Free-running pressure wave supercharger driven by gas forces

In a free-running pressure wave supercharger driven by the gas forces, nozzles (27) are provided in the gas casing (6) and possibly also in the air casing (5), which nozzles are connected--via a drive line (26)--with a position in the air casing (5), preferably with the high-pressure air port (2), at which position a surplus pressure relative to the nozzle entry occurs during the run-up phase of the pressure wave supercharger. A control device 15 actuates a supercharge air flat (14) in the port (2) and a valve device (23+25) in the drive line (26) in the opposite sense, i.e. if the supercharge air flap (14) holds the port (2) closed, the valve device (23+25) frees the flow through the drive line (26) to the nozzle (27) and vice versa. The diaphragm capsule (17) of the control device (15) is subjected, on one side, to the pressure in a compression pocket (11) via a control pressure line (19) and, on the other side, to the pressure before the supercharge air flap (14) in the port (2). During the run-up phase, the pressure in the compression pocket (11) exceeds the pressure in front of the supercharge air flap (14) and the nozzle (27) receives drive air. As soon as the pressure in front of the supercharge air flap (14) exceeds the pressure in the compression pocket (11), the supercharge air flap (14) opens and simultaneously closes the valve device (23+25). The nozzle (27) is switched off and the further drive is then mainly provided by the high-pressure exhaust-gas jet from the port (3) entering obliquely to the direction of the rotor peripheral velocity.

The present invention relates to a free-running pressure wave supercharger 
driven by gas forces. 
BACKGROUND OF THE INVENTION 
In the use of pressure wave superchargers as supercharge air compressors 
for internal combustion engines, the drive of the pressure wave 
supercharger rotor in the currently practiced state of technology takes 
place at a constant transmission ratio from the engine itself. The 
rotational speed of the rotor is therefore proportional to the engine 
rotational speed. The drive elements conventionally used for this purpose 
are V-belts, V-belt pulleys and belt tensioners. Although this type of 
drive has been proven in practice, there are still extra requirements, 
mainly because of the high transmission ratio between the engine and the 
pressure wave supercharger and the associated high belt and bearing 
peripheral speeds and also because of the severe transverse bearing loads 
due to the belt tension. The forces from the engine vibrations transferred 
via the belts to the pressure wave supercharger also contribute to the 
bearing loads. The pressure wave superchargers intended for the engines of 
passenger cars are also fairly small at relatively high engine powers. 
They do not therefore provide sufficient installation space for large 
rolling contact bearings capable of carrying heavy loads instead of the 
currently used rolling contact bearing sizes, whose dimensions have to be 
kept as small as possible for the reasons given below and whose rolling 
bodies therefore often run even without an inner race directly on a 
hardened section of the rotor shaft. These bearing designs make it 
possible to keep the rotor with its pressure exchange cells as small as is 
permitted by the exhaust gas and air throughput necessary for a specified 
power range of an engine. The smaller the shaft, bearing and thus also the 
rotor hub can be designed, therefore, the smaller the external dimensions 
of the rotor and hence of the complete pressure wave supercharger can be 
kept. In the case of direct mechanical drive of the rotor by the engine, 
however, lower limits are set to the bearing dimensions by the 
abovementioned factors of high transmission ratio, high bearing peripheral 
speed (and by the large amount of frictional heat caused by the high 
bearing peripheral speeds, which is difficult to remove because of the 
compact dimensions) and, especially because of the severe transverse 
loading due to the drive belts and the engine vibrations. The requirement 
for a particular minimum life of the bearings is thus a factor opposing 
further reduction of the bearing dimensions in this drive concept. 
If the belt tension is avoided or if no use is made at all of any other 
driving element which causes transverse loading on the bearings, the 
mechanical and hence also the thermal bearing loads are reduced and, 
consequently, the bearing life is increased for the currently usual 
bearing dimensions. In a particular case, the bearings can be dimensioned 
so as to economize in space at a life which is otherwise the same. The 
transverse loading can, for example, be avoided by direct co-axial 
coupling of the rotor shaft to an electrical, hydraulic or similar drive 
source and, of course, also by coupling to an intermediate drive which 
accepts the transverse load due to the belt tension or the like and whose 
shaft has a coupling flange at the supercharger end and, at the other end, 
as usual preferably a belt pulley. Chain and gearwheel drives are 
practically out of the question as drive because of the large transmission 
ratios between the engine crankshaft and the rotor shaft of the pressure 
wave supercharger. 
