Project

Aim:

To study and analyze the Baja All Terrain (ATV) model using Simulink.

Objective:

To prepare a technical report of Baja ATV model with and Lookup Table.

All-Terrain Vehicle:

An ATV also known as quad (cycle), three-wheeler, four-wheeler, four-track, four-wheeler, or quadricycle 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. It is designed to handle a wide variety of terrain than most other vehicles.

Baja ATV (SAE):

The Baja ATV SAE Series is an event for an undergraduate student, organized globally by the society of Automotive Engineers, USA. The events originated in the name of Mini-BAJA, in the year 1976 at University of California. Since then, the event has spanned across six countries – USA, Mexico, South Africa, Korea, Brazil and India. The BAJA SAE tasks the student to design, fabricate and validate a single seater four-wheeled off rolled vehicle to take part in series of events spread over a course of 3 days that test the vehicle for the sound engineering practices that have gone into it, the agility of the vehicle in terms of gradeability, speed, acceleration maneuverability characteristics and finally its ability to endure that back breaking durability test.  

Major components used in this Simulation:

Generic Engine:

The generic engine block represents a general internal combustion engine (IC) which is a type of Spark Ignition (SI-Petrol) or Compression Ignition (CI-Diesel). The speed torque and speed power parameters are provided.

Ports:

1. B – Rotational Conserving Port representing the Engine Block.
2. F - Rotational Conserving Port representing the Engine Crankshaft

• T – Physical Signal Port specifying the normalized engine throttle valve

1. P – Physical signal output port reporting the instantaneous engine power, in W
2. FC – Physical signal output port reporting the fuel consumption rate, in kg/s

Simple Gear:

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

Gear Ratio =(followed gear speed/base gear speed)

Ports:

1. B – Base gear or driver gear
2. F – Follower gear or driven gear

CVT Transmission:

In CVT a 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 is connected to the crankshaft of the engine. The driving pulley is also called the input pulley because its 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 pulleys to where the belt makes the contact in the groove is known as the pitch radius. When the pulleys are far apart, the belt rides lower and the pitch radius decreases. 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:

1. B – Base pulley or drive pulley
2. 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 geometry (CG) that is at or below the plane of travel.

Ports:

1. NR – Rear axle normal force (N)
2. NF – Front axle normal force (N)

• Beta – Road incline angle (rad)

1. V – Longitudinal velocity (m/s)
2. W – Head wind speed (m/s)
3. 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 surface cause the rotating drum to decelerate.

Ports:

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

Tire:

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

Ports:

1. N – Normal force
2. S – Tire slip

• A - Axle

1. H – Mechanical translational port associated with the wheel hub that transmits the thrust generated by the tire to the remainder of the vehicle.

Types of Models:

1. BAJA ATV model without dashboard
2. BAJA ATV model with dashboard

• BAJA ATV model – Lookup table data extraction

1. BAJA ATV model – Mapped Lookup table without dashboard
2. BAJA ATV model – Mapped Lookup table with dashboard

Simulink Model:

First step is giving input to the engine with the help of a signal builder. We have one input to the engine which a throttle, in signal builder we are giving constant throttle for half-press of the throttle for 80s. As we are not considering the braking condition for the vehicle, we kept the input brake zero. The inputs in the signal builder are as shown in the following figure.

Now we define the inputs for the engine, for representing the engine we are using the Generic Engine block which is available in Simulink. We have to give some parameters of the engine like speed vector, torque vector, inertia, ideal RPM which is shown in the figure below,

The speed vector and torque vector re the variables defined in the Matlab workspace, the data for the speed vector and torque vector is taken from the graph which is as shown in the below diagram with the grabit program.

Now the output of the engine which is the crankshaft is connected to ideal rotational motion sensor to measure the RPM of the engine and plot the graph by using Scope Block. The output of the engine is also connected to the input shaft (Base) of the variable ratio transmission which acts as the CVT.

As we know the output of the engine is connected to the input shaft which acts as the primary shaft of CVT. As we know that in CVT there is a continuous change in ratio so for that we have to give input CVT ratios for the given range which depends on the CVT model. So the input for variable ratio transmission block to act as CVT is given with the help of signal builder to the port ‘r’ as shown in below graph and diagrams,

We have defined the inertia for input and output shaft with the help of the following formulas,

For input shaft inertia=

m1 . (((18.6e-2)/2)`square` + ((2.5e-2)/2)`square`)/2

For output shaft inertia=

m2 . (((19.8e-2)/2)`square` + ((1.9e-2)/2)`square`)/2

whereas, m1=3.5kg and m2=3.2kg which is defined in the Matlab workspace. We have connected the ideal rotational motion sensor to the input and output shaft i.e., primary and secondary pulley of the CVT to measure the RPM of both pullies to the graph. Now the output of the CVT i.e., Secondary pulley is connected to the input of the simple gearbox which is having a gear ratio of 10.

Last step is to connect the output of the gearbox shaft to the rear wheel of the BAJA ATV for which we have to make the BAJA ATV model which is as shown in the diagram,

We are considering rear wheel drive system for our BAJA ATV model so we have connected the output of the gearbox to rear wheels only. We are also connecting double-shoe brake to rear wheels. Now to define the rear wheel and front wheel and other parameters of the vehicle we are using vehicle body block which is available in Simulink. The input parameters for the vehicle body are shown in the diagram,

We are considering Headwind speed and inclination plane values zero for this model. The V port is output to get the speed of the vehicle and to get the distance we connect the integer block to velocity output to get the distance.

Now to plot the outputs we are using Goto and from block to connect the scope.

