Method to optimize fuel economy by preventing cylinder deactivation busyness

A method of transitioning an engine to a cylinder deactivation mode may include determining a ratio of time that the engine is operating in the cylinder deactivation mode for an engine operating condition relative to a total time of engine operation in the operating condition, determining a number of transitions from a full cylinder mode to the cylinder deactivation mode during the operating condition, determining a transition modifier based on the ratio and number, and modifying a transition criterion based on the transition modifier.

FIELD

The present disclosure relates to control of internal combustion engines, and more specifically to control of a transition from a full cylinder mode operation to a cylinder deactivation mode operation of an internal combustion engine.

BACKGROUND

Internal combustion engines may be operable at a full cylinder operating mode and a cylinder deactivation operating mode. In such engines, a number of cylinders may be deactivated (non-firing) during low load conditions. For example, an eight cylinder engine may be operable using all eight cylinders during the full cylinder mode and may be operable using only four cylinders during the cylinder deactivation mode.

Operating the engine in the cylinder deactivation mode during low load conditions may reduce an overall fuel consumption of the engine. However, excessive transitioning between the full cylinder mode and the cylinder deactivation mode may reduce the fuel economy gains associated with engine operation in the cylinder deactivation mode. Excessive transitioning may also be adverse to vehicle drivability.

SUMMARY

A method of transitioning an engine to a cylinder deactivation mode may include determining a ratio of time that the engine is operating in the cylinder deactivation mode for an engine operating condition relative to a total time of engine operation in the operating condition, determining a number of transitions from a full cylinder mode to the cylinder deactivation mode during the operating condition, determining a transition modifier based on the ratio and number, and modifying a transition criterion based on the transition modifier.

A control module may include a cylinder deactivation evaluation module, a transition modifier determination module, and a transition threshold evaluation module. The cylinder deactivation evaluation module may determine a ratio of time that an engine is operating in a cylinder deactivation mode during an engine operating condition relative to a total time of engine operation in the operating condition and a number of transitions to the cylinder deactivation mode during the engine operating condition. The transition modifier determination module may be in communication with the cylinder deactivation evaluation module and may determine a transition modifier based on the ratio and number. The transition threshold evaluation module may be in communication with the transition modifier determination module and may modify a transition criterion based on the transition modifier.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, 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.

Referring now toFIG. 1, an exemplary vehicle10is schematically illustrated. Vehicle10may include an engine12in communication with an intake system14, a fuel system16, and an ignition system18. Engine12may be selectively operated in a full cylinder mode and a cylinder deactivation mode. The cylinder deactivation mode of engine12may generally include operation of engine12firing less than all of the cylinders. For example, if engine12includes eight cylinders (not shown), full cylinder mode operation includes operation of engine12firing all eight cylinders and cylinder deactivation mode generally includes operation of engine12firing less than eight cylinders, such as four cylinder operation of engine12.

During the cylinder deactivation mode, fuel, air, and spark may be cut off to the deactivated cylinders. The inlet and exhaust ports (not shown) of the deactivated cylinders may be closed to reduce pumping losses. Closure of the inlet and exhaust ports may be provided by a lost motion coupling between inlet and exhaust valves and a camshaft (not shown).

Intake system14may include an intake manifold20and a throttle22. Throttle22may control an air flow into engine12. Fuel system16may control a fuel flow into engine12and ignition system18may ignite the air/fuel mixture provided to engine12by intake system14and fuel system16.

Vehicle10may further include a control module24and an electronic throttle control (ETC)26. Control module24may be in communication with engine12to monitor an operating speed thereof and a number and duration of cylinder deactivation events. Control module24may additionally be in communication with ETC26to control an air flow into engine12. ETC26may be in communication with throttle22and may control operation thereof. A manifold absolute pressure sensor28and a barometric pressure sensor30may be in communication with control module24and may provide signals thereto indicative of a manifold absolute pressure (MAP) and a barometric pressure (PBARO), respectively.

Control module24may control a transition of engine12between the full cylinder mode and the cylinder deactivation mode. With reference toFIG. 2, control module24may include an engine operating zone determination module32, a cylinder deactivation evaluation module34, a transition modifier determination module36, and a transition threshold evaluation module38. Engine operating zone determination module32may include a look-up table such as Table 1 below including a series of engine operating zones (discussed below) associated with a range of engine speed and load points. It is understood that Table 1 is included for illustration purposes only and is not intended to limit the present disclosure in any way.

