Patent ID: 12233841

DETAILED DESCRIPTION

In the manual mode, auto-up control in which upshift is performed such that the input rotational speed of the continuously variable transmission does not exceed the allowable rotational speed and over-revolution determination in which upshift is performed such that the engine speed does not exceed the allowable rotational speed may be used in combination.

When the auto-up control and the over-revolution determination are used in combination, upshift by the auto-up control and upshift by the over-revolution determination are successively performed under a specific condition, causing two-gear upshift, which is problematic.

It is desirable to provide a transmission controller capable of preventing two-gear upshift.

Hereinbelow, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values described in the embodiment are merely examples for ease of understanding of the disclosure and do not limit the disclosure unless otherwise specified. In the specification and the drawings, elements having substantially the same functions and structures are denoted by the same reference numerals, and repeated description thereof will be omitted. In addition, elements not directly related to the present disclosure are not illustrated.

FIG.1schematically illustrates the configuration of a vehicle1according to the embodiment of the present disclosure. The vehicle1is a hybrid vehicle such as a hybrid electric vehicle (HEV) and includes an engine10and a driving motor11. The vehicle1may further include various components besides the components described in this embodiment.

The engine10has a crankshaft10apassing therethrough. An explosion pressure in a combustion chamber causes pistons to reciprocate, rotating the crankshaft10a. A gear10band a pulley10care provided at the ends of the crankshaft10a.

The driving motor11is, for example, a synchronous rotary electric machine. When the driving motor11serves as a power source, the driving motor11rotates a primary shaft11awith electric power supplied from a high-voltage battery12. When the driving motor11serves as a generator, the generated electric power is supplied to the high-voltage battery12to charge the high-voltage battery12.

A starter13and an integrated starter generator (ISG)15are provided near the engine10. The starter13starts the engine. However, the starter13is used only at the initial start of a drive cycle. A gear13bis provided on a shaft13aof the stator13. The gear13bis engaged with the gear10bprovided on the outer circumference of a torque converter16, so that the power is transmitted between the shaft13aand the crankshaft10a.

The integrated starter generator (ISG)15assists the driving force of the engine10. The ISG15also serves as a motor for starting the engine10that has been stopped to avoid idling, for example. When the ISG15serves as the starting motor, the ISG15rotates a shaft15awith electric power supplied from an auxiliary battery14. A belt15cis stretched between a pulley15bprovided on the shaft15aand the pulley10c. The driving force of the ISG15is transmitted to the crankshaft10avia the shaft15a, the pulley15b, the belt15c, and the pulley10c, to start the engine10. The ISG15also serves as an alternator. When the ISG15serves as the alternator, the ISG15transmits the driving force of the engine10to the shaft15avia the crankshaft10a, the pulley10c, the belt15c, and the pulley15bto generate electric power. The ISG15charges the auxiliary battery14with the generated electric power.

A transmission18is coupled to an end of the crankshaft10avia the torque converter16and an input clutch17.

The torque converter16includes a front cover16acoupled to the crankshaft10aand a pump impeller16bfixed to the front cover16a. In the front cover16a, a turbine runner16cis opposed to the pump impeller16b. A turbine shaft16dis coupled to the turbine runner16c. A stator16eis disposed between the pump impeller16band the turbine runner16c, on the inner circumferential side of them, and the inside of the torque converter16is filled with a working fluid.

In the torque converter16, when the pump impeller16brotates, the working fluid forced to the outer circumferential side flows into the turbine runner16c, rotating the turbine runner16c. This way, the power is transmitted from the crankshaft10ato the turbine runner16c.

The stator16echanges the direction of flow of the working fluid flowing from the turbine runner16cand guides the working fluid back to the pump impeller16bto promote the rotation of the pump impeller16b. Thus, the torque converter16can amplify the torque transmitted to the turbine shaft16d.

