RADIAL PISTON TYPE HYDROSTATIC MACHINE

Abstract: A hydrostatic machine, for use as a motor or pump, has a number of radial pistons and cylinders (5, 4) mounted in a cylinder block (1) surrounding an eccentric (8) which is supported upon a rotary shaft (9) within a housing (2). In order to balance the forces acting upon the eccentric due to the pressures in the cylinders in operation of the machine hydrostatic bearing pockets (14) are formed in the surface of the eccentric (8) or the surrounding block (1), the pockets being supplied with hydraulic pressure fluid through restrictor devices to produce a hydrostatic reaction force on the eccentric balancing the piston forces, and avoiding metal-to-metal contact between the cooperating surfaces of the eccentric and the block.

Description: RADIAL PISTON TYPE HYDROSTATIC MACHINE } DESCRIPTION This ^ Lnyention relates to hydrostatic machines, including both hydrostatic motors and pumps. A known type of hydrostatic machine includes an eccentric carried within a housing by a relatively rotatable shaft having inlet and outlet fluid passages communicating with inlet and outlet ports on the surface of the eccentric, a cylinder block surrounding the eccentric and formed with a number of cylinders extending radially with respect to the axis of the eccentric, and' respect ve pistons slidable in the cylinders, the arrangement being such as to establish a phase relationship between the movement of each piston and, the opening and closing of the inlet and outlet ports to operate the machine as a*, pump or motor, during which the cylinder block moves orbitally on the shaft. The shaft supports the cylinder block on a bearing. The force on the bearing in use of the machine due to the load of one or more of the pistons may be balanced approximately by so proportioning the ports on the surface of the eccentric that the pressure in either port, coupled with the pressure gradient due to fluid leakage from the port, results in a hydrostatic reaction force opposing the piston loading on the bearing. The piston loading varies cyclically and in extreme cases, for example with a very close-fitting bearing, this variation may result in metal-to-metal contact. Since the fluid transfer from the ports and across the surfaces of the eccentric is controlled mainly by the pressure of the fluid, the mean gap between the surfaces and the viscosity of the fluid, the gap is not amenable to precise determination. An object of the present invention is to provide a fluid film bearing for the cylinder block of a hydrostatic machine in which, the bearing film is maintained at a predetermined thickness and has a OMPI high radial stiffness so that the film thickness remains substantially constant, while avoiding metal-to-metal contact between the cooperating surfaces of the eccentric and the cylinder block. According to the invention there is provided a fluid film bearing in a hydrostatic machine of the type referred to above, in which the surface of the eccentric within the cylinder block is provided with or communicates with bearing pockets spaced apart circumferentially in at least one surface portion of the eccentric or the block and spaced axially from either or- both of the-ports, the said pockets communicating with a hydrostatic pressure duct within the eccentric or the block so as to produce a hydrostatic reaction force on the eccentric balancing the force thereon due to the pressure in the cylinders in communication with the said port or ports in use of the machine. The fluid film bearing can function with minimal clearance between the bearing surfaces, without the risk of failure which would result from metal-to-metal contact between the surfaces. The hydrostatic force^ resulting from the fluid pressure supplied to the ports of the eccentric and to the bearing pockets are arranged in operation * of the machine to be such as to react the fluctuating load on the eccentric due to the pistons spaced around the axis of the latter which, at any given time, are exerting a force on the eccentric. The hydrostatic fluid supplied to the bearing pockets produces and cooperates with a hydrostatic bearing film between the surfaces surrounding said pockets, reacting the nett forces between the eccentric and the block, the said film having a mean thickness which is maintained substantially constant and provides a hydrostatic balancing force on the shaft which lies between the OM maximum and minimum forces on the eccentric due to the cyclically varying piston loads. By this means it is ensured, that the hydrostatic bearing of the eccentric has a high radial stiffness, so that in the 5 plane of the external piston load, the vector direction of which can ascillate.through a small but significant angle from a mean position, the bearing clearance is maintained at a predetermined value with close precision, thereby controlling leakage of hydraulic fluid and 10 avoiding metal-to-metal contact between the bearing surfaces under the cyclic loadings. The bearing-may be-provided wit -the said bearing pockets in two surface portions arranged symmetrically on opposite axial sides of the port in the .eccentric. 