Cable protection method and cable protection device

Abstract

A cable protection method for protecting a cable used to supply electrical power from a power source (Vdc) to a load (LOAD), the method comprising the following steps: a) detecting a current (I(n)) applied to the load (LOAD) at each predetermined time (n); b) calculating a temperature change in the cable per predetermined time by substituting the value of the detected current (I(n-1)) into a comparison expression (ΔTw(n), Fig. 4) concerning the heat radiation and heat generation of the cable using the applied current (I(n-1)) detected in step a); c) estimating a temperature of the cable, wherein the estimation includes calculating a temperature rise of the cable using the cable temperature change per predetermined time calculated in step b) and adding the cable temperature rise to a reference temperature set at a start time (0) of the cable temperature estimation; d) determining whether the cable temperature estimated in step c) is lower than a predetermined upper limit temperature of the cable; e) re-estimating the cable temperature according to step c) upon determining in determining step d) that the estimated cable temperature is lower than the predetermined upper limit temperature, wherein the re-estimation according to step c) includes calculating the cable temperature change per next predetermined time, re-calculating the cable temperature rise using the calculated cable temperature change per predetermined time, and adding the new cable temperature rise to the reference temperature; and f) stopping the supply of electrical power from the power source to the load upon determining in the determining step d) that the cable temperature estimated according to step c) or e) is equal to or higher than the predetermined upper limit temperature, wherein in the step c) or e) the estimation of the cable temperature includes the calculation of the cable temperature rise using the following formula 1 as a comparison expression: Δ Tw ( n ) = Δ Tw ( n − 1 ) × exp ( − Δ t / τ w ) + Rthw × Rw ( n − 1 ) × I ( n − 1 ) 2 × ( 1 − exp ( − Δ t / τ w ) ) , where: I(n) is a detected applied current value (A) at the n-th detection, where n is an integer equal to or greater than 1, ΔTw(n) is the cable temperature rise (°C) at the n-th detection, Δt is the predetermined time (s), τw is a heat radiation time constant (s) of the cable, and Rw(n) is a resistance (Ω) of the cable at the n-th detection, which is calculated according to the following formula 2: Rw ( n ) = Rw ( 0 ) × ( 1 + κ w × ( Tw − To ) ) , where: Rw(0) is a resistance (Ω) of the cable at a temperature To, Rthw is a thermal resistance (°C / W) of the cable, ĸw is a resistance temperature coefficient ( / °C) of the cable, and Tw = {reference temperature} + ΔTw(n), where Tw is the cable temperature (°C) at the n-th detection, wherein estimating the cable temperature includes setting the reference temperature as the highest of the ambient temperatures at the locations where the cable runs.

Description

TECHNICAL FIELD

[0001] The present invention relates to cable protection methods and cable protection devices, or more particularly to a cable protection method and a cable protection device wherein the cable is used to supply electrical power from a power source to a load. STATE OF THE ART

[0002] A vehicle wiring harness may deteriorate or wear, causing a core wire to come into electrical contact with a vehicle body, etc., and cause a short circuit. To prevent the wire coating and a current control element (a switching element) from burning out due to such a short circuit, a thermal fuse has been conventionally used. The thermal fuse detects an overheating condition and blows out. However, with the increasing number of electrical components, it has become difficult to provide sufficient space for the thermal fuses when using such thermal fuses. Furthermore, resuming operation after a fuse blowout requires replacing with a new thermal fuse, making maintenance difficult.Furthermore, if current is repeatedly supplied to a load (e.g., a headlight) with a high inrush current, a thermal fuse tends to wear out, and its response time becomes shorter. Since the response time also changes due to initial changes and temperature-dependent characteristics, the response should not occur during normal operation. Consequently, a thermal fuse with a larger current capacity is used. This poses the problem of requiring a thicker cable, which has a higher inrush current and can be protected by the thermal fuse.

[0003] In recent years, it has also been proposed in the prior art, for example, by the unexamined Japanese patent application JP H11 - 139 223 A, to attach a temperature sensor directly to the cable to measure a temperature of the cable and, when the cable reaches an abnormal temperature, to interrupt an applied current.

[0004] JP 08-242533 A discloses a method for protecting an overhead power line. RJ Millar's dissertation, published in Helsinki 2006 (ISBN 9512284162), discloses a general thermodynamic model, focusing specifically on buried cables.

