Note: Descriptions are shown in the official language in which they were submitted.
,,.,.21?0.59~
r
ELECTRO-HYDRAULIC ~RARE SYSTEM
3.~.CKGROU~J~ RY Cr T~r T~E~ITIO~.
J ' The presen~ ~ven~ion relates ;_ 2n ^i~ctr~-
hydraulic brakir._ system in wnich the ~rimary ~raking
force is sup~Liei t~ brake cyLinders by a ~ump moved 5v
~n electric mot~-.
'~One su~n ei~ o-hyaraulic braki~a syst~m s snown
in US Paten~ ~ a_~ 777. ~ sim~ ie~ version o~ an
electro-hydraul_^ ~r~king sys~em is sno~n in F-~GURE 1.
The system comDr ses a pump 12 powered ~y a motor 14 ir. -~
~esponse to cer._-~i sianals generated v an ele~rronic
_ control unir (~ 16. The pump direc-ly ~ressurizes
a brake cilinaer ~ cyiinders generallv s;nown as 18.
The speed ce the mo~or 14/pump 1~ is controile~ so as
to modulate brz:~G system pressure in ac~o_danc~ with a
commanded brake ~ressure signal. A by-pass orifice 20
2 a is provided acr~ss ;he pump 12 whic-. e~hances the
srability of mocc-~pump speea and 2110ws ~5- the rapi~
reiease o_ ora~_ c;linder pressure ~:nen ~e~uire~
-IGURE ~ illus~r__es an improvement ~c .ne sim li~ied
system shown ir. r-~U-~E 1 in whicn a mascer cylinder 22
~5 has been added ;_ provide brake system redundancy in
the event that .:~e Dump 12 or electronics fail. In
this system the ~otor control signal is generated by
comparing master cvlinder pressure as generated by a
pressure senso- 2~, co a signal indicative o~ the
pressure ln~ the brake cylinder 18 as determined by
pressure sensor ~. This technique cou!d also be used
in the system of FIGURE 1. An isolation valve 28 is
used to communica~e either the master cylinder or the
output of the pump to one or more braka cylinders 18.
The isolation valve may be a pressure piloted isolation
valve responsive to pump outpuc pressure. The syscem
SUBST;TUTE SHEET
2120~.91~
illustr~tea u~ es, in a genera! sense, c flow
control d~vic~ ~0 across tne pump ~his flow con~rol
devic~ mav be lmpiemented i?. manv differen~ ways,
inciuding the fixea orifice snown i-, EIGURE 1 or the
solenoid valve shown _n FIGURE 2 Whiie either or the
systems showr in FIGUREs 1 and 2 work well, cer~ain
time delays will exis~ until the pums OU~pUt pressure
builds satisfactorily To reduce an~r time deiay thes-
systems require an ex~remely fas. responding mo~or and
also require motor speed con~rol elec_ronics whLc;n are
useful in re~ulating .he speed or t;~ ~ump suc~; tha~
auring in the s~eadv state the outpu- ?ressure of the
pump is eoual tO the commanded G- master c~flinder
pressure
It is an 02jec~ of the present inven~ion to provide
a more rapid responding, less exDensive
electro-hydraulic system than that ~!us~rated in the
above figures
2C
Accordins, the invention comDrises an
eLectro-nyaraulic brake syst~m comorising a master
cylinder; 2 pump tne ou~put communicated to a ~ressure
regulating valve means; a motor for rotating the pump
~5~ at a determinable speed; isolation valve means
selectively connecting one of the mas~e~ cylinder and
pump to a brake cylinder or group o- brake cvlinders
and first means for generating a signal indicative of
operator in~tiated brake activity to cause ac~ivation
of the pump The valve means, is connected between the
master cylinder and pump and reguiates the output
pressure of the pump at a decerminable level in
proportion to the pressure generaced by the master
cylinder and ~or providing a path to ~rain the brake
cylinder(s) to a reser~oir during intervals of
decreasing master cylinder pressure The system may
SU8S~ITUTE SHEET
- 2120~.9fi
.
also include an excess flow valve(s) which will pr~ven~
the reservoir from being drained bv the pump in the
even.t o a malfunccion such as a derective or leaky
brake cyLinder or a hole (leak) in a hydraulic line.
Various embodiments of the valve means are aescribed
which add additional failure mode protection to the
system.
~.
Many other objects and purposes of the invention
will be clear from the foliowing detailed descriptior.
of the drawings.
BRIEF DESCRTPTION OF THE DRAWINGS
In the drawings:
FIGUREs 1 and 2 illustr.ates simplified versions of
an electro-hydraulic braking system.
FIGURE 3 illustrates an improved electro- hydraulic
system incorporating features of the present in~ention.
