JPH08175405A - Motor-driven power steering device - Google Patents

Abstract

PURPOSE: To provide a motor-driven power steering device with good steering feeling which can generate steering assist force with a good balance kept on the right and left for steering wheel operation. CONSTITUTION: This motor-driven power steering device is provided with a motor control means 12 which has an offset correction means 20 for taking in a motor current detection signal IMD (=ΔIMD) corresponding to the offset value of the motor current IM detected by a motor current detection means 14 with a target current signal ISD where motor current 13 is taken as 0 kept at 0, storing it as an offset correction signal ΔIMD, computing a deviation (IMD-ΔIMD) between the motor current detection signal IMD and the offset signal ΔIMD the target current signal ISD is a finite value, and outputting a correction current sill IMC (=IMD--ΔIMD) to a deviation determination means 17.

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 for directly applying the power of an electric motor to a steering system to reduce the steering force of a driver.

[0002]

2. Description of the Related Art In a conventional electric power steering apparatus, a steering torque sensor detects a steering torque to be steered by a driver, converts the steering torque signal into a steering torque signal, and uses the steering torque signal as a target current of a motor current for driving the motor. Generates the corresponding target current signal and feeds back (negatively feedbacks) the motor current detection signal corresponding to the actual motor current flowing in the motor detected by the motor current detection means to the target current signal to detect the target current signal and the motor current. Based on the deviation signal of the signal, the actual motor current flowing to the motor is controlled so as to quickly match the target current to drive the motor, and the power of the motor corresponding to the steering torque of the driver acts on the steering system as steering assist force. Those configured to let are known.

An outline of the configuration and operation of a conventional electric power steering apparatus will be described. FIG. 10 shows a block diagram of a main part of a conventional electric power steering device. FIG.
At 0, the electric motor control means 53 of the conventional electric power steering device 50 converts the steering torque T detected by the steering torque sensor 51 into a digital signal, the steering torque signal T _D, and the vehicle speed V detected by the vehicle speed detection means 52. based on the vehicle speed signal V _D which is converted into a digital signal 11 to show the vehicle speed signal _{V D (V L, V M} , V H) steering torque signal and a parameter (T _D) - target current signal (I _SD) properties Target current signal generation means 57 for converting the data into the target current signal I _SD , target current signal I _SD , and motor current detection means 55
Deviation signal ΔI (= I _SD − from the electric motor current detection signal I _MD converted into a digital signal of the electric motor current I _M detected by
Deviation determination means 58 for calculating I _MD ) and the deviation signal ΔI
The electric motor control signal V _O for improving the characteristics through the ID controller, and PWM-controlling the electric motor 56 through the electric motor driving means 54 by the drive signal with the improved characteristics to quickly converge the deviation signal ΔI to 0. The drive control means 59 which generate | occur | produces is provided.

The electric motor control means 53 is basically a microprocessor and has a sequence function of soft program control and a digital processing / arithmetic function, and reads the steering torque signal T _D and the electric motor current detection signal I _MD at a predetermined timing. , Deviation signal ΔI in a preset order
Arithmetic and control (= I _SD -I _MD), perform the operation and processing of the motor control signal V _O on the basis of the calculation result of [Delta] I, the motor voltage V _M is supplied to the electric motor 56 via the motor driving unit 54 , The electric current I _M of the electric motor 56 is controlled to be equal to the target current I _SD corresponding to the steering torque T.

The electric motor current detecting means 55 detects the electric motor current I _M according to the forward rotation and the reverse rotation of the electric motor 56 as a voltage. For example, the output voltage of the resistor and the differential amplifier and the differential amplifier is the electric motor detection current. The differential amplifier is equipped with a current signal converting means for converting into a signal I _MD
The midpoint of the voltage E _O (E _O / 2) is set to virtual ground, and the negative voltage (corresponding to the reverse rotation of the motor) and the positive voltage (corresponding to the positive rotation of the motor) detected by the resistor are respectively 0 to E _O. / 2, E _O /
It is configured to output 2~E _O.

As described above, in the conventional electric power steering apparatus 50, the actual electric motor current I flowing through the electric motor 56 is obtained.
The _M detected by the motor current detecting means 55 as the motor current detection signal I _MD, fed back to the deviation determining means 58 (negative feedback) to the deviation signal ΔI between the target current signal I _SD (= I _SD
-I _MD ), the drive of the electric motor 56 is controlled by the electric motor control means 53 so that the electric motor current is quickly matched with the target current, and an appropriate steering assist force corresponding to the steering torque is applied from the electric motor 56 to the steering system. Can be made.

