DE10323314B4 - Combustion engine assembly with operating method therefor - Google Patents

Abstract

Method for operating an internal combustion engine unit with an internal combustion engine (1) and a catalytic converter (9) which is arranged in an exhaust gas flow of the internal combustion engine and has a load range (H) in which the catalytic converter (9) overheats if a measure to cool the catalytic converter is neglected , and combustion exhaust gases are recirculated into a combustion chamber (2) of the internal combustion engine (1) for cooling the catalytic converter, characterized in that the amount of recirculated exhaust gas and the air-fuel ratio are determined in the load range (H) so that a substantially uniform temperature of the catalytic converter (9) results for all load values of the load range (H).

Description

The present invention relates to an internal combustion engine assembly having an internal combustion engine and a catalyst arranged in an exhaust gas stream of the internal combustion engine, and an operating method for such an internal combustion engine assembly. Such internal combustion engine units are known from a variety of writings, among which DE 43 28 085 A1 can be mentioned as an example.

In early designs of these units, the catalyst was located in an exhaust conduit spaced from the internal combustion engine and was heated substantially only by heat entrained in the combustion exhaust gases. The result of this design was that a fairly long warm-up period was required after starting the internal combustion engine until the catalyst reached an operating temperature at which it caused effective degradation of the pollutants in the combustion exhaust gases.

The amount of pollutants that the engine of a motor vehicle may deliver is limited by statutory requirements. Specifically, upper limits for the overall emissions of a vehicle are set during a standardized test cycle that includes different load conditions within a predetermined period of time, each starting with a cold engine, at predetermined time intervals. A significant contribution to total emissions during such a test cycle is made in the period after the engine is started and before the catalyst has reached operating temperature. To limit pollutant emissions during such a test cycle is a very effective means of accelerating catalyst heating. This has led to a tendency in the design of internal combustion engine assemblies to place the catalyst ever closer to the engine itself, on the one hand to minimize heat losses of the exhaust gas on the way from the engine to the catalyst, on the other hand to be heated by the exhaust gas masses such as manifold and to minimize exhaust pipes. However, this design has the disadvantage that heating of the engine during operation under high load is also transferred to the catalyst, so that it can lead to exceeding the permissible operating temperature of the catalyst and thus to irreversible damage, unless measures for cooling the Catalyst are taken.

A z. B. off DE 10043687 A A known method for protecting sensitive parts of an internal combustion engine from overheating is to grease the air-fuel mixture supplied to the engine, ie to set an air-fuel ratio λ <1. When such a mixture is used, the oxygen contained in a combustor charge is insufficient to burn all the fuel supplied, and the exhaust gas stream contains unburned hydrocarbons, the evaporation of which extracts heat from the exhaust gas flow. It is obvious that this method entails increased fuel consumption and increased pollutant content of the combustion exhaust gases. However, as long as load conditions of the engine in which such cooling is required are not included in the test cycle prescribed for determining the pollutant emissions of the vehicle, a combustion engine assembly, in which the mixture is enriched for cooling, complies with the state exhaust gas regulations. D. h., There may be motor vehicles on the market, the internal combustion engine units meet the statutory emission requirements and thus give the impression of being low in pollutants, but which can have very unfavorable consumption and pollutant levels when operating under high load.

One known technique for reducing pollutant emissions of an internal combustion engine is exhaust gas recirculation. It is conventionally used in the low to medium load range to reduce the emission of nitrogen oxides. The recirculated exhaust gas dilutes the charge air. As a result, however, the combustion deteriorates, and above a critical exhaust gas recirculation rate, the content of hydrocarbons in the exhaust gas and the fuel consumption increases with poorer running smoothness of the engine. There is therefore a limit to the exhaust gas recirculation rate above which the emission of all pollutants can not be further reduced. Accordingly, it is common for the exhaust gas recirculation rate, i. H. To optimize the proportion of recirculated exhaust gas to the charge of the combustion chambers, to low, "balanced" pollutant values and low consumption.

Such optimization is conventionally made for stoichiometric combustion on an engine test bench for a prototype engine, and the results obtained are incorporated into the programming of the control units of the in-line engines. It shows that the advantages of exhaust gas recirculation decrease with increasing engine load, and that in most engines there is a load limit above which the exhaust gas recirculation increases consumption.

