770G and 772G Off-Highway Truck Hydraulic and Braking System: Pump and Motor (Parking Brake Release, Secondary Steering) & Control Manifold (Brake Accumulator Charge)

1.-Pump and Motor (Parking Brake Release, Secondary Steering)

(A) Brake retraction section(B) Secondary steering system

The electric drive pump for the secondary steering and the parking brake release is located on the front, right corner of the truck. The electric drive pump is mounted to the inside of the right frame rail just behind the bumper. The electric drive pump provides oil in order to steer the front wheels if the normal flow is lost from the primary steering system.

The electric drive for the secondary steering and the parking brake release operates according to the position of the brake release and secondary steering switch. The switch is located in the cab. During normal machine operation, the brake release and secondary steering switch is placed in the AUTO position. The electric drive pump for the secondary steering and the brake release will only operate when additional pressure oil is needed in the steering system.

When the engine is started, the Power Train Electronic Control Module (Power Train ECM) activates a relay that is located behind the cab. The relay behind the cab activates a larger relay that is located on the inside of the left frame rail next to the engine. Then, the larger relay activates the electric drive pump for the secondary steering and the brake release. The electric drive pump for the secondary steering and the brake release will operate for 3 seconds. Secondary steering indicator light will turn on when the pump is operating.

The brake release and secondary steering switch is moved to the MANUAL position only when the machine is towed. This switch sends a signal to the Power Train ECM. The Power Train ECM then activates electric drive for the secondary steering and the brake release and the secondary steering indicator.

If the steering system pressure decreases to the deactuation pressure of the pressure switch, then the steering pump pressure sensor will send an electrical signal to the Power Train ECM . The advisor monitor display for the secondary steering will flash when the steering pressure is low. Secondary steering indicator will turn ON when the pump is operating. The secondary steering indicator light will turn ON when the pump is operating. The Power Train ECM will then activate electric drive for the secondary steering and the brake release.

2.-Control Manifold (Brake Accumulator Charge)

Port locations for the Control Manifold (Brake Accumulator Charge)(1) Port to the Brake Valve (Front Service Brake)

View A - A (2) Port to the bottom of the Brake Accumulator (Parking), the Control Manifold (Parking Brake Release), and the Brake Valve (Parking) (3) Port for the low brake oil pressure sensor (4) Outlet to the brake cooling system or optional rear axle lube motor (5) Outlet to the hydraulic oil tank(6) Service brake system relief valve

View B - B (7) Port to the Brake Valve (Rear Service Brake, Retarder Control, Traction Control) and to the tap at the bottom of the Brake Accumulator (Service)(8) Inlet from the brake charging section of the Gear Pump (Brake, Brake Cooling, Hoist)

Schematic of the Control Manifold (Brake Accumulator Charge) (1) Port to the Brake Valve (Front Service Brake) (2) Port to the bottom of the Brake Accumulator (Parking), the Control Manifold (Parking Brake Release), and the Brake Valve (Parking) (3) Port for the low brake oil pressure sensor (4) Outlet to the brake cooling system or optional rear axle lube motor (5) Outlet to the hydraulic oil tank (6) Service brake system relief valve (7) Port to the Brake Valve (Rear Service Brake, Retarder Control, Traction Control) and to the tap at the bottom of the Brake Accumulator (Service) (8) Inlet from the brake charging section of the Gear Pump (Brake, Brake Cooling, Hoist) (9) Spool for cut-in and cutout pressure (10) Check valve (11) Unloading valve (12) Check valve to isolate the parking brake system from the service brake system(13) Parking brake system relief valve

The brake charging section of the Gear Pump (Brake, Brake Cooling, Hoist) supplies hydraulic oil to the brake system. The oil first flows to the Control Manifold (Brake Accumulator Charge). The Control Manifold (Brake Accumulator Charge) maintains the pressure in the accumulators between predetermined cut-in and cut-out pressures while the engine is running. If the machine has lost power or the hydraulic pump has failed, the pressure in the accumulator will permit several applications of the service brakes.

When the accumulator oil pressure decreases below 16100 ± 345 kPa (2335.1 ± 50.0 psi), the Control Manifold (Brake Accumulator Charge) reaches the cut-in pressure setting.

When the hydraulic oil flows from the Control Manifold (Brake Accumulator Charge) to the accumulators, the pressure after check valve (10) decreases. The pressure decrease allows the spring force to move spool (9) . The new location of spool (9) causes hydraulic oil to flow to unloading valve (11) . In this position, the orifice in unloading valve (11) restricts the pump flow to outlet (4) . In this position, the orifice in unloading valve (11) also restricts the pump flow to the brake cooling system. Oil flow to the brake accumulators increases and the accumulators are charged.

When the Control Manifold (Brake Accumulator Charge) is at the cut-in pressure setting, the oil flows to ports (1) , (2) , (3) , and (7) . Port (3) connects to a low brake oil pressure sensor. The low brake oil pressure sensor alerts the operator when the brake oil pressure drops below the minimum operating pressure.

The cut-out pressure setting for the Control Manifold (Brake Accumulator Charge) is 19600 ± 345 kPa (2842.8 ± 50.0 psi).

When the accumulator oil pressure increases to the cut-out pressure setting, the supply pressure increases. The pressure increase causes spool (9) to overcome the spring force. This causes spool (9) to open a passage for oil to flow from unloading valve (11) to the tank.

When the pressure from spool (9) to unloading valve (11) decreases, unloading valve (11) overcomes the spring force. This causes pump oil to flow through unloading valve (11) out of outlet (4) to the brake cooling system or optional rear axle lube motor.

Check valve (10) prevents high-pressure oil from the accumulators from flowing to the brake cooling system or to the optional rear axle lube motor.

The Control Manifold (Brake Accumulator Charge) remains in the position of the cut-out pressure setting until the pressure in the accumulators decreases to the cut-in pressure setting of 16100 ± 345 kPa (2335.1 ± 50.0 psi).

Service brake system relief valve (6) regulates the pressure of oil to the brake circuit. Any excess oil that is not required by the brake cooling system, the brake circuit, or the optional rear axle lube motor is diverted back to the hydraulic oil tank. The pressure setting of service brake system relief valve (6) is 22100 ± 345 kPa (3205.4 ± 50.0 psi). Service brake system relief valve (6) is set much higher than cut-out pressure and is used as a backup relief valve.

Parking brake relief valve (13) limits pressure in the parking brake circuit. Check valve (12) prevents oil in the parking brake circuit from flowing to the service brake circuit.

If you need more information, You can visit:

http://www.cat.com

770G and 772G Off-Highway Truck Hydraulic and Braking System: Pump and Motor (Parking Brake Release, Secondary Steering) & Control Manifold (Brake Accumulator Charge) 2012-12-26T20:09:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown