Challenge

SYSTEM-LEVEL SIMULATION OF AN ALL-TERRAIN VEHICLE

SSidharth Chakrapani7 Jan 2023

PROJECT - SYSTEM-LEVEL SIMULATION OF AN ALL-TERRAIN VEHICLE

AIM:

To create a technical report on the BAJA All-Terrain Vehicle's (ATV) simulation in various scenarios.

OBJECTIVES:

Perform a system-level simulation of an all-terrain vehicle and create a technical report outlining the model's characteristics and providing feedback on the findings.

THEORY:

ALL TERRAIN VEHICLE:

According to the American National Standards Institute (ANSI), an All-Terrain Vehicle (ATV), sometimes referred to as a quad(cycle), Light Utility Vehicle (LUV), is a vehicle that rides on low-pressure tires, has a seat that the operator straddles and handlebars for steering. Unlike most other vehicles, it is built to tackle a greater variety of terrain.

BAJA ATV(SAE):

The Society of Automotive Engineers, USA, hosts an international competition for undergraduate engineering students called the BAJA SAE series. At the University of Caroline, the competition was first held in 1976 under the name Mini-BAJA. The event has since expanded to include six nations: the USA, Mexico, South Africa, Korea, Brazil, and India. The BAJA SAE challenges the students to design, build, and validate a single-seater, four-wheeled off-road vehicle to participate in a series of events spread over three days that test the vehicle's agility in terms of gradeability, speed, acceleration, and maneuverability characteristics, and finally its capacity to withstand those backbreaking durability test.

MAJOR COMPONENTS IN SIMULATION:

GENERIC ENGINE:

Generic Internal Combustion (IC) Engines using Spark Ignition (SI-Petrol) or Compression Ignition are represented by the Generic Engine block (CI-Diesel). The Generic Engine block represents a general internal combustion engine for spark-ignition and diesel. Optional dynamic parameters include crankshaft inertia and response time lag. Speed-power and speed-torque parameterizations are provided. Optional idle speed and red line controllers prevent engine stall and enable cruise control.

where Ports are;

B – Rotational Conserving Port symbolizes the Engine Block
F – Rotational Conserving Port symbolizes the Engine Crankshaft
T – Physical signal input port that designates the normalized engine throttle level
P – Physical signal output port that reports the engine's current power in Watts (W)
FC – Physical signal input port reporting the fuel consumption rate, in kg/s

SIMPLE GEAR:

A simple gear is a combination of a driver and driven gear where the speed is reduced by the gear ratio. 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. You choose whether the follower axis rotates in the same or opposite direction as the base axis.

Ports:

B – Base Gear or Driver Gear
F – Follower Gear or Driver Gear

CVT TRANSMISSION:

The variable diameter pulley is crucial to transmission in CVT (Continuous Variable Transmission). Pulleys with variable diameter must always be purchased in pairs. The drive pulley, often referred to as the driving pulley, is attached to the engine's crankshaft. Due to the fact that it is the point at which engine energy enters the transmission, the driving pulley is also known as the input pulley. Because the first pulley is turning the second one, it is known as the driven pulley. The driven pulley transmits power to the driveshaft as an output pulley.

The pitch radius is the distance from the pulleys' centers to the point where the belt contacts the groove. The belt rides higher and the pitch radius widens when the pulleys are close together. The gear is determined by the pitch radii of the driving and driven pulleys in relation to one another. When the driven pulley's pitch radius is larger than the driving pulley's, the driven pulley's rotational speed slows down, resulting in a lower "gear." When the driving pulley's pitch radius is large while the driven pulley's pitch radius is small, the driven pulley's rotational speed increases and a higher "gear" is produced. So, theoretically, a CVT has an infinite number of “gears” that it can run through at any time, at any engine or vehicle speed.

Ports:

B – Base pulley ore Drive Pulley
F – Follower Pulley or Driven Pulley
r – Variable Transmission Ratio (Input)

VEHICLE BODY:

Vehicle having two axles, longitudinal dynamics, and configurable mass, geometry, and drag characteristics. The number of wheels on each axle of the car may be the same or different. two wheels on the front axle and one wheel on the back, for instance. The size of the vehicle's wheels is presumptively the same. The vehicle's center of gravity (CG) may also be on, near, or below the plane of movement.

