Control method for closed loop operation with adaptive wave form of an engine fuel injector oil or fuel control valve

A method and system controls motion of an armature 112 of a fuel injector 100. The armature moves between an open coil 118 and a close coil 116 of the injector. Acceleration current of a certain polarity is applied to the open coil 118 with the armature disposed at the close coil 116. De-latching current of a polarity opposite of the certain polarity is applied to the close coil 116 to release magnetic latch on the armature thereby accelerating movement of the armature towards the open coil 118. Deceleration current is applied the close coil 116 thereby decelerating the armature prior to reaching the open coil. Latching current of the certain polarity is applied to the open coil 118 prior to or just after impact of the armature 112 with the open coil 118 to magnetically latch the armature to the open coil 118 thereby reducing bounce of the armature at impact.

FIELD OF THE INVENTION

This invention relates to oil activated fuel injectors and, more particularly, to a system and method to control motion of an armature of the injector using closed loop operation with adaptive current or voltage wave forms.

BACKGROUND OF THE INVENTION

In hydraulically actuated fuel injection systems, a control valve body is provided with a valve system having grooves or orifices which allow fluid communication between working ports, high pressure ports, and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.

In current configurations, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift an armature into the open position so as to align grooves of the control valve body and the armature. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.

However, in such a conventional system, the armature has a tendency to bounce or repeatedly impact against the open coil during the opening stroke. During this bouncing, it is difficult to control the armature motion and hence results in the inability to efficiently control the supply of fuel to the combustion chamber of the engine. For example, in conventional systems it is not possible to quickly move the armature away from the open coil in order to minimize the bouncing effect during an injection of a pilot quantity of fuel. Accordingly, the initial quantity of fuel provided during the pre-stroke event cannot be easily controllable, resulting in a larger injection quantity of fuel than desired. This may result in a retarded start of injection, as well as the inability to control the armature and hence the injection of a small, pilot quantity of fuel. That is, during this bouncing or repeated impact, a small quantity of fuel cannot be metered accurately in order to efficiently inject this small quantity of fuel into the combustion chamber of an engine. Additionally, it is also very difficult, if not impossible, to vary the amount of fuel during this small injection.

Thus, injection shot-to-shot variations can occur on a single fuel injector.

It is also known that the bouncing phenomenon may differ from injector to injector, and over time. For example, different manufacturing tolerances may affect the bouncing phenomenon from, for example, small variations in armature diameter to different coil characteristics. Additionally, over time, in the same injector, variations may result from different operating conditions such as temperature and wear on the parts due to aging and other factors. Hence, the control of fuel quantity may vary from fuel injector to fuel injector, as well as over time with the same fuel injector. This also may lead to higher emissions and engine noise. Thus, injector shot-to-shot variations can occur on the same engine between multiple injectors.

The shot-to-shot variations mentioned above can cause idle stability issues that are detectable by the vehicle's operator and can cause decreased engine efficiency and increased emissions. Currently, manufacturing tolerances of the injector require sorting or rework to improve shot-to-shot variations.

Thus, there is a need to reduce injector shot-to-shot variations in an injection system by reducing the bounce of an armature of a control valve of the system.

SUMMARY OF THE INVENTION

An object of an embodiment is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by a method of controlling motion of an armature of a fuel injector. The armature is constructed and arranged to move between an open coil and a close coil of the injector. The method applies acceleration current of a certain polarity for a certain amount of time to the open coil with the armature disposed at the close coil. A de-latching current of a polarity opposite of that of the certain polarity is applied for a certain amount of time to the close coil to release magnetic latch on the armature thereby accelerating movement of the armature towards the open coil. A deceleration current is applied for a certain amount of time to the close coil thereby decelerating the armature prior to reaching the open coil. A latching current of the certain polarity is applied for a certain amount of time to the open coil prior to or just after impact of the armature with the open coil to magnetically latch the armature to the open coil thereby reducing bounce of the armature at impact.

