Marine propulsion device with hydrolock and stall prevention

1. A marine propulsion device comprising: an internal combustion engine driving a driveshaft into rotation, configured to propel a marine vessel;

a starter-generator motor in a torque transmitting relationship with the driveshaft, wherein the starter-generator motor is alternately operable in a positive torque mode where it is powered by a battery to exert a positive torque on the driveshaft, and in a negative torque mode where it exerts a negative torque on the driveshaft and generates a charge to the battery;

a control module configured to:

receive an engine RPM;

determine an engine RPM drop rate;

determine that the engine RPM drop rate exceeds a threshold drop rate; and

operate the starter-generator motor in the positive torque mode based on the engine RPM drop rate when the engine RPM drop rate exceeds the threshold drop rate.

2. The marine propulsion device of claim 1 , wherein the control module is further configured to operate the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on the engine RPM drop rate, wherein the positive torque amount increases as the engine RPM drop rate increases.

3. The marine propulsion device of claim 2 , wherein the positive torque amount is calibrated to maintain the engine RPM drop rate below the threshold drop rate.

4. The marine propulsion device of claim 3 , wherein the control module determines the positive torque amount by accessing a lookup table containing positive torque amounts based on engine RPM drop rate values.

5. The marine propulsion device of claim 1 , wherein the control module is further configured to:

determine that the engine RPM is below an idle target RPM; and

operate the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on the difference between the engine RPM and the idle target RPM.

6. The marine propulsion device of claim 5 , wherein the control module determines the positive torque amount by accessing a lookup table containing positive torque amounts based on engine RPM values and engine RPM drop rate values.

7. The marine propulsion device of claim 1 , wherein the control module is further configured to:

receive a throttle demand value;

determine whether a reverse gear position is demanded; and

if a reverse gear position is demanded, operate the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on at least the engine RPM drop rate.

8. The marine propulsion device of claim 1 , wherein the control module is further configured to:

receive a gear position;

operate the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on at least the engine RPM drop rate until the gear position is neutral.

9. The marine propulsion device of claim 1 , wherein the control module is further configured to:

receive a vessel speed; and

operate the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on at least the engine RPM drop rate and the vessel speed.

10. The marine propulsion device of claim 1 , wherein the control module is further configured to:

determine that the internal combustion engine has stalled; and

operate the starter-generator motor in the positive torque mode to exert a maximum torque amount on the driveshaft to prevent negative rotation of the driveshaft.

11. The marine propulsion device of claim 10 , wherein the control module is further configured to operate the starter-generator motor in the positive torque mode until the internal combustion engine is restarted or a gear system is in a neutral position.

12. The marine propulsion device of claim 10 , wherein the control module is further configured to:

receive a gear position;

determine that the gear position equals a reverse gear position;

determine that the engine RPM is above a shift threshold RPM; and

operate the starter-generator motor in the negative torque mode to apply a negative torque amount on the driveshaft based on the engine RPM until the engine RPM is below the shift threshold RPM.

13. A method of controlling a starter-generator motor on a marine propulsion device containing an internal combustion engine and configured to propel a marine vessel, wherein the starter-generator motor is alternately operable in a positive torque mode where it is powered by a battery to exert a positive torque on a driveshaft, and in a negative torque mode where it exerts a negative torque on the driveshaft and generates a charge to the battery, the method comprising:

receiving an engine RPM;

determining an engine RPM drop rate;

determining that the engine RPM drop rate exceeds a threshold drop rate; and

operating the starter-generator motor in the positive torque mode based on the engine RPM drop rate when the engine RPM drop rate exceeds the threshold drop rate.

14. The method of claim 13 , further comprising operating the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on the engine RPM drop rate, wherein the positive torque amount is a calibrated torque amount intended to maintain the engine RPM drop rate below the threshold drop rate.

15. The method of 14 , further comprising determining the positive torque amount by accessing a lookup table containing positive torque amounts based on engine RPM drop rate values.

16. The method of claim 13 , further comprising:

determining that the engine RPM is below an idle target RPM; and

operating the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on the difference between the engine RPM and the idle target RPM.

17. The method of claim 13 , further comprising:

receiving a throttle demand value;

determining whether a reverse gear position is demanded; and

operating the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based at least on engine RPM drop rate until the engine RPM is consistent with the throttle demand value for a predetermined period of time.

18. The method of claim 13 , further comprising:

receiving a gear position; and

operating the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on at least the engine RPM drop rate until the gear position is neutral.

19. The method of claim 13 , further comprising:

receiving a vessel speed; and

operating the starter-generator motor in the positive torque mode to exert a positive torque amount on the driveshaft based on at least the engine RPM drop rate and the vessel speed.

20. The method of claim 13 , further comprising:

determining that the internal combustion engine has stalled; and

operating the starter-generator motor in the positive torque mode to exert a maximum torque amount on driveshaft to prevent negative rotation of the driveshaft.