Trick for P&G On an automatic.. Hint, you need Cruise Control
 

I think I discovered the answer for those who would like to do pulse and glide on an automatic. While I have not tried this on any other cars thus far, I believe it will certainly work with Toyotas equipped with cruise control. I have an automatic, actually at the moment, all the cars I have are automatics. One problem is, if you wanted to do Pulse and Glide, you have to shift into neutral in order to coast which is fine but to shift BACK into drive while you're still moving WILL damage the transmission, for an automatic at least. Now if you tried to do the Pulse and Glide with out turning off the engine and just letting off the gas, you'll end up with engine braking which is BAD because that prevents you from GLIDING.

I noticed something when I have cruise control enabled and I catch a slope. For me, at 55mph the tach reads around 1500rpm, that is what it takes in order for it to maintain speed on the highway due to gearing of the transmission, fair enough. So I have cruise control set at 55mph and I catch a slope, now the car is accelerating to 60mph, but if I watch the tach, something happens. Instead of the RPMS increasing in line with the higher speeds which would lead to engine braking and the quick slow down to 55mph, something else happens. Since an automatic can engage and disengage the transmission at any time with degrees of engagement in between, what I'm about to tell you make makes perfect sense. So what I see are the RPMs drop to 1200, then 1000 and I think at one point 800. This means that the transmission goes into neutral when the car accelerates faster than the set speed of the cruise control and when the throttle isn't used, i.e. when coasting down a hill. I'm sure it does this in order to prolong your coast and for you to enjoy the extra speed you're picking up by coasting down the hill.

This is great news, when I'm going faster than my set cruise controlled speed, the transmission goes into neutral in order to not cause engine braking which means it won't hurt my coasting at the higher speed. Ok so how can this help a hypermiler who wants to glide for long as possible while at the same time not damage their automatic transmission? Well.... since noticing this while I'm driving on the highway, before I get off I disengage the cruise control and try to coast for as long as I can. Unfortunately if I disengage it too quickly, I'll slow down so quickly and will end up having to speed up temporarily. The reason I'd slow down faster than I'd want to is because of the engine braking that normally occurs when your foot is off the throttle and cruise control isn't enabled.

If you look at the cruise control knob on a Toyota, you'll see three arrows, one pointing up, one down and one outward. The up means "accelerate" and the down means "decelerate" and outward meaning cancel. One tip people have mentioned is using cruise control to accelerate at a very moderate pace in order to save fuel. Well cruise control can come in handy for another thing, for when you want to GLIDE. Gliding is a problem on an automatic unless you have no respect for your transmission or all your routes are down hill on at least 5% grade because of engine braking.

So when I discovered that the transmission disengages when the car goes faster than the set speed of cruise control so that you will coast while at the higher speeds, I figured I'd try something else. Instead of canceling the cruise control right before I got off the highway in order to coast, I instead held the cruise control knob downward in order to keep telling the cruise control to "decelerate", meaning to reduce my set cruise control speed. What this did was effectively do the same thing as when I had the cruise control set to 55mph and the car accelerates to 60mph due to other forces besides the throttle such as being on an incline. So by telling the cruise control to decelerate, the transmission basically goes into neutral and I was then able to glide a much farther distance since there was no engine braking.

Summary: Pulse and Glide doesn't work with an automatic unless you have no respect for your drivetrain. You can shift out of gear while moving but to shift back on an automatic while moving WILL destroy your transmission. You can't easily glide on an automatic because you will have some sort of engine braking somewhere except in one case. If you're going 55mph, have cruise control enabled and then hold "decelerate" on the cruise control continuously, the car will not use engine braking. It will not use engine braking because in this specific scenario the transmission will self disengage and effectively be in neutral, therefore permitting an actual glide.

I have found this only to be true on one car which is a Lexus, but the cruise control functions similarly on all toyotas. I plan to test this on my other cars when given the chance and I believe they will all peform the same due to them acting the same in similar circumstances. I do not know if this will work for you but there is no harm in trying. I would not be surprised if this was limited to only new toyota based cars and that were made in the last 5 years.

So if you put your transmission in neutral it will explode, but if your cruise control does it it won't? oooookayyyyyy...

I can't imagine why shifting from N to D will cause damage. Has it happened to you?

I've been P&Ging in my GMC for a while now (1 month, ~1200 miles) and had no problem, even though the transmission I have is supposedly weak. I've also used N randomly (mainly out of boredom) since I began driving 12 years ago. I've never had a transmission problem.

Also, I seriously doubt that your computer shifts the transmission into neutral when the cruise control is set. Try the following experiment:
- First, try your recommended procedure, and note the exact RPM it eventually settles to at a given speed
- Then, try it without cruise control, just take your foot off the gas, and again note the RPM it settles to at the same speed

I doubt they will differ.

