Method and system for controlling a gear change in response to a change in driving mode

Abstract

A method for controlling a gear change in response to a change in a driving mode, the method comprising: (a) determining a maximum number of permissible low gearshift steps according to a result of determining a state of a transmission based on information about an accelerator pedal operation (a signal from an accelerator pedal position sensor (APS; 20)) when a request to change a driving mode to a sport mode is detected during driving, (b) calculating a turbine wheel speed expected immediately after the gear change for each stage included in the maximum number of permissible low gear shift stages using a current speed of an output shaft of the transmission and a gear ratio of each stage, and comparing the calculated expected turbine wheel speed (a speed of an input shaft of the transmission) with a preset permissible turbine wheel speed for each stage, (c) setting the lowest gear shift step from gear shift steps for which the expected turbine speed and the permissible turbine speed satisfy a predetermined condition, such that it is a target gear shift step within the maximum number of permissible low gear shift steps, and (d) executing a gear shift control to downshift a current gear shift stage to the target gear shift stage, wherein in (a) determining the maximum number of permissible low gearshift steps, if an output signal of an APS (20) is at or above a set value at a time when the request to change the driving mode is detected, it is determined that the transmission is in an engaged state, and if the output signal of the APS (20) is below the set value, it is determined that the transmission is in a disengaged state, wherein, when the transmission is in the engaged state, the number of low gearshift steps lower than a set gearshift step determined via a gearshift pattern associated with a sport mode is determined as the maximum number of permissible low gearshift steps, and when the transmission is in the disengaged state, the maximum number of permissible low gearshift steps is determined as 1, such that a low gearshift is only possible to a low gearshift step (a set gearshift step number minus 1) that is one step lower than the set gearshift step determined via the gearshift pattern associated with the sport mode.

Description

BackgroundField of InterestThe present disclosure relates to a method and a system for controlling a gear shift in response to a change in a driving mode, and more particularly to a method and a system for controlling a gear shift in response to a change in a driving mode, the method and the system being capable of controlling the gear shift in a case where a shift from an operation mode (for example, an eco mode, a normal mode, a comfort mode, or the like) other than a sport mode to the sport mode occurs during driving, and an automatic transmission vehicle having the system for controlling the gear shift in response to a change in a driving mode.BackgroundConventionally, an automatic transmission is a mechanical device capable of automatically achieving a result of optimum torque conversion according to a running speed of a vehicle and a load. The automatic transmission is configured to shift gears by operating a shift solenoid and a clutch under the control of a transmission control unit (TCU)) that outputs a shift control command upon request of a driver or based on a driving state of the vehicle.The transmission control unit (TCU) that controls the automatic transmission receives information on a state of the vehicle from an engine control unit (ECU)), and outputs a control command for controlling the shift solenoid and the clutch to perform the shift based on the received information. Moreover, the transmission control unit issues a request to the engine control unit for a power change at a time for a gear change according to operations of the gear shift solenoid and the clutch.For example, when the driver operates an accelerator pedal to accelerate the vehicle, the transmission control unit requests the engine control unit to reduce the engine torque to perform a smooth gear shift operation for upshift or downshift. Then, a request for increasing the engine torque is output to the engine control unit after the request for decreasing the engine torque is output to synchronize a rotation speed of an input shaft of the automatic transmission and a rotation speed of an output shaft of an engine.The gear shift control unit also determines an optimum gear shift stage suitable for an amount of work on an accelerator pedal and a speed of the running vehicle, using a gear shift pattern (a gear shift map) set from a relationship between the amount of work on the accelerator pedal and an output speed of the transmission, i.e., a vehicle speed. Then, the optimum gear shift stage is set as a target gear shift stage, and a target hydraulic pressure (a solenoid duty value) for gear shifting to the target gear shift stage is determined. The shift solenoid is controlled based on the target hydraulic pressure.The automatic transmission vehicle satisfying predetermined specifications has a function of selecting a running mode. The driver may select a desired driving mode via a dedicated switch that is mounted at an appropriate location within the vehicle and functions to select a driving mode. When the running mode is selected, a gear shift pattern matched with the selected running mode is retrieved, and gear shift is performed according to the gear shift pattern. Thus, according to the driver's preference, an increased responsiveness of the vehicle and another shift feeling can be obtained.Typically, the selectable driving modes include an eco mode, a normal mode, a comfort mode, a sport mode, and the like depending on the type of the vehicle. Among these modes, the sport mode is a mode in which a reference point for the gear shift is set to be at a higher speed than the other modes. The gear shift to a high stage is made at the expense of fuel efficiency in a state where the vehicle gains sufficient driving force. In this way, the driver can enjoy a more dynamic driving style and feel a higher responsiveness of the vehicle.However, when a change of the driving mode to the sport mode occurs during driving, the gear shift is smoothly performed in accordance with a gear shift reference point set to be in the gear shift pattern associated with the sport mode (a gear shift map associated with the sport mode having influence amounts of a vehicle speed and an amount of work on a pedal.DE 10 2007 002 035 A1 discloses a method for operating an automatic transmission, having an automatic gear change, wherein gear changes are determined in a transmission control device of the automatic transmission on the basis of an accelerator pedal actuation and on the basis of a travel speed.DE 10 2007 000 536 A1 shows a control device which can execute a program for calculating a sport travel counter on the basis of a state of a vehicle according to an actuation by a driver. Further, the operation for executing a sport driving can be changed by the program.Summary of the InventionIn one aspect, a method and system for controlling a gear shift in response to a change in a driving mode are now provided, the method and system being capable of performing a downshift by setting a target gear shift stage to a low stage lower than a gear shift stage set to be a gear shift pattern (a gear shift map) associated with a sport mode when a shift from a driving mode other than a sport mode to the sport mode occurs during driving. The driver's desire to enjoy dynamic driving may be satisfied.In one aspect, there is provided a method for controlling a gear shift in response to a change in a running mode, the method comprising: (a) determining a maximum number of allowable low gear shift stages according to a result of determining a state of a transmission based on information on an accelerator operation (an accelerator position sensor (APS) signal) when a request for a change in a running mode to a sport mode is detected during the running; (b) calculating a speed of a turbine wheel expected immediately after the gear shift for each stage included in the maximum number of allowable low gear shift stages, using a current rotational speed of an output shaft of the transmission and a gear ratio of each stage, and comparing the calculated expected rotational speed of the turbine wheel (a rotational speed of an input shaft of the transmission) with a preset allowable rotational speed of the turbine wheel for each stage, (c) setting the lowest gear shift stage from gear shift stages in which the expected rotational speed of the turbine wheel and the allowable rotational speed of the turbine wheel satisfy a predetermined condition to be a target gear shift stage within the maximum number of allowable low gear shift stages, and (d) executing gear shift control to down-shift a