Читать книгу Piston Engines of the New Generation (Without turbo – supercharging) - Anatoly Matveevich Druzhinin - Страница 7

The work of (that is most widespread among autotractor internal combustion engines (diameters of cylinders up to 140 mm)), the four-stroke engine consists in effective implementation of all 4 steps of an operating cycle:

– “admission” of a fresh air charge;

– “compression” of the task environment above the piston;

– the piston “working stroke” transforming the huge pressure of working gases to the mechanical work;

– “release” of spent working gases and residues, of the combustion products.

We will consider each of them in the form of a separate project, with its differences and peculiarities. But, as a result, integrated in the integral design of efficient use of the engine.

– The working stroke “admission” (suction) in the cylinder of the engine, or compressor, the estimated amount of fresh air charge.

The task of developers of any constructive element are: define the shape and size of the product, and select the workpiece material based on the conditions in which the element will work. This is a very important stage of the design, from which much will depend on the work of the product. As the initial data, developers only know one size – the diameter of the cylinder.

The principal drawback of many domestic designs (including ICE) is that the designers in their calculations take the safety factor not 1.10 or 1.20, as it should be, but 1.50 or 2.0, sometimes more than that. How important this is to the economy are known to most professionals. In the case of mass production, which we are considering, this is simply unacceptable.

Proceeding from the purpose of the working stroke “admission”, it is necessary to remember, than consolidation between the piston and the cylinder is more reliable, excluding any suction from the crankcase, the extent of discharge of space over the piston is more, the more actively there is a filling of the cylinder with rated quantity of an atmospheric air.

At the beginning of the movement of the piston in the lower position, taking into account the huge speed of displacement of the piston, above it and, accordingly, in the upper piston groove, a certain discharged space is formed. “Admission” is the only step of an engine motoring run to which influence of the gas dynamic scheme presented on fig. 1 doesn’t extend. On this step the gas dynamics is neutral therefore it is possible to approach on other design of pressure rings, proceeding only from the tasks imputed to a step “admission”.

Making rather difficult calculation of elastic forces of the piston rings, developers shouldn’t forget that on all steps of an engine motoring run the sealing (compression) piston ring has to carry out two main task and one compulsory condition:

to condense space between the piston and the cylinder, to provide transfer of heat from a superheated piston crown to the cooled cylinder, at minimum possible mechanical losses on friction.

For the piston ring, which is pressed to the lower flange of the piston groove with the previous stroke, the admission is the relaxation time, one moment. For example, with a piston stroke of 80 mm and a crankshaft rotation speed of 3000 min ^-1, the piston travel speed is 6 m / s, on the Formula 1 engines the average piston speed is 22.5 m / s. For an extremely short period of time, the piston ring should assume its natural position relative to the piston groove and cylinder wall. The technologists, on this occasion, have the expression: the piston ring shall “be installed” on the cylinder wall. In the process of moving to the lower dead point by friction of the ring surface of the cylinder, it is shifted to the top flange of the piston groove and is pressed to the cylinder wall with its own elasticity of the ring.

In this case it is worth using the recommendation of the domestic scientist Orlin A.S, therefore, we can take the recommended value of ring pressure on the cylinder walls 0,05 … 0,3 MPa (0,5 … 3 kg / cm²) and more [6]. As studies have shown, the expression of the scientist “… gases are pressed the ring against the wall of the cylinder” is not entirely correct with respect to modern piston rings, because they do not correspond to reality. It turns out that they lost their elasticity and were pressed against the lower flange of the piston groove with the superior gas-dynamic force F₀.

In the technical conditions for the production of the “the compression piston ring” KAMAZ engine 740.1004032 is recorded: “The load applied to the arrows K, when the ring is compressed by a flexible tape to the gap in the lock, equal to the gap in the calibre of 120 mm, should be 2.3 … 3.1 kgf”. From this it follows that, despite the obvious difference in the methods of measuring the elasticity of a piston seal ring, the values of the recommended values in the textbook and the developers of the KAMAZ engine are of the same order.

It is worth noting that it makes no sense to rely neither on the recommendations of the scientist nor on the value of the “load” practiced by the KAMAZ engine manufacturers in the development of engines with cylinder dimensions about 120 mm. When calculating the elements of the kinematic system “cylinder-piston ring-piston” in modern engines, developers take into account the wear amount of each of them, thereby prolonging the warranty periods of operation of the piston rings.

The permissible value wear of the cylinder 0,15 mm, increases the gap in the lock of the compression ring of the KAMAZ engine to a size of 0.94 mm. When only the working surface of the piston ring is worn by 0.5 mm, the gap in the lock of the ring increases by 3.14 mm. In large engines, wear of the working surface of the piston ring is permitted up to 1.0 mm, which corresponds to an increase in the gap in the ring lock by 6.28 mm. Total “allowable” increase in the gap in the compression ring lock will be 7.22 mm! This is without thermodynamic, i.e. thermal extensions [4].

