Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle subsystem or accessory control
Reexamination Certificate
2002-08-26
2004-05-18
Nguyen, Tan Q. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle subsystem or accessory control
C701S042000, C180S446000
Reexamination Certificate
active
06738699
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to a steering system for a vehicle and more particularly to a vehicle steer-by-wire control system using a model-matching strategy.
2. Discussion of Related Art
In a steer-by-wire control system, the traditional steering column, steering shaft, and steering gear are replaced by an electronically controlled actuation system. The actuation system receives a steering command from a controller and accordingly turns the front road wheels using an electric motor. The vehicle driver provides the steering command through a steering wheel control system using a steering wheel or a joystick. As part of a steer-by-wire control system, a steering wheel control system with a force feedback motor actuator provides the direction reference signal for the road wheel actuation system and the familiar steering feel experienced in the conventional steering systems with a mechanical connection. Such a steer-by wire control system can improve a vehicle's handling performance and stability by providing new features such as adjustable driver steering feel, variable steering effort, variable steering ratio, and active steering wheel return.
FIG. 1
schematically shows a typical steer-by-wire control system
100
. As shown in
FIG. 1
, the steer-by-wire control system
100
includes a steering wheel unit
102
, a road-wheel actuation unit
104
and a controller
106
. The steering wheel unit
102
includes a steering wheel
108
that is actuated by the driver, a steering wheel angle sensor
110
, a steering wheel actuator
112
with electric motor, a motor amplifier
114
and a steering column and connecting shaft
116
. The road-wheel actuation unit
104
includes one or more road wheels
118
, a road wheel actuator
120
with electric motor, a motor amplifier
122
and a road wheel angle sensor
124
. Typically, there are two road wheels
118
, one or two road wheel actuators
120
or one or two road wheel angle sensors
124
.
The controller
106
controls the steering wheel unit
102
and the road-wheel actuation unit
104
via control algorithms that are implemented in the controller
106
. In this system, the required steering functions are realized by using various control system design techniques. In current steer-by-wire control systems, driver's steering feel is realized by controlling the reaction torque of a DC electric motor actuator
112
attached to the steering wheel
108
. Typically, this reaction torque is a function of the steering wheel angle, vehicle speed, and road wheel torque (wheel's self-aligning moment). It is a challenge for a control system designer to realize the required steering feel by controlling the reaction torque. In addition, in current steer-by-wire control systems, the steering feel and all other steering functions, such as steering wheel returnability, are coupled together. In other words, the controller parameters that affect the steering feel also influence the steering wheel returnability. This coupling between various controlled variables makes the design of a control system and tuning of the controller parameters very difficult and challenging.
BRIEF SUMMARY OF THE INVENTION
A first aspect of the present invention regards a steer-by-wire control system that includes a road wheel actuation control system controlling road wheel angles to track a road wheel reference angle and a steering wheel control system producing a steering wheel angle to the road wheel actuation control system, steering feel for the vehicle driver and active steering wheel return. The steering wheel control system further including a steering wheel model matching controller that receives an input signal from the steering wheel control system and an input signal from the road wheel control system and generates a control output signal based on a model-matching control law, wherein the control output signal controls a reaction torque of the steering wheel control system to produce the steering feel for the driver and the return rate of a steering wheel or a joystick.
In a variation of the first aspect of the invention, the model matching controller has two degrees of freedom and receives a steering wheel angle signal and a road wheel torque signal.
A second aspect of the present invention regards a method of designing a steering wheel model matching controller using a model-matching control methodology. The design of the steering wheel model matching controller requires a reference steering dynamic model which provides a relationship between a steering wheel torque and a steering wheel angle. This reference steering model is representative of a relationship between a steering wheel reaction torque and a steering wheel angle which is applied as a typical evaluation for the steering feel. On the other hand, the steering wheel control system with the steering wheel model matching controller is designed as a closed-loop control system with the steering wheel angle as output and the steering wheel torque as input. With same input and output variables, the steering wheel control system matches the reference steering dynamic model using the different minimization criterions in the model-matching control design such that the steering wheel model matching controller is obtained by minimizing the error between the reference steering model and the steering wheel control system.
In a variation of the second aspect of the invention, the model matching controller with two degrees of freedom is determined using H
∞
norm-based minimization criterion
Each aspect of the present invention provides the advantage of improving a driver's steering feel, and the active steering wheel returnability.
Each aspect of the present invention provides the advantage of improving stability of a closed loop control system.
Each aspect of the present invention provides the advantage of improving the robustness of a steer-by-wire control system to disturbances and system parameter variations.
Each aspect of the present invention provides the advantage of adjusting parameters of a two-degree-of-freedom steering wheel model matching controller independently for improving the steering feel and steering wheel returnability.
Each aspect of the present invention provides the advantage of controlling the feel and rate of return of a steering wheel or joystick independently of one another.
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Pending patent application Assigned to Visteon Global Technologies, Inc.: Ser. No.: 10/037,059, Filing Date: Dec. 31, 2001, Inventor: Yao et al.
Pending patent application Assigned to Visteon Global Technologies, Inc.: Ser. No.: 10/037,060, Filing
Ashrafi Behrouz
Yao Yixin
Nguyen Tan Q.
Visteon Global Technologies Inc.
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