MH3037 Material Handler Machine System Caterpillar

The machine maybe equipped with an optional hydraulic oil warming circuit. The hydraulic oil warming circuit warms the hydraulic oil to 16° C (60° F). The hydraulic oil warming circuit is activated through the master controller and monitor. When the hydraulic oil warming circuit is activated, the master controller and monitor will set the engine speed at 1300 rpm and electronic control module 2 will energize the hydraulic oil warming solenoid valve. The hydraulic oil warming circuit will stay on until another throttle function such as "Auto Throttle" or "Engine Idle" is selected through the master controller and monitor. The hydraulic oil warming valve will not function when the hydraulic oil temperature becomes greater than 16° C (60° F). If the hydraulic oil warming circuit is on and the hydraulic oil temperature falls below 12.8° C (55° F), the engine speed will increase and the hydraulic oil warming solenoid valve will activate.

Illustration 1	g03650565
Right side view of machine undercarriage (1) Control manifold and solenoid valve (hydraulic oil warming)

Control manifold and solenoid valve (1) for hydraulic oil warming is located in a compartment, on the right side of the machine undercarriage.

Hydraulic Oil Warming (OFF)

Illustration 2	g06054870
Partial schematic (1) Control manifold and solenoid valve (hydraulic oil warming) (2) Hydraulic warming solenoid valve (3) Relief valve (4) Port "T" - return oil (5) Port "LS" - load sense signal oil (6) Port "P" - main pump oil (7) Port "PIL" - pilot oil

Main pump oil from port "P2B" of the lower main control valve enters port "P" (6) of hydraulic oil warming manifold (1). When hydraulic warming solenoid valve (2) is de-energized, the spool is held in the closed position by spring force. As a result, the main pump oil from port "P" (6) is blocked by the check valve within solenoid valve (2).

Hydraulic Oil Warming (ON)

Illustration 3	g06054924
Partial schematic (1) Control manifold and solenoid valve (hydraulic oil warming) (2) Hydraulic warming solenoid valve (3) Relief valve (4) Port "T" - return oil (5) Port "LS" - load sense signal oil (6) Port "P" - main pump oil (7) Port "PIL" - pilot oil

When hydraulic warming solenoid valve (2) is energized, the spool shifts to the open position allowing main pump oil to flow through hydraulic warming solenoid valve (2). The main pump oil that flows through hydraulic warming solenoid valve (2) is used to create a load sense signal.

The load sense signal flows from port "LS" (5) to port "X" of the main pump. The load sense signal upstrokes the main pump, allowing for an increase in supply oil to flow through the system.

Load sense signal relief valve (3) keeps the load sense signal pressure less than 17,237 kPa (2,500 psi). If the load sense signal pressure becomes greater than 17,237 kPa (2,500 psi), the load sense signal pressure works against the spring to shift the spool of load sense signal relief valve (3). The shifting of the spool for load sense signal relief valve (3) allows excess hydraulic oil pressure from the load sense signal to be released out port "T" (4) to port "T2B" of the lower main control valve and through the anti-cavitation valves and return to tank.

For more information on the operation of the main hydraulic pump, refer to System Operation, "Pump Control (Main Hydraulic)".