AU2019202225A1

AU2019202225A1 - Sinusoidal cam axial piston pump

Info

Publication number: AU2019202225A1
Application number: AU2019202225A
Authority: AU
Inventors: Callum Samuel Mainstone
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-04-01
Filing date: 2019-04-01
Publication date: 2020-10-15

Abstract

SINUSIODAL CAM AXIAL PISTON PUMP ABSTRACT A hydraulic pump driven by a rotating, axial, multi-lobed sinusoidal cam with a race suitable for ball-end piston rods that pulls and pushes pistons within a cylinder barrel. The cylinder block is in a fixed position and each cylinder has a separate valve controlling fluid intake and discharge. The number of strokes completed by each cylinder per rotation of the cam is equal to the number of peaks and troughs within the cam. This aspect of the design allows for useful hydraulic power to be extracted from an oscillating driveshaft. C\i 000 -~ (0 l 0

Description

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SINUSIODAL CAM AXIAL PISTON PUMP DESCRIPTION

[001] Hydraulic pumps are one of the most commonly used mechanical devices for transferring fluids or for transmitting power through a pressurised fluid medium. There are two broad categories of pump being described as either positive displacement or dynamic. Characteristics that influence which pump is selected for a given application include; energy efficiency, cost, output pressure, flow rates, the viscosity and solids content of the pumped fluid, volume efficiency and whether a variable or constant flow is required.

[002] Axial piston pumps have cylinders in a circular array around and aligned parallel to a driveshaft. This design leads to smaller pump diameters than crankshaft driven and radial piston pumps for a given displacement making them attractive in space constrained applications.

[003] As cranks are not used, the reciprocation of pistons within in-line axial piston pumps is accomplished with swashplates; static, angled disks that guide piston rods up and down in a rotating cylinder block. Contact is maintained between the swashplate and piston rods with springs within the cylinder bore or by charging the intake with pre-pressurized fluid. Changing the angle of the swashplate will change the stroke length and the volume of displaced fluid per revolution of the pump.

[004] Replacing the static swashplate and rotating cylinder block of an axial piston pump with a rotating sinusoidal cam (1) as depicted in Figure 1 and a static cylinder block (2) can act as an alternative drive mechanism to move a piston (3) within a cylinder (4). This can achieve the same displacement of fluid per revolution as swashplate pumps while enabling a higher-pressure output from an oscillating or single-direction rotary input. Figure 2 presents a front, top and isometric view of the assembled pump.

[005] During the 2 0 th century there were several examples of sinusoidal cams used in axial piston devices such as the Dynacam Engine which contains 12 chambers and 6 double-ended pistons. The pump covered in this patent is distinct from prior designs in its use of a single-sided axial cam (1) with a ball bearing race (5) to control the positioning of multiple pistons.

[006] Piston rods (6) have ball-ends (7) that fit within the cam's race (5) and are constrained by inner (8) and outer (9) race rings that are mounted onto the cam (1) with bolts (10). Mechanically controlling the ascent of the pistons (3) within the cylinder barrel (4) replaces the typical usage of springs or pre-pressurised intake fluid. The cross-sectional profile of the assembled sinusoidal cam is shown in Figure 3. The gap between the ball-end (7) and race (5) permits the addition of lubrication to reduce friction. The cam (1), piston rods (6), inner (8) and outer (9) race rings are manufactured from high strength, hard-wearing materials often used in bearings including chrome steel, stainless steel or ceramics like silicon nitride. Separate components can be made from different materials providing they do not accelerate degradation from abrasion or corrosion.

[007] As the piston rods (6) align with the troughs (11) of the cam, the piston will be at bottom dead centre (12) where the volume within the cylinder is at its maximum. Conversely, the piston will be at top dead centre (13) when the piston rod is aligned with the peaks (14) of the cam's lobes (15). At this position the volume within the cylinder is at its minimum. The stroke length of the pistons (3) is determined by the amplitude of the cam's lobes (15).

[008] Cylinder blocks (2) can be manufactured from a single component where the bores of the block (16) form the cylinders walls for the piston (3). The cylinder block (2) should be made from forged or cast, hard-wearing materials like iron or aluminium alloys.

[009] As the cylinder block (2) is stationary, the pump can incorporate prefabricated single acting (17) or double acting hydraulic cylinders. Figure 4 is a simplified, exploded view of a prefabricated hydraulic cylinder. With the bore (18) of the cylinder in this case separate from the cylinder block (2), the cylinder block (2) can also be constructed from layers of sheet metal (19). The cylinder barrels (4) will be constrained to the cylinder block (2) by being bolted at base plate mounting holes (20) to a bottom layer (21) and capped by a top layer (22). As the block layers (19, 21, 22) will not be in direct contact with moving components, the hardness of the layers' material is not as critical a property as compressive strength and density. Aluminium and nylon are both suitable materials that satisfy these requirements.

[010] With the flow of hydraulic fluid controlled by valves connected to each cylinder port (23) rather than a shared port plate in swashplate driven axial pumps, leakage is reduced, and the maximum output pressure can be increased.

[011] The inclusion of both high and low-pressure valves connected to each cylinder's port (23) allows for the selective idling of cylinders and a variable displacement output. Two separate fluid circuits will allow for high pressures of output to be maintained with lower flow rates when the pump is run at part-load.

[012] The pump's driveshaft (24) can be extended into the cylinder block's central bore (25) where the layered assembly of the sheet metal cylinder block (2) enables the placement of radial bearings (26) to reduce unwanted vibrations. When the individual layers of the cylinder block (19, 21, 22) are bolted together with threaded rods (27) inserted through alignment holes (28) and are secured with nuts (29), disassembly of the cylinder block (2) enables servicing or replacement of radial bearings (26) and individual cylinders when internal seals are worn. An exploded view of the disassembled cylinder block (2) containing two radial bearings (26) is shown in Figure 5. The driveshaft (24) is welded to the cam (1) or both components can be cast as a single part.