current gear shift stage to the target gear shift stage. Here, in (a) the determination of the maximum number of allowable low gear shift speeds, when an output signal of an APS at a time when the request for changing the traveling mode is detected is at or above a setting value, it is determined that the transmission is in an on state, and when the output signal of the APS is below the setting value, it is determined that the transmission is in an off state.Then, when the transmission is in the on state, the number of low gear shift stages lower than a setting gear shift stage determined via a gear shift pattern associated with a sport mode is determined as the maximum number of allowed low gear shift stages, and then, when the transmission is in the off state, the maximum number of allowed low gear shift stages is determined as 1, such that low-stage gear shifting is allowed only to a low gear shift stage (a setting gear shift stage number minus 1), which is one stage lower than the setting gear shift stage determined via the gear shift pattern associated with the sport mode.Here, the "expected rotation speed of the turbine" is understood to mean a value obtained by assuming the rotation speed of the input shaft of the transmission directly connected to the turbine as an expected rotation speed value of a torque converter turbine disposed between an engine and a transmission. This value can be derived from a simple equation in which the actual rotational speed of the output shaft of the transmission (a vehicle speed) is multiplied by the reciprocal of a gear ratio of the target gear shift stage.The term "allowable speed of the turbine wheel", one of the terms used to describe an embodiment of the present disclosure, means an allowable speed of the input shaft of the transmission. The allowable rotational speed of the turbine wheel means a maximum value of a rotational speed of the input shaft of the transmission at which the driving force of an engine can be stably output by gear shifting without losing load reception at each gear shifting stage. The allowable rotation speed of the turbine wheel is a fixed value to be set in a recording device such as a memory so as to change with the gear shift stage (because a gear ratio changes with the gear shift stage).In a further preferred aspect, in the method of (b) calculating the speed of the turbine wheel expected immediately after the gear change, the speed of the turbine wheel expected immediately after the gear change for each stage may be a value (the current speed of the output shaft of the transmission / the transmission ratio of each stage) resulting from dividing the current speed of the output shaft of the transmission by the transmission ratio of each stage.In another preferred aspect, in the method of (c), in the setting of the lowest gear shift stage, the predetermined condition may be that the expected rotational speed of the turbine wheel does not exceed the allowable rotational speed of the turbine wheel.In certain preferred aspects, the method may further include: (e) comparing the time (a gear shift control time) required for the gear shift control to downshift the current gear shift stage to the target gear shift stage at (d) the execution of the gear shift control with a preset set gear shift control time.In preferred aspects, in the method, when the gear shift control time exceeds the set gear shift control time, a process in such a state may be ended without further executing the gear shift control, and when the gear shift control time is shorter than the set gear shift control time, it may be determined whether or not the gear shift to the target gear shift stage is completed, and when the gear shift is completed within the set gear shift control time, the process may be ended.In preferred aspects, in the method, in a case where the gear shift control time is shorter than the set gear shift control time and where the gear shift to the target gear shift stage is not completed, the return to (d) the execution of the gear shift control and (d) the execution of the gear shift control and (e) the comparison of the time required for the gear shift control may be repeatedly performed.In certain preferred aspects, the method may further include: (f) executing control to restrict gear shifting to a high gear shift stage after gear shifting to the target gear shift stage is completed.In certain preferred aspects, in the method (f), the executing the gear shift restriction control includes: (f-1) making a request for prohibiting the gear shift to the high gear shift stage to restrict the gear shift to the high gear shift stage after the gear shift to the target gear shift is completed; and (f-2) comparing the current gear shift stage (a gear shift stage corresponding to the target gear shift stage) with a setting gear shift stage determined via a gear shift pattern associated with a sport mode according to a current output signal of the APS and a current vehicle speed, and determining whether the prohibiting of the gear shift to the high gear shift stage is canceled or maintained according to a result of the comparison.In certain preferred aspects, in the method (f-2), comparing the current gear shift stage with the setting gear shift stage may include: (f-2-1) immediately cancelling the prohibiting of the gear shift to the high gear shift stage because the control for prohibiting the gear shift to the high gear shift stage is unnecessary when the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is equal to the setting gear shift stage or is the high gear shift stage, and (f-2-2) maintaining the prohibiting of the gear shift to the high gear shift stage when the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is a lower gear shift stage than the setting gear shift stage, and determining a timing, In addition, the prevention of the gear shift to the high gear shift stage is canceled by using additional information.In certain preferred aspects, in the method in (f-2-2) of maintaining the prohibition of the gear shift, a current engine speed may be compared with a preset allowable engine speed to prohibit engine thrust; when the current engine speed is higher than the allowable engine speed, forced gear shifting to a high gear shift stage that is one stage higher than the current gear shift stage may be performed, and then the resultant high gear shift stage may be compared with the setting gear shift stage determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS and the current vehicle speed; and when the high gear shift stage that is one stage higher than the setting gear shift stage, the prohibition of the gear shift to the high gear shift stage may be canceled.In certain preferred aspects, in the method of (f-2-2), when the current engine speed is lower than the allowable engine speed, the gear shift prevention maintenance may be determined whether or not a driver has an intention to experience acceleration based on an output signal of the APS and the time over which the output signal thereof is further provided, wherein when the output signal of the APS is further provided in a state of being on or above the setting value for a set time or longer, it may be determined that the driver actually has an intention to experience acceleration so that a timer may be operated and, at the same time, an increase in vehicle speed obtained after a time at which the gear shift to the current gear shift stage is completed may be determined, According to the invention, there is provided a method of comparing the same with a preset reference value for the increase of the vehicle speed, wherein when the increase of the vehicle speed is at or above the reference value for the increase of the vehicle speed, this situation can be recognized as an increase of the vehicle speed due to a gradient of a road rather than an intention of undergoing acceleration, and thus forced gear shifting to a high gear shift stage which is one stage higher than the current gear shift stage can be performed immediately, and thereafter the resultant high gear shift stage can be compared with the set gear shift stage which is determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS and the current vehicle speed, and when the high gear shift stage which is one stage higher is higher than the set gear shift stage, preventing the gear shift to the high gear shift stage can be canceled.In certain preferred aspects, in the method, as a result of comparing the increase in the vehicle speed obtained after the time when the gear shift is completed with the reference value for the increase in the vehicle speed, when the increase in the vehicle speed is below the reference value for the increase in the vehicle speed, a value of the time over which the timer is operated may be compared with a preset time reference value, and at a time when the time value is higher than the time reference value, the forced gear shift to a high gear