OK, maybe I am a non-friction-braking junkie.

Today, I had a discussion with a friend who owns a Tesla model S. The single motor type, but with the complete performance pack. As we started to talk about braking, we figured the S’s stategy is quite different than on the Zoe and is actually closer to the Fluence and Kangoo. In simple terms, on the S, touching the braking pedal does friction braking, period. Regeneration is applied through not, or barely touching the accelerator. He calls this “one foot driving”.

He also told me the “average” tesla driver doesn’t do any aiming-braking. With that I mean unpowered coasting, letting the motor basically run free. It seems to be popular with Fluence hyperdrivers to avoid the regen-use cycle.  I have to assume this is because hyperdriving is less of an issue with a 80kW battery.

The regenerative braking strategy itself is different too. The Zoe seems to aim at fixed torque, mimicking a traditional car. It is transparent to the driver if that torque is generated through regeneration or friction braking. The S seems to aim at a fixed regeneration power level (up to 60kW, which is lower than the Zoe per kg). As I explained in the previous post, that means increasing torque as the speed bleeds off. When the car reaches roughly 50km/h it seems to switch to constant torque, probably as otherwise the braking would get too brisk and uncomfortable. It is an interesting approach (irrespective to whether it is controlled through a braking pedal or not) as it is the behaviour I am trying to mimic through following the blue bar in the driving screen.

I got an interesting question about the blue “Aim bar” in the new driving screen. Confusion arose how, when increasing speed, the maximum braking torque aim bar actually shrinks, while common sense would dictate it should stay the same or even grow a bit.

Well, common sense is not always right! Assume we are running at a speed where the motor itself can apply it’s maximum braking torque. The power this potential braking would generate is the torque multiplied by the angular velocity. So, as the speed of the vehicle goes up, by definition, the power regenerated with this maximum torque goes up too. Pretty quickly we will hit the limit of the battery: 43kW, and that is under ideal circumstances. At any speed above that, you’d have to actually decrease torque not to go over this maximum, and this is exactly what the power management does and what is displayed through the blue bar..

Consequently, if you “follow” the bar coming down from i.e. 120 km/h, you will find you’ll easily hit that maximum with only a little bit of braking pressure. While speed bleeds off you’ll find yourself braking harder and harder following the blue bar, chasing the maximum power. That goes on until you reach the maximum torque the motor itself can apply. For a short moment, this is a fixed value. As the car decelerates further, now at a constant rate, at constant pedal pressure and with decreasing power generation, it reaches the point where the motor is simply turning too slowly to apply its maximum generating torque and the ability to brake through the motor collapses. I you don’t do anything, the friction brakes will kick in. This is the “traffic light effect”.

Hope this helps.

When time is money (both re. your own time as well as how the operator calculates the rates), the following guidelines will help you, especially in winter. The’re all fairly obvious:

1. Try to avoid fast-charging starting at a high SOC to avoid entering the area where the car squeezes the charging power. This squeezing can start as low as 35% SOC when it is cold. Drive as far as possible to keep the charging power high for as long as possible.

2. Try to charge with the highest possible battery compartment temperatures. As driving increases the temperature substantially, try to fast-charge at the end of a drive, not i.e. the following morning. Fast charging itself also increases the temperature.

3. Quit fast charging as soon as you can. If there is a slow-charger at your destination, just fast charge until you can reach it.  This ensures fast-charging at the highest possible power and trades “real” waiting time (twisting thumbs) against “virtual” waiting time (car is charging for a longer time, but you’re not waiting for it doing nothing).

A rule of thumb is that squeezing from 43 kW starts at 30% SOC plus twice the battery compartment temperature for a Q210, and from 22 kW at 65% SOC plus the battery temperature for an R240. Note that this is for the 22 kWh battery. The 41 kWh battery behaves substantially different, but we don’t have enough data yet.

