EP2711552B1 - Geared machine with low pressure connection deviating from the circular form - Google Patents

Description

The invention relates to a gear machine according to the preamble of claim 1.

From the DE 10 2009 012 853 A1 is a gear machine known, which can be operated as a pump or as a motor. The gear machine comprises two meshing with each other in external engagement gears, which are surrounded by a housing. The housing has opposite a high and a low pressure port.

When the gear machine is operated as a pump, one of the gears is rotated, for example, with an electric motor in rotary motion, wherein pressurized fluid, in particular hydraulic oil, flows from the low to the high pressure port. When the gear machine is operated as a motor, the pressurized fluid flows from the high to the low pressure port, thereby causing the gears to rotate.

The low-pressure connection has a constant cross-sectional shape in the direction of a central axis, which is circular. The corresponding circle diameter is attempted to be as large as possible at the low-pressure connection so that low flow velocities of the pressure fluid occur there. This avoids cavitation at the low-pressure connection, especially for pumps with high-speed gears.

The diameter of the low-pressure connection can only be increased so far as there is still a sufficient seal between the high and the low pressure connection is given to the tooth tips of the gears.

In this context, reference should be made to the pressure equalization bevel on the bearing bodies. The bearing bodies are arranged on both sides next to the gears and are pressed by the pressure fluid sealingly against the side surfaces of the gears. The gears are mounted with circular cylindrical bearing pin in the bearing bodies. The bearing body on one side of the gears may be integrally formed, but it is equally conceivable to assign each gear a separate part of the bearing body.

Each gear is associated with at least one Druckausgleichsfase on the bearing bodies, which is arranged opposite to the side surfaces of the gears and the inner peripheral surface. The inner peripheral surface is the surface against which the tooth tips of the gear wheels sealingly abut. The pressure equalization bevel extends from the high pressure port towards the low pressure port. In all interdental spaces of the gears, which are the Druckausgleichsfase opposite, there is therefore the pressure at the high pressure port, so that the gears are pressed with a good predictable force sealing against the inner peripheral surface of the housing in the region of the low pressure port to effect a seal there.

When dimensioning the diameter of the low-pressure connection, it must be ensured that there is no fluid exchange connection between the pressure equalization phase and the low-pressure connection in any rotational position of the gears via the interdental spaces.

From the DE 10 2007 031 909 A1 is another gear machine known. The low-pressure port, referred to as the inlet, extends into the region of the casing-gear wrap.

The object of the invention is to avoid at high-speed gear machines, especially pumps, cavitation at the low-pressure connection or to use only at higher speeds of the gears.

According to the independent claim, this object is achieved in that both gears on the inner peripheral surface of the housing is associated with an imaginary boundary line which intersects the end of the Druckausgleichsfase, wherein it is parallel to the line of contact between the tooth tips of the gears and the inner peripheral surface, wherein the cutting edge between the two boundary lines is arranged, wherein the minimum distance between the cutting edge and the boundary lines is at least one pitch of the gears, wherein the cross-sectional shape of the low pressure port deviates from the circular shape such that its cross-sectional area covering the gears is greater than the cross-sectional area of an imaginary one covering the gears circular low pressure port, which has the same minimum distance to the boundary lines. As far as a gear two Druckausgleichsfasen are assigned, they are preferably designed so that they define the same boundary line. If this is not the case in exceptional cases, then the boundary line which has the smallest distance to the low-pressure connection is decisive.

The proposed gear machine has a low-pressure port, which has a larger cross-sectional area than the prior art. As a result, the flow velocities are reduced at the low pressure port, so that cavitation occurs only at higher speeds of the gears.

It should be noted that said minimum distance along the inner peripheral surface of the housing is measured, namely in the circumferential direction with respect to the axis of rotation of the respective gear. The same applies to the pitch of the gears, so the distance between two tooth heads, too.

In the dependent claims advantageous refinements and improvements of the invention are given.

The cross-sectional shape of the low-pressure connection may be formed so that the cutting edge has a constant distance to the associated boundary line.

