Control system and method for governing turbocharged internal combustion engines

A control system and method for governing turbocharged internal combustion engines is disclosed including an electronic control unit, a fuel flow control valve, an engine speed sensor, and a bypass valve to control exhaust gas flow through an exhaust bypass conduit. When engine speed is above a first predetermined engine speed, the electronic control unit controls the bypass valve to regulate exhaust gas flow through the bypass conduit, thereby limiting exhaust gas flow through the turbocharger. When the engine speed reaches a second, predetermined engine speed value that is higher than the first predetermined engine speed value, the electronic control unit completely opens the bypass valve allowing virtually total bypass of the turbocharger, and limits fuel flow to the engine by controlling the fuel flow control valve.

BACKGROUND OF THE INVENTION 
This invention relates in general to a control system for an internal 
combustion engine with turbocharger, and more specifically to a governing 
system to limit engine speed and output torque in response to certain 
operating conditions. 
In the field of internal combustion engines, the self-limiting 
characteristics of the unsupercharged or normally aspirated petrol engine 
will usually prevent excessive engine speed. In most cases, the 
self-limiting characteristics establish a balance between the torque 
required to overcome friction and windage losses and the torque developed 
in the unloaded engine at full throttle at a speed sufficiently low to 
prevent self-destruction. However, in applications where an air 
supercharging device is used to increase engine output a maximum engine 
speed limiting device becomes a virtual necessity. Typically, a governor 
is the device used to control the maximum engine speed. 
A governor can be a mechanical or electromechanical device for 
automatically controlling the speed of an engine by regulating the intake 
of fuel. The governor limits the amount of fuel delivered to the engine 
once a predetermined engine speed is reached. When an engine is operated 
close to the governor engine speed setting, the engine speed oscillates 
above and below the governor setting due to delays in engine response to 
the reduction in fuel. Oscillation around the governor engine speed 
setting is an undesirable operating condition known as "hunting". 
The simplest method of achieving stability in the system and eliminating 
hunting is to add a control system that will provide speed droop in the 
governor. Speed droop is a sharp decrease in engine output torque above 
the governor set point. The sharp decrease in output torque caused by the 
speed droop of the governor acts to provide stability at the governor set 
point. 
Speed droop in a simple mechanical governor can be provided by a mechanical 
interconnection between servo movement and governor speed setting such 
that, as fuel is increased, the speed setting is decreased. The servo is 
positioned in response to movement of the throttle. Such a device may 
consist simply of a lever of suitable ratio between servo and speeder 
spring. The equilibrium relationship between speed setting and servo 
position for such a system may be represented by a line sloping or 
"drooping" downward to indicate a lower speed setting with movement of the 
servo toward the higher fuel delivery position. 
While the governing systems placed on internal combustion engines provide 
overspeed protection and the desired droop curve, there is the added cost 
and expense of installing a separate governor. This extra expense is 
sometimes prohibitive, especially on economy class model vehicles. 
Further, engines with separate governing systems require additional 
maintenance, resulting in increased costs. 
It would be desirable to provide a governing system which uses components 
of existing engine control systems. The use of existing components will 
reduce the cost of governing systems and reduce maintenance costs for the 
engine. 
