Patent GB-639148-A (GB)
Title: Hydraulic transmission
IPC: B23Q5/06
Filed: 1947-08-05
Abstract: 639,148. Hydraulic transmission of power. OILGEAR CO. Aug. 5, 1947, No. 21265. Convention date, Dec. 21, 1942. [Class 69 (ii)] In a hydraulic transmission comprising a hydraulic motor, formed, for example, by cylinder 2 and piston 3, a pump 6 for delivering liquid to the motor to energize it, a resistance, such as the valve 10, normally effective to resist the discharge of liquid from one side of the motor pistons 3 to impose a back-pressure thereon, electrically-operated means, which may be the valve 11, adapted when operated to render the resistance ineffective, a switch 40 adapted when closed to effect operation of the means 11 and means, such as a piston 43 operated by pump pressure for closing the switch 40, a magnet 47 which constantly urges the switch to the open position, is so located that a high pump pressure is required to enable the pistons 43 to overcome the pull of the magnet and close the switch whilst a much lower pump pressure is sufficient to enable the piston 43 to hold the switch 40 closed. When the reversible variable-delivery pump 6 is idling, the piston 3, which operates a broaching machine tool slide 1, is maintained in the upper position by the column of liquid trapped underneath the piston 3 by valve 10, which latter has a check valve 9 in parallel with it that opens in the opposite direction to the valve 10. When the pump 6 is adjusted to discharge into a conduit 8, the liquid, after moving to the left the plunger 17 of a differential valve 5, then traverses chamber 18 and conduit 19 and commences to move the piston 3 in a working stroke. The liquid discharged from the underside of the piston 3 passes through the valve 10 to the intake of the pump 6 and since the quantity of the liquid is in excess of the pump requirements the surplus liquid flows through a conduit 7, a passage in the plunger 17 and a low-pressure resistance valve 21 to exhaust, so that pump 6 is supercharged. The necessary back-pressure on the piston 3 to maintain a substantially constant rate of tool movement is therefore effected by both resistance valves 10 and 21 and the tool resistance. When the load on the piston 3 reaches a predetermined value and the pump pressure has increased correspondingly the liquid in conduit 19 acts on piston 43. Movement of the latter overcomes a spring 45 and magnet 47 to close switch 40 and so energizes a solenoid 37 thereby moving rightwardly the spring-loaded plunger of valve 11 so that liquid discharged from the underside of piston 3 may byepass the valve 10. Under these conditions the supercharging of pump 6 and the back-pressure on the piston 3 is not effected by valve 10. When the piston 3 approaches the end of its downward stroke the load on the piston decreases, since the tool is nearly clear of the work, and the piston 43 is forced upwards by its spring so de-energizing solenoid 37. To cause a high-speed upstroke of the piston 3 the pump 6 is reversed to supply liquid to the underside of the piston through the valve 9. Pressure in the conduit 7 causes the plunger 17 to move to its rightward position so that liquid discharged from the upper side of the piston 3 is directed through conduit 19, valve 5, conduit 7 and valve 9 to the under side of the piston 3. The pump 6 now draws liquid from a reservoir 23 and only supplies a volume of liquid equal to the displacement of the rod of piston 3. In a modification, the separate check valve 9 is dispensed with and the valve 11 acts as a pilot valve, which, through chokes, controls the position of a spring-loaded differential piston, the latter having attached to it a valve stem that in conjunction with a valve seat acts as the byepass for the valve 10 as well as a check valve. The chokes permit the valve 11 to open more quickly than it can close.