JP4040309B2 - Control device for electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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 particularly when a high assist gain characteristic is adopted, before and after exceeding the motor output limit. The present invention relates to a control device for an electric power steering device that avoids a sudden change in steering force.
[0002]
[Prior art]
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. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). The feedback control adjusts the motor applied voltage so that the difference between the current control value and the motor current detection value becomes small. The adjustment of the motor applied voltage is generally performed by a PWM (pulse width modulation) control duty. This is done by adjusting the tee ratio.
[0003]
Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 10. The shaft 2 of the handle 1 is coupled to a tie rod 6 of a traveling wheel via a reduction gear 3, universal joints 4 a and 4 b, and a pinion rack mechanism 5. Has been. The shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1, and a motor 20 that assists the steering force of the handle 1 is coupled to the shaft 2 via the reduction gear 3. Electric power is supplied from a battery 14 via an ignition key 11 and a relay 13 to a control unit (ECU) 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 sensor 12. The steering assist command value I of the assist command is calculated on the basis of the vehicle speed V detected in step S1, and the current supplied to the motor 20 is controlled based on the calculated steering assist command value I.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 11 shows general functions executed by a program inside the CPU.
[0005]
The function and operation 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 improve the stability of the steering system, and the phase-compensated steering torque. TA is input to the steering assist command value calculator 32. 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 calculates a steering assist command value I, which is a control target value of the current supplied to the motor 20, based on the input steering torque TA and vehicle speed V, by using a preset data table or function formula. To determine. 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. At the same time, it is input to an integration calculator 36 for improving the characteristics of the feedback system. The output of the proportional calculator 35 is input to the adder 30B, and the outputs of the differential compensator 34 and the integral calculator 36 are also added to the adder 30B, and the current control value E that is the addition result of the adder 30B is obtained. The motor drive signal 37 is input 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 detected motor current value i is input to the subtractor 30A and fed back.
[0006]
As described above, in a general electric power steering apparatus, a motor current corresponding to at least a steering torque is calculated, and this calculated appropriate current is given to the motor. The most important part is a steering assist command value calculator 32, which is obtained from the normal steering torque T using a preset data table or a predetermined function equation (for example, Japanese Patent Laid-Open Nos. 10-59203 and 8). -150954).
[0007]
[Problems to be solved by the invention]
As described above, when the current command value is obtained from the steering torque T using a preset data table or function equation, the current command value may be higher than the steering torque T depending on the characteristics of the vehicle or the steering mechanism. May need to be set (high assist gain as in a hydraulic power steering device). In such a case, the output limit of the motor is often reached, and when the output limit is reached, the amount of assist with respect to the steering force suddenly decreases, and the steering feeling near this steering torque is worsened. is there.
[0008]
The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a motor output limit when an electric power steering device adopts a high assist gain characteristic like a hydraulic power steering device. It is an object of the present invention to provide a control device for an electric power steering apparatus that avoids a sudden change in steering force before and after exceeding.
[0009]
[Means for Solving the Problems]
The present invention provides the motor for applying a steering assist force to a steering mechanism based on a current control value calculated from a steering assist command value calculated by a calculation means based on a steering torque generated in a steering shaft and a current value of the motor. The above object of the present invention is to control the motor from the motor current and the voltage between the motor terminals , or from the motor current and the motor angular velocity. This is achieved by providing a function of multiplying the steering assist command value by a coefficient that gradually decreases as the output limit is approached.
[0010]
Further, the above object of the present invention can be achieved more effectively by making the function expression a nonlinear function by making the coefficient a function expression greater than 0 and less than or equal to 1.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the electric power steering apparatus, a motor current corresponding to the steering torque is calculated and an appropriate current is given to the motor. This current value is calculated using a data table or a function formula set in advance based on the steering torque. It is determined. In this case, depending on the characteristics of the vehicle and the steering mechanism, the assist gain must be set so that the current command value becomes higher with respect to the steering torque.In this state, when the motor output limit is reached, The assist amount with respect to the steering force is rapidly reduced, and the steering feeling is deteriorated. However, in the present invention, in order to smoothly reduce the assist gain, whether or not the motor output limit is approached is detected from the motor rotational speed, the motor current and the motor voltage. By multiplying a coefficient that becomes smaller, a sudden decrease in assist gain is prevented. Thereby, it is possible to maintain a good steering feeling even near the output limit of the motor.
[0012]
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a control function block diagram of the present invention, in which a steering torque T from a torque sensor is input to a steering assist command value calculation unit 100 and a center response improvement unit 101, and each output is input to an adder 102. The addition result is input to the torque control calculation unit 103. A vehicle speed V is also input to the steering assist command value calculation unit 100. The center responsiveness improvement unit 101 ensures stability in the assist characteristic dead zone and compensates for static friction. The output signal of the torque control calculation unit 103 is input to the motor loss current compensation unit 104, and the output is input to the maximum current limiting unit 106 via the adder 105, and the maximum current value is limited by the maximum current limiting unit 106 to control the current. Input to the unit 110. The motor loss current compensator 104 adds a current that does not appear in the motor output even when the motor current flows to improve the rise from the motor output torque 0, and the maximum current limiter 106 has a maximum current command value rated. The current is limited. The output of the current control unit 110 is input to the current drive circuit 112 via the H bridge characteristic compensation unit 111, thereby driving the motor 113.
