U.S. patent application number 09/969543 was filed with the patent office on 2003-11-06 for fluid accumulator for use in a vehicle anti-lock brake system.
Invention is credited to Cassidy, John, Maloney, Brian, Starr, Joseph A..
Application Number | 20030205283 09/969543 |
Document ID | / |
Family ID | 25515667 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030205283 |
Kind Code |
A1 |
Maloney, Brian ; et
al. |
November 6, 2003 |
FLUID ACCUMULATOR FOR USE IN A VEHICLE ANTI-LOCK BRAKE SYSTEM
Abstract
A hydraulic control unit (HCU) for a vehicle brake system having
an HCU body and an accumulator mounted in the HCU body. A grommet
is provided for mounting the HCU body to a vehicle body and
resiliently separating the HCU body from the vehicle body. The
grommet defines a vent path for the accumulator and includes a
hollow generally cylindrical shaft. The shaft has a closed end and
an open end, and the closed end has an opening therethrough. An
enlarged annular head is formed on the open end of the shaft and
has an inner surface defining an axial bore therethrough. The axial
bore is in fluid communication with the hollow shaft, the annular
head further has a crown cut geometry providing radially extending
grooves within an axial face of the annular head, the radially
extending grooves being in fluid communication with the axial bore
of the annular head.
Inventors: |
Maloney, Brian; (Allen Park,
MI) ; Cassidy, John; (Brighton, MI) ; Starr,
Joseph A.; (Plymouth, MI) |
Correspondence
Address: |
MACMILLAN SOBANSKI & TODD, LLC
ONE MARITIME PLAZA FOURTH FLOOR
720 WATER STREET
TOLEDO
OH
43604-1619
US
|
Family ID: |
25515667 |
Appl. No.: |
09/969543 |
Filed: |
October 2, 2001 |
Current U.S.
Class: |
138/31 |
Current CPC
Class: |
F15B 2201/413 20130101;
B60T 8/3685 20130101; Y10S 303/11 20130101; F15B 1/08 20130101;
F15B 2201/312 20130101; B60T 8/34 20130101; F15B 2201/21
20130101 |
Class at
Publication: |
138/31 |
International
Class: |
F16L 055/04 |
Claims
What is claimed is:
1. A fluid accumulator comprising: an accumulator body having an
inner surface defining an axial bore extending from an open end of
said accumulator body to a closed end of said accumulator body; a
generally cup-shaped cylindrical piston having an inner surface
defining an axial bore extending from an open end of said piston to
a closed end of said piston, said piston being slidably received
within said axial bore of said accumulator body; a cap having a
generally cylindrical body portion having an inner surface defining
an axial passageway through said body portion, said cap further
having a circumferential, radially outwardly extending flange
formed on one end of said body portion, said cap being mounted in
said bore of said accumulator body to retain said piston in said
bore of said accumulator body; a spring disposed between said cap
and said piston, said spring urging said piston relatively away
from said cap and toward said closed end of said accumulator body;
and a grommet having a shaft and an enlarged annular head formed on
a first end of said shaft, said shaft being disposed to seal
against said inner surface of said cap, said grommet having an
inner surface defining an axial bore extending from said head
through an open end of said shaft at said first end of said shaft
to a closed end of said shaft at a second end of said shaft, said
closed end of said shaft having a closable passageway
therethrough.
2. The fluid accumulator according to claim 1, said accumulator
body forming a portion a hydraulic control unit (HCU) of a brake
system.
3. The fluid accumulator according to claim 1, said closed end of
said body further including a plurality of apertures
therethrough.
4. The fluid accumulator according to claim 1 wherein said piston
includes a plurality of bosses extending axially from an outer
surface of said closed end of said piston, and a circumferential
groove formed in an outer surface of said piston.
5. The fluid accumulator according to claim 4 further including an
O-ring disposed in said circumferential groove of said piston for
fluidly sealing said piston and said body.
6. The fluid accumulator according to claim 1 wherein said spring
is a helical coil spring.
