Auto manufacturers and suppliers are pulling out all the stops to find creative ways to boost gas mileage and reduce emissions, and Dow Corning technology is playing a part in many ways. Dow Corning materials can be found in dozens of new and emerging applications. The company’s technical centers around the world are delivering process engineering, testing and even prototyping to help customers speed product development and reduce time to market.
“Start-Stop” Braking System
Among recent gas-saving advances is an innovative design for a combination starter-alternator that significantly outperforms the conventional starter and alternator as separate components. The device is at the heart of the aptly named “start-stop” system, which conserves fuel and reduces pollution by automatically shutting off the engine when a vehicle is not in motion. The system immediately and silently restarts the motor as soon as a gear is engaged, or in the case of a car with automatic transmission, whenever the driver releases the brake.
Economic Benefits of “Start-Stop” Braking System
In starter mode, the belt drive and low inertia of the device mean it starts three times faster than a conventional starter, and with a fraction of the noise. When the vehicle stops, noise and tailpipe emissions drop to zero. The approach is so effective that it’s been estimated to reduce consumer fuel consumption up to 10% in urban traffic conditions, operating discreetly and without disrupting normal driving habits. Reduced weight from the dual-function unit contributes to the gain.
Unfortunately, the under-hood environment presents some of the toughest operating conditions in any automotive application, where below-zero ambient temperatures can quickly rise to 150°C (302°F) or even higher. Fuel, oil, glycol coolant and solid contaminants can all interfere with sensitive electronics, forcing device manufacturers to protect circuits and components from the harsh service conditions.
Adhesive/Sealant for Critical Lid Sealing Design
To achieve the reliability and longevity needed in the starter/alternator combo, a French manufacturer has specified Dow Corning® 7091 Adhesive/Sealant for critical lid sealing of its designs. The silicone formulation easily withstands the temperature range and repeated thermal shock, remaining virtually unaffected by automotive fluids and cleaners.
Custom Prototype Design
Dow Corning's role wasn’t limited to material supply in this application, however. Once the customer finalized and tested the design, the company faced significant costs and lead time to develop the 40 prototypes needed for limited customer trials. Instead, the Dow Corning Applications Center in Seneffe, Belgium, was able to fabricate the prototype units, helping to reduce expenses and shorten development time.
Summary
The lid sealing operation was completed using automated dispensing equipment with a 6-axis robot, controlling the location, application speed and volume of the 1-part silicone formulation. Fittingly, the non-slumping RTV material requires no energy to cure. Once the adhesive skins over, it cures from the surface inward, typically requiring about 24 hours (at room temperature and 50% humidity) for sections 2 mm thick. The material reacts with moisture in the ambient air, ultimately forming a tough, flexible elastomer that remains stable from -55°C to 180°C (-67°F to 356°F).
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This information has been sourced, reviewed and adapted from materials provided by Dow Corning.
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