Composite supersets tame wiring harness engineering complexity
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.
Process overview
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.
Data-centric design tools
The part number-based harness design approach has worked for decades, but emerging data-centric design tools and database technologies are changing the landscape. They enable the composite harness flow, which has several important advantages as summarized in Table 1 below.
This is a job for supersets!
Modern data-centric EDS design solutions are architected to encourage composite harness development practices. A single data entry creates the composite superset comprising the entire vehicle’s diversity. Most importantly, the toolset automates the process of engineering individual, fully validated derivative harness products that are ready for manufacturing. Figure 2, below, summarizes the many automated functions that transform the data of a superset into a collection of individual derivative harnesses. The process works because the superset is the universe that contains every wire, connector, and attachment that any derivative will need. The superset together with the complexity table implies every derivative.
Figure 2: A data-centric environment automates many of the most time-consuming and error-prone derivative development steps.
Figure 2 itemizes the automation-related features of a data-centric flow in the context of developing derivatives from the composite. The underlying flow is also a valuable ally in documentation (particularly for diagrams) and reporting. A data-driven BOM inherently reflects the actual design data, and because it is automatically generated it doesn’t tax the engineers’ time or patience.
Advanced data-centric design tools can also divorce style from content. The graphical display of harness design data can be configured to present the needed visual appearance at the click of a button. It can maintain multiple views for a single design, including engineering views, OEM standard-compliant views, and scaled views for formboards.
Reporting, too, gains new efficiencies. Figure 3, below, depicts a harness design in four separate diagram representations. These can be displayed simultaneously on a computer screen of appropriate size; each view is accessible with just one or two mouse clicks. Equally important, edits made on any diagram automatically appear on all diagrams. If, for example the bundle length is changed on the non-scaled diagram (Figure 3-1) the length changes accordingly on the formboard view (Figure 3-3). Fixtures and drill-points are automatically modified as well, based on rules recorded in the database.
Figure 3: Changes in any harness view are automatically reflected in all views.
Change management is a fact of life in every engineering organization. In the automotive industry, changes are sometimes submitted daily. Change management is one of the most compelling reasons to move from a harness drawing-based process to a data-centric flow exploiting composite supersets. Imagine the difficulty of analyzing a daily stream of changes and their effect on hundreds of individual harness implementations and cost estimates!
The composite superset approach transforms the discipline of change management by inherently preserving consistency among derivatives. The composite design maintains a clearly-designated master for the propagation of design changes. The system automatically assesses the design change impact and how the changes are applied to each harness derivative—helping to control the flow of data between design stages and ensuring the consistent integration of the modifications.
A composite data container also speeds the process of reviewing and revising the derivative mix. A composite-based approach to managing harness diversity can dramatically improve flexibility in changing the derivatives mix. Take rates can be compared periodically against forecasts, and the derivatives mix can be revisited through the complexity table alone. This greatly simplifies what otherwise would be a major engineering change.
Costing automation
Harness manufacturing is a low-margin, labor-intensive business. The difference between profit and loss rests on the ability to accurately and reliably cost the material content plus the machine and labor time involved in manufacturing. Traditionally, harness cost estimating has been performed by experts who use in-house tools or spreadsheets to analyze the content of harness designs.
But this is changing with the acceptance of data-centric processes and the composite superset methodology. Just as derivatives processing is automated and controlled by engineering rules, the costing rules are integral to the process.
For example, the costing engineer maintains an order price and a selling price for each component. Expenses such as exchange rates and freight values also can be incorporated. For every assembly step, the times and rates for wire cutting, crimping, connector assembly, etc. are recorded and standardized. As a result the costing engineer can focus on analyzing rather than executing costing reports and comparisons, leaving the tedious calculations to the computer.
Reporting includes supplier analysis, costing comparisons, cost center analysis and even more. It is even possible to simulate different environments, techniques, volumes and overheads when assessing the harness.
Automated costing applied to each individual derivative within a composite superset reduces the lead time for quotes. This is a key competitive differentiator in OEM business transactions. The OEM can trust that the supplier has a robust process to perform repeatable quotes with a quick turn-around, and the supplier has all the data needed to ensure business profitability.
Conclusion
Composite supersets can make harness design, engineering, and production more efficient, accurate, and profitable. One-time data entry and automated processing work together to eliminate many time-consuming steps in the overall process. Automation of manufacturing reports and formboard diagrams improves quality, since the production line receives consistent data from engineering. Change management, too, benefits because design changes automatically ripple through derivatives from the composite master. And lastly, the automation of costing on a derivative basis with no resource overhead dramatically improves business partners’ relationships and profitability.
About the author
Elisa Pouyanne is the automotive business development manager for Mentor Graphics Integrated Electrical Systems Division. Elisa has been with Mentor Graphics for 12 years, where she has held a number of customer-facing roles, working with most of the major automotive OEMs and wire harness manufacturers deploying Mentor’s flagship EDS design platform, Capital. These engagements include redefining processes, making recommendations on design methods, managing deployment projects, and compressing time-to-value for corporations adopting Capital.
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