The all-terrain vehicle is made according to a design that has proven itself well on the Kirovets tractor. It has the same “breakable” frame and drive on both axles. What does this give? Firstly, cross-country ability. The frame, constantly bending, seems to follow the terrain. All four drive wheels are constantly in contact with the surface. This eliminates overloading of individual wheels and their slipping on uneven ground. Secondly, maneuverability. The articulated frame reacts sensitively to even minor steering deviations and allows you to turn almost on the spot. Thirdly, constructive simplicity. In this scheme, you can use exactly the same front and rear axles. The engine mount is also simple.

The frame consists of two main parts connected in the middle by a hinge with a vertical axis of rotation. Its front part is a rigid welded assembly on which the axle, engine, fuel tank, control pedals and driver's seat are installed. The left supporting arc of the frame also serves as a muffler.

The hinge with a vertical axis of rotation consists of two forks connected by powerful fingers. The pins are bolted to the rear fork lugs, and the front fork pivots around them in thrust and needle bearings.

Chassis(in the top view the engine and seat are not shown):

1 - fuel tank, 2 - engine, 3 - steering column mounting bracket, 4 - exhaust pipe, 5 - central engine mounting bracket, C - differential housings, 7 - steering column, B - steering rod. 9, 10 - frame bend angle limiters, 11 - body mounting bolt limiter, 12 - steering worm drive, 13 - front driveshaft housing, 14 - connecting link. 15 - rear propeller shaft housing, 18 - body mounting loop, 17 - gear shift lever. 18 - gas pedal, 19 - lower engine mounting bracket, 20 - clutch pedal, 21 - kickstarter, 22 - muffler inlet pipe, 23. 29 - axle shaft flanges. 24 - step. 25 - supporting arc of the frame (muffler). 26 - exhaust pipe. 27 - steering rocker. 28 - supporting arc of the frame. 30 - brake cable, 31 - brake drum, 32 - rear driveshaft. 33 - steering gear bracket, 34 - front driveshaft. 35 - chain drive casing, 36 - rear engine mounting bracket. 37 - brake handle.

To prevent the wheels from rubbing against each other when the frame “breaks” around the vertical axis, the hinge has limiters installed respectively on the front and rear forks: a slightly bent and flattened tube for rigidity and two studs at the ends of the channel brackets. The rear part of the frame - the bridge, brake and removable body are attached to it - is movable, its hinge is with a horizontal axis of rotation. But it is designed somewhat differently: a fixed casing with an internal thread is riveted to the rear fork, into which a bronze bushing is screwed. It serves as a sliding bearing for the movable casing of the rear part of the frame.

This casing is held in the sleeve by a pin screwed into the reinforcing lining. It is also the limiter of the angle of “break” of the frame relative to the longitudinal axis of the all-terrain vehicle. The size of the angle depends on the length of the groove cut into the fixed casing and sleeve.

The VP-150M engine is installed transversely so that it takes up less space, and the air-cooling fan has the most favorable operating conditions.

1 - bevel gear drive, 2 - differential housing, 3, 7 - tapered roller bearings, 4 - spacer, 5 - adjusting shim, 6, 12 - MB studs, 8 - cuff, 9 - bearing housing, 10 - M4 bolt, 11, 18 - casing halves, 13 - internal flange, 14 - 0 3 mm rivet, 15 - driven sprocket, 16, 20 - M4 vitae, 17 - lining, 19 - steering gear bracket hinges, 21 - nut M 14X1.5, 22 - outer flange, 23 - front driveshaft.

The mounting brackets are located as follows: the central and most powerful one is on the differential casing, under the engine cylinder, the lower one is on the right axle beam, under the crankcase, and the rear one is on the chain drive casing.

A metal fuel tank with a capacity of 5.5 liters is attached to the engine crankcase; Fuel enters the carburetor by gravity.

The controls are located on the front axle beams: the clutch pedal on the left, the gas pedal on the right. For the driver's convenience, footrests are installed next to the pedals.

1 - rear propeller shaft, 2 - outer flange, 3, 8. 12 - M6 studs, 4 - brake drum, 5 - inner flange, 6 - M14 nut, 7 - brake disc, 9 - bearing housing, 10 - collar, 11, 15 - tapered roller bearings. 13 - adjusting shim, 14 - spacer, 16 - differential casing, 17 - bevel gear drive.

Gears are switched by hand using a lever with a ball at the end, welded to the gear sector.

The engine is started by a kickstarter with a crank instead of a pedal.

Exhaust gases from the cylinder through a corrugated pipe enter the left supporting pipe of the frame like a muffler and exit from the exhaust pipe under the seat.

