Improved valve rotation arrangement

Abstract: An improved valve rotation arrangement for providing valve rotation for a pressure medium valve in an internal combustion engine, especially a large diesel engine or gas engine, whereby the valve is opened under positive guidance, for instance under the influence of a rocker arm (18), and is closed by means of a spring (6). The valve rotation arrangement comprises a bearing arrangement for turnably journalling the upper part of a valve stem (2) to the valve spring (6) and a rotation mechanism (10) supported to the cylinder head (1) of the engine and arranged to provide valve rotation. The bearing arrangement comprises a slide bearing between a rotation element (4), at the upper part of the valve stem (2), and a bearing housing element (5) supported to the valve spring (6).

Description: This invention relates to a valve rotation arrangement of an internal combustion engine, especially a large diesel engine of gas engine, the arrangement being of the kind referred to in the preamble of claim 1. In this specification the term "large diesel engine" is intended to refer to such an engine that can be used, for example, as the main propulsion engine or an auxiliary engine for a ship or in a power plant for producing electricity and/or heat energy. The term "gas engine", on the other hand, is intended to refer to a combustion engine in which the basic fuel used is a gaseous fuel, for example natural gas. Such a gas engine may operate either on the OTTO-principle or on the diesel-principle. The purpose of valve rotators is to improve the operational qualities and the lifetime of engine valves. They may be used for both inlet and outlet valves. With outlet valves blow-bys at the sealing surface and burning off of the valve can be prevented by means of valve rotation. With inlet valves, valve rotation decreases wear so as to balance the temperature gradient. There are a relatively large number of different constructional variations for achieving valve rotation depending on where and how the actual rotation is accomplished and where and in which way the bearing arrangement between the valve and the cylinder head is provided. A problem with known valve rotation arrangements is that due to their construction, and especially the use of ball bearings between the movable parts, the lifetime is not sufficient to be in proportion with the other components in the valve mechanism of the engines. In particular the ball bearings are damaged by vibrations and high static load when the valve is in its closed position, by the impulse caused through the closing of the valve and by the small rotations to the valve. With increased damage to the bearings the rotation is hampered or alternatively is totally blocked. A further problem is the fact that in practice there is only a limited possibility to enlarge the dimensions of the bearings so as to increase their strength. Another known valve rotation arrangement of the kind referred to is disclosed in GB-A-761,405. An aim of the invention is to provide an improved valve rotation arrangement having an uncomplicated and economic construction and which eliminates the drawbacks described above. The invention seeks to extend the lifetime of the bearing in valve rotators between the valve spring and the valve. The bearings should with reasonable costs and compact design be able to endure high static and dynamic loads under vibration without being damaged over a long operation period. A further aim is to provide a valve rotation arrangement which can be used in, and is especially suitable for, large diesel engines and gas engines of the kind referred to above. According to the present invention there is provided a valve rotation arrangement as claimed in the ensuing claim 1. A compact design, and at the same time a low specific surface pressure, can be achieved with such an arrangement since the whole available space can be used as a bearing surface, whereby damage can effectively be avoided in the bearing even if it vibrates during operation. Thus operation of the arrangement causes little wear in the valve thereby increasing its lifetime. Furthermore an uncomplicated design is also made possible for elements located near-by, i.e. for instance the rotation element and the bearing housing element. In addition the arrangement according to the invention can easily be replaced. All these features permit a cost effective construction. Although the arrangement according to the invention also brings about a somewhat higher coefficient of friction than, for example, a construction based on ball bearings, this has no negative effect on the operation as such. A simple and effective construction can be achieved when the rotation mechanism comprises the valve spring itself. Such an embodiment makes use of the screw-like movement of the valve spring during, especially, the compression operation, with additional assistance being provided by vibration of the engine. Alternatively the rotation mechanism may comprise a positively guided mechanism arranged to force or allow rotation of the valve in one direction but to block valve rotation in the opposite direction. In