Electronic fuse with dynamic turn-off current

Abstract

The invention relates to an electronic fuse with dynamic turn-off current. An electronic fuse is configured to sense a measurement current flowing through the electronic fuse and calculate a sum based on an amount of the measurement current over time. The electronic fuse evaluates the sum with respect to an area defined according to a graph of current square and time (I2t) for wire specifications. If the sum exceeds the area, the electronic fuse switches off the current flowing through the electronic fuse. The electronic fuse is capable of controlling the flow of current to a device through a wire according to the wire specification. The electronic fuse can be part of a vehicle, such as a pure electric vehicle.

Description

[0001] Related patent applications

[0002] This application claims the benefit of U.S. Application Serial No. 63 / 643,406, filed May 6, 2024, entitled “ELECTRONIC FUSE WITH DYNAMICSHUTOFF CURRENT”. Background Technology

[0003] This disclosure relates to an electronic fuse (eFuse). Summary of the Invention

[0004] This disclosure describes techniques for implementing electronic fuses. In one aspect, an electronic fuse is configured to sense a measured current flowing through the electronic fuse and to calculate a sum based on the amount of the measured current over time. In various embodiments, the electronic fuse is relative to the current squared over time according to the conductor specification. 2 The sum is evaluated using the area defined by the curve t). If the sum exceeds the area, the electronic fuse shuts off the current flowing through it. Attached Figure Description

[0005] Figure 1A Example vehicles that can operate according to certain implementation schemes are shown.

[0006] Figure 1B An example is shown of a vehicle chassis having multiple operable drive units according to certain embodiments.

[0007] Figure 2 It is a schematic block diagram of components used to operate a vehicle according to certain implementation schemes.

[0008] Figure 3 This is a schematic diagram illustrating the transfer of current to a device via an electronic fuse according to certain implementation schemes.

[0009] Figure 4 This is a cross-sectional view of the conductor.

[0010] Figure 5 This is a process flow diagram of a method for controlling an electronic fuse according to certain implementation schemes.

[0011] Figure 6 It is an I for the conductor according to certain implementation schemes. 2 The t-curve and the area used to dynamically determine when to turn off the electronic fuse.

[0012] Figure 7 It is a current versus time graph used for evaluation based on certain implementation schemes.

[0013] Figure 8 It is a graph of the sum of the square of the overcurrent over time, used in certain implementation schemes to determine when to shut off an electronic fuse. Detailed Implementation

[0014] Vehicles rely on fuses to avoid dangerous current levels that could arise from damaged wiring or malfunctions in components drawing current from the fuse. The amount of current that can be safely transmitted through a wire is time-dependent. A component can temporarily draw a large amount of current, and even if the wire cannot sustain that current indefinitely, the large amount of current can still be safely transmitted through the wire.

[0015] By using electronic fuses that consider the duration of current spikes rather than simply their amplitude, vehicle wiring can be made smaller and correspondingly lighter, cheaper, and more flexible. In various embodiments, the electronic fuses disclosed herein calculate the sum of currents exceeding the rated current for the wiring, and where this sum exceeds the If value for the wiring. 2 t-relationship (e.g., I) 2 The current is turned off when the area is defined by the t function or graph.

[0016] Figure 1A Example vehicle 100 is shown. (e.g.) Figure 1A As shown, vehicle 100 has multiple external cameras 102 and one or more front displays 104. Each of these external cameras 102 can capture a specific view or perspective of the exterior of vehicle 100. The images or videos captured by the external cameras 102 can then be displayed on one or more displays in vehicle 100, such as one or more front displays 104, for the driver to view.

[0017] refer to Figure 1B The vehicle 100 may include a chassis 106, which includes a frame 108 that provides the main structural components of the vehicle 100. The frame 108 may be formed by one or more beams or other structural components, or it may be integrated with the vehicle body (i.e., a monocoque construction).

[0018] In embodiments where vehicle 100 is a battery electric vehicle (BEV) or possibly a hybrid vehicle, a large battery 110 is mounted to the chassis 106 and may occupy a significant portion (e.g., at least 80%) of the area within the frame 108. For example, battery 110 may store 100 to 200 kWh. Battery 110 may be a lithium-ion battery or other types of rechargeable battery. The battery may be substantially planar in shape.

