Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates generally to
hydraulic braking systems of motor vehicles and, more
particularly, to fluid pre~sure regulating devices to be
incorporated in such braking systems.
More particularly, this invention relates to a
load-responsive pressure reducing valve assembly which is
so constructed that a starting pressure for the pressure
reducing operation thereof whereby an input hydraulic brake
pressure from a master cylinder is changed to an output
hydraulic brake pres~ure in a prede~ermined ratio, is
. , - .
controlled by means of a pressure proportioning valve which
restricts the flow of fluid from the master cylinder to a
~ brake wheel cylinder during a predetermined range of
;', increasing fluid pre~sure supplied to the wheel brake
,, cylinder. The device is capable of distrib-~ting the
hydraulic brake pressure, corresponding to a transient
weight transfer from rear wheels of the vehicle to the front
.,.;'j - . :,
wheels caused by the braking operation, to front and rear
. '1 . .
,; braki~g means by varying the star~ing pressure for brake
.'.1 ' 1
~ 20 fluid pres ure reduction to the rear braking m~ans in
.".. ~ .- . .
~ response to load and deceleration of the vehicle.
, ~ .
It is a well known fact that when a wheeled
~-1 vehicle such as an automobile or truck having a brake system
on the ~ront and rear wheels is brakedO the braking causes a
forward transfer of the load which occurs due to the
deceleration iner~ia of the vehicle and thereby reduces the
~ load on the vehicle rear wheels and consequently reduces
; the contact of the rear wheels with the ground surface~
Thus, the road holding ability of the rear wheels decreases,
causing the rear wheels to lock under braking application
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~ which, in turn, causes dangerous skidding and possible
',~ loss of control of the vehicle. It is also known ~hat
this tendency is even more likely to be observed in small
siæed truc~s which have a large ratio of load variation
and which also ha~e a shor~ wheel base or distance between
the front and rear wheel axles.
A number of attempts have been proposed for ,'
~' accomplishing the above-described pre~sure reduction operation
,: .
wherein the fluid pressure supplied to the rear wheel
brake~ is reduced to prevent such skidding and provide
maximum brake efficiency under varying vehicle load
;. conditions. One such apparatus is illustrated in U.S.
'- Patent No. 3,802,750, wherein ~he starting point of pressure
reduction in a reducing valve is delayed under conditionq
, o a heavy vehicle load by utiliæing the characteristic
,;j that the vertical distance between the rear wheel axle
'', and the loading platform of the vehicle is shortened with
~' the application of the load. Another apparatus of the
',~,.~ prior art is disclosed in U.S. Patent No. 3,317,251,
wherein ~he operation of the reducing valve is initiated
only when the hydraulic pressure from the master cylinder
prevented from being tran~mitted to the rear wheel
brake cylinders by mean,~ of an inertia ball valve member
which moves in response to the deceleration of the vehicle.
, Another known method is illustrated in U.S. Patent
No. 3,944,292, wherein the pressure reducing operation at the
time o~ a heavy load condition is delayed by controlling the
starting presqure of the pressure reduction operation of the
''' reducing valve in response to or in accordance with the
hydraulic presoure of the master cylinder at the time the
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inertia sensor senses the braking deceleration and moves.
Another example of this type of sensor is also illustrated in
U.S. Patent No. 3,825,303. However, in load-responsive
pressure reducing valves of this type, a shortcoming is
. ,
observed when used in vehicles which display a tendency of
not exhibiting any signiicant or definite difference in the
relationship between braking hydraulic pres~ure and braking
deceleration when it has a light load condition and when it
has a heavy load condition. In this situation, the pressure
reducing valve is thus apt ~o display the pres~ure reducing
characteristic or a light load when, in fact, the vehicle
is under a heavy load condition. This type o~ pressure
reducing valve thus has the shortcoming that the braking
.
~ force applied to the rear wheels tends to be insufficient
,,' undex heavy load conditions notwithstanding its relatively
sophisticated and complicated construction.
, It is a principal object of the present invention
,.
;;~,,, to provide a load-responsive pressure reducing valve assembly
which i~ devoid of the aforementioned disadvantages and to
provide such a reducing valve assembly wherein the starting
point of pressure reduction is controlled by detecting ~he
i deceleration of the vehicle and further aims at providing an
inexpen~ive load-responsive reducing valve of simpler
construction and which further allows variation~ in the
; starting point of pressure reduction in response to
deceleration.
