GB1567100A - Flow control assembly for multi-piston pumps - Google Patents

Description

(54) FLOW CONTROL ASSEMBLY FOR MULTI-PISTON PUMPS (71) We, CATERPILLAR TRACTOR CO., a corporation organized and existing under the laws of the State of California, United States of America, of 100 N. E.

Adams Street, Peoria, Illinois 61629, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following state ment: - The hydraulic system is responsible for a sizable portion of the noise produced by many machines. The pump in most cases is the major exciting component in the hydraulic system. The energy from the pump which produces sound is transmitted in three ways: airborne, structure-borne, and fluid-borne.Air and structure-borne noise can be reduced by barriers and isolation of the pump, but reduction of the fluid-borne noise is more difficult The fluid-borne energy consists of pressure pulsations which act on the walls of lines, valves and other components (and through them to the supporting structure) to produce noise. The pressure pulsations are caused in large part by changes in flow emanating from the pump and other dynamic elements of the system. The changes in flow are translated into pressure pulsations based on the impedance of the system.

In a multiple piston hydraulic pump of either the axial or radial type, fluid is positively displaced by the reciprocating stroking motion between the pistons and cylinders.

During the time each piston moves toward the open end of each cylinder, fluid enters the cylinder from an inlet port to fill the increasing volume. As the piston moves toward the closed end of the cylinder, fluid is forced out of the cylinder to a discharge port. The velocity of each piston with respect to its cylinder is harmonic in nature and is representative of the delivery (flow rate from each cylinder. It is zero at BDC (bottom dead centre), increases to a maximum in an inward direction about mid stroke in discharge, decreases to zero at TDC (top dead centre), increases to a maximum in an out ward direction about mid stroke in inlet, and decreases to zero again at BDC. The sum of the flow rates for the multiple of individual cylinders engaged in inlet or discharge is not constant but varies in a cyclic manner with rotation of the body containing the cylinders.

Hence, because of pump geometry, total delivery is constantly changing in a cyclic fashion. Variations in input and output pressures are created as the fluid has to accelerate and decelerate to change velocity.

A second source of pump delivery variation is due to compressibility of the oil. The cylinder fills during travel from TDC to BDC.

Beyond BDC the piston starts to compress the oil in the cylinder and raises the pressure. If the cylinder is connected to the discharge port before the cylinder pressure is up to discharge pressure, oil flows in a reverse direction from the discharge port to the cylinder until the two pressures are equalized.

Conversely, if opening to the discharge port is delayed until the cylinder pressure is higher than discharge pressure, flow will surge from the cylinder when the port opens.

Even when the cylinder opens to the discharge port just as cylinder pressure is equal to discharge pressure, there is a sudden increase in the discharge flow because the flow from the cylinder is added to the discharge flow. Any of these conditions results in a disruption in the discharge flow which could produce pulsations and fluid-bome noise.

Similarly, expansion of the oil under pressure in the cylinder at TDC results in a disturbance in the input flow.

The usual method for smoothing the flow disturbances over a wide range of operating conditions is to connect the cylinders to the port through a bleed slot prior to opening to the port. This lowers the flow rate into and out of the cylinders during the transition by spreading it out over a longer period.

Nevertheless, there remains a sizable flow ripple that can not be removed by this method.

According to the invention, in a fluid pressure energy translating device (i.e. a pump or motor) having a housing, a body rotatably positioned within the housing and having a first valving surface and a plurality of cylinders, each of the cylinders having a passage opening at the first valving surface, the passages being circumferentially spaced a first preselected arcuate distance one from the other, and a plurality of pistons slidably positioned within the cylinders for reciproc able stroking movement between TDC and BDC in response to rotation of the body, each of the passages being swept in a circular pathway from BDC through TDC and back to BDC in response to rotation of the body; a flow control member is connected to the housing and has a second valving surface positioned in sliding, sealing engagement with the first valving surface, with first and second arcuate ports opening at the second valving surface, the first port being arranged for direct communication with at least two of the passages and for initiating direct communica tion with one passage substantially upon the termination of direct communication with an other passage during rotation of the body, the initiating of direct communication with the one passage being at a second preselected arcuate distance after the one passage has passed one of the BDC and TDC, and the termination of the direct communication with the other passage being at a third preselected arcuate distance before the other passage reaches the other of the BDC and TDC, the sum of the second and third preselected arcuate distances being within the range of between 35% and 60% of the first preselected arcuate distance.

