US2333698A

US2333698A - Fuel injection apparatus

Info

Publication number: US2333698A
Application number: US271291A
Authority: US
Inventors: Albert T Bremser
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1939-05-02
Filing date: 1939-05-02
Publication date: 1943-11-09
Anticipated expiration: 1960-11-09

Description

. Nov. 9, 1943.

A. T. BREMSER 2,333,698

INVENOR.

fvwww M ATTORNEY.

Patented Nov. 9, 1943 UNITED STATES PATENT oFFl-cE asssss y `Eahsttzfnfs2vshmh Appuuoamy 2, 1939, serial No. 271.291

19 claims. 'This invention relatesto pumping apparatus and more particularly to liquid pumping means such as fuel injection pumps for use in connection with solid fuel injection internal combustion engines.

In port-controlled fuel pumps heretoforev provided for injecting solid liquid fuel into internal combustion engine cylinders, considerable diillculty Ahas been .experienced in providing an eillcient seal at the intake and by-pass ports in the pump cylinder without causing undue wear of the 'pump piston and cylinder wall which in turn shortens the life of the pump and alters the fuel metering characteristics thereof. Furthermore, in pumps of the above character heretofore provided 4the personal attention of an operator is required to start the flow of fuel through the pump when a substantial quantity of air collects in the pressure chamber thereof.

One of the objects of the present invention is to provide'novel fuel injection apparatus whereby the foregoing diiculties and disadvantages are obviated.

'Another object of the invention is to provide novel liquid pumping means wherein the fluid pressure acting on the side walls of the pump plunger is controlled in a novel manner.

Another object is to provide a novel port con'- trolled fuel injection pump which is so constructed as to minimize erosion of the edges of the fuel ports and the edges of the metering grooves in the pump plunger.,

Still another object is to provide novel valve means in combination with a fuel injectionpump whereby the latter is prevented fram becoming air-bound.

A further. object is to provide novel retraction valve means in thefuel injection system `of an internal combustion engine.

A still further object is to provide novel fuel pumping apparatus which is so constructed that wearis reduced to a minimum and accurate metering, which entails good sealing, is assured. Still another object is to provide a novelty constructed pump, the eilicient operating fe of which will be comparatively greater'than e life of similar devices heretofore provided.

The above and further objects and novel features of the inventionwill more fully appear from Vthe followingdetailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of, illustration only and are not intended to define .the

of the invention, reference for this latter purpose being had primarily -to the appended claims.

In the drawing wherein like reference characters refer to like parts throughout the several l0 parts broken away, the section being taken substantially on line 2-2 of Fig. 1.

Fig. 3 is a sectional view with parts broken away, the section being taken substantially on line 3-3 of Fig. 1.

1B A single embodiment ofthe invention is illustratedimthe drawing, by way of example, in the form of a fuel injection pump assembly having a novel delivery valve in combination therewith. In the form shown, said pump assembly com- `prises a tubular casing 5 having laterally projecting 'ears 6 by means of which the same may be connected to an engine or other support (not shown) in the usual manner. Mounted in casing 5 intermediate the ends thereof is a pump cylinder 1, th latter being supported on anA internal shoulder 8 in the casing and held against rotary i movement therein by a screw 9 which threadedly engages the casing wall and extends into an axially extending groove III-in the cylinder wall.

A-pair of axially spaced ports Il and I2 are provided in the wall of cylinder 1 adjacent the upper end thereof, as viewed in the drawing, for directing the flow of fuel to a'nd from the pump cylinder in a manner to more fully appear hereafter.

SlidabLv extending into the lower end of cylinder 1 is a pump plunger or piston I3 which also -functionsoas Sa slide valve for controlling the flow of fuel through ports II and 1'2. For a purpose which will more fully appear from the 40 description of the operation which follows,

plunger I3 is provided with an axially extending passage Il and a radial passage I5 which continuousw connects the upper end or pressure chamber of cylinder I to a helical groove I6 in the surface of piston I3, which groove cooperates with port I 2 and constitutes a metering or cut-off groove. If desired, a somewhat smaller helical groove I1 may be provided in the surface of piss ton Il diametrically opposite groove I8, the latter 5o having continuous communication with passage Il and being adapted to act'asja lubricating pressure balancing groove.

