DE102008023806A1 - Exhaust gas system for internal combustion engine of motor vehicle, has control device to control switching elements based on temperature of thermo-electric generator and/or internal-combustion engine and/or exhaust gas pressure in system - Google Patents

Abstract

The system has an exhaust gas channel (2) with two partial-exhaust gas channels (2.1, 2.2), where the channel (2.1) is thermally coupled with a thermo-electric generator (3). Controllable switching elements (4, 4.1, 4.2) e.g. exhaust flaps, are present in the channel (2) to control an exhaust gas stream such that the stream flows exclusively or proportionately through the channels (2.1, 2.2). A control device (6) controls the elements based on a temperature of the generator and/or an exhaust gas pressure prevailing in the system and/or a temperature of an internal-combustion engine (BKM). An independent claim is also included for a method for operating an exhaust gas system for an internal combustion engine.

Description

The The invention relates to an exhaust system according to the preamble of claim 1 and a method for operating such Exhaust system.

Under a thermoelectric generator (also abbreviated as TEG) is understood within the meaning of the invention means the effect of the so-called "Seebeck effect" heat energy converted into electrical energy (this energy conversion arises in that two points of an electrical conductor are different Temperatures are exposed, creating a voltage is generated between these two points).

From the US 2005/0268598 A1 For example, a motor vehicle is already known which has a so-called thermoelectric generator (TEG) in its exhaust gas line, viewed in the flow direction in front of a catalytic converter device for purifying the exhaust gas. In this case, the exhaust gas channel between the outlet of the internal combustion engine and the catalyst is partially formed with two channels with two parallel partial exhaust ducts, being integrated in one of the two partial exhaust ducts of the TEG. At the upstream branching point of the exhaust passage in the two partial exhaust ducts, a controllable switching element for steering the exhaust gas flow is provided (in one or the other part exhaust passage). In this case, the switching element is controlled by a control unit such that during a warm-up phase of the internal combustion engine, in which the catalyst has not reached a predetermined temperature, the entire exhaust gas flow over the partial exhaust duct without TEG (the so-called bypass) is passed, and only when the predetermined catalyst temperature is reached, the exhaust stream is passed through the other part exhaust passage having the TEG. The aim of this arrangement is to dissipate excess heat during periods of operation in which the catalyst is exposed to temperatures at which it may be damaged, in order to protect the catalyst from destruction and at the same time generate valuable electrical energy.

In addition, numerous documents are known in which the structure and operation of a TEG mentioned above are described. Representatives may be mentioned at this point the previously unpublished German patent applications: DE 10 2007 063 168 . DE 10 2007 063 172 . DE 10 2007 063 173 . DE 10 2007 063 196 , whose contents are referred to in full with regard to a possible structure of a TEG.

Of the Invention is based on the object, a generic Exhaust system for an internal combustion engine of a motor vehicle indicate that the energy efficiency of the motor vehicle is significantly improved.

According to the invention the problem is solved by the entirety of the features of claim 1, while in the dependent claims preferred developments the invention are given. According to the invention it is proposed in an exhaust system for an internal combustion engine, which at least partially executed two channels is, with the two Teilabgaskanäle downstream merged in a common exhaust duct section are, and in one of the two partial exhaust ducts an energy conversion agent (hereinafter referred to as thermoelectric Generator or TEG called) is implemented, and in which over at least a arranged in the exhaust passage switching element of the exhaust stream such It can be controlled exclusively by a the two or split by both partial exhaust ducts flows through a control device for control of the at least one switching element, the at least one switching element depending on the temperature of the TEG and / or in Dependence on that in the exhaust system at a predetermined Position present exhaust back pressure and / or as a function of the temperature of the engine (in particular internal combustion engine) head for. It goes without saying that instead of the above named quantities (in their dependency a control of the at least one switching element takes place) representatively also one each correlating with this size Size can be used. It is also conceivable alternatively to the sizes described above a control of the switching element in dependence of Vehicle environment conditions - especially depending from the outside or ambient temperature and / or the ambient pressure or the like - make.

In a particularly preferred embodiment of the invention, the TEG is integrated into the exhaust system of a motor vehicle, in which the so-called warm side (first point, arranged between two points of different temperature, working according to the Seebeck effect energy conversion agent / TEG) of the TEG with an exhaust leading line of the exhaust gas heat is conductively connected. The cold side (second point) of the TEG can be thermally coupled, for example, with a coolant line leading to a coolant line of the engine cooling system of the motor vehicle. In a particularly simple embodiment of the TEG, a plurality of thermocouple modules are disposed around an exhaust passage portion of the corresponding sub-exhaust passage. In a further development, the thermally active surface of the TEG can be increased by the exhaust duct is partially ribbed inwards (al so z. B. rib-shaped elements of the exhaust passage or the thermocouples are arranged in the interior of the partial exhaust gas duct section).

