JPH10157646A - Controller for electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a power steering function when torque sensor outputs a saturation output beyond a measurement range by providing convergent controller which inputs an angular speed found by means of an angular speed estimating device and a vehicle speed and decreases an output when a saturation output is detected by means of a torque saturation sensor. SOLUTION: Steering torque T from a torque sensor 10 is inputted to a phase compensation apparatus 31 and a steering wheel returning controller 310, and a vehicle speed V from a vehicle speed sensor 12 is inputted to the steering wheel returning controller 310 and a convergent control unit 351 inside a convergent controller 350. A saturation output of torque T from the torque sensor 10 is detected by means of a torque saturation sensor 360. When the torque saturation sensor 360 detects torque saturation, the torque saturation sensor outputs a saturation torque signal ST and inputs a gain outputted convergent signal AS to an adder-subtractor 321. In this way, vibration due to disturbance is damped, and a power steering function can be secured even if steering torque cannot be detected by means of the torque sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric power steering device which applies a steering assisting force by a motor to a steering system of an automobile or a vehicle, and more particularly to a control device for a case where the measurement range of a torque sensor is saturated. The present invention relates to a control device for an electric power steering device that does not lose a power steering function.

[0002]

2. Description of the Related Art An electric power steering apparatus for energizing a steering apparatus of an automobile or a vehicle with an auxiliary load by the rotational force of a motor uses a transmission mechanism such as a gear or a belt through a speed reducer to transmit the driving force of the motor to a steering shaft or the like. An auxiliary load is applied to the rack shaft. here,
The configuration of a general electric power steering device will be described with reference to FIG. The shaft 2 of the steering handle 1 is connected to a tie rod 6 of a steering wheel via a reduction gear 3, universal joints 4a and 4b, and a pinion rack mechanism 5.
The shaft 2 is provided with a torque sensor 10 for detecting a steering torque of the steering wheel 1. A motor 20 for assisting the steering force of the steering wheel 1 is coupled to the shaft 2 via a clutch 21 and a reduction gear 3. Have been. The control unit 30 that controls the power steering device includes a battery 1
4 through the ignition key 11, the control unit 30 controls the steering torque T detected by the torque sensor 10 and the vehicle speed V detected by the vehicle speed sensor 12.
The steering assist command value I of the assist command is calculated on the basis of
Control the current supplied to the The clutch 21 is ON / OFF controlled by the control unit 30 and is ON (coupled) in a normal operation state. The clutch 21 is turned off (disengaged) when the control unit 30 determines that the power steering device has failed, and when the power of the battery 14 is turned off by the ignition key 11.

The control unit 30 is mainly composed of a CP
FIG. 10 shows general functions executed by a program inside the CPU. For example, the phase compensator 31 does not indicate a phase compensator as independent hardware, but indicates a phase compensation function executed by the CPU. Incidentally, the control unit 30 may not be constituted by the CPU, but each functional element may be constituted by independent hardware.

The general function and operation of the control unit 30 will be described. The steering torque T detected and input by the torque sensor 10 is phase-compensated by a phase compensator 31 to enhance the stability of the steering system. The phase-compensated steering torque TA is input to the steering assist command value calculator 32. The vehicle speed V detected by the vehicle speed sensor 12 is also input to the steering assist command value calculator 32. The steering assist command value calculator 32 determines a steering assist command value I which is a control target value of the current supplied to the motor 20 based on the input steering torque TA and the vehicle speed V. Is provided with a memory 33. The memory 33 stores a steering assist command value I corresponding to the steering torque using the vehicle speed V as a parameter, and is used for calculating the steering assist command value I by the steering assist command value calculator 32. The steering assist command value I is input to a subtractor 30A, and is also input to a feedforward differential compensator 34 for increasing the response speed, and the deviation (I-i) of the subtractor 30A is input to a proportional calculator 35. The proportional output is input to an adder 30B, and an integral calculator 36 for improving the characteristics of the feedback system.
Is input to The outputs of the differential compensator 34 and the integration compensator 36 are also added to the adder 30B, and the current control value E, which is the result of the addition in the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. The motor current value i of the motor 20 is detected by the motor current detection circuit 38, and the motor current value i is input to the subtractor 30A and fed back.

