JP3191520B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus suitable for use in a vehicle, and more particularly to a power steering apparatus for assisting a steering force by a rotation output of a motor.

[0002]

2. Description of the Related Art In recent years, electric power steering devices using motors have been used in place of hydraulic power steering devices, and motors are increasing in the future because of their advantages such as small size and light weight as actuators. In a conventional power steering device, a torque sensor detects a steering torque of a steering system, a vehicle speed sensor detects a vehicle speed, and controls a driving force of a motor connected to the steering system based on these detection results. I am assisting. The vehicle is generally of a vehicle speed sensitive type, and the assist force is controlled in accordance with the input of the torque sensor so that the vehicle is light at a low vehicle speed and heavy at a high vehicle speed. In general, it is a speed-sensitive type, and the assist force is controlled in accordance with the input of the torque sensor so as to be light at a low vehicle speed and heavy at a high vehicle speed.

In the conventional power steering apparatus, a feedback current control method using software is adopted as a motor control method. In this control method, a feedback operation is performed according to an electric time constant of the motor. Since control must be performed at a high speed, control of a motor having a small electrical time constant, such as a low-voltage DC motor, requires an increase in the speed of a control system. For this reason, it is necessary to use a high-speed processor, and there is a problem that the controller becomes expensive. In order to solve this problem, the present applicant has devised a control device that feeds forward a disturbance having a configuration including a target value response unit and a disturbance compensation unit for control in the current control unit.

Further, in the conventional power steering device, the torque of the assist motor is reduced by a gear and transmitted to a rack shaft or the like, so that the moment of inertia of the assist motor is large. The convergence at high vehicle speed is deteriorated due to the influence of gear friction, and the steering wheel return characteristics at low vehicle speed are deteriorated. In order to solve this problem, the present applicant has devised a device for adding a viscosity command value (at high vehicle speed: adding viscosity, at low vehicle speed: canceling viscosity) according to the steering angular speed (for example, Japanese Unexamined Patent Application Publication No. Hei 3 (1990) -1991). 178868
Reference).

[0005]

However, the conventional electric power steering apparatus improved by the present applicant has the following problems. In other words, in the control method for controlling the disturbance value in a feedforward manner, the current portion can be made inexpensive, but the convergence at high vehicle speed and the steering wheel return characteristic at low vehicle speed are not good. In this control system, sufficient response characteristics can be obtained during normal steering, but when sudden disturbance fluctuation occurs, such as when the steering wheel hits the lock end or when the tire hits the curb. In such a case, an excessive current flows through the motor. On the other hand, in the control method of adding the viscosity command value according to the steering angular speed, the convergence at a high vehicle speed and the steering wheel return characteristic at a low vehicle speed can be improved, but the use of a steering speed sensor or the like increases the cost, Further, the control system becomes complicated.

Accordingly, an object of the present invention is to provide an electric power steering apparatus which is inexpensive and has a simple structure, has a good steering feeling, and does not cause an excessive current to flow even when a sudden disturbance fluctuation occurs. .

[0007]

In order to achieve the above object, an electric power steering apparatus according to the present invention is connected to a steering system to generate a steering assist torque, and a vehicle speed detecting a vehicle speed. Detection means, target value response means for determining an operation amount for motor control according to a given current target value, and motor drive means for driving the motor according to the operation amount given from the target value response means And a disturbance estimating means for estimating a disturbance based on a difference between an operation amount applied to the motor and a motor current obtained from the motor. A feedforward means for changing the output value of the disturbance estimating means and feedforward controlling the result to the current target value. To.

An electric power steering apparatus according to a second aspect of the present invention has a disturbance change amount detecting means for detecting a change amount of the disturbance estimated value, and according to an output value of the disturbance change amount detecting means. The output value of the disturbance estimating means is changed, and the result is fed-forward controlled to the current target value.

