Patent Grant
8378273
This invention relates to a ceramic heater and a glow plug, and, more specifically, to a ceramic heater and a glow plug which have excellent quick heating performance, can reduce power consumption, and are also excellent in durability, all being realized at high levels. This invention realizes a ceramic heater and a glow plug which exhibit particularly excellent durability when the ceramic heater and the glow plug are increased in temperature within a shorter time than in the past (also called “super quick temperature raising”).
In order to assist startup or allow quick activation, diesel engines, various types of sensors, etc. employ a glow plug, a heater for a sensor, a heater for a fan, and the like. For example, in a diesel engine, air taken into a cylinder is compressed, and fuel is injected into the air whose temperature has increased as a result of adiabatic compression, whereby a resultant air fuel mixture spontaneously ignites and burns. However, in a case where such a diesel engine is started in winter or in a cold environment or a like case, since the temperatures of outside air, the engine, etc. are low, it is not easy to heat, only by means of compression, the air within the combustion chamber to a temperature required for spontaneous ignition. In order to overcome such a problem, a glow plug is used in such a diesel engine as means for igniting fuel.
A known heater which is used as a heater for a glow plug, a heater for a sensor, a heater for a fan, or the like has a structure in which a heating resistor element formed of, for example, an electrically conductive ceramic is embedded in an electrically insulative ceramic substrate. Specifically, Patent Document 1 discloses a ceramic-heater-type glow plug in which a resistor element formed of different types of electrically conductive ceramics which differ from each other in temperature coefficient of resistance is embedded in a substrate formed of an electrically insulative ceramic. As described above, Patent Document 1 proposes provision of a ceramic-heater-type glow plug which has quick heating performance and a self temperature controlling function, by means of combining resistor elements having different resistivities.
In the case of a glow plug, in order to realize quick heating performance and perform fine temperature control, a controller is used to control supply of electricity to the glow plug. However, at the time of startup, the voltage of a battery may drop in some cases, with a resultant failure to supply a sufficiently high voltage to the glow plug. In order to overcome such a drawback, a glow plug having low resistance may be used. However, in this case, since the resistance of the glow plug at room temperature is low, a large rush current flows when the supply of electricity is started. This problem can be solved through combined use of different materials having different resistances. Specifically, the resistor element may be configured such that only a front end side portion (heat-generating portion) of the resistor element is formed of a material having a relatively high resistivity, and a rear end side portion (including lead portions) of the resistor element is formed of a material having a relatively low resistivity. However, since this configuration increases cost, if possible, it is desirable to realize quick heating performance through sole use of a single material.
Patent Document 2 discloses a ceramic heater designed to reduce power consumption. The disclosed ceramic heater is characterized in that a heat-generating portion and lead portions of the ceramic heater are formed of the same electrically conductive ceramic, and the ratio of cross sectional area therebetween is determined to fall within a predetermined range. The document states that this configuration reduces power consumption. However, when the ratio of cross sectional area is increased, the surface temperature of a support member varies greatly among positions in its cross section. This problem can be mitigated by proper setting of the ratio of cross sectional area. However, when the temperature at the surface of the support member (substrate) is desired to be more uniform, the temperature of the interior (resistor element) of the support member must be increased excessively such that a portion on the surface of the support member which is low in temperature is heated to such a degree as to provide a satisfactory heating function of the ceramic heater. In such a case, energization durability (the durability of the ceramic heater as determined through a durability test in which the ceramic heater is energized repeatedly) may drop. That is, since a tradeoff relation exists between power consumption and energization durability, improving the power consumption and the energization durability simultaneously is actually difficult although its technical significance is large.
Incidentally, in the case of the ceramic heaters disclosed in Patent Documents 1 and 2, their heat-generating portions (a “first heating element 20” in Patent Document 1 and a “folded portion 3d” in Patent Document 2) assume a shape as shown in
Further, in recent years, a ceramic heater for glow plug has been demanded to have improved heating performance and durability and to further reduce power consumption. In particular, such a ceramic heater has been demanded to further reduce power consumption, while securing a sufficient amount of heat radiation in order to prevent deterioration in the startup performance of an engine. In addition, there has been increasing demand for a ceramic heater which has an excellent durability, can realize a temperature increasing performance such that the heater can reach 1000° C. within 1 sec upon supply of a small amount of power (also called “super quick temperature raising”) in order to contribute to new engine control, and can maintain such temperature increasing performance even when the power supply voltage drops to, for example, about 7 V.
Patent Document 1: Japanese Patent No. 3044632
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. 2006-24394
An object of this invention is to provide a ceramic heater and a glow plug which have excellent quick heating performance, can reduce power consumption, and are excellent in durability. In particular, an object of this invention is to provide a ceramic heater and a glow plug which have practical durability even when they are used for super quick temperature raising which imposes a large load on the ceramic heater and the glow plug.
