US3785250A

US3785250A - Piston-type machine

Info

Publication number: US3785250A
Application number: US00182708A
Authority: US
Inventors: A Steiger
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1971-07-07
Filing date: 1971-09-22
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15
Also published as: DE2134944B2; GB1370840A; AT314280B; DE2134944A1; SE369214B; ES404600A1; IT962327B; BE785869A; CH540427A; JPS54704U; FR2145298A5

Abstract

The pistons are reciprocally mounted within cylinders which are disposed to rotate about a given axis perpendicularly disposed to the longitudinal axes of the cylinders. In addition, an annular support surface or ring surrounds the piston to rotate about an axis parallel to and eccentrically spaced from the axis of rotation of the cylinders. This annular support surface includes flat sliding surfaces on which each piston can slide during rotation of the cylinders and support surface.

Description

United States Patent 1191 Steiger 1451 Jan. 15, 1974 1 PISTON-TYPE MACHINE 3,663,124 5/1972 Schultz 91 491 x [75] Inventor: Anton Steiger, lllnau, Switzerland FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Sulzer Brothers Ltd., Winterthur, 1,528,416 11/1969 Germany 91/491 Switzerland 1,816,435 6/1970 Germany 91/491 1,901,248 7/1970 Germany 91/491 [22] Filed: Sept. 22, 1971 2 Appl, 132,703 Primary Examiner-Martin P. Schwadron Assistant Examiner-Abe Hershkovitz Alt rne Ken on and Ken on Reill Carr and [30] Foreign Application Priority Data y y y y Chapm July 7, 1971 Switzerland 10030/71 52 US. or. 92/72, 91/491 7] B A T [51] Int. Cl F01!) l/00 The pistons are reciprocally mounted within cylinders [58] Field of Search 92/2, 68, 72; which are disposed to rotate about a given axis pep 91/491 pendicularly disposed to the longitudinal axes of the cylinders. in addition, an annular support surface or [56] References Clted ring surrounds the piston to rotate about an axis paral- UNITED STATES PATENTS lel to and cccentrically spaced from the axis of rota- 3,320,902 5/1967 Paschke 91/472 x tion of the cylinders- This annular pp Surface 3,398,698 8/1968 Eickmann 91/491 X cludes flat sliding surfaces on which each piston can /1958 Crane 91/491 X slide during rotation of the cylinders and support sur- 3,151,529 /1964 Leath 91 491 x f 3,628,425 12/1971 Chikushino-machi 92/72 X 3,630,019 12/1971 Kress 92/68 x 3 Claims, 12 Drawing Figures X11 y r,

l 126 1 99 pg 1 had 115 PATENTEDJAH 15 I974 SHEET 1 [IF 9 PATENTEBJAHIS 914 3,785,250

saw u 059 PATENTEDJAB 1 s 1911 s; 785250 SHEET 7 OF 9 Fig.9

13g 118 I 116 120 108' 131. m 132 A+B T PISTON-TYPE MACHINE This invention relates to a piston-type machine and, particularly, to a machine in which a piston is reciprocated within a rotating cylinder.

A piston-type machine has been known in which at least one piston has been mounted to reciprocate within a cylinder while the cylinder has been able to rotate about a journal having an axis of rotation which intersects the cylinder axis. Such machines have generally had channels in the journal for supplying and removing a medium under pressure to the interior chamber of the cylinder in which the piston reciprocates.

However, this machine has had the disadvantage, among others, that lateral forces have been imposed on the piston during the transmission of power, or motion, to the piston or away from the piston. As a result, these lateral forces have created losses through mechanical friction and wear of the piston and cylinder. Further, a simple compensation of these forces by means of hydrostatic pressure has not been possible.

Accordingly, it is an object of the invention to provide a piston-type machine which eliminates any significant lateral forces on the piston during operation.

It is another object of the invention to permit relatively small sliding movements between the piston and the drive for the piston in a piston-type machine.

It is another object of the invention to compensate for a relative sliding motion between a piston and the piston drive means in a piston-type machine with a hydrostatic means.

It is another object of the invention to provide a piston-type machine which can be used as a hydrostatic pump, a hydraulic motor, a compressor for gas or a motor driven by gaseous mediums.

