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Terry953

Differences Between P And N

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Another interesting point to address has arisen on this post and that is the technical difference between P and N positions ?

Ian Rooke raises the issue and is correct in assuming that conventional automatic gearboxes like Borg-Warner 35 and I think 45 models [i.e. those with a torque converter coupled to an epicyclic gear train] are mechanically locked in P.

These have a ‘sprag’ which is a metal pawl that mechanically engages with an externally toothed ring on the gear train to positively lock the train to the gearbox case with no gear being selected in the P position. But the handbrake should also be applied for correct vehicle parking not just rely on the P position.

In the N position, again no gear is selected but the spring is not engaged so if the handbrake was off the vehicle could be pushed or would move. Again the handbrake should be applied. [as a matter of interest I had a SAAB 99 Auto and you could not remove the ignition key until you had selected the P position.]

In both N and P the engine, gearbox and torque converter are relieved of stresses compared to the situation with if a gear was engaged and brakes applied - release the brake and the vehicle will creep without throttle application - great for traffic jams.

I consider this an asset of auto gearboxes.

NOW concerning our hybrids, despite research I have yet to dig up much real technical detail of our systems, but the driving symptoms are similar as follows :---

Select P - release brakes - the vehicle can be rocked. So I would assume that there is a similar positive mechanical lock as in the Borg-Warners.

Select N - release brakes - the vehicle will move - but remember NO Charging takes place.

Select D - release brakes - with no throttle the vehicle will creep - great for traffic jams.

In this attitude there is definitely stress on the engine, Battery/transmission, if you then

select N or P the vehicle gives a sort of sigh of relief. I am not saying this is detrimental

but as in the Borg-Warners there is a case for not holding it in gear for long waits.

I would say select P [not N remember no charging especially if at night] and apply the hand brake. It only takes milliseconds to select D when you are ready to drive off anyway.

Cheers Terry

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I agree Terry, I think that seems to be the correct way to proceed with the Prius and Auris.

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When in Drive and stationary with the brake pedal pressed, the Hybrid system will after a short time cut all power to the electric motors (creep function is disabled), so there isn't the stress as in a conventional automatic.

The Hybrid Synergy Drive in the Auris Hybrid is the same as the Prius Gen 3, and is a refinement of the Gen 2 and Gen 1 before that, all the Toyota Hybrids work the same basic way, so you shouldn't have any trouble finding technical explanations of how stuff works.

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Just addiing to the thread....

P engages a mechanincal lock on the transmission, so if you are in "P", the car will not move.

N does not engage the electric motor/generator, and does not engage the transmission lock, so the car will move (you need to be in "N", and in "READY" to enable the car to be pulled through a carwash, or to push it around by hand)

Thanks to all the "fly-by-wire" computer magic on the car, the gear selections are actually managed by the computer, so..... if you are driving along and try to select "R", or "P" the system will put you in "N" so as not to do any damage

If, as you are driving along, you engage "N" you won't recharge the batteries

I also seem to remember (but am happy to be corrected) that if you select "B" (engine braking) then you will not recharge the batteries either.

When you switch off the ignition "press START", the system puts you in "P" automagically

So, if you are bone idle,(like me), once you get to your destination, you don't bother touching the gear lever or engaging the foot-operated parking brake, you simply press "start" to shut down all systems. The computer will lock the transmission, so the car won't go anywhere. If I'm on a steep hill, then I may get cautious and engage the parking brake.

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(you need to be in "N", and in "READY" to enable the car to be pulled through a carwash, or to push it around by hand)

Just thinking. What happens if you have broken down (the hybrid system has failed for what ever reason) and you can't get the car into 'ready'? How would you push by hand then?

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Just thinking. What happens if you have broken down (the hybrid system has failed for what ever reason) and you can't get the car into 'ready'? How would you push by hand then?

Yes that's a nice one Gav18, I presume your total failure happens when you were in 'P'.

Good tip about the car wash 'Dave R' and I'm sure you are correct about 'B'.

My reaction would be :--

1. Call up Club Toyota rescue service.[i suspect they would recover the car with a front suspended tow.]

2. If you just happened to have a trolley jack in the boot you could jack up the front and drag it around.

A point here though is that Toyota don't recommend towing or pushing with the front wheels on the ground because the road wheels would rotate the M/G 2 [Motor Generator] and produce a charging current to the HV Battery with possible dire results.

Will just add a follow up to the pro's and cons of the parking/waiting in D - P or N saga.

After some further research :--

By studying various third party and Toyota Nomographs into the N and P differences in our HSDs I have come to the following conclusions.

SITUATION :--

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.e. READY] -

Transmission in ‘N’ =

Nothing moves, meaning =

The Engine is OFF -

The M/G [Motor/Generator] 1 is stationary - so not charging -

The M/G 2 is stationary. So vehicle is not moving.

