Patent Publication Number: US-2017361296-A1

Title: Fuel reformer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application No. 2015-4422 filed on Jan. 13, 2015, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a fuel reformer that causes a steam reforming reaction between fuel and water on a reforming catalyst. 
     BACKGROUND ART 
     A vehicle having a fuel reformer has been proposed (e.g., Patent Document 1 below), and an intense effort is being made to advance development toward its practical use. The fuel reformer produces a reaction (steam reforming reaction) between water contained in exhaust gas discharged from an internal-combustion engine of the vehicle, and fuel such as ethanol, on a reforming catalyst to supply hydrogen obtained by this reaction to the internal-combustion engine. 
     Such a fuel reformer can recover the heat energy of exhaust gas by the steam reforming reaction, which is an endothermic reaction, and can convert the recovered heat energy into chemical energy such as hydrogen or carbon monoxide to reuse the heat energy. The use of fuel energy with high efficiency can restrain the fuel consumption amount of the vehicle. 
     To efficiently cause the steam reforming reaction on the reforming catalyst, the fuel needs to be supplied (injected) into the reforming catalyst, with the temperature of the reforming catalyst maintained at an approximately catalyst active temperature or at a temperature higher than this temperature. However, since the steam reforming reaction is an endothermic reaction, as the reaction progresses, the temperature of the reforming catalyst decreases to be lower than the catalyst active temperature, and thus the steam reforming reaction may be inhibited. 
     For this reason, at the time of the low temperature of the reforming catalyst, the fuel reformer described in Patent Document 1 below increases the temperature of the reforming catalyst beforehand prior to the steam reforming reaction. Specifically, an exothermic reaction between fuel and oxygen is initiated by supplying oxygen to the reforming catalyst. The temperature of the reforming catalyst increases by this reaction, so that the steam reforming reaction can be subsequently produced. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: JP2013-133253A 
       
    
     Nevertheless, because the fuel reformer is for recovering and reusing the heat energy included in exhaust gas thereby to restrain the fuel consumption amount, the consumption of a part of fuel to increase the temperature of the reforming catalyst is undesirable. To effectively use the energy, it is desirable to consume all the fuel injected in the fuel reformer for the steam reforming reaction. 
     SUMMARY OF INVENTION 
     The present disclosure addresses the above issues. Thus, it is an objective of the present disclosure to provide a fuel reformer that can efficiently achieve energy recovery by a steam reforming reaction without consuming a part of fuel for an exothermic reaction. 
     To achieve the objective, a fuel reformer in an aspect of the present disclosure produces a steam reforming reaction between fuel and water on a reforming catalyst, and includes a fuel injection part that injects and supplies fuel into the reforming catalyst, and an injection control part that controls an injection amount of fuel by the fuel injection part. The injection control part controls the injection amount in order that a temperature of the reforming catalyst is not lower than a preset given temperature. 
     In the fuel reformer having such a configuration, the fuel injection amount is controlled appropriately by the injection control part in order that the temperature of the reforming catalyst is not lower than a preset given temperature. For example, setting a catalyst active temperature of the reforming catalyst as this given temperature can constantly produce the steam reforming reaction in the reforming catalyst with high efficiency. 
     Thus, in the fuel reformer in this aspect, it is not that the temperature of the reforming catalyst is increased beforehand, and then the steam reforming reaction is caused. Instead, only such an amount of fuel that the temperature decrease amount of the reforming catalyst is negligible is injected into the reforming catalyst. Since a part of the injected fuel is not consumed for an exothermic reaction, the energy recovery by the steam reforming reaction is efficiently achieved. 
     This aspect provides the fuel reformer that can efficiently achieve the energy recovery by the steam reforming reaction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a diagram schematically illustrating a configuration of a fuel reformer in accordance with an embodiment; 
         FIG. 2  is a flow chart showing a flow of processing performed by a control part of the fuel reformer illustrated in  FIG. 1 ; 
         FIG. 3  is a graph showing a temperature change of a reforming catalyst according to the embodiment; and 
         FIG. 4  is a diagram showing a modification to the fuel reformer illustrated in  FIG. 1 . 
     
    
    
     EMBODIMENT FOR CARRYING OUT INVENTION 
     An embodiment will be described below with reference to the accompanying drawings. To facilitate the understanding of explanation, the same reference numeral is given as far as possible to the same component in each drawing to omit repeated explanations. 
