DE112018002559T5 - Dynamic valve control in an engine with skip fire control - Google Patents

Abstract

Various methods and arrangements are described for improving fuel efficiency and noise, vibration and roughness (NVH) in an engine with skip fire control. An engine control dynamically selects a gas spring type for a switched off ignition opportunity. The setting of the skip / fire pattern and the type of gas spring can take place from ignition opportunity to ignition opportunity.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Patent Application 62 / 508,020 (P064P), filed May 18, 2017, the contents of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the operation of an internal combustion engine with skip fire control. Various embodiments relate to changing the timing of cylinder intake and exhaust events to form different types of gas springs within the cylinders of the engine.

BACKGROUND OF THE INVENTION

Most of the vehicles used today (and many other devices) are powered by internal combustion engines. An internal combustion engine typically has an evasive piston that reciprocates within a cylinder. The combustion takes place inside the cylinder and the resulting torque is transmitted to a crankshaft by the piston via a connecting rod. In a four-stroke engine, air and, in some cases, fuel are introduced into the cylinder through an intake valve, and combustion exhaust gases are exhausted through an exhaust valve. In typical engine operation, cylinder conditions vary cyclically and meet an intake, compression, expansion and exhaust stroke in that order in a repeating pattern. Each repeating pattern can be referred to as a cylinder duty cycle.

Internal combustion engines usually have a plurality of cylinders or other working chambers in which an air-fuel mixture is burned. The duty cycles associated with the various engine cylinders are interlocked at times so that the expansion stroke associated with the various cylinders is approximately equally spaced to provide the smoothest engine operation. The combustion that occurs during the expansion stroke generates the desired torque and various exhaust gases. The expansion stroke is often referred to as a combustion or work stroke because it is the power generating stroke.

In normal driving, the torque generated by an internal combustion engine must vary over a wide range in order to be able to meet the operational requirements of the driver. Various methods for regulating the torque of internal combustion engines have been proposed and used over the years. Some of these approaches involve varying the actual engine stroke volume. Two different engine control approaches that vary the actual engine stroke volume include: (1) the use of multiple fixed stroke volumes; and (2) skip fire engine operation. In the case of regulation with several fixed stroke volumes, a fixed cylinder set is deactivated under low load conditions; For example, an 8-cylinder engine can be operated with the same 4 cylinders under certain conditions. In contrast, the skip fire control works by sometimes turning a cylinder off and sometimes firing it. In some internal combustion engines, all cylinders are capable of being switched off or ignited, while in other engines only a certain subset of the engine cylinders have the skip fire capability. In general, skip fire engine control offers several possible benefits, including the potential to provide significantly improved fuel economy in many applications. Although the concept of skip-fire motor control has existed for many years and its advantages are known, skip-fire motor control has only recently developed a certain economic success.

It is well known that engine operation tends to be a source of significant noise and vibration, which is often referred to in the art as NVH (noise, vibration and harshness). Generally speaking, a typical stereotype associated with skip fire engine control is that skip fire operation of an engine results in the engine being significantly rougher, i.e., increased, compared to a conventionally operated engine NVH, running. For many applications, such as automotive applications, one of the biggest challenges with skip fire engine control is vibration control. Indeed, the inability to satisfactorily resolve NVH issues is one of the major obstacles that have prevented the widespread use of skip-fire engine controls to date.

U.S. Patents 7,954,474, 7,886,715, 7,849,835, 7,577,511, 8,099,224, 8,131,445, 8,131,447, 8,616,181, 8,701,628, 9,086,020 9,328,672, 9,387,849, 9,399,964, 9,512,794, 9,745,905, and other methods describe a variety of engines, a variety of engines, a wide range of combustion engines enable in a skip fire operating mode. Alles these patents and patent applications are incorporated herein by reference. Although the controls described work well, there is ongoing effort to improve the performance of these and other skip fire controls to further mitigate NVH problems and improve fuel economy in skip fire engines. The present application describes additional skip fire control features and enhancements that can improve engine performance in a variety of applications.

SUMMARY

In various embodiments, a system and method for varying the types of gas springs in a deactivated working chamber of an engine with skip fire control are described. Various embodiments relate to changing the timing of cylinder intake and exhaust events to modify the nature of gases trapped in the work chamber during a shutdown duty cycle. The timing of fuel injection and ignition can also be modified. The nature of the gas spring can be varied to improve NVH levels and fuel economy. Oil consumption and exhaust emissions can also be taken into account when determining the type of gas spring.

In one aspect, a method for controlling the nature of the gases trapped in a work chamber during a shutdown work cycle is described. Depending on the opening and closing sequence of the inlet and outlet valves, the enclosed gases have different masses and constituents, which effectively form gas springs during the switched off working cycle (s). A shutdown cycle may include a low pressure exhaust spring (LPES), a high pressure exhaust spring (HPES), or an air spring (AS). The type of gas spring can be selected to optimize fuel efficiency and provide an acceptable NVH level.

In another aspect, engine control establishes a fire / skip sequence that is appropriate for providing desired engine power. The fire / skip sequence includes information about the type of gas spring that is present in off-duty cycles and the timing that is available for valve deactivation.

In another aspect, a method of operating an engine in response to a "no torque" request is described. All of the engine's working chambers are shut down in response to the “no torque” request. During the deactivation period, each working chamber functions for at least one working cycle of the switched-off working cycles with an air spring or a gas spring of the high-pressure outlet spring type.

The various aspects and features described above can be implemented either individually or in any combination.

list of figures

• 1 ist ein schematisches Beispieldiagramm, das einen Teilbereich eines Motorsystems zeigt.
• 2 ist ein charakteristisches Schaubild der Beziehung von Druck und Volumen in einem Zylinder während eines Arbeitszyklus.
• 3 ist ein charakteristisches Schaubild der Beziehung von Druck und Volumen einer Gasfeder der Art Niederdruck-Auslassfeder in einem Zylinder.
• 4 ist ein charakteristisches Schaubild der Beziehung von Druck und Volumen einer Gasfeder der Art Hochdruck-Auslassfeder in einem Zylinder.
• 5 ist ein charakteristisches Schaubild der Beziehung von Druck und Volumen einer Gasfeder der Art Luftfeder in einem Zylinder.
• 6 ist ein charakteristisches Schaubild, das Drehmomentkurven von Luftfeder-, Hochdruck-Auslassfeder-, Niederdruck-Auslassfeder-Gasfedern zeigt, die einem einzelnen Zylinder zugeordnet sind.
• 7 ist ein charakteristisches Schaubild der Gesamt-Motordrehmomentkurve eines Skip-Fire-geregelten Achtzylindermotors, der mit einem Zündungsanteil von ½ mit einer Gasfeder der Art Niederdruck-Auslassfeder und Hochdruck-Auslassfeder betrieben wird.
• 8 ist ein schematisches Beispieldiagramm, das ein beispielhaftes Motorregelsystem zeigt.
• 9 ist ein Schaubild des Bremsmoments in Abhängigkeit des Einlasskrümmer-Absolutdrucks bei einer Gasfeder der Art Niederdruck-Auslassfeder und Luftfeder eines charakteristischen Motors.
• 10 ist ein Schaubild des Bremsmoments in Abhängigkeit der Luftmassenladung bei einer Gasfeder der Art Niederdruck-Auslassfeder und Luftfeder eines charakteristischen Motors.
• 11 ist ein Schaubild des bremsspezifischen Kraftstoffverbrauchs in Abhängigkeit des Bremsmitteldrucks bei einer Gasfeder der Art Niederdruck-Auslassfeder und Luftfeder eines charakteristischen Motors.
• In den Zeichnungen werden gelegentlich identische Bezugszeichen zur Bezeichnung identischer Strukturelemente verwendet. Es versteht sich zudem, dass die Darstellungen in den Figuren schematisch und nicht maßstabsgerecht sind.

