Fork lift truck having means to test overload protective system
AssigneeAllis-Chalmers Corporation
InventorsTerry R. Downing, Allois F. Geiersbach
Life of this patent
Estimating the term…
Abstract
A fork lift truck has a safety system for inhibiting further raising of the carriage or further forward tilting of the mast when an excessive tilting moment is acting on the truck and permits the truck operator to selectively simulate an overload on the truck and provides a visual indication that the safety system has responded properly to such simulated overload, thereby permitting the truck operator to test whether or not the truck is protected from picking up an overload.
Claims14
In a fork lift truck having a tilting mast, a load supporting carriage, a mast tilting motor, a carriage elevating motor for raising and lowering said carriage on said mast, overload protective means including sensor means for generating an electrical tilting-moment signal which is a function of the tilting moment acting on said truck and which tilting moment is dependent upon the elevation of said carriage, the weight of the load on the carriage and the angle of inclination of the mast, means receiving said tilting-moment signal as an input for disabling said carriage elevating motor and said mast tilting motor in response to a predetermined value thereof indicative of an overload on said truck, means for providing an indication that said disabling means has operated to disable said carriage elevating and mast tilting motors, and overload simulating means for selectively causing said sensor means to generate a tilting-moment signal having a value equal at least to said predetermined value, thereby permitting the truck operator to simulate an overload on said truck and ascertain from said indication whether or not said truck is protected from picking up on overload.
In combination, a lift truck having a tilting mast, a load supporting carriage, a hydraulic lift jack for raising and lowering said carriage on said mast, a hydraulic tilt jack for tilting said mast, overload protective means including sensor means for deriving an electrical tilting-moment signal whose magnitude is proportional to the tilting moment acting on said truck as a result of a load on said raised carriage, a comparator for deriving an overload signal in response to a predetermined magnitude of said tilting-moment signal indicative of an overload on said truck, means coupled to said comparator for disabling said lift jack and said tilt jack in response to said overload signal, means for providing an indication that said jack-disabling means has operated to disable said lift jack and tilt jack, and overload simulating means for selectively causing said sensor means to derive an electrical tilting moment signal equal at least to said predetermined magnitude, thereby permitting the lift truck operator to test whether or not said lift truck is protected from picking up an overload.
In a fork lift truck having a tilting mast, a load supporting carriage, a mast tilting motor, a carriage elevating motor for raising and lowering said carriage on said mast, a load supporting member which resists the tilting moment acting on said truck as a result of a load on the raised carriage, sensor means including a plurality of strain gages mounted on said load carrying member and arranged in an electrical bridge for generating a tilting-moment electrical signal whose magnitude varies as a function of the mechanical strain in said load carrying member and thus as a function of said tilting moment, a differential amplifier having its inputs coupled across a diagonal of said bridge, comparator means coupled to the output of said differential amplifier for deriving an overload signal when said tilting-moment signal from said bridge exceeds a predetermined magnitude indicative of an overload on said truck, disabling means coupled to the output of said comparator means and being responsive to said overload signal to disable said mast tilting motor and said carriage elevating motor, said disabling means includes a normally conductive transistor switch and electrically operated hydraulic valves having operating coils in series with said transistor switch and which valves respectively control flow of fluid to said mast tilting motor and to said carriage elevating motor, overload simulating means for selectively unbalancing said bridge sufficiently to cause said comparator to generate said overload signal, and indicating means for providing a visual indication when said transistor switch is turned off, thereby permitting the truck operator to selectively test whether or not said lift truck is protected from picking up an overload.
Dependencies are inferred from the claim text.