Method for controlling regenerative braking of vehicle

Abstract

A method for controlling regenerative braking of a vehicle is provided, in which a driving area of a motor is decided when shifting gears during regenerative braking, and an amount of regenerative braking is determined based on the decided result. The method includes a first process of deciding whether motor torque is in a constant power mode, a second process of deciding whether the motor torque is in a constant torque mode, and a third process of deciding whether the mode of the motor torque is converted into the constant torque mode from the constant power mode.

Claims

1. A method for controlling a regenerative braking execution when shifting gears in a vehicle during regenerative braking, the method comprising: a first process of deciding whether motor torque is in a constant power mode: a second process of deciding whether the motor torque is in a constant torque mode; and a third process of deciding whether a mode of the motor torque is converted into the constant torque mode from the constant power mode, wherein an amount of regenerative braking is determined based on a decided result of the first to third processes.

2. The method of claim 1, wherein, when the motor torque is in the constant power mode, the regenerative braking amount is determined using motor torque before torque intervention of a transmission control unit (TCU) and a gear ratio during gear shifting in the constant power mode.

3. The method of claim 1, wherein, when the motor torque is in the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyPower=T.sub.m.sub._.sub.BeforeInt*GR.sub.cal, and a gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}=\frac{{}_{\mathrm{Tmin}}}{{}_{\mathrm{TmOut}}},$ wherein GR.sub.cal is the calculated gear ratio during gear shifting, .sub.Tmin is a transmission input speed, .sub.TmOut is a transmission output speed, REGEN.sub.AV.sub._.sub.StadyPower is the amount of regenerative braking in the constant power mode, and T.sub.m.sub._.sub.BeforeInt is motor torque before torque intervention.

4. The method of claim 1, wherein, when the motor torque is in the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyPower=T.sub.m.sub._.sub.BeforeInt*GR.sub.cal*Eff.sub.TM, and a gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}=\frac{{}_{\mathrm{Tmin}}}{{}_{\mathrm{TmOut}}},$ wherein GR.sub.cal is the calculated gear ratio during gear shifting, .sub.Tmin is a transmission input speed, .sub.TmOut is a transmission output speed, REGEN.sub.AV.sub._.sub.StadyPower is the amount of regenerative braking in the constant power mode, T.sub.m.sub._.sub.BeforeInt is motor torque before torque intervention, and Eff.sub.TM is a transmission efficiency.

5. The method of claim 1, wherein the motor torque is in the constant torque mode, the amount of regenerative braking is determined using motor torque before torque intervention of a transmission control unit (TCU) and a gear ratio during gear shifting in the constant torque mode.

6. The method of claim 1, wherein, when the motor torque is in the constant torque mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyTorque=T.sub.m.sub._.sub.BeforeInt*GR.sub.cal, and a gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT},$ wherein GR.sub.cal is the gear ratio during gear shifting in the constant torque mode, GR.sub.before is a gear ratio before gear shifting, is a gear ratio slope in the constant torque mode, REGEN.sub.AV.sub._.sub.StadyTorque is the amount of regenerative braking in the constant torque mode, T.sub.m.sub._.sub.Before Int is motor torque before torque intervention, and T.sub.shift.sub._.sub.end is a shift end time.

7. The method of claim 1, wherein, when the motor torque is in the constant torque mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyTorque=T.sub.m.sub._.sub.BeforeInt*GR.sub.cal*Eff.sub.TM, and a gear ratio during gear shifting uses a value calculated ${\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT},$ wherein GR.sub.cal is the gear ratio during gear shifting in the constant torque mode, GR.sub.before is a gear ratio before gear shifting, is a gear ratio slope in the constant torque mode, REGEN.sub.AV.sub._.sub.StadyTorque is the amount of regenerative braking in the constant torque mode, T.sub.m.sub._.sub.BeforeInt is motor torque before torque intervention, T.sub.shift.sub._.sub.end is a shift end time, and Eff.sub.TM is a transmission efficiency.

8. The method of claim 6, wherein the gear ratio slope in the constant torque mode is determined by $=\frac{{\mathrm{GR}}_{\mathrm{diff}}}{T_{\mathrm{shift}}},$ and a differential gear ratio uses a value calculated by GR.sub.diff=GR.sub.afterGR.sub.before, wherein GR.sub.after is a gear ratio after gear shifting, and T.sub.shift is a shift time.