A ceramic heater according to the present invention which solves the above-described problem comprises a substrate formed of an electrically insulative ceramic, and a resistor element buried in the substrate, wherein the resistor element includes a single heat-generating portion formed of an electrically conductive ceramic and folded into a U-like shape, and a pair of lead portions which are joined to opposite end portions of said heat-generating portion, the end portion facing rearward with respect to a direction of an axis XA, and which extend straight rearward with respect to the direction of the axis XA. A first structural feature of the ceramic heater resides in that
said resistor element includes intermediate portions located between said heat-generating portion and said lead portions;
when, on cross section S1 and S2 of said ceramic heater taken along a plane perpendicular to said axis XA at a front end side point P1 and a rear end side point P2, which are arbitrary two different points on said axis XA, imaginary circumscribed circles CG1 and CG2 are drawn such that the imaginary circumscribed circles CG1 and CG2 circumscribe and contain two cross sections HS1a and HS1b and two cross sections HS2a and HS2b, respectively, of said resistor element appearing on the cross section S1 and S2, respectively, diameter CL1 and CL2 of the circumscribed circles CG1 and CG2 satisfy a relation CL1<CL2; and
the total cross sectional area HS1S of the two cross sections HS1a and HS1b of said resistor element and the total cross sectional area HS2S of the two cross sections HS2a and HS2b of said resistor element satisfy a relation HS1S<HS2S.
A second structural feature of said ceramic heater having said first structural feature resides in that the cross sectional areas S1S and S2S of the cross sections S1 and S2 of said ceramic heater satisfy a relation S1S<S2S.
A third structural feature of said ceramic heater having said first or second structural feature resides in that
said ceramic heater is inserted into and held in a tubular member formed of metal such that a front end portion of said ceramic heater is exposed;
each of said intermediate portions has a portion having a thickness tXVex equal to or less than ⅔ a maximum thickness txXVmax of said resistor element; and
a portion of said resistor element whose thickness is 2 (tXVmax)/3 is exposed from said tubular member formed of metal.
A fourth structural feature of said ceramic heater having any one of said first through third structural features resides in that a relation θ2>θ1 and a relation L1>L2 are satisfied, where θ1 represents an angle formed between said axis XA and each of radially outer side outlines of said intermediate portions which outlines determine a width of said intermediate portions, L1 represents a length of said intermediate portions as measured along the direction of said axis XA, θ2 represents a largest angle among angles formed between said axis XA and radially outer side outlines of said intermediate portions which outlines determine a thickness of said intermediate portions, and L2 represents a length of the outlines of said intermediate portions forming the largest angle, as measured along the direction of said axis XA.
A fifth structural feature of said ceramic heater having any one of said second through fourth structural features resides in that an outline of said substrate in which the portions of said intermediate portions having the thickness tXVvex are buried is tapered off toward the front end thereof.
A sixth structural feature of said ceramic heater having any one of said second through fifth structural features resides in that said angle θ1 and an angle θ3 satisfy a relation |θ3−θ1|≦10°, where the angle θ3 represents an angle formed, in a XV direction view, between said axis XA and an outline of said substrate at a position along the direction of said axis XA where said intermediate portions are located.
A seventh structural feature of said ceramic heater having any one of said first through sixth structural features resides in that a maximum spacing GL between said pair of lead portions and a maximum spacing GM between said intermediate portions having the thickness tXVex satisfy a relation GL<GM.
A glow plug according to the present invention comprises a ceramic heater having the above-described structure.
Since the ceramic heater according to the present invention is formed such that its heat-generating portion has intermediate portions configured as described above, the heat-generating portion can have a reduced volume, has excellent quick heating performance, can reach a predetermined temperature through consumption of a small amount of electric power, and can avoid concentration of stresses or the like forces produced, for example, as a result of thermal expansion when a voltage is applied to the ceramic heater, whereby the ceramic heater exhibits enhanced energization durability and mechanical durability. Therefore, the present invention can provide a ceramic heater which has excellent quick heating performance, can reduce power consumption, and is excellent in durability. Further, since the glow plug according to the present invention includes a ceramic heater according to the present invention, the glow plug according to the present invention can realize quick heating performance, low power consumption, and durability at higher levels.
A ceramic heater which is one embodiment of the ceramic heater according to the present invention will be described with reference to the drawings.
The resistor element 30 includes a single heat-generating portion 33 having a U-shaped folded portion on the front end side with respect to the direction of the axis XA of the substrate 60, and a pair of lead portions 31, 31 connected to corresponding rear ends of the heat-generating portion 33 and extending in the axis XA direction. The pair of lead portions 31, 31 are located on opposite sides of the axis XA of the substrate 60, and extend, in generally parallel with each other, along the axis XA to a rear end surface 75 of the substrate 60, so that the lead portions 31, 31 are exposed on the rear end surface 75 of the substrate 60. As shown in
Next, the shape of the front end portion of the ceramic heater 12 will be described.
