Patent Publication Number: US-8113178-B2

Title: Apparatus and method for controlling quantity of fuel over common rail diesel engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Korean Patent Application No. 2008-0119211 filed on Nov. 27, 2008, the entire contents of which are incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and method for controlling the quantity of fuel over a common rail diesel engine, and more particularly, to an apparatus and method for controlling the quantity of fuel over a common rail diesel engine, which make it possible to reduce a deviation in the quantity of injected fuel using a map having a fuel temperature and a rail pressure as variables of a pressure wave correction (PWC) logic, reduce exhaust gases from the common rail diesel engine, and improve fuel efficiency of the common rail diesel engine. 
     2. Description of the Related Art 
     In general, the fuel injection system of a common rail diesel engine includes an injection pressure generating process and an injecting process, both of which are completely separated from each other. Thus, the common rail system can freely design burning and injecting processes because the injection pressure generation of fuel can be regarded separately from injection of fuel in the design of the engine. In detail, since both injection pressure and injection timing of the fuel can be regulated according to conditions of engine operation using an engine map, the fuel can be injected at high pressure even when revolutions per minute (rpm) of the engine is low, so that complete combustion can be accomplished. Further, pilot injection allows exhaust gases and noise to be further reduced, and the fuel injection is hydraulically controlled by a nozzle needle, so that it can be rapidly controlled until the injection is completed. 
     With the development of diesel engine technologies, there has recently been developed technology that performs multiple injections on diesel fuel during each combustion stroke. 
       FIG. 1  is a graph showing a change in the pressure of fuel during injection of fuel. 
     As can be seen from the graph of  FIG. 1 , in the case of multiple injections of fuel, a quantity of fuel injected later is affected by a quantity of fuel injected previously as well as a time difference between two injections of fuel, because the pressure is varied in a rail, a high-pressure pipe, and injectors. 
     This variation of the pressure causes a difference between quantities of injected fuel. In order to correct the difference between quantities of injected fuel, correction logic is used. 
       FIG. 2  conceptually illustrates the correction logic of a conventional apparatus for controlling the quantity of fuel over a common rail diesel engine. 
     As illustrated in  FIG. 2 , the correction logic properly corrects the quantity of fuel using a base map and an amplitude map. The base map is adapted to obtain a normalized reference valve on the basis of a time difference between two fuel injections and a fuel quality required for the second injection. The amplitude map is adapted to obtain a correction weight of the quantity of fuel by both a fuel quality required for the first injection and pressure in the rail. 
       FIG. 3  is a graph showing a change in the quantity of fuel caused by rail pressure of a conventional common rail diesel engine. 
     In  FIG. 3 , the change in the quantity of fuel is measured with respect to five rail pressures of 250 bar, 300 bar, 800 bar, 1200 bar and 1400 bar. This data is used when the base map of an existing logic is prepared. However, depending on a change in pressure, a waveform showing the change in the quantity of fuel is shifted, and a period (or frequency) of the waveform is varied. As such, the preparation of a map representative of all the cases using a single curve not only provides very low accuracy, but also requires much time and high expenses to a future verification test and re-correction. 
     Further, all of the existing correction logics are adapted to prepare the base and amplitude maps on the basis of the same time, so that the maps prepared so as to be well matched on some time sections are not well matched on other time sections. 
     The information disclosed in this Background of the Invention 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 OF THE INVENTION 
     Various aspects of the present invention are directed to provide an apparatus and method for controlling the quantity of fuel over a common rail diesel engine, in which a correction logic is equipped with a wave speed correction map having a fuel temperature and a rail pressure as input variables, thereby making it possible to remarkably reduce a deviation of the quantity of injected fuel, reduce exhaust gases from the engine, and improve fuel efficiency. 
     In an aspect of the present invention, an apparatus for controlling a fuel quantity over a common rail diesel engine may include a wave speed correction map correcting a wave speed, a first adder multiplying the corrected wave speed by an injection time difference, a base correction map using an output of the first adder and a former injection quantity as input variables, an amplitude map using a following injection quantity and a rail pressure as input variables, and a second adder multiplying a base correction map value of the base correction map by an amplitude map value of the amplitude map, and outputting a finally corrected value of the fuel quantity. 
