Abstract:
A spring brake actuator having a push rod plate and a diaphragm is provided. A rim projects from the diaphragm for engaging a housing containing the push rod plate. A sidewall is connected to the rim, which is connected to a bottom surface, forming an outer diameter of the diaphragm. Flanges, perpendicular to the diaphragm, extend from the diaphragm forming an inner diameter for which the push rod plate is inserted into. An adhesive is placed between the diaphragm and the push rod plate, wherein the adhesive maintains an attachment and a seal between the diaphragm and the push rod plate keeping the diaphragm and the push rod plate in line with each other.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to braking systems and, more specifically, to brake diaphragms. Even more particularly, the present invention relates to the attachment of the disk brake push rod plate to the diaphragm using an adhesive. 
       BACKGROUND OF THE INVENTION 
       [0002]    Braking systems, such as air brake systems, have generally been used to control movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, trailers, and buses, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles, in combination with the high speeds at which they travel, often requires a braking system which responds rapidly with substantial braking power. One system component which may be instrumental in the operation of air brake systems is the brake actuator. The brake actuator typically provides the necessary force when braking the vehicle. 
         [0003]    Air-operated brake actuators are either piston type or diaphragm type. In the diaphragm type spring brake actuator, two air-operated diaphragm brake actuators are typically arranged in a tandem configuration, which includes an air-operated service brake actuator for applying the normal operating brakes of the vehicle, and a spring brake actuator for applying the parking or emergency brakes of the vehicle. Both the service brake actuator and the spring brake actuator include a housing having an elastomeric diaphragm dividing the interior of the housing into two distinct fluid chambers. On the other hand, the piston brake actuator operates under basically the same principles as above described, except that instead of a diaphragm, a piston with a sliding seal at the outside diameter reciprocates in a cylinder for applying the normal and/or parking brakes of the vehicles. 
         [0004]    In a typical service brake actuator, the service brake section is divided into a pressure chamber and a push rod chamber. The pressure chamber is fluidly connected to a source of pressurized air and the push rod chamber mounts a push rod, which is coupled to the brake assembly, whereby the introduction and exhaustion of pressurized air into the pressurized chamber reciprocates the push rod into and out of the actuator to apply and release the operating brakes. 
         [0005]    In a typical spring brake actuator, the spring brake section is divided into a pressure chamber and a spring chamber. A push rod plate is positioned in the spring chamber between the diaphragm and a strong compression spring, whose opposing end abuts the housing. In one well-known configuration, a push rod extends from the push rod plate, through the diaphragm, into the pressure chamber, and through a dividing wall separating the spring brake actuator from the service brake actuator. The end of the actuator is fluidly connected to the pressure chamber of the service brake actuator. 
         [0006]    When applying the parking brakes, the spring brake actuator pressure is discharged from the pressure chamber and the large force compression spring pushes the push rod plate and the diaphragm toward the dividing wall between the spring brake actuator and the service brake actuator. In this position, the push rod connected to the push rod plate is pushed forward extending into the service section through the dividing center wall applying the parking or emergency brakes and thus forcing the vehicle to stop or remain parked. To release the parking brake, the pressure chamber is closed to the atmosphere and pressurized air is introduced into the pressure chamber of the spring brake actuator which expands the pressure chamber, moving the diaphragm and push rod plate toward the opposing end of the spring brake actuator housing, thereby compressing the strong compression spring. 
         [0007]    One known problem in association with service brake actuators of this design is that the push rod plate of an actuator is known to slip, and to move. During normal weather, the push rod plate may move out of alignment with the diaphragm. During wet weather, water mixed with road oil and dirt migrates between the push rod plate and the diaphragm, and acts as a lubricant. The push rod plate can slide radially out of center position, which can restrict the actuator stroke and/or reduce the force output of the actuator. This presents a problem as the service brake will not work as efficiently as under normal conditions, which can lead to longer stopping distances, and eventual malfunction of the service brake. 
         [0008]    Prior art designs have attempted to solve this problem and provide an improved modification to accommodate misalignment of the push rod plate in the interior surface of the diaphragm of the service brake actuator. Different designs for diaphragms exist to solve this problem. However, prior art designs are limited as they do not efficiently and cheaply keep the push rod plate aligned with the diaphragm. 
         [0009]    Typically, diaphragms for service brake actuators are made from a layer of fabric that forms an integral structure of the diaphragm. Diaphragms in service brake actuators are generally supported at their periphery within a housing of the actuator. Upon introduction of a fluid pressure on one side of the diaphragm, the diaphragm moves a push plate or piston to actuate a braking mechanism. The diaphragm is returned to its normal position when compressed air is released exerting an opposite force on the push rod plate. 
