Abstract:
A disclosed microwave heating apparatus includes a casing part configured to accommodate an object to be heated; a microwave generator configured to generate a microwave; an electromagnetic wave generator configured to generate an electromagnetic wave whose frequency is different from that of the microwave; an electromagnetic wave sensor configured to measure power of the electromagnetic wave, the power of the electromagnetic wave being measured after the electromagnetic wave incident on the casing part from the electromagnetic wave generator has passed through the object to be heated; and a controller configured to control, based on the power measured in the electromagnetic wave sensor, the microwave generator to generate the microwave.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This present application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-079489, filed on Apr. 12, 2016, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The present disclosure is related to a microwave heating apparatus and an exhaust gas purification apparatus. 
       BACKGROUND 
       [0003]    At present, an exhaust gas purification apparatus using DPF (Diesel Particulate Filter) has been put to practical use as an apparatus for collecting fine particles such as PM (Particulate matter) contained in exhaust gas. In such an exhaust gas purification apparatus, the fine particles such as PM, etc., are deposited on the DPF by use, and thus it is required to regenerate the DPF. As a method for regenerating the DPF, for example, a method of using a high frequency electromagnetic wave such as a microwave, etc., emitted from a microwave heating apparatus is disclosed (for example, Patent Document 1). Specifically, according to the disclosed method, the DPF is regenerated by irradiating the DPF with an electromagnetic wave such as a microwave, etc., to heat fine particles such as PM, etc., accumulated in the DPF and burn the fine particles. 
         [0004]    [Patent Document 1] Japanese Laid-open Patent Publication No. 2006-140063 
         [0005]    [Patent Document 2] Japanese Laid-open Patent Publication No. 2011-252387 
         [0006]    [Patent Document 3] Japanese Laid-open Patent Publication No. 10-220219 
         [0007]    [Patent Document 4] Japanese Laid-open Patent Publication No. 9-112249 
         [0008]    In the exhaust gas purification apparatus described above, the regeneration of the DPF is carried out, after the fine particulates such as PM, etc., have been accumulated in the DPF to some extent, by irradiating the DPF with electromagnetic waves such as microwaves, etc., which causes the fine particulates such as PM, etc., to be heated and oxidized and decomposed. However, since the DPF is covered by a casing, it is unknown from the outside whether or not fine particles such as PM, etc., have been accumulated in the DPF. 
         [0009]    For this reason, for example, a method of judging a regeneration timing of the DPF and performing the regeneration using a regeneration timing judgment map for estimating the regeneration timing based on a relationship between intensity of the microwave detected by a microwave sensor and an operation time of an internal combustion engine (For example, Patent Document 3). However, according to the method disclosed in Patent Document 3, since the regeneration timing of the DPF is estimated from the intensity of the microwave and the operation time of the internal combustion engine, the regeneration timing may not be correctly detected in some cases. If the regeneration timing of the DPF is not correctly detected, such problems that the microwave is radiated at an unnecessary timing, the DPF is not regenerated even after the fine particulates such as PM, etc., have been accumulated in the DPF, etc., occur. Further, according to the method disclosed in Patent Document 3, it is necessary to prepare the regeneration timing judgment map and the like, and it is necessary to memorize the regeneration timing judgment map and the like. Furthermore, according to the method disclosed in Patent Document 3, the control circuit for judging the regeneration timing also becomes complicated, and it takes time to implement the judgment, which leads to cost increase. 
       SUMMARY 
       [0010]    According to one aspect of the disclosure, a microwave heating apparatus is provided, which includes: 
         [0011]    a casing part configured to accommodate an object to be heated; 
         [0012]    a microwave generator configured to generate a microwave; 
         [0013]    an electromagnetic wave generator configured to generate an electromagnetic wave whose frequency is different from that of the microwave; 
         [0014]    an electromagnetic wave sensor configured to measure power of the electromagnetic wave, the power of the electromagnetic wave being measured after the electromagnetic wave incident on the casing part from the electromagnetic wave generator has passed through the object to be heated; and 
         [0015]    a controller configured to control, based on the power measured in the electromagnetic wave sensor, the microwave generator to generate the microwave. 
