Related Applications This application claims the benefit of U. S. Provisional Application No. 60/243,784, filed October 27,2000.

Technical Field The present invention relates generally to solenoid actuation devices, and more particularly, to a dual coil solenoid device used for controlling the flow of fuel to an engine.

Background Of The Invention Solenoid devices such as for controlling the flow of fuel used by an engine have been disclosed in the past. In particular, U. S. Patent No. 5,592, 356 discloses one such solenoid. Dual coil solenoid devices, given their high level of reliability and remote operation, are often used with fuel-injected engines to actuate fuel injection pumps. Such devices use a high current pull coil and a low current hold coil which are customarily energized by way of a keyswitch, the keyswitch also operates the starter for the engine. A problem can occur when the

engine operator energizes the pull coil for prolonged periods of time by continually engaging the keyswitch during extended engine cranking. This can cause burn-out of the pull coil and related circuitry.

One approach to solving this problem, as disclosed in U. S. Patent No. 4,219, 861, is to provide a solid state protector means which operates as a function of temperature to interrupt energizing the solenoid before thermal destruction of the solenoid. In particular, the protector means includes a voltage divider and a PTC current-limiting device. The solenoid is connected in series with the power circuit of an S. C. R. whose control electrode is connected to the voltage divider. When the PTC current-limiting device is cool, the S. C. R. allows current flow through the solenoid. At a predetermined temperature, the current-limiting device exhibits a switch-like increase in resistance, thereby causing the potential applied to the switching electrode of the S. C. R. to fall below the S. C. R. gate threshold and prevent the S. C. R. from conducting. The de-energization of the solenoid is executed very rapidly to prevent thermal destruction of the solenoid.

The protector means and the S. C. R. are placed in the solenoid housing ; however, because there is limited space within the solenoid housing, and the PTC current-limiting device expands slightly when heated, additional space is required to accommodate the expansion of the PTC current-limiting device.

Another approach directed to solving these problems involves packaging a solenoid protector circuit for the pull coil of the solenoid within a housing enclosing the protection circuit with the external wiring of the solenoid.

The protector circuit is located away from the solenoid. The housing around the protection circuit and the wiring reduces the flexibility of the protector circuit.

Due to the lack of flexibility, the protection circuit cannot be used in space confining environments.

In addition, attempts have been made to attach the protection

circuitry to the solenoid itself by potting the circuitry to the side or end of the solenoid. However, problems arose because the potting creates a thermally conductive path and the heat from the solenoid contributes to the internal heat generated by the electronics. As a result, the electronics are likely to overheat and destruct.

Although locating the protector circuit closer to the solenoid increases its applicability, the close proximity to the solenoid increases the chance of damaging the circuitry due to the high temperature generated by the solenoid.

The present invention is provided to solve these and other problems.

Summary Of The Invention One embodiment of the present invention is directed to a switch assembly for a solenoid. The switch assembly comprises a thermally non-conductive sleeve having an open end, a closed end, and an interior. A protection circuit is operably connected to the solenoid and contained within the sleeve. A thermal barrier is positioned within the sleeve and about the open end.

Another aspect of the present invention comprises a switch assembly having an open receiving end for mounting onto the solenoid. A thermal barrier is mounted about the receiving end. The switch assembly includes a protection circuit encapsulated within an encapsulate material. The encapsulate material provides an outer surface for the switch assembly.

Yet a further aspect of the present invention is directed to a switch for a solenoid. The switch comprises a thermally non-conductive cap having a surface, an open end, a closed end, and an interior. The interior is defined within the surface, the open end, and the closed end. A protection circuit resides within the cap and is operably connected to the solenoid. A thermal barrier is located within the interior of the cap between the solenoid and the protection circuit wherein the barrier thermally isolates the protection circuit from the solenoid.

Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.

Brief Description Of The Drawings FIGURE 1 is a diagram of the circuitry utilized in one embodiment of the present invention; FIGURE 2 is a schematic diagram of the protection switch circuitry utilized in one embodiment of the present invention; FIGURE 3 depicts the thermally insulated cap; FIGURE 4 is an alternative embodiment of the thermally insulated cap shown in FIGURE 3; FIGURE 5 is a semi-cross-sectional view of one embodiment of the present invention; FIGURE 6 is a semi-cross-sectional view of an alternative embodiment of the present invention; FIGURE 7 is a photograph of the circuitry of the present invention in preparation of being inserted within the cap; FIGURE 8 is a photograph depicting various stages of assembly of one embodiment of the present invention; FIGURE 9 is an assembled embodiment of the present invention attached to a solenoid; FIGURE 1 Oa depicts one embodiment of the thermal barrier; and, FIGURE 1 Ob depicts an alternative embodiment of the thermal barrier.

Detailed Description While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the

invention and is not intended to limit the broad aspect of the invention to the embodiment illustrated.

