JP2008164559A

JP2008164559A - Pressure detection circuit

Info

Publication number: JP2008164559A
Application number: JP2007000066A
Authority: JP
Inventors: Hirokazu Araki; 博和荒木; Osamu Shimoe; 治下江; Kentaro Ino; 健太郎猪野; Masahiro Mita; 正裕三田; Hideko Fukushima; 英子福島
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2007-01-04
Filing date: 2007-01-04
Publication date: 2008-07-17

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit for converting efficiently an electric resistance value changing by a pressure into a voltage, and delivering with high sensitivity a voltage change portion changed by the pressure to an amplifier, when using a washer-shaped pressure detection element whose electric resistance value is changed by the pressure. <P>SOLUTION: In the pressure detection element whose electric resistance value is changed by the pressure, a pressure change is reread efficiently as a change of a voltage value by driving with a constant current both ends of each electrode mounted on the upper and lower sides of the washer-shaped pressure detection element. A capacitor 12 is inserted in series just thereafter, and hereby a disturbance changing in a DC manner such as a change of the electric resistance value independent of a pressure change is removed, and the change of the electric resistance value caused by the pressure change can be delivered with high sensitivity as a voltage change to an input of the amplifier 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、圧力を印加すると電気抵抗率が変化する圧力検出素子において、検出する電気抵抗値の検出方法と圧力変化の受渡し回路方法に関する。 The present invention relates to a method for detecting an electrical resistance value to be detected and a pressure change delivery circuit method in a pressure detection element whose electrical resistivity changes when pressure is applied.

従来から、金属または半導体素子を用いた圧力または荷重検出素子が一般的に使用されており、中でもシリコン単結晶や炭化珪素等からなる半導体圧力検出素子は、金属歪ゲージと比較し、圧力感度が数桁優れることから幅広い応用がなされている。しかしながら、従来の半導体圧力検出素子は機械的強度が弱く、高温・高圧下では単体で使用することが出来ないため耐圧容器に組み込んで測定を行っており、検出装置の構成が複雑になるとともにコスト高となる問題があった。 Conventionally, a pressure or load detection element using a metal or a semiconductor element has been generally used. Among them, a semiconductor pressure detection element made of silicon single crystal, silicon carbide or the like has a pressure sensitivity compared to a metal strain gauge. Since it is several orders of magnitude superior, it has a wide range of applications. However, conventional semiconductor pressure sensing elements are weak in mechanical strength and cannot be used as a single unit at high temperatures and pressures, so measurements are performed by incorporating them in a pressure vessel, which complicates the configuration of the detection device and reduces costs. There was a problem that would be high.

またこれらの検出素子は抵抗値が相対的に変動するのを直流的に観察する必要があるために直流フルブリッジ回路を構成して検出されている。特許文献１に代表されるのが直流フルブリッジ回路である。これらは直流的に安定であるが部品点数が多くなると共にブリッジのバランスを取るために性能がそろったペアとなる素子が必要となる。 These detection elements are detected by constituting a direct current full bridge circuit because it is necessary to observe the relative fluctuation of the resistance value in a direct current manner. A typical example of Patent Document 1 is a direct current full bridge circuit. Although these are stable in terms of direct current, the number of parts increases and a pair of elements with uniform performance is required to balance the bridge.

また別の圧力検出素子には特許文献２に開示されている。これは多結晶セラミックス材料であり、Ｓｉ_３Ｎ_４を主成分とする多結晶セラミックス材料に析出させたＳｉＣの有するピエゾ抵抗効果、すなわち、材料に圧力を加えると電気抵抗が変化する現象を利用して圧力を検出するものである。主成分であるＳｉ_３Ｎ_４が高強度であるため耐圧容器等で圧力検出素子を保護しなくても高温高圧下で使用可能となる。
特開２００２−２４３５６６号公報特開２００４−２０３５５号公報 Another pressure detection element is disclosed in Patent Document 2. This is a polycrystalline ceramic material, utilizing the piezoresistance effect of SiC deposited on a polycrystalline ceramic material mainly composed of Si ₃ N ₄ , that is, the phenomenon that the electrical resistance changes when pressure is applied to the material. The pressure is detected. Since Si ₃ N _{4 as the} main component has high strength, it can be used under high temperature and high pressure without protecting the pressure detection element with a pressure vessel or the like.
JP 2002-243666 A JP 2004-20355 A

