U.S. patent application number 09/766384 was filed with the patent office on 2001-10-25 for control of a variable geometry turbocharger by sensing exhaust pressure.
Invention is credited to Murphy, Brian J., Seiberlich, Mathew J., Terry, Wesley J..
Application Number | 20010032465 09/766384 |
Document ID | / |
Family ID | 22651065 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010032465 |
Kind Code |
A1 |
Terry, Wesley J. ; et
al. |
October 25, 2001 |
Control of a variable geometry turbocharger by sensing exhaust
pressure
Abstract
There is provided a system and method for using an engine's
exhaust back pressure to control a variable geometry turbocharger.
The control system determines a desired exhaust back pressure based
on engine speed and engine load. The desired exhaust back pressure
is compared with a measured exhaust back pressure to determine the
difference between the measured and desired exhaust back pressures.
The difference value is used to determine the duty cycle. In an
alternate embodiment, the exhaust gas pressure is used to adjust
the duty cycle determined by other operating parameters. A base
duty cycle is determined from the engine speed and the engine load.
The difference between the measured and desired exhaust back
pressures is used to determine an exhaust pressure control duty
cycle. The base duty cycle is then adjusted by the exhaust pressure
control duty cycle to give a turbocharger duty cycle.
Inventors: |
Terry, Wesley J.; (Union,
IL) ; Seiberlich, Mathew J.; (Elgin, IL) ;
Murphy, Brian J.; (Chicago, IL) |
Correspondence
Address: |
INTERNATIONAL TRUCK AND ENGINE CORPORATION
Suite 1300
455 North Cityfront Plaza Drive
Chicago
IL
60611
US
|
Family ID: |
22651065 |
Appl. No.: |
09/766384 |
Filed: |
January 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60178071 |
Jan 25, 2000 |
|
|
|
Current U.S.
Class: |
60/602 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02D 41/1448 20130101; F02D 2250/34 20130101; F02D 41/0007
20130101; F02B 37/24 20130101 |
Class at
Publication: |
60/602 |
International
Class: |
F02D 023/00 |
Claims
We claim:
1. A method for controlling a variable geometry turbocharger,
having an operatively connected turbine and compressor housings,
used in an internal combustion engine, the method comprising the
steps of: determining a total desired exhaust back pressure;
determining a measured exhaust back pressure; determining a
difference )EBP between the total desired exhaust back pressure and
the measured exhaust back pressure; determining a duty cycle based
upon the difference )EBP; and actuating turbocharger nozzles based
upon the calculated duty cycle; whereby the nozzles are positioned
to achieve the total desired exhaust back pressure.
2. The method of claim 1, wherein the nozzles operate incrementally
in relation to nozzle positions existing prior to actuation.
3. The method of claim 1, wherein the nozzles assume predetermined
nozzle positions irrespective of nozzle position existing prior to
actuation.
4. The method of claim 1, wherein the total desired exhaust back
pressure is a base desired exhaust back pressure, a temperature
desired exhaust back pressure, braking desired exhaust back
pressure, or an EGR desired exhaust back pressure.
5. The method of claim 1, wherein the total desired exhaust back
pressure is any combination of a base desired exhaust back
pressure, a temperature desired exhaust back pressure, braking
desired exhaust back pressure, and an EGR desired exhaust back
pressure.
6. The method of claim 1, wherein the total desired exhaust back
pressure comprises: the base desired exhaust back pressure; the
temperature desired exhaust back pressure; the braking desired
exhaust back pressure; and the EGR desired exhaust back
pressure.
7. The method of claim 1, wherein the difference )EBP is calculated
in a controller.
8. The method of claim 7, wherein the controller is an electronic
control module, an engine microprocessor, or a turbocharger
microprocessor.
9. The method of claim 8, wherein the controller generates a pulse
width modulated signal to a pulse width modulated driver which will
determine the duty cycle.
10. The method of claim 9, wherein the pulse width modulated driver
provides the duty cycle to a control device for the nozzles.
11. The method of claim 10, wherein the control device is a control
solenoid or a pneumatic valve.
12. The method of claim 1, wherein the nozzles are fully open at a
duty cycle at or below 25 percent, and fully closed at a duty cycle
at or above 75 percent.
13. A method for controlling a variable geometry turbocharger,
having operatively connected turbine and compressor housings, used
in an internal combustion engine, the method comprising the steps
of: determining a base duty cycle; determining a total desired
exhaust back pressure; determining a measured exhaust back
pressure; determining a difference )EBP between the total desired
exhaust back pressure and the measured exhaust back pressure;
determining an exhaust pressure duty cycle based upon the
difference )EBP; determining a turbocharger duty cycle by adjusting
the base duty cycle by the exhaust pressure duty cycle; and
actuating turbocharger nozzles based upon the turbocharger duty
cycle.
14. The method of claim 13, wherein the nozzles operate
incrementally in relation to nozzle positions existing prior to
actuation.
15. The method of claim 13, wherein the nozzles assume
predetermined nozzle positions irrespective of nozzle position
existing prior to actuation.
16. The method of claim 13, wherein the base duty cycle is
determined through a base duty cycle set-point table based on
engine speed and engine load.
17. The method of claim 13, wherein the base duty cycle is
determined through a base duty cycle set-point table based on
engine temperature, engine speed and engine load.
18. The method of claim 13, wherein the base duty cycle is
determined through a base duty cycle set-point table based on
braking parameters, vehicle speed, engine speed and engine
load.
19. The method of claim 13, wherein the base duty cycle is
determined through a base duty cycle set-point table based on an
EGR signal, engine speed and engine load.
20. The method of claim 13, wherein the base duty cycle is
determined through a base duty cycle set-point table based on
engine temperature, braking parameters, vehicle speed, an EGR
signal, engine speed and engine load.
