System for controlling fuel supply for internal combustion engine

A system for controlling supply of fuel to a hybrid fuel powered engine during starting. The system has a sensor detecting the alcohol concentration of the fuel, a device for calculating an alcohol correction factor from the detected alcohol concentration, a device for correcting a basic amount of fuel supply in accordance with the alcohol correction factor, a device for increasing or decreasing the factor in increments of a magnitude determined on the basis of the engine coolant temperature once per interval determined on the basis of the engine coolant temperature, and a device for reversing the direction of the increments each time the factor reaches an upper limit value or a lower limit value, whereby the factor is swept over a prescribed range until the engine starts.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a system for controlling the amount of fuel 
supplied to an engine that uses a fuel containing alcohol, more 
particularly to such a system for controlling the amount of fuel supplied 
at the time the engine is started. 
2. Description of the Prior Art 
Engine fuels containing alcohol and the like are being used increasingly as 
substitutes for gasoline and other more conventional fuels. Some of these 
new fuels are blends including a conventional fuel. For example, a mixed 
gasoline-methanol fuel containing 85% methanol has become generally known 
as M85. Others are used without blending. 
The characteristics of these alternative fuels differ from those of 
conventional fuels in various ways. For example, the stoichiometric 
air-fuel ratio of methanol is about 6.5:1, compared with about 15:1 for 
gasoline, and its latent heat of vaporization is about 280 kcal/kg, 
compared with about 80 kcal/kg for gasoline. These differences are 
substantial. In particular, the higher heat of vaporization of methanol 
means that the amount of heat required for fuel vaporization will increase 
with increasing methanol concentration of the fuel. As a result, the fuel 
does not vaporize easily when the engine coolant temperature is low and 
the engine becomes difficult to start. 
Japanese Laid-Open Patent Publication No. Sho 56-104131 teaches a system 
for improving the start performance of an engine that uses a hybrid fuel 
containing alcohol. In the proposed system, the amount of fuel to be 
supplied to the engine is determined on the basis of the alcohol 
concentration of the fuel detected by an alcohol sensor and when the 
engine fails to start when supplied with the so-determined amount of fuel, 
the amount of fuel is increased or decreased until starting is achieved. 
As was pointed out above, an engine using an alcohol-containing fuel is 
fundamentally hard to start and, therefore, the probability of its 
starting is not necessarily high even when the fuel supply is adjusted to 
the optimum amount for starting. In the aforesaid prior art system, 
therefore, there is a fairly high possibility that the engine will fail to 
start at the time the amount of fuel supply is optimum for starting the 
engine. If this should happen, the amount of fuel supply will thereafter 
deviate further and further from the optimum, making it even more unlikely 
that the engine will start. 
Moreover, if something should go wrong with the system's alcohol sensor, 
the amount of fuel supplied will be determined on the basis of an alcohol 
concentration that is different from the actual concentration. As the 
system is incapable of determining whether the amount of fuel supply 
should be increased or decreased in such circumstances, the adjustment is 
likely to be made in the wrong direction. In this case the probability of 
the engine starting becomes almost nil. 
This invention was accomplished in view of the foregoing problems and has 
as its object to provide a system for controlling the amount of fuel 
supplied for starting an engine that uses a fuel containing alcohol, which 
system ensures reliable engine starting even when an alcohol sensor 
constituting a part of the system malfunctions or breaks down. 
SUMMARY OF THE INVENTION 
This invention achieves this object by providing a system for controlling 
fuel supply for internal combustion engine provided with a blended fuel of 
gasoline and alcohol. The system has a first device for determining an 
alcohol correction factor and a control device for correcting an amount of 
fuel supply at engine starting at least in response to the determined 
alcohol correction factor. The improvement in the system comprises the 
first device includes a second device for increasing or decreasing the 
alcohol correction factor until it reaches a predetermined reference value 
unless the engine is started.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
An embodiment of the invention will now be explained with reference to the 
drawings. 
