Abstract
Throughout previous practice, estimating the life of aviation hydraulic drive assemblies has been utilizing a variant, which requires conducting long-lasting studies of the drive assemblies until they move to the unfitness state. Such studies, which enable estimating life a posteriori, are costly and long-lasting. Hence the need to look for new strategies for estimating life. The article presents a method of estimating the durability of a hydraulic drive assembly based on the control of its change in technical condition. Inspection of the technical condition enables timely detection of the condition before the emergency hydraulic assembly. The novelty of the method is to use, to detect the condition before the emergency team, the principle of determining the pre-emptive control parameter tolerance. Pre-emptive tolerances are a set of control parameter values between threshold levels and pre-emergency (allowable) levels. The intensity of depletion of durability (intensity of aging, wear) is random. The paper presents a stochastic description of the control parameter change and the resulting empirical relationships between the control parameter verification time probability density (verification periodicity) and the control parameter value change probability density. The inter-relations between these two functions were described. It also presents empirical relationships enabling the determination of the permissible value for the control parameters and the periodicity of the control parameter checks after exceeding the limit value. An example of estimating the life of a hydraulic piston pump on-board an aircraft operated in the Polish Air Forces was shown. The permissible values and the time for the first control parameter verification after exceeding the limit value were determined for selected control parameters of the hydraulic pump. The proposed method binds life (fitness time) with the physical wear mechanisms concerning the assemblies. It can be applied in work aimed at determining the resource life of technical equipment. Furthermore, it enables utilizing technical equipment according to a technical state strategy with monitoring the parameters.
Highlights
Estimating the life of aviation hydraulic drive is a broad forecasting issue at the engineering stage of their operational behaviours, as well as forecasting the change of their technical state throughout the operation stage
The method presented in this article is based on the observation of a selected control parameter of the hydraulic drive assembly during its use
The limit value of the hydraulic drive unit control parameter is determined at the stage of its construction and design
Summary
Estimating the life of aviation hydraulic drive is a broad forecasting issue at the engineering stage of their operational behaviours, as well as forecasting the change of their technical state throughout the operation stage. Based on the results of wear tests and taking into account safety factors, normative durability is determined [1, 26] Another approach for estimating the durability of hydraulic units using the concept of safe durability are operational reliability tests [17, 27]. The method presented in this article is based on the observation of a selected control parameter of the hydraulic drive assembly during its use The purpose of this check is to detect in advance the pre-emergency (allowable) condition. The limit value of the hydraulic drive unit control parameter is determined at the stage of its construction and design It results from the design conditions of hydraulic precision pairs (plunger pairs, distribution pairs, control pairs) and functional conditions of the entire hydraulic assembly. It should be added here that in the case of renewable assemblies it can be subjected to a renovation procedure
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