Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2002-08-29
2004-10-19
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S006000, C429S006000, C429S010000
Reexamination Certificate
active
06805984
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cooling fan system for a vehicle with fuel cell propulsion, wherein air is moved by means of a cooling fan for cooling purposes through a heat exchanger and can thereafter be supplied to the environmental air either directly or indirectly after satisfying one or more further cooling tasks. The invention relates furthermore to a method for the operation of a fuel cell system.
BACKGROUND OF THE INVENTION
Many proposals have already been made for the equipping of vehicles with fuel cell propulsion systems. Such vehicles are already being constructed and tested.
With such fuel cell propulsion systems, the fuel cells deliver electrical energy which, after appropriate processing, is applied to one or more drive motors which take care of the propulsion of the motor vehicle.
For fuel cell propulsion systems for vehicles, PEM (Proton Exchange Membrane) fuel cells are currently preferred which are connected in parallel and/or in series to one another and form a so-called stack. The fuel cells are supplied, on the one hand, with hydrogen from a suitable source. Protons which originate from the hydrogen and pass through the membranes of the fuel cells combine in the fuel cells with the oxygen of the air which is supplied to form water with the simultaneous generation of electrical energy.
The vehicle can be equipped with a hydrogen storage tank, and may, however, also be fed with a synthesized hydrogen-rich gas which is obtained from a hydrocarbon such as methanol. In this case, the hydrocarbon is processed in a processing device in the form of a so-called reformer to form the synthesized hydrogen-rich gas. When a reformer is used, it also requires air.
Fuel cells are also known which are directly fed with methanol, with the methanol consisting of up to 97% water. Such fuel cell systems require oxygen for the power generating reaction and must be supplied with air by a compressor.
Independently of the type of fuel cells which are used, a compressor is always required which makes available the compressed air for the fuel cells or for the reformer. Part of the output power of the fuel cell system is also applied to an electric motor which is required in operation to drive the compressor.
In practice, problems arise with the starting of a fuel cell system.
One known solution involves the use of a traction battery with, for example, 288 V operating potential. This traction battery has in principle three different tasks:
On the one hand, it is used to drive the main compressor in order to feed air compressed by this compressor into the fuel cell system, so that power is generated which then replaces the traction battery as the power source for the electric motor driving the compressor.
The second task of the traction battery is to assist dynamically the electric motor or electric motors which propel the vehicle so that, for example, with fast acceleration or at elevated speeds, the power of the traction battery supplements the electrical output power of the fuel cell system.
The third task lies in the fact that a traction battery can be used in order to realize regenerative braking for example. That is to say, on braking of the vehicle, the kinetic energy which is present is partly converted into electrical energy which can then be stored in the traction battery.
Although a traction battery can be useful for these different purposes, it represents an expensive and heavy component, so that one would be pleased to dispense with it. If, however, the traction battery is dispensed with, it could no longer be used to start up the fuel cell system.
For the starting of the fuel cell system, air is required. The air compressor is normally driven from the fuel cell potential; however, this is not yet available. In the absence of a traction battery, it has already been proposed to supply the fuel cell system with sufficient air by means of a 12 V auxiliary fan, i.e., a so-called start-up blower, so that the power generation starts there and the system can be gradually run up until the power generation by the fuel cell system is sufficient in order to maintain the system in operation.
Irrespective of whether one operates with a traction battery or with an auxiliary blower, many components which make the system more complicated or more expensive, such as fans, radiators, pipes, 288 V batteries, etc., are necessary which one would prefer to do without.
SUMMARY OF THE INVENTION
The object of the present invention is to make sufficient air available so that the fuel cell system can be started and run up without using a traction battery or an auxiliary fan.
In order to satisfy this object, provision is made, in accordance with the invention, for an air branching device to be provided which supplies at least a part of the air delivered by each fan to a duct and thereby enables the use of the branched-off air for the starting of the fuel cells and/or for the maintenance of the operation of the fuel cells.
In other words, it has been recognized, in accordance with the invention, when using a fuel cell propulsion system in which a cooling fan driven by the normal onboard battery is used for the cooling of liquid flowing through a heat exchanger, with the throughflowing air also being capable of being used for further cooling tasks, that the system consisting of the cooling fan and heat exchanger is unnecessary per se during the starting of the fuel cell system, since the heat which then arises is restricted, and that the cooling fan associated with the heat exchanger can thus be exploited for the starting of the fuel cell system until the fuel cell system delivers sufficient power to drive the compressor itself. That is to say, the cooling fan is used in the short term for the starting of the fuel cell system.
This can in principle take place in such a way that an air branching device, which is simply formed by a fixed guide wall, is provided and always branches off a part of the air flow produced by the cooling fan and supplies it via a suitable line to the fuel cells and/or to a reformer. On operation of the system, a device must then be provided in order to close off the duct when the compressor starts to run in order to prevent the compressed air generated by the compressor from escaping through the corresponding duct in the form of a reverse flow. This need could indeed be avoided if the branched-off air flow generated by the cooling fan is supplied to the inlet of the compressor and thus via the compressor to the fuel cells and/or the reformer.
A further possibility is to make the air branching device movable so that it can be switched between a first substantially inactive position and a second position which brings about the branching off of the air. In this manner it is not only possible to use part of the air flow delivered by the cooling fan, but rather the entire air flow can be used for the starting of the fuel cell system.
The cooling fan can in principle be a suction fan which is arranged downstream of the heat exchanger and sucks the air through the latter, with the air branching device then being arranged downstream of the suction fan. Such suction fans are customary with fuel cell propulsion systems.
It is, however, more favorable if each cooling fan is a pusher fan which is arranged in front of the heat exchanger. A fan of this kind is better able to deliver the airflow required for the starting of the fuel cells because it operates more efficiently under backpressure conditions.
When using a pusher fan, it is preferably connected to the heat exchanger by means of a housing which avoids air losses.
It is particularly favorable when an air guiding housing is arranged downstream of the heat exchanger directly adjacent to the latter so that all the air flowing through the heat exchanger enters into the air guiding housing.
Various possibilities exist in accordance with the invention in order to realize the air branching device. This can, in particular, be realized by adjustable plates, which, in a first position, permit the air moving through the
Bell Bruce F.
Brooks Cary W.
General Motors Corporation
Wills M.
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