Project 1

Aim: To develop a vehicle model in Simulink including Engine, Transmission, Differential, Wheels, Vehicle dynamics and run-on different drive cycles like udds, hwfet, ftp or wltp etc.

Goal: The main goal of this project is to get familiar with the modelling process, writing scripts in MATLAB, modelling in Simulink, analysing data and generating plots.

Objectives:

• Tabulate the fuel economy numbers (kmpl) for UDDS and HWFET cycle. This forms the baseline numbers for comparing with the future hybrid version
• 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.
• Writing down appropriate brief comments on each of these plots, describing the vehicle behaviour throughout the drive cycle.
• Generate the plots for both drive cycles.

Conventional Vehicle - conventional vehicles use an internal combustion engine fuelled by gasoline or diesel to power the wheels. Electricity is used for some accessories, but is not used to move the vehicle.

Basically, conventional vehicle consists of following subsystems:

• Controller unit - Engine control, Transmission control, Brake control unit.
• Powertrain - Engine, Transmission, Differential, Wheels and vehicle dynamics.
• Driver unit.

MATLAB script:

% Project 1 - Conventional Vehicle Model

%% Initialization File

% Initialization file for loading the variables for the Conventional vehicle simulation model

%% Vehicle Parameters

M = 1500; % Vehicle weight [kg]

Cr = 0.015; % Rolling resistance coefficient

Rw = 0.35; % Rolling radius [m]

Cd = 0.33; % Drag coefficient

Af = 2; % Frontal area [m2]

rhoa = 1.225; % Air density [kg/m3]

Vwind = 0; % Wind velocity [kmph]

g = 9.81; % Gravitational acceleration [m/s2]

theta = 0; % Slope [deg]

myu_road_tire = 1; % Coefficient of friction between tire - road interface

%% Powertrain Parameters

FDR = 3.73; % Final Drive Ratio / Diff Ratio

DiffEff = 0.99; % Differential efficiency (assumed independent of operating conditions)

NumGear = 4; % Number of gears in transmission

TransGear = [1:NumGear]; % Transmission Gears

TransRatio = [3.06, 1.62, 1, 0.7]; % Corresponding Transmission ratios

TransEff = 0.90; % Transmission efficiency (assumed independent of operating conditions)

TC_SR = [0, .5, .6, .7, .8, .87, .92, .94, .96, .97, 1]; % Torque Converter Speed Ratio (Matlab default) -> TurbSpd/PumpSpd

TC_TR = [2.232, 1.5462, 1.4058, 1.2746, 1.1528, 1.0732, 1.0192, 1, 1, 1, 1]; % Torque Converter Torque Ratio (Matlab default) -> TurbTrq/PumpTrq

TC_Cf = 1e-4 * [.72558, .66322, .63463, .59042, .51331, .4144, .29287, .22444, .12186, .04386, 0]; % Torque Converter Capacity Factor

%(Matlab default) -> PumpTrq/PumpSpd^2 [Nm/rpm^2]

load Vehicle_Data/Engine_data_1_9L_Saturn_95kW

load Vehicle_Data/Trans_Shift_map

%% Driver Parameters

Kp = 10; % P gain for driver PI model

Ki = 1; % I gain for driver PI model

Drive_Cycle_Select = 2; % Drive cycle selection

% Drive cycle values in m/s

if Drive_Cycle_Select == 1

load DriveCycles/UDDS;

elseif Drive_Cycle_Select == 2

load DriveCycles/HWFET;

elseif Drive_Cycle_Select == 3

load DriveCycles/FTP;

elseif Drive_Cycle_Select == 4

load DriveCycles/US06;

elseif Drive_Cycle_Select == 5

load DriveCycles/NEDC;

elseif Drive_Cycle_Select == 6

load DriveCycles/WLTP;

end

time_end = cyc_time(end);

vel_end = cyc_vel(end);

vehicle model:

Driver model:

Controller unit:

Powertrain unit:

Engine unit:

Now, the Vehicle dynamics block is developed using the equations:

• Equations for aerodynamic drag, rolling resistance, and gradient are created and summed up to get the road load
• Road load is subtracted from the tractive force to get the force
• This force is then divided by the mass to get the acceleration component
• Integrator is used to integrate the acceleration and get the velocity component
• Road load and velocity are multiplied to get the power required for the vehicle
• Power is then multiplied by the total time to get the energy required
• All the blocks of velocity, acceleration, road load, the power required, and energy required are attached to the 'scope' block to see the output variations with respect to the time.

