Improvement in methods of supercharging an engine, preferably a diesel engine in such supercharged engines, and in supercharging units for

Claims

I claim:

1. A method of supercharging an internal combustion engine of the expansible chamber type having a turbo-compressor system with at least one compressor and at least one turbine for driving the compressor, said engine having a combustion chamber system connected between the outlet of said compressor and the inlet of said turbine having an airflow capacity which varies as a function of engine r.p.m. and load, said method comprising the steps of:

a. directly communicating the outlet of said compressor with the turbine inlet by connecting a bypass passageway between said outlet and inlet in parallel airflow relation with the engine combustion chamber system;

b. establishing a substantially constant total airflow capacity between the compressor outlet and the turbine inlet for any given compressor outlet pressure by providing an airflow capacity in said bypass passageway adequate to automatically responsively compensate for the variations in the airflow capacity of the engine combustion chamber system caused by engine r.p.m. and load variations whereby the pressure difference, if any, between the compressor outlet and turbine inlet is generally independent of the ratio of the flow rate of the air traversing said bypass passageway to the total airflow delivered from said compressor;

c. matching said turbo-compressor system to the total airflow capacity of said engine combustion chamber system and of said bypass passageway such that the plot of the ratio of the compressor output pressure to the compressor input pressure versus the airflow delivered by the compressor, during self-sustaining operation of said turbo-compressor system and conjoint operation of the engine under its own power in response to any variation in engine load and r.p.m. within the complete operating range of the engine, lies at least within a narrow area approximating a predetermined curve located in a high yield area generally near to, but which does not exceed, the surge line characteristic of the compressor; and

d. operating the engine under its own power and simultaneously operating the turbo-compressor system in a self-sustaining mode so as to deliver air from said compressor to said engine combustion chamber system and to said bypass passageway such that the aforementioned plot of the matched turbo-compressor lies within said narrow area.

2. The method of claim 1 wherein step (b) is performed by maintaining a fixed dimension of the flow controlling cross section of the bypass passageway and selecting such dimension so as to permit the whole of the flow of air delivered by the compressor to pass through said bypass passageway without appreciable pressure drop when the engine is stationary.

3. The method set forth in claim 1 wherein step (b) thereof is performed by controlling the flow characteristics of said bypass passageway so as to cause a pressure drop in the air passing through the said bypass which is an increasing function of the pressure existing at the compressor outlet.

4. The method set forth in claim 3 wherein said flow characteristics are controlled such that said pressure drop is an increasing linear function of the pressure existing at the compressor outlet.

5. The method set forth in claim 1 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber system at ambient temperature and pressure conditions, and wherein step (d) is performed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbo-compressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine combustion chamber system is produced.

6. The method set forth in claim 3 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber system at ambient temperature and pressure conditions, and wherein step (d) is performed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbocompressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in th engine combustion chamber system is produced.

7. The method set forth in claim 5 wherein step (d) is further performed by heating the gases before entering the turbine inlet by burning of fuel in the air stream delivered from the compressor outlet and downstream thereof and separately from the burning of fuel in said engine.

8. The method set forth in claim 7 wherein step (d) further includes the step of starting the turbo-compressor in rotation so as to initiate gas flow through said bypass passageway with sufficient input energy so that the turbo-compressor system becomes self-sustaining and delivers air to the engine combustion chamber system at said correlated minimum temperature and pressure conditions.

9. A method of operating a supercharged internal combustion engine of the compression ignition type which is subject to speed and load variations and which is supercharged by an associated turbine-compressor supercharger wherein the turbine drives the compressor such that the supercharger drive is mechanically independent of the engine, said engine having an air intake communicating with the compressor output and an exhaust conduit communicating with the turbine inlet and a gas flow path from the compressor to the turbine in bypass relation to said engine intake, said method comprising the steps of:

a. maintaining the rotational speed of the turbine-compressor supercharger, at least when engine is running under its own power, at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine is produced, said minimum threshold speed having a fixed value for an engine having a given compression ratio, said minimum threshold speed being lower for an engine having a higher compression ratio and being higher for an engine having a lower compression ratio with all other conditions affecting self-ignition being constant;