However, the abovementioned drives with intermediate drive, which are free 
from transverse forces, are also associated under certain circumstances 
with a decisive disadvantage for practical application. This is the 
limited freedom in the choice of the arrangement of the pressure wave 
supercharger in the engine compartment of a motor vehicle. In the case of 
belt drive, with or without intermediate drive, for example, the rotor 
shaft must be located parallel to the engine crankshaft--if unfavorable 
angle drives are not to be accepted. Electrical and hydraulic drives offer 
more freedom in this respect but are in turn more complicated, therefore 
more expensive and are also more difficult to deal with from a control 
point of view. Because the belt drive, together with the belt tensioning 
device, occupies one belt plane in the engine compartment, it makes the 
accommodation of the belt drive for the other auxiliaries more difficult. 
Full freedom in the arrangement of a pressure wave supercharger at 
economically justifiable cost is therefore provided, in practice, only by 
exhaust-gas drive, as in the case of exhaust-gas turbochargers. The supply 
of the exhaust gases to the exhaust gas casing of the pressure-wave 
supercharger, with its control edges and ports, can be carried out without 
any problems by an easily designed exhaust-gas duct and many possibilities 
are conceivable for converting the flow energy of the exhaust gases into 
the rotational motion of the rotor. Examples of such possibilities are 
tangential action on the rotor cell walls or on rows of blade rings 
specially provided for this purpose in association with elements fixed to 
the casing for the deflection and, if required, locally distributed 
concentration of the exhaust-gas flow into the rotor casing or into a ring 
of blading provided for that purpose in order to generate a tangential 
component of the inlet velocity of the exhaust-gas flow. 
As a further disadvantage of the positively driven pressure wave 
supercharger, which has to be avoided, is the risk of a crack in the belt 
which demands expensive measures for emergency operation which must still 
ensure safe return home of the vehicle under its own power. 
There is also difficulty in controlling the belt tension, which can be too 
large or too small and can therefore overload the bearing or lead to slip 
and, in consequence, premature belt wear. Because of the high rotational 
speed of the pressure wave supercharger, the problem of low pressure 
scavenging arises in the higher idling speed range of the engine and, 
similarly, incorrect flows to the rotor with corresponding inlet flow 
losses occur due to the fixed drive transmission ratio in certain 
operating ranges. 
As already stated, an important advantage of the exhaust-gas-driven 
pressure wave supercharger with rolling contact bearings is that it can be 
arranged in any given position relative to the engine, including 
transversely or at any given angle or even at right angles to it. 
Still further advantages should, however, be mentioned. The disappearance 
of the transverse load on the bearings permits the use of smaller 
bearings; in consequence, as also already mentioned, the peripheral 
velocity of the rolling bodies and hence, at the same rotational speed, 
the thermal loading becomes smaller relative to pressure wave 
superchargers with larger bearings. The smaller bearing diameters make it 
possible to increase the free cell cross-section for the same external 
dimensions of the supercharger, i.e. to increase the usable flow 
cross-section of the rotor. The supercharger can therefore be used for a 
larger engine. Advantages also appear with respect to the critical 
rotational speed, which appears at a greater distance from the rotational 
speed range at which the supercharger is mainly operated. Similarly, the 
response behavior becomes better during all acceleration procedures, 
provided the charging limit of the rotor is not exceeded. At low full-load 
rotational speeds of the engine, the exhaust-gas-driven rotor will also 
run more rapidly than one driven at a fixed transmission ratio from the 
engine. This reduces the pulsation of the charge air supply otherwise 
present at low rotational speeds and permits a smaller receiver volume, 
which in turn reduces the thermal inertia and makes the exhaust-gas 
receiver cheaper. 
Pressure wave machines whose rotor is driven by a gas which has to be 
expanded independently of a prime mover are known from the patent 
literature. In contrast to the pressure converters mainly used as charging 
machines and which convert the energy contained in the exhaust-gas flow of 
an engine to increase the pressure of a supercharge airflow of 
approximately the same weight, the pressure of this supercharge air flow 
being above that of the exhaust-gas flow, the patents mentioned concern 
pressure exchangers, in which the air to be compressed is brought 
approximately to the pressure of the expanding medium, i.e. the exhaust 
gases of an engine, for example, or, in the case of the use of a pressure 
exchanger as the high pressure stage of a gas turbine, air heated in a 
combustion chamber or by a heat exchanger. In such a pressure exchanger, 
the energy of the exhaust gases or of the heated air serves to compress a 
quantity of cold air which is larger than the quantity of the exhaust 
gases or heated air to be expanded. Since in an engine, the supercharge 
airflow is approximately equal to the exhaust-gas flow, there is generally 
no requirement for the surplus air so that pressure exchangers are 
scarcely considered for supercharging but are considered, as stated, as 
the high pressure compressor or gas turbine in association with a 
conventional axial or centrifugal compressor as the low pressure 
compressor part and also for refrigerating machines, heat pumps, chemical 
processes, pressure fired steam boilers, etc. 