An example of the configuration of the motor drive circuit 37 will be described with reference to FIG. 11. The motor drive circuit 37 uses a field effect transistor (FE) based on the current control value E from the adder 30B.
T) An FET gate drive circuit 371 for driving the gates of FET1 to FET4, an H bridge circuit composed of FET1 to FET4, a boost power supply 372 for driving the high side of FET1 and FET2, and the like. FET1 and FET2 are turned ON / OFF by a PWM (pulse width modulation) signal having a duty ratio D1 determined based on the current control value E.
It is turned off, and the magnitude of the current Ir actually flowing to the motor is controlled. FET3 and FET4 have a duty ratio D
In a small area of 1, the duty ratio D2 defined by a predetermined linear function expression (D2 = a.D1 + b where a and b are constants)
In the region where the duty ratio D1 is large, it is turned ON / OFF according to the rotation direction of the motor determined by the sign of the PWM signal. For example, when the FET 3 is in the conductive state, the current flows through the FET 1, the motor 20, the F
The current flows through the ET3 and the resistor R1, and a current flows in the motor 20 in the positive direction. When the FET 4 is in the conductive state, the current flows through the FET 2, the motor 20, the FET 4, and the resistor R2, and a negative current flows through the motor 20. Therefore, the current control value E from the adder 30B is also a PWM output. The motor current detection circuit 38 detects the magnitude of the positive current based on the voltage drop across the resistor R1, and detects the magnitude of the negative current based on the voltage drop across the resistor R2. The motor current value i detected by the motor current detection circuit 38 is input to the subtractor 30A and fed back.

[0006]

In the above-described conventional electric power steering apparatus, when steering such that the front wheels are skid on a Belgian road, as shown by T0 in FIG. The disturbance torque having a high frequency is input to the electric power steering device from the rack shaft side. In such a state, even if the steering operation is performed and the torque input to the electric power steering apparatus is shifted from the disturbance torque T0 in FIG.
The torque measured by the torque sensor 10 is Td0 in FIG.
From Td1 to Td1, and hardly changes in a saturated state. For this reason, the torque sensor 10 cannot detect the steering torque and does not generate steering assist torque.
There was a problem that the power steering function was lost.

The present invention has been made in view of the above circumstances, and an object of the present invention is to lose the function of power steering when the torque sensor of an electric power steering device has a saturation output beyond the measurement range. An object of the present invention is to provide a control device for an electric power steering device which is not required.

[0008]

According to the present invention, there is provided a torque sensor for detecting a steering torque of a steering wheel, a motor for urging a steering shaft integrally provided with the steering wheel to apply an auxiliary load, and a magnitude of the steering torque. The control object of the present invention relates to a control unit of the electric power steering device, comprising: a control unit that drives the motor in accordance with the control unit, wherein the control unit estimates an angular speed of the motor; A torque saturation sensor that detects that the torque sensor has saturated output, and an angular velocity and a vehicle speed that are obtained by the angular velocity estimator are input to improve the yaw convergence of the vehicle, and the torque saturation sensor detects the saturation output. And a convergence controller that attenuates the output when the power is turned off. Further, detection of the saturation output of the torque saturation sensor
This is performed when the value of the steering torque detected by the torque sensor exceeds a predetermined value and continues for a predetermined time or more, and the torque sensor is alternately repeated a predetermined number of times in the positive and negative directions.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The steering is performed such that the front wheels are skid on a Belgian road, and the steering wheel is held even when the steering torque of the saturation output is measured by the torque sensor as shown at T0 in FIG. When the proportional gain of the motor angular velocity in the convergence control of the convergence controller for improving the convergence of the yaw of the vehicle is increased, T in FIG.
Disturbance torque such as 0 becomes like T2 in FIG. 2, and the disturbance torque can be attenuated. Accordingly, the fact that the steering was performed and the torque changed from T2 to T3 in FIG.
A change from Td2 to Td3 in FIG. 3 can be measured by the torque sensor, and an assist torque can be generated. In the present invention, the state in which a disturbance having a high frequency and a large torque is input from the rack shaft, the state in which the steering torque from the torque sensor exceeds a predetermined value continues for a predetermined time or more, and the state changes in the positive and negative directions of the torque sensor. It is detected by being alternately repeated a predetermined number of times or more. In this case, the detected motor angular velocity is input to the convergence controller, and the steering assist torque is increased by increasing the output gain of the convergence controller based on the output of the torque saturation sensor that detects torque saturation from the output of the torque sensor. Because it generates
Even when the steering torque cannot be detected by the torque sensor, it can function as power steering. The control according to the present invention can be easily performed only by changing the program of the CPU in the control unit.

