A method and system for matching the current-carrying capacity of an automobile wiring harness fuse wire

Abstract

The present application belongs to the field of automobile electronics, and provides a kind of automobile wire harness fuse wire current carrying capacity matching test method and system, comprising: establishing standardization pulse loading profile, constant current test is extended to cover the composite dynamic test sequence of peak thermal shock and average thermal accumulation;Collect fuse thermal accumulation integral value and wire insulation layer multi-point temperature, introduce three-dimensional evaluation index, identify thermal response asynchronous condition;Pulse peak and duty cycle are gradually increased, respectively, approach the limit of wire transient temperature rise and fuse thermal accumulation melting boundary, determine the safe matching interval by cross comparison;According to the safe matching interval, divide the matching level, select the optimization for asynchronous risk and overheating priority failure combination respectively, and feed back the optimization result to the selection specification.The test distortion problem caused by the asynchronous thermal response of fuse and wire under dynamic pulse current is solved, and the matching reliability and test accuracy of automobile electrical system are improved.

Description

Technical Field

[0001] This invention belongs to the field of automotive electronics technology, specifically a method and system for testing the current carrying capacity matching of automotive wiring harness fuse wires. Background Technology

[0002] In automotive electrical system design, verifying the compatibility of fuses and conductors is a crucial step in ensuring the safe and reliable operation of circuits. Traditional matching tests typically employ a constant current loading method, continuously applying current at proportions of 125% and 150% of the conductor's nominal current carrying capacity, and assessing the suitability of the match by monitoring the fuse's melting time and the conductor's temperature rise. This test method assumes a steady-state, continuous load in actual operating conditions. However, modern automotive electrical systems exhibit significant dynamic characteristics, such as the start-stop of the air conditioning compressor and peak current surges in the motor, all of which generate pulsed, fluctuating currents. These pulsed currents have alternating peak-valley characteristics, resulting in a fundamental asynchrony in the thermal response mechanisms of fuses and conductors. Specifically, the fuse's tripping threshold primarily depends on the heat accumulation effect determined by the average current, and its melting mechanism is based on the principle of heat integration; while the transient temperature rise of the conductor is dominated by the instantaneous Joule heating of the peak current, resulting in significant differences in thermal inertia and response time between the two. Under constant current test conditions, the thermal coupling relationship between the fuse and conductor tends to be consistent, and the matching results usually appear normal. However, under dynamic pulse current loading, existing testing methods are difficult to accurately reflect the actual failure risk, mainly manifested in two misjudgment scenarios: First, the peak current causes the conductor temperature to rise sharply, which may exceed the temperature resistance limit of the insulation layer, while the fuse does not trip because the average current does not reach the threshold, resulting in the latent aging of the insulation layer; Second, the current drops sharply during the pulse valley phase, and the fuse does not accumulate enough heat, so it cannot melt in time before the conductor overheats.

[0003] Therefore, the present invention provides a method and system for testing the current carrying capacity matching of automotive wiring harness fuse wires. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0005] The technical solution adopted by this invention to solve its technical problem is: a method for matching the current carrying capacity of automotive wiring harness fuse wires, comprising the following steps:

[0006] Step S10: By extracting key parameters from the current waveform of a typical load on a real vehicle, a standardized pulse loading profile is established, extending the constant current test into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation.

[0007] Step S20: Under the loading of the composite dynamic test sequence, the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points are collected. A three-dimensional evaluation index of temperature-time-current is introduced. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, the asynchronous thermal response condition is identified.

[0008] Step S30: Based on the asynchronous thermal response condition, the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse are approached by gradually increasing the pulse peak value and duty cycle. By cross-comparing the two sets of critical conditions, the safe matching range of the fuse reaching the dangerous temperature rise before the conductor is determined.

[0009] Step S40: Based on the safety matching range, identify asynchronous risk and overheating priority failure level combinations in the fuse-conductor combination; for asynchronous risk combinations, optimize and adjust the fuse fusing characteristics and conductor current carrying capacity; for overheating priority failure combinations, optimize the fuse rated current level and selection, so that the fusing action is advanced before the conductor insulation layer reaches the temperature resistance limit, and finally feed the optimization results back to the selection specification.

[0010] As a further aspect of the present invention: the method for establishing the standardized pulse loading profile in step S10 is as follows:

[0011] Based on the extracted key parameters, the pulse shape, the ratio of peak current to average current, the typical range of duty cycle, and the typical value of pulse period are statistically formed. The constant current test is expanded into a combination of four types of tests: single pulse impact test, continuous pulse accumulation test, variable duty cycle gradual test, and operating condition cycle test.

[0012] As a further aspect of the present invention: the method for simultaneously acquiring the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points in step S20 is as follows:

[0013] A voltage probe is connected in parallel across the two ends of the fuse and a current probe is connected in series at the front end to collect voltage and current at a sampling rate of not less than 10kHz and calculate the thermal cumulative integral value in real time; multiple temperature sensors are installed on the conductor insulation layer, including the conductor center point, the insulation layer interface and the outer surface of the insulation layer, to collect the temperature of each monitoring point simultaneously.

[0014] As a further aspect of the present invention: the process of identifying the asynchronous thermal response condition in step S20 is as follows:

[0015] Temperature curves are constructed based on the temperatures at each monitoring point and plotted on the same time axis coordinate system as the thermal cumulative integral curve. The time point T_temp when the conductor temperature reaches the short-term temperature resistance limit of the insulation layer and the time point T_fuse when the thermal cumulative integral of the fuse reaches the melting threshold are marked respectively. The time difference Δt = T_temp - T_fuse is calculated. When Δt is less than zero and exceeds the preset allowable deviation range, it is determined to be an asynchronous thermal response condition.

[0016] The temperature data from the monitoring points are filtered, and the temperature values ​​of each monitoring point are connected into a continuous curve along the time axis. The point with the highest temperature in each cross-section is selected as the representative temperature of the cross-section, and the maximum value of the representative temperature curves of all cross-sections is extracted to form a temperature curve.

