DE1950338A1 - Hydraulic pump - Google Patents

Description

P. 1320

Sundstrand Corporation Eockford, Illinois, V.St.A.

Hydraulic pump

The invention relates to a variable displacement hydraulic pump having a selectively actuatable charge relief valve having.

In the past, high-speed pumps of the Hehr piston type had the disadvantage of insufficient pump filling creating a high inlet vacuum and cavitation, particularly in open circuit pumps where fluids is drawn from a reservoir at the pump inlet by a charge pump.

The present invention avoids this difficulty with a charge pressure relief valve which allows the pump to to work at higher speeds with sufficient pump filling and elimination of cavitation, in particular where the pump is in the open circuit with the central valve closed (closed center valving).

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In particular, the invention creates a hydraulic pump system which contains:

A cylinder block with a plurality of therein Cylinders, pistons displaceable in these cylinders, a cam device for the reciprocating movement of the pistons Rotation of the cylinder block relative to the Noekeneinriehtung, a valve device with inlet and outlet channels, the one behind the other can be brought into connection with the cylinders, displacement changing means for the inlay, which are fluid-actuated Means to control the movement of the cam means includes a charge pump to at least one a portion of the fluid of said fluid actuatable ones Supply device and at least a portion of the fluid to said inlet channel device and valve means to divert the charge fluid to said fluid-actuated device only after the demand of the pump has been satisfied.

In a preferred embodiment, the pump system includes a charge pressure relief valve which communicates with the pump inlet passage which receives fluid from a charge pump, which is normally fluid sucks out of a reservoir and delivers the same to the main pump inlet.

The charge relief valve operates on a priority basis so that it is only producing fluid on one stroke Influence Piston delivers when the needs of the pump have been fully satisfied and for as long as the needs of the If the pump has not been satisfied, the manipulation piston allows the pump cam to move towards the neutral position move, reducing the need for the pump. Such a situation can arise when there is a line in the charge pump circuit breaks or when the charge fluid filter becomes clogged »βΦ. Furthermore, there will be no cold weather if that

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hydraulic oil flows very slowly, the stroke of the cam only increased to the degree that the pump can remain fully filled, thus preventing damage to the pump.

Another advantage of the invention is that after the pump is adequately filled and the influencing piston has supplied charge flow means, the charge relief valve hydraulic KuH) I for the circulating Components of the pump supplies. Eventually, excess fluid from the charge pump is sent directly to the inlet of the charge pump bypassed to maintain the predetermined desired inlet fluid pressure to the main pump, as well as reducing the inlet vacuum on the charge pump. There is also a separate passage for relaxation with the influence piston and cylinder device connected, which allows the cam to move towards the neutral position even if the charge relief valve is otherwise Fluid flow from the manipulating piston and cylinder device would block.

In the drawings showing an example embodiment are:

Fig. 1 is a schematic representation of the fluid pump and the associated hydraulic circuit,

Figure 2 is a subassembly view of a charge relief valve in a first position with fluid only going to the low pressure side of the main pump,

3 is a partial view of the charge relief valve in a position in which the flow is blocked by the influencing piston,

Fig. 4 is a partial view of the charge relief valve in a position in which fluid is on the interference sko Ib en is delivered,

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5 is a partial view of the charge relaxation

valvesβ in a position in which fluid is supplied to the cooling circuit and

Pig. 6 is a partial view of the Ladungsentspannungsven tile B, with additional fluid to the Charge pump inlet is bypassed.

In the drawings and in particular in Pig. 1 shows a hydraulic axial piston pump 10 with a pressure compensation valve 12 which is suitable for the displacement of the pump 10 to control a substantially constant Maintain pressure in the high pressure pump outlet port 13. Bas control valve 12 causes this {control by Supply of fluid to a displacement control motor 16, which on the cam 17 against the influencing force of a Influence piston and cylinder device 18 acts.

To the pump 10 filled with hydraulic fluid and to create a hydraulic piston return device as well as other punctures is a charge pump provided which draws fluid from a reservoir 22 and the same through the inlet passage 24 to the Inlet channel 26 of the main pump 10 supplies.