this case the rotation element is suitably arranged to be in force transmitting connection with the rotation mechanism. To minimise the oscillating mass, the bearing housing element and/or the rotation element may with advantage be selected to be of a material serving as bearing metal, which is of advantage for the whole valve mechanism. Advantageously the bearing housing element is bowl-shaped and includes a circular cylindrical protrusion which surrounds the rotation element and preferably extends somewhat above the upper surface of the rotation element. Additionally the protrusion and the rotation element may be so dimensioned that an annular slot remains between these members. If a valve yoke is provided for force transmission from said valve opening means, e.g. a rocker arm, to the valve stem, the valve yoke may be provided with at least one oil duct to feed oil to the top of the valve so that an oil pocket is formed between the bearing housing element and the rotation element. With such a construction the bearing arrangement is always well lubricated and an effective lubrication of the bearing surfaces is ensured, which decreases friction in the bearing and prolongs its lifetime. In order to make the lubrication even more effective, at least one of the bearing surfaces may be provided with a number of radial grooves. Embodiments of the invention will now be described, by way of example only and with particular reference to the accompanying drawings, in which: Figure 1 is an axial section through one embodiment of a valve rotation arrangement which illustrates the valve rotation principle of the invention; Figure 2 is a section taken on the line II-II of Figure 1; Figure 3 is an enlarged section on the line III-III of Figure 1; Figure 4 is a partial sectional view of an embodiment of a valve rotation arrangement according to the invention; Figure 5 is a plan of a bearing washer shown in Figure 4 and provided with radial grooves for lubrication of bearing surfaces; Figure 6 is a sectional view of an arrangement comprising two valves with rotation arrangements in accordance with Figure 1 and guided by a valve yoke; and Figure 7 shows a sectional view of another embodiment of a valve rotation arrangement according to the invention. In the drawings there is shown a valve rotation arrangement in which 1 designates a cylinder head of an internal combustion engine which supports, by means of a valve guide 9, a valve with a valve stem 2. The valve is opened in a known manner under positive guidance, for instance through a rocker arm 18 and a valve yoke 19 (as shown in Figure 6) which, for their part, are guided by a camshaft (not shown) of the engine. The valve is closed by means of a spring 6 which lies against a bearing housing element 5 at the upper part of the valve stem 2. The valve stem 2 is fixed to a rotation element 4 by means of two frusto-conical segmental elements 3a and 3b. The valve rotation arrangement also comprises a cylinder element 7 which, by means of a bearing washer 8 fixed thereto, is rotatably supported with regard to the valve guide 9, and a rotation mechanism 10. The rotation mechanism 10 allows rotation in one direction only, rotation in the other direction being blocked as will be described more fully below with reference to Figure 3. As is apparent from Figure 2, the cylinder element 7 comprises a number of bar-like splines or guiding elements 7a which extend helically about the valve stem axis. The guiding elements 7a interengage with corresponding, radially projecting, helical guiding elements 4a of the rotation element 4. Due to the inertia of the valve and friction forces in the tangential direction, it follows that when the valve is opened, and the valve stem 2 moves downwards in Figure 1, the guiding elements 7a and the corresponding guiding elements 4a in the rotation element 4 force the cylinder element 7 to turn in the direction allowed by the rotation mechanism 10. The slide bearing washer 8 provides a bearing between the cylinder element 7 and the valve guide 9. When the valve is closed, turning of the cylinder element 7 in the opposite direction is blocked by the rotation mechanism 10. As a consequence the cylinder element 7 forces the rotation element 4 as well as the valve itself to turn with respect to the bearing housing element 5 and the spring 6. In order to make this possible, there is a slide bearing between the rotation element 4 and the bearing housing element 5, whereby either one or both of these elements may with advantage be of a material serving as a bearing metal. The rotation mechanism 10 shown in Figure 3 comprises a ratchet wheel 12 non-rotatably mounted on the cylinder head 1 and a number of spring elements 13, which are carried by a support element 11 fixed to the cylinder element 7 and which are arranged to cooperate with the ratchet wheel 12. The application of the present invention is, however, by no means restricted to this particular type of rotation mechanism and many different variations are feasible to force rotation in one direction and to block rotation in the other direction. Figure 4 shows an embodiment of a valve rotation arrangement