In accordance with another aspect of an embodiment, a control system for controlling motion of an armature of a fuel injector includes at least one fuel injector having an armature constructed and arranged to move between an open coil and a close coil, and a controller constructed and arranged to apply 1) acceleration current of a certain polarity for a certain amount of time to the open coil with the armature disposed at the close coil, 2) de-latching current of a polarity opposite of that of the certain polarity for a certain amount of time to the close coil to release magnetic latch on the armature thereby accelerating movement of the armature towards the open coil, 3) deceleration current for a certain amount of time to the close coil thereby decelerating the armature prior to reaching the open coil; and 4) a latching current of the certain polarity for a certain amount of time to the open coil prior to or just after impact of the armature with the open coil to magnetically latch the armature to the open coil thereby reducing bounce of the armature at impact.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

With reference toFIG. 1, an overview of a fuel injector in accordance with the invention is shown. It should be understood, though, that the injector shown inFIG. 1is provided as one illustrative example, and that other configurations, features and the like may also be equally used with the invention. Accordingly, the fuel injector ofFIG. 1and the features described herein are not to be considered a limiting feature of the embodiment.

The fuel injector, generally indicated at100, can be of the type disclose din U.S. Pat. No. 7,216,630 B2, the content of which is hereby incorporated by reference into this specification. The fuel injector100includes a control valve body102as well as an intensifier body120and a nozzle140. The control valve body102includes an inlet area104which is in fluid communication with working ports106. At least one groove or orifice (hereinafter referred to as grooves)108is positioned between and in fluid communication with the inlet area104and the working ports106. At least one of vent hole110(and preferably two ore more) is located in the control body102which is in fluid communication with the working ports106.

An armature112, in the form of a spool, having at least one groove or orifice (hereinafter referred to as grooves)114is slidably mounted within the control valve body102. An open coil118and a closed coil116are positioned on opposing sides of the armature112and are energized via a driver (not shown) to drive the armature112between a closed position and an open position. In the open position, the grooves114of the armature112are aligned with the grooves108of the valve control body102thus allowing the working fluid to flow between the inlet area104and the working ports106of the valve control body102.

The intensifier body120is mounted to the valve control body102via any conventional mounting mechanism. A seal122(e.g., o-ring) may be positioned between the mounting surfaces of the intensifier body120and the valve control body102. A piston124is slidably positioned within the intensifier body120and is in contact with an upper end of a plunger126. An intensifier spring128surrounds a portion (e.g., shaft) of the plunger126and is further positioned between the piston124and a flange or shoulder129formed on an interior portion of the intensifier body120. The intensifier spring128urges the piston122and the plunger126towards a first position proximate to the valve control body102. A pressure release hole130is formed in the body of the intensifier body120. The pressure release hole130may be further positioned adjacent the plunger126.

As shown inFIG. 1, a check disk134may be positioned below the intensifier body120remote from the valve control body102. The combination of an upper surface134aof the check disk134, an end portion126aof the plunger126and an interior wall120aof the intensifier body120forms the high pressure chamber136. A fuel inlet check valve138is positioned within the check disk134and provides fluid communication between the high pressure chamber136and a fuel area (not shown). This fluid communication allows fuel to flow into the high pressure chamber136from the fuel area during an up-stroke of the plunger126. The pressure release hole130is also in fluid communication with the high pressure chamber136when the plunger126is urged into the first position; however, fluid communication is interrupted when the plunger126is urged downwards towards the check disk134. The check disk134also includes a fuel bore139in fluid communication with a fuel bore135in the intensifier body120. The fuel bore135is in fluid communication with the high pressure chamber136.

FIG. 1further shows the nozzle140and a spring cage142. The spring cage142is positioned between the nozzle140and the check disk134, and includes a fuel bore144in fluid communication with the fuel bore139of the check disk134. The spring cage142also includes a centrally located bore148having a first bore diameter148aand a second smaller bore diameter148b. A spring150and a spring seat152are positioned within the first bore diameter148aof the spring cage142, and a pin154is positioned within the second smaller bore diameter148b. The nozzle140includes an angled bore146in alignment with the bore139of the spring cage142. A needle156is preferably centrally located with the nozzle140and is urged downwards by the spring150(via the pin154). A fuel chamber152surrounds the needle150and is in fluid communication with the bore146. In embodiments, a nut160is threaded about the intensifier body120, the check disk134, the nozzle140and the spring cage142.

With reference toFIG. 2, conventional fixed coil waveforms are shown with period control between pulses to control fuel quantity. Current waveform D is of the open coil118and current waveform E is of the close coil116. Waveform F is of accelerometer impact forces. Portion B of the waveforms D and E indicates the bounce of the armature resulting in wasted energy.

