#How Injectors pump works

23 / February 2022
How Injectors pump works

Seletron Performance

How our chip tuning units for injector-pump engines work

Welcome back; we have returned (as promised) to discuss in detail how chip tuning units work on diesel engines that use PDEs, or injector pumps, as their injection system. We previously described other injection systems, namely, the first electronic injection control system via an electronically controlled rotary pump, then the second evolution of centralized injection pump, i.e., the one with a radial piston pump. Today we will discuss the first non-centralized diesel injection system, i.e., one made with independent modules for each cylinder. These elements consist of a high-pressure pump mounted in the same housing as the electronically controlled injector.

In the early 2000s, we began to receive many requests to electronically tune the first diesel engines using this new injection system. The VAG group pioneered this technology and introduced it on the 4-cylinder 1.9TDIs that ditched the electronically controlled rotary injection pump in favor of this system, which promised better efficiency and performance. The previous 1900TDI with rotary injection pump had 110hp and about 235Nm of maximum torque depending on the version.

The first 1900TDI (again with two valves per cylinder and with variable geometry turbocharger) had 115hp and (most importantly) the remarkable maximum torque of 280Nm. One appreciates the remarkable elasticity and easy use of high gears when driving. There is so much torque that it is rarely necessary to downshift, and the ride is very smooth, even uphill. Shortly thereafter, the 1900TDIs appeared with power outputs increased to 130hp, 150hp, and up to 160hp. Depowered versions with 101hp and 105hp were also released. We received many requests to tune these engines with chip tuning additional modules.


How the injector-pump diesel injection system works

Now, let's discuss the differences from the previous 1900 TDIs with electronic rotary injection pumps. Everything is different. Yes, everything, because there is virtually nothing left in common from before. The VAG group uses injector pumps to achieve higher injection pressure (they can work with pressures around 2000 bar) and to have more flexibility in managing the injection stages. With this system, the injection timing is partially freed from the position of the crankshaft. In addition, multiple injections can be produced, including pre-injection.

Now, for the technical aspect. The novelty lies in the fact that with this system, each injector has its own pumping element driven by the overhead camshaft. This makes it possible, as mentioned above, to generate very high injection pressures and to be able to control the injection stages much more precisely. Each solenoid injector features a pumping element per head that generates high diesel pressure. The ECU controls the opening of the injector plug through a solenoid (electromagnetically operated) that creates an imbalance of diesel pressure such that the injector opens and finely atomizes the high-pressure diesel fuel.

This injection, thanks to the high pressure and the option of generating a pre-injection (a small injection of diesel fuel that raises temperature and pressure in the combustion chamber to prepare the environment for subsequent main injections), provides a reduction in particulate generation, higher output, and the chance for tuning to generate more power. In addition, the injector-pump system allows the use of particulate filter technology.


How the first Diesel particulate filters worked

This is a technology that serves to trap particulate matter generated by the combustion of diesel fuel in the diesel engine and requires a special cleaning step to regenerate the filter itself. Regeneration of the particulate filter (which tends to become clogged the more kilometers you drive) occurs through post-injections or small injections of diesel fuel implemented during the exhaust phase that trigger combustion inside the particulate filter by cleaning it out. The ECU detects the need to regenerate the particulate filter through the pressure imbalance detected by a differential pressure sensor connected via two small tubes before and after the filter cells. When the pressure imbalance reaches a certain threshold, it means that the filter cells are excessively clogged and must be regenerated through post-injections to avoid creating excessive exhaust back-pressure.


How chip tuning units work for engines with injector-pumps

In principle, ur chip tuning units for diesel engines with injector-pumps work in a similar way to those for radial piston injection pumps. The main difference is that this type of chip tuning is sequential and incorporates the management of 4 radial piston pumps (in the four cylinders). Basically, the CHIPBOX chip tuning unit connects in parallel to all injector-pumps and reads their control signals. Based on the standard controls implemented by the ECU, an extension of the injection phase occurs for each engine cycle and individually for each electro-injector.

The chip tuning incorporates four solid-state output stages made with Mosfet/Hexfet type semiconductors plus a common output stage acting on the injector-pump power supply. These chip tunings also have a connection to the accelerator pedal position sensor, which is used to detect the rider's demand for torque/power delivery. The assembly of these chip tuning modules is quite simple as the supplied wiring harnesses have round connectors for the electrical connection of all the injector-pumps (located on the side of the engine head). As already mentioned, the only connections needed are those to the power supply and the accelerator pedal position sensor.


Diesel engines that have used injector-pumps

The first engines to employ this technology were those of the VAG group on the 1900TDI. In later years, 5-cylinder 2500TDI and larger displacement engines with this same injection system were also produced with V8 architecture. Then came the 2.0TDI 16V (8-valve in versions with FAP) with 140 horsepower. These injection systems were also used in the heavy-duty truck sector, for example, on the Cursors produced by IVECO. However, even in this sector, this injection system was eventually abandoned in later years to convert all engines to the common-rail system.

Before closing the topic related to chip tunings for diesel engines with pump injectors, we would like to mention that the first electro-injectors of this type were electromagnetically controlled, meaning that to control the injector opening, the ECU modulated solenoids that would generate a controlled magnetic field to attract a ferromagnetic element that acted as a mechanical control for the injector. In subsequent years, the VAG group introduced new piezoelectrically controlled injector-pumps to provide greater control and opening command speed.

In this case, the control element does not consist of an electromagnet but of specific piezoelectric effect crystals, i.e., crystals capable of changing their physical state in the presence of EDP (electrical potential difference) and also of doing the opposite, i.e., generating EDP when mechanically stressed. On this second series of electro-injectors (a technology later also employed on common-rail injectors), the ECU control is different in terms of voltage (higher) and current values. Needless to say, while the logic of operation remains unchanged, over the years, we have had to completely readjust the entire output stage of our chip tunings. This technology is subsequently even more complex and intricate. In fact, in addition to working with voltages that can vary from 100V to 150V, there is also the fact that, while for the classic electro-injectors it was enough to remove the control and the injector would automatically close, in this new system, the challenge was to keep the injector open and then close it via a dedicated Mosfet, while also managing the discharge current so as not to stress the piezoelectric core too much.

We said earlier that the piezoelectric effect is reversible, so here are a couple of contrasting examples to understand its applications. Do you remember piezo tweeters used specifically on large-power acoustic speakers? They operate according to the same principle as piezo electro-injectors. When stressed by a potential difference, they change their physical state. In this application, a membrane connected to piezoelectric crystals "vibrates" following the sinusoidal pattern of musical signal and thus reproduces high sound frequencies. In contrast, when applied in situations such as kitchen gas lighters and some cigarette lighters, when we press the button, it compresses a spring that, when released, mechanically stresses the piezoelectric crystals, which, in turn, produce a high EDP (electrical voltage) that generates the arc to ignite the flame!

Did you like this article? Share it with your friends and come back to read the next one. Soon, we will discuss the most sophisticated and modern diesel injection system, the common-rail!


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