Air volume estimation method for electric supercharger system [Technical Field] [0001] The present invention relates to an air volume estimation method for an electric supercharger system, and more specifically relates to an air volume estimation method for an electric supercharger system which estimates the air volume by dividing the engine operating zone into a throttling zone and a supercharging zone in an engine system in which an electric supercharger is positioned downstream of the throttle valve. [Background Art of the Invention] [0002] Engine systems utilizing an electric supercharger are used for the purpose of reducing turbo lag and improving output and fuel efficiency (downsizing) by being applied upstream of the engine throttle valve. [0003] When the engine system consists of a supercharging system by applying only an electric supercharger, an effect of reducing the fuel efficiency and harmful exhaust gases compared to a turbocharger system comprising a turbine in the exhaust flow path can be obtained. [0004] Also, when a supercharger is applied upstream of a throttle valve in an engine system using an exhaust gas recirculation (EGR) apparatus, it is common for the EGR supply unit to be positioned upstream of the supercharger in order to supply EGR gas from the supercharging zone (intake manifold pressure > atmospheric pressure). In this case, the advantages of reducing knocking and improving fuel efficiency through the EGR supply in the supercharging zone too can be obtained. [0005] The Saint Venant equation is typically used with respect to the throttle valve for estimating (modeling) and controling the air volume supplied in a conventional engine system. In order to apply the Saint Venant equation, the precondition of the pressure ratio between upstream of the throttle valve and the intake manifold being less than 1 (0.95 or less) should be satisfied, and in the case of a system where the supercharger is applied upstream of the throttle valve the condition described above (intake manifold pressure < upstream pressure of the throttle valve) is satisfied and can be used for air volume control and modeling. [0006] Meanwhile, in the case of a system where a conventional EGR supply unit is positioned upstream of the supercharger and the supercharger is positioned upstream of the throttle valve, there are issues in that a time delay occurs in the EGR supply due to the long flow path between the EGR supply unit and the cylinder inlet, and an error between the target value for the EGR supply and the actual EGR supply value occurs in a transitional section of the engine operational zone so the fuel efficiency improvement due to the use of EGR deteriorates. [0007] On the other hand, in the case of a system where the supercharger is positioned downstream of the throttle valve and the EGR supply unit is positioned downstream of the throttle valve and upstream of the supercharger, the time delay in the EGR supply can be minimized as the flow path between the EGR supply unit and the cylinder inlet is short, and the EGR supply flow rate can be further increased through throttle valve control. [0008] Meanwhile, in the case of a system where the supercharger is applied downstream of the throttle valve, the precondition of the pressure ratio between upstream and downstream of the throttle valve being less than 1 (0.95 or less) in the operating zone where the supercharger is operating is not satisfied, thus there are issues with using the Saint Venant equation for air volume control and modeling as described for the prior art. [0009] With regard to the background art of the present invention, "Device and method for adjusting air supply amount of engine having supercharger" is disclosed in the Korean Registered Patent Publication No. 10-1382767 (April 01, 2014). [Details of the Invention] [Problem to be Solved] [0010] The present invention has been proposed to improve upon the problems described above, and the object according to one aspect of the present invention is to provide an air volume estimation method for an electric supercharger system in which the engine operating zone is divided into a throttling zone and a supercharging zone in an engine system where an electric supercharger is positioned downstream of the throttle valve, and, in the throttling zone, control and modeling of the air volume supplied is performed on the basis of the Saint Venant equation, while, in the supercharging zone, control and modeling of the air volume supplied is performed on the basis of the actual number of revolutions, the pressure and temperature values of the electric supercharger that is being driven during supercharging. [Means of Solving the Problem] [0011] The air volume estimation method for an electric supercharger system according to one aspect of the present invention is characterized by comprising steps of: detecting a weighting factor which divides the engine operating zone into a throttling zone and a supercharging zone; estimating the air volume in the throttling zone and supercharging zone respectively; and estimating the intake manifold air volume using the weighting factor and the air volume estimated for each engine operating zone. [0012] The present invention is characterized in that the weighting factor divides the engine operating zone into a throttling zone and a supercharging zone on the basis of ratio between the upstream pressure of the throttle valve and the intake manifold pressure. [0013] The present invention is characterized in that the step of estimating the air volume in the throttling zone and supercharging zone respectively comprises steps of: estimating the air volume in the throttling zone on the basis of the Saint Venant equation with respect to the throttle valve; and estimating the air volume in the supercharging zone by applying the operational data of the electric supercharger to the compressor map of the electric supercharger. [0014] The present invention is characterized in that the step of estimating the air volume on the basis of the Saint Venant equation with respect to the throttle valve comprises steps of: calculating the air volume in the throttling zone by applying at least one of the temperature upstream of the throttle valve, the pressure of the upper portion of the throttle valve, the pressure downstream