Internal combustion engine with throttle tipout dilution reduction

An internal combustion engine with a throttle valve, fuel supply and dilution (EGR) control includes apparatus effective to detect a throttle tipout condition comprising a rate of throttle closing exceeding a predetermined reference rate and decrease the dilution from the scheduled value to its minimum value during the existence of the throttle tipout condition and further apparatus effective to detect the end of the throttle tipout condition and return the dilution to its scheduled value at a controlled rate. Thus, a sudden unscheduled increase in dilution caused by a throttle tipout associated increase in intake manifold vacuum is reduced and driveability improved.

BACKGROUND OF THE INVENTION 
This invention relates to internal combustion engines of the type having a 
throttle controlling airflow to a combustion chamber, fuel supply 
apparatus for forming a combustible charge in the combustion chamber and 
EGR apparatus for introducing recirculated exhaust gasses to the fuel 
charge to control the dilution thereof. In particular, it relates to such 
engines in which the rapid closing of the throttle, in a throttle tipout 
condition, produces increasing intake manifold vacuum and thus causes an 
unscheduled temporary increase in dilution. This may occur with a 
separately controlled EGR valve or with internal EGR control using a 
variable valve lift apparatus for combustion chamber exhaust valve 
control. 
SUMMERY OF THE INVENTION 
The invention is an internal combustion engine of the type described above 
which comprises apparatus effective to detect a throttle tipout condition 
comprising a rate of throttle closing exceeding a predetermined reference 
rate and decrease the dilution from the scheduled value to its minimum 
value during the existence of the throttle tipout condition and further 
apparatus effective to detect the end of the throttle tipout condition and 
return the dilution to its scheduled value at a controlled rate. In the 
case of an external EGR valve, the minimum EGR value generally corresponds 
to a complete closure of the valve. In the case of a variable valve lift 
apparatus, the minimum value will reduce valve lift to produce minimum EGR 
consistent with other engine operating considerations. The reduction in 
the sudden unscheduled increase in dilution results in improved 
driveability. Further details and advantages will be apparent from the 
accompanying drawings and following description of a preferred embodiment.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, an internal combustion engine 10 is of the standard 
type having a plurality of cylinders or combustion chambers. In this 
embodiment, there are four such cylinders, each provided with air and fuel 
through standard fuel supply apparatus 11. Fuel supply apparatus 11 
comprises normal air intake apparatus including air cleaner, intake 
manifold, throttle valve and intake valves, and normal fuel injection 
apparatus including fuel injectors and injector drivers which are 
activated in response to timed, sequential signals from a control computer 
13. The air and fuel forms a combustible fuel charge within the combustion 
chamber which has a composition controlled in the normal manner through 
the duration of the injector pulses relative to the mass of air in the 
cylinder and by dilution control apparatus. The air/fuel ratio control may 
be stoichiometric in response to a standard oxygen sensor in the exhaust 
system of engine 10. 
The dilution control apparatus may include an exhaust gas recirculation 
(EGR) valve 12 to control the rate of inert exhaust gases fed back to the 
air supply apparatus. The degree of opening of EGR valve 12 is controlled 
through a range from closed to maximum open by a stepper motor or 
equivalent means for accurate control of EGR flow, the stepper motor 
receiving positioning signals from computer 13. Other forms of dilution 
control apparatus may be used, either alternatively or in addition. For 
example, a variable lift adjusting device for the exhaust valves of engine 
10 is described in U.S. Ser. No. 834,791, Variable Valve Lift/Timing 
Mechanism, filed Feb. 28, 1986 by Duane J. Bonvallet and issued on Jan. 
27, 1987 as U.S. Pat. No. 4,638,773. This device, actuated by a stepper 
motor or other actuator means, will also be effective to control the 
dilution of the fuel charge within the associated combustion chamber. 
Control computer 13 may be a standard digital microcomputer having a 
microprocessor, RAM, ROM, input/output apparatus and a clock and typified 
by a microcomputer of the Motorola (R) 6800 series. It includes, in ROM, a 
stored program for controlling fuel supply system 11, EGR valve 12 and an 
ignition system, to be described below, in response to values of engine 
operating parameters from a plurality of sensors. An engine speed (RPM) 
sensor 15 may be based on a 180 tooth wheel turning with the engine 
harmonic balancer and a magnetic or other pickup to generate electrical 
pulses as it is passed by teeth of the rotating wheel. Control computer 13 
or other dedicated apparatus may measure the time between consecutive RPM 
pulses and generate an engine speed signal therefrom. In addition, the 
counting of the RPM pulses can be used along with absolute crankshaft 
reference pulses from the standard distributor, not shown, of engine 10 to 
indicate absolute crankshaft rotational position at any time. If the arcs 
of the teeth and the spaces between the teeth are equal, a pulse can be 
generated every degree of crankshaft rotation. A coolant temperature 
sensor 16 of the normal type supplies a coolant temperature signal to 
computer 13. A mass airflow sensor 17 generates a signal of the mass air 
flow rate to the cylinders; and throttle position sensor 18 generates a 
throttle position signal, both said signals being provided to computer 13. 
