JPH0450075A - Electric power steering device - Google Patents

Abstract

PURPOSE:To obtain the assist characteristic with no action incompatibility by calculating the compatibility level of the output current value for each control rule based on multiple quantities of state affecting the steering property and the control rules of the output current value to an electric motor, and determining the final output current value. CONSTITUTION:When a vehicle is driven, detected signals (quantities of state) outputted from the first steering angle sensor 12, the second steering angle sensor 13 for backup, a vehicle speed sensor 19, a crank angle sensor 20 and a reverse switch 21 are inputted to a controller 18 to read out the corresponding control rule from a ROM 34 storing multiple control rules indicating the control tendency of the output current value to an electric motor 14 set for the magnitude of the quantity of state in advance. The compatibility level of the output current value to the quantity of state in the rule is calculated based on the detected quantities of state and the read-out control rule to determine the final output current value. The excitation quantity of the electric motor 14 is controlled to obtain the determined final output current value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power steering device for a vehicle, and more particularly to a power steering device that corrects an assist force applied to a steering wheel operation.

(Conventional technology) In addition to hydraulic type power steering systems for vehicles,
An electric power steering device is known in which an electric motor generates an assist force. For example, according to Japanese Patent Application Laid-open No. 132465/1982, the operation of the electric motor that generates an assist force when operating a steering wheel is controlled by a steering wheel. By controlling according to the steering angular velocity detected by the angle sensor, a predetermined assist force is generated in accordance with the steering state.

(Problem to be Solved by the Invention) Incidentally, the electric power steering device as described above is designed to generate a predetermined assist force depending on the driving condition, but the operating force of the steering wheel depends on the driving condition. Or it will depend on the road surface conditions, etc. For example, when the speed of the vehicle is low, a large amount of resistance acts on the steering wheel due to road surface resistance, so a large assist force is required to provide a light steering feel. On the other hand, when the vehicle speed is high, even the slightest steering wheel operation can significantly change the vehicle's direction of travel, and even in such cases, if the same level of assist force as when driving at low speeds is applied, the steering wheel may turn too much in the opposite direction. It doesn't look like a nice town.

To solve this problem, we can detect various state variables that affect steering performance, such as vehicle speed and steering angle, and also detect a large number of target energization amounts that are set in advance in response to various driving conditions. One idea is to select a current value as the output corresponding to the state quantity and perform feedback control on the amount of current applied to the electric motor so as to achieve this output current value.

However, conventionally, in this type of control method, the control target value is determined based on so-called binary logic, so the control target value must be expressed in the form of an approximate expression. If a rough approximation formula is used, errors will accumulate during the calculation process, making it impossible to obtain good control accuracy. On the other hand, if the accuracy of the approximation formula is increased in order to improve control accuracy, the amount of data to be stored becomes enormous and a large capacity memory is required. A computer is also required, which increases the cost of the vJ# controller and also makes the controller larger. Therefore, in the past, the reality is that approximate expressions for control are set within a reasonable range in consideration of accuracy, cost, etc.

Moreover, in the conventional M4 system, hunting is likely to occur due to a delay in response after steering wheel operation, etc., and there is room for improvement in terms of operability, such as making the driver feel uncomfortable.

In view of the above problems, this invention solves the so-called fuzzy
The purpose of this invention is to provide an electric power steering device at a low cost that provides assist characteristics that do not make the user feel uncomfortable when operating the vehicle.

(Means for Solving the Problems) That is, the electric power steering device according to the present invention has a configuration including an electric motor that applies assist force to a steering system, and a plurality of components that affect steering performance such as steering angle and vehicle speed. state quantity detection means for detecting state quantities, respectively; and control rule storage means for storing a plurality of control rules indicating a control tendency of the output current value to the electric motor, which is set in advance for the magnitude of the state quantity. and, based on the state quantity detected by the state quantity detection means and the control rule stored in the control rule storage means, for each control rule, calculate the degree of conformance of the output current value to the state quantity in that rule. a determining means that determines a final output current value based on the calculated conformity degree for each control rule; The present invention is characterized in that it has an energization amount control means.

