DE102023113312B3 - Compressor protection function to maintain the compressor outlet temperature, control device, internal combustion engine and vehicle - Google Patents

Abstract

Model-based protection method for maintaining a limit temperature of a compressor component in a compressor for an internal combustion engine, comprising determining a cylinder charge based on a compressor model that applies the isentropic compression of a gas, a pressure upstream of the compressor, a temperature upstream of the compressor and a target efficiency of the compressor and setting an operating state of the internal combustion engine based on the determined cylinder charge such that the limit temperature of the compressor component is not exceeded.

Description

The invention relates to a compressor protection function for maintaining the compressor outlet temperature, a control device, an internal combustion engine and a vehicle.

It is known that driving situations such as fast gear shifting when driving uphill under full load can cause the upper temperature limit specified by the component manufacturer to be exceeded on the compressor wheel. The temperature measurement technology that is installed as standard cannot detect these temperature exceedances due to the low dynamics of the measured values (or inertia of the measurement) and a temperature offset. The sensor in question is primarily used to control (monitor) the charge air cooling and is positioned at the inlet of the charge air cooler. This sensor cannot therefore be used to prevent the temperature from being exceeded on the compressor.

There are already design solutions for reducing the component temperature using external cooling. In a biturbo engine, there is also the option of intermediate cooling of the charge air after the first compression stage. This means that the temperature at the inlet of the high-pressure compressor can be reduced and, as a result, the temperature at the outlet of the high-pressure compressor can also be reduced.

There are also software-based concepts for limiting cylinder filling. However, these do not relate to protecting the compressor.

DE 10 2017 212 280 A1 discloses a method for protecting a compressor in which a maximum target boost pressure is determined.

DE 101 11 774 A1 discloses a method and a corresponding device for determining the air outlet temperature of the compressor of an exhaust gas turbocharger of a motor vehicle. The air outlet temperature is derived from the speed of the compressor and the air inlet temperature of the compressor, with a speed-dependent compressor efficiency map being used in particular.

DE 10 2009 000 896 B4 discloses a method for determining the outlet temperature of the compressor of a turbocharger of an internal combustion engine, wherein the outlet temperature is determined from the inlet temperature of the compressor, the efficiency of the compressor and the compressor pressure ratio, wherein the efficiency of the compressor is determined by means of a predetermined two-dimensional function of the efficiency of the rotational speed and a further operating parameter of the turbocharger, characterized in that the further operating parameter on the basis of which the efficiency of the compressor is determined is the compressor pressure ratio.

DE 10 2017 222 593 A1 discloses a method for determining a target intake manifold pressure of an internal combustion engine by means of an iterative method, wherein a cylinder charge is determined for an intake manifold pressure iterated during the iterative method and the target intake manifold pressure is determined as a function of the determined cylinder charge. Furthermore, a control device for carrying out the method is disclosed.

The object of the present invention is to provide a compressor protection function for maintaining the compressor outlet temperature, which at least partially overcomes the above-mentioned disadvantages.

This object is achieved by the model-based protection method according to the invention according to claim 1. This object is also achieved by the control device according to the invention according to claim 8, the internal combustion engine according to the invention according to claim 9 and the vehicle according to the invention according to claim 10.

Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

The design solutions are disadvantageous in terms of the integration of additional components for packaging and thus cause additional effort in production. A software-based protection function (protection procedure) by modeling the temperature or boost pressure at the compressor outlet can be used flexibly in various engine variants according to the Euro 7 emissions standard - such as mono- or biturbo engines - with control (regulation) using a cylinder-filling-based gas system.

The target cylinder charge is limited based on a modeled temperature or a modeled pressure at the compressor outlet. The system does not react to a measurement of a temperature being exceeded, but rather uses target values to determine whether an operating state of the internal combustion engine that has yet to be set is an operating state in which the limit temperature of the compressor would be exceeded, whereupon the cylinder charge is limited. Sensor-based solutions have the disadvantage that protective intervention is often only carried out when a Exceeding the limit temperature is already measured. This is due to the inertia of the sensor or the installation position (temperature transport effect).

A model-based protection method according to the invention for maintaining a limit temperature of a compressor component in a compressor for an internal combustion engine, comprising determining a cylinder charge based on a compressor model that applies the isentropic compression of a gas, a pressure upstream of the compressor, a temperature upstream of the compressor and a target efficiency of the compressor and setting an operating state of the internal combustion engine based on the cylinder charge so that the limit temperature of the compressor component is not exceeded.

