Method of determining the composition of fuel in a flexible fueled vehicle without an O.sub.2 sensor

The present invention is directed towards a method of controlling combustion parameters of an internal combustion engine prior to oxygen sensor feedback availability for a flexible fueled vehicle. If the vehicle has previously been running on ethanol or has been using ethanol in the recent past, a first strategy is employed which basis engine fueling on the minimum of a theoretically appropriate fueling value and a theoretically calculated value. If the vehicle has not previously been running on ethanol or has not been using ethanol in the recent past, a second strategy is employed which basis engine fueling on the minimum of the theoretically appropriate fueling value, the theoretically calculated value and a roughness calculated value.

BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates generally to fuel control systems and, more 
particularly, to a method of determining the percent alcohol content of a 
fuel used in a motor vehicle capable of operating on more than one type of 
fuel. 
2. Discussion 
Environmental and energy independence concerns have stimulated the 
development of alternative transportation fuels, such as alcohol fuels, 
for use in automobiles. Alcohol fuels include methanol and ethanol. A 
flexible fueled vehicle capable of operating on gasoline, or alcohol fuel, 
or any mixture of the two fuels, is therefore in demand. Modifications to 
the engine are necessary when operating on different fuels because of the 
different characteristics of each fuel. For example, an engine operating 
on ethanol or E85 (a blend of 85% ethanol and 15% gasoline) requires 
approximately 1.4 times the amount of fuel relative to gasoline at 
stoichiometry due to a lower energy content of the ethanol. 
Air/fuel ratio in internal combustion engine design is typically considered 
to be the ratio of mass flow rate of air to mass flow rate of fuel 
inducted by an internal combustion engine to achieve conversion of the 
fuel into completely oxidized products. The chemically correct ratio 
corresponding to complete oxidation of the products is called 
stoichiometric. If the air/fuel ratio is less than stoichiometric, an 
engine is said to be operating rich, i.e., too much fuel is being burned 
in proportion to the amount of air to achieve perfect combustion. 
Likewise, if the air/fuel ratio is greater than stoichiometric, an engine 
is said to be operating lean, i.e., too much air is being burned in 
proportion to the amount of fuel to achieve perfect combustion. Alcohol 
fuels have a lower air/fuel ratio than gasoline at stoichiometric, so that 
the engine must be compensated for in the rich direction as the percentage 
of alcohol in the fuel increases. 
U.S. Pat. No. 5,255,661, entitled "Method for Determining Fuel Composition 
Using Oxygen Sensor Feedback Control", hereby expressly incorporated by 
reference, discloses a method for determining the percent alcohol content 
of fuel in the fuel tank utilizing an oxygen sensor feedback control loop 
to sense changes in air/fuel ratio and relay that information to the 
engine controller so that dependant variables can be adjusted accordingly. 
However, oxygen sensors take a predetermined amount of time to warm-up to 
a reliable state, particularly on cold starts. As such, fuel composition 
learning systems cannot be used until an oxygen sensor is functioning 
correctly after the vehicle has been filled with fuel. 
A potential for drivability deficiencies exist during the warm-up time 
frame if the vehicle has been recently filled with a fuel blend (i.e., 
alcohol and gasoline) which differs from the old fuel blend in the fuel 
tank. Drivability deficiencies often occur if the blended fuel after the 
fill has entered the intake manifold and new fueling parameters have not 
yet been determined. Therefore, it would be desirable to provide a method 
for determining the percent alcohol content of a newly blended fuel prior 
to its delivery to the intake manifold and prior to oxygen sensor feedback 
availability. 
SUMMARY OF THE INVENTION 
It is, therefore, one object of the present invention to provide a system 
of flexible fuel compensation. 
It is another object of the present invention to provide a flexible fuel 
compensation system which minimizes drivability deficiencies when a change 
in the percent alcohol content of the fuel occurs on a fill. 
It is yet another object of the present invention to provide a flexible 
fuel compensation system which correctly and effectively uses learned 
percent alcohol content information concerning the fuel used to fill the 
vehicle. 
