EXHAUST VALVE FOR INTERNAL COMBUSTION ENGINES

Abstract: An exhaust valve for internal combustion engines comprises a cylindrical valve stem (1) with a longitudinal cooling duct (2), and a circular, substantially disc-shaped head (3) securely connected to the valve stem (1), the head (3) having at least one cooling duct (4) which extends from the bottom (5) of the valve stem's cooling duct (2) to an outlet (6) on the head's surface (7), in order to conduct coolant through the valve stem (1), through the head (3) to exhaust gases from the engine. In the valve stem's cooling duct (2) there is inserted a cross section-reducing insert (8).

Description: Exhaust valve for internal combustion engines The invention concerns an exhaust valve for internal combustion engines, comprising a cylindrical valve stem with a longitudinal cooling duct with an internal wall surface, and a circular, substantially disc-shaped head securely connected to the valve stem, the head (3) having at least one cooling duct which extends from the bottom of the valve stem's cooling duct to an outlet on the head's surface, in order to conduct coolant through the valve stem, through the head to exhaust gases from the engine. In Norwegian patent application no. 972301 a valve of this kind is described, where there extends through the valve stem and the valve head a passage which leads into a valve surface portion which communicates with the downstream side of the valve. In order to achieve high efficiency in an engine the valve must be capable of withstanding high temperatures, thus entailing the choice of a valve material which can withstand high temperatures. In addition, it is advantageous to cool the valve. With the above-mentioned valve, satisfactory cooling of the valve head is obtained, but the cooling of the valve stem is not satisfactory. An object of the invention is to provide a valve of the type mentioned in the introduction where the cooling of the valve stem is better than in the case of known valves. The object is achieved with a valve of the type mentioned in the introduction, characterized by the features which are indicated in the claims. The valve will now be described in more detail with reference to the drawing, in which: fig. 1 is a longitudinal section through a valve according to the invention. Fig. 2 is a cross section along the intersecting line II-II in fig. 1. Fig. 3 is an enlarged cross section of a valve insert for use in a valve according to the invention. Fig. 4 is an enlarged longitudinal section through a valve head for a valve according to the invention. The same reference numerals are used for corresponding parts or portions of the different figures. Fig. 1 illustrates an exhaust valve for internal combustion engines, comprising a cylindrical valve stem 1, and a circular, substantially disc- shaped head 3 securely connected to the valve stem. When the valve is used in a combustion engine, the head 3 will be brought into alternating contact with a not shown valve seat, and heated by passing exhaust gases. Depending on the engine's design, the same exhaust gases will also heat the valve stem to a greater or lesser degree. The valve stem 1 has a longitudinal cooling duct 2, which is connected at its bottom 5 to cooling ducts 4 in the head 3. The cooling ducts 4 lead to an outlet 6 on the head's surface 7. When the engine is running, coolant, generally air, is passed through the cooling ducts in the valve stem 1 and the head 3 to the outlets 6, where the coolant is mixed with the engine's exhaust gases. By this means both the valve stem and the head are cooled. According to the invention there is inserted in the valve stem's cooling duct 2 a cross section-reducing insert 8. The insert causes the coolant to flow at a higher rate along the insert, which results in better heat transfer from the valve stem 1 to the coolant in the area in which the insert is located. This improved heat transfer is assumed to be due to the fact that by flowing at a high rate the coolant breaks down a greater portion of the boundary layer along the cooling duct's wall surface 12 than it does at a low rate. It is obvious per se that a high rate of flow in the coolant can also be obtained by increasing the amount of coolant supplied, but this will entail increasing the dimensions of the coolant's supply pipe and the device, generally a compressor, which supplies the coolant. An increase in the amount of coolant would also necessitate an increase in the dimensions of the engine's outlet pipe. Such an size increase is undesirable. It is, of course, also possible to obtain an increase in the rate of flow of the coolant by reducing the cross sectional area of the valve stem's cooling duct 2, but this will simultaneously reduce the area of the cooling duct's wall surface 12, thus reducing the heat transfer from the valve stem 1 to the coolant. Consequently, it is desirable to have a cooling duct with a large cross sectional area. In a preferred embodiment, see fig. 1, the insert 8 is located in such a manner that it extends from or approximately from the bottom 5 of the valve stem's cooling duct and along the valve stem 1 for a length \\ which corresponds to at least half of the valve stem's length I2. Improved cooling of the valve stem 1 is thereby achieved in an area where it is most exposed to the hot exhaust gases. In a further preferred embodiment the insert 8 is located in such a manner that it extends from or approximately from the bottom 5 of the valve stem's cooling duct and along the valve stem 1 for substantially the entire length I2 of the valve stem. Improved cooling of the whole valve stem 1 is thereby achieved. Fig. 2, which is a cross section through the cooling duct 2 and the insert 8, illustrates a further preferred embodiment where the insert 8 is composed of a longitudinally centrally located, solid central section 9 with longitudinal, outwardly projecting ribs 10 along the circumference, thus providing between the outwardly projecting ribs 10 longitudinal grooves 11 for the coolant. This causes the coolant to be passed along the cooling duct's wall surface 12, resulting in a high degree of heat transfer from the valve stem 1 to the coolant. In a further preferred embodiment, see fig. 2, the valve stem's cooling duct 2 has a circular or polygonal cross section, while at the same time the insert's central section 9 has a circular or polygonal cross section, and is located in the middle of the cooling duct 2. The outwardly projecting ribs 10 extend radially from the central section 9 to the cooling duct's wall surface 12. A uniform distribution is thereby obtained of the grooves 1 1 along the cooling duct's wall surface 12, resulting in a uniform heat transfer from the valve stem 1 to the coolant. Fig. 3 illustrates a further preferred embodiment where the number of outwardly projecting ribs 10 amounts to at least 6. A uniform distribution is thereby obtained of coolant along the cooling duct's wall surface 12, thus ensuring a uniform heat transfer from the valve stem 1 to the coolant. In a further preferred embodiment, see fig. 3, the outwardly projecting ribs 10 have a constant thickness t from the central section 9 to the cooling duct's wall surface 12, i.e. over its entire area, indicated by ri . This gives the insert adequate strength, while at the same time the grooves 1 1 obtain a trapezoidal cross section with the largest side of the trapeze located against the cooling duct's wall surface 12, thus ensuring satisfactory heat transfer from the valve stem 1 to the coolant. In a further preferred embodiment, see fig. 3, the outwardly projecting ribs 10 have a radial extension τ\ which is approximately equal to the radius r2 of the central section 9. The result of this is that the grooves' 11 trapezoidal cross section obtains a shape which provides a reasonable compromise between the desire for high rate of flow for the coolant, low flow resistance in the cooling duct 2 and good heat transfer from the valve stem 1 to the coolant. Fig. 4, which is an enlarged longitudinal section through the valve head, illustrates a further preferred embodiment where the insert 8 is passed right down to the bottom 5 of the valve stem's cooling duct 2, and a portion 13 of the insert which is located at the bottom 5 of the valve stem's cooling duct is tapered or graduated in order to permit passage of coolant to the cooling ducts 4 in the valve head 3. This provides an advantageous attachment of the insert 8 in the cooling duct 2, since the insert can be passed right down to the bottom of the cooling duct, to abut against it. The other end of the insert may be attached to the valve stem's upper portion in various ways, for example by welding or insertion of an internal plug in the cooling duct 2. Such means of attachment are prior art and will not be discussed further. In a further preferred embodiment the insert 8 is inserted into the valve stem's cooling duct 2 with a light force fit. A simple installation of the insert is thereby achieved, while at the same time providing a valve stem in which the insert is at rest in the cooling duct and follows its movement without any play, which could cause undesirable wear on the insert and the cooling duct and flow problems for the coolant. The invention has been described above with reference to a specific embodiment. It is obvious, however, that variants of the invention may be designed within the scope of the claims, for example associated with the number of ribs, since it will be possible to replace the illustrated number of ribs with a larger or smaller number, which will lead to slight alterations in the cooling and flow conditions, thus enabling the invention to be adapted to the engine concerned.

