VALVE UNIT FOR AN INTERNAL COMBUSTION ENGINE INTAKE DUCT, COMPRISING NON-RETURN FLAP VALVES

Abstract: The valve unit comprises non-return valves disposed within the intake duct (18) and formed from longitudinal channels (22) and flaps (28) which engage these latter. The channels are provided with seal gaskets (36) at their edges and are formed with their base walls shaped on their outer side in such a manner as to improve the valve reliability and life. The flaps (28) comprise fixing tabs (27) which are clamped between ledges (25) and support surfaces (26) of the superposed channels (22).

Description: This invention relates to a valve unit for arrangement in series with an intake valve in an intake duct feeding an internal combustion engine cylinder. It is well known that in internal combustion engines with fixed timing, the chosen opening advance and closure retardation angles for the valves, in particular the intake valves, are such as to be optimised only at determined engine speeds, whereas at other speeds they represent a compromise which is sometimes only just acceptable. The intake valves are made to open while the exhaust valves are still open (cross-over), and while this facilitates discharge of the gaseous combustion products at certain engine speeds, at other speeds it results in return flow of these gaseous combustion products from the exhaust ducts into the cylinders and intake ducts, so reducing the volumetric efficiency of the engine. The intake valves can also be made to close after the compression stroke has commenced in order to improve cylinder filling at high speeds, by inertial and resonance effects. However at low speeds, because of the reduced inertia of the feed charge entering the cylinders, at the commencement of the compression stroke a considerable part of the feed charge can be forced to again enter the intake ducts through the still open intake valves, so worsening cylinder filling. To obviate these drawbacks it has been proposed to provide the intake ducts with non-return valves which allow the air or air-fuel mixture to flow towards the cylinders but not in the reverse outward direction, by retaining in the intake ducts any feed charge which has flown back from the cylinders. The non-return valves may be combined into a valve unit to be arranged within the intake duct. A valve unit of this type and having the features of the preamble of claim 1 is known from GB-A-2 125 483. In the valve unit of this prior document the arcuate base walls of the channels have a completely arcuate profile from one end to the other and a same thickness all along their extension. The flexible flaps are clamped only on a small end surface against the flat edges at the inlet of the channels. At the outlet of the channels the flaps abut against metallic edges defining small contact areas. Another valve unit having flexible flaps acting as non-return valves in an intake duct is known from GB-A-512 632. In this valve unit the arcuate base walls have longitudinal ribs protruding therefrom in such a manner that the flaps adhere against these ribs in the open position of the valves, i.e. they adhere on a limited contact areas, so preventing sticking of the flaps to the arcuate base walls. The ribs terminate adjacent the inlet opening of the intake duct, where the arcuate base walls form stepped regions and end with a surface aligned with that of the ribs in order to form a continuous resting surface for the flaps. FR-A-2 320 484 discloses a laminar valve for an intake or exhaust duct of an internal combustion engine, wherein the valve has an opening in a valve body surrounded by a gasket of elastic material. The opening can be closed by a flexible metallic flap which in the fully open position can abut against an arcuate abutment member. A layer of a resin is applied either on the elastic material or on the surface of the flap facing the valve opening, to prevent sticking between the flap and the elastic material of the valve seat. This construction is however not suitable for valve units composed of a plurality of superposed flaps. The object of the present invention is to further improve the valve arrangement of GB-A-2 125 483, particularly with regard to its reliability and life, while retaining its already excellent characteristics of permeability and fast response. The present invention provides therefor a valve unit having the features recited in claim 1. With this construction the sealing material is disposed only in certain of the contact regions between the flaps and the channel edges, namely where it serves to provide effective sealing and to deaden the impact against the flaps, whereas it is not provided in the flap clamping regions where it would reduce the cross-section at the inlet of the channels, but where in any case good sealing