A charge relief valve 28 acts on a priority basis to (1.) allow fluid to be supplied to the pump inlet, (2.) to deliver fluid to the manipulating piston 18 after the needs of the pump 10 have been met, (j.) Cooling fluid for the circulating Supply components of the pump and (4 ·) bypass flow means from the * charge pump back to the charge pump inlet through passage 36, all of these cases in sequential order Wise to enter into an essentially predestined one Pressure in main pump inlet passage 24 and passage 36

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“To describe the above items in greater detail the pump 10 is an axial piston pump, which is only shown schematically in Pig. 1 is shown and which has a rotatable cylinder block 39 with a plurality of axially arranged pistons 40 which are slidably received in cylinders in the block 39. The cylinder block 39 rotates against a normally stationary valve plate 41 'which has an inlet port 26 and an outlet port 42 therein which are connected in series with the cylinders in the block 39 can be brought into communication when the block rotates.

To move the pistons back and forth and to change the displacement of the hydraulic system, a swash plate or squat assembly 17 is provided which is pivotable is mounted in a housing, not shown, for rotation about an axis 43, generally transversely and vertically to the axis 45 about which the cylinder block 39 rotates. The cylinder block is driven by a suitable drive device through a shaft that revolves around the axis 45 rotates.

For the purpose of influencing the cam 17 against a maximum displacement position on one side of the neutral Position the influencing piston and cylinder device 18 is provided, and it can be seen that the same one stationary cylinder 50 with an enlarged piston 51 therein which is hinged to the cam assembly 17 by an Connection 53 is connected. The piston 51 is sized so that the hydraulic pressure fluid, which on the Piston from charge pump 20 acts, generating a force on cam member 17 about axis 43 in excess of that that is required to overcome the spring 56 and also the inherent fluid pressure torque acting on the swashplate assembly 17 through the pistons 40. Of this

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Fluid pressure torque is known that ea acts in a stroke-reducing direction and is due to the delay im Pressure change causes after each piston the sealing part of the valve member 41 between the channels 26 and 42 crosses.

The control motor 16 forces the cam selectively in the ear pointer direction against the influencing force of the piston and cylinder device 18. From the control motor 16 it can be seen that it includes a cylinder 58 with a piston 59 slidable therein and engaging a separate linkage 62, which is connected at one end to the squat assembly 17. In addition to the influencing force of the piston 59, the Handlebar assembly 62 influenced by the spring 56 in a stroke-reducing sighting. This spring comes with a suitable one Dimensioned spring constants to the swash plate 17 to a zero stroke stop, not shown, against the moments of inertia press, which act on the swash plate 17 caused by the reciprocating movement of the pistons 40. The piston moment of inertia is proportional to the pump stroke or the displacement at any fixed speed and the spring 56 is sized to overcome this moment and the swash plate returned to a zero lift position in the absence of other forces affecting the movement of the cam assembly.

When the cam 17 through the piston and cylinder device 18 is pushed against a maximum displacement position, leads the pressure compensator control valve 12 optionally supplies fluid the control motor 16 to reduce the displacement of the hydraulic system 10 to maintain a constant pressure in the outlet passage 13. The control valve 12 consists of a valve housing 63 with a valve bore 64 which slidably receives a valve member 66 with surfaces 68, 69 and 70, which are separated by reduced shaft parts 71 and 72. The valve member 66 is urged to the left by a spring 65, the tension of the same by a spring seat 73 through

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the adjustment screw 75 is adjustable, the thread-wise in the right end of the valve housing 63 is added. she Valve bore 64 communicates with high pressure passage 13 through passage 74 and branch passages 74a and 74b. Parts of the valve bore 64 normally communicate with a container 76 or the interior of the pump housing, not shown through passages 77 and 78 which are connected to and communicate with a passage 79, which in turn communicates with a depression valve 80.

The outlet fluid pressure from line 13 becomes optional via valve member 66 to control motor 16 and exhaust passage 82 (which through surface 69 in position of the valve member 66 shown in Fig. 1 is blocked).

The adjustment of the spring 65 sets the previously determined pressure level in the outlet passage 13. The movable valve member 66 compensates for the high pressure acting on the left end thereof through passage 74a against spring 65 by the pressure head in the exhaust passage 82 and the control motor 16 to control.

