Isolated temperature sensing for electrical terminals

Abstract

A method for detecting the temperature of an electrical terminal (20, 120). The method comprises: applying a material sheet (24, 124) to the surface of the electrical terminal (20, 120), wherein the thermal mass of the material sheet (24, 124) is less than 25%, 20%, 15%, 10%, or 5% of the thermal mass of the electrical terminal (20, 120), so that the material sheet (24, 124) does not significantly increase the resistance or thermal capacity of the electrical terminal (20, 120); and remotely sensing the change of the material sheet (24, 124 using an electrical isolation circuit (50, 150) outside the electrical terminal (20, 120) to determine whether the electrical terminal (20, 120) is operating at a safe temperature, thereby optimizing the current on the electrical terminal (20, 120).

Description

Technical Field

[0001] The present invention relates to an apparatus and method for remote and isolated temperature sensing of electrical terminals. Background Art

[0002] The current rating of an electric vehicle (EV) charging port connector is currently limited by the contact temperature. A contact temperature approach to connector derating allows the charging system to maximize charging current (and minimize charging time) while avoiding damage to the charging port connector. Key attributes of a suitable temperature sensor include high accuracy, fast response time, and low cost.

[0003] The accuracy and response time of traditional sensors, such as resistance temperature sensors (RTDs) or thermocouples, can be limited because they require electrical isolation of the contact pins. The additional material required for electrical isolation increases the thermal resistance and thermal capacitance of the sensing system. The additional resistance reduces the absolute measurement accuracy. The additional thermal resistance and capacitance increase the system time constant, resulting in longer sensor response times.

[0004] Previous improvements to temperature sensing have been based on temperature sensors such as phase-change wax capsules or Nitinol wire spirals embedded in the center of a pin. The electrical isolation required for these sensors does not add thermal resistance or capacitance, minimizing their response time, and their location in the center of the pin ensures high absolute accuracy. However, a drawback of any such embedded sensor is the reduction in the pin cross-sectional area required to accommodate the volume of the sensor, which results in increased resistance and increased ohmic heating.

[0005] The problem to be solved is to provide a remote sensing circuit and method wherein the components provide galvanic isolation without increasing the measurement system time constant and without reducing the pin cross-sectional area resulting from the above mentioned prior solutions. Summary of the invention

[0006] This problem is solved by an external circuit and method that senses temperature-driven changes in the material applied to the contacts. The external circuit does not contact the pins and is therefore electrically isolated. The material is applied directly to the pin surface, adding little or no thermal mass to the system. The two components combined provide electrical isolation without increasing the measurement system time constant, and they do so without reducing the pin cross-sectional area.

[0007] One embodiment is directed to a method for detecting the temperature of an electrical terminal. The method includes: applying a material sheet to the surface of the electrical terminal, the thermal mass of the material sheet being less than 25%, 20%, 15%, 10%, or 5% of the thermal mass of the electrical terminal, so that the material sheet does not significantly increase the resistance or thermal capacitance of the electrical terminal; and remotely sensing changes in the material sheet using an electrical isolation circuit external to the electrical terminal to determine whether the electrical terminal is operating at a safe temperature, thereby optimizing the current on the electrical terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will now be described by way of example with reference to the accompanying drawings:

[0009] Figure 1 is a perspective view of an illustrative charging port connector incorporating the electrical terminals of the present invention and isolated temperature sensing of the electrical terminals.

[0010] Figure 2 is a schematic diagram of an exemplary electrical terminal having a thermochromic material disposed thereon and an exemplary remote temperature sensing system.

[0011] Figure 3 is with Figure 2 A schematic diagram of an illustrative detector circuit associated with a remote temperature sensing system.

[0012] Figure 4 is from Figure 3 Schematic diagram of an illustrative circuit of the detector circuit output.

[0013] Figure 5 is a schematic diagram of an alternative illustrative electrical terminal with conductive material disposed thereon and an illustrative remote temperature sensing system.

