Patent Application
20070228030
The present invention concerns a device for bearing on a pressure sensor mounted on a glow plug.
It is known to integrate a pressure sensor in a glow plug in an internal combustion engine, in particular a diesel engine. This sensor makes it possible to measure the internal pressure of the engine. The knowledge of this pressure enables the progression of the combustion in that engine to be better controlled. Better efficiency of that engine is thus attained and limitation is achieved not only of its fuel consumption but also of its polluting emissions.
A glow plug generally comprises a tubular body having on its outer surface a threaded portion enabling it to be fixed into a corresponding bore formed in a cylinder head. One portion of that body is located within the combustion chamber and the other portion outside it. The portion within the combustion chamber bears a finger within which is located a heater electrode. The latter is supplied by a core which passes through the tubular body of the glow plug. The portion outside the engine is also referred to as glow plug head. At that head, the core is connected to a source of electrical energy. It is also known to place the pressure sensor in that head.
One form of embodiment of such a glow plug has been provided in a patent application that has not yet been published at the time of filing the present application. This application was later published under the number FR 2 861 836. That embodiment is illustrated in
In the embodiment represented in
In this embodiment, the spacer is formed of ceramic and has a tubular circular cylindrical form. The spacer does not bear directly against the sensor but is separated therefrom by an electrically insulating member as well as by a bearing part used to distribute the pressure from the spacer over the whole surface of the pressure sensor.
This solution has the drawback that at least three parts are situated between the finger and the glow plug and the pressure sensor. This implies a cost both for the production of these different parts as well as for their assembly. Furthermore, it has been noted that the presence of several contact surfaces (between the pressure sensor and the insulating member, between the insulating member and the bearing part and between the bearing part and the spacer) had a negative effect on the sensitivity of the pressure sensor.
The present invention thus concerns a glow plug equipped with a pressure sensor implementing a spacer for transmitting forces to the sensor but of which the production cost is less than the embodiment presented earlier. Preferably, the structure of this glow plug will not weaken the sensitivity of the pressure sensor used.
To that end, it provides a force transmitting device for a pressure sensor associated with a glow plug in an internal combustion engine, having the form of a tubular member of substantially circular section.
According to the invention, the device comprises a zone in which its outer diameter increases towards one of its ends, and the front face of the device corresponding to that flared end is a bearing face adapted to receive a pressure sensor.
Such a force transmitting device is thus also adapted to service as a bearing part. It is possible in this way to eliminate a part between the origin of the force (pressure) to measure and the sensor.
In an advantageous embodiment, this force transmitting device is produced from a ceramic material. Thus, it may also serve as an electrically insulating member for the pressure sensor when this a piezo-electric sensor. This is because it may also be a resistive piezo-electric sensor or any other type of pressure sensor.
To enable the passage of a conductive core, this device preferably has a central hole of substantially constant diameter.
The present invention also concerns a glow plug comprising a piezo-electric pressure sensor and characterized in that it comprises a force transmitting device as described above.
In such a glow plug, the flared end of the force transmitting device bears for example against a face of the pressure sensor and substantially corresponds to the surface of that sensor. In this way, the forces to transmit are perfectly so transmitted and the sensor can operate in good conditions.
The glow plug may in particular be of the type comprising at one of its ends a finger incorporating a heater electrode, and the force transmitting device is then for example disposed between that finger and the pressure sensor. In this embodiment, the finger may be fixed within a tubular part, at one end thereof, and that tubular part may have an interior shoulder against which the force transmitting device rests. The tubular part concerned here may be the body of the glow plug but it may also be another part, such as an intermediate part between the body and the finger of said glow plug.
In the case in which the finger is fixed into a tubular part, the outer diameter of the force transmitting device is preferably less than the inner diameter of the tubular part within which it is housed such that the force transmitting device is free at its periphery, in particular with respect to the tubular part. Thus the risk of transmitting extraneous forces is diminished.
Similarly, when a conductive core supplies the heater electrode of the glow plug with electrical energy, that core preferably passes freely within the force transmitting device.
The present invention lastly concerns an internal combustion engine, in particular an engine of diesel type, characterized in that it comprises at least one glow plug as described above.
Details and advantages of the present invention will appear more clearly from the following description, made with respect to the accompanying drawings in which:
The body 8 is adapted to be fixed to the engine 4 by screwing. To that end, the cylinder head 6 comprises a threaded bore passing through it and opening into a combustion chamber of said engine. Concerning the body 8, this has a screw thread 16 on its other surface corresponding to the bore formed in the cylinder head 6. When the screw thread 16 cooperates with the threaded bore of the cylinder head 6, the glow plug being in its mounted position in the engine 4, a portion of the body 8 extends inwardly of the engine, that is to say towards the combustion chamber, whereas another portion extends outwardly the engine. The body 8 is a tubular body and is for example formed from steel.
In this embodiment, the finger 10 is mounted within the tubular body 8, within which it has an interference fit, and projects into the combustion chamber. This finger 10 incorporates a heater electrode (not shown). The core 12 is adapted to supply that electrode with electrical energy and passes through the body 8 from the finger 10 as far as the opposite end of the body 8 from that at which the finger 10 projects. This core 12 is then connected, by means not shown, to a supply conductor.
The pressure sensor 14 is provided for measuring the pressure within the corresponding combustion chamber. In the embodiment of
In this embodiment, the pressure sensor 14 also comes to bear on the body 8 via a bearing part 24. The pressure sensor 14 is connected to the body 8 by its upper surface and bears against the finger 10 such that the pressure exerted on that finger compresses it against the body 8. To that end, the pressure sensor 14 bears on a spacer 38 which rests on the finger 10 and which is disposed in the body 8, without contact with the latter. This spacer 38 surrounds the core and is not in contact with it either.
