HYDROSTATIC AXIAL PISTON MACHINE

Abstract: The invention relates to a hydrostatic axial piston machine, which has a compact construction with a high power-to weight ratio of several kW/kG, high overall efficiency higher than 90 % and considerably reduced working noise. Its working pressure exceeds 42 MPa and machine working as a pump is self-sucking. The machine in accordance with the invention is characterised in that the shaft (2) is equipped with an axial cam (6), which drives the elements controlling the working medium's flow between working chambers and the low- or high-pressure channels (12, 13) and with immovably attached on the shaft (2) support plate (3) with a fixed inclination angle, while the flow controlling element's shape is preferably a sleeve (9) with at least one hole (10) and a projection (11) supported on the cam's (6) running surface, and the internal surface of the sleeve (9) with at least one piston (5) head form together the working chamber.

Description: Hydrostatic axial piston machine This invention relates to a new type of hydrostatic axial piston machine. Typical axial piston machine consists of a cylinder block with axial pistons inside, mounted on a drive shaft and pressed against it's face fixed fluid collector providing supply and drainage of working medium. An inclined support plate mounted independently on a shaft together with a piston slipper forms hydrostatic support for each piston. This hydrostatic support is supplied with working medium from working chamber through a narrow hole in the piston and slipper. The plate's inclination angle can be changed from 0 to 15-20° providing stepless control of the piston's stroke and thus control of machine's flow volume ratio. The principal drawback of such a construction is a large energetic loss caused by influence of fixed oil collector on rotating cylinder block. The main components are : friction force caused by hydrostatic unbalance, leakage and pressure drop due to rapid flow deflection in supply and drain channels caused by fast rotation. Together they are responsible for about 50% of total power loss in such a machine. The next disadvantage of a typical axial piston machine is a big value of dead volume, usually between 100 and 200 % of stroke volume when the machine is adjusted at full displacement. Reducing the displacement causes further growth of dead volume. Due to volume elasticity of working medium dead volume is a source of a significant volumetric loss and burdensome noise. The control of the machine's flow by changing the inclination angle of highly loaded by piston ' s axial force support plate needs a lot of energy to achieve. It makes necessary to use a hydraulic servo control mechanism with the response time usually longer than 0,2 s. A linear narrow damping hole through the piston,which supplies the hydrostatic support unit with working medium because of its limited length gives a small pressure drop, about 1% of working chamber pressure. It results in a small stiffness of hydrostatic support and a big leakage through the clearance between the slipper and the support plate. In accordance with the invention hydrostatic axial piston machine with a drive shaft, a cylinder block with pistons and at least one support plate is characterised in that shaft is equipped with an axial cam which drives elements controlling working medium's flow between the working chambers and low or high pressure channels and with immovably attached on shaft support plate with fixed inclination angle, while flow controlling element's shape is preferably a sleeve with at least one hole and projection supported on the cam's running surface, while the internal surface of the sleeve and at least one piston head form together the working chamber. The cam is axially shifted and/or rotated on the shaft. A controlling element has a form of a slide valve or a cock with the projection supported on the cam's running surface. . Each piston is equipped inside with a screw throttle located on the slipper's hydrostatic support inlet. Another construction of a hydrostatic axial piston machine with a drive shaft, cylinder block with pistons and at least one support plate in accordance with the invention is characterised in that the shaft is equipped with a radial cam which drives the elements controlling working medium's flow between the working chambers and low- or high pressure channels, and with immovably attached on shaft support plate with fixed inclination angle, while flow controlling element's shape is preferably a slide valve supported on the cam's running surface. The cam is axially shifted and/or rotated on the shaft. Each piston is equipped inside with a screw throttle located on the slipper's hydrostatic support inlet. According to performed tests, full hydrostatic discharge of the controlling elements and the cam, their low mass and small friction force between the pistons and the controlling elements caused an unpredictable effect that machine's flow change by cam's displacement needs much less energy (ten times or more) in comparison with all known constructions and additionally dynamic characteristic of control process is significantly better. It allows to control the machine's flow by means of a simple low energy mechanism e.g. proportional electromagnet. The reduction of dead volume to about 8 % of stroke volume, thanks to the applied sleeve shaped controlling elements, decreases volumetric loss. What is more it occured thar lowering of machine's flow wolume ratio doesn't increase its dead volume, i.e. the dead volume is small indepenently of the current flow volume ratio as an effect of support plate's constant inclination angle. Due to the applied changes in design the cylinder block is fixed. Thus, fluid collector is eliminated and mechanical loss due to friction between collector and block together with pressure drop due to fluid stream deflection are excluded. Successively, screw throttles assemblied in the pistons not only reduce the dead volume, but also enable to obtain pressure drop of 10-15 % of working chamber's pressure, which improves the hydrostatic support characteristics and decreases leakage through clearance between the slipper and the support plate. As a result this invention allows to obtain a compact construction with a high power-to- weight ratio of several kW/kG, high overall efficiency higher than 90% and considerably reduced working noise. Working pressure exceeds 42 MPa and the machine as a pump is self- sucking. Figures 1 and 2 show axial cross-sections of two embodiments of the invention. Fig. 1 shows machine with sleeves while fig.2 shows machine with slide valves. Fig.1 illustrates case 1 with drive shaft 2 and two symmetrically attached on it support plates 3 with fixed inclination angle. Immovably assemblied in case 1 between plates 3 is the cylinder block 4 with double pistons 5 . Shaft 2 is equipped with an axial cam 6. Each piston 5 ends with a ball joint 7 connecting it with a slipper 8 hydrostatically supported on plate 3. Pistons 5 are placed inside sleeve 9. Internal surface of the sleeve 9 together with piston's 5 heads form the working chamber.Each sleeve 9 equipped with a hole 10 in shape of circumferential, parted clearance and a projection 11, is an element controlling the flow of working medium between working chambers and low pressure 12 or high pressure 13 channels. Projection 11 is supported on cam's 6 running surface. In axial boring in shaft 2 there is a pusher 14 which cooperates with proportional electromagnet 15 to shift axially and/or rotate cam 6 on shaft 2. Inside every piston 5 there is a screw throttle 16 located on the inlet of hydrostatic support between slipper 8 and plate 3. Fig. 2 shows another construction with one fixed angle support plate 3 and the radial cam 6. Slide valve 17 situated between working chamber and channels 12 and 13 is supported on cam's 6 running surface. Each slide valve 17 cooperates with one piston 5. The machine driven by energy in the form of a torque driving shaft 2 acts as a pump transporting working medium between channels 12 and 13 through the working chambers, in direction depending on shaft's 2 rotation direction. Otherwise, the supply of energy in form of pressurized fluid stream to 12 or 13 channels causes rotation of shaft 2 in direction depending on the fluid's flow direction and machine acts as a motor. Construction in accordance with fig.1 is characterized in that the cam 6, rotating together with shaft 2 and the support plates 3 , due to its running surface shape shifts axially sleeve 9 thus displacing the hole 10 from full connection of the working chamber to channel 12 to a full connection of this chamber to channel 13 . Cam's 6 displacement along and/or around shaft's 2 axis shortens this phase of working cycle, while the working chamber is connected to the high pressure channel 12 and simultaneously lengthens period of the working chamber's connection to the low pressure channel 13. As a result a part of working medium reaches the low pressure channel 13 instead of the high pressure channel 12, thus allowing to reduce steplessly the machine's flow until the working chamber is continuously connected to the low pressure channel 13. In this construction symmetrical arrangement of two support plates 3 cooperating with two sets of pistons 5 allows to relief the shaft's 2 bearings from piston's 5 axial forces.