従来の抵抗値が変化する検出素子の出力は多くの部品から構成した図６のような直流フルブリッジ回路で検出されている。直流フルブリッジ回路は素子に直流電流を流し、出力もコンデンサを用いない回路である。圧力検出素子２１，２２と抵抗素子２３，２４でブリッジ回路を構成し、その出力を増幅して出力ｅ１として出力するのが従来の圧力検出回路の基本構成である。このようなブリッジ回路はブリッジの組合わせとなる素子を４個、相対するブリッジの辺に配置することを必要とする。しかしながら温度によって抵抗値が変化するような検出素子においてはブリッジ回路のバランスを保つことが難しく、またブリッジ回路では排除できないその他の外乱を多く含むため所望の出力を得ようとすると測定範囲外に外れてしまう困難があり、所望の圧力変化のみを観測することが難しかった。例えば、ペアとなる素子のバランスがある一点で取れても、次の変化、例えば温度変化では異なった動きとなる場合や、圧力変化の傾きが異なる場合などが外乱となる。本発明は、圧力によって電気抵抗値が変わる座金形状の圧力検出素子を用いるとき、圧力によって変化する電気抵抗値を効率良く電圧に変換するとともに圧力によって変化した電圧変化分を感度良く増幅器に受け渡すことのできる圧力検出回路を提供することを目的とする。 The output of the conventional detecting element whose resistance value changes is detected by a DC full bridge circuit as shown in FIG. A direct current full bridge circuit is a circuit in which a direct current is passed through an element and an output does not use a capacitor. The basic structure of the conventional pressure detection circuit is to form a bridge circuit with the pressure detection elements 21 and 22 and the resistance elements 23 and 24, amplify the output and output as an output e1. Such a bridge circuit requires that four elements to be combined in the bridge are arranged on opposite bridge sides. However, it is difficult to maintain the balance of the bridge circuit in a detection element whose resistance value changes with temperature, and it contains many other disturbances that cannot be eliminated by the bridge circuit. It was difficult to observe only the desired pressure change. For example, even if the paired elements are balanced at a single point, disturbance occurs when the next change, for example, a temperature change causes a different movement or the pressure change has a different slope. In the present invention, when a washer-shaped pressure detecting element whose electric resistance value changes with pressure, the electric resistance value changing with pressure is efficiently converted into voltage, and the voltage change changed with pressure is transferred to the amplifier with high sensitivity. An object of the present invention is to provide a pressure detection circuit that can perform the above-described operation.

本発明は、まず圧力によって抵抗値が変化する圧力検出素子に電流を一定に流し込む定電流回路を用いた。この定電流の流れによって圧力検出素子の抵抗値を精度良く電圧値に読替えることができる。これは４つの素子でバランスを取り、これに直流電流を流し、コンデンサを介さず直流で出力する回路、すなわち直流的にフルブリッジ回路を組むより、部品点数が少なくてすむこと、抵抗値及び特性の揃ったブリッジ回路を構成する部品が不要であり、工業的な回路生産上有利である。 In the present invention, a constant current circuit is used in which a current is supplied to a pressure detecting element whose resistance value changes with pressure. With this constant current flow, the resistance value of the pressure detecting element can be accurately read as a voltage value. This circuit is balanced by four elements, and a direct current is passed through it, and a direct current output is output without passing through a capacitor. That is, the number of parts is smaller than a full bridge circuit in a direct current, resistance value and characteristics. Thus, there is no need for the parts constituting the bridge circuit, and this is advantageous in industrial circuit production.

すなわち本願第一の発明は、印加する圧力に応じて電気抵抗が変化する圧力検出素子と、該圧力検出素子を定電流駆動する定電流源と、前記圧力検出素子に発生する電圧を取り出すことを特徴とする圧力検出回路である。 That is, the first invention of the present application is to extract a pressure detection element whose electric resistance changes according to the applied pressure, a constant current source for driving the pressure detection element at a constant current, and a voltage generated in the pressure detection element. It is the pressure detection circuit characterized.

さらに圧力によって抵抗値が変化する圧力検出素子から抵抗値の変化を電圧に読替えた後、直後にコンデンサにおいて直流成分を取り除く。本発明では直流成分を取り除くため圧力変化以外の温度変化、湿度変化、経年変化など時間的にゆるやかな変化を出力成分から排除することができる。これにより圧力の変化に寄与しない直流電圧を扱うこと無く、精度良く増幅器の初段に圧力検出素子からの圧力変化のみを反映した信号を受け渡すことができ、直流的なフルブリッジの入力回路に用いられる差動増幅などの複雑な増幅回路を不要として、工業的に有利な回路構成である。 Further, after the change in the resistance value is read as a voltage from the pressure detecting element whose resistance value changes depending on the pressure, the direct current component is removed from the capacitor immediately after. In the present invention, since a direct current component is removed, a gradual change such as a temperature change, a humidity change, and a secular change other than the pressure change can be excluded from the output component. As a result, a signal reflecting only the pressure change from the pressure detection element can be accurately transferred to the first stage of the amplifier without handling a DC voltage that does not contribute to the pressure change, and used for a DC full-bridge input circuit. The present invention is an industrially advantageous circuit configuration that eliminates the need for complicated amplification circuits such as differential amplification.

