BRUSH ASSEM. 3Y1256 - Caterpillar

Illustration 1 g06020882
(1) Steering and transmission controls
(2) Parking brake switch
(3) Throttle switch
(4) Traction control switch
(5) Hydrostatic piston pump
(6) Fan pump
(7) Final drive
(8) Hydrostatic piston motorThe hydrostatic power train is a dual path hydrostatic transmission with high pressure, closed drive loops.The drive loops consist of a piston pump with a rotating group for each track and of a separate piston motor for each track. The piston pump is an overcenter pump and the piston pump provide oil flow for forward travel and for reverse travel. Travel direction is determined by the direction of flow from the piston pump. The piston motors are infinitely variable and the piston motors provide a range of ground speeds. The piston pump also affects the ground speed of the machine. First, the pump upstroke to provide the desired speed. The motors will destroke if more speed is commanded.The electronic hystat control system controls the hydrostatic transmission functions. The hydrostatic transmission responds to inputs from the operator. Also, the hydrostatic transmission responds to inputs from the sensors.The system also provides engine overspeed and underspeed protection. In an overspeed condition, the system automatically adjusts the current that is supplied to the hydrostatic transmission pump and motors to slow the machine. Engine underspeed protection is provided by decreasing the control currents to the hydrostatic transmission pump and motors. This protection is in response to the low engine speeds and to the engine lug.Refer to Troubleshooting, M0064356, "Connector Contact Description" for pin descriptions on electrohydraulic schematics.