DE102010017791A1 - Method for controlling and reducing thermal load of internal combustion engine e.g. diesel engine of motor car, involves reducing air ratio when temperature of cylinder head exceeds predetermined upper limit temperature - Google Patents

Abstract

The method involves providing a cylinder head (6) with a cylinder (3), and determining temperature of the cylinder head by a sensor unit (16). Air ratio is reduced when the temperature (Tcyl) of the cylinder head exceeds predetermined upper limit temperature based on stoichiometric operation of a combustion engine (1). The air ratio is increased when the temperature of the cylinder head falls below of predetermined lower limit temperature based on under-stoichiometric operation of the combustion engine. The combustion engine is equipped with a liquid cooling unit (12).

Description

The invention relates to a method for limiting and reducing the thermal load of an internal combustion engine having at least one cylinder head having at least one cylinder.

Furthermore, the invention relates to an internal combustion engine for carrying out such a method

Internal combustion engines of the type mentioned are used as a drive for motor vehicles. In the context of the present invention, the term internal combustion engine includes diesel engines and gasoline engines, but also hybrid internal combustion engines, d. H. Internal combustion engines operated by a hybrid combustion process.

Internal combustion engines have at least one cylinder head, which is used to form the at least one cylinder, d. H. Combustion chamber, is connected to a cylinder block. As part of the charge exchange, the exhaust of the combustion gases via the outlet openings and the filling of the combustion chamber, d. H. the intake of the fresh mixture or the fresh air, via the inlet openings of the at least one cylinder. To control the charge cycle four-stroke engines almost exclusively lift valves are used as control members that perform an oscillating lifting movement during operation of the internal combustion engine and thus release the inlet and outlet ports and close. The required for the movement of the valves valve actuating mechanism including the valves themselves is referred to as a valve train.

The cylinder head is used to hold the controls and overhead camshaft to accommodate the entire valve train. In spark-ignited internal combustion engines, moreover, the required ignition device, in direct-injection internal combustion engines beyond the injection device can be arranged in the cylinder head.

To form a functional, d. H. the combustion chambers sealing connection of the cylinder head and cylinder block are sufficiently many and provide sufficiently large holes, which significantly affects the structural design of the cylinder head.

If the internal combustion engine has liquid cooling, a plurality of coolant channels or at least one coolant jacket are generally formed in the cylinder head, which guide the coolant through the cylinder head, resulting in a very complex cylinder head structure.

The above statements make it clear that the cylinder head of an internal combustion engine is a thermally and mechanically highly loaded component. The demands on the cylinder head continue to increase. It should be noted in this context that an increasing proportion of internal combustion engines - by turbocharger supercharger or mechanical supercharger - is charged. Due to the increasingly dense packaging in the engine compartment and the increasing integration of components and components in the cylinder head, for example, the integration of the exhaust manifold, in particular increases the thermal load of the internal combustion engine or the cylinder head, so that increased cooling requirements and measures to are seize that prevent a thermal overload of the internal combustion engine safely.

In principle, it is possible to carry out the engine cooling in the form of air cooling or liquid cooling. In the air cooling, the internal combustion engine is provided with a fan, wherein the heat dissipation takes place by means of a guided over the surface of the cylinder head air flow.

Due to the higher heat capacity of liquids compared to air can be dissipated with a liquid cooling much larger amounts of heat than is possible with an air cooling. For this reason, internal combustion engines are increasingly equipped with a liquid cooling.

Liquid cooling requires the equipment of the internal combustion engine or the cylinder head with a coolant jacket, d. H. the arrangement of the coolant through the cylinder head leading coolant channels. The heat given off to the coolant is withdrawn from the coolant in a heat exchanger, which is preferably arranged in the front-end region of the vehicle.

In general, the interpretation of the engine cooling, regardless of whether it is designed as air cooling or liquid cooling, with regard to the maximum cooling demand occurs. The result of this approach is an engine cooling, which in terms of normal driving, d. H. is oversized in view of the average cooling demand.