         [0016]    The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]      FIG. 1  is a diagram illustrating a structure of a microwave heating apparatus and an exhaust gas purification apparatus according to a first embodiment. 
           [0018]      FIG. 2  is a diagram illustrating a structure of a semiconductor device used for a microwave generator. 
           [0019]      FIG. 3  is a flowchart of a control way of the exhaust gas purification apparatus according to the first embodiment. 
           [0020]      FIG. 4  is a diagram illustrating a structure of a microwave heating apparatus and an exhaust gas purification apparatus according to a second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    In the following, embodiments are described in detail with reference to appended drawings. It is noted that the same elements, etc., are given the same reference numbers, and an explanation thereof is emitted. 
       First Embodiment 
       [0022]    [Microwave Heating Apparatus and Exhaust Gas Purification Apparatus] 
         [0023]    A microwave heating apparatus and an exhaust gas purification apparatus according to a first embodiment are explained with reference to  FIG. 1 . It is noted that the microwave heating apparatus according to the present embodiment is mounted on the exhaust gas purification apparatus according to the present embodiment. 
         [0024]    The exhaust purification device according to the embodiment includes a fine particulate collection unit  10 , an oxidation catalyst unit  11 , a casing part  20 , a microwave generator  30 , an electromagnetic wave generator  41 , a microwave sensor  50 , a first electromagnetic wave sensor  51 , a second electromagnetic wave sensor  52 , a temperature measurement part  70 , a control part  80 , etc. 
         [0025]    The fine particulate collection unit  10  serves as an object to be heated by the microwave heating apparatus in the present embodiment, and is formed of a DPF or the like. For example, the DPF is formed in a honeycomb structure in which adjacent vent holes are alternately closed, and the exhaust gas is discharged from the vent holes different from the vent holes for the inlet. The oxidation catalyst unit  11  is formed of an oxidation catalyst such as DOC (Diesel Oxidation Catalyst), etc. 
         [0026]    The casing part  20  is formed of a metal material such as stainless steel and includes a casing body part  20   a  covering the periphery of the fine particulate collection unit  10  and the oxidation catalyst unit  11 , an inlet port  20   b  and an outlet port  20   c  coupled to the casing body part  20   a.  In the exhaust gas purification apparatus according to the present embodiment, the exhaust for exhaust gas etc., from an engine etc., enters into the casing part  20  from the inlet port  20   b  from the direction indicated by the broken line arrow A, and passes through the oxidation catalyst unit  11  and fine particulate collection unit  10  provided in the casing body part  20   a  to be purified. Thereafter, the exhaust purified in the oxidation catalyst unit and the fine particulate collection unit  10  is discharged from the outlet port  20   c  in a direction indicated by a broken line arrow B. 
         [0027]    In the casing part  20 , the oxidation catalyst unit  11  and the fine particulate collection unit  10  are arranged in this order from the inlet port  20   b  toward the outlet port  20   c.  The oxidation catalyst unit  11  oxidizes the components contained in the exhaust gas entering through the inlet port  20   b.  For example, the oxidation catalyst unit  11  converts NO contained in the exhaust gas into NO 2  having stronger oxidizing power. In the fine particulate collection unit  10 , fine particles such as PM, etc., are collected. In removing the collected fine particles such as PM, etc., by burning, the NO 2  generated in the oxidation catalyst unit  11  is used. The fine particulates such as PM, etc., collected in the fine particulate collection unit  10  are soot or the like, and contain a large amount of C (carbon). When burning and removing the fine particulates such as PM, etc., collected in the fine particulate collection unit  10 , by flowing NO 2 , C and NO 2  chemically react to produce CO 2 . As a result, the fine particulates such as PM, etc., collected in the fine particulate collection unit  10  can be efficiently removed. 
