EP0105473A2 - Hydraulic circuit with two variable flow pumps controlled by excess flow - Google Patents

Abstract

The adjustment controls (70, 72) of a first, support foot and driving functions of an excavator with oil flow adjusting pump (66) and a second, the pivoting device of the driver's cab of the excavator with oil flow adjusting pump (68) are connected to pressure selection valves (88, 112) connected, which work in such a way that a pressure drop in the excess oil flow resulting from the control valves (14, 16, 18) for the driving and pivoting functions is passed on to the adjusting devices. A bypass circuit (132) is provided in order to connect the excess oil flow coming from the swivel control valve (14) to the delivery flow coming from the first variable displacement pump (66) when the pressure of the last-mentioned excess oil flow corresponds to that of the driver Control functions due to pressure drop. Line compensators (136, 138) are provided in order to make the adjusting devices (70, 72) more sensitive to the switching requirements; A pressure limiting valve (172) is also provided in order to automatically establish a pressure connection so that the variable displacement pumps (66, 68) are brought down somewhat and thereby relieve the machine somewhat when the machine speed drops below a predetermined limit.

Description

The invention relates to a hydraulic system with two variable displacement pumps, each of which feeds a group of control valves with an excess outlet, wherein a pressure medium can be fed from one system to the other.

Such a hydraulic system, known for example from US-A-4,024,710, has two hydraulic pumps with a variable delivery rate (variable displacement pumps), the displacement of which is automatically controlled as a function of the requirements of a plurality of hydraulic functions, represented by excess currents generated by the different radio certain control valves.

Surplus is a typical option for most. Valves for. Available that are used in open or closed hydraulic systems. If a large number of control valves are connected in series, this option gives priority to the first control valve with regard to the available oil flow, which when it is not required is fed from the excess outlet to the next valve instead of returning it to the oil tank as it is is the case with conventional open hydraulic systems.

In open hydraulic systems, spool valves with an open center position are mostly used for function control for excess valves. The control spools are closed in the middle position and block the oil flow coming from the pump, so that there is an increase in pressure. The oil flow is divided between the open center position and the work outlets, the oil flow being directed through the open center position into the excess outlet while the oil return is returned to the reservoir. Current sharing of this type makes it difficult for an operator to control the speed of a function to be performed since changes in the functional load must be compensated for by shifting the slide valve.

This control problem can be somewhat reduced by using a special valve with an open middle position and excess outlet, which comprises a flow control slide which works as a flow divider depending on the oil requirement of a function controlled by the valve. The oil flow depends on the displacement of the control spool; the oil flow is kept constant for changing loads and is also limited to a predetermined proportion. Examples of pressure compensated Ven Tile with an open center position and upper weft outlet can be found in US Pat. Nos. 3,455,210 (corresponds to DE-PS 16 50 375 3,465,519 (corresponds to DE-AS 17 51 934) and 3,718 159 (corresponds to DE-OS 22 01 839).

For efficiency reasons, hydraulic systems with open center valves use variable displacement hydraulic pumps that are automatically controlled to meet the fast demands of the system. An example of a system with a variable displacement pump controlled in this way is disclosed in the aforementioned U.S. Patent No. 3,465,51. This known system comprises a single adjustment pump, a variety of functions to be performed, for the control valves are provided, in which the excess flow of the last control valve is directed to a pressure-dependent adjustment control in order to reduce the pump delivery rate as a function of the increasing excess flow. This system avoids connecting functions of equal priority in parallel to a common oil supply or, in situations where a second pump is required, supplying the highest possible amount of oil that the functions could require.

The invention has for its object to add the excess flow of the first variable displacement pump to the flow of the second variable displacement pump when the pressure of the excess flow of the control valve originating from the first variable displacement pump is greater than the pressure of the excess flow of the control valve originating from the second variable displacement pump.

This object is achieved according to the invention in that a pressure selection valve with its second and first inlet to a first pressure-dependent pump displacement control of the first variable displacement pump, to a downstream excess outlet of a downstream control valve and the second privileged upper shot outlet of a second privileged control valve and with its outlet to the second pressure-dependent pump adjustment control of the second variable displacement pump and transmits a pressure drop at its first and second inlet to its outlet.

Further features and advantages of the invention are the subject of the dependent claims and are explained using an exemplary embodiment.

