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'''Knock Sensing''' BMW M102/M106 engines (similar to M30 + turbo) are factory equipped with two knock sensors. I'm trying to utilize them... - Unfortunately at the moment there's only support for one sensor at-a-time in firmware. I'd definitely like to utilize both of them in the future, but for now I need to stick with the second one which is located between cyl. 5-6. It is the well-known place of knock, more than the first sensor location, since cyl.6 is the hottest one. '''PLAN''' '''How to set up the characteristic knock frequency?''' Bore is 92mm, so r=46mm. '''1. Theory''' The expected knocking frequency is around 900/(pi*r) = 900/(3.14*46) = 6.2kHz See TPIC8101 datasheet (using 4 MHz crystal; for reference, 0x29 = decimal 41 = appr 7 kHz) '''2. Experience''' * record the knock-sensor output with notebook soundcard while knock sensor is connected (with a 50k series resistor) to the microphone input of a laptop. * recommended: '''cling the block with a wrench''' when engine not running. Record the sound from the knock-sensor with your notebook sound input '''counterrecommended:''' * adjust the ignition advance (usually upto 36 degrees in 4..5 steps) at idle until slight knock happens. * This is very hard without WideBand closed-loop EGO control, because the engine will want to stop before any knocking, and adjusting the fuel manually at the same time ignadv is adjusted is hard. * note that the MAP should be low, 25..40 kPa (max 55kPa), otherwise the engine is endangered. RPM also low (<1500 RPM). * play back the sound after the engine stopped. You'll be surprised how well the ping sound can be heard without the loud exhaust sounds. * just read the characteristic frequency from the FFT diagram. '''Config''' From TPIC8101 datasheet config value 39 stands for 6.37kHz, which is probably close to current typical knock freqency. * from global.h: uint8_t knock_conf; // knock, config. bit0 o FF means knock2... ?? o FD means knock1... (DEFAULT!) # Overall System Settings # Knock selection knock_conf = FF # enable knock-detection, will use Channel2! knock_sampling_window = e2 # ??? # Use knock sensing in this RPM range # FF for both means no knock sensing/control??? knock_minrpm = 05 # FF=No minimum RPM. 0x01=100rpm knock_maxrpm = FF # FF=No maximum RPM knock1_frequency = 27 # dec 39, 6.37kHz knock1_gain = 40 # ??? knock1_integrator = 14 # ??? knock2_frequency = 27 # dec 39, 6.37kHz knock2_gain = 40 # ??? knock2_integrator = 14 # ??? # Trigger level knock_threshold = 50 # ??? knock_noise_scale = 10 # ??? # Ignition effects # # Knock getting louder knock_max_retard = 50 # 20 degreees, 0x01=0.25 crank degrees. knock_default_retard = 10 # *0.25 crank degrees. knock_retard_step = 08 # 3.2 degrees knock_retard_delay = 10 # 0x01=15ms Retard delay. # Knock getting softer knock_advance_step = 02 # *0.25 crank degrees. knock_advance_delay = 10 # 0x01=15ms I'm '''totally lost''' with these config values. Couldn't find any usable info for those ??? values. Any idea? See lcd_display.c for the displayed knock values. Most importantly: lcd_knock_diff ("d:...") and you'll see that increasing gain increases this. We like to set gain so above d:100 means knock. There are no sharp limits here.
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