Patent Publication Number: US-2020276901-A1

Title: Method for Determining the Temperature of an Active Layer of a Heating Resistor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/EP2018/076068 filed Sep. 26, 2018, which designates the United States of America, and claims priority to DE Application No. 10 2017 217 194.4 filed Sep. 27, 2017, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to heating resistors. Various embodiments may include methods for determining a temperature of an active layer of a heating resistor for a recuperation system of a motor vehicle and to a method for operating a recuperation system, heating resistors for a recuperation system of a motor vehicle, and/or a recuperation system having the heating resistor and to a vehicle having the recuperation system. 
     BACKGROUND 
     Electric vehicles may have a heating resistor to continue to allow a recuperation mode even with a traction battery that is no longer able to absorb energy (for example due to temperature conditions or excessively high state of charge). This allows less mechanical brake wear and higher overall energy efficiency of the vehicle. Generated electrical energy is in particular able to be converted, via the heating resistor, into heat that is able to be dissipated via a cooling circuit. However, in order to ensure stable operation, the temperature of the active layer of the heating resistor must not exceed certain limit values. In order to be able to guarantee this, the active layer of the heating resistor typically has an integrated temperature sensor. In addition, a certain minimum temperature gap must be maintained in order to avoid excess temperatures owing to the always sluggish measurement of thermal variables. Such excess temperatures may lead to irreversible damage or to a drastic reduction in the service life of the heating resistor. 
     If no temperature sensor is installed in the active heating layer or in the active heating wire (for example for cost reasons or packaging reasons), then the gap between the estimated temperature and the permitted maximum temperature must be selected to be even greater in order to avoid possible excess temperatures. This leads to the heating wire being used in a less than optimum manner, since a possible capacity is not able to be exploited for safety reasons. Furthermore, owing to the highly dynamic current load on the heating resistor, it is possible to predict or forecast the absorption capacity of electrical energy only with difficulty. 
     SUMMARY 
     As an example, some embodiments of the present disclosure include a method for determining a temperature (T 1 ) of an active layer ( 2 ) of a heating resistor ( 1 ) for a recuperation system of a motor vehicle, the method comprising the steps of: determining an instantaneous value of a current (I 1 ) flowing through an active layer ( 2 ) of a heating resistor ( 1 ) at a first time (t 1 ), determining an instantaneous value of a voltage (U 1 ) that is present on the active layer ( 2 ) of the heating resistor ( 1 ) at the first time (t 1 ), calculating an instantaneous value of an electrical resistance (R 1 ) from the determined instantaneous value of the current (I 1 ) and from the determined instantaneous value of the voltage (U 1 ) and determining an instantaneous value of a temperature (T 1 ) of the active layer ( 2 ) from the calculated value of the electrical resistance (R 1 ). 
     Some embodiments include determining a future thermal absorption capacity of the active layer ( 2 ) based on the determined instantaneous value of the temperature (T 1 ) of the active layer ( 2 ). 
     As another example, some embodiments include a method for operating a recuperation system of a motor vehicle having a heating resistor ( 1 ), having the steps of: determining a temperature (T 1 ) of an active layer ( 2 ) of the heating resistor ( 1 ) for the recuperation system with the steps as claimed in claim  1 , determining a future thermal absorption capacity of the active layer ( 2 ) based on the determined instantaneous value of the temperature (T 1 ) of the active layer ( 2 ), predicting an anticipated braking time, determining an amount of thermal energy to be absorbed by the heating resistor ( 1 ) based on the predicted anticipated braking time, and activating a friction brake of the recuperation system if the determined thermal energy to be absorbed by the heating resistor ( 1 ) exceeds the determined thermal absorption capacity of the active layer ( 2 ). 
     Some embodiments include determining a ratio of a friction braking force to be set to the recuperation braking force depending on a ratio of the determined thermal absorption capacity of the active layer ( 2 ) of the heating resistor ( 1 ), on the one hand, and an expected generated braking energy, on the other hand. 
     In some embodiments, determining the instantaneous value of the temperature (T 1 ) of the active layer ( 2 ) comprises the following steps: storing pairs of values that each comprise a value of an electrical resistance (R i ) and a value of a temperature (T i ) in a database, determining that value of the electrical resistance (R x ) stored in the database that comes closest to the calculated instantaneous value of the electrical resistance (R 1 ) of the active layer ( 2 ), and selecting the associated value of the temperature (T x ), stored in the database in the same pair of values, as the instantaneous value of the temperature (T 1 ) of the active layer. 
     In some embodiments, the instantaneous value of the current (I 1 ) and the instantaneous value of the voltage (U 1 ) are determined by way of power electronics ( 3 ) of the heating resistor ( 1 ). 
