1. A method of controlling the operation of a vertical reciprocating conveyor having a drive motor to move a carriage, comprising the steps of:
operating the drive motor to initially move the carriage from a resting location;
sensing the amount of current drawn by the motor to initially move the carriage from the resting location;
defining a threshold current value based upon the sensed amount of current drawn by the drive motor during the initial movement of the carriage;
comparing a present value of current drawn by the drive motor to the threshold current value and stopping the drive motor when the present current value varies from the threshold current value by more than an operating limit;
updating the threshold current value to be the present current value when the present current value is within the operating limit; and
continuously repeating the steps of comparing and updating as long as the present current value is within the operating limit.
2. The method of claim 1 wherein the operating limit is defined as an amount of current both below and above the threshold current value.
3. The method of claim 2 wherein the amount of change is a predetermined percentage of the threshold current value.
4. The method of claim 1 wherein the present value of current is an average of multiple current measurements taken over a measurement period.
5. The method of claim 4 wherein the threshold current is updated after a predetermined number of measurement periods.
6. The method of claim 4 wherein the multiple current measurements are the most recent current measurements.
7. The method of claim 1 wherein the threshold current is defined after an initial operating period.
8. The method of claim 5 wherein the threshold current is set as the most recent current measurement.
9. A method of controlling the operation of a vertical reciprocating conveyor having a drive mechanism to lift a carriage, comprising the steps of:
operating the drive mechanism to move the carriage in either an upward direction or a downward direction;
continuously sensing a sensed value created by the drive mechanism in moving the carriage;
continuously comparing the present sensed value to a threshold sensed value during movement of the carriage in either the upward or downward direction;
stopping the drive source when the present sensed value varies from the threshold sensed value by more than an operating limit; and
updating the threshold sensed value to be the present sensed value when the present sensed current value is within the operating limit.
10. The method of claim 9 wherein the operating limit is defined as an amount of change both below and above the threshold sensed value.
11. The method of claim 10 wherein the amount of change is a predetermined percentage of the threshold sensed value.
12. The method of claim 9 wherein the threshold sensed value is updated on a predetermined periodic basis.
13. The method of claim 12 wherein the threshold sensed value is updated to be the most recent sensed value at the end of the predetermined periodic basis.
14. The method of claim 9 wherein the sensed value is current and the drive mechanism is a drive motor.
15. The method of claim 9 wherein the sensed value is pressure and the drive mechanism is a hydraulic pump.
16. A control system for a vertical reciprocating conveyor having a drive motor for lifting a movable carriage, the system comprising:
a sensing module configured to sense the amount of current drawn by the drive motor during movement of the carriage in either an upward or downward direction; and
a controller configured to continuously sense the amount of current drawn by the drive motor and compare the sensed current to a threshold current value, wherein the control unit stops operation of the drive motor when the sensed current value varies from the threshold current value by more than an operating limit and wherein the controller updates the threshold current value to the sensed current value when the sensed current value is within the operating limit.
17. The control system of claim 16 wherein the control unit updates the threshold current value on a periodic basis.
18. The control system of claim 16 wherein the sensed current value is determined as an average of multiple current value measurements.
19. A method of controlling the operation of a vertical reciprocating conveyor having a hydraulic pump to supply pressurized hydraulic fluid to hydraulic cylinders to move a carriage, comprising the steps of:
operating the hydraulic pump to initially move the carriage from a resting location;
sensing the pressure of the hydraulic fluid required to initially move the carriage from the resting location;
defining a threshold pressure value based upon the sensed pressure value of the hydraulic fluid during the initial movement of the carriage;
comparing a present value of pressure of the hydraulic fluid to the threshold pressure value and stopping the hydraulic pump when the present pressure value varies from the threshold pressure value by more than an operating limit;
updating the threshold pressure value to be the present pressure value when the present pressure value is within the operating limit; and
continuously repeating the steps of comparing and updating as long as the present pressure value is within the operating limit.
20. The method of claim 19 wherein the operating limit is defined as an amount of pressure both below and above the threshold pressure value.
21. The method of claim 19 wherein the threshold pressure value is updated after a predetermined number of measurement periods.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method of operating a dual fuel engine, comprising the steps of:
operating a dual fuel common rail system in a regular mode;
operating the dual fuel common rail system in a limp home mode;
leaking more liquid fuel into a gaseous fuel portion of the dual fuel system when operating in the limp home mode versus the regular mode;
injecting liquid fuel from a first nozzle outlet set and injecting gaseous fuel from a second nozzle outlet set into an engine cylinder when operating the dual fuel common rail system in the regular mode;
injecting liquid fuel from the first nozzle outlet set and injecting liquid fuel, but not gaseous fuel, from the second nozzle outlet set into the engine cylinder when operating the dual fuel common rail system in the limp home mode.