Means are provided -for angularly -adjusting piston I3 to change the relation between metering groove I6 and cut-off or by-pass port I2 and Y shoulder in casing 5 and is held thereby vary the edective pumping stroke of the Piston. In the form shown; said means comprise a sleeve I8 loosely surrounding the lower end of cylinder I in an enlarged portion of casing 5, Gear teeth IS are formed on the upper end of sleeve I8 for cooperation with a rack 2B slidably mounted in casing 5, the movement oi' said rack being limited by any suitable means well-known in the art. such as a set fscrew extending through the wall of casing 5 into a groove in said rack. The lower end of sleeve I8 is axially slotted. as at 22, for slidably receiving a cross-bar 23 rigidly connected to plunger I3. Sleeve I8 is held against axial movement relative to cylinder 'I by an internal shoulder I8' which engages the lower end of `saidicylinder and an external shoulder which rests on the upper surtace of an inwardly extending flange on a ring 2t. The latter is positioned against an internal in place by any suitable means, such as a snap ring 25. It'wlli thus be seen that by reciprocating rack 2u, alignlar adjustment of sleeve I8 and hence plunger I3 may be eiected without hindering the longitudinal or pumping movement of the latter.

Means are-also provided for reciprocating piston I3 in cylinder l without subjecting the former to any lateral force or pressure which would cause unnecessary friction and binding. Said means in the illustrated embodiment include a tappet cup 2S slidably positioned in the lower end of casing for engagement with an enlarged headV portion 21 at the lower end of piston I3. The

latter may be moved upwardly by a rotating cam or other suitable means (not shown) which is adapted to engage the closed end of tappet cup 26 in a manner well understood in vthe art. The return or downward movement of piston I3 is effected by a spring 28 interposed between the internal flange of ring 2li and a slotted 'washer 29 which engages the upper shoulder of head 2l.

The upper end or pressure chamber of cylinder I may be connected by any suitable means toV an injection nozzle (not shown) at an internal combustion engine cylinder. The means shown for this purpose comprise an adapter element 33 which constitutes a guide and seat for a novel delivery valve 3|. Adapter 30 rests upon the upper end of cylinder I and is held in fluid tight engagement therewith by la nipple or a sleeve nut 32 which engages internal threads in the upper end of casing 5. Adapter 30 thus completes the pressure chamber vof the pump and, in effect, forms a part of the pump cylinder. A suitable packing washer 33 may be interposed between the inner end of member 32 and an eirternal flange 'on adapter 3B to further insure uid tightness. The upper' end of member 32 terminates in a threaded portion 3d having a delivery passage 35 therein whereby a delivery conduit (not shown) leading to a fuel injection nozzle Vof an engine cylinder maybe attached.

Adapter has a differential cylindrical passage therein through Which the flow of fuel from cylinder 'I into member 32` and delivery conduit is controlled by the novel delivery valve 3| which functions in a 4novel manner to -prevent the pump from becoming airbound and to relieve the /pressure in the delivery passages between the pump and injection nozzle during the suction stroke of piston I3. As shown, the central portion of valve 3| which is provided with axial flutes or grooves 36 (Fig. 3) serves to guide the valve in the central passage in adapter 3Q and yet permits the-flow of fuel through the latter when the valve is in fully open position. Adjacent the upper` end of valve 3| is a; piston portion 3l -of limited extent which .is adapted to slidably t into said adapter passage and at its lower end said valve is provldedwith a tapered head portion 38 adapted to engage a valve seat formed in the adapter adjacent the pressure chamber of pump 1, I3. Valve 3| is yieldingly held on said seat by a coll spring 39 that engages piston portion 31 and is centered within member 32 by a tubular member 40. The latter has continuous communication with the interior of member '32.and with passage 35 and, in addition, may flmction as a stop for limiting the opening movement of valve 3|.

ln order to minimize erosion and the effects thereof and to insure smooth and consistent suction by pump I3, means are provided in casing 5 for directing the ow of fuel to and from cylinder 'I through ports and I 2. Preferably said means are constituted by an insert or lining 4I of stainless steel or other hard material, cast or otherwise fixed, in a peripheral groove or recess formedin casing I5. Lining 4| and said casing are provided. with registering openings 42 and 63, respectively, which communicate with a source of liquid fuel (not shown) through conduits do and 45, said openings being circumferentially spaced from and preferably diametrically opposite ports I I and I2.

Lining 4|=is channel-shaped in radial cross-section to provide a fuel passage around cylinder I and is provided with a radially extending internal vrib 46 which engages the outer wall of cylinder 'I To further insure against erosion adjacent cut,

oi port I2, a hardened steel screw 50 may be threaded into casing 5 with the pilot tlp thereof extending through insert 4I radially outward from y said cut-od port. Screw or plug 5I! may also be used as a vent plug when the pump is mounted in a horizontal position. A vent plug 5| is provided for this latter purpose when the pump is mounted in an upright position.- Screw 50 may also be replaced by a pipe Vtting and this tting connected to an outside conduit so that the fuel which is by-passed through port I2 may be returned to the fuel supply tank without first entering the Supply line attached to fitting 45. In the latter case. internal rib 4I may completely surround cylinder I so that

grooves

41 and 48 may communicate with each other only by way of ports Hand i2, passage I4, I5 and groove I6.

Novel means are provided in the pump comprehended by the present invention to insure a tight seal at ports Il and I2 during the-effective pumping stroke of plunger I3 and thus prevent leakage and erosion of the sharp edges of said ports and metering groove I s without breaking the lubricating iilm vbetween the plunger and cylinder walls on the side of-said ports. Said novel means comprise one or more small pressure relief ports 52, one such port being shown diametrically opposite and in a plane between ports ii and i2.

in pumps of the character described above, a slight clearance is provided between plunger I3 and the walls* of cylinder 'i so that a lubricating Passage 'stroke bylsuitable cam means the upward minimize wear and prevent seizing. During the effective pumping stroke of the plunger this luv bricating nlm is naturally under high pressure due to the high pressure in the pressure chamber of the pump and if relief port 52 is not provided. a, momentary leakage from ports II and I2 occurs and reduces the film pressure on the left side of plunger I3, as viewed in mitting the undiminished film pressure on the right side to press the plunger firmly against the ported side. This insures a good seal at said ports but if the fuel contains even a slight amount of grit or dirt, as most fuels do, considerable wear of the plunger and cylinder wall occurs adjacent the parts due to the absence of a lubricating film in this region. Too much\ wear and lack of lubrication may cause seizing and cutting. By providing relief port 52 which opens into the supply Il or other low pressure chamber the fuel nlm pressure on the right side. of plunger I3 lmay be controlled and reduced so that suiiicient pressure is exerted thereby in the direction of ports II and I2 to insure a good seal at said ports without breaking the lubricating film on that side of the plunger. Some leakage through port 52 will occur .but this leakage is constant and does not affect the metering accuracy of the pump.

In the operation of the above-described assembly, plunger I3 is reciprocated with a constant and spring 23 ln a manner well understood in the art and fore briefly described. On the of the plunger, as soon as the latter completely covers intake port Il, pressure is built up in the upper end of cylinder 1 which is suflicient to lift valve 3| oif its seat and continue the movement heretoupward movement I maybe of adapter Il a quantity of the compressed air will be trapped in the cut away portions or iiutes the drawing, thereby per- V thereof until piston portion 31 moves out ofthe passage in adapter 30. Continued upward movement of the pump plunger forces fuel. past the head 3l of valve member 32 and passage 35 to the injection nozzle.