     In some embodiments, the instantaneous value of the voltage (U 1 ) is determined on a battery of the recuperation system. 
     In some embodiments, a voltage pulse is emitted to the heating resistor ( 1 ) after the expiry of a defined period of time within which the heating resistor ( 1 ) has not been used. 
     In some embodiments, the determined instantaneous value of the temperature (T 1 ) of the active layer ( 2 ) of the heating resistor ( 1 ) is transmitted to a drivetrain of the vehicle via a vehicle communication network (CAN). 
     Some embodiments include storing a temperature model in a database, wherein the temperature model comprises thermal inertias ( 12 ,  14 ,  16 ) and heat transfers ( 13 ,  15 ) of the heating resistor ( 1 ), and calculating a future electrical or thermal absorption capacity of the heating resistor ( 1 ) based on the temperature model stored in the database and the determined instantaneous value of the temperature (T 1 ) of the active layer ( 2 ). 
     As another example, some embodiments include a heating resistor ( 1 ) for a recuperation system of a motor vehicle, the heating resistor ( 1 ) comprising: an active layer ( 2 ), a heat sink ( 6 ), and power electronics ( 3 ), wherein the active layer ( 2 ) is configured so as to absorb electrical energy that is no longer able to be absorbed by a battery of the recuperation system, the heat sink ( 6 ) is arranged and designed such that a coolant is able to be channeled through the heat sink ( 6 ) and that heat is able to be transferred from the active layer to the heat sink ( 6 ) and the coolant, and the power electronics ( 3 ) are configured so as to perform a method as described above. 
     As another example, some embodiments include a recuperation system comprising a heating resistor ( 1 ) as described above. 
     As another example, some embodiments include a vehicle comprising a recuperation system as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the teachings of the present disclosure are discussed in more detail below on the basis of the schematic drawing. In the figures: 
         FIG. 1  shows a longitudinal sectional illustration of one exemplary embodiment of a heating resistor incorporating teachings of the present disclosure for a recuperation system of a motor vehicle; 
         FIG. 2  shows a resistance-temperature graph for metals, non-metals and superconductors; and 
         FIG. 3  shows a circuit diagram with heat transfers on one exemplary embodiment of a heating incorporating teachings of the present disclosure for a recuperation system of a motor vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The teachings of the present disclosure describe an alternative method for determining a temperature of an active layer of a heating resistor for a recuperation system of a motor vehicle, wherein the method increases the measurement speed and the measurement accuracy and allows an accurate forecast regarding the electric power still able to be absorbed, such that the heating wire is able to be operated closer to its maximum power without damage processes occurring due to an excess temperature. 
     In some embodiments, a method includes measures the voltage U 1  that is present on an active layer of a heating resistor and the current I 1  flowing through the active layer at a first time t 1 . Based on the measured voltage U 1  and the measured current I 1 , the electrical resistance R 1  at the first time is determined in accordance with Ohm&#39;s law (R 1 =U 1 /I 1 ). Since the ohmic resistance is temperature-dependent, it is possible in particular to use values stored in the power electronics to compare the average temperature T 1  prevailing in the active layer at the first time t 1 . It is therefore proposed to determine a first temperature T 1  of the active layer at the first time t 1  from the determined electrical resistance R 1 . Said method steps may be repeated continuously such that the temperature T of the active layer is able to be determined continuously. 
     In some embodiments, it possible to dispense with the temperature sensor, which has the disadvantages of thermal inertia. By virtue of the combined current and voltage measurement, which may be provided in particular via the power electronics, it is possible to increase the measurement speed and the measurement accuracy. Furthermore, it is possible to make an accurate forecast regarding the electric power still able to be absorbed. As a result, the heating resistor is able to be operated closer to its maximum power without the risk of damage processes due to excess temperatures. 
     In some embodiments, a method for determining a temperature of an active layer of a heating resistor for a recuperation system of a motor vehicle includes an instantaneous value of a current flowing through an active layer of a heating resistor is determined. This determination, in particular measurement, takes place at a first time. Furthermore, an instantaneous value of a voltage that is present on the active layer of the heating resistor is determined. This determination, in particular measurement, also takes place at the first time. An instantaneous value of an electrical resistance is calculated from the determined instantaneous value of the current and from the determined instantaneous value of the voltage. An instantaneous value of a temperature of the active layer is determined from the calculated value of the electrical resistance. These method steps may in particular be performed by way of power electronics of the heating resistor. These method steps may furthermore be performed repeatedly in succession, such that the temperature of the active layer of the heating resistor is determined continuously or virtually continuously. The possibility of the high measurement speed due to the absence of thermally sluggish sensors and the provision of the current and voltage measurements allow the temperature of the active layer and thus also the power absorption capacity of the heating resistor to be determined in a highly dynamic manner. 
