Method for energy-saving, low-wear operation of a gas bearing

Abstract

A method (100) for operating a gas bearing (1), wherein the gas bearing is formed by a rotor (11) and a stator (12), wherein when there is rotation against a stator (12) with a lift-off rotational speed n.sub.L the rotor (11) changes from mixed friction with the stator (12) into fluid friction with a medium (13) located between the stator (12) and the rotor (11), wherein the rotational speed of the rotor (11) is kept at or above an idling rotational speed n.sub.I, wherein—in response to a first information item (21), on the basis of which a change ΔF is to be expected in the acceleration forces F acting on the gas bearing (1), a new value of a safety factor r.sub.N:=n.sub.I/n.sub.L between the idling rotational speed n.sub.I and the lift-off rotational speed n.sub.L is determined (110), and/or—in response to a second information item (31), on the basis of which a change Δn.sub.L is to be expected in the lift-off rotational speed n.sub.L, a new value n.sub.L,neu is determined for the lift-off rotational speed n.sub.L (120), wherein the idling rotational speed n.sub.I of the gas bearing (1) is adapted to the changed value of the safety factor r.sub.N, and/or to the changed value n.sub.L,neu of the lift-off rotational speed n.sub.L, (130). The invention further relates to an associated computer program.

Claims

1. A method (100) for operating a gas bearing (1), wherein the gas bearing (1) is formed by a rotor (11) and a stator (12), wherein as the rotor (11) rotates against a stator (12) at a lift-off rotational speed n.sub.L said rotor transfers from a state of mixed friction with the stator (12) into a state of fluid friction with a medium (13) located between the stator (12) and the rotor (11), wherein the rotational speed of the rotor (11) is held at or above an idling rotational speed n.sub.I, wherein: in response to a first piece of information (21) on the basis of which a change ΔF in the acceleration forces F that are acting on the gas bearing (1) is to be expected, a new value of a safety factor r.sub.N:=n.sub.I/n.sub.L between the idling rotational speed n.sub.I and the lift-off rotational speed n.sub.L is determined (110), wherein the first piece of information (21) includes at least one measured value from an acceleration sensor (22) and the idling rotational speed n.sub.I of the gas bearing (1) is adapted to the amended value of the safety factor r.sub.N.

2. The method (100) as claimed in claim 1, wherein the acceleration forces F that are to be expected are evaluated during a prognosis time period T.sub.P that lies in the future from a history that is collected during an observation time period T.sub.B of measured values (22a) that are provided by the acceleration sensor (22) (105).

3. The method (100) as claimed in claim 2, wherein the first piece of information includes at least one evaluation (23) of a state of the road surface section on which a vehicle that has the gas bearing (1) is located, and/or of a road surface section that said vehicle is approaching.

4. The method (100) as claimed in claim 3, wherein the evaluation (23) and/or a measured variable that is related to the evaluation (23), are obtained from a digital card (23a), and/or from an information service (23b), which can be accessed by way of a network or from another vehicle (23c).

5. The method (100) as claimed in claim 4, wherein the first piece of information (21) includes a piece of information (24) that a vehicle that has the gas bearing (1) is expected to be at a standstill for at least a predetermined time period.

6. The method (100) as claimed in claim 5, wherein the idling rotational speed n.sub.I is updated in addition to a current or future load requirement on a device that has the gas bearing (1) (130), and wherein the actual rotational speed of the gas bearing (1) is controlled and/or regulated by virtue of controlling a drive of the rotor-shaft unit of the gas bearing (1) to the adapted idling rotational speed n.sub.I.

7. The method (100) as claimed in claim 1, wherein the first piece of information includes at least one evaluation (23) of a state of the road surface section on which a vehicle that has a gas bearing (1) is located and/or of a road surface section that said vehicle is approaching.

8. The method (100) as claimed in claim 7, wherein the evaluation (23) and/or a measured variable that is related to the evaluation (23), are obtained from a digital card (23a), from an information service (23b), which can be accessed by way of a network, and/or from another vehicle (23c).

9. The method (100) as claimed in claim 1, wherein the first piece of information (21) includes a piece of information (24) that a vehicle that has the gas bearing (1) is expected to be at a standstill for at least a predetermined time period.

10. The method (100) as claimed in claim 1, wherein in response to a second piece of information (31) on the basis of which a change Δn.sub.L in the lift-off rotational speed n.sub.L is to be expected, a new value n.sub.L,new of the lift-off rotational speed n.sub.L is determined (120), wherein the idling rotational speed n.sub.I of the gas bearing (1) is adapted to the amended value of the rotational speed n.sub.L,new of the lift-off rotational speed n.sub.L (130), and wherein the second piece of information (31) includes a measured value (32) that relates to the ambient conditions under which the gas bearing (1) is being operated.

