FR2771139A1 - Injector supply circuit for liquid petroleum gas engines - Google Patents

Abstract

The fuel injected IC engine (40) is supplied with fuel through the supply circuit, which consists of a fuel tank (28), which feeds fuel through the supply pipe (32) by means of the pump (34), which supplies pressurized fuel to the fuel injector (36), at a flow rate greater than that required by the engine. A fuel return line (42) is also provided.

Description

 The present invention relates to a supply circuit for an internal combustion engine with liquefied gaseous fuel, in particular liquefied petroleum gas, as well as a fuel injector intended for such a supply circuit.

 The invention is described with reference to liquefied petroleum gas "LPG" used as fuel, by way of example of liquefied gaseous fuel. However, the invention applies to other liquefied gaseous fuels. All these fuels have the property of remaining in the liquid state under a relatively low pressure (for example 7 to 12 bar) so that they can be transported and stored easily in this state. These fuels are kept in a liquid state, from production to consumption. Vehicle tanks are filled in liquid form.

 The liquefied petroleum gas used as fuel is a mixture of hydrocarbons essentially composed of butane and propane. It also contains a certain amount of butenes, ethane and ethylene. However, in the present specification, the expression "main component" refers only to butane and propane, in the case of liquefied petroleum gas, that is to say the components which are generally present in at least quantity equal to 30% by weight.

 Liquefied petroleum gas fuel has a number of advantages over other fuels for internal combustion engines.

 The first advantage is that this fuel has advantageous performances from the point of view of the environment. It is not toxic, it contains practically no sulfur, lead, or benzene, and the exhaust gases it produces contain only much less CO, hydrocarbons and NOx than give petrol engines. In addition, combustion does not produce particles, so this fuel is particularly efficient in urban conditions.

 A second advantage of liquefied petroleum gas fuel is that the combustion carried out in the engines is clean and does not leave a scale which can foul the engines.

In addition, since it is a fuel in the gas phase during combustion, the "leaching" of the cylinders by an excess of liquid fuel during a cold start does not occur. The engine lubricant is therefore not diluted and retains its optimum characteristics for longer.

 A third important advantage of liquefied petroleum gas fuel is that driving comfort is increased compared to traditional fuels. Indeed, for mechanical performance roughly equal to that of a gasoline engine, a liquefied petroleum gas engine gives a significantly reduced noise.

 It should also be noted that the amount of energy of the liquefied petroleum gas housed in a fuel tank of a motor vehicle is practically equal to that which is obtained with the other liquid fuels.

 All the aforementioned advantages are obtained independently of the ratio of butane and propane contained in the liquefied petroleum gas. Depending on the country, these proportions vary, generally between 40/60 and 60/40.

 The disadvantages of using these liquefied gaseous fuels are essentially the size of the tank, and the cost of the particular equipment of the vehicle. The first drawback, the bulk of the tank, has recently been eliminated by a technique for manufacturing the tank from a composite honeycomb material which allows the production of tanks having practically the same configuration and the same size as the tanks for others. liquid fuels.

 Another disadvantage is the cost due to the necessity of using, according to the known technique, a solenoid valve, a vaporizer-regulator and a gas carburetor. It should be noted that this equipment is in addition to that which is normally present in the vehicle, since the regulations of most countries consuming liquefied petroleum gas fuel require the vehicle to be produced with two supply circuits, the one for liquefied petroleum gas, and the other for another liquid fuel, such as gasoline.

 FIG. 1 shows an example of a supply circuit for liquefied petroleum gas of the prior art. The liquefied petroleum gas is stored under pressure in a cylindrical tank 10 provided with a safety relief valve 12. The fuel, at a pressure determined essentially by the temperature of the fuel in the tank 10 and which is generally of the order of 5 to 8 bar and more, is transmitted by a line 14 to a vaporizer 16. The vaporized fuel is introduced into the intake manifold 18 of the engine 20. Usually, the vaporizer 16 is heated by the heat of the fluid of the circuit 22 for cooling the motor 20.

 Also shown by way of example are fuel injectors 24 opening into the intake manifold 18 just upstream of the engine 20, these injectors being supplied by a normal fuel injection circuit 26.

