Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO90~12717 2 ~ 5 3 2 2 ~ PCT/GB90/00640
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VEHICLE BRAKI~G SY~
The invention relates to vehicle braking systems. ',
Almost all moder~ vehicles, particularly motor cars, ~'
have hydraulically operated fioot brakes operating on all
wheels. The systems generally comprise either d mm or disc
brakes with a brake pedal connected to a piston in a master
cylinder whence the hydraulic operating pressure originates.
Depression of the brake pedal forces the hydraulic brake fluid
along a network of pipes and hoses to wheel cylinders which
urge brake calipers or shoes into contact with a brake disc or
drum to provide the ~raking action.
Hydraulic systems' have many advantages, such as heing
self-lubricating (reducing the chance of seizure), having a low
`rate of wear and low fri'~tion,"'and enabling et~ual pressures to
be eserted on all '~the~ br~ake''~shoes` or 'calipers, even
compensating ~' for '~unequal: wear~'or adjustment. 'Further,
installation ~-is generally''' eaæier-than ~or mechanical s~stems
because of the~fle~ibility of'the~hoseæ ~`'':' ''` ' - -
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'The" principal~disa~vantage`'~of''hydraulic brakingisystems
;is ;~:that ~a~:leakage~'`in''':the'lsystem'i or''-!''contamination of the
hydraulic fluld used can r0nder the hrakes ine~fective or in-
opera~ive. '~
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'''One':solution to ~'th'is proble'm is~prov~ide'd''by having a
tandem master-tcylinder, and: splitting'~'he'system"into"two`parts
WO90/12717 PCT/GB90/00640
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so that if one part fails the other part can still function.
Obviously, in the event of failure of one part braking
efficiency is reduced, and there are situations when this can
be dangerous.
Sometimes it would be preferable to control the separate
brakes individually for e~amyle if one tyre has been worn more
than its a~ial counterpart. In standard systems both a~ial
brakes would be operated identically. It would also be useful
in braking systems to be able to control the f~.el at the
braking, as some drivers prefer sharp braking and others prefer
to have to move the brake pedal some distance before ma~imum
braking is achieved.
Advances in braking technology have been restricted '.
because of the problems in distribution of the fluid in the
brake mechanisms.
7'',, '~ Accord,ing to the invention there is provided a vehicle
..., braking system comprising a braking element operable by a
: .driver of-~ the vehicle; control signal generating . means
responsive to.operat1on of the,.braking.element; means braking
at least one wheel of,,the: vehicle in re~ponse to control
,...... ...... ... ........ -,sign,als,generated.by,the control.signal generating maans; and
,reaction means ,responsive~,.to,,ithe.control~signals.to, provide a
force .on the braking ,element to~provide a variable, artifical
s feel to the driver through the braking element.
~3,; ~re~erably ~the control, signals are ,proportional to a
; forcejapplied to the.braking element by the driver.
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In a preferred embodiment the system comprises means for
sensing the force appiied to the braking element and providing
input signals proportional thereto to the control signal
generating means, the sensing means preferably comprising an
electrical load cell.
Preferably the system comprises means for sensing the
position and~or movement of the braking element and providing
input signals to the control -signal generating means
proportionaI thereto, said sensing means preferably comprising
one or more linear vari'able displacement transducers.
Preferably the reaction means comprises a hydraulic
actuator coupled to the braking element, the actuator
preferably being a double acting hydraulic actuator having a
pair of opposed piston faces.
The actuator is preferably controlled by a servo-valve
responsive to the control signals to control the application of
hydraulic fluid pressure to the opposed piston faces to operate
the actuator. ' '' ' "' '~
' ''' The braking element can be a brake pedal.
Another preferred 'embodiment includes error detection
means operative to check whether 1the;artiical ~eel is being
provided to the braking element and to provide input'signals to
~'the contr~l signal generatin~msans in'dependence thereon. On
~'detection -or~an error`~by''~the~error dete'ction means outside a
;I' pre-set ~limit~`l t'he -control signal~generating- means-,preferably
'gen'erates con~rol signals to operate a sa~e~y system.
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WOgo/12717 '~ PCTtGB90/00640
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The control signal generating means is preferably acomputer which can be programmable to generate control signals
dependent on requirements of the driver or the condition of the
vehicle .
A vehicle braking system according to the invention will
now be described by way of e~ample with reference to the
drawings, in which:- ,
Figure l is a schsmatic representation of the layout of
the system;
Figure 2 is a part sectional front elevation of a brake
reelN actuator assembly ~which is a part of the system of
Figure l;
Figure 3 is a sectional view of Figure 2 on III-III;
Figure 4 is a part sectional front elevation of a
distribution valve which is a part of the system of Fi~ure 1;
and . . .
