State of the art As is well known, a four-stroke diesel engine goes through a compression phase, an expansion phase, an exhaust phase and an inlet phase, and the work done during the expansion phase is available for utilisation as useful work (at least partially).

Conventionally, the expansion phase is brought to an end naturally at the piston bottom dead centre point, in a situation where gas under pressure is still present in the cylinder, by exhaust ports opening and these pressurised gases being released to the atmosphere. In a modern diesel engine for a heavy vehicle this residual pressure is typically between 6 and 10 bars during normal operation and at engine cruising speed. Conventionally, this energy has thus not been utilised, resulting in poor engine efficiency.

A number of different proposals have been put forward for trying to utilise the energy in the gases in the cylinder at the bottom dead centre point, the most usual approach probably being turbocharging. However, the turbine unit for recovering the energy is relatively inefficient, partly because the turbine utilises only some of the residual energy.

In addition, the turbo unit incorporates a compressor driven by the turbine to create a charging pressure. This compressor is typically of low efficiency which means, taken together with further deficiencies, that only a small proportion of the remaining energy can be utilised by turbocharging.

Objects and most important characteristics of the invention One object of the present invention is to provide a method and an arrangement whereby energy remaining at the end of the expansion phase is utilised more efficiently than is the case in the state of the art.

This object is achieved with a method and an arrangement of the kind mentioned in the introduction by the features in the characterising parts of patent claims 1 and 8 respectively.

The result is that the remaining energy contained in gases under pressure at the end of the expansion phase is utilised very efficiently by the gases in a cylinder being used for pressure supercharging of a cooperating cylinder which is phase-shifted by 360°. This provides an economically advantageous solution in that the expensive turbo unit can be dispensed with and hence also its installation. A further advantage is that well-known components which experience has shown to be reliable can be used. In addition, the invention involves a more efficient and more fuel-saving solution than the turbo unit, since a larger proportion of the total energy content of the fuel is utilised as useful work.

Cooling the fresh air in the duct creates the possibility of more efficient supercharging, and using an air flow smoother to align the gases results in the establishment of a well- defined boundary between fresh air and exhaust gases so that undesirable mixing of fresh air and exhaust gases in the duct is prevented or reduced. An air flow smoother also provides the possibility of better cooling, so it is advantageous for these functions to be integrated.

Dimensioning the duct so that EGR gases can also be transferred with the fresh air makes it possible to utilise the advantages of EGR transfer and set a desired amount of incorporation of EGR for the application concerned.

The control valves being cam-controlled results in a solution which is economic and simple, even if not freely adaptable, while the adoption of variably controllable valves

makes it possible to adjust opening times and hence adapt supercharging and EGR transfer to the prevailing operating parameters.

Adoption of a low-pressure pump device for the fresh air ensures scavenging of not only the cylinders concerned but also the duct during the inlet phase.

Brief description of the drawings The invention will now be described on the basis of an embodiment and with reference to the attached drawings, in which: Figs. la-lf illustrate the invention schematically in connection with two cooperating cylinders in various of their phase situations.

Description of an embodiment In Fig. 1 a, reference 1 denotes part of a four-stroke combustion engine of which the diagram depicts two cylinders A and B in which in a usual manner pistons 2 and 2' respectively are movable by means of crank configurations 3 and 3'respectively.

Cylinders A and B have inlet lines 4 and 4'respectively to provide them with inlet air (or fresh air) which is supplied at a slight overpressure of, for example, 0.2 bar by a pump device P. The inlet lines 4 and 4'are closed in a usual manner by means of inlet valves 6 and 6'respectively.

Between cylinders A and B is arranged a connecting duct 10,5,10'which at least partly exhibits a cooling jacket and internal air flow smoothing elements. In this case the duct 10,5,10'coincides in the vicinity of cylinders A and B with their respective exhaust ducts 10 and 10', and the respective cylinder heads incorporate in a conventional manner exhaust valves 7 and 7'respectively. The respective exhaust ducts 10,10'also incorporate at a short distance from each of the exhaust valves 7 and 7'a bifurcation whereby the upper ducts 8 and 8'respectively in the diagram lead the exhaust gases out to the atmosphere via an undepicted exhaust system. In this region the connecting duct 10,

5,10'is provided with valve configurations so that the outlet ducts 8 and 8'can be closed by means of valves 9 and 9'respectively.

The function of the invention will now be explained with reference to Figures la-If.