Briefly, the invention provides a piston-type machine in which a reciprocating piston reciprocally mounted in a rotatable cylinder is allowed to slide on a plane surface located on a rotatable means while the rotatable means rotates eccentrically relative to the cylinder.

In one embodiment, a single piston is reciprocally mounted in a cylinder which is rotatably mounted on a journal or pivot pin while a rotatable annular housing is positioned about the piston and cylinder to rotate about an axis parallel to and offset from the axis of the journal by a selected eccentricity. The housing includes a flat supporting surface on which the end of the piston furthest from the journal bears. This supporting surface is perpendicularly disposed to the axis of the piston.

In this form of construction, wherein the housing together with the cylinder rotates, and wherein the two turn about axes separated from one another by the selected eccentricity, there occur, apart from an axial loading of the piston, only slight sliding movements between the piston and the supporting surface of the housing. Apart from the acceleration forces when starting up, the only lateral forces acting on the piston are caused by friction between the piston and the supportsurfaces. These forces are kept to a minimum through an axial hydrostatic force equalization.

In another embodiment, a machine includes a plurality of pistons which are disposed radially of a journal and guided in an annular cylinder-block while a housing is provided in the form of a drum with a cylindrical part in which are formed flat support-surfaces for the pistons. In this way, a light-weight and yet sturdy construction of the housing is obtained which is suitable for transmitting large forces during operation.

In this embodiment, the drum may be provided at one side with a shaft for the supply or the take-off of mechanical power, and can be installed in a fixed housing. The drum is also provided at the opposite side with a hollow bearing-journal that surrounds the journal and that can likewise be installed in a fixed housing.

In addition, where a number of pistons are disposed radially of the journal, provision is made for a drive part with guideways situated perpendicularly of one another in a plane perpendicular of the axis of rotation of the machine. This drive part is, on the one hand, connected with the drum and, on the other hand, with the cylinder-block in such a way that radial movement of the cylinder-block relative to the drum occur, while a relative turning movement is prevented.

By means of such a drive part, it is possible to avoid the occurrence of lateral forces between the cylinders and the piston upon rapid accelerations of the drum because such forces are then absorbed by the drive part.

According to the invention, it is advantageous to make the cylinder-bores in the cylinders as continuous bores of the same diameter. Through this, the hydraulic losses, during the run-in and run-out of the pressure medium into or out of the cylinders, are reduced to a minimum.

In another embodiment, the journal is formed with a spherical bearing surface which cooperates with a corresponding spherical bearing surface of the cylinderblock. This provides a construction wherein any bending of the journal, under hydraulic forces having a onesided action, has no influence on the operation of the machine. In this case, the cylinder-block is divided in the axial direction, into at least two parts which are then connected with one another by means of lockrings. This allows installation of the cylinder-block in a simple way on the spherical surface of the journal.

It is also possible to form the journal on a part that is adjustable perpendicularly of the axis of rotation of the machine. As a result, it is possible to change the eccentricity from one extreme value passing through zero, to the other extreme value. By this means, it is possible to select the eccentricity. Thus, during operation as a pump of constant rotary speed, it is possible to adjust the quantity pumped and direction in which it is pumped.

In the case of a construction having a vertical journal it is possible, for the run-in or run-out of the medium under pressure, to provide sealing elements at the connections of the channels in the displaceable part and in a fixed housing having the slidesurfaces. This allows a perfect connection of the channel to be obtained in each position of the displaceable part with the journal.

It is also possible to provide the housing with a protrusion which acts as a stop and prevent a lifting of the piston away from the respective surface. Such a lift-off might, for example, occur during a stoppage of the machine.

Equalization-pockets for equalization of the hydrostatic pressure can be provided centrally in the slide surfaces of the piston. These pockets are each connected through a bore in the piston with the face of the piston turned toward the journal. By a suitable and known dimensioning of the equalization pockets, perfect equalization of the forces acting on each piston can be obtained. In this way, there is obtained minimum friction and wear of the pistons, and under certain circumstances perfect functioning of the piston-type machine is made possible. Because the hydrostatic installation eliminates friction at the sliding surfaces of the piston, the occurrence of disturbing lateral forces acting on the piston is also avoided.

Segment-like equalization pockets for hydrostatic pressure equalization can also be provided at the periphery of the journal along the control ports. These pockets are, in each case, connected by connecting holes with the channel of the other control port. Thus, by simple means and with suitable dimensioning of the equalization pockets, equalization of the forces acting on the journal is obtained, so that minimum friction and wear of the journal occur.