- Finally, try it in N (if you're not afraid to). See if it settles to even lower RPM.

Automatic transmissions are equipped with a torque converter, which doesn't mechanically connect the engine to the transmission. Instead, it connects them (this explanation is a bit simplified but gets the point across) using two opposed turbines pushing transmission fluid at eachother. This means that, at any given speed, the engine can go a lot faster or slower than if it was connected with a clutch from a manual transmission. It also means that you can be in gear at a complete stop and the engine doesn't stall. It also means that you can be in gear, coasting down a hill, and the engine can settle down to near idle speed without the transmission having to disengage the gear.

The transmission shifts in and out of neutral all the time, especially when shifting gears, the difference is, it's in a controlled manner and it's by design. It's not part of the design for you to manually shift it into neutral and then shift it back into gear while moving. When was the last time you moved a lever in order to get the transmission to lock up the torque converter? You don't, it does it for you when the conditions are right. It's far different to move the shifting in and out of neutral than for the transmission to do it for you.


Here is an example: You're cruising at 25MPH in 5th gear, you floor it in your automatic, what happens? The transmission smoothly shifts into a lower gear, and how low depends on a lot of factors but may go as low as 1st gear. Now if you read the manual, it says not to press on the accelerator when shifting into a lower gear. But isn't that the same thing? Well it is and it isn't, when the manual speaks of not accelerating while shifting into a lower gear, it's because the driver took the shifter and put it into a lower gear while accelerating, BAD IDEA. But when you simply press on the throttle and have the transmission shift for you, then it's ok. This is less of a problem on newer automatics since in my experience will prevent you from shifting into too low of a gear by giving an audible alert and staying in gear. On an older automatic, there is no such protection and it WILL let you shift into a lower gear even if that means redlining it. There are a lot more protections now than there were 10 years ago.

If you've ever accelerated while moving the shifter into a lower gear (not saying you should, it's a BAD IDEA!) you'll hear some bad sounds and it'll feel very wrong, because it is. But when I floored it in my automatic, it downshifted AS I was accelerating yet it doesn't sound wrong or funny by any measure and that's because it's in a controlled manner while shifting into neutral and then back into Drive is NOT.

I don't think you read my post, read it again.

I think it means that you don't need to use the throttle pedal to rev match when using the lower gear for engine braking on hills.

Pop quiz hotshot, to bring out your inner auto tranny expertise, what's better hard firm shifts or smooth as butter shifts you can barely feel?

Oh oh I know! Can I answer?

Last Friday, although it was a button instead of a lever, and it's a mod that I put in. ;)

Toyota automatics generally disengage the TCC but remain in gear at closed throttle. The lower engine speed that you're seeing is the engine being backdriven through the torque converter, which is dissipating kinetic energy in the TC fluid and engine. If you compare high speed coasting distances (e.g. 60-40 MPH) at "decel" and in neutral you should find that the coastdown distances in neutral are longer.

Even though my car isn't rated for flat towing, I've been EOCing for at least 15,000 miles without any problems so far (knock on wood).

15,000 miles is nothing, just like the above poster who said 1500 miles. Anyhow the point was, using the cruise control to keep the car in neutral with out actually shifting in neutral would be better for the transmission than actually shifting it for the reasons I outlined above. And to further add that 15,000 miles is nothing, I know of a guy who drove around 100,000 with out ever changing his transmission oil before something went wrong. This was on a very old GMC Sierra so it wasn't one of those vehicles that are meant to go 100,000 miles between transmission fluid changes.

I going to give this a try on the "Do Not Flat Tow" iAWD auto SX4. There's not many hypermiling techniques that I can do with this car, but this might work. Thanks for the tip!

You still haven't explained why you think N->D will destroy an automatic transmission, nor why you think you're in neutral instead of merely having the torque converter unlocked.

The behavior you observed, regardless of its actual nature, is not universal (nor did you suggest that it is). Here's one data point: I tested in my 2002 GMC, and the torque converter does not unlock at 65mph when I use the "coast" cruise control function, when cruise is on while going downhill, or when I merely take my foot off the gas. At tbat speed, the only conditions that will cause the torque converter to unlock are a throttle-induced downshift (whether from cruise or my foot), or me manually selecting "N".

Just because the torque converter is unlocked, it does not mean that power is not being transferred from the engine to the transmission or vise versa. It wasn't until the late 70s or early 80s I believe where you saw vehicles being equipped with torque converter lockup. If anything, having the torque converter UNLOCKED would mean higher RPMs, not lower. The torque converter locks up at steady speeds, not when accelerating, and or if accelerating, at a moderate pace. More modern vehicles today support not only full torque converter lockup, but some even partial lockup at half way and then some where the torque converter lockup is variable much like a CVT transmission's gear ratios are to an extent.

