JP2005344943A - Glow plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug incorporating a pressure sensor without increasing a cross-sectional area of a through hole. <P>SOLUTION: This glow plug 10 capable of being mounted on the through hole 13 penetrated through an engine head 14 and facing a combustion chamber 12, comprises a housing 23 screwed and fixed to a wall of the engine head 14 defining the through hole 13, an axis 34 partially projecting into the combustion chamber 12 and fixed in the housing 23, a heat generating member 36 mounted on the projecting part, and a pressure sensor 40 having a diaphragm 42 and detecting the pressure acting on the diaphragm. The axis 34 is provided with a hollow space 38 extended from a combustion chamber 12 side to an anti-combustion chamber side. The combustion chamber 12 side of the hollow space 38 is communicated with the combustion chamber 12, and the anti-combustion chamber side is sealed by the diaphragm 42. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glow plug (starting auxiliary device) used for an internal combustion engine. More particularly, the present invention relates to a glow plug incorporating a combustion pressure sensor for measuring the combustion pressure of an internal combustion engine.

There is a need to measure the combustion pressure of internal combustion engines such as diesel engines. If the combustion pressure can be measured, the measured value can be used for feedback control of the fuel supply device and the internal combustion engine, which is expected to be effective for reducing fuel consumption and purifying exhaust gas.
On the other hand, this type of internal combustion engine has a problem that it is difficult to secure a space for installing the combustion pressure sensor in the engine head. Therefore, a glow plug having a combustion pressure sensor provided in the glow plug housing has been developed, and the glow plug is described in Non-Patent Document 1.
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  The glow plug described in Non-Patent Document 1 is a glow plug that is attached to a through hole that penetrates the engine head and faces the combustion chamber, and is a substantially cylindrical housing that is fixed to the wall of the engine head that defines the through hole. It has. A central shaft provided with a sheath tube in which a heat generating coil is embedded on the combustion chamber side is fixed in the housing, and a part thereof projects into the combustion chamber. Further, in this housing, a combustion pressure introduction hole is formed extending from the combustion chamber side to the anti-combustion chamber side in parallel with the axial direction of the central shaft. The central shaft and the pressure introduction hole are formed in a positional relationship that is offset when the through hole is viewed in cross section. A combustion pressure sensor is provided on the side of the combustion pressure introduction hole opposite to the combustion chamber. The combustion pressure propagates through the combustion pressure introduction hole and is detected by a combustion pressure sensor.

In the above glow plug, when the through hole is viewed in cross section, the center shaft and the combustion pressure introduction hole are formed in a positional relationship in which they are offset. For this reason, the cross-sectional area of the through hole must be made larger by the space required to form the combustion pressure introducing hole. Due to the increased cross-sectional area, the volume of the concave portion of the through hole on the combustion chamber side (the through hole existing between the attached glow plug and the combustion chamber) increases. This adds extra volume to the combustion chamber. Due to the added volume, the ignitability of the combustion gas, the effect of spreading the flame, and the like are deteriorated, resulting in a situation in which the combustion efficiency is lowered.
On the other hand, if the hole diameter of the combustion pressure introduction hole is made small so as to suppress the above situation, the speed at which the combustion pressure propagates becomes slow and the responsiveness decreases, or unburned components accumulate in the combustion pressure introduction hole. However, the problem that errors are gradually superimposed on the measured combustion pressure becomes prominent. Therefore, when the structure in which the pressure introduction hole is provided separately from the central shaft is employed, there is a problem that the additional volume increases.
The present invention was created in view of the above problems. That is, an object of the present invention is to provide a glow plug in which a pressure sensor is incorporated without increasing the cross-sectional area of the through hole.

