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“Beaming” in trucks is due to a bending vibration of the frame resulting in a fore-aft motion at the driver location. It has been found that beaming motions are relatively unaffected by the suspension type or components, and, in particular, by the shock absorbers. Since beaming is due to a distributed dynamic effect, it is believed that modal nodes exist near the suspension attachments to the frame thus rendering the suspension ineffectual at controlling beaming. Another explanation of beaming is that an overall system dynamic mode exists such that at a specific frequency the relative velocity across the suspension is near zero thus producing little damping for that mode. This concept is developed here through the use of some simple models. The sensitivity of beaming to system configuration is then demonstrated through use of a rather complete overall tractor/trailer model.

Large vehicles such as buses and trucks suffer from a dynamic resonance problem due to flexure of the vehicle frame. This type of vibration is called “beaming”. Unlike smaller, (relatively) stiffer automobiles, this flexural vibration occurs in these large vehicles at a frequency very close to the wheel-hop frequency and body motion frequencies, and thus is excited easily by typical roadway inputs. The effect of beaming on ride quality differs from one vehicle type to another due to the mounting of the passenger compartment to the frame. A model that provides insight into the beaming problem is formulated using bond graphs. Bond graphs allow coupling of lumped dynamic effects with the distributed dynamics of the frame, and they permit virtually automated computer coding so that different vehicle types can be simulated using basically the same model. The model utility is demonstrated for some simple automatic control strategies aimed at controlling beaming.