phidauex

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In my theme of trying to answer common questions about MachE behavior with actual data, here are the results of an hour long drive up the Colorado front range, with a few interesting data points logged.

In particular, I was watching Brake Pressure, which tells us the pressure at the brake master cylinder. The pressure is 0 bar when the hydraulic brakes are not engaged, but goes up to 5+ bar as the hydraulic brakes engage. This lets us tell exactly when the system decides to apply friction braking, because it doesn't change with the pedal position, it changes with the actual pad engagement.

What I can now say with confidence is that in 1 PD mode, in Whisper, Engage or Unbridled, the MachE will not apply friction brakes at all (not including collision avoidance). It simply doesn't, even when coming to a complete stop. If you look at my datalog, I applied the brakes before leaving, just to show the data spiking, and I applied them once at a stoplight where I pushed the brake pedal firmly. All the rest of the driving, through three cities, was just in Unbridled 1PD, in quite a bit of stop and go. I let off the pedal entirely many times, and several times applied the brake pedal directly, and even with moderate pressure on the brake pedal the friction brakes never engaged, except for the one time when I was already at a complete stop. I made no attempt to hypermile - it was too busy to drive very fast, but I just drove it like a normal car and didn't think about optimizing regen or anything.

What does this mean by the numbers? The maximum deceleration achieved in 1PD without touching the brake pedal is 0.2g. Pressing the brake pedal got me to 0.3g without the friction brakes. Maximum regen power was 91kW. I'll take some more logs later where I actually apply more and more brake pedal to see at what deceleration the brakes will actually come on.

Over 50 miles, the system regenerated about 22% of the total energy consumed, which is pretty impressive. My mi/kWh would have been about 2.29 mi/kwh, but regeneration brought it back up to 2.92 mi/kwh. (Note that these values are fairly coarse because I didn't measure the Energy Remaining field directly, but instead am integrating over 560ms datapoints, with some error). More important is the relative percentages.

I was having trouble logging the battery temperature points (something is acting up in CarScanner), but I was able to spot check them and was seeing favorable values around 30C.

Attached is the full datalog for your amusement, and some stats from the drive below.

Ford Mustang Mach-E Mach-E Brake Pressure Data for Each Drive Mode 1636510429203
 

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Mach-Lee

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Wondering if perhaps the pressure sensor was only measuring the input hydraulic pressure rather than the output pressure? The HCU is very complicated so it wouldn't surprise me if the input pressure is kept isolated from the output. I find it suspicious that you didn't see any hydraulic braking under 3 mph or during collision avoidance, I would expect it in those situations. I don't think it can hold the car still using the motors alone?

What does it do during ABS engagement? You should see huge pressure fluctuations obviously.
 

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Great info. Nice to see hard data that explains what the car is doing. I'm very interested to see the comparison to 2 pedal driving. Thanks for doing this and posting your results.
 
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phidauex

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Wondering if perhaps the pressure sensor was only measuring the input hydraulic pressure rather than the output pressure? The HCU is very complicated so it wouldn't surprise me if the input pressure is kept isolated from the output. I find it suspicious that you didn't see any hydraulic braking under 3 mph or during collision avoidance, I would expect it in those situations. I don't think it can hold the car still using the motors alone?

What does it do during ABS engagement? You should see huge pressure fluctuations obviously.
Iā€™ve been watching the point for a few weeks, and comparing it against the pedal position point, and the brake light switch point, and Iā€™m fairly certain it is showing actual brake system pressure. Would there really be two hydraulic systems operating at different pressures? I havenā€™t collected data during any collision avoidance events (trying not to trigger those lightly, lol) but Iā€™m assuming the brakes would hit then for sure.

I suppose I could prove it by putting a sharpie dot on one of the rotors and then doing a few 60-0 mph 1PD slow-downs.

ABS would be interesting to test as well, maybe I can get it out on a loose gravel road and do some hard stops from 30mph or so to trigger ABS. Should get snow here soon which will help too. Iā€™ll try to collect some data on our first sloppy day here.
 

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Sharpie test is a good idea.
I pretty sure I saw ABS signal around 3 mph or so......right about the same time as when the Brake Coach appears.

Where does all the brake dust come from if the friction brakes aren't being applied?
 


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I've always assumed 1PD never touched friction braking, it never really feels like its using the friction brakes. Good to see actual data that shows it.

