JPH0891237A - Electric power steering device - Google Patents

Abstract

PURPOSE: To provide a motor driven power steering device high in responsiveness, and excellent in a feeling of steering by preventing the occurrence of magneto-strictive sound and vibration followed by the incidental oscillation of a steering system. CONSTITUTION: There is provided a motor driven power steering device equipped with a steering torque detection means 10, a vehicle speed detection means 15, a control means 20 provided with a digital control means 21, a timing setting means 22, and with a reference clock generating means 23, a motor drive means 13, a motor current detection means 14, and with an electric motor 8.

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 system for reducing the steering force of a driver by directly applying the power of an electric motor as a steering assist force to a steering system.

[0002]

2. Description of the Related Art In a conventional electric power steering apparatus, a steering torque signal detected by a steering torque detecting means is converted into a corresponding target current signal, while a motor current detecting signal detected by a motor current detecting means is negatively fed back. , The electric motor is controlled based on the deviation signal between the target current signal and the electric motor current detection signal, the deviation signal is quickly converged to 0 to drive the electric motor with the electric motor current equal to the target current, and the desired power is supplied by the electric motor. It is known to be configured to exert an auxiliary steering force on the steering system.

An outline of the configuration and operation of a conventional electric power steering apparatus will be described. FIG. 5 is an overall configuration diagram of a conventional electric power steering device, and FIG. 6 is a block diagram of essential parts of the conventional electric power steering device.

In FIG. 5, a conventional electric power steering apparatus 1 includes a steering wheel 2, a steering shaft 3, a hypoid gear 4, a rack and pinion mechanism 5 including a pinion 5a and a rack shaft 5b, a tie rod 6, a front wheel of a steering wheel. 7. Steering torque detecting means for detecting the steering torque acting on the electric motor 8 for generating the steering assist force and the steering wheel 2 and outputting the steering torque signal T _D converted into an electric digital signal corresponding to the steering torque ( (Sensor) 10, control means 12 for driving and controlling the electric motor 8 based on the steering torque signal T _D , electric motor driving means 13, electric motor current detecting means 14 and the like.

When the steering wheel 2 is steered, a steering torque detecting means (sensor) 10 provided on the steering shaft 3 detects the steering torque and converts it into a corresponding electric digital signal to control the steering torque signal T _D. Means 1
Send to 2. Further, in the rotation applied to the steering shaft 3, the rotational force of the pinion 5a is converted into a linear movement in the axial direction of the rack shaft 5b via the rack and pinion mechanism 5, and the steering of the front wheel 7 is changed via the tie rod 6. Let

The control means 12 supplies a drive control voltage signal V _O to the electric motor drive means 13 based on the steering torque signal T _D , and the electric motor drive means 13 supplies an electric motor voltage V _M corresponding to the drive control voltage signal V _O. Then, the electric motor 8 is driven.

Electric motor 8 driven by electric motor voltage V _M
Is configured so that a steering assist force corresponding to the level and sign of the electric motor voltage V _M acts on the steering system via the hypoid gear 4 to reduce the steering force applied to the steering wheel 2.

In FIG. 6, the control means 12 of the conventional electric power steering apparatus 1 is the steering torque detecting means 10.
Based on the steering torque signal T _D obtained by converting the steering torque T detected by the vehicle into a digital signal and the vehicle speed signal V _D obtained by converting the vehicle speed V detected by the vehicle speed detecting means 15 into a digital signal, a vehicle speed signal V _D ( V _L, V _M, the steering torque signal and V _H) of the parameter (T _D) - target current signal (I _SD)
Target current setting unit 16 for converting the target current signal I _SD of characteristic diagram, and the target current signal I _SD, and the motor current detection signal I _D which is converted into a digital signal of the motor current I _M which motor current detecting means 14 detects Deviation signal ΔI (= I _SD −
Deviation determination means 17 for calculating I _D ), the deviation signal ΔI is converted into a voltage, and the motor drive means 13 is PWM-controlled to generate a drive control voltage signal V _O for quickly converging the deviation signal ΔI to 0. The drive control means 18 is provided.