Out DE 19858990 A are known a method or a combustion engine assembly according to the preambles of claims 1 and 9. This document proposes to use exhaust gas recirculation to prevent heating in a NOx storage catalyst to a temperature at which stored NOx desorbs.

The object of the present invention is to specify an operating method for a combustion engine assembly or a combustion engine assembly with a catalyst which achieves a high long-term durability of the catalyst and at the same time low fuel consumption and low pollutant values in the exhaust gas.

The object is achieved by a method having the features of claim 1 and an internal combustion engine having the features of claim 9.

The present invention is based on the finding that it is also possible by exhaust gas recirculation to reduce the temperature of the catalyst and thus to protect it from overheating. Such overheat protection is particularly required in a high load area where a lack of temperature limiting measures could result in overheating damage to the catalyst. By properly selecting the amount of recirculated exhaust gas and the value of the air-fuel ratio, the catalyst is operated at a uniform temperature throughout the overheated load area.

Exhaust gas recirculation makes it possible, at least in a first subinterval of that load range in which measures for catalyst cooling are required to dispense with the conventional, consumption and pollution-increasing technique of enrichment.

In another sub-interval of the overheating-prone load range, it has proven to be favorable for the consumption to combine the exhaust gas recirculation with an enrichment of the air-fuel mixture. Although in stoichiometric operation, the consumption in this load range with exhaust gas recirculation may still be slightly higher than without, but this will be acceptable, since it is a low Anfettung the prerequisite for being able to operate the catalyst at all. The extent of enrichment is the lower, d. H. the higher the amount of recirculated exhaust gas, the greater the air-fuel ratio.

Since in the present catalyst compositions the long-term durability rapidly decreases at operating temperatures above 950 ° C, on the other hand, at low temperatures, the effectiveness of the catalyst is impaired, this uniform temperature is preferably in a range of 900 ° C to 950 ° C, preferably about 930 ° C, select.

Since both the exhaust gas recirculation and the enrichment of the mixture are effective per se to limit the temperature of the catalyst, there are a plurality of value pairs of the amount of recirculated exhaust gas and the air-fuel ratio, for load values of the second sub-interval where the desired catalyst temperature is reached. Among these pairs of values, it will be expedient to choose the one in which a minimum fuel consumption results.

The invention is applicable both to external exhaust gas recirculation, i. H. On designs of the internal combustion engine unit, in which an exhaust gas recirculation line is guided by an exhaust pipe via a valve to the intake manifold of the engine, and applicable to internal exhaust gas recirculation, be controlled in the intake and exhaust valves of a combustion chamber of the engine so that in each combustion cycle, a certain amount of exhaust gas is forced back into the suction line through the inlet valve.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures. Show it:

1 a schematic representation of a first embodiment of the internal combustion engine assembly according to the invention with external exhaust gas recirculation;

2 a second embodiment with external exhaust gas recirculation;

3 the principle of internal exhaust gas recirculation;

4 Exhaust gas recirculation rates as a function of load in a conventional and a control according to the invention;

5 Catalyst temperatures and air numbers as a function of load in a conventional and a controller according to the invention; and

6 the fuel consumption as a function of load in a conventional and a control according to the invention.

1 shows a block diagram of an internal combustion engine exhaust gas recirculation engine assembly according to a first embodiment of the invention. Shown is an engine block 1 with four combustion chambers in the example considered here 2 in which pistons 3 for driving a crankshaft 4 are displaceable. Every combustion chamber 2 has two by a (not shown) camshaft in time with the rotation of the crankshaft 4 operated valves 5 . 6 of which one 5 the combustion chamber with an intake manifold 7 and the other 6 she with an exhaust manifold 8th combines. The exhaust manifold 8th derives from the combustion chambers 2 discharged exhaust gas a catalyst 9 , which serves to reduce pollutant levels in the exhaust gas such as nitrogen oxides, carbon monoxide and unburned hydrocarbons. The engine is an electronic control unit 10 associated with a plurality of recorded on the engine or elsewhere on the vehicle parameters such as the position of an accelerator pedal 15 Operating variables of the engine such as the air ratio λ, opening time and duration of injectors 16 , Ignition angle, etc. regulates.

