RE: McLaren P1: Driven

Author
Discussion

DonkeyApple

55,763 posts

170 months

Friday 21st February 2014
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Justices said:
Less than 10 minutes into this video. I very much want this car. I mean, really, really want this car.

What a fantastic job they've done.
It's quite impressive when you think that all you really see for the first ten minutes and most of the rest of the film is Monkey's mug. wink

UK952

764 posts

260 months

Friday 21st February 2014
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Just (well about an hour ago) returned to this thread after being presented with an open can of worms on the video thread smile can see why now.
My feeling was that with wheel braking carrying out the slip limiting duties energy is lost whereas with a differential based slip limiting device the energy is transferred (I realise this transfer will also cost some energy).
The discussion has educated a bit further on the negatives of a traditional LSD as both types of car I have driven with one have been brilliant - 944turbo and corolla ae86, especially compared to those I have driven without 944 tr7 rx8(more lack of torque than lack of LSD). I realise these in no way compare to a P1 and I need to get into more rwd cars wink


I suspect when you are trying to put 900bhp through 2 wheels a bit of energy lost through braking is not an issue and Maxtorque has explained the engineering advantages of this approach.

I also find it interesting that us car geeks can become so focussed and passionate about the little details, resulting in a thread about a really exciting new car being mostly about a fairly insignificant part of it that obviously actually works brilliantly! (in this application at least)




zeppelin101

724 posts

193 months

Friday 21st February 2014
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Am I one of the few who has no preference? I had a knackered old E36 328i ages ago and that had an open diff. Was much, much nicer to drive than the one I had about 8 months later that had an LSD. Turn in was nicer and it still slid absolutely fine. Very rare that I found myself lacking traction on the way out.

By comparison, my 180SX has a welded diff and apart from some initial turn-in understeer, it's wonderfully predictable. Takes a few adjustments to the line on the way into a corner but you just get on the power early and deal with whatever happens next. Which, surprisingly, isn't always a big slide.

At the end of it, it comes down to what the intention of the car is I think. Is it supposed to be fun to drive? Or fking fast? I'd pick entirely different systems for either requirement and an e-LSD or brake steer just appears to be a middle ground between the two. I don't believe either is better than the other necessarily, it's just at the discretion of whoever designs the drive system as a package.

Mr Whippy

29,113 posts

242 months

Friday 21st February 2014
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Peloton25 said:
Man what a mess this became. Let me help... teacher

iloveboost said:
I think the reason they use an E-LSD instead of a mechanical limited slip differential is that... <snip>
Who is this "they" you are referring to? If in our minds we were supposed to assume "McLaren" then...

iloveboost said:
All of the above could be wrong but that's the way I understand it.
...that final statement of yours is no longer 'could be' but is in fact 'is'. There is no E-LSD or E-Diff in the McLaren P1.

Now look what you have done:

Mr Whippy said:
So I have a new appreciation for the P1's diff.
Revert to your earlier appreciation (though still flawed) as what he wrote was not an accurate description of what the P1 uses.

Mr Whippy said:
You'd have thunk that the contents of this thread if they discussed things in such detail would have found their way into the latest article but nope. Still Chris Goodwin tells Chris Harris that the car has an open differential, and Chris talks as if the P1 has some other kind of diff to a mechanical locking one, with computer control, which is apparently what it DOES have?

This is a mechanical infinitely variable locking differential then? Or not?
Or not! The differential where torque is passed from the transmission to the driveshafts in the McLaren P1 is open, not mechanically nor electronically controlled in any form or fashion to balance torque output directly inside the diff itself. All the magic to replicate what a limited slip differential would do is provided by McLaren's Brake Steer technology to put it in the simplest of terms.

Mr Whippy said:
...my points were all based upon an open differential and wheel braking which is clearly completely wrong.
...and yet it is working so well for McLaren with the P1. Hmmmm...

isaldiri said:
E65Ross said:
No idea, but CH has driven all those cars except the LaFerrari and says there is no questions that the McLaren system is better....
My take on what CH said on his comments earlier was that he felt that the calibration of brake steer on the P1 had advanced from that on the 12C (which as much as I like the car, would be improved with superior calibration or a proper diff IMO) to the point that it now equaled the feel of the LSD equipped cars, which is pretty impressive but not quite the same as saying that he thought it was better...
Should not a system be considered 'better' if it can perform a highly similar function without the weight penalty or cost penalty of another system? Perhaps the end result from a functional standpoint is equal, but one has to look at all factors when determining which system is 'better' as function is hardly the only variable. This is what McLaren have done to arrive at their preferred choice of solutions.

