Project
BAJA ALL Terrain Vehicle (ATV) Model
Aim :
To carry out the system level simulation of an all terrain vehicle and preparing a technical report for explaining the model and properties and results.
Objective :
To prepare a technical report on BAJA ATV explaining model properties of the following conditions,
- without using Lookup table
- with using Lookup table
Theory :
BAJA ATV (SAE)
The BAJA SAE Series is an event for the undergraduate engineering students, organized globally by the Society of Automotive Engineers, USA. The event originated in the name of mini BAJA, in the year 1976 at University of Carolina. Since then the event has spanned across six countries -USA, Mexico, South Africa, Korea, Brazil and India.
The BAJA SEA tasks the students to design, fabricate and validate a single seater four - wheeled off road vehicle to take part in series of events spread over a course of 3 days that test the vehicle for the sound engineering practices that have gone into it, the ability of the vehicle in terms of gradeability, speed, acceleration and manoeuvrabability characteristics and finally its ability to endure that back breaking durability test.
ALL Terrain Vehicle :
An all terrain vehicle (ATV), also known as a quad, three-wheeler,four-track, four-wheeler, or quadricycle as defined by the American National Standards Institude(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. It is designed to handle a wider variety of terrain than most other vehicles.
This vehicle runs on low pressure tires. It has handlebars instead of wheel for controlling the steering. As the name indicates, an ATV is designed to handle a broader variety of terrain than regular vehivles. In some countries it is a street-legal motor vehicle and licenced for use public roads.
The riders ride an ALL Terrain Vehicle by siting on it just like a motorcycle. you don't need much effort to balance it because extra wheels give more stability at slower speeds. Generally most ATVs come with three or four wheel. some specialized applications require six-wheel models. Engine size of AVTs range from as low as [49 cc to 1000 cc]. However, the size of the engine depends upon the application.
Continuously Variable Transmission (CVT) :
A CVT or continuously variable transmission is an automatic single speed and gearless transmission that can shift through an infinite number of gear ratios. A continuously variable transmission (CVT) is a transmission that operates on an ingenious pulley system that automatically varies the transmission ratio, allowing an infinite variability between highest and lowest gears with no discreate steps or shift. CVT is provide more useable power, better fuel economy and smoother driving experience than traditional transmissions that use gearboxes with fixed numbers of gear sets.
1. BAJA ATV Model without lookup table
a)Without Dashboard
A Simulink model for the BAJA Model is as following figure
This model consist with common blocks as follows,
Signal Builder :
The signal builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a model.you can quickly switch the signal groups into and out of a model to facilitate testing.
Generic Engine :
Represents a system level model of spark-ignition and diesel engines suitable for use at initial stages of modeling when only the basic parameter are available. Optional idle speed and red line controllers are included.
The throttle input signal T lies between zero and one specifies the torque demanded from the engine as a fraction of the maximum possible torque. If the engine speed falls below the stall speed ,the engine torqe is blended to zero. If the engine speed exceeds the maximum speed the simulation stops and issues an error message.
Engine Sensor :
Ideal Rotational motion sensor :
The block represents an ideal mechanical rotational motion sensor. It is a device that converts an across variable measured between two mechanical rotational nodes into a control signal proportional to angular velocity or angle. The sensor is ideal since it does not account for inertia, friction, delays, energy consumption and so on.
Connections R and C are mechanical rotational conserving ports and connections W and A are physical signal output ports for velocity and angular displacement respectively.
Simple Gear :
This simple gear represents a fixed ratio gear or gear box. No inertia or compliance is modeled in this block. we can optionally include gear meshing and viscous bearing losses.
Connection B and F are mechanical rotational conserving ports. Specify the relation between base and follower rotation directions with the output shaft rotates parameter. Follower (F) to base(B) teeth ratio(NF/NB) :4
CVT Subsystem :
This subsystem has the following blocks,
Inertia :
The block represents an ideal mechanical rotational inertia. this block has one mechanical rotational conserving port. The block positive direction is from its port to the reference point. This means that the inertia torque is positive if the inertia is a positive direction.
Variable Ratio Transmission :
This represents a variable ratio gearbox such as implemented by mechanical belt CVT, electric or hydraulic transmissions. The physical signal input r defines the ratio of input to output angular shaft velocities. connection B and F are mechanical rotational conserving ports. specify the relation between base and follwer rotation directions with the output shaft rotates parameter.
