Hydraulic Schematic for the Brake System
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| Illustration 1 | g01051934 |
Hydraulic Schematic for the Brake System (1) Implement pump (2) Steering and brake pump (3) Check valve (4) Pressure switch (5) Wire to the light on the dash (6) Steering and brake manifold valve (7) Flow control valve (8) Check valve (9) Relief valve (10) Pilot unloading spool (11) HMU supply line (12) Load sensing line to HMU (13) Accumulator Manifold (14) Accumulators (15) Brake Valve (16) Hydraulic pump signal line (17) Front service brakes (18) Rear service brakes | |
The hydraulic pump is a two-section pump that consists of an implement pump (1) and a steering and brake pump (2). The steering and brake pump (2) is a gear pump that supplies the hydraulic oil to the steering system and the brake system.
Oil flows from the steering and brake pump (2) to a check valve (3). Some of the oil flows to the pressure switch (4). The pressure switch (4) sends a signal to the light on the dash through wire (5) if the pressure is low. Most of the oil flows through check valve (3). The check valve prevents oil from flowing back to the pump (2) .
From check valve (3), oil flows to the metering pump (HMU) through supply line (11). Also, oil flows to the steering and brake manifold valve (6). The steering and brake manifold valve (6) controls the flow of load signal oil to the metering pump. The steering and brake manifold valve (6) controls the flow of oil to the accumulators (14). The steering and brake manifold valve (6) contains a relief valve (9), a check valve (8), a flow control valve (7), and a pilot unloading spool (10).
The pressure relief valve (9) limits the signal oil pressure that flows to the HMU. Check valve (8) helps maintain the pressure in the brake system when the accumulators are charged. Check valve (8) prevents oil from flowing back to flow control valve (7). The flow control valve (7) provides the oil in order to charge the accumulators when the pressure reaches the cut-in pressure. Flow control valve (7) provides the load signal oil to the metering pump. The pilot unloading spool (10) controls the flow of load signal oil to the HMU. Any excess oil flows back to the hydraulic oil tank.
Oil flows from the steering and brake manifold valve (6) to accumulators (14). Both accumulators (14) contain a precharge of dry nitrogen. When oil flows into an accumulator, the increase in oil pressure moves the piston inside the accumulator. The piston moves against the charge of dry nitrogen gas. This compresses the dry nitrogen until the oil pressure reaches the cut out pressure. The oil also flows to the brake valve (15) .
Depressing either brake pedal from the first 25 mm to 50 mm (1.0 inch to 2.0 inch) shifts both spools downward. The bottom spool actuates the inching mode. The inching mode reduces the travel speed of the machine to zero. This occurs while full engine rpm is maintained by gradually destroking the hydrostatic pump and upstroking the motor.
Brake valve (15) is located between the accumulators and the service brakes. When either brake pedal is pushed, both spools shift downward. The top spool causes oil from each accumulator 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 is dissipated by the oil in the axle housings. The downward movement of the bottom spool drains the speed sensing to the hydraulic tank. This causes the pump to destroke and this causes the motor to upstroke. This results in a decrease in the machine speed.
When the brake valve (15) is released the lines from the accumulators are blocked. The brake lines between the brake valve and the service brakes are connected to the drain port. This allows the service brakes to release. The supply oil flows to the hydraulic oil tank and the oil for speed sensing to the hydraulic tank is blocked.
Each brake application removes some 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 steering and brake manifold valve (6) permits oil from the brake pump (2) to flow to each accumulator (14), until the pressure increases to the cut out pressure.