Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11~77'Q3
The invention relates to an improved brake propor-
tioning apparatus for limit;ng, restricting and proportioning
the application of brake pressure to the wheels of a vehicle
under certain conditions.
Devices commonly used to program fluid pressure
in brake systems comprise fixed ratio pressure reducing valves.
These devices ~unction as a result of an area relationship and
as such are capable of only respond~ng linearly to a linear in-
put. Further, as the reduction ratio approaches either unity
or zero, the devices become s~gnificantly difficult to design
and to maintain within prescribed operating conditions.
It is an object of the present invention to obviate
or mitiyate the above disadvantages.
According to the present invention there is provided
a proportioning valve for a fluid operated brake system, the
valve comprising a body having an inlet to receive pressurized
fluid from a source, an outlet to deliver pressurized fluid to
a brake actuator, a valve member located between the inlet and
the outlet and moveable from an open position in which flow
from the inlet to the outlet is permitted to a closed position
in which the valve member engages a valve seat to prevent flow
from the inlet to the outlet, an operating member having a pis-
ton surface hydraulically connected to the source so as to be
subjected to variations in pressure of fluid delivered to the
inlet, resilient biasing means operatively connecting the valve
member and the operating member and operable to bias the valve
member toward the closed position, the valve being arranged so
that an increas~ in fluid pressure at the inlet above a predeter-
mined pressure causes the operating member to increase the force
exerted upon the valve member by the biasing means.
1~77~3
~ ccording to a further aspect of the present invention
t}-ere is provlded a proportioning valve for a motor vehicle hy-
draulic brake system, the vehicle haviny a brake actuator and a
source of hydraulic pressure, the valve comprising a body having
an inlet connected to the hydraulic pressure source and an out-
let adapted to be connected to the brake actuator, a valve mem-
ber located between the inlet and the outlet and moveable from
an open position in which flow from the inlet to the outlet is
permitted to a closed position in which the valve member engages
a valve seat to prevent flow from the inlet to the outlet, piston
means adapted to operate the valve member and hydraulically con-
nected to the source so as to be subjected to variations in pres-
sure of fluid delivered to the inlet, resilient non-uniform bias- .
ing means operatively connectin~ the valve member and the piston
means and operable to bias the valve member toward the closed po-
sition, wherein the biasing means is operable upon increases in
fluid pressure from the source to non-linearly proportion the
flow of fluid pressure past the valve member to ~he brake actua-
tor and wherein the valve member is arranged so that an increase
in fluid pressure at the inlet above a predetermined pressure
causes the piston means to increase the force exerted upon the
valve member by the biasing means.
Preferred embodiments of the present invention will now
be described by way of example only with reference to the accom-
panying drawings, in which.-
Figure 1 illustrates schematically one embodiment of a
brake proportioning apparatus;
Figure 2 illustrates another embodiment of a brake yro-
portioning apparatus;
3C Figure 3 illustrates still another embodiment of a
- 2 ~
77~3
brake proportioning apparatus of the invention;
Figures 4-9 are graphs illustrating the manner in which
the embodiments of the invention operate;
Figures 10 and 11 illustrate further embodiments of
the invention;
Figures 12 and 13, which appear on the same sheet as
Figure 10, are graphs illustrating the operation of the embodi-
ments shown in Figures 10 and 11; and
Figure 14, which is on the same sheet as Figure 11,
10 illustrates an automatically adjusting brake proportioning
- 2a -
77~3
device.
Ir, ~'iyure 1, a piston 20 is slidably mounted in a
housing 22. The housing 22 has a central chamber 24, flanked
by two smaller chambers 26 and 28. The piston 20 extends
through all three chambers in the housing 22. The chamber 26
on the left side of the housing (as viewed in accordance with
Figure 1) has an inlet 30 which is connected to the master
cylinder of the brake system and exposed to i~let pressure
PI. One end of the piston 20 is positioned in the chamber 26
and has a cross-sectional area Al exposed to the inlet pressure
PI. The opposite end of piston 20 extends outside the housing
22 and is exposed to atmospheric pressure PATMos
An O-ring 34 or similar sealing member is positioned
around piston 20 in d cavity 36 and prevents fluid from
passing between chambers 24 and 26. Similarly, an O-ring 38
is positioned around piston 20 in a cavity 40 at the right side
of the housing 22; this prevents fluid in chamber 28 from
leaking out of the end of the housing.
