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VACUUM
ATMOSPHERf
56.36
Fig. 2
-
Applying and Holding
4 - Pi<!o
n
rod
5
-
V.he ,od .pri ng
5
-
V~h'e
rod
8 -
!'o.;u
J,,'er
cro
..
p in
12
-
Sr.ke
pedal ph'ot
poi
nt
I
~
-
I'owet
le
,'cr
p
i
,'ot
poill
t
14
-
S",
ke
perlal
I~
-
~I
u
'er
q1i
ndcr
pu.
h ,od
Jfj
-
Power le,-er
17
-
S rake
pedal
return opring
18
-
Pi"
"l1
return
.
pring
19 - Po",'''' pi
"
"n
20 - Poppe! aSKmbly
22 - V
. h'e
,,,d
ha
lan
ci
n
g
d
i.
pht:l
g
m pi
n
23
-
Diaphragm
jected to vacuum.) Rod spring (5) is aided at
this
point by the balancing diaphragm (23)
and balancing diaphragm pin (22) which
ex-
erts a force to the right against the rod. This
allows the use of a lighter rod spring (5) and
consequently allows the use of a
lighter
pedal
return spring (17).
With a partial vacuum now existing in the
right cylinder chamber, the
differ
ence in pres-
sure across piston (19), moves the piston to the
right compressing return spring (18).
Piston
r od (4) pushes against pin (8) of power lever
(16) forcing master
cylinder
push rod (15)
into the master
cylinder.
As in a conventional
hydraulic brake system, the fluid pressure from
t he
master cylinder applies the
brakes.
When the degree of
br
aking desired is
r
eached,
poppet
assembly (20)
r
eaches a lap
or
holding position; at this point, the poppet as-
sembly is seated on both the atmosphere port
of piston (19) and the vacuum port seat on the
end
of rod (6),
Any increase in foot
pr
essure on the brake
pedal allows rod spring (5) to again move rod
(6) away from poppet assembly (20). This
again
connects
the right cylinder chamber to
vacuum thus increasing the force from
piston
(19) and consequently
incr
easing the master
cylinder hydraulic
pressure.
98
Any decrease
in
foot pressure on the
br
ake
pedal allows the force from master cylinder
push rod (15) and pedal return spring (17)
to
move plunger (6) to the left lifting poppet
as~
sembly (20) from the atmosphere seat on
p
i s~
ton (19). This admits
at mospher
e
f
rom the left
cylinder chamber to the right cylinder
cham~
bel',
decreasing the force f
r
om piston (19)
,
and
consequently decreasing the master cylinder
hydraulic pressure.
The driver senses the degree of braking by
the fo
r
ce f
r om
the brake pedal acting back
against his foot.
T
his force is transmitted back
as follows: -
T
he
f or
ce to
the
right from the
master
cylinder
acting through rod (15) forms
a
counter~clockwise
movement about pivot
point (13). This is balanced by a clockwise
movement about pivot point (13) by the
for
ce
from cylinder piston (19)
acting
on pin (8).
A
r
esulting force to the right is therefore
con~
centrated at pivot point (13)
.
Since pivot point
(13) is supported on brake pedal (14)
,
the
force is actually transmitted back
to
the brake
pedal. The brake pedal, however, pivots at point
(12) so that the force at (13) causes a
counter~
clockwise movement around point (12)
.
This
must be balanced by a clockwise movement
around point (12) utilizing the force from the
driver's foot
on
the pedal pad. The driver,
however, has the advantage of the pedal
rat
io
as can be seen by comparing the distance from
point (12) to point (13) with the distance
f
r
om point (12) to the pedal pad.
Full Applied
When the power cylinder is fully applied
(Fig.
3), trigger a
r
m (7) allows valve rod
spring (5) to move the rod to the right, away
from poppet assembly (20). This connects the
right cylinder chamber to manifold vacuum.
The maximum possible pressure differential
now exists across piston (19)
.
Any additional
force on
master
cylinder
r
od (15) must come
from foot pressure on the pedal pad. In this
case, pin
(11
) has moved to the right side of
slot (10) of
the
power
lever.
The
power lever
is
now locked in with t he brake pedal and add i-
tional clockwise movement of the power lever
is therefore dependent on the brake pedal.
Releasing
When the
driver r
emoves foot
pr
essure
f
rom
the brake pedal pad, the force against pivot
pin (13) r otates the
pedal
counte
r
~clockwise
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