The drum bearing can also be formed with segmentlike equalization pockets at the periphery. These pockets are connected, by connecting holes, with a channel, situated at the same side, for the run-in or run-out of the medium under pressure. In this way, hydrostatic relief of the drum bearings is obtained.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIGS. 1 and 2 diagrammatically illustrate a simplified piston-type machine according to the invention with one cylinder;

FIG. 3 illustrates an axial section through a first industrial form of construction of the machine of the invention taken on line IIIIII of FIG. 6;

FIG. 4 illustrates a view taken on line IV-IV of FIG.

FIG. 5 illustrates a view taken on line VV of FIG. 4 of a journal according to the invention;

FIG. 6 illustrates a view taken on line VI-VI of FIG.

FIG. 7 illustrates a view taken on line VII-VII of FIG. 3 ofa drive part between a drum and cylinder according to the invention;

FIG. 8 illustrates an axial section similar to FIG. 3 of a further form of construction of the machine of the invention taken on line VIII-VIII of FIG. 11;

FIG. 9 illustrates a partial section taken on line IXIX of FIG. 11;

FIG. 10 illustrates a partial view taken on line X of FIG. 9;

FIG. 11 illustrates a partial section taken on line XI of FIG. 8; and

FIG. 12 illustrates a partial section taken on line XII of FIG. 8.

Referring to FIG. 1, a piston-type machine comprises a cylinder 1 and a piston 2 which is able to move in reciprocating manner in the cylinder 1 while being guided in a sealed manner. The cylinder 1 is mounted to pivot about a pivot-pin 3 which has

channels

4, 5 for conducting a medium under pressure, e.g., hydraulic oil, in and out, respectively. The pin 3 has, as is known, a pair of recesses 6, 7 which are separated from one another by a partition wall 8 and which are located within the plane of the cylinder 1. The cylinder 1 includes a cylindrical bore 10 in which the piston 2 is mounted and to which is connected a connecting bore 11. As shown, the diameter of the connecting bore 11 is substantially the same in size as the thickness of the partition wall 8, so that no short-circuit connection of the two recesses 6, 7 can occur because of the connecting bore 11.

The piston 2 is, at the end farthest from the pivot-pin 3, provided with a flange 12 which has a sliding surface 13 that slides on a support surface 14 of a mobile part 15 of a machine housing. This housing part 15 is mounted to pivot about a pivot-pin 16 which is shown by dash-lines. The axis A of the pivot-pin 3 of the cylinder 1 and the axis B of the housing part 15 are spaced apart by an eccentricity 2, so that, in operation, the piston 2 moves in the cylinder 1 with a stroke s equal to twice the eccentricity (2e).

Referring to FIGS. 1 and 2, pairs of forces P P, as well as turning moment of torque M are imposed on the machine during rotation in the direction indicated by the arrow 11 when operating as a pump.

In the case of the position shown in FIG. 1, the two forces P set in opposite directions are situated in one line. This means that the piston-type machine is in a dead-center position and takes no turning moment. With the position shown in FIG. 2, which is offset in comparison with FIG. 1, a lever arm having the magnitude of the eccentricity e is formed between the two forces P. When the machine rotates in the direction indicated by the arrow n, the corresponding turning moment M Re must be overcome and the machine operates as a pump.

In comparison with previous machines of this kind, the machine shown in principle in FIGS. 1 and 2 has the advantage that, without special supplementary measures, the piston 2 is always loaded in a purely axial manner, so that no primary tilting moment or lateral forces occur. Apart from the acceleration forces, the only lateral forces acting on the piston 2 are produced by friction resulting from the relative sliding movement between the

surfaces

13 and 14. As is explained in the following practical examples of construction, it is possible to reduce this friction by means of an axial hydrostatic equalization of forces to a negligibly small amount.

Referring to FIGS. 3 and 6, the hydraulic piston-type machine includes a number of pistons 33 disposed radially ofa pivot-pin or journal 32 for use as a pump. Individual cylindrical bores 30 for receiving the pistons 33 are formed in an annular cylinder-block 31, which is mounted so as to rotate on the pin or journal 32. The pistons 33 which are guided in the cylinder bores 30 each has a flange 34 that bears by means of a sliding surface 35 against a respective support or abutment surface 36 of a mobile housing part which is in the form of a drum 37.

