DE102019123261B4 - Method for determining the fan overrun actually required in the reheating mode of a vehicle - Google Patents

Abstract

Method for determining an actually required fan overrun (100) in the reheating mode of a vehicle when a predetermined temperature level in the exhaust system is exceeded, the actually required fan overrun (100) being determined by calculating the residual thermal energy (123) in the exhaust system, the calculation of the residual thermal energy (123) in the exhaust system by determining the heat input (1) into the engine compartment depending on the exhaust gas flow through the exhaust system of the vehicle, by determining the heat discharge (2) from the engine compartment depending on at least the Cooling air mass flow, as well as by determining a temperature level (3) of the components during vehicle operation, as well as a calculation of a maximum permitted temperature increase (34) in the engine compartment in reheating mode, the determination of the temperature level (3) of the components during vehicle operation based on a calculation of the vehicle speed , the ambient temperature, the coolant temperature and the engine power based on applicable characteristic curves, and whereby the actually required fan overrun (100) is determined such that the maximum temperature reached due to the temperature increase (34) in reheating operation remains smaller than a maximum permitted Component temperature (4).

Description

The invention relates to a method for determining the fan overrun that is actually required in the afterheating mode of a vehicle.

In modern vehicles with combustion engines, a wide variety of sources generate heat, which must be dissipated by appropriate cooling systems in order to keep the entire vehicle system at a certain operating temperature. Since these systems are usually only active while the combustion engine is operating, but high thermal stress can occur on components even after the engine has been switched off, the vehicle's electric fan must handle the so-called overrun operation. The fan supplies the components in the engine compartment with the required cooling air even when the engine and the vehicle are at a standstill.

Since the thermal load on the critical components is drastically increased when the internal combustion engine is in regeneration mode, i.e. in cleaning mode of the particle filter by means of greatly increased exhaust gas temperatures, a follow-up operation of the fan is particularly provided here. This particularly applies to diesel vehicles with diesel particulate filters. However, other vehicles that require appropriate cooling may also be affected.

Fan overrun strategies are currently known that calculate a fan overrun requirement based on the average driving speed and the average exhaust gas temperature over a specific observation period. This strategy is designed to ensure that the system reacts in the same way as in the thermal worst-case scenario, especially during particle filter regeneration, in almost all operating points. However, this often results in unnecessary cooling.

In addition, from the DE 10 2014 222 304 A1 a method for operating an engine compartment fan for an engine compartment of a motor vehicle is known, in which at least one component, in particular for driving the motor vehicle, is arranged, with the following steps: determining a current engine compartment temperature depending on a thermal energy balance of a thermal energy input into the engine compartment and a thermal energy discharge from the Engine compartment, activation of the engine compartment fan depending on the determined current engine compartment temperature.

It is therefore an object of this invention to provide a method that provides an improved fan tracking strategy. This object is achieved according to the invention by the features of the independent patent claims. Advantageous refinements are the subject of the dependent claims.

A method is proposed for determining an actually required fan overrun in the reheating operation of a vehicle when a predetermined temperature level in the exhaust system is exceeded, characterized in that the determination of the actually required fan overrun operation is carried out in such a way that a calculation of the residual thermal energy in the exhaust system, as well as a calculation of a maximum permitted temperature increase in the engine compartment in the afterheating mode, the actually required fan overrun being determined in such a way that the maximum temperature reached due to the temperature increase in the afterheating mode remains smaller than a maximum permitted component temperature.

By keeping the fan running as needed, the frequency of the fan running can be reduced and energy can therefore be saved. Acoustic optimization can also be achieved by adjusting the speed and run-on time of the fan accordingly.

Furthermore, it is provided that the calculation of the residual thermal energy in the exhaust system is carried out by determining the heat input into the engine compartment depending on the exhaust gas flow through the exhaust system of the vehicle, by determining the heat discharge from the engine compartment depending on at least the cooling air mass flow, and by determining a temperature level of the Components occur during vehicle operation. Optionally, the heat output is also determined depending on the air temperature. The temperature level of the components during vehicle operation is determined based on a calculation of the vehicle speed, the ambient temperature, the coolant temperature and the engine power based on applicable characteristic curves. By calculating the residual energy depending on parameters that were not previously monitored by the motor control or motor monitoring and are therefore unknown, a more precise calculation of the thermal cooling requirement can be determined and the fan run-on can thus be optimized.

