Provided is an automatic transmission with which a switching mechanism thereof is hardly damaged even if the hydraulic pressure supplied to a hydraulic pressure control circuit temporarily changes. A control part ECU of the automatic transmission TM switches the first brake B1 to the reverse rotation preventing state when a signal indicating that the slider is at a position corresponding to the reverse rotation preventing state is received while the control unit ECU recognized that it has switched the first brake B1 to the fixed state.

The present invention provides an automatic transmission capable of properly judging faults of a switching mechanism. A control part ECU of the automatic transmission TM has an actual change gear ratio calculating part 10 and a fault judging part 11. Under a condition that the control part ECU has recognized that the first brake device B1 is switched to a reverse rotation preventing state, if the actual change gear ratio is kept to be an actual change gear ratio prior to a reduce of a rotational speed of a drive source ENG when the rotational speed of the drive source ENG is reduced, then the fault judging part 11 judges that a first brake B1 has a fault.

A planetary gear train of an automatic transmission for a vehicle is provided. The planetary gear train includes an input shaft receiving power of an engine and an output shaft outputting the power. Additionally, four planetary gear sets are provided. Various shafts the connect the elements of the gear sets either selectively or directly. The planetary gear set maximizes driving efficiency of the engine and improves power delivery performance and fuel consumption through the achievement of the more shift-stages of the automatic transmission

Ten or more forward speeds and at least four reverse speeds are achieved by a planetary gear train of an automatic transmission for a vehicle including an input shaft, an output shaft, four planetary gear sets respectively having three rotational elements, and six control elements for selectively interconnecting the rotational elements and a transmission housing.

A planetary gear train of a transmission for a vehicle is provided. The planetary gear train includes an input shaft that receives power of an engine and an output shaft that outputs power. Multiple planetary gear sets are provided each having three rotation elements. Various shafts then either directly or selectively connect the rotation elements. The transmission is then capable of maximizing engine driving efficiency and improving a power delivery performance and fuel consumption.

An apparatus of an automatic transmission includes a control unit controlling engagement and release of engaging mechanisms. One of the engaging mechanisms is a mechanical engaging mechanism which can be switched to a first state and a second state in which rotation of a rotational element in both directions is restricted. In a reverse range, the mechanical engaging mechanism is set in the second state. If a shift range is switched to the reverse range when the mechanical engaging mechanism is in the first state, the control unit starts engagement corresponding to the reverse range after executing preparation processing. If the shift range is switched from the reverse range to a forward range in the preparation processing, the control unit establishes a forward gear range by controlling the engaging mechanisms according to a degree of progress of the preparation processing.

A planetary gear train of an automatic transmission for a vehicle may include: an input shaft receiving torque of an engine; an output shaft outputting changed 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; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements. The planetary gear train improves power delivery performance and fuel economy by achieving at least ten forward speed stages and one reverse speed stage, and widens gear ratio span and secures linearity of step ratios.

A planetary gear train of an automatic transmission for a vehicle may include: an input shaft receiving torque of an engine; an output shaft outputting changed 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; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements. The planetary gear train improves power delivery performance and fuel economy by achieving at least ten forward speed stages and one reverse speed stage, and widens gear ratio span and secures linearity of step ratios.

The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed 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; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements.

The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed 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; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements.