Patent ID: 8544577

Claim:
A control system for a hybrid vehicle that comprises an engine, a motor generator, a torque converter with a lock-up clutch and a ratio-change mechanism and that is driven by a driving force being transmitted from at least one of said engine and said motor generator through said torque converter and said ratio-change mechanism to wheels; said control system comprising: slip-detecting means, which detects a slip ratio of said torque converter; and lock-up-controlling means, which controls engagement of said lock-up clutch; wherein: while said hybrid vehicle is moving along with an accelerator pedal being released from a stepped down condition; a driving force from said wheels is transmitted through said ratio-change mechanism and said torque converter to said motor generator for energy regeneration; if the slip ratio of said torque converter detected by said slip-detecting means is larger than a first threshold value and equal to or smaller than a second threshold value, which is greater than said first threshold value by a predetermined value, then an engagement control of said lock-up clutch is initiated whereby said lock-up clutch is controlled into engagement only by said lock-up-controlling means while said motor generator is being operated by said control system in cooperative operation for reducing said slip ratio; and if the slip ratio of said torque converter detected by said slip-detecting means is larger than the second threshold value, the cooperative operation of said motor generator is terminated and control of said lock-up clutch into engagement by said lock-up-controlling means is terminated.