Fuel valve.

0001The invention relates to a fuel valve with a fuel inlet, a metering device and a fuel outlet.

0002Valves of this type are available in numerous versions for the metered delivery or injection of fuel in combustion systems, internal combustion engines, burners for the regeneration of particle filters and the like (see, for example, GB-A-1 526 385 or FR-A-476 333).

0003In some applications, such as regeneration burners of particle filters, the valves have narrow cross sections for fuel delivery due to the small power required. This has the disadvantage with diesel fuel, particularly in cold seasons, that the valve becomes blocked due to the failure of paraffins from the fuel.

0004The invention has for its object to provide a fuel valve of the type mentioned, in which malfunctions in diesel fuel do not occur.

0005The object is achieved by the features of claim 1.

0006The housing forms a reservoir of fuel around the valve, in which it is warmed up by the heatable housing to such an extent that paraffin flocculation no longer occurs in winter operation.

0007With a continuous flow of fuel, its heating can be ensured even in very cold seasons by the housing being designed with surface-enlarging devices such as ribs, balls, partition walls and the like.

0008A heating resistor or heating wire, which can be wound around the housing or embedded in the housing wall, preferably provides the thermal energy to be supplied. It must be ensured that temperatures that ignite the fuel are not reached. This is done, for example, by suitable selection of a heating resistor with a positive temperature characteristic (PTC characteristic) or by supplying the heating resistor with a pulse-width modulated voltage.

0009The energy supply to the heating device can be regulated as a function of the housing temperature and / or the ambient temperature by means of a controller.

0010Exemplary embodiments of the invention are shown schematically in the drawing. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a fuel valve with associated control device,</dd><dt>2 and 3</dt><dd>one embodiment of the valve housing,</dd><dt>Fig. 4</dt><dd>a voltage-time diagram.</dd></dl>

00111 shows a fuel valve 10 which has a controllable valve needle 11 which, in cooperation with a fuel outlet 12, forms a quantity metering device for the fuel 10 entering through inlet openings 13. The fuel valve 10 is surrounded by a housing 15 which encloses an annular space 16 around the valve 10, which is filled with fuel 14 during operation. The housing 15 also has an inlet connection 20 through which the fuel flows from a fuel tank into the annular space 16 of the housing 15. The fuel 14 'metered by the valve 10 reaches the consumer, such as a burner nozzle or the like, via an outlet connection 21.

0012An electrical heating winding or a resistance wire 25 is embedded in the housing wall and is connected to a direct current source 27 via a control device 26. When using the fuel valve in a vehicle, the power source 27 is the on-board battery.

0013A resistance thermometer is preferably used to measure and monitor the temperature of the fuel valve or its surroundings, in which the resistance of the heating winding 25 is measured by means of a Wheatstone bridge, and the temperature on the housing 15 via a processor 29 on the basis of the resistance / temperature characteristic of the resistance wire 25 calculated. For this purpose, a PTC thermistor, ie a material with a PTC characteristic, such as copper or nickel, is used as the resistance wire 25. A heating winding of this type simultaneously ensures that the heating temperature of the valve housing 15 is limited.

0014It goes without saying that any other temperature measurement method, for example using a sensor, can also be used. Instead of the housing temperature, the control of the valve can also be monitored depending on the ambient temperature.

0015The control unit 26 is started up, for example, by means of a pulse 30 that can be triggered by hand if required. The processor 29 will then close a temperature measuring circuit 31 which applies the current source 27 to the measuring bridge 28. The potential U₃₄ and U₁₂ of the measuring points 32 and 33 of the bridge 28 are registered and evaluated in the processor 29 to determine the temperature of the valve housing 15.

0016For temperature measurement recordings, the temperature measurement switch 31 is closed by means of a control pulse and thus the resistance bridge to the voltage U._B placed, the potentials U₃₄ and U₁₂ recorded by the processor 29 and evaluated to calculate the instantaneous resistance value R₄ of the heating wire 20 according to the following formula:<maths id="math0001" num=""><img file="EP0503263B1_D0001.tif" /></maths> which can be derived from the ratio U₁₂ / U₃₄. The instantaneous temperature T in the housing 15 is finally calculated via the resistance value R₄ of the wire 25 and the resistance temperature function below.<maths id="math0002" num=""><img file="EP0503263B1_D0002.tif" /></maths> In the formula, R₄₀ is the resistance value of winding 25 at 0 ° C, n is an integer dependent on the resistance material and a_i a temperature coefficient.

0017Depending on the temperature measured in this way, the heating power for the housing heating 25 is regulated by the processor 29. This is done by changing the pulse widths of a pulse-like voltage application for the resistance wire.

00184 shows the voltage U applied to the heating wire 25 as a function of the time t. During the measuring period, ie with the temperature measuring switch 31 closed, a voltage U₃₄ is applied to the heating wire 25. For temperature measurements, measuring pulses 34 of constant time t_T spent. For the load application, the switch 35 is closed, whereby the heating wire 25, the battery voltage U_B receives. This load application takes place in a pulsed manner with a time period t (T) which depends on the measured temperature T. By means of a fixed specification of the maximum current value for the heating wire 25, a current limitation for the load circuit can thus be achieved by appropriate pulse width modulation. A temperature measurement can be carried out in each case in the time span Δt between two load pulses 51. In this case, it is advantageous if the temperature measurement and the load application are carried out alternately at a predetermined clock frequency. The period D of the cycle depends on the maximum required pulse width t (T)_Max of the load pulse 51.

0019Of course, other types of control are possible, such as, for example, that the resistance or temperature measurement is carried out regularly but not after every load pulse 51. Continuous voltage regulation for load operation is also possible, load operation being briefly interrupted for temperature measurements.

0020On the basis of the predefined resistance values ​​of the heating wires 25 or windings, the state of the resistance wire 25 can also be monitored from the resistance measurement, in that interruptions and short circuits can be detected.

0021The temperature determination can be repeated periodically at predetermined time intervals. If the measured temperature drops to a predetermined value, the processor 29 actuates a heating switch 35, as a result of which the current source 27 is applied to the heating winding 25 for heating the housing 15.

0022Many process methods are possible for the heating process. One possibility is to precalculate the heating duration for the individual case on the basis of device parameters (such as volume and thermal conductivity) of the valve or the housing 15 and to utilize it for the switch-off process. The heating period can also be changed depending on, for example, the ambient temperature. Another possibility is that the temperature of the housing 15 or the valve 12 is monitored continuously or at intervals even during the heating period and the heating switch 35 is opened again when a predetermined temperature limit is reached.

0023The configuration for coupling heat into the fuel surrounding valve 10 can also be varied. 2 and 3 show further embodiments of the housing 15, in which the contact area between the housing 15 and the fuel 14 is increased by appropriate measures in order to improve the heat transfer.

0024FIG. 2, in which the left half of a housing 15 'is shown in longitudinal section, shows an embodiment with lamellae which extend into the fuel-filled annular space 16'. 2 concentrically arranged annular inserts are provided, which are alternately attached to the upper and lower front ends 41 and 42 of the housing 15 'and which leave a passage 43 for the fuel 14 at the respective free end. The fuel is guided in a labyrinthine manner between the inserts 40 to the valve 10 and thereby absorbs the thermal energy which is coupled in through the heating winding 25 and passed on via the inserts 40. Lamellar or rod-like inserts are also possible, which can also be arranged perpendicular to the valve axis.

00253, the heat transfer area is enlarged by balls 50, which can be sintered in the housing. The use of balls 50 can be supplemented by using ribs 51. However, sieve inserts 52 are also conceivable which traverse radially or axially in the interior 16 of the housing 15.