Title:
FUEL SYSTEM
Document Type and Number:
United States Patent 3759234
Abstract:
Fuel vapors from the fuel system of an internal combustion engine are absorbed in the uppermost layer of a body of material capable of reversibly absorbing fuel vapors. Desorption of the material occurs during engine operation.
Inventors:
Buckton, Keith Stewart (Wantage, EN)
Fraser, Ian Rowland (Oxford, EN)
Fraser, Ian Rowland (Oxford, EN)
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Application Number:
05/201849
Publication Date:
09/18/1973
Filing Date:
11/24/1971
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Export Citation:
Assignee:
Esso Research and Engineering Company (Linden, NJ)
Primary Class:
International Classes:
F02M25/08; F02M37/02
US Patent References:
Other References:
The Lamp, 30 Rockefeller Plaza NY, 10020 (pg. 21)..
Primary Examiner:
Goodridge, Laurence M.
Parent Case Data:
This is a continuation of application Ser. No. 733,395, filed May 31, 1968.
Claims:
We claim
1. A fuel system for an internal combustion engine comprising:
2. The system according to claim 1 in which the second conduit has a part which extends upwardly substantially to the level of the uppermost layer of the body of material.
3. The system according to claim 1 in which the first conduit includes an expansion tank which is disposed in said first conduit intermediate said fuel reservoir and said canister.
4. The system according to claim 1 in which the fuel reservoir comprises a fuel storage tank containing a filling orifice and a cap capable of sealing the orifice, said tank being sealed and not in communication with the atmosphere during such time that the cap seals the orifice.
5. The system according to claim 1 in which the engine contains an air filter or air cleaner and the second conduit is connected at its other end to the air filter or air cleaner.
6. The system according to claim 1 in which there are two fuel reservoirs, one of said reservoirs being the fuel storage tank and the other reservoir being the bowl of a carburetor, and there are two first conduits, one of which has its one end connected to the vapor area of the fuel storage tank and its other end imbedded in the uppermost layer of said body of material, and the other first conduit has its one end connected to the vapor area of the carburetor bowl and its other end imbedded in the uppermost layer of said body.
7. The system according to claim 6 wherein:
1. A fuel system for an internal combustion engine comprising:
2. The system according to claim 1 in which the second conduit has a part which extends upwardly substantially to the level of the uppermost layer of the body of material.
3. The system according to claim 1 in which the first conduit includes an expansion tank which is disposed in said first conduit intermediate said fuel reservoir and said canister.
4. The system according to claim 1 in which the fuel reservoir comprises a fuel storage tank containing a filling orifice and a cap capable of sealing the orifice, said tank being sealed and not in communication with the atmosphere during such time that the cap seals the orifice.
5. The system according to claim 1 in which the engine contains an air filter or air cleaner and the second conduit is connected at its other end to the air filter or air cleaner.
6. The system according to claim 1 in which there are two fuel reservoirs, one of said reservoirs being the fuel storage tank and the other reservoir being the bowl of a carburetor, and there are two first conduits, one of which has its one end connected to the vapor area of the fuel storage tank and its other end imbedded in the uppermost layer of said body of material, and the other first conduit has its one end connected to the vapor area of the carburetor bowl and its other end imbedded in the uppermost layer of said body.
7. The system according to claim 6 wherein:
Description:
The present invention relates to fuel systems for internal combustion engines. More particularly this invention concerns liquid fuel systems for engines which utilise a combustible mixture of fuel and an oxidant.
In order to form a relatively homogeneous fuel-oxidant mixture, it is desirable in many instances for the liquid fuel to be relatively volatile. The combustion of the fuel-oxidant mixture during the operation of the engine produces heat which tends to volatilise the lighter constituents of the fuel. If the engine is stopped after a period of operation, the fuel adjacent the engine continues to receive heat and to volatilise, and it is necessary to allow the volatilised fuel to escape to avoid any increase in the pressure in the fuel system.