according to the invention in which a separate bearing washer 16 is arranged between the bearing housing element 5 and the rotation element 4. Several such bearing washers may be provided each possibly having a number of radial grooves 17 as shown in Figure 5 so as to improve lubrication of the bearing surfaces. Naturally, the bearing surfaces in the embodiment according to Figure 1 may also be provided with similar grooves when necessary. With reference to Figures 1, 6 and 7, the bearing housing element 5 comprises an upper circular cylindrical protrusion 5a enclosing the rotation element 4, and preferably extending somewhat above the upper surface of the rotation element 4, a lower circular cylindrical part of smaller diameter than the protrusion 5a and an annular part connecting these two circular cylindrical parts. The annular connecting part and the protrusion 5a provide the housing element with a substantially bowl-shaped form. The protrusion 5a and the rotation element 4 are so dimensioned that an annular slot 14 remains therebetween, i.e. the outer diameter of the element 4 is less than the inner diameter of the protrusion 5a. If the valve yoke 19 is provided with at least one oil duct 20 for each valve, the or each oil duct 20 can serve to feed oil to the top of the valve in question so that an oil pocket is formed between the bearing housing element 5 and the rotation element 4. Because of the static pressure provided by the oil pillar in the oil pocket the bearing is always well lubricated, which decreases friction in the bearing and increases the lifetime of the bearing. In this way, any surplus oil will drain down between the segment member halves 3a and 3b into the space below the segment members between the valve stem 2 and the rotation element 4 to thereafter drain through a number of small holes 15 bored into the rotation element 4 and thereby also to lubricate the guiding elements 7a and 4a. In accordance with another embodiment of the invention shown in Figure 7, the valve rotation mechanism 10 comprises the actual valve spring 6, which has a screw-like movement, especially during the compression stroke and with the assistance of the vibrations of the engine. The embodiment is of a simple, uncomplicated construction and functions well in spite of the fact that the rotation is not similarly under positive guidance as according to the other embodiments described above.

Claims: A valve rotation arrangement of an internal combustion engine, the arrangement comprising an engine cylinder head (1), a pressure medium valve having a valve stem (2), means for opening the valve under positive guidance, a valve spring (6) acting to close the valve, a bearing arrangement for turnably journalling the upper part of the valve stem (2) to the valve spring (6) and a rotation mechanism (10) arranged to provide valve rotation, the bearing arrangement comprising a slide bearing between a rotation element (4), at the upper part of the valve stem (2), and a bearing housing element (5) supported by the valve spring (6), characterised in that at least one separate bearing washer (16) is arranged between the bearing housing element (5) and the rotation element (4). An arrangement according to claim 1, characterised in that the rotation mechanism (10) comprises the said valve spring (6). An arrangement according to claim 1, characterised in that the rotation mechanism (10) comprises a positively guided mechanism arranged to allow rotation of the valve in one direction and to block rotation of the valve in the opposite direction, and in that the rotation element (4) is in force transmitting connection with the rotation mechanism (10). An arrangement according to any of the preceding claims, characterised in that the bearing element (5) and/or the rotation element (4) is/are a bearing metal material. An arrangement according to any of the preceding claims, characterised in that the bearing housing element (5) is bowl-shaped and includes a circular cylindrical protrusion (5a) enclosing the rotation element (4), and preferably extending somewhat above the upper surface of the rotation element (4), and in that the protrusion (5a) and the rotation element (4) are additionally so dimensioned that an annular slot (14) remains between them. An arrangement according to claim 5, characterised in that a valve yoke (19) is provided for force transmission from said valve opening means, e.g. a rocker arm (18), to the valve stem (2), the valve yoke (19) being provided with at least one oil duct (20) for feeding oil to the top of the valve so that an oil pocket is formed between the bearing housing element (5) and the rotation element (4). An arrangement according to any of the preceding claims, characterised in that at least one of the bearing surfaces of the bearing arrangement is provided with a number of radial grooves (17) for making the lubrication thereof more effective. An internal combustion engine having a valve rotation arrangement according to any one of the preceding claims.

Inventors: JOHANSSON PETER, JOHANSSON, PETER
Applicants: WAERTSILAE NSD OY AB
Application year: 1996
Main classification: F01L1
IPC codes: F01L1