Arrangement for operating an internal combustion engine with different fuels

p0001The invention relates to a for alternate operation designed with different fuels internal combustion engine, according to the preamble of claim 1.

p0002The use of alternative energy sources for operating an internal combustion engine, especially an internal combustion engine for driving a motor vehicle wins with regard to the limited oil reserves and of compliance with the requirements prescribed by law, in future even lower limits for pollutants is becoming increasingly important.

p0003As a way to conventional fuel (gasoline) as power for motor vehicles to replace at least in part, to the gas operation of motor vehicles has been found.

p0004Of the types of gas commercial representations to all the Liquified Petroleum Gas (LPG) and Compressed Natural Gas (CNG) have been found.

p0005Since these gases are free of lead and sulfur compounds and have excellent combustion properties with excellent mixture formation and mixture distribution, the emissions reduce CO, HC, NO_x and CO₂ respect to motor vehicles, which are equipped with gasoline-powered internal combustion engines.

p0006Due to the still not widely developed in most countries gas supply network, a combination of gas and operating conventional petrol in cars seems sensible.

p0007In order to allow, in addition to petrol and the LPG operation, usually the standard with a device equipped for the petrol motor vehicle is retrofitted with LPG installation on dual-mode operation. Besides the necessary for the storage, distribution and sale of auto gas components (eg gas tank with valves, pipes, thrusters, injection and gas-petrol switch) while an additional electronic control unit with associated sensors and actuators is required, which controls the gas operation.

p0008Moreover, it is known, motor vehicles as standard to provide them with internal combustion engines that can run on different fuels.

p0009In WO 92/08888 a for bivalent operation with petrol and Liquefied Petroleum Gas (LPG) is described, designed as a second fuel internal combustion engine. This system includes for each of the two fuels in separate reservoirs that are each have their own supply lines with a single fuel rail connected. At this fuel rail, a single set of injectors is arranged so that these injectors attach both the fuel petrol and LPG fuel of the intake air. Excess fuel that is not sprayed from the injectors, is returned via return lines in the respective reservoir. care, depending on the fuel type individually controllable electromagnetic valves and self-acting check valves being used ensure that the excess fuel is returned to the right reservoir. The known arrangement further includes a conventional control means, inter alia, for determining the injection time for petrol operation, is connected downstream of a further control means for determining the injection time in gas mode. If the internal combustion engine powered by gasoline, it is calculated in a conventional manner depending on the load and the speed of the Brenkraftmaschine the injection time and the injection pulses are passed on unchanged by the downstream control device for the gas operation of the injectors.

p0010however, the internal combustion engine is operated with LPG, as calculated by the electronic control unit for petrol injection times are corrected in the downstream control device for gas operation and then passed on in the form of injection pulses to the injectors, which now inject LPG. Such a correction calculated for the gasoline operating injection times is necessary because in order to achieve an ignitable fuel-air mixture for the combustion chambers of the internal combustion engine as well as for the purpose of maintaining a certain range of the air ratio for reasons of limitation of the pollutant component in the exhaust gas of the engine, the properties of the fuel to be injected, namely car gas must be considered.

p0011By using one and the same injectors for the fuel currently does result in a cost-effective and space-saving solution, the structural design, the valves can represent (eg different pressures, density) only a compromise due to the different characteristics of the injected fuel. Moreover, it can come from one fuel to the other fuel when using a single set of injectors for the fuel currently in problems during the transition. Another disadvantage is that separate control devices are needed for the different fuel types.

p0012The invention has for its object to provide an arrangement for controlling a provide with different fuels operated internal combustion engine, both the switching between the modes of operation ensured with different fuels in a simple manner with high operational reliability, as well as a simple retrofitting of a vehicle equipped with such an internal combustion engine motor vehicle given is.

p0013This object is achieved according to the features of claim 1. Advantageous embodiments of the invention describe the dependent claims.

p0014The invention is further illustrated by the single figure.

p0015Which shows schematically only the parts of a motor vehicle and an internal combustion engine, which are necessary for understanding the invention.

p0016By the reference numeral 10 is a Bezintank is referred to, by which a suction line 11 leads to an electrically operated fuel pump 12th These electric fuel pump, for example a roller vane pump which is activated via a signal from an electronic control device 23 can also be arranged directly in the gasoline tank 10th It generates the necessary injection pressure, and promotes fuel via a fuel filter 13 and a feed pipe 14 to a common rail 15 close to the intake pipe of the internal combustion engine. At the end of the distribution strip 15 is a pressure regulator 20 is disposed which maintains the pressure differential across the metering gap of the injectors, independently of the injected amount of fuel constant. This ensures that the injected fuel quantity is determined solely by the opening duration of the injector. On the rail 15 of the cylinder of the internal combustion engine electromagnetic injection valves are in a known manner according to the number 16,17,18,19 angeordnet.Überschüssiges gasoline that is not sprayed from the injectors, passes via a return line 21 back to the fuel tank 10. A level sensor 22 outputs a the filling level of the fuel tank 10 corresponding signal for further processing to the electronic control device 23rd