So, you're saying that while you're decelerating downhill, that if the TC was unlocked, the engine would rev up faster???? mmmmkay.

I have a feeling you're confused about the purpose of a torque converter and when the torque converter is unlocked and should be locked. In Older vehicles since the torque converter was unable to lockup, downshifting and going down a hill would result in weak engine braking. But in newer vehicles, supposedly the torque converter is suppose to lockup to result in BETTER engine braking.

In simplest terms, think of a torque converter like a clutch, it allows slippage between the engine and the drivetrain. It's not a perfect example but it's good enough for the purpose of this discussion I feel.

Nope. totally clear on what a TC is thanks.

So you understand that if the TC is unlocked while going downhill, with a closed throttle the revs would drop?

Good so now we can get back to...

How do you know it's going into neutral and not just unlocking the TC?

Actually I don't, I really really have absolutely nothing concrete to prove this, it's really just my intuition. But it is my understanding that a torque converter that is slipping the most that it can would still yield higher engine RPMS than having the transmission in neutral. And when I held the cruise control downward in order for it to "reduce speed" the RPMS dropped to what I believe is idle for this car, effectively being in neutral.

If it's not shifting into neutral and simply just telling the torque converter to slip" or even to completely disconnect which I'd say is basically neutral, then what we should be asking ourselves is this:

What would put more stress on an automatic transmission? Shifting it into neutral while moving and then shifting it back into Drive, something the manual tells us NOT to do. Or when attempting to glide, telling the cruise control to "decelerate" which we speculate either shifts the transmission into neutral for us, in a controlled manner and or causes the torque converter to slip and or entirely disengage.

Modern toyotas seem to have a funny way of defining "idle speed". When I coasting, I shifted the car into neutral and even though it indicated I was in neutral, the "idle speed' was around 1000RPM despite the engine being fully warmed up. Also getting the car to be at its lowest idle speed has been quite a challenge and for the most part I've found it to idle around 1000rpm but sometimes 800rpm even when fully warmed up.

I confirm that you have only moderate knowledge of how your automatic transmission works *************. an automatic does NOT have to shift to neutral between gears. being in only one gear at a time is solely an issue of manual gearboxes, regular or sequential. an automatic uses 1-3 planetary gearsets with clutch packs and brake bands to control gears, all that's required to shift gears in an automatic is to engage or disengage. if it's in X gear and wants to go to the next gear and it's in the same gearset, all it may have to do is release a brake band and viola it's in the next gear. the power drop between shifts is slippage of the clutch packs themselves with low line pressure (which most cars, especially GM products, have). If you do like me and play with the throttle position tranny cable (miscalled the kickdown cable usually) my toyota A340LE transmission would engage with enough pressure to accelerate during upshifts from the raised line pressure as the engine revs were brought down.

they also do NOT shift to neutral when coasting or stopping. the automakers and insurance companies decided that having engine braking automatically combined with DFCO was the best trade off of safety/FE. all you're seeing is torque converter slippage (you also need to look up how these work) which on most cars is around 2k rpm difference. My toyota A340 stall speed with the 7MGE is 2100 rpm. that means if you hit the brakes and floor it, the engine rill rev as high as 2100 rpm without moving the car. why is this relevant? it means that by design, the engine speed can be +/-2100 rpm from what it would be if the torque converter clutch were locked up in a given gear.

be careful making sweeping statements like "shifting from N-D WILL destroy your transmission". It won't usually. maybe if you have crappy gearboxes from the start. I have a buddy that's been beating his Toyota A340 gearbox for 70k miles with 170k on the car. that's frequent redlining, manual holding gears to redline (with both normal and tweaked line pressure), manual shifting, and redline neutral drops (that's launching from a stop by flooring it then going from neutral to drive) N-D =bad is an insurance/CYA (cover your ***) thing. it usually doesn't do any harm especially if you give it a little gas to rev match. (the torque converter make it VERY forgiving).

ALL cars have a very funny way of defining idle speed... generally you have a cold-idle speed to warm up, hot idle speed when not moving which is the lowest you'll get it, and moving hot idle speed which is a little higher to facilitate N-D shifts and also partially because most cars have a cold-air snorkel to somewhere on the front of the car, which is gonna have higher pressure if only half a psi.

There are some many falsehoods in this thread based on "intuition" that's its embarrassing. An automatic does not select gears the same way a manual does. Yeah. I thought this thread would have information useful to help me with P&G, but it seems I will continue with my own avenue of experimentation.

