Abstract:
A cooling system of a motor vehicle may include a coolant circuit including an exhaust-gas recirculation path and an exhaust-gas recirculation cooler arranged therein. A pressure detection device may be provided for detecting a coolant pressure in the coolant circuit. An actuating device may be connected communicatively to the pressure deduction device. A valve device may be connected communicatively to the actuating device and configured to control an exhaust-gas stream passing into the cooler. The actuating device may be configured to at least partially close the valve device and reduce the exhaust-gas stream flowing to the cooler in response to the pressure detection device detecting a predefined pressure drop.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to German Patent Application No. 10 2015 210 646.2, filed Jun. 10, 2015, the contents of which are hereby incorporated by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a cooling system of a motor vehicle, having a cooling circuit, having an exhaust-gas recirculation path and having an exhaust-gas recirculation cooler incorporated into said exhaust-gas recirculation path. The invention also relates to a motor vehicle having a cooling system of said type and to a method for operating a cooling system of said type. 
       BACKGROUND 
       [0003]    US 2014/0288801 A1 has disclosed a generic cooling system of a motor vehicle, having an exhaust-gas recirculation arrangement and having an exhaust-gas recirculation cooler integrated into the exhaust-gas recirculation arrangement. 
         [0004]    A generic cooling system of a motor vehicle is also known from JP 2008-261297 A. In general, cooling components, such as in particular exhaust-gas coolers manufactured from high-grade steel, which are incorporated into a coolant circuit of a motor vehicle have a relatively high replacement value. This is based not only on the high material costs but also on likewise high manufacturing costs. For this purpose, it is desirable for such cooling components to be effectively protected against damage, even if, as a result of faults in the motor vehicle, they are operated not in the intended manner. Here, in particular in the case of an exhaust-gas recirculation cooler, there is a high risk of damage if a fault occurs in the coolant circuit. This may be caused for example by faults in the actuation arrangement, or failures of valves or pumps, or else as a result of selection of, or damage to, relatively inexpensive components in the line system, such as hoses, clamps, screw connections or the like. Here, exhaust-gas recirculation coolers are at particular risk because they exhibit relatively high power and simultaneously relatively low thermal inertia, and, for example in the event of a fault in the coolant circuit, heat up within a few seconds to such an extent that they can sustain damage. Even if it is the case here that the engine switches over very quickly into an emergency running mode, for example associated with a power reduction, it cannot be ensured that the exhaust-gas cooler remains undamaged. Special protection of the exhaust-gas recirculation cooler has therefore hitherto not been provided at all. 
       SUMMARY 
       [0005]    The present invention is therefore concerned with the problem of specifying, for a cooling system of the generic type, an improved or at least alternative embodiment which is distinguished in particular by specific protection for an exhaust-gas recirculation cooler. 
         [0006]    Said problem is solved according to the invention by way of the subject matter of the independent claim(s). The dependent claims relate to advantageous embodiments. 
         [0007]    The present invention is based on the general concept, in a cooling system of a motor vehicle, such as is known per se, having a coolant circuit, having an exhaust-gas recirculation path and having an exhaust-gas recirculation cooler incorporated into said exhaust-gas recirculation path, of monitoring a coolant pressure and at least reducing an exhaust-gas stream flowing to the exhaust-gas recirculation cooler immediately if a predefined pressure drop, and thus a deficiency in a coolant supply, are detected. For this purpose, the cooling system according to the invention has a pressure detection device for the detection of the coolant pressure in the coolant circuit, and also has an actuating device which is connected communicatively to the pressure detection device. The actuating device in turn is connected communicatively to a valve device for the control of an exhaust-gas stream passing into the exhaust-gas recirculation cooler, and is at the same time designed such that it at least partially, preferably entirely, closes the valve device, and thus at least reduces, preferably stops, the exhaust-gas stream flowing to the exhaust-gas recirculation cooler, if the pressure detection device detects a predefined pressure drop. In this way, it is possible, in the event of a fault occurring in the coolant circuit, for the exhaust-gas recirculation cooler to be directly and immediately separated from the hot exhaust-gas stream and thereby protected against overheating and damage. This may furthermore be performed independently of hitherto known emergency running modes, which for example reduce the power of an engine. With the cooling system according to the invention, it is thus possible for the exhaust-gas recirculation cooler, which is at particular risk owing to the hot inflowing exhaust-gas stream in the event of a fault in the coolant circuit, to be protected in an effective manner and, in this way, for the operational reliability thereof to be ensured even in the long term and for the maintenance costs thereof to be reduced. 