[0017] As a further aspect of the present invention: the approximation process of the transient temperature rise limit of the conductor in step S30 is as follows:

[0018] Using a standardized pulse loading profile as a reference, with a fixed duty cycle, the pulse peak value is increased step by step at a fixed step size. The instantaneous temperature rise peak value of each temperature measurement point of the conductor insulation layer is recorded. When the temperature rise of any temperature measurement point first reaches the short-term temperature resistance limit of the insulation material, the pulse peak value is recorded as the transient temperature rise limit of the conductor under the current duty cycle. The above process is repeated by changing the duty cycle to obtain the conductor temperature rise limit curve.

[0019] As a further aspect of the present invention: the process of approaching the fuse thermal accumulation melting boundary in step S30 is as follows:

[0020] With a fixed pulse peak value, the duty cycle is increased step by step. After each increase, a continuous pulse sequence is applied, and the fuse thermal accumulation integral value is monitored in real time. When the integral value first reaches the design fusing threshold and fuses, the duty cycle is recorded as the fuse thermal accumulation fusing boundary under the current pulse peak value. The above process is repeated by changing the pulse peak value to obtain the fuse fusing boundary curve.

[0021] As a further aspect of the present invention: the method for determining the safe matching interval in step S30 is as follows:

[0022] The conductor temperature rise limit curve and the fuse melting boundary curve are plotted on the same coordinate system. The conductor temperature rise limit curve represents the maximum allowable pulse peak value of the conductor under different duty cycles, and the fuse melting boundary curve represents the minimum duty cycle that causes the fuse to melt under different pulse peak values. The two curves divide the coordinate system into the fuse non-operation region, the conductor temperature rise exceeding the limit region, and the intersection region between the two curves. This intersection region is the safety matching interval.

[0023] As a further aspect of the present invention: the method for identifying the combination of asynchronous risks and overheating priority failure levels in step S40 is as follows:

[0024] Substitute the actual operating point of the fuse-conductor combination into a coordinate system with duty cycle as the x-axis and pulse peak value as the y-axis. If the operating point is within the safe matching range, it is determined to be a fully matched combination. If the operating point is below the fuse fusing boundary curve, it is determined to be an asynchronous risk combination. If the operating point is above the conductor temperature rise limit curve, it is determined to be an overheating priority failure combination.

[0025] As a further aspect of the present invention: the optimization method for asynchronous risk combination in step S40 is as follows:

[0026] Select a fuse with a rated current rating one level lower, or replace a slow-blow fuse with a fast-blow fuse; on the conductor side, select a conductor with a cross-sectional area one specification larger, or select an insulation material with a higher temperature resistance rating. After optimization, re-perform boundary approximation tests to verify that the operating point enters the safe matching range.

[0027] The optimization method for the overheat-preferred failure combination in step S40 is as follows:

[0028] Select fuses with a rated current rating reduced by one or two levels, or replace slow-blow fuses with fast-blow fuses. After optimization, re-perform boundary approximation tests to confirm that the fuse blowing time and the time when the conductor reaches the temperature rise threshold meet the preset allowable deviation range. Incorporate the optimized and verified matching combinations into the selection specifications.

[0029] A current-carrying capacity matching test system for automotive wiring harness fuse wires includes the following modules:

[0030] The pulse load construction module extracts key parameters from the current waveform of a typical load on a real vehicle and establishes a standardized pulse loading profile, extending constant current testing into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation.

[0031] The asynchronous monitoring and identification module collects the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points under the loading of the composite dynamic test sequence. It introduces a three-dimensional evaluation index of temperature-time-current. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, it identifies the asynchronous thermal response condition.

[0032] The matching interval definition module, based on the asynchronous thermal response condition, uses a method of gradually increasing pulse peak value and duty cycle to approach the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse respectively. By cross-comparing the two sets of critical conditions, it determines the safe matching interval in which the fuse reaches the dangerous temperature rise before the conductor.

[0033] The combined hierarchical optimization module identifies asynchronous risk and overheating priority failure level combinations in fuse-conductor combinations based on the safety matching range. For asynchronous risk combinations, it optimizes and adjusts the fuse's fusing characteristics and the conductor's current carrying capacity. For overheating priority failure combinations, it optimizes the fuse's rated current level and selection, so that the fusing action is brought forward before the conductor insulation layer reaches its temperature resistance limit. Finally, the optimization results are fed back to the selection specifications.

[0034] The beneficial effects of this invention are as follows:

[0035] By acquiring current waveforms from typical loads on real vehicles and establishing standardized pulse loading profiles, the traditional constant current test is expanded into a composite dynamic test sequence covering single-pulse impact, continuous pulse accumulation, variable duty cycle gradual change, and operating condition cycles. This allows the test loading conditions to simultaneously reflect the instantaneous thermal shock of peak current on the conductor and the thermal accumulation effect of average current on the fuse, avoiding test distortion caused by simplified operating conditions. By simultaneously acquiring the fuse thermal accumulation integral value and the real-time temperature of the conductor insulation layer at multiple points, a three-dimensional evaluation index of temperature-time-current is introduced. A time-domain comparison mechanism is established between the conductor temperature rise curve and the fuse I²t accumulation curve. Combined with a preset allowable deviation range, the asynchronous thermal response of the fuse and conductor under dynamic pulse operating conditions is quantitatively identified, solving the problem that traditional tests cannot capture the hidden failure mode of "conductor overheating but fuse not blowing". By gradually increasing the pulse peak value and duty cycle to approximate the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse, two critical curves are obtained and cross-compared to determine the safe matching range. This transforms the asynchronous failure problem into a visualized range determination problem, providing a quantitative boundary basis for the graded evaluation of fuse-conductor combinations. Based on the safe matching range, fuse-conductor combinations are divided into three levels: fully matched, asynchronous risk, and overheat-priority failure. Different optimization strategies are adopted for different levels: for asynchronous risk combinations, replacing fuses with smaller I²t values ​​or conductors with larger cross-sectional areas is used; for overheat-priority failure combinations, reducing the rated current rating of the fuse or replacing it with a fast-blow fuse is used to advance the melting action before the conductor insulation layer reaches its temperature resistance limit. Finally, the optimization results are fed back to the selection specifications, forming a closed-loop iteration from testing and verification to design specifications. This ensures that the fuse and conductor always meet the "break first, heat later" safety logic under dynamic pulse conditions, effectively improving the reliability and safety of automotive electrical systems. Attached Figure Description

[0036] The invention will now be further described with reference to the accompanying drawings.

