A clutch that includes a friction plate; a separator plate; a clutch hub; and a piston that presses the friction plate and the separator plate, wherein the clutch hub includes a hub on which an inner peripheral portion of the friction plate or the separator plate is fitted, a tubular shaft that movably supports the piston, and an engagement oil chamber defining wall that together with the piston defines an engagement oil chamber to which an engagement oil pressure is supplied, the hub is spline-fitted on a gear of a planetary gear so as to rotate with the gear, and the tubular shaft is rotatably supported by a central shaft and is fitted by a spigot joint in the gear.

A planetary gear train of an automatic transmission for a vehicle having an input shaft for receiving torque of an engine; an output shaft for outputting torque; a first planetary gear set including first, second, and third rotation elements; a second planetary gear set including fourth, fifth, and sixth rotation elements; a third planetary gear set including seventh, eighth, and ninth rotation elements; and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, improves power delivery performance and fuel economy by achieving at least ten forward speed stages.

An automatic transmission, which is configured such that there is no difference of rotation between a third sun gear and an intermediate shaft in a state where a second clutch is brought into a release state and a seventh speed stage is established, is provided. In the automatic transmission, at the time of a gear shift from a tenth speed stage where second and third clutches and a first brake are brought into an engagement state to a seventh speed stage where first, third, and fourth clutches are brought into an engagement state, the fourth clutch is engaged and the first brake is released to establish the seventh speed stage with the second clutch in the engagement state. Then, the first clutch is engaged and the second clutch is released to make transition to the seventh speed stage with the second clutch in the release state.

An automatic transmission has a first clutch shaft that constantly connects first and fourth planetary gear sets, a second clutch shaft that constantly connects second and third planetary gear sets, and a third clutch shaft that constantly connects the third and first planetary gear sets. A drive shaft is constantly connected to the fourth planetary gear set; an output shaft is constantly connected to the third planetary gear set. The first planetary gear set is directly connected to two shift elements, the second planetary gear set is directly connected to four shift elements, the third planetary gear set is directly connected to two shift elements, the fourth planetary gear set is directly connected to four shift elements. The drive shaft is directly connected to only one shift element. The output shaft is directly connected to only one shift element.

An automatic transmission has eight rotatable shafts, four planetary gear sets and seven shift elements for shifting several forward gears and one reverse gear. A first element of the second planetary gear set forms the first shaft designed as the drive shaft of the transmission. A second element of the third planetary gear set forms the second shaft designed as the output shaft of the transmission. A second element of the first planetary gear set forms the third shaft. A first element of the first planetary gear set forms the fourth shaft. A third element of third planetary gear set forms the fifth shaft. As the sixth shaft, a third element of the first planetary gear set, a second element of the second planetary gear set and a first element of the third planetary gear set are constantly connected. A third element of the second planetary gear set forms the seventh shaft. A first brake is arranged in the power flow between the third shaft and the housing. A second brake is arranged in the power flow between the fourth shaft and the housing, a third brake is arranged in the power flow between the fifth shaft) and the housing. A first clutch (C1) is arranged in the power flow between the first and the seventh shafts. A second clutch is arranged in the power flow between the first and third shafts. A third clutch is constantly connected to the eighth shaft. A fourth clutch is in the power flow between the first and fourth shafts.

A method of controlling an automatic transmission is provided. The automatic transmission includes a piston having first and second surfaces opposite from each other, friction plates, engaging and disengaging hydraulic pressure chambers for supplying and discharging hydraulic pressure and directing the piston to push the friction plates to be engaged and disengaged, a hydraulic pressure control valve for supplying and discharging hydraulic pressure to and from the chambers, first and second oil paths communicating the valve with the chambers, and a pressure reducing valve disposed in the second oil path and for preventing hydraulic pressure of the disengaging hydraulic pressure chamber from exceeding a given set pressure. The second surface has a larger area for receiving hydraulic pressure than an area of the first surface for receiving hydraulic pressure. The method includes changing the given set pressure according to information regarding a state of the automatic transmission.

A method for operating a vehicle drivetrain (1) includes decoupling, in the presence of a demand for realizing a sailing operating state of the vehicle drivetrain (1) during which a drive machine (2) is active and the power flow between the drive machine (2) and a drive output (3) is disconnected in a gearbox (4), the active drive machine (2) from the drive output (3) by opening of one of a plurality of shift elements (A to F) that is held in a closed operating state in order to realize the operating state present before the demand for decoupling of the active drive machine (2). The method also includes then actuating the plurality of shift elements (A to F) in a manner dependent on the present operating state profile of the vehicle drivetrain (1) and with the active drive machine (2) decoupled from the drive output (3).

A method for operating a vehicle drivetrain (1) having a drive machine (2), an output (3) and a gearbox (4) with the gearbox (4) arranged in power flow between the drive machine (2) and the output (3) includes opening, in the presence of a demand for activation of a sailing operating function of the vehicle drivetrain (1) and a simultaneously activated engine start-stop function, a positively engaging shift element (F) while the drive machine (2) is left both decoupled from the output (3) and shut down.

A method of controlling an automatic transmission mounted on a vehicle having an automatic engine stop mechanism for automatically stopping and restarting an engine, is provided. The transmission includes a piston having first and second surfaces, friction plates, engaging and disengaging hydraulic pressure chambers, a hydraulic pressure control valve for supplying/discharging hydraulic pressure to/from the chambers, first and second oil paths communicating the control valve with the chambers, a pressure reducing valve for preventing pressure of the disengaging chamber from exceeding a given set pressure, a hydraulic pressure supply device for supplying pressure to the control valve in the automatic stop state, and a mechanical oil pump for supplying pressure to the control valve while the engine is driving, the second surface having a larger pressure receiving area than the first surface. The method includes adjusting the set pressure to be lower in the automatic stop state than while driving.

A method for operating a vehicle drivetrain (1) includes proceeding, in the presence of the demand for activation of the engine start-stop function of the vehicle drivetrain (1) and a simultaneously shut-down drive machine (2), from an operating state of the vehicle drivetrain (1) during which a sailing operating function of the vehicle drivetrain (1) is active, during which the drive machine (2) is decoupled from the drive output (3), during which the positively engaging shift element (F) is open and during which a rotational speed (n_ab) of the drive output (3) is higher than a defined rotational speed at which a rotational speed difference between shift element halves of the positively engaging shift element (F) lies within a rotational speed range within which the positively engaging shift element (F) is transferrable into the closed operating state, and actuating the positively engaging shift element (F) in a closing direction no later than when the defined rotational speed is reached.