GB2278640A

GB2278640A - Direct injection engine with stratified exhaust recirculation

Info

Publication number: GB2278640A
Application number: GB9410612A
Authority: GB
Inventors: Winfried Oppermann
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1993-05-27
Filing date: 1994-05-26
Publication date: 1994-12-07
Anticipated expiration: 2014-05-26
Also published as: JPH0791271A; DE4317660C1; FR2705729A1; FR2705729B1; GB2278640B; GB9410612D0

Abstract

Each cylinder in the area of BDC (UT) of the piston movement has two exhaust gas inlet apertures for exhaust, gas feed-back channels (30, 30') which are connected to other cylinders. Additionally, each cylinder has at least two further exhaust gas inlet apertures, which are arranged displaced radially to the cylinder periphery. The exhaust gas inlet apertures are so arranged that with their aid back-fed exhaust gas into the cylinder forms a rotating, somewhat pot-shaped gas collection with a limit line (17), in the inner space of which fresh air (15) from the air inlet valve (18) can be concentrated. ADVANTAGE - Lowers the fuel consumption of a direct injection internal combustion engine to that of a diesel engine.

Description

2278640

DESCRIPTION A DIRECT INJECTION INTERNAL COMBUSTION ENGINE AND A METHOD OF OPERATING SAID ENGINE

The present invention relates to a direct injection internal combustion engine and a method of operating an internal combustion engine of this type.

The Automobile Technical Magazine No. 50. 1989, Pages 426 to 430, discloses a direct injection Otto four-stroke engine, in which the combustion air is compressed in a motor cylinder with the aid of an engine piston which has a piston recess in the centre of its side towards the spark plug. Fuel is injected into this piston recess with the aid of a fuelinjection nozzle in the proximity of the top dead centre position of the piston. This fuel mixes with the combustion air, which has been drawn into the cylinder with an intensive turbulence, to form an ignitable mixture which is ignited by a spark plug located above the piston recess.

At the end of the 1980's it was possible with the aid of this design of combustion chamber in a test engine to reduce fuel consumption by up to 25% in comparison to comparable engines. A disadvantage with this type of combustion chamber proved to be the comparatively high NOX emissions from the engine, which emissions could not be reduced by the -2contemporary catalytic convertors to the legally prescribed limit value.

Moreover, DE-OS 32 48 918 discloses an internal combustion engine having a carburettor and exhaust gas recirculation, and also a method of operating this engine, in which a part of the exhaust gas of the engine is directed to the cylinders as desired. The exhaust gas is drawn in a tangential manner into the engine cylinder with the aid of an exhaust gas recirculation duct by way of a plurality of inlet ports in the region of the bottom dead centre position of the engine piston in such a way that the exhaust gas passes along the inner wall of the respect engine cylinder in a turbulent manner and in so doing the combustion air mixture previously drawn in is concentrated in the central region of the cylinder below the spark plug. As the piston moves upwards in the direction of the spark plug, the annular exhaust gas column and the cylindrical fuel/air column enclosed therein compresses. The fuel/air mixture is ignited in the region of the top dead centre position of the piston by the spark plug and the piston is moved downwards in a known manner by the increased combustion pressure, thus opening the exhaust gas outlet valve. As soon as the piston during its downward movement passes the inlet port for the -3recirculating exhaust gas, a part of the exhaust gas flow from the previous combustion process is directed to a further cylinder of the engine and pushed in by way of a tangential inlet port as described. In this manner, a cylindrical column of exhaust gas is likewise formed in this further cylinder, as described above, and the fuel/air mixture is concentrated in the centre of the said column. The exhaust gas is fed into the individual engine cylinders by way of a plurality of exhaust gas inlet ports which open in a tangential manner into the engine cylinder in the bottom dead centre region of the piston movement. These exhaust gas inlet ports are connected to the exhaust gas recirculating ducts in such a manner that the cylinders are interconnected in the firing sequence of 360. That is to say, the first cylinder can exchange exhaust gas with the third cylinder and the fourth cylinder can exchange exhaust gas with the second engine cylinder.

