JP2006010306A - Glow plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glow plug integrated with a pressure sensor measuring a combustion pressure without using elastic deformation of a housing itself. <P>SOLUTION: The glow plug is provided with substantially cylindrical housings 42 and 44 coupled to an inner wall defining a through hole, an inner shaft 20 slidably housed in the housings 42 and 44, the pressure sensor 50 fixed between a side of the inner shaft 20 opposite to a combustion chamber and the housings 42 and 44, and a support member 30 provided between the inner shaft 20 and the housings 42 and 44 to slidably support the inner shaft 20 along an axis. Combustion chamber side ends of the housings 42 and 44 are adhered to an inner wall of an engine head 12 when the glow plug 51 is attached to the through hole, and the support member 30 is provided with an inner shaft fixing members 33 and 35 fixed to the inner shaft 20, a housing fixing part (a protruding part 36) fixed to the housing 42, and straining parts 32 and 34 provided between the inner shaft fixing parts 33 and 35, and the housing fixing part to change axial distances between the inner shaft fixing parts 33 and 35, and the housing fixing part by elastically deforming. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a glow plug (starting auxiliary device) attached to 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.

For example, there is a demand for measuring the combustion pressure of an internal combustion engine such as a diesel engine. If the combustion pressure can be measured, it is possible to feedback control the fuel supply device, the internal combustion engine, etc. using the measured value, and it 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. In order to solve this problem, a technique for forming a combustion pressure sensor integrally with a glow plug has been developed, and this type of glow plug is described in Patent Document 1.
JP 2002-327919 A (refer to FIG. 1 of that publication)

FIG. 12 shows a cross section of a glow plug 251 in which the combustion pressure sensor disclosed in Patent Document 1 is incorporated. The glow plug 251 has a structure that can be attached to the engine head 212, and includes a housing 242, a middle shaft 220, a piezoelectric element 250, and the like. The glow plug 251 is screwed into a through hole 213 that passes through the engine head 212 and faces the combustion chamber 215.
The housing 242 has a substantially cylindrical shape and is coupled to an inner wall that defines the through hole 213 by using a screw portion 241. The middle shaft 220 is slidably accommodated in the housing 242. A heating coil (not shown) is built in the tip of the middle shaft 220 (on the left side in the drawing). The middle shaft 220 and the housing 242 are fixed at the fitting press-fit portion 218. The rear end (right side of the drawing) of the middle shaft 220 protrudes outward from the housing 242, and the nut 202 is screwed into that portion.
A ring-shaped piezoelectric element 250 and a ring-shaped insulating bush 204 are inserted between the housing 242 and the nut 202. A predetermined load is applied to the piezoelectric element 250 by tightening the nut 202 with a predetermined torque.
In a state where the combustion pressure is not applied to the glow plug 251, a voltage corresponding to the electric charge stored in the piezoelectric element 250 is output from the piezoelectric element 250. When the combustion pressure acts on the glow plug 251 from the front end side, the housing 242 is compressed in the axial direction in a region 216 between the fitting press-fit portion 218 and the screw portion 241 of the housing 242 based on the combustion pressure acting on the intermediate shaft 220. The middle shaft 220 is displaced to the anti-combustion chamber side. As a result, the load acting on the piezoelectric element 250 decreases, and the amount of charge stored in the piezoelectric element 250 varies. The fluctuation of the charge amount can be detected as a fluctuation of the voltage value. The combustion pressure can be measured by measuring this voltage fluctuation.

Since the glow plug 251 measures the combustion pressure using the elastic deformation of the housing 242 itself, the following improvements are required.
In the glow plug 251, combustion gas is prevented from entering between the outer periphery of the housing 242 and the inner periphery of the through hole 213 by bringing the tapered end surface 242 a of the housing 242 into close contact with the stepped surface 212 a of the through hole 213. The structure to be adopted is adopted.
However, in the glow plug 251, when the region 216 of the housing 242 is elastically deformed by the combustion pressure and contracts in the axial direction, the tapered surface 242a of the housing 242 and the stepped surface 212a of the through hole 213 are separated. If the shrinkage of the housing 242 is increased in order to obtain a large output, the tapered surface 242a of the housing 242 and the stepped surface 212a of the through hole 213 are greatly separated. If the shrinkage of the housing 242 is reduced so that the tapered surface 242a and the stepped surface 212a are not separated from each other, the sensitivity of the measured combustion pressure is lowered. Therefore, if a predetermined measurement sensitivity is to be maintained, a phenomenon in which the tapered surface 242a of the housing 242 and the stepped surface 212a of the through hole 213 are separated is unavoidable.
As a result, in the glow plug 251, when the combustion pressure acts and the region 216 of the housing 242 contracts in the axial direction and the tapered surface 242 a and the stepped surface 212 a are separated from each other, the outer periphery of the housing 242 and the inside of the through hole 213 Combustion gas permeates between the surroundings and accumulation of unburned components is unavoidable, resulting in deterioration of engine performance and failure. Further, if unburned components accumulate between the outer periphery of the housing 242 and the inner periphery of the through hole 213, the phenomenon that the housing 242 contracts in the axial direction in the region 216 due to the combustion pressure is prevented. When the glow plug 251 is used for a long time, an error is added to the measured value of the combustion pressure. In particular, if the measurement sensitivity is increased by causing the housing 242 to contract greatly due to a change in the combustion pressure, this problem becomes prominent.
The inventors of the present invention have focused on the fact that the above problem arises because the combustion pressure is measured using the elastic deformation of the housing itself in the prior art, and the present invention has been made.
An object of the present invention is to provide a glow plug integrated with a combustion pressure sensor in which the housing itself does not substantially elastically deform.

The present invention is embodied in a glow plug that passes through the engine head and is attached to a through hole that faces the combustion chamber.
The glow plug of the present invention is fixed between a housing having a substantially cylindrical shape coupled to an inner wall defining a through hole, a middle shaft slidably accommodated in the housing, and an anti-combustion chamber side of the middle shaft and the housing. The pressure sensor is provided.
The glow plug of the present invention further includes a support member that supports the middle shaft so as to be slidable along the axis. The supporting member is provided between the middle shaft and the housing. The middle shaft fixing portion fixed to the middle shaft, the housing fixing portion fixed to the housing, and the axial direction between the two by elastically deforming between the two. An elastic part for changing the distance is provided.
The housing is not substantially elastically deformed by the combustion pressure, and when the glow plug is attached to the through hole, the end of the housing on the combustion chamber side is kept in close contact with the inner wall of the engine head.
Typical examples of the central shaft used in the present invention include a member in which a heating coil is embedded in a sheath tube (an example of a metal glow plug), and a member in which a conductive ceramic and a lead wire are included in an insulating ceramic tube. (An example of a ceramic glow plug). Instead of the structure in which the heat generating member is built in the tip of the center shaft, the tip of the center shaft itself may be formed by the heat generating member.
The support member may be formed using a part of the housing. In the case where the support member is formed as a part of the housing, a member disposed between the housing constituting the outer shell and the center shaft can be evaluated as the support member. The support member and / or the housing may be composed of a plurality of members. Moreover, there is no restriction | limiting in particular regarding the number of support members, You may be 1 piece, 2 pieces or more.
Here, the elastic portion refers to a portion in which the elastic deformation is positively utilized in order to displace the central axis in parallel along the axis. The elastic characteristic of the elastic part along the axis is sufficiently soft with respect to the elastic characteristic of the housing. Therefore, when the combustion pressure is applied, the elastic portion preferentially elastically deforms without substantially elastically deforming the housing.
Typical examples of the pressure sensor used in the present invention include a piezoelectric type pressure sensor in which electric charges generated by distortion caused by an applied force change, and a resistance value changed by an applied force. Piezoresistive pressure sensor, capacitive pressure sensor that changes the distance between a pair of electrode plates due to applied force, and optical distance measurement that changes due to applied force A pressure sensor etc. can be mentioned.