2. The method of claim 1 including the steps of:
maintaining a ratio of liquid fuel common rail pressure to gaseous fuel common rail pressure high when operating the dual fuel system in the limp home mode;
maintaining the ratio of liquid fuel common rail pressure to gaseous fuel common rail pressure low when operating the dual fuel system in the regular mode.
3. The method of claim 2 including a step of blocking movement of liquid fuel into the gaseous fuel common rail.
4. The method of claim 3 including isolating gaseous fuel supply and pressure control devices from the gaseous fuel common rail in the limp home mode, but not in the regular mode.
5. The method of claim 4 including controlling at least one of timing and duration of injection of liquid fuel from the second nozzle outlet responsive to the gaseous fuel common rail pressure.
6. The method of claim 5 including controlling at least one of timing and duration of injection of liquid fuel from the second nozzle outlet without consideration of the gaseous fuel common rail pressure.
7. The method of claim 1 including a step of blocking movement of liquid fuel into the gaseous fuel common rail.
8. The method of claim 1 including isolating gaseous fuel supply and pressure control devices from the gaseous fuel common rail in the limp home mode, but not in the regular mode.
9. The method of claim 1 including controlling at least one of timing and duration of injection of liquid fuel from the second nozzle outlet responsive to the gaseous fuel common rail pressure.
10. The method of claim 1 including controlling at least one of timing and duration of injection of liquid fuel from the second nozzle outlet without consideration of the gaseous fuel common rail pressure.
11. A dual fuel common rail system comprising:
a gaseous fuel common rail;
a liquid fuel common rail;
a plurality of fuel injectors each fluidly connected to each of the gaseous fuel common rail and liquid fuel common rail;
liquid fuel supply and pressure control devices fluidly connected to the liquid fuel common rail;
gaseous fuel supply and pressure control devices fluidly connected to the gaseous fuel common rail;
an electronic controller in control communication with the plurality of fuel injectors, the liquid fuel supply and pressure control devices, and the gaseous fuel supply and pressure control devices, and including a limp home algorithm configured to communicate liquid injection control signals to inject liquid fuel from a first nozzle outlet set and gaseous injection control signals to inject liquid fuel from a second outlet set, and including a regular algorithm configured to communicate liquid injection control signals to inject liquid fuel from the first nozzle outlet set and gaseous injection control signals to inject gaseous fuel from the second outlet set.
12. The dual fuel common rail system of claim 11 wherein the limp home algorithm is configured to maintain a ratio of liquid fuel common rail pressure to gaseous fuel common rail pressure high;
wherein the regular algorithm is configured to maintain the ratio of liquid fuel common rail pressure to gaseous fuel common rail pressure low.
13. The dual fuel common rail system of claim 12 including a check valve operably positioned to block movement of liquid fuel from each of the plurality of fuel injectors to the gaseous fuel common rail.
14. The dual fuel common rail system of claim 13 including an electronically controlled isolation valve operably positioned between the gaseous fuel supply and pressure control devices and the gaseous fuel common rail.
15. The dual fuel common rail system of claim 14 including a gaseous rail pressure sensor in communication with the electronic controller; and
wherein the limp home algorithm is configured to control at least one of timing and duration of injection of liquid fuel from the second nozzle outlet responsive to a gaseous fuel common rail pressure.
16. The dual fuel common rail system of claim 11 includes a check valve operably positioned to block movement of liquid fuel from each of the plurality of fuel injectors to the gaseous fuel common rail.
17. The dual fuel common rail system of claim 11 including an electronically controlled isolation valve operably positioned between the gaseous fuel supply and pressure control devices and the gaseous fuel common rail.
18. The dual fuel common rail system of claim 11 including a gaseous rail pressure sensor in communication with the electronic controller; and
wherein the limp home algorithm is configured to control at least one of timing and duration of injection of liquid fuel from the second nozzle outlet responsive to a gaseous fuel common rail pressure.
19. The dual fuel common rail system of claim 11 including a coaxial quill assembly fluidly positioned between each of the plurality of fuel injectors and each of the gaseous fuel common rail and the liquid fuel common rail.