An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, a control unit as shown in FIG. 1 is employed to maintain the power steering function at all times. FIG. 1 corresponds to FIG. The steering torque T from the torque sensor 10 is input to the phase compensator 31 and the steering wheel return controller 310, and the vehicle speed V from the vehicle speed sensor 12 is sent to the steering wheel return controller 310 and the convergence controller 351 in the convergence controller 350. At the same time, the steering assist command value I is input to the steering assist command value calculator 320, and the output of the steering assist command value I is input to the adder / subtractor 321 as an assist command. The saturation output of the torque T of the torque sensor 10 is detected by a torque saturation sensor 360. The steering assist command value Iref output from the adder / subtractor 321 is input to the subtractor 30A, and the current control value E from the adder 30B and the battery 14
Is input to the inter-terminal voltage estimator 340, and the inter-terminal voltage estimation value Vm from the inter-terminal voltage estimator 340 is input to the angular velocity estimator 331 in the estimator 330. Further, the motor current detection value i from the motor current detection circuit 38 is input to the subtractor 30A and also to the angular velocity estimator 331 in the estimator 330, and the estimated value PR1 estimated by the estimator 330 is used for convergence control. Switch 35 in the vessel 350
2 to the convergence control unit 351 and the estimated value PR
2 is input to the loss torque compensator 312 and the estimated value PR3
Is input to the inertia compensator 313. Since the angular velocity ω estimated by the angular velocity estimator 331 in the estimator 330 is directly output as the estimated value PR1, the estimated value PR1 indicates the motor angular velocity ω. Further, since the angular velocity ω is input to the encoder 332 and its sign is determined, the estimated value PR2 indicates the motor rotation direction, and the motor angular velocity ω is converted into the approximate differentiator 333.
The estimated value PR3 differentiated by means the motor angular acceleration. The handle return signal HR output from the handle return controller 310 is added to the adder / subtractor 321 and the convergence signal AS calculated and output from the convergence controller 351 using the estimated value PR1 and the vehicle speed V is output to the adder / subtractor 321. The subtraction input, the loss torque compensation signal LT from the loss torque compensator 312 and the inertia compensation signal I from the inertia compensator 313
N is added and input to the adder / subtractor 321.

The convergence controller 350 is a convergence controller 3
51, a changeover switch 352 and a gain control section 353. The changeover switch 352 is normally an a contact,
The convergence control unit 351 calculates and outputs the convergence signal AS (assuming that the gain constant that changes with the vehicle speed V is KV, AS = KV · PR1) with the estimated value PR1 and the vehicle speed V. The saturation torque signal ST from the torque saturation sensor 360 is input to the changeover switch 352, and when the saturation torque signal ST is input, the changeover switch 352 is switched from the contact a to the contact b, and the estimated value PR1 is changed to the gain control unit 353. Is multiplied by a predetermined gain K1, and the convergence signal AS (= K1 · PR
Output as 1).

