Want to really know when friction brakes are used ?

MrFixit

MrFixit

Well-Known Member
All:

Having obtained some Clarity PID's, and getting set up with Car Scanner, here is an example of something very cool that we can now do:

(see this thread for more of the how: https://www.insideevsforum.com/community/index.php?threads/budget-battery-capacity-readout.10531/)

Many have been interested in the nature of the Regen and the use of friction brakes. There is a parameter that can answer this question once and for all !! Among the wealth of OBD2 parameters, there is the brake pressure. This is a sensor in the hydraulic system that can truly indicate when friction brakes are actually being applied. There is also a brake switch which indicates exactly when you just begin to touch the brake pedal. This, coupled with vehicle speed and the HV battery current (indicative of when regen is occurring) can make for some very interesting displays...

I recorded these parameters during a drive yesterday. This example is just scratching the surface of what we can do with this new-found instrumentation...

I am going to show you two examples. First, a "normal" stop from 55 mph to zero in around 25 seconds. This was approaching a light that we knew was red from a long distance away...

upload_2021-3-13_8-23-55.webp
At around 520 seconds, our speed begins to drop. The brakes are applied (red curve - look at the flat value of 10, ignoring the spikes). The Regen kicks in (-50 amps, secondary axis). The car reaches virtually 0 mph before the brake pressure shows application of friction brakes. The friction brakes are only engaged in this case while the vehicle is stopped and we are waiting for the light to turn green.

Now - Here is a "Panic Stop" where the light changed unexpectedly and we stopped very quickly (this time from about 35 mph to zero in about 5 seconds...
upload_2021-3-13_8-28-34.webp
In this case, the brakes are applied (red, ignore the spikes). The friction brakes kick on immediately up to 20 bars (~300 psi). Regen is also applied (-40 amps). After we are stopped, the brake pressure again goes up to 10 bars just to hold the vehicle while waiting for a green light again.

These parameters were recorded using Car Scanner, and exporting a .csv file for plotting in a spreadsheet. During the drive, all this was visible real-time on a 'dashboard' within Car Scanner.

Note, on our drive, I saw HV Battery current that ranged from -120 Amps (very high regen) to +200 Amps (high acceleration). The first 4 ticks on the dash display corresponded to 30, 60, 120, and 200 Amps.
 
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WOW! This is some incredible data and I'd love to see more examples when you can provide them. I'm a former physics teacher so these kinds of velocity/time graphs + EV data is fun for me to analyze!

One question I had in regard to your "normal" stop - how much brake pressure were you applying during the deceleration? It doesn't seem like it was much. The chart shows a pretty constant deceleration from 50 mph beginning at about the 517 second mark (and you can see -20 A regen beginning at that mark, which suggest that you lifted off the throttle at that point). The brake switch doesn't activate until about the 524 second mark, and I don't see much change in the deceleration at that point. So it seems to me that this was pretty light braking for this example, with all of the slowing being done by regenerative braking only until the car comes to a stop.

It would be really interesting to see an example that is somewhere between this light braking case and the second "Panic Stop" example that you provided.
 
Amazing awesome work finding and experimenting with all this data! I think your normal stop data confirms that there isn't an energy efficiency difference between slowing using the paddles to induce regeneration and using the brake gently to achieve the same level of deceleration. Nothing wrong with using the paddles (I do occasionally and find myself missing the paddles on our other cars), but also perfectly fine to just drive and brake with your foot as always.

I know I was suspicious because the Clarity has far a smoother feel on the brake pedal than other hybrids I've driven. On our Highlander Hybrid you feel the brake pedal "tighten" and "loosen" as you use them, and the Chevy Bolt I tried was disconcerting how as you came close to a stop it felt like the brakes released and needed significantly more pressure to keep slowing. The Clarity feels just as linear as my non-hybrid Civic, making me wonder if it applied some friction braking always to better mix, but if it does it's negligible.
 
Kendalf said:
So it seems to me that this was pretty light braking for this example, with all of the slowing being done by regenerative braking only until the car comes to a stop
Click to expand...

Yes, that was the point of this example. It's not like we contrived this situation.
In fact, it was my wife driving, and she had no idea what I was doing with all the graphs on my tablet.
This was a normal reaction to a common driving situation (as was the 'panic' example). The light just happened to turn red and she chose to stop pretty abruptly. I may have sped up to beat the light !
 
This makes sense, and I love the data, keep it coming!

Do you have any compilation yet of how much power increases when different features of the car are used, like heat, AC, seat warmers etc?
 