15 The bearing-pockets- in the or each surface, portion would preferably be spaced apart circumferentially and arranged symmetrically. To provide a controlled reaction to the applied loads the bearing pockets, in preferred embodiments 20 of the invention, communicate with the hydrostatic fluid pressure duct through flow restrictor means, preferably in the form of laminar flow chokes. Thus in one embodiment of the invention the fluid pressure duct extends longitudinally within the 25 eccentric and the shaft and communicates with the pockets in one half of the circumference of the eccentric through respective passages in the eccentric provided with flow restrictor devices. The invention will be further described, by way 30 of example only, with reference to the accompanying purely diagrammatic drawings, in which: -- ■ --- . ■ * - Figure 1 is a schematic transverse section of a rotary hydrostatic machine of a type to which the present invention is applicable; 35 Figure 2 is a side elevational view of the eccentric and associated shaft of a machine such as that shown in OMPI - Figure 1, incorporating one embodiment of the present invention, and Figure 3 is a composite cross sectional view of the eccentric shown in Figure 2, the cross section to the left of the line S-S being taken on line A-A in Figure 2 and the cross section to the right of the line S-S being taken on the line B-B in Figure 2. The description which follows refers to a rotary hydrostatic motor, but it will be understood that the invention is applicable also to a rotary hydrostatic pump. Figure 1 shows diagrammatically a rotary hydrostatic machine comprising a non-rotating cylinder block 1 of cast iron constrained by an Oldha coupling (not shown) to effect orbital movement within a fixed cylindrical housing 2. The block 1 has a central cylindrical bore 3 and is formed with a number of (in this example, five) cylinders 4 the axes of which extend radially with respect to the centre of the bore 3 and are spaced apart at equal angular intervals in a common plane. Respective pistons 5 slide within the cylinders 4, the radially inner ends of which communicate with the central cylindrical bore 2 through respective radial ports 6. The pistons 5 project radially beyond the outer ends of the respective cylindrical bores in the block 1 and are in sliding contact with respective fla thrust pads 7 affixed to the inside surface of the housing 2 surrounding the block 1. An eccentric 8 of generally cylindrical shape having an axis X rotatable within the central cylindrical bore 3. The eccentric 8 is carried by an integral shaft 9 the axis Y of which is displaced from the axis X of the eccentric 8 and bore 3, as shown in Figure 1. The shaft 9 is rotatably supported within the housing 2 by tapered roller bearings 10, shown in broken, outline in Figure 2, on opposite axial sides OMPI of the eccentric 8, the axis Y of the shaft 9 being coaxial with the axis of the cylindrical housing 2. A peripheral inlet port 11 is formed in the surface of the eccentric 8 in the plane of the ports 6 5 and extends ove .less than half of the circumference of the eccentric 8, so that it is in communication with a maximum of, three of the ports 6, as shown in Figure 1. An hydraulic pressure fluid supply duct 12 extending longitudinally within the eccentric 8 and the shaft 9 0 communicates with the port 11 so as to supply hydraulic fluid under pressure to the respective cylinders 3 with which the port 11 communicates at any given position of the block 1 relative to the eccentric 2. An outlet-port ll<a of similar geometry to the inlet port 5 11 is formed on the eccentric 8 diametrically opposite the port 11 and communicates with an outlet duct 12a_ extending longitudinally within the eccentric 8 and the shaft 9 to conduct exhaust fluid from the machine. When the machine as described is used as a motor, 0 fluid under pressure is supplied to the duct 12 and communicates through the port 11 with the ports 6 in the cylinder block 1. The fluid pressure acting on those pistons 4 in communication with the port 11 causes rotation of the shaft 9 and corresponding sliding 5 movement of the outer ends of the pistons 5 on the thrust pads 7 accompanied by orbiting non-rotational movement of the cylinder block 1 within the housing 2. The hydraulic force exerted upon the shaft 9 due to the piston loads is indicated diagrammatically by 0 arrow F in Figure 1- The vector direction of this - - -force--F- ca -swing through a small but significant angle from the mean position illustrated, due to the sequential pressurization of the cylinders 4. This force F is balanced by the pressure in the port 11 and, 5 according to the present invention, by hydrostatic pressure supplied to balance pockets 14 arranged OMPI , WIPO . symmetrically on opposite axial sides of the port 11 in the surface of the eccentric 8, as illustrated in Figures 2 and 3. On each axial side of the port 11 there are four hydrostatic balance pockets 14, arranged symmetrically - and spaced apart circumferentially. Each pocket 14 communicates with a duct 15 extending longitudinally through the eccentric 8 and shaft 9 by way of drillings 16 in which respective laminar flow restrictor devices . 