JPH03182873A - Electrically driven power steering device - Google Patents

Abstract

PURPOSE:To reduce the burden of a CPU by separating the signal component of an assist command into a low frequency component and a high frequency component, processing the respective components by a low frequency control means and a high frequency control means so as to be synthesized thereafter, and thereby controlling an assist motor by the signal synthesized as described above. CONSTITUTION:An assist torque value which is obtained based on the detected torque and the detected vehicle speed, is corrected by a viscosity compensation value and an inertia compensation value so that an assist command value is thereby mae, and the assist command value is inputted into a current control section 50 as a target current command value. In this place, the target current command value is separated into a low frequency component and a high frequency component by means of a LPF 51 and a HPF 54, and the difference between the separated low frequency component and a low frequency component outputted from a LPF 59 which inputs the output signal of a current detector 60 detecting the armature current of a motor 10, is computed by an operating section 52. The respective output signals of a low frequency control section 53 processing the aforesaid difference and a high frequency control section 55 processing the output of the HPF 54 are then synthesized by a control section 56 so that the assist motor 10 is thereby controlled.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device that assists steering force by the rotational output of a motor, and more particularly to a drive control device for the motor.

Prior Art and Its Problems In a conventional electric power steering device, a steering assist (auxiliary) motor is controlled based on a detected steering torque value and a detected vehicle speed value to generate steering assist torque. inertia of the motor and steering mechanical system;
Some perform inertia compensation, viscosity compensation, etc. that take into account viscosity, friction, etc.

In any case, an assist command is given to a motor control device that drives and controls the assist motor. The motor control device responds to the assist command.

Proportional (P) control, integral (1) control, proportional differential integral (PI)
D) Perform motor current feedback control such as control.

When a motor control device is implemented using computer software, the control period must be at least a fraction of the motor's electrical time constant (normally, the motor's electrical time constant is several msec, so (need to have a control period of several hundred μsec), high-speed calculation is required, and the load on the CPU is heavy, and if a CPU capable of high-speed processing is used, it will be expensive. In addition, noise from the motor current detection unit is instantaneously fed back to the control unit, causing unnecessary current to flow through the assist motor, causing noise and heat generation due to current fluctuations, and in some cases leading to malfunction. There is a problem.

Summary of the Invention Purpose of the Invention This invention reduces the burden on the CPU that controls the motor.
It is an object of the present invention to provide an electric power steering device that is inexpensive and includes a motor control device that is resistant to noise in a current detection section.

Arrangement 1 of the Invention Functions and Effects This invention provides an electric power driver that creates an steering command based on detected steering torque, detected vehicle speed, etc., and controls a steering assist motor that generates steering assist torque using this assist command. In the steering device, a motor control device that controls the assist motor includes a filter unit that separates the signal component of the assist command into a low frequency component and a high frequency component, and a first low frequency control unit that processes the low frequency component. , combining the processing results of the second high-frequency control means for processing the high-frequency component, the first low-frequency control means, and the second high-frequency control means; and 6 driving the assist motor based on the combined result. The present invention is characterized in that it includes a third control means for controlling.

Further, according to the present invention, the motor control device further includes means for detecting a motor current of the assist motor, and a low-pass filter means for passing a low frequency component of the detected motor current. It is characterized in that the component is configured to be fed back to the first low frequency control means.

According to this invention, since the signal component of the assist command is divided into a low frequency component and a high frequency component, low-speed processing is sufficient for the low frequency component, and relatively simple processing is required for the high frequency component. Even though it is relatively fast, it does not require much CPU.
It will not be a burden to you. In this way, according to the present invention, when the motor control device is realized by computer software, the load on the CPU can be reduced, and a relatively low-speed and inexpensive CPU can be used, so that the power steering device can be This will lead to lower prices.

In particular, if the feedback control is performed by low frequency control means, the burden on the CPU will be significantly reduced. Further, since the current detected by the current detection means is fed back to the low frequency control means through the low pass filter means, high frequency noise components are cut, making the device resistant to noise.

Description of examples First, the first invention will be explained.

FIG. 1 is a block diagram functionally showing the entire embodiment of an electric power steering device according to the first invention.

FIG. 2 is a configuration diagram showing an example of a steering mechanical system to which this power steering device is applied.

First, the power steering mechanical system shown in FIG. 2 will be explained.