[0007]

The conventional electric power steering apparatus 50 feeds back (negatively feeds back) the motor current detection signal I _MD corresponding to the motor current I _M to the target current signal I _SD to obtain the target current signal I _SD. And the drive current of the electric motor 56 is controlled based on the deviation (I _SD −I _MD ) between the electric motor current detection signal I _MD and the electric current I _M of 0, the electric motor current detection means 55 uses the differential amplifier. When the electric motor current detection signal I _MD is output by an offset such as the above, and the electric motor 56 is controlled based on the deviation signal ΔI fed back from the electric motor current detection signal I _MD , the electric motor 56
There is a problem that the steering assist force due to the power of is unbalanced by an amount corresponding to the offset, and the steering force corresponding to the driver's right and left steering wheel operation is also unbalanced.

For example, as shown in the characteristic diagram of the current detection signal (V _MD ) -motor current detection signal (I _MD ) of the motor current detection means of FIG. 12, the current detection signal V of the differential amplifier of the motor current detection means 55 is shown. _MD is 2.5 V when the motor current I _M is 0 if the power supply (battery) voltage E _O driving the differential amplifier is 5 V and there is no offset in the differential amplifier,
With this current detection signal V _MD (2.5 V) as a center value, a negative motor current I _M (reverse rotation of the motor 56) is detected at a voltage value below 2.5 V (0 ≦ V _MD <2.5 V), The positive motor current I _M (positive rotation of the motor 56) is detected at a voltage value exceeding 2.5 V (2.5 V <V _MD ≦ 5 V).

Output of differential amplifier (current detection signal V _MD )
Is converted into the motor current detection signal I _MD of FIG. 12 by the current signal conversion means. When the current detection signal V _MD is 2.5 V, the motor current detection signal I _MD is 0 and the current detection signal V _MD is 2. When it exceeds 5V, it becomes a positive value, and when it falls below 2.5V, it becomes a motor current detection signal I _MD which changes with a straight line (solid line display) of a negative value.

On the other hand, when the differential amplifier has an offset, for example, V _MDK indicated by the straight line (dashed line) in FIG. 12, the current detection signal V _MD at the neutral position of the steering wheel is 2.
At the point of 5V, the negative electric motor current detection signal ΔI _MD has already been generated due to the offset. For example, when steering the steering wheel to the left, the steering current is 0 and the negative electric motor current detection signal ΔI _MD is dealt with. Since the steering assist force is already applied, the driver's steering wheel operation becomes light, but when steering the steering wheel to the right, the steering wheel operation of the driver may be unnecessarily heavy, and the steering force to the left and right cannot be applied. It is not preferable because it causes a balance.

Further, when the drive control means 59 and the electric motor drive means 54 shown in FIG. 10 have variations and changes with time, the electric motor current detection means 55 allows the electric motor current I _M of the electric motor 56 to be regarded as zero. Since the electric motor current detection signal I _MD is detected, there is a problem that the steering force corresponding to the driver's right and left steering wheel operation becomes unbalanced, as in the case of the offset of the differential amplifier of the electric motor current detection means 55.

Further, due to variations in the drive control means 59 and the motor drive means 54, changes with time, and offsets of the differential amplifier, the drive motor 59, the motor drive means 54, and the motor current detection means 55 shown in FIG. The electric motor current detection signal I _MD is detected even in a state where the electric motor current I _M is regarded as 0, and there is a problem that the steering force corresponding to the driver's left and right steering wheel operation becomes unbalanced.

The present invention has been made to solve such a problem, and an object thereof is to correct a deviation signal based on a motor current detection signal detected in a state where the motor current is considered to be 0, thereby generating a motor. An object of the present invention is to provide an electric power steering device that balances the steering assisting force to improve the steering feeling.

[0014]

In order to solve the above problems, the electric motor control means of the electric power steering apparatus according to the present invention uses the value of the electric motor current detection signal in a state where the electric motor current is regarded as 0 as an offset correction value, It is characterized in that it comprises an offset correction means for correcting the deviation signal based on the offset correction value.

Further, the offset correction means of the electric power steering apparatus according to the present invention comprises a timer means and an offset value storage means, and stores the offset correction value when the target current signal remains at 0 for a predetermined time. It is characterized by

Also, in the electric power steering apparatus according to the present invention, the offset correction means is provided with the offset reference value storage means for storing the offset reference value and the comparison means, and when the offset value is within the range of the offset reference value. Is characterized by storing an offset value.

[0017]

The electric motor control means of the electric power steering apparatus according to the present invention uses the value of the electric motor current detection signal when the electric motor current is regarded as 0 as an offset correction value, and corrects the deviation signal based on the offset correction value. Since the correction means is provided, the electric motor current in a state where the electric motor current is considered to be 0 can be set to 0.

