A method of controlling a solenoid operating fuel injector

Abstract

A method of controlling a fuel injector, said injector including an electrically controlled actuator, said actuator adapted to control a needle valve by the movement of a needle to and from a valve seat of said needle valve, said method comprising : a) determining for said fuel injector, a plot of fuel quantity delivered (Q) by said fuel injector against the pulse width of an actuator actuation pulse sent to said actuator; b) providing a modified plot of fuel quantity delivered by said fuel injector against the pulse width of the actuator actuation pulse based on the plot of step a); c) using said modified plot to subsequently control activation of said fuel injector; wherein step b) comprising the steps of d) identifying spoons regions in said plot of step a), and e) reproducing the plot of step a) without any data from the spoon regions of the plot of a).

Description

TECHNICAL FIELD

[0001] This application relates to a method of controlling a solenoid controlled fuel injector. It has particular but not exclusive application to direct acting fuel injectors and solenoid actuated fuel injectors. It relates further to a method of applying trim in the control of a fuel injectors.BACKGROUND OF THE INVENTION

[0002] Modern fuel injectors typically use electrical actuators (such as piezo or solenoid operated actuators) which are used to operate a needle valve, the valve opening and closing in order to dispense fuel to a combustion chamber via movement of a needle of a needle valve away from a seat. Typically an activation pulse(s) of certain duration (pulse width) is sent to the electrical actuator (e.g. solenoid actuator) operate the fuel injector. The quantity of fuel injected into a combustion space is dependent on the duration of the pulse(s). Fuel injectors may be of the type where the actuator directly moves a pintle / needle (arrangement) away from the valve seat to dispense fuel; e.g. against the biasing spring means; this is referred to as a direct injector, and such injectors are used for both gasoline and diesel. Note typically the actuator is adapted to move a pintle / needle arrangement where a needle is connected to the pintle as is well known in the art and reference to a pintle can be interpreted as reference to a needle and vice versa. The invention has particular application to such direct injectors. The actuator may be solenoid or piezo controlled actuator. An example of fuel injector control method is shown in DE-A- 10 2006 009920.

[0003] In an alternative design many modern fuel injectors are hydraulically operated in that rather than the (e.g. solenoid) actuator actuating the needle directly, the actuator to operate a hydraulic valve (system) so as to control pressure in the fuel injector so as to indirectly move the needle from the valve seat so as to selectively dispense fuel.

[0004] Such (e.g. gasoline) injectors are is compensated over time doing learning, analyzing behavior, computing correction values and applying these trims during subsequent injector operation. This strategy is called ICLC (Injector Close Loop Compensation)

[0005] Most injector control doesn't consider physical pintle rebound of gasoline injector resulting in "spoons" which are spoon shaped regions or "dips" which occur in the plot of pulse length against fuel injected. These occur in the plot at the beginning of pulse duration which leads to full lift area in injector flow curve (pulse versus flow delivery curve) or later. The term "spoon(s)" should be construed hereinafter to mean one or more dips or spoon regions in the plot of fuel delivered Q against (activation) pulse duration (sent to an e.g. solenoid actuator) from the first timepoint where the fuel delivered decreases with marginal increase in pulse duration, until the time point where with further increase in pulse duration brings the amount of fuel delivered Q back up to the (local) peak value it has at the first timepoint i.e. before falling.

[0006] In ECU control of fuel injection, spoons cause problems as more than one pulse width applied to the injector in the spoon area will lead to the same fuel delivery which makes control difficult. It is preferable to have just one quantity linked to one pulse duration and no more. In order to overcome such problems, for the purposes of control, a fuel quantity (delivery) against (e.g. solenoid) pulse width control chart or plot (e.g. stored in the ECU as a MAP or relationship) is provided, where the plot is such that with increasing pulse width, the injected fuel quantity only increases i.e. it increased in the plot monotonically. So, the injector behavior is then mapped using a monotonic pulse versus fuel quantity curve in order to fulfill this condition.

[0007] Such a modified monotonic curve / plot is then used for ICLC trims determination (pulse corrections). This can be done by e.g. making a comparison with a target behavior (called MASTER) at some given fuel delivery learning points (ICLC breakpoints).

