Abstract:
A modular electronic control system for a differential is described. Such a control system can contain an actuator and sensor in the differential casing and a connection between these elements in the differential casing and a controller outside the differential. The controller can be in the form of a printed circuit board residing in a control housing attached to the differential casing. In alternative embodiments, the controller may also be more distally located in the vehicle, where the controller housing contains means for conducting electrical signals from the interior of the differential casing to the vehicle without containing a printed circuit board. The controller may also contain a thermally conductive portion for dissipating heat generated by the controller.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a modular electronic control system for a differential. 
     BACKGROUND OF THE INVENTION 
     A vehicle differential carrier (commonly known merely as a “differential”) is a device employing differential gears therein, which typically are connected to its exterior by three shafts. An input shaft transmits torque and rotation into the differential gears from a vehicle engine. In turn, each of the other two shafts separately transmit a portion of the torque and rotation from the differential gears out to separate external wheels. Regarding the operation of the differential, when a vehicle is being driven straight the differential rotates with an axle, while side and pinion gears mate but do not rotate relative to each other. However, when the vehicle turns the differential still rotates but the side and pinion gears mate and slightly rotate so that one wheel can turn faster than the other. 
     Hence, the differential is needed because when a vehicle is turning, as it quite often does, the outside wheel makes a larger radius than the inside wheel. As a result, the outside wheel goes a farther distance, moves faster and turns more revolutions than the inside wheel. If, however, both wheels were on the same axle shaft, in this instance, one or both wheels would have to skid or slip to make a turn. Consequently, the function of the differential allows the wheels to turn at different speeds, but at equal torque. 
     In certain situations it is desirable to modify the action of the differential. For instance it may be desirable to lock the differential. Those skilled in the art will recognize that there are a number of different mechanisms to lock the relative rotation between a differential gear case and one of the output side gears. Control of the locking differential involves several actions. Engagement of the differential is controlled by an actuator. The actuator is in turn powered and signaled by the vehicle through a controller. In addition, it is beneficial to have a sensor that can relay information regarding the differential back to the controller. It would be beneficial to have a differential control system including an actuator, sensor and controller that was modular. Such a modular control system would facilitate manufacture and installation. It would also provide for feedback to the vehicle about the action and status of the differential. In addition, placement of the controller in close proximity to the differential allows for calibration to be done before installation of the differential. Further, specific placement of the controller can reduce noise (usually from electromagnetic currents) found in the system. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a modular electronic control system for a differential is described that comprises an actuator capable of selectively inducing engagement of a differential, a sensor capable of sensing engagement of a differential, a control housing, wherein the control housing comprises means of conducting electrical signals, and a connector which provides for electrical connectivity between (i) the actuator and sensor and (ii) the means of conducting electrical signals of the control housing. 
     In one embodiment, the control housing further comprises a printed circuit board in electrical connectivity with the connector. 
     In an alternative embodiment, the control system further comprises a port which provides for electrical connectivity between (i) the means of conducting electrical signals of the control housing and (ii) a vehicle wherein the control system resides. 
     Other embodiments include use of a Hall type sensor, an encapsulation around conducting wires between the sensor, actuator and the connector. Still other embodiments include a control housing that extends through the casing of the differential. 
     In an alternative embodiment, the controller has a thermally conductive portion that acts to transfer heat generated by the controller to a heat sink. 
     In other embodiments, the controller is attached to the axle housing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description when considered in the light of the accompanying drawings in which: 
         FIG. 1  is a schematic of an embodiment of the modular electronic differential control system in accordance with the present invention, including a cross-sectional view of the actuator and sensor along the axle axis as shown. 
         FIG. 2  is a schematic of an embodiment of a controller having a thermally conductive portion in accordance with the present invention. 
         FIG. 2A  shows a magnification of the area encircled in  FIG. 2 . 
         FIG. 3  is a schematic of another embodiment of a controller having a thermally conductive portion in accordance with the present invention. 
         FIG. 3A  shows a magnification of the area encircled in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting. 
       FIG. 1  illustrates a schematic of the modular electronic differential control system  2 . Within the differential casing  10  is found a connector  12  that electrically connects the actuator  14  and sensor  16  to the control housing  18 . 
     As is known in the art, the actuator  14 , within the context of a differential, converts electrical current into mechanical force. Electrical current is conducted through a coil of wire  20  that is wound around the pole piece  22 . The flow of electrical current creates a magnetic field that draws the actuator plunger  24  toward the pole piece  22 . Each end of the coil of wire  20  is attached to its own individual connector conductor wire  26 . Typically, a spring (not shown) is placed to act on the plunger  24  in a way to hold it away from the pole piece  22  when current is not flowing through the coil of wire  20 . In applications with actuators  14  in a differential the plunger  24  is attached to a face gear (not shown) arranged in a dog clutch configuration (not shown) as is known in the art so as to allow clutch engagement and disengagement control through coil current control. 
     The position sensor  16  provides a signal that is indicative of the plunger  24  position relative to the pole piece  22 . In one embodiment of the invention, the plunger  24  is made of ferromagnetic material, or has a ferromagnetic attachment. In another embodiment of the invention, the position sensor  16  is a Hall type sensor (magnetic field detector), but any suitable sensor  16  capable of sensing the position of the plunger  24  can be used in accordance with the invention. In embodiments with a Hall type sensor, the sensor  16  is positioned between a magnet  28  and the plunger  24 . The output of the sensor  16  changes states when the plunger  24  moves to a position, relative to the sensor  16 , that permits magnetic flux to flow from the plunger  24  to the magnet  28 . The sensor  16  and magnet  28  are molded into the encapsulation  30  of the actuator coil  20 . In one embodiment, the encapsulation  30  is a plastic material, but any insulating material capable of protecting the sensor  16  from the environment can be used without going beyond the scope of the invention. 
