Title:
Rapidly pumping out an enclosure while limiting energy consumption
Kind Code:
A1


Abstract:
A vacuum pumping device of the invention comprises a motor (1) driving a multi-stage dry mechanical pump (2) in which the stages (5, 6, 7, 8) are connected successively in parallel and then in series in a plurality of successive configurations, each of which is selected to optimize the pumping speed in the current pressure range. This makes it possible to lower pressure inside an enclosure (100) quickly while reducing the volume of the pump and the energy consumed by the pump by about 40% compared with a traditional pump having a speed that is sufficient to obtain the same rapidity of pumping.



Inventors:
Rival, Jean-luc (Villaz, FR)
Application Number:
11/396574
Publication Date:
10/05/2006
Filing Date:
04/04/2006
Assignee:
ALCATEL
Primary Class:
International Classes:
F04B41/06
View Patent Images:
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Primary Examiner:
BAYOU, AMENE SETEGNE
Attorney, Agent or Firm:
SUGHRUE MION, PLLC (WASHINGTON, DC, US)
Claims:
1. A vacuum pumping device for lowering the pressure of an enclosure (100), the device comprising a motor (1) driving a multi-stage dry mechanical vacuum pump (2), each stage (5-8) having an intake (5c-8c) and an outlet (5d-8d), and the pump including pipes (9-11) for interconnecting the stages (5-8) in the circuit for pumping gas out from the enclosure, the device being characterized in that it includes fluid flow connection means (12-19) that interconnect the stages (5-8) so as to pass from a first configuration in which the stages are connected in parallel at least in pairs during a first pumping step (E1), to a last configuration in which the stages are connected in series in a last pumping step (E3), and passing via at least one intermediate configuration, during an intermediate pumping step (E2), pumping speed being optimized in each current pressure range, and in which at least one stage (5) is connected in parallel with at least one other stage (6), while at least one stage (7) is connected in series with at least one other stage (8).

2. A device according to claim 1, in which the fluid flow connection means (12-19) comprise valves (16-19) controlled by electronic control means (22) and inserted in the pipes (9, 11, 13, 15).

3. A device according to claim 2, in which the electronic control means (22) actuate the valves (16-19) to pass from one configuration to the following configuration in response to variation in the gas pressure inside the enclosure (100).

4. A device according to claim 2, in which the electronic control means (22) actuate the valves (16-19) to pass from one configuration to the following configuration in response to variation in the power consumed by the motor (1) of the pump.

5. A device according to claim 2, in which the electronic control means (22) actuate the valves (16-19) to pass from one configuration to the following configuration after a predefined duration.

6. A device according to claim 2, in which the valves (16-19) and the inter-stage pipes (9-11) are integrated in the body of the vacuum pump (2).

7. A device according to claim 2, in which, in the last pumping step (E3), the electronic control means (22) increase the velocity of the motor (1).

8. A device according to claim 2, in which, when the desired pressure state is reached inside the enclosure (100), the electronic control means (22) reduce the velocity of rotation of the motor (1) to provide pressure-maintaining pumping.

9. A device according to claim 2, in which, when the desired pressure state is reached inside the enclosure (100), the electronic control means (22) connect an additional low-speed pumping stage to the outlet (4) in order to maintain pressure.

10. A device according to claim 1, comprising four stages (5-8) connected in the following successive configurations during pumping: a) in a first configuration, during a first pumping step (E1), the first and second stages (5, 6) are connected in parallel with each other forming a first pair of stages, the third and fourth stages (7, 8) are connected in parallel with each other forming a second pair of stages, and the two pairs of stages (5-6 and 7-8) are connected in series on the gas-flow path; b) in a second configuration, during an intermediate pumping step (E2), the first and second stages (5, 6) remain connected in parallel with each other, the third and fourth stages (7, 8) are connected in series with each other, and the first pair of stages comprising the first and second stages are connected in series with the second pair of stages (7-8) comprising the third and fourth stages; and c) in a third configuration, during a last pumping step (E3), all four stages (5-8) are connected in series with one another.

11. A device according to claim 1, comprising five stages (102, 103, 104, 107, 108) connected in the following successive configurations during pumping: a) in a first configuration, during a first pumping step (E1), the first, second, and third stages (102, 103 and 104) are connected in parallel forming a group of stages (102-104), the fourth and fifth stages (107-108) are connected in parallel with each other, forming a pair of stages (107-108), and the group of stages (102-104) and the pair of stages (107-108) are connected in series with each other on the gas-flow path; b) in a second configuration, during a first intermediate pumping step (E2), the first and second stages (102, 103) are connected in parallel with each other, forming a first pair of stages (102-103), the third and fourth stages (104-107) are connected in parallel with each other, forming a second pair of stages (104-107), and the first and second pairs of stages (102-103 and 104-107) are connected in series with each other and with the fifth stage (108); c) in a third configuration, during a second intermediate pumping step (E3), the first and second stages (102, 103) are connected in parallel with each other forming a pair of stages (102-103), and the third, fourth, and fifth stages (104, 107, 108) are connected in series with one another, and with the pair of stages (102-103); and d) in a fourth configuration, during a last pumping step (E4), all five stages (102, 103, 104, 107, 108) are connected in series with one another.

