GB2042064A - Radial piston pump or motor - Google Patents

Abstract

Passages 44, 46, 48, 50 in either the pintle bridges 28, 30 or the rotor of a radial piston pump or motor connect each cylinder 40 to the supply and return zones 18, 20 of the pintle shaft during the parts of each cylinder cycle when the rotor ports are otherwise closed by the bridges 28, 30 but are not at the dead centre positions. The passages provide controlled fluid flow to and from each cylinder, thus reducing cavitation and fluid and mechanical noise. <IMAGE>

Description

SPECIFICATION Radial piston pump or motor This invention relates to hydraulic pumps and motors of the radial piston type, that is to say having pistons co-operating with cylinders extending radially from a rotor mounted for rotation on a pintle shaft having longitudinal passages for the supply and return of hydraulic fluid to the respective cylinders as the rotor rotates, the pistons co-operating with a surrounding reaction structure to produce the inter-conversion of the reciprocatory and rotary motions. Thus, when operating as a pump, rotary drive applied to the rotor is converted to a reciprocatory pumping action of the pistons and, when operating as a motor, the reciprocatory action of the pistons resulting from the supply of hydraulic fluid under pressure is converted to rotary motion.

In pumps and motors of this type, the flow of fluid to and from the cylinders is controlled by valving comprising fixed supply and return ports in the pintle shaft and co-operating ports in the rotor leading to the respective cylinders, which periodically open to the pintle shaft ports in timed relation to the operating cycles of the pistons. At both top and bottom dead centre positions of the pistons, the rotor ports are closed by the "land" areas of the "bridges" which separate the fixed ports, such occlusions of the rotor ports constituting the necessary points of separation between the high and low pressure phases of the piston cycles.The high pressure fixed ports alternate with the low pressure fixed ports, and the land areas between adjacent high and low pressure fixed ports and the land areas between the rotor ports generally overlap each other on either side of each rotor port at the piston dead centre positions to reduce leakage between the high and low pressure ports. An example of a pump-motor operating in this way is disclosed in U.S. patent no: 3,709,104.

The specific design of the valving of pumps and motors of the radial piston type involves a number of problems. Theoretically, maximum hydraulic efficiency should be attained by keeping the rotor ports open at all times except at piston top and bottom dead centre, thereby using the entire displacement of each cylinder for supply and return of fluid. In practice, the leakage across each bridge between the fixed ports via each rotor port at and near the dead centre positions greatly reduces efficiency and is generally, therefore, impractical. Leakage is reduced and efficiency improved, in general, by increasing the width of the bridge on either side of rotor port dead centre to provide overlaps between the land areas of the fixed valve element and the rotor on either side of each rotor port dead centre position, the overlaps providing sealing zones which restrict fluid passage.

An improvement in efficiency by providing overlaps at the bridges to reduce leakage is, however, gained at the expense of increased cavitation and of both hydraulic and mechanical noise resulting from the pressure pulses produced by piston displacement with the rotor port occluded. There are several manifestations of the cavitation and noise problem.

Perhaps the most serious effect occurs at the beginning of the intake stroke in a pump; the piston tries to suck in fluid with the rotor port closed and instead draws a vacuum and hence produces cavitation and the associated noise. Other examples of important effects of closing a rotor port are: (1) pump-piston displacement with ports closed near the end of intakecavitation and hydraulic noise and energy loss; (2) pump-piston displacement with port closed near the beginning and end of delivery pressure pulse accompanied by generation of both hydraulic and mechanical noise and energy loss resulting from extra work required to force fluid past the overlaps to accommodate piston displacement;; (3) motor-piston displacement with port closed near the beginning or end of working (high pressure supply) strokc pressure drop in cylinder with possible cavitation and noisc cnergy loss because fluid is not "working" on the piston; (4) motor-piston displacement with port closed near the beginning or end of exhaust (low pressure return) stroke--pressure pulse (because fluid is trappedFhydraulic and mechanical noiseenergy loss in working on trapped fluid.

The degree to which overlaps adversely affect efficiency and result in cavitation and noise depends upon the size of the overlaps and the amount of clearance between the fixed valve element and the rotor. If the amount of overlap is decreased, the clearance increased, or both, cavitation and noise are reduced, but leakage increases and any gain in overall efficiency due to longer effective piston stroke may be offset by a reduction in efficiency due to increased leakage.