         [0010]    Diaphragms for brake actuators generally are cup shaped with a bottom wall or base merging into a conical sidewall. The conical sidewall terminates at a rim which is clamped between an upper and lower portion of a housing unit. A force is exerted by the diaphragm upon a push rod plate, and the diaphragm is typically in direct contact with the push rod plate. Problems occur when the push rod plate slips laterally with respect to the diaphragm, limiting the direct touching, and proper force placement, between the diaphragm and push rod plate. This can restrict the actuator stroke and/or reduce the force output of the actuator. 
         [0011]    It is thus desirable to develop an attachment of the push rod plate to the diaphragm for a brake actuator that is easily and cheaply manufactured, and that maintains the alignment between the push rod plate and the diaphragm. 
       SUMMARY OF THE INVENTION 
       [0012]    The invention is directed to an adhesive attachment of the push rod plate to the diaphragm for use in a spring brake actuator. The design allows for the push rod plate to be easily and cheaply adhered to the diaphragm without the need for an expensive mechanical connection between the push rod plate and the diaphragm. 
         [0013]    Another object of the present invention is to provide a spring brake actuator having the above characteristics and which is simple in design as compared with known spring brake actuators. 
         [0014]    A further object of the present invention is to provide a spring brake actuator having the above characteristics and which is relatively easy and inexpensive to produce and assemble. 
         [0015]    Still another object of the present invention is to provide a spring brake actuator having the above characteristics and which does not require special machinery to assemble. 
         [0016]    Yet a further object of the present invention is to provide a spring brake actuator having the above characteristics and which can be made of conventional materials. 
         [0017]    These and other objects of the present invention are achieved by provision of a spring brake actuator having a push rod plate adhesively attached to a diaphragm. A brake diaphragm in accordance with the present invention has a projecting rim for engaging a housing containing a piston, a bottom wall having an interior surface for engaging the piston, and a sidewall connecting the projecting rim with the bottom wall. An adhesive is placed between on the diaphragm such that when the push rod plate engages the diaphragm, an adhesive seal is created between the push rod plate and the diaphragm. During operation of the brake by the spring brake actuator, the adhesive maintains a constant attachment between the push rod plate and the diaphragm, keeping both in line with each other. As a result, brake operating is not impaired by a misaligned push rod plate and diaphragm. 
         [0018]    Preferably, a single portion of adhesive is used at the center of the push rod plate to attach the push rod plate to the diaphragm. In a second embodiment, the adhesive covers the entire surface of the push rod plate that is to be attached to the diaphragm. In another preferred embodiment, multiple smaller portions are space around the surface of the push rod plate to be attached to the diaphragm. 
         [0019]    The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a side elevation view, partially in section, of a spring brake actuator in accordance with the present invention; 
           [0021]      FIG. 2  is an enlarged side view of a push rod, push rod plate, and diaphragm of  FIG. 1   
           [0022]      FIG. 3  is an enlarged view of a push rod plate with a single adhesive area; 
           [0023]      FIG. 4  is an enlarged view of a push rod plate with multiple adhesive areas 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The exemplary embodiments of the present invention may be further understood with reference to the following description and the related appended drawings, wherein like elements are provided with the same reference numerals. 
         [0025]    Referring first to  FIG. 1 , a brake actuator  100 , in a double diaphragm spring brake, according to the present invention is shown. It should be noted, while further description relates to a double diaphragm spring brake, the present invention can be used in any braking system containing a diaphragm and a pushrod plate, including a single diaphragm system. The embodiment shown is an air-operated dual diaphragm spring brake actuator  100 , which includes a housing  112  containing a service chamber  114  and a spring chamber  116  in tandem. The service chamber  114  is defined by a cup-shaped service housing  118  and a flange case  120 . The flange case  120  is double cup-shaped and includes a divider wall  122  separating a service side  124  of the flange case  120  from a spring side  126  of the flange case  120 . The service housing  118  is secured to the service side  124  of the flange case  120  using a conventional bolted clamp  128 , or any other of numerous means as are known in the art. An elastomeric service brake diaphragm  130  is clamped in fluid tight engagement between the service housing  118  and the service side  124  of the flange case  120 . The service brake diaphragm  130  contains flanges  190  (further seen in  FIG. 2 ) protruding from the surface of service brake diaphragm  130  forming an inner diameter. Although not shown, an aperture is provided in the flange case  120  for providing communication between a source of compressed air and a portion of the service chamber  114  between the diaphragm  130  and the divider wall  122  of the flange case  120 , also as is known in the art. 
