Abstract:
A charge air cooling device is provided for a combustion engine with a first heat exchanger configured to transmit thermal energy of a charge airflow to a coolant and with a second heat exchanger by which thermal energy of the coolant can be discharged into the surroundings. The first heat exchanger is designed as coaxial tube heat exchanger, which directly connects a compressor provided for the combustion air to the engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102010047092.9, filed Oct. 1, 2010, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a charge air cooling device for a combustion engine in order to cool down the combustion air compressed by a compressor or charger prior to being fed into the combustion chamber of the engine. 
       BACKGROUND 
       [0003]    In charged combustion engines, the combustion air fed to the engine can be cooled down by means of a charge air cooler. By cooling the combustion air, its density can be increased and thus an increased amount of gas fed to the engine with the pressure remaining the same. In this manner, combustion processes, but particularly the power of the engine can be optimized or increased. 
         [0004]    Popular charge air coolers are mostly designed as air-air heat exchangers. Since, in addition the cooled-down combustion air exiting the charge air cooler should have a temperature level below the temperature of the cooling water level of the combustion engine, known air-air charge air heat exchangers are to be typically arranged upstream of the radiator in the engine compartment of the motor vehicle. Furthermore, for example in DE 10 2009 028 487 A1 a cooler for cooling a gas flow of a combustion engine by means of a cooling medium is described, which comprises a first channel for conducting a gas flow and a second channel for conducting the cooling medium. First and second channel in this case are in thermal contact with each other, while a housing is designed as extruded part. On both the ends alongside the housing end caps are arranged, in which inlets to the first or the second channel located in the housing are formed. 
         [0005]    The geometrical configurations of known charge air coolers restrict the flexibility of a charge air routing between compressor or charger and engine-end air supply sometimes substantially so. If for example instead of an air-air heat exchanger a fluid-cooled heat exchanger is provided as charge air cooler, this is accompanied by a substantial integrative effort. Thus, the entire engine package and the engine installation space distribution have to be adapted to the given shape of the heat exchanger. It is additionally desirable to continually improve the cooling output of a charge air cooler with the least possible installation space requirement. 
       SUMMARY 
       [0006]    The charge air cooling device is designed for a combustion engine of a motor vehicle. It comprises a first heat exchanger for transmitting thermal energy of a charge air flow to a coolant and a second heat exchanger, by means of which thermal energy of the coolant can be discharged to the surroundings. The first heat exchanger in this case serves for the cooling of the combustion air to be fed to the engine and compressed. The first heat exchanger bringing about a heat exchange between coolant and compressed combustion air in this case is designed as coaxial tube heat exchanger, which directly connects a compressor or charger provided for the combustion air to the combustion engine. 
         [0007]    Here, it is more preferably provided that a gas-conducting tube of the coaxial tube heat exchanger comprises the entire gas-conducting section downstream of the compressor as far as to the intake manifold of the engine. This means, the entire intake tract of the combustion engine is designed as cooling section of a coaxial tube heat exchanger downstream of the compressor or charger as far as to the inlet in the engine. To that extent it is more preferably provided to adapt the coaxial tube heat exchanger to a predefined geometrical shape of the air supply and in the process optimize the effective length of the coaxial tube heat exchanger to improve its cooling output. Thus, in an advantageous further development the coaxial tube heat exchanger at one end is connected to an intake manifold of the engine and at the other end to the compressor or charger, which compresses the combustion air supplied from the outside to a predefined dimension. 
         [0008]    According to a further embodiment it is furthermore provided that a cooling section of the coaxial tube heat exchanger comprises the entire or substantially the entire combustion air supply section located between the compressor and the combustion engine. Advantageously, the coaxial tube heat exchanger comprises an inner tube conducting the charge air and an outer tube radially enclosing the inner tube. The intermediate space formed by inner and outer tube roughly ring-shaped in cross section can be subjected to the admission of a coolant. The coolant is preferably present in liquid form or as a fluid, for example as a cooling water mixed with antifreeze agent. 
         [0009]    By means of such a coaxial tube heat exchanger through which a cooling liquid flows the discharge of thermal energy from the first heat exchanger to a cooling circuit as against an air-air heat exchanger can be improved. In addition, the configuration of a heat exchanger that can be subjected to the admission of a cooling fluid makes possible almost any arrangement within the engine compartment. Thus, the heat exchanger—in contrast with an air-air heat exchanger—need not of necessity be arranged in an airflow. 
         [0010]    According to a further embodiment a coolant inlet is provided on an engine end and a coolant outlet on a compressor end of the coaxial tube heat exchanger. To that extent, the coaxial tube heat exchanger is operated in the counter flow mode. While the combustion air to be cooled flows from the compressor to the engine, the coolant fed in via the inlet flows in the opposite direction to the coolant outlet in the ring-shaped intermediate space formed by inner tube and outer tube. This configuration of opposing liquid and gas flows in the inner and outer tube of the coaxial tube heat exchanger is provided to increase the overall cooling output of the first heat exchanger. 
