Project
Aim: to study and analyze BAJA ATV vehicle model using Simulink and compare between models
Types of models:
- BAJA ATV MODEL WITHOUT DASHBOARD
- BAJA ATV MODEL WITH DASHBOARD
- BAJA ATV MODEL MAPPED LOOKUP TABLE WITH DASHBOARD
- BAJA ATV MODEL MAPPED LOOKUP TABLE WITHOUT DASHBOARD
ATV
An all-terrain vehicle (ATV), also known as a light utility vehicle (LUV),[1] a quad bike, or simply a quad, as defined by the American National Standards Institute (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. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles.
BAJA 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 SAE 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 agility of the vehicle in terms of gradability, speed, acceleration and manoeuvrability characteristics and finally its ability to endure that back breaking durability test.
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
IMPORTANT BLOCKS
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 choice of fuel consumption model.
Main ports:
- B - Rotational Conserving Port: representing the Engine Block(should be connected to rotational motion reference)
- F- Rotational Conserving Port: representing the Engine Crankshaft
- T- Physical signal input port: specifying the normalized engine throttle level
- 4.P - Physical signal output port: reporting the instantaneous engine power, in W
- 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 co-rotate with a fixed ratio that is specified.
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 TRANSMISSION
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 control that you control. We can choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, WF and wg have the same sign. If they rotate in opposite directions, WF and Wg have opposite signs.Transmission compliance introduces internal time delay between the axis motions. Therefore, unlike a gear, a variable transmission does not act as a kinematic constraint.
Main ports:
- B - Base Pulley or Drive Pulley
- F- Follower Pulley or Driven Pulley
3.r-Variable Transmission Ratio (Input)
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 ports:
- Beta - Road Incline Angle (rad): physical signal input port for road incline angle
- W - Head Wind Speed (m/s): physical signal input port for road incline angle
- CG-center of gravity(m): physical signal input port of externally defined mass relative to the cg of vehicle only available with externally defined additional mass is set to on)
- M-mass(kg): physical signal input port for mass of the externally defined mass (only available with externally defined additional to on mass is set
- J-Externally defined moment of inertia (in kg*m^2): physical signal input port of the externally defined mass
Output ports:
- NR - Rear Axle Normal Force (N): physical signal output port for the rear axle which is considered positive acting downward
- NF - Front Axle Normal Force (N): physical signal output port for the front axle which is considered positive acting downward
3.V - Longitudinal Velocity (m/s): physical output signal of vehicle velocity
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:
- Contact angles smaller than 45º 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.
Input ports:
F- Physical signal input port associated with the applied actuating force
Conserving ports:
S - Rotational conserving port associated with the rotating drum shaft
TIRE BLOCK
The Tire (Magic Formula) block models a tire with longitudinal behavior given by the Magic Formula, 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 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 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.
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 Cex and damping bfx. The Tire-Road Interaction (Magic Formula) block models the longitudinal force Fy 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, lwr2w. 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.
Input ports:
N - Normal Force: Physical signal input port associated with the normal force acting on the tire. The normal force is positive if it acts downward on the tire, pressing it against the pavement.
M- Magic formula coefficients: Physical signal input port associated with the Magic Formula coefficients. Provide the Magic Formula coefficients as a four-element vector, specified in the order (B, C, D, E).( Port M is exposed only if the Main > Parameterize by parameter is set to Physical signal Magic Formula coefficients)
Common tyre parameters:
Magic Formula B coefficient 10
Magic Formula C coefficient: 1.9
Magic Formula D coefficient: 1
Magic Formula E coefficient: 0.97
Output ports: S- Tire Slip: Physical signal output port associated with the relative slip between the tire and road.
Conserving ports: A- Axle: Mechanical rotational port associated with the axle that the tire sits on.
H - Mechanical translational port associated with the wheel hub that transmits the thrust generated by the tire to the remainder of the vehicle
Other Blocks used:
- Solver Configuration
- Signal Builder
- Simulink to PS Converter
- PS to Simulink Converter
- Mechanical Reference
- Rotational free end: The Rotational Free End block represents a mechanical rotational port that rotates freely, without torque.