Further, the offset correction means of the electric power steering apparatus according to the present invention comprises a timer means and an offset value storage means, and stores the offset correction value when the state of the target current signal is 0 for a predetermined time. Therefore, a stable offset correction value can be set.

Further, in the electric power steering apparatus according to the present invention, the offset correction means is provided with the offset reference value storage means for storing the offset reference value and the comparison means, and when the offset value is within the range of the offset reference value. Stores the offset value, it is possible to correct the motor current within the allowable range of the offset value.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention. The electric power steering device 1 includes a steering wheel 2, a steering shaft 3, a hypoid gear 4, a pinion 5a, and a rack shaft 5.
The steering torque acting on the rack and pinion mechanism 5 including b and the like, the tie rod 6, the front wheel 7 of the steered wheels, the electric motor 8 for generating the steering assist force, and the steering wheel 2 is detected and converted into an electric signal corresponding to the steering torque. The steering torque sensor 10 that outputs the generated steering torque signal T, the vehicle speed sensor 11 that detects the vehicle speed and outputs the vehicle speed signal V converted into an electric signal corresponding to the vehicle speed, the steering torque signal T, and the vehicle speed signal V A target current signal I _MD that determines the target current of the electric motor 8 is set based on the target current signal I _MD.
Motor control means for generating a motor control signal V _O corresponding to _MD 12, the electric motor driving unit 13 is driven by supplying a motor voltage V _M to the motor 8, the motor current I _M which corresponds to the forward rotation and reverse rotation of the motor 8 _{Is included} and is converted into a motor current detection signal I _MD .

When the driver steers the steering wheel 2, the steering torque sensor 10 provided on the steering shaft 3 detects the steering torque and supplies the steering torque signal T converted into an electric signal to the electric motor control means 12. Also,
The steering torque applied to the steering shaft 3 is rack &
The rotational force of the pinion 5a is converted into a linear movement in the axial direction of the rack shaft 5b via the pinion mechanism 5, and the steering of the front wheels 7 is changed via the tie rod 6. On the other hand, vehicle speed sensor 1
1 detects the speed of the vehicle, converts it into a corresponding electric signal, and supplies a vehicle speed signal V to the electric motor control means 12.

The motor control means 12 to the motor drive unit 13 based on the steering torque signal T and the vehicle speed signal V, for example, supplies the motor control signal V _O of PWM (pulse width modulation), the motor drive means 13, for example 4 It is composed of individual switching elements (power FET, etc.), and the motor control signal V _O
The motor voltage V _M corresponding occurred, and drives the motor 8 in the two-way motor current I _M which corresponds to the absolute value and direction of the steering torque T. The electric motor torque generated by the electric motor 8 is converted into a boosted steering assist force (assist torque) via the hypoid gear 4 and acts on the steering shaft 3.

The motor current detecting means 14, the motor current I _M actually flowing through the motor 8 is converted into a voltage by such as a resistor or a Hall element which will be described later, and converts the converted voltage to the corresponding motor current detection signal I _MD It is supplied to the electric motor control means 12 and is fed back (negative feedback) to the target current signal I _SD .

FIG. 2 is a block diagram of the essential parts of the electric power steering apparatus according to the present invention. In FIG.
The electric power steering device 1 includes a steering torque sensor 1
0, vehicle speed sensor 11, electric motor control means 12, electric motor drive means 13, electric motor 8, electric motor current detection means 14 and the like. In the electric power steering device 1, when the electric motor current I _M is regarded as 0 by the electric motor control means 12,
Basically, it differs from the conventional electric power steering apparatus 50 shown in FIG. 10 in that an offset correction means 20 for correcting the electric motor current detection signal ΔI _MD caused by the offset detected by the electric motor current detection means 14 is provided.

The steering torque sensor 10 is composed of, for example, a differential transformer, and supplies the steering torque signal T converted into an analog electric signal to the electric motor control means 12 corresponding to the direction and magnitude of the steering force of the driver. . The vehicle speed sensor 11 is composed of, for example, a speedometer including a rotary disk having a slit and a photocoupler, and supplies the vehicle speed signal V converted to a digital signal having a pulse waveform of a cycle corresponding to the vehicle speed to the electric motor control means 12. .

The electric motor control means 12 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 target current signal generation means 16, the deviation determination means 17, and the drive control means are provided. 18 and offset correction means 20.

The target current signal generating means 16 is provided with a memory such as a ROM, and the vehicle speed signal V _D (V _L ,
Steering torque signal (T _D ) with V _M and V _H as parameters
-Target current signal (I _SD ) characteristic data is set in the memory, and when the steering torque signal T and the vehicle speed signal V are input, the target current corresponding to the steering torque signal T _D obtained by digitally converting the steering torque signal T Deviation determining means 1 for signal I _SD
7 and offset correction means 20.