The control means 12 is based on a microprocessor and has a sequence function of soft program control and a digital processing / arithmetic function. The steering torque signal T _D and the electric motor current detection signal I _D are read at a predetermined timing and are stored in advance. The deviation signal ΔI (= I _SD −I in the set order
_D ) calculation and control, calculation and processing of the drive control voltage signal V _O based on the calculation result of ΔI, and the motor drive means 1
The motor voltage V _M is supplied to the motor 8 via 3 to control the motor current I _M of the motor 8 to be equal to the target current I _S corresponding to the steering torque T.

FIG. 7 shows an operation sequence explanatory diagram of the control means of the conventional electric power steering apparatus. In Figure 7,
The read timing of the steering torque signal T _D , the electric motor current detection signal I _D and the vehicle speed signal V _D , and the drive control voltage signal V _O
3 shows the order relation of the calculation / processing timing of.

First, when the steering torque signal T _{D is} output from the steering torque detection means 10, the control means 12 reads the steering torque signal T _D at a predetermined timing and stores it as steering torque signal (T _D ) data.

Next, the electric motor current detection signal I _D output from the electric motor current detection means 14 is read at a predetermined timing in the calculation / processing sequence other than the steering system and stored as electric motor current detection signal ( _ID ) data. . Incidentally, reading of the motor current detection signal I _D performs a plurality of times of read operation as long as the vacant time during the sequence run, rewrites the motor current detection signal (I _D) data, the latest at the end of the sequence Configured to store data.

Further, the vehicle speed signal V _D is read at a predetermined timing into a calculation / processing sequence other than the steering system from the vehicle speed detecting means 15 at a predetermined cycle and stored as vehicle speed signal (V _D ) data.

Subsequently, in the calculation / processing sequence of the drive control voltage signal V _O , the steering torque signal (T _D ) data that has been read and stored is used as the vehicle speed signal (V _D ) data as a parameter, and the data table of FIG. From the target current signal (I _SD ) data to the deviation signal ΔI (= I _SD −I _D ) from the target current signal (I _SD ) data and the motor current detection signal (I _D ) data that is read and stored. Data is calculated, the drive control voltage signal V _O is calculated based on the calculated deviation signal ΔI, and output processing is executed. In addition, a series of sequence control is performed in a predetermined serial cycle (for example,
0.5 ms).

As described above, in the conventional electric power steering apparatus 1, the control means 12 is basically a microprocessor, has a sequence function of soft program control and a digital processing / arithmetic function, and has a steering torque signal according to a preset sequence. Each of T _D , the motor current detection signal I _D, and the vehicle speed signal V _D is read at a predetermined timing, and the drive control voltage signal V _O is read at a predetermined cycle (for example, 0.5).
Since it is configured to calculate and output every ms), it is said that an appropriate steering assist force corresponding to the steering that changes every moment can be obtained.

[0016]

The conventional electric power steering apparatus 1 is constructed so that, in the series of sequence operations of the control means 12, the reading of the electric motor current detection signal I _D is executed in the calculation / processing sequence other than the steering system. Therefore, the drive control voltage signal V _O is calculated and output based on the target current signal I _SD and the motor current detection signal I _D converted from the steering torque signal T _D in the calculation / processing sequence of the drive control voltage signal V _O. At this time, a time delay from the reading of the motor current detection signal I _D to the output of the drive control voltage signal V _O (delay time Td shown in FIG. 7) occurs, and the motor current detection signal I _D at the time of output of the drive control voltage signal V _O There or changed from the value at the time of loading, parasitic at higher frequencies outside the steering region the phase lag of the motor current I _M due to the delay time Td There is a problem that vibration to unpleasant sound (magnetostrictive sound) to the steering system and vibration occurs.

