LEXUS RX 300

1998-2003 of release

Repair and car operation

Application of an oscillograph for supervision of signals in chains of control systems

Digital multimeters perfectly approach for check of electric chains being in a static condition, and also for fixing of slow changes of traced parametres. At carrying out of the dynamic checks which are carried out on the working engine, and also at revealing of the reasons of periodic failures by absolutely irreplaceable tool there is an oscillograph.

Some oscillographs allow to keep oscillograms in the built in module of memory with the subsequent conclusion of results to the press or their copying to the digital carrier already in stationary conditions.

The oscillograph allows to observe periodic signals and to measure characteristics of rectangular impulses, and also levels of slowly varying pressure. The oscillograph can be used for:

• Revealings of failures of astable character;
• Checks of results of the made corrections;
• Monitoring of activity of a ljambda-probe;
• The analysis of the signals developed by a ljambda-probe which deviation of parametres from norm is the unconditional certificate of infringement of serviceability of functioning of a control system as a whole, - on the other hand, correctness of the form of impulses given out by a ljambda-probe can serve as a reliable guarantee of absence of infringements in a control system.

Reliability and simplicity of operation of modern oscillographs do not demand from the operator of special special knowledge and experience. Interpretation of the received information can be easily made by elementary visual comparison of the oscillograms removed during check with the time dependences resulted more low typical for various gauges and actuation mechanisms of automobile control systems.

Parametres of periodic signals

Each signal removed by means of an oscillograph can be described by means of the following key parametres:

• Amplitude – a difference of the maximum and minimum pressure () a signal within the period;
• The period – duration of a cycle of a signal (мс);
• Frequency – quantity of cycles in a second (Hz);
• Width – duration of a rectangular impulse (мс, мкс);
• Porosity – the relation of the period of repetition to width (In foreign terminology return is applied porosity parametre named a running cycle, expressed in %);
• The signal form – sequence of rectangular impulses, individual emissions, a sinusoid, sawtooth impulses, etc.

Usually characteristics of the faulty device strongly differ from reference that allows the operator easily and quickly visually to reveal the refused component.

Direct current signals - pressure of a signal is analyzed only.

Alternating current signals - are analyzed amplitude, frequency and the signal form.

The gauge of detonations

The frequency-modulated signals - are analyzed amplitude, frequency, the form of a signal and width of periodic impulses.

Inductive gauge CKP

Inductive gauge CMP

Inductive gauge VSS

Gauges of turns and the positions of shaft working on effect of the Hall

Optical gauges of turns and position of shaft

Digital gauges MAF and MAP

The signals modulated on width of an impulse (ШИМ) - are analyzed amplitude, frequency, the form of a signal and porosity of periodic impulses.

Fuel injector

The device of stabilisation of turns Х/Х (IAC)

Primary winding of the coil of ignition

Э/м the valve of a purge of an adsorber of system EVAP

System EVAP valves

The form of a signal given out by an oscillograph depends on set of various factors and can change appreciably.

In a kind told before to start replacement of a suspected component in case of discrepancy of the form of the removed diagnostic signal with the reference oscillogram, it is necessary to analyse the received result carefully.

Pressure

Zero level of a reference signal cannot be considered as absolute basic value, - "zero" of a real signal depending on concrete parametres of a checked chain can appear shifted concerning reference (1 the range see an illustration the Digital signal) within a certain admissible range (2 the range see an illustration the Digital signal and 1 on an illustration the Analog signal).

The full amplitude of a signal depends on pressure of a food of a checked contour and also can vary concerning reference value in certain limits (2 the range see an illustration the Digital signal and 2 on an illustration the Analog signal).

In chains of a direct current the amplitude of a signal is limited to pressure of a food. As an example it is possible to result a chain of system of stabilisation of turns of idling (IAC) which alarm pressure does not change in any way with change of turns of the engine.

In chains of an alternating current the amplitude of a signal already unequivocally depends on frequency of work of a source of a signal so, the amplitude of the signal which is given out by the gauge of position of a cranked shaft (CKP) will increase with increase of turns of the engine.

In a kind told if the amplitude of a signal removed by means of an oscillograph appears excessively low or high (up to trimming of top levels), it is enough to switch only a working range of the device, having passed to a corresponding scale of measurement.

