Project 2

Aim:

Development of a forward energy-based fuel consumption model of a Hybrid vehicle.

Objective:

• Tabulate the fuel economy numbers (kmpl) for UDDS and HWFET cycle. This forms the baseline numbers for comparing with the conventional vehicle model.
• Plot the time trace for engine, transmission input, transmission output and wheel speed on one plot.
• Plot engine torque, engine power, fuel rate and fuel consumption using subplots.
• Plot accelerator and brake pedal, gear command, vehicle desired and actual speed, vehicle distance using subplots.
• Plot the engine operating points on the engine fuel map.
• Plot motor speed, torque, motor input power using subplots.
• Plot pack voltage, current and SoC using subplots.
• Plot the motor operating points on the motor input power map, with the motor max motoring and generating torque curves.
• Write down appropriate brief comments on each of these plots, describing the vehicle behavior throughout the drive cycle.
• Generate the plots for both drive cycles.

Introduction –

A hybrid vehicle is one that uses two or more distinct types of power, such as Gasoline or diesel and batteries. Like submarines that use diesel when surfaced and batteries when submerged. Hybrid powertrains are designed to switch from one power source to another to maximize both fuel efficiency and energy efficiency. In hybrid electric vehicles, for instance, the electric motor is more efficient at producing torque, or turning power, while the combustion engine is better for maintaining high speed. Improved efficiency, lower emissions, and reduced running costs relative to non-hybrid vehicles are three primary benefits of hybridization.

Forward model of Hybrid vehicle:

The forward modelling is also known as cause-effect, engine-to-wheel or rear-to-front method. The direction of calculation is the same as the direction of positive power flow which is from engine to wheels.

A forward-facing vehicle model features a driver model that provides torque demand in the form of a desired ICE torque and brake torque, to meet the speed trace from a drive cycle. A basic driver model typically uses one or more Proportional- Integral (PI) controllers to achieve the torque demand, with reference to the desired speed trace. The torque produced by the ICE propagates through the transmission and final drive ratios, before ending up as torque applied at the wheels. This is then exerted to the vehicle mass via force on the tyre contact patch. The vehicle speed that results from the applied force is propagated back through the drivetrain, and returns to the ICE as angular velocity at the crankshaft. Brake torque is applied directly at the wheels.

This model can be used to compare the fuel efficiency of different vehicles, or to identify opportunities for improving the fuel efficiency of a particular vehicle. For example, if you are trying to improve the fuel efficiency of a vehicle, you could modify its design or driving behavior to reduce its energy consumption, and then use the forward energy-based fuel consumption model to estimate the resulting improvement in fuel efficiency.

Hybrid Powertrain Efficiency:

For normal steady state operating condition, hybridization gives an extra degree of freedom to allow the engine to operate at the peak efficiency point.

As transmissions give the degree of freedom to change the operating condition subject to same power input, hybridization gives extra degree of freedom to change the operating power if the engine keeping the same output power.

For Hybrid vehicle, the wheel power is supplied either by engine or motor through the transmission drivetrain,

The power for electric motor comes from the electric energy stored in the battery. The direction of power flow depends on whether energy is being drawn from or supplied to the battery by the electric drive unit.

Now, for pure hybrid electric vehicle, the vehicle battery cannot be charged by an external energy source. This is known as charge-sustaining strategy, where charge in battery energy for a given trip is essentially zero.

Fuel Consumption for a hybrid vehicle is calculated as,

As seen, an extra power unit gives the ability to dynamically change the power operating point of the engine

In some cases, the engine, the engine power output might be higher than desired and in some lower, based on which point is more efficient, subject to keeping the net battery energy change 0.

This means, the local instantaneous fuel consumption minimization might not necessarily result in the global fuel consumption minimization. This makes hybrid vehicle complex, requiring the information of the entire trip beforehand to produce the most efficient control.

MATLAB Script for Initialization:

%% Skill-Lync -> Hybrid Drives Development

% Project 2 - Conventional Vehicle Model

% By - Ganeshram D

The Simulink model for the convection vehicle model having 3 main subsystems 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, torque, brake and power 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 Proportional and integrator controls the error between desired output and actual speed through feedback controls

Controller Model:

The controller takes in all the current conditions like acceleration, break, engine speed, SOC of battery, Velocity and the clutch lockup values and then analyses it and provide output to each controllers to perform as desired.

The Controller block has 4 controller : Engine control unit, Transmission Control unit, Electric Motor Control unit and the Brake Control unit.

All the control units are supervised or controlled by a Supervisory control unit.

Two scop blocks were used here to monitor the Mode shifting and Engine torque required, Gear command and Bake Torque required.

All the output of this block is fed to the 'bus creator' which will be fed to the power train as control signal.

Supervisory Controller:

• The supervisory controller is modelled using State flow.
• The chart takes in Acceleration, Brake, Engine speed, SOC, Velocity, Clutch lockup values and depending on the conditions modelled inside the chart block it gives out the when all the engine should be kept on, what should be engine throttle and what should be the Electric motor throttle.
• The supervisory controller shifts between 4 modes: Stop, Start, Driving and Regeneration mode.
• It analyses and decide when to give the electric motor input and when to keep the engine on and off and when to do the regeneration while breaking.

Engine Control Unit &

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.

Idle Speed Controller:

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.

Transmission Control Block:

Powertrain Model:

Scope Results of Engine:

Transmission Model:

Differential Model:

Listing forces different applicable as per the scenario:

Tractive effort and resistance are the two main forces that oppose one another and determine the performance of roadway vehicles. Tractive effort is the force exerted against the roadway surface to allow a vehicle to move forward. Resistance encompasses all forces that push back and impede motion. Both of these are in units of force.

Rolling Resistance

Rolling resistance is caused by the interaction of tires with the roadway surface. Three main causes exist that create this resistance. The first is the rigidity of the tire and the roadway surface. The second is tire pressure and temperature. The third is vehicular operating speed.

Aerodynamic Resistance

Aerodynamic resistance is a force that is produced by turbulent air flow around the vehicle body. This turbulence is dependent on the shape of the vehicle, as well as the friction of air passing over the vehicle's surface. A small portion of this resistance comes from air flow through vehicle components, such as interior ventilation.

Grade Resistance

Grade resistance is the simplest form of resistance. It is the gravitational force acting on the vehicle. This force may not be exactly perpendicular to the roadway surface, especially in situations when a grade is present. Angle created between horizontal and the slope is θ. Several industrial vehicle manufacturers call the ability of the vehicle to run on a slope as Gradeability. Unit for gradeability is percent. Gradeability is calculated by multiplying tan θ with 100%.

Acceleration –

Inertia is force that inhibits the vehicle to reach a certain speed in a certain time. It is impossible for vehicle to achieve a certain speed from its idle position without acceleration. Therefore, to get to certain speed, the vehicle should be able to perform acceleration.

Power required at wheels is given by:

The power required at the wheels of a vehicle can be calculated using the formula P = Fv, where P is power, F is force, and v is velocity.

Post-Processing P1 Hybrid Vehicle in simulation model: