Method for managing thermal load on an engine

Information

  • Patent Grant
  • 6789517
  • Patent Number
    6,789,517
  • Date Filed
    Monday, November 19, 2001
    23 years ago
  • Date Issued
    Tuesday, September 14, 2004
    20 years ago
Abstract
A method for adjusting the timing of an internal combustion engine having a crankshaft and a camshaft to manage the thermal load on the engine. The method includes the step of altering the timing of the camshaft with respect to the timing of the crankshaft to reduce thermal load on the engine. Preferably, the step of altering the timing of the camshaft is accomplished with a variable camshaft phaser.
Description




FIELD OF THE INVENTION




The present invention relates generally to a method for managing the thermal load on an internal combustion engine, and more particularly to a method for selectively altering the output horsepower of the internal combustion engine by adjusting the timing of a camshaft relative to the crankshaft.




BACKGROUND OF THE INVENTION




Internal combustion engines are continuously subjected to thermal loads that are a product of the combustion process and its inherent inefficiencies. Excessive thermal loads can reduce engine efficiency and reliability, which may cause thermal damage to engine components. It may be necessary to use increased flow rate/capacity fuel injectors to lower the temperatures of the thermally affected engine components. Increased flow capacity fuel injectors, however, have the undesirable characteristic of exhibiting decreased fuel control at low load conditions, which may diminish catalytic converter efficiency and increase the amount of precious metals that are needed to manufacture the converter.




The thermal load on an internal combustion engine is directly proportional to the horsepower that is produced by the engine. The largest thermal loads typically occur while the engine is producing maximum horsepower. However, because there is a time delay between the onset of a high thermal load and its potentially damaging effects, an engine can typically withstand a potentially damaging thermal load for a period of time before experiencing a significant reduction in engine performance or damage to its components. Consequently, excessive thermal load is primarily a concern when an engine is operated at high horsepower for an extended period of time.




Since the thermal load on an engine is directly proportional to the horsepower that is generated, one method for reducing excessive thermal loads is to derate the engine, which limits the maximum horsepower that the engine can produce throughout its operating range. Although doing so would certainly reduce the thermal load on the engine, it will also unnecessarily limit the horsepower available at operating conditions that normally do not produce excessive thermal loads. Consequently, it would be desirable to selectively reduce an engine's output only under those conditions in which an engine is likely to be subjected to an excessive thermal load.




Known methods for selectively reducing the thermal load on an engine consist of retarding spark advance and/or increasing an engine's fuel/air mixture. Both of these methods, however, have limited effectiveness in reducing the horsepower produced by an engine and may not be capable of sufficiently reducing the thermal load on an engine at all operating conditions. Accordingly, there is a need for selectively reducing the horsepower output of an engine beyond that which can be achieved by merely adjusting spark advance and the fuel/air mixture.




SUMMARY OF THE INVENTION




The present invention is directed to a method for selectively adjusting the horsepower generated by an internal combustion engine to reduce the thermal load on the engine by adjusting the timing of a camshaft relative to a crankshaft. For a given engine operating condition, there is typically an optimum camshaft phase angle (i.e., timing) that will maximize engine performance. Operating the engine with its camshaft phase angle set to something other than its optimum degrades engine performance and reduces the horsepower output of the engine. The reduced horsepower produces a corresponding decrease in the thermal load on the engine.




In another feature of the invention, a camshaft phaser is used to adjust the timing of the camshaft. The camshaft phaser varies the phase angle of the camshaft relative to the phase angle of the crankshaft. An engine controller, utilizing a control algorithm, controls the operation of the camshaft phaser. The present invention incorporates additional functions in the control algorithm that modify the timing of the camshaft to control the thermal load on the engine.




The camshaft phaser is used to selectively adjust the timing of the exhaust camshaft relative to the timing of the crankshaft. Setting the exhaust camshaft phase angle to something other than its optimum degrades the volumetric efficiency of the engine and reduces the horsepower output of the engine. Moreover, the drop in horsepower produces a corresponding reduction in the thermal load on the engine.




In another feature, the camshaft phaser is used to selectively adjust the timing of an intake camshaft relative to the crankshaft. As is the case with the exhaust camshaft, de-optimizing the timing of the intake camshaft decreases engine performance and horsepower output, which in turn produces a corresponding reduction in the thermal load to the engine.




In yet another feature, two separate camshaft phasers, one attached to the exhaust camshaft, the other to the intake camshaft, simultaneously adjust the timing of both camshafts relative to the crankshaft. Adjusting both camshafts simultaneously allows for a greater reduction in the thermal load to the engine than is possible by only adjusting the timing of one or the other.




Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.











