Patent Description:
The use of a thermocouple for temperature measurement in a car is well known. Temperature sensors with one or more thermocouples are characterized by the ability to detect a wide temperature range of -<NUM> to <NUM>. The so-called thermoelectric effect is used here: If two electrically conductive measuring wires made of different metallic materials are connected to one another and if this connection point and the free ends of the measuring wires are exposed to different temperatures, a thermal voltage is generated between the free ends, the strength of which is directly proportional to the temperature difference between the measuring point and a reference temperature at a reference point or junction at the free ends of the measuring wires. If the temperature at the reference junction and the characteristic thermally induced electrical voltage of the different measuring wires are known, the temperature at the junction can be determined.

Compared to other temperature sensors, thermocouples offer the advantage that they can be made comparatively small and compact and the thermoelectric voltage can be transmitted over a greater distance. They are therefore able to measure the temperature even in places that are difficult to access, for example in the exhaust system of a motor vehicle or in a cooling water or oil circuit of the vehicle.

A temperature sensor for a motor vehicle engine with a thermocouple, a printed circuit board and an integrated circuit is known from <CIT>. The temperature sensor comprises a protective housing made of a polymer material, in which the circuit board is arranged. The free ends of the thermocouple are connected to terminals on the circuit board by means of connecting means which are made of the same material as the respective measuring wire of the thermocouple.

A temperature sensor for a motor vehicle is known from <CIT>. The temperature sensor has a thermocouple, which is connected to metallic transmission elements in a first housing. The temperature sensor also has a second housing in which a printed circuit board with an evaluation circuit is arranged, the second housing encasing the first housing. The metallic transmission elements connect the free ends of the thermocouple with the printed circuit board. Each connection point is surrounded by a sealing element. The first housing supports the junction between the free ends of the thermocouple and the metallic transmission bodies.

<CIT> discloses a temperature sensor with a thermocouple and an evaluation circuit as well as a manufacturing method for such a temperature sensor. The temperature sensor comprises a printed circuit board, a housing, a thermocouple and a connecting element. The circuit board includes an electrical circuit configured to receive a sensor signal and to generate a sensor characteristic in response to the received sensor signal. The housing includes a body and a cavity defined by inner surfaces of the body and configured to receive the circuit board, the circuit board being positioned in the cavity. The input line is configured to receive the signal from a sensor and can be formed with an insulated solid or stranded conductor. The connecting element comprises a unitary body with a first end, which is attached directly to one end of the measuring wire of the thermocouple, and with a second end, which is positioned in the cavity and is attached directly to the printed circuit board.

The disadvantage of the known solutions, however, is that they are complex to manufacture and therefore comparatively expensive. Furthermore, the distance between the free ends of the thermocouple, at which the thermoelectric voltage of the thermocouple is detected, and a reference temperature sensor on the circuit board causes a measurement error, because the temperature at the free ends of the thermocouple differs from the temperature on the circuit board. The measuring accuracy of the temperature sensor is reduced by partition walls and other boundaries.

The invention is based on the object of improving the measurement accuracy of a temperature sensor and of overcoming the disadvantages known from the prior art.

This object is solved by a temperature sensor with the features of claim <NUM> or of claim <NUM>. According to the invention, it is provided that the housing has a cavity in which the integrated circuit, in particular the application specific integrated circuit (ASIC), and connections with which the stranded wires are electrically conductively connected to the transmission elements are arranged. By arranging the printed circuit board (PCB), the transmission elements as well as the stranded wires of the thermocouples in a common cavity of the housing, the measuring point for the thermoelectric voltage can be located close to the measuring point for a reference temperature on the printed circuit board. In addition, this arrangement avoids partition walls which could have an insulating effect and thus lead to a deviation between the temperature at the strands of the thermocouple and the reference temperature on the circuit board. Thus, the deviation between the temperature at the stranded wire of the thermocouple and the resulting thermoelectric voltage to the measured reference temperature on the circuit board can be reduced. By more precisely determining the reference temperature at the "cold ends" of the thermocouple, the measuring accuracy at the connection point of the measuring wires of the thermocouple, i.e. the "hot end" of the thermocouple, can be improved. The housing preferably completely surrounds the printed circuit board in order to protect the printed circuit board from mechanical damage, dirt or splash water.

