Abstract:
A pressure switch employs electrical contacts isolated from pressure media. By employing a snap action blade in a snap over center configuration, it is possible to provide a hysteresis effect in which the switch actuates at one pressure and deactuates at a different pressure.

Description:
TECHNICAL FIELD  
       [0001]     This disclosure relates generally to a pressure switch and, more particularly, to a pressure switch that can be actuated by high pressure and in which the contacts are isolated from the pressure media.  
       BACKGROUND  
       [0002]     A pressure switch is a type of switch in which the switching action is triggered by pressure in the surrounding environment. Pressure switches have been proposed for use in various kinds of electromechanical devices. The pressure detection mechanism in a typical pressure switch is a diaphragm configured in the pressure switch to be impinged upon by the pressure media (such as air or gas under pressure), and upon reaching a particular pressure the diaphragm is translated to cause the switch contacts of the pressure switch to be actuated.  
         [0003]     However, conventional pressure switches tend to operate only at relatively low pressure levels (50-150 PSIG).  
         [0004]     Another problem of conventional pressure switches is that they are not sufficiently miniaturized and they frequently occupy too much space in the electro-mechanical device.  
       SUMMARY  
       [0005]     The present disclosure provides a pressure switch that can effectively avoid the above-noted disadvantages of conventional pressure switches.  
         [0006]     In one example of this disclosure, a pressure switch with contacts that are isolated from the pressure media is provided.  
         [0007]     In another example of the present disclosure, a pressure switch is provided in which the switch contacts are isolated from the pressure media and a snap actuation blade mechanism is provided to be actuated in response to the pressure.  
         [0008]     By constructing the snap actuation blade mechanism in an exemplary configuration described and shown herein, it is possible to provide a hysteresis response in which the deactuation pressure level is different from the actuation pressure level. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The features of the present disclosure can be more readily understood from the detailed description below with reference to the accompanying drawings wherein:  
         [0010]      FIG. 1  is a front elevational view of a high-pressure miniature switch without covers according to an example of the present disclosure;  
         [0011]      FIG. 2  is cross sectional view of a high-pressure miniature switch according to an example of the present disclosure; and  
         [0012]      FIG. 3  is an exploded view of a high-pressure miniature switch according to an example of the present disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0013]     In describing examples and preferred embodiments in connection with the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.  
         [0014]     An example of a pressure switch which avoids the disadvantages of convention pressure switches includes a pressure detection mechanism coupled to a contact driving mechanism, a first terminal, and a second terminal coupled to a snap action blade. The first terminal has a first contact attached thereto, and the snap action blade of the second terminal has a second contact coupled thereto. The second contact is normally (that is, when no force is being applied to the snap action blade) in electrical contact with the first contact. When the pressure detection mechanism detects a pressure media at or above an actuation pressure level, the pressure detection mechanism causes the contact driving mechanism to drive the snap action blade into a deflected position whereby the second contact becomes no longer in electrical contact with the first contact. An output of the switch through the terminals switches when the electrical contact between the first contact and the second contact is discontinued by the deflection of the snap action blade. The combination of the pressure detection mechanism and the contact driving mechanism isolates the pressure media from the remainder portions of the pressure switch, including in particular the snap action blade.  
         [0015]     The pressure detection mechanism may be any of the known pressure detection devices. One example of a pressure detection mechanism is a diaphragm configured to detect pressure media through a pressure channel. The diaphragm may be mechanically coupled to a plunger assembly which actuates the snap action blade in response to force applied to the diaphragm.  
         [0016]     Such an example of a pressure switch  10  will be discussed with reference to  FIG. 1 . Electrical switching of the switch  10  occurs when a force is applied to a rubber diaphragm  12  which is coupled to a lower (or bottom) plunger portion  14 . The plunger also includes an upper portion  18  complementary to the lower portion  14 .  
         [0017]     A first terminal  26  carries a fixed contact  28 . A common terminal  30  has a snap action blade  32  attached thereto with a movable contact  34  attached thereto. The terminals  26  and  30  are securely held between upper plunger portion  18  and lower plunger portion  14 . The moveable contact  34  is normally (that is, when little or no force is applied to the diaphragm) in a closed position such that it is in contact with the fixed contact  28 .  
