Apparatus and method for learning a gear ratio control of CVT transmissions

Abstract

A device for learning a gear ratio control of a CVT (Continuously Variable Transmission), comprising an APS (110) (Acceleration Position Sensor) configured to detect a change in an accelerator pedal in a vehicle with a CVT, a gear ratio detector (120) configured to detect a pulley gear ratio of the CVT, a timer (130) configured to measure a time during which the learning of the gear ratio control is carried out during the power-off upshift of the CVT, and a controller (140), characterized in that the controller (140) is configured to receive values ​​detected via the APS (110), the gear ratio detector (120), and the timer (130), and to control the CVT in such a way thatthat it shifts gears at a target gear ratio learned via the gear ratio control learning during the power-off upshift while sailing, wherein the controller (140) enters the gear ratio control learning during the power-off upshift while sailing, detects the current gear ratio and the target gear ratio, and actuates the timer (130) to check a gear change time.,

Description

The present invention relates to an apparatus and method for learning a transmission ratio control of a CVT (continuously variable transmission) transmission, and more particularly to an apparatus and method for learning a CVT transmission transmission ratio control that can prevent a problem by means of target transmission ratio control learning, the problem occurring when a turbine shift curve is decelerated or advanced during the pulley gear change, in which a transmission ratio is significantly changed due to the running state of a CVT vehicle or the wear and degradation of a contact surface between a pulley and a belt.Generally, an automatic transmission vehicle is driven under the control of an electronic controller called a TCU (Transmission Control Unit (Transmission Control Unit)), and the TCU controls the overall operation of the automatic transmission. At present, the TCU electronically controls the automatic transmission to shift gears depending on the speed of the vehicle and the opening degree of the throttle valve. When the vehicle is driven by the power of the engine during the gear shift, the state is referred to as a power-on state. When the vehicle is driven (coasting) not by the power of the engine but by the inertia of the vehicle, the state is referred to as a power-off state. Since an engine speed, an engine torque, and an engine power are different during the power-on state and the power-off state, gear shift controls suitable for the power-on state and the power-off state must be performed.For example, DE 100 20 803 A1 discloses a transmission ratio control system for a continuously variable transmission of a vehicle. The transmission control system has a downhill decision means that determines a downhill travel of the vehicle from a road gradient, a target acceleration setting means, and a learning correcting unit. In this case, the learning correction unit determines, on the basis of the time between actuations of the accelerator pedal or brake pedal, whether the set engine braking is too strong or weak.Furthermore, DE 43 30 391 A1 shows a transmission arrangement of a vehicle, which has a computer and sensors connected to the computer, such as a speed sensor and a throttle valve angle sensor. The computer controls a continuously variable transmission of the vehicle such that the speed of the vehicle corresponds to a stored setpoint speed.Generally, when a driver takes the foot from the accelerator pedal (raises the foot) while driving, the operating state of the vehicle is switched from the state where the engine drives the vehicle to the power-off state where the vehicle drives the engine, and the speed stage is changed to a high speed stage higher than the current speed stage by one or more stages. At this time, the number of turbine revolutions decreases, and the gear shift control accompanying this case is commonly referred to as power-off upshift.A typical automatic transmission is automatically synchronized with a target speed stage set according to changes in vehicle speed and throttle opening degree, for example, through a gear shift pattern of a map table. The automatic transmission adopts the power-off upshift control method in which the speed stage is changed to a speed stage higher by one or more stages than the current speed stage to preclude occurrence of shocks due to momentary engine output reduction in the case of the power-off state in which the driver takes the foot from the accelerator pedal.However, in the existing CVT, no speed ratio control learning is performed for a certain pulley speed change, but only a pulley control pressure learning of comparing control pressures and pressure sensor values of an input shaft and an output shaft in the parking position P or the neutral position N is performed as the learning used for the pulley. Since the gear ratio control learning for the pulley gear change is not performed, gear change correction in which the intention of a driver depending on the wear of the transmission or the surrounding environment is inputted is not performed. Therefore, the gear change of the transmission can be delayed or rapidly performed, thereby causing a shock during the gear change control.Therefore, the gear ratio control learning is required to execute transmission control in which, via the target gear ratio control learning process (i.e., the target gear ratio learned), the intention of a driver (for example, an intention of letting the vehicle sail) is more reliably reflected.The related art of the present invention is disclosed in KR 2006 0 108 867 A.Embodiments of the present invention are directed to an apparatus and method for learning a CVT transmission ratio control capable of preventing a problem by target transmission ratio control learning, the problem occurring when a turbine shift curve is decelerated or advanced during the pulley gear change, in which a transmission ratio is significantly changed due to the running state of a CVT vehicle or wear and degradation of a contact surface between a pulley and a belt.In one embodiment, an apparatus for learning a gear ratio control of a CVT transmission may comprise the features of claim 1.The learned target gear ratio may indicate a target gear ratio by which a slope indicating a time required to reach the target gear ratio with respect to the current gear ratio is set to a gentle slope or a steep slope to prevent a rapid change in the current gear ratio when the current gear ratio is controlled to follow the target gear ratio.The controller may check whether an APS change is less than a preset APS value or a target gear ratio change is less than a preset gear ratio change, and determine a power-off upshift point upon coasting.During the power-off upshift upon coasting, the control enters the gear ratio control learning, detects the current gear ratio and the target gear ratio, and operates the timer to check a gear change time.Then, when the absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is larger than a first gear ratio, the controller may determine that the power-off upshift upon coasting has been removed and the gear ratio control learning stops.Then, when the absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is less than a first gear ratio, the controller may continuously increase the timer value to check the gear change time while the learning is performed.The controller may compare the absolute amount of the difference between the current gear ratio and the target gear ratio acquired at the time of entering the gear ratio control learning with a second gear ratio, compare the timer value with a preset timer value 1 when it is determined that the current ratio approaches the target gear ratio acquired at the time of entering the gear ratio control learning within a preset range, determine that the gear ratio has been changed too early when the timer value is less than the timer value 1, and drive the slope of the learned target gear ratio to a gentler slope than the slope of the target gear ratio.Then, when the timer value is between the timer value 1 and a preset timer value 2, the controller may determine that the gear ratio has been changed at a designated appropriate time and maintain the slope of the learned target gear ratio at the current slope.Then, when the timer value is larger than the timer value 2, the controller may determine that the gear ratio has been changed after the designated appropriate time, and increase the slope of the learned target gear ratio to a slope near the target gear ratio.In another embodiment, a method of learning a gear ratio control of a CVT transmission may include the features of claim 10.To determine a power-off upshift point during coasting, the controller may check whether the APS change is less than a preset APS value and a target gear ratio change is less than a preset gear ratio change.During the power-off upshift upon coasting, the control enters the gear ratio control learning, detects the current gear ratio and the target gear ratio, and operates the timer to check a gear change time.Then, when the absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is larger than a first gear ratio, the controller may determine that the power-off upshift has been removed upon coasting and stop the gear ratio control learning.Then, when the absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is less than a first gear ratio, the controller may continuously increase the timer value to check the gear change time while the learning is performed.The controller may compare the absolute amount of the difference between the current gear ratio and the target gear ratio acquired at the time of entering the gear ratio control learning with a second gear ratio, compare the timer value with a preset timer value 1 when it is determined that the current ratio approaches the target gear ratio acquired at the time of entering the gear ratio control learning within a preset