Further, in order to prevent the generation of unpleasant sound (magnetostrictive sound) or vibration, if a low-pass filter or phase compensating means is provided in the feedback loop of the motor current detection signal I _D to prevent parasitic oscillation, steering area Although the gain of the frequency band outside can be reduced to prevent oscillation, the gain of the frequency band in the steering region is also reduced, and there is a problem that a desired steering assist force cannot be obtained.

[0018] This invention has been made to solve the above problems, its object is read motor current detection signal I _D immediately before the drive control voltage signal V _O operation, the drive control voltage signal V _O output when By reducing the delay time Td of the electric motor current detection signal I _D , a sound (magnetostrictive sound) and vibration associated with parasitic oscillation of the steering system are prevented and the electric power steering device with excellent responsiveness and excellent steering feeling is provided. To provide.

[0019]

In order to solve the above problems, the control means of the electric power steering apparatus according to the present invention sets the timing of reading the signal from the electric motor current detection means immediately before the arithmetic processing for determining the control signal. It is characterized in that it is provided with a digital control means.

[0020]

In the electric power steering apparatus according to the present invention, the control means for determining the drive control signal of the electric motor is set to the digital control for setting the timing of reading the signal from the electric motor current detecting means immediately before the arithmetic processing for determining the control signal. Since the means is provided, the delay time Td for detecting the electric motor current detection signal _ID can be shortened when the drive control voltage signal V _{O is} calculated, and parasitic oscillation of the steering system can be prevented,
A steering assist force with a quick response can be generated.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an essential part of an electric power steering apparatus according to the present invention. In FIG.
The electric power steering device includes steering torque detecting means 1
0, vehicle speed detection means 15, control means 20, electric motor drive means 13, electric motor current detection means 14, and electric motor 8.

The steering torque detecting means 10 and the vehicle speed detecting means 15 respectively detect a steering torque T, a differential transformer, wheels or an engine mission rotation speed (vehicle speed V).
An A / D converter for converting the analog steering torque signal T and the vehicle speed signal V detected by the rotation speed sensor, the differential transformer and the rotation speed sensor into a digital steering torque signal T _D and a vehicle speed signal V _D. The steering torque signal T _D and the vehicle speed signal V _D are supplied to the digital control means 21 of the control means 20.

The motor current detecting means 14 is arranged in a feedback loop between the motor driving means 13 and the control means 20, and a resistor for detecting the motor current I _M by a voltage, a differential amplifier, an A / D.
The control means 2 is provided with a converter or the like and detects the analog electric motor current I _M as a digital electric motor current detection signal I _D.
0 to the digital control means 21.

The control means 20 is basically composed of a microprocessor and comprises various arithmetic functions, memories and processing functions which are operated by an instruction execution program of a software program. The digital control means 21, the timing setting means 22, the reference clock generating means 23, The control means 20 is provided with a sequence means (not shown) for controlling the operation sequence of the whole.

The digital control means 21 reads and stores the steering torque signal T _D , the vehicle speed signal V _D, and the electric motor current detection signal I _D , which are digital values, according to the plurality of timing signals T _KI provided from the timing setting means 22. , And PID control are performed to calculate a drive control voltage signal V _O that is a combination of an ON signal and a PWM (pulse width modulation) signal, and the drive control voltage signal V _O is supplied to the motor driving means 13. The digital control means 21 sets the reading of the electric motor current detection signal I _D at the timing immediately before the calculation and output of the drive control voltage signal V _O , and the electric motor current I _M actually flowing through the electric motor 8 is set to the electric motor. Current detection signal I _D
Try to reduce the delay time of reading.

The timing setting means 22 is composed of a plurality of timer means composed of, for example, a frequency dividing circuit, divides the reference clock C _L from the reference clock generating means 23 into a predetermined frequency, and controls the sequence means (not shown). A plurality of timing signals T _KI are supplied to the digital control means 21.

