Project 1

Answer:-

Conventional Vehicle:-

• Conventional vehicles use an internal combustion engine fueled by gasoline or diesel to power the wheels.
• In this the heat engine uses the principle of heat release through combustion of a fuel with an oxidizer in a combustion chamber to create expanding gases which pushes against a piston creating forcce and torque output.
• In this vehicle engine converts chemical energy stored in the fuel into heat which is used to produce useful work. Typically use fossil fuels like petroleum (petrol and diesel).
• The most popular type of engine is used in this system is 4 stroke reciprocating engine.
• Engine in cyclinder process can be represented by ideal thermodynamic cycles such as Otto cycle, Diesel cycle.
• Otto cycle is a ideal cycle thet describes the cycle process for spark ignited SI engine. and the Diesel cycle is the ideal cycle thet describes the cycle process for a compression ignited CI engine.

Energy and performance of vehicle:-

• In this system trge power demand on the wheel need to instant supplied by the powertrain.
• In otyher word the power coming from the powertrain dictates the power demand on the wheels (as per performance viz, acceleration, speed etc is determined by it.
• In tis vehicle the powertrain is consists of an engine connected to the wheels through a transmission therefore the power comes from the engine through the transmission.

Conventional powwertrain efficiency:-

• The engine generates power by converting chemical energy stored into the mechanical energy by the process of combustion.
• This process of energy conversion also has an efficiency and the energy input is in the form of fuel consumption.

- Instantaneous fuel consumption is given as-

mf = Pe/(eff.e*eff.t*Qlhv)

Where,

mf = mass flow rate in [kg]

pe = Engine Power

pt = Transmission Power

eff.t = Transmission efficiency

eff.e = Engine efficiency

Qlhv = Calorific value/ lower heating value of fuel.

• In this system of IC engine if tge power at the wheels is zero the engine is idling and still consumes some fuel to overcome the engine drag loss and keep it spinning this is the idling fuel consumption and know as idling process.
• Above mentioned formula is applicable only when the wheel power is strictly power. When the wheel power is negative either th engine is disengaged and idling or the engiune is engaged and providing some engine braking due to the engine drag losses.
• The engine is consuming fuel when it is idling but even for engine braking the engine might be consuming some fuel.
• The fuel consumption not only depend on the power requirement at the wheels but also is required to generate power to run the various engine and vehicle accessory loads.

System Dynamics:-

• It deals with the modeling of multi domain systems through the use of a unified approach based on a ordinary differential and algebraic equation describing the static and dynamic effects.
• Each systems has are two generalised variables-

1] Efforts:- It is generalised force variable. ex- torque, force, voltage, heating value.

2] Flow:- It is the generalised flow/velocity variable. ex:- velocity, current, mass flow rate.

3] Power:- It is the product of the effort and flow variable. It is interchangeable between energy domains.

Energy based models- Element models:-

To models the internal physical properties of the element and the losses there are basically two kinds of approach.

Map based models-

Elements are modeled using maps which characterized the relationship between the input and output , output and losses etc.

Analytical models-

Elements are modeled using physical equation that represent the internal dynamics. These are the two extremes most models are a combination of the two with some dynamics models analytically and for some using maps.

Statistical models-

Statistical models are built based on real world driving data analysis to derive empirical relationships between the different factors affecting Vehicles energy consumption.

Computational models-

There are mainly two kinds of computational models for energy consumption estimation: Artificial Neural Networks (ANN) based model. Clustering based models.

Architecture of the forward conventional vehicle model-

• It also known as dynamic simulation. Dynamic models are used for detailed simulations. In this model force/torque/power is the input and the vehicle state variable velocity and acceleration are outputs.
• The models and simulatios are more realistic due to phhysical casualty hence appropriate for control development.
• There is feedback loop to meet the desired vehicle state. It is mainly used to simulate a vehicle on a driving cycle to analyse the dynamic behaviour of the system helps significantly in control development.

