SE540383C2

SE540383C2 - Temperature sensor device and method for determining the temperature of exhaust gases from an internal combustion engine

Info

Publication number: SE540383C2
Application number: SE1651609A
Authority: SE
Inventors: Gromov Andrey; Thornblad Johan
Original assignee: Scania Cv Ab
Priority date: 2016-12-07
Filing date: 2016-12-07
Publication date: 2018-09-04
Also published as: DE102017010810A1; SE1651609A1

Abstract

The present invention relates to a temperature sensor device (30) and method for determining the temperature of exhaust gases (25) from an internal combustion engine (2) and comprising a housing (32), a central heat-conducting element (34), a space (36) between the central heat-conducting element and the wall of the housing, the space encapsulated by means of a first and second insulator elements (31; 32). The device further comprises a first heat-conductive end component (35) arranged at a first end (341) of the central heatconducting element and a second heat-conductive end component (37) arranged at a second end (342) of the central heat-conducting element and at a pre-determined distance L from the first heat-conductive end component (35). A first temperature sensing element (311) is connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is below 250°C and a second temperature sensing element (312) is connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is below 150°C in vicinity of the first end (341) of the central heat-conducting element and at a pre-determined distance X from the first temperature sensing element. The first and second temperature sensing elements, respectively, are connected to a control unit (40) comprising means to determine the temperature (T) of the exhaust gases based on measurement data from the temperature sensing elements and the pre-determined distances X and L.

Description

Temperature sensor device and method for determining the temperature of exhaust gases from an internal combustion engine TECHNICAL FIELD The invention relates to a temperature sensor device for determining the temperature of exhaust gases from an internal combustion engine, an exhaust gas system comprising the temperature sensor device, a vehicle comprising the exhaust gas system, a method for determining the temperature of exhaust gases, a computer program for performing the method steps and a computer readable medium comprising a program code for performing the method steps.

BACKGROUND ART Generally there is a need to measure temperature of exhaust gases from an internal combustion engine for example to be able to optimize engine's operation. Today in the automotive industry there are many applications that require measurement of high temperatures, i.e. temperatures in the range of from 500 to 1000°C, in the exhaust gas flow. The dominant technology to measure the highest temperatures is today thermocouple technology in which an electrical device, which uses two different conductors that produce a temperature-dependent voltage as a result of the thermoelectric effect and this voltage can be interpreted to measure temperature. However, the thermocouple devices are sensitive to process environment in which they are used and need their own electronics to function.

Problems with measuring temperatures of at least 1000°C have also been discussed in prior art. For example US4355909 discloses problems relating to maintaining brightness of the materials in the measurement body. The problem has been solved by an alternative measurement apparatus in which the temperature of the measuring body is maintained at a constant temperature by means of connecting heat tubes in contact with the hot fluid with heat-conducting rods which in turn are connected to cooled heat rods. In this way the temperature of the heat tubes in contact with the fluid can be kept at a pre-determined level below the temperature of the hot fluid. Alternatively, measuring bodies may be cooled by means of passing a liquid cooling agent through them. The device suggested by US4355909 is complex and requires control of the cooling fluid so that the temperature of the measurement body is constantly kept below the hot fluid temperature and requires several measurement points for calculation of the hot fluid temperature.

Thus, it is known in the technical field that measuring temperatures upwards 1000°C puts high demands on robustness in the materials and processes used. Further problems are for example that the variation in heat expansion coefficient between materials causes fatigue failures. Also, the high temperatures cause sensors to age and become un-tight against moisture. Furthermore, conditions for example in exhaust systems of vehicles are demanding due to vehicle vibrations and soot and particles in the exhaust gas flow. Therefore, it is desirable to find a more robust and simple technology that can be used in demanding conditions, especially in connection with exhaust gas systems in vehicles.

SUMMARY OF THE INVENTION Despite known solutions in the technical field, there is still a need to develop a device and method for measuring and estimating the temperature of exhaust gases when the gas temperature is high, i.e. more than 300°C and suitably more than about 500°C to optimize engine efficiency, fuel consumption and which device and method are robust and economical. Furthermore, there is a need for a measurement device which is reliable also in the demanding environment of exhaust gas systems in vehicles.

The objective of the present invention is thus to provide a temperature sensor device for determining the temperature of exhaust gases from an internal combustion engine which is robust and simple. It is also an objective to provide a temperature sensor device and measurement method which both are affected as little as possible by the exhaust gases and which can provide information about the temperature of the exhaust gases in a reliable way. It is also an objective of the present invention to provide a sensor device which can be easily connected to existing control systems of a vehicle, which is economic and space saving.

Furthermore, it is an objective to provide a measurement device which is reliable also in the demanding environment of exhaust gas systems in vehicles.

