Mode and KERS setting thoughts

[rogerco]

Having driven my original SR 25k miles over 2 years I often find myself musing as I drive on how the drive mode and KERS settings are actually implemented (I used to be a software engineer / system and HCI designer)

If I was building it with the spec to do what it does I think I would keep it simple.

Firstly for driving mode (sport|normal|eco) I think all that has to be done is adjust the sensitivity (gain) on the accelerator. ie change the amount of power applied for each degree of rotation of the pedal. No change to the max power that can be achieved, just in sport mode you need a smaller movement for a given change.

Secondly for the KERS modes I think that when releasing the pedal the point at which kers begins to be applied is shifted. ie apply an offset to the the accelerator position when power is being decreased (no change when pressing down, only when releasing pressure)

Zero kers only happens when the state of charge is over 96% and then all of the braking has to be mechanical and there is no offset. In all other modes applying the brake pedal starts by using kers and when that runs out uses physical braking.

I suspect that in kers 1 there is no offset so kers is only used when applying the brake (the power meter doesn't go into the blue until you apply the brake). In kers 2 and 3 there is an offset on releasing the accelerator so that kers starts to be used at some point before you take the foot off the pedal. There is no change to the brake pedal operation.

In other words there is no real difference between the modes from the car's point of view - it is just changing the way the driver interacts with the pedals. There will be no difference between power used (or recovered) for a given road and external conditions and speed/acceleration/deceleration. If you think you are getting 'better' performance between combinations of modes and kers that is simply because the external conditions are almost never the same and you have become acclimatised to particular response from the pedals in your previous mode and when you switch you are over or under compensating.

So it is simply an interface change. No change to the underlying system whatever the mode. Just pick the one that works best for you which is probably affected by your body conformation and muscle strength and driving position.

Does this make sense? Or is it more complex than that?

 

[Gomev]

No idea but nice musings. I do know in the real world of what actually happens Kers1 does go into the blue without braking, so maybe your model needs a little tweak

 

[slmorgan42]

Having driven my original SR 25k miles over 2 years I often find myself musing as I drive on how the drive mode and KERS settings are actually implemented (I used to be a software engineer / system and HCI designer)

If I was building it with the spec to do what it does I think I would keep it simple.

Firstly for driving mode (sport|normal|eco) I think all that has to be done is adjust the sensitivity (gain) on the accelerator. ie change the amount of power applied for each degree of rotation of the pedal. No change to the max power that can be achieved, just in sport mode you need a smaller movement for a given change.

Secondly for the KERS modes I think that when releasing the pedal the point at which kers begins to be applied is shifted. ie apply an offset to the the accelerator position when power is being decreased (no change when pressing down, only when releasing pressure)

Zero kers only happens when the state of charge is over 96% and then all of the braking has to be mechanical and there is no offset. In all other modes applying the brake pedal starts by using kers and when that runs out uses physical braking.

I suspect that in kers 1 there is no offset so kers is only used when applying the brake (the power meter doesn't go into the blue until you apply the brake). In kers 2 and 3 there is an offset on releasing the accelerator so that kers starts to be used at some point before you take the foot off the pedal. There is no change to the brake pedal operation.

In other words there is no real difference between the modes from the car's point of view - it is just changing the way the driver interacts with the pedals. There will be no difference between power used (or recovered) for a given road and external conditions and speed/acceleration/deceleration. If you think you are getting 'better' performance between combinations of modes and kers that is simply because the external conditions are almost never the same and you have become acclimatised to particular response from the pedals in your previous mode and when you switch you are over or under compensating.

So it is simply an interface change. No change to the underlying system whatever the mode. Just pick the one that works best for you which is probably affected by your body conformation and muscle strength and driving position.

Does this make sense? Or is it more complex than that?

As mentioned above kers 1 does regen without breaking.

But in general I have come to the same conclusion as you. It’s just a matter of how you feather the throttle.

 

[Kompins]

Also had our car 2 years and rapidly came to the conclusion that drive mode/KERS setting makes no difference to efficiency. ECO might help stretch the last percentage of battery when running low but the throttle response is so horribly woolly I'd rather resort to my feather light right foot ?

 

[Robf]

I now always drive on KERs 3 (ZS 2nd gen) and use the accelerator to control the level (I can coast at 0 regen and up to max regen with full release of pedal).
Problem for those using 1 or 2 is that on release of accelerator pedal and use of brake it seems to only be capable of using assist regen to brake at the regen level set (less than -20 which is level 3).
Using brake should be capable of always using the max regen regardless of set level, only depending on brake pressure.

 

[Wibble]

I find the KERS 2 is best for economy but this is based on you letting your foot off the volts really early to maximise the regen. This isnt always practical and that is where KERS 3 comes in.

ECO/Normal/Sport does not make as much difference to economy really, its how your drive.

 

[Robf]

I find the KERS 2 is best for economy but this is based on you letting your foot off the volts really early to maximise the regen. This isnt always practical and that is where KERS 3 comes in.

ECO/Normal/Sport does not make as much difference to economy really, its how your drive.

Used to be my feeling as well, until it was pointed out that you can control all KERs levels by having on 3 and controlling through accelerator position.

 

[Deep purple]

To get maximum range you should drive to minimise use of regeneration by very early anticipation of the need to slow down, Regeneration is not 100% efficient at recovering energy, although it is hugely better than using the actual brakes.

 

[kevin ellard]

To get maximum range you should drive to minimise use of regeneration by very early anticipation of the need to slow down, Regeneration is not 100% efficient at recovering energy, although it is hugely better than using the actual brakes.

While that is sort of true it isn't really very much fun. I've had my MG5 about 6 months now and it still puts a smile on my face each time I drive it - partly because I can accelerate quite hard knowing that if I have to slow back down I'll get quite a bit of that energy back (and without all the noise and fuss that would happen in an ICE car).

 

[johnb80]

Having driven my original SR 25k miles over 2 years I often find myself musing as I drive on how the drive mode and KERS settings are actually implemented (I used to be a software engineer / system and HCI designer)

If I was building it with the spec to do what it does I think I would keep it simple.

Firstly for driving mode (sport|normal|eco) I think all that has to be done is adjust the sensitivity (gain) on the accelerator. ie change the amount of power applied for each degree of rotation of the pedal. No change to the max power that can be achieved, just in sport mode you need a smaller movement for a given change.

I have spent many years designing motor speed control systems and writing software for them. I dont know the inner workings of the MG control system but I do know what happens on other EV's. The different driving modes usually make adjutments to acceleration ramps, current limit and maximum speed. They often also make adjustment to ancillaries such as HVAC adjusting the maximum power demand they can make.

 

[Petriix]

Yes, your conclusions are pretty accurate. However, the adjustments to the response to the user input do have some (limited) effect on the overall energy consumption. It's possible to drive economical in 'sport' but it requires more precision while 'eco' gives a greater margin for error by requiring larger movements to deliver the same power. With KERS 3, it's easier to accidentally slow more than intended, especially when momentarily lifting from the power. Ultimately it's about encouraging efficient driving at the expense of precise control.