|Title of Invention||
SHEATHED-ELEMENT GLOW PLUG
|Abstract||The sheathed-element glow plug (10) for arrangement in the combustion chamber of air-compressing internal combustion engines has a tubular plug housing (11) in whose longitudinal bore a glow plug (16) is fixed in a sealing fashion with a part of its length. Formed between the longitudinal bore (12) and the sheathed element (16) in a specific, lower region which faces the combustion chamber is an annular gap (21) which serves the purpose of thermal decoupling between the plug housing and sheathed element.|
ROBERT BOSCH GMBH, 70440 Stuttgart
Sheathed-element glow plug
The invention process from a sheathed-element glow plug for arrangement in the combustion chamber of air-compressing internal combustion engines according to the generic concept of the main claim. In known sheathed-element glow plugs of this type, the annular gap between the sheathed element and plug housing is realised by a sheathed element of constant diameter in the press fit region and a cylindrical bore, facing the combustion chamber, in the plug housing. This bore is characterized by a diameter which is greater than the press fit diameter of the sheathed element.
Advantages of the Invention
The task of the sheathed-element glow plug according to the invention and having the characterizing features of the main claim is largely to decouple the sheathed element thermally at the appropriate depth of annular gap, and thus to ensure the desired heating characteristic. Depending on the so-called dimension of projection, that is to say the free length of the sheathed element from the lower edge of the plug housing up to the heater tip, the depth of the annular gap is to be matched to the dimension of projection for a standard plug of constant geometry and heating characteristic. This means that the plug housing has a great multiplicity of parts which vary only in the depth of the annular gap.
By contrast with the prior art, the main advantage is that the annular gap is realised by a sheathed element which is appropriately offset in the region of the press fit and has an expanded diameter
and a plug housing without a diameter step. As a result the number of the plug housings, which vary in their geometry only in the depth of the annular gap, can be reduced to a housing which can be used universally for this feature. At the same time, it is possible as before to use a standard plug of constant geometry which is pressed into the plug housing to an appropriate depth in order to produce the desired depth of annular gap.
The implementation of the annular gap by means of a sheathed element offset in the region of the press fit enlarges the press fit diameter of the sheathed element by comparison with the press fit diameter of the present prior art. This expansion in diameter leads to an enlargement of the overall space available for sealing the sheathed element. The expansion in diameter reduces in this region the required degree of reforming of the hot tube as well as of the seal pressed in. This significantly reduces the risk of crack formation in the seal during the process of hammering the sheathed element in order to shape it.
An exemplary embodiment of the invention is represented in the drawing, in which:
Figure 1 shows a sheathed-element glow plug, partly in longitudinal section, and Figures 2 and 3 show the annular gap zone designated by X on an enlarged scale.
Description of the exemplary embodiment
The sheathed-element glow plug 10 comprises an elongated cylindrical housing 11 with a central bore 12 which has a conical expansion towards the upper end. Somewhat below this expansion an annular offset 15 is formed on the bore 12, specifically by virtue of the fact that the diameter of the bore 12 above this offset 15 is somewhat smaller than the diameter in the subnequent region 12A of the bar tower. Located in the
housing 10 is the sheathed element 16, which protrudes with its tip 17 into the combustion chamber of the prime mover. The joint between the sheathed element and plug housing has so far been designed as a press fit 12A of constant bore diameter on the combustion chamber side. The dimension of projection V of the sheathed element 16 of the sheathed-element glow plug is defined as the distance between the heater tip and the test diameter at the sealing cone of the plug housing.
