Vamos Automotive Simulator git

//  A clutch for the drivetrain.
//
//  Copyright (C) 2001-2019 Sam Varner
//
//  This file is part of Vamos Automotive Simulator.
//
//  Vamos is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  Vamos is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with Vamos.  If not, see <http://www.gnu.org/licenses/>.

#include "Clutch.hpp"

#include <cmath>

namespace
{
    /// The locking threshold.  The clutch is fully engaged when engine speed transmission
    /// speeds < m_threshold * normal force.
    const double m_threshold = 0.01;
} // namespace

Vamos_Body::Clutch::Clutch(double sliding, double radius, double area, double max_pressure)
    : m_sliding_friction(sliding),
      m_radius(radius),
      m_area(area),
      m_max_pressure(max_pressure)
{
}

double Vamos_Body::Clutch::drag(double engine_speed, double drive_speed)
{
    double normal = m_pressure * m_area;
    if (std::abs(engine_speed - drive_speed) < m_threshold * normal)
    {
        // Setting m_engaged to true will cause the drivetrain to ignore the return value
        // and act as though the clutch is fully engaged.
        m_engaged = true;
        return 0.0;
    }
    double force = m_sliding_friction * normal * (engine_speed > drive_speed ? 1.0 : -1.0);
    // The pressure is considered to be concentrated at m_radius from the center.
    return force * m_radius;
}

void Vamos_Body::Clutch::position(double factor)
{
    m_engaged = factor > 0.99;
    m_pressure = (m_engaged ? 1.0 : factor) * m_max_pressure;
}