Single valve intake/exhaust device for a direct injection internal combustion engine

Abstract

An intake and exhaust device for an internal combustion engine with direct injection comprises an intake and exhaust valve (11) with a stem (13), a head (12), and a seat (24) facing a combustion chamber (CC) of the engine (M), an intake duct (42) for the intake of air into the combustion chamber (CC), and an exhaust duct (38, 57) for the discharge of the exhaust gases, the exhaust duct (38, 57) being connected to the intake duct (42) upstream of the valve seat (24). The exhaust duct (38, 57) is arranged so as to be coaxial with the valve (11) and the intake duct (42) extends radially. The connection between the intake duct and the exhaust duct (38, 57) is in the vicinity of the seat (24) of the valve (11) so that the exhaust gas-flow conveyed through the connection has a radial velocity component directed towards the valve stem (13). The air is drawn in from the intake duct (42) as a result of the gas-flow passing through the exhaust duct (38, 57) during the exhaust phase and as a result of the movement of a piston (P) in the cylinder during the intake phase.

Description

The present invention relates to an intake and exhaust device for an internal combustion engine with direct injection, of the type described in the preamble to Claim 1.

There are known internal combustion engines comprising single valve devices in which the intake and exhaust ducts intersect upstream of an intake and exhaust valve. In addition to this valve, it is necessary to provide another, switching valve which puts the valve duct into communication with the intake duct and with the exhaust duct alternately. However, these devices generally lead to problems of reliability and performance connected with the complexity of their structure.

There are also known internal combustion engines having completely separate intake and exhaust ducts in which the exhaust valves are controlled by a camshaft whilst the intake valves are automatic. However, the operation of these engines at high speeds is not efficient since the automatic valves do not permit optimal filling of the cylinders.

The object of the invention is to provide a single valve device which is of simple and robust construction and which permits efficient operation even at high speeds.

This object is achieved, according to the invention, by an intake and exhaust device for an internal combustion engine with direct injection having the characteristics defined in the claims.

In comparison with engines in which the intake and exhaust ducts are completely separate, the present invention has the advantage that a much larger duct area can be achieved for both exhaust and intake. Moreover, since the hot exhaust gases and the cool supply air flow through the valve alternately, the valve is not subjected to the dangerous thermal stresses of exhaust valves with separate ducts and remains free of deposits. Moreover, the emission of noxious exhaust gases is reduced by virtue of the fact that these gases come into contact with the cool air directly at the output from the cylinder, which favours the oxidation of carbon monoxide.

A preferred but non-limiting embodiment of the invention will now be described with reference to the appended drawings, in which:

FIG. 1 is a longitudinal section view through a single valve device for an internal combustion engine with direct injection according to the present invention,

FIG. 2 is a cross-section view through the device of FIG. 1, taken on the line II-II of that drawing,

FIG. 3 is a diagram of the timing of an engine provided with the device of FIG. 1,

FIG. 4 is a schematic view showing the operation of the device of FIG. 1 in an exhaust phase, and

FIG. 5 is a schematic view showing the operation of the device of FIG. 1 in an intake phase.

With reference to FIGS. 1 and 2, a single valve device 10 according to the invention is mounted on an internal combustion engine M with direct injection and is housed in the cylinder head T. The engine M comprises a combustion chamber CC arranged in the head T in known manner and a piston P movable inside a cylinder C of the engine.

The combustion chamber CC is delimited at the top by a mushroom valve 11 of known type comprising a head 12 and a stem 13.

According to the phase of the operating cycle, the valve 11 can isolate the combustion chamber CC or connect it with the exterior by virtue of a control system comprising a camshaft (not shown) and a biasing spring 14.

The single valve device according to the invention comprises a central element 20 which is fixed to the engine block B above the combustion chamber CC and houses the above-described valve 11 slidably.

The central element 20 comprises a base portion 21 which can be mounted on the block B by means of through-holes 22 formed in the base portion 21 for the engagement of screws 23 for fixing to the block B. In the base portion 21 of the central element 20 there is a substantially conical, conventional seat 24 of the valve 11, surrounding an intake and exhaust opening 24a.

The base portion 21 houses an injector, schematically indicated IN, of the type used in direct injection apparatus, communicating with the combustion chamber CC.

The central element 20 of the single valve device 10 further comprises a central portion 25 in which a duct 26 is formed for guiding the stem 13 of the valve 11. The central portion 25 of the central element 20 houses the biasing spring 14 of the valve 11 at its upper end.

The central element 20 of the single valve device 10 further comprises a rib portion 27 which connects the base portion 21 to the central portion 25. This rib portion 27 comprises a plurality of ribs 28 which extend radially and axially from the central portion 25 of the central element 20 and are connected to the base portion 21.