An electric power steering apparatus according to a third aspect of the present invention is connected to a steering system and generates a steering assist torque, a vehicle speed detecting means for detecting a vehicle speed, and a current target value. A target value response unit that determines an operation amount for motor control in accordance with the operation amount; a motor drive unit that drives the motor according to an operation amount given from the target value response unit; an operation amount to be applied to the motor; An electric power comprising: disturbance estimating means for estimating disturbance based on a difference from a motor current obtained from a motor; and feedforward means for feedforward controlling an output value of the disturbance estimating means to the current target value. In the steering device, a motor speed estimating unit that estimates the speed of the motor from the disturbance estimated value, and an output value of the motor speed estimating unit. Flip characterized in that a current target value changing means for changing the current target value.

Further, the electric power steering apparatus according to the present invention has a motor speed estimated value varying means for changing an output value of the motor speed estimating means in accordance with an output value of the vehicle speed detecting means. Features.

An electric power steering apparatus according to a fifth aspect of the present invention is connected to a steering system and generates a steering assist torque, a vehicle speed detecting means for detecting a vehicle speed, and a current target value provided. A target value response unit that determines an operation amount for motor control in accordance therewith; a motor drive unit that drives the motor in accordance with an operation amount given from the target value response unit; and a voltage operation amount applied to the motor. And a disturbance estimating means for estimating a disturbance based on a difference from a motor current obtained from the motor, wherein a low pass for feedforward controlling an output value of the disturbance estimating means to the current target value is provided. A filter, wherein the low-pass filter changes a cutoff frequency according to an output value of the vehicle speed detecting means.

[0012]

According to the present invention, the feedforward amount of the disturbance estimation value to the current target value changes according to the detected vehicle speed. Therefore, at a high vehicle speed, a braking force is applied, so that the steering characteristics are stable and the steering characteristics are stable, and the convergence is improved. At a low vehicle speed, a sufficient current in the return direction flows when the steering wheel returns, so that the return characteristics are improved.

According to the second aspect of the invention, the amount of change in the disturbance estimation value is detected, and the amount of feedforward of the disturbance estimation value to the current target value changes according to the amount of change in the disturbance. Therefore, even if a sudden disturbance change occurs when the handle is brought into contact with the lock end or when the tire hits a curb, an excessive current is not generated in the motor.

According to the third aspect of the present invention, the motor speed is estimated from the estimated disturbance value, and the current target value changes according to the estimated motor speed. Therefore, since the inertia, viscosity, dynamic friction, and the like of the motor are controlled based on the estimated motor speed from the estimated disturbance, the steering characteristics (convergence, return characteristics, responsiveness) are improved.

According to the invention, the estimated motor speed changes according to the detected vehicle speed. Therefore, at a high vehicle speed, the steering characteristics have a firm response and a sense of stability, and the convergence is improved. At a low vehicle speed, a sufficient current in the returning direction flows when the steering wheel returns, so that the return characteristics are improved.

According to the fifth aspect of the present invention, the disturbance estimation value is feed-forward controlled to the current target value through the low-pass filter, and the cut-off frequency of the low-pass filter is changed according to the detected vehicle speed. Word amount changes. Therefore, at the time of high vehicle speed, the steering characteristic has a stable response and stable sensitivity, and the convergence is improved. ,

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a configuration diagram illustrating an example of a steering mechanical system to which an embodiment 1 of an electric power steering apparatus according to the present invention is applied. In this figure, the steering wheel 1
Is transmitted to the steering gear 2 including the pinion gear via the handle shaft, transmitted to the rack shaft 3 by the pinion gear, and further turned the wheel 4 via the knuckle arm and the like. The rotational force of a steering assist (auxiliary) motor (DC motor) 6 controlled and driven by the control device 5 is transmitted to the rack shaft 3 by meshing the steering gear 7 including a pinion gear with the rack shaft 3, and the steering wheel 1 This will assist steering. The handle 1 and the rotating shaft of the motor 6 are mechanically connected by gears 2 and 7 and a rack shaft 3.

A steering torque is detected by a steering torque sensor 21, and a vehicle speed is detected by a vehicle speed sensor 22. Then, the control device 5 controls the motor 6 based on the detected torque, vehicle speed, and the like. The control device 5 and the motor 6 include a battery 8 mounted on the vehicle.
Supplies its operating power. Control device 5
Is a current detector, a driving circuit for driving the motor 6, a motor 6
(CPU, for example, a microprocessor), a memory, an interface circuit between the computer and the input / output device, and the like.

