Automotive "Engine fuel consumption map" without the torque possible?

AI Thread Summary
The discussion revolves around the challenge of creating an engine fuel consumption map without direct torque measurements, as the OBD PID 98 outputs a constant value of -125. Participants suggest that the OBD Calculated Engine Load Value (PID 4) could be used to estimate torque, but the exact formula linking this value to torque remains elusive. It's noted that while engine torque can be derived from engine power and RPM, the current power is not measured during tests, complicating the calculations. Estimations of power based on vehicle speed, incline, and air density are proposed, but they require experimental validation. The correlation between calculated load values and actual torque appears to be weak, raising concerns about the reliability of using these values for accurate mapping.
joker1319
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Hello,
I am currently facing a problem.
I'm on a project and trying to create an "engine fuel consumption map (engine torque / engine speed)" among other things. Unfortunately, the engine torque is not measured in my measurements. More specifically, the "actual engine - percent torque (OBD PID 98)" outputs only "-125".

Therefore, I wonder if it is possible to derive the torque (approximately) with the following information I have:
  • Velocity GPS km/h
  • Velocity ECU km/h
  • Engine Speed rpm
  • Ambient Temperature degC
  • Relative Humidity %
  • Ambient Pressure kPa
  • GPS Altitude m
  • Altitude Amb, Pressure m
  • Exhaust Temperature degC
  • Exhaust Mass Flow g/s
  • Exhaust Volume Flow (1atm 20degC) m3/s
  • Coolant Temperature degC
  • Intake Manif, Pressure Abs kPa
  • Intake Manif, Pressure Rel kPa
  • Intake Manif, Temperature degC
  • Oil Temperature degC
  • Throttle Position %
  • Intake Mass Flow g/s
  • OBD_Accelerator_Pedal_Position_D_(PID_73) %
  • OBD_Ambient_air_temperature_(PID_70) °C
  • OBD_Barometric_pressure_(PID_51) kPa
  • OBD_Calculated_engine_load_value_(PID_4) %
  • OBD_Commanded_throttle_actuator_(PID_76) %
  • OBD_Control_module_voltage_(PID_66) V
  • OBD_Relative_throttle_position_(PID_69) %
  • OBD_Run_time_since_engine_start_(PID_31) s
  • va m2/s3
  • va_pos m2/s3
  • Acceleration m/s²
  • m_CO2 g
  • m_CO g
  • m_NOx g
  • n_PN -
  • y_CO2 %
  • y_CO ppm
  • y_NO ppm
  • y_NO2 ppm
  • y_NOx ppm
  • y_O2 %
  • ndot_PN #/s
  • mdot_CO2 g/s
  • mdot_CO g/s
  • mdot_NO g/s
  • mdot_NO2 g/s
  • mdot_NOx g/s
  • mdot_O2 g/s

Some people claim that with the "OBD_Calculated_engine_load_value" somehow the engine torque can be derived. Unfortunately I have not yet found the formula of "Calculated_engine_load" which does not include the torque.
 
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joker1319 said:
Unfortunately I have not yet found the formula of "Calculated_engine_load" which does not include the torque.
Huh? If you want to calculate torque you need a formula with torque in it.

Engine torque * engine rpm * 2 pi/minute = engine mechanical power
The 2 pi/minute is converting rpm to an angular velocity. You have rpm, if you have the mechanical power of the engine you get torque.
 
The problem is that the power of the car is not measured. It is only the power according to the vehicle documents known, but not the currentl power during the test.
 
What is OBD_Calculated_engine_load_value_(PID_4) then?

It is possible to estimate the power based on other values, like the speed of the car, the incline of the road, the density of air and some car-specific constants, but that will probably need experimental input.
 
CWatters said:
According to this..

http://obdcon.sourceforge.net/2010/06/about-pid-calculated-load-value/

It indicates the percentage of available peak torque.
1Wj900B.png


i know that it indicates the percentage of available peak torque...but when you look at the pic you will see that the correlation of them is pretty poor
 

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