The above and other objects are provided by a method of determining the 
percent alcohol content of a fuel used in a flexible fueled vehicle prior 
to oxygen sensor feedback availability. According to the present 
invention, a fueling strategy is employed which bases the engine fueling 
on the minimum of a theoretically appropriate fueling value and a 
theoretically calculated value if the vehicle has been running on ethanol 
fuel since the last tank fill or has been using ethanol in the recent 
past. If the vehicle has not been running on ethanol since the last tank 
fill or has not been using ethanol in the recent past, a different 
strategy is employed which bases the engine fueling on the minimum of a 
roughness calculated value, the theoretically appropriate fueling value, 
and the theoretically calculated value. As such, drivability deficiencies 
are accommodated when a vehicle is started cold after a fuel fill and 
before the learned percent alcohol content can be determined based on 
oxygen sensor feedback.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed towards a method of determining the 
percent alcohol content of a fuel used in a flexible fueled vehicle prior 
to oxygen sensor feedback availability. The methodology allows the 
flexible fueled vehicle to run effectively until a closed loop operating 
mode occurs or until a more accurate determination of the percent alcohol 
content of the fuel has been made. For instance, a detailed explanation of 
a method for accurately determining the percent alcohol content of the 
fuel may be found in U.S. Ser. No. 08/958,411, entitled "Method of 
Determining the Composition of Fuel in a Flexible Fueled Vehicle" to 
Nankee II et al. which is hereby expressly incorporated by reference 
herein. For the purposes of this specification, a closed loop operating 
mode refers to a state of engine operation in which feedback and fuel 
control changes are based on a functioning, accurate oxygen sensor. As is 
known, a vehicle may run for a significant time after a fuel tank fill 
before a closed loop operating mode occurs during very cold starts. The 
present invention provides an effective means of accommodating vehicle 
operation so as to avoid vehicle die-outs and drivability deficiencies 
during this period of time. 
If the vehicle has previously been running on ethanol fuel (i.e., since the 
last fuel tank fill), or has been using ethanol in the recent past, a 
first control strategy is employed. The first control strategy basis the 
engine fueling parameters on the minimum of either a predetermined 
theoretically appropriate fueling value or a theoretically calculated 
blend value. The appropriate fueling value allows the vehicle to run 
adequately, but may sacrifice performance abilities on certain percentages 
of ethanol in the tank. The theoretically calculated blend value 
accomplishes the same operational goals, while sacrificing less 
performance abilities. 
The theoretically appropriate fueling value varies with engine displacement 
but is commonly near E65 (65% ethanol and 35% gasoline). Furthermore, the 
theoretically calculated blend value includes an E0 blend value (0% 
ethanol and 100% gasoline) and an E85 blend value (85% ethanol and 15% 
gasoline). The theoretically calculated E0 blend value is used if E0 fuel 
was added to the tank and the theoretically calculated E85 blend value is 
used if E85 fuel was added to the tank. The type of fuel added to the tank 
is determined by a prediction technique based on a preliminary output from 
the oxygen sensor. The theoretically calculated values are determined by 
the following equations: 
EQU E0 possibility=(old concentration)*(old vol.)/(new vol.); and 
EQU E85 possibility=(old concentration)*(old vol.)+(85% ethanol)*(added 
vol.)!/(new vol.). 
A second control strategy is employed if the vehicle has not previously 
been running on ethanol or has not been using ethanol in the recent past. 
The second control strategy basis the engine fueling parameters on the 
minimum of either the predetermined theoretically appropriate fueling 
value, the theoretically calculated blend value or a roughness calculated 
value. Under both control strategies, the theoretically calculated blend 
value assumes that pure ethanol fuel was added to the tank. 
The roughness calculated value corresponds to the roughness of engine 
operation and is based on the second derivative of engine speed (RPM). As 
is known in the relevant art, acceleration is the first derivative of RPM 
and jerk is the second derivative. Accordingly, the roughness calculated 
value is a filtered jerk value. During cold starts, when the oxygen sensor 
is not active, the roughness calculated value is determined every 
120.degree. of crank rotation on a six cylinder engine or every 
180.degree. of crank rotation on a four cylinder engine. If the roughness 
calculated value becomes greater than a predetermined level, the 
methodology of the present invention assumes that the vehicle is running 
on fueling parameters set according to an incorrect fueling value (i.e., 
percent alcohol content). 
When the error is detected, the roughness calculated value is incremented 
by a preselected percentage. If a certain number of engine pick-up pulses 
have elapsed since incrementing the roughness calculated value, and the 
rough engine operation does not improve by a preselected amount, the 
methodology assumes that the problem is something other than the 
determination of the percent ethanol content. At this point, the 
previously incremented percentage of the roughness calculated value is 
decremented out and the roughness calculation is no longer trusted. 
