Monday 5 August 2013

Explosive Bonnets

Be careful what you bump into
One of the styling features of the NC Roadster is that long and sleek bonnet that shouts sports car. Unfortunately cars with this design tend to have almost no space between the bonnet and the engine components beneath. This is true of the NC where in pursuit of the classic roadster shape everything is packaged very tightly. The engine is mounted as far back as it will go, but there is still little room for impact absorption. This creates a small problem for wayward pedestrians who may happen to be hit by the NC, they're going to get hurt.

In an attempt to lessen the effects of such an impact, the NC was designed with a bonnet that featured "shock cones". These were incorporated to provide extra energy absorption compared to a flat sheet of aluminium. They also make a pretty pattern if you have a look under the sound absorption material.
The shock cones were an admirable attempt to solve the problem, or at least minimise it. With road safety regulations becoming increasingly strict another solution was needed for the later models of Roadster. With the 2013 NC3 (Mk3.75) revisions came a whole new safety concept - the Deployable Hood System (DHS). Or in other words, and for a bit of drama - Explosive Bonnets!

This system works by having sensors fitted to the front bumper that detect an impact speed of 20kph (12.4mph) or more and send a signal via the PCM to some hydraulic actuators to deploy. These actuators instantly raise the bonnet away from the engine to increase the space for energy absorption in an attempt to minimise injuries to pedestrians. The diagram below explains the concept.
And here is what the actuators look like under the bonnet of the NC3.
The system sounds like a great idea, but what if the DHS activates accidentally when you leave the handbrake off and your car rolls into your own garage door? I know that sounds stupid but it could happen and there are many stories around the internet of premium sports cars being left with large repair bills after relatively minor bumps because the systems cannot differentiate between hitting a person and the car in front reversing into you. Something to think about anyway.