Abstract:
A pressure switch comprises a switch lever  8  equipped with a switch contact and a working shaft contact portion  82 , and a working shaft  6  driven by the pressure of a fluid so as to close or open said switch contact, wherein said contact portion  82  has a spherical surface with a radius of curvature in the range of 2.0 mm to 0.5 mm.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a structure of a pressure switch mainly used in a refrigeration cycle of a cooling device mounted on a vehicle, which is set to stop a compressor and protect the system when a refrigerant pressure in the refrigeration cycle becomes either more than or equal to a predetermined pressure or less than or equal to a predetermined pressure. 
     DESCRIPTION OF THE RELATED ART 
     A conventional pressure switch of this kind is shown in FIGS. 2 and 3. 
     FIG. 2 is a vertical cross-sectional view showing the structure of a pressure switch. FIG. 3 is an enlarged cross-sectional view showing a portion of FIG. 2 encircled by a broken line A. In both drawings, the pressure switch is shown in an inverted position from the actual position of use. 
     In the drawing, the pressure switch  100  comprises a housing  1  including an inner space, a switch case  2 , a diaphragm  3 , a first snap disk  41 , a second snap disk  42 , a receive member  5 , a working shaft  6 , a first switch lever  7  and a second switch lever  8 . 
     The housing  1  comprises a passage  11  equipped to one end for introducing fluid, an inner space  12  opening to the other end, a stopper  15  for fixing a seal member  29 , and a seal support member  16 . 
     The seal member  29  is formed as an annular elastic body formed for example of nitrile butadiene rubber, and the member is supported by the seal support member  16 . 
     The switch case  2 , made of an electric insulating material such as a polybutyl terephthalate resin reinforced by glass fiber, has an opening portion formed to one end thereof which is mechanically press-fixed to the other end of the housing  1  with the seal member  29  placed therebetween. 
     The switch case  2  comprises an inner space  21  with one end being opened and to which a pressure switch mechanism is placed, and an opening  22  formed on the other end for electrical connection. The inner space  21  and the opening  22  are separated by a partition wall. 
     A guide wall  24  for guiding a receive member  5  is formed around the inner space  21 . On the guide wall  24  in the partition wall-side is formed a limiting step  25  which protrudes inwardly so as to limit the movement of the receive member  5  toward the partition wall. 
     Moreover, a supporting step  26  with a smaller diameter for supporting the rim portion of a second snap disk  42  is formed inwardly on the partition wall-side of the limiting step  25 . 
     The pressure switch mechanism stored inside the inner space  21  of the switch case  2  comprises a diaphragm  3  made for example of polyimide resin film, a first snap disk  41  made of steel, a receive member  5  made for example of polybuthylene terephthalate (PBT) resin, a second snap disk  42  made of steel, a working shaft  6  made for example of ceramic, a first switch lever  7 , a second switch lever  8 , and a pair of terminals  9 . 
     The peripheral of the diaphragm  3  in the pressure switch mechanism is mounted to an end  27  of the surrounding wall of the inner space  21  in the switch case  2 , which is airtightly fixed through a seal member  29  to the seal support member  16  equipped to the housing  1 . 
     The receive member  5  is disk-shaped, and on the rim portion of the surface of the disk is formed an outer wall  51  protruding upwards. A penetrating hole  52  is formed to penetrate through the front surface and the back surface of the receive member at the center area, and a central protrusion  53  is formed to protrude around the penetrating hole  52  on the back surface. 
     The receive member  5  is stored in the inner space so that it slides in the central axis direction of the switch case, guided by the guide wall  24  of the switch case  2 . 
     The first snap disk  41  is placed so as to contact the diaphragm  3 , being supported by the surface of the receive member  5 , and further being positioned by the outer wall  51 . The working shaft  6  is stored inside the penetrating hole  52  of the receive member  5  and is contacted to the back surface of the first snap disk  41 , and it is further extended toward the second switch lever  8 . 
     To the exterior of the central protrusion  53  of the receive member  5  is assembled a central opening  43  formed to the center of the convex-shaped second snap disk  42 . The end of the central protrusion  53  is placed opposite to the center surface of the first switch lever  7 . 
     The working shaft  6  is made for example of ceramic, and the peripheral area of the end surface thereof may be chamfered. The chamfering may either be linear, as is shown in the drawing, or may be arc-like. 
     The first switch lever  7  is formed of an elastic body having conductivity, such as phosphorus bronze, and one end portion of the lever  7  is fixed to the surrounding wall of the inner space  21 . A contact  71  is equipped to the other end of the first switch lever  7 , and an opening  72  is formed to the intermediate area of said one end and the other end, through which the working shaft  6  penetrates. 
     The second switch lever  8  is formed of an elastic body having conductivity, such as phosphorus bronze, and one end portion of the lever  8  is fixed to the surrounding wall of the inner space  21 . A contact  81  is equipped to the other end of the second switch lever  8 , and a contact portion  82  is formed to the intermediate area between said one end and the other end, to which the end surface of the working shaft  6  touches. 