The glow plug embodied in the present invention is a glow plug that can be attached to a through hole that penetrates the engine head and faces the combustion chamber. The glow plug includes a support member having a portion fixed to the wall of the engine head that defines the through hole and a portion protruding into the combustion chamber. A heating member is provided at the protruding portion of the support member. Further, the glow plug has a diaphragm and is provided with a pressure sensor for detecting a pressure acting on the diaphragm. A hollow space extending from the combustion chamber side to the anti-combustion chamber side is formed in the protruding portion. The combustion chamber side of the hollow space communicates with the combustion chamber, and the anti-combustion chamber side is sealed with a diaphragm. The diaphragm only needs to be present between the hollow space of the support member and the pressure sensor, and may be formed directly on the support member, as a member of the pressure sensor, or The configuration, shape, and the like are not particularly limited, such as when formed on another member other than the support member and the pressure sensor. In short, it is only necessary to seal the hollow space of the support member.
The fixing portion and the protruding portion of the support member may be configured by separate members. For example, the fixed part is a housing or the like, and the protruding part is a center shaft or the like provided with a heat generating member at the tip.
Typical examples of the pressure sensor used in the present invention include a piezoelectric type pressure sensor in which an electric charge generated by a distortion of a piezoelectric element due to an applied force changes, and a piezoelectric type due to an applied force. Piezoresistive type pressure sensor in which resistance value of resistance element changes, capacitive type pressure sensor in which the distance between a pair of electrode plates changes due to applied force, or deformation due to applied force Mention may be made of a pressure sensor that detects the quantity with light.

In the above glow plug, the combustion pressure in the combustion chamber propagates through the hollow space of the support member, and deforms the diaphragm provided on the anti-combustion chamber side. In conjunction with the deformation of the diaphragm, the piezoelectric element and the piezoresistive element provided in the pressure sensor are distorted, or when an electrode plate is provided, the combustion pressure can be measured by changing the distance. . That is, the hollow space of the support member of the present invention functions as a combustion pressure introduction hole. And this hollow space is formed in the protrusion part in which the heat generating member is provided.
In a conventionally known glow plug, the protruding portion where the heat generating member is provided and the combustion pressure introducing hole are formed in an offset positional relationship when the through hole is viewed in cross section. Therefore, the cross-sectional area of the through hole has to be increased.
In the present invention, the protruding portion provided with the heat generating member and the hollow space (combustion pressure introducing hole) are formed coaxially when the through hole is viewed in cross section. The function of introducing the combustion pressure is also used in the protruding portion where the heat generating member is provided. Therefore, the cross-sectional area of the through hole does not increase.
By adopting the configuration of the present invention, a glow plug incorporating a pressure sensor can be obtained without increasing the cross-sectional area of the through hole.

The protruding portion is preferably formed of a substantially cylindrical insulating ceramic, and the insulating ceramic is preferably embedded with a conductive ceramic constituting the heat generating member.
A current is passed through the conductive ceramic, whereby the conductive ceramic generates heat and functions as a heat generating member that ignites the combustion gas. Further, this projecting portion has a feature that it is easy to mold because it uses ceramic as a material. The projecting portion of the present invention has succeeded in providing both the functions of a substantially cylindrical shape and a heating member at the same time by using ceramic as a material.

It is preferable that the hollow space communicates with the combustion chamber on the side surface of the protruding portion.
The projecting portion of the present invention has both a function of having a combustion pressure introducing hole for propagating the combustion pressure and a function of surely igniting the combustion gas, which is the original function of the glow plug. Is preferred.
Since the hollow space communicates with the combustion chamber at the side surface of the protruding portion, the hollow space is not formed at the tip portion of the protruding portion on the combustion chamber side. Therefore, a sufficient heat generating member can be provided at the tip, and a sufficient heat generation amount can be ensured. Therefore, the combustion gas can be reliably ignited. At the same time, the combustion pressure propagates through the hollow space from its side and can act accurately on the diaphragm. A protruding part having both functions can be obtained.

  The glow plug of the present invention can incorporate a pressure sensor without increasing the cross-sectional area of the through hole.

The main features of the examples will be described.
(Embodiment) The combustion pressure sensor preferably uses a semiconductor piezoresistive element. The combustion pressure sensor is reduced in size, and the combustion pressure sensor can be accommodated in the glow plug housing. Therefore, the middle shaft and the combustion pressure sensor are arranged in a straight line along the axis of the through hole. The cross-sectional area of the through hole can be reduced. A recess (additional volume) on the combustion chamber side of the through hole can be reduced.

