Abstract:
First and second collars cooperate with first and second seal members separated by a retaining ring assembled onto a valve piston. The collars selectively engage the valve housing at one end and the retaining ring at the other end to limit the travel of the piston between first and second positions. Moreover, the assembly offers a cost effective alternative to the bonded rubber seals provided on known piston arrangements.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a control valve assembly and more particularly to an isolation valve that requires a two-way seal. 
     2. Discussion of the Art 
     One common use of an isolation valve is to provide a pneumatic backup in the event of an electronics failure associated with an electronic braking system (EBS). The isolation valve includes first and second seal assemblies on a movable piston that alternately and selectively isolate supply pressure to an outlet or delivery port from either a traditional pneumatic braking system or the electronic braking system. Typically, the two supply ports that communicate with a valve chamber are axially spaced apart. Consequently, movement of the piston between first and second positions alternately isolates one of the supplies from the delivery port. 
     An insert and bonded rubber sealing element is commonly used on the piston to engage the valve seat associated with the first and second positions of the piston. That is, opposite faces of the insert have an elastomer or rubber material integrally bonded thereon. Although an effective seal is provided, the insert and bonded rubber sealing element is a relatively expensive item. Thus, a need exists for a suitable substitute that provides effective isolation, i.e., two-way seals, at a significantly reduced manufacturing cost. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems associated with the prior art arrangements and provides an effective, economical assembly. 
     According to a preferred embodiment, a valve housing has a chamber with first, second, and third ports in communication therewith. A piston is received in the chamber and moves between first and second positions, providing selective communication between the first and third ports or between the second and third ports. A seal assembly on the piston includes a retaining ring that cooperates with first and second collars, and first and second seal members mounted on the piston. 
     According to a further aspect of the invention, the retaining ring is disposed between the collars and dimensioned for abutting engagement therewith and the collars maintain the seal members in place on the piston. 
     According to another aspect of the invention, the retaining ring is a split ring, while the first and second collars are complete annuli, wherein the retaining ring has an internal diameter less than an inner diameter of the first and second collars. 
     According to a preferred method of installation, a first seal member is received in a first groove on the piston. Subsequently, a first collar and then the retaining ring are advanced on the piston. A second seal member is received in a second groove. A second collar is subsequently positioned in place abutting the retaining ring previously secured to the piston. 
     A further aspect of the method of assembly includes the step of installing the second seal member prior to installing the second collar. 
     A primary benefit of the invention resides in the substantially reduced costs to manufacture the valve assembly. 
     Another benefit of the invention resides in the effective operation of the valve assembly. 
     Still another benefit of the invention resides in the ease with which the valve is assembled without any loss in valve performance. 
    
    
     Still other features and benefits of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged, cross-sectional view of a prior art insert and bonded rubber sealing element. 
     FIG. 2 illustrates the valve assembly, partially in cross-section. 
     FIG. 3 is an enlarged view, in cross-section, of the piston in a first position. 
     FIG. 4 is a view similar to FIG. 3 with the piston shown in a second position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning first to FIG. 1, a prior art insert and bonded rubber sealing element  10  used in an isolation valve is shown in cross-section. The insert has a first or lower face  12  and a second or upper face  14 . As noted above, in the isolation valve environment, it is required that the piston be able to seal along both the first and second surfaces. In the prior art of FIG. 1, this is achieved through use of a bonded rubber sealing element  16  that presents a first elastomeric seal  18  on the first face of the piston and a second elastomeric seal  20  on the second face of the piston. Although effective in operation, this part has come under scrutiny because of the high cost associated with its manufacture. 
     FIG. 2 illustrates one preferred use of the present invention, namely, in the environment of an isolation valve  30 . The valve includes a housing  30 , having a first or primary supply port  32 , a second or backup port  34 , and a third port, also referred to as an outlet or delivery port  36 . All three ports communicate with a valve chamber  38 . Dimensioned for movement in the chamber  38  is a valve member or piston  50 . The piston includes first and second seal members  52 ,  54 , respectively, that provide a slidable, sealing engagement with internal bores of the housing in a manner generally well known in the art. A control port  60  provides a constant supply of pressurized air. A solenoid actuator  62 , the details of which are conventional in the art, is selectively actuated to allow the supply air from the control port to reach an upper face  64  of the piston. For example, this occurs when the electronic braking system (EBS) actuates the solenoid and establishes a flow path from the control port to the upper side of the piston. The pressure acting on the upper face of the piston exerts a downward force that overcomes an upward or biasing force of spring  66 . Thus, in the absence of control pressure reaching the upper face  64  of the piston, the spring urges the piston to the position illustrated in FIG.  2 . 
