US3485175A - Liquid fuel pumping apparatus - Google Patents

Description

Dec. 23, 1969 K. A. w. KEMP ET A LIQUID FUEL PUMPING APPARATUS Filed March 13, 1968 Q mm KEN ETH 87M 1- 3,485,175 LIQUID FUEL PUMPING APPARATUS Kenneth Albert Walters Kemp and Terence Redvers Wheeler, London, England, assignors to 'C.A.V. Limited, Acton, London, England Filed Mar. 13, 1968, Ser. No. 712,771 Claims priority, application Great Britain, Mar. 28, 1967, 14,060/67 lint. Cl. F04b 23/04, 19/02, 3/02 US. Cl. 103-5 2 Claims ABSTRACT OF THE DISCLOSURE A liquid fuel pumping apparatus for supplying fuel to a combustion engine, and comprising a pumping piston reciprocably accommodated within a bore, means for moving the piston in one direction to reduce the volume of the pumping chamber, a passage extending from the pumping chamber, a one way delivery valve mounted in said passage, and a spill path extending from the passage at a point intermediate the pumping chamber and the delivery valve, said spill path being arranged to be opened at a predetermined point during the movement of the piston in said one direction to release the pressure in the pumping chamber, thereby to permit said valve to close, and the effective area of said spill path diminishing during continued movement of the piston in said one direction.

This invention relates to liquid fuel pumping apparatus for supplying fuel to internal combustion engines and of the kind comprising a pumping piston reciprocably accommodated within a bore, means for moving the piston in a direction to reduce the volume of the pumping chamber defined by the piston and the bore, a passage extending from said chamber and through which fuel flows in a direction from said chamber to the engine and a one way delivery valve mounted in said passage, said valve being opened by the pressure of fuel created in said chamber when the piston is moved in said one direction the valve when closing serving to displace fuel in the direction opposite to said one direction.

The object of the invention is to provide such an apparatus in a simple and convenient form.

According to the invention in an apparatus of the kind specified a spill path extends from said passage at a point intermediate the pumping chamber and the delivery valve, said spill path being arranged to be opened at a predetermined point during the movement of the piston in said one direction thereby to relieve the pressure in the pumping chamber to permit said valve to close, the effective area of said spill path diminishing during continued movement of the piston in said one direction thereby to restrict the rate of flow therethrough.

One example of a liquid fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawing which is a part sectional side elevation of part of an apparatus in accordance with the invention.

Referring to the drawing there is provided a body part 10 in which is mounted a rotary cylindrical distributor member 11. The distributor member is coupled to an input shaft not shown and is arranged to be driven in timed relationship with the engine to which fuel is to be supplied. At one end of the distributor member is formed a transverse bore 12 in which is mounted a pair of reciprocable plungers 50. Moreover, surrounding the distributor member at this point is an annular cam 51 and having a plurality of diametrically disposed inwardly extending cam lobes. As the distributor member rotates the cam lobes act on rollers 52 respectively the rollers nited States Patent 0 imparting inward movement to the plungers. The plungers 50 together with the cam and rollers define a pressure pump.

The transverse bore 12 is in communication with one end of a bore 13 which extends longitudinally Within the distributor member. The opposite end of the bore is closed by means of a plug 14 and this end of the distributor member is coupled to the rotary part of a fuel feed pump 15. The outlet of the feed pump is in communication with a passage 16 formed Within the body part and the inlet of the feed pump communicates with a source of fuel.

The passage 16 is in communication with an annular feed gallery 17 which is formed on the body part and from which at one point, extends a cylindrical chamber 18. This chamber accommodates an angularly movable throttle member 53 which is arranged to proportion the flow of fuel through a pair of passages 19, 20. The passage 19 communicates with an annular passage and passages 19a and these together with the passage 20 extend to the cylindrical bore in the body part in which the distributor member 11 is mounted. Moreover, for registration with the passages 19a, passage 21 is provided and for registration with the passage 20 a passage 22. is formed in the distributor member. The passages 21 and 22 communicate with the opposite ends of the bore 13. The communication between the passages 19a, 20 and 21, 22 is arranged to take place during the filling stroke of the apparatus.

Mounted within the bore 13 is a reciprocable pumping piston 23 having an annular groove 24 defined in its periphery intermediate its ends. Moreover, the end portions of the pumping piston are of reduced diameter. The space defined by the pumping piston, the bore 13 and the plug 14 constitutes a pumping chamber 25 and from this chamber extends a delivery passage 26. The delivery passage is arranged to register in turn as the distributor rotates, with a plurality of outlet ports 27 formed in the body part and in communication respectively with nozzles 54 mounted so as to direct fuel into the combustion chambers respectively of the associated engine.

Also formed in the distributor member is a spill path which is constituted by a radial passage 27a which is in communication with the outlet passage 26 by means of a longitudinal groove 28 formed on the periphery of the distributor member, the groove 24 formed in the pumping piston 23 and a further radial passage 29 extending from the bore 13 at a point axially removed from the passage 2.7a. The further radial passage 29 during an injection stroke of the apparatus communicates with a spill port 30 defined in the body part. Furthermore, another radial spill passage 31 is formed in the distributor member and extends from the bore 13 at a point axially removed from the passage 29. The passage 31 is arranged to register during an injection stroke of the apparatus, with a spill port 32 formed in the body part and which is provided with a pressurizing valve 55.

The relative positions of the various passages in the distributor member will become apparent from the description of the mode of operation of the apparatus.

