Modelling and Vibration Analysis of a Parallel Hydraulic Hybrid Vehicle

In this paper, the vibration characteristics of a parallel hydraulic hybrid vehicle (PHHV) powertrain are investigated. A powertrain model is built to capture the natural frequencies and mode shapes before model reduction is conducted to simplify the system complexity. The natural frequencies and the mode shapes of the PHHV are compared with the original vehicle. Results show that with a hydraulic pump/motor (HPM) added on the powertrain, the dynamic response to engine excitation is increased only at the first natural frequency. Due to the minimum engine excitation frequency being higher than the first natural frequency of the system, resonance is avoided. The HPM also introduces excitation to the PHHV powertrain due to its instantaneous torque fluctuations. As HPM excitation is much smaller than the engine excitation, it does not produce excessive vibrations even though the powertrain frequency response is near its lowest resonant frequency. These results indicate that the NVH characteristics of the powertrain are not significantly influenced by the significant changes to the system architecture resulting from the addition of the HPM. Additionally, the HPM is not exposed to significant sources of vibration from the forced responses of the engine. Consequently, the need for substantive vibration isolation for the HPM is reduced.