The objects above are attained by a temperature sensor device according to the present invention which is adapted to be placed in a wall of an exhaust gas pipe. The sensor device comprises: - a housing having a wall radially surrounding a central heat-conducting element, wherein the wall is arranged radially at a distance from the central heat-conducting element so that a space is formed between the central heat-conducting element and the wall of the housing; - a first insulator element and a second insulator element arranged at a respective first and second longitudinal end portion of the housing to thereby encapsulate the space between the central heat-conducting element and the wall of the housing, the space being arranged with an inert environment; - a first heat-conductive end component arranged at a first end of the central heatconducting element, which first end component is arranged to be cooled to a temperature of below 150°C, suitably from about -40 to 100°C; - a second heat-conductive end component arranged at a second end of the central heatconducting element and at a pre-determined distance L from the first heat-conductive end component and arranged to be in contact with the exhaust gases from the internal combustion engine, - a first temperature sensing element connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is arranged to be below 250°C, such as from 60 to 200°C; and - a second temperature sensing element connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is arranged to be below 150°C, such as from -40 to 100°C, the second temperature sensing element being arranged at a pre-determined distance X from the first temperature sensing element and at an area where the temperature is lower than the area for the first temperature sensing element, wherein the first and second temperature sensing elements, respectively, are connected to a control unit comprising means to determine the temperature of the exhaust gases based on measurement data from the temperature sensing elements and the pre-determined distances X and L. The second temperature sensing element is suitably connected to the central heatconducting element at an area in vicinity of the first heat-conductive end component. The temperature sensor device of the present invention is robust, simple in construction and economical.

The first and second temperature sensing elements, respectively, are arranged to measure at least one of resistance, voltage and/or temperature and the control unit is arranged with means to convert the measured resistance or voltage values to temperature values by means of at least look-up-table (LUT). Thus, the sensor device of the present invention is flexible.

Suitably the exhaust gas temperature is determined based on a linear temperature distribution in the central heat-conducting element (34) according to the following equation Image available on "Original document" in which X is the distance between the second temperature sensing element and the first temperature sensing element; L is the distance between the second heat-conductive end component and the first heat-conductive end component; T1is the temperature measured by the first temperature sensing element T2is the temperature measured by the second temperature sensing element.

The calculation is simple, and provides an estimated temperature for the exhaust gases which is sufficiently accurate.

Suitably, the thermal conductance of the central heat-conducting element is lower than the thermal conductance of the first and second heat-conductive end components, respectively. In this way one can provide correct thermal flow at the interfaces of the central heatconducting element maintaining the right temperatures on both ends. The difference between the thermal conductance can be obtained for example by varying the diameter or thermal conductivity of the central heat-conducting element.

Preferably the surface of the central heat-conducting element is polished to prevent heat transfer by radiation. The material of the central heat-conducting element suitably comprises ceramic material, which tolerates high temperatures. However, the material could be metallic, and comprise or consist of metal, such as stainless steel.

The first heat-conductive end component is according to one embodiment arranged to be cooled to the temperature of from about -40 to 100°C by means of a cooling system of the internal combustion engine. In this way reliable cooling can be provided. According to another embodiment, the cooling may be arranged by means of ambient conditions and/or a radiator.

Suitably, the inert environment in the space is vacuum. Thereby, gas convention can be prevented in the space.

At least the second heat-conductive end component preferably comprises metal selected from tungsten (W) and copper (CU) alloys. These metals tolerate high temperatures well while they have excellent thermal conductance.

Preferably, the first and second temperature sensing elements are thermistors and suitably negative temperature coefficient (NTC) thermistors. These sensing elements or sensors are simple, reliable and economic. The first temperature sensing element is suitably connected to the central heat-conducting element at an area inside the encapsulated space. In this way it is protected by the surrounding environment. The second temperature sensing element is suitably connected to the central heat-conducting element at an area outside the encapsulated space, whereby it can be connected to the central heat-conducting element in proximity of the first heat-conductive end component, which is cooled and thereby a more accurate calculation of the temperature of the exhaust gases can be provided. The accuracy can be further improved if the distance X between the temperature sensing elements is increased. This on the other hand may imply higher requirement on thermal threshold of the first temperature sensing element. According to another variant, also the second temperature sensing element is connected to the central heat-conducting element at an area inside the encapsulated space.

The present invention also relates to an exhaust gas system for an internal combustion system comprising an exhaust gas pipe connected to an exhaust gas manifold of the internal combustion engine, wherein a temperature sensor device as defined above is fixed to a wall of the exhaust gas pipe such that at least the second temperature sensing element is located outside an interior of the exhaust gas pipe and such that the second heat-conductive end component is arranged to be in contact with the exhaust gases inside the interior of the exhaust gas pipe. Preferably, both the first and the second temperature sensing elements are located outside an interior of the exhaust gas pipe.

The present invention also relates to a vehicle comprising the exhaust gas system above.

Furthermore, the present invention relates to a method for estimating the temperature of exhaust gases from an internal combustion engine by means of a temperature sensor device which comprises a central heat-conducting element having a pre-determined length and radially surrounded by a housing arranged at a distance from the central heat-conducting element so that a space between the central heat-conducting element and the housing is formed, and wherein a first insulator element and a second insulator element are arranged at a respective first and second longitudinal end portion of the housing to thereby encapsulate the space, the space having an inert environment. A first heat-conductive end component is arranged at a first end of the central heat-conducting element, and a second heat-conductive end component is arranged at a second end of the central heat-conducting element at the pre-determined distance L from the first heat-conductive end component and in contact with the exhaust gases from the internal combustion engine. A first temperature sensing element is connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is arranged to be below 250°C, such as from 60 to 200°C and wherein a second temperature sensing element is connected to the central heat-conducting element at an area where the temperature of the central heat-conducting element is arranged to be below 150°C, such as from -40 to 100°C. The second temperature sensing element is arranged at a pre-determined distance X from the first temperature sensing element and at an area where the temperature is lower than the area for the first temperature sensing element. The second temperature sensing element is suitably connected to the central heat-conducting element at an area in vicinity of the first heat-conductive end component. The method comprises the steps of: - processing measurement data obtained from the first temperature sensing element and second temperature sensing element, respectively, by means of a control unit connected to the first and second temperature sensing elements; - determining the temperature of the exhaust gases by means of the control unit based on the processed measurement data from the temperature sensing elements and the pre-determined distances X and L.