[0014] Figure 6 is with Figure 5 A schematic diagram of an illustrative detector circuit associated with a remote temperature sensing system.

[0015] Figure 7 is from Figure 6 Schematic diagram of an illustrative circuit of the detector circuit output. DETAILED DESCRIPTION

[0016] refer to Figure 1 , a representative charging port connector 10 is shown, which has an electrical terminal 20 and an isolated temperature sensing system, as will be described more fully, for sensing the temperature of the electrical terminal 20. The connector 10 has a housing 12, and a terminal receiving cavity 14 is disposed in the housing 12. The terminal receiving cavity 14 is configured to receive the terminal 20 therein. The specific configuration and shape of the connector may vary without departing from the scope of the present invention.

[0017] exist Figure 2In the illustrative embodiment shown, the terminal 20 is in the shape of a pin having a free end 22 that is configured to mate with a mating connector (not shown) provided in a vehicle, etc. The size and shape of the terminal 20 may vary depending on the application and the amount of current that the terminal 20 must carry.

[0018] The sheet of material 24 is applied to the area 26 of each terminal 20. The size and shape of the sheet of material 24 can vary depending on the application and the amount of current that the terminal 20 must carry. The sheet of material 24 is applied directly to the surface 28 of each terminal 20 and adds little or no thermal mass to the terminal 20. For example, the length of the sheet of material 24 can be in the range of 0.6 mm to 10 mm, the width in the range of 0.6 mm to 10 mm, and the thickness in the range of 0.005 mm and 1 mm. The thermal mass of the sheet of material 24 is less than 25%, 20%, 15%, 10%, 5% of the thermal mass of the terminal 20.

[0019] exist Figure 2 In the illustrated embodiment, the material sheet 24 is a thermochromic ink. Thermochromic inks undergo a temperature-driven phase change, wherein the ink will change color or change from colored to colorless at a temperature that depends on the specific ink chemistry. For example, various dyes undergo a reversible chemical transformation that results in a reversible change between colored and colorless within a temperature range of approximately 10°C to 60°C.

[0020] The isolated temperature sensing system 40 positioned in the charging port connector 10 near the terminals 20 includes at least one detector 44 and at least one illuminator 42 for each terminal 20. The illuminator 42 and the detector 44 are located in the connector housing 12, near or in the terminal receiving cavity 14, and near and aligned with the terminal 20. In the illustrative embodiment shown, the illuminator 42 is a white LED that illuminates the material sheet 24 with white light. The detector 44 is a colored LED operating in a photodetector mode.

[0021] As the current through the terminal 20 changes, the temperature of the terminal 20 changes, causing the piece of material 24 to change color. When the temperature of the terminal 20 is within an acceptable range, photons with energy lower than the detector bandgap are reflected, and the photoinduced current or photocurrent 46 in the detector 44 is low, resulting in almost no conduction in the detector 44. When the temperature change of the terminal 20 is outside the acceptable range, photons with energy higher than the detector bandgap are reflected, resulting in a corresponding color change in the piece of material 24, and the photoinduced current 46 or photocurrent in the detector 44 is high, thereby generating a detectable photocurrent 46. By matching the color change of the piece of material 24 to the bandgap of the detector 44, a photocurrent will flow when the piece of material 24 and the terminal 20 are above their specified temperature.

[0022] The sensing system 40 includes a detector circuit 50, such as Figure 3 As shown, the expected output 52 is as follows Figure 4 As shown. Detector circuit 50 is located in charging port connector 10 near detector 44. Light generated by illuminator 42 and reflected from material sheet 24 to detector 44 generates photoelectrons, which cause current to flow into operational amplifier 54. Feedback through resistor 56 results in a voltage output signal proportional to the light flux at detector 44. Since the output of detector 44 is sensitive to wavelength, the output of operational amplifier 54 is sensitive to temperature. Figure 4 As best shown in FIG. 6 , the detector circuit 50 has a sharp transition 62 from a small voltage output 60 produced by reflected light below the bandgap wavelength to a maximum voltage output 64 produced by reflected light shorter than the bandgap wavelength.

