Intake system for an internal combustion engine

An intake system for a multicylinder internal combustion engine includes a manifold having inlet runners for conducting charge air into the cylinders of an engine, and at least one secondary throttle valve situated within at least one of the inlet runners. An actuator positions the secondary throttle valve, with the actuator being operated by a controller. The controller receives a sensed value from at least one engine operating parameter sensor, determines an appropriate position for the secondary throttle valve and predicts an optimum transition point at which the secondary throttle valve transitions to the appropriate position. The controller then initiates operation of the actuator at a point before the transition point such that the engine smoothly transitions between a first operating condition and a second operating condition.

FIELD OF THE INVENTION 
This invention relates to an intake system for an internal combustion 
engine, and, more particularly to, a system for controlling a secondary 
throttle valve in one of the inlet runners of the intake system. 
BACKGROUND OF THE INVENTION 
Variable geometry intake systems employing deactivatable ports are 
desirably used for controlling burn rate by allowing a primary port 
passage to remain open at all times, while having secondary port passages 
which may be deactivated. Such deactivation has been accomplished by means 
of throttle valves in the secondary ports. This throttle valve generally 
has two positions--"SC" for secondary closed and "SO" for secondary open. 
With the "SC" position, swirl is induced in the air charge thus increasing 
the combustion burn rate in the cylinder, improving tolerance to lean 
air/fuel mixtures and increasing torque and fuel economy at a given oxides 
of nitrogen (No.sub.x) level. However, as is well known to those skilled 
in the art, imparting an angular momentum on the air charge usually 
reduces the volumetric efficiency at relatively high engine speeds. For 
peak torque at high engine speeds, then the secondary throttle valve is 
switched to the "SO" position. 
To determine when to switch from the "SC" position to the "SO" position, 
prior art systems typically utilize engine speed. That is, at a discrete 
engine speed, the secondary throttle valve moves between the "SC" and "SO" 
positions. 
The inventors of the present invention have found certain disadvantages 
with prior art systems. For example, a finite time delay exists between 
the time when the secondary throttle is commanded to move between the "SC" 
and "SO" positions and the time when the secondary throttles actually 
move. If, for example, the vehicle is accelerating, this time delay may 
cause the secondary throttles to open when the engine is operating past 
the optimum switch point, thereby causing undesirable drivability. That 
is, a torque bump or spike may occur when the engine transitions between a 
first, relatively low speed operating condition and a second, relatively 
high speed operating condition. 
Another disadvantage with prior art systems is the failure to recognize 
that the optimum switch point changes with changes in ambient air and 
engine temperature. As previously stated, failing to switch at the optimum 
point results in an undesirable torque bump. 
Additionally, the inventors of the present invention have found that the 
prior art systems suffer from alternately switching between "SC" and "SO" 
if the engine is operating near the optimum switch point. This phenomenon 
is termed "hunting" and should be avoided. 
In general, it is desirable to make the transition between the "SC" and 
"SO" positions as smooth as possible. This will assure that the positive 
effects of such a system, such as burn rate control and high tolerance for 
exhaust gas recirculation at low and moderate engine loads, will be 
achieved while at the same time allowing high power operation with both 
the primary and secondary runners open. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a smooth transition 
between the "SC" and "SO" positions while reducing the possibility of 
"hunting" between positions. 
This object is achieved and disadvantages of prior art approaches overcome 
by providing a novel intake system for a multicylinder internal combustion 
engine. In one particular aspect of the invention, the system includes a 
manifold having a plurality of inlet runners for conducting charge air 
into the cylinders of an engine and at least one secondary throttle valve 
situated within an inlet runner. The system also includes an actuator for 
positioning the secondary throttle valve and at least one sensor for 
sensing at least one operating parameter of the engine. A controller 
operates the actuator so as to move the secondary throttle valve between a 
first, relatively restricting position, and a second, relatively 
unrestricting position. The controller receives a sensed value from the 
sensor, determines an appropriate position for the secondary throttle 
valve and predicts an optimum transition point at which the secondary 
throttle valve transitions to the appropriate position. The controller 
then initiates operation of the actuator at a point before the optimum 
transition point such that the engine smoothly transitions between engine 
operating conditions. 
