This invention relates to an improved fuel injector apparatus which includes a displacement sensor.

Fuel injectors are well known as an apparatus for introducing fuel into an internal combustion engine, permitting a high degree of control of the timing of the fuel injection into the engine as well as the quantity of fuel injected.

A fuel injector is a valve which may be opened and closed under command of a central control unit. A typical fuel injector is shown in Figures 14(a) and (b) and comprises an injector body which houses a control piston. The control piston is connected at one end to an injector needle that has a tip which in a closed position of the fuel injector is pressed onto an outlet port by the control piston, blocking the outlet. When in an open position, the control piston is retracted which in turn allows the needle to move away from the outlet. In this position, high pressure fuel that is present within the body of the fuel injector may pass though the outlet port to enter the combustion chamber of the internal combustion engine. In a diesel engine, for example, the injector will initially provide a pilot injection of fuel followed by a main injection, the two occurring during each combustion cycle. Movement of the control piston is typically achieved passing a current through a coil that surrounds a part of the control piston, the coil and control piston together forming a solenoid.

For high efficiency of the combustion engine, it is desirable to have a high level of control of the fuel injector and hence the amount and timing of a fuel injection. For this it is known to be beneficial to measure the displacement of the needle of the fuel injector. Various arrangements have been proposed for taking such measurements. Conventional wired sensors are generally considered impractical as there is a minimal accessibility to the needle vicinity, making it difficult to take the signal wires out of such position. The high pressure acting within the injector body makes it a hostile environment for taking direct measurements.

For this reason, so far the sensors developed for this purpose detect the movement of the control piston motion rather than the needle movement directly. Such methodology is justifiable by the fact that control piston and needle always remain in contact.

Eddy current sensors are commonly used to measure the position of the control piston, but the scientific literature clearly showed their inadequacy, given the presence of electromagnetic disturbance. This phenomenon can be accredited to the current pulse delivered to the injector solenoid coil. Electromagnetic fields arise from these currents and concatenate with sensor voltages, affecting strongly the data acquisition and causing frequent the loss of data.

An object of the present invention is to provide a fuel injector apparatus that includes a displacement sensor which may in at least one arrangement enable the accurate measurement of the displacement of the control piston within the fuel injector apparatus during use.

According to a first aspect the invention provides a fuel injector apparatus of the kind comprising a fuel injector having a fixed body and a movable part that is located at least partially within the body and in use is movable to open and close an outlet port of the injector, the fuel injector apparatus further comprising a displacement sensor for the measurement of the displacement of the movable part of a fuel injector relative to the fixed body of the fuel injector, the displacement sensor comprising:

A light source;

A detector that has a detection area which is sensitive to light and which generates an output signal having a value that varies as a function of the amount of light that is incident upon the detection area of the detector; and

an optical waveguide which has a first end that in use receives light from the light source and a second end through which the light exits as a light beam, and in which the optical waveguide is fixed to the movable part of the fuel injector such that movement of the movable part of the fuel injector causes relative movement of the second end of the optical waveguide relative to the detector thereby varying an amount of overlap between the light beam and the detection area of the detector.

The apparatus in use will vary the amount of light incident on the detector by moving the second end of the waveguide which in turn varies the output of the detector, enabling the position of the movable part to be determined. The amount of overlap of the light beam onto the detection area of the detector may vary from zero overlap where the illuminated area of the light beam output from the optical waveguide does not align with any of the detection area to a complete overlap where all of the light from the light beam is incident on the detector, or a complete overlap where all of the detector area receives light. The latter case will arise if the detector region is smaller than the illuminated region of the light beam.

The optical waveguide may emit a conical light beam such that the area of the detection are that is illuminated by the beam is dependent on the distance between second end of the optical waveguide and the detector, and in use the second end may be moved by the moving part of the injector to generate substantially a translational movement of the second end of the waveguide relative to the detector, in turn causing the light beam to be translated relative to the detector. In use this translation movement scans the beam to and fro across the detector as the moving part reciprocates within the body of the injector apparatus.

The optical waveguide may comprise an elongate optical cable or other light waveguide, the function being to carry light from the first end to the second end.

The second end of the optical cable may have a circular perimeter such that the light beam in a plane containing the optical detector covers a circular area.

The detection area of the detector may also be circular and may have a diameter substantially equal to the diameter of the light beam in the plane of the detector area. Of course, other shapes can be provided and the shape of the detector and the sensitivity of each part of the detector will determine the way the output signal varies with relative movement of the beam and the detector. Through suitable selection of beam profile and detector size and sensitivity a substantially linear output with the position of the moving part may be provided.

