Dual Solenoids on a Single Circuit and Fuel Injector Using Same

The present invention relates generally to electromechanical devices having two or more electrical actuators, and more particularly to the use of two solenoids that are controllable as part of a single electrical circuit in a fuel injector.

Many electromechanical devices employ two or more separate electrical actuators in their operation. For instance, some fuel injectors use two independently controllable solenoids to control such performance parameters as injection timing and fuel pressurization. While the use of two separately controllable solenoids can improve injector performance, there has been some hesitation in the industry to adopt two or more solenoids in a fuel injector because the benefits do not always outweigh the costs. In addition to financial costs, there are the increased complexity and hardware required to provide each solenoid with a separate electrical circuit. Two separate electrical circuits also tend to undermine robustness and long term reliability in most fuel injector applications. On the other hand, use of a single solenoid to control two separate electrical actuators can lead to a highly sensitive system that requires "glitch" detection in the controller as well as very tight tolerances on the injector assembly.

The present invention is directed to these and other problems associated with the use of two or more electrical actuators in an electromechanical device, such as a fuel injector.

In one aspect, an electronically controlled device includes a first electrical actuator and a second electrical actuator attached to a body. An electrical circuit is attached to the body, and includes a positive terminal and a negative terminal connected to the first electrical actuator and the second electrical actuator. The electrical circuit permits energization of one of the first electrical actuator and second electrical actuator when electrical current flows in either direction between the first terminal and the second terminal. However, the electrical circuit permits energization of the other of the first electrical actuator and the second electrical actuator when current flows in a single direction between the first terminal and the second terminal.

In another aspect, the device is an electronically controlled fuel injector that includes an injector body that defines a fuel pressurization chamber and a nozzle outlet. A first solenoid and a second solenoid are attached to the injector body. An electrical circuit is attached to the injector body, and includes a positive terminal and a negative terminal connected to the first solenoid and the second solenoid. The electrical circuit permits energization of one of the first solenoid and the second solenoid when electrical current flows in either direction between the first terminal and the second terminal. However, the electrical circuit permits energization of the other of the first solenoid and the second solenoid when current flows in a single direction between the first terminal and the second terminal.

FIG. 1 is a partial front sectioned diagrammatic view of a fuel injector according to one embodiment of the present invention.

FIG. 2 is a partial side sectioned diagrammatic view of the fuel injector shown in FIG. 1.

FIG. 3 is an electrical circuit diagram according to one aspect of the present invention.

FIGS. 4a-d are graphs of circuit current, spill valve position, needle control valve position, and fuel injection mass flow rate, respectively, versus time for a single injection event according to one aspect of the present invention.

Referring now to FIGS. 1 and 2, a fuel injector 10 includes an injector body 11 made up of a plurality of components attached to one another in a manner well known in the art. Injector body 11 defines a plunger bore 12 within which a plunger 13 is driven to reciprocate by some suitable means, such as hydraulic pressure or a cam driven tappet assembly, etc. A portion of plunger bore 12 and plunger 13 define a fuel pressurization chamber 14 that communicates with a nozzle outlet 17 via a high pressure passage 15 and a nozzle chamber 16. A needle valve member 20 is normally biased by a spring 22 to a position that blocks nozzle outlet 17. During an injection event, needle valve member 20 lifts to an open position to open nozzle outlet 17.

When plunger 13 is undergoing its downward pumping stroke, pressure is unable to build in fuel pressurization chamber 14 while a spill valve assembly 40 is in its open position. Spill valve assembly 40 includes a solenoid 41 that has an armature 42 attached to a spill valve member 43. A biasing spring 45 normally biases spill valve member 43 away from high pressure seat 44 to open fluid communication between high pressure spill passage 46 and low pressure spill passage 47. In other words, when spill valve solenoid 41 is de-energized, fuel pressurization chamber 14 is open to an annular low pressure area 28 within injector body 11 via a portion of high pressure passage 15, high pressure spill passage 46 and low pressure spill passage 47. Thus, when spill valve 40 is open, the fuel displaced from fuel pressurization chamber 14 is recirculated for later use, and pressure within the fuel injector is unable to build to the relatively high injection pressures. When spill valve solenoid 41 is energized, armature 42 and spill valve member 43 are lifted to close high pressure seat 44, which causes fuel pressure in fuel pressurization chamber 14, high pressure passage 15 and nozzle chamber 16 to rise rapidly. Thus, in order to raise fuel pressure to initiate an injection event, spill valve solenoid 41 must be energized to close spill valve assembly 40.

