Internal combustion engine with improved efficiency and filling by recovery of part of the energy of the blasts which are produced during the opening of the exhaust ports

The invention uses the supersonic blast occurring when the exhaust is opened in an internal combustion engine having a variable volume combustion chamber. A transfer conduit is provided between the exhaust pipe and the intake pipe, the volume of this conduit being greater than the cubic capacity of the cylinder, as well as a supply channel and a discharge channel, of a smaller section than the conduit, between this latter and the combustive air intake manifold and the burnt gas exhaust manifold. The invention applies principally to supercharged diesel engines with low compression rate.

The present invention relates to internal combustion engines having a 
variable volume combustion chamber, not only of the reciprocating type but 
also of the rotary type. It is particularly, but not exclusively, 
appropriate for supercharged engines. 
It can be applied as well to engines of the diesel type, i.e. with ignition 
by compression, as to engines with controlled ignition fed with a 
fuel-combustive gas mixture, called in practice "explosion engines", 
whether these two types of engine are two- or four-stroke. 
The invention aims at improving the efficiency and the filling of such an 
engine by recovering part of the energy of the blasts which are produced 
during the opening of the exhaust port, particularly of an exhaust valve 
or aperture, of each cylinder of the engine. It has also the advantage of 
reducing the noise of the engine. 
It is in fact known that the opening of an exhaust port of an internal 
combustion engine cylinder releases an energy-bearing supersonic blast; 
this energy is all the greater the lower the expansion rate of the gases 
in the cylinder, which is the case with low-compression engines, such as 
supercharged low-compression diesel engines. 
It has been suggested using the energy of this blast to raise the pressure 
in the air intake manifold of an engine. In particular a process is known, 
called the Comprex process, for supercharging a diesel engine by 
compressing the air, before its admission into a cylinder, by means of the 
exhaust gases. This process, described for example in a document of the 
"Society of automotive engineers" of Detroit (Mich., U.S.A.), titled 
"Comprex supercharging of vehicle diesel engines", dated Feb. 24-28, 1975 
and having as author Mr. Peter K. Doerflan, uses a rotary member formed by 
an elongated cylinder separated into several elongated compartments, which 
are distributors for the exhaust gases, on the one hand, and the 
combustive air, on the other, between the inlet ports, the outlet ports, 
the air intake manifold at substantially atmospheric pressure and the gas 
exhaust manifold at substantially atmospheric pressure, the pressure of 
the exhaust gases at the outlet of the exhaust ports being transferred, in 
this rotary member, to the air before its arrival at the inlet ports. 
This known process requires this rotary member to be driven in rotation (in 
practice this drive, which must be synchronized with that of the pistons 
of the engine, is provided from the crankshaft of the engine) and sealing 
means between the compartments of hot burnt gases and fresh air, which are 
at different pressures in said rotary member. 
It has moreover been proposed U.S. Pat. No. 3,800,763 of Mr. Robert Jean 
Pouit), in internal combustion engines of the explosion type, having 
several cylinders, to connect the exhaust of each cylinder to the inlet of 
another cylinder shifted in phase by a half-cycle of operation of the 
engine, in relation to the first cylinder, by means of a one-way pipe; 
with this arrangement, the depression which follows the exhaust blast of 
the first cylinder accelerates by suction the inlet air of the second 
cylinder. It will be noted that this pipe has a reduced volume, smaller 
than the volume of each cylinder, and that the air travels therethrough in 
a single direction only, without the exhaust blast ever penetrating 
therein. The pipe serves essentially in this American patent for 
transmitting the depression which follows the blast, from the exhaust side 
of a first cylinder to the suction side of a second cylinder, which 
accelerates the intake of carburetted air into this first cylinder while 
supercharging it. 
The present invention, on the other hand, uses directly the exhaust blast 
of an internal combustion engine cylinder of any type, for compressing the 
inlet air (possibly carburetted) of the same cylinder or of another 
cylinder of the engine without using any rotary member as in the Comprex 
process, but by means of an entirely static transfer conduit connected 
between the exhaust pipe of a cylinder and the inlet pipe of the same 
cylinder or of another cylinder of the engine, this conduit having a 
volume at least equal to that of the cylinder and communicating through 
passages with the intake and exhaust manifolds of the engine so that, 
during one period of the operating cycle of the engine, there may pass 
therethrough the air coming from the intake manifold which will be 
directly forced into the cylinder, contrary to what happens in the engine 
according to the above-mentioned American patent. 
