Fuel metering device for internal combustion engines

Abstract

A fuel metering device for an internal combustion engine having a fuel reservoir from which a fuel line leads to an air-intake suction tube of the engine, wherein the amount of fuel metered into a given amount of air flowing through the suction tube is determined by the air pressure in the air space of a fuel reservoir and in the suction tube as well as by the output signal of a measuring sensor adapted for detecting the composition of the exhaust gas produced by the engine, and emitting corresponding intermittent output signals, is improved by the combination of A. sources for detecting differences in air pressure in the suction tube, B. communicating means between the sources, and C. means for controlling air flow through the communicating means as well as the air pressure in the air space in the fuel reservoir by means of intermittent output signals emitted by the sensor.

Description

BACKGROUND OF THE INVENTION

This invention relates to a fuel metering device for an internal combustion engine having a fuel reservoir from which a fuel line leads to an air-intake suction tube of the engine, wherein the amount of fuel metered into the quantity of air flowing through the suction tube is determined by the pressures in a fuel reservoir and in the suction tube, as well as by the output signal of a measuring sensor adapted for detecting the composition of the exhaust gases of the engine.

In known fuel metering devices of this type, the output signals of the sensor which show abrupt changes of voltage are integrated in an electric circuit and the resulting integrated voltages will serve as regulating signals for a fuel metering valve.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a fuel metering device of the type initially described, wherein integration of the output signals is achieved using a minimum number of electrically operating parts, while avoiding the intermittent output signals of the measuring sensor which have a disadvantageous effect on the running of the engine and/or on the composition of the exhaust gases.

This object is attained according to the invention by providing, in a fuel metering device as initially described; control means adapted for controlling by means of intermittent output signals from a measuring sensor, communicating means between sources of different air pressure, on the one hand, and a fuel reservoir, preferably that of a carburetor, on the other hand, and thereby the air pressure prevailing in the air space of the fuel reservoir; and air chamber means enlarging the total volume of the air space in the fuel reservoir, for integrating the changes in the air pressure.

According to a preferred embodiment of the invention, the air space is connected via air duct means, the cross sectional areas of which are controllable by means of solenoid valves, with the parts of the suction tube sections upstream and downstream of a throttle passage arranged in the suction tube and being preferably devised as an air flow measuring device. The desired integration constant is determined, on the one hand, by the resistances to air flow due to throttling means disposed in the air duct means and/or by the cross sectional areas of the solenoid valves at opening times, and on the other hand, by the air volume in the fuel reservoir. To this end, it can be advantageous to use valves having large cross sectional areas when opened, and to open these valves only for a short time. The air space in the fuel reservoir, which is usually held constant in carburetors having the fuel level in the reservoir controlled by a float valve, is in most cases of insufficient volume to achieve the desired integration of fluctuations in air volume. In order to achieve the desired storage effect, this air space can, therefore, be in free communication with a separate air chamber, thereby enlarging the total available air volume.

According to a further embodiment of the improved fuel metering device according to the invention, the output signals of a measuring sensor can serve for the simultaneous pressure control of the fuel reservoirs of several fuel metering devices. For this purpose, the electrical control input is required only once, and by means of this control, multiple enrichment of fuel in the fuel-air mixtures can be attained uniformly by the several carburetors of the engine.

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

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows in a schematic view a preferred embodiment of the improved fuel metering device according to the invention.

DESCRIPTION AND OPERATION OF THE EMBODIMENT

In an air-intake suction tube 1 of an internal combustion engine, a carburetor 2 operating at continuous pressure and a butterfly valve 3 are mounted successively in the direction of air flow through the suction tube 1 indicated by an arrow. The air space 4 in a fuel reservoir 5 is connected by a line 6 with the part of the suction tube 1 upstream of the carburetor 2, and by a line 7 with the part of the suction tube 1 downstream of the carburetor 2. Specifically, line 7 is connected to the air space 8a behind the rear end of a carburetor regulating piston 8, which is arranged transverse to the direction of air flow to serve as a throttle member therefor and is suspended for axial displacement by means of a membrane 9. The space 8a rearward of this regulating piston 8 is connected by way of an orifice 10 with the part of the suction tube downstream of carburetor 2 so that air pressure prevailing in that part can act on membrane 9 and on regulating piston 8 affixed thereto. The chamber 9a between the membrane 9 and suction tube 1 surrounding regulating piston 8 is connected by way of a bore 11 to the part of suction tube 1 upstream of the carburetor 2 whereby the air pressure in that part of suction tube 1 also prevails in chamber 9a. To the carburetor regulating piston 8 there is affixed a metering needle 12, which controls the opening 13 of a tube 14 dipping into the fuel in reservoir 5.

