Abstract:
A non-contact pressure switch assembly for sensing pressure in, e.g., a vehicle. A piston with integrated magnet in a housing is moved under fluid pressure to change a magnetic field in which a Hall sensor is disposed inside the housing. The field changes polarity at the Hall sensor at a predetermined piston position.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to pressure switches, and more particularly to non-contact pressure switches for vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Pressure switch manifolds are used in automotive transmission applications for direct sensing of fluid pressure. Applications include hydraulic feedback gear selection, shift timing/feel control, torque converter clutch control, solenoid feedback control, solenoid fault detection, and improved idle control. 
         [0003]    As understood herein, contacting technology, in which case hydraulic pressure deflects or moves a diaphragm or spring loaded piston to create a short circuit condition that closes the contacting switch at a predefined hydraulic pressure valve, can be used but these structures are susceptible to contamination, corrosion, and wear. Furthermore, conductive particle contamination can generate the close (short switch) condition without pressure actuation, and corrosion and wear can prevent the close with pressure actuation. 
       SUMMARY OF THE INVENTION 
       [0004]    A pressure switch assembly has a housing disposable in a fluid and an opening in the housing and in fluid communication with the fluid when the housing is disposed therein. A piston is disposed adjacent the opening for reciprocal movement in the housing. As set forth further below, a magnet is coupled to the piston and a Hall effect sensor is in the housing to output a signal that is affected by the position of the magnet in the housing. A spring urges the piston toward the opening, with fluid pressure urging the piston away from the opening. 
         [0005]    In non-limiting embodiments the Hall effect sensor establishes a Hall switch which changes output state from negative to positive at a predetermined position of the magnet in the housing. If desired, the spring and motion of travel of the piston together can establish a pressure switch value. Thus, the magnetic field of the magnet in effect switches polarity relative to the Hall switch at a predetermined position of the magnet relative to the Hall switch. 
         [0006]    In some implementations the housing includes a bottom and a base plate flush against the body and defining the opening. A diaphragm can be disposed between the body and base plate. 
         [0007]    In another aspect, a method for sensing pressure includes moving a piston under fluid pressure to change a magnetic field in which a Hall sensor is disposed. The field changes polarity at the Hall sensor at a predetermined piston position. 
         [0008]    In still another aspect, a non-contact pressure switch assembly for sensing pressure in a vehicle includes a housing, one or more Hall sensors associated with the housing, and one or more respective pistons with respective integrated magnets in the housing. Each piston with magnet is moved under fluid pressure to change a magnetic field in which the Hall sensor is disposed. As contemplated herein, the field changes polarity at the Hall sensor at a predetermined piston position. 
         [0009]    The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an exploded perspective view of a pressure switch assembly that may incorporate plural pressure switches of the present invention; 
           [0011]      FIG. 2  is an exploded perspective view of a single pressure switch in accordance with present principles; 
           [0012]      FIG. 3  is a side elevational cut-away view of a non-limiting switch in accordance with present principles in the depressurized configuration; 
           [0013]      FIG. 4  is a side elevational cut-away view of a non-limiting switch in accordance with present principles in the pressurized configuration; 
           [0014]      FIG. 5  is a side elevational cut-away view of an alternate non-limiting switch that uses an o-ring; and 
           [0015]      FIG. 6  is a side elevational cut-away view of an alternate non-limiting switch that uses a lip seal. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    The present invention overcomes the drawbacks associated with contacting switches by using a non-contacting magnetic switch. As contemplated herein, the present switch may be used but is not limited to an automotive transmission. 
         [0017]      FIG. 1  illustrates a pressure switch assembly, generally labeled  10 , and a solenoid body  12  that in non-limiting embodiments holds plural pressure switch assemblies, a single one of which is described as follows for clarity. A filter magnet (not shown) can be provided in each passageway of the solenoid body  12  that holds one of the below-described switches to filter out ferrous contamination. 
         [0018]    As shown in  FIGS. 1-4 , a magnet  14  is integrated as by, e.g., press fitting into a side of a piston  16 , which together snugly fit into a piston holder  18 , made from a medium such as nylon. Upward pressure through a port  20  in the solenoid body  12  urges against a flexible diaphragm  22 , in non-limiting embodiments made from woven backed Vamac. 
