Nissan's Continuously Variable Transmission

[Guest]

I was out car shopping the other day.

One of the models I looked at was the Nissan Murano. Nice SUV.

The salesman was touting the benefits of the tranny. It's a CVT - no perceptible shifts. I thought to myself, "this is just like my '63 Buick". I asked the salesman if he'd ever heard of a Dynaflow. He hadn't.

I guess what's old is new !

[Matt Harwood]

I was just wondering how the Dynaflow is different than an ordinary planetary automatic transmission. I've heard that there are significant differences, but I don't exactly know what they are.

It can't be a CVT like the Nissan's, so what is it?

Thanks in advance!

[Guest]

I'll try from a lay perspective - and hopefully some of our more technical members will embellish!

As I understand, the stator blades in the Dynaflow's torque converter can "switch their pitch". The result is a range of available torque multiplications. The behavior is like that of the CVT. No shifts - but different apparent "gearings" for lack of a better word. I.E. - it feels "lower" if you nail the acceleraor - but it has not actually downshifted.

[Guest 31tudor]

Man, if it's anything like riding a hot snowmobile, <span style="font-weight: bold">I'M THERE!!!</span> Oh wait, it's a Nissan? So in other words the manufacturer claims roughly DOUBLE the horsepower that the truck actually has! Here in lies a political Nissan issue, which shouldn't be disucussed here, but why are their truck engines so ridiculously gutless when the Maxima has been an excellent performer for the last 15 years? It's like Nissan cars and Nissan trucks come from two totally different manufacturers, but get the same badge. So where does that leave the new Murano SUV? Is it a car or a truck? Please, don't answer. It's not a Buick.

[Matt Harwood]

Actually, 31Tudor, it IS based on the Maxima (actually the Altima platform, but they're pretty much the same today). The engine is the same 3.5L V6 that powers the new Z, the Infiniti G35, the Altima and the Maxima. It's a crossover, like the Buick Rendezvous, more car like than a truck, less car like than a car. Somewhere in-between.

The CVT has been a long time coming and I'm guessing that they gave it some "steps" in the progression of torque so that it wouldn't feel strange to drivers accustomed to regular gearboxes (this is what Audi does with their CVT, which pretty much simulates a 6-speed transmission). It should be vastly more efficient than regular transmissions because it can keep the engine in its powerband without big downshifts or upshifts that pull the engine down. Nail the throttle, and I bet the engine zings right to its power peak and stays there while the car accelerates.

Pretty cool.

And thanks for the switch-pitch explanation, guys. I thought I read something about that in a recent Bugle.

[Guest]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Man, if it's anything like riding a hot snowmobile, <span style="font-weight: bold">I'M THERE!!!</span> Oh wait, it's a Nissan? So in other words the manufacturer claims roughly DOUBLE the horsepower that the truck actually has! Here in lies a political Nissan issue, which shouldn't be disucussed here, but why are their truck engines so ridiculously gutless when the Maxima has been an excellent performer for the last 15 years? It's like Nissan cars and Nissan trucks come from two totally different manufacturers, but get the same badge. So where does that leave the new Murano SUV? Is it a car or a truck? Please, don't answer. It's not a Buick. </div></div>

Yeah, but at least Nissan is benefiting the U.S economy more these days by manufacturing in the United States rather than shipping work down to Mexico like GM. Plus its too bad Buick has been going downhill the past 20 or so years. They just make old people cars now. They even messed up the number of portholes on the Park Avenue!