Returning toFIG. 1, a control “C” is used to control and monitor different parameters of the injector100. The control “C” may, for example, control, monitor and/or regulate the current provided to the open coil118and closed coil116. In this way, the control “C” can control, monitor and/or regulate the movement of the armature112between a closed position and an open position. By way of example, the electronic properties, e.g., back EMF, can be monitored by the control “C”. Thus, closed loop operation is performed by measuring the voltage created by the motion of the armature112as it is pulled from the non-energized coil (e.g., coil116) to the energized coil (e.g., coil118). The resultant signals can then be used to estimate the movement of the armature112in either direction, and impact of the armature and will be explained more fully below. The control C can be considered to be a controller that is preferably part of an engine control unit (not shown) of a vehicle. The controller can control all the fuel injectors of the vehicle.

With reference toFIG. 4, a “negative current” can be used to counteract residual magnetism in a coil and thus reduce the bounce of armature112. Adaptive current waveform D shows the initial acceleration current of a certain polarity provided to the open coil118. At T1, a peak pulse of 25 amps accelerates the armature112. Current waveform E is of the close coil116and N1indicates a first application of “negative current” on the close coil116. The application of the negative current N1can occur slightly before or generally simultaneously with the application of the acceleration current D.

As used herein, the “negative current” is a de-latching current of a polarity opposite of that of the acceleration current to release the armature112from the close coil116, allowing an earlier motion and increase acceleration of the armature112toward the open coil118. More particularly, on simple coil pole piece and armature, when the coil is energized, the coil pulls the armature to the coil. When electrical power is removed, the armature continues to be latched to the pole piece as the stored magnet field holds the parts. By applying an opposite polarity current (the negative current), the stored magnetic field is removed. The application of this negative current allows the opposite coil and pole piece assembly to pull armature with less magnetic resistance from unpowered coil resulting in faster acceleration and improved stability of motion.

The acceleration current D to open coil118can be stepped down to 20 amps at T2. Also at T2, a second application of negative current N2(or deceleration current) is applied on the close coil116to decelerate the armature112by applying electromagnetic force on the close coil116when the armature is moving in the opposite direction toward the open coil118. The polarity of the N2is shown to be opposite that of the acceleration current D, but the polarity of N2is immaterial once the magnetic field is drained from the close coil116. The acceleration current D to open coil118can be stepped down to12amps at T3. Stepping-down of the current D helps control bounce of the armature112. At T4, a peak pulse of 25 amps as a latching current is applied to the open coil118prior to or just after impact of the armature112with the open coil118to magnetically latch the armature112to the open coil118thereby eliminating or at least reducing the bounce of the armature112at impact.

As should be known to those of skill in the art, inductance is a property associated with the wire wound about the open coil or the closed coil. The origin of inductance is that the current flowing through the wire builds up a magnetic field around the wire. Energy is stored in this field and when the current changes in the coil, some energy must be transferred to or from the field which occurs by the field causing a voltage drop across the conductor while the current is changing. The voltage drop (back EMF) will be proportional to the derivative of the current change over time, and the sign of the voltage will be such as to try to resist the change in current. By monitoring this back EMF, an indication of the armature112travel and impact can be obtained (by knowing the current provided to the open coil and the distance the armature must travel to the open coil).

With reference toFIG. 3, the current waveform D ofFIG. 2is shown. Waveform G shows the back EMF (electro-magnetic force) voltage generated by solenoid motion and indicates armature112impact with a coil. The waveform H shows the detection of the impact at the end of armature travel. By using sample-based feedback back by utilizing back EMF signals, changes of the armature motion over the lifetime of the injector can be compensated for due to, for example, temperature changes, wear conditions, magnetic properties, all surface related effects (adhesion, cohesion, friction), fluctuations in working fluid pressure and the like, by adjusting the timing values for the open coil and close coil, e.g., adjusting the timing of the current provided to the open coil and close coil. More particularly, closed-loop operation is used to adjust the timing or amplitude of the deceleration current to maintain consistent end of motion time.

Advantages of the embodiment include:1. Compliance with new, more restrictive customer specifications on injector shot-to-shot variations to meet new emissions requirements.2. Compliance with new more restrictive customer specifications on injector shot-to-shot variations between injectors to meet new emissions requirements.3. Increased injector life with improved stable performance over the increased life.