[0019] Power from battery 110 can be supplied to one or more drive units 112. Each drive unit 112 may consist of an electric motor and possibly a gear train providing gear reduction. In some embodiments, a single drive unit 112 drives either the front or rear wheels of vehicle 100. In another embodiment, two drive units 112 are present, each driving either the front or rear wheels of vehicle 100. In yet another embodiment, four drive units 112 are present, each driving one of the four wheels of vehicle 100.

[0020] Power from battery 110 can be supplied to drive unit 112 by power electronics 114 in each drive unit 112. Power electronics 114 may include inverters configured to convert direct current (DC) from battery 110 into alternating current (AC) supplied to the motor of drive unit 112. Power electronics 114 also facilitate the use of the drive unit's motor as a generator to provide regenerative braking. Power electronics 114 also facilitate the transfer of regenerative current to battery 110.

[0021] A drive unit 112 is coupled to two or more wheel hubs 116 to which wheels can be mounted. Each wheel hub 116 includes a corresponding brake 118, such as a disc brake as illustrated. Each wheel hub 116 is further coupled to a frame 108 via a suspension 120. The suspension 120 may include metal or pneumatic springs for absorbing shocks. The suspension 120 may be implemented as a pneumatic or hydraulic suspension capable of adjusting the ground clearance of the chassis 106 relative to a supporting surface. The suspension 120 may include a damper, wherein the characteristics of the damper are fixed or electronically adjustable.

[0022] exist Figure 1B In the implementation scheme and in the discussion below, vehicle 100 is a battery electric vehicle. However, the systems and methods disclosed herein can be used in any type of vehicle, including vehicles powered by an internal combustion engine (ICE), a hybrid powertrain, a hydrogen fuel cell powertrain, or other types of powertrains that may have a portion that idles during some operating modes. For example, the front or rear differential of an all-wheel-drive vehicle. In another example, in a hybrid powertrain, according to the methods described herein, the idle drive unit including the electric motor can be heated using waste heat from the ICE.

[0023] Figure 2 Examples Figure 1A Example components of vehicle 100. (e.g.) Figure 2As shown, vehicle 100 includes a camera 102, one or more front displays 104, a user interface 200, one or more sensors 202, a motion sensor 204, and a positioning system 206. The one or more sensors 202 may include ultrasonic sensors, radio detection and ranging (RADAR) sensors, light detection and ranging (LIDAR) sensors, or other types of sensors. The positioning system 206 may be implemented as a Global Positioning System (GPS) receiver. The user interface 200 allows a user (such as a driver or passenger in vehicle 100) to provide input.

[0024] The components of vehicle 100 may include one or more temperature sensors 208. Temperature sensors 208 may include sensors configured to sense ambient air temperature, battery 110 temperature, power electronics 114 temperature, temperature of each drive unit 112 and / or each motor of each drive unit 112 temperature, temperature of coolant fluid entering or leaving the coolant system, oil temperature within drive unit 112 temperature, or temperature of any other component of vehicle 100.

[0025] The vehicle 100 may include a friction braking system 210. The friction braking system 210 may include any components of a hydraulic braking system, such as a rotor, brake pads, calipers, caliper pistons, and a master cylinder connected to the caliper pistons and the brake pedal via brake lines. The friction braking system 210 may also include a pump and / or valves for automatically applying hydraulic pressure to the caliper pistons. The friction braking system 210 may be implemented as a drum braking system or any friction braking system known in the art.

[0026] Control system 214 executes instructions to perform at least some of the actions or functions of vehicle 100, including those related to... Figures 3 to 6 The described function. For example, such as Figure 2 As shown, the control system 214 may include one or more electronic control units (ECUs) configured to perform at least some of the actions or functions of the vehicle 100, including regarding... Figures 3 to 6 The functions described. In some implementations, each ECU in the ECU is dedicated to a specific set of functions. Each ECU may be a computer system, and each ECU may include the functionality described below.

[0027] Certain features of the implementation scheme described herein can be controlled by a telematics control module (TCM) ECU. The TCM ECU can provide a wireless vehicle communication gateway to support functionalities such as (by way of example and not limitation) over-the-air (OTA) software updates, vehicle-to-internet communication, vehicle-to-computing device communication, in-vehicle navigation, vehicle-to-vehicle communication, vehicle-to-landscape features (e.g., automatic toll collection sensors, automatic toll booths, power distributors at charging stations), or automatic calling functionality.