[0008] The monotonic curve is thus mandatory to determine ICLC trim, but the physical behavior of this injector is somewhat different because of the assumptions made by producing the monotonic curve. This difference is not compensated for and gives a local error

[0009] At the end, this phenomenon leads to a poor ICLC performance in this specific area, whatever the number of ICLC quantity learning point is selected.

[0010] The usual approach to overcome such problems is to minimize this effect by injector hydraulic optimization which can cause higher part to part sensitivity or requires excessive force margin and hydraulic damping.

[0011] It is an object of the invention to overcome such problems.SUMMARY OF THE INVENTION

[0012] In one aspect is provided a method of controlling a fuel injector, said injector including an electrically controlled actuator, said actuator adapted to control a needle valve by the movement of a needle to and from a valve seat of said needle valve, said method comprising : a) determining for said fuel injector, a plot of fuel quantity delivered (Q) by said fuel injector against the pulse width of an actuator actuation pulse sent to said actuator; b) providing a modified plot of fuel quantity delivered by said fuel injector against the pulse width of the actuator actuation pulse based on the plot of step a); c) using said modified plot to subsequently control activation of said fuel injector; wherein step b) comprising the steps of d) identifying spoons regions in said plot of step a), and e) reproducing the plot of step a) without any data from the spoon regions of the plot of a).

[0013] The plot produced in step d) may have gaps in the regions of the spoon(s). That is to say there may be no data in the stored relationship / MAP / plot in these regions.

[0014] The spoon regions are indicative of a pintle / needle rebound.

[0015] Step c) may comprise comparing data from plot produced in step b) with data from a reference plot, in order to determine trim data for said subsequent control.

[0016] Said actuator is a solenoid controlled actuator or a piezo controlled actuator.

[0017] The term stored "plot" or "curve" (e.g. with regards to fuel quantity Q delivered against (actuator) pulse width) can be construed as relationship data related parameters (e.g. a stored relationship)BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 shows a plot / curve of pulse width applied to a solenoid of a solenoid actuated fuel injector; Figure 2 shows such a monotonic curve / plot based on the figure 1 plot; Figure 3 shows control dependent on nominal (e.g. ideal) fuel injector response; Figure 4 illustrates errors in the plot of figure 2; Figure 5 shows the relation of fuel error with fuel demand; Figure 6 and 7 illustrates examples of the invention; Figure 8 illustrates identification of spoon regions; Figure 9 shows the improved results of examples of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As mentioned, an ECU control, spoons cause problems as more than one pulse width applied to the injector in the spoon area will lead to the same fuel delivery which makes control difficult.

[0020] Figure 1 shows a plot / curve 1 of pulse width applied to a solenoid of a solenoid actuated fuel injector and the consequential fuel quantity injected with respect to a typical injector. It should be noted that aspect of the invention are equally applicable to injector with piezo actuators rather than solenoid actuators.

[0021] As can be seen there may be one or more spoon regions 2 where the fuel quantity dips for a marginal increase in pulse width. The main spoon area is shown with reference numeral 2a.

[0022] To recap, in order to overcome such problems, for the purposes of control, a fuel quantity (delivery) against pulse width control chart / plot (e.g. stored in the ECU as a MAP) is provided, where the plot is such that with increasing pulse width the injected fuel quantity only increases i.e. it increased in the plot monotonically . So, the injector behavior is then mapped using a monotonic pulse versus fuel delivery (quantity Q) plot / curve in order to fulfill this condition. Figure 2 shows such a monotonic curve / plot 3, superimposed with the plot 1 of figure 1.

[0023] This modified monotonic curve is then used for control of the injector, for example for ICLC trims determination (pulse corrections) making a comparison with a target behavior (called MASTER) at some given fuel delivery learning points (ICLC breakpoints). Figure 3 shows such control where reference numeral 4 refers to a nominal (e.g. ideal) fuel injector response.

[0024] The trims to be applied are shown as arrows 5.

[0025] The monotonic curve is mandatory to determine ICLC trim, but the physical behavior of this injector is the curve 1. This difference is not compensated and gives a local error shown by the shaded areas 6 in figure 4 (ref. numerals as before).

[0026] Figure 5 shows the relation of fuel error with fuel demand; errors which are prevalent in the spoon area shown by broken oval 7. At the end, this phenomenon leads to a poor ICLC performance in this specific area, whatever the number of ICLC quantity learning point is selected.Invention

[0027] In general, in aspects of the invention the problem of poor ICLC performance at the beginning of full lift is solved by spoon avoidance.