The compressor is, for example, the compressor of an exhaust gas turbocharger. The compressor component can be, for example, a compressor wheel. The limit temperature of the compressor component (the compressor) can be a maximum temperature that is specified for the compressor component.

If the temperature after the compressor is not measured by a temperature sensor directly on the compressor, but rather, for example, with a temperature sensor in front of the charge air cooler, the measured values are subject to a temperature offset and delayed dynamics. This temperature sensor is therefore not suitable for a limit temperature on the compressor that is also dynamically effective.

Instead of constructive solutions such as a second temperature sensor or cooling of the compressor, a software-based approach offers a reduction in the number and complexity of components. In general, the protection procedure intervenes when an extreme driving situation occurs, for example under full load, in a hot environment, with a hot engine, when towing a trailer, driving uphill or a combination of the aforementioned driving situations. Constructive solutions also reach their limits in such situations. For example, cooling of the compressor housing or cooling of the charge air between two compressors may be reduced because the coolant or cooling air is already warm. This means that protection against overheating of the compressor cannot be guaranteed under such circumstances.

The limit temperature is based on an upper thermal load limit of the compressor component (the compressor). Such a limit temperature can also be maintained if no sensor is installed directly on the compressor.

The cylinder charge is the amount of all gases per stroke that are filled (flow) into the cylinder (the cylinder volume) of the internal combustion engine. This happens in the intake stroke (intake event) with the prevailing intake manifold pressure. The intake manifold pressure is the pressure before the cylinder and after the intercooler and depends on the boost pressure. The boost pressure is generated by the compressor. This is reduced as a result of the charge air cooling by a pressure drop due to flow losses and a pressure drop due to cooling and increased density of the gas as well as the possible pressure reserve via the throttle valve - which is also located between the compressor and the cylinder inlet. The intake manifold pressure is therefore always lower than the boost pressure. The cylinder charge must therefore be determined using the intake manifold pressure. Limiting the target cylinder charge also limits all other target values in the intake tract of the internal combustion engine, for example the target for the fresh air taken in, the exhaust gas recirculation rate and the compression or target boost pressure. The specific cylinder charge is a cylinder charge that is less than a cylinder charge that would be set without the protection method according to the invention when setting the operating state of the internal combustion engine. Alternatively, the specific cylinder charge is only set if it is less than the cylinder charge that would be set without the protection method according to the invention when setting the operating state of the internal combustion engine.

Thus, this type of limitation has no unwanted influence on the composition of the cylinder charge and thus on the composition of the exhaust gas and can be used in parallel with other controls of the intake tract and exhaust gas of the internal combustion engine or can be integrated into them.

There are designs in which the determination is also based on a pressure after the compressor and, using the compressor model, a temperature after the compressor is determined, on the basis of which the cylinder filling is determined.

The target boost pressure, which is also limited due to the limited cylinder filling, also limits the compression in the compressor and thus the temperature after the compressor. Thus, with a model-based temperature value after the compressor, the temperature of the compressor is kept below a limit temperature.

The model-based temperature is determined based on the isentropic compression of the gas in the compressor. Thus, the cylinder filling is limited by a modeled temperature after the compressor.

As a result, the heat generated during compression is reduced. As a result, the component temperature, for example of the compressor or the compressor wheel, can also be reduced.

The basis of the compressor model is the formula of isentropic compression, which is adjusted according to the temperature after the compressor and takes into account the efficiency of the compressor. $$T_{nV}=T_{vV}\left(1+\frac{1}{{\eta }_{isen}}\left[{\left(\frac{p_{nV}}{p_{vV}}\right)}^{\frac{\kappa -1}{\kappa }}-1\right]\right).$$

Here, p _vV is the pressure before the compressor, p _nV is the pressure after the compressor, T _yV is the temperature before the compressor, η _isen is the isentropic target efficiency of the compressor and ĸ is the isentropic exponent of the intake air. The modeled temperature T _nV after the compressor is used to comply with the thermal load limit of the component. The load limit can be variably adjusted depending on the component. The other input values are measured or model values. In particular, the input values can be determined from target values of the intake tract of the internal combustion engine. This makes it possible to detect an exceedance of the load limit or limit temperature in an operating state of the internal combustion engine that has yet to be set and to prevent this by limiting the cylinder filling.

The limitation concept can be used for various engine concepts that are equipped with single- or two-stage charging and whose gas system is designed based on cylinder filling. For an engine with single-stage charging, the conditions before the compressor are assumed as input variables. For two-stage charging, however, the conditions between the two compressors are included as input variables in the formula for isentropic compression. These input variables can in turn be determined using the formula for isentropic compression.

