Experimental Vibration Assessment of a Fuel Cell Transit Bus 2005-01-3449

Energy efficiency and vehicle emissions have been the primary emphasis in comparisons of conventional vehicles to battery electric and fuel cell electric vehicles. Other basic aspects, however, also need to be evaluated between these technologies. One such aspect is the comparison between the vibrations that each system imposes to the vehicle, its operator and passengers. Comfort level, as well as operator fatigue, is increasingly being considered as a problem in on-road transit systems today. The problem is particularly critical considering applications such as long-haul trucking and public transportation systems, and increasing distances in daily commutes. It is widely understood that battery electric and fuel cell electric vehicles provide a smoother ride than vehicles equipped with conventional internal combustion engines. Intuitively, the internal combustion engine imposes higher vibration levels to the vehicle than the battery and/or fuel cell systems, thus causing increased stress to the operator and passengers. Interestingly, there has not been extensive public quantitative comparisons of the vibration aspects inherent to these vehicles.

In this study, two transit buses of comparable size were operated and their vibration characteristics were measured. A conventional 9-m diesel bus and a 9-m fuel cell/battery electric hybrid were selected for these tests. Stationary idling conditions, as well as steady state dynamic road operation, were tested with both buses to simulate normal operating conditions. Accelerometers were installed at five locations of highest interest throughout each bus. The driver's floor location was monitored for vibration levels along with two passenger's floor locations at the mid and rear of the passenger compartment. One accelerometer was also installed at the top of each bus engine for measurement of the primary vibration levels and another on the rear axle to quantify the amount of vibration induced to each bus from the roadway. The buses were monitored under the same driving conditions in an effort to decrease measurement error due to variability from the road tests.

The results of this study showed significant differences in total root-mean-square (rms) vibration levels between the buses. As expected the fuel cell electric vehicle showed lower vibration amplitudes. This study supports the claims that vibration reduction is feasible with the adoption of fuel cell technology.