Method for heating an exhaust gas sensor in the exhaust system of an internal combustion engine

Abstract

Method for heating an exhaust gas sensor (26) in the exhaust system (20) of an internal combustion engine (10), wherein an electrically heated catalyst (24) is arranged in the exhaust system (20) and an exhaust gas sensor (26) is arranged upstream of the electrically heated catalyst (24) and is spaced apart from the electrically heated catalyst (24), wherein the electrically heated catalyst is heated by an electric heating element and the waste heat of the electrically heated catalyst (24) is used to heat the exhaust gas sensor (26) to its release temperature (T) by means of heat conduction via a thermal bridge (28) made of copper or a copper alloy. F ) to heat up.

Description

[0001] The invention relates to a method for heating an exhaust gas sensor in the exhaust system of an internal combustion engine and to an exhaust system with an electrically heated catalyst and an exhaust gas sensor according to the preamble of the independent claims.

[0002] Current and increasingly stringent emissions legislation places high demands on raw engine emissions and exhaust aftertreatment in combustion engines. The requirements for further reductions in fuel consumption and the tightening of emissions standards regarding permissible nitrogen oxide emissions pose a challenge for engine developers. In gasoline engines, exhaust gas purification is achieved in the familiar manner via a three-way catalytic converter, as well as additional catalysts upstream and downstream of the three-way converter. Diesel engines currently employ exhaust aftertreatment systems that include an oxidation catalyst or a NOx storage catalyst, a catalyst for the selective catalytic reduction of nitrogen oxides (SCR catalyst), a particulate filter for the separation of soot particles, and possibly additional catalysts.To meet the stringent requirements for minimal nitrogen oxide emissions, exhaust aftertreatment systems are known which have two SCR catalysts connected in series, with a metering element for adding a reducing agent upstream of each SCR catalyst. A synthetic aqueous urea solution is preferably used as the reducing agent, which is mixed with the hot exhaust gas stream in a mixing device upstream of the SCR catalyst. This mixing heats the aqueous urea solution, causing it to release ammonia into the exhaust gas duct. A commercially available aqueous urea solution generally consists of 32.5% urea and 67.5% water.

[0003] With the introduction of EU6 emissions standards, a limit for particle number is prescribed for gasoline engines, which in many cases necessitates the use of a gasoline particulate filter (GPF). These soot particles are produced particularly after a cold start of the combustion engine due to incomplete combustion combined with a substoichiometric air-fuel ratio and cold cylinder walls during the cold start. The cold start phase is therefore crucial for compliance with the legally prescribed particle limits. During normal driving, the GPF continues to accumulate soot. To prevent excessive exhaust backpressure, the GPF must be regenerated continuously or periodically. An increase in exhaust backpressure can lead to increased fuel consumption, reduced power output, impaired engine smoothness, and even misfires.To thermally oxidize the soot trapped in the gasoline particulate filter with oxygen, a sufficiently high temperature level combined with the simultaneous presence of oxygen in the exhaust system of the gasoline engine is necessary. Since modern gasoline engines are normally operated without excess oxygen at a stoichiometric air-fuel ratio (λ=1), additional measures are required. These measures include, for example, increasing the temperature by adjusting the ignition timing, temporarily leaning out the mixture, injecting secondary air into the exhaust system, or a combination of these measures. Currently, retarding the ignition timing in combination with leaning out the mixture is preferred, as this method requires no additional components and can supply a sufficient amount of oxygen at most operating points of the gasoline engine.

[0004] Exhaust gas sensors are used to monitor the operation of exhaust aftertreatment components and to optimize the air-fuel ratio in the combustion chambers of the internal combustion engine. These sensors measure the oxygen content or pollutant concentration in the exhaust system and control the exhaust aftertreatment accordingly. Furthermore, these sensors control the combustion of the fuel in the combustion chambers of the internal combustion engine. To optimize this combustion, it is necessary for the exhaust gas sensors to reach their operating temperature as quickly as possible after a cold start of the internal combustion engine in order to achieve emission-optimized combustion.

[0005] From DE 10 2011 101 676 A1, an exhaust aftertreatment system for an internal combustion engine is known, comprising an electrically heated catalyst and a three-way catalyst downstream of the electrically heated catalyst. The three-way catalyst is heated by convection, conduction, and / or radiation through the electrically heated catalyst.

[0006] German patent application DE 10 2011 018 293 A1 discloses an internal combustion engine with an exhaust aftertreatment system in which an electrically heated catalyst and a three-way catalyst arranged downstream of the electrically heated catalyst are arranged. The three-way catalyst is heated convectively by the heat of the electrically heated catalyst.

[0007] German patent DE 10 2018 129 684 A1 describes an exhaust aftertreatment system with a heating device for heating a probe during the warm-up phase or during a cold start. The exhaust aftertreatment system comprises an exhaust pipe, a NOx storage catalyst arranged in the exhaust pipe, a probe arranged in the exhaust pipe, and a heating device arranged in the exhaust pipe, wherein the heating device is configured such that the probe can be heated during the warm-up phase or during a cold start.

