 | |
| Illustration 1 | g01793673 |
(1) Front service brakes (2) Wires to transmission electronic control module (3) Left brake pedal (4) Wires to stop lamps (5) Right brake pedal (6) Service brake control valve (7) Accumulator for the front service brakes (8) Accumulator for the rear service brakes (9) Parking brake (10) Parking brake actuator (11) Rear service brakes (12) Brake oil pressure switch (13) Parking brake control valve (14) Parking brake pressure switch (15) Piston pump (16) Breaker relief valve (17) Hydraulic oil tank (18) Control manifold (19) Hydraulic oil filter (20) Hydraulic oil cooler (21) Gear motor (22) Fan (AA) Pressure tap for the rear service brakes (BB) Pressure tap for the front service brakes (CC) Pressure tap for the service brake accumulators | |
 | |
| Illustration 2 | g01793675 |
Left side view of the machine (1) Rear service brakes. (11) Front service brakes. (16) Breaker relief valve. (17) Hydraulic oil tank. (21) Gear motor. | |
 | |
| Illustration 3 | g01793676 |
Right side view of the machine (6) Service brake control valve. (7) Accumulator for the front service brakes. (8) Accumulator for the rear service brakes. (9) Parking brake. (10) Parking brake actuator. (12) Brake oil pressure switch. (13) Parking brake control valve. (14) Parking brake pressure switch. (15) Piston pump. (18) Control manifold. (AA) Pressure tap for the front service brakes. (BB) Pressure tap for the rear service brakes. (CC) Pressure tap for the brake accumulators. | |
Piston pump (15) supplies the hydraulic oil that is required in order to operate the brake and the hydraulic fan system. Oil flows from the pump (15) to the control manifold (18) . The control manifold includes the following components: a pressure relief valve, a shuttle valve, an inverse shuttle valve, a cut in valve, a cut out valve and a priority valve.
The control manifold (18) controls the flow of oil from the pump (15) to the brake accumulators (7) and (8) . The control manifold (18) also controls the flow of oil to the gear motor (21) for the hydraulic fan. A pressure relief valve that is located in the control manifold (18) limits the oil pressure that flows from the pump (15) .
The control manifold (18) contains a priority valve. When this valve is closed, oil flows to an inverse shuttle valve that is located in the control manifold (18) . The oil then flows to the brake accumulators (7) and (8) . When the accumulators are charged, the priority valve opens. Oil then flows to the gear motor (21) for the hydraulic fan system. A port in the control manifold (18) connects to the brake oil pressure switch (12) . The brake oil pressure switch (12) monitors the oil pressure in the brake accumulators. If the oil pressure in either brake accumulator drops below the minimum threshold, switch (12) actuates.
Brake accumulators (7) and (8) contain a precharge of dry nitrogen. When oil flows into an accumulator, the pressure oil moves the piston inside the accumulator. The piston moves against the charge of dry nitrogen gas. This puts compression on the dry nitrogen until the oil pressure reaches the cut out pressure. The oil also flows to the service brake control valve (6) .
Service brake control valve (6) is in the circuit from the accumulators to the service brakes. When a brake pedal is pushed, oil from each accumulator flows to the service brakes. The service brakes are then applied.
When service brake control valve (6) is released, the lines from the accumulators are blocked. The brake lines are connected to the drain port. This allows the service brakes to release. The supply oil is then dumped back into the hydraulic oil tank (17) .
Each brake application removes a quantity of oil from the accumulators. The piston in each accumulator moves toward the oil end until the oil pressure decreases to the cut-in pressure. The control manifold (18) then permits oil from the pump (15) to flow to brake accumulators (7) and (8) . This occurs until the pressure increases to the cut out pressure.
The hydraulic circuits for the front service brakes and for the rear service brakes are completely separate. Applying force to a brake pedal causes the tandem spools in service brake control valve (6) to move. This allows oil from both accumulator (7) and accumulator (8) to flow to the disc brakes in each axle housing. The pressure of the oil causes the wet disc brakes that are enclosed in each axle to engage. The heat from the friction of the brakes is removed by the oil in the axle housings.
Parking brake control valve (13) connects to the rear brake accumulator (8) for the rear service brakes (11) . Parking brake control valve (13) can be actuated manually by pulling out on the parking brake control knob.
A decrease in brake oil pressure causes pressure switch (12) to actuate. This causes a Warning Category 3 alarm to occur. At the same time, a spool in parking brake control valve (13) is overcome by the force of a spring in the control valve. This spool movement is due to a lack of adequate oil pressure. With no oil pressure in the brake system, actuator (10) engages parking brake (9) .
If brake oil pressure is lost during machine operation, the transmission shifts to neutral. However, the transmission only shifts to neutral when the machine is in either first speed forward or first speed reverse.
A drive-through feature allows an operator to engage the transmission in either first speed forward or reverse. This can be accomplished by first moving the transmission direction selector to the NEUTRAL position. Then move the transmission direction selector to either first speed forward or reverse. For example, move the transmission direction selector to the following positions, 1F-N-1F or 1R-N-1R.