| 摘要 |
1,203,404. Masted lift trucks. CLARK EQUIPMENT CO. 21 Feb., 1969 [26 March, 1968], No. 9464/69. Heading B8H. The three-section mast of a lift truck is extendible at two speeds, and is provided with a control system which permits high speed extension only when the mast is extended above a predetermined height. As shown, the mast ram 24 is extended by actuating a pump P 1 alone or pumps P 1 , P 2 together. The return circuit from the ram to the reservoir 18 includes a restrictor 72 which may be by-passed through a valve 78 and line 76 to produce higher speed lowering of the mast. In operation, to extend the mast, the operator closes switches in the electrical control circuit, Fig. 3 (not shown), to actuate the motor of pump P 1 . After a predetermined extension of the mast, a cam closes a switch in the circuit of the motor of pump P 2 whereby, closing of a further switch by the operator causes the pump P 2 to operate, after a time delay, to produce high speed extension of the mast. As the mast approaches within a predetermined distance of its full extension, a cam opens a further switch to de-energize both pump motors. To move the mast to its fully extended position, the operator then closes further switches to complete the circuit of the motor of pump P 1 to produce low-speed extension of the mast. To retract the mast, the operator closes switches in a circuit containing solenoids of valves 74, 78. Initially, valve 74 opens to allow low-speed retraction of the mast and then, after a time delay, valve 78 opens to by-pass the restrictor 72 to allow high-speed retraction of the mast. |