In FIG. 1, a four-cylindered vehicle internal combustion engine 10 has an 
air intake passage 12. Air drawn in through an air cleaner, not shown, has 
its flow rate controlled by a throttle valve 14 and passes through a 
manifold 16 integrally connected to the passage to a combustion chamber 
18, only one shown. A fuel injection nozzle 20 is provided in the vicinity 
of the chamber for supplying fuel. The intake air and the fuel are mixed 
and the resulting air-fuel mixture enters the chamber when an intake 
valve, not shown, is opened. After it is compressed in the chamber by a 
piston 22, the air-fuel mixture is ignited by a spark plug 24, whereupon 
it burns explosively to drive the piston down and the burnt gas is passed 
to the exterior through an exhaust passage 26 during engine exhaust 
stroke. 
The air intake passage 12 is provided with a throttle position sensor 30 
for generating a signal indicative of the opening degree .theta.th of the 
throttle valve 14 and a manifold absolute pressure sensor 32, at a 
position downstream of the throttle valve 14, for producing a signal 
indicative of a manifold absolute pressure Pb. A crankshaft angle sensor 
34 is provided to produce a reference signal .theta.cr-ref once per 720 
crankshaft degrees and a unit signal .theta.cr-unit per a predetermined 
degrees. Further, a coolant temperature sensor 36 is provided to generate 
a signal indicative of a coolant temperature Tw. The exhaust passage 26 
has an oxygen sensor 38 for generating a signal corresponding to the 
oxygen content Vo.sub.2 of the exhaust gas. The fuel injection nozzle 20 
is connected, via a fuel supply conduit 40, with a fuel tank 42 containing 
a blended fuel composed of gasoline and methyl alcohol. An alcohol sensor 
44 is equipped in the conduit for generating a signal indicative of the 
alcohol concentration Va of the fuel. 
The output signals from all of the aforesaid sensors are sent to a control 
unit 50 made up of a microcomputer. In the unit, analog sensor signals are 
converted into digital signals through an A/D converter 50a and are 
temporarily stored at a RAM 50b, a portion of which is backed up even when 
the engine is stopped. The outputs of the crankshaft sensor 34 are 
wave-shaped by a circuit 50c and the signal .theta.cr-unit is then input 
to a counter 50d to measure an engine speed Ne. The outputs of the sensors 
38,44 are sent to the detection circuits 50e,50f respectively. Based on 
the detected values, a CPU 50g calculates, in accordance with instructions 
stored in a ROM 50h, the amount of fuel to be supplied in a manner 
described later and out puts a signal Tout expressing the fuel supply 
amount in terms of an injection period, to a drive circuit 50i through an 
I/O port 50j, in order to drive the nozzle 20 to inject the fuel for the 
period. 
The signal Tout is obtained by using an alcohol correction factor Kc 
calculated from the alcohol concentration Va and other such correction 
factors to correct a basic fuel supply amount set in advance on the basis 
of the engine coolant temperature Tw and other engine conditions and 
stored in the RAM 50b of the control unit 50. If the alcohol sensor 44 
should fail (malfunction or break down), the aforesaid correction of the 
basic fuel supply amount is conducted using an estimated correction factor 
determined from the actual air-fuel ratio calculated from the aforesaid 
oxygen content Vo.sub.2 during operation of the engine 10. The alcohol 
correction factor is stored as a backup value Kb in the backup portion of 
the RAM 50b of the control unit 50. 
The actual alcohol concentration of the fuel does not change when the 
vehicle equipped with the engine is being driven since fuel cannot 
normally be supplied to the fuel tank 42 at such times. Therefore, the 
determination as to whether or not the alcohol sensor 44 has failed can be 
made on the basis of whether or not the fluctuation in the output value of 
the alcohol sensor 44 exceeds a prescribed value. This is only one 
example, however, and various other methods of detecting sensor failure 
are also usable. 
Next, mode of operation of the system will now be explained with reference 
to the flowchart of FIG. 2 and the graphs of FIGS. 3 to 5. 
