CAN-bus data - Live if ignition turned off?
Discussion
I am using a CANM8 connect RPM interface to pick up an RPM signal from the CAN-bus system and convert to a Hz output that is compatible with our speed switch. Can anyone confirm if the Can-bus signal will continue to be live and produce this signal if the key is removed from the ignition but the engine is still running.
I install a shut down device on diesel engines that work in hazardous areas to control a runaway caused by hydrocarbons. The device is controlled using a module that picks up a speed signal from the alternators W terminal so works even if the ignition is off and the engine speed increasing. Modern automotive alternators are becoming more inaccessible so am looking for an alternative source for the speed signal but am concerned that the signal may be lost through CAN bus if key is removed?
Thanks
I install a shut down device on diesel engines that work in hazardous areas to control a runaway caused by hydrocarbons. The device is controlled using a module that picks up a speed signal from the alternators W terminal so works even if the ignition is off and the engine speed increasing. Modern automotive alternators are becoming more inaccessible so am looking for an alternative source for the speed signal but am concerned that the signal may be lost through CAN bus if key is removed?
Thanks
So if the CAN-bus network gives an rpm output when ignition is off will depend on the manufacturer and is not standard for all vehicles? I have not had much luck getting a response from the couple of manufacturers I have contacted and as far as I know there is no way of testing this scenario.
one, or more of the CAN buses will stay alive for a short while after keyoff. However, it would be extremely foolish to rely on this for a safety critical system. Usually, for passenger car ecu's they ecu will keep itself alive until it detects engine speed = 0, so if you key off whist doing 70 on the motorway systems stay live till you've stopped!!
a basic, cheap accelerometer bolted to the block would give you a valid "engine firing" indicator that can be easily after market fitted.
BTW, what does your system do? A run away due to oil or other contaminant in the combustion system cannot be stopped without removing the oxygen it is using to burn, either via choking (CO2 injected into intake) or blocking (intake completely blocked)
a basic, cheap accelerometer bolted to the block would give you a valid "engine firing" indicator that can be easily after market fitted.
BTW, what does your system do? A run away due to oil or other contaminant in the combustion system cannot be stopped without removing the oxygen it is using to burn, either via choking (CO2 injected into intake) or blocking (intake completely blocked)
Our system closes a butterfly valve in the engines air intake system to stop the engine in the event of a runaway caused by an external fuel source such as hydrocarbons produced an oil and gas sites.
The speed signal we currently use comes from the alternator which continues to produce an output if the ignition is off and engine turning, an alternative source for this speed signal needs to be 100% guaranteed so looking at the CAN-bus data to see if this is a possible option - but not if signal is lost when key removed
The speed signal we currently use comes from the alternator which continues to produce an output if the ignition is off and engine turning, an alternative source for this speed signal needs to be 100% guaranteed so looking at the CAN-bus data to see if this is a possible option - but not if signal is lost when key removed
Chalwyn1 said:
Our system closes a butterfly valve in the engines air intake system to stop the engine in the event of a runaway caused by an external fuel source such as hydrocarbons produced an oil and gas sites.
The speed signal we currently use comes from the alternator which continues to produce an output if the ignition is off and engine turning, an alternative source for this speed signal needs to be 100% guaranteed so looking at the CAN-bus data to see if this is a possible option - but not if signal is lost when key removed
Have you thought about piggybacking the signal from an ABS sensor? Or adding an ABS sensor if there isn't one?The speed signal we currently use comes from the alternator which continues to produce an output if the ignition is off and engine turning, an alternative source for this speed signal needs to be 100% guaranteed so looking at the CAN-bus data to see if this is a possible option - but not if signal is lost when key removed
You could easily take the ABS pulse signals and interpret them into speed, but would need to speed check/calibrate once installed.
ABS sensor -> Microcontroller -> Speedo or LCD readout. You'd just need to program the microcontroller to interpret the sensor signal (may need attenuation before input to microcontroller depending on specs), and include a few buttons to make it tunable.
You could easily do this with a Raspberry Pi Zero, I bet my 10 year old could do it. £4 for a Pi Zero.