With Advantage are for controlling the exhaust gas flow a total of two switching elements provided, wherein in each of the two partial exhaust ducts a switching element can be arranged. Preferably, the switching element, which is to be arranged in the partial exhaust duct having the TEG, As seen in the flow direction behind the TEG arranged.

The Control device for controlling the at least one switching element is in particular designed such that in each case an interruption the exhaust flow through full closed position the at least one switching element is prevented. In the preferred Embodiment with one switching element per partial exhaust duct must be ensured by the controller accordingly that at no time of operation, both switching elements in a complete closed position to be transferred.

The Operating strategy, via the appropriate control the switching elements should be realized and on the a significant increase in the efficiency of a per Internal combustion engine driven motor vehicle can be achieved is to maximize the conversion of thermal Energy from the exhaust system aligned in electrical energy. At the same time always the reliability of the motor vehicle and the TEG.

about a particular experimentally determined map in the for a particular internal combustion engine of a particular Motor vehicle, the load over the speed of the internal combustion engine mapped for various stationary operating states and in each load speed state via the map is assigned a particular switching element state, the at least a switching element for steering the exhaust stream adjusted accordingly. As a result, a kind of precontrol of the at least one switching element (exhaust flap (s)) depending on the respective set operating point ensures the internal combustion engine. This feedforward control is preferably suitable for dynamic operation of Internal combustion engine in which a predetermined "warm-up temperature" (in particular an average of the temperature of the internal combustion engine or TEG - or a correlated size (such as exhaust gas temperature o. d.). already reached - with Advantage a temperature at the TEG its best efficiency has reached. This has the consequence that on the map feedforward control the exhaust valves, starting from a cold operating condition of TEG and a still warm or a certain residual heat having the internal combustion engine, the at least one exhaust flap can not be set optimally. To the TEG also with different Ambient conditions (pressure, temperature) and vehicle or TEG operating parameters operate in an optimal temperature range, a controller module (eg PID controller) is provided via which in particular depending on the temperature of the TEG and / or the temperature of the prime mover (or a hereby correlating size) the exhaust flaps if necessary can be set differently than provided by the pilot control. For example, starting from a cold operating condition of the TEG and not yet cooled internal combustion engine (and thus with an increased temperature of the exhaust gas) due the map pilot control via the exhaust duct with TEG less Exhaust gas are led (around this lt. Kennfeld not dangerous to heat) than this due to the actual overall thermal state (warmer exhaust due to not cooled internal combustion engine) it is possible. About the controller module can the exhaust valves are set deviating from this, so that based on the information that the TEG the in the pilot control map underlying temperature has not yet reached, the exhaust stream in the partial exhaust duct with TEG by deviating control of the exhaust flaps increases and thus increases the efficiency in the warm-up phase can be.

For control of the at least one exhaust gas flap dependent on the exhaust gas back pressure, the control device is designed with a control module for exhaust gas backpressure limiting, whereby an excessively high mass flow of exhaust gas through the control module in certain driving situations (such as during the heating phase of the TEG) is prevented Part exhaust duct with TEG out and thereby a high exhaust back pressure is set. Due to the exhaust gas back pressure-dependent control of the at least one switching element, the setting of an excessively high exhaust backpressure (which in turn would result in a poorer efficiency of the internal combustion engine) is effectively prevented. The exhaust gas back pressure-dependent control of the at least one switching element is particularly useful in the event that the partial exhaust duct in the region of the TEG arrangement has a Innenberippung described above. Although this inner ribbing ensures improved heat transfer into the TEG, on the other hand, at higher loads, an increased exhaust gas counterpressure is disadvantageously produced. In order to avoid this exhaust back pressure at higher loads, the control unit for controlling the at least one switching element may be designed such that the control takes place in dependence on the adjusting exhaust back pressure. In this case, the exhaust back pressure modellba be determined or metrologically determined.

By the temperature-dependent control of at least one Switching element, in which the control in dependence of the temperature of the prime mover or a correlated therewith size takes place, effectively overheating the prime mover prevented.

in the Frame of temperature-dependent control of at least a switching element in which the control in dependence from the temperature of the TEG or a variable correlated therewith takes place, a thermal protection of the TEG is effectively achieved.