Furthermore, in the torque converter16, a lock-up clutch16ffixed to the turbine shaft16dis opposed to the inner surface of the front cover16a. The lock-up clutch16fcan directly engage the crankshaft10awith the turbine shaft16d. In other words, the lock-up clutch16fis switchable between a closed state in which the crankshaft10aand the turbine shaft16dare directly engaged with each other and an open state in which the crankshaft10aand the turbine shaft16dare not directly engaged with each other.

When the lock-up clutch16fis open, the torque of the crankshaft10ais amplified and transmitted to the turbine shaft16d. When the lock-up clutch16fis closed, the torque of the crankshaft10ais directly transmitted to the turbine shaft16d.

As described, when the lock-up clutch16fis open, the torque converter16amplifies the torque of the crankshaft10aand transmits the torque to the turbine shaft16d. This in turn makes the rotational speed of the turbine shaft16dlower than the rotational speed of the crankshaft10a. This gives a driver a sense of slip that the vehicle1does not accelerate immediately even if the driver applies the accelerator pedal to increase the rotational speed of the engine10.

In this case, by closing the lock-up clutch16f, the crankshaft10ais directly engaged with the turbine shaft16dto cancel the function of the torque converter16. Doing so eliminates the amplification of the torque transmitted from the crankshaft10ato the turbine shaft16d, and the rotational speed of the engine10is directly transmitted to the turbine shaft16d. This allows the driver to enjoy driving without a sense of slip. Hereinbelow, the operation of directly engaging the crankshaft10awith the turbine shaft16dby means of the lock-up clutch16fis referred to as lock-up.

In the input clutch17, a fixed case17afixed to the turbine shaft16dand a moving member17bfixed to the primary shaft11aare opposed to each other. The moving member17bis moved toward the fixed case17aby the pressure of working oil supplied from an oil-hydraulic pump (not illustrated).

The input clutch17disconnects transmission of power between the turbine shaft16dand the primary shaft11ain a disengaged state in which the fixed case17aand the moving member17bare separated from each other. The input clutch17transmits power between the turbine shaft16dand the primary shaft11ain an engaged state in which the moving member17bis pressed against the fixed case17aby the oil pressure.

The transmission18includes a primary pulley19, a secondary pulley20, and a belt21. The primary pulley19is provided on the primary shaft11a. The secondary pulley20is provided on a secondary shaft22disposed in parallel with the primary shaft11a. The belt21is, for example, a chain belt formed by coupling link plates with pins, and is stretched between the primary pulley19and secondary pulley20. The belt21transmits power between the primary pulley19and the secondary pulley20.

The primary pulley19includes a fixed sheave19aand a movable sheave19b. The fixed sheave19aand the movable sheave19bare opposed to each other in the axial direction of the primary shaft11a. The opposing faces of the fixed sheave19aand the movable sheave19bare substantially conical, forming a groove over which the belt21is stretched.

Similarly, the secondary pulley20includes a fixed sheave20aand a movable sheave20b. The fixed sheave20aand the movable sheave20bare opposed to each other in the axial direction of the secondary shaft22. The opposing faces of the fixed sheave20aand the movable sheave20bare substantially conical, forming a groove over which the belt21is stretched.

The position of the movable sheave19bof the primary pulley19in the axial direction of the primary shaft11acan be changed by the pressure of oil supplied from an oil-hydraulic pump (not illustrated) via an oil-pressure control valve. The position of the movable sheave20bof the secondary pulley20in the axial direction of the secondary shaft22can be changed by the pressure of oil supplied from an oil-hydraulic pump.

As described, the distance between the fixed sheave19aand the movable sheave19bof the primary pulley19is changeable, and the distance between the fixed sheave20aand the movable sheave20bof the secondary pulley20is changeable. The width of the groove in which the belt21is stretched is wide at the radially outer side and is narrow at the radially inner side of the fixed and movable sheaves19aand19band the fixed and movable sheaves20aand20b. Hence, when the distance between the opposing conical faces is changed to change the width of the groove in which the belt21is stretched, the position where the belt21is stretched is changed.

