Fuel Metering Device

This invention relates to a fuel metering device for low fuel feed pressures and adapted for use in externally ignited internal combustion engines of the air/fuel mixture-compressing type with conduit means for conveying fuel to the suction pipe of the engine, in which conduit means at least one throttle passage of determinable cross-sectional area is arranged.

In an internal combustion engine, such a fuel metering device serves for attaining, automatically and under all operational conditions, a favorable fuel/air mixture ratio, in order to burn the fuel as completely as possible and thereby to avoid or substantially reduce the production of toxic exhaust gases while maintaining an optimal performance of the internal combustion engine with the smallest possible consumption of fuel. To this end, it is necessary that, when starting a cold engine, the fuel/air mixture is "richer" during the warming-up phase, i.e., the fuel portion in the mixture must be larger, than when the engine is warm. However, even in a hot engine it is necessary to meter the fuel in amounts corresponding very accurately to the requirements of every operating condition of the internal combustion engine. Therefore, the proportionality of the amounts of air and fuel in the mixture must be variable, in dependence on such engine data as speed, load, and temperature, as well as on environmental data such as air humidity, atmospheric pressure, and ambient temperature.

In the case of a known fuel metering device of the initially described type, complicated control systems must be provided to meet the above-stated requirements.

It is an object of the invention to provide a fuel metering device in which the actual value of the fuel/air mixture is continually measured, and the desired value can be varied by very simple means, in particular by making use of all the possibilities of electrical control.

This object is achieved according to the invention, by providing a fuel metering device of the type described initially, wherein the conduit means which convey fuel to the suction tube serving as air-intake means of the engine, has at least one by-pass duct, by-passing the throttle means provided in the conduit means, which by-pass duct can be switched into the fuel conduit means; such switch-in takes place as a function of engine data, whereby the fuel/air ratio is rendered variable. The switch-in can be effected by electrically operating means, and may occur in the sense of an intermittent cyclic process whose cycle frequency may correspond to the suction frequency of the engine. In order to ensure a better control of the amount of fuel flowing through the by-pass duct, a throttle of determinable cross-section may also be arranged in the bypass duct.

The invention will be better understood and further objects and advantages will become apparent from the ensuing detailed specification of preferred but merely exemplary embodiments taken in conjunction with the drawings.

FIG. 1 shows a first embodiment of the fuel metering device according to the invention in which the air measurement is carried out by means of a Venturi;

FIG. 2 shows another embodiment of a fuel metering device, similar to that shown in FIG. 1 in which two conduits serve as fuel conveying means;

FIG. 3 shows yet another embodiment which is controlled by means of a Stromberg measuring member;

FIG. 4 shows a further embodiment, similar to that shown in FIG. 3, in which two simultaneously controlled throttles are arranged in the main conduit for correcting non-linear fluctuations of the air/fuel ratio.

The fuel is conveyed by means of a fuel prefeed pump (not shown) via a conduit 1 to a float tank 2, wherein the discharge opening of conduit 1 is controlled by means of a float-actuated ball valve 3. From the float tank 2, the fuel flows into the suction pipe 6 via a conduit 4 in which there is provided a throttle passage 5. A throttle valve 7 which can be adjusted as desired, and an air-flow measuring member (not shown) are successively arranged in the direction of air flow in suction pipe 6.

The conduit 4 is provided with a by-pass duct 10 which circumvents the throttle passage 5 and is controlled by a solenoid valve 11. The solenoid valve 11 is open when deenergized, however, it is also possible to use a valve which is closed when deenergized. A throttle passage 12 is disposed in the by-pass duct 10 downstream of the solenoid valve 11. To the metered amount of fuel whose flow is influenced by the throttle passage 5 and which can be determined by means of the pressure conditions in the suction pipe, there is fed an additional fuel amount which is controlled by an electrical control means in the form of the solenoid valve 11 and the flow of which is influenced by the throttle passage 12; such additional fuel supply occurs always, when the measured values of the engine data (e.g., of an oxygen detector electrode in the exhaust gas) cause a switch-in of the by-pass duct 10. Control and any resulting adjustment are preferably achieved by means of an electronic control device (not shown). Although the oxygen detector electrode is not shown an the electronic control device is only shown schematically by the reference numeral 18, they are nevertheless known in the art. For example, the oxygen detector electrode can be similar to that disclosed in either U.S. Pat. No. 3,464,008 or U.S. Pat. No. 3,738,341; and the electronic control device can be similar to that disclosed in U.S. Pat. No. 3,620,196.

Whereas only one fuel feed line 4 is provided in the embodiment shown in FIG. 1, the embodiment shown in FIG. 2 has two such fuel feed lines 4' and 4". Accordingly, two throttle passages 5' and 5" are also provided in the respective feed lines. The by-pass ducts 10' and 10" are controlled in common by a single solenoid valve 11, but they have each a throttle passage 12' and 12" respectively, and share the fuel admitted to valve 11 from float tank 2 via a common conduit 10a.

Into the embodiment shown in FIG. 3, the air amount flowing through the suction pipe 6 is measured by means of a Stromberg measuring member 13 which comprises a needle 15 rigidly mounted on a metering piston 14 and which controls the cross-sectional area of a fuel metering nozzle 16.

In the embodiment shown in FIG. 4, needle 15 controls additionally the diameter of a throttle bore 17 which is interposed upstream of nozzle opening 16 in fuel feed line 4. In this embodiment, by-pass duct 10b discharges into fuel feed line 4 in a zone thereof between the two control points at 16 and 17. A complete compensation of non-linear fluctuations between the amount of air flowing through the suction pipe and the fuel amount to be added, is achieved by thus controlling the diameter of throttle bore 17 as a function of the diameter of nozzle opening 16.