In order to control the precise timing at which an injection event will begin, needle valve member 20 includes an annular closing hydraulic surface 21 exposed to fluid pressure in a needle control chamber 23, which may be alternately exposed to low or high pressure. Needle valve member 20 includes a needle portion 25, a spacer portion 27, a pin stop portion 35 and a needle control piston 24. Depending upon the position of a needle control valve member 33, a needle control chamber 23 is either connected to a high pressure passage 26 or a low pressure passage 29. Needle control valve member 33 is a portion of a needle control valve assembly 30 that includes a needle control solenoid 31, which has an armature 32 attached to valve member 33. A biasing spring 36 normally biases armature 32 and needle control valve member 33 downward toward a position that opens high pressure seat 34. When needle control solenoid 31 is de-energized, needle control chamber 23 is in fluid communication with fuel pressurization chamber 14 via a portion of high pressure passage 15 and high pressure passage 26, past high pressure seat 34. When needle control solenoid 31 is energized, needle control valve member 33 lifts to close high pressure seat 34. When this occurs, needle control chamber 23 is fluidly connected to the annular low pressure area 28 via low pressure passage 29, and a small annular clearance area existing between the outer surface of valve member 33 and inner bore 37. Thus, when needle control solenoid 31 is energized, annular closing hydraulic surface 21 is exposed to low fluid pressure, which causes needle valve member 20 to behave as an ordinary spring biased check valve. However, closing hydraulic surface 21 is preferably sized to hold needle valve member 20 in its closed position, even in the presence of high fuel pressures, when solenoid 31 is de-energized.

Those skilled in the art will appreciate that spill valve solenoid 41 and needle control valve solenoid 31 must sometimes be energized and de-energized at different times through the injection cycle in order to gain the full benefit produced by independent control of fuel pressurization and injection timing. Thus, in the prior art devices, there has been a tendency to provide two complete electrical circuits that have the ability to independently energize the two solenoids. The present invention, however, includes a single electrical circuit 50 of the type shown in FIG. 3 that includes features that enable the two solenoids 31 and 41 to be energized in a manner suitable for use in a fuel injector of the type shown in FIGS. 1 and 2. Electrical circuit 50 is attached to injector body 11 and includes a positive terminal 52 and a negative terminal 51 that are exposed outside of fuel injector 10 for connection to an engine electrical system in a manner well known in the art.

Electrical circuit 50 includes a plurality of diodes 53, 56, 58, 60 that are attached in a plurality of respective electrical branches 54, 55, 57 and 61 in order to permit injector behavior of the type illustrated in FIGS. 4a-d. The positioning of these diodes and branches results in an electrical circuit that permits energization of spill valve solenoid 41 when electrical current flows in either direction between positive terminal 52 and negative terminal 51. It should be noted that current flows through spill valve solenoid 41 in the same direction regardless of the applied voltage polarity. Thus, when a positive voltage is applied, current flows from positive terminal 52 into branch 61 through diode 60, through spill valve solenoid 41 along branch 59, into branch 55 through diode 56, and then to negative terminal 51. In the presence of a positive voltage polarity, diode 53 prevents electric current flow into branch 54 to energize needle control solenoid 31. When a negative voltage is applied to the terminals, electric current flows from negative terminal 51, through needle control solenoid 31 in branch 54, through diode 53, into branch 59 through spill valve solenoid 41, then into branch 57 through diode 58, and then out at positive terminal 52. Thus, the arrangement of the branches and diodes permit energization of spill valve solenoid 41 regardless of the voltage polarity, but permits energization of needle control solenoid 31 only when a negative voltage is applied across terminals 51 and 52. When a negative voltage polarity is applied, the two solenoids are serially arranged. It should also be noted that needle control solenoid 31 decays quickly when a positive voltage is applied; however, both solenoids 31 and 41 tend to decay slowly when an open condition exists.

