Patent Application
20120121450
The invention relates to a screw spindle pump arrangement in accordance with the preamble of patent claim 1.
Screw spindle pumps usually have two or three spindles which are arranged parallel to one another, mesh with one another and are set in rotation by a mobile machine (for example, electric motor). The spindles are received in a housing, there being only minimum spacings between the outer sides of the spindles and the housing.
As a result of the rotation, the fluid to be conveyed is conveyed along the spindles in the spaces which result in the helical threads which engage into one another in the manner of a screw thread between the spindles and the housing. This results in a low pressure region at one end of the spindles or the housing and a high pressure region at the other end. At the same time, the fluid to be conveyed penetrates into the minimum spacings between the spindles and the housing and produces a supporting and lubricating film.
Document DE 39 20 901 A1 discloses a screw spindle pump having three spindles. A central drive spindle meshes with running spindles which are arranged on both sides and along the helical threads of which a fluid is conveyed.
In the case of a double pass design of the screw spindle pump, in contrast, the spindles are not continuously helical, but rather are divided into two sections which are wound in opposite directions and the spaces of which move toward one another during rotation. This results in two low pressure regions at the two ends of the spindles and a high pressure region in the center of the spindles.
Document DE 10 2006 061 971 A1 discloses a double pass screw spindle pump of this type with two spindles.
A disadvantage of screw spindle pumps in accordance with DE 39 20 901 A1 which are driven by constant electric motors is their low flexibility with regard to pump output pressure and volumetric flow.
In contrast, the invention is based on the object of providing a screw spindle pump arrangement which can be adapted simply to different requirements with regard to pump output pressure and volumetric flow.
This object is achieved by a screw spindle pump arrangement as claimed in patent claim 1.
Further advantageous refinements of the invention are described in the dependent patent claims.
The screw spindle pump arrangement according to the invention has a high pressure connection, a low pressure connection, a drive spindle and at least one running spindle. A conveying section of the running spindle can be divided into two conveying sections which can be operated or have flow passing through them either in parallel or in series. As a result, a screw spindle pump arrangement is provided with low outlay, in which screw spindle pump arrangement two operating states can be selected without regulating technology (higher output pressure with a lower volumetric flow or lower output pressure with a higher volumetric flow).
In one particularly preferred development of the screw spindle pump arrangement according to the invention, two tapping connections which can be connected by a connecting line are provided on the housing in a central region of the conveying section. The connecting line can be shut off, and it is possible here for the first tapping connection in the conveying direction to be connected to the high pressure connection and for the second tapping connection in the conveying direction to be connected to the low pressure connection. As a result of the open connecting line, there is a series circuit (higher pressure, lower volumetric flow) which corresponds to a screw spindle pump according to the prior art. In the case of the shut off connecting line and the simultaneous abovementioned divided pressure medium flow paths, the screw spindle pump arrangement can be operated simply in the parallel circuit (lower pressure, higher volumetric flow).
In order to divide the end of the first conveying section from the start of the second conveying section (and/or the pressure medium situated therein), the spacing of the two tapping connections along the conveying section corresponds at least to the width of the lands of the running spindles. At least one land therefore prevents an exchange of pressure medium between the regions of the two tapping connections.
In one particularly preferred development, a directional valve is arranged in the connecting line, which directional valve is connected via a high pressure connecting line to the high pressure connection and via a low pressure connecting line to the low pressure connection. A switchover between series circuit and parallel circuit can thus be carried out by valve actuation.
The pressure medium flow path between the tapping connections via the connecting line is preferably shut off in a spring prestressed basic position of a directional valve body. Instead, the first tapping connection is connected to the high pressure connection and the second tapping connection is connected to the low pressure connection. In a switching position of the valve body, in contrast, the two tapping connections are connected to one another via the connecting line.
In one advantageous embodiment, a nonreturn valve is arranged in the high pressure connecting line, which nonreturn valve opens from the directional valve to a high pressure line which connects the high pressure connection to a pump outlet.
For reasons of operational safety, a pressure limiting valve which relieves to a tank can be arranged on the high pressure line. Here, the pressure limiting valve can be pilot controlled pneumatically.
Depending on the design, it can be advantageous if the screw spindle pump arrangement has two running spindles, the threads of which are wound in the same direction.
For cost reasons, the drive spindle can be driven by a constant two pole electric motor, the manufacturing costs of which are lower than those of a controllable electric motor.
As an alternative, in order to increase the flexibility and/or the adaptability of output pressure and volumetric flow, the drive spindle can be connected to a speed-controlled electric motor, it being possible for a pressure sensor which is connected to said electric motor to be arranged on the high pressure line.
