JP2011509367A - Fluid heater - Google Patents

Abstract

[Objective] To improve environmental conservation, especially from hydrocarbon emissions from vehicles.
[Configuration Requirements] The fluid heater 1 has heating elements 2 and 2 'made of a conductive monolith, and the heater 1 has a fluid passage that is heated by the fluid flow direction determined during the heating operation. The heater 1 has at least two heating elements 2 and 2 'arranged adjacent to each other in the passage, and these heaters 1 and 2' are arranged so as to be parallel to the flow of the fluid. One of the heating elements 2, 2 ′ is a controlled heating element 2 ′ and has a slightly higher heating power than the others, and the temperature at or near the downstream end 23 of the controlled heating element 2 ′. A sensor 19 is provided, and the temperature sensor 19 is connected to the control means 11 that performs temperature control during the heating operation of the heater 1. The present invention also relates to a method for operating such a heater 1.
[Selection] Figure 1

Description

  The present invention relates to a fluid heater having a heating element made of a conductive monolith, the heater having a fluid passage heated by a fluid flow direction defined during a heating operation, and the heater is disposed in the passage. It has two heating elements arranged adjacent to each other, these are arranged so as to be parallel to the liquid flow, and the present invention further includes a fuel vapor storage and recovery device having such a heater, , How to drive it.

  One such heater is known from US 2007/0056954. In particular, as an application of such a heater, a purge heater for a fuel vapor storage and recovery device for reducing steam exhaust from an automobile is described. The disclosed purge heater has one or more electrical heating elements, which are connected to an electrical energy source such as a car battery, for example. The purge heater has, for example, a conductive ceramic as a heating element.

  Alternatively, the purge heater has conductive carbon, preferably porous monolithic carbon. Such porous monolithic carbon is disclosed in, for example, US Application Publication No. 2007-0056954 (A1). These monolithic carbon heating elements have a channel structure that allows air flow from the heating elements and can facilitate heat release directly through purging air absorbed from the atmosphere.

  An important application of such a heater is a fuel vapor storage and recovery device for reducing steam emissions from automobiles. Fuel vapor storage and recovery devices having fuel vapor storage canisters have been widely known in the art for many years. Gasoline fuel used in many internal combustion engines is very volatile. Vaporous emissions of fuel vapor from a vehicle having an internal combustion engine are generated primarily by ventilation of the fuel tank of the vehicle. When the vehicle is parked, the air will carry hydrocarbons escaped from the fuel tank due to changes in temperature and pressure. Some fuel will necessarily evaporate against the air in the tank and take the form of steam for this purpose. If the air released from the fuel tank can flow out and flow untreated around, it will definitely carry this fuel vapor. There is government regulation on how much fuel vapor is emitted from the vehicle fuel system.

  Normally, to prevent fuel vapor loss to the surroundings, the vehicle fuel tank is vented through a passage to a canister containing a suitable fuel adsorbent such as activated carbon. Fine particles of activated carbon with a large surface area are widely used to temporarily adsorb the fuel vapor.

  A fuel vapor storage and recovery system having a fuel vapor storage canister (so-called carbon canister) is stopped during an extended period of time when the vehicle is refueled and the steamed air is discharged from the fuel tank (refueling discharge: refueling) emissions), it is necessary to deal with fuel vapor emissions.

  Fuel recovery systems for the European market usually do not play an important role because these refueling emissions are not generally discharged via carbon canisters. However, in an integrated fuel vapor storage and recovery system for the North American market, refueling emissions are emitted via carbon canisters.

  Obviously, due to the nature of the adsorbent in the carbon canister, the carbon canister has a limited packing capacity. While it is desirable to use a carbon canister with a high carbon operating capacity, it is desirable to use a relatively small volume carbon canister for design purposes. Typically, a certain negative pressure is applied to the interior of the canister from the engine intake system through the fuel vapor discharge port of the carbon canister to ensure sufficient carbon operating capacity of the carbon canister at all times during operation of the internal combustion engine. As a result, the atmosphere is guided to the canister and reaches the atmosphere intake port, and the captured fuel vapor is captured and conveyed to the intake manifold of the engine intake system via the fuel vapor discharge port. During the canister purge mode, the fuel vapor stored in the carbon canister is combusted in the internal combustion engine.