The pressure upstream of the compressor can be calculated, for example. The pressure upstream of a high-pressure compressor, i.e. the second stage, can be calculated using isentropic compression. The temperature upstream of the first compressor depends on the fresh air mass flow and its temperature as well as the EGR mass flow and its temperature.

The temperature after the first compressor depends on an optional compressor housing cooling, an EGR rate, the temperature before the compressor, the compressor efficiency (isentropic) and the pressure ratio across the compressor. This corresponds to the dependencies of the isentropic compression model of the compressor, where the EGR rate influences the isentropic exponent of the gas.

There are designs in which the determined temperature after the compressor is mixed with a measured temperature after the compressor to determine a synthesis temperature after the compressor, on the basis of which the cylinder charge is determined, wherein a mixing factor between the determined and measured temperature after the compressor is determined from an engine torque and, on the basis of the synthesis temperature after the compressor, a correction factor for the cylinder charge is determined which limits the determined cylinder charge.

For example, the temperature measured after the compressor can only be valid when the internal combustion engine is in stationary operation, as the temperature measurement is subject to a certain inertia. This is the case, for example, if a temperature sensor after the compressor is installed primarily to control the charge air cooling.

This stationary valid temperature sensor can then be mixed with the modeled temperature determined from the compressor model, which is more accurate than the temperature sensor in a dynamic operating state of the combustion engine. A synthesis temperature is obtained from the mixture.

Any parameter that describes how dynamic or static the operating state of the internal combustion engine is can be used as a decision criterion as to which of the two temperatures - modeled or measured - is averaged to the synthesis temperature and with what weight. For example, the engine torque or the target boost pressure can be used to form a decision criterion. The decision criterion can also be based on the time derivative of the engine torque or the time derivative of the target boost pressure.

Based on the synthesis temperature determined in this way, a correction factor can then be determined using a characteristic map, which corrects and thus limits the cylinder filling. If, for example, the operating state of the internal combustion engine is dynamic, the modeled temperature is given greater weight in the synthesis temperature or the synthesis temperature corresponds to the modeled temperature. If the modeled temperature exceeds a limit temperature, the cylinder filling is limited.

There are versions in which the determination is also based on a limit temperature of the compressor and a maximum boost pressure after the compressor is determined using the compressor model, on the basis of which the cylinder filling is determined.

Based on the isentropic compression of the gas in the compressor, it is determined which pressure can exist after the compressor without exceeding the limit temperature.

By limiting the boost pressure, the heat generated during compression is also reduced. In the process, the component temperature, for example of the compressor or the compressor wheel, can also be reduced.

The basis of the limitation concept for the boost pressure is the formula of isentropic compression, which is adapted to the limited pressure after the compressor and takes into account the efficiency of the compressor. $$p_{Grenz}=p_{VV}{\left[\left(\left(\frac{T_{Grenz}}{T_{us}}-1\right){\eta }_{isen}\right)+1\right]}^{\frac{\kappa }{\kappa -1}}.$$

Here, p _vV is the pressure before the compressor, T _{limit is} the limit temperature of the compressor, T _vV is the measured temperature before the compressor, η _{isen is} the isentropic target efficiency of the compressor and ĸ is the isentropic exponent of the intake air. The limit temperature T _limit after the compressor describes the thermal load limit of the component and can be variably adjusted depending on the component. The other input values are measured or model values. In particular, the input values can be determined from target values of the intake tract of the internal combustion engine. This means that an exceedance of the load limit or limit temperature can be detected in an operating state of the internal combustion engine that has yet to be set and can be prevented by limiting the cylinder filling.

There are further embodiments comprising selecting a minimum of the calculated maximum boost pressure and a predetermined target boost pressure, determining the cylinder charge for the internal combustion engine based on the selected minimum.

The calculated limit pressure after the compressor (or limited target boost pressure) is compared with the target boost pressure on the control device side in a minimum selection. This ensures that the limitation is only carried out in areas in which the limited target boost pressure is below the target boost pressure on the control device side. If the calculated target boost pressure is above the target boost pressure on the control device side, no limitation is carried out. The value resulting from the minimum selection therefore represents the temperature-limited target boost pressure to be regulated.

The limitation concept is applicable to various engine concepts that are equipped with single- or two-stage charging and whose gas system is designed based on cylinder filling. For an engine with single-stage charging, the conditions before the compressor are assumed as input variables. For two-stage charging, however, the conditions between the two compressors are used as input variables in the formula for isentropic compression to calculate the limited target boost pressure.

