Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2002-08-23
2004-03-09
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S520000, C123S488000
Reexamination Certificate
active
06701906
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system and method for controlling fuel injection, and more particularly, to a system and method for controlling fuel injection, in which a MAP (manifold absolute pressure) sensor is used to calculate variations in intake pressure in a purge interval to control the amount of fuel that is injected.
BACKGROUND OF THE INVENTION
An ECU (electronic control unit) is typically provided in an engine to perform overall control of the engine. For example, the ECU receives various inputs such as vehicle speed, engine rpm, etc., and controls a fuel injector based on the received data.
Since the majority of air pollution caused by vehicles is a result not only of exhaust gases but of fuel vapors, measurements are taken in most vehicles to minimize the escape of fuel vapors into the atmosphere. In particular, hydrocarbons evaporated from the fuel tank are stored in a canister and then supplied at suitable times to the engine through a purge control solenoid valve (PCSV). Accordingly, the amount of fuel vapors released into the atmosphere is greatly reduced. For ease of explanation, evaporated hydrocarbons in the canister will be referred to as “purge fuel”. Similarly, fuel injected from the canister will be referred to as fuel “purged” from the canister.
The amount of fuel purged to the engine through the PCSV directly influences engine operation, thereby controlling the amount of purge fuel supplied to the engine. If an excessive amount of fuel vapors or pure air is purged to the engine at idle speed, the air-fuel mixture becomes too rich or lean, respectively, which may result in stalling of the engine.
To remedy this problem, when the purge fuel is supplied to the engine, purge fuel feedback control is performed such that if the concentration of hydrocarbons in the purge fuel is high, a purge fuel feedback value is increased, and the amount of fuel injected into the engine through the fuel injector is decreased by the feedback value.
FIG. 3
shows a block diagram of a conventional system to control fuel injection. In the conventional system, an ECU
51
receives signals from a PCSV
53
, an engine rpm sensor
55
, a throttle position sensor
57
, an oxygen sensor
59
, and a coolant temperature sensor
61
, and then controls a fuel injector
63
according to the received signals.
FIG. 4
shows a flow chart of a method for controlling fuel injection using the above system.
The ECU
51
receives a purge duty signal from the PCSV
53
to detect a purge interval in step S
100
. That is, a signal value greater than 0 when a coolant temperature is greater than or equal to a predetermined value, and basic fuel feedback conditions are not satisfied indicating that fuel is not being purged.
If conditions for a purge interval are satisfied in step S
100
, it is determined whether fuel feedback control is being performed in step S
110
. That is, fuel feedback control is performed if the oxygen sensor
59
is activated and the coolant temperature is greater than or equal to a predetermined value, and in fuel feedback control, feedback gains including an integral gain (I-gain) and a proportional gain (P-gain), are measured. The feedback gains establish an acceleration fuel injection quantity determined to be suitable during acceleration when there is a change from a throttle-off state (i.e., when a throttle valve is closed) to a throttle-on state (i.e., when the throttle valve is open), after which the fuel injection amount is supplied to the engine through the fuel injector
63
. The feedback gains are also implemented during acceleration such that harmful elements in the exhaust gases are reduced.
If it is determined that fuel feedback control is being performed in step S
110
, the ECU
51
calculates a purge ratio Pr and a purge concentration Pc in step S
120
. The purge ratio Pr is a ratio of purge air to intake air (purge air/intake air), while the purge concentration Pc is a ratio of a purge fuel amount to a purge amount (purge fuel amount/purge amount). The following are equations for calculating the purge ratio Pr and the purge concentration Pc.
A
/
F
=
(
amount
of
intake
air
×
air
density
)
+
(
amount
of
purge
air
×
air
density
)
(
base
fuel
amount
×
liquid
fuel
density
)
+
(
purge
fuel
amount
×
gaseous
fuel
density
)
[
Equation
1
]
If feedback control is performed, an average A/F (air/fuel ratio) is maintained at the stoichiometric value 14.7. Equation 1 is used for Equation 2 below.
Pc
=
1
+
Pr
-
(
I
-
gain
×
purge
fuel
amount
compensation
value
)
Pr
×
(
1
+
14.7
×
gaseous
fuel
density
air
density
)
[
Equation
2
]
Here, I-gain is assumed to be 1.0, the gaseous fuel density is assumed to be 3.21 g/l, and the air density is assumed to be 1.29 g/l. Consequently, Equation 2 becomes as follows:
Pc
=
1
+
Pr
-
purge
fuel
amount
compensation
value
37.6
×
Pr
[
Equation
3
]
After the calculation of the purge ratio Pr and the purge concentration Pc in step S
120
, a purge fuel amount compensation value (% fuel_purge) is calculated using the purge ratio Pr and the purge concentration Pc values in step S
130
. The purge fuel amount compensation value (% fuel_purge) is calculated using Equation 4 below.
% fuel_purge=1
+Pr−
37.6
×Pr×Pc
[Equation 4]
Subsequently, a final fuel amount (% fuel_final) for supply to the fuel injector
63
is calculated in step S
140
. The final fuel amount (% fuel_final) is calculated using Equation 5 below.
% fuel_final=base fuel amount×(1−% fuel_purge) [Equation 5]
However, with the control of fuel injection using the above method, in a high temperature state or in an idle state, for example, where a fuel of a high volatility is used and/or if the vehicle is left idling for long periods, a large amount of purge gas (mostly hydrocarbons) accumulates in the canister. If the vehicle is then driven in this state, a significant amount of purge gas is supplied to the engine through the PCSV. At this time, the purge fuel amount compensation value (% fuel_purge) increases such that the final fuel amount (% fuel_final) supplied through the fuel injector
63
decreases. This result is evident from Equation 5.
If the vehicle is driven from an idle state under such conditions, (a) a difference between an intake pressure during idle and an intake pressure in a part load state causes a difference in pressure variation values between opposing ends of the PCSV
53
, (b) a calculated amount (a desired amount) of purge fuel is not supplied to the engine, and (c) the final fuel amount (% fuel_final) is decreased such that the engine air to fuel ratio (A/F) becomes lean and the driver experiences hesitation or a jerky forward motion.
Further, in a low temperature state or when a fuel of a low volatility is used, since there are almost no fuel vapors in the fuel tank, hydrocarbons do not accumulate in the canister. Accordingly, during the supply of purge gas to the engine, it is mostly air that is being supplied. If feedback is performed under such conditions, a negative value results for the purge fuel amount such that the final fuel amount (% fuel_final) increases. At this time, if the vehicle is operated in an idle state, a difference in pressure variation values between opposing ends of the PCSV
53
results, and the amount of purge fuel supplied to the engine is greater than that calculated (desired) such that a rich air to fuel ratio results, thereby causing the combustion of unneeded fuel.
S
Hoang Johnny H.
Hyundai Motor Company
Morgan & Lewis & Bockius, LLP
Wolfe Willis R.
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