Added can the presented operating strategy by a forward-looking Element, by the control of the at least one switching element additionally depending on vehicle environment conditions he follows. In particular, be mentioned here, the use of navigation data and traffic information. This should be effective prevents the TEG in certain operating phases too cools strongly.

In Another embodiment of the invention is additionally for controlling the switching elements for steering the exhaust gas flow also the coolant pump (water pump) of the cooling system the drive machine controlled. This is the cooling power available for the drive machine as needed while accelerating the warm-up of the TEG slowing down the cooling of the TEG at low engine load. For this purpose, the coolant pump in dependence from the temperature of the TEG (or depending on the Temperature of the TEG and depending on the temperature the prime mover) controlled. Alternatively, instead of the coupling of the TEG via its cold side to the coolant circuit of the motor vehicle and a separate self-sufficient cooling circuit be provided for the cold side of the TEG and accordingly the control by controlling an additional water pump respectively.

One Embodiment of the invention is in the drawing and will be described in more detail below. It demonstrate:

1 : An exhaust system according to the invention together with coupled internal combustion engine and coupled electrical system in a schematic representation, and

2 The control device for controlling the at least one, the exhaust gas flow directing switching element, in a schematic representation.

1 shows a schematic overall view of an exhaust system according to the invention along with various peripherals such as prime mover BKM and wiring system BN. The exhaust system includes an exhaust line A with an exhaust passage 2 the at least partially - between a first exhaust passage AKS_1 and one, from the first exhaust passage AKS_1 downstream spaced second exhaust passage AKS_2 - two parallel partial exhaust ducts 2.1 . 2.2 having. It is a partial exhaust duct 2.1 with funds 3 for the conversion of thermal energy into electrical energy (hereinafter also referred to as thermoelectric generator or TEG) thermally coupled, while the other partial exhaust duct 2.2 acts as a bypass for the controlled evasion of the TEG. In the exhaust duct 2 is at least one controllable switching element 4 ; 4.1 . 4.2 for steering the exhaust gas flow present - in the present embodiment, however, each partial exhaust duct 2.1 . 2.2 a separate switching element 4.1 . 4.2 on. By the at least one, via a control device 6 controllable switching element 4 ; 4.1 . 4.2 (hereinafter also referred to as exhaust flap) is the exhaust gas flow of an internal combustion engine BKM either exclusively through the first part of the exhaust duct 2.1 , exclusively through the second partial exhaust duct 2.2 or proportionately through both partial exhaust ducts 2.1 . 2.2 directed. The exhaust line A is substantially divided into three subregions, wherein in a first portion A1, which is formed only a single channel, a catalyst device is arranged Kat for purifying the exhaust gas. The second, adjoining subarea A2 of the exhaust line A is through the two between the exhaust duct AKS_1 and AKS_2 parallel partial exhaust channels 2.1 and 2.2 educated. In the present case, the last subarea A3 of the exhaust line A is once again of a single-channel design and comprises two silencer devices SD1, SD2 connected in series. The exhaust line A may deviate from the structure described also be constructed differently. All that is essential is that the exhaust gas duct is dual-channeled in one subarea and brought back together downstream (AKS_2). The exhaust duct A may be formed from the outlets of the internal combustion engine BKM to said merge two channels. The exhaust duct A can be led out of the outlets of the internal combustion engine BKM - as shown - also one-channel, in order then to form two channels until the said downstream merge (AKS_2). Even after the downstream merging of the exhaust duct A can be formed arbitrarily formed (single or multi-flow).

The TEG is integrated into the exhaust system A, in which the so-called warm side of the TEG with a exhaust gas leading line of the exhaust line A (here: partial exhaust system 2.1 ) and the cold side of the TEG with a cooling liquid leading cooling Central line 8th (shown in dashed lines) of the cooling system KS of the internal combustion engine BKM is thermally coupled. The cooling system KS is constructed in a conventional manner and comprises a coolant pump P and a radiator arrangement K.

Electrically, the TEG is via a DC voltage coupling device 10 in the form of a DC-DC converter in the electrical system BN of the motor vehicle coupled (alternatively, the coupling via a simple diode is conceivable). The on-board network BN comprises, for example, an electric machine EM operating at least as a generator, an electrical energy storage device in the form of an on-board battery Batt, a capacitor device or the like, and electrical consumers V. The electric machine EM is advantageously designed as a so-called crankshaft starter generator via which the internal combustion engine BKM is included motor operation of the electric machine EM can be started, and over which in braking or coasting phases of electrical energy for feeding into battery Batt and / or in the electrical system BN can be generated. The electric machine EM can also be designed for an electric or hybrid drive of the motor vehicle provided at least temporarily.