A drawback of this introduction of petroleum gas into the intake manifold in the gaseous state is that the volume of gas introduced is large. This admission must therefore be carried out sufficiently upstream relative to the engine. In the case of a multipoint petrol injection engine, that is to say having one injector per cylinder or group of two cylinders, the introduction of gaseous fuel far upstream in the intake manifold may pass on to the power supply of the other cylinders, taking into account the relative inertia of the currents formed. In addition, given this injection in the gaseous state, it is necessary to modify the intake circuit so that this large volume can be introduced upstream of the engine ("gas fuel")
The invention relates to a liquefied gaseous fuel supply circuit which differs from known supply circuits in that the liquefied gaseous fuel is introduced by injection in the liquid state.

 According to the invention, the liquid fuel is discharged at a high pressure (20 to 25 bar) such that the fuel is in the liquid state and is injected into the intake manifold just upstream of the intake valves of the cylinders, at one or more points. This injection is preferably carried out with injectors according to the invention which allow the simultaneous injection of two liquid fuels, the liquefied gaseous fuel and another fuel such as petrol.

 More specifically, the invention relates to a circuit for supplying an internal combustion engine with liquefied gaseous fuel containing at least one main component, of the type which comprises a pressure tank connected to the engine by a pipe; according to the invention, the internal combustion engine is an injection engine which comprises at least one injector introducing the fuel into the intake circuit, and the pipeline comprises, between the tank and the engine, a liquefied gaseous fuel pump intended putting the fuel at a pressure which, during operation, is constantly greater than or equal to the vapor pressure of the most volatile main component at the highest temperature reached by the injector.

 Preferably, the circuit further comprises a return line for liquefied gaseous fuel between the engine and the tank, and the flow rate of the pump is greater than twice the flow rate of fuel consumed by the engine.

 It is also advantageous for at least the injector to have an inlet and an outlet, so that the liquefied gaseous fuel circulates in the injector and cools it.

 Preferably, the liquefied gaseous fuel is liquefied petroleum gas, and the liquefied petroleum gas contains butane and propane in proportions of between 60/40 and 40/60, with the usual secondary components.

 It is also advantageous for the pressure created by the pump at the level of the injector at least to be greater than or equal to approximately 20 bar.

 In an exemplary embodiment, the engine comprises several injectors each placed in the intake circuit upstream of an intake valve of at least one cylinder, and each injector is mounted in parallel with the others, at an orifice of each of the injectors.

 The invention also relates to a fuel injector intended for a supply circuit of an internal combustion engine object of the preceding paragraphs, which comprises an internal needle intended to cooperate with a first seat and to be moved relative to the first seat by a first operating member, an external needle disposed concentrically with the internal needle and intended to cooperate with a second seat and to be moved relative to the second seat by a second operating member, and a body surrounding the external needle, the first and second seats being concentric.

 Preferably, the first seat is placed on the external needle and the second seat on the body.

 It is further advantageous for the body to have a liquefied gaseous fuel inlet orifice and a fuel outlet orifice, and for the two orifices of the injector body to be substantially opposite with respect to the central axis of the injector.

 In an exemplary embodiment, the first operating member comprises a control member carried by the external needle and a controlled element carried by the internal needle, and, in another exemplary embodiment, the first operating member comprises a member control carried by the body and a controlled element carried by one internal needle.

 In another exemplary embodiment, the second operating member comprises a control member carried by the body and a controlled element carried by the external needle.

 In one embodiment, the control member is a solenoid coil and the controlled element is a magnetic core. In another embodiment, the operating member is of the piezoelectric type.

 In an exemplary embodiment, the first operating member is of the electromagnetic type and the second operating member is of the piezoelectric type.

 It is advantageous that only one of the two operating members is controlled at a given time, and that the operating members are controlled by a computer of the vehicle in which the engine is mounted.

Other characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended drawings in which
Figure 1, already described, is a diagram of a supply circuit for liquefied petroleum gas of known type
FIG. 2 is a diagram of a circuit for supplying liquefied petroleum gas according to the invention, in an advantageous exemplary embodiment
Figure 3 is a schematic plan view showing the fuel supply to the injectors shown in Figure 2; and
FIG. 4 is a section through an example of an injector of two fuels, petrol in the central part and liquefied petroleum gas in the peripheral part.

 FIG. 2 represents a supply circuit according to the invention.