shift stage that is one stage higher than the current gear shift stage may be performed, and thereafter, the resultant high gear shift stage may be compared with the setting gear shift stage, determining the gear shift pattern associated with the sport mode according to the current output signal of the APS and the current vehicle speed, and when the high gear shift stage, which is one stage higher, is higher than the set gear shift stage, the prohibition of the gear shift to the high gear shift stage may be canceled.In certain preferred aspects, in the method, the forced gear shift to a high gear shift stage that is one stage higher than the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) may be performed, and then the resultant high gear shift stage may be compared with the setting gear shift stage determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS and the current vehicle speed; as a result of the comparison, when the high gear shift stage that is one stage higher is lower than the setting gear shift stage, the forced gear shift to a high gear shift stage that is one stage higher may be performed; and thereafter, returning to comparing the resulting high gear shift stage with the setting gear shift stage may take place, and the comparing of the resulting high gear shift stage and a subsequent operation may be repeatedly performed.One or more of the aforementioned steps may be performed by using a processor or a control unit.According to another aspect of the present disclosure, there is provided a system for controlling a gear shift in response to a change in a driving mode, the system comprising: a mode change switch for changing a driving mode; an accelerator position sensor (APS)) configured to detect an operation of an accelerator pedal by a driver and output a corresponding signal; a vehicle speed detector configured to detect a rotational speed of an output shaft of a transmission; and a transmission control unit (TCU)) configured to control the transmission based on information provided from the mode change switch, the APS, and the vehicle speed detector, wherein, when a shift from a driving mode other than a sport mode to the sport mode is detected during driving, the transmission control unit performs a control for shifting down to a low gear shift stage that is a stage lower than a setting gear shift stage determined via a gear shift pattern associated with the sport mode.In certain preferred aspects, in the system, the transmission control unit may include: a gear shift mode change detecting unit configured to receive information on a driving mode change from the mode change switch and acquire a gear shift pattern matching a driving mode to which a change is made; a low gear shift stage number determining unit configured to determine a maximum number of allowable low gear shift stages according to a result of determining a state of the transmission based on information on an accelerator operation (a signal of an APS) when the gear shift mode change detecting unit detects the change of the driving mode to the sport mode during the driving; and a turbine wheel expected speed calculating unit configured to calculate an expected rotational speed of a turbine wheel, calculating a speed of a turbine wheel expected immediately after the gear shift (a speed of a drive shaft of the transmission) for each stage included in the maximum number of allowable low gear shift stages, using a current speed of an output shaft of the transmission and a gear ratio of each stage, a target gear shift stage determining unit configured to set the lowest gear shift stage as the target gear shift stage among gear shift stages in which the calculated expected speed of the turbine wheel for each stage included within the maximum number of allowable low gear shift stages and a preset allowable speed of the turbine wheel for each stage satisfy a predetermined condition, and a transmission control device configured to execute gear shift control to downshift a gear shift stage to the target gear shift stage.In certain preferred aspects, in the system, when an output signal of the APS at a time when a request for changing the driving mode is detected is at or above a setting value, the low gear stage number determination unit may determine that the transmission is in an on state, and determine, as a maximum number of allowable low gear stages, the number of low gear stages lower than the setting gear stage determined via the gear shift pattern associated with the sport mode, and when the output signal of the APS is below the setting value, the low gear stage number determination unit may determine that the transmission is in an off state, and determine, as a maximum number of allowable low gear stages, the maximum number of allowable low gear stages as 1, such that, enabling low-stage gear shifting only to a low gear stage (a set gear stage number minus 1), which is one stage lower than the set gear stage determined via the gear shift pattern associated with the sport mode.In certain preferred aspects, in the system, the turbine wheel expected speed calculation unit may calculate the turbine wheel expected speed immediately after the gear change for each stage by dividing the current rotation speed of the output shaft of the transmission detected by the vehicle speed detector by the gear ratio of each stage (the current rotation speed of the output shaft of the transmission / the gear ratio of each stage).In certain preferred aspects, in the system, the predetermined condition may be a condition that the expected rotational speed of the turbine wheel does not exceed the allowable rotational speed of the turbine wheel.In certain preferred aspects, in the system, the transmission control unit may further include a timing comparison unit configured to count the time (a gear shift timing) required for the gear shift control to downshift a current gear shift stage to the target gear shift stage and compare the counted gear shift timing with a preset setting gear shift timing, wherein when the gear shift timing exceeds the setting gear shift timing, the timing comparison unit may make a request to the transmission control device to prevent the gear shift control.In certain preferred aspects, in the system, the transmission control unit may include a gear shift prohibition request unit configured to make a request to the transmission control device for prohibiting the gear shift to a high gear shift stage to restrict the gear shift to the high gear shift stage after the gear shift to the target gear shift stage is completed.According to an embodiment of the present disclosure, when switching from a driving mode other than the sport mode to the sport mode occurs during driving, the target gear shift stage is set to a stage lower than the gear shift stage set to be in the gear shift pattern (the gear shift map) associated with the sport mode (gear shift to the lowest gear shift stage is permitted based on the allowable rotational speed of the turbine wheel for each stage). Thus, the driver can enjoy dynamic driving.Further aspects are disclosed below.Brief Description of the DrawingsThe above and other objects, features and other advantages of the present disclosure will become more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic view illustrating an embodiment of a vehicle with automatic transmission having a gear shift control system responsive to a change in a driving mode according to an embodiment of the present disclosure, FIG. 2 is a table showing a process of setting a target gear shift stage, FIG. 3 is a flowchart sequentially illustrating gear shift control processes in a sequence performed by the gear shift control system in FIG. 1 ; and FIG. 4 is a flowchart showing control for prohibiting an upshift to a high speed shift stage, wherein control is performed immediately after the downshift is performed in response to a change of the running mode to a sport mode during running.DETAILED DESCRIPTIONA preferred embodiment of the present disclosure will be described below in detail with reference to the drawings.The terms used throughout the present specification are merely for describing the preferred embodiment and are not intended to limit the present disclosure in any way. A noun in the singular has the same meaning as when used in the plural, unless it has a different meaning in the context.Moreover, the term "include", "have", or the like in the present application is intended to indicate that there is a feature, a number, a step, an operation, a constituent element, a component, or a combination thereof described in the specification. It should be understood, therefore, that the term does not exclude in advance the likelihood that one or more other features, numbers, steps, operations, components, components, or combinations thereof are present and added.In addition, the terms first, second, etc. are used to describe various constituent elements, but