Designer Yin Meets Engineer Yang

May 1, 2016

Dan Carney

The interface between design and engineering may be the oldest yin-and-yang in vehicle development. And while there are numerous challenges in turning the stylists’ work into practical, manufacturable and affordable cars and trucks, the two camps are working together early, often, and continuously throughout the product development process.

That’s the message from engineers involved with high-profile programs such as the Chevrolet Corvette, Ford Mustang and Lexus LC 500 and even for more mainstream machines like the new GMC Acadia. They say the legendary, ego-driven battles exemplified by General Motors design czar Bill Mitchell and Corvette engineering boss Zora Arkus-Duntov decades ago are becoming a thing of the past.

“Zora and Mitchell hated each other,” chuckled Tadge Juechter, the current Corvette Chief Engineer. Today, the Corvette engineering team has so many members embedded in the design studio that “Ed [Welburn, GM’s Vice President of Global Design] feels like engineering has taken over the studio,” he said.

Identifying common goals

Getting all parties to the same table is the only way of getting them all to recognize the same goal, rather than the narrow goals of their own interests, said Tom Barnes, Vehicle Engineering Manager for the 2015 Ford Mustang.

The challenge was that Mustang is an iconic product and the all-new ’15 car would be debuting on the nameplate’s fiftieth anniversary, putting even more pressure on the team to deliver a vehicle with the styling pizzazz its enthusiasts demand. Additionally, the company planned to expand Mustang into global markets, making the launch even more critical than ever.

“It had to be great-looking,” Barnes emphasized. That is easier said than done when a car has to be buildable and have an accessible price, two classic Mustang attributes. “One of the key things is that somehow you’ve got to get everyone to realize what the common goal is,” said Barnes.

“It all comes down to chemistry [between the design and engineering teams],” agreed Giles Taylor, Director of Design for Rolls-Royce Motor Cars Ltd. “You can’t stay diverted; you have to have a common goal.” Easier said than done, he acknowledged. “It may cause compromises. Those things are hard-fought.”

In the case of the Mustang, designers wanted a zoomy-looking high beltline to give the car visual excitement, while engineers — always the more practical discipline — wanted it to have acceptable outward visibility. They also wanted to deliver the time-honored, elbow-atop-the-door cruising pose that many felt was essential for the convertible version.

Achieving those targets required close collaboration. The team developed a new lip for the window opening that let it sit 3 mm (.12 in) lower than would have otherwise been possible. This helped enable a usable beltline that also looks good, he said.

Similarly, stylists created a hoodline that is 35 mm (about 1.4 in) lower than the outgoing car’s, a decklid that is 70 mm (2.75 in) lower and a very “fast” A-pillar that appears to reach back to interconnect the hood and decklid via the roof line.

Achieving this new, contemporary Mustang look while meeting roof-crush standards demanded new solutions. Ford body engineers used ultra-high strength boron steel in a ring around the car’s daylight opening to provide the needed crush strength while keeping the roof pillars acceptably slim.

Further, they had to mount the cross-car beam as well. The solution for this came from a combination of extensive FEA modeling and laser welding. “At first [the engineers] were like, ‘There is no way. It is not going to work,’” said Barnes. But keeping everyone at the same table maintained the pressure to find solutions.

Ignoring conventional expectations

Sometimes, intuition is misleading. It suggests things like that having a grille in place will reduce the flow of cooling air to the radiator, or that an asymmetrical intake duct won’t flow air as well as a symmetrical one. But both of those assumptions are undercut by the shape of the inlet area, making possible for a grille or asymmetrical vent to actually flow a greater volume of air.

One such discovery on the C7 Corvette was made by a designer who ignored conventional expectations, Juechter noted. The team was tasked with developing a rear intake vent for the production car similar to the one used by the factory racing team to cool the transaxle and rear brakes. But the race team’s [aesthetically] “brutal” solution wouldn’t fly in production, which demanded “beautiful,” said Juechter.

The aerodynamic challenge, however, was so tough that the engineering team couldn’t devise a solution that looked good. So a designer asked to try to produce an asymmetric vent that was half conventional vent, half NACA duct.

“I was mocking them,” Juechter admitted. Until the design worked in practice. “Now it is studied physics,” he said.

The GMC Acadia’s grille, on the other hand, was produced by sheer number crunching, according to Paul Spadafora, Vehicle Chief Engineer for the Cadillac XT5 and Acadia. While a bold, heavily sculpted design with a lot of depth and surface interest was desired, the Acadia is an SUV and, as such, it needs surplus cooling capacity for towing, he pointed out.

The carefully developed result is a grille that flows more air through the Acadia’s radiator than does an empty opening, because it tailors the airflow for the space it is entering. Bring into play some advanced rapid-prototyping technology and test it in the wind tunnel early and often.

To verify their computational fluid dynamics (CFD) models, GM used additive manufacturing (3D printing) to produce prototypes for wind tunnel testing early in the process. “Getting these rapid prototype parts into our wind tunnel, we were able to confirm [the CFD analysis] very quickly,” Spadafora said. “It was no small feat, no lack of hours to come up with that.”

Other parts are tougher to produce because they aren’t bolt-on trim. In the case of the Cadillac XT5, Spadafora points to the sharply creased body side panel. “Getting that depth of draw is very challenging,” he said. To achieve that, “You want to have consistent die quality.”

For the XT5, that meant plenty of analysis. “You have the advantage of the latest analytical tools to predict the stress strain on the panel,” said Spadofora. “We used a lot of work and math, a lot of experience, and we brought in the die experts. This was all before we could ever produce a panel. That is upfront work in the studio.”

Engineering around obstacles

Another solution is to make subtle changes to a car’s design in consultation with the concept’s stylists to develop a production model that looks the same to customers, but has easier-to-build features. That was how the Lexus LF-LC concept car became the LC500 production model, said Chief Engineer Koji Sato.

“We were keeping the taste of the vehicle unique,” Sato said of the LC500. “You think the LF-LC concept is very close [to the LC500’s appearance]. But the dimensions are totally different. The concept is lower and wider, but [the LC500] still has the same taste.”

Some of that taste comes, as with the Cadillac XT5, in the form of distinctive surface interest due to deep sheetmetal stampings. “Normally the pressing makes some cracks in the sheetmetal if it is too deep,” noted Sato. By carefully controlling the conditions of the stamping process and determining the correct number of times for the die to strike the metal, Sato’s team came to a workable solution by “trying and trying and trying,” he said.

That was his same solution for developing an effective radio antenna embedded in the car’s glass, eliminating the protrusion from the LC500’s body. Embedded antennae are infamous for giving unsatisfactory reception, but Sato insists that the LC500’s antenna is good. How could they achieve this? “We checked it a lot!” he replied.

But the LC500’s most critical aspect is its most visible styling feature; the extremely low hood. Compared to the incumbent RC500, the LC500’s hoodline above the wheel is several inches lower. That space normally contains suspension components, and Sato admitted that a higher upper arm is better for ride compliance. The solution meant six months of refining the design of the upper control arm and the precise location of the ball joint. Ultimately this permitted the ultra-low hoodline.

Once the car was mechanically possible, then it was time to address legal requirements, in the form of pedestrian protection. The solution for the LC500 is one that engineers try to avoid because it’s complex and expensive: a hood that pops up at all four corners using pyrotechnic charges in the event of a pedestrian-protection collision, providing crucial impact-mitigating crush space between the hood and the top of the engine.

In this instance, the engineers’ ability to support their design colleagues’ desires with technology that overcomes a regulatory obstacle shows the value of close cooperation between the groups. And maybe earns the engineers a little goodwill in the next tussle with design.

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