In the case of automobile engines powered by gasoline-air mixtures, the volatilised gasoline from the carburettor bowl after a period of operation of the engine is vented to atmosphere from the carburettor. Legislation is now in force or proposed in various countries to limit the amount of gasoline which may thus be lost from the carburettor. Legislation is also in force or proposed in various countries to limit the quantity of gasoline which may be lost from the main fuel storage reservoir or tank, of automobiles. The losses in this case are due to diurnal temperature variations and a heating of the tank during operation of the automobile.
It is an object of the present invention to provide a fuel system in which fuel volatilisation losses from the system or the engine are minimised.
The present invention provides a fuel system for an internal combustion engine comprising a reservoir for fuel, a duct having a mixing zone in which, in operation of the engine, the fuel is mixed with an oxidant (such as air) to form a combustible mixture which passes through the duct to the engine, a body of material which is capable of reversibly absorbing fuel volatilised from the reservoir, first means which enable the reservoir to communicate with the body of absorbent material, second means which enable the body of absorbent material to communicate with the mixing duct upstream of the mixing zone, and third means enabling the body of absorbent material to communicate with the oxidant at substantially its full static pressure.
The term "absorbing" is intended to include both physical absorption and the physicochemical phenomenon of adsorption. "Reversibly absorbing" is intended to convey that the absorption is reversible.
When the oxidant is passing through the mixing duct, there is a depression in its pressure relative to the pressure in the reservoir and the body of material. Oxidant will be drawn from the third means through the body of material into the duct and thus serve to carry desorbed fuel through the second means towards the mixing duct.
In cases where the fuel vapour is denser than the oxidant, preferably the first means comprises a first conduit having one end at or near the upper end of the body of material, the second means comprises a second conduit which has one end at or near the lower end of the body of absorbent material, and the said one end of the first conduit lies between the said one end of the second means and the third means. This arrangement ensures that the fuel vapour passes out of the first means at or near the top of the body of absorbent material and sinks into the body of material where it is absorbed. During desorption, the oxidant also passes downwardly from the third to the second means, thus desorbing fuel from the top of the body of material first, so that the top is relatively free of fuel and capable of absorbing more fuel vapour passing out of the first means, when the passage of oxidant diminishes or ceases.
Moreover, where the said reservoir is the carburettor of a carburetted internal combustion engine, the disposition of the said one end of the first means at or near the upper end of the body of material enables the oxidant, usually air, to communicate with the carburettor bowl through the first means with substantially no pressure drop due to the body of material. Thus the performance of a carburettor designed for operation in a previously known fuel system devoid of a body of absorbent material will be substantially unchanged when incorporated in a fuel system in accordance with the invention.
The second conduit preferably has a part which extends upwardly substantially to the level of the upper end of the body of absorbent material. The said part of the second conduit serves, in effect, as one upwardly extending limb of a U-tube, of which the other limb is provided by the body of material. Heavy fuel vapour forms a trapped layer in the U-tube, the top of the layer being substantially no higher than the level of the upper end of the body of material. The trapping of the fuel vapour increases the chance of absorption of the vapour by the body of material.
The body of material may be disposed in a container and the third means may be provided by an orifice in the container.
In one fuel system in accordance with the invention, the second means comprises a valve which provides a path for any fuel volatilised from the reservoir to pass to the body of absorbent material when the pressure in the mixing duct is greater than a selected pressure, and which interupts the path when the pressure in the mixing duct is less than the selected pressure and provides an alternative path for any volatilised fuel to pass directly from the reservoir to the mixing duct upstream of the mixing zone. The duct may incorporate a throttle control for regulating the fuel-oxidant flow to the engine and the said valve may operate in accordance with the pressure downstream of the throttle control.
Where the invention is applied to automobile engines, the reservoir referred to may be either the carburettor bowl or the tank or both.
The invention will now be described by way of non-limitative example only and with reference to the accompanying drawings in which:
FIG. 1 shows schematically one form of fuel system in accordance with the invention, for use in a carburetted automobile engine,
FIG. 2 shows a part of FIG. 1 to a larger scale,
FIG. 3 depicts an alternative construction of the part of FIG. 2, and
FIG. 4 shows another form of fuel system in accordance with the invention.