The transmission of the all-terrain vehicle is symmetrical relative to the vertical axis of the “kink” of the frame. The torque from the engine is transmitted by a chain to the cardan shafts, and from them through bevel gears and differentials to the axle axles. Cardan shafts are machined from rod. In the middle they have necks for sealing cuffs, and at the ends there are slots. Cardan shafts with crosspieces (including those for the connecting link) were taken from the Ural motorcycle. They rotate in bronze bushings, which are lubricated from time to time through thin oil nipple tubes brought out.

With external splines, the cardan shafts fit into the outer flanges connecting them to the shanks of the drive gears of the bevel gears. The rear shaft is equipped with a brake from the Vyatka scooter: the brake disc is attached with pins to the bearing housing

unit, and the drum - to the flanges. The control cable from the disk is routed to the steering column.

The axle differentials on the all-terrain vehicle are of a traditional design: with two satellite gears (from the Moskvich-412 car). The side gears are homemade, and the bevel gear is taken from a Ural motorcycle.

The cracker, unlike the Moskvich one, does not have a spherical surface facing the differential housing, but a cylindrical one, for simplicity.

Bridges are attached to the frame using bolts, liners and shims. Only on the rear axle are the bolts holding the body mounting loops, and on the front axle are the gas and clutch pedal brackets.

The steering consists of a removable steering wheel, a vertical column, a steering worm drive, two rockers and an adjustable rod. The drive ratio is 1:4, which allows you to “break” the frame not only in motion. but also in the parking lot. The force from it is transmitted by a rod to the rocker attached to the fork of the rear part of the frame, and causes it to deviate in one direction or another.

The wheels are also structurally simple and completely identical. The supporting element of each of them is an aluminum step-

center, to the ends of which disks of the same material are screwed.

1 - plug, 2 - M3 screw (4 pcs.), 3 - cuff body, 4 - cuff, 5 - front driveshaft, 6 - front casing, 7 - trim, 8 - seat post. 9 - seat height adjuster, 10 - front fork, 11 - frame limiter tube, 12 - needle bearing housing, 13 - bushing. 14 - stud-limiter of the angle of "break" of the frame, 15 - brackets of the stud-limiters, 16 - pin-axis of the "break" of the frame, 17 - thrust ball bearing. 18 - needle bearing, 19 - steering rocker, 20 - rear fork, 21 - oil nipples, 22 - body mounting limiter bolt, 23 - reinforcing lining, 24 - movable casing, 25,27,33 - bronze bushings-bearings, 26- fixed casing, 28 - M5 screw (2 pcs.), 29 - Mb bolt for fastening the pin-axis (6 pcs.), 30 - Mb bolt (8 pcs.), 31 - connecting link, 32 - Mb bolt (4 pcs. ), 34 - cardan.

1, 3 - front axle axle shafts, 2, 10 - differentials, 4 - engine output shaft, 5 - chain drive, 6 - front driveshaft, 7 - connecting link, 8 - rear propeller shaft, 9, 11 - rear axle axle shafts.

1 - wheel flange, 2 - oil seal, 3 - cover, 4 - bearing housing, 5 - axle bearing. 6 - cuff, 7 - retaining ring, 8 - bridge beam, 9 - axle shaft. 10, 17 - differential housing flanges, 11 - cover, 12 - driven bevel gear, 13 - M8 tie rod, 14 - block pin, 15 - pinion pin, 16 - satellites. 18 - MB studs. 19 - differential bearing. 20 - axle bearing housing, 21 - gasket, 22 - halves of the differential housing, 23 - frame supporting arc, 24 - plug, 25 - adjusting spacer. 26 - liners. 27 - M8 coupling bolt, 28 - body fastening loop.

1 – M8 bolts for fastening to the axle flange, 2 – hook (wire Ø 3 mm). 3 - canvas belt, 4 - bracket (wire Ø 4 mm), 5 - hole for the valve. 6 - hub, 7 - disks. 8 - cover.

1 - front bracket, 2 - side brackets, 3 - rivets Ø 3 mm. 4 - M4 screws.

Eight canvas belts holding the tire are attached to the disks with wire hooks and staples - two chambers measuring 720 X 310 mm, nested one inside the other and protected by a canvas tape with lug tucks.

The outer end of the hub is covered with a cover, which protects its cavity from contamination, and the inner end is equipped with four bolts for attaching the wheel to the axle shaft flange.

The body is assembled from a welded steel frame and fiberglass panels. The floor is given the necessary rigidity

three channels with brackets for installation on the frame of an all-terrain vehicle.

The weight of the body is only 6.5 kgf, but its dimensions are such that they allow an adult to sit without experiencing any particular inconvenience.

Maintenance of the all-terrain vehicle is practically minimal. It is enough to monitor the level of fuel in the tank, transmission oil in the axles and air pressure in the tires. Yes, occasionally lubricate the bronze bushings-bearings through oil nipples - that’s all.