         [0008]    In an advantageous refinement of the solution according to the invention, the valve device is in the form of a flap. A flap of said type may for example be arranged in an exhaust-gas-conducting inlet line to the exhaust-gas recirculation cooler and close off said inlet line if the pressure detection means detects a pressure drop, which exceeds or overshoots a predefined threshold value, in the coolant circuit. In this way, it can be ensured that, owing to pulsations, the pressure fluctuations that commonly arise during operation also do not lead to a shut-off of the exhaust-gas recirculation cooler. 
         [0009]    In a further advantageous embodiment of the solution according to the invention, the valve device is preloaded into its closed position by way of a spring. A spring of said type thus serves as a fail-safe element, such that the actuating device holds the valve device in its open position during normal operation, wherein, in the presence of a corresponding signal of the pressure detection device, the actuating device moves the valve device into its closed position or into an at least partially closed position. In the event of a failure of the actuating device, it should however nevertheless be ensured that overheating of, and thus damage to, the exhaust-gas recirculation cooler is reliably prevented, such that, in the event of a failure of the actuating device, said actuating device loses its holding force which holds the valve device in its open position, and the valve device is moved, by way of the above-described spring, into its closed position. In this case, it would self-evidently be necessary for a corresponding warning signal to be transmitted to an engine control unit. 
         [0010]    In a further advantageous embodiment of the solution according to the invention, the pressure detection device has at least two pressure sensors which are arranged in the coolant circuit. Here, the two pressure sensors may for example be arranged at the inlet side and outlet side of the exhaust-gas recirculation cooler and thus connected in space-saving fashion thereto. In this case, it would be possible for the two pressure sensors to not only in each case individually detect a pressure drop but also detect the pressure drop of the coolant through the exhaust-gas recirculation cooler. In this way, it is possible in particular for a coolant volume flow in the cooler and/or exhaust-gas recirculation cooler to be checked, whereby it can be ensured that an inadequate coolant supply, for example in the event of damage to or failure of a coolant pump or an incorrectly set coolant valve, is detected, and damage is prevented. Such faults are not inevitably associated with a drop in pressure in the coolant circuit, and therefore cannot be reliably detected by way of a single pressure sensor. However, by way of a differential pressure sensor, it is made possible for the coolant throughflow to be measured, as a pressure drop across the exhaust-gas recirculation cooler or a measurement path situated downstream of the cooler (for example an aperture, V cone or the like), by way of a single sensor. Said measurement signal may also be utilized for directly actuating a pressure capsule on the valve device for the cooler. Since the differential pressure is dependent not only on the throughflow rate but significantly also on the viscosity and thus the temperature and composition of the coolant, it is however predominantly only possible for intense damage to be detected by way of the differential pressure. A moderately reduced coolant stream cannot be reliably detected by way of the differential pressure alone. If the differential pressure signal is applied directly to a pressure capsule, it can be ensured that the exhaust-gas recirculation cooler/cooler is not completely deprived of a coolant supply, which offers protection until the onset of the emergency running mode in the engine. A comparison of the differential pressure, in the ECU, with setpoint values which must not be undershot would be advantageous. 
         [0011]    The valve device is expediently integrated into an exhaust-gas recirculation valve. An exhaust-gas recirculation valve, which is commonly connected to an engine control unit (ECU), in this case controls the exhaust-gas fraction to be supplied for combustion again, wherein, in this case, the valve device could be integrated in space-saving fashion in the exhaust-gas recirculation valve. It is self-evidently also conceivable for the exhaust-gas recirculation valve itself to be the valve device, such that, for the valve device, it is possible to resort to the exhaust-gas recirculation valve that is provided in any case, and not only the variety of parts but also costs can be reduced. 
         [0012]    Expediently, the pressure detection device and the actuating device are integrated in a pressure capsule or in a differential pressure capsule. In this way, the pressure detection device and the actuating device can be easily and inexpensively combined in a common component, wherein it is alternatively self-evidently also conceivable for the pressure detection device to be in the form of a pressure switch, in particular a so-called piezo element, and for the actuating device to be in the form of an electric actuator. Here, the pressure drop causes a mechanical force to be exerted on the piezo element, which mechanical force is converted by the piezo element into an electrical voltage, and the electric actuator is actuated by way of said electrical voltage. Further alternative embodiments are self-evidently also conceivable. 