One characteristic of the load-responsive ~-
pressure reducing valve assembly of the present invention is
... ,. ,; .
-~ that it adopts the type o deceleration detector in which
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~ 30 the entire reducing valve body is installed on the vehicle
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at a predetermined angle of inclination to provide an
incline for movement thereon of the inertia ball or inertia-
responsive valve member, and dispenses with complicated
mechanisms of the prior ar~ wherein the angle o~ inclination
of the reducing va~ve body or housing is varied for light
load conditions and heavy load conditions. The pressure
reducing valve of the present invention also does away
with complicated mechanisms which restrict the movement
of the inertia ball or inertia-responsive valve member.
Another characteristic of the load-responsive
pressure reducing valve assembly of the present invention is
that the starting point or reduction starting pressuxe of
the pressure reduction operation varies first of all in
correspondence to the distance which the inertia ball or
,.
inertia-responsive valve member, which is detecting decleration
c o~ the vehicle, must travel, and secondly in correspondence to
`~ the master cylinder hydraulic pres~ure at hat time. The
distance over which the inertia ball or inertia responsive
valve member rolls or moves and the propagation velocity of
the hydraulic pressure filling the space surrounding the
inertia-responsive valve member are controlled~
Another characteris~ic of the pressure reducing
valve assembly of the present invention is tha~ when a
predetenmined hydraulic pressure from the master cylinder
; is exceeded, a piston within the valve assembly housing is
depressed by th~ pressure ~hereby increasing the distance
; ov~r which the iner~ia ball or inertia-responsive valve
member must travel as the inertia ball is always in contact
with the piston until such time that a preset or predetermined
deceleration i~ exceeded.
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. Yet another characteristic of the reducing valve
.. assembly of the present invention is that the operating hydraulic
pressure of the master cylinder itself is utilized as the press-
. ing or bias means to control the starting point of the pressure
~: reduction operation. Accordingly, it is thus made possible to
. .:.. : .
control this hydraulic pressure over a very broad range with the
use of small or limited mechanical space, whereas many of the
conventional reducing valve assemblies require the use of a
coil spring for this function which creates problems of increased
required space for installation and manufacturing error.
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Broadly speaking, therefore, the present invention
provides, in a brake system provided with a reducing valve having
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a brake fluid inlet and a brake fluid outlet respectively
connected to a brake fluid motor and a wheel brake cylinder in
the rear wheel.s of a vehicle: a deceleration-responsive reducing
valve including therein; a plunger which has one end exposed to
the brake fluid inlet and the other end exposed to the brake
fluid outlet of the reducing valve for restricting fluid pressure .
applied to the wheel cylinder when an operation-starting pressure
at the outlet is attained; means to determine the operation-
starting pressure of the plunger in relation to the weight of
the vehicle and any load carried thereby and including an inertia :
ball resting on an incline for rolling up the incline upon
vehicle deceleration to seal braking fluid from the brake system ::
. . .
, ....
under a then existing pressure in a cavity, which sealed flui~ ~.
communicates with the plunger to determine the operation-start- ~ .
.~ ing pressure thereof; and means to vary this then existing sealed
;~. pressure of the sealed fluid in the cavity and including a
,.. .
. piston provided downward on the incline and against which the ..
. ':
inertia ball normally rests when not rolling up the incline, the
piston displaceable against a bias by brake. fluid under pressure
from the brake system to displace the piston in a direction to
increase the roll travel of the inertia ball when a predetermined
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.:; fluid pressure at the inlet of the reducing valve is exceeded to
,- .
` ; thereby increase the operation-starting pressure of the plunger
: in proportion to an increase of load on the vehicle.
,~ If it is desired to make the inertia-responsive valve
~ member a variable deceleration detection type, then the afore-
,... .
mentioned incline upon which the valve member must travel is
provided with a curved convex surface to thereby increase the
predetermined magnitude of detected vehicle deceleration with
. an increase of travel surface.
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The following description and the accompanying
drawings will serve as an illustration but not as a limita-
, tion of this invention.
FIG. 1 is a schematic diagram of a vehicle braking
,~ system utilizing a load-responsive pressure reducing ~alve
assembly according to the teachings of the present invention.
FIG. 2 i~ a cross~sectional view ~howing the load-
~ responsive pressure reducing valve assembly of the present
`~ invention.