The processing step may comprise arranging the first and second temperature sensing elements, respectively, to measure at least one of resistance, voltage and/or temperature, and the step of determining comprises converting the measured resistance or voltage values to first and second temperature values, respectively, obtained from the first and second temperature sensing elements, respectively, by means of at least one look-up-table arranged in the control unit. In this way, the method is flexible and it is not necessary to measure temperature per se. Also cheaper sensing elements can be used if for example resistance is measured instead of temperature.

The determination step may be based on linear temperature distribution calculation using the difference between first and second determined temperatures T1and T2, the measured temperature T2and the pre-determined distances X and L being based on the following equation: Image available on "Original document" in which X is the distance between the second temperature sensing element and the first temperature sensing element; L is the distance between the second heat-conductive end component and the first heat-conductive end component; T1is the temperature measured by the first temperature sensing element T2is the temperature measured by the second temperature sensing element.

The present invention also relates to a computer program, wherein said computer program comprises program code for causing an electronic control unit or a computer connected to the electronic control unit to perform the steps according above.

Further, the present invention relates to a computer-readable medium comprising a program code stored on the computer-readable medium for performing the method steps above, when said computer program is run on an electronic control unit or a computer connected to the electronic control unit.

Further aspects, details and advantages are described below with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically illustrates a vehicle comprising an exhaust gas system in which a temperature sensor device of the present disclosure can be used; Fig. 2 schematically illustrates an internal combustion engine with an exhaust gas system and an exhaust gas pipe in which a temperature sensor device of the present disclosure is attached; Fig. 3 schematically illustrates a temperature sensor device of the present disclosure; Fig. 4 schematically illustrates a flow chart for a method for determining the temperature of exhaust gases from an internal combustion engine by means of a temperature sensor device according to an embodiment of the invention; and Fig. 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION Internal combustion engines are used in various types of applications and vehicles today, e.g. in heavy vehicles such as trucks or buses, in cars, motorboats, steamers, ferries or ships. They may also be used as industrial engines and/or in engine-powered industrial robots, power plants, e.g. electric power plants provided with a diesel generator, and in locomotives. The temperature sensor device according to the present invention is intended for an internal combustion engine and may be employed in a vehicle, e.g. in a truck or bus or as a freestanding industrial engines.

According to the present invention a vehicle is provided with an internal combustion engine and Fig. 1 depicts the vehicle 1 in a schematic side view. The vehicle is driven by an internal combustion engine 2 which powers the vehicle's tractive wheels 4 via a gearbox 6 and a propeller shaft 8. The engine 2 is provided with an exhaust system 10 in which a silencer 12 including different components of the exhaust gas system is fitted. The engine 2 is powered by fuel 14 supplied to it via a fuel system 16 which comprises a fuel tank 18.

Fig. 2 shows a schematic view of an internal combustion engine 2 which comprises six cylinders 2', wherein only one is depicted with the reference sign. The engine 2 comprises an inlet 21 for fresh air. Fresh air is distributed to the cylinders 2' via an inlet manifold 20. Exhaust gases from the combustion of a fuel are then collected in an exhaust gas manifold 22 from which the exhaust gases are fed via an exhaust gas pipe 24 to a silencer 12 comprising components to purify the exhaust gases. The exhaust gas pipe 24 comprises a sensor device 30 according to the present invention for determining the temperature of the exhaust gases from the internal combustion engine. The sensor device 30 comprises two temperature sensing elements which are connected to a control unit 40 via a communication connection or link 41 which may be a physical connection such as a communication cable or an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The control unit is suitably connected to or comprises a computer 42. The control unit 40 comprises means to determine the temperature (T) of the exhaust gases based on measurement data from first and second temperature sensing elements (311; 312) and pre-determined distances X and L (see fig. 3). From the data the temperature of the exhaust gases can then be determined by for example using a look-up table which has been calibrated for the specific sensor device and conditions in which the sensor device is used. These means can be contained in the computer 42. The sensor device is described more in detail below in connection with Fig. 3.