With this arrangement it is possible to reduce pump flow variation resulting from compressibility of the oil. The flow disrup tion created when a cylinder enters a port and begins delivering flow is offset by cutting off a similar amount of flow from another cylinder leaving the port Two examples of pump constructed in accordance with the invention are illustrated in the accompanying drawings, in which:: Figure 1 is a diagrammatic sectional view of an axial piston pump; Figure 2 is a diagram taken generally along the line II--II of Figure 1 showing the operating face of a flow control member with the relative position of the cylinders indicated thereon; Figures 3, 4 and 5 are similar views of the flow control member shown in Figure 2 but with the cylinders indicated in different rotational positions of distribution thereon; Figure 6 is a diagrammatic view of a radial piston pump; and, Figures 7, 8, 9, and 10 are displacement diagrams illustrating the phase relationship of the flow control member and cylinders at various rotational positions of the cylinders.

Referring now to Figure 1, a variable displacement overcentre axial piston pump 10 has a drive shaft 11 extending through a stationary housing 12 while being coupled in driving relation with a rotatable flange assembly 13. The flange assembly is journalled within the stationary housing by a bearing 14. The drive shaft and flange assembly are coupled in driving relation with a rotatable pumping assembly 16 by means of a universal joint 17. Both the stationary housing 12 and the pumping assembly 16 are positioned within a nonrotating housing 18.

The pumping assembly 16 includes a plurality of cylinders 19 in a cylinder body 20 with each of the cylinders opening at a control or valving surface 21 through a passage 22. The cylinders and hence the passages are arranged in a circular row and are cir cumferentially spaced about a longitudinal axis of the cylinder body. Referring to Fig.

2, the passages are shown in broken lines at 22a, 22b, 22c, 22d, 22e, 22f and 22g with adjacent passages being spaced a preselected arcuate distance or angle "A" one from the other. The preselected angle is determined by the number of cylinders and for a 7-cylinder pump illustrated by the drawings, the angle "'A" is 51.4 degrees. The arcuate length of the passages is depicted by the preselected arcuate distance or angle "B".

A plurality of pistons 23 are slidably positioned within the respective cylinders 19.

Each of the pistons is coupled with the flange assembly 13 by means of a connecting rod 24. A stationary head plate 26 is secured to the non-rotating housing 18 by cap screws 27.

A flow control member 28 is seated in a recess 29 formed in the head plate and has a flat control or valving surface 31 positioned in sliding and sealing engagement with the control surface 21 of the cylinder body 20 Referring to Fig. 2, a pair of symmetrica arcuate ports 32 and 33 are formed in the control surface 31 of the flow control member 28 and connect with a pair of inletoutlet passages, not shown, formed in the head plate 26 in the usual manner. With the housing 12 and flange assembly 13 in the position shown in Fig. 1, the port 32 is considered a low pressure intake port and the port 33 is considered a high pressure discharge port. The identity of the intake and discharge ports is established by rotation of the cylinder body 20 in a clockwise direction relative to the flow control member 28 as viewed in Fig. 2.

A pair of metering slots 34, 36 in the control surface 31 communicates with the intake and discharge ports 32, 33, respectively.

In operation, rotation of the pumping assembly 16 and hence the cylinder body 20 relative to the flow control member 28 causes each of the passages 22, for example 22a, to be swept in a circular pathway from the bottom dead centre position indicated at BDC in Fig. 2, past the discharge port 33, through the top dead centre position indicated at TDC in Fig. 2, past the intake port 32 and back to the BDC position. Fluid is drawn into the respective cylinder 19 from the intake port 32 in response to passage 22a moving from TDC to BDC and fluid is discharged from the cylinder through the discharge port 33 in response to passage 22a moving from BDC to TDC.

In an overcentre axial pump, the intake and discharge ports 32, 33 and the metering slots 34, 36 are substantially identical and are constructed and positioned relative to the TDC and BDC points according to the follow ing parameters. As hereinafter used, the term "direct communication" or its equivalent refers to a condition in which at least a por tion of the passage 22 opens into the ass ciated port 32 or 33 and the term "indirect communication" refers to a condition in which the passage 22 is connected to an asso ciated port through one of the metering slots 34 or 36.