FIG. 3 is a block diagram showing various functions of a computer built in the control device 5 together with block diagrams showing other input / output devices and various circuits. In this figure, an assist command unit 10 includes a detected torque Vt of a torque sensor (steering torque detecting means) 21.
And a vehicle speed Vs detected by a vehicle speed sensor (vehicle speed detecting means) 22. The assist torque instruction function unit 13 in the assist instruction unit 10 outputs a command value indicating the assist torque to be generated by the motor 6 according to the detected torque Vt.
The multiplication constant function unit 14 generates a constant according to the detected vehicle speed Vs, and the multiplication operation unit 15 multiplies the constant by the above-described assist torque command value. As a result, the assist torque value output from the multiplication operation unit 15 becomes a value determined by the detected torque Vt and the detected vehicle speed Vs as shown in FIG.

FIG. 2 shows that a motor current approximately proportional to a certain range of steering torque Vt flows according to the steering torque Vt (assist torque is generated). In accordance with the vehicle speed Vs, an assist command for controlling the motor 6 is generated so that the motor current is reduced when the vehicle speed Vs is high and the motor current is increased when the vehicle speed Vs is low. Is represented.

On the other hand, the detected torque Vt is also given to the phase compensator 16. The phase compensator 16 calculates the differential value of the detected torque Vt, and outputs a signal obtained by multiplying the differential value by a constant corresponding to the vehicle speed Vs generated by the differential multiplication constant function unit 17. This output is added to the output of the multiplication operation unit 15 by the addition unit 18 so that the assist command unit 10
Is supplied to the current control unit 25. The current control unit 25 includes, for example, a PWM (Pulse With Modulatio) according to an H-bridge driving method including four switching elements.
n) The motor 6 is driven and controlled by a chopper operation using a pulse.

The current control unit 25 includes a target value response unit 26 and a disturbance compensation unit 27. Target value response unit 26
At the current target value (assist command unit 10
And the disturbance compensation value given from the disturbance compensator 27 are added by the adder 28 to obtain a current manipulated variable. This current manipulated variable is converted into a voltage manipulated variable by the applied voltage calculator 29. Specifically, the applied voltage calculator 29
Calculates the voltage operation amount by multiplying the input current operation amount by the armature resistance R of the motor 6. The polarity of the voltage operation amount is determined by the polarity determination unit 30, and the duty ratio of the PWM pulse is determined by the duty calculation unit 31 based on the operation amount. The determined polarity and the determined duty ratio are provided to the motor drive unit 32. The motor drive unit 32 drives the motor 6 by controlling ON / OFF of four switching elements wired in an H-bridge type based on these values.

The disturbance compensating unit 27 includes the armature current detecting unit 3
3, subtraction unit 34, current manipulated variable detection unit 35, compensation element 3
6, a vehicle speed calculation constant function unit 37 and a feedforward amount calculation unit 38 are included. In this embodiment, the disturbance estimation is performed based on the difference between the current manipulated variable and the current detection value. The gains of the current manipulated variable detector 35 and the armature current detector 33 are both set to “1”, for example. The current manipulated variable obtained through the current manipulated variable detector 35 and the armature current detector 3
3 is different from the armature current detected by the
Given to. Compensation element 365 is provided by "1" or a filter element. The armature current detecting unit 33, the subtracting unit 34, and the current manipulated variable detecting unit 35 constitute a disturbance estimating unit 100.

The value obtained by multiplying the disturbance estimation value by the compensation element is supplied to the feedforward amount calculation section 38. The feed forward operation unit 38 multiplies the input value by a vehicle speed operation constant determined by the vehicle speed Vs as shown in FIG. Then, the result is fed-forward controlled to the target value response unit 26 as an output of the disturbance compensation unit 27. When the estimated disturbance value increases, the feedforward amount calculation unit 38 calculates
Reduce the amount of feed forward. FIG. 5 shows the characteristics. The output of the feedforward amount calculation unit 38 is provided to the addition unit 28 of the target value response unit 26, and is added to the current target value. When the disturbance estimation value increases, the feedforward amount decreases, and when the rotation speed of the motor is high, a control force acts. As described above, in this embodiment, the feedforward amount of the disturbance estimation value is changed according to the output value Vs of the vehicle speed sensor 22. Therefore, at a high vehicle speed, a braking force is applied, so that the steering characteristics are stable and the steering characteristics are stable, and the convergence is improved. Further, at the time of low vehicle speed, a sufficient current flows in the return direction when the steering wheel returns, so that the return characteristics are improved.