In order to reliably prevent the overheating of the engine, the cooling performance of the engine cooling is designed for operating conditions with very high or maximum cooling demand, which are characterized by high loads at the same time low vehicle speeds, so in terms of operating conditions such as in Acceleration and uphill driving occur to provide the requested cooling capacity even under the most adverse conditions. Under such conditions, the engine cooling has to cope with a very large amount of heat, ie dissipate, without the required for the heat dissipation air flow is available.

The design of the engine cooling with respect to the scenario described above leads to disproportionately large, d. H. oversized cooling. As a result, the fan of air cooling or the heat exchanger, d. H. the radiator, a liquid cooling very large dimensions and that, although this is not necessary for normal driving, d. H. apart from a few extreme driving situations would actually be unnecessary.

In particular, such a design results in a liquid cooling to an excessively large radiator, which can be difficult to accommodate in the front-end area of a vehicle.

To take into account in this context also that the radiator can not be increased arbitrarily, as usually more heat exchangers, in particular cooling devices are provided to ensure safe, trouble-free operation of the internal combustion engine or to optimize the operation of the internal combustion engine, and an oversized cooler greatly limits the other heat exchangers in arrangement and dimensioning.

In the following some examples for further heat exchangers are called and described, in order to clarify the problem.

The heat released as a result of the combustion of the fuel is not only delivered to the walls delimiting the combustion chamber, the exhaust gas flow and optionally to the engine coolant, but also partially to the engine oil. In order to comply with the maximum permissible oil temperature, the heat dissipation via the oil pan due to heat conduction and natural convection is often not sufficient, so that an additional oil cooler is provided.

On the intake side of an internal combustion engine often a charge air cooler is arranged, which lowers the temperature of the fresh air sucked or the fresh mixture sucked in and thus increases the density of the fresh cylinder charge. In this way, the intercooler contributes to a better filling of the combustion chamber with air or with fresh mixture. Usually supercharged internal combustion engines are equipped with a charge air cooler.

In addition to the charge air cooler, internal combustion engines often have further heat exchangers, in particular cooling devices.

Modern internal combustion engines are increasingly being equipped with exhaust gas recirculation (EGR). The exhaust gas recirculation, d. H. the recirculation of combustion gases from the exhaust side to the intake side of the internal combustion engine is considered to be effective in meeting future emissions limits, particularly nitrogen oxide emission limits. Since the formation of nitrogen oxides requires high temperatures, there is a concept for reducing nitrogen oxide emissions, combustion processes, i. H. Combustion process to develop with lower combustion temperatures, the exhaust gas recirculation is a means to reduce the temperatures.

With increasing exhaust gas recirculation rate, the nitrogen oxide emissions can be significantly reduced. In this case, the exhaust gas recirculation rate x _{AGR is} determined as x _AGR = m _AGR / (m _AGR + m _{fresh air} ), where m _AGR denotes the mass of recirculated exhaust gas and m _{fresh air} the supplied and possibly compressed fresh air or charge air.

In order to achieve a significant reduction in nitrogen oxide emissions, high exhaust gas recirculation rates are required, which can be on the order of x _AGR ≈ 50% to 70%.

To realize such high recirculation rates, cooling of the recirculated exhaust gas, i. H. a compression of the exhaust gas by cooling, imperative to increase the density of the recirculated exhaust gas. The internal combustion engine is therefore equipped with an additional cooling device for cooling the recirculating exhaust gas.

Other coolers can be provided, for example for cooling the transmission oil in automatic transmissions and / or for cooling hydraulic fluids, in particular hydraulic oil, which is used in the context of hydraulically actuated adjusting devices or for steering assistance.

Another heat exchanger is the air conditioning condenser of an air conditioner, which usually works after the cold vapor process. The temperature of the passenger compartment supplied air flow is lowered when flowing around an evaporator, wherein the air flow evaporates an evaporator inside a flowing refrigerant heat and thereby evaporates itself.

The above statements make it clear that modern internal combustion engines are equipped with a large number of heat exchangers, which invariably with to fulfill their function a sufficiently large heat-transferring surface must be formed, which is often problematic in the dimensioning and arrangement of the individual heat exchanger in the front-end area due to the limited space available, that leads to conflicts.

