FR2913491A1 - Heat exchanger i.e. charge air cooler, for diesel engine of motor vehicle, has unit distributing gas between cooling stages to modify number of canals, so as to adapt exchange surface of each stage with operating conditions of engine - Google Patents

Abstract

The exchanger (28) has cooling stages (24, 26) assembled in housing, and respectively defined by two series of canals. A distribution unit distributes gas e.g. air, between the cooling stages to modify number of canals in one of the series of canals, so as to adapt an exchange surface of each cooling stage with instantaneous operating conditions of a diesel engine. A movable shutter (70) is placed in the housing between a flow line bundle (62) and gas inlets (50, 54) or gas outlets (52, 56).

Description

Heat exchanger, including intake air cooler for

supercharged heat engine

  The invention relates to the field of heat exchangers, in particular for motor vehicles.

  It relates more particularly, but not li-5 mitative, an intake air cooler for a turbocharged supercharged engine with two stages.

  Thermal engines used on motor vehicles: The, and in particular diesel engines, are most often equipped with a supercharging system.

  To improve performance, particularly at low speeds, it is known to use two stages of supercharging respectively comprising a first compressor and a second compressor. Depending on the needs and limits of the engine, it is possible to derive or not. one and / or the other of these compressors so as to optimize the operation of the device.

  However, since the air coming from the compressor is at a high temperature, it is necessary to cool it before sending it to the engine inlet, so that it can operate under optimum conditions.

  This is the reason why an organ called a charge air cooler or RAS is used, which cools the intake air (charge air) by heat exchange with, for example a flow of liquid, which can be water. This device, also known as Water / Charged-Air Cooler or WCAC, is placed at the outlet of the compressor to lower the temperature of the air, which makes it possible in particular to increase the density and to provide more large amount of engine intake air for a given displacement.

  In the case of a supercharged supercharged engine with two stages of supercharging, the air heated by the compression can be cooled by a single heat exchanger, or by two heat exchangers: their mounted at the outlet of each compressor, when these the latter are mounted in series. This known configuration improves the efficiency and protects: The drive wheel of the second compressor when the temperature at the outlet of the first compressor is too high.

  Such a two-stage cooler integrated in the same functional module is described in particular in publication FR-A-2 886 340 (Valeo Thermal Systems).

  The heat exchanger described in this document comprises a bundle of pipes traversed by a cooling fluid and delimiting between them circulation channels for a gas to be cooled. It comprises, in a same housing, a first and a second cooling stage, said first and second stages being defined respectively by a first and a second series of channels.

  This heat exchanger can consist in particular of a stack of sandwiches each consisting of a corrugated intercalar through which the intake air passes, associated with two half-plates, or two half-tubes according to the recom- holding, in which passes through the cooling fluid, usually consisting of engine coolant.

  In general, it is known that the flow rate, the temperature and: The inlet air pressure at the inlet of each stage - and therefore the cooling requirements - vary according to the speed, the load and the the size of the different compressors. : It is also known that, depending on the configuration of the supercharging system and: The point of use of the engine (rpm / power, or rpm / torque), there are optimal size ratios between the two stages of the cooler module. Charge air. In the cooler described by the aforementioned publication FR-A-2 886 340, the dimensions of the two stages, and therefore the number of sandwiches assigned to each stage, are fixed, whereas the cooling requirements may vary according to the regime and charge.

  To take account of this fact, the charge air cooler is oversized compared to the majority of the typical operating points of the various engines to which this supercharger air cooler is likely to be associated.

  This dimensioning is therefore, concretely, the result of a compromise between several conflicting requirements: the first stage must sufficiently cool the air delivered to the second compressor to protect it, in particular the compressor wheel; - The second stage must sufficiently cool the air delivered to the engine to protect the cylinder head and the combustion chamber of the latter, and to maintain a sufficient rattling guard in the particular case of gasoline engines; --The two combined stages must create an increase in sufficient density of air to ensure the power performance of the engine, while maintaining a low weight and dimensions to reduce clutter and consumption.