21. The method of claim 16, wherein the total desired exhaust back
pressure is a base desired exhaust back pressure, a temperature
desired exhaust back pressure, braking desired exhaust back
pressure, or an EGR desired exhaust back pressure.
22. The method of claim 16, wherein the total desired exhaust back
pressure is any combination of a base desired exhaust back
pressure, a temperature desired exhaust back pressure, braking
desired exhaust back pressure, and an EGR desired exhaust back
pressure.
23. The method of claim 16, wherein the total desired exhaust back
pressure comprises: the base desired exhaust back pressure; the
temperature desired exhaust back pressure; the braking desired
exhaust back pressure; and the EGR desired exhaust back
pressure.
24. The method of claim 13, wherein the difference )EBP is
calculated in a controller.
25. The method of claim 24, wherein the controller is an electronic
control module, an engine microprocessor, or a turbocharger
microprocessor.
26. The method of claim 24, wherein the controller generates a
pulse width modulated signal to a pulse width modulated driver
which will determine the duty cycle.
27. The method of claim 26, wherein the pulse width modulated
driver provides the duty cycle to a control device for the
nozzles.
28. The method of claim 27, wherein the control device is a control
solenoid or a pneumatic valve.
29. The method of claim 13, wherein the nozzles are fully open at a
duty cycle at or below 25 percent, and fully closed at a duty cycle
at or above 75 percent.
30. A control system for a variable geometry turbocharger, having
operatively connected turbine and compressor housings, for use in
an internal combustion engine, the control system comprising: an
exhaust back pressure sensor able to generate an exhaust back
pressure measurement signal; a control device able to actuate a
turbocharger nozzle; and a controller able to process the exhaust
back pressure measurement signal; whereby the controller generates
a control signal to the control device, based upon the exhaust back
pressure measurement signal and at least one predetermined engine
parameter, to thereby actuate the turbocharger nozzle.
31. The control system of claim 30, wherein the at least one
predetermined engine parameter is vehicle speed, engine speed,
engine load, engine temperature, or ambient air temperature.
32. The control system of claim 30, wherein the controller is an
electronic control module, an engine microprocessor, or a
turbocharger microprocessor.
33. The control system of claim 30, wherein the control device is a
control solenoid or a pneumatic valve.
34. The control system of claim 30, wherein the measurement signal
is electronic, magnetic or optical.
Description
[0001] This patent application claims the benefit of Provisional
U.S. Patent application Ser. No. 60/178,071 filed on Jan. 25,
2000.
FIELD OF THE INVENTION
[0002] This invention relates generally to control systems for
turbochargers. More particularly, this invention relates to control
systems that sense the exhaust gas pressure to control variable
geometry turbochargers on internal combustion engines.
BACKGROUND OF THE INVENTION
[0003] Many internal combustion engines use turbochargers to
improve engine performance. A turbocharger increases the density of
the intake air into the engine. The higher density air increases
the amount of fuel the engine may combust. As a result, the power
output of the engine increases.
[0004] Turbochargers typically have a turbine and a compressor
connected by a common shaft. The turbine has blades attached to a
wheel, which is mounted on the shaft. A turbine housing encloses
the turbine and connects to the exhaust gas manifold of the engine.
The turbine housing has vanes for directing the exhaust gases
against the turbine blades. The compressor has blades attached to
another wheel, which also is mounted on the shaft. A compressor
housing encloses the compressor and connects to the intake air
manifold of the engine. The compressor housing has vanes for
assisting the compressor to pressurize intake air. The compressor
housing is isolated from the turbine housing.
[0005] In operation, exhaust gases pass through the exhaust gas
manifold into the turbine housing. The vanes in the turbine housing
direct the exhaust gases against the turbine blades. The exhaust
gas pressure causes the turbine to spin, which causes the
compressor to spin. The spinning compressor pressurizes the intake
air. As a result, higher density air is provided to the intake air
manifold.
[0006] In a turbocharger, the exhaust gas pressure has a direct
effect on the intake air pressure. As the exhaust gas pressure
increases, the turbine and consequently the compressor spin faster.
A faster spinning compressor increases the intake air pressure. The
opposite effect occurs as the exhaust gas pressure decreases.
[0007] Many turbochargers have a fixed geometry. The vanes in the
turbine and compressor housings are stationery. By design, a
fixed-geometry turbocharger operates efficiently at a particular
engine speed and load. Conversely, it operates less efficiently at
engine speeds and loads for which it is not designed.
[0008] At low engine speeds, the exhaust gas pressure is low. It
may be below the minimum necessary for operating the turbine. As
the engine accelerates from idle or slow speeds, there is a delay
from the time when the engine load increases to the time when there
is sufficient exhaust gas pressure to spin the turbine. Even when
the turbine spins, the exhaust gas pressure may not reach a high
enough pressure fast enough to spin the turbine as fast as it is
necessary for the compressor to produce the desired intake air
pressure.
[0009] The exhaust gas pressure increases as engine speed
increases. At some point, the pressure becomes high enough to
overpower the turbocharger. An overpowered turbocharger reduces
engine performance. Additionally, the high exhaust pressure
associated with an overpowered turbocharger may cause the
turbocharger to fail from fatigue, broken seals, and similar
problems.
[0010] To improve efficiency, fixed-geometry turbochargers are
sized to provide high compressor speeds at low engine speeds. The
vanes in the turbine housing usually narrow to increase the exhaust
gas pressure. The vanes also direct the exhaust gas flow toward a
portion of the turbine blades. While these changes improve the
performance of the turbocharger at low engine speeds, they
adversely affect the performance of the turbocharger at high engine
speeds. The narrowing of the vanes lowers the exhaust gas pressure
at which the turbocharger becomes overdriven.
[0011] To avoid overdriving, fixed-geometry turbochargers have a
waste gate or similar valve positioned between the turbine and the
exhaust gas manifold. When the exhaust gas pressure reaches a
certain level, the waste gate opens to divert exhaust gases away
from the turbine. This approach responds and corrects for an
overdriving condition. However, it waits for the condition to occur
before responding. It also wastes energy and requires additional
equipment.