The pressure upstream of the compressor can be calculated, for example. The pressure upstream of a high-pressure compressor, i.e. the second stage, can be calculated using isentropic compression. The temperature upstream of the first compressor depends on the fresh air mass flow and its temperature as well as the EGR mass flow and its temperature.

The temperature after the first compressor depends on an optional compressor housing cooling, an EGR rate, the temperature before the compressor, the compressor efficiency (isentropic) and the pressure ratio across the compressor. This corresponds to the dependencies of the isentropic compression model of the compressor, where the EGR rate influences the isentropic exponent of the gas.

There are embodiments in which determining the maximum boost pressure includes filtering the determined maximum boost pressure, selecting the minimum is based on the filtered maximum boost pressure, determining the maximum cylinder charge includes selecting a further minimum from the calculated maximum cylinder charge and a predetermined target cylinder charge, and setting the operating state of the internal combustion engine is based on the further minimum.

Since the boost pressure does not have to be the highest priority variable (reference variable) in the gas system, it can happen that in gas systems whose reference variable is the cylinder filling, all other target values in the gas system remain unchanged and only the target or actual boost pressure are limited. Due to the reduced actual boost pressure in the limitation case, the other target values cannot be regulated due to the limitation. The remaining control deviations in a individual sections result in a limitation of the cylinder filling taking into account the maximum permissible compressor temperature.

With the target cylinder charge as the reference variable, all other target values along the charge air path are calculated and adjusted. This also includes the target boost pressure. In contrast to a pure boost pressure limitation, a cylinder charge-based limitation offers the advantage that all target values along the charge air path are consistent with one another and thus no deviations between target and actual values that are not the target or actual boost pressure arise as a result of the limitation intervention.

The limited target cylinder charge is based on the temperature-limited target boost pressure to be regulated. The target values can be calculated back along the charge air path to the cylinder charge. This means that all actual values along the charge air path are regulated to the corresponding target values consistent with the limited cylinder charge due to the limited target cylinder charge.

The limited target boost pressure is used to calculate the cylinder charge (reference variable) via the intake line. This results in the limited cylinder charge. The charge limitation concept is therefore based on the boost pressure limitation concept, so that this represents an extension. For various charging units - such as the compressor of a turbocharger - it is possible to adjust the thermal load limit accordingly without having to make changes to the function.

This thermal load limit is also dynamically effective. Furthermore, the stationary thermal load limit for the compressor - based on the temperature sensor on the charge air cooler - can also limit the cylinder filling.

Determining the maximum cylinder charge includes selecting a further minimum from the calculated maximum cylinder charge and a predetermined target cylinder charge and adjusting the operating state of the internal combustion engine based on the further minimum.

The resulting limited cylinder filling can in turn be compared with a target cylinder filling from a control device using a minimum selection and adjusted if necessary. In this way, a limitation is only carried out in the necessary areas.

There are embodiments in which determining the maximum boost pressure includes filtering the determined maximum boost pressure and selecting the minimum is based on the filtered maximum boost pressure.

By filtering the determined maximum boost pressure, the minimum selection functions more stably as a decision criterion - whether a limitation needs to be implemented or not.

There are embodiments in which determining the maximum cylinder filling includes filtering the calculated maximum cylinder filling and selecting the further minimum is based on the filtered maximum cylinder filling.

By filtering the determined maximum cylinder filling, the minimum selection functions more reliably as a decision criterion - whether a limitation must be implemented or not.

There are designs where the limit temperature is a maximum permissible compressor outlet temperature.

The outlet temperature of the compressor is equated with the temperature that the compressor or the compressor wheel assumes from the compressed gas.

There are designs in which setting the operating state of the internal combustion engine is regulating the operating state of the internal combustion engine and the cylinder charge is the reference variable for regulating the operating state of the internal combustion engine.

A control device according to the invention is designed to carry out a method according to one of the above embodiments.

An internal combustion engine according to the invention with at least one compressor, a temperature sensor in front of the compressor and a control device as described above.

A vehicle according to the invention with an internal combustion engine as described above.

• 1 schematisch eine Signalsynthese für einen Temperaturwert nach dem Verdichter zur Begrenzung einer Zylinderfüllung nach einem Ausführungsbeispiel;
• 2 schematisch eine Zylinderfüllungskorrektur zur Begrenzung einer Zylinderfüllung nach einem Ausführungsbeispiel;
• 3 ein Flussdiagramm nach einem Ausführungsbeispiel einer Bestimmung einer begrenzten Zylinderfüllung;
• 4 schematisch den Gasfluss durch eine Verbrennungskraftmaschine nach einem Ausführungsbeispiel; und
• 5 ein Fahrzeug mit einer Verbrennungskraftmaschine und einer Steuervorrichtung nach einem Ausführungsbeispiel.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawing.