         [0019]    As best shown in cross-reference to  FIGS. 3 and 4 , the upward force turns the diaphragm  22  inside out and moves the piston  16  and integrated magnet  14  upward, thereby compressing a spring  24 , oriented to be partially contained in the piston  16 , against a fixed cover  26  ( FIG. 1 ). Screws  28 , cover  26 , and springs  24  can all be made from steel. That is, when pressure is applied to the diaphragm  22  when in the configuration shown in  FIG. 3  (with the holder  18  providing the low pressure stop), the piston  16  with integrated magnet  14  move upward to the position shown in  FIG. 4  (in which the cover  26  provides the high pressure stop). The movement of the magnet changes the field through a Hall switch  30  and crosses the sense element&#39;s field threshold “T”, shown in  FIGS. 3 and 4  by a dashed line. The Hall switch can be fixed into a printed circuit board  34  as shown in  FIG. 1 , which in turn can be fixed either on top of, or on the side of, the open pressure ports. 
         [0020]    As the pressure moves the piston  16  across the sense threshold “T”, the magnetic field at the Hall switch  30  changes direction from a negative to a positive value. It may now be appreciated that the Hall switch  30  changes output state at the threshold “T”, with the spring  24  being pre-loaded to a pre-defined pressure value between the solenoid body  12  and the cover  26  accordingly. Thus, spring  24  selection and piston  16  travel define the pressure switch value, while the Hall switching field and magnetic circuit define the switching position. This magnetic implementation, consisting of using switches in the polarity of the field and a narrow pressure actuation window, provides accurate pressure switching capability. An array of Hall switches  30 , 32  can be arranged on the printed circuit board  34  or load-frame to detect pressure changes at critical positions within the automotive transmission. 
         [0021]      FIG. 2  displays the embodiment that the magnet  14  would be oriented in, more specifically the piston  16 . The spring  24  fits into the piston  16 , which in turn rests in the non-moving holder  18 . The three components, situated in a stacked position, are set on the diaphragm  22 . 
         [0022]    As mentioned above, the dashed line “T” in  FIG. 3  and  FIG. 4  represents the position of the magnet  14  at which the magnetic field at the Hall switch  30  switches polarity. In  FIG. 3 , the magnet  14  is situated below the Hall switching field threshold position “T”. In  FIG. 4 , the magnet  14  is situated above the Hall switching field threshold “T” due to applied pressure on diaphragm  22  that moves the piston  16  and magnet  14  up, thereby compressing the spring  24  against the cover  26 . The difference in position of the magnet  14  between above or below the Hall switching field defines the output of the Hall switch  30 . 
         [0023]      FIGS. 3 and 4  also show that if desired, the piston  16  may be formed with one or more exhaust slots  16   a  to provide an exhaust path for fluid during piston actuation. In non-limiting implementations the holder  18  may include annular crush ribs  18   a  to compress the diaphragm  22  for better engagement. If desired, the cover  26  may include a central alignment dome  26   a  to align the spring  24 , while the piston  16  may include a central annular wall  16   b  for the same purpose. 
         [0024]      FIGS. 5 and 6  show alternate embodiments for the spring  24 , piston  16 , holder  18 , and diaphragm  22 . The arrow “A” represents the upward pressure that moves the diaphragm  22 . The diaphragm  22  is compressed between body and base plate to prevent fluid leakage and pressure losses into the reference cavity. 
         [0025]    In  FIG. 5 , an o-ring  52  is provided between the diaphragm  22  and holder  18  to compress the diaphragm, with the diaphragm sealing the holder from pressure. In  FIG. 6 , on the other hand, an annular seal  54  that is “V”-shaped in cross-section replaces the o-ring. Also,  FIG. 6  illustrates that a non-circular interface  56  can be provided between the piston and holder to prevent rotation of the piston if desired. 
         [0026]    While the particular NON-CONTACT PRESSURE SWITCH ASSEMBLY is herein shown and described in detail, it is to be understood that the subject matter which is encompassed by the present invention is limited only by the claims.