圧力検出素子の出力はコンデンサにおいて直流成分が取り除かれ交流成分だけが通る。交流成分は僅かに振動や回路のノイズ等を含むものの、その圧倒的に多くが圧力変化を反映する信号である。挿入したコンデンサと回路定数とにより直流成分だけでなく、周波数の極低い低周波領域も除かれる。本発明では圧力変化は高周波成分に多く含まれるため、その高周波成分を取り出すことを目的にしている。更に言えばエンジン内の圧力変化の周波数は大体分かっているのでそれを取り出すのに適したハイパスフィルタ又はバンドパスフィルタを設計すればよい。エンジンの型式、構成、目的などによって圧力検出素子から得られる圧力信号の周波数成分は異なる。また必要とする周波数も異なると考えられる。回路上も帯域を広くとることはＳ/Ｎの悪化を招きやすいため、現実的には先頭のコンデンサで下側の周波数を決め、回路上の他のコンデンサで上側の周波数を決めたバンドパスフイルタを構成して高いＳ/Ｎを得るように設計する。 The direct current component is removed from the output of the pressure detecting element in the capacitor, and only the alternating current component passes. Although the AC component slightly includes vibration, circuit noise, etc., the overwhelming majority is a signal reflecting a pressure change. The inserted capacitor and circuit constants remove not only the DC component but also the low frequency region with a very low frequency. In the present invention, since a large amount of pressure change is included in the high frequency component, the object is to extract the high frequency component. Furthermore, since the frequency of the pressure change in the engine is roughly known, a high-pass filter or a band-pass filter suitable for extracting it may be designed. The frequency component of the pressure signal obtained from the pressure detection element varies depending on the model, configuration, purpose, and the like of the engine. Also, the required frequency is considered to be different. A wide band on the circuit is likely to cause S / N deterioration, so in reality, a bandpass filter in which the lower frequency is determined by the first capacitor and the upper frequency is determined by another capacitor on the circuit. Are designed to obtain a high S / N.

すなわち本願第二の発明は、印加する圧力に応じて電気抵抗が変化する圧力検出素子と、該圧力検出素子を定電流駆動する定電流源と、前記圧力検出素子に発生する電圧をコンデンサの一端に供給し前記コンデンサの他端から取り出すことを特徴とする圧力検出回路である。 That is, the second invention of the present application is a pressure detecting element whose electric resistance changes according to an applied pressure, a constant current source for driving the pressure detecting element at a constant current, and a voltage generated in the pressure detecting element at one end of a capacitor. The pressure detection circuit is characterized in that it is supplied to and taken out from the other end of the capacitor.

さらに圧力検出素子の駆動電流は、その電流によって圧力検出素子に発生する電圧が使用できる電源電圧の約１／２であることが望ましい。これによって圧力検出素子の無負荷時抵抗が多少ばらついても定電流の値を変更することなく、圧力と電圧出力の関係が保たれると共に高い圧力検出感度も保たれる。 Furthermore, it is desirable that the drive current of the pressure detection element is about ½ of the power supply voltage at which the voltage generated in the pressure detection element by the current can be used. As a result, even if the no-load resistance of the pressure detection element varies somewhat, the relationship between the pressure and the voltage output is maintained and the high pressure detection sensitivity is also maintained without changing the constant current value.

さらに検出した圧力検出素子の抵抗変化を電圧に読替えた圧力変化信号をその直後にコンデンサを設置することにより増幅器に入力されるさいにはすでに不要な直流成分を取り除くと共に、不要な周波数成分も適宜カットすることができ、実行感度の高い圧力検出素子回路が構成される。 Furthermore, when a pressure change signal obtained by reading the detected resistance change of the pressure detection element into a voltage is placed immediately after the capacitor, an unnecessary DC component is removed and an unnecessary frequency component is appropriately selected. A pressure detecting element circuit that can be cut and has high execution sensitivity is configured.

