EP2924293B1 - Roller piston vacuum pump - Google Patents

Description

The invention relates to a Roots vacuum pump with a housing having a suction flange and a discharge flange.

Roots vacuum pumps are known in practice. In Roots pumps, two counter-rotating rotors rotate without contact in a housing. The rotors may have the shape of an "8" and are separated from each other and from the stator by a narrow gap. The conveyed gas is transported from an intake port to an exhaust port.

A shaft is driven by a motor. The synchronization of the other shaft via a gear pair in a gear compartment. The lubrication is limited to the gear compartment separated from a pump chamber by sealing elements.

Since no friction occurs in the pump chamber, a Roots pump can be operated at high speed up to 9,000 revolutions per minute. The symmetrical mass distribution of the rotors about the shaft axis also allows a perfect dynamic balancing, so that the pump runs very quiet despite high speed.

The bearings of the rotor shafts are arranged in two side parts, the end shields of the housing. On the one hand, the bearings are advantageous as a fixed bearing, running on the other as a floating bearing to allow for uneven thermal expansion between the housing and piston. The lubrication of the bearings and gears is usually done with oil. The passage of the drive shaft to the outside is sealed in the standard versions with radial oil seals overlaid with blocking oil. To protect the shaft, the sealing rings on a protective bush, which can be replaced when worn run.

In continuous operation and for constant conditions, equilibrium is established for introduced power and waste heat. The various components of the Roots vacuum pump, the length of which depends on the temperature, in this state have a constant gap size between the parts. The gap size between pump-effective rotor and stationary housing components are of particular importance for the reliability of this pump.

In exceptional cases, the parts, for example, as a result of impurities or rapid changes in temperature, beat against each other. The resulting forces must be absorbed by the housing forming components and the associated fasteners.

The prior art ( DE 198 12 222 A1 ) includes a twin-shaft flow machine having a pair of rotors disposed in a housing. The housing has a rotor chamber in which the rotors are rotatably mounted. The housing consists of several housing components, which are releasably secured together by means of screws.

This belonging to the prior art housing should be further improved to the effect that in case of a crash inside the pump ensures that the housing components hold together.

The technical problem underlying the invention is to provide a Roots vacuum pump having a housing which ensures in the event of a crash inside the pump that hold the housing components together.

This technical problem is solved by a Roots vacuum pump with the features of claim 1.

The Roots vacuum pump according to the invention with a housing having at least two housing parts, in which the housing parts are releasably secured together by means of a plurality of screws in which at least one screw is designed as a screw with a strength class of 8.8 or higher, characterized in that the Housing parts from the pump housing and / or formed at least one end plate and / or at least one cover are and that are provided for the arrangement of each end plate and / or each cover two heavy-duty pins.

The strength class for screws consists of two numbers separated by a dot. The number left corresponds to 1/100 of the nominal tensile strength R _m in MPa (Mega-Päscal).

The number to the right of the point indicates ten times the ratio between yield strength R _e and tensile strength R _m (yield ratio). This results, for example, in the following values: 0.6 / 0.8 / 0.9. These ratios are multiplied by 10 and then give the value after the point.

For example, a screw having the tensile strength R _m = 1,000 MPa and a yield ratio of 0.9 has a tensile strength of 10.9.

Streckgrenze $$R_e:\left(1.\mathit{Zahl}\times 100\right)\times \left(2.\mathrm{Z}\mathit{ahl}÷10\right)$$

The determination of the strength class thus takes place as follows:
tensile strenght $$R_m:1.\mathrm{number}\times 100$$

Stretch limit $$R_e:\left(1.\mathit{number}\times 100\right)\times \left(\mathrm{Second}\mathrm{Z}\mathit{ahl}÷10\right)$$

For a screw with the strength class 10.9 it is valid
Tensile strength R _m : 10 × 100 = 1,000 MPa
Yield strength R _e : (10 × 100) × (9 × 10) = 1,000 × 0.9 = 900 MPa

Bolts with a grade greater than 8.8 are also referred to as high strength bolts.

Usually, the structure of a housing of a Roots vacuum pump is such that bearing shields and then a cap or a lid are screwed to the pump housing. In the event of a crash, high forces and moments occur, which act in different directions.

Screws absorb the axial load. The screws are, however, sensitive to shearing. The Threads act in the area or parting planes as predetermined breaking points.

If the screws are designed as high-strength screws according to the invention with a strength class of 8.8 or higher, the screws hold much greater loads, such as shear forces, so that thereby the so-called containment, that is, the holding together of the housing components is better ensured.

