[0001] The present invention relates to a heater for fluids comprising heating elements
of an electrically conductive monolith, wherein the heater comprises a passageway
for the fluid to be heated with a defined flow direction of the fluid during heating
operation, the heater comprising at least two heating elements arranged side by side
inside the passageway, so that they are arranged in parallel with respect to the fluid
flow, a fuel vapor storage and recovery apparatus comprising such a heater, and a
method of operating the same.
[0002] A heater of that kind is known from
US 2007/0056954 A1. Particularly, the application of such a heater is described with respect to a purge
heater for a fuel vapor storage and recovery apparatus for the reduction of evaporative
emissions from motor vehicles. The purge heater disclosed may comprise one or more
electric heating elements which are connected to the source of electric energy, such
as for instance the battery of the car. The purge heater may, for instance, comprise
electrically conductive ceramic as heating elements.
[0003] Alternatively, the purge heater may comprise electrically conductive carbon, preferably
porous monolithic carbon. Such porous monolithic carbon is, for instance, disclosed
in
US 2007/0056954 A1. These monolithic carbon heating elements have a channel structure allowing air flow
through the heating elements and thus allowing an enhanced heat transfer directly
to the purging air sucked from the atmosphere.
[0004] An important application of such heaters is a fuel vapor storage and recovery apparatus
for the reduction of evaporative emissions from motor vehicles. Fuel vapor storage
and recovery apparatuses including a fuel vapor storage canister are well known in
the art since years. The gasoline fuel used in many internal combustion engines is
quite volatile. Evaporative emissions of fuel vapor from a vehicle having an internal
combustion engine occur principally due to venting of fuel tanks of the vehicle. When
the vehicle is parked changes in temperature or pressure cause air laden with hydrocarbons
to escape from the fuel tank. Some of the fuel inevitably evaporates into the air
within the tank and thus takes the form of a vapor. If the air emitted from the fuel
tank were allowed to flow untreated into the atmosphere it would inevitably carry
with it this fuel vapor. There are governmental regulations as to how much fuel vapor
may be emitted from the fuel system of a vehicle.
[0005] Normally, to prevent fuel vapor loss into the atmosphere the fuel tank of a car is
vented through a conduit to a canister containing suitable fuel absorbent materials
such as activated carbon. High surface area activated carbon granules are widely used
and temporarily absorb the fuel vapor.
[0006] A fuel vapor storage and recovery system including a fuel vapor storage canister
(so-called carbon canister) has to cope with fuel vapor emissions while the vehicle
is shut down for an extended period and when the vehicle is being refuelled, and vapor
laden air is being displaced from the fuel tank (refuelling emissions).
[0007] In fuel recovery systems for the European market normally refuelling emissions do
not play an important role since these refuelling emissions are generally not discharged
through the carbon canister. However, in integrated fuel vapor storage and recovery
systems for the North American market also these refuelling emissions are discharged
through the carbon canister.
[0008] Due to the nature of the absorbent within the carbon canister it is clear that the
carbon canister has a restricted filling capacity. It is generally desirable to have
a carbon canister with a high carbon working capacity, however, it is also desirable
to have a carbon canister with a relatively low volume for design purposes. In order
to guarantee always sufficient carbon working capacity of the carbon canister typically
under operation of the internal combustion engine a certain negative pressure is applied
to the interior of the canister from an intake system of the engine through a fuel
vapor outlet port of the carbon canister. With this atmospheric air is let into the
canister to the atmospheric air inlet port to pick up the trapped fuel vapors and
carry the same to an intake manifold of the intake system of the engine through the
fuel vapor outlet port. During this canister purging mode the fuel vapors stored within
the carbon canister are burnt in the internal combustion engine.
[0009] Although modern fuel vapor storage and recovery systems are quite effective there
is still a residual emission of hydrocarbons led into the atmosphere. These so-called
"bleed emissions" (diurnal breathing loss/DBL) are driven by diffusion in particular
when there are high hydrocarbon concentration gradients between the atmospheric vent
port of the carbon canister and the absorbent. Bleed emissions can be remarkably reduced
when it is possible to reduce the hydrocarbon concentration gradient. It is quite
clear that this can be achieved by increasing the working capacity of the carbon canister.
[0010] However, it should also be clear that only a certain percentage of the hydrocarbons
stored in the carbon canister can effectively be purged or discharged during the purging
mode. This can be an issue for cars where only a limited time for purging is available,
for instance in electro hybrid cars where the operation mode of the internal combustion
engine is relatively short.
[0011] Another issue arises with the use of so-called flexi fuels which comprise a considerable
amount of ethanol. Ethanol is a highly volatile fuel which has a comparatively high
vapor pressure. For instance, the so-called E10 fuel (10% ethanol) has the highest
vapor generation currently in the market. That means that the fuel vapor uptake of
the carbon canister from the fuel tank is extremely high. On the other hand, during
normal purging modes of a conventional carbon canister only a certain percentage of
the fuel vapor uptake may be discharged. As a result the fuel vapor capacity of an
ordinary carbon canister is exhausted relatively fast. The bleed emissions of a fully
loaded carbon canister normally then increase to an extent which is beyond the emission
values given by law.
[0012] In order to improve the purge removal rate during the purging mode few vapor storage
and recovery devices have been proposed which use so-called purge heaters. By heating
the atmospheric air which is led into the canister through the atmospheric air inlet
port the efficiency of removing the hydrocarbons trapped in the micropores of the
absorbent is enhanced remarkably.
[0013] For instance,
US 6,230,693 B1 discloses an evaporative emission control system for reducing the amount of fuel
vapor emitted from a vehicle by providing an auxiliary canister which operates with
a storage canister of the evaporative emission control system. The storage canister
contains a first sorbent material and has a vent port in communication therewith.
The auxiliary canister comprises an enclosure, first and second passages, a heater
and a connector. Inside the enclosure a second sorbent material is in total contact
with the heater. During a regenerative phase of operation of the control system the
heater can be used to heat the second sorbent material and the passing purge air.