     The apparatus for controlling a fuel quantity over a common rail diesel engine may further include a time corrector disposed between the first adder and the base correction map, wherein the time corrector corrects a difference between a calculated valve open/close time and an actual hydraulic valve open/close time on a basis of a result of the first adder, the rail pressure, and a fuel temperature, and outputs a corrected injection time difference as a variable to the base correction map. 
     The time corrector may include a hydraulic movement correction map using the rail pressure and the fuel temperature as input variables, and a summer summing a hydraulic movement correction map value of the hydraulic movement correction map and the result of the first adder, and outputting the corrected injection time difference as a variable. 
     Each of the correction maps may include a fuel temperature and the rail pressure as input variables. 
     The injection time difference may be a difference between a previous injection time and a current injection time. 
     The injection time difference may be a difference between a previous injection time and a current injection time. 
     The correction map may include a fuel temperature and the rail pressure as input variables. 
     In another aspect of the present invention, an apparatus for controlling a fuel quantity over a common rail diesel engine, may include a wave speed correction map configured to correct a wave speed based on at least one input parameter, wherein an output of the wave speed correction map is configured to correct a first input parameter, a base correction map configured to correct the corrected first input parameter based on a second input parameter, and an output member configured to output a finally corrected value of the fuel quantity, based on an output of the base correction map and an output of an amplitude map, wherein the amplitude map includes one of the at least one input parameter of the wave speed correction map and a third input parameter as input values. 
     The first input parameter may be an injection time difference determined by a difference between a previous injection time and a current injection time. 
     The second input parameter may be a former injection quantity. 
     The third input parameter may be a following injection quantity. 
     The one of the at least one input parameter of the wave speed correction map may be a fuel pressure in a common rail. 
     The other of the at least one input parameter of the wave speed correction map may be a fuel temperature. 
     The wave speed correction map may be configured to correct the wave speed based on the one and the other of the at least one input parameter of the wave speed correction map, wherein the other of the at least one input parameter of the wave speed correction map is a fuel temperature. 
     The apparatus for controlling a fuel quantity over a common rail diesel engine may further include a time correcting member configured to correct the corrected first input parameter wherein the corrected first input parameter is corrected based on the one and the other of the at least one input parameter of the wave speed correction map so as to correct a time difference between a calculated valve open/close time and an actual hydraulic valve open/close time, wherein the time correcting member includes a hydraulic movement correction map having the one and the other of the at least one input parameter of the wave speed correction map as input variable, wherein the one and the other of the at least one input parameter of the wave speed correction map are a fuel pressure in a common rail and a fuel temperature respectively. 
     In further another aspect of the present invention, a method for controlling a quantity of fuel over a common rail diesel engine, may include multiplying a weight of a wave speed, which is corrected by a wave speed correction map having a fuel temperature and a rail pressure as input variables, by an injection time difference as a variable, calculating a corrected injection time difference, which corrects a difference between a calculated valve open/close time and an actual hydraulic valve open/close time, using the value obtained by multiplying the wave speed weight by the injection time difference, calculating a base correction map value using the calculated corrected injection time difference and a former injection quantity of fuel, calculating an amplitude map value using a following injection quantity of fuel and the rail pressure, and determining a finally corrected value of the fuel quantity using the base correction map value and the amplitude map value. 
     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 of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph showing a change in the pressure of fuel during injection of fuel. 
         FIG. 2  conceptually illustrates the correction logic of a conventional apparatus for controlling the quantity of fuel over a common rail diesel engine. 
         FIG. 3  is a graph showing a change in the quantity of fuel caused by rail pressure of a conventional common rail diesel engine. 
         FIG. 4  schematically illustrates the configuration of an exemplary common rail fuel injection system according to the present invention. 
         FIG. 5  conceptually illustrates a PWC logic in an apparatus for controlling the quantity of fuel over an exemplary common rail diesel engine according to the present invention. 
         FIG. 6  is a graph representing a change in the quantity of fuel when an injection time difference is corrected on the basis of a wave speed according to various embodiments of the present invention. 
         FIG. 7  is a graph representing a change in the quantity of fuel when an injection time difference is corrected on the basis of a wave speed, and when a difference between a calculated valve open/close time and an actual hydraulic valve open/close time is additionally corrected, according to various embodiments of the present invention. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various 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 INVENTION 
     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. 
       FIG. 4  schematically illustrates the configuration of a common rail fuel injection system according to various embodiments of the present invention. 