In an exhaust gas recirculation line 11 between the exhaust manifold 8th and the intake manifold 7 is one through the control unit 10 controlled valve 12 arranged, which provides a regulated reflux of exhaust gas from the exhaust manifold 8th in the intake manifold 7 allows. To those of the control circuit 10 Controlled operating variables of the engine also includes a desired exhaust gas recirculation rate or an opening degree of the valve required for realizing this rate 12 , The control unit 10 calculates this rate based on a variety of operating parameters of the engine such as speed, load, outside temperature, etc ..

The control circuit 10 must regulate the various operating variables of the engine so that overheating of the catalyst is avoided. For this purpose, a temperature sensor can be provided on the catalyst. In practice, however, an at least partially empirically derived temperature model is used, which is the control circuit 10 allows to calculate the catalyst temperature from other operating parameters of the engine. Because the catalyst temperature follows changes in parameters affecting it, it allows such a model to recognize and counteract parameter combinations that can lead to overheating even before overheating has actually occurred.

The operation of the controller 10 is the same for all embodiments of internal combustion engine engines shown here and will be discussed later.

2 shows a preferred development of the aggregate 1 in a schematic plan view in the direction of movement of the piston 3 in the combustion chambers 2 , intake manifold 7 and exhaust manifold 8th are each other here on both sides of the row of combustion chambers 2 and have the form of a manifold with a plurality of each to one of the combustion chambers 2 leading branch lines. A return line 11 that one from the control unit 10 controlled valve 12 contains, is in each case between a same combustion chamber 2 associated branch lines of the intake manifold 7 and the exhaust manifold 12 arranged. This modification is more complex than that of the 1 as it has its own return line for each individual combustion chamber 2 requires, but allows, the exhaust gas in the immediate vicinity of the inlet valve of each combustion chamber 2 recirculate. As a result, the residence time of the recirculated exhaust gas in the intake manifold 7 kept short, and the return rate can be under the control of the controller 10 be adapted very quickly to changed operating conditions of the engine.

3 shows the principle of internal exhaust gas recirculation based on a schematic section through a combustion chamber 2 , At the head of the combustion chamber 2 There is an inlet valve 13 that is coupled to the rotational position of the crankshaft 4 is opened or closed to when a downward movement of the piston 3 Fresh gas in the combustion chamber 2 let in, and an exhaust valve 14 , which is opened after each combustion to the combustion exhaust gases in the exhaust manifold 8th drain. The internal exhaust gas recirculation occurs during the upward movement of the piston 3 after combustion, in 3 illustrated state, a phase in the inlet valve as shown 13 and exhaust valve 14 at the same time or just the inlet valve 13 open to a portion of the combustion exhaust gases in the intake manifold 7 to displace. The in the intake manifold 7 displaced exhaust gas amount, which accounts for only a few percent of the total exhaust gas volume, in the subsequent intake phase of the combustion chamber 2 almost completely absorbed in this. This allows extremely fast control of the recirculated exhaust gas quantity.

4 is a graph that is parameterized as a function of engine load, here parameterized as the speed of a motor vehicle in which the engine is installed, when driving on a level track, under the control of the control unit 10 repatriated exhaust gas quantity represents. Above a vehicle speed of 140 km / h is a load range H, in which the engine heats up so much that the amount of heat released via the exhaust gases to the catalyst heated it so much that the durability of the catalyst is impaired, unless action is taken to cool the catalyst.

The curve 20 in 4 shows a conventional pollutant and consumption optimized characteristic of the exhaust gas recirculation rate in percent as a function of the engine load (here the vehicle speed). The return rate in the low load range between 0 and 100 km / h is approx. 13%. From about 100 km / h, a consumption-increasing effect begins to make noticeable, so that in the range between 100 and 140 km / h, below the overheating endangered load range H, the return rate is gradually reduced to zero. To one To avoid overheating of the catalytic converter when the engine is under a high load in the H range, this must be done to the combustion chambers 2 fed air-fuel mixture to be greased.