In the prior art, therefore, coolers are already arranged in series, spaced from each other and partially overlapping. Optionally, flow baffles are used to guide the flow of air through the engine compartment.

In this context, the radiator of the liquid cooling is of particular importance, since this cooler is indispensable for safe operation of the internal combustion engine and has to cope with large amounts of heat.

To the heat exchangers of the cooling systems, d. H. the cooling devices, even at a standstill, d. H. provide a sufficiently high air mass flow when the vehicle is stationary, or at low vehicle speeds, some cooling systems modern motor vehicle drives are equipped with powerful fan motors that drive a fan, d. H. set in rotation. The fan motors are usually operated electrically and can support the heat transfer in the heat exchangers in principle at any operating point. The control of such fan motors by means of motor control.

Nevertheless, further measures are required to limit the thermal load of the internal combustion engine even under the most adverse conditions.

In order to avoid a thermal overload of individual components of the internal combustion engine, enrichment (λ <1) is frequently always carried out according to the prior art whenever high exhaust gas temperatures are to be expected. In this case, more fuel is injected than can be burned at all with the amount of air provided, wherein the excess fuel is also heated and evaporated, so that the temperature of the combustion gases decreases. Although this procedure is considered to be disadvantageous in terms of energy aspects, in particular with regard to the fuel consumption of the internal combustion engine, and with regard to the pollutant emissions, it is nevertheless recognized as permissible and expedient.

The exhaust gas temperatures can in principle also be reduced by leaning (λ> 1) of the fuel-air mixture. The effect is similar to an enrichment. While too much fuel is injected during enrichment (λ <1), less fuel is injected in an emptying than could be burned with the amount of air provided, that is to say, in the case of enrichment. H. more air is provided than is needed to burn the fuel, with the excess air participating in the combustion process, i. H. is heated with. This reduces the temperature of the combustion gases. The decrease in temperature due to leaning is much lower than when enriched, because the excess air, unlike the excess fuel does not have to be evaporated.

In the context of the present invention, enrichment is occasionally also mentioned when the air ratio is reduced on the basis of a superstoichiometric operation of the internal combustion engine.

In the prior art, the exhaust gas temperature is used as an input variable or controlled variable in the control or regulation of enrichment in order to limit the component temperatures of individual components of the internal combustion engine. Here, the primary goal is not to limit the temperature of the internal combustion engine as a whole or to reduce or relieve the cooling system.

Against the background of the above, it is an object of the present invention to provide a method for limiting and reducing the thermal load of an internal combustion engine according to the preamble of claim 1, which is further improved compared to the cooling methods known from the prior art, and in particular takes into account the fact that the entire internal combustion engine is the actual object of the cooling process.

Another object of the present invention is to provide an internal combustion engine for carrying out such a method.

• – eine Temperatur T_cyl des Zylinderkopfes ermittelt wird, und
• – das Luftverhältnis λ verringert wird, falls die Zylinderkopftemperatur T_cyl eine vorgebbare obere Grenztemperatur T_Grenz,up übersteigt mit T_cyl ≥ T_Grenz,up.

The first sub-task is solved by a method for limiting and reducing the thermal load of an internal combustion engine with at least one cylinder head having at least one cylinder, which is characterized in that

• - A temperature T _{cyl of} the cylinder head is determined, and
• - The air ratio λ is reduced, if the cylinder head temperature T _{cyl exceeds} a predetermined upper limit temperature T _{limit, up} with T _cyl ≥ T _{limit, up} .

_{According to the} invention, the air ratio λ is varied as a function of the cylinder head _temperature T _cyl . In order to limit or reduce the thermal load of the internal combustion engine, enrichment of the fuel-air mixture, ie Reduction of the air ratio λ, as soon as the cylinder head temperature T _cyl exceeds a critical value.

Thus, the method _{according to} the _{invention depends} directly on the internal combustion engine to be cooled, namely the cylinder head _temperature T _{cyl of} the internal combustion engine, and thus on the component, which is the immediate subject of the method for cooling. Whether an enrichment is made or not, is decided based on the currently existing temperature of the cylinder head T _cyl .