• 1 schematically shows a signal synthesis for a temperature value after the compressor for limiting a cylinder filling according to an embodiment;
• 2 schematically shows a cylinder filling correction for limiting a cylinder filling according to an embodiment;
• 3 a flow chart according to an embodiment of determining a limited cylinder filling;
• 4 schematically the gas flow through an internal combustion engine according to an embodiment; and
• 5 a vehicle with an internal combustion engine and a control device according to an embodiment.

1 shows schematically a signal synthesis for a temperature value after the compressor for limiting a cylinder filling according to an embodiment.

The signal synthesis 100 comprises a sensor value 101 for the temperature before the charge air cooler, an engine torque 102, a compressor model 103 for the temperature after the compressor, a low-pass filter 104, a subtraction point 105, a modeled temperature 106, an interpolation factor determination 107, a mixer 108 and a synthesis temperature value 109 based on sensor value 101 and the modeled temperature 106.

The sensor value 101 is transmitted to a first signal input of the mixer 108 and the modeled temperature 106 is transmitted to a second signal input of the mixer 108. The mixer 108 mixes (linearly interpolates) a synthesis temperature value 109 based on an interpolation factor determined from the engine torque 102.

The modeled temperature 106 is determined in the compressor model 103. The basis of the compressor model 103 is the formula of isentropic compression, which is rearranged according to the temperature after the compressor and takes into account the efficiency of the compressor. $$T_{nV}=T_{vV}\left(1+\frac{1}{{\eta }_{isen}}\left[{\left(\frac{p_{nV}}{p_{vV}}\right)}^{\frac{\kappa -1}{\kappa }}-1\right]\right).$$

Where p _vV is the pressure before the compressor, p _nV is the pressure after the compressor, T _vV is the temperature before the compressor, η _{isen is} the isentropic target efficiency of the compressor and ĸ is the isentropic exponent of the intake air.

The motor torque 102 is transmitted to the low-pass filter 104, the subtraction point 105 and the interpolation factor determination 107. The low-pass filter 104 filters the motor torque based on a predetermined time constant and transmits the low-pass filtered motor torque to the subtraction point 105.

The subtraction point 105 forms the difference between the low-pass filtered engine torque from the low-pass filter 104 and the engine torque 102. The difference is transmitted to the interpolation factor determination 107.

The interpolation factor determination 107 determines an interpolation factor based on the engine torque 102 and the difference from the subtraction point 105. The interpolation factor is transmitted to the mixer 108.

As described above, the mixer 108 then mixes the sensor value 101 and the modeled temperature 106 based on the interpolation factor and outputs the synthesis temperature value 109. This mixing in the mixer 108 can, for example, be a linear mixing where an interpolation factor that is zero means that the mixed temperature value 109 corresponds to the sensor value 101, an interpolation factor that is one means that the mixed temperature value 109 corresponds to the modeled temperature 106, and an interpolation factor that is 0.5 means that the mixed temperature value 109 corresponds to the average of the sensor value 101 and the modeled temperature 106.

The sensor value 101 of the temperature sensor on the charge air cooler is valid in stationary situations, but is not meaningful in dynamic situations due to the inertia of the temperature measurement. The modeled temperature 106 shows deviations from the actual temperature at the compressor outlet and is "less accurate" than the sensor value 101, particularly in stationary situations. In dynamic situations, however, the modeled temperature 106 is significantly closer to the temperature at the compressor outlet than the sensor value 101.

This results in the combination of both pieces of information, so that in stationary situations the sensor value 101 is adopted and in dynamic situations the modeled temperature 106. The fusion of both values is done via linear interpolation between the two values depending on an interpolation factor.

As shown above, the interpolation factor is generated from the time derivative of the torque (change in torque), which is generated by the difference after the low-pass filtering. Alternatively, the target boost pressure can be used to form the interpolation factor, and the time derivative of the target boost pressure (change in the target boost pressure value) can also be formed. The interpolation factor is also dependent on the absolute values. ten, i.e. on the torque and the target pressure ratio across the compressor.

