PREVENTION OF SLACK LIFT CHAINS ON A MAN-UP LIFT TRUCK

摘要

The present invention features a method and anapparatus for preventing lift chains from becoming slack ina lift truck with a "man-up" feature installed. Lift trucksare generally those vehicles that feature hydraulicallycontrolled lift masts with a chain supported fork carriage.Operators of these lift vehicles with the remote lift andlower feature are generally lifted and lowered by thesemasts, known in the trade as a "man-up" condition. It isquite desirable to prevent a slack chain condition in theman-up mast position. The invention features a pressuretransducer for monitoring a drop in hydraulic fluid pressureestablished by the flow control valve that regulates thelowering speed of the mast during the remote mode, i.e.,when the fork carriage is being lowered by the operator inthe platform attached to the fork carriage. The inventionturns off the normally closed load-holding valve when thehydraulic pressure drops below a predetermined value, whichstops the flow of hydraulic fluid back into the reservoir.This, in turn, stops the cylinder(s) from lowering and keepsthe fork carriage lift chains from becoming slack.