Abstract:
A sealed, electrically controlled compressor provides for two way optical data transmission to and from its sealed interior. An optical window, securely sealed through the compressor shell, and a pair of optical devices located to either side of the window, allow data transfer with no separate lines piercing the shell.

Description:
TECHNICAL FIELD 
     This invention relates to automotive air conditioning systems in general, and specifically to an electrically controlled compressor that has control communication through the compressor housing without a direct wire connection. 
     BACKGROUND OF THE INVENTION 
     A recent trend toward electrically driven, rather than engine belt driven compressors, promises to provide better and more efficient control, as well as eliminating clutches and seals around the drive shafts. Since a mechanical drive shaft with its rubbing seal no longer pierces the compressor housing, such compressors are sometimes referred to as being hermetically, completely sealed. This is somewhat of a misnomer, since a power carrying wire, instead of a shaft, must pierce the compressor shell to carry current to the motor. While not a moving part, the power wire must still be sealed at its interface with the housing. It is desirable to drive such compressors with a brushless electric motor, often referred to as a brushless DC motor, though it is actually an AC type motor. Since an automotive vehicle has only a DC primary electric source, an inverter is necessary to effectively convert the DC current to AC current, to act, in essence, as the equivalent of a conventional mechanical brush and commutator assembly to switch the current. There are also potential advantages to physically incorporating the inverter and its associated electronics inside the compressor shell, providing a compact package, short interconnections, and even the ability to cool the power electronics with the inlet refrigerant. Other sensors may be incorporated within the compressor shell, also. In that case, another wire or even wire bundle would, conventionally, have to pierce the compressor shell to provide two way communication between the vehicle controller and the compressor control electronics. This would require yet another pressure tight seal at the interface. 
     SUMMARY OF THE INVENTION 
     The invention provides a compressor having a shell that incorporates control electronics internally, but which does not require that a deparate data carrying line physically pierce the compressor shell, with its associated seal. Instead, an assembly consisting of a first optical transmission device inside the compressor housing acts across a suitably transparent, small window through the compressor shell, transmitting and or receiving data to or from a corresponding second optical device outside the compressor shell. The optical window is a solid piece which can effectively be made integral to the compressor shell itself, and is thus very tightly sealed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the invention will appear from the following written description, and from the drawings, in which: 
     FIG. 1 is a partially broken away side view of a compressor housing incorporating an embodiment of the invention; 
     FIG. 2 is a view of one embodiment of the invention, with the components disassembled; 
     FIG. 3 is a view of the embodiment of FIG. 2 assembled; 
     FIG. 4 is a view of an alternate embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, an electrically driven compressor, indicated generally at  10 , has a non-illustrated internal motor and scroll compressor device contained within a cylindrical shell  12 . Shell  12  is closed at the end by a removable end cap  14  sealed by an O ring type seal  16 . A basic power connection  18  necessarily pierces the end cap  14  to carry current to the internal motor, and this must be suitably sealed at its interface to cap  14 . As rioted above, that motor is preferably the “brushless” variety, in which an inverter commutates electronically the phases of the motor. This avoids wear and provides for more complete and precise electronic control of the motor. An inverter uses power transistors that produce a good deal of heat. Here, the inverter and its associated circuitry, indicated generally at  20 , is incorporated within the end cap  14 , where it can be exposed to a cooling stream of inlet refrigerant. This also provides a compact and protected package for the electronics. The inverter  20  must have the on-off time of its power transistors precisely controlled, and this necessitates an exchange of data between the vehicle&#39;s control system and the inverter  20 . For example, the vehicle controller might send to the compressor  10  a coded request for a desired RPM or maximum power value. The compressor  10  could send to the vehicle a value for actual RPM, or data about its temperature, voltage, or power consumption, from internal sensors other than the inverter  20 . If a wire or series of wires also had to pierce cap  14  to carry these data back and forth, it would represent several additional possible leak points that would have to be rigorously sealed. The subject invention allows a data exchange across the shell  12 , effectively without piercing it. 
