Broadly Consider Alternative Solutions with a Set-Based Approach

April 25, 2009 - Tags:

As a young Toyota engineer, you attack a problem with relish. You carefully identify the cause of the problem, taking care to do a thorough five-why analysis. You then think and think and come up with a brilliant solution. You detail the solution and run in to share it with your mentor. Instead of evaluating the idea on its merits and congratulating you, he asks, “What other alternatives have you considered? How does this solution compare with those alternatives?” You are stopped dead in your tracks, as you were convinced you had the best approach.

When my colleagues and I started to study Toyota’s product development system, we noticed a distinguishing feature of Toyota, compared not only with U.S. auto companies but also with other Japanese companies, like Mazda and Nissan. Toyota senior engineers and managers were trained to think in sets of alternative solutions. Moreover, they could think concurrently about how things like the design of the product and the manufacturing system fit together. We called this “set-based concurrent engineering” (Ward et al., 1995). It seemed paradoxical that considering such a broad array of alternatives required so much time and delayed decisions, yet Toyota was consistently faster in product development than its competitors.

There are many examples of this in the Prius development discussed in The Toyota Way in The Prius Blueprint:

  • In developing the new suspension needed for Prius, Uchiyamada decided to hold a competition. Instead of using trial and error and testing one suspension alternative at a time, the competition led to over 20 different suspensions tested simultaneously.
  • There were many hybrid engine technologies to choose from. The team began with 80 different hybrid types and systematically eliminated engines that did not meet the requirement, narrowing it down to 10 types. The team carefully considered the merits of each of these and then selected the best four. Each of these four types was then evaluated carefully through computer simulation. Based on this, they were confident in the one alternative selected.
  • The styling of the vehicle was also based on a competition among design centers in California, Europe, Tokyo, and Toyota City. Over 20 designs were put forward in the first wave of the competition, which were narrowed down to five sketches and then four life-sized models. Two were then selected as exceptional and each was revised based on feedback from a wide range of employees until one was finally selected.

Recall that there was extreme time pressure in the development of Prius. For any of these decisions, Uchiyamada could have asked for an opinion up front on the best choice and then developed the one option and refined it through iteration. But the iterative approach, what we called “point-based,” might have completely missed a much better alternative. Part of spending the 80% of time planning that Warren spoke of in the opening quote is considering a broad range of alternatives before deciding on one. Senior managers at Toyota have told us that one of the hardest and most important lessons they teach young engineers is to delay decisions until they have considered a broad array of alternatives. One of the advantages of getting many opinions from many different people (through nemawashi, discussed next) is that many alternatives are brought to light that can then be systematically evaluated.