ARM 4B8421 - Caterpillar

Illustration 3 g03556716Electronic Primary Steering Control
The machines are equipped with an electro-hydraulically controled steering system. The following components make up the steering electro-hydraulic system:
Implement Electronic Control Module (ECM)
Transmission ECM
Left-hand steering and transmission control
Steering pump
Steering control valve
Steering cylinders
Steering accumulator
Brake and fan manifold
Hydraulic tankThe implement ECM controls the primary steering system. The implement ECM uses a closed loop system with cylinder position feedback in order to control the steering angle. The ECM determines the desired steering angle based on the position of the steering axis on the left-hand joystick. The ECM sends control signals to the primary steering valve solenoids to change the position of the steering cylinders to achieve the desired steering angle. As the steering cylinders reach the commanded position, the ECM will decrease the control signals to the solenoids until movement of the cylinders are stopped. The cycle repeats as the position of the steering axis on the left-hand joystick changes. The implement ECM outputs to the steering valve control the primary steering solenoid valves and the primary steering supply on off solenoid. The implement ECM receives inputs from the steering valve position sensor based on the position of the valve spool.When the key start switch is in the ON position, the implement ECM will turn ON the primary steering pilot supply ON/OFF solenoid. This action will result in available pilot pressure being passed through the primary steering solenoid valves. For more information on the implement ECM refer to Systems Operation, "Steering Control (Control Systems)".Left-Hand Steering and Transmission Control
Illustration 4 g03668479
(26) Speed range upshift and downshift
(27) Transmission forward, neutral, and reverse
(28) Left steering
(29) Right steering The left-hand steering and transmission control combines the steering functions and the transmission functions for the machine. Move the control to the left or to the right to articulate the machine.The transmission direction switch (27) is located on the front of the control. The speed range thumb roller (26) is located near the top of the steering and transmission control. For more information on left-hand steering and transmission control refer to Systems Operation, "Steering Control (Control Systems)".Steering Pump
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Right side view of machine
(20) Steering pump The steering pump (20) is located on the left side of the machine. The variable displacement piston pump senses both pressure and flow requirements for the system. The steering pump draws oil from the hydraulic tank (21) and sends flow through the supply hose to the steering control valve (7). The pump compensator valve controls pump flow and maximum system pressure.Steering Valve Operation
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(5) Left secondary steering solenoid
(6) Right secondary steering solenoid
(7) Steering valve
(9) Steering primary pilot supply solenoid
(10) Right primary steering solenoid
(11) Left primary steering solenoid
(12) Steering control valve spool position sensor
(14) Back-up relief valve
(14) Steering workport relief valve The steering control valve (7) is mounted to the front of the transmission near the articulation hitch. Directional steering control is accomplished by the actuation of the machines articulation cylinders by the steering valve. The implement ECM is the primary control of the steering valve with the transmission ECM