Engine operating zone determination module32may be in communication with manifold absolute pressure sensor28, barometric pressure sensor30, and engine12. Engine operating zone determination module32may receive a signal indicative of the operating speed of engine12and may determine engine operating vacuum based on the difference between MAP and PBARO. Engine operating zone determination module32may be in communication with transition modifier determination module36and may provide the operating zone of engine12based on a look-up table, such as Table 1 above. The operating zone of engine12may generally be defined as a function of the operating speed of engine12and a value indicative of the operating load of engine12, such as engine operating vacuum.

Cylinder deactivation evaluation module34may be in communication with transition modifier determination module36and may provide a number and duration of cylinder deactivation events occurring during an engine operating zone. More specifically, cylinder deactivation evaluation module34may track the number of transitions from full cylinder mode to cylinder deactivation mode and the cumulative operating time of engine12in each zone, as well as the percent (or ratio) of the operating time in each zone associated with the cylinder deactivation mode relative to the total engine operating time. The engine operating time may generally be defined from an engine start condition and may begin at zero at each engine start.

Transition modifier determination module36may be in communication with transition threshold evaluation module38. Transition modifier determination module36may include a series of look-up tables corresponding to the zones in Table 1 and including transition modifier values. An exemplary table is illustrated as Table 2 below. It is understood that Table 2 is included for illustration purposes only and is not intended to limit the present disclosure in any way.

TABLE 2Busyness Threshold Modifier (kPa)Number ofPercent of Time in Deactivation ModeDeactivation Events17335067831001000−0.75−1.5−2−32000−0.5−1−1.5−23032100−14054200−1

Transition modifier determination module36may determine a value for adjusting a transition threshold (discussed below) based on the values determined from the look-up table associated with the operating zone of engine12. For example, Table 2 may include transition modifier values associated with zone 5 from Table 1. Transition modifier determination module36may include similar look-up tables for each of zones 1, 2, 3 and 4.

The transition modifier values for each zone may generally be a function of the number of transitions from full cylinder mode to cylinder deactivation mode (deactivation events) and duration of cylinder deactivation mode operation relative to operating time during a given engine operating zone (percent of time in deactivation mode). Transition modifier values may generally include engine load modification values, as discussed below. More specifically, transition modifier values may include engine vacuum modification values.

Transition threshold evaluation module38may include the transition threshold criterion for the transition from full cylinder mode to cylinder deactivation mode. More specifically, the transition threshold criterion may include a range of engine loads associated with a range of engine speeds. More specifically, the range of engine loads may include a range of engine vacuum levels. Transition threshold evaluation module38may evaluate a given engine speed and load condition and determine if transition from full cylinder mode to cylinder deactivation mode is appropriate. Transition threshold evaluation module38may additionally receive the transition modifier value from transition modifier determination module36and adjust the transition threshold, as discussed below.

With reference toFIG. 3, control logic100for reduction of cylinder deactivation busyness of engine12is illustrated. Control logic100may begin at block102where an operating zone of engine12is determined. Block102may determine the current operating engine speed and current operating engine vacuum (engine load). As discussed above, the operating zone of engine12may be determined by referencing a look-up table, such as Table 1 above, including operating zone as a function of engine speed and engine vacuum (engine load). Control logic100may then proceed to block104where the percent of cylinder deactivation time for the zone determined at block102is determined.

Block104may generally determine the ratio of time of engine operation in the determined zone that engine12is operating in the cylinder deactivation mode relative to the total amount of time that engine12has operated in the determined zone. As indicated above, engine operating times may be determined relative to an engine start condition and may begin at zero at each engine start. For example, if engine12has operated in zone 1 for a total of 10 minutes and has operated in cylinder deactivation mode for 2 minutes during operation in zone 1, the ratio of cylinder deactivation time may generally be ⅕, or 20 percent. The operating time of engine12in a particular zone and ratio of cylinder deactivation time for the zone may be updated throughout engine operation. Control logic100may then proceed to block106.