[0028] As apparent from the characteristics of FIG. 11, the vehicle speed signal V (V _L: low vehicle speed range, V _M: Medium speed region, V _H: high vehicle speed range) regardless of the steering torque signal T _D is 0 In this case, the target current signal I _SD also becomes zero. This target current signal I _SD
Is 0, the motor current I _M of the motor 8 is naturally 0.
In this state, when the motor current detection means 14 detects the motor current detection signal ΔI _MD , this motor current detection signal ΔI _MD is stored as an offset correction value by the offset correction means 20 which will be described later. It is configured to correct the deviation signal ΔI.

The deviation calculating means 17 is composed of a calculating means having a subtracting function, and calculates the deviation between the target current signal I _SD and the correction current signal I _MC supplied from the offset correcting means 20 to calculate the deviation signal ΔI (I providing _SD -I _MC) to the drive control unit 18. The correction current signal I _MC is the motor current detection signal I _MD supplied from the motor current detection means 14 and the motor current detection signal ΔI _{MD in} which the target current signal I _SD is 0.
It is the deviation (I _MD −ΔI _MD ) from the (offset signal ΔI _MD ).

The drive control means 18 uses the deviation signal ΔI (= I
Proportional to the _SD -I _MC) (P), integral (I) and differential (D)
The deviation signal Δ
A PID controller that controls I to 0 quickly and stably, and a motor control signal V that is a mixed signal of an ON signal and a PWM (pulse width modulation) signal from the signal of this PID controller depending on the direction and magnitude of the torque generated by the motor 8. A signal generator for generating _O is provided, and the motor control signal V _O is supplied to the motor driving means 13.

The offset correction means 20 has a motor current I
_In the state where the target current signal I _{S D, in} which _M is considered to be 0, is 0, the motor current detection signal Δ detected by the motor current detection means 14
Is stored as the offset correction value is captures and I _MD (offset signal [Delta] I _MD), if the target current signal I _SD is finite value, the motor current detection signal I _MD and the offset signal [Delta] I _MD deviation (I _MD -.DELTA.I _MD ) Result of the correction current signal I _MC
(= I _MD −ΔI _MD ) and outputs it to the deviation determining means 17.

The electric motor current detection signal I _MD detected in the normal steering state includes an offset signal ΔI _MD (I _MD
= I _MDO + ΔI _MD), so the correction current signal I _MC by correcting an offset signal [Delta] I _MD is offset signal Δ
The signal does not include I _MD (I _MC = I _MDO ), and the offset value (ΔI _MD ) can be corrected.

The motor driving means 13 is a switching element,
For example, it is configured by a bridge circuit composed of four FETs (field effect transistors), and the FETs (field effect transistors) are drive-controlled by a motor control signal V _O such as an ON signal or a PWM (pulse width modulation) signal, and the drive direction and size are increased. A motor voltage V _M having a certain level is supplied to the motor 8 to drive the motor 8 with a bidirectional motor current I _M.

The electric motor 8, for example, a DC motor, constituted by a brushless motor or the like, is the motor voltage V _M is supplied, the motor current I _M motor torque T _M corresponding to the direction and magnitude of the
To the rack shaft 7 shown in FIG.

The motor current detecting means 14, for example resistors, detected by the detection or inserted in series in the path of the motor current I _M elements, corresponding voltage bidirectional motor current I _M in a non-contact, such as a Hall element Then, a detection voltage having a positive or negative polarity is output as a voltage of a single polarity by using a differential amplifier driven by a single power source, and the output voltage is converted into a current of positive and negative polarities to drive the motor. The current detection signal I _MD is supplied to the offset correction means 20.

FIG. 3 shows an embodiment of motor current detection using a resistor as a current detection element. In FIG. 3, a resistor R _D for detecting the motor current I _M is inserted in series in the motor 8, and a potential difference V _DR (V _D1 − between the voltages V _D1 and V _D2 across the resistor R _D is inserted.
V _D2 ) is taken into the motor current detection means 14 and the potential difference V _DR
The motor current detection signal I _MD corresponding to is output.

The electric motor drive means 13 is composed of power FETs (field effect transistors) Q1 to Q4, and the electric motor control signal V supplied from the drive control means 18 in FIG.
For example, by driving the gate G1 of Q1 with an ON signal V _G1 and the gate G4 of Q4 with a PWM signal V _G4 at _O , a motor current I _{M +} (solid line arrow) flows and the motor 8 is
For example, the potential difference V is positively rotated and the voltage V _D2 is positive (+) and the voltage V _D1 is negative (-) across the resistor R _D.
DR (V _D1 −V _D2 ) is generated.

