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P1 Drive Train / Motor Tech

24K views 43 replies 19 participants last post by  SilverstoneSyd 
#1 · (Edited)
Hi all,

As most of you know I asked a bunch of questions to McLaren higher-ups and techs because I felt there was confusion about the drive train tech used in the P1.

To start this thread, I think it is best for me to get a few basic physics explanations out there so words or things I use in the actual post will not be misunderstood or maybe understood better than before by some. :) Very low level... hope thats ok, not saying you guys are all physic-idiots, just better to establish a level playing field :)

Watt is a "unit of power". Short form: W
kW = kilo Watts, ie 1 kW = 1000 Watts
One Watt is the rate at which work is done when an OBJECT is kept at the velocity of 1 meter per second against the opposing force of 1 Newton.
Maybe a bit better example (which removes weird physics things like Newton that maybe not everyone understands): A person weighing 100kg, climbing a 3 meter high ladder in 5 seconds time does 600 Watts of work. {(kg * m^2) / s^3 - if anyone cares...}
1 HP is the old "unit of power" which was originally defined as the amount of work one horse could do pulling the wheel in a mill.
1 HP = 0.746 kW or 1 kW = 1.34 HP.

HP in a motor is calculated from its Torque and RPM. HP = Torque * RPM / 5252. So if an engine delivers 200 Nm of Torque and 2000 RPM, it delivers 76 HP at that RPM.

1 Watt is also 1 VA. Volt Ampere when looking at electrical units. So an electric motor converts VA into power and thus torque at a certain RPM of that motor. It can also be used as a generator by applying power to the shaft from outside which generates VA or Watt.

A BATTERY stores power. The power stored is measured in Wh. Meaning how many Watts it can produce over one hour period. So if you want to know how long it can deliver a certain amount of Watts, you divide the Wh by the Watts asked for. A battery has a certain max power output based on the Volts and Ampere it can deliver.

An electric motor converting electric power into kinetic power will always have a loss of conversion. So even if a battery can deliver 100kW and the motor can take it without issues (structural/heat issues in the end only) the power on the shaft will not be 100kW but a little less than that. How much depends on how well the circuits can convert the energy. How much heat is produced in the wiring and so on...

In my post below, note that when I talk about the ENGINE I will be talking about the PETROL ENGINE. When I talk about a MOTOR I will be talking about the ELECTRIC MOTOR.
 
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#2 ·
As we all know, the motor (electric motor) in the P1 delivers around 176HP and 130Nm. Its 176HP converts to 132kW (131.2 converted exactly, but it produces a bit more than 176HP; the 132kW is the more accurate number).

The engine (petrol engine) delivers 727HP at 7500 rpm, and its top torque is 720Nm at 4000 rpm.

Now to the important stuff...

The electric energy needed for the motor to deliver 132kW is roughly 140kW.
The BATTERY stores 3.4kWh of energy.

Therefor, pretending you would find a long enough stretch the electric motor could be powered at full 132kW (needing 140kW electric) for 87 seconds. (3.4kWh / 140kW = 0.024h = 87s)

Within those 87s clearly the P1 can reach vMax, so I asked what will happen at that point with the drive train. The P1 does not need its full engine and motor torque to sustain vMax once reached, it needs to to get there faster. The ECU will therefor reduce torque of the motor to 0. It needs to increase the torque of the engine to compensate a little, which it can. vMax is maintained!

The moment the driver lifts its foot off the throttle, the ECU will IMMEDIATELY start charging the battery.

To recharge the battery, the P1 uses the motor as a generator, by applying negative torque to it through its set of 3 clutches between the motor, engine and gearbox. That means it turns the motor backwards generating energy. As a generator the engine, depending on the RPM applied, can regenerate as little as a couple kW all the way up to roughly 120kW. Which would mean, at max kW it would take 3.4kWh / 120kW = 102s to fully recharge the battery.

The biggest questions came from the comments regarding use and regen of the battery around the Ring, and the comment in their press kit stating that it does NOT use regenerative braking.

So to settle this once and for all, I have confirmation from McLaren on the following (btw, this is all exactly as I explained it before):

1) The battery supplies full power throughout the whole lap of the Ring! It never runs out of juice!
2) During one lap the P1 is able to put almost as much charge back into the battery as they take out of it.

It regenerates in _two_ ways:
1) The ECU applies negative torque to the motor, unless the battery is full, when you are off throttle. Some people call this "regenerative braking" but it is NOT! Because it does not depend on BRAKING. It simply depends on NO THROTTLE. To the driver, this simply feels like more engine braking than just the petrol engine would bring. The power taken depends on the motor speed, the gear and the power train mode the P1 is in. I did not ask for details but I guess the negative torque applied changes depending on power train mode, thus together with speed and gear it generates more or less power.
2) If you drive steady speed, the ECU will also, to regen, turn off the motor, then increase the engine torque and subtract that torque via negative torque applied to the motor, which will in turn generate energy stored in the battery. While driving the car you will notice this since the motor will rev higher without you asking for more power or the car speeding up.