When combustion pressure acts on the glow plug, the elastic portion provided on the support member is elastically deformed in the axial direction of the central shaft. That is, the axial distance between the middle shaft fixing portion fixed to the middle shaft and the housing fixing portion fixed to the housing changes. The elastic part of the support member provided between the housing and the middle shaft is elastically deformed, and the housing itself hardly undergoes elastic deformation. Thereby, the position of the middle shaft is displaced with respect to the housing. Since the pressure sensor is fixed between the housing and the center shaft, the position of the center shaft is displaced with respect to the pressure sensor. Thereby, the displacement amount of the center shaft can be measured from the output of the pressure sensor, and the combustion pressure can be measured from the displacement amount.
With the above glow plug, the combustion pressure can be measured with almost no elastic deformation of the housing itself. Therefore, when the glow plug is attached in the through hole, it is not necessary to finely adjust the insertion condition. By inserting it sufficiently tightly, the end of the housing on the combustion chamber side and the engine head can be brought into close contact with each other. The contact portion between the end of the housing and the inner wall of the engine head does not separate. Therefore, no unburned component is deposited between the outer periphery of the housing and the inner periphery of the through hole, and the deposit does not change the measured value of the combustion pressure. Even if the measurement sensitivity is increased by greatly displacing the central shaft, the end of the housing on the combustion chamber side and the engine head can be kept in close contact with each other.

In one glow plug of the present invention, a structure is used in which the center shaft is slidably supported using one support member. The support member includes a front-end-side middle shaft fixing portion fixed to the front-end side of the middle shaft, a housing-fixing portion fixed to the housing, a front-end side elastic portion between the two, and a rear-end side fixed to the rear end side of the middle shaft. An end side middle shaft fixing portion and a rear end side elastic portion between the housing fixing portion and the rear end side middle shaft fixing portion are provided. Note that the terms “front end side” and “rear end side” in the present specification indicate the relative positional relationship between the two. For example, it should be noted that the front end side of the middle shaft means that it exists on the front end side rather than what is called the rear end side, and does not indicate the front end of the middle shaft.
Since the housing fixing portion of the support member is constrained, when the combustion pressure is applied, the tip side elastic portion is elastically deformed based on the applied stress. As a result, the middle shaft slides toward the anti-combustion chamber. Since the rear end side elastic portion is also elastically deformed, sliding of the central shaft is not prohibited. At this time, since the middle shaft is supported at two positions on the front end side and the rear end side, it can slide while maintaining parallelism.
Also in this case, since the housing itself does not substantially elastically deform, the problem that the front end of the housing separates from the engine head is avoided. Accurate combustion pressure can be measured over a long period of time.

It is preferable that the front end side elastic portion includes a portion extending from the front end side middle shaft fixing portion toward the combustion chamber side. The front end side elastic part should just extend toward the combustion chamber side rather than the direction orthogonal to the central axis. The tip side elastic part should just extend in the angle range from the direction orthogonal to the middle axis to the direction parallel to the middle axis.
The support member is exposed to the flame during the combustion stroke of the internal combustion engine. It has been found by our studies that when the support member is exposed to a flame, it undergoes thermal expansion within a short time of the combustion process. Especially, the support member which exists in the combustion chamber side rather than the edge part by the side of the combustion chamber of a housing raise | generates thermal expansion toward the combustion chamber side, when exposed to a flame. Since the support member is connected to the center shaft via the distal end side center shaft fixing portion, when the support member undergoes thermal expansion, the center shaft moves toward the combustion chamber. For this reason, since the preload applied in advance to the pressure sensor is lost (or the initial state varies depending on the type of pressure sensor), the measured value of the pressure sensor based on the combustion pressure may deviate from the true value. I understand.
Therefore, a structure is adopted in which the tip side elastic portion constituting the support member includes a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side. When this structure is adopted, the tip side elastic portion tends to undergo thermal expansion toward the anti-combustion chamber within a short period of the combustion stroke. Therefore, the direction in which the support member other than the tip side elastic portion tries to cause thermal expansion and the direction in which the tip side elastic portion tends to cause thermal expansion are reversed and cancel each other. Therefore, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates during the combustion stroke is suppressed, and an accurate combustion pressure can be measured.

In the case where the tip side elastic portion includes a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side, it is preferable that the tip side elastic portion further includes a portion extending from the housing fixing portion toward the combustion chamber side. . That is, it is preferable that the tip side elastic portion has a structure that turns back toward the combustion chamber between the tip side middle shaft fixing portion and the housing fixing portion.
If this structure is adopted, the tip side elastic portion has a mechanical spring structure, so that it can be elastically deformed with high sensitivity to the combustion pressure. Therefore, not only the fluctuation of the preload (or the initial state of the pressure sensor) can be suppressed, but also the displacement amount of the central shaft based on the combustion pressure can be improved, and a highly sensitive pressure sensor can be obtained.

It is preferable that the rear end side elastic portion includes a portion extending from the rear end side middle shaft fixing portion toward the anti-combustion chamber side.
When the glow plug is energized, that is, when the middle shaft itself reaches a high temperature by the heater function, the middle shaft undergoes large thermal expansion. At this time, the present inventor is that the leading end side of the middle shaft is thermally expanded toward the combustion chamber side, and the rear end side of the middle shaft is thermally expanded toward the anti-combustion chamber side, with the substantial center of the middle shaft as a boundary. It has been understood by their research. In particular, if the rear end of the middle shaft undergoes thermal expansion toward the anti-combustion chamber, an additional load is added to the preload previously applied to the pressure sensor (or the initial state of the pressure sensor varies). It has been found that the measured value of the pressure sensor based on the combustion pressure deviates from the true value.
Therefore, a structure is adopted in which the rear end side elastic portion includes a portion extending from the rear end side middle shaft fixing portion toward the anti-combustion chamber. When this structure is adopted, at least the side near the rear end side middle shaft fixing portion of the rear end side elastic portion receives heat from the middle shaft when the glow plug is energized, and causes thermal expansion toward the combustion chamber side. Try to. That is, the direction in which the rear end side of the middle shaft attempts to cause thermal expansion is opposite to the direction in which the rear end side elastic portion attempts to cause thermal expansion. Thereby, the thermal expansion of the rear end side of the middle shaft is offset by the thermal expansion of the rear end side elastic portion. Therefore, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates when the glow plug is energized is suppressed, and an accurate combustion pressure can be measured.

The spring constant of the front end side elastic part is preferably smaller than the spring constant of the rear end side elastic part.
As described above, when the glow plug is energized, if the rear end side of the central shaft undergoes thermal expansion toward the anti-combustion chamber side, the true value of the pressure sensor based on the combustion pressure is shifted. If the tip side elastic part has a spring constant smaller than the spring constant of the rear end side elastic part, the tip side elastic part preferentially elastically deforms, so that the thermal expansion on the rear end side of the central shaft is caused by the combustion chamber. It comes to occur toward the side. Therefore, even when the glow plug is energized, even if the middle shaft thermally expands, the phenomenon that the preload (or the initial state of the pressure sensor) applied to the pressure sensor fluctuates is suppressed, and an accurate combustion pressure is suppressed. Can be measured.

The rear end side middle shaft fixing portion is preferably fixed to the rearmost end of the middle shaft.
Assuming that the rear end side middle shaft fixing portion is not fixed to the rearmost end of the middle shaft, when the middle shaft located at the rear end of the rear end side middle shaft fixing portion undergoes thermal expansion, the middle shaft is moved to the rear end. Preload applied to the pressure sensor in advance because the thermal expansion toward the anti-combustion chamber is more dominant than the expansion toward the combustion chamber because it is constrained by the side center shaft fixing portion. (Or the initial state of the pressure sensor) varies greatly.
In the present invention, by adopting a structure in which the rear end side middle shaft fixing portion is fixed to the rearmost end of the middle shaft, the rear end side middle shaft fixing portion is made to have no middle shaft at the rear end. Thereby, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates based on the expansion of the middle shaft is remarkably suppressed, and an accurate combustion pressure can be measured. .