         [0026]    A service push rod assembly including a push rod  132  extends through the service housing  118  into the service chamber  114 , and mounts a service push rod plate  134  at an inner end thereof. The service push rod  132  for a Disc Brake system, (shown) is thrust into a cupped lever arm in a caliper (not shown). The service push rod plate  132  for a Drum Brake system, (not shown) is threaded with a clevis and pin to the lever to actuate the brake. In addition, bolts  136  are provided for mounting the service housing  118  to the vehicle. A service return spring  138  extends between the service housing  118  and the service push rod plate  134  to bias the service push rod plate  134  and thus push the service push rod  132  into the service chamber  114  to release the brake. The service push rod plate  134  is of a diameter slightly smaller than that of the flanges  190  such that the service push rod plate  132  fits into the diameter formed by flanges  190 . The spring biased service push rod plate  134  normally forces the service brake diaphragm  130  against the divider wall  122  of the flange case  120  in the brake release position. 
         [0027]    When air pressure is supplied through the aperture in the service side  124  of the flange case  120  as, for example, when the brakes are applied by a vehicle operator, compressed air is introduced between the service brake diaphragm  130  and the divider wall  122 , thereby forcing the diaphragm toward the service housing  118 . In this manner, the service push rod  132  is extended outwardly of the service chamber  114  to apply braking pressure to the vehicle brakes in a conventional fashion. 
         [0028]    The spring chamber  116  is defined by the spring side  126  of the flange case  120  and a head  140 . The head  140  includes, a shoulder portion  144  and a collar  146  extending therebetween. The collar  146  tightly fits over, and is secured to, a radially outwardly extending flange portion  148  of the spring side  126  of the flange case  120 , as described below in detail. A spring diaphragm  150  has a rim  152  clamped in a fluid tight manner between radially outwardly extending flange portion  148  of the spring side  126  of the flange case  120  and collar  146  of the head  140 . 
         [0029]    An aperture (not shown) is provided within the spring side  126  of the flange case  120  to connect a portion of the spring chamber  116  between the dividing wall  122  and the spring diaphragm  150  with a source of compressed air (not shown). A flange case push rod  154  extends between the spring chamber  116  and the service chamber  114 , and has a first reaction plate  156  rigidly mounted to one end, and a second reaction plate  158  mounted to the other end thereof. A return spring  160  is mounted within the spring chamber  116  between the divider wall  122  and the first reaction plate  156  to bias the flange case push rod  154  into the release position. 
         [0030]    A pressure plate  162  bears against the spring diaphragm  150 , and a power spring  164  is positioned between the pressure plate  162  and the head  140  to bias the pressure plate  162  and the push rods  132 ,  154  to a brake actuating position. The flange case  120  is typically cast aluminum and the head  140  is typically stamped or spun low-carbon steel. The actuator  100  may include a release tool  166  that extends within the head  140  for mechanically drawing the pressure plate  162  against the head  140  such that the power spring  164  assumes a retracted or “caged” position. The release tool can thus mechanically release the brake after a loss of power or air pressure, as is known in the art. 
         [0031]    In operation, air pressure is continually supplied to the spring chamber  116  through the aperture (not shown) to maintain the spring diaphragm  150  in a position to compress the power spring  164 . In this position, the service push rod  132  normally is operated as described above by selective pressurization of air into the service chamber  114 . However, in the event of failure of the air pressure system, the pressure in the spring chamber  116  will be decreased so that the service return spring  138  and flange case return spring  160  would no longer be able to overcome the pressure of the much larger and stronger power spring  164 . Thus, the pressure plate  162  forces the spring diaphragm  150  and thus the flange case push rod  154  outwardly, thereby also forcing the service push rod  132  outwardly to apply braking pressure to the brakes. 
         [0032]    The power spring  164 , therefore, must be compressed between the pressure plate  162  and the head  140  during normal driving and normal service brake mode, as shown in  FIG. 1 . In these modes, the power spring  164  exerts substantial force on head  140  in the direction away from flange case  120 . 
         [0033]    Referring now to  FIG. 2 , there is an enlarged side view of a push rod, push rod plate, and diaphragm of  FIG. 1 . Diaphragm  130  is composed of a rim  152  which is clamped between an upper and lower portion of a housing unit. Rim  152  is connected to sidewall  230  which tapers towards bottom wall  240 . An outer diameter  220  is formed at the connection between sidewall  230  and bottom wall  240 . 
