Implement an Automatic Transmission Gear System by Using the duration Operator
This example models an automotive transmission system by using the Stateflow® temporal logic operator duration to automatically shift gears based on the vehicle's throttle requirements and speed. For more information, see Control Chart Execution by Using Temporal Logic.
Model Description
There are five major blocks in this model.
User Inputs: Provides two inputs to the model, brake and throttle.
Engine: Calculates engine RPM based on impeller torque value and throttle.
Gear_logic: Calculates next gear based on current gear, throttle, and current vehicle speed.
Transmission: Calculates impeller and output torque based on RPM, gear and transmission speed.
Vehicle: Calculates vehicle and transmission speed based on output torque and brake.
Chart Description
The Stateflow chart models the shifting of gears based on throttle and speed of the vehicle. The down_threshold and up_threshold outputs represent minimum and maximum speed values that throttle and current gear are able to handle. The Simulink function calculate_thresholds calculates these two values using throttle and gear as inputs. If the actual speed is higher than up_threshold for longer than TWAIT, then the chart transitions to higher gear. Conversely, if the actual speed is lower than down_threshold for longer than TWAIT, then the chart transitions to a lower gear. At each time step, the chart calls the duration operator to find the amount of time for which speed is higher than up_threshold. If this time exceeds TWAIT then boolean variable up is set which in turn transitions chart from current gear to a higher gear. Conversely the chart transitions to a lower gear based on the value of down_threshold.
Active State Data
Active State Data is the enumerated data that represents the current active state during simulation. In this chart, the output data gear maintains the current active state which in turn represents the current gear. This data automatically updates when a transition is taken. The data is used by downstream blocks as well as by the Simulink® function calculate_thresholds. For more information, see Monitor State Activity Through Active State Data.
Simulation
To visualize these changes, simulate the model and open the scope.
