DE102010017790A1 - Method for limiting and decreasing thermal load of liquid-cooled internal-combustion engine, involves determining temperature of cooling agent - Google Patents

Abstract

The method involves determining a temperature (T-cooling) of a cooling agent. The air ratio is reduced, if the cooling agent temperature exceeds a given upper limit temperature. The air ratio is reduced by a stoichiometric operation of an internal-combustion engine (1). An independent claim is also included for a liquid-cooled internal-combustion engine with a cylinder head.

Description

The invention relates to a method for limiting and reducing the thermal load of a liquid-cooled internal combustion engine having at least one cylinder head, the at least one cylinder and to form a liquid cooling at least one integrated in the cylinder head coolant jacket, wherein the coolant jacket belongs to a coolant leading coolant circuit.

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-like the internal combustion engine according to the invention-also has liquid cooling, a plurality of coolant channels or at least one coolant jacket are usually formed in the cylinder head, which guide the coolant through the cylinder head. This requires 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 engine or the cylinder head, so that increased demands are placed on the cooling.

The heat released during combustion by the exothermic, chemical conversion of the fuel is partly dissipated via the walls delimiting the combustion chamber to the cylinder head and the cylinder block and partly via the exhaust gas flow to the adjacent components and the environment. In order to keep the thermal load of the engine within limits, a part of the introduced into the cylinder head or in the block heat flow must be withdrawn from the cylinder head or block again. The amount of heat dissipated from the surface of the internal combustion engine via radiation and heat conduction to the environment is not sufficient for efficient cooling, which is why, as a rule, cooling is deliberately brought about by means of forced convection.

In principle, it is possible to carry out the 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 the liquid cooling much larger amounts of heat than is possible with air cooling. Therefore, internal combustion engines are increasingly being equipped with liquid cooling. Such, d. H. Liquid-cooled internal combustion engine is also the subject of the present invention.

Liquid cooling requires the equipment of the internal combustion engine or the cylinder head with a coolant jacket, ie the arrangement of the refrigerant through the cylinder head leading coolant channels, which is a complex Structure of the cylinder head construction conditionally. The heat must not be directed to the cylinder head surface as in air cooling, to be dissipated. The heat is already in the interior of the cylinder head to the coolant, usually mixed with additives added water. The coolant is conveyed by means of a pump arranged in the cooling circuit, so that it circulates in the coolant jacket. The heat emitted to the coolant heat is dissipated in this way from the interior of the cylinder head and removed from the coolant in a heat exchanger again. The heat exchanger is this often and preferably arranged in the front-end region of the vehicle, where a sufficiently large air flow ensures the required heat exchange between the coolant and air.

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.

In order to ensure a safe, trouble-free operation of the internal combustion engine or to optimize the operation of the internal combustion engine, further heat exchangers, in particular cooling devices, are provided.

On the intake side of an internal combustion engine, a charge air cooler is often arranged. The intercooler lowers the temperature of the intake fresh air or of the sucked fresh mixture and thus increases the density of the cylinder fresh charge. In this way, the cooler 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.

The cooling of the charge air by means of intercooler is used primarily to increase the performance of the internal combustion engine. The air required for the combustion process is compressed due to the cooling, whereby each cylinder per cycle can be supplied with a larger air mass. As a result, the fuel mass and thus the medium pressure can be increased.

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.

In order to provide a sufficiently high air mass flow to the heat exchangers of the cooling systems, ie the cooling devices, even at a standstill, ie 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, ie set in rotation. The fan motors are usually operated electrically and can heat transfer in the Always support heat exchangers at any operating point. The control of such fan motors is done according to the prior art by means of motor control.

The large number of heat exchangers and the constant increase in the amount of heat to be dissipated often lead to conflicts, in particular with regard to the dimensioning and arrangement of the individual heat exchangers in the engine compartment.

The heat transfer surfaces of the heat exchangers can not be increased arbitrarily and the arrangement of the individual heat exchangers in the front-end area and each other is often problematic due to the limited space available.

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 heat exchanger, d. H. 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.

Ideally, the cooling capacity of the liquid cooling system, including the heat dissipating surface, should be designed for operating conditions characterized by high loads coupled with low vehicle speeds, such as those encountered during acceleration and upheaval, even in the most adverse conditions To deliver cooling power. Under such conditions, the radiator has to dissipate comparatively large amounts of heat without the airflow required or sufficient for heat dissipation being sufficiently available in the front-end region of the vehicle.