More precisely, the invention has as its aim an internal combustion engine 
comprising at least one work chamber, particularly a cylinder, with an 
intake pipe for the intake of air, possibly carburetted, into the work 
chamber and an exhaust pipe for discharging burnt gases from the work 
chamber, an air intake manifold for the engine and a manifold for 
exhausting the burnt gases from the engine, characterized by the fact that 
it comprises, in combination, a transfer conduit connecting directly the 
exhaust pipe of one work chamber to the intake pipe of the same work 
chamber or of another work chamber of the engine, the volume of said 
conduit being at least equal to that of said work chamber or of each of 
said work chambers, and two passages communicating said conduit with each 
of said manifolds, i.e. an exhaust passage in the vicinity of said exhaust 
pipe and an intake passage in the vicinity of said intake pipe, the flow 
permeability from the intake manifold towards the exhaust manifold through 
said intake passage, said conduit and said exhaust passage in series 
allowing, in operation, the substantially complete discharge towards the 
exhaust manifold of the burnt gases produced during the preceding cycle in 
the work chamber and forced into this conduit from the exhaust pipe of 
this chamber and the replacement of these gases by air, possibly 
carburetted, coming from the intake manifold, during the period of the 
cycle during which said exhaust pipe and said supply pipe are 
substantially isolated from the chamber or the chambers with which they 
are associated. 
It will be noticed that, in accordance with the invention, the pressure 
wave of the exhaust blast is transferred directly, by means of a transfer 
conduit, as far as the intake port of the same cylinder or of a different 
cylinder, and this without using any distributing rotary member, contrary 
to the Comprex system in which the transfer conduits are isolated, during 
the pressure exchange phases, from the supply manifolds (atmospheric or 
enclosure already supercharged) and from the exhaust manifolds 
(atmospheric or under supercharging pressure in front of the turbine). 
According to the present invention the transfer channel communicates 
permanently with the intake and exhaust manifolds. Thus, the instantaneous 
pressure rise is limited to the amplitude of the pressure wave of the 
exhaust blast and could not form a high-pressure supercharging device. 
Nevertheless this pressure wave is sufficiently efficient to accelerate the 
passage of the air through the intake ports of the engine. 
This overpressure aids in filling the engine (during the scavenging phase 
for a two-stroke engine and during the induction phase of a four-stroke 
engine with, in this case, the benefit of positive operation of the piston 
during this intake). 
The invention, furthermore, due to this collecting by the cylinder of the 
exhaust waves, limits the sound radiation and provides the engine with an 
appreciably silent operation.

According to the invention and more especially according to that one of its 
modes of application, as well as according to those of the embodiments of 
its different parts, to which it seems preference should be given, 
desiring for example to construct a device adapted to use the blast 
generated during the opening of an exhaust port, such as an exhaust valve 
or aperture, of an internal combustion engine, the following or similar is 
the way to set about it. 
Reference is first of all made to FIG. 1 on which there is shown 
schematically and in section: 
the upper part of two cylinders 1a, 1b of an internal combustion engine 
having at least two cylinders, 
the upper part of piston 2a, 2b reciprocating in the cylinder respectively 
1a, 1b, 
the cylinder head 4a, 4b of each cylinder 1a, 1b respectively, 
the intake 5a and exhaust 6a pipes of cylinder 1a and the intake 5b and 
exhaust 6b pipes of cylinder 1b, 
the intake 7a and exhaust 8a valves of cylinder 1a, adapted to close and 
open, according to their position, the intake 9a and exhaust 10a openings 
respectively of cylinder 1a, 
the intake 7b and exhaust 8b valves of cylinder 1b, adapted to close and 
open, according to their position, the intake 9b and exhaust 10b openings 
respectively of cylinder 1b, these valves 7a, 8a, 7b, 8b being actuated by 
a camshaft (not shown) in a way known per se, 
a manifold 11 for the intake or admission of combustive air, carburetted in 
the case of a so-called explosion type engine, 
a manifold 12 for removing the exhaust gases or burnt gases. 