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.e. READY] -

Transmission in ‘P’ =

Nothing moves, meaning =

The Engine is OFF - so not charging - But if the computer senses that power is required it will start up to charge the Battery.Bear in mind that our Atkinson engines idle &1000 rpm no less.]

The M/G 1 [Motor-Generator] is stationary - But if the computer senses that power is required the engine will start up and drive M/G 1to charge the Battery.

The M/G 2 is stationary. So vehicle is not moving.

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.E READY] -

Transmission in‘D’=

The Engine is OFF - so not charging - But if the computer senses that power is required it will start up to charge the Battery.

The M/G [Motor-Generator] 1 is stationary - But if the computer senses that power is required the engine will start up and drive M/G 1 to charge the Battery.

As ‘D’ is engaged the computer wants to energise M/G 2 to move the vehicle but can’t because the parking or foot brake is applied. So energy is wasted, and the generated heat is dispersed by the transmission cooling system.

[Can’t find any reference to any inhibitors that will combat the build up of excessive heat in this situation. But it must waste energy anyway.]

Release the Brake = The vehicle moves off.

Conclusions for the vehicle stationary / waiting situation :--

1.Don't stay in 'N' for too long or excessive Battery drain will occur [especially at night].

2.Don't stay in 'D' for too long as transmission overheating could occur and fuel/electrical energy waste will occur.

3.Select 'P' for long waits ex. road works traffic lights etc.

Or am I being pessimistic?

Must now do some practical testing.

Cheers TerryB

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<snip>

Vehicle Stationary - Parking or foot brake ON - Electrics switched ON [i.E READY] -

Transmission in‘D’=

The Engine is OFF - so not charging - But if the computer senses that power is required it will start up to charge the battery.

The M/G [Motor-Generator] 1 is stationary - But if the computer senses that power is required the engine will start up and drive M/G 1 to charge the battery.

As ‘D’ is engaged the computer wants to energise M/G 2 to move the vehicle but can’t because the parking or foot brake is applied. So energy is wasted, and the generated heat is dispersed by the transmission cooling system.

[Can’t find any reference to any inhibitors that will combat the build up of excessive heat in this situation. But it must waste energy anyway.]

Release the Brake = The vehicle moves off.

Conclusions for the vehicle stationary / waiting situation :--

1.Don't stay in 'N' for too long or excessive battery drain will occur [especially at night].

2.Don't stay in 'D' for too long as transmission overheating could occur and fuel/electrical energy waste will occur.

3.Select 'P' for long waits ex. road works traffic lights etc.

Or am I being pessimistic?

I am not convinced that your assumption that the computer in always trying to energise MG2 when your foot is on the brake is correct. The appropriate ECU can determine if the brake pedal is pressed and can therefore decide to cut power to the motor. My Observation on a Gen 2, is that with very light brake pedal pressure when stopped, the yellow lines will be displayed on the MFD, but if you press the brake pedal a little more then yellow lines go out, which would seem to indicate that the power is no longer being directed to MG2. (Granted the MFD may be dampened down not to show small current consumption).

If you haven't found this article already, you may find it interesting, look at page 18 about the Inverter power transistors being switched off when in Neutral.

2007_TSSN_Fall.pdf (or search google for 2007_TSSN_Fall.pdf it's a pdf link at www.toyotapartsandservice.com)

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If you haven't found this article already, you may find it interesting, look at page 18 about the Inverter power transistors being switched off when in Neutral.

http://www.toyotapartsandservice.com/pub/pdf/TechCenterLibrary/ToyotaStubikrviceNews/2007/2007_TSSN_Fall.pdf

We may be at cross purposes here comparing a Gen2 Prius with a month old Auris HSD.

I don't have any yellow lines on my MFD to check on.

Your link wouldn't work, I did try shortening it and got through to the library, but gave up when the pick list only went to 2008, and it didn't even list the Auris in other pick lists. In fact all my research is on Prius data as I can't yet find anything specifically Auris.

I know the technology is basically the same, but look at the differences between 01-03 Prius and the 04 and later versions when you start digging into the detail.

The only way to sort this is to do a practical test and see what happens, I'll post when I get a result.

TerryB`

OOps! left a bit out:--

You are correct that in 'N' no power goes to the M/G2,

[Most jurisdictions require automotive transmissions to have a neutral gear that decouples the engine and transmission. The HSD "neutral gear" is achieved by turning the electric motors off.]

However my concerns are with 'D' selected and the vehicle braked by the park or foot brake, this is when I assume current is supplied to MG2 and stress is put on the transmission.

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Oh dear, the link must have been too long - I've edited my previous message with a tinyurl.com link instead (hope that works never used the service before), but it doesn't contain Auris HSD specific information.