FIGURE 4 illustrates an alternate embodiment or z
pressure regulating valve.
FIGURE 5 illustrates another brake system.
FIGURE 6 illustrates another embodiment of a valve.
25 ~
SUBSTITUTE SHEET
W0~3/09012 PCT/US92/08g22
2i20~i!1fi
DETAILED DESCRIPTION OF THE DRAWINGS
FIGURE 3 schematically illustrates an
electro-hydraulic brake system 30. The system
includes a master cylinder 32 and a pump 34 such as
a positive-displacement pump rotated by a motor 36.
The motor 36 is activated through a relay 38 by a
control signal generated by an ECU 40. As shown the
output signal from a brake light switch 80 ~or
similar command) is used to activate the relay 38.
While an ECU 40 is shown, this could be eliminated.
The ECU 40 may in its simplest form include
electronic filters and a buffer or amplifier circuit
for powering the relay 38. The output of the pump
34 and the output of the master cylinder 32 are
communicated to an isolation valve generally shown
as 42 similar in function to the isolation valve 28
of FIGURE 2. If the pump does not produce adequate
pressure, isolation does not oc~ur and conventional
manual braking is still available via the master
cylinder. In this sense, the failure of the pump is
similar to the failure of a vacuum booster found in
conventional power brake systems. The system 30
further includes a pressure regulator which is also
~5 referred to as valve 50. As will be seen the valve
50 regulates pump pressure i.e., the pressure
supplied to the brake cylinder(s) at a determinable
ratio of master cylinder pressure. FIGURE 3 shows
one e~mbodiment of the valve 50 which comprises a
,__
first piston 52 exposed to master cyli~der pressure,
movable within a piston passage 56. The piston
includes a pin or closure element 54. One end 60 of
the piston ~assage 56 is communicated to the ~ump 34
as well as to the brake cylinder or cylinders 44.
The piston passage 56 includes a by-pass passage 58
wo 93/0gol2 2 1 2 0 .~ 9 fi PCT/US92/08922
communicated to a reservoir 62. A first orifice 70
is provided in the piston passage 56 and defines a
flow area Al which is equal to or less than the area
A2 of the first piston 52 that is exposed to master
cylinder pressure. As can be seen, the first
orifice 70 is located between the by-pass passage 58
and the end 60 of the piston passage 56.
The system 30 additionally includes a means for
generating a signal indicative of operator initiated
brake acti~ity. As illustrated in FIGURE 3, and as
mentioned above, an indication that the operator has
stepped on the brake pedal 82 is sensed by the
closure of a brake light switch generally shown as
80. The brake light switch is communicated to the
ECU 40 which in turn activates relay 38 to cause the
motor 36 to rotate at a relati~ely constant speed
defined ~y the pump pressure needed to create a
force balance across the first piston 52.
Alternatively, an indication of braking activity can
be generated by utilizing a force sensor 84 to
measure brake pedal force or a pressure sensor 86 to
measure developed master cylinder pressure. One
ad~antage of using the brake light switch 80 as
~5 opposed to a force transducer 84 or pressure sensor
86 is that the brake li$ht switch 80 will generate a
signal slightly before a force sensor or pressure
sensor will generate its corresponding signal.
Usin~ the brake light switch as a measure of brake
activity reduces time delays permittin~ a more rapid
energization of the motor 36/pump 34.
In operation, when the operator depresses the
brake pedal 82 pressure in the ma~ter cylinder will
increase. The output preqsure of the master
WO93~09012 PCT/US92/08922
21 2 O~i '3 ~ -6-
cylinder is communicated to the brake cylinder or
cylinders 44 through the isolation valve. The
nonactivated state of the isolation valve is shown
in FIGURE 3. When the brake pedal 82 is depressed,
the brake light switch 80 output signal is
communicated to the motor relay 38. During the
initial moments of operation of the system, the
master cylinder pressure will exceed the pressure
generated by the pump 34. During this time, the
master cylinder pressure acts upon the first piston
52 causing the element 54 to fully close the orifice
70. With the orifice 70 closed the full output flow
capacity of the pump 34 is directed to flow to the
isolation valve 42.
The isolation valve 42 should typically be
designed to change its state at a relatively low
output pump pressure such as 30-50 psi. When the
isolation valve changes state, it isolates the
master cylinder 32 from the brake cylinder 44 and
directly communicates the output of the pump to the
brake cylinder 44. As the output pressure of the
pump builds, this pressure acts upon the lower end
of the element 54, moving it from the first orifice
70 in opposition to the forces generated on the
first piston 52 by master cylinder pressure. It is
desirable to regulate the output pressure of pump 34
to a determinable pressure and as a function of
mast~r cylinder pressure. In its equilibrium
condition, the valve 50 will regulate pump pressure
P to be equal to: P = A2/A~ x P~c
where P~c is master cylinder pressure. If A2 is
greater than A1 a boosted pump pressure is generated
analogous to the output of a conventional power
brake.