It is preferable that the front end side middle shaft fixing portion makes a round around the middle shaft, the housing fixing portion rounds the housing, and the front end side elastic portion makes a round between them.
Since the distal end side middle shaft fixing portion is formed around the middle shaft, combustion gas is prevented from leaking from between the middle shaft and the support member. Since the housing fixing part goes around the housing, combustion gas is prevented from leaking between the middle shaft and the housing. Furthermore, the tip side elastic part is formed in a circle between them. As a result, the tip side elastic portion can be elastically deformed in a balanced manner along the axis of the central axis, and the central axis can be displaced in parallel in a balanced manner along the axis. Accurate combustion pressure can be measured.

Another blow plug of the present invention employs a structure that supports the center shaft using two support members. In this case, the front end side support member includes a front end side middle shaft fixing portion fixed to the front end side of the middle shaft, a front end side housing fixing portion fixed to the front end side of the housing, and a front end side elastic portion between them. have. The rear end side support member includes a rear end side middle shaft fixing portion fixed to the rear end side of the middle shaft, a rear end side housing fixing portion fixed to the rear end side of the housing, and a rear end side between the two. And an elastic portion.
In the above support member, the front-end side elastic portion and the rear-end side elastic portion are simultaneously compressed or stretched and elastically deformed to allow the middle shaft to slide. It may be compressed or expanded.
Since the front end side and the rear end side of the middle shaft are supported using the two support members, the middle shaft can be supported more stably in the through hole.
Also in this case, since the housing itself is not substantially elastically deformed, the problem that the front end of the housing is separated from the engine head is avoided. Accurate combustion pressure can be measured over a long period of time.

Even when two support members are used, it is preferable that the tip side elastic portion includes a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side.
When this structure is employed, the tip side elastic portion tends to thermally expand toward the anti-combustion chamber within a short period of the combustion stroke during the combustion stroke. Therefore, the direction in which the tip-side support member other than the tip-side elastic portion tries to undergo thermal expansion and the direction in which the tip-side elastic portion tries to cause thermal expansion are reversed and offset. Therefore, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates during the combustion stroke is suppressed, and an accurate combustion pressure can be measured.

When the two support members are used and the tip side elastic portion has a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side, the tip side elastic portion further moves from the housing fixing portion toward the combustion chamber side. It is preferable to have an extending part. In other words, it is preferable that the tip elastic portion has a structure that turns back toward the combustion chamber between the tip-side middle shaft fixing portion and the tip-side housing fixing portion.
When this structure is adopted, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates during the combustion stroke is suppressed, and the amount of displacement of the central shaft based on the combustion pressure is reduced. Can also be improved. A highly sensitive pressure sensor can be obtained.

Even when two support members are used, it is preferable that the rear end side elastic portion includes a portion extending from the rear end side middle shaft fixing portion toward the anti-combustion chamber side.
When this structure is adopted, when the glow plug is energized, the direction in which the rear end side of the central shaft tends to cause thermal expansion is opposite to the direction in which the rear end side elastic portion tends to cause thermal expansion. Thereby, the thermal expansion of the rear end side of the middle shaft is offset by the thermal expansion of the rear end side elastic portion. Therefore, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates when the glow plug is energized is suppressed, and an accurate combustion pressure can be measured.

Even when two support members are used, it is preferable that the spring constant of the front end side elastic portion is smaller than the spring constant of the rear end side elastic portion.
If the tip side elastic part has a spring constant smaller than the spring constant of the rear end side elastic part, the tip side elastic part preferentially elastically deforms, so that the thermal expansion on the rear end side of the central shaft is caused by the combustion chamber. It comes to occur toward the side. Therefore, even when the glow plug is energized, even if the middle shaft thermally expands, the phenomenon that the preload (or the initial state of the pressure sensor) applied to the pressure sensor fluctuates is suppressed, and an accurate combustion pressure is suppressed. Can be measured.

It is preferable that the front end side middle shaft fixing portion makes a round around the middle shaft, the front end side housing fixing portion rounds the housing, and the front end side elastic portion makes a round between them.
Since the distal end side middle shaft fixing portion is formed around the middle shaft, combustion gas is prevented from leaking from between the middle shaft and the support member. Since the distal-side housing fixing part makes a circuit around the housing, the combustion gas is prevented from leaking from between the middle shaft and the housing. Furthermore, the tip side elastic part is formed in a circle between the two. As a result, the tip side elastic portion can be elastically deformed in a balanced manner along the axis of the central axis, and the central axis can be displaced in parallel in a balanced manner along the axis. Accurate combustion pressure measurement is achieved.

Another glow plug of the present invention employs a structure in which the middle shaft fixing portion is formed on the side opposite to the combustion chamber from the substantial center of the middle shaft.
The phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates due to thermal expansion of the central shaft accompanying energization of the glow plug is caused by thermal expansion on the rear end side of the central shaft. Has been found to have a significant effect. The direction of thermal expansion occurs in each direction on the front end side and the rear end side with the portion constrained by the central shaft fixing portion as a boundary. The direction of thermal expansion of the central shaft on the rear end side occurs toward the rear end side. Therefore, if the middle shaft fixing portion is formed on the side opposite to the combustion chamber than the center of the middle shaft, the portion on the rear end side relative to the middle shaft fixing portion is relatively reduced. Therefore, the thermal expansion on the rear end side of the middle shaft is reduced, and the influence on the pressure sensor can be significantly reduced.

Another glow plug of the present invention employs a structure including a support member that slidably supports the center shaft with respect to the housing. The support member is fixed to either the middle shaft or the housing and supports the front end side of the middle shaft so as to be slidable with respect to the housing, and the rear member fixed to the rear end side of the middle shaft. An end side middle shaft fixing portion, a housing fixing portion fixed to the housing, and a rear end side elastic portion between the rear end side middle shaft fixing portion and the housing fixing portion are provided. The tip-side middle shaft support portion may be structured such that the tip-side middle shaft support portion and the middle shaft are in contact with each other and the tip-side middle shaft support portion and the housing are fixed, or the tip-side middle shaft support portion and the middle shaft are fixed. It is good also as a structure where the side center shaft support part and the housing are in contact. In the case of the structure in which the distal-side middle shaft support portion and the middle shaft are in contact with each other and the distal-side middle shaft support portion and the housing are fixed, the portion fixed to the housing by the distal-side middle shaft support portion may also serve as the housing fixing portion. .
When this structure is employed, even if the middle shaft undergoes thermal expansion, the tip end side of the middle shaft is not constrained, and therefore, thermal expansion of the middle shaft occurs toward the combustion chamber side. Therefore, even if the central shaft is thermally expanded, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates is remarkably suppressed, and an accurate combustion pressure can be measured. .

  According to the glow plug of the present invention, by adopting a configuration that does not use elastic deformation of the housing itself, the end portion of the housing on the combustion chamber side can be kept in close contact with the inner wall of the engine head, and the combustion gas flows into the housing. It is possible to prevent intrusion between the outer periphery and the inner periphery of the through hole. Accurate combustion pressure can be continuously measured even if the deposit is used for a long time without changing the sliding resistance of the central shaft.

First, the main features of the present invention are listed.
(First embodiment) As an example of the elastic portion, a structure in which a strain-generating portion having a smaller film thickness than the remaining portion is formed in the support member, or a structure in which the support member itself is formed in a diaphragm shape and is itself an elastic portion. Can be mentioned.
(2nd form) You may support a center axis | shaft back and forth by the combination of the support member which has an elastic part, and the member which supports a center axis | shaft so that sliding is possible.
(3rd form) In the 2nd form, it is preferable that the support member which has an elastic part is provided in the rear end side, and the member which supports a center axis | shaft so that sliding is possible is provided in the front end side. Since the thermal expansion of the central shaft can be preferentially generated toward the combustion chamber, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates can be suppressed and accurate. The correct combustion pressure can be measured.

