DE102019133518A1 - Exhaust system, motor vehicle and method for operating an exhaust system - Google Patents

Abstract

An exhaust system (14) for an internal combustion engine of a motor vehicle is described, which has an exhaust line (16), a coolant line (20a, 20b) and a heat storage unit (18). The heat storage unit (18) is coupled to the exhaust pipe (16) in a thermally conductive manner and is designed to store thermal energy that is provided by an exhaust gas flow within the exhaust pipe (16). The coolant line (20a, 20b) is movably supported with respect to the heat storage unit (18). Furthermore, a motor vehicle with such an exhaust system (14) and a method for operating such an exhaust system (14) are presented.

Description

The invention relates to an exhaust system for an internal combustion engine of a motor vehicle, with an exhaust line, a coolant line which is connected in a coolant conducting manner to a cooling system of the internal combustion engine, and a heat storage unit which is thermally coupled to the exhaust line and is designed to store thermal energy generated by an exhaust gas flow is provided within the exhaust pipe.

The invention also relates to a motor vehicle with such an exhaust system.

The invention is also directed to a method for operating an exhaust system.

Such exhaust systems and methods are known from the prior art. The same applies to motor vehicles that are equipped with such exhaust systems.

In such exhaust systems, the thermal energy stored within the heat storage unit is used to heat a coolant flowing within the coolant line. This is particularly advantageous shortly after a cold start of the internal combustion engine in order to bring it to its operating temperature as quickly as possible, at which it works efficiently and, in particular, with low emissions. However, there are also operating situations in which additional heating of the coolant by means of the heat storage unit is not desired. In this context, overheating of the coolant in particular must be avoided.

The invention is therefore based on the object of providing an exhaust system in which the coolant can be heated in a manner appropriate to the situation by means of a heat storage unit. The coolant should therefore only be heated by means of the heat storage unit if this is sensible and desired. Otherwise such heating should not take place.

The object is achieved by an exhaust system of the type mentioned at the outset, in which the coolant line is movably mounted with respect to the heat storage unit. A distance between the coolant line and the heat storage unit can thus be changed. In this way, the thermal coupling of the coolant line with the heat storage unit is also changed. If the coolant line is at a great distance from the heat storage unit, no or only a small amount of heat is transferred from the heat storage unit to the coolant flowing in the coolant line. If the coolant line has no or only a small distance from the heat storage unit, thermal energy stored by the heat storage unit can be reliably transferred into the coolant flowing in the coolant line. As a result, the heating of the coolant can be adjusted easily and reliably depending on the situation. The exhaust system can therefore be operated as appropriate to the situation.

The heat storage unit can comprise a phase change material. The heat storage unit then absorbs heat in that the phase change material changes its physical state, for example is liquefied starting from a solid phase. The heat is released in reverse, for example when the liquid phase change material solidifies. Alternatively, the heat storage unit can also have a material which, when heat is supplied, disintegrates as part of an endothermic reaction and in this way can absorb heat. In order to release the stored heat, such a material can be recombined in the course of an exothermic reaction. One then speaks of a thermo-chemical heat storage unit. An example of such a material is magnesium hydroxide, which decomposes into magnesium oxide and water vapor when exposed to heat. If the stored heat is to be released again, water vapor has to be fed back into the magnesium oxide so that these components react exothermically to form magnesium hydroxide. In this example, the reaction of magnesium oxide and water vapor can be specifically influenced by controlling the amount of water vapor. The heat emission can therefore be controlled easily and precisely.

The coolant line is preferably spaced apart from the heat storage unit in an insulating position and lies against the heat storage unit in a coupling position. In particular, the coolant line rests against the heat storage unit under prestress. The distance between the heat storage unit and the coolant line means that they are thermally isolated from one another in the insulation position. In particular, there is an air gap between the heat storage unit and the coolant line. If the coolant line is in contact with the heat storage unit, i.e. if they are not spaced apart from one another, they are reliably thermally coupled to one another so that thermal energy stored in the heat storage unit can be reliably transferred to a coolant within the coolant line. This is based on the phenomenon of heat conduction. In addition, it has been shown that there is a particularly good thermal coupling, that is to say with only low losses, when the coolant line rests against the heat storage unit under pretension, that is to say these lie against one another under pressure. Such a preload can be implemented by spring loading. So it can be set exactly when Heat is released from the heat storage unit to a coolant within the coolant line and when not.