are not intended to limit the meaning of the constituent elements in any way. These terms are used only to distinguish one element from another.In addition, the term "unit", "module", or the like used throughout the specification refers to a single component that performs at least one function and may be implemented in hardware, software, or a combination of both.Further, the control logic of the present disclosure 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 computer readable media include ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer readable medium may also be distributed in network coupled computer systems such 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).It will be understood that the term "vehicle" or "vehicular" or other similar term as used herein is inclusive of motor vehicles in general such as passenger cars including sports utility vehicles (SUVs)), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, as well as hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and vehicles having other alternative fuels (e.g., fuels derived from resources other than petroleum). As used herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example, vehicles that operate both gasoline and electric.Like constituent elements are denoted by like reference numerals, and redundant descriptions thereof are omitted. In this way, the preferred embodiment of the present disclosure will be described with reference to the accompanying drawings. A detailed description of a technology known in the related art will be omitted when it is determined that this makes the gist of the present disclosure unclear.The main terms used to describe a preferred embodiment of the present disclosure have the following meanings.The term "expected rotation speed of a turbine wheel", one of the terms used to describe the embodiment of the present disclosure, denotes a value obtained by assuming a rotation speed of a drive shaft of a transmission directly connected to the turbine wheel as an expected rotation speed value of a torque converter turbine wheel disposed between an engine and a transmission. This value can be derived from a simple equation in which a current rotational speed of an output shaft of the transmission (a vehicle speed) is multiplied by the inverse of a gear ratio of a target gear shift stage.The term "allowable speed of the turbine wheel", one of the terms used to describe the embodiment of the present disclosure, denotes an allowable speed of the input shaft of the transmission. The allowable rotation speed of the turbine indicates a maximum value of a rotation speed of the input shaft of the transmission at which the driving force of an engine can be stably output by gear shifting without requiring no load input at each gear shifting stage. The allowable rotation speed of the turbine wheel is a fixed value to be set in a recording device such as a memory so as to change with the gear shift stage (because a gear ratio changes with the gear shift stage).First, with reference to the accompanying drawings, an arrangement of a gear shift control system responsive to a change in a running mode according to an embodiment of the present disclosure will be described.FIG. 1 is a schematic view illustrating an embodiment of a vehicle with automatic transmission having the gear shift control system responsive to the change of the driving mode according to the embodiment of the present disclosure.Referring to FIG. 1, a gear shift control system 1 responsive to the change of the driving mode according to the embodiment of the present disclosure includes a mode change switch 10 for changing the driving mode and an accelerator position sensor (APS)) 20 that detects the operation of an accelerator pedal by a driver and outputs a corresponding signal. In addition, the gear shift control system 1 includes a vehicle speed detector 30 that detects the rotational speed of the output shaft of the transmission, i.e., the vehicle speed, and a transmission control unit (TCU)) 40.The mode change switch 10 may preferably be mounted in the vicinity of a driver's seat and configured to select a desired driving mode, for example, an eco mode or a normal mode or a comfort mode or a sport mode, through an input method by a push button or a knob. The transmission control unit 40 controls a transmission based on information supplied from the mode change switch 10, the APS 20, and the vehicle speed detector 30.According to the embodiment, specifically, when the shift of the driving mode to the sport mode is detected during driving in a driving mode other than the sport mode, for example, the eco mode, the normal mode, or the comfort mode, the transmission control unit 40 performs a downshift to a low gear shift stage that is a stage lower than a setting gear shift stage determined via a gear shift pattern (a gear shift map associated with the sport mode) associated with a current output signal of the APS and a current vehicle speed. Thus, the driver can enjoy more dynamic driving and feel an increased responsiveness of the vehicle.To this end, the transmission control unit 40 used according to the present disclosure includes a plurality of processors. The plurality of processors are programmed to execute a control sequence in a stepwise manner. When the change of the running mode to the sport mode is detected during the running in a running mode other than the sport mode, the command sequence is executed so that the forced down shift is made to a low gear shift stage, which is one stage lower than the set gear shift stage determined via the gear shift pattern associated with the sport mode.The multiple processors included in the transmission control unit 40, which are programmed to execute the control sequence stepwise, include a gear shift mode change detection unit 400 and a low gear shift stage number determination unit 410. In addition, the plurality of processors includes a turbine wheel expected speed calculation unit 420, a target gear shift stage determination unit 430, and a transmission control device 440. In addition, the plurality of processors may further include a timing comparison unit 450 and a gear shift prohibition request unit 460.The gear shift mode change detection unit 400 receives information on a running mode change from the mode change switch 10 and retrieves a gear shift pattern matched to a running mode to which a change takes place. Then, when the gear shift mode change detection unit 400 detects a change of the driving mode to the sport mode during traveling, the low gear shift stage number determination unit 410 determines a maximum number of allowable low gear shift stages according to a result of determining a state of the transmission based on information on the accelerator pedal operation (a signal of the APS 20).Specifically, at a time when a request to change the driving mode to the sport mode is recognized, when an output signal of the APS 20 is at or above a setting value (when the condition that the output signal of the APS 20≥the setting value is satisfied, that is, when a state in which an accelerator pedal is operated is entered), the low gear shift stage number determination unit 410 determines that the transmission is in an on state. Then, the number of lower gear shift speeds lower than the set gear shift speed determined via the gear shift pattern associated with the sport mode is determined as the maximum number of allowed lower gear shift speeds.For example, in a state where the transmission is on and the output signal of the APS 20 responsive to the accelerator operation is thus at or above the setting value, when the setting gear shift stage determined via the gear shift pattern associated with the sport mode is the fifth stage at the time when the request for the change of the driving mode to the sport mode is detected, the total number of the lower gear shift stages lower than the fifth stage is 4 (the fourth stage, the third stage, the second stage, and the first stage). Therefore, in this case, the low speed speed speed stage number determination unit 410 determines that the maximum number of allowable low speed speed speed stages is set to 4, and thus determines that all speed speed speed stages lower than the fifth stage are included in a target speed speed speed stage list.Conversely, in a case where the output signal of the APS 20 at the time when the request for the driving mode to be changed to the sport mode is detected is below the setting value, the low speed stage determination unit 410 determines that the transmission is in a power-off state. At the same time, the low speed speed speed stage number determination unit 410 determines that the maximum number of allowable low speed speed speed stages is set to 1, such that a downshift is allowed only to the speed speed speed stage (a set speed speed speed stage number minus 1), which is one stage lower than the set speed speed speed stage determined