Mr Whippy said:
But Chris Harris said this car has an open diff and uses brakes to control slip, but it doesn't.

I really enjoy what Chris Harris has to say about cars and he's a great entertaining guy, but can he really isolate his experiences so clearly and say anything like that with any authority?
In case it is still not clear, Mr Harris was always correct. Make it habit of listening to the people in the discussion who don't end their posts (or their statements to their millions of viewers in the case of Chris) with "All of the above could be wrong..." and you'll do much better.

>8^)
ER

Edited by Peloton25 on Friday 21st February 00:14
I give up then.

You can't discuss a car without knowing how it works, never mind in a forum where everyone seems to think it works differently hehe smile


So we're back to the diff action on the P1 basically scavenging regenerated and engine provided energy and pumping heat into brakes in order to operate.

On track the hybrid system must just be redundant most of the time. The weight added probably needs the hybrid system to push it around. The extra power generated by it out of bends where traction is an issue just powers the 'braking' differential in essence.

It's a finely integrated system and I'm sure the end result is lovely, but it does seem overly complex for the sake of a low EU cycle CO2 rating, which seems to be all this whole hybridisation affair seems to offer vs just fitting a big NA engine and dumping the hybrid stuff!?

Dave

GreatGranny

9,169 posts

227 months

Friday 21st February 2014
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Did you not listen to the video?

The emotor isn't just for the sake of a low CO2 rating, it fills the gaps in torque in the engine delivery eg. turbo lag so there is instant throttle response.

Lets not get back to the "wish they would dump all the hybrid stuff and save 200kg blah, blah, blah..."

Its a monumental car BECAUSE of the hybrid stuff together with everything else.
It wouldn't be a better car without it.

Of course this ia all IMO, I don't understand how it all works, not sure if i want to get bogged down in all the technical stuff.
I found the technical stuff on the video interesting because its at the laymans level but I also enjoy hearing and seeing it in action and the pure joy Chris was experiencing when he "spanked it".

Peloton25

986 posts

239 months

Friday 21st February 2014
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Mr Whippy said:
I give up then.

<insert four more paragraphs>
Dave - with all due respect, you'd do better to find good sources and read as much as you can. People on forums are not always the best educators - you have to be selective on what you take as fact as supposition is rampant. Also, using what you think you understand and broad brushing 'What must be' is never the best plan.

...especially when it is "A Whole New Thing". wink

>8^)
ER


stevesingo

4,861 posts

223 months

Friday 21st February 2014
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RE: Locking diff vs Brake steer.

When a car turns a corner the inside wheel follows a tighter radius than the outside wheel and therefore travels a shorter distance.

Due to the weight transfer to the outside wheel whilst cornering there is less pressure on the inside tyre contact patch and therefore less grip.

As we accelerate the torque at the wheel increases and also the speed increases. The speed increase creates more cornering force and therefore more weight transfer and consequently less inside tyre contact patch pressure and therefore grip.

These three facts are a given.

With an open diff, as the inside wheel looses grip the wheel starts to spin and drive is lost as the open diff can only transmit equal torque across the axle. No grip on the inside=no torque being transferred to the road on that tyre and all the drive is lost, although the speed will increase on the inside wheel as the power has to go somewhere. This manifests itself in the fizzing inside wheel we some times see/experience. This will continue until grip is restored to the inside wheel.

With a non active LSD, the torque applied to the diff caused clutches to lock up which transfers torque across both axles by effectively locking the axles together so that the speed of the wheels is more equal. This allows acceleration as the wheel speed is being kept equal and the inside wheel is prevented from spinning the power away. As the car is continuing to accelerate in the corner it is lateral grip that gibes up first and the read begins to slide sideways.

With an Active LSD, the locking of the clutches is not controlled by the torque applied to the diff, but in this case there are hydraulic actuators which lock the clutches independently from torque applied. This gives the engineers the opportunity to vary the amount of lock from 0-100% and therefore allow the wheel speeds to be 100% equal across the axle. It is worth noting that the inside wheel of an LSD equipped car is still not transferring torque to the road as the tyre has no grip due to the effect of weight transfer.

With any LSD the wheel speeds across the axle can only ever be equal, i.e in a 100% lock. So our inside wheel which needs to be travelling slower than the outside wheel is in fact travelling at the same speed and effectively slipping.

What if we control this cross axle speed difference with the brakes and an open diff, and not clutches within a diff?

If our inner wheel starts to spin, we can brake the wheel and this will transfer drive to the outer wheel through the diff. We can now control the wheel speed so they are equal to the theoretical correct speed for the corner radius (derived from steering angle sensor/yaw sensor).