Well considering a lot of vehicles aren't meant to be dinghy towed combined with shifting constantly from gear to neutral and back again while still moving sounds like a disaster waiting to happen with driver's manuals stating this. Also I doubt many people would be perfectly rev matching since that would mean more work and less benefit to mileage.

That's a dumb way at looking at what you've read. Just because the theory behind the idea is incorrect, it doesn't make the idea itself any less valid. Furthermore how the transmission shifts is completely irrelevant to my discovery because when gliding, the tach maintains a constant speed, as if it was in neutral which goes back to what my "intuition was".

Long post, hope you find it useful reading.

Very well then, that's a fair statement. I will proceed to study what you have said and reply based upon your observations of your particular vehicle and the replies of others. I may truncate posts to minimize the length of this post.
I applaud you for taking the time to study your vehicle and how best to gain mpg with P&G. However, taking it personally when someone has a different situation or has a greater knowledge about the subject seems callow. Why am I writing in red? There, that's better.

I think you have the right attitude about researching your vehicle for better mileage, but how you presented it could have been better. You're right about coasting downhill, cruise off, TC unlocked. The speed causes drag, raising the rpms of the engine. RoadWarrior raised a valid point as the first reply: What's the difference between the Cruise engaging neutral or you? If you're coasting downhill, and Cruise ON, 1000rpms, what happens when you reach the bottom and the Cruise has to raise the rpms to match the vehicle speed? I don't believe it does anything different than what manual shifting to neutral does. Both cases the TC has unlocked, slowing the fluids within, removing the majority of the connection between tranny and engine.

I could theorize and state more scenarios, but honestly I'm getting bored with writing this post (I say that jokingly). There are a lot more variables to test and remove to figure out exactly how the tranny reacts, in all situations. I myself will be on a roadtrip next weekend, and I plan to test some of these things you've brought up; it's made me think about how my tranny reacts to the different situations.

Again, I'm apologize for saying this thread is worthless. After reading all of it several times, I see even I have some things I need to test and prove regarding P&G in an automatic, specifically mine.

This thread is giving me a headache.

*************, I can understand why you feel like you're under attack. However please know that that is not the case; while I can't speak for everyone in this thread, I doubt anyone has any different intentions than I do. I merely want to find out what new information you have and how you got it, and either change my own practices or educate you on how you may be misinformed.

As such, I am concerned about my own practice of P&G in my automatic. You still haven't backed up this statement:
with any theory or anecdotes. Can you say why you believe that? If it's going to destroy my transmission I'd rather stop.

It sounds like you think the TC can slip in only one direction. Perhaps this is where things are unclear? The TC happily allows slippage in either direction -- the engine could move faster or slower than the transmission.

Theoretically there could be more wear from shifting in and out of N/D vs. just unlocking the TC (which in most vehicles can be done with the gas pedal just as easily as with the cruise control). In practice I don't think the wear is significant, especially if you rev-match.

This was discussed pretty thoroughly in another thread just a couple days ago. It was decided that either friction in the transmission (due to the transmission fluid) is turning the engine a little faster (I think this is the case; if you put the car on blocks, start the engine, and put it in N, the wheels will start to turn a little) or the computer is idling it a little faster (as it does under other conditions, such as cold idle, or limp mode, or when the A/C is on).

Dinghy towing is done with the engine off. This whole time, have you been talking about EOC? Most automatics should not be used for EOC; they depend on the input shaft for their oil to be pumped to keep them cool. I P&G in my automatic but I do not EOC.

Nice thing about automatics: They have that torque converter, and bands/clutches in the transmission, that take up small RPM differences without breaking a sweat (and do a damn good job on large RPM differences too).

As for anecdotes related to why you don't shift into D from neutral while you're still moving, well apparently those who were drag racing, after finishing a race would shift into neutral and then later shift into D, only to have their transmission to explode from doing this.

Here are some links supporting this:
https://www.elantraxd.com/forums/arch...p/t-10957.html
https://forums.evolutionm.net/archive...p/t-28943.html
https://www.dieselplace.com/forum/sho....php?p=2696485
Last one being funny
Just search for something like this: drag racing shifting into drive from neutral

Dude, all that stuff is about dropping it in to Neutral after deliberately revving the engine high while the car is STOPPED for the purpose of taking off from a line. Drag racing is completely different from what we are talking about.

Also, the difference in force on the TC and tranny are substantial, especially if you bother rev-matching at all. Difference between stopped car and high revs (links specifically mentioned 4000+ RPM), is the full force 4000 RPM the TC has to absorb. Difference between cruising RPM (2000-2500) and neutral idle RPM (600-1000) is at most 1900 RPM. I'm also fairly certain that inertia and other factors make the difference more than linear (in other words, 4000 RPM difference is going to cause more than twice the wear & tear that a 2000 RPM difference would cause. If that is true, then the few hundred RPM difference that happens when you rev-match is virtually meaningless.

