Title of Invention	AN OVERSPEED PROTECTION CONTROL SYSTEM AND A METHOD OF INHIBITING AN OVERSPEED IN A VEHICLE POWERTRAIN
Abstract	A method of inhibiting an overspeed condition in a vehicle powertrain includes monitoring at least one of an engine speed and a transmission input shaft speed of a torque converter that transfers drive torque between an engine and a transmission and determining an operating condition of the vehicle powertrain. The method further includes determining a first threshold speed based on the operating condition and reducing an engine torque request when the at least one of the engine speed and the transmission input shaft speed exceeds the first threshold speed.

Title of Invention

AN OVERSPEED PROTECTION CONTROL SYSTEM AND A METHOD OF INHIBITING AN OVERSPEED IN A VEHICLE POWERTRAIN

Abstract

A method of inhibiting an overspeed condition in a vehicle powertrain includes monitoring at least one of an engine speed and a transmission input shaft speed of a torque converter that transfers drive torque between an engine and a transmission and determining an operating condition of the vehicle powertrain. The method further includes determining a first threshold speed based on the operating condition and reducing an engine torque request when the at least one of the engine speed and the transmission input shaft speed exceeds the first threshold speed.

Full Text	POWERTRAIN OVERSPEED PROTECTION FIELD [0001] The present disclosure relates to a powertrain having a transmission driven by an internal combustion engine through a torque converter, and more particularly to an overspeed protection control for a powertrain. BACKGROUND [0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. [0003] Vehicle powertrains typically include a prime mover, such as an internal combustion engine, a transmission and a coupling device that transfers drive torque from the prime mover to the transmission. The transmission multiplies the drive torque by an applied gear ratio to drive the vehicle's drivetrain. Exemplary transmissions include an automatic transmission having fixed gear ratios and a continuously variable transmission (CVT) having infinitely variable gear ratios. [0004] The coupling device often includes a torque converter that provides a fluid coupling between an output shaft of the prime mover and an input shaft of the transmission. As the output shaft accelerates, the input shaft is induced to accelerate through the fluid coupling. Once the input shaft speed is sufficiently near to the output shaft speed, a torque converter clutch (TCC) is engaged to provide a direct drive between the output shaft and the input shaft. General Motors No. GP-307904 Attorney Docket No. 8540P-000404 [0005] In some instances, an overspeed condition can arise, wherein an uncontrolled speed flare occurs in the powertrain. Such overspeed conditions can result in damage to engine, torque converter and/or transmission components. SUMMARY [0006] Accordingly, the present invention provides a method of inhibiting an overspeed condition in a vehicle powertrain. The method includes monitoring at least one of a transmission input shaft speed and an engine speed and determining an operating condition of the vehicle powertrain. The method further includes determining a first threshold speed based on the operating condition and reducing an engine torque request when the at least one of the transmission input shaft speed and the engine speed exceeds the first threshold speed. [0007] In one feature, the method further includes providing a fixed torque reduction amount. The engine torque request is reduced by the fixed torque reduction amount. [0008] In another feature, the method further includes determining a torque reduction amount based on a difference between the at least one of the transmission input shaft speed and the engine speed and the first threshold speed. The engine torque request is reduced by the torque reduction amount. [0009] In another feature, the method further includes determining a second threshold speed based on the operating condition, and determining the engine torque request without a reduction when the at least one of the transmission input shaft speed and the engine speed is less than the second threshold speed. [0010] In other features, the first threshold speed is determined based on one of an attained gear speed, a commanded gear speed and a commanded speed profile. The operating condition is one of an upshift and a downshift of a gear ratio of the transmission. [0011] In still another feature, the operating condition is one of a garage shift condition and a neutral idle condition and the first threshold speed corresponds to a maximum engine speed limit. [0012] In yet another feature, the transmission is one of an automatic transmission and a continuously variable transmission. [0013] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. DRAWINGS [0014] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. [0015] Figure 1 is a functional block diagram of an exemplary vehicle powertrain that is regulated based on the overspeed protection control of the present invention; [0016] Figure 2 is a schematic illustration of an exemplary torque converter implemented in the exemplary vehicle powertrain of Figure 1; [0017] Figure 3 is a graph illustrating exemplary operating parameters for a neutral condition in accordance with the overspeed protection control of the present invention; [0018] Figure 4 is a graph illustrating exemplary operating parameters for a first upshift condition in accordance with the overspeed protection control of the present invention; [0019] Figure 5 is a graph illustrating exemplary operating parameters for a second upshift condition in accordance with the overspeed protection control of the present invention; [0020] Figure 6 is a graph illustrating exemplary operating parameters for a first downshift condition in accordance with the overspeed protection control of the present invention; [0021] Figure 7 is a graph illustrating exemplary operating parameters for a second downshift condition in accordance with the overspeed protection control of the present invention; [0022] Figure 8 is a graph illustrating exemplary operating parameters for a garage shift condition in accordance with the overspeed protection control of the present invention; [0023] Figure 9 is a graph illustrating exemplary operating parameters for a steady gear condition in accordance with the overspeed protection control of the present