I know only the Gen 2 has the colour display, I was using it as an example to show what I and others have observed on the Gen 2 when stationary on the brakes.

Q. Why do you believe that the Auris HSD operates differently from the Prius Gen 2 and 3 with regards to control of the MG2 when stationary on the brakes?

I can't see how you can prove this unless you hook up a laptop to measure the HV amperage usage? I imagine, not an easy task as you'd probably have to figure out if any of the Toyota specific CAN bus codes have changed.

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I can't see how you can prove this unless you hook up a laptop to measure the HV amperage usage? I imagine, not an easy task as you'd probably have to figure out if any of the Toyota specific CAN bus codes have changed.

From practical tests I have confirmed the following :---

1. Ready ‘ON’ - ‘N’ selected - any brake ON or OFF - No throttle = No charge to HV

Battery - vehicle free to move, [i.e. pushing - coasting downhill - rolling backwards

etc].

2. Ready ‘ON’ - ‘D’ selected - No throttle = HV Battery discharges to MG2.

If a brake is OFF vehicle moves in EVO mode.

If a brake is ON discharge is dispersed as wasted energy = [fuel and HV Battery

capacity].

Select N - HV discharge stops - vehicle bucks as load is removed, if engine is

running the speed drops audibly.

ALL the above is visibly demonstrated on the Auris ‘Multi Information Display’ in the ‘Energy Monitor’ mode.

Additionally, in traffic queues, if you creep forwards in ’D’ you quickly drain the HV Battery capacity, so the engine will start up to charge the HV Battery , there is no indication that this is happening [apart from engine noise] but it must be or in a long queue the HV Battery would be drained.

To avoid the obvious stress to the system of keeping it in ’D’, I select ’N’

[in this situation you are not going to charge the Battery by regenerative means anyway, even if you are in ‘D‘] .

When it is time to move again it’s back into ’D’ to creep [basically in ECO mode] forward and stop - then back into ’N’.

I was unfortunate to-day to be caught in traffic queues and evaluated the above over the 1½ hours I was trapped to cover around 6 miles.

This episode has given me further confidence in my Auris and has defined for me the correct useages of 'N' & 'D'.

If your Prius performance / information display doesn’t match my Auris as above then there are some differences to start with.

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Additionally, in traffic queues, if you creep forwards in ’D’ you quickly drain the HV battery capacity, so the engine will start up to charge the HV battery , there is no indication that this is happening [apart from engine noise] but it must be or in a long queue the HV battery would be drained.

To avoid the obvious stress to the system of keeping it in ’D’, I select ’N’

[in this situation you are not going to charge the battery by regenerative means anyway, even if you are in ‘D‘] .

When it is time to move again it’s back into ’D’ to creep [basically in ECO mode] forward and stop - then back into ’N’.

Hmmm. In the effort to ease strain on the car in stop-start traffic, I started to move the car in D, then knock it into N and freewheel to a stop. Then I read these warnings in the manual:



Do not under any circumstances shift the shift lever to “R”, “N” or push the “P” position switch while the vehicle is moving. Doing so can cause significant damage to the transmission and may result in a loss of vehicle control. *

Do not shift the shift lever to “N” while the vehicle is moving. Doing so may cause the engine brake not to operate properly and lead to an accident.


* So if the car is doing a "runaway" then you cannot knock it into neutral? Why not? (Not that I am concerned about my Prius doing a sudden "runaway" on me in spite of the US instances (or, I should say, alleged instances).

Anyway, the point is that, seemingly, N is verboten when the car is moving, does that include freewheeling forward at 2MPH?

To be honest, if the car can only go into N when stationary, I don't see the point of using it in traffic. One might as well simply press the P button. To get moving, one still has to press on the brake pedal to engage D. I would love to be able to simply engage D without having to put my foot on the brake. But I suspect there are safety reasons why manufacturers do not allow it e.g. to ensure that a person is actually sitting in the driver's seat and the shift lever has not been knocked into D by a passenger brushing against it.

R04drunner1

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Hmmm. In the effort to ease strain on the car in stop-start traffic, I started to move the car in D, then knock it into N and freewheel to a stop. Then I read these warnings in the manual:

Anyway, the point is that, seemingly, N is verboten when the car is moving, does that include freewheeling forward at 2MPH?

To be honest, if the car can only go into N when stationary, I don't see the point of using it in traffic. One might as well simply press the P button. To get moving, one still has to press on the brake pedal to engage D. I would love to be able to simply engage D without having to put my foot on the brake. But I suspect there are safety reasons why manufacturers do not allow it e.g. to ensure that a person is actually sitting in the driver's seat and the shift lever has not been knocked into D by a passenger brushing against it.