In FIG. 1, the fuel system is generally indicated by reference 10 and comprises an air-filter 11 of known type, a choke tube 12, into which air from the filter 11 is drawn when the engine (not shown) is in operation, a carburettor 13 comprising a bowl 14, which serves as a reservoir for the gasoline fuel, and one or more jets 15 providing communication between the carburettor and a narrow mixing zone 16 of the choke tube 12. The fuel is supplied to the carburettor 13 from a main storage tank or reservoir 17 by a pump 18 and the level of fuel in the carburettor bowl 14 is substantially maintained by a well-known valve-and-float mechanism (not shown).
The passage of air through the choke tube 12 causes a fall in the static pressure in the tube 12 as compared with the pressure in the carburettor 13 and gasoline is induced through the jet(s) 15 into the zone 16 of tube 12 where it mixes with air to form a combustible mixture. The combustible mixture passes to the engine via an intake manifold 19, the quantity of this mixture being regulated by a butterfly valve 41 upstream of the manifold 19.
The fuel system 10 further comprises an open-topped container or canister 20 containing a bed 21 of charcoal granules. A perforated pipe 22 is disposed at the top of, and just within, the bed and connected by a tube 23 to the top of the carburettor 13.
If the carburettor 13 should become so heated that gasoline contained therein vapourises, the vapours pass via the tube 23 and a perforated pipe 22 into the top of the bed 21. Since the gasoline vapours will be very largely heavier than air, they tend to sink from the pipe 22 downwardly through the charcoal bed 21 where they will be trapped and at least partially absorbed. Substantially none of the gasoline vapours will rise upwardly from the perforated pipe 22, but a thin layer of charcoal is provided above the perforated pipe 22 to ensure that any vapours which do tend to rise due to unusual operating conditions will have their upward passage resisted and may be absorbed in the thin layer or deflected downwardly. In practice, a significant amount of gasoline is vapourised from the carburettor during the so-called "hot soak" period of about half an hour following operation of the engine.
By disposing the perforated pipe at or near the top of the bed 21, it is ensured that efficient utilisation of the bed by the descending vapours takes place. Furthermore, the disposition of the perforated tube 22 substantially at the top of the bed 21 of charcoal enables air to be drawn into the carburettor 13 via the tube 23 and the perforated tube 22 from the open top of the canister 20 with substantially no impedance to its passage: accordingly, the carburettor 13 need not be particularly adapted for incorporation in the fuel system in accordance with the invention as variations of pressure can take place within the carburettor substantially as freely as in the absence of the canister 20 and the interconnecting tubes 22,23.
The lower end of the canister 20 is connected to the air filter 11 by a tube 24 which extends from the bottom of the canister 20 at least to the level of the top of the canister 20 before its connection to the air filter 11. During operation of the engine, the depression of air pressure in the air-filter 11 is communicated to the bottom of the canister 20, causing air to be drawn downwardly through the charcoal bed 21 from the open top of the canister 20. The air upsets the absorption equilibrium of the vapours and the charcoal in the bed 21 and causes gasoline vapours to be de-sorbed and entrained in the air. The air and the entrained vapours pass via the tube 24 to the air filter 11 and thence through the choke tube 12 to the engine. By arranging that the tube 24 extends upwardly from the bottom of the canister 20 to about the level of the top of the canister 20, the effect is as if the tube 24 and the canister 20 are the limbs of a U-tube ensuring that any vapours which arrive in the canister 20 from the perforated tube 22 will be trapped, very largely in the canister 20, and unable to escape of their own accord either via the open top of the canister 20 or via the tube 24. The charcoal bed 21 will thus have an improved change of absorbing the gasoline vapours.
