When Land Rover designed its highly successful Range Rover Evoque premium compact SUV in 2007-2008, it created 3-door coupe and 5-door versions. But a convertible was not on the alternative body style list.
So when the company’s Board decided in 2011 that such an arguably unlikely option should be added, it was a serious challenge for the company’s designers and engineers.
“Even though the car just looks as if the roof has been chopped off the Coupe, it wasn’t quite that simple!” said Andy Wheel, Land Rover’s Chief Exterior Designer.
It had to be engineered to meet Land Rover’s high level of structural rigidity and torsional stiffness requirements and to provide the same wide breadth of all-terrain capability of metal-roof Evoques. Although no specific figures have been released, Land Rover states that the convertible has “only a 15% reduction in body stiffness compared to that of the coupe.”
A choice of diesel and gasoline engines—with up to 177 kW (237 hp) and a best EU combined fuel consumption of 5.1 L/100 km (46.1 mpg) and CO2 emissions of 149 g/km—are offered.
In a global SUV market forecast to grow by some 20% over the next five years, the Evoque convertible will occupy an unusual niche, Land Rover reckoning its Z-fold fabric roof is the longest and widest currently fitted to any production car on sale today. The roof is also fast acting, with a stowage time of 18 sec, and raising—at speeds up to 48 km/h (30 mph)—in 21 sec.
From concept to reality
With nothing quite like it on the market, Land Rover initially pursued the idea of a convertible Evoque by building a concept and revealing it at the 2012 Geneva Motor Show, to test both public opinion of the design, and to help decide if there was a business case.
“It received a very positive public reaction,” said Wheel. So Land Rover elected to develop the concept for production. “The challenge was how we were going to do it in reality; we decided to go back to basics.
“One aspect of the concept car with which we were not happy concerned the extra shut lines in the rear quarters where the tonneau panel fitted,” he explained. “We realized we needed a more efficient roof system in terms of space efficiency and mass but also regarding any compromises to the aesthetics of the vehicle. So it was a very holistic approach. We decided a Z-fold system made more sense than the concept’s K-fold. With Z-fold we could optimize interior space, produce an uninterrupted rear quarter panel, and make the whole thing look ‘effortless.’”
The roof Z-fold also maximizes load space, and although the trunk opening is relatively narrow, it gives access to 25 L (0.88 ft³) of space.
The work was all done in-house because Land Rover could borrow sister brand Jaguar’s convertible design know-how and associated technology expertise: “Although Jaguar and Land Rover are separate (beneath the corporate umbrella of JLR) we all know each other and can ‘cross-brand,’ which is important in a project like this, where knowledge sharing is very important.”
Even so, it has taken three years to bring the Evoque Convertible to production, partly because a “no compromises” convertible premium SUV is so mechanically unusual but also to be absolutely sure of its sales and marketing positioning.
Creating an entire frameless door system was a major challenge. Although the Evoque Coupe’s components were used as much as possible for the convertible, the doors had to be entirely re-engineered and a different solution for holding the glass designed.
The windshield needed an entirely new header rail design, and the A-pillars strengthened. Although the windshield of the convertible looks exceptionally steeply raked, the angle is exactly that of the coupe, said Wheel.
Cd of the Evoque Convertible is 0.39; the coupe achieves 0.36.
The trunk lid was difficult because the required non-intrusive hinge points would be on the car’s exterior, which was aesthetically unacceptable.
A neat solution emerged; aerodynamic testing in a wind tunnel to minimize wind buffeting of rear-seat occupants when the roof was open resulted in a spoiler fitted immediately above the trunk opening. The hinge problem was solved by integrating them within the spoiler.
Said Wheel: “We had a two-for-one solution: improved aerodynamics and improved aesthetics! With design, you know you’ve got it right when everything acts together like a house of cards. But if you have to change one thing it upsets so many others; with the hinges and spoiler we didn’t have to do that.”
There was another associated aesthetic issue, but that, too, was solved simply. The spoiler was large and positioned in an area where it was very prominent: “So we effectively divided it in two; the top part is gloss black, the lower, body color,” he said.
Design and engineering had a further success. An option for the Coupe Evoque is “Dynamic” styling, which includes sill extensions. These are used on the convertible to hide strengthening components.
Overall, the convertible is 270 kg (595 lb) heavier than the coupe.
Danella Bagnall, Vehicle Programs’ Director for the Evoque, detailed some of the major engineering, technology, and testing challenges the convertible brought to her team, the most significant being that the convertible was not planned from model conception.
“The roof of the coupe is large and taking it off for the convertible meant we had to replace all of the torsional stiffness and rigidity that it, and the coupe’s framed doors, provided. We had to find that contribution to the convertible’s stiffness in other ways without compromising the interior package and off-road clearances, etc. But it has been great to solve it and to work closely with the design team.”
A lot of additional structure was needed for the A-pillars and the half B-pillars. Boron steel and high-strength steel (HSS) were used extensively. The outer door skin is the same as the coupe, but inside the door there is additional reinforcement, again using boron and HSS.
Bracings were placed under and within the car laterally, which was difficult to achieve because it required packaging items such as the exhaust system. Changing extant components from the coupe was kept to a minimum, however.
The car has been tested to the same level as the tin-top Evoque. Said Bagnall: “But we had to create some new test standards including operation of the roof while the car is at steep angles off-road. Quite fun but a bit challenging!”
Working with supplier Webasto (which also supplies the folding roof of the Jaguar F-type) and the design team, a lot of engineering effort went into ensuring that the roof did not encroach into the trunk space.
Controlling aerodynamic noise with the roof up was a priority, with particular attention to sealing, explained Bagnall: “We made refinement an ‘anchor’ for the convertible. We have delivered that via the materials we use and the sections of our seals—for example, around the top of the A-posts and between door glasses.”
Expertise and processes used by the F-type convertible engineers paid dividends in meeting the company’s criteria to ensure the roof will operate in all conditions that a Land Rover might experience, including open top in the Arctic, of course.Continue reading »