The screws 23 for fixing the central element 20 of the single valve device 10 to the engine block B are extended axially upwards. A plurality of rings or annular discs 30 are mounted on these screws 23, and are arranged above one another, around the central portion 25 of the central element 20. Each ring 30 comprises a body 31 provided with a plurality of peripheral through-holes 32 for the engagement of the screws 23 and with a central opening 33 coaxial with the central portion 25 of the central element 20. The rings 30 are substantially flat and the central opening 33 preferably has a rim 34 shaped so as to be curved, or in any case bent, upwards. These rings 30 also have a plurality of radial slots 35 for housing the ribs 28 of the central element 20.

The stacked rings 30 are kept clamped axially by nuts 36 screwed onto the screws 23 and are spaced apart by cylindrical spacer elements 37 mounted coaxially on the screws 23 between one ring 30 and the ring disposed above it. The diameters of the central openings 33 of the rings 30 increase in the direction away from the seat 24 of the valve 11 and, between the rims 34 of the openings 33 and the side wall of the central portion 25 of the central element 20, there is an axial duct the cross-section of which increases in the direction away from the seat 24 of the valve 11 and which defines a proximal portion 38 of an exhaust duct for the exhaust gases.

The single valve device according to the invention also comprises a casing 40 mounted or formed integrally on the base portion 21 of the central element 20 and surrounding the central portion 25 of the central element 20. The side wall of the casing 40 has a plurality of slots 41 which define radially an air-intake duct 42, in cooperation with the walls of the casing 40 and of the base element 21 of the central element 20. The duct 42, or more precisely the plurality of radial ducts 42, is connected to the proximal portion 38 of the exhaust duct in the vicinity of the valve 11, upstream of the valve seat 24.

Finally, the combined valve device according to the invention comprises an exhaust-outlet element 50 mounted on the central element 20 and on the casing 40 and suitable for connection to an exhaust manifold CS (shown schematically in FIGS. 4 and 5). The exhaust-outlet element 50 comprises a central portion 51 which can be mounted on the central portion 25 of the central element 20 by means of through-holes 52 formed in the central portion for the engagement of fixing screws 53. The central portion 51 of the exhaust-outlet element 50 is shaped so as to allow the camshaft (not shown) to operate the valve 11.

The exhaust-outlet element 50 further comprises a flared wall portion 54 which can be mounted on the casing 40 in a leaktight manner and a rib portion 55 which connects the wall portion 54 to the central portion 51 of the exhaust-outlet element 50. This rib portion 55 comprises a plurality of ribs 56 which extend radially so as to be aligned with the ribs 28 of the central element 20. The exhaust-outlet element 50 thus defines a distal portion 57 of the exhaust-gas duct, which has a cross-section that increases in the direction away from the seat 24 of the valve 11 and which is aligned with the above-described proximal portion 38.

The operation of the combined valve device according to the present invention will now be described with reference to FIGS. 3 to 5.

FIG. 3 is a diagram of the timing of an engine provided with the device according to the invention, operating in accordance with a Diesel cycle. The direction in which the cycle is performed is indicated by the arrow A. The advance of the opening of the valve 11 as well as the delay of its closure are those conventionally adopted in internal combustion engines.

As shown in FIG. 4, at the moment at which the valve 11 is opened for the discharge of the gases as a result of the expansion, the exhaust gases leave the combustion chamber CC through the opening 24a (along the path shown by the hatched arrows indicated N) with a component of their velocity directed radially towards the axis of the mushroom valve 11, owing to the shape of the seat 24 and of the head 12 of the valve. The gas-flow then passes through the proximal portion 38 of the exhaust duct, is guided further owing to the deflection provided by the curved rims 34 of the openings 33 of the rings 30, and finally passes through the distal portion 57 of the exhaust duct. By virtue of its velocity and of the above-described radial velocity component, the exhaust gas-flow emerging from the opening 24a draws cool air through the slots 41 of the casing 40 and between the rings 30 (along the path indicated by the blank arrows indicated W); this cool air is mixed with the exhaust gases. By virtue of the shape of the exhaust duct, which has a cross-section that increases in the direction of the exhaust gas-flow from the narrow cross-section of the opening 24a, the exhaust gas-flow increases the vacuum in the connection between the exhaust duct and the intake duct, further favouring the drawing-in of cool air.

The arrangement of the rings 30 promotes the mixing of the exhaust gases with the cool air whilst the ribs 28, 56, arranged along the exhaust duct 38, 57 prevent swirling of the gases. The mixing of the cool air with the hot exhaust gases in turn promotes oxidation of the carbon monoxide that is present therein.

