Reduction of cold-start emissions and catalyst warm-up time with direct fuel injection

An internal combustion engine employs fuel injectors positioned to inject fuel directly into combustion chambers of the engine, and an electronic engine controller (EEC) to control operation of the engine. The EEC implements a cold start routine which controls the amount of fuel injected, the time at which the fuel is injected and spark timing to achieve a rapid increase in temperature of the engine and the exhaust system components, thereby decreasing tailpipe hydrocarbon emissions during cold start.

FIELD OF THE INVENTION 
This invention relates to the field of electronic engine control and more 
particularly to the field of reducing hydrocarbon emissions during cold 
start in a spark ignited internal combustion engine which employs direct 
fuel injection. 
BACKGROUND OF THE INVENTION 
A disproportionately large amount of the hydrocarbons produced by a vehicle 
are emitted during cold starting of the vehicle engine. The temperature of 
the intake passages and the combustion chambers of the engine during the 
early stages of a cold start inhibit the proper vaporization of fuel. As a 
result, during cold start, a stoichiometric air/fuel ratio is difficult to 
achieve with intake port fuel injection. In addition, unburned fuel vapor 
is delivered to the catalytic converter together with the normal 
by-products of combustion. During the early stages of a cold start, the 
catalyst material in the catalytic converter has not reached a sufficient 
temperature in order to sufficiently process the unwanted, and 
uncombusted, by-products of combustion. Tailpipe emissions of hydrocarbons 
thus increase as a result of all three of the foregoing factors. 
One solution to reducing hydrocarbon emissions during a cold start is the 
use of an Electrically Heated Catalyst (EHC). The EHC employs resistive 
elements which heat the catalyst prior to starting the engine. In cold 
start, the heated catalyst is thus better able to process the unwanted 
by-products of combustion. Unfortunately, use of the EHC adds additional 
cost, extra complexity, and requires a delay prior to engine starting to 
allow the EHC to preheat the catalyst. 
The inventors herein have recognized that direct fuel injection may be used 
to advantage in reducing hydrocarbon emissions during cold start. Direct 
fuel injection offers control of fuel delivery unachieveable with intake 
port fuel injection, where the fuel injector is positioned outside of the 
combustion chamber. Others have utilized direct fuel injection to achieve 
engine control strategies unachievable in engines utilizing intake port 
fuel injection. For example, Sasaki et al. in U.S. Pat. No. 5,207,058 
entitled Internal Combustion Engine describe an engine which utilizes 
direct fuel injection and which employs a control strategy to raise the 
temperature of the catalytic converter if it is found to be below a 
predetermined minimum temperature. However, Sasaki et al. do not 
contemplate reduction of hydrocarbon emissions by achieving immediate 
combustion as quickly as possible upon cold start. Moreover, Sasaki et al. 
appear to contemplate an engine which has achieved stable combustion. 
Thus, the approach contemplated by Sasaki et al. has limited use in cold 
start of an engine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to reduce hydrocarbons produced 
during cold start of a spark ignited internal combustion engine by 
employing direct fuel injection to achieve rapid combustion and reduce 
catalyst warm-up time. 
In accordance with the primary object of the invention, in a preferred 
embodiment, hydrocarbon emissions during cold start are reduced by 
employing an internal combustion engine which includes fuel injectors 
positioned to inject fuel directly into combustion chambers of the engine, 
a high pressure fuel supply pump for pumping fuel to the fuel injectors, 
and an engine controller for controlling operation of the engine. At 
engine start, upon initiation of electrical power to the engine, the 
electronic engine controller allows a predetermined period of time to 
elapse to allow the high pressure fuel supply pump to reach a 
predetermined operating pressure. Upon the first engine cycle, for each 
cylinder of the engine, the quantity of fuel injected into each cylinder 
and the ignition timing is controlled to achieve combustion in the first 
engine cycle by injecting a quantity of fuel to compensate for combustion 
chamber wall wetting effects and to achieve a substantially stoichiometric 
air/fuel ratio in each combustion chamber, and controlling spark timing 
according to an empirically determined value which provides the greatest 
probability for ignition. For a first predetermined number of subsequent 
engine cycles, the quantity of fuel injected into each cylinder and the 
spark timing is controlled to rapidly increase the temperature of surfaces 
of the combustion chambers by injecting a quantity of fuel into each 
combustion chamber to achieve an air/fuel ratio substantially equal to or 
marginally leaner than a stoichiometric air/fuel ratio and advancing spark 
timing in each cylinder by a predetermined number of degrees of crankshaft 
rotation from a predetermined optimal ignition timing point. For a 
subsequent, second predetermined number of engine cycles, the quantity of 
fuel injected into each cylinder and the spark timing is controlled to 
rapidly increase the temperature of the surfaces of the exhaust system 
components of the engine, by injecting a first quantity of fuel for each 
engine cycle during the intake stroke of the engine cycle and injecting a 
second quantity of fuel later in the same engine cycle during the 
combustion stroke of the engine cycle, and retarding spark timing for each 
cylinder from the predetermined optimal ignition timing point. 