本発明によれば、圧力によって抵抗値が変化する圧力検出素子の出力を使用する部品点数を増やすことなく感度良く電圧に読替えできる。また読替えた電圧の直後にコンデンサを接続することによって効率良く圧力変化を電圧変化に受渡し、かつ必要な周波数特性を簡便に求められ、圧力検出装置の構造を簡素化でき、工業的に有効な圧力変化信号を提供可能となる According to the present invention, it is possible to read the voltage with high sensitivity without increasing the number of parts using the output of the pressure detecting element whose resistance value changes with pressure. In addition, by connecting a capacitor immediately after the replaced voltage, the pressure change can be efficiently transferred to the voltage change, and the required frequency characteristics can be easily obtained, the structure of the pressure detection device can be simplified, and industrially effective pressure. Change signal can be provided

本発明をその実施例によって具体的に説明するが、これら実施例により本発明が限定されるものではない。 The present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

以下本発明の実施態様について図面を参照しつつ説明する。図１は本発明の圧力検出回路の検出原理を示す模式図である。図２は図１の圧力検出回路に用いる圧力センサの一部を構成する圧力検出素子の概略構成を示す斜視図である。図３は図１の圧力検出回路に用いる圧力センサの概略構成を示す斜視図である。図４は図３の圧力センサが内燃機関であるエンジンに取り付けられた状態を示す斜視図である。図５は図１の圧力検出回路および図４のようにエンジンに取り付けた圧力センサを用いて得られた出力波形である。なお、以下記載する実施態様及び実施例ではガソリンエンジンに装着される点火プラグのハウジング螺子部に組み込まれる圧力センサを主体として本発明を説明しているが、当該実施態様及び実施例に本発明は限定されず、発明として同一の範囲は本発明に含まれる。 Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the detection principle of the pressure detection circuit of the present invention. FIG. 2 is a perspective view showing a schematic configuration of a pressure detection element constituting a part of the pressure sensor used in the pressure detection circuit of FIG. FIG. 3 is a perspective view showing a schematic configuration of a pressure sensor used in the pressure detection circuit of FIG. FIG. 4 is a perspective view showing a state in which the pressure sensor of FIG. 3 is attached to an engine which is an internal combustion engine. FIG. 5 shows an output waveform obtained by using the pressure detection circuit of FIG. 1 and the pressure sensor attached to the engine as shown in FIG. In the embodiments and examples described below, the present invention is mainly described with reference to a pressure sensor incorporated in a housing screw portion of a spark plug attached to a gasoline engine. However, the present invention is not limited to the embodiments and examples. Without being limited, the same scope as the invention is included in the present invention.

圧力センサ６について図２，３に基づき説明する。セラミックスで構成される感圧体２は円環形状をなしている。感圧体２はセラミックスからなる第１の粒子を主体とした母材中に前記第１の粒子とは導電性が異なるセラミックスからなる第２の粒子を分散させたものであり、第１の粒子と第２の粒子との加圧による接触状態の変化により電気抵抗が変化する特性を有している。この第１の粒子としては、炭化珪素、窒化珪素、サイアロン、窒化アルミニウム、シリカ、アルミナ、ムライト、ジルコニア、マグネシア、コージェライト、アルミニウムチタネートのいずれか一種またはそれらの二種以上を含むセラミックスを選択することができる。また、第２の粒子としては、カーボン、炭化珪素、酸化錫、酸化インジウム、酸化銀、酸化銅、IV、V、VI族の遷移金属元素の炭化物、窒化物、ホウ化物、珪化物、酸化物及びこれらの化合物で構成される複合化合物の一種、または、それらの二種以上を含むものを選択することができる。導電性が高い材料から第２の粒子を選択することにより、第１の粒子と第２の粒子の導電性の差が大きくなり、加圧時に接触抵抗が変化した際の電気抵抗変化率を大きくすることができる。その結果、より圧力感度の高い圧力センサを構成することができる。 The pressure sensor 6 will be described with reference to FIGS. The pressure sensitive body 2 made of ceramic has an annular shape. The pressure-sensitive body 2 is obtained by dispersing second particles made of ceramics having different conductivity from the first particles in a base material mainly composed of first particles made of ceramics. And the second particles have a characteristic that the electric resistance changes due to a change in the contact state caused by pressurization. As the first particles, silicon carbide, silicon nitride, sialon, aluminum nitride, silica, alumina, mullite, zirconia, magnesia, cordierite, aluminum titanate or a ceramic containing two or more thereof is selected. be able to. Second particles include carbon, silicon carbide, tin oxide, indium oxide, silver oxide, copper oxide, carbides, nitrides, borides, silicides, oxides of group IV, V, and VI transition metal elements. In addition, one of complex compounds composed of these compounds, or one containing two or more of them can be selected. By selecting the second particles from a material having high conductivity, the difference in conductivity between the first particles and the second particles increases, and the rate of change in electrical resistance when the contact resistance changes during pressurization is increased. can do. As a result, a pressure sensor with higher pressure sensitivity can be configured.

