Abstract:
A control method of a hybrid vehicle that includes engages a second clutch and in response outputs a torque through an output shaft that is connected to the second carrier via torque supplied from an engine and a first and second motor-generators. Accordingly, the speed of the engine is controlled via the first motor-generator, and a torque of an output shaft is control via the second motor-generator. Accordingly, the second motor-generator is used to control an operating point of the engine so that a base motor torque is effectively set.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation in Part of U.S. patent application Ser. No. 13/534,777, filed Jun. 27, 2012, which claims priority to and the benefit of Korean Patent Application No. 10-2011-0134871 filed in the Korean Intellectual Property Office on Dec. 14, 2011, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a control method for a hybrid vehicle that enables a continuous shift of a transmission by using an engine, a first motor-generator, and a second motor-generator. 
     (b) Description of the Related Art 
     Generally, an automatic transmission utilizes hydraulic pressure to shift gears in multiple steps to output the appropriate amount of torque from a rotation torque of an engine/motor based on various driving conditions. Some hybrid vehicles utilize two motor/generators (MG) and one engine that are connected through a planetary gear. In particular, the motor/generator is control in order to achieve a continuously variable shifting. 
     The engine, the first and second motor/generators, and two planetary gear sets are used to continuously vary the output speed of a transmission according to various driving conditions. Here, the speeds of each the first and second motor/generators are controlled. 
     The first motor/generator is speed-controlled according to the driving conditions of the engine and the second motor/generator is torque-controlled together with the engine to control the entire torque output. Meanwhile, while the first motor-generator is being used to control a driving point control of the engine, in a flexible hybrid system (FHS4) there is still no method for effectively setting a base motor torque. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a control method for a hybrid vehicle having advantages of effectively setting a base motor torque when a first motor-generator in a flexible hybrid system (FHS4) is used to control an operating point of an engine. 
     In an exemplary embodiment of the present invention, a control method of a hybrid vehicle includes i.) a first planetary gear set having a first sun gear, a first planetary gear, a first ring gear, and a first carrier, ii.) a second planetary gear set having a second sun gear, a second planetary gear, a second ring gear, and a second carrier, iii.) an engine of which an output shaft thereof is connected to the first carrier, iv.) a first motor-generator that is configured to rotate the first ring gear, v.) a second motor-generator that is connected to the second sun gear to rotate the second sun gear and the first sun gear, vi.) a first brake configured to brake the first ring gear, vii.) a second brake configured to brake the second ring gear, viii.) a first clutch that selectively connects the first ring gear with the first carrier, and ix.) a second clutch that selectively connects the first carrier with the second ring gear. 
     In particular, in the exemplary embodiment of the present invention, the second clutch is engaged and torque is output through an output shaft, outputting torque through an output shaft that is connected to the second carrier via torque supplied from engine and the first and second motor-generators. Then the speed of the engine is controlled via the first motor-generator, and the torque of the output shaft is controlled via the second motor-generator. 
     The rotation speed of the first motor-generator is controlled such that the engine reaches a predetermined target speed. 
     The target speed of the engine may be calculated by Formula 2 below. 
     
       
         
           
             
               
                 
                   
                     ω 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             1 
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         ENG 
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         out 
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     A torque of the output shaft may be calculated by Formula 3 below. 
     
       
         
           
             
               
                 
                   
                     τ 
                     out 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
               
             
           
         
       
     
     A target torque for a speed control of the first motor-generator may be calculated by Formulas 4, 5, and 6 below. 
     
       
         
           
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     SpdControl 
                   
                   = 
                   
                     
                       τ 
                       
                         MG 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       
                         F 
                         / 
                         F 
                       
                     
                     + 
                     
                       τ 
                       
                         MG 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       
                         F 
                         / 
                         B 
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       F 
                       / 
                       F 
                     
                   
                   = 
                   
                     
                       
                         
                           K 
                           
                             
                               F 
                               / 
                               F 
                             
                             , 
                             ENG 
                           
                           
                             EVT 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             - 
                             
                               
                                 R 
                                 1 
                               
                               
                                 1 
                                 + 
                                 
                                   R 
                                   1 
                                 
                                 + 
                                 
                                   R 
                                   2 
                                 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         τ 
                         ENG 
                       
                     
                     + 
                     
                       
                         
                           K 
                           
                             
                               F 
                               / 
                               F 
                             
                             , 
                             
                               MG 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           
                             EVT 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             - 
                             
                               
                                 
                                   R 
                                   1 
                                 
                                 ⁢ 
                                 
                                   R 
                                   2 
                                 
                               
                               
                                 1 
                                 + 
                                 
                                   R 
                                   1 
                                 
                                 + 
                                 
                                   R 
                                   2 
                                 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         τ 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       F 
                       / 
                       B 
                     
                   
                   = 
                   
                     
                       f 
                       PI 
                       
                         EVT 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           ω 
                           
                             MG 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           Target 
                         
                         - 
                         
                           ω 
                           
                             MG 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
           
         
       
     
     A target torque for a torque control of the second motor-generator may be calculated by a below formula 8. 
     