via the speed shift pattern associated with the sport mode.For example, in a state where the transmission is shut down and therefore the output signal of the APS 20 responsive to the operation of the accelerator pedal is below the set value, the set gear shift stage determined via the gear shift pattern associated with the sport mode is the fifth stage as in the above example, at the time when the request for the shift to the sport mode is detected, the maximum number of the allowable low gear shift stages is 1. The gear shift down to the lower gear shift stage, i.e., to the third or lower gear shift stage, is determined to be impermissible. This maximum number of allowed low gear shift speeds information is provided to the turbine wheel expected speed calculation unit 420. The turbine speed expected calculation unit 420 calculates a turbine speed expected immediately after the gear shift (the speed of the input shaft of the transmission) for each stage included in the maximum number of allowable low gear shift stages, based on the supplied information (the information on the maximum allowable low gear shift stage number) from a current speed of the output shaft of the transmission and a gear ratio of each stage.Preferably, as described above, the turbine wheel speed immediately after the gear change is derived for each stage by a simple calculation in which the actual transmission output shaft speed (the vehicle speed) is multiplied by the inverse of the gear ratio of each stage included in the maximum number of the low gear shift stages allowed. That is, the turbine speed expected immediately after the gear change is a value (the current speed of the output shaft of the transmission / the gear ratio of each stage) obtained by dividing the current speed of the output shaft of the transmission (the vehicle speed) by the gear ratio of each stage.Information on the speed of the turbine wheel expected immediately after the gear shift for each stage included in the maximum number of the low gear shift speeds allowed is supplied to the target gear shift stage determination unit 430. The target gear shift stage determination unit 430 compares the calculated expected rotational speed of the turbine wheel for each stage included in the maximum number of the low gear shift stages allowed and a preset allowable rotational speed of the turbine wheel for each stage with each other. The target gear shift stage determination unit 430 sets the lowest gear shift stage as a final target gear shift stage among gear shift stages satisfying a predetermined condition.The predetermined condition may be a condition that the speed of the turbine wheel for each stage expected immediately after the gear change does not exceed the corresponding allowable speed of the turbine wheel for each stage. As described above, the allowable rotational speed of the turbine wheel refers to a maximum value of a rotational speed of the turbine wheel at which the driving force of the engine can be stably output by gear shifting without sacrificing load reception. Therefore, when the rotational speed of the turbine wheel which results immediately after the gear shift (the downshift) is performed to a low gear shift stage is higher than the corresponding allowable rotational speed of the turbine wheel, a large load is applied to the transmission.FIG. 2 is a table required for describing a process in which a target gear shift stage is set. In FIG. 2, an example is illustrated in which, in a state in which the transmission is on (the output of the APS 20≥the setting value), the setting gear shift stage determined via the gear shift pattern associated with the sport mode is the fifth stage at the time when the request to change the traveling mode to the sport mode is detected and when the current rotational speed of the output shaft of the transmission is 2000 min -1.As seen in FIG. 2, in the state where the transmission is on (the output of the APS 20≥the setting value), the setting gear shift stage determined via the gear shift pattern associated with the sport mode is the fifth stage at the time when the request to change the driving mode to the sport mode is detected, when the target gear shift stage is set, the first stage target gear shift stage determination unit 430, which is the lowest gear shift stage among the low gear shift stages below the fifth stage, gives the highest priority. However, when the actual rotational speed of the output shaft of the transmission is used as a reference, the first stage does not satisfy the above-mentioned condition because the expected rotational speed of the turbine exceeds the allowable rotational speed of the turbine.In contrast, the second stage immediately above the first stage satisfies the condition that the expected rotational speed of the turbine wheel does not exceed the allowable rotational speed of the turbine wheel (the expected rotational speed of the turbine wheel<the allowable rotational speed of the turbine wheel). Therefore, in this case, the target gear shift stage determination unit 430 excludes the first stage as the lowest gear shift stage that does not satisfy the above-mentioned condition from the setting of the target gear shift stage, and sets the second stage that is the lowest gear shift stage among gear shift stages that satisfy the above-mentioned condition as the final target gear shift stage.When the final target gear shift stage is determined through this operation, the transmission controller 440 executes gear shift control for shifting down the gear shift stage to the final target gear shift stage. For example, in the case of the situation in FIG. 2, the transmission controller 440 performs the gear shift control (controls a corresponding gear shift actuator) to shift the gear shift stage from the fifth stage to the second stage.While the transmission controller 440 performs the gear shift control, the timing comparison unit 450 performs the following operation: counting the time (a gear shift timing) required by the gear shift control to downshift a current gear shift stage to the target gear shift stage (for example, the downshift from the fifth stage to the second stage), and comparing the counted gear shift timing with a preset setting gear shift timing.In a case where the gear shift control time (the time required to shift down a current gear shift stage to the target gear shift stage) reaches the setting gear shift control time that is at a setting input value but the gear shift control is not yet completed, the control time comparison unit 450 determines that an appropriate gear shift time is exceeded, and requests the transmission controller 440 to prohibit the gear shift control.When the forced down shift is completed along with a transition to the sport mode by the above-described processing sequence, it is necessary to maintain such a down shift state for a predetermined time for the driver to feel a sufficient sense of acceleration. For this purpose, a request is made from the gear shift prohibition request unit 460 to the transmission controller 440 to prohibit the gear shift to the high gear shift stage to restrict the upshift after the gear shift is completed.Hereinafter, a process for controlling the gear shift in response to the change of the running mode will be described in detail to provide an understanding of the request for prohibiting the gear shift to the high gear shift stage and canceling the request thereof, which are performed in cooperation with the gear shift prohibition request unit 460 and the transmission controller 440.FIG. 3 is a flowchart sequentially illustrating gear shift control processes in a sequence performed by the gear shift control system in FIG. 1.Referring to FIG. 3, the method for controlling a gear shift in response to a change in a driving mode according to an embodiment of the present disclosure is a method for controlling a transmission in a case where a shift from a driving mode other than a sport mode to the sport mode is performed during driving. The method starts with step S 100 of determining a maximum number of allowable low gear shift speeds according to a result of determining a state of a transmission based on information on accelerator operation (a signal of an APS) when a request for a shift of the driving mode to the sport mode is detected during driving.Specifically, in step S 100, when an output signal of the APS at a time when the request for switching the traveling mode is recognized (in a state in which an accelerator pedal is held pressed to a preset level or above) is at or above a setting value, it is determined that the transmission is in an on state. Then, the number of low gear shift speeds lower than a current gear shift speed set according to a gear shift pattern associated with the sport mode is determined as the maximum number of allowed low gear shift speeds.For example, in a state where the transmission is on and the output signal of the