A steering assist command value calculator 320 calculates and outputs a steering assist command value I as an assist command from the steering torque T and the vehicle speed V based on an assist characteristic defined in advance by a polynomial as shown in FIG. , Handle return controller 310
In order to improve the steering wheel return characteristics at middle and low speeds, the steering wheel return signal HR is output when the steering wheel is in the steering wheel return state, and the steering wheel is assisted in the returning direction. The convergence controller 350 outputs a convergence signal AS from the estimated value PR1 and the vehicle speed V in order to improve the convergence of the yaw of the vehicle, and applies a brake to the operation of turning the steering wheel. Therefore, the handle return controller 31
The vehicle speed V from the vehicle speed sensor 12 is input to the zero and the convergence controller 350. When the torque sensor 10 is saturated, K1 · PR1 multiplied by the predetermined gain K1 is output as the convergence signal AS as described above.

The loss torque compensator 312 outputs a loss torque compensation signal LT to cancel the influence of the loss torque of the motor 20, and outputs a loss torque compensation signal LT corresponding to the loss torque of the motor 20, ie, the rotation direction of the motor 20. Perform assist. The inertia compensator 313 assists the amount of force generated by the inertia of the motor 20 and outputs an inertia compensation signal IN so as to prevent a feeling of inertia or a deterioration in control response. Therefore,
The estimated value PR2 input to the loss torque compensator 312 indicates the motor rotation direction, and the estimated value PR3 input to the inertia compensator 313 indicates the motor angular acceleration.

By the way, as disclosed in, for example, Japanese Patent Application Laid-Open No. 8-67262, the motor angular velocity ω can be obtained from the estimated value of the motor back electromotive force. That is, the estimated value K _T · ω of the motor back electromotive force is obtained from the following equation 1 with the resistance between the motor terminals as R from the motor terminal voltage Vm and the motor current detection value i. However, the frequency component of the angular velocity ω of the motor is sufficiently lower than the electric response characteristics of the motor.

[0016]

_KT · ω = Vm−R · i _KT : Back electromotive force constant The angular velocity ω of the motor 20 can be obtained from the above equation (1). When there is a difference between the actual electric characteristics of the motor and the electric characteristics defined by the mathematical model, the estimated value ω of the motor angular velocity causes an estimation error e in the direction having the offset. In an actual motor, the motor inductance L
A characteristic when the inductance L is ignored is represented by a mathematical model, and is represented by Vm = R · i. With this offset error e, when a correction signal is generated using the estimated value, for example, the motor 20
Is incorrectly determined to be rotating, and an erroneous correction signal is output. Actually, since the electrical characteristics of the motor 20 are affected by variations during manufacturing and temperature fluctuations, the occurrence of the offset error e is inevitable. In order to solve such a problem, it is conceivable to set a fixed dead zone DZ to the estimated value K _T · ω of the motor back electromotive force as shown in FIG. There is a problem that the electromotive force cannot be estimated.

As described above, the estimation error e of the motor angular velocity ω
The factor is the difference between the electrical characteristics K _T · ω'that are defined in the actual motor electrical characteristics K _T · omega and mathematical models. That is, the following equation 2 holds for the resistance R between the motor terminals.

[0018]

[Mathematical formula-see original document] R = Rm + [Delta] Rt + [Delta] Rp Rm: resistance value of the model, [Delta] Rt: resistance value variation due to temperature, [Delta] Rp: resistance value variation due to manufacturing variation. Number 3
Substituting

Vm = (Rm + △ Rt + △ Rp) ・ i + K _T・ ω. On the other hand, in a mathematical model that does not take into account variations during manufacturing and temperature changes, the following formula 4 is obtained.

[0019]

Vm = Rm · i + K _T · ω ′ Accordingly, the estimation error e of the back electromotive force is obtained from the above equations 3 and 4.

