JP4660988B2 - 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 apparatus that applies a steering assist force by a motor to a steering system of an automobile or a vehicle, and more particularly to remove discontinuity when the duty ratio for driving the motor is near zero. The present invention relates to a control device for an electric power steering apparatus that generates and controls a voltage dither signal to improve the steering performance near the steering wheel neutral point.
[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. 13. The shaft 2 of the steering handle 1 is connected to the tie rod of the steering wheel via the reduction gear 3, the universal joints 4 a and 4 b, and the pinion rack mechanism 5. 6. 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 device is out of order and when the power supply (voltage Vb) of the battery 14 is turned off by the ignition key 11.
[0004]
The control unit 30 is mainly composed of a CPU, and FIG. 14 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 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. 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 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.
[0006]
A configuration example of the motor drive circuit 37 will be described with reference to FIG. 15. The motor drive circuit 37 is a FET gate that drives the gates of the field effect transistors (FETs) FET1 to FET4 based on the current control value E from the adder 30B. A drive circuit 371, an H bridge circuit composed of FET1 to FET4, a boost power source 372 for driving the high side of FET1 and FET2, and the like. The FET1 and FET2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E, and the magnitude of the current Ir that actually flows through the motor 20 is controlled. FET3 and FET4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function equation (D2 = a · D1 + b, where a and b are constants) in a region where the duty ratio D1 is small, and the duty ratio D2 is also 100%. After reaching the value, it is turned ON / OFF according to the rotation direction of the motor 20 determined by the sign of the PWM signal.
[0007]
Here, the relationship between the duty ratio and the motor current I is as shown in FIG. 16, and a dead zone UB is provided in the vicinity of the duty ratio to make the running feeling of steering feel.
[0008]
[Problems to be solved by the invention]
As shown in FIG. 16, since the dead zone is provided near the duty ratio of zero, the friction characteristic becomes discontinuous when the motor angular velocity ω is near zero, and if the steering angle is completely stationary at any timing, the steering wheel There is a problem of receiving a feeling of sticking to the position. That is, in the electric power steering device, in order to improve the steering performance, compensation of motor inertia and various compensations for removing the influence of friction are performed, and such compensation control is performed based on the motor angular velocity. It is not possible to compensate for the effect when the motor is completely stationary, that is, the effect of static friction that the electric power steering device has. In most cases, the automobile is often going straight, and the automobile is controlled by a delicate steering operation near the steering wheel neutral position. Therefore, in control, it is particularly important to compensate for a feeling of friction and a feeling of inertia in delicate steering near the neutral position.
[0009]
The present invention has been made under the circumstances as described above, and an object of the present invention is to control the electric power steering apparatus so as to obtain a continuous and stable steering feeling even near the handle neutral point of the electric power steering apparatus. To provide an apparatus.
[0010]
[Means for Solving the Problems]
The present invention PWM-controls the motor based on a current control value calculated from a steering assist command value calculated based on a steering torque generated in a steering shaft and a current value of a motor that applies a steering assist force to the steering mechanism. The above-mentioned object of the present invention is to provide a duty ratio of the PWM control in order to make the duty ratio having a dead zone region vs. the motor current characteristic apparently continuous. Is provided with a voltage dither signal generation / control means for generating and controlling a voltage dither signal for the H-bridge circuit that drives the motor when the value falls below a predetermined value, and the predetermined value corresponds to the dead zone region. The voltage dither signal is expressed as K · sin ω ₀ t, where K is a constant and ω ₀ is a dither angular frequency. It is achieved by a sinusoidal der Rukoto.
[0011]
Further, by setting the dither angular frequency ω ₀ to 500 Hz , the above object of the present invention can be achieved more effectively.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, in a region where the duty ratio is small, by applying a fine voltage dither signal to the duty signal of the H-bridge circuit and controlling it, the duty ratio versus the motor current characteristic is apparently continuous, and near the motor angular velocity of zero. The effect of static friction characteristics is removed. In other words, in the present invention, the voltage dither signal that changes minutely and repeatedly is added to the duty ratio signal that drives the gate of the FET in which the H bridge circuit is ON, so that the driver does not feel the vibration of the motor. As shown in FIG. 1, the motor is slightly vibrated, and the duty ratio vs. motor current characteristic is continuous. As a result, even at a neutral point where the rudder angle is completely stationary, the handle does not stick to that position as in the prior art.