  One of the aims of the invention is to propose a heat exchanger capable of dynamically modifying the configuration of the two stages of the supercharger air cooler according to the operating point of the engine, to take account of the fact that it There are optimal ratios of variable size between: The two stages of the charge air cooler, depending on the instantaneous operating conditions of the engine (that is to say mainly according to the speed and the load of the engine). engine).

  For this purpose, the exchanger of the invention is characterized in that it comprises distribution means for said gas between said two stages, for modifying the number of channels of said first series of channels and / or said second series of channels, so as to adapt the clean exchange surface of each stage to the instantaneous operating conditions of the engine.

  By modifying the number of channels according to the point of operation of the engine, it is thus possible to increase or decrease the exchange surface of each stage according to the instantaneous needs of the engine.

  More specifically, the use of the charge air cooler according to the invention ensures an optimal increase in the density of the intake air as a function of the load and the engine speed, which provides the following correlative advantages. : for the same motive power, the compression ratio and therefore the work done by the compressor will be lower, the latter can then be resized with a smaller footprint; for the same compression ratio, the engine power can be increased; for the same power and for the same compression rate, the size of the charge air cooler can be reduced because each stage will be optimized.

  Most advantageously, the distribution means between the two stages are means for increasing the number of water of the first series of channels and reducing the number of channels of the second series of channels, or vice versa, so as to adapt the relative exchange surface of the two stages to the instantaneous operating conditions of the engine. If the first and second separate cooling stages are separated by a partition, the distribution means may in particular comprise a movable member of said common partition, and an actuator for controlling the position of this movable member. This movable element is preferably located in the housing between the bundle of pipes and inputs, and / or outlets, gas.

  In one particular embodiment, the movable element comprises a pivoting switching flap, the free end of which is displaceable facing the outlets of the circulation channels of the exchanger, so as to direct variable proportions of the flow. gas between the respective channels of the first and second series of channels.

  It is also possible to provide a configuration with two pivoting switch flaps, mounted respectively facing opposite outlets of the circulation channels of the exchanger.

  An embodiment of the invention will now be described with reference to the appended drawings, in which the same reference numerals designate, from one figure to the other, identical or functionally similar elements: FIG. 1 schematically represents a thermal motor. -20 that and a two-stage monoblock supercharger; Figure 2 is an end view of a charge air cooler according to the invention; Figure 3 is a sectional view along III-III of Figure 2, showing in particular the means for distributing the intake air flow between the two stages.

  FIG. 1 shows the general configuration of a cooling circuit in which a two-stage charge air cooler according to the invention can be included.

  The engine 10, for example a motor vehicle engine, comprises an intake manifold 12 and an exhaust manifold 14. The inlet manifold 12 is supplied by an intake line 16 with a compressor upstream 18 fed by outside air AE, a charge air cooler 20 and a downstream compressor 22.

  The charge air cooler 20 is a monobloc functional module comprising a first cooling stage 24 and a second cooling stage 26, these two stages sharing a common heat exchanger 28 comprising a bundle of pipes through which the cooling fluid flows. motor (for clarity of the figure, this engine coolant circuit has not been shown). The assembly is grouped in the same housing 30.

  The compressors 18 and 22 have respective wheels 32 and 34 disposed in an exhaust line 36 connected to the exhaust neck-reader 14, these wheels being driven by the gases from the engine. A three-way valve 38 allows, in a first position, to send the exhaust gases from the manifold 14 to the wheel 34, and from there to the wheel 32, to drive the two compressors 18 and 22. In a second position , the valve 38 directly sends the exhaust gases from the manifold 14 to the wheel 32, to drive only the compressor 18.

  In the first position of the valve 38, the outside air AE at atmospheric pressure is compressed at low pressure by the upstream compressor 18, and then cooled in the first stage 24 of the charge air cooler 20; it is then compressed at high pressure by the compressor 22 and cooled again in the second stage 26 of the cooler 20, to reach the intake manifold 12.

