PADLOCK 2F2791 - Caterpillar

Gearshift Valve
Illustration 1 g00672500
Location of Gearshift Valve
Illustration 2 g00673426
Location of Accumulator
Illustration 3 g00918488
Gearshift Valve (1) Gearshift valve (2) First speed solenoid valve (3) Accumulator (4) Solenoid valve (transmission brake) (5) Pressure control valve (transmission brake) (6) Second speed solenoid valve (7) Accumulator and modulating valve (clutch) (8) Accumulator and modulating valve (transmission brake) (9) Power train motor (10) Gear pump (11) Temperature sensor (B) Oil line from the implement pump (pressure (B) reduced) (C) Oil line to pressure sensor (D) Return oil line
Table 1
Gearshift Valve    
    Solenoid (2)     Solenoid (4)     Solenoid (6)    
First Speed     Inactive     Active     Active    
Second Speed     Active     Inactive     Active    
Transmission Brake     Inactive     Inactive     Inactive    Gearshift valve (1) is mounted on the right side of the front frame near the transmission gearbox. The gearshift valve has one solenoid valve for each of the clutches. The IQAN Monitoring and Control System uses the solenoid valves to direct oil pressure to each clutch. These solenoid valves are on/off solenoid valves.Reference: For more information on the IQAN Monitoring and Control System, refer to Systems Operation, RENR6127, "IQAN Monitoring and Control System".The solenoid valves are controlled by the outputs of the IQAN. The IQAN uses the solenoid valves to direct oil pressure to each clutch.Oil flows from the implement pump to the differential lock control valve. The pressure reducing valve in the differential lock control valve reduces the oil pressure to 2800 kPa (400 psi).The oil then flows to gearshift valve (1) through oil line (B). When the operator makes a speed selection, the IQAN will activate the appropriate speed selection solenoid valve. Table 1 indicates the solenoid valves that are required to engage the clutches. When the operator makes a speed selection, solenoid valve (4) and a gear selection solenoid valve are activated. This causes pressure oil to flow to the clutch piston and accumulator (3) .Accumulator (3) maintains the oil pressure to the transmission gearbox. This ensures that the clutches will remain engaged if there is a sudden drop in the supply pressure.Accumulator (3) and pressure control valve (5) maintain a minimum oil pressure of 1500 100 kPa (220 15 psi) to the clutches when the transmission is in neutral.Oil flows through port (C) to the gearshift pressure sensor. The gearshift pressure sensor senses the pressure supply to the clutches, and the signal from the IQAN.If the gearshift pressure is below 2600 kPa (380 psi), the IQAN will not allow the machine to move. Then, the IQAN will engage the parking brake in order to prevent the machine from moving. The IQAN will display an alarm.The temperature sensor for the transmission gearbox also protects the transmission gearbox. If the temperature of the oil in the transmission gearbox is below -35 °C (-95 °F) or above 125 °C (257 °F) the IQAN will not allow the transmission to shift. As a result, the IQAN will display an alarm.