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| Illustration 1 | g03590040 |
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(1) Rear service brakes
(2) Wires to transmission electronic control module (3) Left brake pedal (4) Wires to stop lamps (6) Service brake control valve (7) Accumulator for the front service brakes (8) Accumulator for the rear service brakes (9) Parking brake control valve (10) Parking brake (11) Parking brake actuator (12) Parking brake pressure sensor (13) Front service brakes (14) Brake oil pressure sensor (15) Control manifold (16) Hydraulic oil filter (17) Piston pump (18) Breather (19) Hydraulic oil tank | |
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| Illustration 2 | g03558937 |
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(DD) Parking brake switch
(EE) Park brake pressure sensor (FF) Right Pedal position sensor (GG) Park brake solenoid (HH) Brake charging solenoid (JJ) Left pedal sensor (KK) Brake accumulator pressure sensor (MM) Brake accumulator pressure sensor | |
Piston pump (17) supplies the hydraulic oil that is required in order to operate the brake and the hydraulic fan system. Oil flows from pump (17) to control manifold (15). The control manifold controls the flow of oil from pump (17) to brake accumulators (7, 8) and piston motor for the hydraulic fan. Control manifold (15) also directs some of the oil to the pilot circuit for the implement and steering systems. A pump control valve limits the oil pressure that flows from pump (17). A pressure relief valve in control manifold (15) acts as a backup to the pump control valve.
Control manifold (15) contains a priority valve and a cut-in/cut-out valve. The priority valve is a proportional valve. Proportional valves do not shift all the way to a particular position. The valve prioritizes the position that the shift is toward. When the cut-in/cut-out valve is shifted to the left, the priority valve is shifted to the right. With the priority valve shifted to the right, oil flows to an inverse shuttle valve that is located in control manifold (15). The oil then flows to brake accumulators (7, 8). When the accumulators are charged, the cut-in/cut-out valve shifts to the right, and the priority valve shifts to the left. Oil then flows to the fan circuit. The oil flows through a pressure reducing valve. From the pressure reducing valve, the oil flows to piston motor for the hydraulic fan system. A port in control manifold (15) connects to brake oil pressure sensor (14). Brake oil pressure sensor (14) monitors the oil pressure in the brake accumulators. If the oil pressure in either brake accumulator drops below the minimum threshold, sensor (14) sends a signal to the power train ECM. The power train ECM will cause a warning to sound in the cab.
Brake accumulators (7, 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 piston pushes 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 the left 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. The drain port allows the service brakes to release. The supply oil is then dumped back into hydraulic tank (19).
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. Control manifold (15) then permits oil from pump (17) to flow to brake accumulators (7, 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 accumulators (7, 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 (9) connects to brake accumulator for front service brakes (7). Parking brake control valve (9) can be actuated by activating the parking brake switch in the cab.
A decrease in brake oil pressure causes pressure sensor (14) to send a signal to the power train ECM. The power train ECM causes a Warning Category 3 alarm to occur. At the same time, a spool in parking brake control valve (9) 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 (11) engages parking brake (10).
If brake oil pressure is lost during machine operation, the transmission shifts to neutral.
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.