The invention and its advantages are best understood by referring to the following description in conjunction with the accompanying figures, in which the figures apply:

• 1 FIG. 12 is a schematic example diagram showing a portion of an engine system.
• 2 is a characteristic graph of the relationship between pressure and volume in a cylinder during a work cycle.
• 3 Fig. 3 is a characteristic graph of the relationship between pressure and volume of a gas spring of the low pressure exhaust spring type in a cylinder.
• 4 Fig. 3 is a characteristic graph of the relationship between pressure and volume of a gas spring of a high pressure exhaust spring type in a cylinder.
• 5 is a characteristic graph of the relationship between pressure and volume of a gas spring of the air spring type in a cylinder.
• 6 Fig. 4 is a characteristic graph showing torque curves of air spring, high pressure exhaust spring, low pressure exhaust spring gas springs associated with a single cylinder.
• 7 is a characteristic graph of the overall engine torque curve of a skip-fire controlled eight-cylinder engine with an ignition percentage of ½ with a Gas spring of the type low pressure exhaust spring and high pressure exhaust spring is operated.
• 8th FIG. 12 is a schematic example diagram showing an example engine control system.
• 9 is a graph of the braking torque as a function of the intake manifold absolute pressure for a gas spring of the type low pressure exhaust spring and air spring of a characteristic engine.
• 10 is a graph of the braking torque as a function of the air mass charge for a gas spring of the type low pressure exhaust spring and air spring of a characteristic engine.
• 11 is a graph of the brake-specific fuel consumption as a function of the brake medium pressure for a gas spring of the type low pressure exhaust spring and air spring of a characteristic engine.
• In the drawings, identical reference symbols are sometimes used to designate identical structural elements. It also goes without saying that the representations in the figures are schematic and are not to scale.

DETAILED DESCRIPTION

The present invention relates to improving the operation of a skip fire regulated internal combustion engine that provides drive torque to power a vehicle. The present invention discloses that as the timing of intake and exhaust events changes, the gases trapped in a work chamber or cylinder during an off ignition opportunity may differ. The enclosed gases form different types of "gas springs" and the type of gas spring used can vary depending on the cylinder load, engine speed and skip fire pattern. In this case, “gas spring type” refers to the amount and type of gas contained in a deactivated cylinder. Different types of cylinder deactivation strategies can be used for skip fire operation. The deactivation strategies can generally be broken down into three types: low pressure exhaust spring (LPES), high pressure exhaust spring (HPES) and air spring (AS). Each category varies the order and timing of deactivation / reactivation of intake valves, exhaust valves, fuel injection, and ignition timing. Within each of these types of gas springs there are different subcategories, which are described below and differ in which valve starts or ends the exhaust sequence.

1 illustrates an exemplary internal combustion engine that includes a cylinder 161 , a piston 163 , an intake manifold 165 and an exhaust manifold 169 includes. Air is drawn in through an intake valve 185 in the cylinder 161 initiated. Combustion fumes are released through an exhaust valve 187 out of the cylinder 161 emptied. A throttle valve 171 regulates the inflow of air from an air filter or other air source into the intake manifold 165 , Expanding gases from the combustion increase the pressure in the cylinder and drive the piston downwards. A reciprocally linear movement of the piston is caused by a connecting rod 189 that with a crankshaft 183 is converted into a rotational movement. A four-stroke engine requires two crankshaft rotations, 720 degrees, to complete a cycle.

The present invention relates generally to methods and apparatuses for regulating the operation of intake and exhaust valves of an internal combustion engine during a skip fire operation. In various embodiments, the valves are controlled using an eccentric cam to open and close the valves. A collapsible valve lifter can be installed in the valve train to enable the valves to be deactivated during a switched off working cycle. This means that the valve remains closed as long as the collapsible valve lifter associated with the valve is in its collapsed state and opens and closes with the cam rotation when the valve lifter is in its rigid state. Collapsible valve lifters are a form of a general class of idle systems in which cam rotation does not result in valve movement. A valve deactivation can alternatively be regulated by means of a sliding cam, collapsible play compensation or collapsible roller cam followers and other methods. The valve timing control can be controlled with a camshaft adjuster, which controls the opening / closing times of the valve depending on the crank angle. In some embodiments, a cam is not required to move the valves. The valve movement can be achieved by electromagnetic, hydraulic or pneumatic means. All of these valve movement systems can be used with the present invention.

In one embodiment, the combustion and gas exchange processes of an internal combustion engine operating in a skip fire mode may be changed so that the net or total torque generation characteristics are modified. In particular, the gas spring type of deactivated cylinders can be modified in order to adapt the torque-time profile. Adequate timing of the gas spring induced torque based on the cylinder firing events can result in an overall engine torque waveform with desired properties. For example, frequencies that are most perceived by vehicle occupants as vibration or noise may have less content. The cylinder can also be operated with higher efficiency depending on the type of gas spring and the cylinder load.

2 shows the relationship between pressure and volume (PV) of a self-priming Four-stroke gasoline engine during an ignition cycle. It should be noted that the vertical axis (pressure) and horizontal axis (specific volume) in this figure and the PV diagrams of the 3-5 are reproduced on a logarithmic scale. Regular engine operation involves a repeating cycle of intake, compression, expansion, and exhaust that occurs over four strokes of a piston movement or two rotations of the crankshaft. Each stroke of piston movement from top dead center (TDC) to bottom dead center (BDC) or vice versa corresponds to one stroke or 180 degrees of crankshaft rotation. An air intake or intake stroke occurs during the first stroke of the piston movement from the TDC to the BDC, in 2 from point A to point B. A compression stroke takes place during the second stroke of the piston movement from the BDC to the TDC, in 2 from point B to point C. The combustion can be triggered by spark ignition and occurs around the TCD near the end of the second bar and the beginning of the third bar. An expansion stroke occurs during the third stroke from TDC to BDC, in 2 from point C to point D. An exhaust stroke takes place during the fourth stroke from BDC to TDC, in 2 from point D back to point A. The PV curve forms two loops. Generally speaking, the area enclosed by the upper loop reflects the amount of work generated by combustion in an ignition cylinder, while the area enclosed by the lower loop reflects the energy losses caused by the Pumping of air into and out of the cylinder occurs (these losses are often referred to as pumping losses). In 2 atmospheric pressure is also shown with the designation P _atm . During most of the intake stroke, the cylinder pressure is below atmospheric pressure because the cylinder introduces air from an intake manifold, the pressure of which is kept below atmospheric pressure by regulating a throttle valve.