No further detail is given on the design of the sheathed element, since it is not essential to the invention. The plug can be expediently pressed into the bore 12. An incandescent filament arranged in the hot tube of the sheathed element is also not represented. The connecting bolt 18 projecting from the plug housing 11 serves to conduct current to the electrical filament. The connecting bolt 18 is fixed by means of a radially pressed seal 20 in the upper, tubular region (not represented further) of the sheathed element 16. The seal 20 seals the sheathed element 16 against the surroundings between the hot tube and connecting bolt 18. The aim of the annular offset 15 on the housing 11 is that the sheathed element 16 together with the connecting bolt 18 cannot be pressed upwards out of the housing 11 when there is an excessive pressure in the combustion chamber. Located at the upper edge of the sheathed element 16 is the seal 20 which seals the heater against the surroundings between the hot tube and connecting belt.
Figure 2 and 3 show the region, of relevance to the invention, of the annular gap 21 and the annular gap zone between the plug housing and sheathed element. This zone is realised between the constant press fit diameter, on the combustion chamber side, of the plug housing and a sheathed element with an offset outside diameter inside the plug housing. In this case, the region of the sheathed element on the combustion chamber side has a smaller diameter 16C below an offset 16B than that of the press fit region 12A.
Figure 2, in particular, shows the arrangement of the sheathed element according to the invention in the plug housing in order to produce a depth of annular gap Rl. Figure 3 shows the arrangement of the sheathed element according to the invention in the plug housing in order to produce a depth of annular gap R2. The sheathed elements according to Figures 2 and 3 can have the; same geometry and heating characteristic, that is to say it is possible to use a standard sheathed element to realised different depths of annular gap (here: Rl > R2), and thus also different dimensions of projection (here: VI
1. Sheathed-element glow plug (10) for arrangement
in the combustion chamber of air-compressing internal
combustion engines, having a tubular, metallic plug
housing (11) in the longitudinal bore (12) of which a
sheathed element (16) is fixed in a sealing fashion
with a part of its length, and having a connecting bolt
(18) which serves to conduct current and is arranged partially in the sheathed element, and there being located at least partially between the sheathed element
(16) and plug housing (11) an annular gap (21) which emerges from the end of the plug housing on the combustion chamber side, characterized in that the annular gap (21) is formed by a zone (16A) of reduced diameter on the sheathed element (16C).
2. Sheathed-element glow plug according to Claim 1, characterized in that different depths (Rl, R2) of annular gap and dimensions (V) of projection can be realised by means of a single standard sheathed element of the same geometry and heating characteristic by means of a varying depth of impression of the sheathed element into the press fit of the plug housing.
3. Sheathed-element glow plug according to Claim 1 or 2, characterized in that in order to implement different depths (Rl, R2) of annular gap use can be made of a single standard plug housing whose press fit and annular gap has in the direction of a combustion chamber a constant diameter or an arbitrary diameter step of constant geometry.
4 . Sheathed-element glow plug according to one of Claims 1 to 3, characterized in that the changing diameter at the annular edge (16B) of the sheathed element (16) has an arbitrary geometrical configuration, and the sheathed element is pressed into
the plug housing in such a way that the diameter step occurs inside the plug housing.
5. Sheathed-element glow plug according to one of
Claims 1 to 4, characterized in that the region of the
expansion of diameter of the sheathed element (16)
inside the plug housing requires a lesser degree of
reforming of the hot tube.
6. Sheathed-element glow plug according to one of
Claims 1 to 5, characterized in that the diameter step
is produced on the sheathed element by, in particular,
hammering, rolling, drawing or cold-impact extrusion.
7. Sheathed-element glow plug according to one of
Claims 1 to 6, characterized in that there is formed in
the interior of the plug housing an annular edge (15)
which is slightly smaller than the outside diameter of
the sheathed element (16) in this region.
|Indian Patent Application Number||2860/MAS/1998|
|PG Journal Number||27/2007|
|Date of Filing||24-Dec-1998|
|Name of Patentee||ROBERT BOSCH GMBH|
|Applicant Address||POSTFACH 30 02 20, D-70442 STUTTGART, FEDERAL REPUBLIC|
|PCT International Classification Number||F23Q7/00|
|PCT International Application Number||N/A|
|PCT International Filing date|