Musk Goes Big!/Tesla Gigafactory

[nctnico]

If the author was balanced he had included this news item and noted that the electric racing car appearantly was much more able to deal with a high speed crash than Tesla's Model-S:
http://green.autoblog.com/2014/07/05/man-steals-crashes-catches-on-fire-tesla-model-s/

It's not even remotely comparable. The structural design of the race car is optimised for collisions into the barrier and has to preserve a single passenger only.  There are also no air bags so the structure of the chassis is even more important. The driver wears a neck brace so the crumple zone design takes this into account.

The point is that sacrificing the car saves the passenger(s).

I'd like to see YOU make a car that didn't have a risk of fire if split in half. You've got fuel lines running in an ICE car down the chassis, plus a high current 12V system available.

They already did that. There is a fuel pump cut-off switch which activates in a collision in every car so only the fuel in the lines itself could catch fire. The negative wire of the battery is the weakest link and will burn out controlled in case the battery is shorted. Over here it is very rare that a car catches fire after an accident.

[tom66]

Plus the oil in the vehicle engine bay... and transmission fluid... and fuel lines in the engine area... and not to mention any flammable coolants... plus you've got a high CCA battery capable of supplying huge energy into a fault. (The Model S battery is a little bigger than a motorcycle battery, and unlike a vehicle system, each major load group is fused at the battery rather than at a distant fusebox.)

It's worth noting that most EVs have coolant too. I don't know if it is flammable, but most coolants are.

[tom66]

If the author was balanced he had included this news item and noted that the electric racing car appearantly was much more able to deal with a high speed crash than Tesla's Model-S:
http://green.autoblog.com/2014/07/05/man-steals-crashes-catches-on-fire-tesla-model-s/

It's not even remotely comparable. The structural design of the race car is optimised for collisions into the barrier and has to preserve a single passenger only.  There are also no air bags so the structure of the chassis is even more important. The driver wears a neck brace so the crumple zone design takes this into account.

The point is that sacrificing the car saves the passenger(s).

Every modern passenger car is built this way - Tesla included.

The differences are with skateboard design EVs are in the overall vehicle packaging which assists with crash safety. For example the "frunk" area contains a large amount of cooling/pumping/HVAC systems, but they are all mounted near the bottom of the chassis. A large crumple zone is made where an engine would go. There are additional crossmembers that are not present in any other front-engined car. Should a frontal collision occur, you would be very safe.  Should a side collision occur, the rigid battery pack adds torsional strength and weight to the bottom of the chassis, reducing the risk of rollover and intrustion into the chassis.

[nctnico]

If the author was balanced he had included this news item and noted that the electric racing car appearantly was much more able to deal with a high speed crash than Tesla's Model-S:
http://green.autoblog.com/2014/07/05/man-steals-crashes-catches-on-fire-tesla-model-s/

It's not even remotely comparable. The structural design of the race car is optimised for collisions into the barrier and has to preserve a single passenger only.  There are also no air bags so the structure of the chassis is even more important. The driver wears a neck brace so the crumple zone design takes this into account.

The point is that sacrificing the car saves the passenger(s).

Every modern passenger car is built this way - Tesla included.

The differences are with skateboard design EVs are in the overall vehicle packaging which assists with crash safety. For example the "frunk" area contains a large amount of cooling/pumping/HVAC systems, but they are all mounted near the bottom of the chassis. A large crumple zone is made where an engine would go. There are additional crossmembers that are not present in any other front-engined car. Should a frontal collision occur, you would be very safe.  Should a side collision occur, the rigid battery pack adds torsional strength and weight to the bottom of the chassis, reducing the risk of rollover and intrustion into the chassis.

Actually you are not safe at all in a rigid car. In extreme tanks suffer from the same problem. Because they are rigid the personel is injured or shaken to death when the tank hits a mine or an IED. The safest car is the one which crumbles up to the passenger compartment. Unfortunately for Tesla the information on how to design a really crash safe car is a closely guarded secret.

