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BRAKES
5 - 57
The exiter r i n g i s t h e sensor t r i g g e r mechanism.
As t h e r i n g rotates, the teeth o n the r i n g w i l l i n t e r -
u p t the magnetic field around t h e sensor pole. T h e
r a t e o f i n t e r r u p t i o n is converted i n t o speed signals
w h i c h are t r a n s m i t t e d t o the control module.
MOUNTING
FLANGE
ACCUMULATOR CLOSED
CONNECTOR
TO CONTROL
MODULE
SINGLE
POLE
SENSOR
J9005-98
Fig. 4 RWAL Speed Sensor
ANTI-LOCK
INDICATOR
LAMP
The amber colored indicator l a m p is located i n the
message center. The l a m p alerts t h e d r i v e r i f an an-
ti-lock system f a u l t occurs.
The anti-lock and brake w a r n i n g lamps are b o t h i n
c i r c u i t w i t h the electronic module. T h e module w i l l
cause the t w o lamps t o i l l u m i n a t e or flash to a l e r t
t h e d r i v e r t h a t system operation is either n o r m a l or
t h a t a f a u l t has occurred.
ANTI-LOCK SYSTEM OPERATION
D u r i n g l i g h t b r a k e applications, rear wheel decel-
e r a t i o n and/or slip i s not sufficient to activate the an-
ti-lock system. B r a k e f l u i d apply pressure a t the rear
wheels is n o r m a l . However, w h e n b r a k i n g effort, de-
gree of wheel slip a n d rate o f deceleration approach
programmed
l i m i t s , sensor
i n p u t s w i l l cause t h e
module t o activate the system.
Normal Braking Mode
I n n o r m a l b r a k i n g mode, t h e h y d r a u l i c valve com-
ponents are inactive. The isolation valve is open and
t h e dump valve a n d accumulator are closed. F l u i d
flows unimpeded t h r o u g h the isolation valve directly
to t h e rear wheel cylinders (Fig. 5).
Start Of Anti-Lock Mode Braking
W h e n h i g h pedal effort b r a k i n g occurs, t h e de-
crease i n exiter wheel r o t a t i n g speed is noted and
converted i n t o a n electronic signal b y t h e sensor.
T h i s signal is t r a n s m i t t e d t o a n d processed by t h e
control module. T h e module determines t h a t accept-
DUMP
VALVE
CLOSED
SPRING
ISOLATION
VALVE
£
OPEN
FROM
MASTER
CYLINDER
TO REAR BRAKES
J9005-93
Fig. 5 Valve Position And Fluid Flow-Normal
Braking
able l i m i t s of wheel slip/deceleration are about t o be
exceeded. T h e module activates t h e h y d r a u l i c valve
at t h i s point.
The control module t r a n s m i t s a signal t o t h e isola-
t o r valve solenoid w h i c h closes t h e valve (Fig. 6).
Closing the valve prevents f u r t h e r f l u i d flow t o t h e
rear wheel cylinders. This action isolates t h e rear
brakes from the master cylinder. The net effect is to
decrease rear brake apply pressure t o t h e p o i n t
where t h e wheels w i l l continue t o rotate a n d n o t
lock.
ACCUMULATOR CLOSED
ISOLATION
VALVE
CLOSED
MASTER
CYLINDER
DUMP
VALVE
CLOSED
TO REAR BRAKES
J9005-94
Fig. 6 Valve Position And Fluid Flow At Start Of
Anti-Lock Mode Braking
Additional Pressure Relief During Anti-Lock Mode Braking
The dump valve and accumulator are h y d r a u l i c a l l y
connected and serve as additional pressure l i m i t i n g
devices. T h e accumulator a n d dump v a l v e r e m a i n
closed d u r i n g i n i t i a l closing o f the i s o l a t i o n valve.
However, i f pressure exerted b y f l u i d captured i n t h e
wheel cylinders and lines is h i g h enough t o lock the
wheels, t h e dump valve and accumulator are a c t i -
vated (Fig. 7).
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