Project

Aim:

• To carry out a system-level simulation of a BAJA ATV

Objectives:

• Analyse all components and understand the relation and flow between the blocks
• Understand the different types of ways to model this BAJA ATV

an ATV is a small motor vehicle with three or four low-pressure tires designed for use on various types of terrain. Recreational acitivites in deserts are usually carried out in ATV. This project is in reference to one of the types of ATV used in BAJA SAE competitions.

BAJA ATV WITH CVT

From this model, the components present are:

ATV is devided into four compartment and each compartment has some there component

1) INPUT BLOCK

1. Braake
2. Throttle
3. CVT gear ratio

2) GENERIC ENGINE

1. Engine sensor
2. simple gear

3) CVT

1. Variable gear ratio
2. shaft inertia

4) Vehicle body

1. Wheels
2. Phusical body
3. shoe breaks

Brake and throttle input signal:

• No brake is provided
• A constant throttle of 0.3 for the first 20 seconds, and full throttle of 1 for the reamining
• These two parameters are fed into the engine

Generic Engine:

• The engine uses a programmed relationship between speed and torque, modulated by the throttle signal. The throttle input is seen above(fed into port T) and the speed-Torque data points are extracted from the graph shown below and fed into the engine through creation fo column vectors in MATLAB.
• Crankshaft (Port f) is connected to an engine sensor, which simply senses the angular velocity and angular displacement of the crankshaft.
• The simple gear between engine and the CVT gear box is to slow down the engine RPM( in case it too high) before it is fed to the CVT. An appropriate gear ratio needs to be selected so that over or under-revving isn't an issue.

Continuously Variable Tansmission(CVT):

• As evident in the media above, two cone-shaped pulleys connected by a steel or composite belt, whose diameters are continusly variabe, work together to provide infinite gear ratios.
• Optimizing engine speed in a variety of road conditions, according to the speed and torque requirements of the terrain.
• Differ form automatic transmissions in the sense that there aren't gears the vehicle needs to step up/down to for different speed/torque requirments. similar to automatic transmissions in the sense that the gears are shifted automatically.

CVT subsystem block:

• The input and output shaft inertia represent primary pulley(driver) and secondary pulley (driven), respectively.
• The variable ratio gear block represents the multiple gears of the CVT, with the gear ratio input given to port R(shown below)
• Two rotational motion sensors are for tracking the angular velocitites of the two pulleys.

Vehicle body subsystem block:

• The Vehicle Body accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile.
• The Double-Shoe Brake is to apply brakes to the rear wheels. With this component, two brake blocks are applied at opposite ends of the drum. This prevents an unbalanced force from acting on the shaft and bearing connecting th drum to the wheel, which would be the case with a single-shoe brake.
• All of the above is applied to the four wheels.

Vehicle speed out put based o throttle and vrake signals:

• There is constant acceleration at throttle of 0.3 from 0 to 20 seconds
• After 20 seconds the car accelerates until peak velocity as throttle hits a max value of 1

CVT Shaft speed output based on CVT gear ratio input:

• The CVT gear ration input is above 1 throughout, which is why we see a lower secondary RPM than primary, because the output shaft iwll rotate slower to provide more torque to the wheels.

Varying CVT gear ratio:

• As soon as the CVT gear ratio falls below1 , the secondary RPM becomes higer than the primary RPM as the velocity of the vehicle also increases with the reduction in torque.

BAJA ATV with CVT and Dashboard

• The thottle and brake inputs are given via graphical representation (dashboard control knobs) blocks while the simulation is running for an indefinite period. This allows us to input various scenarios.

BAJA ATV with Lookup table

• The only difference with this study is that the CVT gear ration is not fed in via a signal builder, but instead via a lookup table
• This lookup table is data regarding the relation between CVT gear ratio and vehicle speed, which is incorporated through a simple MATLAV script.
• In study#1, a CVT gear ratio had to be inputted manually to see the effect on the vehicle's velocity. However, this isn't feasible in reality and doesn't mimic wicht happens in real time. Through this lookup table, the CVT can be modeled based on the vehicle speed as feedback is taken form vhicle velocity to claculate gear ratio.

Conclusion:

The BAJA ATV with CVT was modelled using two main studies. with the focus pruely on CVT, this project is able to show the effect of CVT on vehicle velocity, although multiple situations for different models of ATV design.