Compressor arrangement

A compressor arrangement for producing compressed air includes a compressor connected through a line to devices using the compressed gas and a supercharger driven by the exhaust of a heat engine. In order to improve the overall efficiency of the arrangement, the compressor is driven by the drive side of the heat engine and the supercharger is arranged in one of an intake line and a pressure line of the compressor. The pressure line forms the connection between the compressor and a pressure reservoir which is connected through another line to the devices using the compressed gas.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a compressor arrangement of any type as it 
is usually used for the compression of a gaseous medium, particularly air. 
More specifically, the present invention relates to a compressor 
arrangement for the compression of a gaseous medium by means of a 
compressor which is driven by the working side of a heat engine and 
connected through a line to consuming devices. The driving side of at 
least one exhaust-driven supercharger is connected to the exhaust side of 
the heat engine and is connected through a line to the compressor. 
2. Description of the Related Art 
Mobile units for supplying compressed gas are required for the operation of 
movable devices which use compressed air and of implements as they are 
used, for example, in construction. 
In view of the fact that natural resources must be used today more 
responsibly, it is necessary that especially commercial users of large 
amounts of energy save a portion of the energy by improved efficiencies of 
the used machines and devices. In the field of compressor technology, many 
attempts have been made to utilize exhaust heat, either within the process 
or outside of the process, in order to improve the energy balance and, 
thus, increase the overall efficiency. 
DE-OS 29 12 190 discloses an arrangement for the production of compressed 
air of the above-described type in which the exhaust side of a multiple 
lifting cylinder internal combustion engine is connected to the driving 
side of an exhaust-driven supercharger. Air which has been taken in by the 
fresh air compressor of the exhaust-driven supercharger and which has been 
compressed is supplied through an intermediate cooler to the intake side 
of the internal combustion engine. Following the intermediate cooler, a 
line branches from the charging line leading to the internal combustion 
engine which is connected to the intake side of an air compressor, for 
example, a reciprocating compressor. The pressure line of the air 
compressor is connected to auxiliary units which in motor vehicles are 
operated by means of compressed air, such as, vehicle brakes, pneumatic 
suspension, door openers, etc. As a result of the proposed arrangement, an 
additional air filter for the air compressor is unnecessary and the 
thermal load acting on the components of the air compressor is lowered 
because of the reduction of the final compression temperature. 
A method for operating a compressor with an internal combustion engine for 
the specific production of high-temperature high-pressure gas is known 
from EP 0 248 640. In this method, the exhaust heat of the internal 
combustion engine is utilized in an advantageous manner for increasing the 
temperature of the compressed gas. However, although this method improves 
the overall efficiency, this manner of operation is limited to the 
described specific field of application and is useless for compressed gas 
which is usually cooled. 
In addition, DE-OS 31 34 844 discloses a multiple-stage compressor with 
coolers which are arranged between the individual stages of the compressor 
and which are integral components of a heat pump. In this case, 
compression heat produced by the process is converted into externally 
usable heat. The heat made available in this manner is not intended for 
internal use. This does improve the energy balance of the compressor 
arrangement, however, external processes are necessary for utilizing the 
recovered energy. Accordingly, this known manner of improving the 
efficiency cannot be used in independent movable compressors of the 
above-described type. 
A structurally very simple solution is disclosed in U.S. Pat. No. 
2,849,173. A heat engine, preferably a multiple-cylinder diesel engine, is 
connected through a coupling to a reciprocating compressor B. A second 
compressor A is arranged in the exhaust gas line of the engine. The second 
compressor A has on the drive side thereof a gas turbine. The compressor 
side is a multiple-stage axial flow compressor whose intake pipe is 
connected to a cleaning filter. The pressure pipe of the axial flow 
compressor is connected through a line to the intake side of the 
reciprocating compressor B. An intermediate cooler is arranged in this 
connecting line. The compressor stage ranged upstream in this arrangement 
is an expensive solution because of the presence of the multiple-stage 
axial flow compressor which, in addition, requires a large mount of space 
and, for this reason, is not particularly suitable for a mobile unit. 
Another disadvantage is the arrangement of the additional compressor stage 
A in front of the main compressor B because a large flow volume must be 
compressed from a very low initial pressure to a medium pressure. Because 
of this large flow volume, the compressor part is also large. 