Chamber 28 on the right side of the housing has an
inlet 32 which is also connected to the master cylinder (inlet)
pressure PI. The fluid pressure introduced into chamber
28 communicates via opening 42 around piston 20 into the
central chamber 24. An outlet 44 transmits the fluid pressure
force in chamber 28 to the brake cylinders ~n the vehicle's
wheels for activation thereof~
In chamber 24, two springs 46 and 48 are mounted
coaxially around piston 20. A plate 50 is securely mounted to the
-- 3 --
, ~.,~'`
~ 9
1~77~3
piston 20 and provides a seat for one end of the springs 46 and 48.
~he opposite end of spring 46 is seated against wall 52 of the hous-
ing 22, while the opposite end of spring 48 engages a cup-shaped
retainer 54 positioned on the piston 20. ~he outer spring 46 is pre-
loaded and reacts against the housing 22 with a force Fl urging the
piston 20 to the left as shown in Figure 1. ~he inner spring 48 is
not preloaded and thus is in a relaxed state when it is positioned
between plate 50 and retainer 54 and the plate and retainer are in
the positions shown in Figure 1. An annular sealing member 56
10 is positioned on piston 20 and held in place by the retainer 54. ~he
seal 56 and retainer 54 are slidably mounted on the piston, When
the brake proportioning apparatus i8 in operation, the seal 56
cooperates with wall 52 around the opening 42 to form a valve 58.
The free length of the ~pring 48, plu9 the thickness of the
seal 56, retainer 54 and spring seat 50, are less than the length of
the central chamber 24 In the housing 22. ~his allows for fluid
communication between chambers 24 and 28 through passagewa~ 42
when the inlet pressure PI has a low value.
When pressure is introduced in the braking system and
20 thus through inlets 30 and 32, a îorce equal to PIAl is developed on
the piston~ 20 urging it rightwardly in Figure 1~ l`his is opposed by
the preloaded force of spring 46 (Fl). When these force~ become
equal, that i6, when PIAl ~ ~1' the pi~ton 2û will be in equilibrium
and will orce the slidable seal 5~ against wall 52. ~he device is
dcsigned so that this will occur at a predetermined pressure level
and the valve 58 will close and fluid communication between the inlet
32 ~nd outlet 44 wil} be interrupted ~n this regard, in order to
11,~77~3 ~ ..
provide a more satisfactory valve seat between seal 56 and wall 52,
an annular lip or projection 60 is provided around the periphery of
the opening 42.
When tl~e piston 20 is in equilibrium, that is, when equal
pressure conditions exist in both the inlet and outlet chambers, all
incremental increases in pressure in the system are introduced
into both inlets 30 and 32 and develop a force of ~ PIA1. As the
piston 20 moves in response to ~ PIAl, the two springs 46 and 48
develop a resisting force (Flr) restoring equilibrium. ~his is writ-
ten as follows:
~ pIA1 = F~ (1)~he total resisting spring force F,I. is comprised of the contribution
of the force of spring 46 (Fl) and the force of spring 4B (F2). Thus:
Fl = Fl + F2 (2)
When the piston 20 has moved rightwardly an incremental distance
~ d", the spring force F1 and F 2 will be a function of deflectlon,
as well as the spring rates Rl and R2 for the springs. l;hus: -
.. , . ... , . ~
= 1 or F1 = ~ d
~ d
and
2 = 2 or F2 = ~d R2
~d
Since the total spring rate (R,~) of springs loaded in parallel is equal
to the sums of the individual spring rates ~Rl + R2), the equation
then is reached:
RT _ FT or F,r = ~ d RT
1 ~ d
77~^3 ~ .:
If it is assumed that:
~T
1, (6)
where K1 is a constant, then substituting from equations (4) and
(5) into equation (6), the following equation results:
~d RT= K1 . ~7)
~d R2
If equations (6) and (7) are equated,
FT ~d RT (8)
F2 a d R2
and the resulting equation is solved for F2,
F2 = FT ~R2 ~ (9)
\RT/
then equation (1) can be substituted into equation (9) to get the
following:
- F~ - aPI~ (10)
~RTJ
At the ~alve 58, the force F2 of spring 48 is opposed
by a force generated by aPI acting against annular area A2 (the
area of opening 42 surrounding piston 20). Within wide limits
in relationship between areas Al and A2, the force F2 will be
~maller in magnitude than the force generated by ~ PIA2. As
a result, the pressure will open the valve 58 allowing a pressure
rise ~PR in the outlet chamber 24, setting up a force ~,PRA
in opposition to .~PIA2 In the equilibrium condition:
~, FX = = F2 ~ ~PRA2 ~PI~2
--6--
~77C~3
Solving for F2,
F2 = A2 ( a PI aPR) (12)
and equa~ing equations (10) and (12), results in the ~ollowing:
R) PIA1 ( 2) ' (13)
or
~2 ( ~PI- ~PR) = aPI (R2) . (14)
Since the ratio of areas Al and A2 is a constant (A2/Al = K2),
the following equation is reached:
K2 ( aPI ~ -~PR) = ~PI ( 2~ (15~
By simplifying and rearranging equation (15), the final equation
is reached: .
