Abstract:
A combined spring brake modulating relay valve integrates the functions of a relay valve and a modulating valve. The housing includes a valve assembly movable in response to air pressure provided to selected ports in the housing. A relay piston selectively communicates with a control port and a primary brake circuit port. A modulating piston includes surfaces selectively pressurized by the primary brake circuit port and a secondary brake circuit port. This modulates the pressure from the delivery port to thereby selectively apply the associated spring brakes if a failure is detected at the primary brake circuit port. The exhaust member selectively controls communication between the supply and delivery ports as necessary.

Description:
RELATED APPLICATIONS 
   This application is a continuation of U.S. Ser. No. 09/579,086, now U.S. Pat. No. 6,769,744 filed on May 25, 2000 entitled “Spring Brake Modulating Relay Valve”. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This application relates to a combined or integrated spring brake modulating valve and relay valve that are contained in a single housing for an air brake system. 
   2. Discussion of the Art 
   It is common in presently available brake circuits to employ a separate modulation valve with a relay valve or with a separate quick-release valve. For example,  FIG. 1  illustrates a six-by-four straight truck, i.e., a non-towing vehicle, that employs spring brakes for parking the vehicle and in which pressurized air is delivered to the spring brakes to release them during normal operation. As shown in  FIG. 1 , each wheel includes a brake chamber connected with a relay valve to provide air pressure to the drive axle and selectively control service application of the brakes. In addition, each wheel includes a spring brake chamber selectively supplied with air to release a large mechanical spring typically used for the park function. Air pressure to these spring brake chambers releases the mechanical spring and allows the vehicle to roll. 
   As is generally known in the art, if a primary circuit fails, it is desirable to take advantage of the spring brakes, yet modulate the operation of the spring brakes through a foot control valve. This is provided by the spring brake modulation valve so that the spring brakes are selectively applied through operation of the foot control valve. The secondary circuit controls the steer axle (not shown). This arrangement provides a desired braking action and modulation of the spring brakes when required. 
     FIG. 2  illustrates a four-by-two or six-by-two straight truck configuration. Again, a spring brake modulation valve is used in conjunction with a separate spring brake quick release valve. It is evident from a comparison of  FIGS. 1 and 2  that different system configurations and plumbing arrangements are thus encountered by truck manufacturers even though the brake needs are not entirely dissimilar. Thus a need exists for simplified plumbing for the truck manufacturers that provides standardized installation across all of its vehicles. In addition, enhanced performance characteristics are always desirable. 
   SUMMARY OF THE INVENTION 
   The present invention provides an integrated spring brake modulating relay valve that simplifies known, multi-component systems. 
   More particularly, the valve includes a housing having a control port, supply port, delivery port, exhaust port, and primary and secondary circuit brake ports that communicate with a chamber in the housing. A first piston received in the housing moves in response to pressure from the control port. A second piston monitors the primary and secondary circuits and modulates spring brake pressure if the primary circuit fails. An exhaust valve is interposed between the supply and delivery ports and controls communication with the exhaust port to selectively supply and release the spring brakes. 
   The first or relay piston is connected to the second or modulating piston through a biasing spring. Thus, the pistons can operate in unison but are also adapted to move relative to one another for their particular functions. 
   A primary benefit of the invention is the ability to integrate separate components into a multi-component arrangement in a single housing. 
   Another benefit of the invention resides in the improved response time, while maintaining all of the features and benefits of known systems. 
   Yet another benefit results from the simplified plumbing and standardized installation for truck manufacturers. 
   Still other features and benefits of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 and 2  are schematic representations of prior art truck brake systems. 
       FIG. 3  is a schematic representation of the spring brake modulating relay valve of the present invention incorporated into an air brake system. 
       FIG. 4  is a sectional view through the spring brake modulating relay valve illustrating relative positions of the valve components during a system charging. 
       FIG. 5  is a view similar to that of  FIG. 4 , where the pressure has been elevated above 105 psi. 
       FIG. 6  illustrates normal service brake application. 
       FIG. 7  illustrates the position of the valve components during system park. 
       FIG. 8  illustrates service brake application where a failure has occurred in the primary brake circuit. 
       FIG. 9  shows the valve components where a failure in the secondary brake circuit has occurred. 
       FIG. 10  illustrates the anti-compounding feature of the subject valve. 