This enables the second and first sorbent material to more readily release the fuel
vapor they absorbed during the previous storage phase of operation so that they can
be burnt during combustion.
[0014] Moreover, the storage canister of the evaporative emission control system according
to
US 6,230,693 comprises two fuel vapor storage compartments side by side connected by a flow passage.
In particular the partitioning of the canister actually means a flow restriction.
Because the driving pressure of the flow through the canister is very low it is an
important design consideration that flow restrictions be kept to a minimum.
[0015] It is an object of the present invention to provide a heater for fluids comprising
heating elements of an electrically conductive monolith, wherein the heater comprises
a passageway for the fluid to be heated with a defined flow direction of the fluid
during heating operation, the heater comprising at least two heating elements arranged
side by side inside the passageway, so that they are arranged in parallel with respect
to the fluid flow, which is simple, compact and reliable in design and allows easy
and efficient controlled operation, and a fuel vapor storage and recovery apparatus
which has an improved fuel recovery efficiency. It is yet another object to provide
a method for operating such a heater which allows easy and efficient controlled operation
[0016] These and other objects are achieved by a heater for fluids comprising heating elements
of an electrically conductive monolith, wherein the heater comprises a passageway
for the fluid to be heated with a defined flow direction of the fluid during heating
operation, the heater comprising at least two heating elements arranged side by side
inside the passageway, so that they are arranged in parallel with respect to the fluid
flow, characterized in that one of the at least two heating elements is a controlled
heating element, which has a slightly larger heating power, and a temperature sensor
is provided at or close to the downstream end of the controlled heating element, and
wherein the temperature sensor is connected to a control means for temperature control
during heating operation of the heater.
[0017] The arrangement according to the invention provides both for improved safety and
improved efficiency of such a heater. The arrangement of the temperature sensor with
a heating element which has a slightly larger heating power ensures that the heater
is effectively controllable to a maximum temperature, thus preventing overheating
of the heater to prevent the risk of fire on the one hand, on the other hand allowing
to control the temperature close to the maximum temperature, thus increasing the efficiency
of the heater. Arrangement of the temperature sensor at or close to the downstream
end of the heating element minimizes the influence of a varying flow rate of the fluid,
i.e. significantly reducing the adverse effects of flow variations on the heating
performance of the heater.
[0018] With the advantages of the invention described above a fuel vapor storage and recovery
apparatus comprising a heater according to the invention is particularly effective
for cars having cycle operation of the engine, e.g. petrol/electric hybrid drive.
It is typical for such kind of drive that the purge air flow through the fuel vapor
storage and recovery apparatus exhibits a rapid change from high to low when the engine
is shut off when switching to electrical drive. With conventional design heater such
rapid change of purge air flow provides a high risk of overheating of the fuel vapor
storage and recovery apparatus with a significant risk of fire, or the heater needs
to be controlled to a temperature well below the critical temperature, thus, providing
bad recovery performance. However, recovery performance is critical with this kind
of application due to the reduced operating time of the petrol engine.
[0019] A particularly useful and fail-safe embodiment of the invention is characterized
in that the at least two heating elements are electrically in series connection with
each other, and the controlled heating element has a larger resistance than the other
heating elements.
[0020] An alternative embodiment is characterized in that at least two of the heating elements
are electrically in parallel connection with each other, and the controlled heating
element has a smaller resistance than the other heating elements.
[0021] Further useful embodiments of the invention are characterized in that the heater
comprises more than two heating elements, and the heating elements are grouped together,
wherein the heating elements of one group are electrically in series connection with
each other, and the groups of heating elements are electrically in parallel connection
with each other group, wherein the group comprising the controlled heating element
has a smaller resistance than the other groups of heating elements, and the controlled
heating element has a larger resistance than the other heating elements of the same
group or in that the heater comprises more than two heating elements, and the heating
elements are grouped together, wherein the heating elements of one group are electrically
in parallel connection with each other, and the groups of heating elements are electrically
in series connection with each other group, wherein the group comprising the controlled
heating element has a larger resistance than the other groups of heating elements,
and the controlled heating element has a smaller resistance than the other heating
elements of the same group.
[0022] A preferred embodiment of the heater according to the invention is characterized
in that the heating elements comprise an electrically conductive carbon monolith,
which carbon monolith is a porous carbon monolith having a cell structure permitting
a significant part of the fluid flow to pass through said monolith inside the passageway
particularly, when the porous carbon monolith has channels with a channel size between
100 µm and 2000 µm, more particularly, when the porous carbon monolith has an open
area between 30 % and 60 % in the cross section perpendicular to the flow path in
the passageway.
[0023] A particularly good performance of the heater according to the invention in a typical
car environment with conventional 12 V DC power supply can be obtained if the heating
elements are arranged to a total resistance not exceeding 2.5 Ohms, preferably not
exceeding 1 Ohm, more preferably about 0.8 Ohms.
[0024] A heater according to the invention is particularly protected against risk of fire
in case of short circuiting of the temperature sensor connection when the temperature
sensor is a thermistor.
[0025] The above and other objects are further achieved by a fuel vapor storage and recovery
apparatus comprising such a heater, and by a method for operating such a heater or
fuel vapor storage and recovery apparatus in a vehicle environment, comprising the
following steps: obtaining a refuelling signal indicating that a vehicle tank in fluid
communication with the heater has been refuelled, and energizing the heater after
refuelling from start of engine for no more than 45 min / 24 hours, preferably for
about 30 min / 24 hours, while controlling electrical power to the heater in response
to a temperature signal from a temperature sensor.
[0026] In a preferred embodiment of the method according to the invention, the method further
comprises the following steps: obtaining a fuel level signal from a fuel gauge, and
preventing the heater from being energized if the fuel level signal indicates the
fuel level being down to a predetermined reading, wherein the predetermined reading
is 1/3, preferably 1/4 of the fuel tank capacity. At such low fuel levels the fuel
vapor generation does not provide significant increase of the pressure in the tank.
