GB2568587A - Tank heater - Google Patents

Tank heater Download PDF

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Publication number
GB2568587A
GB2568587A GB1815529.1A GB201815529A GB2568587A GB 2568587 A GB2568587 A GB 2568587A GB 201815529 A GB201815529 A GB 201815529A GB 2568587 A GB2568587 A GB 2568587A
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United Kingdom
Prior art keywords
posistors
range
electrical resistance
tank heater
overall electrical
Prior art date
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Application number
GB1815529.1A
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GB201815529D0 (en
Inventor
Schwarz Mathias
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Robert Bosch GmbH
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Robert Bosch GmbH
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Publication of GB201815529D0 publication Critical patent/GB201815529D0/en
Publication of GB2568587A publication Critical patent/GB2568587A/en
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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
    • F01N3/2013—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating using electric or magnetic heating means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H9/00—Details
    • F24H9/18—Arrangement or mounting of grates or heating means
    • F24H9/1809—Arrangement or mounting of grates or heating means for water heaters
    • F24H9/1818—Arrangement or mounting of electric heating means
    • F24H9/1827—Positive temperature coefficient [PTC] resistor
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1927—Control of temperature characterised by the use of electric means using a plurality of sensors
    • G05D23/193—Control of temperature characterised by the use of electric means using a plurality of sensors sensing the temperaure in different places in thermal relationship with one or more spaces
    • G05D23/1931—Control of temperature characterised by the use of electric means using a plurality of sensors sensing the temperaure in different places in thermal relationship with one or more spaces to control the temperature of one space
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/30—Automatic controllers with an auxiliary heating device affecting the sensing element, e.g. for anticipating change of temperature
    • G05D23/303—Automatic controllers with an auxiliary heating device affecting the sensing element, e.g. for anticipating change of temperature using a sensing element having a resistance varying with temperature, e.g. thermistor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/10—Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/10—Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
    • F01N2610/105—Control thereof
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
    • F01N2610/1406—Storage means for substances, e.g. tanks or reservoirs
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
    • F01N2610/1486—Means to prevent the substance from freezing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/16—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements
    • G01K7/22—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using resistive elements the element being a non-linear resistance, e.g. thermistor
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Thermal Sciences (AREA)
  • Remote Sensing (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Resistance Heating (AREA)
  • Control Of Resistance Heating (AREA)

Abstract

A tank heater 1 for a reducing agent tank 2 of an SCR system comprises a plurality of electrically parallel-connected posistors (positive temperature coefficient, PTC, resistors) 12, 13. At a first average temperature T1 of the posistors, in the range of 30.0°C to 70.0°C, the posistors have a first overall electrical resistance RGes_1 in the range of 1.40 Ω to 1.60 Ω. The first overall resistance may be the minimum overall electrical resistance. At a second average temperature T2 of 70.5°C to 81.5°C, the posistors may have a second overall electrical resistance RGes_2 greater than or equal to the first overall resistance. An electric control device 3 may control a current feed of the posistors such that the overall electrical resistance RGes of the posistors is limited to a temperature dependent characteristic curve determined by a theoretical value of the first overall resistance being compared with a value of the first overall resistance measured during operation of the tank heater.