The procedure according to the invention is therefore characterized by the fact that exactly the temperature is used as the input variable or control variable for controlling or controlling the enrichment, which is to be limited or reduced in the context of cooling the internal combustion engine, namely the cylinder head _temperature T _cyl , whereas conventional Procedures monitor the exhaust gas temperature and use as an indication of enrichment, to avoid overheating only individual components of the internal combustion engine.

According to the invention, cooling by enrichment also takes place when this is not considered necessary in a conventional manner because of the instantaneous exhaust gas temperatures, but the cylinder head temperature T _{cyl exceeds} a predetermined upper limit temperature T _{limit, up} .

In this way it is avoided that less heat is extracted from the internal combustion engine than is actually required and the internal combustion engine overheats. Once the cylinder head temperature T _{cyl reaches} a maximum allowable temperature, enrichment is performed as an additional measure to lower the temperature to satisfy a current cooling demand and limit or reduce engine thermal load, even if the exhaust gas temperatures do not cause richening index.

With the method according to the invention, the first problem underlying the invention is solved, namely to show a method for limiting and reducing the thermal load of an internal combustion engine, which is further improved in comparison with the cooling methods known from the prior art and in particular takes into account the circumstance, the internal combustion engine is the actual object of the cooling process.

Regardless of the procedure _{according to} the invention, ie the enrichment indicated by the cylinder head _temperature T _cyl, enrichment can still be carried out or carried out for other reasons, for example enrichment for lowering the exhaust gas temperature for protecting an exhaust aftertreatment system from overheating.

Further advantageous variants of the method are discussed in connection with the subclaims.

Advantageous embodiments of the method in which the air ratio λ is only reduced when the cylinder head temperature T _{cyl exceeds} the predetermined upper limit temperature T _{limit, up} and for a predetermined period .DELTA.t _{up is} greater than this upper limit temperature T _{limit, up} .

The introduction of an additional condition for the lowering of the air ratio λ is to prevent a too frequent or hasty change of the operating parameters, in particular a transition to a rich, ie stoichiometric operation of the internal combustion engine, if the cylinder head temperature T _cyl only briefly a predetermined upper limit temperature T _{limit , up} and then falls again or fluctuates around the predetermined limit temperature, without exceeding would justify an enrichment of the fuel-air mixture.

It should be considered in this context that an enrichment according to the invention should advantageously be made only if this is necessary for the protection of the internal combustion engine from overheating, because under energetic aspects, in particular with regard to the fuel consumption of the internal combustion engine, and in terms of pollutant emissions enrichment is disadvantageous , In particular, enrichment does not always allow the internal combustion engine to be operated in the manner required, for example, for a proposed exhaust aftertreatment system. In principle, enrichment should only be carried out if this is actually necessary.

Advantageous embodiments of the method in which the air ratio λ, starting from a stoichiometric operation (λ ≈ 1) of the internal combustion engine is reduced, whereby the internal combustion engine in a substoichiometric operation (λ <1) is transferred.

In the prior art, internal combustion engines are equipped with various exhaust aftertreatment systems to reduce pollutant emissions. In gasoline engines catalytic reactors are used, which ensure the use of catalytic materials oxidation of HC and CO, even at low temperatures. If additional nitrogen oxides are to be reduced, this can be achieved by using a three-way Catalyst can be achieved, but this requires a running within narrow limits stoichiometric operation (λ ≈ 1). The nitrogen oxides NO _{x are} reduced by means of the existing unoxidized exhaust gas components, namely the carbon monoxides and the unburned hydrocarbons, wherein at the same time these exhaust gas components are oxidized.

If the air ratio λ is reduced starting from a stoichiometric operation (λ≈1) of the internal combustion engine, an enrichment takes place directly, in which more fuel is injected than can be burnt. The running in the context of the combustion of the fuel-air mixture evaporation of the excess fuel causes a lowering of the process temperatures, ie the combustion temperatures. This is accompanied by a reduction of the cylinder head _temperature T _cyl . The thermal load of the internal combustion engine is reduced.

