Today’s electrical system designers are dealing with burgeoning complexity, much of which is due to the many electrical options and physical variants that arise with every high volume automotive platform. End users want ever more features and capabilities, and these must be interconnected, powered, monitored, and controlled. A long list of mandatory safety features and emission controls also adds to the burden of complexity.
Potential configurations for a single platform may number in the millions. While hardware components ranging from window motors to ECUs are involved, and software plays a crucial and growing role, the electrical distribution system (EDS) harness is at the heart of the complexity challenge.
Not surprisingly, enterprises have turned to dedicated harness design software tools to manage their processes. These solutions are proving to be indispensable in helping vehicle makers plan, design, document, produce, and cost their products, automating many of the necessary steps along the way. But designers still must find ways to cost-effectively produce many, many variations of each of the harnesses interconnected within a vehicle.
One effective way to accomplish this is to use composite supersets. This approach takes advantage of the fact that, though there are potentially thousands of harness permutations for a given vehicle model, many of them differ only minutely.
To define the term composite supersets, it’s useful to consider the meaning of each word separately: Composite means “combining the characteristics of two or more elements of a group;” while a superset is a set that includes one or more subsets. So a composite data superset describes a hypothetical harness product that encompasses all usable configurations with all the associated wires, connectors, clips, and tape.
Note that this superset harness is unlikely to be built in physical form because it is likely to contain mutually exclusive elements such as wiring for both gasoline and diesel engines. The composite data set is described as the “master”, the “harness family” or the “150%” harness definition. All wires and related components such as clips or insulation runs are option-tagged in the composite design. They are described with combinations of codes that associate them with the options they support. A harness product supporting a given combination of options is known as a derivative harness of the composite superset.
Figure 1, below, illustrates (in simplified form) the composite design and its relationships with a collection of derivative harness products, each supporting one or more end-product configurations. It is the complexity table which identifies these individual harness part numbers and their respective optional electrical content.
Figure 1: The composite superset harness implies multiple derivatives, dramatically simplifying the tasks of design and documentation.
At the inception of the process, the OEM defines harness requirements. Specifics include:
- The wiring connectivity
- The partitioning of the vehicle EDS into harness families for each zone within the vehicle
- The physical routing of harnesses within the vehicle, which may include variants for different body shapes
- Information about the options and variants product mix
The requirements are submitted to wire harness suppliers for engineering and quote. Full service providers, in-house or external, engineer the product. They implement the requirements in such a way as to support all the option-driven variations. Usually this includes deriving the part numbers for each harness family. Business-wise, the wire harness manufacturer’s goal is to produce a 100% accurate, error free bill-of-materials—per derivative—that can be fully costed and passed on to production for assembly. The accuracy of costing is of course critical because it provides the visibility the harness supplier needs to set a competitive, but profitable, price level.
In the real world, the OEM’s requirements are likely to change over the course of a project, which means that the harness supplier must have a means to quickly and accurately re-quote the deliverables and adapt the production process.
Until recently, most enterprises have relied on part number-based harness design flows wherein each configured harness is engineered independently of other harnesses, irrespective of their common and differing features. Over the past 15 years, this entrenched behavior has been changing. A single master harness design can be maintained, encompassing all the specifications that the supplier must meet when delivering an entire family of derivative harnesses—each supporting one or several target configurations.