The industry-wide adoption after the Second World War of monocoque construction for passenger cars, in place of the earlier body-on-a-chassis layout, slashed the cost of each car - but made the development of new models very, very expensive.
So, ever since the advent of computer-aided design, car companies have tried to regain some of the earlier, coach-built flexibility by (virtually) splitting the monocoque into two slices. The expensive bits in the lower slice - engine, drivetrain, steering and suspension - remain the same (or at least off-the shelf replacements) as do their strengthened mounting points on the shell, forming what is now known as a platform.
Meanwhile the designer is free (within limits) to change the upper slice - the passenger cabin, doors and, of course, the outer panels - to create a new model without, so to speak, re-inventing the wheel.
But it is still an expensive and time-consuming process.
It usually takes about four years from the first sketches to the dealer's showroom - and every auto manufacturer in the world is trying for as much commonality as possible across its range, without having all its products look exactly the same (or worse, exactly the same as those of its competitors).
Which has led the white-coated wizards at the Renault-Nissan Alliance to turn conventional thinking on its ear, by splitting their new basic bodyshell design vertically into modules such as the engine bay, cockpit, front underbody, rear underbody and electrical/electronic architecture, rather than horizontally.
The advantage, they say, is that the common module family (CMF) isn't a new platform: with a bit of mix-and-match it can be a number of quite different platforms, at a 30-40 percent saving in development costs.
14 NEW MODELS
In fact, the first new family of common-module 'building blocks' will stretch across the compact and large-car segments to produce 11 new Renault and three Nissan models - a total of 1.6 million vehicles a year! - by 2020, starting with replacements for the current Nissan Rogue, Qashqai and X-Trail later this year, and new versions of the Renault Espace, Scénic and Laguna late in 2014 (probably at the Paris motor show).
The idea is to create a 'parts bank' with an increasing number of pre-engineered modules, that can be assembled like Lego to create a new platform in a matter of days rather than years, with the maximum possible commonality of components.
LONG-TERM BENEFIT
Not only that, each module will be designed from the start to fit the alliance's integrated manufacturing system, a combined Renault-Nissan measurement protocol that ensures that a door made at a Nissan plant in Indonesia will fit a bodyshell built in Renault factory in Mexico, reducing development costs and even making it possible to shift production of models or individual components from plant to plant depending on demand.
Car companies recover their development costs by adding them into the prices of the production cars (which is what makes limited-edition cars such as the McLaren MP4-12C so insanely expensive) so anything that makes new models quicker and easier to develop will also benefit you and me in the long run.