Project

Carry out a system-level simulation of an all-terrain vehicle. 

Download the model from the given link: 

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

Prepare a technical report explaining the model properties & comments on the results.

AIM:

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

Key words:

         CTV, lookup table,dashboard,Baja ATV

Software:

         Matlab,Simulink

Objectives:

 1. Study of Baja ATV model when both brake and throttle kept constant

2. Study of Baja ATV model with when brake kept constant and and throttle increased

3. Study of Baja ATV model with when throttle kept constant and and brake increased

All-Terrain Vehicle:

        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.

A typical ATV is shown in the below picture.

Introduction:

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

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

         A continuously variable transmission,or CVT, is a type of automatic transmission that provides more suitable power,better fuel economy and a smoother driving experience than a traditional automatic transmission. A CVT is a sysytem that makes it possible to vary stepless the transmission ratio without interruption of torque flow. Therefore an infine number of ratios are possible. It is an automatic,single speed and gearless transmission that can shift through an infinite number of gear ratios. This ability to seamlessly shift through these different gears provides a number of benifits including smooth shift and exceptional fuel economy.A CVT draws top engine power from small engine, which gives driver quicker acceleration than standard automatic transmission. Because of their greater ability to control the engine speed range,CVTs produce fewer emissions.CVTs are also lighter weight than traditional automatic transmission.

        To study the above objectives let us take the example of a simulink model which is shown below in Fig.1.The simulink model of CVT consists of signal builder,generic engine,motion sensor,vehicle transmission,vehicle body,tyres and solver configuration etc.The CVT subsystem includes transmission block,input and output shaft inertia and motion sensors as shown in the Fig.2. The vehicle body subsystem includes vehicle body block,double drum brake and tyres as shown in the Fig.3.

Simulink model for Baja ATV with CTV:

                                                                                          Fig.1

CVT Block:

                                                                                         Fig.2

Vehicle Body:

                                                                                     Fig.3

Major Components in the 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 high gears can maximize fuel economy. CTVs 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 pulleys are alligned with the pointed ends of  the cones touching. Theese 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 hydraulic cylinder. The cylinder can increase or decrease the amount of space between two sides of the pulley. This allow the belt to ride lower or higher along the walls of the pulley, depending on the driving condition, thereby changing the "gear" ratio.

Variable Tranmission Ratio:  

         Reprents a variable ratio gearbox such as implemented by mechanical belt CVT, electrical or hydraulic transmission. The physical signal input 'r' defines the ratio of input and output angular shaft velocities. Connections B (Base) and F (Follower) are mechanical rotational conserving parts. Specify the relation between base and follower rotaion directions with the output shaft rotates parameter.

 Engine:

        Represents a system level model of spark-ignition and diesel engines suitable for 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 by the engine as a fraction of maximum possible torque.

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

Input Signal: 

CVT Gear Ratio:

Torque Vs Engine Speed input:

Case-1:

Study of Baja ATV model when both brake and throttle kept constant

         The given model contains a dashboard which contains knob to control throttle and the brake. A knob is provided to control both the parameters in real-time for the user. So, For the first case we have given throttle input as 0.5 and brake input as 0 by using the knob provided in the dash board and the simulation is made run for 100 seconds. It can be seen from the graph that for a constant throttle value of 0.5 and 0 brake value, the vehicle attains a gradual speed and reaches a maximum speed of 53.5 kmph. Since the simulation is run only for 100 seconds the distance travelled by the ATV is measured as 1350 m. As the brake input value is zero, hence it has no effect on velocity.

These graphs shows the variation in angular velocities of input and output shafts with respect to input parameters of the variable gear transmission system. These value differ with respect to gear ratio.From the graph we get the speed as 3421 rpm from primary shaft and 4878 rpm from secondary shaft.

Case-2:

Study of Baja ATV model with when brake kept constant and and throttle increased

          For the second case let us keep the break value to zero and throttle value is made 0.9 by using dashboard knob. Compared to the first case the throttle vaue is been incresed from 0.5 to 0.9 value. From the above graph it is clear that the vehicle attains a maximum speed of 59.5 kmph the throttle value of 0.9 value. And also the distance covered by the ATV is noted as 1590 m.As the brake input value is zero, hence it has no effect on velocity. 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 inturn increases the power of the engine. Therefore for the second case the Velocity attained and distance covered by the ATV is more compared to the case-1. 

As we know from the case-1 the angular velocities of input and output shafts differs with respect to the gear ratio. From this graph we get speed of primary and secondary shaft as 3800 rpm and 5428 rpm respectively. In the above figure the primary shaft speed compared to case-1 (i,e 3421 rpm) increases by increasing the throttle, which defines that the throttle can flow more amount of fuel which increases the power of engine and similar to secondary shaft. Hence it can be said that the shaft speed is directly propotional to the throttle value.

Case-3:

Study of Baja ATV model with when throttle kept constant and and brake increased

           In this case we have given a constant throttle value of 0.5 and the brake value is increased to 0.1 from the default value by using dashboard to with the help of variable knob. From the above graph we can see that the ATV speed is reduced to 17 kmph and the distance covered by the vehicle is 37.5 m compared to the default case-1. From the graph we can conclude that by keeping contant throttle value and increase in brake value reduces the speed of the vehicle and gradually it reduces to zero. And also the distance covered by the vehicle will be less as compared to case-1 and case-2 due to brake applied, the vehicle will travel a small distance and stop after some distance covered.

From this graph, it is seen that primary and secondary shaft velocity increases for the initial period and gradually it reduces to zero as the brake value increased with contant throttle value. 

Conclusion:

1) As the throttle increases, the velocity also increases which inturn the power in the engine also increases. 

2) As the brake input increases the velocity decreases and engine power also decreases. At a certain brake input value the engine may shutdown and there is no power output. The engine power is inversly propotional to the brake input.

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

In the above figure, the torque is increasing by increase in engine speed. At a perticular point the torque is decreasing when the gear ratio increases in order to achieve maximum velocity.