     With continued reference to FIG. 2, and additional reference to FIGS. 3 and 4, the details of the present invention will be described. FIG. 3 illustrates the piston in a first position when the solenoid is actuated and supply pressure from control port  60  reaches the upper face of the piston. The piston moves to the position shown in FIG.  3  and establishes communication between the primary supply port  32  and the delivery port  36 . Simultaneously, communication between the backup port  34  and the delivery port  36  is precluded. Specifically, a first seal member, such as O-ring  70 , that is received in groove  72  in the piston engages valve seat  74 . The O-ring is dimensioned relative to the first groove so that it protrudes outwardly and is adapted for sealing engagement with the valve seat. A first collar  76 , which includes first and second inner tapers  76   a ,  76   b , at opposite ends thereof, partially covers the O-ring  70  and maintains it in the groove even under relatively high pressure conditions. 
     The collar  76  is a continuous annulus that has an inner diameter adapted to freely slide over the outer diameter of the piston and an outer diameter that selectively engages a retaining ring, such as split ring  80 , that is received in a second groove  82  in the piston. The retaining ring provides a stop surface that engages the first collar and limits further advancement of the piston once the opposite end of the first collar engages a surface adjacent the valve seat  74 . The first collar further includes a tapered region  74   a  at one end that cooperates with and retains the first O-ring in the groove. Preferably, the first collar includes a tapered region  74   b  at its opposite end for the same purpose. In this manner, the first collar can be inserted over the piston in either direction and assure that the retaining function is achieved. 
     A second seal member or O-ring  90  is received in a third groove  92  in the piston. It selectively cooperates with a second valve seat  94  in a second position of the piston (FIG.  4 ). The second position of FIG. 4 represents an inoperative state, e.g., a failure, in the EBS system. If the solenoid does not actuate, pressurized air from the control port fails to reach the upper face of the piston. Under those circumstances, the spring  66  urges the piston upwardly so that the second seal member  90  engages the seat  94 . 
     Similarly, a second collar  96  is partially received over the second seal member. Like the first collar, it is a continuous annulus that has an inner diameter greater than the maximum diameter of the piston. This allows the collar to freely slide thereover. However, its inner diameter is slightly less than the unstressed, outer diameter of the seal member. In addition, the second collar has tapers  96   a ,  96   b , one of which will cooperate with the seal member to continually urge it into its respective groove  92 . This is particularly evident in FIG. 4, where the piston is shown in the second position and the seal member  90  is disposed in sealing relationship with the valve seat  94 . The second collar engages the housing at one end adjacent the valve seat  94  and engages the retaining ring  80  at its other end. This precludes further movement of the piston in that direction. 
     The valve body is a typically a conventional die-cast aluminum component. The piston and the first and second collars are likewise aluminum. The O-rings are preferably formed of rubber using conventional molding techniques or any suitable elastomeric substitute. 
     Through careful dimensioning of the first and second collars, the following method of assembly is achieved. First, one of the seal members, for example, the second seal member  90  is inserted into its associated groove  92 . The associated collar  96  is then slid over the piston because of the dimensional relationship noted above. Thereafter, the retaining ring  80 , which is a split ring assembly, is received in place in groove  82 . The assembled collar will abuttingly engage the second seal member at one end and the retaining ring at its other end. 
     The other seal member, in this instance the first seal member, is then inserted into its associated groove  72  on the piston. Due to the elastomeric nature of the O-ring, the first collar  76  can be advanced to its assembled location between the O-ring and the retaining ring by urging the collar over the second seal member (i.e., squeezing the first collar over the second O-ring with some predetermined force). Once assembled, the first collar is disposed in abutting engagement with the O-ring at one end and with the retaining ring at the other end. 
     It is also contemplated that the first collar  76  can be assembled onto the piston prior to installing the first seal member  70  into its groove  72 . However, it is rather difficult to accurately locate the seal member in its groove so that the preferred method of initially mounting the first O-ring into its groove followed by assembling the first collar thereover is preferred. 
     As briefly described above, the retaining ring acts as a shoulder for both collars and in combination with the collars limits travel of the piston. During normal operation the piston is actuated and the lower O-ring seals on a lower seat which is formed into a cap nut. This blocks flow from the traditional pneumatic braking system and allows air from the electronic braking system to be delivered to the brake chambers. In the event of an electronics failure, the upper O-ring seals on an upper seat that is formed in the valve body. This allows air from the pneumatic backup braking system to be delivered to the brake chambers. 
     The invention has been described with reference to the preferred embodiments. Modifications or alterations will occur to others upon a reading and understanding of this specification. The invention is intended to include such modifications and alterations insofar as they fall within the scope of the appended claims or the equivalents thereof.