Such a pressure exchanger is known from Swiss Patent No. 225,426. In the 
rotor of this pressure exchanger, the cell walls are inclined relative to 
an axial section plane, approximately in the form of a helical surface, or 
are curved in blade shape. The actual desired objective of cell walls 
formed in such a way consists in avoiding or reducing the shock losses of 
the gases taking place in the pressure exchange process at entry into or 
outlet from the rotor cells. The absolute outlet velocity relative to the 
rotor receivers a peripheral component so that the absolute outlet 
velocity is reduced; in contrast, the inlet of the gas can take place with 
shock, which drives the rotor. 
A further pressure exchanger, which is located as the high pressure 
compressor between a low pressure axial compressor and a gas turbine and 
whose rotor can be either coupled to the turbine shaft or provided with 
its own drive independent of the gas turbine, is described in Swiss Patent 
No. 550,937. There is no mention of self-drive in this patent 
specification. It describes, rather, how the pressure difference between 
the expanding hot gas and the cold gas to be compressed in the low 
pressure zone can be increased by means of a special design of the rotor 
cells without simultaneously increasing the corresponding pressure 
difference on the high pressure side, in order to unload the compressor 
and, by this means, to increase the useful power and efficiency of the 
installation. 
A pressure exchanger with self-drive by the pressure transmitting medium 
is, on the other hand, described in British Patent No. 921,686. In this, 
the cell walls on the inlet side are curved over one third of their length 
but are parallel to the axis in the other part and the associated inlet 
ports are inclined relative to the end surface of the rotor in such a way 
that they enter tangentially into the curved section of the rotor cells. 
The force driving the rotor arises due to the deflection of the inflowing 
medium on the curved part of the cell walls of the rotor. 
The previously mentioned pressure wave machines are pressure exchangers 
which, as stated, can hardly be considered for the supercharging of 
internal combustion engines. This is reserved for pressure wave 
superchargers acting as pressure converters, in which achievement of the 
drive by the engine exhaust gases requires a series of measures which 
extend beyond the shaping of the cell walls of the rotor to deflect or 
change the direction of the exhaust gas flow and which may not previously 
have been proposed because a usable concept of a pressure converter which 
satisfies the operational requirements to be met by a supercharging unit 
is not known. There should, therefore, be hardly anything to discover in 
the relevant state of technology. A practically usable pressure wave 
supercharger with self-drive includes inter alia, a starting valve device, 
by means of which satisfactory engine starting and accelerating from rest 
under load in the cold condition, restarting the hot engine and driving 
away under load without delay is possible. It must ensure that the rotor 
supplies the supercharge airflow necessary for a sufficiently large 
acceleration torque and that for the particular part-load. Acceleration 
difficulties of the pressure wave supercharger in the case of a cold 
engine are caused by the fact that the grease in the rolling contact 
bearings is still stiff and/or by dirt in the rotor and hence increased 
friction between the casing and the end surfaces of the rotor. Such a 
starting valve, in association with other elements, also has to ensure 
satisfactory low idle running because otherwise, the rotor rotational 
speed would be so low that the particles contained in the exhaust-gas flow 
could pass over onto the air side. Devices such as throttle valves, 
wastegate and the like matched to the characteristic of the free-running 
pressure converter have to be provided for the control of the supercharge 
airflow over the whole of the load range. 
In principle, the exhaust gas flow can be used without further measures to 
drive a rotor with cell walls parallel to the axis because of the swirl 
flow always present. This "natural" swirl flow is not, however, capable of 
accelerating the rotor sufficiently rapidly and to sufficiently high 
rotational speeds corresponding to the particular load conditions. 
As stated and as appears from the relevant publications discussed, the 
known relevant means for driving a free-running rotor consist of cell 
walls curved or oblique to the rotor axis or cell wall parts in 
association with exhaust-gas inlet flow ducts correspondingly inclined to 
the rotor axis for increasing the velocity component of the exhaust-gas 
flow acting in the peripheral direction of the rotor. These means alone, 
however, do not suffice in their known form to meet the requirements 
placed on an actual pressure wave supercharger. They therefore have to be 
adapted to these requirements, more effectively designed and supported by 
elements to concentrate the exhaust-gas flow. Since the exhaust-gas flow 
energy necessary to drive the rotor is not, of course, available for the 
compression work to be transferred to the air, the increase in the leakage 
gaps (caused by the different amounts of heating and the different 
material expansion coefficients of the rotor and casing) between the end 
surfaces of the rotor and the gas and air casings during unsteady state 
operating conditions, such as starting and acceleration, must be kept as 
evenly small as possible in the interest of good compression efficiency. 
