JP5602026B2 - Pressure measurement glow plug - Google Patents

Description

  The present invention relates to a glow plug having the characteristics described in the preamble of claim 1. A glow plug of this kind is known from German Offenlegungsschrift 10 2004 044 727 A1 and has a pressure measuring device for measuring the pressure in the combustion chamber. Also called pressure measurement glow plug.

  In the glow plug known from DE 10 2004 044 727 A1, a bellows-shaped metal sealing thin film is arranged between the glow plug body and the heating rod, which is a combustion gas. Prevents it from exiting the combustion chamber through the plug housing. This metal sealing thin film can sufficiently withstand the temperature of the combustion gas in the combustion chamber, and can improve the axial mobility of the heating rod, so that the pressure in the combustion chamber reduces the heating rod's pressure. Via the pressure measuring device.

  The object of the present invention is to show a method by which the pressure in the combustion chamber can be measured more accurately using a glow plug.

  This object is achieved according to the invention by a glow plug having the features described in claim 1. Further advantageous further configurations of the invention are the subject matter of the dependent claims.

  Within the framework of the present invention, it has been recognized that the accuracy of pressure measurement in the combustion chamber using a pressure measuring device is limited by the natural vibration of the glow plug. A vibration absorber in the form of a ring or sleeve is arranged between the glow plug body and the heating rod, so that the natural vibration acting in the radial direction of the glow plug can be mitigated, thus improving the measurement accuracy. Can be made. Advantageously, the vibration damper can achieve not only the relaxation of the natural vibrations but also the transition of the natural vibrations to higher frequencies which are not easily excited and therefore have a small vibration amplitude.

  Vibration dampers made of perfluoroelastomer have good temperature resistance and advantageously have a lower coefficient of friction, so that the axial mobility of the heating rod in the glow plug housing is almost unaffected by the vibration damper. I do not receive it. Particularly suitable is perfluoro rubber. A sufficiently suitable perfluoro rubber is commercially available under the name Kalrez.

  In the glow plug of the present invention, the natural vibration having the amplitude in the radial direction can be relaxed in a particularly significant frequency range of 1 kHz to 20 kH, particularly 3 kHz to 5 kHz, and can be shifted to a higher frequency.

  The vibration damper is preferably formed as an O-ring. Surprisingly, this kind of simple strategy can obviously mitigate the natural vibration of the heating rod. Preferably, the vibration damper is arranged behind the sealing membrane when viewed from the combustion chamber side, so that the vibration damper is protected from the direct action of hot combustion gases by the sealing membrane. The sealing thin film is preferably made of metal and is formed, for example, as a bellows or corrugated tubular pressure measuring device.

  The natural vibration can be reduced particularly efficiently by virtue of the fact that the vibration damper is arranged at the antinode of the natural vibration. Preferably, the vibration dampers are arranged at the antinodes of the harmonics that act most strongly in the radial direction. Surprisingly, this is usually a 3rd or 4th natural vibration, so that the vibration damper acts on the antinodes of the 3rd or 4th natural vibration, causing the radial motion of the heating rod to vibrate. Can be mitigated particularly efficiently.

  Preferably, the vibration damper surrounds a narrow portion of the heating rod. Thereby, the heating rod is thicker on both sides of the narrowed part than the narrowed part itself. This is advantageous because the position of the vibration damper can be easily set. Preferably, the narrowed portion is limited on one side by a ring surface that is inclined with respect to the length direction of the heating rod. This makes it easier to slide the vibration damper. On the other side, the narrowed portion is preferably defined by a ring surface which is preferably perpendicular to the length direction of the heating rod. This vertical ring surface is advantageous because it forms a stopper for the vibration damper. In this case, the inclined surface is preferably present on the narrow portion side closer to one end of the heating rod.

  Preferably, the heating rod is surrounded by at least two vibration dampers. The advantage of this strategy is that the relaxation effect can be further enhanced. In particular, various natural vibrations can be efficiently mitigated by employing a plurality of vibration dampers. Preferably, the vibration damper is arranged at the strongest antinode of both harmonics acting in the radial direction.

