of the fluctuation of the motor terminal voltage Vm in Equation 5 is set as the proportional coefficient. Therefore, the angular velocity estimation value does not always have the offset error e. Further, even in a region where the actual motor angular velocity is small, the angular velocity estimator 331 can estimate the motor angular velocity ω. Further, when the angular velocity ω of the motor does not coincide with the direction of the current i, that is, when the steering wheel is returned, no offset error occurs as shown in Equation 7 below. Therefore, it is desirable not to perform dead zone correction when the steering wheel return state is detected.

(Equation 6)
K _T · ω ′ = K _T · ω− (ΔRt + ΔRp) · | i |
It is. If | i | ≈0,

(Equation 7)
K _T・ ω ′ ＝ _KT・ ω
It becomes.

FIG. 8 shows an operation example in which the estimator 330 detects the angular velocity ω, the rotation direction, and the stop state of the motor 20. First, the motor current detection circuit 38 detects the motor current value i (step S 1), and the battery 14. Based on the voltage Vb and the current control value E, the terminal voltage estimator 340 calculates the terminal voltage Vm according to Vm = Vb · E (step S2). Then, the angular velocity estimator 331 obtains the angular velocity ω, executes the above equation 1 (step S3), determines whether or not the steering wheel is returned based on the angular velocity ω and the motor current value i (step S4), and returns the steering wheel. In order to determine whether or not the absolute value of the motor back electromotive force K _T · ω is equal to or greater than the dead band width DZ = K · i.

(Equation 8)
| K _T · ω | − | K · i | ≧ 0
Is calculated (step S10). And when the motor back electromotive force is more than the dead band width,

(Equation 9)
ω = sign (K _T · ω) · (| K _T · ω | − | K · i |)
(Step S12), otherwise, the estimated angular velocity value ω = 0 (step S11). In the above Equation 9, if the counter electromotive force _{K T} · omega is positive a sign _{(K T} · _ω) +1, if the counter electromotive force _{K T} · omega is negative sign _{(K T} · ω) is -1. Thereafter, it is determined whether or not the motor angular velocity ω is 0 (step S13), and if it is 0, the motor stop state is detected (step S17). If ω is not 0, it is determined whether or not ω is positive (step S14). For example, if it is positive, it is determined to rotate right (step S16), and if it is negative, it is determined to rotate left (step S15). .

  In the present invention, the rotational state of the motor 20 is detected using the estimated angular velocity value ω of the motor in the angular velocity estimator 331 described above. The estimated value of the angular velocity of the motor has an offset type estimation error e as described above, and there is a drawback that the rotation of the motor is detected despite the steering being maintained, but the dead zone DZ = proportional to the current i. After K · i is provided and offset correction is performed, it is possible to accurately detect the motor stop state and rotation direction.

  By the way, from the number 1

(Equation 10)
R = (Vm−K _T · ω) / i
If the back electromotive force K _T · ω of the motor is 0 or sufficiently small, the resistance between terminals (winding resistance) R of the motor 20 can be calculated.

(Equation 11)
R = Vm / i
Therefore, when the motor stop state is detected using the above-described motor rotation state detection signal, the winding temperature t of the motor 20 is estimated. Further, in estimating the motor angular speed ω, if the resistance R between the terminals of the motor is subject to temperature fluctuations, an estimation error occurs. Therefore, using the estimated temperature value of the resistance between the terminals of the motor, It is good to correct the numerical value. That is, the temperature protection control of the motor includes temperature correction of the inter-terminal resistance R and the counter electromotive force coefficient _KT , and monitoring of the motor rated temperature t _max or less. In this way, the temperature protection control is performed using the estimated temperature value t of the motor. Equation 12 is an example in which the reference temperature is set to 20 ° C., but any temperature can be obtained as the reference temperature.

(Equation 12)
t = (R−R ₂₀ ) / α + 20 (° C.)
R ₂₀ : Resistance value between motor terminals at 20 ° C. α: Temperature coefficient of motor winding FIG. 9 shows an operation example of motor temperature protection according to the present invention. First, the motor rotation state is determined according to the detection operation described above. (Step S20) When the motor stop is determined, the inter-terminal voltage estimator 340 obtains the inter-terminal voltage Vm according to the following equation (13) (Step S21).

(Equation 13)
Vm = E ・ Vb
Then, the motor inter-terminal resistance R is obtained from the motor current value i by the estimator 330 and the inter-terminal voltage Vm obtained by the above equation 13 according to the above equation 11 (step S22). The resistance R between the motor terminals thus determined is set as a mathematical model correction value Rm (step S23), the winding temperature t is calculated according to Equation 12 (step S24), and whether or not it is equal to or lower than the limit temperature value _tmax. Is determined (step S25). When the winding temperature t is larger than the limit temperature value _tmax , motor protection control is performed (step S26). The motor protection control is to prevent the motor 20 from being damaged by self-heating of the motor 20, and examples of the damage include a thermoplastic deformation of a brush holder and a commutator, a motor short circuit due to a breakage of a winding insulator, and the like.

FIG. 10 shows an operation example in the case of obtaining the angular velocity ω, and the resistance R between terminals is set as a correction value Rm of the mathematical model (step S30), and the estimated temperature value t obtained as described above is expressed by the following equation (14). substituted by correcting the counter electromotive force constant _{K T} (step S31).

(Equation 14)
K _T1 = {1 + 0.002 (t−20) / β} · K _T20
Where β is the temperature coefficient of the back electromotive force constant,
K _T20 : The counter electromotive force constant at 20 ° C. and the temperature-corrected counter electromotive force constant K _T1 are used to determine the angular velocity ω according to Equation 1 (step S32). Since the angular velocity ω is obtained using the temperature-corrected constant in this way, the angular velocity ω with higher accuracy can be obtained.

It is a block block diagram which shows an example of an electric power steering apparatus. It is a block diagram which shows the general internal structure of a control unit. It is a connection diagram which shows an example of a motor drive circuit. It is a block diagram which shows the structural example of the control unit by this invention. It is a characteristic view showing an example of the relationship between steering torque and steering assist command value with vehicle speed as a parameter. It is a figure which shows the relationship between a motor back electromotive force and a motor angular velocity. It is a figure which shows the example of a relationship between a motor electric current value and a dead zone width | variety. It is a flowchart which shows the operation example which detects the stop state of a motor. It is a flowchart which shows the operation example of motor protection. It is a flowchart which shows the operation example of the temperature correction of a back electromotive force constant.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 5 Pinion rack mechanism 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 31 Phase compensator 37 Motor drive circuit 38 Motor current detection circuit 330 Estimator 340 Terminal voltage estimator

Claims (1)

A torque sensor for detecting a steering torque of the steering wheel; a motor for biasing a steering shaft provided integrally with the steering wheel; and a control unit for driving the motor in accordance with the magnitude of the steering torque. In the control device for the electric power steering device,
In the control unit,
The detected between terminals on the basis of the voltage and the motor current detection value seek motor terminal resistance value of the motor has a determined Me was motor terminal resistance, motor terminal used in the mathematical model to determine the motor angular velocity resistance and,
Estimating the winding temperature of the motor based on the calculated resistance value between the motor terminals,
Temperature correction of the back electromotive force constant based on the estimated winding temperature, the back electromotive force constant at a predetermined reference temperature, and the temperature coefficient of the back electromotive force constant,
The temperature-corrected back electromotive force constant is one of the parameters used in the mathematical model,
A control device for an electric power steering device , wherein the motor angular velocity is estimated based on the mathematical model .

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