Bendix Commercial Vehicle Systems ATR-2 ANTILOCK TRACTION VALVE 6/04 - Manual (Page 2)

2
OPERATION
GENERAL
Because the ATR-2 ™ valve is actually a relay valve, the
following description of operation refers to its function in the
vehicle’s air brake system and does not address all of the
separate antilock components and their operation. For a
description of antilock operation refer to the appropriate
Service Data Sheet covering the electronic controller used
with the ATR-2
™ valve.
INITIAL CHARGING
During the initial build up of tractor system air pressure,
reservoir air flows into the supply port and through internal
body and cover passages to the blend back piston and
from there to the supply of the normally closed (NC) traction
control solenoid. When sufficient air pressure is applied to
the blend back piston, it moves against the resistance of
its spring until it comes to rest against the service piston.
Activating the trailer supply valve (dash control with red
octagonal button), simultaneously charges the trailer and
the ATR-2
™ valve’s control port. Air entering the ATR-2 ™
valve’s control causes the proportioning piston to move
toward its stop in the cover. The integral inlet and exhaust
valve is carried along with the piston until it seats and seals
the exhaust passage. Continued movement of the
proportioning piston opens the inlet seat. With the tractor
and trailer air system fully charged the vehicle may be
operated.
SERVICE BRAKES APPLYING - TRACTOR/
TRAILER COMBINATION (FIGURE 4)
Brake application air enters the ATR-2 ™ valve’s service port
and is conducted to the single check valve. The check
valve diaphragm flexes in response to application pressure
and seals the passage to the open exhaust of the traction
solenoid. Air flows through the service piston then through
the center of both the blend back and proportioning pistons
to the inlet and exhaust valve. Flowing around the inlet
valve, application air moves through a passage in the cover
to the top of the service relay piston. In response to air
pressure, the relay piston moves into contact with the
exhaust portion of its inlet and exhaust valve. With the
exhaust passage sealed, continued movement of the piston
unseats the inlet portion of the inlet and exhaust valve,
allowing supply air from the reservoir to flow out the ATR-2
™
valve’s delivery ports to the brake chambers.
SERVICE BRAKES HOLDING - TRACTOR/
TRAILER COMBINATION (FIGURE 5)
The air pressure being delivered to the brake chambers is
also present beneath the relay piston. When the air pressure
above and below relay piston is equal, the piston moves
slightly allowing the inlet valve to return to its seat. The
exhaust valve remains closed. With both the inlet and
exhaust valves closed, air pressure in the brake chambers
is held stable and neither increases nor decreases.
SERVICE BRAKES RELEASING - TRACTOR/
TRAILER COMBINATION (FIGURE 6)
When the brake application is released, air from above the
relay piston, flows back through the proportioning, blend
back and service pistons to the foot brake valve and is
exhausted. As air pressure is reduced above the relay
piston, pressure beneath it lifts the piston away from the
exhaust valve and opens the exhaust passage. Air from
the service brake chambers returns to the ATR-2
™ valve
and flows out the open exhaust.
ATR-2 ™ ANTILOCK
TRACTION RELAY
CONTROLLER
FIGURE 2 - ANTILOCK TRACTION ASSEMBLY
TRACTION CONTROL
SOLENOID
SUPPLY
SERVICE
DOUBLE
CHECK
VALVE
DELIVERY
EXHAUST
RELAY PISTON
INLET-EXHAUST
VALVE
BLEND
BACK
PISTON
SOLENOID
CONNECTOR
FIGURE 3 - SECTIONAL ATR-2 ™ ANTILOCK TRACTION ASSY.
INLET-EXHAUST
VALVE
CONTROL
PROPORTIONING
PISTON