Block106may generally determine the number of transitions of engine12from full cylinder mode to cylinder deactivation mode during the determined zone from block102. The number of transitions may be cumulative throughout engine operation. Control logic100may then proceed to block108where the cylinder deactivation busyness modifier is determined.

Block108may generally include referencing a look-up table, such as Table 2 above, including cylinder deactivation busyness modifiers as a function of the ratio of cylinder deactivation time from block104and the number of cylinder deactivation events from block106. As the ratio of cylinder deactivation time increases, the value of the cylinder deactivation busyness modifier may generally decrease. As the number of cylinder deactivation events increases, the value of the cylinder deactivation busyness modifier may generally increase. The determined cylinder deactivation busyness modifier may generally include an engine operating load modifier, more specifically, an engine operating vacuum modifier. The determined cylinder deactivation busyness modifier may be applied to a cylinder deactivation criterion at block110to adjust the likelihood of transitioning to the cylinder deactivation mode.

Block110may adjust the cylinder deactivation criterion by increasing, reducing, or maintaining a threshold value for transition of engine12from full cylinder mode to cylinder deactivation mode. For example, transition threshold evaluation module38may include a transition threshold corresponding to the engine speed determined at block102. The transition threshold may include an engine vacuum (engine load) corresponding to the determined engine speed. The determined cylinder deactivation busyness modifier may be applied to the transition threshold to increase, reduce, or maintain the transition threshold and to create a modified transition threshold.

Block110may then proceed to block112where the engine operating mode is evaluated. Evaluation of the engine operating mode may generally include comparing the engine operating vacuum from block102to the modified transition threshold. If the engine operating vacuum is greater than the modified transition threshold, then engine12may remain in full cylinder mode. If the engine operating vacuum is less than the modified transition threshold, engine12may transition from full cylinder mode to cylinder deactivation mode. Therefore, when the original transition threshold is increased by the determined cylinder deactivation busyness modifier, the resulting modified transition threshold may be greater than the original transition threshold, resulting in a decreased likelihood of engine12transitioning from full cylinder mode to cylinder deactivation mode. Conversely, when the original transition threshold is decreased by the determined cylinder deactivation busyness modifier, the modified transition threshold may be less than the original transition threshold, resulting in an increased likelihood of engine12transitioning from full cylinder mode to cylinder deactivation mode.

For illustration purposes, according to the present disclosure, engine12may be operating at an engine speed of 2000 RPM and a vacuum pressure of 44 kPa. According to Table 1, the operating engine speed and vacuum pressure may generally correspond to zone 5. For exemplary purposes, engine12may be determined to have operated in zone 5 for 100 minutes, and in cylinder deactivation mode for 83 of the 100 minutes, (83 percent of time in deactivation mode) and may have transitioned from full cylinder mode to cylinder deactivation mode 10 times (10 deactivation events) during the 100 minutes of operation in zone 5.

Referencing Table 2, the cylinder deactivation busyness modifier may generally be equal to −2 kPa. Therefore, the cylinder deactivation transition threshold may be reduced by 2 kPa. For example, if the cylinder deactivation transition threshold was originally 45 kPa for an engine speed of 2000 RPM, the cylinder deactivation transition threshold may be modified to 43 kPa (modified transition threshold). The operating vacuum (44 kPa) of engine12may then be compared to the modified transition threshold (43 kPa). Since the operating vacuum (44 kPa) is greater than the modified transition threshold (43 kPa), engine12may transition to or maintain full cylinder operation.

As illustrated above, as the modified transition threshold increases relative to the original cylinder deactivation transition threshold, the less likely it is for engine12to transition to cylinder deactivation mode. Conversely, as the modified transition threshold decreases relative to the original cylinder deactivation transition threshold, the more likely it is for engine12to transition to cylinder deactivation mode. Accordingly, a positive cylinder deactivation busyness modifier may correspond to an increased likelihood of engine operation in a full cylinder mode and a negative cylinder deactivation busyness modifier may correspond to an increased likelihood of engine operation in a cylinder deactivation mode. While the example above has been described with respect to values specifically found in Tables 1 and 2, it is understood that values between those in tables may be interpolated to determine engine operating zone and cylinder deactivation busyness modifiers.

Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure 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.