In the case illustrated in FIG. 1, i.e. of an engine supercharged by 
turbocompressor, the exhaust gases which pass through manifold 12 in the 
direction of arrow s rotate the rotor of a turbine 21 before escaping as 
shown by arrow S. This turbine rotor drives through shaft 26 the rotor of 
a compressor 20 which receives the atmospheric air, as shown by arrow E, 
and compresses it. The compressed air flows in the direction of arrow e 
through the intake manifold 11; it is generally cooled by a cooling device 
22 which compensates for the heating due to the compression and increases 
the specific weight of the air. 
In a supercharged compression engine of the prior art, manifold 11 supplies 
directly intake pipe 5b, whereas exhaust pipe 6a feeds directly the 
exhaust gases into manifold 12. 
In accordance with the invention, there is provided a transfer conduit 
between exhaust pipe 6a of cylinder 1a and the intake pipe 5b of cylinder 
2a, the volume of this conduit being, for reasons outlined above, at least 
equal to the volume of cylinders 1a, 1b; furthermore, the section of the 
transfer conduit 13 is preferably close to that of exhaust pipe 6a. 
There is furthermore provided, between this transfer conduit 13 and the 
exhaust 12 and intake 11 manifolds, exhaust 15 and intake 14 passages 
respectively, having a reduced section in relation to the section of said 
transfer conduit and of said manifolds, so as to reduce to a minimum 
radiation towards the manifolds 11 and 12 of the blast wave which occurs 
when the exhaust valve 8a of cylinder 1a opens and which passes through 
conduit 13; however the flow permeability of the fluids from the intake 
manifold towards the exhaust manifold successively through the intake 
passage, said conduit and the exhaust passage in series, is sufficient to 
allow the substantially complete discharge, towards the exhaust manifold 
12, of the combustion gases produced during a cycle of cylinder 1a and 
discharged into said conduit during the period when valve 8a is open, and 
the replacement of these combustion gases by fresh air coming from 
manifold 11, during the period of the cycle of the engine during which the 
transfer conduit 13 is isolated from cylinders 1a and 1b, valves 8a and 7b 
being substantially closed. 
Said passages may be provided in different ways. 
In the case of FIG. 1, exhaust passage 15 is formed by the annular space 
between two cones or convergent portions (in the direction of arrow F) 15m 
and 15n fitted one into the other with clearance, whereas the intake 
passage 14 is formed by holes 14g, which are illustrated on a larger scale 
in FIG. 1a which shows a preferred embodiment promoting the passage of 
gaseous fluids from the intake manifold to the transfer conduit with 
respect to the passage thereof in the opposite direction. 
The operation of an internal combustion engine having at least cylinders 1a 
and 1b with the system equipped with the improvements of the invention 
shown in FIG. 1 will now be described. It will be assumed that it is a 
two-stroke motor, of the diesel type or of the so-called "explosion" type. 
For the description of the operation which follows, there will be taken, as 
origin of the angles of the crankshaft and as origin of the strokes, top 
dead-center, corresponding to the combustion, in cylinder 1a. 
The power stroke in cylinder 1a, with the two valves 7a and 8a closed, 
takes place between the point of origin (crankshaft angle 0.degree.) and a 
position of piston 2a somewhat above bottom dead-center for example at 
130.degree., when the exhaust valve 8a opens. 
There reigns at that time inside cylinder 1a a pressure, for example of the 
order of 15 bars, which is distinctly greatly than the pressure which 
reigns at that moment in transfer conduit 13, for the example of the order 
of 4 bars. Thus, a supersonic blast passes from inside cylinder 1 into 
transfer conduit 13, in the direction of arrow F, pushing before it the 
mass of fresh air which is present therein and sucking in, because of the 
depression which follows the supersonic pressure wave, burnt gases from 
inside cylinder 1a. The pressure wave arrives at the intake valve 7b of 
cylinder 1b a little later (the time, expressed as a crankshaft angle, 
which the wave takes to travel, in the direction of arrow F, through 
transfer conduit 13 from the exhaust valve 8a to the intake valve 7b 
depending on the length of the transfer conduit 13, on the speed of 
rotation of the engine and on the speed of sound in the gases present in 
this conduit). Meanwhile, a part of the burnt gases from cylinder 1a has 
penetrated into conduit 13 compressing the combustive air which is 
initially present therein (angle of 130.degree. of the crankshaft). The 
rest of the burnt gases is discharged from the cylinder 1a by scavenging 
with fresh air, possibly carburetted, arriving in intake pipe 5a through 
another transfer conduit (not shown) connected to this pipe 5a, as 
explained hereafter for scavenging cylinder 1b. 