  In the second position of the valve 38, the outside air AE is compressed at low pressure by the compressor 18 and successively cooled by the first stage 24 and the second stage 24 of the charge air cooler 20 to gain the collector. intake 12, without being compressed by the downstream compressor 22, or even bypassing this compressor by appropriate bypass means for isolating the two cooling stages 24 and 26.

  Referring now to FIGS. 2 and 3, which describe an embodiment of the charge air cooler 20 according to the invention.

  The first stage 24 and the second stage 26 of cooling comprise respectively a first chamber 40 and a second chamber 42 separated by a common partition 44. In the example shown, the first chamber 40 is placed above the second chamber 44 and the partition 44 extends in a median plane, generally horizontal, of the cooler housing, which has an elongated shape with two opposite ends 46 and 48. The first chamber 40 has an inlet 50 and an outlet 52 formed respectively at the end 46 and end 48. Second chamber 42 includes inlet 54 and outlet 56 formed respectively at end 46 and at end 48.

  As a result of this configuration, the inlets 50 and 54, and the outlets 52 and 56, of the first and second chambers are located respectively on the same side 46, or 48, of the charge air cooler housing. In this way, the intake air circulates in the same direction, that is to say in co-current, in the two chambers 40 and 42 (thus in the two cooling stages) as indicated by the arrows on Figure 3.

  The heat exchanger 28 of the charge air cooler module 20 includes a first portion 58 and a second portion 60 extending respectively into the first chamber 40 and the second chamber 42.

  This heat exchanger 28 consists of a stack of plates 62 arranged in pairs, and insulated tabs 64 (visible in particular in Figure 2). The plates 62 delimit between them channels for the admission air, which circulates in the gap formed between the corrugations of the spacers. The various plates, which are traversed by a cooling fluid, are connected to an inlet pipe 68 and to an outlet pipe 66 to allow the circulation of this cooling fluid, usually constituted by the cooling liquid. of the motor. Reference can be made to the above-mentioned FR-A-2 886 340, which describes in detail the arrangement of such a heat exchanger bundle.

  In a characteristic manner of the invention, instead of intangibly defining the two chambers 40 and 42 by a predetermined configuration of the two parts 58 and 60 of the heat exchanger bundle, the distribution of a certain number of channels between the two cooling stages depending on the instantaneous operating conditions of the engine.

  For this purpose, the charge air cooler of the invention comprises means for selecting some of the air circulation channels located in the central portion of the heat exchanger 28, to assign them as needed. either on the first floor 24 or on the second floor 26.

  It is particularly possible, as illustrated in FIG. 3, to provide a movable flap 70 upstream of the exchanger 28, this vo-let pivoting between two end positions 74 and 76 about an axis 72 articulated on a fixed part of partition 44 separating the two chambers.

  In cross section in a longitudinal plane (the plane of the figure), the flap 70 is configured to extend over the width of a circular sector, so that its distal end 78 extends over the width of the one of the channels, thus playing the role of a concealment member of equal width, or slightly greater, to a passage section of the air in one of these channels.

  In the example illustrated, there is further provided between vo-let 70 and the ends of the channels a fixed mask 80 pierced with orifices for the passage of air (as can be seen in particular in Figure 2), this to prevent air leakage between the distal end 78 of the flap 70 and the outlet of the channel in front of which is placed this end.

  The rotary axis 72 is connected to an actuator 82 (FIG. 2) making it possible to control the angular position of the shutter 70, and therefore the choice of the channel obscured by the end 78 of the latter.

  A comparable mechanism is provided downstream, with a symmetrical configuration comprising a downstream flap 70 'movable about an axis 72' connected to a fixed portion 44 'of the central partition separating the two chambers, between two extreme positions 74' and 76 . The distal end 78 'of the vo-let downstream 70 is movable facing a mask 80' to ensure continuity between the outlets vis-à-vis the various lines and the distal end 78 of the mobile vo-let 70 .