From the perspective of the heat storage unit, the coupling position can be used for a discharge operation, since the heat storage unit gives off heat to the coolant line. This can take place in particular when the internal combustion engine is not running, i.e. there is no exhaust gas flow within the exhaust gas line. The insulation position can be used accordingly for a charging operation of the heat storage unit. Thermal energy provided by an exhaust gas stream flowing in the exhaust pipe is transferred to the heat storage unit. After the coolant line is thermally decoupled from the heat storage unit in this situation, the heat storage unit is charged without affecting the coolant.

The coolant line and the heat storage unit can lie flat against one another in the coupling position. In cross section, at least the side of the heat storage unit facing the coolant line is flat. The same applies to the coolant line. In cross section, at least the side of the coolant line facing the heat storage unit is flat. In particular, the coolant line is polygonal in cross section, e.g. B. rectangular. The areal system also results in an area for heat transfer, which is again based on the phenomenon of heat conduction. A comparatively large amount of heat can thus be transferred comparatively loss-free.

According to one variant, an actuating unit is provided for the optional transfer of the coolant line and the heat storage unit to the insulation position or the coupling position. The actuating unit is thus an actuator for the targeted influencing of the distance between the coolant line and the heat storage unit. Thus, the coolant line and the heat storage unit can optionally be transferred to the isolation position or the coupling position. The heating of the coolant within the coolant line can therefore be controlled specifically and appropriately for the situation.

The actuating unit advantageously comprises a temperature sensor for detecting a temperature within the coolant line. The temperature sensor can have a wax chamber and / or a shape memory alloy, preferably a shape memory spring. The isolation position and the coupling position are therefore set as a function of a temperature within the coolant line, that is to say a temperature of the coolant present there. Overheating of the coolant can thus be prevented by moving the coolant line and the heat storage unit to insulation positions in good time. A wax chamber, a shape memory alloy and, in particular, a shape memory spring represent simple and at the same time robust sensor elements that function reliably at high temperatures.

If the temperature sensor has a wax chamber, the actuating unit equipped with it is a so-called wax actuator.

In an alternative, the heat storage unit is provided with a heat-conducting layer on its side facing the coolant line, in particular the heat-conducting layer comprising graphite. By means of such a heat-conducting layer, the efficiency of the heat conduction between the heat storage unit and the coolant line can be further improved. So comparatively few thermal losses occur at the transition between the heat storage unit and the coolant line. This allows the coolant within the coolant line to be heated comparatively quickly.

According to one embodiment, at least one heat storage unit section of the heat storage unit is arranged between the exhaust gas line and the coolant line. In particular, the heat storage unit surrounds the exhaust pipe circumferentially. As a result, there is an efficient thermal coupling of the heat storage unit with the exhaust pipe on the one hand and the coolant pipe on the other hand. At the same time, such a structure is comparatively compact.

At least one section of the exhaust line facing the coolant line can be flat. In particular, the exhaust pipe has a polygonal cross section. For example, the exhaust pipe has a rectangular cross-section. There can therefore also be a two-dimensional thermal contact between the exhaust gas line and the heat storage unit. This also results in a low-loss thermal coupling at this point.

An exhaust pipe with a polygonal cross section also makes it possible to arrange several coolant pipes on the circumference of the exhaust pipe. In particular, a coolant line is assigned to each surface segment of the polygonal cross section with the interposition of the heat storage unit.

The object is also achieved by a motor vehicle of the type mentioned at the outset which has an exhaust system according to the invention. After the coolant in a motor vehicle of this type has been heated appropriately for the situation within a cooling system of an associated internal combustion engine can, the motor vehicle can be operated efficiently and, in particular, with low emissions.

