STATE OF THE ART A known practice in combustion engines is to feed exhaust gases back to the engine inlet in order to reduce the nitrogen oxides content of the exhaust. The exhaust gases fed back have the effect of lowering the combustion temperature and hence reducing the proportion of the sulphur in the inlet air which can be converted to nitrogen oxides. In Otto engines, this technique, usually called EGR (exhaust gas recirculation), has become widely used as a relatively simple way of reducing the content of harmful exhaust emissions. In diesel engines, however, this technique has not become so widely used, because diesel engines have particular problems which make it impossible to apply directly to them solutions which apply to Otto engines.

One of these particular problems is that combustion in diesel engines normally takes place with excess air. This results indirectly in relatively large volumes of exhaust gases having to be transferred for a relatively large proportion of engine operating range if the intended function is to be achieved. This problem is exacerbated in the case of engines of the supercharged type in that the pressure in their inlet system is greater than the pressure in their exhaust system for a large proportion of their operating range.

Among known solutions usable in supercharged engines, a distinction may be made between two main principles usually referred to respectively as"short route EGR"and "long route EGR". In short route EGR, the exhaust gases are taken from a point upstream from an exhaust turbine arranged in the exhaust system and are fed back at a point downstream from an inlet air compressor arranged in the inlet system. In long route EGR, the exhaust gases are taken from a point downstream from the exhaust turbine and are fed back at a point upstream from the inlet air compressor. Both principles have advantages and disadvantages. An advantage of the short route solution is the possibility

of avoiding fouling of a charge air cooler for the inlet air. A disadvantage of the short route solution is that it requires some form of pressure-increasing arrangement because the exhaust gases are fed back at a point where the pressure is normally higher than the pressure prevailing in the exhaust manifold of the exhaust system.

A known practice is to use a separate supercharging unit to bring about this increase in the pressure of the exhaust gases, as described, for example, in W096/18030 and W096/18031. A disadvantage of those solutions is the need for the extra supercharging unit or some other pressure-increasing device, which makes those solutions both expensive and bulky. The power used for driving these arrangements increases the engine's fuel consumption.

Known technology with regard to the present invention which has also to be mentioned is JP 08232771-A, which refers to an engine with an EGR line which incorporates a directional valve, an EGR chamber and an EGR control valve. That arrangement is intended, however, to reduce exhaust pulse fluctuation so that a steady flow is achieved.

OBJECT OF THE INVENTION An object of the present invention is to eliminate the problems of the state of the art when using a solution for exhaust gas feedback according to the short route alternative in a supercharged diesel engine. The invention thus aims to make effective exhaust gas feedback possible without using a separate supercharging unit or other pressure- increasing device for the exhaust gases fed back.

According to the invention, this is achieved in an arrangement of the kind mentioned in the introduction by its being provided with the features indicated in the characterising part of patent claim 1.

The invention makes it possible for the momentary pressure peaks which normally occur in the exhaust manifold to be used for transferring exhaust gases to the engine's inlet pipe, which, owing to supercharging, has a relatively high inlet pressure. The need to provide a charging compressor or the like for feeding the EGR gases in is thus eliminated,

thereby simplifying and reducing the cost of the installation, while at the same time maintaining low fuel consumption. Providing check valves at the connection to each turbine inlet duct is a simple and effective means of utilising a considerable proportion of the pulse energy deriving from all the cylinders connected to the respective exhaust manifold section.

The dependent patent claims indicate advantageous embodiments of the invention.

Inserting an EGR control valve in the transfer line makes it possible to modulate the flow and optimise both the quantity and timing of the feedback. Incorporating the EGR control valve in the EGR chamber makes the installation simple and economic.

Arranging a deflector which penetrates into each turbine inlet duct ensures effective utilisation of the pulse energy. It may be mentioned here that the design of the deflectors can be optimised to achieve a desired EGR flow, possibly even so that in certain applications the EGR control valve becomes superfluous.

The invention results in easy assembly and freedom from maintenance. Arranging the check valves so that during operation they are closed by (oblique) flow in the opposite direction makes it possible to dispense with return springs and the like, thereby also resulting freedom from losses as the gases pass the check valves.

Connecting the transfer line after the charge air cooler means that fouling, obstruction and corrosion are avoided at that point.

Further features and advantages distinguishing the invention are indicated in the embodiment described below.

DESCRIPTION OF THE DRAWINGS An embodiment exemplifying the invention will now be described in more detail with reference to the attached drawings, in which: Fig. 1 depicts an arrangement according to the invention in a turbine adapter, and Fig. 2 depicts schematically a diagram of the pressure in an exhaust manifold as a function of time.

DESCRIPTION OF AN EMBODIMENT The embodiment described relates to a four-stroke turbocharged combustion engine of diesel type intended as the drive engine for a heavy-duty vehicle such as a truck or a bus.

The engine is multi-cylinder and has the cylinders divided into two groups, e. g. as is usual in engines of V8 type or in an in-line six-cylinder engine in which the cylinders are correspondingly divided into two groups.