:~ ,- -.. Figure -S~,is a:-front elevation of the distribution valve
: of Figure 3 with parts omitted for clarity.
;~ Referring first .to Figure l there is shown a braking
~ system lO~.,for~use -,iin a:-motor vehicle .such as a ~motor car,
!,: having ~ steerable.wheels.(not~shown). ~ ",
:,. :.:,,'..The .~otor,,vehicle,~has ,~our wheels each itted ; with
.,.~ standard hydraulically operated diæc or drum brakes., Althou~h ~.
. the .brakes., hemQel~es are not~,~shown "in the ,drawings,~,.the
: ~ operable ~calipers,;or~,shoes..or each.~,wheel (hereinafter brake
~, mechanism).are attached to a,respective servo,valve ll,, 12, l~,
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WO90/12717 2 0 5 3 2 2 4 PCT/GB90/00640
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14, which independently controls the pressure to the brake
mechanism at the associated wheel.
The system 10 combines a primary active brake system and
a secondary brake override system that provides the braking
effort in the event of a system failure or when the active
system is turned off.
The Prima,ry,Active Bra~ina System
The active system is a fully active "feel" system
including a braking element in the form of a brake pedal 15
which is physically decoupled frorn the braking mechanisms. The
brake pedal 15 is mounted to the vehicle body to be pivotal
about its polnt of attachment. Attached to the brake pedal 15
is a "feel" actuator 16.
Referring now to Figure 2 also, the feel actuator 16 is
a double acting,;,hydraulic actuator comprising a moveable piston
17 ha~ing a pair of opposed ,piston faces and contained.in a
, cylinder 18.: Mounted on the piston :17 is a piston head 17a
which provides-the piston faces. One end of the piston ~17 is
- coupled, to~ the brake pedal 15 by means of a linkage element 20
" ,which ~includes 'a-~load cell~.21 (or other ,sui~able;~device) ~which
.~is pre~erably~,a duple~,.,sensor,~,for sensing,,the force,applied by
a driver,o~,the,,vehicle,,to:the ,-brake :pedal 15. The,load cell
21 is,electrically connected~to a control ,unit 25, such as a
mir,~opracessor,;and.sends, input signals_thereto-,relating-to the
force.applîsd to the brake,pedal' 15.. -~`m~ a."~
:~ , Also attached to, the.linkage~lement~20 is a rod.22
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woso~l27~ PCT/GB90/00640
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which enters a hol~er 23 of a linear variable differential
transformer (LVDT) 24. The LVDT holder 23 is fi~ed adjacent to
the cylinder 18 on a manifold block 75 housing the feel
actuator 16. The LVDT 24 converts the mechanical displacement
of the linkage element 20 (and therefore the displacement of
the brake pedal 15) into an electrical signal which is
transmitted to the microprocessor 25 to which the LVDT 24 is
Plectrically connected. Other suitable devises may of course
be used for converting the displacement into an electrical
signal.
; The feel actuator 16 is hydraulically connected to servo
valve 28. Hydraulic transfer tu~es 9 are provided in the
manifold block 75 linking the hydraulic fluid lines ~rom the
servo valve ~ to each end of cylinder 18 so that the servo
valve 28 may be used to control the movement of the piStOTI 17
by hydraulic pressure to either side o~ the piston head 17a.
; As will be seen in Figure l a~non-return valYe ~9a is
. 'included in the hydraulic fluid line between the servo valve 2a
and feel actuator~. 16, for reasons described below. The
-non-return valve~ 29a:is also connected'ito the pressure supply
l~ ~ line~33 via an isolating valve 31"~describ~d below.' The non-
... . returnlvalve!29a opens on'application of pressurè thereto.`
` The servo valve 28 is colnected to' h~draulic fluid.. suppl~ ,pressure and~:~return lines 33,:34 via an isolating valve
~: 31 which is pre~erably ^a solenoid val~e. When' the solenoid
valve:31 is energised the pressure supply line 33 is connected
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WO90/~2717 PCT/GB9~/00640
- 72~3224
to the servo valve 28 and when it is de-energised the return
line 34 is connected to the servo valve 28. A prPssure
reducing valve 30 is incorporated in the pressure supply line
33 leading to the isolating val~e 31 so that the servo valve 28
uses a pressure lower than the system pressure.
An anti-cavitation valve 27 is also included.