The pressure wave arrives at intake valve 7b which has just opened, for 
example for an angle of the crankshaft of 155.degree.. Thus, the fresh air 
initially contained in conduit 13 penetrates into cylinder 1b pushing out 
by scavenging the rest of the burnt gases which are present in this 
cylinder, these burnt gases following the transfer conduit (not shown) 
connected to exhaust pipe 6b. 
Because the expansion of the pressure wave in cylinder 1b is used, the 
scavenging of the burnt gases is considerably accelerated, which allows 
the duration of the scavenging to be reduced and the two valves 8a and 7b 
to be closed for example at about 240.degree.. 
When these two valves are closed, transfer conduit 13 is isolated from 
cylinders 1a and 1b. Since the pressure of the air in manifold 11 is 
greater than the pressure of the gases in manifold 12, conduit 13 is 
scavenged and the burnt gases which are present therein are replaced by 
air possibly carburetted, the air arriving under pressure through passage 
14 formed by holes 14g, flowing in conduit 13 in the direction of arrow f 
and pushing back the burnt gases which leave this conduit, through passage 
15 between cones 15m and 15n, to reach the exhaust manifold 12 from where 
they pass to the turbine 21 (arrow s). 
It can be seen that there remains about 250.degree. of rotation of the 
crankshaft to achieve this scavenging of the burnt gases in conduit 13 and 
their replacement by fresh air. 
Then a new cycle can begin with the opening of exhaust valve 8a of cylinder 
1a. 
As we have seen, the exhaust pipe 6b of cylinder 1b is connected by a 
transfer conduit to the intake pipe 5a of cylinder 1a, or to the exhaust 
pipe of another cylinder of the engine. 
Thus we see that passages 15 and 14 must allow the diffusion of only the 
smallest possible fraction of the pressure wave moving, in the direction 
of arrow F, in conduit 13 between the exhaust opening 10a, when valve 8a 
opens, and the intake opening 9b, valve 7b having closed, so that this 
wave is best used for scavenging cylinder 1b. 
On the other hand, passage 14 must allow compressed fresh air to pass from 
the intake manifold 11 to the transfer conduit 13, whereas passage 15 must 
allow the burnt gases (coming from cylinder 1a) to pass from this transfer 
conduit 13 (flowing in the direction of arrow f under the effect of fresh 
compressed air arriving through passage 14) towards the exhaust manifold 
12. 
Holes 14g are preferably particularly adapted (shape illustrated in FIG. 
1a) to form a one-way passage 14 (little diffusion of the pressure wave 
and the gases--air or burnt gases--from 13 towards 11, but a relatively 
easy passage of the compressed fresh air from 11 towards 13); similarly 
the structure with two cones 15m, 15n fitted one in the other with 
peripheral clearance forming passage 15 presents a flow permeability of 
the transfer conduit 13 towards exhaust manifold 12 which is low when the 
exhaust gases are flowing in this conduit in the direction of arrow F, but 
which is high when the exhaust gases and the air flow in this conduit in 
the direction of arrow f. 
The device illustrated in FIG. 1 and using the improvements of the 
invention may also be applied to the case of a four-stroke engine, for 
example a six-cylinder in-line engine (as illustrated in FIG. 6) in which 
the connected cylinders are out of phase by 240.degree., the order of 
firing being 1, 5, 3, 6, 2, 4. 
If we also take as origin of the strokes the combustion top dead-center of 
cylinder 1a, lagging by 240.degree. behind cylinder 1b, the expansion in 
cylinder 1a will take place between 0.degree. and 140.degree.. 
