EP0009318B1

EP0009318B1 - Carburettor

Info

Publication number: EP0009318B1
Application number: EP19790301645
Authority: EP
Inventors: Albert Saunders
Original assignee: Saunders J & F Carburettor Co Ltd
Current assignee: Saunders J & F Carburettor Co Ltd
Priority date: 1978-09-27
Filing date: 1979-08-14
Publication date: 1982-03-17
Also published as: EP0009318A1; JPS5546087A; GB2030215A; DE2962288D1

Description

This invention relates to a carburettor.
It is well known that a spark ignition engine requires a practically homogeneous mixture of fuel and air to the cylinder of the engine with 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 rich 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 16 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.
These requirements are met 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.
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/ftoat 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.
Some of these points are taken by United States patent Application 3,102,152 and by United States patent Application 3,331,360.
US - A - 3 102 152 describes a fuel-handling device injecting fuel into the air stream of an engine by means of a positive pressure, having a metering system to regulate the fuel when the engine is idling and having a second metering system to regulate the fuel when the engine is running. This floatless device comprises a fuel inlet, a throttle control means by which the area or an air passage is progressively opened and closed to vary said area, an adjustable self-regulating pressure means via which fuel is fed from said fuel inlet to air passage and one fuel outlet to the air passage adapted to admit air from the atmosphere and discharge it to an engine.
US - A - 3 331 360 describes an anti-smog carburettor and comprises two separate fuel outlets to an air passage. The first outlet controls the fuel flow rate at engine speeds above the idle range, the second outlet controls the fuel flow rate at engine speeds in the idle range.
In contradistinction to these known devices there is provided according to the present invention a floatless carburettor having in combination a fuel inlet, two separate fuel passageway and 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, an adjustable self-regulating pressure means via which fuel is fed from the said fuel inlet to the carburettor and wherein each of said fuel passageways is adjustable by a valve, one fuel outlet being an idling outlet and the other having a V shaped 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 V shaped throat and said air passage opening both cooperating with said throttle control means that directly opens and closes said opening of said air passage and via an adjustable flat cam. gives a linear movement of the said V shaped 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.
The invention will be more fully understood from the following description of one floatless carburettor given 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 II of Figure 2.
- Figure 1 A is a sectional view of a self regulating fuel inlet pressure means to a larger scale than that of Figure 1 on the section station I_A, I_A 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.

In the Figures of the drawings a floatless carburettor is seen to comprise a body 10 having an integral extension 10A screwed at 11 E to a flange body 11 D having a flange 11 provided with bolt fixing holes 11 A, 11 B (Figure 3) and screwed to the body at 11 C. 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 having at its extremity a bolt fixing hole 12D. The manifold 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 11 D progressively opens and closes the openings 13A, 13B.
In Figure 2 the flange body 11 D is closely cross hatched diagonally specially to show the openings 13A, 13B which are not fully open in the position shown in said Figure.
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 1 A) 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 1 5G. 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 15L, which is a main 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 1 5p 1, 1 5p2, 1 5p3. 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 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 24A 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 and at its most narrow toward the upper part as shown in Figure 1. A hexagonal headed screwed member 24G retains the spring 24C and 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 24H, and locknut 24H_z screwed onto a screw threaded part 24K of stem 24B. 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 11 D. The box 25D has a screw cap spring seat 25E. The rod 25B rests upon flat face 26A of a cam 26 that is adjustable in its inclination to axis A (Figure 3) as shown by line Yl Y2 in the plane of the flat face 26A of cam 26. 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 a to a line Z-25F normal to line Y1-Y2. 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, 27B_P 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, 27B_P. 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.
The modus operandi of the floatless carburettor shown in Figures 1, 1 A, 2, 3 and 4 is as follows:-

First we identify passageway 16 centre line B with fuel outlet at F2 as the idling or slow running fuel outlet, and passageway 19 centre line A with fuel outlet at F3 as the intermediate and fast running fuel outlet or the normal running outlet.

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.
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 which 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.
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 11 D 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 a of cam face 26A
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.

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 (t 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.
If the carburettor is now fitted to another engine making different demands upon it then the valves 15, 17 and 24 are re-adjusted, the angle a 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 and 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.
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 1 A) 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 1 5A, 15B and restore the pressure in the carburettor to the preset pressure p.
To prevent leakage of fuel at screwed connections in the carburettor, double screwed glands may be employed.
The path of the fuel jets to the air discharged to the engine is of interest. Both jets F2, F3 project the fuel substantially parallel to the air at discharge via the passageway.
The carburettor of the invention will not catch fire.

Claims

1.. A floatless carburettor having in combination a fuel inlet (14), two separate fuel passageways (16, 19) and outlets (F2, F3) 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, an adjustable self-regulating pressure means (15) via which fuel is fed from the said fuel inlet (14) to the carburettor and wherein each of said fuel passageways (16, 19) is adjustable by a valve (17, 24) one fuel outlet (F2) being an idling outlet and the other (F3) having a V shaped throat (24F) variable in area that is progressively increased and decreased as the opening of said air passage (13A, 13B) is progressively increased and decreased in area, said V shaped throat (24F) and said air passage opening (13A, 13B) both co-operating with said throttle control means that directly opens and closes said opening of said air passage and via an adjustable flat cam (26) gives a linear movement of the said V shaped throat (24F) to provide an air/fuel relationship at said discharge that is adjustably predeterminable by said cam (26) 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 (26).

2. The floatless carburettor according to claim 1 wherein the adjustable self-regulating pressure means (15) includes an adjustable ball valve (15A) and a compensatory cup (15E) actuated by back pressure from the fuel.

3. A floatless carburettor according to claim 1 or claim 2 wherein the fuel from the V throat (24F) is dependent upon the inclination (α) of the cam (26), 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.

4. The floatless carburettor according to claim 3 wherein the inclination of the cam (26) is adjustable by means of at least one eccentric (27A, 27B).