The invention relates to a thrust bearing of the Michell type for absorbing axial thrust which from a propeller for the propulsion of a vessel is transferred through a shaft to the thrust bearing, comprising a journal bearing for supporting the shaft section of the thrust bearing, a first set of thrust segments for transferring the forwards directed axial thrust occurring while the propeller propels the vessel ahead, and a second set of thrust segments for transferring the axial thrust directed astern occurring while the propeller turns astern, either set of thrust bearings being able to slide against an associated axially directed thrust face rigidly connected with the shaft section of the thrust bearing. From a traditional point of view such a bearing is designed so that a thrust shaft is journalled in two journal bearings in such a manner that a thrust collar with two axially opposed thrust faces is disposed bet¬ ween said two journal bearings. The first and the second set of thrust segments are arranged on either side of the thrust collar in an associated segment holder which in the axial direction abuts on a plane, axially directed lateral face on the journal bearing housing which is integral with the base of the thrust bearing. The segment holder is in the radial direction fixed in position by means of three single point sup¬ ports which in the rotational direction of the shaft are spaced apart by approximately 90°. The segment holder and the thrust segments accommodated therein are prevented from rotating in the rotational direction of the shaft by means of a crossbar or a segment stopper which as a separate unit extends across the top section of the shaft and is clamped against the segment holder

by means of two bolts fastened in threaded holes in the journal bearing housing.

When the propeller propels the ship ahead, the forward set of thrust segments will slide against the forwards facing thrust face of the thrust collar and transfer the axial thrust to the segment holder and further on to the housing of the forward journal bearing and down into the base of the thrust bearing. When the propeller reverses, the aft set of thrust segments transfers in a corresponding manner the axial thrust through the segment holder and the housing of the aft bearing journal and down into the base of the thrust bearing.

The object of the invention is to diminish the axial length required for the installation of the thrust bearing so that the total length of installation of the propelling engine with the thrust bearing becomes smaller.

With a view to this, the thrust bearing according to the invention is characterized in that the first and the second sets of thrust segments with asso¬ ciated thrust face are arranged axially on either side of the ournal bearing.

By arranging the thrust segments on either side of one journal bearing the other journal bearing may be dispensed with, resulting in that the thrust bearing according to the invention has a substantially shorter axial length than hitherto known thrust bearings of the Michell type. With the view of further reducing the axial extension of the thrust bearing the thrust segments of the second set transferring the axial thrust while going astern may preferably have a smaller axial thickness than the thrust segments of the first set. The axial length of the thrust bearing is here dimi¬ nished a distance corresponding to the thickness reduc¬ tion of the segments of the second set.

In an embodiment which owing to its simplicity is preferred, the upper part of the journal bearing is designed as a segment stopper which when mounted pre¬ vents at least one set of thrust segments from rotating about the axis of rotation of the shaft. The previously known, separate segment stopper may thus be fully dis¬ pensed with, thereby partly reducing the cost of manu¬ facturing and mounting because the bearing has a fewer number of components and, partly making it possible to further reduce the axial length of the bearing, since a clearance zone for mounting a separate segment stopper is no longer necessary.

In accordance with a further embodiment of the invention the axial length of the bearing may be fur- ther reduced by completely leaving out the previously known segment holder. The radial movement of the seg¬ ments is instead restricted in that the first engage¬ ment members on the segments interact directly with second engagement members designed in the structure that is integral with- the base of the thrust bearing and absorbs the axial thrust. The axial length of the thrust bearing may thus be reduced with the thickness of the segment holder.

The invention also relates to a piston engine for the propulsion of a ship and with a crankshaft pro¬ vided with main bearing journals carrying crank arms and in which the engine has a thrust bearing of the above mentioned type. According to the invention this engine is characterized in that either the first or the second set of thrust segments slides against one axial¬ ly directed lateral face of the crank arm. The thrust bearing becomes then an integral part of the engine proper, and no separate, bulky journal bearing is required for the thrust bearing. The second set of thrust segments transferring the axial thrust while reversing may advantageously

be arranged between the aft main bearing in the engine and the rearwards directed lateral face on. the aft crank arm, this arm being then merely subjected to the reverse thrust and not to the substantially larger axial thrust that may occur while the propeller propels the ship ahead.