During this pumping stroke the pressure of thev I3 is so distributed by reason of relief ports 52 tained at ports II and I2 without film onthe side of said ports. When the desired quantity of fuel engine cylinder, as -determined by the angular seating of piston cut-off port i2, thereby permitting' a free dis charge of fuel and relieving the pressure in the pump, whereupon delivery valve 3| isv closed by spring 39 and the fuel pressure acting on the upper end thereof. o

VfoAiEter the lower edge of piston portion 31 of valve 3| enters adapter or `closing movement of the valve to seated position increases the available space for fuel b'etween the upper end tion nozzle without increasing the volume of fuel in the delivery passages. Accordingly, the pressure of the fuel remaining in thev delivery passages is reduced by the retraction of valve 3| and obviates any dribbling of fuel at the nozzlenA It will also be seen that retraction valve 3| is novelly constructed to insure operation of pump 1, I3 under circumstances pumps having retraction valves of the tofore known type herechamber of cylinder 1 stroke vof piston I3 and lift valve II of! its seat. Even though the lift of the valve 3l, along flutes or grooves 30 in the walls of the valve and, thence, through has been injected into the 30 continued downward of the valve and the injecto become air-bound. If. for exam.4 ple, a quantity of air accumulates in the pressure it will be compressed on breaking said I3, metering groove I6 overlaps changes the point which would cause` It when metering groove Itregisters with port I2 and permits valve 3| to snap back on. its seat. Thus, on the next downward or suction stroke of plunger I3 some fuel is drawn into the pump pressure chamber to replace the air trapped by the delivery-valve. This process continues-until the air ls sulciently compressed to fully open valve 3|, i. e., to move piston 3 1 out of adapter 30, and permit the air to discharge through the delivery passages into the engine cylinder. The necessity for manually venting the pump is thus obviated.

The instant that metering groove Il moves into overlapping relation pressure stroke of plunger I3 the fuel in the upper end of cylinder 1, passages Il, Ii and grooves I6 and I1. is under tremendous pressure. Accordingly. fuelis discharged through thesmall initial opening of port I2 at an extremely high velocity and strikes the walls of casing i, 4I. This sudden rush of fuel through the initially small opening tends to result in erosion of the pump casing and a. breaking up or atomization of the fuel, as well as a setting up f fuel turbulence. The provision of the hard metallic insert di and hardened steel plug 50 substantially reduces erosion caused by the discharge of the high pressure fuel through cut-o port I2 and permits the' use oflight alloys, such as aluminum alloys. for pump casing 5 and'theprvision of'rib' or partition I6 in of the discharged fuel or the atomization thereof from materially affecting` the intake of fuel through port II.' Accordingly, after plunger I3 reaches the top of its stroke and is moved downwardly by spring 28, metering groove I6 is moved out of registry with port I2 so that further movement of the plunger creates a vacuum in cylinder 1. When the plunger uncovers intake port II the comparatively undisturbed vsolid fuel adjacent said port in groove 41 is drawn intocylinder completely lling the space therein so that the pumping of a predetermined charge to the engine cylinder during the nextupstroke of the pump piston is insured.

To vary the effective pumping stroke, and, hence, the quantity of. fuel pumped into the engine cylinder during each pressure stroke of plunger I3, rack 20 is moved to the right or left, as viewed in the drawing,- to thereby angularly adjust sleeve i8 and hence plunger I3.' It will be clear that angular movement of the latter in the upward stroke ofthe plunger at which helical groove I6 begins to overlap cut-off port I2 and accordingly varies the eiective pumping stroke of the plunger. For

idling, piston I3 is turned Vsuillciently in a counter-clockwise direction, as viewed from the top so that groove I6 will register with port I2 durthe full upward movement of is so constructed as to operate efficiently with minimum wear over a long period of time and which is adapted to maintain accurate metering over4 long` periods of use. The novel pump construction provided includes means; whereby a 1ubricating film is maintained at all times completeinsunlcient to move piston portion 31 out with pOl't l2 0n the.

said insert prevents the turbulence plunger while insuring at. the same time good sealing vat the inlet and by' pass ports controlled by the plunger. Addition- Y ally, a novel retraction or delivery valve is provided in combination with the pump whereby the latter will not become air-bound.