[0005] DE 102 57 425 A1 discloses a device and a method for protecting cables, e.g. in vehicles, wherein the temperature of the cable is estimated using a thermodynamic model, wherein the temperature in the region of the cable end is measured and the temperature over the longitudinal extent of the cable is calculated. DESCRIPTION OF THE INVENTION (Problem to be solved by the invention)

[0006] The method that attaches a temperature sensing element (e.g., a linear thermistor) to the wire harness itself and directly measures the temperature of the wire harness, as described in the above-mentioned publication, causes inconvenience due to its complex structure and increased cost. Furthermore, in a case where the temperature rises in a single wire located near the center, accurate temperature tracking is impossible.

[0007] The present invention was therefore made on the basis of the circumstances explained above and, starting from DE 102 57 425 A1, its object is to provide a cable protection method and a protection device, wherein the method and device are capable of protecting a cable with a simple structure from a temperature rise due to different short-circuit currents. (Means of solving the problem)

[0008] As a means for achieving the above-mentioned object, the cable protection method according to one aspect of the present invention is a cable protection method for protecting a cable used to supply electric power from a power source to a load. The method comprises the following steps: a) detecting an applied current to the load at any predetermined time; b) calculating a temperature change in the cable per predetermined time by substituting the value of the detected current into a comparison expression concerning the heat radiation and the heat generation of the cable using the applied current detected in step a); c) estimating a temperature of the cable, wherein the estimation includes calculating a temperature rise of the cable using the cable temperature change per predetermined time calculated in step b) and adding the cable temperature rise to a reference temperature set at a start time of the cable temperature estimation; d) determining whether the cable temperature estimated in step c) is lower than a predetermined upper limit temperature of the cable; e) re-estimating the cable temperature according to step c) upon determining in determining step d) that the estimated cable temperature is lower than the predetermined upper limit temperature, wherein the re-estimation includes calculating the cable temperature change per next predetermined time, re-calculating the cable temperature rise using the calculated cable temperature change per predetermined time, and adding the new cable temperature rise to the reference temperature; and f) stopping the supply of electrical power from the power source to the load upon determining in the determining step d) that the cable temperature estimated according to step c) or e) is equal to or higher than the predetermined upper limit temperature, wherein in step c) or e) the estimation of the cable temperature includes the calculation of the cable temperature rise using the following formula 1 as a comparison expression: ΔTw(n)=ΔTw(n−1)×exp(−Δt / τw)+Rthw × Rw(n−1)×I(n−1)2×(1−exp(−Δt / τw)) where: I(n) is a detected applied current value (A) at the n-th detection, where n is an integer equal to or greater than 1 (one), ΔTw(n) is the cable temperature rise (°C) at the n-th detection, Δt is the predetermined time (s), τw is a heat radiation time constant (s) of the cable, Rw(n) is a resistance (Ω) of the cable at the n-th detection, which is calculated according to the following formula 2: Rw(n)=Rw(0)×(1+κw×(Tw−To)), where: Rw(0) is a resistance (Ω) of the cable at a temperature To, Rthw is a thermal resistance (°C / W) of the cable, ĸw is a resistance temperature coefficient ( / °C) of the cable, and Tw = {reference temperature} + ΔTw(n), where Tw is the cable temperature (°C) at the n-th detection, wherein estimating the cable temperature includes setting the reference temperature as the highest of the ambient temperatures at the locations where the cable runs.

[0009] In this configuration, the applied current is detected per predetermined time, a present cable temperature is estimated using the applied current, and the present cable temperature and the upper limit temperature that the cable allows are compared. This makes it possible to detect the cable temperature even in a case where the cable temperature rises due to a short-circuit current that repeatedly switches on and off, as in Fig. 11, reliably detects the temperature rise and interrupts the applied current before the cable reaches the smoking temperature, thus preventing the cable from smoking. While a conventional thermal fuse degrades due to the inrush current, such a degradation factor is not present in the present configuration. Furthermore, the present configuration provides an accurate temperature estimate. Thus, the current can be kept flowing and used until just before the cable smokes.

[0010] Since the cable temperature is only estimated by detecting the applied current, the design of the cable protection is simple.