SUMMARY OF THE INVENTION 
An apparatus, according to one aspect of the present invention, for 
governing an internal combustion engine having a turbocharger with an 
exhaust inlet and an exhaust outlet, the apparatus comprises an engine 
speed monitoring means for monitoring rotational speed of the engine, the 
engine speed monitoring means producing an engine speed signal 
corresponding to the rotational speed of the engine, an exhaust bypass 
conduit with a first end and a second end, the first end connected to the 
exhaust inlet of the turbocharger and the second end connected to the 
exhaust outlet of the turbocharger, a flow control means, including a 
control input, situated within the exhaust bypass conduit for controlling 
exhaust gas flow through the exhaust gas conduit, the flow control means 
controlling exhaust gas flow through the exhaust gas conduit in accordance 
with signals supplied at the input of the flow control means, a fuel 
control means having a control input, for controlling fuel flow to the 
engine, the fuel control means controlling fuel flow to the engine in 
accordance with signals supplied at the input of the fuel control means, 
first circuit means responsive to the engine speed signal, the first 
circuit means supplying a first control signal to the input of the flow 
control means to cause the flow control means to increase flow through the 
exhaust gas bypass conduit when the engine speed signal is above a first 
predetermined RPM limit, and second circuit means responsive to the engine 
speed signal, the second circuit means supplying a second control signal 
to the input of the fuel control means to cause the fuel control means to 
reduce fuel to the engine when the engine speed signal is above a second 
predetermined RPM limit, wherein the second predetermined cranking limit 
is higher than the first predetermined cranking limit. 
A method for governing an internal combustion engine having a turbocharger, 
according to another aspect of the present invention, comprises the steps 
of monitoring the speed of the engine, limiting exhaust gas flow through 
the turbocharger in response to an engine speed above a first 
predetermined engine RPM limit, and limiting fuel flow into the engine in 
response to an engine speed above a second predetermined engine RPM limit, 
wherein the second predetermined RPM limit is higher than the first 
predetermined RPM limit. 
It is therefore an object of the present invention to provide a governing 
system for an internal combustion engine with a turbocharging device that 
can provide the proper reduction (droop) in engine output torque above a 
predetermined engine speed, using existing engine components. 
It is another object of the present invention to provide a control system 
for an engine with a turbocharger that provides an economical alternative 
to the installation of independent electronic governing systems. 
Related objects and advantages of the present invention will become more 
apparent from the following description of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the embodiment illustrated in the 
drawings and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations and further modifications 
in the illustrated device, and such further applications of the principles 
of the invention as illustrated therein being contemplated as would 
normally occur to one skilled in the art to which the invention relates. 
Referring now to FIG. 1, a diagrammatic illustration of a microprocessor 
controlled governing system for a turbocharged internal combustion engine 
in accordance with the preferred embodiment of the present invention. In 
the preferred embodiment, the governing system includes an electronic 
control unit 10. The electronic control unit 10 includes a microprocessor 
(not shown) including a program ROM, RAM, and analog I/O and digital I/O. 
The electronic control unit 10 is connected to a power source 60 by signal 
paths 62 and 66. The control unit 10 receives sensory input signals from a 
variety of engine sensors, as shown in FIG. 2, and produces output control 
signals that control several engine operating functions. 
The internal combustion engine of the preferred embodiment is a spark 
ignited engine fueled by natural gas. The natural gas fuel is delivered 
from a fuel supply tank (not shown) through a fuel supply line 34. Fuel 
flow is regulated by fuel control valve 38. The fuel control valve 38 has 
electronic controls and receives flow control signals from the electronic 
control unit 10. The fuel control valve 38 regulates the amount of fuel 
supplied to the fuel manifold 32 in response to the flow control signals 
produced by electronic control unit 10. 
Turbocharger 12 is mechanically actuated by the flow of exhaust gases. 
Exhaust gases enter through the turbocharger exhaust gas inlet 26 and 
strike the turbine fan 16. The exhaust gases exit the turbocharger through 
the turbocharger exhaust gas outlet 24. The rotational forces created by 
the exhaust gas flowing through turbine fan 16 are transferred via turbine 
drive shaft 18 to the turbocharger compressor wheel 14. The turbocharger 
compressor wheel 14 compresses the air from the fresh air inlet 20 and 
delivers the compressed air to the air manifold 22. 
The compressed air of the air manifold 22 is mixed with fuel supplied via 
fuel manifold 32. The mixture moves through the intake manifold 36 to the 
combustion chamber 44. The air-fuel mixture is delivered to the combustion 
chamber 45 through intake port 40. The air-fuel mixture is then compressed 
and spark ignited. For illustration purposes only one combustion chamber 
is shown in FIG. 1. However, is apparent to those skilled in the art, the 
engine may have a plurality of such combustion chambers. 
