Stop-start control systems for engines with fully flexible valve actuation system

1. A vehicle system comprising:

a stop-start command module configured to detect an autostop request and generate a mode signal based on the autostop request;

a cylinder control module configured to sequentially disable cylinders of an engine during an autostop mode based on the mode signal, wherein the cylinders of the engine include respective intake valves and exhaust valves, and

wherein the cylinder control module is configured to maintain the intake valves in a closed state and the exhaust valves in an open state during the autostop mode and during a plurality of cycles of a crankshaft of the engine;

a timer module configured to (i) measure an amount of time that a speed of the engine is equal to 0 during the autostop mode, and (ii) based on the measured amount of time, determine whether the speed of the engine is equal to 0 for a predetermined period during the autostop mode,

wherein the timer module is configured to store a first position of the crankshaft in response to the speed of the engine being equal to 0 for at least the predetermined period; and

a crankshaft module configured to determine a second position based on the first position during an autostart mode.

2. The vehicle system of claim 1 , further comprising a pressure module configured to set a fuel pressure in a fuel rail of the engine to a predetermined fuel pressure based on a fuel command signal and during the autostop mode, wherein:

the cylinder control module is configured to generate the fuel command signal when the intake valves are closed; and

the predetermined fuel pressure is a maximum fuel pressure.

3. The vehicle system of claim 1 , wherein the cylinder control module is configured to sequentially disable the cylinders during the autostop mode and in a predetermined firing order of the cylinders.

4. The vehicle system of claim 1 , further comprising a first firing cylinder (FFC) module configured to determine a FFC,

wherein the cylinder control module is configured to sequentially reactivate the cylinders during the autostart mode beginning with the FFC and based on a predetermined firing order.

5. The vehicle system of claim 4 , wherein the FFC module is configured to identify one of the cylinders, which is closest to approaching top dead center, as the FFC.

6. The vehicle system of claim 4 , further comprising a pressure module configured to detect a fuel pressure in a fuel rail of the engine, wherein:

the stop-start command module is configured to detect an autostart request and generate the mode signal based on the autostart request; and

if fuel to the cylinders of the engine is disabled and the fuel pressure is greater than a predetermined pressure, the FFC module is configured to determine the FFC based on the detected fuel pressure.

7. The vehicle system of claim 4 , further comprising an engine control module configured to crank the engine during the autostart mode indicated by the mode signal, wherein:

during the autostart mode, the crankshaft module is configured to determine the second position of the crankshaft of the engine based on the mode signal;

the stop-start command module is configured to detect an autostart request and generate the mode signal based on the autostart request to initiate the autostart mode; and

the FFC module is configured to determine the FFC based on the second position.

8. The vehicle system of claim 1 , further comprising an engine control module configured to close an exhaust recirculation valve and open a throttle valve during the autostop mode,

wherein the engine control module is configured to maintain the exhaust recirculation valve in a closed state and the throttle valve in an open state until an autostart is requested.

9. A method comprising:

detecting an autostop request and generating a mode signal based on the autostop request;

sequentially disabling cylinders of an engine during an autostop mode based on the mode signal, wherein the cylinders of the engine include respective intake valves and exhaust valves;

maintaining the intake valves in a closed state and the exhaust valves in an open state during the autostop mode and during a plurality of cycles of a crankshaft of the engine;

measuring an amount of time that a speed of the engine is equal to 0 during the autostop mode;

based on the measured amount of time, determining whether the speed of the engine is equal to 0 for a predetermined period during the autostop mode;

storing a first position of the crankshaft in response to the speed of the engine being equal to 0 for at least the predetermined period; and

determining a second position based on the first position during an autostart mode.

10. The method of claim 9 , further comprising:

setting a fuel pressure in a fuel rail of the engine to a predetermined fuel pressure based on a fuel command signal and during the autostop mode; and

generating the fuel command signal when the intake valves are closed,

wherein the predetermined fuel pressure is a maximum fuel pressure.

11. The method of claim 9 , further comprising disabling the cylinders sequentially during the autostop mode and in a predetermined firing order of the cylinders.

12. The method of claim 9 , further comprising:

determining a first firing cylinder (FFC);

sequentially reactivating the cylinders during an autostart mode beginning with the FFC and based on a predetermined firing order;

detecting a fuel pressure in a fuel rail of the engine;

detecting an autostart request;

generating the mode signal based on the autostart request;

determining the FFC if the fuel pressure is greater than a predetermined pressure; and

identifying one of the cylinders, which is closest to approaching top dead center, as the FFC.

13. The method of claim 9 , further comprising:

determining a first firing cylinder (FFC);

sequentially reactivating the cylinders during an autostart mode beginning with the FFC and based on a predetermined firing order;

cranking the engine during the autostart mode indicated by the mode signal, wherein the crankshaft is in a first position prior to or at a beginning of the autostart mode;

during the autostart mode, determining a second position of the crankshaft based on the mode signal and the first position;

detecting an autostart request and generating the mode signal based on the autostart request to initiate the autostart mode; and

determining the FFC based on the second position.

14. The method of claim 9 , further comprising:

closing an exhaust recirculation valve and opening a throttle valve during the autostop mode; and

maintaining the exhaust recirculation valve in a closed state and the throttle valve in an open state until an autostart is requested.

15. The vehicle system of claim 2 , wherein the cylinder control module is configured to:

disable fuel to the cylinders; and

if the intake valves are closed, generate the fuel command signal (i) subsequent to disabling fuel to the cylinders, (ii) prior to the speed of the engine decreasing to 0, and (iii) prior to maintaining the exhaust valves in the open state.

16. The vehicle system of claim 15 , wherein, if the speed of the engine is 0, the first position of the crankshaft is stored (i) subsequent to an end of the predetermined period, and (ii) subsequent to maintaining the exhaust valves in the open state.

17. The method of claim 9 , wherein:

the sequentially disabling of the cylinders of the engine includes leaving the exhaust valves in respective open positions;

at least one of the open positions is different than the other ones of the open positions; and

maintaining the exhaust valves in the respective open positions during the autostop mode, wherein the respective open positions are based on a velocity of the crankshaft.

18. The method of claim 9 , further comprising reducing a deceleration rate of a velocity of the crankshaft including maintaining the exhaust valves in a fully open positions during the autostop mode, wherein sequentially leaving the exhaust valves open includes leaving the exhaust valves in the fully open positions.