void CARENGINEINFO::SetTorqueCurve(
const btScalar redline,
const std::vector<std::pair<btScalar, btScalar> > & torque)
{
torque_curve.Clear();
//this value accounts for the fact that the torque curves are usually measured
// on a dyno, but we're interested in the actual crankshaft power
const btScalar dyno_correction_factor = 1.0;//1.14;
assert(torque.size() > 1);
//ensure we have a smooth curve down to 0 RPM
if (torque[0].first != 0) torque_curve.AddPoint(0,0);
for (std::vector<std::pair<btScalar, btScalar> >::const_iterator i = torque.begin(); i != torque.end(); ++i)
{
torque_curve.AddPoint(i->first, i->second * dyno_correction_factor);
}
//ensure we have a smooth curve for over-revs
torque_curve.AddPoint(torque[torque.size()-1].first + 10000, 0);
//write out a debug torque curve file
/*std::ofstream f("out.dat");
for (btScalar i = 0; i < curve[curve.size()-1].first+1000; i+= 20) f << i << " " << torque_curve.Interpolate(i) << std::endl;*/
//for (unsigned int i = 0; i < curve.size(); i++) f << curve[i].first << " " << curve[i].second << std::endl;
//calculate engine friction
btScalar max_power_angvel = redline*3.14153/30.0;
btScalar max_power = torque_curve.Interpolate(redline) * max_power_angvel;
friction = max_power / (max_power_angvel*max_power_angvel*max_power_angvel);
//calculate idle throttle position
for (idle = 0; idle < 1.0; idle += 0.01)
{
if (GetTorque(idle, start_rpm) > -GetFrictionTorque(start_rpm*3.141593/30.0, 1.0, idle))
{
//std::cout << "Found idle throttle: " << idle << ", " << GetTorqueCurve(idle, start_rpm) << ", " << friction_torque << std::endl;
break;
}
}
}
bool CarEngineInfo::Load(const PTree & cfg, std::ostream & error_output)
{
std::vector<btScalar> pos(3, 0.0f);
if (!cfg.get("displacement", displacement, error_output)) return false;
if (!cfg.get("max-power", maxpower, error_output)) return false;
if (!cfg.get("peak-engine-rpm", redline, error_output)) return false;
if (!cfg.get("rpm-limit", rpm_limit, error_output)) return false;
if (!cfg.get("inertia", inertia, error_output)) return false;
if (!cfg.get("start-rpm", start_rpm, error_output)) return false;
if (!cfg.get("stall-rpm", stall_rpm, error_output)) return false;
if (!cfg.get("position", pos, error_output)) return false;
if (!cfg.get("mass", mass, error_output)) return false;
position.setValue(pos[0], pos[1], pos[2]);
// fuel consumption
btScalar fuel_heating_value = 4.5E7; // Ws/kg
btScalar engine_efficiency = 0.35;
cfg.get("fuel-heating-value", fuel_heating_value);
cfg.get("efficiency", engine_efficiency);
fuel_rate = 1 / (engine_efficiency * fuel_heating_value);
// nos parameters
cfg.get("nos-mass", nos_mass);
cfg.get("nos-boost", nos_boost);
cfg.get("nos-ratio", nos_fuel_ratio);
// friction (Heywood 1988 tfmep)
friction[0] = btScalar(97000 / (4 * M_PI)) * displacement;
friction[1] = btScalar(15000 / (4 * M_PI)) * displacement;
friction[2] = btScalar(5000 / (4 * M_PI)) * displacement;
std::vector<btScalar> f(3, 0);
if (cfg.get("torque-friction", f))
{
friction[0] = f[0];
friction[1] = f[1];
friction[2] = f[2];
}
// torque
int curve_num = 0;
std::vector<btScalar> torque_point(2);
std::string torque_str("torque-curve-00");
std::vector<std::pair<btScalar, btScalar> > torque;
while (cfg.get(torque_str, torque_point))
{
torque.push_back(std::pair<btScalar, btScalar>(torque_point[0], torque_point[1]));
curve_num++;
std::ostringstream s;
s << "torque-curve-";
s.width(2);
s.fill('0');
s << curve_num;
torque_str = s.str();
}
if (torque.size() <= 1)
{
error_output << "You must define at least 2 torque curve points." << std::endl;
return false;
}
// set torque curve
torque_curve.Clear();
if (torque[0].first > stall_rpm)
{
btScalar dx = torque[1].first - torque[0].first;
btScalar dy = torque[1].second - torque[0].second;
btScalar stall_torque = dy / dx * (stall_rpm - torque[0].first) + torque[0].second;
torque_curve.AddPoint(stall_rpm, stall_torque);
error_output << "Torque curve begins above stall rpm.\n"
<< "Extrapolating to " << stall_rpm << ", " << stall_torque << std::endl;
}
for (const auto & tp : torque)
{
torque_curve.AddPoint(tp.first, tp.second);
}
if (torque[torque.size() - 1].first < rpm_limit)
{
btScalar r = torque[torque.size() - 1].first + 10000.0f;
btScalar t = 0.0f;
torque_curve.AddPoint(r , t);
error_output << "Torque curve ends below rpm limit.\n"
<< "Extrapolating to " << r << ", " << t << std::endl;
}
// calculate idle throttle position
for (idle_throttle = 0.0f; idle_throttle < 1.0f; idle_throttle += 0.01f)
{
if (GetTorque(idle_throttle, start_rpm) > -GetFrictionTorque(idle_throttle, start_rpm))
break;
}
// calculate idle throttle slope
btScalar stall_throttle;
for (stall_throttle = idle_throttle; stall_throttle < 1.0f; stall_throttle += 0.01f)
{
if (GetTorque(stall_throttle, stall_rpm) > -GetFrictionTorque(stall_throttle, stall_rpm))
break;
}
idle_throttle_slope = 1.5f * (idle_throttle - stall_throttle) / (start_rpm - stall_rpm);
return true;
}
