Methods and means of diagnosing a diesel engine 3
Diesel engine diagnostic equipment 10
Any machine (mechanism) can be in two states – serviceable and faulty. The machine is serviceable if it meets all the requirements for it.
The reliability of units and components installed on modern tractors is so high that with timely replacement of worn parts and parts that have failed as a result of aging of materials, the probability of their sudden failure is extremely small. Failures rarely occur spontaneously and are usually the result of the sometimes prolonged development of a defect. The same components that can fail unexpectedly are usually not vital to the functioning of the main components and systems of the tractor, or are easily replaced on the road.
A fundamental step in identifying the causes of any failure is the choice of a starting point for the search. Often the reason is on the surface, but in some cases you have to work hard, doing a little research. A tractor driver who has made half a dozen random checks, replacements and corrections has a good chance of finding the cause of the failure (or its symptom), but this approach is by no means reasonable, due to its laboriousness and waste of time and money. A calm, logical approach to finding a failed node or component is much more effective.
It is imperative to take into account all the symptoms and warning signals that preceded the breakdown, sometimes insignificant, such as: loss of power developed by the engine, changes in meter readings, the occurrence of unusual sounds and smells, etc.
Diagnosis – in-place determination of the technical condition of mechanisms, systems and units of the tractor using measuring instruments, the main purpose of which is to identify the causes and external signs of malfunctions; determination of parameter values characterizing the technical condition of the object; identification of faulty products. The result of the diagnosis is a conclusion (diagnosis) on the technical condition of the tractor or its individual
Knots, compiled on the basis of the analysis of parameter values; forecasting the probability of recoilless operation of the tractor (residual resource) at specified intervals of operating time and the appointment of repair and maintenance actions that allow restoring the technical condition parameters that have gone beyond the allowable limits. An increase in the volume of control and diagnostic operations during pre-sales, warranty and post-warranty service helps to reduce tractor downtime due to technical malfunctions, save money on maintenance and repairs, and reduce the consumption of spare parts and fuel and lubricants.
Tractor diagnostics are carried out by a master diagnostician who has undergone special training and knows the design and operation of tractor systems and mechanisms, the device of diagnostic tools and the rules for their use. To help the master-diagnostician, a locksmith (driver) of the repair and diagnostic
A workshop that, under the guidance of a master diagnostician, performs simple control and diagnostic, adjustment and repair operations.
Based on the results of the diagnosis, a diagnostic map is compiled.
The process of diagnosing at the post consists of preparatory, main and final stages. The preparatory stage includes questioning the driver (operator) about the operation of the machine; cleaning the points of attachment of diagnostic tools; external examination and elimination of detected malfunctions that prevent the correct diagnosis; preparation and installation of diagnostic instruments (sensors) on the tractor; to the main one – the establishment of a certain mode of operation of the machine, its units; measurement of technical condition parameters; entering the values of the measured parameters into the technical log; to the final – forecasting the residual life of components, assemblies and the machine as a whole; diagnosis; appointment of the type, volume, place and period of repair and maintenance work, as well as the removal of diagnostic tools from the machine.
The post of instrumental diagnostics should be placed in an isolated room equipped with an inspection pit and a supply and exhaust
To reduce the efficiency of diagnosing, reduce the duration of troubleshooting or defects, the technical condition of the tractor must be checked at the post of the following sequence
ñ interrogate the tractor driver and get information about the technical condition of the tractor, any malfunctions or external signs of their manifestation;
ñ analyze the accompanying documents that characterize the work performed by the machine, its operating time (mileage), fuel consumption;
ñ during external inspection detect leaks of fuel, oil, electrolyte, cooling and brake fluids and check their levels, determine the condition of fasteners;
ñ assess the external signs of malfunctions during the operation of the tractor and its components: beating of rotating parts, vibration and heating of body parts, extraneous noise, color of exhaust gases.
Methods and means of diagnosing the diesel engine of the MTZ tractor.
The devices of the diesel engine power system are fundamentally different from those for a carburetor engine. Therefore, the use of diagnostic equipment for power supply systems of carburetor engines is impossible for power systems of diesel engines.
The diesel engine power system includes devices that affect fuel consumption, such as an air cleaner, pre- and fine fuel filters, a booster pump, a high-pressure fuel pump and injectors, an engine speed controller and a drive. The plunger pairs of the fuel pump and injectors are subjected to the most intense wear, and the springs lose their elasticity. Violation of the tightness and clogging of the elements of the fuel system leads to interruptions in the operation of the engine, and a violation of the adjustments of the start, magnitude and uniformity of the fuel supply, the injection advance angle, the pressure of the start of the injector needle lift, as well as the minimum crankshaft speed in idling mode – to an increase in consumption fuel and smoky exhaust gases.
The control of the operation of filters for preliminary and fine fuel purification and technical impacts consist in the daily draining of sludge, washing the filter elements during TO-1 and replacing them when performing TO-2 operations.
A clogged air cleaner will reduce engine power and waste fuel. The air cleaner is checked when working on dusty roads at TO-1, in the conditions of the winter period at TO-2.
The fuel pressure in the low pressure line is checked by connecting a control pressure gauge between the fine filter and the fuel pump; at a camshaft speed of 105010 rpm, the maximum pressure must be at least 4 kgf / cm 2 .
Fuel pump diagnostics.
The high pressure fuel pump must provide a uniform supply of metered portions of fuel to the high pressure injectors in the order of engine operation at the moment corresponding to the end of the compression stroke in the cylinders.