Description

Description
Tank heater
The present invention relates to a tank heater for a reducing agent tank of an SCR system.
Prior Art
Methods and devices for operating an internal combustion engine, in particular in motor vehicles, are known, in the exhaust gas area of which a selective catalytic reduction (SCR) catalytic converter is disposed, which reduces the nitrogen oxides contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. In this way, the proportion of nitrogen oxides in the exhaust gas can be considerably reduced. Ammonia which is admixed with the exhaust gas is required in order for the reaction to proceed. Thus ammonia or ammonia-splitting reagents are used as reducing agents. As a rule, for this purpose an aqueous urea solution is used which is sprayed into the exhaust gas system upstream of the SCR catalytic converter. Ammonia is formed from this solution and acts as a reducing agent. The aqueous urea solution, which can be obtained commercially under the name AdBlue®, consists of one third urea and two thirds water. It has a freezing point of 11.5°C.
At low temperatures, the urea solution in the reducing agent tank of the SCR system must be thawed out. For this purpose a tank heater can be provided which is designed as an electric heater. It has a metal profile and two parallel-connected electric heating elements and a surrounding synthetic material injection moulding which protects the metal profile and the heating elements from the corrosive effect of the urea solution. The electric characteristic curve of the heating elements is non-linear and is selected in such a way that, starting from a normal operating point, the electrical resistance increases as temperatures increase. Therefore, the heating output decreases. During heating, as much heating output as possible should be discharged to the urea solution. Limiting factors are the maximum admissible current and the temperature load on the surrounding synthetic material injection moulding.
At a set electric voltage, an equilibrium is established after some time between the electric output and the thermal capacity to discharge this output to the environment. This equilibrium depends on the design of the metal profile and on the filling level in the reducing agent tank and on the ambient temperature. The tank heater must function under many different operating conditions and must generate as much heating output as possible depending on the filling level and temperature but in so doing it must not damage the surrounding synthetic material injection moulding. The non-linear resistance characteristic curve is therefore selected such that the thermal load on the surrounding synthetic material injection moulding is not too high.
Disclosure of the invention
In accordance with the present invention, a tank heater for a reducing agent tank of an SCR system, which tank heater comprises a plurality of electrically parallel-connected posistors, is characterised in that, at a first average temperature (Ti) of the posistors, which is in the range of 30.0°C to 70.0°C, the parallel-connected posistors have a first overall electrical resistance (Rces_i) which is in the range of 1.40 Ω to 1.60 Ω.
The tank heater for a reducing agent tank of an SCR system comprises a plurality - in particular two - electrically parallel-connected posistors. Posistors, which are also referred to as PTC resistors or PTC thermistors (PTC = Positive Temperature Coefficient), are temperaturedependent resistors. They have a positive temperature coefficient and conduct electric current better at low temperatures than at high temperatures. For use as self-regulating heating elements in a tank heater, the posistors are based in particular on a ceramic material such as e.g. barium titanate (BaTiO3).
The parallel connection of the posistors is distinguished by an electric characteristic curve in which the overall resistance of the parallel-connected posistors is applied over the average temperature thereof. The average temperature is thus the average of the individual temperatures of the posistors. In order to achieve a maximum heating output during heating and at the same time to ensure that the thermal load on the surrounding synthetic material injection moulding is not too high the posistors are designed in such a way that, at a first average temperature of the posistors which is in a range of 30.0°C to 70.0°C, the latter have a first overall electrical resistance in the range of 1.40 Ω to 1.60 Ω.
This first overall electrical resistance is preferably within the typical operating range of a tank heater, which is in a temperature range of -30°C to 128°C, preferably the minimum overall electrical resistance of the parallel-connected posistors. The first average temperature is in this case also referred to as the reference temperature, from which the overall electrical resistance increases sharply as the temperature increases. This leads to self-regulating properties in the tank heater so that this is regulated back to the reference temperature in the event of deviations from the reference temperature by an increase in the overall resistance. Even when the temperature falls below the reference temperature the overall electrical resistance increases.
In order to obtain optimal heating output over the whole operating range of the tank heater, the resistance characteristic curve preferably has further characteristic reference points described hereinunder:
At a second average temperature of the posistors in the range of 70.5°C to 81,5°C, the parallelconnected posistors preferably have a second overall electrical resistance in the range of 1.40 Ω to 1.60 Ω. Since this range coincides with the range of the first overall electrical resistance it should be observed as a further condition that the second overall electrical resistance is greater than or equal to the first overall electrical resistance.
At a third average temperature of the posistors in the range of 82.0°C to 104.0°C, the posistors have a third overall electrical resistance in the range of 1.48 Ω to 1.82 Ω. Since this range overlaps with the range of the second overall electrical resistance it should be observed as a further condition that the third overall electrical resistance is greater than the second overall electrical resistance.
A fourth overall electrical resistance is in the range of 1.97 Ω to 2.35 Ω. This arises at a fourth average temperature of the posistors in the range of 90.0°C to 110.0°C. Since this temperature range overlaps with the range of the third average temperature it should be observed as a further condition that the fourth average temperature is higher than the third average temperature.
