422f2 Side Shift Backhoe Loader Lyf00001-Up (Machine) Powered b (2)

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Bienvenido: r095gcr Producto: BACKHOE LOADERModelo: 422F2 BACKHOE LOADER LYFConfiguración: 422F2 Side Shift Backhoe Loader LYF00001-UP (MACHINE)POWERED BY C4.4 Engine

Operación de Sistemas422F2, 427F2, 428F2, 432F2, 434F2 and 444F2 Backhoe Loaders Axles, Differential andBrakesNúmero de medio -UENR3745-00 Fecha de publicación -01/12/2014 Fecha de actualización -04/12/2014

i05823753

Service Brake Control

SMCS - 4257; 4258; 4291

Illustration 1 g02743057

(1) Plunger(2) Pilot Supply Port

(3) From Pilot Circuit



(4) Reservoir(5) Secondary Piston Spring Chamber

(6) To Brake Actuator

(7) Both Released(8) Primary Piston

(9) Drain Port(10) Passage

(11) Large Spring Chamber

(12) Compensation Port(13) One Engaged

(14) From Pilot Circuit

(15) Reservoir(16) To Brake Actuator

(17) Primary Piston

(18) Feedback Spring Chamber(19) Check Valve

(20) Secondary Piston

(21) Both Engaged

The boosted brake valve group, which uses oil from the pilot accumulator to add boost to the master

cylinder.

The hydraulic force multiplies the pedal effort so the operator can get more braking force with less effort.

The left brake is released (top Illustration) and the right brake (bottom illustration) is engaged.

Compensation check valves in the compensation ports are used to equalize the pressures in both brake

actuators when the brake pedals are depressed together.

With the brake pedal released, the pilot oil is blocked from flowing to the left end of the secondary piston.

The pilot oil is also blocked from flowing to the center of the primary piston. The center of the primary

piston and feedback spring chamber are also open to tank through the drain port.

Oil from the hydraulic tank is connected to the large spring chamber in the middle of the boosted brake

group. This oil flows through a passage in the secondary piston. The oil is free to fl ow between the large

spring chamber and the secondary piston spring chamber. The check valve in the secondary piston isunseated. The secondary piston spring chamber is connected by lines to the brake actuator.

When the brake pedal is depressed, the brake linkage moves the primary piston to the right. Pilot oil is no

longer blocked and flows to the left end of the secondary piston, to the center of the primary piston, and to

the feedback spring chamber. As pressure increases on the left end of the secondary piston, the pressure

assists the primary piston in moving the secondary piston to the right. Pressure sensed in the feedback spring

chamber works with the spring to supply feedback or feel to the operator.

As the secondary piston moves to the right, the check valve seats, blocking the oil in the secondary piston

spring chamber. Oil in the secondary spring chamber is forced out of the chamber to engage the brake. The

distance that the brake pedal is depressed determines the amount of oil flow to the brake actuator. The

amount of flow determines how fully the brake is applied. The distance the pedal is pushed also determineshow much pressure is in the secondary spring chamber and is felt at the brake actuator.

Also, as the secondary piston moves to the right, oil fl ows into the compensation ports. When both brakes

are applied, both compensation check valves will unseat to equalize the pressure to both brake actuators.

When one pedal is depressed, both compensation check valves will move. However, one check valve will

seat to block the pressurized oil from entering the other brake cylinder (cutaway view - middle right).



When the pedal is released, springs move the secondary piston and primary pistons back to the left. this

action reduces the pressure being sensed at the brake actuator. The check valve in the secondary piston

unseats and the oil in the chamber on the right end of the secondary piston is free to mix with the reservoir

oil in the large spring chamber.

If the engine stops while roading the machine, the brakes can still be applied, but more effort may be

required. With the engine stopped, the pilot accumulator will still provide some boost for a limited number

of brake applications.

Illustration 2 g03690324

Boosted brake system(22) Master cylinder

(23) Brake pedals

(24) Supply line(25) Return line

(26) Brake feed lines

The brake boost valves are connected to the master cylinder (22) at each brake pedal (23). Oil enters the

master cylinder through the supply line (24) and exits the master cylinder through the return line (25). The

oil flows to the service brakes through the brake feed lines (26) at the bottom of the master cylinder.

The master cylinders can be removed from the machine from inside the operators compartment.

Copyright 1993 - 2016 Caterpillar Inc.Todos los derechos reservados.Red privada para licenciados del SIS.

Sun Apr 17 2016 23:33:59 GMT-0500 (Hora est. Pacífico, Sudamérica)

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422f2 Side Shift Backhoe Loader Lyf00001-Up (Machine) Powered b (2)