is provided by the fixing of the extended tab portions of the flaps between the ledges and the elongate flat portions of the base walls of the superposed channel modules. The flaps when in their end-of-travel position are properly supported by the base walls of the overlying channels, so minimising any deformation arising from fatigue stress which could damage them, compromise their life and impede their movement into a completely open position, so reducing the air passage cross-section. In addition, the provision of said step-shaped regions enables the stresses on the flaps in proximity to their fixing to be controlled very precisely because the surfaces of the step-shaped connection region can be machined to very narrow tolerances and can therefore be constructed with perfectly definable dimensions to limit the stresses to within design specifications. The non-return valves constructed in this manner form very compact units which can be mounted in those portions of the intake ducts provided within the cylinder bead, to minimise the space between the intake valves and the non-return valves. Characteristics and advantages of the invention will be apparent from the description given hereinafter with reference to Figures 1-4 which show a preferred embodiment of the invention by way of non-limiting example. Figure 1 is an axial section through an internal combustion engine intake duct fitted with a valve unit according to the invention; Figure 2 is a detailed view of the valve unit of Figure 1; Figure 3 is a section on the line III-III of Figure 2; Figure 4 is a front view partly sectioned on the line IV-IV of Figure 2. In Figure 1 the reference numeral 10 indicates overall the cylinder head of a four-stroke internal combustion engine which is provided with an explosion chamber such as that indicated by 11, and intake valves such as the valve 12, and which also comprises intake duct terminal portions such as that indicated overall by 13. To the cylinder head 10 there are flanged by way of gaskets, such as that indicated by 14, intermediate intake duct portions, such as that indicated by 15, in which fuel injectors such as that indicated by 16 are disposed. The usual feed throttle valve or valves are not shown. The ducts 15 are connected to an air filter, also not shown. The duct 13 comprises an inlet portion 18 of substantially rectangular cross-section and a terminal portion 19 of substantially circular cross-section. In the portion 18 there is mounted a non-return flap valve unit indicated overall by 20 for opening and closing the passage through the channels 22. As can also be seen from Figures 2 and 4 the unit 20 is formed from superposed modules 21 each consisting of three longitudinal channels 22 with substantially arcuate base walls 23. At their inlet sections 24 the base and side walls of the channels 22 form flat ledges 25 and support surfaces 26, between which extended fixing tab portions 27 of elastically flexible flaps 28 are clamped when the modules 21 are assembled in superposed position by means of screws 29 and 30. Specifically, the base walls 23 have at the inlet section 24 elongate flat portions mating superficially with the ledges 25 and clamping the extended tab portions 27 therebetween. A gasket 31 embraces the contour 32 of the unit 20 after the modules 21 and flaps 28 have been assembled, and provides sealing for the unit 20 when in the seat 17 of the duct 18. At their outlet section 33, the base and side walls of the channels 22 form edges 34 for abutment of the free portions of the flaps 28 in the position thereof closing the channels 22. In the edges 34 of the base walls 33 and the side walls of the channels 22 there are provided grooves 35 to house sealing material like gaskets 36, for example of vulcanised rubber. On their inner side, the base walls 23 of the channels 22 have each a curved surface 37 suitable for guiding the air stream passing through the channels 22, whereas on their outer side they comprise each an end-of-travel surface 38 for halting the flaps 28 when in their open position. The end-of-travel surfaces 38 of the base walls 23 have the same shape as the flaps 28 when deformed under a uniformly distributed load (corresponding to a determined pressure difference). However, the base walls 23 have regions of reduced thickness adjacent their flat portions and are joined therewith by step-shaped regions 39. The grooves in the side walls of the channels 22 terminate at a distance from the ledges 25, so leaving edge portions free of sealing material in the proximity of the reduced-thickness and step-shaped regions 39. The flaps 28 close the channels 22 by being urged by their own elastic reaction against the edges of the channels 22, this also happening when the engine is operating without a positive pressure difference