This results in a low-pressure connection, which has the largest possible cross-sectional area.

The cross-sectional shape of the low pressure port may include two first straight lines each extending substantially parallel to an associated boundary. The first straight lines can be made much simpler than the ideal cross-sectional shape described above. As far as helical gears are used, the cutting edge between the inner peripheral surface and the low-pressure connection no longer runs exactly parallel to the boundary lines. However, the deviation is so small that no appreciable deterioration in terms of cavitation formation is to be feared. When even toothed gears are used, the ideal state proposed above is realized.

The two first straight lines may be connected by at least one, preferably two, second straight lines which run in alignment with the side surfaces of the toothed wheels. This results in the largest possible cross-sectional area of the low-pressure connection.

The two first straight lines can be connected to one another by at least one, preferably two, circular arcs. This cross-sectional shape is preferably used when a standardized flange is provided at the low pressure port outside the housing, which is provided for a circular passage opening for the pressurized fluid. The larger of said arcs is preferably formed in alignment with the standardized circular passage opening, in particular having the same radius.

The cross-sectional shape of the low pressure port may have rounded corners, so that it can be easily manufactured with an end mill. The radius of the corners corresponds to the radius of the end mill.

The cross-sectional shape of the low-pressure connection can be formed by a plurality, preferably two or three, intersecting circles which offset one another Have midpoints. As a result, compared to the cross-sectional shapes described above, a further simplification of the production is to be achieved. In particular, it is intended to produce said circles by separate drilling operations, wherein the axis of rotation of the respective drill are offset from each other. With the preferred two or three holes already a significant improvement in cavitation tendency can be achieved.

The low-pressure connection can cover at least one bearing body. For the function of the gear machine, it is harmless if the low-pressure connection covers the bearing body. Although this does not directly improve the cavitation behavior can be achieved. However, it is easier to approach the cross-sectional shape of the low pressure port in the area of the gears optimally to the boundary lines.

Fig. 1

einen Längsschnitt einer erfindungsgemäßen Zahnradmaschine;

Fig. 2

einen Querschnitt einer erfindungsgemäßen Zahnradmaschine;

Fig. 3

eine grobschematische Vorderansicht der Zahnräder und der Lagerkörper, wobei die ideale Form des Niederdruckanschlusses gezeigt ist;

Fig. 4

eine Vorderansicht des Niederdruckanschlusses gemäß einer ersten Ausführungsform der Erfindung;

Fig. 5

eine Vorderansicht des Niederdruckanschlusses gemäß einer zweiten Ausführungsform der Erfindung; und

Fig. 6

eine Vorderansicht des Niederdruckanschlusses gemäß einer dritten Ausführungsform der Erfindung.

The invention will be explained in more detail below with reference to the accompanying drawings. It shows:

Fig. 1

a longitudinal section of a gear machine according to the invention;

Fig. 2

a cross section of a gear machine according to the invention;

Fig. 3

a rough schematic front view of the gears and the bearing body, wherein the ideal shape of the low pressure port is shown;

Fig. 4

a front view of the low pressure port according to a first embodiment of the invention;

Fig. 5

a front view of the low pressure port according to a second embodiment of the invention; and

Fig. 6

a front view of the low pressure port according to a third embodiment of the invention.

Fig. 1 shows a longitudinal section of a gear machine 10 according to the invention. The gear machine 10 comprises a housing 20, which consists of a main body 30; a drive cover 21 and an end cover 22 is composed, which preferably consist of aluminum or gray cast iron. The drive and the end cover 21; 22 abut on flat end surfaces at the opposite ends of the main body 30, wherein at the end faces O-rings 24 are provided made of an elastomer, so that no pressure fluid can escape from the corresponding joint. The drive and the end cover 21; 22 are aligned over cylindrical pins 26 relative to the main body 30 and screwed (not shown) with these bolts firmly.

In the housing 20, two gears 50 are rotatably received with respect to an associated axis of rotation 51, wherein the gears 50 mesh with each other in external engagement. The aforementioned axes of rotation 51 run parallel to one another. The gears 50 are present helically toothed, but they can also be formed straight toothed. It should be noted that the invention underlying Kavitationsproblematik occurs primarily in helical gears.

