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(11) | EP 0 009 318 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Carburettor |
| (57) A floatless carburettor comprising in combination a fuel inlet (F1), two separate
fuel outlets (F2, F3) to an air passage (13C) adapted to admit air from the atmosphere
(A1, A2) and discharge it to an engine, a throttle control means (12C) by which the
area of said air passage is progressively opened and closed (13A, 13B) to vary said
area and an adjustable self-regulating pressure means (15) via which fuel is fed from
the said fuel inlet (F1) to the carburettor. |
[0002] It is well known that a spark ignition engine requires a practically homogeneous mixture of fuel and air to the cylinder of the engine witn the relative proportion of each by weight controlled to within narrow limits. The theoretically correct ratio of air to petrol is about 15 : 1 but it is not possible to obtain a completely homogeneous mixture at this ratio under all engine conditions. Hence the engine will give maximum power on ricn mixtures of air to petrol of about 10 to 1 to about 13 to 1 and economic running on lean mixtures of air to petrol of 14 to 1 to 1b to 1 for complete burning of the fuel. Under difficult engine starting conditions the air/fuel ratio may be unity owing to the poor evaporation of the fuel.
[0003] These requirements are not generally by a suction carburettor mounted at the entrance to the engine inlet manifold simultaneously to control the admission of air and fuel. A simple suction carburettor essentially comprises a venturi and one or more fuel jets fed from a float chamber. A butterfly throttle valve is generally used to control the amount of the mixture that passes into the engine from the induction system. As air is drawn through the venturi and past the metering jet, its velocity increases and the pressure at the venturi is reduced in proportion to the air flow. Meanwhile the pressure acting on the fuel bowl is substantially atmospheric, so that the resultant pressure differences forces the fuel through the metering jet into the air stream where it is atomized by the high velocity air. Once the venturi and fuel jet sizes have been selected, the amount of fuel drawn from the jet depends on the pressure drop produced by the venturi.
[0004] Since the fuel metered depends on the pressure drop of the air passing through the venturi the air-fuel ratio with a suction/float carburettor is self-compensating for atmospheric air pressure and temperature to some extent. The simple suction/float carburettor has been provided with supplementary devices to attempt to give the correct air/fuel ratios under various operating conditions in an engine but without success; thus the suction/float carburettor used inter alia in automobiles and motor cycles has a number of disadvantages. It remains an unsatisfactory fuel/air control device since the volume of the fuel and the air is not correlated for slow, intermediate and fast running conditions of an engine to which it is fitted. Consequently, fuel is generally used uneconomically in the said engine, which with present fuel shortages and high prices is not only a serious misuse of fuel but one that causes serious atmospheric pollution.
[0005] We have found surprisingly that a carburettor can be produced to overcome or at least to reduce the above noted difficulties.
[0006] According to the present invention we provide a floatless carburettor comprising in combination a fuel inlet, two separate fuel outlets to an air passage adapted to admit air from the atmosphere and discharge it to an engine, a throttle control means by which the area of said air passage is progressively opened and closed to vary said area and an adjustable self-regulating pressure means via which fuel is fed from the said fuel inlet to the carburettor.
[0007] The invention will be more fully understood from the following description of one floatless carburettor giver by way of example only in relation to the Figures of the accompanying drawings in which:-
Figure 1 is a sectional elevation on the section station I I of Figure 2.
Figure 1A is a sectional view of a self regulating fuel inlet pressure means to a larger scale than that of Figure on the section station I,, IA of Figure 1.
Figure 2 is a sectional plan on the section station II II of Figures 1 and 3.
Figure 3 is a side elevation in the direction of arrow III of Figure 1, and
Figure 4 is a detail to a larger scale of the operational character of the cam and its associated parts referred to by arrow IV of Figure 3.
[0008] In the Figures of the drawings a floatless carburettor is seen to comprise a body 10 having an integral extension 10A screwed at 11E to a flange body 11D having a flange 11 provided with bolt fixing holes 11A, 11B (Figure 3) and screwed to the body at 11C. Engine manifold air enters as shown by arrows A1.A2 (Figure 2) via ports 12A. 12B. in an accelerator sleeve 12 that is provided with throttle control means in the form of an integral lever arm 12C naviug at its extremity a bolt fixing hole 12D. The manifuld air passes via the ports 12A, 12B respectively to opening 13A, 13B in flange body 11D and discharges to an engine via passageway 13C making a right angle turn in so doing. Clearly rotation of accelerator sleeve 12 about flange body 11D progressively opens and closes the openings 13A, 13B.
[0009] In Figure 2 the flange body 11D is closely cross hatched diagonally specially to show the openings 13A, 13B which are not fully open in the position shown in said Figure.
