US2449468A

US2449468A - Fuel injection system for internalcombustion engines

Info

Publication number: US2449468A
Application number: US638129A
Authority: US
Inventors: Greenland Leonard Sidney
Original assignee: HM Hobson Ltd
Current assignee: HM Hobson Ltd
Priority date: 1945-02-12
Filing date: 1945-12-29
Publication date: 1948-09-14
Anticipated expiration: 1965-09-14

Description

Sept. 14,1948.

L.. s. GREENLAND FUEL'INJECTION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed Dec. 29', 1945 s Sheets-Sheet 1 Sept. 14, 1948. L. s. GREENLAND' 2,449,463

FUEL mmcnon SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed Dec. 29, 1945 I 3 Sheets-sheaf? Sept; 14, 1948. L. s. GREENLAND 2,449,468

' FUEL INJECTION SYSTEM FOR INTERNAL-COMBUSTION ENGINES Filed Dec. 29, 1945 3 sheets -sheet 3 Patented Sept. 14. 1948 FUEL INJECTION SYSTEM FOR INTERNAL- COMBU STION ENGINES Leonard Sidney Greenland, Weston-super-Mare, England, assignor to H. M. Hobson Limited, London, England, a company of Great Britain Application December 29, 1945,"Serial No.

i In Great Britain February 12, 1945 4 Claims. (Cl. 123-119) This invention relates to fuel injection systems for internal combustion engines of the type in which fuel is fed under pressure by an engine driven fuel pump to a metering unit, comprising a variable area fuel metering orifice, means for varying the area of said orifice as a desired function of boost pressure and preferably also of exhaust back pressure and induction temperature,

' and means controlled by a centrifugal impeller coupledto the pump for establishing across the metering orifice a metering pressure which is some fraction of the pressure difference developed by the impeller. In injection systems of this type, as is well known, the metering pressure is substantially proportional to the square of the.

engine speed and the now of fuel through the orifice varies as a substantially linear function of engine speed.

It has hitherto been the practice to construct the fuel pump and impeller as a single unit-separate from the metering unit and connected thereto by pipes for carrying the main fuel supply and transmitting the metering pressure. This is disadvantageous for the fol owing reason. The

pressure difference generated across the impeller According to the invention the fuel pump and iil'ipeller are built into the metering unit and a readily detachable coupling is provided between the fuel pump and the impeller. so that the pump can be removed, if required, without disturbing the impeller. This arrangement has two advantages. Firstly the connections for applying the metering pressure from the impeller to the orifice can be constituted by short drilled passages in the housing of the metering unit, which will reduce pressure losses to a minimum and dispense with the many variables inherentin the use of pipes. Another advantage is that once the impeller is 'built into the metering unit, it remains with the unit, and when the fuel pump is changed the fuel metering system is not interfered with in any way. Thus a pump could bechanged on an engine in service without any fear ofthe fuel flow characteristics being altered in any way. In

' however, if the pump is changed the-impeller is the case of a separate pump and impellerunit,

changed with it and the accuracy of the metering system with the new pump will depend upon the similarity of the two metering impellers.

In service it is much more usual for a fuel pump 4 to failthan for the fuel metering unit to fail. Apart from the impeller, there are no parts in the injection system subjected to high speed movement and the impeller itself is not likely to be subjected to wear; on the other hand, a fuel pump unit with its gears or vanes and glands,-

is subjected to wear and has to be removed more frequently than the metering unit. a It is also subject to mechanical breakdown due to foreign matter entering the pumping unit.

One specific form of fuel injector for aircraft engines according to the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which:

Fig. 11s a diagram illustrating the operation of the injector,

Fig. 2 is an exploded perspective'view of the injector, and

Fig. 3 is a horizontal section, through the in- :Iector.

Like reference characters designate like parts throughout the figures.

The general operation of the injector will first be described with reference to Fig. 1, and the specific construction of those parts of the apparatus which are concerned with the ready removal and interchange of the fuel pump will thereafter be described with reference to Figs. 2 and 3.