Preferred embodiments of the thrust bearing and the piston engine according to the invention will now be described in more detail with reference to the schematical drawings, in which

Fig. 1 is a longitudinal section of a known thrust bearing of the Michell type,

Fig. 2 is a longitudinal section through a first embodiment of a thrust bearing according to the inven- tion,

Fig. 3 is a longitudinal section through a second embodiment of a thrust bearing according to the invention,

Fig. 4 is an end view viewed from the crank- case of a thrust bearing according to the invention, the shaft and a pair of the thrust segments being left out for the sake of clearness, and

Fig. 5 is a longitudinal section through a sec¬ tion of a third embodiment of a thrust bearing accord- ing to the invention.

The thrust bearing in Fig. 1 includes a shaft section 1 extending from a bolt flange 2 to be bolted together with a corresponding flange on an intermediate shaft or a propeller shaft and forwards to a crank arm 3 firmly shrinked on the forward end of the shaft section 1.

The shaft section 1 is supported in a forward journal bearing 4 and an aft journal bearing 5. For the sake of clearness the upper parts of the journal bearings are not shown. Between the two journal bear¬ ings the shaft section 1 has a radially projecting

thrust collar 6 with a forward and an aft axially directed thrust face 7, 8, transferring the axial thrusts occurring in the shaft either to a forward set of thrust segments 9 for the transfer of a forwards directed axial thrust (thrust directed to the left in Fig. 1) or to an aft set of thrust segments 10, for the transfer of axial thrusts directed astern. The two sets of thrust segments are mounted each in a respect¬ ive segment holder 11, 12 which in the axial direc- tion abuts on a plane lateral face 13, 14 of the structure constituting the bottom part of the associ¬ ated journal bearing and being connected with the base 17 of the thrust bearing. When the thrust collar 6 on the rotating shaft section 1 presses towards the segments 9 or 10, the friction between the segments and the associated thrust face 7 or 8 attempts to pull the segments along to rotate in the rotational direction of the shaft. To prevent this, the segment holder and the segments are held stationarily in the rotational direction by means of a segment stopper 18 or 19 detachably connected with the associated structure 15 or 16.

The bearing is cooled and the segments are lubricated by means of oil supplied through oil pipes 20, 21 extending to nozzles which may sprinkle oil on the segments.

The thrust bearing in Fig. 2 is arranged around the aft main bearing 21 in the engine, the bottom part of said bearing being integral with the engine bed plate which serves as base for the thrust bearing and whose upper part is divided into two bearing upper parts 22, 23 clamped together with the bottom part by means of bolts 24. The first set of thrust segments 25 may slide against the forward thrust face 7 of the thrust collar 6 and is controlled in the radial direction by a segment holder 26 abutting on an

axially directed lateral face 27 on the bottom part of the main bearing. A segment stopper 28 is bolted to the bed plate of the engine and prevents the segments 25 and the holder 26 from moving in the rotational direction of the shaft.

A second set of thrust segments 29 is arranged on the opposite side of the main bearing between the aft or rearwards directed lateral face or thrust face 30 on the crank arm 3 and an opposite, axially directed lateral face 31 on the bottom part of the main bearing.

The shaft section 1 of the thrust bearing extends in a similar manner as in Fig. 1 from a bolt flange 2 to the fixing point in the crank arm 3, but in the bearing according to the invention the shaft section 12 is substantially shorter. The shaft sec¬ tion 1 may alternatively be a separate thrust shaft which forwards has a bolt flange for connection with a shaft part on the propulsion engine, on a clutch or on a gearing.

A removable end cover 51 with a sealing ring 52 engaging the shaft prevents dirt and other impuri¬ ties from penetrating into the engine and ensures that oil does not leak from the engine. It is evident that the bearing according to the invention includes substantially fewer components than the previously known bearing and, consequently, cost savings are obtained besides the advantageously short length of installation, because the manufacture and installation of the thrust bearing is more simple.