Equation 5] _{e = K T · ω'-K} T · ω = Vm-Rm · i- {Vm- (Rm + △ Rt + △ Rp) · i} = (△ Rt + △ Rp) · i , and the current i A proportional offset error e is generated. Accordingly, for example, by performing a dead zone process proportional to the current i in a relationship as shown in FIG. 6, when the current i is small, the offset value is also small, and accordingly, the dead zone width D
Since Z = K · i also decreases, the motor back electromotive force can be estimated even in a region where the motor angular velocity ω is low.

The current control value E, which is a PWM output,
When estimating the angular velocity ω from the motor current value i, the dead zone width DZ is assumed to be proportional to the motor current value i. That is, DZ = K · i is established with K as a constant. In this case, a value K equal to or larger than the maximum value of the variation of the motor terminal voltage Vm in Equation 5 is set as a proportional coefficient. Therefore, the estimated angular velocity does not always have the offset error e. Then, even in a region where the actual motor angular velocity is small, the angular velocity estimator 3
In step 31, the motor angular velocity ω can be estimated. Further, when the angular velocity ω of the motor does not match the direction of the current i,
That is, when the steering wheel is returned, no offset error occurs as in the following equation (7). Therefore, it is desirable not to perform the dead zone correction when the steering wheel return state is detected.

[0021]

KT · ω ′ = KT · ω− (△ Rt + △ Rp) · | i | And if | i | ≒ 0,

KT · ω ′ = KT · ω

FIG. 7 shows an operation example in which the estimator 330 detects the angular velocity ω, the rotation direction, and the stop state of the motor 20. First, the motor current detection circuit 38 detects the motor current value i (step S1). The terminal voltage estimator 340 calculates the terminal voltage Vm according to Vm = Vb · E based on the voltage Vb of the battery 14 and the current control value E (step S2). Then, the angular velocity estimator 331 obtains the angular velocity ω, and executes the equation (1) (step S3). Based on the angular velocity ω and the motor current value i, it is determined whether or not the steering wheel is returned (step S4). If it is in the state, the process is terminated. If it is not in the steering wheel return state, it is determined whether or not the absolute value of the motor back electromotive force KT · ω is equal to or more than the dead zone width DZ = K · i.

| KT · ω | − | K · i | ≧ 0 is calculated (step S10). If the motor back EMF is equal to or greater than the dead zone width,

Ω = sign (KT · ω) · (| KT · ω | −
| K · i |) is executed (step S12), and if not, the estimated angular velocity ω = 0 (step S11).
In the above equation (9), when the counter electromotive force _{K T-omega} is positive is sign _{(K T} · _ω) +1, - the counter electromotive force _{K T}
When ω is negative, sign (K _T · ω) is −1.
Thereafter, it is determined whether or not the motor angular velocity ω is 0 (step S13), and if it is 0, the motor stop state is detected (step S17). If ω = 0, it is determined whether or not ω is positive (step S14). For example, if ω is positive, right rotation is determined (step S16). If negative, left rotation is determined (step S15). .

In the present embodiment, the angular velocity ω of the motor 20 is detected by the above-described angular velocity estimator 331, but it may be detected by providing a sensor. The estimated value of the angular velocity of the motor causes an offset type estimation error e as described above,
There is a disadvantage that the rotation of the motor is detected in spite of the fact that the steering is maintained, but a dead zone DZ = K · i proportional to the current i is provided, and after the offset correction is performed, the stop state and the rotation direction of the motor are changed. Can be accurately detected.