[0012] New turbocharger designs have a variable geometry. The
turbine and/or compressor housings have variable nozzles, which
move to change the flow area and flow direction. In many designs,
only the turbine has variable nozzles.
[0013] A variable nozzle turbine (VNT) turbocharger typically has
curvilinear nozzles, which rotate between open and closed positions
about a pivot. In some designs, the closed position leaves a small
gap between the nozzles. In other designs, the nozzles touch when
they are closed, which essentially stops the flow of exhaust gas to
the turbine. The nozzles connect to each other by a ring or similar
apparatus to move in unison. An electronic control module sends an
electronic signal to activate a solenoid, pneumatic valve, or
similar device.
[0014] When the exhaust gas pressure is low, the nozzles close to
create a narrower area for the exhaust gases to flow. The narrower
area restricts gas flow through the turbine housing, thus
increasing exhaust gas pressure. The nozzles also direct the
exhaust gases optimally at the tips of the turbine blades. The
directed flow and higher pressure enables the turbine to start
spinning sooner and at a faster rate. As a result, a VNT
turbocharger provides the high compressor speeds desired at low
engine speeds.
[0015] As the exhaust gas pressure increases, the nozzles open to
reduce the restriction to the gas flow. The gas flow also is
directed toward the entire length of the turbine blades. With less
restriction and broader gas flow, the turbine and consequently the
compressors pins slower than if the nozzles were closed under these
conditions. As a result, the turbocharger is able to respond and
correct for overdriven conditions.
[0016] Proper nozzle control is necessary to optimize performance
of a VNT turbocharger. Internal combustion engines, especially
those in vehicles, have constantly changing demands. One moment,
the engine is at low speed. The next moment, the engine is at high
speed. Engine load and other parameters change almost constantly.
Accordingly, the nozzles must adjust to new operating conditions
quickly. If the nozzles delay closing, such as when the engine goes
from high to low speeds, the turbocharger will not provide the
desired intake air pressure. If the nozzles delay opening, such as
when the engine goes from low to high speeds, the turbocharger will
be overdriven.
[0017] In most designs, VNT turbochargers are controlled by the
intake air pressure. The measured intake air pressure is compared
to a desired intake air pressure. A sensor is located in the intake
air manifold to determine the measured intake air pressure. The
engine's electronic control module (ECM) or other microprocessor
determines the desired intake air pressure based on engine
operating parameters such as engine speed, engine load, ambient air
pressure, etc. If the measured intake pressure is higher then the
desired intake pressure, the ECM opens the nozzles until the
measured and desired intake pressures are equal. Conversely, if the
measured intake pressure is lower than the desired intake pressure,
the ECM closes the nozzles until the intake pressures are
equal.
[0018] To open or close nozzles, the ECM sends an electric signal
to the solenoid, pneumatic valve, or other device controlling the
nozzles. The strength of the electric signal or duty cycle
determines the position of the nozzles. The duty cycle is a
percentage of the total electrical signal necessary to move the
nozzles into their closed position. While the duty cycle is
indicative of the nozzle position, the duty cycle for a particular
nozzle position varies from turbocharger to turbocharger.
[0019] Intake air pressure is not suitable for optimizing the
performance of a VNT turbocharger. Generally, the intake air
pressure increases as the nozzles close. However, there is position
where the intake air pressure reaches a maximum level and then
decreases if the nozzles close further.
[0020] FIG. 1 shows the relationship between the intake air
pressure and the turbine duty cycle (nozzle position). As the
turbine duty cycle increases from 20 to 60 percent, the intake air
pressure increases from 7 to 28 in. Hg. As the turbine duty cycle
increases above 60 percent, the intake air pressure decreases. The
nozzles have restricted the flow of gases to the turbine
sufficiently to slow the compressor. Consequently, the intake air
pressure decreases to 19 in. Hg at a duty cycle of 80 percent. At
this point and beyond, the nozzles are closed.
[0021] As the nozzles close beyond the position of maximum air
intake pressure, they prevent exhaust gases from flowing across the
turbine. The turbine and compressor turn slower with less exhaust
gas flow. However, the exhaust gas pressure increases dramatically.
This combination of a slower compressor and higher exhaust gas
pressure decreases the engine torque and increases fuel
consumption. The turbocharger is providing excess exhaust pressure
to the engine. The excess exhaust pressure effectively "steals"
work from the engine to produce the high exhaust gas pressure. It
turns the engine into an air compressor, thus diverting power from
the transmission.
[0022] The maximum intake air pressure is dependent largely upon
the exhaust gas volume. At lower engine speeds, the maximum intake
air pressure occurs at higher duty cycles (the nozzles are more
closed). At higher engine speeds, the maximum intake air pressure
occurs at lower duty cycles (the nozzles are more open). This
affect is more noticeable on VNT turbochargers where the nozzles
close completely.
[0023] It is difficult to control a VNT turbocharger based on the
intake air pressure. At many intake air pressures, the ECM cannot
properly determine whether to open or close the nozzles. For
example in FIG. 1, an intake air pressure of 25 in. Hg occurs at
two duty cycles. Depending on the duty cycle, opening the nozzles
may decrease or increase the intake air pressure. Similarly,
closing the nozzles also may decrease or increase the intake air
pressure. The problem worsens if the turbocharger has nozzles that
close completely.
[0024] In addition to control problems, controllers based on the
intake air pressure do not identify and address the excessive
exhaust gas pressure conditions when the turbocharger may be
overdriven. These conditions may occur prior to the intake air
pressure reaching a maximum.
[0025] To address excessive exhaust gas pressure, some
turbochargers include an exhaust gas pressure sensor in the exhaust
gas manifold. In one approach, the ECM opens the nozzles when the
exhaust gas pressure reaches a certain level. The ECM keeps opening
the nozzles until the exhaust gas pressure returns to a proper
level. Another design compares the intake air pressure with the
exhaust gas pressure. When the difference between the pressures
reaches a certain level, the ECM opens the nozzles until the
difference returns to a proper level.
