2007-2008年，路虎推出了揽胜极光豪华版紧凑型SUV。当时该车型有三门轿跑版和五门版可供消费者选择，并在市场上获得巨大成功，但那时并未推出敞篷版。

2011年，路虎董事会决定在这款车型上采用难度极高的敞篷版设计。对于公司的设计师和工程师而言，这是一个巨大的挑战。

路虎的首席外饰设计师Andy Wheel表示，“看起来敞篷版只是把轿跑版的车顶去掉了而已，但其实并没有这么简单！”

在结构刚度和扭转刚度方面，敞篷版设计必须符合路虎的高标准严要求，也必须拥有与揽胜极光的金属天窗版相同的各种地形驾驶性能。尽管具体数据尚未发布，但路虎表示，敞篷版 “与轿跑版相比，车身刚度仅下降了15%”。

路虎的敞篷版车型搭载的是柴油和汽油发动机，最高输出功率可达177 kW（237 hp），综合油耗符合欧洲最佳标准，为每100公里5.1 L （46.1 mpg），二氧化碳排量为每公里149g。

据预测，全球SUV市场将在未来五年内增长20%左右，同时，揽胜极光敞篷版也将占据引人注目的市场份额。路虎表示，在市场上所有的量产车型中，揽胜极光敞篷版的“Z”形折叠软顶是最长最宽的。车顶开合速度很快，仅需18秒就可以完成开启和关闭，在车速高达48 km/h（30 mph）时，21秒内就可以完成开合。

从概念到实车

由于市场上还没有类似车型，因此路虎最初打造了一辆揽胜极光敞篷版概念车，并在2012年的日内瓦车展上正式发布，目的是测试市场对敞篷设计的反应，并决定是否量产该车型。

“市场反应非常好，”Wheel表示。所以，路虎决定对这款概念车进行量产。“具体怎样实现该车型的量产是一个难题，我们最后决定从最基础的工作开始做起。”

“我们对于概念车的后翼子板处凸起的流线型设计并不满意，”Wheel解释道。“当时我们已经认识到，我们需要设计一个更高效的车顶系统，不仅能优化空间效率，减轻整备质量，也能兼顾车辆美学特征，所以要采用一体化的设计方式。我们最终决定采用‘Z’型折叠天窗，这种造型比概念车的‘K’型系统更加合适。‘Z’型折叠天窗可以优化车内空间设计，有助于打造出流线型更优美的后翼子板，让车辆整体线条更加流畅。”

 “Z”型折叠天窗也实现了汽车载荷空间的最大化，尽管后备箱开口相对较窄，但仍可以保证容积达到25L（0.88 ft³）。

由于路虎可以借鉴其姊妹品牌“捷豹”敞篷车的设计经验和相关专业知识，因此所有的设计工作都可由路虎独立完成，无需外部机构的参与。“尽管捷豹和路虎是（捷豹路虎旗下的）两家独立公司，但我们彼此非常了解，可以进行‘跨品牌’合作，对于揽胜极光敞篷版这样需要大量专业知识支持的项目，这一点非常重要。”

但即便如此，路虎也用了三年时间才实现了揽胜极光敞篷版的量产。这是由于这款敞篷版豪华SUV在性能上丝毫没有妥协，并且要求该车型的市场定位明确，销量也必须有所保证。

在设计方面，工程师们面对的主要挑战是打造出一个完整的无框车门系统。尽管敞篷版尽可能多地保留了轿跑版的部件，但车门必须彻底重新设计。路虎也为车窗玻璃的固定设计了特别的解决方案。

此外，设计团队还需要为挡风玻璃设计全新的上框导轨，并加固A柱。Wheel表示，尽管敞篷版的挡风玻璃看起来倾斜度较大，但实际上其角度与轿跑版是相同的。

揽胜极光敞篷版的空气阻力系数（Cd）为0.39，而轿跑版则为0.36。

后备箱盖很难设计，因为箱盖的非侵入型铰接点在汽车外部，而这不符合美学规律。

最终采用的解决方案非常简洁有效，扰流板在后备箱开启处的位置设计得恰到好处，并与铰接点进行了整合。风洞空气动力实验的结果显示，这一设计可以在车顶开启时让后座乘员承受的风振降到最低，问题得到了顺利解决。

Wheel表示：“这一解决方案可以说是一箭双雕——在空气动力学性能和美学特征上都获得了最佳的效果！对设计师来说，如果某种设计方法能让车辆的所有部件可以如有机整体般协调运行，那么这个设计一定是对的。而如果某个部件的设计必须做改变，那么其他部件就很可能受到影响。通过集成铰接装置和扰流板，我们就不必牵一发而动全身了。”

另外还有一个与美学相关的问题——扰流板尺寸很大，并且在一个非常明显的位置，因而非常显眼。这一问题也得到了有效解决。Wheel 说：“我们把扰流板分成了两部分，上部是亮黑色，下部则与车身颜色一致。”

在设计和工程方面还有另一个成功之处。揽胜极光的轿跑版可选择“动感”外观，该款式车门下边梁包含扩展部件，可用于遮挡敞篷版，以遮挡加固件。

敞篷版的整备质量比轿跑版重270 kg（595 lb）。

工程挑战

Danella Bagnall是揽胜极光的汽车项目总监，她详细介绍了项目团队在工程、技术、与测试方面遇到的主要挑战。其中最大的难题是，量产敞篷版的设计并非基于概念车而进行的，而是必须进行大幅度的修改。

 “轿跑版的车顶很大，而敞篷版没有金属车顶，因此也必须更换所有配套的抗扭刚度和硬度部件，框架车门也要一并更换。我们必须另辟蹊径，解决敞篷版的刚度问题，并且不能损害内饰部件和越障性能等。我们与设计团队通力合作，最终成功地解决了这些问题。”

A柱和半B柱结构需要额外加强，硼钢和高强度钢在这里得到了广泛的应用。敞篷版的车门外部与轿跑版相同，但内部则用硼钢和高强度钢进行了特别加固。

车身支架水平置于车内和车身下方，这一点是很难做到的，原因是采用这种布局需要对排气系统等其他系统部件进行调整，但敞篷版已经尽可能多的保留了轿跑版的原有部件。

敞篷版的测试等级与揽胜极光的金属车顶车型持平。Bagnall表示：“但我们必须专门增设一些新的测试标准，包括在陡峭越野路面上行驶时的车顶的开合性能。这很有趣，但也很有挑战性！”

工程团队与供应商伟博思通（Webasto，该公司也是捷豹“F”车型折叠车顶的供应商）和设计团队通力合作，进行了大量工作，以确保车顶系统不会占据后备箱的空间。

控制天窗升起时的空气动力噪声也很重要，而密封性更是重中之重，Bagnall解释道：“我们为敞篷版车型的精心设计完全可以保证这些方面的高性能，为此我们采用了特殊材料和密封结构，比如在A柱顶部周围和车门玻璃之间的设计。”

工程师们之前设计“F”型车顶时积累了许多专业知识和技术工艺，得益于此，路虎现在可以打造出这款能在全路况中保持良好性能的车顶系统，甚至在北极地区也可以完全打开。

作者：Stuart Birch
来源：SAE《汽车工程杂志》
翻译：SAE上海办公室

How Land Rover took the lid off the Evoque

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 brandJaguar’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.

Engineering challenges

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.

Author: Stuart Birch
Source: SAE Automotive Engineering Magazine