The two gears 50 have on both sides of a circular cylindrical bearing pin 52 which is rotatably mounted in a bearing shell 61 made of a sliding bearing material such as brass or bronze, wherein the bearing shell 61 is in turn firmly received in an associated bearing body 60 made of steel. In the present embodiment, each bearing pin 52 is associated with a separate part of the bearing body 60, wherein two adjacent parts abut each other on flat surfaces and are aligned by means of a cylindrical pin 26 to each other. The bearing body 60 may also be integrally formed. The bearing bodies 60 are pressed by the pressure of the pressurized fluid, for example hydraulic oil, in the gear machine 10 against the flat side surfaces 55 of the gears 50 to effect a lateral sealing of the gears 50. The pressurized fluid acts In this case, in a pressure field on the bearing body 60, which is bounded by an associated axial seal 62.

One of the bearing journals 52 of a toothed wheel 50 is formed integrally with a drive pin 53 which projects out of the housing 20 through the drive cover 21. The corresponding passage opening is sealed with a radial shaft sealing ring 25, so that no pressure fluid can escape. The drive pin 53 can be rotatably connected, for example, with the drive shaft of an electric motor (not shown) when the gear machine 10 is operated as a pump.

The inner circumferential surface 31 of the main body 30 has a constant cross-sectional shape along the axes of rotation 51 prior to the run-in process, which is adapted to the circular cylindrical tip diameter of the gears 50 with very little play.

Next is on the pressure equalization bevel 64 at the in Fig. 1 indicate left bearing body 60. The pressure equalization land 64 is disposed opposite to the side surface 55 of an associated gear 50 and opposite to the inner peripheral surface 31 of the housing 20.

Fig. 2 shows a cross section of a gear machine according to the invention 10. The high and the low pressure port 32; 33 are disposed opposite to the housing 20, having a common center axis 34 along which they have a constant cross-sectional shape. The high-pressure port 32 preferably has a circular cross-sectional shape, wherein the cross-sectional shape of the low-pressure port 33 deviates according to the invention from the circular shape.

The already mentioned pressure compensating bevel 64 extends from the high pressure port 32 in the direction of the low pressure port 33. It has an end 65 which is arranged at a distance from the low pressure port 33. In the interdental spaces 54, which are arranged in the region of the pressure equalization bevel 64, there is therefore everywhere a pressure equal to the pressure at the high pressure port 32. In the remaining interdental spaces there is a lower pressure, resulting in As a result, the gears 50 are acted upon by a hydraulic force 84, which presses its tooth tips 56 against the inner circumferential surface 31 of the housing 20 in a sealing region 11 on the low-pressure connection 34. Only there takes place at the tooth tips 56 a sealing contact with the housing 20. The remaining tooth tips 56 run with a small distance to the inner peripheral surface 31 to the housing 20 so that there pressure fluid between the interdental spaces 54 can be replaced.

The Druckausgleichsfase 64 may be present as shown only on one side of the gears 50, but it may also be provided on both sides of the gears 50. In the latter case is to be considered in helical gears 50 that the two pressure equalization bevels 64 must be designed to have different lengths, so that they end at the same tooth of the associated gear 50.

Fig. 3 shows a rough schematic front view of the gears 50 and the bearing body 60, wherein the ideal shape of the low pressure port 33 is shown. The viewing direction is parallel to the central axis of the low-pressure connection 33, so that its cross-sectional shape coincides with the cutting edge 85 with the inner peripheral surface of the housing.

The two imaginary boundary lines 80 run parallel to the helical contact lines 83 between the tooth tips of the gears 50 and the inner peripheral surface of the housing. The boundary lines 80 therefore extend on the inner peripheral surface of the housing. The border lines 80 each begin at the end 65 of an associated pressure equalization bevel 64 on the bearing body 60.