of the throttle valve, and the effective area with respect to the current degree the throttle valve is open, to the Saint Venant equation; and calculating the air volume in the EGR by applying at least one of the temperature upstream of the EGR valve, the pressure upstream of the EGR valve, the pressure downstream of the EGR valve, and the effective area with respect to the current degree the EGR valve is open, to the Saint Venant equation. [0015] The present invention is characterized in that the effective area with respect to the current degree the throttle valve is open changes depending on the air volume learning control in the throttling zone. [0016] The present invention is characterized in that the step of estimating the air volume by applying the operational data of the electric supercharger to the compressor map of the electric supercharger involves deriving the volume flow of the air flowing in the electric supercharger by applying the operational data of the electric supercharger to the compressor map of the electric supercharger, and calculating the air volume in the supercharging zone on the basis of the volume flow. [0017] The present invention is characterized in that the operational data of the electric supercharger comprises at least one of the temperature upstream of the electric supercharger, the pressure upstream of the electric supercharger, the pressure downstream of the electric supercharger, and the current value of the number of revolutions of the electric supercharger, and the current value of the number of revolutions of the electric supercharger and the pressure upstream of the electric supercharger change depending on the air volume learning control. [0018] An air volume estimation method for an electric supercharger system according to another aspect of the present invention characterized by comprising steps of: detecting a weighting factor which divides the engine operating zone into a throttling zone and a supercharging zone; estimating the air volume in the throttling zone and supercharging zone respectively; and learning control of the error between the intake manifold air volume measured on the basis of the air volume estimated by the weighting factor and the engine operating zone and the actual intake manifold air volume so as to correct the air volume in the throttling zone and the supercharging zone. [0019] The present invention is characterized in that the weighting factor divides the engine operating zone into a throttling zone and a supercharging zone on the basis of ratio between the upstream pressure of the throttle valve and the intake manifold pressure. [0020] The present invention is characterized in that the step of estimating the air volume in the throttling zone and supercharging zone respectively comprises steps of: estimating the air volume in the throttling zone on the basis of the Saint Venant equation with respect to the throttle valve; and estimating the air volume in the supercharging zone by applying the operational data of the electric supercharger to the compressor map of the electric supercharger. [0021] The present invention is characterized in that the step of estimating the air volume on the basis of the Saint Venant equation with respect to the throttle valve comprises steps of: calculating the air volume in the throttling zone by applying at least one of the temperature upstream of the throttle valve, the pressure of the upper portion of the throttle valve, the pressure downstream of the throttle valve, and the effective area with respect to the current degree the throttle valve is open, to the Saint Venant equation; and calculating the EGR air volume by applying at least one of the temperature upstream of the EGR valve, the pressure upstream of the EGR valve, the pressure downstream of the EGR valve, and the effective area with respect to the current degree the EGR valve is open, to the Saint Venant equation. [0022] The present invention is characterized in that the step of estimating the air volume by applying the operational data of the electric supercharger to the compressor map of the electric supercharger involves deriving the volume flow of the air flowing in the electric supercharger by applying the operational data of the electric supercharger to the compressor map of the electric supercharger, and calculating the air volume in the supercharging zone on the basis of the volume flow. [0023] The present invention is characterized in that the operational data of the electric supercharger comprises at least one of the temperature upstream of the electric supercharger, the pressure upstream of the electric supercharger, the pressure downstream of the electric supercharger, and the current value of the number of revolutions of the electric supercharger. [0024] The present invention is characterized in that the step of correcting the air volume in the throttling zone and the supercharging zone comprises a step of: converting the estimated intake manifold air volume to an intake manifold pressure model value, and generating an effective area correction value for the throttle valve on the basis of the error between the intake manifold pressure model value and the actual measured intake manifold pressure and applying same to the estimation of the air volume in the throttling zone. [0025] The present invention is characterized in that the step of correcting the air volume in the throttling zone and the supercharging zone comprises a step of: converting the estimated intake manifold air volume to an intake manifold pressure model value, and calculating a revolution number correction value for the electric supercharger on the basis of the error between the intake manifold pressure model value and the actual intake manifold pressure and applying same to the estimation of the air volume in the supercharging zone. [0026] The present invention is characterized in that the step of correcting the air volume in the throttling zone and the supercharging zone comprises a step of converting the estimated intake manifold air volume to an intake manifold pressure model value, and calculating an upstream pressure correction value for the electric supercharger on the basis of the error between the intake manifold pressure model value and the actual intake manifold pressure and applying same