range, determine that the gear ratio has been changed too early when the timer value is less than the timer value 1, and drive the slope of the learned target gear ratio to a gentler slope than the slope of the target gear ratio.Then, when the timer value is between the timer value 1 and a preset timer value 2, the controller may determine that the gear ratio has been changed at a designated appropriate time and maintain the slope of the learned target gear ratio at the current slope.Then, when the timer value is larger than the timer value 2, the controller may determine that the gear ratio has been changed after the designated appropriate time, and increase the slope of the learned target gear ratio to a slope near the target gear ratio. FIG. 1 illustrates a schematic embodiment of an apparatus for learning a gear ratio control of a CVT transmission according to an embodiment of the present invention. FIG. 2 illustrates an operation of an actuator of the CVT transmission in FIG. 1. FIG. 3 is a flowchart illustrating a method for learning a power-off upshift of a CVT transmission according to the embodiment of the present invention. FIG. 4 is a diagram illustrating the relationship between a current gear ratio and a learned target gear ratio and a target gear ratio depending on a learning start and a learning end in FIG. 3.Hereinafter, an apparatus and a method for learning a transmission ratio control of a CVT (Continuously Variable Transmission) transmission according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.It should be appreciated that the drawings are not exactly to scale and may be exaggerated in the thickness of lines or the size of components for purposes of illustration and clarity only. Moreover, the terms used herein are defined in consideration of functions of the invention, and may be changed according to habit or intention of users or operators. Therefore, the terms should be defined according to the overall disclosures set forth herein.Referring now to FIG. 1, there is shown a schematic embodiment of a device for learning a speed ratio control of a CVT transmission according to an embodiment of the present invention.As illustrated in FIG. 1, the apparatus for learning the gear ratio control of a CVT transmission according to the embodiment of the present invention may include an accelerator position sensor (accelerator position sensor)) 110, a gear ratio detector 120, a timer 130, a controller 140, and an actuator 150.The APS 110 may detect the position (displacement) of an accelerator pedal.For example, when a driver steps on the accelerator pedal, the APS attached to the accelerator pedal may detect the position (displacement) of the pedal and transmit the detected position to the controller 140. The controller 140 may calculate an opening degree of a throttle valve using another input signal from the APS information, and may change the opening degree of the throttle valve to an opening degree appropriate to the operating state of the engine by driving an engine mounted on the throttle valve.The transmission ratio detector 120 may detect a pulley transmission ratio of the CVT.For example, as shown in FIG. 2, the pulley of the CVT transmission may include a first pulley (or input pulley) 151 and a second pulley (or output pulley) 152, and the pulley transmission ratio may indicate the ratio of key slot widths (or diameters) of the first and second pulleys 151 and 152, respectively.The timer 130 may measure a gear shift time during which the gear ratio control learning is performed, the gear shift time indicating a period from a learning start point to a learning end point.The controller 140 may receive the values detected via the APS 110, the gear ratio detector 120, and the timer 130, and perform transmission control in which the driver's intention (for example, the driver's intention to let the vehicle sail) is inputted via the gear ratio control learning during the power-off upshift according to the embodiment of the present invention.The actuator 150 may perform a gear change at a learned target gear ratio while changing the gear ratio (or pulley gear ratio) according to a control signal output from the controller 140.The learned target gear ratio may indicate a target gear ratio at which an inclination with respect to the target gear ratio (i.e., the time required to reach the target gear ratio) may be set to a gentle or steep inclination to prevent a rapid gear ratio change when the current gear ratio is controlled to follow the target gear ratio.As illustrated with reference to FIG. 2, the actuator 150 of the CVT transmission (variator) may include the first pulley (drive pulley) 151, the second pulley (driven pulley) 152, and a transmission belt 153. The CVT may be installed on a power transmission path between an input shaft and an output shaft.The first pulley 151 may be mounted on the drive shaft and have a variable effective diameter. The second pulley 152 may be mounted on the output shaft and have a variable effective diameter. The