Development of a generic methods for prognostics of hydraulic systems in off-road vehicles

A high amount of fixed costs of hydraulic and mechanical systems of mobile applications are caused by maintenance. Mainly the static predefined check intervals are responsible for both the prophylactic replacement of components that are often still intact, and the breakdown of the system due to not detected failures of single components. Condition based maintenance in terms of an individual service schedule for each machine might be a solution to extend the useful life especially of expensive components and to plan service breaks during a mission of a machine. The aim of this project is to generate a condition monitoring system that allows the diagnostic of impending failures in an early stage, to estimate the remaining operating lifetime, to schedule check intervals and to allow a general use for any hydraulic system of mobile machines. To achieve the aim of a general applicability of the condition monitoring system, a modular setup is required. Starting from the planed hydraulic circuit of a wheel loader five hydraulic modules (generator, motor, accumulator, valve controlled actuator and reservoir) were extracted that consists of the critical components and the system information. For each module the amount on available system information, such as sensor and control signals, is specified. The methods that will be the result of this project part, determine so called indicators that contain the information of impending failures for certain modules. Methods based on thermodynamic measurements, investigation of structure borne noise, contamination control and logging of extreme operational conditions are currently under investigation on two different test rigs. The condition monitoring methods are designed to give module specific indicators that can monitor a change of the system behaviour. For application on the mobile machine the indicators are collected during a setup phase for the healthy system. During operation the indicators can be evaluated and compared with the indicators of the initial (healthy) system as well as with the status of the indicators of the remaining modules.