Controller for a fuel injector and a method of operating a fuel injector

A controller for controlling the operation of a fuel injector having a piezoelectric actuator, the actuator being operable by an application of a voltage drive profile across the actuator, the controller comprising:

• inputs for receiving data relating to one or more engine parameters;
• a processor for determining a voltage drive profile for controlling the actuator in dependence upon the one or more engine parameters, the voltage drive profile being arranged to comprise a first pilot injection event, a second pilot injection event, a main injection event, an activating voltage component to initiate the second pilot injection event and a deactivating voltage component to terminate the second pilot injection event, the activating and deactivating voltage components being separated by a time interval TON;
• outputs for outputting the voltage drive profile as determined by the processor to the actuator;
• and
• a function map of a predetermined pressure wave time period (TP) of a pressure wave cycle within the injector in dependence upon engine parameters, wherein
• (i) the processor is arranged to set the time interval TON greater than or equal to the predetermined pressure wave time period (TP);
• (ii) the processor is arranged to set TON=nTP, where n=1, 2, 3 . . . ;
• and
• (iii) the controller is arranged to refer to the function map when setting TON.

A method of operating a fuel injector having a piezoelectric actuator operable by applying an activating voltage level across the actuator to initiate an injection event and a deactivating voltage across the actuator to terminate an injection event, the method comprising:

• determining a voltage drive profile for controlling the actuator, the voltage drive profile comprising a first pilot injection event, a second pilot injection event, and a main injection event;
• applying an activating voltage to the actuator so as to initiate the second pilot injection event, and, after a predetermined time interval (TON);
• applying a deactivating voltage to the actuator so as to terminate the second pilot injection event;
• wherein the predetermined time interval (TON) is selected to be greater than or equal to a predetermined pressure wave time period (TP) of a pressure wave cycle within the injector.

A controller for controlling the operation of a fuel injector having a piezoelectric actuator, the actuator being operable by an application of a voltage drive profile across the actuator, the controller comprising:

• inputs for receiving data relating to one or more engine parameters;
• a processor for determining a voltage drive profile for controlling the actuator in dependence upon the one or more engine parameters, the voltage drive profile being arranged to comprise a first pilot injection event, a second pilot injection event, a main injection event, an activating voltage component to initiate the second pilot injection event and a deactivating voltage component to terminate the second pilot injection event, the activating and deactivating voltage components being separated by a time interval TON;
• outputs for outputting the voltage drive profile as determined by the processor to the actuator,
• wherein the processor is arranged to set the time interval TON substantially equal to a predetermined pressure wave time period (TP) of a pressure wave cycle within the injector.