For better fuel efficiency, it is desirable to keep pumping losses as low as possible. This is achieved by opening the throttle valve, which shifts the section of the PV curve between points A and B closer to atmospheric pressure. Reducing pumping losses is a major reason that skip-fire operation provides better fuel efficiency, since engine performance is essentially controlled by the ignition density and not by throttling the airflow into the engine.

2 also shows characteristic opening and closing times for the intake and exhaust valve (s) of the cylinder. Point 1 corresponds to the opening time of the intake valve. Point 2 corresponds to the closing time of the intake valve. Point 3 corresponds to the opening time of the exhaust valve. Point 4 corresponds to the closing time of the exhaust valve. As shown, the intake valve opens shortly before the TDC and the exhaust valve opens shortly after the TDC, resulting in a short overlap of the intake / exhaust valve, which is typical of a modern engine. Point 2 , at which the intake valve closes, usually occurs shortly after the BDC in order to use the gas moment in the cylinder, to force more air into the cylinder and to increase the filling level. Point 3 where the exhaust valve opens usually occurs just before the BDC. It will be appreciated that strategies for variable cam timing and valve lift can delay opening / closing the intake / exhaust valve either just before or after TCD or BDC. The fuel injection can take place either directly in the cylinder (direct injection, DI) or indirectly in the cylinder by injecting fuel into the inflowing air charge outside the cylinder (intake manifold fuel injection, PFI) and occurs in PFI processes before the intake stroke (point A) and with DI processes during the intake and compression cycles (point A to point B). The spark ignition that triggers a combustion takes place around the end of the compression stroke as in 2 listed. Other control strategies are possible, for example recompression, in which air that was introduced at the beginning of a work cycle is held in the cylinder during the cycle and is burned or emptied in a subsequent cycle.

If a cylinder is switched off or deactivated instead of being ignited in a work cycle, the PV curve is different than in 2 shown. In particular in the case of engines which are able to deactivate intake and / or exhaust valves, different amounts and types of gases can be enclosed in a cylinder and form different types of gas springs during a switched off working cycle.

One type of gas spring is a low pressure outlet spring (LPES), whose PV properties are in 3 are shown. A low pressure exhaust spring gas spring is implemented by deactivating the intake valve directly on an intake stroke that follows an exhaust stroke after a combustion stroke. In this case, the intake valve remains closed, although it would normally open for another intake event, resulting in the cylinder never being open to the intake manifold vacuum. Instead of the PV curve dropping below atmospheric pressure, the PV curve stays at point A ' at or slightly above atmospheric pressure. Since the enclosed cylinder volume at the end of the exhaust stroke when the cylinder is sealed (point 4 ' ), is low, the use of a low pressure Exhaust spring at the end of the intake stroke, when the enclosed cylinder volume is maximized (point E), to very low pressures in the cylinder. The cylinder contains mostly residual gases from the previous cycle. The included remaining exhaust gases then go through a compression cycle and move back along the PV curve to the point A ' or in the vicinity. No fuel is injected during the compression stroke. Sparks may appear near the TDC, but need not; however, combustion would not occur because there is no combustible air or fuel in the cylinder. Due to the absence of fuel and fresh air charge, no energy would be released and the piston would begin an expansion stroke by moving away from point A ' or its proximity back to point e emotional. At the BDC, the exhaust valve would be deactivated, and the piston would go off during the exhaust stroke, which is from point e back to point A ' or moving near it, compact the mixture again. All valves would remain disabled and fuel injection would not occur for as long as desired.

In practice, the peak pressure of the low pressure exhaust spring would slowly increase until thermodynamic equilibrium was reached. Depending on the crankcase pressure and combustion chamber pressure, vapors from the crankcase can flow from the crankcase around the piston rings and into the cylinder and increase the mass and pressure of gas trapped in the cylinder volume. If the decision is made to reactivate this cylinder, one option is to reactivate the intake valve first, which causes the mixture of other exhaust gases and crankcase vapors in the cylinder to be enhanced by a fresh air charge. Fuel injection and spark, if necessary, are reactivated and combustion resumes. Finally, the exhaust valve is reactivated and the cylinder is again in the regular ignition mode.

A variant of the emptying process for cylinders by means of low-pressure outlet spring control is a low-pressure outlet spring with re-outlet. In this case, the exhaust valve is reactivated before the intake valve. This leads to two exhaust strokes without an intermediate intake stroke. In this reactivation strategy, the exhaust valve is reactivated first, followed by the intake valve, and then fuel and spark. There are mutliple reasons for this. First, by causing a re-exhaust event to occur first, gases that have spilled into the cylinder can be evacuated prior to induction, making the charge initiated more similar to that of a cylinder that is operated without deactivation. A regular ignition engine is dependent on valve overlap and gas flow torque in order to discharge as much excess exhaust gas as possible from the cylinder. This does not apply to a low-pressure outlet spring without re-outlet and leads to a lower degree of filling during the first reactivated cycle. Second, in the event that combustion, possibly faulty, occurred during a shutdown cycle, the re-exhaust would prevent the intake valve on a high pressure exhaust spring from opening and potentially causing valve train damage. A re-exhaust could be integrated into a safety function that requires the exhaust valve of any cylinder to open before the intake valve is allowed to open. If the outlet valve fails to open or is deactivated, the inlet valve would be deactivated automatically. A disadvantage of this method is that its pumping loop is larger and thus the energy efficiency is lower than the normal low pressure outlet springs when the number of cycles switched off is small. When the number of cycles switched off increases, the performance of the two methods essentially balances out, since most of the clocks have identical conditions.

A second type of gas spring is an HPES, a high pressure outlet spring whose PV properties are in 4 are shown. When a cylinder is deactivated using the high pressure exhaust spring method, the intake, compression and expansion strokes are regular and the exhaust stroke is skipped by the exhaust valve in front of the point D is deactivated, resulting in an exhaust valve opening 3 prevented and trapped exhaust gas under high pressure in the cylinder. The exhaust gas under high pressure would then be caused by the cylinder being out of point during the exhaust stroke D to point F moved, compressed again, so that the gases in the cylinder are compressed again to peak pressures that are slightly above that of the previous expansion stroke. The intake valve would be deactivated during the subsequent intake stroke to prevent possible damage to the valve train that could occur due to the valve opening at such high pressure. The piston would then expand the high pressure gas a second time while moving from point to what would be the intake stroke F to point G emotional. The fuel injection would be deactivated at this point, so that the compression and expansion strokes would only compress and expand the included high pressure exhaust gases. Compression and expansion of the gas under high pressure would continue as long as the cylinder is switched off, ideally between the same two pressures at TDC and BDC. In practice, heat and mass transfer from the cylinder would cause the cylinder pressure to drop rapidly, so everyone on it following pressure / volume curve would be somewhat lower. If the decision is made to reactivate the cylinder, the exhaust valve can be reactivated first, followed by the intake valve and finally the fuel injection. This would allow the high pressure gas to be exhausted regularly, and would allow a fresh load to enter the cylinder and allow regular combustion the next time it is fired.