     Conducting wires  26  that carry the signals to/from the sensor  16  and coil  20  exit the encapsulation  30  and connect to the pins/receptacles (not shown) housed within the electrical connector  12 . The electrical connector  12  joins with to the control housing  18  on the interior  36  of the differential casing  10 . 
     The connector  12  can be mechanically attached or detached, lending to the modular nature of the control system  2  described herein, from the control housing  18  as needed. When attached, the connector  12  should be designed in such a way to also provide electrical connectivity between the conducting wires  26  and the conducting bars  32  residing in the control housing  18 . 
     In one embodiment of the invention, the control housing  18  is made from a molded plastic, but any suitable material known in the art can be used without departing from the scope of the invention. The electrical signals of the actuator  14  and sensor  16  conduct through wires  26 , into the electrical connector  12 , and through to conducting bars  32  that are molded in to the controller housing  18 . The conducting bars  32  are usually made of metal, but can be made of any conducting material as known in the art. Likewise, signals to/from the vehicle can be conducted through conductor bars  32 ′. The control housing  18  and conducting bars  32 ,  32 ′ are formed in a manner that realizes a standard vehicle connector (not shown). A port  34  for a standard vehicle connector is shown in  FIG. 1 . 
     In one embodiment of the invention, intact conducting bars  32  carry signal to/from the standard vehicle connector to/from the electrical connector  12  in the interior of the differential casing  10 . In this situation, the electrical signals travelling along the conducting bars  32  are not processed locally at the differential. This embodiment is not specifically shown in  FIG. 1 , but can easily be deduced by having a continuous electrical communication through  32 ,  38  and  32 ′. 
     In an alternative embodiment, the conductor bars  32  are not intact and are cut in such a way as to leave vertical portions  38 , as shown in  FIG. 1 , upon which a printed circuit board (PCB)  40  is lowered and then attached so as to provide electrical connectivity between the PCB  40  and the conducting bars  32 ,  32 ′. In this embodiment, the PCB  40  allows for local processing of signals to/from the actuator  14  and sensor  16 . The PCB  40  can provide processing, sensor interfacing, or coil drive capabilities. The PCB  40  is part of the electronic control system  2  and that receives signals and power from the vehicle, processes them and controls the actuator  14  in a manner that is defined by a control strategy. The PCB  40  also provides processing for signals back to the vehicle in a way that is determined by the control strategy. 
     In either alternative embodiment described above, a cover  42  can be situated on the control housing  18  so as to provide electrical insulation and seal the components housed in the control housing  18  from the environment. Another embodiment, not specifically shown in  FIG. 1 , but easily deduced, allows for a potting or encapsulation to be placed in the control housing  18 . Any material known in the art can be used as long as it provides the necessary electrical insulation and sealingly protects the components housed in the control housing  18  from the environment. 
     In the embodiment shown, the PCB  40  is shown attached to both control bars  32  continuing on to the interior of the differential and control bars  32 ′ continuing on to the standard vehicle connector. The control housing  18  is shown with a cover  42 . The control housing  18  and cover  42  may be unitary. 
     The cover  42  and control housing  18  may be in contact with the exterior  44  of the differential casing  10 . The control housing  18  may also be in contact with the differential casing  10 . The control housing  18  can extend through an opening  46  in the differential casing  10 . 
     In alternative embodiments, the controller  2  is attached to the axle housing (not shown) instead of differential casing  10 . The general concept is the same, however and may be used in designs where the actuator  14  for the differential is external to the differential casing  10 . 
     One issue arising from having the controller  2  in such close proximity to the differential is heat build-up. Differentials are composed of moving parts and generate a lot of heat and are generally bathed in oil to reduce heat generated by friction as well as to help dissipate any heat that is generated. Aside from differentials and axles creating hot environments, the controller  2  itself has at least one heat generating component  100 , as shown in  FIGS. 2 and 3 . The heat generating component  100  is usually a transistor. In specific embodiments, these are field effect transistors. In order to aid in the extra heat generated by the heat generating component  100 , the controller  2  should have a heat transfer mechanism which can transfer heat from the heat generating component  100 . The first portion of the heat transfer mechanism shown in both  FIGS. 2 and 3  are thermal vias  106  built into the PCB  40 . These thermal vias  106  are in conductive contact with a thermally conductive tape  102 . The thermally conductive tape  102  is in conductive contact with a heat transfer device  104  or  108 . The embodiment shown in  FIG. 2  allows for heat passing through the heat transfer mechanism (combination of  102 ,  104 , and  106 ) to the differential casing  10  (or in further embodiments, the axle housing (not shown)). 
     In  FIG. 3 , the heat transfer mechanism (combination of  102 ,  108 , and  106 ) allows for heat to transfer to the fluid surrounding the differential casing  10  or, in alternative embodiments) the axle housing (not shown). This fluid can be either a gas or liquid and is most preferably ambient air or oil used in lubrication of the differential or axle. 
       FIG. 2A  and  FIG. 3A  show magnifications of the area encircled in  FIGS. 2 and 3 , respectively. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.