[0026] While these approaches respond to excessive exhaust gas
pressure, they do so after the overdriving conditions already
exist. They also require additional equipment, namely a sensor and
associated control interfaces. In addition, they create a "seesaw"
effect when operating the turbocharger. When the intake air
pressure is lower than the desired intake air pressure, the ECM
closes the nozzles. This action increases the exhaust gas pressure
to drive the turbine and compressor faster. When the exhaust gas
pressure exceeds a certain level, the ECM opens the nozzles to
reduce the exhaust gas pressure. At that point, if the measured
intake air pressure is below the desired intake air pressure, the
ECM closes the nozzles to increase the intake air pressure. This
seesaw effect continues until the operating parameters of the
engine change.
[0027] In another design, a VNT turbocharger is controlled by
sensing the position of the variable vanes. A predetermined map
provides a desired vane position based upon engine conditions such
as engine speed and load. As these engine conditions change, the
variable vanes are moved to the desired vane position for those
conditions. Theoretically, the desired vane position should provide
the desired intake boost pressure. However, the vane position does
not adequately adjust for the variability in exhaust gas volume and
pressure associated with changing engine conditions. In addition,
the vane position to intake boost pressure relationship will have
errors unless manufacturing tolerances are small between
turbochargers.
[0028] Accordingly, there is a need for a turbocharger control
system that maximizes the available intake boost pressure while
avoiding excessive exhaust gas pressure and overdriving conditions
under variable and changing engine operations.
SUMMARY OF THE INVENTION
[0029] The present invention provides a system and method for using
an engine's exhaust back pressure to control a variable geometry
turbocharger. The control system determines a desired exhaust back
pressure based on engine speed and engine load. The desired exhaust
back pressure is compared with a measured exhaust back pressure to
determine the difference between the measured and desired exhaust
back pressures. The difference between the desired and measured
pressures is used to determine the duty cycle for the
turbocharger.
[0030] The exhaust back pressure provides greater controllability
over the prior art. This enhanced controllability enables
additional embodiments for controlling turbochargers with cold
weather warm-up, engine braking, and exhaust gas recirculation
(EGR) capabilities. In cold weather, "extra" exhaust pressure will
cause the engine to increase fuel consumption thus shortening the
time to warm-up of the engine.
[0031] During braking, the engine may be used to slow the vehicle.
Higher exhaust gas pressures increase negative torque and thus slow
the engine. The decrease in engine speed slows the vehicle when the
transmission is engaged. Engine braking is desirous to augment
cruise control. For engines with EGR, the control system ensures
the exhaust gas pressure is always higher than the intake air
pressure. This enables the exhaust gas to enter the intake air
manifold as desired. It also avoids additional equipment associated
with EGR.
[0032] While these embodiments use the exhaust back pressure to
determine the duty cycle for the turbocharger, an alternate
embodiment uses the exhaust gas pressure to adjust the duty cycle
determined by other operating parameters. In the alternate
embodiment, a base duty cycle is determined from the engine speed
and the engine load. The difference between the measured and
desired exhaust back pressures is used to determine an exhaust
pressure control duty cycle. The base duty cycle is then adjusted
by the an exhaust pressure control duty cycle to provide an
adjusted duty cycle to the turbocharger.
[0033] The following drawings and description set forth additional
advantages and benefits of the invention. More advantages and
benefits are obvious from the description and may be learned by
practice of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The present invention may be better understood when read in
connection with the accompanying drawings, of which:
[0035] FIG. 1 is a chart comparing the intake air pressure to the
turbine duty cycle for a VNT turbocharger;
[0036] FIG. 2 is a perspective view of a diesel engine having a
turbocharger with a turbocharger control system according to the
present invention;
[0037] FIG. 3 is a close-up perspective view of the turbocharger in
FIG. 2;
[0038] FIG. 4 is a schematic view of the turbocharger in FIG.
2.;
[0039] FIG. 5 is a block diagram of the turbocharger control
interface according to the present invention;
[0040] FIG. 6 is a block diagram showing a first embodiment of the
closed-loop control strategy for a turbocharger according to the
present invention;
[0041] FIG. 7 is a set-point table for determining the desired
exhaust back pressure according to the present invention;
[0042] FIG. 8 is a chart comparing the exhaust gas pressure to the
turbine duty cycle for a VNT turbocharger;
[0043] FIG. 9 is a chart comparing the intake air pressure and
exhaust gas pressure to the turbine duty cycle for a VNT
turbocharger;
[0044] FIG. 10 is a block diagram showing a second embodiment of
the closed-loop control strategy for a turbocharger according to
the present invention;
[0045] FIG. 11 is a block diagram showing a third embodiment of the
closed-loop control strategy for a turbocharger according to the
present invention;
[0046] FIG. 12 is a method for controlling a VNT turbocharger
according to the present invention;
[0047] FIG. 13 is a method for controlling a VNT turbocharger with
cold weather warm-up capabilities according to the present
invention;
[0048] FIG. 14 is a method for controlling a VNT turbocharger with
engine braking capabilities according to the present invention;
[0049] FIG. 15 is a method for controlling a VNT turbocharger with
exhaust gas recirculation capabilities according to the present
invention; and
[0050] FIG. 16 is an alternate method for controlling a VNT
turbocharger according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0051] FIGS. 2-4 show an internal combustion engine 100 having a
turbocharger 110 controlled by sensing the exhaust gas pressure
according to the present invention. FIG. 2 is a perspective view of
the turbocharger 110 mounted on the engine 100. FIG. 3 is a
close-up perspective view of the turbocharger 110 in FIG. 2. FIG. 4
is a schematic view of the turbocharger 110 mounted on the engine
100 (only one side of the engine is shown).
