Cooling Systems Of Supercharged Diesel Engines

Abstract

This invention applicable notably to supercharged Diesel engines consists essentially in utilizing the engine exhaust gas having already worked in the turbine of the supercharging turbo-compressor for inducing in a pump the air necessary more particularly for partially cooling the lubricating oil and the engine supercharging air.

Description

The present invention relates to Diesel engines and has specific reference to improvements in the cooling system of supercharged Diesel engines.

It is already known to use the exhaust gas of Diesel engines for cooling these engines either through the medium of a radiator in the case of a water-cooled engine, or directly in the case of a direct air-cooled engine.

This procedure proved to be extremely efficient due to the considerable amount of energy normally available in the engine exhaust gas. Unfortunately, the noise was unbearable since the system constituted a free exhaust one. Attempts have been made with a view to fit silencers of mufflers in the duct conveying the gas-air mixture issuing from the pump, but on the one hand this additional device must have very large dimensions and on the other hand the residual energy decreases considerably and thus compromises the cooling efficiency.

The present invention consists in utilizing the exhaust gas having already worked in the turbine of the turbo-supercharger for inducing through a pump the air required more particularly for partially cooling the lubricating oil and the engine supercharging air.

It is known that the exhaust noise, even in the case of a free exhaust engine, is reduced considerably and eventually becomes quite tolerable because an appreciable expansion already took place in the turbine and the pulsation is merged into a single whistling noise, to such an extent that many supercharged engines are operated without any muffler. As a counterpart, the residual energy available in the exhaust gas is strongly reduced and the pump efficiency would not be sufficient to induce the whole of the air required for properly cooling the engine.

In view of the foregoing, and according to a specific feature characterizing this invention, the pump action is limited to a cooling circuit separated from the general cooling system of the engine and adapted to cool in particular the supercharging air and the lubricating oil with more energy than the engine unit as a whole. According to another feature of this invention a pump of the annular peripheral induction type is used. Moreover, this invention provides means for regulating the temperatures in the cooling circuit as a function of the supercharging pressure, as already contemplated in the French Pat. application No. 69/22756 of July 4, 1969, so that the circuit temperature be high when the supercharging pressure is low and the temperature be as low as possible when the supercharging pressure is high. This arrangement is applicable to both liquid-cooled engines and direct-flow air-cooled engines.

The engine proper is cooled as usual by means of a separate radiator and fan system, in the case of a liquid-cooled engine, and by means of a fan and separate duct means in the case of engine cooled by direct-air circulation.

The present invention will now be described with reference to the attached drawings illustrating diagrammatically by way of example two typical forms of embodiment of the invention. In the drawings:

FIG. 1 is a general diagram of the cooling system in the case of an engine cooled by means of an intermediate liquid fluid;

FIG. 2 is a cross section taken along the line A--A of FIG. 1;

FIG. 3 is a detail section showing the thermostat;

FIG. 4 is a detail section of the pressure-responsive valve, and

FIG. 5 is a general diagram showing the cooling system in the case of an engine cooled by direct-air circulation.

Referring first to FIG. 1, the internal combustion engine, in this case a supercharged Diesel engine, comprises an exhaust pipe 2 through which the gas is directed to the turbine 5 driving in turn the compressor 6 of the turbo-compressor unit. The supercharger compressor 6 takes atmospheric air from an inlet 7 and forces same through a duct 8 leading through a heat exchanger 9 to the pipe 10 supplying combustion air to the engine 1. This engine 1 comprises an oil pump 11 and an oil filter 12. The oil pump 11 forces oil through a pipe 13 for lubricating the engine and cooling the pistons. If desired, part of this oil may also be forced through another pipe line 14 into a Root supercharger associated with the engine, for example as disclosed in the Applicants' patent application Ser. No. 47,331 of June 18, 1970. Finally, the pump 11 is adapted, through another pipe line 15, to supply oil under pressure to a heat exchanger 16, this oil returning via another pipe line 17 to the engine sump 18. Both heat exchangers 9 and 16 receive a circulation of cooling liquid therethrough, for example, water and a glycol additive. This cooling circuit is separate from the normal or conventional engine water-cooling system illustrated diagrammatically in the form of a radiator 45 connected through lines 46 and 47 to the engine cylinder block. In this specific circuit water accumulates in a reservoir 19 located at the highest possible level. A water pump 20 draws water through a pipe line 21 and forces same into a pair of branch pipes 22, 23. Pipe 22 extends through a thermostat 3 of which a detailed view is shown in FIG. 3. The other pipe 23 extends through a pressure-responsive valve 4 of which the details are shown in FIG. 4, and pipes 22 and 23 merge into a common pipe 24 passing firstly through the heat exchanger 9 and then through the other heat exchanger 16, before leading to the radiator 25; the coolant emerges from radiator 25 and is forced into reservoir 19. It will be seen that the pressure-responsive valve 4 is connected via a pipe 27 to the delivery side of compressor 6.