Accordingly, there is only a small vapor load of a fuel vapor storage and recovery
apparatus and the recovery efficiency is well sufficient with no heating at any ambient
temperature. Further, when the tank will be refueled subsequently, and fuel vapor
will flow through the carbon canister at high flow rates in integrated systems, the
emission reduction efficiency of the carbon canister is much better with a cold carbon
bed in the canister due to exothermic effects during adsorption.
[0027] Energy saving can also be reached by de-energizing the heater under all operating
conditions if environmental temperature is below a predetermined figure, preferably
below - 7°C, more preferably, below - 10°C. At such low temperature, fuel vapor generation
inside the fuel tank is relatively low and the fuel vapor storage and recovery apparatus
will be sufficiently effective even with no heating.
[0028] Energy loss through heat sink can be minimized and, thus, electrical power be saved
when the controlling of electrical power supplied to the heater comprises pulse-width
modulation of the electrical power supplied to the heater.
[0029] In a particularly preferred embodiment the method further comprises the step of performing
at least one test cycle, and de-energize heater, and send fault signal to an on board
diagnostics system if one or more of the following conditions are met: fault detected
in temperature sensor circuitry, self test of heater control failed, increase of resistance
of monolith heater element arrangement beyond a predetermined figure detected, and
supply voltage exceeds or falls below a predetermined maximum/minimum figure. More
preferably, the fault detected in temperature sensor circuitry comprises one of the
following: open circuit of a thermistor circuitry, short circuit of a thermistor circuitry,
and poor thermistor contact. Considering the fact that improper operation, particularly
uncontrolled heating, may cause the risk of fire, this embodiment provides for improved
fail-safe operation.
[0030] The detection of an increase in the resistance of the monolith heater element arrangement
is an indication of a failure in one of the heater elements or a disconnection. This
is further an indication that failure of operation of the heater is to be expected,
and thus, of a fuel vapor storage and recovery apparatus, such a heater is used with.
With this embodiment of the method according to the invention the legal requirements
of on board diagnosis of emission control equipment can be met.
[0031] Best recovery performance and secure operation is obtained when electrical energy
to the heater is controlled to a temperature at the temperature sensor of about 132°C
to about 145°C, preferably to about 140°C.
[0032] The invention will hereinafter be described by way of a non-limiting example with
reference to the accompanying drawings, in which:
- Fig. 1
- shows a schematic view of a heater according to the invention including a simplified
wiring scheme;
- Fig. 2
- shows an enlarged cross-sectional view of two adjacent heater element end sections;
- Fig. 3
- shows a cross-sectional view in the plane indicated in Fig. 2; and
- Fig. 4
- shows a cross-sectional view through a carbon canister comprising a heater according
to the invention.
[0033] Figure 1 depicts schematically a heater for fluids according to one embodiment of
the invention, generally designated as 1. The heater 1 comprises heating elements
2 of an electrically conductive monolith. The heater 1 according to the invention
may be good used with a fuel vapor storage and recovery apparatus 3 as illustrated
in figure 4. Such a fuel vapor storage and recovery apparatus 3 is usually called
a carbon canister and typically employed as a part of an emission control system of
a motor vehicle having a petrol feeded engine. The illustration is schematic and the
components are not drawn to scale.
[0034] The fuel vapor storage and recovery apparatus or carbon canister 3 comprises a vapor
inlet port 4 connected to a fuel tank (not shown), a vent port 5 communicating with
the atmosphere and a purge port 6 connected to an internal combustion engine of a
motor vehicle (also not shown). The carbon canister 3 is packed with an adsorbent
in the form of granulated activated carbon.
[0035] During shut-off of the engine of the motor vehicle the carbon canister 3 is connected
via vapor inlet port 4 to the fuel tank of the motor vehicle and via vent port 5 to
the atmosphere. During engine running cycles of the car a flow path between the vent
port 5 and the purge port 6 will be established. The internal combustion engine sucks
a certain amount of air to be burnt within the combustion chambers of the internal
combustion engine from the atmosphere via vent port 5 through the carbon canister
3 into the purge port 6, thereby purging the absorbent of the carbon canister 3 and
feeding the hydrocarbons removed from the carbon canister to the combustion chamber
of the engine. In the drawings arrows indicate the air flow path during purging of
the carbon canister 3. The terms "downstream" and "upstream" in the context of this
application always refer to the airflow during purging of the carbon canister 3, that
is defined as the flow direction of the fluid during heating operation.
[0036] The carbon canister 3 comprises first 7, second 8 and third 9 vapor storage compartments.
The first vapor storage compartment 7 is with regard to the airflow during upload
of hydrocarbons to the carbon canister 3 the vapor storage compartment next to the
vapor inlet port 4 and is also the biggest vapor storage compartment.
[0037] It will be readily apparent from Fig. 4 that the vapor storage compartments 7, 8,
9 have a circular cross-section and are arranged in concentric relationship to each
other. The first vapor storage compartment 7 surrounds the vapor storage compartments
8 and 9. Next to the vent port 5 at the upstream side of the third vapor storage compartment
9 there is arranged a purge heater compartment 10 which has also a cylindrical shape,
i.e. a circular cross-section.
[0038] The purge heater compartment 10 has at its upstream face two inlet openings 12 allowing
atmospheric air to be drawn into the purge heater compartment 10. The purge heater
compartment 10 has a relatively thin-walled surrounding wall 13 which is designed
such that heat radiation from the heater 1 may be transferred into the surrounding
carbon bed of the first vapor storage compartment 7. The surrounding wall 13 of the
heater 1 defines a passageway for the fluid, that is the air-flow through the heater
1.
[0039] As can be easily seen from figures 1 and 4 the heater 1 preferably comprises four
heating elements 2 arranged side by side inside the heater compartment 10 forming
the passageway. With respect to the air flow through the heater compartment 10, the
heating elements 2 are arranged in parallel.