         [0018]      FIG. 2  shows in a cross-sectional view an illustration of an example of operation of the combination of the contacts and the snap action blade. In  FIG. 2 , the pressure-actuated switch  10  is shown with its components installed in a casing (as it typically will be in operation). The casing includes an upper cover portion  40  arranged on a lower or base portion  42  of the casing. The diaphragm is held between the base portion  42  and a stem  44 . The switch elements are protected from the pressure media by the casing, with the diaphragm portion  12  being exposed to the external environment via channel  48  in the stem  44  so that it may be subjected to applied force from the pressure medium. The diaphragm in the example of  FIG. 2  is installed in the lower base portion  42  in a plate-like element which forms a cover for the bottom of the case.  
         [0019]     As seen in  FIG. 2 , the movable contact  34  mounted on the snap action blade  32  is in contact with the fixed or normally closed contact  28  that is connected to the terminal  26 .  
         [0020]     A spring  20  is preferably included to abut an upper surface of the upper plunger portion  18 . The spring  20  provides a spring force against the plunger that is controlled by a threaded screw  22 . The threaded screw  22  may be adjusted by use of a nut  24  threaded onto the screw  22  such that the spring force is increased or decreased depending on the desired pressure at which the pressure switch  10  is to respond.  
         [0021]     The screw  22  in the example of  FIG. 2  is a socket head cap screw that is threadedly engaged in the nut  24  and is captured in the upper cover portion  40 . Upon turning the screw  22 , the force of spring  20  on the upper (or top) plunger portion  18  is changed, which in turn changes the amount of force needed to be exerted on the diaphragm  12  and thereby on the lower (or bottom) plunger portion  14  to cause the snap action blade  32  to change position. In the operations of the switch shown in  FIGS. 1 and 2 , when the deforming force of the rubber diaphragm  12  causes the snap action blade  32  to deflect, electrical switching occurs in a circuit connected to terminals  26  and  30 . The snap action blade mechanism configured as shown in  FIG. 2  is called a “snap over center” mechanism. The snap over center mechanism creates a concavo-convex portion on the snap action blade, allowing the snap action blade to deflect when force from diaphragm  12  is applied to the snap action blade. By putting the pivot point, shown generally at  46  in  FIG. 2 , off center, the snap action blade results in a pressure hysteresis response. That is, the actuation pressure level at or above which the switch actuates differs from the deactuation pressure level at or below which the switch deactuates by the value of the pressure hysteresis. Adjusting screw  50  can be used to change the pressure hysteresis response value by adjusting the stopping point for the snap over center mechanism.  
         [0022]     When an optional spring assembly is provided, the pressure level at which the switch actuates can be controlled by adjusting the screw  22  to change the bias force of the compression spring  20 . The bias force is translated through the upper (or top) plunger portion  18  to preload the snap action blade  32 , thereby establishing the threshold pressure at which the switch actuates.  
         [0023]     The diaphragm  12  expands in response to applied force from the external pressure and acts in response to such pressure to drive the lower plunger portion  44  towards the snap action blade  32 . The diaphragm, after being installed in the housing formed by the base  42  and the stem  44 , is retained within the housing such that the diaphragm  12  is positively captured.  
         [0024]      FIG. 3  shows the switch assembly including housings in an exploded view. The fixed contact  28  fits into a suitable aperture (not shown) in the first terminal  26 . In addition, the snap action blade  32  is captured between the upper (or top) plunger portion  18  and the lower (or bottom) plunger portion  14 , and is actuated by the flexing of the diaphragm  12 . The lower base  42  and the stem  44  are held together by fasteners (not shown) to form the housing.  
         [0025]     A high pressure switch according to this disclosure has many uses. For example, it can be used in an air compressor to shut-off the compressor motor when a maximum tank pressure is achieved and to start the compressor motor once the tank pressure falls below a predetermined level. In that regard, a high pressure switch having a construction similar to that described herein can be configured for switching action in the range of 50 PSIG to 200 PSIG. By suitably arranging the snap action blade, the differential between the actuation point and the deactuation point can be set to be approximately 25 to 30 PSIG. Furthermore, by providing a switch in which the contacts can be quite robust (such as provided in the present disclosure), the switch can switch between 15 and 20 amperes. The switch can be configured in a preferred embodiment as a miniature (or micro) high pressure switch, for example, dimensioned at approximately 1.5″ OAL and 1.5″ diameter.  
         [0026]     The above specific examples and embodiments are illustrative, and many variations can be introduced on these embodiments without departing from the spirit of the disclosure or from the scope of the appended claims. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.