Embodiment 2 FIG. Next, FIG. 6 is a block diagram illustrating various functions of a computer built in the control device 5 of the electric power steering apparatus according to the second embodiment of the present invention, together with other input / output devices and various circuits. Things. In this figure, the same parts as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a disturbance change amount detection unit 39 which detects a change amount of disturbance and outputs a value corresponding to the change amount to a disturbance compensation unit 27, and a disturbance change amount output from the disturbance change amount detection unit 39. Compensation factor 3 of disturbance estimated value
6 is added to the value having passed through 6, and the result thereof is provided as an output of the disturbance compensating section 27 to the target value responding section 26, and a feedforward amount calculating section 38 for performing feedforward control is provided.

The detection of the amount of change in disturbance is performed, for example, by calculating a differential value. Specifically, it can be calculated by calculating the difference between the disturbance in the previous control cycle and the disturbance calculated this time. As another method, a value corresponding to the disturbance change amount may be added to the value after passing through the compensation element of the disturbance estimated value only when the disturbance change amount is equal to or more than a certain threshold value. Thus, in this embodiment, the feedforward amount is changed according to the change amount of the disturbance estimated value. Therefore, even if a sudden disturbance fluctuation occurs when the handle 1 is brought into contact with the lock end or when the tire hits a curb, an excessive current is not generated in the motor 6. Further, this makes it possible to easily detect a failure in the electric circuit by checking for an excessive current, thereby improving the reliability of the system. In addition, since unnecessary excessive current can be prevented from being generated and heat generation can be reduced, the life of the motor and the control device can be extended, and the fuel efficiency can be improved.

Embodiment 3 FIG. Next, FIG. 7 is a block diagram illustrating various functions of a computer built in the control device 5 of the third embodiment of the electric power steering device according to the present invention, together with a block diagram illustrating other input / output devices and various circuits. Things. In this figure, the same parts as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof will be omitted. This embodiment includes a motor speed estimating unit 40 that estimates a motor speed from a disturbance estimation value, a friction compensating unit 41 that performs friction compensation based on the estimated motor speed, and a viscosity compensating unit that performs viscosity compensation based on the estimated motor speed. Compensation unit 42
A motor acceleration calculation unit 43 that calculates a motor acceleration by differentiating the estimated motor speed, an inertia compensation unit 44 that performs rotor inertia compensation of the motor 6 based on the motor acceleration,
A subtraction unit 45 that calculates a difference between an output of the inertia compensation unit 44 and an output of the viscosity compensation unit 42; and an output of the subtraction unit 45 and the friction compensation unit 41.
And an adder 47 that adds the output of the adder 46 to the current target value (generated based on the assist command unit 10).

The motor speed is estimated by passing the disturbance estimated value through a high-pass filter. In this case, since disturbance such as power supply voltage fluctuation and motor parameter fluctuation fluctuates slowly, information on the motor speed can be extracted from various disturbances included in the disturbance estimation value by using a high-pass filter. Thus, in this embodiment, the current target value is changed according to the motor speed estimated value. Therefore, since the inertia, viscosity, dynamic friction, and the like of the motor 6 are controlled based on the estimated motor speed value from the estimated disturbance value, the steering characteristics (convergence, return characteristics, responsiveness) are improved.
In addition, since the configuration is such that the current target value and the actual current are controlled to be identical, design and adjustment are easy, and an abnormality in the device is easily detected by comparing both values.