     A fuel reformer  100  of the embodiment will be described with reference to  FIG. 1 . The fuel reformer  100  is attached to a part of a vehicle GC including an internal-combustion engine  10 , and is a device for recovering and reusing the heat of exhaust gas discharged from the internal-combustion engine  10 . 
     First, the configuration of the vehicle GC will be explained. The vehicle GC includes the internal-combustion engine  10 , an intake pipe  20 , an exhaust pipe  30 , and an EGR pipe  40 . 
     The internal-combustion engine  10  is a four-cycle reciprocating engine having cylinders, for generating driving force by combusting liquid fuel in the cylinders. The configuration of each cylinder is generally the same, and only a single cylinder is thus illustrated in  FIG. 1  as the “internal-combustion engine  10 .” 
     Various sensors such as a coolant temperature sensor  11 , a knock sensor  12 , and a crank angle sensor  13  are attached to each cylinder of the internal-combustion engine  10 . The coolant temperature sensor  11  is a temperature sensor for measuring the temperature of coolant circulating between a radiator (not shown) and the internal-combustion engine  10 . The knock sensor  12  is a sensor for detecting a knocking (abnormal combustion) caused in the cylinder of the internal-combustion engine  10 . The crank angle sensor  13  is a sensor for measuring a rotation angle of a crankshaft of the cylinders. The measurement values obtained by these sensors are inputted into an ECU (not shown) that controls the entire vehicle GC. 
     The intake pipe  20  is a pipe for supplying air into the internal-combustion engine  10 . An air cleaner  21 , an air flow meter  22 , a throttle valve  23 , a surge tank  25 , and a first injector  27  are provided for the intake pipe  20  in this order from the upstream side (left side in  FIG. 1 ). The internal-combustion engine  10  is connected to the downstream end part (right side in  FIG. 1 ) of the intake pipe  20 . 
     The air cleaner  21  is a filter for removing foreign substances from the air, which is introduced from the outside of the vehicle GC. The air flow meter  22  is a flow meter for measuring a flow rate of air supplied into the internal-combustion engine  10  through the intake pipe  20 . The flow rate measured by the air flow meter  22  is inputted into the ECU of the vehicle GC. 
     The throttle valve  23  is a flow regulation valve for regulating the flow rate of air through the intake pipe  20 . In accordance with the operation amount of an accelerator pedal (not shown) of the vehicle GC, the opening degree of the throttle valve  23  is adjusted thereby to regulate the flow rate of air. The throttle valve  23  includes an opening degree sensor  24 . The opening degree of the throttle valve  23  is measured by the opening degree sensor  24  and is inputted into the ECU of the vehicle GC. 
     The surge tank  25  is a box-shaped container that is formed at the intake pipe  20 . The intake pipe  20  is divided into more than one branch on a downstream side of the surge tank  25 . Each branched flow passage is connected to a corresponding cylinder. The internal space of the surge tank  25  is larger than the internal space of the other part of the intake pipe  20 . The surge tank  25  prevents an influence of a pressure change by one cylinder on the other cylinders. The surge tank  25  includes a pressure sensor  26 . The pressure in the intake pipe  20  is measured by the pressure sensor  26  and is inputted into the ECU of the vehicle GC. 
     The first injector  27  is an electromagnetic valve for injecting fuel into the intake pipe  20 . The fuel pressurized by a fuel pump (not shown) is supplied to the first injector  27 . When the first injector  27  is put into an open state, the fuel injected through the end of the injector  27  is mixed with air and supplied into the cylinder of the internal-combustion engine  10 . The ECU of the vehicle GC controls the opening and closing operations of the first injector  27  to adjust the amount of fuel supplied to the internal-combustion engine  10 . 
     The exhaust pipe  30  is a pipe for discharging exhaust gas, which is produced in the cylinder of the internal-combustion engine  10 , to the outside. The upstream end part (left side in  FIG. 1 ) of the exhaust pipe  30  is connected to the internal-combustion engine  10 . A catalytic converter  31  for purifying exhaust gas is provided at the exhaust pipe  30  (downstream side of the internal-combustion engine  10 ). 