The degree of de-sorption of vapours from the bed 21 depends on the rate of air-flow through the canister 20, which in turn depends upon the depression of pressure and the rate of air flow in the air filter 11. The air flow in the filter 11 is greatest during acceleration or high speed operation of the engine, and it is believed that the amount of de-sorbed fuel entering the engine from the air filter 11 under such conditions is so small in proportion to the fuel from the jet(s) 15 that no significant change takes place in the hydrocarbon or carbon monoxide content of the engine exhaust gas. The air passing through the canister 20, the bed 21 and the tube 24 to the air filter does not substantially change the quantity of air which would otherwise be induced by the engine.
When the engine is operated at low speeds after a hot-soak period, the air passing through the canister 20 may initially de-sorb considerable quantities of gasoline which may then constitute a significant proportion of the air vapour stream reaching the air filter 11. In order to avoid a substantial change in the composition of the combustible mixture reaching the manifold 19, the tube 24 may incorporate a calibrated orifice 25 to restrict the rate of flow to the air filter 11.
The fuel system 10 further comprises a tube 26 connecting the air space of the fuel tank 17 with a perforated pipe 27 disposed adjacent the perforated pipe 22 at, or just beneath, the top of the bed 21. The cap 28 closing the filling tube 29 of the tank 17 is devoid of the usual breather orifice. Vapours from the tank 17 enter the tube 26 and pass via pipe 27 into the bed 21 where they are trapped and adsorbed, at least in part. Desorption of the vapours takes place in the manner described in relation to vapours originating from the carburettor 13.
An expansion tank 47 is incorporated in the tube 26 to prevent the passage of liquid gasoline into the canister 20 from the tank 17. Liquid gasoline might otherwise tend to pass through tube 26 due to splashing in the tank 17, or due to thermal expansion of vapour in the tank 17 forcing liquid gasoline into the tube 26, particularly when the tank 17 is full and the automobile in which the fuel system 10 is installed is on a steep slope.
It is estimated that for an automibile of European manufacture having an engine capacity of the order of 1,500 c.c. the gasoline losses which need to be taken up by the canister 20 amount to up to about 8 grams per hot soak and up to about 20 grams per day from the tank 17.
FIG. 2 shows the canister 20 in greater detail. The perforated pipes 22 and 27 may be of any convenient configuration, e.g., ring-like or spiral: one convenient form resembles, apart from the perforations, the pressure tube of a Bourdon-type gauge, and the pipes 22,27 may be concentrically arranged in the same plane. In tested embodiments of the canister 20, the perforated tube 27 from the fuel tank 17 has been arranged to surround the perforated tube 22 from the carburettor 13.
The bed 21 comprises about 700 grams of coco-nut charcoal resting on a screen 31 of inert, fine mesh, textile material supported by a dished metal mesh screen 32. The top of the bed 21 is similarly confined by a screen 33 of fine mesh textile material, with a thin metal mesh screen 34 pressed down on the screen 33 by the action of a resilient metal mesh packing 35 trapped under the top of the canister. The pressure of the packing 35 prevents movement of the charcoal granules in the bed 21 so as to minimise attrition.
The tube 24 is of plastics material reinforced with nylon thread.
Another form of canister 20 shown in FIG. 3 is similar to that of FIG. 2 but differs in that the upwardly extending part of tube 24 is disposed within the canister 20 instead of outside. The upwardly extending part of the tube 24 may be integral with the canister 20.
FIG. 4 shows a fuel system 100 basically similar to the system 10 of FIG. 1, but incorporating a pressure-balance valve 37 in the tube 23. The valve 37 comprises a plunger 38 urged to the left (as viewed in FIG. 3) by a spring 39. The plunger 38 moves against the spring 39 when the pressure on its right-hand face (as viewed in FIG. 3) is reduced. A pipe 40 communicates the pressure in the manifold 19 from downstream of a throttle control butterfly valve 41 to the right-hand side of the plunger 38. Thus, when the pressure in the manifold 19 is low, as during engine operation, the plunger 38 will move to the right. Attached to the left-hand face of the plunger 38 is a valve member 42 which moves in a chamber 43 communicating with the choke tube 12 upstream of the jet(s) 15 via a tube 44. An apertured plate 45 in the valve 37 provides communication between the left and right-hand parts of the tube 23 on each side of the valve 37.