         [0034]    Diaphragm  130  further contains flanges  190  which form an inner diameter  250 , which is smaller than outer diameter  220 . As shown, diaphragm  130  has two flanges  190  protruding from the inside of bottom wall  240 . It should be noted, however, that there could be any number of flanges protruding from bottom wall  240  including a single flange forming a complete circle inside outer diameter  220 , or there can be no flanges protruding from bottom wall  240 . As shown, flanges  190  are perpendicular to diaphragm  130  and portray a constant inner diameter. However, flanges  190  may be at an angle other than 90 degrees, with respect to diaphragm  130 , such that inner diameter  250  becomes smaller towards the edges of flanges  190 . 
         [0035]    Push rod plate  134  is sized such that the diameter of the push rod plate  134  is smaller than the inner diameter  250 . This allows push rod plate  134  to fit inside inner diameter  250  and thus inside flanges  190 . Flanges  190  help keep push rod plate  134  from sliding laterally. If inner diameter  250 , represented by tapering flanges  190 , becomes smaller at the edges of flanges  190 , then Flanges  190  surround push rod plate  134  and help prevent push rod plate  134  from pulling away from bottom wall  240 . Push rod plate  134  is further attached to push rod  132 , which is used to actuate the brake. 
         [0036]    Adhesive  210  is placed between push rod plate  134  and diaphragm  130  to immovably connect push rod plate  134  to diaphragm  130 . Adhesive  210  helps to maintain constant contact between push rod plate  134  and diaphragm  130 , and maintains the position of push rod plate  134  in relation to diaphragm  130 . The result is the prevention of push rod plate  134  from sliding laterally with respect to diaphragm  130 , and maintains better, more constant brake power. In the embodiments show, adhesive  210  is placed on push rod plate  134 , and then push rod plate  134  is attached to diaphragm  130 . However, it should be noted, that adhesive  210  can be placed on the diaphragm  130  and not on push rod plate  134 . 
         [0037]    Adhesive  210  can be any know adhesive. For example, adhesive  210  can be heat curable or can be cured at room temperature. Adhesive  210  can be an epoxy adhesive or a polyurethane adhesive. Finally, adhesive  210  can be water based or solvent based. It should be noted, that the above exemplary adhesives are used as examples of adhesives, and that any adhesive can be used to connect push rod plate  134  to diaphragm  130 , not limited to the list above. 
         [0038]    Referring now to  FIG. 3 , is an enlarged view of the bottom surface  310  of push rod plate  134 . Bottom surface  310  has adhesive  210  placed at the center of the push rod plate  134 . Push rod plate  134  is then placed inside inner diameter  250  and against diaphragm  130 . Adhesive  210  is a single portion of adhesive placed at the center of push rod plate  134 . As the force generated by the attachment of push rod  132  to push rod plate  134  is concentrated at the center of push rod plate  134 , only a small amount of adhesive  210  placed at the center of push rod plate  134  is required. However, any amount of a single portion of adhesive  210  can be used including covering a smaller or larger surface area of push rod  134  then represented in  FIG. 3 , including the entire surface area of push rod plate  134 . A larger adhesive will help maintain better stability and may be better at preventing push rod plate  134  from sliding laterally with respect to diaphragm  130 . However, any amount of adhesive can be used. 
         [0039]    Referring now to  FIG. 4 , there is a second enlarged view of push rod plate  134  with bottom surface  310 . Smaller amounts of a plurality of portions of adhesive  210  are placed on bottom surface  310  of push rod plate  134 . Smaller amounts placed over the entire surface allow less adhesive to be used than covering the entire bottom surface  310  of push rod plate  134 . Adhesive  210  can be placed at random, or predetermined locations on the bottom surface  310  of push rod plate  134 . Smaller amounts, of strategically placed adhesive  210 , may allow for better resistance to the lateral forces exerted by push rod plate  134  in relation to diaphragm  130  by spreading out the resistance across bottom surface  310 . In the exemplary embodiment of  FIG. 4 , 4 portions of adhesive  210  are used to cover bottom surface  310 , however, it should be noted that any amount of a plurality of portions can be used to cover bottom surface  310 . 
         [0040]    The present invention, therefore, provides a spring brake actuator which uses an adhesive to attach a push rod plate to a diaphragm to prevent the lateral movement of the push rod plate with respect to the diaphragm. 
         [0041]    Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.