US3805748A

US3805748A - Cooling system for an internal combustion engine

Info

Publication number: US3805748A
Application number: US00223440A
Authority: US
Inventors: G Garcea; D Radaelli
Original assignee: Alfa Romeo SpA
Current assignee: Alfa Romeo SpA
Priority date: 1971-02-05
Filing date: 1972-02-04
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23
Also published as: DE2205280A1; DE2205280C2

Abstract

In a liquid-coolant cooling system for an internal combustion engine, of the kind in which a piping by-passing the radiator and put in parallel with respect thereto, is provided, connected by a three-way valve to the radiator inlet piping, the improvement comprising a special throttling valve for the coolant, installed in the radiator-by-passing piping. The special valve allow the rate of flow of liquid through the radiator-by-passing pipe to be increased as the pressure therein is increased. The advantages of the device are to prevent localized overheatings in the engine block and reducing the emission of unburned hydrocarbons when the engine is running cold.

Description

United States Patent 91 Garcea et a1.

[ COOLING SYSTEM FOR AN INTERNAL COMBUSTION ENGINE [75] Inventors: Giampaolo Garcea, Milan; Dario Radaelli, Legnano, both of Italy [73] Assignee: ALFA Romeo S.p.A., Milan, Italy [22] Filed: Feb. 4, 1972 [21] Appl. No.: 223,440

[30] Foreign Application Priority Data Feb. 5, 1971 Italy 20236/71 [52] US. Cl. 123/41.1, 123/41.13 [51] Int. Cl. F0lp 7/14, FOlp 3/00, F01p 7/16 [58] Field of Search 1215/41.], 41.13, 41.08

[56] References Cited UNITED STATES PATENTS 1,253,695 l/19l8 LaPorte 123/4113 1,649,248 11/1927 Muir 123/41.13 1,785,207 12/1930 Page 123/4108 2,500,472 3/1950 Sohler l23/41.1 2,808,038 10/1957 Scherenberg 123/4l.1

[451 Apr. 23, 1974 3,459,161 8/1969 Kolle l23/4l.1

2,622,572 12/1952 Nallinger 123/4l.13 X

FOREIGN PATENTS OR APPLICATIONS 27,127 3/1967 Japan l23/4l.l

Primary Examiner-Al Lawrence Smith Attorney, Agent, or FirmHolman & Stern ABSTRACT In a liquid-coolant cooling system for an internal combustion engine, of the kind in which a piping bypassing the radiator and put in parallel with respect thereto, is provided, connected by a three-way valve to the radiator inlet piping, the improvement compris ing a special throttling valve for the coolant, installed in the radiator-by-passing piping. The special valve allow the rate of flow of liquid through the radiatorby-passing pipe to be increased as the pressure therein is increased. The advantages of the device are to prevent localized overheatings in the engine block and reducing the emission of unburned hydrocarbons when the engine is running cold.

8 Claims, 10 Drawing Figures COOLING SYSTEM FOR AN INTERNAL COMBUSTION ENGENE BACKGROUND OF THE INVENTION This invention relates to improvements in or relating to the cooling system of an internal combustion engine, of the kind employing a liquid coolant, more particularly for motor vehicles.

Systems of this kind usually comprise a radiator, which forms the heat-exchanger for exchanging heat with the surrounding atmosphere, and a non-metering pump, driven by the engine, sends the liquid from: the radiatorto appropriate channels formed in the engine block. The liquid flowing through these channels is brought back to the radiator in such a way as to make up a closed loop.

The radiator is proportioned consistently with the maximum amount of heat which is to be dissipated. In order that the optimum temperature of the liquid coolant may be attained within the shortest possible time, and to maintain this temperature in the different conditions of use of the engine, a deflecting valve is provided, as controlled by an element responsive to the temperature of the liquid emerging from the channels of the engine block, in the cooling system, the automatic operation of this valve thus permits the temperature of the liquid may to be maintained virtually constant, so that the engine temperature may stay within an acceptable range, inasmuch as the increase in the resistance in the cooling loop as a consequence of throttling, reduces the rate of flow of the pump. In order to prevent over-pressure build-up and a complete stagnation of water when the thermostatic valve is closed, it has been suggested than an auxiliary piping be provided which permanently by-passes the throttling valve and the radiator, offering hydraulic resistance which is greater than that of the radiator, so that, when the valve is open, the rate of flow in the above mentioned auxiliary piping is not significant as compared with that flowing through the radiator.

