Hydraulic Drive for Cryogenic Fuel Pump

Abstract

A system for delivering cryogenic fuels to an engine uses a plurality of cryogenic pumps operating in offset phases to deliver high pressure fuel with a minimum of pressure ripple. The cryogenic pumps use engine oil and a hydraulic pump for actuation via electrohydraulic valves. A charge pump maintains pressure in the feed line so that the cryogenic pumps can be located away from the cryogenic fuel tank. A control strategy for the hydraulic pumps allows output pressure and flow rate to be closely controlled and regulated.

What is claimed is: 
     
         1 . A system for delivering cryogenic fuel from a cryogenic fuel tank to an engine, the system comprising:
 a plurality of cryogenic pumps that are hydraulically operated coupled to the cryogenic tank;   a plurality of electrohydraulic valves, each of the plurality of electrohydraulic valves coupled to one respective cryogenic pump of the plurality of cryogenic pumps, each of the plurality of electrohydraulic valves configured to selectively supply or drain a hydraulic fluid to its respective cryogenic pump; and   a controller coupled to each of the plurality of electrohydraulic valves, the controller configured to activate each of the plurality of electrohydraulic valves in a sequence according to a fuel requirement of the engine.   
     
     
         2 . The system of  claim 1 , further comprising a feed pump that maintains pressure in a feed line that couples the cryogenic fuel tank to each of the plurality of cryogenic pumps. 
     
     
         3 . The system of  claim 1 , further comprising a hydraulic pump that supplies the hydraulic fluid to each of the plurality of electrohydraulic valves. 
     
     
         4 . The system of  claim 3 , wherein each of the plurality of electrohydraulic valves has a drain that channels the hydraulic fluid from its respective one of the plurality of cryogenic pumps to a reservoir for engine lubricating oil. 
     
     
         5 . The system of  claim 3 , wherein the one of the plurality of cryogenic pumps and one of the plurality of electrohydraulic valves are combined into a single electrohydraulic (EH) valve-pump unit. 
     
     
         6 . The system of  claim 1 , wherein each of the plurality of cryogenic pumps is an intensified pump wherein an first area of a first piston in contact with the hydraulic fluid is greater than a second area of a second piston in contact with the cryogenic fuel. 
     
     
         7 . The system of  claim 1 , further comprising a first check valve disposed in a feed line coupling the cryogenic tank to the each of the plurality of cryogenic pumps, the first check valve configured to prevent cryogenic fuel output from any of the plurality of cryogenic pumps from returning to the fuel tank, and a second check valve that prevents flow of the cryogenic fuel from any of the plurality of cryogenic pumps to another of the plurality of cryogenic pumps. 
     
     
         8 . The system of  claim 1 , wherein each of the plurality of cryogenic pumps has a hydraulic chamber with a first piston and a cryogenic chamber with a second piston, the first and second pistons coupled by a shaft, the cryogenic chamber having a gas bleed outlet on a shaft-side of the second piston. 
     
     
         9 . The system of  claim 1 , wherein the plurality of cryogenic pumps has three cryogenic pumps. 
     
     
         10 . A method of delivering a cryogenic fuel from a cryogenic tank to an engine, the method comprising:
 providing a plurality of cryogenic pumps, each cryogenic pump having a hydraulic chamber coupled to a hydraulic pump via a respective electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine, each of the cryogenic pumps having a first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber;   supplying a hydraulic fluid under pressure to the hydraulic chamber of each of the plurality of cryogenic pumps via its respective electrohydraulic valve responsive to a signal from a controller; and   for each of the plurality of cryogenic pumps, pumping the cryogenic fuel from the cryogenic tank to the engine via the second piston of the cryogenic chamber responsive to application of pressure of the hydraulic fluid at the first piston in the hydraulic chamber.   
     
     
         11 . The method of  claim 10 , further comprising supplying cryogenic fuel under pressure to each of the plurality of cryogenic pumps using a feed pump. 
     
     
         12 . The method of  claim 10 , further comprising:
 for each of the plurality of cryogenic pumps, draining the hydraulic fluid from the hydraulic chamber to a reservoir for engine lubricating oil.   
     
     
         13 . The method of  claim 10 , wherein supplying hydraulic fluid under pressure comprises disposing an accumulator between the hydraulic pump and each of the plurality of cryogenic pumps. 
     
     
         14 . The method of  claim 10 , wherein for each of the plurality of cryogenic pumps, a surface area of each first piston is greater than a surface area of each second piston. 
     
     
         15 . The method of  claim 10 , further comprising:
 preventing backflow of cryogenic fuel from any of the plurality of cryogenic pumps to the cryogenic tank; and   preventing backflow of cryogenic fuel from any of the cryogenic pumps to any other of the plurality of cryogenic pumps.   
     
     
         16 . The method of  claim 10 , further comprising:
 bleeding fuel vapor that bypasses the second piston from a shaft-side of the cryogenic chamber.   
     
     
         17 . A system for delivering cryogenic fuel from a cryogenic fuel tank to an engine comprising:
 a hydraulic pump coupled to an engine oil reservoir;   a first electrohydraulic valve of a plurality of electrohydraulic valves coupled to the hydraulic pump;   a first cryogenic pump of a plurality of cryogenic pumps, the first cryogenic pump including a hydraulic chamber coupled to the first electrohydraulic valve and a cryogenic chamber coupled to the cryogenic tank and the engine, the first cryogenic pump having a first piston in the hydraulic chamber coupled by a shaft to a second piston in the cryogenic chamber; and   a controller coupled to the first electrohydraulic valve, the controller configured to activate the first electrohydraulic valve in a sequence with the other of the plurality of electrohydraulic valves according to a fuel requirement of the engine, wherein the activation of the first electrohydraulic valve causes delivery of the cryogenic fuel to the engine via the first cryogenic pump.   
     
     
         18 . The system of  claim 17 , further comprising a feed pump that maintains pressure in a feed line that couples the cryogenic fuel tank to each of the plurality of cryogenic pumps. 
     
     
         19 . The system of  claim 17 , wherein the first electrohydraulic valve has a drain that channels hydraulic fluid from first cryogenic pumps to a reservoir for engine lubricating oil. 
     
     
         20 . The system of  claim 17 , wherein the cryogenic chamber has a pump-side and a shaft-side relative to the second piston, the shaft side including a gas bleed outlet that vents vaporized fuel that escapes around the second piston from the pump side to the shaft side.