     An air-fuel ratio sensor  32  is provided at the part of the exhaust pipe  30  on an upstream side of the catalytic converter  31 , and an oxygen sensor  33  is provided at the part of the exhaust pipe  30  on a downstream side of the catalytic converter  31 . These are all sensors for monitoring the oxygen concentration of exhaust gas passing through the exhaust pipe  30 , and their measurement results are inputted into the ECU of the vehicle GC. Based on the measurement results by the air-fuel ratio sensor  32  and so forth, the ECU controls, for example, the amount of fuel injected by the first injector  27  so that the combustion in the internal-combustion engine  10  is carried out at a theoretical air-fuel ratio. 
     The EGR pipe  40  is a pipe for returning a part of exhaust gas passing through the exhaust pipe  30  into the intake pipe  20  to supply the gas to the internal-combustion engine  10  again (for performing “exhaust gas recirculation”). The upstream end part of the EGR pipe  40  is connected to the position of the exhaust pipe  30  between the internal-combustion engine  10  and the catalytic converter  31 . The downstream end part of the EGR pipe  40  is connected to the position of the intake pipe  20  between the throttle valve  23  and the surge tank  25 . 
     An EGR cooler  42  and an EGR valve  43  are provided at the EGR pipe  40  in this order from the upstream side. A reforming unit part  110 , which is a part of the fuel reformer  100 , is provided at the part of the EGR pipe  40  on an upstream side of the EGR valve  43 . The reforming unit part  110  will be described later. 
     The EGR cooler  42  is a cooler for cooling high-temperature exhaust gas to reduce its temperature beforehand, and then for supplying the gas to the intake pipe  20 . The EGR valve  43  is a flow regulation valve for regulating the flow rate of exhaust gas passing through the EGR pipe  40 . The ECU of the vehicle GC regulates the opening degree of the EGR valve  43  to adjust a rate of the exhaust gas flowing into the EGR pipe  40  to the exhaust gas passing through the exhaust pipe  30 , i.e., an EGR rate. 
     The specific configuration of the vehicle GC is not limited to the above, and the fuel reformer of the present disclosure can be disposed in a variously-configured vehicle. For example, the connecting position of the EGR pipe  40  at the exhaust pipe  30  may be on a downstream side of the catalytic converter  31 . The vehicle GC may include a supercharging device. 
     The configuration of the fuel reformer  100  will be described. The fuel reformer  100  includes the reforming unit part  110  and a control part  120 . The reforming unit part  110  is provided at the part of the EGR pipe  40  on an upstream side of the EGR cooler  42  (exhaust pipe  30 -side). The reforming unit part  110  includes therein a space leading to the EGR pipe  40 , and is configured such that this space is filled with a reforming catalyst  111 . 
     The reforming catalyst  111  is a “monolithic” catalyst that is formed from alumina. Grid-like flow passages are formed along the passage direction of the EGR pipe  40  at the reforming catalyst  111 , and a catalyst material is supported on the inner wall surface of each flow passage. 
     A temperature sensor  113  for measuring a temperature of the reforming catalyst  111  is provided at the reforming unit part  110 . The temperature of the reforming catalyst  111  is measured by the temperature sensor  113 , and is inputted into the control part  120 . 
     A second injector  112  is provided at the part of the reforming unit part  110  on an upstream side of the reforming catalyst  111 . The second injector  112  is an electromagnetic valve configured similar to the first injector  27 , which is provided for the internal-combustion engine  10 , and can inject fuel (ethanol) into the space on an upstream side of the reforming catalyst  111 . The opening/closing operation of the second injector  112 , i.e., the fuel injection, is controlled by the control part  120 , which will be described later. 
     The injection of fuel from the second injector  112  is carried out when EGR control is performed by the ECU of the vehicle GC, i.e., when the EGR valve  43  is in an open state and exhaust gas passes through the EGR pipe  40 . When fuel is injected by the second injector  112 , the water contained in exhaust gas and the fuel are supplied into the reforming catalyst  111  in a mixed state in the reforming unit part  110 . 
     The reforming catalyst  111  is heated by the exhaust gas passing through the reforming unit part  110  to have high temperature. When the water and fuel (hydrocarbon) come into contact with the high-temperature reforming catalyst  111 , a steam reforming reaction is triggered between these to produce hydrogen and carbon monoxide. 