Generally, the exhaust gas system may comprise one or more of the following components. The components are suitably placed in the silencer of a vehicle. The sensor device according to the present invention may be fixed to the exhaust gas pipe anywhere in the exhaust gas system, but is preferably used to determine high temperatures, i.e. temperatures of above 500°C. The silencer comprises an inlet for leading an exhaust gas flow into the silencer. The silencer may comprise a diesel oxidation catalyst (DOC) which may be arranged downstream of the inlet. A DOC is a unit designed to oxidize carbon monoxide, gas phase hydrocarbons and soluble organic fraction (SOF) of diesel particulate matter to CO2and H2O. A diesel particulate filter (DPF) may be arranged downstream of the DOC. A DPF is a unit designed to remove diesel particulate matter or soot from the exhaust gas flow. The DPF can for example be a catalysed soot filter (CSF). A reducing agent arrangement for adding a reducing agent to the exhaust gas flow in order to reduce NOxcontents of the exhaust gas flow is arranged downstream of the DPF. The reducing agent may be for example a mixture of water and urea, e.g. a product with the trade name AdBlue<®>. A mixing and vaporisation arrangement, which comprises a vaporisation chamber, for mixing of the exhaust gas flow and reducing agent and for vaporization the reducing agent is arranged downstream of the reducing agent arrangement. Further, a selective catalytic reduction (SCR) purification system is arranged downstream of the mixing and vaporisation arrangement. The SCR purification system comprises a SCR-substrate which may comprise a vanadium, iron or copper catalyst, which breaks NOxdown to water vapour and nitrogen. An ammonia slip catalyst (ASC), which is designed to convert the NH3 slip to N2and H2O, may be arranged downstream of the SCR purification system. An outlet for leading the exhaust gas flow out from the silencer is arranged downstream of the ASC. The silencer may comprise several outlets.

The temperature sensor device according to the present invention is schematically shown in Fig. 3. Generally, the sensor device is aimed for determining the temperature of exhaust gases 25 from an internal combustion engine, wherein the temperatures are high, i.e. above about 300°C, suitably above 500°C. The higher the temperature to be measured is, the higher are the economical savings with the present sensor device. This is due to the fact that prior art sensor devices, which are used for temperatures above e.g. 700°C, have required the use of thermocouple devices, which are complicated and expensive. With the present device, the use of thermocouple devices can be avoided, whereby the structure of the sensor device can be simpler and thus manufacturing costs can be minimized. With the present temperature sensor device temperatures of up to about 1000°C can be determined.

The temperature sensor device is placed in a wall of an exhaust gas pipe 24, and as explained above, the device can be placed anywhere in the exhaust gas system including the silencer, but is suitably placed in the wall of the exhaust gas manifold 22 or downstream of and in proximity to the exhaust gas manifold 22. As shown in Fig. 3, the device is fixed to the exhaust gas pipe 24 perpendicular to a longitudinal extension of the exhaust gas pipe. The sensor device comprises a housing 32 having a wall which surrounds radially a central heatconducting element 34. The wall may comprise ceramic material or any other heat tolerant material, such as but not limited to alumina 60, zirconium oxide, cordierite or steatite. By radially is meant that both the central heat-conducting element 34 and the housing 32 are essentially concentric and thus have a common central point. The shape of the housing 32 is suitably cylindrical, preferably essentially circular cylindrical. The central heat-conducting element 34 may be thread like and may have a substantially cylindrical shape and has a smaller diameter than the housing 32. It is essential that the wall of the housing is arranged radially at a distance from the central heat-conducting element 34. Thereby a space 36 is formed between the central heat-conducting element 34 and the wall of the housing 32. A first insulator element 31 and a second insulator element 33 are arranged at a respective first longitudinal end portion 321 and second longitudinal end portion 322 of the housing 32 to thereby encapsulate the space 36 between the central heat-conducting element 34 and the wall of the housing 32. The space 36 has an inert environment and is preferably arranged with vacuum. In this way, there is an inert gas, i.e. noble gas (e.g. He, Ne, Ar) environment, or no matter in proximity of the central heat-conducting element 34 that can affect the properties of the element 34 chemically and/or physically. Further, in case of vacuum, there is no gas convection in the space 36. Therefore, the temperature gradient over the length of the central heat-conducting element 34 will be substantially constant or close to constant, whereby calculation of temperature variation in the central heat-conducting element 34 will be substantially linear.

The temperature sensor device 30 is fixed to the exhaust gas pipe 24 for example so that an orifice is provided in the wall of the pipe 24 and the device 30 is placed in the orifice so that the first longitudinal end portion 321 is located outside the interior of the exhaust gas pipe 24 and the second longitudinal end portion 322 is located inside the interior of the pipe 24. To obtain a temperature gradient over the central heat-conducting element 34, a first heatconductive end component 35 is arranged at a first end 341 of the central heat-conductive element 34. The first end component 35 is suitably arranged to be cooled to a temperature of below 150°C, suitably from about -40 to 100°C. The cooling may be obtained by means of a cooling system used for engine cooling, or the first end component may be subjected to cooling by the surrounding environment. In case of the ambient conditions serving as cooling conditions, a simple radiator may be provided for the cooling. The use of ambient conditions is useful especially if the sensor is slow, i.e. when the thermal conductance of the central heatconducting element is low. The use of the engine cooling system is especially advantageous when the sensor is fast, i.e. when the thermal conductance of the central heat-conducting element is high. Also, a second heat-conductive end component 37 is arranged at a second end 342 of the central heat-conducting element 34 at a pre-determined distance L from the first heat-conductive end component 35. The pre-determined distance essentially corresponds to the length L of the central heat-conducting element 34. The second heat-conductive end component 37 is arranged to be in contact with the hot exhaust gases 25 from the internal combustion engine, which travel in the direction of the arrow in Fig. 3. The first and second heat-conductive end components 35, 37 are arranged outside the housing 32. Suitably also a certain length, e.g. from about 1-10% of the length of the central heat-conducting element 34 extending in a longitudinal direction at each end 341, 342 of the central heat-conducting element 34 is arranged outside the housing and in contact with the surrounding environment. Thus, the second end 342 of the central heat-conducting element 34 is arranged to be in contact with the hot exhaust gases together with the second end component 37. In this way, the central heat-conducting element 34 will have two different end temperatures.