[0008] From JP H04-314 911 A, an internal combustion engine with an exhaust gas channel is known in which an exhaust gas probe, an electric heating element and a catalyst are arranged.

[0009] WO 2019 / 063 301 A1 discloses a method for operating a catalyst which can be electrically heated by means of an electric heating element and which includes an exhaust gas sensor.

[0010] From EP 1 510 672 A1, a heating device for an oxygen sensor integrated into a catalyst for exhaust aftertreatment is known. The heating device comprises an electrical heating element arranged to transfer a heating effect to at least one area within the catalyst.

[0011] Furthermore, JP H07-238 823 A describes an exhaust aftertreatment system with an electric heating element and a catalyst following the direction of flow of an exhaust stream, wherein an oxygen sensor is arranged downstream of the electric heating element and upstream of the catalyst.

[0012] The invention is based on the objective of heating the exhaust gas sensors to their release temperature as quickly as possible after a cold start of the combustion engine, thus enabling improved control of the combustion after the cold start of the combustion engine.

[0013] According to the invention, this problem is solved by a method for heating an exhaust gas sensor in the exhaust system of an internal combustion engine, wherein an electrically heated catalyst and an exhaust gas sensor spaced apart from the electrically heated catalyst are arranged in the exhaust system, the electrically heated catalyst being heated by an electric heating element, and the waste heat from the electrically heated catalyst being used to heat the exhaust gas sensor to its release temperature by means of heat conduction via a thermal bridge made of copper or a copper alloy. The method according to the invention makes it possible to heat the exhaust gas sensors independently of the exhaust gas flow of the internal combustion engine. Thus, the sensors can reach their release temperature faster than if heated by the exhaust gas flow.Furthermore, the sensor can be made free of an electrical heating element, thus reducing its cost. The earlier release of the sensors results in improved fuel combustion during the cold start phase, which can reduce fuel consumption and / or raw emissions from the combustion engine.

[0014] The features mentioned in the dependent claims enable advantageous improvements and non-trivial further developments of the method for heating an exhaust gas sensor.

[0015] In an embodiment not part of the invention, the exhaust gas sensor is arranged downstream of the electrically heated catalyst and is heated convectively to its release temperature by the exhaust gas flow of the combustion engine. A large amount of heat can be transferred from the electrically heated catalyst to the exhaust gas sensor via convective heat transfer. However, this requires that the electrically heated catalyst be arranged upstream of the exhaust gas sensor.

[0016] In an advantageous embodiment of the method, the exhaust gas sensor is additionally heated to its release temperature by the thermal radiation from the electrically heated catalyst. This thermal radiation also enables effective heat transfer from the electrically heated catalyst to the exhaust gas sensor. However, it is important to note that the thermal radiation decreases significantly with distance from the heat source. Therefore, when using thermal radiation for heat transfer, the exhaust gas sensor should be positioned as close as possible to the electrically heated catalyst. Since thermal radiation acts in all directions, it can heat both exhaust gas sensors located upstream of the electrically heated catalyst in the exhaust system (in the direction of exhaust gas flow) and exhaust gas sensors located downstream of the catalyst.In the case of an exhaust gas sensor located downstream of the electrically heated catalyst, heat transfer can also occur convectively and via thermal radiation, enabling very efficient heat transfer and allowing the exhaust gas sensor to heat up particularly quickly.

[0017] According to the invention, the electrically heated catalyst is connected to the exhaust gas sensor via a thermal bridge, whereby the exhaust gas sensor is heated to its release temperature via the thermal bridge by means of heat conduction. The heat from the electrically heated catalyst can be transferred to the exhaust gas sensor very effectively and efficiently by means of heat conduction via the thermal bridge. The exhaust gas sensor can be arranged both upstream and downstream of the electrically heated catalyst. Furthermore, the distance can be greater compared to heat transfer by thermal radiation, since efficient heat transfer can also be achieved over longer distances via heat conduction.

[0018] Another aspect of the invention relates to an exhaust system with an electrically heated catalyst and an exhaust gas sensor arranged upstream of the electrically heated catalyst and spaced apart from it, wherein the electrically heated catalyst is connected to the exhaust gas sensor via a thermal bridge made of copper or a copper alloy, and to a control unit configured to carry out such a process when a machine-readable program code is executed by the control unit. In such an exhaust system, particularly rapid and efficient heating of the exhaust gas sensors is possible.

[0019] It is particularly advantageous if the exhaust gas sensor is designed as a lambda sensor or an oxygen sensor. This allows for particularly precise control of the air-fuel ratio in the combustion chambers of the internal combustion engine. The timely activation by a lambda sensor or oxygen sensor can thus reduce raw emissions and / or fuel consumption of the internal combustion engine.

[0020] Alternatively, it is advantageous for the exhaust gas sensor to be designed as a NOx sensor or as a combined NOx / NH3 sensor. This allows the emissions in the exhaust stream of the combustion engine to be determined, enabling the combustion process in the combustion chambers to be adjusted to reduce raw nitrogen oxide emissions.