7. The fluid accumulator according to claim 1 wherein an outer
surface of said shaft of said grommet includes a plurality of
circumferential ribs for sealing engagement with said axial
passageway of said cap.
8. The fluid accumulator according to claim 7 including a plurality
of axial grooves formed in said inner surface of said grommet.
9. The fluid accumulator according to claim 8 wherein said closable
passageway formed in said closed end of said shaft of said grommet
comprises a narrow slit, said slit providing fluid communication
between said axial grooves of said grommet and said axial bore of
said piston.
10. The fluid accumulator according to claim 9, wherein said
annular head includes an annular side surface and an end surface,
said end surface having a plurality of equiangular spaced V-shaped
grooves extending radially from said axial bore of said grommet,
the base of each groove extending at an angle from a plane defining
said end surface of said head, adjacent ones of said grooves
defining radially extending ridges therebetween, said V-shaped
grooves fluidly communicating with said axial grooves of said
grommet.
11. The fluid accumulator according to claim 1 further including a
pin having a length less than the length of said axial bore of said
grommet, the length of said pin further being less than the length
of said axial grooves of said grommet, said pin being mounted
within said axial bore of said grommet.
10. The fluid accumulator according to claim 11 including an
axially extending groove formed in at least one of said inner
surface of said grommet and an outer surface of said pin.
13. A grommet for a fluid accumulator, comprising: a hollow
generally cylindrical shaft having a closed end and an open end,
said closed end of said shaft having an opening therethrough; and
an enlarged annular head formed-on said open end of said shaft,
said annular head having an inner surface defining an axial bore
therethrough, said axial bore being in fluid communication with
said hollow shaft, said annular head further having a crown cut
geometry providing radially extending grooves within an axial face
of said annular head, said radially extending grooves being in
fluid communication with said axial bore of said annular head.
14. The grommet according to claim 13 wherein said inner surface of
said hollow shaft includes a plurality of axial grooves formed
therein, said axial grooves providing fluid communication between
said radially extending grooves of said head and said opening in
said closed end of said shaft.
15. The grommet according to claim 13 farther including a plurality
of circumferential ribs formed on an outer surface of said
shaft.
16. The grommet according to claim 13 wherein said opening through
said closed end of said shaft is self-closing.
17. A hydraulic control unit (HCU) for a vehicle brake system
comprising: an HCU body; an accumulator mounted in said HCU body;
and a mount for mounting said HCU body to a vehicle body, said
mount including a grommet for resiliently separating said HCU body
from said vehicle body, said grommet defining a vent path for said
accumulator.
18. The hydraulic control unit according to claim 17 wherein said
grommet includes a hollow generally cylindrical shaft having a
closed end and an open end, said closed end of said shaft having an
opening therethrough, and an enlarged annular head formed on said
open end of said shaft, said annular head having an inner surface
defining an axial bore therethrough, said axial bore being in fluid
communication with said hollow shaft, said annular head further
having a crown cut geometry providing radially extending grooves
within an axial face of said annular head, said radially extending
grooves being in fluid communication with said axial bore of said
annular head.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates generally to a low pressure
accumulator and more particularly, to a low pressure accumulator
assembly for receiving and temporarily storing fluid in a vehicle
anti-lock brake system.
[0002] Braking a vehicle in a controlled manner under adverse
conditions such as rain, snow, or ice generally requires precise
application of the brakes by the vehicle driver. Under these
conditions, or in panic stop situations, a driver will often apply
excessive brake pressure, thus causing the wheels to lock such that
excessive slippage between the wheels and the road surface takes
place. Wheel lockup conditions can lead to loss of directional
stability and, possibly, uncontrolled vehicle spinout.
[0003] In a continuing effort to improve the operational safety of
vehicles, many companies have been involved in the development of
anti-lock braking systems. While typically such systems are adapted
to control the braking of each braked wheel of a vehicle, some
systems have been developed for controlling the braking of only a
portion of the braked wheels. Examples of prior art anti-lock brake
systems are disclosed in U.S. Pat. Nos. 3,515,440; 3,731,979;
3,870,376; and 3,880,474 and are herein incorporated by
reference.
