745 & 740 GC Articulated Truck Caterpillar

Illustration 1	g06196174
(C) to Clutch (P) Supply oil (T) to Tank (1) ECPC Valve for Clutch 1 (2) ECPC Valve for Clutch 2 (3) ECPC Valve for Clutch 3 (4) ECPC Valve for Clutch 4 (5) ECPC Valve for Clutch 5 (6) ECPC Valve for Clutch 6 (7) ECPC Valve for the Lock-up Clutch (8) Transmission Hydraulic control manifold (9) Suction screen (10) Oil sump (11) Scavenger pump (12) Lubrication Relief Valve (13) Transmission lubrication circuit (13a) Output transfer gear (OTG) lubrication (13b) Flywheel Lubrication (13c) Planetary lubrication (14) Transmission Oil Cooler (15) Torque Converter Temperature Sensor (16) Torque converter (and Lock Up Clutch) (17) Inter axle differential lock ECPC solenoid valve (18) T/C inlet relief valve (19) Transmission oil pump (20) Transmission oil filter (21) Main relief valve

The "Transmission ECM" controls the operation of the "Electronic Clutch Pressure Control" (ECPC) solenoid valves ( (1) through (7)) for control of the transmission. The ECM uses the transmission clutch proportional solenoid valves to shift the transmission. The transmission solenoid valves control the hydraulic circuits that engage the transmission clutch pressures. The ECM supplies electrical current to the appropriate transmission solenoid valves to change the direction and speed of the truck.

The ECM controls the modulation of clutch pressure by sending a variable output current to the appropriate proportional clutch solenoids. The ECM uses input information from the following to determine the correct output current for the solenoids:

• the controls

• the transmission speed sensors

• the transmission temperature sensor

The Transmission ECM will output a pulse width modulated (PWM) signal to vary the current to the solenoid. The current to the solenoid determines the amount of pilot oil pressure that is applied to the hydraulic valve spool. The travel of the spool is proportional to the electrical current that is supplied to the solenoid. The position of the valve spool controls the amount of hydraulic oil pressure that is applied to the clutch. The pressure will determine the engagement of clutch. An increase in the electrical output current of the ECM will result in an increase of the engagement pressure of the clutch.

To control the shifting of the transmission, the "Transmission ECM" will energize one clutch solenoid when the machine is in PARK or NEUTRAL. The ECM will energize different combinations of clutch solenoids when the machine is in one of the available gears.