[0052] The internal combustion engine 100 is a compression ignition
or diesel engine with a v-configuration. The turbocharger 110 is a
variable nozzle turbine (VNT) turbocharger. While FIG. 4 shows only
four cylinders, the present invention may be used with any number
of cylinders. Additionally, the engine may have a spark ignition
and an in-line or other configuration. The present invention is
applicable to any variable geometry turbocharger including those
with variable compressor nozzles. While only one turbocharger is
shown, the present invention may be applied to engines with
multiple turbochargers.
[0053] The turbocharger 110 has a turbine housing 210 connected to
a compressor housing 220. The turbine housing 210 is connected to
the exhaust manifold 230 of the internal combustion engine 100. The
compressor housing is connected to the air intake manifold 235.
While the figures show a particular scheme for mounting
turbocharger 110 on engine 100, other mounting schemes may be
used.
[0054] The turbine housing 210 encloses a turbine 245 mounted on a
shaft 250. The turbine has variable nozzles (not shown) operated by
a control solenoid 240. A pneumatic valve or other control device
may be used in place of the control solenoid 240. The control
solenoid 240 opens and closes the nozzles, which have little or no
gaps between them when they are closed completely. Other
turbochargers may be used where the nozzles are not able to close
completely.
[0055] The compressor housing 220 encloses a compressor 222 mounted
on the shaft 250, which connects the compressor 222 to the turbine
245. Except for the shaft 250, the compressor housing 220 is
isolated from the turbine housing 210. The compressor housing 220
has vanes (not shown) to assist in pressurizing the intake air for
the engine 100. The vanes are optional and various types may be
used.
[0056] An exhaust back pressure sensor 255 is operatively mounted
on the exhaust manifold 230 for sensing the exhaust gas pressure.
The exhaust back pressure sensor 255 provides a pressure signal
indicating the measured exhaust back pressure to an electronic
control module (not shown). While a sensor is used, other means may
be used to determine and provide a signal of the exhaust back
pressure. While the figures show a position for the exhaust back
pressure sensor 255, it may be placed elsewhere on the exhaust gas
manifold 230 and the portion of the turbine housing 210 connecting
with the exhaust gas manifold 230.
[0057] The electronic control module provides a control signal to
the control solenoid 240 to open and close the nozzles based upon
the measured exhaust back pressure. The electronic control module
may be the microprocessor used to control the engine. However,
there maybe separate microprocessors to control the engine and the
turbine. In that scenario, the engine microprocessor would be
connected to the turbocharger microprocessor for monitoring and
control purposes.
[0058] FIG. 5 is a block diagram of the control interface for a
turbocharger according to the present invention. A speed sensor 505
and a load sensor 510 provide electronic signals of the engine
speed and engine load respectively to the electronic control module
(ECM) 515. The exhaust back pressure sensor 255 provides an
electronic signal of the measured exhaust back pressure (MEBP) to
the ECM 515.
[0059] Other pre-determined engine parameters 520 may be provided
to the ECM 515. The other pre-determined engine parameters 520 may
include the ambient air pressure, the vehicle speed, the engine
temperature, and other common operating parameters of the engine
and vehicle.
[0060] While sensors are shown as providing electronic signals,
other means may be used to provide the necessary inputs into the
ECM 515. In addition, the inputs may be signals other than
electronic signals such as magnetic or optical signals as long as
the ECM 515 may interpret them to control the turbocharger.
[0061] The ECM 515 includes or is connected to electronic or data
storage media 525, which are capable of temporary or permanent
storage Such electronic or data storage media includes PROM, EPROM,
EEPROM, flash memory, magnetic, optical, and combinations of these
devices. The electronic or data storage media function in the
control system as read-only memory, random access memory,
keep-alive memory and the like.
[0062] The ECM 515 compares the measured exhaust back pressure
(MEBP) with the desired exhaust back pressure (DEBP). The ECM 515
determines the DEBP by comparing the engine speed and engine load
to map data in the electronic or data storage media 525. The ECM
515 determines the difference (.DELTA.EBP) between the MEBP and the
DEBP. Based on the .DELTA.EBP, the ECM 515 provides a pulse width
modulated signal to a pulse width modulated (PWM) driver 530. While
a pulse width modulated signal and driver are used, other types of
signals and drivers may be used.
[0063] The PWM driver 530 determines and provides a duty cycle to
the control solenoid 240 on the turbocharger 110. The control
solenoid 240 opens and closes the turbine nozzles based upon the
duty cycle.
[0064] FIG. 6 shows a first embodiment of the closed-loop control
strategy for a turbocharger according to the present invention. The
engine speed and engine load signals are sent to a set-point table
605 after they pass through a first low-pass filter 610 and a
second low-pas filter 615 respectively. The set-point table 605
determines the desired exhaust back pressure (DEBP) based on the
engine speed and engine load. The DEBP is then sent to summer 620.
Notably, the DEBP of FIG. 6 is a special case, or the base case, of
the various cases shown in FIG. 10. Thus, in the base case, the
DEBP of FIG. 6 is the base desired exhaust back pressure of FIG.
10, and the set point table 605 of FIG. 6 is the base set-point
table 605 of FIG. 10.
[0065] Other pre-determined engine parameters may be used to
determine the DEBP in place of or in addition to the engine speed
and load, e.g., as will be discussed with respect to FIG. 10. If
other or additional engine operating parameters are used, the
operating data identifies the desired exhaust back pressure based
on those parameters.
[0066] Continuing with FIG. 6, the measured exhaust back pressure
(MEBP) then passes through a low-pass filter 625 and is sent to the
summer 620. The summer 620 determines the difference (.DELTA.EBP)
between the MEBP and the DEBP. The summer sends the .DELTA.EBP to
the pulse width modulated (PWM) driver 630.
