Advances are letting designers spec connectors that deliver high-speed data transfer in harsh environments.
By GERAINT DAVIES
Modern rail vehicles feature an ever-increasing range of technology designed to both enhance passengers’ traveling experience and improve the overall quality of rail operations. Closed-circuit television (CCTV) systems, at-seat information displays, audio and video passenger information systems, and Wi-Fi wireless networking are now commonplace onboard many rail services, and their takeup is being driven by a combination of passenger expectations, operational needs, and profit expectations.
Onboard information displays and video monitors are proving particularly popular in today’s rail and urban-transit industries. Capable of providing real-time journey information, including destination and station stops, as well as news and weather information, security and safety advice, entertainment and even advertising, these onboard systems are no longer seen as optional extras by vehicle manufacturers and operators. Indeed, they help to fulfill safety policies, respond to demand from an increasingly sophisticated public, and cater to passengers with hearing impairments who may otherwise not hear standard audio announcements. If entertainment and advertising are offered, onboard systems also serve to reduce the boredom of tedious commutes and create an additional revenue stream for the many transit authorities currently facing financial deficits.
Growth in onboard technology is spurring the development of electrical components designed with the specific needs of the rail industry in mind. Connectors and interconnection systems are no exception. Onboard information systems are becoming increasingly sophisticated, and use a wide variety of communications media, including GPS, GSM, WiMax, and UHF, to allow voice and data transmission to-and-from the moving train, even when the vehicle is underground or in a tunnel.
Connectors have to be capable of delivering high-speed data transmission while withstanding conditions such as vibration, shock, oscillations in temperature, wind, rain, corrosion, water and salt ingress, dust, flying ballast, and frequent coupling and uncoupling.
A troubled past
In the past, connectors and interconnection systems in the rail industry have been associated with unreliability issues. Their historical inability to withstand harsh conditions represented a major weak spot, and the problem was exacerbated by the frequent use of standard industrial or commercial connectors.
Solving this issue has become a priority for operators, train builders, and manufacturers. With trains carrying increasingly more onboard electronics, the failure of a basic component can completely halt a service, resulting in a knock-on impact on performance, reputation, and operating profits.
To meet the demands imposed by the harsh environments of rail applications, manufacturers of connectors for the transportation market are increasingly looking to the principles used in the design and manufacture of military connectors, which often are subject to similar or even harsher conditions. Tougher and more durable materials are being used to improve reliability. Aluminum outer shells plated with cadmium or zinc cobalt offer extremely high resistance to corrosion, as does tough thermoplastic, which has the added benefit of ensuring full insulation. When it comes to inner shell, components created from plated aluminum give increased strength, as well as provide electrical continuity for screening purposes.
Choice of materials is also important for safety. For example, reducing the risk of fire by incorporating low-fire-hazard thermoplastic insulators is crucial in the mass transportation marketplace. But consideration also must be given to the behavior of the materials should a fire occur. With this in mind, some connector and harness manufacturers, including AB Connectors, manufacture products for rail vehicles using zero halogen, a material designed specifically for the passenger rail market that does not produce harmful or toxic fumes in the event of a fire. Transit authorities worldwide generally require all materials used on vehicle components to be fire-retardant and free of toxic smoke when heated to extreme temperatures; this is particularly important on subway trains, which operate in extremely confined spaces.
Innovative design features provide further protection against harsh environments. Sealing against water and dust ingress can be achieved with a gasket between shells, peripheral seals on the insulators, and grommet wire sealing at the rear of the connector. Rubber coatings protect against the common problem of flying ballast, which can cause significant damage to electrical components. And stainless steel pins incorporated at the critical wear points on the cam track of fixed connectors minimize the stress and wear caused by constant vibration and the train’s motion.
 FIGURE 3: This test cage at AB Connectors’ factory in South Wales, U.K. is part of the company’s lean manufacturing process. |
The need for frequent coupling and uncoupling as vehicles are cleaned and maintained must also be taken into account. For example, connectors that produce an audible snap or click help depot staff and engineers assembling interconnection systems know the connectors are fully mated, and incorporating alignments of colored dots provides further reassurance. Additionally, bayonet pins with locating “windows” in the coupling nut help to guarantee both safe installation and positive coupling in densely packed configurations.
These features are particularly important for subway vehicles, which experience extremely high levels of vibration; any connectors that are not properly mated would quickly become damaged, resulting in service disruption. Ensuring ease of coupling and uncoupling also helps maintenance staff achieve the rapid turnarounds often required in depots, since any cars with technical faults can be disengaged quickly and then replaced.
Lean manufacturing
Vigorous component testing is key to meeting the rail industry’s reliability requirements. To reduce component failure and associated delays, costs, and operating difficulties, all components must be fully tested before leaving the factory, either with autotesters or functional test rigs.
Lean manufacturing techniques can also reduce the incidence of component failure, and several lean processes have proven particularly effective at our organization. Among them are 8D-a corrective procedure to deal with customer complaints, which are captured in the process and immediately contained. Then, the intensive introduction of preventative countermeasures eliminates the possibility of a recurrence.
We also use Poke Yoke principles, which create products that are designed to be assembled in a single manner. By introducing design features and assembly procedures to ensure products cannot be assembled improperly, human error is greatly reduced. We have also increased the use of automation to carry out 100 percent checking, using probes, sensors, and camera vision systems, thereby improving product quality and reliability.
Finally, we use design and process failure mode effect analysis (FMEA) to check if products are actually designed to fail. Examining whether the customer may encounter faults during daily operations enables adaptation of designs to eliminate potential problems. In the two years since we introduced FMEA, the defect rate fell from 4,000 to 5,000 parts per million down to 300 to 400 parts per million.
On the right track
With transit authorities in the United States and elsewhere in the world looking to introduce further information systems and other technologies, it is clear that the need for reliable and high-performance electrical components designed specifically for rail applications is greater than ever. The technology is already being used in the United Kingdom and other European countries. Additionally, Atlanta, Washington D.C., Boston, and Denver all have announced plans to install TV screens on subway cars and commuter rail services.
Manufacturers are investing in research-and-development necessary to meet their needs and, through a combination of durable materials, innovative design features, and advanced testing procedures, connectors may finally be able to shake off their reputation as the Achilles heel of onboard electronics.
GERAINT DAVIES is project manager at AB Connectors, part of TT Electronics PLC (www.ttabconnectors.com).