A variation of the high pressure exhaust spring control method is the high pressure exhaust spring with renewed fuel supply. The main difference is that once the decision is made to reactivate a deactivating cylinder, the fuel is reactivated first, followed by the exhaust and intake. This requires direct injection and assumes that sufficient combustible charge has either run out of the crankcase into the cylinder or has remained in the residues that still need to be left out after the last combustion event. This variant is particularly applicable to a lean mix engine, in which considerable amounts of excess oxygen can remain in the enclosed residues.

Another variation of the high pressure exhaust spring control method is the high pressure exhaust spring with re-inlet. With this strategy, when a deactivating cylinder is reactivated, the intake valve is reactivated first, followed by fuel and exhaust. This is similar to the reactivation process of the low pressure exhaust spring without re-emptying. As stated above, this strategy has the potential to cause significant damage to the valve train since the intake valve is opened at a cylinder pressure that is at a level near the combustion peak pressure. This can be prevented by an appropriate design of the intake valve and its associated valve train. By opening the inlet valve on a high-pressure outlet spring, the high-pressure exhaust gas residues in the cylinder are blown down into the intake manifold, which leads to considerable heating of the incoming charge. The fill level may be low on the first reactivated cycle. The intake valves, intake pipes and manifold should be designed to deal with pressure and temperature levels that are higher than normal. This method has very high expansion / compression losses during deactivation, which lead to a high negative mean spring working pressure and accordingly a low fuel efficiency if the number of cycles switched off is small. This mode of operation can be particularly useful for engines where some duty cycles use homogeneous compression ignition (HCCI) or similar types of combustion strategies.

A third type of gas spring is an air spring (AS), whose PV properties are in 5 are shown. In the air suspension method of cylinder deactivation, the first stroke that is modified when a deactivation is decided is the expansion stroke. With a direct injection engine, an intake would occur regularly, but no fuel would be injected. The piston would compress the charge, which is mainly made up of air, without combustion and out of point B to point H move. From point H the air would point up 1 expand. At point 1 the exhaust valve would be deactivated and the piston would compress the air a second time. At the TDC, the intake valve would be deactivated and the piston would expand the air a second time. This compression and expansion of predominantly air would last as long as the cylinder is to be switched off. Ideally, the cylinder would work like an air spring. In practice, heat and mass transfer from the cylinder to the environment cause the cylinder mass and pressure to decrease over time, so that each subsequent pressure / volume curve would be somewhat lower until the average pressure during a cycle is approximately atmospheric. If the decision is made to ignite the cylinder, fuel injection and ignition sparks are first restored in a direct injection engine. This would likely result in a lower torque charge, lower torque combustion, and less charge movement, which would typically aid fuel evaporation and mixing, due to a lower air charge resulting from gas leakage. The operation of the exhaust valves would next be restored and the cylinder would resume normal operation.

A variant of an air spring is a fuel / air spring. For a PFI engine, intake and fuel injection would occur regularly, but the spark would be deactivated if a shutdown decision was made. In this scenario, the air spring would be more of a fuel / air spring, since the gas introduced in a PFI engine is an air / fuel mixture. In the absence of auto-ignition, the mass and pressure of the fuel-air mixture in the cylinder would in turn decrease over time, since mass and heat losses to the crankcase and the cylinder wall would still occur. Exhaust and intake valves are deactivated in the same way as for the direct injection engine. If the decision is made to restart the ignition, the ignition spark would be restored. In this case too, the occurrence of a weak one would be Combustion event likely and the exhaust and then the intake valves would be reactivated.

In a further variant of an air spring, air spring with re-inlet, both direct injection engines and PFI engines would first stop fuel injection if the decision to switch off was made. Admission would still be regular, but no combustion would occur in the absence of fuel and possibly ignition sparks. The outlet would be deactivated, and eventually the inlet would be deactivated, and the engine would operate in an air spring mode until the decision to reactivate is made. Once this happens, the first step is to reactivate the fuel injection intake valve. This would fill the cylinder again with a fresh charge. The spark would be activated if necessary and regular combustion would occur. Eventually, the exhaust valve would be reactivated. This strategy has the advantage that the lower combustion air charge associated with a regular air spring is avoided. The disadvantage is that the pumping loop can be very large if the number of cycles switched off is small.

An air spring with a re-outlet method differs from other air spring methods in that when the decision is made to end the shutdown and restart the ignition, the exhaust valve is reactivated first, followed by the inlet and fuel injection. Like re-inlet air springs, this avoids the lower air charge and the resulting weak combustion event that would occur on the first reactivated cycle. Unlike re-inlet air springs, re-outlet air springs can avoid the large pumping loop if the number of cycles disabled is small. However, this process pumps unburned air into the outlet. When only one cycle is turned off, this method essentially never deactivates the valves and a significant amount of air is pumped through the cylinder, which can affect the exhaust emissions control systems.

The torque-time profile or the corresponding curves of the different types of gas springs differ considerably. 6 shows characteristic torque curves of air spring, high pressure exhaust spring and low pressure exhaust spring gas springs associated with a single cylinder. For comparison, the torque curve is also shown, that of an ignition cylinder 610 assigned. The magnitude of the torque resulting from the high pressure gas spring 620 is very high, comparable to or higher than the order of magnitude of an ignition cylinder, in both a positive and a negative direction. The torque curve of the low pressure spring 630 has a very small order of magnitude due to the very small amount of gas trapped in the cylinder. For most of a duty cycle, the entrapped gas has a pressure below atmospheric pressure, as in the discussion of FIG 3 is executed. The magnitude of the torque that an air spring 640 is between the high pressure exhaust spring and low pressure exhaust spring cases, but generally closer to the low pressure exhaust spring case since no hot combustion gases are trapped in the cylinder.

The air charge associated with an intake stroke after an ignition opportunity is turned off varies with the type of gas spring that preceded the intake event. The amount of residual charge during a subsequent cycle is, among other parameters, a function of whether the intake and exhaust valves are open at the same time and the respective timing. In addition, the relative temperature of the residual charge varies based on several factors including the length of time that the residual charge is present in the combustion chamber and leakage in and out of the cylinder. Furthermore, pressure fluctuations in the intake and exhaust exhaust manifolds differ based on when and whether intake and exhaust valves open and close in both a given and other engine cylinders. From these and other effects, combustion parameters such as the amount of fuel injected and the ignition point adjustment can be adjusted in order to compensate for the adjustment to the introduced air charge. The amount of fuel injected can be controlled to provide a stoichiometric or near stoichiometric air-fuel ratio required for the efficient operation of certain pollution control devices such as a three-way catalyst. The ignition point setting can be adjusted in order to obtain the greatest possible braking torque from the air-fuel charge, so that the fuel efficiency is optimized.