There are further differences that could be elaborated, but I suspect I'm only feeding the troll, so I won't bother...

like theholycow said, this isn't a personal attack and most of us aren't saying you're a bad person. I congratulate your experimentation. I'm just informing you that some of your theories are wrong and some need some expansion based on my not insignificant knowledge of cars and their workings. again, not a personal attack.

OK I didn't feel like taking 10 mins apiece to read your links but quite frankly, ones' a hyundai forum (not known for strength/reliability), one's a lancer forum (some mitsu trannies aren't the strongest either), and ones a diesel forum (bajillion ftlb of torque). You mentioned all of them under the category of "drag raced, shifted to neutral, then back to D and the trans blew up". trust me, an auto shifting while at WOT acceleration is taking a LOT more abuse than low rpm N-D. During regular driving, even at highway speeds, N-D with the vaguest attempt at rev-matching will be perfectly fine for MOST transmissions. certainly toyota transmissions.

I had the line pressure on my old A340 high enough it'd chirp the tires and surge forward shifting into 2nd and 3rd at WOT with under 200 hp in a 3400lb car. I know people that regularly drag race turbo cars with the exact same transmission for years. it wouldn't bat an eyelash at my antics. going from N-D from idle at 80 mph was noticeable but hardly harsh.

Thanks for the links. I'll have to look at them individually...

https://www.elantraxd.com/forums/arch...p/t-10957.html
This is called a "Neutral drop", and is done to spin the tires like you can do by revving up and popping the clutch in a manual transmission. N->D in P&G is quite the opposite of this.

https://forums.evolutionm.net/archive...p/t-28943.html
Another neutral drop.

This one has a few interesting pieces in it...
https://www.dieselplace.com/forum/sho....php?p=2696485
Those protections do not exist in most vehicles, but are not necessary for N->D under P&G conditions.

Ah, this might explain the question of why the engine revs higher in N at speed than in N at a stop.

Those terms will always return results about neutral dropping.

There's something that can happen with a pressure spike in modified transmissions with the line pressure set wayyyyy high if you shift to neutral above 2500-3000 RPM. But unless you're running a line pressure of near 200psi you don't typically need to worry about it.

Ok did it again today, and I think it will be my preferred method to coasting (before I'd let off the gas only). I tried shifting into neutral and compared the RPMs between holding the cruise control down and neutral, neutral did result in lower RPMS of 800RPM though this was done at around 35mph only. However inspite of the neutral having lower RPMS, I found that once again, holding the cruise control does help prolong the glide from a higher speed say 55mph all the way till 20mph much much better than just letting off the gas since I usually have more engine braking. So I guess people were right, it never went into neutral, it just disengaged somewhat, resulting in RPMS of 1000/1200 all through the glide vs a gradual decline from 1700RPMs on the highway, resulting in engine braking.

I need to do a lot more experimenting to understand this transmission better, I'm just annoyed I have to use an automatic at all since from what I understand, manuals perform universally the same with the only differences being with how the clutch is handled and whatnot. There are far too many quirks to document with these automatics it's mind numbing.

*************, guys, thanks for this thread.

I wanna try this technique and see if the cruise control can be of use for P&G.

Other ideas:

- Have you tried P&G, say between 30 and 40MPH by setting your cruise control at 30MPH, accelerate to 40 with the pedal, then coasting back to 30? Would that yield a good glide with your Toyota with the same drop to 1000RPM? If so, there's no need to hold the "decel" button.

- if this N-D can be electronically controlled, maybe we could also make a convinient "N glide" button on the steering wheel. Maybe better than the "decel" button if that one doesn't really achieve "N".

- Would precing "Decel" for long periods of time cause problems to the car computer (ECU)? It's not designed to be used like that and maybe it could lead the car to enter a weird mode... Like disable cruise control, throw a code, go open loop or something.

Anyway, I'm kind of surprised at your findings.

My AT car when in cruise control mode holds its speed even in a downhill (not too steep I guess). So I assume it uses engine braking and throttle to stay a constant speed (but no @!$# fuel cutoff from what the Scangauge says so no gas savings).
So it would mean that when you press "Decel", the car will just coast instead of engine braking... Hmmm.

Other AT P&G problems:

- Shifting gears is awkward, and maybe even dangerous (P and R are a sort distance away)

- Shifting gears annoys passengers not used to this (I went into an argument about that - pfff), the shift clunks are noisy and cause the driver to make a lot of movement.

- Shifting gears is slow and impractical because the levers are not designed for doing that constantly.

So if I can find a more practical and quiet solution, I'm all for it...

