Hiluxforever
SILVER Star
It's pretty annoying as Instrumentation Engineer. Like I just want to nudge the PID loop a little.The problem is the algorithms on regular cruise are predictive and can't factor in hills and so forth properly. It basically sets a range that if you go under desired speed by X amount then you will add torque to achieve set speed, but on the other hand overspeed can't do anything on a downhill without active braking. Some other manufacturers allow a lot more underspeed which results in even more overspeed. The feedback loop isn't the best and it depends if they are looking at output shaft speed or wheel speed. Wheel speed is more accurate but older generations are not torque secure sensors meaning they can't use it per CARB regulations. And most newer vehicles with radar cruise or adaptive will brake for you if you do overspeed which results in changing the brakes more often. It's a complicated system lol. I drive a lot of various vehicles for my job and can attest that the Lexus is one of the better systems for a basic non-adaptive cruise control. It does what it is supposed to, but some people prefer more gradual control rather than reactive. My prior vehicle had a slow to react system and imo it was worse than a more reactive one. Both end up overspeed, just one doesn't downshift when you request it. Likely you could improve a lot of this with trans schedule changes since your cruise control is just a torque request PID and the reason it will or won't downshift is if you request enough torque. Just need to update the thresholds to get a smoother performance. They are set high for each gear for better fuel economy so you don't shift as frequently meaning you need to dig deeper into the pedal to get a downshift.