If the air ratio λ is reduced starting from a superstoichiometric operation (λ> 1) of the internal combustion engine, the process temperature or cylinder head _temperature T _{cyl may} initially _increase in the individual case, since initially the excess air of the lean fuel-air mixture is reduced before a transition to a rich sub-stoichiometric mixture takes place.

Advantageously, embodiments of the method in which the air ratio λ, starting from a stoichiometric operation (λ <1) of the internal combustion engine is increased again, if the cylinder head temperature T _cyl a predetermined lower limit temperature T _{limit, down} below T _cyl ≤ T _{limit, down} .

As already stated in another context, enrichment with regard to the fuel consumption of the internal combustion engine and with regard to pollutant emissions is disadvantageous. The excess fuel is discharged unburned from the cylinders of the internal combustion engine, which is why in a rich operation, in particular, the concentration of unburned hydrocarbons in the exhaust gas is significantly increased.

An enrichment should therefore only be made if it is indispensable or recommended for the protection of the internal combustion engine from overheating. For the same reasons, a rich operation should be maintained only if such operation is indispensable.

It is therefore advantageous to increase the air ratio λ according to the method _{variant in question} as soon as the cylinder head temperature T _cyl permits this, ie, _{falls below} a predefinable lower limit temperature T _{limit, down} . In this case, the fuel-air mixture is emaciated again and transferred the internal combustion engine in the stoichiometric or superstoichiometric operation.

The predetermined lower limit temperature T _{Grenz, down} are also advantageous in this respect, embodiments of the method in which the air ratio is increased only again λ, when the cylinder head temperature T _cyl below and is smaller for a predetermined period of time .DELTA.t _down than this lower limit temperature T _{limit , down} .

The above condition for increasing the air ratio λ should help to avoid too frequent or over-hasty change of the operating parameters. Reference is made to what has already been said in connection with the time span Δt _up . _Following the approach in question can be adequately responded to scenarios in which the cylinder head temperature T _{cyl falls} only briefly below the _threshold temperature T _{limit, down} and then rises again or fluctuates around the predetermined limit temperature.

_Embodiments of the method in which the temperature T _{cyl of} the cylinder head is determined by calculation are advantageous.

The arithmetical determination of the cylinder head _temperature T _cyl takes place, for example, by means of simulation, in which models known from the prior art, for example dynamic heat models and kinetic models, are used for determining the heat of reaction generated during the combustion. As input signals for the simulation operating parameters of the internal combustion engine are preferably used, which are already present, that are determined in another context.

The simulation calculation is characterized in that no further components, in particular no sensors, have to be provided in order to determine the temperature, which is favorable in terms of cost. On the other hand, it is disadvantageous that the cylinder head temperature determined in this way is merely an estimated value, which can reduce the quality of the control or regulation of the air ratio λ.

Also advantageous are embodiments of the method in which the temperature T _{cyl of} the cylinder head is _detected by measurement technology directly or indirectly by means of a sensor.

The metrological detection of an exhaust gas temperature is often difficult, since during operation of the internal combustion engine very high temperatures in the exhaust gas can be achieved, and in some Cases, for example, in the interior of an exhaust aftertreatment system, not even possible. In addition, the arrangement of a temperature sensor in the exhaust system can affect the charge exchange in individual cases.

The metrological detection of the cylinder head _temperature T _cyl, however, presents no difficulties. A cylinder head has comparatively moderate temperatures, even when the internal combustion engine has warmed up, and also offers a multitude of possibilities, ie different locations, for arranging a sensor without impairing the functionality of the internal combustion engine.

Process variants are advantageous in which the internal combustion engine is equipped with an engine control and the cylinder head _temperature T _{cyl detected} by means of the sensor is provided as the input variable.

For estimating the cylinder head _temperature T _cyl, it is also possible to use another component temperature, in particular a cylinder block temperature, which, for example, is detected by means of a sensor or calculated by means of a simulation calculation. According to this variant, the temperature of the cylinder head is determined indirectly - using a different temperature.

