anyway to know when old school friction brakes are used?

Braking under 8 mph is always friction. Any hard braking is also mostly or all friction. There isn't an indicator to tell you on the dash, other than looking for the regen meter that regen brakes are being used and charging the traction pack. But that also could mean that a mix of friction and regen is going on too. Light braking is regen for the most part.

There's evidence that many have gone 130,000 miles before needing brake work, if a hybrid isn't driven hard.

 

Hybrid Assistant has an indicator and my latest video showing that has lots of braking in it...

 

I don't know of a way to do it without adding a device to create the readout.

A phone or tablet can do it as @john1701a shows above. A Scangauge can also be programmed to show stats.

The car has live data for pedal position, hydraulic pressure, regen force requested by ECU and regen force actually created. Up to you to compare these values and make a useful gauge out of it.

 

Superb illustration! Thanks.

For the record, I gather that the Hybrid Assistant is only available for Android devices.

I confess I’d been thinking about deliberately adding some sort of squeak (strictly temporary of course), just to verify that it for-sure that it doesn’t add friction braking any sooner than strictly necessary.

 

Do you have any easy way of posting the first 2-3 minutes of this at 100% speed, or even 50% speed, rather than time lapse? I’d like to see a little more timing detail on when friction braking kicks in.

 

Easy:

1. Hand wash car, and be sure to hose the wheels good.
2. Let the car sit a few days, the longer the better.
3. Go for a drive.

Due to surface rust building up on the rotors, you'll hear every time the "real" brakes are used. It'll be an eye opener.

Just go easy on the brakes, keep a good following distance, anticipate slow downs, coasting where possible, and let the car figure out the rest.

 

The simple means for you to slow the footage is to use the playback-speed feature on YouTube. Change it to 0.25x

 

It won't surprise you that the question's been taken up before on PriusChat.

The answers are "more than you'd guess", "if you think you know the simple answers you don't", and "but less than in a car with no regen."




You can see they are used at low speeds (where the MGs aren't generating enough power for useful regen), and at higher speeds (when too much regen power would be available for the battery to handle), and there are also various conditions that trigger the ECU into changing the proportions. The details change between Prius generations.

It's already been suggested that you could datalog the line pressures, etc., using the OBD-II port, but that involves periodic messages being sent over the bus, so what you see has discrete updates and a bit of a lag. Brake business happens really fast. Old-timer member hobbit once built a little circuit that tapped the pressure sensors electrically and varied the brightness of LEDs on the dash, to have a more real-time display. I don't have time at the moment to search up that thread, but it's out there.

The LEDs were saying "more than you'd guess", "if you think you know the simple answers you don't", and "but less than in a car with no regen."

 

Well, OK, but again, was kinda hoping to see a little more timing detail. Reducing the frame rate does slow down the action, but doesn’t help with timing detail. Also kinda hoping to see it slower than 1/4 speed.

Nevertheless, the stop in traffic at time index 0:58 or so is very telling. The friction brakes most definitely did not come on until the very end.

 

@ ChapmanF Thanks for remembering Hobbit, I wonder what he's driving these days.
@ john1701a Thanks for another great video, as always... The first one I've watched in slow mo. I gotta check the colors for the Energy Usage Graphic on the MID and hoping they're the same as the similar graphic on the MFD screen below.

 

What do the five green/yellow/red dots below the friction-brake icon ... indicate?

 

I have a theory. The line on the re-gen side of the meter is re-gen and friction braking. I made a picture to explain better. the yellow part is pure re-gen braking and the red is re-gen + friction brakes. It might be a palcebo effect but i always seem to get about 1-1.5% more when i stay above the line (in the yellow.)

Prime Displays Regen theory by Diemaster posted Jan 6, 2020 at 10:44 AM

 

I read that somewhere else, but I think it's not that simple. It does seem to be possible to use the full space past the dotted line and get mostly regen. Especially on the highway where maximum regen (40kw) produces a relatively gentle deceleration. It's harder to use exclusively regen as you get close to the limit because the car is more likely to activate the friction brakes, so staying above the dotted line probably just gives you some extra margin. But I don't have any good way to tell when the friction brakes are being used, so I don't know for sure.

If you press the brake pedal fast the friction brakes seem more likely to come on right away, even if the braking force is moderate. Or if the amount of regen becomes limited the friction brakes will come on. For example on my commute every morning I have to make a right turn at a traffic light at the bottom of a hill, so I have to decelerate from 55 to 25 (if turning) or 0 (if stopping). I've noticed that by the time I get to the light the Charge Current Limit often drops from 40kW to around 26kW, so presumably the friction brakes came on to help.

I also suspect that once the friction brakes come on, they stay on as long as your foot is on the pedal, even if they are no longer needed or if you back off on the pedal slightly. So if you go just past the end of the charge bar at the beginning of braking, it seems like the friction brakes will be used slightly and continue to stay active at least that much until you take your foot off the pedal.

Some indicators that the friction brakes are active: red brake icon on Hybrid Assistant, sound of the brake booster running, or scraping noise at low speed. None of them are perfectly reliable.

 

With my rusty rotors scenario, I hear the brakes every time I press the pedal. My sense is that they're almost always used, at least to some degree; with the car's computers varying the proportion, brakes vs regen.

 

I'm not sure if that's entirely accurate, since brake pads tend to always sit extremely close to the rotors. The slightest force would be enough to make the pads drag, but if they are being used significantly the rust should wear off really quickly. Sometimes I get rusty rotors from the car just sitting, but by the time I'm out of my neighborhood (two stops) I can't hear it anymore.

 

That's my experience as well.

Yes, and accordingly I think they are being used significantly.

Maybe 50/50, or some other ratio, and it likely varies.

 

See post #9 if you're visually inclined.

 

It occurred to me that this could be measured indirectly. The car seems to accurately report motor power for braking and acceleration. Someone could make an app that measures the car's deceleration and compares that to the expected amount given the braking power. The difference would presumably mostly be as a result of the friction brakes. Acceleration could be used to calibrate it to account for drag, tire pressure, etc. The main source of error I can think of would be changing drag (a gust of wind) or terrain (hills).