[0014]
The motor current i of the motor 113 is input to the motor angular velocity estimation unit 121, the current drive switching unit 122 and the current control unit 110 through the motor current offset correction unit 120 and also to the motor output limit detection unit 200. The motor terminal voltage Vm is input to the motor angular velocity estimation unit 121 and also input to the motor output limit detection unit 200. Further, the angular velocity ω estimated by the motor angular velocity estimation unit 121 is input to the motor angular acceleration estimation unit / inertia compensation unit 123, the motor loss torque compensation unit 124 , the yaw rate estimation unit 125, and the motor output limit detection unit 200 , and the yaw rate estimation is performed. The output of the unit 125 is input to the convergence control unit 126, the outputs of the convergence control unit 126 and the motor loss torque compensation unit 124 are added by the adder 127, and the addition result is input to the adder 102.
[0015]
The motor angular acceleration estimator / inertia compensator 123 eliminates the torque for accelerating / decelerating the motor inertia from the steering torque so as to make the steering feel without inertia, and the convergence control unit 126 improves the convergence of the behavior of the vehicle in the yaw direction. Therefore, the brake is applied to the movement of the steering wheel, and the motor loss torque compensator 124 assists the loss torque of the motor 113, that is, the assist equivalent to the loss torque with respect to the rotation direction of the motor 113. Do. The loss torque is a friction loss based on the motor structure and a loss based on a magnetic factor among the output torque of the motor. Such a loss torque is a steering direction when a slight steering is performed during straight traveling. On the other hand, an unintended force is added, or a force in the opposite direction is added, which deteriorates the steering feeling. Also, a current dither signal generation unit 130 is provided, and outputs of the current dither signal generation unit 130 and the motor angular acceleration estimation unit / inertia compensation unit 123 are added by the adder 131, and the addition result is added to the adder 105. Have been entered. The current dither signal generator 130 prevents the motor from sticking due to static friction.
[0016]
Furthermore, the motor terminal voltage Vm to the motor output limit detection unit 200, and the motor angular velocity omega, and the motor current i is inputted, adapted to detect the motor output limit, the steering assist command value limit detection signal LS Input to the arithmetic unit 100. The limit detection signal LS outputs a difference (PLIM-P) from the limit value when the motor output limit is PLIM [W] and the motor output is P [W].
[0017]
Here, the motor output limit detection unit 200 of the present invention performs the following calculation.
[0018]
The motor output P can be obtained by the following equation (1), where T _m [N · m] is the motor output torque and ω [rad / s] is the angular velocity of the motor.
[0019]
P = T _m × ω (1)
The motor output torque T _m is expressed by the following equation (2), where K _T [N · m / A] is the motor torque constant and i [A] is the motor current.
[0020]
T _m = K _T × i (2)
When the above equation (2) is substituted into the equation (1), the motor output P becomes the following equation (3).
[0021]
P = KT × i × ω (3)
Since the torque constant KT is known, the motor output P can be estimated from the motor current i and the angular velocity ω. The estimation of the angular velocity ω is described in , for example, Japanese Patent Laid-Open No. 10-109655, and the angular velocity ω estimated by the motor angular velocity estimation unit 122 may be used.
[0022]
On the other hand, the motor angular velocity ω is expressed by the following equation (4) when the voltage between the motor terminals is Vm [V], the motor winding resistance is Rm [Ω], and the electromotive force constant of the motor is Ke [V · s / rad]. Desired.
[0023]
ω = (Vm−i · Rm) / Ke (4)
Here, since the torque constant _KT and the electromotive force constant Ke are the same value in the same motor, when the equation (4) is substituted into the equation (3), the motor output P is expressed by the following equation (5).
[0024]
P = i · (Vm−i · Rm) (5)
Since the winding resistance Rm is known, the motor output P can be estimated also by the motor current i and the motor terminal voltage Vm. Further, when there is a motor angular velocity sensor or a steering angle sensor, the angular velocity may be obtained from this.
[0025]
As described above, the limit detection signal LS (= P _LIM −P) indicating the motor output limit is input from the motor output limit detection unit 200 to the steering assist command value calculation unit 100. As shown in FIG. 2, the steering assist command value calculator 100 calculates a steering assist command value SS1 based on the steering torque T, and gains the steering assist command value SS1 based on the vehicle speed V. The vehicle speed gain multiplication unit 100B that multiplies and outputs the steering assist command value SS2 and the output limit range gain multiplication unit 100C that gain-multiplies the steering assist command value SS2 by the limit detection signal LS. The multiplication of the vehicle speed gain is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-150954.
