Neutral Or Drive?

[monya]

Having bought the Auris 3 days ago I'm no expert on hybrids but on previous automatics I've moved the selector into neutral when waiting in traffic queues. However, reading the handbook suggests the car to be left in drive as no Battery charging occurs in neutral.

Is this the usual practise? Prius owners should know as it's the same drivetrain so come on and tell!

[Jan&tone]

Having bought the Auris 3 days ago I'm no expert on hybrids but on previous automatics I've moved the selector into neutral when waiting in traffic queues. However, reading the handbook suggests the car to be left in drive as no battery charging occurs in neutral.

Is this the usual practise? Prius owners should know as it's the same drivetrain so come on and tell!

Monya, see the 'roundabouts' thread, lots of discussion there, basically lots of different opinions, take your choice!

[Terry953]

Having bought the Auris 3 days ago I'm no expert on hybrids but on previous automatics I've moved the selector into neutral when waiting in traffic queues. However, reading the handbook suggests the car to be left in drive as no battery charging occurs in neutral.

Is this the usual practise? Prius owners should know as it's the same drivetrain so come on and tell!

Read the previous post for a variety of ideas [thanks to all who contributed].

However I still maintain that the correct and safest method for most situations is to leave the gear in DRIVE and apply the Handbrake.

I see some references to a 'foot operated parking brake', in previous posts, is this a feature on the Prius?

I have a wonderful Auris which only has the clicky lever thingy with a knob to release it. [and before you comment on that - I don't let it click when applying it. Although I have been told that in some Honda Civics that is what they recommend !!]

Oh! as to my pet hate re brake lights - Yes I agree with all of what you collectively said there are lots of other issues to have a coronary by, but my brake light obsession was related to the subject in hand.

I also apologise for making derogatory remarks about neanderthals - not fair on genuine neanderthals.

Cheers TerryB

[Cord77]

One of the things I love so much about automatic cars (and I suspect more so in the Hybrids due to electric only power at low speeds) is how easy it is to creep along with stop start traffic. If its slow enough you only have to use one pedal. Of course if the traffic isn't going anywhere for a while then it makes sense to go into neutral with handbrake on. Since the petrol engine has probably long since switched off anyway, I don't think there is regenerative loss.

I notice the HSD has a B setting also which invokes engine braking, so maybe its possible to use that if going down a hill during traffic (I don't really know yet, getting my HSD on Wednesday).

[Jan&tone]

One of the things I love so much about automatic cars (and I suspect more so in the Hybrids due to electric only power at low speeds) is how easy it is to creep along with stop start traffic. If its slow enough you only have to use one pedal. Of course if the traffic isn't going anywhere for a while then it makes sense to go into neutral with handbrake on. Since the petrol engine has probably long since switched off anyway, I don't think there is regenerative loss.

I notice the HSD has a B setting also which invokes engine braking, so maybe its possible to use that if going down a hill during traffic (I don't really know yet, getting my HSD on Wednesday).

In 'N' the Prius and Auris do not charge, indeed will tell you so on the display. If you are stopped for any length of time you should either leave in 'D' with footbrake on (which nicely boils the brake fluid) or put the car in 'P'.

The 'B' indeed produces extra engine braking downhill and also gives extra charge to the traction Battery.

[Chris Dance]

Terry953. The "hand brake" on the Prius is foot operated. I suppose it is a foot operated parking brake.

When I was doing a forces driving test I recall failing the test for ratcheting the hand brake. You cannot avoid this when operating the foot operated brake on the Prius but I have never ratcheted a normal car hand brake since.

Chris.

[Sagitar]

leave in 'D' with footbrake on (which nicely boils the brake fluid)

I would be obliged if you would explain how? Perhaps I have misunderstood what you are saying?

Boiling brake fluid implies the transfer of heat from the friction surfaces - they generate heat only when they move relative to each other. With the brakes applied and the car stationary, there is no motion, hence no work, hence no heat generated.

[Jan&tone]

leave in 'D' with footbrake on (which nicely boils the brake fluid)

I would be obliged if you would explain how? Perhaps I have misunderstood what you are saying?

Boiling brake fluid implies the transfer of heat from the friction surfaces - they generate heat only when they move relative to each other. With the brakes applied and the car stationary, there is no motion, hence no work, hence no heat generated.