A. GROMOV, A. TIMCHENKO

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In 1961, an unusual “car” called Ferguson P99 entered the start of the British GP. It differed from its rivals... 4-wheel drive: this has not been seen in the Formula 1 world championships for a long time. It must be said that the pioneering P99 did not achieve any noticeable success; immature design. However, the idea was in the air, and in 1965 the all-wheel drive Jensen FF appeared - a “piece” British GT with a powerful Chrysler “eight” under the hood. Its 4WD transmission essentially repeated the design of the hapless Ferguson P99, but the car turned out wow. He laid the foundation for an interesting trend in the automotive industry: the creation of high-speed passenger cars with all-wheel drive transmission.

Why 4WD?

And why, one might ask, do fast cars need 4 driven wheels? With all-terrain vehicles, it’s clear, but does the Jensen FF need an all-wheel drive transmission?

Even so, British engineer Henry Ferguson realized the advantages of all-wheel drive early on. G. Ferguson, not only a qualified technician, but also a major industrialist, had considerable opportunities to realize his plans. One of the embodiments of his plans was the racing Ferguson P99.

Still, why 4WD? For what? First of all, driving safety on wet and slippery roads. Almost the same as with braking, only in reverse. For an inexperienced driver, slipping of the drive wheels under the “gas” is dangerous: the so-called “power” skid when the rear ones slip - or drift when the front ones slip. Whereas the probability of slipping with 4-wheel drive is much lower; That was G. Ferguson's idea.

The essence of the matter is clarified by the so-called Kamm “circular diagram”: the circle (see figure) outlines the limits of tire adhesion in the contact patch with the running surface. Let's say the maximum force that rubber can transmit (due to static friction) on a dry road is 4 thousand newtons. In any direction: forward (acceleration), backward (braking), sideways (centrifugal force in a turn). It makes no difference, but no more than 4 thousand N! There is only one frictional force in the contact patch - for everything. And if, during intense acceleration, a traction force of 8 thousand N falls on the (rear) drive wheels, then it “selects” the adhesion force of the tires to the road almost entirely. There is nothing left for lateral forces: the car fidgets “astern” - a “forceful” skid that is dangerous for an inexperienced driver.

As for sports and racing cars, we have a special conversation about them. The main thing here is the grip weight: the proportion of the car’s weight that falls on the drive wheels. Let's say 58% on the rear drive axle for a central-engine "formula". Not bad, but far from 100%. And the maximum acceleration of the car from the start depends on the adhesion weight: the rear wheels slip from excess traction, and the “car” does not accelerate as quickly as the engine allows. Whereas all-wheel drive gives 100% of the grip weight - by design.

Here are (at least) two reasons that justify the use of complex and expensive 4WD drivetrains. Isn't it enough? In short, it is better to distribute engine thrust not over two, but over all 4 wheels - for the sake of safety and dynamics. And from the mid-60s the process began: the high-speed Jensen FF with an all-wheel drive transmission according to the “Ferguson formula” appeared. What's the other formula? Isn't the diagram clear: transmission shafts transmit torque to both drive axles - and that's it. Why complicate things?

Unfortunately, it is simple only at first glance; in reality, a 4WD transmission will not do without such unpleasant things as differentials. Moreover, two are not enough; all 3 are needed: a pair of drive axles - plus a central (interaxle) differential. And then an acute toothache arises...

Differ's vagaries

It is difficult to imagine a car without any differential: for example, driving in a turn. All 4 wheels roll along different curve radii and travel different paths. If you do not allow the drive wheels to spin unevenly, one or another of them will have to slip (or even both); the car will become difficult to control. Remember how an all-terrain vehicle behaves when the center differential is rigidly locked... .

Okay, since we can’t do without them, we’ll install 3 differentials. Order? I'm afraid not yet... Here you need to figure out what a difer is? The divider is one of the simplest mechanisms - somewhere after the lever and the gate: it divides the torque (but not the power!) among two output shafts in a given proportion - and allows them to spin at unequal speeds. When a differential divides the input torque in half, it is called - symmetric. However, they are also made asymmetrical: 60/40%, 70/30% – whatever you say. It all depends on the number of teeth on the driven gears - the same or different. But when the difer is assembled, its properties no longer change - 50 to 50 (or whatever it is made of).

A simple gear mechanism, but the gears are made differently. And differentials too - conical (the most common), cylindrical, worm... Accordingly, but the idea is the same. Brilliant simplicity: we install a differential (symmetrical or not) into the drive axle - go ahead and sing! On a straight line, the wheels on the sides spin at the same frequency, and in a turn, the differential allows the outer wheel to run ahead (or lag behind the inner one). Moreover, traction is constantly transmitted to both drive wheels; isn't it harmony? .