The compression of the pressure sensor 14 against the finger 10 (via the spacer 38 and the bearing part 24) as well as its connection to the body 8 is provided by a nut with external screw threading 36. This nut is of course not in contact with the core 12 but cooperates with an internal thread formed on the internal face of the side wall 46 of a housing 34 formed in the body 8 for receiving the sensor 14.
In the embodiment of FIGS. 2 to 4, similar members take the same reference numbers as those used in
On the external view of
In the example embodiment of FIGS. 2 to 4, the finger bears the reference 10′. This is a finger of a different type to that represented in
In FIGS. 2 to 4, a tubular intermediate part 30 is provided between the body 8 and the finger 10′ to insulate the finger 10′ from the body 8.
Between the finger 10′ and the pressure sensor 14 is a spacer 38′. There is no bearing part 24 to be found here, nor any electrically insulating member 22 between the spacer 38′ and the pressure sensor 14, or more specifically a contact element 20 of that sensor.
The spacer 38′ is a tubular part which allows the core 12 to pass through its center. As in the embodiment of
In its upper portion, the diameter of the spacer 38′ is adapted to the diameter of the lower face of the pressure sensor 14. Thus, the spacer 38′ has, on its upper portion, a frusto-conical zone 40 enabling the outer diameter of the spacer 38′ to progressively pass from a diameter corresponding approximately to the diameter of the finger 10′ to the diameter of the pressure sensor 14 on approaching the end of the spacer 38′ against which the pressure sensor 14 bears.
As has just been seen, by virtue of its frusto-conical portion 40, the spacer 38′ thus provides the function that is given by the bearing part 24 in the embodiment of
In the embodiment of FIGS. 2 to 4, the tubular intermediate part 30 has an interference fit with the lower end of the body 8, adjacent a fixing zone 32. Between that fixing zone 32 and the zone in which the finger 10′ has an interference fit within the tubular intermediate part 30, there is a deformation zone 42. The latter promotes the transmission of the forces exerted by the ambient pressure in the combustion chamber on the finger 10′ to the pressure sensor 14.
The variant embodiment of
The spacer 38′ is of the same type as that described with reference to FIGS. 2 to 4. It thus comprises a tubular circular cylindrical portion and ends with a frusto-conical portion 40 located adjacent the pressure sensor 14. It can be seen in
At its other end, the spacer 38′ comes to rest against a shoulder 50. The latter is formed in the vicinity of the end of the finger 10 located within the body 8. Thus, the opposite end of the spacer 38′ to the frusto-conical zone 40 is located close to the finger 10 but does not rest thereon. The spacer 38′ nevertheless passes on the forces exerted by the ambient pressure in the corresponding combustion chamber to the pressure sensor. This is because the body 8 has a deformation zone 42′ located between the zone in which the finger 10 fits with an interference fit within the body 8 and the screw thread 16. It is considered that the screw thread is not deformable since it is mounted in the cylinder head 6 which is of high stiffness. As the shoulder 50 against which the spacer 38′ rests is located close to the finger 10 and to the zone in which that finger 10 has an interference fit with the body 8, it enables the pressure sensor 14 to nevertheless to experience the stresses exerted on the finger 10. This is because the pressure sensor 14 is located between the nut with an external screw thread 36 and the spacer 38′. The nut with outer screw thread 36 is fastened to the wall 46 which is fixed with respect to the cylinder head. This is because this wall is situated to the exterior of the cylinder head and is not subject to any significant stress. If it is then considered that the ceramic material of the spacer 38′ is stiff and does not deform, the forces exerted on the finger 10 are passed on to the pressure sensor 14 by the spacer 38′.
As is apparent from the above description, adjacent the pressure sensor 14, the spacer 38′ flares such that its outer diameter adapts itself to the diameter of the pressure sensor. Thus the spacer 38′ may come to bear on the whole surface of the pressure sensor 14. This flared form is preferably produced close to the pressure sensor 14. This is because, in this way, the mass of the spacer 38′ is limited. Furthermore, this embodiment is adapted to the internal form of the body, or more generally of the tubular part, in which the spacer 38′ is found.
In the embodiment of
In
In
As can be noted in the embodiments provided in FIGS. 2 to 7, no part other then the spacer 38′ is situated between the finger of the glow plug described and its pressure sensor. In this way the number of parts necessary to manufacture the glow plug provided with its pressure sensor is limited as is the number of interfaces in the transmission of the force exerted by the ambient pressure within the combustion chamber as far as the pressure sensor.
It is thus achieved to limit the production cost of the glow plug equipped with a pressure sensor and despite the reduction in cost, the sensor equipping that glow plug may have better sensitivity when making a pressure measurement.
The present invention is not limited to the embodiments described above by way of non-limiting example. It concerns on the contrary all the variant embodiments accessible to the person skilled in the art.
Thus, for example, the spacer according to the invention could be produced from a material other than ceramic. An electrically conductive material may even be envisaged. To electrically insulate the sensor on the spacer side, when the sensor is for example a piezo-electric sensor, all means may be envisaged. A surface treatment may for example be suggested making it possible to render the bearing face of the spacer electrically insulating, on which face the pressure sensor rests.
The widening of the outer diameter of the spacer is preferably made in the immediate proximity of the pressure sensor. However, this widening may be made at another place on the spacer.
The spacer according to the invention is described with respect to two different types of glow plug. Of course, this spacer may be used on other types of glow plug comprising a sensor, for example a piezo-electric sensor, and a spacer for the transmission of forces towards that sensor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0404466 | Apr 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/00934 | 4/19/2005 | WO | 3/7/2007 |