An advantage of certain preferred embodiments is that combustion is 
achieved on the first engine cycle, thus reducing the emission of unburned 
gasoline vapors. Moreover, by controlling the quantity of fuel delivered 
and the spark timing in a manner to rapidly warm-up the surfaces of the 
combustion chamber, combustion stability and efficiency is further 
enhanced, resulting in further reductions of tailpipe emissions of 
hydrocarbons. Finally, by then controlling the quantity of fuel delivered 
and the spark timing in a manner to rapidly warm-up the catalytic 
converter, even further reductions in tailpipe hydrocarbon emissions are 
achieved without the cost and complexity imposed by additional hardware 
components such as an electrically heated catalyst. 
These and other features and advantages of the present invention may be 
better understood by considering the following detailed description of a 
preferred embodiment of the invention. In the course of this description, 
reference will frequently be made to the attached drawings.

DETAILED DESCRIPTION 
FIG. 1 of the drawings shows an Electronic Engine Controller (EEC) 10 and 
an internal combustion engine 100, which comprises a plurality of 
cylinders, one of which is shown in FIG. 1. Engine 100 draws an aircharge 
through an intake manifold 102, past a throttle plate 104, and intake 
valve 106 and into combustion chamber 108. An air/fuel mixture which 
consists of the aircharge and fuel injected by fuel injector 130, is 
ignited in combustion chamber 108, and exhaust gas produced from 
combustion of the air/fuel mixture is transported past exhaust valve 110 
through exhaust manifold 112. A piston 114 is coupled to a crankshaft 116, 
and moves in a linear fashion within a cylinder defined by cylinder walls 
118. 
A crankshaft position sensor 120 detects the rotation of crankshaft 116 and 
transmits a crankshaft position signal 118 to EEC 10. Crankshaft position 
signal 118 preferably takes the form of a series of pulses, each pulse 
being caused by the rotation of a predetermined point on the crankshaft 
past sensor 120. The frequency of pulses on the crankshaft position signal 
118 are thus indicative of the rotational speed of the engine crankshaft. 
A Mass AirFlow (MAF) sensor 122 detects the mass flow rate of air into 
intake manifold 102 and transmits a representative signal 124 to EEC 10. 
MAF sensor 122 preferably takes the form of a hot wire anemometer. A 
throttle position sensor 124 detects the angular position of throttle 
plate 104 and transmits a signal 126 indicative of throttle position to 
EEC 10. Throttle position sensor 124 preferably takes the form of 
potentiometer. An engine coolant temperature sensor 126 detects the 
temperature of engine coolant circulating within the engine and transmits 
a representative signal 128 to EEC 10. Engine coolant temperature sensor 
126 preferably takes the form of a thermistor. 
A fuel injector 130 is positioned to inject fuel directly into combustion 
chamber 108. Fuel injector 130 receives fuel from a high pressure fuel 
supply pump 132, and injects fuel into combustion chamber 108 in response 
to an injector control signal 134 received from injector driver 136, which 
operates under control of EEC 10. Fuel injector 130 preferably takes the 
form of a solenoid valve. A spark plug 138 operates in a conventional 
manner, under control of a spark timing signal 140 generated by the EEC 10 
to ignite the air/fuel mixture in the combustion chamber 108. A Heated 
Exhaust Gas Oxygen (HEGO) sensor 142, positioned to sense exhaust gas 
flowing through exhaust pipe 144, transmits an exhaust composition signal 
146, which is indicative of the oxygen concentration of the exhaust gas, 
to EEC 10. A three-way catalytic converter 148 processes exhaust gases to 
reduce hydrocarbon, nitrous oxide and carbon monoxide tailpipe emissions. 
