System and method for diagnosing output power of an internal combustion engine

• US 6,185,996 B1
• Filed: 11/14/1997
• Issued: 02/13/2001
• Est. Priority Date: 11/14/1997
• Status: Expired due to Term

• Current Assignee: Cummins Engine Company Incorporated (Cummins Incorporated)
• Original Assignee: Cummins Engine Company Incorporated (Cummins Incorporated)
• Inventors: Smith, Steven G., Johnston, Richard D., Wang, Yue Y., Sweetland, Emma, Rupp, James A., Roettgen, Leslie A., He, Chuan, Bares, Mark F., Zhu, G. George, Bradley, Eric K., Taylor, Dennis O.
• Primary Examiner(s): DOMBROSKE, GEORGE M
• Application Number:
  US08/970,821
• Time in Patent Office: 1,187 Days
• Field of Search: 701/110, 701/111, 731/02, 731/19.A, 731/15, 731/16, 731/172, 731/173
• US Class Current: 73/114.13
• CPC Class Codes: G01M 15/044 by monitoring power, e.g. by operating the engine with one of the ignitions interrupted; by using acceleration tests

Abstract

A system and method for diagnosing output power of an internal combustion engine includes means for diagnosing potential causes of low engine output power or torque and means for estimating actual engine output power or torque. In a preferred embodiment of the diagnosis of engine output power, low engine output power is first investigated for authenticity to verify whether a low engine output power condition exists. If one exists, a zero fueling engine cranking test is conducted to determine whether relative compression values for each of the cylinders are within specification, and any problems associated therewith are corrected by service personnel. If the low engine output power problem is not corrected in accordance with the engine cranking test, a snap-throttle cylinder balancing test is conducted to balance the relative power contribution from each cylinder. If the cylinder balancing test does not correct the low engine output power problem, a road test is conducted to estimate the actual engine output power for comparison with a rated engine output power over a desired range of engine speeds.

Claims

1. A method of diagnosing output power of an internal combustion engine having a number of cylinders, a fueling system responsive to fueling signals to fuel the engine and means for providing the fueling signals, the method comprising the steps of:

investigating existence of a low engine output power condition and performing the following steps only if said low engine output power condition exists;

correcting relative compression values of each of the number of cylinders having a relative compression value below a predefined relative compression value;

adjusting the fueling signals to balance a relative contribution to engine output power of each of the number of cylinders; and

operating a vehicle carrying the engine along a drive path, including accelerating and coasting the vehicle through a desired vehicle speed range, and estimating an actual engine output power over the desired engine speed range using data collected during the accelerating and the coasting.

2. The method of claim 1 further including the step of:

comparing the estimated actual engine output power over the desired engine speed range to a rated engine output power over the desired engine speed range and verifying existence of the low engine output power condition if the rated engine output power over the desired engine speed range exceeds the estimated actual engine output power over the desired engine speed range by an error value.

3. The method of claim 2 wherein the engine further includes engine calibration data associated therewith;

and wherein existence of said low engine output power condition is conditioned upon the engine calibration data matching engine calibration data appropriate for the engine and vehicle.

4. The method of claim 1 wherein the engine includes a cranking system operable to crank the engine and means for sensing engine speed and providing an engine speed signal corresponding thereto;

and wherein the step of correcting relative compression values of each of the number of cylinders includes;

commanding the fueling signals to produce a zero engine fueling condition;

commanding the cranking system to crank the engine;

sensing engine speed; and

processing the engine speed data to determine a relative compression value for each of the number of cylinders.

