A power transmission system includes a first transmission provided in a first power transmission path, a second transmission provided in a second power transmission path, a first engagement device, a second engagement device, a third engagement device, a fail-safe valve, and an electronic control unit. The third engagement device selectively connects or interrupts one of the first and second power transmission paths. The electronic control unit is configured to, during traveling in a state where the third engagement device is released, output hydraulic pressure commands for simultaneous engagement of the first engagement device and the second engagement device. The electronic control unit is configured to, when it is determined that both the first engagement device and the second engagement device are engaged, prohibit traveling using the one of the first and second power transmission paths which is selectively connected or interrupted by the third engagement device.

When the speed ratio of a belt-type continuously variable transmission is equal to or larger than a predetermined threshold value, switching between a first power transmission path including a gear transmission mechanism and a second power transmission path including a belt-type continuously variable transmission is performed by means of clutches, so as to reduce a difference in an input shaft rotational speed applied to the clutches before and after the switching.

An upshift target turbine rotational speed and a target primary rotational speed are calculated based on a target input shaft rotational speed restricted in a range of an upper limit guard value to a lower limit guard value. Thus, the difference between the upshift target turbine rotational speed and the target primary rotational speed is suitably decreased. When a torque transmission path is switched from a second transmission path to a first transmission path, the difference between an actual turbine rotational speed at a switching start time point and the actual turbine rotational speed at a switching completion time point is reduced.

A continuous and reversible mechanical transmission system with a power branch, with an input shaft (17) and an output shaft (16), formed by a continuously variable transmission (1) connected to the shaft of the motor and by at least one planetary gear train (2) linked to the shaft of the motor (17) and to the continuously variable transmission. The continuously variable transmission includes a first pair of gears (3 and 4) linked by means of a transmission (5). The gear train (2) comprises a second pair of gears (6-7) linked by a transmission (8) and at least a first and second transmission step (9-10), each one of which comprises an epicyclic gear carrier (9-13) and a pair of epicyclic gears (12-14).

An automatic transmission where an engagement mode in which the forward engagement element is put in the engagement state is executed when the vehicle travels forward in the second mode in which the second engagement element is put in the engagement state and the first engagement element is put in a release state.

Mechanical infinitely variable transmissions (IVTs) and vehicles employing such IVTs are discussed. The IVT can comprise a planetary gearset with a sun gear driven based on an input angular velocity and an annulus gear driven based on a combination of the input angular velocity and a variable gear ratio of a pulley system, wherein the variable gear ratio of the pulley system can be electrically controlled by an actuator. A drive element can be driven based on a carrier of the planetary gearset.

In a vehicle in which a continuously variable transmission and a gear mechanism are provided in parallel on a power transmission pathway between an input shaft and an output shaft, (i) an electronic control unit performs CVT shifting, in view of shift characteristics of C to C shifting in which the speed ratio is changed in stages, or (ii) then electronic control unit performs C to C shifting, in view of shift characteristics of CVT shifting in which the speed ratio is steplessly changed.

When neutral control is started by placing a CVT drive clutch in a semi-engaged state while a vehicle is decelerating in a state where a second power transmission path is established, a clutch mechanism that is semi-engaged in neutral control while the vehicle is decelerating is changed from the CVT drive clutch to a forward clutch before a stop of the vehicle, so it is possible to continue the neutral control until a stop of the vehicle. At a stop of the vehicle, a power transmission path is already changed to a first power transmission path that establishes a gear ratio (EL) higher than a highest gear ratio (max) that can be established by the second power transmission path. Thus, right after a stop of the vehicle, it is possible to execute idle stop control.

An automatic transmission where an engagement mode in which the forward engagement element is put in the engagement state is executed when the vehicle travels forward in the second mode in which the second engagement element is put in the engagement state and the first engagement element is put in a release state.

In a region in which a rate of change in slip ratio of a transmission belt with respect to a change in input torque exceeds a permissible slip ratio rate of change set in advance, a steep change in the slip ratio is suppressed by limiting the rate of change in the input torque.