Abstract: The invention relates to a drive circuit for an injector arrangement comprising a first fuel injector in parallel with a capacitive component. The drive circuit comprises: a selector means (SQ1, SQ2) and diagnostic means. The selector means (SQ1, SQ2) is operable to select the first fuel injector and/or the capacitive component into the drive circuit and to deselect the first fuel injector and/or the capacitive component from the drive circuit. When the capacitive component is selected and the first fuel injector is deselected, the diagnostic means is operable to sense a current (Isense) through the first fuel injector. When the sensed current (Isense) is at variance from a first threshold current (Ilimit) the diagnostic means is operable to provide a first signal on detection of a stack terminal short circuit fault associated with the first fuel injector. The capacitive component may be a second fuel injector.

Abstract: The invention relates to a method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump. The piezoelectric actuator body is housed within a volume of fuel. The method comprises determining a temperature (T—INJ IN, T—PUMP IN) of fuel upstream of the fuel volume, determining a temperature (T—CYL) of the engine housing, and estimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the upstream temperature (T—INJ IN, T—PUMP IN) and the temperature (T—CYL) of the engine housing. By considering the heat transfer between the piezoelectric actuator body, the injector and fuel within the volume, and the heat transfer due to fuel flow through the volume for an injection, the temperature of the piezoelectric actuator body can be estimated by modelling or mapping.

Abstract: A method of detecting faults in an injector arrangement in an engine. The injector arrangement comprises at least one fuel injector having a piezoelectric actuator, and the method comprises: charging the piezoelectric actuator during a charge phase (tC); attempting to recharge the piezoelectric actuator during a test phase (tT) which commences after a time interval (?t) following the end of the charge phase (tC); sensing a current (IS) that flows through the piezoelectric actuator during the test phase (tT); and generating a short circuit fault signal if the sensed current (IS) reaches a first predetermined threshold current (ISC) which is indicative of a short circuit in the piezoelectric actuator.

Abstract: The invention relates to a drive circuit for an injector arrangement comprising a fuel injector, and method of detecting faults in the drive circuit. The drive circuit comprises diagnostic means (RH, RL) that is operable to sense a measured voltage (VBIAS) between the injector and a known voltage level (VBAT, VGND). The measured voltage (VBIAS) is biased with respect to the known voltage (VBAT, VGND) to a predicted voltage (VPinjN, VBcalc) unless the drive circuit has a fault. A fault signal is provided on sensing of a measured voltage (VBIAS) that differs from the predicted voltage (VPinjN, VBcalc). The drive circuit may additionally, or alternatively, comprise diagnostic means (RF). The diagnostic means (RF) is operable to sense a detected current (Idect) and to provide a fault signal on detection of a fault, when the detected current (Idect) is at variance from a threshold current (Itrip).

Abstract: The invention relates to a method of estimating the temperature of a piezoelectric actuator body for controlling the operation of a fuel injector mounted within an engine housing and supplied with fuel from a high pressure fuel pump. The piezoelectric actuator body is housed within a volume of fuel. The method comprises determining a temperature (T—INJ IN, T—PUMP IN) of fuel upstream of the fuel volume, determining a temperature (T—CYL) of the engine housing, and estimating a temperature (T—STACK STEADY STATE; T—STACK DYNAMIC) of the piezoelectric actuator body based on the upstream temperature (T—INJ IN, T—PUMP IN) and the temperature (T—CYL) of the engine housing. By considering the heat transfer between the piezoelectric actuator body, the injector and fuel within the volume, and the heat transfer due to fuel flow through the volume for an injection, the temperature of the piezoelectric actuator body can be estimated by modelling or mapping.

Abstract: A control method for controlling the timing of fuel injection in a fuelling system for an engine comprising a fuel injector supplied with fuel from a source of fuel at high pressure, comprises varying a drive current which is supplied to the fuel injector at a first time so as to initiate or terminate a primary injection of fuel and monitoring the pressure of fuel within the source so as to detect when a variation in fuel pressure occurs. A time delay is measured, which represents the difference in time between the first time and a second, later time at which a variation in fuel pressure within the source is detected.

Abstract: A method of controlling the operation of an engine fuel system including at least one fuel injector, a high pressure fuel pump for delivering fuel to the injector and a pressure sensor arranged to provide an output signal indicative of the pressure of fuel delivered to the injector, comprises the steps of controlling the rate of flow of fuel delivered from the pump to the injector by means of a metering valve arrangement supplied with a control current, measuring the speed of the engine and monitoring the status of the pressure sensor so as to determine whether a fault condition has occurred within the sensor. In the event that a fault condition has occurred in the pressure sensor, the control current supplied to the metering valve arrangement is varied in response to the measured engine speed signal so as to maintain operation of the engine at a substantially constant, predetermined engine speed. The invention also relates a fuel system for implementing the control method.

Abstract: A method of controlling the operation of an engine fuel system including at least one fuel injector, a high pressure fuel pump for delivering fuel to the injector and a pressure sensor arranged to provide an output signal indicative of the pressure of fuel delivered to the injector, comprises the steps of controlling the rate of flow of fuel delivered from the pump to the injector by means of a metering valve arrangement supplied with a control current, measuring the speed of the engine and monitoring the status of the pressure sensor so as to determine whether a fault condition has occurred within the sensor. In the event that a fault condition has occurred in the pressure sensor, the control current supplied to the metering valve arrangement is varied in response to the measured engine speed signal so as to maintain operation of the engine at a substantially constant, predetermined engine speed. The invention also relates a fuel system for implementing the control method.

Abstract: A control method for controlling the timing of fuel injection in a fuelling system for an engine comprising a fuel injector supplied with fuel from a source of fuel at high pressure, comprises varying a drive current which is supplied to the fuel injector at a first time so as to initiate or terminate a primary injection of fuel and monitoring the pressure of fuel within the source so as to detect when a variation in fuel pressure occurs. A time delay is measured, which represents the difference in time between the first time and a second, later time at which a variation in fuel pressure within the source is detected. The measured time delay is used to adjust the time at which the drive current is varied so as to initiate or terminate a subsequent injection of fuel, thereby to ensure initiation or termination of the subsequent injection of fuel occurs at a required time.