Abstract:
A diesel engine may be stably controlled without an exhaust gas temperature at an upstream side of a turbocharger, by a method for controlling a diesel engine that includes: detecting an engine rotation speed; detecting or estimating a lambda value; estimating an exhaust gas temperature at an upstream side of a turbocharger by using relationship between the lambda value and an exhaust temperature; determining whether the estimated exhaust gas temperature exceeds a first predetermined reference value; and limiting an engine output power and/or regeneration of a CPF when the estimated exhaust gas temperature exceeds the first predetermined reference value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2007-0113221, filed in the Korean Intellectual Property Office on Nov. 7, 2007, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a diesel engine, and more particularly, a method and apparatus for controlling a diesel engine equipped with a turbocharger. 
         [0004]    (b) Description of the Related Art 
         [0005]    A diesel engine may be provided with a turbocharger in order to increase an output power of the engine, to reduce the emission, or to enhance fuel consumption. 
         [0006]    When the turbocharger is overheated, oil used for lubrication and cooling of the turbocharger may catch a fire. 
         [0007]    The diesel engine shows merits on fuel consumption and output torque, but it shows drawbacks in exhaust gas. That is, although the diesel engine produces less carbon monoxide CO and hydrocarbon HC, it produces more nitrogen oxide (typically, called NOx) and particulate matters because of its high temperature of the combustion chamber caused by its high compression ratio. 
         [0008]    Typically, particulate matters can be reduced by combustion control. However, an emission control scheme for reducing NOx may result in an increase of particulate matters, and an emission control scheme for reducing particulate matters may result in an increase of NOx. Therefore, it is very difficult to reduce both the NOx and particulate matters at the same time. 
         [0009]    Usually, a diesel engine is provided with a diesel catalyzed particulate filter (CPF) for reducing the particulate matters. 
         [0010]    The CPF collects the particulate matters exhausted by the engine, and when more than a predetermined amount of the particulate matters are collected, the CPF is regenerated by burning the particulate matters collected in the CPF in increasing the exhaust gas by employing a post-injection. 
         [0011]    On the other hand, a diesel engine is typically provided with an exhaust gas temperature sensor that senses an exhaust gas temperature at an upstream side of a turbocharger. Such a detection of the exhaust gas temperature is useful for preventing an overheating of the turbocharger, for limiting the exhaust gas temperature, and for preventing an overheating of the CPF. 
         [0012]    In addition, a lambda sensor is typically provided at a downstream side of the turbocharger in order to measure an air/fuel ratio for the purpose of controlling EGR and adjusting fuel injection. 
         [0013]    Thus, an engine control unit (ECU) controls the fuel injection and post-injection, based on the data obtained by the exhaust gas temperature sensor and the lambda sensor located at the upstream and downstream sides of the turbocharger respectively. 
         [0014]    However, the exhaust gas temperature sensor located at the upstream side of the turbocharger may have a very short lift time and may be easily become malfunctioned because it is always exposed to very hot exhaust gas and it may easily gather particulate matters. In the case of malfunctioning of the exhaust gas temperature sensor, the exhaust gas temperature may not be controlled such that the turbocharger may be overheated to catch a fire, and the regeneration of the CPF may not be appropriately controlled. 
         [0015]    Furthermore, such an employment of the exhaust gas temperature sensor at the upstream side of the turbocharger increases the total work process and thus decreases productivity for manufacturing a vehicle. 
         [0016]    Recently, some researches are made in order not to employ the exhaust gas temperature sensor but instead, to employ a method to estimate the exhaust gas temperature. 
         [0017]    As an example, Japanese Patent Laid-Open Publication No. 2005-351106 discloses that the exhaust gas temperature can be measured by a heater resistance of an air/fuel ratio sensor. 
         [0018]    In addition, Japanese Patent Laid-Open Publication No. 2006-161625 discloses that the exhaust gas temperature can be estimated based on an impedance of the lambda sensor and the heating amount of the heater installed therein. 
         [0019]    In addition, Japanese Patent Laid-Open Publication No. 1997-049448 discloses that the exhaust gas temperature can be estimated based on an intake air amount and a target air/fuel ratio. 
         [0020]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0021]    The present invention has been made in an effort to provide a method and apparatus for controlling a diesel engine having advantages of stably controlling the diesel engine including stably controlling regeneration of a CPF without an exhaust gas temperature sensor at an upstream side of a turbocharger. 
