DE102005024984A1 - Diesel engine for motor vehicle, has controller which adjusts throttle valve under throttling of fresh air quantity supplied into engine, during warm up and/or in light load operation of engine, to increase exhaust gas temperature - Google Patents

Abstract

The engine has a high pressure exhaust gas recirculation system (10) connecting an exhaust gas block with an intake system, where an exhaust gas purification mechanism is arranged in the system. A controller adjusts a throttle valve (38) under throttling of fresh air quantity supplied via the system into the engine, during warm up and/or in light load operation of the engine, to increase the exhaust gas temperature in the block. An independent claim is also included for a method for the operation of the internal combustion engine.

Description

The The invention relates to an internal combustion engine according to the preamble of claim 1 and a method for operating an internal combustion engine according to the preamble of Claim 6.

The controlled exhaust gas recirculation in internal combustion engines is a commonly used technique, which serves primarily to reduce the NOx content in the exhaust gas by lowering the combustion temperature in the combustion chambers of the internal combustion engine. In exhaust gas recirculation systems with high-pressure exhaust gas recirculation, hot exhaust gas under relatively high pressure is branched off immediately after it exits the combustion chambers in the exhaust manifold and possibly after passage through an exhaust gas recirculation cooler and / or a cooling channel in the cylinder head to cool the exhaust gas immediately before the internal combustion engine fed back through an exhaust gas recirculation valve in the intake. An internal combustion engine of the type mentioned with such a system is for example from the DE 103 13 503 A1 known.

There but that from the exhaust manifold branched off exhaust gas is polluted by diesel soot, can at a poor design or malfunction in the intake ports of the Intake tract contamination occur. To this as much as possible avoid and above all the amount of total recirculated exhaust gas to increase and thus to reduce the NOx content in the exhaust significantly come Exhaust gas recirculation systems with an additional one Low-pressure exhaust gas recirculation for Use where part of the exhaust gas is just behind the particulate filter in the purified state branched off from the exhaust system and then again fed into the intake tract becomes. Since the temperature of the recirculated exhaust gas through the low-pressure exhaust gas recirculation is lower, in the intake tract in front of the internal combustion engine one Overall, lower mixing temperature is achieved and thus the amount of the resulting NOx reduced.

The compared to pure high-pressure exhaust gas recirculation significantly lower temperature the exhaust gas in the low-pressure exhaust gas recirculation can However, for example, during warm-up of the internal combustion engine cause that is arranged upstream of the particulate filter in the exhaust system oxidation catalyst the for its proper function required light-off temperature reached later, or may at Low load operation of the internal combustion engine excessive cooling of the Catalyst to below its light-off temperature result. This in turn ensures compliance with the required emission limit values for HC and CO endangered, Since this depends crucially on the efficiency of the catalyst, the itself depends on the catalyst or exhaust gas temperature.

Similar Problems, albeit to a lesser extent, can also occur in pure high-pressure exhaust gas recirculation, where the light-off temperature the oxidation catalyst during warm-up also after a period of time required to comply with the prescribed Emission limit values should be as short as possible.

Advantages of invention

The Internal combustion engine according to the invention having the features specified in claim 1 or the method according to the invention with the features specified in claim 6 have the other hand Advantage that by increasing the Exhaust gas temperature and thereby improved efficiency of a Oxidation of the exhaust gas purification device early during the Warm-up or in low-load operation compliance with the prescribed Emission limit values becomes.

By the throttling of the intake air sucked through the intake in the pure high-pressure exhaust gas recirculation or by throttling the combined in a high-pressure and low-pressure exhaust gas recirculation the intake tract in the internal combustion engine supplied gas quantity, consisting of the intake fresh air and the low-pressure exhaust gas recirculation in the intake tract recirculated exhaust gas, can the exhaust gas temperature increases because of the boost pressure of the internal combustion engine and thus their efficiency drops significantly, so that to deliver the same Engine power significantly more fuel must be injected, which in turn the exhaust gas temperature and thus the temperature in the Oxidation catalyst increases. In other words, the temperature in the oxidation catalyst by the deterioration of the efficiency the internal combustion engine increased as a result of additional throttling.