Dislin said:
This makes sense, and I love the data, keep it coming!

Do you have any compilation yet of how much power increases when different features of the car are used, like heat, AC, seat warmers etc?
Click to expand...

Not yet... We only recently acquired this kind of capability. These are also interesting questions.
I have observed however, that it is not always clear what the impact of any individual load is. It is a little tricky because this is all pretty dynamic and loads are coming and going. If you just watch the current without intentionally changing anything, it varies some and thus it is sometimes hard to isolate an individual contributor.

You are of course welcome to join us in investigating what you find the most interesting. The two threads about how to do this should be helpful, and we are happy to assist if you encounter any obstacles.
 
MrFixit said:
Not yet... We only recently acquired this kind of capability. These are also interesting questions.
I have observed however, that it is not always clear what the impact of any individual load is. It is a little tricky because this is all pretty dynamic and loads are coming and going. If you just watch the current without intentionally changing anything, it varies some and thus it is sometimes hard to isolate an individual contributor.

You are of course welcome to join us in investigating what you find the most interesting. The two threads about how to do this should be helpful, and we are happy to assist if you encounter any obstacles.
Click to expand...
Are you in an area with a winter? I think playing with the heater temperatures while you are at a steady speed in HV would be very good info. The manual seems to indicate that no electric heat should be used when engine heat is available but the reduction in mpg in winter seems to potentially indicate otherwise.
 
Yes, this would be an interesting test.
It is cold here.

To minimize the number of variables, I think the test could be done while stopped. On a cold day, before leaving, turn on the heater for maybe 30 seconds and record the current. Then go for a drive in HV to get the engine warmed up well. Then stop somewhere and turn on the heater for another 30 seconds while recording the current.
 
I don't know who wrote this article, but this statement makes NO sense:

"For electric vehicles (EVs), fuel economy can drop roughly 39% in mixed city and highway driving,
and range can drop by 41%. About two-thirds of the extra energy consumed is used to heat the cabin"

This person needs to be informed that EV's do not use any fuel.
 
BTW - Don't forget that you can convert Watts to HP.

Although the friction brake plots did not show it, I was also recording HV battery voltage. While I (my wife) never pushed acceleration, we did hit a peak current of 188 Amps. At that time, the HV Battery voltage was 325.5 Volts. This equates to 61.2 kW or 82 Horsepower.

The Clarity traction motor is supposedly capable of 181 HP. To obtain this (with a 325V battery), you would need to draw ~135 kW (or 415 Amps)

The next time I go out recording, I will capture these values while flooring the car (in normal mode, so the engine doesn't come on). Stay tuned.
 
MrFixit said:
I don't know who wrote this article, but this statement makes NO sense:

"For electric vehicles (EVs), fuel economy can drop roughly 39% in mixed city and highway driving,
and range can drop by 41%. About two-thirds of the extra energy consumed is used to heat the cabin"

This person needs to be informed that EV's do not use any fuel.
Click to expand...

That would be our government at work. The same ones that brought us MPGe. It is reasonable, in my opinion, to consider electricity a fuel. They did state “fuel economy” not gas mileage.
 
MrFixit said:
The next time I go out recording, I will capture these values while flooring the car (in normal mode, so the engine doesn't come on). Stay tuned.
Click to expand...

Without the engine coming on, you should see numbers that equate to 121hp. Presumably, that is the maximum amount of horsepower the electric motor can produce from the electricity provided by the batteries. The rest of the current to produce the 181hp figure,would be provided by the generator.
 
MrFixit said:
I don't know who wrote this article, but this statement makes NO sense:

"For electric vehicles (EVs), fuel economy can drop roughly 39% in mixed city and highway driving,
and range can drop by 41%. About two-thirds of the extra energy consumed is used to heat the cabin"

This person needs to be informed that EV's do not use any fuel.
Click to expand...
Electricity is the fuel.
If they did not use any fuel they would be perpetual motion machines.
 
Well, I had good intentions of doing the heater testing (Power consumption of the heater with a cold ICE and with a hot ICE). Unfortunately a technical error on my part resulted in no data when I had gotten the ICE warmed up.

I do have data with a cold scenario with the heater turned on, then off...

upload_2021-3-15_17-7-50.webp
Parked in the garage, and powered on. Turned heater on for ~ 30 seconds.
I would call the current ~ 18 Amps. The HV Voltage was 342 yielding a load of 6.2 kW.
This is quite hefty (as expected).

Will try again to do this same thing with a warmed-up ICE to see if the vehicle effectively uses the waste heat instead of the electric resistance heaters.
 
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