Fluid-pressure and analogous brake systems – Pulsation neutralizers
Reissue Patent
2000-10-11
2003-07-01
Butler, Douglas C. (Department: 3683)
Fluid-pressure and analogous brake systems
Pulsation neutralizers
C138S031000
Reissue Patent
active
RE038163
ABSTRACT:
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'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'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'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.
REFERENCES:
patent: 3451431 (1969-06-01), Royer
patent: 3757825 (1973-09-01), Givens et al.
patent: 3931755 (1976-01-01), Hatridge
patent: 4166655 (1979-09-01), Spero
patent: 4220376 (1980-09-01), Spero
patent: 5078455 (1992-01-01), Washington
patent: 5-39022 (1993-02-01), None
Butler Douglas C.
Peterson Richard E.
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