In lines 6 and 7 there are disposed solenoid valves 16 and 17 which are controlled by the upper and lower threshold values of a sensor 19 set in the exhaust pipe 18 of the engine. This sensor 19 comprises a small tube closed at one end and which is made of a solid electrolyte material, e.g. of zirconium dioxide. The tube is vapor-plated externally and internally with layers of microporous platinum which are provided with contactors (not shown) to which an electrical potential can be applied. This tube of sensor 19 has one side in contact with the ambient air and its other side in contact with the exhaust gases of the internal combustion engine. At the higher temperatures prevailing in the flow of exhaust gases, the solid electrolyte material is oxygen-ion conducting. When the oxygen partial pressure of the exhaust gases differs from the oxygen partial pressure of the ambient air, a potential difference will occur between the two platinum layers, and correspondingly between the two connectors (not shown), which potential follows a characteristic curve corresponding to the air factor .lambda.. This potential difference depends logarithmically on the quotient of the oxygen partial pressures on both sides of the solid electrolyte of sensor 19. Therefore, the output voltage of the oxygen sensor 19 changes abruptly in the range in which the air factor .lambda. is close to or equal to 1.0; for, when .lambda. is greater than 1.0, unburned oxygen suddenly appears in the exhaust gases. Because of the fact that the output voltage of the sensor 19 is strongly dependent on the air factor .lambda., this sensor is exceptionally well suited for the control of the above-mentioned solenoid valves 16 and 17. The voltage of sensor 19 is large in the range of .lambda. greater than 1, and small in the range of .lambda. smaller than 1. In the fuel metering device according to the invention, only these large and small voltages, above or below a predetermined threshold value, respectively are used for the control of solenoid valves 16 and 17. Thereby, the pressure in air space 4 of fuel reservoir 5 is adjusted until an air factor .lambda. proportional to 1 is attained. The latter air factor has proved to be particularly favorable and corresponds to a stoichiometrical mixture of the amounts of air and fuel. To obtain the desired adjustment of solenoid valves 16 and 17, solenoid valve 16 is controlled by the lower sensor voltages, below the lower threshold value, and the solenoid valve 17 is controlled by the higher sensor voltages, above the upper threshold value. When valve 16 is opened, the air pressure in fuel reservoir 5 increases, and the fuel ratio in the fuel-air mixture increases likewise, while, when opening solenoid valve 17, the fuel ratio decreases. In the electrical circuit between sensor 19 and solenoid valves 16 and 17, Schmitt-triggers 20 and 21 are provided. These are connected, each in series, to control amplifiers 23 and 24. Trigger 20 receives the voltages below the lower threshold value, and trigger 21 receives the voltages above the upper threshold value. Optionally, a single Schmitt-trigger may be sufficient for receiving voltages above and below the upper and the lower threashold values, respectively.

The fuel pressure from fuel reservoir 5, exerted on valves 16 and 17 can be reduced by throttle means 25, 25' and 25", of which throttles 25 and 25' can be arranged in lines 6 and 7, respectively, leading to the suction tube 1, and throttle 25" in a bypass line 26 connecting lines 6 and 7 with one another.

Usually, the volume of the air space 4 in the fuel reservoir 5 is not sufficient to achieve a satisfactory integration of the pressure pulses. For this reason, air space 4 is connected via a line 27 with an air chamber 28. The total volume of air in air space 4 and air chamber 28, the throttle means 25, 25' and 25" as well as the cross sectional area of the solenoid valves 16 and 17 at opening determine the integration constant for the entire fuel metering device.

Claims

What is claimed is:

1. In a fuel metering device for an internal combustion engine having an air-intake suction tube and an exhaust pipe, the device comprising, a carburetor having a fuel reservoir within which an air space is defined and including a fuel line leading from the fuel reservoir to the air-intake suction tube, and a measuring sensor located within the exhaust pipe and adapted for detecting the composition of the exhaust gas produced by the engine and emitting corresponding intermittent output signals, wherein the amount of fuel metered into a given amount of air flowing through the suction tube is determined by the air pressures in the air space of a fuel reservoir and in said suction tube as well as by the output signal of the measuring sensor, the improvement comprising, in combination,

a. air pressure measuring sources connected at least at two locations to the suction tube for detecting differences in air pressure in said suction tube,

b. communicating means connected between said sources and to said air space,

c. means connected to said measuring sensor and to said communicating means for controlling air flow from said sources through said communicating means as well as the air pressure in said air space in said fuel reservoir by means of intermittent output signals emitted by said sensor,

d. means defining an air chamber, and

e. means connecting the air chamber to said air space, wherein said air chamber serves to smoothen the air fluctuations in said air space.

2. The improvement as described in claim 1, wherein said carburetor includes throttle means provided in said suction tube, one of said sources being located upstream, and another downstream of said throttle means, and wherein said communicating means comprise duct means leading from said air space in said fuel reservoir to the parts of said suction tube containing said sources upstream and downstream of said throttle means.

3. The improvement as described in claim 2, wherein said throttle means are adapted for producing a substantially constant pressure drop in said suction tube.

4. The improvement as described in claim 2, wherein said throttle means comprise an air flow-measuring means.

5. The improvement as described in claim 4, wherein said air flow-measuring means comprise a regulating piston disposed for axial displacement in a direction transversely to the direction of air flow in said suction tube, and a fuel metering needle affixed to said piston, and wherein said regulating piston has surfaces attached thereto which act in the respective directions of regulation of said piston, and said communicating means comprise means for applying the air pressures prevailing upstream and downstream of said air flow-measuring means to respective ones of said surfaces.

6. The improvement as described in claim 2, wherein said duct means comprise constant throttle means which are adapted for determining, together with the total volume of the air space in said fuel reservoir, the integration constant of changes in air pressure in said fuel reservoir.