Further, the gate G2 of Q2 is turned on signal V _G2 ,
By driving the gate G3 of Q3 with the PWM signal V _G3 respectively, a motor current I _M- (broken line arrow) flows, the motor 8 is rotated in the reverse direction, and the voltage V _D1 is added (+) to the both ends of the resistor R _D, and the voltage is increased. V _D2 minus (-) potential difference V
_DR (V _D1 −V _D2 ) is generated.

The potential difference V _DR (V _D1 − detected by the resistor R _D
V _D2 ) has a different polarity depending on the direction (I _{M +} , I _M- ) of the motor current I _M , and the motor current detection means 14 has a potential difference V _DR.
(V _D1 −V _D2 ) Motor current detection signal I _MD corresponding to the polarity
Is output.

Here, the offset signal ΔI _MD detected by the electric motor current detection means 14 means that the ignition switch IG is turned on and the power supply voltage E _O of the battery 15 is applied to each part of the electric power steering device 1. and the target current signal I _{S D} is the motor current at 0 I _M in FIG. 2
Occurs when a small amount of motor current I _{M +} or I _M- flows and is detected by the resistor R _D when is also considered to be zero.

Further, even if the motor currents I _{M +} and I _M- are 0, there is an offset signal ΔI _MD detected by the offset of the differential amplifier or the like which constitutes the motor detecting means 14.

As described above, when the target current signal I _SD of the offset signal ΔI _MD is 0 and the motor current I _M is also regarded as 0, the drive control means 18, the motor drive means 13 and the motor current of FIG. The signal output from the electric motor current detection means 14 is shown by the offset of the detection means 14 or the like.

FIG. 4 shows an embodiment of motor current detection using a Hall element as a current detection element. 4, the Hall element HD for detecting a motor current I _M are arranged in a non-contact in the path of the motor current I _M, bidirectional motor current (I M _+,
I _M- ) is a positive or negative voltage V corresponding to each polarity
Configure to detect by _DH . Motor current detection means 14
Is a corresponding motor current detection signal I by taking in the voltage V _DH
Output _MD .

FIG. 5 shows another embodiment of electric motor current detection using a resistor as a current detection element. In FIG. 5, the resistor R
_A and resistor R _B are respectively connected between Q2 of FET (field effect transistor) and ground (GND), and between Q4 and ground (GND).
The resistor R _A is inserted between the resistors R _A to detect the motor current I _M- (broken line arrow) for rotating the motor 8 in the reverse direction with the voltage V _DA ,
_B is configured to detect the electric motor current I _{M +} (solid line arrow) that causes the electric motor 8 to rotate forward with the voltage V _DB .

The voltage V _DB detected by the resistor R _{B and the} resistor R _B
There crowded preparative potential difference of the voltage V _DA that has been detected (V _DB -V _DA) is the motor current detecting means 14, and outputs a corresponding to the potential difference (V _DB -V _DA) motor current detection signal I _MD.

FIG. 6 shows a block diagram of an embodiment of the motor current detecting means. In FIG. 6, a motor current detecting means 14 is a differential amplifier 14A driven by a single power source E _O with a virtual ground point being E _O / 2, and a current detection signal V _MD which is an output of this differential amplifier.
To a motor current detection signal I _MD .

The differential amplifier 14A has, for example, a single power supply E _O.
Composed of the inverting type operational amplifier OP1, the potential difference V _DR (V
_D1− V _D2 ) is amplified and 2.5 when the potential difference V _DR is 0.
When the potential difference V _{DR of the} V current detection signal V _MD and the motor current I _{M +} has a negative (-) polarity, it exceeds 2.5 V (2.5
V <V _MD ≦ 5V) the current detection signal V _MD, the motor current I _M- potential difference V _DR is in the case of positive (+) polarity below _{2.5V (0V ≦ V MD <2.5V} ) current detection signal Output V _MD respectively. The input polarity of the differential amplifier 14A is a minus (-) polarity when the motor current I _{M +} flows in the potential difference V _DR of the resistor R _{D in} FIG. 3, and a polarity when the motor current I _M- flows. On the other hand, the polarity of the current detection signal V _MD of the differential amplifier 14A is positive (+) when the potential difference V _DR is negative (-).
When the polarity and the potential difference V _DR are positive (+), the negative (-) polarity is output.

The input of the differential amplifier 14A is not limited to the potential difference V _DR of the resistor R _D of FIG. 3, but the Hall element HD of FIG.
There resistor R _B of the voltage V _DH or 5, in which the detected voltage V _DB of R _A, may be deviation V _DB -V _DA of V _DA.

