ONCE STEP, TWO STEPS …
TODAY AT THE MAXIMUM SPEED, HAVE TO STEP THROUGH SIX, And THAT … THROUGH 32 STEPS
TEXT / ALEXEY SPARROW-SHOES
WHY ARE TRANSMISSIONS REPRODUCED?
The climb began with the simplest gearboxes: just two steps! Then the number of gears was constantly growing. Already in the 50s, many passenger cars had four gears, and another twenty years later they were replaced by the popular five-step vehicles. However, at the turn of the century, six-speed, if not stepless, boxes begin their victorious procession. The main trucks left the farthest: 14-16 gears do not surprise anyone today, and the latest ZF Ecosplit boxes have up to 32 steps.
The fact that a box with gears is generally needed by a car is related to the peculiarities of internal combustion engines that can satisfactorily work only in a relatively narrow range of revolutions, while the speed should vary from zero to maximum. So you have to break the entire speed range into narrow segments, and even put in the transmission an element that is capable of slipping - otherwise it does not move smoothly. And yet - where is the limit to the number of necessary programs, why even five of us are not always satisfied? To some extent, this is due to an increase in maximum speed (the range is expanding), requirements for acceleration dynamics, but economical considerations are no less important: getting into profitable, but narrower engine speed ranges is much easier with a large number of gears (see graph).
LET THE DRIVER'S HEAD NOT HURT
When you learn to drive a car, you have to remember for a long time the position of the shift lever for each gear. Is the sixth also added to the fifth position on mass machines? The designers, however, are not sadists and have come up with a way to get around this obstacle on the way to an ever-increasing number of steps.
Actually, this has long been known to riders and motorcyclists. The bottom line is that the box control is in the neutral position all the time and to switch up or down you just need to briefly push it back or forward. The included gear will be shown by an indicator on the instrument panel, so you can use the joystick lever by touch and not think too much. (Apparently, it was no accident that Ford named its system in Russian unequivocally “Durashift.”) Such boxes with sequential switching were called sequential ones (ZR, 2001, No. 4).
It is not necessary, however, to think that motorcycle units have come to modern cars. The tricky Latin word refers, rather, to the control method, and the design of the box itself can be any. These are often ordinary car sets made of shafts and gears, but managed in a different way: with the help of separate actuators receiving from the lever (or buttons on the steering wheel) only switch-on commands previously processed by a computer. Well, where the computer is, there is automation, so sequential boxes almost always have an automatic mode of operation.
Today, such transmissions can be found in Alfa Romeo, BMW, Ferrari, Smart, Volkswagen Lupo, FIAT, Mercedes-Benz, Ford … It is estimated that by 2003 they will be equipped 3% of all new cars, and by 2005 it is planned to increase this share to 8%.
THERE IS A PROBLEM…
If everything is so good, then why are car manufacturers not in a hurry to equip their new products with sequential switching boxes? As in every new business, there are problems. One of them is speed. Did you know that the test drivers “Driving” during the races, by definition of accelerating dynamics, manage to shift gears manually in just 0.12 s - this is how dispassion recorders show. And in Smart, for example, a pause when torque is not supplied to the wheels reaches 0.5–0.8 s!
The developers are trying to reduce this delay by trying different versions of the software, changing actuators from pneumatic to hydraulic or to stepper motors. And success is evident: the Isitronic of LuK switches in 0.3 seconds; in addition, the driver, if he chose the manual control mode, can “skip” through unnecessary gears, passing, say, immediately from fifth to third. “Lupo” learned to manage only 150 ms, but perhaps today the latest development of the BMW SMG is ahead of all, taking place in the M3 compartment since June this year.
A driver who is not stingy with an extra $ 2, 800 can choose between five switching modes - from soft to hard sports. In the latter case, all processes, including clutch control, proceed in … 0.08 ms! Frankly speaking, the electronic “brains” have something to work on in these moments. Here is a far from complete list of control unit inputs: the state of the parking brake, the position of the gas pedal, the speed of rotation of the input shaft of the gearbox, the oil temperature in it, the position and speed of the control joystick, the position of the clutch disc, the pressure in the hydraulic system, lateral and longitudinal acceleration of the car, position of the brake pedal, sensors for closing doors and hood, ignition, setting the temperature …
We will not go into the details of a program that guarantees smooth, gear-free shifting. Let's just see why the box needs to know about the doors and the hood? It turns out that this is the so-called protection from the fool. For example, the driver decided to go out and give way to a colleague with the gear already engaged. Then the automation will not allow the clutch to engage until the door closes or the gas pedal is pressed. In anticipation of a “leadership change, " however, the clutch will not be squeezed for too long. After a while, the box itself will switch to “neutral”, and the driver will be notified of this by light and sound indicators. Well, what about the hood? Suppose you decide to dig into the engine with the gear engaged and pulled the throttle cable. Do not be this lock …
So, the more gears, the better. Ideally, there should be an infinite number of them, so that the engine all the time works in an economical and high-torque mode. Therefore, various variator systems have long attracted the attention of developers. The first V-belt variator was invented by the Englishman Joseph Abott, and a very long time ago. Theoretically, the device is not complicated: two pulleys, whose cheeks can be moved and moved apart, displacing the V-belt by a larger or smaller diameter. The gear ratio varies over a wide range completely stepless.