The thermal conductance of the central heat-conducting element 34 is pre-determined and known, and as mentioned above, due to the inert atmosphere or vacuum inside the space 36, the thermal conductance is not affected by chemical or physical factors in the exhaust gas system. In this way the temperature gradient will be substantially constant.

To determine temperatures, two temperature sensing elements are used. There is no need for more temperature sensing elements, which makes the device simple and robust. A first temperature sensing element 311 is connected to the central heat-conducting element 34 at an area where the temperature of the central heat-conducting element is below 250°c, such as from 60 to 200°C. This temperature range is obtained in the region between a second temperature sensing element 312 located in proximity or vicinity of the first heat conductive end component 35, which is cooled, and the second heat conductive end component 37, which is heated by the hot exhaust gases. The area is closer to the second heat conductive end component 37 than to the first heat conductive end component 35, and is suitably located inside the housing. A second temperature sensing element 312 is connected to the central heat-conducting element 34 at a distance X from the first temperature sensing element 311 and is located closer towards the first heat conductive end component 35 than the first temperature sensing element 311 and is located at an area where the temperature of the central heat-conducting element 34 is lower than at the position of the first temperature sensing element 311, and is below 150°C, such as from -40 to 100°C. The specific positions for the temperature sensing elements 311, 312 can be calculated or experimented, and are dependent on the heat conductivity, diameter and the length of the central heat-conducting element 34.

When the sensor device is assembled, the second temperature sensing element 312 is suitably connected before the first temperature sensing element 311 to the central heat-conducting element 34. The second temperature sensing element 312 is suitably connected to the central heat-conducting element 34 at an area in vicinity of the first heat-conductive end component 35. Suitably, the second temperature sensing element is connected to the central heatconducting element 34 at an area between the first the first longitudinal end portion 321 of the housing 32 and the first end 341 of the central heat-conducting element 34. The second temperature sensing element 312 is arranged at a pre-determined distance X from the first temperature sensing element 311.

Generally, the thermal conductance of the central heat-conducting element is suitably lower than the thermal conductance of the first and second heat-conductive end components, respectively. In this way one can provide correct thermal flow at the interfaces of the central heat-conducting element maintaining the right temperatures on both ends of the central heatconducting element 34. The difference between the thermal conductance can be obtained for example by varying the diameter or thermal conductivity of the central heat-conducting element. For example, the central heat-conducting element can be a thread of ceramic material having a diameter of up to about 1 mm, but can be even thicker. For example the second heat-conductive end component 37 comprises metal selected from tungsten (W) or copper (Cu)-alloys. The first heat-conductive end component 35 may comprise the same metals or different metals, for example stainless steel or aluminum, since the environment at the first end is not as demanding as in connection with the exhaust gases. In this way, the end components easily adapt to the surrounding cooling or exhaust gas temperatures and affect the end point temperatures of the central heat-conducting element 34 at the respective end 341, 342.

To protect the central heat-conducting element 34 against heat transfer by radiation, the surface of the central heat-conducting element 34 is preferably polished. Since most of the element 34 is located inside the housing 32 and surrounded by inert atmosphere or vacuum, the element and the surface thereof will be protected against physical and chemical factors in the exhaust gas flow, such as soot. The material of the central heat-conducting element 34 comprises preferably ceramic material, which tolerates the high temperatures in the exhaust gas flow. Other materials, such as metals, may be included in the material. For example, the material could be metallic, and comprise or consist of metal, such as stainless steel.

The first heat-conductive end component 35 is suitably arranged to be cooled to a temperature of from about -40 to 100°C by means of a cooling system of the internal combustion engine. By using the existing cooling system, a robust, space saving and reliable cooling can be provided. Alternatively, ambient conditions possibly combined with a radiator can be used for cooling.

The first and second temperature sensing elements 311, 312, respectively, are connected to a control unit 40. The temperature sensing elements are suitably thermistors or resistors which means that the resistance in the thermistor changes when the temperature changes.

Preferably, the thermistor is a negative temperature coefficient thermistor or resistor (NTC-resistor), wherein the resistance decreases when the temperature increases. Such devices are simple and reliable in use, and the cost of such devices is low. The control device 40 receives resistance values from the first and second temperature sensing elements 311, 312, respectively, via the connection. The control device 40 comprises means to determine the temperature of the exhaust gases based on the measurement data. In case of NTC-resistors, the measured data corresponds to measured resistances. The measurement data obtained from the first temperature sensing element 311 and second temperature sensing element 312, respectively, is processed by means of the control unit 40. By processing is meant that it includes a procedure in which the measurement data is converted to temperature data. The temperature (T) of the exhaust gases is then determined by means of the control unit 40 based on the processed measurement data from the temperature sensing elements 311; 312 and the pre-determined distances X and L. Determination can be done for example by using a look-up-table (LUT) for each temperature sensing element 311, 312, respectively, received from the manufacturer. The LUT includes respective data in which temperature has been determined as a function of the measured or sensed resistance value: T1= f(R1) and T2= g(R2).