[0004] Generally, prior art anti-lock brake systems include a
central control unit for monitoring the speed of the controlled
wheels to determine the deceleration of the controlled wheels. When
the brakes of the vehicle are applied and the wheel deceleration of
the monitored wheels exceeds a predetermined deceleration
threshold, indicating that there is wheel slippage and the wheels
are approaching a lockup condition, the central control unit
functions to control the application of hydraulic pressure through
a control valve means to the associated brakes to prevent lockup of
the controlled wheels. Typically, the anti-lock brake system
includes means for cyclically reducing and reapplying pressure to
the associated brakes to limit wheel slippage to a safe level while
continuing to produce adequate brake torque to decelerate the
vehicle as desired by the driver. While some systems utilize a
separate hydraulic pump as the means for reapplying pressure, other
systems, such as disclosed in U.S. Pat. No. 4,418,966, do not
require the use of a separate hydraulic pump. U.S. Pat. No.
4,418,966 is herein incorporated by reference.
[0005] In controlling the application of pressure to selected wheel
brakes, many systems utilize a low pressure accumulator which is
operative to temporarily receive and store brake fluid during
pressure reduction phases of the anti-lock operation. The low
pressure accumulator typically maintains fluid stored therein at a
predetermined minimum pressure determined by a compression spring
acting on an accumulator piston, generally in the range of 30-60
p.s.i. This minimum pressure represents the lowest pressure to
which the controlled brakes can be reduced during anti-lock
operation. However, it has been found that, in certain braking
situations, it is necessary to reduce the controlled pressure below
this minimum pressure in order to achieve the desired control. U.S.
Pat. No. 4,976,501, incorporated herein by reference, describes an
accumulator which maintains brake fluid stored therein at or near
zero pressure. Thus, if necessary, fluid pressure to the controlled
wheel brakes can be reduced to near zero pressure.
[0006] Referring now to FIG. 1, a pair of conventional low pressure
accumulators are generally shown at 100. Each low pressure
accumulator 102 includes a generally cup-shaped piston 104 slidably
received within an axial bore 106 of a hydraulic control unit (HCU)
108 of a braking system. An end cap 110 is sealingly mounted at an
open end of the bore 106. Typically, the end cap 1 10 includes an
aperture for receiving an elastomeric boot 112. The elastomeric
boot 112 is generally cup shaped and has a closed end and an open
end. The open end includes an inwardly extending flange for
attaching to a lip portion (not shown) formed about the aperture of
the end cap 110. The boot 112 may include a passageway, such as a
narrow slit, for the passage of air in the closed end thereof. In
operation the elastomeric boot 112 allows a small volume of air to
flow between the boot 112 and the end cap 110 as the piston moves
from a top dead center to a bottom dead center position. The flow
of air is further facilitated in boots 112 having a narrow slit in
the closed end. The very small opening between the boot 112 and the
end cap 110 further inhibits, but does not eliminate, the flow of
water or contaminants into the accumulator. The boot 112 thereby
allows for the passage of air as the piston 104 moves and provides
an environmental seal which prevents water and contaminants from
entering the accumulator 102.
[0007] Conventional braking system hydraulic control units are
typically mounted to vehicle frame by a plurality of bolts.
Elastomeric grommets are typically mounted between each bolt and
the frame to absorb vibrations. Such conventional braking system
hydraulic control units typically require three or more mounting
bolts and associated elastomeric grommets, washers, and nuts.
