Engine control in fuel and/or cylinder cut off modes based on intake manifold pressure
Methods and arrangements for transitioning an engine between a deceleration cylinder cutoff (DCCO) state and an operational state are described. In one aspect, transitions from DCCO may begin with reactivating cylinders to pump air to reduce the pressure in the intake manifold prior to firing any cylinders. The number of pumping cycles, if any, is based on intake manifold absolute pressure (MAP).
1. A controller configured to control operation of an engine in a vehicle, the controller configured to:
deactivate all working chambers of the engine in a cylinder cut off mode such that none of the working chambers are fired and no air is pumped through the working chambers from an air intake manifold to an exhaust system of the vehicle;
determining when the operation of the engine is to transition from the cylinder cut off mode to a second operational mode in response to an input to the controller;
measure intake manifold absolute pressure (MAP) in the air intake manifold; and
if the measured MAP is larger than a threshold MAP:
determine, based on the measured MAP, a number of working cycle(s) needed to pump down the measured MAP to below the threshold MAP;
operate the engine so as to pump air from the air intake manifold to the exhaust system through one or more of the working chambers of the engine for the determined number of working cycle(s); and
operate the engine in the second operational mode after the pumping of the air for the determined number of working cycle(s).
2. The controller of claim 1 , further configured to receive the measured MAP from a sensor provided in or adjacent to the air intake manifold.
3. The controller of claim 1 , further configured to determine the number of working cycle(s) based on one or more of the following factors:
the MAP prior to pumping;
the threshold MAP;
relative size of the air intake manifold compared to the working chambers of the engine;
intake and exhaust valve timing;
engine speed; and/or
rate of air leakage past a throttle arranged to supply air to the air intake manifold.
4. The controller of claim 1 , further including a look-up-table to determine the number of working cycle(s) needed to pump down the measured MAP to below the threshold MAP.
5. The controller of claim 4 , wherein the lookup table includes a range of MAP values, each MAP value defining a corresponding number of working cycle(s) needed to pump down the MAP value to below the threshold MAP.
6. The controller of claim 1 , wherein the input to the controller is a signal indicative of a torque request and, in response, the controller is further configured to delay engine torque generation until after the pumping over the determined number of working cycle(s) is completed before transitioning the engine to the second operational mode.
7. The controller of claim 1 , wherein the input to the controller is a signal indicative of a torque request and, in response, the controller is further configured to operate the working chambers of the engine in a skip fire mode to deliver the requested torque while pumping air through at least one of the skipped working chamber(s) over the determined number of working cycle(s).
8. The controller of claim 1 , further configured to operate the engine in the second operational mode, the second operational mode including one of the following:
(a) a full displacement mode;
(b) the skip fire mode; or
(c) a reduced displacement mode.
9. The controller of claim 1 , wherein the controller is further configured to directly transition to the second operational mode when the input signal is a “pedal stomp” torque request by activating all of the working chambers of the engine in lieu of reducing the MAP by pumping.
10. The controller of claim 1 , wherein the controller is further configured to transition to the second operational mode, in lieu of reducing the air pressure in the air intake manifold by pumping, if the measured MAP is less than a desired manifold pressure associated with the second operational mode.
11. The controller of claim 1 , further configured to directly transition the operation of the engine to the second operational mode, in lieu of reducing the air pressure in the air intake manifold by pumping, if the measured MAP is equal to or less than the threshold MAP.
12. The controller of claim 1 , wherein the input to the controller is a signal indicative of engine speed and, in response thereto, the controller is further configured to:
ascertain if the engine speed is below a cylinder cut off mode threshold engine speed;
if the engine speed is below the cylinder cut off mode threshold engine speed, pump air through the one or more working chambers for the determined number of working cycles; and
transition the engine operation to the second operational mode after pumping the air for the determined number of working cycles,
wherein the second operational mode is an engine idle mode.
13. The controller of claim 1 , wherein the determined number of working cycles ranges from one to twelve working cycles.
14. The controller of claim 1 , wherein the air pressure in the air intake manifold is reduced to the MAP threshold by the pumping in 0.1 to 0.2 seconds.
15. The controller of claim 1 , wherein the threshold MAP is in the range of 0.3 to 0.5 bar.
16. A method of operating a vehicle having a crankshaft, an intake air manifold, and a plurality of working chambers of an engine, the method comprising, during operation of the engine:
deactivating all of the working chambers in response to a no engine torque request such that none of the working chambers are fired and no air is pumped through the working chambers as the crankshaft rotates;
measuring the crankshaft rotational speed;
measuring intake manifold absolute pressure (MAP) when the measured crankshaft rotational speed falls below a crankshaft rotational speed threshold;
ascertaining a number of air pumping working cycles needed to reduce the measured MAP to below a threshold MAP; and
pumping air through the engine for the ascertained number of working cycles prior to firing any working chambers.
17. The method of claim 16 , wherein the threshold MAP is based at least in part on the engine having acceptable NVH characteristics upon firing any working chambers.
18. The method of claim 16 , wherein the number of ascertained air pumping working cycles is zero if the measured MAP is below the threshold MAP.
19. The method of claim 16 , wherein the number of ascertained air pumping working cycles varies between 0 and 12.
20. The method of claim 16 , further comprising entering an engine idle state after pumping air through the engine for the ascertained number of pumping working cycles.
21. The method of claim 16 further comprising firing a working chamber after pumping air through the engine for the ascertained number of pumping working cycles.
22. The method of claim 12 , wherein execution of the ascertained number of pumping working cycles is interspersed with execution of deactivated working cycles where no air is pumped through the engine.
23. A controller configured to control operation of an engine in a vehicle, the controller configured to:
deactivate all working chambers of the engine in a cylinder cut off mode such that none of the working chambers are fired and no air is pumped through the working chambers from an air intake manifold to an exhaust system of the vehicle;
determining when the operation of the engine is to transition from the cylinder cut off mode to a second operational mode in response to an input to the controller;
measure intake manifold absolute pressure (MAP) in an air intake manifold associated with the engine;
measure engine speed;
determine, based on the measured MAP and engine speed, a time needed to pump air down the MAP to below a threshold MAP;
operate the engine so as to pump air from the air intake manifold to the exhaust system through one or more of the working chambers of the engine for the determined time; and
operate the engine in the second operational mode after the pumping of the air for the determined time.