The sensitivity of the detector may therefore be substantially uniform over the whole of the detector area but may not be uniform, and similarly the pattern of light distribution within the light beam. The second end of the optical waveguide may be supported such that it faces directly towards the detector and in use translates in a direction parallel to the face of the second end of the optical waveguide.

The movable part of the fuel injector may comprise a fuel injector control piston which may be connected to a fuel injector needle. This enables the displacement sensor to directly measure the movement of the control piston and from that the movement of the needle.

The control piston may comprise an elongate cylindrical element which moves axially within a complimentary elongate bore provided in the fixed injector body, and a portion of the optical waveguide adjacent the second end may pass through at least one opening in one of the control piston and fixed body.

Preferably the waveguide is elongate and passes through holes in both the body and the cylindrical element.

The optical waveguide may be secured to the control piston so that any axial movement of the control piston during use of the injector, as required to open and close the injector, causes a translational or other movement of the optical waveguide.

To allow the waveguide to move freely with the control piston, it may pass through one or more openings in the injector body sized such that the injector body does not impede the movement of the second end of the fibre induced by movement of the control piston.

The width of each opening may be substantially the same as the width of the waveguide so as to allow the waveguide to move up and down in the direction of movement of the needle but not to move from side to side.

The length of each opening may be chosen to exceed the expected range of travel of the injector needle. For example, if the needle has 0.5mm of travel openings that are lmm in length may be chosen.

In a most preferred arrangement, the injector body may include two openings or through holes with one on each side of the control piston, the opening on the side closest to the second end of the cable being oversized to permit movement of the fibre, and the optical waveguide extending through both openings.

Where the optical waveguide passes through an opening in the body furthest from the second end of the optical waveguide the fibre may be rigidly secured to the body at that opening. For instance, the optical waveguide and opening may be complimentary so that the waveguide is a snug fit with the optical waveguide.

When secured in this manner, a portion of optical waveguide between the opening in the body furthest from the second end of the optical waveguide and the second end of the waveguide may be flexible to allow the optical waveguide to move with the control piston.

The fuel injector apparatus may be configured such that such that movement of the movable part generates a larger movement of the second end of the optical waveguide.

In one preferred arrangement the assembly may be arranged such that the waveguide pivots or otherwise deforms about a pivot point or fulcrum, , such that movement of the movable part generates a larger movement of the second end of the optical waveguide.

The fulcrum about which the optical waveguide pivots may be located on the opposite side of the movable part to the detector. In a preferred arrangement the waveguide may pivot about the region where it passes through opening in the body furthest from the second end of the optical waveguide.

Alternatively, the waveguide may be considered to pivot about the region where it is secured to the control piston, portions of the guide extending one way to the second end and the other way towards the first end being considered to be the two arms of the lever.

The shape of the through hole on the injector body may be characterized by a slot, so to enable the motion of the end of optical waveguide. The optical waveguide may pass through the control piston in a direction that is orthogonal to the long axis of the control piston.

The apparatus may include a support element that includes a groove or channel which is located at the detection region of the detector and receives the second end of the optical waveguide. The support element may restrain the optical waveguide so that it is free to move in the axial direction of the control piston as the control piston is operated but prevented from moving orthogonal to that. This helps control the overlap of the light beam and the detection region of the detector.

The optical waveguide may be flexible to permit relative movement between the first end and the second end. In use, the optical waveguide may bend as the movable portion moves.

The optical waveguide may comprise one or more elongate optical fibres or may comprise a bundle of optical fibres arranged in parallel. Where there is more than one fibre, every fibre may transmit light which forms a part of the light beam, end faces of every fibre together forming the second end of the optical waveguide.

The fibre may comprise a continuous length optical fibre between the first end and the second end.

The optical source and optical detector may be provided on a single electronic circuit board in a common housing.

In a most preferred arrangement the light source may comprise a light emitting diode, or a laser diode or a laser source.

The detector may comprise a photodetector that is sensitive to light at the frequency emitted by the light source.

The detector may comprise a single detector element, or may comprise multiple detector elements. Where there is more than one element, each detector element may have a detection area which forms part of the overall detection area of the detector and may generate an output signal having a value that varies as a function of the amount of light that is incident upon the detection area of the detector device.

To minimise contamination it is preferred that the second end of the light waveguide is supported in close proximity to the detector, ideally with nothing between the second end and the detector. It is also preferred that the length of optical waveguide extending from the control piston to the second end is kept as short as possible.