Claims: Claims 1. Hydrostatic axial piston machine with a drive shaft, a cylinder block with pistons and at least one support plate, characterised in that the shaft (2) is equipped with an axial cam (6), which drives the elements controlling working medium's flow between the working chambers and the low- or high pressure channels (12,13), and with immovably attached on shaft (2) support plate (3) with fixed inclination angle, while flow controlling element's shape is preferably a sleeve (9) with at least one hole (10) and a projection (1 1) supported on the cam's (6) running surface, and the internal surface of sleeve (9) with at least one piston (5) head form together the working chamber. 2. A machine as claimed in claim 1, characterised in that the cam (6) is axially shifted and/or rotated on the shaft (2). 3. A machine as claimed in claim 1 characterised in that the flow controlling element has a form of a slide valve or a cock equipped with projection (11) supported on the cam's (6) running surface. 4. A machine as claimed in claim 1, characterised in that each piston (5) is equipped inside with a screw throttle (16) located on the slipper's (8) hydrostatic support inlet. 5. Hydrostatic axial piston machine with a drive shaft, a cylinder block with pistons, and at least one support plate, characterised in that the shaft (2) is equipped with a radial cam (6) which drives the elements controlling working medium's flow between the working chamber and the low- or high pressure channels (12,13), and with immovably attached on the shaft (2) support plate (3) with fixed inclination angle, while the flow controlling element's shape is preferably a slide valve (17) supported on cam's (6) running surface. 6. A machine as claimed in claim 5, characterised in that cam (6) is axially shifted and/or rotated on the shaft (2). 7. A machine as claimed in claim 5 characterised in that the flow controlling element has a form of a cock with projection (11) supported on the cam's (6) running surface. 8. A machine as claimed in claim 5, characterised in that each piston (5) is equipped inside with a screw throttle (16) located on the slipper's (8) hydrostatic support inlet.

Inventors: OSIECKI ANDRZEJ, OSIECKI LESZEK, OSIECKI, ANDRZEJ, OSIECKI, LESZEK
Applicants: OSIECKI ANDRZEJ, OSIECKI LESZEK, OSIECKI, ANDRZEJ, OSIECKI, LESZEK
Application year: 1995
Main classification: F04B1
IPC codes: F04B1, F04B7, F04B49