Patent GB-1446590-A (GB)
Title: Hydroacoustic oscillator
IPC: B25D9/18
Filed: 1973-08-16
Abstract: 1446590 Percussive tools HYDROACOUSTICS Inc 16 Aug 1973 [31 Aug 1972] 38751/73 Heading B3H [Also in Division B4] An oscillator for pile driving or for delivering impacts to a percussive tool 68 comprises a movable mass in the form of a piston 14 having one end exposed to a first cavity 32 containing pressurised fluid (hydraulic oil) for providing unidirectional driving forces and its opposite end communicating with a second cavity 34, a valve element 70 being bi-directionally movable by the piston for opening and closing ports 26, 28 to abruptly switch the pressure in the second cavity between supply and discharge pressures to produce square wave driving forces on the piston in a direction opposite to said unidirectional driving forces. As shown the housing 10 is divided into upper and lower chambers 32, 34 by the piston 14 having an upper working surface and a lower working surface 17 the valve element 70 being slidable in the bore of the lower chamber and provided with axial passages 30, Fig. 2 to prevent division of the chamber as it is moved up and down by collars 22, 24 on an extension 20 of the piston. The housing also includes an inlet passage 36 and annular port 26 and an outlet passage 44 and annular port 28 as well as passages 48, 52 leading to and from the upper chamber and provided with a control valve 50 and restrictor 54 for adjusting the equilibrium position of the piston 14. Square waveform forces (F N ), Fig. 11 (not shown), may be achieved by a lost motion arrangement formed by the valve element 70 being shorter than the distance between the collars 22, 24 as illustrated in Fig. 6. In Figs. 1 to 4 (not shown) this distance is the same and the net force (F N ) driving the piston is plotted in waveform (d), Fig. 5 (not shown). In operation, the piston 14 is set oscillating about the equilibrium position. After impact with the anvil 68, the piston 14 is moved upwardly by fluid pressure supplied through the port 26 to the piston surface 17. When lifted by the collar 24, the valve element 70 shuts off port 26 and opens the outlet port 28. The pressure in the chamber 34 drops to the pressure in the outlet cavity 42 and decelerates the piston. The forces due to the fluid spring so formed by the oil in the chamber 32 cause the piston to move down and pass the equilibrium position to strike the anvil, the valve element being moved down by the collar 22 to shut off the outlet port 28 and open the inlet port 26 again. The amplitude of oscillation builds up gradually. The inlet 36 may be fed from a pump and the outlet 44 may be fed to a tank or to the suction side of the pump, the cavities 38, 42 serving to absorb flow pulsations. If desired, these cavities may include a diaphragm and a compressed air portion for absorbing flow pulsations, Figs. 12 to 14 (not shown) and a diaphragm (81) and compressed air portion (80) may be included in the chamber (32). In the embodiment illustrated in Fig. 13 (not shown) a separate and smaller piston (90) is placed upon the piston (14) so that this smaller piston co-acts with the oil in the chamber (32), the upper end of the chamber 34 being vented at (94) and the passages 48, 52 replaced by a single non-valved passage (96) extending between the cavity (38) and the chamber (32).