System level Simulation of a BAJA All Terrian Vehicle(ATV) using Simulink

Aim:

To carry out a system-level simulation of a BAJA all-terrain vehicle and preparing a technical report explaining the model properties & comments on the results.

Theory:

ATV:

An all-terrain vehicle (ATV), also known as a quad (bike), three-wheeler, four-track, four-wheeler, or quadricycle, as defined by the ANSI is a vehicle that travels on low-pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles.

CVT:

A continuously variable transmission (CVT), also known as a shiftless transmission, stepless transmission, pulley transmission, or, in case of motorcycles, a 'twist-and-go', is an automatic transmisson that can change seamlessly through a continuous range of effective gear ratios. This contrasts with other mechanical transmissions that offer a fixed number of gear ratios. The flexibility of a CVT with suitable control may allow the input shaft to maintain a constant angular velocity even as the output speed varies.

Procedure:

1) In this project we carry out a system level simulation of a pre-built model of an CVT run ATV which is commonly used in BAJA events carried out SAE India.

2)

Main Components of a BAJA ATV Simulink Model:

1) Engine

2) CVT Block

3) Vehicle Block

The above model is the mapped BAJA ATV Model with dashboard.

3) We are providing the Brake input and Throttle input as 0 and 0.3 as initially the braking is in zero condition and the throttle is slowly released.

4) These Inputs are provided to an engine which is a generic engine or a simple engine setup.

5) After that the signal is sent to an engine sensor which consists of an RPM Sensor which basically the Ideal Rotational Motion Sensor. Here we connect Casing to a rotational reference and we only find and plot the angular velocity (W). The angular displacement (A) signal is terminated using a PS Terminator.

6) Then we connect the simple gear setup in which the gear ratio is considered as 4. We are considering gear ratio as 4 since the maximum engine rpm of baja vehicle is 3840 rpm and velocity of vehicle remains constant only after reaching 3840 rpm.

7) Then we move to the CVT Block which is basically consists of a primary pulley, secondary pulley, variator and belt. Here if radius of the variator in the primary pulley increases the speed is reduced. If the radius of the variator in the primary pulley decreases then drive speed increases and overdrive process takes place.

8) Inside the CVT Block there are input and output shafts which are basically the primary and secondary pulleys. A lookup table has been provided which basically creates an relationship between the inputs and outputs. After that we connect the output to the variable ratio gear whihc allows outptut shaft to run in same direction of the input shaft. There are also primary and secondary pulley rpm provided using the rotational motion sensor for both pulleys and displayed as an output.

9) The next body we are learning is about the vehicle body and its components. The vehicle body consists axles, brakes, wheels or tires. The vehicle body is first connected to the front and rear tires and it is connected double shoe brakes. The Normal forces of front and rear tires are connected to the vehicle body and hub mounting is done for the tires. Then there is no slip considered hence it terminated using a PS terminator. Inclination angle and wind velocity are considered as constant. The velocity output is taken as output.

10) The velocity output is plotted and if the optimum velocity is not provided by the CVT the output velocity is sensed and it runs in a closed loop. Thus provides the required input velocity and produces the optimum output velocity for the mapped model and for normal model there is CVT signal input.

OUTPUT:

11) On running the system level simulation the output curves have been formed respectively.

12) We are having an engine torque speed curve which represents the max rpm reachable by baja atv is 3840 rpm.

13) Initially the CVT Ratio is 2.3 for 20 secs then it decreases gradually wrt increase in the speed of the vehicle.

14) After attaining the maximum speed the CVT Ratio is reduced to 1.9 as shown in the below figure.

15) When the program is ran the velocity (max) and the brake and throttle inputs are displayed in graph below.

16) When the throttle input is provided as maximum the maximum speed is obtained. If the brake input is changed the vehicle comes to an ideal position.

17) Finally the CVT's Primary Pulley RPM and Secondary RPM are plotted which are mentioned in the below graph.

Conclusion:

By carrying out the system level simulation of the BAJA ATV we understand that this model can be very useful in building a real world ATV by providing variable user inputs to the model and could be also tested in different conditions by variying the engine speed, torque, throttle input etc.