Читать книгу Piston Engines of the New Generation (Without turbo – supercharging) - Anatoly Matveevich Druzhinin - Страница 8

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 piston’s 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 piston’s 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, weren’t 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 shouldn’t 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, didn’t 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 621—87 for cylinder diameters of 88 mm and 130 mm “determined” the height of the sealing rings for both 2.0 mm. It’s 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 author’s publications.

To prove the published and patented objective fact, let’s show the calculation of the sealing (compression) piston ring, of a virtual motor which could be used for domestic AvtoVAZ models.