Project
AIM: To study and analyze the BAJA All Terrain Vehicle (ATV) model using simulink and compare between different models.
Objectives:-
1. To prepare a technical report explaining the functionsof the subsystem & blocks used for preparing the model.
2. To explain the details between all models.
Introduction:
All Terrain Vehicle:
An all-terrain vehicle is defined as a motorized off-highway vehicle designed to travel on four low-pressure tires, having a seat designed to be straddled by the operator and handlebars for steering control. ATVs are subdivided into two types as designated by the manufacturer. Type I ATVs are intended by the manufacturer for use by a single operator and no passenger and Type II are intended by the manufacturer for use by an operator and a passenger and are equipped with a designated seating position behind the operator.
Continously Variable Transmission (CVT):
A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This goes against the other transmission that provide a limited number of gear ratios in fixed steps. The most benificial flexibilty of a CVT is its control that allows the engine to operate at a constant RPM while the vehicle moves at varying speed.
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 are also present which include crankshaft inertia and response time lag. A physical signal port outputs engine fuel consumption rate based on choice of fuel consumption model. Optional speed and redline controllers prevent engine stall and enable cruise control.
Main ports:
1. B - Rotational conserving port: representing the engine block (should be connected to rotational motion reference).
2. F - Rotational conserving port: representing the engine's 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 is specified.
The follower-base gear ratio is:
gFB=rF/rB=NF/NB
where:
- NB is the number of teeth in the base gear.
- NF 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 withthe follower or output shaft.
Varaible Ratio Transmission Block:
The variable ratio transmission block represents a gearbox that dynamically transfers motion and torque between the two connected driveshaft axes base and follower.
Excluding the dynamics of transmission compliance, the driveshafts are constrained to corotate with a Variable Gear Ratio control that is handled by user. You can choose whether the follower axis rotates in the same or opposite direction as the base axis. If the direction is same ωf and ωb have the same sign otherwise they have opposite signs.
Unlike a gear, a variable transmisson does not act as a kinematic constrain. You can also control torque loss caused by transmission and viscous losses.
Main port:
1. B - Base pulley or drive pulley.
2. 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 numbers of wheel on each axle. For example, two wheels are assumed identical in size. The vehicle can also have a centerof gravity (CG) that is at or below the plane of travel.
The block accounts for the 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:
1. Beta - Road incline angle (rad): physical signal input port for road incline angle
2. W - Head Wind Speed (m/s): physical signal input port for road incline angle.
3. CG: centre 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 mass is set to on).
J - Externally defined moment of inertia (in kg*m^2): physical signal input port of the externally defined mass.
Output ports:
1. NR - Rear Axle Normal Force (N): physical signal output port for the rear axle which is considered positive acting downward.
2. 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.
Conserving ports:
H - Horizontal Motion: conserving port related to the horizontal motion of vehicle body (tyres should be connected 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 fricition paramters.
Limitations:
- Contact angles smaller than 45° produce less accurate results.
- Brake uses the long-shoe approximation.
- Brake geometry does not self-lock.
- Modeldoes not count for actuatorflow consumption.
Input ports:
F - Physical signal input ports associatedwith the applied actuating force.
Conserving Ports:
S - Rotational conserving port associated with the rotating drum shaft.
Tire(magic formula) block:
The tire(Magic Formula) block models a tire with longitudinal behavior given by the magic formula, an emperical equation based on four fitting coefficients. The block can model tire dynamics under constant or variable pavement conditions.
The longitudinal direction of the tire model, you can specify properties such as tires compliance, inertia and rolling resistance. However, these properties increase the complexity of the tire model and can slowdown simulation.
Equivalent Model:
The full tire model is equivalent to this Simscape/Simscape Driveline component diagram. It simulates both the transient and steady state behavior and correctly represents starting from, and coming to, a stop.
The transational spring and transational damper are equivalent to the tire stiffness C(FX) and damping b(FX). The tire-road interaction(Magic Formula) block models the longitudinal force F(x) on the tire as a function of F(z) and k' using the Magic Formula, with k' as the independent slip variable.
The wheel and axle radius is the wheel radius r(w). The mass value is the effective mass, Iwr^2w. The tire characterstic function f(k',F(z) determines the longitudinal force F(x).Together with the driveshaft torque applied to the wheel axis F(x) 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 Port:
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].
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 block used:
- Solver Configuration - To specify the solver parameters before starting the simulation.
- Signal Builder - To input the Brake, Throttle and CVT Ratio.
- Simulink to PS Converter - To convert the simulink signal to simscape environment.
- PS to Simulink Converter - To convert simscape signal to simulink environment.
- Machanical Reference - To make sure all the components are clamped to the ground.
- Rotational free end - Represents a mechanical rotational port that rotates freely, without torque.
- Scope - To display different graphs.
- Display - To view the calculated engine power.
- Inertia -To represent solid inertia.
- Rotational Motion Sensor - To sense the rotational motion from the engine and give output as rpm.
- PS terminator - Terminator for unconnected physical signal outputs.
- PS Constant - Generate constant physical signal.
- Rotational free end - For mechanical component (Tire)
- Custom Measure Gauge - To measure the brake and throttle input.
- Knob - To increase, decrease and vice versa of the 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.
