US3053191A

US3053191A - Gear pumps and like hydraulic machines

Info

Publication number: US3053191A
Application number: US46636A
Authority: US
Inventors: Weigert Wilhelm
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1959-09-15
Filing date: 1960-08-04
Publication date: 1962-09-11
Anticipated expiration: 1979-09-11

Description

Sept. 11, 1962 w. WEIGERT GEAR PUMPS AND LIKE HYDRAULIC MACHINES 2 Sheets-Sheet 1 Filed Aug. 4, 1960 INVENTOR. WILHELM WE/GERT HIS A TTORNEV Sept. 11, 1962 w. WEIGERT 3,053,191

GEAR PUMPS AND LIKE HYDRAULIC MACHINES Filed Aug. 4, 1960 2 Sheets-Sheet 2 Fig.3

INVEN TOR W/LHELM WE/GERT Wsm HIS rron/way United States Patent C) 3,053,191 GEAR PUMPS LIKE HYDRAULIC MACS Wilhelm Weigert, Stuttgart, Germany, assignor to Robert Bosch G.m.b.I-Ii., Stuttgart, Germany Filed Aug. 4, 1960, Ser. No. 46,636 Claims priority, application Germany Sept. 15, 1959 15 Claims. ((31. 103-126) The present invention relates to hydraulic machines in general, and more particularly to hydraulic machines of the type comprising an open-ended casing which is sealable by a cover and which is formed with two bores each adapted to receive a rotary liquid displacing element and two or more bearings for the shaft of the respective liquid displacing element. Many hydraulic gear pumps are typical examples of such machines.

It is already known to center the covers of the above described hydraulic machines by providing in the casing a suitable recess adapted to receive a peripheral flange which forms part of the cover. Alternately, the cover may be centered by the provision of suitable sleeves which are recessed into the casing and each of which is adapted to receive a bolt, these bolts serving as a means for releasably securing the cover to the casing. A disadvantage of such hydraulic machines is that the centering means for the cover must be machined in one or more additional time consuming operations or that the centering is brought about by one or more additional parts which increase the initial cost of the machine, particularly since they must be machined with sufficient precision to avoid any leakage when the machine is in actual use. This holds equally true when the cover is centered by sleeves and bolts as well as when the flange of the cover is received in a recess or groove of the casing which forms the main body portion of the hydraulic machine. In addition, it is rather diflicult to obtain a tight fit between the casing and the flange if one must simultaneously insure that the cover is properly centered with respect to one of the bores provided in the casing for the liquid displacing elements.

An important object of the present invention is to provide a hydraulic machine of the type whose casing is formed with two bores for the reception of liquid displacing elements and bearings which rotatably mount the shafts of the liquid displacing elements, and wherein no separate bores, grooves or recesses must be machined to properly position the cover with respect to the casing.

Another object of the invention is to provide a hy draulic machine of the just outlined characteristics which is constructed and assembled in such a way that the cover is properly centered by partially extending into one of the bores for the liquid displacing elements.

A further object of the invention is to provide a hydraulic machine of the above described type whose construction is such that the means which insures proper axial positioning of the liquid displacing elements simul taneously contributes to proper positioning of the cover.

A concomitant object of my invention is to provide an improved gear pump of the type whose casing is formed with two axially parallel bores, wherein the cover is properly positioned and retained with respect to the casing by extending into at least one of said bores and wherein the cover may contribute to proper sealing and proper axial positioning of the parts normally received in said bores.

With the above objects in view, the invention resides in the provision of a hydraulic machine, such as a gear pump or the like, which comprises essentially an openended body or casing formed with two axially parallel bores each of which receives a liquid displacing element, e.g. a gear, and at least two bearings for rotatably "ice mounting the shaft of the respective liquid displacing element, and a cover or cap which is centered with respect to the casing in a novel way in that the cover comprises a projection which extends into at least one of the aforementioned bores so that the casing need not be machined with a view to properly hold the cover in such position that the open end of the casing is sealed and that the drive shaft connected with one of the liquid displacing elements will be properly centered in a customary bore of the cover.