Such an approach involves serious drawbacks when high powers are required ofa cold engine: as a matter of fact, the thermostatically controlled valve cuts off the radiator and the high pressure drop undergone by the coolant as it flows through the auxiliary piping, drastically reduces the rate of flow of the liquid as delivered by the pump: under these conditions, when the engine is running at full load, localized overheating areas may be formed, which originate serious failures. On the contrary, if the hydraulic resistance of the auxiliary piping which bypasses the radiator is decreased, the time which is required for the liquid coolant, and thus for the engine, to attain the steady state temperature, is undesirably extended.

SUMMARY OF THE INVENTION According to the present invention these defects have been overcome by causing the rate of flow of the liquid which, when the engine is cold, by-passes the radiator, to be increased as the power delivered by the engine is increased.

It has thus become possible to shorten the time requred by the engine to attain the steady state temperature, local over-heating possibilities being thus prevented.

A further result as attained by the present invention is to reduce to a considerable degree the emission of unburned fractions with the engine exhausts, as compared with the conventional approaches affording similar overheating prevention features.

The liquid coolant circulation loop according to the present invention comprises a first piping which includes a radiator, and a second piping mounted in parallel with respect to the radiator by the agency of valve means controlled by means responsive to the temperature of the liquid coolant, to deflect the liquid from the first to the second piping when. the temperature is below a preselected value, and is characterized by a valve, placed in the second piping and governed by means responsive to the power delivered by the engine, the valve being adapted to reduce the flow crosssectional area of said second piping when the engine is running at a low power.

According to a preferred embodiment, the cooling loop according to the present invention comprises a radiator, a first branch of said first piping which connects the liquid delivery side of the radiator to the intake side of a pump whose rate of flow is decreased as the pressure supplied thereby is increased, said pump sending the liquid to the input side of the ducts placed in the interior of the engine block, a second branch of the first piping connecting the output of the liquid of the engine block to the radiator input, the second piping connecting the first branch to the second branch of the first piping, a three-way valve arranged in either of two points of connection of the second piping with the first piping, the three-way valve being controlled by an element sensitive to the temperature of the circulating liquid so that the liquid is circulated through the radiator for temperatures above a preselected level, and, for temperatures below another value which is somewhat lower than the first is circulated through the second piping, whereas for intermediate temperatures it is cir' culated partly through the radiator and partly through the second piping, there being provided in the second piping a throttling valve for the liquid flowing therethrough, the valve being controlled so as to vary the flow cross-sectional area of the liquid by the agency of means sensitive to the power delivered by the engine, so as either to widen or to restrict the cross-sectional area as the power delivered by the engine is either increased or decreased, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the advantages and features of the cooling loop according to the present invention may be better understood, a practical embodiment thereof will be described by way of example only with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatical showing of a conventional cooling system;

FIG. 2 is a diagram of the operation of the system of FIG. 1;

FIG. 3 is a diagrammatical showing of an alternative conventional embodiment of the cooling system.

FIG. 4 is the working diagram of the system of FIG.

FIG. 5 shows the cooling system according to the present invention;

FIG. 6 is the working diagram of the circuit of FIG.

FIG. 7 is a cross-sectional view of a valve of the system of FIG. 5, and

FIG. 8 is a detail of FIG. 7;

FIG. 9 shows the valve of FIG. 7 connected to the throttling valve of the engine feed;

FIG. 10 shows a further alternative embodiment for controlling the valve of FIG. 7.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, there are diagrammatically shown at l the engine block, at 2 the head and at 3 the oil sump tank of a conventional reciprocating internal combustion engine, to whose shaft 4 a flywheel 5 is keyed. The engine block, consisting of the engine crankcase l and the head 2 has a net of inner channels therethrough (not shown) for circulating the cooling liquid, these channels being connected to a delivery piping 6 and a discharge piping 7. The latter feeds, through a thermostatic valve 8, a piping 9 which opens into a manifold 10 of a bundle of gilled tubes 11 which is the member which exchanges the heat with the atmosphere. The tubes ll, or anyhow the ducts having a high external surface, open into a manifold 12 from which starts a piping 13 which feeds a pump 14 feeding with liquid the piping 6: the whole makes up a closed hydraulic loop.

A piping 15, having a reduced cross-sectional area then connects directly the

pipings

6 and 13.

The non-metering pump 14, for example of the centrifugal type, is driven by the engine, and it is shown in the drawing, for the sake of simplicity, as keyed to the crankshaft 4. At any rate, it can be connected to the crankshaft by any rotational drive, such as by a belt. For simplifying the drawing, further conventional members which complete the cooling system have been omitted, such as the fan which thrusts air through the radiator so as to sweep the tubes 11.

The operation of the conventional circuit as shown in FIG. 1 will now be briefly described, with further reference to the diagram of FIG. 2, in which the abscissae indicate the rates of flow and the oridnates the pressures of the circuit of FIG. 1.

As the engine is started at the temperature of the ambient atmosphere, that is when the engine is cold, the valve 8 is closed by the agency of thermostatic means sensitive to the temperature of the liquid in the piping 7, that is, the liquid flowing out of the engine.

Under these conditions, the liquid flows through a loop formed by the pump 14, the piping 6, the engine inner channels, the piping 7, l5 and a portion of the piping 13 to the pump again. Due to the presence of the reduced flow cross-sectional area piping 15, the hydraulic resistances of this path are rather high and shown by the line R, of the plot of FIG. 2, as a function of the rate of flow Q.

A small permanent rate of flow of liquid through the valve 8, even when the latter is closed, permits the thermostatic control means to be mounted within the valve which are thus always swept by the water emerging from the engine; this rate of flow, however, is wholly negligible.

As the engine has attained an appropriate temperature, the liquid emerging from the engine is also at a high temperature, for example 85C; the thermostatic valve is then opened and the liquid is allowed to be circulated from the piping 7 through the piping 9, the

tubes 11, the piping 13 and the pump 14: the resistence of the loop in hot conditions is shown by the curve R of the plot.

The same plot shows two characteristic curves for the pump, at an average rate of rotation, curve s, and at a high rate of rotation, curve r.

It is apparent that, in cold conditions, the rates of flow of the liquid pumped through the engine at either an average or a high rate of rotation, are q and Q8, respectively and, in hot conditions, q and q". respectively. When the valve 8 is only half-way open, the resistance in the circuit will be intermediate between the curves R; and R, the same being true of the rates of flow, for example at an intermediate rate of flow, where they will be intermediate between (1;, and q The valve 8 begins to open slightly before the optimum temperature, for example at C and is fully open at temperatures, for example higher than C.

The principal defect of the cooling loop so embodied has proven to be the small magnitude of the rate of flow q that is, the rate of flow in cold conditions at a high engine rate of rotation. As a matter of fact a small rate of flow has proven to be insufficient to prevent hazardous local overheating whenever a cold engine is required to supply high power. That is to say, the velocity of the water flowing through the internal channels of the engine is inadequate to remove the necessary amount of heat from certain areas. On the other hand, the valve 8 enters action for increasing the rate of flow, since its thermostatic control member is responsive only to the temperature of the water emerging from the pipe 7, the water being at an intermediate temperature with respect to that of the different areas of the engine swept thereby. The troubles which can be originated by such over-heating, for example in correspondence of the explosion chambers, are extremely serious and can even cause jamming or perforation of the pistons.

In order to overcome these drawbacks, a system of the kind shown in FIG. 3 has been suggested: parts equal to those of the system depicted in FIG. I have been indicated by equal reference numerals. In this case the piping 7 is terminated by a three-way valve 16, which is thermostatically controlled and, when hot, establishes a communication between the tubing 7 and the tubing 9 and, in cold conditions, establishes a communication between the piping 7 and a tubing 17 which, in turn, is in communication with 13 and offers to the liquid a hydraulic resistance which is substantially equal to that of the tubes 11. In cold conditions, thus, the liquid flows from the piping 7 to the piping 13 directly via the duct 17 and, in hot conditions, through the

ducts

9, 10, 11 and 12, though with the same pressure drop in both cases.

