FR3049308A1 - COOLING AIR COOLER FOR ELECTRIC COMPRESSOR - Google Patents

Abstract

The disclosure relates to a supercharging system 1 of an internal combustion engine 2, comprising an air circuit 3 having at least one electric supercharger 4, the electric compressor providing a temporary overpressure of the air supplying the engine 2 with internal combustion, during a compression period of a predetermined maximum duration, characterized in that it comprises at least one air cooler 8 placed upstream and / or downstream of said electric compressor 4, able to cool the air for the duration of said compression period.

Description

The invention relates to the field of the automobile and more particularly to electric compressor electric engines. The invention relates in particular to the improvement of the operation, in particular of the efficiency of a motor cooperating with such an electric compressor, in particular in a transient regime at low speed under heavy load.

In the automotive field, it is known to equip an internal combustion engine with a turbocharger to improve its performance. Such a turbocharger produces pressurized air, also called "charge air", which is subsequently introduced into the combustion chamber of the engine. The general principle of the turbocharger is thus to increase the power density of the engine to increase the combustion efficiency or to reduce its consumption by the implementation of equivalent power of a smaller engine displacement. As such, a turbocharger is driven by a turbine, itself driven by the enthalpy of the engine exhaust gas. One of the disadvantages of the turbocharger lies in its low-end response time. This latency corresponds to the time required for engine exhaust to provide sufficient energy to drive the turbine of the turbocharger.

Many solutions have been proposed to address this problem. An electric supercharger or e-turbo compressor is also known, also known as an electric compressor in the present description, intended in particular to supplement a turbocharger, during this latency time. . Unlike the turbocharger, this electric compressor is driven by an electric motor and can therefore be implemented very quickly, regardless of the exhaust gas, and therefore whatever the speed of the engine. It can for example go up between 250 and 350 milliseconds, against 1 to 2 seconds for a turbocharger.

It is particularly envisaged to use it in addition to a turbocharger, although independent applications can also be envisaged.

The recent electrical architectures of motor vehicles make it possible to have sufficient electrical energy to operate during short cycles of use, for example of the order of 10s maximum, but can be repeated. An electric compressor thus reduces vehicle consumption by 8 to 20%, depending on the type of engine, the dimensions of the engine and that of the turbocharger.

It is known that it is undesirable for the air supplying the engine to be at a temperature that is too high. An increase in temperature is reflected in particular by a decrease in filling and an increase in the risk of self-ignition.

For this reason, it is generally expected, for cooling the supercharged air supplying an engine, a charge air cooler (RAS) placed downstream of the turbocharger. SARs are usually air-to-air or air-to-liquid heat exchangers. Each time the turbocharger is used, the boost air increases in pressure and temperature. It is thus possible to observe at the output of the turbocharger temperature peaks of the charge air that can rise up to 240 ° C when using the turbocharger. These large increases in temperature therefore require the use of materials resistant to these high temperatures, the implementation of material thicknesses consistent for the mechanical strength of the elements and also the use of adapted RAS to cool the air around. 50 ° C.

In the case of an air / air RAS, the electric compressor is placed downstream of the main RAS. Compressed air and heated by the electric compressor does not benefit from the cooling of the RAS, and between hot in the engine in the phases of use of the electric compressor.

Indeed, unlike the turbocharger, the electric compressor is only operational for a very short period of time, for example of the order of 10s, which corresponds to a transient phase during which the engine is at low speed. and does not allow optimal implementation of the turbocharger. Once this time interval has elapsed, the turbocharger usually takes over from the electric compressor which then stops its compression work. During the transient phase of air compression by the electric compressor, a period referred to in this description as the "discharge phase", the compressed air has been heated by about 40 ° to 80 ° C., comparison with the temperature peaks representing an increase of about 220 ° C output of the turbocharger.

On the other hand, the cooling must be carried out very rapidly, during this transient phase, which does not effectively ensure the conventional SAR, in particular because of these dimensions, adapted to the turbocharger.

There is therefore a need for improved cooling of the charge air, when an electric compressor is implemented. 3. Summary

The proposed technique meets this need.

More particularly, in at least one embodiment, the proposed technique relates to a supercharging system delivering supercharging air to an internal combustion engine, comprising an air circuit having at least one electric supercharger, the electric compressor providing a temporary overpressure of the air supplying the internal combustion engine during a compression period of a predetermined maximum duration.

