Today's automakers are working hard to reduce the weight of their vehicles, helping to reduce carbon dioxide (CO2) emissions and improve fuel efficiency. Design engineers are working hard to develop new techniques and design techniques to reduce the weight of the wiring harness in the car without sacrificing system reliability. The emerging wire technology is a technology that can significantly reduce weight, which allows for greater current carrying capacity with smaller wire diameters. Today, automotive R&D engineers are reinventing well-known proven technologies that use polymer positive temperature coefficient (PPTC) overcurrent protection devices in distributed architectures to improve system reliability while reducing the weight of the entire vehicle wiring harness. .
Revisit distributed solutions
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Although the use of PPTC devices for distributed protection in distributed solutions has become a well-known design option since the 1990s, the popularity of this technology has become very slow among OEMs. In fact, as the functionality of automobiles has increased dramatically, the functionality of automotive electrical and electronic circuits has increased. Today, cabling systems in automobiles have become larger, more cumbersome, and more complex than ever before. In addition to the resistance to changing traditional design methods, the thick lines traditionally utilized also limit the benefits of using PPTC devices.
In the past, due to mechanical strength, the minimum wire diameter of the wires used in the vehicle was 0.35 mm 2 (22 in American wire gauge), and the maximum current carried was 8 to 10 amps. As a result, for circuit applications where the signal current is small (eg, current is less than 8 amps), some of the advantages of using a PPTC device are not reflected. However, today's wire technology is being able to carry larger currents while carrying larger currents, for example, wires with a wire diameter of only 0.13 mm 2 (26 in the US wire gauge), capable of carrying currents up to 5 amps. . This wire technology allows for a further significant reduction in wire weight when using distributed architecture and PPTC overcurrent protection.
Research in the automotive industry has shown that this distributed solution offers significant advantages over traditional centralized fuse-protected architectures. According to the results of the research, in the mid- to high-end passenger vehicles, using the distributed architecture shown in Figure 1 and Tyco Electronics' polymer switching device (PolySwitchTM), the weight of the copper wire can be reduced by about 50%. In addition, design flexibility has been greatly improved.
Figure 1: Comparison of wire weights used in both conventional fuse and distributed architectures. In the calculation of the wire weight, the reference copper material density is 8.96 x 10-6 kg/mm3.
Reduce wire weight associated with trailer lighting circuits
The harsh, mixed maintenance of the application environment, the short circuit and overload caused by water immersion, all determine the light circuit of the trailer is a high-risk application. In order to improve reliability, redundant connecting wires are usually used in the trailer circuit, and each wire is connected to a separate fuse and a power supply circuit. In this design, all lights are usually protected by a separate fuse, which is located in a centralized fuse holder.
However, in a distributed protection architecture, the PPTC device can be placed in a lamp assembly, connector or bond block, thus reducing three fuses, one relay, three sets of long wires and corresponding connectors. The design also simplifies brake design, steering design, hazard warning light modules, and switch design. Figures 2 and 3 compare the traditional centralized solution (left) and distributed protection technology (right). In a distributed solution, only one polymer switching device is needed on each respective node to protect each lighting circuit.
Figure 2: A traditional centralized protection solution.
Figure 3: Distributed solution using polymer switched PPTC devices.
Reduce the wire diameter of the LED high-position brake light
The use of light-emitting diodes (LEDs) reduces power consumption and increases design flexibility, making them increasingly popular in today's various lighting circuits, including the central high-position brake light (CHMSL). In this solution, the use of LEDs instead of incandescent lamps offers the advantage of low current conductors with small gauges that can be easily routed into the trunking of the roof and flexible Ground is connected to the hinge point as shown in Figure 4.
Figure 4: Distributed protection solution in LEDCHMSL applications.
Due to the potential high motor stall current, in a centralized architecture solution, a large circuit fuse or fuse is usually used for protection. Therefore, in the design, large wire gauge wires, large connector ends and connectors must be used. Therefore, it is necessary to arrange a larger interface device installation area, so that space and weight have become factors that must be considered.
In addition, since the motors used for the rear door window, the rear door lock, and the rear panel electric antenna are not able to be close to their respective control switches, the power supply of the motor will be relatively long and the current is large. In contrast, distributed architecture allows designers to flexibly install PPTC devices into the switches, relays, or drive circuits of these motors. Thus, the wire diameter of the power supply feeder used will be greatly reduced. For example, in power window circuits, the power supply feeder conventionally used is 3.0 square millimeters, while a circuit fuse is required upstream to protect it.
However, by integrating the PPTC device into the motor control switching circuit, the power feeder wire diameter can be greatly reduced to 0.8 square millimeters due to the voltage drop. Due to the reduced wire diameter, smaller termination modules, smaller interface connectors and switches can be used. In addition, in the driver circuit, the micro control circuit can select a transistor that is lower in cost, smaller in power, and does not require protection. This will significantly reduce the cost of the cabling system and its associated hardware. The use of a small wire gauge can reduce the size of the wire harness, thereby increasing the flexibility of the wiring and improving the appearance and uniformity of the wiring. In addition, this reduces the force required to route the vehicle, which in turn reduces the chance of damage during installation.
in conclusion
The combination of a distributed architecture and PPTC overcurrent protection in automotive design can significantly reduce wiring weight. Although distributed solutions have been around for many years, today's solutions are clearly superior to traditional fuses as they can now take on more wires with smaller wire diameters and are motivated by emerging industries. technology. PPTC devices have a resettable function, low-resistance characteristics, and a wide range of rated currents, which can help automotive designers reduce line length and weight, simplify design, increase design flexibility, and improve vehicle system reliability.
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