GB1250892A - - Google Patents

Abstract

1,250,892. Percussive drills. A.F. HYDRAULICS Ltd. 13 Jan., 1969 [16 Jan., 1968], No. 2434/68. Heading B4C. [Also in Division F1] A chamber 14 at one side 16 of a vibrating piston 10 suitable for driving a rock drill bit or a grass mower is connected cyclically with a highpressure hydraulic fluid line 38 and a lowpressure exhaust line 40 by means of a shuttle valve member 36 located in a housing having end chambers 48, 50 which are cyclically connected by lines 62, 64 and a bi-stable element 72 to a branch 60 of supply line 38 when an annular groove 31 of piston 10 momentarily connects cylinder ports 59, 61 to give a first position signal (right hand end position) in line 62 and when a piston groove 28 connects cylinder ports 58, 63 to give a second position signal (left-hand end position) in line 64. Element 72 which is a flip-flop element and may be a pure fluid switch or may comprise two three-way piston valves, is such that once a pressure pulse has been applied to one or other line 62, 64 the element remains switched in one position until a pressure pulse is applied to the other line. Thus if at the end of the outward stroke the groove 31 overshoots ports 59, 61 and so re-connects them at the start of the return stroke which is effected by fluid in a spring chamber 18, the pulse so generated in line 62 is stopped by element 72. Similar considerations apply when groove 28 overshoots ports 58, 63. The piston 10 may be stopped in either the forward or return position by closing a valve (not shown) in lines 62, 64 respectively, and the piston is stopped in an arbitrary position by closing a valve in supply line 38. As shown, the piston is started and stopped according to the presence or absence of a control signal in lines 77, 78 leading to AND gates 74, 75 in lines 62, 64, respectively. Thus if a control signal is not present in line 78 the pulse in line 64 will be blocked so that valve 36 will not be switched to the position shown and the piston 10 will stop in its left-hand position. In a modification, gates 74, 75 receive control signals through a sensor (84), Fig. 3 (not shown), connected to chamber 14, whereby the first position signals are only passed to the bi-stable element 72 when chamber 14 is pressurized and the second position signals are only passed to the element 72 when the chamber 14 is de-pressurized. In a further modification both ends of the piston are cyclically pressurized and exhausted and both ends are also connected to spring chambers.