The intake system also includes an engine speed sensor for sensing engine 
speed. The controller predicts the optimum transition point by receiving 
sensed values from the engine speed sensor indicative of engine speeds and 
calculates a rate of change of engine speed over time based on the sensed 
values. The controller then calculates an engine speed representing the 
point before the transition point when the controller initiates operation 
of the actuator. 
The controller may also determine whether the calculated engine speed is 
increasing or decreasing. The controller operates the actuator so as to 
move the secondary throttle valve between the "SC" and "SO" positions such 
that the point before the transition point when the controller operates 
the actuator is different depending upon whether the engine speed is 
increasing or decreasing so as to form a hysteresis. 
In addition, the optimum transition point may be altered depending upon 
ambient air and engine temperature. The controller alters the optimum 
transition point based on a difference between the actual delivered 
ignition timing and the optimal ignition timing for best torque. 
An advantage of the present invention is that a smooth transition between 
engine operating conditions may be obtained. 
Another advantage of the present invention is that the optimum transition 
point may be determined based on a variety of engine operating parameters. 
Yet another advantage of the present invention is that peak engine torque 
can be produced at any engine speed, ambient air temperature and engine 
temperature. 
Still another advantage of the present invention is that alternating 
between the secondary closed position and the secondary open position may 
be reduced. 
Yet another advantage of the present invention is that peak torque with 
reduced NO.sub.x may be obtained. 
Other objects, features, and advantages of the present invention will 
become apparent to the reader of this specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Multicylinder reciprocating internal combustion engine 10 has a plurality 
of cylinders 12, which may be arranged either in an in-line configuration, 
as shown in FIG. 1, or in a V configuration or other configuration known 
to those skilled in the art and suggested by this disclosure. Engine 10 is 
equipped with exhaust valves 14 and one or more intake valves 16. 
Sparkplugs 18 initiate the combustion event. Intake ports of engine 10 
comprise primary runners 22 and secondary runners 24, which feed each 
intake valve 16. The primary and secondary runners are defined in part by 
vertical dividing wall 26, which separates the runners and which extends 
entirely from the bottom to the top of the runners. Fuel injector 28 is 
disposed in primary runner 22 to inject fuel therein. In the example 
described herein, primary and secondary runners 22, 24 are fed by plenum 
30, which is throttled by primary engine throttle valve 32. Alternatively, 
those skilled in the art will recognize in view of this disclosure that 
primary and secondary runners 22, 24 may be fed by separate plenums. In 
the case of a two intake valve configuration (not shown), runners 22, 24 
may each have an intake valve, respectively. Flow through secondary runner 
24 is controlled by secondary throttle valve 32 as will be further 
described hereinafter. As defined herein, the term "runner" refers to 
either the illustrated passages extending from a plenum to a cylinder, 
either directly, or a crossover passage between two plenums, or any of a 
plurality of passages used in intake systems of modern internal combustion 
engines. 
The flow of charge through primary runners 22 produces a rotational flow 
about the outermost portion of each cylinder 12. This rotational flow, 
sometimes referred to as swirl, is counterclockwise, shown as arrow 32 as 
viewed in FIG. 1. Flow through secondary runners 24 causes much less swirl 
within cylinders 12 because the charge flows into a radially inward 
portion of cylinder 12. The reduced rotational impetus attributable to 
flow through runner 24 is acceptable because secondary throttle valves 34, 
which control flow through secondary runners 24, are opened at higher 
engine speeds which are accompanied by vigorous rotational flow produced 
by primary runners 22. 
Secondary throttle valves 34 are operated by actuator 36, such as an 
electrically driven motor or an engine manifold vacuum driven motor. 
Actuator 36 drives secondary throttle valves 34 via shaft 38 and a 
geartrain (not shown). In a preferred embodiment, actuator 36 drives 
secondary throttle valves 34 to their fully open position and torsion 
spring 40 is used to return secondary throttle valves 34 to their closed 
position. 
Continuing with FIG. 1, actuator 36 is controlled by controller 42 having 
memory storage device 44. A plurality of sensors 46 sense numerous engine 
operating parameters such as engine speed, engine load, spark timing, EGR 
rate, fuel delivery rate, engine air charge temperature, engine coolant 
temperature, intake manifold absolute pressure, the operating position of 
secondary throttle valves, the operating position of primary engine 
throttle valve, vehicle gear selection, vehicle speed, intake manifold air 
mass flow rate, accelerator position, and other parameters known to those 
skilled in the art and suggested by this disclosure. 