[0037] Figure 1 This is a flowchart of a module of a method for matching the current carrying capacity of automotive wiring harness fuse wires according to Embodiment 1 of the present invention.

[0038] Figure 2This is a flowchart of a module of an automotive wiring harness fuse wire current carrying capacity matching test system according to Embodiment 2 of the present invention. Detailed Implementation

[0039] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0040] Example 1, please refer to Figure 1 As shown in the embodiment of the present invention, a method for matching the current carrying capacity of automotive wiring harness fuse wires includes the following steps:

[0041] Step S10: By extracting key parameters from the current waveform of a typical load on a real vehicle, a standardized pulse loading profile is established, extending the constant current test into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation.

[0042] In step S10, the typical load in a real vehicle refers to electrical equipment in the automotive electrical system whose current waveform exhibits obvious pulse characteristics, specifically including:

[0043] Inductive loads include air conditioning compressor clutches, cooling fan motors, blower motors, window lift motors, fuel pump motors, etc. These components generate peak currents several times higher than their rated currents at startup, and the current drops back to a lower level after steady-state operation.

[0044] Capacitive loads: Electronic control units (ECUs), inverters, etc., whose internal capacitors generate short-term peak currents during instantaneous charging;

[0045] Switching loads: solenoid valves, relays, actuators, etc., generate current spikes and reverse induced currents at the moment of activation and deactivation;

[0046] For example, the typical load of a real vehicle is illustrated in Table 1 below;

[0047] Table 1: Typical Loads in Real Vehicles;

[0048] Load type Specific components Current characteristics Inductive load Air conditioning compressor clutch The peak current during startup can reach 5-8 times the rated value, lasting for 50-200ms, after which the steady-state current drops back to the rated value. Inductive load Cooling fan motor The peak starting current is 4-6 times the rated value, the duration is 100-300ms, and the duty cycle varies with temperature control. Inductive load Car window lift motor The peak current during stall can reach 10 times the rated value, lasting 1-3 seconds. Frequent start-stop cycles result in dense pulses. capacitive load Electronic control unit (ECU) Upon power-on, capacitor charging generates a microsecond-level current spike, with the peak value reaching 3-5 times the rated value. Switching load Solenoid valves, relays A millisecond-level current spike is generated at the moment of attraction, and a reverse induced current is generated at the moment of release.

[0049] In step S10, the current waveform of a typical load on a real vehicle is acquired using the following method:

[0050] Using a current clamp (such as TCP0030A) in conjunction with an oscilloscope or data acquisition card, with a sampling rate of not less than 1MHz and a bandwidth of not less than 50MHz, ensure the capture of microsecond-level current spikes. Insert acquisition points in series on the wires at the rear end of the fuse and the front end of the load to obtain the real current flowing through the fuse and wiring harness. In the whole vehicle road test or bench simulation, collect the complete current waveform of the load under a typical working cycle (such as the air conditioning compressor starting and stopping 10 times continuously and the motor switching forward and reverse 5 times), record no less than 30 seconds of continuous data, and obtain the current waveform of a typical load in a real vehicle.

[0051] In step S10, key parameters are extracted from the acquired current waveform, specifically including:

[0052] Peak current: The maximum current value within a pulse period (unit: A);

[0053] Peak duration: The time it takes for the current to drop from its peak value to 90% of its peak value (unit: ms or s).

[0054] Duty cycle: The ratio of pulse width to pulse period (unit: %).

[0055] Rise slope: The rate of change of current from valley to peak value (unit: A / ms);

[0056] Average current: The root mean square value of the current over a complete cycle (unit: A).

[0057] Pulse period: The time interval between the start points of two adjacent pulses (unit: seconds);

[0058] For example, the extraction of key parameters from the collected current waveform is explained using an air conditioner compressor as an example, as shown in Table 2 below;

[0059] Table 2: Key parameters extracted from the current waveform;

[0060] Parameter name symbol unit Example value Extraction method Peak current Ip A 45 Maximum value within pulse period Peak duration tp ms 120 The time it takes for the current to drop from its peak value to 50% of its peak value. Ascending slope di / dt A / ms 300 Rising current change rate Duty cycle D % 15 tp / T × 100% Pulse period T s 3 Interval between adjacent pulse start points Average current Iavg A 9.5 RMS value of current during the cycle

[0061] In step S10, the standardized pulse loading profile is established as follows:

[0062] Based on the extracted key parameters, a standardized pulse loading profile is statistically formed, specifically including:

[0063] Pulse shape (rectangular wave, triangular wave, or exponentially decaying wave).

[0064] The ratio of peak current to average current (e.g., peak / average = 3:1);

[0065] Typical duty cycle values ​​(e.g., 10%, 25%, 50%, 75%).

[0066] Typical values ​​for the pulse period (e.g., 1s, 2s, 5s, 10s).

[0067] In step S10, the constant current test is extended to a composite dynamic test sequence covering peak thermal shock and average thermal accumulation as follows:

[0068] Single-pulse impulse test: A single peak pulse is applied, the instantaneous temperature rise of the conductor is measured, and the peak current withstand capability of the insulation layer is evaluated;

[0069] Continuous pulse accumulation test: Apply pulses continuously at a set duty cycle for more than 10 cycles, and measure the change of fuse thermal accumulation integral and wire temperature rise over time;

[0070] Variable duty cycle gradual test: The duty cycle is gradually increased from 10% to 90%, and the change in the critical point between fuse blowing and wire temperature rise is observed.

