Peak & Hold Injector Outputs

Overview

Some GEMS ECUs provide dedicated on-board “Peak & Hold” injector outputs that provide a specially shaped pulse to drive injector solenoids.

Tip

Fuel Injector settings need either the manufacturer’s data (often restricted) or flow bench test results. GEMS may be able to provide Calibration Aspect files for specific injectors or the layout may include selectors for common injector types.

Peak and Hold Injector Drive

Instead of a simple ON/OFF signal driving an injector solenoid, the drive transistor is first driven hard on for a specified time to ensure opening, then the current is dropped to a holding current, minimising heat dissipation in both injector and transistor. When the injector is closed, the driver circuit recirculates energy from the collapsing magnetic field of the injector coil, preventing abrupt closure of the injector which can lead to physical injector damage (fuel leakage) and unpredictable fuel delivery due to pintle bounce.

The peak & hold injectors are active if option iconInjector Peak & Hold = ON.

Note

Note if injector outputs 4 to 8 are not used as injectors their recirculation diodes may be turned on, to reduce currents when used as PWM outputs, so these outputs must not connect to permanently powered devices. Active if not an injector drive when e.g. option iconFuel 1 Recirculate = ON.

Peak

The table iconInjector Peak Time table specifies the time that the drive transistor is fully ON for, prior to entering hold mode. The peak time is dependent on battery voltage, since this directly affects the rate at which the magnetic field within the injector builds.

Some ECUs may include table table iconInjector Peak Decay Time, which is currently unused, future versions may implement this as a smoother transition from peak to hold.

Hold

The frequency and duty of hold signal is given by option option iconInjector Hold Frequency, and table table iconInjector Hold Duty.

Recirculation

The recirculation diode is controlled per injector driver by options option iconFuel 1 Recirculate … option iconFuel 8 Recirculate. Recirculation manages the current flow when the injector is turned off to smooth the closing.

Compensations

Tables table iconInjector Volts comp and table iconInjector Volts comp Secondary allow for additional compensation in response to battery voltage changes.

Compensations are displayed by channels channel iconInjector Comp Fuel Primary and channel iconInjector Comp Fuel Secondary.