The drawing shows an exemplary embodiment of the invention. The drawing schematically shows a hydraulic control system for an excavator.

The hydraulic system as a whole is identified by the reference number. 10 designates and includes a plurality of control valves that are pressure compensated, have an excess outlet, and are substantially the same as the embodiment of U.S. Patent No. 3,718,159, except that some control valves only include a function control section mated to a supply section, while the patented one Embodiment control parts for three functions disclosed, which are plugged together with a supply part.

The control system 10 comprises a support foot control valve 12, a control valve 14 for pivoting the cabin, and a right and a left travel control valve 16, 18, all of which are shown in a simplified representation as a block.

The support foot control valve 12 comprises a supply part 20 which is connected to a main boom, a bucket boom and a bucket control part 22, 24 and 26. The supply part 20 has an inlet 28 and an excess outlet 30 and encloses a pressure-compensated flow control valve, not shown, which divides the oil flow entering the inlet between the excess outlet and an outlet leading to the function control part in accordance with the arrangement of corresponding control slide valves in the control parts and the Need a function to be controlled. The Hauptausleger-, Kübelausleger- and bucket control portions each have a pair of _A uslaßanschlüsse to 32,34,36, each of which serves to connect the opposite ends of double-acting hydraulic cylinder.

The control valve 14 for pivoting the cabin has a supply part 38 which is plugged together with a pivot control part 40. and corresponds approximately to the supply part 20 of the control valve 12, that is to say also has an inlet 42 and an excess outlet 44. The swing control member 40 includes a pair of outlet ports 45 for connecting the opposite outputs of an invertible swing motor.

The right and left travel control valves 16, 18 are of identical design and each include a supply part 46 and 48 and travel control valves 50, 52. The supply parts 46, 48 have inlets 54, 56 and excess outlets 58, 60. The travel control valves 50, 52 each comprise a pair of outlet ports 62, 64 to which the opposite ports of a reversible right and left travel motor can be connected.

A first and a second hydraulic pump 66, 68 with a variable delivery rate (variable pump) are used to apply oil to the control valves, which are each connected to a pressure-dependent adjustment control 70, 72, which increase the delivery rate of the pumps as a function of pressure drop signals.

The variable displacement pump 66 is connected with its inlet to a pump sump 74 and with its outlet to the inlet 28 of the supply part 20 of the support foot control valve 12 via a feed line 76. A first excess line 78 is connected at one end to the excess outlet 30 of the supply part 20 and at the other bifurcated end to the inlet connections 54, 56 of the drive control valves 16, 18. The excess outlets58, 60 of the. Both travel control valves 16, 18 are connected via a second and a third excess line 80, 82 to the first inlet 84 and the second inlet 86 of a pressure selection valve 88, respectively. The latter has an outlet 90 which communicates with the two inlets 84, 86 via a central valve bore 92 stands. In the latter, a first and a second shut-off ball 94, 96 are arranged on both sides of the connection for the outlet 90 and act together with a first and a second valve seat 98, 100 to prevent oil flow from the inlets 84, 86 to the outlet 90. In the valve bore 92 a reciprocating plunger 102 is arranged between the two shut-off balls 94, 96, which is longer than the distance between the two valve seats mentioned, so that only one of the two shut-off balls at the same time on the valve seat assigned to them can be applied (see also FIG. 3 of US Pat. No. 3,863,449). Therefore, any increase in pressure in the upper weft lines 80, 82 causes one of the two shut-off balls 94, 96 to be pressed against its valve seat, thereby lifting the other shut-off ball from its valve seat, so that a pressure drop in the lines 80, 82 is transmitted to the outlet 90 . The latter is connected via a control line 104 to the pressure-dependent adjustment control 70 of the adjustment pump 66.