[0028] Certain features of the implementation described herein can be controlled by a Central Gateway Module (CGM) ECU. The CGM ECU serves as the vehicle's communication hub, connecting various ECUs, sensors, cameras, microphones, motors, displays, and other vehicle components, and transmitting data to and from these components. The CGM ECU may include a network switch providing connectivity via a Controller Area Network (CAN) port, a Local Interconnect Network (LIN) port, and an Ethernet port. The CGM ECU can also function as the master controller for different vehicle modes (e.g., road driving mode, parking mode, off-road mode, towing mode, camping mode), thereby controlling certain vehicle components associated with placing the vehicle in one of these vehicle modes.

[0029] In various implementations, the CGM ECU collects sensor signals from one or more sensors of the vehicle 100. For example, the CGM ECU may collect data from camera 102, sensor 202, motion sensor 204, positioning system 206, and temperature sensor 208. The sensor signals collected by the CGM ECU are then transmitted to the appropriate ECU for performing operations and functions, as described below.

[0030] The control system 214 may also include one or more additional ECUs, such as (by way of example and not limitation): Vehicle Dynamics Module (VDM) ECU, Experience Management Module (XMM) ECU, Vehicle Entry / Exit System (VAS) ECU, Near Field Communication (NFC) ECU, Body Control Module (BCM) ECU, Seat Control Module (SCM) ECU, Door Control Module (DCM) ECU, Rear Zone Control (RZC) ECU, Autonomous Control Module (ACM) ECU, Autonomous Safety Module (ASM) ECU, Driver Monitoring System (DMS) ECU, and / or Winch Control Module (WCM) ECU.

[0031] If vehicle 100 is an electric vehicle, one or more ECUs may provide functionality related to the vehicle's battery pack, such as a Battery Management System (BMS) ECU, a Battery Power Isolation (BPI) ECU, a Balanced Voltage and Temperature (BVT) ECU, and / or a Thermal Management Module (TMM) ECU. In various implementations, the XMM ECU sends data to the TCM ECU (e.g., via Ethernet, etc.). Additionally or alternatively, the XMM ECU may send other data (e.g., audio data from microphone 216, etc.) to the TCM ECU.

[0032] The ECU may include one or more ECUs configured to control the friction braking system 210. For example, the ECU may include a traction control module, a stability control system, an automatic emergency braking (AEB) module, an anti-lock braking system (ABS), an adaptive cruise control (ACC) module, and / or an advanced driver assistance system (ADAS). The traction control module controls braking and acceleration to control wheel slip according to any method known in the art. The traction control module may also control the torque applied to each wheel, i.e., torque vectoring control. According to any method known in the art, the stability control system controls braking and acceleration to prevent vehicle 100 from rolling over. According to any method known in the art, the AEB module stops vehicle 100 in a controlled manner in response to a predicted collision. The ABS adjusts the braking to maintain traction. The ACC maintains the vehicle's speed while also maintaining a prescribed following distance relative to other vehicles. The ADAS controls the steering, acceleration, and braking of vehicle 100 according to any autonomous driving method known in the art to reach the destination.

[0033] refer to Figure 3 Electricity can be supplied to the device 300 of the vehicle 100 via the electronic fuse 302 (“eFuse”). The electronic fuse 302 is an electronic switch capable of measuring the current flowing through the electronic fuse 302 and evaluating the measured current according to logic to determine whether to disconnect the switch to prevent damage to the device 300 from the current supplied by the electronic fuse 302.

[0034] Device 300 can be a light, motor, heating element, ECU, or any other component of vehicle 100. Device 300 can be a motor of drive unit 112, a pump for adjusting suspension 120, etc. Electronic fuse 302 can also be used in non-vehicle applications, allowing device 300 to be any device that draws current.

[0035] Electronic fuse 302 may be incorporated into zone controller 304, which controls the power supply to components or one or more types of components (e.g., those with common supply voltage and / or current requirements) within a specific zone of vehicle 100. Zone controller 304 may include on-board power supply 306. On-board power supply 306 may receive current from power source 308 (such as battery 110) and perform voltage reduction. For example, battery 110 may output 400 volts, 800 volts, or higher, while the output of on-board power supply 306 is much lower, such as 12 volts, 24 volts, or 48 volts.

