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A variety of methods and arrangements for controlling the exhaust gas temperature of a lean burn, skip fire controlled internal combustion engine are described. In one aspect, an engine controller includes an aftertreatment system monitor and a firing timing determination unit. The aftertreatment mo

A variety of methods and arrangements for controlling the exhaust gas temperature of a lean burn, skip fire controlled internal combustion engine are described. In one aspect, an engine controller includes an aftertreatment system monitor and a firing timing determination unit. The aftertreatment monitor obtains data relating to a temperature of one or more aftertreatment elements, such as a catalytic converter. Based at least partly on this data, the firing timing determination unit generates a firing sequence for operating the engine in a skip fire manner such that the temperature of the aftertreatment element is controlled within its effective operating range.

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1. An engine controller for operating a lean burn internal combustion engine including a plurality of working chambers with at least one working chamber having a deactivatable intake and/or exhaust valve, the engine controller comprising: a firing fraction selector arranged to select one of more tha

1. An engine controller for operating a lean burn internal combustion engine including a plurality of working chambers with at least one working chamber having a deactivatable intake and/or exhaust valve, the engine controller comprising: a firing fraction selector arranged to select one of more than two firing fractions for operating the engine in a skip fire manner, each of the more than two firing fractions defining different effective engine displacements that are each less than full displacement of the engine;an aftertreatment monitor arranged to obtain data relating to a temperature of an aftertreatment element in an engine exhaust system; anda firing timing determination unit that is arranged to determine a firing sequence for operating the at least one working chamber of the engine having a deactivatable intake and/or exhaust valve in the skip fire manner in accordance with the selected firing fraction, wherein the firing sequence is generated at least in part based on the aftertreatment element temperature data; andwherein the engine controller is configured to selectively direct one or both of the associated intake valve and/or exhaust valve(s) to be deactivated during each skipped working cycle such that air is not pumped through the working chamber into the engine exhaust system,wherein, for a given effective engine displacement corresponding to the selected firing fraction, the firing sequence for operating the at least one working chamber is determined on a firing opportunity by firing opportunity basis such that a selection of which working cycles to either fire or skip is individually made each firing opportunity in accordance with the selected firing fraction. 2. An engine controller as recited in claim 1 wherein the aftertreatment element temperature data is obtained from one selected from the group consisting of an aftertreatment element temperature model and a sensed aftertreatment element temperature. 3. An engine controller as recited in claim 1 wherein: the aftertreatment element temperature data is obtained from an aftertreatment element temperature model; andthe aftertreatment element temperature model is based on one or more selected from the group consisting of oxygen sensor data, NOx sensor data, exhaust gas temperature, ambient temperature, mass of airflow through the engine, injected fuel, timing of fuel injection, manifold pressure, camshaft position, residual trapped exhaust gas, recirculated exhaust gas, ambient humidity, barometric pressure, and engine coolant temperature. 4. An engine controller as recited in claim 1 wherein the aftertreatment element is a catalytic converter. 5. An engine controller as recited in claim 4 wherein the aftertreatment element is a catalytic converter that uses a selective catalytic reduction catalyst. 6. An engine controller as recited in claim 1 wherein the aftertreatment element is a lean NOx trap. 7. An engine controller as recited in claim 1 wherein the lean burn internal combustion engine is one selected from a group consisting of a stratified compression ignition engine, a homogeneous charge compression ignition engine, a partial homogeneous charge compression ignition engine and a lean burn spark ignition engine. 8. An engine controller as recited in claim 1 wherein the engine controller is configured to deactivate the working chamber farthest from the aftertreatment element during engine start-up. 9. An engine controller as recited in claim 1 wherein the internal combustion engine has no throttle to control air flow into the working chambers. 10. An engine controller as recited in claim 1, wherein, for the given engine displacement corresponding to the selected firing fraction, the determination of the firing sequence for operating the at least one working chamber on the firing opportunity by firing opportunity basis results in the at least one working chamber being fired, skipped or either skipped or fired over successive working cycles. 11. A method for controlling a temperature of an element in an aftertreatment system using skip fire engine control of a lean burn internal combustion engine having a plurality of working chambers, the method comprising: obtaining data relating to a temperature of an aftertreatment element in an exhaust system; anddetermining a firing sequence for operating the working chambers of the engine in a skip fire manner such that some working chamber working cycles are skipped and some working chamber working cycles are fired, wherein the firing sequence is generated at least in part based on the aftertreatment temperature data, andfor one or more of the skipped working chamber working cycles, initiating injection of fuel into the working chamber late in a power stroke of the working cycle, the late injection in the power stroke resulting in no internal combustion in the working chamber, causing unburnt hydrocarbons to be introduced into the exhaust system. 12. A method as recited in claim 11 wherein the temperature of the aftertreatment element is temporarily elevated to actively regenerate the aftertreatment element. 13. The method as recited in claim 12 wherein the aftertreatment element is a particulate filter. 14. The method as recited in claim 11 wherein the lean burn internal combustion engine is one selected from a group consisting of a stratified compression ignition engine, a homogeneous charge compression ignition engine, a partial homogeneous charge compression ignition engine, and a lean burn spark ignition engine. 15. The method as recited in claim 11 wherein during selected skipped working cycles, the corresponding working chambers are deactivated such that no air is pumped through the corresponding working chamber during skipped working cycles. 16. The method as recited in claim 11 wherein the decisions to skip or fire each working chamber working cycle are made individually every firing opportunity during skip fire operation of the engine. 17. A method as recited in claim 11 wherein the aftertreatment element is a catalytic converter. 18. A method as recited in claim 17 wherein the catalytic converter uses a selective catalytic reduction catalyst. 