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Why Did Matiz Cry? Expert Competition

2024

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Video: Why Did Matiz Cry? Expert Competition

Video: Why Did Matiz Cry? Expert Competition
Video: ЛОБ в ЛОБ! ПРИОРА против МАТИЗА! 2024, March
Why Did Matiz Cry? Expert Competition
Why Did Matiz Cry? Expert Competition
Anonim

TASK No. 124

Slippery slurry

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Styopa went to an important meeting. I washed my old Matiz, polished my shoes to shine. But something went wrong right away: the heels on the rug began to slide. He stopped, looked - the mat was oily for some reason. Rubbed Styopa rug, then drove on. Arrived, locks the car and suddenly notices that one boot in a liquid is some kind. On the way back, the story repeated: the rug is slippery, the boot is dirty. And the brake pedal is flooded with something! Styop thought that he would have to dig into the brake system. I bought a brake on topping up. It looks, but the tank is full. Styopa was completely at a loss. And only the next day I realized that it was not the brakes. Did you guess what was wrong?

Send the answer marked “Competition” until June 1, 2018 at the address: 107045, Moscow, Seliverstov per. 10 - or by e-mail: [email protected]. Indicate your contact phone number or other quick contact method.

We undertake to read all your posts on the topic of the contest. The prize will be awarded not only the correct, but also the most complete solution of the competitive problem with a detailed answer.

And now to summarize the “Expert Competition” from the February issue of the magazine “Behind the Wheel”

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Competition of experts: where does the wedge come from?

The task began with the story of an unlucky car enthusiast, in whose engine the crank pin of the crankshaft was lifted. He remembered with an unkind word both a clogged channel and an oil wedge that was absent for this reason. And one of the participants in the conversation noted that there are engines, and powerful ones, which do not have an oil wedge on the connecting rods by definition! We invited readers to name such motors, recall the oil wedge, and be as attentive as possible to the wording.

Someone remembered motors with a split crankshaft and roller bearings in the lower connecting rod head. These are mainly motorcycle and boat engines, and they are relatively low power. Other readers claimed that bearings filled with babbitt do not need pressure lubrication and do not have an oil wedge. This is not true, because babbitt is only one of the materials that are used to form the surface of the bed for the crankshaft neck. And the principle of operation is the same as in modern designs with steel-aluminum inserts.

This concludes with the wrong options - let's move on to the answer that the winner of our contest sent.

The rotation of the crankshaft in the main and connecting rod bearings is made possible thanks to the oil wedge that occurs between the liners and necks. The bottom line is that under the rotating neck of the shaft the oil is tightened due to viscosity. A layer of oil forms on which the neck floats. The pressure diagram in this layer resembles a wedge in shape - hence the name. The shaft journal does not touch the surface of the liner at all. This mode of operation is called hydrodynamic, friction and wear are practically absent.

But the possibility of the appearance of an oil wedge depends on the pressure under which the oil is supplied to the bearing, on the size of the gap between the neck and the liner, as well as on the amount of oil supplied, its viscosity and temperature. The magnitude of the load on the necks as a result of inertial forces and forces from the combustion of fuel in the cylinders is also important. And in the absence of an oil wedge, the necks rub against the liners, which causes severe wear and heat. In such a situation, called oil starvation, the liners cannot work for a long time - under the influence of high temperatures, the antifriction material of the liner begins to melt. If the oil starvation is long, grab the liners (they can even weld to the necks), which will lead to their rotation and jamming of the engine.

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How to choose engine oil? Expert advice Most often, the oil wedge is broken due to too large clearance in the bearing. The reason is obvious - wear liners and necks. With a larger clearance, oil flows out of the bearing faster. And shock loads that occur at the moment of combustion in the cylinder squeeze the oil out of the gap even more, which leads to direct contact of the neck with the liner. This is possible with a normal gap - when the oil becomes too liquid due to overheating or mixing with fuel or antifreeze. However, the main danger is dirt - both falling into the engine from the outside, and formed during operation. In the proposed problem, it is the clogging of the oil channel and the violation of the oil supply to the bearings that led to the motor failure.

Then the fun begins. After all, the connecting rod has two heads - the lower and the upper. The bottom rotates relative to the necks of the crankshaft, and the top only deviates a small angle relative to the piston pin. No rotation - no oil wedge! Moreover, on some engines (for example, Lada) finger completely pressed into the connecting rod. What an oil wedge!

But there are engines in which the oil wedge does not form in the lower heads. Similar designs were common in aviation. Take, for example, star-shaped piston motors. Nine cylinders are located by a star, and it is impossible to attach nine connecting rods to one neck of the crankshaft. Therefore, they created such a scheme: one main connecting rod sits on the neck of the crankshaft, and the remaining eight are attached to it. They are called so - trailed connecting rods. In the connection of the main connecting rod and crankshaft journal, an oil wedge arises, but trailed ones do without it. Indeed, trailed connecting rods both in the upper head and in the lower have no rotation - only small deviations are possible.

Now about which machines used this scheme. The B-2 diesel engine of the famous T 34 tank had twelve cylinders arranged V-shaped, and six connecting rods in it were trailed. The descendants of this motor worked on many heavy cars and tractors, including BelAZ 540.

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