Patent ID: 12215614

DETAILED DESCRIPTION

InFIG.1, a drive system for a vehicle is denoted in general by10. As drive unit, the drive system10includes a hydrogen combustion engine12, to which hydrogen, or a hydrogen-containing gas, and oxygen, or an oxygen-containing gas, for example air, are fed. The hydrogen and the oxygen are burned in the hydrogen combustion engine12. The engine exhaust gas which arises during this combustion is discharged to the surrounding area via an engine exhaust gas line16, receiving an engine exhaust gas from the hydrogen combustion engine12, and an exhaust gas system14, including an engine exhaust gas outlet line18, for the hydrogen combustion engine12.

If a hydrogen combustion engine12of this type is operated in an operating type with a lambda value in the region of 1, its combustion characteristic corresponds approximately to that of a gasoline internal combustion engine. Therefore, in the case of an operating type like this, a catalytic converter can be provided for exhaust gas purification in the engine exhaust gas outlet line18, which catalytic converter corresponds to a 3-way catalytic converter used in conjunction with a gasoline internal combustion engine.

In the case of hydrogen combustion engines, operation with a lambda value greater than 1 is preferred on account of a higher degree of efficiency, that is, operation with an excess of oxygen. In the case of the combustion with an excess of air, the engine exhaust gas contains not only traces of unburned hydrogen, but also nitrogen oxides. The concentration of the hydrogen which is still contained in the engine exhaust gas can be so high here that an output to the surrounding area is not permissible. Therefore, a catalytic converter unit which forms an embodiment of an oxidation unit20, that is, an oxidation catalytic converter, can be arranged in the engine exhaust gas outlet line18, in which catalytic converter unit the residual hydrogen contained in the engine exhaust gas is oxidized with oxygen fed into the engine exhaust gas outlet line18via a feed line. Via this feed line, for example, air can be introduced into the engine exhaust gas outlet line18.

In order to decrease the nitrogen oxide proportion in the engine exhaust gas, a catalytic converter unit22which is configured, for example, in the form of an SCR catalytic converter is provided in the engine exhaust gas outlet line18. The reactant which is required to carry out a reaction of this type can be injected in a mixing section26arranged upstream of the catalytic converter unit22via a reactant dispensing unit28which is generally called an injector. The reactant which is generally injected as a spray mist into the engine exhaust gas, for example a mixture of urea and water, is mixed with the engine exhaust gas. The ammonia which is formed during this thorough mixing from the urea/water mixture leads to NOx reduction in the reduction reaction which proceeds in the catalytic converter unit22. In order to remove ammonia from the engine exhaust gas which is possibly still present after the reduction reaction in the engine exhaust gas, what is known as a clean-up catalytic converter for reducing the still existing ammonia can be provided downstream of the catalytic converter unit22. As an alternative, the NOx reduction can also be carried out with the use of hydrogen as reducing agent.

In order as far as possible to suppress the emission of noise arising during the operation of the hydrogen combustion engine12via the exhaust gas system14or the engine exhaust gas which flows through the latter, a muffler24is arranged in the engine exhaust gas outlet line18, for example, downstream of the catalytic converter unit22. As in the case of mufflers which are assigned to gasoline or diesel internal combustion engines, the muffler24can include one or more chambers which are connected to one another and can be flowed through by the engine exhaust gas and/or one or more resonator chambers.

The engine exhaust gas line16leads to a first engine exhaust gas cooling unit30. The first engine exhaust gas cooling unit30can include a first heat exchanger32, in which the engine exhaust gas which flows through the first engine exhaust gas line16transfers heat to a liquid or gaseous cooling medium K and is cooled as a result. As a result of this cooling, a part of the water or water vapor contained in the engine exhaust gas condenses in a separating unit34following the first engine exhaust gas cooling unit30, and can be dispensed in liquid form to the surrounding area.