In the left-most position of the plunger 38, the valve member 42 closes the entrance to the tube 44 and any vapours generated in the carburettor 13 will pass through the aperture in the plate 45 along tube 23 to the canister 20 where they are trapped and absorbed in the manner previously described. These vapours can be de-sorbed later in the same manner as described in relation to FIG. 1.
When the pressure in the manifold 19 is reduced due to engine operation, the plunger 38 moves to the right causing the valve member 42 to close the aperture in the plate 45 so that any vapours from the carburettor are drawn along the left-hand parts of the tube 23 through the chamber 43 and the tube 44 and into the choke tube 12 from where they proceed to the engine. Thus during engine operation, vapours arising in the carburettor 13 are drawn directly into the engine instead of passing first to the canister 20. When the engine is inoperative, the vapours are absorbed in the canister 20 as described in relation to FIG. 1.
Some European automobile engines are provided with a carburettor vent which communicates with the choke tube so that vapours arising in the carburettor will pass to the choke tube during engine operation. The embodiment of Figure incorporates such a vent (corresponding to the left-hand part of tube 23 and tube 44) so that carburettors of this type may be employed in a fuel system in accordance with this invention without substantially affecting the designed performance of the carburettor.
In this embodiment, as in the embodiment of FIG. 1, the vapour tube 26 from the fuel tank 17 incorporates an expansion tank 47 so as to minimise the risk of liquid fuel passing to the canister 20 and saturating the charcoal bed 21.
Although coco-nut charcoal has been specifically described hereinabove as the material in which fuel vapour is absorbed, it will be appreciated that other materials, such as coal or peat charcoal or silica gel, may also be employed.
The features disclosed hereinbefore may be employed in various combinations without thereby departing from the invention.
In order to form a relatively homogeneous fuel-oxidant mixture, it is desirable in many instances for the liquid fuel to be relatively volatile. The combustion of the fuel-oxidant mixture during the operation of the engine produces heat which tends to volatilise the lighter constituents of the fuel. If the engine is stopped after a period of operation, the fuel adjacent the engine continues to receive heat and to volatilise, and it is necessary to allow the volatilised fuel to escape to avoid any increase in the pressure in the fuel system.
In the case of automobile engines powered by gasoline-air mixtures, the volatilised gasoline from the carburettor bowl after a period of operation of the engine is vented to atmosphere from the carburettor. Legislation is now in force or proposed in various countries to limit the amount of gasoline which may thus be lost from the carburettor. Legislation is also in force or proposed in various countries to limit the quantity of gasoline which may be lost from the main fuel storage reservoir or tank, of automobiles. The losses in this case are due to diurnal temperature variations and a heating of the tank during operation of the automobile.
It is an object of the present invention to provide a fuel system in which fuel volatilisation losses from the system or the engine are minimised.
The present invention provides a fuel system for an internal combustion engine comprising a reservoir for fuel, a duct having a mixing zone in which, in operation of the engine, the fuel is mixed with an oxidant (such as air) to form a combustible mixture which passes through the duct to the engine, a body of material which is capable of reversibly absorbing fuel volatilised from the reservoir, first means which enable the reservoir to communicate with the body of absorbent material, second means which enable the body of absorbent material to communicate with the mixing duct upstream of the mixing zone, and third means enabling the body of absorbent material to communicate with the oxidant at substantially its full static pressure.
The term "absorbing" is intended to include both physical absorption and the physicochemical phenomenon of adsorption. "Reversibly absorbing" is intended to convey that the absorption is reversible.
When the oxidant is passing through the mixing duct, there is a depression in its pressure relative to the pressure in the reservoir and the body of material. Oxidant will be drawn from the third means through the body of material into the duct and thus serve to carry desorbed fuel through the second means towards the mixing duct.
