RESEARCH ANALYSIS: Review of electrical and electronic distribution systems
The feature content of new cars is increasing on a daily basis. Yet features like multimedia systems, cell hones, rear seat entertainment, remote keyless entry and tyre pressure monitoring systems all consume more energy. How is this impacting on vehicle electrical and electronic architectures? Matthew Beecham reports.
"In the European market, a lot of new vehicle functions are coming in the direction of higher levels of security, driver assistance systems, and in-car entertainment," said Pascal Degardins, managing director of INTEDIS. This is 'complexifying' vehicle electrical and electronic architectures. Another challenge is the need for low-cost architectures. For instance, Renault has launched the US$5,000 Logan but now targeting a US$3,000 car for the Indian market. All the other OEMs are following suit."
Manufacturers are, therefore, developing novel, cost-effective ways in which to integrate those new features. On the one hand, that means they must continually review the EEDS (electrical and electronic distribution systems) architecture and push back the technical boundaries with innovative integration solutions. On the other hand, they must ensure costs are kept under control by reusing modules, functionalities, hardware and software parts wherever possible.
In addition to cost pressures, manufacturers report the two major forces driving the EEDS market today relate to safety and environmental concerns. They are developing more and more technologies aimed at assisting the driver to avoid critical situations. More specifically, they are combining active with passive safety systems in order to create a complete safety solution, aided by telematics. The other major driving force is the need to improve fuel consumption and cut emissions. We are seeing more and more hybrid and electric vehicles supporting this trend. Both of these trends can be only be solved by the increasing use of electronics.
Hybrid vehicles also make tough demands on the electrical and electronic distribution systems, and these have significant effects upon the architecture. For instance, the additional voltage level for the electric drive must be safely distributed between the assemblies of equipment. Furthermore, the already existing demand for weight reduction becomes far more critical when the extra weight of electro-motor and hybrid battery is considered. In today's hybrid vehicles, the conventional electrical system and the hybrid electrical system are for the most part separate.
Technically speaking, the basic function of an electrical distribution system (EDS) is to provide the electrical interconnections necessary to distribute electrical power and signals around the car. An EDS consists of a fusion of tightly bundled round wire harness assemblies, terminal and connector products, fuse boxes and junction boxes. This network winds its way to virtually every part of a vehicle, from the front lighting through the engine compartment, cockpit, interior to the boot. The wire harness itself consists of raw, coiled wire that is cut to length and terminated. Wiring assemblies are typically a combination of round wire, flat wire, ultra thin wall cable and connection systems into complete systems for the distribution of power and signal throughout a vehicle.
Although conventional round wire harnesses continue to evolve to support additional electronic content in vehicles, the technology has remained much the same over the last 50 years. Despite there being currently no other more cost-efficient way in which to transmit electric current than through copper wire, manufacturers are addressing ways in which to reduce the weight of the conventional round wire harness to serve the increasingly number of electrical features in cars. They are also considering the use of alternative solutions to the traditional wire harness loom such as multiplexing, fibre optics and flexible printed circuit boards.
Multiplexing separates power and signal requirements, simplifying the signal wiring. In other words, multiplexed systems need fewer wires, thereby reducing bulk and weight. Information is shared rather than duplicated, improving service repair, diagnostics and the flexibility to change options. A number of companies are developing multiplex systems, including Delphi Corp. Edmund Erich, European head of E/EA advanced engineering for Delphi Corp, said: "Multiplex systems are usually very close to the microchip industry. Multiplex systems cannot be done on your own. You need a couple of different companies onboard in order to have the right power to implement it. We are part of consortia and pushing these activities."
Fibre optic systems transmit information and data throughout the vehicle for signaling and communication. Optical fibre would have a higher information rate than a conductive medium of comparable size, and would not be affected by electromagnetic interference. The optical fibre technology is engineered to support large and rapid data transmission requirements such as mobile multimedia applications. These innovations accommodate large bandwidth, provide electromagnetic compatibility, reduce weight and provide speed, signal clarity and cost improvements over copper-based technologies. The benefits of optical fibre are ideally suited to integrated safety systems. Claimed advantages of using fibre optics over copper wires include weight saving and higher data quality, reliability and integrity.
Not only is it possible to send large volumes of data through the network at the speed of light, it also guarantees excellent electromagnetic compatibility. On the downside, however, fibre optics is more expensive than traditional wire harness technology as it requires more parts to convert electrical signals to light pulses and back again. Erich added: "Usually, fibre optic systems are used for telematics for high speed data interchange. The problem is that this technology is still expensive compared to conventional solutions. However, we see in the future increasing use of plastic clad fibre optic systems, similar to that used to that used in the telecommunications industry. There are improvements being made to that technology that will make it more cost competitive for automotive applications."
Another novel departure in wiring materials is the flexible printed circuit (FPC). FPCs enable larger sections of the wiring harness to be made in a flat printed circuit board (PCB) configuration. Because of its PCB construction, FPCs can integrate switches and LEDs. Benefits of FPCs include weight and space saving, increased automation of production, improved consistency of performance and added value through mounting components on the harness.
Flexible circuits are said to be more expensive than the wire harnesses they replace, although they can save cost elsewhere in the vehicle's electrical system. They can also reduce the number of connectors required. However, given that FPC connectors have current capacity of a few amps, applications are limited. Most applications have been confined to instrument clusters and, more recently, headliners in some vehicles. Other applications include door wiring, seat wiring, HVAC, antenna and mirror systems. Given that flexible circuits cannot tolerate high temperatures, their use in the engine compartment is ruled out altogether.
In terms of the outlook for flat flexible cables as an alternative to conventional wire harnesses, Erich added: "Flat wire technology provides significant advantages in areas of the vehicle where there is very limited space. This technology also provides more possibilities to integrate additional electronics. So in specific areas, we shall always have the flat wires. At the end of the day, they have to compete from a cost point of view. But I think that there is a future for flat wires."
Going forward with steer-by-wire and brake-by-wire technologies emerging, can the current wiring harnesses technology cope? Degardins concluded: "When we talk of x-by-wire applications, we need very reliable energy distribution and this means a second battery in the vehicle or a hybrid solution. This might mean higher currents in the vehicle. So maybe this is an opportunity for aluminium cable which has the advantage of being relatively flat in terms of prices. If you compare the price increase of aluminium to copper, aluminium is a little more stable. That is a very important factor for the OEMs when they launch a car which will last 6 - 7 years then it is very important to know that the price will not be doubled for the wiring harness.
"The wiring harness of the car is the second most expensive part in the car after the engine. It is very price sensitive so that is why we and our competitors are quite worried now about the increasing price of copper and the instability. Aluminium is also a very light weight metal. So I am quite sure that when x-by-wire comes, that aluminium will come together. The drawback of aluminium which has to be considered in the cost of ownership is that the material itself is very sensitive to pollution - a lot more so than copper. All the solutions that you can see today on the market are completely over-moulded. And that is quite expensive to realize. So when you want to compare copper and aluminium wires you should not only compare the price of the raw material but also compare the price of the manufactured product."