Embodiments will be described in detail below with reference to the drawings.
First Embodiment FIG. 1 schematically shows a cross-sectional view of a glow plug 10 according to a first embodiment. It should be noted that this cross-sectional view describes only the main components and the shape is deformed.
The left side of the figure is a combustion chamber 12, and a glow plug 10 is attached to a through hole 13 that penetrates the engine head 14 and is desired in the combustion chamber 12.
The glow plug 10 includes a substantially cylindrical housing 23 (an example of a fixing portion) that is screwed and fixed to a wall of the engine head 14 that defines the through hole 13 by a screw coupling portion 29. An end portion of the housing 23 on the combustion chamber 12 side has a tapered surface 22 processed into a tapered shape. Corresponding to the shape of the tapered surface 22, a stepped surface 24 is formed on the inner wall of the engine head 14. When the housing 23 is screwed and fixed in the through hole 13, the tapered surface 22 and the stepped surface 24 are brought into close contact with each other, thereby preventing the combustion gas in the combustion chamber 12 from leaking to the outside.

A middle shaft 34 (an example of a projecting portion) is fixed in the cylindrical housing 23, and a part of the tip of the middle shaft 34 projects into the combustion chamber 12. A protective metal pipe 32 is fixed to the center shaft 34 by brazing (or press-fit), and the housing 23 is fixed to the metal pipe 32 by brazing (or press-fit). Has been. If the middle shaft 34 and the metal pipe 32 are evaluated as a single unit, it can be evaluated that the middle shaft 34 is fixed to the housing 23 (the middle shaft 34 and the housing 23 can be evaluated as a single support member. The middle shaft 34 and the housing 23 may be formed of a single member.) Further, since the space between the housing 23 and the metal pipe 32 and the space between the metal pipe 32 and the middle shaft 34 are all fixed, it is possible to prevent the combustion gas in the combustion chamber 12 from leaking to the outside.
The middle shaft 34 is an insulating ceramic and has a cylindrical shape. A conductive ceramic heating member 36 is embedded on the combustion chamber 12 side. The heat generating member 36 is also formed in a cylindrical shape. In either case, silicon nitride (SiN) having excellent corrosion resistance is used as a material.
The middle shaft 34 is cylindrical and has a hollow space 38 extending from the combustion chamber 12 side to the anti-combustion chamber side. The hollow space 38 communicates with the combustion chamber 12 at the tip of the middle shaft 34. The anti-combustion chamber side of the hollow space 38 is sealed from the outside with a diaphragm 42. In addition, this diaphragm 42 is comprised as one member of the combustion pressure sensor 40 demonstrated later.

FIG. 2 is a perspective view of a main part near the tip of the middle shaft 34 on the combustion chamber 12 side. This perspective view is shown as a cross-section in which a part is cut out and a part of the hollow space 38 is exposed.
As shown in FIG. 2, the center shaft 34 of this embodiment is cylindrical, and a hollow space 38 is formed therein. Compared with the conventional central shaft, the overall size is almost the same. The middle shaft 34 of the present embodiment can be evaluated as having a hollow space 38 formed on the conventional middle shaft.
Moreover, the hole diameter of the hollow space 38 can ensure a hole diameter sufficient for propagating the combustion pressure even when the strength of the middle shaft 34 is taken into consideration. There is no problem that the speed at which the combustion pressure propagates is slowed down and the responsiveness is lowered, and the problem that the unburned components of the combustion gas are accumulated. Accurate combustion pressure can be measured.