invention; [0024] Figure 10 is a flowchart illustrating exemplary steps executed by the overspeed protection control of the present invention; and [0025] Figure 11 is a functional block diagram of exemplary modules that execute the overspeed protection control of the present invention. DETAILED DESCRIPTION [0026] The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. [0027] Referring now to Figure 1, an exemplary powertrain 10 is illustrated and includes an engine 12 that drives a transmission 14 through a coupling device 16. More specifically, air is drawn into an intake manifold 18 of the engine 12 through a throttle 20. The air is mixed with fuel and the air/fuel mixture is combusted within cylinders 22 to reciprocally drive pistons (not shown) within the cylinders 22. The pistons rotatably drive a crankshaft 24 (see Figure 2) to provide drive torque. Exhaust generated by the combustion process is exhausted from the engine through an exhaust manifold 26. Although 4 cylinders are illustrated, it is appreciated that the present invention can be implemented in vehicles having any number of cylinders. [0028] The drive torque drives is transferred through the torque converter 16 to drive the transmission 14. The transmission 14 multiplies the drive torque by a desired gear ratio to provide a modified drive torque. The modified drive torque is transferred to a vehicle driveline (not shown) by a transmission output shaft 28. The transmission 14 can include one of a manual transmission, an automatic transmission, an automated manual transmission and a continuously variable transmission (CVT). An automatic transmission includes a plurality of pre-defined, fixed gear ratios. A common CVT includes a belt and adjustable pulley system that enables an infinite variability between gear ratios without discrete steps or shifts. [0029] A control module 30 regulates operation of the powertrain based on vehicle operating parameters. More specifically, the control module 30 regulates an effective throttle area (Aeff) via a throttle actuator 32. A throttle position sensor 34 generates a throttle position signal (TPS) based on the angular position of the throttle 20. The control module 30 determines a requested engine torque (TREq) and adjusts the throttle position and other engine operating parameters to achieve TREq. The other engine operating parameters include, but are not limited to, a fueling rate, spark timing, a camshaft phase and/or an intake/exhaust valve lift or timing. [0030] The control module 30 also regulates operation of the transmission 14 based on vehicle operating parameters. More specifically, a crankshaft position sensor 36 generates a crankshaft position signal, which is used to determine an actual engine speed (RPMEng)- A transmission output shaft speed (TOSS) sensor 38 generates a TOSS signal, which is used to determine a vehicle speed (Vveh), and a transmission input shaft speed (TISS) sensor 39 generates a TISS signal. The control module 30 adjusts a gear ratio of the transmission 14 based on the throttle position (i.e., TPS) and VVeh- In an automatic transmission, the gear is shifted accordingly, and in a CVT, the pulley ratio is adjusted accordingly. [0031] Referring now to Figure 2, the coupling device 16 is illustrated as a torque converter that provides a fluid coupling between the engine 12 and the transmission 14. Although the present invention will be described with respect to a torque converter, it is appreciated that the overspeed protection control of the present invention can be implemented with vehicle powertrains having alternative coupling devices including, but not limited to, a dual-clutch coupling device and a starting clutch coupling device. [0032] The torque converter 16 includes a housing 50 that is fixed for rotation with the crankshaft 24 via a flywheel 52. An impeller 54 is fixed for rotation with the housing 50 and a turbine 56 is fixed for rotation with a transmission input shaft 58. A stator 60 is also provided and is fixed from rotation. The interior of the torque converter 16 is filled with a viscous fluid. Rotation of the impeller 54 induces corresponding motion of the viscous fluid, which is directed towards the turbine 56 by the stator 60 to induce rotation of the turbine 56. The torque converter 16 includes a torque converter clutch (TCC) (not shown), which is selectively engaged to proved a direct drive between the crankshaft 24 and the input shaft 58. [0033] As the crankshaft 24 rotates at an idle speed (RPMidle), the impeller 54 is induced to rotate. RPMidle, however, is normally insufficient to overcome braking forces that inhibit the turbine 56 from rotating. As the braking forces are reduced and/or RPMeng increases, the impeller 54 drives the viscous fluid into the turbine 56 and the turbine 56 is induced to rotate. As a result, drive torque is transferred through the transmission 14 to propel the vehicle. Upon achieving a point where there is little or no RPM difference between the turbine 56 and impeller 54, the TCC is engaged to provide a direct drive between the engine 12 and the transmission 14. Under this condition, the rotational speed of the turbine 56 (RPMturb) is equal to RPMeng- Generally, RPMturb is determined based on the TISS signal and is equivalent to the TISS (RPMTiss)- [0034] The overspeed protection control of the present invention protects the engine 12, torque converter 16 and/or transmission 14 from damage in an overspeed condition. An overspeed condition occurs when at least one of RPMeng and RPMturb flares and exceeds a theoretical or expected engine or turbine speed (RPMengexp, RPMturbexp)- It is anticipated that RPMnss can replace RPMturb, and, as a result, the overspeed protection control of the present invention can be implemented in vehicle powertrains that do not include a torque converter. An overspeed condition can damage the engine 12, the torque converter 16 and/or the transmission 14. The overspeed protection control determines whether at least one of RPMeng and RPMturb exceeds an upper threshold (RPMuthr) and reduces TREq to until it falls below a lower threshold (RPMlthr)- [0035] Treq can be reduced by a fixed amount. Alternatively, TREq can be reduced by an amount that is determined based on the difference between RPMturb and RPMuthr. In this manner, the overspeed condition can be more rapidly resolved thereby reducing the potential for damage to the powertrain components. By regulating TREq, a quicker, more accurate control is provided to better