In accordance with one embodiment of my invention, the projection of the cover engages with a suitably configurated spacer element which is inserted into the casing and simultaneously serves as a means for limiting axial movements of the liquid displacing elements and of their bearings. Alternately, the projection of the cover may be received in a complementary recess provided in the outer bearing or bearings and, since the recessed bearing or bearings are held against rotation with respect to the casing, the cover is also held against angular displacement in a very simple and reliable way.

Certain more specific features of the invention reside in the provision of novel sealing elements which are disposed between the cover and the remaining parts of the hydraulic machine, in the provision of a specific spacer element which insures proper axial positioning of the liquid displacing elements and of the bearings for the shafts of the liquid displacing elements, in the provision of special retaining means for the spacer element, and in the provision of a specific projection on the cover which is adapted to engage with and to be thereby held against angular displacement by the spacer element.

The novel features Which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of two specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal central section through a hydraulic machine embodying one form of my invention;

FIG. 2 is a section taken along the line IIII of FIG. 1, as seen in the direction of the arrows; and

FIG. 3 is a longitudinal central section through a slightly modified hydraulic machine.

Referring now in greater detail to the illustrated embodiments, and first to FIGS. 1 and 2, there is shown a hydraulic machine in the form of a gear pump P which comprises an open-ended body or casing 1 formed with two axially parallel blind bores 2, 2' whose diameters are such that they overlap in a central zone 3 indicated in phantom lines in FIG. 2. The bottom or rear portions of bores 2, 2' receive a first bearing in the form of a journal box 4 which preferably assumes the shape of the numeral 8 and is adjacent to the bottom wall 1a of the pump body 1. A similar second hearing or journal box 4' is inserted into the bores 2, 2' close to the end face 30 at the open end of the pump body 1 so that the journal boxes 4, 4' define therebetween a space for a driving spur gear 7 and for a meshing driven spur gear 8. The driving gear 7 is mounted on a comparatively long input or drive shaft 5 which is rotatably mounted in aligned

bores

4a, 4a of the journal boxes 4, 4', respectively. The driven gear 8 is mounted on an idler shaft 6 which is rotatably received in a second set of aligned

bores

4b, 4b respectively provided in the journal boxes 4 and 4'. The idler shaft 6 extends only to the front end face 23 of the outer journal box 4 while the drive shaft 5 projects beyond the end face 23 and through a suitable bore or opening 12 provided in the cover 9. FIG. 1 shows that the outer journal box 4 is slightly spaced from the cover 9. As is well known in the art, the outer or forward end of the drive shaft 5 carries a driving gear element 5;: which, is rotated by another gear element, not shown, the latter receiving rotary motion from the crankshaft of an internal combustion engine if the gear pump P isutilized as an oil pump in an automotive vehicle or the like. The

gears

7, 8 constitute two cooperating liquid displacing elements, the liquid being introduced at one side of their intermeshing teeth and being discharged at a higher pressure at the other side.

The outer journal box 4 is axially shiftable in the bores 2, 2' and is retained in a requisite axial position in a novel manner as will be fully explained hereinafter. The cover 9 has a substantially ring shaped projection 10 which fits into a free space left by the bearing 4' at the outer end of the bore 2 and which abuts against the wall bounding the free space in this bore. This projection is interrupted atits side adjacent to the bore 2 so as to define a space for the reception of a plate like spacer element 11, this spacer element constituting a means for retaining the journal box 4' in a given axial position. As clearly shown in FIG. 2, the projection 10 extends into the non-overlapped portion of the bore 2. The spacer element 11 is of uniform thickness and has a substantially rectangular contour. Its longitudinal end faces 17, 17' are formed with concave recesses 18, 18' for the

shafts

5, 6, respectively. Also, in order to be properly received in the space defined by the projection 10, the spacer elemeat 11 is formed with rounded corner portions 19 two of which abut against the projection 10 when the spacer element assumes the position of FIG. 2. The curvature of all four corner portions 19 is the same so that the spacer element 11 may be turned through 180 degrees and will again fit into the space formed by the projection 10. Adjacent to each of its rounded corner portions 19, the spacer element is formed with inwardly oriented arcuate faces 21 whose curvature equals the curvature of bores 2, 2 so that two of these faces abut against the Wall of the bore 2 and the other two faces abut against the wall of the bore 2'. It will-be noted that the arcuate faces 21 are provided in the transverse end faces of the spacer element 11. Between each pair of adjacent faces 21, there is provided a convex face 22 which abuts against the adjacent wall portion of a complementary concave boring 22' formed for the spacer element 11 in the body 1. Thus, the spacer element 11 is positively retained against rotation with respect to the pump body 1 by partially extending into the bores 2, 2' (faces 21) and by being received in the boring 22 (faces 22). Owing to the symmetric arrangement of the

