One Pedal Driving

[My car]

Hi, we’ve had our MG4 Extended Range for just over a month and I am starting to use the one pedal drive mode but would love someone to tell me the advantages. Also, when sat on a slight incline the other day waiting to turn up a hill I noticed the car was using 3% power - why? Thanks

 

[siteguru]

Ref. 3% power - unless you're pressing the brake then the motor has to use some power to hold the car on the incline; it doesn't just magically hold itself.

The "advantage" of OPD is that you (may) never need to use the brake pedal - maybe it helps to promote "thinking ahead" so you control the car's speed and position so you don't need to use the brake.

 

[My car]

Ref. 3% power - unless you're pressing the brake then the motor has to use some power to hold the car on the incline; it doesn't just magically hold itself.

The "advantage" of OPD is that you (may) never need to use the brake pedal - maybe it helps to promote "thinking ahead" so you control the car's speed and position so you don't need to use the brake.

Thanks for that, I realised the 3% was probably about the car holding itself and so I suppose in a city of seven hills it will be worth using the brake on those inclines possibly.

 

[lsb777]

Once you get the hang of it, OPD makes an EV so simple to drive. You get regen braking as you go downhills without any effort and can virtually drive for miles without using the brake pedal. Although saying that, it's worth testing the brakes first thing on your drive (slip it into neutral briefly) and applying them to get any rain/dust build-up off the discs & pads.

 

[YaR]

Ref. 3% power - unless you're pressing the brake then the motor has to use some power to hold the car on the incline; it doesn't just magically hold itself.

I think this is actually just a software bug displaying the last reading prior to the stop.. The car doesn't need any energy if it has applied the regen brake, at least on all but the steepest inclines. I was using OPD today and when I stopped at some lights going downhill the display was reading -3%. It's not charging unless the physicists have got something fundamentally wrong about how the universe works.

 

[siteguru]

Regen brake? What is this magical item of which you speak?

Regen = regenerative braking = retardation force effected by turning the motor into a generator and converting kinetic energy into electrical energy and sending it to the motor. No motion (kinetic energy) = no regen = no means of stopping the car nevermind holding it on an incline.

Maybe OPD automatically applies the physical brake (I don't have OPD on my Phase 1 car so I don't know), and that is what you mean. But it's not a regen brake.

 

[YaR]

Fine. The friction based effect used to slow a car down and then stop it.

 

[My car]

Thanks for all that, I think! When I read YaR’s response I thought okay, great; then came Siteguru’s response too and I'm back to being confused. Maybe leaving it there is best.

 

[Brettus]

In my experience it tends to show an energy value for holding steady (positive or negative depending on incline direction) and after 20 seconds or so it switches to 0 with a barely perceptible change I suspect this is the physical brake going on but there’s no sound like the parking brake makes of course.

 

[siteguru]

0 speed = 0% regen ... it's physics. The battery (a big energy store) can supply power to the motor to hold the car on an upwards incline, but holding the car on a downwards incline requires braking force; if there's no speed there's no kinetic energy to convert to electrical energy.

tl;dr - the brakes are being used to bring the car to a stop and to hold it on a downwards incline.

 

[crunchy]

As far as I know, the OPD uses regen for braking at "higher" to moderate speeds. At very low speeds, when the braking force is not sufficient, it also uses the normal brakes (up to 100% for full stop). I suspect that it must be difficult to get the interaction between the two brakes to work smoothly, but it works well in my Leaf.
So, OPD can use both type of brakes simultaneously.

 

[lsb777]

As far as I know, the OPD uses regen for braking at "higher" to moderate speeds. At very low speeds, when the braking force is not sufficient, it also uses the normal brakes (up to 100% for full stop). I suspect that it must be difficult to get the interaction between the two brakes to work smoothly, but it works well in my Leaf.
So, OPD can use both type of brakes simultaneously.

I'm not sure it uses the friction brakes at all for OPD. From personal experience, when I park on my drive (facing downhill on slope) it comes to a slow halt with a whirring noise and I've not applied footbrake and the noise sounds like it's coming from the motor rather than mechanically from the brakes. I'm sure someone will correct me though. (pic info from MG attached)

 

[siteguru]

That doesn't explain how OPD is effected - just than you don't have to touch the brake pedal.

I will 99.99% guarantee that the physical brakes are being used at slow speed / coming to a stop. It is simply, physically impossible for regen to provide a braking force at low speeds / stopped - it just can't happen. As I've said several times, regen braking is effected by the conversion of kinetic energy to electrical energy - at low speeds there is very little kinetic energy so virtually no braking effect; when stopped there is none at all.

 

[lsb777]

That doesn't explain how OPD is effected - just than you don't have to touch the brake pedal.

I will 99.99% guarantee that the physical brakes are being used at slow speed / coming to a stop. It is simply, physically impossible for regen to provide a braking force at low speeds / stopped - it just can't happen. As I've said several times, regen braking is effected by the conversion of kinetic energy to electrical energy - at low speeds there is very little kinetic energy so virtually no braking effect; when stopped there is none at all.

Just passing on the info from MG, not trying to prove a point. Thanks for trying though, I knew someone would. When you brake at low speed and haven't used the pads & discs for a while, just get that scraping noise as the disc surfaces are "cleaned". I don't get that same noise when coming to a halt and the feeling of stopping is different from actually braking.

 

[Ayoull]

That doesn't explain how OPD is effected - just than you don't have to touch the brake pedal.

I will 99.99% guarantee that the physical brakes are being used at slow speed / coming to a stop. It is simply, physically impossible for regen to provide a braking force at low speeds / stopped - it just can't happen. As I've said several times, regen braking is effected by the conversion of kinetic energy to electrical energy - at low speeds there is very little kinetic energy so virtually no braking effect; when stopped there is none at all.

A motor will be able to stop the vehicle due to friction within the motor itself, given enough distance to achieve this and in addition to the presence of a permanent magnetic flux due to the permanent magnets in an EV motor, this will increase the loss of speed, as no other forces are being impacted or power to alter the excitation of the rotor.

Else you're defining the EV motor as perpetual motion machine.

The holding will however always be through engagement of the physical brakes however.

 

[crunchy]

OK, try to compare braking with OPD and without OPD, but in "neutral gear" at very low speeds. I doubt that MG4 will have the same deceleration. Motor and transmission friction cannot have the same deceleration as the actual brake (which should be used by OPD at very low speeds).

 

[lsb777]

OK, try to compare braking with OPD and without OPD, but in "neutral gear" at very low speeds. I doubt that MG4 will have the same deceleration. Motor and transmission friction cannot have the same deceleration as the actual brake (which should be used by OPD at very low speeds).

If you put it in neutral, OPD is disengaged.

 

[fshuk1]

Simple question that I am sure is answered somewhere on this enormous forum. Do we get OPD in UK sometime? I haven't got it.

 

[My car]

We have it on our MG4 Trophy Extended Range

 

[siteguru]

Phase 2 cars should have it (the ones with the rear wiper) - Phase 1 cars don't, and likely won't according to feedback from MG that other's have received.