ABS sensor only works if vehicle is moving, and they are now smart, and need to be "excited" by the ABS module, which won't be driving them when key;d off.
Same issue for crank sensor. Old cars used basic VR sensor that generates an output voltage proportional to target speed, but modern cars use smart hall effect sensors that can detect crank rotation direction as well as speed down to zero rpm so the engine position can be monitored to allow fast firing on restart (stop-start) With the ignition off, those won't work either.
As i said, i'd monitor block vibration, as the sensor can be cheap, robust, and should work across a wide range of engines as all you need to know is if combustion is taking place when it shouldn't be! ie, use a bolt on knock sensor (cheap & automotive rated/qualified) through an pre-amplifier (op-amp etc) with some gain, then a simple peak hold and/or threshold detector. Set the thresholds nice and low, because the sensor output will be very low (just thermal noise / emc pickup) when the engine is off.
Same issue for crank sensor. Old cars used basic VR sensor that generates an output voltage proportional to target speed, but modern cars use smart hall effect sensors that can detect crank rotation direction as well as speed down to zero rpm so the engine position can be monitored to allow fast firing on restart (stop-start) With the ignition off, those won't work either.
As i said, i'd monitor block vibration, as the sensor can be cheap, robust, and should work across a wide range of engines as all you need to know is if combustion is taking place when it shouldn't be! ie, use a bolt on knock sensor (cheap & automotive rated/qualified) through an pre-amplifier (op-amp etc) with some gain, then a simple peak hold and/or threshold detector. Set the thresholds nice and low, because the sensor output will be very low (just thermal noise / emc pickup) when the engine is off.
Thinking laterally, could you use any kind of optical sensor? e.g. to measure a white 'spot' left on the auxiliary belt or similar.
Otherwise, what about reading from both CANbus and the nominal system voltage? Is it the case that if the ignition is off but the engine is still running on the hydrocarbons that the alternator would continue to generate power and thus the electrical system would be at a voltage of 13.8v, rather than ~12.6v of a fully charged lead acid battery? If this is reliably detectable, there's your solution: if voltage over 12.6 (or so) and canbus signal interrupted, shut down.
Otherwise, what about reading from both CANbus and the nominal system voltage? Is it the case that if the ignition is off but the engine is still running on the hydrocarbons that the alternator would continue to generate power and thus the electrical system would be at a voltage of 13.8v, rather than ~12.6v of a fully charged lead acid battery? If this is reliably detectable, there's your solution: if voltage over 12.6 (or so) and canbus signal interrupted, shut down.
Why bother with the CAN?
Engine running + ignition off = emergency situation.
Ignition signal can be taken from many locations - but actually the CAN is about the last place I would take it from. (Complexity / reliability / unforseen circumstances etc)
To answer the question, the CAN system is live for a fair time (5 - 10minutes) after ignition off, and will 'wake up' if any of the security features are activated (eg, doors opening, windows changing state, remote operating, door handle operating etc etc).
Engine running + ignition off = emergency situation.
Ignition signal can be taken from many locations - but actually the CAN is about the last place I would take it from. (Complexity / reliability / unforseen circumstances etc)
To answer the question, the CAN system is live for a fair time (5 - 10minutes) after ignition off, and will 'wake up' if any of the security features are activated (eg, doors opening, windows changing state, remote operating, door handle operating etc etc).
Bedini in yorkshire did quite a bit of work interpreting the output of a generic petrol knock sensor fitted to a wide range of diesel engines, when they were attempting to develop their diesel lpg additive kits, they might be a source of info, they made a few revisions to the input signal conditioning side of their custom ecu along the way, but i don't think the overall project ever amounted to much.
Max_Torque said:
optical sensor underbonnet, in industrial environment, er, i don't think so! Way too unreliable.
And modern "smart" alternators don't charge or put out a signal when powered down, hence the need to change from the current alternator based sensing.
Damn and double damn! Ah well And modern "smart" alternators don't charge or put out a signal when powered down, hence the need to change from the current alternator based sensing.
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