• This model includes a driver model that provides input commands acceleration and brake torque depending on the drive cycle and the actual speed of the vehicle.
• A control model that controls the engine torque to the desired range and changes the gear command and control brake torque according to the driver input.
• The transmission model that gives the actual speed of the vehicle as feedback to the driver model. The model includes the engine, transmission, differential, wheel and vehicle dynamics models separately.

MATLAB scripts:-

Pre-Processing-

A MATLAB script has been created to load all the variables needed to run and post-process the Simulink model. Drive cycle selection is also done from here. Before running the Simulink vehicle model, the script is initialized at MATLAB to load all the variables in the workspace.

The simulink model of conventional vehicle-

• 'Project1_InitFile.m' is a Matlab script used to load all the variables required for running the Simulink model and for post-processing. The drive cycle selection is also done here. Before running the Simulink vehicle model, run this initialization script.
• In this project, a typical midsize car with a 1.9L engine and a 4-speed automatic transmission is considered`
• Data is taken from ADVISOR data base developed by NREL, USA. Transmission shift map and controller is taken from Matlab/Simulink example database.
• The model developed has the capability to simulate the vehicle on different drive cycles like-

1	UDDS
2	HWFET
3	FTP
4	US06
5	NEDC
6	WLTP

• The Simulink model for the convection model is created using 3 main subblocks for the driver model, control model and powertrain block.
• The actual vehicle speed is given as feedback to the driver block, and the driver block gives the controller block the required acceleration or brake output, while the controller block provides control signals for engine torque, gear shifting and brake torque to the Powertrain model.

Driver Model-

• Driver Model is a basic PI controller that generates accelerator and brake pedal outputs to match the desired and actual vehicle speeds.
• The PI controller controls the error between the required drive cycle and actual vehicle speed by providing acceleration and brake pedal output to the controller.
• In this we use drive cycles fro the based on these results of fuel consumption and emissions the vehicle gets certified and it also forms a basis of uniform asessment.

Controller Model-

• The ‘Controller’ block is the brains of the vehicle, representing the electronic controls units.
• Based on the driver inputs, it generates desired engine torque, desired transmission gear and desired brake torque.
• These inputs are fed to the ‘Powertrain’ block which represents the drivetrain of the vehicle.
• The controller consists of an engine control unit, a transmission control unit and a brake control unit.

Engine Control Unit-

Idle Speed Controller-

• Engine Control Unit Compare engine speed with the maximum torque and minimum torque curves of the lookup table and give the required torque command to the engine block.
• The throttle input is combined with the idle speed throttle and gains with the torque output from the lookup table to estimate the torque input required for the engine.
• Throttle input, idle throttle and their sum can be scoped from this block.

Transmission Control Unit-

• The Gear shifting is Controlled according to the vehicle speed and throttle input.
• The gear command is passed to the Transmission block to select the desired gear ratio.

Shift Logic-

Brake Control Unit-

• Brake Control unit Produce required brake torque according to the brake pedal input and passes the brake torque in to the wheel block in the transmission model.

Powertrain Model:-

• The powertrain model includes all the components that convert the power of the engine into vehicle motion.
• This includes Engine, Transmission, Differential, Wheels and the vehicle body dynamics subsystems.

Engine Model-

• Based on the Engine speed The required torque from the controller is saturated between Max torque curve and min torque curve and passes the Engine torque to the Transmission block
• The 2D lookup table is used to calculate the fuel flow rate based on engine speed and engine torque. The fuel flow rate is then integrated to find the fuel consumption.
• Estimated fuel flow rate, fuel consumption, engine torque and engine speed are passed to the MATLAB workspace using the to-workspace block.
• Engine fuel flow rate and Fuel consumption are scoped.

Transmission Model-

• In this model we take engine torque, gear selector from controller for transmission of gear ratio.
• The ratio is multiply by transmission input torque and then the transmission efficiency positive torque and negative torque gives transmission input speed.
• In this case torque converter connects the engine to transmission it is part of transmission. In it basically engine dynamics and that is decoupled.

Torque Converter-

• The engine block is connected to the automatic transmission via a torque converter. The output of the transmission is connected to the differential.
• The gear selection from the transmission control unit is multiplied by the engine torque in this block, and the efficiency and engine dynamics of the torque converter are applied in this model.

Differential Model-

• The transmission output torque is multiplied by the differential ratio and differential efficiency in this block and the torque is transmitted to the wheel as the axle torque.

Wheel Model-

• The brake torque from the control model is subtracted from the Axle torque and divides from the rolling radius to determine the Tractive force.
• The Wheel speed is calculated from the vehicle velocity and saved in the workspace.

Vehicle Dynamic Model-

• Tractive Force and Road loads are used to calculate the vehicle velocity-

Where

ρ a - Air Density

A f - Frontal Ares

C d - Drag Coefficient

C r - Rolling Coefficient

M - Mass of Vehicle

g - Acceleration due to gravity

θ - Slope

• The longitudinal dynamics of the vehicle along with the road load is represented in the ‘Vehicle Dynamics’ block-

• The variables are loaded on the workspace using MATLAB Script.
• The Acceleration, Velocity and Distance travelled are Calculated and stored in the workspace.

Simulink Model Results-

1. For UDDS Drive Cycle-

Drive Cycle and Actual Velocity-

Control Signals (Engine Torque, Transmission Gear and Brake torque)-

Engine Torque-

Throttle and Idle Spped controller-

Engine Fuel Rate , Engine Fuel Consumption-

Pump Speed and Turbine Speed-

K-factor and Pump Torque-

Turbine Torque and Pump Torque-

Gear ratio, Transmission input Speed , Transmission output Speed-

Tractive force, Acceleration, Road load,Velocity-

Different load-

2. HWFET Drive Cycle-

Drive Cycle and Actual Velocity-

Control Signals (Engine Torque, Transmission Gear and Brake torque)-

Engine Torque-

Throttle and Idle Spped controller-

Engine Fuel Rate , Engine Fuel Consumption-

Pump Speed and Turbine Speed-

K-factor and Pump Torque-

Turbine Torque and Pump Torque-

Gear ratio, Transmission input Speed , Transmission output Speed-

Tractive force, Acceleration, Road load,Velocity-

Different Road Loads-

Post-Processing Program-

• A MATLAB script is Created to analyse data and to generate plots. Here we rename the variables loaded from the model, do some basic post-process calculations and generate results and plots.

RESULT-

1. Drive Cycle-

For UDDS-

For HWFET-

2. The time trace for engine, transmission input, transmission output and wheel speed-

For UDDS-

For HWFET-

• Much of the fluctuating input speed is facilitated by the torque converter, and the transmission input speed fluctuates according to the engine torque required to achieve the drive cycle.
• Wheel speed and transmission output speed vary according to gear and differential ratio.

3. Engine torque, engine power, fuel rate and fuel consumption-

• The torque requirements of the drive cycle are different, so the fuel flow rate varies and fuel consumption is calculated.
• The HWFET drive cycle has higher power and torque requirements and less negative torque and power.

For UDDS-

For HWFET-

4. Accelerator and brake pedal, gear command, vehicle desired and actual speed, vehicle distance-

Acceleration and brake pedals are used more because the drive cycle is not very smooth and the gear has to be shifted frequently

For UDDS-

For HWFET-

2. Fuel economy numbers (kmpl) for UDDS-

for UDDS-

for HWFET-

• The City Fuel Economy is much lower than the highway drive as the brake pedal engagement and idle time on the drive cycle is less.

4. The engine operating points on the engine fuel consumption map-

For UDDS-

Use P4-

Use P2-

For HWFET-

• The engine operating points are plotted on the fuel map and the operating point is under the maximum torque curve.

CONCLUSION

• Hence, the forward energy-based fuel consumption model of a conventional vehicle has been successfully Simulated using MATLAB and Simulink.
• Analyses and understands vehicle operating points based on engine speed, torque, transmission speed, pedal positions, gear, and distance travelled.
• Post process calculations were performed and the required graphs were successfully plotted.
• Successfully calculated vehicle fuel efficiency numbers (kmpl) for the given city cycle (UDDS) and highway cycle (HWFET).