Abstract:
A gear shifting method of a hybrid vehicle may include releasing a clutch and brake of a transmission and determining a neutral condition status, controlling torque of an engine connected to one operational element of a first planetary gear set in a neutral condition, and controlling speed of a first motor/generator connected to the other operational element of the first planetary gear set. Accordingly, a speed of the first and second motor/generator are controlled and a torque of the engine is controlled in a neutral or parking state of a shift lever such that a mode change becomes easy and the torque of the engine is continuously controlled to improve a shift quality and a driving performance and to save fuel, while the neutral or parking state is changed to a drive or reverse state or the drive or reverse state is changed to the neutral or parking state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0123585 filed Dec. 6, 2010, the entire contents of which application is incorporated herein for all purposes by this reference. 
     BACKGROUND OF INVENTION 
     1. Field of Invention 
     The present invention relates to a gear shifting method of a hybrid vehicle that combines an engine and a motor to generate a rotation torque and to transfer the rotation torque to an output shaft through a transmission. 
     2. Description of Related Art 
     Generally, an automatic transmission uses a hydraulic pressure to shift gear in a multi steps so as to output appropriate torque from a rotation torque of an engine/motor according to a driving condition. 
     One type of hybrid vehicles uses two motor/generators (MG) and one engine that are connected through a planetary gear and controls the motor/generator to achieve a continuous variable shifting. 
     Meanwhile, clutches and brakes are released so as to prevent a torque from being transferred to an output shaft of the transmission in a parking (P) or neutral (N) condition. 
     When it is transferred from a parking or neutral condition of a transmission to a drive (D) or reverse (R), slip is formed in the clutch and the brake by a rotation speed difference such that vibration/noise is formed by the frictional force and the durability of the transmission is decreased. 
       FIG. 4  is a table showing a gear shifting method of a conventional hybrid vehicle. 
     Referring to  FIG. 4 , an engine is controlled in an idle speed in a neutral (N) or parking (P). In other words, output torque of the engine is controlled according to an idle target speed. Further, a speed of the first motor/generator is controlled so as to prepare an EVT 1  mode or an EVT 2  mode for a next drive (D) or reverse (R) and an output torque of the second motor/generator is controlled for charging and discharging according to a target torque. 
     Meanwhile, since an engine is controlled to have an idle target speed in a neutral or parking state and an engine is controlled to output a predetermined torque in a driver or reverse state, there is a problem that a shift shock is generated and fuel consumption is increased. 
     The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art. 
     SUMMARY OF INVENTION 
     Various aspects of the present invention provide for a gear shifting method of a hybrid vehicle having advantages of reducing vibration/noise that is generated while an engine is changed to a torque control from a speed control and saving fuel while a transmission is changed to a drive or reverse from a parking or neutral. 
     A gear shifting method of a hybrid vehicle according to various aspects of the present invention may include releasing clutch and brake of a transmission and determining whether a neutral condition is or not, controlling torque of an engine connected to one operational element of a first planetary gear set in a neutral condition, and controlling speed of a first motor/generator connected to the other operational element of the first planetary gear set. 
     A second planetary gear set is disposed at one side of the first planetary gear set and a speed of a second motor/generator that is connected to one operational element of the second planetary gear set is controlled. A torque of the engine is controlled, a speed of the first motor/generator is controlled, and a torque of the second motor/generator is controlled in an EVT 1  mode that the second ring gear of the second planetary gear set is fixed. 
     A torque of the engine is controlled, a speed of the first motor/generator is controlled, and a torque of the second motor/generator is controlled in an EVT 2  mode that a speed of the second ring gear of the second planetary gear set is controlled to be equal to that of the rotation speed of the engine. 
     As stated above, in a gear shifting method of a hybrid vehicle according to the present invention, a torque of the engine is controlled and a speed of the first and second motor/generator is controlled in a parking or neutral state such that a shift shock is minimized and fuel consumption is reduced. 
     That is, a speed of the first and second motor/generator are controlled and a torque of the engine is controlled in a neutral or parking state of a shift lever such that a mode change becomes easy and the torque of the engine is continuously controlled to improve a shift quality and a driving performance and to save fuel, while the neutral or parking state is changed to a drive or reverse state or the drive or reverse state is changed to the neutral or parking state. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an exemplary shift system of a hybrid vehicle according to the present invention. 
         FIG. 2  is a speed diagram showing an EVT 1  mode and EVT 2  mode in an exemplary gear shifting method of a hybrid vehicle according to the present invention. 
         FIG. 3  is a speed diagram showing a parking/neutral state in an exemplary gear shifting method of a hybrid vehicle according to the present invention. 
         FIG. 4  is a table showing a conventional gear shifting method of a hybrid vehicle. 
         FIG. 5  is a table showing an exemplary gear shifting method of a hybrid vehicle according to the present invention. 