[0071] Operating condition cycle test: The load is cycled according to the actual vehicle load start-stop logic (such as the compressor running for 3 minutes and stopping for 1 minute) to simulate the heat accumulation and heat dissipation process under real operating conditions;

[0072] By organically combining the above four types of tests, a composite dynamic test sequence covering peak thermal shock and average thermal accumulation is formed.

[0073] For example, the extension of constant current testing to a composite dynamic test sequence covering peak thermal shock and average thermal accumulation can be seen in Table 3 below;

[0074] Table 3: Construction of Composite Dynamic Test Sequences;

[0075] Test type Loading method Example parameters Test objective Single-pulse impact test Stop after applying a single peak pulse IP=45A, tp=120ms Measure the instantaneous temperature rise of the conductor to assess the insulation's ability to withstand peak current. Continuous pulse accumulation test Ten pulses are applied continuously at a fixed duty cycle. Ip=45A, D=15%, T=3s Measuring the thermal cumulative integral of the fuse and the change in wire temperature rise over time Variable duty cycle gradient test The duty cycle gradually increases from 10% to 90%. Ip=45A, D=10%→90%, 5 pulses per level Observe the change in the critical point between fuse blowing and wire temperature rise. Operating condition cycle test Loading in a loop according to the actual vehicle start-stop logic Run for 3 minutes (including the start pulse), stop for 1 minute, repeat 10 times. Simulates the alternating process of heat accumulation and dissipation under real-world working conditions.

[0076] By organically combining the above four types of tests, a composite dynamic test sequence covering peak thermal shock and average thermal accumulation is formed.

[0077] Understandably, the significance of step S10 lies in: by acquiring the current waveform of a typical load on a real vehicle and extracting key parameters such as peak current, duty cycle, and pulse period, a standardized pulse loading profile is established, extending the traditional constant current test into a composite dynamic test sequence covering single-pulse impact, continuous pulse accumulation, gradual change of duty cycle, and cyclic operation. This step solves the fundamental problem of the disconnect between traditional test conditions and real vehicle conditions, enabling laboratory loading conditions to simultaneously reflect the instantaneous thermal shock of peak current on the conductor and the thermal accumulation effect of average current on the fuse, providing a truly equivalent excitation input for subsequent asynchronous identification and boundary approximation.

[0078] Step S20: Under the loading of the composite dynamic test sequence, the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points are collected simultaneously. A three-dimensional evaluation index of temperature-time-current is introduced. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, the asynchronous thermal response condition is identified.

[0079] In step S20, the process of synchronously acquiring the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points is as follows:

[0080] A voltage probe is connected in parallel across the fuse, and a current probe is connected in series at the front end of the fuse to collect the voltage drop across the fuse and the instantaneous current flowing through it in real time. The acquisition system continuously records the current and voltage waveforms at a sampling rate of no less than 10kHz, and calculates the thermal accumulation integral value in real time through an embedded algorithm. That is, starting from the start of the test, the square value of the current is continuously integrated over time to obtain the thermal accumulation integral I²t curve that changes with time.

[0081] Multiple temperature sensors are installed at various points on the conductor insulation layer, including the conductor center point, the junction of the insulation layer and the conductor, the outer surface of the insulation layer, and multiple cross sections distributed along the conductor axis, to collect the instantaneous temperature changes at each monitoring point in real time.

[0082] In step S20, a three-dimensional evaluation index of temperature-time-current is introduced. When the conductor temperature approaches the short-term temperature resistance limit of the insulation layer and the fuse integral does not reach the fusing threshold, the process of identifying asynchronous thermal response conditions is as follows:

[0083] Establish a three-dimensional evaluation index system of temperature-time-current to quantify and compare the thermal response processes of fuses and conductors in the same coordinate system, specifically including:

[0084] The temperature dimension uses the instantaneous temperature of the conductor insulation layer as an evaluation index and sets the short-term temperature resistance limit of the insulation material as a safety threshold. The threshold is determined according to the insulation material. For example, the short-term temperature resistance limit of polyvinyl chloride insulation is 125℃, and that of cross-linked polyethylene is 150℃. Exceeding this temperature will cause irreversible aging or failure of the insulation layer.

[0085] The time dimension uses the test duration as the horizontal axis to record the dynamic process of temperature change and thermal accumulation over time, focusing on two key time points: the moment when the temperature of the conductor insulation layer first reaches the short-term temperature resistance limit, and the moment when the thermal accumulation value of the fuse first reaches the design fusing threshold.

[0086] The current dimension uses the thermal accumulation integral value of the fuse as the evaluation index. This integral value is continuously calculated from the real-time acquired current waveform. Its fusing threshold is determined by the I²t parameter in the fuse specification, which represents the thermal accumulation critical value required for the fuse to fuse under a given current waveform.

[0087] The synchronously acquired temperature curve and the thermal cumulative integral curve are plotted on the same time axis coordinate system. The time point T_temp when the conductor temperature reaches the short-term temperature resistance limit and the time point T_fuse when the fuse I²t reaches the melting threshold are marked respectively, and the time difference Δt=T_temp-T_fuse is calculated.

[0088] It should be noted that the temperature curves are obtained by plotting the temperatures at each monitoring point. Specifically, the raw temperature data of each measurement point is filtered to remove abnormal peaks introduced by electromagnetic interference. Next, the temperature values ​​of each measurement point are connected into a continuous curve along the time axis to obtain the temperature curve of each monitoring location changing over time. Then, the point with the highest temperature in each cross-section (usually the center point of the conductor) is selected as the representative temperature of that cross-section. Finally, the maximum value of the representative temperature curves of all cross-sections is extracted to form the temperature curve.

