Dual lip rod wiping seal
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to seal members, and is particularly concerned with piston rod wiping or scraping seal members for cleaning dust and other foreign matter from reciprocating piston rods as the rod enters a cylinder chamber to prevent contamination of the chamber. 
     2. Description of the Prior Art 
     A particular problem that occurs with piston and cylinder assemblies is that of preventing contamination of the chamber formed between the piston head and the end wall of the cylinder. As the piston reciprocates within the chamber, the piston rod moves in and out of the chamber. Dust and other foreign matter can collect on the surface of any portion of the piston rod externally of the chamber. When the rod moves back into the chamber on a return stroke, the dust and other foreign matter must be cleaned from the surface of the rod. If it isn&#39;t, the foreign matter may not only enter the working chamber within the cylinder, but can damage the seal or packing assembly surrounding the piston rod in the end wall of the cylinder. 
     It is conventional to mount in a groove in the end wall of the cylinder a scraping or wiping seal member of resilient material (sometimes also referred to as excluders) for wiping or scraping dust and other foreign matter from the surface of a piston rod on an inward stroke of the piston. 
     Among the problems associated with such rod wiping seals is providing a construction that can be easily installed and removed, and one that will stand up under adverse operating conditions without an unacceptable failure rate. 
     Another problem with prior art rod wiping seals is that premature failure of the seal frequently results from the accummulation of dirt and other foreign matter between the walls of the packing housing and the wiping seal. The accummulated dirt forces the wiper toward the rod which results in excessive friction between the rod and wiping seal. Furthermore, when the bearings used to maintain alignment of the rod wear, transverse movement of the rod results. This increases the likelihood of dirt and foreign matter entering the cylinder between the surfaces of the packing housing and the wiping seal because of the transverse forces tending to cause distortion of the wiping seal when the rod moves transversely. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a one-piece rod wiping seal of resilient or elastomeric material that can be snap fitted into a mounting groove of a cylinder end wall, and that can withstand adverse operating conditions such as transverse movement of the reciprocating rod with which it is engaged. 
     A further object is to provide a rod wiping seal that, when installed, can maintain substantially uniform wiping pressure on the rod regardless of transverse movement of the rod with respect to the seal to prevent the occurrence of excessive friction between the seal and rod. 
     Another object is to provide a rod wiping seal that, when installed, can maintain substantially uniform sealing pressure on the wall of the packing housing regardless of transverse movement of the rod to reduce the likelihood of the entry of dirt and other foreign matter into the cylinder between the seal and packing housing. 
     In carrying out the foregoing, and other objects, a seal member according to the present invention includes an endless body portion having a pair of spaced end walls and inner and outer side walls extending therebetween. The side walls are concentric with the central axis of the body. Projecting from one end wall is a pair of sealing lips each having an inner end joined integrally to the end wall and projecting therefrom to an outer free end. One of the lips constitutes a rod engaging lip and has an inner side surface that projects axially and radially inwardly for engaging the surface of a piston rod. The other lip constitutes a cylinder engaging lip and has an outer side surface that extends axially and radially outwardly from the end wall. The outer side wall of the body portion, the portion of the end wall from which the lips extend between the outer side wall and the cylinder engaging lip, as well as the other end wall of the body portion serve as mounting groove engaging surfaces to be received in the mounting groove of an end cap for the cylinder. 
     When installed, clearances are provided between the outer side wall of the body portion and the corresponding wall of the groove, as well as between the inner side wall of the body portion and the surface of the piston rod so that lateral movement of the piston rod will not over stress the sealing lips, without at the same time interfering with the sealing and scraping function of the two lips. 
     Other objects, advantages and features of the invention will become apparent from the following description taken in connection with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of a piston and cylinder assembly having a rod wiping seal member embodying the present invention; and 
     FIG. 2 is an enlarged sectional detailed view of the portion of FIG. 1 enclosed by circle 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, reference numeral 10 collectively designates a piston and cylinder assembly. The assembly 10 includes a cylinder 12 having a piston 14 reciprocably mounted therein. The piston 14 has a body 16 extending through an end wall or cap 18 of the cylinder. Reference numeral 20 indicates a working chamber in the cylinder defined between the reciprocating piston 14 and the end wall 18. 
     Reference numeral 22 collectively designates a conventional packing assembly including a plurality of V-type seals 24. The seals 24 are nested together between end plates in a conventional manner. The specific construction of the packing assembly 22 forms no part of the present invention. 
     The end wall member 18 is formed with an opening 26 for receiving the reciprocating piston rod 16. Reference numeral 28 collectively designates a piston rod wiping seal which is mounted in a groove formed in the wall of the opening 26 of the end wall member 18. The groove receiving the wiping seal member 28 has a top wall 30, an annular side wall 32, and a bottom wall 34 as illustrated in FIG. 2. 