  Modern fuel vapor storage and recovery systems are very efficient, but they still release hydrocarbons that remain in the atmosphere. These so-called "bleed emissions" (diurnal breathing loss / DBL) are caused by diffusion, especially when there is a high concentration gradient of hydrocarbons between the carbon canister air vent port and the adsorbent. Brought about. When the hydrocarbon concentration gradient can be reduced, bleed emission can be significantly reduced. Obviously, this can be achieved by increasing the operating capacity of the carbon canister.

  However, only some percentage of the hydrocarbons stored in the carbon canister is effectively swept away or released during the purge mode. This is a problem for a car that has a limited time for purging. For example, in an electric hybrid car, the operation mode of the internal combustion engine is relatively short.

  Another problem is associated with the use of so-called flexi fuels with large amounts of ethanol. Ethanol is a highly volatile fuel with a relatively high vapor pressure. For example, so-called E10 fuel (10% ethanol) is currently the most easily vaporized on the market. This means that the carbon canister fuel vapor uptake from the fuel tank is extremely high. On the other hand, in the normal purging mode of conventional carbon canisters, only some percent of the fuel vapor wicking is released. As a result, the fuel vapor capacity of a typical carbon canister is used up relatively early. The bleed emission of a full carbon canister then increases to a degree that usually exceeds the emission values given by law.

  In order to improve the purge removal rate during the purging mode, a steam storage / recovery device using a so-called purge heater has been proposed. By heating the air introduced into the canister via the air intake port, the efficiency of removing hydrocarbons trapped in the fine pores of the adsorbent is significantly improved.

  For example, U.S. Pat.No. 6,230,693 (B1) describes a fuel evaporative gas control system that reduces the amount of fuel vapor discharged from a vehicle by using an auxiliary canister that operates with a storage canister of the fuel evaporative gas control system. Disclose. The storage canister includes a first adsorbent and has a vent port in communication therewith. The auxiliary canister has a main body, first and second passages, a heater, and a connector. Inside the main body, the second adsorbent contacts the heater all over. In the regeneration phase of operation of the control system, the heater heats the purge air passing through the second adsorbent. This can more easily release the fuel vapor adsorbed during the previous storage phase in operation by the second and first adsorbents, and the fuel vapor will burn during combustion.

  Further, according to US Pat. No. 6,230,693, the storage canister of the fuel evaporative gas control system has two adjacent compartments for storing fuel vapors connected by a flow path. In particular, partitioning the canisters actually means flow suppression. Since the driving pressure of the flow through the canister is very low, minimizing flow suppression is an important design consideration.

  An object of the present invention is to provide a fluid heater having a heating element made of a conductive monolith, and the heater is a fluid passage that is heated by a fluid flow direction determined during a heating operation. The heater has two heating elements arranged adjacent to each other in the passage, and these heaters are arranged so as to be parallel with respect to the liquid flow, which is simple, compact and It is reliable and enables easy and efficient controlled operation. Another object of the present invention is to provide a fuel vapor storage and recovery device having improved fuel recovery efficiency. Furthermore, it is a further object to provide a method for operating such a heater that allows a simple and efficient controlled operation.

  These and other objects are achieved by a fluid heater having a heating element made of an electrically conductive monolith, said heater having a fluid passage heated by a fluid flow direction defined during heating operation. And the heater has at least two heating elements arranged adjacent to each other in the passage, and is arranged so that they are parallel to the liquid flow. One of the heating elements is controlled and has a slightly higher heating power than the other, and a temperature sensor is provided at or near the downstream end of the controlled heating element, and the temperature sensor is connected to the heater. It is connected to the control means which controls temperature during heating operation.

  The arrangement according to the invention provides both improved safety and improved efficiency of such a heater. The configuration of the temperature sensor for the heating element with a little larger heating power allows the heater to be efficiently controlled to the maximum temperature, preventing overheating of the heater and avoiding the risk of fire, while The temperature can be controlled close to the maximum temperature to increase the efficiency of the heater. The temperature sensor structure disposed at or near the downstream end of the heating element can minimize the effect of changes in fluid flow velocity, i.e. greatly reduce the adverse effects of flow changes in the heating operation of the heater. be able to.

