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| Illustration 1 | g06120507 |
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(1) Rear service brakes.
(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) Front service brakes. (12) Brake oil low-pressure sensor. (13) Parking brake control valve. (14) Parking brake pressure sensor. (15) Gear pump. (16) Breather. (17) Hydraulic oil tank. (18) Brake/Fan charge valve. (19) Hydraulic oil filter. (20) Hydraulic oil cooler. (21) Gear motor. (22) Fan. (23) Fan reversing valve (if equipped). (24) Service brake pressure sensor. (25) Cold start bypass (if equipped) (26) Quick coupler supply (if equipped) (27) Speed control valve (AA) Pressure tap for the rear service brakes. (BB) Pressure tap for the front service brakes. (CC) Pressure tap for the service brake accumulators. | |
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| Illustration 2 | g06124633 |
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Left side view of the machine (AA) Pressure tap for the front service brakes. (BB) Pressure tap for the rear service brakes. (1) Rear service brakes. (6) Service brake control valve. (11) Front service brakes. (16) Breather. (17) Hydraulic oil tank. (21) Gear motor. | |
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| Illustration 3 | g06124626 |
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Right side view of the machine (CC) Pressure tap for the brake accumulators. (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 sensor (13) Parking brake control valve. (14) Parking brake pressure sensor (15) Gear pump. (18) Brake/Fan charge valve. (behind tire) | |
Gear 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 brake/fan charge valve (18). The brake/fan charge valve is a control manifold that 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. An optional cold start bypass valve ((25)) may be installed on the machine. The valve will redirect flow from the fan/brake pump (15) directly back to the hydraulic tank ((17)) during cold engine cranking to allow the engine to start more easily in cold-weather conditions. During the cold start condition, the engine ECM energizes the solenoid valve during cranking and maintains the oil flow bypass condition until the engine is running. Once the engine is running, the solenoid is then de-energized allowing the flow to be directed to the brake/fan charge valve (18).
The brake/fan charge valve (18) controls the flow of oil from the pump (15) to the brake accumulators (7) and (8). The brake/fan charge valve (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 brake/fan charge valve (18) limits the oil pressure that flows from the pump (15).
The brake/fan charge valve (18) contains a priority valve. When this valve is closed, oil flows to an inverse shuttle valve that is located in the brake/fan charge valve (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 brake/fan charge valve (18) connects to the brake oil pressure sensor (12).
Brake accumulators (7) and (8) contain a precharge of dry nitrogen. When oil flows into an accumulator, the oil moves the piston inside the accumulator. The piston moves against the charge of dry nitrogen gas. This action 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 action 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 brake/fan charge valve (18) then permits oil from the pump (15) to flow to brake accumulators (7) and (8). This flow 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 separate. Applying force to a brake pedal causes the tandem spools in service brake control valve (6) to move. This movement 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). The parking brake control valve ((13)) consists of a spool that is manually controlled by the operator. A bias spring keeps the spool in the "brake applied" position when the brake system pressure is low. When the system reaches acceptable pressure, the bias spring is compressed allowing the operator to shift the spool to the "brake release" position.
When the parking brake control valve ((13)) is placed in the "brake release" position, oil will flow to the parking brake actuator ((10)). The pressure overcomes the internal spring force of the actuator allowing the parking brake to release. The transmission ECM detects the oil pressure rise in the parking brake actuator by the parking brake pressure sensor ((12)). When the pressure is enough to overcome the actuator spring force, the parking brake indicator in the dash will turn off.
If there is a loss of brake oil pressure during operation, the bias spring in the parking brake control valve ((13)) will force the spool to open the parking brake actuator oil port to the hydraulic tank and the parking brake will apply. The transmission will also shift to neutral if 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 drive-through feature 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.