11. The method (100) as claimed in claim 10, wherein the second piece of information (31) includes at least one measured value (33) that relates to a state variable of the medium (13).

12. The method (100) as claimed in claim 10, wherein the second piece of information (31) includes at least one usage indicator (34) of the gas bearing (1).

13. The method (100) as claimed in claim 10, wherein the second piece of information (31) is determined by a model (35) of the gas bearing (1).

14. The method (100) as claimed in claim 1, wherein the idling rotational speed n.sub.I is updated in addition to a current or future load requirement on a device that has the gas bearing (1) (130).

15. The method (100) as claimed in claim 1, wherein the actual rotational speed of the gas bearing (1) is controlled or regulated by virtue of controlling a drive of the rotor-shaft unit of the gas bearing (1) to the adapted idling rotational speed n.sub.I.

16. The method (100) as claimed in claim 1, wherein the gas bearing (1) is located in a compressor for the supply of a combustion gas or oxidizing agent to a fuel cell.

17. A computer program that has machine-readable instructions that, when implemented on a computer and/or on a control device, cause the computer and/or the control device to perform the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features that improve the invention are illustrated in detail below together with the description of the preferred exemplary embodiments of the invention with the aid of the figures.

(2) In the drawings:

(3) FIGS. 1a-c illustrate the principle structure of a gas bearing and the dependency of the coefficient of friction μ on the rotational speed n;

(4) FIG. 2 exemplary embodiment of the method 100;

(5) FIGS. 3a-c illustrate exemplary adaptations of the safety factor r.sub.N or rather of the lift-off rotational speed n.sub.L.

DETAILED DESCRIPTION

(6) FIG. 1a illustrates a sectional drawing of the principle structure of a gas bearing 1 at a standstill or in a state in which the prevailing rotational speed n is less than the lift-off rotational speed n.sub.L. The rotor 11 is rotatably supported against the stator 12 and lies against it. Moreover, the intermediate space between the rotor 11 and the stator 12 is filled with the medium 13, for example air. If the rotor 11 is rotated against the stator 12, which is indicated by the arrow, then a mixed friction occurs between the rotor 11 and the stator 12 on account of the solid body contact.

(7) FIG. 1b illustrates the same gas bearing 1 in the state in which the prevailing rotational speed n is equal to or greater than the lift-off rotational speed n.sub.L. The medium 13 now forms an all-round pressure cushion between the rotor 11 and the stator 12. In the event that the rotor 11 deflects radially against the stator 12, the pressure of the medium 13 is increased at the site where the rotor 11 approaches the stator 12. This exerts a restoring force that is directed against the deflection.

(8) FIG. 1c illustrates the progression of the coefficient of friction μ in the gas bearing 1 as a function of the rotational speed n. In the range I of the mixed friction, the solid body friction between the rotor 11 and the stator 12 dominate. As the rotational speed n increases, the shape of the pressure cushion of the medium 13 increasingly acts against the force that pushes the rotor 11 against the stator 12. Consequently, the coefficient of friction μ reduces on balance. The minimum of the coefficient of friction μ is realized in the case of the lift-off rotational speed n.sub.L in the transition range II between the mixed friction and the pure fluid friction. In this case, precisely the solid body friction between the rotor 11 and the stator 12 is eliminated while simultaneously the fluid friction of the rotor 11 against the medium 13 is not yet very pronounced.

(9) An idling rotational speed n.sub.I is now selected for a low-wear operation of the gas bearing 1, said idling rotational speed being in the range III of the pure fluid friction between the rotor 11 and the medium 13. In so doing, it is cost-effective with regard to the energy consumption if n.sub.I is as close as possible to n.sub.I since the fluid friction increases considerably as the rotational speed n increases. On the other hand, as n.sub.I moves closer to n.sub.L, there is the risk that in the event of a sudden effect of force on the gas bearing 1 solid body contact could occur between the rotor 11 and the stator 12. The method in accordance with the invention provides in this case an optimal trade-off, i.e. the idling rotational speed n.sub.I is reduced as far as possible in the case of an acceptable risk of solid body contact occurring.

(10) FIG. 2 illustrates an exemplary embodiment of the method 100. In accordance with step 110, a new value of the safety factor r.sub.N between the idling rotational speed n.sub.I and the lift-off rotational speed n.sub.L is determined in response to a piece of information 21 that a change ΔF is to be expected in the acceleration forces F that are acting on the gas bearing. The piece of information 21 can originate from different sources that can also be combined with one another.