[0036] Electronic fuse 302 is coupled to device 300 via wire 310. Wire 310 can be as follows: Figure 4 The conductor shown comprises one or more bundles 400 of metal strands surrounded by an insulator 402. The bundles 400 may include copper wires that can be stranded or braided together. The insulator 402 is typically a polymer having dielectric properties.

[0037] When current is conducted through conductor 310, the resistance to the flow of current through the metal of one or more wire bundles 400 will cause heat to accumulate. Under acceptable operating conditions, the heat will be dissipated through insulator 402. As the current increases, heat will be generated more rapidly than heat that can be dissipated to the surrounding materials (i.e., adiabatic heating). The temperature of one or more wire bundles 400 can reach the smoke temperature of insulator 402, at which point insulator 402 will begin to decompose.

[0038] The current required for conductor 310 to reach its smoke temperature is a function of ambient temperature, the square of the current (I), and the duration of the current (t). Therefore, for standard ambient temperatures, such as 25 degrees Celsius or higher, each conductor 310 specification has a corresponding square current versus time (I). 2 t) relationship. I 2 The t-relationship shows the amount of time that conductor 310 can conduct a given amount of current before reaching the smoke temperature. The rated current for conductor 310 is the amount of current that conductor 310 can carry indefinitely at standard ambient temperatures without failure.

[0039] Device 300, which receives current from electronic fuse 302 via conductor 310, may have irregular current draw. For example, most components will initially draw a large current but then stabilize at a much lower current draw. Electric motors, for example, exhibit this behavior. Using the methods described herein, electronic fuse 302 can consider the duration of a current higher than the rated current of conductor 310 to determine whether to cut off the current to device 300. Therefore, conductor 310 can be made smaller, which reduces the cost and weight of conductor 310 and improves the flexibility of the wiring harness including conductor 310.

[0040] Figure 5 A method 500 that can be performed by an electronic fuse 302 is illustrated. Method 500 may include measuring the current flowing through the electronic fuse 302 at step 502. The measurement may be performed periodically, such as with a sampling period Δt. Method 500 may include updating the sum at step 504. The sum may approximate the square of the measured current for a current sample. The square of the rated current of conductor 310 The integral of the difference between them over time. For example, the sum (S) can be calculated according to (1), where S is initialized to zero before the first iteration in step 504. As is evident in (1), the sum can be constrained to be positive.

[0041]

[0042] The method may include, at step 506, relative to I based on wire 310 2 The sum S is evaluated using the area (A) determined by the t-relationship. If S > A, the electronic fuse 302 can be tripped at step 508, thereby cutting off the current supply to device 300. Otherwise, a subsequent iteration of method 500 can begin at step 502. If the electronic fuse 302 trips, method 500 can end until further action is performed. The electronic fuse 302 can remain tripped until it is closed by another entity, such as being reset by a human operator or other software component, for example, resetting control system 214. In some embodiments, whether the electronic fuse 302 can be reset by control system 214 depends on I M For example, if there is no I current higher than the threshold current before the electronic fuse 302 trips. M If so, automatic reset by control system 214 is permitted. Otherwise, a human operator may be required to reset it. Control system 214 may be permitted to reset a maximum of a predetermined number of times, after which a human reset will be required.

[0043] The area A can be a fixed value or can be determined dynamically. For example, A can be determined by evaluating whether the measured current is higher than the rated current at step 510, and if so, at step 512, it is determined based on I for conductor 310. 2 The area A is calculated using the t-relationship (see...). Figure 6 (and the corresponding discussion). The area A calculated for this measurement at step 502 can then be used to perform the evaluation of step 506 for the measurement at step 502. Without invoking step 512, area A can be either the default area A or the area A calculated for the previous iteration of method 500.

