14. January 2016

Customised wire-free solution for on-board safety systems

Vossloh Rail Vehicles wanted a new, simplified and more reliable solution for two safety critical Relay Racks on board its Euro 3000 locomotives that would replace the existing hard-wired chassis. The latter was relatively labour-intensive to trouble-shoot and maintain and required a long lead time when ordering new units. The solution developed by HARTING Integrated Solutions employed direct connections between the relay cards and I/O connectors to eliminate all internal wiring, resulting in a unit that is quicker and more simple to manufacture, smaller in size, lighter weight and simpler to maintain, therefore showing considerable cost benefits all round.

Now in service for almost a decade, the Euro 3000 passenger locomotives are a core product for Vossloh Rail Vehicles. As part of the ongoing improvements such a product undergoes, Vossloh wanted to upgrade a pair of custom-designed Relay Racks that are an integral part of the locomotives’ on-board safety systems.

The two identical racks, with a standard imperial width and height (19" x 3U), hold the 160 mm relay cards that govern various safety-related functions like fire alarms, braking systems and traction convertors. Each card slotted vertically into the rack contains three safety relays. Input signals to the relay contacts come from the locomotive’s control cabinet. The relay contacts provide signal outputs via rear connectors on the chassis to the various safety subsystems distributed throughout the train. Each card has a status LED that must be on when the relay contact is activated.

Hard wiring: Labor intensive

The existing Euro 3000 rack design features hard-wired DIN 41 612 connections from each relay card to the backside connectors and also between the relay cards as a bus connection. This represented an enormous amount of wiring – and for the two racks combined a total of 960 hard-wired connections. That reliance on hard-wiring has made the existing labour-intensive to build, troubleshoot and repair, hence relatively expensive. Manufacturing new units has required a long lead time due in part to the need to order float mounted connectors for all those hard-wired connections throughout the chassis.

Focus on cost

Vossloh wanted a new design that would reduce the cost per unit while retaining the flexibility of the original wired design to reconfigure each rack for changing technology or operator requirements. It sought proposals from qualified manufacturers including the makers of relay products, as well as HARTING Integrated Solutions.

Vossloh engineers had envisioned a stream-lined replacement concept that would include hard-wiring the bus connection of the relay cards to the rear connectors for the output signals. This would have reduced the number of hard-wired connections per unit in half. However, the actual RFP provided only railway standard specifications, not project specifications. This gave HIS, the only provider with both system design capability and extensive connectivity expertise, the latitude to propose an even more ambitious solution ultimately accepted by Vossloh: a relay rack based entirely on direct connectivity without any wiring whatsoever.

Simpler, cleaner design

Using HARTING’s PCB adaptors and proven reliable Han® DD connectors for the input/outputs, the six rear  connectors of the HIS design are mounted on the same backplane used for bus connections and to which the relays are attached. That way, all connections are managed through the single board, eliminating the need for any wiring or a second PCB. This achieved a rack design that reduces the depth by 30 %, because there is no need to accommodate cable looms between the rear connectors and the relay cards. That shorter depth also provides easier access to the rear connector from the front of the cabinet and contributes to the new units weighing almost 40 % less.

Easier to maintain, manufacture

The absence of wired connections increases the reliability of the unit, making it easier to maintain and troubleshoot in the field, translating into significant labor cost savings over time. The HIS design can be assembled much faster using an easily repeatable process. The wire-free design doesn’t lend itself to the same manufacturing errors that plagued its hard-wired predecessor and often necessitated an exhaustive fault-finding exercise before many of the latter were ready for delivery.

Meets customer’s goals

The entire design and production of the HIS concept, including extensive design reviews by the customer and both lab and field testing of the prototypes, took six months. On an all-in cost basis including testing, the HIS design represents a cost saving of more than 20 % for Vossloh, with no compromise to the quality of the Vossloh product. Despite the size and weight reductions, the unit is as rugged as the one it replaces. By eliminating all internal wiring, including all jumper links among the cards, it offers enhanced flexibility to re-configure the system for different projects. “We are encountering this type of application more and more where we can use our extensive experience in PCB design and the various methods of reducing or removing hard-wiring,” says Ben Davies, HARTING Integrated Solution’s’ European Sales Manager. “HARTING also has a unique breadth of connector solutions to maximize that potential. Add to this powerful combination the close cooperation with the customer and our local sales organization in Spain and this project provides a perfect example of what HARTING can achieve.”

This Relay Rack solution also underscores the HIS philosophy to look beyond a customer’s specifications for a solution that exceeds its expectations. The success of the project has led to an order from Vossloh to provide Relay Racks for 24 Euro 3000 locomotives for Israel Railways: 48 relay racks in all.

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