Fluid handling – Processes
Reexamination Certificate
2000-05-13
2001-09-11
Lee, Kevin (Department: 3753)
Fluid handling
Processes
C251S129040
Reexamination Certificate
active
06286532
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a control system and a method for controlling a valve. In particular, the invention relates to a control system and a method that compensates for hysteresis in the valve caused by coulombic friction and static friction.
BACKGROUND OF THE INVENTION
Valves have long been used to control the flow of gases and/or fluids through conduits. In particular, EGR valves have been used to control the amount of recirculated exhaust gas in an automotive engine to thereby reduce the level of nitric oxides Nox) in the exhaust gas. A relatively fast EGR valve response is necessary to maintain low emission levels during transient operation of the engine. EGR valves and valves in general frequently exhibit severe hysteresis impeding a rapid valve response. The hysteresis in a valve may be caused by (i) the paramagnetic behavior of an electrically actuated valve, (ii) dead travel time for a pneumatically actuated valve, and (iii) soot deposits impeding the motion of a closure member within the valve. Regardless of the specific cause of the hysteresis, the hysteresis includes two types of friction: static friction and coulombic friction.
The static friction force (hereinafter referred to as static friction) acts to impede the initial motion of a valve closure member within the valve. Referring to
FIG. 1
, a diagram illustrating the static friction is provided. The static friction is at a maximum value when the valve closure member is not moving. Once the valve closure member begins moving in either a first direction or a second direction, the static friction is no longer present.
The coulombic friction force (hereinafter referred to as coulombic friction) acts to impede the motion of a valve closure member whenever the closure member is moving.
Referring to
FIG. 2
, a diagram illustrating coulombic friction is provided. The coulombic friction has a constant amplitude whose sign is dependent on the direction of the velocity of the closure member.
One known throttle valve control system is utilized to control a rotatable throttle valve. The control system includes a control means that increases the effort supplied to the throttle valve when the valve closure member approaches a closed position. A first problem associated with the known control system is that the system only compensates for static friction and friction when the closure member approaches a closed position. Accordingly, when the closure member is at an operational position that is not near the closed position, the control system does not compensate for the static friction. A second problem with the known control system is that the control system does not compensate for coulombic friction. As a result, when the closure member is moving, the response time of the valve may be increased due to the coulombic friction.
There is thus a need for a control system and a method for controlling a valve closure member that minimizes or reduces one of more of the above-mentioned deficiencies.
SUMMARY OF THE INVENTION
The present invention provides a control system and a method of controlling a valve closure member that compensates for hysteresis caused by static friction and/or coulombic friction. In particular, the control system and the method may be utilized to control any type of valve closure member including linearly actuated valve closure members and rotatably actuated valve closure members.
A method for controlling a valve closure member in accordance with the present invention includes the steps of determining a control value indicative of an uncompensated target position of the closure member. The method further includes the step of calculating a friction compensation value associated with the closure member. The friction compensation value may comprise a static friction compensation value or a coulombic friction compensation value. The friction compensation value may be used to increase or decrease a compensating control value and an associated compensating control signal to compensate for the static friction and/or coloumbic friction. The method further includes the step of calculating the compensating control value responsive to the control value and the friction compensation value. Finally, the method includes the step of actuating the closure member responsive to the compensating control value.
A control system for controlling a valve closure member in accordance with the present invention includes an actuator that variably controls a position of the closure member. The system further includes a controller configured to determine a control value indicative of an uncompensated target position of the closure member. The controller is further configured to calculate a friction compensation value associated with the closure member. The controller is further configured to calculate a compensating control value responsive to the control value and the friction compensation value. Finally, the controller is configured to actuate the closure member responsive to the compensating control value.
A control system and a method in accordance with the present invention represent a significant improvement over conventional systems and methods. In particular, the inventive control system and method compensates for hysteresis caused by static friction and/or coulombic friction resulting in a relatively fast valve response. Further, the inventive control system and method compensates for hysteresis over the entire operational position range of a valve closure member.
These and other features and advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.
REFERENCES:
patent: 5771000 (1999-06-01), Matsumoto et al.
patent: 5992383 (1999-11-01), Scholten
patent: 6044857 (2000-04-01), Stege
patent: 6148837 (2000-11-01), Irokawa et al.
patent: 0495295A2 (1992-07-01), None
Syed Fazal Urrahman
van Nieuwstadt Michiel Jacques
Buckert John F.
Coughlin William J.
Ford Global Technologies Inc.
Lee Kevin
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