(Function) According to the above configuration, a plurality of state quantities that affect steering performance, such as vehicle speed and steering angle, detected by the state quantity detection means and the above-mentioned electric motor control set in advance with respect to these state quantities are detected by the state quantity detection means. Based on the control rule for the output current value to the motor, the calculation means calculates, for each control rule, the degree of conformity of the output current value to the state quantity in that rule, and
The determining means determines a final output current value based on the calculated conformity degree for each control rule. Then, the energization amount control means controls the amount of energization to the electric motor so that the determined final output current value is achieved. This makes it possible to smoothly operate the steering wheel regardless of the driving state of the vehicle, and provides assist characteristics that do not make the operation feel strange.

In particular, the above-mentioned control rule storage means only needs to store simple control trends of output current values for state quantities that affect steering performance, such as vehicle speed and steering angle, and therefore does not require a large storage capacity. Resource conservation will be achieved. However, although the final output current value is calculated based on simple control rules, it does not require large computational power.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic configuration diagram of a power steering device 1 according to the present invention, and the power steering device 1 includes a first steering shaft 3 having a steering wheel 2 attached to one end, and a first steering shaft 3.
a second steering shaft 5 connected to a lower end of the second steering shaft 5 via a universal joint 4; a third steering shaft 7 connected to a lower end of the second steering shaft 5 via a universal joint 6; an output shaft 8 connected to the shaft 7 via a torsion bar (not shown);
A steering rod 11 is formed with a pinion 9 formed at the lower end of the output shaft 8 and a rack 10 that meshes with the pinion 9.
Left and right front wheels (not shown) are connected to both ends of the steering rod 11 via tie rods and knuckle arms.

The third steering shaft 7 has a conventionally known configuration for electrically detecting the rotation angle of the steering shaft 7, in other words, the steering angle of the left and right front wheels using a sliding resistance transducer. A pair of first and second steering angle sensors 12 and 13 are provided. The second steering angle sensor 13 is used for bank-up when the first steering angle sensor 12 is out of order.

Further, a DC motor 14 and an electromagnetic clutch 15 are provided that apply an assist force to the output shaft 8 when the steering wheel 2 is operated. and a steering column (not shown) that rotatably supports the output shaft 8. A disk member 16 is also integrally attached to the output shaft 8, and the upper surface of the disk member 16 A gear 17 meshing with a gear (not shown) formed on the outer peripheral edge is rotationally driven by the DC motor 14 via an electromagnetic clutch 15. Therefore, electromagnetic clutch 1
By rotating the DC motor 14 in forward and reverse directions with the output shaft 8 connected to the
6 is rotated, thereby making it possible to apply an assisting force to rotate the output shaft 8 in the rightward turning direction or the leftward turning direction.

Next, the control system of the power steering device 1 will be explained.

As shown in FIG. 2, a controller 18 with a built-in microcomputer is provided, and the first and second steering angle sensors 12 serve as sensors and switches for inputting various signals to the controller 18. .13, at least a vehicle speed sensor 19, a crank angle sensor 20, and a reverse switch 21 are provided.

The vehicle speed sensor 19 is, for example, a sensor that electrically detects the rotational speed of the automatic transmission output shaft (that is, the rotational speed of the propeller shaft), but may also be a sensor that detects the rotational speed of the front wheels or rear wheels.

Further, the crank angle sensor 20 is provided in conjunction with the distributor or crankshaft of the engine, and electrically detects the rotational speed of the crankshaft.

Furthermore, the reverse switch 21 is a switch that is provided in the automatic transmission and is turned on when the gear position is changed to "reverse".

The reverse signal from the reverse switch 21 is input to the waveform shaping circuit 23 via the digital buffer 22, where it is converted into a pulse signal and input to the CPU 24. Further, the generated voltage signal from the output side terminal 25 of the alternator is inputted to the waveform shaping circuit 26 via the digital buffer 22, converted into a pulse signal by the waveform shaping circuit 26, and inputted to the CPU 24. Furthermore, the signal from the vehicle speed sensor 19 and the signal from the crank angle sensor 20 are input to the CPU 24 via a digital buffer 22.

