Note: Descriptions are shown in the official language in which they were submitted.
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The presen~ invention re]ates to a valve m~ber
in a hydraulic brake booster.
In Canadian Patent No. 1,0~0,281, issued June 24,
1980, a hydrauLic brake booster includes a piston which
is movable in response to pressurized fluid in a pressure
chamber to initiate a braking application. In order to
conserve space and weight, the piston is hollow to
substantially define a storage chamber within the piston.
If the pressure of the pressurized fluid within the
lO pressure chamber is insufficient to move the piston during
- braking, the storage chamber is communicated to the
pressure chamber to assist in moving the piston, thereby
providing a power assist to the braking application.
Generally, the storage chamber is communicated to the
pressure chamber when a spool valve within the brake
booster fails to communicate pressurized fluid to the
pressure chamber, either because of an inoperable pressure
source or the spool valve becoming wedged in the brake
booster housing.
With the pressure source rendered inoperable, the
communication of pressurized fluid to the pressure chamber
from the storage chamber is re~uired to provide a power
assist to braking in order to bring a vehicle to a stop.
Consequently, a reliable valve member ~hich operates to
communicate the storage chamber within the piston with
the pressure chamber is believed to be an improvement
in the state of the art~ Moreover, during assembly it
is desirablè to remove only valve members which are not
satisfactory without scraping any other parts of the
30 hydraulic brake booster.
The present invention resides in a hydraulic
`~ brake booster having a housing defining a pressure chamber,
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a movable piston mounted in the hollsing and clefining a
storage chamber within the piston, a contrvl valve mounted
in the housing, an operator ac~uator cooperating with
the control valve to communicate pressurized fluid to
the pressure chamber, and a valve member carried by the
piston. In the present invention the valve member includes
a unitary assembly for attachment with the piston, the
unitary assembly providing for opening and closing
communication between the pressure chamber and the storage
chamber in response to a pressure differential across
the unitary assembly.
In a specific embodiment of the invention, the
piston includes a plug which is exposed to the pressure
chamber and a passage through the plug receives a valve
member. A blind bore in the plug receives an operator
actuator and the passage is radially spaced from and
offset relative to the blind bore. The valve member
comprises a unitary assembly for insertion within the
passage, the unitary assembly including a sleeve with a
~0 stepped bore therethrough, a seat member biased against
a shoulder formed by the stepped bore and a stem extending
through a bore in the seat member.
Also in a specific embodiment of the invention,
the operator actuator includes a lever which engages a
pin extending through an aperture in the plug. The pin
carries a finger which is engageable with the valve
member sten. When the pressure of the fluid within the
pressure chamber is insufficient to move the piston to
a braking position, the lever pivots to urge the finger
via the pin into engagement with the stem. As the stem
is moved relative to the seat member, the storage chamber
is communicated with the pressure chamber to increase the
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pressure of pressurized fluid within the pressure chamber,
thereby providing a power assist to braklng.
It is a primary object of the present invention
to provide a unitary assembly which is separate from
the piston, but easily connected to the piston for
controlling the communication of pressurized fluid from
the pressure chamber to the storage chamber and vice versa.
BRIEF DESCRIPTIO~ OF THE DRAWINGS
Figure 1 is a schematic view of a brake system
showing a side cross-sectional view of a hydraulic brake
booster constructed in accordance with the present
invention;
Figure 2 is a side cross-sectional view of the
valve member used in the hydraulic brake booster of
Figure l; and
Figure 3 is a cross-sectional vlew taken along
line 3-3 of Figure 1.
D~T~ILED DESCRIPTION
A hydraulic brake booster 10 provides a power
assist during braking to increase the force applied to
a master cylinder in a vehicle, thereby assisting an
operator in stopping the vehicle~ In the hydraulic
brake booster of Figure 1, a housing 12 includes a pair
of bores 14 and 16 and substantially defines a pressùre
chamber 16. A piston 18 disposed in bore 14 is movable
- relative to the housing 12 in response to pressurized -~
fluid within the pressure chamber 16. A conventional
master cylinder (not shown) connects with the left side
of the housing so that movement of the piston 18 causes
the master cylinder to communicate brake fluid to a set
of wheel cylinders (not shown) to initiate braking of
the vehicle.