In Fig. l the reference notation 1 denotes generally an arrangement for exhaust gas feedback (EGR feedback) whereby a two-part exhaust manifold (not depicted in its entirety), referable to the engine and the respective cylinder groups, incorporates respective first and second turbine inlet ducts 2 and 2'. The arrows 3,3'denote the direction of flow to the turbine (and thereafter also to an exhaust pipe) and the arrows 4 and 4'respectively denote the direction of the exhaust gases leaving the respective groups of cylinders.

Each turbine inlet duct forming part of the respective exhaust manifold sections has connected to it an EGR draw-off duct 5,5' which incorporates a deflector 6,6'directe against the direction of flow in the exhaust manifold sections. The EGR draw-off ducts should be as short as possible and without unnecessary bends and be such that exhaust pressure pulses in the exhaust manifold sections effectively drive the gases through these EGR draw-off ducts to a check valve 8,8' provided at the end of each duct. The check valves are themselves fastened to respective articulated arms 9,9' which are articulatedly connected by hinge pins 10,10'to the inside wall of a housing which delineates an EGR chamber 7. To limit the movement of the check valves in the opening direction, stop devices are provided, in the form in this embodiment of supporting projections 12 mounted on a supporting bracket 11. Fig. l shows the lower portion of the check valve 8' resting against the associated supporting projections, while the check valve 8 in the upper part of the diagram is sealing off the EGR draw-off duct.

The check valves 8,8' are of poppet valve type so that when gas pressure inside the EGR chamber 7 exceeds the pressure in the EGR draw-off duct the result is check valve closure, while the opposite condition results in check valve opening. For this purpose it is

important that the respective check valve in the open position presents a clear surface facing the EGR chamber so that this effect can be achieved in practice. For this reason, the extent of the surface of the stop devices is limited to avoid masking the valve bodies.

It is preferable to ensure that the EGR draw-off ducts 5,5' are so designed and the check valves 8,8' are so positioned relative to one another that an exhaust pulse from an exhaust manifold section which passes one of the check valves is steered towards the rear of the second check valve in order to bring about said closure. At the same time, the inlet to the EGR chamber 7, the geometric configuration of the EGR chamber and the suspension of the check valves are adapted so that this steering occurs in practice.

According to the embodiment depicted in Fig. 1, the outlet from the EGR chamber 7 is controlled by an EGR control valve 13 which closes against a valve seat 14 which faces into the chamber. This design is preferred for ensuring sufficient and reliable tightness during exhaust braking. Reference 15 denotes the outlet from the EGR chamber to the other part of the transfer duct. The EGR control valve is advantageously controlled separately and preferably pneumatically in response to signals indicating the operating state of the engine.

Fig. 2 depicts schematically the relationship between the pressure p in the exhaust manifold as a function of time t. It shows that the pressure fluctuates over time. Also, pm denotes the mean pressure in the exhaust manifold, pl denotes the charge air pressure and po denotes the desired pressure in the transfer line which is necessary and also desirable for achieving the intended EGR transfer. According to the invention, the energy in the exhaust gas pulse peaks (marked by shading in Fig. 2) is thus utilised, which means that there is no need to use any pressure-increasing device such as a supercharging unit or the like.

The invention is not limited to the embodiments indicated above but may be modified within the scope of the patent claims, which means that in certain applications the EGR control valve may be omitted, e. g. if the deflectors 6 are matched so that an acceptable EGR flow can be achieved. Exhaust braking, however, needs some form of shutoff valve,

which may nevertheless, at least theoretically, be situated anywhere along the extent of the transfer line.

For operation with mutually cooperating check valves 8,8' it is important that the valve bodies move easily and yet be reliable and provide a reliable tightness. This may be achieved, for example, by the articulations 10,10' being made somewhat loose, which means that movements will automatically result in the articulations being subjected to some cleaning effect. The check valves should in addition be as light as possible and preferably unsprung. Titanium alloys are suitable materials for the moving parts in order to limit the moving mass. Other materials used in connection with exhaust brake valves/waste-gate valves may also be used, and in this context it may be noted that the smaller the moving mass, the quicker the reaction, i. e. the opening/closing of the check valves. Absence of springing minimises the flow resistance. The hinge pins may be oriented vertically, horizontally or at any intermediate angle depending on the characteristics desired for the opening process. If the hinge pins run vertically, the weight of the valves is absorbed by the supports in such a way that gravity does not affect the opening or closing force required. With horizontally oriented hinge pins, gravity acts in a closing or opening direction, depending on the orientation of the device. The design indicated thus makes the articulation loose while still resulting in reliable tightness at the check valve seats. This reduces the risk of jamming and results in insensitivity to temperature changes.

In an inherently conventional manner, the transfer line after the EGR chamber 7 incorporates an EGR cooler (not depicted) to bring the temperature of the EGR gases down to a desired low level. Connecting the inlet from the transfer line downstream from the charge air cooler means that fouling of the latter can be avoided.