We get a lot of questions about the braking system. Here is how it really works.
- Coasting without braking is not a braking function and is performed entirely by the EVC (the motor management computer);
- As the driver starts pushing the brake pedal, the requested torque is computed by the UBP (braking computer) based on main cylinder pressure and pedal position. This requested torque is passed to the ESC (the ABS computer that controls the oil valves to the friction brakes);
- The EVC permanently sends messages to the UBP stating the maximum torque of the motor. This is determined by gear, SOC and temperature;
- The UPB requests the EVC to apply braking torque. In principle this is the same as the driver requested torque, up until the maximum the motor can deliver;
- The EVC sends the truly applied torque to the ESC. The ESC computes the difference and applies friction braking for any difference.
Note that if you put the car in N, no motor braking is possible and the ESC will command all braking through the friction brakes.
In normal operation this means braking is almost entirely regenerative, with the following exceptions:
- very fast braking: the hydraulic system is faster than the electrical system (see below for some more details);
- very powerful braking: the hydraulic brakes are more capable than the electrical system;
- related to the above: if fast, powerful braking is applied, it’s hydraulics all the way as the car might want to apply any form of EPS which requires individual control of all 4 wheels;
- when the electrical system cannot apply the requested torque (max charging power reached, you can see this in the driving and braking screen);
- at very low speeds, when the motor simply cannot brake.
Here is a revealing graph: yellow (hard to see, hidden under purple and red) line is the driver requested torque. The blue line is the regenerative torque and you can see the hydraulic system (red line) compensating for any difference. Note that the final cut over is at a very low energy state (roughly last half second before full stop, 10% of the time, 1% of the energy).
*) Other than this graph shows, when serious braking is applied very fast (3rd bullet above), and therefore, the hydraulics kick in immediately and substantially, they are not released anymore and replaced by motor torque. So, for economical, max regen braking, it is better to not only push the braking pedal not too deep, but do do it gently too.
ps: look here for a description of the computers in the Zoe.
pps: there is a ton of information in this document on scribd.
ppps: Here is some more info on braking.
We have some exciting news this week.
CanZE is now available in the Google Play Store. Once installed that way, updates will come to you a tiny bit slower, but fully automated. We will maintain a weekly release schedule as long as features are changed or added as frequently as they are now. When we’re confident that the updates in the Play Store come through fast enough, we might close the download page here.
We were able to shed a lot of code that was no longer necessary, meaning easier to maintain, and less error prone. We hope to have added again a bit of stability.
Also, we have gained a lot of information about the Zoe this week, straight from Renault. Consequently, we also now know that a few things in CanZE are simply wrong. Friction braking is far smarter in the car than we anticipated, and that code needs to be rewritten. The information
came in too late to make to this weeks release, just know that the friction braking bars are not correct for now JUST made it in time for today’s release.
Also, the firmware screen was unfortunately picking up a wrong field. This has been corrected, but of course we need to work on reference versions again based on your input. Please do report newer versions if you see them in your car.
Today I have spoken with a Renault specialist and to make a long story short: my definition of friction braking is WRONG. In normal operation, the brake system is entirely “fly by wire” and does not perform friction braking as CanZE reports. I will fix this, but I doubt it will make this weekend-release. Long story short, Zoe uses far more motor braking than anticipated. To be continued.
The weekly build we have coming up for you is mostly one of serious un-cluttering. We have moved all experimental and playground stuff out of the way and to a new screen. This can be accessed through the “three dots” menu, just next to the settings. Developers now have each have their own playground. Go there at your own risk!
A very nice enhancement is that time-plots are now saved, so their data is not lost when switching screens.
The driving screen now displays a real time kWh/km. I’ve been running this for a few drives and I’d say it is more pressing than the raw kW in the dash. Quite the eye opener!
For the UK drivers, there is now a “Miles” tick in the settings screen, and it already works for the text based screens.
Maybe somewhat boring but still worthy news is that we have significantly stabilized and speed up ELM again. And as we’re getting more confident about CanZE restoring order when things go wrong, there is now an option in the setting screen to change the log level, enabling you to get rid of those blasted warnings popping up. For the daring, builder people, the Due based hardware is getting more integrated too and is VERY responsive. See Bob’s blog post below this one.
We discovered that Firmware versions can be dependant on the hardware version of certain components. We’re not ready to take up that challenge for several reasons. Just know that the dealer might be right if he tells you that really no, there is no update for your car while CanZE says there is.
Enjoy and stay tuned!
Here’s a little video I made (no good conditions I know), but it should be enough to show how fast the custom based interface is compared to the ELM327.
Don’t forget: buying a ELM327 is cheaper and does not need to build anything at all and for 90% of the users this is enough.