- Scope
- Display
- Inertia
- Rotational Motion Sensor
- PS Terminator
- PS Constant
- Rotational Free End - For mechanical component (Tire)
- Custom Measure Gauge
- Knob - To increase, decrease and vice-versa of throttle and brake inputs
- Lookup Table - To insert the CVT values from the workspace
- Step - To increase or decrease an input value for a defined time interval
ATV MODEL WITHOUT DASHBOARD
Steps:
i.The throttle signal is generated by signal builder block and inputted to generic engine.
ii.The torque and speed vector are inputted from the matlab workspace Rotational
iii. The engine will generate the output rpm which can be taken from the crankshaft output. This speed will be given to the Ideal Motion Sensor to sense the output rpm.
iv.The same output speed will be given to a simple gear mechanism to reduce the speed where the Gear Ratio is -4
v.Then the output speed from the gear reducer will be given to the Variable Ratio Transmission block (CVT).
vi.The CVT ratio is provided to the Variable Ratio Transmission (CVT) block through Signal Builder.
vii. The speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle.
viii. The brake signal is generated by the signal builder and inputted to the vehicle body (Double Shoe Brake) for applying the brake to axle.
ix.The power from the CVT is inputted to the axle and the vehicle accelerates according to the speed.
x.Then the Velocity is taken as output from the vehicle body for further analysis.
INPUT SIGNALS
CVT RATIO
CVT SUB BLOCK
This subblock gives input and output shafts of the cvt with inertia and measures input and output shaft rpm
VEHICLE BODY SUBBLOCK
It appears that this a rear wheel drive vehicle as the power input is transferred to the rear axle, inertia is added to simulate rear axle, the front tires are free to rotate. The hub ports of all the wheels are connected together and connected to vehicle h port. The body takes road inclination and wind velocity from physical constants.
RESULTS
Engine vs torque speed curve
CVT SHAFT SPEED GRAPH
Engine speed is controlled by various cvt ratios it becomes maximum after 40 seconds.
VELOCITY VS DISTANCE VS THROTTLE INPUT VS BRAKE GRAPH
THROTTLE INPUT IS A CONSTANT 0.5 WHILE BRAKE INPUT IS 0 THROUGHOUT, MAXIMUM VELOCITY ATTAINED IS 53.53 KPH.
ENGINE RPM
Maximum engine rpm attained is 3400 the initial peaks are before the clutch is disengaged in a cvt as the clutch operated on purely centrifugal force.
ATV MODEL WITH DASHBOARD
The outputs can be controlled by the knobs in the display present
To understand the outputs three cases are done where throttle is kept constant
Throttle is kept 1
Brake is turned to-
CASE 1= 0.2
CASE 2= 0.3
CASE 3= 0.5
PLOTS
CASE1
ENGINE RPM
ENGINE TORQUE SPEED CURVE
CVT SHAFT SPEED
CASE 2
CVT SHAFT SPEED
VEHICLE SPEED, DISTANCE, INPUTS GRAPH
ENGINE RPM
CASE 3
CVT SHAFT SPEED
VEHICLE SPEED, DISTANCE, INPUTS GRAPH
ENGINE RPM
SIMULINK MODEL OF ATV WITH LOOKUP TABLE WITH DASHBOARD
In this model we change the throttle value constant and keep the brake value constant
The brake is kept constant at 0.35
Case1= throttle 0.5
Case2=throttle 0.78
Case3=throttle 0.95
Vehicle speed
Inputs
CVT SHAFT SPEED
CASE 2
Vehicle speed
Inputs
Cvt values
Cvt ratio
CASE 3
Vehicle speed
Inputs
Cvt ratio
Cvt values
Observation
- Based on different inputs to get different behaviour of the vehicle speed, the power output at the CVT shaft speed and the change in torque speed curve
- The graph changes more smoothly using lookup table values, while manual output values provide a more rougher graph
ATV MODEL WITH LOOKUP TABLE WITHOUT DASHBOARD
ENGINE RPM
CVT RATIO
VEHICLE SPEED AND INPUTS
CVT SHAFT SPEED
LOOKUP TABLE VISUALISATION
OBSERVATIONS
- Using the lookup table, the vehicle speed increase gradually and takes longer time to become constant at a certain level
- There is gradual increase in speed of secondary gear of cvt as initial speed is picked by driving gear.
- Lookup table graph shows cvt ratio wrt output power at wheel
SUCCESSFULLY STUDIED AND CARRIED OUT SYSTEM LEVEL SIMULATION OF BAJA SAE VEHICLE