12. A device according to claim 1, comprising six stages (202, 203, 204, 207, 208, 209) connected in the following successive configurations during pumping: a) in a first configuration, during a first pumping step (E1), the first, second, and third stages (202, 203 and 204) are connected in parallel forming a first group of stages (202-204), the fourth, fifth, and six stages (207, 208, 209) are connected in parallel forming a second group of stages (207-209), and the first and second groups of stages (202-204 and 207-209) are connected in series with each other on the gas-flow path; b) in a second configuration, during a first intermediate pumping step (E2), the first, second, and third stages (202, 203, 204) are connected in parallel forming a group of stages (202-204), the third and fourth stages (207, 208) are connected in parallel with each other, forming a pair of stages (207-208), and the group of stages (202-204) and the pair of stages (207-208) are connected in series with each other, and with the sixth stage (209); c) in a third configuration, during a second intermediate pumping step (E3), the first, second, and third stages (202, 203, 204) are connected in parallel forming a group of stages (202-204), and the fourth, fifth, and sixth stages (207, 208, 209) are connected in series with one another, and with the group of stages (202-204); d) in a fourth configuration, during a third intermediate pumping step (E4), the first and second stages (202, 203) are connected in parallel with each other forming a pair of stages (202-203), and the third, fourth, fifth, and sixth stages (204, 207, 208, and 209) are connected in series with one another, and with the pair of stages (202-203); and e) in a fifth configuration, during a last pumping step (E5), all six stages (202, 203, 204, 207, 208, 209) are connected in series with one another.

13. A device according to any one of claims 1 to 9 claim 1, comprising six stages (302, 303, 304, 307, 310, 311) connected in the following successive configurations during pumping: a) in a first configuration, during a first pumping step (E1), the first, second, and third stages (302, 303, 306) are connected in parallel forming a first group of stages (302-306), the fourth, fifth, and six stages (307, 310, 311) are connected in parallel forming a second group of stages (307-311), and the first and second groups of stages (302-306 and 307-311) are connected in series on the gas-flow path; b) in a second configuration, during a first intermediate pumping step (E2), the first and second stages (302, 303) are connected in parallel with each other forming a first pair of stages (302-303), the third and fourth stages (306, 307) are connected in parallel with each other forming a second pair of stages (306-307), the fifth and sixth stages (310, 311) are connected in parallel with each other forming a third pair of stages (310-311), and the first, second, and third pairs of stages (302-303, 306-307, and 310-311) are connected in series with one another; c) in a third configuration, during a second intermediate pumping step (E3), the first and second stages (302, 303) are connected in parallel with each other forming a first pair of stages (302-303), the third and fourth stages (306, 307) are connected in parallel with each other forming a second pair of stages (306-307), and the fifth and sixth stages (310-311) are connected in series with each other, and with the first and second pairs of stages (302-303, 306-307); d) in a fourth configuration, during a third intermediate pumping step (E4), the first and second stages (302, 303) are connected in parallel with each other forming a pair of stages (302-303), and the third, fourth, fifth, and sixth stages (303, 307, 310, 311), are connected in series with one another, and with the pair of stages (302-303); and e) in a fifth configuration, during a last pumping step (E5), all six stages (302, 303, 306, 307, 310, 311) are connected in series with one another.

14. A vacuum pumping method using a multi-stage dry mechanical pump (2) for lowering the pressure inside an enclosure, in which the stages (5-8) of the pump (2) are interconnected in a plurality of successive configurations to pass from a first configuration in which the stages are connected in parallel at least in pairs during a first pumping step (E1) to a last configuration in which the stages are connected in series during a last pumping step (E3), and passing via at least one intermediate configuration (E2), each configuration being selected to optimize pumping speed in the current pressure range, and in which in the or each intermediate configuration at least one intake stage (5) is connected in parallel with at least one other intake stage (6) and at least one outlet stage (7) is connected in series with at least one other stage (8).

15. A method according to claim 14, in which, during the last pumping step, the velocity of the pump is temporarily increased above its nominal velocity.

Description:

The present invention relates to vacuum pumping devices capable of establishing and maintaining a suitable vacuum in an enclosure.

It is a common practice to establish a vacuum in an enclosure, in particular in industrial processes for fabricating semiconductors, in which some of the fabrication steps need to be performed in a vacuum.

In such processes, the substrates are placed in a loading chamber (known as a “load lock”) that is connected to a vacuum pumping device for lowering the pressure inside the loading chamber to a value that is satisfactory for subsequently transferring the semiconductor substrates into a process chamber in which there is a vacuum suitable for fabrication purposes.