BTW: the coolants used in a car are not flammable; they consist mostly of water. Oil won't burn that easely either. You can throw a burning match in a bucket with oil and it won't ignite. I already wrote the battery is connected to the chassis with a fuseable link. Please read more about how cars are built and work.

[tom66]

The low mounted battery helps keep the passenger cell intact. That's not to say it doesn't crumple (the edges of the pack have a crash structure designed to crumple, and the cell arrays aren't entirely rigid), but that's not what the battery pack is intended to do. The battery pack would also increase the force required to split the car in half. (Obviously, if you throw enough force at a vehicle, you will be able to split it in half. This applies for any vehicle. There's very little any engineer can do about a ~120mph impact into a rigid pole. Something will give; quite frankly, it's amazing the guy didn't die at the scene.)

Detail of Tesla battery pack diagrams.
https://patentimages.storage.googleapis.com/US20120160583A1/US20120160583A1-20120628-D00007.png - cross members providing rigidity
Detail of battery wall showing crash structure
https://patentimages.storage.googleapis.com/US20120160583A1/US20120160583A1-20120628-D00004.png

Tesla has hired many vehicle engineers from VW, Lotus (including their former chief engineer Peter Rawlinson, and Nick Sampson, vehicle and chassis engineering), Mazda and GM. I am sure they know how to engineer a vehicle for crash safety.

Here's an interesting clip (from Tesla) showing the front crash members. You can see that you wouldn't be able to fit these in any vehicle with a large engine up front. This is an obvious  benefit that arises from moving the powertrain and batteries onto the "skateboard".

[Dago]

BTW: the coolants used in a car are not flammable; they consist mostly of water. Oil won't burn that easely either. You can throw a burning match in a bucket with oil and it won't ignite. I already wrote the battery is connected to the chassis with a fuseable link. Please read more about how cars are built and work.

You can actually throw a burning match to gasoline too and it probably won't ignite Oh youth... had to test everything.

[nctnico]

BTW: the coolants used in a car are not flammable; they consist mostly of water. Oil won't burn that easely either. You can throw a burning match in a bucket with oil and it won't ignite. I already wrote the battery is connected to the chassis with a fuseable link. Please read more about how cars are built and work.

You can actually throw a burning match to gasoline too and it probably won't ignite Oh youth... had to test everything.

I can even set sand on fire but throwing a match into gasoline is something I wouldn't try 

[dannyf]

This is an obvious  benefit that arises from moving the powertrain and batteries onto the "skateboard".

That would suggest that mid-engined cars are safer than front-engined cars - that's statistically not true.

What you want, from passenger safety point of view, is to drive around in a rigid passenger compartment surrounded by soft structures. When the X5 was introduced, BMW ran a crash test commercial showing a X5 after a collsion - the engine bay is completely gone, yet the markers on the passenger compartment are still well aligned.

Front engines are not a big issue today as the engine mounts are designed to break in a collision to allow the engine to slide out. On high(er) end cars anyway.

[tom66]

You've still got that huge engine in there, which is a rigid, heavy body. It will impede on the passenger cabin despite the best efforts of the engineers. (They can just hope to make it move as little as possible, or to move down and under, so you only risk injury to your legs.)

Mid engined is a rare configuration in a four-door passenger vehicle. Rear engined would be benefical - like Porsche 911 or early VW beetle, but I don't think either have crash safety as a critical factor (the 911 is a performance vehicle, so weight reduction is key. I'm not sure if NHTSA have tested it.)

GM had a skateboard design in 2002 - Hydrogen fuel cell concept. Neat design comes from packaging things into such a compact chassis. Great for performance, keep the CoG as low as possible. Of course, fuel-cell EV is a non-starter and one of those great things for car manufacturers to use as a "look, we're trying to be green" excuse,
http://www.supercars.net/cars/2109.html

[dannyf]

It will impede on the passenger cabin

Anything will "impede" the passenger compartment, a bird will, an insect will. The fact that they will impede the passenger compartment does not make them a safety threat, let along a "material" safety threat.

