In detail: DIY repair of bosch piezo injectors from a real master for the site my.housecope.com.
Piezoelectric injectors are now increasingly used in common rail fuel systems in modern diesel engines. Designers receive a tool to fine-tune their engines, while car owners and mechanics receive a bunch of financial and technical nuances. So what are the advantages and disadvantages? The engine will deal with the issue.
The introduction of the Common Rail system, which took place in the late nineties, was a new milestone in the development of the Diesel engine. The in-line high pressure fuel pump (TNVD) replaced the main pump, and the hydraulic injectors gave way to injectors with electronically controlled solenoid valves.
Unlike the previous design, where the opening of the nozzle needle was only due to pressure, electro-hydraulic nozzles work in a slightly different way. At rest, the fuel pressure on the cone of the nozzle needle and in the chamber of the control valve located above the needle is the same, the spring-loaded needle closes the nozzles, and injection does not occur. When a signal from the control unit is received, the solenoid valve is triggered, the pressure above the needle is released, it rises, opening the nozzles, and injection is carried out.
Piezo injectors work in a similar way, in which instead of an electromagnet with a moving core, another performer is used - a piezoelectric element. It has the shape of a square column, consisting of a plurality of ceramic plates stacked on top of each other and sintered together. Under the influence of current, a piezoelectric effect arises in them, due to which the structure is able to quickly change its length, acting on the control valve. Compared to an electromagnet, the piezoelectric element provides faster response, the time of which is about 0.1 ms (versus 0.5 ms for a nozzle with an electromagnet), and is also capable of creating a greater force on the control valve and has a higher stroke accuracy for fast cut-off. fuel supply.
The use of a piezoelectric element in the injector allowed the designers to implement up to ten injections per engine cycle - preliminary, main, post-injection. At the same time, the portions themselves, their volume and frequency can be flexibly adjusted here, based on the engine operating modes. Thus, the smoothness and completeness of fuel combustion is achieved in the engine, noise and toxicity are reduced. For modern diesel engines in passenger cars, piezoelectric injectors are becoming an integral element in the design of the fuel system. But high technology comes at a price.
From the point of view of service, the main feature of piezo injectors is the high complexity of repair, which requires special equipment. In some cases, repairs are completely impossible. At the same time, the piezo injectors themselves are very demanding on the quality of the fuel, its composition and the degree of purification, with a decrease in which they quickly fail.
Piezo injectors for passenger car engines are manufactured by companies such as Bosch, Delphi, Denso and Siemens. But they are in no hurry to give this market to third-party repair services, offering a replacement entirely. This component is quite expensive: depending on the brand and model, a piezo injector can cost from 16,000 to 40,000 rubles. Therefore, repairs, the average cost of which is half or less of the price of a new nozzle, is in demand. But not every service can handle it.
The control valve most often fails.In this case, the part is manufactured with high precision and dimension at the micron level.
Difficulties begin already from the moment of diagnostics, which cannot be carried out in a garage workshop. For example, a transfusion test, when pipes with glasses are connected to the drain fittings in the return line, in a system with piezo injectors it is simply impossible to do that, since there must be a back pressure in the return line.
As servicemen say, the most vulnerable is the control valve, which fails most often. Moreover, it is one of the most important components - its malfunction can lead to the failure of the entire nozzle. The valve is either replaced as a whole, or restored by grinding and lapping the working edge of the valve itself and the working edge of the valve seat. But this is not easy to do. The valve has a very high, precision manufacturing accuracy with micron-level measurement parameters. For example, the shoulder at the top of the valve plug is about one hundred microns (one tenth of a millimeter) wide, and there must be a certain chamfer angle. And the more accurately the factory parameters are reproduced, the easier it will be to adjust the injector and the longer its service life will be.
Dmitry Efremenko, director of the company> - "Europrom":
- Rolling bearings in the units of domestic machine tools have greater tolerances for backlash and clearances than the valves of piezo injectors. Accordingly, it is impossible to achieve the required accuracy on such machines. Therefore, we had to design the equipment for the restoration ourselves, the individual units and elements of which had to be bought in Switzerland.
It is also possible to restore the sprayers, in which the needle and the saddle are processed and rubbed, the nozzles are blown out. If the atomizer is irreversibly damaged (for example, when the nozzle overheats), then a part from another nozzle is taken, where the atomizer can be restored. They do the same with valves, the varieties of which, in contrast to the types of sprayers, are ten times smaller, which greatly facilitates the selection. For example, Bosch piezo injectors can use the same valve in more than ten different injectors.
