Cruise control - adjust sensitivity based on engine load

[Davidv]

Hey,

Just a few thoughts about cruise control. Firstly it's very cool and I love it

Over the last few weeks my speedo signal has been very jumpy, which obviously prevents the cruise control from working well.
I'm working to resolve it this weekend, but this had me thinking... It would be cool if you could set the cruise control to use engine RPM as the input rather than vehicle speed.
Obviously would only work in a manual transmission car but would be cool to have the option of it seeking a goal rpm.
Because the rpm signal is a lot more precise, and potentially a lot more stable too.

Also I've found that cruise control will work nicely at a given speed (say 100kph) but then be too jerky at lower speeds.
Thinking about this, I think it needs to scale its sensitivity based on engine load.
If I have the car up on engine stands and in 5th gear so car is doing 80kph or whatever with hardly any load applied, holding that speed.
If I turn on cruise control it will blip the throttle and it will rev up, then revs fall again and then a rev right up, it's quite jerky on settings that are otherwise fine while driving on the road.
I think this is part of why cruise control seems to work nicely on the flat or uphill, but becomes a bit jerky on downhill, as this is when there is the least amount of load on it and it overcompensates with its throttle plate movements when it actually only needs very very fine changes in throttle angle. Maybe it could have a scaling sensitivity based on throttle angle or something like that. I think this would help it make it drive better at all speeds, including downhill sections.

Also as previously mentioned it would be cool to have a button allocated to populate the target speed, for example have a button that sets cruise control to 55kph or 105kph or whatever.
Rather than having to pay attention to speedo to set a speed, when there's only likely to be 2-3 goal speeds that you're ever trying to set.

Edited August 13, 2016 by Davidv

[Scott]

Hi David,

Thanks for the suggestions and feedback. I'll pass them on to the engineering team. 

When you have low load (up on axle stands or downhill) if you adjust the PID values are you able to achieve satisfactory response? If yes, I'm guessing the response uphill or on the flat is not as good?

Scott

[Davidv]

I had my car up on axle stands for other reasons where I was time limited, so didnt test that unfortunately.
However I do remember that my car was more jerky on the fllat initially but fine uphill, on default PID settings.
Then it seemed to improve its behaviour everywhere once I'd toned down the settings. But is still a bit jerky on downhill.
This isnt a particularly scientific observation though so I'll get some better data.

Once I've fixed my speedo sensor, hopefully tonight or some time this week, I'll go out for a drive with some diffferent PID settings on the same uphill/downhill sections and report back.