Another solution is proposed in U.S. Pat. No. 3,204,859. Also in this 
proposal, a precompressing compressor stage in the form of an exhaust gas 
supercharger is arranged in the exhaust gas line of a heat engine. The 
working side of the heat engine is connected through a shaft to the actual 
compressor unit. The airflow produced by the precompressing compressor is 
divided for charging the diesel engine, on the one hand, and to increase 
the quantity of the compressor, on the other hand. The supply of the 
precompressed gas takes place an intermediate portion of the compressor. 
This arrangement has the disadvantage that only a portion of the 
precompressed air flow is available for the secondary compression. In 
addition, the supply of air in the intermediate portion poses problems 
with respect to sealing and design of the machine because the compressor 
must be designed in the intake area for a small airflow and for a greater 
airflow for the area extending from the location where the additional 
supply takes place to the discharge. 
An arrangement which includes two exhaust gas superchargers arranged in the 
intake line of the compressor is known from U.S. Pat. No. 4,563,132. The 
multiple-cylinder heat engine, for example, a V8 engine is divided into a 
motor portion and a compressor portion. The two exhaust gas superchargers 
are located on the drive side in series in the exhaust pipe of the motor, 
while the compressor sides of the two superchargers are connected 
parallel. As is the case in the proposal discussed above, the 
precompressed airflow is divided to the motor and the compressor. The 
proposed division of a heat engine into a motor portion and a compressor 
portion has the disadvantage that the two units operate at the same rate 
of rotation. This makes it impossible to vary the pressure and the 
quantity delivered. As a rule, such a combination machine is designed for 
motor operation, so that the compressor side does not have the optimum 
design. 
SUMMARY OF THE INVENTION 
Therefore, it is the object of the present invention to improve the overall 
efficiency of mobile compressor arrangements and to provide a mobile 
compressor arrangement of compact construction. In this regard, the 
overall efficiency is considered to be the ratio of the required drive 
energy to the quantity of compressed gas. 
In accordance with the present invention, various types of arrangements of 
at least one or more exhaust-driven superchargers are provided, wherein, 
in the simplest case, the energy contained in the exhaust gas of the heat 
engine is utilized partially in at least one exhaust-driven supercharger 
for recompressing the compressed gas. 
The compressor referred to above is essentially a compressor of any type 
which is suitable for the compression of a gas. Among such compressors are 
all compressors with adjustable compression space, such as, reciprocating 
compressors and screw-type compressors, and also all compressors which 
operate in accordance with a different system of compression, such as, 
superchargers. The heat engines referred to above are lifting piston 
engines, such as diesel engines and gasoline engines, as well as rotary 
piston engines and gas turbines of any type. The gas to be compressed is 
particularly air, however, the gas may also be any other gaseous medium 
which is suitable for compression. Suitable as intermediate coolers are 
heat exchangers of any type which are capable of cooling a gas, 
particularly air. Used as cooling medium may be ambient air as well as any 
other medium suitable for cooling in an open system as well as in a closed 
system. Suitable as exhaust-driven superchargers are particularly those 
having a radial wheel on the compressor side and turbine side, however, 
all other exhaust-driven superchargers are suitable, for example, those 
having an axial turbine wheel. Such exhaust-driven superchargers can be of 
compact construction, so that they require little space. 
Starting from a known compressor which receives the gas to be compressed 
through a filter and an intake line and which feeds a pressure reservoir 
through a pressure line and which is operated by the working side of a 
heat engine, at least one exhaust-driven supercharger is provided. This 
exhaust-driven supercharger is arranged following the compressor for 
carrying out recompression. The supercharger is operated by the exhaust 
gas of the heat engine. It is particularly advantageous if the gas to be 
compressed is precompressed as well as recompressed because the overall 
efficiency is further improved due to the small compression ratio of each 
individual compression stage. The overall efficiency is further improved 
by arranging a heat exchanger as intermediate cooler between the 
individual compression stages be, cause the lowering of the temperature of 
the gas to be compressed lowers the energy required for the compressor 
arrangement. 
For an improved division of the required flow volumes, an advantageous 
feature of the present invention provides that the two exhaust-driven 
superchargers are arranged in series or parallel in the intake line or the 
pressure line. In the case of a parallel division of the exhaust gas flow 
to two superchargers, it may be advantageous to arrange a control valve in 
each of the branching-off areas. Even an arrangement of three or more 
superchargers may still be advantageous for improving the overall 
efficiency of the composer arrangement, even though this makes the 
arrangement more complicated and expensive. 