Suitably, and as described above, the first temperature sensing element 311 is connected to the central heat-conducting element 34 at an area inside the encapsulated space 36 and the second temperature sensing element 312 is connected to the central heat-conducting element 34 at an area outside the encapsulated space 36. However, the second temperature sensing element 312 could be connected to the central heat-conducting element 34 at an area inside the encapsulated space 36.

The present invention also relates to an exhaust gas system 10 for an internal combustion engine 2 comprising an exhaust gas pipe 24 connected to an exhaust gas manifold 22 of the internal combustion engine 2, and reference is made to Fig. 2 and 3. The temperature sensor device 30 is fixed to a wall of the exhaust gas pipe 24 such that the first and second temperature sensing elements 311, 312 are located outside an interior of the exhaust gas pipe 24 and such that the second heat-conductive end component 37 is arranged to be in contact with the exhaust gases 25 inside the interior of the exhaust gas pipe 24. The invention also relates to a vehicle comprising the exhaust gas system 10.

Further, the present invention relates to a method for determining the temperature of exhaust gases from an internal combustion engine 2 by means of a temperature sensor device 30 as suitably configured as shown in Fig. 3 and as described above. The steps of the method are illustrated in a flow chart in Fig. 4. The method comprises the following steps - processing s101 measurement data obtained from the first temperature sensing element 311 and second temperature sensing element 312, respectively, by means of a control unit 40 connected to the first and second temperature sensing elements 311; 312; - determining s102 the temperature T of the exhaust gases by means of the control unit 40 based on the processed measurement data from the temperature sensing elements 311; 312 and the pre-determined distances X and L.

In the step s101, the first temperature sensing element 311 measures at least one of resistance, voltage and/or temperature. The step s102 comprises converting the measured resistance or voltage values to first and second temperature values T1; T2, respectively, obtained from the first and second temperature sensing elements 311; 312, respectively, by means of at least one look-up-table (LUT) arranged in the control unit 40. The control unit may according to one embodiment comprise means for determining a temperature difference between the first measured temperature (T1) and the second measured temperature (T2). In the step s102, the control unit can then determine the temperature of the exhaust gases based on linear temperature distribution calculation, in which the temperature of the exhaust gases 25 is calculated based on the determined difference between the first and second temperatures T1and T2, the measured temperature T2and the pre-determined distances X and L and the fact that the temperature distribution in the central heat-conducting element is linear. The method steps are thus suitably performed by means of the control unit 40 connected to the sensor device 30 and preferably also connected to the internal combustion engine 2 and the cooling system of the engine.

Basically, the linear temperature distribution calculation can be based on the following equation: Image available on "Original document" in which X is the distance between the second temperature sensing element and the first temperature sensing element; L is the distance between the second heat-conductive end component and the first heat-conductive end component; T1is the temperature measured by the first temperature sensing element T2is the temperature measured by the second temperature sensing element.

Thus, the first and second temperatures T1and T2can be calculated separately based on intrinsic resistance measurement using nonlinear functions T=f(R) which is different in case of different temperature sensing elements, such as NTC sensors. The gas temperature can then be obtained by the above formula: Image available on "Original document" , where L and X are saved in the control unit 40 as constants. However, there may be error sources in this implementation. For example the accuracy of the temperature sensing elements, which is multiplied by factor of Image available on "Original document" due to two independent measurements, may be unsatisfactory. Also the scale factorImage available on "Original document" for total error coming from formula may be a source for errors. Further tolerances for L and especially for X in serial production process and the nonlinearity due to imperfect construction and losses may be error sources.

The major part of the final errors is the systematic error and can be eliminated in a calibration process, individual or common batch calibration as a final step in sensor production. By the calibration process it is thus possible to minimize errors and thus improve accuracy of the exhaust gas temperature determination. The calibration may be performed according to any method known by the skilled person and for example take into account trueness, precision and/or accuracy values received by the provider of the sensing elements.

The accuracy of the temperature sensor device can be further improved if the distance X between the temperature sensing elements is increased. This on the other hand implies higher requirement on thermal threshold of the first temperature sensing element. For example according to one variant but not limited thereto, the distance X can be equal or larger than about 0.1L. In this way, better accuracy for the calculation can be provided.

Thus, the control unit 40 software will have calibrated function of two variables: T = f(R1,R2), where R1and R2are directly measured resistances.

The function can be recorded in memory of the control unit as a table (or matrix), and continuous values can be extrapolated from it. In order to reduce number of wires, the calculation function can be performed in own electronics of the sensor.

In the present control device 40, according to one variant, voltage is used instead of resistance to determine the temperature. Thus, the control device 40 further comprises means to determine voltage based on the measured resistance values. The voltage may according to an example for voltage divider be calculated from the resistance values as: U = U0*R/(R+ R0), wherein resistance is calculated in k?.

