Project
AIM: To Study and analyze the BAJA All Terrain Vehicle (ATV) model using Simulink.
OBJECTIVES:
To prepare a technical report of Baja ATV model with and without Lookup Table.
THEORY:
ALL TERRAIN VEHICLE:
An All-Terrain Vehicle (ATV), also known as a quad(cycle), Light Utility Vehicle (LUV), 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 wider variety of terrain than most other vehicles. Although it is a street-legal vehicle in some countries, it is not street-legal within most states, territories, and provinces of Australia, the United States, or Canada. By the current ANSI definition, ATVs are intended for use by a single operator, although some companies have developed ATVs intended for use by the operator and one passenger.
These ATVs are referred to as tandem ATVs. 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 exist for specialized applications. Multiple-user analogs with side-by-side seating are called utility terrain vehicles (UTVs) or side-by-sides to distinguish the classes of vehicles. Both classes tend to have similar powertrain parts.
BAJA ATV(SAE):
The BAJA SAE series is an event for the undergraduate engineering students, organized globally by the Society of Automotive Engineers, USA. The event originated in the name of Mini – BAJA, in the year 1976 at University of Caroline. Since then, the event has spanned across six countries – USA, Mexico, South Africa, Korea, Brazil and India. The BAJA SAE tasks the students to design, fabricate and validate a single seater four – wheeled off road 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 and maneuverability characteristics and finally its ability to endure that back breaking durability test.
COMPONENTS USED IN THIS SIMULATION:
- Generic Engine Block:
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. 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.
Ports given in the above block:
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 Block:
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 given in the above block:
B – Base Gear or Driver Gear
F – Follower Gear or Driver Gear
- CVT Transmission Block:
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.
In the below figure the CVT subsystem diagram is given.
Ports given in the above block:
B – Base pulley ore Drive Pulley
F – Follower Pulley or Driven Pulley
r – Variable Transmission Ratio (Input)
- Variable Ratio Transmission Block:
The Variable Ratio Transmission block represents a gearbox that dynamically transfers motion and torque between the two connected driveshaft axes, base and follower.
Ignoring the dynamics of transmission compliance, the driveshafts are constrained to corotate with a Variable Gear Ratio control that you control. You can choose whether the follower axis rotates in the same or opposite direction as the base axis. If they rotate in the same direction, ω and ω have the same sign. If they rotate in opposite directions, ω and ω have opposite signs.
Transmission compliance introduces internal time delay between the axis motions. Therefore, unlike a gear, a variable transmission does not act as a kinematic constraint. You can also control torque loss caused by transmission and viscous losses.
Ports given in the above block:
B – Base Pulley or Drive Pulley
F – Follower Pulley or Driven Pulley
r – Variable Transmission Ratio (Input)
- Vehicle Body Block:
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.
The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. Optionally include pitch and suspension dynamics. The vehicle does not move vertically relative to the ground.
The block has an option to include an externally-defined mass and an externally-defined inertia. The mass, inertia, and center of gravity of the vehicle body can vary over the course of simulation in response to system changes.
Ports given in the above block:
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 Block:
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.
Double-shoe brakes provide high braking torque with small actuator deflections in applications that include motor vehicles and some heavy machinery. The model employs a simple parameterization with readily accessible brake geometry and friction parameters.
Ports given in the above block:
S – Rotational conserving port associated with the rotating drum shaft
F – Physical signal input port associated with the applied actuating force
- Tire (Magic Formula) Block:
The Tire (Magic Formula) block models a tire with longitudinal behavior given by the Magic Formula, an empirical equation based on four fitting coefficients. The block can model tire dynamics under constant or variable pavement conditions.
The vehicle body is connected to 4 tires each per axle to move the vehicle according to the power input to the axle.
Ports given in the above block:
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.
- Other 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 without Dashboard
- BAJA ATV model – Mapped Lookup Table with Dashboard
1)BAJA ATV MODEL WITHOUT DASHBOARD (cvtModel)
Main Model:
Steps:
The throttle signal is generated by signal builder block and inputted to generic engine. The torque and speed vector are inputted from the matlab workspace The engine will generate the output rpm which can be taken from the crankshaft output. This speed will be given to the Ideal Rotational Motion Sensor to sense the output rpm.
The same output speed will be given to a simple gear mechanism to reduce the speed where the Gear Ratio is ‘4’. Then the output speed from the gear reducer will be given to the Variable Ratio Transmission block (CVT). The CVT ratio is provided to the Variable Ratio Transmission (CVT) block through Signal Builder.