The apparatus shown in Fig. 1 is fully described in my copending U. S. application Serial No. 638,128. filed December 29, 1945, and now Patent No. 2.438,631, and it will be suflicient here to explain that fuel is pumped from an inlet ill by an engine-driven gear wheel pump H to a high pressure chamber 12 and thence through a I 6, linked by a bell crank lever ll, pivoted at It.

to a pressure regulating valve I9. The fuel leaves chamber. Ii via the pressure regulating valve and passes on through a pipe 20 and past a balanced discharge valve 2 i to a discharge nozzle 2?! through which it is injected into the induction pipe 23.

The pressure difference across the meterin orifice i3 is maintained substantially proportional to the square of engine speed by utilising the difference of pressure generated across a centrifugal impeller 24 coupled to the pump i I by a dog clutch 25 and deriving movement from the engine by 3 means of a shaft 26. The pressure at the tip of the impeller 24 is applied via a conduit 21 to the entry side of the metering orifice and the pressure at the eye of the impeller is applied by a conduit 28 to chamber I4. The diaphragm I6 and pressure regulating valve I9 therefore operate, as described in U. S. Patent No. 2,374,844, to maintain across the metering orifice I3 some fraction of the pressure difference developed by the impeller 24. 29 is a vent orifice for allowing air or vapour which may collect at the eye of the impeller to vent forward to the downstream side of the metering orifice I3. A biasing spring 30, operating on the diaphragm I6 serves to enrich the mixture at slow running as described in my copending U. S. application Serial No. 638,128, filed December 29, 1945. Adjustment for initial tuning is provided by an orifice 3| adjustable by a screw 32, through which a small quantity of fuel can by-pa-ss the metering orifice.

The effective area of the metering orifice I3 is controlled by a needle valve 33, which is varied in position as a Joint function of boost pressure, exhaust back pressure and induction temperature. The first two corrections in the area of the metering orifice are provided by a pair of

balanced capsules

34, 35 located in the fuel chamber I2. Capsule 34 is exposed internally to boost pressure, being connected to the induction pipe '23 by a pipe 36. The greater part of capsule is evacuated, but the rear section thereof 31 communicates with the exhaust pipe 38 via conduit 39. To a trunnion 40 on a rod 4I connecting the free ends of the two capsules is pivoted a a forked lever 42, pivoted at 43 to the stem of the needle valve 33, and at 44 to a Bourdon tube assembly 45 which adjusts the position of the pivot 44 to conform with alterations in induction temperature under the control of a thermometer bulb 46. Capsules 34, 35 are anchored at their outer ends to the walls of chamber I2. Axial movement of rod 4| in response to expansion or contraction of the capsules, effects an appropriate change in the position of needle valve 33 by causing lever 42 to rock about pivot 44. On change in induction temperature, lever 42 adjusts needle valve 33 by rocking about trunnion 40.

41 is a lever, coupled to the pilot's throttle lever, and arranged, when moved rapidly in the direction to accelerate the engine (1. e. anticlockwise between the sloW running position S. R. and the full throttle position F. T.) to operate through link 48 an accelerator pump 49, so as temporarily to supply extra fuel to the engine through pipe 50. Link 48 is coupled to a bell crank I48. and as lever 41 is moved towards the full throttle position, a piston I49 is moved by bell crank I49 to the right. The resultant fall of pressure to the right of diaphragm I50 causes the latter to be displaced to the right, opening a valve I5I and allowing a temporary additional supply of fuel to flow to the pipe 20 via pipe 50. The diaphragm I50 slowly returns under the action of spring I52, displacing fuel from its left to its right hand side via a restricted orifice I53. A restriction I54 regulates the quantity of fuel supplied to the pump 49 during acceleration. A non-return valve I55 permits of unobstructed movement of piston I49 to the left when the lever 41 is moved to decelerate. When the lever 41 is moved clockwise beyond the S. R. position, it closes a cut-off valve 52 which is normally held open by a spring 5I.

The pump II is provided with a diaphragm engine is stationary.

operated relief valve 52 for returning excess fuel valve, through which fuel can be supplied to the engine by a. priming pump at times when the 56 is a normally closed the capsules and is formed with an aperture 92 by which atmospheric pressure-which in this instance is taken as a measure of exhaust back pressure-is applied to the interior of capsule 31. To the front of housing 51 is fitted a fuel pump body 63, which fits over threaded studs 94 on the 7 housing 51, and is held in position by nuts (not shown) fitted to said studs. A fuel pump assembly fits inside the body 33 being located in position by a cover plate 66 and bolts '81 which pass through holes 88 in the assembly 33 and are screwed into tapped holes 69 in the body 83. The

whole is covered by a screwed ring 19 which screws over threads II on the body 33.