Recently, new Chinese-made spare parts (valves, hydraulic lifters, sprayers) have appeared on the market. But their quality "floats" a lot, it is difficult to figure out where the non-original, suitable for repair, and where the thrown away money is.
The Chinese offer in the form of a spare part and a piezoelectric element, which is also one of the weak points of the piezo injector. But, as servicemen say, replacing it does not justify itself in terms of labor costs. Part of the piezoelectric element is firmly soldered to the connector block, which, in turn, is pressed onto the body, which forms a non-separable structure. Therefore, it is easier to replace this part of the body entirely.
The piezo injector is a high-tech component, originally intended for replacement as a whole and difficult to repair. But life dictates its own rules - services appeared in which they learned how to restore these parts so that the client was satisfied. It remains to say their word to the manufacturers of the non-original and start producing analogs. And also to the manufacturers of original piezo injectors themselves, offering proprietary restoration technologies and spare parts for repairs.
Alexey Zubikov, Head of Network Development, Bosch Diesel Center / Service in Russia, Transcaucasia and Central Asia:
- For the repair of piezo injectors in Bosch Diesel Service workshops, the company does not yet have the technology, sets of special tools and spare parts are not ready. At the moment, we can only diagnose this type of injector. It is planned that we will start providing piezo injectors repair services from 2017–2018.
In our time, the rapid development of technology contributes to the discovery of more practical and environmentally friendly inventions. Diesel fuel system manufacturers are constantly improving their units.If earlier the injectors were controlled, let's say, mechanically, then then electrical elements appeared in the control of the fuel system. This made it possible to more accurately monitor and control the injection system. But the nozzles themselves still remained a purely mechanical product, and the speed of their operation depended on the parameters of the dynamism of the operation of these mechanical units.
In the electromagnetic injectors of the first generations, the fuel supplied to the cylinder was divided into a preliminary and main dose. But the injection system turned out to be more efficient, where, in one working stage of the injector, the fuel is divided into the maximum possible number of micro-portions.
For this, it was necessary to increase the response speed of the control and actuating mechanisms of the injector. For this purpose, a piezoceramic nozzle was designed, which works four times faster than a traditional electromagnetic one.
Considering the specifics of the design of this type of injectors, they add their own specific ones to all the "sores" of traditional electromagnetic nozzles.
Basically, they manifest themselves in this way: the car does not start well (it will not start at all); stalls in load; troite; stalls at idle; traction is lost under load; the appearance of gray smoke at idle and black in the load.
The reasons for such defects in the operation of the car can be varied, but quite often we observe the root cause in the injectors. Therefore, if such symptoms are found on your diesel engine, the first thing to do is go through computer diagnostics. It is inexpensive and will save you a good amount of money in your case.
If the diagnostics determine a loss (excess) of pressure in the system, a short circuit on the injectors or a significant imbalance in the operation of the cylinders, then first pay attention to the injectors. They are often the reason for these problems.
Piezo injector does not hold pressure - the precision part of the switching valve is damaged. As a result, the car will not start well. It can also stall under load.
Short circuit of the nozzle to ground - the insulating layer of the piezoelectric element is damaged. In this case, the car does not start at all, or it starts up and after a short period of time stalls right at idle speed. Sometimes, with such a breakdown, the car stalls only under load. Most often we see such a defect on Trafic 2.0, less often on cars of the Volkswagen and Audi group.
Failure of the sprayer... There are, in principle, two options: either the sprayer pours or wedges in the closed position. In the first case The low pouring nozzle produces light smoke at idle speed, which disappears completely under load. It manifests itself on non-working sprayers after removing the particulate filter. Cars of the Mercedes group, less often Audi, Crafter, love to be sick with such a light smoke.
If the sprayer pours heavily (open wedge), there will be more smoke. Also, black smoke appears in the load, which is accompanied by a knock. But such a defect has so far been observed very rarely.
At closed wedge of the sprayer, the car troit at idle (the wedge is more felt with a small pressure in the system).
Depressurization of the drain line - mechanical damage to the elements of the drain line, failure of the check valve of this line. With such a breakdown, the car starts up, works, but stalls with a small load. Quite often we see such damage on Trafic 2.0.
Ninsufficient capacitance of the piezoelectric element (or weak resistance) - the piezoceramic element is out of order. If this happened on one injector, then the machine is troit. If the piezoelectric element loses capacity across multiple injectors, then the vehicle may lose traction.
We successfully repair all the listed breakdowns of piezo injectors since 2014. A guarantee is given for the repair of piezo injectors, and a record of the repaired cars is kept. To date, more than two thousand injectors have been serviced for Trafic 2.0 only.
