CA1219142A - Injector tester - Google Patents

Abstract

ABSTRACT
"INJECTOR TESTER"
A device for testing fuel injectors in situ. The device comprises a detector having a piezo-electric crystal which converts mechanical impulses caused by the fuel injector valve needle snapping back onto its seat into electrical signals. The signals are fed to electronic processing means which detects the signal amplitude and displays it on an LED
bar graph display as an indication of the operating efficiency of the fuel injector. A timing system using the detector as a generator of timing signals is also disclosed.

Description

2~42 INJECTOR TESTER
The present inveneion relates to a device for testing fuel injec~ors such as those used in diesel engines. The invention al50 relates to a timing system for fuel injected engines.
BACKGROUND ART
Fuel injectors with atomiser nozzles have between 4 and 7 small holes in ~he nozzle, approximately 0.2mm in diameter. In use, these holes are frequently reduced in size, or blocked entirely, causing an imbalance in the spray pattern of atomised fuel into the cyclinder and a consequent imbalance in the air-fuel ratio, resultin~ in incomplete combustion.
This incomplete combustion manifests itself in power loss and black smoke emission from the exhaust. Continued operation of an engine under such conditions results in irrepairable damage to the injector, the piston and the cylinder head, in that sequence.
A faulty injector still in the engine can only be detected when it has failed completely. The engine is run at idle and each injector fuel supply connection is eased, in turn, until fuel leaks out. Under this condition, the injector will fail to operate. If, when the nut is eased, the idle speed is markedly affected then that injector is operating properly. Con~ersely, easing the nut on a faulty injector has no affect on the idle speed. This known method of testing fuel injectors is a time consuming inefficient method.
The most widely practiced method of detecting faulty ~0 injectors before failure thereof is to remove and replace all injectors at specified service intervals. Another common detection method for a faul~y injector is the "black smoke"
test (a vehicle expelling 10 seconds or more of black smoke detected against the sky line). A loss of power under load is ~lso an indication of fuel injection problems. However, these methods are either inefficient or unreliable.
It is also difficult to determine the moment of fuel injection/combustion in a diesel engine for the purpose of ~219~2 establishing an engine timing system. U.S. Patents Nos.
4,130,013; 4,231,251; 4,088,916; 3,978,721; 4,251,209 and 9,137,720 disclose devices having transducers for sensing pulsating ~luid flow in the fuel line. However these devices sense fuel pressure waves in ~he fuel line rather than vibrations in the detector head itself caused by the snap action of the ~alve needle at fuel injectionO U.S. Patent No. 4,102,181 discloses a process for determining the point of fuel injection by sensing the ~ibrations caused by abutments of the needle in the valve against a stroke limiter using a sensing element such as a vibration acceleration indicator or micrQphone. Although the use of a piezo-electric crystal as a sensing element is not disclosed in U.S. Patent No. 4,102,181, its use is disclosed in the device of U.S~ Patent No. 4,228,680 as a transducer for producing an electrical signal related to the position of the valve needle. As much vibration is produced during normal operation of a diesel combustion engine, the vibra~ions of the engine are sensed by the piezo-electric sensor along with the vibrations caused by t~e valve needle~ It is then necessary to use sophisticated and expensive frequency discriminators to distinguish the desired vibration from background noise.
DISCLOSURE OF INVENTION
It is an object of the present invention to overcome or substantially ameliora~e the above described problem by providing apparatus for testing the fuel injectors in situ for faulty operation.
It is another object of the present invention to provide a timing system for a fuel injected engine using a frequency selective transducer to detect the injection of fuel into the engine.
According to one aspect of the present invention, there is disclosed apparatus for testing a fuel injector, said apparatus comprising a transducer adapted to be placed on said fuel injector to convert mechanical impulses to electrical signals, electronic proces~ing means connected to th~ output of said transducer and comprising an amplitude 1~:19~42 detecting circuit for detecting the amplitude of the received electrical signals, and display means connected to the output of said amplitude detecting circuit for providing a display proportional to the detected amplitude, wherein the S transducer comprises a piezo-electric crystal sandwiched between two magnetic members.
Due to the configuration of the transducer, its frequency response is limited to a "window" which includes the frequencies of interest but excludes other unwanted vibrations, i.e. it is frequency selective.
Preferably, the display means comprises a series of light emitting diodes.
According to another aspect of the present invention, there is provided a timing system for a fuel injected engine, said timing system comprising a transducer adapted to be placed on a ~uel injector or fuel line in said engine to convert mechanical impulses to electrical signals, and timing signal generating means connected to the ou~put of said transducer for generating timing signals in response to the output signal from the transducer, wherein the transducer comprises a piezo-electric crystal sandwiched between two magnetic members.
The transducer used in the fuel injector tester can also be u~ed as part of the timing system. The mechanical impulse generated when the fuel injector valve needle snaps back onto its seat is detected by the transducer and an electrical signal is generated. ~he electrical signals received from the transducer indicate the precise instants of time when ehe injector injects fuel into the combustion chamber, and the output signals can be used to operate a timing system such as an engine speed tachometer or a strobe light for checking timing. Consequently, a fuel injected engine, such as a diesel engine, can be strobe light timed onto the fly wheel timing mark~ in the same fashion and with the same ease as an elec~ric ignition engine. Accurate and dynamic tuning of the diesel engine can thereby be obtained.
BRI EF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention will RIS~607C

