JP2007139397A - Glow plug with combustion pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce output variation of a combustion pressure sensor due to vibration or acceleration and delay of transfer of combustion pressure by installing a piezoelectric element in a front side of a fixing screw of a glow plug, reducing length and weight of a pressure carrier and solely using a sheath tube as a pressure transfer medium. <P>SOLUTION: In this glow plug with the combustion pressure sensor, the piezoelectric element 5 is arranged in a space formed between an end of the sheath tube 2 held inside a housing 1 and a combustion chamber side end part of an electrode 4. With accompanying generation of the combustion pressure of an internal combustion engine, the combustion pressure is approximately directly transferred to the piezoelectric element from the sheath tube. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a glow plug with a combustion pressure detection function that can be used as an auxiliary start device for an internal combustion engine such as a diesel engine and can detect a change in combustion pressure of the internal combustion engine.

  As this type of glow plug with a combustion pressure sensor, for example, a glow plug with a combustion pressure detection function described in JP-A-2004-278934 has been proposed. This includes a plug case, a glow plug main body held inside the plug case, and a combustion pressure detecting mechanism, and the glow plug main body includes a housing, a sheath member, a heater member, and a central shaft. The combustion pressure detection mechanism includes a piezoelectric element that converts an axial displacement generated in the housing and the middle shaft of the glow plug body into an electric signal due to a change in the combustion pressure of the internal combustion engine, and the piezoelectric element is an inward protruding portion of the plug case. Is formed between the case base end portion of the plug case and the middle shaft 6.

For example, in the glow plug with an ignition sensor described in Japanese Utility Model Publication No. 4-57056, an elastic member for pressing the piezoelectric element toward the sheath is an elastic member (bush) between the piezoelectric element and the support (bush). Spring) is installed.

Furthermore, in the glow plug with a combustion pressure sensor described in, for example, Japanese Patent Application Laid-Open Nos. 2002-327919 and 2004-124911, a piezoelectric element in which both the pressure transmission unit and the support unit are sandwiched by a rigid body is used. Proposed.
Japanese Utility Model Publication No. 4-57056 JP 2002-327919 A JP 2004-124911 A JP 2004-278934 A

  The problem to be solved is that, for example, in the prior art disclosed in Patent Document 2 to Patent Document 4 described above, the housing and the pipe member are fixed and further restrained because they are deformed minutely using the elastic force of the housing. Since the force is increased, the piezoelectric element is directly sandwiched between the rigid bodies and there is no pressurizing adjustment spring, the pressurization is likely to change due to the tightening of the glow plug and the thermal expansion of the housing and internal components. As a result, there is a problem that the output of the combustion pressure sensor with respect to the combustion pressure to be detected becomes small and the S / N ratio is large.

  Further, the conventional technique disclosed in Patent Document 1 has a problem in that the transmission of combustion pressure is delayed because the support of the piezoelectric element includes a spring.

  Further, in the prior art disclosed in Patent Document 2 to Patent Document 4 described above, since the piezoelectric element is arranged in the vicinity of the mounting screw of the glow plug, the length of the pressure transmission body becomes long. As a result, the vibration and acceleration sensitivity are increased, the S / N ratio of the combustion pressure sensor is large, and the combustion pressure is delayed.

The present invention has a cylindrical housing attached to the internal combustion engine so that one end side is located on the combustion chamber side of the internal combustion engine, and is held inside the housing so as to be exposed from the one end side of the housing, A sheath tube having one end exposed in the combustion chamber; a heating element provided in the sheath tube that generates heat when energized; and a portion that is housed in the housing so as to protrude from the other end of the housing; From a metal electrode rod that is electrically connected to the heating element and a piezoelectric element that detects the combustion pressure by transmitting a force acting on the sheath tube as the combustion pressure of the internal combustion engine is generated. In a glow plug with a combustion pressure sensor, comprising a combustion pressure sensor
The piezoelectric element is disposed in a space portion sandwiched between an end portion of the sheath tube held inside the housing and an end portion on the combustion chamber side of the electrode rod, and accompanying the generation of combustion pressure of the internal combustion engine , Being transmitted from the sheath tube almost directly to the piezoelectric element.

