U.S. patent application number 09/928699 was filed with the patent office on 2002-03-07 for thermal management of fuel-cell-powered vehicles.
This patent application is currently assigned to GENERAL MOTORS CORPORATION. Invention is credited to Skala, Glenn William.
Application Number | 20020027027 09/928699 |
Document ID | / |
Family ID | 24006309 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027027 |
Kind Code |
A1 |
Skala, Glenn William |
March 7, 2002 |
Thermal management of fuel-cell-powered vehicles
Abstract
Thermal management of a fuel-cell-powered electric vehicle
having at least one high temperature heat transfer circuit and one
low temperature heat transfer circuit each using the same
dielectric heat transfer medium as the other. The circuits are in
flow communication with each other so that hot heat transfer medium
can flow form the high temperature circuit into the low temperature
circuit, and cooler heat transfer medium can flow from the low
temperature circuit into the high temperature circuit under
controlled conditions for heating the fuel cell when it is cold,
cooling a fuel processor when it is hot, and otherwise meeting the
thermal demands of the vehicle.
Inventors: |
Skala, Glenn William;
(Churchville, NY) |
Correspondence
Address: |
LAWRENCE B. PLANT
General Motors Corporation
Legal Staff-Intellectual Property
P. O. Box 300, Mail Code 482-C23-B21
Detroit
MI
48265-3000
US
|
Assignee: |
GENERAL MOTORS CORPORATION
|
Family ID: |
24006309 |
Appl. No.: |
09/928699 |
Filed: |
August 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09928699 |
Aug 13, 2001 |
|
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09504450 |
Feb 16, 2000 |
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Current U.S.
Class: |
180/65.22 |
Current CPC
Class: |
B60L 58/33 20190201;
Y02T 90/16 20130101; Y02E 60/50 20130101; B60L 58/34 20190201; H01M
2250/20 20130101; H01M 8/04029 20130101; Y02T 90/40 20130101; B60L
1/02 20130101; H01M 8/0612 20130101 |
Class at
Publication: |
180/65.2 |
International
Class: |
B60K 006/00 |
Claims
1. In a fuel-cell-powered vehicle having a fuel cell system for
generating electricity from hydrogen and oxygen, a traction motor
energized by said electricity for propelling said vehicle, power
electronics for controlling said traction motor, a heat exchanger
for controlling the environment in an occupant compartment of the
vehicle, and a radiator for expelling excess heat from said
vehicle, the improvement comprising: a high temperature heat
transfer circuit including a heat-generating fuel processor for
converting a liquid hydrocarbon into hydrogen for fueling a PEM
fuel cell, at least one endothermic device extracting heat from
said high temperature circuit, and a first pump for circulating a
dielectric liquid heat transfer medium through said high
temperature circuit; a low temperature heat transfer circuit
including said fuel cell, said traction motor, said electronics,
said radiator, and a second pump for circulating said heat transfer
medium through said low temperature circuit; a first valve
communicating said high and low temperature circuits and adapted,
when open, to direct a first quantity of said medium from one of
said circuits to the other of said circuits; a second valve
communicating said high and low temperature circuits and adapted to
direct a second quantity of said medium equal to said first
quantity from said other circuit to said one circuit when said
first valve is open; and a controller responsive to the thermal
requirements of said vehicle for controlling the opening and
closing of said first valve to change the temperature of the medium
in each circuit.
2. The vehicle according to claim 1 including a single motor for
driving both said first and second pumps.
3. The vehicle according to claim 1 wherein said firsts valve is
selected from the group consisting of pulse-width-modulating
valves, proportioning valves and variable orifice valves.
4. The vehicle according to claim 1 wherein said second valve is a
check valve.
5. The vehicle according to claim 1 wherein said fuel cell includes
a first sensor for determining the temperature of said fuel cell
and said controller is responsive to said first sensor.
6. The vehicle according to claim 1 wherein said fuel processor
includes a second sensor for determining the temperature of said
fuel processor and said controller is responsive to said second
sensor.
7. The vehicle according to claim 1 wherein said medium comprises
an oil which is liquid at 300.degree. C., pumpable at -40.degree.
