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Latest DuPont automotive materials technology in Mercury Marine outboard engine

Du Pont Engineering Polymers : 25 May, 2004  (Company News)
A new category of outboard engine, produced by Mercury Marine (Wisconsin, US) and using high-performance DuPont polymers in 21 key parts of its new four-stroke engines, was launched in the US in February 2004.
With up to 275 horsepower, the Verado™ supercharged engine is one of the Mercury’s most powerful and quietest outboard ever produced. The new engine also holds a three-star emission compliance rating from the California Air Resources Board and is positioned to comply with new US emission requirements due to come into effect in 2006.

“We leveraged the best from automotive engine design to deliver a new category of outboard engine that is dazzling the boating industry,” said Rick Davis, Mercury’s chief technology officer. He credits DuPont polymers and technical support for making crucial contributions to the successful development of the Verado™. “DuPont high-performance materials deliver major benefits over metals and thermosets in holding down weight and cost, combating corrosion and enabling us to set new standards for outboard engine performance and durability,” he said.

“Strategic application of polymers in this engine has helped Mercury Marine derive significant benefits in the areas of improved Noise, Vibration and Harshness (NVH), with excellent quality and durability. Significant cost reductions due to elimination of paint, machining operations and reduced assembly costs have been attributed to the application of polymers,” said Mitesh Sheth, polymer materials engineer for Mercury.

In March 2004, the Verado™ outboard boat engine captured four top awards for innovation and groundbreaking design at the Product Design Competition sponsored by The Society of the Plastics Industry’s Structural Plastics Division. The cowl won the Conference Award selected by the judges and the People’s Choice Award picked by conference attendees as the most innovative entry in the competition.Engine subsystems using

DuPont high-performance polymers on Verado™ include cowling, supercharger, fuel delivery, cam cover, air-handling, powertrain and electrical/electronic controls.

Cowl assembly: Big injection-moulded parts deliver big benefits

In the cowl assembly of Verado, six innovative parts made of DuPont high-performance polymers provide a combination of structural, protective and aesthetic functions.

The top cowl is the largest component ever injection-moulded from glass reinforced nylon. Made of a 33 percent glass-reinforced DuPont™ Zytel® nylon, it is shaped like a giant scoop measuring 851 millimeters (33.5 inches) front to back, 582 millimeters (22.9 inches) across and up to 417 millimeters (16.4 inches deep). It weighs just 11.3 pounds (5.13 kilogram), far less than a metal or a thermoset plastic housing.

The rear cowl, and a structural rib that is adhesive-bonded to it, are moulded from the same Zytel® resin. The front cowl is moulded from DuPont™ Minlon® mineral/glass reinforced nylon for added flatness. The lower cowling, or chaps, consists of two mating parts moulded from DuPont™ Surlyn Reflection Series® ionomer alloys for superior gloss without paint.

These components meet several demanding requirements and deliver major benefits over alternative materials. For example, they:

• Mate precisely to prevent water from entering the engine compartment.
• Provide improved NVH – Verado is the quietest and lowest vibration engine in its class.
• Provide excellent structural strength and impact resistance.
• Resist motor fuel, oil, various cleaning agents and corrosive salt-water.
• Stand up to temperatures ranging up to 200ºF in the upper cowl.
• Weigh about 30 percent less (15.2 kilogram, 33.5 pounds) than thermoset SMC (sheet moulding compound) parts.
• Cost 46 percent less than SMC cowls, thanks to the integration of assembly and functional features in part designs, and due to reduced costs of painting attributed to less paint consumption, reduced surface preparation and higher first pass paint line yields.

The cowl parts made of Zytel® and Minlon® are finished in a three-coat system providing first-pass acceptance yields of 95 percent or better at each stage, according to Mercury Marine. By contrast, SMC cowling parts used for other Mercury engines require application of filler to deal with porosity, a primer and two finish coats. Adding to cost, painting yields are low, as each coat requires multiple passes to repair defects caused by porosity and solvent popping.

The lower cowl moulded from DuPont™ Surlyn Reflection Series® ionomer alloy has high-gloss finish and integral colour. It incurs no painting costs at all.

