Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of Patent Application 375,136,
filed April 9, 1981.
The present invention relates to improvements in load
sensing hydraulic brake pressure control apparatus for use in
the hydraulic circuit between the master cylinder and the rear
wheel brake cylinders. The apparatus is adapted for sensing
variations in the distance between the vehicle chassis and the
suspended axle shaft.
It is known that changes in vehicle loading cause
changes in braking capability. For example, when a vehicle
is fully loaded, the rear wheels will have nearly the same brak-
ing capability as the front wheels. However, when the vehicle ~ -
is lightly loaded, the rear wheels may exhibit less braking
capability than the front wheels. Thus the potential for pre-
mature rear wheel lock up is much greater when stopping the
lightly loaded vehicle than when stopping the fully loaded
vehicle. In order to compensate for the inherent imbalance
between front and rear braking action, it has been customary
in past years to provide a proportioning valve which restricts
fluid communication to the rear wheel brake cylinders after
a predetermined pressure level is generated. However, such
proportioning valves represent a compromise between the de-
sirable system characteristics for the full load condition and
those for the light load condition. Thus the selected pro-
portioning valve characteristic in neither suitable for the -
full load condition nor the light load condition. Many load
sensing or vehicle height sensing valve mechanisms have hereto-
fore been presented in the prior art, however, they are un-
necessarily complex or other~ise unsuitable for modern vehicle
30 use. For example, see U.S. E~atents 3,362,758; 3,503,657;
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3,649,084; 3,684,329; 3,734,~,74; 3,768,876; 3,848,932;
4,150,855 and 4,159,855.
The present invention relates to improvements in load
responsive hydraulic brake pressure control apparatus which
is placed in the hydraulic circuit upstream of the rear wheels
and senses changes in the dic;tance between the chassis and the
axle of an automotive vehicle and controls the hydraulic pres-
sure delivered from the master cylinder to the rear wheel brake
cylinders in response to such changes.
The present invention provides for a first and second
proportioning valve assembly hydraulically in series with each
other, the first proportioning valve assembly being positioned
downstream of the master cylinder and the second positioned
between the first valve assembly and the vehicle rear brakes.
The first proportioning valve produces an output pressure
suitable for a vehicle under a full load condition. The second
proportioning valve, which receives the first valve's output
pressure as input pressure, acts to modify or proportion the
pressure received from the first valve producing an output
pressure suitable for a lightly loaded vehicle.
In a preferred embodiment of the invention, the second
proportioning valve assembly is rigidly attached to the vehicle
frame and includes a rotatable digital cam driven by mechanical
linkage attached to the vehicle axle. As the vehicle is loaded,
compression of the suspension system reduces the distance be~
tween the vehicle frame and the axle. The mechanical linkage
j in response to the reduction in distance rotates the digital ;
3 cam to a position whereby the second proportioning valve mech-
anism is disabled. Thus the output pressure of the first pro~
portioning valve is passed undisturbed through the second pro-
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portioning valve assembly to the rear wheel brakes.
The digital cam is rotatingly seated upon an axial
drive shaft so as to allow relative rotation therebetween. A
torsional spring affixed to the digital cam has one leg anchored
thereon and the other leg engaging a flat diametric camming
surface provided in the drive shaft. Thus the digital cam is
caused to rotate in concert with the drive shaft. However,
by reason of the torsion spring a unique drive mechanism is
provided which accommodates relative motion between the vehicle
frame and the axle during vehicle operation by permitting rela-
tive rotation between the cam and the drive shaft whenever rota-
tion of the cam is restricted by the functional operation of
the proportioning valve mechanism.
Although the load sensing proportioning valve assembly
is herein described as being in series with a first proportion-
ing valve assembly it is to be understood that the load sensing
valve may be used alone in systems where the master cylinder
output pressure is suitable, without an intervening proportional
valve, for direct transmissi~n to the vehicle brakes in the
heavily loaded condition.
