Project

AIM : To understand all model  of BAJA ATV by carrying out system-level simulation. 

OBJETIVE:

• To carry out a system level simulation of all -terrain vehicle.
• To prepare a technical report explaining the model properties and outputs.

THEORY :

BAJA ATV :

• BAJA is basically an ATV (all terrain vehicle) competition where students gets to design and develop their own ATV keeping in mind various considerations of design as well as safety . An ATV is design in order to run on various terrain such as soil, Gravel , Pebbles , etc . 
• It is organised by the society of Automotive Engineers , USA.
• The BAJA SAE tasks the student 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 differnt conditions.
• An ATV is a motorized single-seated tri r quardricycle bike and buggy that is designed for off road travel and activities.
• these vehicles consist of handlebars and low-pressure tires that have deep- threaded structure , which assist in driving over muddy , rocky ,wetlend etc.

 

CONTINUOUSLY VARRIABLE TRANSMISSION (CVT)  :

• A CVT , or continuously variable transmission , seamlessly changes through an unending range of effective gear ratios while you drive , whereas other kinds of mechanical transmissions offer a fixed number of gear ratios and have hard shifts between each .
• CVT transmission system are also known as single-speed , shiftless , and stepless transmissions .
• The shiftless nature of a CVT offers unparalled flexibility that maintains constant angular velocity regardless of output speed . Additionally , a continuously variable transmission makes accelerating smooth and offers enhanced fuel economy.
• while a traditional transmission uses a wide variety of intricate parts to shift between a range of present gears,most CVT system works through a pulley system .
• This system consists of cones at each pulley connected via  a chain belt.
• The cones can move to increase or decrease the belt diameter to change gear ratios , allow for quick shifting into the needed ratio for increased power , and boost fuel economy.
• One pulley in the CVT is connected to the engine and the other directs power to the wheels . The width of these pulleys changes based on the needed power ; as one gets larger , the other gets smaller . This allows a CVT to deliver strong and seamless acceleration .

 Various model BAJA ATV are as follow :

1. BAJA ATV model  without dashboard.
2. BAJA ATV model  with dashboard.
3. BAJA ATV model with lookup table and without dashboard .
4. BAJA ATV model with lookup table and with dashboard.

 1 ) BAJA ATV Model without  dashboard :

• This is the simplest model of BAJA CVT model .

A simulink model for the baja ATV model is shown below :

The model consist of main blocks are as follow :

Signal Builder :

 The signal builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a modle . 

Generic Engine :

• Represent a system - level model of spark - ignition and diesel engines suitable for use at initial stages of modeling when only the basic parameters are available . Optional idle speed and red line controller are included .
• 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 . If the engine speed falls below the stall speed , the engine torque is blended to zero . If the engine speed exceeds the maximum speed , the simulation stops and issues an error message .
• connection F and B are mechanical rotational conserving ports associated with the engine crankshaft and engine blocks, respectively . Connections p and FC are physical signal output ports through which engine power and fule consumption rate are reported.

Speed vector and torque vector are assigned parameters :

 

   

Simple Gear : 

• Simple gear of base and follower wheels with adjustable gear ratio , frictional losses and triggered faults . 
• The simple gear block represents a gearbox that constrains the connected driveline axes of the base gear B and follower gear F , to corotate with a fixed ratio that you specifies.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 and angular velocity of the base have the same sign . If they rotate in opposite directions , it will have opposite sign . 
• Represents a fixed - ratio gear or gear box . No inertia or compliance is modeled in this block you can optionally include gear meshing and viscous bearing losses. 
• Connections B (base ) and F (follower ) are mechanical rotational coserving ports . Specify the relation between base and follower rotation directions with the output shaft rotates parameter . Optionally includes thermal effects and expose thmal conserving port H by setting friction model to a temperature - dependent setting .

Engine sensor subsystem :

RPM Sensor :

• The ideal rotational motion sensor block represents an ideal mechanical rotational motion sensor , that is , a device that convert an across variable measured between two mechanical rotational nodes into a control signal proportional to angular velocity or angle . You can specifie the initial angular position ( offset ) as a block parameter.
• The sensor is ideal since it does not account for inertia , friction , delays , energy consumption , and so on .
• Connection R and C are mechanical rotational conserving ports that connect the block to the nodes whose motion is being monitered . connection W and A are physical signal outputs ports for velocity and angular displacement , respectively .
• This block measure angular velocity or angle in a mechanical rotational network . The sensor is ideal since it does not account for inertia , friction , delays , energy consumption and so on .
• The physical signal ports W and A report the angular velocity and angle , respectively , of port R relative to port C . The measured angular velocity is positive when the angular velocity at port R is greater than the angular velocity at port C . 

Subsystem of CVT :

Input shaft inertia  and output shaft inertia :

• Input shaft inertia generally represent the primary shaft of CVT.
• output shaft inertia generally represent the secondary shaft of CVT.
• The block represent an ideal mechanical rotational inertia .
• The block has one or two mechanical rotational conserving ports . The difference is purely graphical , as the port are rigidly linked . The block positive direction is from its port to the reference point . This means that the inertia torque is positive if the inertia is accelerated in the positive direction . 

