Jumping off the Diesel Bandwagon - UPDATED

BenK wrote:

Me Again wrote:
snip....

Well to correctly state it, electric motor have max torque(100%)at start up from zero RPM and less after that. There is nothing to create torque multiplication! Max is 100% and everything after that is less. There are drive system considerations that will have to be handled. Driving in low traction situations will need a complex computer torque management system.

Chris

Electrics should have 100% torque throughout it's RPM range...from Zero RPM to specified max RPM

As for the higher torque than spec...it depends on the controller. Good to great controllers
can over drive to attain +300% torque...but the down side is thermal and the reduced
duty cycle

That great controller will have regenerative braking and understand coasting to several
levels of braking. That also depends on the battery or storage device's ability to
absorb (recharge rate). Why many will have resistive disapation to suppliment the
storage device's recharge for high rates of regenerative braking

Your comments/thoughts/thinking is common and is from ICE's, gear multiplication
and hydraulic multiplication (TC). Had the same issues with the two large OEMs engineers
when consulting on the, then, next gen hybrid SUV

Terminated that contract when I realized that there were not going to use my teams
stuff and just cramming knowledge from my engineers. Mostly regenerative stuff.

Plus when their marketing folks laughed at my suggestion to put in a charge cord
as my controller system could recharge with little changes...they said their customers
don't want a charge cord....guess what...most all hybrids now come with a charge cord...

Great thread ib516. My apologies for our sidejack.

I think you two (Chris, Ben) are talking about two different things. Chris is correct in that a motor cannot put out more than 100% (all its capability), but Ben is correct in that a motor can put out 300% of its 100% duty cycle"torque rating" for a short period of time.

In Bens case, if a motor can be fed more voltage as it rises in rpm (and creates what is sometimes known as a back-voltage*), the maximum rated current can be sustained or even exceeded, and that means it can sustain max torque throughout its useful rpm range, or even exceed it for a shorter duty cycle. The reasoning is that current, and current only, determines magnetism, therefore torque. And the "thickness" of the wire normally determines the resistance, therefore max current, without overheating. This can be partially cheated in a couple of ways:
1) by ever more efficient cooling within a practical limit
2) by initially supercooling (near 0 degrees Kelvin) where resistance drops to zero and current could theoretically go infinate

The *back-voltage I refer to above is a phenomenon whereas when a motor spins acting as a motor, it is also "generating" an opposite voltage at the same time. An example will be an electric drill running full speed without load where barely any current flows because the "generated" back-voltage matches the applied line voltage preventing any more current. The max "free" speed is determined by this match. Any load slows the drill and decreases back-voltage, allowing the applied voltage to force current through the windings, and remember, current produces torque. The drill torques into its load, perhaps twisting ones hand. If one stalls the drill with overload, heavy current flows, and it then produces max (100%) torque at zero rpm (max for the applied voltage that is).

We used ancient hybrids at work. The diesel locomotive has been largely powered by diesel driven generators since the 1950's. Each axle has its own motor and they are fed the same main generator voltage. This hybrid technology came from true-hybrid pre-50's WWII submarines that used a diesel powered drive generator/motor system as a transmission for the prop(s). The beauty of it was the generator also charged lead-acid batteries which allowed the sub to move stealthily underwater with the noisy, air-hungry diesel shut down.

The locomotives don't have battery storage systems to recover momentum. When the axle/traction-motors regenerate, the power is dissipated by huge "toaster" grids cooled by fans aiming scorching heat straight up (the short little round towers you see on top). This regeneration has become so efficient the entire downhill train speed can usually be controlled by this generating which is called dynamic braking (Saves the 1000 or so brakeshoes per train). The other advantage is the 100% zero rpm torque that Chris and Ben refer to. The electric form of power transmission allows the train to start from scratch without slipping the clutch (wheel traction control is used) or overheating hydraulic torque converter oil. Waste "slippage" motor heat is still produced, but other powerfull blowers force copius air down around the traction motors for cooling. The diesel combustion engines are fairly muffled nowadays. What we hear is mostly blowers.

And back to earth, yeah I understand the conversion back to the newest gasoline offerings. This is an exciting time to be an automotive fan.

Wes
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