Project 8 - SIMULINK - SIMULATION - All-Terrain vehicle (CVT)

AIM :  To study system-level simulation of an all-terrain vehicle and explain the results.        

OBJECTIVE: Generate a Simulink model various graphs for different input vs output ration   Results & generate reports. 

SOLUTION: 

All-Terrain Vehicle –

              An All-Terrain is a vehicle that travels on low-pressure tires, with a seat that is straddled by the operator, along with handlebars for steering control. It is designed to handle a wider variety of terrain than most other vehicles. ATVs come in many different shapes and sizes. The different types of ATVs are designed and manufactured for different uses including racing, pit-vehicles, recreation, hunting, ranching, military, emergency services, and industrial usage.

Continuously Variable Transmission –

A continuously variable transmission (CVT), also known as a shiftless transmission, step-less transmission, pulley transmission is an automatic transmission that can change seamlessly through a continuous range of effective gear ratios. The CVT does not strictly require the presence of a clutch. Nevertheless, in some cases, a centrifugal clutch is added to facilitate a "neutral" stance, which is useful when idling or manually reversing. A belt-driven design offers approximately 88% efficiency.

The model taken for the study is the BAJA ATV model with Continuously Variable Transmission(CVT)

Explanation: Here we need to do the following study: 

BAJA ATV model without dashboard

BAJA ATV model with dashboard

BAJA ATV model using the lookup table without a dashboard BAJA ATV model using the lookup table with a dashboard 

Study 1 -

The study based on the BAJA ATV model with CVT consists of signal Builder with throttle and brake input for a driver, generic Engine, motion sensors, simple Gear, vehicle transmission, vehicle body with tire and solver configuration blocks as shown in the figure below.

The CVT subsystem consists of a Variable Ratio Transmission block, Ideal rotational motion sensor, input shaft inertia, motion sensors, and output shaft inertia as shown in the figure below

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.

The models consist of common blocks.

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.

 Signal Builder:

The Signal Builder block allows you to create interchangeable groups of piecewise linear signal sources and use them in a model. You can quickly switch the signal groups into and out of a model to facilitate testing. 

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. Speed vector and Torque vector are the assigned parameters.

Engine Sensor:

Ideal Rotational 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 ports for velocity and angular displacement, respectively. 

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 

The vehicle body sub-system includes vehicle body block, double drum brake, and tires as shown below:

Vehicle body:

Initial engine rpm: 2100 rpm

Mechanical rotation for driven and driver pulley =0.8 and 0.7

Mass of the vehicle = 250 kg Front and rear axle with 4 wheels.

The input is provided using the signal builder for brake, throttle, and gear ratio: Here the value for the brake is taken as zero for entire simulation, throttle value is given as 0.3 to 20 sec and value increases to 1 for overall simulation ie,c80 sec.

As we know that as throttle increases then the power increases by excess input of fuel into the system and shows in the output also increasing. The value of gear ratio is maintained as 2.3 for the first 5 sec and decreases to 1.8 up to 35sec linearly so after that a constant value of that 1.8 is maintained all out the time span ie, 80 sec   

CVT Model _ input throttle & Break

CVT Model/CVT ratio

Study - 2 

The study is based on 'Baja ATV with dashboard' as shown in the figure above here the input data like throttle and brake input are given from the dashboard instead of inputted with the help of a signal builder. All the remaining blocks are the same as in study above (ie, study-1)

The main intention behind the usage of the dashboard is to study the output value with the variation in the inputted values of throttle and brake which will give the value of rpm and velocity of the engine in the digital reading.

The study is based on 'Baja ATV with dashboard' as shown in the figure above here the input data like throttle and brake input are given from the dashboard instead of inputted with the help of a signal builder. All the remaining blocks are the same as in study above (ie, study-1)

The main intention behind the usage of the dashboard is to study the output value with the variation in the inputted values of throttle and brake which will give the value of rpm and velocity of the engine in the digital reading

The value of gear ratio is maintained as 2.3 for the first 5 sec and decreases to 1.8 up to 35sec linearly so after that a constant value of that 1.8 is maintained all out the time span ie, 80 sec. the value for the brake can be varied from 0 to 0.5 for the entire simulation. As we know that as throttle increases then the power increases by excess input of fuel into the system and shows in the output also increasing and vice versa.

Study-3

The above Simulink model of Baja ATV with CVT includes the step time, generic engine, motion sensors, vehicle transmission, vehicle body, tires, and solver configuration.

The CVT system includes a look-up table, an array of data that maps input values to output values, thereby approximating a mathematical function. If we give an input set of values, a look-up operation retrieves the corresponding output values from the tables. If the look-up table does not explicitly define the input values then the Simulink can estimate output value using interpolation, extrapolation or rounding: 

Interpolation: It is the process of estimating values that lie between known data points

Extrapolation: It is the process of estimating values that lie beyond the range of known data points. Rounding: It is the process of approximating the values by altering its digits according to a known value.

The brake and throttle input is given by step time, which depends on the run time and it varies accordingly. By using the loop-up table for the gear ratio and it gives the input to the CVT part and accordingly obtains the output. This method works in a closed-loop and the inputs are given with the loop-up table data. Here the Simulink gets the input values from the look-up tables and according to the values from the input, the output is got in terms of gear ratio.

its the gear ratio varies from the range of 2.3 to 1.8 and the output in terms of velocity is got as for the range of gear ratio at a maximum value of nearly 56kmph

Study- 4

The above study based on the Baja ATV with the dashboard model using the look-up table which consists of throttle and brake meters in the dashboard. With the help of the dashboard, we can see the variation of the output with the input values been varied. Here as we know the gear ratio is inputted from the look-up table and the Simulink will give the output with respect to inputted values. The gear ratio is directly proportional to the torque. As we know that as throttle increases then the power increases by excess input of fuel into the system and shows in the output also increasing.

Output: Study -1 (Without dashboard)

Here the brake value is set as a constant ie, zero and the throttle value from 0.3 to 1 in a time range of 20 second and such that the fuel injection happens in a time basics and the velocity part shows as raise as the throttle values increase by a constant linear line. From the above velocity vs time graph as the velocity part increases and set to a constant value due to throttle values is constant

So,

Here the ratio is determined by the outer to input diameter so that when the radius of the output part is high then the rpm will decreases which is incase reflecting in the above graph.

Output: Study -2 (Without dashboard)

From the above graph, the brake is applied in this case we can see the decrease in the velocity part. Herewith the value of the throttle is increased in instant to 0.3 and maintained so that the velocity

also increases rapidly to a value of nearly 47kmph and being at a constant as the throttle value increases the fuel input increases and the velocity increases and here shows as the throttle increases the vehicle velocity also increases from the graph above.

Here the ratio is determined by the outer to input diameter so that when the radius of the output part is high then the rpm will decreases which is incase reflecting in the above graph.

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.

- System-level simulation of a Baja ATV with and without dashboard and Look-up Table has been carried out and a detailed study report of the model has been prepared.