  Due to the above-described advantages of the present invention, the fuel vapor storage and recovery apparatus equipped with the heater of the present invention is particularly effective for a vehicle that performs engine cycle operation, that is, hybrid driving of gasoline and electricity. In this type of drive, it typically occurs that the purge air flow through the fuel vapor storage and recovery device changes rapidly from high to low when the engine stops when switched to electric drive. With heaters of conventional design, this rapid change in purge air flow results in a high risk of excessive heating of the fuel vapor storage and recovery system with a great risk of fire, or the heater is well below the critical temperature. It is necessary to control the temperature, and this makes the recovery operation worse. However, the recovery operation is very important in this kind of application in order to reduce the operating time of the gasoline engine.

  A particularly beneficial and fault-tolerant embodiment of the present invention is that at least two of the heating elements are electrically connected in series with each other and the controlled heating element has a greater resistance than the other heating elements. Features.

  An alternative embodiment is characterized in that the at least two heating elements are electrically connected to each other in parallel, and the controlled heating element has a smaller resistance than the other heating elements.

  A further advantageous embodiment of the present invention is that the heater has more than two heating elements, which are grouped together, and the heating elements of one group are electrically connected to each other. Connected in series, the groups of heating elements are electrically connected in parallel with each other, the group having the controlled heating elements has a smaller resistance than the group of other heating elements, and the control The heating elements having a higher resistance than other heating elements in the same group, or the heating elements of one group are electrically connected to each other in parallel, and the groups of heating elements are mutually connected A group electrically connected in series and having the controlled heating element has a greater resistance than the other heating element group, and the controlled heating element has a smaller resistance than the other heating element in the same group. It is characterized by having .

  In a more preferred embodiment of the heater according to the invention, the heating element comprises a conductive carbon monolith, the carbon monolith having a cell structure allowing the monolith to pass through most of the liquid flow in the passage. The porous carbon monolith has a channel size between 100 microns and 2000 microns, and the porous carbon monolith has a 30% to 60% open area in a cross section perpendicular to the liquid flow in the passage. It is characterized by having.

  The particularly good operation of the heater according to the invention in a typical vehicle environment supplied with a conventional 12 V DC voltage is that the heating element has an overall resistance of 2.5 ohms, preferably 1 ohm, more preferably 0.8 ohms. Can be obtained.

  The heater of the present invention is particularly avoided from the risk of fire when the temperature sensor connection is short-circuited when the temperature sensor is a thyristor.

  The above and other objects are further achieved by a fuel vapor storage and recovery apparatus having such a heater and by an operating method of operating such a heater or fuel vapor storage and recovery apparatus in a vehicle environment. The method includes the steps of obtaining a refueling signal indicating that a vehicle tank communicating with the heater has been refueled, and after refueling from engine start within 45 minutes per 24 hours, more preferably about 30 minutes per 24 hours. A step of energizing the heater, and the power supplied to the heater is controlled in accordance with a temperature signal from the temperature sensor.

  In a more preferred embodiment of the method according to the invention, the method of operation comprises the steps of obtaining a fuel level signal from a fuel gauge and if the fuel level signal indicates that the fuel level has dropped to a predetermined reading, the heater And the predetermined number is a third of the fuel tank capacity, and preferably a quarter of the fuel tank capacity. At such low fuel levels, the generation of fuel vapor does not result in a large increase in pressure in the tank. Accordingly, in the fuel vapor storage and recovery apparatus, only a small amount of steam is introduced, and sufficient recovery efficiency can be obtained without heating at any ambient temperature. Furthermore, when the tank is continuously refueled, the fuel vapor flows through the carbon canister at a high flow rate in the integrated system, and the carbon canister's emission reduction effect is better using the cold carbon bed of the canister due to the heat generation effect at the time of absorption. It becomes.

  By de-energizing the heater, under all operating conditions, if the environmental temperature is lower than a predetermined value, preferably lower than minus 7 degrees Celsius, more preferably lower than minus 10 degrees Celsius, Energy savings are made. At such a low temperature, the generation of fuel vapor in the fuel tank is relatively low, and the fuel vapor storage and recovery device is sufficiently efficient even without heating.

  Energy loss through the heat sink can be minimized and power can be saved when the control of power supplied to the heater consists of pulse width modulation of the power supplied to the heater.