When the passage 22a is at the BDC posi tion as shown in Fig. 2, direct communica tion between the passage 22a and either of the ports 32, 33 is blocked. After the cylinder body 20 and thus the passage 22a is rotated from the BDC position a preselected arcuate distance or angle "C", (Fig. 3) direct com munication is initiated between the passage 22a and the discharge port 33. The pre selected angle "C" is sufficient to allow cylin der pressure to reach a preselected pressure level (normally near discharge port pressure) before direct communication is established between the passage 22a and the discharge port 33.About the same time the passage 22a begins direct communication with the discharge port, direct communication between passage 22d and the discharge port 33 is being terminated, such termination occurring a preselected arcuate distance or angle "D" (Fig. 4) before the passage 22d reaches the TDC position. This reduces flow variation from the discharge port 33 because as cylin der 22a begins to deliver flow to the discharge port cylinder 22d stops supplying flow and the two disturbances balance each other.Because the flow area is very small between the passage 22a and the discharge port 33 during the first couple degrees of opening, some overlap occurs between the point at which direct comet munication between one passage 22a and the discharge port is initiated and the point at which direct communication between another passage 22d and the discharge port is terminated.

Shortly before direct communication between the passage 22d and the discharge port 33 is terminated, indirect communication between passage 22d and the intake port 32 is initiated through the metering slot 34. This indirect communication occurs at a preselected arcuate distance or angle "E" (Fig. 3) before direct communication between passage 22d and the discharge port is terminated. The indirect communication prevents excessive pressure build-up as the piston continues to move into the cylinder to TDC and also regulates the expansion of the fluid before direct communication between the passage and the intake port is initiated. The passage 22d eventually passes through TDC and direct communication between the passage 22d and the intake port 32 occurs at a preselected arcuate distance after passage 22d has passed by TDC.For an overcentre pump as shown in the drawings, this preselected arcuate distance will be the same as the preselected angle "C".

Referring to Fig. 5, direct communication between one of the passages, for example passage 22g, and the intake port 32 is terminated at a preselected arcuate distance or angle "F" before passage 22g reaches BDC.

The termination of direct communication between passage 22g and the intake port before BDC provides more time for cylinder pressure to build up to discharge pressure. It also reduces the flow variation in the intake port because at the time cylinder 22e begins to accept flow from the inlet port 32, cylinder 22g stops accepting flow from that port. The two disturbances offset each other. Shortly before direct communication between the passage 22g and the intake port is terminated, indirect communication between the passage 22g and the discharge port 33 is initiated through the metering slot 36. This indirect communication between the passage 22g and discharge port is helpful in keeping the cylinder full as the associated piston 23 continues to move out of the cylinder to BDC.The metering slot controls rate of pressure rise in the cylinder, provides reasonable pressure transition characteristics over the range of operating pressures and displacements, and meters fluid in and out of the cylinder preventing sudden changes in delivery of large magnitude.

The sum of angles "C" and "D" is sub- stantially one-half of angle "A". By the term "substantially one-half" it is meant to be from about 35% to about 60% of angle "A".

The relationship between angles "C" and "D" can be within the range of angle "C" being substantially equal to angle "D" to angle "C" being approximately 4 times angle "D". In one example, angle "B" is 400, onehalf angle "A" is 25.70, angle "C" is 140, angles "D" and "F" are each 90 and angle "E" is 20. Thus, starting with one passage 22a at BDC and making one revolution and returning to BDC, the timing between passage 22a and the ports 32, 33 and slots 34, 36 is as follows: 1. Direct communication with port 33 is initiated at 140 past BDC.

2. Indirect communication with port 32 through slot 34 is initiated at 110 before TDC (angles "D" and "E").

3. Direct communication with port 33 is terminated at 90 before TDC.

4. Direct communication with port 32 is initiated at 140 after TDC.

5. Indirect communication with port 33 through slot 36 is initiated at 110 before BDC.

6. Direct communication with port 32 is terminated at 90 before BDC.

Referring to Fig. 6, an overcentre radial piston pump 41 can have a general construc- tion essentially similar to that of a conventional pump except insofar as the construction and position of the intake and discharge ports relative to TDC and BDC. Accordingly, the overall construction of the pump aside from the positioning of the intake and discharge port will be only briefly described.

The pump 41 typically has a stationary cylindrical pintle or flow control member 42 having a valving surface 43, and a pair of arcuate ports 44, 46 opening at the valving surface. An orifice 47 connects the port 44 with the valving surface 43 intermediate the ports 44, 46 while an orifice 48 connects the port 46 with the valving surface 43 at a point intermediate the ports 44, 46.