Vehicle dynamics block:

Transmission:

Wheel:

Tractive force on wheels:

After running the model for 2000seconds, we get the following output:

MATLAB file-2:

% Project 1 - Conventional Vehicle Model

%% Post-Processing File

% File for post-processing the Conventional vehicle simulation model data

Time = out.tout;

Acc_Pdl = out.Acc_Pdl; % Accelerator pedal [%]

Brk_Pdl = out.Brk_Pdl; % Brake pedal [%]

Gear_Cmd = out.Gear_Cmd; % Transmission gear

Trans_In_Spd = out.Trans_In_Spd*30/pi; % Transmission input speed [rpm]

Trans_Out_Spd = out.Trans_Out_Spd*30/pi;% Transmission output speed [rpm]

Eng_Spd = out.Eng_Spd*30/pi; % Engine speed [rpm]

Eng_Fuel_Rt= out.Eng_Fuel_Rate;

Eng_Fuel_Consump = out.Eng_Fuel_Consumption; % Engine fuel consumption [g]

Veh_Dist = out.Veh_Dist/1000; % Distance traveled by vehicle [km]

Veh_Spd = out.Veh_Spd*18/5; % Vehicle speed [kmph]

Eng_Speed = Eng_Spd*30/pi;

Veh_Distance = Veh_Dist/1000;

Wheel_Spd=out.Wheel_Speed;

Veh_Speed = Veh_Spd*18/5;

% Eng_Spd=0.1;

Eng_Trq= out.Eng_Trq1;

%% Data Analysis

Eng_Pwr = Eng_Spd*pi/30*Eng_Trq/1000; % Engine brake power [kW]

rho_petrol = 0.7197; % Density of petrol [kg/L]

kmpl = Veh_Dist(end)/(Eng_Fuel_Consump(end)/1000/rho_petrol); % Fuel economy [kmpl]

%% Plotting vehicle characteristics time trace

figure(1)

subplot(3,1,1)

hold on

grid on

plot(Eng_Speed, 'linewidth', 1, 'Color', 'red');

xlabel('time (s)')

ylabel('Engine Speed [rpm]')

xlim([0, Time(end)]);

subplot(3,1,2)

hold on

grid on

plot(Time, Trans_In_Spd, 'linewidth', 1, 'Color', 'G');

plot(Time,Trans_Out_Spd, 'linewidth', 1, 'Color', 'Red');

xlim([0, Time(end)]);

legend('Transmission input','transmission output')

xlabel('Time [s]');

ylabel('Trans Speed');

subplot(3,1,3)

hold on

grid on

plot(Wheel_Spd, 'linewidth', 1, 'Color', 'red');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Wheel Speed');

%% Plotting Engine an Fuel characteristics time trace

figure(2)

subplot(4,1,1)

hold on

grid on

plot(Eng_Trq, 'linewidth', 1, 'Color', 'b');

ylabel('Engine Torque')

xlim([0, Time(end)]);

subplot(4,1,2)

hold on

grid on

plot(Eng_Pwr, 'linewidth', 1, 'Color', 'black');

ylabel('Engine power')

subplot(4,1,3)

hold on

grid on

plot(Eng_Fuel_Consump, 'linewidth', 1, 'Color','Red');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Fuel Consumption');

subplot(4,1,4)

hold on

grid on

plot(Eng_Fuel_Rt, 'linewidth', 1, 'Color','Red');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Fuel Rate');