     One pair of terminals  9  are connected to the first switch lever  7  and the second switch lever  8  respectively, which penetrate through the partition wall  23  and are taken out from the opening  22 . 
     The first switch lever  7  and the second switch lever  8  constitute the switch mechanism. 
     As shown in FIG. 3, the contact portion  82  equipped to the second switch lever  8  is formed for example through press-working, and the surface of the contact portion  82  is formed as a flat surface  89 . 
     The operation of the pressure switch of the prior art will now be explained. 
     The fluid pressure loaded to the diaphragm  3  through the fluid passage  11  pushes the diaphragm  3  downward, and the receive member  5  supporting the first snap disk  41  is pushed down. When this pressure reaches 0.25 MPa for example, the second snap disk  42 , which is originally in its first position in which the disk protrudes toward the diaphragm (as shown in the drawing), is shifted to a second position in which the center portion of the disk is displaced toward the partition wall. When the snap disk  42  is displaced, the receive member  5  is pushed by the fluid pressure and moves toward the partition wall, and the central protrusion  53  presses the first switch lever  7 , thereby making the switch. 
     The receive member  5  being moved toward the partition wall will bump against the limiting step  25  formed to the inner wall of the switch case  2 , which limits further movement of the receiver member toward the partition wall even when fluid pressure rises. Therefore, the second snap disk  42  will not receive further force, and the disk  42  will be free from any unnecessary deformation which may damage its function. 
     When pressure is reduced and the fluid pressure lowers to 0.21 MPa, the second snap disk  42  shifts from the second position to the first position (shown in the drawing), the receive member  5  moves toward the passage  11 , and the central protrusion  53  will no longer be pressed against the first switch lever  7 . Thus, the switch is opened. 
     When fluid pressure rises to 2.7 MPa during the state the receive member  5  is bumped against the limiting step  25  and the switch is made, the first snap disk  41  shifts from the first position in which the disk is protruded toward the diaphragm (as shown in the drawing) to the second position in which the center portion protrudes toward the partition wall. The displacement is transmitted through the working shaft  6  to the second switch lever  8 , which is pushed down, thus opening the switch. 
     As explained, the prior art pressure switch is operated to make the switch at a predetermined pressure, and to open the switch at two pressure values, one higher than and one lower than the predetermined pressure. 
     SUMMARY OF THE INVENTION 
     The prior art pressure switch  100  as explained above has a contact portion  82  formed to the second switch lever  8  with a flat surface  89 . When the accuracy of the members forming the pressure switch is poor, or the accuracy of assembling the switch structure is poor, the end surface of the working shaft  6  may not be placed parallel to the surface of the contact portion  82  as shown for example in FIG. 4, which causes an offset of the shaft  6 . 
     FIG. 4 is a drawing showing a typical state of contact of the working shaft and the contact portion formed to the switch lever, in which the continuous line shows the state where the working shaft is not positioned parallel to the surface of the contact portion (offset), and the chain double-dashed line shows the state where the working shaft contacts the surface of the contact portion in a parallel position. As could be seen from FIG. 4, it is clearly preferred that a wide area of the end surface  61  of the working shaft  6  touches the surface  89  of the contact portion  82  formed to the second switch lever  8 . 
     However, when the accuracy of assembly of the switch or the accuracy of the members is poor, the center axis  63  of the working shaft  6  is likely to tilt and not cross the surface  8  of the contact portion  82  perpendicularly, as shown by the continuous line of FIG.  4 . In such case, the working shaft  6  will be offset, and only a point  62  on the peripheral of the end surface  61  of the shaft  6  will contact the surface  89  of the contact portion  82 . 
     When offset occurs, only one point  62  on the peripheral of the end surface  61  of the shaft  6  contacts the surface  89  of the contact portion  82 , and point  62  will receive collected pressure repeatedly. After a long term of use, a portion of the point  62  may be chipped and lost. 
     When such problem occurs, not only will the accuracy of the switch operation be damaged, but the function of the contact may be ruined as well. 
     The present invention is aimed at solving the above problems. The object of the present invention is to provide, without changing the design of the prior art pressure switch greatly, a pressure switch which may be assembled easily without having to unnecessarily improve the accuracy of assembly of the members, and which has a high reliability. 
     In order to achieve the above object, the present invention discloses in claim  1  a pressure switch comprising a switch lever equipped with a switch contact, and a working shaft driven by fluid pressure to open or close said switch contact, said switch lever including a contact portion to which said working shaft contacts, wherein said contact portion is formed to have a spherical surface. 
     The present invention discloses in claim  2  a pressure switch according to claim  1 , wherein said spherical surface has a radius of curvature in the range of 2.0 to 0.5 mm. 