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A control valve 20 disposed within housing ~ore
16 moves relative to the housing to cooperate with an
in].et 22, an outlet 24, and a return 26, in order to
control communication of pressurized fluid to the p~essure
chamber 16. The control valve preferably comprises a
spool valve 30 with a passage 32 communicating with the
pressure chamber 16. A sleeve 34 carried by the spool
valve 30 is movable from a normal position to close the
passage 32.
An operator actuator 40 comprises an input rod 42
and a l.ever 44. The lever is pivoted about a pin 46 on
the sleeve 34 and about a pin 48 on the piston 18. -A
spring 50 biases the sleeve 34 and pin 46 to one end of
the spool valve 30 and a spring 52 biases the pin 48 to
one side of a transverse axially elongated aperture 54
on the piston 18. A pair of pins 47 connects the i.nput
rod 42 with the lever 44.
In accordance with Canadian Patent No. 1,080,281,
the piston 18 forms a storage chamber 60 internally of
the piston 18. A diaphragm 62 separates the storage .
chamber 60 from a compressible medium 64 such that
pressurized fluid communicated to the storage chamber 60
compresses the medium to maintain the storage chamber 60
under pressure. The piston 18 preferably comprises a
stepped cylindrical casing 66 termi.nating in an open
end 68 which receives a plug 70. The plug receives the
input rod 42 in a blind bore 72 so that it is possible
to manually move the piston 18 to a braking position
by urging the input rod 42 into the blind bore 72 until
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the input rod abuts the boctom of the blind bGre 72, whereupon urther
movement of the input rod transMlts movement to the piston 1~.
In accordance with the present invention, a valve Member 71~ is
carried in 3 passage ?6 in the plug 70. Viewin~g Figure 2, the val~e
member 74 co~prises a unitary assembly for easy ascembly with the pl;lg 70.
The unitary assemblv includes a sleeve 78 with a stepped tDre 50 therethrou~h
defining a shoulder 82. A seat member 84 i5 biased into sealing engagement
~ith the shoulder 82 by a spring 86 which is retained within the stepped
bore 80 by a ring 88 secured to the sleeve 78. A tapered bore 91 extending
through the seat member 84 receives a stem 9û with a head 92~ The stm
extends through a polygonal opening 94 in the ring 88 which supports the
stem and permits co~munication between the stem and polygonal opening gl,.
When urged to the righ~ in Figure 2, the stem he3d ~2 sealingly engages
the seat member 84 and a plura1ity of tabs ~6 Gn the sleeve 7~ oppose
the head 92 to define the left pos;tion of the stem head~ ;
The lever 44 is pivotally ~ounted on the pin 48 whict) extends
through the ~ransverse axially elongated aperture 54~ The pin 48 carries
a finger lûO which is slida~ly mounted in an undercut slot iO2 in the plug 70.
The finger lOû opposes the stem 90, such th3t movement of the 'in~er 100
2~ to the left moves the stem 90 to th~ left also.
Turning to Figure 3~ the valve mernber 74 is disposed to the
left side of the blind bore 7~ and radially belo~l the centerlina of ~he
blind ~ore. rhe plag 70 includes an enlarged d?ameter portion 104 whlch
sealingly engages the casing ~6 at the open end 68 and a red~ced diameCer
portion 106. The passage 76 ext2nds through the enlargsd diameter por~
ti~n 104 and opens to the pra;sure chamber 16. The reduced dianletzr por-
tion 106 forms ~he transvers* axlally elongated apertwre 54 and includes a
pocket 108 for receiving the spring 52 which biases the pin 48 and ths
finger 100 to~ard one end or the aperture 54. Moreo~er, the reduced
3~ dia~,eter portion lOc extends from the bottom of the enl2rged portion 104
and forms the blind hore 72 For receiving tke ?nput rod 42.
