Mach-E Brake Pressure Data for Each Drive Mode

[phidauex]

In 1PD, is there measurable energy harvesting all the way to zero mph?

Yes, it is a bit hard to catch, since there is an overhead draw of around 2kW on the battery, but I’m seeing values as low as 0.8 kW of regen all the way down to 2 to 0 mph on a very gentle coast. It does appear to be using regen all the way to the end.

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[phidauex]

Fascinating thread. I continue to be impressed by what I would call the “engineering” skills (for lack of a better phrase) of folks here and their willingness to roll up their sleeves and probe the inner workings of the MME to educate us. So here’s perhaps a dumb question but I don’t think I’ve seen it addressed: what happens if you depress the accelerator pedal and the brake pedal at the same time? Does it depend on how much pressure you put on the brake pedal? This is something one can do in an ICE vehicle (simultaneously brake and rev the engine) both with manual transmission (heel and toe shifting) and I think even with automatics, but was wondering what would happen with the MME.

Thanks, I think for many of us we work all day engineering one kind of system, and then for fun go reverse engineer another after work… I do work on grid scale battery systems, but automotive applications are relatively new to me.

As for brake-holding, people have been using that as a launch technique - press the brake firmly, push the accelerator all the way down, feel the power build as the motors try to fight the brakes, then release the brakes to get a faster launch. Unlike an ICE vehicle, there is nothing to slip - no clutch or torque converter, so what happens is the motors just build up current trying to move (same as it would if you were pulling something, or starting on a steep hill).

Presumably if you held it too long the motors would back off on their own to prevent overheating, but for the half-second the brake hold is in effect the motors will still try to turn. This results in a slightly faster launch since the initial current-ramp has already happened.

I don’t have great data on it since some of that happens faster than the 0.5s most of my logs are at, but in my driving dynamics thread (link in the OP) there is a datalog showing a few launches, one of which is using the brake hold. You can see power spike before the vehicle starts moving, then a rapid acceleration once I let off the pedal. Still probably not a great thing to do to the car, but probably less damaging than doing it to an automatic.

 

[SnBGC]

Yes, it is a bit hard to catch, since there is an overhead draw of around 2kW on the battery, but I’m seeing values as low as 0.8 kW of regen all the way down to 2 to 0 mph on a very gentle coast. It does appear to be using regen all the way to the end.

Interesting.
Have you tried the sharpie test with 1PD turned off as well? When does energy harvesting stop with 1PD turned off? Does the overhead remain the same 2kW down to zero with 1PD off?

 

[phidauex]

Interesting.
Have you tried the sharpie test with 1PD turned off as well? When does energy harvesting stop with 1PD turned off? Does the overhead remain the same 2kW down to zero with 1PD off?

I haven’t done any tests with 1PD off, though it is a good idea. I’d think that 1PD being off won’t use the friction brakes on coasting either, since it slows down more gradually than in 1PD (feels more like a “regular car” coasting down). It might use brakes differently when pressing the brake pedal, but I suspect not - the efficiency doesn’t seem wildly different between 1PD and normal, meaning it still has to be mostly slowing with regen (if it wasn’t, the consumption would be up to 20% more with 1PD off, which I think everyone would notice).

The overhead tends to remain the same based on the climate situation. In today’s case, it was cool out, I had the heat set to auto 2, 68F, seat heater low. I’ve seen overheads as low as 800W when there is no climate control going on, and as high as 2.5-3 kW when the AC is blasting.

 

[breeves002]

From all this, I’m still standing by my original claim that 1PD does not use the friction brakes, unless you are already stopped (as confirmed by @Mach-Lee and @breeves002), or unless traction control, collision avoidance, or some other system is taking over (still needs some testing).

Great work, I think this is solved for any AWD Mach E - GT included.

The only variable is RWD only models. Since they don't have a front motor to regen...does it blend the friction brakes, especially in unbridled, to add additional stopping power? My guess is no but I would like someone to find out

 

[breeves002]

Interesting.
Have you tried the sharpie test with 1PD turned off as well? When does energy harvesting stop with 1PD turned off? Does the overhead remain the same 2kW down to zero with 1PD off?

It will turn off when you reach the "creep" speed. Then it will maintain power or regen to creep at the appropriate speed - unless you're in drive going down a big hill then it may speed up.

You probably realize that though and I may have misunderstood your question.

 

[RMoore]

Thanks, I think for many of us we work all day engineering one kind of system, and then for fun go reverse engineer another after work… I do work on grid scale battery systems, but automotive applications are relatively new to me.