Claims: PATENT CLAIMS 1. An exhaust valve for internal combustion engines, comprising a cylindrical valve stem (1) with a longitudinal cooling duct (2) with an internal wall surface (12), and a circular, substantially disc-shaped head (3) securely connected to the valve stem (1) the head (3) having at least one cooling duct (4) which extends from the bottom (5) of the valve stem's cooling duct (2) to an outlet (6) on the head's surface (7), in order to conduct coolant through the valve stem (1), through the head (3) to exhaust gases from the engine, characterized in that in the valve stem's cooling duct (2) there is inserted a cross section-reducing insert (8). 2. An exhaust valve according to claim 1 , characterized in that the insert (8) extends from or approximately from the bottom (5) of the valve stem's cooling duct and along the valve stem (1) for a length (lι ) which corresponds to at least half of the valve stem's length (I2). 3. An exhaust valve according to claim 1 or 2, characterized in that the insert (8) extends from or approximately from the bottom (5) of the valve stem's cooling duct and along the valve stem (1) for substantially the entire length (I2) of the valve stem. 4. An exhaust valve according to one of the preceding claims, characterized in that the insert (8) is composed of a longitudinally centrally located, solid central section (9) with longitudinal, outwardly projecting ribs (10) along the circumference, thus providing between the outwardly projecting ribs (10) longitudinal grooves (11) for the coolant. 5. An exhaust valve according to claim 4, characterized in that the valve stem's cooling duct (2) has a circular or polygonal cross section, that the insert's central section (9) has a circular or polygonal cross section, and that the outwardly projecting ribs (10) extend radially from the central section (9) to the cooling duct's wall surface (12). 6. An exhaust valve according to claim 4 or 5, characterized in that the number of outwardly projecting ribs (10) amounts to at least 6. 7. An exhaust valve according to one of the claims 4-6, characterized in that the outwardly projecting ribs (10) have a constant thickness (t) from the central section (9) to the cooling duct's wall surface (12). 8. An exhaust valve according to one of the claims 4-7, characterized in that the outwardly projecting ribs (10) have a radial extension (ri ) which is approximately equal to the radius (r2) of the central section (9). 9. An exhaust valve according to one of the preceding claims, characterized in that the insert (8) is passed right down to the bottom (5) of the valve stem's cooling duct (2), and that a portion (13) of the insert which is located at the bottom (5) of the valve stem's cooling duct is tapered or graduated in order to permit passage of coolant to the cooling ducts (4) in the valve head (3). 10. An exhaust valve according to one of the preceding claims, characterized in that the insert (8) is inserted in the valve stem's cooling duct (2) with a light force fit.

Inventors: HILDRE HANS PETTER, KVAMSDAL ROLF, HILDRE, HANS, PETTER, KVAMSDAL, ROLF
Applicants: HILDRE HANS PETTER, KVAERNER ASA, KVAMSDAL ROLF, HILDRE, HANS, PETTER, KVAMSDAL, ROLF
Application year: 1998
Main classification: F01L3
IPC codes: F01L3