function force = engine_force_CJP (vel_ms, gear)

%ENGINE_FORCE Determines forward force provided by the engine
%   FORCE = ENGINE_FORCE (VEL_MS, GEAR) computes the total forward force
%   provided by the engine when driving at a velocity VEL_MS in gear GEAR.
%
%   Inputs:
%      VEL_MS: a vector of car velocities expressed in [m/s]
%      GEAR:   the gear number; i.e., 1, 2, 3, or 4
%
%   Outputs:
%      FORCE: a vector of resistance forces expressed in [N].  FORCE has
%      the same dimensions as VEL_MS.
%
%   Assumptions: 
%         - the car is driving in a straight line -- differential is
%         modeled as a simple gear reduction
%         - there are no loses in the drivetrain (e.g., friction)
%         - the tires roll without slipping
%         - the car characteristics correspond approximately to those of a
%           Ford Taurus

%%
%% ME 2016
%% Fall 2007
%%
%% AUTHOR:  Chris Paredis
%%

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

% compute the engine speed and corresponding torque
engine_speed = vel_ms/wheel_radius*differential_ratio*gear_ratios(gear);
engine_torque = engine_model_CJP(engine_speed);

% convert torque back to forward force on car body
force = engine_torque*gear_ratios(gear)*differential_ratio/wheel_radius;

return;