AS A CONSEQUENCE OF increased requirements concerning pleasant working conditions, the system designer of today is facing challenges besides the traditional performance related ones. Subjects such as cleanliness, low sound and vibration levels etc. play important roles in modern system development. The requirements have resulted in considerable improvements on machineries in general, but still the noise often reaches unacceptable levels. In many applications of today, the noise emitted by the hydraulics can be identified through the totally emitted noise, and the trend towards increasing working pressure, which is directly correlated to noise and vibrations, seems to last. Therefore, studies regarding noise from hydraulic systems are still highly relevant.

The primary noise source in a hydraulic system is the hydrostatic machine, working with large pressure differences. Being exclusively of displacement type, the hydrostatic machine divides the flow into separate volumes, which are pressureized or de-pressurized. This working principle will cause phenomena such as pressure peaks, flow ripple and internal force and torque ripple, all contributing to noise and vibrations. However, when considering the complete system it becomes evident that noise is normally created by joint effort from different origins and their interaction with external hydraulic and mechanical systems. It is therefore difficult to point out one origin solely.

This thesis aims to survey and summarize work accomplished in the area of noise and vibrations in hydraulic systems. In the work, effort has been concentrated to the internal workings of the axial piston machine, mainly the pump. To map the couplings between geometric design and dynamic behaviour, simulation technique is frequently used. The most common design features are de­ scribed and discussed. A rating system, grading the different noise reducing devices mutually, which gives the designer the ability to chose the most beneficial design feature regarding to high reduction of flow ripple in relation to implementation cost, is presented.