I have always understood that the pressure of foot on pedal compresses the fluid in the pipes etc and thereby generates heat. I could be wrong but was told this 45 years ago when learning to drive. This was given as the reason not to keep your foot on the brake pedal longer than necessary. Hence the reason to use P in an auto or N + handbrake in a manual car.

[timberwolf]

Maybe getting confused with a regular automatic with a torque converter where you could boil the transmission fluid - although I thought that was more about under load such as towing rather than sitting in traffic??

[Sagitar]

I have always understood that the pressure of foot on pedal compresses the fluid in the pipes etc and thereby generates heat. I could be wrong but was told this 45 years ago when learning to drive. This was given as the reason not to keep your foot on the brake pedal longer than necessary. Hence the reason to use P in an auto or N + handbrake in a manual car.

Then I am afraid you have been labouring under a misapprehension for all that time.

Static pressure alone will not generate heat. Heat is energy and in a static high pressure system no energy is expended. Leave you car sitting on a hydraulic jack for an hour and the jack will be no hotter at the end of the hour than it was at the beginning.

Hydraulic fluid has a high bulk modulus but will still compress a little under pressure. There are other flexible components in the braking system that allow some small movement in the system if you vary the pedal pressure with the brakes applied, but the movement is very small and the work done in creating that movement is equally small; certainly not enough to heat the hydraulic fluid significantly.

Putting a conventional auto in P or N is much more likely to be about disengaging the torque converter and saving petrol. In a manual car it's about saving wear on the clutch disengagement mechanism and preparing for the necessary balancing of handbrake, clutch and accelerator when starting off.

With the car stationary, and the brakes applied, the only energy going into the braking system is that from any movement of your foot (aided by the brake intensifier system). Imagine how hard and with what frequency you would have to pump the pedal to generate enough heat to boil the fluid.

[Jan&tone]

Physics was never my favorite subject! I have indeed been under a misapprehension but I still prefer P instead of the footbrake

[dwilson]

Physics was never my favorite subject! I have indeed been under a misapprehension but I still prefer P instead of the footbrake

I was told by a mechanic many years ago that coming to rest and then leaving the footbrake engaged at lights etc caused a lot of problems with discs warping because the heat generated in braking couldn't be dissipated.

[Grumpy Cabbie]

Physics was never my favorite subject! I have indeed been under a misapprehension but I still prefer P instead of the footbrake

I was told by a mechanic many years ago that coming to rest and then leaving the footbrake engaged at lights etc caused a lot of problems with discs warping because the heat generated in braking couldn't be dissipated.

You're quite right - on a car with a conventional engine and brakes. With the Prius you use the regen braking most of the time so the friction brakes don't get anywhere near as hot - IMHO. My experience so far shows no warped discs and I'm still on the original pads at 32k miles which for my job would be great on a manual car, yet alone an automatic.

I keep my car in Drive all the time, though will use Park if I know I'll be sat at the lights for some time. At first I was frightened that the Prius would be delicate, but the last year has shown it to be as hardy as any normal car - probably more so.

[kithmo]

The 'B' indeed produces extra engine braking downhill and also gives extra charge to the traction battery.

True "B" produces more engine braking, but reduced regeneration to the traction Battery.

[timberwolf]

You're quite right - on a car with a conventional engine and brakes. With the Prius you use the regen braking most of the time so the friction brakes don't get anywhere near as hot - IMHO. My experience so far shows no warped discs and I'm still on the original pads at 32k miles which for my job would be great on a manual car, yet alone an automatic.

I keep my car in Drive all the time, though will use Park if I know I'll be sat at the lights for some time. At first I was frightened that the Prius would be delicate, but the last year has shown it to be as hardy as any normal car - probably more so.

Do heavy braking or an emergency stop and the proportion of overall braking required from the friction will be much higher than under light braking. In an emergency stop (I think the Americans like to call it a panic stop) I'm not sure if the regenerative braking is used?

[Grumpy Cabbie]

You're quite right - on a car with a conventional engine and brakes. With the Prius you use the regen braking most of the time so the friction brakes don't get anywhere near as hot - IMHO. My experience so far shows no warped discs and I'm still on the original pads at 32k miles which for my job would be great on a manual car, yet alone an automatic.