In order to operate this internal combustion engine, a combustible fuel/air mixture or an air flow is drawn in a turbulent manner into the engine cylinder during the inlet stroke in the first step of the process. Subsequently the exhaust gas is introduced in a tangential manner into the cylinder, which exhaust gas leaves a cylinder at a spacing of -4360 from the ignition sequence of the engine, in order to provide a stratified filling comprising air or a fuel/air mixture and exhaust gas. The stratified filling is subsequently compressed by the upwards movement of the piston following the ignition of the combustible fuel/air mixture and an expansion of the contents of the cylinder. The exhaust gas is vented from the cylinder during a final operation by way of the exhaust gas outlet valve and the exhaust gas outlet ports.

A disadvantage with this internal combustion engine and the method of operating an engine of this type is the fact that it is not possible therewith to achieve the fuel consumption values required nowadays and the exhaust gas emission values do not correspond with the current legal regulations. In addition, it has become evident that in the 'part load' range or even idling, range of the engine, the exhaust gas pressure is insufficient to allow sufficient exhaust gas to overflow in the intake cylinder. In the higher 'Part load' range of the engine, there is also the danger of the exhaust gas and fresh gas mixing in the intake cylinder for the fresh gas, if the exhaust gas should allow the return flow of the fresh gas which has previously flowed into the cylinder.

Finally, DE-OS 35 16 038 discloses a carburettor engine, in which a stratification of fresh air or a fresh air/exhaust gas mixture is achieved by means of various inlet valves in the cylinder head of an engine cylinder of this type. This stratification is built up in one embodiment in such a way that at the cylinder base and at the cylinder walls there is a weak mixture and in the centre below the spark plug the combustible fuel/air mixture is concentrated.

An aim of the present invention is therefore to propose a direct injection internal combustion engine wherein the combustion chamber is filled in layers and a method of operating an engine of this type wherein the fuel consumption can be reduced to the level of fuel consumption of a diesel engine and with which greatly reduced exhaust gas emission values are achieved in all load ranges.

According to the present invention there is provided a method of operating a multi-cylinder internal combustion engine so as to optimise the exhaust gas emissions and fuel consumption, in which method prior to a compression stroke of each piston a rotating stratification of recirculated exhaust gas and fresh air is produced within the engine cylinder, exhaust gas being directed in various quantities in dependence upon the engine load in a controlled manner into the engine cylinder, the exhaust gas for filling -6an engine cylinder being drawn off from an exhaust gas emptying cycle of a further engine cylinder, in the region of the bottom dead centre position of the associated piston, the piston of this further cylinder being disposed on a crankshaft journal of an identical angle of crank, a quantity of exhaust gas dependent upon the load being initially metered in a substantially tangential manner into the engine cylinder with the aid of at least one exhaust gas control valve in order to fill the engine cylinder, a top-up quantity of fresh air being subsequently drawn in for the purpose of completely filling the cylinder, the quantity of drawn-in fresh air being metered by opening an inlet valve together with the previously added exhaust gas and the quantity of fuel to be injected in such a manner that independently of the engine load a valueA=1 is continuously set, the stratified contents of the cylinder being subsequently compressed by the piston of the cylinder, fuel being then directly injected into the fresh air located in the cylinder and the fuelair mixture produced being ignited, an exhaust gas outlet valve in the cylinder being first opened in the subsequent expansion phase dependent upon the load when the cylinder internal pressure is still sufficient for the necessary quantity of exhaust gas to be drawn off to fill said -7further cylinder.

According to a further aspect of the present invention there is provided a direct injection internal combustion engine, comprising engine cylinders disposed in an engine block, pistons being articulated at a crankshaft in such a way as to move in a cyclic and reciprocating manner in said cylinder, each cylinder being sealed at its upper end by a cylinder head, at least one air inlet valve and an exhaust gas outlet valve as well as a fuel injection valve and a spark plug being disposed respectively in the cylinder head for each cylinder, each cylinder comprising in the region of the bottom dead centre UT of the piston movement at least two exhaust gas inlet ports disposed tangentially to the cylinder periphery, which inlet ports are for exhaust gas recirculating ducts, which are connected to the other cylinders, each cylinder also comprising at least two further exhaust gas inlet ports which are disposed radially offset at the cylinder periphery, and with respect to each other in such a way that with the aid thereof the recirculated exhaust gas flowing into the cylinder preferably forms a rotating, approximately cup-shaped collection of exhaust gas with a limit line and the fresh air being metered by the or each air inlet valve into the inner space of the said collection of exhaust -8gas can be concentrated, and wherein by virtue of the fuel-injection valve fuel can be injected directly into the cylinder and ignited by means of the spark plug.