         [0022]    An exemplary embodiment of the present invention provides a method for controlling a diesel engine that includes: detecting an engine rotation speed; detecting a lambda value; estimating an exhaust gas temperature at an upstream side of a turbocharger by using relationship between the lambda value of the detected engine rotation speed and the exhaust gas temperature; determining whether the estimated exhaust gas temperature exceeds a first predetermined reference value; and limiting an engine output power and regeneration of a CPF when the estimated exhaust gas temperature exceeds the first predetermined reference value. 
         [0023]    The method may further include: determining whether the estimated exhaust gas temperature is below a second predetermined reference value; and releasing the limitation of the engine output power and/or the stoppage of the CPF regeneration when the estimated exhaust gas temperature is below the second predetermined reference value. 
         [0024]    The first predetermined reference value may be greater than the second predetermined reference value. 
         [0025]    The first predetermined reference value may be about 800° C., and the second predetermined reference value may be about 750° C. 
         [0026]    Another exemplary embodiment of the present invention provides a method for controlling a diesel engine that includes: detecting an engine rotation speed; estimating a lambda value; estimating an exhaust gas temperature at an upstream side of a turbocharger by using relationship between the estimated lambda value of the detected engine rotation speed and the exhaust gas temperature at the detected engine rotation speed; determining whether the estimated exhaust gas temperature exceeds a first predetermined reference value; and limiting an engine output power and/or regeneration of a CPF when the estimated exhaust gas temperature exceeds the first predetermined reference value. 
         [0027]    The method may further include: determining whether the estimated exhaust gas temperature is below a second predetermined reference value; and releasing the limitation of the engine output power and the stoppage of the CPF regeneration when the estimated exhaust gas temperature is below the second predetermined reference value. 
         [0028]    In the estimating of the lambda value, an intake air amount into a combustion chamber of the engine may be detected and the lambda value may be estimated based on the detected intake air amount and the detected engine rotation speed. 
         [0029]    The first predetermined reference value may be greater than the second predetermined reference value. 
         [0030]    The first predetermined reference value may be about 800° C., and the second predetermined reference value may be about 750° C. 
         [0031]    An exemplary embodiment of the present invention provides an apparatus for controlling a diesel engine that includes: an engine speed sensor that detects an engine rotation speed; a lambda sensor that detects an air/fuel ratio at a downstream side of a turbocharger; an air flow sensor that detects an intake air amount drawn into a combustion chamber; an injector that injects fuel into the combustion chamber; and an engine control unit that controls the injector based on signals from the engine speed sensor, the lambda sensor, and the air flow sensor, wherein the engine control unit executes a program comprising instructions for the above described method for controlling a diesel engine according to an exemplary embodiment. 
         [0032]    According to an exemplary embodiment, a fuel injection, an air amount, and an exhaust gas temperature may be stably controlled without an exhaust temperature sensor at an upstream side of a turbocharger of a diesel engine. 
         [0033]    The above features and advantages of the present invention will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated in and form a part of this specification, and the following Detailed Description of the Invention, which together serve to explain by way of example the principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The above and other features of the present invention will now be described in detail with reference to certain exemplary embodiments thereof illustrated the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0035]      FIG. 1  shows a schematic block diagram of an apparatus for controlling a diesel engine according to an exemplary embodiment of the present invention; 
           [0036]      FIG. 2  shows a flowchart for a method for controlling a diesel engine in the case of lambda sensor correctly-functioning according to an exemplary embodiment of the present invention; 
           [0037]      FIG. 3  shows a flowchart for a method for controlling a diesel engine in the case of lambda sensor malfunctioning according to an exemplary embodiment of the present invention; and 
           [0038]      FIG. 4  shows a relationship between lambda sensor values and exhaust temperature values of a diesel engine. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
       [0039]      
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 101: engine speed sensor 
                 102: lambda sensor 
               