faces

21, 22 and of the wall portions in the boring 22, the spacer element '11 may be turned through 180 degrees to be again received in the pump body in a position as shown in FIG. 2. Itwill be readily understood that the cover 9 is immediately centered with respect to the pump body 1 as soonlas its projection 10 is received in the bore 2 because the rounded corner portions 19 of the spacer element prevent any angular displacements of the projection 1t}. Thus, no special bores must be provided for centering of the cover 9'because the latter may be centered right in the bore 2 whose main purposeisto receive the driving gear 7 and certain portions of the journal boxes 4, 4'.

As stated before, in addition to properly retaining the cover 9 in centered position, the spacer element llalso serves asa means for controlling the axial movements of the outer journal box 4'. In other Words, the plate like element 11 serves as-a means for compensating for eventual inaccuracies in the axial length of thebores 2, 2', in thethickness or axial length of the

journal boxes

4, 4, land in the axial length of the

gears

7, 8. A certain amount of axial play must be provided for the outer journal box 4', and the extent of this axial play is controlled by the plate 11. In order to enable an operator to rapidly assemble the pump P, it is preferred to manufacture the spacer elements 11 in a series of different thicknesses so that one can rapidly locate the spacer element of requisite thickness such as will permit just the right amount of axial play for the journal box 4. Of course, it is equally possible to utilize two or more comparatively thin spacer elements instead of a single spacer element 11.

The central portion of the front end face 23 of the journal box 4 is formed with a groove 23a which preferably assumes the shape of the numeral eight and receives an elastic sealing ring 25 which bears against the rear side 27 of the spacer element 111 and seals the outer end of a pressure chamber 26. In other words, the ring 25 seals the hydraulic pressure chamber 26 from a space 26a formed between the cover 9 and that portion of the journal box 4' which surrounds the spacer element 11. The chamber 26 communicates with a channel 28 leading to the pressure side of the pump P so that the pressure prevailing at the pressure side of the pump is communicated to the chamber 26 to tightly press the journal boxes 4, 4' against the

gears

7, 8 when the pump is in operation. This is a self-sealing feature which is brought about in a fully automatic Way whenever the pump P is in actual use.

The outwardly projecting portion of the drive shaft 5 is sealingly received in a special elastic sealing ring 13 which is inserted into the bore 112 from the rear or inner side of the cover 9 and abuts against an internal shoulder 12 provided in the bore 12. The annular outer portion 14 of the sealing ring 13 assumes the shape of an elastic circular sleeve whose inner side bears against a metallic stiifenin g annulus 15 formed with sharp edges and whose outer side bears against a cylindrical wall 16 of the bore 12. The cylindrical wall 16 extends between the shoulder 12' and the rear or left-hand side of the cover 9, as viewed in FIG. 1. The sealing ring 13 further comprises an elastic annular lip 13a which is in sealing engagement with the periphery of the shaft 5 and which, together with the sleeve 14, defines an annular compartment for the stiffening annulus 15. The annulus 15, the annular outer portion 14 and the annular lip 13a insure that the bore 12 is properly sealed even if the drive shaft 5 has a certain amount of radial play with respect to the cover 9.

The plane front end face 30 'of the pump casing 1 is formed with a groove 30a for a further sealing ring 29 which bears against the rear side of the cover 9 and constitutes an outer seal for the space 26a formed between the cover 9 and the journal box 4. The remaining openings leading into this space 26a are sealed by the

aforementioned sealing elements

13 and 25.

