Market technology tailoring by Prodrive

  • 22-Sep-2009 10:12 EDT
Prodrive Brera Matt Taylor 2.jpg

A frustration with post-release modifications is that there is limited design freedom for fundamental changes, said Prodrive's Matt Taylor.

Creating a successful “world car” is difficult to achieve. Twenty or more years ago, such a concept was seen as ideal for achieving phenomenal economies of scale, but the reality proved different, not just for national legislative requirements reasons but also because of the need to meet specific (and changing) individual market tastes and expectations.

And some of those markets are simply resistant to, and cautious of, vehicles that may sell well elsewhere. The U.K.’s failure to accept Cadillac’s offerings in large numbers is an example, even when the designs had been tailored by General Motors to anticipated aesthetic and dynamic requirements. Chrysler, though, did manage it with the 300C, but that was particularly because the car could be specified with a Daimler diesel engine.

The lack of specific characteristics necessary for success in individual markets is notably significant with regard to sports cars. So when Alfa Romeo introduced the Brera sports coupe internationally, Alfa Romeo U.K. decided an upgrade package was necessary as a special edition to make the car less of a long-distance tourer and more of a “pure” sports car suitable for British roads, with ride quality a secondary consideration.

To achieve that, together with some other modifications, it went to the specialist design and engineering consultancy, Prodrive, which has a high international profile both in motorsports (racing and rallying) and for road car projects. Most of the focus was on chassis dynamics improvements to achieve a sporting “feel.”

“Modifying it after Type Approval presented an interesting set of challenges as we had a very limited range of options available to us,” said Roland Cherry, Prodrive’s Automotive Technology Commercial Director. Setting the dynamic character of the vehicle, including an improvement of steering feel and feedback, was the base point of Prodrive’s work, making the suspension firm enough to limit roll and pitch—it was also lowered 10 mm (0.4 in)—but with sufficient compliance for comfort and to avoid losing grip on broken surfaces.

“Ride quality is a technology area with significant regional variation; it is an area that highlights the importance of understanding how end-users evaluate the vehicle,” added Cherry.

Bespoke Eibach springs, 50% firmer than standard, were fitted, together with Bilstein monotube gas dampers. Static geometry was changed to improve steering feel and then the whole suspension calibrated. Wheels (19 in) and tires (235/40ZR-19) received special attention. Extensive FEA (finite-element analysis) work on the wheels saw reduced weight achieved plus higher stiffness. Unsprung weight is particularly important in U.K.-specification cars; the lighter the wheel, the better it tracks undulations without needing additional damping.

Many of these finer points are often impractical for an OEM to achieve for individual market requirements, said Cherry, mainly because of design and development departments’ time and financial limitations. “We engineer vehicles both pre- and post-Type Approval—the latter more difficult and more limited technologically, the former calling for special skills of team integration.”

While improved over the standard car, the Prodrive Brera still had to be something of a compromise, stressed Matt Taylor, the company’s Head of Vehicle Dynamics. One aspect of that compromise is the stiffened suspension’s performance over lateral ridges. Prodrive’s modifications were limited to vertical, not horizontal, movement.

A frustration with post-release modifications is that there is limited design freedom for fundamental changes, stated Taylor: “For example, dealing with lateral ridges requires fore and aft wheel movement to absorb energy from the events. An obvious alternative is to use softer bushings, but that reduces some control. Also, the stiffness of the metalwork to which they are attached is significant. Ideally to cope effectively with the effect of lateral ridges would require a prior decision on the cost target of a subframe, but that is way back in the design process. Dealing with this type of issue post-Type Approval ranges from extremely expensive to completely unfeasible. So this demonstrates that the earlier we are involved with a project, the better when a specific market requirement is needed. Then we can get firmness without harshness.”

With almost every car created—even one-offs—there are always multiple design targets for an OEM. A vehicle might be designed initially to have “perfect” dynamics with a short wheelbase and precise balance, but through the design process, it is always subject to change: a longer wheelbase for greater high-speed stability, more cabin and trunk space; systems packaging; and aesthetic requirements (not the least of which is larger wheels which have become a styling element with mechanical penalties including greater unsprung weight). Through all of this, dynamic purity is almost inevitably compromised and in some cases lost.

“What we can do is to help recover as much of the potential overall dynamic performance of the car as possible,” explained Cherry. “Car companies invariably believe—rightly—that they have highly competent design and development engineers. So, as transformation specialists, when we become involved upstream in a project, we need to be ahead technologically but also to get an OEM’s engineering teams on board and then demonstrate an independent interpretation of what is required to make a car more appropriate to a particular market or customer group. And we can do that quickly and flexibly with no departmental inertia. We work to integrate systems and designs—and to do that we have to be integrated, too.”

Prodrive is now becoming involved in most upcoming vehicle technologies, notably EVs and hybrids. One problem with many hybrid systems is driveline shake. Prodrive has had a development program in place for 18 months to help obviate it. In NVH terms, that may be complex to solve, but it is clear when it has been tackled satisfactorily.

In some other areas, the nuances of development work can be somewhat less definitive. Said Taylor: “It’s always worth remembering that one test driver’s steering feel is another driver’s kick-back!”

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