inhibit or resolve the overspeed condition. In this manner, a high level of powertrain protection is provided. [0036] As described in further detail below, RPMUThr and RPMlthr are determined based on a powertrain operating condition. The powertrain operating conditions include, but are not limited to, a neutral condition, an upshift condition, a downshift condition, a garage shift condition and a steady gear condition. In the case of an automatic transmission, each of these conditions can be present, wherein the overspeed protection control of the present invention includes corresponding control strategies. In the case of a CVT, the overspeed protection control for garage shift and neutral conditions can be combined under a first control strategy and the remaining conditions are combined under a second control strategy. [0037] Referring now to Figure 3, the TREq is reduced when at least one of RPMeng and RPMturb exceeds RPMuthr, during the neutral condition. In this manner, RPMENG and/or RPMturb is maintained equal to or below RPMuthr- If RPMENG and/or RPMturb falls below RPMlthr, the overspeed protection control is exited and TREq is regulated based on normal TREq control. Under the normal TrEq control, Treq is determined based on operating parameters including, but not limited to, MAP and RPMeng, and TPS. [0038] Referring now to Figures 4 and 5, the overspeed protection control implements one of a first strategy (see Figure 4) and a second strategy (see Figure 5) during the upshift condition. With particular reference to Figure 4, the overspeed protection control determines RPMUThr and RPMLThr based on the engine and/or turbine RPM associated with the attained gear ratio (RPMAg)- For example, in the case of an automatic transmission, if a shift from 2nd to 3rd gear is being performed, the overspeed protection control determines RPMuthr, such that RPMeng and/or RPMturb does not exceed a corresponding 2nd gear RPM. RPMag is the desired RPM profile corresponding to the gear that the transmission shifts to as a result of the upshift (e.g., 3rd gear for the above example). With particular reference to Figure 5, the overspeed protection control determines RPMuthr and RPMlthr based on a commanded RPM profile (RPMcom). [0039] Referring now to Figures 6 and 7, the overspeed protection control can implement one of a first strategy (see Figure 6) and a second strategy (see Figure 7) during the downshift condition. With particular reference to Figure 6, the overspeed protection control determines RPMuthr and RPMlthr based on the engine and/or turbine RPM associated with the commanded gear ratio (RPMcg)- For example, in the case of an automatic transmission, if a shift from 3rd to 2nd gear is being performed, the overspeed protection control determines RPMuthr, such that RPMeng and/or RPMturb does not exceed a corresponding 2nd gear RPM. With particular reference to Figure 7, the overspeed protection control determines RPMUTHr and RPMlthr based on a RPMcom for the downshift. [0040] Referring now to Figure 8, the overspeed protection control determines RPMuthr and RPMlthr based on a maximum engine speed limit (RPMengmax) because there is no profile to follow during the garage shift / neutral idle operation. Referring now to Figure 9, the overspeed protection control determines RPMuthr and RPMlthr based on a turbine speed profile for the actual gear (RPMqear)- During a steady gear condition, the actual RPMeng and/or RPMturb should not vary from respective theoretical RPMeng and RPMturb values. [0041] Referring now to Figure 10, exemplary steps that are executed by the overspeed protection control of the present invention will be described in detail. In step 100, control determines RPMeng and/or RPMturb In step 102, control determines the powertrain condition. Control determines RPMuthr and RPMlthr based on the powertrain condition in step 104. [0042] In step 106, control determines whether at least one of RPMeng and RPMturb is greater than RPMuthr- If RPMeng and/or RPMturb is not greater then RPMuthr, control ends. If RPMeng and/or RPMturb is greater than RPMuthr, control decreases TREq in step 108. As discussed above, TREq can be reduced by a fixed amount or by an amount that is determined based on the difference between RPMeng or RPMturb and RPMuthr. In step 110, control determines whether RPMeng and/or RPMturb is less than RPMlthr- If RPMeng and/or RPMturb is not less then RPMlthr, control loops back to step 108. If RPMeng or RPMturb is less than RPMlthr, control resumes normal Treq control in step 112 and control ends. [0043] Referring now to Figure 11, exemplary modules that execute the overspeed protection control will be described in detail. The exemplary modules include, but are not limited to, a powertrain control module 200, an RPMeng and/or RPMturb determining module 202, an RPMuthr and RPMlthr determining module 204, a Treq calculating module 206 and an engine control module 208. The powertrain control module 200 regulates general operation of the powertrain components and outputs powertrain information to the RPMturb determining module 202 and the TREq calculating module. More specifically, the RPMENg and/or RPMturb determining module receives the TISS signal as an input, and both the RPMuthr and RPMlthr determining module and the Treq calculating module 206 receive the powertrain operating condition. [0044] The RPMeng and/or RPMturb determining module 202 determines RPMeng and/or RPMturb- The RPMuthr and RPMlthr determining module 204 determines RPMuthr and RPMlthr based on the powertrain operating condition. The TREq calculating module 206 calculates TREq based on either the overspeed protection control of the present invention, or the normal Treq control. Under the overspeed protection control, the TREq calculating module 206 determines TREq based on RPMeng and/or RPMturb, the powertrain operating condition, RPMuthr and RPMlthr Under the normal TREq control, the TREQ calculating module 206 determines TREq based on operating parameters including, but not limited to RPMENg, MAP and TPS. The engine control module 208 regulates operation of the engine 12 to achieve TREq. [0045] Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims. CLAIMS What is claimed is: 1. An overspeed protection control system that inhibits an overspeed condition in a vehicle powertrain, comprising: a first module that monitors at least one of an engine speed and a transmission input shaft speed; a second module that determines an operating condition of said vehicle powertrain; a third module that determines a first threshold speed based on said operating condition; and a fourth module that reduces an engine torque request when said at least one of said engine speed and said transmission input shaft speed exceeds said first threshold speed. 