C., and has a DC volume resistivity of at least about 250
ohm-cm.
8. The vehicle according to claim 7 wherein said oil is a paraffmic
hydrocarbon.
9. The vehicle according to claim 1 wherein said endothermic device
comprises a vaporizer for vaporizing said hydrocarbon and/or water
for use in said fuel cell system.
10. A method of operating a fuel-cell-powered vehicle having (a) a
fuel cell for generating electricity from hydrogen and oxygen, (b)
a traction motor energized by said electricity for propelling said
vehicle, (c) power electronics for controlling said traction motor,
(d) a heat exchanger for controlling the environment in an occupant
compartment of the vehicle, (e) a radiator for expelling excess
heat from said vehicle, (f) a heat-generating fuel processor for
converting a liquid hydrocarbon into hydrogen for fueling said fuel
cell, (g) at least one endothermic device, (h) a first pump for
circulating a liquid heat transfer medium in a high temperature
circuit between said fuel processor and said endothermic device,
and (i) a second pump for circulating said heat transfer medium in
a low temperature circuit through said fuel cell, said traction
motor, said electronics, and said radiator, said method comprising
the steps of: determining the temperature of said fuel cell;
pumping a first quantity of said medium from said high temperature
circuit into said low temperature circuit to elevate the
temperature of the medium in said low temperature circuit and
warm-up said fuel cell when it is too cold; and displacing an equal
quantity of said medium from said low temperature circuit into said
high temperature circuit when said first quantity is being pumped
into said low temperature circuit .
11. A method of operating a fuel-cell-powered vehicle having (a) a
fuel cell for generating electricity from hydrogen and oxygen, (b)
a traction motor energized by said electricity for propelling said
vehicle, (c) power electronics for controlling said traction motor,
(d) a heat exchanger for controlling the environment in an occupant
compartment of the vehicle, (e) a radiator for expelling excess
heat from said vehicle, (f) a heat-generating fuel processor for
converting a liquid hydrocarbon into hydrogen for fueling said fuel
cell, (g) at least one endothermic device, (h) a first pump for
circulating a liquid heat transfer medium in a high temperature
circuit between said fuel processor and said endothermic device,
and (i) a second pump for circulating said heat transfer medium in
a low temperature circuit through said fuel cell, said traction
motor, said electronics, and said radiator, said method comprising
the steps of: determining the temperature of said fuel processor;
and pumping a first quantity of said medium from said high
temperature circuit into said low temperature circuit and an equal
quantity of said medium from said low temperature circuit into said
high temperature circuit to cool the medium in the high temperature
circuit and thereby cool the fuel processor when it is too hot.
Description
BACKGROUND OF THE INVENTION
[0001] The automobile industry is investigating the commercial
feasibility of powering electric vehicles with hydrogen-oxygen
fueled fuel cells, and particularly with so-called PEM fuel cells
(a.k.a. SPE fuel cells). PEM fuel cells are well known in the art,
and comprise a membrane-electrode-assembly which is a thin,
proton-transitive, solid polymer membrane-electrolyte (e.g.
perflourinated sulfonic acid) having an hydrogen electrode (i.e.
anode) on one of its faces and an oxygen electrode (i.e. cathode)
on the opposite face. The hydrogen is preferably provided by
catalytically decomposing liquid hydrocarbons (e.g. methanol,
gasoline etc.)into H.sub.2 and CO.sub.2 in a reactor known as a
"fuel processor". Fuel processors can take several different forms,
but generally comprise a steam reformer section where the
hydrocarbon and steam react endothermically to form a reformate
that includes H.sub.2, CO.sub.2, and some CO. The heat for the
reaction is provided from either (1) an external combuster that
burns a fuel to produce a heated exhaust stream that heats the
reformer, or (2) a partial oxidation (POx) reactor, upstream of the
steam reformer, that preheats the hydrocarbon-steam inputs to the
steam reformer. The fuel processor also includes a CO clean-up
section that reduces the CO content of the reformate to a
sufficiently low level that it will not poison the anode catalyst
of the fuel cell. The fuel processor's clean-up section typically
includes: (1) a water-gas-shift reactor that exothermically reacts
the CO in the reformate with water to form more H.sub.2; and (2) a
preferential oxidation (PrOx) reactor that selectively
exothermically reacts the CO in the reformate with oxygen from the
air. The CO clean up typically reduces the CO content to below
about 50 PPM which the fuel cell can tolerate. This substantially
CO-free is then sent to the fuel cell where it electrochemically
and exothermically reacts with oxygen (from air) to produce
electricity for powering the vehicle's traction motor(s). The
traction motor(s) and the power electronics in the controller that
controls the motor(s) are both exothermic devices in that they
produce heat while in use, and must be cooled.