And in fact - until one of the drive wheels jumps on uneven surfaces or hits a slippery surface. Have you seen how one of the driving wheels grinds the ice in an angry way, while the other remains motionless? The whole character of the differential is here; that's just the way it's designed. The differential not only divides the input torque, but (if it is symmetrical) equalizes the torques on the output shafts. And when - God forbid! – the rolling resistance on one of the wheels drops to almost 0 (hung on a jack), it conscientiously balances the moments on both. That is, it will also leave the wheel that rests securely on the running surface without traction. All the power (the differential does not share it) flies into the frantic spin of the idle wheel; are you satisfied?

A free differential causes a lot of trouble, even when there is only one - in the (rear or front) drive axle. And when there are 3 of them, it’s like in an all-wheel drive transmission! And everyone is ready to give a damn at any moment: as soon as one of the 4 wheels loses traction, the power will immediately go to it. That is, a 4WD transmission with a central differential (without locking in one way or another) is practically inoperative: free differentials continuously drive one or the other of the wheels. Or even a couple (on board) at the same time - in vain.

And it’s not just a matter of loss of traction; the wheel jumped into the air - and immediately spun wildly with all the power of the engine. When landing, sudden braking and slipping are inevitable - with a violation of the stability of the car on the trajectory, and so on almost every second. Etc., but try to do without a central differential: the car becomes difficult to control in turns. Collision.

Ferguson formula

Simple moral: a 4WD drivetrain cannot be built with free differentials; it will be inoperative. The freedom of the defenders (at least the central one) must be limited. But wisely! So to speak, tolerantly: within some (narrow) limits, let the center differential remain free - and not impair the handling of a high-speed car. And only when the defender threatens to show his malicious temper, bring him to his senses - through a “soft” blocking.

That is, the central differential is complemented by a peculiar device that delicately (!) limits its freedom; This is what the “Ferguson formula” is. So, both Ferguson P99 and Jensen FF were equipped with a special “transfer case” - called Duolok. Quite an intricate design with an asymmetrical (planetary) differential: torque distribution along the axes is approximately 37/63%. However, the main thing is different: two (ball) overrunning clutches. They do not jam until the difference in revolutions of the front and rear transmission shafts exceeds a specified threshold. And then the running shaft is “grabbed” by its overrunning clutch: “soft” tolerant blocking - up to 100%..

1. input shaft;
2. overrunning clutch carriage;
3. chain drive sprockets;
4. planetary center differential;
. output shaft to rear axle;
6. chain drive;
7. output shaft to the front axle;
8 and 9. overrunning clutches;
10. Maxaret anti-lock sensor.

And the Duolok dispenser worked! In any case, in the Jensen FF transmission: a highly dynamic car with a powerful “eight” behaved perfectly on slippery roads. And for the 1969 season, the Formula 1 teams unanimously prepared each all-wheel drive car. Lotus 63, Matra MS84, McLaren M9A... Still the same “Ferguson formula”: center differential with tolerant locking. Alas, again without any success: “active” aerodynamics (“anti-wings”) gave no less effect - using relatively simple means. And in the early 70s, 4WD transmissions were completely banned in Formula 1; the issue was removed from the agenda. .

1. engine;
2. Automatic transmission;
3. “handout” Duolok;
4. front transmission shaft;
5. rear axle;
6. front main gear.

Rally sports are a different matter: by the end of the 70s, the coolest WRC cars acquired all-wheel drive transmissions - according to the Ferguson formula. On high-speed sections, their advantage turned out to be so great that single-wheel drive designs soon dropped out of competition. The 4WD era began in rally sports and continues to this day. The idea of ​​G. Ferguson (he left in 1960) justified itself 100%.

AP photo, Audi, Lancia.

In the first half of the 30s, the awkward all-wheel drive Bugatti 53 took to the race tracks. To no avail.

Transnational corporation Massey Ferguson: tractors and road construction machines.

Wunibald Kamm, German automotive engineer and aerodynamicist (1st half of the last century).

The differential divides the torque in a given ratio - and only the differential! When they say that when the 2nd axle is rigidly connected, the thrust is distributed in a 50/50 ratio, this is a school mistake. Nothing of the kind.

Power is equal, as is known, to the product of torque and shaft revolutions. Therefore, if one of the shafts is stopped, then the power on it, by definition, is 0 (although the torque is quite decent).

Car manufacturers write with great pleasure in their catalogs about the possibility of purchasing various car models with all-wheel drive on all four wheels (4 x 4). Unfortunately, this definition often hides systems that operate differently. So, we suggest finding out what the seller actually means when he says “4 wheel drive”.

4 driving wheels, this is...

The first type of four-wheel drive (4 x 4) is a permanent drive of all four drive wheels, when the torque is always distributed over two axles. This distribution is ensured by the central distribution mechanism. For example, the following models have permanent 4-wheel drive: Audi Allroad, Mitsubishi Lancer Evolution and Pajero, Toyota Land Cruiser or Land Rover Discovery.