Better than that, because we are cornering the outside wheel has more grip, so we can now brake the inside wheel even more and transfer more drive to the outside wheel gaining acceleration and increasing turn in (yaw).

If anyone is in doubt of how this effects the direction of the car, try pushing a supermarket trolley in the middle (it will go straight enough), and then push it from the rear corner (it will start to turn/yaw)

The key is controlling the system so it feels natural. Wasn't quite right on the 12C, but seemingly better on the P1.

PhillipM

6,524 posts

190 months

Friday 21st February 2014
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Mr Whippy said:
Things like brake steer effectiveness will be intertwined with things like the presence of a super fancy differential that the P1 has, along with numerous other systems too no doubt.

Dave
The entire point of brake steer is that you don't need a fancy diff - that why even a set of spanner monkeys like us can use it on the buggy.
You can have a nice lightweight, standard diff, with no friction plates throwing debris in the oil, no heat load from clutch packs to dissipate, and just leave the heat load at the brakes - which is what they were designed for at the outset. The reason most people don't use them is the speed and control alogorithms needed for the traction control under transients and yaw takes a lot of time and refinement to get it working properly compared to a mechanical plate diff (or hydraulically controlled version) - and to get it feeling natural and predicatable is another ball game for a road car (as you start to move the centre of yaw backwards to the rear axle line)

Edited by PhillipM on Friday 21st February 11:53

CraigyMc

16,492 posts

237 months

Friday 21st February 2014
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With regards to the charging/discharging of the battery on the P1, I have read various things and I think the following is true.
Can anyone who is familiar with the P1 confirm or reject with explanation each of these points?

  • The P1 powertrain has the following modes: E-mode, Normal, Sport, Track and Race
  • E-mode is electric only. It's the mode with up to about 6 miles of range, and only uses the power of the battery/eMachine to motivate the car. The output of this system is be circa 176bhp and would result in rough performance figures in the ballpark of 0-60mph in 7.5 seconds or so, with a max speed certainly over 100mph, and more likely peaking around 140mph (assuming you don't care about battery life!).
  • The other modes -those with the IC engine active - are Normal, Sport, Track and Race.
  • At the limited vMax (217mph aka 350km/h) common to all these P1 settings except race mode, the IC engine has enough power to charge the battery, but not at the maximum charge rate possible for the eMachine, inverter, or battery. In other words, at 217mph, the 727bhp-capable IC engine doesn't actually have to produce the peak 727bhp, it can do this speed with less power and the remainder can and does go into charging the battery until it's full.
  • At the limited vMax (205mph aka 330km/h) in race mode, the IC engine has enough reserve power to charge the battery at around the maximum rate the inverter and battery can handle, while travelling at 205mph (short of driving it up huge incline).
  • At any time when the P1 is not at peak engine demand (eg. part throttle through a corner, or no throttle under braking, or when at one of the limited vMax speeds: 205mph or 217mph), the IC will be driving both the rear wheels, propelling the car, and the eMachine will be charging the battery unless it's already full.
That's how I understand it. Anyone care to comment?

Edited by CraigyMc on Friday 21st February 12:14

Ollywood

173 posts

142 months

Friday 21st February 2014
quotequote all
stevesingo said:
RE: Locking diff vs Brake steer.

When a car turns a corner the inside wheel follows a tighter radius than the outside wheel and therefore travels a shorter distance.

Due to the weight transfer to the outside wheel whilst cornering there is less pressure on the inside tyre contact patch and therefore less grip.

As we accelerate the torque at the wheel increases and also the speed increases. The speed increase creates more cornering force and therefore more weight transfer and consequently less inside tyre contact patch pressure and therefore grip.

These three facts are a given.

With an open diff, as the inside wheel looses grip the wheel starts to spin and drive is lost as the open diff can only transmit equal torque across the axle. No grip on the inside=no torque being transferred to the road on that tyre and all the drive is lost, although the speed will increase on the inside wheel as the power has to go somewhere. This manifests itself in the fizzing inside wheel we some times see/experience. This will continue until grip is restored to the inside wheel.

With a non active LSD, the torque applied to the diff caused clutches to lock up which transfers torque across both axles by effectively locking the axles together so that the speed of the wheels is more equal. This allows acceleration as the wheel speed is being kept equal and the inside wheel is prevented from spinning the power away. As the car is continuing to accelerate in the corner it is lateral grip that gibes up first and the read begins to slide sideways.