The gear pump has two gear wheels I2, I3

mounted on spindles 14, II respectively. When the parts are assembled, as shown in Fig. 3, spindle 14 engages via dog clutch 25 with the drive shaft 26 carrying the impeller 24, and spindle I5 abuts via a washer I6, with the priming valve 55. A spring 11 is provided adjacentthe dog clutch, and the shaft 29 carries a pinion I8 by which it derives motion from the engine. Spring 11 urges shaft 28 to the right as seen in Fig. 3, to maintain a bearing member I9 adjacent the impeller 24 pressed against a carbon disc 89. Spring I1 thus prevents the shaft 29 from moving to the left suificiently for the lefthand face of the impeller to foul the right-hand face of the pump body 63. Spring ll forms part of a seal for preventing leakage of fuel along the shaft 26. Spring 8I presses a sealing housing 22 against a carbon ring 83 anda bearing member 84 against a carbon ring 85. A sealing element- 33 is disposed between the housing 92 and the shaft 28.

It will be apparent that the pump II can readily be removed and changed without disturbing the impeller 24, by unscrewing the cap I0 and removing the cover plate 66. If the gear wheels only are damaged, the assembly 95 and gear wheels are removed and replaced, but if the damage to the pump is .more extensive the pump body 63 is also removed. In either case the impeller 24 is undisturbed, and the new pump is at once coupled to the impeller by means of the dog clutch. The weakest section of the drive shaftis arranged to be at the location I14 on the pump driving spindle 14 on the pump side of the dog clutch 25 so that in the event of the gear pump seizing up, the shaft will break at I" in the gear pump, and the drive shaft 26 running through the metering unit and carrying the impeller 24 will not be damaged.

During priming of the engine, fuel is pumped by a priming pump into the inlet I9 and passes thence through the hollow spindle II and the then open priming naive to the chamber l2 and thence to the engine.

What I claim as my invention and desire to segine driven fuel pump, an enginedriven' cen-.

trifugal impeller; a. metering unit, and means for supplying fuel from the fuel pump to the metering unit, said metering unit comprising, within an enclosing housing. a variable area fuel metering orifice, means for varying the area of said orifice as a desired" function of boost pressure and means controlled by said impeller forestablishing across the meteringorifice a metering pressure which is some fraction of the pressure diiference developed by said impeller, characterised in that said fuelpump and impeller are built into the housing of the metering unit and in that a readily detachable drive connection is provided between said pump and said impeller which permits of removal of said pump from said housing without disturbing said impeller and the means controlled thereby for establishing said metering pressure.

2. A metering unit for use in a fuel injection system for an intemai combustion engine, said unit comprising, within an enclosing housing, a fuel pump, a centrifugal impeller, a clutch connecting said pump and said impeller, a variable area fuel metering orifice. a conduit for supplying fuel from the pump to the metering orifice and thence to an outlet, means for varying the area of said oriflceas a desired function of boost pressure, mean for maintaining across said oriflce a metering pressure which is some'fraction of the pressure diflerence developed by said impeller, and a shaft for. driving the impeller, which shaft projects from said'housing and is adapted to be driven by the engine, a removable cover plate being fitted to saidhousing, which plate, when removed,'perrnits of withdrawal of said pump from thehousing by disengagement of the clutch and without disturbing theimpellere 3. A metering unit as claimed in mama, in

"which the pump has a drivespindlefor trans-.

drive spindle being weaker than the impeller mitting the driv theretofrom the clutch, said drive shaft, "so that it will break in preference to the impeller driv seizure.

4. A metering unit as claimed in claim 2,5111 1 which the fuel pump is agear wheel pumpand the clutch is a dog clutch. a

LEONARD SIDNEY GREENLAND.

REFERENCES cITnn The following references are of record in the file of this patent:

UNITED STATES PATENTS England v July 25, 1940 shaft in the eventof pump;