According to the present invention, there is provided
in a vehicle hydraulic brake system including a master cylinder,
wheel braking means, and fluid transmission means for conveying
hydraulic pressure from the master cylinder to the wheel braking
means, the improvement comprises a first and second proportional
valve means between the master cylinder and the wheel braking
means, the proportional valve means being hydraulically in series
one to the other with the second proportional valve means hy-
draulically downstream of the first proportional valve means,
the first proportioning valve means adapted to proportion the
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input to output hydraulic pressure pursuant to a first input
to output relationship and the second proportional valve means
adapted to proportion the input to output hydraulic pressure
pursuant to a second input tc, output relationship, vehicle load
sensing means adapted to disable the second proportioning valve
means when the vehicle is loaded to a predetermined load con- -
dition.
Embodiments of the invention will now be described
with reference to the accompanying drawings, in which:=
Figure 1 is a schematic view of a hydraulic brake
system incorporating a load sensing proportioning valve and
embodying the present inventlon.
¦ Figure 2 is a graphical illustration of the perfor-
mance of a brake proportioning system incorporating the present
invention.
Figure 3 pictorially depicts a typical vehicle instal-
lation of the load sensing proportioning valve.
Figure 4 is a part:Lal cross-sectional view of the
load sensing proportioning valve used in the braking system
illustrated in Figure 1.
Figure 5 is a cross-sectional view taken along line
5-5 in Figure 4.
Figure 6 is a partial cross-sectional view taken along
line 6-6 in Figure 4.
Figure 7 is a partial cross-sectional view taken along
line 7-7 in Figure 4.
Figure 8 is an exploded pictorial view showing the
assembly of elements comprising the digital cam portion of the
load sensing proportioning v~lve.
Figure 9 is an isolated pictorial view of the digital
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cam rotated 180 from that 3hown in Figure 8.
Figure 10 is a schematic illustration of the load
sensing proportioning valve configuration when the vehicle
is lightly loaded.
Figure 11 is a schematic illustration of the load
sensing proportioning valve configuration when the vehicle
is heavily loaded.
Figures 12 and 13 present schematic illustrations
of load sensing proportioning valve configurations accom-
modating over-rotation of the digital cam driveshaft.
Figure 14 presents a partial cross-sectional view -
of the load sensing proportioning valve, similar to that
of Figure 6, wherein the digital cam mechanism is con-
figured activation by clockwise rotation of the digital
cam driveshaft.
Referring to the drawings a vehicle hydraulic
braking system embodying the invention is shown in Figure
1. Master cylinder 11 provides brake activating hydraulic
fluid pressure by means of conduit F to the vehicle front
wheel brakes 13L and 13R first passing through a metering
valve assembly, not shown, contained in combination valve
12. Conduit R similarly provides an independent source
of brake activating hydraulic fluid presssure to a first
proportioning valve assembly 14, shown schematically in
combination valve 12, for ~;upply to the vehicle rear wheel
brakes 15L and 15R.
Proportioning va]ve 11 may be of any known design
~ to the art, such as shown in U.S. Patent 3,423,936, having
i~ a single split point relationship between input hydraulic ; -~
pressure and output hydrau:ic pressure. The
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proportioning valve 14 is des:igned to produce an output pressure
relationship to input pressure as shown in Figure 2 and
identified as "LOAD~D". The split point at which valve 14
begins proportioning being indicated as point L. The curve
identified as "LOAD~D" in Figure 2 represents a master cylinder
to rear brake pressure relationship acceptable for a vehicle
loaded beyond a given mid-load condition and up to its full gross
vehicle weight (GVW). The output hydraulic fluid pressure from ~-
proportioning valve 14 is transmitted to the vehicle rear brakes
by conduits Rl and R2 passing through load sensing proportioning
valve (LSPV) device 20.
LSPV 20 includes a second proportioning valve assembly
16, hereinafter described in greater detail, having a similar
construction as that of proportioning valve assembly 14 contained
in combination valve 12. Proportioning valve assembly 16,
when permitted to function, operates upon the output hydraulic
pressure received from proportioning valve 14 such that the
relationship between master c~linder pressure (input to
proportioning valve 14) to rear brake pressure (output from
proportioning valve 16) is represented by the curve identified
as "EMPTY" in Figure 2. The "EMPTYU curve shown in Figure 2
represents a master cylinder to rear bra~e pressure
relationship acceptable for a vehicle load condition falling below
the sel~cted mid-load condition.
