Car engine

Fri 21 March 2014
By Bram


I like car racing simulations. I spent a lot of time playing Gran Turismo Prologue on my PS3 years ago. So I thought it would be time for me to try making my own racing game. After coding a Hover Bike and all sorts of Heavy Machinery that should be easy, not?

Well, it turns out to be a lot more difficult than I expected. Just some high school physics will not cut it. The image above is my prototype in action. I'm pleased with the suspension, the steering and the traction models. Most of which you get for free by using the OpenDE physics engine. But how can I create a simulation model for the engine?

OpenDE lets me speed up/dn the wheels by simply specifying:

  • Desired wheel velocity.
  • Torque available to achieve this wheel velocity.
  • Mass of the wheel.
  • Moment of inertia of the wheel.

So how do I go about this? How do I determine what speed the wheel wants to turn, and how much torque is available for this?

In real life, things are more complicated. The engine primarily speeds up the fly wheel, not the car wheels. Depending on the state of the clutch, the gearbox, it will result in wheel acceleration. Do I need to model a flywheel in my simulation? And somehow transfer kinetic energy between flywheel and car wheels depending on clutch and gearbox? How does the accelerator fit in here? And what about the torque curve of the engine, and the rpm of the engine? I am beginning to think a few simple equations are not going to suffice.

How does the accelerator affect the engine RPM? Well, that depends on engine load. How do I calculate that? It seems that there is also a circular dependency in here somewhere:

With an engaged clutch, you can only increase wheel velocity if you increase engine RPM. But engine RPM can only go up if wheel velocity goes up. I think I need to study up on what is actually engine load, and how I can measure it in my sim.