     The seal member 28 is of one-piece construction of elastomeric material. The seal member 28 includes a main body portion 36, which, as shown is of generally rectangular construction in cross section. The body portion has a mounting section 36a for mounting seal member 28 in the groove in the wall of opening 26 by flexibly distorting the body portion and snap-fitting the mounting section 36a in the groove. The body portion also includes a sealing section 36b extending radially from the mounting section 36a. The main body portion 36 includes a top end wall 38, a bottom end wall 40, and inner and outer annular side walls 42 and 44, respectively, extending between the end walls 38 and 40. The end walls 38 and 40 extend over both of the mounting and sealing sections. The inner side wall 42 is located on the sealing section 36b and the outer side wall 44 is located on the mounting section 36a. First and second sealing lips 46 and 48 project from the end wall 38 at the sealing section 36b. The first sealing lip 46 constitutes a rod engaging lip for engaging the surface of the piston rod 16. The second sealing lip 48 constitutes a cylinder engaging lip for engaging the wall of the opening 26. The unstressed position of the annular sealing lips 46 and 48 is illustrated in phantom lines in FIG. 2. The installed position of the lips 46 and 48 is illustrated in full lines in FIG. 2 as the sealing lips 46 and 48 respectively engage the piston rods 16 and end wall 18. 
     The lips 46 and 48 each have inner ends joined integrally to the end wall 38. The sealing lips 46 and 48 each project from their inner ends at the end wall 38 to outer free ends 50 and 52, respectively, which are radially spaced from each other as illustrated in the drawings. 
     The rod engaging lip 46 has an inner side surface 54 for engaging the piston rod 16. As illustrated in the drawing, the inner side surface extends axially and radially inwardly (i.e., toward the axis of rod 16) approximately from the junction between the end wall 38 and the inner side wall 42. The sealing lip 46 has an outer side surface 56 extending between the end thereof. The inner end of the outer side surface 56 has its inner end located at the end wall 38 at a location spaced radially outwardly of the inner side wall 42 and radially inwardly of the outer side wall 44. 
     The cylinder engaging lip 48 has an outer side surface 58 extending between the ends thereof. The inner end of the outer side surface 58 is joined to the end wall 38 at a location spaced radially outwardly from the lip 46 and radially inwardly from the outer side wall 44. The side surface 58 extends axially and radially outwardly (i.e., away from the axis of rod 16) from the end wall 38. This position is more pronounced in the unstressed condition as illustrated in the phantom line position. The lip 48 has an inner side surface 60 extending between the ends thereof with its inner end joined to the end wall 38 adjacent to the inner end of the side surface 56 of lip 46. 
     The portion of the end wall 38 extending radially outwardly of lip 48 to the side wall 44, the end wall 40 and the side wall 44 of the main body portion 36 constitute groove engaging surfaces of the body 36 for retaining the sealing member 28 in the end wall 18. 
     A clearance a is illustrated between the side wall 32 of the groove and the outer side wall 44 of the sealing member 28. Similarly, a clearance b is provided between the surface of the rod 16 and the inner side wall 42 of the sealing member 28. A clearance c is indicated between the lower portion of the side surface 58 of the cylinder engaging lip 48 and the wall of the opening 26. By way of example only, clearances a and b may be on the order of 0.010-0.015 inches. 
     The sealing member 28 is installed by inserting the body portion 36 into the groove as illustrated in FIG. 2. When the piston rod is installed, the lips 46 and 48 are compressed toward each other. Sealing pressure is applied between the surface of opening 26 and the other side surface 58 of lip 48. Similarly, sealing pressure is applied between the surface of rod 16 and the inner side surface 54 of the sealing lip 46. As the rod reciprocates, the rod engaging lip 46 scrapes dust and other foreign material from the surface of the rod as the rod moves from an inward stroke into the chamber 20. The clearances a, b and c accommodate transverse movement of rod 16 to prevent overstressing and reduce fatigue on the lips 46 and 48. 
     The length of the cylinder engaging lip 48 is less than the rod engaging lip 46 in the illustrated embodiment. However, if, for example, opening 26 were of greater diameter, the length of the cylinder engaging lip 48 could be greater than illustrated, and possibly as great as that of lip 46, depending upon the size of opening 26. 
     The rod 16 will tend to move transversely as the bearings (not shown) supporting the rod wear through use. With prior art wiping seals, the resulting stresses on the seal tends to distort the seal and permit dirt to enter around the seal along the walls 26, 30, 32 and 34 into the cylinder. Furthermore, such transverse movement of the rod increases the friction between the rod and prior art seals, and the excessive friction causes premature failure of the prior art seals. The sealing lip 48, in the arrangement illustrated, provides substantially uniform sealing pressure on surface 26 regardless of transverse movement of the rod 16. Furthermore, the ability of the seal 28 to shift transversely because of the clearances a, b and c prevents the occurrence of excessive pressure between the sealing lip 46 and the surface of rod 16. 
     While a specific form of the invention is described in the foregoing specification and illustrated in the accompanying drawings, it should be understood that the invention is not limited to the exact construction shown. Variations and alterations in the construction and arrangement of parts, all falling within the scope and spirit of the invention will be apparent to those skilled in the art.