Permanent 4-wheel drive can be further divided into symmetrical and asymmetrical. An asymmetric drive is available, for example, in the Land Rover Defender model, in which torque is distributed equally across two axles. With the asymmetrical version, torque is transmitted to the axles depending on the need - this distribution is ensured by an axle distribution mechanism or a multiplex clutch.

Another type of all-wheel drive (4 x 4) is a mechanically connected drive with 4 driving wheels. In this case, we are talking about the phenomenon where one axis is constantly the driving one, and the second axis can be connected by turning on the corresponding lever or pressing the corresponding button. Connectable all-wheel drive can be seen, for example, in Suzuki Jimmy, Jeep Wrangler or Nissan Patrol models, which have permanent drive to the rear axle, and you can connect the front axle yourself. However, it is recommended to use this function only in off-road conditions. If the movement is carried out under normal conditions, all 4 driven wheels will interfere more than help.

The third type of all-wheel drive (4 x 4) is an automatically connected drive. This solution is an intermediate option between permanent 4-wheel drive and mechanically connected drive. We will see such a drive in the following cars: Mitsubishi Outlander, Toyota RAV4, Volvo AWD, Suzuki SX4, Audi A3 or BMW X5. Here, one axle is constantly and directly driven, and thanks to the multiplex clutch, the drive can also be automatically transferred to another axle if necessary.

Advantages and disadvantages of 4 x 4 all-wheel drive

It is true that in general, a four-wheel drive vehicle is more versatile than single-wheel drive vehicles, both in terms of surface quality and weather conditions. With all-wheel drive (4 x 4), you can probably go further than without it. However, this does not mean that we will achieve every goal at any time. Of course, 4 x 4 all-wheel drive provides better traction than a single-axle drive, but if the car becomes uncontrollable and starts to slide, which is possible, it will be very difficult to cope with the situation. Because in cars with four driven wheels, the rear end may begin to slide, and then the front part will also become uncontrollable.

It will also not be possible to hide the fact that 4 x 4 all-wheel drive vehicles are significantly more expensive than vehicles with a single drive axle. Maintaining such cars is also more expensive. You will have to visit gas stations more often, especially if your car has permanent four-wheel drive with all driving wheels.

Thanks to this system, your car becomes heavier, and accordingly, fuel consumption will be higher. You will also pay more for potential repairs. You will have a complex system that, like any other part of the car, will eventually malfunction.

Therefore, a car with two driving axles should not be bought for economic reasons. Such a vehicle will most likely be useful to those people who often drive on difficult roads, for example, those who live or work in the mountains or forests, or to tourists who regularly visit high-altitude ski resorts.

Four-wheel drive vehicles (4 x 4) available on the market

Finally, let's also take a look at our selection of new 4x4 vehicles. We find one of the most popular Lithuanian ad sites. We select vehicles with all four driving wheels:

• Audi A5, A6, A7, Q2, Q3, Q5 and Q7;
• BMW, 4, 5 and 7 series, X1, X3, X4 and X5;
• Mercedes C-, E- and S-class, as well as models: CLA, GLC, GLE and GLS;
• Volkswagen Amarok, Golf, Multivan, Tiguan, Touareg.
• Subaru Impreza, Forester, Outback and XV;
• Mini Clubman, Cooper S, Countryman;
• Jeep Grand Cherokee.

If we change the filter settings to show cars with an automatically connected second axle, we see the following models: BMW, Audi, Volvo, Volkswagen, Mercedes, Porsche and Honda. The fewest offers for the sale of cars with a mechanically connected second axle. After installing such a request, we will see Nissan, Mitsubishi, Toyota, Suzuki, Jeep, Isuzu and Hyundai on the screen.

In general, there is plenty to choose from. Of course, there is no shortage of interesting models on the used car market. But remember that it is better to avoid used four-wheel drive vehicles (4 x 4) offered for several thousand zlotys. A low price usually indicates that soon after purchase you will have to leave a lot of money at the car service center.

Skoda is one of the few brands that offers all-wheel drive on half of its models, excluding very compact ones. Of course, the Czechs inherited such enthusiasm from the parent concern Volkswagen, as, in fact, all the technical “stuffing”.

The basis for all Skoda all-wheel drive transmissions is the Haldex coupling, introduced in the fifth generation. In general, the Driving Experience event was dedicated not so much to the presentation of cars, each of which we had already tested in a single-wheel drive version, but rather to the updated 4x4 system.

Updated, because fundamentally nothing new has appeared in Haldex 5. This is the result of modernization of the previous generation system, aimed at reducing weight and increasing speed. If we omit all the technical details, we can say that the system has a little less hydraulics and a little more electrics.

