Abstract:
An improved brake equalizer apparatus for equalizing fluid pressure and damping shock waves or pressure surges in fluid lines of a fluid pressure-actuated system, such as a hydraulic brake system. The apparatus has a shorter reaction time than a conventional brake equalizer, and can be manufactured with smaller overall length and weight. An important feature of the apparatus which results in reduced brake equalizer reaction time is an improved brake equalizer piston. The piston of the invention is shorter than a conventional brake equalizer piston (the ratio of the inventive piston&#39;s length to the length of the shock absorber which it abuts is substantially less than 0.5, and is preferably equal to about 0.23). The piston of the invention is also lighter than a conventional brake equalizer piston, and is preferably made of a hard, non-compressible, self-lubricating material. The brake equalizer of the invention does not employ any O-ring or other seal between the piston and the surrounding housing along which the piston slides, thus eliminating friction that would otherwise exist between such a seal and the housing as the piston slides along the housing.

Description:
FIELD OF THE INVENTION 
     The invention relates to brake equalizer apparatus for equalizing fluid pressure and damping shock waves or pressure surges in fluid lines of a fluid pressure-actuated system, such as a hydraulic brake system. 
     BACKGROUND OF THE INVENTION 
     Devices (sometimes referred to as “brake equalizers”) have been used to equalize fluid pressure and damp shock waves and pressure surges, in fluid lines of hydraulic brake systems. Brake equalizers are described in U.S. Pat. No. 4,166,655, issued Sep. 4, 1979 to the present inventor, U.S. Pat. No. 4,220,376, issued Sep. 2, 1980 to the present inventor, and U.S. Pat. No. 5,078,455, issued Jan. 7, 1992 to Washington, for example. 
     The brake equalizer described in U.S. Pat. No. 4,220,376 includes a rigid piston  48  attached to an elastomeric shock absorber  50 . Piston  48  and shock absorber  50  are enclosed within a bore in a rigid housing  56 . One end of piston  48  is exposed to fluid within chamber  42 , and the other end of piston  48  abuts a first end of shock absorber  50 . The other end of absorber  50  rests against a closed end of the bore. A volume between the sides of absorber  50  and housing  56  is partially filled with liquid (such as oil). An O-ring seal  84  between piston  48  and housing  56  prevents this liquid from escaping into chamber  42 , and prevents fluid in chamber  42  from reaching absorber  50 . Absorber  50  is said to be preferably molded from a rubber-like elastomer, such as neoprene having a Shore hardness of about  65 . 
     The apparatus opposes pressure surges in the fluid in chamber  42  as follows. In response to each pressure increase in chamber  42 , piston  48  effectively increases the volume of chamber  42  by sliding toward absorber  50 , thereby compressing absorber  50  against the closed end of the bore. As absorber  50  deforms, it absorbs the energy imparted to it by moving piston  48 . 
     When the fluid pressure drops in chamber  42 , piston  48  opposes the pressure decrease by effectively decreasing the volume of chamber  42  as it slides away from absorber  50 . 
     U.S. Pat. No. 4,166,655 discloses an improved version of the brake equalizer of U.S. Pat. No. 4,220,376. The apparatus of U.S. Pat. No. 4,166,655 differs from that of U.S. Pat. No. 4,220,376 primarily by including a diaphragm  18  between the piston (piston  16 ) and the chamber within which fluid pressure variations are to be equalized (chamber  60 ). Diaphragm  18  is comprised of resilient elastomer, and preferably includes a metal plate bonded to the elastomer to protect the elastomer from damage by contaminants in flowing fluid in chamber  60 . The function of diaphragm  18  is to seal the piston/shock absorber assembly from fluid in chamber  60 , while transmitting pressure variations in such fluid to the piston. 
     Also, the U.S. Pat. No. 4,166,655 apparatus includes annular rubber shims ( 98 ,  100 ) around the piston, in addition to an O-ring seal  96 , for the stated purpose of improving the fluid seal between the piston and the housing against which the piston slides. U.S. Pat. No. 4,166,655 teaches that the housing (including body  20  and cap  22 ) has a preferred length of 6.4 inches, and that absorber  14  is preferably molded of neoprene having a Shore hardness in the range between  62  and  65 . 
     The brake equalizer of U.S. Pat. No. 5,078,455 is similar in relevant respects to that of U.S. Pat. No. 4,166,655. The piston of U.S. Pat. No. 5,078,455 has two O-ring seals  12  around it (in counterbores  92  and  93 ) rather than one, for providing a fluid seal between the piston and the surrounding cylindrical housing surface. 