Advantageously, the at least one screw is designed as a screw with a strength class of 10.9 or higher. As a result, the object of the invention, the containment, namely to ensure the holding together of the housing components, even better solved.

A further advantageous embodiment of the invention provides that the at least two housing components with the screws with a bolt tightening torque of at least 80 Nm (Newton meters) are interconnected.

This increased bolt tightening torque ensures that there is high friction between the housing components. As a result, the energy from transverse loads is consumed stretched to a longer period of time. Load peaks are "smoothed", so that the risk of shearing off the screws is reduced.

A further advantageous embodiment of the invention provides that at least one cylindrical pin is provided in connection planes of the at least two housing parts.

Cylinder pins absorb lateral forces and thus prevent the screws from shearing off. Because of the cylinder pins have no thread, no predetermined breaking points are available in the cylinder pins, so that the cylinder pins can absorb large lateral forces or shear forces.

According to a further advantageous embodiment of the invention, the at least one cylindrical pin is designed as a cylinder pin arranged in bores of adjacent housing parts. This means that two adjacent housing parts have bores which have congruent openings. The housing components have at least one pair of these corresponding holes, so that the cylinder pin can be arranged in this at least one pair of holes.

According to an advantageous embodiment of the invention, the cylinder pin has a strength class equal to or less than 8.8. This means that the cylindrical pins are advantageous not high strength, but rather tough. The cylindrical pins are therefore advantageously not hardened. As a result, the cylinder pins absorb the lateral forces better.

According to a further advantageous embodiment of the invention, at least one screw is replaced by a cylinder pin, wherein a maximum of n-3 screws are replaced by cylindrical pins, where n is the number of screws for fixing a housing part to another housing part.

This means that there are at least three screws for fixing the housing part. The screws are needed to achieve the necessary preload with a tightening torque of, for example, at least 80 Nm or even over 140 Nm, so that preferably a large part of the Number of screws is used. Nevertheless, it is possible to replace a part of the screws by cylindrical pins and thus absorb lateral forces through the cylinder pins.

According to the invention, the housing parts of the Roots vacuum pump are formed from the pump housing and / or at least one bearing plate and / or at least one cover.

The pump housing takes up the pistons and forms the so-called suction chamber.

The at least one bearing plate carries the bearings with which the shaft, which in turn carries the piston, is rotatably mounted. The at least one cover closes off the pump housing on the bearing plate side in a vacuum-tight and / or fluid-tight manner.

The pump housing may be formed in one or more parts according to an advantageous embodiment. The advantage is the part of the pump housing, which receives the Wälzkolben, one or more parts formed. If the pump housing is designed in several parts, these parts of the pump housing are advantageously also connected to each other with screws with a strength class of 8.8 or higher. In addition, the arrangement of cylindrical pins can be provided.

A further advantageous embodiment of the invention provides that the screws are arranged in a screw bushing and that the screw bushing is arranged in a bore of a housing part or in two opposite bores of two housing parts to be connected is. By the embodiment with a screw bush, these sockets can additionally absorb shear forces, whereby the cohesion of the housing parts is guaranteed even better in the event of a crash.

It is also possible to widen or adjust through holes for receiving the screws, that is, they may be conical or stepped. As a result, more transverse movements are possible without shearing the screws, wherein the axial bias is maintained.

According to a further advantageous embodiment of the invention, the fits of the cylindrical pins in the holes are smaller than the clearance between the at least one screw and the screw receiving holes. This also ensures that in the event of a crash, the cylinder pins are the first to absorb the transverse forces. After deforming or partially deforming these cylindrical pins, the transverse forces on the screws attack.

The invention provides that two heavy-duty pins are provided for the arrangement of each bearing plate and / or each lid. The heavy-duty pins are used to align the bearing plate to the housing. Usually, after the orientation of the bearing plate fixation with screws. These heavy duty pins absorb additional lateral forces.

According to a preferred embodiment of the invention it is provided that the game is formed by the screws to the cylinder pins to the heavy-duty pins in their respective holes decreasing. As a result, it is ensured that first absorb the shear forces pins shear forces. Next, the shear forces on the cylinder pins and last but not least the transverse forces on the screws.

By this embodiment, the peak load (peak) of the forces occurring in the event of a crash is stretched, so that a cohesion of the housing components is ensured.

The construction of the housing of the Roots vacuum pump is advantageously such that the at least one bearing plate is screwed to the pump housing. Preferably, a lid is screwed against the bearing plate. As a result, a vacuum-tight or fluid-tight closure is formed. These housing parts are connected according to the invention with at least one screw having a strength class of 8.8 or higher. In principle, it is possible that screws with different strength classes are provided for connecting the housing parts, which means that at least one screw with a strength class of 8.8 or higher is formed, however, that further screws can be formed with a lower strength class.

