Project

Aim:

Carry out a system-level simulation of an all-terrain vehicle (BAJA ATV).

Objective:

Technical report explaining the simulation of all-terrain vehicle (BAJA ATV).

All terrain vehicle:

An all-terrain vehicle (ATV) is defined as a motorized off highway vehicle designed to travel on four low-pressure or non-pneumatic tires, having a seat designed to be stardlled by the operator and handlebars for steering control.

BAJA All Terrain vehicle

CONTINUOUSLY VARIABLE TRANSMISSION (CVT):

A CVT or Continuously Variable transmission is an automated, single-speed and gearless transmission that can shift through an infinite number of gear ratios. A CVT is a transmission that operates on an ingenious pulley system that automatically varies the transmission ratio, allowing an infinite variability between highest and lowest gears with no discrete steps or shifts. CVTs provide more useable power, better fuel economy and smoother driving experience than tradtional transmissions that use gearboxes with fixed number of gear sets.

CVT

Working of CVT

SIMULINK MODEL:

BAJA ATV Model Without Dashboard:

Components present here are,

Vehicle body

1. Physical body
2. Tire
3. Shoe brake

CVT

1. Variable transmission
2. Inertia for rotating parts

Generic Engine

1. Engine sensor
2. Simple gear

Input blocks

1. Throttle
2. Brake
3. CVT Gear shoe

Blocks used in the simulink model are,

Signal builder: The signal builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a model.

Generic engine: This represents a general internal combustion engine. This block is suitable generic engine for spark-ignition and diesel. Speed-power and speed-torque parameterizations are provided. A throttle physical signal input specifies the normalized engine torque.

Engine settings: For this particular model we have specified the initial inertia of 1kg*m^2, and initial velocity of 2100rpm. We have used a limit of 100rpm as speed threshold. Here we are not using any fuel consumption model or speed control model.

Engine sensor: It is a subsystem created using many blocks they are, ideal rotational motion sensor, mechanical rotational reference, PS-Simulink converter, Scope, PS terminator.

Here the 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.

Simple gear:

Represents a fixed-ratio gear or gearbox. No inertia or compliance is modeled in this block. we can optionally include gear meshing and viscous bearing losses.

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. Optionally include thermal effects and expose thermal conserving port H by right-clicking on the block and selecting Simscape block choices to switch between variants.

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

Continuously variable transmission:

Here the two inertia blocks represent the primary pulley and the Output shaft inertia represents the secondary pulley inertia.Then the variable gear ratio block is used to model continuously variable transmission. It 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 relation between base and follower rotation directions with the output shaft rotate parameter.

Inertia: The block represents an ideal mechanical rotational inertia. The block has one mechanical rotational conserving port. The block 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 relation between base and follower rotation directions with the Output shaft rotates parameter.

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.

Tire:

Wheels work on the magic formula:

N- Normal Force, S- Slip, A- Axle, H-Hub

The Tire (Magic Formula) block models a tire with longitudinal behavior given by the Magic Formula, an empirical equation based on four fitting coefficients. The block can model tire dynamics under constant or variable pavement conditions.The Tire (Magic Formula) block models the tire as a rigid wheel-tire combination in contact with the road and subject to slip.When torque is applied to the wheel axle, the tire pushes on the ground (while subject to contact friction) and transfers the resulting reaction as a force back on the wheel. This action pushes the wheel forward or backward.

Double shoe brake:

There are four wheels in which the rear wheels are connected to the output shaft from the CVT through the axles making it a rear wheel drive. A double shoe breaks is also connected to the rear wheel axels which is used to apply break power to the rear wheels.

Torque vs Speed characteristics:

Brake and Throttle input:

Brake input is constant i.e. zero throughout the time of 80 sec. Throttle input is 0.3 for first 20 sec, accelerates to 1 at the same and remains constant throughout the remaining time till 80 sec.

CVT Ratio:

The CVT gear ratio 3.5 for the first 4 secs, then drops down to .5 till 35 secs and remains constant thereafter till 80 sec.

Result:

Velocity:

CVT Shaft speed:

BAJA ATV Model With Dashboard:

The above model is as same as the BAJA ATV model without dashboard but here in this case it has dashboard with it,

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.

Result:

Velocity:

CVT Shaft Speed:

CONCLUSION:

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

1. Velocity, CVT Shaft Speed and Engine Speed are directly proportional to the Throttle input and inversely proportional to the Brake input.
2. CVT Primary speed is greater than CVT Secondary speed as they are directly proportional to their shaft diameter.
3. The variation in vehicle velocity can be observed with change in throttle and brake inputs.
4. With increase in braking value, the speed of vehicle decreases. On the other hand, increasing the throttle leads to increased vehicle velocity.