The screw spindle pump arrangement according to the invention is preferably used for supplying a machine tool with cooling lubricant. In this field of use, the switchover possibility according to the invention is particularly advantageous. The series circuit (higher pressure with lower volumetric flow) is required in larger tools and the parallel circuit (lower pressure with higher volumetric flow) is required in smaller tools. These two operating states of the pump can also advantageously be used in the case of different chip removal yields of the machine tool.
In the following text, one exemplary embodiment of the screw spindle pump arrangement according to the invention will be described in detail using a single FIGURE.
This FIGURE shows a screw spindle pump arrangement according to the invention. It has a screw spindle pump 1, the basic construction of which is known from the prior art and which is shown (in the FIGURE) on the left and in section.
Furthermore, the arrangement has enhancements and/or modifications according to the invention which are shown as a symbolic circuit diagram and are shown (in the FIGURE) largely on the right.
The screw spindle pump has an elongate housing which consists substantially of a housing main section 2 and two end-side housing covers 3, 4.
Two running spindles 6 which are at minimum spacings from the adjacent sections of the inner wall 8 of the housing main section 2 are arranged in the interior of the housing 2, 3, 4.
The running spindles 6 have circumferentially wound grooves or threads 10. Likewise circumferentially wound lands 12 remain between the windings of the threads 10.
A drive spindle 14 which likewise has a circumferentially wound land 16 is arranged centrally in the housing main section 2 and between the running spindles 6. The land 16 is wound in the opposite direction to the lands 12 of the running spindles 6, the drive spindle 14 meshing with both running spindles 6.
A shaft section 18 is formed at the upper (in the FIGURE) end section of the drive spindle 14, which shaft section 18 is mounted via an antifriction bearing 20 in the upper (in the FIGURE) housing cover 4 and has a connection section 22 outside the housing 2, 3, 4. The drive spindle 14 can be driven by an electric motor (not shown) via the connection section 22, it being possible for the electric motor to be a constant motor for cost reasons or to be controllable for reasons of higher flexibility.
As a result of the meshing engagement of the drive spindle 14 with the two running spindles 6, the latter are set in rotation when driven. Here, those threads 10 of the running spindles 6 which are delimited by the inner wall 8 of the housing main section 2 are divided by the land 16 of the drive spindle 14 into sections or spaces which move from top to bottom (in the FIGURE) during the rotation of the running spindles 6. As a result, pressure medium which is sucked in at a low pressure connection 24 can be conveyed to a high pressure connection 26 and can be compressed in the process.
According to the invention, two tapping connections 28, which are spaced apart axially are provided in the housing main section 2 in a central region of the conveying section which extends from top to bottom (in the FIGURE). Their dimension transversely with respect to the conveying direction is selected in such a way that they have a pressure medium connection to the corresponding thread sections of both running spindles 6. Here, the two tapping connections 28, 30 are at an axial spacing from one another in the conveying direction, which axial spacing corresponds at least to the thickness of the lands 16. As a result, a division of the two tapping connections 28, 30 and/or of the pressure medium which is situated in the corresponding thread sections is ensured.
Furthermore, the screw spindle pump arrangement according to the invention has a 4/2-way valve 32. In a spring prestressed position (a) of a valve body of the directional valve 32, the low pressure connection 24 is connected to the second tapping connection 30 via a low pressure line 34, a low pressure connecting line 36 and via a second tapping line 38. Furthermore, in the abovementioned switching position, the first tapping connection 28 is connected to a high pressure line 44 via a first tapping line 40 and a high pressure connecting line 42. The high pressure line 44 connects the high pressure connection 26 to a pump outlet P.
In a switching position (b) of the valve body, which switching position (b) can be selected via a switching magnet 46, a pressure medium flow path from the first tapping connection 28 via the first tapping line 40, the directional valve 32 and the second tapping line 38 to the second tapping connection 30 is opened.
A nonreturn valve 48 which opens from the directional valve 32 to the high pressure line 44 is provided in the high pressure connecting line 42.
In the following text, the function of the screw spindle pump arrangement according to the invention will be explained.
As a result of the tapping connections 28, 30 according to the invention and the hydraulic circuit according to the invention, the conveying section of the two running spindles 6 can be operated substantially continuously or, as an alternative, can be divided into two conveying sections 45a, 45b which can be operated in parallel.
