GB2333132A - Spill valve control method. - Google Patents

Abstract

A method of controlling the operation of an electromagnetically actuated spill valve 16, to relieve pressure in a fuel injector 15 pump chamber 14, comprises energising an actuating coil 18 and monitoring the rate of rise of the current in the coil to calculate a time of flight correction factor for the valve. Coil inductances are calculated using current time to rise data and compared with time of flight measurements to arrive at the correction factor. This enables the timing of triggering valves to be adjusted so that movement of the valve is completed at the desired instant e.g. for synchronising two valves.

Description

CONTROL METHOD This invention relates to a method of operating a valve, in particular a valve for use in controlling the operation of a fuel injector for use in supplying fuel to a cylinder of an internal combustion engine.

Figure 1 illustrates, diagrammatically, part of a fuel system for use in supplying fuel to a cylinder of a compression ignition internal combustion engine. The fuel system comprises a pumping plunger 10 reciprocable within a bore 11 under the influence of a cam arrangement 13 and return spring 12. The plunger 10 and bore 11 together define a pump chamber 14 which is connected to a fuel pressure actuable injector 15. The chamber 14 also communicates with an electromagnetically controlled spill valve 16 including an armature 1 7 and actuating coil 18, the spill valve 16 controlling communication between the pump chamber 14 and a fuel reservoir 19.

In use, during inward movement of the plunger 10, when the spill valve 16 is open, fuel from the pump chamber 14 is displaced through the spill valve 16 to the reservoir 19 without significantly raising the fuel pressure within the chamber 14. Upon closing the spill valve 16, fuel is no longer able to flow to the reservoir 19, thus continued inward movement of the plunger 10 pressurizes the fuel within the chamber 14 and a point is reached beyond which the pressure is sufficient to open the injector 15 commencing injection. In order to terminate injection, the spill valve 16 is reopened allowing the fuel pressure within the chamber 14 to fall to a level insufficient to maintain the injector 15 in its open condition.

It is important to be able to control the operation of the injector 15 accurately, hence the operation of the spill valve 16 must be accurately controlled. One major source of variations in the operation of spill valves results from variations in the distance moved by the valve members of the spill valves when moving between their fully open and closed positions. Such gap errors result in the times of flight of the valve members between their fully open and closed positions varying between spill valves. Other errors, for example valve stiction, inertia and the work involved in overcoming valve spring forces are dependent upon the voltages applied to the actuating coils of the spill valves. In practice, the applied voltage is held relatively constant so these errors are of relatively little significance compared to the time of flight errors.

An object of the invention is to provide a method of controlling the operation of a valve permitting correction of such time of flight errors.

According to the present invention there is provided a method of controlling the operation of a valve of the type comprising a valve member moveable with respect to a seating under the influence of an electromagnetic actuator including an actuating coil and an armature, the method comprising the steps of energizing the coil, monitoring the rate of rise of current in the coil, and using the rate of rise of current to calculate a time of flight error correction factor.

The rate of rise of current is conveniently determined by sensing the time taken for the current to rise from a first predetermined value, conveniently OA, to a second predetermined value.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of a fuel system; Figure 2 is a diagram illustrating a circuit for use in performing the method of the present invention; and Figures 3a to 3 are graphs illustrating control currents applied to two valves and the corresponding movement of the valve members.

Figure 2 illustrates a control circuit for controlling the operation of a plurality of injectors, each injector having associated with it a spill valve, for example of the type illustrated in Figure 1. Each spill valve includes an actuating coil 18 connected between a first terminal 20 and a terminal of an associated switch 22, for example in the form of a transistor, each switch 22 also being connected to a second terminal 24.

The voltage across the first and second terminals is approximately 90V.

The switches 22 are controlled by a controller 26, for example in the form of a microprocessor. In use, at an appropriate time, the controller 26 closes one of the switches 22 whereby a current starts to flow within the actuating coil 18 connected to that one of the switches 22. The flow of current within the actuating coil 18 generates a magnetic field which causes movement of an associated armature. As illustrated in Figure 1, the armature is connected to the valve member of the spill valve thus the energization of the coil 18 results in movement of the valve member of the spill valve.

