American Ergonomics Corporation

Innovative Seat Technology for Comfort and Safety

New Seat Mechanics to Reduce

Occupant Injury and Enhance Comfort

Hector Serber
American Ergonomics Corporation

Copyright © 1998 Society of Automotive Engineers, Inc.

Injury Load Trade Offs
CBM Seat Mechanics
Sled Test Results
Optimization Methodology
MADYMO Crash Simulations
Road Test
Performance Summary


The Counter Balanced Motion (CBM) design utilizes the seat cushion as a crash safety restraint. Just as the air bag becomes a cushion to absorb deceleration forces on the upper body, the seat cushion is used to absorb deceleration forces on the lower body.

Crash simulations of the CBM yield a 33 to 70% reduction in injury loads to the chest and legs. This brings applied forces below bone and joint failure loads.

In addition, impact loads applied to the lower leg become negligible by retracing the feet away from the toe pan and Head Injury Criterion values are reduced 13 to 30%.

The appearance and posture alignment of seats equipped with the CBM mechanism are identical to current production seats. Figure 1.

Figure 1: Seats Equipped with CBM Mechanism

This paper describes the CBM Seat mechanics, design and function. The functional capabilities are verified by three different, independently performed approaches: 1. dynamic analysis, 2. sled tests, and 3. Madymo crash simulations.

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