R = 1 - 2 . (16)
PI K2RT
In this last equation, P~,IPI is the proportioning
ratio of the apparatus and K2 is the ratio of the areas chosen
which is one of design for any given mechanism. As a result,
given a certain ratio of areas in a valve, the proportioning ratio
may be obtained (and/or chan~ed) by changing the spring rates
Rl and R2.
The effect of varying the spring rates on the brake
0 proportioning device shown in Figure 1 is illustrated in the graphs
c~f Figures 4-8 For example, if both spring rates Rl and R2
are linear, the device will proportion the nOw of bral;e pressure
to the wheel cylinders in accordance with F'i~ure 4. In that graph,
! ~ 77~3
line I indicates tlle situation where pressure is applied to the front
and rear brakes at an equal rate. Point A is the "split point",
that is, the point at which the device begins to proportion or limit
the flow of fluid pressure through it. The proportioned pressure
is in~licated by line II,
The total spring force FT can only react up to a
maximum pressure, at which point the piston 20 i~ stopped.
If the outer spring 46 is designed such that the coils abut together
("go solid") at a certain point and thus stop the piston 20, the
force F2 Of the inner spring 4~ will remain constant for all
additional increases in input pre.ssure. This situation i6 ~hown
in Figure where point B on line II indicates the point at which
spring 46 goes "solid". The portion of line II subsequent to
point B has a slope parallel to the slope of line I and the device
merely acts as a check valve during this stage of its operation.
Figure 6 illu~trates the situation where the device
is designed such that the inner spring 48 "goes solid" at a certain
point (point El on line II), At this point, the valve 58 will remain
closed despite further increa~es in inlet pressure PI and the outlet
pressure will remain at a constant value for the remainder of
the braking application.
It is also possible to wind either or both of the
springs 46 and 48 with variable pitches. In a variable pitch
spring, the number of active coils decreases as the spring is
compressed This produces a spring with an increasing spring
rate resulting in a non-linear output for the device The
J
77~3
functioning of a valve with a variable pitch spring 48 is shown in
Figure 7. After the split point A, the rate of pressure to the
wheels ctlanges in a non-linear manner (as shown by curved
line II). Point B in Figure 7 refers to the situation where one
or the otller of the springs is compressed to a "solid" condition
and the valve either stays open (line II') or closed (line Il")
The functioning of the device in either of these situations is
~imilar to that discussed above relative to Figures 5 and 6
Figure 8 is similar to Figure 7, except that it
illustrates the device where the outer spring 46 has a varable
pitch instead of the inner spring 48 ~resulting in an upwardly
curved line II)
It is often desirable to provide a proportioning
device in which the proportioning ratio can be varied or adiusted
for use on different vehicles or in different applications, In
thls manner, a ~ingle type and size of device can be manufactured
and used in a whole line of vehicles having different sizes,
weights and loading capabilities Such a device iB ~hown in
Figure 2. In this em1~odiment, all of the elements which are
similar to the elements of the device shown in Figure 1 are
numbered in the same manner. The primary difference between
the devices of Figures 1 and 2 is that the piston 20 in Figure 2
has a ~piral or screw shaped rib 62 on it which mates and
nests with the coils of thé inner spring 48 The piston 20 also
has a knob 64 mounted on its end outside of the housing so that
it can be manually rotated. The end 4g of the spring 4B closest to
~l~77n3 J
the plate 50 is secured to the piston 20. Thus, when the piston 20
is rotated vi~ knob 64, the ~;piral rib 62 compresses or extends the
length of the spring 48 along piston 20 adding or deleting the num-
ber of active coils in it. In this manner, the spring 48 can either
S be compressed or extended, as desired, changing its rate of spring
force and the resulting proportioning function of the braking device.
