Project
Aim - To study and analyze the BAJA All Terrain Vehicle(ATV) model using Simulink and compare different models.
Objectives - 1.To prepare a technical report explaining the functions of the subsystem and blocks used for preparing the model
2.-To explain in detail all the differences between all the models provided
3.To understand and comment on the results
Types of model studied:-
1.Baja ATV model without Dashboard(cvtModel)
2.Baja ATV model with Dashboard(cvtModel_dashboard)
Introduction:
All Terrain Vehicle:
An all terrain vehicle(ATV) is defined as a motorized off-highway vehicle designed to travel on four low-pressure or non-pneumatic tires, having a seat designed to be straddled by the operaator and handlebars for steering control.ATVs are subdivided into two types as designated by the manufacturer.Type 1 Atvs are intended by the manufacture for use by a single operator and no passenger.Type 2 ATVs are intended by the manufacturer for use by an operator and a passenger, and are equipped with a designated seating position behind the operator.
BAJA SAE:
Baja SAE is an collegiate design series competition run by the society of automotive engineers(SAE International).Teams of students from universities all over the world design and build small off road cars.The cars all have engines of the same specifications.As of 2018 the engine has been an unmodified briggs and stratton Model 19 Vanguard engine single cylinder with a displacement of 305cc and power output of approximately 10 bhp(7.5 KW).
The goal in Baja SAE racing is to design, build and race off-road vehicles that can withstand the harshest elements of rough terrain.The vehicles used in Baja SAE racing are often similar in appearance to dune buggies. Before 2007 , the events were called "Mini Baja".
Continuously Variable Transmission(CVT):
A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.
CVTs are used in automobiles, tractors, motor scooters, snowmobiles, and earthmoving equipment.
The most common type of CVT uses two pulleys connected by a belt or chain; however, several other designs have also been used at times.
Main and critical blocks used:
Generic Engine block:
The Generic Engine block represents a general internal combustion engine. Engine types include spark-ignition and diesel. Speed-power and speed-torque parameterizations are provided. A throttle physical signal input specifies the normalized engine torque. Optional dynamic parameters include crankshaft inertia and response time lag. A physical signal port outputs engine fuel consumption rate based on a choice of fuel consumption model. Optional speed and redline controllers prevent engines to stall and enable cruise control.
Main ports:
1.B- Rotational Conserving Port : representing the engine block(should be connected motion reference)
2.F-Rotational Conserving Port : representing the Engine Crankshaft
3.T- Physical signal input port : specifying the normalized engine throttle level
4.P-Physical signal output port:reporting the instantaneous engine power, in W
5.FC- Physical signal output port: reporting the fuel consumption rate, in Kg/s
Simple Gear 
The Simple Gear block represents a gearbox that constrains the connected driveline axes of the base gear, B, and the follower gear, F, to corotate with a fixed ratio that you specify. You choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, the angular velocity of the follower, ωF, and the angular velocity of the base, ωB, have the same sign. If they rotate in opposite directions, ωF and ωB have opposite signs.
The kinematic constraint that the Simple Gear block imposes on the two connected axes is
rFωF=rBωB
where:
rF is the radius of the follower gear.
ωF is the angular velocity of the follower gear.
rB is the radius of the base gear.
ωB is the angular velocity of the base gear.
The follower-base gear ratio is
gFB=(rF)/(rB)=NF/NB
where:
NB is the number of teeth in the base gear.
NBF is the number of teeth in the follower gear.
Main Ports:
B-Base:Rotational mechanical conserving port associated with the base, or input, shaft
F-Follower:Rotational mechanical conserving port associated with the follower , or output, shaft.
Variable Ratio Transmission block:
Description
The Variable Ratio Transmission block represents a gearbox that dynamically transfers motion and torque between the two connected driveshaft axes, base and follower.
Ignoring the dynamics of transmission compliance, the driveshafts are constrained to corotate with a variable gear ratio that you control. You can choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, ωF and ωB have the same sign. If they rotate in opposite directions, ωF and ωB have opposite signs.
Transmission compliance introduces internal time delay between the axis motions. Therefore, unlike a gear, a variable ratio transmission does not act as a kinematic constraint. You can also control torque loss caused by transmission and viscous losses. For model details, see Variable Ratio Transmission Model.
Ports
B and F are rotational conserving ports representing, respectively, the base and follower driveshafts.