In a liquid-cooled internal combustion engine, it is furthermore possible to determine, ie estimate, the cylinder head temperature T _cyl using the temperature of the coolant or a mixing temperature of a component temperature and a coolant temperature.

Process variants in which the temperature is determined at the location of the head at which a very high or the maximum head temperature is reached or expected are advantageous.

Also, a cylinder head temperature T _cyl are detected at a site to determine the temperature T _cyl elsewhere in the head, ie estimated, namely for a place to which the predetermined limit temperature applies. This procedure, ie to detect the temperature at one point by measurement and to specify the limit temperature for another location, is basically possible, but requires the transformation of the temperature for comparison.

Advantageous embodiments of the method in which the internal combustion engine is equipped with a liquid cooling, wherein at least one coolant jacket is integrated to form the liquid cooling in the at least one cylinder head, which belongs to a coolant coolant circuit. Due to the high heat capacity of a liquid can be removed with a liquid cooling very large amounts of heat.

In this connection, embodiments of the method are advantageous, in which water, preferably water mixed with additives, is used as the coolant.

Water has the advantage over other coolants that it is non-toxic, readily available and inexpensive and also has a very high heat capacity, which is why water is suitable for the removal and removal of very large amounts of heat, which allows the use of a comparatively small sized radiator ,

However, embodiments of the method may also be advantageous in which oil, preferably the engine oil of the internal combustion engine, is used as the coolant. Oil has a lower heat capacity compared to water, whereby the cooling performance of the liquid cooling is noticeably reduced, which may be desirable in individual cases.

The use of oil as a coolant has advantages, especially since oil is used in the operation of an internal combustion engine for lubrication and in general already as a process fluid. When using oil as a coolant, the coolant circuit can - contrary to its original purpose - be used after a cold start advantageously for the rapid heating of the oil. As a result, the friction of the internal combustion engine can be reduced during the warm-up phase.

As already mentioned, in internal combustion engines equipped with liquid cooling process _variants may be advantageous in which the temperature T _{cyl of} the cylinder head is determined using a coolant temperature.

Also advantageous in a liquid-cooled internal combustion engine are embodiments of the method in which the temperature T _{cyl of} the cylinder head is determined using a mixing temperature of a component temperature and a coolant temperature.

If the cylinder head temperature is determined by means of a sensor, in the case of liquid-cooled internal combustion engines, it is also advantageous to have process variants in which the sensor for detecting the cylinder head temperature is arranged in the at least one coolant jacket of the cylinder head.

If the at least one cylinder head has two or more coolant jackets, the outlet-side coolant jacket can be water-cooled and the inlet-side coolant jacket can be made oil-cooled.

If the internal combustion engine has two or more coolant shells, an exhaust-side coolant jacket or coolant shroud of the exhaust system can also be oil-cooled for the purpose of faster oil heating during the warm-up phase.

The second sub-task, namely to provide an internal combustion engine for carrying out a method of the type mentioned above, is achieved by an internal combustion engine with at least one cylinder head, which has at least one cylinder and which is characterized in that a sensor is provided which has a temperature T _cyl of Cylinder head detected.

The statements already made for the method according to the invention also apply to the internal combustion engine according to the invention, which is why reference is generally made at this point to the statements made with regard to the method.

In accordance with the method according to the invention, the air ratio λ is controlled or regulated as a function of a cylinder head _temperature T _cyl . For detecting the temperature, the internal combustion engine according to the invention is equipped with a sensor. The basis of decision for the enrichment of the fuel-air mixture is the cylinder head temperature detected with this sensor and not the exhaust gas temperature as in the prior art.

Embodiments of the internal combustion engine in which liquid cooling is provided are advantageous, with at least one coolant jacket, which belongs to a coolant-carrying coolant circuit, in which at least one cylinder head is integrated in order to form the liquid cooling.

Embodiments of the liquid-cooled internal combustion engine in which the sensor for detecting the cylinder head temperature is arranged in the at least one coolant jacket of the cylinder head are advantageous.