The pump P is assembled as follows:

In the first step, the operator inserts the inner journal box 4, the

shafts

5, 6 with the

gears

7, 8, respectively, and the outer journal box 4'. In the next step, the sealing ring 29 is inserted into the groove 30a, followed by the sealing ring 25 which is placed into the groove 23a, and by the spacer element 11 which then assumes the position of FIG. 2 and abuts against the exposed side of the sealing ring 25. As stated before, the spacer element 11 automatically assumes a position as shown in FIG. 2 because its faces 21, 22 come into abutment with the walls of thebores 2, 2' and with the wall portions of the boring 22', respectively. In fact, this is the only way of inserting the spacer element 11 into the pump body 1. As fully explained hereinabove, the thickness of the spacer element 11 is selected in such a way that it peronly a given axial play for the parts received in the bores 2 and 2, i.e. the spacer element 11 must cause a certain compression of the ring 25 so that this ring will properly seal the pressure chamber 26 even if the pump P is not in actual use and no pressure prevails in the chamber 26. Thus, the plate like spacer element 11 and the elastic ring 25 will exert a centainpressure against the journal box 4 which presses the

gears

7, 8 against the other journal box 4, but the member 4' is still free to float to a given extent in the bores 2, 2'.

In the next step, the operator inserts the sealing ring 13 into the bore 12 of the cover 9 so that the ring comes into abutment with the shoulder 12' and that the elastic sleeve 14 bears against the cylindrical wall 16. The ring 13 is then forced over the outwardly projecting portion of the drive shaft 5 until the projection enters the outer end of the bore 2 to assume the position of FIG. 2 in which it abuts against two rounded corner portions 19 of the spacer element 11. Thus, the cover 9 is now properly centered with respect to the pump body 1 and may be secured thereto by a series of headed bolts 9a extending into tapped bores 1b formed in the pump body. This completes the assembly of the gear pump P.

It will be readily understood that the means for holding the spacer element 1-1 in the pump body 1 may assume a number of forms other than that described in connection with FIGS. 1 and 2. For example, the boring 22' may be replaced by inwardly extending pins, studs or lugs receivable in complementary cutouts provided in the transverse end faces of the spacer element 11. Such complementary cutouts then replace the inclined faces 21 and the convex faces 22.

The improved centering arrangement for the cover of a hydraulic machine is equally useful in such types of pumps wherein each of the S-Shaped journal boxes 4, 4' is replaced by two cylindrical or nearly cylindrical bearing sleeves. As is shown in FIG. 3, a modified hydraulic machine P comprises an open-ended casing or body 45 which is formed with two partially overlapping axially parallel blind bores 39, 39'. The bore 39 receives a nearly cylindrical bearing sleeve 31a, a driving gear 7, and a second nearly cylindrical bearing sleeve 31. The other bore 39' receives a nearly cylindrical bearing sleeve 31a, a driven gear 8, and a further nearly cylindrical bearing sleeve 31. The driving gear 7 is mounted on an outwardly extending drive shaft 42 which is coaxially received in the aligned bores of the bearing

sleeves

31, 31a. The idler shaft 6 of the driven gear 8 is rotatably received in the bearing sleeves 31', 31a. The

sleeves

31, 31' and 31a, 31a are formed with abutting fiat peripheral faces 31b, 31b, respectively, which prevent angular displacements of these sleeves in the bores 39 and 39'. The front end faces 33, 33 of the outer bearing sleeves 31, 31' are formed with

annular grooves

34, 34 for elastic sealing O-

rings

35, 35, respectively. The rings 35, 35' constitute the innermost barriers of two annular

hydraulic pressure chambers

36, 36", respectively. It will be noted that the ring 35 surrounds and is spaced from the shaft 42, and that the other ring 35' is mounted in similar fashion with respect to the shaft 6. The cover 32 is formed at its inner or rear side 37 with a rearwardly extending projection 38 which extends into a free space left by the bearing 31 at the outer end of the bore 39 so that the annular groove 34 and the 'O-ring 35 are surrounded by this projection, i.e. the diameter of the projection 38 is greater than the diameter of the ring 35.

The pressure chambers 36, 36', are connected with the pressure side of the pump P in a manner not shown in the drawing. The cover 32 is formed with an inclined channel 40 which connects a compartment 40a With an axial bore 5a formed in the idler shaft 6 to relieve the pressure at the inner side of the sealing ring 41, the latter surrounding the drive shaft 42 and received in a suitable bore or opening 43 of the cover 32. The sealing ring 41 is somewhat similar to the sealing ring 13 with the exception that it is inserted into the bore 43 from the outer or front side of the cover. The compartment 40a is defined by the wall 43a surrounding the smaller-diameter rear portion of the bore 43, by the periphery of the driving shaft 42, by the sealing ring 41, and by a portion of the front end face 33 of the bearing sleeve 31.