During a filling stroke of the apparatus when the plungers 50 are permitted to move outwardly by the cam lobes .fuel is fed by way of the passages 21 and 22 to the bore 13. The relative quantities of fuel flowing through these passages determines the amount by which the pumping piston moves towards the transverse bore 12. The quantity of fuel which enters by Way of the passage 22 determines the quantity of fuel which will be supplied during the next injection stroke of the apparatus. It should be pointed out that during the filling stroke the passages 26, 27a, 29 and 31 are closed. At the end of the filling stroke the pumping piston 23 will have assumed a position to the left of that in which it is shown in the' drawing and the bores 12, and 13 will be completely filled with fuel.

As the distributor rotates the delivery passage 26 will be brought into register with an outlet port 27 and the passages 21 and 22 will be moved out of register with the passages 19:: and 20 respectively. During continued rotation of the distributor member inward movement will be imparted to the plungers 50 and fuel under pressure will act on the left hand end of the pumping piston 23- and cause it to be moved towards the plug 14. During this movement fuel is expelled from the pumping chamber 25 and flows by Way of the delivery passage 26 to the outlet port. It should be mentioned that each outlet port is provided with a delivery valve 56 which is spring loaded and which opens to permit the flow of fuel to the injection nozzles. Moreover, when the pressure in the pumping chamber is relieved as will be described, the delivery valve 56 closes and in so doing a predetermined small quantity of fuel is urged in the reverse direction to that in which it flows during the delivery of fuel to the engine to provide rapid relief of pressure at the injection nozzle to terminate delivery abruptly but to retain a controlled residual pressure in the delivery pipe.

At a predetermined position in its movement towards the plug 14 the groove 24 on the pumping piston 23 is exposed to the radial passage 27a. Moreover, the groove 24 is exposed to the further radial passage 29 and this is in communication with the spill passage 30. The result of this is that the pressure of fuel within the pumping chamber is relieved and the delivery valve 56 closes. The fuel which is forced back by the delivery valve flows through the spill path previously defined and in addition to this quantity of fuel the surplus fuel from the pumping chamber 25 also flows throgh the spill path.

The pumping piston continues its movement towards the plug 14 and during this movement the effective area of the spill path is reduced so that the rate at which fuel can flow through the spill path is reduced. The reduction in the area of the spill path is brought about by the fact that the groove 24 is moving out of register with the further radial passage 29. At the same time the end of the pumping piston is covering the delivery passage 26 and as soon as this passage is completely covered by the pumping piston an hydraulic lock is created in the pumping chamber 25. The hydraulic lock prevents further movement of the pumping piston and this is brought to a halt in a predetermined position. As soon as the pumping piston is halted surplus fuel contained Within the bore 12 and the end of the bore 13 in communication therewith, flows through the passages 31 and 32, past the pressurising valve 55 which is located in this passage.

The restriction of the spill passage as described minimises the risk of cavities forming in the respective outlet ports 27 when the delivery valves 56 therein contact their seats. The closing of the delivery passage 26 to create an hydraulic lock in the pumping chamber likewise prevents cavitation in this chamber.

At the end of the injection stroke the pumping piston is therefore in a predetermined position and there are no cavities in the pumping chamber, so that the quantity of fuel which flows through the passage 22 during the next filling stroke is exactly the quantity of fuel which will be supplied to the engine during the next delivery stroke neglecting the leakage which takes place.

Having thus described our invention What we claim as new and desire to secure by Letters Patent is:

1. A liquid fuel pumping apparatus for supplying fuel to an internal combustion engine and comprising a member in which is defined a bore, a pumping piston reciprocably accommodated within the bore, a pressure pump for supplying liquid under pressure to one end of said bore thereby to move the pumping piston in one direction towards the other end of the bore, the pumping piston and the other end of the bore defining a pumping chamber, the volume of which is reduced during movement of the pumping piston in said one direction, a delivery passage extending from said pumping chamber and through which fuel flows from the pumping chamber to the associated engine during movement of the pumping piston in said one direction, a one Way delivery valve mounted in said passage, said valve being opened by the pressure of fuel created in said chamber when the piston is moved in said one direction, the valve closing when said pressure is relieved and acting to allow a small quantity of fuel to flow towards the pumping chamber, a spill path extending from said passage at a point intermediate the pumping chamber and the delivery valve the spill path being arranged to be opened at a predetermined point during the movement of the piston in said one direction thereby to relieve the pressure in the pumping chamber to permit said valve to close, the effective area of said spill path diminishing during continued movement of the piston in said one direction thereby to provide increasing restriction to the flow of fuel therethrough.

2. A liquid fuel pumping apparatus as claimed in claim 1 in which said delivery passage extends laterally from said bore at a position to be covered by said piston at the end of the movement thereof in said one direction, and in which said spill path as defined by a pair of passages which break into said bore at axially spaced points and by a groove formed in the periphery of the piston, one of said pair of passages communicating with the first mentioned passage and the other of said pair of passages communicating with a drain, said groove serving to place said pair of passages in communication with each other at said predetermined point during the movement in said one direction of the piston, further movement of the piston serving to move the groove out of registration with one of said pair of passages thereby to restrict the rate of flow of fuel through said spill path.

References Cited UNITED STATES PATENTS 2,178,902 11/1939 Clausen 103-41 2,384,011 9/1945 Bremser 103-41 3,115,838 12/1963 Koester 103-4l 3,320,893 5/1967 Koster 10341 3,356,031 12/1967 Glikin 103-2 WILLIAM L. FREEH, Primary Examiner U.S. Cl. X.R. 1032,

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