A digital cam mechanism 25 is provided within LSPV 20
to selectively disable proportioning valve assembly 16 in the
full open configuration when the vehicle is heavily loaded. Thus
when the vehicle is loaded beyond the selected mid-load condition,
proportioning valve 16 is disabled by action of digital cam 25
thereby permitting, undisturbed, the transmission of hydraulic
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pressure therethrough and resulting in the desired "LOADED"
pressure relationship shown in Figure 2. However, when the
vehicle is lightly loaded proportioning valves 14 and 16
function in series and produce a master cylinder pressure to
rear brake pressure relationship as indicated by the curve
"EMPTY" in Figure 2.
Figure 3 pictorially depicts a typical vehicle
installation of the load sensing proportioning valve. LSPV 20
is rigidly affixed to a non-suspended portion of the vehicle ~'
frame 35. Driveshaft 50 is firmly attached to linkage 30 so
that as linkage 30 rotates driveshaft 50 rotates digital cam
25 by a drive mechanism hereinafter described in greater detail.
Linkage 30 is firmly attached to the vehicle axle tube 31 or
any other suitable element of the suspended portion of the rear
wheel assembly.
Digital cam 25, through action of linkage 30 attached
to vehicle axle 31 responds to compression or expansion of the
vehicle suspension system (not shown). When the linkage is
extended, as indicated by the numeral 30, the vehicle is lightly
loaded and proportioning valve 16 is permitted to function.
~Iowever, when the linkage is compressed, as indicated by
numeral 30', the vehicle is heavily loaded and digital cam 25 is
rotated into position so as to disable the operation of the ;~
proportioning valve 16.
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Referring to Figure 5 proportioning valve assembly 16
as shown and described herein is merely representative of known
proportioning valve mechanisms and does not represent a part of
my invention. Recognizing that any known proportioning valve 1~ -
mechanism which may be modified to function as herein described
is suitable for use with the present invention, the operation
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of proportioning valve assembLy 16 will be described only to
the extent necessary to understand its interrelationship with
my digital cam and its function with respect to the overall
bra~e hydraulic system.
Proportioning valve assembly 16 comprises valve piston 40 ~-
positioned axially within bore 45 and extending into bore 45a of
smaller diameter which in turn opens into digital cam cavity 70.
O-ring seal 47 is provided to hydraulically seal bore 45 from
bore 45a thereby preventing tne flow of hydraulic fluid into
bore 45a. Piston 40 is provided with a pin like extension
48 projecting into bore 49. Piston 40 is permitted to axially
translate within bore 45a so that pin 48 may project into the
digital cam cavity 70 as will be described hereinafter.
The opposite end of piston 40, includes valve head 43
which is less in diameter than that of bore 45b thus permitting
the unrestricted flow of hydraulic fluid thereby. Piston 40 is
further provided extension cap 41 having notch 42 therein.
Piston 40 is normally biased to the left by action of spring
46 such that extension 41 is urged abuttingly against the end of
bore 45b. Hydraulic fluid is thus permitted to enter inlet port
Rl, ~reely pass between piston 40 and elastomeric valve seat 44,
'~ past valve head 43, through notch 42 and exit through outlet
port R2. Thus in the configuration as shown in Figure ~ the
fluid pressure at outlet port R2 will be equal to the fluid
pressure at inlet port Rl.
During brake application the above described fluid
path through proportioning valve 16 remains open until the fluid
pressure delivered at inlet port Rl attains a predetermined ;~
`7 level. At this time valve head 43 will close against valve seat
~ 30 44. The level of pressure at which this occurs is dependent
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upon the force of spring 46 as compared to the effective area of
the valve piston 40, acted up~n by inlet fluid pressure in a
direction opposing the force of spring 46. This effective area
is equal to the diameter D of piston 40 since the right hand end
of piston 40 projecting into :bore 45a is sealed off from the
inlet fluid pressure by O-ring seal 47 while the inlet fluid
pressure acts against all of the remaining portions of piston 40.
