Abstract:
A diaphragm for a turbo charger actuator includes a layer of fabric having upper and lower surfaces. A first layer of elastomeric material coats at least a portion of the upper surface of the fabric to prevent pressurized air from passing through. A second layer of elastomeric material coats at least a portion of the lower surface of the fabric to form a plurality of ribs thereon. The ribs reinforce the fabric and prevent dirt or other abrasive particles from wearing holes in the elastomeric material and the fabric. When the fabric has woven strands, the ribs protect some of the points where the strands intersect in key areas on the diaphragm.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to diaphragms. In particular, this invention relates to a diaphragm for an actuator connected to an engine turbo charger. The invention may also be applicable to other diaphragm applications. 
     Diaphragms made of fabric coated with elastomeric material are known. In automotive use, such diaphragms are exposed to a high number of pressure cycles and a significant amount of dirt from the surrounding environment. Dirt often collects on the underside of the diaphragm. Abrasive particles in the dirt tend to cut or abrade the crossing fibers or strands of the fabric, which allows the air pressure from the pressure side of the actuator to cause a hole to form through the diaphragm. The fabric surrounding the hole is then required to hold the air pressure. This tends to weaken the fabric and lead to its premature failure, making the actuator ineffective. Therefore, there is a need for a more dirt-resistant diaphragm for such actuators. 
     A primary objective of the present invention is the provision of a dirt-resistant diaphragm for an actuator. 
     Another objective of this invention is the provision of an actuator diaphragm having ribs formed thereon for additional strength and resistance to leaks. 
     Another objective of this invention is the provision of an actuator diaphragm having ribs formed on its low pressure or fabric side. 
     Another objective of this invention is the provision of an elastomer-coated, fabric-based diaphragm having ribs thereon which improve the penetration and adherence of elastomer and the life of the diaphragm. 
     Another objective of this invention is the provision of a diaphragm with ribs thereon which tend to channel contaminants away from the zone or zones of the diaphragm where failures can sometimes occur. 
     Another objective of this invention is the provision of an actuator having ribs which extend beyond the piston contact area. 
     Another objective of this invention is the provision of an actuator diaphragm having a greater life, in terms of pressure cycles, than existing actuator diaphragms. 
     Another objective of this invention is the provision of an actuator diaphragm that is economical to produce, durable, and reliable in use. 
     These and other objectives will be apparent from the drawings, as well as from the description and the claims which follow. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a diaphragm. In particular, this invention relates to a diaphragm for a turbo charger actuator. The diaphragm includes a layer of fabric having upper and lower surfaces. A first layer of elastomeric material coats at least a portion of the upper surface of the fabric to prevent pressurized air from passing through. A second layer of elastomeric material coats at least a portion of the lower surface of the fabric to form a plurality of ribs thereon. 
     The ribs reinforce the fabric and prevent dirt or other abrasive particles from wearing holes in the elastomeric material and the fabric. When the fabric has woven strands, the ribs protect some of the points where the strands intersect in key areas on the diaphragm. The ribs also channel contaminants away from the zone(s) of the diaphragm where failures can sometimes occur. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view of a turbo charger waste gate valve actuator equipped with the diaphragm of this invention; 
     FIG. 2 is a perspective view of one embodiment of the diaphragm of this invention; 
     FIG. 3 is a central vertical sectional view of the diaphragm of FIG. 2; 
     FIG. 4 is a plan view of the interior surface of the diaphragm of this invention shown in FIG. 2; 
     FIG. 5 is an enlarged view of the area designated  5 — 5  in FIG. 3; 
     FIG. 6 is a sectional view, taken along line  6 — 6  in FIG. 7, of another embodiment of the present invention in which the diaphragm has an elevated or convoluted brim; and 
     FIG. 7 is a plan view of the interior surface of the diaphragm of FIG.  6 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The diaphragm of this invention is generally designated by the reference numeral  10  in the drawings and the description below. In FIG. 1, the diaphragm  10  is shown installed on an actuator  100  having a piston  102  connected to a turbo charger waste gate (not shown) by an actuator rod  104 . A housing  106  encloses the piston  102 , and has housing portions  108 ,  110  that are joined along a continuous seam  112 . The diaphragm  10  is searingly interposed between the housing portions  108 ,  110  along the seam  112  by crimping, clamping, or other known methods. 
     A pressure inlet  114  is provided through the upper housing portion  108  and puts the chamber  116  above the diaphragm  10  in fluid communication with the turbo charger outlet (not shown). The diaphragm  10  has a downwardly directed or interior surface  12 . The piston  102 , urged by a spring  118 , engages the interior surface  12  to define a piston contact area thereon. The diaphragm  10  also includes an upwardly directed or exterior surface  14  on which the pressure in a chamber  116  acts. 
     Thus, during the operation of the turbo charger and the associated actuator  100 , the diaphragm  10  reacts to the pressure in the chamber  116  and moves the piston  102  and the attached actuator rod  104  accordingly against the spring  118 . When the force of the spring  118  is overcome, the actuator rod moves vertically and thereby opens the waste gate valve to modulate the turbo charger pressure. 