The rotational force of the steering handle 71 is transmitted through the handle shaft to a steering gear 72 including a pinion gear, and further transmitted to the rack shaft 74 by the pinion gear.
The wheel 75 is turned through the knuckle arm and the like. Further, the rotational force of a steering assist (auxiliary) motor (DC motor) 10 controlled and driven by the control device 11 is transmitted to a steering gear 73 including a pinion gear and a rack shaft 7.
4, the signal is transmitted to the rack shaft 74 and assists steering with the handle 71. handle 71
The rotating shafts of the motor 10 and the motor 10 are mechanically connected by gears 72, 73 and a rack shaft 74. A steering torque sensor 21 detects steering torque (torsion torque).

Further, the vehicle speed is detected by the vehicle speed sensor 22, and the control device 11 controls the motor 10 based on the detected torque, vehicle speed, etc., as described later. The control device 11 and the motor lO are equipped with a battery 1 mounted on the vehicle.
Its operating power is supplied from 2.

As will be described later, the control device 11 includes a current detector, a drive circuit that drives the motor 10, a computer (CPU, for example, a microprocessor) that controls the overall control of the motor 10, a memory, a computer, and the above-mentioned people.
It consists of an interface circuit with output equipment, etc. FIG. 1 can be viewed as a block diagram of various functions of the computer built into the control device 11, together with blocks showing other people, output devices, and various circuits.

In FIG. 1, the assist command unit 20 includes the detected torque VT of the torque sensor 2J and the detected vehicle speed V of the vehicle speed sensor 22.
8 is given. Assist in the assist command unit 20
The torque value instruction function unit 23 outputs a command value representing the assist torque to be generated by the motor 0 in accordance with the detected torque VT. Further, the multiplication constant function unit 24 has a detected vehicle speed v
8, and this constant is multiplied by the above-mentioned assist torque command value in the multiplication calculation section 25. As a result.

As shown in FIG. 3, the assist torque value (or motor current command value) output from the multiplication calculation unit 25 is a value determined by the detected torque V 1 and the detected vehicle speed Vs. Figure 3 shows that in response to the steering torque V, a motor current flows (assist torque is generated) that is approximately proportional to the steering torque VT within a certain range (another curve may be used). , so that when the above range is exceeded, a certain constant motor current flows (assist torque is generated), and according to the vehicle speed V, when the vehicle speed Vs is high, the motor current (assist torque) is decreased, and the vehicle speed V8 This indicates that when the motor 0 is slow, an assist command is generated to control the motor 0 to increase the motor current (assist torque). Detected torque VT is detected by phase compensation section 2
The differential value of the detected torque V1 is added to the output of the multiplication calculation unit 25 by the phase compensator 26, thereby finally becoming the output (reference current command value) of the assist command unit 20.

The viscosity compensator 30 calculates a viscosity compensation value based on the detected steering angular velocity (rotational speed of the assist motor 0) θ and, if necessary, the vehicle speed v8. This viscosity compensation value is added to (or subtracted from) the assist command value of the assist command unit 20. This suppresses the instability that tends to occur when the vehicle is released and returns at high speeds, and compensates to reduce viscosity at low vehicle speeds, reducing the sense of activation of the steering wheel and providing a good feeling. It becomes like this.

The inertia compensator 40 controls the rotor inertia of the motor IO as if it were reduced, and it eliminates the weight caused by the motor IO not following the rotation of the steering wheel when the steering wheel is suddenly turned, and adjusts the return speed when the hand is released. It acts to speed up the process. The steering angle acceleration (rotational acceleration of the motor 10) θ is detected in the inertia compensator 40, and an inertia compensation value is calculated based on this detected acceleration. The calculated inertia compensation value is added to the assist command value of the assist command unit 20.

The assist command value corrected by the viscosity compensation value and the inertia compensation value in this way is given to the current control unit 50 as a target current command value. All functions of the current control section 50 are realized by computer software and executed by the CPU.

The current control unit 50 is, for example, a PWM (Pulse
Width Modulation) using a pulse
0 The motor 10 is driven and controlled by chopper operation, and current feedback control is performed.

The target current command value given to the current control unit 50 (which is actually data because it is software processed by CPH, but is described like a signal for ease of explanation) is passed through a low-pass filter (LPF) 51 and a high-pass filter (LPF) 51. Each signal is applied to a pass-pass filter (HPF) 54 and separated into a low frequency component and a high frequency component. For example, L P F 51 is 5
Cuts frequency components above Hz. HP F 54 allows passage of frequency components of 5 Hz or more, but an upper limit of about 500 Hz is sufficient.