In cases where the fuel vapour is denser than the oxidant, preferably the first means comprises a first conduit having one end at or near the upper end of the body of material, the second means comprises a second conduit which has one end at or near the lower end of the body of absorbent material, and the said one end of the first conduit lies between the said one end of the second means and the third means. This arrangement ensures that the fuel vapour passes out of the first means at or near the top of the body of absorbent material and sinks into the body of material where it is absorbed. During desorption, the oxidant also passes downwardly from the third to the second means, thus desorbing fuel from the top of the body of material first, so that the top is relatively free of fuel and capable of absorbing more fuel vapour passing out of the first means, when the passage of oxidant diminishes or ceases.
Moreover, where the said reservoir is the carburettor of a carburetted internal combustion engine, the disposition of the said one end of the first means at or near the upper end of the body of material enables the oxidant, usually air, to communicate with the carburettor bowl through the first means with substantially no pressure drop due to the body of material. Thus the performance of a carburettor designed for operation in a previously known fuel system devoid of a body of absorbent material will be substantially unchanged when incorporated in a fuel system in accordance with the invention.
The second conduit preferably has a part which extends upwardly substantially to the level of the upper end of the body of absorbent material. The said part of the second conduit serves, in effect, as one upwardly extending limb of a U-tube, of which the other limb is provided by the body of material. Heavy fuel vapour forms a trapped layer in the U-tube, the top of the layer being substantially no higher than the level of the upper end of the body of material. The trapping of the fuel vapour increases the chance of absorption of the vapour by the body of material.
The body of material may be disposed in a container and the third means may be provided by an orifice in the container.
In one fuel system in accordance with the invention, the second means comprises a valve which provides a path for any fuel volatilised from the reservoir to pass to the body of absorbent material when the pressure in the mixing duct is greater than a selected pressure, and which interupts the path when the pressure in the mixing duct is less than the selected pressure and provides an alternative path for any volatilised fuel to pass directly from the reservoir to the mixing duct upstream of the mixing zone. The duct may incorporate a throttle control for regulating the fuel-oxidant flow to the engine and the said valve may operate in accordance with the pressure downstream of the throttle control.
Where the invention is applied to automobile engines, the reservoir referred to may be either the carburettor bowl or the tank or both.
The invention will now be described by way of non-limitative example only and with reference to the accompanying drawings in which:
FIG. 1 shows schematically one form of fuel system in accordance with the invention, for use in a carburetted automobile engine,
FIG. 2 shows a part of FIG. 1 to a larger scale,
FIG. 3 depicts an alternative construction of the part of FIG. 2, and
FIG. 4 shows another form of fuel system in accordance with the invention.
In FIG. 1, the fuel system is generally indicated by reference 10 and comprises an air-filter 11 of known type, a choke tube 12, into which air from the filter 11 is drawn when the engine (not shown) is in operation, a carburettor 13 comprising a bowl 14, which serves as a reservoir for the gasoline fuel, and one or more jets 15 providing communication between the carburettor and a narrow mixing zone 16 of the choke tube 12. The fuel is supplied to the carburettor 13 from a main storage tank or reservoir 17 by a pump 18 and the level of fuel in the carburettor bowl 14 is substantially maintained by a well-known valve-and-float mechanism (not shown).
The passage of air through the choke tube 12 causes a fall in the static pressure in the tube 12 as compared with the pressure in the carburettor 13 and gasoline is induced through the jet(s) 15 into the zone 16 of tube 12 where it mixes with air to form a combustible mixture. The combustible mixture passes to the engine via an intake manifold 19, the quantity of this mixture being regulated by a butterfly valve 41 upstream of the manifold 19.
The fuel system 10 further comprises an open-topped container or canister 20 containing a bed 21 of charcoal granules. A perforated pipe 22 is disposed at the top of, and just within, the bed and connected by a tube 23 to the top of the carburettor 13.
If the carburettor 13 should become so heated that gasoline contained therein vapourises, the vapours pass via the tube 23 and a perforated pipe 22 into the top of the bed 21. Since the gasoline vapours will be very largely heavier than air, they tend to sink from the pipe 22 downwardly through the charcoal bed 21 where they will be trapped and at least partially absorbed. Substantially none of the gasoline vapours will rise upwardly from the perforated pipe 22, but a thin layer of charcoal is provided above the perforated pipe 22 to ensure that any vapours which do tend to rise due to unusual operating conditions will have their upward passage resisted and may be absorbed in the thin layer or deflected downwardly. In practice, a significant amount of gasoline is vapourised from the carburettor during the so-called "hot soak" period of about half an hour following operation of the engine.
