Deceleration cylinder cut-off in a hybrid vehicle
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 begin with reactivating cylinders to pump air to reduce the pressure in the intake manifold prior to firing any cylinders. In another aspect, transitions from DCCO, involve the use of an air pumping skip fire operational mode. After the manifold pressure has been reduced, the engine may transition to either a cylinder deactivation skip fire operational mode or other appropriate operational mode. In yet another aspect a method of transitioning into DCCO using a skip fire approach is described. In this aspect, the fraction of the working cycles that are fired is gradually reduced to a threshold firing fraction. All of the working chambers are then deactivated after reaching the threshold firing fraction.
1. A method of operating a vehicle having a drive train, an electric motor/generator and an engine, the engine having a crankshaft, an intake manifold and a plurality of working chamber, and wherein the electric motor/generator and engine cannot independently mechanically engage with the drive train, the method comprising:
while the engine is operating with the crankshaft rotating in a first direction, deactivating all 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 continues to rotate in the first direction through multiple engine cycles with the working chambers deactivated;
disengaging the engine from the drive train so that the vehicle motion and crankshaft rotation are not mechanically coupled during at least a portion of the time in which all of the working chambers are deactivated, whereby the electric motor/generator is disengaged from the drive train when the engine is disengaged from the drive train; and
allowing the crankshaft rotation rate to drop below a shift speed for multiple engine cycles while the engine is disengaged from the drive train with all of the working chambers deactivated.
2. A method as recited in claim 1 wherein the electric motor/generator and engine are mechanically coupled such that they rotate together.
3. A method as recited in claim 2 wherein the mechanical coupling of the engine to the electric motor/generator is a fixed mechanical coupling selected from the group consisting of a belt, a chain, a common shaft and gears.
4. A method as recited in claim 1 wherein the intake manifold pressure is at substantially atmospheric pressure while the crankshaft rotation rate is below an engine idle speed.
5. A method as recited in claim 1 wherein the working chamber deactivation, the engine disengaging and the crankshaft rotation rate dropping below the shift speed all occur while the vehicle is in motion.
6. A method as recited in claim 1 wherein the crankshaft rotation rate is allowed to drop to zero.
7. A method as recited in claim 1 wherein the crankshaft rotation rate is allowed to drop to an engine idle speed and is maintained at the engine idle speed by the electric motor/generator while the engine is disengaged from the drive train.
8. A method as recited in claim 1 wherein the crankshaft rotation rate is allowed to drop to an engine ignition speed and is maintained at the engine ignition speed by the electric motor/generator while the engine is disengaged from the drive train.
9. A method as recited in claim 1 wherein the crankshaft rotation rate is controlled by adding or removing torque from the crankshaft by the electric motor/generator while the engine is disengaged from the drive train.
10. A method as recited in claim 9 wherein the crankshaft rotation rate is maintained above an engine ignition speed by the electric motor/generator while the engine is disengaged from the drive train.
11. A method as recited in claim 1 wherein the working chambers each have an intake valve and an exhaust valve and each working chamber is deactivated by holding at least one of the intake valve and exhaust valve closed through at least one associated working cycle.
12. A method of operating a vehicle having a drive train, an electric motor/generator and an engine, the engine having a crankshaft, an intake manifold and a plurality of working chambers, and wherein the engine and motor/generator are mechanically coupled such that they rotate together, the method comprising:
while the vehicle is operating and the crankshaft is rotating, deactivating all of the working chambers such that none of the working chambers are fired and no air is pumped through the working chambers as the crankshaft rotates in response to an engine torque request that can be supplied by the electric motor/generator; and
using the electric motor/generator to supply the requested torque during a period in which all of the working chambers are deactivated thereby causing the crankshaft to continue to rotate while all of the working chambers are deactivated, whereby the crankshaft continues to rotate through a multiplicity of engine cycles with all of the working chamber deactivated and the electric motor/generator supplying the requested torque.
13. A method as recited in claim 12 wherein the requested torque supplies motive power to creep the vehicle forward.
14. A method as recited in claim 12 wherein the requested torque supplies motive power to sustain the vehicle motion at a cruising speed.
15. A method as recited in claim 12 wherein the mechanical coupling of the engine to the electric motor/generator is a fixed mechanical coupling selected from the group consisting of a belt, a chain, a common shaft and gears.
16. A method as recited in claim 15 wherein the mechanical coupling is configured such that the engine and the electric motor/generator rotate at the same speed.
17. A method of operating a vehicle having a drive train, an electric motor/generator and an engine, the engine having a crankshaft, an intake manifold and a plurality of working chambers, the method comprising:
while the engine is operating, deactivating all 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; and
disengaging the engine from the drive train so that vehicle motion and crankshaft rotation are no longer mechanically coupled, wherein the crankshaft rotation rate is controlled while the engine is disengaged from the drive train by adding or removing torque from the crankshaft by the electric motor/generator, the crankshaft rotation rate being controlled to ensure that the crankshaft continues to rotate throughout the duration of the no engine torque request.
18. A method as recited in claim 17 wherein the engine and motor/generator are mechanically coupled so that they rotate together and have have the same rotation rates.
19. A method as recited in claim 17 wherein the engine and the electric motor/generator are mechanically coupled via a mechanical coupling selected from the group consisting of a belt, a chain, a common shaft and gears.
20. A method as recited in claim 17 wherein the crankshaft rotation rate is allowed to drop to an engine idle speed and is maintained at the engine idle speed by the electric motor/generator while the engine is disengaged from the drive train.
21. A method as recited in claim 17 wherein the crankshaft rotation rate is allowed to drop to an engine ignition speed and is maintained at the engine ignition speed by the electric motor/generator while the engine is disengaged from the drive train.
22. A method as recited in claim 17 wherein the crankshaft rotation rate is maintained above an engine ignition speed by the electric motor/generator while the engine is disengaged from the drive train.
23. A method as recited in claim 17 wherein the working chambers each have an intake valve and an exhaust valve and each working chamber is deactivated by holding at least one of the intake valve and exhaust valve closed as the crankshaft rotates.