Project

AIM:

To study the system-level simulation of an all-terrain vehicle.

OBJECTIVE:

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

INTRODUCTION

Transmission, which transmits the power from engine to the wheels through the shafts. It consists of 4 types mainly,

• Manual transmission
• Continous variable transmission
• Semi-automatic transmission
• Automatic transmission

BAJA All-terrain vehicle (ATV) that uses CVT and CVTs differ from traditional automatic transmissions in that they don't have gears that provide "steps" between low- and high-speed operation. Instead, the majority of them work via a pair of variable-diameter, cone-shaped pulleys connected by a steel or composite belt. The step-less nature of its design allows the CVT to work to keep the engine in its optimum power range, increasing efficiency, and fuel mileage by delivering an infinite number of smooth transitions from low to high.

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 straddled by the operator and handlebars for steering control.

CASE1:

SIMULINK MODEL FOR BAJA ATV WITH CVT:

PARTS OF MODEL

Continuously Variable Transmission drive (CVT):

It is better to have more gears in a transmission since it can optimize engine speed in a variety of driving conditions. That means low gears can provide better acceleration while higher gears can maximize fuel economy. CVTs differ from traditional automatic transmissions in that they don't have gears that provide "steps" between low- and high-speed operations. Instead, the majority of them work via a pair of variable-diameter, cone-shaped pulleys connected by a steel or composite belt. The halves of each pulley are aligned with the pointed ends of the cones touching. These form a V-shaped groove in which the connecting belt rides. One side of the pulley is fixed, and the other side is movable, actuated by a hydraulic cylinder. The cylinder can increase or decrease the amount of space between the two sides of the pulley. This allows the belt to ride lower or higher along the walls of the pulley, depending on driving conditions, thereby changing the "gear" ratio.

CVT Block:

VARIABLE TRANSMISSION RATIO:

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.

ENGINE:

Represents a system-level model of spark-ignition and diesel engines suitable for use at initial stages of modelling 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.

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 rate are reported.

INPUT SIGNAL:

The signal builder is used as input for brake, throttle, and gear ratio. Brake input is maintained as 0 for overall simulation. The throttle input is given as 0.3 for20 secs and increases to 1 for overall simulation. The throttle valve is mainly to control the flow or amount of fuel into the engine, if the throttle value increases the flow of fuel increases to the IC engine which in turn increases the power of the engine. The gear ratio is maintained as 2.3 for 5 secs and linearly decreases to 1.8 and maintained constant for overall simulation

CVT Gear Ratio Input:

Torque vs Engine Speed input:

As the gear ratio increases, torque increases which inturn the velocity decreases.

VEHICLE BODY SUBSYSTEM

OUTPUT

VEHICLE SPEED:

CVT SHAFT SPEED

In the above figure, the primary shaft reaches high speed and the secondary shaft as low rotational speed because the radius of the primary shaft as more than the secondary shaft, the speed is directly proportional to the radius of the shaft. As the radius increases the speed of the shaft also increases. In other words angular velocities of input and output shafts of the variable gear transmission system. These values differ with respect to the gear ratio.

CASE 2:

SIMULINK MODEL FOR BAJA ATV WITH CVT USING DASHBOARD:

The above figure shows the 'Baja ATV with dashboard' model which consists of throttle meter and brake input in the dashboard instead of giving input through the signal builder. The rest of the blocks and subsystems are common in the above Baja ATV model without dashboard as shown in figure A knob is provided to control both the parameters in real-time for the user. The main concept of using the dashboard is study the result by varying the input of the brake and throttle, which shows that the velocity and speed of the engine by increasing the throttle, the velocity, and speed of the engine & shaft increases.

OUTPUT

VEHICLE SPEED

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 0. Once the braking value increases from 0.1 to 0.5, the velocity of the vehicle decreases to 0 at a constant throttle value. This explains the direct relation of vehicle velocity with respect to throttle and brake inputs.