In an engine exhaust gas heating unit36which follows the separating unit34downstream, the engine exhaust gas which has had water vapor removed is heated again. This heating can take place by virtue of the fact that heat is transmitted by way of a heating medium H to the engine exhaust gas which flows through the engine exhaust gas heating unit36, if the engine exhaust gas heating unit36is configured as a second heat exchanger38. As an alternative or in addition, the engine exhaust gas heating unit36can include an electrically excitable heater40which is flowed through by the engine exhaust gas which has had water vapor removed, and transfers heat to the latter in the process.

In the drive system10which is shown inFIG.1, a part, in particular a relatively great part, of the water vapor contained therein is first of all removed by cooling from the engine exhaust gas which is output via the engine exhaust gas line16. On account of its comparatively low temperature, the engine exhaust gas which has had water vapor removed has a high relative humidity which can lie close to 100%. The relative humidity of the engine exhaust gas is lowered by way of the heating of this engine exhaust gas which has had water vapor removed but nevertheless has a high relative humidity, with the result that the engine exhaust gas which is discharged to the surrounding area via the engine exhaust gas outlet line18has a relative humidity which lies considerably below 100%. Even if this engine exhaust gas which is then discharged to the surrounding area comes into contact with comparatively cold ambient air or comparatively cold objects which are situated in the surrounding area of a vehicle, a spontaneous formation of mist arising as a result of condensing of water is avoided, since, even before the temperature of the engine exhaust gas which is discharged to the surrounding area falls below the dew point, comparatively pronounced thorough mixing with ambient air and therefore comparatively pronounced dilution of the engine exhaust gas will take place.

In the case of the drive system10which is shown inFIG.1, the decrease in the water vapor quantity contained in the engine exhaust gas takes place upstream of the oxidation unit20, configured for example as an oxidation catalytic converter, and of the catalytic converter unit22, configured for example as an SCR catalytic converter. This means that they are loaded with an engine exhaust gas which is mixed with a considerably lower water vapor proportion, which is particularly advantageous with regard to the ageing of catalytic converters of this type. Furthermore, the engine exhaust gas which is introduced into the engine exhaust gas outlet line18can be heated again by way of the operation of the engine exhaust gas heating unit36in such a way that its temperature corresponds approximately to the temperature, at which it is ejected from the hydrogen combustion engine12and which also lies in the region of the operating temperature of the oxidation unit20and/or the catalytic converter unit22. Therefore, the catalytic reactions can proceed reliably and with high efficiency.

An embodiment of the drive system10which is modified, in particular, in the region of the first engine exhaust gas cooling unit30and the engine exhaust gas heating unit36is illustrated inFIG.2. In the case of this embodiment, heat is withdrawn in the first engine exhaust gas cooling unit30, configured as a first heat exchanger32, from the engine exhaust gas which flows through it, via a heat transfer medium M which is also conducted, in a circuit which is for example closed, through the engine exhaust gas heating unit36which is configured as a second heat exchanger38. Therefore, the engine exhaust gas which flows further downstream in the exhaust gas system14can be heated via the engine exhaust gas which flows further upstream in the exhaust gas system14. As an alternative or in addition, the engine exhaust gas which flows through the engine exhaust gas heating unit36can be heated in this engine exhaust gas heating unit36by way of a heating medium H and/or an electrically excitable heater40.

In order for it to be possible to further cool the engine exhaust gas, a second engine exhaust gas cooling unit50is arranged downstream of the first engine exhaust gas cooling unit30. This second engine exhaust gas cooling unit50can include, for example, a third heat exchanger52, in which the engine exhaust gas which has already been cooled in the first engine exhaust gas cooling unit30can transfer heat to the cooling medium K. As has already been described in the preceding text, water condenses in the separating unit34, with the result that engine exhaust gas which has had water vapor removed flows in the direction of the engine exhaust gas heating unit36which follows downstream.