In the transmission18, when the position where the belt21is stretched is changed, the diameters of the pulleys19and20over which the belt21is wound are changed. In other words, the effective diameters of the primary pulley19and the secondary pulley20are variable. The transmission18transmits power between the primary shaft11aand the secondary shaft22while changing the gear ratio therebetween. Thus, the transmission18serves as a continuously variable transmission that continuously changes the torque transmitted between the primary shaft11aand the secondary shaft22.

The secondary shaft22is coupled to an output shaft24via a gear mechanism23. The output shaft24includes a first output shaft24aand a second output shaft24b. The gear mechanism23couples the secondary shaft22and the first output shaft24ato each other to rotate them together. The first output shaft24aand the second output shaft24bare coupled to each other via an output clutch25. The output clutch25includes a fixed case25afixed to the second output shaft24band a moving member25bprovided on the first output shaft24a. The fixed case25aand the moving member25bare opposed to each other. The moving member25bis moved toward the fixed case25aby the pressure of working oil supplied from an oil-hydraulic pump (not illustrated).

The output clutch25disconnects transmission of power between the first output shaft24aand the second output shaft24bin the disengaged state in which the fixed case25aand the moving member25bare separated from each other. The output clutch25transmits power between the first output shaft24aand the second output shaft24bin the engaged state in which the moving member25bis pressed against the fixed case25aby the oil pressure. The power is output to a drive wheel26coupled to the second output shaft24b. The output clutch25can adjust the capacity of torque transmitted between the first output shaft24aand the second output shaft24baccording to the pressure of the working oil.

The output clutch25, which has a smaller torque capacity than the transmission18, transmits torque from the transmission18to the drive wheel26. When a torque, such as a disturbance, larger than the torque capacity of the output clutch25is input from the drive wheel26, the moving member25bslips with respect to the fixed case25a. Thus, the torque transmitted to the output clutch25is limited to a level smaller than or equal to the torque capacity of the output clutch25. Therefore, the output clutch25does not transmit, to the transmission18, a torque larger than the torque capacity of the transmission18. Hence, the output clutch25serves as a torque fuse.

The vehicle1is provided with a crank angle sensor S1, a primary rotational speed sensor S2, a secondary rotational speed sensor S3, a vehicle speed sensor S4, and an accelerator opening sensor S5. The crank angle sensor S1, the primary rotational speed sensor S2, the secondary rotational speed sensor S3, the vehicle speed sensor S4, and the accelerator opening sensor S5are electrically coupled to the controller30by signal wires.

The crank angle sensor S1is provided on the crankshaft10a, detects the rotational speed of the crankshaft10a, that is, the rotational speed of the engine10(hereinbelow, the engine speed), and outputs a signal indicating the engine speed to the controller30.

The primary rotational speed sensor S2is provided on the primary shaft11a, detects the rotational speed of the primary shaft11a(hereinbelow, the primary rotational speed), and outputs a signal indicating the primary rotational speed to the controller30.

The secondary rotational speed sensor S3is provided on the secondary shaft22, detects the rotational speed of the secondary shaft22(hereinbelow, the secondary rotational speed), and outputs a signal indicating the secondary rotational speed to the controller30.

The vehicle speed sensor S4detects the vehicle speed of the vehicle1and outputs a signal indicating the vehicle speed to the controller30. The accelerator opening sensor S5detects the depression amount of an accelerator pedal (not illustrated) provided in the vehicle1and outputs a signal indicating the depression amount to the controller30.

The controller30is coupled to the respective components, including the engine10and the driving motor11, described above and controls the entire vehicle1. In this embodiment, details of the control of the transmission18performed by the controller30will be mainly described in detail.

