Project

AIM:

To do detailed case study on continuous variable transmission(CVT)using BAJA ATV vechile and present our observvations on it.

THEORY:

All Terrian Vechile:

       An all-terrian vechile(ATV),also known as a quad (cycle),three-wheeler,four-track,four-wheeler,or quadricycle,as defined by the Ameican National Standars Institute (ANSI) is a vechile that travels on low-pressure tires, with a seat that is straddled by the operator,along with handelbars for steering control.it is designed to handle a wider variety of terrian than most other vechiles.

BAJA ATV(SAE):

The BAJA SAE series is an event for the undergraduate engineering students,organised 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  the event has spaned across six countries-USA,Mexico, south Africa,korea,Brazil and india.The BAJA  SAE tasks the students to design,fabricate and validate a single seater four-wheeled off road vechile to take part in series of events sppread over that the test the vechile for the sound  engineering practises that have gone into it.The ability of the vechile in terms of gradebility,speed, accelaration and manoeuvrability charactersics and finally its ability to that back braking durability test

CONTINOUS VARIABLE TRANSMISIION(CVT):

Is an automatic transmission that can change seamlessly through a continuous range of gear ratios.This contrasts with other transmission 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 vechicle moves at varying speed.

CVTS are used in automobiles, tractors,motor scooters,snowmobiles,and earth moving 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.

MODEL:(simple CVT model

This submission contain a set of models created with simulink,simscape,and simscape Driveline.More specifically,the file contained includes 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 comlete the system.The engine data used in the model is provided as an image which shows the Engine speed (RPM)vs Torque curve.This is an open loop model of CVT.

we can see in the above model the input for engine is acceleration(Throttle).Then the engine was connected with CVT and gave RPM input to CVT.The secondary pulley of CVT gave input to simple gear and then simple gear input to vechile body block in vechile body subsystem.all output from system is given to output with the help of Goto and from block..Input for engine ,CVT and vechile body from the signal builder block

MAIN COMPONENTS OF ATV SIMULATION:

CVT ratio:it is signal builder block used to give the input signal to the main CVT system.Figure below shows the input given by it

SIMPLE GEAR:it represents a fixed-ratio gear or gear box.

VECHILE BODY:it is the actual body of the vechile.Figure below shows the subsystem vechile body

here we can see that an inertia output shaft is used which is actually a secondary pulley of the CVT,a double-shoe brake with a gain,left-right front and rear tires where the rear tires are connected with the double-shoe brake and the CVT secondary pulley and front tires are rotating at free end, and the vechile body block which considers wind velocity and  inclination that are kept as constants.

SCOPE:it is used to observe the output results of vechile speed and CVT shaft speed.

Goto From constants used for brake and throttle inputs and a solver configuration are the miscellaneous blocks used in this simscape model.

Generic Engine:

engine here used generic engine inbuild block .The Generic Engine block represents a general internal combustion engine.This block is suitable generic engine for spark-ignition and diesel.speed-power and speed-torque parameter izations are provided.A throttle physical signal input specifies the normalized engine torque.optional dynamic parameters include inertia and response time lag.The Throttle input signal T lies between zero and one and specifies the torque demanded from the engine as a fraction of the maximum possible torque.

Connections F and B are mechanical rotational conserving ports associated with the engine crankshaft and engine block respectively.connections p and FC are physical signal output ports through 

Figure below shows the moddel after it is simullated at initial conditions.

CVT SUBSYSTEM:

the cvt subsystem uses a variable gear ratio block.

Inside the CVT subsystem,2 INERTIA blocks are connected to ensure proper inertial motion.

Two ideal rotational motion sensors are connected,one on either side of the variable Gear Ratio.The angular velocity outputs of these are then transfered to the main model with the help of Goto blocks.

For CVT there is not any block so here sub system for that was created.which contains the following blocks.

GO  to:

send signals to from blocks that have the specified tag.if tag visibility is scoped then a goto tag visibility block must be used define the visibility of the tag.The block icon displays the selected tag name (brackets[]and braces{})

inport:Provide an input port for a subsystem in braces{}).

Inertia:The block represents an ideal mechanical rotational inertia.

PMC-port:The block represents an ideal mechanical rotational inertia.

Variable ratio gear transmission:

Represents a variable ratio gearbox such as implemented by mechanical belt CVT.electric or hydrulic transmissions.The physicalsignal input are defines the ratio of input to output angular shaft velocities.connections B and (base)and F (follower)are mechanical rotational conserving ports.

PS -Simulink converter:

converts the input physical signal to a simulink output signal.