The proposed engine design achieves a direct injection multi-cylinder internal combustion engine, in which a/\ = 1 control is possible in the 'part load' range without restricting the intake. To this end, when filling each cylinder of the internal combustion engine, recirculating exhaust gas is introduced into the cylinder in such a manner that a rotating, approximately cup-shaped concentration of recirculated exhaust gas is formed therein. A top-up quantity of fresh air is then introduced into the inner chamber of this cup-shaped gas structure, and top-up quantity fuel is injected in the region of the top dead centre of the piston movement, directly into the compressed fresh air, in such a way that independently of the engine loading a value of A=1 is continuously set in the combustion chamber. The quantity of exhaust gases introduced is continuously reduced from the loading points "idling" to "full load" with the aid of control valves by way of the A=1 control. The combustion chamber is therefore continuously completely filled with gas, so that in the combustion chamber of the cylinder there is an 1 -9optimum compression end pressure and an optimum compression temperature over the entire operating range of the engine. Consequently the thermal efficiency and thus the fuel consumption is improved, which has a noticeably positive effect especially in the idling and part load range.

Unrestricted operation, especially in the almost idling 'part load' range, causes the C02 emissions to be considerably reduced owing to the greatly reduced fuel consumption. As the exhaust gas recirculating line from one cylinder to another cylinder is "closed for a short time" the raw emission among other things of NOX in the part load range is further reduced in comparison to engines according to the prior art. In addition, the permanent A=1 control in this layerfilled internal combustion engine also enables tried and tested 3-port catalytic convertors to be used in the 'part load, and 'idling, range, so that with reduced raw emissions it is possible to achieve future exhaust gas limit values.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view through an engine block of a multi- cylinder engine in the region of an engine cylinder, constructed according to the _10present invention; Fig. 2 is a cross-sectional view of part of the engine cylinder of the engine of Fig. 1, showing the exhaust gas inlet ducts, Fig. 3 is a cross-sectional view through Fig. 2 taken along the line III- III in Fig. 2; Fig. 4 is a longitudinal sectional view through Fig. 2 taken along line IV-IV; Fig. 5a to Fig. 7b show a cross-sectional view of a layer-filled engine cylinder, in the filling and compressing phases respectively, and Fig. 8 is a schematic illustration of the arrangement of the exhaust gas recirculating ducts between the cylinders of a four cylinder internal combustion engine, according to the present invention.

Fig. 1 illustrates a schematic cross-sectional view through a multicylinder internal combustion engine with an engine block 1 and a cylinder 2 being shown. The engine cylinder 2 is sealed towards the top by a cylinder head 3, with a fresh air feed line 8 which can be closed by an inlet valve 18, and an exhaust gas line 9 which can be closed by an outlet valve 19, extending therethrough. In addition, a fuel-injection valve 10 and a spark plug 11 extend through the cylinder head 3 into in the cylinder 2, the fuel injection valve 10 being for the purpose of _11injecting fuel directly into the cylinder 2 and the spark plug 11 being for the purpose of ignition. The inlet and outlet valves 18,19 are controlled mainly with variable control times in order to achieve the stratification of the exhaust gas in the cylinder in accordance with the present invention.

The lower part of the cylinder 2 is sealed by a piston 5 arranged to move in a reciprocating manner in the cylinder, the piston being connected to a crankshaft 7 of the engine by way of a piston rod 6.

In the region of the bottom dead centre UT of the piston movement, exhaust gas recirculating ducts 30, 301 are indicated, which ducts open into the engine cylinder 2. Exhaust gas can be pushed through the said ducts out of another cylinder of the internal combustion engine directly in "short-close" operation, and into the engine cylinder 2, as soon as the piston 5 exposes the exhaust gas inlet ports of the exhaust gas recirculating ducts 30, 30'. Exhaust gas inlet ports 20, 201F 21, 21'F22f 22, are disposed in the engine cylinder in such a way that when the engine is operating in a preferred manner a rotating, approximately cup- shaped concentration of exhaust gas occurs, as shown by concentration limit line 17. The fresh air 15 necessary to completely fill the engine cylinder 2 is thus located directly below the fuel- -12injection nozzle 10 and the spark plug 11.