The parallel circuit of the two conveying sections 45a, 45b is achieved in the switching position (a) (shown in the FIGURE) of the valve body of the directional valve 32. Here, the pressure medium volumetric flow which is sucked in at a suction connection S is divided firstly via the low pressure line 34 to the low pressure connection 24 and secondly via the low pressure connecting line 36 and the second tapping line 38 to the second tapping connection 30. The two conveying sections 45a, 45b of the running spindles 6 are therefore operated in parallel, a first high pressure volumetric flow flowing from the first tapping connection 28 via the first tapping line 40 and via the high pressure connecting line 42 to the pump outlet P, while a second volumetric flow flows from the high pressure connection 26 via the high pressure line 44 to the pump outlet P. This ensures that approximately the same pressure prevails in the high pressure connecting line 42 and in the high pressure line 44. The volumetric flow at the pump outlet P is therefore comparatively high, while the output pressure at the pump outlet P is comparatively low.
The series circuit of the two conveying sections 45a, 45b and/or conventional operation of the screw spindle pump arrangement according to the invention are/is achieved by the switching magnet 46 having current applied to it and displacing the valve body of the directional valve 32 into the switching position which is labeled by b. As a result, the two tapping connections 28, 30 are connected to one another, the pressure loaded pressure medium flowing out of the first conveying section 45a via the two tapping lines 40, 38 into the second conveying section 45b of the running spindles 6. The second part of the pressure increase then takes place in the second conveying section 45b, the pressure medium flowing with maximum pressure out of the high pressure connection 26 via the high pressure line 44 to the pump outlet P.
In this case, the volumetric flow is comparatively low, while the pressure increase is comparatively high.
The nonreturn valve 48 which is arranged in the high pressure connecting line 42 closes in the case of a series circuit of the two conveying sections 45a, 45b and opens in the case of a parallel circuit of the two conveying sections 45a, 45b if approximately the same pressure prevails in the high pressure connecting line 42 and in the high pressure line 44.
Furthermore, a line 49 branches off from the high pressure line 44, in which line 49 a pressure limiting valve 50 is provided which, if an adjustable maximum pressure is exceeded, relieves the high pressure line 44 to a tank T. The pressure limiting valve 50 is pilot controlled pneumatically and has an infinitely adjustable proportional pressure valve.
Furthermore, an electronic pressure sensor 52 and a manometer 54 for monitoring the pump outlet pressure are provided on the high pressure line 44, the pressure loading of the manometer 54 taking place via a throttle 56.
The screw spindle pump arrangement according to the invention is particularly suitable for conveying cooling lubricant in machine tools. In this field of use, screw spindle pumps are preferred, since they have the highest possible resistance to partially abrasive particles which accumulate in the cooling lubricant.
In the case of tool changes of the associated machine tools or in the case of a change in the chip removal yield, changes in the pressure and the volumetric flow of the cooling lubricant are required which can be achieved by way of the screw spindle pump arrangement according to the invention, without a speed-controlled electric motor being necessary. Thus, for example, in the case of a small tool, the comparatively high pressure with the comparatively low volumetric flow is produced by the series circuit (switching position b), while, in the case of a relatively large tool, the comparatively low pressure with the comparatively high volumetric flow is produced by the parallel circuit (switching position a).
The maximum drive power of the electric motor (not shown) can be reduced here in the abovementioned use range by approximately 40% with respect to the prior art.
In comparison with a speed-controlled screw spindle pump, the screw spindle pump arrangement according to the invention has the advantage, in addition to the lower costs, that a volumetric flow reduction is not produced by a speed reduction, as a result of which the supporting property of the cooling lubricant could be impaired in the regions between the lands 12 and the housing main section 2.
A screw spindle pump arrangement is disclosed having a low pressure connection, a high pressure connection, a drive spindle and at least one running spindle. A conveying section of the running spindles can be divided into two conveying sections which can be operated either in parallel or in series. As a result, a screw spindle pump arrangement is provided with low outlay, in which screw spindle pump arrangement two operating states can be selected without regulating technology.
Two tapping connections which can be connected by a connecting line are provided in a central region of the conveying section. The connecting line can be shut off, and here the low pressure-side tapping connection can be connected to the high pressure connection and the high pressure-side tapping connection can be connected to the low pressure connection. As a result of the open connecting line, there is a series circuit (higher pressure, lower volumetric flow) which corresponds to a screw spindle pump according to the prior art. In the case of the connecting line being shut off and the simultaneous abovementioned pressure medium flow paths, the screw spindle pump arrangement can be operated simply in the parallel circuit (lower pressure, higher volumetric flow).
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 015 685.2 | Mar 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/001096 | 2/23/2010 | WO | 00 | 12/30/2011 |
