Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
1998-12-04
2001-03-06
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S278000
Reexamination Certificate
active
06198369
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to proportional control devices, and more particularly, to proportional actuators for proportional control devices.
Proportional control devices include a proportional actuator for positioning an armature within the case of the proportional control device. The proportional actuator causes the output of the proportional control device to be related directly to the applied current and independent of a function being controlled. For example, one application of proportional control devices is in control of fluid flow. In such application, a proportional control valve monitors pressure and the rate of flow of fluid through the valve is proportional to the magnitude of the applied current and is independent of changes in pressure of the fluid.
Typically, proportional actuators include a solenoid coil which is wound on a stationary magnetic pole. Current applied to the solenoid coil creates an attractive field in the stationary pole for moving an armature to operate a spool valve for communicating a supply port with a control port. The response time of the proportional actuator as well as the turn-on threshold are a function of the amount of force produced by the device. The amount of force which can be generated by proportional actuators of this type is related to the coaxial diameters of the magnetic pole and the armature, the number of turns of solenoid coil and the current that is applied to the solenoid coil. The solenoid coil size generally determines the dimensions of the device because the solenoid coil is wound on the magnetic pole. Thus, methods of maximizing the force generated by such devices are usually directed to optimizing the magnetic circuit of the device.
For example, the operating efficiencies of proportional actuators can be increased to some extent by improving the magnetic flux coupling between the magnetic pole piece and the armature. To this end, an element, which is commonly referred to as a saturation tip, is provided for directing magnetic flux through the pole piece to the armature. The saturation tip bridges the gap that exists between the opposing surfaces of the armature and the pole piece when the device is not actuated. In known proportional actuators, the saturation tip is formed on the stationary pole piece and the armature moves axially within the saturation tip. This construction, together with the configuration of the solenoid coil of such actuators, limits the coaxial diameters of the pole piece and the armature, thereby limiting the amount of force that can be generated for an proportional actuator of a given size.
In some known proportional actuators, the saturation tip was provided by brazing a tubular member of a magnetic material to the stationary magnetic pole piece as an extension of magnetic shoulder portion of the pole piece. In another known proportional actuator, which is disclosed in U.S. Pat. No. 5,377,720, the magnetic flux is directed by brazing the pole piece to a non-magnetic stainless steel sleeve which, in turn, is brazed to the valve body. However, the brazing operations required by these prior art arrangements add to the cost of the proportional actuator.
Proportional actuators can be incorporated into various types of control devices, and are particularly suitable for application in proportional fluid flow control devices for providing a proportional relationship between applied current and the fluid flow output of such devices. One problem associated with known proportional control valves is their tendency to overshoot a target position. Typically, such valves incorporate some type of damping mechanism which minimize overshoot, but slow the response time of the valve.
SUMMARY OF THE INVENTION
The present invention provides a proportional actuator for proportional control devices. The proportional actuator comprises a magnetic pole piece having a pole end portion, and an armature adapted for movement relative to the magnetic pole piece between first and second positions. The armature has an armature end portion which is located adjacent to the pole end portion and which is spaced apart from the pole end portion when the armature is in the first position. One of the end portions defines a saturation tip which projects from the one end portion. In one preferred embodiment, the saturation tip is configured to overlap at least a portion of the other one of the end portions when the armature is moved away from the first position. The proportional actuator further comprises a coil assembly including a step-wound coil for moving the armature relative to the magnetic pole piece. The step-wound coil includes a first coil portion and a second coil portion having an inner diameter that is larger than the inner diameter of the first coil portion. The inner diameter of the second coil portion in some highly preferred embodiments is also larger than the outer diameter of the end portion that includes the saturation tip, defining a region of increased diameter for allowing the saturation tip to overlap the other end portion. Providing a region of increased diameter for accommodating the end portion that includes the saturation tip allows the working diameters of the armature and the pole piece to be increased for a given size actuator, with a corresponding increase in the amount of force that is produced by the magnetic circuit of the device. In one preferred embodiment, the saturation tip is tapered to optimize magnetic flux coupling between the magnetic pole piece and the armature.
In another embodiment, the saturation tip is located on the armature and is dimensioned for telescopic engagement with an end portion of the magnetic pole piece as the armature is being moved relative to the magnetic pole piece. In yet another embodiment, the saturation tip is located on the magnetic pole piece and is dimensioned for telescopic engagement with an end portion of the armature as the armature is being moved relative to the magnetic pole piece.
In accordance with a further aspect of the invention, the bobbin of the coil assembly functions as a containment structure for the proportional actuator, sealing fluid within the interior of the proportional actuator. One or more sealing elements are interposed between opposing surfaces of the bobbin and the magnetic pole piece and between opposing surfaces of the bobbin and an enclosing member of the proportional actuator.
Further in accordance with the invention, there is provided a proportional control valve which includes a proportional actuator including a magnetic pole piece, an armature supported for movement relative to the magnetic pole piece, and a step-wound solenoid coil for moving the armature relative to the magnetic pole piece. The armature includes a saturation tip. The proportional control valve further includes a pressure inlet port which is adapted to be coupled to a source of the fluid, the source defining a system pressure and a pressure outlet port which is adapted to be coupled to the device the operation of which is to be controlled in accordance with the output pressure of the valve. A valve spool is coupled to the armature and movable therewith relative to the pressure inlet and outlet ports. A pressure balance mechanism includes a pressure sensing chamber in fluid communication with the pressure outlet port. The pressure balance mechanism is configured and arranged for causing a back pressure force to be produced on the valve spool during regulation of the output pressure at the outlet port of the valve in accordance with the energy level of the solenoid coil. As a result, the pressure balance mechanism allows the position of the valve spool and the armature to be determined solely in response to the average current flow to the solenoid coil and maintains the position of the valve spool and the armature, as set by the average current, regardless of the changes in the system pressure.
Highly preferred embodiments of the proportional control valve include a damping mechanism for minimizing overshoot. The damping mechanism provide
Dahlgren Derek A.
Ward James R.
Donovan Lincoln
Reinhart, Boerner, Van Deuren, Norris & Reiselbach, s.c.
TLX Technologies
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