INDUCTION DEVICE FOR MULTI-CYLINDER INTERNAL COMBUSTION ENGINE

Abstract: In a multi-cylinder engine, equipped with at least two induction valves (11,12) per cylinder, with one (11) of said valves having a narrower induction and crossing stroke, and wih another (12) of said at least two valves having a wider induction and crossing stroke, and with a choke valve (22) per each cylinder, the invention provides for a fuel injector (24) to be installed substantially in correspondence of the induction valve (11) having the narrower induction stroke and crossing.

Description: The present invention relates to an induction device for a multi-cylinder internal combustion engine, which is equipped with a plurality of induction valves, and with at least one exhaust valve per each cylinder, in particular with two induction valves per cylinder, and which is equipped with driving means for said valves, wherein said induction device comprises individual induction manifolds, one induction manifold per each cylinder, and with at least two induction ducts branching off from each individual manifold and leading to the corresponding cylinder through said induction valves, and wherein the two induction valves of each cylinder are driven with lift laws respectively optimized for low revolution speed running conditions and for high revolution speed running conditions of the engine. Engines equipped with a plurality of induction valves per each cylinder, and, possibly, with more than one exhaust valves, have, as compared to engines with only one induction valve and one exhaust valve per cylinder, a larger actual surface area of passage through the valves; this fact favours the exchange of the gases inside the combustion chamber, because a larger amount of air, and consequently, of gasoline, can be introduced, and a larger amount of flue gases can be exhausted, during a time unit. From the above, a better filling of the cylinders, and a higher volumetric efficiency derives, with an increase in the specific power of the engine. However, in these engines too, it may happen that a crossing of the induction and exhaust valves, optimized in order to take advantage, for filling purposes, of inertial phenomena and resonance waves, at determined revolution speeds, can result inadequate under other operating conditions, and, in particular, at low revolution speeds, because a portion of fresh mixture may go, unburnt, directly to the exhaust port, or a portion of the exhaust gases can flow back to the induction port, according to whether, during the crossing, between the induction port and the exhaust port, either a positive or a negative pressure difference is established. From such an occurrence an irregular combustion, a larger fuel consumption and an increase of polluting substances in the exhaust gases results. In order to improve the operation of these engines, in particular under low load conditions, it was proposed to drive the two induction valves of each cylinder by means of two different cams, with one of said cams being driven according to a lift law optimized for low revolution speeds, and the other being operated according to a lift law optimized for high revolution speeds, as it results from FR-A-1 511 586. This patent also provides for a respective choke valve to be installed inside each induction duct, with one of said choke valves being operated by the accelerator pedal, and the other being operated by a suitable actuator, in such a way that it may remain closed under low revolution speed conditions. By such an arrangement, the negative effects of the crossing at low revolution speeds is minimized, because each cylinder is fed through one induction duct and one induction valve only, which is precisely characterized for low revolution speed operation conditions. However, such an arrangement is rather complex and expensive. DE-A-35 11 382 discloses an induction device in which the two induction valves of each cylinder are controlled with different lift laws and in which in the induction duct leading to the induction valve having the lift law adapted to low revolution speed conditions of the engine there is arranged a fuel injector, whereas in the induction duct leading to the induction valve having the lift law adapted to high revolution speed conditions of the engine there is arranged a throttle valve. This valve is controlled to close the respective duct at low speed operating conditions of the engine and to open the same duct at high speed operating conditions. The two induction ducts branch from an induction manifold which is the same for all the cylinders of the engine and which is controlled by the throttle valve operated by the accelerator pedal. Also this known device therefore operates with one induction duct only at low speed and with both induction ducts at higher speeds. This creates unfavourable conditions