The output of the L P F 51 is given to the current deviation calculation section 52 . On the other hand, the armature current of the motor 10 is detected by an armature current detection section (current detector) 60 and is applied to the LPF 59 . L P F 59 also. For example, 5Hz
It has filter characteristics that cut off frequency components above. LP
The output of F59 is given to the current deviation calculation section 52. The current deviation calculation section 52 calculates the difference between the target current command value given from both LPFs 51.59 and the low frequency single wave component of the detected current, and provides this difference to the low frequency control section 53. The low frequency control section 53 controls P in feedback control.
, I, PID operation, etc., and its output is input to the control section 58.

The output of the HPF 54 is given to a high frequency control section 55.

The high frequency control section 55 performs gain calculations on the high frequency components of the manually input target current command value, and provides the results to the control section 56 .

The control unit 56 calculates, for example adds, the low frequency control value input from the low frequency control unit 53 and the high frequency control value input from the high frequency control unit 55. This addition result is on the one hand given to the polarity determining section 57, and its polarity (positive, negative) is determined.
On the other hand, it is applied to the duty calculating section 58, and the duty ratio of the PWM pulse is determined based on the above addition result. The generated duty ratio and the determined polarity are given to the motor drive unit 61, and the motor drive unit 61 controls on/off four switching elements wired in an H-bridge type based on these to turn the motor 0. drive

The above configuration realizes the function of the current control unit 50 2 The control cycle of the CPU can be significantly slowed down.

For example, if the cutoff frequency of the LPF 51.59 is set to about 5Hz as described above, the control period for realizing the functions of the current deviation calculation section 52 and the low frequency control section 53 surrounded by the broken line will be equal to the cutoff frequency. A cycle with a frequency of 1/10, that is, about 20 m5ec is sufficient, and C
The burden on the PU will be about 1/1.00 of the conventional one. Further, the control by the high frequency control section 55 is performed in about several msec, but this calculation is relatively simple, and even if the amount of calculation is added, the load on the CPU will be several tenths of that of the conventional system. This allows C
An inexpensive PU can be used. Further, even if some noise enters the armature current detection section 60, it is cut off by the LPF 59 and fed back, so that unnecessary current may flow to the motor 10 due to the noise.

No malfunctions will occur.

In this way, the high frequency control section 55 is
A faster response can be obtained with the output of Also, when holding the rudder, etc.
When it is necessary to flow a constant current to the motor 10 in order to obtain a constant torque, a current deviation calculation section 52 compares the low frequency components of the target current command value and the detected current value and makes the difference zero. Since the motor drive voltage is determined by the low frequency control section 53, the motor current can be passed according to the command value even if there are fluctuations in the power supply voltage or fluctuations in armature resistance due to heat generation in the motor. Furthermore, since the detection current is fed back only through a low-pass filter, the structure is resistant to noise.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing an embodiment of the present invention. FIG. 2 is a configuration diagram showing an example of a power steering mechanical system. FIG. 3 is a graph for determining the reference current command value based on the steering torque and vehicle speed. lO: Steering assist motor. 20...Assist command unit 21...Torque sensor. 22...Vehicle speed sensor. 4 30...Viscosity command section. 40... Inertia compensation section 50... Current control section. 51, 59...Low pass filter. 52...Current deviation calculation unit. 53...Low frequency control section. 54...High-pass filter. 55...High frequency control section. 56...control unit. 60... Armature current detection section. 61...Motor drive unit.

Claims (2)

[Claims] (1) In an electric power steering device that creates an assist command based on detected steering torque, detected vehicle speed, etc., and uses this assist command to control a steering assist motor that generates steering assist torque, the above-mentioned assist motor A filter means for separating a signal component of the assist command into a low frequency component and a high frequency component. A first low frequency control means for processing the low frequency component, a second high frequency control means for processing the high frequency component, and the processing results of the first low frequency control means and the second high frequency control means are synthesized. and third control means for driving the assist motor based on the synthesis result. (2) comprising means for detecting a motor current of the assist motor and a low-pass filter means for passing a low frequency component of the detected motor current, the low frequency component of the detected motor current being controlled by the first low frequency control; The electric power steering device according to claim 1, wherein the electric power steering device is configured to be fed back to the means.