SUMMARY OF THE INVENTION
[0008] The invention relates to a fluid accumulator, especially a
low pressure fluid accumulator of a hydraulic control unit of a
vehicle brake system. The accumulator body has an inner surface
defining an axial bore extending from an open end to a closed end
of the accumulator body. A generally cup-shaped cylindrical piston
has an inner surface defining an axial bore and extends from an
open end to a closed end of the piston, and is slidably received
within the axial bore of the accumulator body. A cap has a
generally cylindrical body portion and an inner surface defining an
axial passageway therethrough. A circumferential, radially
outwardly extending flange is formed on one end of the body portion
of the cap. The cap is mounted in the bore of the accumulator body
with the outer edge of the flange of the cap pressed into or
otherwise fixed relative to the bore of the accumulator body and
retains the piston therein. A spring is disposed between the cap
and the piston and urges the piston relatively away from the cap
and toward the closed end of the accumulator body. A grommet has a
shaft and an enlarged annular head formed on a first end of the
shaft. The shaft is disposed to seal against the inner surface of
the cap. The grommet has an inner surface defining an axial bore
extending from the head through an open end of the shaft at the
first end of the shaft to a closed end of said shaft at a second
end of the shaft, the closed end of said shaft having a closable
passageway therethrough.
[0009] The low pressure accumulator of the invention provides an
advantageous integration of the mounting of a braking system
hydraulic control unit, and venting of a low pressure accumulator
into one component. Assembly of a hydraulic control unit within a
vehicle is simplified because, for example, one or more fasteners,
such as a bolt and an associated grommet, washer, and nut, is
eliminated. Further, the mechanical features of the grommet create
a "dual-rate" effect that is more compliant for low amplitude
vibration.
[0010] Various objects and advantages of this invention will become
apparent to those skilled in the art from the following detailed
description of the preferred embodiment, when read in light of the
accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is an elevational view, partially in cross section,
of a pair of low pressure accumulators as known in the prior art
including a rubber boot.
[0012] FIG. 2 is an elevational view in cross section of a low
pressure accumulator in accordance with this invention with the
components of the accumulator shown in position after the
introduction of fluid into the accumulator reservoir.
[0013] FIG. 3 is a perspective view of the grommet of FIG. 2.
[0014] FIG. 4 is an end view of the grommet taken along line 4-4 of
FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Referring now to the drawings, there is illustrated in FIG.
2 a low pressure accumulator, generally shown at 14. The low
pressure accumulator 14 includes a body 34. The body 34 typically
forms a portion of a hydraulic control unit (HCU) of a brake
system. The body 34 has an axial bore 36 extending from an open end
38 to a closed end 40. The closed end 40 of the bore 36 includes
one or more apertures 42 for providing fluid communication between
the bore 36 and the brake lines of the brake system in which the
accumulator is installed.
[0016] A generally cup-shaped cylindrical piston 45 has an inner
surface defining an axial bore 46 extending from an open end 47 to
a closed end 48 of the piston 45. The piston 45 is slidably
received within the axial bore 36 of the body 34. Preferably, a
plurality of generally cylindrical bosses 49 extend axially from an
outer surface 50 of the closed end 48. The piston 45 and the body
34 cooperate to define an accumulator reservoir 15. A
circumferential groove 56 is formed in an outer surface of the
piston 45. An O-ring 58 is disposed within the groove 56 for
fluidly sealing between the piston 45 and the inner surface of the
body 34 defining the axial bore 46.
[0017] A cap 60 has a generally cylindrical body portion 62. The
body portion 62 is generally tubular having an inner surface
defining an axial passageway 63 therethrough. The body portion 62
further has an inner end 62a (closest to the closed end 40 of the
bore 36) and an outer end 62b. A circumferential, radially
outwardly extending flange 64 is formed on the outer end 62b of the
body portion 62. The cap 60 is mounted in the bore 36 of the
accumulator body 34 to retain the piston 45 in the bore 36.
Preferably the cap flange 64 is press fit within the open end 38 of
the body 34, however any other suitable form of mounting may be
used. A helical compression spring 68 is disposed between the cap
flange 64 and the closed end 48 of the piston 45. The spring 68
urges the piston 45 relatively away from the cap flange 64 and
toward the closed end 40 of the accumulator body 34.