According to the invention, the system comprises at least one air cooler placed upstream and / or downstream of said electric compressor, suitable for cooling the supercharging air during the duration of said compression period.

Thus, during the compression period, generally a transient period of short duration (a few seconds for example) a dedicated and fast cooling (compared to conventional cooling) is occasionally applied, to improve the efficiency of the system.

The present invention is based on a novel and inventive approach of providing a dedicated cooler adapted to the cooling of the supercharging air of the electric compressor. Such a charge air cooler (RAS) thus effectively reduces the temperature of the compressed air by the electric compressor, improving the combustion efficiency of the engine and limiting the risk of auto-ignition in particular. The air cooled by the RAS also has an increased density, which further improves the performance of the engine. The resizing of the cooler limits the space under the hood of the vehicle, while allowing the conservation of satisfactory responsiveness of the charge air circuit driven by the electric compressor.

In the present description, the terms "upstream" and "downstream" refer to the flow direction of the flow concerned. Two parts are considered placed "close" to each other when they are not separated by any major mechanical component (turbocharger, engine, cooler) that can significantly vary the characteristics of the charge air.

The predetermined maximum duration of the compression period may notably correspond substantially to the maximum discharge duration of the electric compressor, for example of the order of 10 seconds. The charge air entering or exiting the electric compressor is for example cooled from 30 ° C to 40 ° C by this dedicated cooler, which can achieve an air temperature downstream of the electric compressor and the upper RAS of 10 ° C to 30 ° C at the air temperature upstream of the electric compressor and the RAS.

According to a particular embodiment, said cooler is placed downstream of said electric compressor.

The mounting of the RAS downstream of the compressor allows in particular to maximize the cooling capacity of the latter, the air expelled by the compressor having a greater temperature difference with the refrigerant than the air drawn upstream of the compressor.

According to a particular embodiment, the air circuit comprises at least one turbocharger connected in series with said electric compressor.

This combines the technical advantages associated with the implementation of an electric compressor and those related to the implementation of a turbocharger. The electric compressor is indeed operational during the transient phase during which the engine is at low speed and does not allow optimal implementation of the turbocharger. Once this time has elapsed, the turbocharger takes the relay of the electric compressor which then stops its compression work.

According to a particular embodiment, the air cooler is adapted to be mounted at the inlet opening, or the expulsion opening of said electric compressor.

Such an air cooler because of its reduced dimensions and / or the implementation of fixing elements to the electric compressor, can thus be at least partly integrated in the intake openings, or expulsion of the compressor . The control electronics of said cooler is also adapted to be mounted at the intake opening or the exhaust opening of said electric compressor.

According to a particular embodiment, at least a portion of said air cooler has a cylindrical shape, adapted to integrate a supply duct or exhaust of the electric compressor.

According to a particular embodiment, the air cooler is supplied with refrigerant fluid by an air conditioning system.

According to a particular embodiment, the refrigerant also cools said electric compressor and / or drive means of said electric compressor and / or control electronics of said cooler.

The refrigerant fluid of the RAS is thus also used to improve the performance of the electric compressor.

According to a particular embodiment, said cooler is supplied with low temperature coolant or with phase change.

According to a particular embodiment, the cooler comprises a heat exchange body between the charge air and said refrigerant fluid, implementing a material of constant pressure thermal capacity (Cp) greater than 40% to 80% the constant pressure thermal capacity required to maintain a constant temperature of the supercharged air output of said cooler.

A material having a high thermal capacity, and in particular a low thermal inertia, allows efficient implementation of the significant heat transfer from the charge air to the coolant, especially in view of the reduced time period corresponding to the discharge. of the electric compressor.

According to a particular embodiment, the material constituting the heat exchange body is aluminum or an aluminum alloy, which have a low thermal inertia. The invention also relates to a motor vehicle comprising a supercharging system such as described above. The invention also relates to a supercharging air cooling method, implemented in a supercharging system as described above and comprising: a charging phase during which said air cooler and the air it contains are cooled to a predetermined temperature, for example from 2 ° C to 13 ° C, • a step of activation of said electric compressor, • a discharge phase during which the supercharging air passes through said cooler to supplying said electric compressor and / or said engine.

Depending on the implementations, the charging and discharging phases can be partly or completely dissociated.

