Abstract:
A method of engine control includes: determining and comparing actual and target supply amounts of EGR gas; sensing an open rate of an EGR valve to control the actual supply amount supplied to an intake line; if the actual supply amount is smaller than the target supply amount and if the EGR-valve open rate is at a maximum, fixing an open rate of a bypass valve installed at a bypass line that bypasses an electrodynamic turbocharger to a minimum open rate; and controlling the EGR-valve open rate in a state in which the bypass-valve open rate is fixed to a minimum open rate. Therefore EGR gas can be more precisely and stably supplied.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority of Korean Patent Application Number 10-2013-0013416 filed Feb. 6, 2013, the entire contents of which application is incorporated herein for all purposes by this reference. 
       BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a method of controlling an engine that recirculates an exhaust gas (or EGR gas) from an exhaust line to an intake line and that more precisely controls the recirculated EGR gas. 
         [0004]    2. Description of Related Art 
         [0005]    In general, in most diesel engines and some gasoline engines that are mounted in a vehicle, an exhaust gas recirculation system is installed to correspond to exhaust gas control. 
         [0006]    Such an exhaust gas recirculation system drops a combustion temperature of an engine and reduces a generation amount of nitrogen oxide (NOx) by returning a portion of an exhaust gas that is exhausted from the engine to an intake device of a cylinder, thereby reducing fuel consumption. 
         [0007]    In a gasoline engine, an electrodynamic turbocharger and an LP-EGR SYSTEM in addition to a mechanical turbocharger are applied, and in order to fully supply an EGR gas, a negative pressure should be formed in a front end portion of the mechanical turbocharger. 
         [0008]    Therefore, in order to form a negative pressure in a front end portion of the mechanical turbocharger, by opening an EGR valve that is installed in an EGR line through which an EGR gas passes to the maximum and by controlling a bypass valve of an intake line, a supply amount of an EGR gas can be controlled. 
         [0009]    However, because it is difficult to precisely control a supply amount of an EGR gas by adjusting an open rate of the bypass valve, a pressure of a front end portion of the compressor may be irregularly changed. 
         [0010]    The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
       BRIEF SUMMARY 
       [0011]    Various aspects of the present invention provide for a method of controlling an engine having advantages of more stably supplying and precisely controlling an EGR gas by more uniformly maintaining a pressure of a front end portion of a compressor. 
         [0012]    Various aspects of the present invention provide for a method of controlling an engine, the method including: sensing or calculating an actual supply amount and a target supply amount of an EGR gas that is supplied from an exhaust line to an intake line and comparing magnitudes thereof; sensing an open rate of an EGR valve that is installed in an EGR line to control an actual supply amount of an EGR gas that is supplied to the intake line; fixing, if the actual supply amount of the EGR gas is smaller than the target supply amount of the EGR gas and if an open rate of the EGR gas is the maximum, an open rate of a bypass valve that is installed at a bypass line that bypasses an electrodynamic turbocharger to a minimum open rate; and controlling an open rate of the EGR valve in a state in which the open rate of the bypass valve is fixed to a minimum open rate. 
         [0013]    The electrodynamic turbocharger may be installed at the intake line of the upstream side further than a point that is joined to the EGR line to charge inhaled air and to be operated by a motor. 
         [0014]    At the controlling of an open rate of the EGR valve, an open amount of a charging control valve that is disposed at the downstream side of the electrodynamic turbocharger to control an intake flux may be together controlled. 
         [0015]    At the exhaust line, a first catalyst unit and a second catalyst unit may be sequentially disposed in an exhaust direction of an exhaust gas, and the EGR line may be branched from the exhaust line between the first catalyst unit and the second catalyst unit. 
         [0016]    The engine may further include a mechanical turbocharger that compresses inhaled air of the intake line separately from the electrodynamic turbocharger, wherein the mechanical turbocharger may include a turbine that is disposed at the upperstream side of the first catalyst unit at the exhaust line to rotate by an exhaust gas; and a compressor that is disposed at the downstream side of a point in which the EGR line and the intake line join to rotate by the turbine. 
         [0017]    At the downstream side of the compressor, an intercooler that cools the compressed inhaled air and a throttle valve that adjusts a flow amount of inhaled air, having passed the intercooler may be disposed. 
         [0018]    As described above, in a method of controlling an engine according to various aspects of the present invention, when an actual supply amount of an EGR gas does not reach a target supply amount, before closing a bypass valve, by fixing the bypass valve to a minimum open rate (step 1) and by simultaneously or selectively adjusting an EGR valve of an EGR line and a charging control valve of the rear end of an electrodynamic turbocharger, an EGR gas can be more precisely and stably supplied. 
         [0019]    The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic diagram of an exemplary engine having an EGR system and a turbocharger according to the present invention. 
           [0021]      FIG. 2  is a flowchart illustrating an exemplary method of controlling an engine according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are 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. 
         [0023]      FIG. 1  is a schematic diagram of an engine having an EGR system and a turbocharger according to various embodiments of the present invention. 
