Abstract:
A device is provided for compressor and charge air cooler protection in an internal combustion engine, such as a Diesel engine. The engine having an intake manifold and an exhaust manifold, first and second EGR routes, a charge air cooler, a turbocharger having a compressor and a turbine. A regulator is also provided for regulating the flow rate of exhaust gas and the splitting of exhaust gas between the first and second EGR route. A temperature sensor is also provided for sensing output temperature of gas at the outlet of said compressor. A method and computer readable medium embodying a computer program product are also provided that have a first phase of monitoring a parameter representative of the gas temperature at the output of the compressor and a second phase in which an activity involving engine components operation is performed. The activity is performed using temperature information determined in the monitoring phase.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to British Patent Application No. 0919782.3, filed Nov. 12, 2009, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The technical field relates to a device and a method for compressor and Charge Air Cooler (CAC) protection in an internal combustion engine, in particular in a Diesel engine having a low pressure EGR system. 
     BACKGROUND 
     A turbocharged Diesel engine system generally comprises a Diesel engine having an intake manifold and an exhaust manifold, an intake line for conveying fresh air from the environment in the intake manifold, an exhaust line for conveying the exhaust gas from the exhaust manifold to the environment, and a turbocharger which comprises a compressor located in the intake line for compressing the air stream flowing therein, and a turbine located in the exhaust line for driving said compressor. 
     The turbocharged Diesel engine system further comprises an intercooler, also indicated as Charge Air Cooler (CAC), which is located in the intake line downstream the compressor, for cooling the air stream before it reaches the intake manifold. The turbocharged Diesel engine systems can also be equipped with a diesel oxidation catalyst (DOC) for degrading residual hydrocarbons and carbon oxides contained in the exhaust gas and, downstream of the DOC, a diesel particulate filter (DPF) for capturing and removing diesel particulate matter (soot) from the exhaust gas. 
     In order to reduce the polluting emission, most turbocharged Diesel engine system actually comprises a first exhaust gas recirculation (EGR) system, for selectively routing back exhaust gas from the exhaust manifold into the intake manifold. In such a way the exhaust gas mixed with the fresh induction air is aspired into the engine cylinders, in order to reduce the production of unburned hydrocarbon (HC), carbon monoxide (CO), soot, and oxides of nitrogen (NO x ) during the combustion process. In order to further reduce the NO x  emission, improved EGR systems comprise an additional EGR conduit, which fluidly connects the exhaust line downstream the DPF with the intake line upstream the compressor of turbocharger, an additional EGR cooler located in the additional EGR conduit, and additional valve means for regulating the flow rate of exhaust gas through the additional EGR conduit. 
     In these improved systems, while the conventional EGR conduit defines a short route for the exhaust gas recirculation, the additional EGR conduit defines a long route for the exhaust gas recirculation, which comprises also a relevant portion of the exhaust line and a relevant portion of the intake line. Flowing along the long route, the exhaust gas is then obliged to pass through the turbine of turbocharger, the DOC, the DPF, the additional EGR cooler, the compressor of turbocharger and the charge air cooler, so that it become considerably colder than the exhaust gas which flows through the short route, reaching thereby the intake manifold at a lower temperature. 
     These improved EGR systems are generally configured for routing back the exhaust gas partially through the short route and partially through the long route, in order to maintain the temperature of the induction air in the intake manifold at an optimal intermediate value in any engine operating condition. 
     In the known art the total amount of exhaust gas and the long route exhaust gas rate are determined by the Electronic Control Unit (ECU) using empirically determined data sets or maps, which respectively correlate the total amount of exhaust gas and the long route exhaust gas rate to a plurality of engine operating parameters, such as for example engine speed, engine load and engine coolant temperature. One drawback of these improved EGR systems is that such data sets or maps are determined during a calibration activity, using an engine system perfectly efficient which is operated under standard environmental conditions, i.e., standard environmental temperature, pressure and moisture. Therefore, the value contained in the data sets or maps are valid only for engine systems that are operated in the same environmental conditions of that used in calibration phase, and completely ignore the reduction in efficiency of the engine system components due to several conditions that may occur during use of the vehicle. 
     For example, it has been observed that in some real use conditions of the vehicle, such as for example high-altitude and/or high-temperature operation and repeated accelerations a series of problems may occur. For example various components may drift from their expected operation parameters leading to sub-optimal control of the engine by the ECU or even components damage. Furthermore, long-route EGR cooler fouling may occur and temperatures out of specifications may be reached downstream of compressor and in the engine intake manifold. It is clear that these problems would lead to components damage due to thermal stress and/or excessive oil cracking and deposition, or at least to a reduced life of engine components with an associated increase of costs. 
