Piezo injector how does it work

Such precise fuel metering makes for improved combustion, which leads to better fuel economy and reduced emissions. Not only are piezo injectors more accurate than conventional solid injectors, they also can perform some tricks that are completely beyond the capabilities of their predecessors.

For one thing, by applying a little less electricity, the piezo crystals expand less so the injectors can open partway. A smaller opening means a longer injection time, which is beneficial when trying to accurately inject a tiny amount of fuel, such as when a car is nearly coasting.

Because they act so quickly, piezo injectors also can inject several times as many as seven in some diesels during a single combustion cycle. This flexibility can reduce emissions in all engines as well as limit soot in diesels. These benefits have secured a home for piezo injectors in many of the latest diesel and direct-injection gasoline engines. Piezo injectors are one of the key devices that will keep internal combustions competitive against these pesky electric upstarts for years to come.

New Cars. Buyer's Guide. This translates into precise fuel measurement and allows for multiple injector events to occur per combustion cycle. Because Piezo injectors are used in common rail injection systems, high pressure fuel is constantly delivered to the tip of the injector where a needle rests and blocks fuel from being injected.

Pressurized fuel is delivered to the top of this needle as well, the force of which keeps the needle closed. When the Piezo crystal is energized, a valve at the top of the needle opens, allowing the pressurized fuel at the top of the needle to return to the tank through the return line.

The key is the innovative injection system: it works with rapid switch, compact piezo-inline injectors. Some advanced common rail fuel systems perform as many as five injections per stroke. Appearance Fig. The operation of piezoelectric injectors is quite similar to that of solenoid injectors, with the difference that they have a ceramic core. This is characterised by its ability to dilate or retract when it receives a pulse of current — the piezoelectric effect.

However, for injectors of this type to be feasible, manufacturers had to circumvent a certain number of problems.

In the first place, the dilation of a piezoelectric element is extremely low. To obtain a useable degree of displacement, it requires a stack of no fewer than ceramic disks to form the active element of the injector. To actuate them, an impulse of a hundred volts is applied to them and a tiny lever arm amplifies their movement. Moreover, as with electromechanical injectors, the piezoelectric disks do not directly command the needle movements.

They also activate a small valve. The major advantage of piezoelectric injectors is their speed of operation and the repeatability of the movement of the valve. The dilation and retraction movements of the piezoelectric elements are almost instantaneous. This reaction speed allows even more precise proportioning of the injected fuel and a greater umber of injections per cycle. Pumped fuel enters the injector via the fuel feed collar and excess can return to the tank via the fuel return collar.

The camshaft follower presses the plunger at the top to pressurise the fuel in the injector. The piezo valve controls the release of this high pressure fuel through the injector nozzle into the combustion chamber.