The controller30includes at least one processor30aand at least one memory30b. The processor30aincludes, for example, a central processing unit (CPU). The memory30bincludes, for example, a read-only memory (ROM) and a random-access memory (RAM). The ROM stores programs, operation parameters, and the like used by the CPU. The RAM temporarily stores data, such as variables and parameters, used for processing executed by the CPU.

FIG.2is a block diagram illustrating an example functional configuration of the controller30according to this embodiment. For example, as illustrated inFIG.2, the controller30includes a gear ratio controller40, an auto-up controller50, an over-revolution determination unit60, and a lock-up controller70.

The processor30aexecutes the program stored in the memory30bto perform various processing, including the processing described below performed by the gear ratio controller40, the auto-up controller50, the over-revolution determination unit60, and the lock-up controller70.

The gear ratio controller40controls the gear ratio of the transmission18. The gear ratio controller40has an automatic shift mode and a manual mode. In the automatic shift mode, the gear ratio is automatically controlled in accordance with the vehicle speed and the accelerator opening. In the manual mode, the gear ratio of the transmission18is controlled in accordance with the gear selected by the driver operating a shift lever (not illustrated) provided in the vehicle1.

In this embodiment, in the manual mode, the gear ratio controller40derives a target gear ratio based on the vehicle speed and the gear. Then, the gear ratio controller40multiplies the secondary rotational speed detected by the secondary rotational speed sensor S3by the target gear ratio to derive a target primary rotational speed. The gear ratio controller40controls the gear ratio of the transmission18such that the primary rotational speed detected by the primary rotational speed sensor S2equals the target primary rotational speed. Hereinbelow, the target primary rotational speed is also simply referred to as a target rotational speed.

In the manual mode, the auto-up controller50upshifts the transmission18when the primary rotational speed or the target rotational speed reaches or exceeds a first threshold. As described above, because the primary rotational speed is controlled so as to be closer to the target rotational speed, when the primary rotational speed and the target rotational speed are close to each other, the auto-up controller50performs upshift control using either the primary rotational speed or the target rotational speed. Hereinbelow, the control for upshifting the transmission18by the auto-up controller50is also referred to as auto-up control (first control).

In the manual mode, the over-revolution determination unit60upshifts the transmission18when the engine speed detected by the crank angle sensor S1reaches or exceeds a second threshold. Hereinbelow, the control for upshifting the transmission18by the over-revolution determination unit60is also referred to as over-revolution determination (second control).

The lock-up controller70controls the lock-up clutch16fsuch that the lock-up clutch16fis in an open state or a closed state. For example, the lock-up controller70controls and opens the lock-up clutch16fwhen the rotational speed of the turbine shaft16dis lower than a certain speed. Meanwhile, the lock-up controller70controls and closes the lock-up clutch16fwhen the rotational speed of the turbine shaft16dis higher than or equal to the certain speed.

In the manual mode, the auto-up controller50performs the auto-up control when the primary rotational speed or the target rotational speed reaches or exceeds the first threshold. In the manual mode, the over-revolution determination unit60performs the over-revolution determination when the engine speed reaches or exceeds the second threshold.

When the auto-up control and the over-revolution determination are performed successively, unintentional two-gear upshift may occur instead of intended one-gear upshift.

FIG.3is a graph illustrating the occurrence of two-gear upshift. InFIG.3, solid lines G1, G2, and G3indicate target gears, in which G1is the first gear, G2is the second gear, and G3is the third gear. The second gear is one gear higher than the first gear, and the third gear is one gear higher than the second gear.

Dashed line R1and two-dot chain line R2indicate the engine speed and the primary rotational speed. Dashed line R1indicates the engine speed and the primary rotational speed when gear change delay occurs, and two-dot chain line R2indicates the engine speed and the primary rotational speed when gear change delay does not occur.

One-dot chain lines Th1and Th2indicate the first threshold and the second threshold, respectively. InFIG.3, line Th1indicates the first threshold, and line Th2indicates the second threshold. The horizontal axis represents time.

