Sizing up accumulators

No other feature of a hydraulic hybrid has more effect on the end performance of the powertrain than the accumulator. Modeling helps to provide specific guidance with regard to establishing pre-charge pressure.

Mobile hydraulic applications are typically constrained by package weight and size. Keeping overall vehicle size and weight within limits are important considerations for most manufacturers. End users are interested in adopting novel technologies, such as hybrid transmissions, because their use lowers total cost of ownership (TCO) for the vehicles in which they are installed. However, if the weight and/or volume of a hybrid system causes a reduction in the functionality of the vehicle, TCO may not be reduced.

Thus, one of the key challenges facing developers of hybrid hydraulic transmission systems: the relatively low energy densities of hydraulic accumulators result in their tending to be large relative to their energy storage capacity.