The angular velocity ω (PR1) obtained by the angular velocity estimator 331 as described above is used for the convergence controller 350.
The convergence signal A which is input to the convergence control section 351 via the changeover switch 352 in the
S or gain control unit 35 when torque sensor 10 is saturated
The convergence signal AS obtained in 3 is input to the adder / subtractor 321. The gain control unit 353 includes the torque saturation sensor 3
Switch 3 according to the saturation torque signal ST from
The contact value is switched at 52, and the estimated value PR1 input is multiplied by a predetermined gain to output the convergence signal AS. The torque saturation sensor 360, as shown in FIG. The state in which the absolute value of the steering torque T exceeds the predetermined value A or −A continues for a predetermined time B or more, and such a state is alternately repeated in the positive and negative directions of the torque sensor 10 a predetermined number of times or more. It detects the torque saturation, that is, the output of the steering torque T beyond the measurement range of the torque sensor 10. When the torque saturation sensor 360 detects torque saturation as described above, it outputs a saturation torque signal ST, switches the contact point of the changeover switch 352 from a to b, and inputs the gain-output astringent signal AS to the adder / subtractor 321. I do.

In a running state such as on a Belgian road, a disturbance occurs. When the disturbance is detected, a signal proportional to the motor angular velocity is subtracted from the current control value when a disturbance input state is detected. By increasing the degree, the torque that attenuates the vibration due to the disturbance is generated from the motor 20 and the steering torque can be detected, and the steering assist torque can be generated. Therefore, even if the steering torque T can be detected by the torque sensor 10, Even without,
Power steering function is not lost.

[0026]

According to the present invention, when a disturbance generated when skid on a Belgian road is input from the rack shaft, the conventional electric power steering apparatus cannot detect the steering torque, and there is a problem that the steering assist torque is not generated. However, according to the control device of the electric power steering device of the present invention, even in the case where the above-described disturbance occurs, the state is detected, and if detected, a signal proportional to the motor angular velocity is subtracted from the current control value. By increasing the degree of proportionality, a torque for attenuating vibration due to disturbance is generated from the motor 20, and the steering torque can be detected. Thus, even when the steering torque cannot be detected by the torque sensor, the steering assist torque can be generated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a control unit according to the present invention.

FIG. 2 is a diagram for explaining the operation of the torque sensor.

FIG. 3 is a diagram for explaining the operation of the torque sensor.

FIG. 4 is a characteristic diagram showing an example of a relationship between a steering torque and a steering assist command value using a vehicle speed as a parameter.

FIG. 5 is a diagram showing a relationship between motor back electromotive force and motor angular velocity.

FIG. 6 is a diagram illustrating an example of a relationship between a motor current value and a dead zone width.

FIG. 7 is a flowchart illustrating an operation example of detecting a stopped state of a motor.

FIG. 8 is a diagram for explaining saturation detection of the torque sensor according to the present invention.

FIG. 9 is a block diagram showing an example of an electric power steering device.

FIG. 10 is a block diagram showing a general internal configuration of a control unit.

FIG. 11 is a connection diagram illustrating an example of a motor drive circuit.

FIG. 12 is a diagram showing a measurement range of a torque sensor and an actual torque value.

FIG. 13 is a diagram showing an output of a torque sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steering handle 5 pinion rack mechanism 10 torque sensor 12 vehicle speed sensor 20 motor 30 control unit 31 phase compensator 37 motor drive circuit 38 motor current detection circuit 330 estimator 340 terminal voltage estimator 350 convergence controller 360 torque saturation sensor

Claims (2)

[Claims] 1. A torque sensor for detecting a steering torque of a steering wheel, a motor for urging an auxiliary load on a steering shaft provided integrally with the steering wheel, and driving the motor in accordance with the magnitude of the steering torque. A control unit for controlling the electric power steering device, the control unit including: an angular velocity estimator for estimating an angular velocity of the motor; a torque saturation sensor for detecting that the torque sensor has output saturation; An angular convergence controller for inputting the angular velocity and the vehicle speed obtained by the estimator to improve the yaw convergence of the vehicle and attenuating the output when the torque saturation sensor detects a saturation output. A control device for an electric power steering device. 2. The detection of the saturation output of the torque saturation sensor continues for a predetermined period of time after the value of the steering torque detected by the torque sensor exceeds a predetermined value, and alternately detects the saturation output of the torque sensor in the positive and negative directions. The control device for an electric power steering device according to claim 1, wherein the control is performed by repeating the number of times or more.