The spring 65 urges the valve member 66 to the left, causing the control motor 16 to evacuate through the passage 82, the reduced shaft portion 72, the passage 77 _f, the passage 79 and the tank 76, which allows the control piston, the swash plate 17 to move into the hub. When the pressure in the high pressure passage 13 rises above the predetermined desired pressure level, the hydraulic force acting on the left end of the valve member 66 will move the valve member to the right compression spring 65 to a position where the surface 69 communicates between the outlet passage and the evacuation passage 77 and providing communication between the high pressure passage 74b and exhaust passage across the reduced stem 71, thereby providing fluid to the control motor 16. This causes a

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influencing force on 'the cam member 17' which is sufficient to overcome the influencing piston and cylinder device 18, and the moments of inertia, so that the displacement of the swash plate 17 is reduced and the pressure in the outlet passage 13 returns to its predetermined desired value.

It is understood that the piston 59 in the control motor 16 is dimensioned so that the by the influencing piston 51, the Spring 56 and the forces created by the moments of inertia and pressure are just balanced to produce the predetermined pressure In the Maintain high pressure passage 13 through the hydraulic fluid flowing to or from the control motor 16 the valve 12 arrives.

The depression valve 80 is provided to selectively reduce the pressure head of the pump 10 when the predetermined high pressure level is no longer desired. The valve 80 includes a valve housing 83 with a valve member 84, which in Jb st and arranged surfaces 86 and 87, which by the reduced Shank part 88 are separated. The valve member 84 is from its inoperative position shown to a left Depression position displaceable by a solenoid 89. In the The position shown connects the valve member 84 that of the spring associated cavity with the tank through passages 78, 79 and the left side of the valve member 84. When the solenoid 89 is energized, the spindle valve member 84 shifted to the left the surface 86 blocks the tank 76 and connects a passage 92 which communicates with the main passage 13, with the normal lower pressure passage 79 »whereby the normal Low pressure passages connected to the pressure compensator valve 12 connected, are pressurized. This resembles that Pressure at both ends of the valve member 66 and the spring 65 brings the forces out of balance, which on the valve member act, shifting the same to the left, and where

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allowing high pressure fluid in passage 77, to be connected to the control motor 16 and to flow to it, through passage 82 across the reduced stem portion 72. This moves the swashplate assembly 17 in Clockwise against the zero stop, the .Druck in the high pressure passage 13 is lowered.

As briefly described above, the charge relief valve is 28 a multipurpose valve between the charge pump 20 and the inlet duct 26 of the hydraulic system 10 * The valve contains a valve housing 90 with a valve member 91 »which is displaceable in the valve bore 93. The valve member 91 has surfaces 94 and 95 through the reduced stem portion are separated. The valve member 91 is to the right against fluid pressure in the chamber 97 by a spring 9 & with Spring seat 99 urged, which engages the left end of the valve member. Chamber 97 communicates with the outlet of charge pump 20 through passage 100. The charge pressure in chamber 97 balances the spindle valve member 91 against ^ ie spring 98 to pressure in the pump inlet passage 24 and passage 26 maintain a predetermined desired inlet level. It should be noted that the inlet passage 24 with the Chamber 97 at the far right end thereof communicates, and in no position of the valve member 91 is blocked the latter the connection between the charge pump outlet and Inlet passage 24.

The charge relief valve 28 performs all of its functions on a priority basis. If the needs of the pump 10 through the supply of sufficient fluid from the charge pump through inlet passage 24 is sufficient charge relief valve 28 to the left in response to further increased pressurized fluid from the charge pump, to sequentially relieve pressure in inlet 24,

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while in successive yfeiae other functions in that hydraulic circuit as follows is explained.

The charge pump 20 is dimensioned such that under normal ' Operation displaces a hydraulic oil volume which is sufficient the needs of the cylinder block 39 and the influencing piston 18 to be delivered during the temporary condition when the swash plate is at its minimum displacement moved to the maximum displacement position without losing hydraulic oil pressure in the low pressure passage 24.