As illustrated inFIG.3, in period P1before time T1, the target gear is set to the first gear G1, and the engine speed and the primary rotational speed R1gradually increase with the vehicle speed.

At time T1, the engine speed and the primary rotational speed R1reach the first threshold Th1. At this time, because the primary rotational speed R1is higher than or equal to the first threshold Th1, the auto-up controller50performs the auto-up control for changing the target gear from the first gear G1to the second gear G2.

In period P2between time T1and time T2, the engine speed and the primary rotational speed R2indicated by the two-dot chain line gradually decrease as a result of the target gear being changed from the first gear G1to the second gear G2. After the change to the second gear G2is completed, the engine speed and the primary rotational speed R2gradually increase with the vehicle speed.

In period P2and period P3after time T2, the engine speed and the primary rotational speed R2do not exceed the second threshold Th2. Hence, the target gear is maintained at the second gear G2in period P3, as illustrated by a two-dot chain line inFIG.3.

In some cases, in period P2, gear change from the first gear G1to the second gear G2is delayed, allowing the engine speed and the primary rotational speed R1to reach or exceed the second threshold Th2. The delay in the gear change from the first gear G1to the second gear G2is the gear change delay caused by, for example, individual differences of the components mounted in the vehicle1and a delayed response to the hydraulic control.

At time T2, the engine speed and the primary rotational speed R1indicated by dashed line reach the second threshold Th2. At this time, because the engine speed R1is higher than or equal to the second threshold Th2, the over-revolution determination unit60performs the over-revolution determination and performs processing for changing the target gear from the second gear G2to the third gear G3.

When the gear change delay occurs like this, the auto-up control and the over-revolution determination are performed successively, causing unintentional two-gear upshift, in which upshift occurs successively, instead of intended one-gear upshift.

To prevent the two-gear upshift, the over-revolution determination unit60according to this embodiment limits the conditions for performing the over-revolution determination. The conditions for performing the over-revolution determination with the over-revolution determination unit60according to this embodiment will be described in detail below.

FIG.4is a graph illustrating processing in the over-revolution determination according to the embodiment. InFIG.4, solid lines G1and G2indicate target gears, in which G1is the first gear, and G2is the second gear. The second gear is one gear higher than the first gear. The first gear G1and the second gear G2illustrated inFIG.4are the same as the first gear G1and the second gear G2illustrated inFIG.3.

Dashed line R1indicates the engine speed and the primary rotational speed when the gear change delay occurs. Two-dot chain line TPR1indicates the target rotational speed of the primary shaft11aderived by the gear ratio controller40. The method for deriving the target rotational speed has been described above.

One-dot chain lines Th1and Th2indicate the first threshold and the second threshold, respectively. InFIG.4, line Th1indicates the first threshold, and line Th2indicates the second threshold. The first threshold Th1and the second threshold Th2illustrated inFIG.4are the same as the first threshold Th1and the second threshold Th2illustrated inFIG.3.

One-dot chain line Th3indicates set values set for the respective gears of the transmission18. The set values are obtained in advance by experiments or the like. In this embodiment, the set value for a gear having a higher gear ratio, i.e., a lower gear, is set to be a smaller value than the set value for a gear having a lower gear ratio, i.e., a higher gear. Furthermore, the set value when the lock-up clutch16fis closed is set to be a smaller value than the set value when the lock-up clutch16fis open.

As illustrated inFIG.4, in period P1before time T1, the target gear is set to the first gear G1, and the engine speed and the primary rotational speed R1gradually increase with the vehicle speed.

At time T1, the engine speed and the primary rotational speed R1reach the first threshold Th1. At this time, because the primary rotational speed R1is higher than or equal to the first threshold Th1, the auto-up controller50performs the auto-up control for changing the target gear from the first gear G1to the second gear G2.