For convenience, the optical waveguide may protrude from the body of the injector but it is within the scope of this invention for it to be located within the body, or within the control piston. In some arrangements of the invention one or more or all of the light source, the detector, the first end and the second end of the light guide may be located within the injector body.

There will now be described, by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which:

Figures 1 a illustrates the key components of the sensor device of an embodiment of a fuel injector apparatus within the scope of the invention

Figure lb is an enlarged view of a part of the apparatus of Figure lb showing the side of the injector body facing the detector;

Figure 2 is a similar view to figure lb showing the side of the injector body furthest from the detector;

Figure 3a is a view corresponding to Figure 1 that is partially cut-away to show the route taken by the optical cable through the body and the control piston;

Figure 3b is an enlarged cut-away view of a part of the injector body and control piston showing the holes the optical cable passes through;

Figure 4 shows the intersection of the beam emitted from the second end of the optical cable and the detector; Figure 5 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection. Injection pressure = 1400 bar, Energizing time = 2000 microseconds, Backpressure = 20 bar.

Figure 6 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Main injection. Injection pressure = 1000 bar, Energizing time = 2000 microseconds, Backpressure = 80 bar.

Figure 7 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Main injection. Injection pressure = 1000 bar, Energizing time = 2000 microseconds, Backpressure = 20 bar.

Figure 8 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Main injection. Injection pressure = 400 bar, Energizing time = 2000 microseconds, Backpressure = 20 bar.

Figure 9 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Main injection. Injection pressure = 400 bar, Energizing time = 2000 microseconds, Backpressure = 40 bar.

Figure 10 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Pilot Injection. Injection pressure = 1400 bar. Energizing time = 400 microseconds, backpressure = 95 bar

Figure 11 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Pilot injection. Injection pressure = 750 bar, Energizing time = 650 microseconds, Backpressure = 20 bar Figure 12 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Pilot injection. Injection pressure = 1000 bar, Energizing time = 650 microseconds, Backpressure = 40 bar.

Figure 13 is a graph showing both the current and needle lift over time as measured using an exemplary apparatus in accordance with the inventions for a Main injection Pilot injection. Injection pressure = 1400 bar, Energizing time = 150 microseconds, Backpressure = 95 bar;

Figure 14 (a) is a cutaway view of a typical prior art fuel injector without a sensor prior to an injection event and (b) during an injection event; and

Figure 15 is a schematic of a sensor circuit including an optical source and a light sensitive detector

Figures 14 (a) and (b) shows a typical fuel injector 100 to which the present invention may be applied. The fuel injector comprises a fixed body 101 and a movable part 102 that is located at least partially within the body and in use is movable to open and close an outlet port 103 of the injector. The body as shown is generally cylindrical with a relatively large inlet 104 for high pressure fuel at one end and the very small outlet port 103 at the other end. The interior of the body defines a bore within which is slidably received a control piston 105 of the movable part 102. The control piston 105 is biased away from the outlet port 103 by a return spring 106, and an injector needle 107 which forms part of the movable part 102 extends from the control piston 105 towards the outlet port.

In an open position the control piston 105 pulls the needle 107 away from the outlet port 103 allowing high pressure fuel to be ejected from the fuel injector. In a closed position the control piston 105 presses the needle 107 onto the outlet port 103 to block it. In the example shown the movement of the control piston 105 is affected by passing a current through a coil 108 formed in the inner wall of the body that surrounds the control piston. The control piston 105 and needle 107 together be considered to represent the movable part of the fuel injector within the scope of this description, although the control piston alone could also be considered to be the movable part.

Figure 2 shows conceptually the arrangement of a fuel injector apparatus 10 within the scope of the present invention. This comprises a fuel injector 20 of the kind shown in Figure 14 (or any other kind of fuel injector) and a displacement sensor 30 for the measurement of the displacement of the movable part of a fuel injector such as the one shown in Figure 1. Only the body 4 of the fuel injector is shown in these figures and the skilled person will understand that the remaining parts will be as shown in Figure 14 or a similar arrangement. Of course, the invention is not to be limited to the arrangement of parts shown in Figure 14 and will apply to a variety of different forms of fuel injector.

