Inyector piezoeléctrico common rail. Funcionamiento detallado.

How Does a Common Rail Piezoelectric Injector Work?

Overview of Common Rail Injectors

• Common rail injectors, both piezoelectric and solenoid types, maintain the same high pressure (around 300-320 bar) at both the bottom and top sides when closed.

• The needle rises due to a pressure difference; higher pressure at the bottom compared to the top pushes the needle upwards, allowing fuel to exit through the nozzle.

Actuation Mechanism

• The injector is actuated by creating a leak from the control chamber to return, resulting in lower pressure on top and higher pressure below, causing needle movement.

• In piezoelectric injectors, an Electronic Control Unit (ECU) sends pulses of 50-60V that increase until reaching 125V due to the piezoelectric effect.

Injection Process

• The voltage amplitude moves a poppet valve downwards, enabling fuel derivation towards return. When ECU stops voltage supply, the piezoelectric remains charged like a condenser.

• To close the injector, a short-circuit is created by ECU between terminals for discharge without inverting polarity.

Oscilloscope Analysis

• An oscilloscope shows voltage (blue line) and current (red line); during idling speed with two pre-injections and one main injection.

• Maximum voltage occurs at zero current; this peak indicates that piezoelectric is charged at 125V before closing via ECU-induced discharge.

Regeneration and Safety Features

• During regeneration phases, post-injections may occur while some pre-injections are canceled to reduce fuel consumption.

• Newer generation injectors have built-in resistance preventing open state if unplugged; it ensures safe closure by discharging any residual charge.

Injector Components Examination

• A common rail injector example from a 1.6 TDI model often fails due to nozzle sticking; internal components include piezoelectrics responsible for control valve operation.

• Resistance measurement of about 200kohms can be taken from piezoelectric terminals; this resistance aids in safe discharge upon disconnection.

Detailed Structure of Piezoelectrics

• The structure includes stacked plates acting as condensers; resistance allows for proper functioning during disconnection scenarios.

• Damage assessment reveals critical components such as contactors for each plate within piezoelectrics which contribute to overall functionality.