[0011] As a further means for achieving the above object, a cable protection device according to one aspect of the present invention is a cable protection device that protects a cable between a power source and a load, which is used to supply electric power from the power source to the load. The device comprises: a semiconductor switching element configured to be arranged in a current application path from the power source to the load and to switch the power supply to the load; a current detection circuit configured to detect a current applied to the load at every predetermined time, the applied current flowing through the semiconductor switching element; an operating circuit configured to calculate a temperature change in the cable per the predetermined time by substituting the detected current into a comparison expression concerning the heat radiation and the heat generation of the cable using the detected applied current, calculate a temperature rise of the cable using the cable temperature change per the predetermined time, and add the cable temperature rise to a reference temperature set at a start time of the cable temperature estimation to thereby estimate the temperature of the cable; and a protection circuit configured to determine whether the estimated cable temperature is lower than a predetermined upper limit temperature of the cable, and upon determining that the estimated cable temperature is lower than the predetermined upper limit temperature, to cause the actuation circuit to calculate the cable temperature change per next predetermined time, to calculate the cable temperature rise using the calculated cable temperature change per the predetermined time, and to re-estimate the cable temperature, wherein the re-estimation includes adding the new cable temperature rise to the reference temperature, wherein the protection circuit is configured to turn off the semiconductor switching element and stop the supply of electric power from the power source to the load when it is determined that the estimated cable temperature is equal to or higher than the predetermined upper limit temperature, wherein the operating circuit (10) is designed to calculate the cable temperature rise using the following formula 1 as a comparison expression: ΔTw(n)=ΔTw(n−1)×exp(−Δt / τw)+Rthw× Rw(n−1)×I(n−1)2×(1−exp(−Δt / τw)) where: I(n) is a detected applied current value (A) at the n-th detection, where n is an integer equal to or greater than 1 (one), ΔTw(n) is the cable temperature rise (°C) at the n-th detection, Δt is the predetermined time (s), τw is a heat radiation time constant (s) of the cable, Rw(n) is a resistance (Ω) of the cable at the n-th detection, which is calculated according to the following formula 2: Rw(n)=Rw(0)×(1+κw×(Tw−To)), where: Rw(0) is a resistance (Ω) of the cable at a temperature To, Rthw is a thermal resistance (°C / W) of the cable, ĸw is a resistance temperature coefficient ( / °C) of the cable, and Tw = {reference temperature} + ΔTw(n), where Tw is the cable temperature (°C) at the n-th detection, further comprising: a reference temperature setting circuit configured to set the reference temperature as the highest of the ambient temperatures at the locations where the cable runs. SHORT DESCRIPTION OF THE DRAWING Fig. 1 is an explanatory view showing a cable protecting method according to the present invention; Fig. 2 is a schematic block diagram showing the configuration of a power protection device according to the present invention; Fig. 3 is an explanatory diagram illustrating a cable temperature estimation model according to the present invention; Fig. 4 is an explanatory diagram illustrating a cable temperature estimating process according to the present invention; Fig. 5 is an explanatory diagram showing a cable temperature estimation expression according to the present invention; Fig. Figure 6 is an explanatory diagram showing test conditions for cable temperature estimation; Fig. 7 is a waveform diagram of a test step current used in a cable estimation test; Fig. Figure 8 is a graphical representation of cable temperature changes with respect to the test current of Fig. 7; Fig. 9 is a graphical representation of a time change of a cable operating temperature according to test step currents with different current values; Fig. 10 is a graphical representation of a relationship between interruption characteristics according to a test result of cable temperature estimations and a melting characteristic of a conventional thermal fuse; and Fig. Figure 11 is a graphical representation of a conventional relationship between a pulsed current and a cable temperature. (Explanation of reference symbols) 10... Microcomputer (operating circuit, protection circuit) 30... Output circuit 33... CR low-pass filter 34... Current / voltage converter circuit 35... N-channel MOSFET (semiconductor switching element) 38... Detection MOSFET (current detection circuit) 40... Reference temperature setting circuit 100... cable protection device BEST MODE FOR CARRYING OUT THE INVENTION<Illustrative Ausführungform>

[0012] An illustrative embodiment of the present invention will be described with reference to the Fig. 1 to 5. Although in this illustrative embodiment, a vehicle wiring harness is intended to be a cable to be protected, the cable to be protected is not limited thereto.

[0013] Fig. Fig. 1 is an explanatory diagram showing a concept of a cable (the wire harness) according to the present invention. According to Fig. 1, in the present invention, a temperature rise ΔTw in the wiring harness is directly calculated from a loss in the wiring harness due to an applied current I, that is, heat generation in the wiring harness, and a heat radiation time constant τw of the wiring harness. Subsequently, a temperature of the wiring harness is estimated from the wiring harness temperature rise ΔTw. This estimated wiring harness temperature and a predetermined threshold (an upper limit) are compared, and then, when the wiring harness temperature is equal to or higher than the predetermined threshold, the applied current I is interrupted, thus protecting the wiring harness.

[0014] More specifically, the applied current I applied to a load via the cable (wire harness) is detected at every predetermined time, and a temperature change in the cable per the predetermined time is calculated using the detected applied current. Subsequently, the cable temperature estimation is performed. The estimation includes: calculating the cable temperature rise using the cable temperature change per predetermined time; and adding the cable temperature rise to a reference temperature. After that, a determination is made as to whether the estimated cable temperature is lower than a predetermined upper temperature limit. Upon determining that the estimated cable temperature is lower than the predetermined upper limit temperature, a new estimation of the cable temperature rise is performed.The new calculation involves calculating the cable temperature change per the next predetermined time, recalculating the cable temperature rise using the calculated cable temperature change per the predetermined time, and adding the new cable temperature rise to the reference temperature. If the estimated cable temperature is determined to be equal to or higher than the predetermined upper limit temperature, the electrical power supply to the load is stopped, thus protecting the cable.