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 51 according to a first embodiment. Note that this cross-sectional view describes only the main components, and the shape is deformed. The glow plug 51 is a type that supports the middle shaft 20 slidably with respect to the housing by using one support member 30.
The glow plug 51 is attached to a through hole 13 that penetrates the engine head 12 and is desired in the combustion chamber 15. The glow plug 51 includes a housing 42. The housing 42 is screwed to the inner wall of the through hole 13 using the screw coupling region 41. The housing 42 is formed in a substantially cylindrical shape, and a hollow space is formed therein. The housing 42 is formed in a shape along the inner wall of the through hole 13. The glow plug 51 includes a sensor housing 44 in the hollow space of the housing 42. The sensor housing 44 is screwed to the housing 42 using the screw coupling region 43. In the glow plug 51, the sensor housing 44 is formed of a member separate from the housing 42. However, the sensor housing 44 can be substantially evaluated as an integral part of the housing 42, and can be referred to as a housing.
The middle shaft 20 is slidably accommodated in the sensor housing 44. The tip of the middle shaft 20 protrudes into the combustion chamber 15. Although not shown in detail, a heater heating wire enclosed in an insulating ceramic is provided at the tip of the middle shaft 20. Furthermore, the middle shaft 20 includes a lead wire electrically connected to the heater heating wire, and the lead wire extends through the insulating ceramic toward the rear end side (the right side in the drawing). For the ceramic, silicon nitride (SiN) having good corrosion resistance is used. For example, a metal glow plug in which a heating coil is embedded in a sheath tube may be used for the middle shaft 20.

A pressure sensor 50 is fixed between the end of the middle shaft 20 on the side opposite to the combustion chamber and the sensor housing 44. As the pressure sensor 50, a type of sensor that uses a piezoresistance effect is used. The pressure sensor 50 includes a hemisphere 52 for receiving force evenly, a semiconductor piezoresistive element 54, and a sensor fixing member 56 for fixing to the sensor housing 44. The sensor fixing member 56 and the sensor housing 44 are fixed by brazing (or fitting press-fitting). The pressure sensor 50 is disposed along the axis of the middle shaft 20. The middle shaft 20 and the pressure sensor 50 are arranged so that their axes coincide when viewed in cross-section on a plane orthogonal to the axis of the middle shaft 20. Further, the pressure sensor 50 is accommodated in the hollow space of the housing 44, in other words, it can be said that the pressure sensor 50 is disposed in place of the middle shaft 20.
A support member 30 is provided between the middle shaft 20 and the sensor housing 44. The support member 30 will be described later in detail.

A deep dish-shaped storage portion is formed on the side of the housing 42 opposite to the combustion chamber. An insulating bush 62, a heater connector 72, and a sensor connector 74 are formed inside the housing portion. The shape of the accommodating portion is not particularly limited, and a circular shape, a polygonal shape, or the like can be adopted. It is preferable that a portion corresponding to the bottom of the deep dish of the housing portion is formed away from the engine head. The vibration from the engine head is not directly transmitted, and the vibration can be mitigated.
The hollow space of the housing 42 is closed from the outside by an insulating bush 62.
The heater wire 82 is introduced from the outside toward the middle shaft 20 via the heater connector 72. The heater wire 82 extends in the hollow space of the housing 42 and in an opening (not shown) formed in the sensor housing 44. The heater wire 82 is electrically connected to the rear end of the middle shaft 20. At the rear end of the middle shaft 20, a lead wire extends from the tip of the middle shaft 20, and the lead wire and the heater wire 82 are electrically connected.
A sensor input line 84 and a sensor output line 86 are introduced toward the pressure sensor 50 via the sensor connector 74. The sensor input / output lines 84 and 86 extend in the hollow space of the housing 42 and are connected to the connection terminal of the pressure sensor 50. The other ends of the sensor input / output lines 84 and 86 are connected to the pressure calculation circuit 92. Further, the combustion pressure calculated by the pressure calculation circuit 92 is input to the control circuit 94. The control circuit 94 performs feedback control of the injector, for example.

Next, the support member 30 will be described in detail. FIG. 2 schematically shows an enlarged cross-sectional view of the support member 30.
The periphery of the middle shaft 20 is protected by a metal pipe 22. The middle shaft 20 and the metal pipe 22 are fixed by brazing (or fitting press-fitting), and gas in the combustion chamber is prevented from leaking between the two. The metal pipe 22 can be evaluated as a part of the middle shaft 20. The metal pipe 22 is electrically conductive, and is also used as a path when a current flowing in the middle shaft 20 via the heater wire 82 is led out toward the engine head 12.
A taper-shaped protruding portion 36 that is tapered toward the combustion chamber 15 is formed at substantially the center of the support member 30. The protruding portion 36 is formed in a shape corresponding to the stepped surface 12a (see FIG. 1) formed on the inner wall of the engine head 12. Therefore, the tapered surface 36 a of the protruding portion 36 is closely fixed to the stepped surface 12 a of the engine head 12. Thereby, it is possible to prevent the combustion gas from entering between the outer periphery of the sensor housing 44 and the housing 42 and the inner periphery of the through hole 13.
The sensor housing 44 is in close contact with the surface opposite to the tapered surface 36a of the protrusion 36 (see FIG. 1). Therefore, the protruding portion 36 can be evaluated as a part of the sensor housing 44. It can also be expressed that the end of the sensor housing 44 is in close contact with the inner wall of the engine head 12. Further, the protruding portion 36 is also a housing fixing portion that fixes the support member 30 to the sensor housing 44.

The support member 30 is located at two locations on the front end side and the rear end side (the front end side and the rear end side along the axis of the intermediate shaft 20, and in this case, the left and right sides in the drawing) across the protrusion 36. The metal pipe 22 is fixed. Thereby, the middle shaft 20 is supported in parallel in the through hole. 33 in the figure is a front end side middle shaft fixing portion, and 35 in the figure is a rear end side middle shaft fixing portion. The middle shaft fixing portions 33 and 35 are fixed by brazing around the middle shaft 20. In particular, the front-end side middle shaft fixing portion 33 prevents combustion gas from leaking from between the metal pipe 22 and the support member 30. Accordingly, since the combustion gas leakage is prevented by the front end side middle shaft fixing portion 33 and the tapered projecting portion 36, the combustion gas does not leak from the support member 30 to the anti-combustion chamber side.
Further, since the metal pipe 22 is fixed at two locations on the front end side and the rear end side, the middle shaft 20 is stably supported in parallel along the axis.

The support member 30 is formed with a distal-side strain generating portion 32 (an example of a distal-end side elastic portion) having a smaller film thickness than the remaining portion between the distal-end-side middle shaft fixing portion 33 and the protruding portion 36. Further, a rear end side strain generating portion 34 (an example of a rear end side elastic portion) having a smaller film thickness than the remaining portion is formed on the support member 30 between the rear end side middle shaft fixing portion 35 and the protruding portion 36. . The distal end side strain generating portion 32 is formed in a circle between both the distal end side middle shaft fixing portion 33 and the protruding portion 36. The rear end side strain generating portion 34 is formed so as to make a round between the rear end side middle shaft fixing portion 35 and the protruding portion 36. Both the strain generating portions 32 and 34 have a thin cylindrical structure. Further, the strain generating portions 32 and 34 are formed to be thinner than the remaining portions in the parallel direction along the axis of the middle shaft 20.
A sensitivity adjustment region 38 having a larger film thickness than the rear end side strain generating portion 34 is formed in front of the rear end side strain generating portion 34. By adjusting the width L of the sensitivity adjustment region 38, the elastic coefficient (spring constant) in the axial direction of the rear end side strain generating portion 34 can be adjusted. For example, if the width L of the sensitivity adjustment region 38 is adjusted to be short, the width of the rear end side strain generating portion 34 is relatively increased, and the elastic strain in the axial direction of the rear end side strain generating portion 34 is increased. On the other hand, if the width L of the sensitivity adjustment region 38 is adjusted to be longer, the elastic strain in the axial direction of the rear end side strain generating portion 34 becomes smaller. In addition, it is preferable that the same structure is also formed in the front end side strain generating portion 32. The adjustable sensitivity range can be increased.