[0018] Referring now to FIGS. 2 through 4, a grommet 70 has a shaft
72 having an inner end 72a (adjacent the inner end 62a of the cap
60) and an outer end 72b. The grommet 70 may be formed of any
suitable material, such as an elastomeric material. An enlarged
annular head 74 is formed on the outer end 72b of the shaft 72. The
grommet 70 includes an inner surface defining an axial bore 75
extending from an open end at the outer end 72b of the shaft 72 to
a closed end 76 at the inner end 72a of the shaft 72. The closed
end 76 of the shaft 72 has a passageway 78, such as, for example, a
narrow slit, formed therethrough. The passageway 78 preferably is
urged closed by the surrounding elastomeric material of the grommet
70. A plurality of spaced apart circumferential ribs 80 are formed
on an outer surface of the shaft 72 of the grommet 70. The outer
diameter of each rib 80 is slightly larger than the inner diameter
of the axial passageway 63 of the cap 60. When inserted into the
passageway 63, the ribs 80 compress radially inwardly and deform to
provide a sealing engagement with the axial passageway 63 of the
cap 60. A plurality of axial grooves 82 are formed within the axial
bore 75 of the grommet 70. As illustrated in FIG. 2, the grooves 82
extend the entire length of the axial bore 75, however the grooves
82 may have a length shorter than the length of the bore 75, as
will be explained in detail below. The narrow slit 78 provides
fluid communication between the axial bore 75 and the enclosed
volume 79 between the piston 48, the cap 60, and the grommet 70, to
vent the volume 79 and thus allow the piston 48 to move freely.
[0019] The head 74 of the grommet 70 has a diameter larger than the
diameter of the shaft 72. The head 74 has a crown cut geometry
providing radially extending V-shaped grooves 84 within an axial
face of the head 74. The V-shaped grooves 84 are equiangular spaced
and extend from an opening of the axial bore 75 of the grommet 70.
The base of each groove 84 extends radially outwardly and at an
angle a away from the plane p of the axial face of the head 74
(e.g., the plane perpendicular to a longitudinal axis of the axial
bore 75 of the grommet). However, it will be appreciated that
satisfactory results may be achieved by grooves having other
shapes, such as grooves with a square or arcuate cross-section.
Similarly, satisfactory results may be achieved by a grommet 70
wherein the base of each groove extends radially outwardly and at
an angle toward the plane of the axial face of the head 74 or
wherein the base of each groove is parallel with the plane of the
axial face of the head 74. Each groove 84 is defined by a pair of
equiangular spaced ridges 86 on either side thereof. The grooves 84
provide radial fluid communication between the atmosphere and the
axial bore 75 of the grommet 70.
[0020] The axial bore 75 is adapted for mounting on a pin 88.
Preferably, the pin 88 is a steel pin attached to a vehicle chassis
90. The pin 88 is preferably mounted within the bore 75 of the
grommet 70 in a line to line fit, however any other suitable
mounting method may be used, such as an interference fit.
[0021] The piston 45 is normally biased upwardly (as viewed in FIG.
2) by the compression spring 68 toward the closed end 40 of the
accumulator body 34. In this position, the piston 45 and the body
34 cooperate to define an accumulator reservoir 15 at minimum
volume. In accordance with the present invention, when the brake
system enters the anti-lock mode and fluid is dumped into the
accumulator reservoir 15, the piston 45 is shifted downwardly (as
viewed in FIG. 2) and compresses the spring 68. During non-braking
conditions, the spring 68 urges the piston 45 upwardly (as viewed
in FIG. 2) such that the bosses 49 on the surface 50 of the piston
45 are seated against the closed end 40 of the accumulator body 35
to maintain the accumulator reservoir 15 at minimum volume.
[0022] An important aspect of the invention is the configuration of
the grommet 70. The grommet 70 is adapted to be mounted in the low
pressure accumulator 14 of a typical ABS brake system and
particularly may be mounted in an HCU arrangement. The HCU (not
shown) is provided with a plurality of internal openings and
passageways formed therein for receiving and interconnecting
various components of the ABS, such as, for example, a dump valve,
and one or more low pressure accumulator 14.