2. The overspeed protection control system of claim 1 wherein said fourth module provides a fixed torque reduction amount, and reduces said engine torque request by said fixed torque reduction amount. 3. The overspeed protection control system of claim 1 wherein said fourth module determines a torque reduction amount based on a difference between said at least one of said engine speed and said transmission input shaft speed and said first threshold speed, and reduces said engine torque request by said torque reduction amount. 4. The overspeed protection control system of claim 1 wherein said third module determines a second threshold speed based on said operating condition and determines said engine torque request without a reduction when said at least one of said engine speed and said transmission input shaft speed is less than said second threshold speed. 5. The overspeed protection control system of claim 1 wherein said third module determines said first threshold speed based on one of an attained gear speed, a commanded gear speed and a commanded speed profile. 6. The overspeed protection control system of claim 5 wherein said operating condition is one of an upshift and a downshift of a gear ratio of said transmission. 7. The overspeed protection control system of claim 1 wherein said operating condition is one of a garage shift condition and a neutral idle condition and said first threshold speed corresponds to a maximum engine speed limit. 8. The overspeed protection control system of claim 1 wherein said transmission is one of an automatic transmission and a continuously variable transmission. 9. A method of inhibiting an overspeed condition in a vehicle powertrain, comprising: monitoring at least one of an engine speed and a transmission input shaft speed; determining an operating condition of said vehicle powertrain; determining a first threshold speed based on said operating condition; and reducing an engine torque request when said at least one of said engine speed and said transmission input shaft speed exceeds said first threshold speed. 10. The method of claim 9 further comprising providing a fixed torque reduction amount, wherein said engine torque request is reduced by said fixed torque reduction amount. 11. The method of claim 9 further comprising determining a torque reduction amount based on a difference between said at least one of said engine speed and said transmission input shaft speed and said first threshold speed, wherein said engine torque request is reduced by said torque reduction amount. 12. The method of claim 9 further comprising: determining a second threshold speed based on said operating condition; and determining said engine torque request without a reduction when said at least one of said engine speed and said transmission input shaft speed is less than said second threshold speed. 13. The method of claim 9 wherein said first threshold speed is determined based on one of an attained gear speed, a commanded gear speed and a commanded speed profile. 14. The method of claim 13 wherein said operating condition is one of an upshift and a downshift of a gear ratio of said transmission. 15. The method of claim 9 wherein said operating condition is one of a garage shift condition and a neutral idle condition and said first threshold speed corresponds to a maximum engine speed limit. 16. The method of claim 9 wherein said transmission is one of an automatic transmission and a continuously variable transmission. 17. A method of inhibiting an overspeed condition in a vehicle powertrain, comprising: monitoring at least one of an engine speed and a transmission input shaft; determining an operating condition of said vehicle powertrain; determining a first and second threshold speeds based on said operating condition; reducing an engine torque request when said at least one of said engine speed and said transmission input shaft speed exceeds said first threshold speed; and determining said engine torque request without a reduction when said at least one of said engine speed and said transmission input shaft speed is less than said second threshold speed. 18. The method of claim 17 further comprising providing a fixed torque reduction amount, wherein said engine torque request is reduced by said fixed torque reduction amount. 19. The method of claim 17 further comprising determining a torque reduction amount based on a difference between said at least one of said engine speed and said transmission input shaft speed and said first threshold speed, wherein said engine torque request is reduced by said torque reduction amount. 20. The method of claim 17 wherein said first threshold speed is determined based on one of an attained gear speed, a commanded gear speed and a commanded speed profile. 21. The method of claim 20 wherein said operating condition is one of an upshift and a downshift of a gear ratio of said transmission. 22. The method of claim 17 wherein said operating condition is one of a garage shift condition and a neutral idle condition and said first threshold speed corresponds to a maximum engine speed limit. 23. The method of claim 17 wherein said transmission is one of an automatic transmission and a continuously variable transmission. A method of inhibiting an overspeed condition in a vehicle powertrain includes monitoring at least one of an engine speed and a transmission input shaft speed of a torque converter that transfers drive torque between an engine and a transmission and determining an operating condition of the vehicle powertrain. The method further includes determining a first threshold speed based on the operating condition and reducing an engine torque request when the at least one of the engine speed and the transmission input shaft speed exceeds the first threshold speed.

Full Text

POWERTRAIN OVERSPEED PROTECTION
FIELD
[0001] The present disclosure relates to a powertrain having a
transmission driven by an internal combustion engine through a torque converter,
and more particularly to an overspeed protection control for a powertrain.
BACKGROUND
[0002] The statements in this section merely provide background
information related to the present disclosure and may not constitute prior art.