With reference to
The following effects are achieved because of presence of the intermediate portions 40, 40 in which the diameters of the imaginary circumscribed circle CG1 and CG2 satisfy a relation CL1<CL2 and the total cross sectional areas HS1S and HS2S of the cross sections (HS1a, HS1b), (HS2a, HS2b) of the resistor element 30 satisfy a relation HS1S<HS2S. That is, since the volumes of the intermediate portions 40, 40 and the heat-generating front end portion 50 decrease, stresses stemming from thermal expansion of the pair of lead portions 31, 31 produced upon application of voltage to the resistor element 30, stresses produced at the time of handling, and other stresses acting on the resistor element 30 are gradually absorbed by the pair of intermediate portions 40, 40, and concentration of these stresses on the heat-generating front end portion 50 can be avoided. Further, since the volume of the heat-generating front end portion 50 decreases, the heat-generating front end portion 50 has more excellent quick heating performance, can reach a predetermined temperature while consuming a slight amount of electric power, and can prevent fracture of the heat-generating front end portion 50, which fracture would otherwise occur due to the above-mentioned stresses. As a result, the resistor element 30; in particular, the heat-generating portion 33, has excellent quick heating performance, can reach a predetermined temperature while consuming a slight amount of electric power, and can have enhanced energization durability and mechanical durability. When electricity is supplied to the ceramic heater 12 so as to cause the ceramic heater 12 to generate heat, the temperature of the heater becomes the highest in a hottest heat-generating portion 55 at which the total cross sectional area of the resistor element 30 and the cross sectional area of the ceramic heater 12 (including the resistor element 30) in a cross section perpendicular to the axis XA direction become the smallest.
The boundaries of the intermediate portions 40, 40 will be described in detail. Since portions in which the cross sections at two different arbitrary points along the axis XA direction satisfy the above-described relations are the intermediate portions, points at which the cross sections fail to satisfy the above-described relations can be the boundaries of the intermediate portions 40, 40. This will be described specifically with reference to
A point Qa is a point along the axis XA direction in the heat-generating portion 33 (the front end portion) of the resistor element 30. A point Pa located rearward of this point Qa is a base point from which an outline 40g on the outer side of the resistor element 30 with respect to the radial direction (hereinafter, the radial direction may be referred to as the “XD direction) starts to expand toward the rear end. From comparison between the cross sectional shapes at these two points Qa and Pa, it is found that the imaginary circumscribed circle containing the pair of cross sections of the resistor element 30 at the point Qa and that at the point Pa have the same diameter. Further, the total cross sectional area of the pair of cross sections of the resistor element 30 at the point Qa and that at the point Pa are the same. Therefore, portions between the points Qa and Pa do not correspond to the intermediate portions (that is, the portions are parts of the heat-generating portion).
Next, the point Pa and a point P1 in
Meanwhile, the lead portions 31, which are approximately constant in cross sectional area, are formed to extend rearward from a point Pb. Therefore, when the point Pb and a point Qd are compared, no difference is found in their cross sectional shapes, etc., and the portions between the points Pb and Qd do not correspond to the intermediate portions. In a region between the point Pa and the point Pb, both the total cross sectional area of the resistor element 30 and the diameter of the imaginary circumscribed circle increase. Therefore, the portions between the points Pa and Pb correspond to the intermediate portions.
Incidentally, in the present invention, which has the above-described structure, preferably, the cross sectional areas S1S and S2S of the ceramic heater 12 at the arbitrary points P1 and P2 satisfy a relation S1S<S2S. That is, the outlines 40g of the intermediate portions 40, 40 narrow toward the front end along with the outline 60g of the substrate 60. Since this configuration reduces the volume of the substrate front end portion, the heat generated by the heat-generating front end portion 50 can be efficiently transmitted to the outer circumferential surface of the substrate 60. Therefore, it is possible to further improve quick heating performance, further reduce power consumption, enhance energization durability, and achieve more uniform heat generation. Further, since the temperature difference between the heat-generating front end portion 50 and the outside of a substrate front end portion 80 decreases, when the substrate front end portion 80 is to be heated to a desired temperature, the resistor element 30 does not need to generate heat excessively. As a result, the ceramic heater 12 is excellent in durability. Furthermore, at the intermediate portions 40, the ratio of the cross sectional area of the resistor element 30 to the cross sectional area of the intermediate portions 40 increases, whereby the stress acting on the resistor element 30 can be mitigated, which contributes to the excellent durability. In the case of conventional ceramic heaters, consideration has been given to employing a structure in which the outline of the substrate 60 narrows toward the front end; however, the shape of the substrate 60, including the shape of the intermediate portions 40, and their synergistic effects have not yet been studied, and no invention was made thereon. The above-described effects are first achieved through the synergistic effects of these configurations.
In the case where the ceramic heater is actually used, the ceramic heater is held by another member for attachment to an object to be heated. This holding is mainly performed by a tubular member 90 formed of metal. The holding structure will be described, while a glow plug 200 is taken as an example. As shown in
In order to satisfy such desire, the ceramic heater may employ the following third structural feature in addition to the above-described configuration. The thickness of the resistor element 30 shown in
The thickness of the resistor element 30 is determined such that a portion of the resistor element 30 projecting frontward (upward in
The shape of the resistor element 30 (in particular, the intermediate portions 40) will be described in detail. In order to make the following description clear,
As shown in
The present embodiment is configured to satisfy a relation θ2>θ1 and a relation L1>L2. Specifically, θ1=1°, θ2=25°, L1=3.5 mm, and L2=2.0 mm. By virtue of this configuration, in the XH direction view in which the U-like shape of the resistor element 30 can be recognized, the resistor element 30 (the intermediate portions 40) has a shape such that it tapers off relatively gradually toward the front end. In contrast, in the XV direction view perpendicular thereto, the resistor element 30 (the intermediate portions 40) has a shape such that it tapers off relatively sharply toward the front end. By virtue of this shape, the resistor element 30 achieves the following effect. Notably, when this shape is formed, preferably, θ1, θ2, and L1 are determined to satisfy respective relations 0.5°≦θ1≦5°, 10°≦θ2≦70°, and 2.5 mm≦L1≦20 mm.