After the combustion cycle, the exhaust gases are expelled through exhaust 
port 42 and enter the exhaust gas manifold 48. The exhaust gas manifold 48 
is connected to the turbocharger exhaust gas inlet 26, such that exhaust 
gases may flow through the turbocharger fan 16. An exhaust bypass conduit 
28 connects the turbocharger exhaust gas inlet 26 to the turbocharger 
exhaust gas outlet 24. The exhaust gas bypass conduit 28 serves to route 
part or all of the engine exhaust gas around the turbocharger 12, thereby 
controlling or limiting the air pressure in the intake manifold 36 and, 
subsequently, the air mass in the combustion chamber 44. 
An exhaust gas bypass valve 30 is located within the exhaust bypass conduit 
28. The valve 30 iis known in the art as a wastegate valve. The bypass 
valve 30 is actuated in such a fashion as to regulate the exhaust gas flow 
through the exhaust gas conduit, thereby controlling the exhaust gas flow 
through the turbocharger. The bypass valve 30 is actuated via pneumatic 
pressure. The pneumatic pressure in the valve assembly is controlled by 
electronic control unit 10, which transmits signals to the bypass valve 
assembly via signal path 54. 
During normal operation, the position of the bypass valve 30 is calculated 
by the electronic control unit 10 to regulate exhaust flow through the 
turbocharger. The position is calculated to optimize the air manifold 
pressure and subsequent air mass in the combustion chamber for maximum 
engine output. 
One object of the present invention is to limit the engine speed when 
engine operation is outside of normal operating conditions and to create a 
sharp decrease in engine output torque above a predetermined governor set 
point. A sharp decrease in engine output torque above the governor set 
point minimizes speed "hunting" around the governor set point. In the 
preferred embodiment of the present invention, the electronic control unit 
10, which is used to control a variety of engine parameters, is 
pre-programmed with two predetermined engine speed values. The first value 
is the rated engine speed, while the second value is midway between the 
rated engine speed and a maximum engine speed. 
Electronic control unit 10 receives engine speed signals from speed sensing 
device 50. When the engine speed reaches a first predetermined engine 
speed value, electronic control unit 10 will calculate a desired position 
for the bypass valve 30 necessary to achieve a specified "droop" in engine 
output torque. The electronic control unit 10 supplies a control signal to 
bypass valve 30 to control the position of the bypass valve. As valve 30 
reduces exhaust gas flow through conduit 26, air flow will be reduced in 
conduit 22 and engine power and torque are reduced accordingly. As the 
engine speed increases above the first predetermined value, the electronic 
control unit 10 supplies signals to the bypass valve 30 controlling it to 
open further and allow more exhaust gas to bypass the turbocharger. Once 
the engine speed has reached the second predetermined engine speed value, 
the bypass valve 30 will be controlled to its fully open position, 
enabling maximum exhaust gas bypass around the turbocharger. 
At or above the second predetermined engine speed value, the electronic 
control unit will calculate an appropriate position for fuel control valve 
38 to create the desired droop in engine output torque. A signal from 
electronic control unit 10 is supplied to fuel control valve 38 to limit 
fuel to the engine. The electronic control unit 10 will continue to reduce 
fuel supplied to the engine until the engine speed reaches a maximum 
engine speed, at which point the electronic control unit will control the 
fuel control valve to an almost completely closed position, whereby fuel 
flow to the engine will be substantially cut-off. 
Referring now to FIG. 2, a block diagram of the electronic control unit 10 
is shown. The engine control unit receives a number of inputs from various 
engine sensors. These include the intake manifold pressure sensor 76, 
intake manifold temperature sensor 78, turbocharger compressor output 
pressure sensor 80, coolant temperature sensor 82, throttle position 
sensor 84, fuel flow sensor 90, and engine speed sensor 50. Electronic 
control unit 10 produces various signals to control the operation of the 
engine. Devices receiving control signals include the idle control device 
94, fuel shutdown valve 88, fuel flow control valve 38, bypass (wastegate) 
valve 30 and the control module 96 which provides signals to the coil 
packs 98. Coil packs 98 provide signals to the spark plugs 99. Gas 
pressure regulator 86 and air/fuel mixer 92 are not directly controlled by 
the electronic control unit 10. 