     In the context of a “braking operating strategy”, it is expedient to determine the electrical resistance and the temperature as described above, and to derive therefrom what braking energy is still able to be absorbed by the heating resistor. If it is predicted or forecast in this case that braking will take place for longer than allowed by the thermal absorption capacity of the heating resistor, a friction brake may already be activated at the time at which this is predicted. In particular, a ratio of the friction braking force to be set to the recuperation braking force may be determined depending on the ratio of the thermal absorption capacity of the active layer of the heating resistor, on the one hand, and the expected generated braking energy, on the other hand. 
     In some embodiments, the method furthermore comprises determining a future thermal absorption capacity of the active layer based on the determined instantaneous value of the temperature of the active layer. 
     In some embodiments, a method for operating a recuperation system, includes: predicting an anticipated braking time, determining an amount of thermal energy to be absorbed by the heating resistor based on the predicted anticipated braking time, and activating a friction brake of the recuperation system if the determined thermal energy to be absorbed by the heating resistor exceeds the determined thermal absorption capacity of the active layer. 
     Determining the instantaneous value of the temperature of the active layer may furthermore comprise the following steps: storing pairs of values that each comprise a value of an electrical resistance and a value of a temperature in a database, determining that value of the electrical resistance stored in the database that comes closest to the calculated instantaneous value of the electrical resistance of the active layer, and selecting the associated value of the temperature, stored in the database in the same pair of values, as the instantaneous value of the temperature of the active layer. 
     In some embodiments, the pairs of values or the database may in particular be stored in the power electronics of the heating resistor, and the power electronics may be configured so as to perform the determination and selection steps additionally provided. Implementing the determination of the instantaneous value of the temperature of the active layer using pairs of values is particularly simple and robust. In some embodiments, a function of the temperature of the active layer may be stored in the database as a function of the electrical resistance of the active layer. 
     In some embodiments, the instantaneous value of the current and the instantaneous value of the voltage are determined by way of the power electronics of the heating resistor. In order to be able to operate the heating resistor, power electronics are required in any case, these supplying the active layer of the heating resistor with regulated current and voltage. These power electronics in this case have to perform a measurement of the transferred current and the applied voltage in order to function correctly. Since the current and voltage are measured in any case, the temperature of the active layer of the heating resistor or its active layer may also be determined in this way. These embodiments thus makes a contribution to being able to dispense with an additional component that performs the voltage measurement and the current measurement, since the power electronics that are typically required in any case for the functionality of the heating resistor are used. 
     In some embodiments, the instantaneous value of the voltage may be determined on a battery of the recuperation system. The voltage measurement may thus also be determined outside the heating resistor at the same voltage level. This results in the possibility for the heating resistor of being able to measure the temperature in the active part of the heating layer or the heating wire very quickly, and therefore also to be able to track high gradients well. If the heating resistor is not used for a relatively long period, the resistance and thus the temperature may be determined using small voltage pulses. In some embodiments, a voltage pulse is emitted to the heating resistor after the expiry of a defined period of time within which the heating resistor has not been used. 
     In some embodiments, the current temperature value may be processed by the power electronics. It is thereby possible to output a very exact value regarding the electric power currently able to be absorbed to the drivetrain via a vehicle communication network (for example CAN). In some embodiments, the determined instantaneous value of the temperature of the active layer of the heating resistor is transmitted to a drivetrain of the vehicle via a vehicle communication network. 
     In combination with a temperature model that is calculated or provided by the power electronics, statements may be made about the future electrical or thermal absorption capacity of the heating resistor. For this purpose, the model must contain the thermal inertias and the heat transfers. The temperature of the active layer of the heating resistor, as determined by way of the current measurement and voltage measurement described above, may likewise be incorporated into this forecast model. 
     In some embodiments, the method comprises the following steps: storing a temperature model in a database, wherein the temperature model comprises thermal inertias and heat transfers of the heating resistor, and calculating a future electrical or thermal absorption capacity of the heating resistor based on the temperature model stored in the database and the determined instantaneous value of the temperature of the active layer. 
     Some embodiments include a heating resistor for a recuperation system of a motor vehicle. The heating resistor comprises an active layer, a heat sink and power electronics, wherein the active layer is configured so as to absorb electrical energy that is no longer able to be absorbed by a battery of the recuperation system, for example since the battery is already fully charged or temperature conditions are too high. The heat sink is furthermore arranged and designed such that a coolant is able to be channeled through the heat sink and that heat is able to be transferred from the active layer to the heat sink and the coolant. The power electronics are furthermore configured so as to perform a method as described above. 