When the piston 5 is moving in the direction of arrow 14 towards the top dead centre OT of the piston movement, the stratified cylinder contents are compressed in such a way that when the piston is positioned in the region of the top dead centre IOTI, fuel can be injected directly into the fresh air concentration 15 by way of the fuel-injection nozzle 10 and subsequently ignited by the spark plug 11. During the subsequent downwards movement of the piston 5, as the piston passes the inlet ports to the exhaust gas recirculating ducts 30, 31, 32, exhaust gas is passed directly in the "short-closed" operation,, to another engine cylinder of the internal combustion engine, the piston of which other cylinder is disposed on a crank journal of the crankshaft 7 with an identical angle of crank. Only then is the remainder of the exhaust gas diverted into the tube 9 by opening the exhaust gas outlet valve 19.

In this way, in the case of a four-cylinder internal combustion engine, the first engine cylinder is connected to the fourth engine cylinder and the second engine cylinder is connected to the third engine cylinder by way of the exhaust gas recirculating ducts 30f301. The exhaust gas can thus flow through these ducts 30, 301 directly from, for -13example, the first cylinder into the fourth cylinder and reverse. This depends upon which cylinder is at the time in the expansion or rather intake phase. After the said another cylinder is now filled as described with recirculated exhaust gas in such a way that a rotating approximately cup-shaped exhaust gas concentration is produced therein, the fresh air necessary for completely filling the cylinder is also supplied by way of the fresh air feed valve 18, so that the compressing step of the said another cylinder can take place as described above.

Fig. 2 illustrate's a sectional side view of part of an engine cylinder in the region of the bottom dead centre position 'UT' of the piston S. in which in a preferred embodiment of the present invention, a total of six inlet ports are provided for the exhaust gas recirculating ducts 30,30'. A total of three exhaust gas inlet ports 20, 21, 22 are visible in Fig. 2, while the other geometrically identical exhaust gas inlet ports 201, 21', 22' are disposed offset by preferably 180 on the other cylinder half (not visible). This arrangement of exhaust gas inlet ports is more clearly shown in the transverse cross section of Fig. 3, it being clearly visible that a total of six exhaust gas recirculating ducts 30, 301, 31, 311, 32, 32' lead to the engine cylinder 2. The respective -14exhaust ducts, which are disposed offset from each other by 1800,have identical cross-section exhaust gas inlet ports.

The shape of the exhaust gas inlet port 20 and its counter port 201 (not illustrated) offset therefrom by 180, is of particular importance for the formation of the stratified contents of the cylinder with exhaust gas. Reference is thus drawn to Fig. 4 wherein it is made clear, that the exhaust gas recirculating duct 30, 301 is cut in an upwards direction with respect to the cylinder 2 and merges tangentially with the cylinder 2 so that when the cylinder is being filled with exhaust gas from these two opposite exhaust gas inlet ports 20, 201, partial exhaust gas flows A. B are superimposed on each other in the form of a spiral. In contrast to the tangential exhaust gas inlet ports known from the prior art, these partial exhaust gas flows A, B do not produce any turbulence amongst themselves. Consequently, it is advantageously possible to prevent a premature mixing of the recirculated exhaust gas and the fresh air in the cylinder chamber.

Figs. 5a to 7b illustrate various stratifications of recirculated exhaust gas 16 and fresh air 15 in an engine cylinder. The figures provided with the suffix "all illustrate the condition of the cylinder 1 i -isstratification at the commencement of the compressing phase by the piston 5, whereas the figures provided with the suffix "b" illustrate the condition of the cylinder stratification in the region of the top dead centre position 'O.T.' of the movement of the piston S.

The various stratifications of the exhaust gas 16 and fresh air 15 in the cylinder 2 can be adjusted by varying the use of the six exhaust gas recirculating ducts 30, 301, 31, 311, 32, 321 provided here at each cylinder. The exhaust gas recirculating ducts 30,301,31,311,32,321, can, as indicated in Fig. 8, be combined to form exhaust gas collecting ducts 34, 35f 36, which are provided in each case with an exhaust gas control valve 29, 29'. These valves render it possible to control both the opening time and also the through-flow quantity of circulated exhaust gas.