Furthermore, in period P2between time T1and time T2, as a result of the above-described gear change delay, i.e., the delay in the gear change from the first gear G1to the second gear G2, the engine speed and the primary rotational speed R1reach the second threshold Th2at time T2.

At this time, the over-revolution determination unit60determines whether the target rotational speed TPR1is higher than or equal to the set value Th3. Then, depending on the determination result, the over-revolution determination unit60determines whether to perform the over-revolution determination.

For example, the over-revolution determination unit60performs the over-revolution determination when the target rotational speed TPR1is higher than or equal to the set value Th3, and does not perform the over-revolution determination when the target rotational speed TPR1is lower than the set value Th3.

At time T2, the target rotational speed TPR1is lower than the set value Th3. Hence, even when the primary rotational speed R1has reached the second threshold Th2at time T2, the over-revolution determination unit60does not perform the upshift control, and the target gear is maintained at the second gear G2.

As described, the over-revolution determination unit60according to this embodiment performs the over-revolution determination when the target rotational speed TPR1is higher than or equal to the set value Th3, and does not perform the over-revolution determination when the target rotational speed TPR1is lower than the set value Th3. This prevents two-gear upshift caused by the gear change delay.

The set values Th3according to this embodiment are set for the respective gears of the transmission18, and the set value Th3for a gear having a higher gear ratio is set to be a smaller value than the set value Th3for a gear having a lower gear ratio. Thus, appropriate set values Th3are set for the respective gears, and two-gear upshift is effectively prevented at every gear.

Furthermore, in this embodiment, the set values Th3differ depending on the state of the lock-up clutch16f. For example, the set value Th3when the lock-up clutch16fis closed is set to be a smaller value than the set value Th3when the lock-up clutch16fis open. The primary rotational speed when the lock-up clutch16fis closed tends to be higher than that when the lock-up clutch16fis open. Thus, to make it difficult for the primary rotational speed to exceed the allowable rotational speed, the set value Th3when the lock-up clutch16fis closed is set to be a smaller value than the set value Th3when the lock-up clutch16fis open.

FIG.5is a flowchart illustrating a flow of processing performed by the controller30according to this embodiment.FIG.5illustrates the flow of processing performed by the controller30in the manual mode. As illustrated inFIG.5, first, the gear ratio controller40determines the target gear based on the gear selected by the driver operating the shift lever (not illustrated) (step S100).

Next, the gear ratio controller40determines the target gear ratio based on the determined target gear and the vehicle speed acquired from the vehicle speed sensor S4(step S200). Note that the target gear ratios are associated with the vehicle speeds and the target gears and are stored in the form of a map in a storage unit (not illustrated) of the controller30. The target gear ratios are lower for higher vehicle speeds and are lower for higher target gears. The gear ratio controller40derives the target rotational speed based on the determined target gear ratio and the value acquired from the secondary rotational speed sensor S3(step S300). For example, the gear ratio controller40derives the target rotational speed by multiplying the secondary rotational speed by the target gear ratio. The gear ratio controller40controls the gear ratio such that the value acquired from the primary rotational speed sensor S2equals the target rotational speed (step S400).

The gear ratio controller40determines whether to perform downshift based on the value acquired from the vehicle speed sensor S4and the value acquired from the accelerator opening sensor S5(step S500). If it is determined that downshift is performed (YES in step S500), the process returns to step S100, and the gear ratio controller40determines that the target gear is a gear that is one stage lower than the current gear.

The auto-up controller50determines whether the primary rotational speed or the target rotational speed is higher than or equal to the first threshold Th1(step S600). If it is determined that the primary rotational speed or the target rotational speed is higher than or equal to the first threshold Th1(YES in step S600), the auto-up controller50performs the auto-up control, and it is determined in step S100that the target gear is a gear that is one gear higher than the current gear.