W093/09012 2 1 2 0 ~ ~ fi PcT/us92/o8922
As can be appreciated, the pressure regulating
- action of the valve 50 works on a force balance
principle. The master cylinder pressure acts on the
working area of its associated piston (piston 52)
- 5 and produces a force which is balanced by the pump
34 acting on an associated element (pin or element
54). The pin 54/piston 52 will move until
sufficient flow passes through the orifice 70 to
produce the required pressure difference.
When using a conventional service brake system
the operator modulates the force applied to the
brake pedal 82 to vary the pressure applied to the
brake cylinder 44. This action also happens in the
present invention. The pressure generated by the
pump will follow master cylinder pressure which is
proportional to brake pedal force.
While FIGURE ~ illustrates a separate master
cylinder and valve ~0, it should be appreciated that
the valve S0 can be incorporated within a modified
master cylinder.
Failure of a portion of the hydraulic system
r 25 downstream of the isolation valve 42 such as a
broken line or leaking brake cylinder could result
in not only a loss of braking to the affected wheel
but also allow the pump to completely drain the
reservoir so that the pump cannot pressurize other
braké cylinders. This undesirable effect can be
circumvented by placing an excess flow valve 90
between the pump 34 and isolation valve 44. It
should be appreciated that FIGURE 3 9hows a ~ingle
brake channel. FIGURE 5 shows a plurality of excess
flow valves and a two channel brake system from
WO93/09012 PCT/~S92/08922
21205.~6 -8-
which the benefit of these valves is more readily
apparent. - -
Reference is made to FIGURES 4 and 5. FIGURE 4
illustrates an alternate valve 50~. FIGURE 5
illustrates an exemplary braking system 30~ for the
control of four brake cylinders 44. The valve 50',
also shown schematically in FIGURE 5, is
functionally analogous in operation to valve 50. An
added feature is that this valve 50' is adapted to
communicate to a master cylinder having primary and
secondary master cylinder chambers 32a and 32b,
respectively providing failure redundancy in
operation. The valve 50~ includes a housing 100
defining a plurality of ports 102, 104, 106 and 108,
adapted to respectively communicate to the primary
master cylinder chamber 32a, pump 34, reservoir 62
and the secondary master cylinder chamber 32b. The
valve 50~ includes the first piston 52 (see FIGURE
4) and closure element 54 and a valve seat 110
defining the orifice 70. Port 104 illustrates the
use of an inverted SAE fitting which may also be
used in any of the various ports of the valve 50~.
The piston 52 is slidably received within a bore 114
which also supports a second piston 116. The valve
50~ includes an additional two ports 120a and 120b
which communicate to the isolation valves 42a and
42b shown in FIGURE 5. The exemplary system of
FIG~E 5 shows a cross-split brake configuration in
which the primary master cylinder 32a is
communicated to the left front and to the right rear
brake cylinders 44 through a proportioning valve
122a. Secondary master cylinder pressure is u~ed to
control the right front and left rear brake
cylinders through a second proportioning valve 122b.
W~g3/0901~ 2 1 2 0 5 9 fi PCT/US92/08922
_g_
Returning to FIGURE 4, the passage 114, between
the connection points of the primary and secondary
master cylinder, is also communicated to the exhaust
port through a passage 126. This passage 126
provides a region of atmospheric pressure about
piston 116. The purpose of this vent or passage 126
is to insure that if any of the regulator seals such
as 128 fail, this failure will be detectable. As an
example, if one of the seals 128 fail the secondary
master cylinder chamber pressure will decrease as
brake fluid will flow to the reservoir. This low
pressure will be detected by a low pressure switch
in the secondary master cylinder chamber. The
pressure switch will typically activate a light on
the dashboard informing the driver of the failure.
If such a failure of a component in the valve were
not detectable then a subsequent failure of, for
example a seal in the primary master cylinder would
result in the loss of complete braking control.
Another feature of the valve 50' is that it is
operable in the event of a failure of one or the
other master cylinder chambers or in the hydraulic
lines connecting these chambers to the valve 50'.
~5
The operatipn of the valve 50' is as follows.
