Speak EV - Electric Car Forums banner
81 - 87 of 87 Posts

·
Registered
Nissan Leaf 40, 2018
Joined
·
25 Posts
And while I have my calculator out........and more on topic .......... is it really the case that you (or the cruise control) can achieve regeneration on motorways while maintaining a constant speed? I suggest not, for all reasonable motorway or trunk road speeds.

In round numbers, travelling at 70mph at constant speed on the level will require about 20kW (@3.5 mile / kWh). To be able to regenerate, the energy input to the car from going downhill needs to be greater than 20kW if you are to maintain speed. Assuming a 1.5 tonne car, that would require a vertical drop of about 1.3m/s = 4.8kph = 3.0mph. So that requires a downhill gradient of at least 3/70 = 4.3%. I don't think there are many motorways in the UK with gradients that steep. The M90 south of Perth has a notoriously steep section but that, I believe, is 4% at maximum. So, even going downhill there, you would struggle to maintain speed at 70mph without applying some power. There would be nothing left over for regeneration.

I am not challenging the usefulness of regeneration on roads where speeds need to vary - slowing down for corners and junctions - but at constant speed, I don't buy the idea that you, or the cruise control, can regenerate significantly on motorways or trunk roads that are not switchbacks. So neither do I buy the idea that using (non-adaptive) cruise control on motorways is inefficient.
 

·
Registered
Joined
·
3,176 Posts
The measure that struck me is that a litre of petrol or diesel gives about 2kWh of work output. (It's more thermally, but an ICE is not 100% efficient.) So, to get a similar range, you need either a 100kWh battery or a 50 litre fuel tank. More significantly, that 2kWh costs you about £1.40 for petrol or about 30p for electricity.
Or 10p on OE Go.
I tell them in work my cost is 1.25p mile in fuel. They say well my car is about that, then they do the actual maths. ;)
 
  • Like
Reactions: Edinburgh 2000

·
Registered
Joined
·
3,176 Posts
And while I have my calculator out........and more on topic .......... is it really the case that you can achieve regeneration on motorways while maintaining a constant speed? I suggest not, for all reasonable motorway or trunk road speeds.

In round numbers, travelling at 70mph at constant speed on the level will require about 20kW (@3.5 mile / kWh). To be able to regenerate, the energy input to the car from going downhill needs to be greater than 20kW if you are to maintain speed. Assuming a 1.5 tonne car, that would require a vertical drop of about 1.3m/s = 4.8kph = 3.0mph. So that requires a downhill gradient of at least 3/70 = 4.3%. I don't think there are many motorways in the UK with gradients that steep. The M90 south of Perth has a notoriously steep section but that, I believe, is 4% at maximum. So, even going downhill there, you would struggle to maintain speed at 70mph without applying some power. There would be nothing left over for regeneration.

I am not challenging the usefulness of regeneration on roads where speeds need to vary - slowing down for corners and junctions - but at constant speed, I don't buy the idea that you can regenerate significantly on motorways or trunk roads that are not switchbacks.
I would agree there. Best i have seen in economy is coming back over the M62 east to west. The continuous and lengthy drop back towards Manchester gives some amazing m/kWh and over a fair distance, not just a short sharp drop.
 
  • Like
Reactions: Edinburgh 2000

·
Registered
2020 Kia Soul First Edition
Joined
·
3,136 Posts
How does the car know if it's going up a hill or not?
My current EV knows if it’s going up or down a hill and will automatically (if switched on) apply regen going down a hill, but turn it off while going up. It must have some sensors to detect this! It will also add as much regen as is required if following another car which slows down and you lift off the throttle. Quite different to my old Leaf 40. (I also have 4 levels of regen!).

The measure that struck me is that a litre of petrol or diesel gives about 2kWh of work output. (It's more thermally, but an ICE is not 100% efficient.) So, to get a similar range, you need either a 100kWh battery or a 50 litre fuel tank. More significantly, that 2kWh costs you about £1.40 for petrol or about 30p for electricity.
Not forgetting the amount of electricity required to make the fuel in the first place. :D
 

·
Registered
Joined
·
5,290 Posts
How does the car know if it's going up a hill or not?
The same way it knows whether to engage automatic hill hold or not when you come to a stop with the foot brake?

All modern cars with stability control have a 6 axis accelerometer and gyro the same as you'll find in your smart phone.