To increase the exhaust gas temperature as a result of throttling during warm-up or in low-load operation may also possibly contribute that the proportion of the exhaust gas supplied by the high-pressure exhaust gas recirculation into the internal combustion engine is increased, which due to the higher temperature This exhaust gas also leads to an increase in the exhaust gas temperature in the exhaust tract and thus in the oxidation catalyst and in the downstream particulate filter.

To A cold start of the internal combustion engine is the throttle preferably as far as possible closed until either the temperature in the oxidation catalyst the light-off temperature of the catalyst reaches or exceeds or a predetermined period has elapsed, previously for the same Type of internal combustion engine as average period has been determined until reaching the light-off temperature.

Dm the former case is preferable for measuring exhaust gas temperature in the region of the oxidation catalyst, a temperature sensor in the exhaust gas tract or provided in the oxidation catalyst, as the controlled variable for the adjustment measures the exhaust gas temperature serving the throttle flap.

in the The latter case may be the control of the throttle for the various Operating points of the internal combustion engine in dependence be done by a map of the exhaust gas temperature in a memory of the engine control unit is stored.

A Further preferred embodiment of the invention provides that the Throttle valve is integrated into a high-pressure exhaust gas recirculation valve, the preferably as well as the throttle itself on electronic Ways of an engine control unit the Internal combustion engine is driven.

drawing

The Invention will be described below in an embodiment with reference to the accompanying drawings explained in more detail. It demonstrate:

1 a schematic representation of a equipped with an exhaust gas turbocharger diesel engine with high pressure and low pressure exhaust gas recirculation;

2 a graph showing the exhaust gas temperature as a function of the air mass measured in the intake manifold for different effective mean pressures of the diesel engine and constant engine power.

description of the embodiment

The in 1 illustrated diesel engine 2 is with an exhaust gas turbocharger 4 equipped and includes an intake tract 6 and an exhaust tract 8th caused by internal or high pressure exhaust gas recirculation 10 as well as by an external or low-pressure exhaust gas recirculation 12 connected to each other.

The intake tract 6 contains an air filter 14 , one in the flow direction of the intake air (arrow AL) behind the air filter 14 arranged hot film air mass meter 16 , one between the air mass meter 16 and an intake air compressor 18 the exhaust gas turbocharger 4 arranged outside or (low-pressure exhaust gas recirculation valve 20 , one behind the intake air compressor 18 arranged intercooler 22 , as well as between the intercooler 22 and the diesel engine 2 arranged inner or high-pressure exhaust gas recirculation valve 24 ,

The exhaust tract 8th contains an exhaust manifold 26 from which part of the diesel engine 2 generated exhaust gases through an exhaust gas turbine 28 the exhaust gas turbocharger 4 and further through an oxidation catalyst 30 and a diesel particulate filter 32 to an exhaust (not shown) are directed (arrow AG).

The high pressure exhaust gas recirculation 10 branches off the exhaust manifold 26 and connects this via an exhaust gas recirculation cooler 34 with the high pressure EGR valve 24 while the low-pressure exhaust gas recirculation 12 behind the diesel particulate filter 32 from the exhaust tract 8th branches off and the low-pressure exhaust gas recirculation valve 20 in the intake tract 6 leads.

The two exhaust gas recirculation valves 20 . 24 Serve to reduce the amount of intake into the intake 6 to control supplied exhaust gases and are to a motor control unit (not shown) of the diesel engine 2 electronically controlled. The two exhaust gas recirculation valves 20 . 24 each contain an integrated throttle 36 respectively. 38 , both also from the engine control unit of the diesel engine 2 electronically controlled. The throttle valves 36 respectively. 38 However, do not need, as shown, in the exhaust gas recirculation valve 20 respectively. 24 be integrated, but also individually in front of each exhaust gas recirculation valve 20 respectively. 24 be arranged.

The throttle 38 of the high pressure exhaust gas recirculation valve 24 Supports the regulation of the high-pressure exhaust gas recirculation 10 in the area behind the intercooler 22 in the intake tract 6 directed exhaust gas amount, if in some operating points of the diesel engine 2 the pressure gradient between the exhaust manifold 26 and an area 27 behind the high-pressure exhaust gas recirculation valve 24 is not enough to exhaust enough through the valve 24 in the intake tract 6 supply. In this case, the intake air flow by adjusting the throttle 38 throttled, so that further sufficient exhaust gas from the exhaust manifold 26 through the high pressure EGR valve 24 in the intake air stream is supplied.