The cross-sectional shape of the low-pressure connection 33 runs parallel to these in the region of the boundary lines 80. The minimum distance 81 from the boundary lines 80 is therefore the same everywhere, so that a maximum cross-sectional area of the low-pressure connection 33 covering the toothed wheels results. This cross-sectional area is in Fig. 3 hatched marked and marked with the reference numeral 79.

Incidentally, the cross-sectional shape of the low pressure port 33 is aligned with the side surfaces 55 of the gears 50. In gears 50 with a very large helix angle, it may happen that the low pressure port 33, the in Fig. 3 right side surface 55 of the gears 50 no longer covered.

Next is in Fig. 3 an imaginary low-pressure port 82 is shown, which has the same minimum distance 81 to the boundary lines 80. The corresponding circle 82 covers the bearing bodies 60, the corresponding surface section 78 not counting the cross-sectional area 79 covering the toothed wheels 50. As can be readily appreciated, the fraction of the hatched area 79 detected by the circle 82 is significantly smaller than the hatched area 79 itself, so that the condition according to the characterizing portion of claim 1 is satisfied.

The minimum distance 81 between the low pressure port 33 and the boundary line 80 is at least one pitch (No. 57 in FIG Fig. 2 ) of the gears, wherein it is preferably selected to be slightly larger, so that regardless of the rotational position of the gears at least one tooth head completely rests against the inner peripheral surface of the housing. By increasing the minimum distance to slightly more than two or three pitches, the internal seal of the gear machine can be improved.

Fig. 4 shows a front view of the low pressure port 33 according to a first embodiment of the invention. The viewing direction is parallel to the central axis of the low pressure port 33. The two boundary lines 80 and the two side surfaces 55 of the gears are shown by dash-dotted lines.

The cross-sectional shape of the low-pressure connection 33 has two first straight lines 70, which run essentially parallel to the associated boundary line 80. The two first straight lines 70 are connected by two second straight lines 71, which are arranged in alignment with the side surfaces 55 of the gears. If the gears have a very large width and / or a very large helix angle, it can occur that the first two lines 70 intersect in the area of the gears. In this case, the in Fig. 4 right straight 71.

The corners between the first and second straight lines 70; 71 are rounded 74, so that the present low pressure connection can be easily made with an end mill. The corner radius 74 is, for example, 5 mm or 7.5 mm. On the rounding 74 but can also be dispensed with.

The low pressure port 33 according to the first embodiment according to Fig. 4 covered with its entire cross-sectional area 79, the gears. The corresponding cross-sectional shape is mirror-symmetrical with respect to a plane of symmetry 86 which contains the central axis of the low-pressure connection 33.

Fig. 5 shows a front view of the low pressure port 33 according to a second embodiment of the invention. Except for the differences described below, this embodiment is consistent with the first embodiment Fig. 4 so that reference is made to the corresponding statements. The viewing direction of Fig. 5 agrees with the one of Fig. 4 match.

The second straight lines were replaced by arcs 73, which are arched outward. The radius of in Fig. 5 Left circular arc 73 corresponds to the radius of the passage opening, which has a standardized flange with a circular passage opening. The entire width of the low-pressure port 33 is preferably equal to or smaller than twice the said radius.

The present low-pressure port 33 covers with the areas 78 and the bearing body of the gear machine. The gear cross-sectional cross-sectional area of the low pressure port 33 is the in Fig. 5 hatched area 79.

Fig. 6 shows a front view of the low pressure port 33 according to a third embodiment of the invention. The viewing direction agrees with that of the 4 and 5 match.

This low pressure port 33 is formed by two circular holes 76 which overlap. The corresponding cross-sectional shape is therefore composed of two circles 76 that overlap, having offset centers 77. The centers 77 are arranged on the plane of symmetry 86 of the low-pressure connection 33. Instead of the illustrated two circles 76, three or more circles 76 may be provided, wherein two or three circles, the optimum compromise between manufacturing costs and the gear cross-sectional area 79 of the low pressure port 33 result.

The in Fig. 6 left circle 76 covered with the area 78 in turn a bearing body, so that the toothed wheels covering cross-sectional area of the low pressure port 33 is the hatched area designated by the numeral 79.