The invention assumes that it is advantageous to erode the kinetic energy and to cushion load peaks over a prolonged period of time.

In the event of a crash, plastic deformations of the bearing plate and cover and / or cap usually occur.

In principle, it is also possible to use a special casting, which withstands higher forces. It is also possible to mesh the housing parts intermeshing to absorb occurring by this training lateral forces.

It is also possible, instead of screws and / or cylindrical pins or in addition to screws and / or cylindrical pins disc-shaped components to be arranged between the housing parts. The disc-shaped components have larger diameter than the cylindrical pins and therefore can absorb larger lateral forces.

Fig. 1

ein Gehäuse einer Wälzkolbenvakuumpumpe in perspektivischer Ansicht;

Fig. 2

ein Lagerschild in Draufsicht;

Fig. 3

einen Querschnitt eines zweibogigen antreibenden und eines zweibogigen angetriebenen Rotors einer zum Stand der Technik gehörenden Wälzkolbenvakuumpumpe.

Further features and advantages of the invention will become apparent from the accompanying drawing, in which an embodiment of a vacuum pump according to the invention is shown only by way of example. In the drawing show:

Fig. 1

a housing of a Roots vacuum pump in a perspective view;

Fig. 2

a bearing plate in plan view;

Fig. 3

a cross section of a two-yoke driving and a two-yoke driven rotor of a prior art Wälzkolbenvakuumpumpe.

Fig. 1 shows a Roots vacuum pump 1 with a first housing part 2, the actual pump housing, which piston (not shown) of the Roots vacuum pump 1 receives.

The Roots vacuum pump 1 also has, as a further housing part on a bearing plate 3 and a cover 4. The bearing plate 3 is fixed with screws 5 to the pump housing 2. The cover 4 is arranged with screws 6 on the bearing plate 3.

The housing of the Roots vacuum pump 1 has a suction flange 33 and a discharge flange 34. The ejection flange 34 is fastened to the housing with screws 35.

The end shield 2 is in Fig. 2 shown. The bearing plate 2 is fastened with six screws 5 to the pump housing 2 (not shown). The screws 5 are designed as so-called high-strength screws with a strength class of 12.9.

In addition, four cylinder pins 7 are provided, which also absorb transverse forces in a crash. Furthermore, two heavy-duty pins 8 are provided, which serve to center the bearing plate and dampen load peaks with transverse forces.

The bearing plate has two openings 9 for the passage of waves (not shown).

Instead of the cylindrical pins 7 and discs can be provided with a larger diameter than the diameter of the cylindrical pins. In the case of the cylindrical pins 7, the diameter is smaller than the length of the cylindrical pins 7. In the case of the discs, the diameter is greater than the length of the discs.

As in Fig. 3 represented, in the rotor chamber 11, that is, in the suction chamber 11, the rotor 27 and the rotor 28 are arranged. The rotors 27, 28 are designed as double-bow rotors. The cross section of the rotors is formed perpendicular to an axis of the drive shaft 21 and the output shaft 22. The drive rotor 27 is driven by a motor (not shown). The output rotor 28 is via a transmission (not shown) synchronized with the drive rotor 27.

The shape of the rotors 27, 28 has approximately the shape of the numeral "8". The drive rotor 27 has two arcuate portions 27a and two recessed portions 27b respectively formed between the two arcuate portions 27a. Likewise, the output rotor 28 has two arcuate portions 28a and two recessed portions 28b respectively formed between the two arcuate portions 28a.

The drive rotor 27 and the output rotor 28 are disposed in the rotor chamber 11 with a minimum distance between a peripheral surface 15a of the rotor chamber 11 and the rotors 27 and 28. That is, the peaks T of the arcuate portions 27a, 28a are along the axes of Drive and output shafts 21, 22 extend and be prevented from coming into direct sliding contact with the inner surface 15a of the rotor chamber 11 or directly engage with it. Moreover, the drive rotor 27 and the output rotor 28, when engaged with each other, have a minimum clearance therebetween to prevent them from directly interfering with each other. In the peripheral wall 12a of the housing 12, a suction port 31a is provided so that a fluid can be sucked into the rotor chamber 11 (suction space) through the suction port 31a. In addition, an outlet port 32 a is provided so that the compressed fluid can escape from the rotor chamber 11. In the operation of the Roots vacuum pump 10, the drive shaft 21 is rotated by an electric motor (not shown). Thereby, the output shaft 22 becomes in the opposite direction to the drive shaft 21 by the engagement relationship between a drive gear and a driven tooth edge rotated and the drive rotor 27 and the output rotor 28 are consequently rotated.