When the car is stopped it knows exactly what angle the car is on to a fraction of a degree and therefore whether it's facing uphill, downhill, is level etc.

When the car is moving it has to take into account acceleration/deceleration from the driving itself (since acceleration will influence the accelerometer as well as gravity) but it knows what that driving induced acceleration is from looking at the change in wheel speed over time and steering wheel angle for sideways acceleration. This can be subtracted from the acceleration reported by the accelerometer to find the remaining vector for gravity and thus the true orientation of the car relative to level while driving to know whether you are driving up hill or down hill and modify regen behaviour accordingly.

A slightly less high tech way for a car to figure out if it is driving up hill or down hill while moving without requiring any accelerometer is to simply compare the engine torque output against measured acceleration/deceleration of the wheels.

This is how early generation, pre-stability control computer controlled automatic gearboxes like the one in my 1997 petrol worked - it knows I'm going uphill if significant torque is being applied but the car is not accelerating like it would be on the level, or conversely if it detects the car accelerating when there is little torque applied it knows it is rolling downhill, and in both cases it automatically adjusts the gear shift points to hold a lower gear vs driving on the level where it will more readily change up a gear.

This simpler method of measuring whether the car is driving uphill or downhill would be perfectly adequate for adjusting lift off regen based on uphill / level / downhill driving, but I suspect EV's that do this regen adjustment simply use the first method and tap into the accelerometer data in the stability control system as it is already there and much more accurate.
 

·
Registered
Joined
·
2,554 Posts
My current EV knows if it’s going up or down a hill ...
My old Skoda Octavia DSG Estate (end of range in 2012) knew. It would make different decisions about changing gear if I was going uphill or downhill, and that was prior to it being able to sense the increased power needed.
 
  • Like
Reactions: ElectricIan

·
Registered
Joined
·
3,176 Posts
My current EV knows if it’s going up or down a hill and will automatically (if switched on) apply regen going down a hill, but turn it off while going up. It must have some sensors to detect this! It will also add as much regen as is required if following another car which slows down and you lift off the throttle. Quite different to my old Leaf 40. (I also have 4 levels of regen!).


Not forgetting the amount of electricity required to make the fuel in the first place. :D
Just the 42 months for a reply there. 😬
The same way it knows whether to engage automatic hill hold or not when you come to a stop with the foot brake?

All modern cars with stability control have a 6 axis accelerometer and gyro the same as you'll find in your smart phone.

When the car is stopped it knows exactly what angle the car is on to a fraction of a degree and therefore whether it's facing uphill, downhill, is level etc.

When the car is moving it has to take into account acceleration/deceleration from the driving itself (since acceleration will influence the accelerometer as well as gravity) but it knows what that driving induced acceleration is from looking at the change in wheel speed over time and steering wheel angle for sideways acceleration. This can be subtracted from the acceleration reported by the accelerometer to find the remaining vector for gravity and thus the true orientation of the car relative to level while driving to know whether you are driving up hill or down hill and modify regen behaviour accordingly.

A slightly less high tech way for a car to figure out if it is driving up hill or down hill while moving without requiring any accelerometer is to simply compare the engine torque output against measured acceleration/deceleration of the wheels.

This is how early generation, pre-stability control computer controlled automatic gearboxes like the one in my 1997 petrol worked - it knows I'm going uphill if significant torque is being applied but the car is not accelerating like it would be on the level, or conversely if it detects the car accelerating when there is little torque applied it knows it is rolling downhill, and in both cases it automatically adjusts the gear shift points to hold a lower gear vs driving on the level where it will more readily change up a gear.

This simpler method of measuring whether the car is driving uphill or downhill would be perfectly adequate for adjusting lift off regen based on uphill / level / downhill driving, but I suspect EV's that do this regen adjustment simply use the first method and tap into the accelerometer data in the stability control system as it is already there and much more accurate.
My current EV knows if it’s going up or down a hill and will automatically (if switched on) apply regen going down a hill, but turn it off while going up. It must have some sensors to detect this! It will also add as much regen as is required if following another car which slows down and you lift off the throttle. Quite different to my old Leaf 40. (I also have 4 levels of regen!).


Not forgetting the amount of electricity required to make the fuel in the first place. :D
Was racking my brain trying to recall what this was about. Suspected I had been doing some drunken posting. Relieved it was as it is a post from just 42 months ago.
 
81 - 87 of 87 Posts
Top