[Guest 31tudor]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Yeah, but at least Nissan is benefiting the U.S economy more these days by manufacturing in the United States rather than shipping work down to Mexico like GM. Plus its too bad Buick has been going downhill the past 20 or so years. They just make old people cars now. They even messed up the number of portholes on the Park Avenue! </div></div>

Wow, maybe you should change your username to NissanMan02

[twinturbine]

Dynaflow is technically a multiple geared turbine torque converter. The first turbine is geared at 1.6 times output shaft speed while the second turbine is directly connected to output shaft. The converter pump drives both turbines from start. As the first turbine over runs the speed of the output shaft the load is gradually transferred to the second turbine alone. Good torque multiplication (3.4 to 1 at stall) with no shifts. The variable pitch stator is used only to provide additional multiplication near WOT. It increases the angle of redirected oil to the pump resulting in higher stall speeds and additional torque multiplication. This is a CVT that operates by hydraulic rather than mechanical means. A beautifully elegant piece of engineering that gave Buicks a unique feel. The last version (61-63) was extremely reliable and very satisfying to drive. The triple turbine or Flight Pitch Dynaflow (58-59) used 2 geared turbines and an infinitely variable pitch stator for even more off line torque multiplication. It was short lived due to the extremely high cost of production.

[Centurion]

TwinTurbine, thank you for helping us understand a bit more about Dynaflow. I own a '59 Electra with the Flight Pitch / Triple Turbine transmission, and the transmission works perfectly. Within the last week, two people have indicated that the Flight Pitch was the same transmission as the Chevrolet TurboGlide. I had always assumed that the Flight Pitch was unique to Buick. Was the Chevrolet transmission the same transmission as Buick's, or did it simply employ some of the same principles? Am I correct in assuming that the Flight Pitch was actually built by Buick rather than another GM corporate entity, such as the Hydramatic Division? Whenever I have seen parts advertised for the Flight Pitch / Triple Turbine on Ebay, there is no indication that any of the parts also fit any Chevrolet transmissions. I would appreciate any knowledgeable responses to this question.

[Matt Harwood]

So there were no gears involved at all? Just a pair of torque converters?

Wow.

[NTX5467]

The TurboGlide was a "poor man's" copy of the Dynaflow concept, but less expensive to build as it was for a Chevrolet, is suspect. I've never heard anyone mention any family lineage between those two transmisisons. Back then, Chevy did their own transmissions and GM Hydramatic did the rest.

The CVTs will probably be found mostly on lower powered vehicles (although the Murano is not weak by any means). The Inifiniti QX45 (the Infinity "Murano") has over 300 horsepower from its V-8 and uses a conventional automatic transmission. The allure of the CVT is greater fuel efficiency with the smooth "feel" probably being an added benefit. As I understand it, when the Murano's shift lever is moved to the lower "geared" position, it just positions the drive belt to a particular location on the pulleys or restricts it from moving past a certain point so it stays in the lower geared area.

One friend related that if you went through a dip too fast (and bottomed out the suspension in the process) in a TurboGlide '58 or so Chevy, it could crack the case as the casting was a little too "light", even though it was aluminum.

The TurboGlide did have a more variable stator torque converter and included a "Grade Retard" position instead of manual low gear. My late uncle had a '61 Impala with a TurboGlide and it worked fine for many years. Performed good even with the 283-2bbl engine. TurboGlide was the "upgrade" from the PowerGlide.

One used car dealer related that whenever he bought some rental cars in the late '50s from Hertz with TurboGlides, the first thing he did was to convert them to PowerGlides so they would not cause problems he'd have to fix later.

Some people had bad names for the DynaFlows too, unfortunately, so it might well have had more to do with who was working on the trans than how it was designed. Back then, it seemed that anything that was new and different was not liked too well, even if it was designed pretty good from the start. New styling was ok, but new mechanical advances might not have received the same reception.

Enjoy!

NTX5467

[Centurion]

NTX5467, I think you raised an excellent point about things that were new or different. When I first began to ask questions about Buick's Flight Pitch / Triple Turbine, one of the BCA Technical Advisors indicated that he had driven a '59 with Triple Turbine in daily service for many years. The car was highly reliable, and his assessment was that the transmission had gained a poor reputation mostly because it was "different" from the other Dynaflows. There is probably some truth to this statement -- although there were indeed some problems with the early '58 Flight Pitch transmissions that were remedied by changes made during the course of '58 model year production. (See Bill Schoening's great article about the Flight Pitch in the April, 2003 Buick "Bugle".)