[0013]
In a region where the motor current is small, there is a dead zone in the duty ratio vs. motor current characteristic, which slows down the response of the control, and there is a problem that friction and inertia are not fully recommended. Since it is impossible to eliminate the dead band of the duty ratio vs. motor current characteristics from the viewpoint of handle operability, the present invention eliminates the dead band by using a voltage dither signal in order to eliminate the control delay in the small current region due to the influence of the dead band as much as possible. Linearize as much as possible. The reason why the voltage dither signal can be linearized to some extent is that when the dither is performed at a frequency higher than the current response determined by the current control response, the duty ratio vs. motor current characteristic is substantially equal to the current amplitude corresponding to the dither. This is because it becomes an effective value.
[0014]
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
FIG. 2 is an overall block diagram of the control function according to the present invention. The steering torque T is input to the steering assist command value calculation unit 100 and the center response improvement unit 101, each output is input to the adder 102, and the addition result is input to the torque control calculation unit 103. 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 and input to the current control unit 110. . The output of the current control unit 110 is input to the current drive circuit 112 formed of an H bridge circuit via the H bridge characteristic compensation unit 111, thereby driving the motor 113.
[0016]
The motor current i of the motor 113 is input to the motor angular speed estimation unit 121, the current drive switching unit 122 and the current control unit 110 via the motor current offset correction unit 120, and the motor terminal voltage Vm is input to the motor angular speed estimation unit 121. . 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, and the yaw rate estimation unit 125, and the output of the yaw rate estimation 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. The motor loss torque compensator 124 provides assist equivalent to loss torque in the direction in which the loss torque of the motor 113 is generated, that is, the rotation direction of the motor 113, and the convergence controller 126 controls the steering wheel to improve the yaw convergence of the vehicle. The brakes are applied to the movement of the swaying. The output of the motor angular acceleration estimation unit / inertia compensation unit 123 is input to the adder 105.
[0017]
In addition, a voltage dither signal generation / control unit 130 that generates and controls a dither signal DS for minutely vibrating the motor 113 to the extent that the driver does not feel is provided. The dither signal DS from the voltage dither signal generation unit 130 is provided. Is applied to the H-bridge characteristic compensator 111. The voltage dither signal generation unit 130 receives the duty ratio Duty from the H-bridge characteristic compensation unit 111, and generates the dither signal DS in a range where the duty ratio Duty is smaller than a predetermined value. The voltage dither signal generator 130 generates a sine wave dither signal DS having a peak value Δω and a frequency of 500 Hz when the motor angular velocity ω is near zero. Note that the frequency of the dither signal DS is not limited to 500 Hz, but may be a large value with respect to the change of the duty ratio Duty, as long as the driver does not feel it.
[0018]
In such a configuration, in the present invention, as shown in FIG. 3, the center responsiveness improvement unit 101 includes a phase lead compensation unit 101A, an approximate differentiation unit 101B, and a gain setting unit 101C, and the phase lead compensation unit 101A is shown in FIG. The approximate differentiation unit 101B has the frequency characteristics shown in FIG. As a result, the combined characteristics of the phase lead compensation and the approximate derivative are as shown in FIG. 6, and a phase characteristic without a phase delay can be obtained.
[0019]
In the present invention, the assist characteristic based on the three representative vehicle speeds (0, 30, 254 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 254 km / h and the resolution is 2 km / h. The basic assist characteristics (torque versus current) are shown in FIG. 7, and are represented as + by 0 km / h = lo characteristics, 30 km / h = la characteristics, and 254 km / h = lb 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 30 km / h, the assist current I is I = la (T) + γ (V) (lo (T) −la (T)), and when the vehicle speed is 32 to 254 km / h, the assist current I is I = lb (T) + γ (V) (la (T) −lb (T)).
[0020]
Here, in the present invention, a voltage dither signal generation / control unit 130 for compensating for a feeling of friction and a feeling of inertia in delicate steering near the steering wheel neutral point is provided, and the duty ratio Duty is in a range of ± d1 near zero. 9 and FIG. 10, a dither signal DS having a peak value Δω corresponding to the angular frequency ω ₀ and a constant K at a frequency of 500 Hz and a constant K K · sin ω ₀ t is generated as shown in FIGS. This is applied to the gate drive signal Vg of the FET of the bridge circuit.
[0021]
FIG. 11 shows the details, and the duty ratio Duty is input to the determination circuit 131 that determines the magnitude of the predetermined value d1, and controls the gates of the FETs 1 to 4 of the H bridge circuit (current drive circuit) 112. The oscillation signal OC is input to the oscillation circuit 132 when the duty ratio Duty is input to the gate control circuit 133 and becomes smaller than the predetermined value d1. When the oscillation signal 132 is input, the oscillation circuit 132 oscillates a sine wave K · sinω ₀ t and applies it to the gate drive signal Vg via the adders 1341 to 1344. As a result, a signal obtained by adding the sine wave K · sinω ₀ t, which is the dither signal DS, to the gate drive signal Vg is supplied to the FET1 to FET4 through the gate control circuit 133. The gate control circuit 133 is synchronized with the duty ratio Duty, and controls ON / OFF of the FET1 to FET4. Thus, the duty ratio Duty is the predetermined value d1 smaller area, the FET being ON is finely driven in accordance with the period of the angular frequency omega _0. For this reason, the characteristic of the duty ratio versus the motor current as shown in FIG. 16 becomes continuous, and the uncomfortable feeling of steering is eliminated. The angular frequency ω ₀ is 450 to 550 Hz, preferably 500 Hz, and the driver does not feel the vibration of the motor in this range.
