What is the most fuel efficient way to accelerate?

Martin D said:

An EV uses the exact same amount of energy to accelerate to 60 mph whether it takes a second or a minute according to CleanTechnica.

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MichBolt said:

Edit: I failed to answer your actual question. Is it better to gun it a little? Why yes it is. In fact, it's even better to gun it a lot.

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Martin D said:

He goes on to say that people are not capable of regulating speed to plateau at and will end up driving faster at any given point ....

What I have noticed is our cruise control. If you hit “resume” at a much lower speed than it is set for, the acceleration is neither sluggish or gentle. I would say more like “brisk” , maybe 50 kW load.

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MisterJJ said:

Put an extra PSI or so in your tires and you will probably save more energy. Sneak over and put an extra PSI in your neighbors ICE and you'll probably save 10x more energy. Some things are not worth worrying about... IMHO.

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MichBolt said:

Here you go:

How EV Range Is Affected By Quick Acceleration

I was recently involved in a discussion about the effect of levels of acceleration an electric vehicle range. This was below one of the articles on CleanTechnica. I was arguing that heavy acceleration will reduce range, while another person was saying that it made no difference whatsoever.

cleantechnica.com

The author did try to test whether hard acceleration made a difference, and for his test, it resulted in 7% more energy used over a 30 mile trip.

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shrox said:

Spinning the tires will reduce the range, but how much?

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electrons said:

Driving Instructions:

A ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal.

How do we get those approx instructions? Below:

Basic physics always applies: Isquared x R is always the power (energy rate) lost in the motor, batteries, and wires. (The other types of losses in the motor also increase a little due to the higher torque needed for brisk acceleration, but we can neglect that extra bearing friction usually.)
"I" is the electric current flowing, which is very high when flooring it. THAT is the main power loss, which creates extra heat in the battery, wires, windings, compared to taking it a bit easy on acceleration.

The main physics consideration above is a good starting place.
There are secondary effects (motor windage, bearing friction, iron losses,etc.), which translate into a motor efficiency map:
View attachment 34247

... that basically tells us to ramp up torque as our fixed-gear ratio vehicle gains speed into the redest region of the graph where we get the highest motor efficiency.
IOTW, make a bee-line to the middle of the red region until you are at the traffic-limited speed target.

Granted, air drag builds as you increase speed too, so best not to accelerate too rapidly into that energy-wasting situation too soon either. And keep currrent (amps) down to avoid the blue region on the left side of the graph during low-speed operation. ......So a ramping launch (not full tilt, but say 3 seconds building up to 1/4 max pedal capability) up to 20 mph, followed by a slower accel 1/3 max pedal for that particular motor, and we assume our motors are at least similar to that efficiency map.

Deeper (Tech Warning: The following article could cause headaches unless you're into physics-engineering.):

EV design – electric motors – x-engineer.org

Tutorial on how to calculate and simulate an electric motor for an electric vehicle (EV) design using Scilab and Xcos block diagrams

x-engineer.org

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Duke Woolworth said:

More control and easier on the machinery the more gentle you are. Works for all, repeat all, things mechanical or electric.

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wonderbolt said:

I am surprised no one has yet suggested just watching the ring color around the speedometer. If you keep it green that is most efficient, if it turns yellow less efficient, the GM engineers know and provided the info to the driver. Keep the ring green for highest efficiency, or yellow for most fun ;-)

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electrons said:

You're right the Bolt runs 1,000 RPM for every 10 mph (7:1 gearing). Electric motors spin faster than gasoline engines, true.

If you look back at the efficiency map graph above, that motor maxes out at around 300 torque, and the center of the red region is around 1/4 to 1/3 of that, approx.
I think pedal position could be more of a power command, not strictly torque or speed, at least apart from 1-pedal driving, I'm not sure what GM is doing exactly.

Acceleration is proportional to excess torque, meaning maybe the better rule of thumb is stated as:
1. Accelerate lightly from a standstill to keep the amps down, within reason, so maybe that's about 1/4 pedal travel gradually eased in over 4 seconds.
2. Once at 20 mph, accelerate a bit harder to reach your target speed, up to 1/3 or 1/2 the max capability.

Main thing is to avoid the blue region of the graph, which says don't floor it right away when going from a full stop, since the current (amps) flow is too high (IsquaredR losses).
To do that, you want to ease into the pedal at first, to keep the initial blast of amps down, but notice the 80 torque line (1/4 of max capability) cuts right down the center of the red high-efficiency region.

The Bolt already limits current some automatically to avoid wheelspin off the line, but they left a lot of low-rpm current flow "peppiness" for customer satisfaction, a selling point in sales test drives and Car and Driver reviews.

The engineers sized the motor & hence the efficiency map to maximize range in the standard EPA range test, which is representative of mixed city & hiway anyway.

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electrons said:

Fun calculation: How much thrust (force, Pounds, lb) does a Chevy Bolt produce at maximum? Usually we think of an F-15 having 'thrust' not a car, but it does, just the same.

266 ft-lbs x 7.05 gearing = 1875 ft lbs at the half shaft. Acting over a 1.06 ft tire radius = 1,769 lbf at the front wheels = 7869 Newtons
7869 Newtons force / 1616 kg mass = 4.87 meters/s2 = almost exactly 0.5 g's acceleration.
Since current & torque is limited at low speeds, you may only get 0.5 g's accel at around 20 mph or so (?). And it's limited by tire grip too, so not sure if you can actually get there. Add a driver and mass goes up, so 0.5 g's is for a hamster driver only....

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electrons said:

Fun calculation: How much thrust (force, Pounds, lb) does a Chevy Bolt produce at maximum? Usually we think of an F-15 having 'thrust' not a car, but it does, just the same.

266 ft-lbs x 7.05 gearing = 1875 ft lbs at the half shaft. Acting over a 1.06 ft tire radius = 1,769 lbf at the front wheels = 7869 Newtons
7869 Newtons force / 1616 kg mass = 4.87 meters/s2 = almost exactly 0.5 g's acceleration.
Since current & torque is limited at low speeds, you may only get 0.5 g's accel at around 20 mph or so (?). And it's limited by tire grip too, so not sure if you can actually get there. Add a driver and mass goes up, so 0.5 g's is for a hamster driver only....

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electrons said:

GM engineers probably limited current at launch to prevent wheelspin with standard all-season tires, keeping the traction control system brakes from having to activate too often when somebody stood on it.

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newboltdriver said:

The most fuel efficient way to accelerate which will give you a higher m/kWh which will give you more miles is to pretend there is an egg between the accelerator and your foot. Keeping the energy use light green will also help.
I read on here about people complaining about not getting at least 259 miles on a charge. If they would drive more efficiently, they would easily get that and more. I don’t charge to 100% anymore since I don’t need the distance or miles, but I would see 350 miles when my m/kWh was in the high 5s or higher.

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