Electric vehicle component package ideation

[marellasunny]

I am in the design phase of a lightweight electric city vehicle with a capacity of 15kWh. I am at a stage where I am moving elements like Electric motors, tranmission, DC-DC converters, Inverters, Battery charger and battery pack in a CATIA software model. In-order to cater to the wide-range of requirements, I aim to create 5 prototypes and later simulate these models for the NCAP crash tests.

My question at this stage is: Can I place the different components of the electric vehicle where-ever I like without constraints? for example: Does it make sense for the battery charging pack(they call it "Batterie Ladegerät" in German) be at the rear of the vehicle and the battery pack at the front like the VW XL1? I mean, how much heavier are the cables going to weigh in particular cases?

Can you suggest a good book on`Electric vehicle component package ideation´.

 

[jedishrfu]

This article may give you some ideas:

http://www.engineering.com/Videos/D...ideoId/2907/Designing-A-Car-From-Scratch.aspx

It seems that early on component weight is more of an issue than placement. Later placement minimizes stress on the wheels and can improve car stability. If you check out modern cars you'll see that left / right placement is more important than front / back placement ie motor weight is in the front more and front wheel drive is more common.

 

[marellasunny]

Inter'part' linking, very interesting approach to design. Will start using this in CATIA right away. Thanks.

 

[jim hardy]

In aircraft, weight concentrated at ends versus middle gives higher moment of inertia for pitch and yaw .
Surely there's some SAE guidelines on that subject for automobiles. It'll affect handling and ride.
Wish i could link some but whenever i try to access SAE papers it asks me for seventy bucks. Surely your company has a subscription.

old jim

 

[AlephZero]

If you are considering crashworthiness, you might want to consider locating expensive and/or hazardous components (e.g. batteries) to minimize the amount of damage.

 

[marellasunny]

In aircraft, weight concentrated at ends versus middle gives higher moment of inertia for pitch and yaw .
Surely there's some SAE guidelines on that subject for automobiles. It'll affect handling and ride.
Wish i could link some but whenever i try to access SAE papers it asks me for seventy bucks. Surely your company has a subscription.

old jim

I think automotive engineers call weight reduction 'Topology optimization', although I haven't come across articles relating structure weight to vehicle handling yet. If I may say so, handling of an automobile has always been related to the roll centre height, am I correct? So,if I find a connection between weight of an automobile structure and the roll centre height, I will find a way to understand handling more precisely.
I am quite weary of positioning components like the Alt.Curre. electric motor, 2-speed gearbox, battery charger at the rear-end of the vehicle and spread-out along a lateral plane. I am weary because this might increase the moment of inertia along the z-axis in a sharp turn, causing oversteer.

 

[jim hardy]

I am quite weary of positioning components like the Alt.Curre. electric motor, 2-speed gearbox, battery charger at the rear-end of the vehicle and spread-out along a lateral plane. I am weary because this might increase the moment of inertia along the z-axis in a sharp turn, causing oversteer.

I'm not a mechanical engineer
my meager understanding of this comes from the courses i took in Statics and Dynamics in 1960's
and thinking about them as i drove various vehicles along twisty Ozark highways, testing for fun their behavior when pushed to the limits of traction.
It's a wonder most of us guys from that time survived the years 15 to 25. There were no seatbelts.

Anyhow

yes weight at the back will make the car want to throw out its stern in a curve
and i found a little bit of understeer to be way more comfortable than oversteer .

When GM brought out the rear engine Corvair, Ford ran an advertisement using a bow and arrow and slow motion photography.
The speaker weighted two arrows one at the rear and one at the front and shot both at a target a few yards away.
The front weighted arrow flew straight and stable
The rear weighted one wobbled about its Y and Z axes as it tried to reverse ends , for as it deviated from straight ahead the feathers at rear reversed its rotation.
A very effective demonstration. It may have sold a few Falcons.

Now - if one releases the steering wheel coming out of a curve he wants the vehicle to return to straight ahead. The Ackermann steering should do that , absent some outlandish moment the other way..
My '53 Ford stationwagon was well behaved in that regard provided it wasn't heavily loaded in the rear, damping seemed about optimal unloaded. Loading it toward rear perceptibly increased overshoot and lowered natural frequency. (no power steering then, and steering wheel inertia itself was significant to stability )

Instability comes from interaction of displacing, restoring, and inertia forces.
So for stability and subjective 'feel', moment of inertia becomes as important as center of gravity.
That's why those legendary high performance Chrysler sedans of the late 1950's had the engine set back a few inches compared to the everyman's version. Their handling astonished the European reviewers.

If I may say so, handling of an automobile has always been related to the roll centre height, am I correct?

Absolutely correct. Roll in corners is the first thing one notices about a car, or at least i do. That's most certainly height of CG, track width, and suspension stiffness .
Lateral stability in turns is next for me.
Note all the SUV stability issues when they tried to make sports cars out of trucks.


Not a big deal, just something to be aware of in your thoughts.
And I'm certainly no expert in your field.

My favorite car of all time was my 1962 Chrysler Newport. Long, low, black, and for an everyman's car, surprisingly stable. Among my friends, it astonished everyone who drove it.
http://www.roadroyalty.com/media/images/member_vehicle/62-chrysler-bbd8-3-large.jpg

old jim

 

[marellasunny]

Thanks old jim.

I have a simple question: Does the transfer of C.G DURING a crash pose any major disadvantage? It seems logical that when the C.g shifts during a crash in a direction where the passengers are sitting, then there is going to be blood. Am I correct?

So,with this simple philosophy, I am going about positioning the heavy components like the HVAC, Motors, Brakes etc. in my EV simulation.

 

[jim hardy]

It seems logical that when the C.g shifts during a crash in a direction where the passengers are sitting,

I assume you mean when something heavy comes loose and goes through the passenger compartment ?

I'd sure think so. I'm no expert but have read about intentional crumple design to deflect parts like engine down and away from passengers. The infamous Pinto got a deflector plate added to keep its gas tank from getting squashed between rear bumper and back axle .
Scouting junkyards I've noticed only a few engines that made it into front seats. Angled firewall usually pushes passenger compartment up and over it.

Mind you i wasn't doing forensics, just looking for used parts.