Control apparatus and control method for reformer

A control apparatus can maintain a substantially constant temperature of a reforming reaction in which a partial oxidation reaction occurs. The control apparatus can be used for a reformer that reforms reformats fuel into fuel by an endothermic reforming reaction and a partial oxidation reforming reaction. The amount of oxygen supplied for the partial oxidation reaction is determined based on an amount of the raw material and on theoretical endothermic values and exothermic values of the respective reforming reaction and partial oxidation reaction.

BACKGROUND OF THE INVENTION
 1. Field of Invention
 The present invention relates to an apparatus and a method for controlling
 a reaction which occurs in a reformer for reforming hydrocarbon and
 reformate fuel into a desired type of fuel with a high concentration of
 hydrogen.
 2. Description of Related Art
 A reformer designed to reform a vapor mixture of methanol and water into
 reformate gas mainly composed of hydrogen is known. In principle,
 according to a reforming reaction occurring in the reformer, methanol
 reacts with water vapor so as to produce hydrogen gas. In other words, a
 water vapor reforming reaction occurs in the reformer. This is an
 endothermic reaction, as can be understood from equation (1) shown below.
EQU CH.sub.3 OH+H.sub.2 O.fwdarw.3H.sub.2 +CO.sub.2 -49.5 kJ/mol (1)
 Further, the activation temperature of a reforming catalyst is relatively
 high (about 300.degree. C.). Therefore, in order to continue the
 above-mentioned reforming reaction, it is necessary to supply a
 corresponding amount of reaction heat.
 On the other hand, as an example of a reforming reaction of methanol, there
 is a partial oxidation reforming reaction wherein hydrogen is produced
 through an oxidation reaction. This is an exothermic reaction, as can be
 understood from the equation (2) shown below.
EQU CH.sub.3 OH+1/2O.sub.2.fwdarw.2H.sub.2 +CO.sub.2 +189.6 kJ/mol (2)
 The reactions represented by the aforementioned formulas (1) and (2) can be
 caused to proceed simultaneously. For example, there is known a fuel cell
 system of a type compatible with partial oxidation, wherein the heat
 generated in the partial oxidation reaction compensates for the heat
 absorbed in the water vapor reforming reaction (Japanese Patent
 Publication No. HEI 7-57756).
 As is apparent from the equations (1) and (2), the amount of heat absorbed
 in the water vapor reforming reaction is greatly different from the amount
 of heat generated in the partial oxidation reaction. Thus, provided that
 these reactions occur simultaneously for methanol of 1 mol, a large amount
 of heat is generated and the catalyst reaches an excessively high
 temperature, so that the catalyst may deteriorate in activity or
 durability. Conversely, if the partial oxidation reforming reaction
 (equation (2)) is at a low ebb, the reforming catalyst falls in
 temperature, so that an undesirably large amount of methanol remains and
 an undesirably large amount of carbon monoxide gas is produced.
 That is, even in the case where the water vapor reforming reaction is
 caused to proceed simultaneously with the partial oxidation reforming
 reaction, the proceeding of the water vapor reforming reaction may be
 adversely affected depending on a degree of the proceeding of the partial
 oxidation reforming reaction. For this reason, the reformer of a type
 compatible with partial oxidation needs to suitably control the partial
 oxidation reaction. However, the above-described known apparatus do not
 control the partial oxidation reaction. Therefore, the known apparatus
 have trouble in constantly maintaining the reforming portion at a
 temperature required for the reforming reaction. In particular, in the
 case where the amount of reformate fuel fluctuates in response to load
 fluctuations in an energy converter such as a fuel cell which consumes
 reformate fuel, the temperature of the reforming portion such as the
 reforming catalyst may become unstable. As a result, the reformate gas may
 deteriorate in quality.
 SUMMARY OF THE INVENTION
 The present invention has been made in consideration of the aforementioned
 disadvantages of known apparatus and methods. It is an object of the
 present invention to provide an apparatus and a method capable of
 constantly maintaining a reformer, that utilizes both a reforming reaction
 and a partial oxidation reforming reaction, at a temperature required for
 the reforming reaction.