[0040] The heating elements 2 may be of cylindrical shape and comprise an electrically conductive
porous carbon monolith, such as for instance, a synthetic carbon monolith. A method
of manufacturing such carbon monolith heating elements 2 is generally disclosed in
US 2007/0056954 A1, and in more detail in paragraphs [0013] to [0024]. The carbon monolith is a porous
carbon monolith having a cell structure permitting a significant fluid flow to pass
through said monolith. Each heating element 2 provides continuous longitudinal channels
(not shown) allowing a gas fluid flow in longitudinal direction through each heating
element 2. The channels inside the porous carbon monolith may have a size between
100 µm and 2000 µm. The porous carbon monolith heating element has an open area between
30 % and 60 % in the cross section perpendicular to the flow path in the passageway.
[0041] A suitable typical heating element 2 may have a diameter of approx. 10 mm and a typical
length of about 50 mm. The heating elements 2 operate as a resistive heating element,
each. In a preferred embodiment shown in the drawings, the four electric heating elements
7 are electrically connected in series and connected to a control and switching means
11, which in tum is connected to a source of electric energy as the generator and
battery of the vehicle through negative and positive power lines 14 and 15.
[0042] The heating elements 2 are connected to the control and switching means 11 via power
line 16 and copper connectors 17. The interconnection of the heating elements 2 is
provided by connectors 18. The arrangement of the heating elements 2 provide a total
resistance of no more than 2.5 ohms, preferably about 0.8 ohms. To provide a heating
power of approx. 75 watts at a supply voltage of 13.7 V some kind of power regulation
is required.
[0043] A suitable method of controlling the power supplied is pulse-width modulation (PWM).
The main advantage of this method is the low power loss in the control and switching
means 11. Although PWM operation requires some additional electrical components to
minimize adverse feedback in the onboard power supply network and to provide electromagnetic
compatibility (EMC), the control and switching means 11 itself could be less expensive.
Additionally, space and probably ventilation for a large heat sink required otherwise
can be saved, giving an overall advantage in costs and space required.
[0044] However, conventional current regulator circuiting can be used as well, but requires
cooling. Conventional current regulation may be advantageous if the dissipated heat
can be used for some other purposes.
[0045] One of the heating elements 2 has a slightly larger heating power than the other
heating elements 2. This heating element defines a controlled heating element 2'.
A temperature sensor in the form of a thermistor 19 is provided at or close to the
downstream end 23 of the controlled heating element 2'. The temperature sensor 19
is connected to the control means 11 via wires 20 and 21 for temperature control during
heating operation of the heater 1. In the depicted embodiment of four heating elements
2, 2' connected in series, the controlled heating element 2' has a slightly larger
length than the other heating elements 2, e.g. 53 mm. With the same diameter, and
thus the same cross sectional area, the controlled heating element 2' shows a slightly
larger resistance than the other heating elements 2. Preferably, the thermistor 19
is mounted approx. 50 mm from the upstream end 22 of the controlled heating element
2', corresponding to the position of the downstream end 23 of the other heating elements
2, inside an opening in the downstream end section of the controlled heating element
2', as shown in more detail in figures 2 and 3. This arrangement is just to ensure
that the thermistor 19 detects the temperature at the hottest part of the heater.
[0046] The control and switching means 11 is further connected to an on board diagnostic
system via data line 24, and other devices of the vehicle, e.g. via CAN bus line 25.
Of course, other suitable wiring is possible as easily apparent for a person skilled
in the art.
[0047] The heating elements 2 will only be activated during the purging operation of the
fuel vapor storage and recovery apparatus 3, as described in more detail below. As
explained above, during shut-off of the car the fuel within the fuel tank evaporates
into the air space above the maximum filling level of the fuel tank. This vapor laden
air flows via vapor inlet port 4 into the carbon canister 3. During refuelling of
the car, where normally the internal combustion engine is also shut off, in so-called
integrated systems the fuel being pumped into the fuel tank causes an air flow through
the vapor inlet port 4 the flow rate of which corresponds to the flow rate of refuelling.
Accordingly, hydrocarbon laden air is pumped with a flow rate of up to 60 liters/min
into the carbon bed of the carbon canister 3. The activated carbons within the carbon
canister absorb the hydrocarbons, hydrocarbon molecules being trapped within the internal
pore structure of the carbon. More or less cleaned air will be discharged from the
vent port 5. Adsorption efficiency at such high flow rates is better if the carbon
bed is cold due to exothermic effects coming with the adsorption. Therefore, suppressing
heating operation of the heater 1 at low fuel levels in the fuel tank is advantageous
in view of refuelling to be expected.
[0048] During running cycles of the internal combustion engine of the vehicle the fuel vapor
storage and recovery apparatus 3 according to the invention is set to purge mode.
Atmospheric air is drawn from the internal combustion engine of the vehicle from the
vent port 5 via inlet opening 12 into the purge heater compartment 10. The heating
elements 2 are electrically energized from the generator or battery of the vehicle
during purging. The air flows through and around the heating elements 2 thereby being
heated up to a temperature below but in any case not exceeding 150°C. At the same
time radiation heat emitted by the heating elements 2 heats up the surrounding carbon
bed of the first vapor storage compartment 7. Heated air flows through the third vapor
storage compartment 9. On its way the atmospheric air will be loaded by the hydrocarbons
stored in the carbon beds. This air flow, as indicated by the arrows in Fig. 4 flows
into and through the carbon bed of the first vapor storage compartment 7 and is finally
drawn through the purge port 6 to a purging line leading to the internal combustion
engine.
[0049] The method of operating a heater 1 used in a fuel vapor storage and recovery apparatus
3 in a vehicle environment comprises the following steps: obtaining a refuelling signal
through CAN bus 25 indicating that the vehicle tank has been refuelled. Such signal
can be obtained from a fuel cap switch detecting a closed fuel cap. If the signal
is present, the heater 1 will be energized from the start of the engine for no more
than 45 min within 24 hours, preferably for about 30 min per 24 hours, while controlling
electrical power to the heater 1 in response to a temperature signal from the temperature
sensor 19. With the embodiment described above, the thermistor 19 is calibrated to
a temperature of 140°C, providing the best compromise between recovery efficiency
and safety.