With an Active LSD, the locking of the clutches is not controlled by the torque applied to the diff, but in this case there are hydraulic actuators which lock the clutches independently from torque applied. This gives the engineers the opportunity to vary the amount of lock from 0-100% and therefore allow the wheel speeds to be 100% equal across the axle. It is worth noting that the inside wheel of an LSD equipped car is still not transferring torque to the road as the tyre has no grip due to the effect of weight transfer.

With any LSD the wheel speeds across the axle can only ever be equal, i.e in a 100% lock. So our inside wheel which needs to be travelling slower than the outside wheel is in fact travelling at the same speed and effectively slipping.

What if we control this cross axle speed difference with the brakes and an open diff, and not clutches within a diff?

If our inner wheel starts to spin, we can brake the wheel and this will transfer drive to the outer wheel through the diff. We can now control the wheel speed so they are equal to the theoretical correct speed for the corner radius (derived from steering angle sensor/yaw sensor).

Better than that, because we are cornering the outside wheel has more grip, so we can now brake the inside wheel even more and transfer more drive to the outside wheel gaining acceleration and increasing turn in (yaw).

If anyone is in doubt of how this effects the direction of the car, try pushing a supermarket trolley in the middle (it will go straight enough), and then push it from the rear corner (it will start to turn/yaw)

The key is controlling the system so it feels natural. Wasn't quite right on the 12C, but seemingly better on the P1.
Great explanation! got it now wishing my shopping trolley had that in sainsbury's I would be doing "ring" times.

Mr Whippy

29,113 posts

242 months

Friday 21st February 2014
quotequote all
PhillipM said:
Mr Whippy said:
Things like brake steer effectiveness will be intertwined with things like the presence of a super fancy differential that the P1 has, along with numerous other systems too no doubt.

Dave
The entire point of brake steer is that you don't need a fancy diff - that why even a set of spanner monkeys like us can use it on the buggy.
You can have a nice lightweight, standard diff, with no friction plates throwing debris in the oil, no heat load from clutch packs to dissipate, and just leave the heat load at the brakes - which is what they were designed for at the outset. The reason most people don't use them is the speed and control alogorithms needed for the traction control under transients and yaw takes a lot of time and refinement to get it working properly compared to a mechanical plate diff (or hydraulically controlled version) - and to get it feeling natural and predicatable is another ball game for a road car (as you start to move the centre of yaw backwards to the rear axle line)
I've driven loads of vehicles with brake steer, but in my case it's essential for turning when the front wheels are off the floor, and it's using a foot for each rear wheel biggrin

I understand all the principles here... my argument has always been the same point people make back to me.

A diff is chosen based on the package firstly, so any diff will be good assuming it's had everything else around it designed with it in mind for the required end goals.

It's very hard to just say diff X is bad, diff Y is good, or better. It's all about how it fits with everything else. Put an LSD with a lot of coast locking on my Z4 and it'd probably be a bit more numb on turn-in on a track for example just because of the pre-load locking both rears together and not allowing a rapid differential speed to occur.




But in this specific case, the algorithms and systems you note are just as present and possible in something like the F458, and no doubt the LaFerrari.

Brake-steer is essentially just a part of another calibrated table set that does X based on Y,Z,A,B,C from a myriad of other tables all looking up other values from yaw sensors, wheel speed sensors, yadda yadda.

And as said, the F458 has all that inside it too, AND has a fancy differential.


I'm happy for McLaren to be happy with their approach, but what frustrates me is when people have to look at the solution like it's better, and everyone else is now wrong. It doesn't work like that.

It fits their package, great. But that is where comparisons should stop on diff X is better than diff Y etc.

Dave

Finlandese

542 posts

176 months

Friday 21st February 2014
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Since I don´t have the expertise to tell McLaren engineers how they should´ve engineered the P1, I´ll pick up on the other main theme of this thread.

Why doesn´t CH have his own tv show?!?

Considering all the inferior produtions that you see on tv, this is a valid question, but after giving it a bit of thought, I think it makes sense only if you assume that the financial benefits for CH would be massively greater on tv than on (in) interweb. Think about it. When you have tv show, you´ll have a format (for example 22 min show that has certain segments that have been approved by the channel), and distribution channel(s) that have their own needs.

What Chris has now, is a complete freedom to do whatever he wants to do (a 10 minute clip about picking baguette and fantasising about Miami Vice - done!), and worldwide following. Based on his car collection, Chris doesn´t excatly have problems providing for his family (the occasional baguette, at least)nor feeding his cardicction.

I am greatful for living in times, when there are means of effective communications that can unite the marginal constituents of this planet to enjoy the kind of content that CH provides.

P.s. If you thought that CH refered to Christian Horner, I doubt that my post made much sense..