[0026]
Here, by measuring the output limit PLIM of the motor in advance, the difference (PLIM-P) between the motor output P and the output limit PLIM calculated by the equation (3) or (5) can be known. A gain characteristic as shown in FIG. 3 is set in advance so that the gain can be reduced (limit detection signal LS) and the difference becomes smaller as the difference becomes smaller. That is, the gain Gain is “1” or a value close to “1” when the motor output P is small, and the gain Gain is smaller than “1” when the motor output P is close to the large output limit PLIM. It is a non-linear function that changes. Then, by multiplying the steering assist command value SS2 after the vehicle speed gain multiplication by a gain characteristic as shown in FIG. 3, the steering assist command value SS3 is increased in a region where the motor output P is small, and the motor output P is set to the output limit. In a region close to PLIM, the steering assist command value SS3 is output small.
[0027]
The characteristics shown in FIG. 3 are merely examples. The gain Gain is large (maximum value “1”) when the motor output P is small, and the gain Gain is small (“0”) when the motor output P is close to the output limit P _LIM. (Large) As long as the function expression changes, it may be non-linear or linear.
[0028]
Next, the configuration of other parts in FIG. 1 will be briefly described. In this example, as shown in FIG. 4, the center response improvement unit 101 is configured by a phase compensation unit 101A, an approximate differentiation unit 101B, and a gain setting unit 101C. The phase compensation unit 101A has frequency characteristics shown in FIG. The differentiator 101B has the frequency characteristics shown in FIG. As a result, the combined characteristics of phase compensation and approximate differentiation are as shown in FIG. The gain setting unit 101C switches and sets the gain according to the vehicle speed V and the steering torque T. Furthermore, in order to reduce the uneasy steering feeling that the steering wheel is suddenly returned and to stabilize the steering, the steering torque is increased and the steering torque change rate is increased, and the gain is decreased in the steering torque decreasing direction.
[0029]
In the present invention, the assist characteristic based on the three representative vehicle speeds (0, V1, V2 Km / h) is set as a basic characteristic in the calculation of the assist amount in the steering assist command value calculation unit 100, and the vehicle speed interpolation gain is set at other vehicle speeds. Accordingly, interpolation is performed between the basic characteristics at a vehicle speed of 2 km / h. The vehicle speed setting range of assist characteristics is 0 to V2 km / h, and the resolution is 2 km / h. The basic assist characteristics (torque versus current) are as shown in FIG. 8, and are represented by 0 km / h = Io characteristics, V1 = Ia characteristics, and V2 = Ib characteristics. The vehicle speed interpolation calculation for other vehicle speeds is performed every 2 Km / h with the vehicle speed (Km / h) vs. vehicle speed interpolation coefficient γ shown in FIG. When the vehicle speed is 0 to V1, the assist current I is I = Ia (T) + γ (V) (Io (T) −Ia (T)), and when the vehicle speed is (V1 + 2) to V2 Km / h, the assist current I is I = Ib (T) + γ (V) (Ia (T) −Ib (T)).
[0030]
【The invention's effect】
In the present invention, whether or not the motor output limit is approached is detected from the motor current and the motor voltage, and when approaching the output limit, a coefficient that gradually becomes smaller than 1 is multiplied so that the sudden assist gain is increased. Prevent reduction. Thereby, it is possible to maintain a good steering feeling even near the motor output limit.
[Brief description of the drawings]
FIG. 1 is a control function block diagram of the present invention.
FIG. 2 is a block diagram illustrating a configuration example of a steering assist command value calculation unit according to the present invention.
FIG. 3 is a diagram illustrating an example of gain multiplication characteristics according to the present invention.
FIG. 4 is a block configuration diagram of a center response improvement unit.
FIG. 5 is a diagram illustrating an example of characteristics of a phase compensation unit.
FIG. 6 is a diagram illustrating an example of characteristics of an approximate differentiation unit.
FIG. 7 is a diagram illustrating a combined characteristic of a phase compensation unit and an approximate differentiation unit.
FIG. 8 is a diagram illustrating basic assist characteristics.
FIG. 9 is a diagram illustrating an example of a vehicle speed interpolation calculation.
FIG. 10 is a mechanism diagram showing a general example of electric power steering.
FIG. 11 is a block diagram showing a general internal configuration of a control unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 100 Steering assistance command value calculation part 100A Steering assistance command value calculation part 100B Vehicle speed gain multiplication part 100C Output limit area gain multiplication part 101 Center response improvement part 103 Torque control calculation part 110 Current Control unit 112 Current drive circuit 113 Motor 121 Motor angular velocity estimation unit 124 Motor loss torque compensation unit 125 Yaw rate estimation unit 126 Convergence control unit 200 Motor output limit detection unit

Claims (3)

The motor that provides steering assist force to the steering mechanism is controlled based on the current control value calculated from the steering assist command value calculated by the calculation means based on the steering torque generated in the steering shaft and the current value of the motor. In the control device for the electric power steering device, the motor current and the voltage between the motor terminals , or the motor current and the motor angular velocity are detected and the motor is approaching the output limit, and gradually as the output limit is approached. A control device for an electric power steering apparatus, which has a function of multiplying the steering assist command value by a coefficient that becomes smaller. The control device for an electric power steering apparatus according to claim 1, wherein the coefficient is a functional expression having a value greater than 0 and 1 or less. The control device for an electric power steering apparatus according to claim 2, wherein the functional expression is a nonlinear function.

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