On the other hand, the signals from the first and second steering angle sensors 12 and 13 are sent to the A/D converter 2 via an analog buffer 27.
8, is converted into a digital signal by this A/D converter 28, and is input to the CPU 24.

Furthermore, the CPU 24 is connected to a ROM 30 and a RAM 31 via a bus 29. A control program for controlling the DC motor 14 and the electromagnetic clutch 15 is stored in the ROM 30.

Further, the ROM 30 stores a plurality of control rules indicating control tendencies of the output current value for the DC motor 14, which are preset according to vehicle speed, steering angle, and the like.

Here, to explain the control rules for the output [flow value] in this embodiment, for example, the following four control rules are used.

First control rule: If the steering angle θ is large, the output current value is increased.

This is because the larger the steering angle θ is, the heavier the steering wheel 2 tends to be, so assisting force is applied to the steering wheel operation.

Second control rule: If the vehicle speed (■) is large and the steering angle speed (S) is large, the output current value (■) is made small.

This is to provide resistance to steering wheel operation, since the larger the vehicle speed (2) and the larger the steering angle speed (2), the larger the change in the steering angle .theta. with respect to the steering wheel operating force.

3rd f Control Rule 2 If the vehicle speed V is large and the steering angle speed is small, the output current value I is made slightly smaller.

This is to compensate for the fact that even if the vehicle speed ■ is high but the steering angular speed is small, if the output current value ■ is made smaller according to the third control rule above, the steering force may become too heavy. .

Fourth control rule: If the steering angular velocity change rate υ is large, the output current value ■ is also increased.

This is to increase the assist force since the larger the steering angular velocity change rate, the greater the steering force required.

In this embodiment, each of the above M rules is represented using the following simple form.

First, for the first control rule with the steering angle θ as a parameter, the membership rf expressing the steering angle θ, which is the antecedent part, is
As the Ij number, as shown by the solid line in Fig. 3 (a), select a triangular functional formula in which the fitted value increases as the steering angle θ increases, and also express the output current value, which is the consequent part. As the membership function, a trapezoidal function expression is adopted in which the adaptive value increases in ten directions starting from the zero point of the output current value, as shown by the broken line in FIG. in this case,
When the steering angle θ shows a value of 360°, the fitness value of the membership function in FIG. 3(a) becomes 1, and correspondingly, the entire range of the number of memberships in FIG. This is a membership function that indicates the inference result of the output current value according to the rules.

Next, regarding the second control rule that uses vehicle speed V and steering angle speed as parameters, as a membership function expressing vehicle speed V, which is one antecedent, vehicle speed is We selected a triangular function equation in which the fitted value increases as V increases, and as a membership function that expresses the other antecedent, the rudder angular velocity, as shown in Figure (b). A triangular function equation is selected in which the fit value increases as the angular velocity increases. The membership rIIj number expressing the output current value ■, which is the rear part #, is as shown by the broken line in FIG.
A trapezoidal functional expression is adopted in which the adaptive value increases in one direction starting from the zero point of the output current value ■.

On the other hand, regarding the third control rule that uses vehicle speed V and steering angle speed as parameters like the second control rule, as a membership function expressing vehicle speed ■ which is one antecedent part,
As shown by the solid line in FIG. 5(a), a triangular function equation is selected in which the fitted value increases as the vehicle speed increases, while a membership function that expresses the other antecedent, the steering angular velocity 6, is selected. As shown in FIG. 3B, a triangular function equation is selected in which the fitted value decreases as the steering angular velocity distortion increases. The membership function expressing the output current value I, which is the consequent part, is shown in the figure (
As shown by the broken line in c), a trapezoidal function formula is adopted in which the adapted value takes the maximum value at the zero point of the output current value, and the output current value I decreases in one direction as the adapted value decreases. There is.