One variant which is advantageous, above all, with regard to the efficient transfer of heat and the simple structural configuration and in the case of which the heat which is contained in the engine exhaust gas is likewise used to heat a further downstream flowing part of the engine exhaust gas is shown inFIG.3. In the case of that embodiment of the exhaust gas system14which is shown inFIG.3, a heat exchanger unit which is denoted generally by54is provided which is configured as a counter current heat exchanger in the embodiment which is shown. The heat exchanger unit54includes an upstream heat exchanger region56which provides the first engine exhaust gas cooling unit30or the first heat exchanger32.

Furthermore, the heat exchanger unit54includes a downstream heat exchanger region58which provides the engine exhaust gas heating unit36or the second heat exchanger38. The two heat exchanger regions56,58can be of channel-like configuration in a heat exchanger unit housing60of the heat exchanger unit54, and can provide flow channels which are separated from one another by way of one or more dividing walls62and in which the engine exhaust gas flows substantially in opposed directions and, as a result, transfers heat from that part of the engine exhaust gas which flows through the upstream heat exchanger region56to that part of the engine exhaust gas which flows through the second heat exchanger region58.

It is to be noted that, even in the case of this embodiment, the engine exhaust gas which flows in the engine exhaust gas heating unit36, that is, in the second heat exchanger region58, can additionally be heated there by way of a heating medium and/or an electrically excitable heater, as has been described in the preceding text.

The engine exhaust gas which flows through the upstream heat exchanger region56and leaves it is conducted to the second engine exhaust gas cooling unit50following the upstream heat exchanger region56downstream or to the third heat exchanger52, where it outputs heat to the cooling medium K and is therefore cooled further. In the separating unit34, the water which condenses from the engine exhaust gas as a result of the further cooling is collected. The engine exhaust gas which has had water vapor removed then flows further to the downstream heat exchanger region58, where it is heated by way of thermal interaction with the engine exhaust gas flowing in the upstream heat exchanger region56and optionally additionally by way of a heating medium and/or an electrically excitable heater.

FIG.4shows one configuration variant, in the case of which the second engine exhaust gas cooling unit50and the separating unit34are combined structurally with the heat exchanger unit54. As can be seen inFIG.5, the third heat exchanger52of the second engine exhaust gas cooling unit50can be integrated into the upstream heat exchanger region56, in particular a downstream end64, of the same. At or downstream of this downstream end64of the upstream heat exchanger region56, a transition in flow terms takes place to the separating unit34and, from the latter, to the downstream heat exchanger region58. Water which has collected at the separating unit34and therefore also in the heat exchanger unit housing60of the heat exchanger unit54can be output to the surrounding area, for example, via a shut-off unit66.

For a highly efficient transfer of heat, the third heat exchanger52can have fins which increase the surface area available for thermal interaction with the engine exhaust gas flowing in the upstream heat exchanger region56.

In the modification, shown inFIG.5, of the construction principle illustrated inFIG.4, the second engine exhaust gas cooling unit50is integrated both into the upstream heat exchanger region56, in particular in the region of the downstream end64thereof, and into the upstream heat exchanger region58, in particular an upstream end68. Therefore, water or water vapor can be condensed by way of cooling of the engine exhaust gas and received or collected in the separating unit34in the entire transition region from the upstream heat exchanger region58, that is, the first engine exhaust gas cooling unit30, to the downstream heat exchanger region58, that is, the engine exhaust gas heating unit36.

The third heat exchanger52can also have fins in the case of this embodiment for a highly efficient transfer of heat, which fins increase the surface area available for the thermal interaction with the engine exhaust gas flowing in the upstream heat exchanger region56. It is to be noted, furthermore, that additional heating of the engine exhaust gas flowing through the downstream heat exchanger region58by way of a heating medium and/or an electrically excitable heater can also take place in the case of this embodiment.