The P1 DOES NOT however use REGENERATIVE BRAKING. What this means is, the negative torque applied to the motor does NOT CHANGE when you brake in order to keep brake-feel 100% based on mechanical braking instead of a mix of the two! They DID consider increasing negative torque when braking, but were concerned with brake feel so stepped away from the idea.

For an idea of how much energy the battery can truly regen via kinetic energy recuperation, in the vMax example above, when you lift off your foot from the throttle, the motor will generate about 100kW. It will not generate more in order not to do too much engine braking. It could do more and it will in certain circumstances, but the ECU would decide on roughly 100kW in that circumstance.
 
#36 · (Edited)
It regenerates in _two_ ways:
1) The ECU applies negative torque to the motor, unless the battery is full, when you are off throttle. Some people call this "regenerative braking" but it is NOT! Because it does not depend on BRAKING. It simply depends on NO THROTTLE. To the driver, this simply feels like more engine braking than just the petrol engine would bring. The power taken depends on the motor speed, the gear and the power train mode the P1 is in. I did not ask for details but I guess the negative torque applied changes depending on power train mode, thus together with speed and gear it generates more or less power.
2) If you drive steady speed, the ECU will also, to regen, turn off the motor, then increase the engine torque and subtract that torque via negative torque applied to the motor, which will in turn generate energy stored in the battery. While driving the car you will notice this since the motor will rev higher without you asking for more power or the car speeding up.

The P1 DOES NOT however use REGENERATIVE BRAKING. What this means is, the negative torque applied to the motor does NOT CHANGE when you brake in order to keep brake-feel 100% based on mechanical braking instead of a mix of the two! They DID consider increasing negative torque when braking, but were concerned with brake feel so stepped away from the idea.
.
What you've described is regenerative braking, the same principle as applied to locomotive DC motors or oil rig drawworks AC motors for example.

What occurs during regenerative braking is a current flow reversal as the motors stop providing drive and instead become driven (by momentum or inertia), thus becoming power generators. The power generated is either dissipated into resistor banks as heat or, as in the case of these hyper cars, stored in batteries. The spinning drive shafts sees the generator as a load that is trying to impart a braking effect on their rotation, thus the term regenerative braking.

Obviously this form of recharging, being free, is much preferred over the other one which requires engine torque (more fuel) which is parasitic.
 
#4 ·
Thanks very much Fabian.... Great explanation..clears up a number of points that were not well understood.

903 for the whole lap when needed. Amazing.
More importantly, also for the 2nd, 3rd, 4th, 5th, 6th lap... :)

I wonder however how fast the petrol engine runs out of fuel.. ;)

But clearly faster than the battery runs out of power with that little loss per lap...
 
#6 ·
It's interesting equally that the recharge time from flat they day is 10 mins after e mode one assumes that this is assuming significantly less torque delivered in town driving,..,

Anyway a true hybrid. Not another electrical boost system..

I wonder how much quicker it will be down dottinger hohe at vmax

It's amazing when you think it doesn't need full power for vmax chat but seeing as we know this is load limited with an electronic top speed not intuitively surprising.. Shows you how pointless top speed figures really are from a useable basis..
 
#13 ·
If you think about it, 10min is a lot to recharge actually... At 100kW the negative torque needed is not a lot, it takes only 102 seconds to recharge. Meaning for 10 minutes, all it needs is about 21kW. 21kW is only 28HP. So all it needs to take is 28HP from the engine to recharge the battery in 10 minutes... Thats not really a problem to do. Especially in the city.
 
#8 ·
What shocks me is that I actually understand what you have written Fabian,thanks for the concise explanation in laymans terms.This clears things up and needed an engineers brain to put it across,rather than some of the guff that has been banded around,thanks again !!
 
#11 ·
Thanks mate, very intriguing and fascinating information delivered in a concise and direct-to-read manner. Good job :)
 
#12 ·
Interesting.. however... The 918 was clearly shown to have run out of electric power per lower top speed down dottinger hohe compared to some earlier straights. And the 918 has considerably higher battery capacity despite a greater electric power output and I think the maths ends up to being full battery power for 115s or something like that (I'm a bit lazy to find the exact figures sorry...) which is longer than the 87 seconds you have for the P1. Given the 918 has the capability to charge the battery through braking as well, it would seem strange the P1 will be able to maintain it's electric capability throughout the lap compared to the 918?

Unless the torque differential between the turbo v8 and the NA engine of the 918 is such that it can charge the battery that much more off throttle.....or the 918 is able to use far more of the full electric power available being awd etc so depletes it's batteries to a far greater extent and is not able to recharge it.
 