When the operation for starting the engine 10 is initiated, the control 
procedure first fetches the backup value stored in the RAM 50b in step S1 
and uses this value as the alcohol correction factor Kc during engine 
starting. The procedure then moves to step S2 in which a flag F 
prescribing that changes to be made in the alcohol correction factor Kc 
are to be made in the increase direction is set to zero. (The alcohol 
correction factor is increased when the flag F is set to 0 and decreased 
when set to 1.) The procedure then advances to step S3 in which the 
coolant temperature Tw, which represents the temperature of the engine 10, 
is used as address data for retrieving a change interval t from a table 
prepared and stored in the ROM 50h of the control unit 50 in advance. A 
timer (down counter) is then set to the retrieved time t and is started. 
An example of the relationship between the coolant temperature Tw and the 
change interval t is shown in FIG. 3, from which it will be noted that 
change interval t increases with decreasing coolant temperature Tw. The 
procedure then goes to step S4 in which the coolant temperature Tw is 
again used as address data for retrieving an increment delta Kc from a 
table prepared and stored in the ROM 50h in advance. As shown in FIG. 4, 
the increment delta Kc increases with decreasing coolant temperature Tw. 
In the following step S5 the alcohol correction factor Kc is maintained at 
backup value Kb and an amount of fuel corrected by the backup value Kb is 
supplied to engine 10 until the timer counted down to zero. (The timer is 
never reset at an intermediate value before counting down to zero.) If the 
engine does not start by the time that the timer reaches zero, i.e. by the 
time that the change interval t has lapsed, the procedure advances to the 
following step S6. In step S6 the setting of the flag F is checked and if 
it is zero, the procedures moves to step S7 in which the alcohol 
correction factor Kc is increased by increment delta Kc. If the flag is 
found to be set to 1 in step S6, the procedure goes to step S8 in which 
the alcohol correction factor Kc is decreased by increment delta Kc. In 
either case, the procedure thereafter advances to step S9 in which the new 
alcohol correction factor is compared with an upper limit H. If it is 
found to be equal to or greater than the upper limit H, the flag is set to 
1 in step S10 so that the direction of change of the factor will be 
reversed from increase to decrease in the next cycle. Then in step S11, 
the alcohol correction factor is compared with a lower limit L and if it 
is found to be equal to or smaller than the lower limit L, the flag is set 
to 0 in step S12 so that the direction of change will be reversed from 
decrease to increase in the next cycle. This brings the procedure to step 
S13 in which the counter is set to a freshly retrieved change interval t 
to run and engine cranking is continued for the period of the new change 
interval t using an amount of fuel supply corrected using the 
increased/decreased alcohol correction factor obtained in step S7 or step 
S8. The foregoing steps are thereafter repeated until the engine 10 
starts. While the alcohol correction factor Kc is increased/decreased from 
the backup value Kb by an increment of delta Kc once every change interval 
t during the cranking operation, as shown in FIG. 5, since the direction 
of the increment is reversed when the value of the factor reaches the 
upper limit H or the lower limit L, the factor Kc is repeatedly swept back 
and forth between the two limits until the engine starts. 
When the engine is cold, it takes a long time for the engine to start even 
when the amount of fuel supply is optimum. Since the aforesaid interval is 
set to be relatively long when the engine temperature is low, this 
minimizes the probability of the engine not starting and the fuel supply 
amount consequently being changed even though the optimum amount of fuel 
is being supplied. Moreover, the fuel supply amount is incremented 
relatively large when the coolant temperature is low so as to ensure the 
optimum amount of fuel supply will be achieved quickly. Therefore, even if 
the engine 10 does not start the first time that the factor Kc is optimum 
for engine starting, eventual starting is ensured by the fact that this 
optimum value will be returned to as many times as necessary. Moreover, 
engine starting is also ensured even if the backup value Kb should deviate 
from the proper value of the for the actual alcohol concentration due to a 
problem with the alcohol sensor 44. 
The present invention has thus been shown and described with reference to 
the specific embodiments. However, it should be noted that the present 
invention is in no way limited to the details of the described 
arrangements but changes and modifications may be made without departing 
from the scope of the appended claims.