The plot of FIG. 4 shows the operability of the loop described immediately above, in the same coordinates as in the loop of FIG. 2. The resistances in the cold and in the hot are represented by the line R R and the rates of flow which pass through the engine either at an average or a high rate of rotation are indicated at q, and q,, respectively. In this case, the quick attainment of the steady state temperature by the engine is due only to the fact that, in cold conditions, the liquid does not flow through ducts having an intensive heat exchange with the external atmosphere. With this second kind of duct it has been made possible to overcome the defects of the system shown in FIG. 1, but the rate of flow has proven to be too high for comparatively reduced delivered powers, that is, in the great majority of cases, since a driver very seldom uses a newly started engine at full power. It has been suggested that such an excess of rate of flow could give rise to an unnecessary and exceedingly high heat removal at the engine head and the engine barrels and thus remove heat from the gas during the combustion of the mixture. It is known, in fact, that the presence of unburned hydrocarbons in the engine exhaust gases is essentially due to the layer of mixture which, by sticking to the combustion chamber walls, is kept cold thereby so as to hinder both the propagation of the flame and the combustion of the mixture layer in question. It is known that the thickness of the cooled layer is greater, the colder the walls, it being also known that among the noxious emissions which are set free during the operation of a motor vehicle, a not negligible fraction is emitted during the engine warm-up. Laws now in force set a limit for emissions, ruling that an emission reading be taken during a test with cold engine start (thus comprising the engine warm up stage). This speculation as based on theoretical considerations, has been confirmed by the results of accurate experimental research which results were that at comparatively reduced powers (such as prescribed in the various laws) the rates of flow of liquid q of the system of FIG. 3, for being considerably higher than those, q,, of the system of FIG. 1, actually gave rise to an exceedingly high cooling of the gases during combustion, especially during the engine warm-up stage, so that the total amount of unburned hydrocarbon emissions from the vehicle (which thus comprised both the emissions of a cold and a warm engine) was increased by at least 10 percent.

As a result of this practical confirmation it has been deemed advisable to study the possibility of providing a cooling system which, with a cold engine, might simultaneously prevent both the possible engine failures at high power delivery, which characterized, as outlined above, the system of FIG. 1, and the high emissions due to an exceedingly high rate of flow of the coolant at low power deliveries by the engine, which are characteristic of the system of FIG. 3.

According to the present invention, the circulation of water in the engine is increased as a function of the power delivered by the engine.

The cooling system according to the present invention is shown in FIG. 5 and equal componentparts are indicated by equal reference numerals with respect to those already employed for the systems of FIGS. 1 and 3. In the present cooling system the piping 17 communicates with the piping 13 through a valve, as generally indicated at 18, which brings about a variable restriction of the cross-sectional area, consistently with the variations of the liquid pressure upstream of the valve.

An example of such a valve 18 is shown in FIG. 7 and consists of a cup 19 integral with the piping l7, and in which an obturator 20 is movable, as biassed by a spring 21 which rests against a bottom wall 22. As clearly shown also by the plan view of the obturator in FIG. 8, when the vlave is closed, as shown in FIG. 7, the liquid flowing through the piping 17 must also flow through the port 23. When the pressure upstream of the valve, top portion of FIG. 7, exceeds a certain value, the spring 21 is compressed as the obturator 20 drops and the liquid flows also through the open spaces 24 of the obturator.

It is now apparent that the operation of the system according to the present invention is the one summarized by the plot of FIG. 6. When the engine is cold and at slow running the hydraulic resistances encountered by the liquid are those of the first portion of the curve R that is, the port 23 acts like a restrictor with a function similar to that of the piping 15 of the system of FIG. 1. However, when the engine has reached such a rate of rotation that the pump operates with a characteristic curve s and thus at a pressure h, the valve 18 begins to open, and is completely open as the pump follows the characteristic curve s and has a pressure h. The valve resistance drop as the valve is open causes the rate of flow to be increased from q to q;,,, the latter being substantially equal to the rate of flow q which obtains in the warm engine, that is, when the valve 16 feeds the piping 9 with liquid.

Thus when the engine is cold the system according to the invention operates, at a low rate of rotation of the engine, like the system of FIG. 1, .and, at a high rate of rotation of the engine, likethe one of FIG. 3, so that fast warm up of the engine is warranted in correspondence with the explosion chambers without any risk of overheating at high rates of rotation.

It is extremely important to note that the opening of the valve 18, and thus the resistance drop in the piping 17, which by-passes the radiator, is determined by the increase of the rate of rotation of the engine. Actually, it would be advisable that the resistance drop would be strictly proportional to the power actually delivered by the engine, although it has proven to be sufficient to have the rate of flow of the liquid coolant proportional to other physical units bound to the engine power, such as, as described above, to the rate of rotation of the engine, or the pressure of the pump when the latter is of the centrifugal type.

None-the-less other physical units which are a function of the engine power can be useful for controlling the throttling valve in the piping 17: for example the position of the engine feed throttling valve. It is thus possible to arrange in the piping 17 a throttling valve which is driven open when the throttling valve of the engine feed is open. This is obtained by a mere meclianical linkage well-know to persons skilled in the art between the two valves as may be seen in FIG. 9. A rod 25, for example is fastened to the obturator 20 of FIG. 7 and to the accelerator pedal 28 of the vehicle. The accelerator pedal also controls the throttle 32 in the ini take duct of the engine, so that when the pedal 28 is depressed, throttle 32 opens, and element 20 of valve 18 is displaced against the action of the spring 21 thus increasing the passage section for the cooling liquid in theduct 17.

The valve in the piping 17 can still be controlled by the pressure obtaining in the engine intake duct, the pressure being increased, as is known, when the throttling valve for the aeriform fluid feeding the engine is opened. To this end, it suffices to connect the intake duct with a chamber having a wall formed by a deformable diaphragm, the latter being mechanically connected to a throttling valve installed in the piping 17, in such a direction as to close the latter as the feeding pressure is decreased.

These diaphragm devices which drive a mechanical memberas a function of the pressure obtaining in the intake duct are well known and in the art are usually mounted on internal combustion engines in order to actuate either adjustment mechanisms or servocontrols. Such a device is shown connected to the valve 18 of FIG. 7, between the valve and the accelerator pedal of the vehicle. The diaphragm 34 of the device together with the rigid wall 35 define a chamber 36 which is connected to the intake duct of the engine. When the intake duct pressure is low, the obturator is held against the wall 19 so that the passage section is almost throttled. However when the pressure in duct 33 is increased the obturator 20 is displaced by spring 21 so that the passage section of duct 17 is increased.

Other physical units which are a function of the power delivered by the engine can be used for controlling the position of the throttling valve mounted in the cooling system, by the agency of appropriate servoing members.

The system according to the present invention affords advantages even when the engine is at its steady state temperature and, however, the valve 16 is in an intermediate position, that is, the liquid partly flows through the radiator and partly through the by-pass piping 17. As a matter of fact, under these conditions, the resistance of the hydraulic circuit has an intermediate value and, likewise, the rate of flow is comprised between the maximum value under hot conditions and the minimum value under cold conditions. At any rate, an abruptincrease of the delivered power causes the rate of flow to be immediately increased, preventing overheating which could be experienced if the increase of the rate of flow should require of necessity the operation of the valve 16. As a matter of fact, this valve has a certain delay at the beginning of its operation due both to thermal inertia and the insertion of thermostatic control means.

Lastly, it is important to note that the three-way valve 16 can merely be replaced by two distinct valves, one on the piping 9 and the other on the piping 17, which are driven open and closed, respectively, by thermostatic means acting in opposite directions. In this case the thermostatically controlled valve installed in the piping 17 could be integral with the valve 18.

In the same way, the position of the pump could 'be varied, by arranging it in any appropriate point of the hydraulic loop.

Further modifications and changes may be introduced in the system described above by way of example, without thereby departing from the spirit and scope of the present invention as defined in the appended claims.

What is claimed is:

l. A liquid-coolant cooling system for an internal combustion engine, more particularly for motor vehicles, comprising a first piping which includes a radiator, and a second piping placed in parallel with the radiator through valve means governed by means sensitive to the temperature of the liquid coolant for deflecting the liquid from the first to the second piping when said temperature is below a preselected value, characterized by a throttling valve placed in said second piping and governed by means sensitive to the power delivered by th engine, said throttle valve being adapted to reduce the cross-sectional area of said second piping when said power is below preselected value.

2. A cooling system according to claim 1, wherein the hydraulic resistance of said second piping with its throttling valve open, is in the same order of magnitude as the hydraulic resistance of the first piping.