     The exhaust gas becomes hydrogen-containing gas by passing through the reforming unit part  110 , and is supplied into the intake pipe  20 . After that, the hydrogen-containing gas (exhaust gas) is supplied into the cylinder of the internal-combustion engine  10  for combustion again. 
     As is well-recognized, the steam reforming reaction produced in the reforming unit part  110  is an endothermic reaction, so that the exhaust gas is cooled to become the hydrogen-containing gas with its temperature lowered. Thus, the heat energy of exhaust gas is recovered by the steam reforming reaction in the reforming unit part  110 , and is converted into chemical energy of hydrogen. The fuel reformer  100  recovers the heat energy of exhaust gas and converts it into the chemical energy, and then uses this chemical energy again in the internal-combustion engine  10  to improve the energy use efficiency of fuel. Such a fuel reformer  100  can improve the fuel efficiency of the vehicle GC. 
     The control part  120  is a computer system including a CPU, a ROM, a RAM, and an input/output interface. The control part  120  includes a temperature obtaining part  121 , a target value calculation part  122 , and an injection control part  123  as functional control blocks. 
     The temperature obtaining part  121  is a part into which the signal from the temperature sensor  113  is inputted. Based on the signal inputted from the temperature sensor  113 , the temperature obtaining part  121  obtains the temperature of the reforming catalyst  111 . 
     The target value calculation part  122  is a part that calculates the target injection amount, which is a target value of the amount of fuel injected by the second injector  112  (hereinafter also referred to simply as an “injection amount”). The specific method of calculating the target injection amount will be described later. 
     The injection control part  123  is a part that controls the opening and closing operations of the second injector  112  by supplying a driving current to the second injector  112 . The injection control part  123  controls the opening and closing operations of the second injector  112  so that the injection amount of the second injector  112  reaches the target injection amount calculated by the target value calculation part  122 . 
     As described above, the signal from the temperature sensor  113  is inputted into the control part  120 , and furthermore, a variety of information is inputted into the control part  120  through communication with the ECU (not shown) of the vehicle GC. For example, the opening degree of the EGR valve  43  or information such as operating conditions (e.g., the rotation speed or the load magnitude of the internal-combustion engine  10 ) of the vehicle GC is inputted into the control part  120  from the ECU of the vehicle GC. 
     The steam reforming reaction has weak reactivity at a low temperature, and is actively produced approximately at a temperature (catalyst active temperature) at which the reforming catalyst  111  is activated or at a temperature higher than this temperature. Thus, the injection of fuel from the second injector  112  is not performed constantly during the EGR control, but is performed only when it is confirmed by the temperature sensor  113  that the reforming catalyst  111  has reached a high temperature. When fuel is injected by the second injector  112 , the temperature of the reforming catalyst  111  decreases under the influence of the endothermic reaction. The control part  120  controls the opening and closing operations of the second injector  112  in order that the temperature of the reforming catalyst  111  is not lower than the catalyst active temperature due to the fuel injection. 
     The specific content of processing performed by the control part  120  will be described with reference to the flow chart in  FIG. 2 . A series of processing illustrated in  FIG. 2  is carried out repeatedly with a predetermined period. 
     At the first step S 01 , it is determined whether the EGR control is performed in the vehicle GC. If the EGR control is performed, i.e., if the EGR valve  43  is in an open state and exhaust gas passes through the EGR pipe  40 , control proceeds to S 02 . If the EGR control is not performed, i.e., if the EGR valve  43  is in a closed state, the series of processing illustrated in  FIG. 2  is ended. 
     At S 02 , it is determined whether the temperature of the reforming catalyst  111  measured by the temperature sensor  113  is higher than a preset lower limit temperature. The lower limit temperature is preset as the temperature that should be ensured at the minimum to sufficiently produce the steam reforming at the reforming catalyst  111  while the fuel reformer  100  is in operation. In the present embodiment, the value (e.g., 500° C.) that is equal to the catalyst active temperature is set as the lower limit temperature. 
     If the temperature of the reforming catalyst  111  is higher than the lower limit temperature, control proceeds to S 03 . If the temperature of the reforming catalyst  111  is equal to or lower than the lower limit temperature, this means that the temperature of the reforming catalyst  111  becomes lower than the lower limit temperature due to the fuel injection, and thus control ends the series of processing illustrated in  FIG. 2 . 
     At S 03 , the target injection amount is calculated by the target value calculation part  122 . The target injection amount is calculated, such that a temperature decrease amount of the reforming catalyst  111  when the fuel injection is carried out does not exceed the temperature difference obtained by subtracting the lower limit temperature from the temperature of the reforming catalyst  111  at the present time (which can also be called a temperature decrease amount permitted in the reforming catalyst  111  and hereinafter also referred to as a “permissible temperature decrease amount”). 
       FIG. 3  illustrates an example of the temperature change of the reforming catalyst  111  when fuel is injected by the second injector  112 . An initial temperature T S  of the reforming catalyst  111  at the time before fuel is injected starts to decrease from the time t 0  that fuel is injected, to eventually reach a generally constant value. If a temperature decrease amount in this case is too great, the temperature of the reforming catalyst  111  becomes lower than the lower limit temperature (hereinafter also written as “lower limit temperature T L ”). 
     The temperature decrease amount becomes larger as the injection amount becomes larger, and becomes smaller as the injection amount becomes smaller. The relationship between the temperature decrease amount and the injection amount is obtained beforehand through experiment or the like, and is stored as a map in a storage device (not shown) of the control part  120 . At S 03 , the target injection amount is calculated based on this map and the permissible temperature decrease amount. 
     In the present embodiment, the target injection amount is calculated so that the temperature decrease amount due to the injection corresponds to a difference ΔT between the initial temperature T S  and the lower limit temperature T L  (i.e., permissible temperature decrease amount). In other words, the target injection amount is calculated, such that the temperature of the reforming catalyst  111  after the fuel injection is carried out is not lower than the lower limit temperature T L  and generally corresponds to the lower limit temperature T L . 
     The relationship between the temperature decrease amount and the injection amount is not constantly the same, and varies according to, for example, the initial temperature T S  of the reforming catalyst  111 , a speed at which exhaust gas and fuel pass through the reforming catalyst  111 , the EGR rate, the operating conditions of the vehicle GC, and the kind of fuel injected from the second injector  112 . Thus, more than one map indicating the relationship between the temperature decrease amount and the injection amount may preferably be provided in view of these factors (or as a multidimensional map). At S 03 , an appropriate map is selected based on the information on the above factor (e.g., flow speed of exhaust gas or the like passing through the EGR pipe  40 ) obtained from the ECU of the vehicle GC, and the target injection amount is calculated more accurately based on this map and the permissible temperature decrease amount. 
     At the step S 04 , which follows the step S 03 , it is determined whether the calculated target injection amount exceeds an upper limit value. The upper limit value is a value that is calculated beforehand by the control part  120  as such an injection amount that the temperature decrease amount of the reforming catalyst  111  is maximized. The upper limit value may also be such an injection amount that the steam reforming reaction caused in the reforming catalyst  111  is saturated (injection amount that maximizes a reforming effect). 
     The upper limit value is not always constant, and varies according to, for example, the initial temperature T S  of the reforming catalyst  111 , the EGR rate, and the operating conditions of the vehicle GC. The relationship between the initial temperature T S  and so forth, and the upper limit value is stored beforehand as a map in the storage device of the control part  120 . When the determination at S 04  is made, the upper limit value is calculated each time by reference to this map beforehand. 
     If the target injection amount exceeds the upper limit value at S 04 , control proceeds to S 05 . If the target injection amount is equal to or smaller than the upper limit value, control proceeds to S 06 . 
     The target injection amount is corrected at S 05 . Specifically, the value of the target injection amount is rewritten into the same value as the upper limit value. 
     At the step S 06 , which follows the step S 04  or the step S 05 , the injection of fuel from the second injector  112  is performed by the injection control part  123 . The injection amount in this case accords with the target injection amount calculated at S 03  (or rewritten at S 05 ). Consequently, the final temperature of the reforming catalyst  111  generally corresponds to the lower limit temperature T L  as in the example of  FIG. 3 . 