The housing of the present invention comprises two bodies, a front housing disposed on the combustion chamber side and a rear housing attached to the internal combustion engine, and the combustion pressure sensor is sandwiched between the front housing and the rear housing. It is arrange | positioned in the open space part.

The piezoelectric element of the present invention has a predetermined pressure through the sheath tube by a pressurizing spring housed between the inside of the step portion of the sheath tube held inside the housing and the inner diameter step portion of the housing. Is applied.

The material of the piezoelectric element of the present invention is a langasite crystal.

In the present invention, a tightening portion is formed on an outer peripheral surface near the other end of the housing, the tightening portion has a storage portion on an inner peripheral side, and an electric signal from the combustion pressure sensor is converted into the storage portion. And an amplifier to be amplified is housed.

The present invention is characterized in that the clearance between the inner diameter surface of the housing and the outer diameter surface of the sheath tube is held flexible and airtight by a seal member.

  In the glow plug with a combustion pressure sensor of the present invention, since the piezoelectric element is installed on the front side of the mounting screw of the glow plug, the length of the pressure transmission body can be shortened and reduced in weight, and the pressure transmission medium is only a sheath tube. The fluctuation in the output of the combustion pressure sensor due to vibration and acceleration can be reduced, and the delay in the transmission of the combustion pressure can also be reduced.

In addition, since the pressurized spring is not included in the combustion pressure transmission path (the pressurized spring and the piezoelectric element are mechanically parallel to the pressure transmission direction), there is no delay in combustion pressure, glow plug tightening and housing And the change in the pressurization due to the thermal expansion of the internal parts is reduced, and the clearance between the inner diameter surface of the housing and the outer diameter surface of the sheath tube is held flexibly and airtightly by the seal member. Since the restraint force in the combustion pressure transmission axis direction can be reduced, the sensitivity is improved and the combustion pressure output is less susceptible to fluctuations due to vibration and thermal expansion, the combustion pressure transmission accuracy is stabilized, and the S / N ratio is improved. .

  Further, since the piezoelectric element is installed in front of the glow plug mounting portion, a storage portion is formed on the inner peripheral side of the tightening portion formed on the outer peripheral surface near the other end of the housing, and the combustion pressure sensor is connected to the storage portion. By storing an amplifier that converts and amplifies the electrical signal, the unit can be miniaturized.

Furthermore, the piezoelectric element is closer to the combustion chamber side than the conventional glow plug with a combustion pressure sensor, so higher heat resistance is required. However, a Langasite crystal having a high Curie point of 1200 ° C. or higher should be used. Can be used without any problem.

  FIG. 1 is an overall longitudinal sectional view of a glow plug with a combustion pressure sensor of the present invention. A cylindrical housing (1) attached to the internal combustion engine so that one end side is positioned on the combustion chamber side of the internal combustion engine, and held inside the housing so as to be exposed from one end side of the housing, and one end side is the combustion chamber An exposed sheath tube (2), a heating element (3) provided in the sheath tube and generating heat when energized, and being housed in the housing so that a part protrudes from the other end of the housing, It consists of an electrically conductive metal electrode rod (4) and a piezoelectric element (5) for detecting the combustion pressure by transmitting the force acting on the sheath tube as the combustion pressure of the internal combustion engine is generated. A glow plug with a combustion pressure sensor comprising a combustion pressure sensor (6), wherein the piezoelectric element is sandwiched between the end of the sheath tube held inside the housing and the end of the electrode rod on the combustion chamber side Placed in an open space It is, with the generation of combustion pressure of the internal combustion engine is substantially transmitted directly to the piezoelectric element from the sheath tube.

In this embodiment, the housing (1) is composed of two bodies, a front housing (7) disposed on the combustion chamber side and a rear housing (8) attached to the internal combustion engine. It arrange | positions in the space part pinched | interposed by the front housing and the rear housing. However, of course, the housing may be integrated, and more than two bodies may be provided depending on the ease of incorporation of the combustion pressure sensor.

