Challenge

Project

WWinnie Raghu23 Jan 2021

MATLAB

BAJA All-Terrain Vehicle (ATV) Model Simulation in MATLAB

AIM

To do a system-level simulation of an all-terrain vehicle and understand the Modelling Techniques.

OBJECTIVE

To understand the modeling of ATV with Continuously Variable Transmission and do the system level simulation.

SIMULINK MODELLING

ATV

An all-terrain vehicle (ATV), also known as a light utility vehicle (LUV), a quad bike, or simply a quad, as defined by the American National Standards Institute (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.

Figure 1: All Terrain Vehicle (ATV)

BAJA All-Terrain Vehicle (ATV) Model

BAJA ATV Model contains a set of models created with Simulink, Simscape, and Simscape Driveline. The most important feature of this Model is the implementation of BAJA ATV model with Continuously Variable Transmission(CVT).
These models show how to build an ATV with CVT which is mostly used in BAJA competitions. Simscape and Simscape Driveline have been used to complete the system. The engine data used in the model is provided as an image which shows the Engine Speed (RPM) Vs Torque curve.

Figure 2: Components of ATV

The main components of ATV are shown in figure 2. The main parts are 1. Engine, 2. CVT, 3. Vehicle Body, 4. Suspension, 5. Tire

All these components are modeled in Simulink to observe the behavior of the vehicle. The Simulink model is shown in Figure3.

Figure 3: Simulink Model of ATV

Brake and Throttle Input

The brake and throttle inputs are provided through a signal builder block as shown below. The Brake applied is zero and full throttle is applied after 20s. Figure 4 shows the brake and throttle input signals.

Figure 4: Brake and Throttle Input

Engine

The engine used in this model is ‘Generic Engine’ available in the library. The characteristics of ATV engine have been mapped through ‘GRABIT’ application available in MathWorks File Exchange.

GRABIT Extracts data points from an image file.
GRABIT starts a GUI program for extracting data from an image file. It is capable of reading in BMP, JPG, TIF, GIF, and PNG files (anything that is readable by IMREAD). Multiple data sets can be extracted from a single image file, and the data is saved as an n-by-2 matrix variable in the workspace. It can also be renamed and saved as a MAT file.

Figure 5: Data point Extraction using GRABIT

The Engine Torque-Speed curve is shown in figure 6.

Figure 6: Torque-Speed Curve of ATV Engine

Continuously Variable Transmission

Figure 7: CVT Operation

The CVT is an automatic transmission that uses two pulleys with a steel belt running between them. To continuously vary its gear ratios, the CVT simultaneously adjusts the diameter of the "drive pulley" that transmits torque from the engine and the "driven pulley" that transfers torque to the wheels. With stepless shifting of gear ratios, the CVT can avoid the shift-shock and deliver smooth driving, making it an exceptional transmission solution.

When Primary pulley expands( Radius decreases), secondary pulley contracts (Radius Increases) thus speed will get reduced. The reverse action will take place to increase speed as shown in figure 8.

Figure 8: CVT Block

Figure 8 shows the CVT block. Input shaft inertia represents Primary pulley and output shaft inertia represents Secondary pulley. Gear ratio has been specified in the Variable Gear Ratio block. There are two sensors used to measure the Primary and Secondary RPM.

Vehicle Body

The Vehicle body model consists of Vehicle body block and 4 wheels. The wheels have given default parameters to make the model simple. ATV has low pressure wheels for off road driving. But for simplicity, we haven’t given tire parameters. Figure 9 shows the vehicle body block.

Figure 9: Vehicle Body

The block parameters of the vehicle body is shown below.

Figure 10: Block Parameters of Vehicle Body

Simple Gear

The CVT and Vehicle body has been connected through a simple gear with gear ratio 12. This gear ratio selection is done by simulating at different gear ratios to find optimum value. The vehicle speed curve, Engine Torque and Engine RPM curves are compared to find optimum gear ratio.

Figure 11: Simple Gear

Figure 12: BAJA ATV Dashboard Model

This model is same as the Simulink model explained previously except the input signals. Here we can change the brake input and Throttle input while simulation is running.

Figure 13: Lookup Table based Model of CVT based ATV

This look up table based model is closed loop model and CVT ratio adjusts with vehicle velocity. A Lookup table for CVT ratio with Vehicle velocity has been provided to the CVT block.

Figure 14: Lookup table visualisation

OUTPUT ANALYSIS

The Vehicle speed has been plotted with time in figure 15. Also the brake and Throttle inputs were also plotted. We can see that velocity increases as throttle increases and it takes some time to settle to the new velocity. Unlike normal gears, there is no jump in CVT and the speed increases gradually. This is one of the main advantage of CVT.Here the applied braking is zero.