b. operating said engine under its own power over a varying speed and load range while continuously supplying air from the compressor to the engine intake at or above said correlated minimum temperature and pressure conditions;

c. automatically maintaining the air flow capacity of said bypass gas flow path at a value correlated with that of said engine such that the combined air flow capacity of the parallel air flow paths provided by said engine and said bypass gas flow path remains substantially constant for any given compressor outlet pressure regardless of the rate of change of speed and load conditions of said engine; and

d. driving the turbine at least after being started solely by sufficiently heating gases admitted to the turbine so as to operate said turbine-compressor supercharger in a high yield mode at or near its characteristic surge line whereby surging of said compressor is prevented despite sudden variations in the airflow capacity of the engine induced by variations in the load and speed conditions of the engine.

10. A method of supercharging an internal combustion engine of the expansible chamber type having a turbo-compressor with at least one compressor and at least one turbine for driving the compressor, said engine having a combustion chamber system connected between said compressor and said turbine, and a bypass passageway communicating with the outlet of said compressor and with the turbine inlet in parallel air flow relation with the engine combustion chamber system, said method comprising the steps of:

a. operating the turbocompressor so as to deliver air from said compressor to said engine combustion chamber system and to said bypass passageway;

b. simultaneously operating the engine under its own power;

c. controlling the pressure difference between the compressor outlet and the turbine inlet by maintaining a sufficient air flow capacity in the bypass passageway so as to permit the entire air flow output of the compressor to pass through said bypass passgeway both when the engine is stationary and when the engine is running under varying conditions of load and speed such that for a given pressure ratio of the compressor or for a given power output of the engine the air flow delivery of said compressor remains generally constant regardless of the rotary speed and load conditions of said engine; and

d. simultaneously operating said compressor such that a plot of the pressure ratio versus the air flow delivery of said compressor is generally along a line generally parallel to and sufficiently near its surge line to optimize the efficiency of said compressor.

11. The method set forth in claim 10 wherein step (c) is performed by selecting a fixed air flow capacity of said bypass passageway sufficient to accept the entire air flow output of said compressor without generating any appreciable pressure drop in said bypass even when the engine is stationary.

12. A method of supercharging an internal combustion engine of the expansible chamber type having a turbocompressor with at least one compressor and at least one turbine for driving the compressor, said engine having a combustion chamber system connected between said compressor and said turbine, and a bypass passageway communicating with the outlet of said compressor and with the turbine inlet in parallel air flow relation with the engine combustion chamber system, said method comprising the steps of:

a. operating the turbocompressor so as to deliver air from said compressor to said engine combustion chamber system and to said bypass passageway with the compressor outlet pressure exceeding turbine inlet pressure;

b. simultaneously operating the engine under its own power and admitting exhaust gases from the engine combustion chamber system to the turbine;

c. generating hot gases as necessary externally of and separately from the burning of fuel in the engine combustion chamber and admitting the same along with the engine exhaust gases to the turbine to provide a supply of motive gases having sufficient temperature to cause the turbocompressor to operate in a self-sustaining mode;

d. maintaining in said bypass passageway an air flow capacity responsive to any variation in the air flow capacity of said engine combustion chamber system caused by variations in engine load and r.p.m. such that the total air flow capacity provided by said bypass passageway and engine combustion chamber system is substantially constant for any given compressor outlet pressure whereby any appreciable pressure difference developed in the air passing through the bypass passageway toward said turbine is generally independent of the ratio of the flow rate of the air traversing said bypass passageway to to the total air flow delivered from said compressor and whereby for a given pressure ratio of the compressor the air flow delivery of said compressor remains generally constant regardless of the rotary speed and load conditions of said engine; and

e. simultaneously operating said compressor such that a plot of the pressure ratio versus the air flow delivery of said compressor is generally within a narrow area generally parallel to its surge line.

13. The method as set forth in claim 9 wherein, in step (c), said bypass gas flow path is maintained in a permanently open condition.