  In a particularly preferred embodiment, the method performs at least one test cycle to de-energize the heater and if a fault is detected in the following conditions, temperature sensor circuit, heater control self-test One of the cases where there is an increase in the resistance of the monolith heating element configuration beyond a predetermined detection value and when the supply voltage exceeds a predetermined maximum value or is below a predetermined minimum value. Alternatively, when more than that is satisfied, a failure signal is transmitted to the mounted diagnostic system. More preferably, the defect detected by the temperature sensor circuit is one of the following thermistor circuit opening, thermistor circuit short circuit, and thermistor contact being insufficient. Considering that improper operation, in particular uncontrollable heating, leads to fire hazard, this embodiment is supposed to be operation resistant to improved defects.

  Detection of an increase in resistance of the monolith heating element configuration indicates that one heating element is defective or disconnected. This further indicates that a malfunction of the heater is expected, and that a malfunction of the fuel vapor storage and recovery apparatus where such a heater is used is also expected. According to an embodiment of the method according to the invention, the legal requirements of the diagnosis on which the emission control device is mounted are fulfilled.

  The best recovery and safe operation is obtained when the electrical energy to the heater is controlled so that the temperature at the temperature sensor is from about 132 degrees Celsius to about 145 degrees Celsius, and preferably about 140 degrees Celsius. It will be.

  The invention will now be described by way of non-limiting example with reference to the accompanying drawings.

FIG. 2 is a schematic diagram of the heater of the present invention including a simplified wiring schematic. FIG. 6 is an enlarged cross-sectional view of end sections of two adjacent heating elements. It is sectional drawing in the plane shown in FIG. It is sectional drawing about the carbon canister which comprises the heater by this invention.

  FIG. 1 is a schematic view of a fluid heater according to an embodiment of the present invention, generally indicated by reference numeral 1. The heater 1 has a heating element 2 made of a conductive monolith. The heater 1 of the present invention is preferably used with a fuel vapor storage and recovery device 3 as shown in FIG. Such a fuel vapor storage and recovery device 3 is usually called a carbon canister and is typically used as part of an emission control system for an automobile having an engine to which gasoline is supplied. The figure is schematic and the parts are not drawn to scale.

  The fuel vapor storage / recovery device or carbon canister 3 includes a steam intake port 4 connected to a fuel tank (not shown), a vent port 5 leading to the atmosphere, and a purge port 6 connected to an internal combustion engine of an automobile (not shown). have. The carbon canister 3 is packed with an adsorbent in the form of finely divided activated carbon.

  During the engine stop period of the automobile, the carbon canister 3 is connected to the fuel tank of the automobile via the steam intake port 4 and connected to the atmosphere via the ventilation port 5. In the vehicle engine operation cycle, a flow path between the ventilation port 5 and the purge port 6 is established. The internal combustion engine sucks a predetermined amount of air from the atmosphere through the ventilation port 5, across the carbon canister 3 and into the purge port 6 for burning in the cylinder of the internal combustion engine, thereby purging the adsorbent of the carbon canister 3. The hydrocarbon removed from the carbon canister is sent out to the combustion chamber of the engine. In the figure, the arrows indicate the air flow during purging of the carbon canister 3. Hereinafter, in the present application, the terms “downstream” and “upstream” always refer to the air flow during the purging of the carbon canister 3 and are defined as the flow direction of the fluid during the heating operation.

  The carbon canister 3 has first, second, and third steam storage partitions 7, 8, 9. The first steam storage partition section 7 is the steam storage partition section adjacent to the steam intake port 4 and the largest steam storage partition section with respect to the air flow at the time of introduction of hydrocarbons into the carbon canister 3.

  As is clear from FIG. 4, the steam storage partitions 7, 8, 9 have a circular cross-sectional area and are arranged in a coaxial relationship. The first steam storage partition 7 surrounds the steam storage partitions 8 and 9. Next to the vent port 5 on the upstream side of the third steam storage partition 9, a purge heater partition 10 is provided, which is also cylindrical and has a circular cross section.

  The purge heater partition 10 has two suction openings 12 on the upstream end face for introducing the atmosphere into the purge heater partition 10. The purge heater partition 10 has a relatively thin peripheral wall 13, and the peripheral wall 13 is designed so that heat release from the heater 1 is transmitted to the carbon bed around the first steam storage partition 7. Has been. A passage of fluid that is an air flow of the heater 1 is defined by the peripheral wall 13 of the heater 1.

  As can be easily seen from FIGS. 1 and 4, the heater 1 preferably has four heating elements 2 arranged adjacent to each other in a heater partition 10 constituting a passage. Regarding the air flow in the heater partition 10, the heating elements 2 are arranged in parallel.