9. The method of claim 1, wherein, when the mode of the motor torque is converted into the constant torque mode from the constant power mode, the amount of regenerative braking Is determined using a virtual motor torque value, which is fixed to the constant torque mode and a gear ratio during gear shifting in the mode conversion.

10. The method of claim 1, wherein, when the mode of the motor torque is converted into the constant torque mode from the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.ModeChange=T.sub.m.sub._.sub.Virtual*GR.sub.cal, and a gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT},$ wherein REGEN.sub.AV.sub._.sub.ModeChange is the amount of regenerative braking in the mode conversion, T.sub.m.sub._.sub.Virtual is a virtual motor torque value, which is fixed to the constant torque mode, GR.sub.cal is the gear ratio during gear shifting in the mode conversion, GR.sub.before is a gear ratio before gear shifting, is a gear ratio slope in the mode conversion, and T.sub.shift.sub._.sub.end is a shift end time.

11. The method of claim 1, wherein, when the mode of the motor torque is converted into the constant torque mode from the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.ModeChange=T.sub.m.sub._.sub.Virtual*GR.sub.cal*Eff.sub.TM, and a gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT},$ wherein REGEN.sub.AV.sub._.sub.ModeChange is the amount of regenerative braking in the mode conversion, T.sub.m.sub._.sub.Virtual is a virtual motor torque value which is fixed to the constant torque mode, GR.sub.cal is the gear ratio during gear shifting in the mode conversion, Eff.sub.TM is a transmission efficiency, GR.sub.before is a gear ratio before gear shifting, is a gear ratio slope in the mode conversion, and T.sub.shift.sub._.sub.end is a shift end time.

12. The method of claim 10, wherein a gear ratio slope () when the motor torque is in the constant torque mode is used as the gear ratio slope () in the mode conversion, and the gear ratio slope () is calculated by $=\frac{{\mathrm{GR}}_{\mathrm{diff}}}{T_{\mathrm{shift}}},$ wherein GR.sub.diff is a differential gear ratio between before and after gear shifting, and T.sub.shift is a shift time.

13. The method of claim 2, wherein, when the motor torque is in the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyPowerT.sub.m.sub._.sub.BeforeInt*GR.sub.cal, and the gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}=\frac{{}_{\mathrm{Tmin}}}{{}_{\mathrm{TmOut}}},$ wherein GR.sub.cal is the calculated gear ratio during gear shifting, .sub.Tmin is a transmission input speed, .sub.TmOut is a transmission output speed, REGEN.sub.AV.sub._.sub.StadyPower is the amount of regenerative braking in the constant power mode, and T.sub.m.sub._.sub.BeforeInt is the motor torque before the torque intervention.

14. The method of claim 2, wherein, when the motor torque is in the constant power mode, the amount of regenerative braking is determined by REGEN.sub.AV.sub._.sub.StadyPowerT.sub.m.sub._.sub.BeforeInt*GR.sub.cal*Eff.sub.TM, and the gear ratio during gear shifting uses a value calculated by ${\mathrm{GR}}_{\mathrm{cal}}=\frac{{}_{\mathrm{Tmin}}}{{}_{\mathrm{TmOut}}},$ wherein GR.sub.cal is the calculated gear ratio during gear shifting, .sub.Tmin is a transmission input speed, .sub.TmOut is a transmission output speed, REGEN.sub.AV.sub._.sub.StadyPower is the amount of regenerative braking in the constant power mode, T.sub.m.sub._.sub.BeforeInt is the motor torque before the torque intervention, and Eff.sub.TM is a transmission efficiency.

15. The method of claim 7, wherein the gear ratio slope in the constant torque mode is determined by $=\frac{{\mathrm{GR}}_{\mathrm{diff}}}{T_{\mathrm{shift}}},$ and a differential gear ratio uses a value calculated by GR.sub.diff=GR.sub.afterGR.sub.before, wherein GR.sub.after is a gear ratio after gear shifting, and T.sub.shift is a shift time.

16. The method of claim 11, wherein a gear ratio slope () when the motor torque is in the constant torque mode is used as the gear ratio slope () in the mode conversion, and the gear ratio slope () is calculated by $=\frac{{\mathrm{GR}}_{\mathrm{diff}}}{T_{\mathrm{shift}}},$ wherein GR.sub.diff is a differential gear ratio between before and after gear shifting, and T.sub.shift is a shift time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated by the accompanying drawings which are given hereinbeiow by way of illustration only, and thus are not limitative of the present disclosure.