Furthermore, it is provided that a calculation of the maximum permitted temperature increase in the engine compartment up to the maximum permitted component temperature in reheating operation is carried out depending on a predetermined, maximum permitted component temperature of one or more components in the engine compartment and a calculated temperature level of the components during vehicle operation. The maximum permitted component temperature is advantageous Maximum permitted component temperature of a specified critical component within the engine compartment. This critical component is usually the component that is most temperature critical. This is identified first, advantageously in experiments. Here it is measured which component is closest to the maximum permitted temperature for the component in various extreme thermal tests, which varies depending on the material of the component. The maximum permitted temperature of the determined critical component then results in the temperature limit, which is defined as the maximum permitted component temperature. By using a maximum permitted component temperature, it can be ensured that no overheating occurs even if the fan overrun is not at its maximum.

Furthermore, it is provided that the last calculated temperature of the components after switching off the engine is used as the temperature level of the components during vehicle operation.

Furthermore, it is provided that the speed of the fan and the duration of the fan overrun are determined in such a way that predetermined criteria are met, at least comprehensively permitted maximum noise development. This means that customer requests can be addressed, e.g. to reduce acoustic pollution.

Furthermore, it is provided that a cooling process is simulated during driving depending on the residual energy and the temperature level and the determination of the actually required fan overrun is carried out until the residual energy has reached or fallen below a predetermined temperature value.

Further features and advantages of the invention result from the following description of exemplary embodiments of the invention, based on the figures of the drawing, which show details of the invention, and from the claims. The individual features can be implemented individually or in groups in any combination in a variant of the invention.

Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawing.

1 shows a flowchart of the method according to an embodiment of the present invention.

During vehicle operation, thermal energy is stored in engine components, specifically in the exhaust system. When the vehicle is at a standstill, thermal energy causes a temperature increase in components located there due to a lack of active cooling, which is referred to as post-heating operation, or NHZ operation for short. This is particularly critical after regeneration operation of a filter, e.g. a diesel particulate filter DPF, due to the increased exhaust gas temperatures. A lack of cooling due to the vehicle being stationary and thus an increase in the temperature acting on these components can lead to damage or failure, particularly for components that are temperature-sensitive and are referred to as critical components. As already described, fan run-on strategies are known for cooling, especially after regeneration operation, which limit a temperature increase in components in NHZ operation, i.e. when the vehicle is at a standstill or after the engine has been switched off.

Currently, the average driving speed during vehicle operation and the exhaust gas temperature essentially determine the fan overrun via a map. However, this is insufficient for an assessment of the thermal conditions in the engine compartment in NHZ operation, as the previous driving profile has so far only been taken into account in the calculation to a small extent. Until now, only the average driving speed was taken into account. Since the exhaust gas temperature during particle filter regeneration is often independent of the driving profile, the actual required cooling capacity has not yet been calculated. Therefore, a method for improving the fan run-on strategy is proposed below, which determines the actually required run-on cooling power.

The basic concept of the invention is as in 1 shown schematically, to mathematically model the critical component temperatures using a physically correct calculation model, to implement a corresponding control in the engine control unit and thereby to optimize the control of the fan overrun 100. For verification purposes, the temperature behavior of the components was characterized based on measurements in a wide variety of driving situations. It can be adapted for different components or vehicles.

Furthermore, measurements were carried out to analyze the temperature behavior of the components in after-run operation at different fan modes. Based on this knowledge, the expected temperature increase of the components in follow-up operation can be calculated based on the previous driving situation.

The process is described in more detail below. The process for determining the fan overrun actually required is started when a predetermined temperature level from a previous driving situation is reached is exceeded or if the exhaust gas temperature in front of the vehicle's particle filter exceeds a predetermined level at which regeneration operation can be concluded. This determination of the actually required fan overrun 100 is carried out by calculating the residual thermal energy 123 in the exhaust system and a calculation of a maximum permitted temperature increase 34 of the temperature in the engine compartment in overrun mode, the actually required fan overrun 100 being determined in this way that the maximum temperature reached in post-heating mode due to the temperature increase remains lower than the maximum permitted component temperature 4.

In parallel to the calculation of the component temperatures 3, the residual thermal energy 123 in components of the exhaust system is calculated using a heat balance calculation. This is achieved on the one hand by calculating the heat input 1 into the exhaust system, i.e. the exhaust gas flowing through at high temperatures, and on the other hand by calculating the heat output 2 through the engine compartment, i.e. the cooling air flowing through while driving.