As described above, concentration of the heater's heat generation on the front end thereof is desirable from the viewpoint of reduction in power consumption. However, in some cases, heat generation in only a small region of the front end is considered not preferred. In particular, in the case of a glow plug used for heating of a diesel engine, in order to realize efficient combustion, heat is preferably generated over a somewhat large range. In order to meet the incompatible requirements, the ceramic heater 12 of the present embodiment has the above-described configuration. Thus, a relatively large portion of the front end portion of the ceramic heater 12 (in
Notably, in order to realize more excellent durability while meeting the above-described requirements, preferably, the outline 60g of the substrate 60 is tapered to narrow toward the front end as in the present embodiment, in a region in which the thickness tXVex of the portions of the intermediate portions 40 projecting from the tubular member 90 is equal to or less than 2(tXVmax)/3. Through employment of this configuration in addition to the tapering-off shape of the intermediate portions 40, the outside contours of the pair of intermediate portions 40, 40 become straight and do not have concave and convex portions or the like. Therefore, when voltage is applied to the resistor element 30, it becomes possible to mitigate concentration of thermal stress and local temperature rise. Further, concentration of thermal stress on the heat-generating front end portion 50 can be prevented. Accordingly, the ceramic heater can have excellent quick heating performance, can reach a predetermined temperature while consuming a small amount of electric power, and can have enhanced energization durability.
This will be described with reference to
Preferably, the above-described tapered shape of the substrate 60 is formed as follows. As shown in
In particular, from the viewpoint of performance in starting a diesel engine, the maximum spacing GL between the pair of lead portions 31, 31 is determined to satisfy a relation GL<GM, where GM represents the maximum spacing GL between the portions of the intermediate portions 40, 40 whose thickness tXVex is equal to or less than 2tXVmax/3. Thus, in a region in which the heat generation temperature is relatively high, the pair of intermediate portions 40, 40 has an increased spacing therebetween, so that the heat generated by the heat-generating portion 33 is efficiently transmitted to the substrate 60, and the amount of heat radiated from the substrate increases. Accordingly, it becomes possible to reduce power consumption while maintaining engine starting performance. Further, since the heat-generating portion 33 does not need to generate more heat than necessary in order to heat the substrate front end portion 80 to a desired temperature, the ceramic heater 12 is excellent in durability as well.
In the above, the structure of the ceramic heater 12 has been described. Next, materials of the ceramic heater 12 and a method of manufacturing the ceramic heater 12 will be described.
An example of an electrically insulative ceramic for forming the substrate 60 of the ceramic heater 12 is silicon nitride ceramic. Also, an electrically conductive mixture of silicon nitride (Si3N4) and tungsten carbide (WC) is used as an electrically conductive ceramic for forming the resistor element 30. These materials and a method of manufacturing the materials are known, and are described in, for example, Japanese Patent Application Laid-Open (kokai) No. 2008-293804.
That is, material powder for forming the substrate 60 and material powder for forming the resistor element 30 are prepared in advance. A green member which is to become the resistor element 30 is formed through injection molding performed by charging the corresponding material powder into a predetermined mold. The mold used for the injection molding is designed such that the resistor element 30 has the above-described shape. Alternatively, a member obtained through injection molding is machined to obtain a green member of the resistor element 30 having the above-described shape. Meanwhile, the material powder for forming the substrate 60 is charged into a different mold, the molded green member is placed on the charged material powder, and the material powder for forming the substrate 60 is further charged. Subsequently, press forming is performed in a state in which the molded green member is buried in the material powder for forming the substrate 60, whereby the molded green member and the material powder are united, and, thus, a green ceramic heater is produced. After having undergone a predetermined debindering process, etc., the green ceramic heater is fired by means of a hot press. The external shape of a resultant ceramic heater is regulated by use of a grinder or the like. At that time, the machining is performed such that the substrate 60 has the above-described shape.
The ceramic heater 12 manufactured as described above can be used as the glow plug 200 shown in
Needless to say, this example is one example of the embodiment of the ceramic heater according to the present invention, and the invention is not limited thereto.