[0044] Figure 6 , Figure 7 and Figure 8 This example demonstrates how to calculate and use area A. Figure 6 An example is given for the square of the current (I) for conductor 310. 2 A graph 600 showing the relationship between time (t) and conductor 310, which may be provided by the conductor manufacturer. Graph 600 may be based on specifications for conductor 310. 2 t-curve. Rated current I R It can also be based on the specifications for conductor 310. The curve 600 can be derated, i.e., indicating limits for the duration of a given current, these limits are artificially reduced to provide a safety margin. The curve 600 can be further derated to obtain curve 602, for example, I. 2 The value decreases by X%, where X is a value between 10 and 20, such as 15%.

[0045] Area A can be the area of ​​a rectangle, which has the following characteristics: Furthermore, the first corner point at t=0 and the depreciation curve in Figure 602 are for values ​​higher than... Selected value I 2 The second corner point. A point on the derating curve 602 can be selected to (a) provide the minimum area A of all possible points on the derating curve 602, or (b) with the measured current I from step 502. M Correspondingly (e.g.) The default value for A can be the minimum area A. In some implementations, step 506 may include using (a) the value of A from the immediately preceding iteration of method 500 and (b) the measured current I from step 502 of the current iteration of method 500. M The smaller of the values ​​of A.

[0046] Figure 7 and Figure 8 This illustrates possible scenarios where method 500 might be used. Figure 7 Graphs 700 and 702 showing the measured current over time are provided. These graphs show I values ​​above the exemplified amplitude and duration. R The pulse then drops below I in the case of curve 700. R The current.

[0047] Figure 8 Examples of possible sums S1 and S2 calculated according to (1) for curves 700 and 702 are shown respectively. As shown by sum S1, the sum rises to a peak value below A, and then decreases to below I as the current drops. R and the items in (1) It becomes negative and decreases. Figure 8This further illustrates that the sum S1 does not fall below zero as defined in (1). For example, in some embodiments, the electronic fuse is configured to calculate the sum such that the sum is never negative. In some embodiments, where the area A is not fixed, once the sum S1 falls below zero, the area A is restored to its default value or set to 0. Subsequently, when the current rises above I... R In this case, the area A can be set in a subsequent iteration of method 500.

[0048] like Figure 8 As shown, the sum S2 does indeed rise above A, at which point the electronic fuse 302 will disconnect and the current will stop flowing through the electronic fuse 302. Using the derating curve 602 to calculate A ensures that any overshoot of area A due to the limited response time of the electronic fuse 302 will not cause a malfunction.

[0049] Various embodiments of this disclosure have been described for illustrative purposes. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein has been chosen to explain the principles of the embodiments, their practical application, or technical improvements to technologies found in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

[0050] In the foregoing, reference has been made to the embodiments presented in this disclosure. However, the scope of this disclosure extends beyond the specifically described embodiments. Rather, any combination of features and elements is contemplated for implementing and practicing the intended embodiments, regardless of whether different embodiments are involved. Furthermore, while the embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, the embodiments may achieve some advantages or no particular advantages. Therefore, the aspects, features, embodiments, and advantages discussed herein are merely illustrative.

[0051] The various aspects of this disclosure may take the form of a completely hardware implementation, a completely software implementation (including firmware, resident software, microcode, etc.), or a combination of software and hardware implementations, all of which may be collectively referred to herein as “circuit,” “module,” or “system.”

[0052] Various aspects of this disclosure are described by narrative text, flowcharts, block diagrams of computer systems, and / or block diagrams of machine logic included in implementations of a computer program product (CPP). Regarding any flowchart, depending on the technology involved, operations may be performed in a different order than that shown in a given flowchart. For example, again depending on the technology involved, two operations shown in consecutive flowchart frames may be performed in reverse order, as a single integrated step, concurrently, or in a manner that at least partially overlaps in time.

