Internal-combustion engines – Charge forming device – Gaseous fuel and air mixer
Patent
1987-12-14
1989-08-22
Cross, E. Rollins
Internal-combustion engines
Charge forming device
Gaseous fuel and air mixer
123 27GE, F02B 4300
Patent
active
048585831
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arrangement for the metering of fuel, in particular liquid gas, to a variable-output consumer, for example a vehicle engine, which comprises a metering device with a reduction valve, a metering valve and a chamber arranged therebetween and means of control (open-loop system) or means of regulation (closed-loop system) for setting the valves as a function of operating variables, in particular for controlling the metering valve as a function of a power requirement signal.
Known arrangements of this type (WO 82/02926, EP-A 64373, EP-A 155538, DE-A 31 49 839, US-A 4,386,594) control the second valve as metering valve as a function of a power requirement signal, for example the pressure in the air duct leading to the consumer and, if appropriate, other operating variables such as engine speed, air and gas temperature. Control in this case is understood as meaning influencing the position of the metering valve in an open-loop system (in contrast to the closed-loop system). Open-loop control has the advantage that it can react virtually without delay to changes in the power requirement signal. It is set up in such a way, taking into account the positioning data of the valve, that the rate of fuel fed to the combustion air stream comes as close as possible to the desired ratio. A precondition here for the desired metering is that the pressure by which the gaseous fuel is fed to the metering valve has a predetermined magnitude which is either held constant or is controlled variably as a function of operating variables, in particular a power requirement signal. However, open-loop controls (unlike closed-loop controls) suffer from the basic disadvantage that, even with the most elaborate account taken of many operating variables, the accuracy of their effect is dependent on the functional constancy of the individual elements of the open-loop system. If, for example, the flow cross-section of a metering valve changes due to soiling or a control signal does not have the intended level owing to a fluctuating voltage supply, or if the metering valve operates in ranges with different characteristic curves due to changing operating conditions, this results in a metering error. Owing to this characteristic, the known arrangements are basically unsuitable for applications in which high-precision metering is demanded, for example for use in conjunction with a controlled catalyzer. It is admittedly known to use closed-loop control systems in engines with fuel injection, directly influencing the metering of the fuel. However, transferring this measure to gas metering has so far not yet proven possible, because it is extremely difficult to meter gases precisely under the effect of highly fluctuating operating influences and different characteristics of the gas itself under extreme load conditions. This also applies to cases where a high precision design is used for the metering valve and the operating variables are electronically processed, because the superposing of different operating conditions on the control of the metering valve results in a shift from its characteristic curve. It is therefore typical that in the only case known (DE-A 34 10 930), in which a lambda control is proposed for a gas-operated motor, it is obviously a stationary motor with slow output variation that is involved, which allows slow adjustment excursions for an exact positioning of the metering valve under the effect of the lambda control (page 6, top), there being no direct actuation of the metering valve under the effect of a power requirement signal. Lambda is the ratio between the quantity (mass) of air avialable for combustion and the quantity of fuel. The stoichiometric relation is characterized by lambda=1.
The invention is therefore based on the object of providing an arrangement of the type mentioned at the start which allows a universal arrangement, in particular including under the conditions of short-term load change in vehicle engines, and in which the accuracy of the metering is not impaired by a shift in the
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patent: 3960126 (1976-06-01), Shinoda
patent: 4141326 (1979-02-01), Wolber
patent: 4386594 (1983-06-01), Szloboda
patent: 4413607 (1983-11-01), Batchelor et al.
patent: 4617904 (1986-10-01), Pagdin
Cross E. Rollins
Hi-Tec-Gas International GmbH
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