Method and apparatus for determining optimum skip fire firing profile
First Claim
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1. A skip fire engine controller arranged to direct operation of an engine in a skip fire manner to deliver a desired engine output, the skip fire engine controller comprising:
- a skip fire profile determination unit arranged to determine an operational firing fraction for delivering the desired engine output,wherein the skip fire profile determination unit is arranged to select the operational firing fraction from among a plurality of candidate firing fractions that are each capable of delivering the desired engine output, each of the plurality of candidate firing fractions having a corresponding maximum allowable cylinder load, wherein each of the corresponding maximum allowable cylinder loads indicates a maximum allowable cylinder torque fraction when the engine is operating at the associated one of the plurality of candidate firing fractions under specified operating conditions,wherein the maximum allowable cylinder torque fraction for at least some of the plurality of candidate firing fractions at some specified operating conditions is less than one, each of the plurality of candidate firing fractions having an associated maximum allowable engine output that is attainable by operating the engine at such candidate firing fraction at the associated maximum allowable cylinder load,wherein at a selected engine speed, the maximum allowable engine output for a first one of the candidate firing fractions is higher than the maximum allowable engine output for a second one of the candidate firing fractions, the second one of the candidate firing fractions being higher than the first one of the candidate firing fraction, andwherein the operational firing fraction is selected at least partially based on the corresponding maximum allowable cylinder load not being exceeded when the engine is firing at the operational firing fraction and operating at the desired engine output; and
a firing control unit arranged to direct firings of cylinders of the engine in the skip fire manner in accordance with the operational firing fraction, the operational firing fraction resulting in the desired engine output of the engine without exceeding the maximum allowable cylinder load associated with the operational firing fraction.
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Abstract
In one aspect, a skip fire engine controller is described. The skip fire engine controller includes a skip fire module arranged to determine an operational firing fraction and associated cylinder load for delivering a desired engine output. The skip fire engine controller also includes a firing controller arranged to direct firings in a skip fire manner that delivers the selected operational firing fraction. Various methods, modules, lookup tables and arrangements related to the selection of a suitable operational firing fraction are also described.
109 Citations
25 Claims
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1. A skip fire engine controller arranged to direct operation of an engine in a skip fire manner to deliver a desired engine output, the skip fire engine controller comprising:
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a skip fire profile determination unit arranged to determine an operational firing fraction for delivering the desired engine output, wherein the skip fire profile determination unit is arranged to select the operational firing fraction from among a plurality of candidate firing fractions that are each capable of delivering the desired engine output, each of the plurality of candidate firing fractions having a corresponding maximum allowable cylinder load, wherein each of the corresponding maximum allowable cylinder loads indicates a maximum allowable cylinder torque fraction when the engine is operating at the associated one of the plurality of candidate firing fractions under specified operating conditions, wherein the maximum allowable cylinder torque fraction for at least some of the plurality of candidate firing fractions at some specified operating conditions is less than one, each of the plurality of candidate firing fractions having an associated maximum allowable engine output that is attainable by operating the engine at such candidate firing fraction at the associated maximum allowable cylinder load, wherein at a selected engine speed, the maximum allowable engine output for a first one of the candidate firing fractions is higher than the maximum allowable engine output for a second one of the candidate firing fractions, the second one of the candidate firing fractions being higher than the first one of the candidate firing fraction, and wherein the operational firing fraction is selected at least partially based on the corresponding maximum allowable cylinder load not being exceeded when the engine is firing at the operational firing fraction and operating at the desired engine output; and a firing control unit arranged to direct firings of cylinders of the engine in the skip fire manner in accordance with the operational firing fraction, the operational firing fraction resulting in the desired engine output of the engine without exceeding the maximum allowable cylinder load associated with the operational firing fraction. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A skip fire engine controller comprising:
