Project 3 - System-Level simulation and technical report preparation of BAJA ATV (All Terrain Vehicle)

QUESTION

Objectives: -

Carry out a system-level simulation of an all-terrain vehicle. Prepare a technical report explaining the model properties & comments on the results.

ANSWER

#Theory

All-Terrain Vehicle

An all-terrain vehicle (ATV), also known as a quad (cycle), three-wheeler, four-track, four-wheeler, or quadricycle, 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. It is designed to handle a wider variety of terrain than most other vehicles.

Baja ATV (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 gradeability, speed, acceleration and maneuverability characteristics and finally its ability to endure that back breaking durability test.

#Components Used

• Generic Engine

The Generic Engine block represents a general Internal Combustion (IC) Engine which is a type of Spark Ignition (SI Petrol) or Compression Ignition (CI-Diesel). The speed-torque and speed-power parameters are provided.

Ports

1. B - Rotational Conserving Port representing the Engine Block.
2. F - Rotational Conserving Port representing the Engine 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

A simple gear is a combination of driver and driven gear where the speed is reduced by the gear ratio. The gear ratio is defined as

Gear ratio = Follower gear speed

Base gear speed

Ports

1. B – Base gear or Driver gear.
2. F – Follower gear or driven gear.

• CVT Transmission

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.

The distance between the center of the pulleys to where the belt makes contact in the groove is known as the pitch radius. When the pulleys are far apart, the belt rides lower and the pitch radius decreases. When the pulleys are close together, the belt rides higher and the pitch radius increases. The ratio of the pitch radius on the driving pulley to the pitch radius on the driven pulley determines the gear, when the pitch radius is small on the driving pulley and large on the driven pulley, then the rotational speed of the driven pulley decreases, resulting in a lower "gear" When the pitch radius is large on the driving pulley and small on the driven pulley, then the rotational speed of the driven pulley increases, resulting in a higher "gear." Thus, in theory, a CVT has an infinite number of "gears" that it can run through at any time, at any engine or vehicle speed.

Ports

1. B – Base Pulley or Driver Pulley.
2. F – Follower Pulley or driven Pulley.
3. r – Variable Transmission Ratio (Input)

• Vehicle Body

Two-axle vehicle with longitudinal dynamics and motion and adjustable mass, geometry, and drag properties. 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 centre of gravity (CG) that is at or below the plane of travel.

Ports

1. NR - Rear Axle Normal Force (N)
2. NF - Front Axle Normal Force (N)
3. Beta-Road Incline Angle (rad)
4. V - Longitudinal Velocity (m/s)
5. W - Head Wind Speed (m/s)
6. H- Horizontal Motion

• Double Shoe Brake

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.

Ports

1. S - Rotational conserving port associated with the rotating drum shaft.
2. F - Physical signal input port associated with the applied actuating force.

• Tire

The vehicle body is connected to 4 tires each per axle to move the vehicle according to the power input to the axle.

Ports

1. N – Normal force.
2. S – Tire Slip
3. A – Axle
4. H – Mechanical Translational port associated with the wheel hub that transmits the thrust generated by the tire to the remainder of the vehicle.

# Blocks Used

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

#Types of Models

• Baja ATV model without Dashboard
• Baja ATV model with Dashboard
• Baja ATV model – Mapped lookup table without Dashboard
• Baja ATV model - Mapped lookup table with Dashboard

# 1) Simulink Model for Baja ATV without Dashboard

Main Model

Engine Sensor

CVT Mechanism

Vehicle Body

Procedure of Simulation

• The Throttle is generated by the signal builder block and input to the generic engine.
• The brake input is generated by the signal builder block and input to the vehicle body (Double Shoe brake) for applying brake to the axle.
• The brake input is kept as zero i.e., no brake is applied, while Throttle input is applied as 0.3 for the first 20 sec and then increased to 1 for the next 20 to 80sec.

• The speed and torque vectors are predefined in Workspace according to the Torque speed characteristics of the vehicle and these are extracted through grabit in MATLAB.

• 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 speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle.
• 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.

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 is common for all the cases because it's a default input to the engine.

Engine (Vehicle) Speed Plot

It is clear from the graph that the vehicle attains its maximum speed (V=55km/h) at full throttle 1 after =35 seconds and then remain constant the brake input value is zero hence it has no effect on velocity.

CVT Shaft RPM

This graph shows the variation in the velocity in input and output shafts of the variable gear transmission system this value differs concerning the gear ratio.

# 2) Simulink Model for Baja ATV with Dashboard

Dashboard

Procedure of Simulation

The model workflow process is same as the process of “Simulink Model of Baja ATV without Dashboard” but the Throttle and brake inputs are controlled by the user with the knob.

Results

Engine (Vehicle) Speed Plot

It can be observed from the graph that the velocity of the vehicle increases drastically from 0 to 50kmph when throttle value is 0.5 & brake input is O. Once the braking value increases from 0.1 to 0.5, the velocity of the vehicle decreases to O at constant throttle value. This explains the direct relation of vehicle velocity with respect to throttle and brake inputs.

CVT Shaft RPM

# 3) Simulink Model for Baja ATV– Mapped lookup table without Dashboard

CVT Mechanism

Procedure of Simulation

1. The model workflow process is same as the process of 'Simulink model for BAJA ATV without Dashboard.
2. Instead of Signal Builder Blocks for Brake and Throttle Input, the Step blocks are used. At 35 sec the brake input will take a step of value '0' and at 20 sec throttle input will increases from 0.3-1 then remains constant throughout.

3) And instead of Signal Builder Block for CVT Ratio the 2-D Lookup Table is used. The interpolations and extrapolation methods are set to linear.

4) At last, the vehicle speed output is given as 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

When we compare the above plot, the ratio varies from 2.3 - 1.8 within timespan of 80 sec which is same as the previous BAJA ATV Models. And from 32 sec it's constant ratio of 1.8.

CVT Ratio vs Vehicle Speed

Here the CVT Ratio changes from 2.3-1.8 and the velocity value also changes w.r.t to the CVT Ratio. Hence, we can conclude that the vehicle accelerates, decelerates and remains constant when the CVT Ratio is being varied. And also, the vehicle attains the constant speed of 55.441 m/s.

Engine (Vehicle) Speed Plot

CVT Shaft RPM

# 4) Simulink Model for Baja ATV– Mapped lookup table with Dashboard

In the above model we the new thing is that this model provides us with the control brake input and throttle input.

Results

Engine (Vehicle) Speed

This graph is similar to the CVT dashboard case study the variation in vehicle velocity can be observed with the change in brake input and throttle input when we increase the break input the speed of the vehicle decrease. In another case we can see that when we increase the throttle input the vehicle velocity also increase.

CVT Shaft RPM

This graph indicates the variation in rpm of primary and secondary shafts with respect to input parameters.

#Conclusion

Thus, we have successfully examined 4 various models of BAJA ATV WITH CVT and recorded the outputs: - (Vehicle velocity & CVT shaft rpm) with respect to variations in input -throttle and brake.

#Simulink Model

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