     As described above, the fuel reformer  100  of the present embodiment controls the amount of fuel injected by the second injector  112  so that the temperature of the reforming catalyst  111  is not lower than the preset lower limit temperature T L  (given temperature). Specifically, the target injection amount (target value) is calculated, such that the temperature of the reforming catalyst  111  after the fuel injection is carried out is equal to or higher than the lower limit temperature T L  (e.g., such that the temperature corresponds to the lower limit temperature T L ). The operation of the second injector  112  is controlled such that its injection amount coincides with the target injection amount. 
     The temperature of the reforming catalyst  111  decreases due to the fuel injection, but this temperature is not lower than the lower limit temperature T L  and generally accords with the lower limit temperature T L . Thus, in the present embodiment, as much fuel as possible is injected in a range in which the reforming catalyst  111  can fulfill its function, and the recovery of heat energy from exhaust gas is thereby made. Since a part of the injected fuel is not consumed for an exothermic reaction, the energy recovery by the steam reforming reaction is efficiently achieved. 
     In the present embodiment, the temperature of the reforming catalyst  111  is measured directly by the temperature sensor  113 , which is provided at the reforming unit part  110 . Instead of such an aspect, an aspect, in which the temperature of the reforming catalyst  111  is calculated by the control part  120  without providing the temperature sensor  113 , may be applicable. For example, the relationship between the operating condition of the vehicle GC and the exhaust gas temperature is stored beforehand as a map. Consequently, the temperature of the reforming catalyst  111  can be calculated (estimated) by reference to the current operating condition and this map. 
     In the present embodiment, the same value as the catalyst active temperature of the reforming catalyst  111  is set as the target value (lower limit temperature T L ) of the temperature of the reforming catalyst  111  after fuel is injected. However, when implementing the present disclosure, another value (e.g., value slightly lower than the catalyst active temperature) may be set as the lower limit temperature T L . 
     The control part  120  may be provided as a separate device from the ECU of the vehicle GC as in the present embodiment, but may be provided integrally with the ECU of the vehicle GC. Thus, the ECU of the vehicle GC may be configured to also serve as the function of the control part  120 . 
     Modifications to the present embodiment will be described with reference to  FIG. 4 . The configuration of a vehicle GCa illustrated in  FIG. 4  is different only in position and structure of the reforming unit part  110  from the configuration of the vehicle GC. 
     In this modification, the reforming unit part  110  is provided at the part of the exhaust pipe  30  on a downstream side of the catalytic converter  31 . The reforming catalyst  111  in the reforming unit part  110  is configured to be heated by the exhaust gas passing through the EGR pipe  40 , and also to be heated by the exhaust gas passing through the exhaust pipe  30 . Thus, the reforming unit part  110  is configured as a part of the heat exchanger to which both the EGR pipe  40  and the exhaust pipe  30  are connected. Such a configuration can also maintain the temperature of the reforming catalyst  111  at a high temperature by the exhaust gas passing through the exhaust pipe  30 . As a consequence, even though a relatively great amount of fuel is injected from the second injector  112 , the temperature of the reforming catalyst  111  can be maintained to be equal to or higher than the lower limit temperature T L . 
     However, in such a configuration, the reforming unit part  110  grows in size and much of the limited space in the vehicle GC is taken by the reforming unit part  110 . 
     In contrast, the fuel reformer  100  configured as illustrated in  FIG. 1  has a structure whereby the reforming catalyst  111  is heated only by the exhaust gas passing through the EGR pipe  40  (flow passage in which the reforming catalyst  111  is disposed), thereby enabling the downsizing of the reforming unit part  110 . 
     The heating amount for the reforming catalyst  111  is smaller than in the modification illustrated in  FIG. 4 , but the temperature of the reforming catalyst  111  does not excessively decrease due to the fuel injection. Thus, the configuration of  FIG. 1  that can further downsize the reforming unit part  110  has greater advantages, and may be a more desirable configuration. 
     The embodiment has been described above with reference to the specific examples. However, the present disclosure is not limited to these specific examples. Thus, those obtained by making appropriate design changes to these specific examples by a person skilled in the art are also included in the scope of the present disclosure as long as they have the characteristics of the present disclosure. For example, the components of each of the above-described specific examples, and their arrangement, materials, conditions, shapes, and sizes are not limited to those illustrated, and can be modified appropriately. In addition, the components of each of the above-described embodiments can be combined as long as technically possible, and the combination of these is also included in the scope of the present disclosure as long as it has the characteristics of the present disclosure. 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.