     The common rail fuel injection system includes an electronic control unit  100 , a high-pressure pump  150 , a fuel feed regulating valve  110 , a common rail  120 , injectors  130 , injector coils  140 , a variety of sensors  161  through  167 , and a pressure wave correction (PWC) logic  200  for controlling the quantity of fuel over a common rail diesel engine. 
     The high-pressure pump  150  is a pump using a rotational force of the diesel engine, and is configured to compress the fuel supplied from the fuel tank  121  up to maximum 1,350 bar, and then feed the compressed fuel to the common rail  120 . The fuel feed regulating valve  110  is mounted in the high-pressure pump  150 , and regulates the quantity of fuel fed to a high-pressure chamber of the high-pressure pump  150  under the control of the electronic control unit  100  to thereby control the quantity of fuel required for the engine. 
     The common rail  120  stores the high-pressured fuel feed from the high-pressure pump  150  and then feeds the fuel to each combustion chamber at the same pressure, and is equipped with a check valve for preventing a backflow and a high-pressure sensor  161 . The pressure of the fuel in the common rail is regulated by an electromagnetic pressure regulating valve, is always monitored by the high-pressure sensor, and is continuously regulated according to conditions required by the engine. 
     Each injector  130  serves to inject the high-pressure fuel into the combustion chamber. Each injector coil  140  is actuated under the control of the electronic control unit  100 , thereby opening/closing a needle valve of each injector  130 . 
     The electronic control unit  100  receives signals detected by the sensors  161  through  167 , thereby actuating a high-pressure fuel pump, the fuel feed regulating valve  110 , the injector coils  140 , etc. to control the quantity of fuel, injection time, injection rate, and so on. 
     According to various embodiments of the present invention, the quantity of injected fuel is corrected using a wave speed correction map, in which both pressure in the common rail and temperature of the fuel are set as input variables, in the PWC logic  200 . This is because the quantity of injected fuel has a variable value depending on a level of the pressure in the common rail. In other words, a pressure wave in the high-pressure fuel pipe is subjected to a change in its period, etc. by a wave speed. The wave speed can be mathematically given as follows. 
     The wave speed “c” of liquid in the pipe is expressed by the following Equation 1:
 
 c=√ {square root over (γ B   T /ρ o )}  Equation 1
 
where γ is the ratio of heat capacity, BT is the isothermal bulk modulus, and ρo is the volume density. All of the three variables possess the property of being varied by temperature and pressure of the liquid. Thus, the wave speed “c” is the function of the rail pressure and the fuel temperature, and the wave in the fuel pipe is subjected to a change in its frequency and wavelength according to pressure. As such, in the case of the graph of  FIG. 3  illustrating a change in the quantity of fuel, an injection separation (i.e. an injection time difference) has also to be corrected on the basis of the rail pressure and the fuel temperature.
 
     According to various embodiments of the present invention, the quantity of injected fuel is corrected using the wave speed correction map, in which the rail pressure and the fuel temperature are set as the input variables, in the PWC logic  200 . 
     Now, the aforementioned PWC logic  200  will be described in detail with reference to the figures. 
       FIG. 5  conceptually illustrates a PWC logic in an apparatus for controlling the quantity of fuel over a common rail diesel engine according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 5 , the PWC logic includes a wave speed correction map  210  correcting a wave speed using the fuel temperature and the rail pressure as the input variables, a first adder  220  multiplying the corrected wave speed by an injection time difference, a time corrector  230  correcting a difference between an electrical valve open/close time (i.e. a valve open/close time calculated by the electronic control unit  100 ) and a hydraulic valve open/close time (i.e. an actual valve open/close time) on the basis of the result of the first adder  220 , the rail pressure, and the fuel temperature, and outputting a corrected injection time difference as a variable, a PWC base correction map  240  using the corrected injection time difference and a former injection quantity as input variables, a PWC amplitude map  250  using the rail pressure and a following injecting quantity as input variables, and a second adder  260  multiplying a PWC base correction map value of the PWC base correction map  240  by a PWC amplitude map value of the PWC amplitude map  250 , and outputting a finally corrected value of the PWC fuel quantity. 
     As described above, the wave speed correction map  210  uses the fuel temperature and the rail pressure as input variables. As in the aforementioned Equation 1, a wave speed corresponding to that of liquid is corrected. In other words, a weight is added to the wave speed. 