Combining the torque curves of each cylinder, which are correctly matched to each other in accordance with the cylinder firing order, leads to a combined torque curve. Depending on the number of cylinders in the engine, all firing opportunities are separated by a nominal amount of crank rotation. For example, in a 6-cylinder engine, successive firing opportunities occur nominally every 120 ° in an engine with an identical distance between firing events. With an 8-cylinder engine with identical distances between Firing opportunities occur consecutive firing events nominally every 90 °. In a 4-cylinder engine with identical intervals between ignition opportunities, successive ignition events occur nominally every 180 °. These crank angles are only setpoints, since the spark control timing can be adjusted individually or in combination to change the profile of the resulting torque curve and to optimize fuel efficiency.

7 shows a characteristic torque curve that results from an 8-cylinder four-stroke engine, which is operated with an alternating skip-fire-skip-fire ... pattern. A course 720 shows a high pressure exhaust spring torque curve of the deactivated cylinders, and the other course 730 shows a low pressure exhaust spring torque curve of the deactivated cylinders. As can be seen, the torque curves differ significantly, with the low-pressure exhaust spring mode having a significantly smaller deviation over an average engine torque. Since NVH is generally related to the smooth provision of engine torque 7 suggests that in this firing pattern, operation in a low pressure exhaust spring mode is preferable to high pressure exhaust spring operation; other factors such as fuel economy are identical. In general, the gas spring type can be selected together with the operational ignition component or the operational ignition sequence in order to smooth out deviations of the torque-time profile below an acceptable level. In addition, the type of gas spring can be selected to reduce the spectral content of the torque curve in a given frequency range. This predetermined frequency range can correspond to a range of specific occupant sensitivity, for example 0.5 to 12 Hz. It can also be selected to avoid excitation of resonances in the vehicle or in vehicle components.

Next referring to 8th becomes a skip fire engine control 130 described according to an embodiment of the present invention. The engine control 130 closes a fire / skip sequence generator 106 , a fire / skip control unit 110 , a powertrain parameter adjustment module 108 and an engine diagnostic module 150 on. The engine control 130 is designed to operate the engine in a skip-fire manner. The engine diagnostic module 150 is designed to detect engine problems (e.g. knock, misfire, etc.) in the engine. All known technologies, sensors or detection processes can be used to detect the problems. In various embodiments, the engine diagnostic module guides 150 if a problem is detected, the fire / skip sequence generator 106 to perform operational steps to reduce the likelihood that the problem will occur in the future. Such procedures may include adjusting the gas spring category on one or more cylinders and / or changing the powertrain parameters.

The engine control 130 receives an input signal 114 that the desired engine power and various operating parameters of the vehicle such as an engine speed 132 and gear position 134 reproduces. The input signal 114 can be treated as a request for a desired engine power or torque. The signal 114 can be received or derived from an accelerator pedal position sensor (APP) or other suitable sources such as a vehicle speed control, a torque calculation unit, etc. An optional preprocessor can send the accelerator pedal signal before forwarding it to the engine control 130 modify. However, it can be assumed that in other implementations the accelerator position sensor works directly with the engine control 130 can communicate.

The fire / skip sequence generator 106 receives the input signal 114 , Engine speed 132 and the gear position signal 134 as well as further inputs, if applicable, and is designed to define a fire / skip sequence and a gas spring type when the ignition opportunities are switched off, which would be suitable for delivering the desired power. In various embodiments, the fire / skip sequence consists of any data indicating whether an opportunity to fire is an ignition or a shutdown and the type of gas spring associated with the shutdown. For engines with dynamic multi-height skip fire control as in the US U.S. Patent 9,399,964 which is fully incorporated herein for all purposes, information regarding whether an ignition is a low or high output ignition may also be determined by the fire / skip sequence generator.

Information regarding the fire / skip sequence (or more generally regarding the air charge sequence when an ignition may have a low or high output) is provided via the signal line 116 to the Fire / Skip control unit 110 directed. The Fire / Skip control unit 110 coordinates the opening and closing of the intake and / or exhaust valves in order to implement the fire / skip sequence and the type of gas spring assigned to the respective switched off ignition opportunity. In the case of cam-operated valves with collapsible idle lifters, the fire / skip control unit actuates magnetic control valves that are located in the engine 112 are located. These solenoid valves regulate the oil pressure in the collapsible valve lifter to determine whether the valve lifter is in its rigid or collapsible state. In 8th is the engine 112 depicted as having eight cylinders, but the engine can have any number of cylinders, for example 2, 3, 4, 5, 6, 8, 10 or 12.

In addition to the Fire / Skip control unit 110 the engine receives 112 also control signals 119 from the powertrain parameter adjustment module 108 , The control signals 119 May include, among other things, ignition point adjustment, injected fuel amount, throttle position, camshaft phaser position (s), cam valve lift, torque converter slip, exhaust gas recirculation valve settings, etc. The powertrain parameter adjustment module provides appropriate adjustment of these various powertrain parameters to ensure stable ignition cylinder combustion. Combustion conditions, such as spark timing, can be optimized to provide maximum fuel efficiency.

In addition to influencing the NVH level, the type of gas spring can also affect engine torque and engine fuel efficiency. 9 compares the engine brake torque with the intake manifold absolute pressure (MAP) of an engine that is operated at 1600 rpm and an operating ignition ratio of the gas springs of 1/3 for air springs (without re-intake) and low-pressure exhaust springs (without re-exhaust) , In both cases, the engine is operated with a stoichiometric air-fuel ratio. The low pressure exhaust spring torque output 910 is significantly higher than the air spring torque output at a given MAP level 920 , This is due, at least in part, to a lower air charge in the cylinder due to gas leakage from the cylinder when acting as an air spring and the absence of re-intake in the air spring case, whereas the low pressure exhaust spring case has an intake stroke just prior to re-ignition.

While the engine output torque for air springs is generally lower compared to the low pressure exhaust spring type gas springs in the re-intake and re-exhaust strategy outlined above, fuel efficiency performance is more complex. 10 compares the engine brake torque with the air mass charge for gas springs of the air spring type and the low pressure exhaust spring type under the same engine operating conditions as in 9 , The low pressure outlet spring curve 1010 shows an almost linear dependence while the air spring curve 1020 this crosses at higher values of the air mass per cylinder. Since the fuel consumption is proportional to the air mass per cylinder, sets 10 indicates that fuel efficiency is greater at low load using an air spring and at high load using a low pressure exhaust spring. One reason that the air spring offers greater utilization at low load is because the air spring maintains conventional valve overlap while the low pressure exhaust spring does not. If the air mass per cylinder increases, a larger proportion of the load is either lost or diluted when operating with a gas spring of the air spring type, which reduces the fuel efficiency. The cylinder load threshold to change the type of gas spring to maximize fuel efficiency may vary engine speed and spark ratio or spark pattern.