As before, the Skoda has all-wheel drive without a center differential, but the clutch constantly works with a slight pretension, always transmitting a small percentage of torque to the rear axle. This allows Skoda to call their all-wheel drive models Full Time - with permanent all-wheel drive.

The main advantage of a system based on the Haldex coupling is not only the speed of torque redistribution among the axles, but also the fact that wheel slip on the driving front axle is not the main argument for connecting the rear axles.

The electronics reads information from a huge number of sensors, starting with the level of pressure on the gas pedal and ending with lateral and longitudinal acceleration. At each moment of time, it is decided whether and how much it is necessary to use all-wheel drive, for example, in order to turn the car in a sharp turn, even if there is dry asphalt under the wheels.

The cross-wheel torque distribution is under full electronic control, both on the front and rear axles. Of course, there are no locks here; they are imitated by the ESP system, braking each specific wheel if necessary.

The most interesting thing is that this whole complex makes Skoda cars not so much more passable, but safer, which is what the organizers of the event first tried to show. So, all-wheel drive Octavias and Superbs versus their front-wheel drive “brothers”.

At a water-filled training ground, they had to undergo three tests in turn, changing every five minutes from a front-wheel drive car to an all-wheel drive one.

The first exercise is entering a gentle turn, which has a surface with a minimum coefficient of friction. In fact, an imitation of one of the most common causes of accidents on the winter highway.

Everything here is quite predictable. When quickly but smoothly entering a bend, the front-wheel drive Octavia immediately “floats” with its front end to the outside of the turn. Instant release of gas for corrective work by the steering wheel is quite sharply stopped by the intervention of the ESP system, which, by braking the corresponding wheels, cuts off the fuel supply until the car is completely “straightened up”.

A more provocative drive under a sharp opening of the throttle in a bend with a turn of the steering wheel at the last moment is immediately reflected by a skid of the stern, which is reflexively extinguished by a counterattack by the steering wheel with the addition of gas... but no, the same stabilization system, and this time knocking out the brakes, chokes the engine, making it impossible to pull the car out on your own. As a result, the same adjustment by the steering wheel for a smooth deceleration and only then a return to the set course.

The all-wheel drive Octavia Combi is actually more stable. Behavior on a slippery curve is avoided without sudden movements on the part of both the car and the driver. You can even gently “sink”, controlling the speed limit by the chirping of the ESP - the system intervenes here more correctly, pinpointing the slipping wheels. And even if it went too fast, the all-wheel drive Octavia slides out more slowly and with its whole “body”, allowing the driver to choose... no, there is no choice: the non-switchable safety “collar” again takes control of everything when the drift develops critically.

The second and third exercises turned out to be similar. It was proposed to walk a “snake” first along a horizontal surface, then along a slippery surface to climb. In both cases, everything is watered abundantly.

The long and massive Superb, even with front-wheel drive, is reluctant to be provoked. An attempt to “loose” the car on wet asphalt occurs as if in slow motion – the rear wheels smoothly begin to slide, which the ESP immediately grabs. But driving up a very slippery slope while simultaneously avoiding obstacles was difficult for the car and nerve-wracking for the driver.

In addition to the stabilization system whirring throughout its entire length with “suffocating” dips in reactions to the accelerator, sharp “blows” on the brakes of the drive wheels of the traction control system were added. As a result, driving up the mountain was a jerky jump with the danger of sliding back to the bottom.

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2 / 3

3 / 3

Or the Skoda Superb Combi 4x4. Yes, the traction control here also works a bit roughly, but due to the fact that the front wheels are pulled uphill and the rear wheels are immediately pushed, the car moves with minimal ESP intervention, that is, smoother, more evenly and... noticeably faster. In general, the advantage is clear and obvious.

For the Skoda Yeti, the test organizers prepared something more serious - off-road. Although, I must say, without our native mud mess, this is somehow not off-road - just geometric obstacles.

But first, bench testing of the Haldex 5 coupling on a roller rack. This is where you can clearly see how the torque is distributed and the speed at which the system detects a “slipping” wheel. Of course, the positive result was predictable, otherwise they would not have driven it, but it cannot be said that Yeti copes with this exercise perfectly.

Already in natural conditions, Yeti easily crawled along sloped mountains, without causing any problems to the driver. And overcoming a steep descent, when the driver and front passenger are literally hanging on their seat belts, became the main attraction - the operation of the electronic system for descending from the mountain was tested. In fact, the crossover, playing with the brakes, moves itself at the minimum possible speed - the driver only needs to decide to release all the pedals.

The most exciting task was overcoming the “snake” inside the ravine. The Yeti, of course, pleased us with its geometric cross-country ability and a fairly successful fight against diagonal hanging, but when it fell on its side it was quite intimidating. The fact is that the maximum lateral tilt angle for a crossover is 45 degrees, after which there is a rollover, and, of course, there is no inclinometer in the car. So when the car fell from one side to the other in free fall, my heart sank a little - suddenly it took more than 45 degrees.