APS responsive to the accelerator operation is thus at or above the setting value, when a setting gear shift stage determined via a gear shift pattern associated with the sport mode is the fifth stage at the time when the request for the change of the driving mode to the sport mode is detected, the total number of the lower gear shift stages lower than the fifth stage is 4 (the fourth stage, the third stage, the second stage, and the first stage). Therefore, in this case, the maximum number of allowable low gear shift stages is set to 4, and thus all gear shift stages lower than the fifth stage are set as included in a target gear shift stage list.Conversely, when the output of the APS is below the set value (in a state where the accelerator pedal is held depressed or is held depressed to less than the set value), it is determined that the transmission is in a power-off state. Then, the maximum number of allowable low gear shift speeds is determined as 1, so that a downshift is allowed only up to a gear shift speed (a number of the set gear shift speeds minus 1) which is one speed lower than the set gear shift speed determined via the gear shift pattern associated with the sport mode.For example, in a state where the transmission is shut down and therefore the output signal of the APS responsive to the operation of the accelerator pedal is below the set value, the set gear shift stage determined via the gear shift pattern associated with the sport mode is the fifth stage at the time when the request for the drive mode to be shifted to the sport mode is detected, the maximum number of the allowable low gear shift stages is 1. The downshift to the lower gear shift stage, i.e., the third or a lower gear shift stage, is set to be limited.If the maximum number of allowed low gear shift speeds is determined by step S 100, step S 200 is then performed. In step S 200, the expected rotation speed of the turbine wheel for each stage included in the maximum number of low speed gear shift allowed stages is calculated using a current rotation speed of an output shaft of the transmission and a gear ratio of each stage, and the calculated expected rotation speed of the turbine wheel (an expected rotation speed of an input shaft of the transmission) is compared with a preset allowable rotation speed of the turbine wheel for each stage.In step S 200, the turbine wheel speed expected immediately after the gear shift is preferably derived for each stage through a simple calculation in which a current transmission output shaft speed (a vehicle speed) is multiplied by the inverse of the gear ratio of each stage included in the maximum number of the allowable low gear shift stages. That is, the turbine speed expected immediately after the gear change is a value (the current speed of the output shaft of the transmission / the gear ratio of each stage) resulting from dividing the current speed of the output shaft of the transmission (the vehicle speed) by the gear ratio of each stage.Next, step S 300 is performed when the expected rotation speed of the turbine wheel for each stage included in the maximum number of the allowable low gear shift stages is derived from the current rotation speed of the output shaft of the transmission (the vehicle speed). In step S 300, out of gear shift stages in which the expected rotation speed of the turbine wheel and the allowable rotation speed of the turbine wheel satisfy a predetermined condition, the lowest gear shift stage within the maximum number of allowable low gear shift stages is set as the target gear shift stage. The predetermined condition is a condition that the expected rotational speed of the turbine wheel does not exceed the allowable rotational speed of the turbine wheel.When the target gear shift stage is finally determined by step S300, step S400 is performed to execute the gear shift control for shifting down the gear shift stage to the target gear shift stage. Subsequently, in step S 500, the time (a gear shift control time) required by the gear shift control to shift the current gear shift stage to the target gear shift stage is compared with a preset setting gear shift control time.Specifically, in step S 500, while the above-described transmission control device performs the gear shift control, the following operation is performed: counting the time (the gear shift control time) required by the gear shift control to downshift a gear shift stage to the target gear shift stage (for example, the downshift from the fifth stage to the second stage), and comparing the counted time for the gear shift control with the preset setting gear shift control time.In a case where the gear shift control time (the time required to downshift a gear shift stage to the target gear shift stage) reaches the setting gear shift control time which is a setting input value but the gear shift control is not yet completed, a corresponding set gear shift time is exceeded. Therefore, in such a state, the process is ended without further executing the gear shift control. When the set gear shift control time is not exceeded, whether or not the gear shift is completed is monitored based on the target gear shift stage (S 510).At this point, in a case where the gear shift timing is equal to or shorter than the setting gear shift timing and the gear shift to the target gear shift stage is not completed, the operation may be set to return to step S 400 and to perform step S 400 and subsequent steps repeatedly.When the forced downshift is completed along with a transition to the sport mode by the above-described processing sequence, it is necessary to maintain such a downshifted state for a predetermined time for a driver to feel a sufficient sense of acceleration. For this purpose, control for completing the gear shift and simultaneously limiting the gear shift to the high gear shift stage is performed (S 600). Preferably, the upshift restraining control is executed until a predetermined required condition described below is satisfied.The control for restricting the upshift will be described in more detail below.FIG. 4 is a flowchart of control for prohibiting the upshift to the high speed shift stage, wherein the control is performed immediately after the execution of the downshift in response to the change of the driving mode to the sport mode during the driving.Referring to FIG. 4, the step S 600 generally includes the step S 610 and the step S 620. In step S 610, a request for prohibiting the gear shift is made to restrict the gear shift toward the high gear shift stage after the gear shift is completed. In step S 620, after completion of the gear shift, a current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is compared with the setting gear shift stage determined via the gear shift pattern associated with the sport mode according to a current output signal of the APS and the vehicle speed, and according to a result of the comparison, it is determined whether the prohibition of the gear shift to the high gear shift stage is canceled or maintained.Specifically, as a result of the comparison by step S 620, when a current gear shift stage is equal to the set gear shift stage or is the high gear shift stage, the control for prohibiting the gear shift to the high gear shift stage is necessary (S 622). When the current gear shift stage is the gear shift stage lower than the setting gear shift stage, by maintaining the prohibition of the gear shift to the high gear shift stage and by using additional information, a timing at which the prohibition of the gear shift to the high gear shift stage is canceled is determined (S 624).Upon entering step S624, a current engine speed is first compared with a preset allowable engine speed to prevent engine thrust (S6240). As a result, when the current engine speed is higher than the allowable engine speed, forced gear shifting to a high gear shift stage, which is one stage higher than the current gear shift stage (the gear shift stage corresponding to the target gear shift stage), is performed (S 6261). Then, the resulting high gear shift stage is compared with the set gear shift stage determined via the gear shift pattern associated with the sport mode according to the output signal of the APS and the vehicle speed (S6246).As a result (a result of the comparison over step S 626), when the high gear shift stage, which is one stage higher, is equal to or higher than the set gear shift stage, the prohibition of the gear shift to the high gear shift stage is immediately canceled (S 6247). When the high gear shift stage, which is one stage higher, is the low gear shift stage, which is still lower than the set gear shift stage, the forced gear shift to a gear shift stage, which is one stage higher, is further performed (S 6248). Then, a return is made to step S6246, at which the resultant high speed shift stage is compared with the set speed shift stage, and then step S6246 and subsequent steps are repeatedly