BTW, friends that are car "savvy" but not hypermiling savvy claim that I'll destroy my tranny shifting back and forth. So yeah, I'd want to make sure that P&G on an AT doesn't end up costing me a nasty repair in the middle of nowhere (I already lost a car in the middle of nowhere, and don't want a repeat).

I wish I understood how AT trannys work. If you guys know of a good simple online tutorial, post a link! I'll start with googling :-)

https://en.wikipedia.org/wiki/Automatic_transmission
https://auto.howstuffworks.com/automa...ansmission.htm

How an A/T works
 

OK, I'm learning... Here's my own wording paraphasing "howstuffworks". Another good explanation is on FamilyCar

planetary gearset
Cutting a cross-section of the trany it's composed of:
- (S) sun gear in the center,
- (R) the ring outside
- (C) the planet carrier (see P)
- (P) the planet gears which are 4 smaller gears working together in lockstep, sandwiched between (S) and (R) and held together by (C)

https://www.familycar.com/classroom/I...Planetary2.gif
Animation

Any of (S), (R), (P) can be engaged to another (or all engaged to each other), changing the gearing ratio, to provide reverse, reduction and overdrive. Depending on the mode, the planet carrier (C) will be stationary (planets gears can rotate on themselves but won't move around the sun) or will rotate too. I don't think it matters for the resulting gearing. It's a mechanical side effect.

To get a full gear set, two planetary gearsets are combined (compound planetary gearset). The design means that there's another set of planets of a different diameter. The planets are all working in lockstep, but now there's 2 gears on the sun of different diameters, contacting either the 1st or the 2nd set of planets. There I get lost.

Gearing gets engaged/released by 2 bands and 4 clutches.

Bands are metal brake bands that wrap around sections, actuated by hydrolic cylinders to lock that section.

Clutches are actuated by hydrolic pistons, and held off normally with a spring.

Park: there's a tooth actuated by a lever going out of the tranny that engages and locks the output shaft so it doesn't move.

Neat details:
- In "2" the tranny never down or upshifts.
- If dowshifting, the tranny goes down only if the car speed is low enough
- Upshifts will happen at lower speeds if you accelerate genlty vs hard.
- The tranny downshifts if you floor the gas
- In overdrive the tranny picks the best gear

Gear pump
Spins at the speed of the engine/ torque converter housing, and forces oil from a sump to the hydrolic system.

The governor
A valve connected to the output shaft. Faster rotation the more the valve opens, the higher the fluid pressure in it.

Throttle
Either through a throttle valve has increased pressure as the pedal is depressed, or a vacuum modulator detects the engine load from the manifold pressure.

manual valve
Hooked to the shifter, it inhibits selected gears.

shift valves
pressurises the clutches and bands, each valve detects when to shift from one gear to the next depending on governor and throttle valves pressure.

Electronic tranny
Shifting is still done with hydrolics, but electric solenoids are used instead of valves.

Note

"Most transmissions will upshift to third gear, or even overdrive, when you take your foot off the gas".

Torque converter

IT sits between the engine and the tranny, and contains
a Pump, a Turbine, a Stator and Transmission fluid.

The centrifugal pump is actually the whole housing with built-in fins, which is bolted to the flywheel and rotates at the same speed of the engine. As the flywheel turns, the fins scoop the oil and pushes it.

The turbine faces the pump, and is linked to the tranny shaft, the
oil is pushed against its fins which makes the turbine and tranny shaft rotate.

the tranny fluid moves from the inside out and outside in as the pump pushes it in, and it escapes through the turbine outwards.
The stator lies in between to optimize the flow of fluids.

https://www.familycar.com/classroom/I...eConverter.gif

A torque converter can multiply 2x to 3x the engine torque when accelerating from a stop, because the engine turns much faster.
On the downside, the tranny shaft will always be a little slower than the engine, yielding lower MPG than a MT, because the trany fluid is moving. A lockup clutch is used in modern cars to avoid the problem.

Wear and tear from P&G, going N to D

Now that I took that crash course, let's see if I understand what happens...

From: Familycar course

"The clutch pack is used, in this instance, to lock the planet carrier with the sun gear forcing both to turn at the same speed. If both the clutch pack and the band were released, the system would be in neutral."

So my take away here is going to "N" to "D" is a simple matter of engaging some clutches and brake bands.
One one side you have the torque converter axle and on the other the driveshaft axle.
When in "N" coasting, the driveshaft rotates fast, and the torque converter rotates at idle RPMs.
When engaging to "D", the torque converter shaft is jolted suddenly from 800RPM to say 3000RPMs.
The torque converter in that case is counter productive because it will oppose a force, increasing the stress on the torque converter shaft.
Once in gear, the torque shaft turns at 3000RPMs, and the torque converter handles the decoupling with the engine flywheel which before that was rotating the torque converter shaft.