[0028] The inventors have determined that the problem and solution may be formulated as being a goal is to create a system with a pulse versus quantity characteristic avoiding spoon area and staying monotonic at the same time.

[0029] In prior art methodology , the monotonic pulse / quantity curve used all the pulse widths to provide the desired fuel quantity within the fuel quantity / width (reference curve)

[0030] Instead according to general aspects, when determining a pulse width to be applied to a fuel injector for a certain quantity fuel, certain areas of the curve / plot 3 are avoided. So namely, the spoon area(s) / regions are avoided, and no such pulse areas (within spoon) are used, as there is no other pulse width which gives the same required fuel quantity. This is effectively performed by producing and storing (e.g. in the ECU) a modified plot of fuel quantity against pulse duration, which is based on the actual plot but with (data) section effectively removed from the plot; the resulting plot is thus still monotonic. This modified plot is then used for control /

[0031] Figure 6 and 7 illustrates the invention. Figure 6 shows a plot of the fuel quantity against pulse curve (without monotonic correction) 1 as before. The spoon regions (designated by reference numeral 8). In examples of the invention, a new curve / plot 9 is created which does not include any data in these spoon regions 8. Thus, a new (inherently monotonic) curve 9 as in figure 7 is provided (essentially with gaps 10 along the regions 8 of the spoons), but this does not matter as a pulse width can still be demined for any fuel delivery quantity.

[0032] The new curve (pulse / quantity characterization) is, by thus by definition, monotonic, and will give only one pulse for one quantity. Due to this when using such a plot 9 for control, some pulse widths will be avoided in order to avoid spoons and then quantity rebound i.e. pintle / needle; rebound. Pulse avoidance can be done using optimal adapted ICLC learning points. With two specific learning points, one placed just before the removed area, and one placed just after, the pulse length will jump to the next useful pulse length

[0033] Spoon areas can be detected by a more precise analysis of Hydraulic Opening (HO) (which is directly related to fuel quantity delivered) measurement versus pulse width, looking at negative slopes. Size (pulse width length) and amplitude (HO amplitude) of each spoon are recorded in order to perfectly know each spoon of each injector. Figure 8 shows an example of a plot showing three spoons (spoon 1, spoon 2, spoon 3 ) of varying parameters. HO is the time between needle valve opening and closing and the skilled person would be aware of various methods to determine these.

[0034] Individual Y-axis (delivery / HO axis) for ICLC can be determined for each injector, for the start and the end of each spoon. That will avoid using unwanted pulse widths (which may be regarded as the time the actuator or on (e.g. at a high-level Ton) and create a single pulse width to Delivery answer perfectly fitted to the injector characteristic. Deliveries between the two horizontal lines are forbidden and rounded to the closest allowed point.

[0035] As a result, ICLC performance on spoon is highly improved. Optimization is done per injector, increasing also ICLC efficiency. Figure 9 shows the relative error using aspects of the invention; to be compared with that of figure 5.

Claims

1. A method of controlling a fuel injector, said injector including an electrically controlled actuator, said actuator adapted to control a needle valve by the movement of a needle to and from a valve seat of said needle valve, said method comprising : a) determining for said fuel injector, a plot of fuel quantity delivered (Q) by said fuel injector against the pulse width of an actuator actuation pulse sent to said actuator; b) providing a modified plot of fuel quantity delivered by said fuel injector against the pulse width of the actuator actuation pulse based on the plot of step a); c) using said modified plot to subsequently control activation of said fuel injector; wherein step b) comprising the steps of d) identifying spoons regions in said plot of step a), and e) reproducing the plot of step a) without any data from the spoon regions of the plot of a).

2. A method as claimed in claim 1 wherein the plot produced in step d) has gaps in the regions of the spoon(s).

3. A method as claimed in claims 1 or 2 where the plot of step b) is monotonic.

4. A method as claimed in claim 3 were spoon regions are indicative of a pintle / needle rebound.

5. A method as claimed in claim 1 to 4 where step c) comprises comparing data from plot produced in step b) with data from a reference plot, in order to determine trim data for said subsequent control.

6. A method as claimed in claim 1 to 5 wherein said actuator is a solenoid controlled actuator or a piezo controlled actuator.

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