BRIEF DESCRIPTION OF THE DRAWINGS




The various features, advantages and other uses of the present invention will become more apparent by referring to the following detailed description and accompanying drawings, wherein:





FIG. 1

is a perspective view of an internal combustion engine having a crankshaft, an intake camshaft, an exhaust camshaft, and an exhaust camshaft phaser;





FIG. 2

is a block diagram of the control elements used to carry out the present invention;





FIG. 3

is a flowchart illustrating the control method of the present invention;





FIG. 4

is a flowchart illustrating a method for adjusting the exhaust camshaft timing to optimize engine performance; and





FIG. 5

is a flowchart depicting a method for adjusting the exhaust camshaft timing to manage the thermal load on the engine.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.





FIG. 1

is a perspective view of an internal combustion engine


10


having a crankshaft


12


, an intake camshaft


14


, and an exhaust camshaft


16


. Attached to the exhaust camshaft


16


is a camshaft phaser


18


of a type known to those skilled in the art. Although persons skilled in the art will appreciate that alternatives may exist for controlling the phase angle of the exhaust camshaft, the present exemplary system preferably utilizes a camshaft phaser that can be controlled to continuously adjust the phase angle of the exhaust camshaft


16


. The camshaft phaser


18


adjusts the phase angle of the exhaust camshaft


16


in response to certain predetermined engine parameters.




Sprockets


20


,


22


, and


24


, which are conventional in design, are attached to one end of the crankshaft


12


, the intake camshaft


14


, and the camshaft phaser


18


, respectively. The intake camshaft


14


, exhaust camshaft


16


, and crankshaft


12


, are coupled together in a conventional manner by entraining a belt or chain (not shown) about sprockets


20


,


22


, and


24


, thereby establishing the initial timing sequence between the intake camshaft


14


, exhaust camshaft


16


, and crankshaft


12


.




Referring to

FIG. 2

, during normal engine operation, the camshaft phaser


18


adjusts, if necessary, the phase angle between the exhaust camshaft


16


and the crankshaft


12


to achieve a desired engine performance for a given operating condition. An engine controller


30


controls the operation of the camshaft phaser


18


. As is conventional, the controller


30


includes a central processing unit (CPU)


32


that executes a control algorithm stored in the controller's memory


34


.




Referring now to

FIG. 3

, a flow chart is shown for a method


40


used to adjust the timing of crankshaft


12


and exhaust camshaft


16


of engine


10


in accordance with the present invention. Method


40


includes a first step


42


that adjusts the timing of the exhaust camshaft


16


with respect to the crankshaft


12


to optimize engine performance. A second step


44


adjusts, if necessary, the exhaust camshaft phase angle that was previously calculated in step


42


to manage the thermal load on engine


10


. The control algorithm, which is designed to optimize engine performance as well as protect the engine from excessive thermal load, controls when and by how much the camshaft timing is altered. The control algorithm is stored in memory


34


of engine controller


30


. Adjustments to the exhaust camshaft timing are made while engine


10


is operating.




The exhaust camshaft phaser


18


is activated in response to one or more predetermined engine parameters that are monitored by the control algorithm. According to a preferred embodiment, the predetermined engine parameters include at least one parameter selected from the currently chosen transmission gear, TCC, barometric pressure, coolant temperature, engine RPM, manifold pressure, engine intake air temperature, and the amount of time engine


10


has operated in a “power enrichment” mode. Power enrichment is a known method for increasing the horsepower output of an engine during high load conditions by increasing the engine's fuel/air mixture.




Referring to

FIG. 4

, a block diagram flow chart is shown depicting a method


50


used by the control algorithm to determine the exhaust camshaft phase angle required to optimize engine performance based on the current engine operating condition. Method


50


is a more detailed description of step


42


of method


40


(see FIG.


3


), whereby the exhaust camshaft timing is adjusted to optimize engine performance. In step


52


of method


50


, the control algorithm determines whether the engine's power enrichment (PE) mode has been activated. As previously noted, power enrichment is initiated when an engine is under high load and additional horsepower is needed. The additional horsepower is obtained by raising the engine's fuel/air mixture. Changing the fuel/air mixture also requires that a corresponding adjustment be made to the exhaust camshaft timing. If power enrichment is activated, the control algorithm proceeds to step


54


where it calculates a base PE exhaust phase angle as a function of engine RPM. This calculation can be accomplished via a look-up table, an algorithm or other suitable methods.




The optimum exhaust camshaft phase angle can also be dependant on the engine coolant and/or engine inlet air temperature. In step


56


the control algorithm adjusts the base PE exhaust phase angle calculated in step


54


to account for the affect of the current engine coolant and/or engine inlet air temperature. Preferably, a look-up table provides a correction factor that is added to or subtracted from the base PE exhaust phase angle determined in step


54


.