 In order to achieve the above-stated object, the present invention has
 focused attention on the fact that the oxygen supplied to the reforming
 portion undergoes the partial oxidation reaction. The amount of oxygen to
 be supplied can be determined based on either a required amount of
 reformate fuel contributing to the exothermic reforming reaction (the
 water vapor reforming reaction), or a required amount of reformate fuel
 contributing to the partial oxidation reaction. In the present invention,
 the amount of oxygen to be supplied is determined based on an amount of
 reformate fuel contributing to the partial oxidation reaction, which
 amount is determined based on a ratio between a theoretical endothermic
 value in the endothermic reforming reaction and a theoretical exothermic
 value in the partial oxidation reaction.
 That is, according to one aspect of the present invention, a control
 apparatus for a reformer includes a controller for controlling the
 introduction of raw material and oxygen into the reformer and promoting an
 endothermic reforming reaction and an exothermic partial oxidation
 reaction, and for determining an amount of oxygen supplied for the partial
 oxidation reaction based on an amount of the raw material and on
 theoretical exothermic values in the reforming reaction and the partial
 oxidation reaction.
 In the above aspect, the endothermic value and the exothermic value are
 balanced with each other in the reforming reaction, so that the portion of
 the reformer where the reforming reaction occurs can be maintained at a
 predetermined temperature. Consequently, the reforming reaction proceeds
 favorably, and high-quality fuel can be obtained.
 In addition to the features of the above aspect, the controller determines
 an amount of time from supply of the raw material to occurrence of the
 reforming reaction and the partial oxidation reaction, and adjusts the
 determined amount of supply of oxygen based on that amount of time.
 Thus, even if there is a fluctuation in the amount of supply of the raw
 material, the amount of supply of oxygen is corrected in accordance with a
 temporal delay of a fluctuation in the reforming reaction resulting from
 the fluctuation in amount of supply of the raw material. Therefore, the
 portion of the reformer where the reforming reaction occurs can be
 maintained at the predetermined temperature with higher precision.
 Further, in addition to the features of the above aspect, the control
 apparatus can include a temperature detector for detecting a temperature
 of a portion of the reformer where the reforming reaction and the partial
 oxidation reaction occur, and the controller can adjust the determined
 amount of supply of oxygen based on the detected temperature. In this
 manner, the portion of the reformer where the reforming reaction occurs
 can be maintained at the predetermined temperature with still higher
 precision. As a result, the reforming reaction is stabilized and
 high-quality fuel can be obtained.
 Further, in addition to the features of the above aspect, the controller
 can estimate a state quantity of oxygen supplied for the partial oxidation
 reaction, and adjust the determined amount of supply of oxygen based on
 the estimated state quantity of oxygen.
 According to the above embodiment, the state quantity such as a feed
 pressure of oxygen is estimated in supplying oxygen, and the amount of
 supply of oxygen is corrected based on the estimated state quantity. Thus,
 the amount of supply of oxygen can be controlled precisely. As a result,
 the reforming reaction is stabilized and high-quality fuel can be
 obtained.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 An exemplary embodiment of the present invention will now be described with
 reference to the accompanying drawings.
 FIG. 2 schematically illustrates a system wherein a reformer that uses
 reformate fuel is employed, and wherein reformate gas generated in the
 reformer is utilized to convert energy in an energy converter. A reformer
 2 reforms reformate fuel, which is the mixture of methanol and water, into
 reformate gas substantially comprising hydrogen and carbon dioxide. The
 reformer 2 is connected to an anode 15 side of a fuel cell 1, which is
 used as an energy converter. The reformer 2 comprises a heating portion 3
 for heating the reformate fuel, a reforming portion 4 and a carbon
 monoxide (CO) oxidation portion 5.
 The heating portion 3 generates vapor of the mixture of methanol and water
 by heating reformate fuel. The heating portion 3 comprises a combustion
 portion 6 for generating heat for heating reformate fuel, and a vaporizing
 portion 7 for vaporizing the reformate fuel using the heat generated by
 the combustion portion 6. The combustion portion 6 may comprise a burner
 that causes heat fuel to burn or a catalyst that oxidizes heat fuel.
 Referring to FIG. 2, a pump 8 for feeding heat fuel, such as methanol, is
 connected to the combustion portion 6 via an injector 9. Further, there is
 provided an air feed portion 10 for feeding a combustion support gas, such
 as air. More specifically, the air feed portion 10 comprises an air pump.
