History of the 80-year-old automatic transmission, the traditional most versatile

(To Gianluca Celentano)

I had previously talked about automatic transmissions, a reality that has also touched the ARs, as we have seen for the J8 destined, apparently, to supplant the manual gearbox also in our armed forces (v.articolo). A change of pace that will still have to take into account a huge audience of users still tied to manual systems that generally hardly ever leave you on foot, as well as instilling a personal feeling between man and a half that no type of automatism can replicate. This should be highlighted for consistency.

Despite training with ZF manuals, I admit that hydrodynamic systems fascinated me since the age of 12, when I requested workshop manuals from manufacturers, and I must say that they sent them to me as well!

How was the automatic transmission born?

Although Leonardo da Vinci had already designed systems to reduce or increase the final speed of an axis, some passages on the development of the automatic gearbox are really curious and various authoritative names gravitate around these.

Tanks and modern armored vehicles on rubber are equipped with flexible automatic transmissions far from those well-founded prejudices of the 80s, a period in which the automatism was associated with the quiet DAF Variomatic or was an unwelcome option if the cavalry under the hood was limited . However, either Mercedes' Borg Warner in the early 90s or the Tiptronic Porsche rather than BMW were precursors that overturned preconceptions.

The invention of a progressive speed system takes its cue from various projects and patents on transmissions, but there is a "central" device that was the basic element to fine-tune the speed progression without the help of man : the transfer of motion from engine to gearbox. Hence centrifugal clutches, hydraulic couplings and torque converters, the optimum initially created for the naval sector in the early 900s by Hermann Föttinger, were the winning ideas in this direction.

E. TRENTA: an Italian, the first inventor of the automatic in the USA

Just think that at the end of the 800th century the French engineers Louis-Rene Panhard and Emile Levassor already had an automatism project which however failed dramatically, while the American brothers Sturtevant in 1904, had developed a centrifugal clutch, more or less like the system that moved the mythical Hello Piaggio or current scooters. But there is no limit to inventiveness, in fact in 1923 a simple system took shape from the ingenious project of the Canadian Alfred Horner Munro which used air instead of oil to pressurize the circuits.

But I don't want to bore you and I'll tell you right away that among these names and projects there is also an Italian, Elio Trenta, an Umbrian engineer who in 32 patented the first epicycloidal unit necessary to have gear ratios with the number 306379.

Trenta presented the invention to Fiat which, however he showed no interest as instead did the American Oldsmobile that made it on the versions Hydra-matic.

In the USA shortly after 39 the driving method revolution was beginning - even with TV commercials - which would deliver the manual gearbox to about 10% of the market over the course of the century. De Soto, Buick in 1947 with Dynaflow Drive and Chrysler with Fluid Torque Drive in 50 they marked the new semiautomatic range with these names.

"Hydraulic" manuals

Remember when we talked about the ATC81 Wagon Transport Tractor (v.articolo)? That concept of semi-automatic transmission (Hydrotrans converter plus clutch) but always with 3 pedals, was the concept on which the first semi-automatic cars made in the USA were based many years before.

It involved associating a two-speed manual gearbox with a hydraulic joint - pump and turbine - and making a clutch controlled by the traditional pedal adhere to the pump. Citroën also did something similar with the DS (shark) semi-auto version, but here the clutch was opened via an electric contact on the gear lever.

We start from the assumption that in the USA in those years the cost of fuel was absolutely not a problem so you could open the carburetor throttle all the way to couple the big cars that had to be comfortable offices on wheels with an unmistakable line to show how a Yankee trophy with stars and stripes. So the final mass was not a drama for chassis-loaded vehicles, with displacements in the order of 4/5 thousand cubic centimeters or more (see carriage M113) with 6 or 8 cylinders arranged V.

Very few horses and a lot of torque were the cure-all of the hydrodynamic joints which also allowed some nervous skidding typical of manuals, albeit with overall and very meager road performance and stability.

How did they work?

Interesting topic. In reality, the clutch on the hydraulic joint had been placed because there was not yet - we were at the end of the 30s - a hydraulically controlled planetary unit with a slide valve unit that arrived from Italy thanks to Elio Trenta. A clutch was therefore required to make manual gear changes (traditional up and down movement with neutral) between first and second and reverse. Once the gear was stationary, the clutch could be raised by pressing the brake and the car remained in motion. Given the pair of engines, you could easily start in second or third - the joy of taxi drivers - without having to press it just before stopping. The downshifts were done to have a little 'engine brake (actually very little) or sprint.