The microprocessor 25 is connected to control the brake
servo valves 11, 12, 13, 14 ana signals g2nerated by the micro-
processor 25 control the pressure applied to the four brake ''
mechanisms independently. The servo valves 11, 12, 13, 14 are
connected to brake lines 56 which are connected to the brake
mechanisms of the front left, rear left, rear right and front
brakes respectively, via a distribution valve 35, as shown in
Figures 4 and 5. - -
The servo valves 11, 12, 13, 14 are connected to the
hydraulic pressure and retur~ lines 33, 34 via connectors 32.
One connector 32`connects a branch-o the pressure and return
lines to one pair of servo~ valves- 11, 14 and the other '
connector 32 to the seco~d pair of servo valYes 1~, 13. ` '
The distribution'~'val've 35~'comprises a' valvè manifold 36
ha~ing ~our separate "chambers` 46; 47, 48, 49 'therein. ' Each
chambe'r 46,;' 47,'48, 49"is connecte~ via a fluid pàssage 50 to a
respective s~rvo'~-valvè 11,"12, 13,'` 14;~;;The manifold 36 has
eight ports 37-44'therein such that~each chamber 46, 4i,'148, 49
has a pair of po'rts ~37', 41), '(~8, 42), ~3g; ~3j, (40,';44j`;'
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WO90/12717 2 ~ ~ 3 2 2 ~ PCT/GB90/00~0
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thPrein. One port 37, 38, 39, 40 of each pair is hydraulically
connected to a master cylinder 45 via a pair of fluid lines 58,
59. The master cylinder 45 is preferably a tandem master
cylinder and has a hydraulic booster 45a attached thereto, the
function of which will be e~plained later.
As shown in Figure 1, one pair of ports 37, 38 feeds
from one fluid line 58 from the master cylinder whilst the
second pair of ports 39, 40 feeds from the second fluid line
59. A balancing valve 60 may be provided in one of the fluid
lines 58, 59.
The other ports 41, 42, 43, 44 are connected to a brake
line 56 leading to a brake mechanism. -.
Within each chamber 46, 47, 48, 49 is a spool 51
comprising a concave~first part 52 which is located in one end
of a concave second part 53, the two parts 52 and 53 being
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secured together by a screw 55. As shown the two parts 52 and
53 are of different materials in view of the possibly differant
fluids acting on the.~.two..parts. The r spool 51 is slidable
within the chamber 46,.47, 48, 49....
A compression spring 54 is also~iocated in each chamber
,46,~47, 48,;.49, with one.end located against~an inside face 55
.of the second spool part 53 so.as to bias the spool 51 outwards
to seal o~ the 1uid passage..50 between~the chamber 46, ~7,
~8, .49 .and .~ the,a5sociated servo valvejll, .1~, 13, 14. The
length of .the;.;spool.j51 .jis such .that.;when it is biased as
mentioned a~ove ~rake fluid from the master cylinder 45 is free
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WO 90/12717 2 ~ 5 3 2 2 ~ P~T/GB90/00640
to enter/leave the chambers 46, 47, 98, 49 via the ports 37-44.
When hydraulic pressure is applied via pressure line 33
to the end face 57 of the spool part 53 the bias of the spring
54 is overcome and the spool 51 moves to compress the spring 54
and seals off the chambers.46, 47, 48, 49 from the ports 37-40.
S~con~ary Brakinq,SYs~em
A secondary braking system is also incorporated, the
secondary system being isolated when the primary active system
is operating and thus providing no braking effort. However,
when the primary active system is turned off or fails the
secondary system is selectively activated, for e~ample by a
pQSitive decision from the driver who operates a manual switeh,
or by automatic decision from the system in the event of a
failure.
The second system utilises a secondary hydraulic
actuator 65 to operate the hooster 45a which in turn operates
the master cylinder 45 in a known manner to:supply pressurised
.
- 1uid to fluid lines 5B, 59.
: ~The actuator 65 comprises a.piston 66 having a single
head 67 within a cylinder. 68. The ;secondary-actuator.65 is
.:~. hydraulically .linked to .the,feel..actuator..).~6..as ~ollows. A
:.hydraulic flu1d.linei69iis connected to the cylinder:68..on.one
- ~ 8ide o the plston.h~ad 67. After the.~luid :line 6g leaves the
: cylinderI68 it~:divides into two, one ~ranch.69a.connecting to
;~ ~ the hydraulic:fluid ~eturn line.,34~via ~a non-return.;valve.:29b~
and the~s~cond branch ~9b leading to a switching valve~i70.i:.The
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WO90/12717 . . PCT/GB90/00640
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switching ~alve 70 has a fluid line 71 which splits into two
branches 71a, 71b; branch 71a leads to the non-return valYe 29a
and branch 71b to the cylinder l8 of the feel actuator 16.