[013] The number of discharge strokes per cylinder for each rotation of the driveshaft is proportional to the number of lobes (15) within the cam. Multiplying this by the number of cylinder barrels (4) housed in the cylinder block (2) yields the total rate of discharge cycles per rotation.

[014] Having multiple strokes per rotation allows piston strokes to be completed with an oscillating driveshaft. Dividing 360 degrees by the number of peaks and troughs within the cam will give the arc travelled per stroke. A cam with 3 peaks and 3 troughs will result in 6 strokes per cam rotation which is equivalent to one stroke, either intake or discharge, per 60 degrees for each cylinder. Having the pump accept bidirectional motion from a driveshaft allows for the extraction of energy from oscillating bodies such as certain designs of wave energy converter.

[015] Under continuous single-directional rotation, the magnitudes of pulsation in output flow should be minimised to create a consistent supply of hydraulic power. Having a pump with an equal number of lobes (15) and cylinder barrels (4) will result in synchronous strokes as the pistons will advance and retract simultaneously. The same effect will be observed if the number of lobes (15) in the cam (1) is a multiple of the number of cylinder barrels (4).

[016] A 3:2 ratio of lobes (15) to cylinder barrels (4) will cause a half-phase separation when there are an even number of cylinders (4). In Figure 6 for example, a pump with 4-cylinders matched to a 6 lobed cam will have 2 sets of 2 cylinders at a one stroke offset. When 2 pistons are at top dead centre (13) the remaining 2 pistons will be at bottom dead centre (12).

[017] The lowest ripples in fluid output can be achieved with a pump that contains an odd number of cam peaks (14) and an even number of cylinder barrels (4). The pump with 4-cylinders and a 3 lobed-cam from Figure 7 will have a quarter-phase separation. When one cylinder is at top dead centre (13), its opposing cylinder will be at bottom dead centre (12) while the other 2 cylinders will be at mid-stroke with one piston (3) ascending (30) and one descending (31).

[018] While the standard driveshaft (24) is suitable for a single input source of rotation to drive the Sinusoidal Cam Axial Piston Pump, two power sources can be utilised in a modified configuration where a dual driveshaft (32) passes though the cylinder block (2) that contains a variation of the bottom layer (21) to include a central bore (25). This configuration allows the dual driveshaft (32) to be driven by power sources located on the pump's cam end (33), port end (34) or both.

[019] The axial piston mechanism from the cam end (33) of the pump can be completely enclosed in a cam housing (35) to prevent dust accumulation and the risk of injury to persons if the pump is used in an exposed environment. The cam housing (35) also provides a barrier that prevents the cam (1) from pulling pistons (3) out of the cylinder barrels (4) in the event of a mechanical failure. Alignment holes (28) allow the cam housing (35) to be attached to the cylinder block (2) with the same threaded rods (27) and nuts (29) used to bond the cylinder block layers (19, 21, 22) together.

[020] Figure 8 is of an assembled pump with the axial piston mechanism covered by a cam housing (35) and a dual driveshaft (32) that extends through both sides of the cylinder block (2). A thrust bearing, not depicted in the drawing, can be placed between the top surface of the cam (1) and the inside face of the cam housing (35) to provide additional vibration control.

[021] Aside from hydraulic pumps, the sinusoidal cam driven axial piston mechanism can be used in hydraulic motors, gas compressors and combustion engines.

EDITORIAL NOTE

2019202225

There is one page of the claims only.

Claims

SINUSIODAL CAM AXIAL PISTON PUMP CLAIMS 1. A circular array of pistons oriented parallel to a driveshaft produces intake and discharge cycles by following the path of a rotating cam with axial sinusoidal lobes facing towards the pistons.
2. The cam of Claim 1 has a race along the sinusoidal surface shaped for ball rolling elements.
3. Piston rods that are connected to the pistons of Claim 1 have ball-ends that conform to the shape of the race in Claim 2.
4. The piston rods of Claim 3 are constrained to the cam of Claim 1 with inner and outer race rings that are fixed to the cam.
5. The pistons of Claim 1 fit within a bore formed in a solid cylinder block or a detachable cylinder that is static relative to the object the pump is mounted to.
6. The detachable cylinder of Claim 5 is fixed to a cylinder block that is comprised of layers of sheet material.
7. One or more ports are attached to each bore of the cylinder block or detachable cylinder of Claim 5 to facilitate the intake and discharge of fluid.
8. One or more valves are connected to the ports of claim 7 to control the pressure of discharge fluid or to selectively restrict fluid intake.
9. The rotation of the cam in Claim 1 is provided by an attached driveshaft.
10.The driveshaft of Claim 9 can extend through the cylinder block of Claim 5 and 6 and accept a rotational input from one or both sides of the pump.
11. The volume within each cylinder of Claim 5 will be at its minimum when the piston rod of Claim 3 aligns with the peak of the cam in Claim 1.
12. The volume within each cylinder of Claim 5 will be at its maximum when the piston rod of Claim 3 aligns with the troughs between cams in Claim 1.
13.The stroke length of the pistons in Claim 1 is limited to the amplitude of the wave in the sinusoidal cam of Claim 1.
14. The number of discharge strokes for each piston from Claim 1 per rotation of the driveshaft in Claim 9 is equal to the number of lobes in the sinusoidal cam in Claim 1.