A fifth overall electrical resistance of the posistors is in the range of 4.75 Ω to 6.11 Ω. This arises at a fifth average temperature of the posistors in the range of 90.0°C to 120.0°C. Since this temperature range fully includes the temperature range of the fourth average temperature it should be observed as a further condition that the fifth average temperature is higher than the fourth average temperature.
A sixth overall electrical resistance of the posistors is in the range of 11.10 Ω to 32.10 Ω. This arises at a sixth average temperature of the posistors in the range of 90.0°C to 128.0°C. Since this temperature range fully includes the temperature range of the fifth average temperature it should be observed as a further condition that the sixth average temperature is higher than the fifth average temperature.
It is further preferred that an electronic control device is provided in order to control current feed of the posistors in such a way that, under preset operating conditions of the tank heater, the overall resistance of the posistors is limited according to a temperature-dependent characteristic curve. The preset operating conditions are in particular an empty reducing agent tank and an ambient temperature which exceeds a preset threshold value. The temperature limitation under these operating conditions has the advantage that the thermomechanical load on the posistors is minimised when normal heating is not taking place.
The characteristic curve stored in the electronic control device is preferably an empirically determined characteristic curve which depicts the deviation of the actual behaviour of the posistors from their theoretical behaviour.
In particular, this characteristic curve was determined by a theoretical value of the first overall electrical resistance being compared with a value of the first overall electrical resistance which was measured during operation of the tank heater. This exploits the fact that the first overall electrical resistance as a minimum overall resistance on the resistance characteristic curve of the tank heater is particularly characteristic for this.
Brief description of the drawings
By way of example only, specific embodiments of the present invention will now be describe with reference to the accompanying drawings, in which:
Figure 1 shows a partially cut-away isometric illustration of a tank heater according to one exemplified embodiment of the invention.
Figure 2 shows an equivalent circuit diagram of a tank heater according to one exemplified embodiment of the invention.
Figure 3 shows a diagram of a resistance characteristic curve of a tank heater according to one exemplified embodiment of the invention.
Figure 4 shows a diagram of admissible tolerances in selecting the resistance characteristic curve of figure 3.
Exemplified embodiments of the invention
Figure 1 shows a tank heater 1 according to one exemplified embodiment of the invention, which is disposed in a reducing agent tank 2 of an SCR catalytic converter system, not illustrated. The tank heater 1 has an aluminium extrusion profile 11 to divert the generated heat to an aqueous urea solution. Two posistors 12, 13 made of barium titanate (BaTiO3) are disposed in the extrusion profile 11. The extrusion profile 11 and the posistors 12, 13 have a polyamide 14 injected around them. An electronic control device 3 outside the reducing agent tank 2 is connected to the tank heater 1 by a contact, not illustrated. The control device controls the current feed of the posistors 12, 13.
As shown in figure 2, the two posistors 12, 13 are electrically connected in parallel. The first posistor 13 has a first electrical resistor R12 and the second posistor 13 has a second electrical resistor R13. The overall resistance RGes of the two posistors 12, 13 is connected in series with the resistor RK of the electric cable via which the posistors 12, 13 are fed with current. This cable resistor RK cannot be disregarded because the posistors 12, 13 are relatively low impedance posistors.
The posistors 12, 13 are selected in such a way that they have a resistance characteristic curve with six reference points. The resistance characteristic curve is shown in figure 3. These reference points meet the conditions according to the following Table 1:
Table 1
i Ti[°C] ±ATj[°C] RGes_i [Ω] ± ARGes_i [Ω]
1 50.0 20.0 1.50 0.10
2 76.0 5.5 1.50 0.10
3 93.0 11.0 1.65 0.17
4 100.0 10.0 2.16 0.19
5 105.0 15.0 5.43 0.68
6 109.0 19.0 21.60 10.50
The tolerance ranges ± ΔΤ, of the average temperatures T, of the posistors 12, 13 and the tolerance ranges ± ARGesj of the overall resistances RGesj at the respective temperatures T, are illustrated in figure 4. Within these tolerance ranges which permit optimal heating behaviour of the tank heater 1, a resistance characteristic curve according to the following table was selected:
Table 2
i Ti[°C] RGes_i [Ω]
1 60.0 1.48
2 75.0 1.51
3 86.0 1.64
4 99.0 2.07
5 116.0 6.00
6 120.0 16.70
In the case of normal heating of the tank heater, this tank heater displays behaviour according to this resistance characteristic curve by reason of the selection of the posistors 12, 13. However, for cases of operation which do not correspond to a case of normal heating, namely an empty reducing agent tank 2 or a media temperature higher than 10°C, a limitation of the heating output is provided in the electronic control device 3. For this purpose, the actuation of the heating elements 12, 13 in these cases of operation is not based on the theoretical resistance characteristic curve according to Table 2. Instead of this, the learned resistance characteristic curve is used which is calculated according to Formula 1:
Raesj learned = F · RGesj (Formula 1)
This learning is carried out using a factor F which is calculated according to Formula 2:
F = Rmess.min (Formula 2)
Rgss_1
In this case, in addition to the overall resistance RGes_i known from Table 2, an actual minimum overall resistance Rmess.min previously measured at the temperature Ti is considered. This can be calculated according to Formula 3:
Rmess, min ~ U(^)
----------- - RK (Formula 3) Imax(Ti)
In this case U(Ti) designates the electric voltage applied at the temperature Ti, Imax (Ti) designates the electric current flowing at the temperature Ti and being at a maximum in this case, and RK designates the cable resistance. While the values U(Ti) and Imax(Ti) can be measured, the cable resistance RK is known. By means of the reference points modified in this way, a resistance characteristic curve for the temperature limitation is determined which is stored in the electronic control device 3. It can then be used under operating conditions with active temperature limitation in order to activate the posistors 12, 13. For example, it is now possible to carry out regulation to an average temperature of the posistors.