In addition, the object is achieved by a method for operating an exhaust system for an internal combustion engine of a motor vehicle, which has a coolant line, which is connected to a cooling system of the internal combustion engine in a coolant-conducting manner, and a heat storage unit, which is thermally coupled to an exhaust line and is designed to carry thermal energy to store, which is provided by an exhaust gas flow within the exhaust line, wherein the coolant line for heating coolant flowing inside the coolant line is selectively applied to the heat storage unit. The coolant line is therefore only applied to the heat storage unit when the coolant flowing in it is to be heated. Otherwise, the coolant line is spaced apart from the heat storage unit, so that no or only a comparatively low heating of the coolant takes place via the heat storage unit. The exhaust system can thus be operated appropriately for the situation by specifically controlling the thermal coupling between the heat storage unit and the coolant line.

The coolant line can be applied to the heat storage unit as a function of a temperature detected in the interior of the coolant line. The temperature of the coolant is thus taken into account when controlling the heat transfer between the heat storage unit and the coolant line. The same is consequently only heated via the heat storage unit when it is actually necessary. In particular, overheating of the coolant can be reliably avoided in this way.

In this context, the coolant line can be applied to the heat storage unit if the detected temperature is less than a limit temperature, and the coolant line can be spaced apart from the heat storage unit if the detected temperature is greater than or equal to the limit temperature. If the recorded temperature is lower than the limit temperature, the heat storage unit and the coolant line thus assume the coupling position. Otherwise they are in the isolation position. The limit temperature is preferably selected such that it lies with a certain safety margin below a temperature at which the coolant is overheated. The limit temperature is preferably 70 ° C to 90 °, and it is more preferably 75 ° C to 85 ° C. In an advantageous example, the limit temperature is approx. 80 ° C. Overheating of the coolant is thus reliably avoided.

• - 1 ein erfindungsgemäßes Kraftfahrzeug mit einer erfindungsgemäßen Abgasanlage,
• - 2 in einer schematischen Darstellung die erfindungsgemäße Abgasanlage in einer Koppelstellung der Wärmespeichereinheit und der Kühlmittelleitung,
• - 3 in einer schematischen Darstellung die erfindungsgemäße Abgasanlage in einer Isolationsstellung der Wärmespeichereinheit und der Kühlmittelleitung,
• - 4 eine Teilansicht der Abgasanlage aus 2 in Richtung des Pfeils IV, und
• - 5 eine der 4 entsprechende Teilansicht einer Abgasanlage gemäß einer alternativen Ausführungsform.

The invention is explained below on the basis of various exemplary embodiments which are shown in the accompanying drawings. Show it:

• - 1 a motor vehicle according to the invention with an exhaust system according to the invention,
• - 2 in a schematic representation of the exhaust system according to the invention in a coupling position of the heat storage unit and the coolant line,
• - 3rd in a schematic representation of the exhaust system according to the invention in an insulating position of the heat storage unit and the coolant line,
• - 4th a partial view of the exhaust system 2 in the direction of arrow IV, and
• - 5 one of the 4th Corresponding partial view of an exhaust system according to an alternative embodiment.

1 shows a motor vehicle 10 with an internal combustion engine 12th that with an exhaust system 14th is coupled.

The exhaust system 14th is in the 2 to 4th shown in more detail.

It includes an exhaust pipe 16 with an exhaust manifold of the internal combustion engine, not shown 12th is connected to conduct the exhaust gas.

The exhaust pipe 16 has an essentially rectangular cross-section in the section relevant here (see 4th ).

There is also a heat storage unit 18th intended.

This has a first heat storage unit section 18a in the illustrations above the exhaust pipe 16 is arranged. There is also a second heat storage unit section 18b provided, which in the illustrations below the exhaust pipe 16 is positioned.

There is an inner area of the heat storage unit 18th also essentially rectangular in cross section and lies directly on an outer circumference of the exhaust pipe 16 at.

This makes the heat storage unit 18th and the exhaust pipe 16 thermally coupled.

An outer area of the heat storage unit also has an essentially rectangular cross section (see 4th ).

It also includes the exhaust system 14th two coolant lines 20a , 20b , of those in the Representations according to 2 , 3rd and 4th one above and one below the exhaust pipe 16 is arranged.

The heat storage unit 18th is the coolant lines 20a , 20b and the exhaust pipe 16 interposed. So it is the first heat storage unit section 18a between the coolant line 20a and the exhaust pipe 16 and the heat storage unit section 18b between the coolant line 20b and the exhaust pipe 16 .