[0050] Further, a fuel level signal will be obtained from a fuel gauge also through CAN
bus 25, and the heater 1 will not be energized if the fuel level signal indicates
the fuel level being down to a predetermined reading, preferably 1/4 of the fuel tank
capacity, for the reasons described above described above with respect to refuelling.
[0051] Energy saving can be reached by de-energizing the heater 1 under all operating conditions
if environmental temperature is below a predetermined figure, e.g. - 10°C. The outside
temperature signal may also be provided via CAN bus 25 or otherwise obtained from
the motor management system. The control and switching means 11 preferably performs
at least one test cycle e.g. prior to energizing the heater 1, and de-energize heater
1, and send fault signal to the on board diagnostics system via data line 24 if one
or more of the following occurs: a fault is detected in the circuitry of the thermistor
19 and wires 20 and 21, a self test of heater control 11 failed, or increase of the
resistance of the monolith heater element 2 beyond a predetermined figure is detected,
thus, indicating a failure in one of the heating elements 2 such as a cracked monolith
or a disconnection, etc. A damaged heating element 2 or disconnection will make the
carbon canister 3 as a part of emission control system ineffective, and malfunction
needs to be indicated to the driver. Preferably; a limp-home mode will be activated
to allow the driver to return home and take the car to a repair shop.
[0052] A fault detected in the temperature sensor circuitry 19, 20, 21 comprises one of
the following: open circuit of the wiring 20, 21, a short circuit of the thermistor
19, and poor thermistor 19 contact. Considering the fact that improper operation,
particularly uncontrolled heating, may cause the risk of fire, this embodiment provides
for improved fail-safe operation.
[0053] In addition, the heater 1 will be de-energized by the control and switching means
11 in case the supply voltage exceeds or falls below predetermined maximum/minimum
voltage figures to avoid damage or malfunction, like overheating.
[0054] Best recovery performance and secure operation is obtained when the electrical energy
to the heater 1 is controlled by the control and switching means 11 to a temperature
at the temperature sensor 19 of about 132°C to about 145°C, preferably to about 140°C,
thus preventing that no part of the heater 1 which is in contact with air/petrol vapor
mixture permanently exceeds 150°C.
1. A heater (1) for fluids comprising heating elements (2, 2') of an electrically conductive
monolith, wherein the heater (1) comprises a passageway for the fluid to be heated
with a defined flow direction of the fluid during heating operation, the heater (1)
comprising at least two heating elements (2, 2') arranged side by side inside the
passageway, so that they are arranged in parallel with respect to the fluid flow,
characterized in that one of the at least two heating elements is a controlled heating element (2'), which
has a slightly larger heating power, and a temperature sensor (19) is provided at
or close to the downstream end (23) of the controlled heating element (2'), and wherein
the temperature sensor (19) is connected to a control means (11) for temperature control
during heating operation of the heater (1).
2. The heater (1) according to claim 1, characterized in that the at least two heating elements (2, 2') are electrically in series connection with
each other, and the controlled heating element (2') has a larger resistance than the
other heating elements (2).
3. The heater (1) according to claim 1, characterized in that at least two of the heating elements (2, 2') are electrically in parallel connection
with each other, and the controlled heating element (2') has a smaller resistance
than the other heating elements (2).
4. The heater (1) according to any preceding claim, characterized in that the heater (1) comprises more than two heating elements (2, 2'), and the heating
elements are grouped together, wherein the heating elements of one group are electrically
in series connection with each other, and the groups of heating elements are electrically
in parallel connection with each other group, wherein the group comprising the controlled
heating element has a smaller resistance than the other groups of heating elements,
and the controlled heating element (2') has a larger resistance than the other heating
elements of the same group.
5. The heater (1) according to any of claims 1 to 3, characterized in that the heater comprises more than two heating elements (2, 2'), and the heating elements
are grouped together, wherein the heating elements of one group are electrically in
parallel connection with each other, and the groups of heating elements are electrically
in series connection with each other group, wherein the group comprising the controlled
heating element (2') has a larger resistance than the other groups of heating elements,
and the controlled heating element has a smaller resistance than the other heating
elements of the same group.
6. The heater (1) according to any preceding claim, characterized in that the heating elements (2, 2') comprise an electrically conductive carbon monolith,
which carbon monolith is a porous carbon monolith having a cell structure permitting
a significant part of the fluid flow to pass through said monolith inside the passageway.
7. The heater (1) according to claim 6, characterized in that the porous carbon monolith has channels with a channel size between 100 µm and 2000
µm.
8. The heater (1) according to claim 6 or 7, characterized in that the porous carbon monolith has an open area between 30 % and 60 % in the cross section
perpendicular to the flow path in the passageway.
9. The heater (1) according to any preceding claim, characterized in that the heating elements (2, 2') are arranged to a total resistance not exceeding 2.5
Ohms, preferably not exceeding 1 Ohm, more preferably about 0.8 Ohms.
10. The heater (1) according to any preceding claim, wherein the temperature sensor is
a thermistor (19).
11. A fuel vapor storage and recovery apparatus (3) comprising a heater (1) according
to any preceding claim, and a control (11).
12. A method for operating a heater (1) according to any of claims 1 to 10 or a fuel vapor
storage and recovery apparatus (3) according to claim 11 in a vehicle environment,
comprising the following steps:
i) obtaining a refuelling signal indicating that a vehicle tank in fluid communication
with the heater (1) has been refuelled, and
ii) energizing the heater (1) after refuelling from start of engine for no more than
45 min / 24 hours,
while controlling electrical power supplied to the heater (1) in response to a temperature
signal from a temperature sensor (19).
13. The method according to claim 12, characterized in that the energizing of step ii) is for about 30 min / 24 hours.
14. The method according to claim 12 or 13, further comprising the step of
iii) obtaining a fuel level signal from a fuel gauge, and
iv) preventing the heater (1) from being energized if the fuel level signal indicates
the fuel level being down to a predetermined reading.