With less new functions being added, a focus on getting things more stable and life beyond things CanZE requiring at least some attention, we are changing our release schedule. Today’s release will be the last mandatory Sunday release and we’ll decide on a per-case basis if a new release is warranted.

Not many visible changes this week. Small changes on the charging and driving screen based on user feedback. In the experimental section, we added s tyres screen for cars equiped with TPMS. If you happen to have this feature on your car, give it a spin and let us know the results through github please (issue #235).

Under the hood we’re still working on strange Bluetooth instabilities and getting things back on track for the Kangoo and Fluence, which needs a lot of research.

We’re also working very hard on getting all the info we have (and not just the fields we use in CanZE today) in our database. It is a lot of tedious, lonely work but it is needed to move on.

 

You will not find many obvious changes this week’s release. We’ve taken a small step back from the rather crazy development cycle and the rest of our efforts have been focussed on fixing issues.

It seems we’ve been pushing the ELM a bit too hard; CanZE appears to freeze now and then, though it is usually the communication between the CanZE and the ELM. Please know it has our full attention, but it’s a hard one to crack as it’s really a bit of a random issue. We believe we’ve made some improvements though. Keep us updated (through github please!) and send us your logs please as it helps is pinning down what’s going on.

We’ve split the “Experimental” section into “Experimental” and “Technical”. Technical contains screens that should work, but are for the users that want to dig a bit deeper. At the same time, we’re cleaning up the “Main” activities to only display the information that matters most.

The Cell Voltages Heatmap has a new function that you should actually never see: if a cell turns bright red, it means it has a serious problem. The algorithm used is borrowed from Nissan: If the delta between the mean and lowest cell voltage is greater than then 1.5 times the delta between the mean and the highest cell voltage, it is considered bad. This check is only valid (and will only be performed) if the pack’s SOC is roughly 25% or lower.

EDIT: I was not aware that the Leaf uses a different chemistry for the battery than the Zoe. The red cell algorithm used may, or may not be valid. Don’t rely on it.

Here is a (faked) example

Screenshot_2015-11-15-23-18-41 (1)

Have a great remainder of your weekend!

Last weeks release was not very stable with respect to the Bluetooth connection. A lot has been done to improve that, but if you have still have problems, please switch on “log to sdcard” in the new setting screen, so we might find some more remedies with the extra logs.

The Consumption screen has changed a lot and we hope you like it!

We removed a lot of overly technical information for the charging and braking screens based on feedback we got. Things are simpler now and more focussed on the things that matter. The old charging screen is still available in the experimental screen and we’re contemplating creating a third menu screen called “Technical” for the more detailed information.

As always, we appreciate your feedback. Enjoy!

This week we have above and under the hood developments for you.

We’ve added two heat-maps, giving a quick overview of your battery temperatures and voltages. Those will give you immediate insight in the overall stability of your battery pack: the colors indicate the deviation of the mean temperature / voltage.

Data for graphs is now retained much longer so your graphs will simply continue once you restart them.

Then there are some graphical updates, a bit better handling of different screen sizes. Also we’ve become a bit more aware of potential licensing issues so you might notice some different wording, removal of copyrighted graphics, stuff like that.

Of course there has been the usual bug fixing but we’ve also improved on the differences between the Zoe, Fluence and Kangoo.

Under the hood significant changes going are on. We’re constantly optimizing speed and memory usage and there are a lot of technical changes that you will notice above the hood too. One notable change is the ability to differentiate better between slow changing parameters, such as temperatures, and fast changing ones, such as speed. This way we can optimize display speed for the fast changing ones.

Also, there is now a setting to let CanZE continue to run in the background instead of closing or pausing. Note that this will use significantly more power on the device.

These enhancements create even more possibilities that we will announce and implement later.

DTC readout is already working for a few ECU’s, you can try in the experimental section (at your own risk!). It certainly works for the TCU (Telematics) and the CLUSTER (instrument panel).

We get a lot of questions about the braking system. Here is how it really works.

Zoe braking system

  • 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).

brake

*) 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.