  The system of distribution of the downstream intake air is identical to the upstream system, and these two systems operate opposite one another, to ensure good air tightness between the two stages.

  The downstream flap 70 'can be controlled by the same actuator 20 as that of the flap 70, thus ensuring a combined operation of the two upstream and downstream flaps 70 and 70'.

  With the configuration just described, it is possible to selectively interconnect some of the central channels of the heat exchanger with either the first chamber 40 or the second chamber 42, i.e. ie to assign these channels, and therefore a corresponding additional cooling capacity, either to the first stage 24 or to the second stage 26 of the charge air cooler 20.

  Thus, in the illustrated example, when the two flaps 70 and 70 'are in the extreme positions 76 and 76', the four most central channels are put into communication with the second chamber 42, thus attributed to the second cooling stage. 26, thus bringing to nine channels (the four center channels plus five side channels), the total number of channels allocated to the second floor, while the first floor will be assigned only five channels.

  For the other extreme position 74, 74 ', the situation is in-poured: nine channels allocated to the first cooling stage 24, and five channels to the second stage 60.

  For the intermediate positions of the shutters 70, 70 ', this ratio can be modified between these two extremes. It should be noted that in the positions between the end positions 74 and 76, the distal ends 78 and 78 'of the flaps 70 and 70' completely obscure one of the central channels, for example the channel 84 in the example shown in FIG. 3. This channel adjacent to the two stages of cooling-in, which will not circulate intake air, thermally isolates the two series of channels 58, 60 corresponding to each of the two stages of the cooler. Still in this example of FIG. 3, out of a total of fourteen channels, six channels are assigned to the first cooling stage and seven channels to the second cooling stage (the channel 84 is not traversed by the air intake).

  The displacement of the flaps 70, 70 'between their two extreme positions thus makes it possible to vary the number of channels, and therefore the capacity of the exchanger assigned to one or other of the two stages, an increase of the number of channels for one of the floors simultaneously resulting in a decrease in the number of channels assigned to the other floor. This makes it possible to dynamically adapt the performance of the exchanger to the instantaneous operating conditions of the engine.

Claims (6)

claims   1. Heat exchanger (28), including an intake air cooler, comprising a bundle of pipes (62) run by a cooling fluid and defining between them circulation channels for a gas to be cooled, said exchanger comprising, in the same housing, a first and a second cooling stage (24, 26), said first and second stages being defined respectively by a first and a second series of channels, characterized in that it comprises means distributing for said gas between said two stages, for modifying the number of channels of said first series of channels and / or said second series of channels, so as to adapt the clean exchange surface of each stage to the instantaneous operating conditions of the motor.   2. Exchanger according to claim 1, characterized in that said distribution means between the two stages are means for increasing the number of channels of said first series of channels and decreasing the number of channels of said second series of channels, or the opposite, so as to adapt the relative exchange surface of the two stages to the instantaneous operating conditions of the engine.   3. Exchanger according to claim 2, wherein the first and second separate cooling stage (24, 26) are separated by a partition (44), characterized in that said distribution means between the two stages comprise a movable element ( 70) of said common partition (44), and an actuator (82) for controlling the position of said movable element. 14   4. Exchanger according to claim 3, characterized in that said movable element (70) is located in the housing between the bundle of pipes (62) and inlets (50, 54), and / or outlets (52, 56). of said gas.   5. Exchanger according to claim 4, characterized in that said movable element (70) comprises a pivoting switching flap whose free end (78) is displaceable facing the outlets of said circulation channels (58) of the exchanger ( 28) so as to direct varying proportions of the flow of said gas between the respective channels of the first (24) and second (26) series of channels.   6. Exchanger according to claim 5, characterized in that said means of distribution between the two stages comprise two pivoting switch flaps (70, 70 '), respectively mounted opposite opposite outlets of the circulation channels (58) of the exchanger.