Returning to FIG. A combustion pressure sensor 40 is fixed on the side of the intermediate shaft 34 opposite to the combustion chamber via a substantially cylindrical sensor housing 27 fixed to the housing 23.
The combustion pressure sensor 40 includes a metal diaphragm 42, a heat insulating rod 43, a hemisphere 44, a piezoresistive element 45, a hermetic terminal 46, and an inner housing 47 containing these components. The diaphragm 42 seals the hollow space 38 of the middle shaft 34. The thermal insulating rod 43 is for suppressing the influence of heat in the combustion chamber 12 mainly on the piezoresistive element 45 and converting the pressure applied to the diaphragm 42 into force. The hemisphere 44 is for uniformly transmitting the force applied to the hemisphere 44 to the piezoresistive element 45. The piezoresistive element 45 is a material whose resistance value changes due to an applied force, and for example, a silicon semiconductor is used. The hermetic terminal 46 is fixed to the inner housing 47 by brazing (or press-fitted) to ensure airtightness, and a connection terminal for taking out an input / output signal of the combustion pressure sensor 40 is provided.
As described above, the size of the central shaft 34 itself is not different from that of the conventional one. Therefore, the size of the cross-sectional area of the through hole 13 does not change regardless of whether or not the combustion pressure sensor 40 is incorporated in the glow plug 10.

An insulator shaft 52 is provided on the side opposite to the combustion chamber from the combustion pressure sensor 40. The insulator shaft 52 is made of, for example, workable ceramic or sealing glass.
A deep dish-shaped housing portion is formed on the side of the housing 23 opposite to the combustion chamber, and an insulating bush 54 and a heater connector and a sensor connector (not shown) are formed therein. The shape of the accommodating portion is not particularly limited, and a circular shape, a polygonal shape, or the like can be adopted. The inside of the housing 42 is closed from the outside by the insulating bush 54 to ensure airtightness.
A heater wire 66 is introduced from the outside toward the heat generating member 36 over the inside of the housing 23 via a heater connector (not shown). By applying current to the heater wire 66, the heat generating member 36 is heated. Further, the current passing through the heat generating member 36 is electrically led to the engine head 12 through the metal pipe 32.
A sensor input line 62 and a sensor output line 64 are introduced across the interior of the housing 23 toward the hermetic terminal 46 of the combustion pressure sensor 40 via a sensor connector (not shown). The other ends of the sensor input / output lines 62 and 64 are connected to the connection terminal of the Herme terminal 46. The sensor input / output lines 62 and 64 are connected to a combustion pressure detection circuit (not shown), and the combustion pressure detection circuit is connected to a control circuit. Based on the result of the combustion pressure detected by the combustion pressure detection circuit, the control circuit feedback-controls, for example, an injector or the like.

Next, the operation of measuring the combustion pressure using this glow plug will be described with reference to FIGS.
The combustion pressure in the combustion chamber 12 propagates through the hollow space 38 of the middle shaft 34 and acts on the diaphragm 42 provided on the anti-combustion chamber side. A deflection stress is applied to the diaphragm 42 according to the magnitude of the combustion pressure, and the diaphragm 42 is distorted by an amount corresponding to the combustion pressure. When the diaphragm 42 is distorted, compressive stress is applied to the heat insulating rod 43 and the hemisphere 44 disposed behind the diaphragm 42, and the piezoresistive element 45 is distorted according to the compressive force. Since the resistance value of the piezoresistive element 45 varies according to the amount of distortion, the variation in the resistance value is detected as a voltage value, and the combustion pressure is measured from the detected voltage value.

In the glow plug described above, the hollow space 38 is formed in the middle shaft 34, so that the function as a combustion pressure introducing hole is also used in addition to the function of igniting the combustion gas in the middle shaft 34 itself. Therefore, unlike the conventional structure, no pressure introduction hole is provided separately from the central shaft, and the cross-sectional area of the through hole 13 does not increase. In other words, it can be evaluated that the hollow space 38 (combustion pressure introduction hole) is formed in the cross-sectional area of the intermediate shaft 34 using the existing intermediate shaft 34, and the cross-sectional area of the through hole 13 is increased. There is nothing.
Further, the structure of this embodiment is extremely simple compared to the conventional structure. In the conventional structure, since the structure is complicated, such as providing a combustion pressure introducing hole separately, it has been difficult to prevent combustion gas leakage. In this embodiment, even if the hollow space 38 is formed in the middle shaft 34, the diaphragm 42 can easily prevent combustion gas from leaking.

