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Decades old sealing problem alleviated with new connector system

08 May 2018

Here Denis O’Sullivan of Molex looks at the subject of downtime in commercial vehicle sealed connector systems and highlights the new solution from Molex.

It’s a common story that is played out across many commercial vehicle applications daily, it has a familiar title – downtime. It is a situation that simply cannot be accepted in any application. Whilst it can be mitigated through predictive maintenance programmes, the unexpected failure of a wiring system component is always a surprise for operators when it occurs. Operational efficiency is key and it can be said that in commercial vehicle applications the only thing that matters is durability. The environment in which they operate can be challenging; therefore, sufficient sealing is required to protect against the ingress of water, dirt, salt and other external contaminants, such as lubricants and fuel. A sealing failure could cause one of the electronic subsystems to malfunction or, worse still, cause the vehicle itself to break down. When selecting a wiring system for use in these harsh environments, one of the several critical elements to consider, is sealing integrity.

Identifying the need

For decades, the same traditional industry standard sealed connector system has been utilised and it appears that ‘failure’ of the seals was just part of the course. However, the more Molex spoke to manufacturers and operators it became obvious that they were frustrated and wanted a more reliable solution. In Molex’s opinion, the only way to validate the need was for the company to embark on a period of research to fully understand the “voice of the customer”. This was done in order to better discern how the de facto industry standard connector system for these low circuit-count applications perform in the real world. During this evaluation period, the journeys of each individual component in the connection system were followed, investigations were made on how the system is typically installed in the factory and on its overall performance in the field. 

Traditionally speaking

The connector system typically incorporates a front and rear IP68, IP69K and J2030 grade seal to protect the inner workings when mated. If the front seals become loose, they may move alignment position or go missing. If the seal drops out unnoticed, the sealing integrity of the mated system may be fully compromised. There may also be a possibility for the seal to drop onto the floor and become contaminated with dust and dirt or, worse still, into a pool of diesel fuel, where it may swell and become misaligned. In both circumstances, the sealing integrity of the mated system may be compromised.

If the rear internal seal becomes loose, it is exposed to commercial vehicle elements. As the rear seal is not protected, leak paths may occur due to loss of seal compression as the cables flex - particularly for two-circuit designs. A cover is available to protect the seal, though it comes at a premium cost and can itself become loose. The covers can be plastic welded to fix them in place, but over time the welded joint may become brittle and crack, causing the cover to drop off.

Enter the ML-XT

When developing the ML-XT system, the number one focus was on enhancing the sealing integrity of the de facto connector system. The engineers at Molex set out to find a solution that was a little bit different than the norm, and the objective was to find a way of covalently bonding the seal to the housing. What Molex have now is a product where the seal is now part of the housing – it simply does not fall off unlike the old design. The one-piece plug housing and seal design - permanently bonded by a cutting edge, two-shot LSR (liquid silicone rubber) moulding technique - prevents the seal from rolling during un-mating and mating processes to guarantee correct seal positioning for variations in wire gauges. Molex also focused on taking away installation risks, and the new bonded seal minimises the risk of a seal being lost or forgotten during build up and becoming contaminated with dust/dirt or aggressive chemicals. When it comes to testing, Molex have found that even under the tough testing of SAE J2030 the bonds stay in place, thus the ML-XT is full approved against this standard. 

The company have also designed an additional essential feature of the ML-XT system, the rear internal seal and cover are permanently bonded with latches to connect securely to the housing, this protects against water ingress. These protective rear covers allow for the bend radius of the cable to be a lot tighter into the connector, thus offering extreme bend radius. A wedgelock or TPA (Terminal Position Assurance) locks the terminals in position for a reliable electrical contact, while the plug housing features an integral locking latch for secure mating of plug and receptacle.

In addition to these design enhancements, the parts are shorter when the rear covers are in position. No ultrasonic welding is required to attach the end caps, which eliminates the risk of the end caps breaking off over time. Furthermore, during routine maintenance the innovative finger grip feature helps ease the unmating of the connector in wet, slippery conditions.

Rated at IP68, IP69K and J2030 power-wash capable, the ML-XT system is delivered fully assembled and tested, so no parts will be lost. The system covers 2-, 3-, 4-, 6-, 8-, 12- and 18-circuit options, providing design flexibility for a vast range of sensor technologies and low circuit-count applications. Molex integrated field-proven XRC terminals, deliver current ratings of up to 13.0A, while the nine colour-coded housings enable easy visual mating of harnesses as well as prevent mis-mating. 

In designing the ML-XT defacto standard connector system, Molex engineers have potentially mitigated all currently known likely sealing challenges. Harness manufacturers, who are keen to reduce warranty bills, and OEMs, who do not want to see their vehicles fail in the field, have already found the system particularly interesting. Designed to perform in the harshest environments, the ML-XT system also has potential applications beyond commercial vehicles. 

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