[0067] Based on the .DELTA.EBP, the PWM driver 630 determines and
provides the duty cycle to the turbocharger 110. The duty cycle
opens or closes the nozzles on the turbocharger as appropriate in
response to the .DELTA.EBP.
[0068] In a first approach, the PWM driver 630 opens and closes the
nozzles incrementally in relation to the current position of the
nozzles. For example, the duty cycle opens the nozzles an
additional three degrees based on the .DELTA.EBP. The incremental
amount for opening or closing the nozzles may be fixed or may vary
in relation to the magnitude of the .DELTA.EBP.
[0069] In a second approach, the PWM driver 630 opens and closes
the nozzles to a specific pre-determined position regardless of
their location. For example, the duty cycle moves the nozzles so
they are open 15 degrees based on the .DELTA.EBP.
[0070] Each approach achieves the desired result, positioning the
nozzles to achieve the DEBP. However, the first approach is better
suited for when incremental adjustments to the nozzle position are
necessary to achieve the DEBP. Conversely, the second approach is
better suited when major adjustments to the nozzle position are
necessary to achieve the DEBP.
[0071] A third approach combines the first and second approaches.
If the magnitude of EBP is large or exceeds a threshold, the duty
cycle will move the nozzles to achieve the DEBP regardless of the
current position of the nozzles. If the magnitude of EBP is small
or below a threshold, the duty cycle will move the nozzles
incrementally depending on the current position of the nozzles.
[0072] The control strategy continuously repeats itself unless
other parameters are provided to disengage the control system.
These other parameters include a turbocharger
engagement/disengagement switch, engine idle control, and similar
control features.
[0073] The preferred execution rate of the control strategy is on
the order of 125 Hz. However, the execution may be slower or faster
especially when the variability of engine conditions change. For
example, slower execution rates may be more suitable when the
engine conditions do not change rapidly.
[0074] FIG. 7 shows an abbreviated set point table 605 for
determining a DEBP for a particular engine load and speed. For
example, the table indicates a DEBP of 63 in. Hg when the fuel rate
is 55 and the engine speed is 1400 RPM. In use, the table is
expanded to include a full range of DEBP values for all operating
engine speeds and engine loads.
[0075] Turbocharger design and size changes the relationship
between the duty cycle and nozzle position. For example, the duty
cycle on one design opens the nozzles 10 degrees. The same duty
cycle on another design opens the nozzles 12 degrees. Turbochargers
of the same design but different sizes show the same
inconsistency.
[0076] In contrast, turbochargers of the same design and size have
a consistent relationship between the duty cycle and nozzle
opening. However, they have a manufacturing variability from one
turbocharger to the next. This manufacturing variability may be
reduced substantially, and maybe statistically eliminated, through
empirical analysis of the turbocharger throughout its operating
range.
[0077] Empirical testing of the turbocharger determines the DEBP
for given engine operating parameters (e.g., engine load and
speed). The testing determines the DEBP or range of DEBP for
maximizing the intake air boost while avoiding excessive exhaust
pressure and overdriving conditions. Proper statistical analysis
virtually eliminates any manufacturing variability between
turbochargers of the same design and size.
[0078] The present invention advantageously senses the exhaust back
pressure to control a variable geometry turbocharger. As shown in
FIG. 8, there is a direct relationship between the exhaust manifold
pressure and the turbine duty cycle (nozzle position). By sensing
the exhaust back pressure, the nozzles may be repositioned more
optimally based on the desired exhaust back pressure.
[0079] In FIG. 8, the nozzles are fully open at a turbine duty
cycle below 25 percent. The nozzles are fully closed at a turbine
duty cycle above 75 percent. While the profile and location of the
curve changes with the volume of exhaust gases, the relationship
holds throughout the engine's different operating levels.
[0080] Of importance are the dramatic changes in the exhaust gas
pressure for relatively small changes in the turbine duty cycle.
These dramatic changes enhance the control capabilities of the
present invention. Ideally, it is desired to operate the
turbocharger at or as close to an optimal operating position--the
highest intake boost pressure without reaching excessive exhaust
pressure or overdriving conditions. In practice, it is very
difficult to consistently achieve or even come close to this
optimal operating position. The operating and manufacturing
variability of the turbocharger as well as changing engine
conditions compound the problem.
[0081] In addition, the intake air pressure does not change
dramatically as the duty cycle changes. Because of these
difficulties, many controllers based on intake air pressure
incorporate large margins of error to avoid excessive exhaust gas
pressure and overdriving conditions. In contrast, the dramatic
changes in the exhaust gas pressure to changes in the duty cycle
enable the present invention to operate closer or at the optimal
operating position. FIG. 9 shows compares the exhaust gas and
intake air pressures with the turbine duty cycle.
[0082] This better control enables a plurality of alternate
embodiments of the present invention. These alternate embodiments
involve adjusting the desired exhaust back pressure (DEBP) to
provide additional features such as cold weather warm-up of the
engine, engine braking, and exhaust gas recirculation (EGR).
Similar features may be added but are not shown. These additional
features include overspeed protection for the turbine, ambient
pressure adjustments, and the like.
[0083] FIG. 10 shows a second embodiment of a closed-loop control
strategy for a turbocharger according to the present invention. The
engine speed and engine load signals are sent to a set-point tables
605, 705, 805, 905 after they pass through a first and second
low-pass filters 610, 615 respectively. The base set-point table
605 determines the base desired exhaust back pressure (DEBP-BASE)
based on the engine speed and engine load. The DEBP-BASE is sent to
a DEBP summer 635.
[0084] To provide cold weather warm-up, an engine temperature
signal is sent to temperature set-point table 705 after it passes
through a third low-pass filter 710. The engine temperature signal
may be provided through a sensor in the engine oil, the engine
coolant, or other similar means. The temperature set-point table
705 determines the temperature desired exhaust back pressure
(DEBP-T) based on the engine speed, load, and temperature. When the
engine is cold and idling, the DEBP-T increases to hasten engine
warm-up. When the engine is running at higher speeds or the engine
load is high, the DEBP-T is low or zero because there is little
need to increase the exhaust back pressure under these conditions.