Preferably, an anti-rotation mechanism should be employed rela-
tive to the spring 48; devices including ~;uch feature are shown in
Figures 10 and 11 which are di~cu~sed below.
. Through the use of the embodiment shown in Figure 2,
it is possible to adjust the proportioning ratio of a braking device
within wide limits. This iB illustrated in Figure ~. The use of
variable pitch springs for either spring 46 or 4B also would add
many variations to the operating characteristic~ of the device.
The devices ~hown in Figures 1 and 2 can be used in a
vehicle with either single or dual braking systems. The pressure --
PI entering inlets 30 and 32 could be either from the same master
cylinder compartment and brake line, or the pressure introduced
into chamber 26 could be from the front brake system, while the
pressure introduced in chamber 2~ could be from the rear brake
~ystem. In the latter arrangement, a failure in the frc>nt brake sys-
tem would render the valve inoperative allowing full pressure to be
applied to the rear wheels, This would provide a safety by-pass
~ystem where needed.
Another embodiment of the invention is shown in Figure
3, ~his is used for dual braking systems, A housing 70
has inlet port5 72 and 74 connected to the front bralce system of
~77~3
a vehicle and another inlet port 76 connected to the rear
brake systern. The housing 70 also has an outlet port 77 which
is connected to and a part of the rear brake system.
Inlet port 74 and passageway 78, which is in fluid
communication with inlet port 76, are both associated with
a differential pressure switch and warning device 80. The
device 80 is situated in the upper portion of the housing 70
and operates towarn the operator of the vehicle in the event of
a failure of either the front or rear brake systems. The
device 80 can be of any conventional type, but preferably is a
diaphragm-type differential pressure warning device in accor-
dance with United States Patent No. 3,985,986 dated October 12,
1976, which is assigned to the same assignee as the present
case.
In accordance with U.S. Patent No. 3,g~5,986, one
diaphragm 82 is acted upon by the front bra~e system and a
second diaphragm 84 is acted upon by the rear brake system.
A movable piston 86 is positioned in a chamber between the
diaphra~ms 82 and 84 and is electrically insulated from the
housing 70 by a pair of insulating rings or washers 88. A
metal xing 90 is positioned on the piston 86 and is adapted to
come into contact with member 92 which is in electrical contact
with an appropriate warning device (not shown) such as a dash-
board light or buzzer. In the event of a failure in either
brake system wherein the pressure in one system is reduced
signi~icantly, the piston 86 will be displaced axially
by the forces acting on the diaphragms toward the
chamber having the lower brake
-- 1~ --
77~3
pressure, When this happens, the ring 90 will come into contact
with the member 92 closing an electrical circuit and in turn acti-
vating the warning device.
The lower portion of housing 70 contains a brake pro-
portioning device, A piston 100 is slidingly contained in stepped
bores 102, 103 and 104. One end 106 of the piston 100 is in direct
communication with inlet port 72 and the other end 108 i~ positioned
in a bore 110. The central portion 112 of the piston 100 ha~ a
redu-~ed diameter and is positioned in boree 103 and 104. Bore
102 is in communication with the i~ilet port 72 and iB maintained
at inlet pressure. Bore 104 is maintained at atmospheric pre~-
sure. O-rings 114 and 116, or other 6imilar sealing members,
are provided at the two ends of bore 104 to prevent brake fluid
from leaking into it. An end plug 118 is secured in one end of
the hou~ing 70 and a~sist8 in introducing pressure from the front
brake system into inlet 72 and against the end 106 of piston 100.
- . ... ~. . .. .
Sealing mernber 122 provides a 8eal between the end plug 118
:, . - - - . .
with the housing 70. An axial projection 120 is included on plug
118 and it helps maintain O-ring 114 in position.