  The heating element 2 can have a cylindrical shape, and a conductive porous carbon monolith such as a synthetic carbon monolith can be used. A method of manufacturing such a carbon monolith heating element 2 is generally disclosed in US Patent Application Publication No. 2007-0056954 (A1), and more particularly in paragraphs [0013] to [0024] The contents are cited here. A carbon monolith is a porous carbon monolith having a cell structure in which most of the flow can pass through the monolith in the passage. Each heating element 2 forms a continuous longitudinal channel (not shown), allowing air flow in the longitudinal direction at each heating element. The channel of the porous carbon monolith is between 100 microns and 2000 microns in size. The porous carbon monolith heating element has an open area of 30% to 60% in a cross section perpendicular to the fluid flow in the passage.

  A suitable and typical heating element 2 has a diameter of approximately 10 mm and a typical length of about 50 mm. Each of the heating elements 2 operates as a resistor heating element. According to the preferred embodiment shown in the figure, four electric heating elements 7 are electrically connected in series and connected to a control switching means 11, which is connected via positive and negative power lines 14, 15. It is connected to an electrical energy source as a vehicle generator and battery.

  The heating element 2 is connected to the control switching means 11 via the power line 16 and the copper connector 17. The wiring of the heating element 2 is formed by the connector 18. The configuration of the heating element 2 is arranged with an overall resistance of 2.5 ohms or less, preferably 1 ohm or less, more preferably 0.8 ohms or less. In order to provide approximately 75 watts of heating power at a supply voltage of 13.7 V, some constant current flow is required.

  A preferred method for controlling the power supply is pulse width modulation (PWM). The main advantage of this method is that the power loss in the control switching means 11 is low. While PWM operation minimizes the reverse feedback of the power supply network implemented with some additional electrical components and provides electromagnetic compatibility (EMC), the control switching means 11 itself can be inexpensive. Furthermore, where ventilation for space and possibly a larger heat sink is required, it can be saved, giving an overall advantage in terms of cost and space required.

  However, conventional current rectifier circuits can be used as well, but require cooling. Conventional current rectification is also beneficial if the dissipated heat can be used for other purposes.

  One of the heating elements 2 has a slightly larger heating power than the other heating elements 2. This heating element is a controlled heating element 2 '. A temperature sensor in the form of a thyristor 19 is arranged at or near the downstream end of the controlled heating element 2 '. The temperature sensor 19 is connected to the control means 11 for temperature control during the heating operation of the heater 1 via wirings 20 and 21. In the depicted embodiment of four heating elements 2, 2 ′ connected in series, the controlled heating element 2 ′ has a slightly longer length than the other heating elements 2, for example 53 mm. Because of the same diameter and thus the same cross-sectional area, the controlled heating element 2 ′ exhibits a slightly higher resistance than the other heating elements 2. Preferably, the thyristor 19 corresponds to the position of the downstream end of the other heating element 2, and the thyristor 19 is controlled in the opening of the downstream end portion of the heating element 2 'controlled as shown in more detail in FIGS. It is mounted at about 50 mm from the upstream end of 2 ′. This arrangement is provided so that the thyristor 19 senses the temperature of the hottest part of the heater.

  The control switching means 11 is further connected to a diagnostic system implemented via a data line 24 and to other devices of the vehicle via a CAN bus line 25, for example. Of course, it will be apparent to those skilled in the art that other suitable wiring is possible.

  The heating element 2 operates only during the purging operation of the fuel vapor storage and recovery device 3, as will be described in detail below.

  As described above, during the vehicle stop period, the fuel in the fuel tank evaporates into the air space above the full liquid level of the fuel tank. The steam carried by the air flows to the carbon canister 3 through the steam intake port 4. When the vehicle is refueled, the internal combustion engine is usually also stopped, and in the integrated system, the air flow through the steam intake port 4 has a flow rate corresponding to the flow rate of refueling by the fuel supplied to the fuel tank. Accordingly, the hydrocarbons carried by the air are pumped into the carbon bed of the carbon canister 3 at a flow rate of up to 60 liters per minute. The activated carbon in the carbon canister adsorbs hydrocarbons, and the hydrocarbon molecules are trapped in the carbon internal pore structure. More or less purified air is released from the vent port 5. Because of the exothermic effect associated with adsorption, if the carbon bed is cold, the adsorption efficiency at such high flow rates will be better. Therefore, suppressing the heating operation of the heater 1 at a low fuel level in the fuel tank is beneficial from the perspective of an expected refueling.