In order to produce an exhaust gas-fresh air stratification as shown in Fig. Sa and 5b, exhaust gas is accordingly fed through the two upwardly cut exhaust gas recirculating ducts 30, 301 which issue in a tangential manner into the cylinder, so that, as already described, two spiral exhaust gas flows A, B are formed at the cylinder inner wall, and the said gas flows A, B with respect to the cylinder wall also form amongst themselves a stratification in the -16recirculated exhaust gas in the vertical direction. The stratification which is produced in this way between the recirculated exhaust gas 16 and the fresh air 15 is extremely more stable than the stratification known from the prior art. A premature mixing is thus prevented in the boundary region between the fresh air zone and the exhaust gas zone, so that in the region of the top dead centre IOTI of the piston movement, a greatly improved fresh gas concentration can occur below the fuel-injection nozzle 10 and the spark plug 11, than was previously possible. Fuel can then, preferably in the idling range and in the lower part load range, be injected directly into this compressed fresh air trough 23 and with the aid of the spark plug is subsequently ignited.

Provided that a stratification of charge is desired in the cylinder, in such a way that a fresh air disc 24 is produced (see Fig. 6b) over the entire cylinder diameter in the top dead centre position of the piston movement, the exhaust gas recirculating ducts 30, 301, 31, 311 are opened by way of the exhaust gas control valves 29, 291, so that exhaust gas is fed into the cylinder 2 in the first intake phase in such a manner that a substantially horizontal exhaust gas concentration 16 is formed (see Fig. 6a).

k -17As the piston 5 continues to move, the necessary fresh air quantities are drawn in at the respective opt' times in dependence upon the load.

In a preferred embodiment of the present invention, the exhaust gas recirculating ducts 30, 30, and 31, 31, are opened by way of the exhaust gas control valves, as shown in Figs. 7a, 7b. In this way, recirculated exhaust gas 16 passes in the first intake phase into the cylinder chamber by way of the exhaust gas inlet ports 20, 20'r 21, 211 in such a manner that a rotating and approximately cup-shaped exhaust gas concentration with a concentration limit line 17 is formed within the cylinder 2. During the course of the subsequent intake process, fresh air 15 can be filled into the inner chamber thereof. At the end of the compressing process by the piston 5, a compressed fresh air lens 25 is produced (see Fig. 7b) in such a way that fuel can then be injected directly with the aid of the fuel-injection valve 10 and the mixture produced can be ignited by the spark plug 11.

In order to explain glearly the arrangement of the exhaust gas recirculating ducts 30, 301, 31, 31', 32, 32' and the cylinder 26, 27, 28, 2 in the engine block, Fig. 8 illustrates a transverse, crosssectional view through an internal combustion engine constructed in accordance with the present invention.

- 18The engine cylinders 26 and 2 or 27 and 28 which are connected to each other by way of the exhaust gas ducts, are those cylinders, the pistons of which are disposed on the crankshaft journal at an identical angle of crank.

Referring to Fig. 8, exhaust gas control valves 29, 29, are provided in each exhaust gas duct, it being possible with the aid of these control valves to shut off each exhaust gas recirculating duct and to adjust the quantity of exhaust gas flowing therethrough. In this way, it is possible to recirculate only that q uantity of exhaust gas into the respective cylinder, which is necessary for a loaddependent ( A=1) control. That is to say, in the part load range the cylinder is filled with a comparatively large quantity of recirculated exhaust gas, whereas in the full-load range no exhaust gas at all is recirculated. Consequently, it is possible to reduce continuously the quantity of recirculating exhaust gas from the load point "idling", as far the load point "full-load" by virtue of the exhaust gas control valves 29,291. The combustion chamber region of the cylinder 2 is thus continuously completely filled, so that even in the part load range it is possible to operate the engine without throttling. The quantity of fuel to be injected directly into the internal 1 _19combustion chamber is metered in this way and the commencement of fuel injection is controlled in such a way that a value ofA=1 is continuously set independently from the engine load.

The operation of an internal combustion engine of this type can be understood, by way of example, by the control flow and current flow of the cylinder pair comprising the first and fourth engine cylinders. The expansion phase commences in the first cylinder in the idling range after ignition. The outlet valve 19 of this cylinder preferably remains closed until the piston 5 has passed the bottom dead centre 'UT', whereas the exhaust gas control valve in the exhaust gas recirculating duct(s) between the first and the fourth cylinder is completely opened.

As the piston 5 moves downwards in the direction of 'UT', the crosssections of the exhaust gas inlet ports 20, 201, 21, 211, 22, 22, are revealed. The exhaust gas thus flows by way of the exhaust gas recirculating ducts into the fourth cylinder, the exhaust gas inlet ports of the fourth cylinder being likewise revealed as a result of the synchronised movement of the piston of the fourth cylinder. Since, particularly in the idling range, the expansion pressure when opening the exhaust gas duct(s) is low, the moment when the inlet valve 18 of the fourth -20intake cylinder and the moment when the outlet valve 19 at the first cylinder is opened, are timed so that sufficient exhaust gas can flow over into the fourth cylinder. In this way, the outlet valve 19 is preferably not opened until 60 after 'UT'.