By disposing the perforated pipe at or near the top of the bed 21, it is ensured that efficient utilisation of the bed by the descending vapours takes place. Furthermore, the disposition of the perforated tube 22 substantially at the top of the bed 21 of charcoal enables air to be drawn into the carburettor 13 via the tube 23 and the perforated tube 22 from the open top of the canister 20 with substantially no impedance to its passage: accordingly, the carburettor 13 need not be particularly adapted for incorporation in the fuel system in accordance with the invention as variations of pressure can take place within the carburettor substantially as freely as in the absence of the canister 20 and the interconnecting tubes 22,23.
The lower end of the canister 20 is connected to the air filter 11 by a tube 24 which extends from the bottom of the canister 20 at least to the level of the top of the canister 20 before its connection to the air filter 11. During operation of the engine, the depression of air pressure in the air-filter 11 is communicated to the bottom of the canister 20, causing air to be drawn downwardly through the charcoal bed 21 from the open top of the canister 20. The air upsets the absorption equilibrium of the vapours and the charcoal in the bed 21 and causes gasoline vapours to be de-sorbed and entrained in the air. The air and the entrained vapours pass via the tube 24 to the air filter 11 and thence through the choke tube 12 to the engine. By arranging that the tube 24 extends upwardly from the bottom of the canister 20 to about the level of the top of the canister 20, the effect is as if the tube 24 and the canister 20 are the limbs of a U-tube ensuring that any vapours which arrive in the canister 20 from the perforated tube 22 will be trapped, very largely in the canister 20, and unable to escape of their own accord either via the open top of the canister 20 or via the tube 24. The charcoal bed 21 will thus have an improved change of absorbing the gasoline vapours.
The degree of de-sorption of vapours from the bed 21 depends on the rate of air-flow through the canister 20, which in turn depends upon the depression of pressure and the rate of air flow in the air filter 11. The air flow in the filter 11 is greatest during acceleration or high speed operation of the engine, and it is believed that the amount of de-sorbed fuel entering the engine from the air filter 11 under such conditions is so small in proportion to the fuel from the jet(s) 15 that no significant change takes place in the hydrocarbon or carbon monoxide content of the engine exhaust gas. The air passing through the canister 20, the bed 21 and the tube 24 to the air filter does not substantially change the quantity of air which would otherwise be induced by the engine.
When the engine is operated at low speeds after a hot-soak period, the air passing through the canister 20 may initially de-sorb considerable quantities of gasoline which may then constitute a significant proportion of the air vapour stream reaching the air filter 11. In order to avoid a substantial change in the composition of the combustible mixture reaching the manifold 19, the tube 24 may incorporate a calibrated orifice 25 to restrict the rate of flow to the air filter 11.
The fuel system 10 further comprises a tube 26 connecting the air space of the fuel tank 17 with a perforated pipe 27 disposed adjacent the perforated pipe 22 at, or just beneath, the top of the bed 21. The cap 28 closing the filling tube 29 of the tank 17 is devoid of the usual breather orifice. Vapours from the tank 17 enter the tube 26 and pass via pipe 27 into the bed 21 where they are trapped and adsorbed, at least in part. Desorption of the vapours takes place in the manner described in relation to vapours originating from the carburettor 13.
An expansion tank 47 is incorporated in the tube 26 to prevent the passage of liquid gasoline into the canister 20 from the tank 17. Liquid gasoline might otherwise tend to pass through tube 26 due to splashing in the tank 17, or due to thermal expansion of vapour in the tank 17 forcing liquid gasoline into the tube 26, particularly when the tank 17 is full and the automobile in which the fuel system 10 is installed is on a steep slope.