The present invention achieves the objective of producing an 
exhaust-gas-driven pressure wave supercharger acting as a pressure 
converter, which pressure wave supercharger satisfies the requirements 
sketched above and avoids the disadvantages described of the pressure wave 
supercharger driven at a constant transmission ratio by the engine.

DETAILED DESCRIPTION 
FIG. 1 is a schematic view of a first design example, the part of a 
free-running pressure wave supercharger essential for understanding the 
invention, i.e., a cylindrical section through the rotor, the gas casing 
and the air casing at half the height of the rotor cells developed in a 
plane. Of the two cycles present in the casings, one is shown with all its 
elements, whereas only the ports of the second cycle adjacent to the first 
cycle are shown. By "cycle" is here meant, as is general in the case of 
pressure wave machines, the totality of the gas and air ports, the 
expansion pockets, compression pockets and other auxiliary ducts necessary 
for the functioning of a pressure wave process. The two cycles are 
displaced at 180.degree. relative to one another in the air casing 5 and 
the gas casing 6. The main ports 1 to 4 enter at plane end surfaces of the 
air and gas casings 5 and 6 in a rotor casing 7, which encloses a cell 
rotor 8 with cell walls 9 with overhung support in known manner in the air 
casing 5. The cell walls 9 form the boundaries of rotor cells 10. The main 
ports are a low pressure air port 1, which induces the air from ambient 
pressure into the rotor cells 10 and which is, therefore, referred to 
below as the induction air port, a high-pressure air port 2, which is 
referred to below as the supercharge air port, a high pressure exhaust-gas 
port 3, through which the combustion gases expelled from the engine are 
fed into the rotor cells 10, where they compress the induced air to the 
supercharge air pressure, and a low-pressure exhaust-gas port 4, referred 
to below as the exhaust port, through which the exhaust gases expanded in 
the rotor cells 10 are led into the open air. The flow arrows belonging to 
one cycle in the ports 1 to 4 are solidly black and those belonging to the 
second cycle are only shown in outline. 
A cycle also includes auxiliary ports in the air casing and the gas casing. 
These auxiliary ports serve to maintain a functioning pressure wave 
process, in a known manner, over the whole of the operating range of an 
engine, i.e. in addition to the particularly important operating range for 
which the ports 1 to 4 and their opening and closing edges are optimally 
designed. These auxiliary ports are, in the present case, a compression 
pocket 11 in the air casing 5 between the induced air port 1 and 
supercharge air port 2. It is located directly in front of the latter, as 
seen in the direction of rotation of the rotor. Another auxiliary port is 
an expansion pocket 12 located between the supercharge air port 2 and the 
induced air port 1 of the following cycle. In the gas casing 6, a gas 
pocket 13 is directly after the high-pressure exhaust-gas port 3, again as 
seen in the direction of rotation of the rotor which is symbolized by the 
thick black arrow in the rotor cell development. 
For practical operation of a pressure wave supercharger for vehicle 
engines, a supercharge air flap 14 centrally pivotably supported is also 
provided in the supercharge air line 16, which connects the supercharge 
air port 2 of the air casing 5 to the air inlet ducts of the engine, which 
is not shown. The supercharge air flap 14 is actuated, for example, by a 
control device 15. The actuator of this control device 15 is formed by a 
diaphragm capsule 17 whose spring-loaded diaphragm 18 is subject, on one 
side, to the pressure in the supercharge air port 2 and, on the other 
side, to the pressure acting in the compression pocket 11 via a control 
pressure line 19. As long as the latter is dominant, the supercharge air 
flow 14 blocks the supercharge air port 2. Other process pressures or a 
suitable vacuum dependent on or controlled by the pressure wave process of 
the operating condition of the engine can also be considered for control. 
