Regenerative Braking

[BusyBee]

My Toyota Yaris hybrid seems to generate a fair amount while braking.  It has a brake mode position on the gear shift but even on a steep hill it works almost too well slowing the car down too much.

I have noticed similar with mine. The 'B' position does seem to give a similar feel to that of the similar position on one of the old automatics though, and I use it similarly.

[peter scott]

My Toyota Yaris hybrid seems to generate a fair amount while braking.  It has a brake mode position on the gear shift but even on a steep hill it works almost too well slowing the car down too much.

The Audi I'm complaining about also has good regenerative action when braking. My issue is that it recovers virtually nothing on the overrun and I tend to avoid using the brakes in a normal car as it just burns your fuel as heat.

Peter.

[ppppenguin]

In theory, pressing the brake on an electric or hybrid should regenerate first and only then actually apply the brakes. Software should make the whole thing seamless. If the ammeter is to be believed, on both Peter's Audi and my Skoda, then this is exactly what's happening. It just feels wrong when you are used to easing off the accelerator to slow down, rather than actually braking. That's why I select the regne mode that best suits my driving style.

I'm not convinced about hybrids. The Toyota Prius has made its name by being as economical in town as in steady driving. Along with utter reliability, this has made it the minicab of choice. Plenty of hybrids don't live up to this. The low CO2 figures claimed for plug-in hybrids are largely an artefact of the test methods. Unless you are doing such short journeys that you can do them largely on battery then they are complete fiction. Because of the small batteries in plug-in hybrids the battery range is small. Often very small in practice because running ancillaries uses a greater fraction of battery if the battery is small.

Pure electric is still not ready for all uses. But the cars are getting better and better. Poor reliability hasn't helped, with expensive brands such as Audi, Jaguar and even Tesla having problems. On the flip side, Kia are making very practical and reliable electric cars. The charging network still leaves much to be desired from what I've read. If you can't charge in your own driveway then charging is expensive too.

[peter scott]

Unfortunately this Audio has no ammeter but I guess I could ask Pam to look at the brake lights but it still doesn't tell me the proportion of regen to actual braking at any level of pedal.

Peter

[Mike Watterson]

Unfortunately this Audio has no ammeter but I guess I could ask Pam to look at the brake lights but it still doesn't tell me the proportion of regen to actual braking at any level of pedal.

Peter

Surely the brake lights ought to come on during purely regenerative braking? They are to warn someone behind.

[ppppenguin]

Peter, if there's no ammeter how do you know you're getting regeneration? I use the term "ammeter" slightly loosely to refer to the dial in my car that shows the rate of charge or discharge on an arbitrary scale.

Michael, I agree with brake lights coming on during heavy regen braking but at what threshold? No brake lights if you coast to a halt. No brake lights if you change down purely to slow down. Though I don't think that's being kind to the gearbox.

[Mike Watterson]

No brake lights if you change down purely to slow down. Though I don't think that's being kind to the gearbox.

My brother did an experiment, long ago on an old car. He claimed cutting brake pipes or similar to disable braking to kill the person coming down the hill only works with automatics (normal in 1950s Hollywood?). So he pretended no brakes and slowed car on steep hill (after reaching a scary speed) so as to be able to stop by turning to kerb at the crossroads at the bottom. It probably did no good to clutch, gearbox or engine. Wasn't good for my nerves.

[Murphyv310]

Glad you recovered from that experience Michael. My dad used to complain about drivers in front that were forever touching the brake pedal even in the slightest of bends. To be fair im the same.
The issue here is of course the fact that de-acceleration on EVs can be far greater when "lifting off" which "could" cause an issue especially with dozy following drivers that see no brake lights, so again that needs a system that would need to match present IC vehicles rate of de-acceleration. In fact these days slowing down is recommended only by the foot brake not using the gears "unless" you are descending a long decent and it's advisable to select a lower gear whether in a manual or auto or decent mode in a CVT even the DAF variomatic has a low setting.

[Mark Hennessy]

In most cases, an accelerometer is involved in the decision to light the brake lights or not.

I don't know if simply touching the brake pedal over-rides that, or if you have to brake to produce a certain amount of retardation first. Different manufacturers will have different ideas.

I had a Ford Puma for a week that uses the 1.0 micro-hybrid. The normal 1.0 Ecoboost is quite a nice engine to drive, but the mild hybrid - just a 48V system, with a belt-driven alternator/motor - made it quite a bit nicer. Mild hybrids generally can't move the vehicle on battery alone, but they fill in at the bottom to give the engine more torque at revs below the point where the turbo can work, and can also assist the engine to give a bit more power, and to cover the initial turbo-lag. That enables the use of a bigger turbo, meaning more power. Currently, the 1.0 Ecoboost can do over 150 bhp with battery assistance!

We've recently gone from a normal 1.0 Ecoboost (125 BHP) to a 1.5 Ecoboost with 150 BHP. The bigger engine obviously has better low-down torque, so is much easier to "launch" and is basically effortless in traffic. Still does between 40 and 50 mpg. We got a peak of 58 mpg from the 1.0 on a long run once. The Puma did a bit better than either of our non-hybrid cars would do, which included a fair bit of town driving, so the mild hybrid definitely helps under those conditions. The tiny battery not adding weight probably helps a lot compared to a conventional self-charging hybrid (which I agree don't really make sense).

One of my recent cars had cruise control with braking. Not a full radar-based active cruise control, just something that would squeeze the brakes for you when going downhill. I wish that was more widespread - the hardware is in every car now. I don't miss the car hugely (we decided to sell it last year as it was worth what we bought it for, and we'd been thinking about going down to one car for a while), but the cruise control with braking is probably the feature I miss most. The auto box was really nice too. Plenty that I don't miss though, so we did make the right decision...

Anyway, that didn't light the brake lights ordinarily. But if you resumed cruise control from a higher speed than previously set, it would brake down to the speed (fairly gently, but positively - not harshly), and under those conditions it often lit the lights. As is the case in many cars, you could see a bit of "spill" around the high-level brake light when it is dark, so it was easy to understand how it worked. Amazing how many sensors are in modern cars - not just accelerometers for braking and stability control, but tilt sensors to help the auto gearbox adapt and light sensors, rain sensors, cameras for city safety and high-beam assist, radar for adaptive cruise and other city safety stuff. Scary really...

[ppppenguin]

Modern car  = computer(s) with 4 wheels.

You might like to see the first few pages of a small book written by one of my Imperial College tutors (John Prigmore) about electric car conversions. Not a computer in sight. I was prompted to dig this out by: https://blogs.imperial.ac.uk/videoarchiv...l-in-1972/