to the estimation of the air volume in the supercharging zone. [0027] The present invention is characterized in that the step of correcting the air volume in the throttling zone and the supercharging zone comprises a step of: storing the cumulative error when the engine operating conditions are steady as a learning value for each engine operating zone for correcting the effective area, a learning value for each engine operating zone for correcting the number of revolutions of the electric supercharger, or a learning value for each engine operating zone for correcting the upstream pressure of the electric supercharger. [0028] The present invention is characterized by further comprising a step of estimating the intake manifold air volume using the corrected air volume in the throttling zone and air volume in the supercharging zone. [Advantages of the Invention] [0029] The air volume estimation method for an electric supercharger system according to one aspect of the present invention, compared to conventional methods which only use the Saint Venant equation, is capable of air volume estimation and control in an engine system even when an EGR and electric supercharger system are applied downstream of the throttle valve and can be operated without using an air flow rate sensor, thus enabling the reduction of system costs. [Brief Description of the Drawings] [0030] FIG. 1 is a drawing illustrating a supercharging and EGR system to which an air volume estimation device of an electric supercharger system according to one embodiment of the present invention is applied. [0031] FIG. 2 is a block diagram for the air volume estimation device of an electric supercharger system according to one embodiment of the present invention. [0032] FIG. 3 is a drawing illustrating the weighting factor for fading between the throttling zone and supercharging zone according to one embodiment of the present invention. [0033] FIG. 4 is a drawing illustrating a compressor map of the electric supercharger according to one embodiment of the present invention. [0034] FIG. 5 is a block diagram of an air volume estimation module according to one embodiment of the present invention. [0035] FIG. 6 is a block diagram of a learning control module according to one embodiment of the present invention. [0036] FIG. 7 is a sequence diagram for an air volume estimation method according to one embodiment of the present invention. [0037] FIG. 8 is a sequence diagram for an air volume learning control method in the throttling zone according to one embodiment of the present invention. [0038] FIG. 9 is a sequence diagram illustrating an example of the air volume learning control method in the supercharging zone according to one embodiment of the present invention. [0039] FIG. 10 is a sequence diagram illustrating another example of the air volume learning control method in the supercharging zone according to one embodiment of the present invention. [Detailed Disclosure for Implementing the Invention] [0040] Hereinbelow, the air volume estimation method for an electric supercharger system according to one embodiment of the present invention shall be described in detail with reference to the accompanying drawings. In this process, the thickness of lines or the size of the components shown in the drawings may be exaggerated for clarity of the description and convenience. In addition, the terms to be described below are terms defined considering the function in the present invention, and may vary according to intentions or customs of a user and an operator. Thus, definitions of such terms should be made based on the content throughout the entirety of this specification. [0041] FIG. 1 is a drawing illustrating a supercharging and EGR system to which an air volume estimation device of an electric supercharger system according to one embodiment of the present invention is applied. FIG. 2 is a block diagram for the air volume estimation device of an electric supercharger system according to one embodiment of the present invention. FIG. 3 is a drawing illustrating the weighting factor for fading between the throttling zone and supercharging zone according to one embodiment of the present invention. FIG. 4 is a drawing illustrating a compressor map of the electric supercharger according to one embodiment of the present invention. FIG. 5 is a block diagram of an air volume estimation module according to one embodiment of the present invention. FIG. 6 is a block diagram of a learning control module according to one embodiment of the present invention. [0042] With reference to FIG. 1, in the supercharging and EGR system to which an air volume estimation device of an electric supercharger system according to one embodiment of the present invention is applied, an electric supercharger (50) and an EGR supply unit (40) are positioned upstream of a throttle valve (30) and the EGR supply unit (40) is positioned between the electric supercharger (50) and the throttle valve (30). [0043] When the EGR supply unit (40) is positioned between the throttle valve (30) and the electric supercharger (50), the pressure of the EGR supply unit (40) is maintained at the pressure prior to supercharging, thus even in the supercharging zone smooth EGR supply is possible, and there is an advantage in that the flow path between the EGR supply unit (40) and the cylinder inlet of the engine (90) can be minimized. [0044] Note the undescribed reference numerals in FIG. 1, 20 is an air cleaner, 10 is an intake pipe, 41 is an EGR cooler, 42 is an EGR valve, 60 is an intake manifold, 70 is an intercooler, and 80 is an exhaust manifold. Each of these operations is the same as those in the prior art so a detailed description thereof has been omitted. [0045] Meanwhile, in the supercharging and EGR system to which an air volume estimation device of an electric supercharger system is applied, due to the electric supercharger (50) being positioned between the intake manifold (60) and downstream of the throttle valve (30) so as to perform supercharging, the pressure ratio of upstream of the throttle valve and the intake manifold (60) is ‘1’ or more. That is, the pressure of the intake manifold is greater than the pressure upstream of the throttle valve. Accordingly, when the electric supercharger (50) is positioned between the intake manifold (60) and downstream of the throttle valve (30), it is not appropriate to use air volume control and modeling using the Saint Venant equation in the supercharging zone. [0046] Also, air volume control and modeling can be applied in the supercharging zone by using an air flow rate sensor, but this has issues in that the time delay due to the long flow path between the installation position of the air flow rate sensor (normally at the rear end of the intake filter) and the cylinder inlet should be considered and the system costs increase. [0047] Hence, the air volume estimation device for an electric supercharger system according to one embodiment of the present invention performs air volume control and modeling based on the Saint Venant equation when the engine operating zone is the throttling zone, and performs control and modelling of the supplied air volume in the supercharging zone on the basis of the operational information of the electric supercharger (50) driven during supercharging, for example, actual number of revolutions, pressure and temperature values, in an engine system where the electric supercharger (50) is positioned downstream of the throttle valve. [0048] With reference to FIG. 2, the air volume estimation device of an electric supercharger system according to one embodiment of the present invention comprises an air volume estimation module (100) and learning control module (200). [0049] First, the air volume estimation module (100) defines the weighting factor for dividing the engine operating zone into a throttling zone and a supercharging zone. [0050] With reference to FIG. 3, the weighting factor can be set to divide the engine operating zone into a throttling zone and a supercharging zone with respect to the ratio of the pressure upstream of the throttle valve and the intake manifold (60) pressure. [0051] The weighting factor is used to fade the division of the throttling zone and the supercharging zone and the transitional section of the estimated air volume. [0052] Next, the air volume estimation module (100) estimates the intake manifold air volume in the throttling zone on the basis of the Saint Venant equation with respect to the throttle value (30) and estimates the intake manifold air volume in the supercharging zone by applying the actual number of revolutions, the pressure and temperature values of the electric supercharger (50) to the compressor map of the electric supercharger (50) shown in FIG. 4. [0053] With reference to FIG. 5, the air volume estimation module (100) comprises a weighting factor detection unit (110), a first air volume estimation unit (120), a second air volume estimation unit (130) and a third air volume estimation unit (140). [0054] The weighting factor detection unit (110) detects the weighting factor for the transitional section between the throttling zone and supercharging zone. [0055] The first air volume estimation unit (120) estimates the air volume in the throttling zone and the EGR air volume. [0056] The first air volume estimation unit (120) calculates in real-time the air volume in the throttling zone by applying the temperature upstream of the throttle valve, the pressure of the upper part of the throttle valve, the pressure downstream of the throttle valve, and the effective area with respect to the current degree the throttle valve is open, to the Saint Venant equation. [0057] Also, the first air volume estimation unit (120) calculates in real-time the EGR air volume by applying the temperature upstream of the EGR valve, the pressure upstream of the EGR valve, the pressure downstream of the EGR valve, and the effective area with respect to the current degree the EGR valve is open, to the Saint Venant equation. [0058] The second air volume estimation module (130) estimates the air volume in the supercharging zone. [0059] The second air volume estimation module (130) derives the volume flow currently flowing through the supercharger (50) by applying the temperature upstream of the electric supercharger (50), the pressure upstream of the electric supercharger (50), the pressure downstream of the electric supercharger (50), and the current value of the number of revolutions of the electric supercharger(50) to the compressor map of the electric supercharger (50), and calculating the air volume in the supercharging zone on the basis thereof. [0060] The third air volume estimation unit (140) calculates the intake manifold air volume using the weighting factor detected by means of the weighting factor detection unit (10), the air volume and EGR air volume in the throttling zone which is calculated by means of the first air volume estimation unit (120), and the air volume in the supercharging zone which is calculated by means of the second air volume estimation unit (130). [0061] The learning control module (200) performs additional air volume learning control in order to correct the error that may occur in the air volume estimation module (100). [0062] The learning control module (200) performs proportional control by receiving input of the error of the air flow measured by means of the pressure sensor (not shown) of the intake manifold (60) or the air flow rate measurement sensor (not shown) of the rear end of the air cleaner (20), or the pressure measured by means of the intake manifold cylinder inlet pressure sensor. [0063] The output value of the learning control module (200) can, in the case of the throttling zone, be applied to the effective area which is input into the Saint Venant equation that the air volume estimation module (100) uses for air volume estimation in the throttling zone, and can, in the case of the supercharging zone, be applied to the number of revolutions of the electric supercharger (50) or the upstream pressure of the electric supercharger (50) which the air volume estimation module (100) uses for air volume estimation in the supercharging zone. [0064] In addition, the cumulative error (integral term) among the output values of the learning control module (200) when the engine operating conditions are steady is used in the learning maps (number of engine revolutions, engine load) of each engine operating zone for correcting the effective area in the case of throttling zone, and in the case of the supercharging zone the cumulative error (integral