EP1630364B1 - Valve seat ring with cylindrical outer surface - Google Patents

Description

The invention relates to a cylinder head of an internal combustion engine having a valve seat ring inserted into a cylindrical bore, wherein the valve seat ring has a cylindrical outer surface and an outer diameter with excess relative to the diameter of the cylindrical bore and the cylinder head is formed of a material with greater thermal expansion than the valve seat ring.

Valve seat rings are usually connected by a shrinking and / or pressing with the cylinder head. In order to ensure a secure hold of the valve seat ring in the bore or annular groove of the cylinder head, a certain excess of the valve seat ring is required. The experts were of the opinion that this oversize must be greater, the more different the thermal expansions of the materials from which the valve seat ring or the cylinder head is made. For example, the thermal expansion of aluminum is almost twice that of steel. Based on US 4,896,638 A is known a valve seat ring made of steel, which is used with excess in a bore of a cylinder head made of aluminum.

wobei

• α_Fe= thermische Ausdehnung von Eisen
• α_Al = thermische Ausdehnung von Aluminium
• D = Außendurchmesser des Sitzrings
• ΔT = Temperaturerhöhung bei Betrieb
• Sicherheit = Sicherheitsfaktor

So far, the required excess of the valve seat ring was calculated using a simple model, assuming that a seat ring made of steel is inserted into a non-distorting aluminum plate. It was a constant temperature and a free elongation of the aluminum plate adopted. The required oversize of the valve seat ring was determined by the following equation: $$\ddot{\mathrm{U}}{\mathrm{bermaß}}_{\min }\mathrm{=}\left({\mathrm{\alpha }}_{\mathrm{Fe}}\mathrm{-}{\mathrm{\alpha }}_{\mathrm{A}\mathrm{1}}\right)\mathrm{*}\mathrm{D}\mathrm{*}\mathrm{.DELTA.T}\mathrm{*}\mathrm{safety}$$

in which

• α _Fe = thermal expansion of iron
• α _Al = thermal expansion of aluminum
• D = outer diameter of the seat ring
• ΔT = temperature increase during operation
• Safety = safety factor

According to this previously used formula for calculating the oversize, very high values for the oversize are obtained. Because of the high excess of the valve seat ring relative to the cylinder head in the associated bore or groove a large effort is required during assembly. The seat rings may need to be frozen, and sometimes it may be necessary to heat the cylinder head. In addition, a high mounting force is necessary. When mounting the valve seat ring, a high tensile load in the valve land area of the cylinder head can occur, whereby critical values can be achieved. The load on the combustion chamber roof is therefore very high, which can even lead to cracking of the cylinder head. In any case, the life of the cylinder head is reduced. Therefore, a higher quality material must be used for the cylinder head or the wall thickness of the cylinder head must be increased. Occasionally, a heat treatment of the cylinder head is required. However, all these measures are associated with an increase in manufacturing costs.

The invention has for its object to overcome the above difficulties by optimizing the interpretation of the excess of the valve seat ring.

According to the invention, this object is achieved in that the valve seat ring has an excess of at most 1.5 parts per thousand.

The invention is based on the finding that the cylinder head due to the uneven temperature distribution in the region of the combustion chamber roof at a free Extension is prevented. For this reason, contrary to the previous opinion, an excess of the valve seat ring of 1.5 parts per thousand or even less is sufficient. The inventors have recognized that a thermal distortion of the combustion chamber roof caused by unequal temperature distribution prevents free expansion thereof. The combustion chamber roof is surrounded by a material region which has a lower temperature. This self-contained material area effectively acts like a lashing or a tire that prevents free thermal expansion of the higher temperature combustion chamber roof. The actual expansion of the cylinder head in the region of the combustion chamber roof is therefore much lower than previously assumed. In operation, the combustion chamber roof is hindered in contrast to the aforementioned model of a zerkungsungsfreien aluminum plate due to the thermal inhomogeneity of a free expansion. This creates compressive stresses in the cylinder head, which counteract the expansion and hold the valve seat rings. It is therefore required a much lower excess than previously thought.

Lower load on the combustion chamber roof due to the reduced excess of the valve seat ring, the life of the cylinder head can be significantly increased. Under certain circumstances, the use of lower-cost alloys for the cylinder head is possible. Also, the assembly of the seat rings is facilitated because they can be mounted because of the smaller excess with less effort. As a result, with the previously required cooling, z. As with liquid nitrogen, associated high costs can be saved.

It has been found that with valve seat rings, which have virtually no oversize, a reliable hold in the cylinder head is guaranteed at operating temperature. With regard to surface roughness and subsidence of the valve seat ring on the one hand and the cylinder head on the other hand, however, the valve seat ring should have an excess of at least 0.1 parts per thousand, preferably 0.5 parts per thousand for safety reasons.

An embodiment of the invention is illustrated in the drawing and will be explained in more detail below.

The sole figure of the drawing shows a longitudinal section through a valve seat ring in the installed state.

In an aluminum alloy cylinder head 1, an annular groove 2 having a diameter D1 is formed. In the annular groove 2, a valve seat ring 3 made of steel with an outer diameter D1 is inserted. At the combustion chamber facing the end face of the valve seat ring 3, a conical valve seat surface 4 is formed for the valve plate of a (not shown) valve.

Since the thermal expansion of aluminum is substantially greater than that of steel, the valve seat ring 3 must be used with excess in the cylinder head 1, to ensure a secure hold at operating temperature. On the other hand, the excess of the valve seat ring for the reasons mentioned above should be as small as possible in order to facilitate the insertion process and to avoid unnecessary stresses in the cylinder head. To meet these two requirements, the valve seat ring has an excess, which is in the range of 0.5 to 1.5 parts per thousand.

LIST OF REFERENCE NUMBERS

1

cylinder head

2

ring groove

3

Valve seat ring

4

Valve seat

D1

Outer diameter of 3

D2

Inner diameter of 2

Claims (2)

1. A cylinder head of an internal combustion engine with a valve seat ring inserted into a cylindrical bore (2), wherein the valve seat ring (3) has a cylindrical outer surface and an outer diameter (D1) oversized relative to the diameter (D2) of the cylindrical bore (2) and the cylinder head (1) is made of a material with greater thermal expansion than that of the valve seat ring (3),
   characterised in that
   the outer diameter of the valve seat ring (3) relative to the diameter of the bore (2) has an oversize of 0.1 to 0.5 per thousand.
2. A cylinder head according to claim 1, characterised in that the oversize is at least 0.5 per thousand.

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