FIG. 3 is a graph showing the relationship between
.: . ,
pre~sure input to the pressure reducing valve apparatus
of the present invention from the master cylinder to pressure
output to the wheel cylinders for light and heavy vehicle
load conditions.
FIG. 4 is a cross-sectional view showing an
.. . .
embodiment variation of the inertia-responsive valve por~ion
.,~,
; of the apparatus illustrated in Fig. 1 wherein the incline -~
ovex which the inertia ball tra~ls is a curved convex surface.
Referring to ~he drawings~ Fig. 1 diagrammatically
illu~trates a vehicle braking sy~tem for a wheeled vehicle
~; utilizing the load-responsive pressure reducing valve
` assembly of the present invention and schematically
illustrates the flcw diagram of the system.
Hydraulic braking pressure is generated in the
conventional tandem master cylinder 1 by means o the brake
".
' pedal and linkage illustrated and the hydraulic fluid i~
directed through conduit 2 and di~tributed through triple
connec~or 3 to the left and right front wheel brake cylinders
4 and 4' respectively. Fluid pressure is distributed to
the rear wheel brake cylinders 9 and 9' from the tandem
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.~ master cylinder 1 through conduit 5 via the reducing valve
~ body or assembly 6 of the present invention and conduit 7.
. The reducing valve assembly housing 6 i~ installed on a
.. portion of the motor vehicle at an angle of inclination
corresponding to the deceleration of the vehicle to be
`' detected. The brake fluid exits the pressure reducing
~ valve assembly 6 via conduit 7 and is then dis~ributed
; through triple connector 8 to the right and left rear
wheel brake cylinders 9 and 9' respectively.
Referring next to Fig. 2, the interior construction
:: of the reducing valve assembly shown in Fig. 1 is disclosed.
.
The body or hou~ing 6 of the reducing valve assembly is
divided into thxee major portions or sections, namely, the
pxoportional pressure reduction section PR, the hydraulic
pressure controlling section PC and the pressure buffer
section BF.
: The proportional pressure reduction section PR
incorporates a fluid pressure proportioning valve for
restricting the flow of fluid fed to the fluid inlet 19
. 20 from master cylinder 1 to the fluid ou~let 20 duri~g a
~i pr~determined range of increasing fluid pressure at the
outlet 20~ This fluid pressure proportioning valve consists
of a plunger 18 which is axially moveable in a first cavity
or chamber 22 within the housing 6. The plunger 18 also
.~ extends to the left toward a second cavity 55 within the
housing 6.
The plunger 18 is provided with a valve head 35
which is cooperable with valve seat 33 to selectively
: establish an interrupt communication between the first fluid
, 30 inlet port 19 and the fluid outlet port 20 as the plunger
18 is axially moved.
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Valve head 35 is received within chambex 21 which
in ~urn is connected to output port 20 which leads to the
rear wheel brake cylinders. The o~her end or stem end of
plunger 18 is exposed to second cavity or chamber ~5 through
a slide fluid seal from ~he first cavity 22 ~or biasing
plunger 18 to a position establishing communication between
fir~t inlet port l9 and outl~t port 20 by ~luid under
pressure in second cavity or chamber 55. Fluid under pressure -'
in chamber 55 will bias plunger 18 to the right so that the
plunger head in chamber 21 does not engage valve seat 32
thereby establishing communication between first inlet port
19 and outlet port 20.
The stem portion of plunger 18 i~ slidably received
in the central bore 25 of seal holder 24 whioh in turn is
seated in bore 23. Spring re~ainer 28 is also held in
po~itio~ within bore 23 in buttlng engagement against
annular shoulder 29 by pressure applied by seal holder 24
which, in tur~, is retained in ~sition by means of end cap
60 which is threadably received in housing 6 ac indicatedO
Seal holder 24 is constructed to block the direct passage
of hydraulic fluid under pressure from the first cavity or
chamber 22 directly into the second cavity or ~hamber 55
by mea~ of the cup seal 26 and O-ring 27.
Preload compression spring 31 is held under
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compres~ion between ~pring retainer 28 and the flange portion
30 of plunger 18 as illustrated.
;: ~he annular 3eal valve or ~alve seat 33 is
~ illustrated and described in detail in United States Patent
No. 3,423,936. This Patent may be referred to to explain
` 30 the basic cooperative pressure reducing ~unction or operation
`, that occurs between valve plunger 18 and valve seat 33.
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10.