Embodiments of the liquid-cooled internal combustion engine in which the sensor for detecting the cylinder head temperature is arranged adjacent to the at least one coolant jacket are also advantageous.

If the cylinder head temperature is to be determined by means of a sensor and if, for example, the sensor is arranged in the coolant jacket of the cylinder head adjacent to a wall of the cylinder head, the sensor generally detects a mixing temperature of component and coolant temperature. The cylinder head temperature to be determined is therefore a cylinder head temperature colored by the coolant temperature, which is also referred to as the mixing temperature in the context of the present invention.

In the following, the invention is based on an embodiment of the internal combustion engine for carrying out the method according to 1 described in more detail. Hereby shows:

1 schematically a first embodiment of an internal combustion engine.

1 schematically shows a first embodiment of an internal combustion engine 1 for carrying out the method for limiting the thermal load.

It is a four-cylinder in-line engine 1 with direct injection, in which the four cylinders 3 along the longitudinal axis of the cylinder head 6 , ie arranged in series, and each with an injector 20 equipped to inject fuel. The injectors 20 are individually via control line 19 by means of motor control 17 activated, ie controlled. The injected amount of fuel serves to adjust the air ratio λ.

For discharging the hot combustion gases is an exhaust pipe 4 and to supply the cylinders 3 with fresh air or fresh mixture a suction line 2 intended. To adjust the load is in the intake pipe 2 a throttle valve serving as a shut-off element 18 also provided by the engine control 17 is controlled or regulated.

The internal combustion engine 1 is for the purpose of charging with an exhaust gas turbocharger 7 equipped, being in the exhaust pipe 4 a turbine 7a and in the intake pipe 2 a compressor 7b are arranged. The turbine 7a the exhaust gas turbocharger 7 has a bypass line. That of the internal combustion engine 1 supplied fresh air is in the compressor 7b compressed, including the enthalpy of the exhaust gas flow in the turbine 7a is being used. The charge increases the thermal load of the internal combustion engine 1 ,

Downstream of the compressor 7b is a charge air cooler 5 in the intake pipe 2 arranged to lower the temperature of the compressed charge air. In this way, the density of the air is increased, resulting in better filling of the cylinder 3 can be realized.

The internal combustion engine 1 is also with an exhaust gas recirculation 8th fitted. A return line 9 branches upstream of the turbine 7a from the exhaust pipe 4 and discharges downstream of the intercooler 5 in the intake pipe 2 , The recirculated exhaust gas is thus not through the intercooler 5 Run and can this cooler 5 do not pollute.

For cooling the recirculated exhaust gas is in the line 9 an additional cooler 10 provided, which lowers the temperature of the recirculated exhaust gas. Also in the return line 9 is for controlling the exhaust gas recirculation rate serving as an EGR valve shut-off 11 arranged.

In the 1 illustrated internal combustion engine 1 is liquid cooled. To form a liquid cooling 12 has the cylinder head 6 via an integrated coolant jacket. The coolant leading coolant circuit is powered by a pump 14 for conveying the coolant and serving as a cooler heat exchanger 13 added.

That in the internal combustion engine 1 or in the cylinder head 6 heated coolant is used in the 1 illustrated embodiment used to the cabin heater 22 a heating cycle 21 with a heated process liquid, namely the heated coolant to supply, in order to heat the interior of a vehicle.

To vent the coolant circuit is a vent line 23 provided, in which a compensating vessel 24 is arranged.

The temperature T _{cyl of} the cylinder head 6 is by means of a sensor 16 metrologically detected and the engine control 17 the internal combustion engine 1 provided as an input variable, wherein for limiting the thermal load of the internal combustion engine 1 the air ratio λ is decreased if the cylinder head temperature T _cyl exceeds a predetermined upper limit temperature T _{Grenz, up} and _up larger for a predetermined period of time .DELTA.t than this upper limit temperature T _{Grenz, up.}