14. The method of claim 9 wherein step (c) is performed by maintaining said bypass gas flow path constantly open via a bypass pipe having a fixed dimension of the flow controlling cross section thereof and selecting such dimension so as to permit the whole of the flow of air delivered by the compressor to pass through said bypass pipe without appreciable pressure drop when the engine is stationary.

15. The method set forth in claim 9 wherein step (c) is performed by controlling the flow characteristics of said bypass gas flow path so as to cause a pressure drop in the air passing therethrough which is an increasing function of the pressure existing at the compressor outlet.

16. The method set forth in claim 15 wherein said flow characteristics are controlled such that said pressure drop is an increasing linear function of the pressure existing at the compressor outlet.

17. The method set forth in claim 9 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber system at ambient temperature and pressure conditions.

18. The method set forth in claim 100 wherein step (a) is further performed by heating the gases before entering the turbine inlet by burning of fuel in the air stream delivered from the compressor outlet and downstream thereof and separately from the fuel burned in said engine.

19. The method set forth in claim 18 wherein step (a) further includes the step of starting the turbocompressor in rotation so as to initiate gas flow through said bypass gas flow path with sufficient input energy so that the turbocompressor becomes self-sustaining and delivers air to the engine combustion chamber system at said correlated minimum temperature and pressure conditions.

20. The method of claim 10 wherein step (c) is performed by maintaining a fixed dimension of the flow controlling cross section of said bypass passageway, maintaining said bypass passageway constantly open and selecting such dimension so as to permit the whole of the flow of air delivered by the compressor to pass through said bypass passageway without appreciable pressure drop when the engine is stationary.

21. The method set forth in claim 10 wherein step (c) is performed by controlling the flow characteristics of said bypass passageway so as to cause a pressure drop in the air passing therethrough which is an increasing function of the pressure existing at the compressor outlet.

22. The method as set forth in claim 21 wherein said flow characteristics are controlled such that said pressure drop is an increasing linear function of the pressure existing at the compressor outlet.

23. The method set forth in claim 21 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber sytem at ambient temperature and pressure conditions, and wherein step (a) is performed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbocompressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine combustion chamber system is produced.

24. The method set forth in claim 20 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber sytem at ambient temperature and pressure conditions, and wherein step (a) is performed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbocompressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine combustion chamber system is produced.

25. The method set forth in claim 107 wherein step (a) is further performed by heating the gases before entering the turbine inlet by burning of fuel in the air stream delivered from the compressor outlet and downstream thereof and separately from the burning of fuel in said engine.

26. The method set forth in claim 25 wherein step (a) further includes the step of starting the turbocompressor in rotation so as to initiate gas flow through said bypass passageway with sufficient input energy so that the turbocompressor becomes self-sustaining and delivers air to the engine combustion chamber system at said correlated minimum temperature and pressure conditions.

27. The method of claim 12 wherein step (d) is performed by maintaining a fixed dimension of the flow controlling cross section of said bypass passageway and selecting such dimension so as to permit the whole of the flow of air delivered by the compressor to pass through said bypass passageway without appreciable pressure drop when the engine is stationary.

28. The method set forth in claim 27 wherein step (d) is further performed by providing said bypass passageway in the form of a constantly wide open pipe having said selected fixed dimension of its flow controlling cross section.

29. The method set forth in claim 12 wherein step (d) thereof is performed by controlling the flow characteristics of said bypass passageway so as to cause a pressure drop in the air passing therethrough which is an increasing function of the pressure existing at the compressor outlet.

30. The method set forth in claim 29 wherein said flow characteristics are controlled such that said pressure drop is an increasing linear function of the pressure existing at the compressor outlet.

31. The method set forth in claim 27 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber system at ambient temperature and presure conditions, and wherein step (a) is prformed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbocompressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine combustion chamber system is produced.

32. The method set forth in claim 29 wherein said engine is of the compression ignition type having a compression ratio less than that necessary to achieve self-ignition of fuel with air admitted to said engine combustion chamber system at ambient temperature and pressure conditions, and wherein step (a) is performed while maintaining, at least when the engine is running under its own power, the rotational speed of the turbocompressor at or above a minimum threshold speed sufficient to cause the compressor to deliver air to the engine combustion chamber system at correlated minimum temperature and pressure conditions high enough such that, when said air is compressed by said engine from a point at or near the beginning of the intake phase of the cycle of said engine to a point at or near the end of the compression phase of said cycle, self-ignition of fuel in the engine combustion chamber system is produced.

