Project
CVT BAJA ATV Test Report
Overview:
This is the model for the BAJA All-Terrain Vehicle which uses a Continuously Variable Transmission as the powertrain (No Manual Gear Shift). The actual vehicle consists of 5 main components Engine, CVT, Vehicle Body, Suspension, and Tire. As in normal vehicle a driver has to manually provide the throttling and breaking action in order to drive the vehicle, this model has used a Signal Builder Block wherein we can provide a range of Throttle and Braking conditions w.r.t time. The second major component in the model is the engine, which is mathematically modelled with the help of Engine Torque-Speed Curve data collected from the actual BAJA field vehicle. This set of data helps the engine block to decide what should be Torque/Speed output depending on the fuel supply. CVT consist of Primary and Secondary Pulley, Variator and Belt, basically the Variator helps to change the pulley dimensions and thus varies the speed for Input and Output shafts. Before feeding the output of the CVT, Simple gear set is used to pull down the angular velocity and increase the torque. While the vehicle is in motion, the vehicle body will experience large amount of forces including aerodynamic drag, normal reactions on the wheel/suspensions (due to vehicle wt.) and vehicle inclination. The Vehicle Body block takes into consideration for all these declared forces, and provides us the vehicle velocity/ Tire velocity for the provided throttling. An important catch here is in real time situation the CVT ratio has to upgrade itself according to the vehicle speed, to take it into consideration the Look-Up Table is used, which uses data from CVT ratio vs Vehicle Speed (data collected from a tested vehicle). Data recorded in this model consists of Throttle and Brake Inputs, CVT Primary and Secondary shafts angular velocities, Vehicle Speed and Distance. As discussed above the Engine Torque- Speed Curve and Lookup Table Visualization are the data, which is feed to engine and CVT block for testing the model in real time situation.
Blocks Used In Model:
To build this model following Simscape and Simulink blocks are used:
Signal Builder Block 1 – To provide input signals i.e. Braking and Throttle inputs w.r.t time
Goto Block – 2 Goto blocks are used to pull the data from 1st Signal Builder block
Simulink to PS convertor – Is used to convert Throttle Signal into physical signal for the engine
Engine block – where T port- Throttle input port whose value ranges between 0-1 and which indicates torque demanded by engine as a fraction of maximum torque
F and B- mechanical rotational conserving ports linked with engine crankshaft and engine block
P and FC- Output ports reporting the engine Power and its Fuel Consumption
Engine sensor subsystem – which includes an Ideal rotational sensor, the F and B mechanical rotational conserving ports are given as the input for the sensor with help of PMC_Port and output RPM is displayed.
Signal Builder Block 2- To provide CVT ratio as an input w.r.t time to the CVT subsystem block
CVT Subsystem- Simscape block Variable Transmission Ratio is the main block here, where input port R defines the ratio of input to output angular shaft velocities. These changes in angular velocities are monitored with help of Ideal Rotational Sensor. Connections B(Base) and F(Follower) are the mechanical rotational ports these are pulled from the Engine Block. Furthermore in order to take inertia of the front and rear axle inertia blocks are also used. Lastly to fetch sensor data outside this subsystem Goto blocks are used.
In Signal Builder Block 2 the CVT ratio decreases w.r.t time, thus the angular velocity of the output shaft increases w.r.t time when compared with the input angular velocity
Simple Gear – The outputs of the CVT Block are connected to simple gear with gear ratio of 10. This is done to pull down the angular velocity in order to increase the torque demanded by the vehicle body block
Vehicle Body Subsystem- This block consists the Tires, Vehicle Body, Brakes, Velocity and Distance trackers.
Tires are basically the units which will experience the distributed vehicle load, the horizontal traction and slip. Tire block consists of 4 ports including A for the mechanical rotational conservation port for the wheel axle, port H is mechanical translational conserving port for the wheel hub through which the traction is applied to the wheel hub. Connection N feeds the normal reaction to the tire and port S accounts for the slip.
Vehicle Body block is an extremely crucial block here it takes into consideration for all the forces acting on the vehicle, it accounts for the rotational torque transferred by the drive train to the wheel, the normal reaction acting on the wheel(Wt. of the vehicle), Horizontal traction force acting on the tire, aerodynamic drag, and inclination. Output of this block is the vehicle velocity, which can be further integrated to find vehicle displacement. For considering the braking effect Double shoe brake and a gain block is used.
About Results:
Here we can monitor the vehicle output speed varying w.r.t to the parameters such as throttle, braking, and loads acting on the vehicle.
With decrease in CVT ratio, the angular velocity for the Secondary shaft in CVT increases and hence the vehicle speed increases.
Throttle valve is kept constant equal to 0.3 w.r.t time. Increasing the throttle input increases the vehicle velocity.
Breaking and Throttle valve effects can be modified in the dashboard mapped model when the system is running.
Increasing the Fixed Gear Ratio increases the vehicle speed, as the data for the engine RPM which is feed to the Engine block is limited the Gear Ratio which is used in this model is also limited. System shows an error when gear ratio is increased beyond certain limit. Velocity outputs are attached for GR14 and GR8.