As shown in FIG. 3, the drum 37 is connected at one side with a shaft 38 which is rotatably mounted in a stationary housing 39. This shaft 38 serves to supply mechanical power. At the other side, the drum 37 connects to a part 40 which has a hollow bearing-pin 40' thereon. The bearing pin 40' is mounted rotatably in a cover 41 which is fastened to the stationary housing 39 as by bolts. The cover 41 is mounted about the journal 32 and is secured thereto by bolts as shown. The shaft 38 and the bearing in the cover 41 are situated on a common axis B, corresponding to the axis B of FIGS. 1 and 2 while the journal 32, about which the cylinder block 31 is able to turn, has an axis A, which corresponds to the axis A of FIGS. 1 and 2.

Referring to FIGS. 4, 5 and 6, the journal 32 has channels which are connected to

channels

44, 45 in the housing cover 41 and provide for the input and output of the medium under pressure. The

channels

42, 43 correspond to the

channels

4, 5 of FIGS. 1 and 2.

As shown in FIGS. 4 and 5, the journal 32 is provided with

recesses

46, 47 within the plane of the pistons 33 which correspond to the recesses 6 and 7 of FIGS. 1 and 2, and which form control ports to transmit flow between the

channels

42, 43 and bores 30. A partition wall 48 is also disposed between the

recesses

46, 47 as above.

The piston-type machine shown in FIGS. 3 to 6 operates in accordance with the principle that was explained by the aid of FIGS. 1 and 2. For example, when this machine operates as a pump, the drum 37 is turned by the shaft 38 so that the cylinder block 31 is caused to rotate on the journal 32. In this case, by means of the connection of the individual cylinder bores 30 with the

recesses

46 or 47, the input and output of the medium under pressure is controlled. As shown in FIG. 6, with a suitable width of the separating wall 48 at the periphery of the journal 32, the entire diameter of the bores 30 can be used as a control cross-section. As a result, particularly low internal losses are obtained in the piston-type machine. It is noted that there is an absence of conduits to the individual bores 30 for the medium under pressure, which conduits would otherwise, because of the pulsating flow concerned, cause particularly high losses of energy.

Referring to FIG. 3, in order to obtain perfect hydrostatic compensation of the forces occurring in the piston-type machine, by means of which minimum friction and wear of the machine can be achieved, the pistons 33 are provided at the sliding surfaces 35 with compen sation pockets 50. Each pocket 50 is positioned concentrically of the axis of the piston 33 and is connected through a bore 51 with the end face of the piston 33. By means of a suitable choice of the area of the compensation pockets 50, it is possible to obtain axial compensation of the forces acting on the pistons 33.

Referring to FIG. 4, the

channels

44, 45 connect over connecting

bores

52, 52' and 53, with

compensation pockets

54, 54' and 55 respectively formed in the individual bearings. In this way, with suitable dimensioning of the compensation pockets 54, 54 and 55, it is possible to obtain hydrostatic compensation of the forces acting in these bearings independently of the direction in which the machine turns and of the direction in which the medium under pressure flows. As shown, the compensation pockets 54, 54' and 55 are formed at the periphery of the bearing concerned, for example, with two opposite compensation pockets in one bearing.

Referring to FIGS. 4 and 5, in order to compensate for one-sided loading of the journal 32 by hydrostatic forces, segment-like compensation pockets 56 and 56' are provided in the periphery of the journal 32 and extend somwhat less than half of the periphery of the journal 32. The compensation pockets 56, 56' are connected by means of connecting

bores

57, 57 with the

channels

42 and 43 respectively, situated at the other side of the journal 32. These compensation pockets 56, 56' allow perfect compensation of the hydraulic forces which would otherwise have a one-sided action on the journal 32.

In the case of rapid accelerations or rapid retardations of the machine because lateral forces could occur between the pistons 33 and the cylindrical bores 30, caused by mass forces, since such forces can considerably exceed the forces caused by friction between the pistons and support or abutment surfaces, the machine according to FIGS. 3 to 6 is provided with a drive part that serves to absorb these forces. This drive part 60, best seen in FIG. 7, has the form of a cardan cross, and consists of a plate in which two sets of guideways are disposed, perpendicularly of one another. The first is formed of two cut-outs 61 the other of two cut-outs 62. Two blocks 63 which are fastened to the drum 37 are piloted in the cut-outs 62 while two projections 64 from the cylinder block 31 are engaged within the cut-outs 61. The drive part 60 is thus able-to permit radial movements of the cylinder block 31 relative to the drum 37 while preventing relative turning movements therebetween.