 Further, a pump 11 serving as a reformate fuel feed portion for feeding the
 liquid mixture of methanol and water is connected to the vaporizing
 portion 7. The vaporizing portion 7 is coupled to the combustion portion 6
 such that heat can be transmitted therebetween through a heat exchanger
 12.
 The reforming portion 4 generates gas substantially comprising hydrogen,
 mainly by reforming reactions of methanol. The reforming reactions are a
 water vapor reforming reaction indicated by the above equation (1) and a
 partial oxidation reaction is indicated by the equation (2). In order to
 cause these reactions, as can be seen from FIG. 3A, a catalytic layer 41
 composed of a catalyst such as a copper-based catalyst with an activation
 temperature, for example, of from about 280-300.degree. C., is provided
 inside a chamber 42. The vaporizing portion 7 is connected to a feed port
 43 of the chamber 42. A partial oxidation air feed pipe 44 for feeding
 oxygen for the partial oxidation reaction is connected to the feed port
 43. An air pump 13 is connected to the partial oxidation air feed pipe 44
 of the reforming portion 4.
 Further, temperature sensors 46 and 47, which detect a temperature of the
 catalytic layer 41 and provide output signals, are disposed on the side of
 the feed port 43 of the chamber 42, and on the side of a discharge port 45
 of the chamber 42, respectively. Still further, a pressure sensor 48 is
 disposed on the side of the discharge port 45.
 The reforming reaction represented by the equation (1) and the partial
 oxidation reaction represented by the equation (2) occur only in ideal
 circumstances. Further, carbon dioxide is reversibly changed into carbon
 monoxide. Therefore, in fact, the inclusion of carbon monoxide into the
 reformate gas is inevitable. Because carbon monoxide would poison a
 catalyst at a fuel electrode of the fuel cell 1, the CO oxidation portion
 5 is provided so as to reduce the carbon monoxide. The CO oxidation
 portion 5 is provided with a CO oxidation catalyst and an air feed portion
 14. The reformate gas generated in the reforming portion 4 is passed
 through the CO oxidation portion 5 so that the carbon monoxide contained
 in the reformate gas is oxidized by oxygen contained in air.
 The fuel cell 1 typically comprises a multitude of unit cells that are
 interconnected to one another. For example, each unit cell can have a
 construction wherein a high-molecular electrolyte film permeable to
 protons is interposed between the anode 15 and a cathode 16. Each of the
 anode 15 and cathode 16 is composed of a diffusion layer and a reaction
 layer. The reaction layer at the anode 15 has a porous structure wherein a
 catalyst such as platinum, platinum alloy or ruthenium is carried, for
 example, on a support such as carbon. The anode 15 communicates with the
 reformer 2, to which reformate gas mainly containing hydrogen gas is fed.
 An air feed portion 17 such as a pump is connected to the cathode 16 so as
 to feed oxygen, which is to react with hydrogen contained in the reformate
 gas.
 External loads such as a battery 18 and an inverter 19 are connected to the
 respective anode 15 and cathode 16 so as to form a closed circuit. The
 closed circuit incorporates a current sensor 20. Furthermore, a motor 21
 is connected to the inverter 19. For example, the motor 21 serves as a
 power source for driving a vehicle.
 The ionization of hydrogen generated in the anode 15 and the oxidation
 reaction through an electrolytic film do not occur as to all of the
 hydrogen supplied to the fuel cell 1. The reaction efficiency is several
 tens of percent, and the exhaust gas discharged from the side of the anode
 15 contains unreacted combustible gas that is irrelevant to the reaction,
 namely, hydrogen gas. In order to take advantage of this fact effectively,
 a return pipe 22 for returning exhaust gas on the side of the anode 15 to
 the combustion portion 6 is disposed such that the fuel cell 1
 communicates with the combustion portion 6. Further, the return pipe 22
 extends across a flow rate regulating valve 23 for controlling the flow
 rate of gas flowing within the return pipe 22. The opening degree of the
 flow rate regulating valve 23 is electrically controlled. Furthermore, the
 return pipe 22 suitably discharges the gas flowing therein to the outside
 instead of supplying the gas to the combustion portion 6.
