%% ME 2016 Section
%% Fall 2007
%%
%% AUTHOR:  Chris Paredis
%%
%% PURPOSE: plot the 5 power curves as a function of car speed,
%%          one for each of the five gear ratios in a transmission
%%
%% This script loads the engine model from an Excel file, computes the
%% engine speed from the car speed for each of the five gears in an
%% automatic transmission, and plots the engine power relative to the car
%% speed
%%
%% ASSUMPTIONS: 
%%         - the torque converter can be ignored
%%         - no friction losses anywhere
%%         - no tire slip


%%
%% define the problem
%%

% to be on the safe side, clear all the variables and close all figures
clear all;
close all;

% define the drivetrain parameters
wheel_radius = 0.332; % in [m]
gear_ratios = [2.77 1.54 1 0.69];
differential_ratio = 4.266;

% conversion constant -- for convenience
ms_to_kmh = 3.6;

% create the engine speed vector across the entire range of speeds
engine_speed = (500:6500)*pi/30; % in [rad/s]

%%
%% solve the problem
%%

% for each engine speed, compute the corresponding power in [W]
% power = speed * torque 
engine_power = engine_speed .* engine_model_CJP(engine_speed);

% compute the total conversion from engine speed in rad/s to car velocity
% in km/h
total_ratios = ms_to_kmh * wheel_radius ./ gear_ratios / differential_ratio;

% compute the car velocities -- one row for each gear
% note: rather than using a for loop, this can be done using an "outer"
% matrix product.  A for-loop over the different gear ratios is an
% acceptable solution here also 
car_velocity = total_ratios' * engine_speed;

%%
%% interpret the results
%%

figure(1)
plot(engine_speed*30/pi, engine_power/1000);
grid on;
xlabel('Engine Speed [RPM]');
ylabel('Engine Power [kW]');
title('Engine power as a function of engine speed (ME 2016 - Chris Paredis)');

figure(2)
plot(car_velocity, engine_power/1000);
grid on;
xlabel('Car Speed [km/h]');
ylabel('Engine Power [kW]');
title('Car power as a function of car speed (ME 2016 - Chris Paredis)');
legend('1st gear','2nd gear','3rd gear','4th gear','Location','SouthEast');