In this phase, with the supercharge air port 2 blocked, the engine operates 
as a normally induced engine by inducing air directly from the environment 
via a weakly spring-loaded breather valve 20. As soon as the rotor 8 of 
the supercharger comes up to high speed and the engine is loaded, the 
pressure wave process functions so that air is already compressed. In 
consequence, the pressure in front of the supercharge air flap 14 
increases, but, at the same time, the pressure in the compression pocket 
11 decreases so that the diaphragm 18 pivots the flap 14 into the open 
position. As soon as the pressure in the supercharge airflow exceeds the 
ambient pressure, the breather valve 20 remains closed and the engine 
receives only compressed air from the supercharger. 
The measures for increasing the acceleration torque during the starting 
phase are first described below. In order to start the rotor moving, the 
supercharge air flap 14 must be closed during the starting phase but the 
supercharge port 2 before the flap 14 must be unloaded by some sort of 
opening because, with the flap 14 closed, air flowing back from the 
supercharge air port 2 into the rotor 8 would adversely affect the action 
of the torque generating exhaust-gas flow. The exhaust-gas flow, which 
flows in at an accute angle, measured between the positive directions of 
the vectors of the rotor peripheral velocity and the inlet velocity of the 
high-pressure exhaust gas, has a driving effect from the initial ignition 
of the engine but would be weakened by the air flowing back. The relief 
flow of the supercharged air through the opening mentioned is utilized at 
an advantageously situated position of the air casing 5 to drive the rotor 
and is thus resupplied to the pressure wave process. 
For the present task of running up the rotor 8 from rest in a free-running 
state without mechanical coupling to the engine, the control device 15 can 
be coupled to an additional device, consisting of a driving line 21, which 
combines the space in front of the supercharge air flap 14 with a position 
in the land between the expansion pocket 12 and the induction air port 1 
and which emerges in this land in a nozzle 22, and with a slide valve 23 
in this driving line, whose slide 24 is connected by a rod to the flap 14. 
The nozzle 22 here forms the opening mentioned for relieving the 
supercharge air port 2 during starting. 
FIG. 1 shows the slide 24 in a position in which it opens the flow 
cross-section of the driving line 21. Since the pressure, in the case of a 
rotor at rest or rotating very slowly, is higher in the supercharge air 
port 2 than at the point of emergence of the nozzle 22, part of the air 
backed up in front of the flap 14, which air is still polluted with 
exhaust gas from the high-pressure exhaust-gas port 3 during this phase, 
flows out of the supercharge air port via the driving line 21 to the 
nozzle 22, which deflects a concentrated driving jet against the cell 
walls of the rotor and accelerates up its rotational speed until the 
pressure in the supercharge air port has reached a level sufficient to 
open the supercharge air flap 14. The resulting pivoting movement of the 
supercharge air flap 14 into its open position causes, via the rod 25, a 
closing movement of the slide 24 which, in consequence, shuts off the 
driving air flow to the nozzle 22. The rotational speed is then 
subsequently maintained mainly by the peripheral components of the 
high-pressure exhaust gas flowing into the rotor space at an acute angle 
and it is increased or reduced to suit the changes in load. The peripheral 
component of the induction air flowing from the port 1 into the rotor 
space, again at an acute angle, also contributes to a small extent. 
The location of the nozzle for the driving jet in the land between the 
expansion pocket 12 and the induction air port 1 has the advantage that 
the air/exhaust-gas mixture blown in at this point reaches the 
low-pressure exhaust-gas port 4 by the shortest route and does not flow 
back into the induction air port 1. The driving jet supports, by this 
means, the scavenging of the exhaust gas from the rotor cells into the 
low-pressure exhaust-gas port 4. 
The design in FIG. 2 based on the same principle differs from that 
described previously in that the driving line 26 emerges from the gas 
casing 6 in the land between the low-pressure exhaust-gas port 4 and the 
high-pressure exhaust-gas port 3. The slot-shaped nozzle 27, which extends 
over the whole of the cell height, is thus provided in the land between 
the high-pressure exhaust-gas port 3 and the low-pressure exhaust-gas port 
4 at a position at which pressure relief to the induction air port 1 can 
take place via the cell subject to the flow because otherwise back-up 
could occur in the relevant cell. The nozzle can be made cylindrical or 
conical in the region where it emerges which, as for the nozzle 22 in FIG. 
1, also applies to all the other nozzles of this type. There is no 
difference relative to the design first mentioned with respect to the mode 
of operation of the control device 15. 
After the supercharge air flap 14 has been opened, the breather valve 20 
remains closed due to the excess pressure of the supercharge air relative 
to the ambient air pressure and the engine receives its combustion air 
exclusively via the pressure wave supercharger. 
