Electronic control unit for the Instant Start System (ISS) for diesel engines
BERU AG has developed the ISS glow system (Instant Start System), comprising electronically controlled steel glow plugs and an electronic control unit in order to meet new customer requirements for diesel engine cold starting.
The main function blocks of the control unit are a microprocessor for controlling all the functions, MOSFET power semiconductor for activating and deactivating the individual glow plugs, an electrical interface for communication with the engine control and an internal voltage supply for the microprocessor and the interface. The microprocessor triggers the power semiconductor, reads its status information and communicates with the engine control via the electrical interface. The power semiconductors are so-called high-side switches with integrated trigger and safety functions such as a load pump, a current limiter and an over-heating safety shut-off. The gate voltage required for triggering the actual switch transistor is generated with the load pump. Status information, such as open or shorted load circuit and activated over-heating safety shut-off, is supplied in the form of an output signal. In order to prevent any electromagnetic compatibility (EMC) interference by the timed action of the high glow plug currents, with frequencies from 30 to 100 Hz, a flank control has been incorporated within the power semiconductors. This prevents voltage or current changes taking place too quickly in the load circuit which might lead to EMC interference. The interface performs the task of adjusting the signals which are needed for communication between engine control and microprocessor. The voltage supply delivers a stable voltage for the microprocessor and the interface.
We recommend installing the glow plug control unit on the engine itself. The advantage of this is that the high-current cable connections for the connections to the glow plugs and the on-board power supply are kept short; this does however create very stringent demands on the mechanical stability of the control unit as well as the electrical structure and connection system. For connecting the control unit Beru, in conjunction with vehicle manufacturers and producers of plug-in connectors, has developed a two-part connector system for the on-board power connection (terminal 30) and the other connections.
The control unit housing consists of a metallic base plate, a plastic frame with two connectors and a cover. The circuit board containing the electronic components is glued onto the base plate, providing thermal conductivity, and linked to the connectors by way of thick wire bond connections. An oxide ceramic, that electrically insulates the circuit against the base plate which is connected to the chassis potential, is used as a base material for the circuit board, ensuring good heat dissipation from the power semiconductors into the base plate.
