Anonim

CLUB OF CAR FANS

FRICTION

SQUIRRING BALLS

Today, the choice of spare parts is quite wide. But this phenomenon, unfortunately, has a downside: each of us runs the risk of buying parts with which the machine will become less stable …

Edward CONOP

REMEMBER THE BIKE

Again, two wheels - say the reader, who does not miss publications of the "Club of motorists." This is usually a person who wants to not only "ride" a car manufactured by a more or less well-known company, but also to know as much as possible about it. By the way, when working with letters, we are again and again convinced that our main reader is just such an intellectual, and not a “pure consumer”, interested only in where and what to buy.

The question that we will discuss today was asked to the author in the parking lot, and then he met in letters from readers. And it sounded like this: how to explain the deteriorating stability of the machine “on course” after replacing the ball bearings, if the new ones are in perfect order, very tight, without the slightest hint of illegal backlash?

“Indeed, ” we recalled, “this happens quite often!” Having overdone in the search for the best supports, a motorist easily makes a traditional mistake, believing simply: the tighter the better! And as a result, he runs the risk of being in a car strangely yawning along the course, hard to drive, and disgustingly noisy, because such supports soon begin to creak unbearably. Attempts to lubricate them do not give a result - the matter most often ends with a replacement for others, sometimes not at all the best.

So, let’s remember all the same a bicycle pedal. We hope that many readers have not yet broken with him today, and therefore remember an important condition for its stability and controllability (here they are closely related): the steering wheel should turn completely freely, without interfering with the bicycle’s “mechanics” to self-install. Remember, that gives us the “overhang” of the front fork, shown in fig. one? The axis of rotation of the fork crosses the road surface in front of the contact patch of the wheel with the road. This "trifle", which once was ingeniously thought of, provides a bicycle or motorcycle with an automatic turn of the fork in the direction where the car accidentally bends. This is the most important point in the theory of stability of single-track machines. "Mechanics", as we see, is embedded in the very layout of the bike and is therefore extremely reliable. It would seem, well, what could stop her? It turns out that it can interfere … excessive friction in the steering wheel bearings. Once they are pulled slightly - and the bike on the go becomes awkward, it is difficult to ride it. The reason is simple: it is impossible to move the steering wheel until you overpower the friction of rest (remember physics!). But then you already overcome the friction of the movement (rolling) of the balls, which is less than the friction of rest. Therefore, every turn of the steering wheel looks like a breakdown - it is not possible to turn it smoothly, to the required, small angle, in order to maintain balance.

The result is well known: a bicycle writes out a certain broken line along the road! A recipe for the treatment of this disease is also known: the tightening of the bearings needs to be loosened somewhat, and at the same time, grease them.

WHAT'S COMMON WITH A CAR

…You ask. There are quite a lot in common. It is hardly necessary to remind why the front wheels have “tricky” installation angles, and the axles of the steering knuckles have a longitudinal and transverse tilt. Despite the apparent complexity of the car (in comparison with a bicycle, of course), this is the same “automation” that allows the car to maintain directional stability even when the driver, having forgotten about the steering wheel, is carried away by the passenger. If the highway is smooth, straight, with a slight transverse slope, then the car goes straight. With a gust of wind on the left, it may deviate slightly to the right (stability requirement). With a large transverse slope, it equally logically deviates "under the slope". (In both of the latter cases, it is better to distract from the neighbor and slightly “tweak” the steering wheel!) At the turn, the car needs to be held by the steering wheel, because all the same mechanics, if you release the steering wheel, will return the wheels to a straight position.

In short, the machine, while in good condition, behaves quite “reasonably”, for which thanks to those who designed and manufactured it. But imagine what threatens the installation of overly tight, "creaking" supports: almost the same thing will happen as was shown in the example with a bicycle. The "self-installation" of wheels is prevented by rest friction in the supports. Until you overcome it, do not turn the steering wheel! On a smooth highway, and then the car prowls to the sides. Moreover, observant readers even note such a “paradox”: on a highway with a not-so-even pavement, it’s easier to drive a car than on a smooth one. However, there is no miracle. The shocks from the road, causing the tight "balls" to slip, create the very friction of the movement, which is less than the friction of rest - and the car rises somehow. On a smooth, new surface, the tight supports seem to stop, forcing the driver to go along some broken path.

The stronger the friction in the steering bearings, the greater the jump when turning it. Imagine that to keep the direction you needed to turn only half a degree, and the steering wheel can be turned only by "doses" of two degrees - and you will understand why the car is unpleasantly scouring. The less friction in the bearings, the more accurate the control.

Of course, the behavior of the car depends on the collapse and toe. However, is it worth it to delve into these subtleties? Today we have a different goal: to show that all this mechanics works only on condition that there is no excessive friction in the suspension. It is easy to imagine how a car would behave with hinges welded tightly and locked in one position - it will go where the wheels are pulled. Of course, this is an extreme case. A pendant with tight joints is better, but not by much.

The car has a whole arsenal of friction sources in the suspension and control system. So, for Zhiguli, there are four ball joints, six (!) Ball joints in the trapezoid, plus the steering gear itself, and even the swingarm with its bushings and rubber seals. Do not forget also the friction in the rubber bearings of the anti-roll bar, the friction between the parts of the shock absorbers. We omit the other small things. All this "good" resists both the suspension and the steering wheel. While the friction is not too great, we consider the behavior of the machine to be normal. But it is worth tightening the nut of the pendulum lever (someone is trying to eliminate its backlash!) Stronger - and the machine, like a jerky horse, does not listen to the “reins”.

This also happens when the owner, frightened by the upcoming technical inspection, specifically buys tight supports and steering rod ends - perhaps, at the same time, they will last longer! Here, in addition to the fact that the steering wheel becomes “heavy”, other unpleasant effects begin to appear. Take a look at the photo.

Everyone who has happened to adjust the “camber” knows that these angles depend on the load on the machine. Before measurements, the suspension is squeezed up and down several times so that it occupies a position corresponding to a static load. With a lot of friction in the suspension, the car acquires the ability to be fixed in a variety of positions. Therefore, in motion, after an accidental push, the car is pulled to the right or left, depending on the acquired “posture” … But it is not possible to steer thinly on it, as we have already shown: friction prevents it.

The problems of a lover of tight joints are not limited to this. Tight suspension makes the car partially "unsprung", likening a village cart. The tighter the hinges, the higher the “sensitivity threshold” of the suspension and the more bumps are rigidly transmitted to the body. First of all, this applies to small variable forces that are not able to overcome the friction forces - for example, acting in the suspension when moving along slightly crushed asphalt, gravel, pavers. The machine is not only uncomfortable, but sometimes dangerous: idle shock absorbers are not able to damp vibrations of tires, wheels, and suspension arms themselves. Tires begin to slip along the road - here the driver risks losing control of the car altogether.