When performing TO-2 in case of increased fuel consumption, it is recommended to remove the high-pressure pump from the site and diagnose it at the stand. Checking and adjusting the start of fuel supply is carried out using a momentoscope (Fig. 1) in the following sequence:
– disable the automatic injection advance clutch;
– turn the camshaft of the pump clockwise (on the drive side). The first section of the adjusted pump starts supplying fuel 38–39° before the axis of symmetry of the cam profile;
– determine the symmetry profile of the cam of the first section, for which purpose install a momentoscope on the section and, turning the pump shaft clockwise, monitor the fuel level in the momentoscope tube;
– the moment of the beginning of the movement of fuel in the momentoscope to fix on a graduated disk fixed on the pump shaft;
– turn the shaft clockwise by 90°. Then turn the shaft counterclockwise until the fuel begins to move in the momentoscope and fix this position on the disk;
– mark on the graduated disk the middle between the fixed points, which determines the axis of symmetry of the cam profile of the first section;
– taking the angle at which the first section starts the fuel supply conditionally as 0 °, determine the start of the fuel supply in the remaining sections of the YaMZ236 engine in the following order: for the fourth section 45 °, the second – 120, the fifth – 165, the third – 240 and the sixth – 285 °.
Rice. 1. Momentoscope:
1 – glass tube; 2 – adapter tube; 3 – high pressure fuel line; 4 – washer; 5 – union nut
The inaccuracy of the angle between the beginning of the fuel supply of any section of the pump relative to the first section is not more than 20°. Adjustment of the beginning of the fuel supply is made by the adjusting bolt of the pusher. When unscrewing the bolt – early feed, when screwing in – late.
For the YaMZ-238 engine, the start of feeding of each subsequent section in accordance with the section operation order should occur through 45 ° in relation to the previous one.
The technical condition of the injectors is determined when performing TO-2.
A faulty injector can be determined by successively disabling the cylinders from operation. To do this, it is necessary to loosen the nut at the high pressure fuel line of the injector being checked so that the fuel comes out, bypassing the injector, which will cause the engine cylinder to turn off. If, when the engine is turned off, there is no change in the operation of the engine, the nozzle is faulty, but if interruptions and uneven operation increase, the nozzle is working.
For an objective check of the technical condition of the nozzle in order to determine the tightness, the pressure of the beginning of the rise of the nozzle needle and the quality of spraying, use the KP1609A device (Fig. 2).
Rice. 2. Device KP1609A for checking and adjusting injectors:
1 – fuel tank, 2 – injector to be checked, 3 – injector to be checked, 4 – lever, 5 – device body
When determining the tightness of the nozzle with the KP1609A device, it is necessary:
– install the nozzle on the device;
– turning the adjusting screw of the injector, at the same time increase the pressure with lever 4 up to 300 kgf/cm 2 ;
– stop pumping, observing the pressure drop;
– when reaching 280 kgf / cm2, turn on the stopwatch, and turn it off at a pressure of 230 kgf / cm2.
The fuel pressure drop time for worn injectors should be at least 5 s, and for new atomizers – at least 15-20 s.
A rapid drop in pressure indicates a leak in the injector interfaces. Moistening of the nozzle of the sprayer indicates a loose fit of the obturator of the needle, which is eliminated by lapping. The exit of fuel from under the spring nut indicates a loose fit of the guide part of the needle to the body of the injector sprayer.
The pressure of the beginning of the rise of the nozzle needle, equal to 150 ± 5 kgf / cm 2 , is checked by its value at the moment of the start of fuel injection in the following sequence:
– install the nozzle on the device;
– remove the nozzle cap and loosen the locknut of the spring adjusting screw;
use the lever 4 of the device to slowly increase the pressure, observing the readings of the pressure gauge 3, and determine the pressure at which the needle begins to rise, at which fuel injection begins;
– set the required nozzle pressure with the adjusting screw. At low injection pressure, the adjusting screw is screwed in with a screwdriver, at high pressure, vice versa;
– tighten the lock nut (tightening torque 7-8 kgf m) and re-check the pressure at the beginning of the needle lift.
The quality of fuel atomization is considered satisfactory if the fuel is injected into the atmosphere in a foggy state and is evenly distributed over the cross section of the jet cone. The beginning and end of the injection should be clear, the pressure drop during fuel injection should be 8–17 kgf / cm 2 , without fuel leakage.
To check the quality of fuel atomization, it is necessary to use lever 4 of the device to make several sharp injections of fuel through the nozzle, and then, shaking the lever 70–80 strokes per minute, observe the nature of the injection. If the atomization quality is poor, the nozzle needs to be repaired or replaced.
Diesel engines, along with high technical and economic indicators, also have negative sides, one of which is the high content of aerosols in the exhaust gases, which determine the start-up smoke. The exhaust gases of a diesel engine contain mainly particles of soot, ash, unburned fuel, oil, water, which pollute the air and have a harmful effect on humans.
To determine the level of smoke in the exhaust gases of a diesel engine , a device model K408 (Fig. 3) was created, powered by an alternating current network with a voltage of 220 V.
The device consists of two units – electrical and gas, which are mounted in a metal case mounted on a stand.
The electrical measuring part includes a photocell, an electric lamp with a voltage of 12 V and a power of 30 W, a microammeter and a potentiometer that regulates the current flowing from the photocell to the microammeter.
The gas part consists of a sampler, switchgear, working and reference pipes and a fan.
Rice. 3. Device K408 for determining the level of smoke in the exhaust gases of a diesel car
The procedure for measuring the smoke level is as follows:
– fix the sampler of the device on the muffler pipe;
– start and warm up the car engine;
– put the shift knob in the “freeze” position;
– on the scale of the microammeter, calibrated in percentage of opacity, determine the level of opacity.
A smoke level of no more than 50 units is considered normal.