The features listed in the dependent claims allow advantageous further developments and improvements of the temperature sensor specified in the independent patent claims.

In a preferred embodiment of the temperature sensor, it is provided that the transmission elements are designed as SMD connectors, wherein the SMD connectors are arranged on the printed circuit board, the SMD connectors connecting the stranded wires of the measuring wires to the printed circuit board in an electrically conductive manner. SMD connectors enable a simple and stable connection between the stranded wires of the thermocouples and the printed circuit board. In addition, the temperature difference between the measuring point for evaluating the thermal voltage of the thermocouple and the reference temperature can be minimized by a connection using SMD connectors. By connecting the SMD connectors to the circuit board via one or more copper layers, the heat transfer can also be improved by conduction, which further reduces the temperature difference. In addition, the excellent heat conduction can reduce the time until a stable measuring temperature is reached.

In a preferred configuration of the temperature sensor, it is provided that two metallic terminals are arranged in the housing, a section of the first measuring wire being connected to the first terminal and a section of the second measuring wire being connected to the second terminal in a material or form-fitting manner in order to form a strain relief. A requirement for such a temperature sensor is that a force acting on the measuring wires of the thermocouple should not be transmitted to the sensitive printed circuit board or the ASIC. The metallic terminals provide strain relief so that a force acting on the measuring wires of the thermocouples can be diverted into the housing. The strain relief leads to a reduction of the mechanical forces acting on the printed circuit board. This reduces the risk of damage to the printed circuit board.

It is particularly preferred if the terminals or the sections connected to the terminals are spaced apart from the printed circuit board. A distance between the terminals and the printed circuit board can prevent the danger of an electrical short circuit. In this way the function of the strain relief and the electrical signal transmission from the measuring wires of the thermocouple to the printed circuit board can be strictly separated.

Alternatively or in addition, it is advantageous to have a layer of insulating material between the terminals or the sections of the measuring wires connected to the terminals and the printed circuit board. This prevents an electric connection between the terminals and the integrated circuit arranged on the printed circuit board. An insulation layer can prevent an electrical short circuit between the stranded wire of the thermocouple and the printed circuit board. In this way, electrical contact between the terminals and the printed circuit board can be reliably prevented, particularly in the event of vibrations, shocks or mechanical impacts.

In a further preferred design of the temperature sensor, the transmission elements are arranged in the housing, with a free end section of each terminal being electrically connected to the circuit board.

In an advantageous design of the temperature sensor it is provided that the stranded wire of the first measuring wire is connected to the first terminal and the stranded wire of the second measuring wire is connected to the second terminal in a material-locking or form-locking manner to form a strain relief.

It is particularly preferred if the terminals are accommodated in the printed circuit board by means of a press-fit connection. This enables a simple and stable connection between the free end sections of the terminals and the PCB, which can be made without additional tools. Further welding or soldering connections can be dispensed with, thus minimising production costs.

In an advantageous design of the temperature sensor, the stranded wire or sections of the measuring wires are welded or crimped to the terminals. By welding the stranded wires of the thermocouple to the respective terminal, a permanent and reliable connection can be established. A welded connection can be produced in particular by an ultrasonic welding process or a resistance welding process. Alternatively, it is advantageous to connect the stranded wires of the thermocouple with the terminals by means of a crimp connection, whereby the connection is made by means of a corresponding plastic deformation on the stranded wire and/or the terminals. A crimp connection can also be used to transmit correspondingly high forces, so that a crimp connection offers sufficient resistance when the measuring wires of the thermocouple are subjected to a tensile load, thus avoiding damage to the connection point.