The throttle 36 the low-pressure exhaust gas recirculation valve 20 , or alternatively one behind the diversion of the low-pressure exhaust gas recirculation 12 in the exhaust tract 8th arranged, controlled by the engine control unit electronically controlled damper 40 , In a similar way, serves a corresponding pressure gradient between the exhaust tract 8th and the intake tract 6 in the area of the low-pressure exhaust gas recirculation valve 20 build.

The task of low-pressure exhaust gas recirculation 12 it is part of the high-pressure exhaust gas recirculation 10 in the exhaust tract 8th supplied unpurified waste gas to be replaced by purified, freed of diesel soot exhaust gas. Due to the freed of diesel soot exhaust on the one hand and the lowering of the mixing temperature in the intake system, the amount of the intake into the intake 6 recycled total exhaust gas and thus the NOx content in the exhaust gas can be reduced.

Because that's behind the particulate filter 32 diverted exhaust gas compared to that from the exhaust manifold 26 However, branched off exhaust gas has a relatively low temperature, is due to the low-pressure exhaust gas recirculation 12 the combustion in the cylinders of the diesel engine 2 changed so that the temperature level of the exhaust gas in the exhaust system 8th in comparison to pure high-pressure exhaust gas recirculation 10 is lowered. This in turn has the consequence that in the oxidation catalyst 30 the reaction rate in the conversion of unburned exhaust gas constituents, such as HC and CO decreases, since the efficiency of the catalyst 30 decisively depends on the temperature of the exhaust gas passed. This is especially true when the exhaust gas temperature in the vicinity of the so-called light-off temperature of the oxidation catalyst 30 below which there is no conversion of unburned exhaust gas constituents in the catalyst 30 takes place. This temperature is in most cases about 180 ° C.

While such a temperature in a medium load spectrum of the diesel engine 2 is usually far exceeded and thus caused by reducing the exhaust gas temperature usually no problems in terms of compliance with the required emission limits, the light-off temperature of the catalyst 30 when cold starting the engine 2 reached only after a certain time, whose duration by lowering the exhaust gas temperature due to the low-pressure exhaust gas recirculation 12 is extended. The same applies to a low load operation of the diesel engine 2 , Such as an inner-city driving or driving operation with high idle share, by which the heating of the catalyst 30 after starting the engine 2 required time is also extended, or to a cooling of an already heated catalyst 30 below the light-off temperature, which causes considerable problems in terms of compliance with the required emission limits.

To avoid these problems, the engine control unit of the diesel engine 2 programmed to the throttle 38 of the high pressure exhaust gas recirculation valve 24 during warm-up and / or during low-load operation of the engine 2 to control so that the amount of the through the intake 6 to the diesel engine 2 supplied gas, ie intake air and relatively cold exhaust gas from the low-pressure exhaust gas recirculation 12 , as much as possible is throttled to the combustion in the cylinders of the diesel engine 2 and thus its efficiency by artificially deteriorate this throttling. This in turn means that due to the poorer efficiency, the exhaust gas temperature in the exhaust system 8th increases and thus the efficiency of the oxidation catalyst 30 and possibly the downstream diesel particulate filter 32 is improved.

After a cold start of the engine 2 can the through the intake tract 6 to the diesel engine 2 supplied gas mixture can be throttled over a predetermined period of time, which corresponds to a substantially for the same engine type previously determined by tests on an engine dynamometer period until reaching or exceeding the light-off temperature. Alternatively, the throttling can also take place as a function of the exhaust gas temperature, which expediently in the region of the oxidation catalyst by means of a tempera ture sensor 42 is measured and serves as a control variable for throttling.

2 shows the dependence of the temperature T of the exhaust gases in the oxidation catalyst 30 at a speed of the diesel engine 2 of 1500 min ^-1 for three different load-dependent mean pressures pe of 0 bar, 3 bar and 5 bar above the air-mass meter 16 measured air mass m. How to get out 2 sees, the temperature T of the exhaust gases can be significantly increased with decreasing air mass m. In particular, it can be seen that the exhaust gas temperature even at zero load (pe = 0 bar) by throttling by about 50 ° C above a light-off temperature of the catalyst 30 can be raised from 180 ° C addition.