According to a particular embodiment, the charging phase is initiated during a deceleration phase of the engine. The energy recovered during the deceleration of the vehicle can thus be used to supply the RAS, thus limiting the fuel consumption by the RAS.

Although not described explicitly, the various aspects described above can be implemented in any suitable combination or sub-combination. 4. Figures Other features and advantages will appear more clearly on reading the following description of a particular embodiment of the disclosure, given as a simple illustrative and nonlimiting example, and the appended drawings, among which: Figure 1 is a diagram illustrating a supercharging system according to a particular embodiment of the invention; Figure 2 is a schematic top view illustrating a motor vehicle according to a particular embodiment of the invention; Figure 3 is a diagram illustrating the mounting downstream of the RAS relative to the electric compressor, according to a particular embodiment of the invention; Figure 4 is a diagram illustrating the mounting upstream of the RAS relative to the electric compressor, according to another embodiment of the invention; FIG. 5 is a flow diagram illustrating the various steps of a supercharging air cooling method, according to a particular embodiment of the invention; FIG. 6 is a diagram illustrating the cycles of activation and of stopping of an electric compressor, according to a particular embodiment of the invention; Figure 7 is a graph illustrating the temperature changes of a refrigerant during the discharge phase, according to a particular embodiment of the invention; FIG. 8 is a graph illustrating the variations of energy absorbed from the supercharging air during the discharge phase, according to a particular embodiment of the invention;

The various elements illustrated by the figures are not necessarily represented on a real scale, the emphasis being more on the representation of the general operation of the invention. 5. Description of a particular embodiment of the disclosure 5.1 Engine boost system

FIG. 1 schematically shows an example of a supercharging system 1 of an internal combustion engine 2 according to a particular embodiment of the disclosure comprises an air circuit 3 having an electric supercharging compressor 4 and a turbocharger 5, both mounted in series. A deflection channel 4 'is connected in parallel with the electric compressor 4 and thus makes it possible to redirect directly to the engine 2 the air intended to supply the electric compressor 4.

Although the implementation of an air circuit 3 comprising both an electric compressor 4 and a turbocharger 5 is particularly advantageous, given their respective technical advantages, those skilled in the art will understand that a supercharging system According to another embodiment of the invention may not include a turbocharger 5. According to other embodiments, several turbochargers and / or several electric compressors may be provided.

As illustrated by FIG. 2, the invention also relates to a motor vehicle 6 comprising, according to a particular embodiment, a supercharging system such as that represented in FIG. 1. In FIG. 2, the supercharging system is not not shown in detail for simplification purposes.

As shown in FIG. 1, a first turbocharger supercharger air cooler (RAS) 7 is mounted downstream of the turbocharger. Such a RAS 7, by its large size, is however not suitable for satisfactorily cooling the supercharging air of the electric compressor 4. For this purpose, a second RAS 8, in turn adapted and dedicated to the electric compressor 4, is mounted downstream of the latter, that is to say between the electric compressor 4 and the motor 2. Such a downstream assembly is also illustrated in Figure 3.

A person skilled in the art will understand that according to an alternative embodiment of the disclosure, and as illustrated by FIG. 4, the second cooler 8 can also be mounted upstream of the electric compressor 4. There can also be several second RASs, and for example one upstream and one downstream. 5.2 Cooling air cooling process

According to one particular embodiment of the invention and as illustrated by FIG. 5, the supercharging system 1 illustrated in FIGS. 1 and 3, for which the RAS 8 is mounted downstream of the electric compressor 4, is used according to the supercharging air cooling process described later.

It comprises a charging step 10 during which the second cooler 8 and the air contained therein are cooled. For example, during this charging phase 10, the second cooler 8, having a coefficient of performance of 0.4, is fed by a refrigerant branch of the air conditioning loop. The cooler 8 and the air present inside are then cooled for example to a temperature of the order of 2 ° C. At the same time, the temperature T1 at the inlet of the electric compressor 4 is brought to about 20 ° C.

In a second step 11, the electric compressor is activated.

Following activation 11 of the electric compressor 4, the supercharging air passes through the electric compressor 4, for example at a flow rate of 50 g / s, during a discharge step 12, of a duration for example between 1 and 3 seconds. During this discharge 12, this air can be compressed for example with a degree of compression of 1.5, and with a coefficient of performance of 0.7. The temperature T2 of the air output of the electric compressor is then of the order of 70 ° C. After passing through the second cooler 8, this air is cooled to a temperature T2 ', for example of the order of 45 ° C. For an equivalent degree of compression, the power required by the electric compressor is then reduced from 1.5 kW to 1 kW.