         FIG. 6 ,  FIG. 7 , and  FIG. 8  are flowcharts showing an exemplary gear shifting method of a hybrid vehicle according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Referring to  FIG. 1 , a gear shifting system of a hybrid vehicle includes an engine (E), a first planetary gear unit, a second planetary gear unit, a first motor/generator MG 1 , a second motor/generator MG 2 , a first clutch CL 1 , a second clutch CL 2 , a first brake BK 1 , a second brake BK 2 , and a transmission output shaft (TM output). 
     The first planetary gear unit includes a first sun gear S 1  in a center thereof, first pinion gears P 1  that are externally meshed with the first sun gear S 1 , and a first ring gear R 1  that the first pinion gears P 1  are internally meshed therewith, wherein the first carrier C 1  connects the first pinion gears P 1  to rotate centering around the first sun gear S 1 . 
     The second planetary gear unit includes a second sun gear S 2  in a center of thereof, second pinion gears P 2  that are externally meshed with the second sun gear S 2 , and a second ring gear R 2  that the second pinion gears P 2  are internally meshed therewith, wherein the second carrier C 2  connects the second pinion gears P 2  to rotate centering around the second sun gear S 2 . 
     An output shaft of the engine (E) is connected to the first carrier C 1  and the engine (E) rotates the first carrier C 1  centering around the first sun gear S 1 . 
     The first motor/generator MG 1  is disposed to rotate the first ring gear R 1 . Further, the first brake BK 1  is disposed to selectively brake (stop) the first ring gear R 1 . 
     The first sun gear S 1  and the second sun gear S 2  are connected by one shaft to rotate together and the second motor/generator MG 2  is disposed to rotate the second sun gear S 2 . 
     The first clutch CL 1  selectively connects the first carrier C 1  with the first ring gear R 1  such that they rotate or stop together and the second clutch CL 2  selectively connects the first carrier C 1  with the second ring gear R 2  such that they rotate or stop together. 
     The second brake BK 2  is fixed to selectively brake the second ring gear R 2 . Further, the second carrier C 2  is connected to an output shaft (TM output) of a transmission to a torque of the engine (E), the first motor/generator MG 1 , and the second motor/generator MG 2  to a wheel. 
     Referring to an upper side speed diagram of  FIG. 2 , the transmission of the hybrid vehicle performs an electronic variable transmission (EVT) mode, in this case, an EVT 1  mode in a predetermined condition (D or R). 
     As shown, referring to a speed diagram for the EVT 1 , the first ring gear R 1 , the first carrier C 1 , the first and second sun gear S 1  and S 2 , the second carrier C 2 , and the second ring gear R 2  are disposed on a horizontal axis according to a predetermined gear ratio. 
     The first motor/generator MG 1 , the engine (E), and the second motor/generator MG 2  are disposed on a line to form a predetermined speed line and the second motor/generator MG 2 , the output shaft (TM output), and the second ring gear R 2  are disposed on a line to form a predetermined speed line. 
     In the EVT 1  mode, the first brake BK 2  is operated, other brake and clutch are released, and the second ring gear R 2  is braked. However, the transmission output shaft (TM output) has a low speed by the first motor/generator MG 1 , the engine (E), and the second motor/generator MG 2 . 
     Referring to a lower side speed diagram of  FIG. 2 , the transmission of the hybrid vehicle performs an EVT 2  mode in a predetermined condition (D or R). 
     As shown, referring to a speed line diagram for the EVT 2 , the first ring gear R 1 , the first carrier C 1 , the first and second sun gear S 1  and S 2 , the second carrier C 2 , and the second ring gear R 2  are disposed on a horizontal axis according to a predetermined gear ratio. 
     The first motor/generator MG 1 , the engine (E), and the second motor/generator MG 2  are disposed on a line to form a predetermined speed line and the second motor/generator MG 2 , the output shaft (TM output), and the second ring gear R 2  are disposed on a line to form a predetermined speed line. 
     The second clutch CL 2  is operated and the other brake and clutch are released in the EVT 2  mode and a rotation speed of the engine (E) is controlled to be equal to that of the second ring gear R 2 . However, the output shaft (TM output) has a predetermined high speed by the first motor/generator MG 1 , the engine (E), and the second motor/generator MG 2 . 
     Referring to  FIG. 3 , if a parking or neutral is demanded, the transmission releases all clutches and brakes so as to perform parking (P) or neutral (N). 
     As shown, referring to a speed diagram for a parking or neutral condition, the first ring gear R 1 , the first carrier C 1 , the first and second sun gear S 1  and S 2 , the second carrier C 2 , and the second ring gear R 2  is disposed on a horizontal axis according to a predetermined gear ratio. 
     The first motor/generator MG 1 , the engine (E), and the second motor/generator MG 2  forms a predetermined speed along one line and the second motor/generator MG 2 , the output shaft (TM output), and the second ring gear R 2  forms a predetermined speed alone one line. 