  Within the framework of the present invention, the heating rod is not only understood to be the heated portion at the end on the combustion chamber side, but the entire rod that extends to the pressure measuring device in the housing tube is also a heating rod. Therefore, it is understood that the portion of the inner rod not surrounded by the housing tube, through which the heating member in the heated portion of the heating rod can be supplied with electric current, is also the heating rod. Is done.

  Further details and advantages of the invention are explained in the embodiments with reference to the attached drawings. In this case, equal and corresponding parts are denoted by the same reference numerals.

It is the figure which showed one Embodiment of the glow plug of this invention, and is sectional drawing partially. FIG. 2 is a detailed view of FIG. 1. FIG. 3 is another detailed view of FIG. 1. It is detail drawing of deformation | transformation embodiment. It is another embodiment of the glow plug of the present invention.

  The glow plug shown in FIGS. 1 to 3 includes a glow plug body 1 having a male screw 2 for screwing into a screw hole of a diesel engine, and a heating rod 3 that is movable in the axial direction in the glow plug body 1. The heating rod 3 has a heatable portion 3a having a smaller diameter, and this portion protrudes from the glow plug body 1, and in the illustrated embodiment, the heating rod 3 is opposite to the normal combustion chamber. The glow plug body 1 extends to the electronic circuit housing 4 at the end of the glow plug body 1.

  A heating rod 3 that can slide and move relative to the glow plug body 1 in the axial direction transmits the pressure in the combustion chamber of the diesel engine to a pressure measuring device (not shown). The greater the pressure in the combustion chamber, the more the heating rod 3 is pushed into the glow plug housing against the restoring force. The relative displacement of the heating rod 3 with respect to the glow plug body 1 by this pressure is preferably between 0.05 μm / bar and 0.25 μm / bar.

  In the illustrated embodiment, the pressure measuring device for measuring the combustion chamber pressure applied to the heating rod is arranged in the housing 4 and may have, for example, a piezoelectric sensor or a strain gauge for pressure measurement. . This pressure measuring device is a cylindrical portion of the glow plug body 1 and may be disposed in a portion in front of the casing 4 as viewed from the combustion chamber side.

  Between the glow plug body 1 and the heating rod 3, a metal sealing thin film 5 is arranged, which is formed as a bellows-like sealing member, which is particularly shown in the detailed view of FIG. It can be seen. The sealing thin film 5 protects the pressure measuring device so that the combustion gas in the combustion chamber does not act directly, but the heating tube 3 is relatively movable in the axial direction with respect to the glow plug body 1. .

  In order to reduce the radial vibration of the heating rod 3, a ring-shaped or sleeve-shaped vibration damper 6 is disposed between the glow plug body 1 and the heating rod 3. Both the glow plug body 1 is pressed. When the heating rod vibrates in the radial direction, the vibration damper is compressed and thus the vibration is mitigated. In order to achieve the greatest possible buffering effect, the vibration damper 6 is arranged at the harmonic antinodal point that acts most strongly in the radial direction. Usually this is the third or fourth order natural vibration of the heating rod 3.

  The vibration damper 6 is made of a perfluoroelastomer, especially perfluororubber, and has a temperature resistance exceeding 300 ° C., preferably a temperature resistance exceeding 320 ° C. Suitable materials are commercially available under the name Kalrez. In the simplest case, the vibration damper 6 can be formed as an O-ring.

  One embodiment of the vibration damper 6 can be seen in particular in the detailed view of FIG. Preferably, the heating rod 3 has a narrow portion, in which a vibration damper 6 is arranged. Due to the narrowed portion, the vibration damper 6 can be easily positioned at the time of manufacture.

  In order to provide better vibration damping, the heating rod 3 can be further surrounded by a second or further vibration damper 6. In such a case, these vibration dampers are preferably arranged at the antinode where the harmonics acting in the radial direction are strongest.

  As illustrated in FIG. 4, the vibration damper 6 may be placed on a bellows-like sealing thin film 6.

  In the illustrated embodiment, the sealing thin film 5 formed as a bellows is disposed in front of the glow plug male screw 2 when viewed from the combustion chamber side. Thereby, the screwing effect and the temperature influence of the material of the glow plug body 3 can be largely eliminated.