After valve head 43 closes against valve seat 44 and
the fluid pressure at inlet port Rl is further increased, the
10 increased pressure will act against piston 40 over an effective
circular area having a diameter equal to the main sealing diameter
of valve head 43 less the cross-sectional area of piston 40
extending into bore 45a. This produces a force acting upon
piston 40 in the same direction as an assisting spring 46 to
reopen valve head 43 so as to deliver at least a portion of the
increased fluid pressure to outlet port R2. However, any
increased fluid pressure delivered to outlet port R2 creates
an opposing force upon piston 40. The opposing force tends to
reclose valve head 43 against valve seat 44. The opposing ;~
20 forces tend to keep valve head 43 closely adjacent to valve seat
44 thereby restricting the flow of fluid from inlet port Rl to
outlet port R2 creating a pressure at the outlet port R2 which
; increases at a lower rate than the pressure at inlet port Rl. `~
The ratio of the pressures is determined by the relationship of
the effective areas previously referred to and hence the fluid :~
pressure passing through proportioning valve 16 r,~ay be propor~
tioned to follow a predetermined relationship.
During that portion of a brake application in which the
l applied pedal e~fort is reduced subsequent to a brake application
30 of sufficient intensity to have moved piston 40 to the restricted
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flow positionthe forces tending to move piston 40 to the left ~-
are reduced and piston 40 tra.nslates to the right under the
influence of the pressure at outlet port R2. As the piston 40
¦ moves right valve head 43 is permitted to slide within the inner
¦ peripheral surface of valve seat 44, thereby increasing the
available volume for the fluid at the rear brake cylinders 15L
and 15R and accomplishing a reduction in pressure at outlet
port R2. The pressure at outlet port R2 can never be greater
than the pressure at inlet port Rl because valve seat 44 also
10 acts as a fluid check valve permitting the flow of fluid from .
port R2 and into bore 45. -
For a more detailec. description relating to propor- -
tioning valve operation and the design of particular propor-
tioning valve elements refer to U. S. Patent No. 3,423,936
issued to William Stelzer on January 28, 1969.
Figures 4 through 9 are to be referred to for the
following description of the digital cam 25, its construction
and operation. LSPV housing 19 is provided with a two step
bore 60. Floor 69 of bore 60 contains recessed therein : :~
20 semicircular slot 67 and journal recess 68. Cam driveshaft 50
is supported and retained as shown in Figure 4. Journal 51 of
driveshaft 50 is rotationally received within journal recess
68. Shaft 50 extends generally normal to bore floor 69 passing
through and rotationally supported by end cap 61. End cap 61
is snugly retained within bore 60a and against shoulder 62 by
action of snap ring 63. O-ring 55 is provided to seal the
digital cam chamber 70 from t.he entrance of any contamination
thereto. Cam driveshaft 50 protrudes externally of end cap 61
sufficiently to permit rigid engagement thereof by linkage 30 ~ -~
(see Figure 3). Thus driveshaft 50 is caused to rotate through
the same angular displacement: as that of linkage 30. :~
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Digital carn 25 is rotationally supported on cam
journal 52 of driveshaft 50 such that cam 25 may rotate relative
I to driveshaft 50. Cam 25 is provided with a peripheral recess
26 and axial directed knurls 24 over at least the working
peripheral portion of cam 25. The working portion of cam 25
will become apparent as the function and operation are further
described hereinafter. Pin 32 projects axially from cam 25
into and slidably engaging slot 67 in bore floor 69 thereby
limiting the angular rotation of cam 25 to that are inscribed by
slot 67. The inboard side 22 of cam 25 is milled providing
inboard facing stepped surface 27. Circular recess 21 extends
axially through cam 25 from the outboard surface 28 and slightl~
past the inboard facing stepped surface 27 thereby providing ~ - ;
passage way 23 between outboard surface 28 and inboard surface ;~
27. Mandrel 33 is axially positioned within circular recess
21 extending outboard and slightly past outboard surface 28.
Torsion spring 34 is seated about mandrel 33 the helical ' ,
portion thereof being seated within circular recess 21 such
that inboard leg 34a extends through passage way 23 in juxta~
posed relation with inboard facing stepped surface 27 and
engages spring retention hole 29. Outboard spring leg 34b
extends in juxtaposed relatic~n with outboard surface 28 of
j cam 25 extending into slot 54 of driveshaft 50 and engaging the ,' ~-
l~ flat camming surface 53. In their normal assembled state as
¦ hereinabove described and shown in Figure 6, torsion spring legs
¦ 34a and 34b are spring loaded so as to apply an angularly
outward force upon spring retention hole 29 and the flat
I c,amming surface 53' of driveshaft 50. Slot 56 is ~rovided at - '
¦ the external and outboard encl of car,l driveshaft 50 to permit
external adjustment.