(2) FIG. 1 is a flowchart illustrating a method for controlling regenerative braking when shifting gears in a vehicle having a discrete variable transmission mounted therein according to the related art.

(3) FIG. 2 is a graph illustrating a problem caused by the related art method.

(4) FIG. 3 is a graph illustrating characteristics of a general driving motor for a vehicle.

(5) FIG. 4 is a graph illustrating a result obtained by controlling an amount of regenerative braking in a constant power mode condition of motor torque, as compared with the conventional method, according to the present disclosure.

(6) FIG. 5 is a graph illustrating a result obtained by controlling an amount of regenerative braking in a constant torque mode condition of motor torque, as compared with the conventional method, according to the present disclosure.

(7) FIG. 6 is a flowchart illustrating a selection method of a gear ratio slope when a mode of motor torque is changed in a method for controlling regenerative braking according to the present disclosure.

(8) FIG. 7 is a flowchart illustrating a selection method of motor torque when a mode of motor torque is changed in a method for controlling regenerative braking according to the present disclosure.

(9) FIG. 8 is a graph illustrating a result obtained by controlling an amount of regenerative braking in a mode change condition of motor torque, as compared with the conventional method, according to the present disclosure.

(10) FIG. 9 is a flowchart illustrating a method for controlling regenerative braking of a vehicle.

(11) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

(12) In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

(13) Hereinafter, reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings and described below. While the disclosure will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the disclosure to those exemplary embodiments. On the contrary, the disclosure is 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 disclosure as defined by the appended claims.

(14) The present disclosure provides a method for determining and controlling a regenerative braking amount by considering characteristics of a motor, when shifting gears during regenerative braking of a vebicie having a discrete variable transmission mounted therein. First, torque characteristics of the motor used in regenerative braking will be described.

(15) As known in the art, the motor is generally divided into a constant torque area and a constant power area according to the driving speed of the motor. In this case, the speed of the motor, which determines two driving areas, is referred to as a base speed (base revolution per minute (RPM)).

(16) As shown in FIG. 3, the motor has constant torque characteristics in a driving area of the base speed or less. That is, motor torque is constant in the constant torque area, and the absolute value of motor power (motor torquemotor speed) constantly increases in proportion to motor speed, in addition, the motor has constant power characteristics in a driving area of the base speed or more. That is, the motor power is constant in the constant power area, and the absolute value of the motor torque (motor power/motor speed) decreases in inverse proportion to the motor speed.

(17) A regenerative braking amount estimates motor torque transmitted to a wheel in regenerative braking. The regenerative braking amount may be calculated as shown in Equation 1.
REGEN.sub.AV=T.sub.m*GR*Eff.sub.TM[Equation 1]

(18) Where, REGEN.sub.AV is a regenerative braking amount, T.sub.m is the motor torque, GR is a gear ratio, and Eff.sub.TM is a transmission efficiency.

(19) However, Equation 1 cannot be used during gear shifting due to the following reasons:

(20) First, since the motor torque is decreased by torque intervention of a transmission control unit (TCU) (transmission input torque for smooth gear shifting is requested by the TCU), the motor has other type of motor torque according to a gear shifting situation. Through such a shifting mechanism, it is difficult to estimate the actual torque transmitted to the wheel using the amount of regenerative braking.

(21) Second, the gear ratio Is also changed during gear shifting. Therefore, in a case where the amount of regenerative braking is calculated as shown in Equation 1, it is impossible to estimate the actual regenerative braking torque transmitted to the wheel using the amount of regenerative braking. In addition, hydraulic braking with a relatively slow reaction does not estimate a target value due to a sudden change in the regenerative braking amount, thereby causing a variation in deceleration sensation.

(22) Accordingly, when shifting gears in regenerative braking, the amount of regenerative braking is constantly increased during gear shifting with consideration of the regenerative braking amount before/after gear shifting, so that hydraulic braking can estimate the target value. In this case, the TCU transmits regenerative braking torque as much as the amount of regenerative braking to the wheel through the torque intervention.