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Seal valve or valve seat 33 is made of an ela~tic
material and i5 sandwiched between the annular shoulder 32
and the righ~ æide or end of plunger 18. Hydraulic fluid
under pressure PM from the master cylinder enters through
the first inlet port 19 into the first cavity or chamber 22
and passes through the crescent shaped passages 34 formed
between plunger 18 and the wall of cavity 22 and then
continues to flow between valve seat 33 and pl~nger 18 on
into chamber 21 and out outlet p~rt 20. This fluid passage
or communication between inlet p~rt l9 and outlet por~ 20 is
interrupted when plunger 18 moves to the left so that the
head 35 of the plunger in chamber 21 engages valve seat 33.
This pressure reducing valve thus proportionally reduce~ the
hydraulic fluid pressure fed to the output 20 and sub~equently
the rear wheel brake cylinders by opening and clo~ing
CDmmunication of valve head 35 with valve seat 33. A more
detailed explanation of the oper,ation of this portion o~
the reducing valve may be obtain~ed by reference to lines
16 through 47 of U.SO Patent No. 3,736,031 issued May 29, 1973.
The ~hird cavity or chamber 37 in the hydraulic
pre~sure controlling seal-in 3ection PC is connected by
second inlet port 36 to the hydraulic fluid under pressure
PM from the master cylinder via the first chamber or cavity
22. Inertia ball 38 is positioned in the center of third
cavity 37. The right side or end of the third chamber or
ball chamber 37 is closed by means of plug 39 that is
threadably received in reducing valve body or hou~ing
6. An airtight seal is maintained between third cavity
37 a~d the exterior by msans of O-ring 40.
In the bore 41 of this plug 39 t a piston 42 is
~lidably received suoh ~hat the left end o the piston 42
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contacts the inertia bal:L 38 at rest. Hydraulic pressure
within the third chamber 37 will ac~ on the piston cup seal
43 via the crescent groove 44 to urge piston 42 to the right
against the compression of preload spring 47 for the maximum
possible displacement of As indicated by the double-headed
arrow. ~his displacement of piston 42 increases the distance - -
of travel for inertia ball 38 over incline 37a.
. . .
Preload spring 47 is sandwiched in position between
the annular shoulder 45 of pis~on 42 and the annular shoulder
or end wall 46 of ~he fourth cavity or chamber 41 within
; housing 6 ox plug 39.
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The installation length of preload spring 47 is
.; .
determined by snap ring 49 inserted in the ring groove 48
~` provided o~ the stem or spindle portion of the piston which
, .,~: " .
extends through plug 39 to the exterior. This snap ring
arrangement provides a stop to limit the extent to which
; piston 42 will be permitted to slide or extend toward third
cavity 37 due to the bias of preload spring 47. The movement
~' of piston 42 on the other hand, is restricted to the right
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20 side by the contact o~ annular ~houlder 50 on the stem
portion of the piston with the annular shoulder 46 of the
fourth cavity or chamber 41. Elastic dust boo~ 51 is provided
,~ with an annular snap fit to plug end plug 39 and slidably
`~ receive the outer circumference of the exposed spindle
,;: . . .
,'~ portion of piston 42 in a sealed manner to prevent the entry
of dust and water into the slide contact between the piston
spindle and end plug 39 and consequently into the fourth
., ; ,
; cavity or chamber 41.
An operating fluid channel 52 is provided in the
30 top of the third or ball cavity 37 and is of a semi-
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120
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cylindrical cross con~iguration and is provided to assist
the rolling of inertia ball 38 to the left on incline 37a,
as this channel 52 permits the free flow of fluid around
inertia ball 38 when it is in motion to reduce pressure
build up as much as possible in front of the ball as it is
rolling to the left.
- Check valve seat 53 of the inertia-responsive
valve is constructed of a plastic tubing or material and has
a central penetrating channel or bore. Check valve seat 53
is retained in the reducing valve housing 6 by means of
retainer 54 at a position to preset or predetermine the small
travel distance 8 which the inertia ball 38 must travel from
~- its engagement with pis~on 42 in order to press the mouth
`~ portion of check valve seat 53 and thereby close the passage
of fluid from third chamber 37 to the central bore of check
valve seat 53.
...:
-; The pressure buffer section BF provides two
functions~ First of all it is the chamber which provides
;~- fluid under pressure to bias the fluid pre~sure proportioning
valve consisting of piston 18 and valve seat 33 in order to
detexmine the pressure reduction starting pressure and in
addition, it also improves the liquid seal function of check
valve 53 when inertia valve 38 seats therewith. More
; definitely, the oil pocket of cavity or chamber 55 is utili~ed
~ as the control cha~ber to apply fluid pressures from there-
" within against the exposed st~m end of plunger 18 in order
to control the starting pressure for the reducing operation.