The DEBP-T is sent to the DEBP summer 635.
[0085] When engine braking is desired, signals for the vehicle
speed and other braking parameters are sent to a braking set-point
tables 805 after they pass through a fourth low-pass filter 810 and
a fifth low-pass filter 815. Other braking parameters can include
ABS brakes, cruise control settings, emergency brake activation,
and other similar signals or related parameters. The braking
set-point table 805 determines the braking desired exhaust back
pressure (DEBP-BRAKE) based on the engine speed, engine load,
vehicle speed, and other parameters. The DEBP-BRAKE is sent to the
DEBP summer 635.
[0086] When exhaust gas recirculation (EGR) is desired, an EGR
signal is sent to an EGR set-point tables 905 after it passes
through a sixth low-pass filter 910. The EGR set-point table 905
determines the EGR desired exhaust back pressure (DEBP-EGR) based
on the engine speed and engine load. The DEBP-EGR is sent to the
DEBP summer 635. While this feature may be used to control the
amount of EGR to the engine, its purpose is to ensure the exhaust
gas pressure is higher than the intake boost pressure. This avoids
costly venturi and similar devices to ensure the exhaust gas has
sufficient pressure to enter the intake air manifold.
[0087] At the DEBP summer 635, the DEBP-BASE, the DEBP-T, the
DEBP-BRAKE, and the DEBP-EGR are combined to yield the total
desired exhaust back pressure (DEBP-TOT). The DEBP-TOT is sent to
summer 620.
[0088] The measured exhaust back pressure (MEBP) passes through a
seventh low-pass filter 625 and is sent to the summer 620. The
summer 620 determines the difference (.DELTA.EBP) between the MEBP
and the DEBP-TOT. The summer 620 sends the .DELTA.EBP to the pulse
width modulated (PWM) driver 630.
[0089] Based on the .DELTA.EBP, the PWM driver 630 determines and
provides the duty cycle to the turbocharger 110. The duty cycle
opens or closes the nozzles on the turbocharger as appropriate in
response to the .DELTA.EBP.
[0090] As previously described, the PWM driver 630 opens and closes
the nozzles incrementally in relation to the current position of
the nozzles. Alternatively, the PWM driver 630 opens and closes the
nozzles to a specific position regardless of their location. These
approaches may be combined.
[0091] The control strategy continuously repeats itself unless
other parameters are provided to disengage the control system. The
preferred execution rate of the control strategy is on the order of
125 Hz. However, the execution may be slower or faster especially
when the variability of engine conditions change.
[0092] While the cold weather warm-up, the engine braking, and EGR
have been described in a single embodiment, they maybe used
separately or in any combination. Other features also may be
similarly incorporated into any of the embodiments. These features
include overspeed protection for the turbine, ambient pressure
adjustments, and the like. The ambient air pressure may be measured
so the turbocharger can be adjusted for various altitude
conditions. In addition, the operating parameters (e.g., engine
speed, engine load, and others) may be used singly, all together,
or in any combination to control the turbocharger 110.
[0093] FIG. 11 shows a third embodiment of the closed-loop control
strategy for a turbocharger according to the present invention. In
this embodiment, the exhaust gas pressure is used to adjust the
duty cycle set by some other pre-determined engine parameter(s). In
contrast, the previous embodiments set the duty cycle based on the
exhaust gas pressure. The engine speed and engine load signals are
sent to a set-point tables 605, and a base duty cycle set-point
table 650 after they pass through a first low-pass filter 610 and a
second low-pass filter 615 respectively. The set-point table 605
determines the desired exhaust back pressure (DEBP) based on the
engine speed and engine load. The DEBP is sent to summer 620.
[0094] The measured exhaust back pressure (MEBP) passes through a
low-pass filter 625 and is sent to the summer 620. The summer 620
determines the difference (.DELTA.EBP) between the MEBP and the
DEBP. The summer sends the .DELTA.EBP to the pulse width modulated
(PWM) driver 630. Based on the .DELTA.EBP, the PWM driver 630
determines and provides an exhaust pressure duty cycle (DUTY
CYCLE-EP) to summer 655.
[0095] A base set-point table 650 determines a base duty cycle
(DUTY CYCLE-BASE) based on the engine speed and engine load. These
parameters are shown as an example because the based duty cycle may
be determined by other parameters. The DUTY CYCLE-BASE is sent to
summer 655.
[0096] Summer 655 combines the DUTY CYCLE-EP and the DUTY
CYCLE-BASE to determine and send the turbocharger duty cycle (DUTY
CYCLE-VNT) to the turbocharger 110. DUTY CYCLE-VNT opens or closes
nozzles on the turbocharger as appropriate. In this manner, the
DUTY CYCLE-BASE is adjusted by the .DELTA.EBP.
[0097] The control strategy continuously repeats itself unless
other parameters are provided to disengage the control system. The
preferred execution rate of the control strategy is on the order of
125 Hz. However, the execution may be slower or faster especially
when the variability of engine conditions change. Of course, the
control strategy may also include the cold weather engine warm-up,
engine braking, and EGR features described in the second
embodiment. Thus, the operating parameters (e.g., engine speed,
engine load, and others) can be used singly, all together, or in
any combination to control the turbocharger 110 similarly to that
described with respect to FIG. 10.
[0098] FIG. 12 shows a method for controlling a variable nozzle
turbocharger using the exhaust back pressure according to the
present invention. In step 1205, the desired exhaust back pressure
(DEBP) is determined from the engine speed and engine load. Other
engine or vehicle parameters may be used in addition to the engine
speed and load. Prior empirical testing provides a map of DEBP's
based on the full operating range of the engine speed and load. In
operation, the map is used to determine the DEBP based on the speed
and load. The DEBP may be adjusted to avoid over speeding the
turbocharger and for changes in ambient air pressure.