Heat is also removed from the engine exhaust gas at the heat exchanger unit54in the case of that configuration variant of an exhaust gas system14which is shown inFIG.6, in the region of the downstream end64of the upstream heat exchanger region56and in the region of the upstream end68of the downstream heat exchanger region58. For this purpose, the first heat exchanger32of the first engine exhaust gas cooling unit30surrounds the heat exchanger unit housing60of the heat exchanger unit54on its outer side, and can be flowed through by the cooling medium K. For boosted thermal interaction and therefore for improved dissipation of heat from the engine exhaust gas flowing through the heat exchanger unit54, heat transfer fins70can be provided on the outer side of the heat exchanger unit housing60, by way of which heat transfer fins70the surface area available for the output of heat to the cooling medium K is increased.

A further alternative embodiment, in the case of which heat can be transferred in a heat exchanger unit54from the engine exhaust gas flowing in a further upstream part of the exhaust gas system14to the engine exhaust gas flowing in a further downstream part of the exhaust gas system14, is illustrated inFIG.7. In the case of this embodiment, the heat exchanger unit54is configured as a cross-flow heat exchanger. A volume which substantially provides the upstream heat exchanger region56is formed in the heat exchanger unit housing60, which volume is flowed through by the engine exhaust gas which is fed in via the first engine exhaust gas line16. The engine exhaust gas which is conducted through this upstream heat exchanger region56then flows through the second engine exhaust gas cooling unit50or its third heat exchanger52, and dissipates heat in the process to the cooling medium K. After flowing through the separating unit34, the engine exhaust gas which has had water vapor removed then flows through a line region which provides the downstream heat exchanger region58, runs in the heat exchanger unit housing60, and on which heat transfer fins72can be provided for boosted thermal interaction with the engine exhaust gas flowing through the upstream heat exchanger region56.

It is also the case in this embodiment that the engine exhaust gas leaves the upstream heat exchanger region56or the heat exchanger unit54in a heated state, and then flows, for example, to the catalytic converter unit44′ and the muffler24before it warms up and is therefore discharged to the surrounding area with a comparatively low relative humidity.

It is also the case in the embodiments shown inFIGS.6and7that the above-described measures can additionally be assigned to the downstream heat exchanger region58for additional heating. Therefore, additional heating of the engine exhaust gas which flows through the downstream heat exchanger region58and has had water vapor removed can take place by way of a heating medium and/or an electrically excitable heater.

In the case of all the above-described embodiments, the cooling medium K and/or the heating medium H can, if used, be provided by way of liquids and/or gases, it being possible, in particular, for the cooling medium K to dissipate the heat received therein to the surrounding area in a further heat exchanger. The cooling medium K can also be provided, for example, by way of the ambient air, with the result that the first heat exchanger can include, for example, a plurality of fins which can be flowed around by ambient air. The heating medium H can be heated, for example, during the catalytic processes which proceed in the oxidation unit20or the catalytic converter unit22. As an alternative, instead of or in addition to the oxidation catalytic converter which provides an oxidation unit20for oxidizing the residual hydrogen still contained in the engine exhaust gas, a burner can be provided as a further example of an oxidation unit of this type, in which burner the residual hydrogen is burned with oxygen. The oxygen can be provided, for example, by way of air being fed into the engine exhaust gas outlet line18upstream of the oxidation unit20. The heat which is produced during the combustion can be transferred in a heat exchanger assigned to the burner to the heating medium H and from the latter to the engine exhaust gas which flows through the second heat exchanger38.

In the case of an exhaust gas system which is constructed according to the disclosure, as illustrated, in particular, by the embodiments ofFIGS.3to6, structural linking or merging of different system regions can be provided, in particular of the first engine exhaust gas cooling unit, the separating unit and the engine exhaust gas heating unit, possibly also with the second engine exhaust gas cooling unit, with the result that these different system regions adjoin one another directly and/or also overlap one another in flow terms. Thus, water vapor or water can already be separated from the engine exhaust gas via the separating unit in the region of the first engine exhaust gas cooling unit and/or also in the region of the engine exhaust gas heating unit, and can be collected in liquid form, for example.

It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.