[0010] The body 10 contains a number of fuel passageways. Fuel enters the carburettor (arrow F1) via pipe 14 from the fuel pump P along a passageway 14A to a self-regulating pressure means shown generally at 15 (Figure 1A) that comprises a ball 15A that seats on a seat 15B in a screwed union 15C and is forced against the fuel flow, shown by arrow F1, by a helical compression spring 15D acting on a compensatory cup 15E having a spigot 15G. A spring cap 15H together with compensatory cup 15E accept the opposed ends of helical spring 15D. Spring cap 15H has a recess 15K for a screw 15L having a head 15L1 which is a mair adjustment head for valve 15. Screw 15L passes through a complex fuel gland comprising a plastics washer 15M a plastics packing 15N which packing is adjustable to prevent fuel leakage by virtue of co-acting parts 15p1, 15p2, 15p3. It is to be noted that the compensatory cup 15E operates by the back pressure of the fuel and extends across centre lines
A,
B of Figure 1 which centre lines define the centres lines define the centres of fuel outlets F2 and F3 of Figure 1. F2 is the idler outlet and F3 is the outlet for normal running. A fuel passageway 16 normal to passageway 14A is adjustable by virtue of a valve shown generally at 17 that comprises essentially a frusto-conical valve end 17A and seat 17B; the said end 17A having therein a hole 17C that extends in line with passageway 16. The frusto-conical valve end 17A has an extension 17D provided with a knurled end 17E and locknut 17F. The said end 17A is able to be forced against its seat 17B by a screwed member 18 having an hexagonal end 18A and locknut 18B. A further fuel passageway 19 normal to 14A is provided with a valve shown generally at 24. Valve 24 comprises a frusto-conical valve 24A in a frusto-conical valve seat 24B. A helical compression spring 24C co-operates with valve 24B that has a complex form since its stem 24E contains parallel to its axis
A a tapered groove 24F providing a V throat progressively increasable in area upon opening and progressively decreasable in area upon closing; the groove is at its most wide toward the lower part 1 and at its most narrow toward the upper part as shown in Figure 1. A hexagonal headed screwed member 24G retains the spring 24C ana has an orifice that receives the said stem 24E. An important refinement in the operation of valve 24 is provided by means of a mechanical linkage that by its disposition inter se is able to give a substantially homogeneous mixture of fuel and air under various engine running conditions. The linkage comprises a lifter arm 25 co-operating with a serrated nut 24H1 and locknut 24H2 screwed onto a screw threaded part 24K of stem 24E. Lifter arm 25 is fixed at 25A to a rod 25B spring urged via helical compression spring 25C in guide box 25D that is integral with flange body 11L. The box 25D has a screw cap spring seat 25E. The rod 25B rests upon flat face 2bA of a cam 26 that is adjustable in its inclination to axis
A (Figure 3) as shown by line Y1Y2 in the plane of the flat face 26A of cam 2b. The flat face 26A may for convenience be set, in respect of end point 25F (Figure 3) of rod 25B, to be at an angle α to a line Z25F normal to line Y1Y2. The adjustability and the setting of angle α of cam 26A is effected by two co-operating eccentrics 27A, 27B, these are shown most clearly in Figure 4. The diameter d1 of eccentric 27A is greater than the diameter d2 of eccentric 27B. The eccentrics co-operate about their respective pivot points 27Ap 27Bp with curved recesses 28A, 28B in the underside of cam 26. The cam 26 has a pair of slots 26B, 26C and these are loosely fitted over bolts B1, B2 (Figure 3) that are co-incident with centres 27Ap 27Bp. Each eccentric 27A, 27B has an extension having a knurled end K1 K2 that may be locked in position on its respective bolt B1 B2 by a locknut L1 L2. Clearly such a linkage offers a multiplicity of accurate settings commensurate with the air/fuel mixtures at different running conditions of the engine.
[0011] The modus operandi of the floatless carburettor shown in Figures 1, 1A, 2, 3 and 4 is as follows :-
First we identify passageway 16 centre line φB with fuel outlet at F2 as the idling or slow running fuel outlet, and passageway 19 centre line φA with fuel outlet at F3 as the intermediate and fast running fuel outlet or the normal running outlet.
[0012] Passageway 16 is adjustable by valve 17. Passageway 19 is adjustable by valve 24. Fuel inlet to the carburettor is adjustable via self regulating pressure valve 15. Consider now that the carburettor in use is fitted to a particular engine then the fuel supply is first adjusted to the requisite pressure p from fuel pump P (not shown). Fuel passes to fuel passageway 16 and the idling or slow running requirement of the engine are adjusted by valve 17 and fuel issues from the outlet at F2, which outlet may be fan shaped if necessary.