The cross-sections of the coolant lines 20a , 20b are essentially rectangular, so that one of the exhaust pipe 16 and thus also the heat storage unit 18th facing section of the coolant lines 20a , 20b is flat.

The coolant lines 20a , 20b are coolant conducting with a cooling system of the internal combustion engine, not shown in detail 12th connected.

The heat storage unit is used for improved heat conduction 18th also on their coolant lines 20a , 20b facing sides with a heat conducting layer 22nd made of graphite.

The coolant lines 20a , 20b are opposite the heat storage unit 18th movably mounted.

In this context is the coolant line 20a about two springs 24 in one housing 26th the exhaust system 14th stored.

The coolant line 20b is in the same way about two springs 28 in the housing 26th stored.

Furthermore, each of the coolant lines is 20a , 20b an actuator 30a , 30b assigned, which are designed as so-called wax actuators in the illustrated embodiment.

Each setting unit 30a , 30b thus comprises a temperature sensor designed as a wax chamber 32a , 32b as well as a plunger 34a , 34b .

The tappets 34a , 34b act on the outer circumference of the heat storage unit 18th and are used to control the associated coolant line 20a , 20b against one of the feathers 24 , 28 provided spring force by the heat storage unit 18th move away.

In this way, the coolant lines 20a , 20b and the heat storage unit 18th starting from a coupling position in which the coolant lines 20a , 20b on the heat storage unit 18th flat and under the action of one of the springs 24 , 28 provided spring force are applied (see 2 ), be transferred to an isolation position.

The coolant lines are in the isolation position 20a , 20b from the heat storage unit 18th spaced (see 3rd ) so that there is an air gap 36 between the coolant lines 20a , 20b and the heat storage unit 18th results. More precisely, the result is the air gap 36 between the coolant lines 20a , 20b and the respective adjacent heat storage unit sections 18a , 18b .

During the operation of the exhaust system 14th the coupling position is used in the heat storage unit 18th stored thermal energy to a coolant flow within the coolant lines 20a , 20b submit. So there is thermal energy from the heat storage unit 18th in the coolant lines 20a , 20b unload. This is by means of the arrows 38 symbolizes.

In this operating state there is usually no exhaust gas flow within the exhaust pipe 16 in front.

The isolation position, however, serves to prevent an exhaust gas flow within the exhaust pipe 16 provided thermal energy in the heat storage unit 18th to record. Thermal energy is thus loaded into the heat storage unit. The exhaust gas flow is indicated by an arrow 40 and heat transfer by arrows 42 symbolizes.

After the coolant lines are in the isolation position 20a , 20b from the heat storage unit 18th are spaced apart, there is no discharge of thermal energy.

The exhaust system 14th can thus be operated in such a way that it is only transferred into the coupling position when a flow of coolant within the coolant lines is heated 20a , 20b is desired. Then thermal energy is drawn from the heat storage unit 18th to that inside the coolant lines 20a , 20b present coolant dispensed (see arrows 38 ).

This operation takes place in particular as a function of a temperature of the coolant flow within the coolant lines 20a , 20b , in the illustrated embodiments by means of the temperature sensors 32a , 32b is captured.

This is in the as temperature sensors 32a , 32b acting wax chambers configured so that it liquefies and expands when a system-specific limit temperature is reached. This causes the plunger 34a , 34b from its withdrawn position ( 2 ) to its extended position ( 3rd ) and the coolant lines 20a , 20b are from the heat storage unit 18th spaced, ie lifted.

It can thus be ensured in particular that the coolant is in the coolant lines 20a , 20b is not heated beyond the system-specific limit temperature and consequently is not overheated.

In one variant, there are temperature sensors 32a , 32b designed as shape memory springs instead of wax chambers, which expand in a defined manner when the system-specific limit temperature is exceeded, and so do the plungers 34a , 34b move to their extended position. When the temperature of the coolant falls below the limit temperature again, the shape memory springs retract into their original position, so that the tappets 34a , 34b take their withdrawn position.