         [0028]    The microwave generator  30  is coupled to the casing part  20 , and can generate microwaves of 2.45 GHz. In the microwave generator  30 , in order to generate high power microwaves necessary for burning and removing fine particulates such as PM, etc., collected in the fine particulate collection unit  10 , a semiconductor element formed of a nitride semiconductor is used. The microwave sensor  50  is provided between the casing part  20  and the microwave generator  30 , and measures power (Pin 0 ) of the incident wave incident on the casing part  20  from the microwave generator  30  and power (Pr 0 ) of the reflected wave returning from the casing part  20 . The power (P 0 ) that is actually output from the microwave generator  30  into the casing part  20  is calculated from P 0 =Pin 0 −Pr 0 . Further, a tuner is provided between the microwave generator  30  and the microwave sensor  50 . In the tuner  60 , by reducing the power (Pr 0 ) of the reflected wave, tuning is performed so as to increase the actually outputted power (P 0 ). 
         [0029]    The electromagnetic wave generator  41  is coupled to the casing part  20  and generates an electromagnetic wave having a different frequency from the microwave generated in the microwave generator  30 . Since the electromagnetic wave radiated from the electromagnetic wave generator  41  is for detecting the amount of the fine particulates such as PM, etc., collected in the fine particulate collection unit  10 , it is preferred that high frequency electromagnetic waves, which are easily absorbed by fine particulates such as PM, etc., are used. Specifically, the frequency of the electromagnetic wave radiated from the electromagnetic wave generator  41  is greater than or equal to 10 GHz and less than or equal to 10 THz. The first electromagnetic wave sensor  51  is provided between the casing part  20  and the electromagnetic wave generator  41 , and measures power (Pin 1 ) of the incident wave incident on the casing part  20  from the electromagnetic wave generator  41  and power (Pr 1 ) of the reflected wave returning from the casing part  20 . The power (P 1 ) that is actually output from the electromagnetic wave generator  41  into the casing part  20  is calculated from P 1 =Pin 1 −Pr 1 . Further, a tuner  61  is provided between the first electromagnetic wave sensor  51  and the electromagnetic wave generator  41 . In the tuner  61 , by reducing the power (Pr 1 ) of the reflected wave, tuning is performed so as to increase the actually outputted power (P 1 ). It is noted that, since the wavelength of the microwave of 2.45 GHz is about 12 cm and the wavelength is relatively long, the microwave may not be absorbed so much depending on the position where fine particles such as PM, etc., exist, and a correlation between the amount of fine particles such as PM, etc., and the amount of microwaves absorbed is not very high. However, the electromagnetic waves of high frequency with short wavelengths are absorbed without substantial dependence on positions where the fine particles such as PM, etc., exist, etc. Therefore, a correlation between the amount of fine particles such as PM, etc., and the amount of microwaves absorbed can be increased. 
         [0030]    The second electromagnetic wave sensor  52  is provided in the casing part  20  at a position where the second electromagnetic wave sensor  52  and the casing part  20  are opposed to each other with the fine particulate collection unit  10  interposed therebetween. The second electromagnetic wave sensor  52  measures power (P 2 ) of the electromagnetic wave component transmitted through the fine particulate collection unit  10 , among the electromagnetic wave components generated in the electromagnetic wave generator  41  and entering the casing part  20 . The electromagnetic waves that have entered the casing part  20  are absorbed by the fine particulates such as PM, etc., accumulated in the fine particulate collection unit  10 . Therefore, when the amount of particulates such as PM, etc., accumulated in the fine particulate collection unit is great, the amount of electromagnetic waves absorbed becomes great, and the power (P 2 ) of electromagnetic waves measured by the second electromagnetic wave sensor  52  becomes low. Further, when the amount of particulates such as PM, etc., accumulated in the fine particulate collection unit  10  is small, the amount of electromagnetic waves absorbed becomes small, and the power (P 2 ) of electromagnetic waves measured by the second electromagnetic wave sensor  52  becomes high. 
