The years in which the vehicles in use at the State were exclusively produced by the mother country are far away and their productions fell mostly among those present in the "basic" versions, this at least until the 90 years, a period in which the technology also arrives on the basic versions used by the public administration.
Simplicity could certainly benefit reliability, especially for vehicles used for operational purposes, and it is also correct to report the technical problems that have followed with the introduction of automatisms and control units that have forced a sort of forced alienation, different vehicles and motorized units also used by the Armed Forces. Some of them are used as a "spare parts warehouse" for working vehicles, while others are sheltered and well aligned in the barracks, on their body, with some sadness, you can see the dust deposited over the years, since perhaps the budget Defense spending has also been withdrawn due to fundamental logistics.
Transmission systems past and present, some of them equipped on military vehicles
It is basic to premise that the family of automatic transmissions is divided into three reality with some sub-groups. There are traditional torque converter hydraulics, continuously variable CVTs and the latest robots.
Probably now you are wondering among these types which ones are the most reliable and cheap and without making you wait, I immediately express my opinion.
The robots are generally the fastest and most sporty, the plumbers the softest but heaviest, while the CVTs are progressive light and cheap.
Robots / automated / sequential. Three appropriate terms to identify the same system; a concept that, unlike the other automatic types, maintains the driving torque in release of the accelerator, getting closer to the type of driving with manual transmission. They are excellent but they are not always up to expectations and this clearly depends on which "robotized" we use and above all on how much we spend. The sports par excellence, Lamborghini, Ferrari, Maserati and BMW have in fact been oriented for double clutch robotic systems, the most similar to mechanical transmissions and born initially for racing in the German DTM championships and then in F1. Many mechanics, about robotized gearboxes, will be able to confirm a certain delicacy, especially in the cheaper versions and continuous interventions of reset control units or for bulk systems, rather than for prematurely worn frictions.
This category of changes have in common regardless of how complex they are, a system a double clutch (with two disks) rather than a pack - heavier - multidisk with clutches in an oil bath, like those of motorcycles to be clear. If we take for example the more expensive DSG Volkswagen, rather than ZF or the Alfa Romeo TCT, we will probably have a positive response in terms of performance, but the medium-sized cars are equipped with simpler systems, comfortable in traffic but with not certain benefits in extra-urban use .
In the 1938 the first "automatic". A system, the hydraulic one that made the history of automotives of automotive transmissions and was applied to American cars from the 38 by Chrysler De Soto who called it fluid drive and shortly thereafter Mercury followed her with theO Matic. The clutch pedal was used only to change gears and nothing was forbidden, consumption aside from starting in the fourth; an innovation for overseas taxi drivers.
The mechanism was actually based on one hydraulic coupling and not on a converter (ie, a called rotismo was missing stator) and this joint was joined by a traditional disc clutch. Perhaps someone will remember the Citroen DS Squalo semiautomatic that equipped a similar system without having the clutch pedal.
A "semi-automatic" system was present in the old Astra trucks used for towing tanks but also on locomotives used by the railway engineers - railcar FS AL 668 1900 - rather than in buses or quarry trucks and the joint use of friction and torque converter, avoided overheating and premature wear of friction materials with really heavy loads.
How does the converter work and how does the multiplication of torque occur? I try to give you a metaphorical example that I hope will be clear. We think of a water mill, with the rotating wheel immersed in part in a river. The river current exerts pressure on the entire surface of the blades and then flows away. If you could imagine that the water, immediately after the thrust on the blades, was conveyed again on them and then went to add up with that already present, on the same blades we would have a mass and a volume of water double compared to the first pass . The impeller of our mill would then acquire a lot more "torque" and therefore force for his work.
This is the principle of the torque converter, which instead of water uses red ATF oil, specific to be placed under pressure. In fact the parts of the converter are three: a pump, driven by the engine (the water course of first) a stator (a conveyor) and a turbine connected to the wheels (the mill).
"Converter lock " ready torque, engine braking, more performance with less consumption. These are the prerogatives to be found in the variegated world of hydraulic transmissions. In fact, if there is not a torque converter exclusion clutch shortly after the start, the sensation in the event of gas release is to have the car in neutral, a situation not very sporty and that relies only on the brakes on the relationship between adherence and stability of the vehicle.
This feature is now assembled on all heavy vehicles, including the special ones used by the Armed Forces. Here, the torque converter as soon as the engine is at a speed of about 1500 revolutions, is excluded through a clutch that makes two elements previously seen, pump and turbine, integral, which start to turn at the same speed and without power losses. Some automotive systems, on the other hand, have the exclusion of the torque converter only in the last gear, a sort of mode over drive highway.