In contrast, if the roughness of the engine operation has improved but the 
engine is still running more rough than a preselected threshold, the 
roughness calculated value is incremented again and the engine is 
re-evaluated for roughness. It should be noted that the roughness 
calculated value is no longer trusted once the flexible fuel control 
system decrements the roughness calculated value. 
Turning now to the drawing figure, FIG. 1 illustrates a flow chart for the 
method of flexible fuel compensation control prior to oxygen sensor 
feedback availability. The methodology starts in bubble 10 and advances to 
decision block 12. In decision block 12, the methodology determines if the 
vehicle's oxygen sensor is functioning. If the vehicle's oxygen sensor is 
operating properly, the methodology advances to bubble 14 where it exits 
the routine so that a standard percent alcohol content learning system 
based on oxygen sensor feedback availability may be employed for 
controlling the fueling parameters of the flexible fueled vehicle. 
Thereafter, the methodology restarts at bubble 10 on a periodic basis 
according to engine crank revolution. 
However, if the oxygen sensor is not functioning at decision block 12, the 
methodology advances to decision block 16. In decision block 16, the 
methodology determines if the percent alcohol content of the newly added 
fuel has been determined. This would be the case when the oxygen sensor 
begins to output a percent alcohol content of the fuel prior to reaching a 
closed loop mode upon which a percent alcohol content (i.e., E0 or E85) of 
the newly added fuel can be based. If so, the methodology advances to 
block 18. In block 18, the methodology implements engine operating 
parameters based on the theoretically calculated E0 blend value or the 
theoretically calculated E85 blend value detailed above. 
From block 18, the methodology advances to bubble 14 where it exits the 
routine until another running thereof is called for by the engine control 
unit based on engine crank revolution. Referring again to decision block 
16, if the percent alcohol content of the newly added fuel has not yet 
been determined, the methodology advances to decision block 20. Ah 
decision block 20, the methodology determines if the vehicle has had a 
recent history of operating on an ethanol-based fuel. This is indicated by 
a counter stored in the engine controller reaching a level indicative of 
ethanol content being detected on previous fuel tank fills. 
If the vehicle has a recent history of operating on an ethanol-based fuel, 
the methodology advances to block 22 and implements engine operating 
parameters based on the minimum of either the predetermined theoretically 
appropriate fueling value or the theoretically calculated E85 fueling 
value. From block 22, the methodology advances to bubble 14 where it exits 
the routine. 
If the engine operating parameters have not been recently based on ethanol 
fuel at decision block 20, the methodology advances to block 24. In block 
24, the methodology determines the roughness calculated value which, as 
described above, is indicative of the level of engine operating roughness. 
From block 24, the methodology advances to decision block 26 and compares 
the level of determined engine roughness to a preselected roughness 
threshold. 
If the roughness calculated value is less than the threshold, the 
methodology is returned to decision block 12. However, if the roughness 
calculated value is greater than the preselected threshold, the 
methodology advances to block 28 and increments the roughness calculated 
value a predetermined percentage so as to increase the amount of fuel 
being delivered to the engine such that a greater fuel to air ratio is 
established. From block 28, the methodology advances to decision block 30. 
In decision block 30, the methodology determines if the level of engine 
operating roughness has improved. If so, the methodology returns to 
decision block 12 and continues the loop. However, if the engine operating 
roughness has not improved, the methodology advances to block 32 and 
decrements out the previous incrementing of the roughness calculated value 
to return the fuel to air ratio to its prior state. From block 32, the 
methodology advances to bubble 14 where it exits the routine. 
According to the above, the present invention provides a flexible fuel 
control system for a flexible fueled vehicle suitable for providing 
theoretical fueling parameters for engine operation prior to oxygen sensor 
feedback data availability. The percent alcohol content of the fuel is set 
according to one of a predetermined appropriate fueling value, a 
theoretically calculated value and a roughness calculated value. As such, 
drivability deficiencies that may occur when the newly blended fuel 
reaches the intake manifold of the vehicle prior to a closed loop mode can 
be avoided. 
Those skilled in the art can now appreciate from the foregoing description 
that the broad teachings of the present invention can be implemented in a 
variety of forms. Therefore, while this invention has been described in 
connection with particular examples thereof, the true scope of the 
invention should not be so limited since other modifications will become 
apparent to the skilled practitioner upon a study of the drawings, 
specification, and following claims.