In contrast to constant operating states, particle and NOx emissions of internal combustion engines are significantly higher during transient operating states, which occur repeatedly at working cycles of mobile machines. This paper therefore deals with the conception, development and testing of hydraulic hybrid systems to reduce these emissions by phlegmatization of the engine. A wheel loader with its machine-typical working cycle serves as an example for the investigation of the benefits of such a system. Therefore, model based development techniques are used. In a holistic machine simulation, four different typical wheel loader cycles were carried out and the optimum size of the hydraulic accumulator for the hybrid system is identified by a parameter variation. The lowest emitted emissions and the smallest construction dimensions are the key elements for the accumulator selection. With an optimal hydraulic accumulator, a reduction in particle emissions of up to 29.4 % is achieved in one of the cycles investigated.