         [0024]    Referring to  FIG. 1 , the engine includes an intake line  132 , an intake manifold  120 , a cylinder block  115 , an exhaust manifold  110 , and an exhaust line  107 . 
         [0025]    At the intake line  132 , an air cleaner box  135 , an electrodynamic turbocharger  147 , a charging control valve  155 , a compressor  102 , an intercooler  130 , and a throttle valve  125  are disposed, and a bypass line  137  that bypasses the electrodynamic turbocharger  147  is formed. At the bypass line  137 , a bypass valve  150  is disposed. 
         [0026]    At the exhaust line  107 , a turbine  104 , a first catalyst unit  105 , and a second catalyst unit  170  are disposed, and an EGR line  167  is formed from the exhaust line  107  to the intake line  132 , and at the EGR line  167 , a low pressure EGR cooler  165  (or EGR cooler) and a low pressure EGR valve  160  (or EGR valve) are disposed. The EGR line  167  is branched at the downstream side of the first catalyst unit  105  to join at the downstream side of a point in which the intake line  132  and the bypass line  137  join. 
         [0027]    An exhaust gas that flows the exhaust line  107  to the mechanical turbocharger  100  rotates the turbine  104 , and the compressor  102  compresses inhaled air of the intake line  132  by a torque of the turbine  104  and supplies the inhaled air to a cylinder. 
         [0028]    The electrodynamic turbocharger  147  includes an electrodynamic turbine  140  and a motor  145 , and the motor  145  has a structure that selectively compresses inhaled air by rotating the electrodynamic turbine  140  according to a driving condition. 
         [0029]    The EGR cooler  165  adjusts a flow amount of an EGR gas that flows the EGR line  167 , the charging control valve  155  adjusts a flow amount of inhaled air flowing the intake line  132 , and the bypass valve  150  adjusts a flow amount of inhaled air flowing the bypass line  137 . 
         [0030]    In order to increase a quantity of an EGR gas (recirculated gas) that is supplied through the EGR line  167 , the bypass valve  150  may be closed. 
         [0031]    However, in various embodiments of the present invention, the bypass valve  150  is fixed or adjusted to a minimum open rate that is not completely closed, and in order to achieve an accurate target supply amount of an EGR gas, an open rate of the EGR valve  160  may be controlled. Further, while an open rate of the EGR valve  160  is controlled, an open rate of the charging control valve  155  may be together controlled. 
         [0032]    In various embodiments of the present invention, in order to obtain an enough differential pressure for recirculating an EGR gas, a minimum open rate in which the bypass valve  150  is not completely closed may be calculated in a separate control unit (ECU) (not shown) or may be selected from preset data. 
         [0033]    In various embodiments of the present invention, a control unit calculates or selects a target supply amount of an EGR gas that is recirculated from the exhaust line  107  to the intake line  132  based on a driving condition, and determines (e.g., calculates or senses) an actual supply amount of an actually recirculated EGR gas. In order to an actual supply amount to follow a target supply amount, the control unit controls the EGR valve  160 , the charging control valve  155 , and the bypass valve  150 . Such a series of control methods are well-known technology and therefore a detailed description thereof will be omitted. 
         [0034]      FIG. 2  is a flowchart illustrating a method of controlling an engine according to various embodiments of the present invention. 
         [0035]    Referring to  FIG. 2 , the control unit compares a target supply amount and an actual supply amount of an EGR gas that is supplied through the EGR line  167  (S 200 ). An actual supply amount may be calculated through a flux sensor or a differential pressure sensor, and a target supply amount may be calculated according to a driving condition or may be selected from preset data. 
         [0036]    The control unit determines whether the EGR valve  160  is opened to the maximum (S 210 ). If the EGR valve  160  is opened to the maximum, the process continues at step S 250 , and if the EGR valve  160  is not opened to the maximum, the process continues at step S 220 . 
         [0037]    The EGR valve  160  and the bypass valve  150  are normally controlled (S 220 ), and the bypass valve  150  is fixed at minimum open rate (S 250 ). That is, the bypass valve  150  operates at several steps and is fixed to a state of step 1 before being closed (S 250 ). 
         [0038]    The control unit determines whether an actual supply amount of an EGR gas reaches a target supply amount (S 230 ), and if an actual supply amount of an EGR gas reaches a target supply amount, the process continues at step S 240 , and if an actual supply amount of an EGR gas does not reach a target supply amount, the process continues at step S 260 . 
         [0039]    The control unit determines whether the EGR valve  160  is opened to the maximum (S 260 ). If the EGR valve  160  is opened to the maximum, the process continues at step S 250 , and if the EGR valve  160  is not opened to the maximum, the process continues at step S 220 . 
         [0040]    In various embodiments of the present invention, even if the EGR valve  160  is completely opened, if an actual supply amount of an EGR gas does not reach a target supply amount, an EGR valve is controlled to inject an EGR gas through a pressure drop of the upstream side of the mechanical turbocharger  100 . For this purpose, the bypass valve is controlled to a minimum open rate, and the EGR valve is controlled. 
         [0041]    For convenience in explanation and accurate definition in the appended claims, the terms upper, front or rear, and etc. are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures. 
         [0042]    The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.