The present invention concerns a glow plug head and a piezo-electric pressure sensor adapted to be located in such a head.
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.
For mounting such a pressure sensor, the Applicants have knowledge, not yet disclosed by them, of disposing that sensor in a housing provided for that purpose in the body of the glow plug. At the opposite end to the finger incorporating the heater electrode, an internal screw thread is formed and the pressure sensor is thus held in its housing by the fitting of a nut with an exterior screw thread. On its other face, the pressure sensor, of piezo-electric type, rests on a bearing member via an electrically insulating member and a spacer connects the finger of the glow plug to the bearing member. Thus, the pressure sensor is held by the nut and the spacer passes on, via the bearing member (and the electrically insulating member), the forces that are exerted on it by the pressure within the corresponding combustion chamber.
This assembly solution has first of all the drawback of requiring substantial machining particularly adjacent the head of the glow plug, and particularly of the body of that glow plug.
During the assembly of the glow plug and its pressure sensor, the various members are put in place and towards the end of the assembly the nut with external screw threading is put in place. It has then been noted that it is sometimes difficult to manage to obtain correct pre-stressing of the piezo-electric pressure sensor. This prestressing depends in particular on the machining tolerances and also on the roughness of the materials.
The present invention is therefore directed to providing an assembly of the sensor which makes it possible to alleviate these drawbacks and which in particular has a lower production cost and preferably giving a good ability to control the prestressing applied to the pressure sensor.
To that end, the invention provides a glow plug comprising a pressure sensor mounted within a tubular member and held in said tubular member by means of a bearing member.
According to the invention, the bearing member is held in the tubular member by plastic deformation of the wall of the tubular member.
In this way, it is possible to limit the machining operations for putting in place the pressure sensor compared with a solution in which the bearing member is screwed or else is held by a screwed member. This is because no screw threading is necessary here at the pressure sensor. Furthermore, by deforming the wall of the tubular member, it is possible to better control the stress exerted on the sensor. Lastly, during the plastic deformation carried out to hold the bearing member, no rotation is necessary and thus the parts within the glow plug are not driven rotationally.
In one embodiment of the invention, the bearing member is held by crimping.
For better holding of the bearing member, the latter advantageously has, at least over a portion of its periphery, a frusto-conical surface, the large diameter base of the frustum being oriented towards the pressure sensor.
An advantageous embodiment provides that the pressure sensor is a piezoelectric sensor comprising a piezoelectric member mounted between two contact members, and in that the piezoelectric member has an annular form having a flat on its periphery. This solution makes it possible to optimize the surface of the pressure sensor without having to modify the wall of the housing receiving the pressure sensor. In this embodiment, the piezoelectric member and the contact members are for example arranged substantially transversally in the tubular member; the contact members each have a connection tab at their periphery extending substantially longitudinally with respect to the tubular member, and the connection tabs are arranged in front of the flat of the piezoelectric member.
In a glow plug according to the invention, the tubular member may comprise an inner wall that is substantially circular cylindrical.
The tubular member receiving the pressure sensor may be a tubular body, generally termed glow plug body, enabling the glow plug to be fixed into an internal combustion engine cylinder head. It may however also be another part comprising a housing to receive the pressure sensor.
In the case in which the pressure sensor is mounted in the glow plug body and the latter is fixed in the cylinder head by screwing and comprises a gripping zone of hexagonal transverse section to facilitate its screwing and unscrewing, then the plastic deformation enabling the bearing member to be held in place is for example carried out adjacent to the gripping zone.
The present invention also 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.
Lastly, the invention also provides a method of mounting a pressure sensor in the head of a glow plug, in which the sensor is installed in a housing of adapted form then held by means of a bearing member.
According to the invention, the holding in place of the bearing member is achieved by plastic deformation of the wall of the housing receiving the sensor and the bearing member.
Details and advantages of the present invention will appear more clearly from the following description, made with reference 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 glow plug is mounted in the engine 4, a portion of the body 8 extends towards the inside of the engine, that is to say towards the combustion chamber, whereas another portion extends towards the outside of the engine. The body 8 is a tubular body and is for example formed from steel.
In this embodiment (
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 member 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.
The compression of the pressure sensor 14 against the finger 10 (via the spacer 38 and the bearing member 24) as well as its connection to the body 8 is provided by a nut with external screw threading 36. This nut is 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 48 formed in the body 8 for receiving the pressure sensor 14.
The present invention provides for holding the pressure sensor 14 differently.
In the following portion of the description, the members of a glow plug according to the invention that are similar to those of the glow plug represented in
The glow plug according to the invention also has a housing 48 similar to the housing 48 of
As can be seen in
The head of the glow plug in
In the embodiment of the glow plug represented here, the piezo-electric pressure sensor is of generally annular form (a central hole is provided for the passage of the core 12) having a flat 56 at its periphery. The piezo-electric member 18, the contact members 20 as well as the second bearing member 50 reproduce this annular form having a flat 56.
The contact members 20, and the piezo-electric member 18, are transversely disposed with respect to the housing 48 which receives them. Each contact member 20 carries a connection tab 58 extending perpendicularly to the plane of the corresponding contact member 20. These connection tabs 58 thus extend longitudinally with respect to the housing 48 and extend substantially parallel to the core 12. As
As can be noted in
Compared with the retaining of the pressure sensor by a threaded plug (case of
First of all, the machining costs for the corresponding glow plug are substantially reduced. More particularly, it is no longer necessary to produce an internal screw thread in the housing receiving the pressure sensor. The assembly is also facilitated, which makes it possible to have a reduced cost of assembly.
In a glow plug according to the invention, it is also easier, compared with glow plugs such as the one in
Lastly during the fitting of the nut with external screw threading, the various components within the glow plug are driven rotationally. Of course, this drawback is not found with a glow plug according to the invention, as described above.
The present invention is not limited to the embodiment described above by way of non-limiting example. It also concerns all the variant embodiments accessible to the person skilled in the art.
Thus, the present invention may in particular apply to numerous glow plug structures incorporating a pressure sensor.
The method provided may apply when the pressure sensor is mounted in the body of the glow plug, but it may also apply when the sensor is mounted in a housing in another part.
Number | Date | Country | Kind |
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0404467 | Apr 2004 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR05/00935 | 4/19/2005 | WO | 2/23/2007 |