【文章內(nèi)容簡介】 icles such as shuttle buses, refuse trucks, and delivery trucks where high power is needed to propel the vehicle and a large amount of energy is availablefor harvesting from braking.The hydraulic hybrid main ponents are a dual function pump/motor (P/M), a lowpressured accumulator (LPA) and a highpressured accumulator (HPA). Hydraulic hybrid vehicles, as shown in Fig. 1, exist in two con?gurations: parallel and series. In the parallel design, which is also called Hydraulic Launch Assist (HLA ) by Eaton Corporation or Hydraulic Power Assist (HPA ) by Ford Motor Company, the hydraulic subsystem (HSS)is integrated in parallel to the drivetrain of a regular vehicle. The main objective is to capture the large amount of the energy that is lost in frictional braking and to utilize that energy to propel the vehicle in its next can be seen as an addon to the conventional powertrain without any fundamental changes of how the vehicle operates. When the brake is pressed, kinetic energy of the vehicle is captured by the P/M to charge hydraulic ?uid from LPA to HPA. When the gas pedal is pressed, the process is reversed. The hydraulic ?ow from HPA back toLPA makes the P/M work as a motor to transform the hydraulic energy to rotational motion at the wheels. In this process, the engine only contributes to the vehicle propulsion when most of the stored hydraulic energy is used.In the series design, as illustrated in Fig. 1, the conventional drivetrain is pletely replaced by the ?uid line connecting two P/M’s. The main hydraulic ponents of this con?guration are the same as the ones of paralle 1 design. The engine only provides the input torque to operate the ?rst P/M. The ?uid power is transferred to the second P/M, which is integrated with the gearbox and located at the rear axel. The hydraulic energy is transformed into rotary motion by the second P/M. This second P/M is also connected to the high and low pressured excess amount of ?uid, during driving cycles, is pumped to the high pressured accumulator and stored regenerative braking process in the series design is done similar to that in the parallel design. In a series HHV the engine can potentially operate at its optimal condition and/or be turned off leading to better fuel economy and less pollution.. Hydraulic hybrid vehiclesHydraulic hybrid technology is being studied at several universities and institutes in the US, Australia, Denmark,and Japan. Matheson and Stecki studied HHV models for heavyduty vehicles such as trucks and buses [21]. They built a regenerative energy powertrain which is similar to the parallel design shown in Fig. 1. It was shown that the performance of HHV is parable to conventional vehicles, while they have a better fuel ef?ciency. As part of this development, a hydraulic hybrid FMTV Army Tactical Vehicle was tested through a series of fuel trials and maximum acceleration test runs to measure the effectiveness of the proposed the use of a HHV model for smaller vehicles such as SUVs and light trucks [19]. With a 7000 lb vehicle and a 150cc pump/motor, analysis showed that it was possible to absorb 72% of the available braking energy in the EPA city cycle with the parallel HHV system. The calculation was done with the assumption of an ideal hydraulic subsystem with no energy loss during liquid ?ow and storage. The vehicle demonstrated even greater bene?ts driving a cycle with more aggressive acceleration and braking events. His study also suggests that HHV architecture may have signi?cant practical potential for fuel economy and performance bene?ts in road vehicles.More recently, the experimental results from the US Environmental Protection Agency (EPA) and its partners have proven the potential of HHV in onroad applications [14]. They introduced the ?rst ever SUV, a Ford Expedition,with the full hydraulic hybrid drivetrain as shown in Fig. 1. It was shown that the fuel economy can be increased by as much as 80%. That bines about 50% improvement in fuel ef?ciency due to hybridization and another 30–40% by switching from a gasoline to a diesel engine. Projected information of acceleration and deceleration time also indicates better performance than the conventional Expedition . Noise and vibration of HHVsAs it is known, hybrid vehicles operate based on the bination of two or more power systems. Those power systems are alternating to provide propulsion for the vehicles. Therefore, each power system is at one of two states during its working cycles. The states are on (operating) and off (idling or shutoff). Besides, the vehicle’s powertrain is experiencing the engagement and disengagement from those power systems when they are turned on or switched off. A signi?cant amount of noise and vibration e from the switching states and the engagement/disengagement mechanism of the hybrid vehicles [30]. Kepner pointed out that one of the main problems with the hydraulic hybrid subsystem is the high level of noise and vibration [19]. This is partly because the system’s operation is based on ?uid ?ow at high velocity and high pressure. The peak pressure in the highpressure accumulator can be as high as 5000 psi. During braking events, pumping noise is noticeable. The primary sources of noise are from the pump/motor pistons passing by the pump ports, and from hydraulic valve opening and closing events. Noise alsocan be generated by hydraulic ?uid ?ow inside the tubing system. Prek investigated the noise problem of hydraulic systems generated by tubing geometry [23]. The research indicated that the geometrical parameters determine the levels and characteristics of noise emission. On the other hand, Johansson et al. suggests dealing with the hydraulic systems noise problem at its origins [18]. The noise and vibration created inside the pump/motor mainly have two different origins. First, the cylinder pressures acting on the pistons will create piston forces inside the P/M. Second, the pump generates ?ow ripple