In accordance with a beneficial further development of the temperature sensor, it is planned that the terminals will be U-shaped or meander-shaped in a cross-sectional plane extending essentially perpendicular in respect to the extension of the printed circuit board. This allows an elasticity to be realized in the direction of tension of the measuring wires, which allows an elastic deformation of the domes, so that a tensile force does not lead to permanent damage to the connection. Furthermore, the U-shape or meander shape allows the dome to be easily accommodated in the housing with a positive fit.

In a preferred embodiment of the temperature sensor, it is provided that the terminals are accommodated positively in the housing at least in sections. The position of the terminals relative to the housing can be defined and fixed by means of a form-fit connection. In addition, comparatively high forces can be transmitted through the positive connection, so that the terminals provide efficient strain relief for the connection points on the PCB. Forces acting on the measuring wires of the thermocouple are transmitted into the housing via the domes, so that the PCB is relieved.

In another preferred embodiment of the temperature sensor it is provided that the printed circuit board is connected by means of further transmission elements with an electrical output contact for contacting the temperature sensor. In order to enable simple electrical contacting of the temperature sensor, the printed circuit board can be connected to the output contact via further transmission elements. The design of the housing makes it easy to seal the cavity against dirt and spray water.

It is particularly preferred if the other transmission elements are connected to the housing by means of an injection moulding process with a material fit and/or form fit connection. By means of a material-locking connection, a sealing between the output contact and the printed circuit board can be achieved in a simple manner, whereby the printed circuit board is protected against splash water and/or contamination. The position of the transmission element can be fixed exactly by means of a positive-locking connection, so that the mounting of the temperature sensor, in particular the electrical connection between the printed circuit board and the electrical output contact can be established in a simple manner.

In an advantageous design of the temperature sensor, a reference temperature sensor is provided on the printed circuit board. By means of a reference temperature sensor on the printed circuit board, in particular as part of the integrated circuit, the measured thermoelectric voltage can be assigned a reference temperature prevailing at the cold ends of the thermocouple. Since there is only a small distance between the cold ends of the thermocouple and the reference temperature sensor, the temperature at the cold ends of the thermocouples essentially corresponds to the temperature at the reference temperature sensor.

Alternatively, the reference temperature sensor can also be arranged at another location in the cavity of the housing. Proximity of the reference sensor to the cold ends of the thermocouple is desired.

Another aspect of the invention concerns a method for manufacturing such a temperature sensor, whereby the printed circuit board, the transmission elements as well as the strands of the measuring wires are arranged in a common cavity of the housing. The method enables the production of a mechanically robust sensor, which has a high measuring accuracy and can be manufactured with low production costs. By arranging the printed circuit board, the transmission elements as well as the stranded wire of the thermocouples in a common cavity of the housing, the measuring point for the thermoelectric voltage can be placed close to the measuring point for a reference temperature on the printed circuit board. In addition, this arrangement avoids partition walls which could have an insulating effect and thus lead to a deviation between the temperature at the stranded wire of the thermocouple and the reference temperature on the circuit board. Thus, the deviation between the temperature at the stranded wire of the thermocouples and the resulting thermoelectric voltage to the measured reference temperature on the printed circuit board can be reduced.

As a further benefit, the proposed temperature sensor allows the design of a very small and compact temperature sensor despite the spatial separation of strain relief and electrical transmission point to the printed circuit board. The material of the terminals can be selected in such a way that a stable fixing of the stranded wire to the terminals by means of a welding or crimping process is possible. The SMD connectors or pressfit connection allows an efficient transmission of an electrical signal to the PCB and from there to the integrated circuit.

The various embodiments of the invention mentioned in this application can be combined with each other to advantage, unless otherwise stated in the individual case.

The invention is described in the following in design examples based on the associated drawings. Identical components or components with the same function are provided with the same reference numbers in the different drawings.

