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Case Study: Drivetrain Complexity

A case of one change to the arrangement of automotive drivetrains turning into a radical change.

drivetrain02.jpgFig. 1: A conventional front-wheel drivetrain.

Consider a conventional front-wheel drivetrain as shown in figure 1. Consider only steering, suspension, power, and braking. Notice how power must be driven from the engine, through the steering and suspension, to reach the wheels.

This induces a great deal of complexity. The drive shafts for the front wheels must not only transmit power from the engine, but also respond to vertical movement/forces for suspension, and rotational movement/forces for steering.

conventionalfrontwheeldrivetrain.jpgFig. 2: A simple system model of the conventional drivetrain.

In figure 2 we have a simple representation of the systems in the conventional drivetrain and the overall complexity of the system, based on a method of complexity analysis. Note its complexity is 1053. The complexity derives mostly from the multiple interfaces between individual subsystems. And the number of interfaces relate significantly to the way the engine is “in parallel” with other subsystems.

This raises the question: What if we could linearize the topology of the drivetrain to cut back on the number of “extra” system interactions?

This question was explored by Michelin when they developed their Hy-Light drivetrain concept. In Hy-light, there is no “engine,” but rather each wheel has an electric motor built into it. This seems pretty obvious when you think about it. A wheel-tire assembly has two basic elements: a tire the rotates about a stationary central hub/shaft. Electric motors have the same basic (albeit inverted) structure: a stator and a rotor.

Michelin designed Hy-light to have this kind of motor, which puts force generation at the very end of a chain of subsystems. But they didn't stop there. Since the so called “wheel motor” now had a sizeable empty space in its centre, they put the suspension system directly into the wheel too, and then arrange the steering system to turn that whole motor+suspension system.

unconventionaldrivetrain.jpgFig. 3: Schematic and complexity of the Hy-light system.

The result is a highly linearized drivetrain, as shown in figure 3. Notice that the complexity of the Hy-light system is now only 294. Complexity has been drastically decreased. This leads to improvements in efficiency, reliability, manufacturability, control and manoeuvrability, cost, and so on.

hylight1.jpgFig. 4 hylight2.jpgFig. 5

In case you're wondering, yes, the Hy-light really exists. In figure 4 and figure 5, you can see some close up images of actual Hy-light drivetrains. All you need is a power cable and a data cable to each wheel, and you're set.

Below is a video showing a car equipped with a Hy-light drivetrain.

design/case_study_drivetrain_complexity.txt · Last modified: 2021.11.23 13:59 by Fil Salustri