FIG. 3 shows a variant of the type first mentioned. It differs from the 
latter in the control of the flow of driving medium from the supercharge 
air port 2 to the nozzle 22 in the land between the expansion pocket 12 
and the induction air port 1. For this purpose, a spring loaded diaphragm 
valve 28 is provided instead of a slide 23 (coupled with the supercharge 
air flap actuation) in the driving line 21. The upper surface of the 
diaphragm 29 can be subjected in operation to the pressure from the 
supercharge air port 2 and its lower surface can be subjected to the 
pressure from the supercharge air line 16 via a control pressure line 30. 
As long as the supercharge air flap 14 is closed, the dominant pressure is 
the supercharge air port 2 pressure, which acts via the line 21 on the 
diaphragm 29, raises the latter from its seal seating and thus frees the 
path to the nozzle 22. As soon as the flap 14 has been opened by a 
sufficiently strong supercharge air flow, the pressures on both sides of 
the diaphragm 29 are the same and the flow to the nozzle 22 is therefore 
shut off so that the drive occurs by the high-pressure exhaust-gas alone. 
FIG. 4 shows a further possibility for using the compressor air from the 
supercharge air port for running up the rotor in the starting phase. The 
device 15 for controlling the supercharge air flat 14 corresponds 
substantially to that of FIG. 1 but the flap 14 has a hook-shaped nose 40 
on its back whose point, when the flap 14 is closed, presses on a closing 
element in the form of a spring-loaded plate 42 of a plate valve 41 
located upstream of the flap 14. By means of this arrangement, the air 
(backed-up in front of the flap 14) is blown against the cell walls 9 via 
a driving line 43, which is connected to the valve 41 and emerges in front 
of the compression pocket 11 in the rotor casing 7. As long as the 
pressure in the compression pocket 11 acting via the control pressure line 
19 on the upper surface of the diaphragm 18 exceeds the supercharge air 
pressure in front of the flap 14, the valve 41 remains open. During this 
period, the combustion air is induced via the breather valve 20. After a 
certain rotor speed, at which a pressure sufficiently high for supercharge 
operation of the engine has built up, has been reached, this pressure 
exceeds the pressure occurring in the compression pocket 11 and presses 
the diaphragm 18 upwards thus pivoting the flap 14 into the opened 
position. The nose 40 simultaneously frees the plate 42, which then shuts 
off the supercharge airflow into the driving line 43. 
In this design, the valve 41 also functions as a safety valve in the case 
of failure of the wastegate through which excess supercharge air is 
normally carried away. 
In all the previously described designs and in those described below, the 
nozzles mentioned for driving the rotor, just as the main and auxiliary 
ports in the air and gas casings mentioned in the introduction, extend 
over the complete height of the rotor cells and correspondingly, in the 
case of multiple flute rotors, over the height of the cells in the 
available flutes with radial interruptions. 
FIG. 5 shows a variant of the previously described design, in which a 
supercharge air flap 44 shuts off the supercharge air line 16 during the 
starting phase and the flow from the port 2 into a driving line 45 during 
operation under load. The flap 44 in this case therefore simultaneously 
also undertakes the function of the plate valve 41 in FIG. 4 with the 
exception of the function as a safety valve when the wastegate fails. This 
position of the flap 44 in operation under load is shown dash-dotted. 
Since, because of the single-sided deflection of the flap 44 to the wall 
of the duct 16, the space 47 subject to supercharge air in the diaphragm 
capsule underneath the diaphragm 18 is located downstream of the flap 44, 
a ventilation line 46 branches off from the port 2 upstream of the upper, 
free edge of the flap 44 and this ventilation line 46 enters into the 
space 47. The space 47 is sealed by a rubber collar 48, which also 
encloses the rod 25 to as to seal it, against the supercharge air line 16. 
The driving line 45 contracts to a nozzle 49 before entering the rotor 
space so as to increase the velocity of the driving jet. 
Another possibility of increasing the drive torque in the starting phase on 
the exhaust-gas side is to restrict the exhaust-gas flow. In the case of 
single-flute pressure wave superchargers with two cycles, this can be 
achieved by temporarily shutting off one of the two cycles and, in the 
case of two-flute superchargers, by shutting off one of the two flutes 
and, if necessary, in addition one of the two cycles of the other flute. 
By "flute" is here meant an independent, functional cell ring of a rotor 
with the associated ports, pockets etc. in the gas and air casings. In the 
case of a double-flute pressure wave supercharger, the rotor has two 
coaxial cell rings on one rotor hub, the exhaust-gas and air-side ports 
and pockets of the cell rings being located in one casing each. 
