The basic object of EGR is better fuel economy and cleaner exhaust gases. It is particularly concerned with fulfilling the stringent environmental requirements regarding emissions which are particularly likely to apply to diesel engines.

In a known EGR device, an EGR pump is used to raise the pressure of the return gases so that they can be fed to the engine's inlet side against the inlet pressure, which in a normally operating diesel engine is higher than the exhaust pressure. A representative case of this state of the art is described in WO 96/18030, in which an EGR turbine arranged after the charging turbine is used for driving a compressor which increases the pressure of the EGR gases and thereby feeds the latter in via the inlet manifold to the engine's inlet side.

PROBLEMS WITH THE STATE OF THE ART The state of the art entails disadvantages owing to the complexity and relatively high cost of manufacturing and installing the additional turbine/compressor. The many parts involved also increase the servicing requirements of the installation.

US-A-4 445 488 refers to a device of the kind mentioned in the introduction in which the EGR gases are led by their own pressure from the exhaust side to the inlet side via a valved recirculating line. This is made possible by the turbine being dimensioned so that there is in the exhaust line a certain desired counterpressure which is used for recirculation. However, the state of the art according to that document does in practice involve a great deal of line laying and valve incorporation.

OBJECTS AND MOST IMPORTANT CHARACTERISTICS OF THE INVENTION An object of the present invention is to provide a device of the kind mentioned in the introduction which eliminates the problems of the state of the art. This is achieved in the device indicated in the introduction by means of the features in the characterising part of patent claim 1.

The result is an integrated unit which reduces the amount of line laying and eliminates inter alia the need in self-transferring EGR systems for an additional separate exhaust manifold.

The invention also makes it possible to use the waste-gate technique which incorporates a bypass line to lead exhaust gases past the turbine in certain operating states. According to the invention, however, this is done in such a way that exhaust gases which would have been intended to be led past the turbine to the exhaust outlet become EGR gases instead.

The invention also makes it possible to use known and proven waste-gate technology, which means that components and control equipment are readily available at low cost.

In an advantageous embodiment of the invention, the turbine housing is also provided with a waste-gate duct which allows the proportion of EGR or bypassing exhaust gases to be controlled so as to achieve optimum combustion in the most diverse operating conditions. Combining the valve functions with the turbine housing results in an uncomplicated and economic design and in easy and extremely service-friendly installation.

Further advantages are achieved by the characteristics in the other dependent claims and are indicated by the following description of an embodiment with reference to the attached drawings.

LIST OF DRAWINGS Fig. 1 shows a skeleton diagram of an installation of a device according to the invention.

Fig. 2 shows in axial section a turbine housing according to a first embodiment of the invention, and Fig. 3 shows in axial section a turbine housing according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS In Fig. 1, reference 1 denotes a schematically depicted six-cylinder turbocharged diesel engine incorporating two exhaust manifolds 2 and an inlet manifold 3. An EGR line (exhaust gas recirculating line) 4 runs in a conventional manner between the exhaust side and the inlet side of the engine and ends in the vicinity of the point where the feed line 5 enters the inlet manifold. The exhaust manifolds 2 lead to and are connected into a turbine housing 6 containing a turbine designed to drive in a conventional manner a supercharging compressor situated in the inlet line 5. The turbine housing 6 incorporates before the turbine a valve-controlled EGR duct section in one of the exhaust lines.

Exhaust gas flows through the turbine housing are indicated by the arrows marked in the respective ducts, of which the large arrow after the turbine represents exhaust gases going to the silencer system (applies also correspondingly to Fig. 2).

Fig. 2 shows the turbine housing 6 with the turbine 7 driven by exhaust gases coming from the engine's respective exhaust manifolds 2 via the duct sections 8 and 9. The reason for two separate exhaust manifolds is to prevent any unfavourable exhaust gas pressure effects between the various cylinders of the engine which might otherwise arise from an undivided exhaust manifold. In one of these duct sections, 9, there is before the turbine impeller a branch leading to an EGR duct section 10 in which a controllable valve device is incorporated. This valve device consists of a valve element 11 and a valve seat 12 and is used for drawing off a certain exhaust gas quantity to the EGR duct. What is used in practice in this respect is a combined waste-gate/EGR valve which combines the EGR principle with the waste-gate principle. The valve is of course controllable according to

the principle of achieving the best possible EGR transfer even when waste-gate draw-off is not taking place.

Controllability means that the valve is controlled with a view to optimising the operation of the engine and/or minimising emissions, e. g. during heavy load the valve is closed so that maximum power is fed to the turbine and hence to the supercharging compressor.

In the embodiment according to Fig. 3, the same reference notations are used as in Fig. 2 for similar elements. The difference from the version according to Fig. 2 is that the ducting is supplemented by a genuine waste-gate duct 13 which is provided with a valve device incorporating a valve element 14 and a valve seat 15. This solution makes it possible for the engine's operating conditions to be controlled for further refined optimisation by the gas flow through the duct section 9 or the whole gas flow being led along the following different paths: -to the turbine, -partly to the turbine and partly to the EGR duct, -partly to the turbine and partly to the waste-gate duct, or -partly to the EGR duct, partly to the waste-gate duct and partly to the turbine.

This enhances engine control possibilities in a variety of operating conditions.

The invention thus makes it possible for various separate functions to be integrated in the turbine housing, resulting in a reduced total cost of production and easier and more logical installation of the unit. Control of the valve/valves in this context is preferably by means of a control system based on such operating data as engine speed, fuel consumption, load, emissions etc. The valves concerned are controlled by means of suitable movement transmitting devices which operate electrically, pneumatically or hydraulically.

A turbine housing according to the invention can easily be manufactured in a manner corresponding to the manufacture of a turbine housing with integrated waste-gate duct.

Incorporating the EGR and/or waste-gate ducts, and the valves situated in them, as integrated units in the turbine housing simplifies assembly and reduces the space requirements of installations.