19. A method as recited in claim 11 wherein the aftertreatment element is a lean NOx trap. 20. A method of cold starting a lean burn internal combustion engine having a plurality of working chambers, each working chamber being arranged to operate in a series of successive working cycles, the method comprising: operating the lean burn internal combustion engine, during a cold start, in a first reduced effective displacement mode by deactivating at least one of the working chambers during selected working cycles such that no air is pumped through the corresponding working chamber(s) during the selected working cycles, wherein the lean burn internal combustion engine is operated in the reduced effective displacement mode at least until an aftertreatment element in an exhaust system associated with the lean burn internal combustion engine reaches a hydrocarbon light off temperature;determining whether the aftertreatment element has reached at least the hydrocarbon light off temperature; andafter it is determined that the aftertreatment element has reached at least the hydrocarbon light off temperature, switching operating of the engine from the first effective reduced displacement mode to an active warm-up skip fire operational mode at least until the aftertreatment element has reached at least a designated operating temperature, wherein during operation in the active warm-up skip fire operational mode, oxygen and unburnt hydrocarbons are caused to be passed into the exhaust system such that at least some of the unburnt hydrocarbons are oxidized by the aftertreatment element to speed warm-up of the aftertreatment element. 21. A method as recited in claim 20 wherein only a subset of the working chambers that are physically closer to the aftertreatment element in the exhaust system are fired during operation in the first reduced effective displacement mode. 22. A method as recited in claim 20 wherein during operation in the first reduced effective displacement mode, the working chambers are operated at a nominally stoichiometric air/fuel ratio. 23. A method as recited in claim 20 wherein skip fire engine operation is utilized in the first reduced effective displacement mode. 24. A method as recited in claim 20 wherein at least some of the unburnt hydrocarbons are introduced by utilizing a rich air/fuel ratio in at least some of the fired skip fire working cycles. 25. A method as recited in claim 20 wherein, during the active warm-up skip fire mode, at least some of the unburnt hydrocarbons is introduced via late fuel injection in at least some of the non combusted skip fire working cycles. 26. An apparatus, comprising: an exhaust sensor for monitoring an operating temperature of an exhaust system for an internal combustion engine of a vehicle;an engine controller for controlling the operation the internal combustion engine, the engine controller configured to receive:(a) a torque signal indicative of a requested torque demand for the internal combustion engine; and(b) a temperature signal, from the exhaust sensor, indicative of the operating temperature of the exhaust system of the vehicle;the engine controller further including a firing fraction calculator that is configured to define two or more firing fractions, each defining a different effective reduced displacement that is less than full displacement of the internal combustion engine,the engine controller further configured to control the firing of the cylinders of the engine in a skip fire manner while operating at a selected reduced effective displacement using a corresponding one of the two or more firing fractions, such that a decision to either fire or skip firing the cylinders is made on a firing opportunity-by-firing opportunity basis so that a given cylinder is fired, skipped and selectively either fired or skipped over successive firing opportunities respectively;wherein the skip fire control causes the internal combustion engine to dynamically: meet varying torque demands as indicated by changes in the torque signal; andadjust the operating temperature of the exhaust system to operate within a predefined temperature range in response to variations in the temperature signal. 27. The apparatus of claim 26, wherein the engine controller is further configured to prevent air from passing through one or more cylinders of the internal combustion engine during skip firing of the one or more cylinders respectively, the prevention of the air passing through the one or more cylinders into the exhaust system acting to increase the operating temperature of the exhaust system. 28. The apparatus of claim 26, wherein the engine controller is further configured to pump air into the exhaust system by opening intake valve(s) and exhaust valve(s), while preventing combustion, for the one or more cylinders respectively, the pumped air acting to decrease the operating temperature of the exhaust system. 29. The apparatus of claim 26, wherein the engine controller is further configured to inject and allow fuel to pass through one or more cylinders, substantially without combustion, so that the passed fuel is ignited in the exhaust system, the ignited fuel increasing the operating temperature of the exhaust system and burning off particulates in the exhaust system. 30. An apparatus as recited in claim 26, wherein the determination of the firing sequence for operating the at least one working chamber on the firing opportunity by firing opportunity basis results in the at least one working chamber being fired, skipped or either skipped or fired over successive working cycles. 31. An engine controller for operating a lean burn internal combustion engine including a plurality of working chambers with at least one working chamber having a deactivatable intake or exhaust valve, the engine controller comprising: a firing fraction selector arranged to select one of more than two firing fractions for operating the engine in a dynamic skip fire manner, each of the more than two firing fractions defining different effective engine displacements that are each less than full displacement of the engine;an aftertreatment monitor arranged to obtain data relating to a temperature of an aftertreatment element in an engine exhaust system; anda firing timing determination unit that is arranged to determine a firing sequence for operating the at least one working chamber of the internal combustion engine having a deactivatable intake or exhaust valve in the skip fire manner in accordance with the selected firing fraction, wherein the firing sequence is generated at least in part based on the aftertreatment element temperature data,wherein, for a given engine displacement corresponding to the selected firing fraction, the firing sequence for operating the internal combustion engine is determined on a firing opportunity by firing opportunity basis such that a selection of which working cycles to either fire or skip is individually made each firing opportunity in accordance with the selected firing fraction. 32. The engine controller as recited in claim 31, wherein the decisions to skip or fire each of the plurality of working chamber working cycles are made individually every firing opportunity during skip fire operation of the internal combustion engine in accordance with the selected firing fraction. 33. An engine controller as recited in claim 31, wherein the determination of the firing sequence for operating the at least one working chamber on the firing opportunity by firing opportunity basis results in the at least one working chamber being fired, skipped or either skipped or fired over successive working cycles.