     The inventor of the present application has recognized that conventional brake equalizers have several limitations, including the following: 
     1. they have slow reaction time, and thus are unable to equalize rapid pressure fluctuations of the type which often occur in brake air line systems; and 
     2. they have large overall length and weight, which renders them impractical to use in certain applications. 
     SUMMARY OF THE INVENTION 
     The invention is an improved brake equalizer apparatus for equalizing fluid pressure and damping shock waves or pressure surges in fluid lines of a fluid pressure-actuated system, such as a hydraulic brake system. The inventive apparatus has a shorter reaction time than a conventional brake equalizer, and can be manufactured with smaller overall length and weight. 
     An important feature of the invention which results in reduced brake equalizer reaction time, is an improved design for a brake equalizer piston. The inventive piston is shorter than a conventional brake equalizer piston (the ratio of the inventive piston&#39;s length to the length of the shock absorber which it abuts is substantially less than 0.5, and is preferably equal to about 0.23). The inventive piston is also lighter than a conventional brake equalizer piston, and is preferably made of a hard, non-compressible, material having a low-friction surface (preferably a hard, castable, self-lubricating material such as “Royal Cast”  ROYALCAST® urethane, which has a hardness of 79 D on the Rockwell hardness scale). 
     The inventive brake equalizer does not employ any seal (such as an O-ring seal) between the piston and the surrounding housing along which the piston slides, thus eliminating friction that would otherwise be present between such a seal and the housing as the piston slides along the housing. Besides reducing the reaction time of the brake equalizer (by reducing the piston assembly&#39;s sliding friction), elimination of seals from around the inventive piston also eliminates the need for providing oil in the volume between the sides of the piston/shock absorber assembly and the surrounding housing. 
     In a preferred embodiment, the inventive piston is molded of “Royal Cast”  ROYALCAST® urethane and has a weight of about 3.5 ounces. The inventive piston is preferably used with, but not bonded to, a shock absorber. The shock absorber is preferably made from a resilient material harder than conventional brake equalizer absorber material. Preferably, the shock absorber has a Shore hardness in the range of about 70 to about 75, and is made of a combination of polyether-based urethane (cured with a liquid diamine) and a quantity of a benzoate ester (rather than BUNA-N hard rubber as in the prior art). 
     The inventive piston design allows the overall length of inventive brake equalizer to be reduced. The inventive piston design enables a preferred embodiment of the brake equalizer&#39;s housing (including body and cap portions) to have a length of 4.2 inches or even less (in contrast with the housing of U.S. Pat. No. 4,166,655 which has a preferred length of 6.4 inches). 
     The inventive brake equalizer design eliminates the need for a metal plate to be bonded to the elastic diaphragm which separates the piston from the variable-pressure fluid (whose pressure is to be equalized). A preferred embodiment of the inventive brake equalizer includes a screen positioned between the diaphragm and the variable-pressure fluid, to prevent contaminants (especially sharp or abrasive particles) from reaching the diaphragm and possibly penetrating through it to the piston/absorber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified, side cross-sectional view of a preferred embodiment of the brake equalizer of the invention. 
     FIG. 2 is a top elevational view of the housing cap of the FIG. 1 apparatus. 
     FIG. 3 is a bottom elevational view of the housing cap of the FIG. 1 apparatus. 
     FIG. 4 is a side elevational view of the housing cap of the FIG. 1 apparatus. 
     FIG. 5 is a bottom elevational view of the housing body of the FIG. 1 apparatus. 
     FIG. 6 is a cross-sectional view of the housing body of FIG. 5, taken along line  6 ′— 6 ′ shown in FIG.  5 . 
     FIG. 7 is a side elevational view of the piston-shock absorber assembly employed in the FIG. 1 apparatus. 
     FIG. 8 is a top elevational view of the piston-shock absorber assembly of FIG.  7 . 
     FIG. 9 is a top elevational view of the screen of the FIG. 1 apparatus. 
     FIG. 10 is a bottom elevational view of the diaphragm of the FIG. 1 apparatus. 
     FIG. 11 is a cross-sectional view of the diaphragm of FIG. 10, taken along line  11 — 11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a simplified, side cross-sectional view of a preferred embodiment of the brake equalizer of the invention. The FIG. 1 apparatus includes a housing (comprising cap  2  and body  4 ) and a piston-shock absorber assembly (comprising piston  8  and shock absorber  6 ). Cap  2  and body  4  are connected together by bolts  14  and nuts  17  (one screw  14  and a mating nut  17  are shown in FIG. 1) so as to enclose volumes  20  and  22 . An elastic diaphragm  10  (composed of resilient elastomer) separates volume  20  from volume  22 , and seals the piston/shock absorber assembly within volume  20  from fluid in volume  22 , while transmitting pressure variations in such fluid to piston  8 . 