You specify the unitless variable gear ratio gFB(t) as a function of time at the physical signal input at port r. If the signal value becomes zero or negative, the simulation stops with an error.
Vehicle Body block
The Vehicle Body block represents a two-axle vehicle body in longitudinal motion. The vehicle can have the same or a different number of wheels on each axle. For example, two wheels on the front axle and one wheel on the rear axle. The vehicle wheels are assumed identical in size. The vehicle can also have a center of gravity (CG) that is at or below the plane of travel.
The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. Optionally include pitch and suspension dynamics. The vehicle does not move vertically relative to the ground.
The block has an option to include an externally-defined mass and an externally-defined inertia. The mass, inertia, and center of gravity of the vehicle body can vary over the course of simulation in response to system changes.
Limitations
The Vehicle Body block lets you model only longitudinal dynamics, parallel to the ground and oriented along the direction of motion. The vehicle is assumed to be in pitch and normal equilibrium. The block does not model pitch or vertical movement. As such, the equations assume that the wheels never lose contact. This constraint can result in negative normal forces.
Input
W — Headwind speed
scalar
beta — Road incline angle
scalar
CG — Center of gravity, in m
two-element vector
M — Mass, in kg
scalar
J — External moment of inertia, in kg*m^2
scalar
Output
V — Longitudinal velocity
scalar
NF — Front axle normal force
scalar
NR — Rear axle normal force
scalar
Conserving
H — Horizontal motion
mechanical translational
Conserving port associated with the horizontal motion of the vehicle body. Connect tire traction motion to this port.
Double shoe brake Block
The Double-Shoe Brake block represents a frictional brake with two pivoted rigid shoes that press against a rotating drum to produce a braking action. The rigid shoes sit inside or outside the rotating drum in a diametrically opposed configuration. A positive actuating force causes the rigid shoes to press against the rotating drum. Viscous and contact friction between the drum and the rigid shoe surfaces cause the rotating drum to decelerate.
Double-shoe brakes provide high braking torque with small actuator deflections in applications that include motor vehicles and some heavy machinery. The model employs a simple parameterization with readily accessible brake geometry and friction parameters.
Limitations and Assumptions
Contact angles smaller than 45° produce less accurate results.
The brake uses the long-shoe approximation.
The brake geometry does not self-lock.
The model does not account for actuator flow consumption.
Ports
Input
F — Actuating force
physical signal
Conserving
S — Drum shaft rotation
rotational mechanical
H — Heat flow
thermal
Tire (Magic Formula)
The Tire (Magic Formula) block models a tire with longitudinal behavior given by the Magic Formula [1], an empirical equation based on four fitting coefficients. The block can model tire dynamics under constant or variable pavement conditions.
The longitudinal direction of the tire is the same as its direction of motion as it rolls on pavement. This block is a structural component based on the Tire-Road Interaction (Magic Formula) block.
To increase the fidelity of the tire model, you can specify properties such as tire compliance, inertia, and rolling resistance. However, these properties increase the complexity of the tire model and can slow down the simulation. Consider ignoring tire compliance and inertia if simulating the model in real-time or if preparing the model for hardware-in-the-loop (HIL) simulation.
Equivalent Model
The full tire model is equivalent to this Simscape™/Simscape Driveline™ component diagram. It simulates both transient and steady-state behavior and correctly represents starting from, and coming to, a stop. The Translational Spring and Translational Damper are equivalent to the tire stiffness CFx and damping bFx. The Tire-Road Interaction (Magic Formula) block models the longitudinal force Fx on the tire as a function of Fz and k′ using the Magic Formula, with k′ as the independent slip variable.
The Wheel and Axle radius is the wheel radius rw. The Mass value is the effective mass,
I
w
r
2
w
. The tire characteristic function f(k′, Fz) determines the longitudinal force Fx. Together with the driveshaft torque applied to the wheel axis, Fx determines the wheel angular motion and longitudinal motion.
Without tire compliance, the Translational Spring and Translational Damper are omitted, and contact variables revert to wheel variables. In this case, the tire effectively has infinite stiffness, and port P of Wheel and Axle connects directly to port T of Tire-Road Interaction (Magic Formula).
Without tire inertia, the Mass is omitted.
Limitations
The Tire (Magic Formula) block assumes longitudinal motion only and includes no camber, turning, or lateral motion.