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In operation cam 25 is caused to rotate with cam
driveshaft 50 by reason of torsion spring 34 applying spring
force upon camming surface 53 of shaft 50. However, should cam
25 be restricted from rotating because of interference between
pin 32 and slot 67 or because of interference between cam 25
and pin 48 on valve piston 40, cam driveshaft 50 may however,
rotate relative to cam 25 by further compressing torsion spring --
34. Thus, a spring drive mechanism is provided between cam
driveshaft 50 and digital cam 25 which allows for over travel of
shaft 50 when rotation of cam 25 is otherwise restricted.
Figures 3, 5 through 7 and 10 depict the configuration -~
of LSPV 20 under conditions o light vehicle loading. The -~
vehicle frame 35 is riding relatively high with respect to
suspended axle 31. Thus linkage 30 positions digital cam 25
such that peripheral recess 26 permits pin 48 of piston 40 to
axially translate in and out of digital cam chamber 70.
Proportioning valve 16 is permitted to freely function resulting
in a master cylinder pressure to rear brake pressure relationship
as shown by the curve identified as "EMPTY" in Figure 2.
So long as the vehi-le is lightly loaded proportioning
valve 16 is function. Peripheral slot 26 accommodates operation
of valve 16. However, should valve piston pin 48 protrude into
cam chamber 70 as a result of vehicle braking and the vehicle
encountered an extreme road condition causing cam dxiveshaft 50
to momentarily, over rotate from excessive compression of the
vehicle suspension system, cam 25 will momentarily engage valve
piston pin 48 stopping the cam's counterclockwise rotation.
llowever, cam driveshaft 50 is permitted to continue its counter- -
clockwise rotation by compression torsion spring 34. Such a
condition is illustrated in Figure 13.
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~ hen the vehicle is loaded heavy the suspension system
is compressed such that the vertical separation between frame
35 and axle 31 is reduced. Linkage 30 assumes a configuration
as depicted in Figure 11 thereby rotating digital cam 25
counterclockwise as shown. In this configuration the outermost
periphery of cam 25 is rotated in a position that disables
proportioning valve 16 by preventing the free translation piston
40. Thus in the loaded condition, as illustrated in Figure 11,
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the master cylinder pressure to rear brake pressure relationship
is as shown by the curve identified as "LOADED" in Figure 2.
So long as the vehicle is in the loaded condition the outer
periphery of cam 25 will remain in the valve piston disabling
configuration as illustrated in Figures 11 and 12. In this ~ -
configuration and when the applied braking load is such that
valve piston 40 attempts to translate to the right valve piston
pin 48 buts against cam 25 and engages the axial ~nurls 24 on
the outer periphery of cam 25. Thus cam 25 is restricted from
freely rotating. Any further rotation of cam driveshaft 50
resulting from road induced vacillations of axle 31 will be
accommodated by compression oE torsion spring 34 as illustrated
in Figure 12.
The angle A (Figure 6) between the pin 48 centerline
and digital cam step 26a determines the vehicle load condition
at which proportioning valve 16 is disabled therefore it is
necessary that this angle be accurately fixed. Angle A is
determined for an unloaded vehicle and represents that angle
through which driveshaft 50 will rotate as the vehicle is loaded
to that mid-load condition at which it is desired to change
from the "EMPTY" curve to the "LOADED" curve as shown in Figure
2. Step 26b is located so as not to interfere with the operation
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of proportioning valve 16; pin 32 and slot 67 may also be
configured so as to limit the clockwise rotation of cam 25
thereby preventing step 26b interfering with the operation of
proportioning valve 16.
The LSPV as illustrated in Figures 1 through 13
accommodate counterclockwise rotation of cam driveshaft 50 upon
compression of the vehicle suspension system. However, the
LSPV may be easily adapted to accommodate clockwise rotation
as is illustrated in Figure 14. By relocation of slot 67 as
shown in Figure 14 the mechanism is adapted for clockwise
rotation.
While an embodiment of the invention has been -
described herein with considerable particularity, it will be
understood that the scope of the present invention is to be
determined by the appended claims.
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