Thus, the LUT with resistance values is further calculated so that the determined temperature is a function of voltage: T1= f1(U1) and T2= f2(U2).

Only to illustrate as an example and not in any way limited to, a LUT could comprise data and values as shown in Table 1 below: Table 1 Image available on "Original document" According to another variant the temperature of the exhaust gases can thus be calculated as a function of the determined voltages: Image available on "Original document" Thus, the exhaust gas temperature T is calculated as a function of the two variable voltages, i.e. generally: T = f(U1, U2) , in which the coefficient L/x is included as a constant value in the formula.

The sensor device can then be calibrated over the measurement range of the first and second temperature sensing devices 311, 312, and an expanded LUT is obtained. The LUT may according to one example include the values as shown in Table 2 below, but is in no way limited to the values: Image available on "Original document" Image available on "Original document" Fig. 5 schematically illustrates a device 500. The control unit 40 and/or computer 42 described with reference to Fig. 2 may in a version comprise the device 500. The term "link" refers herein to a communication link which may be a physical connection such as an optoelectronic communication line, or a non-physical connection such as a wireless connection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile memory 520 has a first memory element 530 in which a computer program, e.g. an operating system, is stored for controlling the function of the device 500. The device 500 further comprises a bus controller, a serial communication port, I/O means, an A/D converter, a time and date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer program P which comprises routines for a method for calculating the temperature of the exhaust gases from an internal combustion engine 2 according to the invention. The computer program P comprises routines for processing measurement data obtained from the first temperature sensing element 311 and second temperature sensing element 312, respectively. The computer program P comprises routines for determining the temperature T of the exhaust gases based on the processed measurement data from the temperature sensing elements 311; 312 and the pre-determined distances X and L. The program P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it means that the data processing unit 510 effects a certain part of the program stored in the memory 560 or a certain part of the program stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. The non-volatile memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the second memory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepared to effect code execution as described above.

Parts of the methods herein described may be effected by the device 500 by means of the data processing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, methods herein described are executed.

The foregoing description of the present invention is provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to restrict the invention to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The embodiments have been chosen and described in order best to explain the principles of the invention and its practical applications and hence make it possible for a skilled person to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims

1. A temperature sensor device (30) for determining the temperature of exhaust gases (25) from an internal combustion engine (2), the temperature sensor device (30) being adapted to be placed in a wall of an exhaust gas pipe (24), characterized in that the sensor device comprises - a housing (32) having a wall radially surrounding a central heat-conducting element (34), wherein the wall is arranged radially at a distance from the central heat-conducting element (34) so that a space (36) is formed between the central heat-conducting element (34) and the wall of the housing (32); - a first insulator element (31) and a second insulator element (33) arranged at a respective first longitudinal end portion (321) and second longitudinal end portion (322) of the housing (32) to thereby encapsulate the space (36) between the central heat-conducting element (34) and the wall of the housing (32), the space (36) arranged with an inert environment; - a first heat-conductive end component (35) arranged at a first end (341) of the central heat-conductive element (34), which first end component (35) is arranged to be cooled to a temperature of below 150°C, suitably from about -40 to 100°C; - a second heat-conductive end component (37) arranged at a second end (342) of the central heat-conducting element (34) and at a pre-determined distance L from the first heat-conductive end component (35) and arranged to be in contact with the exhaust gases (25) from the internal combustion engine (2), - a first temperature sensing element (311) connected to the central heatconducting element (34) at an area where the temperature of the central heat-conducting element is arranged to be below 250°C, such as from 60 to 200°C; and - a second temperature sensing element (312) connected to the central heatconducting element (34) at an area where the temperature of the central heat-conducting element is arranged to be below 150°C, such as from -40 to 100°C, the second temperature sensing element (312) being arranged at a pre-determined distance X from the first temperature sensing element (311) and at an area where the temperature is lower than the area for the first temperature sensing element (311), wherein the first and second temperature sensing elements (311; 312), respectively, are connected to a control unit (40) comprising means to determine the temperature (T) of the exhaust gases based on measurement data from the temperature sensing elements (311; 312) and the pre-determined distances X and L.

2. The temperature sensor device of claim 1, characterized in that the first and second temperature sensing elements (311; 312), respectively, are arranged to measure resistance, voltage and/or temperature and the control unit is arranged with means to convert the measured resistance or voltage values to temperature values by means of at least look-up-table (LUT).

3. The temperature sensor device of claim 1 or 2, characterized in that the exhaust gas temperature is determined based on a linear temperature distribution in the central heat-conducting element (34) according to the following equation: Image available on "Original document" in which X is the distance between the second temperature sensing element (312) and the first temperature sensing element (311); L is the length of the central heat-conducting element (34); T1is the temperature determined from the measurement data from the first temperature sensing element (311); T2is the temperature determined from the measurement data from the second temperature sensing element (312).

4. The temperature sensor device of claim 1 to 3, characterized in that the thermal conductance of the central heat-conducting element (34) is lower than the thermal conductance of the first and second heat-conductive end components (35; 37), respectively.