Next, the operation when the combustion pressure acts on the glow plug 51 will be described. FIG. 3 is a diagram showing, in a simplified manner, only a configuration that can exhibit an elastic action among the configurations shown in FIGS. 1 and 2. Referring to FIGS. 1, 2 and 3 at the same time, it is easy to understand the operation of the glow plug 51.
When the combustion pressure is applied to the middle shaft 20, the protrusion 36 of the support member 30 is constrained, so that stress is applied to the distal end side strain generating portion 32 on the distal end side. Since the distal end side strain generating portion 32 is formed thin in parallel with the axial direction, the distal end side strain generating portion 32 is compressed and elastically deformed. On the other hand, the rear end side strain generating portion 34 provided on the rear end side with respect to the protruding portion 36 extends along the axial direction and elastically deforms. Accordingly, the middle shaft 20 slides toward the anti-combustion chamber side in parallel with the axis. At this time, as shown in FIG. 3, the housing 42 and the sensor housing 44 are also elastically deformed in a strict sense, but this elastic strain is sufficiently smaller than the strain generating portions 32 and 34, It can be evaluated that it is not substantially elastically deformed.
Therefore, the middle shaft 20 greatly distorts the hemisphere 52 and the semiconductor piezoresistive element 54 of the pressure sensor 50. Corresponding to this distortion, the resistance value of the semiconductor piezoresistive element 54 varies, and this is measured as a variation in voltage value. The measured voltage value is input to the calculation circuit 92 and converted into a combustion pressure. The result of the combustion pressure is input to the control circuit 94, and the control circuit 94 adjusts the fuel injection timing and the injection amount of the injector based on the result.
As described above, in the present embodiment, by providing the support member 30, the center shaft 20 is preferentially displaced without substantially elastically deforming the housing 42 and the sensor housing 44. The housing 42 and the sensor housing 44 existing at the position along the axial direction of the middle shaft 20 from the contact portion between the tapered surface 36a of the projecting portion 36 and the stepped surface 12a of the engine head 12 are not elastically deformed. The front-end-side strain-generating portion 32 and the rear-end-side strain-generating portion 34 provided between 20 are elastically deformed, thereby successfully displacing the middle shaft 20. Since the housing 42 and the sensor housing 44 are not elastically deformed, the contact portion between the tapered surface 36a of the projecting portion 36 and the stepped surface 12a of the engine head 12 is not separated. Therefore, unburned components do not accumulate between the outer periphery of the housing 42 and the sensor housing 44 and the inner periphery of the through hole 13, and the deposit does not change the measured value of the combustion pressure. By using the glow plug 51 in which the pressure sensor 50 is incorporated, an accurate combustion pressure can be measured over a long period of time.

The above embodiment has the following other features.
(1) Compared to the conventional method of measuring the combustion pressure using the elastic deformation of the housing, if the elastic deformation of the strain generating portions 32 and 34 is used as in the present embodiment, the displacement of the central shaft 20 The amount increases, and the combustion pressure can be measured with high sensitivity.
(2) Since the sensor housing 44 is interposed between the housing 42 and the pressure sensor 50, the vibration of the engine head 12 transmitted to the pressure sensor 50 is well mitigated, and noise is reduced.
(3) When the glow plug 51 is installed in the through hole 13, it is inserted sufficiently tightly to strengthen the adhesion to the engine head 12, and a preload is applied to the housing 42 and the sensor housing 44 itself. No preload is applied to the strain generating portions 32, 34 of the support member 30. Accurate combustion pressure can be measured. Further, by suppressing the rattling of the housing 42 and the sensor housing 44 itself, a more accurate combustion pressure can be measured.
(4) By adopting the pressure sensor 50 in which the semiconductor piezoresistive element 54 is used, the pressure sensor 50 is miniaturized, and the pressure sensor 50 has been successfully accommodated in the through hole 13. Therefore, the middle shaft 20 is configured shorter than the conventional structure. Thereby, the vibration of the middle shaft 20 itself is suppressed, and the noise is reduced from being superimposed on the measurement value.
Further, the above embodiment may be the following modification.
There may be only one of the strain generating portions instead of the two on the front end side and the rear end side. In this case, it is preferable to have a structure in which the other middle shaft fixing portion supports the metal pipe so as to be slidable. As a result, the middle shaft can be slidably supported along the axis without inhibiting the elastic deformation of one of the strain-generating portions. In addition, it is preferable to provide the structure which supports a metal pipe so that sliding is possible in the front end side. In this case, even if the central shaft undergoes thermal expansion, the thermal expansion of the central shaft occurs toward the combustion chamber. Therefore, even if the central shaft is thermally expanded, the phenomenon that the preload (or the initial state of the pressure sensor) previously applied to the pressure sensor fluctuates is suppressed, and an accurate combustion pressure can be measured.