for operations at low speeds and constructional problems because of the installation of the injectors and throttle valves in the induction ducts. The main purpose of the present invention is a simpler and cheaper solution, featuring an as satisfactory performance. In particular, the present invention aims at achieving a high torque, together with reduced fuel consumptions and minimum emissions of polluting substances, when the engine operates at low speeds, and at increasing the peak power at high revolution speeds. This purpose and aim are achieved by an induction device as claimed in claim 1. By installing a choke valve inside each induction manifold, a higher freedom is reached in the selection of the timings of the valves, above all of the crossings, because possible refluxes of exhaust gases to the induction port of a cylinder, possible under low-load conditions, do not affect the fuel feed to the other cylinders. With the off-centre positioning of the fuel injectors, through the induction valve having a narrower opening stroke and a minimum crossing relatively to the corresponding exhaust valve, air enters, which is strongly carburetted by all, or nearly all, the fuel delivered by the injector; whilst through the induction valve having a wider opening stroke and a wide crossing relatively to the corresponding exhaust valve, air, or only weakly-carburetted air, enters. In this way, it is prevented that under low load conditions, a portion of the mixture of air and gasoline may be expelled from the combustion chamber to the engine exhaust; moreover, an improvement of the combustion is additionally obtained, under all operating conditions, due to the turbulence effect, and the consequent stirring up of the charge inside the combustion chamber, due to the air stream which enters in advance through a valve, and has assumed a certain speed, and a whirling behaviour when it comes to interfere with the heavily carburetted air stream which subsequently enters through the other valve. Characteristics and advantages of the invention are now illustrated by referring to the hereto attached Figures 1-3, wherein for exemplifying, non-limitative purposes, a preferred form of practical embodiment of the same invention is depicted. Figure 1 shows a partially sectional plan view of an induction device according to the present invention; Figure 2 shows a partially sectional view along the path plane II-II of Figure 1; Figure 3 shows charts of the lift laws of the valves of the engine of the invention. In Figures 1 and 2, a diagram is shown of an internal combustion engine equipped with four valves per cylinder, wherein two cylinders 10 are shown each having two induction valves 11 and 12 and two exhaust valves 13 and 14. The spark plugs are indicated at 15. To each cylinder there is associated an individual induction manifold 16, branching off into two induction ducts 18 and 20, which lead to the combustion chamber of the same cylinder through the valves 11 and 12 and define a constantly open fluid communication between the valves 11, 12 and the associated manifold 16. By the reference numerals 17, 19, 21, the respective longitudinal axes of the manifold 16 and of the ducts 18 and 20, are indicated. Inside each manifold 16, a respective feed choke valve 22 is installed; the choke valves 22 are connected with each other by a diagrammatically represented shaft 23, and are operatively linked with the accelerator pedal, not shown in the figures, as usual in the art. Inside each manifold 16, downstream the respective choke valve 22, at least one electroinjector 24 is installed upstream of the place where the manifold 16 branches off into the induction ducts 18, 20. Each electroinjector 24 is mounted off-centre relatively to the longitudinal axis 17 of the respective manifold 16, i.e., shifted towards the side of the duct 18. The electroinjector 24 can also be mounted coaxial with the axis 19 of the duct 18. Advantageously, as it results from Figures 1 and 2, the induction duct 18 towards which the injector 24 is shifted, has a first portion 18' having its axis in a vertical plane substantially parallel to the vertical plane containing the axis of the manifold 16 from which the duct 18 branches off, and a second portion having its axis 19 in a vertical plane forming an angle with said vertical plane containing the axis of the manifold 16; the axis of the electroinjector 24 and the axis of the first portion 18' of the induction duct 18 may lie on a same vertical plane, and the electroinjector 24 may be located with its axis being skew relatively to the axis 19 of the second portion of the induction duct 18. The induction valves 11 and 12 and the exhaust valves 13 and 14 are operatively connected with respective cam shafts, not shown in the figures, constituting the driving means for these valves. In the particular