When the charge pump 20 is operating below its normal "capacity", the valve member 91 will assume a position shown in FIG. 1, which allows all hydraulic fluid from the charge pump 20 to flow into the low pressure passage to the cylinder block 39, the same This condition may occur at start-up when the cylinder block is being filled, even if the charge pump is supplying fluid at its aforementioned designed capacity. After the oil supplied is sufficient or the charge pump begins to supply fluid at its designed capacity, the pressure in chamber 97 will increase 4, where valve surface 94 opens channel 103, the connection between chamber 97 and servo cylinder 50 being created through passage 105. The charge relief valve is located so on priority ^M 2 ", with hydraulic fluid being fed to the influencing tub 51 ührt is what causes the influencing piston to move the cam assembly against the full stroke against the counteracting force of the spring 56 and the flow smitteldruckmomente, which act on the swash plate. This second puncture is very important if the oil flow to the low-pressure passage 24 is insufficient,

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To fill the cylinder block 39, the valve member 91 will not move to the position shown in Fig. 4 and will be in remain in the position of Figure 2 where fluid is not being delivered to the manipulating piston and the cam will stay against the zero stroke stop. A second importance of this feature is that in cold weather, if the hydraulic oil flows very slowly, the stroke of the swash plate assembly only increased to the extent that the cylinder block can remain completely filled and in this way Damage to the pump is prevented.

If the flow from the charge pump 20 further increases the pressure acting on the valve member 91, it becomes further to the left move to the position shown in Fig. 5, where the surface 95 moves sufficiently into the enlarged part of bore 92, to the connection between the bore part 106 and the chamber 97 through the transverse slot 108 and axial slot 109 which are both located in the valve member 91. A throttle 112 in passage 109 allows only limited cooling flow through that passage. The purpose of the fluid flow in the enlarged bore 106 consists in the fact that it goes out of the channel 111 and over the circumferential components the pump is sprayed by suitable means not shown to cool these parts. This creates a means to dissipate the heat generated by the 'rotating components. The cooling oil is then drained through a container drain line 115 through a heat exchanger 116 and then to the reservoir 22 led. Hydraulic fluid is supplied from the reservoir to the charge pump through a suction filter 118 in the passageway 119 which leads to the charge pump inlet.

The fourth function and priority of the charge relief valve 28 is to allow relaxation directly on the suction of the charge pump 20. Assume the

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Delivery-of-the-pump 20 continues to increase, so will it Valve member 91, assume the position shown in Fig. 6, wherein the valve surface 94 opens the passage 36 to the chamber 97, wherein a portion of the fluid flow from the charge pump is allowed to return directly to the inlet of the charge pump through passage 36. This is for the purpose of the charge pump 20 to operate in passage 119 under conditions of low inlet vacuum.

In the event that the pressure in passage 24 should drop below the predetermined desired value, spring 98 will move to the right, progressively cutting off the priority functions in the reverse order to those previously described. When the ■> poppet moves back to the position shown in Fig. 2 position, the channel being 103r as shown in Fig. 3, blocked, the influence is ineffective skolben 18 to empty via the valve member 91. To allow the manipulation piston 51 to move to the right, allowing a rapid reduction in displacement under these circumstances of excessive pump demand (in excess of that in passage-'24

> supplied fluid), the fluid in the Piston and cylinder device 18 or in particular in the Cylinder 50 can be expelled therefrom through passage 120 which communicates with low pressure passage 24. A Check valve 121 is provided in passage 120 to prevent the flow of fluid from passage 24- to the To prevent influencing piston, before the point in time when the valve surface 94 opens the channel 103, so the Maintain priority integrity of charge relief valve 28 will. When the valve member moves further to the right to the position shown in Fig. 2 in response Moving another decrease in pressure in passage 24 may result in the

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Influence piston and cylinder device 18 then through passage 105 via reduced stem portion 96 and Passage 36 can be emptied, allowing the swash plate 17 to de-stroke, so the Main pump 10 is protected against damage. As previously explained, the reduction in pressure in passage 24 could result A variety of causes occur, including the rupture of the inlet pipe, the clogging of the filter etc. include.

It can be seen that the charge relief valve 28 controls the stroke of the swash plate 17 in a manner to the main pump during cold weather starts or low hydraulic To protect pressure in the main inlet passage 24 to the pump, the check valve 121 and 121 also allows the passage 120 the rapid relaxation (de-stroking) of the cam 17 when the relaxation valve is in its in Fig. The blocking position shown is located. That way did the pump has the ability to operate at much higher speeds than those previously obtained without a high inlet vacuum or cavitation, as well as the ability to operate in open circuit applications with or without closed central valves to work using a suction filter at the charge pump inlet

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Claims (8)