The cool air is drawn in from the exterior throughout the upward stroke of the piston P and also continues, owing to inertia, when the piston P reverses its direction of movement in order to start the intake phase: the radial component of the air drawn in, towards the axis of the valve 11, is maintained both during expulsion and during intake, producing an almost continuous supply flow.

The valve 11, which is opened for the expulsion of the exhaust gases, still remains open throughout the intake phase (shown in FIG. 5).

When the piston P starts its descent in order to perform the intake phase, it draws in from a large volume of cool air which is present in the space inside the casing 40.

Cool air is drawn in in greater quantities in the region closest to the valve head and then in quantities which gradually decrease away from the head until a region is reached in which the suction due to the presence of the velocities of the last traces of the exhaust gases which are being removed still prevails.

Evacuation is favoured by the diverging cross-section of the distal portion 57 of the exhaust duct in the exhaust-outlet element 50 and by the shape of the exhaust manifold CS which also diverges.

As will be appreciated, since the supply air-flow in the intake duct is substantially continuous, optimal filling of the cylinders can be achieved even at high speeds.

Moreover, since the valve performs a single complete stroke for every two revolutions of the engine shaft, performing the exhaust and intake phase by itself, the power required of the camshaft is practically halved in comparison with conventional systems.

By virtue of its particular shape and by virtue of the presence of the annular discs 30, the device according to the invention also operates as a silencer, since a considerable attenuation of the noise is achieved upon the outlet of the gases from the cylinder.

The air entering through the slots 41 of the casing 40 may be at ambient pressure or, in a supercharged engine, under pressure.

If particularly high compression ratios are to be achieved, in order to allow the piston to come closer to the head, the camshaft may be profiled in a manner such as to cause the valve to retract slightly when the piston approaches top dead centre (during the exhaust/intake transition) but without completely closing the opening through the seat 24.

Claims

1. An intake and exhaust device for an internal combustion engine (M) with direct injection, comprising an intake and exhaust valve (11) with a stem (13) and a head (12), the seat (24) of which faces a combustion chamber (CC) of a cylinder (C) of the engine (M), at least one intake duct (42) for the intake of air into the combustion chamber (CC), and one exhaust duct (38, 57) for the discharge of the exhaust gases, the exhaust duct (38, 57) being connected to the intake duct (42) upstream of the valve seat (24), wherein the exhaust duct (38, 57) is arranged so as to be substantially coaxial with the valve (11) and the at lease one intake duct (42) extend substantially radially, the connection with the exhaust duct (38, 57) being arranged in the vicinity of the seat (24) of the valve (11) in a manner such that the exhaust gas-flow conveyed through the connection has a radial velocity component directed towards the stem (13) of the valve (11) so that the air is drawn in from the intake duct (42) as a result of the gas-flow passing through the exhaust duct (38, 57) during the exhaust phase and as a result of the movement of a piston (p) into the cylinder (C) during the intake phase, characterized in that at least one annular disc-like element (30) with a central opening (33) is arranged around the exhaust duct (38, 57) in the region of the connection with the intake duct (42) to promote the mixing of the air drawn in with the exhaust gases.

2. A device according to claim 1 in which at least a portion of the exhaust duct (38, 57) has a cross-section which increases progressively in the direction away from the valve seat (24).

3. A device according to claim 1, wherein the at least one intake duct (42) is defined by a casing element (40) arranged around the valve (11) and provided with a plurality of air-inlet slots (41) arranged radially in the walls of the casing (40).

4. A device according to claim 1 in which a plurality of annular disc-like elements (30) are arranged along the exhaust duct (38, 57) in a manner such that their respective central openings (33) are aligned coaxially.

5. A device according to claim 4 in which the central openings (33) have cross-sections which increase in the direction away from the seat (24) of the valve (11).

6. A device according to claim 1, wherein the intake duct (42) comprises deflector means (34) which are suitable for conveying the exhaust gas-flow through the exhaust duct (38, 57) and which are arranged in the region of the connection of the intake duct with the exhaust duct (38, 57).

7. A device according to claim 6 in which the deflector means are formed on a rim (34) of the central opening (33) of each annular disc-like element (30).

8. A device according to claim 7 in which the deflector means comprise a rim (34) of the central opening (33) of each annular disc-like element (30), which rim is curved or bent in the direction of the exhaust gas-flow through the exhaust duct (38, 57).

9. A deviced according to claim 1, wherein a plurality of radial ribs (28, 56) for preventing gas turbulence are arranged inside the exhaust duct (38, 57), extending along the length of the exhaust duct (38, 57).

10. A device according to claim 9 in which the radial ribs (56) also extend in the intake duct (42).

11. An internal combustion engine, comprising the device according to claim 1.

12. (Canceled)