The cover 32 is held against rotation by the bearing sleeve 31 whose front end face 33 is formed with an arcuate recess 33a for the projection 38. The projection 38 is of annular shape with an outer diameter corresponding to the diameter of the bore 39' but does not form a complete annulus so that, when received in the complementary recess 33a, it prevents the cover from angular displacement about the drive shaft 42 and with respect to the pump body 45. Thus, as soon as the projection 38 is received in the recess 33a, the cover 32 is properly positioned with respect to the pump body 45 and may be secured thereto in a manner as shown in FIG. 2.

The plane inner side 37 of the cover 32 is parallel with the plane front end face 44 of the casing 45, i.e. the sealing ring 46 in the front end face 44 and the sealing rings 35, 35' abut against a pair of parallel surfaces.

It will be noted that the bearing sleeve 31 performs the function of the spacer element 11 by engaging with the projection 38 and by holding this projection against rotation with respect to the pump body 45. Of course, by engaging the projection 38, the bearing sleeve 31 simultaneously prevents angular displacements of the cover 32.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications Without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a hydraulic machine, in combination, a casing having an open end and a pair of bores extending inwardly from said open end, said casing comprising wall means bounding said bores; a liquid displacing element rotatably received in each of said bores, each liquid displacing element having a shaft; bearing means received in each of said bores for rotatably mounting said shafts, said bearing means having peripheral surface means and at least a portion of said peripheral surface means located entirely within and abutting against the respective Wall means for locating said bearing means against transverse movements in said bores, said bearing means leaving within at least one of said bores a free space along the Wall means bounding said one bore and said free space adjacent to the open end of said casing; and a cover sealingly connected with said casing, said cover having a projection extending into said free space and abutting against the wall means bounding said free space for locating the cover with respect to said casing, said cover and said projection thereof spaced from the peripheral surface means of the bearing means in said one bore.

2. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel bores extending inwardly from said open end, said casing comprising wall means bounding said bores; a first liquid displacing element rotatably received in one of said bores; a second liquid displacing element rotatably received in the other bore; a shaft connected with each of said liquid displacing elements, the shaft of said first liquid displacing element extending beyond the open end of said casing; bearing means received in each of said bores for rotatably mounting said shafts, said bearing means having peripheral surface means and at least a portion of said peripheral surface means located entirely within and abutting against the respective Wall means for locating said bearing means against transverse movements in said bores, said bearing means leaving within at least one of said bores a free space along the wall means bounding said one bore and said free space adjacent to the open end of said casing; and a cover sealingly connected with and adjacent to the open end of said casing, said cover formed with an opening for loosely receiving the shaft of said first liquid displacing element and the cover comprising a projection extending into said free space and abutting against the wall means bounding said free space for locating the cover with respect to said casing, said cover and said projection thereof spaced from the peripheral surface means of the bearing means in said one bore.

3. In a hydraulic machine, in combination, a casing having an open end and a pair of overlapping axially parallel bores extending inwardly from said open end, said casing comprisingwall means bounding said bores; a first liquid displacing element rotatably received in one of said bores; a second liquid displacing element rotatably received in the other bore and engaging with said first liquid displacing element; a shaft connected with each of said liquid displacing elements, the shaft of said first liquid displacing element extending beyond the open end of said casingg bearing means received in each of said bores for rotatably mounting said shafts, said bearing means having peripheral surface means and at least a portion of said peripheral surface means located entirely within and abutting against the respective wall means for locating said bearing means against transverse movements in said bores, said bearing means leaving within .at least one of said bores a free space along the wall means bounding said one bore and said free space adjacent to the open end of said casing; a cover sealingly connected with and adjacent to the open end of said casing, said cover formed with an opening for loosely receiving the shaft of said first liquid displacing element and the cover comprising a projection extending into said free space and abutting against the wall means bounding said free space for locating the cover with respect to said casing, said cover and said projection thereof spaced from the peripheral surface means of the bearing means in said one bore; and an elastic sealing ring received in said opening, the elasticity of said sealing ring being such that the latter seals said opening despite a limited radial play of said last mentioned shaft.