transmission belt 153 may be looped around the first and second pulleys 151 and 152 so as to extend between the first and second pulleys 151 and 152. The force may be transmitted via a frictional force between the first and second pulleys 151 and 152 and the transmission belt 153.The first pulley 151 may include a fixed pulley 151 a, a movable pulley 151 b, and a first hydraulic actuator 151 c. The fixed pulley 151 amay serve as a rotating body fixed to the drive shaft. The movable pulley 151 bmay serve as an input-side movable rotating body that can be moved in the axial direction while preventing relative rotation about the axial line of the drive shaft. The first hydraulic actuator 151 cmay generate a thrust to move the movable pulley 151 bto change the spline width between the fixed pulley 151 aand the movable pulley 151 b.The second pulley 152 may include a fixed pulley 152 a, a movable pulley 152 b, and a second hydraulic actuator 152 c. The fixed pulley 152 amay serve as a rotating body fixed to the output shaft. The movable pulley 152 bmay serve as a driven-side movable rotating body that can be moved in the axial direction while preventing relative rotation about the axial line of the fixed pulley 152 a. The second hydraulic actuator 152 cmay generate a thrust to move the movable pulley 152 bto change the spline width between the fixed pulley 152 aand the movable pulley 152 b.Therefore, while the spline widths of the first and second pulleys 151 and 152 are changed or the diameters of the first and second pulleys 151 are substantially changed according to the change of the widths, the winding diameter (effective diameter) of the transmission belt 58 can be changed.Thus, while the spline widths of the first and second pulleys 151 and 152 are changed or the diameters of the first and second pulleys 151 are substantially changed according to the change in the widths, the gear ratio (or speed ratio=rotation speed of the input shaft / rotation speed of the output shaft) can be continuously changed. For example, when the spline width of the first pulley 151 is decreased, the gear ratio may be decreased to upshift the CVT. On the other hand, when the spline width of the first pulley 151 is increased, the transmission ratio may be increased to downshift the CVT.The operation of the controller 140 will be described in more detail below with reference to FIGS. 3 and 4.FIG. 3 is a flowchart illustrating a method for learning a power-off upshift of a CVT transmission according to the embodiment of the present invention, and FIG. 4 is a diagram illustrating the relationship between a current gear ratio and a learned target gear ratio and a target gear ratio depending on the start of learning and the end of learning in FIG. 3.Referring to FIG. 3, the controller 140 may check whether an APS change (i.e., the position of the accelerator pedal) is less than a preset APS value and a target gear ratio change is less than a preset gear ratio change.For example, if the driver determines that the vehicle is travelling at high speed, he may not step on the accelerator pedal to let the vehicle sail. Therefore, the controller 140 may determine whether the driver intends to sail the vehicle or a power-off upshift is performed at step S 101.Thus, when the APS change (i.e., the position of the accelerator pedal) is less than the preset APS value and the target gear ratio change is less than the preset gear ratio change (Yes at step S 101), or when the driver intends to sail the vehicle or a power-off upshift will be made, the controller 140 may acquire the current gear ratio and the target gear ratio (see (A) of FIG. 4 ) and simultaneously operate the timer 130 at step S 102. That is, learning may be started.If the APS change is still less than the preset APS value or the vehicle is still coasting, the controller 140 may check whether a difference between a target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point is less than a preset first gear ratio at step S 103. In reality, the absolute amount of the difference may be applied.For example, the controller 140 may check whether the driving situation of the coasting vehicle has not changed. When it is assumed that the vehicle is traveling on a flat road, the target gear ratio corresponding to the current traveling situation and the target gear ratio acquired at the learning start point may be similar to each other without a significant difference or within a preset range. However, if the vehicle encounters an upward-going road during coasting, the desired transmission ratio corresponding to the current driving situation is changed. Thus, there occurs a large difference between the target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point (A of FIG. 4 ).Thus, when the difference between the target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point is larger than the first gear ratio (No at step S 103), this may indicate that the current driving situation has been changed to a situation in which the vehicle cannot sail. Therefore, the