感圧体２としては上記の構成に限定されず圧力に対して電気抵抗が変化するものであれば使用することができるが、内燃機関内の圧力計測に適用するためには高温においても特性の変化の少ないセラミックスで構成された感圧体である必要がある。したがって、ＳｉＣに窒素をドープした材料や、Ｓｉ_３Ｎ_４に導電性物質をドープした材料等ピエゾ抵抗効果を有するセラミックスから構成された感圧体を圧力センサに組み込むこともできる。 The pressure-sensitive body 2 is not limited to the above-described configuration, and any pressure-sensitive body can be used as long as its electric resistance changes with respect to pressure. It is necessary to be a pressure sensitive body composed of ceramics with little change. Therefore, a pressure-sensitive body made of ceramics having a piezoresistance effect, such as a material in which SiC is doped with nitrogen or a material in which Si ₃ N ₄ is doped with a conductive material, can be incorporated into the pressure sensor.

感圧体２の上面と底面には電極３，３が形成されており、その電極３からリード線３ａが取り出されている。電極３としては、銅又は銀等の導電性を有する金属を使用することができる。電極３として金属片を使用する場合には、ロウ付け又は導電性接着剤などで感圧体２の上面と底面に金属片を接合することにより電極３，３を形成することができる。また、感圧体２の上面及び底面に銀ペースト等を塗布し、焼成して電極３，３を形成するようにしてもよい。 Electrodes 3 and 3 are formed on the top and bottom surfaces of the pressure-sensitive body 2, and lead wires 3 a are taken out from the electrodes 3. As the electrode 3, a conductive metal such as copper or silver can be used. In the case where a metal piece is used as the electrode 3, the electrodes 3 and 3 can be formed by bonding the metal piece to the upper surface and the bottom surface of the pressure-sensitive body 2 by brazing or a conductive adhesive. Alternatively, the electrodes 3 and 3 may be formed by applying a silver paste or the like to the top and bottom surfaces of the pressure-sensitive body 2 and firing the paste.

電極３，３に隣接してそれぞれ円環形状の絶縁体４，４が設けられる。この絶縁体４は、電気的絶縁性を有するものであれば例えば樹脂等で構成してもよいが、圧力センサ６に負荷される締付圧力に対応するという点からはアルミナやジルコニア等のセラミックスを採用することが好ましい。 Toroidal insulators 4 and 4 are provided adjacent to the electrodes 3 and 3, respectively. The insulator 4 may be made of, for example, a resin as long as it has electrical insulation, but ceramics such as alumina and zirconia are suitable from the viewpoint of corresponding to the tightening pressure applied to the pressure sensor 6. Is preferably adopted.

座金５が上記電極３と絶縁体４を介して感圧体２に密接される。座金５は金属製でありヤング率が７０〜２２０ＧＰａであるもの、例えばアルミニウム、真鍮、銅、鋼及びそれらの合金等を主体とした金属で形成することができる。 A washer 5 is brought into close contact with the pressure sensitive body 2 through the electrode 3 and the insulator 4. The washer 5 is made of metal and has a Young's modulus of 70 to 220 GPa, for example, a metal mainly composed of aluminum, brass, copper, steel and alloys thereof.

図４に示すように点火プラグ７はそのハウジング雄螺子部７ａがガソリンエンジンのシリンダヘッド９に形成された雌螺子部にねじ込まれて、先端がシリンダ内に貫通する状態でシリンダヘッド９に装着される。圧力センサ６を構成する座金５、絶縁体４、電極３、感圧体２、電極３、絶縁体４、座金５はこの順序でハウジング座面７ｂとシリンダヘッド９の取付面９ｂとの間に挟み込まれ、所定の締め付けトルクで固定される。 As shown in FIG. 4, the spark plug 7 is mounted on the cylinder head 9 with its housing male screw portion 7a screwed into a female screw portion formed in the cylinder head 9 of the gasoline engine, with its tip penetrating into the cylinder. The The washer 5, the insulator 4, the electrode 3, the pressure sensitive body 2, the electrode 3, the insulator 4, and the washer 5 constituting the pressure sensor 6 are arranged in this order between the housing seat surface 7b and the mounting surface 9b of the cylinder head 9. It is sandwiched and fixed with a predetermined tightening torque.