It is estimated that for an automibile of European manufacture having an engine capacity of the order of 1,500 c.c. the gasoline losses which need to be taken up by the canister 20 amount to up to about 8 grams per hot soak and up to about 20 grams per day from the tank 17.
FIG. 2 shows the canister 20 in greater detail. The perforated pipes 22 and 27 may be of any convenient configuration, e.g., ring-like or spiral: one convenient form resembles, apart from the perforations, the pressure tube of a Bourdon-type gauge, and the pipes 22,27 may be concentrically arranged in the same plane. In tested embodiments of the canister 20, the perforated tube 27 from the fuel tank 17 has been arranged to surround the perforated tube 22 from the carburettor 13.
The bed 21 comprises about 700 grams of coco-nut charcoal resting on a screen 31 of inert, fine mesh, textile material supported by a dished metal mesh screen 32. The top of the bed 21 is similarly confined by a screen 33 of fine mesh textile material, with a thin metal mesh screen 34 pressed down on the screen 33 by the action of a resilient metal mesh packing 35 trapped under the top of the canister. The pressure of the packing 35 prevents movement of the charcoal granules in the bed 21 so as to minimise attrition.
The tube 24 is of plastics material reinforced with nylon thread.
Another form of canister 20 shown in FIG. 3 is similar to that of FIG. 2 but differs in that the upwardly extending part of tube 24 is disposed within the canister 20 instead of outside. The upwardly extending part of the tube 24 may be integral with the canister 20.
FIG. 4 shows a fuel system 100 basically similar to the system 10 of FIG. 1, but incorporating a pressure-balance valve 37 in the tube 23. The valve 37 comprises a plunger 38 urged to the left (as viewed in FIG. 3) by a spring 39. The plunger 38 moves against the spring 39 when the pressure on its right-hand face (as viewed in FIG. 3) is reduced. A pipe 40 communicates the pressure in the manifold 19 from downstream of a throttle control butterfly valve 41 to the right-hand side of the plunger 38. Thus, when the pressure in the manifold 19 is low, as during engine operation, the plunger 38 will move to the right. Attached to the left-hand face of the plunger 38 is a valve member 42 which moves in a chamber 43 communicating with the choke tube 12 upstream of the jet(s) 15 via a tube 44. An apertured plate 45 in the valve 37 provides communication between the left and right-hand parts of the tube 23 on each side of the valve 37.
In the left-most position of the plunger 38, the valve member 42 closes the entrance to the tube 44 and any vapours generated in the carburettor 13 will pass through the aperture in the plate 45 along tube 23 to the canister 20 where they are trapped and absorbed in the manner previously described. These vapours can be de-sorbed later in the same manner as described in relation to FIG. 1.
When the pressure in the manifold 19 is reduced due to engine operation, the plunger 38 moves to the right causing the valve member 42 to close the aperture in the plate 45 so that any vapours from the carburettor are drawn along the left-hand parts of the tube 23 through the chamber 43 and the tube 44 and into the choke tube 12 from where they proceed to the engine. Thus during engine operation, vapours arising in the carburettor 13 are drawn directly into the engine instead of passing first to the canister 20. When the engine is inoperative, the vapours are absorbed in the canister 20 as described in relation to FIG. 1.
Some European automobile engines are provided with a carburettor vent which communicates with the choke tube so that vapours arising in the carburettor will pass to the choke tube during engine operation. The embodiment of Figure incorporates such a vent (corresponding to the left-hand part of tube 23 and tube 44) so that carburettors of this type may be employed in a fuel system in accordance with this invention without substantially affecting the designed performance of the carburettor.
In this embodiment, as in the embodiment of FIG. 1, the vapour tube 26 from the fuel tank 17 incorporates an expansion tank 47 so as to minimise the risk of liquid fuel passing to the canister 20 and saturating the charcoal bed 21.
Although coco-nut charcoal has been specifically described hereinabove as the material in which fuel vapour is absorbed, it will be appreciated that other materials, such as coal or peat charcoal or silica gel, may also be employed.
The features disclosed hereinbefore may be employed in various combinations without thereby departing from the invention.