BENDIX ATR-2 ANTILOCK TRACTION VALVE Scheda tecnica del servizio - Pagina 2

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CONTROLLER

ATR-2

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ANTILOCK

TRACTION RELAY

FIGURE 2 - ANTILOCK TRACTION ASSEMBLY

OPERATION

GENERAL

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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

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valve.

SOLENOID

CONNECTOR

PROPORTIONING

PISTON

CONTROL

INLET-EXHAUST

VALVE

BLEND

BACK

PISTON

SUPPLY

FIGURE 3 - SECTIONAL ATR-2

TRACTION CONTROL

SERVICE

SOLENOID

DOUBLE

CHECK

RELAY PISTON

INLET-EXHAUST

VALVE

DELIVERY

EXHAUST

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ANTILOCK TRACTION ASSY.

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

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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

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

VALVE

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

and flows out the open exhaust.

valve's control port. Air entering the ATR-2

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valve's service port

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valve