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,~IODE OF OPERATIO~I
The hydraultc brake booster 10 operates 'n a conventional manner
to provide a power assist to a braking appliration. For example, ~hen the
5nput rod 42 is moved to the left to initiate braking, the connecti~g pins ~7
cause tha le~er 44 to pivot akout the pin 48 thereby ~ving the eontrol
valve 20 to open co,~nunication between ~he inlet 24 and the pressure
chamber 16. Pressurized fluid communicated to the pressure chamber 16
imparts a force on the piston 18 to move the piston to the left, thereby
actuating the master cylinder to &ommunicate brake fluid to a wheel cylinder,
which effectuates a braking application. With pressurized fluid communi-
cated to the pressure chamber 16, the storage chamber 60 is charged if
the pressure within the pressure chamber is greater than ~he pressure
within the storage chamber~ The pressure differential across the valve
member 74 causes the stem 90 to be biased against the tabs 96 so tha~
fluid is communicated through the opening ~4, 3 slot 95 in the seat
member 84, the clearance between the stem 90 and ~he bore 91 on the seat
member, and the clearance between the head 92, and the stepped bore 80
tn order to cvmmunicate the pressurized fluid to the storage chamber 60.
If the pressure in the pressure chamber is less ~han that in the storage
cnamber, the head 92 is biased into sealing engagement with the seat
member 84 to trap pr~ssurlz~d fluid in the storage chamber 60. If, d~lring
braking, the pressure of the pressurized fluid within ~he pres~ure ~hamber
is tnsufficient ~o move the pis~on 18, further m~vement of the input rod 42
causes the pivoting lever 44 to move the spsol valve 30 in abutment w~th a
stop 31 and to move the stee~e 34 relati~/e to the spool valv~ 30 theraby
closing the passage 32~ Continued movement of thé inpu~ rod 42 pivo~s
the lever about the pin 46 and urges the pin 4~ and finger 100 to !nove
agains~ the spring 52~ The finger 100 engages the stem 90 to move the
stem head ~ away frsm the seat member 84, thereby openirlg communication
betw~en the storage chamber arld the pressure ehamber. Consequently
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pressurized fluid is communicat~d from the storage chamber to the pressure
chamber to create d force urging the piston to move to the left. There-
fore, a power assist is provided during braking by the storage chamber,
even though the control valve fails to commllnicate enough pressurized
fluid to the pressure chamber.
If the pressurized fluid wirhin the s~oraye chamber 60 is
exhausted after a few brake applications without the control valve
operating properly, a brake application is still possible, as continued
movement of the input rod 42 abuts the latter with the bottom of the
blind bore 72, so that movement of the input rod 42 imparts movement
to the piston 18 to actuate the master cyl;nder.
When brakTng is ter~inated, the spool valve and sleeve retur~
to their normal position to communicate the pressure chamber w7th the
return 26 via passage 37. Consequently, if ~he pressure of the pressurized
fluid within the s~orage chamber 60 increases due to he.at or other means
to a pressure above a predetermined value, the pressure differential
across the stem and seat member causes the stem head and seat menber
to move against the spring 86 to open the storage chamber to the pressure
chamber in order to relieve the increased pressure in tha storage chamber~
Because the pressure chamber is in communication with the return ~6, the
venting of incr~ased pressure to the pressure chamber does not initia~e
braking, as the increased pressure communicatsd from the s~or-age chamber
to pressure cha0ber is communicated to the return via passage 32
Because the valve member 74 is a unitary assemD1y, the valve .
member can be tested independently of the plug 70 so that defective
valve members can be isc7ated before the pluy and attached valve member
ars engaged with th~ çasing ~6 to form the piston 18.
Viawing Figure 2, the slseve 78 terminates in a fl3nge 110
which forms a tapered side edge 112. The axial width or the flange
is narrower at the junction with the sleeve and the passage 76 is tapered
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at the snd receiving the valve member 74 so that an excessive buildup
of pressure within the storage chamber coupled with a ~lfunction of the
venting cf the storage chamber causes the flange 110 to deforrn in response
to the force of th~ excessive pressure in the storage chamber. The flange
deforms to engage the tapered side edge 112 with the tapered passage
~i portion~ thereby rMVing the valve member to the right. This r^overrent
urges the stem 90 into engagement with the finger 100 to rnove the
stem away from the seat member 84 in order to vent the excessive buildup
of pressure within the storage chamber to the pressure chamber.
Although many variations of the present invention are possible
by one skilled in the art it is intended that these variations are included
wiehin the scope of the appended claims.
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