  FIG. 5 shows a further embodiment of the glow plug, in which a bellows-like sealing thin film 5 is arranged at the end of the glow plug body 1 on the combustion chamber side. In this embodiment, therefore, the vibration damper 6 is arranged behind the sealing thin film 5 when viewed from the combustion chamber side. A further difference from the embodiment in FIGS. 1 to 4 is that the outer sleeve of the heating rod 3 does not extend to the pressure measuring device 7. Therefore, in FIG. 5, the inner rod 3b of the heating rod 3 can be seen. The first vibration damper 6 is in the form of an O-ring and is arranged between the inner rod 3b of the heating rod 3 and the glow plug body 1, and the second vibration damper is around the bellows-like sealing thin film 5. Surrounding.

  The inner bar 3b is a conductor, which supplies current to the heating coil in the heatable part 3a of the heating rod 3. It is also possible to surround the inner bar 3b with a ceramic insulator, for example magnesium oxide or aluminum oxide, for electrical insulation. The grounding of the heating coil can be performed via the glow plug body 1 and outside the portion of the heating rod 3 protruding from the glow plug body 1.

  The signal of the pressure measuring device 7 is guided through the connection wiring of the electronic circuit in the housing 4. With the electronic circuit in the housing 4, the obtained signal can already be evaluated. However, this signal does not necessarily have to be evaluated in the glow plug, but may instead be transmitted directly to the engine control device.

DESCRIPTION OF SYMBOLS 1 Glow plug body 2 Male screw 3 Heating rod 3a Heatable part 3b Heating rod inner part 4 Housing rod 5 Sealing thin film 6 Vibration buffer 7 Pressure measuring device

Claims (13)

A glow plug for a diesel engine,
A glow plug body (1) having a male screw (2) for screwing into a screw hole of a diesel engine;
A heating rod (3) movable axially in the glow plug body (1) and projecting from the glow plug body (1);
A pressure measuring device (7) for measuring the combustion chamber pressure acting on the heating rod (3);
In a glow plug comprising a sealing thin film (5) disposed between the glow plug body (1) and the heating rod (3),
The heating rod (3) includes a narrowed portion, and has a thickness on both sides of the narrowed portion than the narrowed portion itself;
In order to reduce the radial vibration of the heating rod (3), a ring-shaped or sleeve-shaped vibration buffer made of perfluoroelastomer is provided between the glow plug body (1) and the heating rod (3). (6) is arranged ,
A glow plug characterized in that the vibration damper (6) surrounds the narrow portion of the heating rod (3) . The glow plug according to claim 1, wherein the vibration damper is an O-ring. The glow plug according to claim 1, wherein the perfluoroelastomer is perfluoro rubber. The glow plug according to any one of claims 1 to 3, wherein the vibration damper (6) is arranged at an antinode of a harmonic that acts most strongly in a radial direction. The glow plug according to claim 4, wherein the harmonic that acts most strongly in the radial direction is a third-order or fourth-order natural vibration. The glow plug according to any one of claims 1 to 5, wherein the vibration damper (6) is arranged behind the sealing thin film (5) when viewed from the combustion chamber side. Glow plug according to any one of the preceding claims, characterized in that the heating rod (3) is surrounded by at least two vibration dampers (6). 8. The glow plug according to claim 7, wherein the two vibration dampers (6) are arranged at the strongest antinodes of both harmonics acting in the radial direction. The glow plug according to claim 1, wherein the at least one vibration damper (6) has a higher elastic modulus in the radial direction than in the axial direction. The glow plug according to claim 1, wherein the sealing thin film is made of metal. The glow plug according to any one of claims 1 to 10, wherein the sealing thin film (5) forms a bellows or a corrugated tube. The heating rod (3) has an inner rod (3b) and a casing tube surrounding the inner rod (3b), and the casing tube is surrounded by the vibration damper (6). The glow plug according to any one of claims 1 to 11 , wherein: 13. A glow plug according to claim 12 , characterized in that the housing tube extends to the pressure measuring device (7).

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