33. The method set forth in claim 12 wherein step (c) is further performed by heating the gases before entering the turbine inlet by burning of fuel in the air stream delivered from the compressor outlet and downstream thereof.

34. The method set forth in claim 31 wherein step (c) further includes the step of starting the turbocompressor in rotation so as to initiate gas flow through said bypass passageway with sufficient input energy so that the turbocompressor becomes self-sustaining and delivers air to the engine combustion chamber system at said correlated minimum temperature and pressure conditions.

The invention relates to supercharging methods for internal combustion engines of the expansible combustion chamber type, preferably a diesel engine with a supercharging unit comprising a compressor supplying fresh air in parallel to the engine and to a combustion chamber, and a turbine supplied with combustion gas by the engine and said combustion chamber, the said turbine driving in rotation the said compressor, independent starting means being provided to bring the turbine-compressor assembly to self-maintaining operation independent of the engine.

The invention also relates to diesel engines supercharged by a supercharging unit comprising a compressor, supplying fresh air in parallel to the engine and to a combustion chamber, and a turbine supplied with combustion gas by the engine and the abovesaid combustion chamber, the abovesaid turbine driving said compressor in rotation, independent starting means being provided to bring the turbine-compressor assembly to self-maintaining operation independent of the engine.

The invention relates also to supercharging units for internal combustion engines, preferably of the diesal type, comprising a compressor supplying fresh air to an auxiliary combustion chamber and also to the engine combustion chamber via first connecting means connected to an intake manifold of an engine, and a turbine supplied with combustion gases provided by said auxiliary combustion chamber and by the engine combustion chamber via second connecting means connected to the exhaust manifold of said engine, said turbine rotating said compressor, independent starting means being provided to bring the turbine-compressor assembly to self-maintaining operation.

As set forth in more detail following the detailed description of the embodiments shown in FIGS. 1-13, it has been appreciated that it would be advantageous, especially from the point of view of specific power/stroke volume ratio and from the point of view of robustness and simplicity, to provide supercharged diesel engines having a low compression ratio, less than 12, and which can be as low a value as 8 or even 6.

Now it is known that, all things being otherwise equal, reduction of the compression ratio of a supercharged diesel engine causes the appearance, below a certain limiting compression ratio, which is situated around 12, of impossibilities of starting and difficulties of low power operation, and this by reason of the fact that the temperature of selfignition of the fuel is no longer reached at the end of the compression stroke.

It is a specific object of the invention to improve the operation of supercharged diesel engines and to permit, for engines whose compression ratio is less than 12, starting without having to resort to any special starting method, and correct operation at idle and low power.

The supercharging method according to a preferred embodiment of the invention is characterized by the fact that, the engine having a compression ratio less than 12, the minimal rotary speed of its supercharging unit is limited to a threshold value sufficient to create, in the intake pipe of the engine, conditions of temperature and of pressure enabling its starting and its operation at low power, this threshold value being all the higher, for a given supercharging unit, as the compression ratio of the engine is lower.

Preferably, the abovesaid threshold value is obtained by limiting, i.e., controlling or regulating, the supply of fuel to the combustion chamber.

The diesel engine according to a preferred embodiment of the invention is characterized by the fact that it has a compression ratio less than 12, by the fact that regulating means for the speed of its supercharging unit are provided and are arranged so that the minimal rotary speed of this supercharging unit is limited to a threshold value sufficient to create, in the intake pipe of the engine, conditions of temperature and of pressure enabling its starting and its operation at slow speed, this threshold value being all the higher, for a given supercharging unit, as the compression ratio of the engine is lower.

Preferably, the abovesaid regulating means are constituted by a supply device limiting, i.e., controlling or regulating, the flow rate of fuel introduced into the combustion chamber.