Throttle position sensor 18 and coolant temperture sensor 16 are useful 
for controlling entry of the system into power enrichment and start/warmup 
operating modes, respectively. 
Each cylinder of engine 10 is provided with a spark plug 20 effective, when 
fired, to initiate combustion of the combustible charge within the 
combustion chamber. Spark plugs 20 are fired by ignition drivers 21 in 
response to signals from computer 13. Spark plugs 20 and ignition drivers 
21 may be of any standard type, with ignition drivers 21 responsive to 
firing pulses to fire spark plugs 20 and further effective to control the 
ignition dwell time. 
Computer 13 includes means, such as stores tables, for storing or 
determining predetermined schedules for fuel injection pulse width 
(combustion mixture air/fuel ratio), ignition timing and dilution (EGR). 
Such tables may use input lookup parameters based on engine speed and load 
and may be subject to modification or trim by other sensed engine 
operating parameters. For example, combustion pressure sensors 22 may be 
provided to sense the pressure within the cylinders of engine 10 and 
generate a signal thereof. A pressure signal processor 23 may be provided 
to detect timing and/or amplitude of peak combustion pressure for use by 
computer 13 in determining any or all of the predetermined fuel, ignition 
or EGR schedules. 
FIG. 3 shows a flow chart which describes the operation of this invention 
in controlling EGR during throttle tipout. Throttle tipout is the closing 
of the throttle valve at a rate defined, in this embodiment, as greater 
than 3 percent. Under this condition, intake manifold vacuum increases 
greatly and causes more exhaust gas to be recirculated through the valve 
for the same opening. To avoid a sudden excess of EGR in the combustion 
chamber, the EGR valve is closed during the tipout and allowed to recover 
afterward at a controlled rate. FIG. 2(a) shows the output over time of 
the throttle position sensor (TPS) for a typical throttle tipout. The 
curve 120 shows a region 121 of sharp decrease in the TPS signal. The 
corresponding region 123 in the curve 122 of FIG. 2(i b), which curve 122 
represents the negative rate of change of the TPS signal, shows a change 
exceeding negative 3 percent. The flow chart of FIG. 3 produces a desired 
result as shown in FIG. 2(c), in which the EGR signal goes to zero (the 
valve closes or is otherwise controlled to minimize EGR), as shown by the 
portion 126 of curve 125 during the existence of the high negative change 
in TPS and is then allowed to return to the normally scheduled EGR value 
at a controlled rate, in portion 127 of curve 125, when the condition 
ends. 
Referring to the flow chart of FIG. 3, if the throttle closing rate exceeds 
a predetermined rate TIPOUT at a decision point 58, a tipout flag is set 
and EGR is set to zero at step 60. TIPOUT is equal, in this embodiment, to 
3 percent per millisecond. This produces portion 126 of curve 125. If no 
throttle tipout is detected at decision point 58, the routine continues to 
decision point 61, in which the tipout flag is checked. If it is set, the 
system is in a recovery mode from a throttle tipout; and the EGR value, 
having previously been set to zero during the tipout itself, is increased 
in step 62 toward the normally scheduled value for the speed and load 
conditions in a predetermined step which produces a recovery, over many 
cycles, at a controlled rate, as shown in portion 127 of curve 125. If it 
is not set, then no throttle tipout or recovery therefrom is in progress; 
and the normally scheduled EGR value is retained. 
After step 62, the new EGR recovery value is compared at decision point 63 
with the regularly scheduled EGR value to see if recovery is complete. If 
the new EGR recovery value is equal to or greater than the scheduled 
value, then recovery is complete. Therefore, the tipout flag is reset at 
step 65 and the EGR value is adjusted, if necessary, to the regularly 
scheduled value. If recovery is not found to be complete at decision point 
63, however, EGR will be left at the latest recovery value. From step 60, 
from decision point 61 if the tipout flag is not set, from step 65 or from 
decision point 63 if EGR is at the scheduled value, the program proceeds 
to step 66, in which the EGR value is output to EGR valve 12, and then 
exits this portion of the control program. 
The minimum value of dilution produced during a throttle tipout condition 
by the apparatus of this invention will vary somewhat according to the 
nature of the dilution control apparatus, as well as other engine 
operating considerations. In the case of an external EGR valve, the 
minimum dilution will generally correspond to a complete closure of the 
valve, wherein the accumulated exhaust gases already within the intake 
manifold will be supplemented by internal EGR associated with the 
combustion chamber exhaust valve or valves. In the case of a variable lift 
exhaust valve, its lift will be reduced to a prdetermined minimum value 
consistent with total desired EGR and other engine operating 
considerations, since the exhaust valve affects more than just EGR. The 
precise values for any given engine will be determined by design and 
calibration.