Method for Operating a Fluid Conveying Device of a Motor Vehicle Comprising at Least One Aerodynamic Bearing

Abstract

A method is provided for operating a fluid conveying device of a motor vehicle having at least one aerodynamic bearing. The method reduces the rotational speed of the aerodynamic bearing to a rest speed, wherein the rest speed is below a lifting speed, in which case the bearing builds up an air film for bearing free of mixed friction, and wherein the rest speed is above a lowering speed, in which case the bearing has reduced the air film such that mixed friction occurs. The fluid conveying device is operated at the rest speed.

Claims

1. A method for operating a fluid conveying device of a motor vehicle having at least one aerodynamic bearing, the method comprising the acts of: reducing a rotational speed of the aerodynamic bearing to a rest speed, wherein the rest speed lies below a lifting speed, at which the bearing forms an air film for mounting free from mixed friction, and the rest speed lies above a lowering speed at which the bearing has reduced the air film in such a manner that mixed friction occurs; and operating the bearing of the fluid conveying device at the rest speed.

2. The method according to claim 1, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when the motor vehicle is operating.

3. The method according to claim 2, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when the motor vehicle continues to move.

4. The method according to claim 1, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when the motor vehicle continues to move.

5. The method according to claim 3, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when the motor vehicle continues to move at a maximum speed of 70 km/h.

6. The method according to claim 5, wherein the maximum speed is 50 km/h.

7. The method according to claim 5, wherein the maximum speed is 30 km/h

8. The method according to claim 3, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when drive energy is provided by a high-voltage storage device.

9. The method according to claim 5, wherein the fluid conveying device is not stopped and the bearing is operated at least at the rest speed when drive energy is provided by a high-voltage storage device.

10. The method according to claim 1, further comprising the acts of: predicting a rest time; and stopping the fluid conveying device when the predicted rest time exceeds a limiting value of the rest time.

11. The method according to claim 10, wherein the act of predicting the rest time comprises the acts of: recording driving behavior information, navigation information, and/or environmental information; and predicting the rest time taking into account driving behavior information, the navigation information, and/or the environmental information.

12. The method according to claim 1, wherein the fluid conveying device is an oxidizing agent conveying device, which conveys oxidizing agent to a fuel cell stack and/or to a regenerator.

13. The method according to claim 12, wherein during the rest time of the oxidizing agent conveying device, the oxidizing agent is diverted so as not to flow through the fuel cell stack or the regenerator.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0040] FIG. 1 is a schematic diagram of torque M due to friction in a bearing as a function of rotational speed n.

DETAILED DESCRIPTION OF THE DRAWING

[0041] FIG. 1 shows schematically the torques M.sub.d caused by friction in the bearing as a function of the rotational speed n. The continuous curve shows the runup from standstill of the bearing. Initially, a breakaway torque M.sub.d los should be applied to set the shaft mounted in the aerodynamic bearing in motion. The air bearing usually has retaining devices, for example, a spring. These retaining devices bear against the shaft when standing. When the shaft is accelerated from standstill, solid-state friction or adhesive friction occurs in the rotational speed range from n=0 to n.sub.fixed acceleration. The retaining devices are in continuous contact with the shaft. In the rotational speed range from n=n.sub.fixed acceleration to n.sub.lift, mixed friction occurs. At or above the lifting speed n.sub.lift, the bearing builds up an air film for mounting free from mixed friction. The fluid conveying device is operated in this rotational speed range above the lifting speed n.sub.lift.

[0042] Usually a certain safety margin is provided for the lifting speed n.sub.lift, in order to reliably avoid any bearing damage. For example, a conveying device can have a conveying range which is defined by a lower limiting operating speed n.sub.operation u and an upper limiting operating speed n.sub.operation o, where the lower limiting operating speed is sufficiently far from the lifting speed n.sub.lift.

[0043] Up to the lifting speed n.sub.lift, the friction torque M.sub.d decreases continuously. In the air friction region (i.e. n greater than or equal to n.sub.lift), the friction torque M.sub.d gradually increases again slightly.

[0044] If the conveying device is now braked again from the conveying region, during the braking process an approximately identical speed-dependent torque profile is established up to the lifting speed n.sub.lift, as for the runup.

[0045] Below the lifting speed n.sub.lift, however, a different speed-dependent torque profile is established, which is shown by the dashed line in FIG. 1. Initially, the region of air friction, i.e. the region in which an air film is present for mounting free from mixed friction, continues to exist as far as the lowering speed n.sub.low. At the lowering speed n.sub.low as far as the speed n.sub.fixed braking, mixed friction occurs before adhesive or solid-state friction occurs at even lower speeds.

[0046] The lowering speed n.sub.low is lower than the lifting speed n.sub.lift. According to the technology disclosed here, the conveying device or the bearing of the conveying device should be operated precisely in this rest region between the lowering speed n.sub.low and the lifting speed n.sub.lift when the conveying device is in rest mode or standby mode. The rest region therefore has comparatively lower speeds than the conveying region of the conveying device. The friction torques are comparatively low in this rest region. Accordingly the energy consumption in the rest mode is also comparatively low.

[0047] It should be noted that the torque profiles in FIG. 1 are merely shown schematically and in a simplified manner. The values for the different speeds such as, for example the lowering speed n.sub.low and the lifting speed n.sub.lift are dependent on the design of the bearing and the applied load. They can be determined experimentally.

[0048] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.