Regarding the fourth control rule that uses the steering angular speed change rate V as a parameter, as shown by the solid line in FIG. 6(a), the steering A triangular function equation is selected in which the fitted value increases as the angular velocity change rate V increases, and as a membership function of the output current value I, which is the consequent, as shown by the broken line in FIG. A trapezoidal equation is used in which the adaptive value increases in the child direction starting from the zero point of the output current value I.

On the other hand, the RAM 31 has a small amount of memory (registers,
flag memory, soft counter memory, etc.).

Further, the battery 32 as a power source is connected to a constant voltage circuit 34 via an ignition switch 33, and a predetermined operating voltage (for example, 5V) is supplied from the constant voltage circuit 34 to the CPU 24. The output voltage of the ten output terminals of the battery 32 for detecting is A
/D converter 28 converts it into a digital signal and converts it into a CP
It is designed to be input to U24.

In addition, in order to control the direction and magnitude of the DC current supplied to the DC motor 14, a D/A converter 35 receives a digital motor drive current control signal from the CPU 24 and converts it into a D/A; In response to an analog control signal supplied from the D/A converter 35 and an analog current detection signal supplied from the current detector 36, the motor drive current is adjusted so that the current has the direction and magnitude specified by the control signal. A current control circuit 37 that performs feedback control using a PWM method.
A driver 38 receives and amplifies an analog command signal supplied from the current control circuit 37, and is connected to the output terminal of the battery 32 via a power supply line 39, and is also connected to the DC motor 14. , and a power circuit 3 that supplies the DC motor 14 with a motor drive current according to the amplified command signal supplied from the driver 38.
9 is provided.

Note that the current detector 36 is interposed in the ground line from the power circuit 39 to the ground, detects the direction and magnitude of the motor drive current, and sends the analog detection signal to the current control circuit 37.
and the A/D converter 28.

Furthermore, in order to control the 0N10FF and magnitude of the excitation current supplied to the electromagnetic clutch 15 incorporated in the DC motor 14, a control signal is received from the CPU 24, and the constant voltage circuit 34 is connected via the power supply line 40. A current control circuit 41 is connected to the input line and connected to the input terminal of the solenoid 15a of the electromagnetic clutch 15, receives control signals from the CPU 24, and is connected to the output terminal of the solenoid 15a to respond to the control signal. The drive circuit 42 turns the excitation current ON or OFF, and the excitation current of the solenoid 15a is monitored and the monitor signal is sent to the CPU.
24 is provided.

Note that when the constant voltage circuit 34 becomes unable to output a predetermined operating voltage due to a drop in the voltage of the battery 32, etc.
Since the operation of the CPU 24 is no longer guaranteed, in this case, the constant voltage circuit 34 outputs the current control circuit 41 heliset signal RST, the excitation current is cut off, and the electromagnetic clutch 15 is turned off.

Next, the operation of this embodiment will be explained.

That is, the CPU 24 calculates the steering angle θ, the steering angle speed θ, and the steering angle speed change rate δ based on the steering angle signal from the first steering angle sensor 12, and also calculates the steering angle speed θ and the steering angle speed change rate δ.
The vehicle speed V is calculated based on the vehicle speed signal from.

Next, by comparing these steering angle θ, steering angular speed θ, steering angular speed change rate δ, and vehicle speed ■ with the first to fourth control rules stored in the ROM 30, the output current for each control rule is determined. Calculate the membership function of each value ■.

In other words, regarding the first control rule, when the steering angle θ shows the value θ1 as shown in FIG.
24, as shown by the hatched area in FIG. 3(b), is the part cut off at the above adaptive value (0, 6) of the output current value I corresponding to the actual steering angle θ1 in this first control rule. Calculated as a membership function.

