Project

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

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

• Study the baja ATV model using lookup table without dashboard.
• Study the baja ATV model using lookup table with dashboard.
• Study the baja ATV model using lookup table without dashboard.
• Study the baja ATV model using lookup table with dashboard.

INTRODUCTION:

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. ATVs are subdivided into two types as designated by the manufacturer. Type I ATVs are intended by the manufacturer for use by a single operator and no passenger. Type II ATVs are intended by the manufacturer for use by an operator and a passenger, and are equipped with a designated seating position behind the operator. Similarly, riders must also consider the various ATV sizes.

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.

CVT-

Unlike traditional automatic transmissions, continuously variable transmissions don't have a gearbox with a set number of gears, which means they don't have interlocking toothed wheels. The most common type of CVT operates on an ingenious pulley system that allows an infinite variability between highest and lowest gears with no discrete steps or shifts.

Peer into a planetary automatic transmission, and you'll see a complex world of gears, brakes, clutches and governing devices. By comparison, a continuously variable transmission is a study in simplicity. Most CVTs only have three basic components:

CVTs also have various microprocessors and sensors, but the three components described above are the key elements that enable the technology to work.

he variable-diameter pulleys are the heart of a CVT. Each pulley is made of two 20-degree cones facing each other. A belt rides in the groove between the two cones. V-belts are preferred if the belt is made of rubber. V-belts get their name from the fact that the belts bear a V-shaped cross section, which increases the frictional grip of the belt.

When the two cones of the pulley are far apart (when the diameter increases), the belt rides lower in the groove, and the radius of the belt loop going around the pulley gets smaller. When the cones are close together (when the diameter decreases), the belt rides higher in the groove, and the radius of the belt loop going around the pulley gets larger. CVTs may use hydraulic pressure, centrifugal force or spring tension to create the force necessary to adjust the pulley halves.

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.

When one pulley increases its radius, the other decreases its radius to keep the belt tight. As the two pulleys change their radii relative to one another, they create an infinite number of gear ratios -- from low to high and everything in between. For example, 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.

The simplicity and stepless nature of CVTs make them an ideal transmission for a variety of machines and devices, not just cars. CVTs have been used for years in power tools and drill presses. They've also been used in a variety of vehicles, including tractors, snowmobiles and motor scooters. In all of these applications, the transmissions have relied on high-density rubber belts, which can slip and stretch, thereby reducing their efficiency.

STUDY CASE 1-

PART 1 - BAJA ATV Model without Lookup Table

Section A- without dashboard

A Simulink model for the BAJA ATV Model is shown below-

This model consists following blocks-

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.

IDEAL ROTANATIONAL MOTION SENSOR-

• The block represents an ideal mechanical rotational motion sensor, that is, a device that 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 inertia, friction, delays, energy consumption, and so on.
• Connections R and C are mechanical rotational conserving ports and connections W and A are physical signal output port.

SIMPLE GEAR-

• Represents a fixed-ratio gear or gearbox. 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 right-clicking on the block and selecting Simscape block choices to switch between variants.
• Follower (F) to base (B) teeth ratio (NF/NB): 4

CVT SUBSYSTEM-

The CVT Subsystem 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.

VEHICLE BODY SUBSYSTEM-

vehicle body system contains following block-

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 the 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.

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.

TIRE-

• Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-RoadnInteraction (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.

OUTPUT-

VELOCITY-

CVT SHAFT SPEED-

CVT GEAR RATIO-

Section B- 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.

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

Baja ATV model

INPUTS-

THROTTLE AND BRAKE-

• 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-

CVT SHAFT SPEED-

ENGINE SPEED-

STUDY CASE 2-

PART 2 - BAJA ATV Model with Lookup Table

Section A- without dashboard

• 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 figure.

• The CVT subsystem includes look up table, Transmission block, input and output shaft inertia and motion sensors as shown in figure.

• The vehicle body subsystem includes vehicle body block, double drum brake and tyres as shown in figure

• The initial engine speed is given as 2100 rpm, mechanical rotation for driven pulley and driver pulley as 0.8 & 0.7 respectively. The mass of the vehicle as 250kg and 2 axles which connects 4 wheel accordingly.

LOOK UP 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:

  1. An interpolation is a process for estimating values that lie between known data points. 2. An extrapolation is a process for estimating values that lie beyond the range of known data points. 3. A rounding is a process for approximating a value by altering its digits according to a known rule.

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

THROTTLE INPUT-

BRAKE INPUT-

CVT RATIO-

VELOCITY-

CVT SHAFT SPEED-

ENGINE RPM-

Section B- with dashboard

• The above figure shows 'Baja ATV with dashboard' model using lookup table which consists throttle meter and brake input in the dash board and indicated as constant block. Rest of the blocks and subsystems are common in the above baja ATV model without dashboard.
• The main concept of using dash board is 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 lookup table, simulink get the input value from the lookup table and obtain the result according to the lookup table.
• As the brake input varies from 0 - 0.5, the velocity and speed decreases accordingly which inturn the gear ratio also decreasing. By increasing the throttle, the velocity and speed of the engine & shaft increases.
• The transmission as primary pulley and secondary pulley, in which the radius of primary pulley increses by compacting and the radius of secondary pulley decreases. As the gear ratio varies, the torque also varies. Gear ratio is directly proportional to the torque, which increases by increasing the gear ratio. At the max torque, the speed and velocity is decreases.

OUTPUT-

VELOCITY-

ENGINE SPEED-

CVT SHAFT SPEED-

CONCLUSION-

1. As throttle input increases, velocity increases & speed of engine increases. Velocity, shaft speed and engine speed are directly proportional to throttle input.

2. As brake input increases, velocity decreases & speed of engine decreases. Velocity, shaft speed and engine speed are inversely proportional to throttle input.

3. CVT Primary speed is greater than CVT Secondary speed as they are directly proportional to their shaft diameter.

4. As the gear ratio increases, torque increases & velocity decreases.

5. With use of lookup table, we can change and increase any input value and also get the output value by using interpolation and extrapolation method which the simulink can solve.