PUMP GP-PISTON 3988977 - Caterpillar

The "Chassis ECM" controls the operation of the "Electronic Clutch Pressure Control" (ECPC) solenoid valves for control of the transmission. The ECM uses the transmission clutch proportional solenoid valves in order 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. On an ECPC controlled transmission, the clutch pressure is modulated electronically. 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 controls, the transmission speed sensors and the transmission temperature sensor to determine the correct output current for the solenoids.The ECM will output a pulse width modulated (PWM) signal in order 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.
Table 1
Assignments for the Transmission Clutch    
Gear     Clutches    
1 2     3     4     5     6     7    
Neutral                 X                
Reverse     X                         X    
First     X                     X        
Second             X             X        
Third         X                 X        
Fourth             X         X            
Fifth         X             X            
Sixth             X     X                
Seventh         X         X                To control the shifting of the transmission, the "Chassis 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