The hydraulic fluid is transmitted under pressure
to the oil pocket or ~econd cavity 55 from the third cavity
or chamber 37 through the central bore of check valve seat
130
: i~ . . .: ,
: ~ 53 and thence through pa~sage 56 ~o the annular groove 57
to the radial communication pa~isage or opening 58 provided
at the left end of seal holder 24.
The pressure bufer means within the s2cond cavity
: or chamber 55 provides a means wherein the second chamber 55
. is enabled to expand its capacity elastically to compen-~ate
-: for an incremental fluid pressure increase created therein
: due to the closure of the iner~ia-responsive check valve,
....
i~e., engagem~nt of inertia ball 38 with inertia check valve
seat 53, thereby improving the cloæure seal of the check
... valve in section PC of the load-responsive pressure reducing
valve assembly.
This pressure buffer consists of an ela-~tic
wall portion 59 in the ~econd chamber or cavity 55 which
is ou~wardly expandable into a sealed air chamber 63. The
expandable wall portion 59 may be designated as an oil
; pocket which is made of an elastic material and which is
centrally held within end plug 60 by annular shoulder 61 and
. the inside bottom 62 of end plug 60 to thus orm the annular
,'. 20 air chamber 63.
: "
::;,, The end plug 60 is threadably secured in the
reducing valve body or housing 6 a~ indicated and thus
`, maintains an air tight seal of both oil pocket or the second
. cavity 55 and air chamber 63 from the exterior. This ~ealed
relationship is insured by the use of O-ring 64 and as
formerly pointed out, end plug 60 also restricts the movement
,.~
~ of seal holder 24 to the left, or as previously indicated,
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.~' plug 60 holds ~eal holder 24 in its prescrib~d fixed position.
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~: Reference numeral 65 generally indicates an air
,` 3C bleeder which is provided for the purpose o~ expelling air
... ..
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14.
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which migh~ be entrapped in ch~ber or cavity 55, third
~- cavity 37, and second inlet port 36 or the first cavity or
chamber 22. In other words, it is designed to purge the
entire reducing valve assembly of air which is accidentally
mixed in with the hydraulic braking fluid.
Fig. 3 illus~rates ideal hydraulic braking pressure
curves for a given vehicle with two different load conditions.
The one-dot broken curve E indicates the ideal curve for a
light load condition for master cylinder hydraulic fluid
pressure Pm versus the output pressure Pr of the pressure
reducing valve assembly of the present invention which is
supplied to the rear wheel brake cylinders. The one-dot
broken line F indicates an ideal curve for heavy load
vehicle conditions. Curves O-Pse-E~ and O-Ps~-F' represent
actual operating curves of the pressure reducing valve
assembly of the present inv~ntion which attempt to closely
correæpond to the ideal curves for light load and heavy
load oDnditions.
In order to automatically force the hydra~lic
i 20 pressure of th~ rear wheel cylinders, as shown by the
- polygonal line O-Pse-E', at the time of liyht load conditions,
..... .
and the polygonal line O-Psf-F' at heavy load conditions, to
correspond to these ideal hydraulic pressure curves
i respectively. Inertia ball 38 is utilized to set the
starting pressure of the fluid pressure reduction operation.
~, Inertia ball 38 controls both of the curves of actual
operation by moving to the left on incline 37a for the
predetermined distance 8 to contact the check valve seat 53
in order to make the actual straight line curves conform
as closely as possible to the ideal curves illustrated in
':
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15.
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,: ....... . , . . : . ' : .
Fig. 3. Inertia ball 38 thus controls the starting point of
the pressure reduction opera~ion by sealing off the master
cylinder hydraulic pressure Pm from the control chamber or
:.
second cavity 55 at the point in time that inertia ball 38
: oontacts the check valve seat 53 by traveling or rolling up
. incline 37a and ~eals the check val~e bore within check valve
seat 53~
If i~ is assumed that Po represents the hydraulic
braking pressure of ~he vehicle brakes and tha~ C represents
the brake fac~or, then the braking force B of the vehicle
may be represented as shown by the following formula:
B = C Pc (1)
In addition, the ratio between the deceleration
~ ~ of the vehicle and the acceleration of gravity g is..
equal to the ratio between the braking ~orce B and the weight
. W of the vehicle. This relationship may be expre~sed as
' follows:
~, B .
g W (2)
; When a deceleration occurs in a vehicle due to
., :
:1 20 braking, the following equilibrium will then occur or be
.