The over-revolution determination unit60determines whether the target rotational speed TPR1is higher than or equal to the set value Th3(step S700). When it is determined that the target rotational speed TPR1is higher than or equal to the set value Th3(YES in step S700), the over-revolution determination unit60permits execution of the over-revolution determination, and, when it is determined that the target rotational speed TPR1is lower than the set value Th3(NO in step S700), the over-revolution determination unit60does not permit execution of the over-revolution determination.

When it is determined that the target rotational speed TPR1is higher than or equal to the set value Th3(YES in step S700), the over-revolution determination unit60determines whether the engine speed is higher than or equal to the second threshold Th2(step S800). When it is determined that the engine speed is higher than or equal to the second threshold Th2, the over-revolution determination unit60performs the over-revolution determination, and it is determined in step S100that the target gear is a gear that is one gear higher than the current gear.

Although the embodiment of the present disclosure has been described above with reference to the accompanying drawings, the present disclosure is not limited to such embodiment. It is apparent that those skilled in the art can conceive various modifications or corrections within the scope described in the claims, and it is understood that such modifications or corrections belong to the technical scope of the present disclosure.

The series of processing performed by the controller30according to this embodiment described above may be implemented by using any of software, hardware, and a combination of software and hardware. A program constituting the software is stored in advance in, for example, a non-transitory storage medium provided inside or outside the device. The program is read from the non-transitory storage medium (for example, a ROM) into a transitory storage medium (for example, a RAM) and is executed by a processor, such as a CPU.

Programs for implementing the functions of the above-described devices may be created and installed in computers of the devices. As a result of processors executing the programs stored in memories, the processing for implementing the above-described functions is executed. At this time, execution of each program may be shared by multiple processors, or may be performed by a single processor. Furthermore, the functions of the devices may be implemented by using cloud computing, in which multiple computers are coupled to one another via a communication network. The programs may be distributed from an external device through a communication network and installed in the computers of the devices.

In the above embodiment, an example in which the auto-up control is performed in the manual mode has been described. However, the present disclosure may be applied to control for performing similar upshift in the automatic shift mode. In the above embodiment, the example in which the auto-up control is performed based on the primary rotational speed or the target rotational speed has been described. However, the present disclosure is not limited thereto, and the auto-up control may be performed based on the rotational speed of the turbine shaft16dor the vehicle speed and the accelerator opening instead of the primary rotational speed or the target rotational speed. In the above embodiment, an example in which the gear shift control is performed based on the primary rotational speed has been described. However, the present disclosure is not limited thereto, and the gear shift control may be performed based on the rotational speed of the turbine shaft16dinstead of the primary rotational speed.

In the above embodiment, an example in which the target rotational speed is derived based on the secondary rotational speed has been described. However, the present disclosure is not limited thereto, and the target rotational speed may be derived based on the rotational speed of the output shaft24instead of the secondary rotational speed.

The present disclosure prevents two-gear upshift.

The controller30illustrated inFIG.2can be implemented by circuitry including at least one semiconductor integrated circuit such as at least one processor (e.g., a central processing unit (CPU)), at least one application specific integrated circuit (ASIC), and/or at least one field programmable gate array (FPGA). At least one processor can be configured, by reading instructions from at least one machine readable tangible medium, to perform all or a part of functions of the controller30including the gear ratio controller40, the auto-up controller50, the over-revolution determination unit60, and the lock-up controller70. Such a medium may take many forms, including, but not limited to, any type of magnetic medium such as a hard disk, any type of optical medium such as a CD and a DVD, any type of semiconductor memory (i.e., semiconductor circuit) such as a volatile memory and a non-volatile memory. The volatile memory may include a DRAM and a SRAM, and the non-volatile memory may include a ROM and a NVRAM. The ASIC is an integrated circuit (IC) customized to perform, and the FPGA is an integrated circuit designed to be configured after manufacturing in order to perform, all or a part of the functions of the modules illustrated inFIG.2.