TRANSMISSION AR-POWER SHIFT 1164860 - Caterpillar

Operation (No Turn)
The steering pump will draw oil out of the hydraulic tank through the strainer and send oil to the SCU. With the SCU three position valve in the center position oil returns to the tank.Operation (While Turning)
Oil from the steering pump outlet flows to the SCU. In the SCU, the three position valve shifts to allow oil flow to the appropriate end of the steering cylinder. The SCU controls the direction and the speed of the turn.Steering Control Unit (SCU) Operation
Steering Control Unit
(1) Outlet port. (2) Inlet port. (3) Pressure relief valve. (4) Internal pump gear. (5) External pump gear. (6) Spool. (7) Centering springs. (8)_Cross pin. (9) Left turn port. (10) Internal check valve. (11) Right turn port. (12) Sleeve. (13) Body. (14) Drive. (A) Control section. (B) Metering section.The steering control unit (SCU) is a pilot operated, open centered type pump. The steering control unit (SCU) has two main sections. They are control section (A) and metering section (B). The two sections are connected inside the unit, both hydraulically and mechanically. These two sections work together to send oil to the steering cylinder.Oil from the steering pump goes through inlet port (2) into control section (A). When the steering wheel is turned, the control section sends oil from metering section (B). Metered oil from section (B) is directed by control section (A) to either left turn port (9) or right turn port (11).Metering section (B) is a small hydraulic pump. It produces a specific amount (metered) of oil flow. This metered oil is then directed by control section (A) to the steering cylinder.The direction and the speed of a turn are controlled by the steering control unit. As the steering wheel is turned faster, there is an increase in the flow of oil from the steering control unit to the steering cylinder. This increased flow causes the cylinder to move farther and faster, which turns the machine faster.Oil Flow
When the steering wheel is not being turned, the SCU is in the center position. Oil from the steering pump enters the SCU through inlet port (2) and spool (6) blocks oil flow to the steering cylinder. The oil flows out of the SCU to the hydraulic tank. The oil cannot flow through the steering control unit to the steering cylinder until the steering wheel is turned.The steering wheel is connected to spool (6) by a shaft assembly and splines. When the steering wheel is turned, spool (6) turns a small amount until centering springs (7) are compressed. Then, sleeve (12) starts to turn. As long as the steering wheel is turned, the spool and sleeve both turn as a unit, but they turn a few degrees apart.When the spool and sleeve are a few degrees apart, oil passages are opened between them. This allows oil to flow from inlet port (2) through passages in body (13) to the metering section.
Pump Gears In Metering Section
(6) Spool. (12) Sleeve. (15) Slots for springs. (16) Holes for pin.