This is to allow for load dependency to be taken into account in the interpolation. The modeled temperature 106 can thus be hidden in all non-critical load ranges (stationary situations), while it has a more dominant influence on the synthesis temperature 109 in critical load ranges (dynamic situations). Furthermore, the synthesis temperature 109 can also correspond to the modeled temperature 106 if a dynamic situation exists. The modeled temperature 106 is based on the modeling of isentropic compression. The fused temperature (synthesis temperature 109) is used either to correct the cylinder filling, which limits the cylinder filling in the operating state of the internal combustion engine.

2 shows schematically a cylinder filling correction for limiting a cylinder filling according to an embodiment.

The cylinder charge correction 200 includes an index 201, an engine speed 202, a torque input value 203, a synthesis temperature 204, an intake manifold temperature 205, a map 206, a map 207, a buffer memory 208, a buffer memory 209, a multiplication point 210 and a corrected cylinder charge value 211.

The index 201 indicates the parameter space of the current combustion mode of the cylinder charge. The combustion mode can be, for example, normal operation, diesel particulate filter regeneration or heating operation of a catalyst for selective catalytic reduction. The torque input value 203 is the torque value that is used for calculations in the cylinder charge path of the static setpoint calculation.

The characteristic map 206 receives the index 201, the torque input value 203 and the engine speed 202 as input values. The characteristic value of the cylinder charge is then determined in the characteristic map 206 as a function of the torque in the current combustion mode. This characteristic value is transmitted to the buffer memory 208.

The synthesis temperature 204 after the compressor is used to correct the setpoint value of the cylinder charge. The synthesis temperature is then used to determine the pressure after the intercooler and further after the throttle valve (if this is installed behind the intercooler). The pressure after the throttle valve can then be used to determine the cylinder charge. The synthesis temperature 204 is as in 1 determined. Here, a correction for the cylinder charge is determined on the basis of this synthesis temperature 204 and this cylinder charge is thus limited. The intake manifold temperature 205 is also used to correct the target value of the cylinder charge.

The map 207 receives the index 201, the synthesis temperature 204 and the intake manifold temperature 205 and determines a correction factor for the cylinder charge depending on the gas temperature in the intake manifold in the current combustion mode. The correction factor is then transmitted to the buffer memory 209.

The buffer memory 208 stores the characteristic value and transmits it to the multiplication point 210. The buffer memory 209 stores the correction factor and transmits it to the multiplication point 210.

In the multiplication point 210, the characteristic value from the buffer memory 208 is corrected with the correction factor from the buffer memory 209 in order to obtain the corrected cylinder filling value 211.

This corrected cylinder filling value 211 is defined for the current combustion mode after the internal combustion engine has started.

The correction is made in 2 by means of the characteristic map 207, whereby the intake manifold temperature 205 is also taken into account. However, only the temperature 204 can be taken into account, whereby the characteristic map 207 is replaced by a characteristic curve which is derived from the 1 certain synthesis temperature (108 in 1 ) depends.

The maps 206 and 207 depend on the operating point (load/speed) and the operating mode.

3 shows a flow chart according to an embodiment of a determination of a limited cylinder filling.

In step S1, input variables are read out for determining a limited cylinder charge. The input variables include a target efficiency of the compressor, a given limit temperature of the compressor (temperature after the compressor), a pressure before the compressor and a measured temperature before the compressor. In addition, the input variables include the isentropic exponent of the intake air that is compressed in the compressor. If the compressor is two-stage, the values for the input variables between the compressors can be determined using isentropic compression or stored from measurements. The target efficiency of the compressor can, for example, be measured or simulated and the pressure before the (second) compressor is determined from the isentropic compression. If the compressor is single-stage, the pressure can be determined from the ambient pressure and the inflowing and outflowing mass flows.

In step S2, the input variables are fed into a model that applies the isentropic compression of a gas (the intake air). A maximum boost pressure p _limit after the compressor is calculated as follows: $$p_{Grenz}=p_{VV}{\left[\left(\left(\frac{T_{Grenz}}{T_{us}}-1\right){\eta }_{isen}\right)+1\right]}^{\frac{\kappa }{\kappa -1}}.$$

Where p _vV is the pressure upstream of the compressor, T _{limit is} the limit temperature of the compressor, T _vV is the measured temperature upstream of the compressor, η _{isen is} the isentropic target efficiency of the compressor and ĸ is the isentropic exponent of the intake air.

The maximum boost pressure is filtered in step S3 to reduce fluctuations in the maximum boost pressure in order to stabilize the subsequent minimum selection.

