FUEL SYSTEM FOR AN INTERNAL COMBUSTION ENGINE

Abstract: Fuel system for an internal combustion engine operated on liquefied gas. This liquefied gas is situated in a storage tank and is supplied from there by way of a pump and a supply pipe to one or more injectors. Excess fuel is returned to the tank. In order to limit heating of the fuel - and thus of the tank - as far as possible, caused by the heat transfer from the pump and heat from the environment of the engine, it is proposed that the quantity of liquefied gas supplied be made to correspond as far as possible to the required quantity of fuel. For this purpose, a pump with variable output is used, and this output is made dependent on the load of the internal combustion engine.

Description: Fuel system for an internal combustion engine. The present invention relates to a fuel system according to the preamble of Claim 1. Such a type of fuel system is known from US Patent Specification 5479906. Gas in the liquid phase is there fed by means of a fuel tank to a common rail for injectors, and excess fuel is returned to the tank by way of a return pipe in which a pressure regulator is fitted. This circulation causes heating of the liquefied fuel in the tank. In order to control the temperature of the tank, it is proposed that a separate circuit be provided, wherein liquefied gas is vaporized in the tank and fed in the gaseous condition upstream of the injectors to the intake port of the internal combustion engine. The fuel pump present in the tank can be controlled by means of a control device, in order to regulate the outlet pressure of the liquefied gas. This control mechanism also controls the injectors. In the case of such a system with return pipe known in the prior art, the quantity of fuel circulated by the electric pump is such that at maximum capacity of the internal combustion engine, i.e. at maximum fuel consumption, just sufficient fuel circulates in the system without an inadmissible lowering of pressure - and therefore vapour bubble formation - occurring. In the case of a conventional fuel system operating on LPG on average over 50% of the fuel fed in is returned over a longer period of time. Such a system operates satisfactorily, and in recent years it has proved possible for the power consumption of the pump used to be reduced to an ever- increasing extent, in other words to increase the efficiency of said pump, and also to bring its service life into line with the service life of the vehicle in which such a fuel system will generally be installed. The greater efficiency of the pump will mean that a smaller quantity of heat will be produced during the pumping, but such a quantity of heat will always be a considerable part of the quantity of energy supplied to the pump. When the pump is fitted in the tank, this heat is given off partly to the tank and partly to the pumped liquefied gas. This liquefied gas then moves through the engine compartment of the particular vehicle in which the internal combustion engine has been installed. Despite insulation measures, some heating will occur, and the heated excess fuel will be supplied to the tank by way of the return pipe. This means that the temperature of the tank increases during operation. Owing to the reduction in the energy consumption of the pump described above, it has proved possible to keep such an increase in the temperature of the tank within acceptable limits, in which case it is clearly essential for the tank to be able to give off heat to the environment. In the case of vehicles, for example, such fuel tanks are fitted underneath the floor, and such giving off of heat does not constitute any problem whatsoever in that case. In the case of other constructions, the tank is fitted in the passenger compartment or in the luggage compartment. In those places the heating can indeed constitute a problem, or it can do so if the tank is made of a plastic. It is the object of the present invention to prevent the heating of the fuel described above to a further extent, making it no longer necessary to take additional measures such as those described in US Patent Specification 5479906, in other words, the provision of a separate circuit for vaporous gas. This object is achieved in a fuel system of the type described above by the characterizing features of Claim 1. Modern internal combustion engines are without exception provided with electronics which control either the petrol part or the LPG part of the engine. The desired quantity of fuel to be injected into the internal combustion engine is measured in some way. This can be carried out, for example, by determining the quantity of air flowing in through the intake pipes. This can be achieved directly either by flowmeters or by means of calculations on the basis of the position of the throttle valve, the movement to which it is subjected, and the r.p.m. of the internal combustion engine concerned. In all cases, a signal which is representative of the quantity of fuel injected is present at the injectors. By linking this "demand" to the "supply" from the pump, it is ensured that as little fuel as possible is supplied, and in the case of a return pipe hardly any more fuel than is necessary for avoiding and removing the vapour bubbles is returned. This means that the heating of the tank can be fully or partially eliminated. It must be understood that during normal operation, apart from the factors described above which produce heating of the tank, cooling occurs because the diminishing volume of liquefied gas is taken up by vaporous gas, and heat is withdrawn from the environment during this vaporization. According to an advantageous embodiment of the invention, the above is synchronized in such a way that no more than 25% of the quantity of fuel supplied is moved through the return pipe. Apart from the return pipe described above, it is possible to fit pressure-regulating means in the pipe system of the fuel system. These can be pressure-regulating means which maintain a constant pressure, but they can also be pressure-regulating means which bring about a determined constant increase in pressure relative to the tank pressure. According to yet another embodiment of the invention, the increase in pressure relative to the tank pressure can be variable in such a way that at higher absolute pressures this increase in pressure is lower. For details, reference is made to Netherlands patent 1009528 in the name of applicant. However, it should be understood that the measures described above ensure that little or no rise in temperature and pressure occurs in the tank, with the result that an increase in pressure relative to the tank pressure does not occur either. It will be understood that the temperature of the tank is dependent on the three factors described above, being the efficiency of the pump, and more particularly the quantity of heat which is consequently thereby supplied to the environment with the exception of the fuel pumped away, and the quantity of heat which is supplied to the tank by fuel coming from the return pipe, minus cooling of the tank by vaporization. Of course, there is an exception to this if a motor vehicle with a tank, in particular in the passenger compartment, is left standing in the sun or the like for quite a long time, in which conditions an increase in the temperature is inevitable. Owing to the fact that it is no longer essential for the tank to give off heat to the environment, it is possible to provide the tank with a lining. A more attractive external appearance can be obtained in this way in certain circumstances. Moreover, it is possible to insulate the tank, with the result that the heating by external influences described above can be reduced considerably. Moreover, with such insulation, it is possible to deaden the noise of the pump further if the latter is situated in the tank. The pump used must, of course, have a variable output. This pump can be in the form of a rotary pump such as a pump with a brushless direct-current motor. In such a case the r.p.m. is variable, and more particularly continuously variable. The invention will be described in greater detail below with reference to an exemplary embodiment shown in the drawing. The sole figure shows very diagrammatically the layout of the fuel system according to the invention. In the sole figure, an internal combustion engine is indicated by 1. Only some parts of it are shown, such as the intake pipes 2 provided with injectors 3 for liquefied gas. If desired, a system can be present which permits running on petrol, but this is not important at present. These injectors 3 are controlled electrically by way of control device 13, to which the various operating parameters of the internal combustion engine are supplied. These parameters can be dependent on a device for determining the quantity of injected petrol, but can likewise be derived directly from the engine. The position of the throttle valve, r.p.m., quantity of air flowing through intake pipes 2 and the temperature of said air and of the internal combustion engine are important in this case. Injectors 3 are fed from a supply pipe 6, which is connected to a pump 5 fitted in a pressure vessel 4. More particularly, such a motor is a brushless direct- current motor, in the case of which more particularly a permanent magnet is disposed in a rotating manner. Such a motor is much simpler to regulate than three- phase motors known in the prior art. More particularly, the electronics required for it are simpler. Operation of the pump 5 is regulated by way of the control device 11, which is connected by way of a pipe 12 to pump 5. Downstream of pipe 6 is a return pipe 8, in which a pressure regulator 7 is accommodated. Return pipe 8 opens out into tank 4. Tank 4 is also provided with noise/heat insulation 10. The construction described above, and more particularly the combination of control device 11 and pump 5, is such that during variable operation a maximum of 25%, and more particularly a maximum of 20%, of the fuel supplied by way of supply pipe 6 always moves back through return pipe 8. In other words, the quantity of fuel consumed by the injectors 3 is in such proportion to the quantity of fuel supplied by way of supply pipe 6 that only about 20% of the fuel is not used and can be recirculated. Some return flow will generally be desirable, in order to counteract the formation of vapour bubbles as far as possible and to guarantee operation in all circumstances. As an example, a pump 5 can be used for an average internal combustion engine with a maximum capacity of 120 kW which has a maximum power consumption of 60 W. Over half of this 60 W will be given off as heat. This heat is given off partly to the tank. For in general, pump 5 will be immersed in the liquefied gas as close as possible to the bottom of the tank. Some of the heat is given off to the fuel introduced into supply pipe 6 and, in view of the fact that a maximum of about 20% is returned, about 80% is given off to the injectors 3. During conveyance of the fuel through pipe 6, pressure regulator 7 and return pipe 8, some further heating occurs. The quantity of heat given off by the pump described above can be considerably reduced by regulating the capacity of the pump. For the maximum capacity for which the pump is designed will seldom be required during normal operation. This makes it possible to meet the requirement of a maximum of 20% returned fuel described above. The result is that the fuel tank does not heat up during operation. Although the invention has been described above with reference to a preferred embodiment, it will be understood that numerous modifications can be made thereto without going beyond the scope of the present invention, as described in the appended claims. For instance, it is possible to integrate the control device of the pump 11 in part 13, and it is possible to base operation directly on the signals supplied to the inj ectors 3.

