This invention relates to circuitry for fuel injectors and specifically for injectors which include an injector switch. Such injectors switches comprises effectively two injector components which move relative to each other such that they come into and out of contact with each other. Circuitry connected to such injector switches allow characterization of the closing and opening responses of the switch and therefore of fuel injector valve.

BACKGROUND OF THE INVENTION

Fuel injectors typically comprise solenoids or piezo actuators which are adapted to actuate a fuel injector valve arrangement in order to open and close the valve and to allow fuel to be injected into a combustion space during a certain time period. Generally speaking the control of such actuators is by means of sending an actuation pulse to the actuator i.e. fuel injector under the control of the ECU. Typically therefore the control of fuel injectors is provided by sending a series of activation pulses form the ECU to the injector, and the duration of valve opening is controlled by e.g. pulse width modulation. In order to provide closed loop control of fuel injectors, typically some fuel injectors include incorporated in them switch means or mechanism referred to as an "injector switch" to determine the operating condition of the fuel injector e.g. valve open or closed. Generally speaking such injector switches use existing or additional wiring to allow determination of when e.g. two metal surfaces of fuel injector components come into contact or close contact with each other. This will be explained in more detail hereinafter.

Thus for an injector with such switches, the fuel injector can be regarded as an "switch injector"; where the switch can be regarded as being e.g. as open or closed depending on the operational state of the fuel injector (open or closed). Typically the switch injector is supplied by an ECU that provides a 5V DC voltage in series with a pull up resistor of e.g. 4k Ohms. A voltage between 0.5 & 100V, 5V will be taken as an example to quantify/illustrate the principle of the invention.

The switch injector resistance/impedance indicates the state of the needle such as e.g. closed or open. In one arrangement and example when the needle (valve is closed) the switch injector has a low resistance/impedance and when high it has high resistance/impedance. Thus voltage monitoring between the pull-up resistor and the switch injector indicate if the injector is closed or opened; e.g. closed when around 0V and open when around 5V. The voltage monitoring is called switch signal. However there are problems with such an arrangement. At opening, e.g. due to parasitic capacitance inside the injector, variable resistance of the switch, and 4 kOhms pull-up resistance in the ECU, the switch signal is not a perfect rising edge, which generates inaccuracy in the opening measurement. At closing, due to fuel film the switch resistance/impedance is not zero.

Further, due to 4 kOhms pull-up resistance in the ECU the switch signal is not zero when the injector is closed. This leads to incorrect closing measurement.

It is one object of the invention to overcome such problems.

SUMMARY OF THE INVENTION

In one aspect is provided circuit arrangement for electrical connection between an ECU and a switch integral within a fuel injector, said circuit arrangement comprising a first resistance, and arranged in parallel with said first resistance, a diode and second resistance arranged in series. Said second resistance has preferably a value which is substantially lower than said first resistance.

Said second resistance has a value which is preferably less than 20% of the value of said first resistance.

In a further aspect is provided a system adapted to detect the operational state of a fuel injector where said fuel injector includes a switch integral within said fuel injector, comprising a circuit arrangement as claimed in claims 1 to 3 electrically connected between an engine ECU and said switch.

Said switch may be formed from two injector components which move relative to each during an injector operational cycle such that the switch is closed when the component come into contact with each other or open when the two components are not in contact with each other.

The system may include means to measure the voltage at a point between the circuit arrangement and said injector switch. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which:

Figure 1 shows a schematic view of a fuel injector which includes an effective "injector switch";

Figure 2 shows a schematic representation of a known arrangement to determine the state of the injector switch;

Figures 3 and 4 shows examples of the switch signal response functions of various resistance values in the circuitry of figure 1 ;

Figure 5 shows an example of the invention;

Figure 6 shows the opening response with the circuitry of figure 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The switch signal of an injector with the aforementioned switches provides valuable feedback on the operating state of the fuel injector. A fuel injector generally comprises metal components, which move relative to each other and e.g. come into contact and non-contact during the operational cycle of the injector. Examples of this are the control valve stem and the armature thereof and the injection needle. In addition the needle tip contacts the valve seat when the injector is closed and when open there is no contact. By using appropriate wiring one or more effective switches can be provided integral with the fuel injectors which allow determination of the operational state of the injector.

An injector (e.g. actuator) includes control wires communicating with the outside of the injector by means of a connector arranged on the body of the injector. With appropriate wiring and circuitry, a contact or injector switch relating to when the surfaces of two fuel injector or valve components come into contact with each other can be provided, where a line from the ECU or injector controller to ground is provided when the switch is closed i.e. when the two relevant metal surfaces of the components of the injector which move relative to each other come into contact. The effective switch is open when the two surfaces are out of contact.