         [0031]    According to the present embodiment, based on the power (P 1 ) of the electromagnetic wave measured and calculated by the first electromagnetic wave sensor  51  and the power (P 2 ) of the electromagnetic wave measured by the second electromagnetic wave sensor  52 , it becomes possible to estimate an accumulated amount Mp of the fine particulates such as PM, etc., in the particulate collecting unit  10 . Specifically, from an equation shown in the following (1), it is possible to estimate the accumulated amount Mp of the fine particulates such as PM, etc., in the fine particulate collection unit  10 . It is noted that k and a are coefficients. 
         [0000]        Mp=k ×In ( P  1/( a×P  2))   (equation 1)
 
         [0032]    The temperature measurement part  70  is attached to the casing part  20  and measures a temperature of the fine particulate collection unit  10  in the casing part  20 . The temperature measurement part  70  may be a radiation thermometer or the like that is capable of measuring the temperature distribution in the fine particulate collection unit  10 . The control part  80  performs control of the exhaust gas purification apparatus according to the present embodiment. 
         [0033]    In the present embodiment, a semiconductor element, specifically, a HEMT using a nitride semiconductor, or the like, is used in the microwave generator  30  in order to generate high power microwaves. As illustrated in  FIG. 2 , the HEMT using the nitride semiconductor is formed by laminating a nitride semiconductor layer on a substrate  210  such as SiC, etc. That is, a buffer layer  211  formed of AlN, GaN or the like, an electron transit layer  212 , and an electron supply layer  213  are deposited in this order on the substrate  210 . The electron transit layer  212  is formed of GaN, and the electron supply layer  213  is formed of AlGaN or InAlN. As a result, in the electron transit layer  212 , a 2DEG  212   a  is generated in the vicinity of the interface with the electron supply layer  213 . A gate electrode  231 , a source electrode  232 , and a drain electrode  233  are formed on the electron supply layer  213 . 
         [0034]    [Control of Microwave Heating Apparatus and Exhaust Purification Apparatus] 
         [0035]    Next, control of the microwave heating apparatus and the exhaust purification apparatus according to the present embodiment is explained with reference to  FIG. 3 . It is noted that the control of the microwave heating apparatus and the exhaust gas purification apparatus in the present embodiment is performed by the control part  80 . 
         [0036]    At first, in step  102  (S 102 ), the power of the microwave generated in the microwave generator  30  is set to zero. Specifically, the power (Pin  0 ) of the incident wave incident on the casing part  20  from the microwave generator  30  is set to zero. When the power (Pin 0 ) of the incident wave incident on the casing part  20  from the microwave generator  30  is already 0, the current state is kept. 
         [0037]    Next, in step  104  (S 104 ), the electromagnetic wave generator  41  generates the electromagnetic wave and sets the power (P 1 ) actually output from the electromagnetic wave generator  41  into the casing part  20  to a predetermined power (Pex 1 ). 
         [0038]    Next, in step  106  (S 106 ), the temperature measurement part  70  measures the temperature T of the fine particulate collection unit  10 , and it is determined whether the temperature T measured by the temperature measurement part  70  is in a temperature range greater than or equal to a temperature Ta and less than or equal to a temperature Tb. When the temperature T is within the temperature range greater than or equal to the temperature Ta and less than or equal to the temperature Tb, the process proceeds to step  108 . When the temperature T is not within the temperature range greater than or equal to the temperature Ta and less than or equal to the temperature Tb, step  106  is repeated. In the case where the temperature T of the fine particulate collection unit  10  is less than the temperature Ta, the temperature does not become a desired temperature even if the fine particulate collection unit  10  is irradiated with the microwaves, and thus the fine particulate collection unit  10  cannot be regenerated. When the temperature T of the fine particulate collection unit  10  is greater than the temperature Tb, the fine particulate collection unit  10  is regenerated without irradiating the microwave. For this reason, it is determined whether the temperature T of the fine particulate collection unit  10  is within the temperature range of not less than the temperature Ta and not more than the temperature Tb. 