As for brake-holding, people have been using that as a launch technique - press the brake firmly, push the accelerator all the way down, feel the power build as the motors try to fight the brakes, then release the brakes to get a faster launch. Unlike an ICE vehicle, there is nothing to slip - no clutch or torque converter, so what happens is the motors just build up current trying to move (same as it would if you were pulling something, or starting on a steep hill).

Presumably if you held it too long the motors would back off on their own to prevent overheating, but for the half-second the brake hold is in effect the motors will still try to turn. This results in a slightly faster launch since the initial current-ramp has already happened.

I don’t have great data on it since some of that happens faster than the 0.5s most of my logs are at, but in my driving dynamics thread (link in the OP) there is a datalog showing a few launches, one of which is using the brake hold. You can see power spike before the vehicle starts moving, then a rapid acceleration once I let off the pedal. Still probably not a great thing to do to the car, but probably less damaging than doing it to an automatic.

Thanks. I was thinking more about what happens when driving as opposed to trying to get a fast start. Since regenerative breaking uses the motor, I would guess that the only way one could brake and have the motor continue to maintain its speed or increase revs is if you pushed hard enough on the pedal to engage the friction brake, though not clear to me why one would do that given the differences in shifting etc with EV vs ICE.

 

[phidauex]

Thanks. I was thinking more about what happens when driving as opposed to trying to get a fast start. Since regenerative breaking uses the motor, I would guess that the only way one could brake and have the motor continue to maintain its speed or increase revs is if you pushed hard enough on the pedal to engage the friction brake, though not clear to me why one would do that given the differences in shifting etc with EV vs ICE.

I think the condition you are thinking about just can't happen - since there is no adjustable transmission, and no slip anywhere in the system, the motor RPM and the road speed are always exactly proportional to each other. There is no such thing as maintaining revs while slowing in a corner, for instance.

Of course, it also isn't necessary - the electric motors have much wider power bands than ICE engines - no need to try to keep boost up by staying at a specific RPM, for instance.

I think that if you pressed both while driving the request to slow the vehicle down would override the request to speed it up, and the vehicle would use the normal regen/friction blend to slow the car down. I suppose you might be able to really confuse it and have the friction brakes start to engage and fight the motor, but that doesn't sound like a safe thing to try.

 

[SnBGC]

It will turn off when you reach the "creep" speed. Then it will maintain power or regen to creep at the appropriate speed - unless you're in drive going down a big hill then it may speed up.

You probably realize that though and I may have misunderstood your question.

Yeah, I could have phrased that question a little better.

I am curious if the sharpie mark remains while using just the brake pedal to bring the vehicle to a complete stop (1PD turned off). I wouldn't expect the pads to scrub the ink off the rotors with just a light application of the friction brakes but I've never tested it to verify. Would be interesting to know either way.

More interesting though is to see what happens during the same test with 1PD turned off and only the brake pedal is used to bring the vehicle to a complete stop. Does the brake system operate the same as when 1PD is enabled or is there different behavior? Maybe the vehicle is slowed all the way down to 2 or 3 miles/hr using just regenerative braking and then the friction brakes blend in or maybe the motors bring the vehicle to a complete stop. Curious to see what the data says.

If I understand the physics correctly....the larger the motor, the more easily it is able to keep the field active for harvesting energy but as the RPMs approach zero then that field has to be maintained by drawing energy from the HVB and when that happens the energy harvested is cancelled out by the energy needed to maintain the electrical field in the windings.

However, I did read something about EV motor design and the early units had a regeneration resistor circuit that makes a bunch of waste heat and newer designs don't have that resistor and they solve the problem some other way. If the MME has that newer design, then I wonder if it exists on the rear motor only. The front motor appears to be more of a legacy design compared to the IDM but I don't know for certain. Haven't seen any patents yet.....

In the early days of EV motors.....regen was about 40% efficient and now it's approaching 70% from what I understand. Seems to be a closely guarded trade secrets though. When I talk to engineers they are super vague with the details. The Jeep Wrangler 4xe has a very unique regenerative braking system and it is very very close to 1PD without using the friction brakes at all. I am not sure how they do that because their motors are not very strong but there is a mechanical device in their MGU2 that might provide a clue. However, that is a topic for a different discussion and I don't want to get us off track with this very interesting thread.

 

[phidauex]

Yeah, I could have phrased that question a little better.

I am curious if the sharpie mark remains while using just the brake pedal to bring the vehicle to a complete stop (1PD turned off). I wouldn't expect the pads to scrub the ink off the rotors with just a light application of the friction brakes but I've never tested it to verify. Would be interesting to know either way.

More interesting though is to see what happens during the same test with 1PD turned off and only the brake pedal is used to bring the vehicle to a complete stop. Does the brake system operate the same as when 1PD is enabled or is there different behavior? Maybe the vehicle is slowed all the way down to 2 or 3 miles/hr using just regenerative braking and then the friction brakes blend in or maybe the motors bring the vehicle to a complete stop. Curious to see what the data says.