[0022]
In FIG. 11, the oscillation circuit 132 is oscillated when the duty ratio Duty becomes smaller than the predetermined value d1, and the dither signal DS is generated and applied. However, the duty ratio Duty is always oscillated. A switching circuit may be provided for applying to each gate drive signal Vg when becomes smaller than a predetermined value d1.
[0023]
FIG. 12 shows an actual operation example of the voltage dither signal generation / control unit 130. It is determined whether or not the duty ratio Duty is within the range of the predetermined value ± d1 (step S1), and the duty ratio Duty is If it falls within the range of ± d1, it is further determined whether or not the magnitude (absolute value) of the torque T is smaller than a predetermined value α (step S2). The predetermined value ± d1 may be in the vicinity of zero of the duty ratio Duty, and is not limited to ± d1. When the torque T is smaller than the predetermined value α, a dither signal DS of K · sin ω ₀ t of a sine wave is generated with K as a constant, and is applied to the gate drive signals Vg of the FET1 to FET4. As a result, the motor can be vibrated minutely to the extent that the driver does not feel it near zero of the duty ratio Duty.
[0024]
【The invention's effect】
In the present invention, a dither signal for causing the motor to vibrate slightly near the zero duty ratio is generated and applied to the gate drive signal of the FET for control. The vibration of the motor due to the dither signal has a frequency and magnitude that the driver does not feel, and the influence of static friction near the duty ratio of zero can be eliminated. Further, since the duty ratio vs. motor current characteristic is continuous near the duty ratio of zero, an unnatural steering feeling can be prevented and a comfortable steering feeling can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a basic concept of the present invention.
FIG. 2 is a block diagram illustrating a configuration example of the present invention.
FIG. 3 is a block configuration diagram of a center response improvement unit.
FIG. 4 is a diagram illustrating a characteristic example of a phase lead compensation unit.
FIG. 5 is a diagram illustrating an example of characteristics of an approximate differentiation unit.
FIG. 6 is a diagram illustrating a combined characteristic of a phase lead compensation unit and an approximate differentiation unit.
FIG. 7 is a diagram showing basic assist characteristics.
FIG. 8 is a diagram illustrating an example of a vehicle speed interpolation calculation.
FIG. 9 is a diagram illustrating a voltage dither signal according to the present invention.
FIG. 10 is a diagram for explaining the operation of the present invention.
FIG. 11 is a diagram showing friction characteristics when the motor angular velocity is zero.
FIG. 12 is a flowchart showing an operation example of the present invention.
FIG. 13 is a block diagram showing an example of an electric power steering apparatus. FIG. 14 is a block diagram showing a general internal configuration of a control unit.
FIG. 15 is a connection diagram illustrating an example of a motor drive circuit.
FIG. 16 is a diagram showing a duty ratio versus motor current characteristic of the electric power steering apparatus.
[Explanation of symbols]
100 Steering assist command value calculation unit 101 Center response improvement unit 101A Phase advance compensation unit 101B Approximation differentiation unit 101C Gain setting unit 103 Torque control calculation unit 104 Motor loss current compensation unit 110 Current control unit 113 Motor 121 Motor angular velocity estimation unit 125 Yaw rate estimation Unit 130 Voltage dither signal generation / control unit

Claims (2)

PWM control of the motor is performed based on a 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 that applies the steering assist force to the steering mechanism. In the control device of the electric power steering device configured as described above,
In order to make the duty ratio having a dead zone region vs. the motor current characteristic apparently continuous , a voltage dither signal is supplied to the H bridge circuit that drives the motor when the duty ratio of the PWM control becomes a predetermined value or less. comprising a voltage dither signal generating / controlling means for controlling to generate,
The predetermined value is a duty ratio corresponding to the dead zone region, and the voltage dither signal is a sine wave represented by K · sin ω ₀ t, where K is a constant and ω ₀ is a dither angular frequency. Control device for electric power steering device. The control device for an electric power steering apparatus according to claim 1, wherein the dither angular frequency ω ₀ is 500 Hz.

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