In step S4, a minimum selection is made from the determined (filtered) maximum boost pressure and a target boost pressure that is specified by a control device. The selected minimum is determined as the limited target boost pressure. Based on the limited target boost pressure, an operating state of the internal combustion engine can be set or regulated in step S5. The compressor is thus protected from exceeding the limit temperature due to a limitation of the boost pressure after the compressor.

Another option for setting or regulating the operating state of the internal combustion engine is to determine a limited target cylinder charge in step S6, which can follow the determination of the limited target boost pressure. The limited cylinder charge is determined on the basis of the limited target boost pressure. For example, the pressure drop across the charge air cooler is determined based on the mass flow, the compressor outlet temperature, and a pressure drop factor. The target pressure after the charge air cooler is then determined from the limited target boost pressure and the pressure drop across the charge air cooler. The pressure after the throttle valve is determined from the target pressure after the charge air cooler, whereupon a target charge is determined using the pressure loss in the intake port and the factor for the pressure at bottom dead center. The limited cylinder charge can be filtered to reduce fluctuations in the limited cylinder charge.

In step S7, a minimum selection is made from the determined limited cylinder filling and a target cylinder filling that is specified by a control device. The selected further minimum is then determined as the limited target cylinder filling.

Based on the limited target cylinder charge, an operating state of the internal combustion engine can then be set or regulated in step S8. The compressor is thus protected from exceeding the limit temperature due to a limitation of the cylinder charge, which is determined from the limitation of the boost pressure after the compressor.

4 shows schematically the gas flow through an internal combustion engine according to an embodiment.

The internal combustion engine 400 comprises an air filter 401, a hot film air mass meter 402, a blowby 403, a low-pressure exhaust gas recirculation (LP-EGR) 404, a low-pressure compressor 405, a high-pressure compressor 406, a compressor bypass valve 407 (a ball valve), a charge air cooler 408, a control flap 409, a temperature sensor 410, an internal combustion engine 411, a high-pressure exhaust gas recirculation (HD-EGR) 412, a high-pressure turbine 413, a bypass valve 414, a low-pressure turbine 415, another bypass valve 416 and an exhaust system 417.

The internal combustion engine 400 sucks in fresh air through the air filter 401 and measures the mass flow of the fresh air with the hot film air mass meter 402. After the hot film air mass meter 401, the sucked in fresh air is mixed with exhaust gases from the LP-EGR 404 and the blowby 403 of the internal combustion engine 411. A mixed gas is thus generated.

The mixed gas is compressed by the low-pressure compressor 405 and then flows on to the high-pressure compressor 406 and the compressor bypass valve 407, which are arranged in parallel in the gas flow. The bypass valve 407 is designed as a ball valve and opens when the pressure of the gas mixture to the right of the bypass valve 407 is greater than to the left of the bypass valve 407. Due to a control device (not shown), either the high-pressure compressor 406 is operated and further compresses the gas mixture or the gas mixture flows through the bypass valve 407.

The compressed gas mixture is cooled in a charge air cooler 408. The charge air cooler 408 is water-cooled, for example. The mass flow of the gas mixture is then regulated with a control flap 409 and the temperature in the regulated mass flow of the gas mixture is measured with the temperature sensor 410.

The gas mixture is then used to burn the fuel in the internal combustion engine 411, thereby producing an exhaust gas stream.

A portion of the exhaust gas flow is fed back to the combustion engine 411 through the HD-EGR 412 and mixed with the gas mixture for fuel combustion.

The remaining exhaust gas flows on to the high-pressure turbine 413 and the bypass valve 414, which are arranged in parallel in the exhaust gas flow. The bypass valve 414 is controlled to adjust how much of the exhaust gas flow flows through the high-pressure turbine 413. The high-pressure turbine 413 extracts energy from the exhaust gas flowing through the high-pressure turbine 413, which is provided by means of a shaft to the high-pressure compressor 406, whereby the latter compresses the gas mixture taken in. Consequently, the compression in the high-pressure compressor 406 can be controlled via the bypass valve 414.

After the high-pressure turbine 413 and the bypass valve 414, the exhaust gas flows to the low-pressure turbine 415 and the bypass valve 416, which are arranged parallel in the exhaust gas flow.

The bypass valve 416 is controlled to adjust how much of the exhaust gas flow flows through the low-pressure turbine 415. The low-pressure turbine 416 extracts energy from the exhaust gas flowing through the low-pressure turbine 416, which is provided by means of a shaft to the low-pressure compressor 405, whereby the latter compresses the gas mixture taken in. Consequently, the compression in the low-pressure compressor 405 can be controlled via the bypass valve 416.