The speed is controlled by the variable CVT ratios and the controlled output speed is inputted to the vehicle axle. The brake signal is generated by the signal builder and inputted to the vehicle body (Double Shoe Brake) for applying the brake to
axle. The power from the CVT is inputted to the axle and the vehicle accelerates according to the speed. Then the Velocity is taken as output from the vehicle body for further analysis.
Engine Sensor Sub Block:
This block measures angular velocity or angle in a mechanical rotational network. The sensor is ideal since it does not account for inertia, friction, delays, energy consumption, and so on.
The physical signal ports W and A report the angular velocity and angular displacement, respectively, of port R relative to port C. The measurement is positive when the motion at R is greater than the motion at C.
CVT System Sub Block:
The cvt subblock provides the input and the output shafts of the cvt with inertia, and measures the input shaft rpm and the output shaft rpm.
Vehicle Body Sub Block:
The model shows that the vehicle is rear wheel drive as the output from the gearbox is inputted to the rear axle, then an inertia is added to simulate axle inertia, then the shoe brake s conserving port is connected to the axle, and then the same axle connects the two rear tyres while the front tyres is free to rotate on a rotational free end.
All the tyres H hub port is connected together and then connected to the vehicle H port, Also the rear tyres N port is connected together and then connected to the vehicle body Nr output ports, while the front are connected to the Nf vehicle body output ports, the vehicle body takes the road inclination and wind velocity from physical constants.
Simulation Process:
Throttle Input Signal:
The throttle signal is generated by signal builder block and inputted to generic engine. Throttle starts at 0.3 and then it steps to 1 at the 20 second.
Brake Input Signal:
The brake input remains zero through the whole simulation
Torque and Speed MATLAB Workspace Input:
CVT Ratio Input:
The engine will generate the output rpm which can be taken from the crankshaft output . This speed will be given to the Ideal
Rotational Motion Sensor to sense the output rpm. The same output speed will be given to a simple gear mechanism to reduce the speed where the Gear Ratio is ‘4’. Then the output speed from the gear reducer will be given to the Variable Ratio Transmission block (CVT). The CVT ratio is provided to the Variable Ratio Transmission (CVT) block through Signal Builder.
Cvt ratio starts at 3.5 ,then 5 sec it gradually reduces until it reaches 0.5 at 35 second and it remains so till the end of the simulation.
Output:
Torque Speed Plot:
The torque and speed are inputted from the MATLAB workspace window to the generic engine block to generate the output RPM accordingly. This plot is common for all the cases because it’s a default input to the engine.
Engine Speed Plot:
The engine rpm generated according to the throttle, speed and torque inputs. It is clearly evident how the step increase in throttle at 20 second resulted in an increase in the engine revolutions from 2,250 to 3,800 RPM.
Engine Speed vs. Gear Reduction Speed Plot:
Here we can see that the engine speed is reduced by the Gear Ratio ‘4’. For verification I calculated the maximum RPM.
Maximum RPM (Before Reducing) = 3833 rpm
Gear Ratio = 1:4
We know that,
Driven = 3833/4
Driven = 95625 rpm
Thus, the reduced maximum rpm is 958.25rpm which can be verified from the plot.
Note: Driven = Secondary CVT Shaft , Driver = Primary CVT Shaft
CVT Speed Reduction Plot:
The engine reduced speed is controlled by various CVT Ratios. For verification the maximum RPM is calculated at 1.8 gear ratio which is applicable from the 35 second.
Maximum RPM (Before Reducing) = 958.25 rpm
CVT Ratio = 1:1.8
The reduced maximum rpm is 532.36 rpm which can be verified from the plot.
Speed vs. Throttle Plot:
From the graph we can infer that the brake is not applied during the drive cycle and the Throttle is constant (0.3) till 20 sec and being increased from 0.3 to 1 from 20 sec where it remains constant for the rest of the run. With the increase in throttle, the vehicle speed also increases from 30 to 55 kmph.
2)BAJA ATV MODEL WITH DASHBOARD (cvtModel_dashboard)
Main Model:
Dashboard:
Flow Process:
The model workflow process is as same as the process of ‘BAJA ATV model without Dashboard’ but the Throttle and Brake inputs are controlled by the user with the Knob. Here, We are also replacing signal builder with two separate constant blocks for Throttle and Brake.
Output:
Engine Speed Plot:
Here the engine speed is generated according to the inputs like throttle, break, torque and speed vectors. The runtime is not defined so that the Throttle and Break are controlled by the user. The step up is throttle and step down is brake input.
Engine Speed vs. Gear Reduction Speed Plot:
We can see that the engine speed is reduced by the Gear Ratio ‘4’. For verification I calculated the constant RPM (42000 – 50000 sec).