[0021] In the exhaust system embodiment according to the invention, the electrically heated catalyst is connected to the exhaust gas sensor via a thermal bridge. This thermal bridge enables particularly efficient heat transfer from the electrically heated catalyst to the exhaust gas sensor.

[0022] According to the invention, the thermal bridge is made of copper or a copper alloy. Copper has a particularly high thermal conductivity compared to other metals. Furthermore, copper exhibits high temperature stability, ensuring it remains dimensionally stable even at the high temperatures occurring in the exhaust system.

[0023] In an advantageous embodiment of the exhaust system, the exhaust gas sensor is positioned in an exhaust duct of the exhaust system at a distance of less than 5 cm, preferably less than 3 cm, from the electrically heated catalyst. This enables particularly efficient heat transfer via thermal radiation.

[0024] Unless otherwise stated in individual cases, the various embodiments of the invention mentioned in this application can be advantageously combined with one another.

[0025] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Identical components or components with the same function are designated with the same reference numerals in the different figures. The figures show: Fig. 1 an internal combustion engine with an exhaust system in which an electrically heated catalyst and an exhaust gas sensor are arranged; Fig. 2. An embodiment not belonging to the invention for an exhaust system with an electrically heated catalyst and an exhaust gas sensor, wherein the waste heat from the electrically heated catalyst is transferred to the exhaust gas sensor by means of convection; and Fig. 3 an embodiment of an exhaust system with an electrically heated catalyst and an exhaust gas sensor, wherein the waste heat from the electrically heated catalyst is transferred to the exhaust gas sensor by means of heat conduction via a thermal bridge.

[0026] Fig. Figure 1 shows an internal combustion engine 10 with at least one combustion chamber 12, wherein a fuel injector 14 and a spark plug 16 are arranged on the combustion chamber 12. The internal combustion engine 10 is connected via its exhaust outlet 18 to an exhaust system 20, in which an exhaust gas sensor 26 and an electrically heated catalyst 24 are arranged in the direction of flow of an exhaust gas stream from the internal combustion engine 10. The electrically heated catalyst 24 is arranged at a distance of less than 5 cm, preferably less than 3 cm, downstream of the exhaust gas sensor 26. The waste heat from the electrically heated catalyst 24 is transferred to the exhaust gas sensor 26, which is arranged upstream of the electrically heated catalyst 24, by thermal radiation. This allows for simple heating of the exhaust gas sensor 26, thus enabling the use of a simpler and more cost-effective exhaust gas sensor 26.In particular, the indirect heating of the exhaust gas sensor 26 eliminates the need for an additional heating element within the sensor. Furthermore, the exhaust gas sensor 26 does not need to be designed to be dew point-free, which further reduces its cost. The electrically heated catalyst 24 and the exhaust gas sensor 26 are connected via signal lines to a control unit 40 of the combustion engine 10, with the control unit 40 controlling the heating of the electrically heated catalyst 24.

[0027] Alternatively, the internal combustion engine 10 can also be designed as a diesel engine. In this case, the spark plugs 16 on the combustion chambers 12 of the internal combustion engine 10 are omitted, while the design remains otherwise identical.

[0028] In Fig. Figure 2 shows an embodiment of an exhaust system 20 not belonging to the invention. In this embodiment, an exhaust gas sensor 26, in particular a lambda sensor 30, a NOx sensor 32, a NOx-NH3 combination sensor 34, or an oxygen sensor 36, is arranged in an exhaust gas channel 22 of the exhaust system 20 downstream of an electrically heated catalyst 24. The waste heat from the electrically heated catalyst 24 is transferred to the exhaust gas sensor 26 by convection through the exhaust gas flow of the combustion engine 10 and by thermal radiation.

[0029] In Fig.Figure 3 shows an embodiment of an exhaust system 20 according to the invention. An exhaust gas sensor 26 is arranged upstream of an electrically heated catalyst 24 and is connected to the catalyst 24 via a thermal bridge 28. The thermal bridge 28 is made of copper or a copper alloy. Copper has high thermal conductivity and correspondingly high temperature stability, making a copper thermal bridge particularly suitable for transferring heat from the catalyst 24 to the exhaust gas sensor 26. Alternatively, in an embodiment not included in the invention, the thermal bridge can also be made of an iron-based material, in particular steel.An iron material also has high temperature resistance and high thermal conductivity in order to withstand the temperatures occurring in the exhaust system 20 and to transfer the heat from the electrically heated catalyst 24 to the exhaust gas sensor 26. Reference symbol list 10 Internal combustion engine 12 Combustion chamber 14 Fuel injector 16 Spark plug 18 Outlet 20 Exhaust system 22 Exhaust duct 24 electrically heated catalyst 26 Exhaust gas sensor 28 Thermal bridge 30 Lambda sensor 32 NOx sensor 34 NOx-NH3 combination sensor 36 Oxygen sensor 40 Control unit

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