Note: Descriptions are shown in the official language in which they were submitted.
s~o
sIMpLIFIF~n ~NTI-LOCK ~RAKING SY~r~'E'M
_C _ OUWD ~ T~IE INVENI'ION
The present invention relates to antt-lock hrak-
ing systems and in partlcular to an anti-lock brakinq
system which incorporates an integrated modulatiny valve
and brake pressure reducing pump, actuated by an elec-
tronic control system responsive to rotational behaviorof a vehicle's wheels, the system being particularly
applicable to anti-lock control of the rear wheels of a
vehicle.
Anti-lock braking systems are well known.
Typically, prior art anti-lock brak~ng ~ys,tems have
_~o~ r , ~;~ G6:1'
evolved from mechanical to s~s~i~l~e~ electronically-
controlled devices which sense the rotational behavior of
a vehicle's wheels during braking and assume control of
braking of the vehicle upon sensing an ~ r-~e~ skid con-
dition to automatically modulate the application of brak-
ing pressure to avoid wheel-lock. Typically, these sys-
tems incorporate a power boosted master cylinder or a
full power hydraulic system to produce the required pres-
surized braking fluid. The systems are normally divided
into a plurality of hydraulic circuits with braking of
the front wheels of the vehicle heing individually con-
trolled and the rear wheels of the vehicle being con-
trolled either individually or as a pair. Such systems
can be highly effective. Such systems are, however,
complex and expensive, a factor which reduces their
availability and widespread implementation.
There exist numerous applications for anti-lock
braking systems in which substantial~improvements in the
braking performance of the vehicle can be enhanced with-
out the requirement of controlling three or more wheelsof the vehicle. Such applications typically include
pick-up trucks and vans. In these applications, due to
the substantial variation in loading of the rear wheels
of the vehicle, it is possible to have a vehicle that is
lightly loaded be very subject to locking of the rear
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wheels. Various brake pressllre proportlonlng dev1ce~
have been proposed to alleviate this prohlem hut sllch
devices have been less than fuliy efectlve, due to sub-
stantial variations in friction materials and other
variable parameters of the braking system.
There therefore exists a need for a simple, low
cost anti-lock braking system which is adaptable for ap-
plications such as pick-up trucks and vans which can sub-
stantially reduce the potential of rear wheel lock with a
minimum of cost and complexity.
There also exists a need for such a system which
can be used with braking systems incorporating vac~um
boosted modulators, and any of various hydraulically
boosted systems.
Broadly, the present invention is an anti-lock
braking system which comprises a master cylinder means
for generating pressurized braking fluid in a hydraualic
circuit which includes at least one wheel cylinder. Means
are provided for sensing the rotational behavior of a ve-
hicle wheel and generating a signal corresponding thereto.
A control circuit is connected to the sensor means for
receiving these signals and generating control signals in
response to an incipient wheel-lock condition. A hrake
pressure modulator is operatively connected to the hy-
draulic circuit between the master cylinder and the wheelcylinder. The pressure modulator includes a pump for
pumping fluid from the wheel cylinder to the master cyl-
inder, and a pressure reducing means connected between
the pump means and the master cylinder for producing a
pressure drop thereacross in response to the flow of
fluid therethrough. An isolating valve is provided, the
valve having an inlet port, wheel cylinder outlet port, a
pump outlet port, and a control port. The ports are
connected to the master cylinder, wheel cylinder, the
inlet of the pump means, and the input of the pressure
reducing means, respectively. The isolating valve
normally establishes fluid communication between the
inlet, wheel cyllnder, and pump inlet ports and lnclude~
an element oper~ble in response to a pressure drop across
the pressure reducing means to isolate the inlet port
from the wheel cylinder and pump inlet ports. The pump
means is responsive to the signa:Ls from the control means
to pump fluid from the wheel cylinder to the master
cylinder to thereby reduce the pressure of hLaking fluid
therein.
It is therefore an object of the invention to
provide an improved anti-lock braking system.
Another object of the invention is to provide an
anti-lock braking system of reduced cost and compiexity.
Still another object of the invention is to pro-
duce an anti-lock braking system particularly well suited
for use in preventing lock of the rear wheels of a
vehicle.
Another object of the invention is to provide an
anti-lock braking system which includes a self-contained
electrically operated pump and an isolating valve operable
in response to signals from a control circuit and fluid
flow from the pumpj-respectively, to pump fluid from a
wheel cylinder and reduce the pressure therein.
These and other objects and purposes of the
invention and the invention itself will he best under-
stood in view of the following detailed descriptionthereof taken in conjunction with the appended drawings
wherein:
Figure 1 shows an anti-lock braking system in
accordance with the present invention, portions thereof
being shown in schematic format; and
Figure 2 is a fragmentary drawing of an alterna-
tive pump for use in the invention.
DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to the drawing there is shown an
anti-lock braking system which comprises generally a
master cylinder 12, typically a dual cylinder displace-
ment type of master cylinder including a reservoir 14 and
actuated by a Eoot pedaL 16. ~laster cylln(ler 12 h~lg two ou~ptll: cLr-
cuits, I, [I. As illustratecl, hy~lrauLlc cLrcuLt I Ls cotlnec~e(l ~o
a palr oE Eront wllee1 brake cyllnders l8, 20 nnd llyclrn~lLIe cLrcllLt
II is connected throllgll n pUIllp ancl moduLator assemhly 22 to a pnir
oE rear wheel cylinders 24, 26. ~laster cyLLnder 12 may be man~laL
or power boosted by means of sueh as a vacuum booster or a hydrallllc
booster (not shown). Ilydraulic circuits I, II are fully hydraulically
isolated, such systems and components being now well known in the
art.
Pump modulator assembly 22 includes a body 28 of irregular
configuration. Body 28 is provided with a generally cylindrical,
stepped diameter valve chamber 30 having a closed end 32 and provided
at its opposite end or master cylinder inlet 34 with a tapered valve
seat 36.
An inlet passage or master cylinder port 38 communicates
axially with valve chamber 30 via the valve seat 36 and is connected
at its opposite end 40 to the hydraulic circuit II of master cylinder
12.
A wheel cylinder outlet passage or wheel cylinder port 42
and a pump inlet passage 44 communicate with chamber 30 adjacent
valve seat 36. Wheel cylinder outlet passage 42 is connected via
fluid conduit 46 to the wheel cylinders 24, 26 associated with the
rear wheels of a vehicle (not shown).
Also formed fluidly in series in body 28 are a pump mani-
fold chamber or pressure fluid inlet port 48, pump cylinder 50, stop
valve chamber 52, connecting passage or pressure reducing means inlet
port 54, pressure relief or reducing valve chamber 56, and a fluid
passage 58 communicating between reducing valve chamber 56 and inlet
passage 38. A solenoid 60 includes a coil 62 electrically connected
to an electronic anti-lock control unit 64, a plunger 66 connected
to a pump piston 68 which extends through a fluid tight bore 70 and
"O" ring seal 72. Alternatively, pressurized fluid can be admitted
to the coil chamber to provide a fluid balanced system, that is,
a system wherein fluid pressure on the opposite ends of piston 68
are balanced. A spring 74 maintains the plunger 66 in its illus-
trated position. Upon energization of the solenoid coil 62, plunger
66 moves upwardly (as viewed in the drawings) causing the piston
68 to move into the pump cylinder 50.
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Stop valve chamber 52 has dispose(l there:Lrl an anl~ lr
stop valve e:lement 76 res:L:L:Lent:ly ma:LIlta:Llle(l aga:L[Ist a slloll.l.(lor 7
oE chatllber 52 by a col:L spr:lng 80.
S:Lm:llarly, a ball valve 82 :ls rece:lvecl:ln red-lc:LIlg va:Lve
chamber 56, ball valve 82 being ma:Lntalned agalnst a valve seat 84
in chamber 56 by a co:Ll spring 86.
~ fluid passage 54 connects stop valve chamber 52 and the
pressure reducing valve chamber 56 to fluid passage 88 and to the
end 90 of valve chamber 30 axially opposite inlet passage 38. Inlet
passage 44 communicates chamber 30 with the pump inlet chamber 48.
~ valve element 92 is reciprocally received in valve chamber
30. Valve element 92 is provided with a valve closure portion 94
movable into engagement with the valve seat 36 to close the inlet
passage 38. Preferably, an "0" ring seal 96 is fitted to the valve
element 92 to provide fluid tight isolation thereacross. The end
98 of the valve element 92 is of reduced diameter to provide a fluid
receiving space between the valve element 92 and the end 90 of
chamber 30.
Lastly, a speed sensing device 95, typically a magnetic
sensor associated with rotating tone wheel or the like is operatively
connected to the drive shaEt of the rear wheels of the vehicle (not
shown). This sensor, as is now well known to those skilled in the
art, provides a signal proportional to the speed of the wheels
associated with wheel cylinders 24, 26. This signal is applied to
the electronic control unit 64. The control unit itself includes
a computing circuit which will analyze the rotational behavior of
the wheels of the vehicle to determine the occurence of an incipient
skid condition. Based on this information, control signals are
generated by the electronic control unit 64 to apply an operating
signal to the solenoid coil 62 to effect reduction in pressure of
fluid applied to the wheel cylinders 24, 26.