WC (average grain size: 0.7 μm), silicon nitride (average grain size: 1.0 μm), and Er2O3 (sintering aid) were wet-blended in a bowl mill for 40 hours, whereby a powder mixture for forming the resistor element was obtained (the WC content of the powder mixture was adjusted within a range of 27 vol. % (63 mass %) to 32 vol. % (70 mass %), whereby the room temperature resistance of a completed heater became about 300 mΩ or higher). The powder mixture for forming the resistor element was dried by a spray dry method so as to prepare powder for granulation. Binder was added to the powder for granulation such that the binder was present in an amount of 40 to 60 vol. %, and the powder was kneaded for 10 hours in a kneader. After that, granules having a grain size of about 3 mm were formed from the obtained mixture by use of a pelletizer. The formed granules were placed in an injection molding machine having a mold capable of forming intermediate portions of Examples 1 to 15 and Comparative Example 1, and a green resistor element having a green heat-generating portion to become a heat-generating portion satisfying the above-described conditions was obtained through injection molding.
Meanwhile, silicon nitride (average grain size: 0.6 μm), Er2O2 (sintering aid), and CrSi2, WSi2, and SiC (thermal expansion adjusters) were wet-blended in a bowl mill, whereby a powder mixture was obtained. Binder was added to the powder mixture, and the resultant mixture was dried by a spray dry method, whereby a substrate-forming powder mixture for forming the substrate was obtained.
Next, the green resistor element was embedded into the substrate-forming powder mixture, which was then press-formed, whereby a molded product to become a ceramic heater was obtained. This molded product was calcined for debindering at 800° C. for one hour in a nitrogen atmosphere, and was fired by a hot press method at 1780° C. under a pressure of 30 MPa for 90 minutes in a nitrogen atmosphere of 0.1 MPa, whereby a fired product was obtained. The obtained fired product was ground into the form of an approximate cylinder having a diameter of 3.1 mm. Further, as desired, the substrate front end portion 80 was tapered, polished, or polished into a rounded shape, whereby each of ceramic heaters shown in Table 1 was manufactured. The manufactured ceramic heaters have shapes identical with that of the above-described ceramic heater 12. However, the ceramic heaters may have modified shapes shown in
The above-described glow plug was manufactured by use of each of the manufactured ceramic heaters, and subjected to various performance evaluation tests, which will be described next. Notably, the characteristic values of the ceramic heaters are also shown in Table 1.
(Measurement of Power Consumption of Glow Plug)
An apparatus shown in
The surface temperature and power consumption of each of the glow plugs of Examples and Comparative Example 1 were measured by use of the apparatus shown in
Further, the voltage applied from the DC power supply 101 to each glow plug and the current flowing through each glow plug were monitored by use of the oscilloscope 105, and the measured temperature, measured as the surface temperature of the ceramic heater by the radiation thermometer 104, was monitored. The oscilloscope 105 can record data of the measured temperature, the applied voltage, and the current in a synchronized manner, while using the applied voltage as a trigger. The data obtained in this manner were processed in the personal computer 106, to thereby calculate the power consumption. Tables 1 and 2 show the results.
(Energization Durability Test for Glow Plug)
An energization durability test was carried out for the glow plugs of Examples and Comparative Example 1. The energization durability test was carried out by repeating a heating and cooling cycle in which a heater voltage was applied to each glow plug such that the heater temperature increased at a rate of 1000° C./sec until the temperature reached a highest temperature of 1350° C. or 1450° C., and the application of voltage was stopped, and the glow plug was cooled by a fan for 30 sec. The heating and cooling cycle was ended when the number of repeated cycles reached 100000. When the resistance changed 10% or more before the number of repeated cycles reached 100000, the test was ended. In this test, a glow plug for which the heating and cooling cycle was repeated over 35000 times was evaluated “Excellent (AA)”; a glow plug for which the heating and cooling cycle was repeated over 15000 times was evaluated “Good (BB)”; and a glow plug for which the heating and cooling cycle was repeated over 5000 times was evaluated “Fair (CC).” The results of this test are shown in Tables 1 and 2.
(Quick Heating Performance Test for Glow Plug)
A quick heating performance test was carried out for the glow plugs of Examples and Comparative Example 1. A DC voltage of 11 V was applied to each glow plug, and the temperature of a hottest-generating portion 21 of the outer circumferential surface of the ceramic heater was measured. A time required to reach 1000° C. was measured as a 1000° C. reaching time, on the basis of which quick heating performance was evaluated. The results of this test are shown in Tables 1 and 2.
(Engine Startup Test for Glow Plug)
For the glow plugs of Examples, an engine starting test was performed in an environment of −25° C. A glow plug which enabled an engine to reach 950 rpm within 10 sec was evaluated “Excellent (AA)”; and a glow plug which enabled the engine to reach 950 rpm within 15 sec was evaluated “Good (BB).” The results of this test are shown in Table 2.
As is apparent from the results shown in Tables 1 and 2, the glow plugs of Examples whose resistor element has a heat-generating portion including a pair of intermediate portions satisfying the requirement of the above-described first structural feature were found to have excellent quick heating performances, can reduce power consumption, and are excellent in durability. In particular, the glow plugs of Examples 1 to 4 and 7 to 15 which satisfy the requirements of the above-described first and second structural features were able to reduce power consumption while being excellent in quick heating performance and durability. In contrast, the glow plug of Comparative Example 1, which does not satisfy the requirement of the above-described first structural feature, consumed as much power as 62 W.