     Due to this situation, the known art has tried to solve the above problems by ensuring protection against excessive temperatures downstream of compressor as well as over-speed are performed in open-loop, with the help of undesirable significant engineering margins. In case of the presence of a long-route EGR system this disadvantage increases, since at mid-load, in the EUDC area, compressor protection is enacted in open loop too, severely limiting the system performance. It appears therefore that these solutions are unsatisfactory and may even be considered palliative. 
     At least one object is to create a device and a method that allows protecting the compressor and downstream pipes from thermal stress, from oil cracking, and allowing operating the compressor with reduced engineering margin with respect to the current situation. At least another object is to provide such protection strategy taking advantage from the computational capabilities of the Electronic Control Unit (ECU) of the vehicle. At least a further object is to meet these goals by means of a simple, rational and inexpensive solution. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     A device is provided for compressor and charge air cooler protection in an internal combustion engine, in particular in a Diesel engine, the engine having an intake manifold and an exhaust manifold and corresponding intake and exhaust lines, first and second EGR routes, a charge air cooler located in the intake line upstream the intake manifold and downstream the second EGR route, a turbocharger having a compressor located in the intake line, the system having regulating means for regulating the flow rate of exhaust gas and the splitting of exhaust gas between the first and second EGR route. A temperature sensor means is also provided for measuring the temperature of gas at the outlet of the compressor. 
     A method is provided for compressor and charge air cooler protection in an internal combustion engine, in particular in a Diesel engine, the engine having an intake manifold and an exhaust manifold and corresponding intake and exhaust lines, first and second EGR routes, a charge air cooler located in the intake line upstream the intake manifold and downstream the second EGR route, a turbocharger having a compressor located in the intake line and a turbine in the exhaust line, the system having regulating means for regulating the flow rate of exhaust gas and the splitting of exhaust gas between the first and second EGR route. The method also comprises at least a phase of monitoring a parameter representative of the gas temperature at the output of the compressor and at least a second phase in which an activity involving engine components operation is performed, the activity being performed using also the temperature value determined in said monitoring phase. 
     In a first embodiment of the method, such activity is directed to reduce gas temperature at the output of the compressor and is performed in case the temperature determined in the temperature monitoring phase is above a predetermined threshold. This activity may comprise a phase of regulating the splitting of flow rate of exhaust gas through the second EGR route with respect to the flow rate of exhaust gas through the first EGR route for a predetermined amount of time if the actual temperature of the gas at the compressor outlet is above the threshold temperature. According to a further embodiment of the invention, an activity comprising a phase of regulating the geometry of the turbine housing for a predetermined amount of time may be performed, if the actual temperature of the gas at the compressor outlet is above the threshold temperature. Activities permitted by the device and method of the invention may also comprise allowing overboost during acceleration in order to optimize engine performance during transients or the monitoring of charge air cooler efficiency during use of the vehicle. 
     The method can be realized in the form of a computer program comprising a program-code to carry out all the steps of the method of the invention and in the form of a computer program product comprising means for executing the computer program. The computer program product comprises, according to a preferred embodiment of the invention, a control apparatus for an IC engine, for example the ECU of the engine, in which the program is stored so that the control apparatus defines an embodiment of the invention in the same way as the method. In this case, when the control apparatus execute the computer program all the steps of the method are carried out. 
     The method can be also realized in the form of an electromagnetic signal, the signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method. 
     The invention further provides an internal combustion engine specially arranged for carrying out the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing FIGURE, and: 
         FIG. 1  is a schematic illustration of a turbocharged Diesel engine system with an embodiment of the device allowing the method according to an embodiment of the invention. 
         FIG. 2  is a flowchart illustrating a method for protection in an internal combustion engine, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     The embodiments hereinafter are disclosed with reference to a turbocharged Diesel engine system. However, the embodiments are applicable to different Diesel engine system and even to spark-ignition engine systems. 
     The turbocharged Diesel engine system comprises a Diesel engine  1  having an intake manifold  10  and an exhaust manifold  11 , an intake line  2  for conveying fresh air from the environment in the intake manifold  10 , an exhaust line  3  for conveying the exhaust gas from the exhaust manifold  11  to the environment, and a turbocharger  4  which comprises a compressor  40  located in the intake line  2  for compressing the air stream flowing therein, and a turbine  41 , preferably Variable Nozzle Turbine (VNT), located in the exhaust line  3  for driving said compressor  40 . A temperature sensor  80  is provided for determining the temperature within the intake manifold  10 . 