[0015] Hereinafter, a cable protection device according to the present invention will be described with reference to Fig. 2 described. Fig. Figure 2 is a schematic block diagram of the cable protection device 100 according to the present invention. The cable protection device 100 includes a microcomputer 10, a plurality of input circuits 20 (eight in this illustrative embodiment), a plurality of output circuits 30 (eight in this illustrative embodiment), a reference temperature setting circuit 40, a regulator IC 50, etc. Note that the number of input circuits 20 and output circuits 30 can be appropriately changed according to the number of cables to be estimated.

[0016] The microcomputer 10 corresponds to an "operation circuit" and a "protection circuit" of the present invention. The microcomputer 10 calculates the temperature rise ΔTw of the wire harness while estimating the temperature Tp of the wire harness, as described below. The microcomputer 10 includes a WDT (watchdog terminal) 11, an oscillator terminal 12, a plurality of I / O terminals 13, a plurality of A / D converter input terminals 14, etc. Note that the microcomputer 10 performs operations (e.g., operation, determination, protection, etc.) of the present invention for protecting the cable (i.e., actions of a cable protection method) according to instructions of a program included in a memory (not shown in the drawing) of the microcomputer 10.

[0017] Each input circuit 20 includes an input I / F circuit (interface). Various input signals for the microcomputer 10 are input to the input circuits 20 and converted into signals that can be processed by the microcomputer 10.

[0018] Each output circuit 30 includes an output I / F circuit 31, an IPS (intelligent power switch) 32, a CR low-pass filter 33, a current / voltage converter circuit (converter circuit) 34, etc.

[0019] The IPS 32 includes a semiconductor switching element 35 (here: an n-channel MOSFET), a charge pump 36, a self-protection circuit 37, and a sense MOSFET 38 (corresponding to a "current detection circuit" according to the present invention). The semiconductor switching element 35 switches on / off the applied current I from the power source Vdc to a load. The charge pump 36 steps up a control voltage toward the semiconductor switching element 35. The self-protection circuit 37 protects the semiconductor switching element 35 from overcurrent. The sense MOSFET 38 generates a sense current that has a certain proportional relationship to the load current I.

[0020] The detection current is converted by the current-to-voltage conversion circuit 34 into a detection voltage signal (conversion signal) Vsens, which has a proportional relationship to the detection current. The current-to-voltage conversion circuit 34 is configured, for example, by a detection current detection resistor. The detection voltage signal Vsens is applied to the CR low-pass filter 33. The CR low-pass filter 33 removes certain high-frequency components from the detection voltage signal Vsens and supplies the detection voltage signal Vsens after removing the high-frequency components to the A / D conversion input terminal 14 of the microcomputer 10. It should be noted here that the time constant of the CR low-pass filter 33 should be larger (or sufficiently larger) than a sampling interval (the predetermined time), which should be smaller (or sufficiently smaller) than the heat radiation coefficient of the wiring harness.In this illustrative embodiment, the time constant of the CR low-pass filter 33 is assumed to be 20 ms. In this case, the speed of the current conversion signal is reduced so that the microcomputer can perform its operation.

[0021] The microcomputer 1 converts the detection voltage signal Vsens into the applied current I. For example, the microcomputer 1 obtains the instantaneous value of the applied current I from a correspondence table between the detection voltage signal Vsens and the applied current I. The correspondence table is included, for example, in the memory (not shown) in the microcomputer 10.

[0022] The reference temperature setting circuit 40 sets the reference temperature at a start time of the cable temperature estimation by the microcomputer 10. The reference temperature setting circuit 40 includes, for example, a temperature sensor (not shown) and an amplifier circuit (not shown). The temperature sensor is located, for example, in the engine compartment of a vehicle. The amplifier circuit amplifies a sensor signal from the temperature sensor and thus generates a temperature signal indicative of the temperature in the engine compartment. The reference temperature setting circuit 40 supplies the temperature signal indicative of the temperature in the engine compartment as a reference temperature to the A / D converter input terminal 14 of the microcomputer 10. Note that, depending on the number of ambient temperatures to be detected, the reference temperature setting circuit 40 includes a plurality of temperature sensors and a plurality of amplifier circuits.Furthermore, the reference temperature setting circuit 40 may also include, for example, a comparison circuit for selecting one of the detected plurality of ambient temperatures as a reference temperature.