The supercharging unit according to a preferred embodiment of the invention is characterized by the fact that first connecting means are provided for the compressor to supply with fresh air, in parallel, the combustion chamber and the intake pipe of a diesel engine with a compression ratio less than 12, by the fact that second connecting means are provided so that the turbine can be supplied with the combustion gas by the combustion chamber and by the exhaust pipe of the abovesaid diesel engine, and by the fact that regulating means of the speed of the supercharging unit are provided and are arranged so that the minimal rotary speed of this supercharging unit is limited to a threshold value sufficient to create, in the intake pipe of the engine, conditions of temperature and of pressure enabling its starting and its operation at low power, this threshold value being all the higher, for a given supercharging unit, as the compression ratio of the engine concerned is lower.

The abovesaid regulating means can comprise an actuating member which can modify the threshold value according to the compression ratio of the engine concerned.

To a first approximation, the power of an engine is proportional to the amount of air inspired. The power of a given engine, whose rotary speed is fixed, hence can only be increased at the cost of an increase in the density of the intake air. So it is necessary to increase the pressure and to reduce the temperature of this air. On the other hand to respect the longevity of the engine, the maximal admissible pressure must not be exceeded and the temperature of the gases in the cylinder must not be unduly raised. A considerable increase in intake pressure is hence only possible at the cost of a correlated lowering of the compression ratio which is accompanied by lesser heating of the air during the compression stroke. Below a limiting volumetric expression ratio of the engine comprised between 12 and 17 according to the bore, this heating may become insufficient to enable self-ignition of the fuel at least at starting, idling or low power operation.

In accordance with one feature of the present invention, such relatively low compression ratios comprised between about 6 and 10, as the case may be, are employed, while around the engine an artificial atmosphere is maintained under sufficient pressure and temperature to palliate the lack of compression in the cylinder and this pressurized atmosphere is established prior to the starting of the engine. The pressure of this atmosphere is sufficiently high to enable easy starting up at the lowest ambient temperatures. The low compression ratio gives the engine a smoothness of operation which is manifested by a considerable reduction in the characteristic knock or chatter of a diesel engine and less wear of the moving connecting parts. It makes possible an excess of air in the cylinder, which in turn lowers the maximal and average temperatures of the gases and hence the thermal load on the engine. Moreover, this excess of air reduces the creation of nitrogen oxide (due to the lowering of temperatures) and the formation of unburnt products and of smoke (due to the excess of oxygen at all speeds).

To provide the high pressure of air required, the turbocompressor is operated within the narrow range of good compression yields, that is to say like a gas turbine. The ability to operate in this high yield mode is achieved by the system of the invention due to the previously described parallel connection in the form of a bypass connecting the compressor outlet to the turbine inlet whose permeability is controlled to maintain the good yield of the compressor. This bypass also supplies fresh air to a combustion chamber which is situated upstream of the turbine and which enables self-sustaining operation of the turboblower. The latter can then be started up prior to the engine and kept above a minimal speed in the whole range of operation of the engine. The artificial pressurized atmosphere defined above is thus realized.

The above features enable, moreover, the obtaining of maximum torque at all rotary speeds, the supercharging pressure being adjustable independently of the engine speed. The increase in power is not obtained by increasing the forces on the connecting rod system but by increasing the duration during which they are applied. Therefore, the basic construction of the engine can be preserved in adapting a conventional engine to the system of the invention. Similarly, since the average temperature of the gases in the cylinder is lower, the water circulation of the original engine is sufficient for the increase in power and hence the original cooling system need not be modified.

The method of the invention is applicable to any existing self-ignition internal combustion engine and enables the obtaining of three to four times the power of the unsupercharged engine without changing is operating life. Relative to conventional supercharging, the power gain thus obtained can go from 50 to 150%, depending upon the ratio of initial supercharging employed. The increase in power is also accompanied by a certain number of secondary advantages: high torque at low speed, much reduced noise level, exhaust of low polluting effect, ease of cold starting, easy correction of atmospheric variations, possibility of idling at very low speed, and reduction in the specific bulk of the cooling system.