Although only a single embodiment of the invention has been illustrated and described in detail it is to be expressly understood that the same is not limited thereto. For example, plug 50 as well as balancing or lubricating groove il may be eliminated if desired. Various changes may also be made in the design and arrangement of parts illustrated, as will now be understood by those skilled in the art, Without departing from the spirit and scope of the invention. For a dellnition of the limits of the invention reference is had primarily to the appended claims.

What is claimed is:

l. In apparatus of the class described, a cylinder having axially spaced inlet and by-pass ports in only one side thereof. a plunger recipthrough said ports, and port means in saidcylinder opposite said mst-named ports for reliev` lng the fiuid pressure between adjacent surfaces of said plunger and cylinder'during the pressure strokes of saidl plunger, said port means being covered by said plunger and connected to a low pressure space outside of the cylinder.

2. In apparatus of the class described, a cylinder having axially spaced inlet and by-pass ports in only one side thereof, a reciprocable plunger having a working' clearance in said cylinder for controlling dow through said ports, and at least one relatively small pressure relief portin the other side of said cylinder opposite said first-named ports -for relieving the fluid pressure in the clearance space between said plunger and cylinder in the vicinity of said relief Dort.

3. A fuel injection pump assembly comprising a cylinder having inlet and by-pass port means .rocable in said cylinder for controlling iiow port with said chamber after the piston reaches a predetermined point during the pressure stroke said ports connecting the interior of the cylinder with a low pressure space outside of the cylinder, said opening being covered at all times by said piston.

6. In a fuel pump, a cylinder having axially spaced inlet and by-pass ports in only one side thereof and a piston in said cylinder adapted to form a pressure chamber therewith, saidY piston having a working clearance in said cylinder for reciprocation therein to vary the volume of said pressure chamber and control iiow through said portstoandfromsaidchamberandagroove on the periphery of the piston in continuous communication with said pressurev chamber and adapted to register with the by-pass port, and said cylinder having a pressure relief port in the other side thereof opposite said mst-named ports connecting the clearance space between said piston and cylinder with the exterior of the cylinder, said relief port having a smaller cross-sectional area 'than said mst-named ports.

7. A fuel injection pump comprising a cylinder and a reciprocating piston having a working clearance in said cylinder and cooperating therewith to form a uid pressure chamber, said cylinder having only one inlet port adapted to communicate with said chamber and an outlet port in the same side thereof as said inlet port, said piston being adapted to cover Said inlet port during the unal portion of the pressure stroke thereof and having parts thereof cut away for connecting said outlet port with said chamber after the piston reaches a predetermined point during the pressure stroke thereof, and said cylinder having a relatively small opening in the in only one side thereof, a plunger reciprocable in said cylinder for controlling iiow to and from the cylinder through said port means, @11d port means covered by said plunger and circumferentially spaced more than 90 from said rst-named port means for relieving, without eliminating, the uid pressure between said plunger and cylin'der opposite said first-named port means which tends to press said plunger toward `said rstnamed port means during a, pressure stroke of theplunger.

4. A iiuid pressure pump comprising a ,cylinder having port means in one side thereof and a reciprocable plunger having a working clearance in said cylinder for controlling the ow through said port means, said cylinder having a small bleed port in the other side thereof continuously covered by said plunger, said port being so located that durlng the eiective pumping stroke of said plunger the iluid pressure in the clearance space between the sides of said plunger and cylinder which tends to press Said plunger toward said port mean is relieved in the vicinity of .said port.

.5. A fuel injection pump comprising a cylinder and a piston reciprocable in said cylinder and cooperating therewith to form a uid pressure chamber, said cylinder having only one inlet port adapted to communicate with said pressure chamber for supplying fuel to the latter and an outlet port in the same side thereof as said inlet port, said piston being adapted to cover said inlet port during the pressure stroke thereof and having parts'cut away for connecting said outlet other side thereof opposite said ports connecting the clearance space between said piston and cylinder with a low pressure space outside the cylinder, the cross-sectional area. of said opening being such in comparison tothe corresponding areas of said ports that a greater iiuid. pressure lwill exist in said clearance space on the side of said opening than-on the side of said ports during the pressure strokes of the piston, said greater uid pressure being adapted to hold said piston lightly against the side of the cylinder containing said ports.

8. Apparatus of the class described comprising a cylinder having an inlet port v-nd anoutlet port at one side thereof, said ports being spaced axially oi the cylinder from each other, and .a reciprocable plunger having in said cylinder for controlling flow to and from the latter through said ports, said cylinder also having other side thereof, said relief port having constant communication with a low pressure chamber outside of said cylinder and being so located as to cause a reduction of the pressure between the plunger and the wall of the cylinder tending to press said plunger toward said pair of ports during the eiective pumping stroke of said plunger, the inner end of said relief port terminating in the inner working surface of the cylinder and being small in comparison to said rst-named ports. f

9. Apparatus of the class described comprising a cylinder having a pair of axially spaced ports in one side thereof and a. relatively small relief port in the other side thereof, the inner end of said relief port terminating in the plane a working clearance at least one pressure relief port in the parlson to of are inner wan of said cylinder and navingsn area smaller than the area of either of said pair of ports, and a plunger reciprocable .in said cylinder for controlling the dow of fluid to and from the latter through said pair of ports and for covering said relief port..the latter being so located as to cause a reduction ofthe pressure between the plunger and the wall of the cylinder tending to press said plunger toward said pair of. ports during the effective pumping stroke of the plunger. 1

10. Inapparatus of the class described, a cyl. inder having a pair of axially spaced ports in one side thereof. and a plunger reciprocable in said cylinder for controlling the iiow of' iiuid to and from the latter through said pair of ports, said cylinder also having a. relatively small pressure reliefport in the other side thereof, said relief port being so located as to eiIect a reduction in. without eliminating. the resultant pressure tending to press said plunger toward said pair of ports during the effective pumping stroke said plunger. the inner end of said relief port terminating in the sliding surface of the cylinderengaged by said plunger and having an area smlatller than the area of either of said pair of P0 11. In apparatus of the class described. a cylinderhavingapairofaxiallyspacedportsinone.

side thereof. and a plunger reciprocable in said cylinder for controlling the flow of fluid to and from the latter through said pair of ports, said cylinder also having a pressure relief port in the other side thereof opposite said pair of ports, said relief port having constant communication with a low pressure space outside the cylinder and being adapted to pressure between the plunger and cylinder in a localized area surrounding the inner end of said relief port. the area of the inner end of said port being smaller than the transverse areaof either ofsaidpairofports.

f 12. In apparatus of the class described. a cyl- Inder having port means in one side thereof, and a reciprocable plunger having a working clearance in said cylinder for controlling ow to and from the latter through said -port means, said cylinder also having at least onepressure relief port in lthe other side thereof having constant communication with a low pressure chamberloutside of said cylinder. said pressure relief port being covered by the same longitudinal portion of the plunger which covers said portl means and being small in comparison to said -port means.

the location of said rellef'port being such as to cause a reductionv in the pressure between the plunger and the wall of the cylinder tending to press said plunger toward said port means durbeing such as to cause a plunger toward said first-named ports during partially relieve the iiuid stant communication with a low pressure chamber outside of said cylinder.