The improvement in fuel efficiency by operating with an air spring in certain low load conditions is in 11 clearly shown. 11 represents the brake specific fuel consumption (BSFC) depending on the brake fluid pressure (BMEP). A consideration of 11 shows that air spring operation (curve 1120 ) at loads below about 1.5 bar BMEP for better fuel efficiency than low-pressure exhaust spring operation (curve 1110 ) leads. The crossing of the curves 1110 and 1120 near 0.6 BMEP is a product of interpolation and should not be interpreted to mean that low pressure exhaust springs are more efficient than air springs under these very low load conditions. Thus, under these loads and at the assumed engine speed, spark ratio, and re-intake / re-exhaust strategy, it is advantageous to operate with an air spring and to operate with a low pressure exhaust spring at other loads to improve fuel economy.

In addition to NVH and fuel efficiency, the selection of the gas spring can also affect oil consumption and emissions. If the cylinder pressure is below atmospheric pressure, oil that lubricates the cylinder walls tends to be drawn into the cylinder. This oil is then present at the next combustion event, where it may evaporate and burn incompletely. The vaporized oil and its combustion components then flow into the exhaust manifold during the exhaust stroke. If left untreated, the oil and combustion components in the exhaust gas stream can lead to undesirable emissions into the environment.

Because of the possible oil entry into the cylinder, it may be desirable to avoid prolonged use of a low pressure exhaust spring type gas spring as this type of spring works at the lowest internal cylinder pressure. A special situation in which cylinders can be deactivated over extended periods of time is during overrun cylinder deactivation (DCCO). This operating mode can be used in driving conditions in which no engine torque is required, for example when rolling freely, driving downhill or stopping a vehicle. A thrust cylinder shutdown event can span many seconds, resulting in many consecutive shutdown firing opportunities. During the overrun cylinder deactivation, all cylinders of the engine are deactivated, so that all ignition opportunities are deactivated and the cylinders are not supplied with fuel. This means that little or no air is pumped through the engine. A thrust cylinder shutdown operation improves fuel economy and reduces the requirements for balancing a catalyst that can be part of an exhaust gas purification system. The benefits and use of thrust cylinder shutdown operation are in the US American Patent 9,790,867 , which is incorporated herein by reference in its entirety for all purposes.

If engine torque is not requested, it may be desirable to avoid using a low pressure exhaust spring only and instead use at least some air spring or high pressure exhaust spring for the duration of the "no torque" request. For example, in order to reduce the use of a spring of the low pressure exhaust spring type in the case of thrust cylinder deactivation, a spring of the air spring or high pressure exhaust spring type can be used during at least one working cycle of the series of switched off working cycles. In one embodiment, a thrust cylinder shutdown event may begin using a low pressure exhaust spring in each cylinder and then switch to using an air spring after a period of time or number of working cycles that have been shut off. In another embodiment, a push cylinder shutdown event may initially use a high pressure exhaust spring on at least some cylinders and then switch to an air spring at a time in the push cylinder shutdown event. It is believed that generally the length of a thrust cylinder shutdown event is not known when the thrust cylinder shutdown event is initiated, so that some thrust cylinder shutdown events, such as longer events, may use different types of gas springs, while other thrust cylinder shutdown events such as Shorter thrust cylinder shutdown events may use only one form of gas spring.

The transition from one type of gas spring to another type of gas spring within the series of deactivated ignition opportunities generally involves opening an intake or exhaust valve at the appropriate time during a work cycle. A high pressure exhaust spring will always require a combustion event to produce high pressure exhaust gases. As long as the intake or exhaust valve remains closed after combustion, a high-pressure exhaust spring remains in the cylinder (regardless of the loss of mass and heat, which naturally occurs). A transition from a high pressure exhaust spring to an air spring can occur after a desired number of high pressure exhaust spring work cycles by first opening the exhaust valve during a stroke and then opening the intake valve during a stroke. A rejection process takes place and an air spring with fresh air charge is present in the cylinder. To prevent combustion, fuel injection and / or ignition sparks must be deactivated. A transition from a high pressure exhaust spring to a low pressure exhaust spring after a desired number of high pressure exhaust spring work cycles can be accomplished by opening the exhaust valve during one stroke. Most of the exhaust gas residues are emptied out of the cylinder, but no new charge is introduced since the intake valve remains closed. The cylinder can be operated as long as desired with a low pressure exhaust spring type gas spring. At least one combustion event is required to return from a gas spring of the air spring or low pressure exhaust spring type to a high pressure exhaust spring.

Transitions between gas springs of the air spring type and low-pressure outlet spring can take place as often as desired, but these changes involve a certain amount of pumping. For the transition from a low pressure exhaust spring to an air spring, the intake valve is deactivated during a stroke at or near top dead center in order to initiate a fresh air charge. Air spring operation can be maintained as long as desired by deactivating fuel injection and / or ignition sparks. To transition from an air spring to a low pressure exhaust spring, the exhaust valve is reactivated during a stroke at or near bottom dead center of an expansion stroke. This empties cylinder gases, which are mainly air in an air spring, into the exhaust system. The intake valve remains closed and the cylinder is now operated with a low pressure exhaust spring for as long as desired.

In certain driving situations, it may be desirable to use a gas spring of the high pressure exhaust spring type for deactivated cylinders. For example, is an operation with a To expect a set set of activated and deactivated cylinders during an extended period of time, a high pressure exhaust spring can be used on the deactivated cylinders. A substantially constant torque request can be expected over a long period; for example while driving at the same speed on a flat, open road with an ignition component, the denominator of which is a factor of the number of engine cylinders; For example, ½ for 4-, 6- or 8-cylinder engines, 1/3, ½, 2/3 for 6-cylinder engines etc. Since the high-pressure outlet spring is to be expected over an extended number of working cycles, there are pumping losses that result from draining the high pressure outlet spring, be small. The use of a high pressure exhaust spring type gas spring reduces the possibility of oil entering the deactivated cylinders and possible exhaust emission problems.

Dynamic control of the gas spring type in vehicles with autonomous vehicle control as in the US American patent applications 15 / 642,132 and 15 / 849.401 which are incorporated herein in their entirety for all purposes. Autonomous vehicle control generally provides more extensive and in-depth information about future engine torque requirements so that the length of successive rows of shutdown cycles can be known or estimated when the row of shutdown cycles is triggered. This allows you to define an optimal gas spring type or gas spring change strategy at the beginning of the series of deactivated working cycles. In addition, in cases without vehicle occupants, the autonomous vehicle control loosens NVH restrictions, which enables the use of different gas spring strategies.

