PRESSURE GRADIENT CONTROLLED ROTARY HYDRAULIC MACHINE

Abstract: A pressure gradient controlled rotary hydraulic machine (10) includes a housing (11) having a low pressure port (4) on one side, a high pressure port (3) on the opposite side, and a pair of meshed gears (14, 15) rotatably mounted in the housing between the two ports. A pressure gradient control is provided for regulating the pressure differential across a portion of the gears, the pressure gradient control comprising a fluid passageway (24) adjacent the teeth (30) of the gears (14, 15), spaced from both the high pressure and low pressure ports, isolated from direct fluid communi­ cation with the two ports, and in fluid communication with the interdental spaces of the gears. The fluid passageway (24) may be provided for in the housing of the machine or, preferably, in a pair of wear plates (20) that are disposed at opposite end faces of the gears (14, 15). The preferred fluid passageway (24) is formed by a chamfer adjacent to the tips of the gear teeth (30) along the peripheral portion of the wear plate (20).

Description: Pressure gradient controlled rotary hydraulic machine This invention concerns improvements in rotary hydraulic machines and, in particular, though not exclusively, concerns improvements in hydraulic gear pumps. Gear pumps and motors are well known hydraulic machines that are used in numerous hydraulic systems where a relatively fixed displacement of fluid flow is desired. Such gear type machines typically include a pair of meshed gears mounted for rotation in a housing, with the housing having low and high pressure ports disposed on opposite sides of the meshed gear teeth. In operation, the gears are thrust toward the low pressure port by the high pressure fluid, thereby generating large loads on the gears, their shafts, the bearings or bushings which support the shafts, and within the housing itself. These relatively large loads can place excessive strains on the aforesaid components, thereby accelerating ordinary wear and tear and contribUting to the premature failure of the machine. There have been a number of attempts to deal with the problem of these loads. These attempts generally comprise some means or other to divert a portion of the fluid at the high pressure port to a lower pressure zone in order to counteract a portion of the high pressure force of the gears. One such attempt is described in U.S. Patent No. 4,087,216 where the device includes a wear plate which has a special fluid channel leading from the high pressure end of the wear plate around the outer periphery toward a zone of lower pressure. It is claimed that such a device will alleviate some of the force placed upon the bearings by transferring some of the high pressure force to the wear plates. Others have used the high pressure fluid not only to counterbalance the high pressure force but also to dampen fluctuating pressures acting on the gear teeth. See, for example, U.S. Patent No. 3,833,319. Still others have placed high pressure fluid passages in the bearings themselves, as is shown in the U.S. Patent Numbers 3,474,736 and 2,624,287. A common feature of all of the above referenced attempts is that the fluid passages which carry the counterbalancing high pressure fluid are all in direct communidation with the highest pressure fluid, i.e. the fluid at the high pressure port. By using such high pressure fluid, additional, large vertical loads are placed upon the gears thereby subjecting them to increased wear and tear. Hence, it would be desirable to have a means for counterbalancing the high pressure force on the gears without using the highest pressure fluid and thereby reducing the detrimental effects of large vertical forces on the gears. According to the present invention there is provided a rotary hydraulic machine having a housing with a low pressure port on one side of the housing and a high pressure port on the other. A pair of gears are rotatably mounted in mesh in a gear chamber inside the housing. In operation, fluid at the high pressure port urges the meshed gears toward the low pressure port. Thus, the housing and the bearings or bushings supporting the gears come under unbalanced forces. Those forces are regulated by a pressure gradient fluid passageway that is positioned adjacent the gears1 in fluid communication with the interdental spaces of the gears, and isolated from direct fluid communication with the high and low pressure ports. In the preferred embodiment, the pressure gradient fluid passageway is provided for in a pair of end or wear plates on opposite ends of the gears. The wear plates have a chamfer on the side of the plate facing the gear, adjacent the peripheral edge of the wear plate. The chamfer in the edge of the wear plate is isolated from direct fluid communication with the high and low pressure ports by the wear plate itself and other sealing means that are well known to one skilled in the art. Accordingly, an interdental fluid communication channel is established adjacent the tips of the teeth of the gears. The interdental channel provides a pressure path across the teeth of the gears. In effect, the chamfers in