Controller 42, which may comprise a conventional engine control 
microprocessor known to those skilled in the art, or a stand-alone 
processor, as desired, is charged with the task of operating actuator 36 
so as to move secondary throttle valves 34 between "SC" and "SO". 
Controller 42 receives sensed values of engine operating parameters from 
sensors 46 and determines an appropriate position for secondary throttle 
valves 34 as will be further described hereinafter. According to the 
present invention, the opening and closing of secondary throttle valves 34 
must be handled correctly in order to assure that objectionable torque 
spike or bump is not felt by the drivers and/or passengers of the vehicle. 
The inventors of the present invention have determined that in order to 
achieve the desired smoothing of torque output of the engine, a prediction 
of the optimum transition point must be made, with the actual transition 
beginning before reaching such optimum transition point. 
For example, referring to FIG. 2, a plot of torque versus engine speed for 
"SC" and "SO" is shown. At relatively low engine speeds, secondary 
throttle valves 34 are in the "SC" position; whereas at relatively high 
engine speeds, secondary throttle valves are moved to the "SO" position. 
In order for a smooth transition to occur between the two torque curves 
shown, the optimum transition point must occur where the two curves 
intersect, shown at point "A" in FIG. 2. As previously described, if 
engine speed is increasing and actuator 36 begins to operate secondary 
throttle valves 34 at point "A", which occurs at a calculated engine speed 
N.sub.1, then by the time secondary throttle valves 34 are fully moved to 
the "SO" position, engine speed may increase to N.sub.2. As a result, the 
aforementioned torque bump may occur, shown as the difference between 
T.sub.1 and T.sub.2. According to the present invention, as will be more 
fully described with reference to FIG. 3, controller 42 predicts the 
optimum transition point at which secondary throttle valves 34 transition 
completely to the appropriate position. Controller 34 then initiates 
operation of actuator 36 to operate secondary throttle valves 34 at a 
point before the optimum transition point, shown at point "B" in FIG. 2. 
Thus, by the time secondary throttle valves 34 are fully moved to the "SO" 
position, engine speed increases from N.sub.3 to N.sub.1 such that engine 
10 smoothly transitions between operating conditions. 
Turning now to FIG. 3, operation of the present system begins with 
enablement of the strategy at block 60. At block 62, the current position 
of secondary throttle valve is sensed. The position of secondary throttle 
valve may be determined by a variety of methods and structures known to 
those skilled in the art and suggested by this disclosure. For example, a 
rotary potentiometer, such as used in throttle positioning in 
electronically controlled internal combustion engines, may be employed. At 
block 64, the engine speed is sensed for at least two discrete points in 
time. At block 66, the rate of change of engine speed, dN/dt, is 
calculated. This rate is used to predict the optimum transition point, to 
determine at what point to actuator 36 begins to operate secondary 
throttle valves 34, and whether the engine speed is increasing or 
decreasing, as will be further described with reference to FIGS. 5 and 6. 
At block 68, controller 42 determines an appropriate secondary throttle 
position. That is, controller 42 determines whether secondary throttle 
valves 34 should be moved from the present position. At block 70, 
controller 42 senses the position of primary engine throttle 32 using, for 
example, a rotary potentiometer. At block 72, controller 42 predicts the 
optimum transition point when actuator 36 completely moves secondary 
throttle valve 34 between "SC" and "SO". 
Continuing now with reference to FIGS. 3 and 4, at block 74, controller 42 
may alter the optimum transition point due to changes in ambient air 
temperature and engine temperature because temperature changes effects the 
ignition timing to minimize engine knock. The optimum transition point 
then may be altered based on a difference between the actual delivered 
ignition timing (SPK.sub.-- ACT) and the optimum ignition timing for best 
torque (SPK.sub.-- MBT). SPK.sub.-- MBT, shown in FIG. 4, represent the 
crank angle when the in cylinder charge is ignited to obtain maximum 
torque. Those skilled in the art will recognize in view of this disclosure 
that SPK.sub.-- MBT depends upon various engine operating parameters such 
as engine speed, engine load, spark timing, EGR rate, fuel delivery rate, 
engine air charge temperature, engine coolant temperature, intake manifold 
absolute pressure, the operating position of secondary throttle valves, 
the operating position of primary engine throttle valve, vehicle gear 
selection, vehicle speed, intake manifold air mass flow rate, accelerator 
position, and other parameters known to those skilled in the art and 
suggested by this disclosure. The inventors of the present invention have 
determined that SPK.sub.-- MBT is also dependent upon the operating 
position of secondary throttle valves. It has been found that SPK.sub.-- 
MBT is more advanced for the "SO" position than the "SC" position. 