BAJA ATV model with CVT system with variable input to the engine by using variable constant which can be controlled by a knob and fixed input to CVT by using the signal builder:

Simulink Model:

This model is similar to above model, the only difference is the only type of input we are providing which is explained as follows:

In this model we can change the input values of throttle and brake with the help of knobs. In this model the simulation runtime is kept at infinity so that we can change the throttle values and brake during the simulation run to get the real-time effect of the input parameters. We also have two circuits gauges which are connected to measure the RPM of the engine and velocity of the velocity of the vehicle as shown in the above figure.

BAJA ATV model with CVT system with fixed input to the engine through the step block and input to CVT ratio is selected based on vehicle speed with the help of lookup table as a close loop system:

In this model we are giving input to the engine with the help of step blocks. As we know that we are considering only accelerating conditions so we are keeping the braking condition zero throughout the simulation. The input to the engine with step values is shown below.

Throttle input:

As per these values, the throttle will be pressed 0.3 for 0 to 20s and at 20s it increases to the final value which is 1 for the rest of the simulation time.

Brake input:

As we can see throughout the simulation time the braking value is zero. Now the output of the throttle and brake is connected to the Goto block and connected to the block by from block. Now the output of the throttle is connected to the input of the engine. We are using a generic engine with parameters as shown below diagram:

The speed and torque vector are variables defined in the Matlab workspace from the below graph points with the help of the grabit program.

The engine inertia is 5 kg.m² and ideal rpm (i.e., Initial velocity) is 1600 rpm. Now the output of the engine is connected to the ideal rotational motion sensor to get the rpm of the engine and next the output of the engine is connected to the input shaft of the variable ratio transmission for the variable CVT ratios we are using the lookup table.

Lookup table:   

We are selecting the CVT ratios according to the velocity of the vehicle which is connected to the input of the Lookup table from the output of the vehicle model. In the lookup table for input, we are taking vehicle array in increasing order and for output values, we are taking CVT ratios, so when we run the simulation CVT changes its ratio according to the vehicle velocity because we have connected input of lookup table to the output of the vehicle velocity of the vehicle body.

To get the values of the vehicle speed and CVT ratios we used the following Simulink model:

As we can see this model is the same as above model but the only difference is that we have connected ‘To Workspace’ blocks at the output of the CVT ratio graph and the output of the vehicle speed at the vehicle body as shown in above diagram marked with the yellow marker. These blocks are connected to collect the data to the workspace so we can use that in the Lookup table.

Now the output of the Lookup table is connected to the input of the Variable ratio transmission and also connected to the GOTO block to get the graph of the output CVT ratios in graph format. Now we have connected the output of the engine to the input shaft of the variable ratio transmission and the output shaft of the variable ratio transmission is connected to the input of the gearbox. Across these two shafts, we have connected the inertia blocks to give the inertia and also connected to the ideal rotational motion sensor block to measure the rpm of the primary and secondary pulley.

Now the output of the secondary pulley is connected to the input shaft of the gearbox. We are using a gearbox with a ratio 12 in this simulation. Next the output of the gearbox is connected to the both rear wheels of the BAJA ATV because we are considering rear wheel drive system and also, we have connected double-shoe brake to the rear wheel as shown in diagram,

As we can in above diagram the front wheel (NF) and rear wheel (NR) are defined by using vehicle body block. The all wheels are connected to the H_port to give only horizontal motion to the wheels. For front wheel we are giving free rotation only. We are not considering headwind speed and road inclination angle for this model so their values is given zero in constant block. Now the output port of the vehicle body which is speed is connected to the GOTO block to connect it to scope by using from block to plot the graph.

BAJA ATV model with CVT system with variable input to the engine which can be controlled by knob and input to CVT ratio is selected based on vehicle speed with the help of lookup table as a close loop system:

This model is different in the way like input we are giving to the engine block i.e., it is a real time simulator. In this model we have connected throttle and brake to engine with the help of constant blocks which are connected to the knob. The throttle knob can be varied to the range of 0.3 to 1 and the brake knob can be varied to the range of the 0 to 0.5. We also connected circular gauge to measure the engine rpm and the vehicle speed.

Outputs:

BAJA ATV model with CVT system with fixed input to the engine and CVT by the signal builder. Graph for the vehicle speed and distance for given value of throttle and brake:

Result:

As we can see that when we press the throttle to 0.5 the vehicle speed increase to its corresponding value with corresponding distance. Graph for primary and secondary rpm of the CVT.

As we can see that as primary pulley rpm increases the corresponding secondary pulley rpm increase w.r.t. the given CVT ratio.

Graph of engine rpm:

From the above graph we can say that as we press the throttle for 0.5 the engine attends its corresponding rpm, first the rpm decreases to get the required torque to move the vehicle then it increases w.r.t. time, now next this engine rpm is transferred to the secondary pulley with the help of the primary pulley. Forgiven vehicle rpm the CVT ratios are selected from the singular builder.

Baja ATV model with CVT system with fixed input to the engine through the step block and input to CVT ratio is selected based on vehicle speed with the help of lookup table as a close loop system.

Graph for vehicle speed with respect to throttle and brake values:

In this graph speed increases continuously according to the throttle input and once the throttle input reaches to its maximum value which is 1 the speed increases to its maximum value.

Graph for primary and secondary pullies RPM of CVT:

As we can see that the secondary pulley rpm is low for starting time compared to the primary pulley rpm because to get initial torque required to move the vehicle. As we are giving input to the CVT w.r.t. to vehicle speed by lookup table so when the input speed is low it select the required CVT ratio to get required secondary pulley rpm.

Graph for engine rpm:

As we know that for first 20s the throttle input is 0.3 so the engine rpm is low once the engine input throttle jumps to 1 value the engine rpm increases rapidly w.r.t. time.

Graph for CVT ratios:

As the engine rpm goes on increasing the CVT ratio decreases to get the required rpm of the CVT secondary pulley.

Graph for CVT ratio from lookup table: