Electrification of vehicles leads to new, non-traditional problems.
Our customer had a problem with a battery pack that had to be ELECTRICALLY isolated from the surrounding components. This involves both system performance and operator safety.
The vibration isolation system is an excellent area to incorporate this added functionality.
As we developed the parts using our standard elastomeric vibration isolation materials, the customer (and then ourselves) learned that assumptions concerning the conductivity of typical rubber materials were not adequate – the mounts would need greater electrical isolation – lower conductivity – than is common for rubber mount materials.
There are elastomeric materials which are very low conductivity – however they are also expensive and tend to have other properties that would lead to higher cost and shorter service life. So the problem for Hutchinson became to develop a new compound family targeted on:
- Reduced electrical conductivity
- With mechanical properties and environmental capabilities that would meet the expectations of the vehicle/transportation market.
Our customer sounded like this:
"Much to our surprise, and against all our pre-conceived assumptions….we have selected an elastomer isolation mount….which is conductive. It was not planned to be this way, neoprene is supposed to be largely electrically resistant, right? We don't have the time to devote to fix this issue, but we can't avoid it. Yet we don't have the space for adding resistant elements, in addition to vibration isolation elements….we have deadlines to meet. The trade show…is upon us. The material of the mount was specifically selected to minimize or eliminate chassis electrical conductivity. This we believed, was nearly a certainty. In our plan, the isolation mount needs to be non-conductive…it is an operator safety concern if the mount is conductive.
"We also need isolation. That is just as critical to the success of the design. Batteries are heavy….they need to be isolated, controlled. A bank of batteries….is very heavy. Rubber shock and vibration isolation mounts are named "isolation" mounts….because they isolate and control physical vibration. Not necessarily electrical current flow. For the most part, unless specifically called for, electrical conductivity…is not even on the radar for an isolation mount manufacturer. They specialize in molding and manufacturing elastomeric mounts for shock and vibration isolation. In order to mold and manufacture effective isolation mounts….additives are needed.
"Clarity Moment: Many of these additives….are conductive. Therein lies the trade-off."
New Mounting Requirements:
Our isolation mount has to effectively isolate from outside vibration, approximately 575 lbs. The mount must also provide a firewall against the potential of an electrical short energizing the chassis. There is a lot of current in the battery bank. There is no packaging space for both an isolation mount AND a resistant element. Too much time and effort has been put into the manufacturing of this prototype, the design was essentially locked in. Time to call the manufacturer.
Once made aware of our situation, Hutchinson circled the wagons around our dilemma. A tiger team comprised of the VP / Engineering, the Materials expert, the manufacturing specialist, and associated support individuals convened with the customer to discuss the effort. Mounts with high electrical resistivity had been manufactured before – we had experience in this area, but the specific mount which we needed for other design factors was not available. The recipe, and the process would have to be initiated and attempted.
We told the customer "give us two weeks".
Within the two week window, the elastomer recipe had been developed, the material was on hand, the mold tool was identified, and new molded parts of new design and materials were on their way to the customer’s testing facility.
Two different elastomer compounds were developed, and two different sets of parts were supplied.
The parts were installed on customer’s test stand. The electrical resistance was impressive, and exceeded requirements by a substantial margin. Customer project is back on track, and headed for their trade show.