FIRING FRACTION MANAGEMENT IN SKIP FIRE ENGINE CONTROL

• US 20140041625A1
• Filed: 08/09/2013
• Published: 02/13/2014
• Est. Priority Date: 01/11/2010
• Status: Active Grant

• Current Assignee: Tula Technology, Incorporated
• Original Assignee: Tula Technology, Incorporated
• Inventors: PIRJABERI, Mohammad R., CARLSON, Steven E., SERRANO, Louis J., YUAN, Xin, CHIEN, Li-Chun
• Granted Patent: US 9,650,971 B2
• Time in Patent Office: Days
• US Class Current: 123/349
• CPC Class Codes: F02D 11/105 characterised by the function converting demand to actuation, e.g. a map indicating relations between an accelerator pedal position and throttle valve opening or target engine torque
• CPC Class Codes: F02D 17/02 Cutting-out cutting-out engines in multiple engine arrangements F02D25/04
• CPC Class Codes: F02D 2250/18 Control of the engine output torque
• CPC Class Codes: F02D 41/00 Electrical control of supply of combustible mixture or its constituents F02D43/00 takes precedence ; control of engine starters F02N11/08, electrical control of engine ignition timing F02P5/145
• CPC Class Codes: F02D 41/0087 Selective cylinder activation, i.e. partial cylinder operation deceleration cut-off F02D41/123
• CPC Class Codes: F02D 41/0225 in relation with the gear ratio or shift lever position
• CPC Class Codes: F02D 41/2422 Selective use of one or more tables

Abstract

The described embodiments relate generally to skip fire control of internal combustion engines and particularly to mechanisms for determining a desired operational firing fraction. In some embodiments, a firing fraction determining unit is arranged to determine a firing fraction suitable for delivering a requested engine output. The firing fraction determining unit may utilize data structures such as lookup tables in the determination of the desired firing fraction. In one aspect the desired engine output and one or more operational power train parameters such as current engine speed, are used as indices to a lookup table used to select a desired firing fraction. In other embodiments, additional indices to the data structure may include any one of: transmission gear; manifold absolute pressure (MAP); manifold air temperature; a parameter indicative of mass air charge (MAC); cam position; cylinder torque output; maximum permissible manifold pressure; vehicle speed; and barometric pressure.

Claims

1. A skip fire engine controller comprising:

a lookup table embodied in a computer readable media;

a firing fraction determining unit arranged to determine a firing fraction suitable for delivering a requested engine output, wherein the firing fraction determining unit utilizes the lookup table to determine a desired firing fraction, wherein the firing fraction determining unit utilizes at least (i) the requested engine output, and (ii) a current engine speed as indices to select a desired firing fraction; and

a firing controller arranged to direct firings in a skip fire manner that delivers the desired firing fraction.

2. A skip fire engine controller as recited in claim 1 wherein an additional index for the lookup table includes transmission gear.

3. A skip fire engine controller as recited in claim 1 wherein an additional index for the lookup table includes at least one selected from the group consisting of:

manifold absolute pressure (MAP);

manifold air temperature;

a parameter indicative of mass air charge (MAC);

a parameter indicative of cam position

cylinder torque output;

engine torque output;

maximum permissible manifold pressure;

vehicle speed;

ambient temperature; and

barometric pressure.

4. A skip fire engine controller as recited in claim 1 wherein the lookup table is a multi-dimensional lookup table that includes a plurality of logically or physically separate lookup tables.

5. A skip fire engine controller as recited in claim 1 wherein the lookup table dictates operation in an all-cylinder operational mode in selected operational states.

6. A skip fire engine controller as recited in claim 5 wherein the selected operational states for all-cylinder operation include engine speeds below a first threshold and engine speeds above a second threshold.

7. A skip fire engine controller as recited in claim 1 wherein each entry in the lookup table includes a firing fraction field that stores a firing fraction indicator indicative of a desired firing fraction associated with such entry.