A pumping assembly 49 is rotatable relative to the pintle 42 and has a valving surface 51 of a rotor 52 positioned in sealing and sliding engagement with valving surface 43 of the pintle. A plurality of spokes 53 extend radially outwardly from a central hub 54 of the rotor, each spoke having a passage 56 opening at the valving surface 51. Each spoke has a piston 57 connected to its outer end. A cylinder 58 is slidably positioned on each piston and communicates with the respective passage 56. The cylinders are positioned in sliding engagement with a race 59 which is in turn positioned within a housing 61. The pump 41 is illustrated as an overcenter pump and is shown at one of its maximum displacement positions with port 44 functioning as an intake port and port 46 functioning as a discharge port.Movement of the race 59 to the right relative to the pintle 42 reduces the volumetric output displacement of the pump and subsequently reverses the fluid flow therethrough so that port 44 becomes the discharge port and port 46 becomes the intake port. For an explanation, however, the operation of the pump will be described in the operating position illustrated wherein the port 44 is the intake port and port 46 is the discharge port.

In operation, rotation of the pumping assembly 49 clockwise about the pintle 42 causes each of the passages 56, for example 56a (Fig. 7), to be swept in a circular pathway from BDC, past the discharge port 46, through TDC, past the intake port 44 and back to BDC. When the passage 56a is at the BDC position, as shown in Fig. 7, direct communication between passage 56a and either of the ports 44 and 46 is blocked. After the rotor 52 and thus the passage 56a is rotated from the BDC position a preselected arcuate distance or angle "C" (Fig. 8) direct communication is initiated between the pas sage 56a and the discharge port 46.About the same time the passage 56a begins direct com munication with the discharge port, direct communication between passage 56d and the discharge port is being such termination occurring at a preselected arcuate distance or angle "D" (Fig. 9) before the passage 56d reaches TDC.

Shortly before direct communication between passage 56d and the discharge port 46 is terminated, indirect communication between passage 56d and the intake port 44 is initiated through the orifice 47. The passage 56d eventually passes through TDC and direct communication between passage 56d and the intake port occurs at a preselected arcuate distance after passage 56d has passed by TDC. For an overcentre pump as shown in Figs. 610, this preselected arcuate distance will be the same as the preselected arcuate distance "C".

Referring to Fig. l, direct communication between one of the passages, for example 56g, and the intake port 44 is terminated at a preselected arcuate distance or angle "F" before passage 56g reaches BDC. Shortly before direct communication between passage 56g and the intake port is terminated, indirect communication between the passage 56g and the discharge port 46 is initiated through the metering slot 48.

The sum of angles "C" and "D" is substantially one-half of angle "A". The relationship between angles "C" and "D" can be within the range of angle "C" being substantially equal to angle "D" to angle "C" being approximately four times the angle "D". In one example, angle "B" is 400, one-half angle "A" is 25.70, angle "C" is 140, and angle "D" and "F" are each 90.

WHAT WE CLAIM IS: 1. A fluid pressure energy translating device having a housing, a body rotatably positioned within the housing and having a first valving surface and a plurality of cylinders, each of the cylinders having a passage opening at the first valving surface, the passages being circumferentially spaced a first preselected arcuate distance one from the other, and a plurality of pistons slidably positioned within the cylinders for reciprocable stroking movement between TDC and BDC in response to rotation of the body, each of the passages being swept in a circular pathway from BDC through TDC and back to BDC in response to rotation of the body; wherein a flow control