Referring to FIGS, 8 to 12, a further form of construction of the piston-type machine is shown. The most important difference, in comparison with the machine of FIGS. 3 to 7 consists in that the eccentricity e, that is, the spacing between the axes A and B, can be varied and in that the journal has a spherical hearing surface 101.

Referring to FIGS. 8 and 12, the journal 100 is connected to an adjusting part 102 in which a screw 103 which can be operated by a hand-wheel is threadably mounted. In addition, the part 102 is piloted in a guideway 104 of the machine housing so as to be displaced only in the plane of the two axes A and B. The guideway 104 is formed in the stationary housing by three

parts

105, 106 and 107. As shown in FIGS. 9 and 12, the adjusting part 102 is provided with

channels

108 and 109 which connect to the

recesses

110 and 111 in the journal 100, and form control ports for the output from and the input into the cylinders of the medium under pressure.

Referring to FIGS. 9, 10 and 12, as the adjustment part 102 is movable, connecting parts 112 are disposed between the housing part 106 and the adjusting part 102. These connecting parts 112 each includes a bore 113 having an elongated mouth 114 and a plane sliding surface 114' at the end which cooperates with a plane sliding surface of the part 102. The connecting parts 112 are sealingly guided in bores in the housing part 106, and are pressed against the slide surfaces of the part 102 by means of springs 112' and also by the hydraulic pressure acting on their end faces. In this way, a perfect connection is retained between the channels in the housing part 106 and in the adjusting part 102, for any position of the adjusting part 102.

Referring to FIGS. 8 ane 9, the annular cylinder block 1 16 has cylindrical bores 117 which extend completely therethrough with a constant diameter. In addition, for installation reasons, the block 116 as split in the radial plane and the two halves of the cylinderblock 116 are clamped tightly together by the lockrings 118. The cylinder block 116 is thus able to move freely to adapt to the spherical slidiing surface 101, so as to prevent binding of the pistons in the bores when the journal 100 bends under a one-sided load. Pistons 115 are guided in the bores 117 and each has a sliding surface 115' for bearing against a support or abutment surface 126 on a drum 120 as above. The drum 120 has a shaft 121 which is mounted in the housing part 105. The drum 120 is fastened to a part 122 similar to the above that has a hollow bearing-pin 123 by which the drum 120 is supported in a bearing-bore in the housing part 106.

Referring to FIGS. 8 and 11, the part 122 is provided with an annular projection 124 which cooperates with a projection 125 on each piston 115 and forms a kind of stop that prevents a lifting of the pistons 115 away from the respective support or abutment surfaces 126 of the drum 120. Such a lifting-off might, for example, become possible during a stoppage of the machine, and could make starting-up again difficult.

Referring to FIGS. 8 ane 9, the machine is also provided with a hydrostatic pressure-compensation in a simple way. For this purpose, compensation pockets 130, 130, 131,131 (FIG. 8) are formed in the housing in the bearingsurfaces for the shaft 121 and pin 123. Each bearing is provided with two segment-like bearing pockets 130, 130', 131 and 131. The bearing pockets of one side are, in each case connected by connecting bores 132 and 132', with the

channel

108 or 109 situated at the same side, for the medium under pressure. As in the machine of FIGS. 3 to 6, provision is made for hydrostatic equalization of pressures to result in practical elimination of friction and of wear of the machine.

For reasons of clarity and of simplification, the drive part for connecting the cylinder block 116 with the drum 120 as discussed above with respect to FIGS. 3 to 7 is not shown. Similarly, the projection for avoiding a lifting of the piston away from the support or abutment surface as discussed with respect to FIGS. 8 to 12, is not shown in FIGS. 3 to 7. It is evident that these elements are not connected with the other characteristics of the form of construction under consideration and may be used independently of one another. Similarly, the hydrostatic pressure equalization for the cylinder block of the design according to FIGS. 8 to 12 by means of compensation pockets in the sliding surfaces 101 can be the same as shown with the FIGS. 3 to 7. The same applies for the axial pressure equalization of the pistons 115.