     Volume  22  is an open chamber having three fluid inlets  3  (shown in FIGS. 1 through 4) and two fluid outlets  5  (shown in FIGS.  1  through  4 ). The FIG. 1 apparatus functions to counteract (equalize) variations in the pressure of fluid flowing within volume  22 . Inlets  3  and outlets  5  are typically connected to fluid lines of a fluid pressure-actuated system, such as a hydraulic brake system. In this case, the FIG. 1 apparatus would function to equalize fluid pressure variations in such lines. 
     Volume  20  is a closed chamber having an annular cross-section, bounded by shock absorber  6  and piston  8  (on the inside) and generally cylindrical side wall  4 b of housing body  4  (on the outside). 
     The FIG. 1 apparatus does not employ an O-ring seal or any other seal between piston  8  and wall  4 b, and thus eliminates friction that would otherwise be present between such seal and housing body  4  during translation of piston  8  along wall  4 b. Use of such a “non-sealed” piston  8  (i.e., elimination of seals from around piston  8 ) eliminates the need to provide oil or other lubricant in chamber  20 , and also reduces the reaction time of the FIG. 1 apparatus (by reducing piston  8 &#39;s sliding friction). Non-sealed piston  8  is preferably made of a hard, non-compressible, material having a low-friction surface (preferably a hard, self-lubricating material such as “Royal Cast”  ROYALCAST® urethane, which has a Rockwell hardness of 79 D). 
     Piston  8  is shorter than a conventional brake equalizer piston. Specifically, the ratio of length L of piston  8  (the dimension indicated in FIG. 7) to length M of shock absorber  6  (the dimension indicated in FIG. 7) is substantially less than 0.5, and is preferably equal to about 0.23. In contrast, the ratio of piston length to shock absorber length in above-cited U.S. Pat. Nos. 4,166,655, 4,220,376, and 5,078,455, is 0.53, 0.92, and 0.55, respectively (as measured from the patent drawings). 
     Piston  8  is not bonded to shock absorber  6 . Thus, piston  8  is free to slide relative to wall  4 b toward a stationary shock absorber  6 . Then (after piston  8  contacts absorber  6 ) piston  8  will either push absorber  6  into engagement with end surface  4 a of body  4 , or piston  8  will compress stationary absorber  6  (if absorber  6  already rests against end surface  4 a), as piston continues to slide along wall  4 b toward end surface  4 a. A previously compressed absorber  6  (compressed between, and engaged with, end surface  4 a and piston) will push piston  8  along wall  4 b away from end surface  4 a as it decompresses back to its original, non-compressed shape. 
     Preferably, shock absorber  6  is made from a resilient material (preferably having a Shore hardness in the range from about 70 to about 75). In one preferred embodiment, shock absorber  6  is made of plastic having a Shore hardness of about 75 (rather than BUNA-N hard rubber as in the prior art). Such plastic is preferably a combination of polyether-based urethane (cured with a liquid diamine) and a quantity of a benzoate ester. If the Shore hardness of absorber  6  is about 75, then a version of the FIG. 1 apparatus (for use in a vehicle hydraulic braking system) can be designed for maximum operating efficiency for braking from a vehicle speed of 30 mph (assuming an application pressure of 30 p.s.i.). 
     Piston  8  is not only shorter, but is preferably also lighter, than a conventional brake equalizer piston. In a preferred embodiment, piston  8  is molded of “Royal Cast”  ROYALCAST® urethane and has a weight substantially equal to 3.5 ounces, and the shock absorber  6  used with such piston is molded of urethane having a Shore hardness of about 70. 
     The inventive piston design allows the overall length of inventive brake equalizer to be reduced. The inventive piston design enables a preferred embodiment of the FIG. 1 apparatus to have a total length (from the top to the bottom of FIG. 1) of 4.2 inches or even less (in contrast with the housing of U.S. Pat. No. 4,166,655 which has a preferred length of 6.4 inches). 
     With reference again to FIG. 1, mounting bracket  19  is fixedly attached to housing body  4  (for example by bolts, not shown), and screen  12  is mounted between diaphragm  10  and volume  22 . Screen  12  prevents contaminants (especially sharp or abrasive particles) in fluid within volume  22  from reaching diaphragm  10  and possibly penetrating through it to volume  20 , piston  8 , and absorber  6 . 
