JP2017191068A - Combustion pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion pressure sensor 1 capable of enhancing the reliability by preventing positional deviation between a diaphragm 3 and a force transmission rod 5 and by preventing a sensor element 4 as a glass component part (for example, a second force transmission block 42) from getting brittle due to being exposed to moisture.SOLUTION: The combustion pressure sensor includes: a guide member 6 which encloses a force transmission rod 5 so as to be displaceable in a transmission direction of a pressing force from a pressure receiving part 32 of a diaphragm 3 to a sensor element 4 (axis X-direction). The guide member 6 is formed using a resin material which has a predetermined water absorption rate or more, for example, a nylon 6, 6 etc.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a combustion pressure sensor that detects the pressure of a combustion chamber of an engine, and more particularly to a structure around a force transmission rod that transmits a force acting on a diaphragm by the combustion pressure to a sensor element.

  Conventionally, a combustion pressure sensor used for an engine such as an automobile has a substantially cylindrical outer housing, a disc-shaped diaphragm fixed to a tip portion thereof, and the like, as described in Patent Document 1, for example. A cylindrical force transmission rod that transmits a force corresponding to the combustion pressure acting on the diaphragm to the sensor element. The sensor element is, for example, a piezoresistive element, and the output value changes according to the pressing force from the force transmission rod.

  More specifically, a cylindrical inner housing is provided integrally and continuously with the outer peripheral portion of the diaphragm, and the force transmission rod and the sensor element are disposed therein. A hermetic seal terminal is fitted and welded to the opening end of the inner housing opposite to the diaphragm, and the signal line is taken out from the sensor element while sealing the internal space in which the sensor element is accommodated. .

JP 2009-008694 A

  By the way, in the conventional sensor, the hermetic seal terminal is pushed into the inner housing at the time of assembly in order to keep the tip surface of the force transmission rod in contact with the center of the back surface of the diaphragm. The rear surface of the diaphragm is pressed. In this state, the outer peripheral surface of the stem of the hermetic seal terminal is welded to the inner peripheral surface of the inner housing, and so-called preload is applied.

  However, even if a preload is applied in this manner, for example, when a large combustion pressure acts on the diaphragm due to abnormal combustion of the engine and the component parts of the force transmission rod and the sensor element resonate, the tip surface of the force transmission rod becomes the diaphragm surface. There was a possibility of moving away from the back surface, and there was a possibility that the positions of both would be displaced at this time. Therefore, it is conceivable to fix the front end surface of the force transmission rod to the back surface of the diaphragm with an adhesive or the like at the time of assembling, but in this case, an adhesive drying step is required, and the tact time is extended.

  In addition, some of the components of the sensor element are made of glass, and when the sensor element is exposed to moisture, the sensor element becomes brittle, and there is a problem that reliability is lowered. On the other hand, when the hermetic seal terminal is assembled to the inner housing as described above, there is a method in which the inner space is filled with an inert gas and welding is performed in an inert atmosphere. turn into.

  In view of such points, the object of the present invention is to suppress the displacement between the diaphragm of the combustion pressure sensor and the force transmission rod, and to make the glass component parts of the sensor element housed in the internal space difficult to become brittle. To improve reliability.

  In order to achieve the above object, the present invention is directed to a combustion pressure sensor for detecting the pressure of a combustion chamber of an engine, and a diaphragm that faces the combustion chamber and a force that transmits a pressing force from the diaphragm to a sensor element. A transmission rod and a guide member surrounding the force transmission rod so as to be displaceable in the transmission direction of the pressing force, and the guide member is formed of a resin material having a predetermined water absorption or more. .

  Examples of the resin material having a high water absorption rate include those having a water absorption rate of approximately 1% or more, such as aliphatic polyamide (nylon), urethane resin, and cellulose-based resin. In view of heat resistance, wear resistance, etc., it is preferable to use nylon 6, nylon 6, 6 or the like.

  The combustion pressure sensor configured as described above is surrounded by a guide member so that the force transmission rod that transmits the pressing force from the diaphragm facing the combustion chamber of the engine to the sensor element is not displaced in a direction orthogonal to the transmission direction of the pressing force. It is. Therefore, even if it does not fix the front end surface of this force transmission rod and the back surface of a diaphragm with an adhesive agent, both position shift can be suppressed. Further, it is not necessary to increase the frictional force by increasing the contact area between the two end surfaces, and at least one of them can be a convex curved surface.