term) is stored in the learning maps (number of engine revolutions, engine load) of each engine operating zone for correcting the number of revolutions of electric supercharger (50) or learning maps (number of engine revolutions, engine load) of each engine operating zone for correcting the upstream pressure of the electric supercharger and then is used for correcting the learning controler output value while driving in each engine operating zone. [0065] With reference to FIG. 6, the learning control module (200) comprises a first learning control unit (210), a second learning control unit (220), and the third learning control unit (230). [0066] The first learning control unit (210) performs air volume learning control for the throttling zone. [0067] The first learning control unit (210) converts the estimated intake manifold air volume (MFL_IM) to an intake manifold pressure model value in order to perform learning control on the error of the estimated intake manifold air volume and the actual intake manifold air volume as described above. [0068] Next, the first learning control unit (210) outputs an effective area correction value of the throttle valve (30) (AR_THR_COR) on the basis of the error of the intake manifold pressure model value and the measured intake manifold pressure. [0069] The effective area correction value of the throttle valve is the sum of the effective area with respect to the degree the throttle valve is open which is input into the first air volume estimation unit (120). Thereby, the air volume estimation error in the throttling zone estimated by means of the first air volume estimation unit (120) can be reduced and learning control can be continuously performed for the air volume estimation error in the throttling zone. [0070] Meanwhile, the first learning control unit (210) stores the cumulative error (integral term) when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) for correcting the effective area. The stored cumulative error when the engine operating conditions are steady can be used to correct the output value of the first learning control unit (210) during driving in each engine operating zone. [0071] The second learning control unit (220) performs air volume learning control in the supercharging zone. [0072] The second learning control unit (220) outputs a revolution number correction value of the electric supercharger (50) on the basis of the error of the intake manifold pressure model value and measurement value which are defined as described above. [0073] The revolution number correction value of the electric supercharger (50) is the sum of the current number of revolutions of electric supercharger (50) which is input into the second air volume estimation unit (130) described. [0074] Thereby, the air volume estimation error in the supercharging zone estimated by means of the second air volume estimation unit (130) can be reduced and learning control can be continuously performed for the air volume estimation error in the supercharging zone. [0075] Meanwhile, the second learning control unit (220) stores the cumulative error when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) for correcting the number of revolutions of electric supercharger (50). [0076] The stored cumulative error when the engine operating conditions are steady can be used to correct the output value of the second learning control unit (220) during driving in each engine operating zone. [0077] The intake manifold pressure measurement value described above can be substituted with a measurement value of the air flow rate sensor, and the error value of the intake manifold pressure model value and measurement value can be substituted with an air volume value. [0078] In another embodiment, the second learning control unit (220) can output the upstream pressure correction value of the electric supercharger (50) on the basis of the error of the intake manifold pressure model value and measurement value. The upstream pressure correction value of the electric supercharger (50) is the sum of the upstream pressure of the electric supercharger (50) which is input into the second air volume estimation unit (130) described above. [0079] Thereby, the air volume estimation error in the supercharging zone estimated by means of the second air volume estimation unit (130) can be reduced and learning control can be continuously performed for the air volume estimation error in the supercharging zone. [0080] In this case, the second learning control unit (220) stores the cumulative error when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) for correcting the upstream pressure value of electric supercharger (50). The stored cumulative error when the engine operating conditions are steady is used to correct the output value of the second learning control unit (220) during driving in each engine operating zone. [0081] The third learning control unit (230) estimates the intake manifold air volume using the value to which learning control of the air volume in the throttling zone and supercharging zone is applied. [0082] Hereinbelow, the air volume estimation method of the electric supercharger system according to an embodiment of the present invention is described in detail with reference to FIGS. 7 to 10. [0083] FIG. 7 is a sequence diagram for an air volume estimation method according to one embodiment of the present invention. [0084] With reference to FIG. 7, the weighting factor detection unit (110) detects the weighting factor (FAC_PRS_AR_THR_CTL) (S110). [0085] In this case, the weighting factor can be defined as the ratio (PQ_IM_UP_THR) between pressure upstream of the throttle valve (PRS_UP_THR) and intake manifold pressure (PRS_DOWN_EL_SCHA) considering the intercooler pressure loss downstream of the electric supercharger. [0086] Furthermore, the weighting factor detection unit (110) determines the pressure ratio (PQ_THR_THD) where the transition starts from the throttling zone to supercharging zone in the zone (PQ_IM_UP_THR < 1) where the psi value is greater than 0 with respect to the psi function in the Saint Venant equation, and defines the transition section window (PQ_THR_THD_WIN). [0087] Next, the weighting factor detection unit (110) calculates the weighting factor (FAC_PRS_AR_THR_CTL) which divides the throttling zone and supercharging