In practice, the engine control 130 , in the 8th is shown, or an engine control with similar functionality dynamically select the type of gas spring used on any deactivated cylinder. This stipulation can be made from shutdown opportunity to shutdown opportunity to optimize fuel efficiency and keep NVH below an acceptable level. Exhaust emissions and oil consumption can also be taken into account when determining the type of spring. The type of spring associated with any shutdown can be algorithmically determined or can be based on one or more look-up tables that list the type of spring to be used under certain operating conditions. It can be assumed that not all cylinders have to have the same type of spring in any given cycle. This means that a deactivated cylinder can be operated with an air spring, while another deactivated cylinder can be operated with a low pressure outlet spring. In addition, if a cylinder is deactivated during successive firing occasions, the nature of the deactivation can be changed, for example, from a high pressure exhaust spring to a low pressure exhaust spring by emptying the cylinder at a certain time during the deactivation sequence.

This type of control is possible using cam operated valves with "idle" deactivation. The valve control can be designed such that a single electromagnet activates / deactivates both the inlet and the outlet valve or that the inlet valve and the outlet valve have activation / deactivation electromagnets that are independent of one another. As in the pending U.S. American patent application 14 / 812,370 Described in more detail, there is a latency between the time a fire / skip decision is made and its implementation. This latency can range from 4 to 12 firing opportunities for cam operated valves. This latency enables the ignition control unit 110 sufficient time to activate / deactivate intake and / or exhaust valves. The latency also allows the powertrain parameter adjustment module sufficient time to adjust powertrain parameters such as throttle, spark point adjustment, fuel quantity injected, converter clutch slip, etc. to provide the requested engine power with optimal fuel efficiency and acceptable NVH levels.

Many control strategies can be used to establish an appropriate skip fire and gas spring pattern that will provide the required engine power while minimizing fuel consumption and providing an acceptable NVH level. For example, a short-term optimal control, also known as model-based predictive control (MPC) or decreasing horizon control (receding horizon control RHC) can be used. This can refer to the optimization of the spring type during the series of ignition decisions that have been made but have not yet been implemented. These can range from 4 to 12 ignition opportunities, but can also include more or less. Because these decisions are known before they are implemented, torque output, fuel consumption, and NVH levels associated with fire / skip sequences and the corresponding sequences of gas spring types can be calculated. The fire / skip sequence generator can compare the properties associated with each sequence and based on Select the best sequence for optimization criteria. Furthermore, predictions regarding torque requests and corresponding ignition decisions beyond this horizon can be integrated into the optimization problem to be solved.

Model-based predictive control is a variant of optimal control that repeatedly solves a simplified mathematical optimization problem while the system is operating, using the most up-to-date sensor information from the system each time to counteract the fact that the optimization problem is often severe is simplified and can only approximate the mathematical formulation for finding the "best" fire / skip sequence and / or shutdown spring type. This combined optimization formulation enables the requested engine power to be generated while maximizing fuel economy and maintaining an acceptable NVH level.

In general, optimization is an estimation process that does not guarantee that it will converge to a fixed number of iterations. To support this situation in real-time implementation, a short-term optimization algorithm that implements a short-term optimization control can be greatly simplified. Since the optimization is resolved repeatedly over time, errors in the solutions obtained for the simplified optimization problems related to the original, more complex optimization problems will use current measurements of engine parameters if the simplifications have been selected accordingly. The use of current parameters can be seen as a kind of feedback control in order to correct the solution in the direction of the original optimization criteria. An alternative method for reducing the computational effort in real-time optimization is to carry out calculations in advance and to arrange parts of the optimization problem in a table. The net result is a computation of computational effort by memory effort, which can be advantageous with certain electronic control units.

It is also believed that all of the operations described herein can be stored in a suitable computer readable medium in the form of executable computer code. The operations are performed when a processor executes the computer code. The computer code can be integrated in an engine control system that coordinates the opening and closing of the intake and exhaust valves.

The invention is primarily described herein in the context of gasoline powered four stroke piston engines suitable for use in motor vehicles. However, it can be assumed that the methods and devices described are also suitable for use in many different internal combustion engines. These include engines for almost any type of vehicle, including automobiles, trucks, boats, aircraft, motorcycles, scooters, etc., and almost any other application involving working chamber ignition and employing an internal combustion engine. The various approaches described work for engines that operate with a wide variety of different thermodynamic cycles, including almost any type of diesel engine, gasoline engine, double cycle engine, Miller cycle engine, Atkinson cycle engine, Wankel engine, and other types of rotary engines, mix cycle engines (such as dual Otto) and diesel engines), hybrid engines, radial engines etc. It is further assumed that the approaches described will work well with newly developed internal combustion engines regardless of whether they are operated using currently known or later developed thermodynamic cycles.

While only a few embodiments of the invention have been described in detail, it should be understood that the invention can be implemented in many other forms without departing from the spirit or scope of the invention. For example, the control strategies described herein can be implemented with a fully flexible valve train that is not dependent on a camshaft in valve event timing. Some of the strategies described herein can also be used in the absence of injection and ignition control, such as homogeneous compression ignition (HCCI) or similar compression or ignition-assisted combustion engines that use premixed or unmixed air / fuel charges. The fire / skip sequence may also contain information in some cases as to whether firing results in either high or low output. Thus, the sequence can be a sequence of high power ignitions, low power ignitions and shutdowns. While the invention is generally described as using an intake and exhaust valve to control intake and exhaust from a cylinder, a cylinder may have multiple intake and / or exhaust valves, and the control strategies may control their movement together. Thus, the present embodiments are to be considered exemplary and not restrictive, and the invention is not to be limited to the details provided here.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 9399964 [0038]
• US 9790867 [0045]
• US 15/642132 [0050]
• US 15849401 [0050]
• US 14/812370 [0052]

Claims (40)