, established around or in relation to the inertia ball 38,
, .,
if the weight o~ the inertia ball in the hydraulic braking
liquid is designated as W: .
: W a cos ~ _ W sin ~ :
> tan ~ ~3)
~ .
.. . The inertia ball 38 will begin to move to the
left as seen in Fig. 2 when the deceleration as shown by
the inequality sign of Formula (3) is exceededO Expressing
this mathematically, the operation of the inertia ball 38
may be expressed as a function of the angle of installation
as follows:
'' .'. . .
., .
16.
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AS a re~ult, the hydraulic pressu_e Pa which
is sealed within the second chamber or oil pocket 55 may
~hus be expressed from Fonmulae (l), (2) and (4) and
mathematically reduced and placed in order as shown in
:~ the following eql7ationO
:~ f (~) :~: pO ~ W (5)
: C
~ On ~he other hand, if inertia ball 38 has traveled
the distance 6 Up the incline 37a in time T at a velocity
V, then,
VT (63
In addition, if the hydraulic pressure of the
master cylinder 1 is designated Pm2 at a givan time and the -
velocity of pressure rise per unit tLme is designated as :
Vp, then Vp may be expressed by the following formula~
~ = Pmi (7)
r',' Thus~ from Formulae 16) and (7), Pm2 ~ay be
.`. designated as followss ~
~., Pm~ = 2 Vp ~ 8 ~8~ :
`"'' V , :,
Furthermore, if the installation load of the
preload spring 47 is F, the spring constant hereof is R
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1 and the distance which ~he piston 42 is pe7~tted to slide ~ .
;. within its bore or chamber 41 is designated as ~8 due to the
applied hydraulic pressure Pm o the master cylinder, which
acts on the cross-sectional area A3 of piston 42 to move
the same to the right, then the equilibrium of force about
. the piston 42 can be expressed by the followi~g ~ormulae: .
, .'' .
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:
~ : - . . . .
Pml A3 = F ~ Q~ K
: F + Q8 ~ K
Pml = __________ (9)
A3
To m~thematically state this relationship in a
more meaningful manner, the hydraulic pre~sure Pc sealed in
.. , the oil po~ket or sQcond chamber 55 may be expressed from
; Formulae (8) and (9) and mathematically reduced and placed
i in oxder as indicated in the following formula:
Pc = Pml + Pm2
`:
;:: F + ~8 K 2Vp
Pc - - + _ (8 ~ ~s) (10)
i,.:
Formula ~10) indicates the hydraulic pressure which
is sealed in the oil pocket or ~econd chamber 55 in the
~"~ situation wherein ~he floor surfaca of the third cavity or
chamber 37 i8 flat as shown in Fig. 2, thus illustxating a
~ constant deceleration detecting type pressure reducing valve
:~ assembly. However, the floor or surface upon which inertia
ball 38 rolls in chamber 37 may be provided in the form of a
,., ; . .
.' convex curved surface as illustrated in Fig. 4 to thus make
the apparatus a variable deceleration detection type wherein . .
~:1 the detected deceleration increases with the angle o~ tangent
~, which indicates the increments of angle increase of the
incline 37b of Fig. 4.
- ~ With reference again to Fig. 3, the operation of
the reducing valve assembly illustrated in Fig. 2 will be
explained with regard to the polygonal line O-Pse-E~, which
represents the pressure reduction characteristics o~ the
apparatu~ or a light load condition.
Re~erring to Fi~. 2 for thi~ example, the input
hydraulic pressure Pm supplied from the master cylinder to
port 19 is tran~mitted directly to the output port 20 via
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the annular gap between plungex 18 and the seal valve or
valve seat 33 as plunger 18 i~ urged under the bi~s of
compression spring 31 to the far right as indicated in the
Figure. Protru~ions on the left side of valve seat 33 permit
the fluid to pass the valve seat to the outle~ port 20.