If the power enrichment mode is not activated, the control algorithm proceeds from decision block


52


to step


58


, where it calculates a base non-power enrichment (non-PE) exhaust camshaft phase angle. The base non-power enrichment exhaust camshaft phase angle is further adjusted based on certain vehicle operating parameters, which may include the transmission gear that is currently selected (step


60


) and the barometric pressure (step


62


). For each case, the control system has predetermined phase angle correction factors that are combined with the base non-PE exhaust phase angle to optimize engine performance. As is the case when the power enrichment mode is activated, step


56


is performed to adjust the corrected base non-PE phase angle to take into account the affect of engine coolant temperature. The output from step


56


is an optimum exhaust camshaft phase angle determination.




Referring now to

FIG. 5

, a flow chart is shown depicting a method


70


used to calculate the exhaust camshaft phase angle that reduces, when required, the horsepower output of the engine to manage the engine's thermal load. The control algorithm uses method


70


in conjunction with method


50


(see

FIG. 4

) to determine the proper exhaust camshaft phase angle. Method


70


is a more detailed description of step


44


of method


40


(see FIG.


3


), whereby the optimized exhaust camshaft timing is adjusted to manage engine performance. It is important to note that method


70


is a continuation of method


50


, and the two methods operate in conjunction with one another to determine the proper exhaust camshaft phase angle for a given engine operating condition.




In step


72


of method


70


, the control algorithm first determines whether the power enrichment mode is activated. Method


70


uses the status of the power enrichment mode as the decisional operator since excessive thermal loads generally occur when power enrichment is activated and engine


10


is producing high horsepower. If the power enrichment mode is activated, the control algorithm sequentially executes steps


74


through


82


of method


70


and calculates the exhaust camshaft phase angle required to reduce the thermal load on the engine. If on the other hand, the power enrichment mode is not activated, the control algorithm will skip steps


74


through


82


and proceed directly to step


84


.




If engine


10


is operating in the power enrichment mode, the control algorithm will execute step


74


and calculate the maximum adjustment that can be made to the exhaust cam phase angle to manage the thermal load on the engine (maximum adjustable phase angle). The maximum adjustable phase angle varies depending on engine RPM and the configuration of the engine. The relationship between the maximum adjustable phase angle and engine RPM is typically determined empirically. The resulting data is included in a look-up table that can be accessed by the control algorithm. The control algorithm references the lookup table to determine the maximum adjustable phase angle as a function of engine RPM.




In step


76


, the control algorithm monitors the amount of time the engine has continuously operated with the power enrichment mode active. Since various engine components do not reach their maximum temperature immediately upon initiation of power enrichment, adjustments to the exhaust camshaft timing as a means for offsetting the increased thermal load may occur over a period of time. The actual time period, however, varies depending on the particular engine component involved as well as the overall engine configuration. The transient temperature characteristics for a given engine component are typically determined empirically. The resulting data is incorporated into a lookup table that can be accessed by the control algorithm. The control algorithm references the table to determine the amount by which to adjust the maximum adjustable phase angle based on the length of time the engine has continuously operated in the power enrichment mode.




The exhaust camshaft timing required to manage the thermal load on an engine is also a function of the engine's manifold pressure (MAP). There is a direct correlation between the horsepower that an engine is producing and MAP. Furthermore, the thermal load on an engine is directly proportional to the horsepower being produced by the engine. Since there is a direct correlation between MAP and horsepower, as well as between horsepower and thermal load, it follows that there is also a direct relationship between MAP and thermal load. Consequently, MAP can be used to accurately estimate the magnitude of the thermal load on the engine. The relationship between horsepower output (which is directly proportional to the thermal load) and MAP is typically determined empirically and varies depending on the particular engine configuration. The resulting data is incorporated into a lookup table that can be accessed by the control algorithm. Referring to

FIG. 5

, in step


78


the control algorithm references the lookup table to determine the amount by which the previously calculated maximum adjustable phase angle can be reduced based on the amount of horsepower the engine is producing.




Continuing to refer to

FIG. 5

, using the results of steps


74


,


76


and


78


, in step


80


the control algorithm calculates the amount of adjustment that needs to be made to the exhaust camshaft phase angle that was previously determined using method


50


. In step


82


the control algorithm calculates the exhaust camshaft phase angle that balances the desire to optimize engine performance with the need to appropriately manage the thermal load on the engine. The optimum exhaust camshaft phase angle is arrived at by subtracting the result of step


80


from the exhaust camshaft phase angle determined in step


56


of method


50


. The resulting camshaft phase angle information is then processed by controller


30


for communication to the power-operated actuator associated with the camshaft phaser


18


via a conventional I/O interface


36


. The camshaft phaser


18


then makes the necessary adjustment to the timing of the exhaust camshaft


16


.