At 140.degree., the exhaust valve 8a of cylinder 1a opens, which creates a 
pressure wave which reaches through transfer conduit 13 (in the direction 
of arrow F) cylinder 1b, for example at 180.degree., i.e. in the middle of 
its induction stroke (for this cylinder) when piston 2b is close to its 
maximum speed. The pressure wave invades cylinder 1b and creates useful 
work which increases the effective average pressure in this cylinder and 
reduces the specific consumption. 
The induction stroke then becomes a power stroke. 
After the exhaust valve 8a of cylinder 1a and intake valve 7b of cylinder 
1b have closed, the replacement of the burnt gases present in transfer 
conduit 13 takes place as in the case of a two-stroke engine, with flow in 
conduit 13 in the direction of arrow f. 
We have seen that, both for a four-stroke engine and for a two-stroke 
engine, the volume of conduit 13 must be at least equal to the cubic 
capacity of a cylinder, so that it contains enough air for supplying a 
cylinder. 
It may be noted that the transfer of energy from the burnt gases coming 
from cylinder 1a to the fresh air for cylinder 1b takes place through the 
mechanism of a gaseous piston with good efficiency and a minimum of 
mixing. 
In the case of a four-stroke engine, the time available for scavenging the 
transfer conduit is about 540.degree. in the crankshaft. 
In FIGS. 2 to 4 there are shown variations of the exhaust 15 and intake 14 
passages: 
in the case of FIG. 2, these two passages are formed by means of holes, 
i.e. exhaust holes 15p having a smaller diameter than the intake holes 
14g; 
for FIG. 3, there is provided for the exhaust passage a channel 15c 
connecting the exhaust manifold 12 to a narrowed portion 13c of conduit 
13, this portion forming the neck of a venturi, channel 15c having a small 
section with respect to that of conduit 13 and manifold 12; it is known 
that in the highly converging part 13d (in direction F) of the venturi the 
pressure wave, produced by the opening of valve 8a, is transformed into 
speed, the speed of the burnt gases passing through (in the direction of 
arrow F) being maximum in the region of neck 13c, resulting in low 
diffusion towards manifold 12 through channel 15c which has furthermore a 
reduced section; on the other hand, the divergent portion 13e (in 
direction F) is longer, which allows the speed of the burnt gases to be 
retransformed into pressure; 
still with the case of FIG. 3, the intake passage is also formed by a 
channel 14c having a section smaller than that of conduit 13 and manifold 
11, but greater than that of exhaust channel 15c, so as to allow the fresh 
compressed air to pass relatively easily from manifold 11 to conduit 13, 
while limiting diffusion from this conduit to manifold 11 when air or 
burnt gases pass through neck 15f of venturi 15g-15h similar to venturi 
13d-13e (converging portion 15g shorter than the diverging section 15h, 
the notions of convergent and divergent corresponding to a flow in the 
direction F); 
in the case of FIG. 4, there are also provided channels 15c and 14c for 
forming the passages, channel 14c having possibly a section larger than 
that of channel 15c; these two channels 15c and 14c have sections less 
than those of manifolds 12 and 11 respectively; on the other hand transfer 
conduit 13 has a uniform section without necks; in order to reduce 
diffusion from conduit 13 to manifold 12, when the flow in the conduit is 
in direction F, without reducing diffusion too much when the flow in this 
conduit is in direction f, an extension is provided, inside conduit 13, of 
channel 15c, this extension 15e comprising a bend 15d and with its end 
directed in direction F, as illustrated with dash lines in FIG. 4. 
In FIGS. 5 and 6 there is shown schematically an engine having six 
cylinders C.sub.1, C.sub.2, C.sub.3, C.sub.4, C.sub.5, C.sub.6 with firing 
order C.sub.1, C.sub.5, C.sub.3, C.sub.6, C.sub.2, C.sub.4, then again 
C.sub.1, C.sub.5, C.sub.3 . . . , with six transfer conduits: 13a between 
the exhaust pipe of cylinder C.sub.1 and the intake pipe of cylinder 
C.sub.2, 13b between the exhaust pipe of cylinder C.sub.2 and the intake 
pipe of cylinder C.sub.3, 13c between the exhaust pipe of cylinder C.sub.3 
and the intake pipe of cylinder C.sub.1, 13d between the exhaust pipe of 
cylinder C.sub.4 and the intake pipe of cylinder C.sub.6, 13e connecting 
the exhaust pipe of cylinder C.sub.5 to the intake pipe of cylinder 
C.sub.4 and finally 13f connecting the exhaust pipe of cylinder C.sub.6 to 
the intake pipe of cylinder C.sub.5. 