Claims (10)

Internal combustion engine, in particular for a motor vehicle, having an intake tract, an exhaust tract, an exhaust gas purification device arranged in the exhaust tract, a high-pressure exhaust gas recirculation connecting the exhaust tract with the intake tract, one in front of the junction of the high Pressure exhaust gas recirculation in the intake tract arranged throttle, and a control for adjusting the throttle, gekkzeichnet in that the control during warm-up and / or in low load operation of the internal combustion engine ( 2 ) the throttle valve ( 38 ) while throttling through the intake tract ( 6 ) in the internal combustion engine ( 2 ) adjusted fresh air quantity to the exhaust gas temperature in the exhaust gas tract ( 8th ) for improving the efficiency of the exhaust gas purification device ( 30 . 32 ) increase. Internal combustion engine according to claim 1, characterized in that the exhaust tract ( 8th ) by a low-pressure exhaust gas recirculation ( 12 ) with the intake tract ( 6 ) and that the control during warm-up and / or in low-load operation of the internal combustion engine ( 2 ) the throttle valve ( 38 ) while throttling the amount of fresh air and / or by the low-pressure exhaust gas recirculation ( 12 ) adjusted exhaust gas quantity to the exhaust gas temperature in the exhaust tract ( 8th ) for improving the efficiency of the exhaust gas purification device ( 30 . 32 ) increase. Internal combustion engine according to claim 1 or 2, characterized in that the throttling by a high-pressure exhaust gas recirculation valve ( 24 ) from the intake tract ( 6 ) in the internal combustion engine ( 2 ) gas quantity used to increase the exhaust gas temperature by more than about 50 ° C and preferably by more than 100 ° C. Internal combustion engine according to one of the preceding claims, characterized in that the throttle valve ( 38 ) Part of a controlled by the control high-pressure exhaust gas recirculation valve ( 24 ). Internal combustion engine according to one of the preceding claims, characterized in that the exhaust gas purification device ( 30 . 32 ) an oxidation catalyst ( 30 ) and a particle filter ( 32 ). Method for operating an internal combustion engine having an intake tract, an exhaust tract and an exhaust gas purification device arranged in the exhaust tract, fresh air being sucked in through the intake tract and exhaust being returned from the exhaust tract to the intake tract, characterized in that the quantity passing through the intake tract ( 6 ) sucked fresh air during warm-up and / or in low-load operation of the internal combustion engine ( 2 ) is throttled to the exhaust gas temperature in the exhaust tract ( 8th ) for improving the efficiency of the exhaust gas purification device ( 30 . 32 ) increase. A method according to claim 6, characterized in that the exhaust gas by a high-pressure exhaust gas recirculation ( 10 ) and by a low-pressure exhaust gas recirculation (12) is returned to the intake tract, and that the amount of the through the intake tract ( 6 ) sucked fresh air and by the low-pressure exhaust gas recirculation ( 12 ) in the intake tract recirculated exhaust gas during warm-up and / or in low-load operation of the internal combustion engine ( 2 ) is throttled to the exhaust gas temperature in the exhaust tract ( 8th ) for improving the efficiency of the exhaust gas purification device ( 30 . 32 ) increase. A method according to claim 6 or 7, characterized in that the amount of the through the intake tract ( 6 ) sucked fresh air and / or by the low-pressure exhaust gas recirculation ( 12 ) in the intake tract ( 6 ) recirculated exhaust gas by adjusting a throttle valve ( 38 ) in a high-pressure exhaust gas recirculation valve ( 24 ) of the high-pressure exhaust gas recirculation ( 12 ) is throttled. Method according to one of claims 6 to 8, characterized in that the amount of the through the intake tract ( 6 ) sucked fresh air and / or by the low-pressure exhaust gas recirculation ( 12 ) in the intake tract ( 6 ) recirculated exhaust gas after a cold start of the internal combustion engine ( 2 ) is throttled over a predetermined period of time. Method according to one of claims 6 to 9, characterized in that the amount of the through the intake tract ( 6 ) sucked fresh air and / or by the low-pressure exhaust gas recirculation ( 12 ) in the intake tract ( 6 ) recirculated exhaust gas is throttled until reaching a predetermined exhaust gas temperature.