[0089] If Δt is less than 0 and the time difference exceeds the preset allowable deviation range, it means that the conductor temperature reaches its respective threshold before the fuse melts, and it is determined to be an asynchronous thermal response condition. Conversely, if Δt is greater than 0, it means that the fuse reaches its threshold before the conductor, and it is determined to be a synchronous matching state.

[0090] It should be noted that the allowable deviation range is set to [-200ms, +500ms]. This setting is based on a comprehensive consideration of three aspects: measurement system error, thermal characteristics of insulation materials, and engineering safety redundancy. The -200ms range serves as the upper limit of the allowable lead time for the conductor. This is primarily due to the inherent 50-150ms delay in thermocouple response, the 100-200ms thermal inertia window of the insulation material after reaching its short-term temperature limit, and the approximately 50ms synchronization error between the current and temperature acquisition channels. These three factors are combined and rounded to 200ms to ensure that when the conductor temperature reaches the threshold, although the actual conductor temperature may have slightly exceeded it, the insulation layer has not yet suffered irreversible damage, thus providing a buffer for fuse activation. +500ms is the upper limit of the allowable advance time for the fuse. Based on the typical dynamic pulse working condition, the conductor temperature rise rate is about 0.5-2℃ / s. The conductor temperature corresponding to the fuse blowing 500ms in advance is 0.25-1℃ lower than the threshold. This temperature difference is within the safety margin and does not affect the matching effectiveness. At the same time, it avoids the frequent malfunctions caused by the fuse selection being too conservative due to the excessive pursuit of early blowing.

[0091] It should be noted that when Δt=0, it indicates that the moment when the temperature of the conductor insulation layer reaches the short-term temperature resistance limit coincides with the moment when the thermal accumulation integral of the fuse reaches the melting threshold. This situation belongs to the theoretical boundary point and will not occur precisely in actual testing, so it will not be elaborated further.

[0092] The significance of step S20 is understandable: by synchronously acquiring the fuse's thermal cumulative integral value and the real-time temperature of the conductor's insulation layer at multiple points, a three-dimensional evaluation index of temperature-time-current is introduced to establish a time-domain comparison mechanism between the conductor's temperature rise curve and the fuse's I²t cumulative curve. By calculating the time difference between the moment when the conductor reaches the short-term temperature resistance limit of the insulation layer and the moment when the fuse reaches the melting threshold, and combining this with a preset allowable deviation range, the asynchronous thermal response conditions are quantitatively identified. This step achieves accurate capture of the asynchronous thermal response of the fuse and conductor under dynamic pulse conditions, providing a clear failure criterion for boundary approximation and hierarchical optimization.

[0093] Step S30: Based on the asynchronous thermal response condition, the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse are approached by gradually increasing the pulse peak value and duty cycle. By cross-comparing the two sets of critical conditions, the safe matching range of the fuse reaching the dangerous temperature rise before the conductor is determined.

[0094] In step S30, the process of gradually increasing the pulse peak value and duty cycle to approach the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse includes:

[0095] S301, the approximation process of the transient temperature rise limit of the conductor is as follows:

[0096] Based on the standardized pulse loading profile established in step S10, the transient temperature rise limit of the conductor is approached by gradually increasing the pulse peak value.

[0097] The initial pulse peak value is set to 80% of the rated current carrying capacity of the conductor, the duty cycle is fixed to a typical intermediate value (e.g., 50%), and the pulse period and duration are taken from the actual measured values ​​of the actual vehicle (standardized parameter values ​​extracted from the typical load of the actual vehicle in step S10).

[0098] The pulse peak value is increased incrementally in fixed steps (e.g., 10% of the rated current carrying capacity). After each increment, a single pulse is applied, and the instantaneous temperature rise peak value at each temperature measurement point of the conductor insulation layer is recorded.

[0099] When the instantaneous temperature rise at any temperature measurement point first reaches the short-term temperature resistance limit of the insulation material, the peak value of the pulse is recorded as the transient temperature rise limit of the conductor under the current duty cycle.

[0100] By changing the duty cycle parameter (e.g., 25%, 50%, 75%), repeating the above process, the transient temperature rise limit points of the conductor corresponding to different duty cycles are obtained, forming a conductor temperature rise limit curve with duty cycle as the abscissa and pulse peak value as the ordinate.

[0101] S302, the process of approaching the thermal accumulation melting boundary of the fuse is as follows:

[0102] The duty cycle is gradually increased to approach the thermal accumulation and melting boundary of the fuse. The initial duty cycle is set to 10%, and the pulse peak value is fixed as the measured peak current of the actual vehicle (the peak current value in the current waveform parameters collected and extracted from the typical load of the actual vehicle in step S10). The pulse period and duration remain unchanged.

[0103] The duty cycle is gradually increased in fixed steps (e.g., 5% or 10%), and a continuous pulse sequence (no less than 10 pulse cycles) is applied after each increase to monitor the thermal accumulation integral value of the fuse in real time.

[0104] When the thermal accumulation integral value first reaches the design fusing threshold and fuses, the duty cycle is recorded as the fuse thermal accumulation fusing boundary under the current pulse peak value.

[0105] If the fuse does not blow even when the duty cycle is increased to 100%, the pulse peak value is increased and the test is repeated. The pulse peak current is changed (e.g., 80%, 100%, 120% of the measured peak value). The above process is repeated to obtain the critical duty cycle for fuse blowing corresponding to different pulse peak values, forming a fuse blowing boundary curve with the pulse peak value as the horizontal axis and the duty cycle as the vertical axis.

[0106] In step S30, the process of determining that the fuse reaches the safe matching range for dangerous temperature rise before the conductor is as follows:

[0107] Plot the conductor temperature rise limit curve and the fuse melting boundary curve on the same coordinate system, with the horizontal axis representing the duty cycle and the vertical axis representing the pulse peak current.