At the opposite end of housing 70, the inlet port 76
associated with the rear brake system is in direct communication
with chamber 130. Bore 132 is formed in chamber 13~. Bore
132 is slightly larger than bore 110 thereby forming a shoulder
134 therebetween, A retainer 136 and sealing member 138 are
2~ positioned in bore 132. ~he retainer 136 and member 138
are 6ecurely positioned against shoulder 134 by end plug 140,
-12-
77~3 ~ ~ :
In this regard, axial projection 142 of plug 140 abuts against a
series of raised projections 144 on sealing member 138 forcing
the retainer and sealing member against the shoulder. Openings
are left between the projections 144 in order to allow nuid to
.
flow freely past projection 142 on plug 140.
A second piston 150 is positioned in the chamber
formed by bore 110, The piston 150 is positioned in an opening
152 in retainer 136. The opening 152 iB ~ufficiently large to
allow the pi~ton 150 to move axially and fluid to pass around the
piston, One end 154 of piston 150 is adapted to engage sealing
member 138 under certain operating conditions; the end 154
and sealing member 138 thus define a valve mechanism which
is generally indicated by the reference number 156. A spring
158 is positioned between piston 150 and plug 140 and provides
a relatively weak spring force in a direction to open the valve
mechamsm 156, Spring 158 maintains valve 156 in its open
position when the brakes are not in operation or at low pressuré
levels, ~ ~ -
Two coaxial springs 160 and 162 are positioned
in bore 110, One end of spring 160 rests against flange 164
., : . ., . ... ;, : . . . ... ..
on piston 100 and the other end rests against retainer 136,
Spring 162, on the other hand, is ~ituated between the flange
164 on piston 100 and a corresponding plate or flange I66 on
piston 150.
The operation of the brake proportioning device
shown in Fi~ure 3 is similar to the devices shown in Figures 1 and 2.
- 1 3 -
~ 377~3 ~ : .
In this regard, b;)re 102 corresponds to chamber 26, bore 110
corresponds to chamber 24 and chamber 130 correspc~nds to cham-
ber 28, Also, the springs 160 and 162 correspond to E;pringS 46
and 48, 1espectivel~. Thus, spring 160 is in a preloaded condi-
tion forcing piston 100 to the left, while spring 162 is in its relaxeù,
free condition. One of the primary difference~ between the embo-
diment of Figure 1 and the embodiment of Figure 3 is the piston
. .
arrangement; in Figure 3, the piston consists of two parts, l00
and 150, while the piston is in one piece in Figures 1 and 2, The
_ _ _
operation is similar, however, as the separate piston 150 i8 simi-
lar in function $o the sliding retainer and sealing member assem-
bly of Figure 1.
In order to vary the operation of the device, varia~le
pitch springs can be used for either or both of the springs 160 and
182. Also, the device ~hown in Figure 3 can be adapted to shorten
or extend the length of spring 162 in order to change the spring
rate in a manner similar to that shown and described with refer-
ence to Figure 2,
Preferably, the adjustable embodiment of the invention
as shown in Figure 2 has an anti-rotation mechanism for the
coaxial springs. A device including this feature is shown in F~e
10. In this embodiment, a ~lidable piston 170 is positioned in a
housing 172. Pressure from the master cylinder is admitted into
housing 172 through inlet 174. The inlet pressure PI is passed
first into chamber 176, coaxially through bore 178 around piston
170, and into chamber 180. Outlet 182 allows the tluid to pass
from the device to the rear wlleels of the vehicle. A valve, desig-
nated generally by the numeral 184, proportions the pressure in
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~77~3
~ . .
a manner described belo~v between the inlet 174 and the outlet 182.
Fluid pressure also is transmitted through central passageway 186
in the piston 170 into chamber 188. Pressure in chamber 188
reacts on one end surface 190 of the piston 170 producing a force
5 on it in a direction to close t~e valve 184 The opposite end 192 o
piston 170 is exposed to the atmosphere outside the housing 172 and
has a knob or similar mechanism on it for rotating the piston. An
O-ring 194 or similar sealing member is positioned around pi~ton
170 in a cavity 196 and prevents fluid from passing between cham-
bers 180 and 188. Similarly an O-ring 198 is positioned around
piston 170 in a cavity 200 at the opposite end of the pist~ to pre-
vent fluid in chamber 176 from leaking out of the housing 172.