According to the present invention a hydraulic pump or motor of the radial piston type (as herein defined), in which the pintle shaft includes fluid supply and return zones opening at ports separated by bridges and communicating sequentially with ports in the rotor leading to respective cylinders, the rotor ports being periodically isolated from the pin tle ports by occlusion of the rotor ports by land areas of the bridges, and each of the land areas having a substantial overlap with land areas of the rotor for effective sealing also includes passages connecting each cylinder sequentially with the pintle supply and return zones during substantially the entire period of each piston stroke when the corre sponding rotor port is occluded by a bridge land area and the piston is not at top or bottom dead centre.In particular, one or more passages is provided for any or all of the following conditions: (1) for the initial part of the fluid supply stroke, a passage or passages connecting each cylinder with the supply zone while the corresponding rotor port is closed by an over lap on the outgoing side of a bridge after leaving bottom dead centre; (2) for the final part of the fluid supply stroke a passage or passages connecting each cylinder with the supply zone while the corresponding rotor port is closed by an overlap on the ingoing side of a bridge before reaching top dead centre; (3) for the initial part of a fluid return stroke, a passage or passages connecting each cylinder with the return zone while the corresponding rotor port is closed by an overlap on the outgoing side of a bridge after leaving top dead centre; and (4) for the final part of a return stroke, a passage or passages connecting each cylinder with the return zone when the corresponding rotor port is closed by an overlap on the ingoing side of a bridge before reaching.top dead centre.

The resultant valving arrangement significantly reduces cavitation and noise, permits effective sealing by large overlaps, thus minimizing efficiency losses due to leakage, and improves efficiency by more effectively using the parts of each piston stroke when the rotor ports are covered by the bridges.

Each of the passages referred to (or group of associated passages when there is a number of passages in parallel) is designed to provide a fluid flow rate not less than that required by the displacement during the part of the stroke in question when the rotor port is closed. That displacement and the period of port closure can easily be calculated, and from that standard fluid flow equations can be used to determine passage sizes that will produce the necessary flow rate. It is preferable, moreover, for the flow rate not greatly to exceed that required by the displacement during port closure.

Although the passages can be in the rotor, the easiest or least costly way of providing them is to drill holes in the bridges. Generally, passages will be provided for all four of the aforementioned situations.

The passages considerably reduce noise and cavitation by providing flow to and from the cylinders at all times during each cycle, thereby reducing or virtually eliminating sharp pressure pulses. The passages can, in fact, be designed to control the rates of pressure changes that occur between supply and return phases and in any case will provide smoother transitions between high and low pressures.

The clearance between the pintle shaft and the rotor can be designed solely for sealing and lubrication rather than as a compromise to obtain required leakage between the cylinders and the pintle supply and return zones.

This is a particularly important advantage in low speed, high pressure machines. Keeping the cylinder filled during the supply strokes and allowing them to empty during the return strokes reduces energy losses without adversely affecting sealing. The passages do not significantly increase leakage because they are small, provide flow rates close to those satisfying displacement and are separated by a distance not less than the corresponding dimension of each rotor port.

Constructions in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevational view of the valve portion of a pintle shaft; Figure 2 is a cross sectional view of the pintle shaft shown in Fig. 1 taken along the lines 2-2 of Fig. 1; Figure 3 is a broken longitudinal sectional view of part of a pintle shaft and a rotor taken along the lines 3-3 of Fig. 4; Figure 4 is a cross sectional view of the pintle shaft and rotor shown in Fig. 3, the section being taken along the lines 4-4 of Fig. 3; Figure 5 is a broken longitudinal sectional view of part of a modified pintle shaft and a rotor, the section being taken along the lines 5-5 of Fig. 6 and in the direction of the arrows; and Figure 6 is a cross sectional view of the pintle shaft and rotor of Fig. 5 taken along the lines 6-6 of Fig. 5 and in the direction of the arrows.

The pintle shaft shown in Figs. 1 and 2 is suitable for use, for example, in a pump or motor of the type described and shown in U.S. patent no: 3,709,104 (referred to above) and has a cylindrical valve portion into which four large passages extend from one end. Two of the passages 10 and 1 2 lead from a fluid supply conduit (not shown) and the other two 14 and 1 6 lead back to a return conduit. At the valve portion, there are cutouts 1 8 and 20 separated by a diametrical wall 22. The cutout 1 8 is a supply zone and is bounded at the circumference of the pintle by a supply port 24, and the cutout 20 is a return zone and is bounded by a return port 26. The side edges of the pintle ports 24 and 26 define bridges 28 and 30 located symmetrically on opposite sides of the pintle at the sides of the dividing wall 22. Longitudinal webs 32 and 32 oriented perpendicular to the wall 22 stiffen the valve section.