 Liquefied petroleum gas is kept in a tank 28, preferably having a configuration adapted to the chassis of the vehicle. The tank includes a safety relief valve 30. A supply line 32 leads the liquefied petroleum gas to a fuel pump 34 which brings the fuel pressure to a pressure which is constantly higher than the vapor pressure of the main component the most volatile of the fuel, at the highest temperature reached by the injector 36. The pressure given by the pump 34 is for example between 20 and 25 bar. This high pressure fuel in the liquid state reaches at least one injector 36. In FIG. 2, a single injector is shown in the intake manifold 38 of an engine 40. It is an injection single point. On the contrary, in Figure 3, there are shown four injectors 36, corresponding to a multipoint injection. Line 32 forms a supply ramp and line 42 a return ramp.

 According to a characteristic of an advantageous embodiment of the invention, the supply circuit comprises a return line 42. Preferably, the pump 34 operates at a constant flow rate which is greater than at least twice the flow rate consumed by the injectors 36 at full load. In this way, a large amount of fuel returns through the line 42 in the tank 28. It is advantageous for this return line 42 to leave from the injector itself, that is to say that the line 32 of supply and return line 42 are both connected to the injector 36 at different locations, so that the body of the injector itself is cooled by the circulation of liquid fuel.

This characteristic is indicated in FIG. 3 which represents an exemplary embodiment of multipoint injection in which each injector 36 is connected to the supply and return pipes 32 in parallel with the other injectors. In this way, all the injectors are practically at the same temperature, and this temperature is relatively low. Indeed, it is desirable that the temperature of the injectors 36, even when it is maximum, is relatively low so that the pump 34 can work at a reasonable pressure.

Thus, when the maximum temperature of the injectors 36 is 50 ° C., a pressure of 25 bar given by the pump 34 is largely sufficient.

 It was indicated, in the supply circuit of FIG. 2, that the circuit 44 for supplying petrol to the engine also joined the injector 36 of the liquefied petroleum gas. It is an advantageous characteristic of the invention since the transformation of a petrol engine into a liquefied petroleum gas engine does not require the addition of an element such as a vaporizer, in the intake manifold, because the injector or injectors of the two fuels can be mounted in the hole or holes provided for mounting the fuel injectors.

 FIG. 4 shows such an injector which can be mounted in a hole provided for a petrol injector, and which however allows the injection either of petrol or of liquefied petroleum gas.

 The injector shown in FIG. 4 has a cylindrical body 46 which ends, at the bottom, with a threaded end piece 48 intended to be screwed into the tapped hole normally provided in a motor for mounting a fuel injector. . A hollow external needle 50 is intended to move in translation in the body 46 and an internal needle 52 is intended to move in translation in the hollow external needle 50. This internal needle 52 carries, along its length, groups of fins 24 guiding the needle 52 in the internal bore of the external needle 50 when the tip of the needle moves away and approaches a seat 56 formed inside the hollow needle 50. The needle 52 therefore closes the orifice by cooperation with the seat 56 when it is brought back down by a spring 58 retained between a shoulder of the internal needle 52 and a shoulder of a cap secured to the external needle 50.

 The internal needle 52 can be moved away from its seat, when a gasoline injection is to be carried out, by attraction of an external magnetic core 60 secured to the needle 52 by a coil 62 which surrounds the upper part of the hollow needle 52 and which receives a current controlled by threads 64. When the internal needle 52 is moved away from the seat 56 by supplying the coil 62 with current, the gasoline which penetrates through the orifice 66 can flow between the 'internal needle 52 and the external needle 50 to the seat 56 to be injected.

The external needle 50 is guided in translation in the body 46 by fins 68 and a seal 70 placed at the top of a sleeve screwed onto the body 46. The external needle 50 is pushed against a seat 72 , formed inside the body 46, by a spring 74 which is pressed against a flange of the external needle and a member secured to the body 46. The external needle also carries, outside, a magnetic core 76 intended to be attracted by a coil 78 of electromagnet when the latter is supplied via wires 80. The liquefied petroleum gas transmitted to the injector enters through an orifice 82 and the excess fuel is evacuated by an orifice 84. In this way, the body 46 and the external needle 50 are cooled by the circulation of liquefied petroleum gas
There have also been indicated, at the lower part of the body 46, holes 86 intended for the passage of the injected fuel.

 Of course, during operation, electrical excitation pulses are transmitted either to the wires 64 or to the wires 80, depending on whether the supply is to be made of gasoline or liquefied petroleum gas.

 The injector shown in FIG. 4 comprises a first operating member which comprises a controlled element constituted by the magnetic core 60, integral with the needle 52, and a control element, constituted by the coil 60 which is integral with the external needle 50.