[0023] The HCU is typically attached to a vehicle frame by a
plurality of bolts, such as, for example three bolts. Each bolt
typically includes a rubber grommet attached thereto and disposed
between the HCU and the vehicle frame to dampen vibrations. Also
associated with each bolt are associated washers and nuts. The
specific construction of the grommet 70 allows the low pressure
accumulator 14 to be used as a mounting point to mount the HCU to
the vehicle frame. Specifically, the pin 88 is preferably a portion
of a mounting bracket and suitably attached to the vehicle chassis
90. The HCU may therefore be attached to the vehicle chassis 90 by
inserting the pin 88 into the bore 75 of the grommet 70. The ridges
86 of the grommet 70 are disposed against the mounting bracket or
the vehicle chassis 90. More specifically, the HCU may be slipped
onto the pin 90 (or pins 90) associated with each of the low
pressure accumulators 14 of the HCU that is provided with an
associated grommet 70 to limit movement in two axes. The HCU is
prevented from slipping back off of the pin(s) 88 (the third axis
of movement) by the use of one or more conventional bolt/nut and
grommet arrangement. The use of the low pressure accumulator 14 and
its associated grommet 70 as a mounting point thereby reduces the
number of mounting bolts and associated rubber grommets, nuts and
washers required to mount the HCU to the vehicle chassis 90 and
speeds the time required to mount the HCU.
[0024] The novel shape of the grommet 70 also facilitates improved
passage of air as the piston 45 moves, and provides an improved
environmental seal which prevents water and contaminates from
entering the accumulator 14. As the piston 45 moves toward the
closed end 40 of the body 34, air is drawn into a cavity between
the closed end 76 of the grommet 45 and the closed end 48 of the
piston 45. Specifically, air flows between the grommet 70 and the
chassis 90, through the grooves 84, through the axial grooves 82
and through the passageway 78. Conversely, as the piston 45 moves
away from the closed end 40 of the body 34 and toward the closed
end 76 of the grommet 45, air flows back through the narrow slit
78, through the axial grooves 82 and though the grooves 84. Note
that the pin 88 has a length shorter than the length of the bore 75
of the grommet 70 and shorter than the length of the axial grooves
82, such that air may flow through the grooves 82 from the V-shaped
grooves 84 to the slit 78.
[0025] As indicated above, the novel shape of the grommet 70
provides an improved environmental seal by providing a circuitous
path for water and contaminates to flow. Further, the narrow slit
78 is normally closed. Any water or contaminate that may flow
through the circuitous path formed by the V-shaped grooves 84 and
the axial grooves 82 is prevented from flowing through the normally
closed narrow slit 78, thus providing an improved environmental
seal.
[0026] The plurality of narrow ridges 86 provide a reduced contact
surface between the grommet 70 and the vehicle chassis 90. The
crown-shaped geometry creates a "dual rate" effect that is more
compliant for low amplitude vibration. That is, the reduced contact
surface allows the grommet 70 to efficiently absorb energy
generated by high frequency, low amplitude vibration typically
generated by the brake system 10 and prevents the transfer of the
energy to the vehicle chassis 90. Additionally, the reduced contact
surface allows the grommet 70 to absorb the energy typically
generated by the vibration of the vehicle during travel on a road
surface and prevents the transfer of road vibration through the
chassis 90 to the brake system 10.
[0027] The accumulator assembly of the present invention has been
explained and illustrated in its preferred embodiment. However, it
will be appreciated that various modifications may be made to the
accumulator assembly without departing from the spirit of the
present invention. For example, while the preferred embodiment of
the invention utilizes axial grooves 82 within the bore 75 of the
grommet 70 for the passage air, other means could be used. For
example, grooves could be formed on an outer surface of the
mounting pin 88.
[0028] The principle and mode of operation of this invention have
been explained and illustrated in its preferred embodiment.
However, it must be understood that this invention may be practiced
otherwise than as specifically explained and illustrated without
departing from its spirit or scope.
* * * * *