  If at least one of the front end surface of the force transmission rod and the rear surface of the diaphragm is a convex curved surface in this way, the spring constant of the system for transmitting the pressing force from the diaphragm to the force transmission rod is reduced, and the natural frequency is reduced. For this reason, even if a large combustion pressure acts on the diaphragm due to abnormal combustion of the engine or the like, resonance of the force transmission rod is less likely to occur, which is advantageous in avoiding damage to the glass component of the sensor element. .

  Further, since the guide member is formed of a resin material having a water absorption rate equal to or higher than a predetermined value, even if moisture remains in the sealed space in which the sensor element is accommodated, the moisture is absorbed by the guide member. Will come to be. As a result, the glass component of the sensor element can be prevented from being exposed to moisture, making it difficult to become brittle and improving reliability. There is no need to work in an inert atmosphere when sealing the sensor element or the like, and the cost is not increased.

  In the combustion pressure sensor according to the present invention, since the force transmission rod that transmits the force from the diaphragm facing the combustion chamber is surrounded by the guide member, the tip surface of the force transmission rod and the back surface of the diaphragm are bonded by an adhesive. Even if it is not fixed, the positional deviation between the two can be suppressed. Further, since moisture can be absorbed by the guide member, it is possible to suppress exposure of the glass component parts of the sensor element to moisture, and it is difficult to become brittle, and reliability can be improved.

It is a longitudinal cross-sectional view which shows the structure of the front-end | tip part of the combustion pressure sensor which concerns on embodiment. It is a perspective view which removes an outer housing and shows the front-end | tip part of a combustion pressure sensor. It is a longitudinal cross-sectional view which shows the assembly process of a diaphragm assembly. It is a longitudinal cross-sectional view which shows the process of assembling | attaching a sensor assembly to a diaphragm assembly and also attaching an outer housing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, the present invention is applied to a combustion pressure sensor 1 that is mounted on an automobile engine (not shown) and detects the pressure (combustion pressure) of a combustion chamber in the cylinder. Note that the description of the embodiment is merely an example, and is not intended to limit the configuration or use of the present invention.

  In FIG. 1, the combustion pressure sensor 1 according to the present embodiment includes a front end side (upper side in FIG. 1) as a longitudinal section (a section including the axis X) of the outer housing 2. For example, it is attached to a cylinder head so that the diaphragm 3 disposed at the tip faces the combustion chamber. The combustion pressure sensor 1 has an output signal that changes as the diaphragm 3 is deformed by receiving the pressure (combustion pressure) in the combustion chamber.

  As shown in FIG. 2, the diaphragm 3 is formed with a disk-shaped pressure receiving portion 32 so as to close the central hole 31 of the donut-shaped support portion 30, and from the outer peripheral surface of the support portion 30. A flange portion 33 projects from the circumference. In the present embodiment, the outer peripheral portion of the pressure receiving portion 32 is continuous with the peripheral portion of the central hole 31, and the pressure receiving portion 32 is formed of a metal material integrally with the support portion 30.

  Further, a cylindrical inner housing 34 is integrally formed so as to extend downward from the base end surface of the support portion 30, that is, the lower surface in FIGS. 1 and 2, and the sensor element 4 and the force transmission rod are formed therein. 5 and the guide member 6 are accommodated. Although only shown in FIG. 1, in this embodiment, an annular seal member 7 is attached so as to cover the distal end side of the diaphragm 3 from the outer peripheral side, and the gap with the screw hole of the cylinder head is closed. ing.

  The outer housing 2 has a cylindrical shape, and a tapered portion 2a is provided on the outer periphery of the front end portion thereof, and subsequently, a screw portion (not shown) is formed in a predetermined range on the outer periphery. The combustion pressure sensor 1 is attached to the engine by, for example, screwing the screw portion into a screw hole of the cylinder head. And the support part 30 of the said diaphragm 3 is engage | inserted by opening of the front-end | tip part of the outer housing 2, The flange part 33 is welded to the peripheral part of opening.

  Thus, the diaphragm 3 fixed to the distal end portion of the outer housing 2 is formed with the pressure receiving portion 32 as described above. When the combustion pressure is applied to the surface (upper surface in FIG. 1), the back side (in FIG. 1) (Lower side). The tip surface 5a (upper surface in the drawing) of the force transmission rod 5 is pressed near the center of the back surface of the pressure receiving portion 32 that bends in this way, and the pressing force due to the combustion pressure is applied to the sensor element 4 via the pressure receiving portion 32. introduce.

  As an example, the force transmission rod 5 is formed in a cylindrical shape with a heat insulating material, and its distal end surface 5a is a spherical convex curved surface, while its proximal end surface is planar, and the first of the sensor element 4 described later. It is in contact with the force transmission block 41. Therefore, when the pressure receiving portion 32 is bent to the back side under the combustion pressure as described above, the force transmission rod 5 is displaced toward the base end side (the lower side in FIG. 1), and the combustion pressure is increased. A corresponding pressing force is transmitted to the sensor element 4 by the force transmission rod 5.