#14 ·
The extra negative torque added through increased negative torque while braking is very little to keep your brake feel! I think the biggest problem is that it needs much more HP from the battery than the P1. And on top of that, above 260kph or something like that the front motor is DISCONNECTED. Its RPM would be too high, so also as a generator it can not be used in high speeds. So although in the most important speeds, ie the lower end below 200kph you need both motors, only one is effective at regenerating at all speeds. This loses regen power from engine/motor braking and the regen brakes does not recoup that.

So the 918's battery is bigger, but is used more and regens less than the P1. P1's regen is much closer to its usage which helps it not to lose too much power during any normal circuit's lap.
 
#18 ·
Makes sense

Does beg the question though whether Mclaren need the hot lap mode of 903 is available all the time on a lap of the ring...

Am sure over the coming weeks well work out what the differences are and why therefore the cars perform differently if indeed they do..
 
#19 ·
The P1 has no "hot lap" mode, and does not need a "hot lap" mode.. wtf is that anyway?!

There is absolutely no reason to not regenerate battery. Are you telling me that the 918 does not slow down before a corner!? If it slows down, it can regen, its very easy.
 
#20 ·
@Ftyl

Not sure if you're joking?

That's what I was saying. Lol.

The P1 appears to have no "hot lap" mode like The 918, or the capacity to do so (at least on the ring).

And I'm not sure you read (if you're responding to me) my post clearly, and why I responded/gave the answer I did. I explained it all.

It appears Mikeyb, read, understood it (Not being rude)?
 
#21 ·
CarMeister, I am neither joking, nor does it matter to me if you said that.. Your post makes it sound like it is somehow "bad" that the P1 has no hot lap mode. But my post is clarifying that it does not matter at all since a hot lap mode is not needed and would add nothing.

So again, I am honestly not sure what you are trying to claim.

You are correct, the porsche needs a "hot lap mode" for some reason to achieve a faster time on the ring. This makes little sense and the P1 does not need it. A "hot lap mode" would add nothing because the P1's ECU does not make the car slower in hybrid mode.
 
#22 · (Edited)
With all due respect. I think you're confused, and didn't read/understand what I was responding to. And I'm to lazy to re-read ISV's question. But quite frankly, I think you're overreacting. "Hot lap" came up; cause ISV mentioned the 918 running out of charge, and speculated why, what it would to on it's further laps (while mentioning the P1 as well)? That was the entire premise for my response.

FYI/According to Porsche: The 918 could to 7-7:02 on the Ring in "Race Hybrid mode" where it regenerates the battery constantly via engine and brake regeneration. As you know, this time is currently faster than anything we know of the P 1. This is a time it should do over and over again as well. As I said in my response: the 918 has ran on various tracks for owners, writers and drivers alike in Race Hybrid, while keeping a steady charge. So what you're implying ("the 918 needs a hot lap mode") is not an issue.

I repeat. It's just the 918's battery is so big, it can practically do the entire ring with out engine regeneration. That's a bonus (and really so hard to understand)!? Though in reality, the overwhelming majority of owners would never need to use it ("Hot Lap"). And it certainly does fine by itself in Race Hybrid. But of course the big battery, has it's benefits on the track and the real world (performance, cabin conveniences, etc.), besides "Hot Lap" mode. It just makes the 918 a versatile vehicle. I was only addressing a question regarding battery depletion, additional laps with the 918. There is/was no "fanboyism".

The P1 was never criticized. That was your interpretation? I was just answering, addressing the two vehicles, regarding the 918's recent Ring Video with Lieb at the helm, in lieu of ISV's comments. "Hot Lap" on the Ring, essentially means the 918 has a bigger battery, which we already knew.

I hope that helps (for good)? Whew! :)
 
#23 ·
CarMeister...

you are right, we know nothing about the P1's ring time. And this whole thread has nothing to do with the time either. It is an explanation of the tech in the P1 that was discussed many times.

Just since you keep bringing up the 918... the battery in the 918 has 6.8kWh. Even ignoring the front engine, taking only the one connected to the gearbox, 115kW. Will only power for 212 seconds. Less than half the time it takes around the lap. Explain to me how it uses "all the power" the whole lap using a "hot lap" feature?!

None of this makes sense. But more importantly, this is a P1 thread about its tech, can we stop discussing 918 tech please?
 
#24 ·
HOT Lap uses selective regeneration compared to Race Hybrid and it's other modes. Generalizations are used (Porsche included) to avoid confusing nomenclature, technical terms, electrical, battery charge, dissipation figures, etc... You know that.

Yes, it's a P1 thread. And I never criticized the P1, or offered a wanton, unprompted opinion on the vehicle. I answered a posters question, in regards to the 918. And I thought I gave a good answer at that, concerning what he was seeking Some how you took offense?

