WINCH HYDRAULIC SYSTEM

TM 5-2410-237-23

WINCH THEORY OF OPERATION - CONTINUED

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WINCH HYDRAULIC SYSTEM - CONTINUED

Winch HOLD Position. In the hold position, the pump draws oil from the reservoir, through a strainer, and discharges

the oil to an inlet port on the pressure control valve. Porting within the pressure control valve and the directional valve

directs the oil flow, under low pressure, to the lubrication circuit. No pressure is applied to any of the clutches.

REEL OUT Position. In the reel out position, the winch drum will be rotated, under power, in the direction necessary to

unspool cable from the drum. To do this, the input clutch must be engaged and the right directional clutch must be disen-

gaged. A sequence valve (17), built into the pressure control valve (2), ensures that the input clutch will be fully

engaged before the directional clutch is allowed to disengage.

NOTE

The lag between input clutch engagement and directional clutch disengagement is of very short duration, by

necessity. Allowing the input clutch to be engaged for any appreciable length of time while the winch shaft

is locked up would stall the engine. In the following description, it is assumed that the control lever is moved

briskly and fully into the REEL OUT position.

Spool (16) moves out of valve body (6) and coupling (11) is moved into valve body (2), as the control lever is

moved into the REEL OUT position. Inward movement of coupling (11) compresses spring (12) and also shifts

spool (14) to the right. Spool (14) ports pump flow through oil passage (15) to chamber (24) and through oil pas-

sage (20) to sequence valve (17). Chamber (24) is connected to the right directional clutch. When pressure in the

chamber below the sequence valve reaches 80 psi (552 kPa), the sequence valve will unseat. Oil then flows around

the sequence valve and through oil passage (13) to load piston (7). The load piston will move spool (8) to the right,

closing off pump flow to the chamber of spool (14) and opening oil passage (5) to pump flow. Oil flows through oil

passage (5) and chamber (22) to the input clutch.

The pressure buildup in chamber (22) is reflected back to the slug chamber of spool (8). This pressure, which is the

input clutch operating pressure, builds quickly. At 300 psi +/- 15 psi (2069 kPa +/- 103 kPa), pressure in the slug

chamber, when combined with the force of the spool return spring, will overcome the force imposed by load piston

(7) and will shift spool (8) to the left.

The pressure in right directional clutch chamber (24) [presently at 80 psi (552 kPa)] will now build quickly toward

its maximum of 275 psi +/- 15 psi (1896 kPa +/- 103 kPa). At a pressure of 180 psi (1241 kPa), the directional

clutch begins to release; at 275 psi (1896 kPa) it is fully released. Spool (14) will be shifted to the left by the com-

bined force of the system pressure felt in the slug chamber and the spool return spring.

So long as the control lever is held in the REEL OUT position, spools (8 and 14) will regulate the respective clutch

operating pressures. In the case of the input clutch, operating pressure of 300 psi +/- 15 psi (2069 kPa +/- 103 kPa)

is determined by the force of the load piston spring.

The operating pressure of the directional clutch is determined by the compression of spring (12), which can be var-

ied by the amount that coupling (11) is moved into the valve body by the control lever. The design of spring (12)

allows the directional clutch operating pressure to be regulated in a range of 180 - 275 psi (1241 - 1896 kPa),

thereby varying winch drum speed

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