So I see that you could prematurely wear the tranny's brake bands and clutches that way, because the "N" to "D" shift is not really protected by the torque converter so those take the force by slipping... Unless indeed you rev-match the engine before engaging to "D".

So would those be designed to handle that kind of beating?

Maybe yes? I expect they take that beating when shifting between gears, unless the shifts happen in a way that when we go from one lockdown to another, the parts that lock together are close to sync'ed when that happens, even when you kick the pedal.

Note: The gears are not impacted because they never disengage from each other. They either get locked together to stop their relative movement or not. So I would not expect a sudden breakage there.

Note2: Going D to N does not seem to be a problem then, as you release all gearing so they just desynchronize smoothly with the planetary gears just moving freely to adjust for the variations.

Here are some things that you (sonyhome) have stated as problems that don't actually have any effect for my vehicle:

1. Hold the decel button and letting the cruise re-engage actually causes a large jump in rpms, sometimes such that it cause jolts. Therefore, I don't let it re-engage; I set my speed with my foot much more gently and then reset the cruise.

2. I never worry about P or R. I have to press the button to go beyond N and 3. So, that means N, D, and 3 are available without pressing the button. It saves me from accidentally shifting fast and being in a gear I don't want: I have to actively think about it.

3. Haha! shifting gears is slow and inpractical? What do you think a manual tranny is? Only dual clutch autos can shift faster than a human, standard slushboxes are slower. No offense meant of course.

4. Shifting from N to D while coasting, to exceed 3000rpms I would need to be traveling at excess of 95mph or stuff it in 3, which puts it in 4th no lockup (knowing these details about your auto is important). Usually when returning to my speed, I match rpms to the speed. I've had much practice to know what rpms = what speed to avoid potential damage.

So a lot of the problems of Neutral coasting in an auto are negated by knowing your vehicle and how the tranny and engine interact. I'm sure I'm causing premature wear to the tranny, and it will likely fail before the motor does. How much sooner than a typical failure? No way to tell, as these trannys have lasted over 200K miles without major service, only fluid/filter changes.

I have also taken 1st, 2nd, and 3rd (4th hits the limiter at 112mph first)to the redline of the motor, to know where the tranny shifts given the physical variables of my car. Bad for it? sure. The knowledge gained about how it works? Worth it.

Here's some details about how the "gold standard"* ( ;) ) in hydraulic automatic transmissions engages gears ...

https://www.allpar.com/mopar/transmis...-tom-hand.html

(*Seriously though, it was much copied and many trannys around today are almost straight cribs off the general design, with an extra gear set cobbled on and a solenoid pack instead of the valve body.)

The lockout (button on a console shifter, or pulling back on a column shifter) should prevent this accident. In my GMC, I end up pulling past the lockout on every shift anyway, but it requires a lot of force to go between any selection so once I get out of D there's not a strong chance I'll even knock at R's door.

Lots of hypermiling practices are annoying for passengers. I try to be extra-smooth with passengers, but sometimes they just have to deal with it...at $4/gallon, they can damn well deal with it!

With a console shifter, if the lever is in a decent position, D->N and N->D should be a tiny nudge away. Waiting for the transmission to shift can get annoying, though.

I think that's just FUD. They've never tried it and don't know. I've been shifting my auto trannies around for hundreds of thousands of mile. I had a friend with a rusted out '82 Mustang who did the hardest, jerkiest shifts he could, downshifting for engine braking every time he stopped (because the brakes on that car were TERRIBLE); I was sure it would blow the tranny in no time, but that car lasted forever.

They wouldn't put all that functionality there if it was going to make stuff blow up under moderate conditions. Don't forget, hypermilers aren't pushing huge amounts of power or using high RPMs. We are moving slow and operating (usually) gently, using little power. Some kinds of stuff that would break it under drag racing conditions will not even wear it under our conditions.

This behavior varies greatly from one car to another. Some are obedient, some don't care what you've asked for. Most, I think, will use 2 except under extreme conditions, such as bouncing against the rev limiter.

This also differs from vehicle to vehicle. I wouldn't depend on it.

Those are very universal, true of all automatic (and new automated manual / sequential manual / dual clutch) trannies.

That depends on your priorities. It rarely picks the gear I'd prefer, but it almost always picks an acceptable gear.

[qote]Gear pump
Spins at the speed of the engine/ torque converter housing, and forces oil from a sump to the hydrolic system.[/quote]

Very important! This is how the transmission is kept cool, as it circulates the oil to a cooler in or near the radiator. It is why EOC is not acceptable for most automatic transmissions.