According to the present invention, the optimum transition point may be 
altered, based on the difference between SPK.sub.-- MBT and SPK.sub.-- 
ACT, where SPK.sub.-- ACT is often retarded from SPK.sub.-- MBT to reduce 
engine knock, especially at high temperatures. That is, SPK.sub.-- ACT is 
retarded at elevated temperatures to reduce engine knock, which also 
results in less torque. The reason the optimum transition point is altered 
is because, under fast burn conditions (with the secondary throttle in the 
"SC" position), the loss in torque due to temperature increase and engine 
knock is less severe. Thus, the effect of temperature is greater when the 
secondary throttles are in the "SO" position. As a result, the engine 
speed at which the optimum transition point occurs is higher when in the 
elevated temperature condition. 
Continuing with FIG. 3, at block 76, controller 42 determines when to 
operate actuator 36, and at block 78, controller 42 operates actuator 36. 
According to the present invention, controller 42 signals actuator 36 to 
initiate moving the secondary throttle valves 34 at a point before the 
optimum transition point. In the example described herein, controller 42 
calculates an engine speed (i.e. the optimum transition point) when 
secondary throttle valves 34 should be completely moved between the "SO" 
and "SC" positions, shown as N.sub.1 in FIG. 2. Then, using the calculated 
engine speed rate, dN/dt, controller 42 determines the engine speed, shown 
as N.sub.3 in FIG. 2, at which to initiate operation of actuator 36. Thus, 
controller 42 initiates operation of actuator 36 at a point before the 
optimum transition point such that a smooth torque transition occurs 
between engine operating conditions. 
Turning now to FIGS. 5 and 6, there is shown graphs of primary engine 
throttle position versus engine speed. The graphs also show when the 
secondary throttle valves 34 are in the "SC" or "SO" positions. Referring 
in particular to FIG. 5, it can be seen that the "SC" and "SO" positions 
are independent of primary engine throttle position. Here, the optimum 
transition between the "SC" and "SO" positions occurs at a calculated 
engine speed, as discussed above. According to the present invention, the 
optimum transition point is different depending upon whether the engine 
speed is increasing or decreasing. Thus, when engine speed is increasing, 
as determined by controller 42, the optimum transition point occurs at 
N.sub.10. However, when engine speed is decreasing, the optimum transition 
point occurs at N.sub.11. This creates a desired hysteresis, shown as 
cross-hatched area H.sub.1 in FIG. 5. Without hysteresis, the secondary 
throttle valves 34 may be alternately switched between "SC" and "SO" if 
the engine is operating at or near the transition point. This phenomenon 
is known as "hunting", which the hysteresis is designed to overcome. 
In FIG. 6, the "SC" and "SO" positions are shown to be dependent upon 
primary engine throttle position. That is, the optimum transition point 
depends upon whether the engine speed is increasing or decreasing and also 
depends upon the position of the primary engine throttle. Thus, for 
example, at wide open throttle (shown as "WOT"), the optimum transition 
point from "SC" to "SO" occurs at N.sub.20 whereas, at less than wide open 
throttle (shown as "TP"), the optimum transition point from "SC" to "SO" 
occurs at N.sub.21. As discussed with reference to FIG. 5, a hysteresis 
may also be provided. Thus, at "TP", when engine speed is decreasing, the 
optimum transition point occurs at N.sub.22, rather than N.sub.21, thereby 
creating the desired hysteresis, shown as cross-hatched area H.sub.2 in 
FIG. 6. 
While the best mode for carrying out the invention has been described in 
detail, those skilled in the art in which this invention relates will 
recognize various alternative designs and embodiments, including those 
mentioned above, in practicing the invention that has been defined by the 
following claims.