Claims Hydraulic pump system with a cylinder block with a A plurality of cylinders located therein, pistons displaceable in the cylinders, a cam device for moving to and fro the piston relative to the rotation of the cylinder block to the cam device and a valve device with inlet and outlet ducts, one behind the other with the cylinders connectable aind, characterized by a displacement changing device for the plant that has a fluid actuatable device (18) for the control movement of the cam device includes a charge pump (20) for delivering at least a portion of the fluid to the fluid-actuated Means (18) and at least a portion of the fluid to said inlet channel means (26), further valve means (28) for supplying the charge fluid to the fluid-actuated Set up only after the needs of the pump (1.0) have been met. 2. Pump system according to claim 1, characterized in that the valve means (28) responsive to fluid or pressure from the charge pump (20) to the fluid-actuated To control means (18) to provide a reduction in the pump displacement at a predetermined reduction in the flow or pressure from the charge pump. 3. Pump system according to claim 1, characterized in that the valve device comprises a charge relief valve which can be actuated in succession (28) is, in order to control the pressure to a predetermined value in the inlet channel means (26), a passage means (100, 24), which the outlet the charge pump (20) and the inlet duct device connects, -15- 009827/1151 wherein the charge relief valve means with the Communicating passage device (100, 24), a device (111) to deliver cooling oil to the pump system, whereby the Charge relief valve (28) to supply charge fluid to the Cooling oil device dispenses according to the needs of the pump (10) and the fluid-actuated device (18) are satisfied. 4. Pump system according to claim 1 or 3 »characterized in that that the valve device is operable one after the other Charge relief valve (28) is to reduce the pressure to a to control predetermined value in the inlet channel device (26), a passage device (100, 24), which the Outlet of the charge pump (20) and the inlet duct means connects, the charge relief valve means communicating with the passage means (100, 24), one Bypass passage (36) »to return charge fluid from the charge pump outlet directly to the charge pump inlet, to reduce the vacuum at the charge pump inlet, with the charge relief valve (28) opening the bypass B passage opens only after the needs of the pump system (10) and the fluid-actuated device (18) have been satisfied. 5 · Pump system according to claim 1 .-, -, characterized by a Passage device (100, 24) which connects the outlet of the charge pump (20) with the inlet channel device (26), wherein the valve means (28) is a movable valve member (91) includes spring means (98) urging the valve member in a first direction, the valve, device (28) with the passage device (100, 24) communicates so that fluid pressure from the charge pump • the valve member (91) .- urges in a second direction, further , a first channel device (103) »the one with said . Valve device. Is connected, a passage device -16- 00982 Λ 115 1- -. (105) r which the first duct means and the fluid actuatable Device (18) connects, wherein the valve member (91), the first channel device (103) to Fluid pressure from the charge pump (20) opens. 6. Pump system according to .Anspruch 5 »characterized in that the valve device (28) comprises a second channel device (108) which is set to open after the first channel device by the valve member (91) when the valve member moves in the second direction moves, a cooling device (111) and the second Channel device (108) in connection with the cooling device stands. 7. Pump system according to claim 5 or 6, characterized in that the valve device (28) has a second channel device (108) which is set to be opened by the valve member (91) after the first channel means (103), when the valve member moves in the second direction, a bypass passage means (36) to bypass charge fluid from the outlet of the charge pump directly to the inlet of the charge pump (20). 8. Pump system according to claim 1, characterized in that the displacement change device for the pump system contains a fluid-actuated control motor (16), an influencing piston and cylinder device (18) to, when pressurized, the cam member (17) against a maximum To push displacement position, a control valve device (12) to admit fluid to the control motor for optional displacement of the pumping system to reduce a passage device (100, 24) »to lead fluid to the inlet channel device (26), wherein the charge pump (20) supplies charge fluid to the Passage device and to the displacement piston and -17- 009827/115 1 Cylinder device supplies, wherein the charge relief valve (28) is in communication with the pass-through facility to place the printout in the pass-through facility on a to control predetermined value, wherein a movable valve member (91) is present, which on fluid pressure from the charge pump responds to transfer some of the fluid from that charge pump to the influencing piston and allow cylinder device. Pump system according to claim 8, characterized by one Return passage (120) from the influencing piston and Cylinder device (18) to the passage device (24) »a check valve device (121) in the aforementioned Return passage which controls the flow of fluid to the piston and cylinder device, the return passage allowing the fluid to escape from the Influence piston and cylinder device flow out when the expansion valve member (91) is in one position which blocks the return of fluid therefrom via the relief valve. 009827/1151