%% Plotting vehicle characteristics time trace

figure(3)

subplot(4,1,1)

hold on

grid on

plot(Time, Acc_Pdl, 'linewidth', 1, 'Color', 'black');

plot(Time, Brk_Pdl, 'linewidth', 1, 'Color', 'red');

ylabel('Pedal [%]')

xlim([0, Time(end)]);

legend('Accel','Brake');

subplot(4,1,2)

hold on

grid on

plot(Time, Gear_Cmd, 'linewidth', 1, 'Color', 'black');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Gear');

subplot(4,1,3)

hold on

grid on

plot(Veh_Spd, 'linewidth', 1, 'Color', 'black');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Vehicle speed');

subplot(4,1,4)

hold on

grid on

plot(Veh_Dist, 'linewidth', 1, 'Color', 'red');

xlim([0, Time(end)]);

xlabel('Time [s]');

ylabel('Vehicle Distance');

%% Plotting engine operating points on engine fuel map

figure(4)

title('Engine Operating Points')

hold on

grid on

title('Engine Operating Points','fontsize',12);

p1=plot(Eng_map_spd*30/pi,Eng_max_trq,'linewidth',2,'color','r');

p2=line([Eng_map_spd(end)*30/pi Eng_map_spd(end)*30/pi],[0 Eng_max_trq(end)]);

set(p2,'linewidth',1,'linestyle','--','color','k');

p3=line([Eng_map_spd(1)*30/pi Eng_map_spd(1)*30/pi],[0 Eng_max_trq(1)]);

set(p3,'linewidth',1,'linestyle','--','color','k');

[c,h] = contour(Eng_map_spd'*30/pi,Eng_map_trq,Eng_fuel_map');

clabel(c,h);

xlabel('Engine Speed [rpm]');

ylabel('Engine Torque [Nm]');

title('Engine Fuel Consumption Map [g/s]');

p4 = plot(Eng_Spd,Eng_Trq,'color','k');

legend([p1 p4],{'Max Curve','Operating Points'});

axis([Eng_map_spd(1)*30/pi Eng_map_spd(end)*30/pi 0 Eng_map_trq(end)]);

Fuel Economy Number

For UDDS cycle:

For HWFET cycle:

As we see, the fuel economy is high in HWFET compared to UDDS, it is because, in urban driving, the vehicle encounters more traffic and it has to stop for fewer distances and it consumes more fuel at the starting. In HWFET, the vehicle encounters no traffic and it moves without use of too much braking, so it will have more fuel economy number.

Outputs for UDDS cycle

Plot of Engine speed, Transmission In-Out Speed, Wheel Speed:

Plot of Engine torque, Engine Power, Fuel Rate, Fuel Consumption:

Engine fuel consumption map:

Plot for acceleration, brake pedal, gear commands, vehicle speed, vehicle distance:

Observation:

• Vehicle consumed more power in the UDDS compared to HWFET cycle because it has too many starts and stops compared to HWFET.
• When starting from the initial condition vehicle requires more power Engine torque is also high in UDDS because while starting from rest, the vehicle requires more torque to overcome the static friction.
• The fuel rate is high in HWFET because the vehicle will be in continuous movement, it consumes more fuel But, fuel economy will be high in HWFET compared to UDDS because there are many stops and starts in UDDS and more fuel is consumed when the vehicle is in an idle position.
• For UDDS, the accelerator and the brake pedal have more fluctuations because of frequent starts and stops. But in HWFET, the brake pedal fluctuations are almost near to the zero line as there will be no frequent stops.
• UDDS cycle mostly runs on 1st, 2nd gears, and uses 3rd, 4th gears very rarely as it does not achieve high speeds in that traffic. In the HWFET cycle, the vehicle mostly runs on 3rd, 4th gears as it will be moving at high speeds. It uses 1st, 2^nd gears very frequently when braking is required.