SPRAY VALVE FOR A COMBUSTION ENGINE

Abstract: A combustion engine with fuel injection system has at least one cylinder with air inlet passage. In said passage a fuel spray valve opens which is connected to a fuel pipe with the pump. In order to improve the mixing of gasoline and air and the spray action of the spray valve in particular when the engine is cold, a fuel heating element is disposed in the fuel pipe or on the spray valve said heating element is provided in the form of a thermistor of material with a positive temperature coefficient; an electrical supply and discharge cable is connected to the thermistor. The thermistor can have the form of a PTC tablet which is connected to a heat sink designed as a metal box with at least one fuel passage.

Description: The invention relates to a spray valve for a combustion engine comprising a fuel heating element positioned in a cylindrical holder upstream of the valve seat, said heating element comprising a heat sink, a thermistor of ceramic material having a positive temprature coefficient (PTC) and electrical supply and discharge means. Such a spray valve is disclosed in DE-A-2750686. Combustion engines with fuel injection are divided into engines with mechanical or electronic gasoline injection and diesel engines with injection of diesel fuel. Compared with gasoline engines with a carburetor, an engine with fuel injection has the advantage that the fuel distribution is more efficient and the engine reacts much more quickly and more accurately to changes in the position of the throttle, this being due to the short time elapsing between the movement of the throttle and the injection of the fuel. The power and acceleration are therefore clearly better in a fuel injection engine than in a carburetor engine. Electronic injection has the not inconsiderable advantage over mechanical injection that one can use temperature and pressure sensors to supply the cylinders with the correct amount of fuel in all circumstances. The quantity of fuel to be injected can be regulated by controlling the pressure (between, for example, 3 and 6 bars) or by controlling the pressure (between, for example, 3 and 6 bars) or by regulation of the time. The outstanding advantages of fuel injection are offset by the disadvantage of a relatively poorer mixing of fuel and air; the air velocity is fairly low and there is litle time available to mix fuel and air. Besides, the spray valve has a sparing spray action. These advantages are particularly felt when the engine is cold. The sparingly sprayed fuel, when poorly mixed with air, precipitates on the cold inlet passage and the cold cylinder wall. Through heating the fuel to a particular temperature (in gasoline engines, for example between 40 and 70°C) when the engine is cold, a much finer spray is obtained. It was also found that where there was spraying the particles under a certain size (about 12 microns) no precipitation occurred on the cold wall. The temperature will have to be kept under such control that vapour condensation does not take place. The correct temperature depends on the boiling range of the fuel in question and the minimum pressure occurring in the system. The winter grade is determinative, because it contains more volatile constituents. The great advantage of the thermistor of PTC material is that on electrical charging thereof the temperature cannot rise above a particular value depending on the chosen material, so that even without an advanced delicate control system the temperature of the thermistor remains with absolute certainty below the chosen value and the fuel temperature can also be selected to be below the value at which vapour condensation within the fuel injector takes place. It is known that the PTC material works on the principle that the electrical resistance at a particular temperature (for example, 80°C) has increased to such an extent that no further temperature increase occurs. PTC material has a very great energy density (water/cu.cm) and has achieved its maximum temperature in a few seconds. In the spray valve of DE-A-275686 the thermistor is made of a number of stagged PTC elements in electric parallel connection, and between the PTC elements fuel ducts are open. As a matter of fact such a construction provides a efficient heat transfer however it is complicate and expensive and takes a lot of space. The invention aims to eliminate this disadvantage and to provide a spray valve in accordance with the preamble which is compact, strong, simple in construction and provides a very efficient heat transfer to the fuel. According to the invention the heat sink is formed as a closed cylindrical metal box, and the thermistor comprises one or more PTC tablets connected to an end face of said box, and that between the cylindrical wall of said box and the inner surface of said holder which is integral with or connected to the spray valve, fuel guiding means are disposed forming one or more spiral-shaped passages or passages parallel to the central axis of the cylindrical box. FR-A-2116047 discloses a spray valve for a combustion engine comprising a fuel heating element positioned in a cylindrical holder upstream of the valve seat and electric supply and discharge means. The fuel heating element is formed as a cylindrical thermistor (PTC) having a great number of capillary tubes of fissures. The fuel is in direct contact with the thermistor and flows through the tubes of fissures. The construction does not have a heat sink and the fuel will be subject to a considerable flowing resistance in the thermistor. In the spiral shaped passages or passages parallel to the central axis of the cylindrical box there is a risk that the fuel will exhibit in essentially laminary flow pattern. In order to improve this, turbulence-generating raised parts and/or recesses are preferably disposed in the wall of the passages. Of course, it is important that the heat taken up by the fuel during its flow to the combustion chamber is released as little as possible to the environment. That is why the holder containing the PTC tablet and the heat sink is preferably thermally insulating and is positioned as near to the spray valve as possible. In this connection it can be advantageous to make the holder with thermistor integral with the spray valve. This combination then has a relatively small mass and is warmed more quickly. This design is particularly suitable for a pressure regulation of the injection system as compared to a timed system, because the injection valve with energizable solenoid needed for this has a large mass. The invention can also be used for a diesel engine, where the injection pressure is much higher and the maximum admissible heating temperature of the fuel can be much higher than in the case of a gasoline engine. Since the fuel heating element can be interposed in a line, a manufacturer of combustion engines will be able to accept the use of the present invention without any problem. In the case of an engine with more cylinders, a number of heating elements can be connected to the same electrical system, for example by means of a bus-bar. The invention will now be explained in greater detail with reference to the figure. Referring to the figure the spray valve shown is fixed in a manner known per sé in the wall of the schematically shown air inlet passage 2 in the cylinder head of a gasoline fuel injection engine. This passage 2 is provided with an air filter (not shown) and a throttle valve (not shown) operated by the accelerator pedal. The spray valve 1 is connected by means of a holder 3 to a fuel pipe 4 with electric pump, which is not shown. The spray valve is of known construction and comprises a valve element 7 pulled by a spring 5 on its seat 6. With a particular fuel pressure (for example, 4 atmosphere), the valve opens and fuel is sprayed into the inlet passage and mixes with air. When the engine is cold a considerable improvement is achieved in this spraying if the fuel is heated to a temperature, say between 40 and 70°C. This heating of the fuel is produced by the contents of the holder 3. The latter contains a heating element in the form of a tablet-shaped thermistor 8 of ceramic material which has a positive temperature coefficient (so-called PTC material), and a heat sink 9 in the form of a closed box made of good heat-conducting metal and with as low a mass as possible. This box has a spiral peripheral groove 10. The tablet 8 is fixed to the top side of the box by means of an adhesive which conducts electricity and heat. By means of two terminals 12, 13 the thermistor is connected to electrical cables 14, 15, which are connected to an electrial voltage supply. Preferably accommodated in the electrical cables is a relay 16 which by means of cable 17 is connected to a thermostatic control unit 18 with a temperature sensor. This sensor ascertains the temperature of the cooling water of the cylinder of measures in some other way a temperature which determines the engine temperature, while the control unit gives signals to the relay 16 to switch off or change the electric current. The heating device works as follows: When the engine is cold the relay will be switched in such a way that electric current runs through the electrical circuit 14, 12, 8, 9, 13, 15 so that the thermistor tablet becomes warm. The carefully chosen ceramic PTC material of this tablet at a particular temperature (for example, 80°C) shows a very steep increase in the electrical resistance, which means that the tablet temperature stabilizes at that temperature and does not become warmer. The heat is transferred to the box 9 (heat sink). The fuel collides with the tablet 8 and flows through the spiral groove 10 on the outer periphery of the box to the spray valve 1. During this spiral flow, the fuel is preferably heated to a temperature at which vapour condensation does not take place. This temperature depends on the fuel pressure and composition. Since the tablet does not become warmer than a particular value selected on the basis of the material composition, vapour condensation in the fuel injector is prevented in a simple manner. Once the engine is at normal running temperature, the control unit 18 will switch off or reduce the electric current. The fuel heated when the engine is cold sprays much better than cold fuel. As a result of this, the period during which fuel enrichment is applied can be reduced. All this leads to lower fuel consumption and cleaner exhaust fumes. The box 9 can be provided with passages parallel to the central axis, instead of a spiral-shaped passage. The holder 3 with its contents could be integral with the injection nozzle. The tablet 8 could be placed between two closed metal boxes 9. Flutes or corrugations could be provided in the passage 10 to increase the turbulence. The fuel is heated to the desired temperature very quickly and the temperature control is further improved by the direct heat contact. By using a holder diposed on the spray valve itself and having therein the thermistor in the form of a PTC tablet which is connected to a heat sink for transfer of heat to the fuel, the heat sink being designed as a metal box with at least one fuel passage, the heat transfer is very efficient and the construction is compact, strong and reliable. Diesel engines can also be used, of course such adaptation of the ceramic PTC material that the temperature of the fuel will be higher than the value of around 40°C which is normal for petrol, since diesel oil is much less volatile.

