Exhaust gas turbine of an exhaust gas turbocharger

An exhaust gas turbine for an exhaust gas turbocharger has a nozzle ring having an inner ring and an outer ring supporting a plurality of guide vanes. The nozzle ring is diagonally supported between a covering ring and the inlet casing, with the outer ring bearing against the covering ring and the inner ring bearing against the inlet casing. The outer ring provides an axial expansion gap with gas inlet casing and a radial expansion gap with the gas outlet casing. The nozzle ring is free to expand into the axial and radial gaps as a result of thermal expansion, without causing stress to the adjacent components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to the exhaust gas turbine of an exhaust gas 
turbocharger which is connected to an internal combustion engine. 
2. Discussion of Background 
During operation of an exhaust gas turbocharger, the exhaust gas turbine of 
the latter is exposed to relatively high temperatures from the internal 
combustion engine connected thereto. High thermal stresses thus arise in 
the turbine-side components, such as for example the gas inlet casing, the 
nozzle ring, the covering ring and the gas outlet casing. Since each of 
these components is at a different distance from the internal combustion 
engine and, moreover, different materials are used, the component 
temperatures differ accordingly. This results in different thermal 
expansions with relative movements between the individual components, 
which may lead to screws breaking, gas leakages and components cracking. 
The design and arrangement of the separating locations of gas inlet 
casing, gas outlet casing, nozzle ring and covering ring thus play an 
important part in the ability of an exhaust gas turbocharger to function. 
DE-A1-4223496 has disclosed a screw connection of the nozzle ring to the 
gas inlet casing. For this connection, the inner ring of the nozzle ring 
is of thickened design and provided with an additional flange which 
receives the screws serving for connection to the gas inlet casing. 
The one-sided screw connection may lead to irreversible distortions of the 
nozzle ring in the event of such a solution. Moreover, there is the risk 
of a bypass flow being formed on the outer ring of the nozzle ring, as a 
result of which the efficiency of the exhaust gas turbine and thus that of 
the turbocharger is reduced. Owing to the high generation of heat on the 
turbine side, the screws serving to fasten the nozzle ring are positioned 
in a very fixed manner and can only be removed with very great difficulty. 
The assembly time required to exchange the nozzle ring is therefore 
considerably lengthened, which is a significant disadvantage for the 
internal combustion engine which is connected to the exhaust gas 
turbocharger and is dependent on the latter in terms of its power. 
EP-B1-191380 shows the exhaust gas turbine of an exhaust gas turbocharger, 
the nozzle ring of which turbine is clamped against the gas inlet casing 
by the covering ring. For this purpose, the outer ring of the nozzle ring 
has an axial projection and the covering ring has a corresponding 
fastening flange. The latter is connected to the gas inlet casing by means 
of a plurality of screws. In the peripheral direction, the nozzle ring is 
fixed on the gas inlet casing by means of positively locking centering 
bolts. 
A drawback which is common to both solutions is that the nozzle ring in 
each case has an additional component for arranging or accommodating 
fastening elements. As a result, its production is complicated and thus 
relatively expensive. Moreover, both the axial projection of the outer 
ring and the flange of the inner ring are at risk from cracking, owing to 
the thermal stresses which have already been described above, as a result 
of which reliable fastening of the nozzle ring and thus the functioning of 
the turbocharger are not ensured in the long term. 
SUMMARY OF THE INVENTION 
Accordingly, one object of the invention is to avoid all these drawbacks by 
designing the exhaust gas turbine of an exhaust gas turbocharger such that 
simple and reliable fastening of the nozzle ring is ensured. 
This is achieved according to the invention in that, the nozzle ring bears 
against the covering ring by means of its outer ring and against the gas 
inlet casing by means of its inner ring. An axial expansion gap is formed 
between the outer ring and the gas inlet casing and a radial expansion gap 
is formed between the outer ring and the gas outlet casing. 
The reasons for the advantages of the invention are that the nozzle ring is 
only braced diagonally between the gas outlet casing and the gas inlet 
casing. Owing to this fastening, the flux of force in the nozzle ring 
starts from the covering ring and passes via the outer ring, the guide 
vanes and the inner ring as far as the gas inlet casing. Due to the two 
expansion gaps, the nozzle ring can expand freely both in the radial and 
in the axial direction. This diagonal bracing of the nozzle ring provides 
the conditions for free thermal expansions between the turbine-side 
components, so that either no thermal stresses are formed or these 
stresses can be compensated. 