       
         
           
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     Base 
                   
                   = 
                   
                     
                       
                         1 
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                       
                       ⁢ 
                       
                         τ 
                         out 
                         Demand 
                       
                     
                     + 
                     
                       
                         1 
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         τ 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     As described above, in a control method for a hybrid vehicle according to the present invention, the second motor-generator is used to control an operating point of the engine such that a base motor torque is effectively set. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a hybrid vehicle gear shifting system according to an exemplary embodiment of the present invention. 
         FIG. 2  is a graph showing a hybrid gear shifting system as a lever type according to an exemplary embodiment of the present invention. 
         FIG. 3  is a graph showing a vehicle speed, an engine rotation speed, and a wheel torque according to an exemplary embodiment of the present invention. 
         FIG. 4  shows formulas for controlling a hybrid vehicle gear shifting system according to an exemplary embodiment of the present invention. 
         FIG. 5  is a flowchart for controlling a first motor-generator for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention. 
         FIG. 6  is a flowchart for controlling a second motor-generator for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention. 
         FIG. 7  shows formulas for controlling first and second motor-generators for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
         
           
             E: engine 
             MG 1 : first motor-generator 
             MG 2 : second motor-generator 
             PG 1 : first planetary gear set 
             R 1 : first ring gear, 
             S 1 : first sun gear 
             P 1 : first planetary gear 
             C 1 : first carrier 
             PG 2 : second planetary gear set 
             R 2 : second ring gear, 
             S 2 : second sun gear 
             P 2 : second planetary gear 
             C 2 : second carrier 
             BK 1 : first brake 
             BK 2 : second brake 
             CL 1 : first clutch 
             CL 2 : second clutch 
             OS 1 : first output shaft 
             OS 2 : second output shaft 
             CU: Control Unit 
           
         
       
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
     It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
     Furthermore, control logic executed by a control unit of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN). The processes executed below may be executed using a plurality of units or a single unit. Thus, the illustrative embodiment is not intended to be limited as such. 
       FIG. 1  is a schematic diagram of a hybrid vehicle gear shifting system according to an exemplary embodiment of the present invention. As shown in  FIG. 1 , a hybrid vehicle includes an engine  100 , a first planetary gear set PG 1 , a second planetary gear set PG 2 , a first motor-generator MG 1 , a first brake BK 1 , a first clutch CL 1 , a second clutch CL 2 , a second brake BK 2 , and a second motor-generator MG 2 . 
     The first planetary gear set PG 1  includes a first sun gear S 1 , a first planetary gear P 1 , a first ring gear R 1 , and a first carrier C 1 , and an output shaft of the engine  100  is configured to rotate the first sun gear S 1 . The output shaft of the first motor-generator MG 1  is configured to rotate the first ring gear R 1 , and the first brake BK 1  selectively brakes the output shaft of the first motor-generator MG 1  and the rotation of the first ring gear R 1 . 
     The first clutch CL 1  selectively connects the first ring gear R 1  with the first carrier C 1 , and the second clutch CL 2  selectively connects the first carrier C 1  with the second ring gear R 2 . The second brake BK 2  is configured to brake the second ring gear R 2 , and the second carrier C 2  is connected to the output shaft. The first sun gear S 1  is directly connected to the second sun gear S 2 , and the second motor-generator MG 2  is configured to rotate the second sun gear S 2 . 
     In a complex divergence condition of the exemplary embodiment of the present invention, the second clutch CL 2  is operated such that the first carrier C 1  is directly connected to the second carrier C 2 , and the engine  100 , the first motor-generator MG 1 , and the second motor-generator MG 2  are operated so that a torque is outputted through the second carrier C 2 . 
       FIG. 2  is a lever graph showing a hybrid gear shifting system according to an exemplary embodiment of the present invention. Referring to  FIG. 2 , the first clutch CL 1  is operated so that rotation speed of the second ring gear R 2  is equal to that of the engine  100 , and the driving point control (e.g., speed control) of the engine  100  is performed by the first motor-generator MG 1 , while the second motor-generator MG 2  is controlled by a requested output torque. 
       FIG. 3  is a graph showing a vehicle speed, an engine rotation speed, and a wheel torque according to an exemplary embodiment of the present invention. The horizontal axis denotes time and the vertical axis denotes torque or speed. A vehicle speed, an engine rotation speed (target, present) and a wheel torque (target, present) are shown as well. The wheel torque is proportional to the torque of the output shaft. 
       FIG. 4  shows formulas for controlling a hybrid vehicle gear shifting system according to an exemplary embodiment of the present invention. The speed of the engine  100  is calculated, by e.g. a control unit installed in the vehicle, by the formulas below. 
     
       
         
           
             
               
                 
                   
                     
                       ( 
                       
                         
                           I 
                           ENG 
                         
                         + 
                         
                           I 
                           
                             C 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         + 
                         
                           I 
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                       
                       ) 
                     
                     ⁢ 
                     
                       
                         ω 
                         . 
                       
