Project

An All-terrain Vehicle (ATV), also known as a quad cycle, Light Utility Vehicle (LUV), that travels on low-pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control. It is designed to handle a wider variety of terrain than most other vehicles.

BAJA ATV Model -

The BAJA SAE series is an event for the undergraduate engineering students, organized globally by the Society of Automotive Engineers, USA. Suspension and chassis play a vital role in the structural performance of an off-road vehicle. The paper focuses on Computer Aided Engineering (CAE) modeling and simulation study of an All Terrain Vehicle (ATV) structure to analyze its static and dynamic behavior. An integrated MBD-FEA approach used for analysis purpose has been presented. 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.

Components used in this Simulation Model -

Generic Engine -

Represents 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 controllers 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.

Connections F and B are mechanical rotational conserving ports.

Connections P and FC are physical signal output ports through which engine power and fuel consumption rate are reported.

Engine Sensor -

This block measures 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.

Consists of -

• RPM Sensor
• Engine RPM Scope

Simple Gear -

Represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in this block. 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.

CVT System -

In CVT (Continuous Variable Transmission), the variable diameter pulley plays a vital role in transmission. Variable – diameter pulleys must always come in pairs. One of the pulleys, known as the drive pulley (or driving pulley), is connected to the crankshaft of the engine. The driving pulley is also called the input pulley because it’s where the energy from the engine enters the transmission. The second pulley is called the driven pulley because the first pulley is turning it. As an output pulley, the driven pulley transfers energy to the driveshaft.

Consists of -

• Input Shaft Inertia
• CVT ratio
• Variable Ratio Gear
• Output Shaft
• CVT Primary RPM
• CVT Secondary RPM

Vehicle Body -

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.

Consists of -

• Double Shoe Brake
• Wheels (Front Left and Right, Rear Left and Right)
• Brake (as Gain)
• Vehicale body block
• Wind input
• Velocity input

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.

Tire -

Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road 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.

BLOCKS USED -

• Signal Builder – To input the Brake, Throttle and CVT Ratio.
• Simulink to PS converter – To convert the Simulink signal to Simscape environment.
• Solver Configuration – To specify the solver parameters before starting the simulation.
• Mechanical Reference – To make sure all the components are clamped to the ground.
• Generic Engine – To run the engine with speed and torque values as input.
• PS to Simulink Converter – To convert Simscape signal to Simulink environment.
• Scope – To view the graph of the parameters for better understanding.
• Display – To view the calculated engine power.
• Inertia – To represent the solid inertia.
• Rotational Motion Sensor – To sense the rotational motion from the engine and give output as RPM.
• Variable Gear Ratio – To vary the speed according to the gear ratios.
• PS Terminator – Terminator for unconnected physical signal outputs.
• Double Shoe Brake – To apply brake to the vehicle when needed.
• PS Constant – Generate constant physical signal.
• Tire – For transportation of the vehicle.
• Rotational Free End – For mechanical component (Tire)
• Vehicle Body – To represent the BAJA ATV model body.
• Custom Measure Gauge – To measure the brake and throttle input.
• Knob – To increase, decrease and vice-versa of throttle and brake inputs.
• Lookup Table – To insert the CVT values from the workspace.
• Simple Gear – To reduce the speed of the engine with pre-defined gear ratio.
• Step – To increase or decrease an input value for a defined time interval.

TYPES OF MODEL:

• BAJA ATV model without Dashboard
• BAJA ATV model – Mapped Lookup Table with Dashboard

BAJA ATV model without Dashboard

Process -

• The throttle signal is generated by signal builder block and inputted to generic engine.
• The torque and speed vector are inputted from the MATLAB workspace.

• The speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle.
• The brake signal is generated by the signal builder and inputted to the vehicle body (Double Shoe Brake) for applying the brake to axle.

Workspace Data -

Speed and Torque Table -

• The engine will generate the output RPM which can be taken from the crankshaft output. This speed will be given to the Ideal Rotational Motion Sensor to sense the output RPM.
• The same output speed will be given to a simple gear mechanism to reduce the speed where the Gear Ratio is ‘4’.
• Then the output speed from the gear reducer will be given to the Variable Ratio Transmission block (CVT).
• The CVT ratio is provided to the Variable Ratio Transmission (CVT) block through Signal Builder.

• The power from the CVT is inputted to the axle and the vehicle accelerates according to the speed.
• Then the Velocity is taken as output from the vehicle body for further analysis.

OUTPUTs -

Speed Vs. Torque -

The torque and speed are inputted from the MATLAB workspace window to the generic engine block to generate the output RPM accordingly.

This plot is common for all the cases because it’s a default input to the engine.

Engine RPM Plot -

Here we can see the engine rpm generated accordingly w.r.t to the throttle, speed and torque inputs.

Speed Vs. Throttle -

From the graph we can infer that the brake is not applied during the drive cycle and the Throttle is constant (0.3) till 20 sec and being increased from 0.3 to 1 from 20 sec where it remains constant for the rest of the run. With the increase in throttle, the vehicle speed also increases.

Note - Here, Signal Builder/2 (Throttle) and Signal Builder/1 (Brake)

BAJA ATV MODEL WITH DASHBOARD

Open Loop Model -

Output (Break, Throttle, Distance, Velocity) -

CVT Shaft Speed Graph -

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BAJA ATV MODEL WITH DASHBOARD

Gear Ratio Selection -

It is observed that providing a gear ratio of equal or less then 10, Engin's getting down as its not withstanding with the current model parameters.

It is also observed that providing a gear ratio of more then 13, Shows a Engin's behaviour where velocity is not moving up more than 60kmph.

Conclusion - It is concluded with a gear ration of 12, as this ration fits the best in this simulation with respect to the model's design parameters.

Plots After analysing the gear ratio with respect to the parameters of the model -

Vehicle Speed -

CVT graph -

BAJA ATV model without Dashboard

Closed Loop Model -

Vehicle Speed -

CVT graph -

CVT Ratio -

References -

BAJA All-Terrain Vehicle (ATV) Model - File Exchange - MATLAB Central (mathworks.com)

(5) Understanding CVT ! - YouTube