Variable Ratio Gear :

• Dynamic gearbox with variable and controlled gear ratio , transmission compliance and friction losses.
• The variable transmission block represent a gearbox that dynamically transfer motion and torque between the two connected driveshaft axes , base and follower .
• Ignoring the dynamic of transmission compliance , the driveshafts are constrained to corotate with a variable gear ratio that you control . 
• Ports B and F are rotational conserving ports representing respectively , the base of follower driveshafts.
•  

Subsystem of vehicle body :

Double -shoe brake:

• Frictional brake with two pivoted shoes diametrically positioned about a rotating drum with triggered faulting .
• Represents a breake arranged as two pivoted rigid shoes symmetrically installed inside or outside a drum and operated by one actuator . The actuator force causes the shoes to exert a friction torque on a shaft connected to the drum .
• connection S is a conserving rotational terminal associated with the drum shaft . Connection F is a physical signal port representing the force input to the actuator . Positive force creates friction torque that resists shaft rotation . Optionally includes thermal effects and expose thermal conserving port H by setting thermal port to model .
• The double - shoe bake block represent a frictional brake with two pivoted rigid shoes that press against a rotating drum to produce break 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 a rotating drum . Viscous and contact friction between the drum and the rigid shoe surface cause the rotating drum to decelerate .
• Double - shoe brakes provide high braking torque with small actuator deflections in application that include motor vehicle and some heavy machinery . The modle employs a simple parameterization with readily accessible brake geometry and friction parameters.
• You can also enable faulting . When faulting occurs, the belt will exert a user - specified force . Faults can occur at a specified time or due to an external trigger at port T .

 Vehicle Body :

• Two -axle vehicle with longitudinal dynamics and motion and adjustable mass , geometry and drag properties.
• Represents a two - axle vehicle body in longitudinal motion .The block account for the body mass , aerodynamics 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 axles. optionally include pitch and suspension dynamics or additional variable mass and inertia. The vehicle does not move vertically relative to the ground .
• Connection H is the mechanical translational conserving port associated with the horizontal motion developed by tires should be connected to this port . Connections V,NF, and NR are physical signal output   port for vehicle velocity and front and rear normal wheel forces , respectively . Wheel forces are considered positive if acting downwards . connections W and beta are physical signal input port corresponding to headwind speed and road inclination angle , respectively . If variable mass is modeled , the physical signal input ports CG and M are exposed .CG accepts a two - element vector representing the x and y distance offsets from vehicle CG to additional load mass CG . M represent the additional mass . if both variable mass and pitch dynamics are included , the physical signal port J accepts the inertia of the additional mass about its own CG.
• The vehicle body represents the 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 wheel can also have a center of gravity that is at or below the plane of travel .

Tire ( Magic formula ) :

• Tire with longitudinal behavior given by magic formula coefficients.

Represents the longitudinal behavior 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 .

connection A is the mechanical rotational conserving port for the wheel axle .

connection H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle .

connection N is aphysical signal input port that applies the normal force acting on the tire .

Explanation : 

• The throttle signal is generated by signal builder block and inputted to generic engine.
• The torque and speed vector are inputted from matlab workspace.
• now from crankshaft output ,the value is passed to engine .
• the speed is sense by ideal rotational motion sensor .
• The output speed will be given to a simple gear mechanism to reduce the speed where the gear ratio is four.
• The output speed from the gear reducer will be given to the CVT .
• the CVT ratio is provided to the CVT block through signal builders.

• The speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle.
• The power from CVT is inputted to the axle and the vehicle accelerated according to the speed .
• Then the velocity is taken as output from the vehicle body for further analysis .

INPUTS :

Torque - speed plot :

• It is taken as default input to the engine.
• The torque and speed are inputted from the matlab workspace window to the generic engine block to generate the output RPM accordingly . 

BREAKE INPUT AND THROTTLE INPUT :

Here the break input is given as 0.

and throttle velocity is is given 0.3 for 30 sec and for 1 after 30 sec and it remains constant .

OUTPUTS :

• From the graph we can see that the brake value is zero throughout the simulation process.
• Throttle velocity is remain constant and is 0.3 for 20 sec.
• After 20 sec ,throttle value becomes 1 and is remain constant after 20 sec .

Primarry shaft and Secondary shaft velocity comparision :

• As we can see from the graph that , velocity of secondary shaft is greater than the velocity of secondary shaft .

 2 ) BAJA ATV model  with dashboard :

•  In this model ,there is only change that we can give break input and throttle input through knob.
• we are replacing signal builder with two seperate constant blocks for throttle and brake .
• All other procedure is same .

CASE 1:

THROTTLE VELOCITY IS 0.3

• As we can see from the graph that due to low throttle value , velocity becomes zero after some sec .

CASE 2:

THROTTLE VELOCITY IS 0.6

• Here from graph we can see that as we have increase throttle valve , speed increase and remain constant at 60 .

CASE 3:

THROTTLE VELOCITY IS 1

•  Here we have given maximum value of throttle ie 1 .
• Velocity increases rapidly and become constant .
• Maximum velocity is 58 kmph.

   3 ) BAJA ATV model with lookup table and without dashboard .

 

In this model lookup table is added .

 Flow process :

• In this model lookup table is added in the subsystem of CVT block.
• CVT ratio and vehicle speed are extracted from matlab workspace. 

Lookup Table :

• A loopup 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 retrive the corresponding output values from the table .
• If the lookup table does not explicitly define the input values , simulink can estimate an output value using interpolation , extrapolation or rounding .

4 )BAJA ATV model with lookup table and with dashboard :

•  This is the latest upgraded model of BAJA ATV model.
• In this model both  dashboard and lookup table is used .

OUTPUTS :

Case 1 :

• Here we have given random value of throttle and brake inputs .
• AS seen from graph , the value of speed is changing accordingly.

Case 2 :

• Here we first increasing value of throttle input to its maximum value.
• Now increasing the brake value to its maximum values.
• The below graph shows the variation of speed according to above condition .

Output of Primary shaft and secondary shaft :

• From the above graph we can see that ,shaft speed in rpm increase upto 7500rpm at throttle value of 1 and break input of 0.

 REFERENCE:

https://www.mathworks.com/matlabcentral/fileexchange/70576-baja-all-terrain-vehicle-atv-model