BAJA ATV MODEL WITHOUT DASHBOARD (cvtMOdel)
Main Model:
Steps:
i) The throttle signal is generated by signal builder block and feeded to generic engine.
ii) The torquw and speed vector are given from matlab workspace.
iii) The engine will generate the output rpm which can be taken from the crankshaft output. This speed will be given to an Ideal Rotatonal Motion Sensor to read 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 Varaible Ratio Transmission (CVT) block through signal builder.
vii) The speed is controlled by the variable CVT ratios and the controlled output speed is transferred to vehicle axle.
viii) The brake signal is generated by the signal builder and given to the vehicle body (Double Shoe Brake) for applying the brake to the axle.
ix) The power from the CVT is transferred 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:
Throttle Input Signal:
Throttle starts at 0.3 and then steps up to 1 at t=20.
Brake Input Signal:
Remains zero the whole simulation.
Torque and Speed Matlab workspace Input:
CVT ratio input:
CVT ratio starts at 3.75 and decreases gradually until it reaches 0.5 at 35th second and remains there throughout.
Engine Sensor Sub-Block:
This sub-block measure engine rotational speed as it takes the output of the engine as its input and outputs engine rpm.
CVT Sub-block:
The CVT sub-block provides the input and the output shafts of the cvt with inertia, and measures the input shaft rpm and the output shaft rpm.
Vehicle Body Sub-Block:
The model shows that the vehicle is rear wheel drive as the output from the gearbox is given to the rear axle, then the same axle connects the two rear tyres while the front tyres are free to rotate on a rotational free end. All the tyres H hub ports are connected together and then connected to the vehicle H port.
Similarly, rear tyres N ports are also connected together and then connected to the Vehicle body Nr output ports, the vehicle body takes the road inclination and the wind velocity from physical constants.
Results:
Torque-Speed plot:
The torque and speed are inputted from the matlab workspace window to the generic engine block to generate the output RPM accordingly. This plot behavior is generic to all ICE.
Engine-Speed Plot:
The engine rpm generated accordingly to the throttle, speed and torque inputs.
CVT shaft speed plot:
Speed-Throttle plot:
BAJA ATV model - Data Extraction (cvtModel_data)
Main model:
Steps:
The model workflow process is same as the process of 'BAJA ATV model without Dashboard'. The small addition is here the CVT Ratio and Vehicle Speed data are extracted using 'To Workspace' block.
Inputs:
Throttle:
Brake:
CVT ratio:
Results:
Vehicle Speed Plot:
An additional output is the Vehicle Velocity to the workspace.
CVT Shaft Speed:
Vehicle speed vs cvt ratio plot:
BAJA ATV Model with Dashboard (cvtModel_dashboard):
Main model:
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.
CVT ratio:
Results:
Engine Speed Plot:
Here the engine speed is generated according to the inputs like throttle, break, torque and speed vectors. The runtime is not defined so that the throttle and break are connected by the user. The step up is throttle and step down is brake input.
Speed-Throttle Input:
From the graph we can infer that the vehicle is accelerating while throttle is applied adn decelerates when brakes are applied. The constant speed areas represent no changes in the throttle or braking.
BAJA ATV model - Mapped Lookup table without Dashboard (cvtModel_mapped):
Main model:
Steps:
The model workflow process is same as the process of 'BAJA ATV model without Dashboard' except that it used step input block instead of signal builder block for brake and throttle input.
Throttle and Brake inputs:
CVT Sub-block:
The cvt sub-block is the same as the previous model "BAJA ATV model without Dashboard' but instead of signal builder block for CVT ratio the 2-D lookup tableis used. The interpolations and extrapolation methods are set to linear. It needs to be loaded in the workspace having the file name as Lookuptable_data.mat.
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 valies, 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.
A lookup table block uses an array of data to map input values to output values, approximating a mathematical function. Given input values, Simulink performs a "lookup" operation to retrieve the corresponding output values from the table. If the lookup table does not define the input values, the block estimates it based on nearby table values.
At last the vehicle speed output is given as a feedback to the 2-D Lookup Table so that we can verify that the velocity of the vehicle is changing perfectly when the CVT Ratio changes. The vehicle speed is converted to m/s from kmph.
Results:
CVT ratio plot:
CVT ratio starts at 3.5 remains constant for 4 second and reduces gradually to 0.5 remaining there throughput.
Engine Speed:
CVT Shaft Speed:
The secondary shaft rpm is higher than the primary.
Speed-Throttle plot:
BAJA ATV model -Mapped Lookup Table with Dashboard (cvtModel_dashboard_mapped):
Dashboard (simulation off):
Dashboard (simulation on):
User controls:
Steps:
The model workflow process is same as the process of 'BAJA ATV model - mapped lookup table without Dashboard' but the throttle and brake inputs are controlled by the user with the knob followed by the vehicle speed is given as feedback to the CVT Ratio lookup table.
Results:
CVT ratio plot:
In this BAJA ATV model, the engine is pre set to run at 3300 rpm with throttle value of 0.3. And the velocity of 45 kmph.
Engine Speed plot:
From the graph we can infer that the vehicle was first running at minimum rpm of 3300 rpm and then a throttle is applied (step-up) then braking (step-down) which released after.
Speed-Throttle plot:
From the plot we can infer that when throttle is applied vehicle speed increases and when brake is applied vehicle speed decreases simultaneously.
REFERENCE:
Matlab Documentation