[0023] The regulator IC 50 converts a specific DC voltage, for example 12 V, into a supply voltage of, for example, 5 V for the microcomputer 10 and supplies the DC voltage of 5 V to the microcomputer 10. <Kabeltemperaturschätzverfahren>

[0024] Hereinafter, the cable temperature estimation method by the microcomputer 10 is described with reference to the Fig. 3 to 5. Fig. Figure 3 is a view illustrating a cable temperature estimation model. In this figure, the cable temperature rise ΔT is represented as the difference between the heat generation T1 of a cable conductor and the heat radiation T2 of the cable. An equivalent circuit of Fig. Figure 3 is a representation of an equivalent circuit with respect to heat.

[0025] The microcomputer 10 calculates the cable temperature rise (temperature rise in the cable) ΔTw by substituting the value of the detected current I into a comparison expression concerning the heat radiation and heat generation of the cable. The comparison expression is shown in Fig. 4 and expressed by the following formula 1. Formula 1 has according to Fig. 4 a term relating to the heat radiation of the cable and a term relating to the heat generation of the cable: ΔTw(n)=ΔTw(n−1)×exp(−Δt / τw)+Rthw× Rw(n−1)×I(n−1)2×(1−exp(−Δt / τw)) where: I(n) is a current value (A) at an n-th sampling (detection), where n is an integer equal to or greater than 1; ΔTw(n) is the cable temperature rise (temperature rise in the cable) (°C) at the n-th sampling; Rw(n) is a resistance (Ω) of the cable at the n-th sampling; Rw(0) is a resistance (Ω) of the wiring harness (cable) at a temperature To; Rthw is a thermal resistance (°C / W) of the wiring harness (cable); τw is a heat radiation time constant (s) of the wire harness (cable); and Δt is the sampling interval (predetermined time) (s).

[0026] The microcomputer 10 estimates the current cable temperature Tp by adding the calculated cable temperature rise ΔTw to the reference temperature. During the estimation, the microcomputer 10 calculates the cable temperature change ΔTs per sampling interval (predetermined time) Δt and calculates the cable temperature rise ΔTw using the temperature change ΔTs per sampling interval Δt.

[0027] Next, the microcomputer 10 determines whether the current cable temperature Tp is lower than the predetermined upper limit temperature Tmax of the cable by comparing the current cable temperature Tp with the predetermined upper limit temperature Tmax. Upon determining that the cable temperature Tp is lower than the upper limit temperature Tmax, the microcomputer 10 again calculates the cable temperature rise ΔTw(n) from the reference temperature so far by calculating the temperature change ΔTs per next sampling interval Δt and adding the temperature change ΔTs per sampling interval Δt to the cable temperature rise ΔTw(n-1) calculated last. The microcomputer 10 adds the calculated temperature rise ΔTw(n) to the reference temperature, thus defining the current cable temperature Tp.The microcomputer 10 repeats the calculation of the temperature rise ΔTw, the estimation of the cable temperature Tp and the comparison of the cable temperature Tp with the upper limit temperature Tmax until the cable temperature Tp becomes equal to or higher than the upper limit temperature Tmax.

[0028] It should be noted that the temperature change ΔTs per sampling interval Δt is expressed by Formula 1A (a transformation of Formula 1), which is as follows: ΔTs=ΔTw(n)−ΔTw(n−1)=(Rthw×Rw(n−1)×I(n−1)2−ΔTw(n−1))×(1−exp(−Δt / τw))

[0029] When determining that the cable temperature Tp is not lower than the upper limit temperature Tmax, i.e., when determining that the cable temperature Tp is equal to or higher than the upper limit temperature Tmax, the microcomputer 10 generates a protection signal and supplies the protection signal to the IPS 32. The protection signal serves to turn off the semiconductor switching element 35 and thus protect the cable. The semiconductor switching element 35 is turned off by the protection signal, and the current applied to the cable is interrupted. This prevents a further temperature increase in the cable.

[0030] Fig. Figure 5 is a diagram that explains Formula 1 in more detail. It should be noted here that according to Fig. 5, and as expressed by the following formula 2, the cable resistance Rw(n) at the n-th sampling is a variable depending on the cable temperature rise ΔTw(n), ie (Tw - To). Rw(n)=Rw(0)×(1+κw×(Tw−To)) where: Tw is the cable temperature (°C) at the n-th detection ĸw is a resistance temperature coefficient ( / °C) of the wire harness (cable); and To is the predetermined temperature (e.g., 20 °C).