PS-terminator:

use this block to terminate physical signal outputs.unconnected physical signal output ports do not generate warnings,but connection to a PS Terminator can be used to indicate that the signal was not inadvertently left unconnected.

Mechanical Rotational Reference:

This block represents a mechanical rotational reference point,that is a frame or a ground .use it to connect mechanical rotational ports that are rigidly affixed to the frame(ground).

VECHILE SUBSYSTEM:

The Vechile Body block represennts a two-axel vechile body in longitudinal motion.The block accounts for body mass, aerodynamic drag, road incline,and weight distribution between axles due to acceleration and road profile.

MASS:250kg

Diistance between CG To Front Axle-1m

Distance between CG to Rear axle-0.35m

Height of CG above ground-0.7m

Eachof the axles consist of two wheels.

ROLLING RADIUS:0.2794m

ROLLING RESISTANCE-0.015

The rear wheels share the same rotational motion so their corresponding rotational ports are connected .since the front wheels are freely rotating,their rotational ports are connected to Rotational free ends.These can be mutually connected to.

since all the wheels share the same translational motion,the corresponding ports of all the wheels are connected to each other.

The driver shaft is given proper rotational input through an inertia(inertia=le-1kg*m^2)block along with the brake input through a Double shoe Brake.

DRUM RADIUS:150MM

SHOE SPAN ANGLE:120degree

The velocity of the vechile Body is taken out as an output in order to get visualised in the main body.

Now depending upon the different types of inputs,five different model simulations carried out.

Model1(A):cvtModel

In this model, the Brake and Throttle inputs are given with the help of Signal Builder block.Here,the brake input value is kept 0throughout and just the throttle input is given a rise,at t=20sec,to study the variation of the vechile speed.

The input cvt ratio is also given with the help of another signal builder block.its value remains constant at 2.3for first 4sec,then is reduced linearly to 1.8 at t=5sec

These are the angular velocities before and after te variable Gear Ratio coming into play in the CVT subsystem.

The 2 signal builder plots are nothing but the Brake and Throttle inputs given to the model.

The veechile speed varies as shown in the plot.Due to the inittial throttle of0.3units the vechile shows a sudden rise in the velocity at the start .For the next 20sec of constant throttle,the vechile speed gradually increases up until the point where the throttle is given a complete push.The vechile accelerates at a higher rate till it reaches the top speed.

Model1(B):cvtModel_Dashboard:

The only difference between this and previous model simulation is-istead of giving a signal builder inputs of Brake and Throttle,these are provided by connecting Knobs.

This enables us to run model as per Real time simulaion,wherein the input can be varied while the simulation running.

Accordingly,the stop time is set to infinite.

While the simulation is being run,the Brake was applied at around t=4sec,while keeping the throttle input constant,the velocity of the vechile quickly fails down to0 it comes to rest.

The next three models are based upon taking the input values for the CVT subsystem from a LookUp Table whis is itself created in one of the models.

MODEL2(A):cvtModel_data:

This is same as model1.(A) discussed above

Here the lookup Table is created by taking the values from CVT Ratio block and the final velocities of the vechile corresponding to the CVT Ratio values.The to workspace blocks are used for this purpose.

By running the model the values of the lookup table are stored in the Base Workspace.

Model.(B):cvt Model_mapped:

This model takes input for the CVT subsystem from the lookup Table created in the previous model,instead of the signal builder block used earlier.

GoTo and from blocks are used in order to visualize the values of CVT Ratio in the output.

Model2.(B):

cvtModel_dashboard_mapped:

This model,as the name suggests,is similar to the model1.(B),wherein the Brake and the Throttle inputs are given from Knobs.(Real time simulation)

Also,the model uses the Lookup tabel for the CVT Ratio values.

The simulation is run while keeping the throttle input constant .Brake is applied at t=2.5sec,accordingly the vechile comes to rest quickly.

BLOCKS used in model:

LOOKUP TABLE:

A look up tabel is an array of data that maps input values to output values, there by approximating a mathmatical function.Given a set of input values there by approximating a mathmatical function.Given a set of input values,a lookup operation retrives 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 methods.

An interpolation is a process for estimating values that lie between known data points.

An extrapolation is process for estimating values that lie beyond the range of known data points.

A rounding is process for approximating a value by altering its digits according to a known value.

An analytical expression is expensive to compute.

No analytical expression exists,but the relationship has been determined empirically.

CONCLUSION:

We can conclude that we have successfully simulated the BAJA all terrain Vechile with different methods like open loop model and close loop model.we got satisfactory results for the simulation.we can use this model to simulate actual data for SAE comepetition.