BRACE 3398572 - Caterpillar

Illustration 1 g01047781
Selector and pressure control valve (1) Speed selection spool (2) Load piston (3) Modulation relief valve (4) Pressure differential valve (5) Torque converter inlet valve (6) Direction selection spool (7) Flow control orificeThe selector and pressure control valve is located inside the top cover of the transmission.Speed selection spool (1) and direction selection spool (6) are connected to the transmission hydraulic control linkage.The basic functions of each valve are listed in Table 1.
Table 1
Valve     Function    
(1) Speed selection spool     This spool directs the oil to a speed clutch.    
(2) Load piston     This piston controls the rate of pressure increase in the clutches.    
(3) Modulation relief valve     This valve controls the maximum pressure in the system.    
(4) Pressure differential valve     This valve keeps a pressure differential between the speed and the direction clutches.
This prevents the movement of the machine if the engine is started with the transmission in a speed and a direction.    
(5) Torque converter inlet valve     This valve limits the maximum pressure to the torque converter.    
(6) Direction selection spool     This spool directs oil to a direction clutch.    On initial start up with the transmission in neutral pump oil flows through the flow control orifice (7) to No.3 clutch (C3), torque converter inlet valve (5) and pressure differential valve (4). The right hand end of the pressure differential valve is open to tank. Clutch numbers (C1), (C2), (C4), (C5) and (C6) are all connected to tank. The right hand end of load piston (2) is also connected to tank. Engine Running, transmission in Neutral
Illustration 2 g01063336
Selector and pressure control valve - Engine running, transmission in neutral (1) Speed selection spool (2) Load piston (3) Modulation relief valve (4) Pressure differential valve (5) Torque converter inlet pressure valve (6) Directional selection spool (7) Flow control orificeThe position of directional selector spool (6) allows oil to flow to clutch (C3), converter inlet valve (5) and pressure differential valve (4). Oil flows through an orifice in the converter inlet valve spool and fills the slug chamber at the right end of the spool. Oil also flows through an orifice in the spool of pressure differential valve (4) and fills the chamber at the left end of the spool.As the pressure in the chamber at the left end of pressure differential valve (4) increases, the spool moves fully to the right against the end cover. This allows oil to flow past the spool to the directional clutch circuit and to fill the spring chamber at the right hand end of the spool. As the directional clutch pressure increases, the spool moves back to the left until flow past the spool is stopped. In this position the pressure in the chamber at the left end of the spool is balanced by the combined effect of pressure in the spring chamber and the springs themselves. The spool is in a balanced position to maintain a constant pressure in the