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| Illustration 1 | g00909196 |
Hydraulic Schematic for the Brake System (1) Front service brakes (2) Wires to the 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) Accumulator charging valve (13) Parking brake pressure switch (14) Line to the implement circuit, pilot circuit, and steering circuit (15) Brake oil pressure switch (16) Breaker relief valve (17) Parking brake control valve (18) Pilot/brake pump (19) Implement pump (20) Steering pump (21) Hydraulic oil tank (22) Implement and pilot/brake pump (23) To filtration circuit (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 | g00294076 |
Left Side View of the Machine (1) Front service brakes. (7) Accumulator for the front service brakes. (8) Accumulator for the rear service brakes. (11) Rear service brakes. (12) Accumulator charging valve. (13) Parking brake pressure switch. (15) Brake oil pressure switch. (17) Parking brake control valve. (CC) Pressure tap for the brake accumulators. | |
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| Illustration 3 | g00294077 |
Right Side View of the Machine (6) Service brake control valve. (9) Parking brake. (10) Parking brake actuator. (16) Breaker relief valve. (18) Pilot/brake pump. (19) Implement pump. (20) Steering pump. (21) Hydraulic oil tank. (AA) Pressure tap for the rear service brakes. (BB) Pressure tap for the front service brakes. | |
The implement and pilot/brake pump (22) are connected in tandem by a common shaft. The two vane pumps are mounted in tandem on steering pump (20). Pilot/brake pump (18) and implement pump (19) share a common inlet port from hydraulic oil tank (21), but each pump has a separate outlet port.
Pilot/brake pump (18) is a vane pump that supplies the hydraulic oil that is required to operate the brake system. Pump (18) also provides the pilot oil for the implement circuit.
Oil flows from pilot/brake pump (18) to brake accumulator charging valve (12). Accumulator charging valve (12) includes the following components. A pressure relief valve, a charge control, a flow control orifice, a spool for cut-in and cut out pressure and an inverse shuttle valve.
Accumulator charging valve (12) controls the flow of oil from pilot/brake pump (18) to brake accumulators (7) and (8). A pressure relief valve that is located in accumulator charging valve (12) limits the oil pressure that flows from pilot/brake pump (18) .
Oil then flows through an inverse shuttle valve that is located in brake accumulator charging valve (12). The oil then flows to brake accumulators (7) and (8). A third port in the inverse shuttle valve connects to switch (15). Switch (15) monitors the oil pressure in the two brake accumulators. If the oil pressure in either brake accumulator drops below the minimum threshold, switch (15) 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 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 hydraulic oil tank (21) .
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. Accumulator charging valve (12) then permits oil from pilot/brake pump (18) 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 (17) connects to the brake accumulator for the front service brakes (7). Parking brake control valve (17) can be actuated manually by pulling out on the parking brake control knob.
A decrease in brake oil pressure causes pressure switch (15) to actuate. This causes a Warning Category 3 alarm to occur. At the same time, a spool in parking brake control valve (17) 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.