Engineering the new V-Rod

Edited by Paul Dvorak, Amy Higgins & Sherri Koucky

The latest motorcycle from HarleyDavidson Motor Company, the V-Rod, is the first member of a brand new family of liquid-cooled performance custom motorcycles.

For the first time, a Harley packs a 115-hp V-twin liquid-cooled engine with fourvalves-per cylinder, overhead camshafts, and quarter-mile times in the 11-sec range. Only about 24 parts are carried over from previous motorcycles, items such as switch gear and brake components. The custom styling shows what happens when styling and engineering departments want to make each other's ideas work.

The V-Rod chassis and engine design were the result of an ongoing collaborative effort between Harley-Davidson's Engineering and Styling departments, combining tradition with technology. From the beginning, the engineering team modeled the bike in Pro/Engineer from PTC, Needham, Mass. While the styling department was creating shapes in clay or on screen in CDRS (the styling module in Pro/E), information and ideas flowed back and forth using CAD as the go between. This was not the case in other projects. "Working closely with styling let us change the way we think as an engineering group," says Robb Dennert, engineering platform lead with Harley.

John Myers, senior project designer points to several significant technology developments on the new bike. "We went with a liquidcooled engine because it produces more power than a similarly sized air-cooled version and delivers more performance. The four-valvesper cylinder provides volumetric efficiency." Some of the engine developments came out of the company's racing experience. Myers says it lead to the 60? V, double-overhead cams, and side-by-side connecting rods.

Another departure from traditional Harley styling puts the gas tank under the seat, not behind the handlebars. "The curved aluminum sheet metal in the conventional tank location covers an engine air intake," says Myers. "It needs a large capacity to provide sufficient airflow and reduce noise." Placing the gas tank here has the added benefit of lowering the center of gravity.

Another benefit from the upper air intake is that it required a frame with tubes running alongside it and the tank, rather than the single tubular backbone that usually nestles under the fuel tank. "That let us make the frame a styling element," says Dennert. "In addition, the perimeter frame provides a higher area moment of inertia and increased torsional rigidity between the steering head and swing arm."

Even the exhaust pipes contribute to the sharp look. "The styling team suggested sweeping the pipes forward and then back," says Dennert. "They don't cover much of the engine. Harley has always gone to great lengths to make the engine a visible part of the style."

The wheels look solid but have a hollow core. Even though they are cast of semipermanent molded aluminum, they weigh less than wheels on other models.

Look at the right side of the bike, says Dennert. It shows a vertical cooling hose in the middle of the V. "The shortest path between the radiator and the water pump is the best engineering solution. The styling department made it clear that a strong vertical element splitting the V of the engine would look impressive. We found a solution that accommodates both goals."

Dennert says to match the bike's good looks with strength, his team used FEA extensively in structural studies. "We did a lot of work to model forming processes on the aluminum body panels with our supplier, and with manufacturing teams in our Kansas City plant on fixturing, holding, and access during assembly. In addition, to simulate factory operations, the team modeled the frame-welding fixture held by a robot. The machine model was developed in manufacturing-robot simulation software from Tecnomatix, Nashua, N.H., with a direct interface to Pro/E. This let the manufacturing team run production simulations with the exact model to be manufactured.

Pro/E also let the design team conduct kinematic studies to see the extent of possible motion for mechanisms such as the compression of the suspension, turning the front end, actuating the foot and hand controls, and flipping up the seat for access to the fuel tank. "Each mechanism was simulated in CAD before it was added to the prototype bike," says Myers.

The skeleton concept in Pro/E is another useful tool. "It let us define the boundaries around the concept vehicle in a relatively small file," says Myers. For example, if someone wanted to know how much the rear swing arm moves up and down, they could examine the skeleton model. Depite its small size, it let the team test ideas, such as changing a value related to the suspension to see how 15 or 20 components would update on the layout.

The V-Rod is built with what's called the vehicle-coordinate system. "That means with a common coordinate system, an engineer can call up any two components to check, for instance, their relationship to each other or the space between them.

What's more, every component in this motorcycle exists as a CAD model and most of them are parametrically defined. "The whole assembly is huge, on the order of gigabytes," says Myers. "But because of simplified representations, we can use the modeler to pull up the systems or components necessary for a given area of work, rather than the entire model."

With such a large model to cope with, the design teams turned to Pro/Intralink, a database manager for the modeling system, to control revisions and make sure that parts and subsystems checked out of the database were the latest revisions.

And to handle an interoperability issue, the company learned to deal with powertrain data in Catia files coming from Porsche of Germany. "A function called Pro/ShrinkWrap takes only the surface of the model, enough information for packaging studies and accurate measurements," says Dennert.

Using a midlevel-accuracy setting, the software trimmed load times by factors up to 10. For example, a designer working on the frame that needed to have the fuel tank and engine in place would "shrink wrap" the extraneous parts to make the working file a more manageable size.

The team engaged the supply chain early enough for their contributions because "everyone knew this would be a big event," says Myers. For instance, the seat supplier bought a copy of Pro/E so we could swap models without translations. "And the supplier on the curved air-box cover, which is difficult to produce, built experimental tooling at his own expense, then bought a press more capable of making the part to ensure there are no production delays," he adds. The bikes are expected to hit Harley dealerships this month.