図１の本発明の圧力検出回路の動作は次のとおりである。
圧力に応じてその抵抗値が変化する圧力センサ６に定電流源１１で一定電流を流し込むことによって前記抵抗値を電圧Ｖ１に効率良く変換し、この圧力によって変化する電圧Ｖ１の変化分のみをコンデンサ１２によって増幅器１３に入力し、増幅器１３によって増幅された信号電圧が出力電圧ｅ１として圧力変化信号となる。 The operation of the pressure detection circuit of the present invention shown in FIG. 1 is as follows.
The constant current source 11 feeds a constant current into the pressure sensor 6 whose resistance value changes according to the pressure, thereby efficiently converting the resistance value into the voltage V1. Only the change in the voltage V1 that changes due to the pressure is converted into a capacitor. 12, the signal voltage input to the amplifier 13 and amplified by the amplifier 13 becomes the pressure change signal as the output voltage e1.

(実施例)
第１の粒子として絶縁性セラミックスであるα‐Ｓｉ_３Ｎ_４粉末（宇部興産製、型番：E１０、平均粒径０．５μｍ）を３８．０ｇ、第２の粒子として導電性のＣ粉末（高純度化学製、型番：ＣＣＥ０１ＰＡ）を３．０ｇ、焼結助剤としてＡｌ_２Ｏ_３（高純度化学製、型番：ＡＬＯ０５ＰＡ）を６．０ｇ、Ｙ_２Ｏ_３（高純度化学製、型番：ＹＹＯ０１ＰＡ）を３．０ｇ秤量し、エタノール中でボールミル混合を２４時間行った。得られたスラリーを乾燥後、Φ３６ｍｍの金型を用い、１００ＭＰａの圧力を加えて、Φ３６ｍｍ、厚さ１０ｍｍの成形体を作製し、次いで、焼結温度１６５０℃、保持時間２時間、加圧力３０ＭＰａ、窒素雰囲気中で、成形体をホットプレスで焼結した。 (Example)
As the first particles, 38.0 g of α-Si ₃ N ₄ powder (made by Ube Industries, model number: E10, average particle size 0.5 μm), which is an insulating ceramic, is used as the second particles. 3.0 g of purity chemical, model number: CCE01PA), 6.0 g of Al ₂ O ₃ (made by high purity chemical, model number: ALO05PA) as a sintering aid, Y ₂ O ₃ (made by high purity chemical, model number: YYO01PA) ) Was weighed and ball mill mixed in ethanol for 24 hours. After drying the obtained slurry, using a Φ36 mm mold, a pressure of 100 MPa was applied to produce a molded body having a Φ36 mm and a thickness of 10 mm, and then a sintering temperature of 1650 ° C., a holding time of 2 hours, and an applied pressure of 30 MPa. In a nitrogen atmosphere, the compact was sintered with a hot press.

得られた焼結体から、外径Φ１９.０ｍｍ、内径Φ１４．０ｍｍ、厚さ２．０ｍｍの円環形状体を切り出し感圧体２を作製した。次いで、感圧体２の上面と底面に外径Φ１９.０ｍｍ、内径Φ１４．０ｍｍ、厚さ０．５ｍｍの両面にロウ材を塗布した円環形状のＣｕ片を配設して電極３，３を形成し、さらに、各電極部３，３の上面と底面に外径Φ１９.０ｍｍ、内径Φ１４．０ｍｍ、厚さ１．０ｍｍのアルミナからなる絶縁体４，４をそれぞれ配設し、さらに絶縁体４，４の上面と底面にロウ材を塗布して外径Φ１９.０ｍｍ、内径Φ１４．０ｍｍ、厚さ２.０ｍｍのＡｌ製の座金５，５をそれぞれ配設し、７６５℃、真空度１０^−１Ｐａ以下、加圧力０.１ＭＰaの条件で１５分間キープしてロウ付けを行い、感圧体２、電極３、絶縁体４及び座金５を接合した。そして電極３にΦ０．３ｍｍのＣｕ線３４をスポット溶接で接合し、図３に示した構造の圧力センサ６を得た。上記ロウ材としては、田中貴金属製のＴＫＣ−５９１ペーストを使用した。得られた圧力センサ６の特性評価を行った。得られた結果を表１に示す。 From the obtained sintered body, an annular body having an outer diameter of Φ19.0 mm, an inner diameter of Φ14.0 mm, and a thickness of 2.0 mm was cut out to produce a pressure-sensitive body 2. Next, an annular Cu piece having a brazing material applied on both sides of an outer diameter of Φ19.0 mm, an inner diameter of Φ14.0 mm, and a thickness of 0.5 mm is disposed on the upper surface and the bottom surface of the pressure-sensitive body 2 to provide electrodes 3 and 3. Furthermore, insulators 4 and 4 made of alumina having an outer diameter of Φ19.0 mm, an inner diameter of Φ14.0 mm, and a thickness of 1.0 mm are disposed on the top and bottom surfaces of the electrode parts 3 and 3, respectively. A brazing material is applied to the top and bottom surfaces of the bodies 4 and 4, and Al washers 5 and 5 having an outer diameter of Φ19.0 mm, an inner diameter of Φ14.0 mm, and a thickness of 2.0 mm are disposed, respectively. The pressure sensitive body 2, the electrode 3, the insulator 4 and the washer 5 were joined by keeping brazing for 15 minutes under conditions of 10 ⁻¹ Pa or less and a pressure of 0.1 MPa. A Cu wire 34 having a diameter of 0.3 mm was joined to the electrode 3 by spot welding to obtain the pressure sensor 6 having the structure shown in FIG. As the brazing material, TKC-591 paste made by Tanaka Kikinzoku was used. The characteristics of the obtained pressure sensor 6 were evaluated. The obtained results are shown in Table 1.

