Bendix ATR-1 User Manual

®

Bendix® ATR-1™ AntiLock Traction Relay Valve

SD-13-4811

CONTROLLER

MOUNTING HOLES (4)

MOUNTING

BRACKET

SERVICE

PORT

BODY

SUPPLY

PORT

COVER PLATE FOR

REMOTE MOUNT

REMOTE MOUNT ATR-1™ RELAY VALVE

FIGURE 1 - ATR-1™ ANTILOCK TRACTION RELAY VALVE

DESCRIPTION

The ATR-1™ antilock traction relay is a specialized air brake
valve developed for use on Bendix antilock/traction equipped
vehicles.

It is essentially three separate valves working in combination
in a single housing. An R-14™ style service relay is the base
valve and is fitted with a modified cover containing a double
check valve and a traction control solenoid. The ATR-1™ valve
contains both air and electric components to provide the
service braking and traction control (differential braking)
functions. A Bendix antilock traction controller can be
mounted to the ATR-1™ valve or a cover plate can be installed
and the antilock controller mounted elsewhere on the vehicle.
When an ATR-1™ valve is combined with an antilock traction
controller the resulting assembly is referred to as an antilock
traction assembly.

The ATR-1™ valve replaces the standard relay valve used to
control the rear axle service brakes and performs the standard
relay function. Like the standard relay valve it replaces, the
ATR-1™ valve (sometimes with attached antilock controller)

TRACTION CONTROL

SOLENOID

UNDRILLED

“CON” PORT

DELIVERY

PORT (4)

2 PIN SOLENOID

CONNECTOR

is normally mounted near the service brakes it serves. A
mounting bracket, furnished with the valve, permits either
frame or cross member mounting. All air connections on
the ATR-1™ valve are identified for ease of installation. The
letter identification and air line connections are shown below
for reference.

EMBOSSED

ATR-1™ VALVE AIR CONNECTION IDENT.

Supply (to reservoir) SUP
Delivery (to brake Chamber) DEL
Service (to brake valve rear delivery) SER
Control (not drilled or threaded on ATR-1™ valve) CON

The ATR-1™ valve is part of the R-12™ family of relay valves
which includes the R-12™, R-14™, BP-R1™, AR-1™.

The internal components of the relay portion of all of these
valves are interchangeable with the R-12™ valve and therefore
the same basic components are used to service all of them.
The ATR-1™ valve is available with various crack pressures
to accommodate specific applications, however the standard
is 4 psi.

SUPPLY

PORT

1

CONTROLLER

ATR-1™ ANTILOCK
TRACTION RELAY

VALVE

FIGURE 2 - ANTILOCK TRACTION ASSEMBLY

OPERATION

GENERAL

Because the ATR-1™ is essentially a relay valve, the following
description of operation refers to its function in the vehicles
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-1™ valve.

SERVICE BRAKES APPLYING (FIGURE 4)

Reservoir air pressure is present at the supply port and flows
through internal body and cover passages to the supply of
the normally closed (NC) traction control solenoid.

Brake application air enters the ATR-1™ 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 the blend back and 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-1
valve’s delivery ports to the brake chambers.

™

SOLENOID

CONNECTOR

BLEND BACK

PISTON

SUPPLY

TRACTION CONTROL

SOLENOID

SERVICE

DOUBLE

CHECK VALVE

RELAY PISTON

INLET-EXHAUST

VALVE

DELIVERY

FIGURE 3 - ATR-1™ ANTILOCK TRACTION ASSEMBLY

2

EXHAUST

CONTROLLER

TRACTION
SOLENOID

BRAKE
VALVE

CHECK VALVE

RELAY PISTON

REAR AXLE

RESERVOIR

FIGURE 4 - SERVICE BRAKE APPLICATION

SERVICE BRAKES HOLDING (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

CONTROLLER

INLET EXHAUST

MODULATOR

SPRING BRAKE

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.

TRACTION
SOLENOID

RELAY PISTON

REAR AXLE
RESERVOIR

FIGURE 5 - SERVICE BRAKES HOLDING

BRAKE

VALVE

CHECK VALVE

INLET EXHAUST

MODULATOR

SPRING BRAKE

3

CONTROLLER

TRACTION
SOLENOID

RELAY PISTON

REAR AXLE

RESERVOIR

FIGURE 6 - SERVICE BRAKES RELEASING

SERVICE BRAKES RELEASING (FIGURE 6)

When the brake application is released, air from above the
relay piston flows back through the 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-1™ valve and flows out the open exhaust.

BRAKE
VALVE

CHECK VALVE

INLET EXHAUST

MODULATOR

EXHAUST

SPRING BRAKE

TRACTION CONTROL SERVICE APPLICATION
(FIGURE 7)

GENERAL

While under the control of an antilock traction controller, the
ATR-1™ valve’s solenoid is able to initiate a brake application
that allows the traction system to control wheel spin upon
acceleration under 25 mph. When wheel spin is detected

CONTROLLER

TRACTION
SOLENOID

RELAY PISTON

REAR AXLE

RESERVOIR

FIGURE 7 - TRACTION CONTROL BRAKE APPLICATION

4

BRAKE
VALVE

CHECK VALVE

INLET EXHAUST

MODULATOR

SPRING BRAKE