     Some embodiments include a recuperation system that comprises a heating resistor as described above. Some embodiments include a vehicle that comprises a recuperation system as described above. The vehicle is for example a motor vehicle, such as an automobile, a bus or a truck, or else a rail vehicle, a ship, an aircraft, such as a helicopter or an airplane, or for example a bicycle. 
       FIG. 1  shows a heating resistor  1  for a recuperation system of a motor vehicle. The heating resistor  1  comprises an active layer  2 , power electronics  3 , a high-voltage connection  4  with a positive pole and a negative pole, a connection  5  to a vehicle communication network in the form of a CAN, and a heat sink in the form of a cooling channel  6 , which runs through a housing  7  of the heating resistor  1  in order to cool the active layer  2  and has an outflow connection  8  for a coolant and a return connection  9  for the coolant. 
     The active layer  2  is configured so as to absorb electrical energy that is no longer able to be absorbed by a battery of the recuperation system, for example since the battery is already fully charged or the temperature conditions are too high. The coolant may be channeled through the cooling channel  6 , wherein heat may be transferred from the active layer  2  to the cooling channel body  6  and the coolant located therein. 
     In some embodiments, the power electronics  3  may perform a combined current and voltage measurement. In this case, a voltage U 1  that is present on the active layer  2  may be measured at a first time t 1 . A current I 1  flowing through the active layer  2  may furthermore likewise be measured at the first time t 1 . In some embodiments, the instantaneous value of the voltage U 1  may be determined on a battery (not shown) of the recuperation system. 
     Based on the measured voltage U 1  and the measured current I 1 , the electrical resistance R 1  at the first time is able to be determined in accordance with Ohm&#39;s law (R 1 =U 1 /I 1 ). Since the ohmic resistance is temperature-dependent (see  FIG. 2 ), it is possible to use values stored in the power electronics, in particular pairs of values or a formula, to compare the average temperature T 1  prevailing in the active layer at the first time t 1 . The determined instantaneous value of the temperature T 1  of the active layer  2  of the heating resistor  1  may be transmitted to a drivetrain (not shown) of the vehicle via the CAN. 
     In some embodiments, the power electronics  3  may have a storage unit on which a plurality of pairs of values are stored in a database. The individual pairs of values each comprise a resistance value R i  and a temperature value T i . The power electronics  3  may compare the determined resistance value R 1  with the resistance values of the pairs of values. By way of example, a resistance value R x  in a pair of values x may come closest to the determined resistance value R 1 . If the power electronics  3  determine this, then they may select the associated temperature value T x  in the pair of values x as the instantaneous value of the temperature T 1  of the active layer  2 . In some embodiments, a function of the temperature T may also be stored in the database as a function of the electrical resistance R (cf.  FIG. 2 ), wherein the power electronics  3  may be configured so as to determine a corresponding instantaneous temperature value T 1  of the active layer  2  of the heating resistor  1  at a time t 1  from a determined instantaneous resistance value R 1 . 
     In the sense of a predictive braking strategy, the power electronics  3  may be configured so as to derive what braking energy is still able to be absorbed by the heating resistor  1  from the determined temperature T 1 . If it is predicted or forecast in this case that braking will take place for longer than allowed by the thermal absorption capacity of the heating resistor  1 , then a friction brake (not shown) of the recuperation system may already be activated at the time at which this is predicted. In some embodiments, a ratio of the friction braking force to be set to the recuperation braking force may be determined depending on the ratio of the thermal absorption capacity of the active layer  2  of the heating resistor  1 , on the one hand, and the expected generated braking energy, on the other hand. If the heating resistor  1  is not used for a relatively long period, the resistance R and thus the temperature T may be determined using small voltage pulses. 
     In combination with a temperature model that is calculated or provided by the power electronics  3 , statements may be made about the future electrical or thermal absorption capacity of the heating resistor  1 . For this purpose, the model must contain the thermal inertia and the heat transfers. The temperature T 1  of the active layer  2  of the heating resistor  1 , as determined by way of the current measurement and voltage measurement described above, may likewise be incorporated into this forecast model. 
     In this regard,  FIG. 3  shows an exemplary temperature model with a heat source  11 , for example caused by current or voltage in the active layer  2  of the heating resistor  1 . A heating wire or a heating surface having the active layer  2  in this case forms a first heat carrier  12 . A first heat transfer  13  takes place from the first heat carrier  12  to the body of the cooling channel  6 , which forms a second heat carrier  14 . A second heat transfer  15  takes place from the second heat carrier  14  to the coolant, which is channeled through the cooling channel  6  and forms a third heat carrier  16 . The cooling channel  6  or a cooling circuit formed thereby forms a heat sink  17 . The three heat carriers  12 ,  14  and  16  form thermal inertias of the heating resistor  1 .