Passages 14 and 15 between each transfer conduit, such as 13a and the 
intake and exhaust manifolds, respectively, may be formed by holes 14g 
having a relatively large section and by holes 15p having a relatively 
small section, respectively (FIG. 5). 
In FIG. 6 the passages between transfer conduits 13a and 13f and the intake 
11 and exhaust 12 manifolds have not been shown. 
The operation is the same, for each transfer conduit of FIGS. 5 and 6, as 
that described with reference to FIG. 1 for a four-stroke engine. 
There will now be described, with reference to FIGS. 7 to 11, the 
implementation of the invention in the case where the transfer conduit of 
the invention connects the exhaust pipe of one cylinder to the intake pipe 
of the same cylinder. 
In FIG. 7 there is shown the application of the invention to one of the 
cylinders of a two-stroke valve engine of the type described and 
illustrated in the French Patent Application No. 2,338,385 filed on Jan. 
15, 1976. 
In this figure piston 2 moves in a cylinder 1 having an intake valve 7 and 
an exhaust valve 8, both inclinably disposed, as described in the 
above-mentioned patent application. 
In accordance with the invention, a transfer conduit 13 connects exhaust 
pipe 6 to the intake pipe 5 of cylinder 1. Furthermore, intake passages, 
formed by a channel 14 having a relatively large section (but more reduced 
than that of conduit 13 and intake manifold 11), and exhaust passages, 
formed by a channel 15 having a relatively small section (smaller than 
that of channel 14), connect conduit 13 to the intake 11 and exhaust 12 
manifolds. 
The operation of the system of FIG. 7 will now be described, taking as 
origin of the angles of the crankshaft and as origin of the strokes top 
dead-center corresponding to combustion in cylinder 1. 
The explosion stroke in cylinder 1, with valves 7 and 8 closed, takes place 
between the stroke origin (top dead-center) and a position of piston 2 
somewhat above bottom dead-center, for example at 130.degree. when exhaust 
valve 8 opens. 
At this time a supersonic blast escapes from inside cylinder 1 and through 
exhaust pipe 6 reaches transfer conduit 13 while displacing, in the 
direction of arrow F, the column of air contained in this conduit and 
while sucking in, because of the depression which follows the supersonic 
pressure wave, burnt gases from inside cylinder 1. 
The intake valve 7 opens, for example for a crankshaft angle of 
155.degree., and fresh air, possibly carburetted, contained in conduit 13 
penetrates into cylinder 1 through opening 10 and pushes out by scavenging 
the rest of the burnt gases which are present in this cylinder, these 
gases leaving the cylinder through exhaust opening 9, valve 8 being still 
open, and reach conduit 13. It can be seen that the volume of this latter 
must be at least equal to that of cylinder 1 so that practically all the 
burnt gases from this latter may be stocked in the conduit during this 
phase of the operating cycle of cylinder 1; if the volume of conduit 13 
were smaller than that of cylinder 1, a part of the burnt gases would be 
returned to the cylinder through conduit 13 and the scavenging of the 
cylinder would not be efficiently accomplished. 
Then valves 7 and 8 close, which isolates transfer conduit 13 from cylinder 
1. The air under pressure from manifold 11, possibly carburetted, reaches 
through the channel or passage 14 conduit 13 and pushes back the burnt 
gases contained therein towards exhaust manifold 12 through channel or 
passage 15 smaller in section than channel or passage 14. This achieves 
the scavenging of conduit 13 (in the direction of arrow f) which is rid of 
the burnt gases. After this scavenging, conduit 13 is again filled with 
fresh air and a new cycle may begin again. 