[0002] Heat management in fuel-cell-powered vehicles is a
challenge. A number of the vehicle's components are exothermic
devices in that they produce heat while in use and require cooling.
Other of the vehicle's components are endothermic devices in that
they require heat to be operational. For example, the fuel cell
system will typically include a number of endothermic and
exothermic devices such as an air compressor (exothermic), water
recovery condensers (exothermic), and vaporizers (endothermic) for
vaporizing water and/or fuel for use in the system, as well as a
variety of other devices that either require (endothermic) or
generate (exothermic) heat. Still further, the vehicle requires a
heating, ventilation & cooling subsystem (HVAC)for occupant
comfort. Moreover, significant differences exist between the
operating temperatures of the vehicle's components. In this regard
for example, the fuel cell, traction motor, and power electronics
are typically maintained at relatively low operating temperatures
in the range of about 80.degree. C. to about 100.degree. C., while
the fuel processor and fuel/H.sub.2O vaporizers are maintained at
relatively high operating temperatures in the range of about
200.degree. C. to about 300.degree. C.
[0003] Heretofore it has been the practice to provide several
discrete heat transfer circuits one for the fuel cell system, one
for the traction motors and power electronics and one for the HVAC
system. Each system had its own componentry (e.g. plumbing, pumps,
and valves), was completely isolated from the other systems, and
used a heat transfer medium adapted to itself and different from
the heat transfer mediums used in the other systems. Such
componentry adds weight and cost to the vehicle.
[0004] The present invention is directed to an efficient, low
weight and cost effective thermal management system for a
fuel-cell-powered vehicle, which system utilizes the same heat
transfer medium throughout, and minimizes the number of components
required to manage the heat produced by the vehicle.
SUMMARY OF THE INVENTION
[0005] The present invention involves a fuel-cell-powered vehicle
that has a fuel cell system for generating electricity from
hydrogen and oxygen, a traction motor energized by the electricity
to propel the vehicle, power electronics that control the traction
motor, a heat exchanger that controls the environment in the
vehicle's occupant compartment , and a radiator that expels excess
heat generated by the vehicle to the ambient. The invention
contemplates such a vehicle having: (1) a high temperature heat
transfer circuit that includes a heat-generating fuel processor
that converts a liquid hydrocarbon into hydrogen for fueling a PEM
fuel cell, at least one endothermic device that extracts heat from
the high temperature circuit, and a first pump that circulates a
dielectric liquid heat transfer medium through the high temperature
circuit; (2) a low temperature heat transfer circuit that includes
the fuel cell, traction motor, power electronics, radiator, and a
second pump that circulates the same dielectric heat transfer
medium as is used in the high temperature circuit through the low
temperature circuit; (3) a controllable first valve that
communicates the high and low temperature circuits and is adapted,
when open, to direct a first quantity of medium from one of the
circuits (i.e. the donor circuit) into the other of the circuits
(i.e. the receiving circuit); (4) a second valve that communicates
the high and low temperature circuits and is adapted to direct a
second quantity of the medium, equal to the first quantity, from
the other (i.e. receiving) circuit to the one (i.e. donor) circuit
when the first valve is open; and (5) a controller, responsive to
the thermal requirements of the vehicle, for controlling the
opening and closing of the first valve to change the temperature of
the medium in each of the circuits as dictated by the thermal needs
of the components in those circuits. Preferably, the vehicle
utilizes a single motor to drive both the first and second
pumps.