5. A method of estimating actual output power of an internal combustion engine mounted in a vehicle and connected to a transmission having a number of selectable gear ratios, the engine having a fueling system responsive to fueling signals to fuel the engine, means for a providing the fueling signals and an engine speed sensor responsive to engine speed to provide an engine speed signal, and a means for sensing vehicle speed and providing a vehicle speed signal corresponding thereto, the method comprising the steps of:

starting and warming up the engine;

engaging the engine with a numerically low gear ratio of the transmission;

accelerating the vehicle along a drive path and through a desired engine speed range while collecting one of engine speed and vehicle speed data;

coasting the vehicle along the drive path and through a desired vehicle speed range corresponding to the desired engine speed range while collecting vehicle speed data; and

processing the speed data collected during the accelerating and coasting steps and computing therefrom an estimate of actual engine output power over the desired engine speed range.

6. The method of claim 5 wherein the step of accelerating the vehicle includes accelerating the engine under maximum fueling conditions through the desired engine speed range.

7. The method of claim 5 wherein the engine includes a first temperature sensor responsive to engine operating temperature to provide an engine temperature signal;

and wherein the step of starting and warming up the engine includes the steps of;

starting the engine;

sensing engine temperature; and

monitoring the engine temperature signal and performing the engaging, accelerating, coasting and processing steps only after the engine temperature exceeds a threshold temperature.

8. The method of claim 5 wherein the vehicle includes a number of tires mounted thereto;

and wherein the method further includes the step of performing a tire rolling radius test to determine a number of tire revolutions for a predefined traveling distance;

and wherein the processing step further includes processing the number of tire revolutions for a predefined traveling distance in computing the estimate of actual engine output power over the desired engine speed range.

9. The method of claim 5 wherein the vehicle includes a climate control system and the engine includes an air compressor associated therewith;

and further including the steps of;

monitoring the climate control system during the accelerating and coasting steps; and

discarding all speed data collected during the accelerating and coasting steps and repeating the accelerating and coasting steps if the climate control system is detected as being active during either of the accelerating and coasting steps.

10. The method of claim 9 further including the steps of:

monitoring the air compressor during the accelerating and coasting steps; and

discarding all speed data collected during the accelerating and coasting steps and repeating the accelerating and coasting steps if the air compressor is detected as being active during either of the accelerating and coasting steps.

11. The method of claim 5 wherein the accelerating step includes accelerating the vehicle along the drive path in a first direction;

and further including the steps of;

accelerating the vehicle along the drive path in a second direction opposite the first direction and through the desired engine speed range while collecting one of engine speed and vehicle speed data; and

averaging the engine or vehicle speed data collected in the two accelerating steps.

12. The method of claim 11 wherein the engine further includes a boost pressure sensor operable to sense boost pressure and provide a boost pressure signal corresponding thereto;

and wherein the two accelerating steps each further include collecting boost pressure data while accelerating the vehicle along the drive path through the desired engine speed range.

13. The method of claim 12 wherein the two accelerating steps each further include collecting fueling data related to the fueling signals while accelerating the vehicle along the drive path through the desired engine speed range.

14. The method of claim 13 wherein the engine further includes an intake manifold air temperature sensor operable to sense intake manifold air temperature and provide an intake manifold air temperature signal corresponding thereto;

and wherein the two accelerating steps each further include collecting intake manifold air temperature data while accelerating the vehicle along the drive path through the desired engine speed range.

15. The method of claim 14 wherein the two accelerating steps each further include collecting data related to the numerically low gear ratio of the transmission engaged with the engine throughout the accelerating test.

16. The method of claim 5 wherein the coasting step includes coasting the vehicle along the drive path in a first direction;

and further including the steps of;

coasting the vehicle along the drive path in a second direction opposite the first direction and through the desired vehicle speed range while collecting vehicle speed data; and

averaging the vehicle speed data collected in the two coasting steps.