controller 140 may stop the gear ratio control learning at step S 111.On the other hand, when the difference between the target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point is smaller than the first gear ratio (Y at step S 103), this may indicate that the driving situation of the coasting vehicle has not been changed. Therefore, the controller 140 may increase the timer value. Thus, the timer value for checking the learning time can be increased by 1.The controller 140 may check whether the difference between the target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point is less than a preset second gear ratio at step S 105.For example, since it is determined at step S 103 that the target gear ratio corresponding to the current driving situation and the target gear ratio detected at the learning start point are similar to each other (the vehicle is coasting) without a large difference or within the preset range, the current gear ratio needs to follow (or approach) the detection target gear ratio detected at the learning start point.Therefore, the controller 140 may check whether the current gear ratio has approached the target gear ratio detected at the learning start point within a preset range (for example, a range corresponding to a difference between A and B of FIG. 4 ) or the gear ratio has been changed to the target gear ratio at step S 105.At this time, the timer value may be increased until the current gear ratio approaches the target gear ratio detected at the learning start point within the preset range (for example, the range corresponding to the difference between A and B of FIG. 4 ) or is changed to the target gear ratio (steps S 103 to S 105 are repeated). Thus, when the current gear ratio approaches the target gear ratio detected at the learning start point within the preset range or is changed to the target gear ratio (Y at step S 105), the controller 140 may check whether the timer value is less than a preset timer value 1 (for example, 10 ms) at step S 106.That is, the controller 140 may check whether the time (timer value) required until the current gear ratio approaches the target gear ratio detected at the learning start point within the preset range (for example, the range corresponding to the difference between A and B of FIG. 4 ) or is changed to the target gear ratio is less than the timer value 1 (for example, 10 ms).If the timer value is less than the timer value 1 of 10 ms (Y at step S 106), this may indicate that the gear ratio has been changed too early. In this case, since a surge may occur, the controller 140 may increase the limit value for the target gear ratio (i.e., the limit amount) at step S 107.For example, it may be limited that the slope of the learned target gear ratio in FIG. 4 follows the slope of the target gear ratio. That is, the slope of the learned target gear ratio may be maintained at a gentler slope than the target gear ratio.If the timer value is greater than the timer value 1 of 10 ms (N at step S 106), the controller 140 may check whether the timer value is less than a preset timer value 2 (e.g., 20 ms), or check whether the timer value is greater than or equal to the timer value 1 and less than the timer value 2 (10 ms≤timer value<20 ms). If the timer value is between the timer value 1 and the timer value 2 (Y at step S 107), this may indicate that the gear ratio has been changed at a predetermined appropriate timing. In this case, the controller 140 may maintain the limit value for the target gear ratio (i.e., the limit amount).For example, it may indicate that the slope of the learned target gear ratio in FIG. 4 is maintained at the current slope.If the timer value is larger than the timer value 2 of 20 ms (No at step S 108), this may indicate that the gear ratio has been changed after the predetermined appropriate time. In this case, the controller 140 may decrease the limit value for the target gear ratio (i.e., the limit amount) at step S 110.For example, it may indicate that the slope of the learned target gear ratio in FIG. 4 is changed to a slope near the target gear ratio.Note that the timer values 1 and 2 of 10 ms and 20 ms, respectively, are merely examples for convenience of description, and are not limited to specific values. Therefore, the timer values 1 and 2 can be changed to other values.According to the present embodiment, when a turbine shift curve is decelerated or advanced during the pulley shifting in which the transmission ratio is largely changed due to the running condition of the vehicle with CVT or the wear and deterioration of the contact area between the pulley and the belt, the device and method for learning the transmission ratio control can equalize this condition through the target transmission ratio control learning operation, thereby preventing occurrence of shock during the transmission speed change control with the transmission speed change being decelerated or carried out early.While preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as defined in the appended claims.