What is claimed is:

1. A piston-type machine comprising a journal having a longitudinal axis and a spherical bearing surface, channels for the respective input and output of a medium, and control ports in the periphery thereof connected to said channels;

a cylinder block movably mounted on said spherical bearing surface of said journal in the plane of said control ports, and cylinder block having an axis intersecting said axis of said journal;

at least one piston reciprocally mounted in said cylinder block for reciprocating radially of said journal, said piston having a flat surface at an end thereof spaced from said cylinder block;

a housing having a part rotatably mounted about an axis parallel to and spaced eccentrically from said longitudinal axis of said journal, said housing part including a flat abutment surface slidably bearing said flat surface of said piston thereof; and

means for adjusting said journal relative to said housing to vary the eccentricity of said journal relative to said axis of said housing part from one extreme value to another about a zero eccentricity.

2. A piston-type machine as set forth in claim 1 which further includes a stationary housing mounting said journal therein, said housing having an opening therein and said journal having a channel communicating with said opening of said housing; and a connecting part disposed between said channel of said journal and said opening of said housing for conveying a medium therebetween, said connecting part having a slide surface abutting said journal about said channel.

3. A piston-type machine comprising a journal having a longitudinal axis, channels for the respective input and output of a medium, and control ports in the periphery connected to said channels;

a cylinder block rotatably mounted on said journal in the plane of said control ports and having a plurality of bores therein;

a plurality of pistons respectively mounted in said bores of said block for reciprocating radially of said journal, each piston having a flat surface at an end projecting from said block;

a drum rotatably mounted about an axis parallel to and spaced eccentrically from said longitudinal axis of said journal, said drum including a plurality of flat abutment surfaces each slidably receiving a flat surface of a respective piston thereon;

a shaft for rotating said drum;

a drive part connected between said drum and said block to permit relative radial movements between said block and drum during rotation thereof; and

a stationary housing about said drum and wherein said drum includes a hollow bearing pin surrounding said journal and rotatably mounted in said housing, channels in said housing connected to said channels in said journal; bearings about said shaft and said pin of said drum, each bearing including segment-like compensation pockets therein facing said respective shaft and drum; and connection bores extending through said housing from said channels in said housing to said pockets to deliver medium thereto for hydrostatic pressure equalizatron.

Claims

1. A piston-type machine comprising a journal having a longitudinal axis and a spherical bearing surface, channels for the respective input and output of a medium, and control ports in the periphery thereof connected to said channels; a cylinder block movably mounted on said spherical bearing surface of said journal in the plane of said control ports, and cylinder block having an axis intersecting said axis of said journal; at least one piston reciprocally mounted in said cylinder block for reciprocating radially of said journal, said piston having a flat surface at an end thereof spaced from said cylinder block; a housing having a part rotatably mounted about an axis parallel to and spaced eccentrically from said longitudinal axis of said journal, said housing part including a flat abutment surface slidably bearing said flat surface of said piston thereon; and means for adjusting said journal relative to said housing to vary the eccentricity of said journal relative to said axis of said housing part from one extreme value to another about a zero eccentricity.

3. A piston-type machine comprising a journal having a longitudinal axis, channels for the respective input and output of a medium, and control ports in the periphery connected to said channels; a cylinder block rotatably mounted on said journal in the plane of said control ports and having a plurality of bores therein; a plurality of pistons respectively mounted in said bores of said block for reciprocating radially of said journal, each piston having a flat surface at an end projecting from said block; a drum rotatably mounted about an axis parallel to and spaced eccentrically from said longitudinal axis of said journal, said drum including a plurality of flat abutment surfaces each slidably receiving a flat surface of a respective piston thereon; a shaft for rotating said drum; a drive part connected between said drum and said block to permit relative radial movements between said block and drum during rotation thereof; and a stationary housing about said drum and wherein said drum includes a hollow bearing pin surrounding said journal and rotatably mounted in said housing, channels in said housing connected to said channels in said journal; bearings about said shaft and said pin of said drum, each bearing including segment-like compensation pockets therein facing said respective shaft and drum; and connection bores extending through said housing from said channels in said housing to said pockets to deliver medium thereto for hydrostatic pressure equalization.