How would regenerative braking work for a long downhill?

[Sequoiasoon]

The new Accord and CRV is revised from the '18 that @fdcg27 has also. And then to put back to OP question on the REGEN braking.

What affects or how would it work if you use the paddle shifters for more or less regen braking? Would the gearsets and generator tie back to motor for engine braking so you don't overheat the brakes coming down longer mountain passes?

Again I have no clue on most of this, just reading/learning and intrigued for future replacements. The traffic by me gets worse daily, my body and legs hurt more daily. If I was stuck in daily stop and go, something like the Accord or CRV Hybrid might be attractive. I work nights so don't hit much traffic either direction.

My son took a "test drive" to where he needs to go for clinicals and when he needs to be there. It took him 2 hours to go 48 miles. Afterward he said he would rather take his automatic Forte than my 6MT Accord. He likes driving stick and takes my Accord often for trips but the constant stop and go was killing him. Basically 1st and 2nd gear the whole time even leaving space to try and reduce clutch use. I-495 Long Island Expressway rush hour traffic, 3 lanes each way and an HOV (but he couldn't take the HOV by himself).

 

[y_p_w]

I certainly understand regenerative braking and have gone down long inclines where the range/charge level seemed to barely budge as a matter or going downhill. But I was wondering if there might be any limit and what might be needed if something happened that would limit regenerative braking. Once that's limited, it's just the brakes and no low gear.

I mean - something like the 18 or so miles down Pikes Peak. Without adequate regenerative braking, that would seem like an iffy proposition in most EVs.

 

[fdcg27]

The new Accord and CRV is revised from the '18 that @fdcg27 has also. And then to put back to OP question on the REGEN braking.

What affects or how would it work if you use the paddle shifters for more or less regen braking? Would the gearsets and generator tie back to motor for engine braking so you don't overheat the brakes coming down longer mountain passes?

Again I have no clue on most of this, just reading/learning and intrigued for future replacements. The traffic by me gets worse daily, my body and legs hurt more daily. If I was stuck in daily stop and go, something like the Accord or CRV Hybrid might be attractive. I work nights so don't hit much traffic either direction.

My son took a "test drive" to where he needs to go for clinicals and when he needs to be there. It took him 2 hours to go 48 miles. Afterward he said he would rather take his automatic Forte than my 6MT Accord. He likes driving stick and takes my Accord often for trips but the constant stop and go was killing him. Basically 1st and 2nd gear the whole time even leaving space to try and reduce clutch use. I-495 Long Island Expressway rush hour traffic, 3 lanes each way and an HOV (but he couldn't take the HOV by himself).

I suspect that the revisions are limited to software and not hardware, but I could be wrong and they'd be real either way.
I use the regen paddles all the time and can usually avoid touching the brake pedal at all.
I've never run out of regen, although it does seem somewhat variable in its retardation.
I've also never driven the car in mountainous terrain, so what would happen with a battery fully charged on regen I don't know.

 

[Kiwi_ME]

On the Hyundai/Kia EVs you can access the kWh cumulative registers on OBD and use those to track regen. These are just like domestic electricity meters but separately register energy going in and out. So, on this 290 km round trip on a hilly road (0 to 2700 ft and back) I can see how much regen helps. In general I expect the returned energy from going up and down the same mountain is roughly about 70% due to power conversion losses, without including aerodynamic losses. The graph is by percent charge so you can see that the net energy used is mostly linear with displayed charge level. The extrapolation of that net energy curve to 100% as-expected matches the advertised capacity of 64 kWh.

 

[PandaBear]

I certainly understand regenerative braking and have gone down long inclines where the range/charge level seemed to barely budge as a matter or going downhill. But I was wondering if there might be any limit and what might be needed if something happened that would limit regenerative braking. Once that's limited, it's just the brakes and no low gear.

I mean - something like the 18 or so miles down Pikes Peak. Without adequate regenerative braking, that would seem like an iffy proposition in most EVs.

No matter what, an EV must have a full size brake that is enough to stop the vehicle, and if going down hill, enough braking power to stop the vehicle like a regular car going down hill (i.e. you cannot reduce the brake so much you cannot stop and it "run away").

The worst case scenario would be to leave a home at the peak of a mountain top fully charged, and start driving downhill. If the regen braking is not happening, it still has to slow down the car enough to be safe.

 

[brianl703]

Wikipedia says:

The simplest transmissions used a fixed ratio to provide either a gear reduction or increase in speed, sometimes in conjunction with a change in the orientation of the output shaft. Examples of such transmissions are used in helicopters, wind turbines and power take-offs (PTOs) for tractors. In the case of a wind turbine, the first stage of the gearbox is usually a planetary gear, to minimize the size while withstanding the high torque inputs from the turbine.[3][4]

Seems there's no need for a gearbox to have multiple speeds to be considered a transmission.