Second Embodiment FIG. 3 schematically shows a cross-sectional view of the glow plug 110 of the second embodiment. It should be noted that this cross-sectional view describes only the main components and the shape is deformed. Further, the present embodiment is different from the first embodiment only in the structure of the central shaft 134. Therefore, description of components other than the central shaft 134 is omitted.
The middle shaft 134 of this embodiment is an insulating ceramic, and the shape thereof is substantially cylindrical. A conductive ceramic heating member 136 is embedded on the combustion chamber 12 side. In either case, silicon nitride (SiN) having excellent corrosion resistance is used as a material.
The middle shaft 134 is substantially cylindrical and has a hollow space 138 extending from the combustion chamber 112 side to the anti-combustion chamber side. The hollow space 138 is connected to a hollow hole 137 formed on the side surface of the central shaft 134. The hollow hole 137 is formed closer to the combustion chamber 112 than the metal pipe 132 that protects the central shaft 134 in a round. Therefore, the hollow space 138 of the central shaft 134 is connected to the combustion chamber 112 via the hollow hole 137. It is communicated to.

FIG. 4 is a perspective view of a main part in the vicinity of the tip of the middle shaft 134 on the combustion chamber 112 side. This perspective view is shown as a cross section in which a part is cut away and a part of the hollow space 138 is exposed.
As shown in the figure, the central shaft 134 of this embodiment is substantially cylindrical, and a hollow space 138 is formed therein, and the hollow space 138 communicates with the combustion chamber 112 through a hollow hole 137 on the side surface. .
The combustion pressure can propagate through the hollow space 138 from the hollow hole 137 and act on the diaphragm 142 on the anti-combustion chamber side. In addition, the hole diameter of the hollow space 138 can ensure a sufficient hole diameter for propagating the combustion pressure even if the strength is taken into consideration, and the speed at which the combustion pressure propagates becomes slow, resulting in a decrease in responsiveness. In addition, there is no problem of accumulation of unburned components of the combustion gas.

By providing the hollow hole 137 on the side surface of the middle shaft 134, the amount of the heat generating member 136 embedded in the tip portion of the middle shaft 134 can be increased. Thereby, when a current is passed through the heat generating member 136, the amount of heat generated from the heat generating member 136 is increased, and the certainty of igniting the combustion gas can be increased.
Therefore, by adopting the configuration of the middle shaft 134, it is possible to effectively provide both the function of causing the combustion pressure to act accurately on the diaphragm and the function of reliably igniting the combustion gas.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

Sectional drawing of the glow plug of 1st Example is shown. The perspective view of the center axis | shaft of 1st Example is shown. Sectional drawing of the glow plug of 2nd Example is shown. The perspective view of the center axis | shaft of 2nd Example is shown.

Explanation of symbols

13: Through hole 14: Engine head 23: Housing 32: Metal pipe 34: Central shaft 36: Heat generating member 38: Hollow space 40: Combustion pressure sensor 42: Diaphragm 43: Thermal insulation rod 44: Hemisphere 45: Piezoresistive element 46: Herme Terminal 47: Inner housing 137: Hollow hole

Claims (3)

A glow plug that can be attached to a through hole that penetrates the engine head and faces the combustion chamber,
A support member having a portion fixed to the wall of the engine head that defines the through hole and a portion protruding into the combustion chamber;
A heat generating member provided at the protruding portion of the support member;
It has a diaphragm and is equipped with a pressure sensor that detects the pressure acting on the diaphragm.
In the protruding portion, a hollow space extending from the combustion chamber side to the anti-combustion chamber side is formed,
A glow plug characterized in that the combustion chamber side of the hollow space communicates with the combustion chamber and the anti-combustion chamber side is sealed with a diaphragm. The protruding portion is formed of a substantially cylindrical insulating ceramic,
2. The glow plug according to claim 1, wherein a conductive ceramic constituting the heat generating member is embedded in the insulating ceramic.   The glow plug according to claim 1, wherein the hollow space communicates with the combustion chamber on a side surface of the protruding portion.

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