(23) A method for constantly increasing the amount of regenerative braking when shifting gears during regenerative braking is as follows:

(24) First, in order to calculate the amount of regenerative braking during gear shifting, motor torque before the torque intervention of the TCU Is used rather than the actual motor torque after the torque intervention of the TCU, Since the motor torque before the torque intervention is changed depending on the motor speed, it is possible to estimate a change in motor torque during gear shifting. Thus, the motor torque before the torque intervention of the TCU is used to calculate the amount of regenerative braking. In this case, the torque intervention of the TCU is a transmission input torque (i.e., motor torque) which is requested by the TCU in order to smoothly shift the gears.

(25) The motor torque (motor torque used in the calculation of the amount of regenerative braking) is divided into a constant power mode, a constant torque mode, and a mode conversion according to the characteristics of the motor. That is, when shifting gears during regenerative braking, the amount of regenerative braking is calculated using the constant power mode, the constant torque mode, and the mode conversion according to the characteristics of the motor. The amount of regenerative braking is appropriately controlled using the value calculated as described above.

(26) A method for controlling (calculating) the amount of regenerative braking in the constant power mode will be described hereinafter.

(27) A gear ratio in the constant power mode uses a gear ratio (GR.sub.cal) during gear shifting, which is calculated using a transmission input speed (.sub.Tmin) and a transmission output speed (.sub.TmOut), closest to the actual gear ratio as shown in the following Equation 2.

(28) The motor torque in the constant power area is changed depending on the motor speed. Hence, when the amount of regenerative braking (REGEN.sub.AV.sub._.sub.StadyPower) is calculated by multiplying the actual gear ratio (GR.sub.cal*Eff.sub.TM) and the motor torque before the torque intervention (T.sub.m.sub._.sub.BeforeInt) as shown in the following Equation 3, the amount of regenerative braking (REGEN.sub.AV.sub._.sub.StadyPower) is constantly increased, so that it is possible to ensure deceleration sensation during gear shifting.

(29) $\begin{array}{cc}{\mathrm{GR}}_{\mathrm{cal}}=\frac{{}_{\mathrm{Tmin}}}{{}_{\mathrm{TmOut}}}& \left[\mathrm{Equation}2\right]\\ {\mathrm{REGEN}}_{\mathrm{AV\_StadyPower}}=T_{\mathrm{m\_BeforeInt}}*{\mathrm{GR}}_{\mathrm{cal}}*{\mathrm{Eff}}_{\mathrm{TM}}& \left[\mathrm{Equation}3\right]\end{array}$

(30) Here, GR.sub.cal is the calculated gear ratio during gear shifting, .sub.Tmin is the transmission input speed, .sub.TmOut is the transmission output speed, REGEN.sub.AV.sub._.sub.StadyPower is the amount of regenerative braking in the constant power mode, T.sub.m.sub._.sub.BeforeInt is the motor torque before the torque intervention, and Eff.sub.TM is a transmission efficiency.

(31) In addition, the amount of regenerative braking (REGEN.sub.AV.sub._.sub.StadyPower) in the constant power mode may be caiculated as shown in the foilowing Equation 3-1 without considering the transmission efficiency. In case where the amount of regenerative braking in the constant power mode (REGEN.sub.AV.sub._.sub.StadyPower) is calculated as shown in Equation 3 by considering the transmission efficiency, a more accurate value is calculated.
REGEN.sub.AV.sub._.sub.StadyPower=T.sub.m.sub.Before Int*GR.sub.cal[Equation 3-1]

(32) Referring to FIG. 4, the amount of regenerative braking during gear shifting is controlled in a constant power mode condition of the motor torque. As a result, in a case where the amount of regenerative braking is controlled based on Equation 3, the amount of regenerative braking is constantly increased, so that it is possible to ensure the deceleration sensation during gear shifting, as compared with the related art.

(33) Next, a method for controlling (calculating) the amount of regenerative braking in the constant torque mode will be described. The gear ratio in the constant torque mode uses a gear ratio during gear shifting (GR.sub.cal) increased using a gear ratio slope () of the following Equation 5 in consideration of a differential ratio (or a differential gear ratio) before/after transmission (GR.sub.diff of Equation 4). In this case, the gear ratio during gear shifting (GR.sub.cal) may be calculated as shown in the following Equation 6.

(34) The motor torque before the torque intervention (T.sub.m.sub._.sub.BeforeInt) is not changed regardless of the motor speed, and the gear ratio during gear shifting (GR.sub.cal) is calculated as shown in the following Equation 6. Thus, in a case where the amount of regenerative braking (REGEN.sub.AV.sub._.sub.StadyTorque) is calculated by multiplying the motor torque before the torque intervention (T.sub.m.sub._.sub.BeforeInt) and the calculated gear ratio during gear shifting (GR.sub.cal), the amount of regenerative braking (REGEN.sub.AV.sub._.sub.StadyTorque) is constantly increased, so that it is possible to ensure the deceleration sensation during gear shifting.