The curve 21 shows a characteristic of the exhaust gas recirculation rate as a function of the vehicle speed according to the invention. It is the result of pollutant and fuel consumption optimization, but included as an additional constraint that a damaging overheating of the catalyst must be omitted. The curve 21 follows in the low load range up to a speed of approx. 100 km / h of the curve 20 but then decreases less strongly and retains, above all unlike those in the area H a non-disappearing return rate up to the speed of 180 km / h, which corresponds to almost full load.

The diagram of 5 again, as a function of vehicle speed, air ratios λ and catalyst temperatures according to the prior art and according to the invention. The catalyst temperature is that of the return rate curve 20 according to the prior art, by a curve 22 and those of the return rate curve 21 according to the invention, by a curve 23 played. curves 24 . 25 each set the curves 22 respectively. 23 corresponding air ratios λ as a function of the speed.

In the speed range up to 100 km / h, in which the return rates of the curves 20 and 21 essentially the same, the temperature curves are also running 22 . 23 essentially congruent. There is an approximately linear relationship between the engine load (or speed) and the catalyst temperature. In the speed range of 100 to 140 km / h, in which the control according to the invention provides for a somewhat increased return rate, the slope of the curve is 23 a bit slower than the curve 22 , At 140 km / h reaches the conventional curve 22 a catalyst temperature of about 930 ° C, which should, in order to avoid damage to the catalyst, should not be exceeded. To be able to operate the engine nevertheless with higher load, the air-fuel mixture must be enriched, whereby load-dependent the fuel surplus is selected in each case so that the catalyst temperature remains essentially constant at 930 ° C. This temperature profile is in 5 through the dotted line 22 ' reproduced for speed greater than or equal to 140 km / h averaged substantially parallel to the abscissa. Accordingly, one recognizes for the curve 24 The air-fuel ratio above 140 km / h, a gradual decrease from the stoichiometric value of 1.0 to less than 0.9 at about 190 km / h.

The inventive strong exhaust gas recirculation according to curve 21 leads to the fact that the catalyst has not yet reached the limit temperature at the beginning of the load range H without overheating prone to overheating. It is therefore not necessary to enrich the mixture in the H1 partial interval of H, which ranges from 140 km / h to approximately 160-170 km / h.

At even higher engine load, maintaining a high exhaust gas recirculation rate of the order of 10% would increase fuel economy or lack of vacuum in the intake manifold 7 difficult to realize, so the return rate according to curve 21 is greatly reduced with increasing load in this area designated H2 and reaches zero at 180 km / h. In the load range H2 between about 160 to 170 km / h and 180 km / h, the catalyst is thus simultaneously cooled by exhaust gas recirculation and enrichment of the mixture.

In 6 is the speed-dependent fuel consumption rate represented by a curve 27 , in control according to the invention with exhaust gas recirculation rate according to curve 21 and air-fuel ratio according to curve 25 the fuel consumption rate of the same engine without exhaust gas recirculation, represented by a curve 26 , faced. The curves 26 . 27 are related to the values plotted on the left ordinate, which indicate the fuel consumption in liters / 100 km. Curve 28 represents, based on the right ordinate, the difference between the two in the curves 26 . 27 shown consumption percentages. Curve 29 shows for comparison the percentage difference between the consumption in conventional control with exhaust gas recirculation rate according to curve 20 and air ratio according to curve 24 , In the low load range up to 150 km / h you can observe on both curves 28 . 29 a slight fuel saving of 2 to 3%. In the high load range H, a significant fuel consumption advantage of the control according to the invention of up to 5, which corresponds to an under-consumption of 0.5 to 1.0 l / 100 km in this speed range for a typical car engine.

Since with the control according to the invention the value of the engine load, above which a mixture enrichment is required to protect the catalyst from overheating, is shifted upwards, not only a reduction of pollutant emissions, especially unburned hydrocarbons, but also a significant fuel consumption advantage is achieved.

It is understood that the velocity values given above as limits of the load ranges H, H1 and H2 are only examples, and that different limits of these intervals may result for different types of motor assemblies depending on the type of engine and the catalyst and the thermal coupling between them , Essential to the present invention is not the location of these intervals, but the fact that under load conditions which require measures to cool the catalyst to prevent damage to it, the exhaust gas recirculation replace or at least assist the conventional enrichment method and thereby fuel consumption and Can reduce pollutant emissions.