[0023] The response of detector 44 may vary with temperature. If such variation results in unacceptable changes in behavior, a compensation diode 58 may be placed in series with resistor 56 in the feedback path of operational amplifier 54.

[0024] The components (illuminator 42, detector 44, and detector circuit 50) are not in physical contact with the terminal 20, and therefore the components are electrically isolated from the terminal 20. As previously described, the sheet of material 24 is applied directly to the terminal surface 28 and adds little or no added thermal mass to the terminal 20 or system 40. This combination provides electrical isolation of the terminal 20 from the components without increasing the measurement system time constant and without reducing the terminal cross-sectional area.

[0025] Reference Figures 5 to 7 , an alternative embodiment is shown. Figure 5 In the illustrative embodiment shown, the terminal 120 is in the shape of a pin having a free end 122 that is configured to mate with a mating connector (not shown) disposed in a vehicle, etc. The size and shape of the terminal 120 may vary depending on the application and the amount of current that the terminal 120 must carry.

[0026] A sheet of material or device 124 is applied or mounted to an area 126 of each terminal 120. The size and shape of the sheet of material or device 124 can vary depending on the application and the amount of current that the terminal 120 must carry. The sheet of material or device 124 is applied directly to the surface 128 of each terminal 20 and adds little or no thermal mass to the terminal 20 or system 140. For example, the length of the sheet of material 124 can be in the range of 0.6 mm to 10 mm, the width in the range of 0.6 mm to 10 mm, and the thickness in the range of 0.005 mm and 1 mm. The thermal mass of the sheet of material 124 is less than 25%, 20%, 15%, 10%, 5% of the thermal mass of the terminal 20.

[0027] exist Figures 5 to 7In the embodiment shown, the material sheet or device 124 is a matrix of a polymeric positive temperature coefficient material, or a device containing a mixture of conductive magnetic particles. The thermal expansion of the polymer matrix causes a magnetic field that is a nonlinear function of temperature. Below the designed transition temperature, the matrix does not expand or has minimal expansion, and the particles are in close mechanical contact. Above the designed transition temperature, the matrix expands, causing the particles to separate and form individual islands.

[0028] The current flowing through the terminal 120 and the material sheet or device 124 causes ohmic heating of the polymer matrix of the material sheet or device 124. The excess current causes the polymer matrix to rise above its designed transition temperature, causing the polymer matrix to expand. The expansion of the polymer matrix causes the particles to separate, thereby blocking the current flowing through the material sheet or device 124.

[0029] This operating principle can be used to sense temperature remotely. As mentioned above, the matrix is ​​loaded with magnetic particles and excited by an AC magnetic field. The AC magnetic field will cause eddy currents to flow in the magnetic particles. This eddy current is a dissipative loss, resulting in ohmic heating of the particles and electrical energy loss. When the matrix is ​​above its designed transition temperature, the eddy currents will flow only within each particle, and the electrical losses will be relatively low. When the matrix is ​​below its transition temperature and the particles are in close mechanical contact, the eddy currents will flow through most of the material, and the losses will be significantly higher. This temperature-related change in the matrix dissipative losses can be detected by an external circuit, such as an oscillator whose inductive element is magnetically coupled to the matrix.

[0030] Inductors may incorporate magnetic cores to increase the energy stored in the inductor's magnetic field. The properties of the magnetic core depend on the design requirements. Power transformers operating at AC line frequencies of about 50-60Hz may use a core constructed from a stack of stamped steel laminations. The stampings are coated with a layer of electrically isolating varnish to reduce eddy currents between the layers, which would cause losses in the core. A matrix of magnetic particles can be used at higher frequencies. Due to their high eddy current losses, conductive matrices excel in suppressing electromagnetic interference (EMI). A core composed of electrically isolating particles in a ceramic matrix will have lower losses and be more suitable for power transmission or energy storage.