The reference clock generating means 23 is composed of an oscillator such as a crystal oscillator which is highly accurate and stable and an oscillating circuit, generates a reference clock C _L and supplies it to the timing setting means 22 and the control means 20 as a whole.

FIG. 2 shows a block diagram of the essential parts of the digital control means of the electric power steering apparatus according to the present invention. In FIG. 2, the digital control unit 21 includes a target current setting unit 24, a deviation calculation unit 25, a drive current setting unit 26, a drive current storage unit 27, and a drive control unit 28.

The target current setting means 24 is provided with a memory such as a ROM, and is synchronized with the timing signals T _KI (T _K1 , T _K3 , T _K5 ) supplied from the timing setting means 22, and the steering torque signal T _D and the vehicle speed signal are supplied. Load the V _D, selected in advance vehicle speed signal V _D in FIG. 8 set in _{ROM (V L, V M,} V H) of the target current signal I _SD data corresponding to the steering torque signal T _D which has a parameters, The target current signal I _SD is output to the deviation calculator 25. For example, the steering torque signal T _D is read with the timing signal T _K1 , the vehicle speed signal V _D is read with the timing signal T _K5 , the target current signal I _SD is selected and the target current signal I _SD is output as the timing signal T _K3. To configure.

The deviation calculation means 25 includes a subtraction function, reads a target current signal I _SD in synchronism with the timing signal T _K3, whereas, the motor current detected in synchronism with the timing signal T _K4 in the timing signal T _K3 period The signal I _D is read, and the deviation (I _SD −I _D ) between the target current signal I _SD and the motor current detection signal I _D is calculated in synchronization with the timing signal T _K3 after the end of the timing signal T _K4 , and the deviation signal ΔI _n (N is the current number of times) is output to the drive current setting means 26.

The drive current setting means 26 has an addition function and a memory drive function, takes in the deviation signal ΔI _n by the timing signal T _K3 , and drives the drive current storage means 27 to drive the previous (n-1) drive current. The signal I _On-1 is read and added to the deviation signal ΔI _n to supply the current (n-th) drive current signal I _On (I _On-1 + ΔI _n ) to the drive control unit 28 and the drive current storage unit 27. The previous (n-1) drive current signal I _On-1 written in (1) is rewritten to the latest (n-th) drive current signal I _On .

The drive current storage means 27 is a rewritable RA.
The previous drive current signal I which is composed of a memory such as M and is stored in the memory under the control of the drive current setting means 26.
_On-1 is output and the current drive current signal I _On is stored instead of the drive current signal I _On-1 .

The drive control means 28 is a PID calculation means 28.
A, the drive control voltage generating means 28B is provided, the drive current signal I _On is PID-calculated in synchronization with the timing signal T _K3 to obtain the drive control current signal I _Pn , and the drive control current signal I _Pn is converted into a voltage. , ON signal and PWM are combined to generate a drive control voltage signal V _O , and this drive control voltage signal V _O is generated.
Is configured to control the electric motor drive means 13.

The PID computing means 28A has a proportional (P), integral (I) and derivative (D) computing function, respectively, and has a proportional coefficient K _P , an integral coefficient K _I and a differential coefficient K preset in a memory such as a ROM. using _D proportional component (K _P ×
ΔI _n ), integral component (K _I × I _On ) and differential component {K _D
After calculating × (ΔI _n −ΔI _n−1 )}, the drive control current signal I _Pn obtained by adding the respective components is added to the drive control voltage generating means 28B.
Output to. The drive control current signal I _Pn is expressed by _equation 1.

[0035]

## EQU1 ## I _Pn = K _P × ΔI _n + K _I × I _On + K _D × (ΔI _n −ΔI _n-1 ) where ΔI _n-1 is the previous deviation signal.