[0108] The conductor temperature rise limit curve represents the maximum allowable pulse peak value of the conductor under different duty cycles, while the fuse blowout boundary curve represents the minimum duty cycle that causes the fuse to blowout under different pulse peak values.

[0109] The conductor temperature rise limit curve and the fuse melting boundary curve divide the coordinate system into three regions: the area below the fuse melting boundary curve is the region where the fuse does not operate, the area above the conductor temperature rise limit curve is the region where the conductor temperature rise exceeds the limit, and the area between the conductor temperature rise limit curve and the fuse melting boundary curve is the region where the fuse reaches its respective threshold before the conductor. This intersection area is the safe matching interval.

[0110] It should be noted that at any operating point within the safety matching range (duty cycle, pulse peak combination), the safety logic of the fuse completing the melting before the conductor insulation layer reaches the short-term temperature resistance limit is met. That is, the fuse melting time at any operating point and the time when the conductor reaches the temperature rise threshold meet the allowable deviation range [-200ms, +500ms] set in step S20.

[0111] The significance of step S30 is understandable: by gradually increasing the pulse peak value and duty cycle, it approximates the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse, respectively, to obtain the conductor temperature rise limit curve and the fuse melting boundary curve. By plotting the two curves on the same coordinate system and cross-comparing them, the region where the fuse does not trip, the region where the conductor temperature rise exceeds the limit, and the safe matching range where the fuse reaches the dangerous temperature rise before the conductor are identified. This step transforms the asynchronous failure problem into a visualized range determination problem, providing a quantitative boundary basis for the graded evaluation and selection optimization of fuse-conductor combinations.

[0112] Step S40: Based on the safety matching range, identify asynchronous risk and overheating priority failure level combinations in the fuse-conductor combination; for asynchronous risk combinations, optimize and adjust the fuse fusing characteristics and conductor current carrying capacity; for overheating priority failure combinations, optimize the fuse rated current level and selection, so that the fusing action is advanced before the conductor insulation layer reaches the temperature resistance limit, and finally feed the optimization results back to the selection specification.

[0113] In step S40, the process of identifying asynchronous risks and overheating priority failure levels in the fuse-conductor combination is as follows:

[0114] The position of the fuse-conductor assembly is determined within a coordinate system. The horizontal axis represents the duty cycle, the vertical axis represents the peak pulse current, and the safe matching range is the intersection of the conductor temperature rise limit curve and the fuse melting boundary curve. The identification process is as follows:

[0115] Substitute the rated parameters of the fuse-conductor combination into the coordinate system to determine the actual operating point, i.e., the combination of duty cycle and pulse peak value. If the actual operating point is within the safe matching range, it is judged as a complete match. If the actual operating point is below the fuse blowing boundary curve, i.e. the fuse will not blow under this condition, but the conductor temperature rise may exceed the limit, it is judged as an asynchronous risk combination. If the operating point is above the conductor temperature rise limit curve, i.e. the conductor temperature rise reaches the danger threshold before the fuse action, it is judged as an overheat priority failure combination.

[0116] In step S40, the process of optimizing the fusing characteristics of the fuse and the current-carrying capacity of the conductor for asynchronous risk combinations is as follows:

[0117] For fuse-side optimization, the thermal accumulation fusing boundary curve is reduced by selecting fuse models with smaller I²t values. Specifically, while keeping the rated voltage unchanged, fuses with a lower rated current rating are selected, or fast-blow fuses with the same rated current but faster fusing speed are selected to replace slow-blow fuses. By comparing the I²t parameters of different fuse models, models with a 20%-30% reduction in fusing time under the same pulse conditions are selected for replacement verification.

[0118] For conductor-side optimization, the transient temperature rise tolerance of the conductor can be improved by increasing the conductor cross-sectional area or increasing the temperature resistance rating of the insulation layer, thus shifting the conductor's temperature rise limit curve upward. Specifically, this involves increasing the conductor cross-sectional area by one specification (e.g., from 1.5mm² to 2.5mm²), or selecting an insulation material with a higher temperature resistance rating (e.g., upgrading from PVC 125℃ to cross-linked polyethylene 150℃). After optimization, the boundary approximation test in step S30 is repeated to verify whether the operating point has entered the safe matching range.

[0119] An example illustrating optimization for asynchronous risk portfolios:

[0120] Taking the air conditioning compressor circuit of a certain car model as an example, the original matching scheme used a 20A slow-blow fuse and a 1.5mm² PVC insulated wire. After the boundary approximation test in step S30, the operating point of this combination was located below the fuse fusing boundary curve, and it was determined to be an asynchronous risk combination. That is, under the pulse condition with a peak current of 45A and a duty cycle of 15%, the wire temperature reached the short-term temperature resistance limit of the insulation layer of 125℃ 180ms after the start pulse, while the fuse thermal accumulation integral value only reached 65% of the fusing threshold, and the fuse did not trip.

[0121] To address this asynchronous risk combination, the following optimization measures were implemented: On the fuse side, while maintaining the rated voltage, the 20A slow-blow fuse was replaced with a 15A slow-blow fuse, reducing its I²t value from 800A²s to 450A²s; on the conductor side, the 1.5mm² PVC insulated conductor was replaced with a 2.5mm² cross-linked polyethylene insulated conductor, increasing the temperature resistance from 125℃ to 150℃. After optimization, a boundary approximation test was conducted again. Under the same pulse condition with a peak current of 45A and a duty cycle of 15%, the fuse reached the fusing threshold and activated 165ms after the pulse started. The conductor temperature at the time of fusing was 118℃, which is below the short-term temperature resistance limit of the insulation layer, and the operating point successfully entered the safe matching range.

[0122] In step S40, the process of optimizing the fuse rated current rating and selection for the overheat-preferred failure combination is as follows:

[0123] By reducing the rated current of the fuse, it can reach the thermal accumulation melting threshold earlier under the same pulse conditions. Specifically, the rated current of the fuse is reduced by one or two levels (e.g., from 20A to 15A), ensuring that the reduced rated current is still greater than the steady-state operating current of the load, thus avoiding accidental melting under normal operating conditions.