Amirhussain

11,490 posts

164 months

Friday 21st February 2014
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CH doesn't have his TV show because apart from some people on PH, no one really knows who he is, pretty much everyone knows who Clarkson, Hammond and May are. And TBH I don't understand some of the praise and arse licking CH gets from some PH'ers.

Also just because he may be part of some alright videos online, doesn't mean its going to take of on the TV screens, Top Gear has more than 300 million viewers in over 100 countries worldwide, how many people you reckon would tune in to watch CH is he was given a TV slot?



Finlandese

542 posts

176 months

Friday 21st February 2014
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^Not Top Gear numbers, but certainly more than any number of other car related cable shows. As far as being PH only star, I´ll have to disagree with you. Just take a look around the webmosphere, and you´ll see that good content spreads like an Ebola!

As far arse liking goes, good product, good feedback. What is so strange about that?

Edited by Finlandese on Friday 21st February 15:21


Edited by Finlandese on Friday 21st February 15:25

The Vambo

6,670 posts

142 months

Friday 21st February 2014
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Mr Whippy said:
And as said, the F458 has all that inside it too, AND has a fancy differential.
stevesingo said:
It is worth noting that the inside wheel of an LSD equipped car is still not transferring torque to the road as the tyre has no grip due to the effect of weight transfer.
I maybe wrong, but the e-diff will stop the spinning wheel from being slowed by the brake steer to a speed to where it has grip and can transfer torque.

Even if it could, It would have the extra weight/complexity of the e-diff to do the exact same job.

If that is correct, one is clearly better than the other,


E65Ross

35,152 posts

213 months

Friday 21st February 2014
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Finlandese said:
^Not Top Gear number, but certainly more than any number of other car related cable shows. As far as being PH only star, I´ll have to disagree with you. Just take a look around the webmosphere, and you´ll see that good content spreads like an Ebola!

As far arse liking goes, good product, good feedback. What is so strange about that?

Edited by Finlandese on Friday 21st February 15:21
Look at 5th gear, that does quite poorly compared to TG, and I bet CH wouldn't get anywhere near the amount of views as that.

I love the videos, but they aren't mainstream TV, the audience isn't there IMO.

Dr JonboyG

2,561 posts

240 months

Friday 21st February 2014
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Amirhussain said:
CH doesn't have his TV show because apart from some people on PH, no one really knows who he is, pretty much everyone knows who Clarkson, Hammond and May are. And TBH I don't understand some of the praise and arse licking CH gets from some PH'ers.

Also just because he may be part of some alright videos online, doesn't mean its going to take of on the TV screens, Top Gear has more than 300 million viewers in over 100 countries worldwide, how many people you reckon would tune in to watch CH is he was given a TV slot?
A: broadcast TV is not the future.

B: in three days that P1 video has been watched by half a million people. I'd say that's more than just a few people on PH.

E65Ross

35,152 posts

213 months

Friday 21st February 2014
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Dr JonboyG said:
Amirhussain said:
CH doesn't have his TV show because apart from some people on PH, no one really knows who he is, pretty much everyone knows who Clarkson, Hammond and May are. And TBH I don't understand some of the praise and arse licking CH gets from some PH'ers.

Also just because he may be part of some alright videos online, doesn't mean its going to take of on the TV screens, Top Gear has more than 300 million viewers in over 100 countries worldwide, how many people you reckon would tune in to watch CH is he was given a TV slot?
A: broadcast TV is not the future.

B: in three days that P1 video has been watched by half a million people. I'd say that's more than just a few people on PH.
Bare in mind those figures are totally skewed by those refreshing the page, watching it more than once etc.

Finlandese

542 posts

176 months

Friday 21st February 2014
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E65Ross said:
Finlandese said:
^Not Top Gear number, but certainly more than any number of other car related cable shows. As far as being PH only star, I´ll have to disagree with you. Just take a look around the webmosphere, and you´ll see that good content spreads like an Ebola!

As far arse liking goes, good product, good feedback. What is so strange about that?

Edited by Finlandese on Friday 21st February 15:21
Look at 5th gear, that does quite poorly compared to TG, and I bet CH wouldn't get anywhere near the amount of views as that.

I love the videos, but they aren't mainstream TV, the audience isn't there IMO.
I might have made my point poorly..

My point is: For all those who hope that CH would have a tv show, don´t. The current format is better for his current, wordwide audience. It´s probably more satisfying for Chris and profitable enough to provide a comfortable life for Chris, doing what he loves.

epom

11,629 posts

162 months

Friday 21st February 2014
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Ah I dunno do I really like it that much ? Spose I'd take one, but only of they gave me a demo for a week or two !!