[0003] Vehicle powertrains typically include a prime mover, such as an
internal combustion engine, a transmission and a coupling device that transfers
drive torque from the prime mover to the transmission. The transmission
multiplies the drive torque by an applied gear ratio to drive the vehicle's
drivetrain. Exemplary transmissions include an automatic transmission having
fixed gear ratios and a continuously variable transmission (CVT) having infinitely
variable gear ratios.
[0004] The coupling device often includes a torque converter that
provides a fluid coupling between an output shaft of the prime mover and an
input shaft of the transmission. As the output shaft accelerates, the input shaft is
induced to accelerate through the fluid coupling. Once the input shaft speed is
sufficiently near to the output shaft speed, a torque converter clutch (TCC) is
engaged to provide a direct drive between the output shaft and the input shaft.
General Motors No. GP-307904
Attorney Docket No. 8540P-000404
[0005] In some instances, an overspeed condition can arise, wherein
an uncontrolled speed flare occurs in the powertrain. Such overspeed conditions
can result in damage to engine, torque converter and/or transmission
components.
SUMMARY
[0006] Accordingly, the present invention provides a method of
inhibiting an overspeed condition in a vehicle powertrain. The method includes
monitoring at least one of a transmission input shaft speed and an engine speed
and determining an operating condition of the vehicle powertrain. The method
further includes determining a first threshold speed based on the operating
condition and reducing an engine torque request when the at least one of the
transmission input shaft speed and the engine speed exceeds the first threshold
speed.
[0007] In one feature, the method further includes providing a fixed
torque reduction amount. The engine torque request is reduced by the fixed
torque reduction amount.
[0008] In another feature, the method further includes determining a
torque reduction amount based on a difference between the at least one of the
transmission input shaft speed and the engine speed and the first threshold
speed. The engine torque request is reduced by the torque reduction amount.
[0009] In another feature, the method further includes determining a
second threshold speed based on the operating condition, and determining the
engine torque request without a reduction when the at least one of the
transmission input shaft speed and the engine speed is less than the second
threshold speed.
[0010] In other features, the first threshold speed is determined based
on one of an attained gear speed, a commanded gear speed and a commanded
speed profile. The operating condition is one of an upshift and a downshift of a
gear ratio of the transmission.
[0011] In still another feature, the operating condition is one of a
garage shift condition and a neutral idle condition and the first threshold speed
corresponds to a maximum engine speed limit.
[0012] In yet another feature, the transmission is one of an automatic
transmission and a continuously variable transmission.
[0013] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the description and
specific examples are intended for purposes of illustration only and are not
intended to limit the scope of the present disclosure.
DRAWINGS
[0014] The drawings described herein are for illustration purposes only
and are not intended to limit the scope of the present disclosure in any way.
[0015] Figure 1 is a functional block diagram of an exemplary vehicle
powertrain that is regulated based on the overspeed protection control of the
present invention;
[0016] Figure 2 is a schematic illustration of an exemplary torque
converter implemented in the exemplary vehicle powertrain of Figure 1;
[0017] Figure 3 is a graph illustrating exemplary operating parameters
for a neutral condition in accordance with the overspeed protection control of the
present invention;
[0018] Figure 4 is a graph illustrating exemplary operating parameters
for a first upshift condition in accordance with the overspeed protection control of
the present invention;
[0019] Figure 5 is a graph illustrating exemplary operating parameters
for a second upshift condition in accordance with the overspeed protection
control of the present invention;
[0020] Figure 6 is a graph illustrating exemplary operating parameters
for a first downshift condition in accordance with the overspeed protection control
of the present invention;
[0021] Figure 7 is a graph illustrating exemplary operating parameters
for a second downshift condition in accordance with the overspeed protection
control of the present invention;
[0022] Figure 8 is a graph illustrating exemplary operating parameters
for a garage shift condition in accordance with the overspeed protection control
of the present invention;
[0023] Figure 9 is a graph illustrating exemplary operating parameters
for a steady gear condition in accordance with the overspeed protection control
of the present invention;
[0024] Figure 10 is a flowchart illustrating exemplary steps executed by
the overspeed protection control of the present invention; and
[0025] Figure 11 is a functional block diagram of exemplary modules
that execute the overspeed protection control of the present invention.
DETAILED DESCRIPTION
[0026] The following description of the preferred embodiment is merely
exemplary in nature and is in no way intended to limit the invention, its
application, or uses. For purposes of clarity, the same reference numbers will be
used in the drawings to identify similar elements. As used herein, the term
module refers to an application specific integrated circuit (ASIC), an electronic
circuit, a processor (shared, dedicated, or group) and memory that execute one
or more software or firmware programs, a combinational logic circuit, or other
suitable components that provide the described functionality.
[0027] Referring now to Figure 1, an exemplary powertrain 10 is
illustrated and includes an engine 12 that drives a transmission 14 through a
coupling device 16. More specifically, air is drawn into an intake manifold 18 of
the engine 12 through a throttle 20. The air is mixed with fuel and the air/fuel
mixture is combusted within cylinders 22 to reciprocally drive pistons (not shown)
within the cylinders 22. The pistons rotatably drive a crankshaft 24 (see Figure
2) to provide drive torque. Exhaust generated by the combustion process is
exhausted from the engine through an exhaust manifold 26. Although 4 cylinders
are illustrated, it is appreciated that the present invention can be implemented in
vehicles having any number of cylinders.