(35) $\begin{array}{cc}{\mathrm{GR}}_{\mathrm{diff}}={\mathrm{GR}}_{\mathrm{after}}-{\mathrm{GR}}_{\mathrm{before}}& \left[\mathrm{Equation}4\right]\\ =\frac{{\mathrm{GR}}_{\mathrm{diff}}}{T_{\mathrm{shift}}}& \left[\mathrm{Equation}5\right]\\ {\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT}& \left[\mathrm{Equation}6\right]\\ {\mathrm{REGEN}}_{\mathrm{AV\_StadyTorque}}=T_{\mathrm{m\_Beforeint}}*{\mathrm{GR}}_{\mathrm{cal}}*{\mathrm{Eff}}_{\mathrm{TM}}& \left[\mathrm{Equation}7\right]\end{array}$

(36) Where, GR.sub.diff is the differential ratio, GR.sub.after is the gear ratio after gear shifting, GR.sub.before is the gear ratio before gear shifting, is the gear ratio slope in the constant torque mode, T.sub.shift is the shift time, GR.sub.cal is the calculated gear ratio during gear shifting, REGEN.sub.AV.sub._.sub.StadyTorque is the amount of regenerative braking in the constant torque mode, T.sub.m.sub._.sub.BeforeInt is the motor torque before the torque intervention, Eff.sub.TM is the transmission efficiency, and T.sub.shift.sub._.sub.end is the shift end time.

(37) The amount of regenerative braking in the constant torque mode (REGEN.sub.AV.sub._.sub.StadyTorque) may be calculated as shown in the following Equation 7-1 in consideration of the transmission efficiency. In a case where the amount of regenerative braking in the constant torque mode (REGEN.sub.AV.sub._.sub.StadyTorque) is calculated as shown in Equation 7 by considering the transmission efficiency, a more exact value is calculated.
REGEN.sub.AV.sub._.sub.StadyTorque=T.sub.M.sub._.sub.BeforeInt*GR.sub.cal[Equation 7-1]

(38) Referring to FIG. 5, the amount of regenerative braking during the gear shifting is controlled in a constant torque mode condition of the motor torque. As a result, in a case where the amount of regenerative braking is controlled based on the value calculated through Equation 7, the amount of regenerative braking is constantly increased. Therefore, it is possible to ensure the deceleration sensation during gear shifting, as compared with the related art.

(39) A method for controlling the amount of regenerative braking in the mode conversion will be described hereinafter. In other words, a method for controlling the amount of regenerative braking when a mode of the motor is converted from the constant power mode to the constant torque mode will be described.

(40) In a case where the motor torque enters into the constant torque mode from the constant power mode according to a change in motor speed when shifting gears during regenerative braking, gear shifting is mostly ended, and simultaneously, the motor torque again enters into the constant power mode from the constant torque mode. If the motor speed is decreased in the constant power mode, the absolute value of the motor torque is increased, but the motor torque in the constant torque mode is maintained regardless of the motor speed. Hence, in the mode conversion of the motor, the gear ratio during gear shifting is calculated by distinguishing the constant torque mode from the constant power mode, and the regenerative braking amount is controlled using the calculated gear ratio during gear shifting.

(41) As shown in FIG. 6, during the gear shifting (S20), it is decided whether the motor torque enters into the constant torque mode or the constant torque area (S21). In a case where the motor torque enters into the constant torque mode, the gear ratio slope (, hereinafter, referred to as a constant torque gear ratio slope) of Equation 5 is selected as a gear ratio slope () in the mode conversion by considering the differential ratio before/after gear shifting (see Equation 2) (S22), so that the gear ratio during gear shifting is increased with the constant torque gear ratio slope (). When the motor torque does not enters into the constant torque mode, i.e., when the motor torque is in the constant power mode, the gear ratio slope (, hereinafter, referred to as a constant power gear ratio slope) which is a value derived through experiments is selected as the gear ratio slope () in the mode conversion (S23), so that the gear ratio during gear shifting is increased with the constant power gear ratio slope ().

