Daimler AG and

Ford Global Technologies, LLC

PUMP AND FUEL CELL SYSTEM WITH SUCH A PUMP

The invention relates to a pump with a shaft and an impeller arranged on the shaft, and a seal arranged between stationary and moving parts of the pump. The invention additionally relates to a fuel cell system having such a pump.

Such a pump is known from EP 1 315 272 A2.

A canned motor is additionally known from DE 40 28 765 C2 which comprises a heating and cooling device. This is arranged outside the canned motor. It consists on the one hand of a heating jacket, which surrounds longitudinal ribs of the stator housing of the canned motor. On the other hand, it comprises a fan driven by an electric motor, the cooling air stream from which fan is guided through a space formed between the wall of the stator housing, the longitudinal ribs and the heating jacket. When viewed in the longitudinal direction of the motor, the external heating jacket is thus positioned below and at a considerable distance from the electric motor and the fan.

In pumps, in particular blowers or compressors, which are arranged in a fuel cell system, it may happen, in the "off' state and at low ambient temperatures, that the rotor in the canned motor of a fan delivering moist wet gases into a fuel cell system freezes up because of water freeze-out. When starting the fuel cell system and thus also when starting the pump, the pump may then not operate at all or only to a limited degree, since proper operation cannot occur or occurs only with significant delay due to the frozen-up components.

It is the object of the present invention to provide a pump and a fuel cell system having such a pump in which operating behavior at low temperatures may be improved.

This object is achieved by a pump comprising the features as claimed in claim 1 and a fuel cell system comprising the features as claimed in claim 7.

A pump according to the invention comprises a shaft and an impeller arranged on the shaft. The pump additionally comprises a seal, which is arranged between stationary and moving parts of the pump. A part of the housing facing the impeller and/or a part of the seal facing the impeller are heatable. In particular, locations between the impeller and the housing and between the impeller and the seal are thus heatable. The adjoining area between the impeller and the housing and/or the adjoining area between the impeller and the seal may thus be heated specifically, in particular operating phase-specifically. In this way, the operating behavior of the pump may be improved significantly, in particular at low ambient temperatures. Precisely when moving components of the pump have become frozen to stationary parts of the pump after the pump has been in the "off' state, this configuration enables very rapid thawing precisely in these critical areas and thus proper operation of the pump within the shortest possible time after activation.

Preferably, at least one heating element is incorporated into the seal and/or at least one heating element is incorporated into the housing. By incorporating electrical heating elements at locations in the pump at risk of freezing, the ice potentially present may be thawed and detached in the shortest possible time in the event of a cold start, in particular within a few seconds, full functionality of the pump thereby being achieved. With prior art pumps several minutes are needed to achieve this scenario, which causes a considerable delay until sufficient operating functionality is achieved.

Preferably, the heating element is a PTC (Positive Temperature Coefficient) heating element. Such an element is of very compact and thus space-saving construction and furthermore is functionally very reliable and inexpensive.

In particular, the housing may be heated on the side facing the impeller and on a side facing the blades of the impeller. Precisely those areas of the housing which thus virtually at least partially enclose the impeller may thus all be heated virtually fully, so making possible very rapid thawing of frozen zones virtually at all locations at risk at the interface between the impeller and the housing.

In particular, the pump takes the form of a side channel compressor. Preferably, an interrupter zone of the side channel compressor is heatable at least in places, in particular fully. An interrupter zone of the side channel compressor comprises inter alia the in- and outlet openings for in- and outflow of the medium delivered and the separation zone therebetween. Thus, preferably all points potentially at risk of freezing between moving and stationary parts of the pump are accordingly heatable. The annular gap or the labyrinth seal and thus the area between the impeller and the motor side and also the area between the impeller shaft and the housing are accordingly preferably heatable. Furthermore, the area between annular gap or labyrinth seal in the area between the impeller and the housing side are heatable. In a side channel compressor, the entire interrupter zone is preferably heatable.

In the case of a frozen-up impeller in a pump, the invention thus enables thawing within a few seconds, since only a very small mass has to be heated at the critical points. In this way, very rapid and reliable thawing is achieved, which has not hitherto been possible. Reliable starting of the pump and thus rapid proper functioning of the pump is thus ensured irrespectively of how the components were operating prior to switch-off.

The invention also relates to a fuel cell system having at least one fuel cell and one pump according to the invention or to an advantageous configuration thereof. The possibility of improving the mode of operation of the pump thus significantly improves the mode of operation in precisely those fuel cells in which, due to the manner in which they function, water arises which may freeze out in the "off' state at low ambient temperatures.

In particular, the pump is associated with the anode branch of the fuel cell or the fuel cell system. In particular, the pump is arranged in a recirculation branch associated with the anode branch for recirculating the anode waste gas.

However, provision may also be made for the pump according to the invention to be used in any other system in which moist medium is conveyed and which is intended for use at temperatures of below or close to 0° C.

