Best Acceleration (Ergonomically)

[robinfisichel]

Im trying to spec the acceleration curve (vs time) for a car i am designing in a project. The car is lightweight (400 kilos) low drag (cd=0.15) and electric (also only one forward gear).

Im trying to come up with what would 'feel' like a good acceleration.
0-60mph is about 9-10 seconds.
Top speed around 100mph

Would most people agree that the 'kick' or greatest acceleration should happen in the first few seconds and then progressively decrease up to the max speed?

If anyone has some accel data logs from a slowish passenger car (both electric and non electric) that would be useful...

 

[Terraloth]

apologies if I've misunderstood this... but if you already know what the 0-60mph time is, don't you already have a accn curve?

 

[xxChrisxx]

Seems like a pointless excerise to me.

More acceleration = better...

Fact is you won't be able to alter 'when' the kick comes in as that determined by the engine, gearing, mass and traction available. Basically no matter what you do, the inital acceleration is likely to be traction limited, then as you get going it'll be power limited.

No matter what you do the biggest 'push' will come at peak torque in gear. There is very little you can do to alter that.

AS an asside 0-60 is a totally pointless measure of real world performance, simply because no one does it. 30/40 - 70 is a fer better target to aim for. (Basically acceleration from normal speed to motorway speeds)

 

[robinfisichel]

Seems like a pointless excerise to me.

More acceleration = better...

Fact is you won't be able to alter 'when' the kick comes in as that determined by the engine, gearing, mass and traction available. Basically no matter what you do, the inital acceleration is likely to be traction limited, then as you get going it'll be power limited.

No matter what you do the biggest 'push' will come at peak torque in gear. There is very little you can do to alter that.

AS an asside 0-60 is a totally pointless measure of real world performance, simply because no one does it. 30/40 - 70 is a fer better target to aim for. (Basically acceleration from normal speed to motorway speeds)

actually i think i have confused myself, my question is probably more to do with throttle mapping, more acceleration = better only if you are putting your pedal to the floor (i.e. want the max performance) though you would want that acceleration early on (you don't want some sort of huge spike at 50mph as its not really expected).

 

[Lsos]

More acceleration is ALWAYS better :)

I must agree with xxChrisxx's aside about the 0-60. While it does tell you something about the car because in general, a better 0-60 means better 30-70, this is not always the case. I've actually seen manufacturers deliberately decrease the overall performance of their cars, simply because it resulted in a better 0-60 time...and that defeats the very point of the measurement.

 

[xxChrisxx]

actually i think i have confused myself, my question is probably more to do with throttle mapping, more acceleration = better only if you are putting your pedal to the floor (i.e. want the max performance) though you would want that acceleration early on (you don't want some sort of huge spike at 50mph as its not really expected).

There's no way you would ever get a 'spike' of acceleration. As acceleration is determined by the torque output of the engine, so unless you had a very large spike in the torque speak you wouldn't get a large sudden rush of acceleration.

In general with cars as opposed to thinking strictly in terms of speeds, it's better to just think in terms of engine revs and gear ratios.

eg. you say you don't want a huge spike at 50mph. You may do, if I put my foot down in 3rd i'd expect some performance. however if I was in top gear, I wouldn't expect to accelerate at all. In the 3rd gear case, you'd be running between peak torque and peak power. In top gear you'd be at low revs.

For thottle mapping you generally want it mapped against load and speed, to be honest my mate is the one to talk to on this as ECU's are just magic little boxes to me.

However in general, at low load and WOT you want lots and lots of fuel being injected (read slightly rich). As that generally signifies that you are traveling slowly and want to get a move on. At high load (speed) and WOT, you want to lean the engine out for good fuel economy. Ie motorway cruising at peak efficiency.