US2756033A - Carburettors for internal combustion engines - Google Patents

Description

1956 c. R. B. SMITH ErAL 2,756,033

CARBUREJTTORS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 8, 1954 4 Sheets-Sheet 1 llllllll ll .F'nankJfp BY July 24, 1956 c. R. B. SMITH L 2,756,033

CARBURETTORS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 8, 1954 4 Sheets-Sheet. 2

FIG. 2

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July 24, 1956 c. R. B. SMITH EI'AL CARBURETTORS FOR INTERNAL COMBUSTION ENGINES Filed Nov. 8, 1954 4 Sheets-Sheet 4 IN VEN T0 Ra: (Zyzyc'ZRevj lleflpllang 77w Izon,

ATTORNEYS.

FIG. 5

United States Patent CARBURETTORS FOR INTERNAL COMBUSTION ENGINES Cyril Reville Bellamy Smith, Sutton Coldfield, and Frank Henry Thomas Izon, Birmingham, England, assignors to Amal Limited, Witton, Birmingham, England, a corporation of Great Britain Application November 8, 1954, Serial No. 467,475

Claims priority, application Great Britain November 19, 1953 3 Claims. (Cl. 261-44),

This invention relates to carburettors for internal combustion engines, particularly those employed in association with motor cycles.

It is an object of this invention to provide an improved carburettor for an internal combustion engine.

According to this invention a carburettor for an internal combustion engine comprises in combination a main body portion, a float chamber for fuel, a float in the float chamber, a fuel-cut-oif device associated with said float to control the admission of fuel into the float chamber in accordance with the volume of fuel in the float chamber, a passage formed through said main body portion, said passage forming an airintake passage, a chamber in which air and fuel may be mixed and a mixture outlet passage, a pistontype throttle adapted to control the amount of air passing along the air-intake passage, a needle jet indirectly connected to the float chamber and in communication with the mixing chamber, a metering needle movable with the piston-type throttle valve and adapted to co-operate with the needle jet to control the amount of fuel entering the mixing chamber in accordance with the amount of air passing along the air-intake passage, a primary air-intake passage separate from, and uninfluenced by any turbulence in, the air-intake passage, said primary air-intake passage communicating with an annular space around said needle jet, a pilot fuel passage discharging into the mixture outlet passage, a pilot air supply associated with the pilot fuel passage, and a bleed hole in the needle jet communicating with the annular space around said needle jet.

According to one feature of the invention, at least one wall of the float chamber is formed by part of the main body portion.

According to another feature of the invention, the float is pivotally-mounted in the float chamber.

A carburettor in accordance with an embodiment of the invention is shown in the accompanying drawings of which:

Figure l is an elevational view'of the carburettor;

Figure 2 is a sectional view of the carburettor taken along the line II--II of Figure 1;

Figure 3 is a sectional view of the float chamber, taken along the line IIIIII of Figure 1;

Figure 4 is a sectional view taken along the line IV--IV of Figure 2; and

Figure 5 is a sectional view taken along the line V-V of Figure 2.

Referring to the drawings, the carburettor comprises a main body portion 1, generally of cruciform cross-section. This body portion has a main transverse bore which provides an air-intake passage 3, and a mixture outlet passage 5. The air-intake passage 3 is bored eccentrically in the part 7 of the main body portion which has screwed to it a funnel 9. The open end-portion of the mixture outlet passage 5 is provided with a flange 11 which will be utilised for attaching the carburettor to an associated internal combustion engine (not shown).

A cup-shaped member 13 co-operates with part of the 2,756,033 Patented July 24, 1956 main body portion in a fluid tight manner so as to form a float chamber and an aperture 15 in that part of the main body portion allows access of fuel from the float chamber to the interior of the main body portion as will be described later.