FIG. 3 illustrates a thermostatic bellows 28 inserted in the pipe line 22 for controlling the valve 29 in such a manner that the circuit is closed when the temperature drops below a predetermined value, for example, 85.degree. C, and open when the temperature is above this value.

FIG. 4 illustrates a manometric bellow 30 controlling a valve 31 balanced by a spring 32.

A pipe line 27 connects the inner chamber of the manometric bellows 30 to the delivery side of compressor 6; the bellows 30 and spring 32 are gauged so that the valve is normally closed when the pressure is inferior to 1.4 psi, and wide open when the pressure value is about 4.2 psi.

Reverting to FIG. 1, it will be seen that the cluster of radiator 25 is cooled by air taken from the outflared upper section 33, constituting the convergent of a pump 34 having a lower divergent 35.

The induction is produced in this pump by means of the exhaust gas from the turbine 5 which is directed through a duct 36 tangentially to an annular chamber 37 as shown in FIG. 2, before penetrating into the pump through blades 38 illustrated in FIGS. 1 and 2. These blades 38 are so shaped that the gas stream is eventually rectified and caused to follow a direction parallel to the generatrices of the mixing body 34 of the pump. Moreover, the total cross-sectional area of the annular chamber 37 is small enough to cause the gas to be accelerated sufficiently for inducing the desired air current. Of course, this cross-sectional area determines for each gas output a counterpressure which must be adjusted reasonably in order to avoid any undesired or abnormal reduction in the power available in the turbine 5. Thus, the dimensions of the annular chamber 37, the cross-section of blade-receiving passage and the angular position of the blades 38 can be selected with a view to obtain a satisfactory compromise between the induced air input and the noise level obtained at the exhaust, provided, of course, that a minimum disturbance is observed at the turbine 5, as already explained hereinabove. It may be emphasized that by mixing the engine exhaust gas with a large amount of air there is obtained at the same time a considerable dilution of the exhaust gas, so that definitely colourless gas emissions are produced.

The mode of operation of this assembly will be readily inferred from the above description. However, a few details are given hereinafter in connection with the functions of the thermostat 3 and the pressure-responsible valve 4.

In case the engine 1 is a conventional Diesel engine simply supercharged through its turbo-compressor 5, 6, the pressure-responsive valve 4 and pipes 23, 27 could be dispensed with so as to maintain only the pipe 22 and thermostat 3 by adjusting the latter at a relatively low temperature, say, of the order of 60.degree. or 55.degree. C. In this case the purpose is to obtain an auxiliary cooling circuit at a general temperature considerably lower than that of the main engine cooling system 45, 46 and 47. Thus, the supercharging air will under all circumstances be strongly cooled by the heat exchanger 9, and the lubricating oil will be strongly cooled by the other heat exchanger 16. The engine circulation water is kept at about 80.degree. to 85.degree. C. The chief advantage of providing a separate cooling of the lubricating oil at a temperature below 60.degree. or 55.degree. C is to relieve the main radiator 45 since the oil heat is no more dispersed in the radiator circuit; besides, this oil can thus pick up more heat than usual from the engine pistons, due to its lower temperature. Besides, the lower temperature of the supercharging air constitutes an essential factor for increasing the engine power output without any excessive strain for the engine parts. Under these conditions it is clear that, in addition to the advantageous technical results obtained from the dual point of view of the increased power output and useful life of the engine, the main radiator is relieved from excessive work while facilitating the mounting, on a given vehicle, of a more powerful engine since the main radiator can preserve reasonable dimensions.

If the engine is a compensated Diesel engine (as disclosed in the U.S. patent application Ser. No. 794,187 of Jan. 27, 1969), i.e., an engine wherein the turbo-compressor 5, 6 is combined with a variable speed ratio volumetric compressor, a fumigation system, etc.., the circuit operation is more complicated. In fact, in this case it is advantageous to use both the thermostat 3 and the pressure-responsive valve 4. The temperature should be kept as low as possible in circuit 24 of the cooling system when the engine is operated under high power output conditions and notably when a high pressure is obtained on the delivery side of centrifugal compressor 6. The pressure in circuit 24 acts via pipe line 27 on the pressure-responsive valve 4 to open the branch line 23 so that the fluid flow be as fast as possible and the radiator 25 operates under its maximum cooling capacity. It may be emphasized that at the same time this high-power operation is attended by a very considerable exhaust gas output at a relatively high pressure so that the pump 34, 35, 36, 37, 38 operates with a high degree of efficiency and yields a considerable air throughput across the radiator 25.

