Daimler AG and

Ford Global Technologies, LLC

Pump and fuel cell system having a pump such as this

The invention relates to a pump having an electric motor, in which a split cage separates the area with the rotor, which revolves in the medium being fed and is arranged on a shaft, from the stator.

A pump such as this is disclosed in EP 1 315 272 A2.

Furthermore, DE 40 28 765 C2 discloses a split-cage motor which has a heating and cooling device. This device is arranged outside the split-cage motor and comprises on the one hand a heating jacket which surrounds longitudinal ribs on the stator housing of the split-cage motor. On the other hand, it has a fan which is driven by an electric motor and whose cooling air flow is passed over an area which is formed between the wall of the stator housing, the longitudinal ribs and the heating jacket. Viewed in the longitudinal direction of the motor, the heating jacket on the outside is therefore positioned underneath and well away from the electric motor and the fan.

In the case of pumps, in particular fans or compressors, which are arranged in a fuel cell system, it is possible when in the switched-off state and in low environmental temperatures for example for the rotor in the split-cage motor of a fan, which feeds moist wet gases into a fuel cell system, to freeze up as a result of water freezing. When the fuel cell system is started and therefore when the pump is started as well, the pump may not operate at all, or may operate only to a restricted extent since the frozen components do not allow normal operation, or allow normal operation only with a significant delay.

The object of the present invention is to provide a pump and a fuel cell system having a pump such as this, in which the operating response at low temperatures can be improved.

This object is achieved by a pump which has the features according to Claim 1 , and by a fuel cell system which has the features according to Claim 12.

A pump according to the invention comprises an electric motor which has a rotor and a stator. Furthermore, the pump comprises a split cage, which separates the area with the rotor, which revolves in the medium being fed and is arranged on a shaft, from the stator. This split cage can be heated. The invention therefore provides for the split cage of the motor of the pump, by means of which the stator of the motor is separated from the moist wet medium being conveyed, to be directly heated in order to thaw out firmly frozen ice or the like between the motor and stator. The capability to heat the split cage means a positive temperature being applied to the split cage by means of an active procedure, which is produced and influenced deliberately. In particular, this is provided with open- loop or closed-loop control by means of electronics. Possible relatively slow and minor heating of the split cage, as is natural as a result of temperature changes in the environment and can occur in a manner which cannot be influenced, is not intended to be meant by this expression, or at best as accompanying it.

The operating response of the pump can in this way be considerably improved. Particularly in low environmental temperatures and possibly with firmly frozen components, this refinement can allow correct operation without delay or directly shortly after starting.

The split cage is preferably itself in the form of a heating unit. This refinement makes it possible to produce a pump whose components are minimized to a major extent, this also making it possible to optimize the heating effectiveness.

The split cage is preferably formed at least in places from electrically conductive plastic, with which electrical contact is made for heating.

In particular, it is possible to provide for the split cage to be formed at least in places from fibre-reinforced plastic to which carbon-black particles are added and with which electrical contact is made for heating.

In particular, the plastic is electrically insulated on the sides facing the housing of the pump. This preferably mea ns that, if the split cage, in particular the split pot, is formed from conductive plastic, this is formed from carbon-fibre-reinforced plastic with carbon-

black particles added to it, in which case this split cage is then appropriately electrically insulated and has electrical contact made with it at the two opposite ends towards the housing of the pump.

It is also possible to provide for heating conductors with which electrical contact is made to be arranged on the split cage. By way of example, the heating conductors can be applied by printing or electroplating. Other types of application are, of course, also possible. In particular, the heating conductors are designed such that their geometry and positioning on the split cage are provided as appropriate for the required operating voltage and heating power.

One refinement, as is provided by way of example for window pane heating in a vehicle, can be provided for this purpose. This is effectively in the form of electrical resistance heating.

It is preferably possible to provide for the heating conductors to be arranged on the outside of the split cage and/or to be integrated in the split cage. They are therefore arranged on the split cage at defined points, which are preferably selected depending on the required operating voltage and the required heating power.

It is also possible to provide for the heating conductors, which are arranged on the split cage or integrated therein, to be heatable via the magnetic field of the stator. Encapsulated or printed-oπ electrical heating conductors which are heated via the stator magnetic field can then preferably be switched on and off by means of a switch, in particular a temperature switch. The temperature switch is preferably in the form of a bimetallic element or a PTC element. A heating conductor can then be activated or deactivated as a function of the temperature.

The shaft is preferably borne by at least one bearing, with the split cage being arranged such that it surrounds at least this one bearing, and the bearing can also be heated by the heating of the split cage. The shaft is preferably borne by two bearings, and the split cage surrounds both bearings and can therefore also heat both bearings. The split cage, or the split pot, therefore preferably surrounds the outer bearing ring entirely or partially, by which means at least one of the two ball bearings above and below the rotor can also be heated.

In particular, the pump may be in the form of a side-channel compressor.

With the aid of the pump according to the invention and an advantageous refinement thereof, the split cage can, for example, be directly electrically heated by a DC voltage of 13.5 volts, and with about 100 W to 500 W. The heating duration starting from a temperature of -15 ⁰ C to above O ⁰ C can then be shortened, for example, to a few seconds, in particular to about 2 seconds. This is a considerable reduction in that time which the pump requires to operate correctly from the state in which components are firmly frozen, since several minutes are required to do this in the case of pumps known from the prior art.