<FIG> and <FIG> show a first design example of a temperature sensor <NUM> with a housing <NUM> and a printed circuit board <NUM> arranged at least partially in the housing <NUM>. The temperature sensor <NUM> further comprises a thermocouple <NUM>, with an integrated circuit <NUM>, in particular an ASIC <NUM>, arranged on the printed circuit board <NUM>. The thermocouple <NUM> comprises a first measuring wire <NUM> and a second measuring wire <NUM>, the first measuring wire <NUM> and the second measuring wire <NUM> being electrically conductively connected to each other with their respective first ends at a connection point or junction <NUM>. The measuring wires <NUM>, <NUM> have an electrically conductive stranded wire or strand <NUM>, <NUM> at their second end. Transmission elements <NUM>, <NUM> for transmitting a measuring voltage Um or a measuring current Im to the printed circuit board <NUM> are arranged in the housing <NUM>. The transmission elements <NUM>, <NUM> are made of a different material than the stranded wires <NUM>, <NUM>. The stranded wires <NUM>, <NUM> are connected to the respective transmission element <NUM>, <NUM> at a connection point or junction <NUM>. The housing <NUM> has a cavity <NUM>, in which the ASIC <NUM> and the connection point <NUM> with which the stranded wire <NUM>, <NUM> are electrically conductively connected to the transmission elements <NUM>, <NUM> are arranged.

The transmission elements <NUM>, <NUM> could be designed as SMD connectors <NUM>, <NUM>, which are soldered to the printed circuit board <NUM>. A reference temperature sensor <NUM> is arranged in the cavity <NUM> preferably on the printed circuit board <NUM>, most preferably on the ASIC <NUM>, with which a reference temperature Tref can be recorded. By means of the reference temperature Tref and the thermoelectric voltage between the two stranded wires <NUM>, <NUM> of the measuring wires <NUM>, <NUM>, a measuring temperature Tm can be determined at the connection point <NUM>.

<FIG> shows the first example of the temperature sensor <NUM> in a further illustration. It can be seen that the housing <NUM> has a cavity <NUM>. The housing <NUM> also has a first connection orifice <NUM> for connecting a first thermocouple <NUM>. The housing <NUM> also has a second connection orifice <NUM> for connecting a second thermocouple <NUM>. The housing <NUM> also has a further orifice <NUM>, which enables an electrical connection of the printed circuit board <NUM> with an electrical output contact <NUM>. The top side of the housing <NUM> could be closed by means of a cover, such that the cavity <NUM> is sealed.

As shown in <FIG>, the strand <NUM> of a first measuring wire <NUM> of the thermocouple <NUM> is connected to the printed circuit board <NUM> by means of an SMD connector <NUM>. A second strand <NUM> of a second measuring wire <NUM> is connected to the PCB <NUM> with a second SMD connector <NUM>.

As shown in <FIG> the housing <NUM> comprises two metallic terminals <NUM>, <NUM>, which are positively connected with the housing <NUM>. The first measuring wire <NUM> of the thermocouple <NUM> is connected to a first terminal <NUM> at a further connection point <NUM> via a weld seam <NUM>. The weld seam <NUM> can be produced in particular by means of an ultrasonic welding process or a resistance welding process. The second measuring wire <NUM> of thermocouple <NUM> is connected at a connection point <NUM> to the second terminal <NUM> by means of a weld seam <NUM>. As an alternative to a weld seam <NUM>, the measuring wires <NUM>, <NUM> can also be connected to the respective terminals <NUM>, <NUM> by means of a crimp connection <NUM>. By connecting the strands <NUM>, <NUM> of the measuring wires <NUM>, <NUM> to the terminals <NUM>, <NUM>, an effective strain relief is created so that the PCB is not damaged when a tensile force is applied to the measuring wires <NUM>, <NUM> of the thermocouple <NUM> and this tensile force is introduced into the housing <NUM> via the terminals <NUM>, <NUM>. The terminals <NUM>, <NUM> could also be referred to as domes.