[0031] The behavior of the quality factor Q of a resonant LC circuit can be used to sense the changes in the eddy current losses of the substrate with temperature. The Q of a resonant system is defined as the ratio of stored energy to energy lost per cycle and can depend on the eddy current losses in the magnetic core. Figure 7 As shown, the resonant circuit or system 150 ( Figure 6 ) to an excitation of frequency f depends on the Q of the system. The resonant circuit 150 is located in the charging port connector 10, close to the inductor 160. A high Q system has a strong response to a narrow range of excitation frequencies (e.g. Figure 7152 in FIG), while a low-Q system has a lower response to a wider range of excitation frequencies (such as Figure 7 154 in FIG. 154).

[0032] refer to Figure 5 , in one illustrative embodiment, the sheet or device 124 of material is a magnetic particle-polymer matrix applied to the terminal 120. The inductor 160 is positioned in the charging port connector 10 close to the sheet or device 124 of material, close enough so that some or all of the inductor magnetic field 162 flows through the sheet or device 124 of material. In this embodiment, the terminal 120 is copper and has little interaction with the inductor 160. The inductor 160 forms part of a resonant system whose Q is a function of the magnetic properties of the sheet or device 124 of material. As the sheet or device 124 of material is raised above its transition temperature, the magnetic particles separate, eddy current losses decrease, and the Q of the resonant circuit or system 150 increases.

[0033] Can be used Figure 6 The circuit 150 shown in block diagram format in FIG. 1 detects Q and thus the temperature of the terminal 120. The inductor 160 and the capacitor 164 form a resonant circuit or tank circuit 150 that is excited by a VCO (voltage controlled oscillator) 168. The frequency of the VCO 168 is swept by a constant current source 172 at about the resonant frequency of the inductor 160 and the capacitor 164, so the rate of change of frequency is linear in time. As the frequency of the VCO 168 is swept at about the resonant frequency of the resonant circuit 150, the amplitude of the signal induced in the resonant circuit 150 will vary, with the highest amplitude occurring at the resonant frequency of the inductor 160 and the external capacitor 164. The envelope detector circuit 174 converts this amplitude into a DC signal. The output of the envelope detector circuit 174 is fed to a peak detector 176 and a comparator 178, and the peak detector 176 captures and holds the highest amplitude. The reference potential of the comparator 178 is set to some fraction of the peak amplitude. The output of comparator 178 is connected to flip-flop 180 , the output of which controls the direction in which VCO 168 sweeps the signal.

[0034] Circuit 150 forms a limit cycle controller. The frequency of VCO 168 will slowly oscillate above and below the resonant frequency. The period of these slow oscillations, or the time between flip-flop 180 switching, will be proportional to the external circuit Q. Figure 7 As shown, a low Q will result in a broad resonant peak that sweeps between f1 and f4, as shown at 154. A high Q will result in a narrow resonant peak that sweeps between f2 and f3, as shown at 152. Since the scan rate is constant over time, the high Q condition will result in more frequent switching, and therefore faster switching cycles, than the broad peak associated with a low Q value.

[0035] The output of peak detector 176 may be allowed to change slowly to allow it to compensate for changes in the amplitude of the circuit response that may occur due to changes in Q

[0036] As exemplified by the illustrative embodiments described above, the sheet or device of material is coupled to the remote sensing circuit, providing electrical isolation without increasing the measurement system time constant and without reducing the terminal cross-sectional area. The external circuit does not contact the terminals and is therefore electrically isolated from the terminals. The sheet or device of material is applied directly to the terminal surface, adding little or no thermal mass to the system.