The piezoelectric element (5) is passed through the sheath tube by a pressurizing spring (9) housed between the stepped inner side of the sheath tube (2) held inside the housing (1) and the inner diameter stepped portion of the housing. A specified pressure is applied, and the material used is a langasite crystal such as langasite, langate, langanite.

Further, a tightening portion (10) is formed on the outer peripheral surface in the vicinity of the other end of the housing (1), the tightening portion has a storage portion (11) on the inner peripheral side, and the combustion pressure sensor (6) in the storage portion. An amplifier (12) that converts and amplifies an electrical signal from the housing is housed, and a gap between the contact portion between the inner diameter surface of the housing and the outer diameter surface of the sheath tube (2) is, for example, a metal foil of 10 μm to 100 μm, for example It is held in a flexible and airtight manner by a seal member (13) using inconel, precipitation hardening type SUS, or the like.

1 is an overall longitudinal sectional view of a glow plug with a combustion pressure sensor of the present invention. It is a fragmentary sectional view near the combustion pressure sensor part of the glow plug with a combustion pressure sensor of the present invention. It is a fragmentary sectional view of the rear end part vicinity of the glow plug with a combustion pressure sensor of this invention. It is a fragmentary sectional view of the seal member vicinity of the glow plug with a combustion pressure sensor of this invention. It is a fragmentary sectional view of the seal member vicinity of the glow plug with a combustion pressure sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Housing 2 Sheath tube 3 Heating element 4 Electrode rod 5 Piezoelectric element 6 Combustion pressure sensor 7 Front housing 8 Rear housing 9 Pressurizing spring 10 Tightening part 11 Storage part 12 Amplifier 13 Sealing member 14 Insulating sleeve 15 Ring 16 Sleeve 17 Spring 18 Lid 19 Rubber washer 20 Insulating ring 21 Nut 22 Electrode film 23 Metal foil 24 Tapered ring

Claims (6)

A cylindrical housing (1) attached to the internal combustion engine so that one end side is located on the combustion chamber side of the internal combustion engine, and held inside the housing so as to be exposed from the one end side of the housing, A sheath tube (2) having one end exposed in the combustion chamber, a heating element (3) provided in the sheath tube and generating heat when energized, and a part projecting from the other end of the housing. The metal electrode rod (4) that is housed and electrically connected to the heating element, and the force acting on the sheath tube with the generation of the combustion pressure of the internal combustion engine is transmitted. In a glow plug with a combustion pressure sensor, comprising a combustion pressure sensor (6) comprising a piezoelectric element (5) for detecting the combustion pressure,
The piezoelectric element is disposed in a space portion sandwiched between an end portion of the sheath tube held inside the housing and an end portion on the combustion chamber side of the electrode rod, and accompanying the generation of combustion pressure of the internal combustion engine A glow plug with a combustion pressure sensor, wherein the glow plug is transmitted almost directly from the sheath tube to the piezoelectric element. The housing (1) includes two bodies, a front housing (7) disposed on the combustion chamber side and a rear housing (8) attached to the internal combustion engine. The combustion pressure sensor includes the front housing and the 2. The glow plug with a combustion pressure sensor according to claim 1, wherein the glow plug is disposed in a space sandwiched between the rear housing. The piezoelectric element (5) is provided by a pressurizing spring (9) accommodated between a step portion inside of the sheath tube (2) held inside the housing (1) and an inner diameter step portion of the housing. The glow plug with a combustion pressure sensor according to claim 1 or 2, wherein a specified pressure is applied through the sheath tube. The glow plug with a combustion pressure sensor according to claim 1, wherein the material of the piezoelectric element (5) is made of a langasite crystal. A tightening portion (10) is formed on the outer peripheral surface in the vicinity of the other end of the housing (1), the tightening portion has a storage portion (11) on the inner peripheral side, and the combustion pressure sensor ( 6. A glow plug with a combustion pressure sensor according to claim 1, wherein an amplifier (12) for converting and amplifying the electric signal from 6) is housed. The gap between the contact portions between the inner diameter surface of the housing (1) and the outer diameter surface of the sheath tube (2) is held in a flexible and airtight manner by the seal member (13). 5. A glow plug with a combustion pressure sensor according to 5.