15. The method according to claim 14, characterized in that the predetermined reading of step iv) is 1/3, preferably 1/4.
16. The method according to any of claims 12 to 15, further comprising the step of
v) de-energizing the heater (1) under all operating conditions if environmental temperature
is below a predetermined figure.
17. The method according to claim 16, characterized in that the temperature of step v) is -7 °C, preferably -10°C.
18. The method according to any of claims 12 to 17, further comprising the step of performing
at least one test cycle, and de-energize heater (1), and send fault signal to an on
board diagnostics system if one or more of the following conditions are met:
a) fault detected in temperature sensor circuitry,
b) self test of heater control (11) failed,
c) increase of resistance of monolith heater element (2, 2') arrangement beyond a
predetermined figure detected, and
d) supply voltage exceeds or falls below a predetermined maximum/minimum figure.
19. The method according to claim 18,
characterized in that the fault detected in temperature sensor circuitry comprises one of the following:
- open circuit of a thermistor circuitry,
- short circuit of a thermistor circuitry, and
- poor thermistor contact.
20. The method according to any of claims 12 to 19, wherein the provision of electrical
energy to the heater (1) is controlled to a temperature at the temperature sensor
(19) of about 132°C to about 145°C, preferably to about 140°C.
21. The method according to any of claims 12 to 20 wherein the controlling of electrical
power supplied to the heater (1) comprises pulse-width modulation of the electrical
power supplied to the heater (1).
1. Heizeinrichtung (1) für Fluide umfassend Heizelemente (2, 2') aus elektrisch leitfähigen
Monolithen, wobei die Heizeinrichtung (1) einen Durchgang für das zu heizende Fluid
mit einer definierten Durchflussrichtung des Fluids während des Heizvorgangs umfasst,
die Heizeinrichtung (1) wenigstens zwei Heizelemente (2, 2') umfasst, die innerhalb
des Durchgangs nebeneinander angeordnet sind, sodass diese bezogen auf den Durchfluss
des Fluids parallel angeordnet sind, dadurch gekennzeichnet, dass eines der wenigstens zwei Heizelemente ein gesteuertes Heizelement (2') ist, welches
eine geringfügig größere Heizleistung aufweist und dass in der Nähe oder an dem stromabwärtigen
Ende (23) des gesteuerten Heizelements (2') ein Temperatursensor (19) vorgesehen ist
und dass der Temperatursensor (19) mit Steuermitteln (11) zur Temperatursteuerung
während des Betriebs der Heizeinrichtung (1) verbunden ist.
2. Heizeinrichtung (1) nach Anspruch 1, dadurch gekennzeichnet, dass wenigstens zwei Heizelemente (2, 2') elektrisch in Serie geschaltet sind und dass
das gesteuerte Heizelement (2') einen größeren Widerstand als die anderen Heizelemente
(2) aufweist.
3. Heizeinrichtung (1) nach Anspruch 1, dadurch gekennzeichnet, dass wenigstens zwei der Heizelemente (2, 2') elektrisch parallel geschaltet sind und
das gesteuerte Heizelement (2') einen geringeren Widerstand als die anderen Heizelemente
(2) aufweist.
4. Heizeinrichtung (1) nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die Heizeinrichtung (1) mehr als zwei Heizelemente (2, 2') umfasst und dass die Heizelemente
gruppenweise angeordnet sind, wobei die Heizelemente einer Gruppe elektrisch miteinander
in Serie geschaltet sind und die Gruppen von Heizelementen mit jeder anderen Gruppe
der Heizelemente elektrisch parallel geschaltet sind, wobei die Gruppe, welche das
gesteuerte Heizelement umfasst, einen geringeren Widerstand aufweist als die andere
Gruppe der Heizelemente und das gesteuerte Heizelement (2') einen größeren Widerstand
als die anderen Heizelemente in der gleichen Gruppe aufweist.
5. Heizeinrichtung (1) nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass die Heizeinrichtung mehr als zwei Heizelemente (2, 2') umfasst und die Heizelemente
gruppenweise angeordnet sind, wobei die Heizelemente einer Gruppe elektrisch parallel
geschaltet sind und die Gruppen der Heizelemente untereinander elektrisch in Serie
geschaltet sind, wobei die Gruppe mit dem gesteuerten Heizelement (2') einen größeren
Widerstand als die andere Gruppe der Heizelemente aufweist und das gesteuerte Heizelement
einen geringeren Widerstand als die anderen Heizelemente der gleichen Gruppe aufweist.
6. Heizeinrichtung (1) nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die Heizelemente (2, 2') einen elektrisch leitfähigen Kohlenstoffmonolithen aufweisen,
wobei der Kohlenstoffmonolith ein poröser Kohlenstoffmonolith ist, der eine Porenstruktur
aufweist, die eine Durchströmung des Monolithen innerhalb des Durchgangs mit dem Fluid
zulässt.
7. Heizeinrichtung (1) nach Anspruch 6, dadurch gekennzeichnet, dass der poröse Kohlenstoffmonolith Kanäle mit einer Kanalgröße zwischen 100 µm und 2000
µm aufweist.
8. Heizeinrichtung (1) nach Anspruch 6 oder 7, dadurch gekennzeichnet, dass der poröse Kohlenstoffmonolith einen geöffneten Bereich von zwischen 30 % und 60
% des Querschnitts senkrecht zum Durchströmungspfad in dem Durchgang aufweist.
9. Heizeinrichtung (1) nach einem der vorstehenden Ansprüche, dadurch gekennzeichnet, dass die Heizelemente (2, 2') so angeordnet sind, dass diese einen Gesamtwiderstand von
2,5 Ohm nicht überschreiten, dass diese vorzugsweise einen Widerstand von 1 Ohm nicht
überschreiten, und dass diese weiterhin bevorzugt einen Widerstand von 0,8 Ohm nicht
überschreiten.
10. Heizeinrichtung (1) nach einem der vorstehenden Ansprüche, bei welchem der Temperatursensor
als Thermistor (19) ausgebildet ist.