5. The temperature sensor device of claim 1 to 4, characterized in that the surface of the central heat-conducting element (34) is polished.

6. The temperature sensor device of any one of the preceding claims, characterized in that the material of the central heat-conducting element (34) comprises ceramic material.

7. The temperature sensor device of any one of the preceding claims, characterized in that the first heat-conductive end component (35) is arranged to be cooled to a temperature of from about -40 to 100°C by means of a cooling system of the internal combustion engine (2).

8. The temperature sensor device of any one of the preceding claims 1-6, characterized in that the first heat-conductive end component (35) is arranged to be cooled to a temperature of from about -40 to 100°C by means of ambient conditions.

9. The temperature sensor device of any one of the preceding claims, characterized in that the inert environment is vacuum.

10. The temperature sensor device of any one of the preceding claims, characterized in that the second heat-conductive end component (37) comprises metal selected from tungsten (W) or copper (CU) alloys.

11. The temperature sensor device of any one of the preceding claims, characterized in that the first and second temperature sensing elements (311; 312) are negative temperature coefficient (NTC) thermistors.

12. The temperature sensor device of any one of the preceding claims, characterized in that the first temperature sensing element (311) is connected to the central heatconducting element (34) at an area inside the encapsulated space (36).

13. The temperature sensor device of any one of the preceding claims, characterized in that the second temperature sensing element (312) is connected to the central heatconducting element (34) at an area outside the encapsulated space (36).

14. Exhaust gas system (10) for an internal combustion engine (2) comprising an exhaust gas pipe (24) connected to an exhaust gas manifold (22) of the internal combustion engine (2) characterized in that a temperature sensor device (30) according to any one of claims 1-13 is fixed to a wall of the exhaust gas pipe (24) such that at least the second temperature sensing element (312) is located outside an interior of the exhaust gas pipe (24) and such that the second heat-conductive end component (37) is arranged to be in contact with the exhaust gases (25) inside the interior of the exhaust gas pipe (24).

15. Vehicle (1) characterized in that it comprises the exhaust gas system (10) of claim 14.

16. A method for determining the temperature of exhaust gases (25) from an internal combustion engine (2) by means of a temperature sensor device (30), which comprises a central heat-conducting element (34) having a pre-determined length L and radially surrounded by a housing (32) arranged at a distance from the central heat-conducting element (34) so that a space (36) between the central heat-conducting element (34) and the housing (32) is formed, and wherein a first insulator element (31) and a second insulator element (33) are arranged at a respective first and second longitudinal end portion (321; 322) of the housing (32) to thereby encapsulate the space (36), the space (36) having an inert environment, wherein a first heat-conductive end component (35) is arranged at a first end (341) of the central heat-conducting element (34), and a second heat-conductive end component (37) is arranged at a second end (342) of the central heat-conducting element (34) at a pre-determined distance L from the first heat-conductive end component (35) and in contact with the exhaust gases (25) from the internal combustion engine (2), wherein a first temperature sensing element (311) is connected to the central heat-conducting element (34) at an area where the temperature of the central heat-conducting element (34) is arranged to be below 250°c, such as from 60 to 200°C, and wherein a second temperature sensing element (312) is connected to the central heat-conducting element (34) at an area where the temperature of the central heat-conducting element (34) is arranged to be lower and below 150°C, such as from -40 to 100°C, the second temperature sensing element (312) being arranged at a pre-determined distance X from the first temperature sensing element (311) and at an area where the temperature is lower than the area for the first temperature sensing element (311), the method characterized by steps of: - processing (s101) measurement data obtained from the first temperature sensing element (311) and second temperature sensing element (312), respectively, by means of a control unit (40) connected to the first and second temperature sensing elements (311; 312); - determining (s102) the temperature (T) of the exhaust gases by means of the control unit (40) based on the processed measurement data from the temperature sensing elements (311; 312) and the pre-determined distances X and L.

17. Method according to claim 16, wherein the step (s101) comprises arranging the first and second temperature sensing elements (311; 312), respectively, to measure at least one of resistance, voltage and/or temperature, and the step (s102) comprises converting the measured resistance or voltage values to first and second temperature values (TI; T2), respectively, obtained from the first and second temperature sensing elements (311; 312), respectively, by means of at least one look-up-table (LUT) arranged in the control unit (40).

18. Method according to any of claims 16 or 17, characterized by the determination step (102) being based on linear temperature distribution calculation using the difference between first and second determined temperatures T1and T2, the measured temperature T2and the pre-determined distances X and L being based on the following equation: Image available on "Original document" in which X is the distance between the second temperature sensing element (312) and the first temperature sensing element (311); L is the distance between the second heat-conductive end component (37) and the first heat-conductive end component (35); T1is the temperature measured by the first temperature sensing element (311); T2is the temperature measured by the second temperature sensing element (312).

19. A computer program (P), wherein said computer program comprises program code for causing an electronic control unit (40; 500) or a computer (42; 500) connected to the electronic control unit (40; 500) to perform the steps according to any of the claims 16-18.

20. A computer-readable medium comprising a program code stored on the computerreadable medium for performing the method steps according to any of claims 16-18, when said computer program is run on an electronic control unit (40; 500) or a computer (42; 500) connected to the electronic control unit (40; 500).