[0053] A Computer Program Product Implementation (“CPP Implementation” or “CPP”) is a term used in this disclosure to describe any set of one or more storage media (also referred to as “medium”) collectively included in a set of one or more storage devices, which collectively include machine-readable code corresponding to instructions and / or data for performing the computer operations specified in a given CPP claim. A “storage device” is any tangible device capable of holding and storing instructions for use by one or more computer processing devices. Without limitation, a computer-readable storage medium can be an electronic storage medium, a magnetic storage medium, an optical storage medium, an electromagnetic storage medium, a semiconductor storage medium, a mechanical storage medium, or any suitable combination of the foregoing. Specific types of storage devices including these media include: magnetic disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), compact disc read-only memory (CD-ROM), digital versatile disc (DVD), memory sticks, floppy disks, mechanical encoding devices (such as punched cards or pits / platforms formed in the main surface of the disk), or any suitable combination of the foregoing. As used in this disclosure, computer-readable storage medium refers to a non-transitory storage device rather than the transient signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides, optical pulses transmitted through fiber optic cables, and electrical signals transmitted through wires and / or other transmitting media. As those skilled in the art will understand, data typically moves at some incidental points in time during the normal operation of the storage device (such as during access, defragmentation, or garbage collection), but the storage device remains non-transitory during these processes because the data remains non-transitory while stored.

[0054] While the foregoing relates to embodiments of this disclosure, other and further embodiments may be devised without departing from the basic scope of this disclosure, the scope of which is defined by the appended claims.

Claims

1. An apparatus comprising: Electronic fuse, the electronic fuse being configured to: Sensing the measured current flowing through the electronic fuse; The sum is calculated based on the amount of the measured current over time; Compared to the current square and time (I) based on the conductor specification 2 The sum is evaluated using the area defined by the relationship t). as well as If the sum exceeds the area, the current flowing through the electronic fuse is cut off.

2. The apparatus of claim 1, wherein the electronic fuse is configured to calculate the sum based on the amount by which the measured current exceeds a rated current over time, the rated current being based on conductor specifications.

3. The apparatus of claim 2, wherein the electronic fuse is configured to calculate the sum as the time difference between the square of the measured current and the square of the rated current.

4. The apparatus of claim 3, wherein the electronic fuse is configured to calculate the sum such that the sum is never negative.

5. The apparatus of claim 2, wherein the electronic fuse is configured to, according to Update I for each sample of the measured current M The sum (S) is used to calculate the sum, where I R It is the rated current, and Δt is the sampling period for the electronic fuse to measure the current flowing through it.

6. The apparatus of claim 2 further includes a wire of the specified wire specification connected to the electronic fuse.

7. The apparatus of claim 6, further comprising a device connected to the wire, the device being configured to draw a current exceeding the rated current during normal operation of the apparatus.

8. The apparatus of claim 7, wherein the device is a component of a vehicle.

9. The apparatus of claim 1, wherein the area is the size of a rectangular region having a first corner point at time = 0 and the rated current, and at the I... 2 The second corner point on the reduced version of the t relation.

10. The apparatus of claim 9, wherein the I 2 The reduced version of the t relationship relative to the I 2 The t-relationship decreases by at least 10%.

11. A method comprising: The electronic fuse senses the measured current flowing through it. The electronic fuse calculates the sum based on the amount of the measured current over time; The electronic fuse is relative to the square of the current and time (I) according to the wire specification. 2 The sum is evaluated using the area defined by the relationship t). The electronic fuse determines that the sum is greater than the area; and In response to determining that the sum is greater than the area, the current flowing through the electronic fuse is turned off by the electronic fuse.

12. The method of claim 11, further comprising calculating the sum by the electronic fuse based on the amount by which the measured current exceeds the rated current over time, the rated current being based on conductor specifications.

13. The method of claim 12, further comprising calculating the sum as the time difference between the square of the measured current and the square of the rated current by the electronic fuse.

14. The method of claim 13, further comprising calculating the sum by the electronic fuse such that the sum is never negative.

15. The method of claim 12, further comprising the electronic fuse being connected according to... Update I for each sample of the measured current M The sum (S) is used to calculate the sum, where I R It is the rated current, and Δt is the sampling period for the electronic fuse to measure the current flowing through it.

16. The method of claim 12, wherein a wire of the specified wire specification is connected to the electronic fuse.

17. The method of claim 16, wherein the device is connected to the conductor, and the device draws a current exceeding the rated current during normal operation of the device.

18. The method of claim 7, wherein the device is a component of a vehicle.

19. The method of claim 11, wherein the area is the size of a rectangular region having a first corner point at time = 0 and the rated current, and at the I... 2 The second corner point at the point on the reduced version of the t relation.

20. The method of claim 19, wherein the I 2 The reduced version of the t relationship relative to the I 2 The t-relationship decreases by at least 10%.

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