In addition, it is also possible to drive not only one but two or more 
mechanical compressors with one heat engine and to arrange one or more 
superchargers in front of, behind and/or between the compressors. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of the disclosure. For a better understanding of the invention, its 
operating advantages, and specific objects attained by its use, reference 
should be had to the drawing and descriptive matter in which there are 
illustrated and described preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The schematic diagrams shown in the figures of the drawing merely include 
some principal structural groups of a compressor arrangement and the 
components necessary with respect to the present invention. All other 
structural components and groups required for operating a compressor are 
independent of the invention and may be inserted as necessary, without 
influencing the gist of the invention. 
FIG. 1 of the drawing shows a known heat engine 40 with a compressor 50 
being connected to the working side of the engine 40. This compressor 50 
produces a pressure difference P2 between its input and its output. The 
exhaust side of the heat engine 40 is connected through an exhaust line 30 
to an exhaust-driven supercharger 20. The expanded exhaust gas of the heat 
engine 40 is removed through another exhaust line 32. The compressor part 
of the exhaust-driven supercharger 20 produces a pressure difference P1. 
This ensures that the energy on the working side of the heat engine 40 is 
converted by means of the compressor 50 and the exhaust energy of the heat 
engine 40 is converted by means of the exhaust-driven supercharger 20 in 
order to arrive at the desired pressure difference or compression ratio. 
Accordingly, by connecting the compressor stages in series, the total 
pressure difference of the compressor arrangement is the sum of all 
pressure differences, in this case P1 plus P2. 
For producing a predetermined pressure difference, a given compressor 
arrangement requires a predeterminable quantity of energy which can be 
removed as a constant quantity from the given heat engine 40. When the 
same quantity of energy is converted in the heat engine 40, the overall 
efficiency of the compressor arrangement is now greater because of the 
increased compression ratios, and the exhaust heat is utilized internally 
within the process. 
The diagram of FIG. 2 shows a compressor arrangement in which the gas to be 
compressed is cleaned by a filter 10 and is taken in by the compressor 50 
through intake line 60. The driver of the compressor 50 is the heat engine 
40. The exhaust gas of the heat engine 40 is conducted through the exhaust 
line 31 to the drive side of the exhaust-driven supercharger 22 and is 
subsequently removed through the exhaust line 33. The compressed gas from 
the compressor 50 reaches the pressure reservoir 80 the pressure line 72, 
73 to the compressor side of the supercharger 22 and then through the 
pressure line 74. The pressure reservoir 80 is monitored by a safety valve 
81. The compressed gas is conducted from the pressure reservoir 80 through 
the pressure line 75 via the pressure-maintaining check valve 82 and the 
pressure line 76 to the output valves 83. 
Depending on the type of arrangement, an intermediate cooler 91 may be 
arranged in the pressure line 72, 73 between the compressor 50 and the 
supercharger 22. The advantage of this arrangement as compared to the 
prior art is to be seen in the fact that recompression is required only 
for a small air volume because the main compression has already taken 
place in the compressor 50. Accordingly, the supercharger 22 may be of 
compact construction. 
Another embodiment of the present invention is illustrated in FIG. 3. In 
the arrangement of FIG. 3, two exhaust-driven superchargers 21, 23 are 
arranged on the drive side connected in series and parallel in the intake 
line 60, 61. As shown in FIG. 3, the gas to be compressed is separately 
cleaned in filters 10, 11 and is supplied through the intake line 60, 61 
on the compressor side to the two exhaust-driven superchargers 21, 23. The 
respectively precompressed quantity of gas is then supplied to the 
compressor 50 through pressure lines 70, 77, 78, 79 arranged at the intake 
of the compressor 50. The compressor 50 is driven, in turn, by a heat 
engine 40. The exhaust gas of the heat engine 40 is initially supplied to 
the drive side of the first exhaust-driven supercharger 21 and 
subsequently, after partial expansion, to the drive side of the second 
exhaust-driven supercharger 23. In this arrangement, the sequence of the 
drive sides of the two superchargers 21, 23 arranged in series is 
insignificant. Depending on the type of arrangement, an intermediate 
cooler 90 may be arranged in the intake line 78, 79 or the compressor 50. 