Supercharger boosts power of compact engine

Verado is the world’s first production outboard featuring a supercharger. According to Mercury, the supercharger enables its 2.6 litre Verado engine to deliver significantly higher torque and acceleration than competitive 3.0 to 3.6 litre four-strokes. Its performance equals that of a 4.0 to 4.5 litre naturally aspirated engine, which would be far too bulky and heavy for an outboard, their engineers say.

The supercharger, a rotary Lysholm-type co-developed by Mercury and IHI Turbo America uses rotors coated with DuPont™ Teflon® fluoropolymer. “Teflon® was critical to our success,” said Davis. “Other materials caused the rotors to quickly corrode and wear out.”

Fuel module meets stringent requirements

Verado has an innovative electrically powered fuel delivery module located outside the engine compartment, between the engine and the propeller. The module is protected in a two-piece housing moulded from DuPont™ Zytel® HTN high performance polyamide. It contains two fuel pumps, one to draw fuel into the housing from the tank and another to pump it to the fuel injection rail.

Thanks to the use of Zytel® HTN and astute part design, the housing can meet demanding requirements and deliver cost and performance benefits over metal housings. It stands up in nearly continuous contact with motor fuel on the inside and seawater on the outside. In certain boat application and running conditions, the fuel delivery module operates continuously immersed in saltwater.

It costs about 15 percent less than an equivalent aluminium module and has numerous integral features that avoid the need for separate parts and/or costly machining that would be required with a metal housing. The module provides a weight reduction of 19.7 percent (0.45 kilogram or 1.0 pounds) compared to an aluminium module.

The housing’s moulded-in assembly features include fittings for in and out fuel lines, a manifold reference line, a groove for the rubber sealing ring, support members for the fuel pumps and a pressure regulator and mounting ears. Integrated fittings reduced the potential for leak paths and polymer materials provided excellent corrosion resistance.

Cam cover seals oil in, water out

The cam cover of the Verado is moulded from DuPont™ Minlon® mineral/glass-reinforced nylon. It provides a 1.8 kilogram (4 pound) weight saving and considerable cost savings compared with an aluminium cover.

The cover draws on the material technology and design principles employed for similar nylon components used on automotive engines, but it overcomes unique oil-sealing challenges posed by the engine’s vertical position and the marine environment.

The integration of functional and assembly features in the cover reduces costs by reducing part count and minimising assembly steps. For example, an oil-air separator is moulded-in. Another cost-saving feature involves separately moulded breather plate, which unlike a metal part can be ultrasonically welded into the cover.

Air handling system helps keep down noise

Verado engines also deliver cost, weight and performance benefits by incorporating automotive industry learning into the design and materials employed for the air intake manifold and resonator. The air intake manifold is a one-piece design that delivers a weight saving of more than 50 percent compared with aluminium, better corrosion resistance, and runners with smoother interior surfaces for improved air flow to the engine. It is moulded from 33 percent glass-reinforced Zytel® nylon.

The resonator efficiently manages noise, vibration and harshness and incorporates an air filter in its design. The resonator is a two-chamber design consisting of a centre tube injection moulded from Zytel® 15 percent glass-reinforced nylon, and a blow moulded outer body also made of Zytel®.

Powertrain components have what it takes

The powertrain of the Verado engine also includes a torsional damper made of DuPont high-performance polymers. The torsional damper, moulded from DuPont™ Vamac® ethylene acrylic elastomer, is pressed into place on the flywheel to dampen torsional harmonic movements. The damper made of Vamac® meets Mercury’s demanding requirements for resistance to hot oil at temperatures ranging up to 150ºC.

Electrical system

Verado comes with state-of-the-art electrical controls and systems. For protection and servicing ease, its modules are consolidated in a control box with a cover, both moulded from a glass-reinforced grade of DuPont™ Crastin® PBT thermoplastic polyester.

Aiming to add to its successes with high-performance polymers, Mercury is working with DuPont on development of a number of components for new engines in its pipeline and existing models as well.
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