However, the control of the changes, on all existing systems, generally takes place according to the speed, load, inclination of the vehicle, engine rpm and throttle position and the control unit has an indispensable role compared to the previous "analogical" hydraulic versions of the 70 / 80 years such as the BorgWarner Mercedes that had a pole with two masses on the sides and that due to the centrifugal effect of the transmission shaft speed, rotated by expanding a rhomboidal device that opened or closed the slide valves designed to change the gears.
CVT, Continuously Variable Transmission, Hub Van Doorne.
Many may think of the Fiat Uno Selecta, but in reality the system is much older and Fiat has only patented a winning metal belt system that today is mounted on all CVT systems, including scooters.
The inventor Van Doorne took a cue looking at the machine tools in their different and variable rotation speeds for the processing of materials. However the first car application, happened on the DAF Variomatic and later on Volvo 343 two and a half volumes.
The system used two pulleys and the mandatory scanning of the moving belt inside the latter, generated tens of variable transmission ratios according to the set acceleration.
He seemed to have no future, but Fiat took it into consideration especially studying the limits that fell on the delicacy of the first rubber belts. Fiat revolutionizes the CVT concept starting from its Achilles heel. With the versions Selecta, a belt made of hundreds of steel links held together (a bit like a zip) by two circular bands of flexible steel appeared. The project was sensational even if in '90 the bias on the "automatic" was quite widespread and sales of this model not really exciting and perhaps overshadowed by the American hydraulic automatic.
Japan contributed to the revitalization of the CVT. After the setback on the Uno, Fiat continued the CVT road with the Punto Sporting in the "automatic" version and the latter had two innovations to transmit the movement from the engine to the CVT pulleys, ie the addition of a torque converter in place of the engine / transmission clutch systems, such as centrifugal, magnetic or pressure clutches. The Fiat system also offered the novelty of the sequential concept applied to a continuous variation system. In fact, it was possible to interact "manually" with the lever of the automatic transmission on the diameters of the pulleys, the one that today, as an option, have several powerful scooters.
In Japan, the Fiat patent takes shape and the association between torque converter and CVT transmission like so much that after some updates, Nissan and Toyota are just some of the houses that have jealously made this innovation that today finds its application and benefits in running costs, even on middle class sedans.
The limits of this system are the powers and the masses, in fact we will never see sports cars or trucks with a CVT but in urban or motorway use the modern systems to variation with sequential use have the green light also as reliability.
Drivers of heavy vehicles they opt in part for the traditional mechanic but in the stalls of robotic options, the system Volvo I Shift seems to have the most "professional" consensus followed by the Scania system Optcruise e As Tronic Zf of Daf.
Excluding the hydraulic converter systems used on the modern military fleet of Iveco Defense Vehicles, power and horses it seems the obstacles, if not proportioned to the mass, that associated with a robot system with numerous gears, can preclude performance especially when climbing with heavy load, where the continuous changes to look for torque, inhibit the acceleration of the vehicle lengthened driving times and the overheating of the parts.
It is therefore important to understand before the purchase of a heavy vehicle, bus or articulated vehicle, the use that you want to relegate to the means, highway, mountain rather than city traffic; admitted clearly that in a difficult profession like that of the driver, always full of unknowns and unexpected events not because of him, there is the margin for the preventive evaluations on the on board technology. The best horses could be from 350 to 450 hp for larger buses, while for a truck from 40 tons the value could start from 500 horses up to 700.
Feature of hydraulic gearboxes is the creep, Or the creep at the minimum generated by the multiplication of torque of the converter. This is one of the main differences between the exchanges hydraulic and robotized. A particularity, among other things very convenient in traffic and parking, which has however misled many buyers of the modern automated system. In fact, the "robotized" vehicles, although having a selection lever often very similar to vehicles with torque converter, do not need with the gear engaged to keep the vehicle braked with the engine running during a stop at a traffic light, just to give an example . Many mechanics were besieged by customers worried about some defect on their new purchase, but in reality everything was working perfectly; to change was only the type of system. Many car manufacturers, however, ran for cover by providing to insert on the most sophisticated robotic systems, a sort of maneuvering clutch, which is grafted by lifting the foot from the brake.
Even the big buses Travego Mercedes produced recently and with robotized transmission, have inserted this clutch of maneuver that eliminates jerks and jolts produced by the electric accelerator during maneuvers.
(photo: web)