LIST OF REFERENCE NUMBERS

10

gear machine

11

sealing area

20

casing

21

drive cover

22

End covers

23

Low pressure port

24

O-ring

25

Radial shaft seal

26

straight pin

30

main body

31

Inner circumferential surface

32

High pressure port

33

Low pressure port

34

Center axis of the high and low pressure connection

50

gear

51

Rotary axis of the gear

52

pivot

53

drive journal

54

Interdental

55

side surface

56

addendum

57

pitch

60

bearing body

61

bearing shell

62

axial seal

63

straight pin

64

Druckausgleichsfase

65

End of the pressure equalization phase

70

first straight

71

second straight line

73

arc

74

rounded corner

76

circle

77

Center of the circle

78

Area that covers the bearing bodies

79

the gear cross-sectional area

80

boundary line

81

minimum distance to the borderline

82

Circle with the same minimum distance to the borderline

83

Touch line between the tooth tip and the inner peripheral surface of the housing

84

hydraulic power

85

cutting edge

86

plane of symmetry

Claims (8)

1. Gear machine (10), in particular a pump or a motor, having two externally intermeshing gear wheels (50), which are enclosed by a housing (20), which comprises a high-pressure connection (32) and a low-pressure connection (33) situated opposite one another, the low-pressure connection (33) having a constant cross sectional shape in the direction of the central axis (34), said connection forming an intersection edge (85) with an inner circumferential face (31) of the housing (30) which bears tightly against the gear tooth tips (56) of the gear wheels (50), an optionally multipart bearing liner (60), in which the gear wheels (50) are rotatably supported, being arranged on both sides of each of the gear wheels (50), the bearing liners (60) bearing tightly on an associated lateral face (55) of the gear wheels (50), at least one pressure equalization chamfer (64) on the bearing liners (60) being assigned to each of the two gear wheels (50), said chamfer extending opposite the relevant gear wheel (50) and the inner circumferential face (31) from the high-pressure connection (32) in the direction of the low-pressure connection (33), where it has an end (65), characterized in that on the inner circumferential face (31) of the housing (20) a notional boundary line (80), which intersects the end (65) of the pressure equalization chamfer (64), is assigned to both gear wheels (50), said line running parallel to the line of contact (83) between the gear tooth tips (56) of the gear wheels (50) and the inner circumferential face (31), the intersection edge (85) being located between the two boundary lines (80), the minimum distance (81) between the intersection edge (85) and the boundary lines (80) being at least one pitch interval (57) of the gear wheels (50), the cross sectional shape of the low-pressure connection (33) deviating from the circular shape in such a way that its cross sectional area (79) overlapping the gear wheels (50) is greater than the cross sectional area of a notional, circular low-pressure connection (82) overlapping the gear wheels (50) at the same minimum distance (81) from the boundary lines (80).
2. Gear machine according to Claim 1, wherein the cross sectional shape of the low-pressure connection (33) is formed so that the intersection edge (85) is at a constant distance (81) from the associated boundary line (80).
3. Gear machine according to either of the preceding claims, wherein the cross sectional shape of the low-pressure connection (33) comprises two first straight lines (70), which each run substantially parallel to an associated boundary line (80).
4. Gear machine according to Claim 3, wherein the two first straight lines (70) are connected by at least one, preferably two, second straight lines (71), which run in alignment with the lateral faces (55) of the gear wheels (50).
5. Gear machine according to Claim 3, wherein the two first straight lines (70) are connected to one another by at least one, preferably two, circular arcs (73).
6. Gear machine according to one of the preceding claims, wherein the cross sectional shape of the low-pressure connection (33) has rounded corners (74).
7. Gear machine according to Claim 1 or 2, wherein the cross sectional shape of the low-pressure connection (33) is formed by more than one, preferably two or three, overlapping circles (76), which have centers (77) offset in relation to one another.
8. Gear machine according to one of the preceding claims, wherein the low-pressure connection (33) overlaps at least one bearing liner (60).

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