There are no components which are at risk of cracking and reinforce the 
nozzle ring. It is thus of relatively resilient, i.e. elastic, design and 
to a certain extent acts as a diaphragm between the components surrounding 
it. Since the nozzle ring has no fastening flanges, it can be manufactured 
in a simple and cost-effective manner. Since as a result no screws are 
required for its fastening, working time is also saved during assembly and 
dismantling. As an additional advantage, the nozzle ring can now be 
mounted from both sides, i.e. both from the compressor side and from the 
side of the internal combustion engine. 
It is particularly expedient if a sealing surface with respect to the gas 
inlet casing is arranged on the gas outlet casing. An assembly gap is 
formed radially outside the sealing surface between the gas outlet and the 
gas inlet casing. By virtue of this design, effective sealing is achieved 
between gas inlet and gas outlet casing. 
Furthermore, it is advantageous if the gap width of the axial and/or of the 
radial expansion gap is designed to be larger than or equal to the maximum 
thermal expansion of outer ring and gas inlet casing and of outer ring and 
gas outlet casing, respectively. 
In this manner it is ensured that the nozzle ring retains its elastic form, 
that is to say no stresses occur, under all operating conditions of the 
exhaust gas turbine. In an extreme case, the outer ring may bear lightly 
in the axial direction on the gas inlet casing and in the radial direction 
on the gas outlet casing, without the resultant pressure leading to wear 
of the material. This has the advantage that gas leakages can be 
prevented. 
Finally, both the outer and also the inner ring each have a significantly 
smaller material thickness than the covering ring and the gas inlet 
casing. The resulting minimal differences in wall thickness between the 
guide vanes of the nozzle ring and its outer and inner ring have the 
consequence of only low thermal stresses. 
It is particularly advantageous if outer and inner ring are made from sheet 
metal. The nozzle ring can thus be manufactured in a very simple and 
cost-effective manner. 
In a second configuration of the invention, a clamping segment, which is 
positively locking with the gas inlet casing and also with the gas outlet 
casing in the axial direction, is arranged on the said gas inlet casing 
and is provided with recesses for the connecting elements. At least one 
radial gap is formed between the gas inlet casing and the clamping 
segment. In contrast to the first configuration, the thermal expansions of 
the gas inlet casing can also be compensated for in this manner. 
Consequently, the connection location of gas inlet and gas outlet casing 
is relieved of load, so that significantly lower operating stresses occur. 
For this reason, the solution is also particularly suitable for 
turbochargers which are subject to high thermal loads.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein like reference numerals designate 
identical or corresponding parts throughout the several views, the exhaust 
gas turbine of a turbocharger has a turbine casing 3, which is formed by a 
gas inlet and a gas outlet casing 1, 2 and is held together by means of 
connecting elements 4 designed as screws. A turbine rotor 6 supported by a 
shaft 5 and having rotor blades 7 is arranged in the turbine casing 3. The 
turbine rotor 6 is outwardly delimited by a covering ring 8 which is 
designed as a diffuser and is in turn fastened on the gas outlet casing 2 
by screws 9. A flow duct 10 is formed between the turbine rotor 6 and the 
turbine housing 3, which flow duct receives the exhaust gases from a 
diesel engine, which is not shown and is connected to the turbocharger, 
and conducts them further to the turbine rotor 6. Of course, a different 
internal combustion engine may also be connected to the turbocharger. 
A nozzle ring 14 comprises an outer ring 11, an inner ring 12 and a number 
of guide vanes 13 arranged between the outer ring and inner ring. The 
nozzle ring 14 is formed as a casting, and is arranged in the flow duct 10 
upstream of the turbine rotor 6. The said nozzle ring is axially braced 
between the covering ring 8 and the gas inlet casing 1 and is arranged 
radially inside the gas outlet casing 2. To this end, the nozzle ring 14 
bears against the covering ring 8 with its outer ring 11 and against the 
gas inlet casing 1 with its inner ring 12. Both its outer and the inner 
ring 11, 12 each have a significantly smaller material thickness than the 
covering ring 8 and the gas inlet casing 1 (FIG. 1). Naturally, the nozzle 
ring 14 may also be made from different materials, such as for example of 
sheet metal or steel profiles, or consist of ceramic. 
An axial expansion gap 15 is formed between the outer ring 11 and the gas 
inlet casing 1 and a radial expansion gap 16 is formed between the outer 
ring 11 and the gas outlet casing 2. The gap width of the expansion gaps 
15, 16 is larger than the maximum thermal expansion of outer ring 11 and 
gas inlet casing 1 and of outer ring 11 and gas outlet casing 2, 
respectively. The ratio of the gap width of the radial expansion gap 16 to 
the gap width of the axial expansion gap 15 is here about 4:1. This ratio 
is produced by the radial and the axial dimensions of the nozzle ring 14. 