  In the car engine operation cycle, the fuel vapor storage and recovery device 3 according to the present invention is set to the purge mode. The air is introduced from the internal combustion engine of the vehicle, and is introduced from the ventilation port 5 to the purge heater partition 10 through the suction opening 12. The heating element 2 is energized by electric energy from a vehicle generator or battery during purging. The air through and around the heating element 2 flows heated to a temperature below 150 degrees Celsius in any case not exceeding it. At the same time, the heat radiation radiated by the heating element 2 also heats the carbon bed around the first vapor storage partition 7. The heated air flows through the third steam storage partition 7. On the way, hydrocarbons stored in the carbon bed are taken out to the atmosphere. As indicated by the arrows in FIG. 4, this air flow flows into or through the carbon bed of the first steam storage partition 7 and is finally introduced into the purging line connected to the internal combustion engine via the purge port 6. Is done.

  The operation method of the heater 1 used in the fuel vapor storage and recovery device 3 in the vehicle environment includes the following steps, which obtain a refueling signal indicating that the vehicle tank has been refueled via the CAN bus 25. It is a process to do. Such a signal can be obtained from a fuel cap switch that detects the closed state of the fuel cap. If there is a signal, controlling the power to the heater 1 in response to the temperature signal from the temperature sensor 19, the time from the engine start to the heater within 45 minutes per 24 hours, more preferably about 30 minutes per 24 hours. 1 is energized. In the embodiment described above, thyristor 19 is zeroed to a temperature of 140 degrees Celsius, providing the best compromise between recovery efficiency and safety.

  In addition, the fuel level signal can also be obtained from the fuel gauge via the CAN bus 25, and if the fuel level has dropped to a predetermined reading, preferably a quarter of the fuel tank capacity, the fuel level If the signal indicates, the heater 1 is not energized for the reasons described above for refueling.

  If the environmental temperature is below a predetermined value, for example minus 10 degrees Celsius, the heater 1 is stopped under all operating conditions, and energy is saved. The external temperature signal is provided via the CAN bus 25 or obtained from a motor management system. The control switching means 11 is preferably mounted if at least one test cycle is performed, for example before the heater 1 is energized, and the heater is de-energized, if one or more of the following conditions are met: A fault signal is transmitted to the diagnostic system via the data line 24. That is, when a failure is detected in the circuit of the thyristor 19 and the wirings 20 and 21, or when the self-test of the heater control 11 is rejected, the resistance of the configuration of the monolith heating element 2 exceeds the predetermined detection value. That is, a case where it is indicated that one of the heating elements 2 is defective, such as a crack or disconnection in the monolith. Damaged heating elements 2 and breaks make the carbon canister 3 that is part of the emission control system inefficient and indicate a malfunction to the driver. Preferably, a limp-home mode is activated so that the driver can return home and bring the car to a repair shop.

  The defect detected by the temperature sensor circuits 19, 20, and 21 is one of the following. These are the opening of the wires 20 and 21, the short circuit of the thermistor 19, and the contact failure of the thermistor 19. In view of the fact of improper operation, especially uncontrollable heating, creates a risk of fire, this embodiment provides improved operation that is resistant to failures.

  In addition, when the supply voltage exceeds or falls below a predetermined maximum or minimum voltage value, the heater 1 is stopped by the control switching means 11 to prevent malfunction such as damage and excessive heating.

When the temperature of the temperature sensor 19 is controlled from about 132 degrees Celsius to 145 degrees Celsius, and preferably about 140 degrees Celsius, the electric energy to the heater 1 is obtained by the control switching means 11 so that the best recovery operation and safe operation can be obtained. And prevents any part of the heater 1 in contact with the mixture of air and gasoline vapor from ever exceeding 150 degrees Celsius.