     The wave speed correction map  210  is to correct the wave speed that is a physical phenomenon. A map prepared for a given engine can be used in common with other engines without great correction. Thereby, test number and time that are required for correction and complement in order to prepare the map can be remarkably reduced. 
     Here, the first and second adders  220  and  260  multiply the mapped values. At this time, the injection time difference refers to that between two sections, i.e. between a former injection time and a current injection time. 
     The time corrector  230  includes a hydraulic movement correction map  231  using the rail pressure and the fuel temperature as input variables, and a summer  232  summing a hydraulic movement correction map value of the hydraulic movement correction map  231  and the result of the first adder  220  to thereby output the corrected injection time difference as a variable. 
     The value output from the time corrector  230 , i.e. the corrected injection time difference, is a value that corrects a difference between the valve open/close time pre-calculated by the electronic control unit  100  and the actually measured valve open/close time. Thereby, a difference between a theoretical value and an actual value can be easily corrected with respect to the valve open/close time. 
     If necessary, the time corrector  230  may be removed. In this case, the PWC base correction map  240  receives the output of the first adder  220  and the former injection quantity as input variables. 
     The PWC base correction map  240  outputs the PWC base correction map value using the former injection quantity of fuel and the corrected injection time difference as input variables. The PWC amplitude map  250  outputs the PWC amplitude map value using a currently measured rail pressure and the following injection quantity of fuel as input variables. 
     In this manner, the PWC base correction map  240  receives the former injection quantity of fuel and the corrected injection time difference that is a new variable, and then outputs a mapping value corresponding to these variables, so that it can easily record its data. Similarly, the PWC amplitude map  250  can easily record its data as well. 
     The operation of the PWC logic  200  having the aforementioned configuration will be described with reference to  FIG. 5 . 
     First, the weight of a wave speed corrected by the wave speed correction map  210  having the fuel temperature and the rail pressure as input variables is multiplied by an injection time difference. 
     A corrected injection time difference, which corrects a difference between a calculated valve open/close time and an actual hydraulic valve open/close time, is calculated using the value obtained by multiplying the wave speed weight by the injection time difference. 
     A PWC base correction map value is obtained using the corrected injection time difference calculated in this way and a former injection quantity of fuel. Subsequently, a PWC amplitude map value using the following injection quantity of fuel and the rail pressure as input variables is obtained, and then the PWC base correction map value is multiplied by the PWC amplitude map value. Thereby, a finally corrected value of the PWC fuel quantity is obtained. 
     In comparison with a conventional PWC logic, the PWC logic can conspicuously reduce a deviation in the quantity of injected fuel. 
       FIG. 6  is a graph representing a change in the quantity of fuel when an injection time difference is corrected on the basis of a wave speed according to an exemplary embodiment of the present invention. 
     In  FIG. 6 , the change in quantity of fuel is measured with respect to five rail pressures of 250 bar, 300 bar, 800 bar, 1200 bar and 1400 bar, and the injection time difference between the two injections (i.e. the first injection and the following second injection) is corrected on the basis of the wave speed. In this manner, when the injection time difference is corrected, it can be seen that the change in quantity of fuel has a more regular form as compared to the graph of  FIG. 3 . 
       FIG. 7  is a graph representing a change in the quantity of fuel when an injection time difference is corrected on the basis of a wave speed, and when a difference between a calculated valve open/close time and an actual hydraulic valve open/close time is additionally corrected, according to various embodiments of the present invention. 
     In  FIG. 7 , the change in the quantity of fuel is measured with respect to five rail pressures of 250 bar, 300 bar, 800 bar, 1200 bar and 1400 bar, and the injection time difference is corrected through the PWC logic in additional consideration of the difference between the electrical valve open/close time and an actual hydraulic valve open/close time of each injector. In this manner, when the injection time difference is corrected in addition to the valve open/close time difference, it can be seen that the change in quantity of fuel has a more regular form with respect to each pressure, as compared to the graph of  FIG. 6 . In particular, positions of wave peaks can be better matched. 
     According to various aspects of the present invention, the apparatus and method for controlling the quantity of fuel over a common rail diesel engine make it possible to easily prepare data of a map through a pressure wave correction (PWC) logic having the wave speed correction map using a fuel temperature and a rail pressure, remarkably reduce number and time of tests that are required for correction and complement in order to prepare the map, reduce a deviation of the fuel quantity as well as exhaust gases, and improve fuel efficiency 
     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.