Safety first - ouch!
This blog continues to attract some fascinating questions and perceptions regarding the philosophies of energy consumption, alternative fuels, well-to-wheel efficiency and other significant issues that affect us all. Then there’s the technology of the car itself with its lithium ion battery pack, onboard charging system, power electronics to handle the immense energy available and that little motor that blasts you towards the horizon at warp speed……Linking all these systems and their safety monitors involves more computing power than the combined total on board all the cars I’ve ever owned. You could probably add your total in too!
So, apart from the new high tech stuff, what else do we do at Tesla Motors to ensure that our customers can enjoy this unique offering?
There are a whole host of development activities from making sure the headlamps point in the right direction to tuning the suspension characteristics so that you have such superb dynamic response that you’ll want to drive straight past your home to make the enjoyment last a little longer.
Unfortunately, one of the other things we do after we’ve built these beautiful (and very expensive) shiny prototypes is re-paint them by hand in a variety of plain matte colors and crash them into walls, hit them in the side, drive a moving barrier at 50 mph into the rear and generally do nasty things to them. Ouch!
It doesn’t look so pretty without the rear body and there’s more to removing it than just to aid fitting the measuring and recording equipment. In addition to the fully instrumented Hybrid III dummies, we also place additional accelerometers in strategic positions to map the deceleration of the structure and key components. All this equipment adds so much mass to our little roadster that we have to leave the rear body off to keep the weight down to the specified maximum.
We also paint the underside components and film from below.
The rainbow colors, targets and marker scales help us identify the relative motion of the components and occupants during subsequent analysis.
I guess that not much of this is news to you. You’ve all heard about crash testing and within the industry we’ve all suffered the jokes about volunteering to be the crash test dummy. But, who’s actually witnessed a test or thought about what it must take to get an occupant that is traveling at 30mph, to zero mph within three feet or so?
You’ve possibly seen crash tests shown on TV where the car starts to crumple, the airbags gently inflate and the occupants gracefully nod their way into those big fluffy cushions and then serenely sit back in their seats….
Now hands up those who have seen one at actual speed and not slowed down 100 times?
The actual event probably took less than 1/10 of a second for the dummies to reach zero from 30 mph. That’s scary!
Just think for a moment. Imagine yourself sitting on a car seat in free space traveling at 30 mph. Now stop the seat within a couple of feet…. OK, don’t think about that! Second thoughts, if there’s anyone out there that doesn’t wear a seat belt …… do think about that.
So what happens in those 100 milliseconds? Firstly, the front of the car starts to crumple, slowing the whole vehicle. The airbag sensor (yup, another computer) which is constantly monitoring acceleration, recognizes that the car is having a significant enough accident that it should deploy the airbags. It has to differentiate this from just hitting a pot hole, re-arranging some unfortunate wildlife or knocking into that bollard in the car park that you hadn’t seen. The sensor fires the airbags at the appropriate moment. Too early and they will start to lose pressure before the occupants need them, too late and … work it out for yourselves. The sensor also fires the seat belt pyrotechnic retractors which pull in a hand full of belt length.
Why? First, the belt will tighten on the reel, effectively lengthening. Secondly, the belt will stretch under the load. (Yup, they do stretch). The retractor takes out the excess length but don’t worry about that belt stretch. Controlled stretch is good. This is all about slowing down the occupants in a progressive manner. Stopping them too quickly hurts.
So together, the seat compression, pyrotechnic retractor, belt extension, airbag inflation rate and pressure are all choreographed to slow the occupants down as progressively as possible within the time available.
Other systems that we have designed to help manage this whole event include a structural crumple zone to absorb energy, slowing the whole vehicle as progressively as possible. There is also a rigid occupant safety cell to resist the huge loads involved and generally keep all the nasty hard bits away from those inside.
As you know, we are still some months away from the start of series production for the Roadster. We are currently deep into the process of design validation, safety, performance and durability testing.
Crash testing progress? Well, we’ve done the theory. We’ve run the computer analysis and simulations. We’ve run the low speed impacts to validate the crash sensor trigger point. Then came the sleepless night before the first high speed crash test itself. There’s no other way, you’ve just got to do it and for a small company like Tesla Motors, this was pretty significant.
Was the sleepless night warranted?
• The crumple zone decelerated the vehicle within the predicted distance.
• The crash sensor recognized the crash event and triggered the bags and belts at the right moment.
• The bags deployed and the retractors retracted.
• The accelerometers within the Hybrid III dummies showed g-levels that met our targets, exceeding the Federal Motor Vehicle Safety Standards (FMVSS) requirements.
• The doors could be opened within the required loads.
• No electrolyte was spilt during the subsequent roll over test (Well spotted! Li-ion wouldn’t spill, would it? So no nasty stuff poured on the ground.)
• The occupant safety cell withstood the loads.
• The vehicle performed as modeled, which gives confidence about the remaining tests that we still have to complete.
I now sleep a lot better.
So having totally destroyed one beautiful prototype, we build more and impact those in the side or crash them from the rear. When the team has put so much effort into designing and building these prototypes, wrecking them within a few milliseconds always seems such a shame. However, it’s all part of ensuring that the Roadster not only meets the Federal Motor Vehicle Safety Standards (FMVSS), but also delivers what we, and our customers, expect from a serious sports car.
Drive carefully :-)