Referring to Figs. 3 and 4 (which show the pintle shaft of Figs. 1 and 2), the valve portion of the pintle shaft receives a rotor 36 which consists of a cylindrical body 38 sur rounding the pintle shaft and a number (five are shown) of radially oriented cylinders 40.

Pistons (not shown) reciprocate radially in the cylinders and, on the working stroke, are driven by (in a pump) or drive (in a motor) a reaction assembly (not shown) positioned eccentrically relative to the axis of the pintle shaft and rotor. The axes of the reaction assembly and pintle shaft are located in a diametrical plane which bisects the bridges 28 and 30; therefore, the top and bottom dead centre positions of each piston occur when the corresponding cylinder axis lies in that plane. For example, if the reaction assembly axis is to the left of the pintle axis (referring to Fig. 4) each piston is at top dead centre when the cylinder axis is at the 9 o'clock position (labelled "TDC") and at bottom dead centre ("BDC") at the 3 o'clock position.As each cylinder rotates (counter-clockwise in this example) from BDC to the TDC position fluid enters through a rotor port 42 at the internal bore of the rotor body 38 and is conducted to the cylinder. The supply stroke ends and the return stroke begins at TDC, the piston moving back toward the pintle from TDC to BDC.

The shapes of various surfaces of the supply and return zones of the pintle shaft, the pintle shaft and rotor ports, and the chargedischarge passages of the pintle shaft and rotor shown in the drawings are the same as those of certain constructions described and shown in the co-pending application no; 46627/78, and reference may be made to that application for a full description. The shapes of the ports and passages ensure smooth, relatively non-turbulent flow to and from the cylinders for quiet, efficient operation.

The bridges 28 and 30 are somewhat wider than the rotor ports 42, and the ends of the rotor body 38 extend lengthwise some distance beyond both ends of the rotor and pintle ports. The overlaps widthwise and lengthwise between the rotor bore and the pintle shaft provide sealing around the ports, since the small radial clearance and great (relative) lengths of the overlaps greatly restrict fluid flow. Some leakage is inevitable and, indeed, is necessary for lubrication between the rotor and pintle shaft. A construction in accordance with the present invention permits the sealing and lubrication to be optimized by the design of the clearance and the bridge width without the need to be concerned about the cavitation and noise resulting from closure of the rotor ports while the pistons are moving.

In the construction of Figs. 1 to 4 there are two passages 46, 48 and 44, 50 respectively (see Fig. 2) in each pintle bridge 28 and 30, located symmetrically with respect to TDC and BDC a distance from the TDC-BDC plane just outside the edges of the rotor port when the corresponding cylinder is at BDC or TDC; the rotor ports are, therefore, fully closed at those positions. To either side of BDC or TDC for a period that depends upon the bridge width, the rotor ports are closed by the bridge, but the passages allow fluid flow to or from the supply of return zones, as the case may be.

The flow rate through each passage for a given fluid viscosity, pressure drop and machine speed is a function primarily of the length and diameter of the passage--length and diameter can be determined mathematically closely to match the flow to the cylinder displacement between BDC or TDC and the opening of the pintle ports to the rotor ports.

Instead of a single passage adjacent either side of the TDC or BDC rotor port positions, multiple passages at each side at different circumferential distances from the BDC-TDC plane and of the same or different sizes can be provided to give a variable flow rate to and from the cylinders during rotor port occlusion by the bridge; the further the rotor port is from dead centre, the greater the number of passages that are open, and vice versa. Different sizes, numbers and positions of passages can be provided to achieve different flow control objectives at the ingoing and outgoing sides of BDC and TDC.

If the pintle shaft and rotor shown in Figs.

3 and 4 are used in a pump, the following effects result from the passages: (1) During the time a cylinder moves from BDC to opening of the corresponding rotor port to the supply zone 18, the passage 44 admits fluid to the cylinder. Cavitation and noise due to the piston sucking against a closed port are greatly reduced or eliminated.

(2) From port closure by the bridge 28 to TDC, the passage 46 admits fluid from the supply zone with essentially the same effect as step (1) above.

(3) A cylinder moving from TDC to opening to the return zone 20 can deliver fluid through the passage 48 and is not subject to a sharp pressure pulse that would occur if the piston were working against a fully closed port; hydraulic and mechanical noise are greatly reduced and the piston produces work.