 

[y_p_w]

No matter what, an EV must have a full size brake that is enough to stop the vehicle, and if going down hill, enough braking power to stop the vehicle like a regular car going down hill (i.e. you cannot reduce the brake so much you cannot stop and it "run away").

The worst case scenario would be to leave a home at the peak of a mountain top fully charged, and start driving downhill. If the regen braking is not happening, it still has to slow down the car enough to be safe.

But they're often sized considering there's regenerative braking. Or at least covered up for better aerodynamics, like the wheel covers on the Model 3.

There was often a distinct wheel style for early hybrids with regenerative braking. They often had smaller brakes and smaller openings (for better aerodynamics) in their wheels for cooling, on the premise that the friction brakes wouldn't need to be as effective when combined with regenerative braking.



If anyone is going up a high peak, there's almost no chance the battery will be at 100% unless somehow there's charging there and someone thinks it's a good idea to charge. I wouldn't since I would want to leave room for regenerative braking, which I understand is more effective at lower state of charge.

That's the thing with my parents' new Model 3. They live on a hill and are following Tesla's recommendation to have it charged to 100% at least once a week. And they'll be starting most drives going downhill. But they get me to set it to 90% most of the time, which should be enough for regenerative braking.

 

[PandaBear]

But they're often sized considering there's regenerative braking. Or at least covered up for better aerodynamics, like the wheel covers on the Model 3.

There was often a distinct wheel style for early hybrids with regenerative braking. They often had smaller brakes and smaller openings (for better aerodynamics) in their wheels for cooling, on the premise that the friction brakes wouldn't need to be as effective when combined with regenerative braking.



If anyone is going up a high peak, there's almost no chance the battery will be at 100% unless somehow there's charging there and someone thinks it's a good idea to charge. I wouldn't since I would want to leave room for regenerative braking, which I understand is more effective at lower state of charge.

That's the thing with my parents' new Model 3. They live on a hill and are following Tesla's recommendation to have it charged to 100% at least once a week. And they'll be starting most drives going downhill. But they get me to set it to 90% most of the time, which should be enough for regenerative braking.

I agree, but I think that most of today's cars have overpowered brakes and brake cooling for regular commutes. Look at the base model vs top trim gas vehicles (i.e. Corolla for example), you will see a lot of the steel wheel hub cap has similar cooling and brake size as the hybrids and EVs.

EV probably are designed with enough braking and brake cooling like a base model vehicle going downhill, in non racing application. I would imagine they have the worst case scenario covered (white knuckle by the time they are at the bottom of the hill) but they are not going to do that for most people going downhill having enough battery capacity to regen braking.

I think a responsible EV design should have "what if the cooling system for the power electronics fail and disable the regen braking, can the car be stopped safely at top speed". If they cannot do that with mechanical braking, then there is a fatal accident waiting for them and will sue them into billions in damage. This doesn't mean the car will stop comfortably, but it will stop safely by smoking your pads and warping your rotors.

 

[y_p_w]

I agree, but I think that most of today's cars have overpowered brakes and brake cooling for regular commutes. Look at the base model vs top trim gas vehicles (i.e. Corolla for example), you will see a lot of the steel wheel hub cap has similar cooling and brake size as the hybrids and EVs.

EV probably are designed with enough braking and brake cooling like a base model vehicle going downhill, in non racing application. I would imagine they have the worst case scenario covered (white knuckle by the time they are at the bottom of the hill) but they are not going to do that for most people going downhill having enough battery capacity to regen braking.

I think a responsible EV design should have "what if the cooling system for the power electronics fail and disable the regen braking, can the car be stopped safely at top speed". If they cannot do that with mechanical braking, then there is a fatal accident waiting for them and will sue them into billions in damage. This doesn't mean the car will stop comfortably, but it will stop safely by smoking your pads and warping your rotors.

That's kind of tricky since these systems tie in both regenerative braking and physical braking. But it's my understanding that there's an actual mechanical link between the brake pedal and the brake hydraulics in most EVs.

I've actually had a car where the power brakes went out. I was tough getting it to stop.

 

[PandaBear]

That's kind of tricky since these systems tie in both regenerative braking and physical braking. But it's my understanding that there's an actual mechanical link between the brake pedal and the brake hydraulics in most EVs.

I've actually had a car where the power brakes went out. I was tough getting it to stop.

My understanding (maybe not up to date) is in the US you must have mechanical linkage between the brake pedal and the mechanical brake, and same for steering (no electrical signal only). This is to avoid losing control and causing accident if the power steering or brake boosting failed. Sure you can't stop or steer as well but at least you still can stop a lot, and steer somehow.

 

[eljefino]

Just took my wife's Prius up and down Mt Washington (6000 vertical feet) with four full sized passengers. Used gear "B" on the way down which wastes electricity by having a motor-generator spin the ICE.

Tried keeping the speed UP to 22-ish MPH on the theory that it was more of a sweet spot for regeneration/ "low gear" wasting compared to, say, 10 MPH which would have been more friction braking.