The operation of the TEG can by controlling the at least one exhaust flap 4 ; 4.1 . 4.2 (either a central exhaust flap 4 in the first exhaust gas passage AKS_1 - or as shown, in each exhaust gas subchannel 2.1 . 2.2 one exhaust flap each 4.1 . 4.2 ) according to one in the control device 6 deposited operating strategy can be optimized so that quite a significant advantage in terms of the CO2 balance of the motor vehicle can be achieved. The control device 6 is preferably integrated into a bus control system such as CAN in the control structure of the motor vehicle. The operation of the controller 6 or the operating strategy stored therein will be described below with reference to FIG 2 explained in more detail.

2 shows a schematic representation of the functionality of the control device 6 or the operating strategy implemented thereby. The control device 6 receives input side via various sensors as well as other control devices within the motor vehicle network a variety of information (vehicle operating and Fahrzeugumgebungsparametern P _B , P _U ). In particular, this information includes: information indicating the state of the TEG (TEG temperature T _TEG , exhaust back pressure in the partial exhaust duct 2.1 , Pressure and temperature in the coupled coolant system, ...) describe information describing the state of the internal combustion engine BKM (BKM temperature, engine speed, engine torque, ...) and information describing the state of the vehicle environment (navigation data, traffic information, ... ). In the control device 6 Thus, at least information about the state of the TEG as well as information from the further information network of the motor vehicle (such as information from the central engine control or the like) read. In the control device 6 At least four (sub) control modules Mod_1, Mod_2, Mod_3, Mod_4 are shown, wherein in a first control module Mod_1 a map for pilot control of the two exhaust valves 4.1 . 4.2 as a function of the operating point of the internal combustion engine BKM, in a second control module Mod_2 a general controller structure for modifying the pilot operated flap position at unsteady operation of the motor vehicle, in a third control module Mod_3 a map for controlling the exhaust valves 4.1 . 4.2 as a function of the exhaust gas back pressure prevailing in the exhaust system p _{exhaust gas} and in a fourth control module Mod_4 an emergency operation of the exhaust valves 4.1 . 4.2 to ensure safe operation.

For the operation of the exhaust system A and the thermoelectric arranged therein Generator TEG via the first control module Mod_1 a Pilot control of the exhaust valves, in the basis of the stored map KF1 as a function of at least one operating parameter (preferably depending on at least two operating parameters) such as exhaust gas mass flow, exhaust gas temperature, load M and / or speed n the internal combustion engine BKM a flap position is determined. Since the pilot control map on experimentally determined values at stationary ambient conditions of the internal combustion engine is based on the pilot control found flap position for the operation of the internal combustion engine at transient Ambient conditions (ambient temperature, ambient pressure, or similar) only partially suitable. To the TEG also in the transient Operation always in the optimum temperature range (temperature range with the best efficiency), the pilot operated damper position by the control module Mod_2 if required modified. By the in the third control module Mod_3 mapped Exhaust backpressure limitation prevents the over the control module Mod_2 mapped knobs in certain situations - such as z. B. in the heating phase of the TEG - an excessive exhaust gas mass flow adjusted by the TEG and thus a high exhaust back pressure. By the illustrated via the fourth control module Mod_4 runflat functionality will ensure that a simultaneous closing Both exhaust valves - and thus a complete closure the exhaust system - is avoided. For this will be the two exhaust flaps positively functionally coupled control technology.

By a not shown further tax ermodul the described operating strategy could be extended to the effect that by controlling navigation and / or traffic information, the control of the exhaust valves and thus the "control" of the TEG is such that excessive cooling of the TEG - especially by temporary high load phases in which the part -Abgaskanal 2.1 is closed with TEG or in temporary relief phases such as traffic light stop (possibly with the internal combustion engine switched off) - is prevented.

About that In addition, the operational strategy can be extended to that the electric coolant pump P is driven in such a way is that a warm-up of the TEG possible done quickly and efficiently and a quick cooling of the TEG is avoided as far as possible. For example, in the Warm-up phase of the TEG the coolant flow as possible be kept low to drain the through the exhaust stream in the TEG consuming introduced heat energy avoid as much as possible. Conversely, when achieved upper limit temperature of the TEG via an acceleration the coolant flow quickly superfluous Heat dissipated by the TEG.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 2005/0268598 A1 [0003]
• - DE 102007063168 [0004]
• - DE 102007063172 [0004]
• - DE 102007063173 [0004]
• - DE 102007063196 [0004]

Claims (8)