11. Kraftstoffdampf-Speicher- und Rückhaltevorrichtung (3) umfassend eine Heizeinrichtung
(1) nach einem der vorgehenden Ansprüche und eine Steuerung (11).
12. Verfahren zum Betreiben einer Heizeinrichtung (1) nach einem der Ansprüche 1 bis 10
oder einer Kraftstoffdampf-Speicher- und Rückhaltevorrichtung (3) nach Anspruch 11
in einer Fahrzeugumgebung, umfassend die folgenden Schritte:
i) Erhalten eines Betankungssignals, welches anzeigt, dass der Fahrzeugtank, der sich
in Fluidkommunikation mit der Heizeinrichtung (1) befindet, betankt wurde und
ii) Einschalten der Heizeinrichtung (1) nach dem Betanken vom Start des Motors für
nicht länger als 45 min./24 Stunden,
wobei die Zufuhr von elektrischer Energie an die Heizeinrichtung (1) als Reaktion
auf ein Temperatursignal von dem Temperatursensor (19) gesteuert wird.
13. Verfahren nach Anspruch 12, dadurch gekennzeichnet, dass die Einschaltung nach Schritt ii) etwa für 30 min./24 Stunden stattfindet.
14. Verfahren nach Anspruch 12 oder 13, weiterhin folgende Verfahrensschritte umfassend:
iii) Erhalten eines Kraftstofffüllstandssignals von einem Kraftstofffüllstandsgeber
und
iv) Verhindern der Einschaltung der Heizeinrichtung (1), wenn das Füllstandssignal
einen Kraftstofffüllstand unter einem vorgegebenen Auslesewert anzeigt.
15. Verfahren nach Anspruch 14, dadurch gekennzeichnet, dass der vorgegebene Auslesewert aus Schritt iv) 1/3, vorzugsweise ¼ beträgt.
16. Verfahren nach einem der Ansprüche 12 bis 15, weiterhin umfassend den Schritt:
v) Abschalten der Heizeinrichtung (1) unter allen Betriebsbedingungen, wenn die Umgebungstemperatur
unter einem vorgegebenen Wert ist
17. Verfahren nach Anspruch 16, dadurch gekennzeichnet, dass die Temperatur aus Schritt v) -7°C, vorzugsweise -10°C beträgt.
18. Verfahren nach einem der Ansprüche 12 bis 17, weiterhin umfassend den Schritt der
Durchführung wenigstens eines Testzyklus und des Abschaltens der Heizeinrichtung (1)
und des Sendens eines Fehlersignals an ein OnBoard-Diagnosesystem, wenn eine der folgenden
Bedingungen erfüllt ist.
a) Fehler im Temperatursensorschaltkreis erfasst
b) Selbsttest der Heizeinrichtungssteuerung (11) versagt
c) Ansteigen des Widerstands der monolithischen Heizelementanordnung (2, 2') oberhalb
eines erfassten vorbestimmten Wertes und
d) Spannungszufuhr überschreitet einen bestimmten Maximalwert oder unterschreitet
einen bestimmten Minimalwert.
19. Verfahren nach Anspruch 18,
dadurch gekennzeichnet, dass der in dem Temperatursensorschaltkreis erfasste Fehler einer der Folgenden sein kann:
- geöffneter Kreis des Thermistorschaltkreises,
- Kurzschluss eines Thermistorschaltkreises und
- schlechter Thermistorkontakt
20. Verfahren nach einem der Ansprüche 12 bis 19, bei welchem die Bereitstellung von elektrischer
Energie an die Heizeinrichtung (1) von dem Temperatursensor (19) bis zu einer Temperatur
von etwa zwischen 132°C bis etwa 145°C gesteuert wird, vorzugsweise bis etwa 140°C.
21. Verfahren nach einem der Ansprüche 12 bis 20, bei welchem die Steuerung der elektrischen
Energie, die der Heizeinrichtung (1) zugeführt wird, eine Pulsbreitenmodulierung der
an die Heizeinrichtung (1) zugeführten elektrischen Energie umfasst.
1. Dispositif de chauffage (1) pour des fluides comprenant des éléments chauffants (2,
2') d'un monolithe électriquement conducteur, dans lequel le dispositif de chauffage
(1) comprend un passage pour le fluide à chauffer avec une direction d'écoulement
définie du fluide pendant une opération de chauffage, le dispositif de chauffage (1)
comprenant au moins deux éléments chauffants (2, 2') agencés côte à côte à l'intérieur
du passage, de sorte qu'ils soient agencés parallèlement à l'écoulement de fluide,
caractérisé en ce que l'un desdits au moins deux éléments chauffants est un élément chauffant commandé
(2'), qui a une puissance de chauffage légèrement plus grande, et un capteur de température
(19) est prévu au niveau de l'extrémité aval (23) de l'élément chauffant commandé
(2') ou à proximité de celle-ci, et dans lequel le capteur de température (19) est
connecté à des moyens de commande (11) pour la commande de la température pendant
une opération de chauffage du dispositif de chauffage (1).
2. Dispositif de chauffage (1) selon la revendication 1, caractérisé en ce que lesdits au moins deux éléments chauffants (2, 2') sont connectés électriquement en
série l'un avec l'autre, et l'élément chauffant commandé (2') a une résistance supérieure
à celle des autres éléments chauffants (2).
3. Dispositif de chauffage (1) selon la revendication 1, caractérisé en ce qu'au moins deux des éléments chauffants (2, 2') sont connectés électriquement en parallèle
l'un avec l'autre, et l'élément chauffant commandé (2') a une résistance inférieure
à celle des autres éléments chauffants (2).