The design of the cooling in view of the scenario described above leads to excessively large radiators, which can be difficult to accommodate in the front-end area of the vehicle, the other heat exchangers in arrangement and dimensioning severely limit and in normal driving are not required , d. H. apart from a few exceptional situations are actually dispensable.

According to the prior art, therefore, further measures are often taken 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 additional 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 temperature 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 reduction in temperature due to emaciation is much lower than when enriched because the excess air, unlike the excess fuel, does not have to be evaporated.

In the prior art, the exhaust gas temperature is used as an input variable or controlled variable in the control or regulation of the enrichment, without taking into account whether the liquid cooling is already operating at the power limit or the requested cooling capacity is still able to provide.

In view of the above, it is an object of the present invention to provide a method for limiting and reducing the thermal load of a liquid-cooled internal combustion engine according to the preamble of claim 1, wherein the operating state of the liquid cooling is taken into account.

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

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

The first sub-task is solved by a method for limiting and reducing the thermal load of a liquid-cooled internal combustion engine with at least one cylinder head having at least one cylinder and for forming a liquid cooling at least one integrated in the cylinder head coolant jacket, wherein the coolant jacket belongs to a coolant-carrying coolant circuit, which is characterized in that

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

According to the invention, the air ratio λ is varied as a function of a coolant temperature T _cooling . In order to limit or reduce the thermal load on the internal combustion engine, the fuel-air mixture is enriched, ie, the reduction of the air ratio λ as soon as the coolant temperature T _cooling exceeds a critical value.

Thus, the inventive method for controlling or regulating the heat balance of the internal combustion engine directly on the liquid cooling. Whether enrichment is carried out or not is decided on the basis of the current operating state of the liquid cooling. In this way, it is avoided that the liquid cooling is operated beyond its power limit and the engine less heat is removed than required or desired. As soon as liquid cooling reaches its maximum cooling capacity in a specific operating point of the internal combustion engine, the enrichment is activated as an additional measure for lowering the temperature, ie. H. used to satisfy a currently available cooling demand and to limit or reduce the thermal load of the internal combustion engine.

The liquid cooling or belonging to the cooling circuit heat exchanger need not be designed in view of the worst possible operating conditions, such as a Berganfahrt to avoid a thermal overload of the engine safely, because the liquid cooling, d. H. the coolant temperature is monitored in the context of the method according to the invention, whereby an overload of the cooling and thus overheating of the internal combustion engine due to insufficient cooling is reliably prevented.

The fact that the coolant temperature and not the exhaust gas temperature is used as the input variable or controlled variable in the enrichment, as already mentioned - an overload of the liquid cooling is prevented. It should be noted that liquid cooling overload is usually associated with overheating of the coolant and excessive evaporation of coolant. Due to the coolant, which is only present in some regions in vapor form, a reduced heat removal occurs, which can lead to material deposits. In addition, it may cause damage due to cavitation. With the method according to the invention, excessive evaporation of the coolant and damage due to cavitation can be reliably prevented.

With the method according to the invention, the first object underlying the invention is achieved, namely to show a method for limiting and reducing the thermal load of a liquid-cooled internal combustion engine, which takes into account the operating state of the liquid cooling.

Regardless of the procedure according to the invention, namely the enrichment as a function of the coolant temperature, 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.

Embodiments of the method are advantageous in which water, preferably water added 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, which noticeably reduces the cooling capacity of the liquid cooling system.

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.

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 coolant temperature T _cooling 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} .

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 coolant temperature T _cooling 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 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, the enrichment does not always allow the internal combustion engine to be operated in the manner required, for example, for a proposed exhaust aftertreatment system.

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, using catalytic materials which increase the speed of certain reactions, ensure oxidation of HC and CO even at low temperatures. If, in addition, nitrogen oxides are to be reduced, this can be achieved by using a three-way catalytic converter, which, however, requires a narrow-flow stoichiometric operation (λ≈1) for this purpose. 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 exhaust gas temperature. This is accompanied by a reduction in component temperatures. 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 exhaust gas temperature or component temperature in the individual case may initially increase, since first the excess air of the lean fuel-air mixture is reduced before a transition to a rich substoichiometric mixture takes place.

Embodiments of the method in which the air ratio λ is increased again starting from a substoichiometric operation (λ <1) of the internal combustion engine are advantageous if the coolant temperature T _cooling falls below a specifiable lower limit temperature T _{limit, down} with T _cooling ≦ 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 coolant temperature T _cooling 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.