zone through the transition section window (PQ_THR_THD_WIN). The process of calculating the weighting factor is the same as the following equation. [0088] The first air volume estimation unit (120) estimates the air volume in the throttling zone (MFL_THR) and EGR air volume (MFL_EGR) (S20). [0089] That is, the first air volume estimation unit (120) calculates the air volume in the throttling zone (MFL_THR) in real-time by applying temperature upstream of the throttle valve (TIG_THR), pressure upstream of the throttle valve (PRS_UP_THR), pressure downstream of the throttle valve (PRS_UP_EL_SCHA), and the effective area (AR_THR) with respect to the current degree the throttle valve (30) is open, to the Saint Venant equation. The process for estimating the air volume in the throttling zone (MFL_THR) is the same as the following equation. [0090] Here, the temperature upstream of the throttle valve (TIG_THR), the pressure upstream of the throttle valve (PRS_UP_THR), and pressure downstream of the throttle valve (PRS_UP_EL_SCHA) can be obtained through modeling or measurement. [0091] The effective area (AR_THR) with respect to the current degree the throttle valve is open can be obtained through experimental values. [0092] In particular, the effective area (AR_THR) with respect to the degree the throttle valve is open can be updated by continuously adding the effective area correction value of the throttle valve input from the first learning control unit (210), and thereby the air volume estimation error in the throttling zone can be reduced. The process for estimating the EGR air volume is the same as the following equation. [0093] Furthermore, the first air volume estimation unit (120) calculates the EGR air volume in real-time by applying the temperature upstream of the EGR valve (TEMP_UP_EGRV), the pressure upstream of the EGR valve (PRS_UP_EGRV), the pressure downstream of the EGR valve (PRS_UP_EL_SCHA), and the effective area (AR_EGRV) with respect to the current degree that the EGR valve is open, to the Saint Venant equation. [0094] The temperature upstream of the EGR valve (TEMP_UP_EGRV), the pressure upstream of the EGR valve (PRS_UP_EGRV), the pressure downstream of the EGR valve (PRS_UP_EL_SCHA) can be obtained through modeling or measurement, while specific value of the effective area (AR_EGRV) with respect to the current degree that the EGR valve is open can be obtained through experimentation. [0095] The second air volume estimation unit (130) estimates the air volume in the supercharging zone (MFL_EL_SCHA) (S130). [0096] The second air volume estimation unit (130) calculates the volume flow (VFL_EL_SCHA) of the air currently flowing in the electric supercharger (50) by applying the temperature upstream of the electric supercharger (50) (TIG_EL_SCHA), the pressure upstream of the electric supercharger (50) (PRS_UP_EL_SCHA), the pressure downstream of the electric supercharger (50) (PRS_DOWN_EL_SCHA), and the current number of revolutions of the electric supercharger (50) (N_EL_SCHA) to the compressor map of the electric supercharger (50) in FIG. 4. [0097] Next, the second air volume estimation unit (130) converts the volume flow (VFL_EL_SCHA) of the air currently flowing in the electric supercharger (50) to an air volume in the supercharging zone (MFL_EL_SCHA) by means of the upstream temperature and pressure values of the electric supercharger (50). [0098] The process of estimating the air volume in the supercharging zone (MFL_EL_SCHA) is the same as the equation below.

[0099] Lastly, the third air volume estimation unit (140) estimates the intake manifold air volume (MFL_IM) (S140). [0100] The third air volume estimation unit (140) calculates the intake manifold air volume (MFL_IM) by using the air volume in the throttling zone and the air volume in the supercharging zone. The process of calculating the intake manifold air volume (MFL_IM) is the same as the equation below. [0101] FIG. 8 is a sequence diagram for an air volume learning control method in the throttling zone according to one embodiment of the present invention. [0102] With reference to FIG. 8, the first learning control unit (210) performs learning control on the air volume in the throttling zone. [0103] The first learning control unit (210) converts the intake manifold air volume (MFL_IM) which is estimated in order to perform learning control of the error between the intake manifold air volume (MFL_IM) estimated as described above and the actual intake manifold air volume into an intake manifold pressure model value (PRS_IM). [0104] Next, the first learning control unit (210) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES). [0105] The first learning control unit (210) receives input of the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES).and outputs an effective area correction value for the throttle valve (30) (AR_THR_COR) and so performs learning control of the air volume estimation error in the throttling zone. [0106] In this case, the first learning control unit (210) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), P-gain, and the effective area correction value (P) of the throttle valve (AR_THR_COR_P) using the weighting factor (S202,S206). Here, the P-gain can be set as at least one of the number of engine revolutions, and the pressure ratio of the upstream pressure of the electric supercharger with respect to the upstream pressure of the throttle valve (PQ_THR, PRS_UP_EL_SCHA/PRS_UP_THR). [0107] Furthermore, the first learning control unit (210) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), I-gain, and the effective area correction value (I) of the throttle valve (AR_THR_COR_I) using the weighting factor (S204,S206). I-gain can be set as at least one of the number of engine revolutions, the effective area correction value (I) of the throttle valve (AR_THR_COR_I) of the previous step, and the pressure ratio of the upstream pressure of the electric supercharger with respect to the upstream pressure of the throttle valve (PQ_THR,PRS_UP_EL_SCHA/PRS_UP_THR). [0108] Note that PI control is described as an example in the present embodiment, and the technical scope of the present invention is not limited thereto. [0109] Next, the first learning control unit (210) calculates the effective area correction valve of the throttle