The non-return valves 29a, 29b and the switching ~alve
are connected to the pressure supply line 33 via the
isolating valve 31.
The Mechanical O~errid~
In the event of a~ undetected failure in the primary
actiYe braking system an override mechanism comes into
automatic operation. Under normal braking conditions the hrake
pedal 15 may be depressed over distance A shown in Figure 2.
When the braking pedal 15 is subjected to a "panic~ force in
the event of a failure undetected by the system lO so that no
braking occurs during the normal travel A of the pedal lS, the
pedal 15 moves through distance B and operates the override
mechanism.
. :The override mechanism comprises a sha~t 76 mounted on
the piston 66 of the actuator 65 and located within a cylinder
77, e~tending between.the actuators 16 and 65. Under normal
?~ conditions-the shaft 76 does not contact-.the cylinder 77. ~.
~ ..An override:compression spring:.79..is..located between the
..e manifold~lock 75~ which:houses the ~actuator l6 and a fi~ed
support 78 on which the cylinder 77 `is ~ounted on a pivotal arm
79;; see ~Figures 2..and ~3. The mani~old block 75 is mounted in
the system~;lO-;to be moveable, but ~:is..held, during normal
braking, stationary by the spring 74 acting between the block 75
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WO90/12717 2 ~ 5 ~ 2 2 ~ PCT/&BgO/00640
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and the support 78.
Figure 2 shows the system in the condition when the
override is operating, although the pedal 15 is shown in solid
line in its normal position.
Primarv Ac~ive Brakina
During primary active braking brake p~dal 15 travels
through distance A (see Figure 2). The .load applied by the
driver to the pedal 15 is measured by load.cell ~l which sends
input sig~als relating to the load to the microprocessor 25.
A reaction to the driver's demand on the brake pedal 15
is provided by the ~eel actuator 16. To do this the
microprocessor 25 sends control signals to the servo valve 28
which is connected to the feel actuator 1'6 to apply pressure to
either side of the piston head 17a. This is used to provide
resistance to movement of the brake pedal 15 and to generally
simulate the ~feel~ of braking. This ~feel" may.be altered by
.programming the microprocessor 25 to provide light or heavy
braking or whatever the'driver prefers.~
: . During primary active braking -the lisolating valve 31 is
energlsed to connect the servo valve ~8 with.the pressure line
: .33.: When the isolating valve 31 is:energised pressure is`'also
~ .. -applied ~to :the ;non-return`valves 29a, 29b~-This causes the
: non~return valves 29a, 29b to open and the switching valve 70
to close which allows the feel actuator ..16.i~ta be.'driven
. directly ~by the servo valve .28 via~:the :fluid.lines to either
side of the:!piston head -17a.: Any residual~fluid~;pressure 'in
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WO90/12717 '; ~'~ PCT/GB90/00640
2~32~ - 12 - ,;
the master cylinder 45 is ve~ted via fluid line 69 through the
open non-return valve 29b to the fluid return line 34.
The feel actuator 16 is capable of simulating a wide
range of characteristics depending on the 'feel' re~uired.
The actual braking is carried out by fluid pressure
supplied by, the four servo valves 11, 12, 13, 14. The
microprocessor 25 sends independent co ~ rol signals to each of
the servo valves 11, 12, 13, 14, according to input siynals
from the load cell 21.
Since the isolating valve 31 is energised the servo
valves 11, 12, 13, 14 are connected to the pressure supply line
via the connectors 32. The fluid pressure is controlled by
each servo valve 11, 12, 13, 14 to operate each brake mechanism
independently. The fluid pressure transmitted from the servo
valves 11, 12, 13, 14 via fluid passages 50 is ~u~ficient to
,o~ercome the preload on the springs.54 causing the spools 51 to
move in the ~hambers 46, .47, 48, 49 to seal them off from the
., :ports ,37-40 from the ma~ter,cylinder 45. The fluid remaining
~ ..the chambers 46.~49 is ,forced out of,the chambers 46-49 via
: the:ports ~,41-~4 by~mo,vement of the spools 51 to,the individual
" , brake,~,mechanisms to operate.:the brakes ~independently.o~ each
,. other.. .~ }
The secondar~braking ,.,s~stem ma~ be activated ,.in two
ways;,either by means..o~:a~manual switch .~not ,shown) operated
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WO 90/127~7 2 ~ ~ 3 2 2 ~ PCI/GB90101)640
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by the driver to de-energise the isolating valve 31, or as a
result of a failure detected in the primary active braking
system.
