Feel force Regen -> Friction on demand

So I was driving home from work yesterday and was wondering what it feels like when you go from full regen braking to pure friction brake, and realized it would be easy to force the car to dump regen while braking so I could feel this transition.

-> Put it into neutral at the right moment

So I set it up -- slowing down and got the regen up to about 600 on my SGII, and pushed it into neutral while keeping constant pressure on the brake pedal. (Neutral free wheels the motors, hence you have zero regen.)

The first time I did this, it felt like I took my foot off the brake pedal. I had very little braking. Odd. That would have certainly resulted in the feeling people have felt with the brake issue.

Since I was going only about 12mph at this time on an empty street, no danger..... A little more pressure and the car stopped normally.

So I did several more runs .... and all I can say is the ECU must have learned something after the first try, because every time after that the transition was perfect. I can feel a very slight blip (a passenger wouldn't even be able to feel it) as the ECU ramps up friction braking to match what I had with regen -- and it was flawless. Braking force was a perfect match and the car slowed normally. I found this pretty amazing the car could gauge exactly how much pressure to apply so you could hardly notice a change!

The car's broke and ICE throttle control is definitely adaptive. I had to reset the battery this past weekend and on the first restart, it was like the ECU didn't know how to properly control the ICE as the idle speed was all crazy. (Much higher than normal and fluctuating.) Also braking felt strange with awkward transitions and braking force changes when slowing down.

So on Sunday I took the car up to Mulholland to "school it" with some high speed "spirited" driving with lots of WOT and heavy braking. I even used the ABS several times as lots of dirt and sand had accumulated on the road, so I took that opportunity to lock up individual wheels. The first ABS application felt strange, with what felt like a very brief loss of braking force even though only the right front wheel was on the sand..... But after that, ABS activations were totally normal and working properly, with the car modulating the slipping wheel while still applying lots of pressure to the other wheels. (When you lose braking traction on a front wheel, you do loose about 40% of your stopping force ... you can't change the laws of physics.)

I love adaptive systems!!

PS: The stability control program on the Prius Gen III is nice in that it isn't hyper sensitive. I expected to activate the alarm while cornering over some sand an dirt a few times.... when hitting the dirt mid corner, the car of course slides out until you hit clean tarmac again ... and I did this a few times without any bothersome warnings or intervention by the car.

 

Back in the "analog" car days, WOT = wide open throttle AKA gas pedal floored.

 

I didn't mean adaptive to the driver -- it's adaptive to the mechanical systems in the car. Any time you are controlling variable analog mechanical devices with electronics and software, you have to be able to adapt. The ratio of stopping force provided by X amount of pressure on each caliper isn't constant, and certainly varies car to car and over time on the same car. Then if you, for instance, change the brake pads to a different brand, they could provide more or less braking force for the same pressure with the old pads. So for a little while the transition from regen to friction might be odd, as the computer expects one thing but something else is happening. I presume the ECU uses the G-force sensors to detect unusual behavior and it starts to compensate by applying the correct amount of pressure when you stop to make the transition seamless.

Think about it this way: If you are used to driving your Prius in ECO mode (with its insensitive throttle pedal) -- and then you get into a rental car with a typical very sensitive throttle, you will probably need a minute or two to adapt to the super sensitive throttle. Once you do, you will be able to start off smoothly from a light.

Same goes for the brakes or steering when you go from car to car. These are analog things and the only way you can figure them out is to try them out a few times. Then you can adapt.

It's the same with the Prius ..... and when you unplug the 12v battery, it forgets what it has learned and has to re-adapt. It doesn't take long before it's mostly adapted, but some situations don't happen very often so it never has a chance to learn them.

By putting the car's mechanical systems through their range of operation, you can help the ECU's learn about how they behave. Kind of like driving a car at the limit.... A driver will never know how a car behaves in a skid if they don't try it out (in a controlled environment, of course.)

Non hybrid cars have a 1:1 mapping between the gas pedal and the physical throttle plate. (Ok, often not 1:1 on new cars as they have curves and sport mode and what not ...) If you put a normal car in neutral and push the pedal down 10%, you might get 5000rpm.... but on another of the same model car, you might get 5500rpm. This difference is unimportant because in day to day operation the car will feel the same to the driver. (Going from one to another.)

But since the Prius ECU sets the engine RPM to a specific value, it needs to know exactly how much to open that throttle to attain that very specific RPM. (Depending on needs ... like charging, battery level, power requested.) The first time you turn on the Prius after the battery has been removed, it doesn't know how much to open the throttle plate so it goes overboard and the revs go way above where they should be ... then it beeps backing off until it gets to the right RPM. It didn't take long for it to learn and soon after when the ICE started to warm up, it went right to 1280rpm without any wasted revving.

Smart stuff!

 

Still on original firmware.

 

The XGAUGE 'RGO' shows you 'Regen Braking Operation' -- This is the actual braking force in NM being provided by MG2 as reported to the ABS ECU.

The other XGAUGE 'RGR' is the requested regen braking force from the ABS ECU to the HV ECU. The numbers are usually pretty similar.

I haven't tried but I should look at RGR and RGO at the same time, then dump the regen by going to neutral and RGO should drop to 0 while RGR should still show the requested value. (Unless, of course, the HV ECU tells the ABS ECU that regen is no longer available so RGR might drop to 0 as well.)

The SGII is the ScanGauge II, by the way.

 

I totally agree. In California, it's so easy to get your driver's license .. it's a bit of a joke. There are lots of people driving around that are utterly clueless.

 

Do you feel a very slight blip?

I did the test again on the way to work yesterday and it was perfect every time. Negative g's felt exactly the same with regen and friction with just the very slight blip at the exact moment of transition. (Seat of the pants) It's so quick it's hard to know for sure, but it feels like just milliseconds of reduced braking force. I could not get it to give me the bad transition again as Fuzzy was able to... just the very first time I tried it.

I will be interested to see your analysis of your high res accelerometer.

 

I have the data to make it now ..... and nope, during regen there is no hydraulic pressure unless you need more braking force than can be provided.

I put up a graph (and my thoughts) on this post:

http://priuschat.com/forums/gen-iii...cussion/76690-regen-braking-observations.html