The “tXVex/tXVmax” in Table 2 represents the ratio of the minimum thickness of the intermediate portion 40 to the maximum thickness of the resistor element 30. Comparison among Examples 7 to 9 reveals that, when the degree of thinness of the intermediate portions 40 as compared with the maximum thickness of the resistor element 30 increases; specifically, when the glow plug has the above-described third structural feature, it is possible to improve quick heating performance while reducing power consumption. Specifically, whereas, in Examples 7 and 8, the thickness of the resistor element 30 (the intermediate portions 40) becomes ⅔ at a portion exposed from the tubular member 90 of the ceramic heater, in Example 9, the thickness of the resistor element 30 (the intermediate portions 40) at the exposed portion thereof is ¾ as measured at the beginning of the exposed portion. Therefore, the glow plug of Example 9 consumed a slightly larger amount of power as compared with those of Examples 7 and 8.
Notably, Example 10 is an example for comparison which has the first and second structural features but does not have the third structural feature. That is, the resistor element 30 has a portion whose thickness becomes ⅔ the maximum thickness inside the tubular member 90. Therefore, heat dissipates from the tubular member 90, which slightly lowers the quick heating performance.
The glow plugs of Examples 8 and 11 to 15 were fabricated such that their ceramic heaters had external shapes substantially identical with or similar to the external shape of the ceramic heater 12, in order to check the influence of the angles θ1 and θ3 on quick heating performance and power consumption. Comparison among these examples reveals that having the sixth structural feature is preferred.
Moreover, comparison between Example 1 and Examples 7 to 15 of Table 2 reveals that engine starting performance can be improved by setting the relation between the maximum spacing GL between the pair of lead portions 31 and the maximum spacing GM between the intermediate portions 40 having the thickness tXVex to satisfy the relation GL<GM.
As shown in Table 1, Examples of the present invention differ from one another in the difference (CL2−CL1) between the diameter of the circumscribed circle CG of the intermediate portions 40 at the frontmost end thereof and the diameter of the circumscribed circle CG of the intermediate portions 40 at the rearmost end thereof. Depending on design, a desirable value is selected for the diameter difference. For example, the diameter difference is selected to fall within a range of 0.1 to 2.5 mm, preferably, 0.3 to 2.0 mm. When the diameter difference falls within this range, the outer diameter of the pair of intermediate portions 40 decreases appropriately toward the front end, and their volumes decrease. Therefore, it is possible to improve quick heating performance and further lower power consumption, while maintaining the durability of the heat-generating portion 33.
Further, the hottest-generating portion 55 is preferably formed such that its total cross sectional area becomes 1/60 to 1/2.6 the total cross sectional area of the lead portions 31. Each of the total cross sectional areas is the sum of areas of cross sections of the resistor element 30 taken along a plane perpendicular to the axis XA. When the cross sectional area of the hottest-generating portion 55 falls with the above-described range, excellent quick heating performance, low power consumption, and excellent durability can be realized, and the heating temperature of the hottest-generating portion 55 can be made more uniform. Accordingly, when this ceramic heater 12 is used as the heater of the glow plug 200, the glow plug 200 exhibits excellent quick heating performance, low power consumption, and excellent durability, and also exhibits excellent engine starting performance.
Further, the degree of taper of the substrate 60 is preferably determined such that the ratio of cross sectional area S1S/S2S between the cross sections S1 and S2 of the ceramic heater becomes about 0.1 to 0.9 (preferably, 0.5 to 0.9). With this, the buried position of the heat-generating front end portion 50 becomes neither too close to nor too far from the outer surface of the substrate front end portion 80, and the wall thickness of the substrate front end portion 80 in which the heat-generating front end portion 50 is buried becomes a proper thickness, whereby the heat generated by the heat-generating front end portion 50 can be transmitted to the outer circumferential surface of the substrate 60 more efficiently and more quickly. Thus, it becomes possible to realize higher levels of quick heating performance, low power consumption, and durability.
Moreover, a verification test was carried out so as to verify the effectiveness of the fourth structural feature of the present invention. A test similar to the above-described test was carried out for ceramic heaters fabricated such that they differed from one another in the terms of the angles θ1 and θ2 and lengths L1 and L2 of the resistor element. The specifications of the ceramic heaters and the test results are shown in Table 3.
The ceramic heater of Example 8 satisfies the requirement of the fourth structural feature. That is, the ceramic heater was formed to satisfy the relation θ2>θ1 and the relation L1>L2. Meanwhile, the ceramic heaters of Examples 16 to 18 were formed such that either one or both of the relations regarding the angle θ and the length L failed to be satisfied. Comparison between Example 8 and Examples 16 to 18 reveals that the ceramic heater of Example 8 can reduce power consumption and is relatively excellent in quick heating performance. This results from configuring the intermediate portions 40 to satisfy the requirement of the sixth structural feature, whereby the resistance of the resistor element 30 concentrates at the heat-generating portion 33 on the front end side.