the wear plates are leakage paths which lower the pressure acting on the gears near the high pressure side of the pump and raise the pressure acting on the gears near the low pressure side of the pump thereby counterbalancing a portion of the horizontal component of the force acting on the gears without substantially increasing the vertical force on the gears. By positioning the chamfer in the peripheral edge of the wear plate, the length dimensions of the chamfer can be relatively small due to the advantage gained from placing it at the tips of the teeth of the gears. Although the pressure gradient control is preferably positioned in a replaceable wear plate, one or more such controls could also be included directly in the housing of the pump and/or in the end or adapter covers, or at some other point on the wear plate closer to the hub of the gears. A fuller understanding of the invention and of features and advantages thereof may be had from the following detailed description of"an exemplary embodiment which is illustrated in the accompanying drawings wherein Figure 1 is a vertical, cross-sectional view of a rotary gear pump or motor; Figure 2 is an elevational view of a wear plate, including the pressure gradient control of this invention; Figure 3 is an elevational view of the opposite side of the wear plate shown in Figure 2; Figure 4 is an end view of the wear plate; Figure 5 is a sectional view of the wear plate; Figure 6 is a graphical representation of thepressure profile of three wear plates, one of which is constructed according to the preferred embodiment of the present invention. With reference to Figure 1 of the drawings, a rotary hydraulic machine in the form of a gear pump 10 includes a central housing 11 having a low pressure or inlet port (not shown) and a high pressure or outlet port indicated by reference numeral 3. In housing 11 are two meshing gears 14, 1.5 that are respectively rotatably mounted on driven gear shaft 6 and idler shaft 7. Gear shafts 6 and 7 are mounted in bushing or bearing assemblies 18 which in turn are positioned in adapter cover 13 and end cover 12. Drive shaft 6 extends beyond adapter cover 13 where it is connectable to a power source (not shown). Centering plates 16, 17 serve to align the bearings 18, gear shafts 6 and 7, covers 12, 13 as well as central housing 11 with one another. Adjacent the end faces of gears 14 and 15 are a pair of wear plates 20, 21 which carry the pressure gradient control chamfer passageway 24 of the preferred embodiment of the invention. As shown in Figure 2, the wear plate 20 has a general figure-eight configuration with openings 22, 23 for accommodating the gear shafts 6 and 7. The gear facing surface 34 of wear plate 20 is usually faced with bronze or other suitable wearing material. The gear teeth 30 of gears 14, 15 are partially superimposed on the representation of wear plate 20 in order to illustrate the relative positioning of pressure gradient control chamfer passageway 24. A zone indicated by Roman numeral I designates a portion of the wear plate adjacent the high pressure port. As can be seen, the gear teeth 30 in zone I effectively isolate chamfer 24 from direct fluid communication with the high pressure port 3. Proceeding clockwise, to the zone indicated by Roman numeral II, there is shown the chamfer portion 24 adjacent a plurality of gear teeth 30. The interdental spaces 31 between gear teeth 30 are placed in fluid communication by means of chamfer 24 of wear plate 20. Proceeding further clockwise to a zone designated by Roman numeral III, the interdental spaces 31 are no longer in fluid communication with each other and the gear teeth 30 effectively seal off the low pressure port 4 from fluid communication with chamfer 24. There is a pressure drop across Zone I due to the restricted fluid passage between the tips of the teeth and the housing. Hence the pressure at the boundary of Zones I and II is at an intermediate value, somewhat less than the outlet pressure. Chamfer 24 transfers that intermediate pressure across to the low pressure side of the gears 14, 15. A consequence of the latter is that the vertical loads imposed on gear shafts 6, 7 and bearing assemblies 18 are less than the vertical loads imposed upon those members in the case where the highest pressure fluid, i.e., the fluid at the high pressure-outlet 3, is diverted back across the wear plate to balance the force at the high pressure port 3. As a further result, the interdental spaces 31 of the gears are effectively tied together and acted upon by the intermediate pressure in chamfer 24. Accordingly, the gears themselves are partially pressure balanced horizontally, thereby relieving a portion of the radial load upon the bearing assemblies 18. The pressure gradient control that is achieved by this invention is graphically illustrated in Figure 6. A comparative test was conducted using an ordinary wear plate without any pressure gradient control chamfer, (A), one with a chamfer extending into the high pressure port 3(B), and one having the chamfer illustrated in Figure 2 (C). The test was conducted at the same inlet temperature, output pressures and speed for all three wear plates. The test results are indicated in polar 0 coordinates, with 90 corresponding to the centre line of the two gears. Pressures were measured at a number of equally spaced angular locations. Pressure measurements are represented on a percentage of maximum pump output pressure as measured at the discharge port 3. 