performed.Conversely, if the result of the comparison through step S6240 is that the current engine speed is lower than the allowable engine speed, it is determined whether or not the driver has an intention to experience acceleration based on the output signal of the APS and information on the time during which his output signal is still provided (S6242). In step S6242, preferably, when the output signal of the APS is further supplied for a preset time or longer in a state at or above the setting value (the setting value used to determine whether the transmission is on or not), it is determined that the driver actually has the intention of undergoing acceleration.When it is determined in step S6242 that the driver actually has an intention of undergoing acceleration (when the output signal of the APS continues to be in the state of being at or above the set value (the set value used to determine whether the transmission is on or not) for the preset time), a timer (an acceleration determination timer) is operated (S6243), and simultaneously, an increase in the vehicle speed obtained after a time point when the gear shift to a current gear shift stage is completed is compared with a preset reference value for the increase in the vehicle speed (S6244).At this point, if the increase in vehicle speed is at or above the reference value for the increase in vehicle speed, then this situation is recognized as an increase in vehicle speed due to a road grade, rather than the intention of the driver to experience acceleration. Therefore, the process immediately shifts to step S 6261. When the increase in the vehicle speed is below the reference value for the increase in the vehicle speed, a value of the time over which the timer is operated is compared with a preset time reference value (S6245). Then, at a time point when the value of the time is higher than the preset time reference value, the process shifts to step S 6241 described above.In the related art, in a case where switching is made from a driving mode other than the sport mode to the sport mode during driving, the gear change is uniformly performed in accordance with a gear change reference point determined in the gear change pattern associated with the sport mode according to a current vehicle state (the vehicle speed and an amount of work on a pedal). Thus, there is a disadvantage in that the driver's desire to enjoy dynamic driving is not satisfied.In contrast, according to the embodiment of the present disclosure, when switching from a driving mode other than the sport mode to the sport mode during driving, the target gear shift stage is set to be a low stage lower than the gear shift stage set in the gear shift pattern (a gear shift map) associated with the sport mode (gear shift to the lowest gear shift stage is permitted based on the allowable rotational speed of the turbine wheel for each stage). Accordingly, the downshift is performed in a wider range. Thus, the driver's desire to enjoy dynamic driving can be satisfied.

Claims

A method for controlling a gear shift in response to a change in a running mode, the method comprising: (a) determining a maximum number of allowable low gear shift stages according to a result of determining a state of a transmission based on information on an accelerator operation (an accelerator position sensor (APS; 20) signal) when a request for a change in a running mode to a sport mode is detected during the running; (b) calculating a rotation speed of a turbine wheel expected immediately after the gear shift for each stage included in the maximum number of allowable low gear shift stages, using a current rotational speed of an output shaft of the transmission and a gear ratio of each stage, and comparing the calculated expected rotational speed of the turbine wheel (a rotational speed of an input shaft of the transmission) with a preset allowable rotational speed of the turbine wheel for each stage, (c) setting the lowest gear shift stage from gear shift stages in which the expected rotational speed of the turbine wheel and the allowable rotational speed of the turbine wheel satisfy a predetermined condition to be a target gear shift stage within the maximum number of allowable low gear shift stages, and (d) executing gear shift control to downshift a current gear shift stage to the target gear shift stage, wherein, in (a) the determination of the maximum number of allowable low gear shift stages, when an output signal of an APS (20) at a time point, wherein the request for changing the running mode is detected to be at or above a set value, it is determined that the transmission is in an on state, and when the output signal of the APS (20) is below the set value, it is determined that the transmission is in an off state, wherein when the transmission is in the on state, the number of low gear shift stages lower than a set gear shift stage determined via a gear shift pattern associated with a sport mode is determined as the maximum number of allowed low gear shift stages, and when the transmission is in the off state, the maximum number of allowed low gear shift stages is determined as 1, such that a low stage gear shift is allowed only to a low gear shift stage (a set gear shift stage number minus 1), the one stage is lower than the set gear shift stage determined via the gear shift pattern associated with the sport mode.The method of claim 1, wherein in (b) the calculation of the turbine speed expected immediately after the gear change, the turbine speed expected immediately after the gear change for each stage is at a value (the current speed of the output shaft of the transmission / the gear ratio of each stage) resulting from dividing the current speed of the output shaft of the transmission by the gear ratio of each stage.The method of any preceding claim, wherein at (c) the setting of the lowest gear shift stage, the predetermined condition is that the expected speed of the turbine wheel does not exceed the allowable speed of the turbine wheel.The method according to any one of the preceding claims, further comprising: comparing the time (a gear shift control time) required for the gear shift control to downshift the current gear shift stage to the target gear shift stage at (d) the execution of the gear shift control with a preset setting gear shift control time, wherein when the gear shift control time exceeds the setting gear shift control time, a process in such a state is ended without further executing the gear shift control, and wherein when the gear shift control time is shorter than the setting gear shift control time, it is determined whether or not the gear shift to the target gear shift stage is completed, and when the gear shift within the setting gear shift control time is completed, the process is ended.The method according to claim 4, wherein in a case where the gear shift control time is shorter than the set gear shift control time and where the gear shift to the target gear shift stage is not completed, the return to (d) the execution of the gear shift control and (d) the execution of the gear shift control and (e) the comparison of the time required for the gear shift control are repeatedly performed.The method according to claim 4 or 5, further comprising: (f) executing control for restricting the gear shift to a high gear shift stage after the gear shift to the target gear shift stage is completed.The method according to claim 6, wherein (f) the executing of the gear shift restriction control comprises: (f-1) making a request for prohibiting the gear shift to the high gear shift stage to restrict the gear shift to the high gear shift stage after the gear shift to the target gear shift is completed; and (f-2) comparing the current gear shift stage (a gear shift stage corresponding to the target gear shift stage) with a setting gear shift stage determined via a gear shift pattern associated with a sport mode according to a current output signal of the APS (20) and a current vehicle speed, and determining whether the prohibiting of the gear shift to the high gear shift stage is canceled or maintained according to a result of the comparison.The method of claim 7, wherein (f-2) comparing the current gear shift stage with the setting gear shift stage comprises: (f-2-1) immediately cancelling the prohibiting of the gear shift to the high gear shift stage because the control for prohibiting the gear shift to the high gear shift stage is unnecessary when the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is equal to the setting gear shift stage or is the high gear shift stage, and (f-2-2) maintaining the prohibiting of the gear shift to the high gear shift stage when the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is a lower gear shift stage than the setting gear shift stage, and determining a timing, In addition, the prevention of the gear shift to the high gear shift stage is canceled by using additional information.The method