Claims (7)

Claims
1 A tank heater for a reducing agent tank of an SCR system, which tank heater comprises a plurality of electrically parallel-connected posistors, characterised in that, at a first average temperature (Ti) of the posistors, which is in the range of 30.0°C to 70.0°C, the parallel-connected posistors have a first overall electrical resistance (Rces_i) which is in the range of 1.40 Ω to 1.60 Ω.
2 A tank heater as claimed in claim 1, characterised in that the first overall electrical resistance (Rces_i) in a temperature range of -30°C to 128°C is the minimum overall electrical resistance of the parallel-connected posistors.
3 A tank heater as claimed in claim 1 or 2, characterised in that, at a second average temperature (T2) of the posistors, which is in the range of 70.5°C to 81,5°C, the parallelconnected posistors have a second overall electrical resistance (Rces_2) which is in the range of 1.40 Ω to 1.60 Ω and is greater than or equal to the first overall electrical resistance (RG es_1)
4 A tank heater as claimed in claim 3, characterised in that, at a third average temperature (T3) of the posistors, which is in the range of 82.0°C to 104.0°C, the parallel-connected posistors have a third overall electrical resistance (RcesjO which is in the range of 1.48 Ω to 1.82 Ω and is greater than the second overall electrical resistance (RGes_2).
5 A tank heater as claimed in claim 4, characterised in that, at a fourth average temperature (T4) of the posistors, which is in the range of 90.0°C to 110.0°C and which is higher than the third average temperature, the parallel-connected posistors have a fourth overall electrical resistance (Rces_4) which is in the range of 1.97 Ω to 2.35 Ω.
6 A tank heater as claimed in claim 5, characterised in that, at a fifth average temperature (T5) of the posistors, which is in the range of 90.0°C to 120.0°C and which is higher than the fourth average temperature (T4), the parallel-connected posistors have a fifth overall electrical resistance (Rces.s) which is in the range of 4.75 Ω to 6.11 Ω.
7 A tank heater as claimed in claim 6, characterised in that, at a sixth average temperature (T6) of the posistors, which is in the range of 90.0°C to 128.0°C and which is higher than the fifth average temperature (Ts), the parallel-connected posistors have a sixth overall electrical resistance (Rces_s) which is in the range of 11.10 Ω to 32.10 Ω.
5 8 A tank heater as claimed in any one of claims 1 to 7, comprising an electronic control device which is designed to control a current feed of the posistors in such a way that, under preset operating conditions of the tank heater, the overall resistance (RGes) of the posistors is limited according to a temperature-dependent characteristic curve.
10 9 A tank heater as claimed in claim 8, characterised in that the characteristic curve was determined by a theoretical value of the first overall electrical resistance (Rces_i) being compared with a value of the first overall electrical resistance (Rces_i) which was measured during operation of the tank heater.
GB1815529.1A 2017-09-26 2018-09-24 Tank heater Withdrawn GB2568587A (en)

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CN110456186B (en) * 2019-07-22 2021-11-26 老肯医疗科技股份有限公司 Heater attenuation test system and test method
DE102019214435A1 (en) * 2019-09-23 2021-03-25 Robert Bosch Gmbh Heating device

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WO2012012519A2 (en) * 2010-07-22 2012-01-26 Watlow Electric Manufacturing Company Combination fluid sensor system
WO2013004692A1 (en) * 2011-07-07 2013-01-10 Nv Bekaert Sa Selective catalytic reduction tank with heating element
DE102015201760A1 (en) * 2015-02-02 2016-08-04 Smk Systeme Metall Kunststoff Gmbh & Co. Kg. Heater with mounted in a mounting element PTC heating element for a tank, in particular for a urea tank
US20170257911A1 (en) * 2016-03-03 2017-09-07 Röchling Automotive SE & Co. KG Electrical heating device with ptc element and electrical supply lines as heat conductor and operating fluid tank with such a heating device

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US20100134120A1 (en) * 2008-12-02 2010-06-03 Robert Bosch Gmbh Procedure for checking the functionality of an electric heating device
WO2012012519A2 (en) * 2010-07-22 2012-01-26 Watlow Electric Manufacturing Company Combination fluid sensor system
WO2013004692A1 (en) * 2011-07-07 2013-01-10 Nv Bekaert Sa Selective catalytic reduction tank with heating element
DE102015201760A1 (en) * 2015-02-02 2016-08-04 Smk Systeme Metall Kunststoff Gmbh & Co. Kg. Heater with mounted in a mounting element PTC heating element for a tank, in particular for a urea tank
US20170257911A1 (en) * 2016-03-03 2017-09-07 Röchling Automotive SE & Co. KG Electrical heating device with ptc element and electrical supply lines as heat conductor and operating fluid tank with such a heating device

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CN109555582A (en) 2019-04-02
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KR20190035533A (en) 2019-04-03

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