(11) It is thus possible for the piece of information 21 to include a measured value 22a that is provided by an acceleration sensor 22. Measured values 22a that are provided by the acceleration sensor 22 can however also be obtained for example during an observation time period T.sub.B and in the optional step 105 they can be used during a prognosis time period T.sub.P that lies in the future to evaluate the acceleration forces F that are to be expected. It is possible in this manner to update the safety factor r.sub.N for example of the changing quality of a road surface which is being driven over by a vehicle that has a gas bearing 1. However, it is also possible for example to obtain an already finished evaluation 23 of a road surface section that is currently being driven over or that will be driven over in the near future from any source, for example from a digital card 23a, from an information service (cloud) 23b, which can be accessed by way of a network, and/or from another vehicle 23c (possibly by way of a vehicle-to-vehicle communication). It is also possible to use a piece of information 24 that it is to be expected that the vehicle that has the gas bearing will be at a standstill for at least a predetermined time period. As previously described, this includes both the case that a prevailing standstill state continues and also the case that the standstill state only occurs in the future. It is therefore possible to use information both regarding the current state of movement of the vehicle and also regarding the predictive state of movement of the vehicle.

(12) As an alternative thereto or also in combination therewith, it is possible in step 120 to determine a new value n.sub.L,new for the lift-off rotational speed n.sub.L in response to a piece of information 31 that the lift-off rotational speed n.sub.L will change. The piece of information 31 can include for example measured values 32 of ambient conditions, measured values 33 of state variables of the medium 13, and/or usage indicators 34 of the gas bearing 1. Furthermore, the piece of information 31 can also be determined using an applied model 35 of the gas bearing 1, which is evaluated for example in the control device. It is possible for example to determine conditions of the gas bearing 1, such as a temperature, at least approximately from such a model 35 in order to forego additional sensors.

(13) Irrespective of whether the step 110 or 120 is performed individually or in combination, the end effect is a new idling rotational speed n.sub.I. This is set in step 130 on the gas bearing 1 and in so doing it is possible in addition to update a current or future load requirement on a device that has a gas bearing 1. It is possible in this manner to more or less avoid that the rotational speed n needs to be suddenly accelerated in order to fulfill the load requirement.

(14) FIG. 3 illustrates as an example different adjustments to the safety factor r.sub.N or to the lift-off rotational speed n.sub.L.

(15) In FIG. 3a, the safety factor r.sub.N is plotted dependent upon the absolute velocity of a vehicle that has a gas bearing 1. The safety factor r.sub.N that is normally 2.4 has considerably reduced to 1.5 for the vehicle at a standstill and rapidly increases back to 2.4 as soon as the vehicle is moved. The method is equally active when the vehicle is traveling forwards or backwards.

(16) FIG. 3b illustrates the effects a temperature change has on the lift-off rotational speed n.sub.L. The rotational speeds n are plotted against the absolute vehicle velocity |v|.

(17) In the case of a cold temperature, the lift-off rotational speed n.sub.I, is at a first level n.sub.L,C. In the case of a warm temperature, the lift-off rotational speed n.sub.L is at a second, higher level n.sub.L,W. In the case of an identical safety factor r.sub.N, this leads to the idling rotational speed n.sub.I at a warm temperature (curve n.sub.I,W) being higher than the idling rotational speed n.sub.I in the case of a cold temperature (curve n.sub.I,C).

(18) Similar to FIG. 3a, the safety factor n.sub.R is reduced for a vehicle that is at a standstill, i.e. when the vehicle is at a standstill, the idling rotational speed n.sub.I both in the case of a cold temperature and also in the case of a warm temperature respectively is considerably lower than when the vehicle is traveling.

(19) In FIG. 3c, as an example, the safety factor r.sub.N is plotted against vehicle velocity v and in fact once for a good road surface state (curve r.sub.N,G) and once for a poor road surface state (curve r.sub.N,P).

(20) When the vehicle is at a standstill, it is not possible for the road surface state as such to produce any shocks on the gas bearing 1. The safety factors r.sub.N,G and r.sub.N,P are therefore identical for the two road surface states under consideration. However, if the vehicle is moved, the safety factor r.sub.N,P increases for a poor road surface to a considerably higher level than the safety factor r.sub.N,G for a good road surface. Furthermore, in contrast to FIG. 3a, the safety factors r.sub.N,G and r.sub.N,P are not constant as the vehicle is moving but rather increase as the velocity v increases. Consequently, consideration is given to the condition that sudden shocks as a result of the vehicle traveling over an uneven road surface at higher velocities lead to greater effects of force on the gas bearing 1.