[0028] The drive torque drives is transferred through the torque
converter 16 to drive the transmission 14. The transmission 14 multiplies the
drive torque by a desired gear ratio to provide a modified drive torque. The
modified drive torque is transferred to a vehicle driveline (not shown) by a
transmission output shaft 28. The transmission 14 can include one of a manual
transmission, an automatic transmission, an automated manual transmission and
a continuously variable transmission (CVT). An automatic transmission includes
a plurality of pre-defined, fixed gear ratios. A common CVT includes a belt and
adjustable pulley system that enables an infinite variability between gear ratios
without discrete steps or shifts.
[0029] A control module 30 regulates operation of the powertrain based
on vehicle operating parameters. More specifically, the control module 30
regulates an effective throttle area (Aeff) via a throttle actuator 32. A throttle
position sensor 34 generates a throttle position signal (TPS) based on the
angular position of the throttle 20. The control module 30 determines a
requested engine torque (TREq) and adjusts the throttle position and other engine
operating parameters to achieve TREq. The other engine operating parameters
include, but are not limited to, a fueling rate, spark timing, a camshaft phase
and/or an intake/exhaust valve lift or timing.
[0030] The control module 30 also regulates operation of the
transmission 14 based on vehicle operating parameters. More specifically, a
crankshaft position sensor 36 generates a crankshaft position signal, which is
used to determine an actual engine speed (RPMEng)- A transmission output
shaft speed (TOSS) sensor 38 generates a TOSS signal, which is used to
determine a vehicle speed (Vveh), and a transmission input shaft speed (TISS)
sensor 39 generates a TISS signal. The control module 30 adjusts a gear ratio
of the transmission 14 based on the throttle position (i.e., TPS) and VVeh- In an
automatic transmission, the gear is shifted accordingly, and in a CVT, the pulley
ratio is adjusted accordingly.
[0031] Referring now to Figure 2, the coupling device 16 is illustrated
as a torque converter that provides a fluid coupling between the engine 12 and
the transmission 14. Although the present invention will be described with
respect to a torque converter, it is appreciated that the overspeed protection
control of the present invention can be implemented with vehicle powertrains
having alternative coupling devices including, but not limited to, a dual-clutch
coupling device and a starting clutch coupling device.
[0032] The torque converter 16 includes a housing 50 that is fixed for
rotation with the crankshaft 24 via a flywheel 52. An impeller 54 is fixed for
rotation with the housing 50 and a turbine 56 is fixed for rotation with a
transmission input shaft 58. A stator 60 is also provided and is fixed from
rotation. The interior of the torque converter 16 is filled with a viscous fluid.
Rotation of the impeller 54 induces corresponding motion of the viscous fluid,
which is directed towards the turbine 56 by the stator 60 to induce rotation of the
turbine 56. The torque converter 16 includes a torque converter clutch (TCC)
(not shown), which is selectively engaged to proved a direct drive between the
crankshaft 24 and the input shaft 58.
[0033] As the crankshaft 24 rotates at an idle speed (RPMidle), the
impeller 54 is induced to rotate. RPMidle, however, is normally insufficient to
overcome braking forces that inhibit the turbine 56 from rotating. As the braking
forces are reduced and/or RPMeng increases, the impeller 54 drives the viscous
fluid into the turbine 56 and the turbine 56 is induced to rotate. As a result, drive
torque is transferred through the transmission 14 to propel the vehicle. Upon
achieving a point where there is little or no RPM difference between the turbine
56 and impeller 54, the TCC is engaged to provide a direct drive between the
engine 12 and the transmission 14. Under this condition, the rotational speed of
the turbine 56 (RPMturb) is equal to RPMeng- Generally, RPMturb is determined
based on the TISS signal and is equivalent to the TISS (RPMTiss)-
[0034] The overspeed protection control of the present invention
protects the engine 12, torque converter 16 and/or transmission 14 from damage
in an overspeed condition. An overspeed condition occurs when at least one of
RPMeng and RPMturb flares and exceeds a theoretical or expected engine or
turbine speed (RPMengexp, RPMturbexp)- It is anticipated that RPMnss can
replace RPMturb, and, as a result, the overspeed protection control of the
present invention can be implemented in vehicle powertrains that do not include
a torque converter. An overspeed condition can damage the engine 12, the
torque converter 16 and/or the transmission 14. The overspeed protection
control determines whether at least one of RPMeng and RPMturb exceeds an
upper threshold (RPMuthr) and reduces TREq to until it falls below a lower
threshold (RPMlthr)-
[0035] Treq can be reduced by a fixed amount. Alternatively, TREq can
be reduced by an amount that is determined based on the difference between
RPMturb and RPMuthr. In this manner, the overspeed condition can be more
rapidly resolved thereby reducing the potential for damage to the powertrain
components. By regulating TREq, a quicker, more accurate control is provided to
better inhibit or resolve the overspeed condition. In this manner, a high level of
powertrain protection is provided.
[0036] As described in further detail below, RPMUThr and RPMlthr are
determined based on a powertrain operating condition. The powertrain operating
conditions include, but are not limited to, a neutral condition, an upshift condition,
a downshift condition, a garage shift condition and a steady gear condition. In
the case of an automatic transmission, each of these conditions can be present,
wherein the overspeed protection control of the present invention includes
corresponding control strategies. In the case of a CVT, the overspeed protection
control for garage shift and neutral conditions can be combined under a first
control strategy and the remaining conditions are combined under a second
control strategy.