A fuel cell system according to the invention comprises a pump according to the invention or an advantageous refinement thereof. The pump is, in particular, arranged in or associated with an anode branch of the fuel cell system. In particular, the pump is arranged in a recirculation branch, which is associated with the anode branch, for feeding back the anode off-gas. Particularly when using the pump in a fuel cell system, when the fuel cell system is in the shut-down state, the water formed therein can freeze at low environmental temperatures, and movable parts of the pump can thus freeze firmly. By means of the fuel cell system according to the invention, the condensation on the media side of the split pot or split cage and thus ice formation on freezing can be overcome not only during a cold-starting phase after deactivation of the fuel cell system but in principle also during continuous operation. The split cage can therefore also be heated in an entirely general form on an operating-phase-specific basis, in which case, in this context, the expression an operating-phase specification also covers normal operation of the pump or of the fuel cell system. In this context, this may also cover heating after shutting down the system, thus providing heating during cooling-down phases immediately after shutdown, in order to make it possible in this context to also prevent water from freezing.

One exemplary embodiment of the invention will be explained in more detail in the following text with reference to a schematic drawing. The single figure shows a section illustration through a subarea of a pump in the form of a side-channel compressor.

The section illustration in the figure shows a partial detail of a pump 1 in the form of a side-channel compressor. The pump 1 is associated with a fuel cell system with at least one 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, where it is positioned, in particular, in a recirculation circuit of the anode branch. The pump 1 is therefore designed to feed anode off-gas.

The pump 1 comprises a rotor 2 which is arranged in a motor area. A stator 3 is also arranged in the motor area and is positioned fixed to the housing. The rotor 2 is attached to a shaft 4, on which an impellor 5 of the pump 1 is also mounted. The impellor 5 in the exemplary embodiment is in the form of a disc, on whose circumference a plurality of blades 6 are arranged. The impellor 5 together with the blades 6 is driven via the shaft 4, and rotates around the axis A of the shaft 4.

A lower side channel 7 and an upper side channel 8 are formed adjacent to the blades 6.

Furthermore, the pump 1 has a labyrinth seal 9, which is arranged at the top of the impellor 5. The labyrinth seal 9 extends between the shaft 4 or the area of the impellor 5 facing the shaft 4 and a blade rear area 12. The labyrinth seal 9 is arranged separately from the impellor 5, and is positioned firmly on a housing 10. This therefore represents a stationary component of the pump 1. The impellor 5 can move relative to the labyrinth seal 9.

The shaft 4 is mounted on an upper bearing 11 and on a lower bearing 12.

The electric motor of the pump, comprising the rotor 2 and the stator 3, is arranged such that the rotor 2 is arranged in a wet area 13, in which the moist wet medium being conveyed, in particular anode off-gas, flows.

A split pot or split cage 14 is arranged in the pump 1 such that it separates the wet area 13 with the rotor 2, which revolves in the medium being conveyed and is arranged on the shaft 4, from the stator 3. This split cage 14 can be heated.

In particular, the invention provides for the split cage 14 to itself represent a heating unit.

As can be seen from the illustration in the figure, the split cage 14 extends over a length (the extent in the Y-direction) such that it surrounds both the upper bearing 11 and the lower bearing 12.

Furthermore, the split cage 14 is designed such that it tapers at its upper end 15.

A lower end 16 of the split cage 14 extends to or even into the labyrinth seal 9.

It is possible for the split cage 14 to be formed from conductive plastic, in particular from carbon-fibre-reinforced plastic, to which carbon-black particles are added, in order to produce the heating unit. This split cage 14 is electrically insulated in places and on the other hand has electrical contact made with it at the ends 15 and 16, in each case towards the housing of the pump 1. The electrical power for heating can be supplied in this way.

It is also possible to provide for the heating to be provided by one or more heating conductors being formed in an integrated form on an outer face 17 and/or in the split pot or the split cage 14. External application can be made possible by printing or electroplating, in which case encapsulation can be provided in the case of an integral embodiment. The number and/or the geometry and/or the positioning of the heating conductors on/in the split cage 14 are/is preferably dependent on the required operating voltage and/or on the required heating power. Electrical contact is then also made with these heating conductors in order to allow the appropriate power to be supplied for heating.

It is possible to provide for the split cage 14 either to be formed completely from conductive plastic or only in places from a material such as this. If the split cage 14 is provided with a conductive plastic only in places, then these points are preferably selected in a defined manner in order in turn to make it possible to predetermine a suitable geometry and positions of this conductive plastic area on the basis of the required operating voltage and the required heating power.

It is also possible to provide for the applied and/or integrated heating conductors to be heatable via the magnetic field of the stator 3. Provision is then preferably made for a switch, in particular a temperature switch, additionally to be provided, allowing the electrical heating conductors to be switched on and off as a function of the temperature.

List of reference symbols

1 Pump

2 Rotor

3 Stator

4 Shaft

5 lmpellor

6 Blade

7, 8 Side channel

9 Labyrinth seal

10 Housing

11 , 12 Bearing

13 Wet area

14 Split cage

15, 16 Ends

A Axis