GB856939A - Fork lift trucks having tilting mast assemblies - Google Patents

Abstract

856,939. Fork lift trucks. ELECTROHYDRAULICS Ltd. Aug. 14, 1958 [May 28, 1957; July 25, 1957], Nos. 16949/57 and 23651/57. Class 78 (3). A fork lift truck is provided with hydraulic rams to tilt the mast and to raise the load on the mast, means being provided to prevent further extension of both these rams and to give visual or audible warning when the tilting moment of the loaded mast about the front axle of the truck reaches a predetermined value. In the embodiment shown in Fig. 4, a ram 103 is pivoted between a point 104 on the truck frame and a point 105 on a link 106 pivoted to the mast 100 at 107, the mast 100 being pivoted at 101 to the truck frame. As the ram 103 is extended, by means of a pump (not shown) connected to a pipe 118, the moment of the mast tends to rotate an arm 110 on link 106 in a clockwise direction against the action of a spring 111 to operate a pump 116 which supplies pressure to the end 124 of a tilt limit valve 119, urging a piston 121 against a spring 126, and to the end 124 of a lift limit valve 131, in the hydraulic circuit of a lifting-ram 102. At a predetermined pressure in the end 124 of valve 119, the piston 121 moves to prevent flow of fluid from the ram 103 to the tilt selector through line 117, thus preventing further extension of the ram 103. Similarly, at the predetermined pressure in the end 124 of lift limit valve 131, this valve closes to prevent fluid flowing from the lift selector to the ram 102. The rams 102, 103 cannot now be extended further, but non-return valves 133, 128 permit fluid to be withdrawn from the lifting ram 102 and to be supplied to the outer end of the cylinder of ram 103, respectively, so that the fork may be lowered or the mast tilted back, thus reducing the tilting moment and allowing the spring 111 to remove arm 110 from pump 116. A warning lamp 140 is actuated by an abutment 113 on arm 110 engaging a switch 114. The pump 116 may be replaced by an electric switch operating solenoids in valves 119, 131. In a modification, Fig. 5 (not shown), the valves 119, 131 are actuated directly by the arm 110. In a further embodiment, Fig. 6 (not shown), the tilt limit and lift limit valves are coupled together mechanically, and the link 106 is replaced by a valve which is operated to supply fluid from the outer end of the tilting ram cylinder to close the limiting valves at a predetermined extension of the tilting ram. In a further modification, Fig. 7 (not shown), the pump 116 of Fig. 4 is mounted on the chassis of the truck and is actuated by a lever on the truck suspension as the weight distribution of the truck changes.