GB2239411A

GB2239411A - Cylinder wall surface treatment

Info

Publication number: GB2239411A
Application number: GB8929305A
Authority: GB
Inventors: Ian Coroon Middleton
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1989-12-29
Filing date: 1989-12-29
Publication date: 1991-07-03
Also published as: GB8929305D0

Abstract

The surface finish of the internal cylinder wall of an internal combustion engine is produced by honing the surface and then after honing applying a sealing composition 14 to the surface to at least partially fill the valleys 12 left in the surface by the honing operation. After the sealing composition has set, pistons with piston rings are assembled in the cylinders and the engine is then run. Peaks 16 will then be removed by the rubbing action of the piston rings. By coating the surface in this way, oil consumption is reduced, which in turn leads to a reduction in engine emissions. <IMAGE>

Description

CYLINDER WALL SURFACE TREATMENT This invention relates to a method of surface treating the cylinder walls of the cylinders of an internal combustion engine, and to an engine with treated cylinder walls. The invention is particularly applicable to diesel engines, but may also be extended to use on petrol engines.

On diesel engines it is desirable to reduce the oil consumption of the engine, because this not only leads to increased running costs and increased maintenance work, but also has a direct effect on engine emissions, particularly particulates and hydrocarbons, which are produced by the burning of the small quantities of oil which pass the piston rings and reach the combustion chambers.

According to the invention, there is provided a method of treating the internal cylinder walls of an engine, wherein the as-cast cylinder walls are first bored and then honed, and then finally a layer of sealing compound is applied to the honed surface, the sealing compound is allowed to set, pistons with piston rings are assembled in the cylinders and the engine is then run.

Sealing compound is preferably applied in the liquid state and is allowed to flow over the surface to partially fill the valleys in the surface as left by the honing operation. Subsequently, when the pistons run in the cylinders, the peaks covered by the sealing compound will be worn down and in places the metal of the cylinder wall will be exposed. However over the majority of the cylinder wall area, the exposed surface will be that of the sealing compound.

A completely smooth cylinder wall surface is to be avoided, because the lubricating oil will not wet a completely smooth surface, and lubricating deficiencies will occur. It is preferred if the cylinder wall surface, after coating with the sealing compound has an Ra dimension of between 0.3 and 0.6 microns. After running the engine, this will be reduced to a figure of 0.2 to 0.4 microns.

The invention is particularly intended for iron cylinder blocks, but may also be useful where the cylinder walls are of different materials.

The sealing compound may be chosen from a wide variety of different, preferably non-metallic materials. The compounds must of course be able to withstand in-cylinder operating temperatures; because particles of the sealing compounds will enter the combustion chamber and enter the exhaust, they must be non-polluting in either of these two locations. Typically liquid compositions sold as iron casting sealers may be used and Lackfabrik Becolin Universal 05612/1 and AG210979C have both been used with success. These compositions can be brushed on or sprayed on to the internal cylinder surface.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a typical section through an as-honed cylinder wall surface; Figure 2 shows the surface of Figure 1 after application of the sealing composition; and Figure 3 shows the same surface after the engine has been run.

Figure 1 illustrates the surface contours on a microscopic level with peaks 10 and troughs 12. This represents the surface as left by the honing operation. If the honing operation is finished, as is typical, using honing stones having a 150/180 grit size, then the average peak/trough distance Ra would be about 1 micron.

To this surface, a layer of sealing composition 14 is applied (Figure 2). This sealing composition forms a thicker layer in the valleys 12 than on the peaks 10 and as a result the Ra dimension would be considerably reduced as compared with the dimension prior to coating and may for example at this stage amount to 0.3 to 0.6 micron.

Finally, Figure 3 shows the surface after the peaks have been removed by the rubbing action of the piston rings as the pistons move up and down in the cylinders. It will be seen that this still further reduces the Ra, to a figure of about 0.2 to 0.4 microns. It will also be seen from Figure 3 that the metal of the cylinder wall is exposed at a few places identified by the numeral 16. However the presence of the metal surface beneath the surface composition 14 is important to provide the support for the coating composition.

By coating the surface in this way, a considerable improvement can be obtained in the oil consumption of the engine which in turn leads to an improvement in engine emissions

Claims

1. A method of treating the internal cylinder walls of an engine, wherein the as-cast cylinder walls are first bored and then honed, and then finally a layer of sealing compound is applied to the honed surface, the sealing compound is allowed to set, pistons with piston rings are assembled in the cylinders and the engine is then run.

2. A method as claimed in Claim 1, wherein the sealing compound is applied in the liquid state and is allowed to flow over the surface to partially fill the valleys in the surface as left by the honing operation.

3. A method as claimed in Claim 1 or Claim 2, wherein when the pistons run in the cylinders, the peaks covered by the sealing compound will be worn down and in places the metal of the cylinder wall will be exposed.

4. A method as claimed in any preceding claim, wherein the sealing compound is non-metallic.

5. Method as claimed in any preceding claim, wherein the surface is honed to produce a surface with an Ra dimension of approximately 1.0 micron.

6. A method as claimed in any preceding claim, wherein the cylinder wall surface, after coating with the sealing compound has an Ra dimension of between 0.3 and -0.6 microns.

7. A method as claimed in any preceding claim, wherein the sealing compound is a liquid composition sold as a casting sealer.

8. A method as claimed in Claim 7 wherein the composition can be brushed on or sprayed on to the internal cylinder surface.

9. A method of treating a cylinder wall surface, substantially as herein described with reference to the accompanying drawings.

10. A cylinder wall treated by the method of any preceding claim.