Also advantageous in this context are embodiments of the method in which the air ratio is increased only again λ, when the coolant temperature T _cooling the predeterminable lower limit temperature T _{Grenz, down} below and is smaller for a predetermined period of time .DELTA.t _down than this lower limit temperature T _{Grenz, 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 proposed procedure, it is possible to react appropriately to scenarios in which the coolant temperature T _cooling falls only briefly below the limit temperature T _{limit, down} and then increases again or fluctuates around the predetermined limit temperature.

Embodiments of the method in which a temperature T _{cooling of} the coolant is determined by calculation are advantageous.

The mathematical determination of the coolant temperature takes place by means of simulation, in which models known from the prior art, for example dynamic heat models and kinetic models, are used to determine 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, d. H. be determined in a different 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 cooling 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.

In order to estimate the coolant temperature T _cooling, it is also possible to use a component temperature, in particular a cylinder head temperature, or a mixing temperature from a component temperature and a coolant temperature, which is detected by means of a sensor, for example by measurement. According to this variant, the temperature of the coolant is determined indirectly - using a different temperature.

Also advantageous are embodiments of the method in which a temperature T _{cooling of} the coolant is detected by measurement technology directly or indirectly by means of a sensor.

The metrological detection of a temperature can often be difficult or even impossible. This applies, for example, to the metrological detection of the temperature of an exhaust aftertreatment system, in which both the extremely high temperatures and the lack of ability to arrange a temperature sensor in the exhaust aftertreatment system cause problems.

The metrological detection of the coolant temperature, however, presents no difficulties. The coolant has comparatively moderate temperatures even when the internal combustion engine has warmed up. The coolant circuit also offers a variety of possibilities, d. H. different locations, for the placement of a sensor, without the functionality of the liquid cooling would be affected.

If the coolant temperature is detected by means of a sensor, embodiments of the method are advantageous in which the sensor for detecting the coolant temperature is arranged adjacent to an outlet of the coolant circuit from the at least one cylinder head.

The arrangement of the sensor downstream of the cylinder head, according to the above embodiment concretely in the region of the coolant outlet from the cylinder head, ensures that the temperature is detected at a point of the cooling circuit, at which the coolant has already undergone a significant increase in temperature, after that Flowed through the cylinder head and absorbed heat. This is advantageous if the coolant temperature is compared with a coolant temperature considered to be maximally admissible for the exit as the upper limit temperature T _{limit, up} .

If, however, the temperature is detected at the inlet to the cylinder head, an estimate of the temperature increase in the cylinder head would be required here in order to determine the coolant temperature T _cooling at the outlet.

Under the aspect mentioned above, it is particularly advantageous to determine the temperature at the point in the cooling circuit where the coolant reaches the maximum temperature.

According to an alternative variant of the method, however, the sensor for detecting the coolant temperature may in principle also be arranged adjacent to an inlet of the coolant circuit into the at least one cylinder head. In this case, an upper limit temperature T _{limit, up} can be specified for the entry or the temperature detected at the inlet is used to determine the coolant temperature elsewhere in the cooling circuit, ie estimate, for a point to which the predetermined limit temperature refers. The latter procedure, ie to detect the temperature at one point metrologically and to specify the limit temperature for another location is basically possible, but requires for comparison purposes the transformation of the coolant temperature. An arrangement of the sensor immediately upstream of a heat exchanger provided in the cooling circuit may also be advantageous.

If the coolant temperature is determined by means of a sensor, it is also advantageous to use variants of the method in which the sensor is arranged near the highest point of the coolant circuit. Preferably, here the venting of the cooling circuit takes place, since the vaporized, superheated coolant collects at the highest point of the cycle.

Embodiments of the method in which the sensor for detecting the coolant temperature is arranged on the cylinder head are advantageous.

In this context, method variants are advantageous in which the sensor for detecting the coolant temperature is arranged in the at least one coolant jacket of the cylinder head.

Process variants in which the internal combustion engine is equipped with an engine control and the coolant temperature or component temperature detected by means of a sensor are provided as an input variable are advantageous.

The second sub-task, namely to provide an internal combustion engine for carrying out a method of the type mentioned above, is achieved by a liquid-cooled internal combustion engine having at least one cylinder head, the at least one cylinder and to form a liquid cooling at least one integrated in the cylinder head coolant jacket, wherein the coolant jacket to a Coolant leading coolant circuit is heard, and which is characterized in that a sensor is provided which detects a temperature T _{cooling of} the coolant.