FIGS. 6 and 7 show diagrammatically, in section, the gas casing 55 of a 
single-flute supercharger with two cycles and a side view of the flange 56 
of the casing 55 corresponding to the projection direction VII shown in 
FIG. 6. A shut-off flap 58 is provided in the high-pressure exhaust-gas 
port 57 of the lower cycle, this flap being pin-jointed to the central 
guide body. In the closed position shown, the port 57 is shut off so that 
the total exhaust-gas flow enters the high-pressure exhaust-gas port 59 of 
the upper cycle. The lower cycle also includes the gas pocket 60 and the 
exhaust gas port 61, the upper cycle similarly including the gas pocket 62 
and the exhaust port 63. 
FIG. 8 shows an axial section through the gas casing 64 of a double-flute 
pressure wave supercharger. The two inlet flow ports 65 and 66 of the two 
flutes are separated by a partition 67. In this case, it is not only the 
inlet flow port 65 of the inner flute which is cut off by a shut-off flap 
68 but also the lower cycle of the outer flute of the exhaust-gas flow. In 
consequence, the upper cycle of the outer flute receives, in the starting 
phase, a multiple of the exhaust-gas flow relative to a design without 
flute and cycle shut-off. The rotor is therefore subjected to four times 
the exhaust-gas velocity and it is correspondingly brought more rapidly to 
a speed permitting the engine to provide power. 
In all the variants shown, nozzles supplied with air, acting together with 
the high-pressure exhaust-gas jet and possibly the induced air jet, ensure 
rotor run-up. The two latter measures then undertake the drive of the 
pressure wave supercharger when the engine is operating under load after 
the nozzles have been switched off. 
In the starting phase, it is important to keep the leakage losses through 
the clearance between the rotor and the casing walls as small as is 
practically possible in order to make the maximum use of the flow of the 
media for driving the rotor. The rotor/casing surface material pair has to 
be matched to this requirement. This suggests, inter alia, pairing a rotor 
in mineral ceramic with a casing surface of steel. During the starting 
phase, the rotor rapidly becomes hot but only changes its dimensions to an 
unimportant extent because of the small thermal expansion coefficient of 
mineral ceramic. Although the steel of the casing surface has a much 
higher thermal expansion coefficient than mineral ceramic, it remains 
cooler than the rotor during the starting phase so that only small casing 
clearances form and the leakage losses remain small. As soon as the casing 
surface has taken up its steady state operating temperature, the 
clearances are of course substantially larger but the leakage losses 
remain small relative to the mass flow in operation under load and can 
therefore be accepted. 
The designs described up to now themselves substantially permit the running 
up of the rotor 8 from the rest condition of the pressure wave machine to 
the point of achieving a supercharge pressure sufficient for satisfactory 
running of the engine with power output. This device has to be combined 
with other means for driving the pressure wave supercharger over the whole 
of the rest of the low range. A most obvious measure to this end is drive 
by means of the high-pressure exhaust gas, supported by the induced air, 
as is described in more detail in the discussion of FIG. 1. 
FIG. 9 shows a suitable device for this purpose which also acts as a run-up 
aid for the rotor during the starting phase and in which the torque at low 
engine speeds, particularly in idling operation, is self-regulating. Since 
the same device as that in FIGS. 1-3 is used for controlling the 
supercharge air flap 14, it is not shown and only the supercharge air flap 
14 itself is shown diagrammatically. Where the other elements agree in 
form and function with the designs analogous to those earlier described, 
they are provided with the same reference numbers. 
In this design, a nozzle 31 is again provided in the air casing 5 but this 
nozzle is located between the induction air port 1 and the compression 
port 33. This nozzle 31 is supplied via a short transfer port 32 from the 
compression pocket 33, in which the pressure is higher than it is upstream 
of it in front of the closing edge of the port 1. Since this applies for 
the whole of the operating range, this nozzle 31, has a driving action 
over the whole of the operating range, particularly at low engine speeds 
and in the lower idling range where the compression pocket 33 is 
particularly effective, to which is added, after the run-up phase, the 
driving action of the high-pressure exhaust gas from the port 3 and, to a 
lesser extent, the induction air from the port 1. 
Another measure which contributes to the driving torque is the formation of 
an expansion pocket 34 with an oblique wall part at least on the side of 
its closing edge 36, but advantageously also with an oblique wall part 37 
on the side of it's opening edge 38. In both cases, the gas enters the 
rotor cells with a clearly defined peripheral component; in the case of 
two oblique wall parts, this peripheral component is even greater because 
the gas after the opening edge 38 already enters the pocket 34 with a 
larger peripheral component from the arriving cells. 
