The invention relates to a cylinder for piston engines and to a process for its production.

The cylinder wall of both the petrol- and Diesel internal combustion engines is subjected to significant mechanical and thermal shocks and has to resist the chemical effects of the combustion products in the combustion chamber. Without loss of its mechanical strength, it must endure the thermal gradient between the temperatures of the combustion chamber and engine blocks, as well as the load of the periodical heat transfer and stationary heat dissipation.

In addition to the chemical and thermal effects, it must display appropriate mechanical strength partly against the normal tangential power effects of the combustion .taking place in the chamber, and partly against those producing abrasion of the piston, providing the optimal sealing.

With regard to these effects and the expecatable properties, the engine designers developed a wide range of alloys. Engines provided with relatively inexpensive an quickly replaceable sleeves were developed to facilitate the efficient operation, when in case of a specific wear of the cylinder wall, the used up sleeve of worn surface is replaceable with a new one.

In case of engines without sleeve, it is possible to eliminate the uneven cylinder surface with fairly complicated and costly processes requiring up-to-date material and personal facilities. In this case the pistions have to be provided with rings suited to the increased cylinder diameter for the sake of proper sealing.

In view of the foregoing, it is vitally important both technically and economically to know the intervals required for repair of the cylinder surface of internal combustion engines, the cost of repair and the degree of operational efficiency.

The object of the present invention is to provide a cylinder ensuring a short period for renewal of the cylinder wall, low cost of πewal. Another object of the present invention is to provide a method for producing said cylinder.

According to the invention, the surface of the piston engines is made of a high density (3.85 - 3.95 g/cιτr) aluminium-oxide ceramic containing 0.2 - 3.0 mass% calcium- and/or magnesium- luoride, or titanium oxide.

There are several methods to provide the cylinders with aluminium-oxide wall.

a) in the sleeve-type engines, the oxide-ceramic wall is placed in as cylinder bush, only by turning the sleeve, without remodelling the engine block, so that the construction need not be changed;

b) according to the second version, the whole sleeve body is made of ceramic; if thickness of the ceramic bush allows, only the two end-parts have to be provided with metal cap;

c) in the third version, the casting material of the cylinder sleeve used for receiving the ceramic is replaced with heat-resistant steel.

Thus in each case, the aluminium-oxide ceramic is placed as

cylindrical body into the cylinder of the interna combustion engine, so that its size and density are forme by sintering at 1450 - 1750°C before insertion.

According to the invention, the life of the metal engin block is extended by insertion of ceramic, i.e. by provid ing with ceramic bush.

According to the experiences, the friction, therma expansion and wear properties of the metals in this fiel are much inferior to those of the ceramic parts.

According to the invention, such pistion bore wa succesfully machined for the internal combustion engines the wear of which is less, its renewal is less expensiv and quicker than in case of the conventional meta surfaces. Due to the more favourable thermal conduction an friction properties, the amount of consumed- lubricant an fuel is reduced.

These effects involve reduction of the amount of pollutant discharged by the internal combustion engines, and at th same time, the proportion of the toxic components of th exhaust gases in compliance with the more favourable an improved combustion conditions is also reduced.

The ceramic coat well resists the acids, lyes, organi solvents even at high temperature. Its water-, steam- an gastightness are high, thus the ceramic coat perfectl seals the cylinder wall from the combustion chamber, whereby the requirement imposed on the quality of th engine block's material is substantially reduced not onl for the sleeve-type engine.

The process according to the invention, the cylinder an

the favourable effect attained thereby are illustrated by the following examples.

Example 1.

A cylinder sleeve lifted out of an engine block was turned on the lathe to the required size, then aluminium-oxide ceramic (density 3.95) sintered at 1750°C containing 3 H titanium-dioxide was diamond-ground to size and placed into the sleeve with shrink joint. The engine was assembled conventionally without any change. The result appearing during operation was as follows.

a) efficiency of the engine improved, b) oil and fuel consumption lowered and c) wear resistance of the sleeves improved (and thus their life was longer.

Example 2,

In the second version, the whole sleeve was made of aluminium-oxide ceramic of 3.85 density containing 0.2 mass% magnesium- and calcium-fluoride in 1:1 proportion, sintered at 1450°C. The lower and upper parts of the sleeve were received by metal cups for the sake of safe assembly.

Remodelling of the engine is not necessary either in this version. The conventional cooling system remains the same, and its assembly is unchanged. In this version, the coolant is in direct contact with the ceramic sleeve, therefore, in addition to the favourable properties experienced in Example 1, heating of the engine will be different, the

coolant ensures the required operating temperature with less cooling, e.g. with shorter operating time of the cooling fan.

Example 3

An engine block was drilled through to form a jacket of adequate thickness, that was capable to provide safe prestress for the ceramic cylinder sleeve.

The cylinder sleeve lining made of heat-resistant steel was essential, because its prestress was safer than that of the casting. The ceramic lining was made of aluminium-oxide containing 2.2 mass ⁵ , titanium-dioxide, burnt out at 1650°C, its density being 3.90. The fitted accurate size was set .on grinding machine with diamond tipped tool by grinding to size. The favourable properties described in Example 1 were in evidence.