case herein depicted, it is provided for the induction valves 11 to be operated by cams having a lift law (a) so computed as to obtain high torques, low consumption rates and reduced emissions of polluting substances under partial-load operating conditions, e.g., such a law as shown in Figure 3 by the curve 311. As regards the induction valves 12, they are operated by means of cams with a lift law (a), so computed as to increase the peak power of the engine, e.g., such as that shown in Figure 3 by the curve 312. In Figure 3, also the curves 313 and 314 are shown, which represent the lift laws (a) of the exhaust valves 13 and 14. As it results from Figure 3, the opening stroke of the valve 11 is narrower than that of the valve 12, with the starting of valve 11 opening being delayed relatively to that of the valve 12, relatively to the top dead centre (TDC), and the crossing (i.e., the simultaneous opening astride the TDC) of the induction valves 11 and exhaust valves 13 is minimum, whilst the crossing of the induction valves 12 and exhaust valves 14 is wide. The induction stroke of a cylinder 10 begins with the opening of the relevant valve 12; through it, a stream of air only, or of weakly carburetted air enters, which assumes a whirling movement with a rather high speed, having a lower specific gravity than the air-gasoline mixture. Then, the valve 11 opens, and through it a stream of strongly carburetted air enters, because all of the fuel delivered by the electroinjector 24 during the injection stroke, or most of it, enters the duct 18. The meeting of the two streams, one of which has already assumed a whirling movement, and a certain speed, causes an effect of turbulence and of stirring up of the charge, which renders more homogeneous said charge, owing to the better fuel distribution in the air, and favours the complete combustion thereof, under all engine operating conditions. Furthermore, the rich-in-fuel mixture is prevented from passing unburnt to the exhaust port, because the crossing between the induction valves 11 and the exhaust valves 13 is small, whilst the crossing between the induction valve 12, which is concerned by an only air stream or a weakly carburetted air stream, and the exhaust valve 14, is wide.

Claims: Induction device for a multi-cylinder internal combustion engine equipped with a plurality of induction valves, and at least one exhaust valve per each cylinder, in particular with two induction valves (11,12) per cylinder, and equipped with driving means for said valves, wherein said induction device comprises individual induction manifolds (16), one induction manifold per each cylinder (10), and at least two induction ducts (18,20) branching off from each individual manifold (16) and leading to the corresponding cylinder (16) through said induction valves (11,12), and wherein the at least two induction valves of each cylinder are driven with lift laws respectively optimized for low-revolution-speed running conditions and for high-revolution-speed running conditions of the engine, characterised in that a respective choke valve (22) is installed inside each induction manifold (16) and the induction ducts (18,20) of each cylinder (10) define a constantly open fluid communication between said induction valves (11,12) and the associated manifold (16), and in that at least one fuel injector (24) is installed inside each individual induction manifold (16), downstream of the respective choke valve (22) and upstream of the place where the induction manifold (16) branches off into said induction ducts (18,20), said fuel injector (24) being positioned in an off-centre position relatively to the longitudinal axis (17) of the same manifold (16) and shifted towards the side of the induction duct (18) equipped with the induction valve (11) having a lift law optimized for the low-revolution-speed operating conditions. Device according to claim 1, characterized in that the induction duct (18) towards which the injector (24) is shifted has a first portion (18') having an axis in a vertical plane substantially parallel to the vertical plane containing the axis of the manifold (16) from which the duct (18) branches off, and a second portion having its axis (19) in a vertical plane forming an angle with said vertical plane containing the axis of the manifold (16). Device according to claim 2, characterized in that the axis of the injector (24) and the axis of said first portion (18') of the induction duct (18) lie on the same vertical plane. Device according to claim 2, characterized in that the injector (24) is located with its axis being skew relatively to the axis (19) of said second portion of said induction duct (18).

Inventors: OLDANI, EMILIO, ROSA, RICCARDO, TRUZZI, SERGIO
Applicants: FIAT AUTO S.P.A.
Application year: 1988
Main classification: F02M35
IPC codes: F02F1, F02M69, F02M35