It is difficult to imagine how such a “thin” seal, in the design of which, by definition, there should not be any gaps, or they should be reduced to an insignificant minimum. Unfortunately, it’s hard to argue with opponents who have disarming arguments. At first, the engines “work fine”, and secondly, the compression piston rings are made exactly in accordance with the instructions of the domestic standards [8] and [9].

In this case, the question arises, why the “modern” internal combustion engine is so “good”? The answer is obvious, if you give an example from everyday life, answering a similar question: can you take a bucket of water with a sieve? Of course you can. It needs to be done very quickly and for a long time, but… the efficiency is too small.

Is the engine has a high efficiency? No! Maybe he has a small rotation speed of the crankshaft? Also, no. On the latest models of VAZ engines, small-gas turns are already over 1000 min^-1!

The engines of the Formula-1 maximum power reach over 22 000 min ^-1, while after each race there is a major repair of the engine.

So, what are the conclusions will be drawn?

Proceeding from a purpose of a working step “admission”, it is necessary to remember, the consolidation between the piston and the cylinder, the excluding, any suction from the crankcase is more reliable, the extent of discharge of space over the piston is more; the more actively there is a fence of an atmospheric air and implementation of rated data.

First of all, it is worth paying attention to the design of the cylinder-piston group and, first of all, the design, shapes and dimensions of the piston rings. It’s incomprehensible! With a complete change in the entourage of the car, the famous AvtoVAZ, which is quite competitive with foreign models, for decades the engines are equipped with permanent piston rings, performed at the will of the standards.

It is worth noting that the equipment and technology for the manufacture of piston rings not only for the AvtoVAZ engines but also for KAMAZ, YaMZ and other engines was used by the world famous German company Goetze, which is under the patronage of the equally famous Federal Mogul concern – “the advanced European manufacturer of the engine gaskets and piston rings”. That is, all claims to poor-quality piston engine compaction should be presented not to the main designers of these engines, but to world-famous specialists with whom the “main” are in solidarity.

To this we must add the following circumstance. From the advertisement of its latest achievement, the manufacturer of the elements of CPG the Kostroma-Motordetal presented “ncMDChr (nanochrome) – a new generation coating is applied to the working surface of the upper compression and oil-removable piston rings”! Especially shocking “… and oil-removable rings”, inefficient, performing a rough operation of removing oil from the cylinder wall, in a continuous oil environment.

It is unclear why to apply “nanochrome” on them, if the working surface of the oil-removable piston ring does not wear out and without “nano”. When it is necessary to change the piston rings, along with the compression rings, oil-removable rings also fall into disassembly, but not because they have a “worn working surface”, but because the waste oil is clogged, sometimes coked, by the spiral extension of the oil-removal ring. This is especially true of the diesel engines. The inefficient oil-removal piston ring becomes generally inoperable.

This is an example of the imperfection of the widely used oil-removable ring with useless “nanochrome”. Nevertheless, Kostroma is pleased, scientific and technological progress all that is needed for the buyer to “appreciate” these innovations.

The design of compression piston rings, subjected to rigid analysis by the author, continue to “live” and “improve.” The achieved results of the research and the proposed measures for the recognized authorities of the car industry are not so “obvious”, there may be other reasons that have nothing to do with science.

The low efficiency of consolidation between the piston and cylinder is one of the most important problems of the ICE. The negative consequences of this decision are obvious, the engine can “earn” and operate normally only at huge speeds of rotation of the crankshaft, boosting the engine work. What leads to “forcing” should be known even to the motorist.

The problem of gaps is only part of the general problem of the “cylinder-piston ring-piston” system. In this case, on a working step “admission”, in the absence of excessive pressure over the piston, the mechanical friction losses of the compression rings affecting the efficiency of the engine or compressor The magnitude of the mechanical losses at the “admission” step depends on the magnitude of the elastic forces of the piston seal ring and the friction coefficient of the two kinematic elements: “Piston ring-cylinder”, more specifically, the working surface of the piston ring and the cylinder wall.

The shape and dimensions of the piston seal ring at the “admission” step depend mainly on the design value of the minimum necessary elastic force of the ring. It is necessary to determine the magnitude of the elastic force of the piston ring and the necessary material from which the ring should be made.

In analysis of the reasons for the low efficiency of internal combustion engines, it was found that in calculating the sizes and permissible deviations in the manufacturing process, in domestic engines, especially in the cylinder-piston group, there is lacks precision; therefore, as one of the measures to increase the efficiency of internal combustion engines, in the system “cylinder – piston ring – piston “was held minimization of gaps [10].

The modern piston rings, depending on their size, are mainly made of steel and cast iron. The researches, the developed theory of designing of the piston rings provide an opportunity of manufacturing of rings from other metals and alloys, and also nonmetallic materials. For example, the domestic company LLC “Compressor Technologies” advertises bronze with various fillers, various plastics as a material for manufacturing sealing and oil-removable piston rings.

At the research stage, to define the shape and dimensions of the sealing (compression) piston rings, using the results of theoretical studies, to recommend various bronze alloys and copper alloys as a material for the preparation of the ring.