Moreover, the following modification can also be employ | adopted for a supporting member.
FIG. 4 schematically shows a cross-sectional view of a support member 30 </ b> A as a modification of the support member. Although an overall view of the glow plug of the modified example provided with the support member 30A is not shown, if the support member 30 shown in FIG. 1 is replaced with the support member 30A, an overall view of the glow plug of the modified example is obtained.
In the support member 30 </ b> A, the distal end side strain generating portion 32 </ b> A extends from the distal end side middle shaft fixing portion 33 toward the combustion chamber side. Further, the rear end side strain generating portion 34A extends from the rear end side middle shaft fixing portion 35 toward the anti-combustion chamber side. The support member 30A can reduce (1) the influence of the movement of the middle shaft 20 based on the flame of the combustion stroke by providing the front end strain generating portion 32A, and (2) energize the glow plug by providing the rear end strain generating portion 34A. This is useful in that the influence of thermal expansion of the middle shaft 20 due to can be reduced.
Regarding the effect of (1) Of the support member 30A, the distal-side strained portion 32A, the first thick portion 37A, the thin portion 37B, and the second portion located on the combustion chamber side of the tapered surface 36a of the protrusion 36. The thick portion 37C is exposed toward the combustion chamber. Therefore, the tip side strain generating portion 32A, the first thick portion 37A, the thin portion 37B, and the second thick portion 37C are exposed to a flame due to combustion during the combustion stroke of the internal combustion engine. As a result, the distal-side strained portion 32A, the first thick portion 37A, the thin portion 37B, and the second thick portion 37C undergo thermal expansion due to a temperature increase based on the flame within a short period of the combustion stroke.
Of the support member 30A, the first thick portion 37A, the thin portion 37B, and the second thick portion 37C, especially the thin portion 37B, cause thermal expansion toward the combustion chamber within a short period of the combustion stroke. On the other hand, the tip side strain generating portion 32A extends from the tip side middle shaft fixing portion 33 toward the combustion chamber side, so that the tip side strain generating portion 32A causes thermal expansion toward the anti-combustion chamber side. That is, the direction in which the first thick portion 37A, the thin portion 37B, and the second thick portion 37C other than the tip side strain generating portion 32A undergo thermal expansion (combustion chamber side direction), and the tip side strain generating portion 32A is heated. The direction in which expansion occurs (the direction opposite to the combustion chamber) is the reverse direction.
FIG. 5 shows sensor output characteristics. The vertical axis is the sensor output, and the horizontal axis is the crank angle. The sensor output of the present embodiment is a solid line 18. A case where the tip side strain generating portion 32A does not extend from the tip side middle shaft fixing portion 33 toward the combustion chamber side is taken as a comparative example, and the sensor output is a broken line 17. As shown by the broken line 17 in FIG. 5, during the combustion stroke, the first thick portion 37A, the thin portion 37B, and the second thick portion 37C other than the tip side strained portion 32A are thermally expanded, particularly the thin portion 37B. As the center shaft 20 moves toward the combustion chamber, the preload previously applied to the pressure sensor 50 is lost, and the combustion pressure is measured to be smaller than the true value. It turns out that it cannot measure. On the other hand, when the tip strained portion 32A is provided, as shown by the solid line 18, the phenomenon that the preload is lost is suppressed, and an accurate combustion pressure can be measured.
Regarding Effect of (2) When the glow plug 51 is energized, that is, when the middle shaft 20 itself reaches a high temperature by the heater function, the middle shaft 20 undergoes thermal expansion. At this time, with the substantial center of the middle shaft 20 as a boundary, the front end side of the middle shaft 20 is thermally expanded toward the combustion chamber side, and the rear end side of the middle shaft 20 is thermally expanded toward the anti-combustion chamber side. In particular, when the rear end side of the middle shaft 20 undergoes thermal expansion toward the anti-combustion chamber side, an additional load is added to the preload previously applied to the pressure sensor 50, so that the measurement of the pressure sensor 50 based on the combustion pressure is performed. The value deviates from the true value.
The support member 30A shown in FIG. 4 includes a rear end side strain generating portion 34A and a thicker portion 39A on the side opposite to the combustion chamber than the rear end side strain generating portion 34A. Since the thick portion 39A is provided, a temperature difference is generated between the thick portion 39A and the rear end side strain generating portion 34A. Further, since the rear end side strain generating portion 34A extends from the rear end side middle shaft fixing portion 35 toward the anti-combustion chamber side, the rear end side strain generating portion 34A has the center shaft when the glow plug 51 is energized. It receives heat from 20 and tries to cause thermal expansion toward the combustion chamber. That is, the direction in which the rear end side of the middle shaft 20 attempts to cause thermal expansion (the anti-combustion chamber side) is opposite to the direction in which the rear end side strain generating portion 34A attempts to cause thermal expansion (the combustion chamber side). Thereby, the thermal expansion of the rear end side of the middle shaft 20 and the thermal expansion of the rear end side strain generating portion 34A are offset. Therefore, when the glow plug 51 is energized, an additional increase in the preload previously applied to the pressure sensor 50 is suppressed, and an accurate combustion pressure can be measured.
Although the tip side strain generating portion 32A shows an example extending in parallel to the middle shaft 20, the tip elastic portion 32A extends toward the combustion chamber rather than the direction orthogonal to the middle shaft 20. That's fine. The tip elastic portion 32 </ b> A may be inclined and extended with respect to the middle shaft 20 in an angle range from a direction orthogonal to the middle shaft 20 to a direction parallel to the middle shaft 20.
In addition, although the rear end strained portion 34 </ b> A also shows an example extending in parallel to the middle shaft 20, the rear end elastic portion 34 </ b> A extends toward the anti-combustion chamber rather than the direction orthogonal to the middle shaft 20. It only has to be. The rear end elastic portion 34 </ b> A may be inclined and extended with respect to the middle shaft 20 in an angle range from a direction orthogonal to the middle shaft 20 to a direction parallel to the middle shaft 20.

FIG. 6 schematically shows a cross section of a support member 30B as another modification of the support member.
The support member 30B includes a first front end side strain generating portion 32B extending from the front end side middle shaft fixing portion 33 toward the combustion chamber side, and a second front end side strain generating portion 32C extending from the protruding portion 36 toward the combustion chamber side. ing. That is, the first front end side strain generating portion 32B and the second front end side strain generating portion 32C form a structure that is folded back toward the combustion chamber between the front end side middle shaft fixing portion 33 and the projecting portion 36.
When this structure is employed, the combined structure of the first tip side strain generating portion 32B and the second tip side strain generating portion 32C functions as a mechanical spring structure. For this reason, the composite structure of the first front end side strain generating portion 32B and the second front end side strain generating portion 32C can be elastically deformed with high sensitivity to the combustion pressure.
Furthermore, the length L2 of the first tip side strain generating portion 32B and the length L1 of the second tip side strain generating portion 32C in the axial direction of the middle shaft 20 are formed longer in the first tip side strain generating portion 32B. . Therefore, thermal expansion in the axial direction of the middle shaft 20 of the composite structure of the first tip side strain generating portion 32B and the second tip side strain generating portion 32C occurs toward the anti-combustion chamber side. Since this thermal expansion is offset between the thermal expansion of the second thick portion 37C toward the combustion chamber, it is possible to suppress the loss of preload. The combined structure of the first front end side strain generating portion 32B and the second front end side strain generating portion 32C can suppress suppression of preload loss, and can also improve the amount of displacement of the central shaft 20 based on the combustion pressure. A highly sensitive pressure sensor 50 can be obtained.
The rear end side strain generating portion 34 </ b> B extends from the rear end side middle shaft fixing portion 35 in a direction orthogonal to the middle shaft 20. In this case, as compared with the rear end side strain generating portion 34A shown in FIG. 4, the displacement amount of the central shaft 20 with respect to the combustion pressure can be increased, and a highly sensitive pressure sensor can be obtained.

FIG. 7 schematically shows a cross section of a support member 30C as another modification of the support member.
The support member 30C is an example in which the rear end side strain generating portion 34B shown in FIG. 6 is changed. The rear end side strain generating portion 34C of the support member 30C extends from the rear end side middle shaft fixing portion 35 toward the anti-combustion chamber side while being inclined with respect to the axis of the middle shaft 20.
The rear end side strain generating portion 34C of the support member 30C has an effect of suppressing an additional increase in preload applied in advance to the pressure sensor 50 when the glow plug 51 is energized, and the center shaft 20 against the combustion pressure. Since both the effects of increasing the displacement amount are provided in a well-balanced manner, an extremely useful pressure sensor can be obtained.

FIG. 8 shows another modification of the glow plug 51. Referring to the structure shown in FIG. 1, it is easy to understand the structure of this modification. In this modification, the rear end side middle shaft fixing portion 35 is fixed to the rearmost end of the middle shaft 20. Although the rear end side middle shaft fixing portion 35 is not shown in FIG. 8, the positional relationship can be understood with reference to FIG. In the modification of FIG. 8, a structure in which the middle shaft 20 does not exist on the rear end side with respect to the rear end side middle shaft fixing portion 35 is employed.
When the middle shaft 20 located on the rear end side with respect to the rear end side middle shaft fixing portion 35 undergoes thermal expansion, the middle shaft 20 is restrained by the rear end side middle shaft fixing portion 35, so that the expansion toward the combustion chamber side is performed. However, thermal expansion toward the anti-combustion chamber side is more likely to occur. For this reason, an additional load is added to the preload previously applied to the pressure sensor 50.
In the modification of FIG. 8, by adopting a structure in which the rear end side middle shaft fixing portion 35 is fixed to the rearmost end of the middle shaft 20, the middle shaft 20 does not exist on the rear end side of the rear end side middle shaft fixing portion 35. can do. For this reason, the influence regarding the thermal expansion of the rear end side middle shaft 20 relative to the rear end side middle shaft fixing portion 35 is eliminated, and the phenomenon that the preload applied in advance to the pressure sensor 50 is additionally increased is remarkably suppressed. Is done.
In the case of the modification of FIG. 8, it is preferable to adopt the structure of the central shaft shown in FIG. FIG. 9 shows a cross-sectional structure of the middle shaft 20. In the middle shaft 20 shown in FIG. 9, a ring-shaped metal electrode 25 extends in the middle shaft 20 along the axis of the middle shaft 20. The periphery of the metal electrode 25 is surrounded by an insulating ceramic 24. A heater wire 82 extending from the outside is connected to the metal electrode 25. By adopting this structure, the heater wire 82 can be connected to the metal electrode 25 exposed from the rear end surface of the middle shaft 20.