Cylinders A and B are phase-shifted 360°, which for Figure la means that cylinder A is approximately halfway through the inlet phase for fresh air, while cylinder B is approximately halfway through the expansion phase. In this situation, the valves 6 and 7 in cylinder A are open, as also the valve 9'in the portion of the connecting duct 10,5,10' situated further away from cylinder A. In this situation, fresh air is fed in by the pump P via the inlet line 4 and the valve 6 to the cylinder space A, and the fact that the fresh air is fed in at a certain pressure means that it also passes through the valve 7 to the connecting duct 10,5 and thence via the valve 9'to the outlet duct 8'. The valves 6,7 and 9'are thus open in this situation, while cylinder B's valves 6'and 7'and the valve 9 situated furthest from cylinder B in the connecting duct are closed.

Fig. lb depicts the cylinders after completion of the inlet phase for cylinder A and the expansion phase for cylinder B. In this situation, substantially fresh air is present in cylinder A at a pressure close to atmospheric pressure, while in cylinder B there is a residual pressure after the expansion phase, typically of the order of 8 bar. In this situation the inlet valves 6 and 6'respectively for both cylinders are closed, as also the respective valves 9 and 9'in the connecting duct 10,5,10'. If the valve 7 in cylinder A is now kept open while at the same time the exhaust valve 7'in cylinder B opens, the gases under pressure in cylinder B, the so-called blown-down gases, will rush from cylinder B through the connecting duct 10,5,10' towards cylinder A. This flow of gases will drive the cooled and aligned fresh air in the connecting duct 10,5,10'into cylinder A until substantially the same pressure prevails in cylinder A as in cylinder B.

Figure lc depicts the next stage, with cylinder A substantially halfway through the compression phase, while cylinder B is approximately halfway through the exhaust phase.

Just after the pressure equalisation depicted in Fig. lb, cylinder A's exhaust valve 7 has closed, while cylinder B's exhaust valve 7'remains open, and at the same time at least the valve 9 in the connecting duct 10,5,10'remains open to allow remaining exhaust gases in

cylinder B to depart to the atmosphere. It is also possible to open the valve 9'in this situation, which would result in reduced counterpressure in cylinder B. It may be noted that according to invention the counterpressure is substantially smaller than in the case of an engine provided with a turbo unit, thus contributing to better efficiency for an engine according to the invention.

Figs. ld-lf depict the continuation of the sequence, with cylinder B in Fig. ld in the inlet phase, while cylinder A is in the expansion phase (corresponding to Fig. la).

It is found that the invention makes it possible for a substantial supercharging pressure of, for example, 4-5 bar for a normal diesel engine for a heavy vehicle to be achieved at a normal operating point, resulting in a corresponding increase in power compared with an unsupercharged engine.

In Fig. le, cylinder B is at the end of the inlet phase, while cylinder A is at the end of the expansion phase (corresponding to Fig. lb). In Fig. If, cylinder B is in the compression phase, while cylinder A is in the exhaust phase (corresponding to Fig. lc).

The invention may be modified within the scopes of the attached claims, and it is thus possible for the connecting duct to be of a different configuration, e. g. separated from the exhaust valves of the cylinders, i. e. with separately controlled valves. The valves 9 and 9' may also be replaced by a single valve situated centrally on the connecting duct, although this allows only a relatively smaller amount of fresh air to be fed into the receiving cylinder.

It is preferable that the connecting duct be well cooled and that the gases which flow through it be aligned via an air flow smoother to create a distinct boundary between fresh air and exhaust gases, but the possibility of cool air being supplied to the connecting duct is not excluded, nor the possibility of this duct having no air flow smoother.

It is also preferable that fresh air be fed in at a certain slight pressure, but the possibility of the engine being constructed entirely on the suction principle is not excluded, which entails ensuring that during the inlet phase the connecting duct has a connection for fresh

air to be drawn into the cylinder concerned via this duct. It is also possible to arrange separate fresh air scavenging of this duct only.

Appropriate choice of dimensions for the duct 10,5,10'enables the supercharging to be optimised and also makes it possible, if so desired, to ensure a certain EGR transfer between the cylinders.

It is possible to control the valves concerned with cam control mechanisms, which entails substantially unadjustable opening and closing periods, but it is also possible for at least some of the valves incorporated in the arrangement to be controlled by variable systems, e. g. electrical, mechanical or hydraulic systems, to make it possible to adapt the pressure supercharging and any EGR transfer to respective operating situations.

An advantageous way of controlling the incorporation of EGR will be to control the pump device P, which may of course be only one pump device for the engine despite two of them being depicted in Fig. la with a view to flow achieving more or less complete scavenging of the duct 10,5,10'. In this way the gas transferred to the receiving cylinder will contain a certain amount of EGR. As specialists are of course aware, variation in EGR content is a significant factor for the combustion process.