図４に示すように点火プラグ７（ＮＧＫ製：ＢＰＲ６ＥＳ）がシリンダヘッド９に形成された雌螺子部を貫通するように、圧力センサ６とともに単気筒400ccエンジン（ヤマハ製オートバイＳＲ４００）のシリンダヘッド９に組み付けた。この時のプラグの絞めつけトルクは、安全率を考慮し規定の締め付けトルクの２倍の５ｋｇｆ・ｍとした。このときにシリンダヘッド９の取付面９ｂに加わる面圧を感圧フィルム（フジフィルム製：プレスケール高圧用）を用いて計測したところ、約１６０ＭＰaであった。次いで圧力センサ６から取り出したリード線３ａ，３ａを測定回路に接続して特性を評価した。 As shown in FIG. 4, the cylinder head 9 of the single cylinder 400cc engine (Yamaha motorcycle SR400) is mounted together with the pressure sensor 6 so that the spark plug 7 (NGK: BPR6ES) penetrates the female screw portion formed in the cylinder head 9. Assembled. The tightening torque of the plug at this time was 5 kgf · m, which is twice the specified tightening torque in consideration of the safety factor. At this time, the surface pressure applied to the mounting surface 9b of the cylinder head 9 was measured using a pressure-sensitive film (manufactured by Fuji Film: for prescale high pressure) and found to be about 160 MPa. Next, the lead wires 3a, 3a taken out from the pressure sensor 6 were connected to a measurement circuit to evaluate the characteristics.

圧力センサ６の特性評価方法について説明する。エンジンを作動させて、得られた圧力センサの出力からシリンダの内圧を計測し、アイドリング時の信号出力とノイズの比率（以下ＳＮ比）を算出した。感圧体２の両端から出したリード線３ａ，３ａに図１に示す本発明の回路を接続し、本発明の回路の出力ｅ１をオシロスコープで観測評価した。エンジンを１時間連続で作動させた後、圧力センサを外して、その感圧体２のクラックの数を目視にて計測した。得られた結果を表１に示す。ＳＮ比は１１５と高い値が得られた。感圧体２にクラックは観察されなかった。 A method for evaluating the characteristics of the pressure sensor 6 will be described. The engine was operated, the internal pressure of the cylinder was measured from the output of the obtained pressure sensor, and the signal output to noise ratio (hereinafter referred to as SN ratio) during idling was calculated. The circuit of the present invention shown in FIG. 1 was connected to the lead wires 3a and 3a extending from both ends of the pressure sensitive body 2, and the output e1 of the circuit of the present invention was observed and evaluated with an oscilloscope. After the engine was operated continuously for 1 hour, the pressure sensor was removed, and the number of cracks in the pressure sensitive body 2 was visually measured. The obtained results are shown in Table 1. The S / N ratio was as high as 115. No cracks were observed in the pressure sensitive body 2.