It can be understood that each substrate loading or unloading operation requires the gas pressure in the loading chamber to be lowered and then raised, thus requiring frequent intervention by the vacuum pumping device.

It will also be understood that a vacuum is not established instantaneously in the pumping chamber, and the time taken constitutes a limit on the overall speed of the fabrication process.

This limit is particularly appreciable when the substrates are of large dimensions. Under such circumstances, and in particular for fabricating flat TV or display screens, the loading chamber must necessarily have a volume that is suitable for containing one or more flat screens.

For example, at present, the loading chambers used for fabricating flat screens are of large volume, generally about 500 liters (L) to 1000 L and sometimes exceeding 5000 L, and these chambers need to be pumped out as quickly as possible.

The solution presently used for pumping out such large-volume loading chambers quickly is to use large pumps fitted with large motors. As a result the pumps and their motors constitute elements that are bulky and expensive, and that consume large quantities of energy.

The problem posed by the invention is to pump out a large-volume enclosure quickly so as to reach a suitable vacuum quickly inside the enclosure, while reducing the dimensions of the vacuum pumping device, and while limiting the energy it consumes to reach a satisfactory vacuum.

The invention results from the observation that a given vacuum pumping device generally presents a characteristic of speed as a function of pressure that presents a maximum in some given pressure range, with the particular pressure range for maximum speed depending on the architecture of the vacuum pumping device.

The invention takes advantage of that observation to devise a vacuum pumping device of variable geometry in which the geometry of the device is caused to change on one or more occasions in order to optimize the speed of the pumping device during each stage of pumping, i.e. during the various successive ranges of pressures within the enclosure that is being pumped out.

The invention thus achieves the looked-for result by using a multi-stage dry mechanical pump with a scheme for intelligently connecting the various stages in series and parallel modes, possibly also in combination with controlling the velocity of the pump.

A plurality of configurations for the pumping stages are thus used in succession, which configurations succeed one another as the intake pressure is reduced, and at all times the configuration that is selected is the configuration that provides the maximum pumping speed for the pumping device.

In practice, a changeover is made from one configuration to the next, either on the basis of timing adapted to the volume that is to be pumped out, or on the basis of the instantaneous electricity consumption of the pump motor, or on the basis of pressure information obtained from a pressure gauge measuring the pressure inside the enclosure that is being pumped out.

As a result, a pump of relatively small size is capable of pumping at higher speed, thus avoiding the need to use larger pumps driven by larger motors and consuming more energy.

The savings in terms of pumping device volume and energy consumption can be as much as about 40%.

To achieve these objects, and others, the invention provides a vacuum pumping device for lowering the pressure of an enclosure, the device comprising a motor driving a multi-stage dry mechanical vacuum pump, each stage having an intake and an outlet, and the pump including pipes for interconnecting the stages in the circuit for pumping gas out from the enclosure. The device includes fluid flow connection means that interconnect the stages so as to pass from a first configuration in which the stages are connected in parallel at least in pairs during a first pumping step, to a last configuration in which the stages are connected in series in a last pumping step, and passing via at least one intermediate configuration, during an intermediate pumping step, pumping speed being optimized in each current pressure range, and in which at least one stage is connected in parallel with at least one other stage, while at least one stage is connected in series with at least one other stage.

In practice, the fluid flow connection means may advantageously comprise valves controlled by electronic control means and inserted in the pipes.

In an embodiment of the invention, the electronic control means actuate the valves to pass from one configuration to the following configuration in response to variation in the gas pressure inside the enclosure. The gas pressure inside the enclosure is a reliable indicator of the pumping capacity of the vacuum pumping device in its current configuration, and it is possible to compare the speed curves of various configurations in order to select at all times the configuration that presents the best pumping capacity.

Alternatively, the electronic control means actuate the valves to pass from one configuration to the following configuration in response to variation in the power consumed by the motor of the pump. In practice, the power consumed by the motor is also a suitable parameter that gives an indication about the optimum or non-optimum state of the current configuration of the stages, since the power consumed by the pumping device increases above some limit value after the maximum of the speed curve has been reached.

In another possibility, the electronic control means may actuate the valves to pass from one configuration to the following configuration after a predefined duration which is a function of the volume of the enclosure being pumped out. For a given volume of enclosure to be pumped out, it is possible by trial and error to determine the times at which it is necessary to switch from one configuration to the next in order to remain continuously in the configuration that optimizes the speed of the vacuum pumping device.

Preferably, the valves and the inter-stage pipes are integrated in the body of the vacuum pump.

During the first pumping step, when the pressure inside the enclosure is still high, a first configuration is selected in which the stages are in parallel. During the last pumping step, when the pressure inside the enclosure is low, a last configuration is selected in which the stages are in series so as to increase the compression ratio and thus reach an even lower pressure inside the enclosure. In addition, during the last pumping step, the electronic control means may advantageously increase the velocity of the motor, and thus the velocity of the pump, above its nominal velocity, it being observed that the nominal velocity can be exceeded without exceeding the power limit since the low pressure stage, which is the stage that limits power, is in a zone of low compression during this step.