Claims (21)

A fluid heater having a heating element made of a conductive monolith,
The heater has a fluid passage heated by a fluid flow direction defined during a heating operation, the heater having at least two heating elements disposed adjacent to each other in the passage; These are arranged so as to be parallel to the fluid flow,
One of the at least two heating elements is a controlled heating element and has a slightly higher heating power than the other, and a temperature sensor is provided at or near the downstream end of the controlled heating element, The fluid heater according to claim 1, wherein the temperature sensor is connected to a control means for performing temperature control during the heating operation of the heater. 2. The fluid heater according to claim 1, wherein at least two of the heating elements are electrically connected to each other in series, and the controlled heating element has a greater resistance than other heating elements. Fluid heater. 2. The fluid heater according to claim 1, wherein at least two of the heating elements are electrically connected to each other in parallel, and the controlled heating element has a smaller resistance than other heating elements. Fluid heater. The fluid heater according to any one of claims 1 to 3, wherein the heater has more than two heating elements, which together form a group,
The heating elements of one group are electrically connected to each other in series, the groups of heating elements are electrically connected to each other in parallel, and the group having the controlled heating elements is A fluid heater having a resistance smaller than the group, wherein the controlled heating element has a higher resistance than other heating elements of the same group. A fluid heater according to any one of claims 3 to 3, wherein the heater has more than two heating elements, these heating elements being grouped together,
The heating elements of one group are electrically connected to each other in parallel, the groups of heating elements are electrically connected to each other in series, and the group having the controlled heating elements is connected to other heating elements. A fluid heater having a resistance greater than a group, wherein the controlled heating element has a smaller resistance than other heating elements of the same group. A fluid heater according to any preceding claim, wherein the heating element comprises a conductive carbon monolith, wherein the carbon monolith allows a majority of the flow of fluid to pass through the monolith in the passage. A fluid heater characterized by being a porous carbon monolith having a cell structure. 7. The fluid heater according to claim 6, wherein the porous carbon monolith has channels having a channel size between 100 microns and 2000 microns. 8. The fluid heater according to claim 6, wherein the porous carbon monolith has an open area of 30% to 60% in a cross section perpendicular to the fluid flow in the passage. A fluid heater according to any preceding claim, characterized in that the heating element is arranged with an overall resistance of 2.5 ohms, preferably 1 ohm, more preferably 0.8 ohm. Heater for fluid. The fluid heater according to any one of the preceding claims, wherein the temperature sensor is a thermistor. A fuel vapor storage and recovery apparatus comprising the fluid heater according to any one of the preceding claims, comprising a control unit. An operation method for operating the fluid heater according to any one of claims 1 to 10 or the fuel vapor storage and recovery device according to claim 11 in a vehicle environment,
i) obtaining a refueling signal indicating that the vehicle tank communicating with the heater has been refueled;
and ii) energizing the heater after refueling from the start of the engine within 45 minutes per 24 hours,
An operation method, wherein power supplied to the heater is controlled according to a temperature signal from the temperature sensor. 13. The operation method according to claim 12, wherein energization in step i) is 30 minutes per 24 hours. The driving method according to claim 12 or 13,
iii) obtaining a fuel level signal from the fuel gauge;
iv) A method of operation characterized by comprising a step of preventing energization of the heater if the fuel level signal indicates that the fuel level has dropped to a predetermined reading. 15. The operation method according to claim 14, wherein the predetermined number in the step iv) is 1/3, preferably 1/4. The driving method according to any one of claims 12 to 15,
v) The operation method further comprising the step of de-energizing the heater under all operating conditions if the environmental temperature is lower than a predetermined value. 17. The operation method according to claim 16, wherein the predetermined temperature in step v) is minus 7 degrees Celsius, preferably minus 10 degrees Celsius. 18. The method of operation according to any one of claims 12 to 17, wherein at least one test cycle is performed to deenergize the heater and if one or more of the following conditions are met:
a) If a defect is detected in the temperature sensor circuit,
b) If the heater control self-test is rejected,
c) if there is an increase in the resistance of the monolith heating element configuration beyond the predetermined detection value; and
d) If the supply voltage exceeds the specified maximum value or is below the specified minimum value,
A driving method characterized by transmitting a failure signal to an on-board diagnostic system. The operation method according to claim 18, wherein the defect detected by the temperature sensor circuit is as follows.
Opening the thermistor circuit,
A method of operation characterized in that one of a thermistor circuit short circuit and a thermistor contact is insufficient. The operation method according to any one of claims 12 to 19, wherein the electric energy is supplied to the heater so that the temperature of the temperature sensor is 132 to 145 degrees Celsius, preferably 140 degrees. A driving method characterized by being controlled. 21. The operation method according to claim 12, wherein the control of electric power supplied to the heater includes pulse width modulation of electric power supplied to the heater.