Help me understand my Leaf's acceleration...

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jehan2256

Member
Joined
Jan 14, 2019
Messages
6
Hi everyone, I just got myself a used 2011 Leaf in December.

I'm loving the car, but the acceleration is... weird.

If the car is at standstill and I put my foot down, the acceleration gradually ramps up until about 50km/h, where it seems to reach its peak. However, if I'm rolling along at 15km/h and put my foot down, it feels much more instantaneous, which is what I expected the acceleration to feel like on an EV.

So, why is there a difference? Why does the acceleration have a ramp-up when starting from standstill? Is it to prevent wheelslip? To reduce wear and tear? And how exactly is the ramp-up programmed? Is it designed to take a certain amount of time to reach maximum power, or is the available power determined by the current speed?

I'd appreciate any information on this, as Google has not been very useful.
 
I'm not as familiar with the 2011 & 2012 cars as the later ones, but assuming you have an "Eco" mode (and I believe you do, but I'm not sure if it's a button or a position on the "shifter") that is probably tuned on, muting the acceleration by remapping the accelerator pedal response. You should get more instant, responsive acceleration in "D" mode.
 
LeftieBiker said:
I'm not as familiar with the 2011 & 2012 cars as the later ones, but assuming you have an "Eco" mode (and I believe you do, but I'm not sure if it's a button or a position on the "shifter") that is probably tuned on, muting the acceleration by remapping the accelerator pedal response. You should get more instant, responsive acceleration in "D" mode.

Nope; this is happening on D mode.
 
Something similar happens on the 2013+ Leafs because of charges in the motor, but the 2011/2012 Leaf is generally considered to be faster off the line. The only other thing I can think of is worn tires that are triggering the traction control.
 
LeftieBiker said:
Something similar happens on the 2013+ Leafs because of charges in the motor, but the 2011/2012 Leaf is generally considered to be faster off the line. The only other thing I can think of is worn tires that are triggering the traction control.

No difference with traction control turned off.

I noticed this behavior on the other 2011 Leafs that I test drove too, so it's not unusual. Maybe there was a software update which toned down the acceleration? BMW did something similar with the i3.
 
Slight update... I've found a thread from 2012 in which the acceleration buildup is mentioned: http://www.mynissanleaf.com/viewtopic.php?f=38&t=8102
 
I'm guessing that you either test drove a Tesla, or have some unrealistic expectations for EVs based on the misleading "100% torque at 0 RPM" description of electric car drive motors. It's also attributed to hub motors used in electric bicycles and motorcycles, but believe me, you don't get neck-snapping acceleration from those, either.
 
What the original poster asks is basic physics. Of course that from a start, the acceleration is slow. 4000 lbs (Mass) of steel at rest will take time (T) for it to accelerate (A)

F=MA, or A=F/M

So then the car is moving, it takes less force for it to accelerate at a faster rate (pick up). Since Acceleration is measured in Meters / Second(squared).
 
jehan2256 said:
Hi everyone, I just got myself a used 2011 Leaf in December.

I'm loving the car, but the acceleration is... weird.

If the car is at standstill and I put my foot down, the acceleration gradually ramps up until about 50km/h, where it seems to reach its peak. However, if I'm rolling along at 15km/h and put my foot down, it feels much more instantaneous, which is what I expected the acceleration to feel like on an EV.

So, why is there a difference? Why does the acceleration have a ramp-up when starting from standstill? Is it to prevent wheelslip? To reduce wear and tear? And how exactly is the ramp-up programmed? Is it designed to take a certain amount of time to reach maximum power, or is the available power determined by the current speed?

I'd appreciate any information on this, as Google has not been very useful.

Be wary of using a "butt-dynomometer" to determine acceleration rates. :)

There is a slight lull when accelerating from a dead-stop. Imho this (initial slew rate) is done to protect the drivetrain.
 
Nubo said:
Be wary of using a "butt-dynomometer" to determine acceleration rates. :)

There is a slight lull when accelerating from a dead-stop. Imho this (initial slew rate) is done to protect the drivetrain.

Agree with both your points. I'd also add that depending on how the motor is synchronized, there may be a limit to the initial acceleration so that the motor can stay in sync. At least with some permanent magnet DC motors, the drive must be turned off during a small time window so the synchronization circuitry can operate. These windows are controlled by computer and during initial acceleration from a dead stop it can be hard to accurately time them while keeping them sufficiently short.

Finally, the derivative of acceleration is jerk and minimizing it will reduce the stress on the mechanical drivetrain.
 
No need for calculus here: F = MA so acceleration A = F/M.

Unless the car nears the speed of light and experiences relativistic effects, the mass will be constant and the F (force) required for any amount of A (acceleration) will be constant.
 