Examples of such injector switches can be found e.g. in European Patent Application EP 14802330. Here those surfaces of the metal components that are in contact with one another are contact surfaces. Resistive surface coatings may be arranged on a number of contact surfaces. The overall electrical resistivity of the injector between the body of the solenoid actuator and the body of the injector may vary by at least three distinct ohm values intermittently according to the kinetics of the injection needle of the injector. The overall electrical resistivity of the injector can be modeled in accordance with the topology of an electric circuit formed of electrical resistors connected in series, these being equivalent to the contact surfaces of the metal components placed in contact with one another and arranged one on top of the other, electrical resistors connected in parallel, these being equivalent to the contact surfaces of the metal components placed in contact with one another and arranged one inside the other, and switches, these being equivalent to the instances of intermittent contact, for example the contact between the injection needle and seat thereof. The intermittent instances of contact change the value of the overall electrical resistivity intermittently according to the kinetics of the movable components of the injector.

Figure 1 shows a schematic view of a fuel injector 1 which includes an effective "injector switch" as described above. The switch designated by reference numeral 2 comprises effectively two injector components 3 and 4 which come in and out of contact with each other during an operational cycle of the injector such that when in contact they provide electrical continuity from a line or wire 5 from the ECU to ground. This line may be provided by using additional wiring or existing wiring from the injector controller or ECU. It is to be noted that any portion of the line 5 may be provided effectively through injector components and the figure is entirely schematic. Depending on the arrangements and which two components comprise the switch, in some arrangements the switch closing (response) represents the valve closing (response) and the switch opening response represents the valve opening (response), e.g. needle and needle seat. In other arrangement the switch opening may represent the closing response of the valve and the switch closing may represent the opening response of the valve. The phrase "switch integral within a fuel injector" should be interpreted as any such arrangements described above. Figure 2 shows a schematic representation of a known arrangement to determine the state of the injector switch where the injector 1 (with injector switch) is connected to the ECU via a pull-up resistor Rl designated with reference numeral 6. The voltage at a point between the injector and pull-up resistor Vmeas is measured as shown to give a switch signal which is monitored with time to determine the operational state of the injector. The injector switch is represented as a switch between a line to the injector (from the ECU) and ground in the figure. As mentioned the switch represents two moving parts of the injector (e.g. valve /actuator) that come into contact or close contact with each other during a point in the operational cycle of the injector such that current can flow through the components from the line to ground. In this case the switch is regarded as closed. At another point in the operational cycle the two components out of contact and so the circuit form the ECU to ground is open (represented by the switch in the open position).

Figures 3 and 4 shows examples of the switch signal response functions (closing and opening respectively) of various resistance values in the circuitry of figure 1. Switch signal measurements were performed with different pull-up resistances for R1 = 2 kΩ (plot 7), 20 kΩ (plot 8), 40 kΩ (plot 9) on a hydraulic rig.

The closing response is detecting the effective closing of the switch 2 i.e. detecting when the two fuel injector components come into electrical contact and the opening response when the two fuel injector components come out of contact . As can be seen a high value of pull-up resistor will push down measured voltage in the pre-fall value of voltage measured in the closing response but also in the post fall region. A high pull up resistor will also push down the rise region on switch opening. Thus there is an improved injector closing detection with a high pull up value and better injector opening detection with a small pull up value of pull up resistor. As mentioned none of these is an ideal situation.

According to one aspect the problems of inaccurate opening measurement and incorrect closing measurement can be solved by changing the circuitry i.e. the voltage supply circuit (ECU) of the switch injector. Circuitry according to aspects provides different voltages / resistances between opening and closing phases.

As mentioned at closing, due to a film of fuel between the needle and the nozzle, the switch resistance/impedance is not zero. The value can be high (200 kOhm). It is possible to detect this high resistance/impedance, only if the pull-up resistance is increased (typically 20kOhms). But if such a high pull-up resistance is used, at opening it will slow down the rising edge and cause inaccurate opening measurement. (A high pull-up resistance in series with a parasitic capacitance (typically 1.5 nF) and a variable switch resistor create a low pass filtration that slows down the switch signal at opening.) In a simple embodiment a diode is incorporated into the circuitry which allows the circuit a low resistance at opening and high resistance at closing. Figure 5 shows an example of the invention which is similar to figure 2 but also includes a diode 10 located in parallel with the pull-up resistor and a further resistance 11 in series with the diode whose value in the example is 2 kOhms.

When injector is closed, Vmeas is 0V and the diode is conductive. Most of the current is passing through the 2 kOhm resistance. When injector starts to open, Vmeas increase progressively. The 2 kOhms resistance stays active up to Vmeas = 4.4V (5V - Vdiode). That means that during the injector opening the 2 kOhm is used and then the switch signal rising edge is sharp enough to reflect accurately the opening (the parasitic capacitor is quickly loaded).

When needle is opened, switch signal goes up to 5V. Above 4.4V the 2 kOhm resistance is no longer more active. The current is fully passing through the 20 kOhm resistance. At beginning of closing, the circuit will then use the high pull-up value which is perfect to detect the injector closing with a film of fuel.

Figure 6 shows the opening response with the circuitry of figure 5, that is the value of Vmeas when the switch . As can be seen the response gives a good result on terms of detecting fairly rapidly the opening of the valve /injector.