Embodiment 4 FIG. Next, FIG. 8 is a block diagram illustrating various functions of a computer built in the control device 5 of the electric power steering device according to the fourth embodiment of the present invention, together with a block diagram illustrating other input / output devices and various circuits. Things. In this figure, the same parts as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, a motor speed estimating unit 40, a vehicle speed calculating constant function unit 37 for outputting a vehicle speed calculating constant determined as shown in FIG. 9 by the vehicle speed Vs, and a multiplication for multiplying the estimated motor speed by a vehicle speed calculating constant An operation unit 48 is provided. The result of multiplying the estimated motor speed by the vehicle speed calculation constant is added to the output of the assist command unit 10 by the adding unit 47 and supplied to the current control unit 25 as a current target value.

As described above, in this embodiment, the current target value is changed according to the estimated motor speed and the detected vehicle speed Vs. Therefore, at a high vehicle speed, the steering characteristics have a firm response and a sense of stability, and the convergence is improved. At a low vehicle speed, a sufficient current in the returning direction flows when the steering wheel returns, so that the return characteristics are improved.

Embodiment 5 FIG. Next, FIG. 10 is a block diagram showing various functions of a computer built in the control device 5 of the electric power steering device according to the fifth embodiment of the present invention, together with a block diagram showing other input / output devices and various circuits. Things. In this figure, the same parts as those in FIG. 3 described above are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment, as shown in this figure, the disturbance estimation value is feed-forward controlled through the compensation element 36 to the current target value. The compensating element 36 here is a low-pass filter that can make the cutoff frequency variable,
This cutoff frequency is changed at a ratio indicated by the vehicle speed calculation constant determined as shown in FIG. 11 by the vehicle speed Vs. Specifically, the calculation cycle of the low-pass filter is made longer as the vehicle speed increases. As another method, the cutoff frequency may be changed by changing the operation constant of the low-pass filter.

As described above, in this embodiment, the feedforward control is performed on the estimated disturbance value to the current target value through the lowpass filter, and the cutoff frequency of the lowpass filter is changed according to the detected vehicle speed. To change. Therefore, when the vehicle speed is high, the control force is generated in the motor by the generation of the back electromotive voltage of the motor, so that the convergence can be improved.

In each of the above embodiments, the present invention is applied to a power steering apparatus. However, other examples include, for example, engine control control, constant driving control, shift control, suspension control, 4WD (four-wheel drive) control, and 4WS.
It can be applied to (four-wheel steering) control and underbody control.

[0034]

According to the first aspect of the invention, the amount of feed-forward of the disturbance estimated value is changed according to the output value of the vehicle speed detecting means. Steering characteristics with a sense of stability and stability can be obtained, and the convergence can be improved. In addition, at the time of low vehicle speed, a sufficient current in the return direction can flow when the steering wheel returns, so that the return characteristics are improved.

According to the second aspect of the present invention, the amount of change in the estimated disturbance value is detected, and the feedforward amount is changed in accordance with the amount of change. Even if a sudden disturbance fluctuation occurs when the tire collides with a curb, an excessive current does not flow through the motor.

According to the third aspect of the present invention, the motor speed is estimated from the disturbance estimated value, and the current target value is changed in accordance with the estimated value. Since the inertia, viscosity, dynamic friction, and the like of the motor can be controlled by the value, the steering characteristics (convergence, return characteristics, and responsiveness) can be improved at low cost.

According to the fourth aspect of the present invention, the current target value is changed by changing the estimated motor speed based on the output value of the vehicle speed detecting means. In addition to the effects, at the time of a high vehicle speed, a firm response and a steering characteristic with a sense of stability are obtained, and the convergence is improved. In addition, at low vehicle speed, sufficient current in the return direction flows when the steering wheel returns,
The return characteristics are improved.

According to the fifth aspect of the present invention, the disturbance estimated value is fed-forward controlled to the current target value through the low-pass filter, and the cut-off frequency of the low-pass filter is changed according to the output value of the vehicle speed detecting means. As a result, at a high vehicle speed, the steering characteristics are firmly responsive and stable, and the convergence is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of a steering mechanical system to which an embodiment 1 of an electric power steering apparatus according to the present invention is applied.

FIG. 2 is a diagram showing characteristics of an assist torque according to the embodiment.