Yes, but unless you're going slow, it will probably already be in 3rd or 4th gear. This, combined with the torque converter, may be why some people think they're automatically shifting to neutral.

That is an in-depth explanation. If you want a simplified one, imagine two window fans pointing at eachother. One is turned on, blowing at the other; you'll see the other spin as a result (just like when the fan is in the window, turned off, and a gust of wind comes through). Modern TCs can lock, which means that both sides get physically connected as if it was just a shaft.

The torque converter acts like a big pillow for all those jarring shocks that you might fear during shifts. It easily absorbs them, preventing the transmission from getting jerked around.

I suppose there could be some cars where it would hit 3000rpm. That's 70mph in my manual tranny VW, and probably about 100mph in my auto tranny GMC which is 2000rpm at 70mph.

The TC is pretty robust, and the concern tends to be about the bands/clutches in the tranny. They don't get a hard jolt, though, because they don't have to accelerate the engine right away; instead, they only have to accelerate the TC, which allows that to happen easily. By the time the engine is pushing back, the bands/clutches are fully engaged and the TC does all the work, which is exactly the sort of work it's designed to do.

No, the engine crankshaft is what's opposing the transmission. The TC cushions that issue as described above.

It doesn't decouple really; it just lets one side spin faster than the other. Like I said, imagine the fans; the engine is attached to the fan that's off and the transmission is attached to the fan that's on. The TC doesn't lockup when the transmission is in N, so it's not physically connected, only through the oil.

Yes, theoretically you could. I can't say that I have enough P&G miles to say for sure but I am confident that you WON'T prematurely wear that stuff, especially if you rev-match (which I do). Rev-matching is actually extremely easy here, since you don't need to be accurate at all, you have lots of time, and you've got the torque converter to cushion it.

My GMC takes ~1 second to execute my N->D request after I shift it. So, I shift, then get on the gas a little, and watch as the tach jumps up to exactly the spot it needs to be in, and that's where it stays.

It is, indeed, designed to handle high-rpm high-power shifts, that's what the TC and all those bands and clutches are for. You shove the pedal down to the floor to dive out onto that busy highway, your engine produces massive amounts of power, and you NEVER interrupt the power while the tranny does its job. It must use those bands and clutches to shift while under FULL power.

Shifting per the user's request is very slow on most automatics. Just ask anyone who thought paddle shifters were going to respond immediately. Most automatics take a second or two to decide if you were serious about your choice. N->D should be even slower due to the usually larger difference in RPM.

Well yes, like the newer grand am (before it was G6) when it got the paddles, it was neat, but no faster than just using the stick on the floor. What I was referring to is in high performance vehicles. Look up the Audi R8. It can shift in a tenth of a second use 2 clutches. It's actually really neat because both gears are engaged for a split second, providing seamless power. Technically its called a clutchless manual, as you have the 6 speed like a regular manual, but no clutch pedal. But yeah, 85% of slushboxes aren't that fast, 1 second to shift into gear from N is how mine is too. I say 85% because Audi/VW Tiptronic is actually pretty fast at shifting manual style. I just haven't seen a domestic with the same speed in an auto.

Yeah, an automated manual is a very different beast. The dual clutch ones, like VW's DSG, supposedly can execute a planned upshift in as little as 8ms, though I think they can still lag quite a bit when an unexpected request comes in from the driver. To tell you the truth, with paddles, I'd WANT it to lag so I have time to choose a gear before it executes...else it has to shift twice just to go from 5th to 3rd.

Gawd yeah, I put a shift kit* in my tranny and I am continually getting advice from various relatives, friends, one time passengers, that maybe I should take it into a tranny shop and get it looked at, or that I should scrap it because the tranny is on it's way out.... AND 90% of these people probably can't even find the oil filler!!!! :rolleyes:

(*Yeah it's "firm", if I floor the gas it will chirp tires going into second, and sometimes going into 3rd if my foot twitches)

One thing is pretty universal: Nearly ANYONE who is well studied insists that firmer shifts (due to shift kit, servo upgrade, increased line pressure, or ECU flash) WILL make the transmission last longer. This is from people who drive slow, people who drive fast, racers, economizers, etc. I have no choice but to believe it. That would be fine, as I enjoy the feel of a firm shift, but my wife will complain if I do it...

That Lucas Tranny fix stuff seems to do good things. It has a bucketload of friction modifiers, increases the viscosity effectively increasing pressure a little, firms the shifts up and appears to run the tranny cooler. Despite being thicker, the other effects appear to improve FE, especially if your tranny is slipping slightly or TC lockup isn't firm. The being thicker improves the TC efficiency out of lockup also I believe. Anyhoo, it's the one bottle of snake oil that actually seems to have real benefits.