[0099] In step 1210, the measured exhaust back pressure (MEBP) is
determined from a sensor placed in the exhaust gas manifold. Other
sensing devices may be used as well as other locations as long as
an electrical or other signal is provided indicative of the exhaust
gas pressure
[0100] In step 1215, the difference (.DELTA.EBP) between the DEBP
and the MEBP is determined. In step 1220, the duty cycle of the
turbocharger is determined based on the .DELTA.EBP.
[0101] FIG. 13 shows a method for using the exhaust back pressure
to control a variable nozzle turbocharger having cold weather
warm-up capabilities according to the present invention. In step
1305, the base desired exhaust back pressure (DEBP-BASE) is
determined from the engine speed and engine load. Other engine or
vehicle parameters may be used in place of or in addition to the
engine speed and load.
[0102] In step 1310, the temperature desired exhaust back pressure
(DEBP-T) is determined from the engine temperature, the engine
speed, and the engine load. The engine temperature may be provided
by a sensor in the engine oil, a sensor in the coolant, or other
suitable means for determining the engine temperature. When the
engine speed or the engine load is high, the DEBP-T is little or
none.
[0103] In step 1320, the total desired exhaust back pressure
(DEBP-TOT) is determined. The DEBP-BASE is adjusted by the DEBP-T
to provide the DEBP-TOT. In step 1330, the measured exhaust back
pressure (MEBP) is determined usually from a sensor placed in the
exhaust gas manifold. In step 1340, the difference (.DELTA.EBP)
between the DEBP-TOT and the MEBP is determined. In step 1350, the
duty cycle of the turbocharger is determined.
[0104] FIG. 14 shows a method for using the exhaust back pressure
to control a variable nozzle turbocharger having engine braking
capabilities according to the present invention. In step 1405, the
base desired exhaust back pressure (DEBP-BASE) is determined from
the engine speed and engine load. Other engine or vehicle
parameters may be used in addition to the engine speed and
load.
[0105] In step 1410, the braking desired exhaust back pressure
(DEBP-BRAKE) is determined from the engine speed, engine load,
vehicle speed, and other pre-determined braking-related engine
parameters. These other engine parameters include ABS brake
operation, emergency brake activation, cruise control activation,
and the like.
[0106] In step 1415, the total desired exhaust back pressure
(DEBP-TOT) is determined. The DEBP-BASE is adjusted by the
DEBP-BRAKE to provide the DEBP-TOT.
[0107] In step 1420, the measured exhaust back pressure (MEBP) is
determined usually from a sensor placed in the exhaust gas
manifold. In step 1425, the difference (.DELTA.EBP) between the
DEBP-TOT and the MEBP is determined. In step 1430, the duty cycle
of the turbocharger is determined.
[0108] FIG. 15 shows a method for using the exhaust back pressure
to control a variable nozzle turbocharger having exhaust gas
recirculation (EGR) capabilities according to the present
invention. In step 1505, the base desired exhaust back pressure
(DEBP-BASE) is determined from the engine speed and engine load.
Other engine or vehicle parameters may be used in place of or in
addition to the engine speed and load.
[0109] In step 1510, the EGR desired exhaust back pressure
(DEBP-EGR) is determined from the engine temperature, the engine
speed, and EGR requirements. While the present invention may be
used to control EGR, it is used to ensure the exhaust pressure is
higher than the intake air pressure. The EGR requirements are
provided by an EGR controller or similar device.
[0110] In step 1515, the total desired exhaust back pressure
(DEBP-TOT) is determined. DEBP-BASE is adjusted by the DEBP-EGR to
provide the DEBP-TOT.
[0111] In step 1520, the measured exhaust back pressure (MEBP) is
determined usually from a sensor placed in the exhaust gas
manifold. In step 1525, the difference (.DELTA.EBP) between the
DEBP-TOT and the MEBP is determined. In step 1530, the duty cycle
of the turbocharger is determined.
[0112] It will be readily understood by those of skill in the art
that the methods described in FIGS. 12-15 may be combined into a
method for using the exhaust back pressure to control a
turbocharger having cold weather warm-up of the engine, engine
braking, and EGR capabilities.
[0113] FIG. 16 shows an alternate method for controlling a variable
nozzle turbocharger using the exhaust gas pressure according to the
present invention. In step 1605, the base duty cycle (DUTY
CYCLE-BASE) is determined from the engine speed and engine load.
Other engine or vehicle parameters may be used in addition to the
engine speed and load.
[0114] In step 1610, the desired exhaust back pressure (DEBP) is
determined from the engine speed and engine load. Other engine or
vehicle parameters may be used in place of or in addition to the
engine speed and load.
[0115] In step 1615, the measured exhaust back pressure (MEBP) is
determined usually from a sensor placed in the exhaust gas
manifold. In step 1620, the difference (.DELTA.EBP) between the
DEBP and the MEBP is determined. In step 1625, the exhaust pressure
duty cycle (DUTY CYCLE-EP) is determined based on the .DELTA.EBP.
In step 1630, the DUTY CYCLE-BASE is adjusted by the DUTY CYCLE-EP
to provide the turbocharger duty cycle (DUTY CYCLE-VNT).
[0116] The invention has been described and illustrated with
respect to certain preferred embodiments by way of example only.
Additional advantages will readily occur to those skilled in the
art, who may make changes without departing from the true spirit
and scope of the invention. For example, the control system of the
present invention may be applied to a turbocharger with a variable
nozzle compressor and with or without a variable nozzle turbine.
The control system may be used on multiple turbochargers. In
addition, the control logic in the system may be replaced by
electronic circuits which perform the same function as the control
logic. Therefore, the invention is not limited to the specific
details, representative devices, and illustrated examples in this
description. Accordingly, the present invention is limited only by
the following claims and equivalents.
* * * * *