[0013] Fuel also passes to fuel passageway 19 and the intermediate and fast running requirements of the engine are adjusted by the arm 12C attached to the accelerator whicn actuates openings 13A, 13B in relation to air ports 12A, 12B and actuates rod 25B in co-operation with surface 26A to vary the position of tapered V groove 24F which by its vertical position in passageway 19 control the V throat opening at fuel outlet F3 which is most clearly shown at F3 in Figure 2.
[0014] When now the operator requires the engine to develop more power the accelerator lever arm 12C is moved in rotation (arrow R1) about flange body 11D and ports 12A, 12B come more into alignment with openings 13A, 13B giving a greater flow of air to the engine manifold. At the same time valve 24 from its setting on spring 24C demands fuel and this is supplied via the variable V throat at F3, which for any given engine is defined by:-
a the inclination α of cam face 2bA
b the depth and width of the tapering V groove 24F in stem 24E.
c the position to which the V groove throat is lifted linearly in the cylindrical bore of circular cross section in member 24G.
[0015] Clearly as the accelerator lever 12C is rotated in direction of arrow R1 (Figure 2) not only do the air ports 13A, 13B open but the inclination α of cam 26 progressively lifts the rod 25B and progressively lifts stem 24B and increases the area of the throat of F3 (Figure 2) with the increased demands on the engine. Thus fuel at F3 is progressively increased in volume with the volume of air which volumes are accurately correlated by the setting of cam 26 about eccentrics 27A, 27B.
[0016] If the carburettor is now fitted to another engine making different demandsupon it then the valves 15, 17 and 24 are re-adjusted, the angle α reset to β1 for the requirements put upon the fast running valve 24. No longer is the fuel metered dependent, as in the orthodox suction float carburettor on the pressure drop generated by the air passing through a venturi, in contra-distinction it is accurately adjusted to the fuel pump delivery for slow intermediate ana fast running conditions with air and fuel volumes correlated to the practical or theoretically correct mixture of air and fuel essential to the engine power.
[0017] We have finally to deal with the self regulating valve shown generally at 15. It is set for a fuel pressure p to the carburettor from the fuel pump P. If now the preset pressure p rises inside the carburettor for any reason to a pressure p1 then the excess or back pressure (p1 - p) acts on compensatory cup 15E and produces a force (arrow F4 Figure 1A) in opposition to the force of the fuel flow shown by arrow F1 (Figure 1A). This force F4 seeks to close the valve 15 at 15A, 15B and restore the pressure in the carburettor to the preset pressure p.
1. A floatless carburettor comprising in combination a fuel inlet, two separate fuel
outlets to an air passage adapted to admit air from the atmosphere and discharge it
to an engine, a throttle control means by which the area of said air passage is progressively
opened and closed to vary said area and an adjustable self-regulating pressure means
via which fuel is fed from the said fuel inlet to the carburettor.
2. The floatless carburettor according to claim 1 wherein the adjustable self-regulating
pressure means includes an adjustable ball valve.
3. The floatless carburettor according to claim 1 or claim 2 wherein the self-regulating
pressure means includes a compensatory cup actuated by back pressure from the fuel.
4. The floatless carburettor according to claim 3 wherein the compensatory cup extends
across the centre lines of the two fuel outlets.
5. The floatless carburettor according to any preceding claim wherein each of said
fuel outlets is adjustable by a valve one fuel outlet being an idling outlet and the
other having a throat variable in area that is progressively increased and decreased
as the opening of said air passage is progressively increased and decreased in area,
said throat and said air passage opening both co-operating with said throttle control
means that directly opens and closes said opening of said air passage and via an adjustable
cam gives a linear movement of the throat to provide an air/fuel relationship at said
discharge that is adjustably predeterminable by said cam for any given engine to which
the carburettor is fitted and which air/fuel relationship once predetermined is varied
automatically with the opening and closing of said throttle control means via said
cam.
6. The floatless carburettor according to claim 5 wherein the throat is a V-shaped
throat defined by a tapering V groove in a valve spindle that is slideable in a cylindrical
bore of circular cross-section.
7. The floatless carburettor according to claim 6 wherein the fuel from the V throat
is projected substantially parallel to the air flow in the air passage at its discharge.
8. The floatless carburettor according to any one of claims 5 to 7 wherein the cam
has a flat surface that is adjustable to allow the inclination of said flat surface
to be varied to the line of action of a cam follower that slides the V groove in its
bore.
9. A floatless carburettor according to claim 8 wherein the fuel from the V throat
is dependent upon the inclination (a) of the cam, the depth and width of the V groove
and the said linear movement of the throat in its bore which movement is controlled
by said inclination.
10. The floatless carburettor according to claim 9 wherein the inclination of the
cam is adjustable by means of at least one eccentric.