LIST OF REFERENCE NUMBERS

1

block

2

combustion chamber

3

piston

4

crankshaft

5

Valve

6

Valve

7

intake manifold

8th

exhaust manifold

9

catalyst

10

control unit

11

Return line

12

Valve

13

intake valve

14

outlet valve

15

accelerator

16

Injector

17

18

19

20

Curve

21

Curve

22

Curve

23

Curve

24

Curve

25

Curve

26

Curve

27

Curve

Claims (15)

Method for operating an internal combustion engine assembly with an internal combustion engine ( 1 ) and a catalyst arranged in an exhaust gas stream of the internal combustion engine ( 9 ), which has a load range (H), in which the catalyst ( 9 ) is overheated when a measure for cooling the catalyst is omitted, and for the cooling of the catalyst, a recirculation of combustion exhaust gases in a combustion chamber ( 2 ) of the internal combustion engine ( 1 ), characterized in that in the load range (H) the amount of recirculated exhaust gas and the air-fuel ratio are set so that for all load values of the load range (H) a substantially uniform temperature of the catalyst ( 9 ) results. Method according to Claim 1, characterized in that at least in a first subinterval (H1) of this load range ( 4 ) a stoichiometric air-fuel ratio combustion is performed. A method according to claim 2, characterized in that in a second sub-interval (H2) of this load range, a combustion with enriched air-fuel ratio is performed. A method according to claim 3, characterized in that in the second sub-interval (H2) with increasing load, the amount of recirculated exhaust gas and the air-fuel ratio can be reduced. Method according to one of the preceding claims, characterized in that the temperature of the catalyst ( 9 ) between 900 ° C and 950 ° C, preferably at about 930 ° C is selected. A method according to claim 5, characterized in that for load values of the second sub-interval (H2), the amount of recirculated exhaust gas and the air-fuel ratio are set so that a minimum fuel consumption results. Method according to one of the preceding claims, characterized in that the recirculation of the combustion gases with respect to the internal combustion engine takes place externally. Method according to one of claims 1 to 6, characterized in that the recirculation of the combustion gases based on the internal combustion engine takes place internally. Internal combustion engine assembly with an internal combustion engine ( 1 ), one in an exhaust gas stream of the internal combustion engine ( 1 ) arranged catalyst ( 9 ) and controllable recycling means ( 11 . 12 ; 13 . 14 Optionally, the recirculation or non-recirculation of exhaust gas from the exhaust stream into a combustion chamber (FIG. 2 ) of the internal combustion engine, and a control unit ( 10 ) for controlling the return means ( 11 . 12 ; 13 . 14 ), wherein the internal combustion engine unit has a load range (H), in which the control unit ( 10 ) the return means ( 11 . 12 ; 13 . 14 ) in order to recirculate exhaust gas and in the absence of the return to the overheating of the catalyst ( 9 ), characterized in that the control unit ( 10 ) is arranged to set the amount of recirculated exhaust gas and the air-fuel ratio so that the temperature of the catalyst ( 9 ) is substantially uniform for all load values of the load range (H). Internal combustion engine unit according to claim 9, characterized in that the control unit ( 10 ), setting means ( 16 ) to the Adjusting an air-fuel ratio to control and at least in a first sub-interval (H1) of the load range so that the combustion takes place with a stoichiometric air-fuel ratio. Combustion engine assembly according to claim 10, characterized in that the control unit the adjustment means ( 16 ) in a second subinterval (H2) of the load range so that combustion takes place with enriched air-fuel ratio. Internal combustion engine assembly according to claim 11, characterized in that in the second subinterval (H2) with increasing load, the amount of recirculated exhaust gas and the air-fuel ratio decrease. Combustion engine assembly according to claim 11 or 12, characterized in that for load values in the second sub-interval (H2), the amount of recirculated exhaust gas and the air-fuel ratio are set so that a minimum fuel consumption results. Internal combustion engine unit according to one of claims 9 to 13, characterized in that the return means ( 11 . 12 ) relative to the internal combustion engine ( 1 ) are arranged externally. Internal combustion engine unit according to one of claims 9 to 13, characterized in that the return means ( 13 . 14 ) are arranged internally relative to the internal combustion engine.

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