According to the invention, the rate of increase of the current within the selected coil is monitored. In this embodiment, the monitoring of the rate of increase of the current is achieved by starting a timer at the instant at which the controller 26 actuates one of the switches 22. The timer continues to run until the current within the coil reaches a predetermined current. Once the predetermined current level is achieved, the timer is stopped. The predetermined current level is determined by the controller 26 which produces a pulsed digital signal which is converted to an analogue voltage using a resistor 28 and capacitor 30. This analogue voltage is supplied to a comparator 32 which is arranged to compare the analogue voltage with the voltage across a sense resistor 34, this voltage being directly related to the current flowing in the coil 18. As illustrated in Figure 2, when the sensed voltage is equal to the analogue voltage, and hence the current within the coil is equal to the predetermined current, a signal is supplied to the controller 26 to stop the timer.

Figure 3a illustrates the detected current waveform flowing through the coils 18 of two spill valves, the full line showing the waveform for a spill valve in which the maximum separation of the valve member from its seating and hence the maximum separation of the armature from the coil, is relatively small, the broken line illustrating the current waveform for a spill valve in which the maximum separation of the valve member from its seating is relatively large. The waveforms clearly show that the location of the armature at the instant that the switch 22 is closed has an effect upon the rate at which the current flowing within the actuating coil increases, the waveform for the valve in which the armature is furthest from the coil showing that the current rises, initially, at an increased rate.

In this embodiment, the rate at which the current increases is measured by sensing the time taken for the current flowing within the coil to rise from OA to 3A. Figure 3g illustrates the location of the valve member during actuation of the valves, and it is clear that it takes significantly longer to close the valve in which, at rest, the valve member is spaced by a relatively large distance from the seating.

The measurements of the time taken for the current to rise to 3A can be used to calculate the coil inductance for each valve using the following equation: E.t Linjector = E.t set where LjnjeCtor is the coil inductance; t is the time taken for the current to rise to the predetermined current level; E is the applied voltage (in this embodiment 90V); and set is the predetermined current level (in this embodiment 3A).

By comparing the calculated coil inductances with time of flight measurements, a correction factor or look-up table can be calculated so that once a value for the coil inductance of a valve of a particular type is known, the switch for that valve can be triggered at an appropriate time to ensure that movement of the valve member is completed at the desired instant.

Figures 3h and 3d illustrate the effect of adjusting the timing of triggering the valves. In Figure 3k, the switch 22 associated with the valve in which, at rest, the valve member is spaced from its seating by a relatively large distance is actuated in advance of that associated with the valve in which, at rest, the valve member is spaced from its seating by a relatively small amount. In particular, in order to ensure that the valves reach their fully closed position at the same time the triggering of the valves is separated by a time equal to the difference in the time taken for the current to rise to the 3A level multiped by an empirically derived correction factor of 7. Figure 3d illustrates the effect of actuating the switches 22 at the times determined using the correction factor of 7, and the traces illustrated in Figure 3d clearly show that the valve members reach their fully closed positions at substantially the same instant.

Although in the embodiment illustrated hereinbefore, the inductance of the coil is determined by monitoring the time taken for the current flowing therein to increase to a predetermined level, in the example 3A, the rate of increase of current could be monitored by monitoring the current level reached during a predetermined time interval. In the embodiment illustrated, the predetermined current level is selected to be the level at which the current is maintained in order to hold the spill valve in its closed position. However, it will be appreciated that other current levels could be used.

Figure 3 indicates that the rate of increase of current is monitored over a period of the current waveform during which movement of the valve is not occurring. Measurement over this part of the current waveform is advantageous in that other uncontrolled errors are reduced thus the results obtained by monitoring the rate of current increase during the part of the current waveform during which valve movement is not taking place are of improved accuracy.

Claims (5)

1. CLAIMS 1. A method of controlling the operation of a valve of the type comprising a valve member moveable with respect to a seating under the influence of an electromagnetic actuator including an actuating coil and an armature, the method comprising the steps of energising the coil, monitoring the rate of rise of current in the coil, and using the rate of rise of current to calculate a time of flight error correction factor.
2. 2. A method as claimed in Claim 1, wherein the rate of rise of current is measured by measuring the time taken for the current to rise from a first predetermined level to a second predetermined level.
3. 3. A method as claimed in Claim 2, wherein the first predetermined level is OA.
4. 4. A method as claimed in any one of the preceding claims, wherein the rate of rise of current is monitored over a period in which movement of the valve member is not occurring.
5. 5. A method of controlling the operation of a valve substantially as hereinbefore described with reference to the accompanying drawings.