         [0039]    Next, in step  108  (S 108 ), it is determined whether the accumulation amount Mp of the fine particulates such as PM, etc., in the fine particulate collection unit  10  exceeds a predetermined accumulation amount Ma. This is because it is unnecessary to perform the regeneration of the fine particulate collection unit when the accumulation amount Mp of the fine particulates such as PM, etc., in the fine particulate collection unit  10  does not exceed the predetermined accumulation amount Ma. When the accumulation amount Mp of the fine particulates such as PM, etc., in the fine particulate collection unit  10  exceeds the predetermined accumulation amount Ma, the process proceeds to step  110 , and if the accumulation amount Mp is less than the predetermined accumulation amount Ma, the process proceeds to step  106 . The accumulation amount Mp of the fine particulates such as PM, etc., in the fine particulate collection unit  10  is measured by measuring the electromagnetic wave generated in the electromagnetic wave generator  41  with the first electromagnetic wave sensor  51  and the second electromagnetic wave sensor  52 , and applying the obtained power P 1  and P 2  to the above-mentioned equation (1). 
         [0040]    Next, in step  110  (S 110 ), the microwave is generated in the microwave generation unit  30 , and the power (Pin 0 ) of the incident wave incident on the casing part  20  from the microwave generator  30  is set to a predetermined power (Pex 0 ). As a result, the regeneration of the fine particulate collection unit  10  is started. 
         [0041]    Next, in step  112  (S  112 ), it is determined whether or not the power (P 0 ) actually output from the microwave generator  30  into the casing part  20  is less than or equal to b×Pin 0 . It is noted that b is a coefficient. In the case where the power (P 0 ) actually output from the microwave generator  30  into the casing part  20  is equal to or less than b×Pin 0 , the proportion of the reflected wave (Pr 0 ) of the microwave is large, and thus the tuning to decrease Pr 0  in the tuner  60  is necessary. When the power (P 0 ) actually output from the microwave generator  30  to the casing part is equal to or less than b×Pin 0 , the process proceeds to step  114 . When the power (P 0 ) actually output from the microwave generator  30  to the casing part  20  exceeds b×Pin 0 , the process proceeds to step  106 . 
         [0042]    Next, in step  114  (S  114 ), the tuning to decrease Pr 0  is performed in the tuner  60 . After the tuning is performed in the tuner  60 , the process proceeds to step  106 . 
         [0043]    It is noted that, in the present embodiment, in the case where it is not necessary to consider the reflected wave of the electromagnetic wave generated in the electromagnetic wave generator or in the case where there is hardly any reflected wave, a single electromagnetic wave sensor corresponding to the second electromagnetic wave sensor  52  may be provided without providing the first electromagnetic wave sensor  51 . 
         [0044]    A case where the exhaust gas purification apparatus in the present embodiment was mounted in a diesel engine with a displacement of 3 L and traveled in an urban area for 8 hours was examined. In this case, according to the experience of the inventor, it is presumed that the accumulation amount of the fine particles such as PM, etc., in the fine particulate collection unit  10  can be reduced to ⅓ as compared with an exhaust gas purification apparatus that is not equipped with the microwave heating apparatus. In addition, the microwave heating apparatus according to the present embodiment can also be used in a food heating apparatus for heating foods, a chemical reaction apparatus, etc. 
       Second Embodiment 
       [0045]    Next, a second embodiment is described. According to the present embodiment, there are a microwave heating apparatus and an exhaust gas purification apparatus in which a plurality of electromagnetic wave generators are provided. The microwave heating apparatus and the exhaust purification apparatus according to the second embodiment are explained with reference to  FIG. 4 . 
