Field of the Invention

This invention relates to actuators such for fuel systems and has particular but non-exclusive application to fuel injectors which are actuated

electronically/electrically under control of, e.g., an Engine Control Unit. The actuators may be solenoid controlled valves.

Background of the Invention

Typically fuel injectors are controlled by electrically actuated valve systems such as solenoid or piezoelectric valve actuators. Such fuel injector systems are controlled by the ECU sending electrical pulses to the actuator, generally the length of which controls the valve opening times.

Without any additional boost injection drive for the ECU, the injectors opening is susceptible to voltage fluctuations from the battery side, due to power consumption by other vehicle components and systems. The inventors have determined that, as a consequence, it may take a (variable) amount of time for the current through the actuator to achieve a certain level, and thus

consequential adequate opening of the valve.

It is an object of the invention to overcome such problems. It is a further object of the invention to improve the injection shot-to-shot performance and therefore engine stability.

Statement of the Invention

In one aspect is provided a method of controlling an electrically/electronically operated actuator for a fuel system or component thereof, wherein in operation said actuator is supplied with electrical pulses, and wherein for each actuation cycle, said actuator is supplied with at least one pulse of duration T _end

comprising: determining the time Tp taken for the current through the actuator to achieve a threshold value, and varying the pulse duration T _end dependent on the value Tp.

The actuator may be a solenoid operated valve.

The actuator may be part of a fuel injector so that in one aspect is provided a method of controlling an electrically/electronically actuated fuel injector where an actuator is supplied with electrical pulses in order to operate said fuel injector, and wherein for each injection cycle, the fuel injector is supplied with at least one injection pulse of duration T _end comprising: determining the time Tp taken for the current through the actuator to achieve a threshold value, and varying the pulse duration T _end dependent on the value Tp.

The method may comprise determining the difference between a currently determined value of Tp and a reference value, Tref, where the reference value Tref is based on one or more values of T determined previously, and varying the pulse duration based on this difference.

Said reference value Tref is preferably based on a moving average of the previous N determinations of Tp.

The pulse may be varied dependent on a percentage of this said difference.

The value of current may be determined from measuring a current or a voltage signal. The signal may be filtered.

The method may be performed per injection and/or per cylinder

The method may be applied to one or more pulses of a multi-injection system. The method may be performed for one particular pulse and the other pulses in an injection cycle of a multi-injection system are varied based on the Tref determined for that one particular pulse. The said particular pulse is the first or pilot pulse.

The electrically/electronically actuated fuel injector may include a solenoid or piezo actuated valve, for example, but the methodology may be applied to any fuel injector.

The invention is also applicable to controlling actuators (valves) in any fuel delivery system or components thereof. For example the methodology can be applied to common rail or other systems, where pulses are sent to actuators (valves) typically used for control of pressure in common rail or any fuel accumulator volumes, or other portions of such systems. Typically in common rail systems, there is a (digital) inlet valve for common rail pressure control on a low pressure side of a pump and sometimes a (digital) high pressure valve on the high pressure side, on rail); the methodology can be applied to such solenoid actuators.

An advantage of the invention is that the need in some cases for a boost supply to stabilise the voltage is not required, and in some examples, the deviation of opening of a actuator valve is compensated for by adjusting the closing.

Brief Description of the Drawings

The invention will now be described by way of example and with reference to the following figures of which:

Figure 1 shows a plot of current pulse applied to a fuel injector valve actuator over time; and Figure 2 compares the results showing variation in the quantity of fuel delivered with and without implementation of an example of the invention.

Detailed description of Examples

Figure 1 shows a plot of current against time for an injector. The time T shows the time for the current to ramp up to a threshold value; the threshold value may be pre-set. As can be seen during this ramp -up time the current measured increases in a fairly steady fashion. During this time the injector valve will start to open. Dependent on the design parameters and control function, no or little actual fuel injection may take may be place as a result of the current not being high enough for the actuator to overcome forces and open the valve to the required amount.

At time T the desired current is achieved. As can be seen, there may be fluctuation in the current as a result of actuation of the valve and the functional characteristics of the electrically operated valve and system. Power /current is then stopped and a point Tend, this is the nominal end of the pulse duration.

In one general example of the invention, the time, T, required for the current supplied to injector (the time for the current through the actuator) to achieve a current threshold, is monitored. Dependent on this, a compensation strategy is implemented which may be "on-the-fly", e.g., by varying the pulse length for a particular cycle based upon this value of T (that for the same cycle).

In a preferred embodiment, the pulse length is varied based on the difference between the present time for the current through the actuator to achieve a current threshold (Tp) and a stored threshold or that value or values of T computed previously, the latter of which can be referred to as Reference Time (Tref). In a further preferred embodiment the pulse length is varied based on the difference between the present time for the current through the actuator to achieve a current threshold (Tp) and that T determined from N previous cycles. Thus the variation to pulse length can be based on the difference between present value Tp and that value of T computed from the average value of T with respect to the previous N cycles (=Tref), i.e. the Reference Time (Tref) is a moving average.