What has already been said for the method according to the invention also applies to the internal combustion engine according to the invention, which is why reference is generally made at this point to the statements made above with regard to the method.

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

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

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

Embodiments of the liquid-cooled internal combustion engine in which the sensor for detecting the coolant 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 coolant temperature is arranged adjacent to a wall of the cylinder head are advantageous.

If the coolant 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 coolant temperature to be determined is consequently a coolant temperature which is colored by the component temperature of the cylinder head and which is also referred to as the mixing temperature in the context of the present invention.

In the following the invention with reference to 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 a liquid-cooled 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 for the injection of fuel are equipped. 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.

The temperature T _{cooling of} the coolant is determined by means of a sensor 16 detected by measurement, wherein the sensor 16 near the exit 15 the coolant circuit from the cylinder head 6 is arranged.

The from the sensor 16 detected coolant temperature T _cooling is 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 coolant temperature T _cooling a predeterminable upper limit temperature T _{Grenz, up} and exceeds _up larger for a predetermined period of time .DELTA.t than this upper limit temperature T _{Grenz, up.}

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

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.

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 _cooling

Coolant temperature

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 a liquid-cooled internal combustion engine ( 1 ) with at least one cylinder head ( 6 ), which has at least one cylinder ( 3 ) and to form a liquid cooling ( 12 ) at least one in the cylinder head ( 6 ), wherein the coolant jacket belongs to a refrigerant circuit leading coolant, characterized in that - a temperature T _{cooling of} the coolant is determined, and - the air ratio λ is reduced, if the coolant temperature T _cooling a predetermined upper limit temperature T _{limit, up} exceeds with T _cooling ≥ T _{limit, up} . A method according to claim 1, characterized in that the air ratio is λ reduced only when the coolant temperature T _cooling the predetermined upper limit temperature T _{Grenz, up} exceeds and larger for a predetermined period of time .DELTA.t _up than this upper limit temperature T _{Grenz, up.} A method according to claim 1 or 2, characterized in that the air ratio λ starting from a stoichiometric operation (λ1) 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 coolant temperature T _cooling falls below a predefinable lower limit temperature T _{limit, down} with T _cooling ≦ T _{limit, down} . A method according to claim 4, characterized in that the air ratio λ is only increased again when the coolant temperature T _cooling the predetermined lower limit temperature T _{limit, down} below and for a predetermined period of time .DELTA.sub.down _down is lower than this lower limit temperature T _{limit, down} . Method according to one of the preceding claims, characterized in that a temperature T _{cooling of} the coolant is determined by calculation. Method according to one of claims 1 to 5, characterized in that a temperature T _{cooling of} the coolant by measurement means by means of sensor ( 16 ) is detected. Method according to claim 7, characterized in that the sensor ( 16 ) for detecting the coolant temperature adjacent to an exit ( 15 ) of the coolant circuit from the at least one cylinder head ( 6 ) is arranged. Method according to claim 7, characterized in that the sensor ( 16 ) for detecting the coolant temperature adjacent to an entry of the coolant circuit into the at least one cylinder head ( 6 ) is arranged. Method according to one of claims 7 to 9, characterized in that the sensor ( 16 ) is arranged to detect the coolant temperature at the highest point of the coolant circuit. Method according to one of claims 7 to 10, characterized in that the internal combustion engine ( 1 ) with a motor control ( 17 ) and by means of sensor ( 16 ) detected coolant temperature is provided as an input. Liquid-cooled 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 ) and to form a liquid cooling ( 12 ) at least one in the cylinder head ( 6 ), wherein the coolant jacket belongs to a coolant-carrying coolant circuit, characterized in that a sensor ( 16 ) is provided, which _detects a temperature T _{cooling of} the coolant. Liquid-cooled internal combustion engine ( 1 ) according to claim 12, characterized in that the sensor ( 16 ) for detecting the coolant temperature adjacent to an exit ( 15 ) of the coolant circuit from the at least one cylinder head ( 6 ) is arranged. Liquid-cooled internal combustion engine ( 1 ) according to claim 12, characterized in that the sensor ( 16 ) for detecting the coolant temperature adjacent to an entry of the coolant circuit into the at least one cylinder head ( 6 ) is arranged. Liquid-cooled internal combustion engine ( 1 ) according to claim 12, characterized in that the sensor ( 16 ) to record the Coolant temperature is located near the highest point of the coolant circuit.

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