[0006] In accordance with one embodiment of the invention, the
endothermic device comprises a vaporizer for vaporizing the
hydrocarbon and/or water utilized in the fuel cell system. In
another embodiment of the invention, the fuel cell includes a
sensor for determining its temperature and the controller is
responsive to that sensor to direct hot heat transfer medium from
the high temperature circuit into the low temperature circuit when
the fuel cell is undesirably cold (e.g. to thaw out the fuel cell
after it has sat idle at subfreezing temperatures). According to
still another embodiment of the invention, the fuel processor has a
sensor for determining the temperature of the fuel processor, and
the controller is responsive to that sensor to direct hot heat
transfer medium from the high temperature circuit into the low
temperature circuit when any part of the fuel processor (e.g. the
combuster or PO.sub.x sections) is too hot (e.g when the electrical
load is removed from the fuel cell before the fuel processor can
slow down H.sub.2 production) to extract excess heat from the
medium by means of the radiator in the low temperature circuit. A
particularly effective heat transfer medium comprises a dielectric
oil which is liquid at 300.degree. C., pumpable at -40.degree. C.,
and has a DC volume resistivity of at least about 250 ohm-cm (i.e.
as determined by ASTM Specification D-1169) in order to prevent any
short circuiting of the fuel cell, or current leakage therefrom to
the rest of the vehicle, via the heat transfer medium. A preferred
such heat transfer medium is a paraffinic hydrocarbon having a DC
volume resistivity of 1.times.10.sup.12 ohm-cm that is sold by the
Paratherm Corporation under the tradename Paratherm OR.TM.
[0007] In accordance with another aspect of the invention, the
invention contemplates a method of operating a fuel-cell-powered
vehicle having (a) a fuel cell for generating electricity from
hydrogen and oxygen, (b) a traction motor energized by the
electricity for propelling the vehicle, (c) power electronics for
controlling the traction motor, (d) a heat exchanger for
controlling the environment in an occupant compartment of the
vehicle, (e) a radiator for expelling excess heat from the vehicle,
(f) a heat-generating fuel processor for converting a liquid
hydrocarbon into hydrogen for fueling the fuel cell, (g) at least
one endothermic device that extracts heat from the vehicle, (h) a
first pump for circulating a liquid heat transfer medium in a high
temperature circuit between the fuel processor and the endothermic
device, and (i) a second pump for circulating the heat transfer
medium in a low temperature circuit through the fuel cell, the
traction motor, the power electronics, and the radiator. According
to one embodiment, the method invention includes the steps of:
determining the temperature of the fuel cell; pumping a first
quantity of the heat transfer medium from the high temperature
circuit into the low temperature circuit to elevate the temperature
of the medium in the low temperature circuit and warm-up the fuel
cell when it is too cold (e.g. thaw out the fuel cell); and
displacing an equal quantity of the medium from the low temperature
circuit into the high temperature circuit when the first quantity
is being pumped into the low temperature circuit . This same
technique can be used to thaw out other components of the fuel cell
system especially those that contain ice. According to another
embodiment, the method invention is similar to that described above
for thawing-out the fuel cell and H.sub.20-containing devices, but
instead is directed to providing extra cooling for an overheating
fuel processor component (e.g combuster or POx) and comprises the
steps of: determining the temperature of the fuel processor; and
pumping a first quantity of the medium from the high temperature
circuit into the low temperature circuit and an equal quantity of
the medium from the low temperature circuit into the high
temperature circuit to thereby cool the fuel processor.
BRIEF DESCRIPTION OF THE DRAWING
[0008] The drawing schematically depicts a preferred embodiment of
the vehicle thermal management system of the present invention
.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0009] The invention will be better understood when considered in
the light of the following detailed description of a preferred
embodiment thereof.