     The turbocharged Diesel engine system further comprises an intercooler (or charge air cooler)  20  located in the intake line  2  downstream the compressor  40  of turbocharger  4 , for cooling the air stream before it reaches the intake manifold  10 , and a valve  21  located in the intake line between the charge air cooler  20  and the intake manifold  10 . The turbocharged Diesel engine system further comprises a diesel oxidation catalyst (DOC)  30  located in the exhaust line  3  downstream the turbine  41  of turbocharger  4 , for degrading residual hydrocarbons and carbon oxides contained in the exhaust gas, and a diesel particulate filter (DPF)  31  located in the exhaust line  3  downstream the DOC  30 , for capturing and removing diesel particulate matter (soot) from the exhaust gas. 
     In order to reduce the polluting emission, the turbocharged Diesel engine system comprises an exhaust gas recirculation (EGR) system, for selectively routing back exhaust gas from the exhaust manifold into the intake manifold. The EGR system comprise a first EGR conduit  50  for directly fluidly connecting the exhaust manifold  11  with the intake manifold  12 , a first EGR cooler  51  for cooling the exhaust gas, and a first electrically controlled valve  52  for determining the flow rate of exhaust gas through the first EGR conduit  51 . The first EGR conduit  51  defines a short route for the exhaust gas recirculation cooler, so that the exhaust gas routed back by the first EGR conduit  51  is quite hot. 
     The EGR system further comprise a second EGR conduit  60 , which fluidly connects a branching point  32  of the exhaust line  3  downstream the DPF  32  with a leading point  22  of the intake line  2  upstream the compressor  40  of turbocharger  4 , and a second EGR cooler  61  located in the additional EGR conduit  60 . The flow rate of exhaust gas through the second EGR conduit  60  is determined by an electrically controlled valve  62 , wherein the valve  62  is located in the second EGR conduit  60  upstream the second EGR cooler  61 . A valve  63  is located in the intake line  2  downstream an air filter  23  and upstream the leading point  22 . The second EGR conduit  60  defines a long route for the exhaust gas recirculation, which comprises also the portion of the exhaust line  3  comprised between the exhaust manifold  11  and the branching point  32 , and the portion of the intake line  2  comprised between the leading point  22  to the intake manifold  10 . 
     Flowing along the long route, the exhaust gas is obliged to pass through the turbine  41  of turbocharger  4 , the DOP  30 , the DPF  31 , the second EGR cooler  61 , the compressor  40  of turbocharger  4  and the charge air cooler  20 , so that it become considerably colder than the exhaust gas which flows through the first EGR conduit  50 , to thereby reaching the intake manifold at a lower temperature. 
     The turbocharged Diesel engine system is operated by a microprocessor (ECU) based control circuit, which is provided for generating and applying control signals to the valves  52 ,  62  and  63 , to thereby adjusting the flow rate of exhaust gas through the first EGR conduit  50  and the second EGR conduit  60 . A pressure sensor  82  and a temperature sensor  83  are provided respectively upstream and downstream of the DOP  30  and DPF  31  group. Furthermore, a temperature sensor  84  is provided downstream of the second EGR cooler  61  in order to measure the temperature downstream of the long route EGR; temperature downstream the charge air cooler may be measured by a dedicated sensor  76 . A temperature sensor  99  is also present in order to measure ambient temperature and temperature sensor  80  is provided in order to measure manifold temperature. 
     A further temperature sensor  98  is placed immediately downstream of the compressor  40  in order to measure gas temperature at the compressor outlet, such temperature sensor  98  being upstream with respect to the charge air cooler  20 . Accordingly, it is therefore possible to monitor intermittently or continuously a parameter representative of the gas temperature at the output of the compressor  40  and, depending to the value of the temperature measured, it is possible to perform through electronic control of the various parameters of the engine system a wide number of activities. In general, such activities involve operations performed on engine components using the temperature value determined in the temperature monitoring phase. 
     Specifically, some activities performed can be directed to reduce gas temperature at the compressor outlet in case the temperature determined in the first phase is above a predetermined threshold. This procedure amounts to a first effective components protection strategy. Moreover, when gas temperature at the output of said compressor is below said predetermined threshold said activity directed to reduce said temperature is deactivated. 