The system of the invention is readily adapted to the majority of self-ignition internal combustion engines. It requires no internal modification other than a different geometry of the combustion chambers. Moreover, the very high pressure necessary for the method is provided by a supercharging system which is used instead and in place of conventional supercharging devices of similar bulk.

In such engines of the invention, the parallel branch of the aforesaid connecting means preferably comprises a bypass pipe enabling direct and permanent passage of fresh air delivered by the compressor to the exhaust gases emerging from the engine. A combustion chamber is then generally provided upstream of the turbine, this combustion chamber being supplied by the exhaust gases and by the fresh air taken from the abovesaid branch pipe.

It is a further object of the invention to adapt the turbo-compressor group to high supercharging pressures due to operation of the compressor close to the surge or pumping line, that is to say with optimum yield.

It is yet another object of the invention to enable good scavenging of the engine due to a difference of pressure maintained between the intake and the exhaust.

It is another object of the invention, in engines of the above character, to reduce the work of discharging exhaust gases, which hence enables the power of the engine to be increased (by increasing the mean effective pressure) and to reduce its consumption.

In order to achieve such scavenging the engine according to another embodiment of the invention is provided with throttle means with variable passage cross section, arranged so as to be traversed by the air passing through the bypass pipe, these throttle means generating between the upstream part of the bypass pipe (the part connected to the compressor) and the downstream part of the bypass pipe (the part connected to the turbine, if necessary through the combustion chamber) a difference in pressure which is an increasing function, preferably linear or substantially linear, of the pressure existing in the upstream part regardless of the engine speed and therefore which is independent of the air flow passing through said throttle means.

It will hence be understood that the work of discharging the exhaust gases being reduced, the brake mean effective pressure (b.m.e.p.) is increased to a value equal to the aforesaid difference in pressure between the pressure upstream of the throttle means and the pressure downstream of said throttle means.

Moreover, it is possible to make the engine operate at high supercharging pressures, the compressor operating close to the pumping limit.

Lastly, the existence of a difference in pressure maintained between the intake (pressure upstream of the throttle means) and the exhaust (pressure downstream of the throttle means) enables good scavenging of the engine.

According to one advantageous embodiment of the invention, the throttle means comprises a throttle member arranged in the bypass pipe and cooperating with a fixed seat.

This throttle member can be operatively coupled to, or may consist of, a balancing piston, one working surface of which is subjected to the pressure existing in the part upstream of the bypass pipe and of which a second working surface is subject to a counter pressure (atmospheric pressure or pressure comprised between atmospheric pressure and the pressure existing in the upstream part of the bypass pipe), and a third working surface of which is subjected to the pressure existing in the downstream part, and elastic return means being able to act in one sense or the other on the movable mechanism constituted by the throttle member and its balancing piston.

According to a particular feature of the invention, which is applied in the case where there is provided a combustion chamber which is supplied, with fresh air, through a primary air intake to introduce fresh air into a combustion zone, and through a secondary air intake to introduce fresh air into a mixing zone, the throttle means comprise, in parallel, first throttle means with variable passage cross section, arranged so as to be traversed by the secondary air, these first throttle means generating between the upstream part of the bypass pipe (the part connected to the compressor) and the downstream part of the bypass pipe (the part connected to the combustion chamber) a pressure difference which is an increasing function, preferably linear or substantially linear, of the pressure existing in the upstream part, and second throttle means with variable outlet cross section subjected to the difference of pressure generated by the first throttle means and arranged so as to be traversed by the primary air, these second throttle means regulating the flow-rate of primary air by offering an outlet cross section to this primary air which is servocoupled to the pressure existing in the downstream part or the upstream part of the bypass pipe, this servocoupling being according to a predetermined relationship.

Preferably, these second throttle means control in addition a regulating device for the flow-rate of fuel injected into the combination chamber so as to preserve, for flow-rates of primary air and of fuel, a ratio ensuring good combustion stability.

The invention, apart from the features which have been considered, consists of certain other objects, features and advantages which will be more explicitly discussed below.