The embodiment of FIG. 8 is similar to that of FIG. 7, except that the 
intake, instead of being controlled by the opening of an intake valve 7, 
is provided by intake ports 10a which are uncovered at a specific moment 
in the cycle by piston 2 during its downward stroke (power stroke) and are 
covered over again at another specific moment by this piston during its 
upward stroke (compression stroke). Furthermore, passages 14 and 15 are 
formed by apertures 14g having a relatively large section and 15p having a 
relatively small section. 
The operation of the embodiment of FIG. 8 is similar to that of FIG. 7. 
The embodiment of FIG. 9 is similar to that of FIG. 7, except that the 
intake and exhaust, instead of being controlled by valves 7 and 8, are 
provided by intake ports 10a and exhaust ports 9a which are uncovered at 
specific moments in the cycle by piston 2 in its downward power stroke and 
are covered over again at other specific moments by this piston in its 
upward compression stroke. Furthermore, passages 14 and 15 are formed by 
apertures 14g (as in the case of FIG. 8) and by a system of two converging 
portions 15m and 15n fitted one in the other between which exist an 
annular passage 15 (passages 14 and 15 are then constructed as in FIG. 1). 
The operation of the embodiment of FIG. 9 is similar to that of the 
embodiments of FIGS. 7 and 8. 
Beyond lines YY and ZZ of the embodiments of FIGS. 8 and 9, and also of 
FIG. 7, there may be provided, in the case of a supercharged engine, the 
fitment of FIG. 10 or that of FIG. 11. 
In these figures we find again the turbine 21-compressor 20 assembly whose 
rotors are fixed to a common shaft 26, the turbine receiving the burnt 
gases (arrow s) which expand therein before leaving (arrow S) while 
rotating the rotor of this turbine, so shaft 21 which rotates the rotor of 
compressor 20 which compresses the incoming air (arrow E); this compressed 
air is cooled in the cooling device 22 (for it has heated up during 
compression), which increases its specific weight. 
In the embodiment of FIG. 10, the cooled compressed gas which leaves device 
22 is again compressed in a second geared compression device 27 to ensure 
the scavenging of the transfer conduit at low powers. 
In the embodiment of FIG. 11, the invention is applied to low compression 
ratio supercharged engines known in the art by the name "Hyperbar engines" 
and described for example in French Pat. No. 2,179,310 filed on Apr. 6, 
1972 and its first certificate of addition No. 2,222,537 filed on Mar. 21, 
1973 (and in the corresponding counterpart U.S. Pat. Nos. 3,988,894, 
4,125,999 and 4,233,815). 
There is provided between the intake manifold 11 and the exhaust manifold 
12 a flame tube 28 in which a part of the compressed air leaving turbine 
20 burns fuel while releasing at 29 hot burnt gases which are mixed at 30 
with burnt gases arriving in the direction of arrow s. A flame tube serves 
essentially for starting up and at low speeds. It may be of the kind 
described in French Pat. No. 2,253,389 filed on Dec. 4, 1973 (and in the 
corresponding counterpart U.S. Pat. No. 4,004,414). A fresh compressed air 
by-pass 31 (closable by means of a valve 32) is also provided according to 
the above-mentioned patent which explains the operation of the unit 
illustrated in FIG. 11. 
In FIG. 12, finally, there is shown a diagram which corresponds to an 
engine conventially supercharged by means of a turbocompressor driven by 
the exhaust gases, the power W (in kilowatts) being shown as abscissa and 
the absolute pressure P (in bars) being shown as ordinates, on the one 
hand, at the intake manifold 11 (curve P.sub.2) and, on the other hand, at 
the exhaust manifold 12 (curve P.sub.3), 
It can be seen that these curves P.sub.2 and P.sub.3 intersect at point A. 
For powers less than a (abscissa of point A), the pressure in the conduit 
of intake manifold 11 is less than the pressure in the conduit of exhaust 
manifold 12, which would produce a counter-scavenging instead of the 
scavenging desired. 
With the unit shown in FIG. 11, this is avoided owing to the presence of 
flame tube 25, the outgoing gases of which rotate turbine 21 which in its 
turn drives compressor 22, resulting in an increase of pressure P.sub.2 so 
that this latter exceeds P.sub.3. It is known that in conventional 
two-stroke engines a coupled compressor is provided which comes into 
operation, if required, when P.sub.2 is less than P.sub.3. 