(4) In a cylinder passing from closure by the bridge 30 to BDC, the passage 50 delivers fluid the the pintle return zone with the same benefits stated in (3) above.

In a motor, the passages 44 and 46 permit high pressure fluid from the supply to enter each cylinder during the periods when the ports are occluded by the bridges but are not at BDC or TDC. The fluid performs useful work, and cavitation and noise due to piston movement in a closed cylinder are reduced considerably. Return flow of fluid begins as soon as a cylinder leaves TDC through the orifice 48, and no noisy, wasteful "bump" against a trapped fluid at high pressure occurs. Similarly, smooth return through the passage 50 continues from rotor port occlu sion by the bridge 30 to BDC.

During each of the partial strokes between port occlusion and dead centre, the fluid flow through the particular passage closely matches the demand of the piston displacement. Leakage is minimized, for the cylinders do not "demand" it. Machine operation is much smoother and quieter; efficiency is increased; sealing is optimized because there are no short paths for fluid flow at the interface between rotor and pintle land areas from high to low pressure.

Figs. 5 and 6 illustrate an alternative construction in which the passages are provided in the rotor rather than the pintle shaft. This is obviously a little more costly because many more holes have to be drilled in less accessible places, but in terms of returns it is equivalent. Each cylinder has two passages 52 and 54 extending obliquely from it in opposed directions and opening at the rotor bore at locations such that they will be located just inside the edges of each bridge when the cylinder is at TDC or BDC. Other than the different location of the passages, the construction of Figs. 5 and 6 is the same as the construction of Figs. 1 to 4.

From the above description it is readily apparent that the construction of Figs. 5 and 6 will function in the same way as the construction of Figs. 1 to 4 and will produce the same results.

Claims (7)

1. A hydraulic pump or motor of the radial piston type (as herein defined), in which the pintle shaft includes fluid supply and return zones opening at ports separated by bridges and communicating sequentially with ports in the rotor leading to respective cylinders, the rotor ports being periodically isolated from the pintle ports by occlusion of the rotor ports by land areas of the bridges, and each of the land areas having a substantial overlap with land areas of the rotor for effective sealing, the pump or motor also including at least one passage connecting each cylinder with the pintle zone specified below during substantially all of one or more of the periods of the corresponding piston strokes specified below:: (a) the pintle supply zone from occlusion of the rotor port up to, but excluding, piston top dead centre; (b) the pintle supply zone from, but excluding, piston bottom dead centre to opening of the rotor port to the pintle supply zone; (c) the pintle return zone from occlusion of the rotor port up to, but excluding, bottom dead centre; and (d) the pintle return zone from, but excluding, top dead centre to opening of the rotor port to the pintle return zone.

2. A hydraulic pump or motor of the radial piston type (as herein defined) in which the pintle shaft includes fluid supply and return zones opening at ports separated by bridges and communicating sequentially with ports in the rotor leading to respective cylinders, the rotor ports being periodically isolated from the pintle ports by occlusion of the rotor ports by land areas of the bridges, and each of the land areas having a substantial overlap with land areas of the rotor for effective sealing, the pump or motor also including passages connecting each cylinder sequentially with the pintle supply and return zones during substantially the entire period of each piston stroke when the corresponding rotor port is occluded by a bridge land area and the piston is not at top or bottom dead centre.

3. A pump or motor according to claim 1 or claim 2 wherein each passage passes through one of the pintle bridges.

4. A pump or motor according to any one of the preceding claims wherein each passage or group of associated passages is of a size such that the fluid flow rate through it is not less than that sufficient to conduct a quantity of-fluid to or from the cylinder during such period of each piston stroke equal to the displacement of such cylinder during such stroke period.

5. A pump or motor according to claim 4 wherein each passage is of a size such that the flow rate through it is not substantially greater than that sufficient to conduct a quantity of fluid to or from the cylinder, during such period of the piston stroke equal to the displacement of such cylinder during such stroke period, thereby to reduce leakage losses.

6. A pump.or motor according to any one of the preceding claims wherein each passage passes through one of the pintle shaft bridges.

7. A hydraulic pump or motor of the radial piston type (as herein defined) having a valving arrangement between the pintle shaft and rotor which is substantially as described and as illustrated with reference to Figs. 1 to 4 or Figs. 5 and 6 of the accompanying drawings.