               
                   
                 103: air flow sensor 
                 104: engine control unit (ECU) 
               
               
                   
                 105: injector 
               
               
                   
                   
               
             
          
         
       
     
         [0040]    It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0041]    Hereinafter reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings and described below. While the invention will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention to those exemplary embodiments. On the contrary, the invention is intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
         [0042]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. 
         [0043]    As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. 
         [0044]    Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0045]      FIG. 1  shows a block diagram of an apparatus for controlling a diesel engine according to an exemplary embodiment of the present invention. 
         [0046]    As shown in  FIG. 1 , an apparatus for controlling a diesel engine according to an exemplary embodiment of the present invention includes an engine speed sensor  101 , a lambda sensor  102 , an air flow sensor  103 , an engine control unit (ECU)  104 , and an injector  105 . 
         [0047]    The engine speed sensor  101  detects a rotation speed of the engine, and it may be realized as a crank position sensor (CPS) that detects an angular position of a crankshaft, or a cam angle sensor (CAS) that detects an angular position of a camshaft. The ECU  104  receives signal from the engine speed sensor  101  and calculate the engine rotation speed from the signal. 
         [0048]    The lambda sensor  102  is arranged at a downstream side of a turbocharger, and detects an oxygen concentration (i.e., air/fuel ratio) of the exhaust gas. The lambda sensor  102  provides a signal (hereinafter called a lambda value) for the detected air/fuel ratio to the ECU  104 . 
         [0049]    The air flow sensor  103  detects an air amount drawn to a combustion chamber of the engine, and provides a signal for the detected air amount to the ECU  104 . 
         [0050]    The ECU  104  estimates an exhaust gas temperature at the upstream side of the turbocharger by using a relationship between the lambda value and the engine rotation speed. The relationship between the lambda value and the exhaust gas temperature is experimentally obtained and is preset in the ECU  104  as a map table for each engine rotation speed. The ECU  104  controls fuel injection amount, air amount drawn into the combustion chamber, and regeneration of the CPF, based on the estimated exhaust gas temperature. 
         [0051]    In addition, the ECU  104  determines whether the lambda sensor  102  is malfunctioning. In the case of the lambda sensor  102  malfunctioning, the ECU  104  estimates the lambda value based on an engine rotation speed and an intake air amount into a combustion chamber of the engine, and then the ECU  104  uses the engine rotation speed and the estimated lambda value instead of actually measuring the lambda value received from the lambda sensor to estimate an exhaust gas temperature at the upstream of the turbo charger. 
         [0052]    The injector  105  injects the fuel into the combustion chamber according to a control signal from the ECU  104 . 
         [0053]    Hereinafter, a method for controlling a diesel engine according to an exemplary embodiment of the present invention is described in detail with reference to the drawings. 
         [0054]    Process for the Correctly-Functioning of the Lambda Sensor 
         [0055]    Firstly, a method for controlling a diesel engine in the case of lambda sensor correctly-functioning according to an exemplary embodiment of the present invention is described in detail with reference to  FIG. 2 . 
         [0056]    While the diesel engine is running at step S 101 , the ECU  104  detects a current engine rotation speed by the engine speed sensor  101  at step S 102 , and detects an air/fuel ratio at the downstream side of the turbocharger by the lambda sensor  102  at step S 103 . 
         [0057]    Subsequently at step S 104 , the ECU  104  estimates the exhaust gas temperature at the upstream side of the turbocharger based on the engine rotation speed detected by the engine speed sensor  101  and the air/fuel ratio detected by the lambda sensor  102 . 
         [0058]    Typically, heat relation between upstream and downstream side of the turbocharger is written as the following Equations 1 and 2. 
         [0000]      Δ Q=Cw×Δm   air amount   ×T 3  (Equation 1) 
         [0000]      Δ Q=Q   LHV   ×Δm   fuel amount   (Equation 2) 
         [0059]    In the above Equation 1 and Equation 2, Cw denotes a specific heat [joule/gram/° K.] of the fluid, Δm air amount  denotes an air amount [gram] drawn into the combustion chamber, ΔT3 denotes a temperature difference between the upstream and downstream sides of the turbocharger, and Q LHV  denotes a minimum heating value. 
         [0060]    The following Equation 3 is obtained from the above Equation 1 and 2. 
         [0000]      Δ T 3 =[Q   LHV   ×Δm   fuel amount   ]/[Cw×Δm   air amount ]=( Q   LHV   /Cw )×(1/λ)  (Equation 3) 
         [0061]    Here, λ denotes the air/fuel ratio. 
         [0062]    As can be understood from the Equation 3, the temperature difference between the upstream and downstream sides of the turbocharger is proportional to an inverse value of the air/fuel ratio, i.e., the lambda value. 
         [0063]      FIG. 4  is a graph that shows a relationship between the exhaust gas temperature difference and the lambda value (λ), at an engine rotation speed of 4,000 rpm with 1.5 liter diesel engine. 
         [0064]    As can be understood from the graph of  FIG. 4 , the lambda value (λ) and the temperature difference between the upstream and downstream sides of the turbocharger is inversely proportional, with variations of the boost pressure, the intake air temperature, and injection amount, although the relationship may vary depending on the engine rotation speed. Such an inversely proportional relationship is experimentally obtained and is preset as a map table in the ECU  104 . 
         [0065]    Therefore, the ECU  104  may estimate the exhaust gas temperature at the upstream side of the turbocharger based on the current engine rotation speed and the lambda value (λ) from the lambda sensor  102 , by using the preset map table depending on engine rotation speeds. 