     In a parking/neutral mode, all clutches and brakes are released, the output shaft (TM output) rotates according to a speed of the vehicle, the engine (E) is controlled to output a predetermined torque, and the first and second motor/generator MG 1  and MG 2  are controlled to output a predetermined speed. 
     Referring to  FIG. 5 , in a neutral or parking state, the engine is feed back or feed forward controlled to output a target torque and the first and second motor/generator is controlled to output a predetermined speed. 
     Further, in the EVT 1  mode of the drive or reverse, the engine (E) is controlled to output a target torque, the first motor/generator MG 1  is controlled to output a predetermined speed, and the second motor/generator MG 2  is charged or discharged according to a target charging torque. 
     In addition, in the EVT 2  mode of the drive or reverse, the engine (E) is controlled to output a target torque, the first motor/generator MG 1  is controlled to output a predetermined speed, and the second motor/generator MG 2  is charged or discharged according to a target charging torque. 
     Referring to  FIG. 6 , a control is stated and a shift lever position, an engine (E) speed, a speed of the first motor/generator MG 1 , a speed of the second motor/generator MG 2 , a transmission output speed, a demand for operating the engine, a target speed of the engine, and related signals are input in a S 101 . 
     It is determined whether the position of the shift lever is neutral or parking state in a S 102  and it is determined whether the speed of the output shaft of the transmission is larger than a predetermined value that EVT 1  mode is changed to EVT 2 . 
     If the speed of the output shaft of the transmission is less than the predetermined value. S 104  is performed and if the speed is larger than that, S 106  is performed. 
     The speed of the first and second motor/generator (MG 1  and  2 ) is controlled, that is, the MG 1  and  2  are speed controlled to output a predetermined speed such that the speed of the second ring gear R 2  is 0 on the speed diagram in the S 104 . As described above, the torque of the engine (E) is controlled, that is, the engine (E) is torque controlled to output a predetermined torque. 
     The speed of the first and second motor/generator (MG 1  and  2 ) is controlled, that is, the MG 1  and  2  are speed controlled to output a predetermined speed such that the speed of the second ring gear R 2  becomes equal to that of the engine in the speed diagram in the S 106 . As described above, the torque of the engine (E) is controlled to output a predetermined torque. 
     The second motor/generator MG 2  is feedback or feed forward controlled to outputs a torque so as to achieve a predetermined speed in a S 105  and S 107 . 
     Referring to  FIG. 7 , if the engine (E) is demanded to operate in a S 108 , a S 109  is performed and if the engine is not demanded to operate therein, a S 112  is performed. 
     A target sped of the first motor/generator MG 1  is calculated in a S 109  and the first motor/generator MG 1  is feedback or feedforward controlled to output a target torque so as to achieve a predetermined speed in a S 110 . 
     A target torque of the engine (E) is calculated by a predetermined formula in a S 111 . 
     A target torque of the first motor/generator MG 1  is 0 in a S 112  and a target torque of the engine (E) is controlled to output a Zero torque in a S 113 . In other words, the output torque of the engine is 0. 
     Referring to  FIG. 8 , if it is determined that the position of the shift lever is not neutral or parking but drive or reverse, a S 114  is performed. 
     It is determined whether an operating of the engine (E) is demanded in the S 114 . If there is not an demand for the operation of the engine (E), a target torque of the first motor/generator MG 1  is 0 in a S 119 , and a target torque of the engine (E) is 0 in a S 120 . In other words, the output torque is 0. 
     A target speed of the second motor/generator MG 2  is calculated by multiplying a target torque, a final gear ratio, and efficiency thereof in a S 121 . 
     A target speed of the first motor/generator MG 1  is calculated by a predetermined formula in the S 115  and a target torque of the second motor/generator MG 2  is feedback or feedforward controlled to achieve a speed thereof in the S 116 . 
     A target torque of the engine (E) is calculated by a predetermined formula in a S 117  and a target speed of the second motor/generator MG 2  is calculated by multiplying a target torque thereof, a final gear ratio, and efficiency and extracting a target torque of the engine from the multiplied value in a S 118 . 
     The EVT 1  mode is performed in a case that the speed of the output shaft is less than a predetermined value, wherein the second brake BK 2  is operated to stop the second ring gear R 2  in various embodiments of the present invention. 
     The EVT 2  mode is performed in a case that the speed of the output shaft is larger than a predetermined value, wherein the second clutch CL 2  is operated such that the speed of the second ring gear R 2  becomes equal to that of the engine (E). The detailed description for the EVT 1  and EVT 2  mode is omitted in various embodiments of the present invention. 
     In various embodiments of the present invention, the engine is torque controlled in a state that the shift lever for shifting is in the neutral or parking and the mode change becomes easier by using a speed control of the first and second motor/generator and the engine is continuously torque controlled such that the gear shifting quality and the driving performance is improved and the fuel is saved, while the transmission mode is changed to a drive or reverse from the neutral or parking or is changed to a neutral or parking from a drive or reverse. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.