valve (AR_THR_COR) using the effective area correction value (P) of the throttle valve (AR_THR_COR_P) and the effective area correction value (I) of the throttle valve (AR_THR_COR_I) which are calculated as described above, and delivers the calculated effective area correction valve of the throttle valve (AR_THR_COR) to the first air volume estimation unit (120). [0110] Meanwhile, the first learning control unit (210) stores the cumulative error when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) for correcting the effective area (AR_THR_AD_COR), and initializes the effective area correction value (I) of the throttle valve (AR_THR_COR_I) of the previous step at 0 (S212). This is used for correction of the output value of the first learning control module (210) during driving in each engine operating zone. [0111] Meanwhile, the first air volume estimation unit (120) estimates the air volume in throttling zone as has been described above. In this case, the first air volume estimation unit (120) calculates the air volume in the throttling zone by summing the effective area correction valve of the throttle value (AR_THR_COR) received from the first learning control unit (210) and the learning value (AR_THR_AD_COR) for each engine operating zone (number of engine revolutions, engine load) with the effective area with respect to the degree that the throttle valve is open (S208,S210). [0112] The process of estimating the effective area correction value of the throttle valve (AR_THR_COR) and the air volume in the throttling zone is the same as the equation below. [0113] FIG. 9 is a sequence diagram illustrating an example of the air volume learning control method in the supercharging zone according to one embodiment of the present invention. [0114] With reference to FIG. 9, the second learning control unit (220) performs learning control on the air volume in the supercharging zone. [0115] The second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value defined above and the measurement value as an input value. That is, the second learning control unit (220) converts the intake manifold air volume (MFL_IM) which is estimated in order to perform learning control of the error between the estimated intake manifold air volume (MFL_IM) and the actual intake manifold air volume into an intake manifold pressure model value (PRS_IM). [0116] Next, the second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES). [0117] Next, the second learning control unit (220) performs learning control in which input of the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES) is received, and a revolution number correction value for the electric supercharger (50) (N_EL_SCHA_COR) is output, to perform learning control of the air volume error in the supercharging zone. [0118] In this case, the second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), P-gain, and the revolution number correction value (P) of the electric supercharger (50) (N_EL_SCHA_COR_P) using the weighting factor (S222,S226). Here, the P-gain can be set as at least one of the number of engine revolutions, and the pressure ratio of the downstream pressure of the electric supercharger with respect to the upstream pressure of the electric supercharger (PQ_EL_SCHA, PRS_DOWN_EL_SCHA/PRS_UP_EL_SCHA). [0119] In this case, the second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), I-gain, and the revolution number correction value (I) of the electric supercharger (50) (N_EL_SCHA_COR_I) using the weighting factor (S224,S226). Here, I-gain can be set as at least one of the number of engine revolutions, the revolution number correction value (I) of the electric supercharger (50) (N_EL_SCHA_COR_I) of the previous step, and the pressure ratio of the downstream pressure of the electric supercharger with respect to the upstream pressure of the electric supercharger (PQ_EL_SCHA, PRS_DOWN_EL_SCHA/PRS_UP_EL_SCHA). [0120] Next, the second learning control unit (220) calculates the revolution number correction value of the electric supercharger (50) (N_EL_SCHA_COR) using the revolution number correction value (P) of the electric supercharger (50) (N_EL_SCHA_COR_P) and the revolution number correction value (I) of the electric supercharger (50) (N_EL_SCHA_COR_I) which are calculated as described above, and the calculated revolution number correction value of the electric supercharger (50) (N_EL_SCHA_COR) is delivered to the second air volume estimation unit (130). [0121] Meanwhile, the second learning control unit (220) stores the cumulative error when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) for correcting the number of revolutions (N_EL_SCHA_AD_COR), and initializes the revolution number correction value (I) of the electric supercharger (50) (N_EL_SCHA_COR_I) of the previous step at 0 (S232). [0122] Meanwhile, the second air volume estimation unit (130) estimates the air volume in supercharging zone as has been described above. In this case, the second air volume estimation unit (130) can estimate the air volume in the supercharging zone by summing the revolution number correction value of the electric supercharger (50) (N_EL_SCHA_COR) received from the second learning control unit (220) and the learning value of each engine operating zone (number of engine revolutions, engine load) (N_EL_SCHA_AD_COR) with the current value of the number of revolutions of the electric supercharger (50) (S228,S230). [0123] The process of estimating the revolution number correction value of the electric supercharger (50) (N_EL_SCHA_COR) and the air volume in the supercharging zone is the same as the equation below. [0124] FIG. 10 is a sequence diagram illustrating another example of the air volume learning control method in the supercharging zone according to one embodiment of the present invention. [0125] The second learning control unit (220) performs learning control in which the error (PRS_IM_DIF) between the intake manifold pressure model value defined above and the measurement value is taken as an input value. That is, the second learning control unit (220) converts the intake manifold air volume (MFL_IM) which is estimated in order to perform learning control of the error between the estimated intake manifold air volume (MFL_IM) and the actual intake manifold air volume (PRS_IM_MES) into an intake