Pumps – Condition responsive control of pump drive motor – Responsive to accumulation of pumped liquid in receiver
Reexamination Certificate
1999-09-10
2001-05-08
Thorpe, Timothy S. (Department: 3746)
Pumps
Condition responsive control of pump drive motor
Responsive to accumulation of pumped liquid in receiver
C417S012000, C417S044100, C417S044200, C417S053000
Reexamination Certificate
active
06227806
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a lift or transfer pump for supplying fuel from a tank to an internal combustion engine. More particularly, the invention relates to a device and method to prevent dry running of a lift pump.
Internal combustion engine powered devices typically include a lift pump to transfer fuel from a remote tank to the engine fuel supply. The engine fuel supply may comprise a carburetor, a fuel injection system, or a high pressure fuel injection pump. While lift pumps may be mechanically driven, electric motor powered lift pumps have become common place. These electric powered lift pumps are energized to operate whenever the engine electrical system is in a start or run condition. The lift pump, or a downstream portion of the fuel system, will include a pressure switch or a pressure regulator and return line to prevent “dead heading” of the lift pump. Thus, it is possible for the fuel pump to continue operating when the ignition is in the on condition but the engine is not operating.
The ability of the lift pump to operate when the engine is not also operating leads to a number of potential problems. In the case of an ignition switch inadvertently left in the on position with the engine not operating, the lift pump will operate and drain the battery. Further, continuous operation of the lift pump circulates fuel through the fuel system and back to the tank leading to fuel heating. More seriously, if the fuel tank empties so that the lift pump runs dry, the continuously operating lift pump motor can overheat. In severe cases of dry running, the motor commutator melts, requiring costly and time consuming replacement of the lift pump before the vehicle can be restarted.
SUMMARY OF THE INVENTION
Briefly stated, the invention in a preferred form is an electric lift pump guard which prevents unintended dry running of the lift pump. In one embodiment, the lift pump guard monitors current flowing through the electric motor powering the lift pump. This is accomplished by monitoring the voltage drop across a precision value sensing resistor within the lift pump guard circuit. This voltage is compared with a standard or threshold voltage. Under normal conditions, when the lift pump is pumping, the measured voltage is greater than the threshold voltage. When the lift pump motor is operating but no fuel is being pumped, the measured voltage falls below the threshold voltage creating a low voltage condition. After a predetermined time the low voltage condition will open the normally closed connection of a relay, thereby disconnecting the electric motor of the lift pump from the power supply circuit. The relay remains in the off condition until it is reset. Resetting of the relay is accomplished by interrupting the power supply to the lift pump guard.
In an alternative embodiment of a lift pump guard for a diesel engine, the pump guard monitors the voltage at an electric shutoff (ESO) solenoid of a high pressure fuel injection pump as well as at an oil pressure switch. The voltages are compared to preestablished values. As long as one of the measured voltages is above the preestablished value, the normally open connection of a relay is held closed, thereby energizing the lift pump electric motor. When the engine runs out of fuel it stalls, the voltage values are below the predetermined level and the relay will de-energize, terminating electricity to the lift pump motor. This embodiment preferably includes a momentary contact switch which can be used to manually activate the lift pump to allow purging of air from the fuel system.
Preferably, the lift pump guard in any embodiment is designed so that it may comprise a sealed housing. Wiring leads or harnesses extend from the housing and via detachable electrical connectors allow the lift pump guard to be added to existing or new electrical systems quickly and inexpensively.
An object of the invention is to provide an automatic shutoff device for a lift pump of a fuel supply system.
Another object of the invention is to provide an automatic shutoff device to prevent dry running of a lift pump which device is compact and can be efficiently incorporated into presently existing wiring harnesses or electrical connections.
A further object of the invention is to provide a new and improved method for monitoring and controlling a lift pump to prevent dry running.
Other objects and advantages of the invention will become apparent from the specification and the drawings.
REFERENCES:
patent: 4430980 (1984-02-01), Pidgeon
patent: 4841404 (1989-06-01), Marshall et al.
patent: 4905641 (1990-03-01), Miller
patent: 5078577 (1992-01-01), Heckman
patent: 5789879 (1998-08-01), Cook
Alix Yale & Ristas, LLP
Gray Michael K.
Stanadyne Automotive Corp.
Thorpe Timothy S.
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