Claims: Spray valve for a combustion engine comprising a fuel heating element positioned in a cylindrical holder (3) upstream of the valve seat, said heating element comprising a heat sink, a thermistor of ceramic material having a positive temperature coefficient (PTC) and electrical supply and discharge means, characterized in that the heat sink is formed as a closed cylindrical metal box (9), and the thermistor comprises one or more PTC-tablets (8) connected to an end face of said box, and that between the cylindrical wall of said box (9) and the inner surface of said holder (3) which is integral with or connected to the spray valve, fuel guiding means (10) are disposed forming one or more spiral-shaped passages or passages parallel to the central axis of the cylindrical box. Spray valve according to claim 1, characterized in that turbulence generating parts are disposed in the wall of said passages. Combustion engine with fuel injection system comprising at least one cylinder with an air inlet passage (2) and a spray valve according to claim 1 or 2 opening in the air inlet passage (2) and connected to a fuel pipe (4) with pump.

Inventors: BUENK, GERRIT, VAN DER ELST, FREDRIK MANNES NICOLAAS, VAN WECHEM, GUSTAAF LOUIS
Applicants: TEXAS INSTRUMENTS HOLLAND B.V.
Application year: 1987
Main classification: F02M53
IPC codes: F02B1, F02M51, F02M53, F02B3