       FIG. 11  is an illustration of another preferred embodiment of a combined spring brake modulating relay valve. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Turning first to  FIG. 3 , a brake system  20  includes a first or primary reservoir  22  and a second or secondary reservoir  24  that provide a supply of pressurized air for the brake system. The reservoirs are periodically charged by a compressor (not shown) and typically an air dryer is interposed between the compressor and the reservoirs to remove moisture and contaminants from the air before it is stored. Lines  26 ,  28  lead from the first and second reservoirs, respectively, to a foot control valve  30 . The valve includes a foot pedal  32  that is selectively depressed by an operator to supply pressure from the foot control valve to a standard service relay valve  40  via line  42 . The relay valve delivers normal service braking to brake chambers  50  via lines  52  associated with each of the drive wheels (not shown). In addition, line  54  extends from the relay valve to a spring brake modulation relay valve  60 . In this manner, and as will be described in greater detail below, operability of the primary brake circuit is communicated to the spring brake modulation valve  60 . 
   The foot control valve also provides a signal through line  62  to the spring brake modulation valve representative of the operation of the secondary brake circuit. Although the secondary circuit is not shown in  FIG. 3  for purposes of simplicity and brevity, it is well known that a separate or secondary circuit controls braking for the steering axle from the foot control valve. 
   Moreover, a separately actuated control valve  70  is typically mounted in the operator compartment, such as on the dashboard. Again, as is known in the art, the control valve  70  provides a control signal (pneumatic signal) through line  72 . That control signal cooperates with a spring brake modulating valve, here combined in the spring brake modulation relay valve  60 , to provide pressurized air through lines  74  to the spring brake chambers  76  and thereby release the mechanical spring brakes (not shown). 
   With this brief overview of the brake system, attention is turned to  FIG. 4  where the details of the structure and function of the combined spring brake modulating relay valve  60  is shown in greater detail. It includes a housing  100  which, in this embodiment, includes a first or lower housing portion  102 , a second or intermediate housing portion  104 , and a third or upper housing portion  106 . An internal cavity or valve chamber  110  selectively communicates with a number of ports provided in the housing. For example, a supply port  112 , delivery port  114 , and exhaust port  116  are all formed in the lower housing portion  102 . In the intermediate housing portion, a primary brake circuit port  120  and a secondary brake circuit port  122  are provided while a control signal port  124  is provided in the upper housing portion. 
   A first or relay piston  130  includes a seal member such as O-ring  132  for sealing, sliding engagement in the housing. A second or modulating piston  134  likewise includes a seal member, such as O-ring,  136  for sliding sealing engagement within the housing. A lower extension of the modulating piston includes an auxiliary piston  138  having an O-ring seal member  140 . A first biasing member or spring  142  engages an internal shoulder  144  of the relay piston  130  at one end and an internal shoulder  146  of the modulating piston at the other end. The spring permits the relay and modulating piston to move as a unit under certain pressure conditions. On the other hand, a retention ring  150  provides an abutment surface for the opposite face of shoulder  144  to define the engagement between the first and second pistons in the absence of air pressure. In addition, a second biasing member or spring  152  is interposed between the housing and the modulating piston for urging the valve assembly toward a first or upper position. 
   The lower end or modulating end of the second piston includes a seat portion  154  adapted to sealingly engage an exhaust valve  160 . As shown in  FIG. 4 , the exhaust valve is closed as a result of the seat portion  154  engaging a seal surface  162  of the exhaust valve. The exhaust valve is normally urged toward a seated position with the housing via spring  164 . When seated against the housing and forming a lap seal therewith, the supply port  112  cannot communicate with the delivery port  114  as will be described further below. 
   A check valve  170  is associated with the control port  124 . In a first position (as shown), the check valve permits communication between the control port and an upper face  172  of the relay piston via passage  174 . In the first position, passage  176  is sealed by the check valve  170  so that the primary brake circuit port (i.e., on the upper face of the second piston  134 ) cannot communicate with the passage  174 . In addition, a check valve  180  is urged by spring  182  toward a closed position and precludes communication between passage  176  and passage  184  that leads to the supply port. 
   The position of the valve components in  FIG. 4  represent the system when it is charging and the pressure is below a predetermined level (here 105 psi). The control valve  70  is actuated by the operator and supplies a pneumatic control signal to control port  124 . This seats the check valve  170  and provides air pressure to the relay piston surface  172 . The air pressure acting over the relay piston surface exerts a force in a downward direction so that the inlet valve and seal surface  162  is lifted or spaced from the housing seat and provides communication between the supply port  112  and the delivery port  114  to the spring brakes. This provides pressurized air that retracts the mechanical spring brakes and releases the spring brakes to allow the wheels to roll freely. 