After the low-pressure turbine 415 and the bypass valve 416, the exhaust gas flows into the exhaust system 417. In the exhaust system 417, part of the exhaust gas is branched off through the LP-EGR 404 and mixed with the fresh air upstream of the low-pressure compressor 405.

5 shows a vehicle with an internal combustion engine and a control device according to an embodiment.

The vehicle 500 includes the internal combustion engine 400 and the control device 501.

The control device controls (regulates) the internal combustion engine 400. More specifically, the control device detects measured values from sensors in the internal combustion engine 400 and regulates the internal combustion engine 400 on the basis of these sensor values, predetermined control variables, predetermined gas models and setpoints obtained therefrom.

The vehicle 500 can be any wheeled vehicle for transporting goods or people, for example. For example, a car or a commercial vehicle such as a truck.

list of reference symbols

100

signal synthesis

101

sensor value

102

engine torque

103

compressor model

104

low-pass filter

105

subtraction point

106

modeled temperature

107

interpolation factor determination

108

mixer

109

synthesis temperature

200

cylinder filling correction

201

index

202

engine speed

203

torque input value

204

temperature

205

intake manifold temperature

206, 207

map

208, 209

buffer storage

210

multiplication point

211

corrected cylinder filling value

300

flow chart

400

internal combustion engine

401

air filter

402

hot-film air mass meter

403

blow-by

404

low-pressure exhaust gas recirculation

405

low-pressure compressor

406

high-pressure compressor

407

compressor bypass valve

408

intercooler

409

control flap

410

temperature sensor

411

combustion engine

412

high-pressure exhaust gas recirculation

413

high-pressure turbine

414, 416

bypass valve

415

low-pressure turbine

417

exhaust system

500

vehicle

501

control device

Claims (10)

Model-based protection method for maintaining a limit temperature (T _limit ) of a compressor component in a compressor (405, 406) for an internal combustion engine (400), comprising determining a cylinder charge (211; S8) based on a compressor model (103; S2) that applies the isentropic compression of a gas, a pressure (p _vV ) upstream of the compressor (405, 406), a temperature (T _vV ) upstream of the compressor (405, 406) and a target efficiency (η _isen ) of the compressor (405, 406) and setting an operating state of the internal combustion engine based on the determined cylinder charge (211; S8) so that the limit temperature (T _limit ) of the compressor component is not exceeded. Model-based protection procedure according to claim 1 , wherein the determination is also based on a pressure (p _nV ) after the compressor (405, 406) and by means of the compressor model a temperature (106) after the compressor (405, 406) is determined, on the basis of which the cylinder filling (211) is determined. Model-based protection procedure according to claim 2 , wherein the determined temperature (106) after the compressor (405, 406) is mixed with a measured temperature (101) after the compressor (405, 406) to determine a synthesis temperature (109) after the compressor (405, 406), on the basis of which the cylinder charge (211) is determined, wherein a mixing factor between the determined and measured temperature after the compressor is determined from an engine torque (102) and on the basis of the synthesis temperature (109) after the compressor (405, 406) a correction factor for the cylinder charge (211) is determined, which limits the determined cylinder charge (211). Model-based protection procedure according to claim 1 , wherein the determination is also based on a limit temperature (T _limit ) of the compressor and by means of the compressor model a maximum boost pressure after the compressor is determined (S2), on the basis of which the cylinder filling is determined (S8). Model-based protection procedure according to claim 4 , further comprising selecting (S4) a minimum from the calculated maximum boost pressure and a predetermined target boost pressure, determining (S8) the cylinder charge for the internal combustion engine (400) based on the selected minimum. Model-based protection procedure according to claim 5 , wherein determining (S2) the maximum boost pressure comprises filtering (S3) the determined maximum boost pressure, selecting (S4) the minimum is based on the filtered maximum boost pressure, determining (S8) the maximum cylinder charge comprises selecting (S7) a further minimum from the calculated maximum cylinder charge and a predetermined target cylinder charge, and setting the operating state of the internal combustion engine (400) is based on the further minimum. Model-based protection procedure according to one of the Claims 1 until 6 , wherein the setting of the operating state of the internal combustion engine (400) is a regulation of the operating state of the internal combustion engine (400) and the cylinder charge is the reference variable for the regulation of the operating state of the internal combustion engine (400). Control device (501) designed to carry out a method according to one of the Claims 1 until 7 to execute. Internal combustion engine (400) with at least one compressor (405, 406) and a control device (501) according to claim 8 . Vehicle (500) with an internal combustion engine (400) according to claim 9 .

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