EEC 10 includes a central processing unit (CPU) 2 1 for executing stored 
control programs, a random-access memory (RAM) 22 for temporary data 
storage, a read-only memory (ROM) 23 for storing the control programs, a 
keep-alive-memory (KAM) 24 for storing learned values, a conventional data 
bus and I/O ports 25 for transmitting and receiving signals to and from 
the engine 100 and other systems in the vehicle. 
A preferred embodiment advantageously implements a cold start routine to 
control the spark timing, the quantity of fuel delivered, along with the 
time in the engine cycle at which fuel is delivered, in a manner to reduce 
hydrocarbon emissions upon cold start. 
FIG. 2 shows the steps executed by the EEC upon cold start of the engine to 
implement the cold-start routine. The cold-start routine may preferably be 
executed on an engine which is started over a range of different initial 
temperatures. The EEC preferably makes a determination of the engine 
temperature prior to entering the cold-start routine. The temperature 
determination may be determined as a function of the engine coolant 
temperature, or alternatively may be determined as a function of the 
temperature of the intake air charge or of the catalyst temperature, or 
may be determined as a combination of two or more of the foregoing 
temperatures. Depending upon the initial temperature, steps 204, 206 and 
207 are altered in a manner to be described below. The steps shown in FIG. 
2 are preferably implemented in the EEC as a program stored in ROM 23 
which is executed by the CPU 21. As used herein the term engine cycle 
refers to a complete cycle of the engine which involves two complete 
rotations of the engine crankshaft and includes all four strokes-intake, 
compression, power and exhaust, completed by a four-stroke engine. 
The cold start routine is entered at 201 and at 202 the EEC waits a 
predetermined period of time to allow the high pressure supply pump to 
reach a predetermined pressure. Typically the predetermined pressure will 
be approximately 90% of its normal operating pressure. 
At step 203, the EEC initiates engine operation, and on the first engine 
cycle, for each cylinder, the quantity of fuel delivered and the spark 
timing are controlled to achieve combustion in the first engine cycle. 
This is preferably performed by injecting a quantity of fuel into the 
combustion chamber which results in an air/fuel ratio substantially equal 
to stoichiometry. In order to achieve a stoichiometric air/fuel ratio, the 
amount of fuel actually injected into the combustion chamber is greater 
than the amount required to achieve a stoichiometric air/fuel ratio in the 
gases, in order to account for combustion chamber wall wetting effects. As 
will be appreciated by those skilled in the art in view of the present 
disclosure, wall wetting effects are more pronounced when the surfaces of 
the combustion chamber are cold, thus preventing effective vaporization of 
the fuel which impacts the surfaces of the combustion chamber. Spark 
timing in the first engine cycle is preferably empirically determined to 
provide the greatest probability for combustion of the air/fuel mixture. 
In a preferred embodiment, the spark timing is approximately ten degrees 
before Top Dead Center (TDC) in the compression stroke. 
At 204, for a predetermined number of cycles, the quantity of fuel injected 
and the spark timing are controlled in a manner to achieve rapid warm-up 
of combustion chamber surfaces. This is achieved by injecting a quantity 
of fuel to achieve an air/fuel mixture which is in a range from a 
stoichiometric air/fuel ratio to a slightly lean ratio. While a 
stoichiometric air/fuel ratio is preferable, an amount of fuel required to 
achieve a slightly lean air/fuel ratio is injected to account for the 
quantity of unvaporized fuel on the surfaces of the combustion chamber 
from the initial engine cycle which will vaporize as the surfaces become 
warmer. Spark timing at step 204 is advantageously advanced from the 
timing which produces the most power. By moving the spark timing to an 
earlier point in the engine cycle, an increased amount of energy released 
from combustion of the air/fuel mixture is used to warm up the surfaces of 
the combustion chamber. Step 204 is preferably executed for approximately 
five to fifty engine cycles. The exact number of cycles is empirically 
determined and is partially a function of the thermal conductivity of the 
material comprising the engine block, cylinder liners and piston. The 
number of cycles is additionally a function of a temperature value 
indicative of initial engine or catalyst temperature upon engine start-up. 