The external needle 50 is itself displaced by a second operating member which comprises a controlled element consisting of the magnetic core 76 and a control element consisting of the coil 78. Each operating member and the associated spring are adapted to the particular fuel (for example petrol at a pressure of 3 to 5 bar, and liquefied petroleum gas at a pressure of 20 to 25 bar).

 Although the operating devices have been shown in the form of electromagnets, they can be replaced by other types of operating device. It is thus advantageous for at least one of the operating members to be of the piezoelectric type. For example, since the circumferential dimension of the seat 72 is much greater than that of the seat 56, the distance from which the outer needle 50 must be moved away from the seat 72 of the body 46 is very small, of the order of a few microns or a few tens of microns, so that it is possible to use a piezoelectric actuator working between the outer needle 50 and the body 46 practically at the location of the coil 78. Such an embodiment has the advantage of solving the problem of fuel tightness between the body and the external needle.

 Although a concentric type injector has been described for injecting two fuels, it is also possible to use separate injectors for the two fuels.

For example, an adapter can be screwed into the hole normally provided in the intake manifold for the single injector of the initial fuel, for example petrol.

The adapter itself has two threaded holes for mounting the two injectors, that of the initial fuel and that of the liquefied petroleum gas.

 The control of the injector or injectors can be easily carried out, as those skilled in the art know, by the injection control computer usually present on an injection motor vehicle. The computer receives, for example, signals from sensors incorporated into or disposed near the injectors so that it can control the pump which is thus regulated. Thus, the pump can work at constant flow, at constant pressure or at constant pressure and flow.

 It is understood that the invention has only been described and shown as a preferred example and that any technical equivalence may be made in its constituent elements without going beyond its ambit.

Claims (10)

 1. Supply circuit for an internal combustion engine with liquefied gaseous fuel containing at least one main component, of the type which comprises a pressure tank connected to the engine by a pipe, characterized in that  the internal combustion engine is an injection engine (40) which comprises at least one injector (36) introducing the fuel into the intake circuit, and  - the line (32) comprises, between the tank and the engine, a pump (34) of liquefied gaseous fuel intended to put the fuel at a pressure which, during operation, is constantly greater than or equal to the vapor pressure of the component most volatile main at the highest temperature reached by the injector (36).  2. Supply circuit according to claim 1, characterized in that it further comprises a pipe (42) for the return of liquefied gaseous fuel placed between the engine (40) and the tank (28), and the flow rate of the pump (34) is greater than twice the flow rate of fuel consumed by the engine (40).  3. Supply circuit according to claim 2, characterized in that the injector at least (36) has an inlet (82) and an outlet (84) so that the liquefied gaseous fuel flows in the injector (36) and cools it.  4. Supply circuit according to any one of the preceding claims, characterized in that the liquefied gaseous fuel is liquefied petroleum gas, and the pressure created by the pump (34) at the level of the injector at least (36 ) is greater than or equal to approximately 20 bar.  5. Supply circuit according to any one of the preceding claims, characterized in that the engine (40) comprises several injectors (36) each placed in the intake circuit (38) upstream of an intake valve at least one cylinder, and each injector (36) is mounted in parallel relative to the others, to an inlet orifice of each of the injectors.  6. Fuel injector intended for a supply circuit of an internal combustion engine according to any one of claims 1 to 5, characterized in that it comprises  an internal needle (52) intended to cooperate with a first seat (56) and to be moved relative to the first seat by a first operating member,  an external needle (50) disposed concentrically with the internal needle (52) and intended to cooperate with a second seat (72) and to be moved relative to the second seat by a second operating member, and  a body (46) surrounding the external needle,  the first and second seats (56, 72) being concentric.  7. An injector according to claim 6, characterized in that the body (46) has an orifice (82) for entering liquefied gaseous fuel and an orifice (84) for leaving the fuel.  8. Injector according to one of claims 6 and 7, characterized in that the first operating member comprises a control member (62) carried by the external needle (50) and a controlled element (60) carried by the internal needle (52), and the second operating member comprises a control member (78) carried by the body (46) and a controlled element (76) carried by the external needle (50)  9. An injector according to any one of claims 6 to 8, characterized in that at least one operating member is of the piezoelectric type.  10. Injector according to any one of claims 6 to 8, characterized in that only one of the two operating members is controlled at a given time, and the operating members are controlled by a computer of the vehicle in which is mounted engine.