Abstract:
A pneumatic actuator canister body employs a press fit cup received over an end portion of the canister to engage mounting studs extending through apertures in the end wall of the body and an end plate internally engaging the end wall. Heads of the studs are constrained between the end plate and a piston plate for the internal actuator spring.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of pneumatic actuators and, more particularly, to a canister employing a closely fitting end cup receiving the canister body housing the actuator. 
     BACKGROUND OF THE INVENTION 
     Pneumatic actuators are used for various duties where relatively high reaction speed, simple devices are needed for linear or cable actuation. One such use has been the control of wastegates and variable nozzle devices for turbochargers. Numerous designs exist for such actuators including those disclosed in U.S. Pat. No. 4,893,474 TURBOCHARGER WITH DUAL FUNCTION ACTUATOR, U.S. Pat. No. 5,172,552 TURBOCHARGER WITH FLEXIBLE CABLE WASTEGATE OPERATING LINKAGE, U.S. Pat. No. 5,487,273 TURBOCHARGER HAVING PNEUMATIC ACTUATOR WITH PILOT VALVE, U.S. Pat. No. 5,746,058 ADJUSTABLE ACTUATOR FOR A TURBOCHARGER, U.S. Pat. No. 5,787,591 TURBOCHARGER ACTUATOR WITH ROLLING O-RING, U.S. Pat. No. 6,155,048 ACTUATOR FOR A TURBOCHARGER. 
     A typical configuration for a prior art actuator is shown in FIG.  1 . The actuator has a canister  10  having a cylindrical body  12  and an end wall  14 . A spring  16  engaging a piston  18  which is covered by and/or attached to a diaphragm  20  to linearly position a rod  22  to provide the actuating mechanism. The actuator canister incorporates a end cap  24  which includes a fitting  26  for attachment of the pneumatic source. The end cap is crimped to the canister body in a joint  28  which also constrains and seals the peripheral circumference of the diaphragm. The spring is constrained opposite the piston by a spring plate  30 . The end wall of the canister is strengthened with a plate  32  inserted between the end wall and spring plate. The spring plate also constrains the seal  34  surrounding the rod. 
     Attachment of the canister to a bracket or other mounting means is accomplished using studs  36  which are held in a mounting plate  38 . The mounting plate is welded to the end wall, either with a continuous circumference weld or with spot or projection welds. In operation, the actuator is subjected to significant cyclical loads which result in a high risk of fatigue in the weld or canister wall resulting in cracking and failure of the actuator. 
     It is, therefore, desirable to have an actuator canister which eliminates the required welding of a mounting plate to the end wall, both for elimination of the fatigue cracking failure mode and as a cost reduction by elimination of the welding requirement. 
     SUMMARY OF THE INVENTION 
     A pneumatic actuator containing the present invention incorporates a canister body having a substantially cylindrical side wall and an end wall. The end wall has multiple apertures arranged around a central aperture. A spring engages a piston which is attached to a diaphragm and to an actuating rod for pneumatic actuation. The diaphragm is attached to the canister wall for the pneumatic seal and the rod extends through the central aperture. 
     A cup is sized to closely receive an end portion including the end wall of the canister body. The cup has matching apertures aligned with the apertures in the end wall and a second central aperture through which the rod extends. An end plate is inserted within the canister body and abuts the end wall. The end plate also has apertures aligned with the apertures in the end wall and a central aperture through which the rod extends. Attachment studs having a shank and head provide the means to attach the actuator to a bracket or other support device. The shank of each stud is inserted through one of the multiple apertures in the end plate, end wall and cup and the head engages the end plate. 
     A spring plate including a substantially circular face engages the heads of the studs to urge the studs against the end plate. An outer cylindrical upset portion of the spring plate engages the spring at a second end and an inner cylindrical portion having a flange extending radially inwardly distal from the face constrains a seal for the rod. The seal rests against the end plate around the central aperture. The inner cylindrical portion of the spring plate constrains the seal radially and the spring plate flange constraining the seal axially in cooperation with the end plate. A standard fitting in the canister end opposite the cup provides a means for supplying pneumatic pressure to the diaphragm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 is a section view of a prior art pneumatic actuator with a conventional welded canister; 
     FIG. 2 is a side section view of an actuator employing the present invention with mounting studs; and, 
     FIG. 3 is a pictorial view of an exemplary installation of an actuator incorporating the present invention on a bracket for a turbocharger control device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, an embodiment of the actuator incorporating the present invention has a canister  40  having a cylindrical body  42  and an end wall  44 . A spring  46  engaging a piston  48  which is covered by and attached to a diaphragm  50  linearly position a rod  52  as the actuating operator in response to pneumatic pressure. The actuator canister incorporates an end cap  54  which includes a fitting  56  for attachment of the pneumatic source. The end cap is crimped to the canister body in a joint  58  which also constrains and seals the peripheral circumference of the diaphragm. 
     The end wall has multiple holes  60  typically arranged in a circular pattern around the central aperture  62  through which the rod passes. A cup  64  is sized to closely receive an end portion including the end wall of the canister body. The cup has matching apertures  66  aligned with the apertures in the end wall and a second central aperture  68  through which the rod extends. An end plate  70  is inserted within the canister body and abuts the end wall. The end plate also has apertures  72  aligned with the apertures in the end wall and a central aperture  74  for the rod. Attachment studs  76  each having a shank  78  and head  80  provide the means to attach the actuator to a bracket or other support device. The shank of each stud is inserted through one of the multiple apertures in the end plate, end wall and cup and the head engages the end plate. In the embodiment shown, the end plate incorporates a cylindrical relief  82  around each aperture in the plate, which is sized to receive the head of the stud. 
     The cup is press fit onto the end portion of the canister and for additional strength in certain embodiments is brazed to the cylindrical wall of the body. This brazing operation is significantly simpler that prior art welding requirements and is achieved by locating a ring of brazing material around the canister and the cap with a process step running the canister through a brazing oven. 
     A spring plate including a substantially circular face  84  engages the heads of the studs to urge the studs against the end plate. In the embodiment shown, the relieved holes receiving the stud heads allow the spring plate to also engage the plate directly to further stabilize the actuating mechanism and the studs. An outer cylindrical upset portion  86  of the spring plate engages the spring at a second end. In the embodiment shown, the upset portion is a channel shape to engage the interior of the cylindrical wall of the canister body to center the spring plate. 
     The spring plate also includes an inner cylindrical portion  88  having a flange  90  extending radially inwardly opposite from the face of the plate constrains a seal  92  for the rod. The seal rests against the end plate around the central aperture. The inner cylindrical portion of the spring plate constrains the seal radially and the spring plate flange constraining the seal axially in cooperation with the end plate. 
     Attachment of the canister to a bracket or other mounting means is accomplished using the studs. As shown in FIG. 3, a mounting bracket  94  for the actuator on a turbocharger  96  engages the studs which can be threaded to accept a nut  98  or the shank can be fixed with star retainers or other frictional retainers. The bracket is, in turn, connected to the case of the turbocharger with bolts  100 . An extension  102  connects the actuating rod through a linkage  104  to the turbocharger wastegate mechanism. 
     Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.