The main failures may be in the form of loss of
electrical power to the system of a drop in the system pressure
below a pre-set safety limit.
Various safety control loops may be incorporated in the
overall braking system which are monitored ~y the
microprocessor 25. An e~ample described earlier in the
provision of the LVDT 24 which checks whether the feel actuator
16 is in fact operating according to the control signals sent
to the servo valve 28 by the microprocessor 2S. The LVDT,'load
cell 21 and other sensors in the system are preferably duple~
sensors. Their-signals are duplicated and the signals'combined
to give a demand and an error~detection signal. Failures in
the control loops can be detected :by' comparing the actual
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output' from the system~with a~ real time model of the system
' running in''parallel. Any deteeted failures ':will result in
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: de-èner~isation of the isolating valve 31. ' ^'
Loss of the electrical~'supply will automatically result
' in de-engerisation.of the isolating'valve' 31. ~he efect of
'' 'loss of 'pressure has`a 'similar e~ect 'which-will' be described
: later'. ' ''"' ' ~'`~' ' " '''
Wh~n the isolating valve' 31:is'~dë-energisëd it conné~ts
:: to: the'~fluid return~ line '34 This ;'resu'lt's ~in a drop in
pressure to'the non-return valves'29a, 29b which ciose and the
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WO90/12717 pcT/GBso/oo~o
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and switching valve 70 which opens. This hydraulically
disconnects the servo valve 28 from the feel actuator 16 and
hydraulically connects the feel actuator 16 to the secondary
hydraulic actuator 65 via switching valve 70 which operates the
booster 45a and master cylinder 45.
Thus pressure applied to the pedal 15 will be
transmittPd by movement of the p'ston 17 with piston head 17a
forcing the fluid out of cylinder 18, via the switching valve
70, into the cylinder 68 of the secondary actuator 68 to act on
the piston head 66 of the secondary actuator 68. Thus, braking
in this mode feels and performs similar to a standard
unmodified hydraulic braking system.
Referring to the distribu~ion valve 35, in secondary
~raking the servo valves 11-14 are connected to the fluid
return line 34 and the pressure applied to the spools 51
drops. The force of springs 54 is sufficient to overcome any
residual pressure and force the spools 51 outwards towards the
servo valves 11-14 to seal off fluid passages 50 from the
..
: chambers 46-49 and the ports 37-40 which communicate with the
: . master cylinder 45 are uncovered.
Thus, as the ~oot pedal..l5.is depressed brake ~luid is
.,forced along the fluid lines 58, 59 from the~master cylinder
45, into chambers 4fi-49 and out of ports 41-44 to the brake
. mechanismi.vla theJbrake ~lines,56. ~ :
Since ports 37, 40 are connected ~to the,fluid li~e 58
and ports 38, 39 are connected to line 59 equal pressures are
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WO90/lZ717 2 ~ ~ 3 2 ~ ~ PCT/GB90/00640
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transferred across each a~le pair of brakes.
~ oss of sys~em pressure below a certain limit will also
allow the springs 54 to recover and return to their original
state and thus has the same ef~ect as if the isolating valve 31
had been de-energised.
Overrid~ Brakinq
In the event of an undetected ~ailure in the feel system
the override mechanism comes into operation. If no braking
occurs when the driver depresses pedal 15 through distance A,
he will use a panic ~orce and the pedal will move through
distance B. The length of the feel actuator cylinder 18 is
such that when the brake pedal 15 has reached the end of travel
distance A, the piston head 17a reaches the end of the cylinder
18. Further movement of the pedal 15, i.e. through travel
distance B on applicaton of a panic force, will cause the
piston head 17a to bear on the end face 80 of the cylinder 18,
which lS attached to the manifold block 75 and thus causes the
manifold block 75~to move aqainst and overcome the pre-load of
spring 74 so that the whole manifold block 7S moves (to the
position shown as Figure 2~. As the manifold block 75 moves
toward the support 78 cylinder 77 moves into contact with shaft
76. Further movement of the block 75 cau~ed ~he shaft 76 to
move the piston 66, which activates the brake booster 45a and
~aster cylinder 45 to operate the brakes.
The system is;thus very versatile, self-monitoring, fail-
safe and may per~orm to a variety o~ control laws, such as anti-
WO90/12717 - i`: PCT/GB90100640
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lock braking, variable balance, deceleration demand and brake
performance feed back to pedal.
Although the system described above operates primarily
in dependence upon the load applied to the brake pedal, with
appropriate modifications to the system it may be made
responsive to the position or movement of the brake pedal or
any other param~ter measurable in the system.
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