Once the desired pressure state has been reached inside the enclosure, the electronic control means can put the vacuum pumping device into a low cost mode of operation either by reducing the velocity of rotation of its motor so as to provide pressure-maintaining pumping, or by connecting an additional pumping stage presenting a low speed to the outlet, likewise so as to maintain pressure.

In a first embodiment of the invention, the device has four stages that are connected in the following successive configurations during pumping:

a) in a first configuration, during a first pumping step, the first and second stages are connected in parallel with each other forming a first pair of stages, the third and fourth stages are connected in parallel with each other forming a second pair of stages, and the two pairs of stages are connected in series on the gas-flow path;

b) in a second configuration, during an intermediate pumping step, the first and second stages remain connected in parallel with each other, while the third and fourth stages are connected in series with each other, and the first pair of stages comprising the first and second stages are connected in series with the second pair of stages comprising the third and fourth stages; and

c) in a third configuration, during a last pumping step, all four stages are connected in series with one another.

In a second embodiment, the device has five stages that are connected in the following successive configurations during pumping:

a) in a first configuration, during a first pumping step, the first, second, and third stages are connected in parallel forming a group of stages, the fourth and fifth stages are connected in parallel with each other forming a pair of stages, and the group of stages and the pair of stages are connected in series with each other on the gas-flow path;

b) in a second configuration, during a first intermediate pumping step, the first and second stages are connected in parallel with each other forming a first pair of stages, the third and fourth stages are connected in parallel with each other, forming a second pair of stages, and the first and second pairs of stages are connected in series with each other and with the fifth stage;

c) in a third configuration, during a second intermediate pumping step, the first and second stages are connected in parallel with each other forming a pair of stages, and the third, fourth, and fifth stages are connected in series with one another and with the pair of stages; and

d) in a fourth configuration, during a last pumping step, all five stages are connected in series with one another.

In a third embodiment of the invention, the device has six stages that are connected in the following successive configurations during pumping:

a) in a first configuration, during a first pumping step, the first, second, and third stages are connected in parallel forming a first group of stages, the fourth, fifth, and six stages are connected in parallel forming a second group of stages, and the first and second groups of stages are connected in series with each other on the gas-flow path;

b) in a second configuration, during a first intermediate pumping step, the first, second, and third stages are connected in parallel forming a group of stages, the third and fourth stages are connected in parallel with each other, forming a pair of stages, and the group of stages and the pair of stages are connected in series with each other, and with the sixth stage;

c) in a third configuration, during a second intermediate pumping step, the first, second, and third stages are connected in parallel forming a group of stages, the fourth, fifth, and sixth stages are connected in series with one another, and with the group of stages;

d) in a fourth configuration, during a third intermediate pumping step, the first and second stages are connected in parallel with each other forming a pair of stages, and the third, fourth, fifth, and sixth stages are connected in series with one another, and with the pair of stages; and

e) in a fifth configuration, during a last pumping step, all six stages are connected in series with one another.

In a fourth embodiment of the invention, the device has six stages that are connected in the following successive configurations during pumping:

a) in a first configuration, during a first pumping step, the first, second, and third stages are connected in parallel forming a first group of stages, the fourth, fifth, and six stages are connected in parallel, forming a second group of stages, and the first and second groups of stages are connected in series on the gas-flow path;

b) in a second configuration, during a first intermediate pumping step, the first and second stages are connected in parallel with each other forming a first pair of stages, the third and fourth stages are connected in parallel with each other forming a second pair of stages, the fifth and sixth stages are connected in parallel with each other forming a third pair of stages, and the first, second, and third pairs of stages are connected in series with one another;

c) in a third configuration, during a second intermediate pumping step, the first and second stages are connected in parallel with each other forming a first pair of stages, the third and fourth stages are connected in parallel with each other forming a second pair of stages, and the fifth and sixth stages are connected in series with each other, and with the first and second pairs of stages;

d) in a fourth configuration, during a third intermediate pumping step, the first and second stages are connected in parallel with each other forming a pair of stages, and the third, fourth, fifth, and sixth stages are connected in series with one another, and with the pair of stages; and

e) in a fifth configuration, during a last pumping step, all six stages are connected in series with one another.

In another aspect, the invention provides a vacuum pumping method using a multi-stage dry mechanical pump for lowering the pressure inside an enclosure, in which the stages of the pump are interconnected in a plurality of successive configurations to pass from a first configuration in which the stages are connected in parallel at least in pairs during a first pumping step, to a last configuration in which the stages are connected in series during a last pumping step, and passing via at least one intermediate configuration, each configuration being selected to optimize pumping speed in the current pressure range. In the or each intermediate configuration at least one intake stage is connected in parallel with at least one other intake stage and at least one outlet stage is connected in series with at least one other stage.