Under normal braking conditions, valve element 92 remains
in its rightmost position as is shown in the drawing. Pressurized
braking fluid in hydraulic circuit II passes through the passage
38, valve chamber 30, and to wheel cylinders 24, 26 via passage 42
and fluid conduit 46. This same pressure is also provided to pump
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inlet chamber 48 via fluid passage 44. When the electronic control
unit 64 determines that the wheels are being braked excessively and
an incipient lock condition exists, a control signal is generated
to energize solenoid coil 62. This moves the plunger 66 vertically
(as shown in the drawing) moving the piston 68 into the piston cylin-
der 50. This forces a quantity of brake fluid from the cylinder
50 past the stop valve 76 and pressure reducing valve element 82.
Action of the pressure reducing valve 82 creates pressure drop in
the fluid as it passes from passage 54 to the inlet passage 38. The
highér pressure in passage 54 is conveyed via passage 88 to the end
98 of valve element 92. Because this pressure is higher than pressure
at the inlet passage 38, valve element 92 moves to the left (as viewed
in the drawings). With repetitive solenoid action, valve element 92
fully travels so that valve closure portion 94 seals against seat
36. This isolates master cylinder 12 from the wheel cylinders 24,
26. Simultaneously, fluid pumped from the cylinder 50 forces a simi-
lar quantity of fluid backwardly through the inlet passage 38 thereby
withdrawing a small quantity of fluid from the wheel cylinders 24, 26
via wheel cylinder outlet passage 42, valve chamber 30, and pump
inlet passage 44. This, accordingly, reduces the pressure in the
wheel cylinders 24, 26. Continued existence of the incipient skid
condition will cause further repetitious operation of the solenoid
plunger 66 thereby further reducing pressure in the wheel cylinders
24, 26O This will continue until the incipient skid condition has
been alleviated.
When the driver lowers pressure in master cylinder 12,
the pressue in passage 38 lowers. If the pressure in the brakes
is greater (less the pressure drop across the regulator valve) fluid
will return to the master cylinder via passages 42 to 44 to 48 past
valve 76 to passage 54, past valve 82 to passage 58 to master cylinder
inlet passage 38. When the pressure in chamber 90 is less than in
chamber 30, piston 92 moves to its rest position reopening full com-
munication from master cylinder to the brakes.
In the illustrated embodiment, the pump has been illustrated
as a solenoid. This configuration provides the least expensive struc-
ture. However, in severe spike applications of brakes, it is possible
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that the solenoid actu.ltecl pump wLll have insuEficlent capncLl:y to
reduce brake pressure rapicl:ly enough to EuLLy avoLcl 1 skLcl or loc:k
cond:itlon oE the vehLcles wheeLs. ~ccorclLng1y, th:Ls l.:l.lll.l.t~lt:LOII (:all
be alLeviatecl by replacLng tlle soleno:Ld p(llllp witll an cLectr1c nlotor
pUIllp as sllown in FLgure 2. The motor pUIllp lO5 Lncorporates a Illotor
(llOt shown) clrivLng an eccentrLc 102 wh1ch Ln turn rec-Lprocates the
plston 68. ~ stop vaLve L04 may be provided. Because oE Lts Illgher
capacity, the pump 105 wilL be able to eliminate locking oE the vehi-
cles rear wheels even under severe spike applications but with an
attendant increase in cost of the system. The system, nonetheless,
represents a substantial reduction in the complexity of anti-lock
braking systems. Because of its configuration, this system is excep-
tionally well adapted for applications such as vans and light trucks
with ~he system being applied to the rear wheels only.
In the operation of the system, it should be observed that
the stop valve element 76 prevents the passage of fluid from the
inlet passage 38 backwardly through pump cylinder 50, chamber 48,
and the wheel cylinders 24, 26 during the brief period when the pres-
sure reducing valve 82 remains open and the solenoid pump begins
to retract. It should also be observed that a pressure build orifice
lO0 may be provided in the valve seat 36 to allow for gradual controlled
building of pressure in the wheel cylinders 24, 26 when the incipient
lock condition has been alleviated and/or the brake pressure in the
wheel cylinders 24, 26 has been reduced by an amount greater than
necessary.
~ lthough the present invention has been illustrated and
described in connection with example embodiments, it will be under-
stood that this is illustrative of the invention, and is by no means
restrictive, thereoE. It is reasonable to be expected that those
skilled in the art can make numerous revisions and additions to the
invention and it is intended that such revisions and additions will
be included in the scope of the following claims as equivalents of
the invention.