17 are located. The hydraulic fluid supplied to the port 11, and that supplied through the restrictor devices 17 to the pockets 14, establishes a hydrostatic bearing film between the cooperating surfaces of the eccentric 8 and the cylinder block 1 -which surround the pockets 14. The pressure in the pockets reacts the nett forces between the eccentric 8 and the block 1. The flow restrictor devices 17 are preferably in the form of laminar flow chokes, for example those available commercially under- he trade name "LEE VISCOJET". Alternatively, the flow restrictor devices 17 may take the form of flow-restricting orifices. It is arranged that the hydrostatic pressures produced in the bearing pockets 14 by virtue of the restricted flow through the laminar flow restrictor devices 17, in cooperation with the pressure in the port 11, are such as to maintain a hydrostatic bearing film of substantially constant thickness, affording a hydrostatic balancing force which balances the hydraulic force F exerted on the shaft 9 due to the piston loads. The size of the flow restrictor devices 17 is selected so as to establish a hydrostatic bearing film thickness which is maintained in operation of the machine at a substantially constant predetermined value, thereby avoiding any tendency for metal-to-metal contact between the surfaces of the eccentric 8 and the bore 3 relative to which the cylinder block 1 slides. OMP WIP

Claims: CLAIMS 1. A hydrostatic machine including an eccentric carried within a housing by a relatively rotatable shaft having inlet and outlet fluid passages communicating with inlet and outlet ports on the surface of the eccentric, a cylinder block, surrounding the eccentric, formed with a number of cylinders extending radially with, respect to the axis of the eccentric, and respective pistons slidable in the cylinders, the arrangement being such as to establish a phase relationship between the movement of each piston and the opening and closing of the inlet and outlet ports to operate the machine as a pump or motor, during which the cylinder block moves orbitally on the shaft, characterised in that the surface of the eccentric (8) within the cylinder block (1) is provided with or communicates with bearing pockets (14) spaced apart circumferentially in at least one surface portion of the eccentric or the block and spaced axially from either or both of the ports (11, 11a) , the said pockets communicating with a hydrostatic pressure duct (15) within the eccentric or the block so as to produce a hydrostatic reaction force on the eccentric balancing the force thereon due to the pressures in the cylinders (3) in communication with the said port or ports in use of the machine. 2. A machine as claimed in claim 1, characterised in that the eccentric (1) or the housing (2) is provided with the said bearing pockets (14) in two surface portions arranged symmetrically on opposite axial sides-.of the. said.-port (11) in the eccentric (8). 3. A machine as claimed in claim 1 or claim 2, characterised in that the bearing pockets (14) in the or each surface portion are spaced apart circumferentially and arranged symmetrically. OMPI 4. A machine as claimed in any one of claims 1 to 3, characterised in that the bearing pockets (14) communicate with the hydrostatic pressure duct (15) through flow restrictor means (17) . 5. A machine as claimed in any one of claims 1 to 4, characterised in that the hydrostatic fluid pressure duct (15) extends longitudinally within the eccentric (8) and the shaft (9) and communicates with the pockets (14) in one half of the circumference of the eccentric (8) through respective passages (16) in the eccentric provided with respective laminar flow restrictor devices. (17) . 6. A machine as claimed in any one of the preceding claims, characterised in that the hydrostatic fluid supplied to the bearing pockets (14) results in a hydrostatic bearing film reacting the forces on the eccentric (8) and the shaft (9) , the said film having a mean thickness which is maintained substantially constant and provides a hydrostatic balancing force on the shaft which lies between the maximum and minimum forces on the eccentric due to the cyclically varying piston loads.

Inventors: CAMERON JOHNSON A
Applicants: CAMERON JOHNSON A, SAUER UK LTD, SAUER UNITED KINGDOM LTD
Application year: 1979
Main classification: F04B1
IPC codes: F04B1