FIG. 4 shows another arrangement with two exhaust-driven superchargers 21, 
23 arranged in the intake area. Contrary to FIG. 3, in this arrangement 
the compressor sides of the two superchargers 21, 23 are connected in 
series. The drive sides are also connected in series. In this arrangement, 
the exhaust gas of the heat engine 40 is initially supplied to the drive 
side of the supercharger 23 immediately in front of the compressor 50 and 
subsequently, after partial expansion, to the drive side of the 
supercharger 21 which is arranged following the cleaning filter 10. It is 
apparent that the exhaust gas flow can also be conducted in reverse 
sequence initially to the drive side of the supercharger 21 following the 
cleaning filter and then to the drive side of the supercharger 23 arranged 
in front of the compressor 50. Depending on the type of arrangement, an 
intermediate cooler 90, 92 each may be provided between the compressor 50, 
on the one hand, and the two superchargers 21, 23, on the other hand. 
Similar to FIG. 3, FIG. 5 shows two exhaust-driven superchargers 21, 23 
which are connected in parallel and arranged in the intake area of the 
compressor 50. However, contrary to FIG. 3, the exhaust gas flow is 
divided, so that the drive sides of the two superchargers 21, 23 are 
parallel. As an alternative, FIG. 5A shows the arrangement of a valve 
control in the branching-off point of the exhaust gas flow. This control 
may be required if the output data of the two superchargers 21, 23 are 
different. 
FIG. 6 shows the compressor arrangement according to the present invention 
in which the compressor sides of the two superchargers 21, 23 are 
connected in series. As an alternative, FIG. 6A shows the arrangement of a 
valve control in the branching-off point of the exhaust gas flow. This may 
be an advantage if it is taken into consideration that the work performed 
by the two superchargers 21, 23 is different. 
Another embodiment of the compressor arrangement according to the present 
invention is shown in FIG. 7. In this arrangement, an exhaust-driven 
supercharger 21 is arranged in front of the compressor 50 and an 
exhaust-driven supercharger 22 is arranged following the compressor 50. 
FIG. 7A additionally shows a control of the exhaust gas flow in the 
branching-off point. As already mentioned above in connection with the 
other embodiments, depending on the type of arrangement, an intermediate 
cooler 90, 91 each can be arranged between the compressor 50 and the two 
superchargers 21, 22. Each intermediate cooler 90, 91 may optionally be 
provided with a condensate discharge. 
FIG. 8 of the drawing shows a compressor arrangement according to the 
present invention similar to the one shown in FIG. 7. In this arrangement, 
the drive sides of the exhaust-driven superchargers 21, 22 are connected 
in series. In principle, it is conceivable that the exhaust gas is first 
supplied to the drive side of the supercharger 21 arranged in front of the 
compressor 50 and then to the drive side of the supercharger 22 arranged 
following the compressor 50. At any rate, the sequence shown in FIG. 8 is 
thermodynamically more advantageous. 
FIGS. 9 and 10 of the drawing show a reverse arrangement of the 
superchargers as compared to FIGS. 3 to 6. In FIGS. 9 and 10, the two 
exhaust-driven superchargers 22, 24 are arranged following the compressor 
50. With respect to the arrangement in series and in parallel, the same 
variations are possible as those shown in FIGS. 3 to 6. In principle, the 
arrangement of FIG. 9 corresponds to that of FIG. 5 and the arrangement of 
FIG. 10 corresponds to that of FIG. 4. Not illustrated are the 
arrangements corresponding to the arrangement of FIG. 3, i.e., drive sides 
in series and compressor sides in parallel, and the arrangement of FIG. 6, 
i.e., drive sides in parallel and compressor sides in series. 
FIG. 11 of the drawing shows together with FIG. 11A a further development 
of the invention in which three exhaust-driven superchargers 21, 22, 23 
are provided. In this arrangement, two superchargers 21, 23 are arranged 
in parallel and in front of the compressor 50 and one supercharger 22 is 
arranged following the compressor 50. In order to be complete, it is 
pointed out that, similar to the examples described above, corresponding 
variations are possible, depending on whether a connection in series or in 
parallel is provided and how the exhaust gas flow is conducted and 
divided. Further combinations of three and more superchargers are 
possible. However, these combinations are not illustrated because they are 
not required for a better understanding of the invention. 
It should be understood that the preferred embodiments and examples 
described are for illustrative purposes only and are not to be construed 
as limiting the scope of the present invention which is properly 
delineated only in the appended claims.