Automotive Design Case Study

As cars started getting smaller, this size reduction affected various storage areas within the cars that typically had sufficient roominess. As an example, the trunks shrunk in volume, and as a result, auto designers looked at the various components in the trunk to see if said components could also be shrunk in size. The largest entity in any car trunk is typically the spare tire. The tire companies were then asked to develop much smaller spare tires, with the new parameter of having only limited needed mileage, rather than the normal tire's standard mileage.

One of the early tire solutions was a unit that had side walls and tread area that folded inwards, so that the overall volume was greatly reduced. The tire was to be supplied with a device to then inflate the tire, causing it to expand in volume to a size comparable to the other tires on the car.

We were asked to design a very cost-effective air compressor that could be used for such a purpose. As well, it could be used for various other functions such as blowing up air mattresses, etc., for the vehicle owner. The compressor was to reach 28 to 30 psi output pressure reasonably quickly, to be able to be stored for years without losing its capability, be user-friendly, and low cost.

The design of a compressor is extremely simple, being typically a piston, a cylinder, an inlet and an outlet check valve, and a hose to distribute the air to the needed device. At this pressure, all this could easily be designed in low cost plastics.

The challenge was to determine a highly cost effective power source to drive the compressor piston. All vehicles have various potential sources of power (electrical, hydraulic, etc.). All these however typically then require some costly componentry (electric for instance usually means an electric motor). We finally settled on using engine vacuum as the driving means, as utilizing it is nearly free (a simple hose connection to the engine manifold is required). So, the unit now became an air-driven, air output device.

As the compressor side was a piston in a cylinder, with its up/down movement, it was logical to create the vacuum drive side with a piston in a cylinder, directly connected to the compressor piston. The design challenge was to create a valving system to cause the engine vacuum to shuttle the driver piston up and down. Finally, the design settled on a vacuum cocked, spring released concept, where the valving system caused vacuum to pull the driver piston down against a spring, at which time the vacuum valve was shut, and atmospheric air flowed into the evacuated area, thereby pressure balancing the driver piston. As the driving spring was fully ‘cocked’, it then drove the piston assembly forward, causing the compressor piston to pressurize the air trapped in the compressor cylinder. At the end of its travel, the driving valve again opened engine vacuum to the driving piston, and the piston again started to compress the driving spring. This happened over and over rapidly, so rapidly that the tire could be fully inflated to 28 to 30 psi in a matter of three minutes or so.

With the exception of the springs (driving spring, check valve springs), all components including the piston seals were made from various plastics, principally polypropylene.

The design was released for production.

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