     In order to avoid jerking and undesirable controller oscillation a time threshold is preferably set, in order to activate or deactivate the control system after a predetermined amount of time has elapsed from the attainment of the temperature threshold condition. The activity directed to reduce said temperature may comprise a phase of regulating the splitting of flow rate of exhaust gas through said second EGR route with respect to the flow rate of exhaust gas through said first EGR route for a predetermined amount of time if the actual temperature of the compressor is superior to a said temperature threshold. Specifically, the electrically controlled valve  62  located in the second EGR conduit  60  may be actuated and regulated in order to adjust flow rate of exhaust gas through the second EGR conduit  60 , realizing a splitting of the flow rate between the first and second EGR conduits that decreasing the flow in the second EGR conduit  60  and eventually increasing correspondingly the flow in the first EGR conduit; this allows a progressive decrease of gas temperature at the outlet of the compressor. 
     A further method to decrease gas temperature at the outlet of the compressor involves intervening directly on the compressor outlet pressure. In other words, an activity directed to reduce said temperature may comprise a phase of regulating the geometry of the turbine  41  housing for a predetermined amount of time in order to reduce outlet compressor pressure, if the actual temperature of the gas at the outlet of compressor is superior to the threshold temperature. Specifically this may be obtained by employing the capabilities of the Variable Nozzle Turbine (VNT), adjusting the movable vane angles to optimize turbine behaviour in relation to desired effect. 
     The activities connected to splitting EGR flow by means of valve  62  regulation and to regulation of turbine housing geometry may also be performed in parallel, for better results. The activities that the presence of the temperature sensor  98  renders possible, may also comprise charge air cooler (CAC) efficiency monitoring. Such activities being able to detect early a faulty condition, also contributing to components protection. In fact, the presence of temperature sensor  98  placed immediately downstream of the compressor  40  allows, in cooperation with temperature sensor  99  (T ambient ) and temperature sensor  80  (T manifold ), to monitor CAC efficiency based on the following relationship: 
               CAC   efficiency     =         T   ⁢           ⁢   com     ,     out   -   Tmanifold           T   ⁢           ⁢   com     ,     out   -   Tambient               
This monitoring is possible when no short-route EGR is used and both T ambient  and T manifold  are measured as explained above.
 
     The CAC efficiency evaluation can be used for detection of internal and external CAC fouling due to soot leakage or dirt, respectively or for detection of conditions prone to moisture condensation. Furthermore such monitoring gives the capability to optimize and extend CAC by-pass operation depending on the operating limits. 
     A further activity that the inventive compressor temperature control allows is the overboost which is made possible during acceleration thanks to system thermal capacity. Also, with the inventive compressor temperature control, limit temperature may be reached in a shorter time with respect to prior art solutions. 
     The embodiments of the invention have several important advantages. A first notable benefit is that it allows optimizing Long Route/Short Route EGR split and boosting level according to the European Extra-Urban Drive Cycle (EUDC). Furthermore, the embodiments of the invention allow protecting the compressor against thermal stress and oil cracking. Another important benefit is that the embodiments of the invention allow reducing the engineering margins with benefits during heavy accelerations and high altitude operation as well as component ageing. Furthermore, the embodiments of the invention allow optimizing performance during transients thanks to the closed-loop temperature control being performed. Finally the invention allows monitoring CAC efficiency during use of the vehicle and preventing operation in critical ambient conditions. 
       FIG. 2  is a flowchart illustrating a method  200  for protection in an internal combustion engine, in accordance with an embodiment. The method  200  may include, but is not limited to measuring a gas temperature at an outlet of said compressor with a temperature sensor (Step  210 ); determining if the gas temperature at the compressor output is greater than a predetermined threshold (Step  220 ); reducing the gas temperature at the output of said compressor when the gas temperature is greater than the predetermined threshold by regulating, via the valve, the splitting of flow rates of the exhaust gas through the first EGR rout and the second EGR rout and maintaining the regulated flow rate of the exhaust gas through the first EGR rout and the second EGR rout for a predetermined time (Step  230 ); deactivating the reducing the gas temperature at the output of said compressor when the gas temperature is less than the predetermined threshold and the predetermined time has elapsed (Step  240 ); and Measuring an ambient temperature and a manifold temperature in order to monitor charge air cooler efficiency on a basis of a relationship as follows under a condition that said first EGR route is substantially closed (Step  250 ). 
     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.