Surplus temperature rise prevention device of torque converter in automatic transmission for vehicle with torque converter

When the heating value per unit time of a torque converter reaches an upper limit, an automatic transmission is down shifted to easily prevent surplus temperature rise of working oil regardless of the characteristics of the torque converter and the engine. When the heating value per unit time of the torque converter reaches the upper limit, the automatic transmission is down shifted to forbid up shift. From the engine speed, the engine torque, the number of revolutions of the input shaft of the automatic transmission, and the performance diagram of the torque converter when a vehicle is running at a lower shifting step, an expected number of revolutions of the input shaft and an expected input torque after up shift are operated. Based on the expected number of revolutions of the input shaft, the expected input torque and the performance diagram, an expected speed ratio and an expected capacity coefficient are operated. Using the expected number of revolutions of the input shaft, the expected speed ratio and t