In contrast thereto, when the engine operates at low speed or under moderate load conditions it is essential that the supercharging air be at a relatively high temperature and that, consequently, the circuit 24 be kept at a considerably higher temperature; in this case the pressure on the delivery side of the centrifugal compressor is relatively moderate and the pressure-responsive valve 4 is closed. Thus, the fluid can flow only through the branch line 22 as permitted by the thermostat, provided that the temperature is not inferior to 80.degree.-85.degree. C.

The air flowing through ducts 8 and 10 must in this case be warm, and the lubricating oil must also preserve a temperature of about 80.degree. C.

The above remarks given in connection with a liquid-cooled engine are also applicable to an assembly wherein the main engine cooling circuit operates by direct air flow as in the case shown in FIG. 5. In this arrangement, as in that illustrated in FIG. 1, there is an engine 1, an exhaust 2, a turbine 5, a compressor 6, a delivery duct 8 extending through a heat exchanger 9', but in this case the exchanger 9' is an air-to-air exchanger provided with fins and disposed within a duct 39. This arrangement also includes the lubrication pump 11 and the oil circuit extending through another heat exchanger 16' of the oil-to-air type provided with fins and also disposed within the same duct 39. Similarly, the outlet 36 of turbine 5 is directed tangentially into the circular duct 37 and acts upon the pump 34, 35, 38 as in the preceding example; the section 33' of the pump convergent is thus connected not to a radiator but to the aforesaid duct 39; the air flow sucked by the pump will thus pass through the upstream portion of the duct 39 in order to cool directly the heat exchangers 9' and 16'. Of course, the regulation is effected on the air through a relatively large by-pass valve shutter 40 which may either close a lateral aperture 49 formed in the wall of duct 39, when it is desired to cause the air to flow through the heat exchangers, or alternatively tend to close the main passage of duct 39 when it is desired to prevent the air from flowing therethrough. In this last case the pump 34, 35, 38 will draw air directly from outside through said aperture 49. The regulation controls, although applied to an air circulation, are of the same order as in the preceding case, notably the thermostatic bellows 28' controlled by the probe 41. This thermostatic bellows controls the linkage comprising the levers 42, 43 acting in turn upon the valve 40; when the temperature rises and exceeds a value of, say, 60.degree. C in the lubricating oil, the thermostat is expanded and, through the levers 42 and 43, tends to close the aperture 49 by actuating the valve shutter 40 so as to derive the maximum efficiency from the circulation of air induced by the pump 34, 35, 38 for cooling the exchangers 9' and 16'.

In the case of an engine equipped with a compensated supercharger (as disclosed in the aforesaid U.S. patent application Ser. No. 794,187 of Jan. 27, 1969), it is also essential that the temperature rises when the engine revolves at low speed and under a moderate load. The pipe line 27' branched off the pipe or duct 8 permits of inducing in the above-described mechanism a correction also tending to close the duct 39 when only a very low supercharging pressure is available.

Although a specific form of embodiment and a modification thereof have been described and illustrated herein, it will readily occur to those convergent with the art that various modifications and variations may be brought thereto without departing from the scope of the present invention.

Claims

What is claimed as new is:

1. An auxiliary system for cooling diesel engines supercharged by means of a turbo-compressor driven from the engine exhaust gas which comprises:

a first heat exchanger in the line from the turbo-charger to the engine to cool the supercharged air;

a second heat exchanger in the engine lubricating oil line to cool the oil;

common cooling fluid means in series heat exchange relation with said first and second heat exchangers;

means sensitive to the pressure of the delivery pipe of the turbo-compressor for controlling the flow rate of the common fluid in heat exchanger relation between said first and second heat exchangers;

means sensitive to the temperature of the diesel system for controlling the flow rate of said common fluid; and

pump means actuated by the turbo-compressor exhaust for inducing air into the auxiliary system to remove the heat absorbed by the system from the diesel engine.

2. A system according to claim 1 wherein said cooling fluid means comprises a liquid which flows in a conduit through a third heat exchanger;

said pump means induces air across said third heat exchanger to cool said liquid; and

said temperature sensitive means comprising a thermostat in a branch of the liquid conduit which is responsive to the temperature of the cooling fluid.

3. A system according to claim 1 wherein said cooling fluid is air which is induced through said auxiliary system by said pump;

said temperature means is responsive to the temperature in the engine lubricating oil line; and

said pressure sensitive flow controlling means and said temperature sensitive flow controlling means are connected via a common linkage to a valve shutter which regulates the amount of air which enters said auxiliary system downstream of said first and second heat exchanger and before said pump whereby the amount of cooling air in the upstream portion of said auxiliary circuit is controlled.

4. A system according to claim 1 wherein said pump comprises:

a circular chamber;

an annular nozzle within said chamber surrounding the neck of a convergent zone through which the cooling air is caused to circulate;

a circular set of rectifying blades in said annular nozzle; and

means to tangentially supply the exhaust gas from the turbine of said turbo-compressor to activate said rectifying blades.