4. Dispositif de chauffage (1) selon l'une quelconque des revendications précédentes,
caractérisé en ce que le dispositif de chauffage (1) comprend plus de deux éléments chauffants (2, 2'),
et en ce que les éléments chauffants sont groupés les uns avec les autres, dans lequel les élément
chauffants d'un groupe sont connectés électriquement en série les uns avec les autres,
et les groupes d'éléments chauffants sont connectés électriquement en parallèle avec
chaque autre groupe, dans lequel le groupe comprenant l'élément chauffant commandé
a une résistance inférieure à celle des autres groupes d'éléments chauffants, et l'élément
chauffant commandé (2') a une résistance supérieure à celle des autres éléments chauffants
du même groupe.
5. Dispositif de chauffage (1) selon l'une quelconque des revendications 1 à 3, caractérisé en ce que le dispositif de chauffage comprend plus de deux éléments chauffants (2, 2'), et
les éléments chauffants sont groupés les uns avec les autres, dans lequel les éléments
chauffants d'un groupe sont connectés électriquement en parallèle les uns avec les
autres, et les groupes d'éléments chauffants sont connectés électriquement en série
avec chaque autre groupe, dans lequel le groupe comprenant l'élément chauffant commandé
(2') a une résistance supérieure à celle des autres groupes d'éléments chauffants,
et l'élément chauffant commandé a une résistance inférieure à celle des autres éléments
chauffants du même groupe.
6. Dispositif de chauffage (1) selon l'une quelconque des revendications précédentes,
caractérisé en ce que les éléments chauffants (2, 2') comprennent un monolithe de carbone électriquement
conducteur, lequel monolithe de carbone est un monolithe de carbone poreux ayant une
structure cellulaire permettant à une partie importante de l'écoulement de fluide
de passer à travers ledit monolithe à l'intérieur du passage.
7. Dispositif de chauffage (1) selon la revendication 6, caractérisé en ce que le monolithe de carbone poreux comporte des canaux avec une taille de canal entre
100 µm et 2000 µm.
8. Dispositif de chauffage (1) selon la revendication 6 ou 7, caractérisé en ce que le monolithe de carbone poreux a une aire d'ouverture entre 30 % et 60 % de la section
transversale perpendiculaire au trajet de circulation dans le passage.
9. Dispositif de chauffage (1) selon l'une quelconque des revendications précédentes,
caractérisé en ce que les éléments chauffants (2, 2') sont agencés avec une résistance totale ne dépassant
pas 2,5 Ohms, de préférence ne dépassant pas 1 Ohm, plus préférablement d'environ
0,8 Ohm.
10. Dispositif de chauffage (1) selon l'une quelconque des revendications précédentes,
dans lequel le capteur de température est une thermistance (19).
11. Appareil de stockage et de récupération de vapeur de carburant (3) comprenant un dispositif
de chauffage (1) selon l'une quelconque des revendications précédentes, et une commande
(11).
12. Procédé de mise en oeuvre d'un dispositif de chauffage (1) selon l'une quelconque
des revendications 1 à 10 ou d'un appareil de stockage et de récupération de vapeur
de carburant (3) selon la revendication 11 dans un environnement de véhicule, comprenant
les étapes consistant à :
i) obtenir un signal de réapprovisionnement en carburant indiquant qu'un réservoir
de véhicule en communication fluidique avec le dispositif de chauffage (1) a été réapprovisionné
en carburant, et
ii) alimenter le dispositif de chauffage (1) après un réapprovisionnement en carburant
depuis le démarrage du moteur pendant une durée ne dépassant pas 45 minutes / 24 heures,
tout en commandant l'énergie électrique fournie au dispositif de chauffage (1) en
réponse à un signal de température provenant d'un capteur de température (19).
13. Procédé selon la revendication 12, caractérisé en ce que l'alimentation de l'étape ii) s'effectue pendant environ 30 minutes / 24 heures.
14. Procédé selon la revendication 12 ou 13, comprenant en outre l'étape consistant à
:
iii) obtenir un signal de niveau de carburant d'une jauge de carburant, et
iv) empêcher l'alimentation du dispositif de chauffage (1) si le signal de niveau
de carburant indique que le niveau de carburant est à une mesure prédéterminée.
15. Procédé selon la revendication 14, caractérisé en ce que la mesure prédéterminée de l'étape iv) est 1/3, de préférence 1/4.
16. Procédé selon l'une quelconque des revendications 12 à 15, comprenant en outre l'étape
consistant à :
v) cesser d'alimenter le dispositif de chauffage (1) dans toutes les conditions de
fonctionnement si la température environnementale est inférieure à un chiffre prédéterminé.
17. Procédé selon la revendication 16, caractérisé en ce que la température de l'étape v) est de -7 °C, de préférence -10 °C.
18. Procédé selon l'une quelconque des revendications 12 à 17, comprenant en outre l'étape
consistant à effectuer au moins un cycle de test, et cesser d'alimenter le dispositif
de chauffage (1), et envoyer un signal de défaut à un système de diagnostic embarqué
si une ou plusieurs des conditions suivantes sont satisfaites :
a) un défaut est détecté dans les éléments de circuit de capteur de température,
b) un autotest de la commande de dispositif de chauffage (11) a échoué,
c) une augmentation de la résistance de l'agencement d'éléments chauffants de monolithe
(2, 2') au-delà d'un chiffre prédéterminé est détectée, et
d) la tension d'alimentation est supérieure ou inférieure à un chiffre maximum/minimum
prédéterminé.
19. Procédé selon la revendication 18,
caractérisé en ce que le défaut détecté dans les éléments de circuit de capteur de température comprend
l'un des éléments suivants :
- circuit ouvert d'un élément de circuit de thermistance,
- court-circuit d'un élément de circuit de thermistance, et
- contact de thermistance médiocre.
20. Procédé selon l'une quelconque des revendications 12 à 19, dans lequel la fourniture
d'énergie électrique au dispositif de chauffage (1) est commandée à une température
au niveau du capteur de température (19) d'environ 132 °C à environ 145 °C, de préférence
à environ 140 °C.
21. Procédé selon l'une quelconque des revendications 12 à 20, dans lequel la commande
de l'énergie électrique fournie au dispositif de chauffage (1) comprend la modulation
par durée d'impulsion de l'énergie électrique fournie au dispositif de chauffage (1).