Allis-chalmers Corporation

Terry R Downing

Allois F Geiersbach

Warren E Herwig

Ronald E Spooner

Winfred C Croft

John M Zorns

An overhead guard is provided for counterweighted lift trucks of different lengths. The overhead guard has a top portion supported at its front end by a pair of laterally spaced front legs extending downwardly to attaching points on the front of the truck and the top portion is supported at its rear end by adjustably positioned laterally spaced rear posts. The top of the rear posts may be attached to different longitudinally spaced points on the upper portion of the guard and the bottom of the rear posts are attachable to support posts on the counterweight which is at different longitudinal positions on different length trucks.

Overhead guard for lift trucks of different lengths

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.

Fork lift truck having means to test overload protective system

An automatic mechanical brake adjuster for a walk-behind lift truck includes a lever (59) with two relatively pivoted parts (58,76) including a ratchet mechanism (96) therebetween. The ratchet mechanism (96) includes a ratchet wheel segment (77) and cooperating pawls (101-104). The brake adjuster also includes an extensible link (126) which determines the brake shoe back-off distance and cooperates with the ratchet mechanism (96) in effecting pivotal adjustment between the lever parts (58,76).

Automatic mechanical brake adjuster

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 override of the safety system so that the overload can be relieved by the operator under certain conditions without requiring the assistance of a second truck.

Lift truck overload protective circuit having override feature

A fork lift truck has an overload protective circuit which is responsive to an excessive tilting moment acting on the truck, as a result of a load on the raised carriage, to disable the mast tilting motor and carriage elevating motor from shifting the load supporting carriage in a direction which would increase the forward tilting moment and also has a crowbar circuit which, upon failure of the protective system to respond properly to such excessive tilting moment, opens an electrical circuit that also results in inhibiting the mast tilting and carriage elevating motors from further raising the carriage or further forward tilting of the mast on the overloaded truck, thereby providing enhanced protection against faulty operation resulting from component failure. One embodiment permits the truck operator to selectively simulate an overload and thereby initiate testing for component failure in the overload protective system. Another embodiment is self-testing and simulates an overload to thereby initiate testing for component failure each time the truck electrical system is turned on.

Lift truck safety system having protection against component failure

An overload protective system continuously monitors the forward overturning moment on a counterbalanced lift truck and prevents further raising of the carriage or further forward tilting of the mast when the overturning moment is excessive. Resistance strain gage sensors mounted on a load carrying tilt jack pin which resists the overturning moment are connected in an electrical bridge which may be inherently unbalanced due to the weight of the unloaded carriage and derives a strain signal proportional to the mechanical strain in the load carrying anchor pin when the carriage supports a load; a high gain differential amplifier raises the level of the strain signal output from the bridge and unbalance compensating adjustment means permit selective variation of the potential difference between the inputs to the differential amplifier until its output voltage is substantially zero to thereby compensate for unbalance in the bridge when the carriage is unloaded; a visual indicator is lighted when the differential amplifier output voltage is substantially zero to thereby indicate that bridge unbalance is compensated for; a comparator derives a trip signal when the differential amplifier output voltage reaches a predetermined magnitude when the carriage supports a load; a shift register receiving clock pulses from an oscillator as a time reference records the history of the comparator output and a decoder analyzes the shift register output and sets a latch when the trip signal comparator output has been present for a predetermined interval of time; and disabling means responsive to setting of the latch de-energize operating coils for blocking valves which inhibit further raising of the carriage or further forward tilting of the mast.

Lift vehicle with fail-safe overload protective system

An overload protective system continuousy monitors the forward overturning moment on a counterbalanced lift truck and prevents further raising of the carriage or further forward tilting of the mast when the tilting moment is excessive. A strain gage sensor connected in an electrical bridge derives a strain signal proportional to the mechanical strain in a load carrying anchor pin for the tilt jack which resists the forward overturning moment acting on the truck; a differential amplifier raises the level of the strain signal; a comparator which receives the output of the differential amplifier derives a trip signal when the strain signal reaches a predetermined magnitude; a shift register receiving clock pulses from an oscillator as a time reference records the history of the comparator output and a decoder analyzes the shift register output and sets a latch when the trip signal comparator output has been present for a predetermined interval of time; and disabling means responsive to setting of the latch de-energize operating coils for blocking valves which inhibit further raising of the carriage or further forward tilting of the mast.

Truck overload protective system having trip signal sampling means

When the load moment on a counterbalanced lift truck exceeds a predetermined magnitude, a blocking valve automatically prevents forward tilting of the mast and elevation of the load. The load moment is sensed by the pressure differential across the tilt jack and the blocking valve is actuated by the pressure differential. In order to prevent the blocking valve from becoming locked up, when the tilt jack is contracted to the end of its stroke, a spring-biased unloading valve is incorporated in the tilt jack piston. Abuse of the truck is reduced and operator safety is improved further by the provision of a second blocking valve which prevents lifting loads when the tilt jack is at the end of its extension stroke, that is when the mast is tilted forwardly as far as permitted by the tilt jack. In this condition the second blocking valve will close preventing further raising of the load. However, retraction of the tilt and lift jacks is permitted even though the blocking valves are in their closed positions. The second blocking valve is biased toward its open position by the pressure in the rod end of the tilt jack and toward its closed position by the pressure in the lift jack. The blocking valves are biased toward their open positions by adjustable spring means which permit the control system to be adjusted to meet the protection requirements of lift trucks with different load carrying capacities. Pressure modulating restrictors are provided in pilot lines to the blocking valves to prevent false actuation when pressure fluctuations occur.

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Hazel Crest, IL, United States of America

Terry R Downing