To form a weld seam <NUM> or a crimp connection <NUM> between the measuring wires <NUM>, <NUM> of thermocouple <NUM> and the terminals <NUM>, <NUM>, the measuring wires <NUM>, <NUM> are each at least partially stripped of insulation. For this purpose, a section <NUM>, <NUM> of the respective measuring wire <NUM>, <NUM> adjacent to the terminal <NUM>, <NUM> is stripped of its insulation. The transmission of the electrical signal from the respective measuring wire <NUM>, <NUM> to the printed circuit board <NUM> is realized as shown in <FIG> and <FIG> via an SMD connector <NUM>, <NUM>.

<FIG> shows another example of a temperature sensor <NUM>, which comprises a housing <NUM> with a cavity <NUM> in which a printed circuit board <NUM> is located. The temperature sensor <NUM> further comprises a thermocouple <NUM>, with an ASIC <NUM> arranged on the printed circuit board <NUM>. The thermocouple <NUM> comprises a first measuring wire <NUM> and a second measuring wire <NUM>, the first measuring wire <NUM> and the second measuring wire <NUM> being electrically conductively connected to each other with their respective first ends at a junction <NUM>. The measuring wires <NUM>, <NUM> have electrically conductive stranded wires <NUM>, <NUM> at their respective second ends.

The housing <NUM> contains transmission elements <NUM>, <NUM> for transmitting a measuring voltage Um or a measuring current Im to the printed circuit board <NUM>. The transmission elements <NUM>, <NUM> are designed as terminals <NUM>, <NUM>, which are positively mounted in the housing <NUM>. A free end section <NUM>, <NUM> of each terminal <NUM>, <NUM> is connected to an electrically conductive contact on the printed circuit board <NUM> e.g. by means of a press-fit connection <NUM>.

On the printed circuit board <NUM>, preferably integrated in the ASIC <NUM>, a reference temperature sensor <NUM> is arranged to determine a reference temperature Tref. In knowledge of the reference temperature Tref and the thermoelectric voltage between the two strands <NUM>, <NUM> of the measuring wires <NUM>, <NUM>, a measuring temperature Tm can be determined at the connection point <NUM>. Both the electrical signal transmission and the strain relief are carried out at a connection point <NUM>, <NUM> between the respective strands <NUM>, <NUM> of the measuring wires <NUM>, <NUM> and the dome <NUM>, <NUM>. The dome <NUM>, <NUM> is electrically connected with its end section <NUM>, <NUM> at a transmission point <NUM>, <NUM> to the printed circuit board <NUM>.

<FIG> shows further views of the first design example for a temperature sensor <NUM>. It can be seen that the connection orifices <NUM>, <NUM> for the thermocouples <NUM> and the further orifice <NUM> for the electrical output contact <NUM> are formed on opposite end faces of the housing <NUM>. It can also be seen that the measuring wires <NUM>, <NUM> of thermocouple <NUM> are connected to the SMD connectors <NUM>, <NUM> at one connection point <NUM> and to the terminals <NUM>, <NUM> at another connection point.

<FIG> shows further views of the temperature sensor <NUM> described in <FIG>. It can be seen that the printed circuit board <NUM> is connected to the electrical output contact <NUM> via further transmission elements <NUM>, <NUM>. The strands <NUM>, <NUM> of the measuring wires <NUM>, <NUM> are welded or crimped to the terminals <NUM>, <NUM>. An insulation layer <NUM> can be provided between the strands <NUM>, <NUM> and the printed circuit board <NUM> to electrically separate the printed circuit board <NUM> from the terminals <NUM>, <NUM>.

The insulation layer <NUM> could preferably be formed by an air-gap or by a material layer e.g. a part of the housing <NUM>.

Preferably, the connection <NUM>, <NUM> where the stranded wires <NUM>, <NUM> are connected to the terminals <NUM>, <NUM> is provided on the underside of the PCB <NUM>. Preferably the connection <NUM>, <NUM> is on one side of the PCB <NUM> and the ASIC <NUM> is on an opposite side of the PCB <NUM>. Thus, ASIC <NUM> and connections <NUM>, <NUM> could be brought together closely, which enhances the accuracy and reliability of the measuring result.