[0031] Furthermore, a formula concerning the cable temperature rise ΔTw(n) is shown, where the formula in Fig. 5, the process according to formula 1 and has identical content to formula 1. It should be noted here that the sampling interval Δt, the harness heat radiation time constant τw, the harness thermal resistance Rthw and the harness resistance (the initial value, e.g., a value at 20 °C) Rw(0) are constants which are set depending on the cable which is the subject of the temperature estimation. <testbeispiel>

[0032] Hereinafter, a test example of the cable temperature estimation according to the present invention will be described with reference to the Fig. 6 to 10 explained. Fig. Figure 6 is an explanatory view showing the test conditions for the cable temperature estimation according to the present invention. In this test, a copper cable (AVSS 0.85 sq) with a cross-section of 0.85 mm 2 and a length of 3 m, and a semiconductor switching element with an on-resistance of 3.5 mΩ was used. The actual cable temperature was measured at a point along the cable. The test cable and the cable temperature estimation test device were placed in a constant-temperature chamber, which provided a static environment at a temperature of 25 °C.

[0033] Fig. Figure 7 is a graph showing the waveform of a step current used in the test. Fig. Figure 8 is a graph showing cable temperature changes and actual measured cable temperature changes in relation to the step current. According to Fig. 8 it was observed that the actuated cable temperature changes are approximately equal to the actually measured cable temperature changes.

[0034] Fig. Figure 9 is a graph showing the actuated cable temperature changes per time with respect to the test stage currents with different current values. Fig. Figure 10 is a graph showing the relationship between a test result of a limiting characteristic and an interrupting characteristic of a conventional thermal fuse by the test stage currents. The upper limit (interrupting temperature) was set to 150 °C. Fig. 9, the step currents have five current values ​​(25.0 A, 29.0 A, 30.0 A, 40.0 A, and 50.0 A) and were used as test step currents, and it could be observed that the currents were interrupted at 194.3 s, 65.6 s, 59.3 s, 24.5 s, and 14.0 s after the test was started. Furthermore, by recording the relationship between the current application times until interruption and the current values ​​through the test, it could be determined that the recording points lie along a smoke line (limit characteristic) of the copper cable. Consequently, compared to the case (according to Fig. 10), which uses a conventional thermal fuse, the cable temperature estimation method according to the present invention does not have a deterioration factor due to the inrush current and still provides an accurate temperature estimate. This makes it possible to apply the current until just before the cable begins to smoke. <effekte>

[0035] As explained above, in this illustrative embodiment, the applied current I is detected at every predetermined sampling interval Δt, the present cable temperature Tp is estimated using the applied current I, and the cable temperature Tp and the allowable upper limit temperature Tmax are compared. Also, in a case where the cable temperature Tp has risen due to a short-circuit current that repeats on and off, as in Fig. As shown in Figure 11, the rise in cable temperature Tp can be reliably detected, so that the applied current is interrupted before the cable reaches the smoking temperature. As a result, smoking of the cable can be prevented.

[0036] Since the cable temperature Tp is estimated solely by detecting the applied current I, the cable protection structure can be easily configured.

[0037] Furthermore, the design of the cable protection circuit 100 according to the present invention can be configured using existing components. Thus, manufacturing costs can be low. Furthermore, modifying an existing protection circuit is easier.

[0038] Furthermore, the cable protection circuit 100 according to the present invention can be applied to protect a plurality of output circuits 10, that is, a plurality of cables under the control of the single microcomputer 10. The number of parts and the cost of the entire cable protection circuit 100 can therefore be reduced. <Andere illustrative Ausführungsformen>

[0039] The present invention is not limited to the illustrative embodiment explained above with reference to the drawings. For example, the following illustrative embodiments are also within the scope of the present invention.

[0040] (1) In the above-mentioned illustrative embodiment, the cable resistance Rw(n) at the n-th sampling is exemplified as a variable depending on the cable temperature rise ΔTw(n) and is found using Formula 2. However, the cable resistance Rw(n) is not specifically limited to this. The cable temperature rise ΔTw can be calculated using the cable resistance Rw, which is a constant value regardless of the temperature. In this case, appropriate selection of the constant value makes it possible to appropriately modify the time before the cable temperature Tp reaches the upper limit temperature Tmax according to the cable protection requirements. That is, cable protection measures can be taken according to the degree of cable protection.

[0041] The temperature rise ΔTw can be calculated, for example, by setting the cable resistance Rw to a value corresponding to the upper limit temperature Tmax. In this case, the temperature rise ΔTw is calculated under conditions where a condition concerning the cable temperature rise is more severe than an actual condition, i.e., under conditions where the cable temperature rise is greater than the actual cable temperature rise. Thus, setting the cable resistance Rw to a value corresponding to the upper limit temperature Tmax is suitable in a case where faster cable protection is desired.