One thing is bad: the life of the belt, especially when transmitting significant torque, is relatively small. Therefore, CVTs for a long time remained the lot of snowmobiles or baby cars. Today, this restriction is being gradually removed. We will not go far for an example - only to Audi: here is the serial A6 with the Multitronic variator, in which a soft belt replaced … a chain.
Of course, electronics could not be avoided here either: it monitors the necessary pressure in the system, preventing too tight a compression of the pulley cheeks and at the same time not allowing the chain to slip. In addition, it became possible to organize virtual transmissions for drivers who are tired of the “trolleybus” traction and want to enjoy manual switching.
In addition to Audi, CVTs can be found on FIAT, Lanche, Honda, Nissan, Rover, Subaru or Volkswagen. Moreover, the V-belt or chain is not a mandatory attribute of the variator, there are other systems, so far, however, at the level of prototypes.
DOES AUTOMATIC RENTAL FOR RENT?
The disadvantage of classic automatic transmissions with a torque converter was considered large energy losses in the latter, which led to an increase in fuel consumption. In planetary systems, usually three, sometimes four fixed gear ratios were implemented, and the torque converter took care of the rest.
And so, the German ZF announced the creation of a new class of planetary automatic transmissions 6НР26 with … six fixed gears that cover the range of gear ratios from 1 to 6.04 (the CVT “Multitronic” has 6.05). The designers managed to reduce the number of switching elements (clutches, brakes) to five, respectively, reducing the weight and dimensions of the new box. As for fuel consumption, it was reduced in the standard European driving cycle by 5-6%.
COMPLEX … SIMPLIFIED
In the transmission of a modern main truck, it is often not less than one and a half dozen steps. You can’t hide such a ladder in one box, therefore, for example, after the main four-stage they put a couple more two-stage. Switching - with a lever and two flags on it … That is, two or three transmission control elements, not counting the clutch!
It is quite natural that sequential boxes with them to the limit by a simple control algorithm are firmly established here. Here, where there is no place for sporting ambitions, all switching is carried out by compressed air. Moreover - there is no need for synchronizers! Probably only drivers with a very long experience remember such words as “double squeeze”, “gas exchange”. Without complex manipulations of the gearbox lever and the clutch pedal in those old years, it was not possible to equalize the rotational speeds of the mating gears, and therefore switching, not accompanied by a "gnashing of teeth", was considered the destiny of the elect. Nowadays, all these routine procedures are undertaken by automation, so the driver of, say, Aktros or Scania does not even suspect how many processes he starts with a slight push of the joystick. In fact, he may not even push it - in automatic mode, the serial box will do everything in the optimal way, so manual mode is probably left as a means of dealing with sleep on a long journey and for difficult maneuvers when unloading.
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To summarize, we dare to assume that the future is most likely in sequential gearboxes and variators. But - only as long as the piston heart of the internal combustion engine beats under the hood. If, say, an electric motor comes in its place, the gearbox will simply disappear as an indispensable vehicle unit. So her fate directly depends on the dispute between … two hydrogen technologies - burning this promising fuel in combustion chambers or directly converting it into electric current. Wait and see!
Typical curves of power, torque and specific fuel consumption of an internal combustion engine, taken with the throttle fully open. To ensure that the car accelerates to high speeds and does not burn too much fuel, it is necessary to keep the engine in a fairly narrow range - transmissions need steps!
manually controlled by a joystick or buttons on the steering wheel, and can also work in automatic mode.
BMW SMG box performance is very fast
(85 atm) pressure
in the hydraulic system.
The control sticks of different cars look different, but the essence is the same - sequential gear shifting.
The principle of operation of the Multitronic variator is simple, but can not be said about the technology of its manufacture