[0037] Referring now to Figure 3, the TREq is reduced when at least
one of RPMeng and RPMturb exceeds RPMuthr, during the neutral condition. In
this manner, RPMENG and/or RPMturb is maintained equal to or below RPMuthr-
If RPMENG and/or RPMturb falls below RPMlthr, the overspeed protection control
is exited and TREq is regulated based on normal TREq control. Under the normal
TrEq control, Treq is determined based on operating parameters including, but
not limited to, MAP and RPMeng, and TPS.
[0038] Referring now to Figures 4 and 5, the overspeed protection
control implements one of a first strategy (see Figure 4) and a second strategy
(see Figure 5) during the upshift condition. With particular reference to Figure 4,
the overspeed protection control determines RPMUThr and RPMLThr based on
the engine and/or turbine RPM associated with the attained gear ratio (RPMAg)-
For example, in the case of an automatic transmission, if a shift from 2nd to 3rd
gear is being performed, the overspeed protection control determines RPMuthr,
such that RPMeng and/or RPMturb does not exceed a corresponding 2nd gear
RPM. RPMag is the desired RPM profile corresponding to the gear that the
transmission shifts to as a result of the upshift (e.g., 3rd gear for the above
example). With particular reference to Figure 5, the overspeed protection control
determines RPMuthr and RPMlthr based on a commanded RPM profile
(RPMcom).
[0039] Referring now to Figures 6 and 7, the overspeed protection
control can implement one of a first strategy (see Figure 6) and a second
strategy (see Figure 7) during the downshift condition. With particular reference
to Figure 6, the overspeed protection control determines RPMuthr and RPMlthr
based on the engine and/or turbine RPM associated with the commanded gear
ratio (RPMcg)- For example, in the case of an automatic transmission, if a shift
from 3rd to 2nd gear is being performed, the overspeed protection control
determines RPMuthr, such that RPMeng and/or RPMturb does not exceed a
corresponding 2nd gear RPM. With particular reference to Figure 7, the
overspeed protection control determines RPMUTHr and RPMlthr based on a
RPMcom for the downshift.
[0040] Referring now to Figure 8, the overspeed protection control
determines RPMuthr and RPMlthr based on a maximum engine speed limit
(RPMengmax) because there is no profile to follow during the garage shift / neutral
idle operation. Referring now to Figure 9, the overspeed protection control
determines RPMuthr and RPMlthr based on a turbine speed profile for the
actual gear (RPMqear)- During a steady gear condition, the actual RPMeng
and/or RPMturb should not vary from respective theoretical RPMeng and
RPMturb values.
[0041] Referring now to Figure 10, exemplary steps that are executed
by the overspeed protection control of the present invention will be described in
detail. In step 100, control determines RPMeng and/or RPMturb In step 102,
control determines the powertrain condition. Control determines RPMuthr and
RPMlthr based on the powertrain condition in step 104.
[0042] In step 106, control determines whether at least one of RPMeng
and RPMturb is greater than RPMuthr- If RPMeng and/or RPMturb is not greater
then RPMuthr, control ends. If RPMeng and/or RPMturb is greater than
RPMuthr, control decreases TREq in step 108. As discussed above, TREq can be
reduced by a fixed amount or by an amount that is determined based on the
difference between RPMeng or RPMturb and RPMuthr. In step 110, control
determines whether RPMeng and/or RPMturb is less than RPMlthr- If RPMeng
and/or RPMturb is not less then RPMlthr, control loops back to step 108. If
RPMeng or RPMturb is less than RPMlthr, control resumes normal Treq control
in step 112 and control ends.
[0043] Referring now to Figure 11, exemplary modules that execute the
overspeed protection control will be described in detail. The exemplary modules
include, but are not limited to, a powertrain control module 200, an RPMeng
and/or RPMturb determining module 202, an RPMuthr and RPMlthr determining
module 204, a Treq calculating module 206 and an engine control module 208.
The powertrain control module 200 regulates general operation of the powertrain
components and outputs powertrain information to the RPMturb determining
module 202 and the TREq calculating module. More specifically, the RPMENg
and/or RPMturb determining module receives the TISS signal as an input, and
both the RPMuthr and RPMlthr determining module and the Treq calculating
module 206 receive the powertrain operating condition.
[0044] The RPMeng and/or RPMturb determining module 202
determines RPMeng and/or RPMturb- The RPMuthr and RPMlthr determining
module 204 determines RPMuthr and RPMlthr based on the powertrain
operating condition. The TREq calculating module 206 calculates TREq based on
either the overspeed protection control of the present invention, or the normal
Treq control. Under the overspeed protection control, the TREq calculating
module 206 determines TREq based on RPMeng and/or RPMturb, the powertrain
operating condition, RPMuthr and RPMlthr Under the normal TREq control, the
TREQ calculating module 206 determines TREq based on operating parameters
including, but not limited to RPMENg, MAP and TPS. The engine control module
208 regulates operation of the engine 12 to achieve TREq.