Modifications of the present invention will be described. The resistor element 30 of the present embodiment has a generally elliptical cross sectional shape. However, the cross sectional shape of the resistor element 30 is not limited thereto, so long as the resistor element 30 is formed through so-called injection molding. For example, the embodiment may be modified without departing from the scope of the present invention such that the resistor element 30 has a generally circular or fan-like cross section, or a rectangular or polygonal cross section with chamfered corners.
Not only the cross sectional shape of the resistor element 30, but also its external shape may be modified.
A ceramic heater 1 shown in
A ceramic heater 2 shown in
A ceramic heater 3 shown in
In the case of a ceramic heater 5 shown in
A ceramic heater 6 shown in
A ceramic heater 7 used in the above-described evaluation test has a shape approximately similar to that of the ceramic heater 2. Different is that the substrate front end portion 80 is formed larger as compared with the ceramic heater 2, and the remaining portion is not changed (not shown).
A ceramic heater 8 is identical with the ceramic heater 2, except that the substrate front end portion 80 has a hemispherical shape (
Although the embodiments of the present invention have been described above, other modifications are possible. For example, a ceramic heater 10 shown in
However, when such a shape is employed, improving the production yield of a manufacturing process becomes difficult. Therefore, needless to say, the intermediate portions are preferably formed to extend straight. In conjunction with the first structural feature, it can be said that “the intermediate portions are preferably formed continuously.”
Further, in the present embodiment, the ceramic heater is configured such that both the substrate and the resistor element are formed of ceramic. However, the configuration of the ceramic heater is not limited thereto, and a conventionally known structure may be additionally employed. Specifically, as in a ceramic heater 11 shown in
Notably, when the present invention is practiced, a ceramic heater may be formed by use of different types of electrically conductive ceramics. In such a case, a specific design as defined by the present invention may become unnecessary, and the effects achieved by the present invention can be attained relatively easily through employment of a simpler design. However, only when a ceramic heater is formed by use of the single electrically conductive ceramic, management of materials used in manufacture and a manufacture process itself can be facilitated, and the above-described action and effects can be attained. Accordingly, the technical importance of the present invention becomes more significant in ceramic heaters which use the single electrically conductive ceramic. However, it is clear that, when the present invention is applied to ceramic heaters which use different types of electrically conductive ceramics, the ceramic heaters exhibit more preferred characteristics. Therefore, application of the present invention is not limited to ceramic heaters in which the resistor element is formed of the single electrically conductive ceramic. However, the present invention, which provides a configuration crucial to ceramic heaters in which the resistor element is formed of a single electrically conductive ceramic, cannot be easily conceived from the design of a ceramic heater which is formed of different types of electrically conductive ceramics.
a), 3(b) and 3(c) are a set of enlarged cross sectional views showing the embodiment of the ceramic heater according to the present invention.
a) and 4(b) are a pair of views relating to the embodiment of the ceramic heater according to the present invention, and each showing a cores section at an arbitrary point P along the axis XA direction.
a) and 5(b) are a pair of partial see-through views relating to the embodiment of the ceramic heater according to the present invention, and showing, in an exaggerated manner, characteristic portions in order to describe the shape of the resistor element 30.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-039203 | Feb 2008 | JP | national |
| 2008-330796 | Dec 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/000707 | 2/19/2009 | WO | 00 | 8/3/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/104401 | 8/27/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4125761 | Churchill | Nov 1978 | A |
