EP0232464B1

EP0232464B1 - Carburetor for internal combustion engines

Info

Publication number: EP0232464B1
Application number: EP86113807A
Authority: EP
Inventors: Pierluigi Dell'orto
Original assignee: Dell Orto SpA
Current assignee: Dell Orto SpA
Priority date: 1985-10-17
Filing date: 1986-10-06
Publication date: 1991-07-24
Anticipated expiration: 2006-10-06
Also published as: IT1185460B; EP0232464A3; ES2023109B3; DE3680509D1; EP0232464A2; IT8522524A0

Description

The present invention relates to a carburetor for internal combustion engines with controlled ignition, designed to equip vehicles, of the type wherein fuel feed can be finely and promptly regulated according to the vehicle running conditions and to the engine working conditions, so as to comply, on one hand, with the strictest anti-pollution rules and to satisfy, on the other hand, the most elaborate working requirements.
As known, the strength of the air/fuel mixture fed by a carburetor to an internal combustion engine depends on the difference between the pressure existing in correspondence of fuel discharge into the main duct of the carburetor and the pressure existing in the constant level float chamber, above level. According to the most commonly known technique, this last pressure corresponds to ambient pressure or to the pressure existing just downstream of the carburetor air filter, and it is substantially constant. Whereas, the pressure in the main duct obviously varies according to the engine running conditions. As a result, it will be possible to obtain a satisfactory value of the strength of the mixture fed to the engine only in some of these conditions.
According to the more advanced known technique, an improvement has already been attempted by varying, at least in certain conditions, the pressure existing at the top of the constant level float chamber. In particular, it is already known, for instance from US-1783214 and from DOS-2900732, to produce a depression into the top of the constant level float chamber of a carburetor, through proper conduits leading into said chamber. In the solution proposed in DOS-2900732.7, said depression is obtained by using separate suction means controlled by sensors detecting the combustion state of the engine mixture.
Although this already developed solution allows to obtain satisfactory results, both against pollution and for a proper engine performance, the increasing requirements in these respects have led designers to seek even better solutions.
In the carburetor according to the present invention, the depression into the top of the constant level float chamber is derived, with possibility of regulation, from the depression produced by engine running into the air intake of the carburetor; this allows - as has been proved by tests - to improve the working of the carburetor according to the conditions of use of the engine and of the vehicle onto which it is mounted.
In substance, the present invetion concerns a carburetor in which a fine and continuous regulation of the feed mixture strength is obtained producing a controlled depression in the top of a constant level float chamber, the carburetor comprising a register throttle valve in an air intake duct and downstream thereof a main duct with a venturi followed by an accelerator throttle valve, the top of said constant level float chamber being connected with external atmosphere by an opening which opens into the air intake duct upstream of the register throttle valve when the register throttle valve is in its closed position, and being connected by a gauged port with the main duct, downstream of the register throttle valve and upstream of the venturi.
This carburetor is characterized in that the opening connecting the top of the constant level float chamber with the air intake duct opens through the wall of the air intake duct and is positioned with regard to the register throttle valve so that it is upstream of the rim of the register throttle valve when the register throttle valve is in its closed position and downstream of the rim when it is in its fully open position, in that said air register throttle valve is asymmetric and has its minor sector corresponding to said opening, and in that the position of said air register throttle valve is determined by an electric motor controlled by sensors detecting the combustion state of the engine.
It should be noted that the devices characterizing the carburetor according to the invention can be advantageously used to perform also the functions of a pickup pump and/or - if suitably integrated with temperature sensors - of an automatic starter.
Moreover, according to the invention, the air register throttle is mounted idle on a shaft, in respect of which it is caused to rotate thanks to a worm drive mechanism operated by said electric motor, with possibility however to act independently from said mechanism when opening.
The invention is now illustrated in further detail, by mere way of example, with reference to a preferred embodiment thereof, shown on the accompanying drawing, in which:

Fig. 1 is a conventional representation of the carburetor according to the invention; and
Fig. 2 illustrates in detail the control of the air register throttle of the carburetor of figure 1.