Maximum RPM (Before Reducing) = 2759.3 rpm
Gear Ratio = 1:4
We know that,
Driven = 2759.3/4
Driven = 689.825 RPM
The reduced constant rpm is 689.825 rpm which can be verified from the plot.
CVT Speed Reduction Plot:
The engine reduced speed is controlled by various CVT Ratios. For verification I had calculated the constant RPM (42000 – 50000 sec)
Maximum RPM (Before Reducing) = 689.825 rpm
CVT Ratio = 1:1.8
We know that,
Driven = 689.825/ 1.8
Driven = 383.23 RPM
The reduced maximum rpm is 383.23 rpm which can be verified from the plot.
Speed vs. Throttle Input:
From the graph we can infer that the vehicle is accelerating while throttle is applied (Step Up) and decelerated while break is applied (Step Down). The constant speed areas represent no changes in throttle or braking.
BAJA ATV MODEL – MAPPED LOOKUP TABLE WITHOUT DASHBOARD (cvtModel_mapped)
Main model:
Steps:
The model workflow process is same as the process of ‘BAJA ATV model without Dashboard’ except that it used instead of Signal Builder Blocks for Brake and Throttle Input Step input blocks are used. At 35 sec the brake input will take a step of value ‘0’ and at 20 sec throttle input will increases from 0.3-1 then remains constant throughout.
CVT Sub Block:
The cvt subblock is the same as the previous model “BAJA ATV model without Dashboard” but instead of Signal Builder Block for CVT Ratio the 2-D Lookup Table is used. The interpolations and extrapolation methods are set to linear. It needs to be loaded in the workspace having the file name as Lookuptable_data.mat
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.
the vehicle speed output is given as a feedback to the 2-D Lookup Table so that we can verify that the velocity of the vehicle is changing perfectly when the CVT Ratio changes. The vehicle speed is converted to m/s from Kmph.
Output:
CVT Ratio Plot:
CVT Ratio vs. Vehicle Velocity:
Engine Speed:
CVT Shaft Speed:
Speed vs. Throttle Plot:
BAJA ATV MODEL – MAPPED LOOKUP TABLE WITH DASHBOARD(cvtModel_dashboard_mapped):
Main Model:
Dashboard (Simulation OFF):
Dashboard (Simulation ON):
Steps:
In this BAJA ATV Model, the Engine is pre-set to run at 3300rpm with the throttle value of ‘0.3’. And the velocity at 45 m/s. The CVT Ratio for minimum and maximum speed of the engine was pre-defined as 2.3 and 1.8 respectively. When the simulation is started the initial throttle value 0.3 is achieved so that the CVT Ratio is nearby to 1.85. When the throttle is being increased the CVT Ratio move towards 1.8 where the state is maximum engine speed. Simultaneously when the throttle is decreasing the CVT Ratio will move towards 1.85. While the braking is applied the CVT Ratio increases so that it can achieve the nearest state of 2.3 (Minimum Engine Speed). When braking is reduced the CVT Ratio move towards 1.85 which is the basic throttle input 0.3 or if any other throttle value is applied it would reach that CVT Ratio state.
The model workflow process is same as the process of ‘BAJA ATV model – mapped lookup table without Dashboard’ but the Throttle and Brake inputs are controlled by the user with the Knob followed by the vehicle speed is given as feedback to the CVT Ratio lookup table.
Output:
CVT Ratio Plot:
Engine Speed Plot:
From the graph we can infer that the vehicle was first running at minimum rpm of 3300 rpm and then throttle is applied (step-up) then braking (step-down) then brake is released so that engine rpm is increased then braking is applied.
CVT Speed Plot:
From the above graph we can understand that the throttle is applied (step-up) and then kept constant, then braking is applied (step-down), and finally brake is released so that the engine speed is increased with the increase in throttle input.
Speed vs. Throttle Plot:
From the plot we can infer that when throttle is applied the vehicle speed increases and when brake is applied, vehicle speed
decreases simultaneously.
SIMULINK MODEL :
https://www.mathworks.com/matlabcentral/fileexchange/70576-baja-all-terrain-vehicle-atv-model
CONCLUSION:
We can understand easily how the vehicle may perform under the provided conditions. We can calculate the time required to attain a certain amount of speed or to stop the vehicle completely. We can also calculate what will be the maximum speed vehicle can achieve. We are also able to observe the performance of the braking system and the throttle system. This model helps us to verify the performance of the vehicle under the constructed brake system and throttle system.
REFERENCES:
Matlab help