[0042] (2) In the above-described illustrative embodiment, temperature is taken as an example of the reference temperature. The reference temperature is not limited to this. For example, if the cable to be protected is installed in a passenger compartment, the passenger compartment temperature may be used as the reference temperature; or, in a case where most of the cable to be protected is installed outside the vehicle, the outside temperature around the vehicle may be used as the reference temperature. What is important is that the reference temperature is set according to the ambient temperature where the cable to be protected is installed.

[0043] Furthermore, if the cable to be protected extends through environments with different temperatures (e.g., the engine compartment and the interior of the passenger compartment), the reference temperature is taken as the highest of the ambient temperatures at the locations where the cable runs (in this case, the temperature in the engine compartment). In this case, the temperature rise ΔTw is calculated under the conditions where the cable rise temperature condition is the most severe, i.e., under conditions where the cable temperature rise is the highest. Thus, the cable is reliably protected at an early stage.

[0044] (3) In the configuration of the above-described illustrative embodiment, the reference temperature setting circuit 40 is separate from the microcomputer 10. The microcomputer 10 may perform the function of the reference temperature setting circuit 40. The microcomputer 10 then receives information about the ambient temperature from separately arranged temperature sensors and sets the reference temperature using the temperature information.

[0045] (4) In the above-described illustrative embodiment, an n-channel MOSFET is used as an example of the semiconductor switching element 35. The present invention is not limited to this. For example, a p-channel MOSFET or a bipolar transistor can also be used as the semiconductor switching element 35.

[0046] (5) In the illustrative embodiment described above, the applied current I is detected, for example, by the detection MOSFET 38. The present invention is not limited to this. For example, the applied current I can also be detected using a shunt resistor.

[0047] (6) In the above-described illustrative embodiment, the operating circuit and the protecting circuit are illustratively configured by the microcomputer, and the operations of the cable protecting method according to the present invention are also performed by the microcomputer, for example. The present invention is not limited to this. The operating circuit and the protecting circuit may also be configured separately, for example, by logic circuits.< / effekte> < / testbeispiel>

Claims

[1] A cable protection method for protecting a cable used to supply electrical power from a power source (Vdc) to a load (LOAD), the method comprising the following steps: a) detecting a current (I(n)) applied to the load (LOAD) at each predetermined time (n); b) Calculating a temperature change in the cable per predetermined time by inserting the value of the detected current (I(n-1)) into a comparison expression (ΔTw(n), Fig. 4) concerning the heat radiation and heat generation of the cable using the applied current (I(n-1)) detected in step a); c) estimating a temperature of the cable, wherein the estimation includes calculating a temperature rise of the cable using the cable temperature change per predetermined time calculated in step b) and adding the cable temperature rise to a reference temperature set at a start time (0) of the cable temperature estimation; d) determining whether the cable temperature estimated in step c) is lower than a predetermined upper limit temperature of the cable; e) re-estimating the cable temperature according to step c) upon determining in determining step d) that the estimated cable temperature is lower than the predetermined upper limit temperature, wherein the re-estimation according to step c) includes calculating the cable temperature change per next predetermined time, re-calculating the cable temperature rise using the calculated cable temperature change per predetermined time, and adding the new cable temperature rise to the reference temperature; and f) stopping the supply of electrical power from the power source to the load upon determining in the determining step d) that the cable temperature estimated according to step c) or e) is equal to or higher than the predetermined upper limit temperature, wherein in the step c) or e) the estimation of the cable temperature includes the calculation of the cable temperature rise using the following formula 1 as a comparison expression: ΔTw(n)=ΔTw(n−1)×exp(−Δt / τw)+Rthw× Rw(n−1)×I(n−1)2×(1−exp(−Δt / τw)), where: I(n) is a detected applied current value (A) at the n-th detection, where n is an integer equal to or greater than 1, ΔTw(n) is the cable temperature rise (°C) at the n-th detection, Δt is the predetermined time (s), τw is a heat radiation time constant (s) of the cable, and Rw(n) is a resistance (Ω) of the cable at the n-th detection, which is calculated according to the following formula 2: Rw(n)=Rw(0)×(1+κw×(Tw−To)), where: Rw(0) is a resistance (Ω) of the cable at a temperature To, Rthw is a thermal resistance (°C / W) of the cable, ĸw is a resistance temperature coefficient ( / °C) of the cable, and Tw = {reference temperature} + ΔTw(n), where Tw is the cable temperature (°C) at the n-th detection, wherein estimating the cable temperature includes setting the reference temperature as the highest of the ambient temperatures at the locations where the cable runs. [2] The cable protection method according to claim 1, wherein: estimating the cable temperature comprises calculating the cable temperature rise with the resistance of the cable at the n-th detection (Rw(n)) in the comparison expression, wherein a constant value independent of a temperature is used for the resistance of the cable at the n-th detection (Rw(n)) instead of the value calculated according to formula 2 in the comparison expression according to formula 1. [3] The cable protection method according to claim 2, wherein: as the value for the resistance of the cable at the n-th detection, the resistance value corresponding to the predetermined upper limit temperature is used as the constant value. [4] A cable protection device (100) which protects a cable arranged between a power source (Vdc) and a load (LOAD) and used to supply electrical power from the power source to the load, the device (100) comprising: a semiconductor switching element (35) configured to be arranged in a current supply path from the power source (Vdc) to the load and to switch the power supply to the load; a current detection circuit (38) configured to detect a current (I(n)) applied to the load at every predetermined time (n), the applied current flowing through the semiconductor switching element (35); an operating circuit (11) adapted to calculate a temperature change in the cable per the predetermined time by inserting the detected current (I(n-1)) into a comparison expression (ΔTw(n), Fig.4) regarding the heat radiation and heat generation of the cable, using the detected applied current (I(n-1)), to calculate a temperature rise of the cable using the cable temperature change per the predetermined time and to add the cable temperature rise to a reference temperature set at a start time (0) of the cable temperature estimation to thereby estimate the temperature of the cable; and a protection circuit (10) configured to determine whether the estimated cable temperature is lower than a predetermined upper limit temperature of the cable, wherein: the protection circuit (10) is designed, upon determining that the estimated cable temperature is lower than the predetermined upper limit temperature, to cause the operating circuit to calculate the cable temperature change per the next predetermined time, recalculate the cable temperature rise using the calculated cable temperature change per the predetermined time, and reestimate the cable temperature, wherein the reestimation comprises adding the new temperature rise to the reference temperature; and the protection circuit (10) is designed to switch off the semiconductor switching element (35) and interrupt the supply of electrical power from the power source (Vdc) to the load (LOAD) upon determining that the estimated cable temperature is equal to or higher than the predetermined upper limit temperature wherein the operating circuit (10) is designed to calculate the cable temperature rise using the following formula 1 as a comparison expression: ΔTw(n)=ΔTw(n−1)×exp(−Δt / τw)+Rthw× Rw(n−1)×I(n−1)2×(1−exp(−Δt / τw)) where: I(n) is a detected applied current value (A) at the n-th detection, where n is an integer equal to or greater than 1 (one), ΔTw(n) is the cable temperature rise (°C) at the n-th detection, Δt is the predetermined time (s), τw is a heat radiation time constant (s) of the cable, Rw(n) is a resistance (Ω) of the cable at the n-th detection, which is calculated according to the following formula 2: Rw(n)=Rw(0)×(1+κw×(Tw−To)), where: Rw(0) is a resistance (Ω) of the cable at a temperature To, Rthw is a thermal resistance (°C / W) of the cable, ĸw is a resistance temperature coefficient ( / °C) of the cable, and Tw = {reference temperature} + ΔTw(n), where Tw is the cable temperature (°C) at the n-th detection, further comprising: a reference temperature setting circuit (40) configured to set the reference temperature as the highest of the ambient temperatures at the locations where the cable runs. [5] The cable protection device according to claim 4, wherein: the operating circuit (10) is designed to calculate the cable temperature rise using the resistance value of the cable at the n-th detection (Rw(n)) in the comparison expression, wherein a constant value independent of temperature is used for the resistance value of the cable at the n-th detection instead of the value calculated according to formula 2 in the comparison expression according to formula 1. [6] The cable protection device according to claim 5, wherein: as the value for the resistance of the cable at the n-th detection, the resistance value corresponding to the predetermined upper limit temperature is used as the constant value. [7] The cable protection device according to any one of claims 4 to 6, wherein the cable protection device (100) further comprises a converter circuit (34) and a low-pass filter (33), wherein the converter circuit (34) is designed to convert an applied current (I) into a voltage (Vsens) and thereby generate a conversion signal, wherein the low-pass filter (33) is designed to filter the conversion signal, wherein: the low-pass filter (33) has a time constant which is greater than the predetermined time and less than the cable heat radiation time constant. [8] The cable protection device according to any one of claims 4 to 7, wherein: the cable is a vehicle wiring harness for arrangement between the semiconductor switching element (35) and the load (LOAD); and the operating circuit and the protection circuit are configured as a microcomputer (10). [9] The cable protection device according to any one of claims 4 to 7, wherein: the operating circuit and the protection circuit are configured by hardware logic.

Images