In such a method, provision can be made for the stages to be connected in parallel at least in pairs during a first pumping step, for the stages to be connected in series during a last pumping step, and optionally for the intake stages to remain in parallel while the outlet stages are in series during an intermediate pumping step.

In addition, during the last pumping step, the velocity of the pump may be temporarily increased above its nominal velocity.

Other objects, characteristics and advantages of the present invention appear from the following description of particular embodiments given with reference to the accompanying figures, in which:

FIG. 1 is a diagram illustrating a prior art structure for a vacuum pumping device in which the multi-stage pump is of the Roots type, with four pumping stages in series;

FIG. 2 is a diagrammatic view of a vacuum pumping device in an embodiment of the present invention, again comprising four stages of the Roots type, the stages being interconnected in a first configuration;

FIG. 3 is a perspective view of the FIG. 2 pumping device shown partially open;

FIG. 4 is a flow diagram showing how the pump stages are interconnected in the first configuration of FIG. 2;

FIG. 5 is a diagram of the pumping device in the embodiment in FIG. 2, in a second configuration;

FIG. 6 is a flow diagram showing the way in which the pump stages are interconnected in the second configuration of FIG. 5;

FIG. 7 is a flow diagram showing how the pump stages are interconnected in a third configuration;

FIG. 8 is a graph plotting the curve of the pumping speed of the device of FIGS. 2 to 7 as a function of the pressure in the enclosure being pumped out;

FIG. 9 is a graph plotting the curve of the electricity consumption of the pumping device of FIGS. 2 to 7 while lowering the pressure in an enclosure;

FIGS. 10A to 10D are diagrams of a vacuum pumping device in an embodiment of the present invention that comprises five stages of the Roots type, shown in four successive configurations while lowering the pressure in the chamber;

FIGS. 11A to 11E are diagrams of a vacuum pumping device in an embodiment of the present invention comprising six stages of the Roots type, in five successive configurations while lowering the pressure in the chamber; and

FIGS. 12B and 12C show an alternative embodiment corresponding respectively to FIGS. 11B and 11C.

Consideration is given initially to the structure of the prior art pumping device shown in FIG. 1.

Such a device comprises a motor 1 which drives a multi-stage Roots type pump 2 that sucks in gas from an enclosure 100 via an intake 3 and exhausts the gas via an outlet 4.

In the embodiment shown, the pump 2 comprises four successive stages respectively 5, 6, 7, and 8, each having a stator stage respectively 5a, 6a, 7a, and 8a, and a double rotor stage respectively 5b, 6b, 7b, and 8b.

Each stage has its own intake respectively 5c, 6c, 7c, and 8c, and its own outlet respectively 5d, 6d, 7d, and 8d.

In that prior art device, the successive stages are connected in series one after another by respective inter-stage pipes 9, 10, and 11. Each inter-stage pipe 9-11 in that prior art pump connects the outlet of the preceding stage to the intake of the following stage. For example, the inter-stage pipe 9 connects the outlet pipe 5d to the intake 6c. This connection is not changed during the pumping process.

With reference now to FIG. 2, there is shown a vacuum pumping device structure in an embodiment of the invention.

This embodiment reproduces the same general structure as a traditional multi-stage Roots pump of the kind shown in FIG. 1, but applies adaptations that make it possible to modify the connections between the stages. Thus, in FIG. 2, there can be found the same main elements as in the pump of FIG. 1, and these elements are identified by the same numerical references.

Thus, there can be seen the four stages 5-8 with their respective intakes 5c-8c, their respective outlets 5d-8d, and the inter-stage pipes 9-11.

The inter-stage pipe 9 connects the outlet 5d to the intake 6c; the inter-stage pipe 10 connects the outlet 6d to the intake 7c; and the inter-stage pipe 11 connects the outlet 7d to the intake 8c.

In the invention, provision is also made for a first bypass pipe 12 between the intake 5c and the inter-stage pipe 9; a second bypass pipe 13 between the inter-stage pipe 9 and the inter-stage pipe 10; a third bypass pipe 14 between the inter-stage pipe 10 and the inter-stage pipe 11; and a fourth bypass pipe 15 between the inter-stage pipe 11 and the outlet 8d, as can be seen in the figure.

Finally, in FIG. 2, there can be seen four valves respectively 16, 17, 18, and 19. The valve 16 is arranged to put the intake 6c selectively into communication either with the bypass pipe 12 or with the inter-stage pipe 9 and the outlet 5d. The valve 17 is arranged to close the bypass pipe 13 selectively. The valve 18 is arranged to put the intake 8c into communication selectively either with the bypass pipe 14 or the inter-stage pipe 11 and the outlet 7d. Finally, the valve 19 is arranged to close the bypass pipe 15, selectively.

