Piston pumps, in particular for the injection of fuel into internal combustion engines

Claim 1

A RECIPROCATING PISTON LIQUID PUMP WHICH COMPRISES, IN COMBINATION, A MAIN CYLINDER AND A RECIPROCATING MAIN PISTON FITTING SLIDABLY IN SAID CYLINDER SO AS TO FORM THEREWITH A VARIABLE VOLUME CHAMBER, THE DISPLACEMENTS OF SAID PISTON WITH RESPECT TO SAID CYLINDER WHICH REDUCE THE VOLUME OF SAID CHAMBER BEING CALLED THE DELIVERY STROKES OF SAID PISTON, A DELIVERY CONDUIT IN COMMUNICATION WITH SAID CHAMBER, AN AUXILIARY CYLINDER FIXED WITH RESPECT TO SAID MAIN CYLINDER, AN AUXILIARY PISTON FITTING SLIDABLY IN SAID AUXILIARY CYLINDER, HYDRAULIC MEANS OPERATIVELY CONNECTED TO SAID MAIN PISTON AND ARRANGED TO ACT ON SAID AUXILIARY PISTON SO THAT EVERY DELIVERY STROKE OF SAID MAIN PISTON CAUSES A DISPLACEMENT OF SAID AUXILIARY PISTON IN ONE DIRECTION, RESILIENT MEANS CONNECTED WITH SAID AUXILIARY PISTON FOR URGING IT IN THE DIRECTION OPPOSED TO SAID FIRST MENTIONED DIRECTION, SAID AUXILIARY CYLINDER AND PISTON BEING ARRANGED TO FORM BETWEEN THEM A VARIABLE VOLUME SPACE WHICH INCREASES DURING THE DISPLACEMENTS OF SAID AUXILIARY PISTON IN SAID FIRST MENTIONED DIRECTION AND DECREASES DURING THE DISPLACEMENTS OF SAID AUXILIARY PISTON IN SAID SECOND MENTIONED DIRECTION, SAID LAST MENTIONED DISPLACEMENTS OF SAID AUXILIARY PISTON BEING CALLED RETURN STROKES THEREOF, A LIQUID FEED PORT OPENING INTO SAID AUXILIARY CYLINDER NEAR ONE END THEREOF, A LIQUID DISCHARGE PORT IN SAID AUXILIARY CYLINDER NEAR THE OTHER END THEREOF, SAID AUXILIARY CYLINDER BEING PROVIDED WITH AN INLET OPENING LOCATED AT A POINT THEREOF INTERMEDIATE BETWEEN SAID PORTS, CONDUIT MEANS LEADING FROM SAID VARIABLE VOLUME CHAMBER OF SAID MAIN CYLINDER TO SAID AUXILIARY CYLINDER INLET OPENING, SAID AUXILIARY PISTON BEING IN THE FORM OF A SLIDE VALVE PROVIDED WITH A PASSAGE ARRANGED TO CONNECT SAID INLET OPENING WITH SAID FEED PORT AT THE BEGINNING OF EVERY MOVEMENT OF SAID AUXILIARY PISTON IN SAID FIRST MENTIONED DIRECTION, THEN TO CUT OFF SAID INLET OPENING FROM BOTH OF SAID PORTS FOR A PORTION OF SAID LAST MENTIONED MOVEMENT AND FINALLY TO CONNECT SAID INLET OPENING WITH SAID DISCHARGE PORT AT THE END OF SAID LAST MENTIONED MOVEMENT, AND LIQUID DISCHARGE MEANS IN COMMUNICATION, DURING THE RETURN STROKES OF SAID AUXILIARY PISTON, WITH THE PORTION OF SAID AUXILIARY CYLINDER LIMITING SAID VARIABLE VOLUME SPACE, SAID LIQUID DISCHARGE MEANS FORMING THE ONLY WAY FOR THE OUTFLOW OF LIQUID FROM SAID SPACE DURING SAID RETURN STROKES OF SAID AUXILIARY PISTON AND SAID LIQUID DISCHARGE MEANS INCLUDING A THROTTLED PASSAGE FOR BRAKING THE OUTFLOW THERETHROUGH OF LIQUID FROM SAID SPACE, WHEREBY, FOR SPEEDS OF RECIPROCATION OF SAID MAIN PISTON ABOVE A GIVEN VALUE, SAID THROTTLED PASSAGE IN SAID LIQUID DISCHARGE MEANS PERMITS ONLY A PORTION OF THE LIQUID PRESENT IN SAID VARIABLE VOLUME SPACE TO BE DISCHARGED THEREFROM DURING EVERY RETURN STROKE OF SAID AUXILIARY PISTON AND THUS LIMITS SAID RETURN STROKE SO THAT ON THE NEXT DELIVERY STROKE OF SAID MAIN PISTON SAID CONDUIT MEANS OPENING IS CUT OFF FROM SAID LIQUID INTAKE PORT AT AN EARLIER TIME DURING EVERY CYCLE OF OPERATION OF THE PUMP.