The period of overflow is limited by the piston 5 of the first and fourth cylinder moving upwards again and passing the bottom dead centre, since no further exhaust gas can overflow from one cylinder into the other cylinder when passing the upper edges of the exhaust gas inlet ports of the exhaust gas recirculating ducts. The quantity of the overflowing exhaust gases can be varied by the exhaust gas control valve in dependence upon the engine load. Once the pistons of the first and fourth cylinders have passed the upper edge of the exhaust gas inlet ports, the exhaust gas outlet valve is opened in the first cylinder and the inlet valve 18 in the fourth cylinder is opened in the proximity of 'UT' for filling the remainder of the cylinder with fresh air. The filling of the remainder of the cylinder with fresh air can be controlled also by means of a restrictor plate in advance of the inlet valve.

In full-load operation the engine is operated as a conventional Otto engine. This is achieved by the exhaust gas control valves in the exhaust gas 1 - 21recirculating ducts between the cylinders being fully closed. In the transition from these two extreme load points ie "idling" and "full-load", aA=l control is achieved by controlling the exhaust gas control valves in such a way that a progressively smaller quantity of gas overflows. This can for example be achieved by a valve stroke which is gradually reducing and a progressively shorter opening period of an exhaust gas control valve.

The stratification, which can be adjusted in this way and varied by means of dimensioning and arranging the exhaust gas inlet ports, between fresh air and recirculated exhaust gas, is compressed by the piston 5 moving in the direction towards the top dead centre and in the "idling" load range in the proximity of the top dead centre IOTI, fuel can be injected directly. This method of operation prevents a part of the fuel being diffused into the exhaust gas layer during premature injection with the result that incomplete combustion is prevented.

In the "full load" load range the fuel is injected directly when the exhaust gas is no longer flowing out through the outlet valve 19. Consequently the in-flowing fresh gas is homogenised well with the directly injected fuel, producing a high performance yield for the "fullload" range of the engine. The -22points in time when fuel is injected between the extreme load values of "idling" and "full-load" lie between the said points in time.

In an advantageous embodiment of the present invention, the fuelinjection valve 10 can be designed as an air-supported fuel-injection valve_ known per se, wherein the fuel is collected from an air flow and pushed through a fuel-injection nozzle. When using a fuel-injection valve of this type, the quantity of air transported with the fuel can be used to control the total air quantity to be introduced into the cylinder for example in the part load range for controlling the A=1 mixture in the region of the spark plug 11.

By means of the engine concept described it is possible for the first time when using direct fuel injection into a stratified combustion chamber to reduce greatly the toxic substances in the exhaust gas, especially during a cold start-up and in the warm running phase. The directly injected fuel no longer moistens the cold walls of the piston and/or cylinder, as is the case in direct injection engines according to the prior art, which inparticular leads to enhanced exhaust gas values in the area of hydrocarbon emissions.

With unrestricted operation, in particular in the almost idling part of the load range, the fuel Z 1 -23consumption is also greatly reduced with respect to engines according to the prior art, so that the quantity of C02 is reduced. The raw emission among other things of NOx, is further reduced in the part load range owing to the exhaust gas recirculating line between the described cylinders being closed for a short period of time. The pe=anent.-\=l control also renders it possible to use a tried and tested 3-port catalytic convertor even in the "part load" range with its stratified contents, so that it also possible to achieve future exhaust gas limit values when the raw emission is reduced.