Referring now in addition to FIGS. 4a-d, between injection events no current is applied to electrical circuit 50. When no current is applied, spill valve 40 is biased to its open position, and needle control valve 30 is biased to a position that opens high pressure seat 34. As plunger 13 begins its downward pumping stroke, the fuel is displaced from fuel pressurization chamber 14 into high pressure passage 15, through spill passage 46, past high pressure seat 44, into low pressure spill passage 47 and then to annular low pressure area 28 for recirculation into fuel inlet 39. When it comes time to build fuel pressure for an injection event, a positive voltage is applied across terminals 52 and 51 to energize spill valve solenoid 41. This moves spill valve member 43 upward to close high pressure seat 44 (FIG. 4a, b) and allow fuel pressure to build to an injection pressure in fuel pressurization chamber 14, high pressure passage 15 and nozzle chamber 16. However, because needle control solenoid 31 remains unenergized, the building high pressure in passage 15 acts upon annular closing hydraulic surface 21 to hold needle valve member 20 in its downward closed position.

When fuel pressure has reached a desired magnitude, voltage polarity across terminals 51 and 52 is reversed to energize needle control solenoid 31 as shown in FIG. 4a-d. When this reversal of voltage polarity occurs, spill valve assembly 40 remains in its closed position, but needle control valve assembly 30 moves from its closed position to its open position to relieve the high pressure in needle control chamber 23. Relatively high fuel pressure in nozzle chamber 16 then lifts needle valve member 20 upward to its open position to commence the spraying of fuel out of nozzle outlet 17.

If a split injection is desired, after an amount of time, the voltage polarity is again reversed to de-energize needle control solenoid 31. When this occurs, needle control valve member 33 moves downward to re-open high pressure seat 34. This connects needle control chamber 23 to the high pressure in high pressure passage 26, which causes needle valve member 20 to quickly move downward to its closed position due to the high hydraulic force acting on annular closing hydraulic surface 21. When it comes time for the main injection event, the voltage polarity is again reversed and the high pressure in needle control chamber 23 is relieved, allowing needle valve member 20 to again move to its upward open position to resume fuel spray out of nozzle outlet 17. The injection event is ended by ceasing all current through electrical circuit 50 so that both solenoids 31 and 41 become de-energized. This causes residual fuel pressure in needle control chamber 23 and the mechanical force from spring 22 to abruptly move needle valve member 20 downward to its closed position to end the injection event.

Although the present invention has been illustrated in the context of a fuel injector 10, the electrical circuitry 50 of the present invention finds potential application in a wide variety of electromechanical devices that include at least two separate electrical actuators that require some independent controllability. Electrical circuit 50 is particularly applicable to fuel injectors of the type shown in FIGS. 1 and 2 because the spill valve assembly 40 needs to be in one position throughout an injection event, but the needle control valve assembly 30 must be controllable within the injection event. This circuitry combined with the presence of biasing springs 22, 36 and 45 ensure that no fuel is injected between injection events and that the valves are reset to a known position before the initiation of each subsequent injection event. Thus, the electrical circuitry 50 of the present invention permits some independent control over two separate electrical actuators. Although the present invention has been illustrated with the use of solenoids, other electrical actuators, such as piezo electric actuators, servo motors, etc., could also be used in an appropriate application with the present invention.

The above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Various modifications and other changes could be made to the illustrated embodiment without departing from the intended spirit and scope of the present invention, which is defined in terms of the claims set forth below.