Project

#Aim:

To perform the simulation of BAJA All-Terrain vehicle model and observe the vehicle speed and CVT shaft speed output graph by changing break and throttle inputs.

Theory:

            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. As the name implies, it is designed to handle a wider variety of terrain than most other vehicles.

 By the current ANSI definition, ATVS are intended for use by a single operator, although some companies have developed ATVs intended for use by the operator and one passenger. These ATVs are referred to as tandem ATVs.

The rider sits on and operates these vehicles like a motorcycle, but the extra wheels give more stability at slower speeds. Although most are equipped with three or four wheels, six-wheel models exist for specialized applications.

Major and Crucial Components:

1.CVT

2.Vehicle Body

3.Generic Engine

4.Simple Gear

5.Tires and Brakes

1.CVT-

      

A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios.This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.

CVTs are used in automobiles, tractors, motor scooters, snowmobiles, bicycles and earthmoving equipment. Its compact size and simplicity of construction mean it's more cost-effective to use in a small car than a conventional automatic gearbox.

A CVT is an automatic, single-speed, and gearless transmission that can shift through an infinite number of gear ratios. A continuously variable transmission (CVT) is a transmission that operates on an ingenious pulley system that automatically varies the transmission ratio, allowing an infinite variability (theoretically) between highest and lowest gears with no discrete steps or shifts. CVTs provide more useable power, better fuel economy, and a smoother driving experience than traditional transmissions that use gearboxes with fixed numbers of gear sets. It has a relatively simple arrangement of two cone-shaped pulleys with a V-shaped drive belt connecting them. One pulley is attached to the engine, while the other is joined to the wheels. When you press the accelerator, the engine revs and the cone moves according to the amount of power asked for. The other cone adjusts accordingly so that the drive belt mainkans the same tension, and this is what determines how the car accelerates.

CVT Subsystem-

• The CVT subsystem uses a Variable Gear Ratio block-
•  Inside the CVT subsystem, 2 Inertia blocks are connected to ensure proper inertial motion.
• Two Ideal Rotational Motion Sensors are connected, one on either side of the Variable Gear Ratio. The angular velocity outputs of these are then transferred to the main model with the help of GoTo blocks

i)Variable Ratio Gear:

The ratio of the follower to base angular speed decreases with gear ratio, and conversely the ratio of the follower to base torque increases with gear ratio. The variable gear is implemented using the Variable Ratio Transmission block which includes compliance

The variable gear arrangements of CVT in this model is represented by the Variable Ratio Gear Block:

Where.

• B-Base Pulley or Drive Pulley.
• F-Follower Pulley or Driven Pulley
• r-Variable Transmission Ratio (Input).

ii)Ideal Rotational Motion sensor-

Where,

• R- Rod(positive prob)
• C- Case (reference probe)
• W- Angular velocity, rad/s
• A- Angular displacement, rad

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 conserving ports and connections W and A are physical signal output ports for velocity and angular displacement, respectively.

2.Vehicle body-

A Baja ATV of a Two-axle type vehicle with longitudinal dynamics and motion: has adjustable mass, geometry and drag properties. The vehicle may 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 center of gravity (CG) that is at or below the plane of travel so that it mitigates the chances of rolling over

Vehicle Subsystem-

Vehile Boody-

Where,

The block accounts for 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.

3.Generic Engine-

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

Where.

• B-Rotational Conserving Port representing the Engine Block
• F-Rotational Conserving Port representing the Engine Crankshaft
• T-Physical signal input port specifying the normalized engine throttle level
• P- Physical signal output port reporting the instantaneous engine power, in W
• FC Physical signal output port reporting the fuel consumption rate, in kg/s

 iii)case-1: Brake input-0.2 and Throttle input-0.8

VEHICLE SPEED PLOT:

in the above Plot,Given input of Brake Input is O.2 and Throttle Input is 0.8 for 100 sec, Velocity will reach 7.56(km/hr) at 0.7sec. By keeping the brake input value constant and throttle input is 0.8 then velocity value will decrease.

CVT SHAFT SPEED PLOT:

In Continously Variable Transmission (CVT) Variator of Primary Pulley goes inward and Secondary Pulley goes outward it will leads to overdrive. Primary Pulley radius increases and Secondary Pulley radius decreases So Speed of Primary pulley is higher than Secondary Pulley.

ENGINE SPEED:

In the above Plot, Brake Input is O.2 and Throttle input is 0.8 for 100 sec, Engine Speed will increase at the  because of decreasing gear ratio which increases the torque and by kepping Throttle input value to 0.8. 

CONCLUSION:-

In real-world application is very important to understand the relation between the engine speed (rpm), the gear ratio, and torque. The acceleration and speed requirements can be met by varying the throttle(engine power) and the gear ratio.

For example in case 2 when the vehicle speed was decreased due to the application of brake we applied  throttle in order to accelerate but due to the less torque at lower gear ratio the acceleration was not achieved, while in case 3 the gear ratio was increased with the decrease in speed to meet the torque requirement and we saw that the vehicle was able to accelerate.