The current signal converting means 14B is composed of voltage-current converting means using, for example, constant current means, and converts the current detection signal V _MD detected by the differential amplifier 14A into a motor current detection signal I _MD and outputs it. To do. Current signal converting means 14B
Outputs a motor current detection signal I _MD of 0 when the current detection signal V _MD is 2.5 V, plus (+) when it exceeds 2.5 V, and minus (-) when it falls below 2.5 V.

FIG. 7 shows the configuration of another embodiment of the motor current detecting means. (A) In the embodiment shown in the figure, the motor current detection means 19 uses the voltages V _D2 , V detected by the resistor R _{D of} FIG.
Buffers BF1 and BF2 for inputting _D1 and voltages V _D2 and V
A / to convert _D1 buffer output to analog / digital
D converter 19A, and calculates the deviation of the digital converted signal Vd ₂ (corresponding to the voltage V _D2) and the signal Vd ₁ (corresponding to the voltage _{V D1) (Vd 2 -Vd 1} ), the current detection signal V _MD Deviation calculating means 19B for outputting and current signal converting means 1 for converting and outputting the current detection signal V _MD to the motor current detection signal I _MD
4B and.

In the embodiment shown in FIG. 5B, the motor current detecting means 19 includes buffers BF1 and BF2 for inputting the voltages V _DB and V _DA detected by the resistors R _B and _{RA of} FIG.
A / D converter 19A for analog / digital converting the buffer outputs of voltages V _DB and V _DA , digitally converted signal V _dB (corresponding to voltage V _DB ) and signal V _dA (corresponding to voltage V _DA ) switching the switching means 19C which operates by a control signal from an unillustrated direction determining means and the like, for example, the motor current when the signal V _dB was selected I _{M +,} motor when the signal V _dA is selected current I _M- Current signal conversion means 1
4B converts into a motor current detection signal I _MD corresponding to the signal V _dB and the signal V _dA and outputs it.

FIG. 8 is a block diagram of the essential parts of the offset correction means of the electric power steering apparatus according to the present invention. In FIG. 8, the offset correction means 20 comprises a switching means 21, a timer means 22, a data access means 23,
Offset value storage means 24, correction current signal output means 25
The provided, target current signal I _SD is stored 0 (signal I _SDL) state of the motor current detection signal I _{M D} (offset signal [Delta] I _MD), the motor current detection signal I of normal steering operation in the offset signal [Delta] I _MD Compensate _MD and compensate current signal I _MC ( _IMD
-ΔI _MD ) is output to the deviation determining means 17 and the deviation signal ΔI
Is configured to correct.

The switching means 21 has a software-controlled switching function, and the timer signal T _K supplied from the timer means 22.
The switch SW1 is turned on for a predetermined time t _K by the control of 1 and the offset signal ΔI _MD is stored in the offset value storage means 24 via the data access means 23.

The timer means 22 divides and generates the reference clock for driving the microprocessor of the electric motor control means 12, and starts the clocking with the signal I _{SDL of} which the target current signal I _SD is 0 as a trigger, and the signal I _SDL becomes and it continues for a predetermined time T _K,
The switch SW is supplied with the timer signal T _K supplied to the switching means 21.
1 is turned on for a predetermined time t _K.

The switching means 21 and the timer means 22 are provided, and the state in which the target current signal I _SD is 0 (signal I _SD L) and the motor current I _M is also considered to be 0 is monitored for a predetermined time T _K. The motor current detection signal I _MD can be stored as the offset signal ΔI _MD .

Incidentally, the state in which the target current signal I _SD is 0 (signal I _SDL ) continues for a predetermined time T _K is a predetermined time period until the driver turns on the ignition switch IG and starts the steering wheel operation. The time may exceed the time T _K , or the vehicle may be traveling straight ahead and the driver may fix the steering wheel at the neutral position for a predetermined time T _K or more.

The data access means 23 is the switching means 21.
The offset signal ΔI _MD supplied from the device is fetched for a predetermined time t _K , and the offset signal ΔI _{M D} is supplied to the offset value storage means 24 to be stored therein. To read the stored offset signal ΔI _MD and output it to the correction current signal output means 25.

The offset value storage means 24 is composed of a rewritable memory such as a RAM, and stores the offset signal ΔI _MD written from the data access means 23 in place of the previously stored previous offset signal to perform data access. The offset signal ΔI _MD is output according to the request from the means 23. Once stored, the offset signal ΔI _MD is stored until the next new offset signal ΔI _MD is written, and the latest offset signal ΔI _MD that is always stored is output.