The heat balance calculation, cumulatively over the period under consideration, results in a thermal residual energy content 123 in the components of the exhaust system, in particular on the particle filter due to the high thermal mass. Measurements confirmed that the thermal residual energy 123 has a direct influence on the temperature rise of the components in follow-up operation. By adjusting the fan overrun 100, i.e. the duration and speed, this temperature increase can be influenced so that the maximum temperature increase 34 specified for the critical components is not exceeded.

Based on these findings, a map can be generated which uses the input variables of the calculated component temperature 3 of components to be considered, in particular critical components, during vehicle operation and the calculated residual thermal energy 123 in the components of the exhaust system to determine the required fan run-on 100 calculated to comply with the component-specific limit temperatures.

In this way, on the basis of the calculated temperature in vehicle operation 3 and the calculated expected temperature increase 34 in the run-on mode, a demand-oriented fan run-on 100 can be implemented, which is designed so that no temperature limit values 4 of the components are exceeded. This is particularly advantageous if the engine is switched off immediately after regeneration operation.

The individual components for determining the demand-oriented fan run-on 100 are explained in detail below.

The calculation of the residual thermal energy 123 in the exhaust system is based on the calculations described below of the heat input 1 into the engine compartment, the heat discharge 2 from the engine compartment and the component temperature 3 of predetermined, advantageously critical, components during vehicle operation. In addition, a specified, maximum permitted component temperature 4 is taken into account.

The calculation of the heat input 1 into the engine compartment and thus onto the components located there, i.e. also temperature-sensitive, i.e. critical, components, is carried out by determining the exhaust gas flow through the exhaust system. To simplify matters, only the convective heat transfer can be considered, since only the temperature behavior of the moving liquids can be meaningfully monitored. The parameters required for the calculation, such as specific heat capacities and temperatures, are known from exhaust gas monitoring.

The heat output 2 from the engine compartment is calculated by modeling the cooling air mass flow through the engine compartment and, if necessary, also the air temperatures, more precisely the cooling air temperatures.

Most of the parameters for calculating the heat input 1 to determine the residual energy 123 are known, for example, by monitoring using suitable sensors, in particular the exhaust gas mass flow, the specific heat capacity of the exhaust gas and the air, the temperature of the exhaust gas before the diesel oxidation catalytic converter DOC, and after the diesel particulate filter DPF as well before selective catalytic reduction SCR in diesel vehicles.

To determine the heat output 2, additional unknown parameters are required that must be modeled. These parameters are the cooling air mass flow and the air temperatures before and after the exhaust components. In most cases, the air temperatures can be neglected because the temperature difference before and after the exhaust system, which has an influence on the heat energy discharged, does not vary significantly, but only the temperature level shifts. This means that only the cooling air mass flow is absolutely required to determine the heat output 2. This is determined via applicable maps with the inputs vehicle speed, air flap position of the air flaps on the radiator and fan speed, whereby the air flap position is usually and to For simplification, it can be assumed to be completely open, especially during a regeneration phase of the particle filter. Another position that can be assumed is a half-open position. The heat output 2 can be calculated directly via the cooling air mass flow.

It has been found that considering the residual thermal energy 123 in the components is not sufficient to determine the fan run-on requirement, as this only reflects the temperature increase. Therefore, a calculation is made of the component temperature or the temperature level of predetermined, advantageously critical, components during vehicle operation. The temperature level of the components when the engine is switched off, i.e. the last value before the engine is switched off, is determined. Together with the residual energy 123, the required fan overrun 100 can now be calculated.

The temperature level of the components during driving is calculated using applicable characteristic curves from the following input variables: vehicle speed, ambient temperature, coolant temperature and engine power. A time average is first formed from these input variables over an applicable observation time horizon, and factors for calculating the temperature level are calculated using the previously mentioned applicable characteristic curves. In addition, an applicable map with the input variables vehicle speed and engine power is required, which calculates an additional correction factor for operating points with high engine power at low driving speeds, such as in the extreme mountain driving test. This factor is added to the calculated temperature level.

The calculated temperature level is subtracted from an applicable critical component temperature, which is defined or specified as a constant value, in order to calculate the maximum permitted temperature increase 34 in the post-heating operation.

From the maximum permitted temperature increase 34 in the post-heating mode and the calculated residual energy 123, a specific, required follow-up control signal is calculated via an applicable characteristic map in order not to exceed the critical values, i.e. the maximum permitted temperature increase 34. The required overrun time and overrun speed of the fan are then calculated from the control signal.