Claims

CLAIMS 1. A method of operating a multi-cylinder internal combustion engine so as to opt'IM'Ise the exhaust gas emissions and fuel consumption, in which method prior to a compression stroke of each piston a rotating stratification of recirculated exhaust gas and fresh air is produced within the engine cylinder, exhaust gas being directed in various quantities in dependence upon the engine load in a controlled manner into the engine cylinder, the exhaust gas for filling an engine cylinder being drawn off from an exhaust gas emptying cycle of a further engine cylinder, in the region of the bottom dead centre position of the associated piston, the piston of this further cylinder being disposed on a crankshaft journal of an identical angle of crank, a quantity of exhaust gas dependent upon the load being initially metered in a substantially tangential manner into the engine cylinder with the aid of at least one exhaust gas control valve in order to fill the engine cylinder, a top-up quantity of fresh air being subsequently drawn in for the purpose of completely filling the cylinder, the quantity of drawn-in fresh air being metered by opening an inlet valve together with the -25previously added exhaust gas and the quantity of fuel to be injected in"such a manner that independently of the engine load a value A=l is continuously set, the stratified contents of the cylinder being subsequently compressed by the piston of the cylinder, fuel being then directly injected into the fresh air located in the cylinder and the fuel- air mixture produced being ignited, an exhaust gas outlet valve in the cylinder being first opened in the subsequent expansion phase dependent upon the load when the cylinder internal pressure is still sufficient for the necessary quantity of exhaust gas to be drawn off to fill said further cylinder.

1

2. A method as claimed in claim 1, in which the recirculated exhaust gas is introduced in the region of the bottom dead centre position 'UT' of the piston in a tangential manner and/or offset radially into the cylinder, so that a cup-shaped exhaust gas concentration is produced in the cylinder, in the centre of which concentration the fresh air is stored.

3. A method as claimed in claim 1, in which the exhaust gas introduced in a tangential manner into the cylinder is stratified in partial exhaust gas flows A, B vertically at the cylinder inner wall.

4. A method as claimed in claim 1 or 2, in which the cylinders of the engine are unrestricted in each -26load range and operated with a continuously completely full cylinder chamber.

S. A direct injection internal combustion engine, comprising engine cylinders disposed in an engine block, pistons being articulated at a crankshaft in such a way as to move in a cyclic and reciprocating manner in said cylinderf each cylinder being sealed at its upper end by a cylinder head, at least one air inlet valve and an exhaust gas outlet valve as well as a fuel injection valve and a spark plug being disposed respectively in the cylinder head for each cylinder, each cylinder comprising in the region of the bottom dead centre UT of the piston movement at least two exhaust gas inlet ports disposed tangentially to the cylinder periphery, which inlet ports are for exhaust gas recirculating ducts, which are connected to the other cylinders, each cylinder also comprising at least two further exhaust gas inlet ports which are disposed radially offset at the cylinder periphery, and with respect to each other in such a way that with the aid thereof the recirculated exhaust gas flowing into the cylinder preferably forms a rotating, approximately cup-shaped collection of exhaust gas with a limit line and the fresh air being metered by the or each air inlet valve into the inner space of the said collection of exhaust gas can be Q -27concentrated, and wherein by virtue of the fuelinjection valve fuel can be injected directly into the cylinder and ignited by means of the spark plug.

6. An internal combustion engine as claimed in claim 5, in which the exhaust gas inlet ports of an individual cylinder are interconnected by way of the exhaust gas recirculating ducts.

7. An internal combustion engine as claimed in claim 5 or 6, in which the exhaust gas recirculating ducts interconnect at least two cylinders, the pistons of which are disposed on crankshaft journals of an identical angle of crank, so that in the case of fourstroke/four-cylinder engine a first cylinder is connected to a fourth cylinder and a second cylinder is connected to a third cylinder by way of these exhaust gas recirculating ducts.

8. An internal combustion engine as claimed in any one of claims 5 to 7, in which at least one exhaust gas control valve respectively is disposed in the exhaust gas recirculating ducts or in the exhaust gas collecting ducts.

9. An internal combustion engine as claimed in any one of claims 5 to 8, in which the exhaust gas recirculating ducts of identical dimensions and inlet position are disposed in the cylinders in each case offset by approx 180 with respect to each other on -28the cylinder periphery.

10. An internal combustion engine as claimed in any one of claims 4 to 9, in which the exhaust gas inlet ports disposed tangentially to the cylinder periphery and are cut vertically in the direction towards the cylinder head in such a way that spiralshaped exhaust gas flows form in the region of the cylinder inner y7all, which exhaust gas flows form layers mutually superimposed on each other.

11. An internal combustion engine as claimed in any one of claims 5 to 10, in which the fuel injection valve is designed as an air-supported fuelinjection valve adapted to collect fuel from a carrier air flow and to break the fuel down into extremely fine particles after passing the valve port.

12. An internal combustion engine constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

13. A method of operating a multi-cylinder internal combustion engine substantially as hereinbefore described with reference to the accompanying drawings.