Two coaxial springs 202 and 204 are positioned around
piston 170. ~hese springs are situated and operate in a manner
similar to springs 46 48 and 160 162 described above with refer-
ence to Figures 1-9. The outer spring 202 is positioned between
-
adjusting nut 206 (situated on piston 170) and end wall 208 of cham-
ber 180; it i5 preloaded and resists the force acting on surface 190
(F1 = A1PI). As mentioned earlier the inner spring twhich in
Figure 10 is ~esignated by the numeral 204) is not preloaded and
thus normally in a relaxed state when there is little or no nuid
pressure applied ~o the device. When the force F1 reaches a mag-
nitude sufficient to overcome the {:reload of spring 2û~ the piston
170 moves rightwardly ~as shown in Figure 10) closing t~le valve
184 and interrupting the ~low between the ir~let 174 and outlet 182.
Further incremental increases in inlet pressure are reduced pro-
portionately .
~ 77~3
A retainer 210 is slidably positioned on piston 170. A
sealing member 212 is situated in and held in position by the
retainer 210, The seal 212 comprises one part of a valve mecha-
nism 184 and operatively acts with the raised annu~ar lip 214 around
bore 178 to form the complete valve. An O-ring 216 is situated in
a cavity 218 in retainer 210 to prevent fluid from bypassing valve
184. A key 222 is positioned on retainer 210 and situated in slot 220
in piston 170. ~he key-and-slot allows the retainer 210 to slide
axially along the piston 170 and at the same time rotate with it. A
key-and-slot mechanism 224, 225 i6 also provided relative to the
nut 206 and housing 180, although this mechanism prevents the
adjusting nut 206 from rotating with the piston,370.
The nut 206 is threadably fastened on pistc)n 170 and
appropriate threads 226, 227 are provided for this purpose. 'The
inner spring 204 is positioned between the nut 206 and a nange 211
on the retainer 210. ~hreads 228 (or a spiral ridge) are provided
on the outer surface of ad~usting nut 206 and are adapted to mate
with the coils of spring 20~ at one end thereof. 'Ihe opposite end
of spring 204 is securel~ fixed in any conventional manner to the
retainer 210, such as by key 230. The pitch and hand of spring 204,
nut adjusting threads 228 and the piston-nut mating threads 226, 227
are the same,
Assuming a right-handed pitch to the threads 226, 227
and 228, rotating the piston 170 in a clockwise direction will advance
the adjusting nut 206 axially along the piston. During rotation, the
piston 170 will remain in it6 stopped position against uall 189 of
housing 172 and the spring 202 will become more and more compressed.
-16-
1~.77~3
The retainer 210, together with the inner spring 204, which are
both keyed to the piston 170, will rotate with the piston. The iden-
tically pitched inner spring 204 will screw onto the mating threads
228 on the advancing nut 206; each full revolution will reduce the
active coils by one.
As the nut 206 advances and compresses the outer spring
202, the initial preload of the spring 202 increases and thus the
split point of the brake proportioning mechanism is raised. As the
elevation of the split point is taking place, the reduction of active
coils of the inner spring 204 serves to lower the proportioning ratio
in synchronization with such elevation. The operation of the Fig-
ure 10 embodiment is shown in Figure 12. Point A represent~ the
split point situation where the nut 206 is not advanced at all; in this
situation, the device operates similar to the device shown and des
cribed relative to Figures 1 and 4 and the proportioned pressure is
indicated by line I. When piston l70 is turned ~uch that the ad~ust-
ing nut 206 is advanced approximately one-half way along the threads
226, the split point is raised to Point B and the proportioned pres-
sure is indicated by line II. When the nut is fully advanced, the
split point is raised to Point C and the proportioned pressure is
indicated by line III.
A further embodiment of an adjustable proportioning
device is shown in Figure 11. Many of the features of Figure ll
are similar to th~se shown and described relative to Figure ~0 and
are numbered in a similar manner. In addition, the fluid path and
proportioning principles are the same. The principal differences
relate to the configuration of the adjusting nut 206 and the retainer
-17-
77~3
210, as well as the addition of an adjusting nut 240 for the
inner spring 204.