3. A cooling system according to claim 1, wherein a first branch of said first piping connects the output of liquid from the radiator with the input side of a pump whose rate of flow is decreased as its pressure' is in creased, said pump sending the liquid to the input side of the ducts internal to the engine block, a second branch of said first piping which connects the output of liquid from the engine block with the radiator input, said second piping connecting the first branch to the second branch of the first piping, a three-way valve arranged in one of the points of connection of the second piping with the first piping, said three-way valve being driven by an element sensitive to the temperature of the flowing liquid so that the liquid circulates through the radiator at temperatures over a predetermined value, and at temperatures below another value which is somewhat lower than the first it circulates through the second piping, whereas at intermediate temperatures it partly circulates through the radiator and partly through the second piping, there being provided in said second piping a throttling valve for the liquid flowing therethrough and driven so as to vary the flow crosssectional area for the liquid by means sensitive to the power delivered by the engine, in the direction as either to widen or to restrict said cross-sectional area as the power delivered by the engine is either increased or decreased, respectively.

4. A cooling system according to claim 3, wherein said pump is of the centrifugal type and is driven to rotation by the engine at a speed which is proportional to the speed of rotation of the engine, said throttling valve comprising a movable obturating member, as biassed by a spring, which can be moved from a first position, wherein it leaves said restricted cross-sectional area free for the liquid flow, to a second position wherein it leaves free for the liquid flow said wider cross-sectional area, said obturator being brought from said first to said second position by the pressure differential upstream and downstream of said valve, when said differential exceeds a preselected value.

5. A cooling system according to claim 1, wherein said throttling valve is mechanically connected with the adjusting member for the flow of the aeriform fluid fed to the engine in the sense of reducing the crosssectional area of said second piping when said member reduces the flow of the aeriform fluid fed to the engine.

6. A cooling system according to claim 1, wherein said engine has at least one combustion chamber and said throttling valve is driven by a device responsive to the pressure of the aeriform fluid fed to said combustion chambers, in the sense of reducing the crosssectional area of said second piping when said pressure of the aeriform fluid is below certain preselected values.

7. A cooling system according to claim 6, wherein said device consists of a chamber placed in communication with a duct through which the aeriform fluid flows towards said combustion chambers, a wall of said chamber being displaceable by the agency of the pressure obtaining in said chamber and being mechanically connected to said throttling valve.

8. A cooling system according to claim 7, characterized in that said movable wall is a resiliently yielding diaphragm.

Claims

1. A liquid-coolant cooling system for an internal combustion engine, more particularly for motor vehicles, comprising a first piping which includes a radiator, and a second piping placed in parallel with the radiator through valve means governed by means sensitive to the temperature of the liquid coolant for deflecting the liquid from the first to the second piping when said temperature is below a preselected value, characterized by a throttling valve placed in said second piping and governed by means sensitive to the power delivered by th engine, said throttle valve being adapted to reduce the cross-sectional area of said second piping when said power is below preselected value.

3. A cooling system according to claim 1, wherein a first branch of said first piping connects the output of liquid from the radiator with the input side of a pump whose rate of flow is decreased as its pressure is increased, said pump sending the liquid to the input side of the ducts internal to the engine block, a second branch of said first piping which connects the output of liquid from the engine block with the radiator input, said second piping connecting the first branch to the second branch of the first piping, a three-way valve arranged in one of the points of connection of the second piping with the first piping, said three-way valve being driven by an element sensitive to the temperature of the flowing liquid so that the liquid circulates through the radiator at temperatures over a predetermined value, and at temperatures below another value which is somewhat lower than the first it circulates through the second piping, whereas at intermediate temperatures it partly circulates through the radiator and partly through the second piping, there being provided in said second piping a throttling valve for the liquid flowing therethrough and driven so as to vary the flow cross-sectional area for the liquid by means sensitive to the power delivered by the engine, in the direction as either to widen or to restrict said cross-sectional area as the power delivered by the engine is either increased or decreased, respectively.

5. A cooling system according to claim 1, wherein said throttling valve is mechanically connected with the adjusting member for the flow of the aeriform fluid fed to the engine in the sense of reducing the cross-sectional area of said second piping when said member reduces the flow of the aeriform fluid fed to the engine.

6. A cooling system according to claim 1, wherein said engine has at least one combustion chamber and said throttling valve is driven by a device responsive to the pressure of the aeriform fluid fed to said combustion chambers, in the sense of reducing the cross-sectional area of said second piping when said pressure of the aeriform fluid is below certain preselected values.