Valves and valve actuation – Electrically actuated valve – Rotary electric actuator
Reexamination Certificate
2000-01-14
2001-06-26
Lee, Kevin (Department: 3754)
Valves and valve actuation
Electrically actuated valve
Rotary electric actuator
C251S124000, C251S903000, C060S039281, C060S243000
Reexamination Certificate
active
06250602
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to metering valves, and in particular, to fuel and ignitor valves for use in air and space vehicles.
2. Description of the Related Art
Valves for metering fuel and other combustible media to engines in aircraft and spacecraft are well known in the art, see for example U.S. Pat. Nos. 3,848,806 and 4,561,468. Such valves are used to control the rate at which pressurized fuel is supplied to metering orifices in the combustion chamber through a fuel line. The valves are relied upon to provide consistent and rapid control of flow rates of fuel at various operational stages, such as ignition and during sustained operation as actuated by a servo motor or the like. Their operation is critical to proper performance of the vehicle. Poor valve operation can result in unintended engine shutdown and failure.
These valves often include movable stemmed valve members, or pintles, aligned with the outlet port of the valve for controlling the rate at which fuel flows to an engine. Pintle type valves are typically less affected by the temperatures and pressures of the fuel passing through the fuel chamber of the valve, due to their contoured head and axial movement. However, even pintle valves can be adversely affected by the high pressure conditions of jet engines. High pressure can cause large forces to act on the pintle so as to alter the flow rate of the fuel through the valve.
In one prior art design, the pintle of a metering valve is actuated by a servo motor mounted at right angles to the pintle axis. The servo motor has a pinion gear engaging a rack attached to the pintle, the rack extending along the pintle axis. The rack and pinion ensure that axial forces on the pintle are translated properly to the radial bearings of the servo motor; however, the rack and pinion provides a relatively high gear ratio that may not provide sufficient force on the pintle when used with smaller high speed servo motors. Accordingly, a helical spring is attached to the free end of the rack to provide a countervailing force on the pintle reducing the peak forces that the servo motor must overcome.
A drawback to the use of a spring is that it may only coincidentally balance the force on the pintle at certain valve openings and operating conditions. Further, it adds mass to the actuation mechanism slowing its response speed. The rack and pinion is complex and requires stabilizing guideways.
SUMMARY OF THE INVENTION
The present invention provides a simple and high speed metering valve using a compact axial drive where a shaft of the servo motor is aligned with the pintle axis. The axial drive is made possible by the use of a force plate and thrust bearing to accept the axial pintle load in lieu of the servo motor bearings. A threaded coupling between the servo motor and pintle shaft provide a simple and reliable drive providing effective high gear ratios with low rotational and translational inertia. The valve has a pintle that when fully extended positively seals a nozzle passageway leading to the outlet port.
Specifically, the present invention is a valve for metering liquid or gaseous fuel from a fuel supply. The valve has a housing defining a fuel chamber in communication with an inlet port coupled to the fuel supply and an outlet port. A nozzle passageway joins the fuel chamber to the outlet port. The nozzle passageway is preferably a venturi opening having a throat through which the fuel flows at sonic velocity. The valve has a pintle extending along a pintle axis concentric with the nozzle passageway. The pintle has a stem at one end and a contoured head at an opposite end. The pintle head has a seal about its circumference. The valve also has an axial drive assembly concentric with the pintle axis and in threaded communication with the pintle stem. The pintle moves along the pintle axis from a retracted position allowing passage of fuel through the outlet port to an extended position in which the circumferential seal closes the passageway so that no fuel can exit the outlet port. The drive assembly has a force plate in communication with a thrust bearing for transferring to the housing pressure forces acting on the pintle.
In one preferred form, the axial drive assembly includes an actuator, preferably a servo motor, having a rotatable shaft concentric with the pintle axis. The drive assembly also includes a drive nut coupled to the actuator shaft at one end and having threads at an opposite end for engaging a threaded end of the pintle stem. This direct, axial drive provides a highly reliable and accurate mechanism for positioning the pintle.
Additionally, the valve may have a fixed member secured to the housing and contacting the pintle such that rotation of the drive nut causes translation of the pintle along the pintle axis between the retracted and extended positions. In one embodiment, the pintle stem has an axially extending transverse slot in which is disposed a pin fixed to the housing for preventing the pintle from rotating. The pin is fixed to the housing at a pintle guide defining a transverse bore aligned with the transverse pintle stem slot.
In another preferred form, the drive assembly is isolated from the fuel. In particular, the pintle is disposed within an axial bore within the housing and the pintle stem includes a seal about its circumference located so as to seal the axial bore throughout the stroke of the pintle. In one embodiment, the axial bore is defined by the pintle guide. The pintle stem seal seals the axial bore of the pintle guide throughout the stroke of the pintle thereby isolating the axial drive assembly from fuel in the fuel chamber. Thus, the drive assembly is not subjected to wear inducing contaminants that may be present in the fuel.
In yet another preferred form, the force plate is an annular flange of the drive nut, and the drive assembly further includes at least one annular thrust washer. Specifically, the drive nut flange is flanked by two annular thrust bearings each disposed between two annular thrust washers. A containment sleeve is disposed about the outer diameter of the thrust washers and bearings, held fixed by an interference fit between the pintle guide and a retaining nut fixed to the housing. This arrangement ensures that the threaded connections will not separate from vibration. Thus, the valve of the present invention provides a simple, axially aligned force distribution assembly that transfers fuel pressure forces acting on the pintle to the housing rather than the motor. This assembly prevents the pressure forces increasing the load on the motor which could reduce its responsiveness and operational life. Moreover, routing the pressure forces away from the motor allows the valve to more accurately adjust the position of the pintle and thereby the fuel flow rate.
In still another preferred form, the pintle head and stem are joined at a threaded connection. In this way, the pintle head may be replaced with a pintle head of different contour so as to change the flow rate of media through the valve. A locking insert is preferably disposed at the mated threads to prevent the pintle head from separating from the pintle stem.
Thus, the highly responsive and reliable axial drive mechanism and positive shut off of the nozzle render the valve of the present invention suitable to meter fuel to gas turbines and jet engines. In particular, these characteristics of the valve allow it to be used in vehicles having supersonic combustion ramjet (SCRAMJET) engines for hypersonic air and space travel. These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow.
REFERENCES:
patent: 3848806 (1974-11-01), Samuelsen et al.
patent: 4383553 (1983-05-01), Platt
patent: 4524914 (1985-06-01), Kaibara et al.
patent: 4561468 (1985-12-01), Kreitchman et al.
patent: 4593881 (1986-06-01), Yoshino
patent: 5706856 (1998-01-01), Lancaster
patent: 5722634 (1998-03-01), Hrytzak et al.
patent: 5806301 (1998-09-01), auBuchon et al.
Jansen's Aircraft Systems Controls, Inc.
Lee Kevin
Quarles & Brady LLP
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