         [0011]    Advantageously, the charge air cooling device comprises a cooling circuit which in terms of flow interconnects the first and the second heat exchanger as well as a coolant pump. This cooling circuit preferably of a closed design is specifically and exclusively provided for cooling the coolant circulating in the circuit by means of the coolant pump. The second heat exchanger in this case is preferably designed as a liquid-air heat exchanger in order to be able to discharge thermal energy from the coolant to the surrounding air. 
         [0012]    According to a further embodiment the coaxial tube heat exchanger comprises substantially straight line sections and/or sections following a curved course. The sections following a curved course in this case can be designed in all three space directions in order to be able to adapt the coaxial tube heat exchanger to a given geometry of the charge air routing. In particular, through the course of the coaxial tube heat exchanger curved at least in sections it can be variably and universally adapted to given installation dimensions of the charge air routing. 
         [0013]    Here it is more preferably provided that the inner tube and/or that the outer tube in the region of curved sections and in the region of straight-line sections have a substantially identical or constant tube diameter. This serves to achieve that the coaxial tube heat exchanger also makes possible a heat exchange in sections following a curved course between the charge air flowing in the inner tube and the coolant flowing in the ring-shaped intermediate space between inner tube and outer tube. 
         [0014]    In terms of manufacturing, such a coaxial tube heat exchanger designed curved in sections can be formed by assembling several inner tube and/or outer tube pieces. Thus, the inner tube and/or the outer tube can each be successively assembled of substantially straight tube pieces and curved tube pieces. Tube diameter and curvature radius in this case however have to be selected in such a manner that curved inner tube pieces and correspondingly curved outer tube pieces can be employed. 
         [0015]    In another embodiment it is provided by contrast to form the inner tube and/or the outer tube as a continuous tube bent in sections. To this extent, inner and outer tubes which unitarily extend from the compressor as far as to the intake manifold of the combustion engine can be used for the coaxial tube heat exchanger. In terms of manufacturing, it is more preferably provided here to manufacture the coaxial tube heat exchanger of inner and outer tube cuts formed substantially straight and arranged nested within each other even before a forming process. The tubes arranged nested within each other in this case have to be brought into a shape that is predefined and curved at least in sections by means of a joint forming process, preferentially by means of a bending process. Here, almost any curvatures, even in different directions, can be realized in order to be able to adapt the coaxial tube heat exchanger as universally as possible to a predefined course of a charge air routing. 
         [0016]    According to a further embodiment the inner tube on its inner wall comprises at least one air swirling element radially protruding to the inside, which for example is designed as swirling rib and/or as air swirling web, if applicable as turbulator. By means of at least one such air swirling element, preferably with several air swirling elements provided spaced in axial direction in the inner tube a specific swirling of the charged air flowing through the inner tube can be created, more preferably in order to intensify a heat exchange with the coolant flowing between inner tube and outer tube. Furthermore, it can be additionally provided to provide at least one end section of the coaxial tube heat exchanger with a length compensating element in order to be able to compensate for thermally induced length changes of the charge air cooling device, particularly of its coaxial tube heat exchanger. 
         [0017]    In another embodiment a method for producing a coaxial tube heat exchanger is additionally provided, wherein for forming a heat exchanger section of curved design having an inner tube and an outer tube, an inner tube cut substantially of straight design is pushed in an outer tube cut of corresponding design and radially fixed in the latter. Following this it is provided to jointly bend the tubes pushed inside each other by means of one or by means of several tools into a predefined shape. 
         [0018]    In order to avoid that the ring-shaped fluid-conducting intermediate space between inner and outer tube is changed through a bending operation, particularly made smaller, individual spaces, for example holding or fixing webs can be provided in the inner and outer tube sections according to a further development. The fixing webs in this case are to be preferably provided either on the outside of the inner tube or on the inside of the outer tube prior to a pushing into each other of inner and outer tube. If applicable, the individual tube cuts can already be provided in advance at least in sections with suitable spacer or holding webs. 
