A diagnostic method of determining clutch failure of a dual clutch transmission (DCT) includes comparing, by a controller, a wheel torque of a vehicle with a driving load torque of the vehicle, confirming, by the controller, whether or not the vehicle is driving, if, as a result of comparing step, the wheel torque is greater than the driving load torque, releasing, by the controller, a gear engaged with a non-drive shaft, if, as a result of the confirming step, the vehicle is in a stopped state, reconfirming, by the controller, whether or not the vehicle is driving, after the releasing step, and judging, by the controller, that a transmission clutch of the non-drive shaft fails, if, as a result of the reconfirming step, the vehicle is driving.

A diagnostic method of determining clutch failure of a dual clutch transmission (DCT) includes comparing, by a controller, a wheel torque of a vehicle with a driving load torque of the vehicle, confirming, by the controller, whether or not the vehicle is driving, if, as a result of comparing step, the wheel torque is greater than the driving load torque, releasing, by the controller, a gear engaged with a non-drive shaft, if, as a result of the confirming step, the vehicle is in a stopped state, reconfirming, by the controller, whether or not the vehicle is driving, after the releasing step, and judging, by the controller, that a transmission clutch of the non-drive shaft fails, if, as a result of the reconfirming step, the vehicle is driving.

The present invention provides a method for searching a touch point of a clutch in a dual clutch transmission, including: (a) a step of checking whether a touch point searching condition for a non-driving clutch and a driving clutch is met or not; (b) when the search condition of the step (a) is met, a step of detecting a searching point at which an absolute value of a difference between an acceleration value of an engine and an acceleration value of the driving clutch is larger than a threshold value after applying a position value of the non-driving clutch to the engine; and (c) a step of determining a position of the non-driving clutch corresponding to the searching point as the touch point.

A clutch torque control method for a dual clutch transmission (DCT) vehicle may include a shift initiation determining step of determining whether power-on downshift in which a driver steps on an accelerator pedal to change a current shift stage to a lower shift stage is initiated, and a torque correcting step of correcting basic control torque according to torque-stroke (TS) curve characteristics for controlling a disengagement-side clutch within a real shift range in which a number of rotations of an engine is changed with observer torque calculated by a torque observer when the power-on downshift is initiated, and determining the corrected basic control torque into control torque of the disengagement-side clutch.

A transmission utilizes an electro-magnetically actuated selectable one-way-clutch. The one-way-clutch prevents rotation of a transmission member in both directions when a current exceeds a threshold and permits rotation in only one direction otherwise. To prevent un-intended engagement, a switch interrupts the current unless a second current exceeds a threshold. In order to engage the one-way-clutch, both currents are set above their respective thresholds by a controller. In the event of a single fault such as a short circuit, the system continues to function normally. The controller may periodically test for a fault by intentionally setting one current above its threshold and the other below its threshold and determining the state of the one-way-clutch by measuring speeds of transmission elements.