I would assume my MME uses the 1PD "brakes" 95% of the time. I hardly EVER touch my actual brake when driving. Now when using cruise control, I'd assume its using the friction brakes a lot more when its adjusting speeds, and that could be where the dust is coming from. I dunno about everyone else, but my MME likes to drive like a 16yr old who just got their license when on cruise control in moderate to heavy interstate traffic. My wife can tell every time I have it turned on, it does not give a very smooth experience. I would also bet if someone is prone to getting car sick, the MME would do it with the CoPilot turned on.
 
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phidauex

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Sharpie test is a good idea.
I pretty sure I saw ABS signal around 3 mph or so......right about the same time as when the Brake Coach appears.

Where does all the brake dust come from if the friction brakes aren't being applied?
I can see there is some skepticism so Iā€™ll do a sharpie test this week. That said, I really donā€™t see much brake dust at all, and my brakes seem to have a light rust film on them most of the time, so it might be driving style or the traffic situation that people are in that would be causing more brake usage.
 

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I can see there is some skepticism so Iā€™ll do a sharpie test this week. That said, I really donā€™t see much brake dust at all, and my brakes seem to have a light rust film on them most of the time, so it might be driving style or the traffic situation that people are in that would be causing more brake usage.
I haven't seen the data log yet.....Will try and download it tomorrow. Is it showing a spike in energy consumption and thermal gain from 3 mph to dead stop? Electric motors can come to a complete stop but they need quite a bit of energy to do that......more than is harvested through regen at those very slow speeds. At least from what I know about them anyway. Doesn't seem like a benefit to consume more energy to come to a complete stop when friction brakes can finish the job for those last few feet. Why throw some of that recovered energy out the window?
 

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What I can now say with confidence is that in 1 PD mode, in Whisper, Engage or Unbridled, the MachE will not apply friction brakes at all (not including collision avoidance). It simply doesn't, even when coming to a complete stop.
Yes, this is exactly what I would expect.
 
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phidauex

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I haven't seen the data log yet.....Will try and download it tomorrow. Is it showing a spike in energy consumption and thermal gain from 3 mph to dead stop? Electric motors can come to a complete stop but they need quite a bit of energy to do that......more than is harvested through regen at those very slow speeds. At least from what I know about them anyway. Doesn't seem like a benefit to consume more energy to come to a complete stop when friction brakes can finish the job for those last few feet. Why throw some of that recovered energy out the window?
No obvious change in power or heat as you approach 0mph, but I donā€™t think youā€™d see it in the logs anyway - there is very little energy at low speeds, and the thermal mass of all the components with temperature sensors is huge.

One thing to note is that for the ā€˜22 model Ford is getting rid of the parking pawl, relying entirely on an electronic braking mechanism. Not sure if that is in the motor or if it is on the rear friction brakes.

Is anyone aware of any other useful brake-related PIDs? There are ABS speed sensors, but Iā€™m not seeing any others of obvious utility.
 

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OK, @breeves002 and I just did an FDRS session to look at the brake pressure. In FDRS there are separate parameters for each wheel's brake pressure. I can confirm the input pressure from the pedal and the output pressure to the wheels are different as I suspected because the HCU decides what it's going to output. In terms of one-pedal, it does not apply brakes at all until just after you come to a stop (slight delay). So you might feel like you roll for a half sec before the brakes grab. Probably more noticeable stopping on a hill. Brake pressure in the wheels is released as you press the accelerator pedal after a stop.

So no brake blending is happening in one-pedal.
 

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One thing to note is that for the ā€˜22 model Ford is getting rid of the parking pawl, relying entirely on an electronic braking mechanism. Not sure if that is in the motor or if it is on the rear friction brakes.
I don't believe this is confirmed. It would honestly surprise me because that's a decent amount of engineering work and possible tooling for only 1 year of use. I think it may be more expensive than leaving it in for a few years. Also it is still in the service manual for the 2022 model year.

If they did get rid of the pawl, it would just use the parking brake to hold the car when you put it in park.
 

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@phidauex , sorry if I didn't understand this correct, what was your SOC? If you can regen 91kW. I have noticed in my previous EV's regen was weak at high state of charge.
I usually charge to 90% and have a lot of brake dust while I drive mostly conservative.
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