14. A port-controlled fuel iniection pump comprising a cylinder having a pair of axially spaced ports in one side lief port in the other side of said cylinder having anareabsmaller than the area of either of said pair of ports, and a slotted plunger reciprocable in saidcylinder for controlling the .now of iiuid to'and from the pressure chamber of the pump through said pair of ports and for covering said relief port, said relief port being so positioned as to reduce, without eliminating. the fluid pressure which occurs between, the plunger and the wall of the cylinder Opposite said pair of ports and tends to press said plunger toward -said pair of ports during the eifective pumping stroke of said plunger. 1

15. In a fluid pressure pump.l a cylinder having axially spacedinletand by-pass ports at only one side thereof, a plunger reciprocable in said cylinder for controlling iiow through said ports. saidplunger having an indented portion adapted to cooperate with said bye-passport to 's relieve the pressurin the pressure chamber in said pump. and at least one additionalport Vof small size in said cylinder having communication with a low pressure space outside of the cylinder. said last-named port being in the opposite side of said cylinder from said mst-named ports and covered by said plunger at ciprocation of the latter. the position of named port relative to 'said first-named ports reduction in, without eliminating. -the pressure tending to presssaid the effective pumping stroke of the plunger.

16. A. fuel injection pump comprising a cylin said cylinder for controlling the flow of fuel to and from said cylinder through said port means, and a single port in the other side of said cylinder, ered by said plunger during the entire eective pumping-stroke thereof and being further so losize as to effect -a reduction in, without eliminatingfthe resultant pressure tending to means during said effective pumping stroke, said port having constant communication with a low pressure chamber outside of said cylinder.

17. In a fuel pump, a cylinder having ow control port means in one side thereof and a piston in said cylinder adapted to form a pressure chamber therewith, said pistonhaving a working clearance in saidl cylinder and being reciprocable therein to vary the volume .of said pressure chaming the eifective pumping stroke of the plunger.

having an inlet port/and ancylinder from each other,l

riphery of said piston ber and to control the ow of fuel through said port means to and from said chamber, the pehaving a recess therein in vcontinuous communication with saidpressure 'chamber' and adapted to register with said port means to relieve the pressure in said chamber. and said cylinder having la nlm-pressure relief y' port in the other side thereof opposite's'aid port cylinder in substantially the salire longiwdmai portion of the latter as so as to cause a reduction in the pressure be tweenthe plunger'andithe wall of the cylinderv l tending to press said plunger,A

toward said ports during the ,effective pumping strokeof the plunger. said pressure relief portbeingsmall in comfirst-named and having consaia mst-named ports. -h

means connecting the'clearance space between said piston and cylinder with' the exterior of thecylinder. said film-'pressure relief port being of such size as to effect a reduction in. without elimmating, the. resultant pressure tending to press said piston toward said port means during the eilective ,pumping stroke of the piston. 18. A fuel injection pump comprisinga cylinder having port in one side thereof and thereof. a. relatively small rei all times during rea* said lastsaid portbeing solocatedastobecovv press said plunger toward said port a nlm-pressure relief port in the other side thereof, and a slotted reciprocating plunger having a working clearance in said cylinder for controiling the flow of fuel to and from the pressure chamber of the pump through said port means and for covering said nlm-pressure relief port during the entire effective pumping stroke thereof, said relief port being so positioned as to effeet a. reduction in, without eliminating. the resultant lm-pressure in the clearance space between said plunger and cylinder tending to press said plunger toward 'said port means during the eiective pumping stroke of said plunger.

19. A port-controlled fuel injection pump comagences prising a cylinder having an inlet port'and an outlet port at one side thereof, said ports being spaced axially of the cylinder from `each other, a reciprocable plunger having aV working clearance in said cylinder for controlling iiowizo and from the latter through said ports, and at least one pressure relief port in the other side of said cylinder and in the same longitudinal portion of the latter as said first-named ports, said pressure relief port being small in comparison to said mst-named ports and having constant communication with a low pressure chamber outside of said cylinder.

ALBERT T. BREMSER.