Ports,

NR – Rear Axle Normal Force (N)
NF – Front Axle Normal Force (N)
Beta – Road Incline Angle 9rad)
V – Longitudinal Velocity (m/s)
W – Head Wind Speed (m/s)
H – Horizontal Motion

DOUBLE SHOE BRAKE:

The Double-Shoe Brake block depicts a frictional brake that works by applying pressure to a revolving drum with two rigid, pivoted shoes. The rigid shoes are positioned diametrically opposed within or outside the revolving drum. The rigid shoes press against the turning drum due to a positive actuating force. The rotating drum slows down due to viscous and contact friction between the drum and the rigid shoe surfaces.

Ports:

S – Rotational conserving port associated with the rotating drum shaft
F – Physical signal input port associated with the applied actuating force

TIRE:

In order to move the vehicle in accordance with the power applied to each axle, the vehicle body is attached to four tires on each axle.

Ports:

N – Normal Force
S – Tire Slip
A – Axle
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:

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 with Dashboard
BAJA ATV model – Mapped Lookup Table with Dashboard

BAJA ATV MODEL WITHOUT DASHBOARD

MAIN MODEL:

ENGINE SENSOR:

This building component calculates the angle or angular velocity in a mechanical rotating network. Since the sensor does not take into account inertia, friction, delays, energy consumption, etc., it is excellent.

The angular displacement and angular velocity of port R with respect to port C are reported by physical signal ports W and A, respectively. When the motion at R is larger than the motion at C, the measurement is positive.

CVT Block:

VEHICLE BODY:

SIMULATION PROCESS:

The signal building block produces the throttle signal, which is then supplied to the universal engine.
The MATLAB workspace is used to input the torque and speed vector.

The crankshaft output can be used to determine the engine's output rpm. The Ideal Rotational Motion Sensor will receive this speed in order to perceive the output rpm.
When the gear ratio is "4", the same output speed will be applied to a straightforward gear system to slow it down.
Then, the Variable Ratio Transmission block will receive the output speed from the gear reducer (CVT).
The Signal Builder provides the CVT ratio to the Variable Ratio Transmission (CVT) block.

The variable CVT ratios regulate the speed, and the vehicle axle receives the controlled output speed.
To apply the brake to the axle, the vehicle body (Double Shoe Brake) receives the brake signal from the signal maker.

The axle receives power from the CVT, which causes the vehicle to accelerate in accordance with the speed.
The Velocity is then extracted from the vehicle body and used for additional analysis.

OUTPUT:

TORQUE-SPEED PLOT:

The generic engine block receives the torque and speed inputs from the MATLAB workspace window and generates the output RPM in accordance. Due to the fact that it is the engine's default input, this plot is shared by all cases.

ENGINE SPEED PLOT:

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

ENGINE SPEED vs GEAR REDUCTION SPEED PLOT:

Here we can see that the engine speed is reduced by the Gear Ratio ‘4’. For verification I calculated the maximum RPM.

Maximum RPM (Before Reducing) = 3833 rpm

Gear Ratio = 1:4

We know that,

Driven = 3833/ 4

Driven = 95625RPM

Thus, the reduced maximum rpm is 958.25rpm which can be verified from the plot.

Note: Driven = Secondary CVT Shaft

Driver = Primary CVT Shaft

CVT SPEED REDUCTION PLOT:

The engine reduced speed is controlled by various CVT ratios. For verification I had calculated the maximum RPM.

Maximum RPM (Before Reducing) = 958.25rpm

CVT Ratio = 1:1.8

We know that,

Driven = 3833/ 4

Driven = 95625RPM

The reduced maximum rpm is 532.36rpm which can be verified from the plot.

SPEED vs THROTTLE PLOT:

The graph indicates that no brake is engaged during the driving cycle and that the throttle is constant (0.3) until the 20-second mark, at which point it increases to 1 and stays steady for the remainder of the run. The vehicle's speed rises as the throttle is opened up.

ACCELERATION PLOT:

From the above plot, we can infer that the vehicle is accelerated from 0-20kmph and then gradually increases till 30kmph(approx..) and it’s accelerated to 55.74kmph where it remains constant throughout the cycle.

BAJA ATV MODEL WITH DASHBOARD

MAIN MODEL:

DASHBOARD:

FLOW PROCESS:

The workflow for the model is identical to that for the "BAJA ATV model without Dashboard," but the user controls the throttle and brake inputs via the knob. Additionally, two distinct constant blocks for throttle and brake are replacing signal builder.