The cup-shaped member 13 (see particularly Figure 3) is provided with an integral upstanding substantially cylindrical hollow boss 17 into which is threaded a hollow plug 19 generally of cruciform cross-section. A fibre gasket 21 is provided between the boss and the plug 19 in order to prevent any leakage of fuel. A connecting plug 23 (which will be secured to a source of fuel) is slipped over the upper end portion of the hollow plug 19 and is secured to it by a screw 25 which is threaded into the upper end portion of the hollow plug 19. Gaskets 27 and 29 prevent leakage of the fuel between the several parts. A cylindrical chamber 31 is provided between the upper end portion of the hollow plug 19 and the connecting plug 23, and a diametral bore 33 connects the cylindrical chamber 31 with the interior of the hollow plug 19. The interior of the hollow plug 19 has a shouldered portion 35 with which a needle-type fuel supply valve 37, triangular in cross-section, co-operates. guided for movement by the hollow plug and passes into the cup-shaped member 13 and its end is supported upon one arm 39 of a lever. The lever is pivotally-mounted upon a pin 41 secured to the internal Wall of the cupshaped member 13 and the other arm 43 of the lever is secured to'a cylindrical float 45. A substantially-cylindrical wire gauze filter 47 is disposed in the chamber 31.

A second integral upstanding substantially-cylindrical boss 49 on the cup-shaped member 13 is internallythreaded and co-operates with a sleeve 51. is resiliently mounted in the sleeve 51 by a spring 55 and a bore 57 in the tickler acts as an air vent for the float chamber.

The cup-shaped member carrying its associated parts is attached to the hollow boss 59 formed on the main body portion by screws 61 (see Figure l) and a circular wire gauze filter (not shown) is disposed within the boss and abuts against the shoulder 63.

The lower part 65 of the main body portion has an inwardly-directed portion 67 and a cylindrical 'jet block 69 is disposed within the main body portion, resting upon the inwardly-directed portion, and is secured in position by a set screw 71 (see Figure 4). The jet block 69 has a substantially-cylindrical bore 73 which is aligned with p the air-intake passage and the mixture outlet passage and which forms a mixing chamber. A hollow plug 75 is threaded into the lower portion of the jet block 69 and this hollow plug has threaded into its upper end portion a needle jet 77 and into its lower end portion a main jet 79. The hollow plug co-operates with a fibre washer 81 to form a fluid-tight joint with the bottom of the main body portion (as shown in Figures 2 and 5). A closure well member 83 is threaded into the lower end portion of the hollow plug 75 so as to seal the bottom of the hollow plug 75.

A fuel-receiving chamber 85 is formed between the hollow plug 75 and the lower part 65 of the main body portion and communicates with the aperture 15. In-

clined holes 87 in the hollow plug 75 connect the fuelreceiving chamber 85 with the closure well member 83 and hence indirectly with the main jet 79 and the needle one not designated, bored in the main body portion and .in the jet block 69 respectively, are associated with the The needle-type valve 37 is v A tickler 53 Pilt i k u p am unt at Pfi 3 I9 1 i pilot fuel jet 89i's Controllable by pilot fuel jet 109 and a screw 101 threaded into a sleeve 193 which, in turn, is aded in a h a he q rrart fi he main-b s ns portion is provided for reaming the pilottu el-j A supplyof pilot air (see FigureA) is suppl ed -to-the passage95, for mixing with the supply ot pilct'iuelby way of passages 105, 107, 109, and 111 bored;-injthe lower part of the main body portion andinflhe jet; block 69 The amount of pilot air supplied is -contro l 1 .10 lable, by a pilotair control screw 113 which ist'hreaded W into a hole in the lower part 65 of the main body portion, therebeinga coiled spring 115 disposed hetweenthe head; of es w and h ma o r tiq ff pas a ew mcnqesin t t P t 7 0 the ma qdy po ion-w ,15 is not bored eccentrical ly and so; lSJll'lll'lllUdlTlQfllbY any turbulence which may occur-inthe, ahtintalge passage 3.,

Primary air is supplied to the mixing chamber side of; the metering tube (see Figures land 4) by Way of passage 117 bored in that part 7 of the main body portion 20 which isnot bored eccentrically, and passage 119 which is bored in the jet block 69 and which communicates with an annular space around the needle jet. A primary air jet tube 121 is provided in the passage 117,'its internal diameter determining the amount of primaryair passing. 2 Since the passage 117 commences in that part 7 of the main body portion which is not bored eccentrically, the supply of primary air is not influenced by turbulence in i the air-intake passage 3.

A bleed hole 123 in the needle jet 77, communicating with the annular space around the needle jet allows fuel 1 to be, mixed with the primary air to be available for rapid acceleration. The bleed hole is arranged tobe slightly below the mean level of the fuel, e. g. of an inch, and slightly above, e. gJA of an inch, the calibrated orifice of the needle jet.

