980L Medium Wheel Loader Power Train, Steering, Braking, Hydraulic, and Machine Systems Control Manifold (Brake, Pilot, Fan) - HMU Steering Caterpillar

Illustration 1	g06073091
Control manifold

The Brake/Pilot/Fan control manifold is responsible for the following pressure/flow generation:

• Implement pilot pressure

• Brake system pressure

• Engine cooling fan motor flow

• HMU steering system pressure (if equipped)

Illustration 2	g03734975
HMU units (1) Inverse shuttle valve (2) Check valve (3) Fan solenoid valve (4) Cut-in/cut-out valve (5) Priority valve (6) Flow control valve (7) Pressure reducing valve (8) Relief valve (AA) Brake accumulator pressure sensor (BB) Brake accumulator pressure sensor (CC) Brake charging solenoid (DD) Demand fan solenoid (A1) Brake accumulator port (Rear service brakes) (A2) Brake accumulator port (Front service brakes) (F) Hydraulic fan port (LS) Load sense port (P) Pump port (P1) Pilot pressure port (PS) Pressure sensor port (T) Tank port

Illustration 3	g03734975
EH units (if equipped) (1) Inverse shuttle valve (2) Check valve (3) Fan solenoid valve (4) Cut-in/cut-out valve (5) Priority valve (6) Flow control valve (7) Pressure reducing valve (8) Relief valve (AA) Brake accumulator pressure sensor (BB) Brake accumulator pressure sensor (CC) Brake charging solenoid (DD) Demand fan solenoid (A1) Brake accumulator port (Rear service brakes) (A2) Brake accumulator port (Front service brakes) (F) Hydraulic fan port (LS) Load sense port (P) Pump port (P1) Pilot pressure port (PS) Pressure sensor port (T) Tank port

Illustration 3 shows the control manifold when the brakes are released and the fan is turning at a reduced speed. Accumulator pressure is below 12,850 ± 700 kPa (1,864 ± 100 psi). The system is in the CUT-IN position. When the system is in the CUT-IN position, the brakes are charging.

The pump draws oil from the hydraulic tank. The oil is sent to pressure reducing valves (7), priority valve (5), relief valve (8), and fan solenoid valve (3). Oil also flows through check valve (2) to cut-in/cut-out valve (4) and inverse shuttle valve (1).

With the brake accumulator charge pressure below 12,850 ± 700 kPa (1,864 ± 100 psi) the accumulator pressure sensors (AA) or (BB) will send a signal to the transmission electronic control module (ECM). The ECM will send a signal to the brake charging solenoid (CC) causing the cut-in/cut-out valve (4) to move to the left. Cut-in/cut-out valve (4) directs oil to the resolver valve and priority valve (5). At the resolver valve, the pressure from cut-in/cut-out valve (4) is higher than pressure from fan solenoid valve (3). The resolver valve allows the pressure from cut-in/cut-out valve (4) to flow to the flow control spool in the pump control valve. The pump upstrokes.

Cut-in/cut-out valve (4) also directs oil to the left port on priority valve (5). This oil assists the spring in shifting the priority valve to the right. This shift reduces the oil flow to the fan motor. The fan speed is reduced since the pump oil flowing to the fan flows through an orifice. The fan speed is reduced temporarily because oil is being redirected to charge the brakes.

Oil from the pump also flows through a screen, check valve (2), and the orifice to inverse shuttle valve (1). Oil flowing into inverse shuttle valve (1) continues until both the accumulators are charged. Inverse shuttle valve (1) maintains equal pressure between both brake accumulators. Inverse shuttle valve (1) also ensures that the lowest pressure of the two accumulators is communicated to the accumulator pressure sensors (AA) or (BB). This communication causes the brake charging solenoid valve to cut-in and charges the accumulators even if only one accumulator pressure is low. Pressure in the brake system is limited to 17,290 – 900 kPa to + 600 kPa (2,508 – 131 psi to + 90 psi) by the ECM and the accumulator pressure sensors (AA) or (BB).

Illustration 4	g03716284
(1) Inverse shuttle valve (2) Check valve (3) Fan solenoid valve (4) Cut-in/cut-out valve (5) Priority valve (6) Flow control valve (7) Pressure reducing valve (8) Relief valve (AA) Brake accumulator pressure sensor (BB) Brake accumulator pressure sensor (CC) Brake charging solenoid (DD) Demand fan solenoid (A1) Brake accumulator port (Rear service brakes) (A2) Brake accumulator port (Front service brakes) (F) Hydraulic fan port (LS) Load sense port (P) Pump port (P1) Pilot pressure port (PS) Pressure sensor port (T) Tank port

Illustration 5 shows the control manifold when the accumulators are charged, brakes are released and the fan is turning at minimum speed.

When the accumulators are charged to 17,290 – 900 kPa to + 600 kPa (2,508 – 131 psi to + 90 psi), the spring moves cut-in/cut-out valve (4) to the right. Cut-in/cut-out valve (4) opens a passage. The passage allows oil sent to the resolver valve and oil on the left side of priority valve (5) to flow to the tank. The resolver valve shifts and flow demand from the fan solenoid valve (3) is once again permitted to reach the pump control valve.

The amount of oil flowing to the fan motor is determined by a signal from the ECM to the demand fan solenoid (DD). Fan solenoid valve (3) directs load sensing oil to the resolver and pump control valve. When the brake accumulators are charged, system oil pressure increases. The increased pressure moves priority valve (5) against spring force. Priority valve (5) opens and supply oil is directed to the fan motor through flow control valve (6). Flow control valve (6) regulates the oil flow to the fan motor.

The ECM monitors the temperatures of hydraulic oil, coolant, and the charge air supply using various sensors. If all of these temperatures are below the default values of the particular sensors, sufficient flow is supplied to rotate the fan at minimum speed. The minimum fan speed is calibrated through AVSpare Electronic Technician (Cat ET).

Illustration 5	g03716330
(1) Inverse shuttle valve (2) Check valve (3) Fan solenoid valve (4) Cut-in/cut-out valve (5) Priority valve (6) Flow control valve (7) Pressure reducing valve (8) Relief valve (AA) Brake accumulator pressure sensor (BB) Brake accumulator pressure sensor (CC) Brake charging solenoid (DD) Demand fan solenoid (A1) Brake accumulator port (Rear service brakes) (A2) Brake accumulator port (Front service brakes) (F) Hydraulic fan port (LS) Load sense port (P) Pump port (P1) Pilot pressure port (PS) Pressure sensor port (T) Tank port

Illustration 5 shows the control manifold when the accumulators are charged, brakes are released and the fan is turning at maximum speed.

As one or more of the key target temperatures increase above the sensor default values, the current to fan solenoid valve (3) decreases. Fan solenoid valve (3) shifts up proportionally to the decrease in current. When fan solenoid valve (3) shifts up, oil flow through the solenoid valve increases. The increased flow also increases oil flow to the flow control spool in the pump.

The pump upstrokes and the fan speed increases. The fan pump can supply sufficient oil flow to rotate the hydraulic motor to the maximum fan speed. The maximum fan speed is controlled by the engine ECM and calibrated through Cat ET.

If the current to fan solenoid valve (3) is interrupted, the pump will continue to upstroke. Upstroking the pump will cause the discharge pressure to increase until the pump reaches high-pressure cutoff. When the pump reaches high-pressure cutoff, the pump will destroke.