The Yeti was the most uncertain when overcoming sandy climbs, which again made me say an unkind word about the work of ESP. As soon as you start to wiggle the steering wheel on an unsteady climb with wheels slipping, choosing the optimal ascent trajectory, the electronics instantly perceive this as a loss of stability and immediately choke the engine even with the Off-road system turned on.

Drive parts from the transfer case of Volkswagen Touareg

Nowadays, it’s hard to catch someone off guard with a question about “all-wheel drive.” They will immediately point out to you an SUV passing by; fortunately, there are more than enough such vehicles on the streets of our cities. And those in the know will also add that ordinary passenger cars can also be all-wheel drive (Audi and Subaru are most often mentioned). And that all-wheel drive can be “permanent” and “plug-in”.

The question “Why?” usually meets with one answer: “For better cross-country ability.” However, regular readers of the automotive press are still aware of “better stability on slippery roads.”

All this, as they say, is true, but not entirely. Therefore, today we will try to systematize our knowledge about all-wheel drive. More precisely, let’s start with it, because this topic, like the entire modern car, is practically inexhaustible.

Divide by more

What moves the car? The engine rotates the wheels, and they are already pushed off the road - just like we do when we take the next step forward. At the point where the tire makes contact with the road (let's call it the “contact patch”), the torque generated by the engine turns into wheel traction. However, if the traction force turns out to be greater than the adhesion force of the tire to the road, the wheel will slip - slip.

It is clear that if a car has two driving wheels, then all the force created by the engine is distributed between the two contact patches.

What if there are four? Then between four. The more driving wheels, the less traction force falls on each wheel, on each contact patch. This means that with the same tire grip on the road, we can develop a much greater total traction force, that is, accelerate faster, drive up steeper hills, and tow a heavier trailer. Or vice versa - with the same (or even greater) traction force we will be able to confidently move on a much more slippery surface.

In general, simple physics. And it is clear that a road car can use all this no less than an off-road vehicle.

Sustainability has a lot to do with all of this. After all, thanks to the adhesion of the tires to the road, the car not only accelerates, but also stops, changes direction, and generally stands on the road, and does not lie in a ditch after the first turn. However, the greater the longitudinal force acting in the contact patch, the less transverse force will be enough to tear the wheel into lateral slip. And a slipping wheel practically does not perceive lateral load.

And, of course, one can imagine many different situations where the practical benefit of all-wheel drive is manifested simply in the fact that any wheel is a drive wheel. For example, several wheels suddenly found themselves in conditions of very poor traction - on snow, ice, or mud. Or they even “dangle” in the air (and this happens when driving over rough terrain).

In such a case, we can only count on the fact that the wheels that maintain traction with the supporting surface are also driving.

However, you have to pay for the benefits of all-wheel drive - a more complex (and more expensive) design, an increase in vehicle weight (and therefore fuel consumption), and a decrease in usable space allocated for passengers and cargo. After all, in order for the wheels to become driving wheels, torque from the engine must be supplied to them. This means that additional units will appear - transfer cases (at least one), main gears with differentials (one for each drive axle), drive shafts. And therefore, throughout most of the 20th century, all-wheel drive became widespread mainly only where it was simply impossible to do without it - in off-road vehicles.

But in most of them, all-wheel drive was used only occasionally - only in difficult conditions. The rest of the time, the inactive units were carried around like a useless load, only worsening the dynamics of the car and increasing fuel consumption. Why?

His Majesty the differential

Even at the dawn of the era of self-propelled carriages, when the drive wheels were fixed on a common rigid axle, designers were faced with the fact that a sharp turn became an insurmountable obstacle for the car. After all, when cornering, the “outer” wheel travels a greater distance than the “inner” wheel (in the same time), which means it must rotate at a higher speed. Or the inner wheel must slip, which the low-power first engines could not provide - and simply stalled. And even if the engine power was enough, the car constantly skidded in turns, the tires wore out very quickly, and the axles broke due to the resulting loads. And therefore, quite quickly, the single axle of the drive wheels was replaced by two axle shafts, between which a differential appeared, a planetary mechanism that provides the right and left wheels with equal torque, but allows them to rotate at different speeds.

But the fact is that the front and rear wheels also travel different distances when turning.

Moreover, in real driving conditions they can travel different distances even in a straight line, because there are bumps on the roads. This means that if we make a car all-wheel drive, then it must have another differential - between the front and rear axles. Otherwise, the tires will quickly wear out, and the loads that arise in the drive will render it unusable.

Of course, a center differential means a more complex and expensive design and, again, extra weight. And, in principle, we can do without it, but under one condition: we will use all-wheel drive only on fairly slippery surfaces and at low speeds, when serious troubles for the tires and drive do not arise. And on hard roads you will have to leave only one drive axle.