図５にSi₃N₄-C系材料を用いた筒内圧センサの3000rpmにおける出力電圧ｅ１を時間に対してプロットしたグラフを示した。出力電圧が高くなるほど筒内圧が高いことを示している。図１からエンジンの吸気-圧縮に伴い圧力が増加し、点火−爆発でさらに圧力が増加、その後、排気によって圧力が減少する過程が確認できた。また、エンジンの回転数を800〜5000rpmの範囲で変化させると回転数に対応した波形が検出され、Si₃N₄-C系材料を用いた感圧素子により筒内圧を検出できることを確認した。 FIG. 5 shows a graph in which the output voltage e1 at 3000 rpm of the in-cylinder pressure sensor using the Si ₃ N ₄ —C material is plotted with respect to time. The higher the output voltage, the higher the in-cylinder pressure. From FIG. 1, it was confirmed that the pressure increased with the intake-compression of the engine, the pressure further increased with ignition-explosion, and then decreased with exhaust. Moreover, when the engine speed was changed in the range of 800 to 5000 rpm, a waveform corresponding to the engine speed was detected, and it was confirmed that the in-cylinder pressure could be detected by a pressure sensitive element using Si ₃ N ₄ -C material.

本発明の圧力検出素子と検出回路構成は機械的な強度が高いことからエンジンの圧力変化だけにとどまらず、機械構造物、建築構造物の圧力変化を検出して計測することも可能である。また、用途に応じて圧力感度を高めたり、機械強度を高めたりすることができる。そのため、エンジン以外の圧力例えばディーゼルエンジンのインジェクターに燃料を供給するコモンレールの圧力計測に適用可能であり、さらに、高圧タンクや高圧ボンベの変動水圧計測にも利用できる。 Since the pressure detection element and the detection circuit configuration of the present invention have high mechanical strength, it is possible to detect and measure not only the pressure change of the engine but also the pressure change of a mechanical structure or a building structure. In addition, pressure sensitivity can be increased or mechanical strength can be increased depending on the application. Therefore, it can be applied to pressure measurement other than the engine, for example, the pressure of a common rail that supplies fuel to an injector of a diesel engine, and can also be used to measure fluctuating water pressure in a high-pressure tank or a high-pressure cylinder.

本発明の圧力検出回路の検出原理を示す模式図である。It is a schematic diagram which shows the detection principle of the pressure detection circuit of this invention. 図１の圧力検出回路に用いる圧力センサの一部を構成する圧力検出素子の概略構成を示す斜視図である。It is a perspective view which shows schematic structure of the pressure detection element which comprises some pressure sensors used for the pressure detection circuit of FIG. 図１の圧力検出回路に用いる圧力センサの概略構成を示す斜視図である。It is a perspective view which shows schematic structure of the pressure sensor used for the pressure detection circuit of FIG. 図３の圧力センサが内燃機関であるエンジンに取り付けられた状態を示す斜視図である。It is a perspective view which shows the state in which the pressure sensor of FIG. 3 was attached to the engine which is an internal combustion engine. 図１の圧力検出回路および図４のようにエンジンに取り付けた圧力センサを用いて得られた出力波形である。5 is an output waveform obtained using the pressure detection circuit of FIG. 1 and a pressure sensor attached to the engine as shown in FIG. 従来の圧力検出回路の検出原理を示す模式図である。It is a schematic diagram which shows the detection principle of the conventional pressure detection circuit.

符号の説明Explanation of symbols

１圧力検出素子
２感圧体
３電極
３ａリード線
４絶縁体
５座金
６圧力センサ
７点火プラグ
１０圧力検出回路
１１定電流源
１２コンデンサ
１３増幅器
１４電圧源
DESCRIPTION OF SYMBOLS 1 Pressure detection element 2 Pressure sensitive body 3 Electrode 3a Lead wire 4 Insulator 5 Washer 6 Pressure sensor 7 Spark plug 10 Pressure detection circuit 11 Constant current source 12 Capacitor 13 Amplifier 14 Voltage source

Claims

印加する圧力に応じて電気抵抗が変化する圧力検出素子と、該圧力検出素子を定電流駆動する定電流源と、前記圧力検出素子に発生する電圧を取り出すことを特徴とする圧力検出回路。 A pressure detection circuit characterized by taking out a pressure detection element whose electric resistance changes according to an applied pressure, a constant current source for driving the pressure detection element at a constant current, and a voltage generated in the pressure detection element.

印加する圧力に応じて電気抵抗が変化する圧力検出素子と、該圧力検出素子を定電流駆動する定電流源と、前記圧力検出素子に発生する電圧をコンデンサの一端に供給し前記コンデンサの他端から取り出すことを特徴とする圧力検出回路。
A pressure detection element whose electrical resistance changes according to the applied pressure; a constant current source for driving the pressure detection element at a constant current; and a voltage generated in the pressure detection element is supplied to one end of the capacitor to supply the other end of the capacitor A pressure detection circuit, wherein the pressure detection circuit is taken out from the pressure sensor.