1. Field of the Invention
The present invention relates to a transmission control apparatus for an infinitely variable transmission in which the transmission control is performed in an open-loop fashion based on transmission control information including a throttle opening position, a vehicle speed, and the like.
2. Description of the Prior Art
A prior art transmission control apparatus of an infinitely variable transmission is disclosed, for example, in U.S. Pat. No. 4,434,675.
This control apparatus is arranged such that a roller supporting body is moved by mechanically manipulating a main control valve in accordance with the position of the accelerating pedal and a negative pressure from the intake manifold, and a desired transmission ratio is obtained by tilting power rollers to desired positions by mechanically feeding back the movement position of the roller supporting body to the main control valve by means of a precess cam.
However, in this prior art control apparatus there are problems in that because it is designed to mechanically transmit the position of the accelerator pedal and the manifold pressure to the main control valve, the control mechanism tends to become large and complicated, and further, because it is unable to perform sophisticated control based on various transmission control information, optimum transmission control adapted to a vehicle running condition cannot be achieved. Moreover, since the control is effected by hydraulic and mechanical means, the transmission ratio is varied due to changes in hydraulic pressure caused by changes in fluid temperature, and thus transmission operation with high precision is impossible. Furthermore, since the control is basically intended to maintain constant engine speed, comfortable ride in the vehicle is not necessarily provided.