Tire compliance implies a time lag in the tire response to the forces on it. Time lag simulation increases model fidelity but reduces simulation performance.
Ports
Input
N — Normal force
physical signal
M — Magic formula coefficients
physical signal | vector | [B, C, D, E]
Output
S — Slip
physical signal
Conserving
A — Axle
mechanical rotational
H — Hub
mechanical translational
Other Blocks used:
1.Solver Configuration - To specify the solver parameters before the simulation
2.Signal Builder- To input the brake, throttle and CVT ratio
3.Simulink to ps converter - To convert the Simulink signal to Simscape environment
4.PS to Simulink converter - To convert Simscape signal to simulink environment
5.Mechanical Reference-To make sure all the components are clamed to the ground
6.Rotational Free end - Represents a mechanical rotational port that rotates freely, without torque
7.Scope-To display different graphs
8.Display - To view the calculated engine power
9.Inertia - To represent the solid inertia
10.Rotational motion sensor- To sense the rotational motion from the engine and give output as rpm
11.PS Terminator- Terminator for unconnected physical signal outputs
12.PS Constant-Generate constant physical signal
13.Rotational free end - For mechanical component(Tire)
14.Custom Measure Gauge- To measure the brake and throttle input
15.Knob-To increase , decrease and vice versa of throttle and brake inputs
16.Lookup Table - To insert the CVT values from the workspace
17.Step- To increase or decrease an input value for a defined time interval.
BAJA ATV WITHOUT DASHBOARD(cvt model)
Main Model
Steps:
1. The throttle signal is generated by signal builder block and inputted to generic engine.
2.The torque and speed vector are inputted from the matlab workspace
3.The engine will generate the output rpm which can be taken from the crankshaft output. This speed will be given to the ideal rotational motion sensor to sense the output rpm.
4.The same output speed will be given to a simple gear mechanism to reduce the speed where the gear ratio is '4'
5.Then the output speed from the gear reducer will be given to the variable ratio transmission block(CVT)
6.The CVT ratio is provided to the variable ratio transmission(CVT) block through signal builder
7.The speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle.
8.The brake signal is generated by the signal builder and inputted to the vehicle body (Double shoe Brake) for applying the brake to axle.
9.The power from the CVT is inputted to the axle and the vehicle accelerates according to the speed.
10.Then the velocity is taken as output from the vehicle body for further analysis.
Input signals
Throttle input signal
Brake input signal
The brake input remains zero through the whole simulation
Torque and speed Matlab workspace input
CVT ratio
Engine sensor Sub Block
This subblock measure engine rotational speed as it takes the output of the engine as its input and outputs engine Rpm
CVT Subblock
The cvt subblock provides the input and the output shafts with inertia and measures the input shaft rpm and the output shaft rpm
Vehicle body subblock
The model shows that the vehicle is rear wheel drive as the output from the gearbox is inputted to the rear axle, then an inertia is added to simulate axle inertia , then the shoe brake is conserving port is connected to the axle, and then the same axle connects the two rear tyres while the front tyres is free to rotate on a rotational free end.All the tyres H hub port is connected together and then connected to the vehicle H port, Also the rear tyres N port is connected together and then connected to the vehicle body Nr output ports, While the front are connectedto the Nf vehicle body output ports, the vehicle body takes the road inclination and wind velocity from physical constants.
Results:
Torque speed plot
Engine torque speed curve
The torque and speed are inputted from the matlab workspace window to the generic engine block to generate the output RPM accordingly. This plot behaviour is generic to all ICE.
Velocity Distance Throttle Brake plot
As the throttle is kept constant at 0.5 and brake is kept at 0 the velocity plot shows increase in velocity and at the same time the distance is also increasing in the distance plot.
CVT shaft speed
The engine reduced speed is controlled by various cvt ratios.
BAJA ATV Model with Dashboard(cvtModel_dashboard)
Dashboard
User Controls
Steps
The model workflow process is same as the process of 'BAJA ATV model without dashboard' but the throttle and brake inputs are controlled by the user with knobs.
Results:
Velocity Distance Throttle Brake
result is same as without dashboard only difference is that throttle and brake can be externally controlled while runnibg the simulation
From the plot we can infer that when throttle is applied the vehicle speed increases and when brake is applied vehicle speed decreases simultaneously.
Please see the uploaded picture for your reference.