The seal arranged in the pump is in particular a seal of metal, in particular of light metal, preferably an aluminum seal. The housing of the pump is preferably produced as a casting.

Exemplary embodiments of the invention are explained in greater detail below with reference to schematic drawings, in which:

Fig. 1 shows a section through a portion of a pump taking the form of a side channel compressor; and

Fig. 2 is a perspective representation from below of a housing part of the pump according to Fig. 1.

In the figures, elements which are the same or have the same function are provided with the same reference signs.

Fig. 1 is a sectional representation of a detail of a pump 1 taking the form of a side channel compressor. The pump 1 is associated with a fuel cell system having at least one fuel cell, in particular a PEM fuel cell, which is arranged in a motor vehicle. The pump 1 is arranged in an anode branch of a fuel cell of the fuel cell system and therein in particular in a recirculation circuit of the anode branch. The pump 1 is thus designed to deliver hydrogen-containing waste gas.

The pump 1 comprises a rotor 2, which is arranged in a motor compartment. Furthermore, a stator 3 is arranged in the motor compartment, this being positioned fixed to the housing. The rotor 2 is attached to a shaft 4, to which an impeller 5 of the pump 1 is also attached. The impeller 5 takes the form, in the exemplary embodiment, of a disk, at whose circumference a plurality of blades 6 are arranged. The impeller 5 is driven, with the blades 6, via the shaft 4 and rotates about the axis A of the shaft 4.

Adjacent the blades 6 there are formed a lower side channel 7 and an upper side channel 8.

In addition, the pump 1 comprises a labyrinth seal 9, which is arranged on the top 11 (Fig. 2) of the impeller 5. The labyrinth seal 9 extends between the shaft 4 or the area of the impeller 5 facing the shaft 4 and a blade back 18. The labyrinth seal 9 is arranged separately from the impeller 5 and positioned firmly on a housing 10. It thus constitutes a

stationary component of the pump 1. The impeller 5 can move relative to the labyrinth sea! 9.

The housing 10 comprises a part 11 which is arranged virtually as the lower portion or as a lower cover of the pump 1.

The seal 9 is heatable at least in the area facing the impeller 5 and additionally in the area facing the shaft 4. This is marked by way of example by the zone 12. Thus, the seal 9 is heatable at least on the side facing the top of the impeller 5 and also on the side facing the shaft 4, this being symbolized by the cross-sectionally angled shape of the zone 12. Preferably, this heatable zone 12 is rotationally symmetrical about the axis A. Provision may also be made for the entire seal 9 to be heatable.

Furthermore, at least a portion of the part 11 of the housing 10 is heatable. This is characterized in particular by the zone 13. Thus, the portion of the part 11 facing the impeller 5 is heatable. The interfaces between the stationary parts 9 and 11 and the moving part, namely the impeller 5, are thus heatable. In particular, the impeller 5 is heatable virtually both from above and from below.

In addition, the exemplary embodiment provides heatability virtually not only in the horizontal direction (x direction) but also in the vertical direction (y direction). In particular, this is brought about by the zone 14, which constitutes a portion of the part 11 of the housing 10 which is formed laterally adjacent the impeller 5.

Provision may be made for the zones 13 and 14 to constitute a single common zone and to be brought about for example by an integral heating element. In this regard, the zone 14 constitutes virtually a circumferential ring about the axis A.

The sizing both with regard to width and length and with regard to the height of the zones 12, 13 and 14 is given merely by way of example and the zones may also be longer, shorter or higher.

In principle, provision may also be made for a heating element to be additionally incorporated in the impeller 5, this being designed to release heat by suitable energy transfer.

In particular, for such heat production heating elements may be provided in zones 12, 13 and 14 which are incorporated into the components mentioned in each case.

Preferably, the heating elements take the form of PTC heating elements.

The zones 12, 13 and 14 may thus also symbolically represent the position of the heating elements in each case arranged therein.

Provision may also be made in particular in Fig. 1 for the zones 12 and 13 also to be heatable at the blade backs 18 of the blades 6 of the impeller 5 in the seal 9 and/or the part 11 of the housing 10. The zone 12 is thus in particular of U-shaped cross section in each case on both sides of the axis A.

Fig. 2 shows in perspective representation a view from below of the part 11 of the housing 10. It shows the heating element which is provided to heat the zone 13. This is of cup- shaped configuration when viewed from below.

Moreover, an interrupter zone 15 may be provided, which is provided in particular in the case of a pump 1 taking the form of a side channel compressor. This interrupter zone also comprises inter alia inlet and outlet openings 16 and 17 respectively and the separation zone located therebetween. The angled arrows P additionally indicate the direction of circulation of the gas conveyed in the pump 1 or of the gas conveyed in the side channels 7 and 8.

List of reference signs

1 Pump

2 Rotor

3 Stator

4 Shaft

5 Impeller

6 Blades

7,8 Side channels

9 Seal

10 Housing

11 Part of the housing

12,13,14 Heatable zones

15 Interrupter zone

16,17 Openings

18 Blade back

A Axis

P Arrows