The piston 170 is slidably positioned in bore 242 on
the left side of the housing 172. Male threads 226 on the piston
170 engage female threads 227 on the adjusting nut 206 for the
outer spring 202. A radial flange 244 on the nut 206 provides
a seat for the outer spring 202 whose initial preload biases
the nut and piston to its leftward stop position against wall
189 of housing 172. Assuming a right-handed pitch of the
mating threads 226 and 227, rotating the piston 170 in
a clockwise direction will advance the nut 206 which is
prevented from rotating by key-and-slot mechanism 224, 225.
This will raise the split point as mentioned above.
The retainer 210 is slidably mounted on the piston 170
but is also keyed to it via key-and-slot mechanism 220, 222 so
that the two parts will rotate together. External male threads
246 are provided on the retainer 210 and engage mating female
threads 248 on the inner spring adjusting nut 240. The pitch
and hand of mating threads 246, 248 are the same as mating
threads 226, 227. A flange 250 extends radially from the ad-
justing nut 240 and a key 252 thereon engages a slot 254 in the
housing 172 preventing rotation of the nut 240. The inner spring
204 is positioned between flange 250 on nut 240 and a radially
extending flange 256 formed on piston 170. The right hand
end of the inner spring 204 is threaded upon male threads 262
on adjusting nut 240. The pitch of threads 262 is the same
as the other two pairs of mated threads. AlsG, the end of
spring 204 adjacent flange 256 is securely fixed thereto, such
as by key 258. The outer spring 202 is positioned between
3~ the flange 244 of nut 206 and shoulder 260 ~f housing 172.
- 18 -
LgD77rA3
Again, assuming right hand threads, clockwise rotation
of the piston 170 will translate outer and inner adjusting nuts 206,
240 rightwardly (in Figure 11) in synchronization. With both adjust-
ing nuts in the fully leftward position (zero advance), the right hand
end of inner spring 204 is fully threaded upon nut 240 abutting radial
nange 250. When the piston is rotated, the inner spring 204 also
rotates, unthreading from the adjusting nut 240. Each full revolu-
tion of the spring 204 adds one active coil to the inner spring. As
the ratio of active coils of the inner spring becomes greater in rela-
tion to the total number of coils of both inner and outer springs,
the proportioning ratio becomes greater,
The operation of the Figure 11 embodiment is shown in
Figure 13. Point A represents the split point where the piston 170
has not been rotated at all. When the piston is turned such that
lS nuts 206 and 240 are advanced approximately one-half way, the split
point is rai~ed to Point B and the proportioned pressure is ~ndicated
by line Il. When the nuts are fully advanced, the split point is raised
to Point C and the proportioned pressure is indicated by line III.
The pistons shown in the above embodiments are rotated
2~ and the ~nternal coaxial springs adjusted in order to adapt the opera-
tion of the brake proportioning device to the loading of the vehicle.
l~his is preferably accomplished by the rotation c~f kno~s secured
to the ends of the proportioning pistons which prc~trude from the
housings. The knobs can be rotated either manually or automati-
2~ cally. If the knobs are rotated manually, this is done b~ the vehicle
manufacturer or operator, depending on the expected use c>r actual
loading of ~he vehicle. If the pistons are rotated automatically,
-lg-
77Q3
then an adjusting mechanism adapted to take into account the
loading of the vehicle and rotate the proportioning piston
preferably is provided.
An automatically adjusted brake proportioning device
iS5hown schematically in Figure 14. A lever or other mechani-
cal linkage 300 is attached to the axle, frame, or suspension
302 of the vehicle and provides a direct input of the loading
of the vehicle into a control system 304. A spring 306 or
other damping mechanism screens out undesired deflections and
input from lever 300. It is also possible to include a time
delay in the control system 304 such that adiustment of the
proportioning device only takes place if the lever 300 remains
deflected for a predetermined length of time. The control
system 304 in turn operates an appropriate mechanism, such
as toothed plate 307, which in turn rotates knob 308 on the
bra~e proportioning device 310. The device 310 can be any of
the adjustable embodiments of the invention described above.
The control 304 can be any conventional type and can
be operated mechanically, electrically, pneumatically or
hydraulically. Satisfactory mechanical linkages and control
systems which could be adapted to operate the present inventive
brake proportioning device are shown, for example, in United
States Letters Patent ~os. 2,807,338; 3,649,084 and 3,379,479.
~ t will be appreciated that the presen~ i.nvention is
susceptible to modification, variation and chanye without
departing ~rom the scope of the invention as defined in
the subjoined claims.
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