Second Embodiment FIG. 10 schematically shows a cross-sectional view of a glow plug 151 according to a second embodiment. It should be noted that this cross-sectional view describes only the main components and the shape is deformed. The glow plug 151 is a type in which two support members are provided on the front end side and the rear end side along the axis of the middle shaft.
The glow plug 151 is attached to a through hole 113 that penetrates the engine head 112 and is desired in the combustion chamber 115. The glow plug 151 includes a housing 142. The housing 142 is screwed to the inner wall of the through hole 113 using the screw coupling region 141. The housing 142 is formed in a substantially cylindrical shape and has a hollow space therein. The housing 142 is formed in a shape along the inner wall of the through hole. A tapered surface 142a that is tapered toward the combustion chamber 115 is formed at the end of the housing 142 on the combustion chamber 115 side. The tapered surface 142a is in close contact with the stepped surface 112a of the opposing engine head 112.
A central shaft is slidably accommodated in the hollow space of the housing 142. For convenience, the middle shaft will be described by distinguishing it from a front-side middle shaft 122, a center-side middle shaft 124, and a rear-end side middle shaft 129. A ceramic glow plug type heat generating member 120 is formed at the tip of the middle shaft. The heat generating member 120 protrudes into the combustion chamber 115.

  The glow plug 151 includes a diaphragm-like front end side support member 133. The distal-side support member 133 includes a distal-side intermediate shaft fixing portion 133a that is fixed to the distal-side intermediate shaft 122, a distal-side housing fixing portion 133c that is fixed to the distal-end side of the housing 142, a distal-side intermediate shaft fixing portion 133a, and a distal-side housing fixing portion. A diaphragm-like distal end side elastic portion 133b extending between the two portions 133c is provided. The distal end side support member 133 can be elastically deformed by applying a bending stress to the distal end side elastic portion 133b.

A deep dish-shaped storage portion is formed on the side of the housing 142 opposite to the combustion chamber. Insulation bushings 162 and 164, a heater connector 130, and a pressure sensor 150 are formed inside the housing portion. The insulating bushings 162 and 164 and the heater connector 130 are formed in an annular shape so as to surround the pressure sensor 150. The insulating bushings 162 and 164 are formed between the heater connector 130 and the housing 142 to achieve insulation and relaxation of vibration.
The heater connector 130 is formed to extend in the hollow space of the housing 142 and is locked by a locking portion 126 formed on the central central shaft 124. Further, the heater connector 130 is screwed to the central central shaft 124 using a screw coupling portion 135 (an example of a rear end side central shaft fixing portion). As a result, the heater connector 130 and the middle shaft are electrically connected. Further, the heater connector 130 is fixed to the housing 142 by using an screw bushing portion 143 (an example of a rear end side housing fixing portion) with an insulating bush 162 interposed therebetween. Thereby, in combination with the distal end side support member 133 on the distal end side, it is possible to stably support the central axis in parallel along the axis. From this, the heater connector 130 can be evaluated as a rear end support member in the sense of supporting the middle shaft.
Further, a strain generating portion 134 (an example of a rear end side elastic portion) having a thickness smaller than that of the remaining portion is formed in the heater connector 130. The strain generating portion 134 is formed in a round in a plane orthogonal to the axis. The strain generating portion 134 has a thin cylindrical structure. The strain generating portion 134 is formed thin along the axial direction. The width of the strain generating portion 134 can be freely adjusted by processing the remaining portion around it. The strain generating portion 134 extends from the screw coupling portion 135 toward the anti-combustion chamber side.

A pressure sensor 150 is fixed between the end of the middle shaft on the side opposite to the combustion chamber and the heater connector 130. The pressure sensor 150 is supported by the heater connector 130 via the insulating member 166. The pressure sensor 150 is a type of sensor that uses the piezoresistive effect, and includes a hemisphere 152, a semiconductor piezoresistive element 154, and a sensor fixing member 156. The sensor fixing member 156 is fixed to the insulating member 166 by brazing (or press fitting). A heat insulating member 157 made of zirconia is interposed between the middle shaft and the hemisphere 152 of the pressure sensor 150.
The pressure sensor 150 is disposed along the axis of the middle axis. The pressure sensor 150 and the central axis are arranged so that their axes coincide when viewed in cross-section on a plane orthogonal to the axis.

A heater wire 182 is connected to the heater connector 130. As a result, the current supplied from the heater wire 182 can energize the heating member 120 via the heater connector 130 and the center shaft.
A sensor input line 184 and a sensor output line 186 are connected to the connection terminal of the pressure sensor 150. The other ends of the sensor input / output lines 184 and 186 are connected to the pressure calculation circuit 192. Further, the combustion pressure calculated by the pressure calculation circuit 192 is input to the control circuit 194. The control circuit 194 controls an injector (not shown).

Next, the operation when the combustion pressure acts on the glow plug 151 will be described. FIG. 11 is a simplified view of only the configuration that can exhibit an elastic action among the configurations shown in FIG. 10. Referring to both FIG. 10 and FIG. 11, it is easy to understand the operation of the glow plug 151.
When the combustion pressure acts on the heat generating member 120 and the middle shaft, the distal end side housing fixing portion 133c of the distal end side support member 133 is restrained, so that the diaphragm-like distal end side elastic portion 133b is elastically deformed. At the same time, compressive stress is applied to the strain generating portion 134, and the strain generating portion 134 is compressed in parallel along the axis. Therefore, the central axis is greatly displaced in parallel along the axis.

On the other hand, in the housing 142, the screw coupling portion 141 is constrained, and a compressive stress is applied to the distal end side, but the elastic coefficient of the housing 142 is extremely higher than the elastic coefficients of the distal end side elastic portion 133b and the strain generating portion 134. Since it is large, it is considered that it hardly deforms elastically. Therefore, the contact portion between the tapered surface 142a and the stepped surface 112a of the engine head 112 is prevented from separating.
Since the housing 142 on the rear end side with respect to the screw coupling portion 141 is not elastically deformed, the heater connector 130 fixed through the screw coupling region 143 on the rear end side is hardly displaced. Therefore, the pressure sensor 150 is hardly displaced. As a result, the central shaft is displaced significantly with respect to the pressure sensor 150. Therefore, the rear end side middle shaft 129 greatly distorts the hemisphere 152 and the semiconductor piezoresistive element 154 of the pressure sensor 150. Corresponding to this distortion, the resistance value of the semiconductor piezoresistive element 154 varies, and this is measured as a variation in voltage value.
The measured voltage value is input to the calculation circuit 192 and converted into the combustion pressure. The result of the combustion pressure is input to the control circuit 194, and the control circuit 194 adjusts the fuel injection timing and the injection amount of the injector based on this result.

