Study on Reliability Design of the Domestic Compressor Subjected to Repetitive Internal Stresses by Parametric Accelerated Life Testing

This chapter explains the parametric accelerated life testing (ALT) to recognize design defects in mechanical products. A life-stress model and a sample size formulation are suggested. A compressor is used to demonstrate this method. Compressors were failing in the field. At the first ALT, the compressor failed due to a fractured suction reed valve. The failure modes were similar to those valves returned from the field. The fatigue of the suction reed valves came from an overlap between the suction reed valve and the valve plate. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan performed the heat treatment to the exterior of the crankshaft made of cast iron. After the design modifications, there were no troubles during the third ALT. The lifetime of compressor was secured to have a B1 life 10 years.

Tribological performance of multi-scale micro-textured H62 brass surface fabricated by micro-milling and wet micro-blasting

The cylinder block/valve plate interface in the axial piston pump has been proven to be easily worn out, which will increase power loss and reduce its efficiency. The valve plate surface is required to be manufactured with low viscous friction and wear. Multi-scale micro-texture has been proven to improve surface tribological properties. However, there are few types of research in the effect of surface topography on the tribological performance of multi-scale micro-textured surfaces. The purpose of this study is to explore how the multi-scale micro-texture on H62 brass affects its sliding friction behavior on 38CrMoAl. Based on micro-milling and wet micro-blasting, the multi-scale micro-textured surface was manufactured on H62 brass. The wet micro-blasting was applied in the H62 brass after the surface micro-texturing. The surface topography of multi-scale micro-textured samples processed by three abrasive grit sizes accompanied by two processing times was comprehensively measured in terms of height, feature, functional, and functional volume parameters. The tribological performance of multi-scale micro-textured H62 brass was characterized by disk-on-disk frictional experiments. Through analyzing the relationship between surface morphology and tribological properties, the anti-friction mechanism of the multi-scale micro-textured surface was analyzed from the perspective of 3D surface roughness parameters. The friction coefficient of the multi-scale micro-textured surface processed by the combination of micro-milling and wet micro-blasting decreased with the increasing grit size and micro-blasting time.

Tribological Properties of Cylinder Block/Valve Plate Interface of Axial Piston Pump on the Tribometer

The tribological properties of cylinder block/valve plate is an important consideration in the design of axial piston pump. The effect of materials and heat treatment on friction and wear properties has been studied in depth. Engineering experiences show that the speed and load also affect the tribological properties, but these have not been systematically analyzed. The purpose of this paper is to evaluate the tribological properties of the commonly used materials (CuPb15Sn5 and 38CrMoAl/42CrMo) for cylinder block/valve plate with different heat treatment and contact pressure at different speed. During the test, tribometer is used to simulate the contact pattern between the valve plate/cylinder block in axial piston pump, the friction coefficient, wear rate and surface topography are analyzed to evaluate the tribological properties of different types of friction samples at different speed. Results indicate that: (1) contact surface of the samples at 1800 r/min is more prone to adhesive wear than those at 500 r/min; (2) in the terms of wear resistance, quench-tempered and nitrided 38CrMoAl (38CrMoAl QTN for short) is better than quench-tempered and nitrided 42CrMo, although they are all commonly used materials in the axial piston pump; (3) 2.5 MPa is the critical contact pressure of the interface between valve plate made of 38CrMoAl QTN and cylinder block made of CuPb15Sn5 on the tribometer, which implies the pressure bearing area at the bottom of the cylinder block should be carefully designed; (4) the valve plate/cylinder block made of 38CrMoAl QTN/CuPb15Sn5 exhibits good tribological properties in a real axial piston pump. This research is useful for the failure analysis and structural optimization design of the valve plates/cylinder block.

Analysis of Characteristics of Damping Valve Based on High-Order Discrete Scheme

In this paper, based on the high-order discrete scheme, a two-way fluid-solid coupling numerical simulation is for the damping valve plate. According to the discrete method, the governing equations of fluid structure coupling of damping valve plate are studied, including the basic conservation laws; Meanwhile, it analyzes the discretization of the control equation, including the discretization method and the high-order discretization format when the finite volume method is adopted. And based on this discrete format, a numerical simulation was performed on the damping valve, the oil flow condition is analyzed, and the velocity of the throttling hole at different time points and the throttling pressure are analyzed.

‘Shuttle’ Technology for Noise Reduction and Efficiency Improvement of Hydrostatic Machines - Part 2

In 2001, INNAS introduced the ‘Shuttle’ technology for noise reduction and efficiency improvement of hydrostatic machines. The current study revisits this technology for application in hydrostatic pumps and motors. In many hydrostatic pumps and motors, commutation is imposed by a fixed component like a valve plate. Designing a valve plate (or comparable component) that ensures good commutation at one specific operating condition, is fairly simple. However, an inherent problem of such a component is that it should ensure good commutation at all of the operating conditions. In an attempt to minimise losses and reduce noise emission caused by improper commutation, so-called shuttles were introduced by INNAS in 2001. These shuttles act as small pistons between two working chambers, essentially providing a connection to the ports while the valve plate is still closed. In theory, this will result in a check-valve like commutation. In the original paper, shuttles were implemented in a hydraulic transformer. This paper discusses and analyses the use of shuttles in pumps and motors. Simulation results show that the introduction of shuttles can reduce commutation losses to negligible levels. Furthermore, the results suggest that the use of shuttles could also reduce noise emissions.