 A controller 24, such as an electronic control unit (ECU) is provided so as
 to control the supply of reformate fuel to the vaporizing portion 7, as
 well as the supply of partial oxidation air. The controller 24 is a
 microcomputer, which includes a central processing unit (CPU), storage
 devices (RAM, ROM) and an I/O interface. An output signal from the current
 sensor 20, detection signals from the temperature sensors 46 and 47, and a
 detection signal from the pressure sensor 48 are input to the controller
 24 as control data. A determination is then made based on the input data
 and preliminarily stored data, and control signals are output to the pump
 11 and the air pump 13, so as to control the amounts of supply of the
 reformate fuel and partial oxidation air.
 The basic operation of the reformer 2 will now be described. A liquid feed
 pump 11 feeds the liquid mixture of methanol as reformate fuel and water
 to the vaporizing portion 7. Combustion methanol is introduced from the
 injector 9 into the combustion portion 6. Alternatively, exhaust gas
 containing unreacted hydrogen gas is supplied from the return pipe 22 to
 the combustion portion 6 simultaneously with the spraying of combustion
 methanol, or instead of combustion methanol. Further, the air pump 10
 feeds air as combustion support gas to the combustion portion 6. The
 combustion methanol and/or the air and heat fuel composed of unreacted
 hydrogen gas undergo an oxidation reaction (that is, burn) in the
 oxidation catalyst and generate heat. This heat vaporizes the liquid
 mixture, so that the vapor mixture of methanol and water is generated.
 The vapor mixture generated in the vaporizing portion 7 is delivered to the
 reforming portion 4. The copper-based catalyst provided in the reforming
 portion 4 causes a reforming reaction of methanol with water.
 Consequently, reformate gas substantially comprising hydrogen gas and
 carbon dioxide gas is generated. Simultaneously, there is caused a partial
 oxidation reaction of the air fed from the air pump 13 to the reforming
 portion 4 with methanol. The partial oxidation reaction is represented by
 the above equation (2). As a result of the partial oxidation reaction,
 hydrogen gas and carbon dioxide gas are generated.
 The reforming reaction of methanol is an endothermic reaction, whereas the
 partial oxidation reaction of methanol is an exothermic reaction. Hence,
 these reactions are controlled such that the endothermic value becomes
 equal to the exothermic value. Thereby, the heat budget in the reforming
 portion 4 is balanced so that the temperature of the reforming portion 4
 is kept substantially constant. Because heat substantially neither enters
 nor leaves the reforming portion 4, the heat generated in the combustion
 portion 6 is exclusively used to heat and vaporize the reformate fuel.
 In principle, the gas generated in the reforming portion 4 is only hydrogen
 gas and carbon dioxide gas. In fact, however, a small amount of carbon
 monoxide (about 1%) is typically also generated. While reformats gas
 passes through the CO oxidation portion 5, most of the carbon monoxide
 reacts with oxygen contained in the air fed from the air feed portion 14
 and then becomes carbon dioxide. The reformate gas with a high
 concentration of hydrogen is delivered to the anode 15 of the fuel cell 1,
 whereby hydrogen ions and electrons are generated in the reaction layer
 thereof. The hydrogen ions permeate the electrolytic film, react with
 oxygen on the side of the cathode 16 and generate water. The electrons
 generate motive power through the external loads.
 In order to maintain the reforming portion 4 at a substantially constant
 temperature during the above-described reforming process, the amount of
 oxygen for the partial oxidation reaction, that is, the amount of air
 supply is controlled as follows. FIG. 1 is a flowchart illustrating an
 exemplary embodiment of such control. First, the amount of partial
 oxidation air is determined based on an amount of reformate fuel (STEP 1).
 The amount of reformate fuel Fk (mol/s) corresponds to an amount of
 hydrogen required in the fuel cell 1. Therefore, the amount of reformate
 fuel is determined based on a load applied to the fuel cell 1.
 Further, in the case where methanol is reformed through water vapor
 reformation and partial oxidation reformation, the endothermic and
 exothermic values are represented by the above equations (1) and (2).
 Hence, about 21% of the methanol fed to the reforming portion 4 is
 subjected to partial oxidation reformation, and the remaining 79% of the
 methanol is subjected to water vapor reformation, whereby the heat budget
 in the reforming reactions is balanced. Furthermore, as is apparent from
 the equation (2), 1/2 mole of oxygen is required to oxidize and reform 1
 mole of methanol. Accordingly, the amount of partial oxidation air Fpo
 (1/s) required for the determined amount of reformate fuel Fk (mol/s) is
 calculated using equation (3) shown below.
