What integral gain does
Cruise control on a Haltech Nexus is a PID controller: it looks at the gap between your set speed and actual speed, and adjusts throttle to close it. Each of the three terms handles a different part of the job. Proportional gain reacts to how big the error is right now. Derivative gain reacts to how fast it's changing. Integral gain reacts to how long the error has been there.
The longer the car sits off target, the more the integral term builds, and the more throttle it adds (or removes). That's what eliminates the small steady error proportional alone leaves behind, like the car holding a couple of mph under set speed on a gentle uphill. Without enough integral, the car never quite gets there.
How to tune it
- Higher integral gain makes the throttle respond faster to a lingering error.
- Too high and it overshoots the set speed, then undershoots, and the car surges.
- Too low and it takes a long time to reach set speed, or sits just below it on hills.
We start low, get proportional working, then raise integral in small steps until the car settles on target in a reasonable time without overshooting. Test on flat road and on a grade.
The table values depend on the speed units chosen in Preferences. If you switch between mph and km/h, recheck your gains.
More in cruise control and our general PID tuning guide.