A piston-type throttle sleeve 125 of orthodox form is; pqssd t e up P r Qt h ma abqd P0 tion and co-operates with the mixing chamber to determinethe amount of air passing from the air-intakepas- 40 sage Stothe mixture outlet passage 5. The pistontype throttle sleeve is controlled by means ofa Bowden wire 127 which passes through a sleeve 129 threaded in acap 131 to the outside of the carburettor, A spring 133 is disposed between the cap 131 and the upperparoofthe throttlesleeve.

A ra l me ber 135 o do f rm. sa pq a ed with the throttle sleeve and is operable againstthe action v of spi n 1. 5 dmw m wh h-pa e ugh a sl e e 1 ea d-in t e an .131- yli der. A F PQ ..%1 I Pa f the sp 1137 v. s;t s= stranglen member durin g its movement,

A m t r aanes e 45 d e o 15mm w t the ia in to n l he ma n amount fs s s pp ied; to the mixing chamberis fastened to the head of the thrpt Q tle sleeve by. a bifurcatedspringplip 147 which engages with one pf a-series of grooves formed at the upperend a,

portion pf the needle.

The cap 131 is secured to the upper part of the main; bodypor-tion by a locking ring 14? which is threadedon to the outer surface of the main body portion. A spring clip 151 secured by a-screw 153 to the cap .ptevents undesired; rotation of the locking ing. u q

A throttle stop 155 is threaded into the body portion (see Figured) and its upper end determines the location of the throttlesleevewhen in its closed position Move ment ot the throttle stop due tovibration is; prevented by; a coiled spring 157 disposed between the head of the throttle sto a e a nrho P on.

It appears that by providingthebleedhole 12 3, a small well of f ue l is always available inthe annular space around the sgdl ti t for s a emig tion; W t is wal et fuel ha bcc w ss n n w nah re on ied ,-.th

consequent leyel drop whichtalgeaplace allows aintq'pass usbthe b e 91 w t a.consequsa twe n nstot,

the mixture at mid-throttle positions. This weakening at the mid-throttle positions leads to an increased performance.

In a modified form of the carburettor just described.

a hollow boss cast inone with the main body portion co; operates with a cover plate to provide the float chamber.

For instance with a motor cycle having a 650 cc. engine,

working-under identical conditions. the followingzresults u With a motor cycle having a 250 cc. engine, tworking under identical conditions, the following resultswere ob:

tained:

Old type Carburottor carburettor in accordance Speed, miles per hour miles pet with lnven gallon tion, miles, per gallon Consequently there-is a 15-20% reductionin fuel consumption with superior acceleration properties.-

We claim:v

1. A carburettor for an internal combustion engine comprisingdn combination a main body portion, a-fioat chamber for fuel, a float in said float chamber, a fuel cut-ofl device associated with said float to control the admission .of fuel into said float chamber in accordance: with the volume of fuel containedtherein, a passage:

formed through said main bodyportion said passageforming an air-intake passage, achamber in which air and fuel may be mixed and a mixture outlet passage,--a

piston-type throttle adapted to control the amount of air passing along the air-intake passage, a needle jet indirectly t connected to the float chamber and in communication with the mixingchamber, a metering needle movable with the piston-typethrottle valve and adapted to cooperate'with l said needle jet to control the amount of fuel entering-the intake passage communicating with an annular space around said needle'jet, a pilot fuel passage discharging i into the mixture outlet passage, a'pilot air supply 3.580% ciated with the pilot fuel passage,- and a bleed hole in said 1 needle jet=communicating with the annularspacearound said needle jet, said bleed hole being disposed slightlyi' belowthe mean level ofthe fuel and slightlyabove the calibrated orifice of the needle jet.

2. The structure defined in claim l wherein at least one i wall of the float chamber is formed by part of the mainbody portion.

3. The structure defined in claim .1 wherein said fioat is pivotally mountedin said float'chamben Referencestfilited in the file of this patent FOREIGN PATENTS mixing chamber in accordance with the amount, of air passing along the air-intake passage,-a primary -air-intake passageseparate from, and uninfluenced by any turbulence r in said first mentioned air-intake passage, said primaryain l

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