~219~L2 now be described with reference to the drawings in which:
Figure 1 is an elevational view of ~he injector tester of the preferred embodiment.
Figure 2 is a cro~s-sectional elevational view taken along C-C (Figure 3) of the detector of Figure 1.
F;gure 3 is a cross-sectional end elevation view taken along B-B of the detector of Figure 1.
Figure 4 is a cross sectional plan view taken along A-A of the detector of Figure 1.
Figure 5 is an enlarged cross-sectional elevational view of the piezo-electric crystal of the detector of Figure 1.
Figure 6 is an enlarged cross-sectional end elevational view of the piezo-electric crystal of the detector of Figure 1.
Figure 7 is a schematic block diagram of the circuitry of the iniector tester of Figure 1.
BEST MODE OF CARRYING OUT THE INVENTION
As illustrated in the drawings, the injector tester of the preferred embodiment comprises a detector 10 which is a passive device incorporating a ferro-magnetic clamp ~or attaching the detector 10 directly to the injector body with sufficient strength to sustain the attachment whilst the engine is running.
The detector 10 uses a transducer which comprises a bilaminar piezo-electric crystal 50 sandwiched between two magnets 30, 40. The piezo-electric cry~tal actually comprises two piezo-electric substrates 52, 54 with a metal layer 55 sandwiched therebetween. Wires connected to the two substrates 52, 54 lead to the electric processing means 15 for proces6ing ehe signals received from the detector.
A~ illustrated in Figure 6, the magnet~ 30, 40 are provided with end plates 32, 34 and 42, 44. The piezo-electric crystal 50 i~ held between the end plates 32, 34 and 42, 44 so that mechanical vibrations of the end plates are transmitted directly to the crystal where they are con~erted to electric signals. A rivet 35 is inserted throuqh the bo~tom ma~net 40 into the detector body to :~2~L9142 prevent the piezo-electric crystal from being crushed between the two magnets by excessive shock. In this manner, although vibrations are sensed by the piezo-electric crystal, it is protected from excessive shock. The crystal/magne~ assembly is coated with epoxy to form a sealed unit and housed in a plastic jacket.
Due to the above described mounting arrangement, the piezo-electric crystal is frequency selective. For example, the low frequency component of the engine vibrating in its mounts falls below the detector's range, and other unwanted noises and vibrations generated by the engine and its components are filtered by the mounting arrangement 50 that the detector is primarily responsive only to the particular band of frequencies within which the vibrations of the injector needle/nozzle assembly fall.
The electronic processing means of the preferred embodiment is a pulse height analyser circuit and is schematically shown in Figure 7. The outpue of the detector 10 is fed to an amplitude range selector 16 which can be a multiple resistance switch which is adjusted to a desired setting so that the detected amplitude falls within the range of the display means 20. The output from the amplitude range selector 16 is amplified in pre-amplifier 17 and then fed to a peak detector 18. A "clamp and hold" circuit can also be incorporated to extend the duration of the recorded pulse so that the peak value can be analysed by an analogue level detector, if desired. If average, rather than peak, value is desired, an average select switch 19 can be enabled to provide an average reading of the detected pulse.
The peak or average value of the detected pulse is fed via buffer amplifier 14 to a display 20 which comprises a display driver (not shown) which drives a series of li~ht e~itting diodefi 24. Thus, the instantaneous vibration level caused by the reseating injector needle is translated into a scaled visual display. The short firing time of the injector is extended so that the operator can see and interpret the information being displayed.
In operation, the detector is placed on an injector ~2~91~

which is known to be operating properly, or if no injector is known to be operating properly, it is placed on the injector giving the highest reading on the visual display 20. The amplitude range select switch 16 is set so that the pulses received from the chosen injector light up substantially all of the diodes in the bar graph display 20. With the amplitude range selector on the same setting, the detector is then placed on an injector suspected of mal~unctioning and the number of light emitting diodes which are illuminated by the suspected injector will provide an indication of its condition. A properly operating injector will light up substantially all of the diodes, whereas a faulty injector will illumina~e fewer diodes.
The pulse height analyser circuit is fabricated in CMOS integrated circuits and a high input impedance ensures limited protection against electrical interference. Power is supplied from a standard 9 volt dry cell battery contained within the processor package, and the processor will function accura~ely so long as there is sufficient power to operate the LED display.
Other than the on/off switch, there are only two controls required to be operated; the amplitude range select switch 28 and the peak/average switch 27. The amplitude select switch adjusts the amplitude of the received pulse so that the displayed value falls within the range of the bar graph display. This switch is incorporated to compensate for different pulse heights from different engines since the pulse height is affected by the speed of the engine, the engine block mass/injector body mass ratio, injector needle valve~nozzle mass ratio, the number of nozzle holes or the shape of the pintle nozzle, and the damping response of the needle return spring. These factors do not have to be considered separately since the optimum range setting can be quickly determined simply by adjusting the peak level in the display to just below full scale.
The peak/average selects a fast or slow decaying display, in order to visually highlight any fault. The ~average~ position reveals constant, injector faults over a number of engine cycles and exposes the most common injector faults such as clogged or carbonized tips, defective valve seating, stuck valve stem, eroded valve stem and incorrect spring tension. Othee intermittent faults are detected with a display which shows the "peak" level on each injector stroke. Thus, the "peak" position allows the display to reveal any fluctuations due to partly sticking valve stem, contaminated fuel, loose debris within the injector body or cracked or sticking valve spring.
Not only will the device test injectors, but it can also be used to detect bearing knock in motors.
A further use of the present invention is in a timing system for a fuel injected engine. In this further application of the invention, the detector 10 is attached to an injector in the engine, and the output electrical pul6es from the detector 10 can be used to drive a timing signal generator.
In one embodiment, the detector 10 is suitably clamped to an injector body or a high pressure fuel line.
The piezo-electric transducer in the detector 10 senses the vibration caused by the in~ector needle snap-action or the pressure wave which causes the injector to fire, respectively. Again, the detector is frequency selective so that the engine's background noise is blanked ou~, and the output will be proportional to the frequency of firing of the particular injector unit. The output can be used to actuate a strobe light unit, a tachometer or an engine diagnos~ic system~
The foregoing describe6 only some embodiments of the present invention, and modifications which are obvious to those fikilled in the art may be made thereto without departing from the scope of the invention as defined in the follow;ng claims.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:

1. Apparatus for testing a fuel injector, said apparatus comprising a transducer adapted to be placed on said fuel injector to convert mechanical impulses to elec-trical signals, electronic processing means connected to the output of said transducer and comprising an amplitude detecting circuit for detecting the amplitude of the received electrical signals, and display means connected to the out-put of said amplitude detecting circuit for providing a display proportional to the detected amplitude, wherein the transducer comprises a piezo-electric crystal positioned between two magnetic members.

2. Apparatus as claimed in Claim 1, wherein one of said magnetic members is located between a pair of rigid plate members bearing on said piezo-electric crystal, one end of at least one plate member adapted to be in physical con-tact with said injector whereby vibrations in said injector are transmitted by said at least one plate member to said crystal.

3. Apparatus as claimed in Claim 2, wherein the display means comprises a bar graph display having a series of light emitting diodes.

4. Apparatus as claimed in Claim 2, wherein said electronic processing means comprises an amplitude range selector for varying the amplitude of the signal received from the detector.

5. Apparatus as claimed in Claim 2, wherein the piezo-electric cyrstal comprises two piezo-electric sub-strates with a metal layer therebetween.

6. A timing system for a fuel injected engine, said timing system comprising a transducer adapted to be placed on a fuel injector or fuel line in said engine to convert mechanical impulses to electrical signals, and timing signal generating means connected to the output of said transducer for generating timing signals in response to the output signal from the transducer, wherein the trans-ducer comprises a piezo-electric crystal positioned between two magnetic members.

7. A timing system as claimed in Claim 6, wherein one of said magnetic members is located between a pair of rigid plate members bearing on said piezo-electric crystal, one end of at least one plate member adapted to be in physi-cal contact with said injector or fuel line whereby vibra-tions in said injector or fuel line are transmitted by said at least one plate member to said crystal.

8. A timing system as claimed in Claim 7, further comprising a tachometer connected to said timing signal generating means.

9. A timing system as claimed in Claim 7, further comprising a stroboscopic light connected to said timing signal generating means.