Analysis of Cavitation Characteristics of High Temperature Fuel Piston Pump in the Process of Suction and Discharge

The fuel piston pump is the core power component of the aircraft engine fuel control system. The key technology of improving the reliability of the pump is the suppressing of the cavitation at the interface between the valve plate and the cylinder block. This article aims to solve the problem of cavitation caused by high temperature in the process of suction and discharge. The theoretical model of cavitation related to the interface is established. The influence of different working conditions and valve plate structures are considered, and the performance such as gas volume fraction and pulsation are analyzed separately. A new valve plate with combined damping groove is proposed. A hydraulic system test rig to verify the performance of the pump is built. In summary, the results of simulation and test show that the new combined damping groove effectively suppress the cavitation at the interface under high temperature. The non-cavitation time of the fuel piston pump is extended from 20h to 450h, which significantly improves its reliability.

Optimization of valve plate applied in secondary unit and noise reduction

Secondary unit, in term of application, is the combination of pump and motor, the valve plate specifically designed for pump or motor may not be suitable for a secondary unit. This paper mainly discusses design of valve plate of secondary unit applied in mobile crane, several critical points needed to be noticed during design have been discussed, furthermore, by adopting the proposed method to optimize a valve plate, which originates from closed-loop pump and now is used in opened-loop system, noise reduction was realized. Firstly, 1D simulation models, including pump condition and motor condition, were established in AMESim to obtain cylinder pressure, flow ripple and other critical parameters; secondly, by using Pumplinx, 3D numerical simulation was conducted to evaluate the cavitation risk; finally, a test bed was set up to validate the simulation result. Simulation result agreed well with the tested one. Both of them verified practicability of the proposed method. This research may provide a guidance for engineers and scholars who are interested in pump and motor.

Reliability Design of Mechanical Systems Such as Compressor Subjected to Repetitive Stresses

This study demonstrates the use of parametric accelerated life testing (ALT) as a way to recognize design defects in mechanical products in creating a reliable quantitative (RQ) specification. It covers: (1) a system BX lifetime that X% of a product population fails, created on the parametric ALT scheme, (2) fatigue and redesign, (3) adapted ALTs with design alternations, and (4) an evaluation of whether the system design(s) acquires the objective BX lifetime. A life-stress model and a sample size formulation, therefore, are suggested. A refrigerator compressor is used to demonstrate this method. Compressors subjected to repetitive impact loading were failing in the field. To analyze the pressure loading of the compressor and carry out parametric ALT, a mass/energy balance on the vapor-compression cycle was examined. At the first ALT, the compressor failed due to a cracked or fractured suction reed valve made of Sandvik 20C carbon steel (1 wt% C, 0.25 wt% Si, 0.45 wt% Mn). The failure modes of the suction reed valves were similar to those valves returned from the field. The fatigue failure of the suction reed valves came from an overlap between the suction reed valve and the valve plate in combination with the repeated pressure loading. The problematic design was modified by the trespan dimensions, tumbling process, a ball peening, and brushing process for the valve plate. At the second ALT, the compressor locked due to the intrusion between the crankshaft and thrust washer. The corrective action plan specified to perform the heat treatment to the exterior of the crankshaft made of cast iron (0.45 wt% C, 0.25 wt% Si, 0.8 wt% Mn, 0.03 wt% P). After these design modifications, there were no troubles during the third ALT. The lifetime of the compressor was secured to have a B1 life of 10 years.

Valve Plate Structural Optimal Design and Flow Field Analysis for the Aviation Bidirectional Three-Port Piston Pump

This paper designed and optimized a bidirectional three-port valve plate structure for solving the matching problem of flow rate and pressure in the aerospace pump-controlled differential hydraulic cylinder. This design aims to make the valve plate work well under the bidirectional high-speed condition. The model was set up using dynamic mesh and sliding mesh, and the simulation is conducted by FLUENT. In addition, the flow field of inlet and outlet flow rate pulsations, pressure pulsation in cylinder, and non-dead-point transition zone of four cases are analyzed to optimize the valve plate in this work. The numerical results show that different angles of non-dead-point transition zones of the valve plate have a big impact on the performance of the piston pump. For example, the flow rate pulsation reaches the minimum when the angle of non-dead point transition zone is greater than or equal to the angle of a cylinder port. However, at this time, the closed compression would occur and the pressure inside the cylinder would rise rapidly as the piston moves to the non-dead point zone, thus resulting in serious pressure overshoot. In addition, if the angle of non-dead point transition zone is reduced within a certain range, the pressure overshoot will be reduced drastically, and the flow pulsation rate will rise a bit. The study suggests that it is necessary to adjust the angle of non-dead point transition zone to balance the pressure overshoot and flow pulsation of the pump to obtain the optimal kidney structure of the valve plate.