As is typically the case, the pressure generated in
the primary master cylinder will be approximately 20
to 50 psi (1.38-3.45 bar) greater than the pressure
generated in the secondary master cylinder. With
the system connected as shown in FIGURE 5, the
~ primary master cylinder pressure is received into
chamber 130 of FIGURE 4. This pressure force urges
piston 52 downwardly and piston 116 upwardly against
stop 132. As can be appreciated, the dynamics of
WO93/09012 PCT/US92/08922
21 2 0 5 9 6 -lo-
valve 50', in this condition, are essentially
identical to those of valve 50. In this operating
condition, secondary master cylinder pressure does
not play an operative role in regulating the output
pressure of the pump. The valve 50~ wfill continue
to operate even in the face of a failure of the
hydraulic system upstream of port 108 i.e. the
secondary master cylinder chamber. In the event of
~ failure of the hydraulic system connected to the
primary master cylinder chamber, no fluid pressure
would be generated within chamber 130, however,
secondary master cylinder pressure is communicated
to chamber 134 which urges piston 116 downwardly and
which in turn will cause piston 52 to close the
orifice 70. As before, this action permits full
pump output to be communicated to the brake
cylinders 44 during pump start-up. In this failure
mode, the valve 50' will regulate pump output
pressure to be proportional to the pressure in the
secondary master cylinder.
Reference is made to FIGURE 6 which illustrates
an alternate embodiment of a pressure regulating
valve 50~. This valve can be substituted into
FIGURE 5. The valve 50 n includes a housing 104 into
which are received three pistons 206, 208 and 212.
A pin 214 is secured to one of the pistons 206 or
208. In FIGURE 6 the pin 214 is secured to piston
208 and is slidably received within a bore 216 of
piston 206. Pistons 206 and 208 are slidably
received within a central bore 220. Pist~n 212 is
- received within another bore 222. Various dynamic
seals such as 224 and 226 are provided to prevent
leakage through the various bores 220 and 222. As
illustrated seal 224 can be a GLYD ring while seal
~ ' !
WO93/09012 2 1 2 ~ 5 9 6 pCT/US92/08922
226 is shown as an O-ring.
Piston 212 supports a valve closure element 230
which is spherically shaped and adapted to seat upon
a valve seat 232 defining an orifice 2~4.
The valve 50l~ includes a plurality of ports
104, 106, 102 and 108 respectively connected to the
pump 34, the reservoir 62, the primary master
cylinder chamber 32a, and the secondary master
cylinder chamber 32b. The valve ~0" also includes a
plurality of vents schematically shown as 242 and
246. As can be appreciated exterior vents are not
necessary. Alternately, the bores 220 and 222 can
be vented to atmosphere through internal passages
(not shown) communicated to the reservoir port which
is typically at atmospheric pressure.
The piston 208 has a first working surface 260
of area A3 which is exposed to primary master
cylinder pressure. The piston 212 has a second
working surface 262 of area Al which is also exposed
to atmosphere through the vent 246.
The operation of the system 200 is as follows.
Fluid from the primary chamber 32a will fill the
chamber 250 between pistons 206 and 208 and act on
the first working surface 260 of piston 208 causing
the piston 208 to press down on the working surface
262 of piston 212 causing element 230 to fully close
orifice 234. This action enables the full output of
- the pump 34 to be communicated to the brake cylinder
44. As the pump pressure builds, it acts upon the
piston 212 to move away from the valve seat 232 in
opposition to the forces exerted on piston 208. As
W093~09012 PCT/US92/08922
2120~ ~ 6 -12-
the piston 212 moves out from the orifice 234, the
output of the pump 34 will be regulated to a
determinable pressure which is a function of master
cylinder pressure and more specifically a function
of the primary master cylinder pressur~.~~ It can be
shown that this determinable pressure equals:
p = [(A3/(A2-A1)] x Ppmc
wherein PpmC is primary master cylinder pressure, A3
is the area across piston 208, A2 the area of t~e
piston 212 and A~ is the area of the orifice 234. As
can be appreciated, the valve S0" shown in FIGURE 6
will permit the pressure generated by the pump to be
greater than the pressure generated by the primary
master cylinder pressure. If it is desired that the
pump pressure be more closely related to master
cylinder pressure, that is, that the relationship
between pump pressure and primary master cylinder
pressure approach unity, then the cross-sectional
areas of the various pistons will be made equal.
As can be seen valve 50~ includes failure mode
protection similar to that employed in valve 50' and
will continue to operate even if primary or
secondary master cylinder pressure is not
communicated to the various ports. In the event of
the failure of the primary master cylinder chamber,
the output pressure of the pump 34 will be regulated
as a function of the secondary master cylinder. The
relationship is as follows:
P = [A4/(A2-AI)l P~c
where P,~c is secondary master cylinder pressure and
- A4 is the area of the piston 206 expoqed to secondary
master cylinder pressure.
W O 93/09012 2 1 2 0 S 9 6 PC~r/US92/08922
~ ,,
-13-
Many changes and modifications in the above
described embodiment of the invention can, of
course, be carried out without departing from the
scope thereof. Accordingly, that scope is intended
to be limited only by the scope of the~appended
claims.