[Guest]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Yeah, but at least Nissan is benefiting the U.S economy more these days by manufacturing in the United States rather than shipping work down to Mexico like GM. Plus its too bad Buick has been going downhill the past 20 or so years. They just make old people cars now. They even messed up the number of portholes on the Park Avenue! </div></div>

Wow, maybe you should change your username to NissanMan02 </div></div>

Actually, it would have to be NissanMan00. I have an 02 Rendezvous and an 00 Xterra.

[Mrbuick714]

The transmission usd in a few 58-59 Buicks is also known as a "Triple-Turbine"

[twinturbine]

Similar in design, Turboglide is a different trans than Flight Pitch (3T) Dynaflow. Turboglide has a two position stator, like 2T Dynaflow. Flight Pitch has an infinitely variable pitch stator. This gives 3T a unique driving feel which some do not like. As more throttle is used the vp stator gradually changes angle - this can give the sensation of slippage - although that is not the case, the trans is simply giving more torque multiplication as the driver commands. 2T remains fairly "tight" until near WOT when the stator changes fully to the performance position - almost gives the feel of a "kickdown shift".

[NTX5467]

The operation of the 2T DynaFlow sounds very much like the switch pitch torque converter used in the Buick and Olds versions of the '64-'66 (might have stayed until '67?) Turbo HydraMatic 400 where the stator angle was switched electrically between "tight" and "performance" angles. Higher stall speed angles were used at idle and also at WOT to decrease creep and add a little extra power at WOT, respectively, yet had the lower stall speed angle (i.e., "tight") for better lockup characteristics during cruise situations.

As good as the various versions of DynaFlow might have been, I suspect they had a good deal of power absorption in them due to the internal rotating mass (including the fluid in the various torque converters and such). This would not have mattered much during cruise conditions, but would have been more critical during lower speed acceleration when all of that rotating mass was being accelerated along with the vehicle itself. Kind of like a manual trans car with a heavy flywheel (DynaFlows) or a lighter weight flywheel (ST300, ST400).

Those earlier versions of the THM400 had some very good shift characteristics yet you could hear the engine speed change with each gear change. Obviously, manufacturing costs were less too. One of our chapter members had his '62 LeSabre converted to a THM400 and was amazed at the increase performance (so was his high school son!) with no other changes.

The 3.4 torque multiplication ratio mentioned would have matched the typical torque multiplication ratio of 2.1-2.2 on most torque converters back then. Similarly, 2.2x2.48 in the THM400 would be more and also more efficient in the process too. This torque ratio would apply only at start-up and diminish as the two halves of the torque converter turbine/stator mechanism approached the same speed (i.e., lockup--but not "lockup" as with the more modern torque converters with an internal mechanical clutch inside of them).

Obviously, the DynaFlows and TurboGlides were after that smoooooth operation with no jerks or such in the process. At the time, they were technical advances and might have lived longer with a little better finesse in some design areas plus the much better fluids we have now. Anytime there is slip in a torque converter or fluid coupling, there will be some additional heat put into the trans fluid. With the "jet" theme of that era, the 3T DynaFlow probably had that feel a little more than did the regular 2D DynaFlow and TurboGlide. Punch the gas and let it soar??

I suspect that where the CVT deal is headed is to allow the engine to get to a particular rpm where it is efficient and then vary the car speed within that more narrow rpm range. Kind of like the more modern non-self-propelled lawn mowers that now have only one engine speed instead of the earlier ones that had throttle controls.

Obviously, the smooooth feel of the DynaFlows were preferable to the various versions of HydraMatic used in other GM lines back then. The 4-speed HydarMatics were probably a little more efficient (or at least felt that way) yet had more noticeable gear changes (especially the first one about 1 car length from the standing start!) Those HydraMatics were also used with open drivelines too, which made them more adaptable to other applications.

I haven't read Bill's article just yet, but look forward to getting the time to digest it all. I did find a Chilton book that was a chronicle of automatic transmissions of the '50s and '60s and how they worked, unlike what you'd find in a Motor manual.

Enjoy!

NTX5467