Regarding the second control rule, when the vehicle speed V shows the value of Vl as shown in FIG. As shown in (b), when the steering angular speed O shows a value of 61, a value of 0.34 is similarly determined as the adaptive value of the steering angular speed O. Then, the CPU 24 operates as shown in FIG.
), the compatible value of vehicle speed V (0,6)
The smaller value of the adaptive value (0, 34) of the steering angular velocity and the steering angle speed, that is, the part cut off by the adaptive value (0, 34) of the steering angular velocity, is calculated as the actual vehicle speed v1 and It is calculated as a membership function of the output current value 1 corresponding to the steering angular velocity Yu1.

Regarding the 3rd M11M rule, since the vehicle speed V indicates the value of Vl as in the second control rule, as shown in FIG. 5(a), a value of 0.6 is determined as the compatible value of the vehicle speed V. . On the other hand, regarding 01 indicating the value of the steering angular velocity υ in this case, a value of 0.68 is determined as the compatible value of the steering angular velocity O, as shown in FIG. therefore,
As shown by the shaded area in FIG.
8>, that is, the adaptive value of vehicle speed V (0, 6> Calculated as a membership function.

Regarding the fourth control rule, when the steering angular speed change rate δ shows the value of υl as shown in FIG. Therefore, the CPU 24 calculates the actual steering angular velocity change rate i in this fourth control rule by converting the portion cut off by the adapted value (0, 6) as shown by the hatched area in FIG. 6(b).
It is calculated as a membership function of the output current value ■ corresponding to 91.

Then, as shown by the shaded area in FIG. 7, the CPU 24 converts the sum of the membership functions indicating the degree of conformity of the output current value I in the first to fourth control rules to the final member of the output current value ■. ship function, and the value of the output current value I corresponding to the center of gravity position P1 of the final membership function is determined as the final output current value i.

Then, the amount of current applied to the DC motor 14 is controlled so that the final output current value i is achieved.

This makes it possible to smoothly operate the steering wheel regardless of the driving state of the vehicle, and provides assist characteristics that do not make the operation feel strange.

(Effects of the Invention) As described above, according to the electric power steering according to the present invention, state quantities that affect steering performance, such as vehicle speed and steering angle, and electric motors that are set in advance for these state quantities are controlled. Based on the control rule for the output current value of The final output current value is determined, and the amount of current applied to the electric motor is controlled so that the final output current value is determined, so that smooth steering operation can be performed regardless of the vehicle's running condition. This means that assist characteristics that do not cause discomfort during operation can be obtained.

In particular, it is only necessary to memorize a control rule that indicates a simple control tendency of the output current value for state variables that affect steering performance such as vehicle speed and steering angle. Therefore, it is possible to save resources without requiring a large storage capacity. In addition, since the final output current value is calculated based on a simple control rule, a large calculation capacity is not required, and the controller of this type of electric power steering device can be configured compactly.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic configuration diagram of a power steering device for a vehicle according to this embodiment, FIG. 2 is an overall system diagram of the control system of the device, and FIG. Each figure is a conceptual diagram showing the calculation method in this embodiment. DESCRIPTION OF SYMBOLS 1... Power steering device, 12... First steering angle sensor, 13... Second steering angle sensor, 14... DC motor (electric motor), 19... Vehicle speed sensor, 24...
・CPU (calculation means, determination means, energization amount control means),
30...ROM (control rule storage means). to) Shukaku e Shooting monument 6 The second day da (t) 1 Denmai 儂

Claims (1)

[Claims] (1) An electric power steering device equipped with an electric motor that applies assist force to the steering system, and a state quantity detection means that detects each of a plurality of state quantities that affect steering performance such as steering angle and vehicle speed; a control rule storage means storing a plurality of control rules indicating a control tendency of the output current value to the electric motor, which is set in advance for the magnitude of the state quantity; and a state quantity detected by the state quantity detection means. and a calculation means for calculating, for each control rule, the degree of conformity of the output current value to the state quantity in the rule, based on the control rule stored in the control rule storage means; An electric motor characterized by having a determining means for determining a final output current value based on the degree of conformity, and an energization amount control means for controlling the amount of energization to the electric motor so that the determined final output current value is achieved. Power steering device.