The drive control voltage generating means 28B has a voltage conversion function and a drive control voltage signal generation function, and after converting the drive control current signal I _Pn into a voltage signal, an ON signal and P
The drive control voltage signal V _O which is mixed a WM signal and outputs to the motor drive unit 13 in FIG. 1.

FIG. 3 shows an operation sequence explanatory diagram of the digital control means of the electric power steering apparatus according to the present invention. FIG. 3 shows the order relation between the reading of the steering torque signal T _D , the electric motor current detection signal I _D and the vehicle speed signal V _D corresponding to the timing signal T _KI , and the calculation / processing of the drive control voltage signal V _O.

First, the steering torque signal T _D is read in synchronization with the timing signal T _K1 . Then, synchronized with the timing signal T _K3, first timing signal T _K1 read the steering torque signal T _D and the vehicle speed signal V based on the vehicle speed signal V _D read on the previous timing signal T _K5 of the timing signal T _{K3 D (V L, V M,} V H) to select a target current signal I _SD corresponding to the steering torque signal T _D which was the parameter.

Subsequently, during the timing signal T _K3 period after selecting the target current signal I _SD , the motor current detection signal I _D is read in synchronization with the timing signal T _K4 . After reading the motor current detection signal I _D, calculates a difference signal [Delta] I _n from the target current signal I _SD and the motor current detection signal I _D in synchronization again with the timing signal T _K3, the drive current of the previous (n-1) The current (n) drive current signal I _On is calculated from the signal I _On-1 and the deviation signal ΔI _n .

Next, in synchronism with the timing signal T _K3 , the deviation signal ΔI _n , the drive current signal I _On, and the deviation (ΔI _n −ΔI _n-1 ) of the deviation signal between the current time (n) and the previous time (n−1) are calculated. PID based on (proportional, integral, derivative) after calculating the drive control current signal I _Pn subjected to calculation, the drive control current signal I _Pn
Is subjected to voltage conversion, and the drive control voltage signal V _{O in} which the ON signal and the PWM signal are mixed is calculated from the voltage converted signal and output.

The vehicle speed signal V _D is read in synchronization with the timing signal T _K5 at every predetermined cycle, and the target current signal I is based on the previous vehicle speed signal V _D until a new vehicle speed signal V _D is read. _SD selection is executed.

Further, the sequence operation is configured to be repeatedly executed from the start of the timing signal T _K1 to the end of the timing signal T _K3 as one cycle (for example, cycle 0.5 ms).

As described above, the reading of the motor current detection signal I _D is performed immediately before the calculation and the output of the drive control voltage signal V _O , and a series of sequences, for example, 0.5 ms.
Of the motor current detection signal I
The time delay of _D is small and the phase delay of the motor current I _M flowing through the motor 8 can be reduced. Although there is a time delay from the reading of the steering torque signal T _D to the calculation of the drive control voltage signal V _O , the change of the steering torque signal T _D is gentle with respect to the period of 0.5 ms and can be ignored.

FIG. 4 is an operation flow chart of the digital control means of the electric power steering apparatus according to the present invention.
When the vehicle is started and the control means 20 enters the standby state (start state), the steering torque signal T _D is read in step S1.

In step S2, the steering torque signal T _D is converted into a target current signal I _SD responsive to the vehicle speed signal V _D (using the vehicle speed signal V _D as a parameter). Subsequently, the motor current detection signal I _D is read in step S3, and the deviation between the target current signal I _SD and the motor current detection signal I _D is calculated in step S4 to calculate the deviation signal ΔI _n .

Next, in step S5, the current (n) drive current signal I _On is calculated from the previous drive current signal I _On-1 and the deviation signal ΔI _n , and in step S6 the deviation signal Δ On.
I _n , the drive current signal I _On, and the current time (n) and the previous time (n-
P) based on the deviation (ΔI _n −ΔI _n- 1) of the deviation signal of ₁ )
ID calculation is performed, and the drive control current signal I represented by the equation 1
_Pn is required.