Accordingly, if the hydraulic pressure Pc within second
chamber or cavity 55 at the tLme inertia ball 38 contacts
check valve seat 53 under the influence o~ an applied
deceleration ~e as shown in Formula (10) is designated as
- 10 P¢e, the equilibrium of plunger 18 may he mathematically
illustrated by the following formula:
Pce A2 + f < P~
wherein A2 ie the cross-sectional area of the
~: stem portion of plunger 18 as indicated
.; ., ,:
in the Figure, and
f i3 the installation load of preload spring 31.
`~1' .
The principal object of preload spring 31 is to :~
restoxe plunger 18 to its original or normal position after ;~
: each time the fluid pressure proportioning valve has made a :
j 20 closure by plunger 18 moving to the left to thereby engage ~ :
'`J' the annular valve head 35 with the inner diameter of valve
seat or seal 33 to reduce or re~rict fluid pressure flow
: from the ma~ter cylinder to the rear wheel brake cylinders~
Another object of preload spring 31 i8 to guarantee minimal
necessary braking force applied to the brake pedal indicated
.
.~. in Fig. 1 even if the installation angle ~ shown in Fig. 2
;~. may become nearly equal to zero when the vehicle is descending
a s~eep slope and the inertia ball 38 thus moves to the left ~ :
a~ seen in Fig. 2 at a deceleration which is les~ than the
.` 30 set or predetermined deceleration rate, wherein a hydraulic
'i . "
`' :,
,....................................... .. ~ :
.. 19. '.'
. . , . :- - :
322~i~
~: ;
., pressure will be sealed in the oil pocket or second cavity
-~ 55 which may eve~ be near to zero.
From the foregoing, one can derive from Formula
(11) the following formula in regard to the master cylinder
..,~
.~ pressure Pm:
: f
Pm ~ Pce ~ A ~12~
~hus, the hydraulic pressure Pm from the master
cylinder at the moment wherein the condition~ of Form~la
`: ll2) are caused to have an equality sign, the pressure
Pm becom2s the pressure Pse required to start the pressure
.~ reducing operation.
When the ma.~ter cylinder pressure Pm increases
, .
a sufficient am~unt to at~ain the equality sign of Formula
. (12) and thereafter increases to attain the inequality sign .:
'. thereof~ the plunger 18 will move to the left due to the
~, . . .
~i partial pressures which act against the larger area Al sf
.. . .
,`, pi8ton head 35 in chamber 21 opp3sed to the smaller areas
exposed to chamber 22~ such that the outer circumference of
:.,
.` valve head 35 seats in the inner circumference of the valve
seat 33 thereby temporarily bloclking the passage of hydraulic
.: fluid from fir~t input port 19 to output port 20. The
equilibrium of hydraulic pressure around or on opposite sides
~ of plunger 18 at this ~oint in time may be expressed as :~
: follows:
Pr Al = (Al - Az) Pm ~ f + Pce A2 (13)
.. where Pr is the output hydraulic pre~sure supplied to the
.' rear wheel brake cylinder through output 20,
`~, Al is the cross-sectional area of valve head 35.
;~ From Formula (13), the output hydraulic pre~sure
.-, 30 may be further reduced and expressed as follows: :
: ,~
... ~
. . .
.
:.'
,;~ 20.
. . ~
~:`
- . .
.,,
.,'`'' ` .
Al - A2 f A2
Pr = ~ Pm ~ Pce (14)
~ Al Al A~
The relationship expressed in this Formula between
the input and the output hydraulic pressures may be seen to
satisfy the polygonal line O-PseoE~ illustrat2d in Fig. 4
for light load conditions.
(Al - A2)/AI in Formula (14) represent~ the ratio
of pressure reduction after commencement of the pressure
, ~ reducing operation.
In a like manner, when piston 42 has moved to the
.
right in Fig. 2 under the influence of Pm for vehicle
; deceleration on the heavy load side9 and the hydraulic
pre~sure Pc shown in Formula (10) has thus become or attained
level Paf, an equilibrium of Formula (14) with P¢e
; substituted by Pcf, will be established and, at the ~ame
time as Pse moves to the level of P~f, E~ makes a parallel
translation to F' as seen in Fig. 3 and thereby effects
load~responsive proportionating pressure reduction for
heavy load ccnditions.