At check of the equipment of chains with э/м management (for example, system IAC) at food switching-off pressure throws (the Digital signal see 4 an illustration) which can be ignored easy at the analysis of results of measurement can be observed.

It is not necessary to worry also at occurrence of such deformations of the oscillogram, as скашивание the bottom part of forward front of rectangular impulses (5 values see an illustration the Digital signal) if, of course, the fact выполаживания front is not a sign of infringement of serviceability of functioning of a checked component.

Frequency

Frequency of repetition of alarm impulses depends on working frequency of a source of signals.

The form of a removed signal can be edited and led to a kind convenient for the analysis by switching on an oscillograph of scale of time development of the image.

At supervision of signals in alternating current chains time development of an oscillograph depends on frequency of a source of a signal (3 the range see an illustration the Analog signal), defined by engine turns.

As already it was told above, for signal reduction to a legible kind it is enough to switch scale of time development of an oscillograph.

In certain cases characteristic changes of a signal appear developed mirror concerning reference dependences that speaks реверсивностью polarity of connection of a corresponding element and, in the absence of an interdiction for change of polarity of connection, can be ignored at the analysis.

Typical signals of components of control systems of the engine

Modern oscillographs are usually equipped only by two alarm wires together with a set various щупов, allowing to carry out device connection practically to any device.

The red wire is connected to a positive pole of an oscillograph and usually connected to plug ECM. The black wire should be connected to reliably earthed point (weight).

Injectors

Management of structure of an air-fuel mix in modern automobile electronic systems of injection of fuel is carried out by timely updating of duration of opening of electromagnetic valves of injectors.

Duration of stay of injectors abroach is defined by duration developed ECM the electric impulses submitted on an input э/м of valves. Duration of impulses usually does not fall outside the limits a range 1 ч 14 мс.

The typical oscillogram of the impulse operating operation of an injector, is presented on an illustration a fuel Injector. Often on the oscillogram it is possible to observe also a series of the short pulsations following directly behind the initiating negative rectangular impulse and supporting э/м the valve of an injector abroach, and also the sharp positive throw of pressure accompanying the moment of closing of the valve.

Serviceability of functioning ECM can be checked easily up by means of an oscillograph by visual supervision of changes of the form of an operating signal at a variation of working parametres of the engine. So, duration of impulses at проворачивании the engine on single turns should be a little above, than at unit work on low turns. Increase of turns of the engine should be accompanied by respective increase in time of stay of injectors abroach. The given dependence is especially well shown at opening throttle заслонки by short pressing a gas pedal.

Fast closing throttle заслонки should lead to the flattening of the oscillogram confirming the fact перекрывания of injectors (for systems with отсечкой fuel givings).

At cold start the engine requires some enrichment of an air-fuel mix that is provided with automatic increase in duration of opening of injectors. In process of warming up duration of operating impulses on the oscillogram should be reduced continuously, gradually coming nearer to value typical for single turns.

In injection systems in which the injector of cold start is not applied, at cold start of the engine the additional operating impulses shown on the oscillogram in the form of pulsations of variable length are used.

In the table resulted more low typical dependence of duration of operating impulses of opening of injectors on a working condition of the engine is presented.

Inductive gauges

Э/м the valve of stabilisation of turns of idling (IAC)

In motor industry electromagnetic valves IAC of set of the various types which are giving out signals also of the various form are used.

The general distinctive feature of all valves is that fact that porosity of a signal should decrease with loading increase for the engine, connected with inclusion of additional consumers of the capacity causing fall of turns of idling.

If porosity of the oscillogram changes with loading increase, however at inclusion of consumers infringement of stability of turns of idling takes place, check up a condition of a chain of the electromagnetic valve, and also correctness given out ECM a command signal.

Usually in chains of stabilisation of turns of idling the 4-polar step-by-step electric motor which description is resulted more low is used. Check of 2-contact and 3-contact valves IAC is made in a similar manner, however oscillograms of alarm pressure given out by them are absolutely unlike.

The step-by-step electromotor, reacting on given out ECM a pulsing operating signal, makes step updating of turns of idling of the engine according to working temperature of a cooling liquid and current loading on the engine.

Levels of operating signals can be checked up by means of an oscillograph, measuring щуп which is connected serially to each of four plugs of the step-by-step motor.

Ljambda-probe (the oxygen gauge)

The detonation gauge (KS)

Ignition signal on an exit of the amplifier of ignition

Primary winding of the coil of ignition