The most common type of system for reducing NOx in the exhaust gases are systems for re-circulating of a certain amount of exhaust gases to the combustion chambers of the engine, so called EGR-systems, have an extra piping which leads from an exhaust outlet on the exhaust manifold via a so-called EGR-valve to the inlet manifold of the engine.

This piping is consequently common for the re-circulation of the exhaust gases of all the cylinders. Such an external EGR-system requires a certain space in the engine compartment. In climates with extremely cold winters the system requires arrangements for preheating in order to prevent water vapour in the exhaust gases condensing and freezing in the inlet manifold and by the throttle. The devices for preheating cause a pressure drop with a consequential impaired volumetric efficiency for the system.

The object with the present invention is to provide an internal combustion engine of the type mentioned in the introduction in which the arrangement for re-circulation of exhaust gases to the combustion chamber of the engine are integrated into the engine construction itself so that the disadvantages associated with an external EGR-system are eliminated.

This is achieved according to the invention through that means for re-circulating exhaust gases comprise, for each cylinder, an evacuation channel formed in the cylinder block, which channel opens out into the cylinder barrel and forms a communicating connection between the cylinder barrel and an inlet channel, that the evacuation channel's opening and the piston are adapted to each other in such a way that the opening is exposed when the piston is at its lower dead centre, and that valve means in the evacuation channel are

arranged to regulate the flow of exhaust from the combustion chamber to an inlet channel.

An obvious advantage with the EGR-system according to the invention is that all the external components of earlier known systems are eliminated which reduces the manufacturing and assembly cost and facilitates the packing of the engine compartment.

The evacuation channel is preferably arranged between the cylinder wall and an adjoining cooling water skirt, which ensures an even, and so high, temperature that the risk of freezing is eliminated without special arrangements for preheating needing to be required.

The re-circulation path of the exhaust gases becomes optimally short and this in combination with that each cylinder has its own channel gives a high volumetric efficiency. The exhaust mixture in the inlet air becomes well-defined. This can be quickly varied without delay and without great differences between different cylinders. The stability of the combustion is improved with increased flow and improved mixing of the EGR-charge during operation with powerfully stratified fuel-air mixtures (in direct- injected petrol engines).

In an improved embodiment of an aspirating engine according to the invention the evacuation channel opens directly into the inlet channel in the cylinder head. The piston is in its basic design a conventional piston which on the side which is facing towards the evacuation channel's opening is provided with a shield which forms shielding towards the opening of the evacuation channel in order to limit the penetration of oil splashes into the channel during the part of the piston stroke from the upper dead centre, where the underside of the piston is above the opening of the channel. Through letting the evacuation channels open directly into the inlet channels in the cylinder head disturbances from residual gases in the volumes of the inlet tubes and the common piping of conventional systems are eliminated.

The invention is described more closely below with reference to the embodiment shown on the appended drawings, where Figure 1 shows a cross-section through a cylinder block of an embodiment of an engine according to the invention, Figure 2 a cross-section

through a cylinder block of an embodiment of an engine according to the invention and Figure 3 a detailed view of a slide valve in a bored hole of the cylinder block in Figure 1.

In Figure 1 the numeral 1 denotes a cylinder block and 2 a cylinder barrel in which a piston 3 is movably mounted. The piston 3 is via a connecting rod 4 joined with a crank shaft 5 which is rotatably mounted in the crank case 6 of the cylinder block 1. A lower main bearing bridge and an oil pan which together close the crank case are left out of Figure 1. In the cylinder block 1 between the wall 7 of the cylinder barrel 2 and a adjoining cooling water skirt 8 a evacuation channel 9 is formed. The channel 9 has a lower end part 10 which opens out into the wall 7 of the cylinder barrel 2. The second end of the evacuation channel 9 opens out into an inlet channel 11 in the cylinder head 12 of the engine (see Figure 2). As is evident from Figure 2 the evacuation channel 9 opens out into the inlet channel 11 relatively close to the inlet valve 13 in the combustion chamber 14. An exhaust channel 15 with an exhaust valve 16 also opens out into the combustion chamber 14. As is further evident from Figure 1 the end part 10 of the channel 9 opens out directly above the upper surface of the piston 3 when the piston is at its lower dead centre. In a bored hole 17 between the end part 10 of the chaimel 9 and the rest of the channel 9 a slide valve 18 is displaceably and rotatably provided in the cylinder block 1. The slide valve 18, which is shown in more detail in Figure 3, is common for all the cylinders and the bored hole 17 intersects all the channels 9. The slide 18 has a number of portions 19 with a reduced diameter, the number of which corresponds to the number of channels 9. When the portion 19 with a reduced diameter lies in front of the channel 10, as shown in Figure 1, the through-flow area of the connections 10,9 between the combustion chamber 14 of the engine and the inlet channel 11 is maximal and the connection is consequently completely open at the piston's lower dead centre. When the slide portion 20 between the portions 19 with the reduced diameters lies in front of the channel 10 then the connection between the combustion chamber 14 and the inlet channel 11 is broken even when the piston is at its lower dead centre.

