The present invention relates to a transmission control apparatus for an automatic transmission of a vehicle, and more particularly to a control apparatus for a continuously variable transmission (CVT) suitable for a vehicle which can accelerate comfortably based on the driver""s intention or the running state of the vehicle and can run with taking the fuel consumption into consideration when the acceleration is not required and a control method thereof.
In a vehicle with the continuously variable transmission, the speed is generally changed by using a control map in which values of the transmission gear ratio pre-determined by the vehicle speed and the throttle opening are represented as a table.
However, in such a control method, it is required to pre-determine a control constant in consideration of various driving conditions when the design or the development of the vehicle is made. It is a task called as tuning or matching, which takes a lot of doing and thus time.
To solve such a problem, it is thought to eliminate the time required to tune by using a control method in which the optimum transmission gear ratio is calculated during run of the vehicle. For example, the method proposed by us is disclosed in Japanese Patent Application Laid-Open No. 7-174219 (1995). However, in this method, the actual driving torque follows the predetermined target value or the target driving torque. There is, therefore, a problem that even though new target driving torque revised according to the situation is preferable, it is impossible to control the transmission gear ratio by setting the new target driving torque as a target value.
An object of the present invention is to provide an improved CVT control apparatus for a vehicle, in which the time required to tune can be remarkably decreased. By using the improved CVT control apparatus, it becomes possible that the drive feeling is constant independently of the running state, the vehicle is accelerated as the driver""s intention if accelerated due to the actuation of an accelerator pedal, and the run of the vehicle is performed so as to improve the fuel consumption rate if the acceleration is not required.
Therefore, by calculating the correct driving torque every time in the present invention, the transmission gear ratio is calculated to obtain the target driving torque set based on the amount of actuation of an accelerator pedal, and the obtained target driving torque is corrected by the gradient of a road obtained from the calculated driving torque. Further, the gear ratio which aims at the improvement of acceleration and the gear ratio which aims at the improvement of the rate of fuel consumption are weighted and combined with each other, and the optimum gear ratio is obtained by using fuzzy inference.
Because the target driving torque is set according to a state at that time during run of a vehicle, and the transmission gear ratio is determined by using the target driving torque, the drive feeling is not changed even if the circumstance of run is changed. Further, the vehicle can be accelerated as the driver""s intention at the time of the acceleration due to the actuation of the accelerator pedal, and run of the vehicle is performed so as to improve the fuel consumption rate if the acceleration is not required.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed several exemplary embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.