         [0066]    When the exhaust gas temperature at the upstream side of the turbocharger is estimated at the step S 104 , the ECU  104  determines at step S 105  whether the estimated exhaust gas temperature exceeds a first predetermined reference temperature, e.g., 800° C. 
         [0067]    When the estimated exhaust gas temperature at the upstream side of the turbocharger exceeds the first reference temperature, the ECU  104  concludes that the exhaust gas temperature is excessively high at step S 106 . 
         [0068]    Then, the ECU  104  limits the fuel injection amount of the injector  105  at step S 107  such that an output power of the engine may be limited and the load of the turbocharger may be reduced. 
         [0069]    At the same time, the ECU  104  stops the regeneration of the CPF by the post-injection at step S 108 , and the ECU  104  limits an air amount drawn into the combustion chamber by activating an air flow control valve (not shown) at step S 109 . 
         [0070]    After that, the ECU  104  determines at step S 110  whether the estimated exhaust gas temperature at the upstream side of the turbocharger is below a second predetermined reference temperature, for example, 750° C. 
         [0071]    When the exhaust gas temperature at the upstream side of the turbocharger is not below the second predetermined reference temperature, the process returns to the step S 107  such that the steps of S 107 , S 108 , and S 109  may be executed until the exhaust gas temperature becomes below the second predetermined reference temperature. 
         [0072]    When the exhaust gas temperature at the upstream side of the turbocharger is below the second reference temperature, the ECU  104  concludes at step S 111  that the exhaust gas temperature has become stable. 
         [0073]    Therefore, the ECU  104  releases the limitation of the fuel injection amount at step S 112  and also releases the limitation of the air amount at step S 113 . Then, the ECU  104  restarts the regeneration of the CPF by restarting the post-injection at step S 114 . 
         [0074]    Process for the Malfunctioning of the Lambda Sensor 
         [0075]    In the above description, the method is described in connection with the case that the lambda sensor is correctly functioning. Hereinafter, the method is described in detail in connection with the case that the lambda sensor  102  is malfunctioning, with reference to  FIG. 3 . 
         [0076]    The malfunctioning of the lambda sensor  102  may be determined by a conventional way known to a person of ordinary skill in the art. For example, the lambda sensor  102  may be understood to be malfunctioning if no signal is obtained from the lambda sensor  102 , or a signal beyond a predetermined range is obtained from the lambda sensor  102 . 
         [0077]    When the malfunctioning of the lambda sensor  102  is detected, the ECU  104  enters a limp-home mode, and executes the following process. The following process corresponds to the process described above with reference to  FIG. 2 . The process for the malfunctioning of the lambda sensor  102  differs from the case of correctly-functioning lambda sensor in that, the lambda value (λ, equivalently, the air/fuel ratio) is estimated based on an intake air amount to the combustion chamber of the engine and the engine rotation speed, whereas the lambda value (λ) is directly detected by the lambda sensor  102  at the step S 103 . 
         [0078]    While the diesel engine is running at step S 201 , the ECU  104  detects a current engine rotation speed by the engine speed sensor  101  at step S 202 . Then at step S 203 , the ECU  104  detects an intake air amount drawn into the combustion chamber by the air flow sensor  103 , and estimates the lambda value (λ) based on the intake air amount and the engine rotation speed by which the ECU  104  is currently driving the injector  105 . 
         [0079]    Subsequently at step S 204 , the ECU  104  estimates the exhaust gas temperature at the upstream side of the turbocharger based on the engine rotation speed detected by the engine speed sensor  101  and the estimated lambda value (λ), i.e., estimated air/fuel ratio. 
         [0080]    Then, at step S 205 , the ECU  104  determines whether the estimated exhaust gas temperature exceeds the first predetermined reference temperature, e.g., 800° C. 
         [0081]    When the estimated exhaust gas temperature at the upstream side of the turbocharger exceeds the first predetermined reference temperature, the ECU  104  concludes that the exhaust gas temperature is excessively high at step S 206 . 
         [0082]    Then, the ECU  104  limits the fuel injection amount of the injector  105  at step S 207  such that an output power of the engine may be limited and the load of the turbocharger may be reduced. 
         [0083]    At the same time, the ECU  104  stops the regeneration of the CPF by the post-injection at step S 208 , and the ECU  104  limits an intake air amount drawn into the combustion chamber by activating an air flow control valve (not shown) at step S 209 . 
         [0084]    After that, the ECU  104  determines at step S 210  whether the estimated exhaust gas temperature at the upstream side of the turbocharger is below the second predetermined reference temperature, for example, 750° C. 
         [0085]    When the exhaust gas temperature at the upstream side of the turbocharger is not below the second predetermined reference temperature, the process returns to the step S 207  such that the steps of S 207 , S 208 , and S 209  may be executed until the exhaust gas temperature becomes below the second predetermined reference temperature. 
         [0086]    When the exhaust gas temperature at the upstream side of the turbocharger is below the second predetermined reference temperature, the ECU  104  concludes at step S 211  that the exhaust gas temperature has become stable. 
         [0087]    Therefore, the ECU  104  releases the limitation of the fuel injection amount at step S 112  and also releases the limitation of the air amount at step S 213 . Then, the ECU  104  restarts the regeneration of the CPF by restarting the post-injection at step S 214 . 
         [0088]    The ECU  104  can be realized by one or more processors activated by predetermined program, and the predetermined program can be programmed to perform each step of a method according to an embodiment of this invention. 
         [0089]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.