  In addition, since the tip end surface 5a of the force transmission rod 5 is a convex curved surface as described above and the contact area with the pressure receiving portion 32 of the diaphragm 3 is reduced, in this embodiment, the force transmission rod 5 is removed from the diaphragm 3. The spring constant of the system that transmits the pressing force to the sensor element 4 via the sensor element 4 is reduced, and the natural frequency thereof is also reduced.

  In the present embodiment, a guide member 6 is provided for guiding the force transmission rod 5 so as to be displaceable in the force transmission direction (direction of the axis X). The guide member 6 has a cylindrical shape that concentrically surrounds the outer periphery of the force transmission rod 5, and the inner peripheral surface thereof and the outer peripheral surface of the force transmission rod 5 are in sliding contact. The guide member 6 is inserted into the central hole 31 of the diaphragm 3 and restricts the force transmission rod 5 from being displaced in a direction orthogonal to the transmission direction.

  The guide member 6 is made of a resin material having a water absorption rate equal to or higher than a predetermined value, and absorbs moisture remaining in the inner housing 34. That is, as an example, in a resin material having a high water absorption rate of 1% or more (for example, nylon, which is an aliphatic polyamide, urethane resin, cellulose resin, etc.), good slidability with the force transmission rod 5 Nylon 6 and 6 that have the necessary heat resistance and wear resistance are used.

  As described above, the sensor element 4 to which the pressing force is transmitted from the force transmission rod 5 includes the force detection block 40 and the two force transmission blocks 41 and 42. The force detection block 40 is mainly composed of a silicon substrate, and a piezoresistive element is formed on the tip surface (the upper surface in FIG. 1). As is well known, the piezoresistive element changes its electrical resistance value in response to an external force, and an electrode group (not shown) for detecting this change in resistance value is formed in the force detection block 40. ing. The force detection block 40 may be constituted by a piezoelectric element.

  Of the two force transmission blocks 41, 42, the second force transmission block 42 in contact with the force detection block 40 is made of glass, and the base end surface (the lower surface in FIG. 1) is the tip of the force detection block 40. It is joined to the surface. On the other hand, the first force transmission block 41 is made of metal such as iron or ceramic and is hemispherical in the present embodiment, and its distal end (upper part in FIG. 1) abuts against the base end surface of the force transmission rod 5. On the other hand, the flat base end surface is bonded to the front end surface of the second force transmission block 42. The first force transmission block 41 may also be formed of silicon or glass.

  The sensor element 4 is attached to the inner housing 34 via the tube 8 and the stem 80. That is, the distal end side of the metal tube 8 is fitted and welded to the proximal end side of the inner housing 34, and the distal end surface (the upper surface in FIG. 1) of the columnar stem 80 fixed inside thereof. The sensor element 4 is bonded and fixed. A plurality of through holes are formed in the stem 80, and a cable 81 inserted therein is fixed by a sealing material 82.

  That is, in the present embodiment, the tube 8, the stem 80, the cable 81, and the sealing material 82 constitute a hermetic seal terminal that seals the inner space of the inner housing 34. One end of the cable 81 is connected to the electrode of the force detection block 40 of the sensor element 4 via a wire 83. The other end of the cable 81 is connected to a power source or a measuring instrument (an ammeter or a voltmeter) through an amplifier circuit or the like (not shown).

  With the above-described configuration, in the combustion pressure sensor 1 of the present embodiment, the pressure receiving portion 32 of the diaphragm 3 is deflected by the action of the combustion pressure, and the force transmission rod 5 is displaced to the sensor element 4 side (lower side in FIG. 1). Then, a pressing force acts on the piezoresistive element of the sensor element 4 to change its electric resistance. Thus, for example, if a constant current is passed from the current source to the piezoresistive element, the output voltage changes according to the change in the electric resistance value, so that the combustion pressure applied to the pressure receiving unit 32 based on this changes. Can be detected.

-Assembly of combustion pressure sensor-
Next, assembly of the combustion pressure sensor 1 of the present embodiment will be described with reference to FIGS. 3 and 4. First, the guide member 6 is prepared by inserting the force transmission rod 5 in advance, and this is inserted into the central hole 31 of the diaphragm 3 through the opening on the proximal end side as shown in FIG. To do. In addition, the force detection block 40 and the force transmission blocks 41 and 42, that is, the sensor element 4 are fixed to the stem 80, and this is fixed in the tube 8 to prepare as a sensor assembly.