manifold pressure model value (PRS_IM). [0126] The second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES). [0127] Next, the second learning control unit (220) performs learning control in which input of the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES) is received, and an upstream pressure correction value for the electric supercharger (50) (PRS_UP_EL_SCHA_COR) is output, to perform learning control of the air volume error in the supercharging zone. [0128] In this case, the second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), P-gain, and the upstream pressure correction value (P) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_P) using the weighting factor (S242,S246). Here, the P-gain can be set as at least one of the number of engine revolutions, and the pressure ratio of the downstream pressure of the electric supercharger with respect to the upstream pressure of the electric supercharger (PQ_EL_SCHA, PRS_DOWN_EL_SCHA/PRS_UP_EL_SCHA). [0129] In this case, the second learning control unit (220) calculates the error (PRS_IM_DIF) between the intake manifold pressure model value (PRS_IM) and the actual intake manifold pressure (PRS_IM_MES), I-gain, and the upstream pressure correction value (I) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_I) using the weighting factor (S244,S246). Here, I-gain can be set as at least one of the number of engine revolutions, the upstream pressure correction value (I) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_I) of the previous step, and the pressure ratio of the downstream pressure of the electric supercharger with respect to the upstream pressure of the electric supercharger (PQ_EL_SCHA, PRS_DOWN_EL_SCHA/PRS_UP_EL_SCHA). [0130] Next, the second learning control unit (220) calculates the upstream pressure correction value of the electric supercharger (50) (PRS_UP_EL_SCHA_COR) using the upstream pressure correction value (P) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_P) and the upstream pressure correction value (I) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_I) which are calculated as described above, and the calculated upstream pressure correction value of the electric supercharger (50) (PRS_UP_EL_SCHA_COR) is delivered to the second air volume estimation unit (130). [0131] Meanwhile, the second learning control unit (220) stores the cumulative error when the engine operating conditions are steady as a learning value of each engine operating zone (number of engine revolutions, engine load) (PRS_UP_EL_SCHA) for correcting the upstream pressure of the electric supercharger (50), and initializes the upstream pressure correction value (I) of the electric supercharger (50) (PRS_UP_EL_SCHA_COR_I) of the previous step at 0 (S252). [0132] Meanwhile, the second air volume estimation unit (130) estimates the air volume in supercharging zone as has been described above. In this case, the second air volume estimation unit (130) can estimate the air volume in the supercharging zone by summing the upstream pressure correction value of the electric supercharger (50) (PRS_UP_EL_SCHA_COR) received from the second learning control unit (220) and the learning value of each engine operating zone (number of engine revolutions, engine load) (PRS_UP_EL_SCHA_AD_COR) with the upstream pressure of the electric supercharger (50) (S248,S250). [0133] Consequently, the third air volume estimation unit (140) performs learning control as described above using the air volume in the throttling zone (MFL_THR) received from the first air volume estimation unit (120), the EGR air volume (MFL_EGR), the air volume in the supercharging zone (MFL_EL_SCHA) received from the second air volume estimation unit, and the weighting factor (FAC_PRS_AR_THR_CTL), and thus can estimate an intake manifold air volume (MFL_IM) corrected on the basis of the learning control results. [0134] The process for estimating the intake manifold air volume (MFL_IM) is the same as the equation below. [0135] As has been described above, the air volume estimation method for an electric supercharger system according to one aspect of the present invention, compared to conventional methods which only use the Saint Venant equation, is capable of air volume estimation and control in an engine system even when an EGR and electric supercharger system are applied downstream of the throttle valve and can be operated without using an air flow rate sensor, thus enabling the reduction of system costs. [0136] The embodiment described in the present specification can be realized as, for example, a method or process, apparatus, software program, data stream or signal. Despite being discussed only in the context of a single form of embodiment (for example, discussed only as a method), embodiments of the discussed feature can also be realized in other forms (for example, an apparatus or program). Apparatuses can be implemented with appropriate hardware, software and firmware etc. The method can be realized in apparatuses such as processors which are generally called processing devices which, for example, include computers, microprocessors, integrated circuits and programmable logic devices. Processors also include communication devices that facilitate communication of information between end-users such as computers, cell phones, mobile/individual information terminals (personal digital assistants, PDAs) and other devices. [0137] The present invention has been particularly described with reference to the embodiments shown in the drawings, but these are merely illustrative and it should be understood by those skilled in the art that various changes and other equivalent embodiments are possible. Accordingly, the true technical scope of protection of the present invention should be defined by the patent claims below. [Description of the Reference Numerals] 10: Intake pipe 20: Air cleaner 30: Throttle valve 40: EGR supply unit 50: Electric supercharger 60: Intake manifold 70: Intercooler 80: Exhaust manifold 90: Engine 100: Air volume estimation module 110: Weighting factor detection unit 120: First air volume estimation unit 130: Second air volume estimation unit 140: Third air volume estimation unit 200: Learning control module 210: First learning control unit 220: Second learning control unit 230: Third learning control unit