CVT SHAFT SPEED

CASE 3:

SIMULINK MODEL FOR BAJA ATV WITH CVT USING LOOKUP TABLE:

CVT BLOCK

By using Simulink model of CVT consists of step time, generic engine, motion sensors, vehicle transmission, vehicle body, tyres and solver configuration blocks, etc., as shown in the figure. The CVT subsystem includes a lookup table, Transmission block, input and output shaft inertia and motion sensors as shown in the figure. The only Difference between this model and the first model is the gear ratio input to CVT is provided using a lookup table. The vehicle velocity and shaft rpm outputs are the same as before.

A lookup table is an array of data that maps input values to output values, thereby approximating a mathematical function. Given a 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:

• Interpolation is a process for estimating values that lie between known data points.
• Extrapolation is a process for estimating values that lie beyond the range of known data points.
• Rounding is a process for approximating a value by altering its digits according to a known rule.

CVT GEAR RATIO

The brake input and throttle input is given by step time, which depends on the run time and varies accordingly. By using a Lookup table for gear ratio which takes as input to the CVT and works according to the input gear ratio and obtained the output. This method is very effective which can avoid the unusual torque at a certain speed and very easy to achieve greater velocity & engine speed. It works as a closed-loop when the input is given by a lookup table. The Simulink get the input value from a lookup table and obtain the result according to the input values of the gear ratio. The gear ratio varies from 2.3 to 1.8 as taken as input and output in terms of velocity. The maximum velocity reached as 57 kmph approximately.

VEHICLE SPEED

In the above figure, the brake is maintained as constant and increase in throttle which shows an increase in velocity. The flow of fuel increases when the throttle increases from 0.3 to 1, thus the power in the engine increases. The torque reaches approximately 7N-m at a 1.8 gear ratio, which defines that the gear ratio is directly proportional to the torque. By this gear ratio, the speed & velocity can achieve maximum. The gear ratio is assigned in the lookup table and given as input to the Simulink which reads every input value and obtain the result according to the input.

CVT SHAFT SPEED

In the above figure, the primary shaft speed increases by increasing throttle and decreasing by increasing brake input value, which defines that the throttle can flow more amount of fuel which increases the power of the engine and is similar to the secondary shaft. The radius of the primary shaft as more than the secondary shaft, the speed is directly proportional to the radius of the shaft. As the radius increases the speed of the shaft also increases.

CASE 4

SIMULINK MODEL FOR BAJA ATV WITH CVT USING LOOKUP TABLE & DASHBOARD

In this model a dashboard is used to control the inputs- ‘Throttle’ & ‘Brake’ with knobs The main concept of using a dashboard is to study the result by varying the input of brake and throttle, which shows that the variation of velocity and speed of the engine. The gear ratio is given by the lookup table, Simulink gets the input value from the lookup table and obtains the result according to the lookup table. The variation in vehicle velocity can be observed with a change in throttle and brake inputs. With the increase in braking value, the speed of the vehicle decreases. On the other hand, increasing the throttle leads to increased vehicle velocity. The transmission has a primary pulley and secondary pulley, in which the radius of primary pulley increases by compacting, and the radius of the secondary pulley decreases. As the gear ratio varies, the torque also varies. The gear ratio is directly proportional to the torque, which increases by increasing the gear ratio. At the max torque, the speed and velocity are decreased.

OUTPUT

VEHICLE SPEED

In the above figure, By increasing the brake input, the velocity of the vehicle decreasing accordingly shown By using a lookup table, it works as a closed-loop by recording the velocity value and we can get at any particular value of gear ratio which is beyond the range or any random value within the range by using extrapolation and interpolation by a lookup table.

CVT SHAFT SPEED

In the above figure, the primary shaft speed increases by increasing throttle and decreasing by increasing brake input value, which defines that the throttle can flow more amount of fuel which increases the power of the engine and is similar to the secondary shaft. The radius of the primary shaft as more than the secondary shaft, the speed is directly proportional to the radius of the shaft. As the radius increases the speed of the shaft also increases. The throttle valve and brake input value can be varying in the dashboard, so we can get any particular value for the input.

CONCLUSION:

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