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May 07,2024

Power Distribution Module (PDM)

In the past, the power distribution module has been built with relays and fuses, in some cases (even today) as a plug-in for a punched grid box. The only function has been to connect and disconnect the battery to the loads and modules. To replace faulty relays or fuses, the box had to be located at easy accessible areas of the car.

Today, the technology and concept of the power distribution module are evolving towards one of a Body Control Module (BCM) or Electronic Control Unit (ECU) where relays and fuses have already been replaced by semiconductors two decades ago. Replacing relays in a power distribution module by semiconductors and adding intelligence to it with a microcontroller has the great advantage of integrating new functions for the power distribution module: supply, communication, control, and actuation. Additionally, it removes the accessibility requirement, thanks to its newly enhanced component protection and reliability.

Finally, one important benefit of such a smart power distribution module lies in the wire harness. The integration of multiple functions and the now possible optimization of its location in the car enables the wire harness to be shorter, thinner, and less complex.

Power distribution module system designs require:

Developing an automotive electrical distribution system: Part 1

By Nigel Hughes, Mentor Graphics 0

The electronic content of a modern car has become one of the key brand differentiators in the market place. Alongside the obvious problems in ensuring that the latest technologies are available to be included is making sure that the associated systems supporting deployment into the vehicle can be developed and integrated into the final production vehicle. Any problems are compounded by the pressure of ever decreasing design cycle times. As can be seen from the graph below, cycles have now been reduced to between 24 and 18 months, with a clear goal for most OEMs to reduce this to 12 months by 2010. Within this cycle the electrical distribution system supporting the electronic content must be designed, validated, and deployed. Doing this is increasingly dependent on developing new processes and tools to support those processes. In order to preserve a reasonable margin, automotive OEMs must also see that an appropriate return is gained from the technology, by specifying vehicle models with an appropriate set of options in order to support accurate pricing. Recently the market has witnessed a dramatic increase in the amount of optional content in vehicles. This trend pushes the need to make the latest technologies available, whilst ensuring basic car models are still available in an extremely price competitive market. Re-use caveats

A key part of these new processes is increasing the amount of re-use of previous designs. Traditionally this has involved a painstaking process of taking existing wiring designs and carefully updating them for new vehicle platforms. This manual process inevitably introduces errors, and demands significant validation and verification. Re-use of previous designs tied to a particular platform is difficult. Almost all details of the wiring will change as it is integrated with a different physical platform. For example, all of the wire lengths will need to change, as will locations of in-lines and splices. However, logical systems can be designed which are re-usable and provide a sufficient level of abstraction to significantly increase the amount of direct re-use whilst still not requiring large amounts of manual re-work. Process overview

We will consider each stage of the high-level process shown below in more detail later in this article, but this diagram provides a useful overview of the broad context in which an electrical distribution system (EDS) is designed.

View a full-size image First, systems are selected from any available libraries that will implement the required functionality. Of course new vehicles will typically deliver at least some new content, and those systems must be developed (sometimes by a Tier 1 supplier). All captured systems are normalized (option and variant expressions from the particular platform applied) and shared connectivity identified. Then the designs must be placed in the context of the harness topology (the physical routes the wires will take through the vehicle), and the nets (signals) converted into actual wires inside harness bundles. Components such as fuses and wires can now be sized appropriately based on the amount of current they are expected to carry. Once this process has been completed, individual wiring diagrams can be generated which are then passed on to service groups, who will re-layout the diagrams ready for service manuals or other distribution channels. The harness designs themselves will be passed onto the harness engineering groups who will further refine the detail of the physical implementation, adding mechanical components such as clips and grommets, as well as specifying terminals, harness dressings, and coverings. We will now consider each of the stages shown in the process overview diagram in more detail.

The starting point in our flow is collecting together existing system designs that will be re-used in the new vehicle model, or platform. In order to make systems more re-usable than their physical implementation in a wiring diagram, a more abstract representation is needed. The devices (or components) are placed together, and connected by nets which carry the signals (e.g. power or sensor readings) between the devices. An example is shown in the figure belowÂin this case an in-vehicle entertainment system.

View a full-size image Signals run from the AUDIO_UNIT to the speakers, as well as providing I/O from separate elements such as the CD CHANGER. With the connectivity captured in this abstract form, it is possible to import them from a library into a specific vehicle platform. These systems must also identify their optional content. For the in-vehicle entertainment system, we can see a number of areas that have been marked out; the additional two speakers (marked 6 speaker), and the sub-woofer. These are purely visual indications that the system contains optional content. What is optional and what is standard is determined by the marketing plan for a particular vehicle. As such, a high-end platform may include all content as “standard;” a low-end platform may have everything as additionally purchased options. Therefore, the content of the design will have to be marked with the applicable option tags for any given platform. Other considerations include grounding and power. Note in the diagram above that all

devices have their own grounds. These are logical grounds that may be combined into a single physical ground when placed inside the vehicle. This process will happen during the physical integration stage described later. Power, and the attendant fusing, also provide some unique challenges. Each device requires power, but we may not wish to represent the ignition system on every diagram, and almost certainly cannot specify a specific fusing implementation in a re-usable system design. As a result a typical process involves placing shared nets (nets that appear in many diagrams that are actually single logical entity) that supply the power. These can be seen in the diagram labelled PWR_IGN_RUN and PWR_IGN_ACC. At a later stage a power system design will be created that connects all of these shared power-supply nets to the fusing architecture being used in the vehicle and associated power-supply components (e.g. batteries and alternators). We might, for example, want to progress to initial topology creation and wire synthesis before coming back to finalize the specification of the fuse architecture. These cycles will require that there are multiple versions of a system during its life-cycle. Releasing and revisioning

The process of managing multiple versions of wiring system designs will be heavily dependant on the requirements of the OEM, however there are some consistent common themes. When releasing a design it becomes read-only, and therefore cannot be edited itself. The intention is that only released designs will be taken forward to the integration stage. Of course, it is unreasonable to assume that no further changes will take place. Therefore, there may be a need to produce a new revision of a design (a copy of an existing design, where the relationships between content in the new design are traceable to the original design), which can then be edited and the changes re-integrated into the vehicle. An example of where this release-revision-release cycle should be expected is the power system design described earlier, which is expected to change as the systems are integrated into a particular platform. Looking back at our flow, we have now collected the existing designs being re-used, and developed the additional system designs required for this platform. Once a set of designs has reached a sufficient level of maturity they can be released and grouped together into a set, or build-list, of versions that are compatible with each other. A change to the power design may necessitate a revision in another system and only those two versions are compatible with each other. This build-list can then be passed onto the integration stage.

The systems are now integrated into a harness topology. Once again the source of this topology will vary from one OEM to another, but a common source is from an MCAD tool. Common tools in use include UGS NX or Dassault CATIA V5. These harnesses must be bridged into the design tool and connected together. The bridging process in modern software tools is no longer a complex and delicate procedure, often allowing manipulation of the data as it is converted from the 3D world into the 2D topology.

View a full-size image The topology could also be drawn manually directly in 2D, and later synchronized with a 3D model as it became available. Location and rules

Now that the topology is complete, we can move to the next stage of the flow and place devices from system designs into the harness topology at their correct locations. For example, our stereo would be placed into the centre console attached perhaps to the instrument panel harness. Some devices may have multiple locations depending on options or variants. For instance, left or right hand-drive configurations will cause an instrument binnacle housing or cluster) to be placed on one side or the other of the vehicle. Rules, the second part of this stage in the flow diagram, can be used to control the automatic placement of components discussed above. A rule is formal description of heuristic used by an actual wiring engineer, such “as place all fuses connected to devices on the engine harness in the engine fuse-box.” The benefit of capturing this in a software tool is that this expertise can be repeatedly and reliably re-applied. Of course, these rules are used not only to constrain where devices are placed, but also how wiring is generated, the next stage in the flow. For synthesis, appropriate rules might include limiting the number of wires that can be spliced together (perhaps changing that limit depending on if it's a wet or dry harness), the distances between splices and their devices, and the maximum length of a wire. These rules, applied to the released systems, which have been integrated into the harness topology, can be used to complete the next stage of the flow, the synthesis of the actual wiring. Wiring generation

Before individual harness derivatives supporting particular vehicle models can be produced, the “150%” or “composite wiring” must be generated, supporting all allowable combinations of options. This composite wiring will never be used in a single car delivered to a customer, and as such is “un-buildable.” To actually define the different buildable configurations we must then generate derivatives of each harness that contain a subset of the generated wiring and splices. The initial set of configurations may produce more derivatives than can be cost-effectively manufactured and therefore decisions will be made about options that may have their associated wiring “given away.” This might perhaps mean that the wiring for a six-speaker system is always included in all harnesses regardless of whether or not the customer has selected that option. Typically each harness will have between 10 and 20 different manufactured derivatives. Although there may be a number of cycles back through the process (applying changes to system diagrams, and re-generating the wiring) a full EDS design has now been completed. It is now possible to hand-off automatically generated wiring diagrams of systems, or parts of systems, to service documentation groups to be included in electronic or printed service manuals. The harnesses themselves now enter a new stage of their development. This is discussed in Part 2 , where simulation and analysis techniques can be applied to an electrical distribution design flow to make it more efficient and less costly. Nigel Hughes is product marketing manager, Integrated Electrical Systems Division, at Mentor Graphics.