17. A method of estimating actual output power of an internal combustion engine mounted in a vehicle and connected to a transmission having a number of selectable gear ratios and a clutch for engaging and disengaging the gear ratios, the engine having a fueling system responsive to fueling signals to fuel the engine, means for a providing the fueling signals, an engine speed sensor responsive to engine speed to provide an engine speed signal and a vehicle speed sensor responsive to vehicle speed to provide a vehicle speed signal, the method comprising the steps of:

engaging the engine with a numerically low gear ratio of the transmission;

accelerating the vehicle along a drive path and through a desired engine speed range under maximum engine fueling conditions while collecting one of engine speed and vehicle speed data;

coasting the vehicle along the drive path and through a desired vehicle speed range corresponding to the desired engine speed range with the clutch disengaged while collecting vehicle speed data; and

processing the speed data collected during the accelerating and coasting steps and computing therefrom an estimate of actual engine output power over the desired engine speed range.

18. The method of claim 17 wherein the vehicle includes a number of tires mounted thereto;

and wherein the method further includes the step of performing a tire rolling radius test to determine a number of tire revolutions for a predefined traveling distance;

and wherein the processing step further includes processing the number of tire revolutions for a predefined traveling distance in computing the estimate of actual engine output power over the desired engine speed range.

19. The method of claim 18 wherein the processing step includes:

processing the speed data collected during the accelerating and coasting steps to produce a vehicle acceleration rate;

computing a total vehicle inertia as a function of at least a mass of the vehicle, engine inertia and tire inertia;

computing a push force of the engine as a function of the vehicle acceleration, the total vehicle inertia and a resistance force of the engine; and

computing the estimate of the actual engine output power as a function of the push force of the engine.

20. A method of diagnosing output power of an internal combustion engine having a number of cylinders, a fueling system responsive to fueling signals to fuel the engine and means for providing the fueling signals, the method comprising the steps of:

providing means for sensing engine speed and providing an engine speed signal corresponding thereto, and means for sensing vehicle speed and providing a vehicle speed signal corresponding thereto;

investigating existence of a low engine output power condition and performing the following steps only if said low engine output power condition exists,

correcting relative compression values of each of the number of cylinders having a relative compression value below a predefined relative compression value,

adjusting the fueling signals to balance a relative contribution to engine output power of each of the number of cylinders; and

operating a vehicle carrying the engine along a drive path and estimating therefrom an actual engine output power over a desired engine speed range, including;

accelerating the vehicle along the drive path and through the desired engine speed range while sensing one of engine speed and vehicle speed;

coasting the vehicle along the drive path and through a desired vehicle speed range corresponding to the desired engine speed range while sensing vehicle speed; and

processing the speed information sensed during the accelerating and coasting steps and computing therefrom estimate of the actual engine output power over the desired engine speed range.

22. The method of claim 20 wherein the engine includes means for sensing engine speed and providing an engine speed signal corresponding thereto;

and wherein the accelerating step further includes accelerating the engine from an idle speed to a maximum engine speed;

and wherein the computing step further includes computing an engine acceleration rate while accelerating the engine from the idle speed to the maximum engine speed.

21. A method of diagnosing output power of an internal combustion engine having a number of cylinders, a fueling system responsive to fueling signals to fuel the engine and means for providing the fueling signals, the method comprising the steps of:

investigating existence of a low engine output power condition and performing the following steps only if said low engine output power condition exists;

correcting relative compression values of each of the number of cylinders having a relative compression value below a predefined relative compression value,

altering the fueling signals to cut fuel delivery to one of the number of cylinders;

accelerating the engine;

computing an engine acceleration rate while accelerating the engine;

altering the fueling signals to cut fuel delivery to different ones of the number of cylinders and repeating the accelerating and computing steps to thereby compute an engine acceleration rate while fuel delivery is cut to a different one of each of the number of cylinders;

comparing engine accelerations rates computed with fuel cut to each of the number of cylinders and computing therefrom a corresponding relative output power contribution of each of the number of cylinders;

adjusting the fueling signals to equalize the relative output power contribution of each of the number of cylinders to overall engine operation; and

operating a vehicle carrying the engine along a drive path and estimating therefrom an actual engine output power over a desired engine speed range.