Claims

An apparatus for learning a transmission ratio control of a CVT (continuously variable transmission) transmission, comprising an APS (110) (acceleration position sensor)) configured to detect a change of an accelerator pedal in a vehicle having a CVT, a transmission ratio detector (120) configured to detect a pulley transmission ratio of the CVT, a timer (130) configured to measure a time during which learning of the transmission ratio control is performed during the power-off upshift of the CVT, and a controller (140), characterized in that the controller (140) is configured to communicate via the APS (110), the transmission ratio detector (120) and the timer (130) receive detected values, and controls the CVT to shift gears at a target transmission ratio learned through the transmission ratio control learning during the power-off upshift during coasting, wherein the controller (140) enters the transmission ratio control learning during the power-off upshift during coasting, detects the current transmission ratio and the target transmission ratio, and operates the timer (130) to check a speed change time.The apparatus according to claim 1, wherein the learned target gear ratio indicates a target gear ratio by which an inclination indicating a time required to reach the target gear ratio with respect to the current gear ratio is set to a gentle or steep inclination to prevent a rapid change of the current gear ratio when the current gear ratio is controlled to follow the target gear ratio.The apparatus according to claim 1 or 2, wherein the controller (140) checks whether an APS change is less than a preset APS value or a target gear ratio change is less than a preset gear ratio change, and determines a power-off upshift point upon coasting.The apparatus according to any preceding claim, wherein, when an absolute value of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is greater than a first gear ratio, the controller (140) determines that the power-off upshift has been removed upon coasting and stops the gear ratio control learning.The apparatus according to any preceding claim, wherein, when an absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is less than a first gear ratio, the controller (140) continuously increases a timer value to check a gear change time while the learning is being performed.The apparatus according to claim 5, wherein the controller (140) compares the absolute amount of the difference between the current gear ratio and the target gear ratio acquired at the time of entering the gear ratio control learning with a second gear ratio, compares the timer value with a preset timer value 1 when it is determined that the current ratio approaches the target gear ratio acquired at the time of entering the gear ratio control learning within a preset range, determines that the gear ratio has been changed too early when the timer value is less than the timer value 1, and drives the slope of the learned target gear ratio to a gentler slope than the slope of the target gear ratio.The apparatus according to claim 6, wherein when the timer value is between the timer value 1 and a preset timer value 2, the controller (140) determines that the gear ratio has been changed at a designated appropriate time and maintains the slope of the target learned gear ratio at the current slope.The apparatus according to claim 6 or 7, wherein when the timer value is larger than the timer value 2, the controller (140) determines that the gear ratio has been changed after the designated appropriate time, and increases the slope of the target learned gear ratio to a slope near the target gear ratio.A method for learning a gear ratio control of a CVT transmission performed by an apparatus for learning the gear ratio control of the CVT transmission, the apparatus comprising an acceleration position sensor (APS) (110)), a gear ratio detector (120), a timer (130), and a controller (140), characterized in that the method comprises: detecting, by the APS (110), a change of an accelerator pedal in a vehicle with CVT transmission, detecting, by the gear ratio detector (120), a pulley gear ratio of the CVT transmission, measuring, by the timer (130), a time during which the learning of the gear ratio control is performed, during the power-off upshift of the CVT transmission, receiving, by the controller (140), values detected via the APS (110), the transmission ratio detector (120), and the timer (130), and controlling the CVT transmission to shift gears at a target transmission ratio learned via the transmission ratio control learning during the power-off upshift during coasting, and entering the controller (140) during the power-off upshift during coasting into the transmission ratio control learning, detecting the current transmission ratio and the target transmission ratio, and operating the timer (130) to check a gear shift time.The method of claim 9, wherein the controller (140) checks, for determining a power-off upshift point upon coasting, whether the APS change is less than a preset APS value and a target gear ratio change is less than a preset gear ratio change.The method according to claim 9 or 10, wherein, when the absolute amount of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is larger than a first gear ratio, the controller (140) determines that the power-off upshift has been removed upon coasting and stops the gear ratio control learning.The method according to any one of claims 9 to 11, wherein, when the absolute value of a difference between a target gear ratio corresponding to the current driving situation and a target gear ratio acquired at the time of entering the gear ratio control learning is less than a first gear ratio, the controller (140) continuously increases a timer value to check the gear change time while the learning is performed.The method according to claim 12, wherein the controller (140) compares the absolute amount of the difference between the current gear ratio and the target gear ratio acquired at the time of entering the gear ratio control learning with a second gear ratio, compares the timer value with a preset timer value 1 when it is determined that the current ratio approaches the target gear ratio acquired at the time of entering the gear ratio control learning within a preset range, determines that the gear ratio has been changed too early when the timer value is less than the timer value 1, and drives the slope of the learned target gear ratio to a gentler slope than the slope of the target gear ratio.The method according to claim 13, wherein when the timer value is between the timer value 1 and a preset timer value 2, the controller (140) determines that the gear ratio has been changed at a designated appropriate time and maintains the slope of the target learned gear ratio at the current slope.The method of claim 13 or 14, wherein when the timer value is greater than the timer value 2, the controller (140) determines that the gear ratio has been changed after the designated appropriate time, and increases the slope of the learned target gear ratio to a slope near the target gear ratio.

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