         [0019]    In a further embodiment a combustion engine arrangement of a motor vehicle is additionally provided, which comprises a combustion engine, a charger or a compressor and a charge air cooling device described before, whose coaxial tube heat exchanger bridges the entire air-conducting section between the charger and the combustion engine. Furthermore, a motor vehicle is provided, which comprises a charge air cooling device described before. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0020]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0021]      FIG. 1  is a schematic representation of a charge air cooling device; 
           [0022]      FIG. 2  is a schematic cross-sectional representation through a coaxial tube heat exchanger; and 
           [0023]      FIG. 3  is an isolated schematic representation of a coaxial tube heat exchanger designed bent in sections. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0025]    The charge air cooling device shown in  FIG. 1  comprises a cooling circuit specifically provided for cooling the charge air, which in the present example is formed by a coaxial tube heat exchanger  11 , a coolant outlet  9 , a charge air cooler  7 , a coolant pump  6 , a coolant expansion tank  10  and a coolant inlet  8  terminating in the coaxial tube heat exchanger. The coaxial tube heat exchanger  11  extends between a compressor or charger  3  and an intake manifold  5  of the combustion engine  1 . The entire section conducting combustion air located between the charger  3  and the intake manifold in this case is designed as cooling section  4  of the coaxial tube heat exchanger  11 . 
         [0026]    To that extent it is provided to form a predefined charge air routing downstream of the charger  3  and upstream of the combustion engine  1  almost entirely as cooling section of a coaxial tube heat exchanger  11 . Because of this, the cooling output of a charge air cooling device can be increased and also flexibly and universally adapted to predefined installation space requirements. The intake tract for the combustion engine  1  is additionally provided with an air filter  2  on the air inlet side. 
         [0027]    Cooling of the charge or combustion air  34  fed in and compressed by the charger  3  is performed according to the counter flow principle. Thus, the coolant  30  cooled down by means of the charge air and low-temperature cooler specifically provided for this purpose is fed to the coaxial tube heat exchanger  11  by means of the cooling pump  6  via the coolant inlet  8  in the vicinity of the intake manifold  5 . The coolant  30  then preferably flows in a fluid-conducting channel against the flow direction of the charge air  34 . The coolant  30  heated by the counter-flowing charge air  34  again flows out of the coaxial tube heat exchanger  11  at the coolant outlet  9  in the vicinity of the charger  3  and via the charge air cooler  7  substantially discharges the thermal energy absorbed by the charge air  34  to the surroundings  32 . 
         [0028]    The coaxial tube heat exchanger  11  is shown in  FIG. 2  in a schematic cross-sectional representation. It comprises tubes arranged concentrically or coaxially to each other, namely an inner tube  22  and an outer tube  20  radially enclosing the inner tube  22 . The inner tube  22  in this case acts as flow channel  26  for the charge air  34 , while in an intermediate space  24  formed ring-like in cross section between inner tube  22  and outer tube  20  the preferably liquid coolant  30  flows in opposite direction. 
         [0029]    Particularly the inner tube is designed for the thermal coupling of its inner space  26  to the ring-shaped intermediate space  24 . Although the tubes  20 ,  22  merely indicated schematically in  FIG. 2  are shown comparatively thin-walled, the wall thicknesses of the tubes  20 ,  22  can deviate from this almost randomly. It can also be provided for example that in particular the outer tube  20  has a wall thickness such that in the outer tube wall individual fluid-conducting channels can be provided in such a manner that the formation of an intermediate space  24  between inner tube  22  and outer tube  20  under certain conditions can also be omitted. The channels provided in the outer tube wall could to that extent also provide an exclusive fluid routing for the coolant  30 . 
         [0030]    Furthermore, a swirling element  28  radially protruding to the inside is indicated in  FIG. 2 , which for example can be designed as swirling rib or web, if applicable also as turbulator. By means of the swirling element  28  the compressed combustion air flowing in the inner space  26  of the inner tube  22  can be subjected to a specific swirling in order to improve the heat exchange between the coolant  30  and the compressed combustion air. The air swirling elements  28  in this case are arranged on the inner wall of the inner tube  22  in such a manner that a preferably optimized heat exchange with simultaneously low pressure loss or with low flow resistance in the interior tube  22  can be achieved. 
         [0031]    In the representation according to  FIG. 3  the coaxial tube heat exchanger  11  is once more shown isolated. In the shown configuration it comprises tube sections  12 ,  14 ,  16  substantially designed straight, while the tube sections  12 ,  14  are connected to one another by means of a curved tube section  13  and the tube section  14 ,  16  via a further curved tube section  15 . The individual tube sections  12 ,  13 ,  14 ,  15 ,  16  can be produced both for the inner tube  22  in each case of a tube piece, which are joined into a single inner or outer tube  22 ,  20  preferentially unchanged in cross section. However, as an alternative, it is also conceivable to achieve the tube arrangement shown in  FIG. 3  by means of pushing into each other of two tube cuts initially designed substantially straight, which in a joint forming process are bent over in the region of the sections  13 ,  15  shown here by approximately 90°. 
         [0032]    On the free end section of the coaxial tube section  16  a length compensating device  18  is additionally indicated, which is to compensate for possible thermally-induced length changes of the coaxial tube heat exchanger  11 . The length compensating device can furthermore simplify the assembly process of the coaxial tube heat exchanger  11  and to that extent serves to facilitate assembly. 
         [0033]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.