For example, a maximum permitted temperature 4 that a critical component can assume is 160 degrees Celsius. If the calculated temperature during vehicle operation is 95 degrees Celsius, the maximum permitted temperature increase 34 in NHZ operation is 160 degrees Celsius - 95 degrees Celsius = 65 degrees Celsius. In order to obtain a safe overtravel strategy, it is advantageous to specify the maximum permitted temperature 4 of the weakest or most critical component, i.e. the component that is closest to its maximum permitted value in experiments, as the maximum permitted component temperature 4. In addition, components can also be considered that have a higher permitted maximum temperature 4, but are located in areas in the engine compartment that are exposed to higher temperature loads.

In post-heating mode, depending on the fan overrun used, a PT1 behavior is preferably used as a cooling curve for the component temperature and the residual energy in order to know in the event of the engine being started again at what level the component temperature and the residual energy are currently and whether or when the calculation will be carried out again needs to be started. During vehicle operation, no PT1 behavior is used as a cooling process, but the calculation of the thermal residual energy 123 continues. If the heat output is greater than the heat input, e.g. B. because the particle filter regeneration has ended, the calculated residual energy is also reduced again. As soon as this is below a threshold value or a specified temperature value, the calculation is ended.

In the event of a new engine start, it is therefore known at what level the component temperature and the residual energy are currently and whether or when the calculation has to be started again because the threshold value or the specified temperature value is exceeded.

After selecting the operation, i.e. duration and speed, the fan overrun 100 is no longer adjusted directly when the engine is switched off due to the calculation model. The temperature value is no longer used for the current fan operation in post-heating mode, it is only estimated mathematically via the PT1 behavior and used as the starting value the next time the engine is started.

The fan overrun 100 can be optimized by adjusting the overrun time and the speed so that specified criteria are met. For example, one criterion can be that the fan run-on should be as quiet as possible. A longer run-on time at a lower speed can be selected here. If the overrun time is specified to be as short as possible, a shorter overrun time can be selected at a higher speed. These settings can be saved as default settings, or the driver can be given a setting option to decide for yourself which follow-up strategy should be carried out.

The proposed method made it possible to reduce the frequency of fan overrun 100 during the measurement runs considered by up to 50%, thereby saving energy. Furthermore, by reducing the fan speed in run-on mode, the acoustic behavior can be improved or the acoustic load can be greatly reduced without incurring thermal risks.

Reference symbols

1

Heat input into the engine compartment

2

Heat discharge from the engine compartment

3

temperature level

4

Component temperature

34

Temperature rise

100

Fan overrun

123

residual energy

Claims (7)

Method for determining an actually required fan overrun (100) in the afterheating mode of a vehicle when a predetermined temperature level in the exhaust system is exceeded, the actually required fan overrun (100) being determined by - a calculation of the residual thermal energy (123) in the exhaust system, the calculation of the residual thermal energy (123) in the exhaust system being determined by determining the heat input (1) into the engine compartment depending on the exhaust gas flow through the vehicle's exhaust system, by determining the heat output ( 2) from the engine compartment depending on at least the cooling air mass flow, as well as by determining a temperature level (3) of the components during vehicle operation, and - a calculation of a maximum permitted temperature increase (34) in the engine compartment in the afterheating mode, the determination of the temperature level (3) of the components during vehicle operation based on a calculation of the vehicle speed, the ambient temperature, the coolant temperature and the engine power based on applicable characteristic curves, and where - The actually required fan overrun (100) is determined in such a way that the maximum temperature reached due to the temperature increase (34) in reheating operation remains lower than a maximum permitted component temperature (4). Procedure according to Claim 1 , whereby the heat output (2) is also determined depending on the air temperature. Method according to one of the preceding claims, wherein a calculation of the maximum permitted temperature increase (34) in the engine compartment up to the maximum permitted component temperature in the reheating mode depends on a predetermined, maximum permitted component temperature (4) of one or more components in the engine compartment and a calculated temperature level of the components occurs during vehicle operation. Procedure according to Claim 3 , whereby the maximum permitted component temperature (4) is the maximum permitted component temperature of a given critical component within the engine compartment. Method according to one of the preceding claims, wherein the last calculated temperature of the components after switching off the engine is used as the temperature level of the components during vehicle operation. Method according to one of the preceding claims, wherein the speed of the fan and the duration of the fan overrun (100) are determined such that predetermined criteria are met, at least including permitted maximum noise development. Method according to one of the preceding claims, wherein a cooling process during driving is simulated as a function of the residual energy (123) and the temperature level and the determination of the actually required fan overrun is carried out until the residual energy (123) reaches or falls below a predetermined temperature value has.

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