The free end sections <NUM>, <NUM> of the terminals <NUM>, <NUM> are each electrically connected to the printed circuit board <NUM> via a clamp connection <NUM>, <NUM>, e.g. a press fit connection.

<FIG> shows another example of a temperature sensor <NUM>, which comprises a housing <NUM> with a cavity <NUM> in which a printed circuit board <NUM> is located. The temperature sensor <NUM> further comprises a thermocouple <NUM>, with an integrated circuit <NUM>, in particular an ASIC <NUM>, arranged on the printed circuit board <NUM>. The thermocouple <NUM> comprises a first measuring wire <NUM> and a second measuring wire <NUM>, the first measuring wire <NUM> and the second measuring wire <NUM> being electrically conductively connected to each other with their respective first ends at a junction <NUM> as shown in <FIG>. The measuring wires <NUM>, <NUM> have electrically conductive stranded wires <NUM>, <NUM> at their respective second ends.

As shown in <FIG> the housing <NUM> comprises two metallic terminals <NUM>, <NUM>, which are positively connected with the housing <NUM>. The first measuring wire <NUM> of the thermocouple <NUM> is connected to a first terminal <NUM> at a further connection point <NUM> via a weld seam <NUM>. The weld seam <NUM> can be produced in particular by means of an ultrasonic welding process or a resistance welding process. The second measuring wire <NUM> of thermocouple <NUM> is connected at a connection point <NUM> to the second terminal <NUM> by means of a weld seam <NUM>. As an alternative to a weld seam <NUM>, the measuring wires <NUM>, <NUM> can also be connected to the respective terminals <NUM>, <NUM> by means of a crimp connection <NUM>. By connecting the strands <NUM>, <NUM> of the measuring wires <NUM>, <NUM> to the terminals <NUM>, <NUM>, an effective strain relief is created so that the PCB is not damaged when a tensile force is applied to the measuring wires <NUM>, <NUM> of the thermocouple <NUM> and this tensile force is introduced into the housing <NUM> via the terminals <NUM>, <NUM>.

Claim 1:
A temperature sensor (<NUM>) comprising
- a housing (<NUM>) which surrounds a printed circuit board (<NUM>) at least in sections, the printed circuit board (<NUM>) carrying an integrated circuit (<NUM>), in particular an ASIC,
- a thermocouple (<NUM>) comprising a first measuring wire (<NUM>) and a second measuring wire (<NUM>), wherein
- the first measuring wire (<NUM>) and the second measuring wire (<NUM>) are connected to each other by their respective first ends at a first connection point (<NUM>), wherein
- the measuring wires (<NUM>, <NUM>) each comprise an electrically conductive stranded wire (<NUM>, <NUM>) at their respective second ends, wherein
- transmission elements (<NUM>, <NUM>) are arranged in the housing (<NUM>) for transmitting a measuring voltage (Um) or a measuring current (Im) from the stranded wires (<NUM>, <NUM>) to the printed circuit board (<NUM>), wherein
- the transmission elements (<NUM>, <NUM>) are made of a different material than the stranded wires (<NUM>, <NUM>) of the measuring wires (<NUM>, <NUM>)
- the housing (<NUM>) has a cavity (<NUM>) in which the integrated circuit (<NUM>) and connection points (<NUM>) with which the stranded wires (<NUM>, <NUM>) are electrically conductively connected to the transmission elements (<NUM>, <NUM>) are arranged
characterized in that
- two metallic terminals (<NUM>, <NUM>) are arranged in the housing (<NUM>), a section (<NUM>) of the first measuring wire (<NUM>) being connected to the first terminal (<NUM>) and a section (<NUM>) of the second measuring wire (<NUM>) being connected to the second terminal (<NUM>) in a material-locking or form-locking manner in order to form a strain relief,
- and in that the terminals (<NUM>, <NUM>) are received positively in the housing (<NUM>) at least in sections, wherein the position of the terminals relative to the housing is defined and fixed by means of a form-fit connection, so that the terminals (<NUM>, <NUM>) provide strain relief for connection points on the printed circuit board (<NUM>).