p0017In addition to the fuel tank 10 in the motor vehicle, a gas tank 24 is provided for receiving and storing liquid petroleum gas (LPG). The pressurized liquefied gas is pressed by means of an electric pump 25, and an open during gas operation of the engine shut-off valve 26 via a feed line 27 to a gas distribution strip 28th At this rail 28 the number of engine cylinders in accordance with electromagnetic injection valves 29, 30, 31, 32 are also arranged. By opening these injectors relaxing the liquefied petroleum gas and is injected as a gaseous fuel into the intake manifold. Excess fuel passes via a return line 33, a pressure transducer 34 and a check valve 38 back to the gas tank 24th

p0018A level sensor 35 is a the filling level of the gas tank 24 corresponding signal for further processing to the electronic control device 23 from. On the electronic control device 23 further from the outputs to multiple sensors and transmitters, of which in the figure only a few outputs are located. These are signals of oxygen sensors upstream and downstream of a catalytic converter lambda 1, 2, from a throttle sensor DKL, of temperature sensors for intake air TAL and coolant temperature TKW and sensors for engine load (eg air mass, intake manifold pressure, speed).

p0019A arranged in the instrument panel of the motor vehicle petrol / gas selector switch 37 allows a choice of petrol or gas operation of the internal combustion engine and is also electrically connected to the controller 23rd

p0020Depending on the switching position of this petrol / gas selector switch 37 may be either the fuel injection valves 16, 17, 18, 19 for petrol operation or the injection valves 29, 30, 31, 32 is activated for gas operation. The switching of the power supply between the two sets of injection valves takes place via an electrically actuatable change-over switch 36, which is preferably implemented as a relay with a switching member. A winding end of the relay coil is connected to ground, while the other end via a control line 39 to the electronic control device 23 and 37 is there to the output of the petrol / gas selector switch in conjunction. The input terminal of the two-way contact of the relay 36 is connected to the terminal 15 (terminal output ignition ride switch), so that 37, the terminal 15 supply voltage to the injectors either, depending on the switching position of the petrol / gas selector switch on all injectors for gas operation 29, 30 31, 32 or is connected to all injectors for gasoline operation 16, 17, 18, 19th

p0021The individual control of the individual injectors for 37 selected by the petrol / gas selector mode petrol or gas is effected via a ground timing of the electronic control device 23rd This purpose is served drive lines 40, 41, 42, 43, wherein one drive line is connected both to a terminal of an injection valve for fuel operation and to one terminal of an injection valve for gas operation. This results in the possibility and to use the same power amplifier for both the driving of an injection valve for fuel operation as well as for driving an injection valve for gas operation. So for example, controls the amplifier 44 via the drive 40 in gas mode of the internal combustion engine, the injector 32, in petrol mode it controls contrast to the injector 19th So despite the sequential control possibility of all eight injectors only four power amplifiers are needed. A switch from petrol to gas or vice versa can not only depend on the driver's request by means of the petrol / gas selector switch are introduced, but can also occur automatically if one of the two tanks 10, 24 has reached a minimum allowable level. For this purpose, the signals of the two level sensors 22, 35 are of the electronic control device 23 is evaluated and it is switched regardless of the currently set switching position of the petrol / gas selector switch to the respective other fuel. A subsequent operation of the fuel / gas selector switch 37 has then provided no more influence on the choice of the mode of the internal combustion engine until the appropriate level sensor again signals an over the minimum permissible level.

p0022As for controlling the alternately operated with different fuel internal combustion engine, a single control device 23 finds use not only the injectors must be switched due to the different characteristics of the two types of fuel when changing the operating mode, but also certain functions and / or data in the electronic control device 23 ,

p0023If you switch from petrol to gas operation, the following should be considered:<ul><li>at the start enrichment shorter injection times are required during gas operation due to absent or very low existing wall film,</li><li>in Nachstartanreicherung / warm-up enrichment lower enrichments are required during gas operation,</li><li>for the basic maps for the injection time calculation other basic data are due to the structurally different injectors during gas operation save,</li><li>When using gas as fuel, the required enrichment / Abmagerungen are much lower at transient operation,</li><li>due to other ignition conditions other ignition timings during gas operation required also gas has a RON greater than 100, ie at full load earlier ignition timings are possible,</li><li>in the lambda control other control parameters must be used,</li><li>the tank venting of fuel system must continue to run even during the gas operation, but may proceed with a reduced amount because no has been heated fuel comes through the return of the fuel injection rail,</li><li>in gas mode no preliminary injection is necessary.</li></ul>

p0024In addition, the fuel supply pump of the other tanks must be switched on when switching from petrol to gas operation at first, so that the pressure in the fuel rail is constructed. Then, only the injection valves are switched. The lambda control is briefly interrupting, not to wallop by brief Lambda deviations regulation.

p0025When switching from gas to petrol operation of the first injection pulse at petrol mode must be increased by a corresponding wall-film quantity depends on the motor load point. This too lean fuel-air mixture is avoided and any possible engine misfire prevented.

p0026The invention has been described using a preferred embodiment, in addition to the petrol mode the gas operation with Liquified Petroleum Gas (LPG) is possible. Likewise, but also bivalent operation with petrol and Compressed Natural Gas (CNG) is possible instead of the gas operation with LPG. This requires a different structural configuration of the injection valves, which must be adapted to the circumstances of the gas used. Furthermore, the inventive arrangement and the method can also be used for internal combustion engines, each having only one injector (single point injection) for petrol and for gas operation.