The slide 18 is loaded towards the latter closed position by a spring arrangement 21 at one end 17 of the bored hole as shown schematically in Figure 3. With the help of a manoeuvring arrangement 22 which can be an hydraulic piston/cylinder arrangement which is controlled by a engine controlling computer (not shown) which controls the fuel injection and ignition, the slide valve 18 is moved in order to open the re-circulation channel. In a preferred embodiment the slide valve 18 has a part 23 with helical grooves and teeth which run in a part (not shown) of the bored hole 17 with corresponding grooves and teeth. When the manoeuvring device 22 is activated and displaces the slide 18, the slide will simultaneously be rotated which reduces the risk for the slide jamming in the bored hole. With the help of the manoeuvring device 22 the slide valve 18 can be moved steplessly so that the evacuation channel's 9,10 through-flow area can be steplessly varied between the position completely closed and the maximally open channel in order to in this way regulate the amount of re-circulated exhaust gases simultaneously in all the cylinders. The slide valve 18 common to all cylinders could be replaced by individual valves for each cylinder. Instead of hydraulically controlled valve members, electrically controlled valve members could be used.

During approximately half of the piston stroke from the piston's 3 upper dead centre the lower edge of the piston is above the opening 10 of the channel. In order to prevent oil splashes from coming into the channel 10 during the upper half of the piston stroke the piston 3 on the side which is facing towards the channel 10 is provided with a shield 24 the extension of which in the direction of movement of the piston is approximately equal to the length of the piston from its upper oil scraper groove 25 to its bottom edge. The width of the shield is so selected that it is greater than the width of the channel opening.

The shield has a small gap towards the wall of the cylinder barrel and is preferably manufactured of a plastic material, e. g. PTFE.

Towards the end of the expansion stroke but before the exhaust valve opens the pressure of the exhaust gases above the piston are very high and the exhaust gases therefore will begin to flow out through the evacuation channels 10,9 to the inlet channel 11 as soon as the piston 3 begins to expose the opening of the channel 10 assuming that the slide valve

18 does not completely close the channels 9,10. The quantity of exhaust gases which flow to the inlet side depends on the position of the valve slide and the piston speed. The higher the engine speed and the piston speed then the shorter becomes the time interval during which the channel 10 is open.

In an engine with a throttle and inlet manifold and with fuel injection in the inlet port to the respective cylinder the respective evacuation channel 9 leads to the inlet port of the same cylinder which it starts from. If the engine on the other hand is a throttle-less petrol engine with fuel injection directly into the combustion chamber the exhaust gases are led to a different cylinder to that from which the evacuation channel starts from. In a throttle- less DI engine the EGR gas is preferably directed to the intake of the cylinder which is currently on an intake stroke, because the EGR gas is difficult to confine until it is required due to the lack of an intake manifold.

In a typical four cylinder engine with the ignition sequence of cylinder one, three, four and two, the exhaust gases are re-circulated according to the following patterns: from cvlinder one (expansion stroke) to cylinder four (inlet stroke); from cylinder three to cylinder two; from cylinder four to cylinder one; from cylinder two to cylinder three.

The cause of events will be the following if re-circulation from the first to the fourth cylinder is chosen as an example: When the piston in cylinder four passes the lower dead centre at the end of the intake stroke the compression begins in cylinder four. As the piston closes the channel 10 before the compression pressure becomes higher than the diminishing exhaust gas pressure in cylinder one reverse flow is prevented. When the respective pistons again close the channels 10 in cylinders four and one the flow to cylinder four is stopped and a new re- circulation cycle begins. As the pressure in the cylinders at the beginning of the exhaust stroke are much higher than the pressure in the exhaust re-circulation piping in

conventional systems and a sudden pressure increase occurs in channel 10 when it is exposed by the piston, in combination with that the speed near the open inlet valve causes a greater vacuum than in the inlet to conventional systems, an intensive gas pulse is formed which contributes to improving vortex formation in direct-injected petrol engines.

Only minor modifications would be required to make the EGR system decribed above function as a crank case ventilation system of the type which is disclosed in SE patent application No. 9704922-5. In fact, the only structural modification required would be the replacement of the shield 24 with a shield leaving a gap between the shield surface facing the cylinder wall and the cylinder wall as shown in SE patent application No. 9704922-5. Preferably said shield surface should be formed with a step so that there would be an upper portion with small clearance and a lower portion with a larger clearance between the shield surface and the cylinder wall. The location of the step determines the opening time while the width of the gap determines the flow rate. In addition, in order to function as a crank case ventilation system the slide valve 18 of the EGR system must not be brought to a completely closed position. It has to leave at least an opening with a size approximatelv 5% of maximum opening size.