Preferably the number of cycles are stored in a table in ROM and are 
indexed by engine or catalyst temperature. As will be appreciated by those 
skilled in the art in view of the present disclosure, rapid heating of the 
combustion chamber surfaces reduces overall tailpipe hydrocarbon emissions 
during cold start by allowing more complete combustion of the air/fuel 
mixture in the combustion chamber. 
At 206, for a predetermined number of cycles, the quantity of fuel injected 
and the spark timing are controlled in a manner to achieve rapid warm-up 
of exhaust system components, including the catalyst material contained in 
the catalytic converter. This is achieved by utilizing a split injection 
mode of fuel injection, seen designated by dotted line 205, in which the 
amount of fuel injected is injected during two discrete portions of the 
engine cycle. The total amount of fuel injected is preferably an amount 
which generates a stoichiometric air/fuel ratio. Approximately 90% of the 
total quantity of fuel to be injected is injected at the normal time in 
the engine cycle, which is preferably during the intake stroke. Normally, 
fuel injection is initiated at 240 to 330 degrees of crankshaft rotation 
before TDC and lasts for approximately 15 to 20 degrees. At step 206, 
approximately 90% of the fuel to be injected is injected at the normal 
injection time and the remaining 10% is injected late in the power stroke 
of the engine cycle. Spark timing at step 206 is advantageously retarded 
from the optimal timing which produces the most power. By moving the spark 
timing to a later point in the engine cycle, and injecting a small portion 
of fuel later in the engine cycle, an increased amount of energy released 
from combustion of the air/fuel mixture is used to warm up the surfaces of 
the exhaust system components step 206 is preferably executed for 
approximately five to fifty engine cycles. As with step 204, the exact 
number of cycles is empirically determined and is partially a function of 
the thermal conductivity of the material comprising the cylinder head 
(exhaust port), the catalyst, and other exhaust system components, and the 
proximity of the catalyst to the engine. Moreover, as explained above, the 
exact number of cycles will preferably vary with initial engine 
temperature in a manner similar to that described in the description 
accompanying step 204. As will be appreciated by those skilled in the art 
in view of the present disclosure, rapid heating of the exhaust system 
components reduces overall tailpipe hydrocarbon emissions during cold 
start by enhancing catalytic conversion efficiency. 
At step 207, the proportion of fuel injected between the first portion, in 
the intake stroke, and the second portion, in the expansion stroke, is 
altered in order to achieve a further increase in the temperature of 
exhaust system components. Spark timing remains as in step 206, but the 
amount of fuel injected during the intake stroke is reduced to 
approximately 80% of the total amount to be injected and the amount of 
fuel injected during the power stroke is increased to approximately 20% of 
the amount to be injected. Step 207 is preferably executed for 
approximately five to fifty engine cycles, with the exact number of cycles 
being empirically determined based primarily on the exhaust system 
components and geometry. As with steps 204 and 206, the exact number of 
cycles will vary with the initial engine temperature. Upon completion of 
step 207, the cold start routine is exited and subsequent engine controls 
are effected by the EEC 10. 
Preferably, the variation in spark timing achieved in the cold start 
routine is limited within predefined boundaries to differences in engine 
operation which are noticeable to the vehicle driver. 
It is to be understood that the specific mechanisms and techniques which 
have been described are merely illustrative of one application of the 
principles of the invention. For instance, as noted above, the exact 
number of cycles for which each of the steps of the cold start routine are 
executed will vary depending upon engine and exhaust system temperature, 
material, size and geometry. Although the preferred embodiment is 
applicable to a spark ignited gasoline engine, the principles of the 
invention may also be used in spark ignited engines utilizing alternative 
liquid fuels. Numerous additional modifications may be made to the methods 
and apparatus described without departing from the true spirit and scope 
of the invention.