     As shown in FIGS. 2-4, housing cap  2  has four holes  15  bored through its outer periphery, for alignment with four corresponding holes  31  (shown in FIG. 5) of housing body  4 . A bolt  14  is positioned through each pair of aligned holes  15  and  31 , for fastening cap  2  to body  4  (after piston  8 , absorber  6 , diaphragm  10 , and screen  12  have been mounted within body  4 ). 
     Housing body  2  has a hollow interior and includes the following orifices which extend outward from its hollow interior through its outer surface: top orifice  16  (across which screen  12  is to be positioned), two fluid inlets  3  which extend downward (opposite top orifice  16 ) and one fluid inlet  3  which extends through the side of cap  2  (the left side in FIG.  4 ), and two fluid outlets  5  which extend through other sides of cap  2  (the left and right sides in FIG.  3 ). 
     As shown in FIGS. 5 and 6, inner wall  4 b of housing body  4  is machined to define four ridges  17   27 . The function of ridges  17   27 is to center shock absorber  6  within body  4 , even at times when absorber  6  is compressed against end surface  4 a by piston  8 . Four holes  31  (discussed above) are bored through the periphery of housing body  4 &#39;s lower end (the end opposite surface  4 a). An annular groove  30  extends around housing body  4 &#39;s lower end, for receiving outer ridge  10 d of diaphragm  10 . When body  4  is assembled with cap  2 , and diaphragm  10  and screen  12  are positioned within them (as shown in FIG.  1 ), diaphragm  10  is held in place because its ridge  10 d is pressed between groove  30  and screen  12  (or groove  30  and a facing portion of cap  2 ). 
     With reference next to FIGS. 7 and 8, the ratio of piston  8 &#39;s length L to shock absorber  6 &#39;s length M is substantially less than 0.5, and is preferably equal to about 0.23. Piston  8  has a large diameter cylindrical portion  8 a, which faces large diameter cylindrical portion  6 a of shock absorber  6 . The outer edge of portion  8 a is designed to slide with low friction along wall  4 b of housing  4 . As indicated above, piston  8  (including portion  8 a) is preferably made of hard, self-lubricating material, such as “Royal Cast”  ROYALCAST® urethane. Piston  8  also has a tapered, frusto-conical, end portion  8 b facing away from absorber  6 . Diaphragm  10  will be draped against piston end portion  8 b during normal operation, because in normal operation, the pressure within chamber  22  exceeds the pressure within chamber  20 . Shock absorber  6  also has a tapered portion  6 b (integrally molded with portion  6 a), which terminates at upper surface  6 c. Surface  6 c will abut end surface  4 a of housing body  4  when piston  8  compresses absorber  6  against surface  4 a. In a preferred embodiment, the diameter of surface  6 c is 1.00 inches, the diameter of portion  6 a is 1.50 inches, the diameter of portion  8 a is 1.975 inches, the minimum diameter of portion  8 b is 1.71 inches, length L  M (of absorber  6 ) is 3.00 inches, and length M  L (of piston  8 ) is 0.7 inches. The ratio, M/L  L/M, is equal to 0.23 in this embodiment. 
     With reference to FIG. 9, screen  12  is preferably composed of SS wire mesh (24 gauge, 8 mesh, 8 wires per inch), and preferably has a diameter of 1.93 inches. 
     With reference to FIGS. 10 and 11, a preferred embodiment of elastic diaphragm  10  is a molded resilient elastomer having the following portions: a relatively thick central portion  10 c, a relatively thin outer rim  10 a, a relatively thick retaining ring portion  10 d (for retention within groove  30  of housing body  4 ), and a relatively thin portion  10 b connecting portion  10 c with portion  10 d. Central portion  10 c lies in a first plane, and portions  10 a and  10 d lie in a second plane (parallel to, and separated from, the first plane). In a preferred embodiment, central portion  10 c has a thickness of about 0.065 inches and diameter of about 1.190 inches, rim  10 a has thickness of about 0.020 inches and outer diameter of about 2.600 inches, ring portion  10 d has thickness of about 0.060 inches, and portion  10 b has thickness of about 0.020 inches. Preferably, diaphragm  10  is made of the material known as “70 BUNA-N rubber,” and no metal plate is bonded to diaphragm  10 . 
     Various modifications and variations of the described apparatus of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments.