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Siemens Intelligent Switching Unit Leads On Power Management

19 October 1998

Siemens Intelligent Switching Unit Leads the Charge On Better Power Management

    DEARBORN, Mich., Oct. 19 -- The latest generation of Siemens
Intelligent Switching Unit (ISU) technology addresses the industry's rapidly
increasing need for optimal electrical power distribution management, while
substantially reducing wiring harness complexity, size and the number of
interconnects.
    "It's not just about more power, it's about better management of that
power," said Joe Fadool, Marketing Manager of Body Electronic Systems, Siemens
Automotive.
    "Whether a vehicle is equipped with a standard 14-volt electrical system,
or transitions to a more powerful 42Vdc (36V battery) power supply, the
crucial need is for optimal management of that power," said Fadool.  "The
ongoing proliferation of electrical/electronic applications throughout the
vehicle will continue to drive the need for a larger power source, and for
optimal, more efficient management and distribution of electricity to the
point(s) where it is needed, at precisely the time when it is needed."
    While providing a method of optimizing electrical distribution, the
Siemens ISU also brings improved efficiencies to the electrical distribution
system resulting in 20 percent less wiring and 15 percent fewer connectors.
The overall result is a package and weight reduction of nearly 25%.
Additionally, quality improvement and cost savings are realized through the
elimination of wiring.
    The ISU contains fuses, Positive Temperature Coefficient devices (PTCs),
relays and semiconductor power for implementing such features as lighting,
remote entry, immobilization, anti-theft, timer and chime functions.  It also
can implement splices in order to simplify further the wiring architecture.
    The average electrical load in many luxury cars is expected to increase by
a factor of three by model year 2005.  Technologies soon to be introduced that
are driving the load increase include: electronic power-assist steering,
electro-mechanical braking systems, electronic throttle control, electronic
valve timing and air conditioning.
    "These new technologies will place much higher demands on the electrical
power source while less load will be placed directly on the engine," Fadool
said.
    Anticipating this growing appetite for power, the 42V power supply is
expected to readily meet the task.  "However, the solution is not as simple as
adding higher voltage and more semiconductors," explained Fadool.

    The ISU Difference
    The benefit of an intelligent system, like the Siemens ISU, translates to
improved fuel consumption, extended battery life and better overall customer
satisfaction.  For example, "the ISU could sense when the state of battery
charge reaches a low level and it would immediately attenuate certain
unnoticeable loads, such as the rear defrost, until enough energy from the
alternator is available again," Fadool explained.
    The concept of the ISU lies in the combination of the power distribution
system and sophisticated body electronics.  The integration of these two
systems is only possible through the deployment of many key technologies
developed by Siemens.  These include: "smart power" using solid-state devices,
in lieu of conventional fuses and relays, to provide improved power and
circuit protection; and the use of flexible (Flex) Printed Circuit Board (PCB)
substrates in place of conventional fiberglass PCBs for improved packaging.
    According to Fadool, electronic advancements such as smart power and Flex
PCBs could only be developed by a world-class wire harness manufacturer and
electronics leader.  "We are one of the few automotive technology companies in
the world able to bring both groups of technology together," Fadool said.
    Siemens Automotive is presently developing its fourth generation ISU
technology.  Through ISU development, Siemens intends to eliminate, entirely,
the need for fuses, which improves serviceability and reliability.