OUTPUT:

ENGINE SPEED PLOT:

Here, inputs like the throttle, break, torque, and speed vectors are used to generate the engine speed. Because the runtime is not specified, the user controls the throttle and break. Step down is input for the break, and step up is for the throttle.

ENGINE SPEED vs GEAR REDUCTION SPEED PLOT:

Here we can see that the engine speed is reduced by the Gear Ratio ‘4’. For verification I calculated the constant RPM (42000 – 50000 sec).

Maximum RPM (Before Reducing) = 2759.3 rpm

Gear Ratio = 1:4

We know that,

Driven = 2759.3/4

Driven = 689.825 RPM

The reduced constant rpm is 689.825 rpm which can be verified from the plot.

CVT SPEED REDUCTION PLOT:

The engine reduced speed is controlled by various CVT Ratios. For verification I had calculated the constant RPM (42000 – 50000 sec)

Maximum RPM (Before Reducing) = 689.825 rpm

CVT Ratio = 1:1.8

We know that,

Driven = 689.825/ 1.8

Driven = 383.23 RPM

The reduced maximum rpm is 383.23 rpm which can be verified from the plot.

SPEED vs THROTTLE PLOT:

From the graph we can infer that the vehicle is accelerating while throttle is applied (Step Up) and decelerated while break is applied (Step Down).

ACCELERATION PLOT:

The graph indicates that the vehicle is initially accelerated to 46 kmph, and that as the operator adjusts the throttle and brake knobs, the status changes. Step-up and step-down are, respectively, acceleration and deceleration. Since the linear one has a constant speed, there are no changes in braking or throttle.

BAJA ATV MODEL – MAPPED LOOKUP TABLE WITH DASHBOARD

SIMULINK MODEL:

DASHBOARD MODEL (SIMULATION OFF):

DASHBOARD MODEL (SIMULATION ON):

FLOW PROCESS:

The workflow is the same as for the "BAJA ATV model with Dashboard" approach. The only change is that the 'To Workspace' block is used to extract the CVT Ratio and Vehicle Speed.

Instead of a Signal Builder block for CVT Ratio, a Lookup Table is used. The interpolation and extrapolation methods are set to linear.

Right Click on the Lookup table block and choose Foundation Library option and then Plot option to visualize the lookup Table.

RELATIONSHIP OF CVT RATIO, THROTTLE AND BRAKE INPUTS:

The engine in this BAJA ATV model is already programmed to run at 3300 rpm with a "0.3" throttle value. Moreover, the speed at 45 m/s. The CVT Ratio was pre-set as 2.3 and 1.8 for the engine's minimum and maximum speeds, respectively. The initial throttle value of 0.3 is attained as the simulation begins, bringing the CVT Ratio close to 1.85. The CVT Ratio moves closer to 1.8 when the throttle is opened up, which is the state of the maximum engine speed. The CVT Ratio will also shift closer to 1.85 as the throttle is depressed. As braking is applied, the CVT Ratio rises to reach the condition that is the closest to 2.3. (Minimum Engine Speed). The CVT Ratio changes as braking is decreased, it move towards 1.85 which is the basic throttle input 0.3 or if any other throttle value is applied it would reach that CVT Ratio state.

CVT RATIO PLOT:

OUTPUT:

ENGINE SPEED PLOT:

The graph indicates that the engine was initially operating at a minimum rpm of 3300 rpm before the throttle was applied (step-up), braking was applied (step-down), and then the brake was released, increasing engine rpm before brakes was applied. Finally, 2900 rpm are set as the constant for the throttle and brake.

CVT SPEED PLOT:

The above graph demonstrates how the throttle is first applied (stepped up), then maintained at the same level, followed by the application of brakes (stepped down), and eventually the removal of the brakes, causing the engine speed to increase along with the increase in throttle input.

INPUT vs VEHICLE SPEED:

From the plot we can infer that when throttle is applied the vehicle speed increases and when brake is applied, vehicle speed decreases simultaneously.

REFERENCES:

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

SYSTEM-LEVEL SIMULATION OF AN ALL-TERRAIN VEHICLE

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Ship work like thisin your own course.

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Ship work like this
in your own course.