Vehicle Body Subsystem :
Vehicle Body :
This vehicle body represents a two axle vehicle body in longitudinal motion. The block accounts for body mass, areodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. The vehicle can have the same or a different number of wheels on each axle.
Connection H is the mechanicla translational conserving port associated with the horizontal motion of the vehicle body. the resulting traction motion developed by tires should be connected to this port. connections V,NF and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces respectively. wheels forces are considered positive if acting downwards. connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively.
parameters are,
mass = 250kg
Number of wheels per axle = 2
Horizotal distance from CG to front axle = 1m
Horizotal distance from CG to rear axle = 0.35m
CG height above ground = 0.7 m
Gravitational accerlation =9.81 m/s^2
Tire :
This tire represets the longitudinal behaviour of a highway tire characterized by the tire magic formula. The block is built from tire-road interaction and simscape foundation library wheel and axle blocks. optionally the effects of tire inertia, stiffness and damping can be included. Physical signal port M accepts a four-element vector corresponding to the B, C, D and E magic formula coefficients.
parmeters are,
Constant Magic Formula coefficients
Magic formula B coefficient = 10
Magic formula C coefficient =1.9
Magic formula D coefficient =1
Magic formula E coefficient =0.97
Double-Shoe Brake :
This double shoe brake represents a brake arranged as two pivoted rigid shoes symmetrically installed inside or outside a drum and operated by one sctuator. The actuator force causes the shoes to exert a friction torque on a shaft connected to the drum.
The parameters are,
Drum radius = 150mm
Actuator location radious = 100m
Pin location radius =125mm
Pin location angle = 15 deg
Shoe beginning angle = 5 deg
shoe span angle = 120 deg
Torque vs Speed characteristics :
Input : 1.1
Brake and Throttle input :
Brake input is constant so it will be zero throught the time of 80 sec. Throttle input is 0.3 for first 20sec, accelerates to 1 at and remains constant throughout the remainning time till 80 sec.
CVT Ratio :
The CVT gear ratio 2.3 for the first 4 secs, then drops down to 1.8 till 35 sec and remains constant thereafter till 80 sec.
Output : 1.1
Velocity :
CVT Shaft Speed :
Engine Speed :
b) With Dashboard :
A simulink model for the BAJA ATV Model including the dashboard is shown below. The rest of the parts and subsystems are common in the above part without dashboard 1.1.
Dashboard :
A dashboard is a control panel usually located directly ahead of a vehicle's driver, displaying instrumentation and controls for the vehicle's operation.
The initial conditions are as follows,
Brake Input = 0
Throattle input =0.3
Input :1.2
It comprises a throttle and brake input through a knob which can be varied unlike the signal builder in the previous model without Dashboard. The Engine RPM gauge and velocity gauge and velocity gauge displays the changes done by the respective knobs.
Output : 1.2
Velocity :
CVT Shaft Speed :
Engine Speed :
2) BAJA ATV Model with lookup table - With Dashboard
Lookup Table :
A lookup table is an array of data that maps input values to output values, thereby approximating a mathematical function. Given a set of input values a lookup operation retrieves the corresponding output values from the table. If the lookup table does not explicity define the input values, simulink can estimate an output value using interpolation, extrapolation or rounding. where,
- Interpolation is a process for estimating values that lie between known data points.
- Extrapolation is a process for estimating values that lie beyond the range of known data points.
- Rounding is a process for approximating a value by altering its digits according to a known rule.
In place of CVT ratio input, a lookup is assigned in the models below. It needs to be loaded in the workspace having the file name as lookuptable_data.mat.
Model with lookup table :
A simulnik model for the BAJA ATV Model including the dashboard and the lookup table is shown below.
Input :
It comprises a throttle and brake input through a knob which can be varied unlike the signal builder in the previous model. The engine RPM gauge and velocity gauge displays the changes done by the respective knobs.
Output :
Velocity :
CVT Shaft Speed :
Engine Speed :
Conclusion :
Hence, the given BAJA AVT Model was simulated successfully and prepared technical report explaining the model.And, from the result graph plot we can say that Velocity, CVT shaft speed and Engine speed are directly proportional to the Throttle input and inversely proportional to the Brake input.
References :
https://in.mathworks.com/matlabcentral/fileexchange/70576-baja-all-terrain-vehicle-atv-model