between the upstream and downstream sides of the valve unit 20. However, during each cylinder intake stroke, the flaps 28 are lifted from the edges of the channels 22 by the effect of the positive pressure difference between the upstream and downstream sides of the unit 20, and allow the air-fuel mixture to flow through the channels 22. At the end of the cylinder intake stroke, the positive pressure difference across the unit 20 reduces and the flaps 28 again close the channels 22. In this condition, if the engine runs at low speed, especially under full induction with the throttle valve or valves completely open, there is a return flow of cylinder mixture into the duct 13, where it is retained and assumes a certain overpressure by the closure of the valve 12 and flaps 28. The unit 20 is very compact and can therefore be located within that portion 18 of the duct 13 provided in the cylinder head 10, so minimising the space between the intake valve 12 and the unit 20 and thus facilitating the pressure rise in the mixture which flows back into the duct 13. The mixture which has flown back into the duct 13 is again drawn into the cylinder 11 during its next intake stroke, and because of its overpressure it contributes to the expulsion of the gaseous combustion products from the cylinder 11 with a scavenging effect which also occurs at low engine speed. An overall increased cylinder filling effect is therefore obtained at low engine speed., The contact between the flaps 28 and gaskets 36 provides a good seal even after many hours of operation, and deadens the impact of the flaps to the advantage of their life. The clamping of the extended tab portions 27 between the ledges 25 and the support surfaces 26 also ensures good sealing at the channel inlet sections 24. There is therefore no need to use seal gaskets, which would lead to a reduction in the area of the inlet sections 24 and reduce the permability of the channels 22. Advantageously, as visible in Fig. 3, the flaps 28 of each module comprise individual flap portions connected by a same tab portion 27. A particular advantage is the shape of the outer side of the base walls 23, comprising end-of-travel surfaces 38 having the same shape as a deformed flap 28, and step-shaped regions 39 joining up with the support surfaces 26. In this manner the flaps 28 rest totally against the end-of-travel surfaces 38 and do not undergo deformation. In addition the stresses to which the flaps 28 are subjected in proximity to their region of clamping between the ledges 25 and support surfaces 26 are precisely controlled because the regions 39 can be machined to very narrow tolerances and can therefore be constructed with perfectly defined dimensions for limiting the stresses to within the design specifications. Complete lifting of the flaps 28 is therefore ensured, together with an extremely satisfactory life.

Claims: A valve unit for arrangement in series with an intake valve (12) in an intake duct (13) feeding an internal combustion engine cylinder (11), comprising a plurality of longitudinal channels (22) defined by substantially arcuate base walls (23) and side walls and assembled into superposed modules, and a plurality of elastically flexible flaps (28) associated with said channels (22) for opening and closing the passage through said channels (22) like non-return valves, wherein at the inlet section (24) of said channels (22) the base and side walls form support surfaces (26) and flat ledges (25) which in the superposed position of the modules clamp between each other fixing portions of said flaps (28), and wherein at the outlet section (33) of said channels (22) the base and side walls form edges (34) for abutment of the free portions of said flaps (28) in the position thereof closing said channels (22), characterised in that said base walls (23) have at said inlet section (24) elongate flat portions mating superficially with said ledges (25) and clamping extended tab portions (27) of said flaps (28) therebetween, in that said base walls (23) have regions of reduced thickness which are adjacent said flat portions and are connected therewith through step-shaped regions (39), and in that the edges (34) of the base walls (23) and the side walls have grooves (35) therein receiving sealing material (gaskets 36), the grooves in said side walls terminating at a distance from said ledges (25), thereby leaving edge portions free of sealing material in the proximity of said reduced-thickness and step-shaped regions (39). A valve unit as claimed in claim 1, characterised in that the flaps (28) of each module comprise individual flap portions connected by a same tab portion (27).

Inventors: D'ANGELO, DOMENICO, VISCONTI, MARCO
Applicants: FIAT AUTO S.P.A.
Application year: 1989
Main classification: F01L3
IPC codes: F01L3