ATC81 Hydrotrans

The Iveco wagon transport truck was equipped with an 8-speed ZF manual gearbox alongside a torque converter on which two clutches worked. A traditional one to control the change of gears (as in the first semiautomatics in the USA) and a second that instead went under pressure to exclude the converter after starting.

The realization of this system Hydrotrans, designed to move exceptional loads in the order of 80 tons, was not really appreciated by drivers for the sudden replacement of clutches and for consumption. However you will have noticed that, when I describe an automatic means, I always specify a particular of the converter, that is, its exclusion. In fact, after the first “hydraulic” start - already a first gear in itself - the automatic vehicle, thanks to the planetary units, can have direct and uninterrupted contact between the engine and transmission.

Better performance, engine braking and lower energy losses and reduced consumption are the main reasons that since the 80s have seen the introduction of a clutch that joins the "pump and turbine" halters initially only on commercial vehicles, and without more on trucks and city buses.

The concept of continuity between engine and transmission is the principle on which the faster, lighter but also more delicate robotic double clutch transmissions were subsequently developed.

It is precisely on reliability that the game of opinions between drivers and enthusiasts is open. In fact, if a modern ZF manual can have its weak point perhaps on the short / long gear program epicycle block, it is also true that it is practically unstoppable and mistreatable as well as very suitable for construction sites, in the mountains or in operational military uses.

Moving on one step below, there are the modern converter plumbers and finally the robotized ones, which however should be conducted as if you were dealing with a manual, but ideal above all on the highways.

The selectors and the abbreviations

If the torque converter has basically given the green light to the traditional development of the epicyclic automatic transmission, it is curious to retrace the history of its selector lever.

The very first "automatics" used the classic cloche gearbox placed on the steering column, so as to be able to insert a front sofa. From what emerges, they drove like traditional cars with two or three gears, but given the presence of the joint, everything could be simpler, forgetting or almost forgetting the clutch.

The perceptual evolution of this system, compared to a traditional H-pattern, was precisely in the yoke that was associated with a slightly deceptive ring nut with the letters, R, Low, N, Dr. In reality, there is "automatic". it was just a hydraulic joint.

Also for the insertion of the back, the movement was the traditional one, that is, pulling the lever towards you and bringing it upwards low.

With the intensification of technology, the abbreviations have undergone shifts, for example: ND Low R but it is curious to remember that the introduction of the P parking position was inserted towards the 60s, while before the car was parked in neutral by pulling vigorously the Park Brake Lever (the handbrake), hence the abbreviation P. The R position was moved from the full scale and put up, to avoid accidentally inserting it, convinced to position it on Low (a term to indicate the first position)

Military selectors

Some of you may be wondering why the VTLM Lince does not have the position of P. Well, even the ACTLs or the automatic buses do not have it because they are equipped with a pneumatic parking lever (the handbrake) that works by unloading quickly air and tightening the drive wheels.

In some models a second lever locks the front axle pair (eg APS 95).

The Park system, among other things, is a particular (a ratchet, a pin inside a straight toothed ring) which, if stressed by slopes, thrusts, etc., can break even more if the vehicle is heavy.

The position of P is instead present on "light" vehicles such as J8 or MUV 70/20 or in any case on common civilian vehicles used as a representative for the Armed Forces.

Opinion on technological excesses

Chapeau to that technology that has allowed us to simplify our lives, making it above all safer and even more so to the one that has not relegated us to true slavery, still allowing us to think about an action without resorting to pre-packaged programs and very often far from reality. 'use. It is the wise theory that separates practice from theory, even more so for the military.

Even in automotive technology today swollen with every sophistication, it should be borne in mind that the initial purchase, certainly sensible, will go against specialized maintenance periods without which the vehicle will not be stopped.

The heart of the problem is very often locked in a box called unit rather than in cabling subject to deterioration of work or even by the time or inactivity of the vehicle, an embarrassing situation especially on large numbers of units.

Traditional automatic gearbox systems now also tested in urban areas - see the mechanical stresses of hyper-loaded buses - offer and guarantee appreciable operating standards even in the hectic operational use envisaged in the Army. An armed force that today, even more so, has to do even more accounts in their pockets before buying, perhaps by launching the basic guidelines first. This, despite the rich and current market offer reflects - not always in small details - the discoveries for purely civilian uses of vehicles.

Photo: web / author