4. In a hydraulic machine, in combination, a casing having an open end and a pair of partially overlapping axially parallel bores extending inwardly from said open end, said casing comprising wall means bounding said bores; a first liquid displacing element rotatably received in one of said bores; a second liquid displacing element rotatably received in the other bore; a shaft connected with each of said liquid displacing elements, the shaft of said first liquid displacing element extending beyond the open end of said casing; bearing means received in each of said bores for rotatably mounting said shafts, said bearing means having peripheral surface means and at least a portion of said peripheral surface means located entirely within and abutting against the respective wall means for locating said bearing means against transverse movements in said bores, said bearing means leaving within at least one of said bores a free space along the ,wall means bounding said one bore and said free space adjacent to the open end of said casing; and a cover sealingly connected with and adjacent to the open end ofsaid casing, said cover formed with an opening for loosely receiving the shaft of said first liquid displacing element and the cover comprising a projection extending into said free space and abutting against the wall means bounding said free space for locating the cover with respect to said casing, said cover and said projection thereof spaced from the peripheral surface means of the bearing means in said one bore.

5. In a hydraulic machine, in combination, a casing having an open end, a bottom Wall opposite said open end and formed with a pair of partially overlapping axially parallel constant-diameter bores extending inwardly from said open end toward said bottom wall; first bearing means inserted into said bores and adjacent to said bottom wall; second bearing means inserted into said bores and having end face means adjacent to the open end of said casing; a'first liquid displacing element rotatably received in one of said bores between said first and second bearing means and comprising a shaft rotatably mounted in said first and second bearing means; a second liquid displacing element rotatably received in the other bore between said first and second bearing means and engaging with said first liquid displacing element, said second liquid displacing element having a shaft rotatably mounted in said first and second bearing means; a cover sealingly connected with the open end of said casing, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of said bores; and first and second sealing ring means disposed between the end face means of said second bearing means and said cover, said first sealing ring means surrounding the shaft of said first liquid displacing element, said second sealing ring means surrounding the shaft of said second sealing element, and at least one of said sealing ring means disposed within said projection. i

6. In a hydraulic machine, in combination, a casing having an open end, a bottom wall opposite said open end and formed with a pair of partially overlapping axially parallel constant-diameter bores extending inwardly from said open end toward said bottom wall; first bearing means inserted into said bores and adjacent to said bottom wall; second bearing means inserted into said bores and having end face means adjacent to the open end of said casing; a first liquid displacing element rotatably received in one of said bores between said first and second bearing means and comprising a shaft rotatably mounted in said first and second bearing means; a second liquid displacing element rotatably received in the other bore between said first and second bearing means and engaging with said first liquid displacing element, said second liquid displacing element having a shaft rotatably mounted in said first and second bearing means; a cover sealingly connected with the open end of said casing, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of said bores; and first and second sealing ring means received in annular grooves formed in the end face means of said second bearing means and sealingly engaging with said cover, said first sealing ring means surrounding the shaft of said first liquid displacing element, said second sealing ring means surrounding the shaft of said second sealing element, and at least one of said sealing ring means disposed within said pro ection.

7. In a hydraulic machine, in combination, a casing having an open end, a plane end face at said open end, a bottom wall opposite said open end, and formed with a pair of partially overlapping axially parallel constantdiameter bores extending inwardly from said open end toward said bottom wall; a first bearing sleeve inserted into each of said bores adjacent to said bottom wall; a second bearing sleeve inserted into each bore and each said second bearing sleeve having an end face adjacent to the open end of said casing; a first liquid displacing element rotatably received between the first and second bearing sleeves in one of said bores, said first liquid displacing element having a shaft rotatably mounted in said last mentioned first and second bearing sleeves; a second liquid displacing element rotatably received between the first and second bearingsleeves in the other bore and engaging with said first liquid displacing element, said second liquid displacing element having a shaft rotatably mounted in saidlast mentioned first and second bearing sleeves; a cover sealingly connected with the open end of and abutting against the end face of said casing, said cover having a centering projection snugly received in at least 9 a one of said bores for properly positioning the cover with respect to said casing and said cover having a plane inner side adjacent to the end faces of said second bearing sleeves and parallel with the end face of said casing, said projection extending to both sides of the plane common to the axes of said bores; and first and second sealing ring means each disposed between the end face of one of said second bearing sleeves and the inner side of said cover, said first sealing ring means surrounding the shaft of said first liquid displacing element and said second sealing ring means surrounding the shaft of said second liquid displacing element.

8. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengaging liquid displacing elements each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing; and at least one rigid spacer element disposed between said outer bearing means and said cover.

9. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengaging liquid displacing elements each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of said bores; and at least one rigid spacer element disposed between said outer bearing means and said cover, said casing and said spacer element formed with means for holding the spacer element against angular displacement with respect to said casing.

*10. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengaging liquid displacing elements each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of said bores; a rigid spacer element disposed between said outer bearing means and said cover, said spacer element and said outer bearing means defining a hydraulic pressure chamber therebetween; and an elastic sealing ring received in a recess formed in said outer bearing means and sealingly engaging with said spacer element, said sealing ring surrounding said pressure chamber.

11. In a gear pump, in combination, a casing having an open end and a pair of axially parallel constant-diameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said a 10 t bores adjacent to said open end; a pair of mating liquid displacing spur gears each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means, one of said shafts extending beyond the open end of said casing; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover formed with an opening for loosely re ceiving said one shaft and the cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of the bores in said casing; and at least one rigid spacer element disposed between said outer bearing means and said cover.

12. In a hydraulic gear pump, having an open end and a pair of partially overlapping axially parallel bores extending inwardly from said open end, said casing comprising wall means bounding said bores; a liquid displacing spur gear rotatably received in each of said bores, each gear having a shaft with one of said shafts projecting beyond the open end of said casing; bearing means received in each of said bores for rotatably mounting said shafts, said bearing means having peripheral surface means and at least a portion of said peripheral surface means located entirely within and abutting against the respective wall means for locating said bear-ing means against transverse movements in said bores, said bearing means leaving within at least one of said bores a free space along the wall means bounding said one bore and said free space adjacent to the open end of said casing; and a cover sealingly connected with said casing, said cover formed with an opening for loosely receiving said one shaft and the cover having a substantially ring shaped projection extending into said free space and abutting against the Wall means bounding said free space for locating the cover with respect to said casing, said cover and said projection thereof spaced from the peripheral surface means of the bearing means in said one bore.

13. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengaging liquid displacing elements each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of the bores in said casing; and at least one rigid spacer element disposed between said outer bearing means and said cover, said spacer element received in a boring formed in said casing between said shafts and engaging with said projection for holding the cover against angular displacement with respect to said casing.

14. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengaging liquid displacing elements each received in one of said bores bet-ween said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casing and slightly spaced from said outer bearing means, said cover having a projection snugly received in at least one of said bores for locating the cover with respect to said casing, said projection extending to both sides in combination, a casing of the plane common to the axesof said bores; and at least one rigid spacer element disposed between said outer hearing means and said cover, said spacer element for-med with recesses for said shafts and having inclined faces engaging with the walls of said bores.

15. In a hydraulic machine, in combination, a casing having an open end and a pair of axially parallel constantdiameter bores extending inwardly from said open end; inner bearing means received in said bores and distant from said open end; outer bearing means received in said bores adjacent to said open end; a pair of interengagaging liquid displacing elements each received in one of said bores between said inner and outer bearing means and each having a shaft rotatably mounted in said bearing means; a cover sealingly connected with the open end of said casingand slightly spaced from said outer bearing means, said cover having a ring shaped projection snugly received in one of said bores for locating the cover with respect to said casing, said projection extending to both sides of the plane common to the axes of said bores; and a substantially rectangular plate like spacer element 12 disposed between said outer bearing means and said cover, said spacer element having rounded corner portions with two of said corner portions engaging and holding said projection against angular displacement with respect to said casing.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,534 Johnson Dec. 23, 1952 2,816,510 Jarvis Dec. 17, 1957 2,824,524 Banker Feb. 25, 1958 2,842,066 Hilton July 8, 1958 2,986,096 Booth et a1. May 30, 1961 FOREIGN PATENTS 523,969 Italy Apr. 19, 1955 546,795 Italy Aug. 1, 1956 552,057 Belgium Nov. 14, 1956 567,301 Belgium May 14, 1958 1,140,520 France Mar. 4, 1957 1,216,737 France Nov. 30, 1959