There was never any disrespect to the P1. And I ONLY brought up the 918's Ring Times in "Race Hybrid" mode, cause you kept repeating 'The 918 needs HOT LAP to record and repeat fast laps', thus alleging it was inferior to McLaren's Hybrid set up (not that it matters). That's all.

This was really never a comparison, competition between the two vehicles in my eyes. And I would be happy to end it right now.
 
#26 ·
@ftyl
Thanks for your post. It really cleared up a lot of the confusion for me.

I suspect the P1 will be much faster then most people think it is considering how much more advanced it aerodynamics are (seem to be) compared to the other two. They may have had to sacrifice a little in terms of aesthetics (subjective, of course) for the sake of aerodynamics but given their stated goals for the P1, they've done the right thing.
I imagine the P1 will be devastating around places like Suzuka, Silverstone or Spa.
 
#27 ·
Great post ftyl, that's the most complete information on the P1 drive train I've read anywhere, thanks for posting.

I suspect the P1 will be much faster then most people think it is considering how much more advanced it aerodynamics are (seem to be) compared to the other two.
I looked up the numbers and the difference is much greater than I anticipated for most cars:

2009 GTR - 176 pounds of downforce at 186 mph
2011 Porsche 911 GT3 RS 4.0 - 426 lbs of downforce at 193 mph
Enzo Ferrari - 1709 lbs of downforce 185 mph (note: it reduces downforce above 186 mph to achieve a higher top speed)

McLaren P1 - 600 kg ( ~ 1323 lbs ) of downforce at 161 mph

They may have had to sacrifice a little in terms of aesthetics (subjective, of course) for the sake of aerodynamics but given their stated goals for the P1, they've done the right thing.
Sacrifice? The P1 is perfect. It's so good it's hard to find the right adjectives to describe it really.
 
#30 ·
ftyl - great write up, thanks for sharing. I like to clarify one detail on the battery charging bit - what you describe

1) The ECU applies negative torque to the motor, unless the battery is full, when you are off throttle.

This is in fact KERS - right? i.e. the energy in this mode is converted kinetic energy?
 
#32 ·
No, it is not KERS as far as I understand the rules of F1. KERS is only allowed while braking I think? It is the same basic tech though, just that the P1 does not modulate the torque based on braking...
 
#38 ·
Yes. In BOOST mode, it turns off electric motor and you choose via the IPAS button when you want it added for extra accel.
 
#40 · (Edited)
I postulate that the folks at McLaren probably have some people better suited than us forum goers to determine how many miles on track / laps on track the P1 can stay at top performance, and I would further postulate that they probably thought of this ahead of time. :)

Thought in 3 steps:

1. Lets say that somewhere on some bend at the 'ring the driver lifts to keep a steady speed. In this moment, the amount of power that the engine develops drops hugely. From full throttle to partial throttle to maintain speed not accelerate.

2. In a car like the P1, the electric motor can add its torque/power to the transmission input, powering the rear wheels.

3. If you were doing a hot lap, as in 1. above, and the driver lifted, and the petrol engine was simply left at wide open throttle, the electric motor could then reverse and DELETE torque from the transmission input and use that torque to power the battery. (edit, poor typing earlier)

Thats how I picture this system working. The engine just runs, in its track/max mode, at a higher level of throttle overall for the course of the lap than it would without the hybrid system. Think of two curves

a) throttle setting without the hybrid system (from zero or near zero to full throttle)
b) throttle setting at WOT the whole lap

The area in between these two curves should be available for battery recharging. And that should be enough to charge an electric system that is generating less than 20% of the total power.

I'm not an engineer, but if this is how the system works one should be able to tell because when braking for turns in those videos the engine would still sound like it was under some strain. Its speed would be changing (with the changing transmission input shaft speed, related to gear and wheel speed), but it would stay under strain when braking for a corner.

Who has good ears? And if a very technically versed person is among us ... is this close to accurate?
 
#41 ·
Minnesota, in the video, the 2nd turn where the car decelerates, you do hear the electric motor is still in very high speed. In line with the engine shifting it seems.
 
#42 ·
Cool.

Any of these cars would ahve all the power for all the laps in the world, probably, if they ran the petrol engine at higher throttle than necessary when the driver lifts and during those periods reverse the electric motor to make it a generator.

The driver would probably experience relatively extreme engine braking under such a circumstance, kind of like driving a Tesla Model S with the regen turned way up or something like that. They may even be able to get it to feel like normal engine braking through some clever mechanism.

But guys, and ladies if present, the assumption that these cars are all out of power before the end of a hot lap is not as conclusively known as the web comments are making it seem. They MAY be out of power, they may run out on some tracks, but if the petrol engine is run at higher throttle than necessary and the electric system reversed, they will not necessarily run out.

If i was clever enough to draw a curve showing what I'm thinking and post it on the internet I would, but I apparently can't even post youtube videos.
 
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