Naturally, the gap widths may also correspond to the maximum thermal 
expansion of the components concerned. 
FIG. 2 shows an enlarged detail of FIG. 1 which approximately illustrates 
the size ratios of the gap widths. A sealing surface 17 with respect to 
the gas inlet casing 1 is formed on the radially inner region of the gas 
outlet casing 2. An assembly gap 18 is arranged radially outside this 
sealing surface 17 between the gas outlet casing 2 and the gas inlet 
casing 1. 
The inner ring 12 is supported on the gas inlet casing 1 in a manner secure 
against torsion by means of a plurality of positioning elements 19 
designed as pins. To receive the pins 19, the inner ring 12 has a 
corresponding number of thickened portions 20 having first recesses 21 on 
its upstream side, while the gas inlet casing 1 has second recesses 22 
corresponding to the latter. Each of the first recesses 21 arranged in the 
thickened portions 20 additionally has an inner gap 23 in the region of 
the pin 19 (FIG. 1). 
During operation of the diesel engine, the hot exhaust gases therefrom pass 
via the gas inlet casing 1 or the flow duct 10 arranged therein to the 
turbine rotor 6 of the exhaust gas turbine. The nozzle ring 14 in this 
case has the task of passing the exhaust gases in an optimum manner to the 
rotor blades 7 of the turbine rotor 6. The turbine rotor 6 driven in this 
manner in turn provides the drive for the compressor which is connected 
thereto and is not shown. The air compressed in the compressor is used for 
turbocharging, i.e. increasing the power, of the diesel engine. 
The nozzle ring 14, which is arranged directly in the flow duct 10, is 
exposed to the high exhaust-gas temperatures in this process. Since its 
guide vanes 13 are relatively thin and the overall nozzle ring 14 moreover 
has a significantly lower mass than the gas inlet casing 1, the gas outlet 
casing 2 and the covering ring 8, the nozzle ring 14 undergoes a 
significantly greater rise in temperature than the said components 
surrounding it. 
The formation according to the invention of the radial and the axial 
expansion gaps 16, 15 allows the outer ring 11 of the nozzle ring 14 to 
expand freely both in the radial and in the axial direction in accordance 
with the actual operating conditions. In this process, the significantly 
greater radial expansion of the material in the region between the outer 
ring 11 and the gas outlet casing 2 compared to the possible axial 
expansion of outer ring 11 and gas inlet casing 1 is taken into account by 
means of the abovementioned ratio of the gap widths of about 4:1. In this 
manner, the thermal stresses formed between the covering ring 8, the gas 
inlet casing 1, the gas outlet casing 2 and the nozzle ring 14 can be 
compensated. The nozzle ring 14 is thus firstly braced diagonally between 
the covering ring 8 and the gas inlet casing 1 and secondly acts as a 
diaphragm between the components surrounding it. Due to the formation of 
the assembly gap 18, the sealing surface 17 always bears against the gas 
inlet casing 1. The sealing surface 17 prevents leakage of exhaust gases 
to the environment. When sheet metal is used as the material for the 
nozzle ring 14, the flexible design thereof is additionally supported. 
If the gap width of the axial and that of the radial expansion gap 15, 16 
corresponds to the maximum thermal expansion of outer ring 11 and gas 
inlet casing 1 and of outer ring 11 and gas outlet casing 2, respectively, 
then the outer ring 11 bears axially against the gas inlet casing 1 and 
radially against the gas outlet casing 2 under full load of the diesel 
engine. As a result, the expansion gaps 15, 16 are closed during operation 
of the exhaust gas turbine. It is thus impossible for any exhaust gas to 
penetrate into the cavity formed between the outer ring 11, the gas outlet 
casing 2 and the diffuser 8. In this manner, both interference with the 
exhaust gas flow and losses through the gap are avoided, which results in 
a higher efficiency. 
In a second exemplary embodiment, a clamping segment 24, which is axially 
positively locking with the gas inlet casing 1 and also with the gas 
outlet casing 2, is arranged on the said gas inlet casing and is provided 
with recesses 25, designed as bores, for the screws 4. Radial gaps 26 are 
formed between the clamping segment 24 and the gas inlet casing 1 (FIG. 3) 
. As a result, the gas inlet casing 1 can also expand radially without 
increasing its operating stresses. The further arrangement and functioning 
of the components is similar to the first exemplary embodiment. 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein.