GB2221305A

GB2221305A - Circuit for evaluating needle displacement in a fuel injector

Info

Publication number: GB2221305A
Application number: GB8818008A
Authority: GB
Inventors: Johannes Sonntag; Herbert Schneider
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-07-28
Filing date: 1988-07-28
Publication date: 1990-01-31
Also published as: GB8818008D0

Abstract

A circuit for evaluating needle displacement in a diesel fuel injector comprises a needle movement sensor 10 which supplies a speed-dependent signal which is integrated by integrator 11 to supply a signal to output circuitry 12 which is representative of needle displacement. An integration window is defined by a timing circuit 14 which is responsive to a threshold detector 13. Timing circuit (14) actuates a switch 142, which by-passes the integrator 11 to terminate integration. <IMAGE>

Description

Circuit for evaluating needle displacement in a fuel injector The present invention relates to means for evaluating the needle displacement in a fuel injection arrangement, and especially to determining the needle stroke in diesel fuel injectors.

As is known from GB 1589913 and GB 2098334A, the need arises to determine as quickly and accurately as possible various parameters of the fuel supply system of an i.c. engine. The present invention seeks to provide a circuit for determining the stroke of the needle without measuring this parameter directly.

According to the present invention there is provided a circuit for evaluating needle displacement in a fuel injector comprising a sensor of needle novement which provides an output signal representative of the speed of the needle and an integrator for integrating said output signal to produce a signal representative of the needle stroke.

An advantage of this circuit is that it readily permits the stroke to be measured. In addition the displacement of the needle with time can be closely followed on a cathode ray tube and accordingly the commencement of fuel injection can be recognised. The circuit has a simple construction and does not require carrier frequency measuring amplifiers or measuring bridges. The circuit may readily be used in conjunction with an already-installed motor; all that is required is that the needle speed sensor is located in a position where it can detect needle movement. The circuit can be incorporated in test apparatus in development, manufacturing and service operations which require a qualitative assessment of the course of the needle's travel.

In a preferred arrangement the output signal is supplied to a threshold circuit the output of which is supplied to a timing circuit which controls the commencement and termination of integration by the integrator. This reduces the effects of noise and drift and ensures uniform starting conditions for each integration process.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig 1 is a block diagram of a circuit in accordance with the present invention; Figs 2a and 2b show curves obtained on a cathode ray tube representing two senor movement outputs and the corresponding needle stroke signals; and Fig 3 is a more detailed circuit diagram.

In Fig 1 there is provided a needle movement sensor 10 which is located adjacent to the needle of a fuel injector in a diesel internal combustion engine, and which produces an output signal which at any particular moment is directly proportional to the speed of the needle. The sensor 10 may have any convenient form, eg a coil. The output of the sensor is fed to an integrator 11 the output of which at any particular moment represents the displacement of the needle. This is supplied to further processing and/or display circuits 12.

In order to prevent erroneous signals, the output of sensor 10 is also supplied to a threshold trigger circuit 13 which, once a predetermined threshold level in the sensor output has been exceeded, switches on a timing circuit 14. Circuit 14 allows integrator 11 to operate for a predetermined period, typically lOm sec.

At the end of this period the output voltage of the integrator is clamped to 0 volts at which value it remains until the next signal from trigger circuit 13.

Thus circuit 14 prevents the problems of drift and determines the initial conditions of the integration process in each case.

In Figs 2a and 2b, curves I show the output of sensor 10 in two cases, representing needle movement or speed, and curves II show the corresponding signals supplied to circuitry 12, representing the course of the displacement of the needle, ie its stroke. Useful data can be extracted from curves II, for example the fuel injection time, the maximum needle displacement and any asymmetries in the course of movement of the needle.

Fig 3 shows the circuit of Fig 1 in more detail. The sensor 10 is connected to a power supply by circuitry 16. Typically this supplies a current of 40mA + 0.5mA to the sensor 10 via a screened cable and a plug. The output of the sensor at point A is supplied to a first input of a comparator 131. The threshold level is adjusted to a desired value by a potentiometer 132 connected to the second input of the comparator.

The comparator output is supplied to a timing chip 141 which supplies a lOm sec pulse to open a by-pass switch 142 for the capacitor 111 of integrating circuitry 11.

At the end of the lOm sec period, switch 142 is closed and integration ceases.

Various modifications can be made to the above described circuit. For example the threshold circuit 13 and the timing circuit 14 may be omitted; in this case means may be provided for automatically setting the output of the integrator 11 to zero at a predetermined interval after initiation of needle movement.

Claims

1. A circuit for evaluating needle displacement in a fuel injector comprising a sensor of needle movement which provides an output signal representative of the speed of the needle and an integrator for integrating said output signal to produce a signal representative of the needle displacement.

2. A circuit according to claim 1, wherein the output signal of the sensor is supplied to a threshold circuit which controls the commencement of integration by the integrator.

3. A circuit according to claim 2, wherein the output of the threshold circuit is supplied to a timing circuit which controls the commencement and termination of integration by the integrator.

4. A circuit according to claim 3 wherein the timing circuit comprises a switch which is closed at a predetermined interval after commencement of integration to by-pass a capacitor of the integrator to terminate integration.

5. A circuit for evaluating needle displacement in a fuel injector substantially as herein described with reference to the accompanying drawings.

6. A test apparatus comprising a circuit according to any preceding claim and a screened cable which has a plug at the end thereof and which supplies power to and receives the output signal from the sensor.

7. A method of determining the needle stroke of a diesel fuel injector employing a circuit according to any of claims 1 to 5.