Application of Hydraulic Body Mounts to Reduce the Freeway Hop Shake of Pickup Trucks

When pickup trucks are driven on concrete paved freeways, freeway hop shake is a major complaint. Freeway hop shake occurs when the vehicle passes over the concrete joints of the freeway which impose in-phase harmonic road inputs. These road inputs excite vehicle modes that degrade ride comfort. The worst shake level occurs when the vehicle speed is such that the road input excites the vehicle 1^st bending mode and/or the rear wheel hop mode. The hop and bending mode are very close in frequency. This phenomenon is called freeway hop shake.

Automotive manufacturers are searching for ways to mitigate freeway hop shake. There are several ways to reduce the shake amplitude. This paper documents a new approach using hydraulic body mounts to reduce the shake. A full vehicle analytical model was used to determine the root cause of the freeway hop shake. Experimental hydraulic engine mounts were installed in place of body mounts on a modified pickup truck to confirm analytical findings and establish the initial tuning strategy for a hydraulic body mount. Three different designs of hydraulic body mounts were prototyped for on-vehicle evaluation. The on-vehicle experimental results demonstrate that hydraulic body mounts can be an effective solution to reduce the freeway hop shake.