Claims

1. A method for detecting the temperature of an electrical terminal (20, 120), comprising: Applying a sheet of material (24, 124) of thermochromic ink to a surface of the electrical terminal (20, 120), the thermal mass of the sheet of material being less than 25% of the thermal mass of the electrical terminal, whereby the sheet of material (24, 124) does not significantly increase the resistance or thermal capacity of the electrical terminal (20, 120); Changes in the sheet of material (24, 124) are remotely sensed using a detector circuit external to and not in physical contact with the electrical terminal (20, 120) to determine whether the electrical terminal (20, 120) is operating at a safe temperature to optimize current flowing through the electrical terminal (20, 120), the detector circuit having a resistor and an operational amplifier.

2. The method according to claim 1, wherein: The sheet of material (24) undergoes a temperature driven phase change wherein the ink will change color or from colored to colorless at a specified temperature depending on the ink chemistry.

3. The method according to claim 2, wherein: A sensing system (40) is provided and in communication with the detector circuit (50).

4. The method according to claim 3, wherein: The sensing system (40) has an illuminator (42) and a detector (44) positioned proximate to and aligned with the terminal (20), and the detector circuit (50) is positioned proximate to the detector.

5. The method according to claim 4, wherein: The illuminator (42), the detector (44), and the detector circuit (50) are not in physical contact with the terminal (20) and are electrically isolated from the terminal (20).

6. The method according to claim 2, wherein: As the current passing through the terminal (20) changes, the temperature of the terminal (20) changes, causing the sheet of material (24) to change color.

7. The method according to claim 4, comprising: When the temperature of the terminal (20) is outside the acceptable range, photons having a higher energy than the band gap of the detector (44) are reflected, whereby the photocurrent (46) induced in the detector (44) is high, indicating that the temperature of the terminal (20) is outside the acceptable range.

8. The method according to claim 4, comprising: generating photoelectrons based on light generated by the illuminator (42) and reflected from the sheet of material (24) to the detector (44); causing current to flow into an operational amplifier (54) of the detector circuit (50); A voltage output signal proportional to the light flux is generated at the detector (44) via a resistor (56).

9. The method according to claim 1, wherein: The sheet of material (124) comprises a polymer matrix having a polymeric positive temperature coefficient material comprising a mixture of electrically conductive magnetic particles.

10. The method according to claim 9, comprising: A magnetic field is generated based on the thermal expansion of the polymer matrix, which magnetic field is a non-linear function of temperature.

11. The method according to claim 10, wherein: Current passing through the terminals (120) and the sheet of material (124) causes ohmic heating of the polymer matrix of the sheet of material (124), wherein excess current causes the polymer matrix to rise above a designed transition temperature, thereby causing the polymer matrix to expand, wherein the conductive magnetic particles move apart, blocking current passing through the sheet of material (124).

12. The method according to claim 10, comprising: exciting the conductive magnetic particles with an AC magnetic field (162) to cause eddy currents to flow within the conductive magnetic particles; Wherein, when the polymer matrix is ​​above the designed transition temperature, the eddy current will flow only within each of the conductive magnetic particles, and the electrical loss is relatively low; Therein, when the polymer matrix is ​​below the designed transition temperature and the conductive magnetic particles are in close mechanical contact, the eddy currents will flow through the conductive magnetic particles and the polymer matrix, and the losses will be significantly higher.

13. The method according to claim 12, comprising: Changes in dissipative losses of the polymer matrix are detected by an external circuit (150) magnetically coupled to the polymer matrix.

14. The method according to claim 13, wherein: An inductor (160) is located near the sheet of material (124), close enough so that some or all of the inductor's magnetic field (162) flows through the sheet of material (124), and the inductor (160) forms part of a resonant system, the quality of which is a function of the magnetic properties of the sheet of material (124), wherein as the sheet of material (124) rises above the designed transition temperature, the conductive magnetic particles of the polymer matrix separate, eddy current losses decrease, and the quality of the resonant circuit (150) or system improves.

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