Mid engined is a rare configuration in a four-door passenger vehicle. Rear engined would be benefical - like Porsche 911

Most of those vehicles are considered mid-engined (aft the passenger compartment but in front of the rear axle) - the porsches, ferraris, or some BMWs (the M1). A true "rear engined" car is very rare - I actually have never seen one.

[tom66]

Anything will "impede" the passenger compartment, a bird will, an insect will. The fact that they will impede the passenger compartment does not make them a safety threat, let along a "material" safety threat.

Ok, for the purposes of this discussion, let's say anything that could lead to leg, foot or knee injury (this includes things such as the throttle pedal moving upwards into the cabin, or the steering wheel moving) is "impeding" into the passenger compartment.  An EV has the benefit that there is no large engine to potentially impede. There are electronics mounted at the bottom of the chassis area, but these are near the floor pan area, mounted very low. (Again CofG being a consideration, also maximising space in frunk area.)

Most of those vehicles are considered mid-engined (aft the passenger compartment but in front of the rear axle) - the porsches, ferraris, or some BMWs (the M1). A true "rear engined" car is very rare - I actually have never seen one.

Didn't know that, thanks - so are these all performance vehicles? I don't think any sedan/saloon/conventional passenger car has been made in a mid/rear-engined configuration in a long time?

[dannyf]

An EV has the benefit that there is no large engine to potentially impede.

I guess I am trying to say that based on the safety record of mid-engined cars, such a benefit, if it exists, is non-material.

[tom66]

Again my point being here that the mid/rear-engined cars are sporty vehicles, so crash safety is not as important as, for example, weight saving and performance. People also tend to drive them far faster than ordinary vehicles. So you might see worse accidents in them because of that.

How can having a massive weight at the front of the vehicle which could potentially intrude into the cabin not increase the risk?

[nctnico]

Again my point being here that the mid/rear-engined cars are sporty vehicles, so crash safety is not as important as, for example, weight

Sports cars tend to be involved in much more severe crashes (the amount of energy released in a crash is a square function of the speed). How on earth do you come to the conclusion that in their design safety has to be a lesser concern to the manufacturer?

[tom66]

Well, it is. That's why for example the Porsche 911 (two-seater Carrera model) only comes as standard with driver and passenger airbags - the minimum legal requirement - despite it costing a lot more than for example a Ford Focus, which as standard comes with side and driver/passenger airbags for the driver as well as rear passengers. (Yes rear passengers don't matter in a 2-seater car; the 911 doesn't have driver side protection either.) This is one example of many. The crumple zones will be minimised as they add weight and size to the vehicle, so the vehicle won't perform as well in a crash.  People who buy such cars understand that they are taking a risk. They consider that risk acceptable. (I probably would too.) 

This is nothing against Porsche. I'm just noting that in general rear or mid engined cars are optimised for performance rather than safety in an accident (less active safety, more passive safety - good brakes/suspension etc.) So it's NOT a valid comparison to say that because mid/rear engined cars appear less safe, does not mean the engine position has made this difference. (Correlation != Causation...)

When a performance car manufacturer moves to a carbon-fibre frame for example, again, that's reducing weight, improving rigidity but reducing crash safety, because it's more likely to crack or shatter in an accident, leading to a faster deceleration.

[zapta]

Well, it is. That's why for example the Porsche 911 (two-seater Carrera model) only comes as standard with driver and passenger airbags - the minimum legal requirement

Some sport cars have seats that are not really intended for use. They are small, barely can fit a child, an are rarely use. The Audi TT for example comes with a warning to be aware of rear passengers heads when you close the rear hatch. ;-)

As for two seater mid engine car being too light and therefore unsafe, I think this is a gross generalization. Take the Cayman 981 for example, 3000lb (heavy), mid engine and good airbag coverage. 

(it has a standard roof, made transparent for illustration).

[tom66]

This discussion really was only about mid/rear engine configurations being safer - I was trying through deductive reasoning to indicate that they are not relevant to skateboard EV design.