As illustrated in FIG. 6, the supercharging air cooling method comprises a succession of activation phases 11 of the electric compressor 4, lasting 3 seconds, and idle phases of the electric compressor 4, lasting 27 seconds. 5.3 Example of material constituting the heat exchange body of the cooler.

According to a particular embodiment, the material constituting the heat exchange body is an aluminum alloy. Since aluminum is one of the solid materials with the lowest thermal inertia, its selection as an interface material allows the implementation of an efficient heat transfer from the charge air to the coolant. in particular the brevity of the discharge phase 12.

FIGS. 7 and 8 make it possible to compare the performance of a conventional permanent cooling system, illustrated by the green curve 13, for which the coolant is kept at a constant temperature during the discharge phase, and the performance of an optimized system to take advantage of the thermal inertia of aluminum, illustrated by the red curve 14 (without additional cooling of the heat transfer fluid during the discharge phase). Thus, in the context of the cooler taking advantage of the thermal inertia of aluminum, FIGS. 7 and 8 show the large amount of thermal energy absorbed during the first seconds of the discharge phase, by the sole action of Aluminum whose thermal inertia is very low. The amount of thermal energy absorbed by the optimized system (without additional cooling) is thus not

reduced by only 27%, from 18.5 kJ to 13.4 kJ.

Constant heat capacity at constant pressure is thus increased from its original value of 1006 J / kg.K to an advantageous value of 1650 J / kg.K, by taking advantage of the thermal inertia of aluminum.

Claims (10)

A supercharging system (1) for supplying charge air to an internal combustion engine (2), comprising an air circuit (3) having at least one electric supercharger (4), the electric compressor providing a temporary overpressure of the air supplying the internal combustion engine (2) during a compression period of a predetermined maximum duration, characterized in that it comprises at least one air cooler (8) placed upstream and or downstream of said electric compressor (4), able to cool the charge air during the duration of said compression period. 2. supercharging system (1) according to claim 1, characterized in that said air circuit (3) comprises at least one turbocharger (5) connected in series with said electric compressor (4). 3. supercharging system (1) according to any one of claims 1 and 2, characterized in that said cooler (8) is adapted to be mounted at the intake opening or the exhaust opening said electric compressor (4). 4. Supercharging system (1) according to claim 3, characterized in that a control electronics of said cooler is also adapted to be mounted at the inlet opening or the exhaust opening of said electric compressor (4). 5. Supercharging system (1) according to any one of claims 1 to 4, characterized in that said air cooler (8) is supplied with refrigerant fluid by an air conditioning system. 6. Supercharging system (1) according to claim 5, characterized in that said coolant further cools said electric compressor (4) and / or motorization means of said electric compressor (4) and / or electronics of controlling said cooler. Boosting system (1) according to any one of claims 1 to 6, characterized in that said cooler (8) is supplied with low temperature coolant or phase change. 8. supercharging system (1) according to any one of claims 5 to 7, characterized in that said cooler (8) comprises a heat exchange body between the supercharging air and said coolant, implementing a material whose constant heat capacity at constant pressure (Cp) is 40% to 80% greater than the constant pressure thermal capacity required to maintain a constant temperature of the supercharged air leaving said cooler (8). 9. Motor vehicle (6) comprising a supercharging system (1) according to one of the preceding claims. 10. A method of cooling (9) charge air, characterized in that it is implemented in a supercharging system (1) of an engine (2) with internal combustion, comprising: • a circuit d ' air (3) having at least one electric supercharger (4), the electric compressor providing a temporary overpressure of the air supplying the internal combustion engine (2), during a compression period of a predetermined maximum duration, at least one air cooler (8) placed upstream and / or downstream of said electric compressor (4), able to cool the air delivered by the latter during the duration of said compression period, and in that said process cooling device (9) comprises: • a charging phase (11) during which said air cooler (8) and the air contained therein are cooled to a predetermined temperature, • an activation step (11) ) of said electric compressor (4), • a phase discharge device (12) during which the charge air passes through said cooler (8) to supply said electric compressor (4) and / or said engine (2).