A method of controlling an internal combustion engine having a plurality of cylinders during a skip fire operation of the engine, the method comprising: Determine that a selected cylinder is deactivated on a first ignition opportunity with an associated first duty cycle; Selecting a first type of gas spring associated with the first ignition opportunity turned off; Controlling valves associated with the selected cylinder to cause the selected cylinder to operate in accordance with the selected first gas spring type during the first duty cycle; Determining that the selected cylinder is deactivated on a second firing opportunity with an associated second duty cycle, the second firing opportunity being different from the first firing opportunity; and Selecting a second type of gas spring which is assigned to the second switched-off ignition opportunity, the second type of gas spring differing from the first type of gas spring. Procedure according to Claim 1 , wherein the selection of the gas spring type, which is assigned to each switched-off working cycle, is made individually from switch-off opportunity to switch-off opportunity. Procedure according to Claim 1 or 2 , wherein the selection of the first type of gas spring is based at least in part on a current cylinder load. Procedure according to Claim 3 , wherein the selection of the second gas spring type is based at least in part on at least one of the following: a period of time that has occurred since the operationally occurring occurrence of the first deactivated ignition opportunity; a number of off-duty cycles in the selected cylinder that have occurred since the first off-ignition opportunity; or an engine speed. A method according to any of the preceding claims, wherein the first and second selected gas spring types are each selected from the group consisting of a low pressure outlet spring, a high pressure outlet spring and an air spring. A method according to any one of the preceding claims, wherein the selection of gas spring type is based at least in part on optimizing fuel economy while delivering the requested engine power and providing an acceptable NVH level. A method according to any one of the preceding claims, wherein cams are used to actuate the valves associated with the selected cylinder. Procedure according to Claim 7 wherein the valves include intake and / or exhaust valves and the intake and / or exhaust valves remain in a closed position when an idle valve spring lifter is in its collapsed condition. Method according to any one of the preceding claims, wherein the determination of the gas spring type is based on a short-term optimization algorithm. Procedure according to Claim 9 , where the short-term optimization algorithm includes the fuel efficiency and NVH optimization criteria that are assigned to the fire / skip sequence. A method of controlling skip fire operation of an internal combustion engine having a plurality of cylinders, each cylinder being configured to operate in a sequence of duty cycles, each duty cycle having an associated ignition opportunity, the method comprising: For each ignition opportunity, determine whether the assigned work cycle should be switched off or ignited; individually select a gas spring type from a plurality of possible gas spring types for each switched off work cycle that can be used in connection with such a work cycle so that the gas spring type for each switched off work cycle is determined from switch-off opportunity to switch-off opportunity, different gas spring types sometimes being used for different switch-off opportunities during the skip -Fire operation of the internal combustion engine can be used. Procedure according to Claim 11 , the possible gas spring types including at least two selected from the group consisting of a low pressure outlet spring, a high pressure outlet spring and an air spring. Procedure according to Claim 11 or 12 , wherein the selected gas spring type is based at least in part on a current cylinder load. Method according to any of the Claims 11 - 13 , with the selected gas spring type based at least in part on a current engine speed. Method according to any of the Claims 11 - 14 , wherein the selected gas spring type is based at least in part on a current operational ignition component. Method according to any of the Claims 11 - 15 wherein air springs are used when the selected cylinder is operating at a cylinder load that is below a predetermined threshold, and low pressure exhaust springs are used when the selected cylinder is operating at a cylinder load that is above the predetermined threshold. Procedure according to Claim 16 , the predetermined threshold varying as a function of at least one of the engine speed and the operational ignition component. A method of regulating the operation of an internal combustion engine having a plurality of cylinders, each cylinder being configured to operate in a sequence of duty cycles, each duty cycle having an associated ignition opportunity, the method comprising: Directing a selected cylinder not to be fueled and ignited during a plurality of duty cycles that continuously follow a fired duty cycle of the selected cylinder; Operating the selected cylinder as a first type of gas spring for a first plurality of the plurality of duty cycles that continuously follow the fired duty cycle of the selected cylinder; and Operating the selected cylinder as a second type of gas spring during at least one additional duty cycle of the plurality of duty cycles following the first plurality of the plurality of duty cycles, the second type of gas spring being different from the first type of gas spring. Procedure according to Claim 18 , wherein the first type of gas spring is a low pressure outlet spring and the second type of gas spring is an air spring. Procedure according to Claim 18 , wherein the first type of gas spring is a high pressure outlet spring and the second type of gas spring is an air spring. Procedure according to Claim 18 , wherein the first type of gas spring is a high pressure outlet spring and the second type of gas spring is a low pressure outlet spring. Method according to any of the Claims 18 - 21 wherein the method is performed when the engine enters a thrust cylinder shutdown (DCCO) operating mode. A method of controlling an internal combustion engine having a plurality of cylinders, each cylinder having associated valves and configured to operate in a sequence of duty cycles, each duty cycle having an associated ignition opportunity, the method comprising: Directing skip fire operation of the engine where some duty cycles are fired duty cycles that are fueled and ignited and other duty cycles are off duty cycles that are not firing; instructing valve actuation while the engine is operating in a skip-fire manner within a first operating range so that the off-duty cycles occurring during the skip-fire operating within the first operating range act as air springs; and while the engine is being operated in a skip-fire manner within a second operating range that is different from the first operating range, directing the valve actuation so that the switched off operating cycles that occur during operation within the second operating range function as a low-pressure outlet spring. Procedure according to Claim 23 , wherein the first operating range is based at least in part on a cylinder load. Procedure according to Claim 23 , wherein the first operating range is a range of a cylinder load map below an air spring threshold line. Method according to any of the Claims 23 - 25 , wherein the first operating range includes lower cylinder loads than the second operating range. A method of operating an engine having a crankshaft, an intake manifold, and a plurality of working chambers, the method comprising during operation of the engine: Disabling all of the work chambers in response to a "no engine torque" request so that all of the work chambers are shut down during subsequent work cycles and no air is pumped through the work chambers as the crankshaft rotates; and Operating each of the plurality of work chambers with a gas spring of the air spring or high pressure exhaust spring type during at least one work cycle of the switched off work cycles. Engine control that is designed to match the operation of an internal combustion engine with any of the preceding claims. Material computer readable storage medium on which programmed instructions are arranged to operate an internal combustion engine in accordance with any of the Claims 1 - 27 to guide. Engine control configured to operate an internal combustion engine having a plurality of cylinders in a skip-fire manner, comprising: a fire / skip sequence generator, the fire / skip sequence generator generating a sequence of skip / fire decisions and defining a type of gas spring for each skip decision that is associated with the shutdown. Engine control after Claim 30 , the type of gas spring being selected from a group consisting of a low pressure outlet spring, a high pressure outlet spring and an air spring. Motor control according to any of the Claims 30 - 31 , wherein the type of gas spring selected is based at least in part on optimizing fuel efficiency. Motor control according to any of the Claims 30 - 32 wherein the type of gas spring selected is based at least in part on reducing NVH to an acceptable level. Motor control according to any of the Claims 30 - 33 , with the type of gas spring being selected from disconnection opportunity to disconnection opportunity. Motor control according to any of the Claims 30 - 34 , the fire / skip sequence generator determining for each firing whether the firing has a high output or a low output. Motor control according to any of the Claims 30 - 35 , wherein the fire / skip sequence generator uses a short-term optimization algorithm to determine a fire / skip sequence and the type of gas spring associated with off-duty cycles in the fire / skip sequence. Engine control after Claim 36 , where the short-term optimization algorithm includes the fuel efficiency and NVH optimization criteria that are assigned to the fire / skip sequence. Engine control after Claim 30 wherein, in response to a no torque request from the internal combustion engine, the fire / skip sequence generator generates a series of successive shutdowns and at least some of these shutdowns use a high pressure exhaust spring or an air spring. A computer readable storage medium that includes executable computer code that is embodied in a physical form and is capable of operating an internal combustion engine in a skip-fire manner that is fuel efficient and has acceptable noise, vibration and roughness (NVH) characteristics, wherein the computer readable medium includes: Executable computer code to generate a fire / skip sequence to provide a desired torque, the fire / skip sequence including the type of gas spring associated with the ignited opportunity. Computer-readable storage medium Claim 39 , wherein the gas spring is selected from a group consisting of a low pressure exhaust spring, a high pressure exhaust spring and an air spring.

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