Project

AIM: To carry out a system-level simulation of an all-terrain vehicle using Simulink.

OBJECTIVE:

To prepare a technical report on BAJA ATV explaining model properties for the following: 

- without using Lookup table

- using Lookup table

THEORY: 

ATV: An all-terrain vehicle (ATV) refers to a motorized single-seated tri or quadricycle bike and buggy that is designed for off-road travel and activities. The vehicle consists of handlebars and low-pressure tires that have deep-threaded structures, which assist in driving over muddy, rocky, wetlands and dune topologies. In comparison to other utility vehicles (UTVs), ATVs offer excellent off-road capabilities and can carry heavy equipment over long distances and narrow access points. They can also be customized for high-performance riding, owing to which they find extensive applications across various industries, including sports, entertainment, agriculture, military and defense

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MAJOR COMPONENTS USED IN THIS SIMULATION:

GENERIC ENGINE:

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

                                    

Ports:

• 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 Watts (W)
• FC – Physical signal input port reporting the fuel consumption rate, in kg/s

 

SIMPLE GEAR:

            The simple gear is a combination of a driver and driven gear where the speed is reduced by the gear ratio. The gear ratio is defined as,

 

Ports:

• B – Base Gear or Driver Gear
• F – Follower Gear or Driver Gear

 

CVT TRANSMISSION:

            In CVT (Continuous Variable Transmission), the variable diameter pulley plays a vital role in transmission. Variable – diameter pulleys must always come in pairs. One of the pulleys, known as the drive pulley (or driving pulley), is connected to the crankshaft of the engine. The driving pulley is also called the input pulley because it’s where the energy from the engine enters the transmission. The second pulley is called the driven pulley because the first pulley is turning it. As an output pulley, the driven pulley transfers energy to the driveshaft.

            The distance between the center of the pulleys to where the belt makes contact in the groove is known as the pitch radius. When the pulleys are close together, the belt rides higher and the pitch radius increases. The ratio of the pitch radius on the driving pulley to the pitch radius on the driven pulley determines the gear when the pitch radius is small on the driving pulley and large on the driven pulley, then the rotational speed of the driven pulley decreases, resulting in a lower “gear”. When the pitch radius is large on the driving pulley and small on the driven pulley, then the rotational speed of the driven pulley increases, resulting in a higher “gear”. Thus, in theory, a CVT has an infinite number of “gears” that it can run through at any time, at any engine or vehicle speed. 

Ports:

• B – Base pulley ore Drive Pulley
• F – Follower Pulley or Driven Pulley
• r – Variable Transmission Ratio (Input)

 

VEHICLE BODY:

            Two – axle vehicle with longitudinal dynamics and motion and adjustable mass, geometry, and drag properties. The vehicle can 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.

Ports,

• NR – Rear Axle Normal Force (N)
• NF – Front Axle Normal Force (N)
• Beta – Road Incline Angle 9rad)
• V – Longitudinal Velocity (m/s)
• W – Head Wind Speed (m/s)
• H – Horizontal Motion

DOUBLE SHOE BRAKE:

            The Double-Shoe Brake block represents a frictional brake with two pivoted rigid shoes that press against a rotating drum to produce a braking action. The rigid shoes sit inside or outside the rotating drum in a diametrically opposed configuration. A positive actuating force causes the rigid shoes to press against the rotating drum. Viscous and contact friction between the drum and the rigid shoe surfaces cause the rotating drum to decelerate.

Ports:

• S – Rotational conserving port associated with the rotating drum shaft
• F – Physical signal input port associated with the applied actuating force

 

TIRE:

          The vehicle body is connected to 4 tires each per axle to move the vehicle according to the power input to the axle.

Ports:

• N – Normal Force
• S – Tire Slip
• A – Axle
• H – Mechanical translational port associated with the wheel hub that transmits the thrust generated by the tire to the remainder of the vehicle.

 

BLOCKS USED:

• Signal Builder – To input the Brake, Throttle and CVT Ratio.
• Simulink to PS converter – To convert the Simulink signal to Simscape environment.
• Solver Configuration – To specify the solver parameters before starting the simulation.
• Mechanical Reference – To make sure all the components are clamped to the ground.
• Generic Engine – To run the engine with speed and torque values as input.
• PS to Simulink Converter – To convert Simscape signal to Simulink environment.
• Scope – To view the graph of the parameters for better understanding.
• Display – To view the calculated engine power.
• Inertia – To represent the solid inertia.
• Rotational Motion Sensor – To sense the rotational motion from the engine and give output as RPM.
• Variable Gear Ratio – To vary the speed according to the gear ratios.
• PS Terminator – Terminator for unconnected physical signal outputs.
• Double Shoe Brake – To apply brake to the vehicle when needed.
• PS Constant – Generate constant physical signal.
• Tire – For transportation of the vehicle.
• Rotational Free End – For mechanical component (Tire)
• Vehicle Body – To represent the BAJA ATV model body.
• Custom Measure Gauge – To measure the brake and throttle input.
• Knob – To increase, decrease and vice-versa of throttle and brake inputs.
• Lookup Table – To insert the CVT values from the workspace.
• Simple Gear – To reduce the speed of the engine with pre-defined gear ratio.
• Step – To increase or decrease an input value for a defined time interval.

TYPES OF MODEL:

• BAJA ATV model without Dashboard
• BAJA ATV model with Dashboard
• BAJA ATV model – Mapped Lookup Table with Dashboard

MAIN MODEL:

The input signal is provided using signal builder in which brake input is provided as 0 and trottel input is provided as 0.3 upto 20sec and varied to 1 for remaining seconds.

                 

• GENERIC ENGINE:

             Represents a system-level model of spark-ignition and diesel engines suitable for use at 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 rate are reported.

          

The value of speed vector and torque vector is obtained from the diagram and logged the values in the workspace of matlab file.

             

          

         

         

• ENGINE SENSOR:

           Engine sensor which sense the rpm of the engine and it is connected to the CVT block 

          

• CVT BLOCKSET:

          

Input shaft represents the primary pulley and output shaft represents the secondary pulley and mechanical rotational sensor is connected to input and output shafts and Variable ratio Gear 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.CVT ratio is generated by signal builder.

• CVT ratio:

         

• SIMPLE GEAR:

         The output from the CVT block is connected to the simple gear which represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in 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 relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by setting Friction model to a temperature-dependent setting.

• 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 forces are considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively. If 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.

     

In Vehicle Body parameter block we can vary the mass of the vehicle and plot the result in data inspector in order to compare the behaviour of vehicle during different mass condition.

Output #1.1:

Velocity:

CVT Shaft Speed:

Engine Speed:

1.2 With Dashboard

A Simulink model for the BAJA ATV Model including the dashboard is 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 displays 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

A 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 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:

A lookup table block uses an array of data to map input values to output values, approximating a mathematical function. Given 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 down to 2.03

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

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

Input #2.1:

They are given in steps using the step block. Parameters are:

Brake Input: Step time: 35 Initial value: 0 Final value: 0 Sample time: 0

Throttle Input: Step time: 20 Initial value: 0.3 Final value: 1 Sample time: 0

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 displays 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. 

- The speed might get null at a particular braking resistance.