EQU Fpo (1/s)=0.105.times.Fk(mol/s).times.22.4
 (1/mol).times.100/21.times.298/273 (3)
 In this formula, "100/21" represents a conversion factor in converting the
 required amount of oxygen into the amount of air, and "298/273" represents
 a volume correction factor for a room temperature of 25.degree. C.
 In changing an amount of reformate fuel, by the time the corresponding
 change in the reforming reaction occurs, adjustment is made in
 consideration of a length of time for transporting reformate fuel and a
 dynamic characteristic in the vaporizing portion 7 (STEP 2). First,
 adjustment is made as to a delay resulting from the transportation of the
 reformate fuel. Provided that the length of delay time is t0, the
 adjustment is made according to the following formula: Fpo1=Fpo (t-t0).
 That is, the amount of air that is determined before the lapse of the
 delay time t0 is adopted as a current amount of partial oxidation air.
 Further, if it is assumed that the dynamic characteristic of the
 vaporizing portion 7 is a primary delay, adjustment is made according to
 the equation (4) shown below.
EQU Fpo2=Fpo2(old).times..tau./(DT+.tau.)+Fpo1.times.DT/(DT+.tau.) (4)
 In this equation,
 DT represents a control cycle,
 .tau. is an amount indicative of a degree of primary delay, and
 Fpo2(old) represents a hysteresis of the value of Fpo2 during a preceding
 control cycle.
 Then, the amount of partial oxidation air is corrected based on the
 temperature detected by the temperature sensor 47 on the side of the
 discharge port 45 of the reforming portion 4, using the equation (5) shown
 below (STEP 3).
EQU Fpo3=Fpo2(old)+Kp.times.(Trot-Tro)+Ki.times..SIGMA.(Trot-Tro) (5)
 In this equation,
 Kp and Ki are control parameters,
 Trot is a target temperature on the side of the discharge port of the
 reforming portion 4, and
 Tro is the temperature detected by the temperature sensor 47.
 That is, if the detected temperature on the side of the discharge port is
 high, the amount of partial oxidation air is reduced. Conversely, if the
 detected temperature on the side of the discharge port is low, the amount
 of partial oxidation air is controlled such that the detected temperature
 becomes a target temperature.
 Furthermore, the amount of partial oxidation air is adjusted based on a
 temperature on the side of the inlet port of the reforming portion 4 (STEP
 4). This step is intended to at least substantially prevent deterioration
 of the reforming catalyst, which especially results from a temperature
 exceeding a predetermined temperature. For example, the value determined
 in STEP 3 is corrected using the equation (6) shown below.
EQU Fpo4=Kdec.times.Fpo3 (6)
 In this equation, Kdec represents a function of a temperature Tri (.degree.
 C.) that is detected by the temperature sensor 46 on the side of the inlet
 port 43 of the reforming portion 4. For example, the value of Kdec is
 determined based on a relationship shown in FIG. 4. The inflection point
 of the graph shown in FIG. 4 represents a threshold value of catalyst
 deterioration resulting from an abnormally high temperature. Accordingly,
 if the temperature of the reformate fuel vapor supplied to the catalytic
 layer 41 is high, the partial oxidation reforming reaction is restricted,
 so that the temperature of the catalyst is reduced down to the target
 temperature. FIG. 3B shows an example of temperature distribution in the
 catalytic layer 41 of the reforming portion 4.
 Then, a command signal is output to the air pump 13 so as to supply the
 reforming portion 4 with partial oxidation air of the thus-corrected
 amount Fpo4 (STEP 5). In this case, if the pressure on the side of the
 inlet port of the reforming portion 4 is high, the output of the air pump
 13 needs to be increased. Therefore, the command value to be output to the
 air pump 13 is set as follows. First of all, the pressure sensor 48
 provided on the side of the discharge port 45 of the reforming portion 4
 detects a pressure. Based on the detected pressure, the pressure of
 partial oxidation air on the side of the feed port 43 of the reforming
 portion 4 (the amount indicative of a state of oxygen supply) is
 estimated. Then, based on a map such as shown in FIG. 5, the air pump
 command value for the amount of partial oxidation air is set using the
 estimated pressure as a state quantity. For example, even in the case
 where the pressure on the side of the feed port 43 is high due to a great
 amount of reformate fuel vapor supplied to the reforming portion 4 from
 the vaporizing portion 7, the output of the air pump 13 increases
 correspondingly. Thus, it is possible to supply a precise amount of oxygen
 required for the partial oxidation reformate reaction.