[0045] Those skilled in the art can now appreciate from the foregoing
description that the broad teachings of the present invention can be implemented
in a variety of forms. Therefore, while this invention has been described in
connection with particular examples thereof, the true scope of the invention
should not be so limited since other modifications will become apparent to the
skilled practitioner upon a study of the drawings, the specification and the
following claims.
CLAIMS
What is claimed is:
1. An overspeed protection control system that inhibits an overspeed
condition in a vehicle powertrain, comprising:
a first module that monitors at least one of an engine speed and a
transmission input shaft speed;
a second module that determines an operating condition of said vehicle
powertrain;
a third module that determines a first threshold speed based on said
operating condition; and
a fourth module that reduces an engine torque request when said at least
one of said engine speed and said transmission input shaft speed exceeds said
first threshold speed.
2. The overspeed protection control system of claim 1 wherein said fourth
module provides a fixed torque reduction amount, and reduces said engine
torque request by said fixed torque reduction amount.
3. The overspeed protection control system of claim 1 wherein said fourth
module determines a torque reduction amount based on a difference between
said at least one of said engine speed and said transmission input shaft speed
and said first threshold speed, and reduces said engine torque request by said
torque reduction amount.
4. The overspeed protection control system of claim 1 wherein said third
module determines a second threshold speed based on said operating condition
and determines said engine torque request without a reduction when said at least
one of said engine speed and said transmission input shaft speed is less than
said second threshold speed.
5. The overspeed protection control system of claim 1 wherein said third
module determines said first threshold speed based on one of an attained gear
speed, a commanded gear speed and a commanded speed profile.
6. The overspeed protection control system of claim 5 wherein said operating
condition is one of an upshift and a downshift of a gear ratio of said transmission.
7. The overspeed protection control system of claim 1 wherein said operating
condition is one of a garage shift condition and a neutral idle condition and said
first threshold speed corresponds to a maximum engine speed limit.
8. The overspeed protection control system of claim 1 wherein said
transmission is one of an automatic transmission and a continuously variable
transmission.
9. A method of inhibiting an overspeed condition in a vehicle powertrain,
comprising:
monitoring at least one of an engine speed and a transmission input shaft
speed;
determining an operating condition of said vehicle powertrain;
determining a first threshold speed based on said operating condition; and
reducing an engine torque request when said at least one of said engine
speed and said transmission input shaft speed exceeds said first threshold
speed.
10. The method of claim 9 further comprising providing a fixed torque
reduction amount, wherein said engine torque request is reduced by said fixed
torque reduction amount.
11. The method of claim 9 further comprising determining a torque reduction
amount based on a difference between said at least one of said engine speed
and said transmission input shaft speed and said first threshold speed, wherein
said engine torque request is reduced by said torque reduction amount.
12. The method of claim 9 further comprising:
determining a second threshold speed based on said operating condition;
and
determining said engine torque request without a reduction when said at
least one of said engine speed and said transmission input shaft speed is less
than said second threshold speed.
13. The method of claim 9 wherein said first threshold speed is determined
based on one of an attained gear speed, a commanded gear speed and a
commanded speed profile.
14. The method of claim 13 wherein said operating condition is one of an
upshift and a downshift of a gear ratio of said transmission.
15. The method of claim 9 wherein said operating condition is one of a garage
shift condition and a neutral idle condition and said first threshold speed
corresponds to a maximum engine speed limit.
16. The method of claim 9 wherein said transmission is one of an automatic
transmission and a continuously variable transmission.
17. A method of inhibiting an overspeed condition in a vehicle powertrain,
comprising:
monitoring at least one of an engine speed and a transmission input shaft;
determining an operating condition of said vehicle powertrain;
determining a first and second threshold speeds based on said operating
condition;
reducing an engine torque request when said at least one of said engine
speed and said transmission input shaft speed exceeds said first threshold
speed; and
determining said engine torque request without a reduction when said at
least one of said engine speed and said transmission input shaft speed is less
than said second threshold speed.
18. The method of claim 17 further comprising providing a fixed torque
reduction amount, wherein said engine torque request is reduced by said fixed
torque reduction amount.
19. The method of claim 17 further comprising determining a torque reduction
amount based on a difference between said at least one of said engine speed
and said transmission input shaft speed and said first threshold speed, wherein
said engine torque request is reduced by said torque reduction amount.
20. The method of claim 17 wherein said first threshold speed is determined
based on one of an attained gear speed, a commanded gear speed and a
commanded speed profile.
21. The method of claim 20 wherein said operating condition is one of an
upshift and a downshift of a gear ratio of said transmission.
22. The method of claim 17 wherein said operating condition is one of a
garage shift condition and a neutral idle condition and said first threshold speed
corresponds to a maximum engine speed limit.
23. The method of claim 17 wherein said transmission is one of an automatic
transmission and a continuously variable transmission.

A method of inhibiting an overspeed condition in a vehicle powertrain
includes monitoring at least one of an engine speed and a transmission input
shaft speed of a torque converter that transfers drive torque between an engine
and a transmission and determining an operating condition of the vehicle
powertrain. The method further includes determining a first threshold speed
based on the operating condition and reducing an engine torque request when
the at least one of the engine speed and the transmission input shaft speed
exceeds the first threshold speed.

AN OVERSPEED PROTECTION CONTROL SYSTEM AND A METHOD OF INHIBITING AN OVERSPEED IN A VEHICLE POWERTRAIN

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