2. Description of the Prior Art The injectors are frequently fed fuel from a common rail which, in turn, receives fuel from an electronic control valve. The fuel is pumped through the electronic fuel valve by a pump and the electronic fuel valve is closed to terminate flow in response to the ignition system being turned off. However, the residual pressure between the electronic fuel valve and the injectors is sufficient for fuel to leak through the injectors and into the combustion chambers thereby causing a fuel rich or"flooded"condition which impedes an engine re-start.

The United States Patent 5,630,399, granted May 20,1997, to Nomura et al. addresses this problem by placing a relief valve in the supply line to the injectors.

SUMMARY OF THE INVENTION AND ADVANTAGES The invention provides a unique method of limiting the leakage of fuel through the injectors and into the combustion chambers of an internal combustion engine after engine shutdown from normal operation during which fuel is supplied to the fuel injector on the upstream side thereof. The method is characterized by applying a negative fuel pressure to the upstream side of the injector in response to engine shutdown to remove fuel on the upstream side of the injector which could leak through the injector and into the combustion chamber after engine shutdown.

A fuel injection assembly for performing the method is characterized by a supply system for supplying fuel to the upstream side of the fuel injector during normal operation of the engine and for applying a negative fuel pressure to the upstream side of the injector in response to engine shutdown to remove fuel on the

upstream side of. injector which could leak through... e injector and into the combustion chamber after engine shutdown.

BRIEF DESCRIPTION OF THE DRAWING Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein Figure 1 is a schematic view of a preferred embodiment of the subject invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 schematically discloses the well components associated with an internal combustion diesel engine 10. As is well known in the art, a fuel injection assembly supplies fuel from a fuel supply tank 12 to a rail manifolds 14 of the engine 10. The manifolds 14 include a plurality of fuel injectors each having an upstream side for receiving fuel and a downstream side for injecting fuel into the combustion chamber of the internal combustion engine.

The assembly is characterized by a supply system 16 for supplying fuel to the upstream side the fuel injector during normal operation of the engine 10 and for applying a negative fuel pressure to the upstream side of the injector in response to engine shutdown to remove fuel on the upstream side of the injector which could leak through the injector and into the combustion chamber after engine shutdown. In addition to the fuel tank 12, the assembly includes a main valve 18 movable between open and closed positions for allowing fuel flow to the injector in the open position and for terminating fuel flow to the injector in the closed position and an injector fuel line 20 for delivering fuel from the main valve 18 to the injector. The main valve 18 is typically an electronic control valve well known for such a use. The fuel tank 12 stores and supplies fuel to the main valve 18 through a main fuel line 22, i. e., the main fuel line 22 for establishes fuel flow between the fuel tank 12 and the main valve 18. A main pump 24 is disposed in the main fuel line 22 for supplying fuel to the injector during normal operation of the engine 10. A pair of filters 26 are also disposed in the main fuel line 22 as is well known in the art.

The assembly includes a switch 28 having an engine ON or closed condition for establishing the normal operation of the engine 10 and an engine OFF or open condition for establishing the engine shutdown, i. e., ignition on and ignition off. The

switch 28 is conne J to and operates an electronic contro. nit 30. The main valve 18 is opened and the main pump 24 is activated to pump fuel in response to the switch 28 being in the ON condition through electrical connections 32,34 and 36 with the electronic control unit 30.

The supply system 16 includes a return fuel line 38 connected in fluid communication between the injector fuel line 20 and the fuel tank 12 and a return pump 40 disposed in the return fuel line 38 and having a vacuum mode of operation for establishing the negative fuel pressure, i. e., a vacuum mode to return fuel from the injector fuel line 20 to the fuel tank 12. The return pump 40 is also controlled by the electronic control unit 30 through an electrical lead 42, which also places a relay 44 and a timer 46 in series with the return pump 40. A return control valve 48 is disposed in the return line 38 for closing the return line 38 during operation of the main pump 24 to prevent return of fuel to the fuel tank 12 normal operation of the engine 10 in response to the switch 28 being in the ON condition. In addition, a check valve 50 is disposed in the return line 38 between the return pump 40 and the fuel tank 12 for preventing fuel flow from the fuel tank 12 through the return pump 40.

In operation, the main pump 24 is activated and the main valve 18 is opened in response to the ignition switch 28 being turned ON to pump fuel from the fuel tank 12 to the injectors in the injector manifold 14. During the ON condition, the return control valve 48 is closed to prevent back flow from the injector manifold 14 to the fuel tank 12.

In response to the ignition switch 28 being turned to the OFF condition, the main valve 18 is closed and the main pump 24 is deactivated and, most importantly, the return control valve 48 is opened and the return pump 40 is activated to place a negative or vacuum pressure on the upstream side of the injectors to return the residual fuel therein to the fuel tank 12. This prevents the residual fuel from leaking through the injectors and into the combustion chambers of the engine 10, which, in turn, would make it difficult to immediately restart the engine 10 because of a fuel rich condition. The control unit 30 is connected to the main valve 18 and the return control valve 48 for maintaining one valve closed while the other valve is open, and vice versa. As the electronic control unit 30 places the return pump 40 in the vacuum mode in response to the switch 28 moving from the ON condition to the OFF condition, it simultaneously activates the timer 46 for terminating operation of the

return pump 40 in., vacuum mode a predetermined time p. iod after the switch 28 is moved from the ON condition to the OFF condition.

The above embodiment is particularly suited for an add-on situation, as in the automotive aftermarket, whereas the concept encompasses use of the invention in an OEM situation as original equipment. In the later embodiment, the return line 38 and return pump 40 would be replaced by a main pump 24 which would be a reversible pump and electronic control valve 18 would have a bypass so that the electronic control unit 30 would simply reposition the electronic control valve 18 to a return by- pass position and reverse the direction of pumping by the main pump 24. In either case, a pump would be activated to positively apply a pressure to the residual fuel at the upstream side of the injectors immediately after engine shutdown. In the embodiment illustrated, the method of implementation is characterized by placing a control valve having a normally closed condition in fluid communication with the injector fuel line 20 and placing a return pump 40 in fluid communication with the control valve. It is further refined by installing a control unit 30 with the return pump 40 and control valve to open the control valve during operation of the return pump 40 and installing a timer 46 with the control unit 30 to cease operation of the return pump 40 after a predetermined time period. In the second embodiment, the implementation is by installing a reversible main pump 24 with a main valve 18 which can be controlled to reverse fuel flow in response to engine shutdown.

Within the bounds of the appended claims are various modifications. The return pump 40 and the solenoid 48 may be replaced with a single positive displacement pump which will prevent backflow. Alternatively, a pumping solenoid could replace the return pump 40 and solenoid 48. Additionally, the relay 44 and timer 46 may be part of the circuit board in the return pump 40.

The invention provides a method of supplying fuel to the fuel injector on the upstream side thereof during normal operation of an internal combustion engine 10 which is characterized by applying a negative fuel pressure to the upstream side of the injector in response to engine shutdown to remove fuel on the upstream side of the injector which could leak through the injector and into the combustion chamber after engine shutdown. The negative pressure is specifically attained by operating a return pump 40 in a vacuum mode. A further step includes timing the operation of the return pump 40 and terminating operation of the pump after a predetermined time

period. The metho.. further defined as preventing the retu. i fuel from the injector fuel line 20 to the return pump 40 during normal operation of the engine 10.

The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.