In the embodiment shown in FIG. 2, the valves 16 and 17 are mechanically coupled to each other by a longitudinal actuator rod engaged in the inter-stage pipe 9 and driven by an actuator 20. Similarly, the valves 18 and 19 are mechanically coupled to each other on a longitudinal rod driven by an actuator 21.

In the first configuration of the pumping device during a first pumping step E1, the actuators 20 and 21 are lowered, and the valves 16-19 are lowered as shown in FIG. 2. The first and second stages 5 and 6 are connected in parallel with each other, forming a first pair of stages, and the third and fourth stages 7 and 8 are in parallel with each other, forming a second pair of stages. The two pairs of stages are connected in series in the gas-flow path between the intake 3 and the outlet 4.

The actuators 20 and 21 are controlled by an electronic controller 22 to which they are connected by lines 20a and 21a. The electronic controller 22 comprises, for example, a processor associated with memories containing a program for appropriately powering the actuators 20 and 21 and ensuring that the valves 16-19 are appropriately positioned during the various operating steps implemented by the device, as described below.

The speed of the motor 1 is also controlled by the electronic controller 22, and it is connected thereto by a line 1a with a speed controller being disposed outside or inside the motor 1 or in the electronic controller 22.

FIG. 3 shows the same elements as FIG. 2, but in a three-dimensional representation. There can thus be seen the motor 1 and the pump 2 with its intake 3 and its outlet 4. There can also be seen the two actuators 20 and 21, the valves 16 and 18, and the Roots-type rotors 5b, 6b, and 7b of the respective stages 5, 6, and 7. The outlet stage 8 is not visible.

FIG. 4 shows the configuration of the FIG. 2 stages, and thus between the intake 3 and the outlet 4 there can be seen the two stages 5 and 6 connected in parallel with their respective intakes 5c and 6c being connected to each other via the bypass pipe 12, and their respective outlets 5d and 6d being connected to each other by the bypass pipe 13. The stages 7 and 8 are likewise connected in parallel, their respective intakes 7c and 8c being connected to each other by the bypass pipe 14, and their respective outlets 7c and 8c being connected to each other by the bypass pipe 15. The two pairs 5-6 and 7-8 are connected to each other in series by the inter-stage pipe 10 on the path followed by the gas from the intake 3 to the outlet 4.

This first configuration shown in FIGS. 2 to 4 having two pairs of parallel stages corresponds the first configuration given to the device during a first step of pumping out an enclosure.

In FIGS. 5 and 6, the system is given a second configuration, during an intermediate pumping step E2. The first and second stages 5 and 6 or “intake” stages remain connected in parallel with each other, while the third and fourth stages 7 and 8 or outlet stages are connected in series with each other. The first pair of stages formed by the first and second stages 5 and 6 is connected in series with the third and fourth stages 7 and 8. To do this, the actuator 20 remains down while the actuator 21 is raised into an up position.

Finally, in the third or last configuration shown in FIG. 7, for use during the last pumping step E3, all four stages 5, 6, 7, and 8 are connected in series with one another in the gas-flow path. To do this, both actuators 20 and 21 are down.

The advantage of the invention is explained below by performing a simulation by calculation.

It is assumed that an enclosure 100 has a volume V of 1000 L, and that it is desired to evacuate it over a duration t of 45 seconds (s); in practice, it is desired to cause the pressure inside the enclosure to go down from a pressure p1 of 1 atmosphere to a pressure p2 of 0.1 millibars (mBar), for example.

By way of comparison, it is assumed initially that a traditional pump is used. The mean speed S of the traditional pump needs to be about 700 cubic meters per hour (m3/h) in application of the formula:
S=(V/t)ln(p1/p2)

The electrical power needed to drive a flow S from 0.1 mBar to 1 atmosphere is given by the formula:
Pw=(p1−p2)S
where Pw is in watts (W), p1 and p2 are in Pascals (Pa) and S is in cubic meters per second (m3/s), which in the present example gives:
Pw=19.5 kilowatts (kW)

Given the way the power drawn increases progressively from the beginning of pumping, the mean electric power required for emptying the volume is about 13 kW (see FIG. 9).

There follows a demonstration by calculation that the invention makes it possible to obtain a speed of close 700 m3/h in three successive steps with a pump initially designed for an optimum speed of 400 m3/h.

It is assumed that the stage 5 has a speed S1 of 400 m3/h, that the stage 6 has a speed S2 of 300 m3/h, that the stage 7 has a speed S3 of 300 m3/h, and that the stage 8 has a speed S4 of 200 m3/h. It is shown below that the mean power consumption remains below 10 kW.

During a first step of pumping out the enclosure 100, the gas pressure inside the enclosure is taken down from 1 atmosphere to a pressure p1. The vacuum pumping device is then in its configuration as shown in FIGS. 2 and 4.