[0010] The figure schematically depicts a thermal management system
2 for a fuel cell powered vehicle. The system 2 includes a high
temperature (i.e. about 200-300.degree. C.) circuit 4 through which
a suitable dielectric, liquid, heat transfer medium such as
Paratherm OR.TM. circulates. The high temperature circuit 4
includes a fuel processor 6 and a vaporizer 8. In its innards, the
fuel processor 6 includes (1) a steam reformer heated by a
combuster that is fueled by H.sub.2-containing anode exhaust gas,
(2) a water-gas-shift (WGS) reactor section, and (3) a preferential
oxidation (PrOx) section. The dielectric liquid flows through heat
exchangers associated with the combuster, WGS and PrOx sections to
extract heat therefrom under normal operations, to heat up the WGS
reactor during system startup, and to cool the combuster when the
load is removed from the fuel cell before the fuel processor can
reduce its production of H.sub.2. The vaporizer 8 is part of the
fuel cell operating system, and serves to vaporize liquid
hydrocarbon for supply to the fuel processor, and/or to vaporize
water for use in the fuel cell system (e.g. in the steam reformer
and water-gas-shift reactor sections). A pump 10, driven by a motor
12, circulates the dielectric heat transfer medium through the
circuit 4 wherein under normal operating conditions (a) the medium
extracts heat from the fuel processor 6, and (b) the vaporizer 8
extracts heat from the medium to cool it for recirculation back
through the fuel processor 6.
[0011] The system 2 also contains a low temperature heat transfer
circuit 14 including (a) a PEM fuel cell 16, (b) a traction motor
18 for propelling the vehicle, (c) a power electronics package 20
for controlling the traction motor 18, (d) a heat exchanger 22 in
the HVAC system for maintaining the temperature of the air in the
occupant compartment of the vehicle at a comfortable level, (e) a
conventional automobile- type radiator 24, or the like, for
discharging heat from the heat transfer medium in the low
temperature circuit to the ambient, (f) a condenser 26 for cooling
the exhaust stream from the fuel cell sufficiently to condense and
recover water therefrom for reuse within the fuel cell operating
system, and (g) a pump 28 for circulating a dielectric liquid heat
transfer medium through the low temperature circuit 14. The heat
transfer liquid in the low temperature circuit is the same as that
used in the high temperature circuit 4, and the pump 28 for the low
temperature circuit 14 is driven by the same motor 12 that drives
the pump 10 for the high temperature circuit 4.
[0012] In accordance with the present invention, the high
temperature heat transfer circuit 4 and the low temperature circuit
24 communicate one with the other via a first conduit 30 containing
a flow control valve 32, and a second conduit 34 containing a flow
return valve 36. The valve 32 controls the flow of heat transfer
medium from one of the circuits (e.g. the high temperature circuit)
into the other circuit (e.g. the low temperature circuit), and will
preferably be a valve such as a controllable pulse-width-modulating
valve, a proportioning valve or a variable orifice valve that
permits varying the amount of heat transfer medium flowing between
the circuits. The flow return valve 36 in the conduit 34 is
preferably a check valve that permits one way flow of the heat
transfer medium from the other circuit (i.e. the receiving circuit)
back to the one circuit (i.e. the donor circuit) in the same
quantity as was transferred from the one circuit to the other
circuit via the control valve 32.
[0013] A temperature sensor, or other temperature indicator, 38
associated with the fuel cell 16, and a temperature sensor, or
other temperature indicator, 40 associated with the fuel processor
6 are coupled to a controller 42. The controller 42 receives
temperature-related signals 44 and 46 from the sensors/indicators
38 and 40 respectively and, in response thereto, emits a control
signal 48 that controls the opening and closing of the valve 32, as
needed, to meet the temperature needs of the system. In one
situation for example when the fuel cell is cold (e.g. frozen), hot
heat transfer medium from the high temperature circuit 4 is
directed through the control valve 32 into the low temperature
circuit 14, an hence the fuel cell 16 for heating or thawing of the
fuel cell 16. With appropriate routing of the low temperature
circuit other cold-sensitive components of the fuel cell system can
be similarly warmed or thawed. In another situation for example
when the combuster in the fuel processor is too hot (e.g.
immediately after the electrical load is removed from the fuel
cell), hot heat transfer medium from the high temperature circuit 4
is directed through the control valve 32 into the low temperature
circuit 14, and hence through the radiator 24, for cooling and
return to the high temperature circuit 4 for cooling the fuel
processor
[0014] While the invention has been described in terms of certain
specific embodiments thereof, it is not intended to be limited
thereto, but rather only to the extent set forth hereafter in the
claims which follow.
* * * * *