Confessions of an Automationeer, Part 15: A Case of Sense and Sensibility
Automationeers like me have to balance capability with cost-effectiveness whenever they design a new car. As such, for most mass-market cars, it is often better to forgo more advanced items in favor of simple alternatives. Consider the common example of an entry-level, transverse-engined, (sub)compact car from 2017, aimed at buyers with limited budgets. Such a vehicle will not only require a low starting price, but must also be developed quickly enough and be cheap to produce, in addition to having low running costs. To that end, the vehicle should utilize simpler components in its construction.
The first step is usually to use a less complex suspension system. Often, this would entail fitting the car with a torsion beam or semi-trailing arm rear suspension, but there are occasions where there is enough left in the budget to install a double-wishbone or even multi-link set-up instead. In addition, the front suspension would usually be a strut-sprung configuration, allowing for the installation of wider engines. Since simpler setups also tend to be more reliable, they are often favored by budget-conscious engineers. Finally, the car itself will usually be front-wheel-drive, and as such the resulting configuration will be space-efficient and cheap to assemble.
The engine should also be designed with sensibility in mind. As such, it will usually have cast internals, one or two throttle bodies, a standard intake, and cast-iron exhaust headers. If economy is of particular concern (which it often is), low-friction pistons can be used at the expense of a shorter redline, while the cam profile (or the initial part of it in particular, if variable valve lift is in use) should be lowered, thereby improving smoothness. The exhaust should also incorporate baffled mufflers and a standard three-way catalytic converter at minimum.
Trim choices are even more important still for low-budget applications. In the case of our everyday compact commuter, comfort is key, and so it will be fitted with an automatic transmission. However, it will only be at its most effective if it has the right number of gears (6-7, although newer models may have 8 or more), with the correct spacing and maximum speed. If the latter is set high enough, top gear can be used as an overdrive, improving economy and comfort even further.
In addition, a comfort-oriented, small-diameter wheel and tire package will be fitted, with stamped-steel or cast-alloy wheels wrapped in all-season or low-rolling-resistance tires. The latter are preferable if, as in our case, fuel efficiency is a major priority. Often, vented disc brakes will be fitted at each corner, although if budgets are particularly tight, solid rear discs may be used instead. Moreover, underbody cladding and spoilers will usually be omitted, and active cooling could also be forgone to save weight and cost.
On the inside, a standard interior and entertainment package will be fitted, sometimes even with advanced safety systems. All driving aids (except for launch control, which is frankly unnecessary in most mass-market cars) will be fitted. The suspension will be tuned mainly for comfort and incorporate progressive springs, monotube dampers and passive sway bars. Anything fancier than this will add a lot of extra cost, weight and complication that potential customers won't need, as well as reducing reliability.
That just about wraps up the steps taken when designing a small car on a small budget. In one of my next few posts I will describe another round of CSR - if not the current one, or a previously concluded round, then the one after that, or, since I haven't won any rounds yet, probably one with an as-yet unused premise. But before that, I shall show off my first car made using the first public release build of the UE4 version of Automation.
