IAC Firmware changes
PWM switched ground to pin1 and pin3 moves the valve to opposite directions, if pin2 has stable 12V+ supply. Connecting pin1 to GND closes the valve.
Control relatively simple. Some changes and things to-check required in idle_solenoid() :
- 2 channels must be used instead of config.iac_sol_channel. However, I don't see a reason to add a config variable to make them independent. Eg. config.iac_sol_channel and config.iac_sol_channel+16 would work well (that means if mdh02/mdh82 is used for one solenoid, mdh12/mdh92 can be used for the other).
- if one solenoid is powered, the other must be unpowered. This can be remembered or done dumbly every time (SRAM/cycles tradeoff).
- iac_conf can be cleaned-up (while merging the unipolar-iac support) as on GenBoard/UnderDevelopment/FirmWare/PowerRelated to make space for the new bit that activates BAC-mode.
Changed the end of idle_solenoid() in iac.c so it sets 2 output channels instead of one: \n
cli();
digitalout(config.iac_sol_channel, output);
sei_nop_cli();
digitalout(config.iac_sol_channel + 0x10, output ^ 0x80 );
sei();
config.iac_sol_channel has been set to 0x36 (stepper channel A)
This way 0x46 (stepper channel B) is inverted. Connections are according to GenBoard/Manual/DigitalOut/Table.
IAC control is somewhat working this way, I can use mdh/mdi commands and idle changes. For warm engine value around mdi70 seems a good approximation for 900 rpm. I've found that small changes to value doesn't reflect in rpm immediately (or at all). Big changes (like mdiff :) are noticeable promptly.
Idle controlled by GenBoard, but the idle controller (reference positions, ign-adv based control, iac-PID) is not yet tuned. Kindof instable now, see logs:
- [config.txt]
- [tables.txt]
- [ Config and data saved in MegaSquirt]
- [Datalog (XLS) from megasquirt. I've made a chart in it also]
Definitely relative heavy actuator couldn't cope with such a high PWMming (2kHz), decreasing control frequency was reasonable. MembersPage/BengtR measured frequency from couple of 'similar' (but different part ie. Bosch part number vice) valves, they all were controlled with 50 to 150 hz signals.
I've modified the firmware to call the idle solenoid code with 100Hz frequency (20 times slower, than original solenoid freq in GenBoard). It seems to be working now, changes like 1-2 (hex) iac values reflected quickly in rpm.
- I've got strange behavior which might be firmware related (IAC setting). Every time I switch the ignition ON idle setting is OK according to iac_*_start_pos. Right before cranking it's jumping to 100% and then (while cranking) jumps back to the preset value. After it jumps again to 100% and slowly falling back to the right value. (Takes seconds, and engine is revving up to 2200 rpm). Engine status bits are suspicious to me but don't see the reason why this 100% IacDC occurs. Please check my [XLS] logfile if interested.
As you might see on the picture, I started the engine, where 100% IAC happened, then falled back to "normal" levels, then fixed the setting to 70(?) manually, and at the end set it to 0.
I think that IAC behaviour (description above) happens quite normally when PID target rpm is not reached. However when cranking and immediately after the engine has started this causes bit high rpm. Note - that this is somewhat the kind of behaviour that original ECU's (Bosch, Weber, Siemens etc.) also has.
Adjusting gain and/or pid integrator values, rpm falling time to regulated idle rpm could be adjusted.
- It seemed to me that this is not related to PID. According to the XLS above, I have iac value series like(in %): 40, 40, 40....40, 100, 100, 40, 40, 40, 100, 100, 99, 98, 97.. 42, 41, 40, 40....
- I've got a new idea about fluctuating idle, it might be related to the fact that I use 6 banks alternating inj config but no cam sync. Maybe it'd be better to fire them all at once while no camsync?
Using similar IAC valve? Check my firmware!
- Download my modified [iac.c] using 2 channels with inverted signals as mentioned above
- Download modified [vems.c] which is calling idle_solenoid() function at a 10ms interval
- or Download my compiled firmware [vems.hex] to burn.
All above is based on firmware v14rc1. Be careful of using the very next channel related to config.iac_sol_channel since it is hardcoded to produce my inverted IAC signal!