'The particular pump used for the comparative test had an inlet port disposed at 18 and a delivery (discharge) port at 2050. The object of the pressure gradient control is to minimize the pressure force applied from the discharge (left) side, and increase the balancing force on the gears in order to thereby reduce the bearing load on the inlet (right) side. The polar graph (A) of a standard wear plate shows relatively little balancing pressure. One can see that the pressure differential on either side of the 900 line 0 changes rapidly and soon falls off to 0 . The wear plate having the chamfer extended to the high pressure port (B) has some balancing force, but the overall applied load is relatively high. The preferred embodiment of the invention (C) has the best overall results, showing lower vertical loads than (B) and increased horizontal balancing force. Those skilled in the art will recognize that the profile of the preferred embodiment (C) can be altered to approach either (A) or (B) by reducing or lengthening the chamfer 24. The remaining details of the construction of wear plate 20 are illustrated in Figures 3, 4 and 5. The opposite or bearing facing surface of the wear plate 20 includes a numeral 3 shaped recess 28 for accommodating a balance seal 29 (partially shown) therein. Such balance seals and recesses are common elements of wear plates and are thus well known to those skilled in the art. The gear facing side of the wear plate has a relief recess 25 extending between the two gear shaft openings 22, 23. A pair of port recesses 26 are disposed adjacent the portion of the wear plate approximate to the inlet and outlet ports 3, 4. Having thus described the preferred embodiment of the invention, those skilled in the art will understand that various modifications of that embodiment may be resorted to without departing from the scope of the invention disclosed and claimed herein. More specifically, those skilled in the art would recognize that the pressure gradient control could be placed directly into the housing 11 adjacent the tips of the gears 14, 15 or combined with another pressure gradient control in the wear plates. Alternatively, the pressure gradient control could be spaced inwardly from the periphery of the wear plate 20; however, such a configuration would require that the chamfer be longer since the gear teeth are wider. If the gear pump did not have wear plates and the gear teeth were adjacent the end and adapter covers, the pressure gradient control could be placed in the covers or the housing, or in both the housing and the covers. With the benefit of the foregoing, it is believed that a person skilled in the art would be able to easily alter such parameters as the location and configuration of the pressure gradient control and thus empirically achieve an improved balancing effect for any given gear pump or gear motor.

Claims: CLAIMS 1. A pressure gradient controlled rotary hydraulic machine comprising a low pressure port and a high pressure port, a gear chamber, and a pair of meshed gears rotatably mounted in the chamber for receiving fluid from one port and expelling said fluid from the other port, and a pressure gradient control including an interdental fluid passage adjacent said gears in fluid communication with the teeth of said gears and isolated from direct fluid communication with said high and low pressure ports. 2. The invention of claim 1 further comprising two end plates, each adjacent one end of said geara and each including a pressure gradient control fluid passageway in fluid communication with the gear teeth and isolated from direct fluid communication with the low and high pressure ports. 3. The invention of claim 2 wherein said pressure gradient control fluid passageway comprises a chamfered peripheral portion of the end plate adjacent the tips of the gear teeth. 4. The invention of claim 1 wherein the rotary hydraulic machine includes a housing enclosing the gear chamber and said pressure gradient control fluid passage is disposed in the housing, in fluid communication with the teeth of the gears, and isolated from fluid communication with said high and low pressure parts. 5. The invention of claim 1 wherein said rotary hydraulic machine has an end cover and an adapter cover disposed on opposite sides of the gear chamber and said pressure gradient control fluid passage is disposed in said covers, in fluid communication with the teeth of the gears, and isolated from direct fluid communication with the high and low pressure parts. 6. A wear plate for a gear-type hydraulic machine having a chamfered peripheral portion on one side thereof adapted to face the gears of such machine.

Inventors: BOWDEN, CHARLES JOHN
Applicants: GENERAL SIGNAL CORPORATION
Application year: 1980
Main classification: F04C2
IPC codes: F04C2, F04C15