The above explanations relate to an exhaust system 14th who have favourited the two coolant lines 20a , 20b includes.

Alternatively, four coolant lines can also be used 20a , 20b , 20c , 20d be provided which has an associated exhaust pipe 16 and a heat storage unit connected to it 18th surrounded on its perimeter (see 5 ). The coolant lines 20c , 20d are then analogous to the coolant lines 20a , 20b each equipped with an actuator so that the functionality already explained is also applicable to the coolant lines 20c , 20d results.

In the embodiment according to 5 surrounds the heat storage unit 18th the exhaust pipe 16 completely to their extent.

Claims (12)

Exhaust system (14) for an internal combustion engine (12) of a motor vehicle (10), with an exhaust line (16), a coolant line (20a, 20b, 20c, 20d) which is connected in a coolant-conducting manner to a cooling system of the internal combustion engine (12), and a Heat storage unit (18) which is thermally conductively coupled to the exhaust pipe (16) and is designed to store thermal energy that is provided by an exhaust gas flow within the exhaust pipe (16), characterized in that the coolant pipe (20a, 20b, 20c, 20d) is movably mounted with respect to the heat storage unit (18). Exhaust system (14) Claim 1 , characterized in that the coolant line (20a, 20b, 20c, 20d) is spaced apart from the heat storage unit (18) in an insulating position and in a coupling position rests against the heat storage unit (18), in particular rests against the heat storage unit (18) under bias. Exhaust system (14) Claim 2 , characterized in that the coolant line (20a, 20b, 20c, 20d) and the heat storage unit (18) lie flat against one another in the coupling position. Exhaust system after Claim 2 or 3rd , characterized by an adjusting unit (30a, 30b) for the optional transfer of the coolant line (20a, 20b, 20c, 20d) and the heat storage unit (18) into the isolation position or the coupling position. Exhaust system (14) Claim 4 , characterized in that the actuating unit (30a, 30b) comprises a temperature sensor (32a, 32b) for detecting a temperature within the coolant line (20a, 20b, 20c, 20d), in particular wherein the temperature sensor (32a, 32b) has a wax chamber and / or a shape memory alloy, preferably a shape memory spring. Exhaust system (14) according to one of the preceding claims, characterized in that the heat storage unit (18) is provided with a heat conducting layer (22) on its side facing the coolant line (20a, 20b, 20c, 20d), in particular wherein the heat conducting layer (22) Includes graphite. Exhaust system (14) according to one of the preceding claims, characterized in that at least one heat storage unit section (18a, 18b) of the heat storage unit (18) is arranged between the exhaust line (16) and the coolant line (20a, 20b, 20c, 20d), in particular wherein the heat storage unit (18) circumferentially surrounds the exhaust pipe (16). Exhaust system (14) according to one of the preceding claims, characterized in that at least one section of the exhaust line (16) facing the coolant line (20a, 20b, 20c, 20d) is flat, in particular wherein the exhaust line (16) has a polygonal cross section. Motor vehicle (10) with an exhaust system (14) according to one of the preceding claims. Method for operating an exhaust system (14) for an internal combustion engine (12) of a motor vehicle (10), which has a coolant line (20a, 20b, 20c, 20d) which is connected in a coolant-conducting manner to a cooling system of the internal combustion engine (12), and a heat storage unit ( 18) which is thermally conductively coupled to an exhaust pipe (16) and is designed to store thermal energy generated by an exhaust gas flow within the exhaust pipe (16) is provided, wherein the coolant line (20a, 20b, 20c, 20d) for heating coolant flowing within the coolant line (20a, 20b, 20c, 20d) is optionally applied to the heat storage unit (18). Procedure according to Claim 10 , characterized in that the coolant line (20a, 20b, 20c, 20d) is applied to the heat storage unit (18) as a function of a temperature detected inside the coolant line (20a, 20b, 20c, 20d). Procedure according to Claim 11 , characterized in that the coolant line (20a, 20b, 20c, 20d) is applied to the heat storage unit (18) when the detected temperature is lower than a limit temperature, and the coolant line (20a, 20b, 20c, 20d) from the heat storage unit is spaced when the detected temperature is greater than or equal to the limit temperature.

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