The forward bearing upper part 22 has suffi¬ ciently large axial width to slightly protrude over the thrust segments 29. As appears from Fig. 4 the upper part is at either side provided with a protruding por- tion 33 which downwardly is terminated in a radially extending abutting face 34 engaging the upper edge of

the upper thrust segment 29' and prevents this seg¬ ment from rotating together with the shaft. The upper part 22 is thus designed as a segment stopper.

In the description of the various embodiments according to the invention the same reference numerals are used for the same type of components.

In the embodiment in Fig. 3 the aft upper part 23' is provided with an axial enlargement directed astern and which projects in over the thrust segments 25'. The axial enlargement is provided with projecting sections and abutting surfaces for the segments in the same manner as illustrated in Fig. 4 in connection with the upper part 22. Thus, the upper part „23' operates as a segment stopper and the previously used separate segment stopper may be dispensed with. In the illus¬ trated embodiments the upper part is formed in two parts 22, 23 in order to facilitate the mounting and dismounting of the top section, but if there is suffi¬ cient space around the bearing, it is of course possible to design the top section in one piece which, if desired, may be designed as segment stopper for one or both sets of thrust segments.

The thrust segments are generally made from cast iron and have a layer of white metal on the side sliding against the thrust surface 7 or 30. The thrust segments must have a sufficiently large axial thickness so as to prevent the segments from being deformed while transferring the axial thrust, such a deformation being detrimental to the oil film between the thrust segment and the rotating face 7 or 30. The thrust segments of the second set 29 have a substantially smaller axial thickness than the segments of the first set 25, 25'. This is possible without subjecting the segments 29 to unacceptable defor- mation because the maximum axial force while going astern is substantially weaker than the maximum axial force during forward propulsion.

As mentioned, the thrust bearing may be designed without the traditionally used segment holder so that the segments abut directly on the lateral face 27 or

31 which absorbs the axial thrust. The movement of the segments in the radial direction is then restricted by means of an engagement member which is placed on the segments and is controlled by engagement with a second engagement member secured on or formed in the thrust absorbing surface 27 or 31. As illustrated in Figs 2 to 4, the first engagement member may be a circularly arched, continuous groove 35 in the lateral face of the segment, and the second engagement member may com¬ prise one or more projecting pins 36 screwed or clamped into associated holes in the lateral face 27 or 31. The groove 35 has suitably a larger width than the diameter of the pin 36, so that the segments have a limited clearance in the radial direction. The paired engagement members may of course be formed in another way, for instance as a circularly arched groove in the stationary lateral face 27, 30 and a corresponding circularly arched rib 38 which may be integral with each of the thrust segments 29', 25", see Fig. 5.

Fig. 5 illustrates a thrust bearing that may be used independently of the engine proper. The thrust bearing is arranged around an ordinary thrust bearing 39 and the first set of thrust segments 25 ^• ' may slide against an ordinary thrust collar 6 whereas the second set of thrust segments 29' for absorbing the axial thrust while going astern may slide against a thrust collar 40 that is shorter in the axial direc¬ tion and is disposed on the opposite side of the journal bearing. Since the thrust bearing according to the invention only requires very little space in the axial direction the bearing may normally always be arranged around one of the journal bearings which necessarily must support the propeller shaft or an intermediary shaft.

The thrust segments according to the invention may in a simple manner be lubricated by means of a cir¬ cularly arched, perforated oil pipe 41 disposed imme¬ diately radially within the thrust segments and capable of sprinkling them with oil. Such a pipe occu¬ pies only little space in the radial direction.

In smaller engines in which the chain wheel is generally positioned at the aft end of the engine the chain wheel may, as illustrated in Fig. 2, be used as thrust collar in the thrust bearing whereas the thrust bearing in larger engines in which the chain wheel is located centrally in the engine must have a separate thrust collar 6', as illustrated in Fig. 3.

It is evident that the illustrated components may be arbitrarily composed when arranging a thrust bearing according to the invention, the thrust segments

25' in Fig. 3 may for instance alternatively be designed as the thrust segments 25 in Fig. 2.