The carburetor according to the invention comprises, in known manner, a main duct 1, with choke 1A, having at one end the air intake 2, protected by a filter element 3, and at the opposite end - of mixture outlet to feed the engine - the throttle 4 controlled by the accelerator, a constant level chamber 5 with float 6, and fuel tubes and jets 7. The carburetor also comprises, in the air intake 2, an air register throttle 8 just downstream of the filter element 3.
According to the invention, the top of the constant level float chamber 5 is connected to external atmosphere - through the air intake 2 of the duct 1 - in two different points: firstly, through the gauged port 9 opening directly into the chamber of the main duct 1, upstream of the choke 1A and downstream of the throttle 8; and secondly, through the tube 10 opening at 11 into the air intake 2 of the duct 1, in correspondence of the rim of said throttle 8.
The throttle 8 (see fig. 2) is mounted idle on a shaft 12, in respect of which it can be caused to rotate thanks to a worm mechanism 13 operated by an electric motor 14 controlled, at 15, by sensors of the engine combustion state, through an electronic pilot circuit. The mechanism 13 acts by pressing onto the throttle 8, which is kept close to said pressure mechanism by a spring 16 acting so as to close said throttle. In this manner, the throttle 8 can open even independently from the pressure of the mechanism 13 and of the motor 14, when the carburetor working conditions so require.
The sensors of the engine combustion state can consist of various devices detecting the environmental and operating features; in particular, a probe will definitely be used to check the presence of oxygen in the exhaust manifold of the engine. The use of temperature sensors will also be required when wishing to adopt the described arrangement in order to facilitate engine startup.
As can be easily understood, in the heretofore described and illustrated carburetor, the air-fuel ratio in the mixture fed to the engine is regulated by varying both the pressure of the air intaken by the carburetor and the pressure of the constant level float chamber. Since the mere metering through the air throttle would create difficulties of regulation when working with low air capacities (for instance, when idling and during the first running steps: in such cases, the throttle would be quite closed and any small movements would lead to excessive variations in the carburation), the invention has provided for two paths apt to connect the constant level float chamber to external atmosphere: the first (9) downstream of the air register throttle, subjected to the same pressure of the air let into the carburetor, and the second (10, 11) ending in correspondence of the throttle rim. During the closing movement of the throttle 8, the opening 11 is initially downstream of the throttle rim. In this way, the pressure on the opening 11 varies from a minimum value, produced by the pressure loss on the throttle, to a maximum value, when the throttle is completely closed.
The pressure in the fuel chamber, which is the sum of the pressures on the two openings 9 and 11, can thus be regulated to a sufficiently wide extent as to allow a proper regulation of the air-fuel ratio in the mixture, in any running condition.
For what concerns the control of the throttle 8, it is evident that the electronic circuit - receiving the signals from the probe checking the oxygen in the exhaust manifold and from the other sensors detecting the environmental and engine parameters - will pilot the motor 14 for the throttle 8, so as to cause the closing of said throttle when the signals indicate that the mixture is weak, and to cause its opening in the opposite event.
The same circuit, besides the functions of regulating the steady state of the engine, can also operate in the engine warming up steps and, when accelerating, to suitably enrich the mixture, so as to perform also the functions of starter and of pickup pump.
The previous description evidently illustrates the invention by mere way of example. It is also understood that, though described in its application to a single carburetor, the invention can also be used to feed internal combustion engines having more carburetors.

Claims

Carburetor for internal combustion engines with controlled ignition, especially designed to equip vehicles, of the type wherein a fine and continuous regulation of the feed mixture strength is obtained producing a controlled depression in the top of a constant level float chamber (5), the carburetor comprising a register throttle valve (8) in an air intake duct (2) and downstream thereof a main duct (1) with a venturi (1A) followed by an accelerator throttle valve (4), the top of said constant level float chamber (5) being connected with external atmoshpere by an opening (11) which opens into the air intake duct (2) upstream of the register throttle valve (8) when the register throttle valve is in its closed position, and being connected by a gauged port (9) with the main duct, downstream of the register throttle valve (8) and upstream of the venturi (1A), characterized in that the opening (11) connecting the top of the constant level float chamber (5) with the air intake duct (2) opens through the wall of the air intake duct (2) and is positioned with regard to the register throttle valve so that it is upstream of the rim of the register throttle valve (8) when the register throttle valve is in its closed position and downstream of the rim when it is in its fully open position, in that said air register throttle valve is asymmetric and has its minor sector corresponding to said opening (11), and in that the position of said air register throttle valve (8) is determined by an electric motor controlled by sensors detecting the combustion state of the engine.
Carburetor as in claim 1, wherein said sensors mainly comprise a probe to check the oxygen, positioned in the exhaust manifold of the engine, as well as detectors of the other engine and environmental parameters.
Carburetor as in claim 1, wherein the register throttle (8) is mounted idle on a shaft, in respect of which it is caused to rotate thanks to a worm drive mechanism (13) operated by said electric motor, (14), with possibility however to act independently from said mechanism when opening.