Category: New cars

Multiply And Divide

2023

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Video: The Soviettes - Multiply and Divide (Official Video) 2023, February
Multiply And Divide
Multiply And Divide
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WHY FOUR

Previously, in all-wheel drive, they saw only a means of increasing patency. However, for two decades now, designers and marketers have been tireless to say: it is required for greater traffic safety and better realization of the capabilities of powerful engines. And therefore, an unprecedented variety of schemes and devices arose, the main task of which was confident control on a slippery road.

A 4x4 car takes better slippery climbs, is more stable on roads with a low coefficient of adhesion, more confidently passes corners, allows more precise control in sliding. No wonder that at one time the Audi Quattro captured the rally crown with lightning speed. However, not for long - it turned out that for sports victories not only all-wheel drive is required …

ORTHODOXES AND RADICALS

Manageability and patency are not the best fellow travelers. Take, for example, Nissan Patrol GR / Nissan Patrol. In its next, 2004 edition, the transmission scheme was left the same as forty years ago. Four-wheel drive without center differential, front wheels that can be switched off. Unlike UAZ - automatic wheel clutches. Advantages: simplicity and reliability. The shortcomings - everything else, from the inability to use four-wheel drive on a good road and high speed to the “two in one” problem - the driver must be prepared for two different types of control in critical situations. It is especially difficult to deal with short cars that are more prone to skidding. However, off-road competition enthusiasts consider the scheme with a rigidly connected front axle to be the only true one - the simpler the mechanics, the less often it breaks.

Over the years, the main stages of improving such a scheme were automatic wheel couplings and a synchronizer, which allows you to turn on the front axle at any speed. However, the Chevrolet Tahoe offers automatic inclusion of the front axle when the rear is slipping (Autotrac 4x4 system).

How to make an all-wheel drive car drive on paved roads in 4x4 mode? Add center differential. Back in 1976, the Niva VAZ 2121 was a discovery in this area. However, paying tribute to the Soviet designers, we recall that the Range Rover with a similar drive scheme appeared earlier, and not only the design advantages, but also the need for maximum unification of the new product with the Zhiguli, as well as problems with handling and a small margin, determined the VAZ choice durability of the rear axle.

TWICE TWO NOT ALWAYS FOUR

The center differential solved one problem and gave rise to another: it must be blocked off-road, otherwise the other three will stop when one wheel is slipping.

However, this is not the most difficult task. It’s more difficult with the behavior of a car with three “free” differentials on a slippery road: until the wheels slip, it’s more or less tolerable, but when skidding, it turns out that even a car with a rigidly connected front axle behaves much more clearly.

Audi was one of the first to solve this problem by using the Thorsen self-locking center differential worm differential. By the way, this is not at all the name of the Swedish inventor, but an abbreviation for the English Torque Sensitive (literally: torque-sensitive). For a long time this solution remained one of the most effective. Its main disadvantage is high cost, high requirements for workmanship and “one for life” setting.

A thorough analysis of the behavior of all-wheel drive sports cars showed that precisely in the distribution of torque - the key to confident handling on any road. Fortunately, another invention arrived in time on time. A viscous coupling is a set of plates immersed in a special fluid. While both parts of the coupling rotate at the same speed, nothing happens, but if one of them brakes, the temperature of the liquid increases and the viscosity rises sharply - the coupling is blocked. Wiskomuft is the perfect solution when you need a “soft” and quick-acting lock for a road car, but it is not suitable for heavy off-road use.

Imagine a simple situation: an all-wheel drive car got stuck, the front wheels fell into the pit, and the rear wheels stalled helplessly. As a lock - viscous coupling. She is desperately trying to crank the stuck wheels, translating the engine power into heat … Many owners of SUVs have seen from their own experience that it’s not difficult to cook roast from viscous coupling, and the cost of the dish is sensitive even for a tight wallet.

However, there are many other couplings that automatically include four-wheel drive. For example, multi-plate clutch controlled electronically or hydraulically, as on the Honda CR-V. The operation of such devices can be regulated within wide limits, avoiding dangerous modes and intervening when their action complicates the work, for example, ABS.

ADVENTURES OF ELECTRONICS

Theoretically, it’s not so difficult to create the perfect all-wheel drive transmission. You just need to combine the technical solutions needed in each case and provide for all possible operating modes. The Mitsubishi company, having created the Super-Select transmission, combined in it the best that was invented in the last century. If you want a “clean” rear-wheel drive, you want it to be full with a center differential with a viscous coupling, if you want it, it’s hard to lock the center differential with a lower gear. In a word, for every taste. Minus, perhaps, one - the price. “Super-Select” is still offered only for the most expensive Mitsubishi off-road vehicles.

Mercedes-Benz is one of the few companies that installed all three “hard” locks on their “Gelendvagenes”. This, combined with the “right” rubber, is a very effective off-road weapon. But the "short-circuited" transmission requires the ability of the driver to handle it - to break the CV joint, for example, a trifling matter. Therefore, the M-class, which appeared in 1996 for the American market, was devoid of mechanical locks: for the first time they turned to electronics. The stalled wheels here simply slow down, redistributing the torque to the stuck ones. It is cheaper and eliminates the shock loads in the transmission - it is almost impossible to break anything.

An M-class example has become contagious. Today, such systems are used everywhere, from impersonating serious Volkswagen-Tuareg and Land Rover Discovery 3 off-road vehicles to the all-road Audi A4 Quattro.

ONLY WHAT WITH RALLY

Those who are seriously engaged in the preparation of rally all-wheel drive cars know that the control of the rear differential lock is point number 2 after the interaxle. A typical example is "Mitsubishi Lancer Evolution /"> Mitsubishi Lancer Evolution VIII ". Its transmission has three differentials, two of which (center and rear) - with electronic adjustments. Depending on the program set by the driver (asphalt / gravel / snow), priority is given to either maximum stability or maximum power realization.

The Subaru Impreza WRX Sti is equipped with an asymmetrical 35/65 center differential with electronic locking metering and a self-locking rear differential. The driver can choose automatic or one of six fixed modes of operation, corresponding to his style of cornering.

FIVE YEARS OLD FORWARD

Hybrids are coming - now a car with a power plant made of internal combustion engines, an electric motor and batteries can be found not only in the salon in Tokyo, but also in the neighboring lane. Off-road vehicles are an ideal object of "hybridization". I want to reduce fuel consumption, improve dynamics, have enough space inside, and the price does not put barriers to new technologies. The Lexus RX 400h is no longer a prototype: it has been sold in America since April 15, 2005 and will soon reach Russia.

This all-wheel drive does not have a mechanical connection between the axles, since the rear wheels are driven by a separate electric motor with a power of 50 kW. Fully electronic traction control allows you to quickly achieve a total power of 270 liters. sec., accelerate to 100 km / h in 8 s and limit the average fuel consumption of 8.5 l / 100 km. VDM (Vehicle Dynamic Management) is responsible for the behavior of the machine in difficult conditions, which for the first time uses not only the selective braking of individual wheels, but also the individual distribution of torque.

INSTEAD OF CONCLUSIONS

For mass vehicles, there is no alternative to electronics. First of all, for the price - because today's systems use the readings of ABS sensors, brakes are also on every car. What is left to add? Several additional sensors and programs.

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