                       ENG 
                     
                   
                   = 
                   
                     
                       τ 
                       ENG 
                     
                     + 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             1 
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                     - 
                     
                       
                         R 
                         2 
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
             
               
                 
                   
                     ω 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   = 
                   
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             1 
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         ENG 
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         out 
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     In particular, R 1  corresponds to a gear ratio of a ring gear of a first planetary gear set  1 , R 2  corresponds to a gear ratio of a ring gear of a second planetary gear set  1 , ω out  corresponds to an output velocity of the second carrier gear and ω ENG  corresponds to an output velocity of the engine. 
     Further, the output shaft torque that is outputted by the system is calculated, by e.g. a control unit installed in the vehicle, by Formula 3 below. 
     
       
         
           
             
               
                 
                   
                     τ 
                     out 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
           
         
       
     
     In particular, T MG2  corresponds to a torque of the second motor minus an inertia torque of the second motor, and T MG1  corresponds to a torque of the first motor minus an inertia torque of the first motor. 
       FIG. 5  is a flowchart for controlling a first motor-generator for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention, and  FIG. 6  is a flowchart for controlling a second motor-generator for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5  and  FIG. 6 , in a complex divergence mode of FHS4 according to an exemplary embodiment of the present invention, when the engine  100  is speed-controlled by the first motor-generator MG 1 , a PI torque is generated through an error from a target speed, and a feed-forward torque that is related to a torque of the engine  100  and a torque of the second motor-generator MG 2  is further added thereto. Simultaneously, the torque of the second motor-generator MG 2  is generated to satisfy the demand torque of the driver. 
       FIG. 7  shows formulas for controlling first and second motor-generators for controlling a hybrid gear shifting system according to an exemplary embodiment of the present invention. 
     A demand torque of the first motor-generator MG 1  is calculated, by at least one control unit installed in the vehicle, by following Formulas 4, 5, 6, and 7. 
     
       
         
           
             
               
                 
                   
                     τ 
                     out 
                   
                   = 
                   
                     
                       
                         ( 
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         ) 
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         T 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
               
             
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       F 
                       / 
                       F 
                     
                   
                   = 
                   
                     
                       
                         
                           K 
                           
                             
                               F 
                               / 
                               F 
                             
                             , 
                             ENG 
                           
                           
                             EVT 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             - 
                             
                               
                                 R 
                                 1 
                               
                               
                                 1 
                                 + 
                                 
                                   R 
                                   1 
                                 
                                 + 
                                 
                                   R 
                                   2 
                                 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         τ 
                         ENG 
                       
                     
                     + 
                     
                       
                         
                           K 
                           
                             
                               F 
                               / 
                               F 
                             
                             , 
                             
                               MG 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           
                             EVT 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ⁡ 
                         
                           ( 
                           
                             - 
                             
                               
                                 
                                   R 
                                   1 
                                 
                                 ⁢ 
                                 
                                   R 
                                   2 
                                 
                               
                               
                                 1 
                                 + 
                                 
                                   R 
                                   1 
                                 
                                 + 
                                 
                                   R 
                                   2 
                                 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         τ 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       F 
                       / 
                       B 
                     
                   
                   = 
                   
                     
                       f 
                       PI 
                       
                         EVT 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           ω 
                           
                             MG 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           Target 
                         
                         - 
                         
                           ω 
                           
                             MG 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
             
               
                 
                   
                     ω 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     Target 
                   
                   = 
                   
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             1 
                           
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         ENG 
                         Target 
                       
                     
                     - 
                     
                       
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         ω 
                         out 
                       
                     
                   
                 
               
               
                 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   7 
                 
               
             
           
         
       
     
     In particular, τ FIF / MG1  corresponds to a feed forward torque of the first motor generator, τ FIB/MG1  corresponds to feedback torque of the first motor generator, K EVT2   /FIF/ENG  corresponds to a torque gain in a EVT 2  mode for an engine, K EVT2   /FIF/ENG  corresponds to a torque gain in a EVT 2  mode for the second motor generator, τ MG2  corresponds to an output torque of the first motor generator, τ ENG  corresponds to an output torque of the engine, f EVT2  corresponds to a function of the EVT 2  mode ω Target   MG1  corresponds to a target velocity of the first motor generator and ω MG1  corresponds to an actual velocity of the first motor generator. 
     The demand torque of the second motor-generator MG 2  is calculated, likewise, by the following Formula 8. 
     
       
         
           
             
               
                 
                   
                     τ 
                     
                       MG 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     Base 
                   
                   = 
                   
                     
                       
                         1 
                         
                           1 
                           + 
                           
                             R 
                             2 
                           
                         
                       
                       ⁢ 
                       
                         τ 
                         out 
                         Demand 
                       
                     
                     + 
                     
                       
                         1 
                         
                           R 
                           1 
                         
                       
                       ⁢ 
                       
                         τ 
                         
                           MG 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                     
                   
                 
               
               
                 
                   Formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     In particular, τ Demand   out  corresponds to a demand torque requested to be out and τ MG1  corresponds to a torque of the first motor generator. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.