     Having briefly described the environment in which the diaphragm is used, greater detail regarding the diaphragm itself will now be provided by reference to FIGS. 2-5. FIG. 2 shows that the diaphragm  10  is shaped like a cup or a top hat, with interior (lower) and exterior (upper) surfaces  12 ,  14 . The diaphragm  10  has a substantially flat crown or top  16  with a generally circular periphery  18  supported by continuous side wall  20 . The side wall  20  connects or joins the periphery  18  of the top  16  with a generally circular outwardly projecting brim  22  which terminates at an outer periphery  26 . The brim  22  and the side wall  20  are joined along a continuous inside fillet or radius  24  when viewing the exterior surface  14 . The diaphragm  10  is substantially symmetrical about a central axis  28 . Shapes other than that just described will not detract from the invention, provided that the shape is selected to generally match the shape of the piston  102 . 
     Referring to FIG. 4, the diaphragm  10  has a plurality of angularly spaced ribs  30  on the interior surface  12 . The ribs  30  extend vertically along the side wall  20 , protruding therefrom. The ribs  30  have an outer end  32  and a lower end  34 . Preferably, the outer ends  32  of the ribs  30  extend radially outward along the inside radius  24  and onto the brim  22 , as shown. Thus, at least some of the ribs  30  extend through the inside radius  24 . Preferably, the ribs  30  extend 360 degrees around the central axis  28 . The ribs  30  are also equally spaced along the inner circumference of the side wall  20 , a full 360 degrees around the central axis  28 . For example, 180 ribs are angularly spaced at intervals of two degrees between centers in FIGS. 2-5. 
     Referring to FIGS. 3 and 5, the diaphragm  10  includes a flexible fabric layer  36 . The fabric layer  36  is formed by a plurality of crossing, preferably woven, strands  37 . The strands  37  extend across each other at intersections  38 , leaving interstices or voids  40  between the intersecting strands  37 . Nylon or Nomex™ (3D604) is the preferred material for the fabric layer  36  of the diaphragm  10  because tightly woven fabrics such as these tend to be able to hold low to moderate air pressure and can easily be molded into specific shapes. The fabric layer  36  is approximately 0.005-0.015 inch thick, more preferably 0.009 inch. The diaphragm fabric is equivalent to Mohawk HT-92. 
     A first elastomeric layer  42  covers at least the piston contact area, and more preferably completely covers the exterior surface  14  or pressurized side of the side of the diaphragm  10 . The first layer  42  is approximately 0.010 to 0.050 inch thick, more preferably 0.017-0.042 inch. A second elastomeric layer  44  at least partially covers the interior surface  12  so as to form the ribs  30 . In the preferred embodiment of FIGS. 2-5, the layer  44  is approximately 0.011 inch thick so as to yield ribs  30  protruding approximately 0.011 inch from the side wall  20 . The elastomer DE42460 (fluorosilicone), available from Dow Chemical Co., has been found to have good mold ability, effectively seal the voids  40  in the fabric layer  36 , and provide suitable ribs  30 . With the geometry shown and the thicknesses stated above, the diaphragm  10  can be molded economically in a single pour. 
     Another embodiment of this invention appears in FIGS. 6-7 and is similar to the embodiment of FIGS. 2-5, but is convoluted around the inside radius. The radius  24 A is much smaller than the radius  24  in the embodiment of FIG.  3 . Consequently, the brim  22 A is elevated above the plane containing the lowermost portion of the inside radius  24 A. This structure is believed to provide easier rolling and unrolling of the diaphragm  10 A as the pressure forces diaphragm  10 A (and the piston  102 ) downward. The ribs  30 A are still equally spaced angularly, with approximately two degrees between centers. Other structural features are labeled similar to FIGS. 2-5, but the suffix “A” is added. 
     The diaphragms  10 ,  10 A are fabricated according to the following process. A sheet of fabric is placed in a performing mold. Depending on the relative size of the diaphragm to the sheet of fabric and the mold dimensions, several diaphragms can be molded and cut from each sheet. Next, the preformed fabric layer  36  is transferred to a compression molding machine where one or more rubber pellets are inserted. Negative impressions of the ribs  30 ,  30 A have been formed in the rubberizing mold. When the mold and/or material is held at an elevated temperature sufficient to melt the elastomeric material, the material flows and/or is injected into all voids in the mold to form the first and second elastomeric layers, as well as the ribs on the second layer. The rubberizing mold can have multiple cavities like the performing mold. Finally, the molded diaphragms  10 ,  10 A are transferred to a trim tool where they are cut to final size. 
     During molding, the diaphragms  10 ,  10 A tend to exhibit greater elastomer penetration into the fabric. The ribs  30 ,  30 A tend to push the fabric side or layer  36  away from the mold slightly so as to allow more elastomer to penetrate and adhere to the fabric layer  36  from both sides, even in areas where the ribs do not extend. 
     In use, actuator diaphragms tend to eventually fail around the crevice or zone near where the top edge of the piston  102  contacts the diaphragm  10 ,  10 A. Applicants have discovered that abrasion from dirt or other contamination that collects in the crevice often causes such failures. The ribs  30 ,  30 A provide natural routes or channels through which the contaminants escape from the zone around the crevice as the diaphragm flexes. 
     Therefore, the present invention at least achieves its stated objectives. 
     In the drawings and specification there has been set forth preferred embodiments of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only, and not for purposes of limitation. Changes in the form and proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims.