SFWR GP-A1015 5298682 - Caterpillar

Illustration 1 g01450189
Cross Section of Control Group (1) Plunger (2) Spool (3) Spool guide (4) Springs (5) Return passage (6) Control passage (7) Orifice (8) Servo piston passage (9) CamThe propulsion control group consists of two sections. Each section contains a plunger and a spool assembly. One section controls oil flow to the forward servo piston in the propulsion pump, and the other section controls oil flow to the reverse servo piston.The propulsion control lever is attached to a cam which contacts the plunger in each control section. When the propulsion control lever is in the NEUTRAL position, the cam maintains the two sections of the control group in the same position relative to each other. In these positions, the spool in each control group blocks the control passage and the spool opens a passage between each servo piston passage and the return passage.Moving the propulsion lever causes the cam to move the plunger in one of the control sections. This action causes the spool and spool guide to move down.Downward movement of the plunger determines the oil pressure in the servo piston passage. Oil pressure moves the spool in the servo piston which seals the pressure inside the servo piston passage. The plunger position can increase the pressure and the machine speed or the plunger position can decrease the pressure and the machine speed. Both control sections operate in this fashion.An orifice in each servo piston passage creates back pressure in the return line from the servo piston in the pump. This back pressure limits erratic movement of the servo piston and the back pressure causes the starts, stops, and speed regulation of the machine to be much smoother.