The displacement sensor 30 comprises three main parts. An exemplary implementation of the sensor 30 is shown schematically in Figure 15 or the accompanying drawings. A light source 1 is provided that in use emits light of a fixed wavelength of set of wavelengths. The light may be visible or infra-red light or a mixture. A detector 2 is provided that has a detection area and which generates an output signal having a value that varies as a function of the amount of light that is incident upon the detection area of the detector 2. The detection area can be seen in Figure 4. Importantly, the detector 2 must be sensitive to at least one of the wavelengths contained in the light emitted by the light source 1. The sensor 30 also comprises an optical waveguide in the form of a single continuous length of dielectric optical fibre 3 which has a first end 3a that in use receives light from the emitter and a second end 3b through which the light exits as a light beam over an illuminated area. The beam of light will exit as a cone which subtends an angle determined by the refractive index of the optical fibre. When incident upon a plane that is parallel to the face of the second end of the fibre the light beam will appear circular. This is shown in Figure 4.

As can be seen, the optical fibre 3 is supported such that the second end faces the detector 2, and is held in place by a guide 9.

To detect movement of the movable part of the fuel injector, a portion of the optical fibre 3 is fixed to the control piston 4 of the fuel injector 20 such that movement of the control piston 5 of the fuel injector 20 causes relative movement of the second end 3b of the optical fibre 3 and the detector 2 thereby varying the amount of overlap between the detection area and the illuminated area. This overlap is shown in Figure 4, and will vary as the relative position of the centres C changes.

The connection of the optical fibre 3 to the control piston 5 can best be seen in Figure 3. The optical fibre 3 is placed into two through holes 6 machined on the control piston 4 and two through holes 7, 8 of the injector body 4. The through holes 6 of the control piston 5 are circular. The shape of the hole 7 on the injector body that is closest to the detector 2 is characterized by a slot, so to enable the motion of the end of optical fibre 3 by bending of the fibre 3.

The other hole 8 on the injector body is circular. As the injection commences, the control piston drags the optical cable 3 up, forcing the cable to move along the vertical slot 7 machined on the injector and receiver cylinder 9. Such cylinder is placed in the cavity of the receiver 3 detecting the motion of the optic cable end 3. The slot width is equal to the optical cable diameter. The Figures 3(a) and 3 (b) illustrate the overall layout of the exemplary sensor.

The reciprocal motion of the control piston 5 during a fuel injection causes the misalignment between the second end 3b of optical fibre 3 and the portion of the detector 2. In the example, an upward motion of control piston 5 results in the increasing alignment between the end of the optical cable 3 and the receiver portion devoted to detect the light intensity. The output signal from the detector will then increase in value. Then, the light intensity and related voltage tend to return to the initial values as the control piston begins its downward motion for injector closing stage. As shown in Figure 4, from a geometrical point of view, the mutual position between the end of optical fibre 3 and detector 2 generates an intersection area, which is indicative of the position of the control piston 5.

The variation in intensity of the light signal passing through such intersection area provides an indication of the control piston displacement. The light intensity is linearly proportional to the voltage output by the detector. Such voltage is in turn linearly proportional to the detected control piston displacement. A robust experimental campaign has been carried out in order to proof the reliability of the sensor. An exemplary sensor was constructed using a single strand of optical fibre which illuminates a single photodetector, light being received by the fibre from a suitable optical source. Figures 5 to 13 show that the exemplary sensor is able to detect all injector events, including Main injection events and Pilot events as well as post injections events. The solid trace in each graph indicates the current applied to the injector and the dashed trace indicates the needle lift as indicated by the output of the sensor. Moreover, the sensor has been proven to be able to detect also the smallest needle displacements.

Furthermore, the tests showed the difference both in needle displacement and injection duration, though the same injection pressure and energizing time. Such discrepancy is accredited to the backpressure, which exerts a strong influence on the rate of momentum transferred by pressurized fuel to the needle as the injection commences. Therefore, it is presumable that low backpressure causes the momentum, transferred from pressurized fuel to the needle, to be wasted in the delivery chamber of the injector, engendering a slower needle lift, though high injection pressure and energizing time.

The assessment of the injection characteristics is a key step for the analysis of spray morphology, which in turn affects the combustion quality. At this regard, the needle lift measurement is of great importance for an accurate study of the injection process, given the strong influence exerted on in-nozzle cavitation and on the injected flow rate. Therefore, the needle lift is a key parameter for the increased understanding of the injection process. In this respect, the proposed technique represents a step ahead towards the real time control of the injection process. Furthermore, the presented invention enables injector diagnosis. The experimental campaign revealed that the sensor detects satisfactorily both single and multiple injections. The experimental tests was carried out varying the injection pressure and energizing time, performing various injection scenarios. This makes the proposed sensor an ideal tool for the research field concerning any fuel injector or for use as a diagnostic tool for evaluating hardware in the loop.