I keep my car in Drive all the time, though will use Park if I know I'll be sat at the lights for some time. At first I was frightened that the Prius would be delicate, but the last year has shown it to be as hardy as any normal car - probably more so.

Do heavy braking or an emergency stop and the proportion of overall braking required from the friction will be much higher than under light braking. In an emergency stop (I think the Americans like to call it a panic stop) I'm not sure if the regenerative braking is used?

Posted a thread on PriusChat about a time when I had to do an emergency stop and the EBA thingy came on - now the car stopped in double quick time with hardly a chirp from the tyres. It almost felt like someone else was stomping on the brakes with me. Didn't check whether regen worked as I was concentrating on not hitting the car in front.

[timberwolf]

My Honda Civics used to add in brake assist going down the hill on the A4 into Maidenhead and I wasn't trying to emergency stop. It was a weird feeling to have the brake pedal move away from your foot.

I've not experienced it yet in my Prius, does the Prius press the pedal further down when applying the brake assist or is it all electronic?

[Grumpy Cabbie]

My Honda Civics used to add in brake assist going down the hill on the A4 into Maidenhead and I wasn't trying to emergency stop. It was a weird feeling to have the brake pedal move away from your foot.

I've not experienced it yet in my Prius, does the Prius press the pedal further down when applying the brake assist or is it all electronic?

Yes

[dwilson]

Physics was never my favorite subject! I have indeed been under a misapprehension but I still prefer P instead of the footbrake

I was told by a mechanic many years ago that coming to rest and then leaving the footbrake engaged at lights etc caused a lot of problems with discs warping because the heat generated in braking couldn't be dissipated.

You're quite right - on a car with a conventional engine and brakes. With the Prius you use the regen braking most of the time so the friction brakes don't get anywhere near as hot - IMHO. My experience so far shows no warped discs and I'm still on the original pads at 32k miles which for my job would be great on a manual car, yet alone an automatic.

I keep my car in Drive all the time, though will use Park if I know I'll be sat at the lights for some time. At first I was frightened that the Prius would be delicate, but the last year has shown it to be as hardy as any normal car - probably more so.

Good to know the brakes are lasting well, that's one less thing to replace too frequently. The Prius really is a most impressive car.

[Ancient Nerd]

Physics was never my favorite subject! I have indeed been under a misapprehension but I still prefer P instead of the footbrake

I was told by a mechanic many years ago that coming to rest and then leaving the footbrake engaged at lights etc caused a lot of problems with discs warping because the heat generated in braking couldn't be dissipated.

You're quite right - on a car with a conventional engine and brakes. With the Prius you use the regen braking most of the time so the friction brakes don't get anywhere near as hot - IMHO. My experience so far shows no warped discs and I'm still on the original pads at 32k miles which for my job would be great on a manual car, yet alone an automatic.

I keep my car in Drive all the time, though will use Park if I know I'll be sat at the lights for some time. At first I was frightened that the Prius would be delicate, but the last year has shown it to be as hardy as any normal car - probably more so.

Good to know the brakes are lasting well, that's one less thing to replace too frequently. The Prius really is a most impressive car.

My last Gen II Prius (2008, 08 reg) is still in the family. Now around 75,000. Still on the original brake pads

[johalareewi]

My Honda Civics used to add in brake assist going down the hill on the A4 into Maidenhead and I wasn't trying to emergency stop. It was a weird feeling to have the brake pedal move away from your foot.

I've not experienced it yet in my Prius, does the Prius press the pedal further down when applying the brake assist or is it all electronic?

The Prius doesn't move the pedal.

If you hit the brakes quickly, the Prius decides you want to stop on a sixpence and does it.

It is very impressive.

[Jan&tone]

My Honda Civics used to add in brake assist going down the hill on the A4 into Maidenhead and I wasn't trying to emergency stop. It was a weird feeling to have the brake pedal move away from your foot.

I've not experienced it yet in my Prius, does the Prius press the pedal further down when applying the brake assist or is it all electronic?

The Prius doesn't move the pedal.

If you hit the brakes quickly, the Prius decides you want to stop on a sixpence and does it.

It is very impressive.

I'd go a bit further than that one johal... basically the Prius does what it says on the tin! endof....