  Then, the sensor assembly is assembled to the diaphragm assembly as shown in the upper part of FIG. At this time, the distal end side of the tube 8 of the sensor assembly is inserted into the inner housing 34 from the proximal end side, and the force transmission rod 5 is pushed in by the sensor element 4. In this way, the front end surface 5a of the force transmission rod 5 is pressed against the pressure receiving portion 32 of the diaphragm 3, and the outer peripheral surface of the tube 8 and the inner peripheral surface of the inner housing 34 are welded with the preload applied.

  Thus, the outer housing 2 is assembled to the diaphragm assembly to which the sensor assembly is assembled as shown in the lower part of FIG. That is, the base end side of the support portion 30 of the diaphragm 3 in the diaphragm assembly is inserted into the outer housing 2 from the opening of the tip portion thereof, and the flange portion 33 on the outer periphery of the support portion 30 is placed on the peripheral portion of the opening of the outer housing 2. Place and weld.

  As described above, in the combustion pressure sensor 1 of the present embodiment, the force transmission rod 5 that transmits the pressing force from the pressure receiving portion 32 of the diaphragm 3 facing the combustion chamber of the engine to the sensor element 4 transmits the pressing force. It is surrounded by the guide member 6 from the outer periphery so that it can be displaced in the direction (axis X direction). As a result, it is possible to suppress the positional deviation between the front end surface 5a of the force transmission rod 5 and the back surface of the pressure receiving portion 32 of the diaphragm 3, so that it is not necessary to fix both of them with an adhesive, and an adhesive drying step is unnecessary. .

  Further, since the displacement can be suppressed by the guide member 6, there is no need to increase the frictional force by increasing the contact area between the front end surface 5 a of the force transmission rod 5 and the back surface of the pressure receiving portion 32 of the diaphragm 3. . Therefore, in the present embodiment, the tip surface 5a of the force transmission rod 5 is a convex curved surface, the spring constant of the system that transmits the pressing force is reduced, and its natural frequency is reduced. Thereby, even if a large combustion pressure acts on the diaphragm 3 due to abnormal combustion of the engine or the like, resonance of the force transmission rod 5 or the like hardly occurs, and the glass configuration like the second force transmission block 42 of the sensor element 4 is achieved. This is advantageous in preventing breakage of parts.

  Furthermore, since the guide member 6 has high water absorption, even if moisture remains in the inner space of the inner housing 34, the moisture is absorbed by the guide member 6. Thereby, it can suppress that the glass-made components like the 2nd force transmission block 42 of the sensor element 4 are exposed to a water | moisture content, and become weak, The reliability becomes high. Further, when the tube 8 is assembled to the inner housing 34 and welded, there is no need to perform an operation in an inert atmosphere, and there is no fear of increasing the cost.

-Other embodiments-
The present invention is not limited to the description of the embodiment described above. For example, in the above-described embodiment, the combustion pressure sensor 1 mounted on an automobile engine has been described. However, the present invention is not limited to this. For example, an engine mounted on a vehicle other than an automobile or a vehicle such as a ship or a stationary type The present invention can also be applied to a combustion pressure sensor mounted on the engine.

  Further, it is not necessary to provide the annular seal member 7 at the tip of the combustion pressure sensor 1 as in the above embodiment, and it is not necessary to have a double structure in which the inner housing 34 is provided inside the outer housing 2. Further, there is no need to have a structure in which the tube 8 is fitted into the inner housing 34, and there is no need to insert the guide member 6 into the central hole 31 of the diaphragm 3, and a specific structure of the combustion pressure sensor 1 of the above-described embodiment. Is merely an example.

  The present invention can suppress the positional deviation between the diaphragm and the force transmission rod in the combustion pressure sensor of the engine, and is advantageous in ensuring the reliability of the sensor element. Therefore, the present invention is applied to, for example, a combustion pressure sensor equipped in an automobile engine. And the effect is high.

1 Combustion Pressure Sensor 3 Diaphragm 4 Sensor Element 42 Second Force Transmission Block (Glass Component)
5 Force transmission rod 6 Guide member X Force transmission rod axis (pressure transmission direction)

Claims (1)

A combustion pressure sensor for detecting the pressure of a combustion chamber of an engine,
A diaphragm facing the combustion chamber;
A force transmission rod for transmitting a pressing force from the diaphragm to the sensor element;
A guide member that surrounds the force transmission rod so as to be displaceable in the transmission direction of the pressing force,
The combustion pressure sensor, wherein the guide member is made of a resin material having a water absorption rate equal to or higher than a predetermined value.

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