(42) That is, one of the constant torque gear ratio slope () and the constant power gear ratio slope () is used as the gear ratio slope () in the mode conversion, as the gear ratio slope (or gear ratio increase slope) to calculate the amount of regenerative braking. The gear ratio during gear shifting (GR.sub.cal) in the mode conversion may be calculated as shown in the following Equation 8.

(43) $\begin{array}{cc}{\mathrm{GR}}_{\mathrm{cal}}={\mathrm{GR}}_{\mathrm{before}}+{}_{T=0}^{T_{\mathrm{shift\_end}}}\mathrm{dT}& \left[\mathrm{Equation}8\right]\end{array}$

(44) Where, GR.sub.cal is the gear ratio during gear shifting in the mode conversion, GR.sub.before is the gear ratio before gear shifting, is the gear ratio slope in the mode conversion, and T.sub.shift.sub._.sub.end is a shift end time.

(45) The motor torque before the torque intervention of the TCU is used as the motor torque in the mode conversion, in the mode conversion, the motor torque during gear shifting mostly enters into the constant torque mode from the constant power mode, and then again enters into the constant power mode as the gear shifting is ended.

(46) According to the present disclosure, if is decided that the mode conversion of the motor torque has occurred when the motor torque during gear shifting enters into the constant torque mode from the constant power mode. In the mode conversion, the motor torque is driven in the constant torque mode from the constant power mode and then again enters into the constant power mode. Thus, a fixed motor torque value is used when the motor torque is assumed to be in the constant torque mode when the motor torque reenters into the constant power mode. The gear ratio during gear shifting also uses the gear ratio calculated using the constant torque gear ratio slope () which is the gear ratio slope in the constant torque mode (see Equation 8).

(47) The fixed value is used by assuming that the motor torque is in the constant torque mode because it is not easy to estimate an exact shift end time due to the influence of the shift time, road condition, and any change in environment. Since the motor is driven in the constant torque area at an actual shift start time, the motor torque value is fixed to the actual shift start time. Therefore, the linearity of the regenerative braking amount and the regenerative braking torque transmitted to the wheel can be estimated as close as the actual values by assuming that the motor torque is in the constant torque mode and the gear ratio slope is the constant torque gear ratio slope ().

(48) Referring to FIG. 7, when shifting gears during regenerative braking (S30), it is decided whether the mode conversion of the motor torque occurs (S31). When the mode is converted into the constant power mode from the constant torque mode, a virtual motor torque (T.sub.m.sub._.sub.Virtual) which is fixed to the constant torque mode during gear shifting, is used as the motor torque (S32), and the amount of regenerative braking is calculated using the virtual motor torque value.

(49) Subsequently, it is decided whether gear shifting is ended while controlling the amount of regenerative braking (S33). When gear shifting is ended, motor torque before the torque intervention is used (S34). When gear shifting is not ended (i.e., during gear shifting), the virtual motor torque (T.sub.m.sub._.sub.Virtual) which is fixed to the constant torque mode, is used as the motor torque during gear shifting (S32).

(50) When the mode is not converted into the constant torque mode from the constant power mode by deciding whether the mode conversion of the motor torque occurs during gear shifting, i.e., when the mode does not convert in the constant torque mode or in the constant power mode, the motor torque before torque intervention is used as the motor torque during gear shifting.

(51) When the regenerative braking amount in the mode conversion (REGEN.sub.AV.sub._.sub.ModeChange) is calculated by multiplying the virtual motor torque (T.sub.m.sub._.sub.Virtual) value and the calculated gear ratio during gear shifting (GR.sub.cal), the amount of regenerative braking in the mode conversion (REGEN.sub.AV.sub._.sub.ModeChange) is constantly increased, so that if is possible to ensure the deceleration sensation,
REGEN.sub.AV.sub._.sub.ModeChange=T.sub.m.sub._.sub.Virtual*GR.sub.cal*Eff.sub.TM[Equation 9]

(52) Where, REGEN.sub.AV.sub._.sub.ModeChange is the amount of regenerative braking, T.sub.m.sub._.sub.Virtual is the virtual motor torque which is fixed to the constant torque mode, GR.sub.cal is the calculated gear ratio during gear shifting, and Eff.sub.TM is the transmission efficiency,