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a lookup table embodied in a tangible computer readable media, the lookup table including a plurality of table entries that indicate maximum allowable cylinder load thresholds at different firing fractions respectively, wherein each maximum allowable cylinder load threshold indicates a maximum allowable cylinder torque fraction when an engine is operating at the associated firing fraction of the different firing fractions under specified operating conditions, and wherein the maximum allowable cylinder torque fraction for at least some of the firing fractions at some specified operating conditions is less than one; a skip fire profile determination unit arranged to determine an operational firing fraction suitable for delivering a requested engine output for the engine, wherein the skip fire profile determination unit utilizes the lookup table to select the operational firing fraction from among a plurality of candidate firing fractions, the operational firing fraction being selected at least partially based on a candidate cylinder load for the candidate firing fraction selected as the operational firing fraction not exceeding the maximum allowable cylinder load threshold associated with the selected candidate firing fraction when the engine is delivering the requested engine output and operating at the operational firing fraction, wherein the skip fire profile determination unit is arranged to determine the candidate cylinder load for at least the selected candidate firing fraction and to compare such candidate cylinder load to the maximum allowable cylinder load threshold associated with the selected candidate firing fraction in the determination of the operational firing fraction; and a firing control unit arranged to direct firings of cylinders of the engine in a skip fire manner in accordance with the operational firing fraction; and wherein the maximum allowable cylinder load thresholds in the lookup table are set such that at a selected engine speed, a maximum allowable engine output for a first one of the candidate firing fractions is higher than a maximum allowable engine output for a second one of the candidate firing fractions, the second one of the candidate firings fraction being higher than the first one of the candidate firing fractions. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A method of selecting an operational skip fire firing fraction suitable for use in operating an internal combustion engine in a skip fire manner to produce a desired engine output, the method comprising, during operation of the internal combustion engine:
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determining the desired engine output; calculating a candidate cylinder load for each of a plurality of candidate firing fractions that are each capable of delivering the desired engine output, wherein each candidate cylinder load represents a cylinder torque fraction at which an associated cylinder would need to operate at an associated candidate firing fraction of the plurality of candidate firing fractions in order to deliver the desired engine output; for each of the candidate firing fractions, determining whether the calculated candidate cylinder load exceeds a maximum allowable cylinder load associated with such candidate firing fraction under selected current engine operating conditions, wherein the maximum allowable cylinder load indicates a maximum allowed cylinder torque fraction when the internal combustion engine is operating at the associated candidate firing fraction under specified operating conditions, and wherein the maximum allowable cylinder load for at least some of the candidate firing fractions at some specified operating conditions is a cylinder torque fraction that is less than one; eliminating one or more of the candidate firing fractions for which the associated candidate cylinder load exceeds the maximum allowable cylinder load under the selected current engine operating conditions, and after the eliminating step, selecting one of the candidate firing fractions that has not been eliminated as the operational skip fire firing fraction; and operating the internal combustion engine in the skip fire manner using the selected operational skip fire firing fraction, wherein at least some of the time, the selected operational skip fire firing fraction has an associated maximum allowable cylinder load that corresponds to a cylinder torque fraction that is less than one when operated to deliver the desired engine output under the selected current engine operating conditions. - View Dependent Claims (17, 18, 19, 20)
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21. An engine controller configured to control an engine to operate in a skip fire manner, the engine controller configured to:
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maintain a table including a plurality of cylinder load thresholds indexed by a plurality of different operational firing fractions and engine speeds respectively; receive an input signal representative of a desired output of the engine; select an operational firing fraction from the table, among a plurality of candidate firing fractions, the selected operational firing fraction resulting in a cylinder load that does not exceed a cylinder load threshold of the plurality of cylinder load thresholds associated with the selected operational firing fraction for the engine operating at the selected operational firing fraction and the desired output of the engine; and cause the firing of cylinders of the engine in the skip fire manner in accordance with the selected operational firing fraction, the selected operational firing fraction resulting in an engine output substantially meeting the desired output of the engine while maintaining the cylinder load below the cylinder load threshold; and wherein the cylinder load thresholds in the table are set such that at a selected engine speed, a maximum allowable engine output for a first one of the plurality of candidate firing fractions is higher than a maximum allowable engine output for a second one of the plurality of candidate firing fractions, the second one of the candidate firing fractions being higher than the first one of the candidate firing fractions. - View Dependent Claims (22, 23, 24, 25)
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Specification