On the contrary in the case of operation under normal running conditions, 
i.e. when power W is greater than a, pressure P.sub.2 in the intake 
manifold is greater than pressure P.sub.3 in the exhaust manifold, which 
allows scavenging to take place. It is precisely this scavenging pressure 
which achieves, in the device of FIG. 11, the rapid discharge of the burnt 
gases present in transfer conduit 13 during the whole of the period when 
the exhaust and intake valves are closed. It is the difference of pressure 
shown by arrow X directed upwardly (in FIG. 12) which is used for 
scavenging conduit 13. 
In the absence of the flame tube of FIG. 11 or of a coupled compressor, the 
pressure difference X.sub.1 directed upwardly in FIG. 12 would produce a 
counter-scavenging of transfer tube 13 from exhaust manifold 12 towards 
intake manifold 11. It is possible to prevent this counter scavenging in 
four-stroke engines by providing a valve (illustrated at 33 by a dash line 
in FIG. 5) which is closed for starting up and during the whole period of 
operation when curve P.sub.3 is below curve P.sub.2 (for a power W less 
than a). 
In some cases the transfer conduit may be scavenged by the return wave 
formed by the blast wave which has been reflected at the intake aperture 
and which pushes back towards the exhaust manifold the burnt gases which 
have just penetrated into said conduit. Such an engine may then operate 
without any external air supply system. 
The invention has been described up to now in the case of an internal 
combustion engine, of the so-called diesel type or of the so-called 
explosion type, with pistons reciprocating in a cylinder, the cycle being 
two- or four-stroke. It also applies to rotary engines in which a work 
chamber plays the role of the cylinder. In the claims which follow, by 
work chamber is meant the chamber of a rotary engine or the cylinder of a 
reciprocating piston engine. 
Thus it can be seen that the invention allows the supersonic blast to be 
used which is normally produced in an internal combustion engine when an 
exhaust valve or port opens, this blast being due to the pressure 
difference which reigns at that moment between the inside of the cylinder 
and the exhaust pipe. 
In accordance with the invention, this blast is used to accelerate the 
intake, in the same cylinder or in another cylinder, of scavenging air 
which is first of all compressed (before the opening of the intake valve 
or ports), then accelerated (after opening of this valve or these ports) 
towards the same cylinder or another cylinder, while ensuring a more rapid 
and a better scavenging of the cylinder in which it penetrates. 
Furthermore, the invention eliminates, or at least considerably reduces, 
the exhaust noise which is produced during the opening of the exhaust 
valves or ports. 
These objects are reached due to a very simple structure only comprising 
fixed elements, contrary to the solution provided by the Comprex process, 
these fixed elements being few in number, i.e. a transfer conduit and 
channels provided between this conduit and the intake and exhaust 
manifolds. In most cases, a considerable reduction in the specific 
consumption of the engine is fully obtained. 
It will be noted that the intake and the exhaust passages are designed to 
reduce to a minimum the radiation, towards the intake and exhaust 
manifold, of the blast wave which appears on the opening of the exhaust 
valve of a chamber and follows said transfer conduit. 
In the case where the engine comprises an air supply system, the flow 
permeability from the intake manifold to the exhaust manifold, 
successively through the intake passage, the conduit and the exhaust 
passage in series, allows, in operation, practically the whole of the 
burnt gases to be discharged towards the exhaust manifold, under the 
effect of the air delivered by the air supply system. 
In the case where the engine does not comprise any external air supply 
system, the flow permeability from the intake manifold towards the exhaust 
manifold, successively through said intake passage, the conduit and the 
exhaust passage in series allows, in operation, practically the whole of 
the burnt gases to be discharged towards the exhaust manifold, under the 
effect of the return wave resulting from the blast wave, which appears 
when the exhaust valve of a chamber opens and follows the transfer 
conduit, and which is reflected back at the intake aperture putting the 
chamber in communication with the intake pipe. 
As is evident and as it follows moreover already from what has gone before, 
the invention is in no wise limited to those of its modes of application 
and embodiments which have been more specially considered; it embraces, on 
the contrary, all variations thereof.