The correction current signal output means 25 is composed of a soft control subtraction function, and is a deviation (I _MD -ΔI _MD) between the motor current signal I _MD from the motor current detection means 14 and the offset signal ΔI _MD from the data access means 23. ) Is calculated, and the correction current signal I _MC (= I _MD −ΔI _MD ) is provided to the deviation determining means 17 in FIG. 2 to correct the offset of the deviation signal ΔI.

Although the correction current signal output means 25 for generating the correction current signal I _MC is provided in this embodiment, the correction current signal output means 25 is omitted and the deviation current determination means 17 subtracts the motor current signal I _MD . , The offset signal ΔI _{MD is} added for input, the deviation signal ΔI (= I _SD −I _MD ) is directly corrected by the offset signal ΔI _MD , and the deviation signal ΔI (= I _SD
-I _MD + ΔI _MD ).

In this way, the offset correction means 20 monitors the state where the target current signal I _{SD in} which the motor current I _M can be regarded as 0 is 0 for a predetermined time T _K , and the motor current detection signal I _MD in this state is offset signal ΔI _MD. Therefore, it is possible to correct the deviation signal ΔI by detecting the highly accurate offset signal ΔI _MD .

FIG. 9 is a block diagram of the essential portion of another embodiment of the offset correcting means of the electric power steering apparatus according to the present invention. In FIG. 9, offset correction means 30
Are switching means 21, timer means 22, data access means 23, offset value storage means 24, correction current signal output means 25, offset reference value storage means 31, comparison means 3
2. The switching means 33 is provided, and the motor current detection signal I _MD (offset signal ΔI _MD ) in the state where the target current signal I _SD is 0 (signal I _SDL ) is within the preset offset reference values I _OMN and I _OMX . storing the offset signal [Delta] I _MD in some cases, the motor current detection signal I _MD of normal steering operation in the offset signal [Delta] I _MD by correcting the correction current signal I _MC (I
_MD- ΔI _MD ) is output to the deviation determining means 17 and the deviation signal Δ
It is configured to correct I. The offset correction unit 30 includes an offset reference value storage unit 31 and a comparison unit 3.
2. The point that the switching means 33 is provided is different from the offset correction means 20 of FIG.

Signal I _SDL when target current signal I _SD is 0
For a predetermined time T _K , the timer means 22 switches to the switching means 21.
Is controlled to turn on the switch SW1, and the offset signal ΔI _MD is supplied to the comparison means 32 and the switching means 33.

The offset reference value storage means 31 is composed of a memory such as a ROM, and the maximum offset reference value I which is allowed as an offset preset from a design value or an experimental value.
_{The OMX} and the offset minimum reference value I _OMN are stored, and the comparison means 32 is provided with the offset maximum reference value I _OMX and the offset minimum reference value I _OMN .

The comparison means 32 has a soft control comparison function, and has an offset signal ΔI _MD and an offset maximum reference value I.
_{The OMX} or the offset minimum reference value I _OMN is compared, and the offset signal ΔI _MD is within the range between the offset maximum reference value I _OMX and the offset minimum reference value I _OMN (I _OMN ≦ ΔI _MD ≦
I _OMX ), the comparison signal H _O of, for example, H level is supplied to the switching means 33 to control ON of the switch SW2.

[0066] Switching means 33 is provided with a switching function of the soft control, the comparison signal H _O (H level) from the comparing means 32
The switch SW2 is turned on based on the above, and the offset signal ΔI _MD is provided to the data access means 23.

The offset signal I _MD written from the data access unit 23 to the offset storage unit 24 is stored in place of the previously stored previous offset signal I _MD, and the offset signal I _MD is requested by the data access unit 23. ΔI _MD is sent to the correction current signal output means 25, and a deviation calculation from the motor current signal I _MD from the motor current detection means 14 is performed, and the correction current signal I _MC (= I _MD −ΔI _MD ).
Is provided to the deviation determining means 17 of FIG. 2 to correct the offset of the deviation signal ΔI. Although the correction current signal output means 25 for generating the correction current signal I _MC is provided in this embodiment,
The correction current signal output means 25 is omitted, and the deviation determination means 17
Alternatively, the motor current signal I _MD may be subtracted and the offset signal ΔI _MD may be added for input.

In this way, the offset correction means 30
The offset signal ΔI _MD is compared with preset offset maximum reference value I _OMX and offset minimum reference value I _OMN, and when the offset signal ΔI _MD is within the range of the offset maximum reference value I _OMX and the offset minimum reference value I _OMN. The offset signal ΔI _MD can be stored as the latest offset value, and the motor current detection signal I _MD or the deviation signal ΔI in the normal steering state can be corrected based on this offset signal ΔI _MD .

