SIMULINK [BAJA ATV Simulation]
Simulink for Mechanical & Electrical Engineers
#PROJECT
OBJECTIVE: To carry out a simulation and technical report on BAJA ATV explaining model properties for -
- with and without Dashboard
- using Lookup table
- without using Lookup table
THEORY :
ATV : 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 operator and handlebars for steering control. ATVs offer excellent off-road capabilities and can carry heavy equipment over long distances and narrow access points. It has applications across various industries, including sports, entertainment, agriculture, military and defense.
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.
PROCEDURE :
- BAJA ATV Model Without Dashboard.
Brake and Throttle Input :
Brake input is constant i.e. zero throughout the time of 80 sec. Throttle input is 0.3 for first 20 sec, accelerates to 1 at the same and remains constant throughout the remaining time till 80 sec.
Signal Builder: The Signal Builder block allows you to create linear signal sources and to use them in a model. You can quickly switch the signal groups into and out of a model to facilitate testing.
The CVT gear ratio 2.3 for the first 4 secs, then drops down to 1.8 till 35 secs and remains constant thereafter rill 80 sec.
Generic Engine:
It represents a model of spark-ignition and diesel engines suitable for use at initial stages of modeling when only the basic parameters are available. 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.
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 which engine power and fuel consumption rate are reported.
Engine Sensor: Ideal Rotational Motion Sensor: The block represents an ideal mechanical rotational motion sensor, that is, a device that converts an across variable measured between two mechanical rotational nodes into a control signal proportional to angular velocity or angle. 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.
CVT Subsystem:
Inertia: The block represents an ideal mechanical rotational inertia. The 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 accelerated in a positive direction.
Variable Ratio Transmission: 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. Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relation between base and follower rotation directions with the Output shaft rotates parameter.
Simple Gear: Represents a fixed-ratio gear or gearbox. 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 conserving ports. Specify the relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by right-clicking on the block and selecting Simscape block choices to switch between variants.
Follower (F) to base (B) teeth ratio (NF/NB): 4
Vehicle Body Subsystem:
Vehicle Body: Represents a two-axle vehicle 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. The vehicle can have the same or a different number of wheels on each axle. 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 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. Wheel 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. If the 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 represents 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.
Parameters are: Mass: 250 kg
Number of wheels per axle: 2
Horizontal distance from CG to front axle: 1 m
Horizontal distance from CG to rear axle: 0.35 m
CG height above ground: 0.7 m
Gravitational acceleration: 9.81 m/s^2
Tire: Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from TireRoad Interaction (Magic Formula) 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 a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports the tire slip. Optionally expose physical signal port M by setting Parameterize by to Physical signal Magic Formula coefficients. Physical signal port M accepts a four-element vector corresponding to the B, C, D, and E Magic Formula coefficients.
Parameters (common for all tires) are:
Parameterize by: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: Represents a brake 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 include thermal effects and expose thermal conserving port H by setting Thermal port to Model.
Parameters are:
Drum radius: 150 mm
Actuator location radius: 100 mm
Pin location radius: 125 mm
Pin location angle: 15 deg
Shoe beginning angle: 5 deg
Shoe span angle: 120 deg
Torque vs Speed characteristics:
OUTPUTS :
- Vehicle Speed
- CVT Shaft Speed
BAJA ATV MODEL WITH DASHBOARD
A dashboard (also called dash, instrument panel (IP), or fascia) 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
Throttle Input = 0.3
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 displays the changes done by the respective knobs.
OUTPUTS :
- Vehicle Speed
- CVT Shaft Speed
BAJA CVT using Lookup Table
- Without 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 explicitly 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.
CVT Ratio vs Vehicle Speed:
They are given in steps using the step block. Parameters are:
Brake Input:
Step time: 35
Initial value: 0
Final value: 0
Sample time: 0
Throttle Input:
Step time: 20
Initial value: 0.3
Final value: 1
Sample time: 0
OUTPUT :
- CVT shaft speed
- Vehicle speed
- Visualization lookup table
WITH DASHBOARD
OUTPUT :
- CVT Ratio
- CVT shaft speed
- Vehicle speed
CONCLUSION:
Hence, the given BAJA ATV Model was simulated successfully-
-Velocity, CVT Shaft Speed and Engine Speed are directly proportional to the Throttle input and inversely proportional to the Brake input.
- CVT Ratio is directly proportional to Torque and inversely proportional to the Throttle input.
- CVT Primary speed is greater than CVT Secondary speed as they are directly proportional to their shaft diameter.
- The speed might get null at a particular braking resistance.