8. A skip fire engine controller as recited in claim 7 wherein each entry in the lookup table further includes a MAC field arranged to store a MAC indicator indicative of a desired operational mass air charge.

9. A skip fire engine controller as recited in claim 8 wherein the MAC indicator is a relative value.

10. A skip fire engine controller as recited in claim 7 wherein each entry in the lookup table further includes a second field arranged to store a value indicative of a second desired operational parameter.

11. An engine controller that includes a skip fire engine controller as recited in claim 1 wherein the engine controller is arranged to sometimes operate the engine in an all cylinder firing mode in which the output of the engine is primarily modulated based on throttle position.

22. A skip fire engine controller as recited in claim 10 wherein the second field stores a value indicative of one selected from the group consisting of:

throttle position;

cam position; and

MAP setting.

12. A skip fire controller comprising a lookup table embodied in a computer readable media, the lookup table having a multiplicity of entries, each entry including a firing fraction field arranged to store an associated firing fraction indicator indicative of a desired firing fraction, wherein indices for the lookup table include:

(i) a desired engine output; and

(ii) a first operational power train parameter.

13. A skip fire controller as recited in claim 12 further comprising an additional index for the lookup table based on a second operational power train parameter that is different than the first operational power train parameter.

14. A skip fire controller as recited in claim 13 wherein the first and second operational power train parameters are selected from the group consisting of:

engine speed;

transmission gear;

manifold absolute pressure (MAP);

manifold air temperature;

mass air charge (MAC);

cylinder torque output;

cam position;

maximum permissible manifold pressure; and

vehicle speed.

15. A method of operating an engine comprising:

determining a desired engine output in terms of a desired torque fraction, wherein the desired torque fraction is indicative of the desired engine output relative to a reference maximum available engine output;

determining a desired operational firing fraction based at least in part on the desired torque fraction; and

directing skip fire operation of the engine at the desired operational firing fraction in a manner that delivers the desired engine output.

16. A method as recite in claim 15 wherein the desired operational firing fraction is determined at least in part using a lookup table that utilizes desired torque fraction as a first indices and current engine speed as a second index.

17. A skip fire engine controller comprising:

a firing fraction determining unit arranged to dynamically determine a desired firing fraction based at least in part upon,

i) a desired engine output;

ii) a current engine speed; and

iii) a current transmission gear; and

a firing controller arranged to direct firings in a skip fire manner that delivers the desired firing fraction.

18. A skip fire engine controller as recited in claim 17 wherein the firing fraction determining unit utilizes a multi-dimensional lookup table in the determination of the desired firing fraction, wherein indices for the multi-dimensional lookup table include desired engine output, current engine speed and current transmission gear.

19. A skip fire engine controller as recited in claim 18 wherein the current engine speed index is arranged in selected ranges of engine speed.

20. A skip fire engine controller as recited in claim 17 wherein the determination of the desired firing fraction is further based on a current maximum manifold pressure that is desirable for use.

21. An engine control unit that includes a skip fire engine controller as recited in claim 17, the engine controller unit further being arranged to sometimes operate the engine in an all cylinder firing mode in which the output of the engine is primarily modulated based on throttle position.

23. A method of controlling skip fire operation of an engine comprising:

determining a desired operational firing fraction by accessing a lookup table having a multiplicity of entries, each entry including a firing fraction field arranged to store an associated firing fraction indicator indicative of a desired firing fraction, wherein indices for the lookup table include;

(i) a desired engine output;

(ii) engine speed; and

(ii) a first operational power train parameter.

directing skip fire operation of the engine at the desired operational firing fraction in a manner that delivers the desired engine output.

24. A method as recited in claim 23 wherein the first operational power train parameter is selected from the group consisting of:

transmission gear;

manifold absolute pressure (MAP);

manifold air temperature;

a parameter indicative of mass air charge (MAC);

a parameter indicative of cam position

cylinder torque output;

engine torque output;

maximum permissible manifold pressure;

vehicle speed;

ambient temperature; and

barometric pressure.