Exhaust system for an internal combustion engine (BKM), comprising - an exhaust duct ( 2 ), the two parallel partial exhaust ducts ( 2.1 . 2.2 ), wherein the partial exhaust gas channels ( 2.1 . 2.2 ) are merged downstream in a common exhaust gas passage section, - wherein one of the partial exhaust gas passages ( 2.1 ) with means ( 3 ) is thermally coupled to the conversion of heat energy into another form of energy, - and wherein in the exhaust gas channel ( 2 ) at least one controllable switching element ( 4 ; 4.1 . 4.2 ) is present for steering the exhaust gas flow, such that in dependence on the switching position of the at least one switching element ( 4 ; 4.1 . 4.2 ) the exhaust gas flow exclusively through the first partial exhaust gas channel ( 2.1 ), exclusively through the second partial exhaust gas channel ( 2.2 ) or proportionally through both partial exhaust gas channels ( 2.1 . 2.2 ), and - a control device ( 6 ) for controlling the at least one switching element ( 4 ; 4.1 . 4.2 ), characterized in that - the control device ( 6 ) is designed such that the activation of the at least one switching element ( 4 ; 4.1 . 4.2 ) depending on the temperature (T _TEG ) of the means ( 3 ) for the conversion of heat energy - and / or depending on a prevailing in the exhaust system (A) exhaust back pressure (p _exhaust ) - and / or in dependence on the temperature of the internal combustion engine (BKM). Exhaust system according to claim 1, characterized in that each of the two partial exhaust ducts ( 2.1 . 2.2 ) a controllable switching element ( 4.1 . 4.2 ) having. Exhaust system according to one of the preceding claims, characterized in that the control device ( 6 ) is formed such that the closed position of the or the switching elements ( 4.1 . 4.2 ), such that the exhaust duct ( 2 ) is completely closed and thus the total exhaust gas flow is interrupted, is prevented. Exhaust system according to one of the preceding claims, characterized in that the control device ( 6 ) is designed such that the activation of the at least one switching element ( 4 ; 4.1 . 4.2 ) depending on data of a navigation or satellite system and / or depending on traffic information. Exhaust system according to one of the preceding claims, characterized in that the control device ( 6 ) is designed such that a pilot control of the at least one switching element ( 4 ; 4.1 . 4.2 ) takes place in dependence on the current operating point of the drive machine. Exhaust system according to one of the preceding claims, characterized in that - the means ( 3 ) for the conversion of heat energy in thermal operative connection with a controllable coolant pump (P) having cooling circuit (KS) for cooling the prime mover are. Exhaust system according to claim 6, characterized in that - the control device ( 6 ) is designed such that - during an operating phase, - during which the means ( 3 ) have not yet reached a predetermined temperature for the conversion of the heat energy, - and during which the at least one switching element ( 4 ; 4.1 . 4.2 ) is controlled such that at least a portion of the exhaust gas stream - preferably the entire exhaust stream - through which the means ( 3 ) for converting the heat energy have partial exhaust duct ( 2.1 ), - the coolant pump (P) as a function of the temperature (T _TEG ) of the means ( 3 ) is driven to convert thermal energy. Method for operating an exhaust system for an internal combustion engine (BKM), the exhaust system comprising: an exhaust duct ( 2 ), the two parallel partial exhaust ducts ( 2.1 . 2.2 ), wherein the partial exhaust gas channels ( 2.1 . 2.2 ) are merged downstream in a common exhaust gas passage section, - wherein one of the partial exhaust gas passages ( 2.1 ) Medium ( 3 ) for the conversion of heat energy into another form of energy, - and wherein in the exhaust duct ( 2 ) at least one controllable switching element ( 4 ; 4.1 . 4.2 ) is present for steering the exhaust gas flow, such that in dependence on the switching position of the at least one switching element ( 4 ; 4.1 . 4.2 ) the exhaust gas flow exclusively through the first partial exhaust gas channel ( 2.1 ), exclusively through the second partial exhaust gas channel ( 2.2 ) or proportionally through both partial exhaust gas channels ( 2.1 . 2.2 ), and - a control device ( 6 ) for controlling the at least one switching element ( 4 ; 4.1 . 4.2 ), characterized by the following method steps - the activation of the at least one switching element ( 4 ; 4.1 . 4.2 ) depending on the temperature (T _TEG ) of the means ( 3 ) for the conversion of heat energy - and / or as a function of a prevailing in the exhaust system (A) exhaust back pressure (p _exhaust ) - and / or in dependence on the temperature of the internal combustion engine (BKM).