Differences between the present value of T (Tp) and the Reference Time may be scaled by a factor (e.g. multiplier k) to determine the amount of adjustment to the pulse length.

Example 1

In a simple embodiment, methodology reads the time on the pulse at a given threshold, in other words determines the time T to achieve a certain (e.g. pre- determined) current (threshold) for the present injection, (i.e. injection currently being performed). This current may be determined by measuring current directly by appropriate circuitry or by determining the voltage with impedance. The voltage or current signal may be filtered in order to filter out small perturbations or fluctuations thereof. The pulse length applied to the injector is then adjusted, e.g. for the present or next/following injection (of the next cycle) dependent on the difference between this time Tp and a Reference Time, Tref. The reference time, Tref , may be one based on the value of T (Tp) from previous injections. In a preferred embodiment, the methodology determines the difference between the currently measured time Tp and a Reference Time (Tref ) which is based on one or more previous values of T, such as the average value of T for the previous N injections/cycles. Generally the longer the difference between Tp and Tref, the longer the pulse length will be made. This total length of the actuation pulse is generally set by the ECU dependent on the operating parameters for the engine. An example of this preferred embodiment will now be described.

Example 2

In case of single injection per cycle, during the 10 first injections, the time to reach the current threshold is measured, and then averaged to provide a

Reference Time, Tref. Thus this may be regarded as a "filtered" measurement of a stable value of the time to reach current threshold. On the 11 ^th injection, the current time (or instantaneous time) to reach the current threshold is again measured. The correction strategy is then applied to the pulse length (of the 11 ^th injection). The time to perform the calculation is very short and far less than the pulse length, and so the adjustment can be made "on the fly" i.e. for the same pulse that is being measured. So the adjustment is based on the difference between the current time (or instantaneous time) of the 11 ^th injection and the reference time (average value of the 10 previous measurements). Alternatively the adjustment is made to the pulse(s) that follows the one for which the value of T is measured (e.g. in the example the 12 ^th injection). Preferably the correction to the pulse length is based on a percentage of the difference and the Reference Time.

For the next injection (12 ^th ), the reference time is computed as the average value of the injection from 2 ^nd to 11 ^th The present time for the current to achieve the threshold is determined for the time to reach current threshold of the 12 ^th injection. A consequential pulse length correction applied on 12 ^th injection based on the difference between the current time (or instantaneous time) of the 12 ^th injection and the reference time (average value of the 10 previous measurement from 2nd to 11th). Preferably the correction is based on the percentage of this difference and the Reference time

So in general terms, the pulse length is adjusted (on the fly) based upon the time difference between Tref and the time for the current to reach the current threshold Tp in the present cycle. This difference may be scaled by a multiplier k. This multiplier k depends on physical parameters optimized by tests and simulations.

So in summary, mathematically in a simple embodiment, the adjustment to pulse length is At _pu i _se where At _pulse = f (Tp-Tref)

Tref is based on one or more values of T previously determined and preferably the average of the previous N values.

Preferably the adjustment is multiplied by a factor k

A ise = k* (Tp-Tref)

Calculations are preferably made per kind of injection (pilot or main or post) and per injector/cylinder.

The invention is also applicable to systems where there are multiple injections per cycle. In one such embodiment each injection pulse is treated separately as above; thus each injection pulse will have its own Tref and this monitored and the pulse for each injector varied as above.

In an alternative embodiment, one of the injection pulses (e.g. the first / pilot injection pulse) is used as a common reference i.e. the Tref is determined based on this and the pulse duration for all pulses varied dependent on this (e.g. other pilots main and post injection pulses). This is preferable done on an injection train/cylinder basis. This embodiment has the advantage that to counter the fact that many correction strategies can only be based on the first injection of a pulse train. In this case, compensation may be applied to the methodology to counter the effects of Eddy current effects.

Figure 2 shows the results of comparison testing for a double injection pattern at high pressure (1800 bar) at an engine speed of 2000rpm and where the voltage source is subjected to a high frequency power fluctuation of +/_ X volts at a frequency of 258Hz at 11 V. The first plot shows the variation fuel delivered without any methodology according to the invention and the plot on the right shows the variation in fuel delivered implementing the (Time to Reference) strategy according to one example. As can be seen the variation in the fuel delivered has been reduced by a third when implementing the strategy according to this embodiment; thus the shot to shot performance has been reduced by three. In general shot to shot (variability) is reduced for high frequency noise on the injector supply voltage with an average 50% shot to shot reduction compared to current methodology. The methodology according to example so the invention provides a system which obviates the need for expensive boost injector drive ECU about shot to shot improvement.