(53) The amount of regenerative braking in the mode conversion (REGEN.sub.AV.sub._.sub.ModeChange) may be calculated as shown in the following Equation 9-1 without considering the transmission efficiency. In a case where the amount of regenerative braking in the mode conversion (REGEN.sub.AV.sub._.sub.ModeChange) is calculated as shown in Equation 9 by considering the transmission efficiency, a more accurate value is calculated.
REGEN.sub.AV.sub._.sub.ModeChange=T.sub.m.sub._.sub.Virtual*GR.sub.cal[Equation 9-1]

(54) Referring to FIG. 8, the amount of regenerative braking during gear shifting is controlled in a mode conversion condition of the motor torque. As a result, in a case where the amount of regenerative braking is controlled based on the value calculated through Equation 9, the regenerative braking amount is constantly increased, thus ensuring the deceleration sensation during gear shifting, as compared with the related art.

(55) Hereinafter, a method for controlling a regenerative braking amount when shifting gears in a vehicle will be described with reference to FIG. 9.

(56) As shown in FIG. 9, if a driver's braking intention is input (S100), a total braking amount is determined based on the driver's braking intention (S110). A regenerative braking allowance amount in the total braking amount is determined (S120), and it is then decided whether regenerative braking is possible (S130).

(57) When it is determined that the regenerative braking is impossible, a hydraulic braking amount is determined similar to the total braking amount. Once it is decided that the regenerative braking is possible, it is decided whether gear shifting of the vehicle occurs (S140), and the amount of regenerative braking is controlled according to a decided result.

(58) Here, the regenerative braking allowance amount is the maximum braking amount which can be generated through the regenerative braking of the vehicle. The amount of regenerative braking is the actual braking amount which is generated through the regenerative braking in the total braking amount determined by the driver's braking intention during vehicle braking. The amount of regenerative braking is determined and controlled as the regenerative braking allowance amount or less.

(59) When there is no gear shifting during regenerative braking, the amount of regenerative braking is calculated/determined (S210) using the actual motor torque and the actual gear ratio (S150). When shifting the gears during the regenerative braking, if is decided whether the motor torque enters into the constant power mode (S160).

(60) When the motor torque enters into the constant power mode, i.e., when the motor torque is in the constant power mode, the regenerative braking amount is determined (S210) using the motor torque before the torque intervention of the TCU and the gear ratio during gear shifting, calculated using and Equation 2 (S170).

(61) In other words, when the motor torque enters into the constant power mode, the amount of regenerative braking is determined using the motor torque before the torque intervention of the TCU and the gear ratio calculated using the transmission input speed and the transmission output speed according to Equation 2. In the constant power mode condition of the motor torque, the amount of regenerative braking may be calculated using Equation 3.

(62) In a case where the motor torque does not enter into the constant power mode, it is decided whether the motor torque enters into the constant torque mode (S180). When the motor torque enters into the constant torque mode, i.e., when the motor torque is in the constant torque mode, the amount of regenerative braking is determined (S210) using the motor torque before the torque intervention of the TCU and the gear ratio during gear shifting calculated using Equation 6 (S190). In the constant torque mode condition of the motor torque, the amount of regenerative braking may be calculated using Equation 7.

(63) In a case where the motor torque does not enters into the constant torque mode, it is decided that the motor torque is under mode conversion (S200), the amount of regenerative braking is determined (S210) using the virtual motor torque which is fixed to the constant torque mode, and the gear ratio during gear shifting, calculated using Equation 8 (S200). In the mode conversion condition of the motor torque, the amount of regenerative braking may be calculated using Equation 9.

(64) After the amount of regenerative braking is determined through the aforementioned procedure when shifting the gears during the regenerative braking (S210), other braking amount except the determined amount of regenerative braking is determined as the hydraulic braking amount (S220). That is, other braking amount obtained by subtracting the determined amount of regenerative braking from the total braking amount is determined as the hydraulic braking amount.

(65) The regenerative braking and the hydraulic braking are controlled according to the regenerative braking amount and the hydraulic braking amount, determined as described above, thus performing stable braking of the vehicle.

(66) In the method for controlling regenerative braking according to the present disclosure, it is possible to maximize regenerative braking of the vehicle by solving a problem of the related art hybrid vehicle having the discrete variable transmission mounted therein, where braking is limited due to variation in deceleration sensation when shifting the gears during regenerative braking.

(67) Accordingly, it is possible to remarkably improve fuel efficiency without any increase in cost and to minimize a change in deceleration sensation, thereby ensuring user's safety and drivability.

(68) The disclosure has been described in detail with reference to exemplary embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.