The present invention is primarily concerned with controlling the bypass 
valve 30 and fuel control valve 38. The electronic control unit 10 is 
programmed to control the bypass valve 30 and fuel control valve 38 in 
such a manner as to reduce the engine output torque above the rated engine 
speed to create a droop curve similar to that produced by a governed 
diesel engine. 
Referring now to FIG. 3, a flowchart of an engine speed control subroutine 
executed by the electronic control unit 10 is shown. This routine is 
executed many times each second during normal engine operation. Upon 
receiving a power signal, the electronic control unit 10 is initialized at 
step 100. At step 102, the electronic control unit inputs the engine speed 
signal from speed sensor 50. At step 104, the electronic control unit 
compares the engine speed of step 102 to the first predetermined value, 
2800 RPM. If the engine speed is less than 2800 RPM then the execution 
returns to step 102 to read the engine speed again. 
If the engine speed is above 2800 RPM at step 104, then step 106 is 
executed and the engine speed is compared to the second predetermined 
value, 2900 RPM. If the engine speed is less than 2900 RPM at step 106, 
then step 108 is executed thereafter and the desired position of the 
bypass valve 30 is determined. Next at step 110 the electronic control 
unit sends a control signal to bypass valve 30 to position the valve in 
accordance with the valve position determined at step 108. Program 
execution continues at step 102 after step 110. 
If the engine speed is greater than 2900 RPM at step 106, then program 
execution continues at step 112 and the bypass valve 30 is sent a control 
signal to position the valve to its fully open position. Next, at step 
114, electronic control unit 10 calculates the desired position of the 
fuel control valve 38. The position of the fuel control valve is 
calculated to limit fuel to the engine to create a reduction in engine 
output torque. After step 118, program flow returns to step 102 to read 
the engine speed. 
Referring now to FIG. 4, a graphical illustration showing the engine output 
torque curve 400 versus engine speed. Idle speed and associated output 
torque are shown at point A. The curve 400 increases to a maximum output 
torque at point B, then steadily decreases to point C, the rated engine 
speed. The first predetermined valve is the rated engine speed, 2800 RPM, 
point C on curve 400. The second predetermined value is 2900 RPM, point D 
on the curve 400. Once the engine reaches 2800 RPM, point C, the 
electronic engine control unit begins to modulate the bypass valve 30, 
thereby decreasing turbocharger action. The electronic control unit 10 
modulates the bypass valve from point C, 2800 RPM, to point D, 2900 RPM, 
thereby reducing the output torque from approximately 360 Ft.Lb. to 
approximately 280 Ft.Lb. At point D, 2900 RPM, the electronic control unit 
10 controls the bypass valve to a full open position, allowing virtually 
total bypass of exhaust gases around the turbocharger turbine fan. 
Electronic control unit 10 begins modulating the fuel control valve 38 
once the engine speed is above 2900 RPM. The fuel valve is modulated to 
continue reduction of the output torque from approximately 280 Ft.Lb. to 
approximately 180 Ft.Lb. The modulation of the fuel control valve 
continues until the engine speed reaches a maximum engine speed at point 
E, 3000 RPM, at which point the fuel flow control valve is positioned to 
allow the minimum fuel flow to the engine, almost completely shutting off 
the fuel supply to the engine. 
While the invention has been illustrated and described in detail in the 
drawing and foregoing description, the same is to be considered as 
illustrative and not restrictive in character, it being understood that 
only the preferred embodiment has been shown and described and that all 
changes and modifications that come within the spirit of the invention are 
desired to be protected.