         [0046]    As illustrated in  FIG. 4 , the exhaust gas purification apparatus according to the present embodiment includes a first electromagnetic wave generator  141 , a second electromagnetic wave generator  142 , a first electromagnetic wave sensor  151 , a second electromagnetic wave sensor  152 , etc. It is noted that, similar to the exhaust gas purification apparatus according to the first embodiment, the exhaust gas purification apparatus in the present embodiment includes the fine particulate collection unit  10 , the oxidation catalyst unit  11 , the casing part  20 , the microwave generator  30 , the microwave sensor  50 , the temperature measurement part  70 , the control part  80 , etc. 
         [0047]    The first electromagnetic wave generator  141  and the second electromagnetic wave generator  142  in the embodiment are the same as the electromagnetic wave generator  41  according to the first embodiment, and the frequency of the generated electromagnetic waves may be different or the same. Like the first electromagnetic wave sensor  51  and the second electromagnetic wave sensor  52  in the first embodiment, the first electromagnetic wave sensor  151  and the second electromagnetic wave sensor  152  are attached to the casing part  20  at positions where the first electromagnetic wave sensor  151  and the second electromagnetic wave sensor  152  are opposed to each other via the fine particulate collection unit  10 . 
         [0048]    A tuner  161  is provided between the first electromagnetic wave generator  141  and the first electromagnetic wave sensor  151 , and a tuner  162  is provided between the second electromagnetic wave generator  142  and the second electromagnetic wave sensor  152 . The tuner  161  and the tuner  162  have the same function as the tuner  61  in the first embodiment. Specifically, the tuner  161  performs the tuning such that the reflected wave of the electromagnetic wave generated in the first electromagnetic wave generator  141  becomes low, and the tuner  162  performs the tuning such that the reflected wave of the electromagnetic wave generated in the second electromagnetic wave generator  142  becomes low. 
         [0049]    In the present embodiment, the first electromagnetic wave sensor  151  measures the incident wave and the reflected wave of the electromagnetic wave generated in the first electromagnetic wave generator  141 , and measures the electromagnetic wave entering the casing part  20  from the second electromagnetic wave generator  142  and transmitted through the fine particulate collection unit  10 . Further, the second electromagnetic wave sensor  152  measures the incident wave and the reflected wave of the electromagnetic wave generated in the second electromagnetic wave generator  142 , and measures the electromagnetic wave entering the casing part  20  from the first electromagnetic wave generator  141  and transmitted through the fine particulate collection unit  10 . 
         [0050]    The control unit  80  calculates, based on the information obtained by the first electromagnetic wave sensor  151  and the second electromagnetic wave sensor  152 , the accumulation amount Mp of the fine particulates such as PM, etc., accumulated in the fine particulate collection unit  10 . In the present embodiment, by providing a plurality of electromagnetic wave generators, it is possible to more accurately calculate the accumulated amount Mp of the fine particulates such as PM, etc., accumulated in the fine particulate collection unit  10 . 
         [0051]    In the exhaust gas purification apparatus according to the present embodiment, the first and second electromagnetic wave sensors corresponding to the first electromagnetic wave generator  141  and the second electromagnetic wave generator  142  may be individually provided. Specifically, a first electromagnetic wave sensor and a second electromagnetic wave sensor corresponding to the first electromagnetic wave generator  141  and a first electromagnetic wave sensor and a second electromagnetic wave sensor corresponding to the second electromagnetic wave generator  142  may be provided. In this case, there are four electromagnetic wave sensors in total. 
         [0052]    In the present embodiment, when the electromagnetic wave generated in the first electromagnetic wave generator  141  and the electromagnetic wave generated in the second electromagnetic wave generator  142  are different from each other in the frequency, electromagnetic waves can be continuously generated. When the electromagnetic wave generated in the first electromagnetic wave generator  141  and the electromagnetic waves generated in the second electromagnetic wave generator  142  have the same frequency, the timings of generating the electromagnetic waves may be shifted to alternately generate the electromagnetic waves. 
         [0053]    It is noted that the contents other than the above are the same as those in the first embodiment. 
         [0054]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.