 As described above, according to the control apparatus of the present
 invention, the amount of supply of oxygen contributing to the partial
 oxidation reforming reaction is set based on an amount of reformate fuel,
 a theoretical endothermic value of the water vapor reforming reaction, and
 a theoretical exothermic value of the partial oxidation reforming
 reaction. Therefore, the endothermic value is balanced with the exothermic
 value in the reforming portion 4, which can be maintained substantially at
 its target temperature.
 In particular, this embodiment adjusts an amount of air based on a delay in
 transportation or reaction of reformate fuel, and based on temperatures on
 the feed and discharge sides of the reforming portion 4. Therefore, the
 amount of oxygen for the partial oxidation reforming reaction, that is,
 the degree of the partial oxidation reformate reaction, can be set to a
 target value. As a result, the reforming portion 4 is set to a temperature
 for maintaining the catalyst in its activated state, which makes it
 possible not only to enhance reforming efficiency but also to obtain
 high-quality reformate gas. Furthermore, according to the above-described
 embodiment, the command value for the air pump 13 is set based on an
 estimated value of a pressure at the location where partial oxidation air
 is supplied, namely, on the side of the feed port 43. Therefore, the
 determined or adjusted amount of air, that is, oxygen, can be supplied to
 the reforming portion 4. Consequently, the proportion of the partial
 oxidation reaction can be set with high precision, and the reforming
 portion 4 can be substantially maintained at its target temperature.
 In the above-described embodiment, the present invention is applied to a
 control apparatus designed for a reformer for supplying the fuel cell 1
 with fuel gas. However, the present invention can also be applied to other
 apparatus for supplying reformate gas.
 Furthermore, although methanol is used as reformate fuel in the
 abovedescribed embodiment, it is also possible to alternatively use
 hydrocarbons other than methanol. In addition, although the pressure on
 the feed side of the reforming portion is adopted as an amount indicative
 of a state of supply of partial oxidation air in the above-described
 embodiment, it is also possible to use other state quantities in other
 embodiments.
 Furthermore, in the above-described embodiment, the amount indicative of a
 state of supply of partial oxidation air is estimated based on a pressure
 on the discharge side of the reforming portion. However, it is also
 possible to directly detect a pressure on the discharge portion of the
 reforming portion for partial oxidation air. Also, the amount indicative
 of a state of partial oxidation air can also be estimated based on a
 pressure at the outlet of the reformer.
 In the above-described embodiments, the controller 24 is implemented as a
 programmed general purpose computer. It will be appreciated by those
 skilled in the art that the controller 24 can be implemented using a
 single special purpose integrated circuit (e.g., ASIC) having a main or
 central processor section for overall, system-level control, and separate
 sections dedicated to performing various different specific computations,
 functions and other processes under control of the central processor
 section. The controller 24 also can be a plurality of separate dedicated
 or programmable integrated or other electronic circuits or devices (e.g.
 hardwired electronic or logic circuits such as discrete element circuits,
 or programmable logic devices such as PLDs, PLAs, s or the like). The
 controller 24 can be implemented using a suitably programmed general
 purpose computer, e.g., a microprocessor, microcontroller or other
 processor device (CPU or MPU), either alone or in conjunction with one or
 more peripheral (e.g., integrated circuit) data and signal processing
 devices. In general, any device or assembly of devices on which a finite
 state machine capable of implementing the programs shown in FIG. 1 can be
 used as the controller. A distributed processing architecture can be used
 for maximum data/signal processing capability and speed.
 While the present invention has been described with reference to what is
 presently considered to be a preferred embodiment thereof, it is to be
 understood that the present invention is not limited to the disclosed
 embodiment or construction. On the contrary, the present invention is
 intended to cover various modifications and equivalent arrangements. In
 addition, while the various elements of the disclosed invention are shown
 in various combinations and configurations, which are exemplary, other
 combinations and configurations, including more, less or only a single
 embodiment, are also within the spirit and scope of the present invention.