If I understand the physics correctly....the larger the motor, the more easily it is able to keep the field active for harvesting energy but as the RPMs approach zero then that field has to be maintained by drawing energy from the HVB and when that happens the energy harvested is cancelled out by the energy needed to maintain the electrical field in the windings.

However, I did read something about EV motor design and the early units had a regeneration resistor circuit that makes a bunch of waste heat and newer designs don't have that resistor and they solve the problem some other way. If the MME has that newer design, then I wonder if it exists on the rear motor only. The front motor appears to be more of a legacy design compared to the IDM but I don't know for certain. Haven't seen any patents yet.....

In the early days of EV motors.....regen was about 40% efficient and now it's approaching 70% from what I understand. Seems to be a closely guarded trade secrets though. When I talk to engineers they are super vague with the details. The Jeep Wrangler 4xe has a very unique regenerative braking system and it is very very close to 1PD without using the friction brakes at all. I am not sure how they do that because their motors are not very strong but there is a mechanical device in their MGU2 that might provide a clue. However, that is a topic for a different discussion and I don't want to get us off track with this very interesting thread.

Ah, I see what you are saying - my current theory is that if you drove at the same speeds, and had the same deceleration profiles, then 1PD and 2PD would behave exactly the same way. Phrased another way, if you drove the same course at the exact same speeds, and all I had to look at was the power data and brake pressure data, I wouldn't be able to tell if you were in 1PD or not.

When I get a little more time to play I'll do some more brake testing. I wanted to do a lot more back-to-back runs with a new sharpie mark added after each run so it would be more clear how a mark wears after brake application. I'll make sure to do some runs in both 1PD and 2PD mode.

As for the motors, I'm sure there is some quiescent field overhead energy, but so far it is small enough that I'm not sifting it out in the data. In a few cases I saw a tiny bump in consumption as I approach 0mph, showing that perhaps at 1mph the motor is consuming more energy to stay active than it is getting from the winding regeneration, but it happens over such a small time scale and small amount (maybe 200W?) that I'm not sure if it is a real effect or just a blip in the data.

How could we determine the regen efficiency? On the drive log I shared, I regenerated ~20% of the energy I consumed, as measured at the battery (so after all motor losses). To determine the actual motor efficiency I'd need to have an estimate of how much of my energy was lost to road friction and air resistance...

 

[65sohc]

Great thread. My wife's car has about 2200 miles, 2100 of which I drove. It took me two months to convince her to start driving it in the first place. The stipulation was that it drive as much like "a normal car" as possible. Converting her to 1PD is the next challenge.

 

[phidauex]

Great thread. My wife's car has about 2200 miles, 2100 of which I drove. It took me two months to convince her to start driving it in the first place. The stipulation was that it drive as much like "a normal car" as possible. Converting her to 1PD is the next challenge.

Well, I hope to do some testing on 2PD "normal" mode soon, but my hope is actually that given how much the car relies on regeneration, driving in 2PD mode might not actually be lower efficiency than 1PD mode, meaning it would be more of a preference thing, and therefore something you could drop entirely, thereby saving your marriage.

 

[BMT1071]

Well, I hope to do some testing on 2PD "normal" mode soon, but my hope is actually that given how much the car relies on regeneration, driving in 2PD mode might not actually be lower efficiency than 1PD mode, meaning it would be more of a preference thing, and therefore something you could drop entirely, thereby saving your marriage.

The claims up to this point are that there's no difference in efficiency. It will be interesting to have data to support or refute.

 

[phidauex]

The claims up to this point are that there's no difference in efficiency. It will be interesting to have data to support or refute.

I'll try to capture some soon! I think the conventional wisdom in the EV world is that 1PD would be more efficient since it makes more use of regen, but that seems to be out of date, maybe from earlier EVs where 2PD mode didn't effectively blend regen, so it actually was less efficient? Not sure, but we'll find out!

 

[SnBGC]

The claims up to this point are that there's no difference in efficiency. It will be interesting to have data to support or refute.

I think generally speaking any slight variations in the different modes are outweighed by the differences in operator driving styles. I use 2PD exclusively and routinely consume 50% S.O.C. for each 150 miles driven so that pretty much means I average around 300 miles of range for an AWD EX. I think there are many others that use 1PD exclusively and have similar numbers.

I think Ford did a pretty good job with the various driving modes. They are slightly different from each other but still remain inside the boundaries of operation that Ford has predetermined for this vehicle. Except for the odd examples in Norway or wherever that big hill is located......it's pretty hard to be reckless with regen on this vehicle. Other EVs flirt with those boundaries a bit more it seems.

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