1. Technical Field
The present invention relates generally to multilayer metal gaskets. The invention relates more particularly to multilayer metal gaskets having a compression limiting feature. Even more particularly, the invention relates to a multilayer metal gasket having a compression limiting feature which varies along the length of a selected sealing surface of the gasket.
2. Related Art
Two common issues exist with multilayer metal gaskets, such as multilayer steel cylinder head gaskets, they relate to the fatigue resistance of the gaskets and joint distortion associated with the use of the gaskets. Multilayer metal gaskets are made from thin sheets of metal, such as steel. In many applications, such as cylinder head gasket applications, these multilayer metal gaskets are subjected to temperature and pressure extremes associated with the operation of the internal combustion engine and the environmental conditions under which it is utilized. Thus, as the engine is operated, the internal combustion processes subject the cylinder head gasket to repeated pressure-induced cyclic motion and stresses and extreme temperatures. Over the operating life of an engine, this cyclical motion and stresses at the extreme operating temperatures can cause fatigue within the metal gasket, particularly fatigue in the region of the embossments which are used to provide the sealing surfaces of the gasket. While a cylinder head gasket is used as an example, other applications of multilayer metal gaskets are also subject to cyclic temperatures associated with their operating environment, and are thus also subject to the fatigue processes described above.
In the case of multilayer metal gaskets used in cylinder head gasket applications, this motion within the cylinder head gasket is known to play a significant role in cylinder bore distortion as the cylinder head gasket is the interface between the cylinder bore located within the engine block and the cylinder head. In operation, the cyclic changes described above also result in distortion of the cylinder bore in the region of the gasket. Cylinder bore distortion can cause high rates of wear on the piston rings or combustion gas blow-by within the head gasket.
One of the primary factors effecting fatigue and cylinder joint distortion is the fact that the common practice of applying a uniform bolt sealing pressure to the cylinder head bolts produces a non-uniform sealing force along the length of the sealing surfaces of the cylinder head gasket. Therefore, at various points along the circumference or length of the sealing surface associated with the cylinder bore opening, there exists a variation in the sealing force applied to and by the gasket. As the gasket is subjected to cyclic temperature variations, this can result in a tendency for fatigue failures at locations within the gasket where the sealing forces are highest.
Therefore, it is desirable to reduce the sealing force peaks along the gasket sealing surface, particularly to levels which are below a threshold associated with fatigue processes within a particular gasket design, so as to improve the fatigue performance of the gasket and reduce joint distortion associated with the gasket.
It is, therefore, desirable to improve the fatigue and joint distortion performance of multilayer metal gaskets. Further, it is desirable to make such improvements by controlling the sealing force along the length of the sealing surface of these gaskets for a particular engine block and cylinder head design, including the bolt pattern, particularly so as to make the sealing force more uniform along the length of the sealing surface.