Project

Aim:- To understand and Carry out a system-level simulation of an all-terrain vehicle.

Objectives:

• Analyse all components and understand the relationship and flow between the blocks
• Understand the different types of ways to model this BAJA ATV

  - without using Lookup table

  - use the Lookup tab

An ATV is a small motor vehicle with three or four low-pressure tires designed for use on various types of terrain. Recreational activities in deserts are usually carried out in ATVs. This project is in reference to one of the types of ATVs used in BAJA SAE competitions.

COMPONENTS OF A BAJA ALL TERRAIN VEHICLE (ATV) :

The main components used in BAJA All Terrain Vehicles (ATV) are given below

• Vehicle Body
• Suspension
• Tire
• Engine
• Continuous Variable Transmission (CVT)

CONTINOUSLY VARIABLE TRANSMISSION (CVT) :

CVT or Continuously Variable Transmission is an automatic, single-speed, and gearless transmission that can shift through an infinite number of gear ratios, making gear change operation an unnoticeable experience.

variable diameter pulley transmission, this transmission uses a belt to transmit power from the input shaft to the output shaft by axial movement of sheaves, the overall gear ratio can be adjusted continuously, this is only possible through the movement of the sheaves, When the pulley sheaves are far apart the pulley is just like a smaal gear when the sheaves are close together it acts as a large gear.

Since the length of the belt must always be the same for both the sheave of the input and the output must be adjusted simultaneously, if a cross section for the belt is created we can see its v-shaped design, that way a movement of the belt is possible.

Study 1a: BAJA ATV with CVT

Common Components of this model are:

Break and Trottle input

Generic engine

Engine sensor

Simple Gear

CVT gear ratio

CVT

Vehicle Body

Break and trottle input (Signal Builder): The Signal Builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a model. You can quickly switch signal groups in and out of a model to facilitate testing in this model signal builder is used to give the input values of break and trottle.

Generic Engine:

Represents a system-level model of spark-ignition and diesel engines suitable for use at the 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. If the engine speed falls below the Stall speed, the engine torque is blended to zero. If the engine speed exceeds the maximum speed, the simulation stops and issues an error message.

Connections F and B are mechanical rotational conserving ports associated with the engine crankshaft and engine block, respectively. Connections P and FC are physical signal output ports through which engine power and fuel consumption rates are reported.

Speed vector and Torque vector are the assigned parameters.

Engine Sensor:

Ideal Rotational Motion Sensor: The block represents an ideal mechanical rotational motion sensor, that is, a device that converts an across variable measured between two mechanical rotational nodes into a control signal proportional to angular velocity or angle. The sensor is ideal since it does not account for inertia, friction, delays, energy consumption, and so on.

Connections R and C are mechanical rotational conservation ports and connections W and A are physical signal output ports for velocity and angular displacement, respectively

Simple Gear: Represents a fixed-ratio gear or gearbox. No inertia or compliance is modeled for this block. You can optionally include gear meshing and viscous bearing losses.

Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relationship between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and exposure to thermal conservation port H by right-clicking on the block and selecting Simscape block choices to switch between variants.

Followers (F) to base (B) teeth ratio (NF/NB): 4

CVT Subsystem:

The CVT Subsystem consists of the following blocks:

Inertia: The block represents an ideal mechanical rotational inertia.

The block has one mechanical rotational conservation port. The block's positive direction is from its port to the reference point. This means that the inertia torque is positive if the inertia is accelerated in a positive direction.

Variable Ratio Transmission: Represents a variable ratio gearbox such as implemented by mechanical belt CVT, electric, or hydraulic transmissions. The physical signal input r defines the ratio of input to output angular shaft velocities.

Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relationship between base and follower rotation directions with the Output shaft rotates parameter.

Vehicle Body Subsystem:

The Vehicle Body Subsystem consists of the following blocks:

Vehicle Body: Represents a two-axle vehicle body in longitudinal motion. 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.