     The present invention discloses in claim  3  a pressure switch according to claim  1 , wherein said spherical surface has a radius of curvature in the range of 2.0 to 1.5 mm. The present invention discloses in claim  4  a pressure switch according to claim  1 , wherein the area that said working shaft contacts said spherical surface is positioned inwardly from the end portion of said working shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged cross-sectional view showing the structure of the main portion (the shapes of the working shaft and the switch lever) according to one embodiment of the pressure switch of the present invention; 
     FIG. 2 is a vertical cross-sectional view explaining the structure of the pressure switch; 
     FIG. 3 is an enlarged cross-sectional view showing in part the structure of the working shaft and the contact portion of the switch lever in the pressure switch; and 
     FIG. 4 is an enlarged cross-sectional view showing in part the contact status of the working shaft and the contact portion of the switch lever in the pressure switch of the prior art. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiment of a pressure switch according to the present invention is explained with reference to FIG.  1 . FIG. 1 is a cross-sectional view showing the structure of the main portion of a pressure switch according to the present invention, wherein the drawing shows in enlarged view a working shaft  6  and a contact portion  82  equipped to a switch lever  8 . Other structures of the present pressure switch not shown in the drawing are the same as those of FIG.  2 . 
     As shown in FIG. 1, the pressure switch  100  of the present invention characterizes in that a contact portion  82  formed to a second switch lever  8  to which the working shaft  6  contacts is formed to have a shape different from that of the prior art pressure switch. 
     As shown in FIG. 1, the contact portion  82  to which the working shaft  6  contacts is formed to have a spherical surface. By forming the surface of the contact portion  82  to a spherical shape, an end surface  61  of the working shaft  6  will contact a spherical surface  83  of the contact portion  82  at a contact point  64 , even when a center axis  63  of the working shaft  6  is tilted due to low assemble accuracy and the like. 
     In other words, the contact point  64  is positioned at a point in which a line  85 , drawn from a center point  84  of the spherical surface parallel to the center axis  63  of the tilted working shaft  6 , crosses the spherical surface  83 . Since the contact point  64  is formed inwardly by distance D from a peripheral  62  of the end surface  61  of the working shaft  6 , no stress will be concentrated around the peripheral  62  area. Therefore, even when the accuracy of assembly is relatively low, the peripheral  62  of the working shaft  6  will not be chipped. 
     Now, the result of the studies performed by the present inventors related to the chipping (breaking) of the working shaft  6  with regard to the radius of curvature of the spherical surface  83  of the contact portion  82  will be explained. 
     With reference to FIG. 1, a test is performed to study the status of the chip generated around the peripheral  62  of the end surface  61  of the working shaft  6 , with regard to the relation between the radius of curvature of the spherical surface  83  of the contact portion  82  and the distance D between the contact point  64  and the peripheral  62  of the working shaft  6 , on condition that the gap between the center axis  63  of the working shaft  6  and the center axis of the contact portion  82  is 0.1 mm. 
     As a result, when the radius of curvature is 2.0 mm or less, the peripheral  62  of the end surface  61  of the working shaft  6  will not be chipped. On the other hand, when the radius of curvature is less then 0.5 mm, it is discovered through experiment that the accuracy of processing the contact portion  82  through press-forming is lowered, and further, the contact portion is likely to be abraded through repeated contact with the shaft, since the area of the contact portion  82  is reduced. 
     That is, as the contact point between the working shaft  6  and the contact portion  82  moves inwardly from the peripheral  62  of the working shaft  6 , in other words, as the contact point approaches the center axis  63  of the shaft  6 , the possibility of pressure being concentrated to the peripheral  62  is reduced, and the possibility of a chip occurring to the shaft  6  is also reduced. However, since the peak area of the contact portion  82  is reduced, the area of contact between the shaft  6  and the contact portion  82  is also reduced, which may cause abrasion of the contact portion  82 . 
     Based on the above studies, the inventors have found that the radius of curvature of the spherical surface of the contact portion  82  equipped to the switch lever  8  should preferably be in the range of 2.0 to 0.5 mm, and from the point of view of preventing abrasion and to improve workability, the radius of curvature should be in the range of 2.0 to 1.5 mm. 
     As explained above, according to the present invention, the peripheral  62  of the end surface of the working shaft  6  will not be chipped even when the working shaft is tilted due to low accuracy in assembling the pressure switch. Therefore, a highly reliable pressure switch which may be assembled easily is provided by the present invention. 
     In the above explanation, a two-action pressure switch is utilized. However, the present invention is not limited to such example, and it may be applied to other pressure switches such as a three-action pressure switch. 
     As explained, the present invention provides a pressure switch which is easy to assemble, and with high reliability, since the working shaft will not be chipped through use. 
     Moreover, the present invention provides a pressure switch capable of an accurate switching operation, having a design not greatly changed from that of the prior art pressure switch.