Smelled my own brakes near the end, but I pulled off a couple times and the calibrated finger knuckle didn't detect too much heat radiating from the rotors. And I've had a scorcher before with a siezed caliper coming off the interstate so I know what to feel for.

The car lacked foresight and charged the tiny hybrid battery in the first few hundred feet of vertical drop then engaged plan B of spinning the ICE up. If I had my Prius Prime and its larger pack I'm confident I could do better. Wonder if it would trigger a panicky battery cooling algorithm.

 

[Sequoiasoon]

But they're often sized considering there's regenerative braking. Or at least covered up for better aerodynamics, like the wheel covers on the Model 3.

There was often a distinct wheel style for early hybrids with regenerative braking. They often had smaller brakes and smaller openings (for better aerodynamics) in their wheels for cooling, on the premise that the friction brakes wouldn't need to be as effective when combined with regenerative braking.

These are the 17" wheels on the '23 Accord Hybrid.

 

[IndyIan]

I am not sure if it will be more efficient, but consider towing uphill you likely don't run as fast (roads are not straight, limiting the speed you can drive on) and as he mentioned the thinner air. I think if he drives on the flat ground with lowered speed he will see a lot of improvement in watt too.

There was no issue with power so if the road is straight I think he’s setup would do 60 mph just like on the flats. Also I suspect his towing setup would out corner a lot of pickups with nothing behind them. He is all about the low centre of gravity you can have with a car tow vehicle and an airstream trailer. I doubt he was driving much faster than the regular flow of traffic though.

 

[Jetronic]

There is, as there has to be, a reduction gearset for when the gas engine is driving the wheels.
There is no torque converter since there's no need for one.
Honda cleverly exploited the torque capabilities of electric drive to dispense with any sort of multi speed gearbox.
A simple design that works well and delivers really good fuel economy in my use.

No there doesn't have to be any reduction gearset. Mitsubishi outlander phev doesn't have one. It can drive the wheels directly only over a certain speed (around 40 mph IIRC)

 

[Owen Lucas]

Here’s my 2020 CRV Hybrid experience. Only happened once though.

I was driving down a long mountain, very steep at some points. Regenerative braking turned off and the engine started revving as if it was engine braking.

I presume it went into engine braking mode because the battery was completely full. I drove at the full mark downhill for quite a while before the revving started which means either:

A. The battery has more capacity than the gage indicates or

B. Some type of battery management or usage of regen I am not aware of.

In the CRV it is not hard to drain and recharge the battery all within a short spirited acceleration or downhill drive to recharge. It is only 1.4kWh.

 

[Astro_Guy]

The long downhill run regeneration is something I have experience with in both the 2010 Prius and 2017 Prius V. Granted these vehicles have very small capacity in contrast to a true EV, but here is what I have experienced. There is a long and steep grade on VT route 9 approaching Bennington from the east that I've run many times. The battery always completely tops up, stops charging and then the cooling system kicks in. I imagine that something similar would happen descending a large mountain with a pure EV, provided that the battery had the capacity to accept the renerative load,

 

[y_p_w]

I’m borrowing a Model 3 today. Not sure why it’s at 100% as I thought I remotely changed it to 90%. But also set it to apply friction brakes. Saw something new today, with a gray bar showing application of friction brakes, including simultaneously with limited regenerative braking in green. But the warning symbol for limited regenerative braking didn’t pop up.

 

[Owen Lucas]

The battery always completely tops up, stops charging and then the cooling system kicks in. I imagine that so

What do you mean the cooling system kicks in and how do you know?

Maybe a resistor is used to take care of the excess energy?

 

[Torrid]

I’m borrowing a Model 3 today. Not sure why it’s at 100% as I thought I remotely changed it to 90%. But also set it to apply friction brakes. Saw something new today, with a gray bar showing application of friction brakes, including simultaneously with limited regenerative braking in green. But the warning symbol for limited regenerative braking didn’t pop up.

Yeah, it'll show you what its doing on the screen. I think it's what you mentioned before with regenerative braking reduced which leaves the green circle indicator on the screen until the battery comes up to temperature. With the brake assist on you won't see that warning anymore. It'll just supplement friction brakes to retain the one pedal driving feel no matter what the regenerative braking status is. It's probably why I've never seen it freak out on really long downhills of regenerative braking either, because unless I was intently watching the screen I'd have no idea that it was reducing regenerative braking and supplementing friction brakes to maintain downhill speed. Typically I'm using cruise in these situations anyway since many of our craziest hills here are on county roads and interstates which would make me even less likely to notice.

 

[fdcg27]

No there doesn't have to be any reduction gearset. Mitsubishi outlander phev doesn't have one. It can drive the wheels directly only over a certain speed (around 40 mph IIRC)

It would still need a differential, no?
The reduction gearing would be that gearset.