SageBrush said:
ROFL !
powersurge said:
What the original poster asks is basic physics.
No, but understanding basic physics is a good thing.
So [w]hen the car is moving, it takes less force for it to accelerate at a faster rate (pick up).
I know you are a Trumper (and thus by definition the bottom of the gene pool and an abject moron) but try anyway: energy is conserved. Kinetic energy is proportional to the velocity squared. I hesitate to use the "calculus" word so just google it: power is proportional to the cube of velocity

You know... Your ignorance and short sightedness is really showing.... I talk about physics and you start throwing out insults about my gene pool.... and Trump...??? #$%^^ WTF??

I think you really enjoy the protection you have from the anonymity of the internet.... You would never talk like that if you were looking right at me.... You are quickly adding names to the list of enemies, and there will be a breaking point on this and other sites you may be trolling. I will just ignore you ,,,
 
goldbrick said:
No need for calculus here: F = MA so acceleration A = F/M.

Unless the car nears the speed of light and experiences relativistic effects, the mass will be constant and the F (force) required for any amount of A (acceleration) will be constant.
One way to explain the error is to realize that a car has constant power, not constant force.

So let's try some 7th grade algebra now:
W: work
t: time
A: acceleration
V: velocity
P: power
F: force
d: distance
M: mass


W = F * d
Now divide both sides by t:
W/t = F * (d/t). This is
P = F * V
F = M * A
Substitute:
P = M * A * V

P and M are constant, so A decreases as V increases
 
I don't see how effective mass or power is constant for the leaf but y'all are entertaining arguing about high school physics.

While actual mass of the vehicle is constant, the effective mass is not when you consider air resistance, friction, and other forces that all increase with speed. You'd be surprised how big a factor this plays above 50mph or so.

While the power is "relatively" constant across a range of speeds for the leaf it is not completely flat either. I've only seen rolling Dyno charts so I really don't know what happens from a stop but if you search Dyno charts for the leaf there is a peak somewhere around 30-40mph then it slowly drops off until the end of the chart around 90 mph or whenever the thing is speed limited...

https://www.flickr.com/photos/tuanies/15103792190/

Generally speaking Sage is right though, some of y'all should check this out for a decent explanation of the work-energy relationship. Power is work per unit time...

https://courses.lumenlearning.com/boundless-physics/chapter/work-energy-theorem/

I've felt what the OP is talking about and suspect there is something in the software that limits the amps in certain situations near 0mph but I can't really say for sure without monitoring current to the motor across a range of speeds, scenarios and throttle positions. It'd be an interesting experiment, which the link the OP posted sort of does for a couple of specific situations, but it is beyond my capabilities.
 
I'm not certain, but perhaps this torque curve explains OP's observation:

uc
 
golfcart said:
While the power is "relatively" constant across a range of speeds for the leaf it is not completely flat either.
Certainly true, though we can pretty easily set up an experiment where the power flowing from the battery is constant, as is the heat coming out of the motor. dW/dt going to the wheels is constant. In fact that situation is a pretty good description of an EV.

Over a time interval the work added is constant and is equal to F*d
Since velocity is increasing the distance traveled over the same time interval increases ... and the force must decrease.

Roh roh
 
SageBrush said:
Certainly true, though we can pretty easily set up an experiment where the power flowing from the battery is constant, as is the heat coming out of the motor. dW/dt going to the wheels is constant. In fact that situation is a pretty good description of an EV.

Over a time interval the work added is constant and is equal to F*d
Since velocity is increasing the distance traveled over the same time interval increases ... and the force must decrease.

Roh roh

Meh, l give u one Scooby snack but I posted the actual Dyno power curve and the work-energy theorem already so I don't know why we're designing idealized experiments.
 
golfcart said:
SageBrush said:

Meh, l give u one Scooby snack but I posted the actual Dyno power curve and the work-energy theorem already so I don't know why we're designing idealized experiments.
To point out two things:

1. That it is easy to see that force is not constant
2. That one does not have to talk about non-conserved forces (e.g., air friction) to realize that acceleration drops in a car as velocity increases.

I agree, it would be nice to just post: P = F * V and have the gallery respond with an "Oh, yeah ..."
 
SageBrush said:
One way to explain the error is to realize that a car has constant power, not constant force.

Electric cars have a torque and a power limit.

At lower RPMs, torque or force is constant. Above some RPM, the torque starts to decrease to keep the power the motor and inverters are handling below the power limit. As the RPMs continue to rise, various stray losses cause the allowable power to fall. The graph below is idealized, but shows the general picture.

Slide1.jpg


(source https://insideevs.com/why-buy-tesla-model-3-long-range/ )
 
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