         [0013]    The invention is furthermore based on the general concept of specifying a method for operating a cooling system of a motor vehicle, in which method a pressure detection device detects a coolant pressure in the coolant circuit and is connected communicatively to an actuating device which at least partially closes the valve device, and thus at least reduces the exhaust-gas stream flowing to the exhaust-gas recirculation cooler, if the pressure detection device detects a predefined pressure drop. By way of the method according to the invention, it is possible for the exhaust-gas recirculation cooler, which is at particular risk owing to the hot inflowing exhaust-gas stream in the event of a fault in the coolant circuit, to be protected in an effective manner and, in this way, for the operational reliability thereof to be ensured even in the long term. 
         [0014]    Further important features and advantages of the invention will emerge from the subclaims, from the drawings and from the associated description of the figures on the basis of the drawings. 
         [0015]    It is self-evident that the features mentioned above and those yet to be discussed below may be used not only in the respectively specified combination but also in other combinations or individually without departing from the scope of the present invention. 
         [0016]    Preferred exemplary embodiments of the invention are illustrated in the drawings and will be discussed in more detail in the following description, wherein the same reference signs are used to denote identical or similar or functionally identical components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    In the drawings, in each case schematically: 
           [0018]      FIG. 1  shows a cooling system according to the invention of a motor vehicle, 
           [0019]      FIG. 2  shows a possible integration of a pressure detection device and of an actuating device into a pressure capsule or a differential pressure capsule. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Corresponding to  FIG. 1 , a cooling system  1  according to the invention of a motor vehicle  2  has, in a coolant circuit  3 , an exhaust-gas recirculation path  4  and an exhaust-gas recirculation cooler  5  incorporated into said exhaust-gas recirculation path. Here, the exhaust-gas recirculation path  4  runs from an exhaust-gas recirculation valve  6  via the exhaust-gas recirculation cooler  5  to a fresh-air path  7 , via which combustion air is supplied to an engine  8  (internal combustion engine). The coolant circuit  3  is furthermore connected to a cooler  9 , by way of which the engine  8  is normally also cooled. To now be able, in an effective manner, to prevent damage to the exhaust-gas recirculation cooler  5  in the event of a fault in the coolant circuit  3 , it is the case, according to the invention, that a pressure detection device  10  having at least one pressure sensor  11  for detecting a coolant pressure in the coolant circuit  3  is provided. Communicatively connected to the pressure detection device  10  is an actuating device  12  which, in turn, is connected communicatively to a valve device  13  for the control of an exhaust-gas stream  14  passing into the exhaust-gas recirculation cooler  5 . Here, according to the invention, the actuating device  12  is designed such that the valve device  12  at least partially, preferably even completely, closes, and thus at least reduces, preferably stops the exhaust-gas stream  14  flowing to the exhaust-gas recirculation cooler  5 , if the pressure detection device  10  detects a predefined pressure drop. Therefore, if a fault occurs in the coolant circuit  3 , for example owing to a burst hose or a burst line, which directly leads to a pressure drop in the coolant circuit  3 , this is detected by the pressure detection device  10  and leads immediately to a reduction or stoppage of the exhaust-gas stream  14 , whereby it is possible to prevent a situation from arising in which hot exhaust gas continues to be supplied to the exhaust-gas recirculation cooler  5  but, owing to the fault in the coolant circuit  3 , said exhaust gas can no longer be adequately cooled. This is of particularly great advantage because, in particular, components of the exhaust-gas recirculation cooler  5 , such as for example a cooler block  21  thereof, are often composed of high-grade material and can thus be replaced only at great expense. 
         [0021]    It has hitherto been the case that such a safety measure tailored specifically to the exhaust-gas recirculation cooler  5  has not been implemented, because, for example, only a temperature of the coolant in the coolant circuit  3  has been monitored. However, if the coolant circuit  3  has a leak, this does not imperatively have to have an influence on the coolant temperature and thus lead to a corresponding warning signal of an engine control unit  24 . Such a leak with coolant circuit  3  however gives rise to only inadequate cooling of the exhaust-gas recirculation cooler  5 , whereby, in the presence of a continuing unhindered inflow of exhaust gas  14 , said exhaust-gas recirculation cooler may overheat and thereby be damaged even in the presence of an emergency running mode triggered by the engine control unit  24 . 
         [0022]    Considering the detail illustration of the valve device  13  in  FIG. 1 , it can be seen that the valve device  13  is for example in the form of, or has, a flap  15 . A spring  16  may additionally be provided, which preloads the valve device  13  or the flap  15  into its closed position and thereby constitutes a type of failsafe safety means. In the event of a failure of the actuating device  12 , which would for example result in a closure of the valve device  13  being permitted, the spring  16  will in this case lead to closure of the exhaust-gas recirculation valve  13  and thus to protection of the exhaust-gas recirculation cooler  5  against overheating. 
         [0023]    Here, in  FIG. 1 , the valve device  13  is arranged in the exhaust-gas recirculation path  4  upstream of the exhaust-gas recirculation cooler  5 , wherein an arrangement of the valve device  13  directly at the inlet side of the exhaust-gas recirculation cooler  5  may self-evidently also be provided, in particular at an inlet diffuser  22 , or alternatively at an outlet diffuser  23 , wherein the arrangement upstream of the exhaust-gas recirculation cooler  5  is more advantageous. Purely theoretically, the valve device  13  may also be arranged downstream of the exhaust-gas recirculation cooler  5  with equal effectiveness, because in that case, too, exhaust gas  14  no longer flows through the exhaust-gas recirculation cooler  5 . 
         [0024]    In general, the pressure detection device  10  comprises at least one pressure sensor  11 , wherein, in the example shown in  FIG. 1 , two pressure sensors  11  are provided, which are arranged at the inlet side and outlet side of the exhaust-gas recirculation cooler  5 . In this way, by way of the pressure detection device  10 , it is additionally possible for a pressure drop in the exhaust-gas recirculation cooler  5  to be monitored, which pressure drop may be used to monitor a free flow cross section in the exhaust-gas recirculation cooler  5 . In this way, too, it is possible to detect a relative pressure between the two pressure sensors  11 , whereby the detected pressure loss in the coolant circuit  3  or in the exhaust-gas recirculation cooler  5  can be utilized for actuation of the actuating device  12 . In this case, it is thus possible for not only a predefined pressure drop but also a reduced coolant throughflow to be utilized for the closure of the valve device  13 . 
         [0025]    In a further advantageous embodiment of the solution according to the invention, the pressure detection device  10  and the actuating device  12  may be integrated in a pressure capsule  17  or in a differential pressure capsule  18 , as illustrated for example in  FIG. 2 . It may likewise be provided that the pressure detection device  10  is in the form of a pressure switch, in particular a so-called piezo element  19 , and that the actuating device  12  is in the form of an electric actuator  20 . In this case, a mechanical change in pressure at the pressure sensor  11  in the form of a piezo element  19 , or at the pressure detection device  10  in the form of a piezo element  19 , would generate an electrical signal, which would be transmitted to the actuating device  12  and specifically, in this case, to the electric actuator  20 , which thereupon controls the valve device  13  correspondingly. 
         [0026]    It is likewise conceivable that, in an alternative embodiment, the valve device  13  is integrated into the exhaust-gas recirculation valve  6 , such that the latter performs not only the open-loop and closed-loop control of the exhaust gas  14  that is supplied for combustion again, but also the protection of the exhaust-gas recirculation cooler  5  against overheating in the event of a fault occurring in the coolant circuit  3 . A valve device  13  integrated in such a manner into the exhaust-gas recirculation valve  6  is in this case illustrated in  FIG. 1  merely by dashed lines, and thus as an option. In this case, too, the valve device  13  is positioned upstream of the exhaust-gas recirculation cooler  5  and shuts off the exhaust-gas flow  14 , preferably completely, if a predefined pressure drop is detected in the coolant circuit  3 . In this case, it would also be possible for the pressure detection device  10  to be connected to an engine control unit  24 , which then closes the valve device  13  in the region of the exhaust-gas recirculation valve  6 , or else the exhaust-gas recirculation valve  6  itself, in the event of a pressure drop being correspondingly detected in the coolant circuit  6 . 
         [0027]    In principle, it is conceivable for at least the pressure detection device  10 , the actuating device  12  and the valve device  13  to be in the form of an autonomously operating system and to thereby be used in the sense of a stand-alone system, without utilization of the ECU (engine control unit  24 ). This offers the great advantage that no modifications to the vehicle are necessary during the integration process. Alternatively, it is also conceivable for at least the pressure detection device  10 , the actuating device  12  and the valve device  13  to be connected communicatively to the engine control unit  24 , and in particular be controlled in closed-loop fashion by the latter, which permits more precise throughflow monitoring. 
         [0028]    In general, in the case of all of the proposed solutions, effective protection of the exhaust-gas recirculation cooler  5  against overheating is possible with only marginal additional outlay in terms of construction, in particular if, for example, the exhaust-gas recirculation valve  6  that is provided in any case is utilized for the valve device  13 .