     Referring next to FIGS. 2 and 3, in one embodiment of the invention, a glass optical window  22  is fixed through the end cap  14 . The term “optical” is used broadly to indicate an area amendable to having light source encoded data passed through it. Window  22  is formed by boring a cylindrical hole through cap  14 , and pouring molten glass therewithin to harden. This creates a very solid optical path through cap  14 , one which acts essentially an integral part of cap  14  and is substantially leak proof. Window  22 , in the particular embodiment disclosed, would be formed of red or “black” glass, a material suitable to pass infrared light. A transparent (or at least translucent) protective housing  24  is closely engaged between the underside of window  22  and a circuit board  26  located just inboard of the underside of cap  14 . Housing  24  is formed of a transparent, oil and temperature resistant material, such as polycarbonate, and should be optically similar to the window  22 , in terms of color and propensity to pass light. Housing  24  covers a first optical device, indicated generally at  28 . Device  28  could be a single paired receiver/transmitter of infrared light, called a transceiver, or could be two separate receivers and transmitters side by side. It may be assumed for purposes of discussion that first device  28  is a transceiver. The receiver portion is a photosensitive diode, while the transmitter portion is a light emitting diode (LED). Devices like  28  are widely commercially available, and the one disclosed is identical to those, but for having a Fresnel lens, which is more compact than a conventional hemispherical lens. First optical device  28  is mounted to board  26 , within housing  24  and directly below window  22 . Its associated circuitry would be mounted to board  26 . As seen in FIG. 3, the lens of first device  28  is protected by housing  24  against oil containing refrigerant within cap  14 . 
     Still referring to FIGS. 2 and 3, above cap  14 , a connector block  30  fits tightly to the top of cap  14 , sealed by an O ring  32  and surrounding the outside of window  22 . Mounted inside connector block  30  is a second optical device  34 , oriented directly above, and optically matched to, first optical device  28 . Second device  34  would be identical to  28 , and matched thereto, that is, respective transmitter and receiver portions would be opposed. Connector terminals  36  extend from the back of block  30 , adapted to be connected to a wiring harness to the rest of the vehicle electrical and control system. 
     Referring next to FIG. 4, an alternative embodiment is described. The compressor end cap  14  and most other components would remain the same, and are given the same number accordingly. Housing  24  and window  22 , however, are replaced by a single part, a window-housing indicated generally at  38 . Window-housing  38  provides both functions of the housing  24  and window  22  in a single part. That is, a lower housing section  40  surrounds and protects first device  28 , and a upper window section  42  integral thereto passes through end cap  14 , with a snap fit to provide a direct light path to the second device  34 . The material used would be similar to that used for housing  24 , that is, a light transmitting and oil resistant material, such as polycarbonate. The fit through the end cap  14  of window section  42  would be as close and tight as physically practicable, potentially aided by a suitable adhesive, but would not be quite as solid to end cap  14  as melted in place glass would be. Therefore, an extra O ring seal  44  is compressed between the top of housing section  40  and the underside of end cap  14  to provide additional sealing integrity. 
     With either embodiment, in operation, coded data would be transmitted between the two optical devices  28  and  34 , such as requested and actual compressor RPM. As disclosed, infrared light is the medium, although other optical devices and light sources could be used, such as visible or even laser light. Data transmission would be simplified by the short transmission paths involved (the two devices  28  and  34  are very close), and by the lack of ambient light in the particular environment (underhood). A carrier frequency could be used for the data transmission, but it is likely that plain binary signals would work just as well. Since simultaneous transmission and sending of data would not be needed, the two devices  34  and  28  could be simply linked in an automatically responsive fashion. For example, the control scheme could be set up so that each time the vehicle control system sent a request for a certain compressor speed and power, the compressor control system, (emitter and associated sensors and circuitry) inside compressor  10  would respond automatically with a reading of actual speed and power. 
     Variations in the disclosed embodiment could be made. Either of the devices  34  or  28  could be just a receiver, or just an emitter, although it is most likely that two way data communication would be desired. As noted, the optical medium could be a source other than infrared light. It is possible that the internal device  28  could be in a location where it did not need environmental protection within the shell  12 , although it is likely that it would, and the translucent housing  24  that provides protection without impairing data transfer is a particularly advantageous solution to that problem. Therefore, it will be understood that it is not intended to limit the invention to just the embodiment disclosed.