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

suction

3

cylinder

4

exhaust pipe

5

Intercooler

6

cylinder head

7

turbocharger

7a

turbine

7b

compressor

8th

Exhaust gas recirculation

9

Line for exhaust gas recirculation

10

cooler

11

Shut-off element, EGR valve

12

liquid cooling

13

heat exchangers

14

pump

15

Coolant outlet

16

sensor

17

motor control

18

throttle

19

control line

20

injector

21

Heating circuit

22

cabin heating

23

vent line

24

Compensation vessel air ratio

T _cyl

CHT

T _{border, down}

predeterminable lower limit temperature

T _{border, up}

predefinable upper limit temperature

Δt _down

predeterminable minimum period for falling below T _{limit, down}

Δt _up

specifiable minimum period for exceeding T _{limit, up}

Claims (15)

Method for limiting and reducing the thermal load of an internal combustion engine ( 1 ) with at least one cylinder head ( 6 ), which has at least one cylinder ( 3 ), characterized in that - a temperature T _{cyl of} the cylinder head ( 6 ), and - the air ratio λ is reduced if the cylinder head temperature T _{cyl exceeds} a specifiable upper limit temperature T _{limit, up} with T _cyl ≥ T _{limit, up} . A method according to claim 1, characterized in that the air ratio λ is only reduced when the cylinder head temperature T _{cyl exceeds} the predetermined upper limit temperature T _{limit, up} and for a predetermined period of time .DELTA.t _{up is} greater than this upper limit temperature T _{limit, up} . A method according to claim 1 or 2, characterized in that the air ratio λ, starting from a stoichiometric operation (λ ≈ 1) of the internal combustion engine ( 1 ), whereby the internal combustion engine ( 1 ) is converted into a substoichiometric operation (λ <1). Method according to one of the preceding claims, characterized in that the air ratio λ, starting from a substoichiometric operation (λ <1) of the internal combustion engine ( 1 ) is increased again, if the cylinder head _temperature T _cyl a specifiable lower limit temperature T _{limit, down} below T _cyl ≤ T _{limit, down} . A method according to claim 4, characterized in that the air ratio λ is only increased again when the cylinder head temperature T _{cyl falls below} the predetermined lower limit temperature T _{limit, down} and for a predetermined period .DELTA.t _{down is} less than this lower limit temperature T _{limit, down} . Method according to one of the preceding claims, characterized in that the temperature T _{cyl of} the cylinder head ( 6 ) is determined by calculation. Method according to one of claims 1 to 5, characterized in that the temperature T _{cyl of} the cylinder head ( 6 ) metrologically by means of sensor ( 16 ) is detected. Method according to Claim 7, characterized in that the internal combustion engine ( 1 ) with a motor control ( 17 ) and by means of sensor ( 16 ) detected cylinder head _temperature T _cyl is provided as an input. Method according to one of the preceding claims, characterized in that the internal combustion engine ( 1 ) with a liquid cooling ( 12 ), whereby to form the liquid cooling ( 12 ) in the at least one cylinder head ( 6 ) at least one coolant jacket is integrated. A method according to claim 9, characterized in that water is used as the coolant. A method according to claim 9, characterized in that engine oil is used as the coolant. Method according to one of the preceding claims for limiting and reducing the thermal load of an internal combustion engine ( 1 ), which are cooled with liquid ( 12 ), characterized in that the temperature T _{cyl of} the cylinder head ( 6 ) is determined using a coolant temperature. Method according to one of the preceding claims for limiting and reducing the thermal load of an internal combustion engine ( 1 ), which are cooled with liquid ( 12 ), characterized in that the temperature T _{cyl of} the cylinder head ( 6 ) is determined using a mixing temperature of a component temperature and a coolant temperature. Internal combustion engine ( 1 ) with at least one cylinder head ( 6 ) for performing a method according to one of the preceding claims, the at least one cylinder ( 3 ), characterized in that a sensor ( 16 ) is provided, which has a temperature T _{cyl of} the cylinder head ( 6 ) detected. Internal combustion engine ( 1 ) according to claim 14, characterized in that a liquid cooling ( 12 ) is provided, wherein to form the liquid cooling ( 12 ) at least one coolant jacket, which belongs to a coolant-carrying coolant circuit, in the at least one cylinder head ( 6 ) is integrated.

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