Claims: Claims 1. Fuel system for an internal combustion engine, comprising a storage (4) for liquefied gas, a pump (5) connected to a supply pipe (6), and one or more injectors (3) connected to said supply pipe, wherein said pump has a variable output controlled by a control unit (11) to which signals indicating the load of said internal combustion engine are supplied, characterized in that the output of said pump is controlled depending on the load of the internal combustion engine. 2. Fuel system according to Claim 1 , comprising a return pipe (8). 3. Fuel system according to one of the preceding claims, comprising pressure- regulating means (1). 4. Fuel system according to one of the preceding claims, in which said pump comprises a rotary pump with variable r.p.m. 5. Fuel system according to one of the preceding claims, in combination with claim 2, wherein the output of said pump is controlled in such a way that a maximum of 25% of the fuel supplied is conveyed through the return pipe. 6. Fuel system according to one of the preceding claims, in which the output of said pump is continuously variable. 7. Fuel system according to one of the preceding claims, in which said storage comprises a metal vessel provided with an insulating lining. 8. Fuel system according to one of Claims 1-6, in which said storage device comprises a plastic tank. 9. Fuel system according to one of the preceding claims, in which said pump comprises a brushless direct current motor.

Inventors: JAASMA SERVATIUS ALFONS MARIA, JAASMA, SERVATIUS, ALFONS, MARIA
Applicants: JAASMA SERVATIUS ALFONS MARIA, VIALLE BEHEER B V, JAASMA, SERVATIUS, ALFONS, MARIA, VIALLE BEHEER B.V.
Application year: 1999
Main classification: F02D19
IPC codes: F02D19, F02M21