FIG. 3 shows a CP built in the control device of the embodiment.
FIG. 3 is a block diagram showing various functions of U.

FIG. 4 is a characteristic diagram showing a vehicle speed calculation constant with respect to a motor speed estimated value in the embodiment.

FIG. 5 is a characteristic diagram showing an output of a feedforward amount calculation unit with respect to a disturbance estimated value according to the embodiment.

FIG. 6 is a block diagram illustrating various functions of a CPU incorporated in a control device of a second embodiment of the electric power steering device according to the present invention.

FIG. 7 is a block diagram illustrating various functions of a CPU incorporated in a control device of a third embodiment of the electric power steering device according to the present invention.

FIG. 8 is a block diagram showing various functions of a CPU incorporated in a control device of a fourth embodiment of the electric power steering device according to the present invention.

FIG. 9 is a characteristic diagram showing a vehicle speed calculation constant with respect to a motor speed estimated value in the electric power steering apparatus of the embodiment.

FIG. 10 is a block diagram showing various functions of a CPU incorporated in a control device of Embodiment 5 of the electric power steering device according to the present invention.

FIG. 11 is a characteristic diagram showing a vehicle speed calculation constant with respect to a motor speed estimated value in the embodiment.

[Explanation of symbols]

22 Vehicle speed sensor (vehicle speed detection means) 36 Compensation element (low-pass filter) 38 Feedforward amount calculation unit (feedforward means) 39 Disturbance change amount detection unit (disturbance change amount detection means) 40 Motor speed estimation unit (Motor speed estimation) Means) 47 adding section (current target value varying means) 48 multiplication calculating section (motor speed estimated value varying means) 100 disturbance estimation means

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B62D 6/00-6/04 B62D 5/04

Claims (5)

(57) [Claims] 1. A motor connected to a steering system for generating a steering assist torque, vehicle speed detecting means for detecting a vehicle speed, and a target value for determining an operation amount for motor control according to a given current target value A response unit; a motor driving unit that drives the motor in accordance with an operation amount given from the target value response unit; and a disturbance based on a difference between an operation amount applied to the motor and a motor current obtained from the motor. And a disturbance estimating means for estimating, wherein an output value of the disturbance estimating means is changed in accordance with an output value of the vehicle speed detecting means, and the result is fed-forward controlled to the current target value. An electric power steering apparatus, comprising: 2. Disturbance change amount detecting means for detecting a change amount of the disturbance estimated value, wherein the feedforward means changes an output value of the disturbance estimating means in accordance with an output value of the disturbance change amount detecting means. 2. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus changes the result and feed-forward controls the result to the current target value. 3. A motor connected to a steering system for generating a steering assist torque, vehicle speed detecting means for detecting a vehicle speed, and a target value for determining an operation amount for motor control according to a given current target value A response unit; a motor driving unit that drives the motor in accordance with an operation amount given from the target value response unit; and a disturbance based on a difference between an operation amount applied to the motor and a motor current obtained from the motor. An electric power steering apparatus comprising: a disturbance estimating unit for estimating; and a feedforward unit for feedforward controlling an output value of the disturbance estimating unit to the current target value. Motor speed estimating means for estimating, current target value varying means for changing the current target value according to the output value of the motor speed estimating means, Electric power steering apparatus characterized by comprising. 4. An electric power steering apparatus according to claim 3, further comprising a motor speed estimated value changing means for changing an output value of said motor speed estimating means in accordance with an output value of said vehicle speed detecting means. . 5. A motor connected to a steering system for generating a steering assist torque, vehicle speed detecting means for detecting a vehicle speed, and a target value for determining an operation amount for motor control according to a given current target value Responsive means; motor driving means for driving the motor in accordance with an operation amount given from the target value responsive means; and a disturbance based on a difference between a voltage operation amount applied to the motor and a motor current obtained from the motor. And a disturbance estimating means for estimating the vehicle speed, wherein a low-pass filter for feed-forward controlling an output value of the disturbance estimating means to the current target value is provided, and the low-pass filter comprises a vehicle speed detecting means. An electric power steering apparatus characterized in that the cutoff frequency changes according to the output value of the power steering.