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 & dashboard.
• without using lookup table & using dashboard.
• using lookup table & without using dashboard.
• using both lookup table & dashboard.

Theory:

ATV:

An All terrain vehicle(ATV), also known as a light utility vehicle(LUV), a quad bike, or simply a quad, 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.

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 exists and existed historically for specialized applications. Multiple-user analogues with side-by-side seating are called utility terrain vehicles(UTVs) or side-by-sides to distinguish the classes of vehicle. Both classes tend to have similar powertrain parts.

ATVs offer excellent off-road capabilities and can carry heavy equipment over long distances and narrow access points. They can also be customised for high-performance riding, owing to which they find extensive applications across various industries,including sports,entertainment,agriculture,military and defense.

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.

The most common type of CVT uses two pulleys connected by a belt or chain; however, several other designs have also been used at times.

In the above image, the pulley connected to the wheel is the secondary pulley and the other one is the primary pulley. When the speed needs to be reduced, the radius of the belt on the secondary pulley increases by moving the pulley set close to each other. And, the vice versa is followed when the speed of the vehicles needs to be increased or when the throttle is given.

Simulink Model:

BAJA ATV Model without lookup table & without dashboard;

The above model consists of the following blocks;

Signal Builder : The Signal Builder is a source block in the Simulink library that lets you quickly develop and modify test input data that you want to incorporate with your model. In this model, it is used to vary the input values of the brake & throttle signal to understand the working of the BAJA ATV.

Generic Engine : The Generic Engine block represents a general internal combustion engine. This block is a 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. Optional dynamic parameters include crankshaft inertia and response time lag. A physical signal port outputs the engine fuel consumption rate based on the fuel consumption model that you choose. Optional speed and redline controllers prevent engine stall and enable cruise control.

In the above image, T is the throttle input whose value lies between zero & one & 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 & issues an error message. Connections F & B are mechanical rotational conserving ports associated with the engine crankshaft and engine block repectively. Connections P & FC are physical signal output ports through which engine power & fuel consumption rate are reported.

The speed vector & torque vector are the assigned parameters;

Engine Sensor: This Sensor has a sub system which contains Ideal rotational motion sensor, this 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 interia,friction,delays,energy consumption & so on. Connections R & C are mechanical rotational conserving ports and connections W & A are physical signal output ports for velocity & angular displacement respectively.

CVT Subsystem : This system consists of the following blocks;

• 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.

Simple Gear : Represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in this block. You can optionally include gear meshing, backlash, 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 Subsystem : This system consists of the following blocks;

• 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.

The parameters of the vehicle body are as follows;

• Tire : Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road Interaction (Magic Formula) and Simscape Foundation Library Wheel and Axle blocks. Optionally, the effects of tire inertia, stiffness, and damping can be included.

  Connection A is the mechanical rotational conserving port for the wheel axle. Connection H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Connection N is a physical signal input port that applies the normal force acting on the tire. The force is considered positive if it acts downwards. Connection S is a physical signal output port that reports the tire slip. Optionally expose physical signal port M by setting Parameterize by to Physical signal Magic Formula coefficients. Physical signal port M accepts a four element vector corresponding to the B, C, D, and E Magic Formula coefficients.

The parameters of the tire are as follows;

• Double-Shoe Brake : Represents a brake arranged as two pivoted rigid shoes symmetrically installed inside or outside a drum and operated by one actuator. The actuator force causes the shoes to exert a friction torque on a shaft connected to the drum.

  Connection S is a conserving rotational terminal associated with the drum shaft. Connection F is a physical signal port representing the force input to the actuator. Positive force creates friction torque that resists shaft rotation. Optionally include thermal effects and expose thermal conserving port H by setting Thermal port to Model.

The parameters of the vehicle body are as follows;

Inputs :

• Brake & 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 2.3 for the firsrt 4 secs, then drops down to 1.8 till 35 secs & remains constant thereafter till 80 sec.

Outputs :

• Velocity :

• CVT Shaft Speed :

• Engine Speed :

BAJA ATV Model without lookup table & with dashboard;

The only difference in this simulink model is that a dashboard is added to the BAJA ATV Model. The simulink model with dashboard is shown below;

Dashboard : A dashboard is a control panel usually located directly ahead of a driver, displaying the instrumentation and controls for the vehicle operation.

Inputs :

The dashboard contains the brake & throttle input knobs to vary the input values, unlike using the signal builder without the dashboard. Therefore, the Engine RPM & velocity output values change with the changes done in the respective knobs.

Outputs :

• Velocity :

• CVT Shaft Speed :

• Engine Speed :

BAJA ATV Model with lookup table & without dashboard;

The simulink model of BAJA ATV with lookup table is shown below;

Lookup table : A lookup table is an array of data that maps input values to output values, thererby approximating a mathematical function. For a given 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.

• 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.

In this CVT model, instead of a constant ratio input, we use lookup table to input the ratio values.

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

Inputs :

• 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

Outputs :

• CVT Ratio :

• Velocity :

• CVT Shaft Speed :

• Engine Speed :

BAJA ATV Model with lookup table & with dashboard;

The simulink model of BAJA ATV with both lookup table & dahboard is shown below;

Inputs :

The dashboard contains the brake & throttle input knobs to vary the input values, unlike using the signal builder without the dashboard. Therefore, the Engine RPM & velocity output values change with the changes done in the respective knobs.

Outputs :

• Velocity :

• CVT Shaft Speed :

• Engine Speed :

Conclusion :

From the above results, we can infer that;

• Velocity, CVT shaft speed & Engine speed are all directly proportional to the Throttle input value & inversely proportional to Brake input value.
• CVT Ratio is directly proportional to Torque & inversely proportional to the Throttle input value.
• 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.