` In either load condition, when Pm reduces from a
value on the line E' or ~' in Fig. 3, Pm does not follow
Formula ~14). Stated in a different man~er, and with
'` reference to Formula (133, the Aydraulic pressure Pm applied
,t, to the difference in area of plunger 18 (A~ - A2) reduces,
the equilibrium of the plunger 18 in accordance with Formula
`;. (13) is broken, and the valve head 35 moves even further to
the le~t while retaining its sealed relationship of closure
- with valve ~eat 33 and the hydraulic fluid or liquid of higher
, pressure in output port 20 flows into the first cavity 22 on
,.~.,
the input port 19 side of the valve seat via the outer
circumference of the seal valve or seat 33 and, thereafter,
: . ,.
21. ~
.
` P~ reduces as Pm reducesO The extreme leftward movement
.. ~ of plunger 18 at this point in time is restricted by means
of the annular shoulder 66 within seal holder 24.
: Even if the hydraulic pressure applied from the
master cylinder to the rear wheel brake cylinders is reduced
~rom high braking pressure by removal of brake application to
the mas~er cylinder such that the vehicle gradually decelerates
,' below the prese~ deceleration at which check valve 53 will
i close, inertia ball 38 will still remain in contact with
check valve 53 as long as the equilibrium o the following
' '
formula holds true, A4 being the cross sectional area of
the central hole o~ the check valve seat 53:
W u sin ~ _ Pm A4 (15)
~owever, if the master cylinder pressure Pm
. reduces~ such that the left side of Formula ~15) becomes
greater than the right side as indicated by the inequality
: sign, the inertia ball then moves to the right as viewed in
~`~ Fig. 2 down incline 37a and the hydraulic pressure within
:~ the third chamber or ball chamber 37 becomes equal to that
;~ 20 of second chamber or control chamber 55.
One of the major section.~ of the pressure reducing
valve assembly, as previously explained, is the pres~ure
~-~ buffer section BF which includes the ~econd cavity or chamber
:: 55~ ~n elastic wall portion in the form o~ an elastic oil
,;
... pocket 59 is provided for chamber 55. The first function of
oil pocket 59 is explained as follows: when i~ertia ball 38
.~ presses against check valve 53, it compresses the elastic
.:
material of the check valve seat such ~hat the hydraulic
pressure Pa which is sealed in the chamber 55 of pressure
;, 30 buffer section BF at that moment becomes slightly higher
:.
... .
22.
'
' .
:~ due to this compression e~fect. Alth~ugh the pressing force
Pm o A4 of inertia ball 38 against the check valve ~eat 53
,. is restricted due to the fact that the outer circumference
,
of the inertia ball contac~s ~he end surface 67 of retainer
54, nevertheless, this increase in pressure of ~Pc would have
the effect of pushing the inertia ball 38 back off its check
valve seat 53. To prevent this displacement of the inertia
`;~ ball from its valve seat, oil pocket 59 elastically protrudes
on air chamber 63 in end cap 60 ~o absorb this small pressure
increase QP¢ and thereby cancels the possible undesirable
effect~ of ~Po on the fluid pressure proportionin~ valve,
: while at the same time improving ~he liquid sealing
capabilities of the check valve consi~ting of inertia ball
38 and check valve seat 53.
The qecond function of the pres~ure buffer section
i~ to ¢ompensate for the event that plunger 18 moves to the
left a~ viewed in the figure to initiate the pressure reduction :-:
operation by having valv~ head 3~ press against seal valve
seat 33 when the condition P~ > ~Pc + f has been attained.
A2
When this occur~, the hydraulic pressure Pc in the chanlber
55 of pressure buffer section BF will increase by ~Pc , due
:. to the leftward displacement of plunger 18 into the chamber.
In order to cancel this effect, oil pocket 59 will elastically
,:
:, protrude into air chamber 63 to the extent nececsary to
. . . .
:: absorb ~Po and thereby stabilize the pressure level of Pc~
By ~irtue of the above-described valve assembly
construction, the load-responsive reducing valve assembly of
the present invention initiates pressure reduction by ~ean~
of the action of inertia ball 38 ~uch that the behavior of
inertia ball 38 determines the pressure reduction starting
'.
.
' ., ~'
.
: . . : : ' ; . . .
`:
: point at the same detected dec~eleration for both light and
:: heavy load conditions as do the inertia detecting reducing
valves of the prior art. ~lowever, due to the displacement
; of piston 42, the point of deceleration at which pressure
, ! .
' reduction will initiate will move in effect to the high
~` side or the situation wherein the vehicle carries a heavy
. load and in addition, thi~ construction further makes it
,;.
possible to control the starting point of pressure reduction
ln accordance with the rate of pressure application to the
.~ 10 vehicle brake pedal.
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