The above embodiment has the following other features.
(1) Compared to the conventional method of measuring the combustion pressure using the elastic deformation of the housing, as in the present embodiment, the diaphragm-like front end side support member 133 and the rear end side strain generating portion 134 are used. If the elastic deformation is utilized, the amount of displacement of the central shaft increases, and the combustion pressure can be measured with high sensitivity.
(2) When the glow plug 151 is installed in the through hole, the tip of the tip side support member 133 is inserted even if it is inserted sufficiently tightly to strengthen the adhesion to the engine head 112 and a preload is applied to the housing 142 itself. No preload is applied to the side elastic portion 133b or the strain-generating portion 134 on the rear end side. Accurate combustion pressure can be measured. Further, by suppressing the rattling of the housing 142 itself, a more accurate combustion pressure can be measured.
(3) The pressure sensor 150 is arranged at a position away from the distal end side support member 133 and the housing 142. Furthermore, since the insulation bushes 162 and 164 and the heater connector 130 are interposed between the pressure sensor 150 and the members, the vibration transmission of the engine head 112 is well mitigated, and the noise is remarkably reduced. Has been. Moreover, as a material that can easily relieve vibration, for example, plastic, glass, rubber, or the like can be preferably used.
(4) In the glow plug 151, the strain generating portion 134 extends from the screw coupling portion 135 toward the anti-combustion chamber. Therefore, when the glow plug 151 is energized, the strain generating portion 134 receives heat from the heat generating member 120 provided at the tip of the center shaft and tends to cause thermal expansion toward the combustion chamber. That is, among the middle shafts, the direction in which the center side middle shaft 124 tends to cause thermal expansion is opposite to the direction in which the strain generating portion 134 tends to cause thermal expansion. Thereby, the thermal expansion of the central middle shaft 124 is suppressed by the thermal expansion of the strain generating portion 134. Therefore, when the glow plug 151 is energized, an additional increase in the preload applied in advance to the pressure sensor 150 is suppressed, and an accurate combustion pressure can be measured.

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.
In the first embodiment, the second embodiment, and the modifications thereof, it is preferable to employ a tip-side elastic portion having a spring constant smaller than that of the rear-end side elastic portion. The spring constant here refers to a spring constant in the axial direction of the central shaft. In order to provide a difference between the two spring constants, different materials may be used in addition to providing elastic portions having different structures. For example, it is preferable to employ a material having a low Young's modulus such as a rubber material for the tip side elastic portion. As long as the pressure of the combustion chamber can be sealed, the structure and material of the tip side elastic portion are not limited. Preferably, a material with low heat conduction that suppresses the transfer of heat in the combustion chamber to the anti-combustion chamber side is employed. If the spring constant of the front end side elastic part is adjusted to be smaller than that of the rear end side elastic part, the front end side elastic part preferentially elastically deforms, so the thermal expansion on the rear end side of the central shaft is directed toward the combustion chamber. Will be generated. Therefore, even when the glow plug is energized, even if the middle shaft thermally expands, the phenomenon that the preload previously applied to the pressure sensor is additionally increased is suppressed, and an accurate combustion pressure can be measured. .
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 expanded sectional view of the support member of the 1st example is shown. FIG. 2 shows a simplified cross-sectional view of the first embodiment. One modification of the support member of the first embodiment is shown. The sensor output characteristic of the modification of 1st Example is shown. Another modification of the supporting member of 1st Example is shown. Another modification of the supporting member of 1st Example is shown. The modification of 1st Example is shown. Sectional drawing of the center axis | shaft of the modification of 1st Example is shown. Sectional drawing of the principal part of the glow plug of 2nd Example is shown. Sectional drawing which simplified 2nd Example is shown. The principal part sectional drawing of the conventional glow plug is shown.

Explanation of symbols

13, 113: Through-holes 12, 112: Engine heads 20, 122, 124, 129: Center shaft 30: Support member 32, 32A: Tip side strain generating portion 32B: First tip side strain generating portion 32C: Second tip side starting Strain portion 133: tip side support member 33, 133a: tip side middle shaft fixing portion 133c: tip side housing fixing portion 133b: tip side elastic portion 35: rear end side middle shaft fixing portions 34, 34B, 34C: rear end side strain generating portion 36: Projection 38: Sensitivity adjustment region 42, 142: Housing 44: Sensor housing 50, 150: Pressure sensor 51, 151: Glow plug 92, 192: Calculation circuit 94, 194: Control circuit 12a, 112a: Stepped surface 36a, 142a: Tapered surface

Claims (16)

A glow plug that passes through the engine head and attaches to a through hole facing the combustion chamber,
A generally cylindrical housing coupled to an inner wall defining a through hole;
A middle shaft slidably housed in the housing;
A pressure sensor fixed between the anti-combustion chamber side of the middle shaft and the housing;
It is provided between the middle shaft and the housing, and includes a support member that slidably supports the middle shaft along the axis.
When the glow plug is attached to the through hole, the end on the combustion chamber side of the housing keeps in close contact with the inner wall of the engine head,
The support member includes an intermediate shaft fixing portion fixed to the intermediate shaft, a housing fixing portion fixed to the housing, and an elastic portion that is between the two and elastically deforms to change the axial distance between the two. Glow plug characterized by   The support member is fixed to the front end side middle shaft fixing portion fixed to the front end side of the middle shaft, the housing fixing portion fixed to the housing, the front end side elastic portion between them, and the rear end side of the middle shaft. The glow plug according to claim 1, further comprising a rear end side middle shaft fixing portion and a rear end side elastic portion between the housing fixing portion and the rear end side middle shaft fixing portion.   The glow plug according to claim 2, wherein the tip side elastic portion includes a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side.   The glow plug according to claim 3, wherein the tip side elastic portion includes a portion extending from the housing fixing portion toward the combustion chamber.   The glow plug according to any one of claims 2 to 4, wherein the rear end side elastic portion includes a portion extending from the rear end side middle shaft fixing portion toward the anti-combustion chamber side.   The glow plug according to any one of claims 2 to 5, wherein a spring constant of the front end side elastic portion is smaller than a spring constant of the rear end side elastic portion.   The glow plug according to any one of claims 2 to 6, wherein the rear end side middle shaft fixing portion is fixed to the rearmost end of the middle shaft.   The tip side middle shaft fixing portion makes a round around the middle shaft, the housing fixing portion makes a round around the housing, and the tip side elastic portion makes a round between them. Glow plug. With two support members,
The front end side support member has a front end side middle shaft fixing portion fixed to the front end side of the middle shaft, a front end side housing fixing portion fixed to the front end side of the housing, and a front end side elastic portion between them,
The rear end side support member includes a rear end side middle shaft fixing portion fixed to the rear end side of the middle shaft, a rear end side housing fixing portion fixed to the rear end side of the housing, and a rear end side between the two. The glow plug according to claim 1, further comprising an elastic portion.   The glow plug according to claim 9, wherein the tip side elastic portion includes a portion extending from the tip side middle shaft fixing portion toward the combustion chamber side.   The glow plug according to claim 10, wherein the distal end side elastic portion includes a portion extending from the distal end side housing fixing portion toward the combustion chamber side.   The glow plug according to any one of claims 9 to 11, wherein the rear end side elastic portion includes a portion extending from the rear end side middle shaft fixing portion toward the anti-combustion chamber side.   The glow plug according to any one of claims 9 to 12, wherein a spring constant of the front end side elastic portion is smaller than a spring constant of the rear end side elastic portion.   The tip side middle shaft fixing portion makes a round around the middle shaft, the tip side housing fixing portion goes around the housing, and the tip side elastic portion goes around between both. Glow plug.   The glow plug according to claim 1, wherein the middle shaft fixing portion is formed closer to the anti-combustion chamber than the center of the middle shaft. A glow plug that passes through the engine head and attaches to a through hole facing the combustion chamber,
A generally cylindrical housing coupled to an inner wall defining a through hole;
A middle shaft slidably housed in the housing;
A pressure sensor fixed between the anti-combustion chamber side of the middle shaft and the housing;
It is provided between the middle shaft and the housing, and includes a support member that slidably supports the middle shaft along the axis.
When the glow plug is attached to the through hole, the end on the combustion chamber side of the housing keeps in close contact with the inner wall of the engine head,
The support member is fixed to either the front end side of the middle shaft or the housing, and supports the middle shaft slidably with respect to the housing, and the rear member fixed to the rear end side of the middle shaft. A glow plug comprising: an end-side intermediate shaft fixing portion; a housing fixing portion fixed to the housing; and a rear-end side elastic portion located between the rear-end side intermediate shaft fixing portion and the housing fixing portion.

Images