| 4563568 | Takizawa | Jan 1986 | A |
| 4636614 | Itoh et al. | Jan 1987 | A |
| 4810853 | Maruta et al. | Mar 1989 | A |
| 4929813 | Masaka et al. | May 1990 | A |
| 5086210 | Nunogaki et al. | Feb 1992 | A |
| 5218183 | Kimata | Jun 1993 | A |
| 5750958 | Okuda et al. | May 1998 | A |
| 5883360 | Tatematsu et al. | Mar 1999 | A |
| 6013898 | Mizuno et al. | Jan 2000 | A |
| 6111223 | Tatematsu | Aug 2000 | A |
| 6236148 | Nasu et al. | May 2001 | B1 |
| 6274853 | Watanabe et al. | Aug 2001 | B1 |
| 6359261 | Watanabe et al. | Mar 2002 | B1 |
| 6433311 | Teramura et al. | Aug 2002 | B1 |
| 6483079 | Sato et al. | Nov 2002 | B2 |
| 6563089 | Watanabe et al. | May 2003 | B2 |
| 6621052 | Watanabe et al. | Sep 2003 | B2 |
| 6646231 | Hotta et al. | Nov 2003 | B2 |
| 6653601 | Taniguchi et al. | Nov 2003 | B2 |
| 6657166 | Funaki et al. | Dec 2003 | B2 |
| 6689990 | Taniguchi et al. | Feb 2004 | B2 |
| 6720530 | Taniguchi et al. | Apr 2004 | B2 |
| 6737612 | Taniguchi et al. | May 2004 | B2 |
| 6759631 | Geissinger et al. | Jul 2004 | B1 |
| 6770850 | Taniguchi et al. | Aug 2004 | B2 |
| 6849207 | Funaki et al. | Feb 2005 | B2 |
| 6881930 | Yoshikawa et al. | Apr 2005 | B2 |
| 7020952 | Watanabe et al. | Apr 2006 | B2 |
| 7122947 | Nasu et al. | Oct 2006 | B2 |
| 7201043 | Yamada et al. | Apr 2007 | B2 |
| 7282670 | Matsubara et al. | Oct 2007 | B2 |
| 8013278 | Kurono et al. | Sep 2011 | B2 |
| 20020036192 | Sato et al. | Mar 2002 | A1 |
| 20020043524 | Taniguchi et al. | Apr 2002 | A1 |
| 20020096802 | Watanabe et al. | Jul 2002 | A1 |
| 20020113052 | Watanabe et al. | Aug 2002 | A1 |
| 20020117492 | Teramura et al. | Aug 2002 | A1 |
| 20020134774 | Funaki et al. | Sep 2002 | A1 |
| 20020148823 | Watanabe et al. | Oct 2002 | A1 |
| 20020162830 | Taniguchi et al. | Nov 2002 | A1 |
| 20020162831 | Taniguchi et al. | Nov 2002 | A1 |
| 20020162834 | Asano et al. | Nov 2002 | A1 |
| 20020175155 | Funaki et al. | Nov 2002 | A1 |
| 20020175156 | Hotta et al. | Nov 2002 | A1 |
| 20030029857 | Taniguchi et al. | Feb 2003 | A1 |
| 20030042242 | Taniguchi et al. | Mar 2003 | A1 |
| 20030042243 | Taniguchi et al. | Mar 2003 | A1 |
| 20030126736 | Watanabe et al. | Jul 2003 | A1 |
| 20040178185 | Yoshikawa et al. | Sep 2004 | A1 |
| 20040183419 | Nasu et al. | Sep 2004 | A1 |
| 20050274707 | Matsubara et al. | Dec 2005 | A1 |
| 20050284859 | Konishi | Dec 2005 | A1 |
| 20060011602 | Konishi et al. | Jan 2006 | A1 |
| 20070210053 | Hotta et al. | Sep 2007 | A1 |
| 20070221661 | Nagasako et al. | Sep 2007 | A1 |
| 20070241092 | Suzuki | Oct 2007 | A1 |
| 20080142496 | Itoh et al. | Jun 2008 | A1 |
| 20090008383 | Kurono et al. | Jan 2009 | A1 |
| 20090194519 | Funaki et al. | Aug 2009 | A1 |
| 20090320782 | Hiura | Dec 2009 | A1 |
| 20100000982 | Allgaier et al. | Jan 2010 | A1 |
| 20100155389 | Yamamoto | Jun 2010 | A1 |
| 20100213188 | Nishihara et al. | Aug 2010 | A1 |
| 20100288747 | Yamamoto | Nov 2010 | A1 |
| 20110068091 | Hiura | Mar 2011 | A1 |
| 20110114622 | Sekiguchi et al. | May 2011 | A1 |
| 20110240625 | Takenouchi | Oct 2011 | A1 |
| 20110253704 | Yamamoto | Oct 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 1255075 | Nov 2002 | EP |
| 1255076 | Nov 2002 | EP |
| 1288572 | Mar 2003 | EP |
| 1288573 | Mar 2003 | EP |
| 1998595 | Dec 2008 | EP |
| 1998596 | Dec 2008 | EP |
| 2117280 | Nov 2009 | EP |
| 2219414 | Aug 2010 | EP |
| 2247156 | Nov 2010 | EP |
| 2257119 | Dec 2010 | EP |
| 61-225517 | Oct 1986 | JP |
| 4-370689 | Dec 1992 | JP |
| 07-239123 | Sep 1995 | JP |
| 09137945 | May 1997 | JP |
| 10300083 | Nov 1998 | JP |
| 10300086 | Nov 1998 | JP |
| 3044632 | May 2000 | JP |
| 2000327426 | Nov 2000 | JP |
| 2001132947 | May 2001 | JP |
| 2001132949 | May 2001 | JP |
| 2001132950 | May 2001 | JP |
| 2002203665 | Jul 2002 | JP |
| 2002246153 | Aug 2002 | JP |
| 2002257341 | Sep 2002 | JP |
| 2002333136 | Nov 2002 | JP |
| 2002-364847 | Dec 2002 | JP |
| 2002349852 | Dec 2002 | JP |
| 2002349853 | Dec 2002 | JP |
| 2003022889 | Jan 2003 | JP |
| 2003074849 | Mar 2003 | JP |
| 2004061041 | Feb 2004 | JP |
| 2006-024394 | Jan 2006 | JP |
| 2006049279 | Feb 2006 | JP |
| 2006127995 | May 2006 | JP |
| 2006351446 | Dec 2006 | JP |
| 2008235034 | Oct 2008 | JP |
| 2009231161 | Oct 2009 | JP |
| 2009287920 | Dec 2009 | JP |
| 2010073417 | Apr 2010 | JP |
| 2012033340 | Feb 2012 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20110114622 A1 | May 2011 | US |