[0124] Fast-blow fuses are selected instead of slow-blow fuses. Fast-blow fuses are more sensitive to pulse current and can accumulate heat and melt faster under peak current impact. After optimization, the boundary approximation test in step S30 is repeated to confirm that the fuse melting time and the time when the wire reaches the temperature rise threshold meet the allowable deviation range set in step S20.

[0125] An example of optimization for the overheat-preferred failure combination is provided:

[0126] Taking the cooling fan motor circuit of a certain vehicle model as an example, the original matching scheme used a 25A slow-blow fuse and a 2.5mm² PVC insulated wire. After the boundary approximation test in step S30, the operating point of this combination was found to be above the wire temperature rise limit curve, and it was determined to be an overheat-priority failure combination. That is, under the pulse condition with a peak current of 60A and a duty cycle of 50%, the fuse melted when the pulse sequence was applied for 8 cycles, while the wire temperature had reached 135℃ at the end of the 5th cycle, exceeding the 125℃ short-term temperature resistance limit of the PVC insulation layer. The wire overheated before the fuse went off.

[0127] To address this overheat-preferred failure combination, the following optimization measures were implemented: the 25A slow-blow fuse was replaced with a 20A fast-blow fuse, the rated current was reduced by one level, and the fusing type was changed from slow-blow to fast-blow. After optimization, a boundary approximation test was performed again. Under the same peak current of 60A and a duty cycle of 50% pulse conditions, the fast-blow fuse reached the fusing threshold and activated during the third cycle of the pulse sequence. At this time, the conductor temperature was 112℃, which is lower than the short-term temperature resistance limit of the insulation layer of 125℃. The fuse fusing time and the time when the conductor reached the temperature rise threshold met the preset allowable deviation range.

[0128] Establish an optimization results database to record the original parameters, optimization adjustment measures, post-optimization test results, and final matching level for each fuse-conductor combination. Database fields include key information such as fuse type, rated current, I²t value, fusing type, conductor cross-sectional area, insulation temperature rating, operating point location before and after optimization, and post-optimization Δt value. Optimized and validated matching combinations will be incorporated into the company's selection specifications for direct reference in subsequent new project selections.

[0129] Understandably, the significance of step S40 lies in classifying the fuse-lead combination into three levels based on the safety matching range: fully matched, asynchronous risk, and overheat-priority failure. Different optimization strategies are then applied to each level—for asynchronous risk combinations, replacing the fuse with one of smaller I²t values ​​or using a lead with a larger cross-sectional area brings the operating point into the safe range; for overheat-priority failure combinations, reducing the fuse's rated current or replacing it with a fast-blow fuse advances the blowing action. Finally, the optimization results are fed back to the selection specifications, forming a closed-loop iteration from testing and verification to design specifications, ensuring that the fuse and lead always meet the "break first, heat later" safety logic under dynamic pulse conditions.

[0130] Example 2, please refer to Figure 2 As shown in the embodiment of the present invention, an automotive wiring harness fuse wire current carrying capacity matching test system includes the following modules:

[0131] The pulse load construction module extracts key parameters from the current waveform of a typical load on a real vehicle and establishes a standardized pulse loading profile, extending constant current testing into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation.

[0132] The asynchronous monitoring and identification module synchronously collects the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points under the loading of the composite dynamic test sequence. It introduces a three-dimensional evaluation index of temperature-time-current. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, it identifies the asynchronous thermal response condition.

[0133] The matching interval definition module, based on the asynchronous thermal response condition, uses a method of gradually increasing pulse peak value and duty cycle to approach the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse respectively. By cross-comparing the two sets of critical conditions, it determines the safe matching interval in which the fuse reaches the dangerous temperature rise before the conductor.

[0134] Based on the safety matching range, asynchronous risk and overheating priority failure level combinations are identified in the fuse-conductor combination; for asynchronous risk combinations, the fusing characteristics of the fuse and the current carrying capacity of the conductor are optimized and adjusted; for overheating priority failure combinations, the rated current level and selection of the fuse are optimized so that the fusing action is brought forward before the conductor insulation layer reaches the temperature resistance limit, and finally the optimization results are fed back to the selection specification.

[0135] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for testing the current-carrying capacity matching of automotive wiring harness fuse wires, characterized in that: Includes the following steps: Step S10: By extracting key parameters from the current waveform of a typical load on a real vehicle, a standardized pulse loading profile is established, extending the constant current test into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation. Step S20: Under the loading of the composite dynamic test sequence, the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points are collected. A three-dimensional evaluation index of temperature-time-current is introduced. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, the asynchronous thermal response condition is identified. Step S30: Based on the asynchronous thermal response condition, the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse are approached by gradually increasing the pulse peak value and duty cycle. By cross-comparing the two sets of critical conditions, the safe matching range of the fuse reaching the dangerous temperature rise before the conductor is determined. Step S40: Based on the safety matching range, identify asynchronous risk and overheating priority failure level combinations in the fuse-conductor combination; for asynchronous risk combinations, optimize and adjust the fuse fusing characteristics and conductor current carrying capacity; for overheating priority failure combinations, optimize the fuse rated current level and selection, so that the fusing action is advanced before the conductor insulation layer reaches the temperature resistance limit, and finally feed the optimization results back to the selection specification.

2. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 1, characterized in that: The method for establishing the standardized pulse loading profile in step S10 is as follows: Based on the extracted key parameters, the pulse shape, the ratio of peak current to average current, the typical range of duty cycle, and the typical value of pulse period are statistically formed. The constant current test is expanded into a combination of four types of tests: single pulse impact test, continuous pulse accumulation test, variable duty cycle gradual test, and operating condition cycle test.

3. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 1, characterized in that: The method for simultaneously acquiring the fuse thermal cumulative integral value and the real-time temperature of the conductor insulation layer at multiple points in step S20 is as follows: A voltage probe is connected in parallel across the two ends of the fuse and a current probe is connected in series at the front end to collect voltage and current at a sampling rate of not less than 10kHz and calculate the thermal cumulative integral value in real time; multiple temperature sensors are installed on the conductor insulation layer, including the conductor center point, the insulation layer interface and the outer surface of the insulation layer, to collect the temperature of each monitoring point simultaneously.

4. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 3, characterized in that: The process of identifying asynchronous thermal response conditions in step S20 is as follows: Temperature curves are constructed based on the temperatures at each monitoring point and plotted on the same time axis coordinate system as the thermal cumulative integral curve. The time point T_temp when the conductor temperature reaches the short-term temperature resistance limit of the insulation layer and the time point T_fuse when the thermal cumulative integral of the fuse reaches the melting threshold are marked respectively. The time difference Δt = T_temp - T_fuse is calculated. When Δt is less than zero and exceeds the preset allowable deviation range, it is determined to be an asynchronous thermal response condition. The temperature data from the monitoring points are filtered, and the temperature values ​​of each monitoring point are connected into a continuous curve along the time axis. The point with the highest temperature in each cross-section is selected as the representative temperature of the cross-section, and the maximum value of the representative temperature curves of all cross-sections is extracted to form a temperature curve.

5. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 1, characterized in that: The approximation process of the transient temperature rise limit of the conductor in step S30 is as follows: Using a standardized pulse loading profile as a reference, with a fixed duty cycle, the pulse peak value is increased step by step at a fixed step size. The instantaneous temperature rise peak value of each temperature measurement point of the conductor insulation layer is recorded. When the temperature rise of any temperature measurement point first reaches the short-term temperature resistance limit of the insulation material, the pulse peak value is recorded as the transient temperature rise limit of the conductor under the current duty cycle. The above process is repeated by changing the duty cycle to obtain the conductor temperature rise limit curve.

6. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 1, characterized in that: The process of approaching the fuse thermal accumulation melting boundary in step S30 is as follows: With a fixed pulse peak value, the duty cycle is increased step by step. After each increase, a continuous pulse sequence is applied, and the fuse thermal accumulation integral value is monitored in real time. When the integral value first reaches the design fusing threshold and fuses, the duty cycle is recorded as the fuse thermal accumulation fusing boundary under the current pulse peak value. The above process is repeated by changing the pulse peak value to obtain the fuse fusing boundary curve.

7. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 6, characterized in that: The method for determining the safe matching interval in step S30 is as follows: The conductor temperature rise limit curve and the fuse melting boundary curve are plotted on the same coordinate system. The conductor temperature rise limit curve represents the maximum allowable pulse peak value of the conductor under different duty cycles, and the fuse melting boundary curve represents the minimum duty cycle that causes the fuse to melt under different pulse peak values. The two curves divide the coordinate system into the fuse non-operation region, the conductor temperature rise exceeding the limit region, and the intersection region between the two curves. This intersection region is the safety matching interval.

8. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 7, characterized in that: The method for identifying the combination of asynchronous risks and overheating priority failure levels in step S40 is as follows: Substitute the actual operating point of the fuse-conductor combination into a coordinate system with duty cycle as the x-axis and pulse peak value as the y-axis. If the operating point is within the safe matching range, it is determined to be a fully matched combination. If the operating point is below the fuse fusing boundary curve, it is determined to be an asynchronous risk combination. If the operating point is above the conductor temperature rise limit curve, it is determined to be an overheating priority failure combination.

9. The method for matching the current carrying capacity of automotive wiring harness fuse wires according to claim 1, characterized in that: The optimization method for asynchronous risk combination in step S40 is as follows: Select a fuse with a rated current rating one level lower, or replace a slow-blow fuse with a fast-blow fuse; on the conductor side, select a conductor with a cross-sectional area one specification larger, or select an insulation material with a higher temperature resistance rating. After optimization, re-perform boundary approximation tests to verify that the operating point enters the safe matching range. The optimization method for the overheat-preferred failure combination in step S40 is as follows: Select fuses with a rated current rating reduced by one or two levels, or replace slow-blow fuses with fast-blow fuses. After optimization, re-perform boundary approximation tests to confirm that the fuse blowing time and the time when the conductor reaches the temperature rise threshold meet the preset allowable deviation range. Incorporate the optimized and verified matching combinations into the selection specifications.

10. A current-carrying capacity matching test system for automotive wiring harness fuse wires, characterized in that: Includes the following modules: The pulse load construction module extracts key parameters from the current waveform of a typical load on a real vehicle and establishes a standardized pulse loading profile, extending constant current testing into a composite dynamic test sequence covering peak thermal shock and average thermal accumulation. The asynchronous monitoring and identification module collects the thermal cumulative integral value of the fuse and the real-time temperature of the conductor insulation layer at multiple points under the loading of the composite dynamic test sequence. It introduces a three-dimensional evaluation index of temperature-time-current. When the conductor temperature is close to the short-term temperature resistance limit of the insulation layer and the fuse integral has not reached the melting threshold, it identifies the asynchronous thermal response condition. The matching interval definition module, based on the asynchronous thermal response condition, uses a method of gradually increasing pulse peak value and duty cycle to approach the transient temperature rise limit of the conductor and the thermal accumulation melting boundary of the fuse respectively. By cross-comparing the two sets of critical conditions, it determines the safe matching interval in which the fuse reaches the dangerous temperature rise before the conductor. The combined hierarchical optimization module identifies asynchronous risk and overheating priority failure level combinations in fuse-conductor combinations based on the safety matching range. For asynchronous risk combinations, it optimizes and adjusts the fuse's fusing characteristics and the conductor's current carrying capacity. For overheating priority failure combinations, it optimizes the fuse's rated current level and selection, so that the fusing action is brought forward before the conductor insulation layer reaches its temperature resistance limit. Finally, the optimization results are fed back to the selection specifications.

Images