according to claim 8, wherein in (f-2-2) the gear shift prohibition maintenance, a current engine speed is compared with a preset allowable engine speed to prohibit engine thrust, when the current engine speed is higher than the allowable engine speed, forced gear shifting is performed to a high gear shift stage that is higher by one stage than the current gear shift stage (the gear shift stage corresponding to the target gear shift stage), and then the resultant high gear shift stage is compared with the setting gear shift stage that is determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS (20) and the current vehicle speed, and when the high gear shift stage that is higher by one stage is higher than the setting gear shift stage, preventing the gear shift to the high gear shift stage is canceled.The method according to claim 9, wherein when the current engine speed is lower than the allowable engine speed, it is determined whether or not a driver has an intention to experience acceleration based on an output signal of the APS (20) and the time over which the output signal thereof is further provided, wherein when the output signal of the APS (20) is further provided in a state of being on or above the set value for a set time or longer, it is determined that the driver actually has an intention to experience acceleration so that a timer is operated and at the same time an increase in vehicle speed obtained after a time at which the gear shift to the current gear shift stage is completed is compared with a preset reference value for the increase in vehicle speed, wherein, then, when the increase in vehicle speed is at or above the reference value for the increase in vehicle speed, this situation is recognized as an increase in vehicle speed due to a gradient of a road rather than the intention of undergoing acceleration, and thus forced gear shifting to a high gear shift stage that is one stage higher than the current gear shift stage (the target gear shift stage) is immediately performed, and thereafter the resultant high gear shift stage is compared with the setting gear shift stage determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS (20) and the current vehicle speed, and when the high gear shift stage that is one stage higher than the setting gear shift stage, the prevention of gear shifting to the high gear shift stage is canceled.The method according to claim 10, wherein as a result of comparing the increase in vehicle speed obtained after the time when the gear shift is completed with the reference value for the increase in vehicle speed, when the increase in vehicle speed is below the reference value for the increase in vehicle speed, a value of the time over which the timer is operated is compared with a preset time reference value, and at a time when the time value is higher than the time reference value, the forced gear shift to a high gear shift stage which is one stage higher than the current gear shift stage is performed, and thereafter the resultant high gear shift stage is compared with the setting gear shift stage, determining the gear shift pattern associated with the sport mode according to the current output signal of the APS (20) and the current vehicle speed, and when the high gear shift stage that is higher by one stage is higher than the set gear shift stage, prohibiting the gear shift to the high gear shift stage is canceled.The method according to any one of claims 9 to 11, wherein the forced gear shift to a high gear shift stage that is one stage higher than the current gear shift stage (the gear shift stage corresponding to the target gear shift stage) is performed, and then the resultant high gear shift stage is compared with the setting gear shift stage determined via the gear shift pattern associated with the sport mode according to the current output signal of the APS (20) and the current vehicle speed, and as a result of the comparison, when the high gear shift stage that is one stage higher is lower than the setting gear shift stage, forced gear shift to a high gear shift stage that is one stage higher is performed, and wherein there is thereafter a return to comparing the resulting high gear shift stage with the set gear shift stage, and the comparing of the resulting high gear shift stage and a subsequent operation are repeatedly performed.A system for controlling a gear change in response to a change in a driving mode, the system comprising: a mode change switch (10) for a change in a driving mode; an accelerator position sensor (APS; 20) configured to detect the operation of an accelerator pedal by a driver and output a corresponding signal, a vehicle speed detector (30) configured to detect a rotational speed of an output shaft of a transmission, and a transmission control unit (TCU) (40) configured to control the transmission based on information provided from the mode change switch (10), the APS (20), and the vehicle speed detector (30), wherein when a shift from a driving mode other than a sport mode to the sport mode is detected during driving, the transmission control unit (40) performs a low gear shift stage shift down control that is a stage lower than a setting gear shift stage determined via a gear shift pattern associated with the sport mode.The system according to claim 13, wherein the transmission control unit (40) comprises: a gear shift mode change detection unit (400) configured to receive information on a driving mode change from the mode change switch (10) and fetch a gear shift pattern matching a driving mode to which a change takes place; a low gear shift stage number determination unit (410) configured to determine a maximum number of allowable low gear shift stages according to a result of determining a state of the transmission based on information on an accelerator pedal operation (a signal of an APS (20)) when the gear shift mode change detection unit (400) detects the change of the driving mode to the sport mode during the driving; and a turbine wheel expected speed calculation unit (420) configured to calculate a turbine wheel speed, calculating a turbine speed expected immediately after the gear shift (a speed of a drive shaft of the transmission) for each stage included in the maximum number of allowable low gear shift stages, using a current speed of an output shaft of the transmission and a gear ratio of each stage, a target gear shift stage determining unit (430) configured to set the lowest gear shift stage as the target gear shift stage among gear shift stages in which the calculated turbine speed expected for each stage included within the maximum number of allowable low gear shift stages and a preset allowable speed of the turbine wheel for each stage satisfy a predetermined condition, a transmission control means (440) configured to execute gear shift control to downshift a gear shift stage to the target gear shift stage, and a gear shift prohibition request unit (460) configured to make a request to the transmission controller (440) to prohibit the gear shift to a high gear shift stage to restrict the gear shift to the high gear shift stage after the gear shift to the target gear shift stage is completed.The system according to claim 14, wherein when an output signal of the APS (20) at a time when a request for changing the driving mode is detected is at or above a setting value, the low gear stage number determination unit (410) determines that the transmission is in an on state, and determines, as a maximum number of allowed low gear stages, the number of low gear stages lower than the setting gear stage determined via the gear shift pattern associated with the sport mode, and wherein, when the output signal of the APS (20) is below the setting value, the low gear stage number determination unit (410) determines that the transmission is in an off state, and determines the maximum number of allowed low gear stages as 1, such, enabling low-stage gear shifting only to a low gear stage (a set gear stage number minus 1), which is one stage lower than the set gear stage determined via the gear shift pattern associated with the sport mode.The system of claim 14 or 15, wherein the predetermined condition is a condition that the expected rotational speed of the turbine wheel does not exceed the allowable rotational speed of the turbine wheel.The system according to any one of claims 14 to 16, wherein the transmission control unit (40) further comprises: a timing comparison unit (450) configured to count the time (a gear shift timing) required for the gear shift control to downshift a current gear shift stage to the target gear shift stage, and compare the counted gear shift timing with a preset setting gear shift timing, wherein when the gear shift timing exceeds the setting gear shift timing, the timing comparison unit (450) makes a request to the transmission control device (440) to prevent the gear shift control.

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