The drive rotor 27 and the output rotor 28 of the Wälzkolbenvakuumpumpe 10 are arranged so that according to the rotation of the drive rotor 27 and the output rotor 28, an arc portion 27 a of the output rotor 27 and a recessed portion 28 b of the output rotor 28 engage with each other and an arc portion 28 a of the output rotor 28 and a recessed portion 27b of the drive rotor 27 engage with each other.

By rotating the drive rotor 27 and the output rotor 28, a fluid is sucked into the rotor chamber 11 through the suction port 31 a, and the fluid is trapped in the space S defined between the outer peripheral surface of the output rotor 28 and the peripheral surface 15 a of the housing 15 of the rotor chamber 11 is in the in Fig. 3 Then, the fluid in the space S is forwarded to the outlet port 32a in accordance with the rotation of the drive rotor 27 and the output rotor 28, and then is discharged from the rotor chamber 11 through the outlet port 32a.

reference numerals

1

Roots

2

pump housing

3

end shield

4

cover

5

screw

6

screw

7

straight pins

8th

Roll pins

9

drilling

10

Roots

11

Rotor chamber (pump chamber)

12

rotor housing

12a

cylindrical peripheral wall

15

casing

15a

Peripheral surface of the rotor chamber 11

21

drive shaft

22

output shaft

27

drive rotor

27a

arc sections

27b

Waist

28

driven rotor

28a

arc sections

28b

Waist

31a

suction

32a

outlet

33

suction flange

34

Ausstoßflansch

35

screw

S

Space (part of the scoop)

T

vertex

Claims (13)

1. Rotary piston vacuum pump (1, 10) having a housing with at least two housing parts (2, 3, 4) wherein the housing parts (2, 3, 4) are firmly connected to one another releasably by means of a plurality of screws (5, 6), wherein at least one screw (5, 6) is configured as a screw with a strength class of 8.8 or greater, characterised in that the housing parts (2, 3, 4) are formed from the pump housing (2) and at least one end shield (3) and/or at least one cover (4) and in that two clamping pins (8) are provided for the arrangement of each end shield (3) and/or each cover (4).
2. Rotary piston vacuum pump according to claim 1, characterised in that at least one screw (5, 6) is configured as a screw with a strength class of 10.9 or greater.
3. Rotary piston vacuum pump according to claim 1 or 2, characterised in that the at least two housing parts (2, 3, 4) are connected to one another with the screws (5, 6) with a tightening torque of at least 80 Nm (Newton metres).
4. Rotary piston vacuum pump according to one of the preceding claims, characterised in that at least one cylindrical pin (7) is provided in the connecting planes of the at least two housing parts (2, 3, 4).
5. Rotary piston vacuum pump according to claim 4, characterised in that the at least one cylindrical pin (7) is formed as a cylindrical pin (7) arranged in bores of adjacent housing parts (2, 3, 4).
6. Rotary piston vacuum pump according to claim 4 or 5, characterised in that the at least one cylindrical pin (7) is formed with a strength class of equal to or less than 8.8.
7. Rotary piston vacuum pump according to one of the preceding claims, characterised in that at least one screw (5, 6) is replaced by a cylindrical pin (7) and that a maximum of n-3 screws (5, 6) are replaced by cylindrical pins (7), wherein n is the number of screws (5, 6) for fastening a housing part (2, 3) to another housing part (3, 4).
8. Rotary piston vacuum pump according to one of the preceding claims, characterised in that the screws (5, 6) are arranged in a screw sleeve and in that the screw sleeve is arranged in a bore of a housing part (2, 3, 4) or in two mutually opposed bores of two housing parts (2, 3, 4) that are to be connected.
9. Rotary piston vacuum pump according to one of the preceding claims, characterised in that bores for receiving screws (5, 6) are formed conically or stepped.
10. Rotary piston vacuum pump according to one of the preceding claims, characterised in that the fits of the cylindrical pins (7) in the bores are smaller than the play between the at least one screw (5, 6) and the bore receiving the screw (5, 6).
11. Rotary piston vacuum pump according to one of the preceding claims, characterised in that the play, in their respective bores, is configured decreasing from the screws (5, 6) to the cylindrical pins (7) to the clamping pins (8).
12. Rotary piston vacuum pump according to one of the preceding claims, characterised in that screws (5, 6) with different strength classes are provided for connecting two housing parts (2, 3, 4).
13. Rotary piston vacuum pump according to one of the preceding claims, characterised in that in addition to the screws (5, 6) with a strength class of 8.8 or greater, screws with a strength class of less than 8.8 are provided.

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