The invention will, in any case, be better understood with the aid of the supplementary description which follows as well as of the accompanying drawings, which description and drawings relate to preferred embodiments of the invention and do not have, of course, any limiting character. In these drawings:

FIG. 1 is a diagrammatic view of a supercharged diesel engine, with one compression stage, constructed according to the invention and constituting a first embodiment.

FIG. 2 is a diagrammatic view of a supercharged diesel engine, with one compression stage, constructed according to the invention and constituting a second embodiment thereof.

FIG. 3 is a diagrammatic view of a supercharged diesel engine, with one compression stage, constructed according to the invention and constituting a third embodiment thereof.

FIG. 4 shows a supercharging unit according to the invention, with one compression stage, and constructed in a manner analogous to the embodiment of the diesel engine shown in FIG. 1.

FIG. 5 shows a supercharging unit according to the invention, with one compression stage, and constructed according to the invention in a manner analogous to the embodiment of the diesel engine shown in FIG. 2.

FIG. 6 shows a supercharging unit according to the invention, with one compression stage, and constructed in a manner similar to that of the embodiment of the diesel engine shown in FIG. 3.

FIGS. 7 and 8 show two variations of a supercharged diesel engine with two compression stages and constructed according to the invention in a manner similar to the embodiment of the supercharged diesel engine with one compression stage which is illustrated in FIG. 2.

FIG. 9 is a diagrammatic view of another embodiment of a supercharged diesel engine equipped with a combustion chamber with a single fresh air intake, and constructed according to the invention.

FIGS. 9A and 9B are diagrammatic views of second and third embodiments of throttle means which are equivalent to and may be substituted for the throttle means shown in FIG. 9.

FIG. 10 is a diagrammatic view of a supercharged diesel engine, equipped with a combustion chamber with two fresh air intakes, and constructed according to an embodiment of the invention for which the combustion chamber comprises a return injector.

FIG. 11 is a diagrammatic view of a supercharged diesel engine, equipped with a combustion chamber with two fresh air intakes, and constructed according to an embodiment of the invention for which the combustion chamber comprises a "nonreturn" injector.

FIG. 12 is a parallel view of an important element of the engine of FIG. 10 showing a modification of the invention.

FIG. 13 is a graph relating to the operation of an engine according to the invention.

FIG. 14 is a schematic diagram of a commercial Poyaud Model 520-6L engine modified in accordance with the present invention.

FIG. 15 is a rear perspective elevational view of a commercial Poyaud Model 520-6L engine also modified in accordance with the present invention and in particular utilizing the system shown in FIG. 2.

FIG. 16 is a front perspective elevational view of the commercial Poyaud Model 520-6L engine incorporating the systems described in conjunction with FIGS. 11-14.

FIG. 17 is a graph showing a plot of engine r.p.m. against horsepower and against specific fuel consumption for nonsupercharged, conventionally supercharged and invention supercharged versions of the engine shown in FIGS. 14-16.

FIG. 18 is a graphic comparative development of supercharging pressure versus crank angle for engines supercharged conventionally and pursuant to the invention, and FIGS. 19, 20 and 21 are corresponding graphic comparative developments of temperature, heat transfer coefficients and thermal flow respectively.

FIG. 22 is a graph of indicated mean effective pressure as a function of the supercharging pressure and of the angular duration of combustion calculated for an engine supercharged pursuant to the invention.

FIG. 23 is a graph of the paths of operative points of a turbocompressor in its characteristic field as operated in conventional supercharging and in supercharging pursuant to the invention.

FIG. 24 is a graphic illustration of three phases of operation of engine operated pursuant to the method of the invention depicted as plot of horsepower versus engine r.p.m.

As shown in FIGS. 1-3, the diesel engine 1 is supercharged by a supercharging unit, with one compression stage, which comprises a compressor 2, supplying fresh air in parallel to the engine 1 and to a combustion chamber 3, and a turbine 4 supplied with combustion gas by the engine 1 and by the abovesaid combustion chamber 3. The turbine 4 rotates the compressor 2 through a connecting shaft 5. Independent starting means 6, which can be constituted by an electric motor associated with a clutch, are provided to bring the turbine 4-compressor 2 assembly into self-maintaining operation independent of the engine.

This en