Patent Application
20080202725
The present invention relates to a cooler arrangement according to the preamble of claim 1.
The amount of air which can be supplied to a supercharged combustion engine depends on the pressure of the air but also on the temperature of the air. Supplying the largest possible amount of air to the combustion engine therefore entails cooling the compressed air in a charge air cooler before it is led to the combustion engine. The compressed air is usually cooled by ambient air flowing through the charge air cooler. The compressed air can thus be cooled to a temperature substantially corresponding to the temperature of the surroundings.
The technique known as EGR (Exhaust Gas Recirculation) is a known way of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for supply of air to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's cylinders in which the combustion takes place. The addition of exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used for both Otto engines and diesel engines. A known practice is to cool the returned exhaust gases in a first EGR cooler by means of the coolant of the vehicle's cooling system and in a second EGR cooler by means of ambient air. The exhaust gases can thus likewise be cooled to a temperature substantially corresponding to the temperature of the surroundings. A further known practice is to arrange the charge air cooler and the second EGR cooler close to one another at a front portion of a vehicle in front of the vehicle's ordinary radiator. The cooled exhaust gases and the cooled compressed air can thus be mixed with one another substantially immediately after the cooling.
In operating situations where the combustion engine's load is low while at the same time there is a low ambient temperature, there is risk of the exhaust gases being cooled to such a low temperature that corrosive substances in the exhaust gases may condense during cooling in the EGR cooler. EGR coolers are usually made of corrosion-resistant material such as stainless steel so that no problems are caused, at least during short periods, by the formation of such condensate in the EGR cooler. Charge air coolers, however, are usually made of material such as aluminium which has good heat-conducting characteristics but less good corrosion-resistant characteristics. As the charge air cooler and the EGR cooler are in this case situated close to one another, there is risk of exhaust gases or condensate from the exhaust gases making their way into and accumulating in the charge air cooler, which is not made of a totally corrosive-resistant material.
The object of the present invention is to provide a cooler arrangement which comprises an EGR cooler for cooling of returned exhaust gases and a charge air cooler for cooling of compressed air which are fitted close to one another and whereby the cooled exhaust gases from the EGR cooler or condensate from the exhaust gases are effectively prevented from making their way into and accumulating in the charge air cooler.
This object is achieved with the cooler device of the kind mentioned in the introduction which is characterised by the features indicated in the characterising part of claim 1. By means of such a tubular element the cooled exhaust gases can be led into the charge air cooler's tank at a position downstream of the point where the cooled air is led into the tank. The air flow present in the tank thus effectively prevents the exhaust gases from moving in an opposite direction and making their way into the charge air cooler's pipelines or accumulating in an upstream portion of the charge air cooler's tank. Since the exhaust gases are thus prevented from accumulating in the charge air cooler, it is therefore possible for the charge air cooler to be made of a less corrosion-resistant material than the EGR cooler. The returned exhaust gases and the compressed air thus already undergo mixing in a downstream portion of the charge air cooler's tank. The inlet line to the combustion engine can therefore be made rather short.
According to a preferred embodiment of the present invention, the tubular element has an extent inside the charge air cooler's tank. There is thus no need for any external lines to lead the cooled exhaust gases from the EGR cooler's tank to the charge air cooler's tank. Alternatively, the tubular element might have an extent at least partly outside the charge air cooler's tank. With advantage, the tubular element has a substantially rectilinear extent inside the first tank. The length of the tubular element can thus be minimised. The tubular element is preferably made of a substantially rigid material. This makes it easier to fit the tubular element in a correct position inside the charge air cooler's tank. The tubular element may have a substantially central extent inside the first tank. The result is a substantially uniform flow of air round the tubular element and its outlet aperture. The risk that any of the exhaust gases from the outlet aperture might be led in an opposite direction is thus eliminated. Central positioning of the tubular element's outlet aperture in the charge air cooler's tank results in effective mixing of exhaust gases and compressed air.
According to a preferred embodiment of the present invention, the charge air cooler's tank has at least one curved portion and the tubular element's outlet aperture is arranged in said curved portion. In a curved portion there is usually a more turbulent flow than in a straight portion. The result is that when the exhaust gases have left the tubular element they undergo effective mixing with the surrounding compressed air, starting in the curved portion. The tubular element's outlet aperture may be defined by an end surface angled in such a way that a radially outermost part of the end surface in the curved portion is situated downstream of a radially innermost part of the end surface. The tubular element is thus provided with an outlet aperture so directed as to facilitate the flow of exhaust gases through the curved portion. Said end surface may have an extent along an inclined plane.
According to a preferred embodiment of the present invention, the charge air cooler's tank is fitted above the EGR cooler's tank. This makes it possible to arrange a tubular element which has an extent from an upper portion of the EGR cooler's tank substantially directly into the charge air cooler's tank via an aperture in a lower portion of the charge air cooler's tank. In such cases, the tubular element will be of substantially vertical extent. Any condensate from the cooled exhaust gases which precipitates on the tubular element's internal wall surfaces will thus run down and accumulate in the EGR cooler's tank.
According to a preferred embodiment of the present invention, the tubular element is made of stainless steel. As there is risk of condensate from the cooled exhaust gases precipitating inside the tubular element, the tubular element needs to be made of a corrosion-resistant material. Stainless steel is a very corrosion-resistant material while at the same time having relatively good heat transfer characteristics. The EGR cooler is also preferably mainly made of stainless steel. In the EGR cooler there is always risk of condensate from the cooled exhaust gases precipitating, e.g. when the ambient air is at a low temperature and the engine is at low load. As stainless steel has the characteristics indicated above, it is advantageous for EGR coolers to be made of this material. With advantage, the charge air cooler will mainly be made of aluminium. The compressed air does not contain the same corrosive substances as the exhaust gases. The first cooler element can therefore with advantage be made of aluminium, which has extraordinary heat transfer characteristics and is a less expensive material than stainless steel.
Preferred embodiments of the invention are described below by way of examples with reference to the attached drawings, in which:
| Number | Date | Country | Kind |
|---|---|---|---|
| 0501403-0 | Jun 2005 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2006/050199 | 6/16/2006 | WO | 00 | 12/10/2007 |