The induction air ports 1 in the design shown in FIG. 9 differ from the 
form shown in FIGS. 1-4 in that they enter the rotor space at a flatter 
angle relative to the peripheral direction of the rotor so that the 
induction air enters with a larger peripheral component relative to the 
designs mentioned and supplies a larger drive torque. The flatter entry of 
the port 1 is obtained by a curved entry section 39 whose side walls, 
shortly before entry, are preferably designed to be approximately parallel 
to the wall part 35 of the expansion pocket 34 and to the nozzle 31 before 
the compression pocket 33. 
FIG. 10 shows how the driving jet can be deflected in a direction with a 
larger peripheral component of the inlet velocity by means of a 
nozzle-type contraction of the high-pressure exhaust-gas port 3 before its 
entry into the rotor space in order to achieve a larger torque in the load 
range. Values of 0-10.degree. and approximately 75-80.degree. have been 
found favorable for the angles .alpha. and .beta., respectively. A driving 
jet deflected in this matter generates a high driving torque and, in 
consequence, provides short response times of the supercharger when the 
load on the engine rapidly increases. 
Even more effective in this respect is a wedge gas-pocket inlet port 50, as 
shown in FIG. 11, which extends from the entry of the port 3 to beyond the 
opposite opening edge 53 of an expansion pocket 52, seen in the direction 
of rotation of the rotor. In other words, the closing edge 51 of the 
supply port 50 is located, seen in the direction of rotation of the rotor, 
after the opening edge 53 of the expansion pocket 52, employing an oblique 
outlet flow wall. Starting from the opening edge 53 as the reference point 
and considering the direction of rotation of the rotor as positive, the 
condition described above may be expressed by saying that .alpha. must be 
greater than 0. Maintaining this condition ensures that, even with a 
stationary rotor, a drive torque is generated via the expansion pocket 52. 
Ths also gives the possibility of allowing the engine exhaust gases to 
flow through the pressure wave supercharger when at rest in order, if 
necessary, to heat it or de-ice it. The inlet flow wall for this expansion 
pocket 52 is located parallel to the axis of the rotor but it can also, as 
in the design of FIG. 9, be oblique--which increases the driving effect of 
the pocket 52. 
In the case of the wedge gas-pocket inlet flow port 50, an angle of 
approximately 75.degree. relative to the direction of the rotor axis has 
been found to be advantageous for the inclination of the outlet flow wall. 
In the case of the outlet flow wall of the expansion pocket 52, 50.degree. 
is correspondingly valid as the favorable value for the obliquity. 
As already mentioned, the induction air flowing from the port 1 can also 
contribute to the drive of the free-running rotor, particularly in the low 
speed range because of its large quantity and high density. So that it 
does not have a braking effect on the rotor, its velocity component in the 
peripheral direction must, at every point, be at least equal to the 
peripheral velocity of the rotor cell walls at the relevant point. For a 
particular inclination of the port axis, a particular air throughput is 
associated with each rotor speed so that shall be the case. If the air 
throughput is higher, the inlet velocity of the air and hence its 
peripheral component is greater than is necessary for shock-free entry--it 
therefore has a driving effect on the rotor. 
FIG. 12 shows how the large quantity of induced air in port 1, which, after 
its entry into the rotor cells, acts initially as scavenging air for 
ejecting the expanded exhaust gases, can be made even more useful for 
driving purposes. By means of one or, as shown, two guide ribs 54, the air 
is accelerated before its entry into the rotor space and the drive torque 
is increased. In order to prevent formation of eddies due to oblique 
instant flow, the leading edges of the guide ribs are well rounded. Due to 
the contraction of the flow in the entry region, the maintenance of the 
favorable cell-wall incident flow angle is also ensured more effectively 
than in the absence of guide ribs. The particularly important point is to 
prevent separation of the flow on the wall part associated with the 
opening edge of the port 1. This means that the guide rib adjacent to the 
opening edge should be located sufficiently near to the wall part 
mentioned that separation of the flow is prevented. This is important 
because the main suction wave occurs on the opening edge, this being a 
precondition for a good scavenging effect. Compared with an eddying, 
undirected flow in this wall region, this provides an increased scavenger 
quantity and, in consequence, an improved drive torque. 
Although only preferred embodiments are specifically illustrated and 
described herein, it will be appreciated that many modifications and 
variations of the present invention are possible in light of the above 
teachings and within the purview of the appended claims without departing 
from the spirit and intended scope of the invention.