Then, in step S7, the drive control voltage signal V _O is calculated from the drive control current signal I _Pn to complete one cycle of the sequence, and the operations of steps S1 to S7 are repeated.

Further, in step S8, the vehicle speed signal V _D is read in a cycle relatively longer than the cycle from step S1 to step S7, and the read vehicle speed signal V _D uses the vehicle speed signal V _D as a parameter in step S2. The target current signal I _SD is updated.

[0049]

As described above, in the electric power steering apparatus according to the present invention, the control means for determining the drive control voltage signal of the electric motor is operated by the operation for determining the timing of reading the signal from the electric motor current detecting means. Equipped with a digital control unit that is set immediately before processing, the delay time of the motor current detection signal can be shortened when the drive control voltage signal is calculated, parasitic oscillation of the steering system can be prevented, and the motor current can be quickly changed to the target current signal. Therefore, the response of the steering assist force can be improved.

Further, since the phase delay of the electric motor current can be improved, the gain of the feedback loop can be set high to further improve the response of the steering assist force.

Therefore, it is possible to provide the electric power steering apparatus which is excellent in steering feeling.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of an electric power steering device according to the present invention.

FIG. 2 is a block diagram of a main part of digital control means of the electric power steering apparatus according to the present invention.

FIG. 3 is an operation sequence explanatory diagram of the digital control means of the electric power steering apparatus according to the present invention.

FIG. 4 is an operation flow chart of digital control means of the electric power steering apparatus according to the present invention.

FIG. 5 is an overall configuration diagram of a conventional electric power steering device.

FIG. 6 is a block diagram of a main part of a conventional electric power steering device.

FIG. 7 is an explanatory diagram of an operation sequence of control means of a conventional electric power steering apparatus.

[8] the steering torque signal and vehicle speed signal as a parameter (T _D) - target current signal (I _SD) characteristic diagram

[Explanation of reference numerals] 1 ... Electric power steering device, 2 ... Steering wheel, 3 ... Steering shaft, 4 ... Hypoid gear, 5
... rack and pinion mechanism, 5a ... pinion, 5b ... rack shaft, 6 ... tie rod, 7 ... front wheel, 8 ... electric motor, 10 ...
Steering torque detecting means (sensor), 12, 20 ... Control means, 13 ... Electric motor driving means, 14 ... Electric motor current detecting means, 15 ... Vehicle speed detecting means, 16, 24 ... Target current setting means, 17 ... Deviation determining means, 18 , 28 ... Drive control means,
21 ... Digital control means, 22 ... Timing setting means, 23 ... Reference clock generating means, 25 ... Deviation computing means, 26 ... Driving current setting means, 27 ... Driving current storing means, 28A ... PID computing means, 28B ... Driving control voltage Generating means, C _L ... Reference clock, I _D ... Motor current detection signal, I _M ... Motor current, ΔI _n ... Deviation signal, I _On ... Drive current signal, I _Pn ... Drive control current signal, I _SD ... Target current signal , T _D ... Steering torque signal, K _D ... Differential coefficient, K _I ... Integral coefficient, K _P ... Proportional coefficient, T _KI (T _K1 , T _K3 , T _K4 ,
T _K5) ... timing signal, V _D ... vehicle speed signal, V _M ... motor voltage, V _O ... driving control voltage signal.

Claims (1)

[Claims] 1. A steering torque detecting means for detecting a steering torque acting on a steering system of a vehicle, an electric motor for applying a steering assist force to the steering system, and an electric motor current detecting means for detecting an electric motor current of the electric motor. An electric power steering apparatus comprising: a signal from the steering torque detecting means and a signal from the electric motor current detecting means, and a control means for determining a control signal for controlling the electric motor based on a deviation signal of both signals, The electric power steering apparatus according to claim 1, wherein the control means includes digital control means for setting the timing of reading the signal from the electric motor current detection means immediately before the arithmetic processing for determining the control signal.