Connection H is the mechanical translational conserving port associated with the horizontal motion of the vehicle body. The resulting traction motion developed by tires should be connected to this port. Connections V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively. Wheel force is considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively. If the variable mass is modeled, the physical signal input ports CG and M are exposed. CG accepts a two-element vector representing the x and y distance offsets from vehicle CG to additional load mass CG. M represents the additional mass. If both variable mass and pitch dynamics are included, the physical signal port J accepts the inertia of the additional mass about its own CG.

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 conservation port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Connection N is a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports a tire slip. Optionally expose the physical signal port M by setting Parameterize by to Physical signal Magic Formula coefficients. Physical signal port M accepts a four-element vector corresponding to the B, C, D, and E Magic Formula coefficients.

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 conservation rotational terminal associated with the drum shaft. Connection F is a physical signal port representing the force input to the actuator. Positive force creates friction torque that resists shaft rotation. Optionally include thermal effects and exposure to thermal conservation port H by setting the Thermal port to Model.

Torque vs Speed characteristics:

Brake and Throttle

In index 1 there is Brake input that is constant at Zero throughout the period of 80 sec.

In index 2 there is throttle input here this at 0.3 from 0 to 20 sec, then accelerates to 1 fro the same and remains constant throughout the

remaining time till 80 sec.

B

CVT Ratio:

The CVT gear ratio is 2.3 for the first 4 secs, then drops from 1.8 to 35 secs and remains constant thereafter until 80 secs

Output #1.1:

Velocity:

CVT Shaft Speed:

Engine Speed:

1.2 With Dashboard

The Simulink model for the BAJA ATV Model including the dashboard shown below. The rest of the parts and subsystems are common in the above part #1.1.

Dashboard: A dashboard (also called dash, instrument panel (IP), or fascia) is a control panel usually located directly ahead of a vehicle's driver, displaying instrumentation and controls for the vehicle's operation.

The initial conditions are as follows:

Brake Input = 0

Throttle Input = 0.3

Input #1.2:

It comprises a throttle and brake input through a knob which can be varied unlike the signal builder in the previous model without Dashboard. The Engine RPM gauge and Velocity gauge display the changes done by the respective knobs.

Output #1.2:

Velocity:

CVT Shaft Speed:

Engine Speed:

Part #2: BAJA CVT using Lookup Table

2.1 Without Dashboard

The Simulink model for the BAJA ATV Model, including the Lookup table, is shown below.

Lookup Table: A lookup table is an array of data that maps input values to output values, thereby approximating a mathematical function. Given the 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 values, Simulink can estimate an output value using interpolation, extrapolation, or rounding, where:

A lookup table block uses an array of data to map input values to output values, approximating a mathematical function. Given the 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 the output values based on nearby table values.

In place of CVT ratio input, a lookup table is assigned in the models below. It needs to be loaded in the workspace having the file name as Lookuptable_data.mat

CVT Ratio vs Vehicle Speed:

0 to 20 km/hr, the CVT ratio is constant at 2.3

20 to 30 km/hr, the CVT ratio drops to 2.03

30 to 50 km/hr, the CVT ratio drops to 1.8

50 km/hr onwards, the CVT ratio is consistent at 1.8

Output #2.1:

CVT Ratio:

Velocity:

CVT Shaft Speed:

Engine Speed:

2.2 With Dashboard

A Simulink model for the BAJA ATV Model including the dashboard and the Lookup table is shown below.

Input #2.2:

It comprises a throttle and brake input through a knob which can be varied unlike the signal builder in the previous model without Dashboard. The Engine RPM gauge and Velocity gauge display the changes done by the respective knobs.

Output #2.2:

Velocity

CVT Shaft Speed:

Engine Speed:

CONCLUSION:

Hence, the given BAJA ATV Model was simulated successfully and from the above results, we can infer that:

- Velocity, CVT Shaft Speed and Engine Speed are directly proportional to the throttle input and inversely proportional to the Brake input.

- CVT Ratio is directly proportional to Torque and inversely proportional to the throttle input.

- CVT Primary speed is greater than CVT Secondary speed as they are directly proportional to their shaft diameter.

REFERENCES:

BAJA ATV Model File

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