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. through slot 34 is initiated at 110 before TDC (angles "D" and "E"). 3. Direct communication with port 33 is terminated at 90 before TDC. 4. Direct communication with port 32 is initiated at 140 after TDC. 5. Indirect communication with port 33 through slot 36 is initiated at 110 before BDC. 6. Direct communication with port 32 is terminated at 90 before BDC. Referring to Fig. 6, an overcentre radial piston pump 41 can have a general construc- tion essentially similar to that of a conventional pump except insofar as the construction and position of the intake and discharge ports relative to TDC and BDC. Accordingly, the overall construction of the pump aside from the positioning of the intake and discharge port will be only briefly described. The pump 41 typically has a stationary cylindrical pintle or flow control member 42 having a valving surface 43, and a pair of arcuate ports 44, 46 opening at the valving surface. An orifice 47 connects the port 44 with the valving surface 43 intermediate the ports 44, 46 while an orifice 48 connects the port 46 with the valving surface 43 at a point intermediate the ports 44, 46. A pumping assembly 49 is rotatable relative to the pintle 42 and has a valving surface 51 of a rotor 52 positioned in sealing and sliding engagement with valving surface 43 of the pintle. A plurality of spokes 53 extend radially outwardly from a central hub 54 of the rotor, each spoke having a passage 56 opening at the valving surface 51. Each spoke has a piston 57 connected to its outer end. A cylinder 58 is slidably positioned on each piston and communicates with the respective passage 56. The cylinders are positioned in sliding engagement with a race 59 which is in turn positioned within a housing 61. The pump 41 is illustrated as an overcenter pump and is shown at one of its maximum displacement positions with port 44 functioning as an intake port and port 46 functioning as a discharge port.Movement of the race 59 to the right relative to the pintle 42 reduces the volumetric output displacement of the pump and subsequently reverses the fluid flow therethrough so that port 44 becomes the discharge port and port 46 becomes the intake port. For an explanation, however, the operation of the pump will be described in the operating position illustrated wherein the port 44 is the intake port and port 46 is the discharge port. In operation, rotation of the pumping assembly 49 clockwise about the pintle 42 causes each of the passages 56, for example 56a (Fig. 7), to be swept in a circular pathway from BDC, past the discharge port 46, through TDC, past the intake port 44 and back to BDC. When the passage 56a is at the BDC position, as shown in Fig. 7, direct communication between passage 56a and either of the ports 44 and 46 is blocked. After the rotor 52 and thus the passage 56a is rotated from the BDC position a preselected arcuate distance or angle "C" (Fig. 8) direct communication is initiated between the pas sage 56a and the discharge port 46.About the same time the passage 56a begins direct com munication with the discharge port, direct communication between passage 56d and the discharge port is being such termination occurring at a preselected arcuate distance or angle "D" (Fig. 9) before the passage 56d reaches TDC. Shortly before direct communication between passage 56d and the discharge port 46 is terminated, indirect communication between passage 56d and the intake port 44 is initiated through the orifice 47. The passage 56d eventually passes through TDC and direct communication between passage 56d and the intake port occurs at a preselected arcuate distance after passage 56d has passed by TDC. For an overcentre pump as shown in Figs. 610, this preselected arcuate distance will be the same as the preselected arcuate distance "C". Referring to Fig. lû, direct communication between one of the passages, for example 56g, and the intake port 44 is terminated at a preselected arcuate distance or angle "F" before passage 56g reaches BDC. Shortly before direct communication between passage 56g and the intake port is terminated, indirect communication between the passage 56g and the discharge port 46 is initiated through the metering slot 48. The sum of angles "C" and "D" is substantially one-half of angle "A". The relationship between angles "C" and "D" can be within the range of angle "C" being substantially equal to angle "D" to angle "C" being approximately four times the angle "D". In one example, angle "B" is 400, one-half angle "A" is 25.70, angle "C" is 140, and angle "D" and "F" are each 90. WHAT WE CLAIM IS:

1. A fluid pressure energy translating device having a housing, a body rotatably positioned within the housing and having a first valving surface and a plurality of cylinders, each of the cylinders having a passage opening at the first valving surface, the passages being circumferentially spaced a first preselected arcuate distance one from the other, and a plurality of pistons slidably positioned within the cylinders for reciprocable stroking movement between TDC and BDC in response to rotation of the body, each of the passages being swept in a circular pathway from BDC through TDC and back to BDC in response to rotation of the body; wherein a flow control

member is connected to the housing and has a second valving surface positioned in sliding, sealing engagement with the first valving surface, with first and second arcuate ports opening at the second valving surface, the first port being arranged for direct communication with at least two of the passages and for initiating direct communication with one passage substantially upon the termination of direct communication with another passage during rotation of the body, the initiating of direct communication with the one passage being at a second preselected arcuate distance after the one passage has passed one of the BDC and TDC, and the termination of the direct communication with the other passage being at a third preselected arcuate distance before the other passage reaches the other of the BDC and TDC, the sum of the second and third preselected arcuate distances being within the range of between 35% and 60% of the first preselected arcuate distance.

2. A device according to claim 1, wherein the second preselected arcuate distance is selected from the range of a distance substan tially equal to the third preselected arcuate distance to a distance of substantially four times the third preselected arcuate distance.

3. A device according to claim 2, wherein the first preselected arcuate distance is substantially 51.40, the second preselected arcuate distance is substantially 140 and the third preselected arcuate distance is substantially 90.

4. A device according to claim 1 or claim 2, wherein the sum of the second and third preselected arcuate distance is substantially one-half of the first preselected arcuate distance.

5. A device according to any one of the preceding claims, including a metering means connected to the first port for initiating indirect communication between a selected passage and the first port at a fourth preselected distance before termination of direct communication between the selected passage and the second port.

6. A device according to claim 5, wherein the fourth preselected distance is about 20.

7. A device according to any one of the preceding claims, wherein the first port is a discharge port and the second preselected arcuate distance is positioned after the one passage has passed BDC.

8. A device according to any one of the preceding claims, wherein the first and second ports are substantially symmetrical.

9. A device according to claim 1, substantially as described with reference to Figures 1 to 5, or to Figures 6 to 10, of the accompanying drawings.