R04drunner1

Hey RO4drunner,

1. Who said anything about selecting D to get vehicle moving and then selecting N to coast to a stop ?

MY TEXT WAS = "When it is time to move again it’s back into ’D’ to creep [basically in ECO mode] forward and stop - then back into ’N’."

2. There is no restriction on moving the vehicle in N that’s the only way it can be pushed or towed.

What about the emergency towing instructions ? =

STEP3 Change the shift position to N

3. After the initial gear selection after start up where the footbrake must be applied, I can select from N to D or P or R or back again without further footbrake applications, as long as the parking brake is applied it is safe.

So applying the foot brake for every gear selection is not necessary.

4. Come on RO4drunner do some research and RTFM.

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Hey RO4drunner,

1. Who said anything about selecting D to get vehicle moving and then selecting N to coast to a stop ?

I said that. Not you. I never said you did.

I was trying to discuss what I thought was a related topic. To make it clear, for the record, I was not suggesting you had encouraged the use of N to coast to a stop. I brought it up because I found your posting about the use of N and P very interesting and useful and I wanted to ask about that related issue.

2. There is no restriction on moving the vehicle in N that’s the only way it can be pushed or towed.

What about the emergency towing instructions ? =

STEP3 Change the shift position to N

I was only quoting the manual that said:

Do not
under any circumstances
shift the shift lever to “R”, “N” or push the “P” position switch while the vehicle is moving...

(emphasis mine).

I would assume the emergency towing instructions you refer to apply when the vehicle is stationary before moving off. Also your earlier posts about using N to allow the car to be manually pushed would be the same scenario. What I wrote as a quote from the manual in no way contradicts what you were saying earlier. In fact, to be honest, I had been wondering just what the point of N was. Your post was very instructive. Thank you for it.

3. After the initial gear selection after start up where the footbrake must be applied, I can select from N to D or P or R or back again without further footbrake applications, as long as the parking brake is applied it is safe.

That is absolutely news to me, I will try it. Thanks for the tip.

4. Come on RO4drunner do some research and RTFM.

I have been reading the fine manual, thank you. As you say, some of the finer details only come out with a bit of trial and error.

Thanks again for your informative posts. As my post evidently gave you the impression I was criticising you or calling your research into question, I do apologise. That was never my intention.

Regards

R04drunner1

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I have been reading the fine manual, thank you. As you say, some of the finer details only come out with a bit of trial and error.

Thanks again for your informative posts. As my post evidently gave you the impression I was criticising you or calling your research into question, I do apologise. That was never my intention.

Regards

R04drummer1

Points taken RO4drunner, and I thank you for your gracious reply to my rather forthright posts, but that's me, forthright and brusque.

I did have a sneaking suspicion you were winding me up though, but obviously not.

The main thing is learning and understanding was achieved by all and isn't that the value and purpose of these forums ? :cheers:

Regards TerryB

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The main thing is learning and understanding was achieved by all and isn't that the value and purpose of these forums ? :cheers:

Very well put Terry: that's exactly it. And I look forward to more!

Cheers B)

R04drunner1

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Hmmm. In the effort to ease strain on the car in stop-start traffic, I started to move the car in D, then knock it into N and freewheel to a stop. Then I read these warnings in the manual:



Do not under any circumstances shift the shift lever to “R”, “N” or push the “P” position switch while the vehicle is moving. Doing so can cause significant damage to the transmission and may result in a loss of vehicle control. *

Do not shift the shift lever to “N” while the vehicle is moving. Doing so may cause the engine brake not to operate properly and lead to an accident.


* So if the car is doing a "runaway" then you cannot knock it into neutral? Why not? (Not that I am concerned about my Prius doing a sudden "runaway" on me in spite of the US instances (or, I should say, alleged instances).

Anyway, the point is that, seemingly, N is verboten when the car is moving, does that include freewheeling forward at 2MPH?

To be honest, if the car can only go into N when stationary, I don't see the point of using it in traffic. One might as well simply press the P button. To get moving, one still has to press on the brake pedal to engage D. I would love to be able to simply engage D without having to put my foot on the brake. But I suspect there are safety reasons why manufacturers do not allow it e.g. to ensure that a person is actually sitting in the driver's seat and the shift lever has not been knocked into D by a passenger brushing against it.

R04drunner1

Accidently pressed "P" whilst driving the other day.... all that happened was that the car put itself in "N".

Following the scares earlier in the year about "runaway Priuses" there were a number of articles published, and Youtube videos showing that the car electronics tend to protect everything, safely putting the car into "N" if you try to do anything out of the ordinary.

Personally, I can't see the point of putting the car into "N" whilst driving (or stuck in traffic). My belief is that the computers "know" to turn the MG1 or MG2 off when the car is stationary with the brakes applied.... it certainly seems to be the case when you look at the MFD on the GEN 3 - nothing flows from Battery to motors when the car has stopped.

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