   It is desired that the pressure to the spring brakes be limited to 105 psi. Accordingly, once that preselected pressure level is reached, the exhaust valve is urged to a sealed position with the valve seat ( FIG. 5 ) and remains in contact with the lower portion of the modulating piston. This lapped position assures that only 105 psi is delivered to the spring brakes. 
   A normal service application is illustrated in  FIG. 6 . Pressure is provided at the control port  124  to urge the relay piston  130  to its lower position as shown. In addition, air pressure is provided at the primary circuit port  120 , as well as the secondary circuit port  122 . This provides a balancing force on the modulating piston  134  so that it does not engage against the lower shoulder (e.g. as it does in  FIG. 4 ), and instead remains in a balanced position as shown in  FIG. 6 . Thus, the pistons have moved relative to one another and the spring  142  is under compression. The spring brakes have already been released and are held in the release position due to the lapped arrangement between the sealing surface  162  and the housing. Likewise, the lower end of the modulating piston  134  is seated against the seal surface  162  to prevent communication with the exhaust port. 
   To effect system park, no pressure is provided to the control port  124  or the primary and secondary circuit ports  120 ,  122 , respectively. The components of the valve adopt the positions illustrated in  FIG. 7 . Note that the relay piston is urged to a second or upper position. Likewise, the modulating piston  134  is urged upwardly by the springs. This lifts the end of the modulating piston from its sealed engagement with the seat  162  and thereby establishes communication with the exhaust port  116 . Thus, the air pressure which released the mechanical spring brakes is now free to communicate with ambient through the exhaust port and the spring brakes are applied. The pressure at the supply port  112  cannot communicate with the delivery port due to the closing force imposed by the spring  164 . 
   If a primary circuit brake failure occurs, the modulation function of the valve  60  comes into play. This is best illustrated in  FIG. 8 . The control port  124  is still pressurized and the air pressure urged the relay piston  130  toward its lower position. Because of the failure, there is no pressure at the primary port  120 . Thus, the pressure at the secondary port  122  moves the modulating piston upwardly as shown. This lifts the modulating end of the piston from its sealed engagement with seal member  162 , again establishing communication between the delivery port  114  and the exhaust port. Consequently, the mechanical springs can be applied through selective depression of the foot valve when the primary circuit has failed. This, of course, is a very desirable and beneficial feature of the valve assembly. 
   If a failure occurs in the secondary circuit, and the primary circuit is still operative, the rear axle or drive brakes can still be operated. The modulating piston moves downwardly, as shown in  FIG. 9 , resulting in the supply reservoir pressure being delivered to the spring brakes. However, no modulation occurs since the service brakes are still operative and can satisfy safe stopping distance requirements. 
   Another feature incorporated into the valve is generally referred to as anti-compounding ( FIG. 10 ). That is, it is undesirable to apply both the spring brake and the normal service braking at the same time, i.e., compounding the brakes. To prevent this undesired result, an anti-compounding feature is incorporated into the valve assembly. For example, if the vehicle is parked, i.e., there is no air pressure at the control port  124 , then air from the primary circuit drives the pistons downwardly by providing pressure to the upper face  172  of the relay piston. The lower end of the modulating piston moves the exhaust valve from its sealed position with the seat and thereby establishes communication between the supply port  112  and the delivery port  114 . As will be recognized, this backs the spring brakes from the applied position and prevents compounding of the brake application. 
   The valve of  FIG. 11  is similar to that shown and described with reference to  FIGS. 4–10 . It is preferred from the standpoint, however, that a more compact assembly is provided since the intermediate housing portion is removed. Instead, an inner static piston  200  is received in a modified upper housing portion. As will be appreciated, the static piston  200  is sealed relative to the upper housing portion via O-ring seals  202 ,  204 . It has an internal cavity that receives the sliding seals  136 ′ and  140 ′ of the modulating piston. In substantially all other respects, the correspondence between the valve of  FIGS. 4–10  and that in  FIG. 11  is exhibited through the use of components identified with a primed suffix (′). Accordingly, operation and function of the combined spring brake modulating relay valve of  FIG. 11  is the same as described above. 
   The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will become apparent to those skilled in the art. It is intended to include all such modifications and alterations insofar as they fall within the scope of the appended claims or the equivalents thereof.