The present invention is directed to a switch for a solenoid. The switch is operably connected to a pull coil of the solenoid. The switch comprises a protection circuit positioned within a thermally non-conductive cap. The cap is attached to the solenoid and a thermal barrier located between the protection circuit and the solenoid thermally insulates the circuit from the solenoid.

Referring to the FIGURES, the switch assembly 10 comprises a thermally non-conductive cap or sleeve 12 having an interior surface 14, an open end 16, a closed end 18, and an interior 20. FIGURE 3. The interior 20 is defined within the surface 14, the open end 16, and the closed end 18. A protection circuit 22 resides within the cap 12 and is operably connected to the solenoid 24.

FIGURE 5. A thermal barrier 26 is located within the interior 20 of the cap 12 between the solenoid 24 and the protection circuit 22. The barrier 26 can be air, a thermally non-conductive material, or a combination thereof. The cap 12 facilitates heat removal via convective air currents while the barrier 26 simultaneously isolates the circuitry 22 from the heat generated by the solenoid 24.

The protection circuit 22 is preferably attached to a printed circuit or wiring board 28. FIGURE 1. The protection circuit 22 is positioned near the closed end 18 of the cap 12. The open end 16 of the cap includes a rim 30.

FIGURES 3 and 4. The rim 30 of the thermally non-conductive cap 12 is attached to the solenoid 24.

The protection circuit 22 controls the energizing of the solenoid's 24 pull coil when power is initially applied to the solenoid. The protection circuit 22 comprises a timing circuit 32 and a switching circuit 34. FIGURE 2. Each circuit 32,34 is designated within a dashed perimeter line. Preferably, the timing circuit 32 comprises a pair of resistors 36 operably connected to a capacitor 38 and

a transistor 40. A reverse voltage protector 42, preferably a rectifier, is connected to the input of the timing circuit 32. The output of the timing circuit 32 is operably connected to the switching circuit 34. The switching circuit 34 comprises a resistor 44, a diode 46, and a transistor 48. The output of the switching circuit 34 is connected to one side of the solenoid's 24 pull coil and to a clamping device 50, preferably a diode, connected to the other side of the pull coil.

Preferably, the cap 12 comprises a continuous inner surface 14 having a closed end 18 and an open end 16. The open end 16 of the cap 12 is defined by a continuous or noncontinuous rim 30. FIGURES 3 and 4. The circuitry 22 is attached to an encapsulate 52 and connected to the surface 14 within the interior 20 of the cap 12 near the closed end 18. An epoxy or similar material can be used to pot or encapsulate the circuitry 22 within the cap 12. The cap 12 is comprised of a high impact plastic material that resists or insulates heat transfer from the solenoid 24. The cap 12 facilitates heat transfer away from the protection circuitry 22.

The thermal barrier 26, e. g. gasket, includes a perimeter 54. The perimeter 54 is attached to the cap 12 and the barrier 26 is positioned within the interior 20 of the cap, between the circuitry 22 and the open end 16 of the cap. The <BR> <BR> perimeter 54 of the barrier 26 can be continuous or non-continuous, e. g. , notched, gapped, etc. FIGURES lOa and lOb. The thermal barrier 26 can be positioned to contact the encapsulated circuitry 22 and/or the solenoid 24. The protection circuit 22 within the cap 12 is physically spaced apart from the solenoid 24. The barrier 26 is affixed within the interior 20 of the cap 12 and is positioned between the solenoid 24 and the circuitry 22 to isolate the circuitry 22 from the thermal conditions associated with the solenoid 24. The barrier 26 allows for the operable connection of the solenoid 24 and the switching circuitry 22.

FIGURE 6 depicts an alternative embodiment of the present invention wherein the cap 12 is not utilized. The protection circuit 22 is operably

connected to the solenoid 24 and resides within the encapsulation material 52. The thermal barrier 26 is located between the encapsulation material 52 and the solenoid 24. The barrier 26 comprises a thermally non-conductive material capable of isolating the circuitry 22 from the heat generated by the solenoid 24.

One method contemplated for manufacturing this embodiment includes placing the circuitry 22, while operably connected to the solenoid 24, into a mold and then inserting the encapsulation material 52 into the mold and allowing it to form around the circuitry. The thermal barrier 26 is positioned between the molded encapsulation material 52 and the solenoid 24. The encapsulate material 52 provides an outer surface for the switch assembly 10. Alternatively, the cap-less encapsulated circuitry can be implemented without the thermal barrier 26 being utilized.

FIGURES 7-9 depict various stages of assembly of the solenoid switch assembly 10. FIGURE 7 shows the circuitry 22 on a printed circuit board 28 in preparation of insertion within the cap 12. FIGURE 8 shows the circuitry 22 just prior to, and after, being inserted into the cap 12. And FIGURE 9 depicts an assembled solenoid 24 and switch assembly 10.

While a specific embodiment has been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection is only limited by the scope of the accompanying Claims.