The expected speed of the pump: S=K(S1+S2)

K=K0/(K0−1+(S1+S2)/(S3+S4))=0.93 with K0=5 at atmospheric pressure

K0 is the compression ratio of the pump at a speed of zero.

S=650 m3/h

Pw=700(p′−p2(in))+500(p(ref)−p′)

with p′=intermediate pressure=p1(in)(S1+S2)/(S3+S4) by the principle of flow conservation.

The power consumption is greater in the high pressure stage. Power increases in each stage with decreasing pressure p1(in).

p1(in) is determined so as to avoid exceeding Pw=10 kW.

If power consumption is calculated for p1=300 mBar by sharing the work between the two stages, then p′=420 mBar and:
Pw=700 m3/h×120 mBar+500 m3/h×580 mBar=10.3 kW

With this new configuration of the pump stages and in this pressure range, the power is again reduced and the pumping speed is close to 700 m3/h.

Reference is made to FIG. 8 which plots the curve of pump speed as a function of pressure in the chamber being pumped out. During step E1, the speed of the vacuum pumping device of the invention in the first configuration follows a curve A that presents a maximum.

When the pressure p1 is reached, the system is switched into the following configuration.

FIG. 9 plots energy consumption for mechanically driving the pump in rotation as a function of the pressure in the enclosure. During step E1, energy consumption increases regularly following a curve B, and then drops suddenly at the pressure p1 when the device is switched into its second configuration.

In the second configuration, shown in FIGS. 5 and 6, the pressure inside the enclosure is taken from a pressure p1 to a pressure p2.

At p1, the parallel outlet stage 7-8 is split into series so as to reduce the power consumed by the high pressure stage.

Speed expected of the pump: S=K′(S1+S2)

K′=0.78 with K0=5 when S=550 m3/h.

The power consumed for p2=50 mBar and assuming the following pressure distribution between the three stages:

50→100→550→1000

Is Pw=700×(100−50)+300×(550−100)+200×(1000−550) i.e. Pw=7.2 kW.

In FIG. 8, it can be seen that during the step E2 between the pressures p1 and p2, the characteristic of the speed S of the device of the invention follows a curve C that presents a maximum. In FIG. 9, it can be seen that during this same step E2, the power characteristic of the device follows a curve D.

Thereafter, the configuration of the device is changed again to take the pressure inside the enclosure down from a pressure p2 to a pressure p3. The configuration is then as shown in FIG. 7, with all four stages 5-8 in series.

At the pressure p2, this configuration of the stages in series enables the compression ratio to be increased.

In order to maintain a high speed of 700 m3/h, it is necessary to increase the nominal pumping velocity by increasing the velocity of rotation.

The velocity is increased by a coefficient Kn.

Expected speed S=400×Kn.

Kn is selected to be 7/4 giving S=700 m3/h.

Power consumption for p3=1 mBar and making an assumption about the compression ratio of the stages as a function of the utilization pressure is as follows:

Stage 5 works from 1 mBar to 10 mBar (K0=10), stage 6 works from 10 mBar to 50 mBar (K0=5), stage 7 works from 50 mBar to 250 mBar, stage 8 works from 250 mBar to 1000 mBar (K0=4).

Pw=Kn (400×9+300×40+300×200+200×750)

Pw=10.9 kW.

In FIG. 8, there can be seen the influence of increasing pump velocity: at constant velocity, the speed characteristic follows curve E, i.e. the speed drops compared with that which was obtained during steps E1 and E2. However, by increasing velocity, the speed characteristic follows curve F, which maintains a pumping speed close to the maximum speed over a significant pressure range.

From the diagram in FIG. 8, it can be seen that curves A, C, and F characterize pumping with a mean speed close to 700 m3/h (curve G representing an ideal pump operating at 700 m3/h), whereas the largest stage of the pump provides only 400 m3/h.

In FIG. 9, it can be seen that the power needed for driving the pump is restricted to about 10 kW, following successive curves B, D, and H, whereas a conventional multi-stage pump having a speed of 700 m3/h would require a power of 19.5 kW as represented by curve I.

The invention thus provides a saving in maximum electric power of 40% to 45%, and a saving in mean energy consumption of 20% to 25%.

It is also considered that the invention provides a saving in the nominal size of the pump of about 40%.

The example described relates to a pumping device having a four-stage Roots-type dry mechanical pump. Naturally, the invention is applicable in the same manner to pumping devices based on a dry mechanical pump having some other number of stages, it being possible for the number of stages to be greater than or equal to four.

FIG. 10 shows an example of successive configurations of a pumping device of the invention as pressure decreases, for a device that has five stages.

In FIG. 10A, there can be seen between the intake 100 and the outlet 101, three stages 102, 103, and 104 connected in parallel, their respective intakes 102c, 103c, and 104c being connected to each other by the bypass pipe 105, their respective outlets 102d, 103d, and 104d being connected to one another by the bypass pipe 106. The two stages 107 and 108 are likewise connected in parallel, their respective intakes 107c and 108c being connected to each other by the bypass pipe 109, their respective outlets 107d and 108d being connected to each other by the bypass pipe 110. The two groups 102-103-104 and 107-108 are connected to each other in series by the inter-stage pipe 111 on the gas-flow path between the intake 100 and the outlet 101.

