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.
Working step compression of a fresh charge of air, fuel-air mix and its ignition
The working step compression is fundamentally different from the previous step admission in that by obtaining a piston ring pressed against the upper flange of the piston groove and to the wall of the cylinder by the force of its own elasticity, at the beginning of the pistons movement to the upper position, the piston ring is shifted downward. The forces of friction of the piston ring working surface against the cylinder wall, as well as the appearing overpressure P0 above the piston and in the piston groove, further enhance the contact of the piston ring with the lower flange of the piston groove and the cylinder wall.
It is important to note, the piston ring being in the lower dead point in rather free state, is fixed in this position, appearing changes and, above all, increasing pressure over the piston. This position of the sealing piston ring relative to the piston and cylinder will remain unchanged on the remaining steps of the engine motoring run.
So, with the beginning of the pistons movement to the upper position on the working step compression, gas dynamics comes into operation, according to the scheme given above to fig. 1. On a working step admission the design of a piston sealing ring, its shape and dimensions, werent of particular importance, solving the main task of effectively consolidation of the free space between the piston and the cylinder with the minimum possible mechanical friction losses.
At this stage, the developer must solve the problem of the correct use of gas-dynamic forces that will preserve the elastic forces of the piston ring, thereby guaranteeing its working capacity [11].
The author to solve this problem developed a formula, the use of which in the calculation of the geometric characteristics of a sealing piston ring allows neutralizing the negative effect of huge gas-dynamic forces on the operation of the piston ring. This formula solved the historical injustice of the subjective decision in assigning the height of the piston ring, although this decision was made by an authoritative German scientist [5].
It was suggested to choose for the engine the free size of the height of the sealing piston ring in an unreasonable range of sizes, relying only on the recommendation of an authoritative scientist: Usually, the ratio of h/a shouldnt be lower than 0,5 0,45 (h height of a piston ring, and the radial thickness of a ring).
The domestic scientists and then developers of the piston cars took these recommendations for an axiom which, obviously, those far sixtieth years of last century, didnt demand any proofs, pilot and other studies which had to be carried out at so basic decision. As a result, instead of an incomprehensible range of sizes of recommendations for the height of the piston ring, there appeared precise indications of the domestic standards. Designers did not have to calculate the height of the sealing ring, thereby removing all responsibility for low-quality products from all general and main ones.
For example, the current GOST 62187 for cylinder diameters of 88 mm and 130 mm determined the height of the sealing rings for both 2.0 mm. Its incomprehensible! Really when developing so responsible document how the technical standard, it was unclear that from the given size of diameter of the cylinder equal to the outer diameter of a piston ring, all other geometrical characteristics of a ring depend?
How can ignore the enormous working pressures in the engine cylinders, reaching 20 MPa (200 kg / cm2) and actively affecting to the free surfaces of the movable piston ring? In these extreme conditions, the minimum change in the height of the sealing ring and its radial thickness is transformed into kilograms of force, reflecting on the performance of the piston ring and, ultimately, on the technical, economic and environmental performance of the engine. Why all this happened in detail described in the authors publications.
To prove the published and patented objective fact, lets show the calculation of the sealing (compression) piston ring, of a virtual motor which could be used for domestic AvtoVAZ models.
§3. The practical solutions from the theoretical conclusions
To comparing two engines of the same purpose KAMAZ and MERCEDES, the author a professional technologist, intuitively (sometimes trusting the designers), was closer the MERCEDES engine. Of course, the importance was not the authority of the firm, but pragmatism, confirmed by many years of searching for the reasons for the low efficiency of the product, the project of which technology is implemented in the metal. Obviously, it is not necessary to convince the designers of the need for difficult searches for a simpler design that is completely would perform the tasks assigned to it.
The main advantage of the German engine, in comparison with the competing engines of KAMAZ OOO (Limited Liability Company) " and YaMZ TMZ of Avtodizel OAO (Open Joint-stock Company), is the size of its cylinder of 128 mm. The difference is small, only 8 mm, but taking into account the huge operating pressures, the power increases significantly, so the competitor was allowed to provide only 6 cylinders, with all the ensuing positive consequences.
Therefore it would be possible to recommend to domestic trucks of a class KAMAZ and YaMZ to use diameter of the cylinder of 130 mm. Kostroma MOTORDETAL OAO(Open Joint-stock Company) is manufactured a similar piston group with a cylinder diameter of 130 mm, for the tractor engines. This measure can be implemented only on condition of fundamental changes in the design of piston devices.
So, back to the calculation of the sealing (compression) piston ring, which could be used for domestic AvtoVAZ models. Considering the strategy of design of similar engines, it was interesting to get acquainted with features of engines of Formula -1. With engine speeds of 18,000 22,500 rpm or more, the engine develops power over 750 PS. with a cylinder diameter of 98 mm, a piston stroke of 39.7 mm, fuel consumption of about 60 litres per 100 km.
It is not enough to copy for our engines from AvtoVAZ series, but the design strategy, taking into account the highest class of skill of the mechanics of Formula-1, should be taken into account. Now we have VAZ engines with diameters of cylinders of 76 82 mm, three and four-cylinder.
Lets finish the interrupted calculation of the effect of gas dynamics on the operation of the compression ring of the VAZ-2190 engine presented above, but already for a virtual engine with the desired initial data.