In another preferred embodiment of the present invention, the camshaft phaser


18


is used to selectively adjust the timing of the intake camshaft


14


relative to the crankshaft


12


. As is the case with the exhaust camshaft


16


, de-optimizing the timing of the intake camshaft


14


will decrease the performance and horsepower output of engine


10


, which will result in a corresponding decrease in the thermal load to the engine. In this embodiment, the camshaft phaser


18


is attached to intake camshaft


14


, rather than the exhaust camshaft


16


. The engine controller


30


, shown in

FIG. 2

, still controls the operation of the camshaft phaser


18


, but the camshaft phaser now controls the timing of the intake camshaft


14


, rather than the exhaust camshaft


16


. Determining the appropriate intake camshaft phase angle is accomplished using the previously described method for determining the phase angle of the exhaust camshaft, which is also shown in

FIGS. 3 through 5

.




In yet another embodiment of the present invention, two separate camshaft phasers


18


are used to simultaneously adjust the timing of both the intake camshaft


14


and the exhaust camshaft


16


relative to the crankshaft


12


. In this embodiment, a separate camshaft phaser


18


is attached to the intake camshaft


14


and the exhaust camshaft


16


. The engine controller


30


, shown in

FIG. 2

, controls the operation of both camshaft phasers


18


. Once again, determining the appropriate intake and exhaust camshaft phase angles is accomplished using the previously described method for determining the phase angle of the exhaust camshaft, which is also shown in

FIGS. 3 through 5

.




While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it shall be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but rather, the invention will include any embodiments falling within the description of the appended claims.



Claims
  • 1. A method for adjusting the timing of an internal combustion engine having a crankshaft and a camshaft, comprising the steps of:altering the timing of the camshaft with respect to the crankshaft to optimize engine performance; determining if the engine is operating in a power enriched mode by comparing a currently delivered fuel/air mixture to a predetermined fuel/air mixture; altering the timing of the camshaft with respect to the crankshaft from the previously optimized position to adjust engine performance in response to the engine entering the power enrichment mode; determining the amount of time the engine has continuously operated within the power enrichment mode; and altering the timing of the camshaft with respect to the crankshaft from the previously altered position to reduce the thermal load on the engine.
  • 2. The method of claim 1 wherein the step of altering the timing of at least one camshaft further comprises performing at least one of advancing and retarding the timing of at least one camshaft relative to the crankshaft to optimize engine performance and reduce the thermal load on the engine.
  • 3. The method of claim 2 wherein the step of performing at least one of advancing and retarding the timing of at least one camshaft further comprises performing at least one of advancing and retarding the timing of at least one camshaft relative to the crankshaft within a range of zero to twenty-five degrees inclusive.
  • 4. The method of claim 1 wherein the step of altering the timing of at least one camshaft further comprises the step of altering the timing of at least one camshaft with at least one camshaft phaser.
  • 5. The method of claim 4 wherein the step of altering the timing of at least one camshaft further comprises activating at least one camshaft phaser in response to at least one predetermined engine parameter.
  • 6. The method of claim 5 wherein the predetermined engine parameters include at least one parameter selected from engine speed, engine load, power enrichment, the currently selected transmission gear, TOG, barometric pressure, engine coolant temperature, engine inlet air temperature, manifold pressure, and the amount of time the engine has operated in a power enrichment mode.
  • 7. The method claim 1 wherein the step of altering the timing of at least one camshaft further comprises altering the timing of at least one camshaft relative to the crankshaft in response to at least one predetermined engine parameter.
  • 8. The method of claim 7 wherein the predetermined engine parameters include at least one parameter selected from engine speed, engine load, power enrichment, the currently selected transmission gear, TCC, barometric pressure, engine coolant temperature, engine inlet air temperature, manifold pressure, and the amount of time the engine has operated in a power enrichment mode.
  • 9. The method of claim 1 wherein at least one camshaft is an exhaust camshaft and the step of altering the timing of at least one camshaft further comprises altering the timing of at least one exhaust camshaft relative to the crankshaft.
  • 10. The method of claim 1 wherein at least one camshaft is an intake camshaft and the step of altering the timing of at least one camshaft further comprises altering the timing of at least one intake camshaft relative to the crankshaft.
  • 11. The method of claim 1 wherein at least one camshaft is an intake camshaft and at least one other camshaft is an exhaust camshaft, and the step of altering the timing of at least one camshaft further comprises altering the timing of at least one intake camshaft and at least one exhaust camshaft relative to the crankshaft.
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