1. Field of the Invention
The present invention relates to an automatic transmission controller and more particularly to the control of a solenoid valve that is used for changing gear ratios of an automatic transmission.
2. Description of the Prior Art
So far, a control method of a solenoid valve that is used for control of an automatic transmission is disclosed in the Japanese Patent Publication No. Hei 05-035293. In this solenoid valve control method, to make the program structure simple, control cycles in the steady state and the speed changing state were set at fixed times.
FIG. 5 (a), (b) and (c) are time charts showing the operations of the above-mentioned conventional transmission controller. The solenoid valve control cycle cannot be made shorter than a certain time from the viewpoint of hydraulic pressure response and to avoid a natural frequency of a vehicle body. So, the control cycle is set at 28.57 ms as illustrated. In contrast to this, in the main routine which computes controlled variables, the solenoid valve is controlled as fast as possible, for instance, at a control cycle of 5 ms as shown in the example in FIG. 5 to improve manpower taking accuracy and control accuracy of a throttle opening sensor, etc., that is, to get new information precisely.
In the above-mentioned automatic transmission control method, the solenoid valve is controlled at an interval of fixed cycle time in the steady state as well as the speed change state and therefore, there was such a problem that the speed change control was delayed to start by maximum one control cycle when changing the steady state to the speed change state. In other words, even when the speed change is judged as required in the program main process, the duty solenoid control started at a time t2 as the next duty solenoid control process is set at the time t2. Therefore, the control is delayed by maximum one cycle.