## Analysis of Slipper Structures in Water Hydraulic Axial Piston Pumps

##### Rokala, Markus (2012)

Rokala, Markus

Tampere University of Technology

2012

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**Julkaisun pysyvä osoite on**

http://urn.fi/URN:ISBN:978-952-15-2872-9

##### Tiivistelmä

This thesis is focused on slipper behaviour during operation, slipper behaviour during swashplate turning and especially the impact of the slipper deformations in water hydraulic axial piston pumps. Experimental research, numerical methods, like computational fluid dynamics and fluid-structure interaction, and simulation are used as research methods. The main target is to find methods to achieve a higher power density of water hydraulic axial piston pumps because better components are necessary to obtain a wider range of applications for water hydraulics. The work is primarily basic research, not the development of an actual water hydraulic pump.

Two different basic structures of slippers with different material combinations are studied and compared through the work. It is shown that it is possible to follow the maximum PV-rate of the material. However, that means that the sizing of the slipper is designed near the limit of the hydrostatic balance. The problem is that the deformations should be accurately known in order to be able to do that.

Basic theory shows the physical base and also that numerical methods are needed if deformation is taken into account. Measurements show that slipper behaviour is smooth during swashplate turning and the problems of realizing a variable displacement pump are not from slipper-swashplate contact. Restrictions in achieving a higher pressure level are the deformation and PV-rate of the material. It is possible to size the slipper near the limit of the hydrostatic balance, which helps to obtain acceptable PV-rate values. In this case the deformations of the slipper have to be accurately known to avoid slipper lift from the surface.

Sliding surface deformations are one of the key factors in industrial plastic-made slipper design. Deformations are so big that the pressure profiles are totally different from the basic equations expected. Consequently, the leakage flow is also higher than expected. The difference of the force of the sliding surface between basic equation and FSI calculation arises when the pressure level rises. With one slipper with a steel core, for example, the force is 11.4 % higher at a pressure level of 10 MPa and 27.1 % higher at a pressure level of 40 MPa than is calculated with the basic equations. Nowadays the power loss is one significant reason to decide the dimensions of the slipper. The optimum ratio is, however, calculated based on the basic equations, the results of which are incorrect.

The results of the study show that FSI calculations are necessary to make the right decisions in slipper design. However, it is not needed to calculate all different situations because the behaviour of the slipper is logical. Slipper behaviour can be predicted with sufficient accuracy with the simulation model based on a few FSI calculations, basic theory and measurements. In this thesis, a simple simulation model is developed to predict the behaviour of two types of slipper structures.

Two different basic structures of slippers with different material combinations are studied and compared through the work. It is shown that it is possible to follow the maximum PV-rate of the material. However, that means that the sizing of the slipper is designed near the limit of the hydrostatic balance. The problem is that the deformations should be accurately known in order to be able to do that.

Basic theory shows the physical base and also that numerical methods are needed if deformation is taken into account. Measurements show that slipper behaviour is smooth during swashplate turning and the problems of realizing a variable displacement pump are not from slipper-swashplate contact. Restrictions in achieving a higher pressure level are the deformation and PV-rate of the material. It is possible to size the slipper near the limit of the hydrostatic balance, which helps to obtain acceptable PV-rate values. In this case the deformations of the slipper have to be accurately known to avoid slipper lift from the surface.

Sliding surface deformations are one of the key factors in industrial plastic-made slipper design. Deformations are so big that the pressure profiles are totally different from the basic equations expected. Consequently, the leakage flow is also higher than expected. The difference of the force of the sliding surface between basic equation and FSI calculation arises when the pressure level rises. With one slipper with a steel core, for example, the force is 11.4 % higher at a pressure level of 10 MPa and 27.1 % higher at a pressure level of 40 MPa than is calculated with the basic equations. Nowadays the power loss is one significant reason to decide the dimensions of the slipper. The optimum ratio is, however, calculated based on the basic equations, the results of which are incorrect.

The results of the study show that FSI calculations are necessary to make the right decisions in slipper design. However, it is not needed to calculate all different situations because the behaviour of the slipper is logical. Slipper behaviour can be predicted with sufficient accuracy with the simulation model based on a few FSI calculations, basic theory and measurements. In this thesis, a simple simulation model is developed to predict the behaviour of two types of slipper structures.

##### Kokoelmat

- Väitöskirjat [3835]