At the beginning and middle of the last century, this approach suited. The all-wheel drive system without a center differential (with a rigid connection in the transfer case and disconnection of one of the drive axles) was popular in off-road vehicles until the end of the 20th century. In fact, it has survived to this day, having been modernized as much as possible.

Now you don’t have to stop to connect the “additional” drive axle (in English literature this is called “shiftonthefly”). Nowadays, a drive with a connected front axle is used in the Isuzu Trooper with a manual transmission, in the Jeep Wrangler, in the Mitsubishi Pajero Sport and many other cars.

Always full!

But “just SUVs” are one thing. Their consumers were quite satisfied with the main advantages of the circuit with a switchable bridge - relative simplicity and, accordingly, low cost, and they were of little concern about the issues of high-speed movement on asphalt. It’s completely different when an all-wheel drive vehicle is not a “conqueror of meadows and deserts,” but a vehicle for everyday use (and mostly on normal roads). In this situation, shortcomings come to the fore. Firstly, the impossibility of constantly using the advantages of all-wheel drive (after all, when driving on hard surfaces, only one axle remains driving). Secondly, there are increased requirements for the driver’s qualifications: he must correctly assess the situation and make a decision whether to turn on the additional bridge or not. And mistakes are fraught with unpleasant consequences: turning a car into an all-wheel drive instantly changes not only the cross-country ability, but also the handling.

So recently, permanent all-wheel drive with a center differential has been used much more often. This scheme is found in most all-wheel drive passenger cars and the latest models of SUVs (all Audi quattro, except A3; all BMW iX, as well as X5; Hyundai Santa Fe; Jaguar XType; all Mercedes-Benz 4matic, M and G-class; Mitsubishi Pajero - in In general, a complete list can take up the entire space allocated for the article).

However, the “differential” drive is not without its drawbacks.

Firstly, on a slippery surface the differential may well fail. Have you ever watched from the side a car skidding in the snow or liquid mud? Then you should have noticed: while the slipping wheel is spinning madly, the other one is making virtually no attempt to move. The differential is to blame for this. And the center differential will behave in exactly the same way when the wheels of one of the axles find themselves on a slippery surface. To prevent this from happening, all-wheel drive vehicles (especially off-road vehicles) must be equipped with differential locking devices. It is clear that this does not make the drive system any simpler or cheaper.

In addition, the transfer case and additional drive shafts still weigh the car down and take up a lot of space. And if for large cars with powerful engines all this is not so significant, then in passenger cars, especially compact ones, dynamics, efficiency and capacity are seriously affected.

As needed

Not without the “help” of compact passenger cars, another all-wheel drive concept was born, used on many modern cars. In Western literature it is called “torqueondemand” (or simply “on demand”) - “a moment of necessity.”

The idea is to add to a simple (without center differential) drive with a switchable axle some kind of automatic device that connects it if necessary (say, when the “main” drive wheels slip). And even better - it transmits exactly as much torque as necessary to the “additional” axle.

Of course, such a scheme is inferior to permanent all-wheel drive, but it is structurally simpler, and most importantly, it is very convenient for making a small car all-wheel drive.

After all, when the engine is in front and the “main” driving wheels are front, you can even abandon a separate transfer case - it’s enough to make a simple power take-off to the rear axle, and install the same automatic device at the front. This drive is compact and quite lightweight, and therefore very popular among passenger cars (Audi A3; Volvo AWD and XC; Volkswagen Golf 4Motion, etc.), as well as models of “intermediate” classes (Ford Maverick, Honda CRV; Nissan X -Trail; Volvo XC 90, etc.).

The first “on demand” systems were created on the basis of a viscous friction clutch (until recently it was still used on all-wheel drive Volvo V70, and is still installed on Chrysler Voyager AWD, Land Rover Freelander and some Mitsubishi Pajero Pinin). Later, several more relatively simple hydraulic-mechanical devices were proposed that operate without any external intervention. We intend to devote separate materials to their design and principles of operation.

But all simple clutches with “internal automation” have significant drawbacks. Firstly, they are triggered upon the fact of slippage, which may be too late. Secondly, their characteristics (operation speed, dependence of the transmitted torque on the slipping speed, etc.) are determined by the design and cannot be changed without disassembly (which is often possible only in the factory). This means that there is no longer any need to talk about adaptation to specific driving conditions.

And since microprocessor technology has become significantly cheaper in recent years, computer-controlled devices are increasingly being used in “on demand” systems. They regulate the torque transmitted to the “additional” bridge not only depending on the current situation, but also on the basis of a forecast of its development. The possibilities of electronically controlled systems are very wide. And therefore, they are increasingly finding use instead of a center differential in transfer cases of large powerful models (Chevrolet Tahoe and TrailBlazer; Infiniti FX, etc.).