[0069]

As described above, in the electric power steering apparatus according to the present invention, the value of the motor current detection signal in the state where the motor current is regarded as 0 is set as the offset correction value, and the deviation signal is calculated based on the offset correction value. Since the offset correction means for correction is provided and the actual electric motor current in a state where the electric motor current is regarded as 0 can be corrected to 0, the steering assist force of the electric motor generated by the driver's operation of the left and right steering wheels is balanced and the steering feel is adjusted. The ring can be improved.

Further, the offset correction means of the electric power steering apparatus according to the present invention is provided with the timer means and the offset value storage means, and stores the offset correction value when the state of the target current signal is 0 for a predetermined time. , A stable offset correction value that is not affected by noise or the like can be set and corrected.

Further, in the electric power steering apparatus according to the present invention, the offset correcting means is provided with the offset reference value storing means for storing the offset reference value and the comparing means, and when the offset value is within the range of the offset reference value. Since the offset value is stored, the electric motor current can be corrected within a preset allowable range of the offset value without being affected by an abnormal phenomenon or the like.

Therefore, it is possible to provide the electric power steering apparatus which is capable of generating the steering assist force which is balanced left and right with respect to the steering wheel operation and has a good steering feeling.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 2 is a block diagram of a container portion of the electric power steering device according to the present invention.

FIG. 3 Example of motor current detection using a resistor as a current detection element

FIG. 4 Example of motor current detection using a Hall element as a current detection element

FIG. 5: Another embodiment of motor current detection using a resistor as a current detection element

FIG. 6 is a block diagram of an embodiment of electric motor current detection means.

FIG. 7 is a block diagram of another embodiment of the motor current detection means.

FIG. 8 is a block diagram of a main part of an offset correction unit of the electric power steering device according to the present invention.

FIG. 9 is a block diagram of the essential part of another embodiment of the offset correction means of the electric power steering device according to the present invention.

FIG. 10 is a block diagram of a main part of a conventional electric power steering device.

[11] the vehicle speed signal _{V D (V L, V M} , V H) steering torque signal and a parameter (T _D) - target current signal (I _SD)
Characteristic diagram

FIG. 12: Current detection signal (V _MD ) of motor current detection means
-Characteristics of motor detection current signal ( _IMD )

[Explanation of symbols]

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 sensor, 11 ... Vehicle speed sensor, 12 ... Control means, 13 ... Motor drive means, 14, 19 ... Motor current detection means, 14A ... Differential amplifier, 14B ... Current signal conversion means, 15 ... Battery, 16 ... Target current Signal generating means, 1
7 ... Deviation determining means, 18 ... Drive controlling means, 19A ... A /
D converter, 19B ... Deviation calculation means, 19C, 21, 33
... switching means, 20, 30 ... offset correction means, 22 ...
Timer means, 23 ... Data access means, 24 ... Offset value storage means, 25 ... Correction current signal output means, 31 ...
Offset reference value storage means, 32 ... comparator, HD ... Hall _{elements, I M, I M +,} I M- ... motor current, I _MC ... correction current signal, I _MD ... motor current detection signal, [Delta] I _MD ... offset signal, I _OMN ... Offset minimum reference value, I _OMX ... Offset maximum reference value I _SD , I _SDL ... Target current signal, R _A , R
_B, R _D ... resistors, T, T _D ... steering torque signal, T _K ... timer signal, V, V _D ... vehicle speed _{signal, V DH, V DA, V} DB ... voltage, V _DR (V _D1 -V _D2 ) ... Potential difference, V _M ... Motor voltage,
V _MD ... current detection signal, V _O ... motor control signal.

Claims (3)

[Claims] 1. A steering torque sensor for detecting a steering torque, an electric motor for applying a steering assist force to a steering system,
Electric motor driving means for driving the electric motor, electric motor current detecting means for detecting electric motor current flowing in the electric motor, and target current signal generating means for determining a target current of the electric motor based on a steering torque signal from the steering torque sensor. ,
An electric motor control means including drive control means for controlling the electric motor drive means based on a deviation signal between the target current signal from the target current signal generation means and the electric motor current detection signal from the electric motor current detection means. In the power steering device, the electric motor control unit sets an offset correction value to a value of the electric motor current detection signal in a state where the electric motor current is regarded as 0, and an offset correction unit that corrects the deviation signal based on the offset correction value. An electric power steering device comprising: 2. The offset correction means comprises a timer means and an offset value storage means, and stores the offset correction value when the state where the target current signal is 0 continues for a predetermined time. Item 2. The electric power steering device according to item 1. 3. The offset correction means is provided with an offset reference value storage means for storing an offset reference value and a comparison means, and stores the offset value when the offset value is within the range of the offset reference value. The electric power steering device according to claim 2, wherein