This first configuration, as shown in FIG. 10A, constitutes the configuration given to the device during a first step E1 of pumping out an enclosure.

In FIG. 10B, the system is given a second configuration in an intermediate pumping step E2. The first and second stages 102 and 103 are connected in parallel with each other as are the third and fourth stages 104 and 107. The first pair of stages formed by the first and second stages 102 and 103 is connected in series with the second pair of stages formed by the third and fourth stages 104 and 107, and also in series with the fifth stage 108.

A third configuration, used in an intermediate pumping step E3, is shown in FIG. 10C. The first and second stages 102 and 103 are connected in parallel with each other, while the third, fourth, and fifth stages 104, 107, and 108 are connected in series with the first pair of stages formed by the first and second stages 102 and 103.

Finally, in the fourth or last configuration shown in 10D, the last pumping step E4 has all five stages 102, 103, 104, 107, and 108 connected in series with each one another on the gas-flow path.

FIG. 11 shows an example of successive configurations for a pumping device of the invention while pressure is being decreased when the device has six stages.

In FIG. 11A, there can be seen between the intake 200 and the outlet 201, three stages 202, 203, and 204 connected in parallel, their respective intakes 202c, 203c, and 204c being connected to one another by the bypass ducts 205, their respective outlets 202d, 203d, and 204d being connected to one another by the bypass ducts 206. The three stages 207, 208, and 209 are likewise connected in parallel, with their respective intakes 207c, 208c, and 209c being connected to one another by the bypass ducts 210, their respective outlets 207d, 208d, and 209d being connected to one another by the bypass ducts 211. The two groups 202-203-204 and 207-208-209 are connected to each other in series by the inter-stage pipe 212 on the gas-flow path between the intake 200 and the outlet 201.

This first configuration shown in FIG. 11A constitutes the configuration given to the device in a first step E1 of pumping out an enclosure.

In FIG. 11B, the system is given a second configuration in an intermediate pumping step E2. The three first stages 202, 203, and 204 remain connected in parallel. The fourth and fifth stages 207 and 208 are connected in parallel with each other. The group 202-203-204, the pair 207-208, and the sixth stage 209 are connected in series.

A third configuration for an intermediate pumping step E3 is shown in FIG. 11C. The first three stages 202, 203, and 204 are still connected in parallel. The fourth, fifth, and sixth stages 207, 208, and 209 are connected in series with one another, and with the group 202-203-204.

A fourth configuration for an intermediate pumping step E4 is shown in FIG. 11D. The first and second stages 202 and 203 are connected in parallel with each other. The third, fourth, fifth, and sixth stages 204, 207, 208, and 209 are connected in series with one another and with the first pair of stages formed by the first and second stages 202 and 203.

Finally, in the fifth or last configuration shown in FIG. 11E, that is used for the final pumping step E5, all six stages 202, 203, 204, 207, 208, and 209 are connected in series with one another on the gas-flow path.

FIG. 12 shows an example of alternative configurations that could be used with a pumping device of the invention having six stages. The first configuration is as shown in FIG. 11A and constitutes the configuration that is given to the pumping device during a first step E1 of pumping out an enclosure.

In FIG. 12B, the system is given a second configuration in an intermediate pumping step E2. Between the intake 300 and the outlet 301, there are the first two stages 302 and 303 connected in parallel, their respective intakes 302c and 303c being connected to each another by the bypass pipe 304, their respective outlets 302d and 303d being connected to each other by the bypass pipe 305. The next two stages 306 and 307 are likewise connected in parallel, their respective intakes 306c and 307c being connected to each other by the bypass pipe 308, while their respective outlets 307d and 308d are connected to each other by the bypass pipe 309. Finally, the last two stages 310 and 311 are likewise connected in parallel, their respective intakes 310c and 311c being connected to each other by the bypass pipe 312, while their respective outlets 310d and 311d are connected to each other by the bypass pipe 313. The three pairs 302-303, 306-307 and 310-311 are connected to one another in series by the inter-stage pipes 314 and 315 respectively on the gas-flow path between the intake 300 and the outlet 301.

A third configuration for an intermediate pumping step E3 is shown in FIG. 12C. The two first stages 302 and 303 are connected in parallel. The third and fourth stages 306 and 307 are also connected in parallel. The last two stages 310 and 311 are connected in series with the pairs 302-303 and 307-308.

The fourth and fifth configurations are analogous to those shown in FIGS. 11D and 11E.

The present invention is not limited to the embodiments described explicitly, and it includes the numerous variants and generalizations that come with the competence of the person skilled in the art.