The pump 68 is connected with its inlet to a pump sump 74 and with its outlet via a flow line 106 to the inlet 42 of the control valve 14. A fourth excess line 108 connects the excess outlet 44 to a first inlet 110 of a pressure selection valve 112, which in its construction is identical to the pressure selection valve 88 described above. The pressure selection valve 112 is connected to the control line 104 with its second inlet 114 and to its outlet 116 pressure dependent on di _e displacement control 72 of the variable displacement pump connected 68 and via a control line 118. a central valve bore 120 connects the terminals 110.114 and 116. in order to control the oil flow from the inlets 110 and 114 to the outlet 116 first and second Absperrkugeln 122,124 are provided, which cooperate with first and second valve seats 126 and 128. Between the shut-off balls 122, 124, a plunger 130 is displaceably arranged back and forth in the valve bore 120, the length of which is dimensioned such that simultaneous contact of the shut-off balls on their valve seats precludes. The pressure Selection valve 112 therefore connects the respectively lower pressure, which exists in the control line 104 or the fourth excess line 108, to the control line 118 and thereby to the adjustment control 72 of the adjustment pump 68.

A bypass circuit comprises a bypass line 132 which is connected between the fourth excess line 108 and the flow line 76 and has a one-way valve 134 which only allows the oil flow in the direction from line 108 to line 76. Thus, if the pressure in line 108 is greater than that in control line 104, pressure selection valve 112 prevents oil flow from line 108 to control line_118; the pressure in the line 108 then opens the valve 134 and thereby connects the excess line 108 to the flow line 76, so that the delivery volume generated by the pump 68 is added to the pump 66.

In order to enable the variable displacement pump 66 to be adapted more quickly to the need changes in the support foot functions operated by the valve 12, a pair of line compensators 136, 138 are provided in the circuit leading to the valve 12 or leading away from this valve. The latter each include stepped cylindrical chambers 140, 142, of which the chamber 140 is connected to the flow line 76 with a small end via a line 144, while the chamber 142 with a small end is connected to the first excess line via a line 146. device 78 is connected. Both chambers 140, 142 are each connected with their large ends to one another and to the control line 104 via a forked line 148. A small and a large piston 150 and 152, which are connected to one another via a piston rod 154, are each displaceably arranged in the small and large sections of the chamber 140. On opposite sides of the large piston 152 a pair of centering springs 156, 158 are provided which urge the piston 152 to a central position in the large portion of the chamber 140. Correspondingly, the chamber 142 also has a small and a large piston 160, 162 which are arranged such that they can be moved back and forth and are connected to one another via a piston rod 164. A pair of centering springs 166,168 is on the opposite. the sides of the large piston 162.

If there is suddenly a high oil requirement for actuating the support leg, which is controlled via the support leg control valve 12, the excess flow in the excess line 78 will decrease and thus reduce the pressure acting on the small piston 160 of the line compensator 138. The piston 160 is then shifted to the left due to the unbalanced forces resulting from an increase in volume in the end of the large section of the chamber 142, which leads to a decrease in pressure in the bifurcated line 180 and, in turn, a pressure drop in the control line 104 . The adjustment control 70 of the adjustment pump 66 will react to this pressure drop by increasing the pump delivery rate. This increased oil flow will initially cause a pressure increase relative to the small piston 150 of the line compensator 136, whereupon the unbalanced forces push the piston to the left so that the large piston 152 pushes oil out of the large end of the chamber 140.

At this time, the initial pressure drop in excess line 78 will likely have made its way through the circuit and become apparent in control line 104 so that any pressure increase in control line 104 due to the left displacement of piston 152 will be overlaid by the pressure drop; the delivery rate of the variable displacement pump 66 is increased in accordance with a possible net pressure drop in the control line 104.

In the bifurcated line 148 is the outlet 170 of a solenoid operated pressure relief valve 172 which has its inlet 174 connected to the flow line 76 via a portion of the bypass line 132 downstream of the one-way valve 134. The pressure relief valve 172 is more commonly decayed Position shown in which there is a flow connection between the line 132 and the control line. tion 104 prevents. The pressure relief valve 172 is expediently actuated to a predetermined minimum as a function of the drop in the output speed of the excavator machine. Any known speed measurement circuit can be used to determine the output speed of the. Measure the machine and energize the solenoid of the pressure relief valve 172 at the predetermined minimum speed. With corresponding excitation, the pressure relief valve 172 provides the connection to the line 132 and thus to the outlet of the pump 66 and the oil flow flowing through the one-way valve 134 into the control line 104. As a result, the pressure in the adjustment control 70 is increased, which in turn reduces the delivery rate of the pump 66, which in turn takes a partial load off the machine and thereby prevents its speed from falling.

The operation of the hydraulic control system 10 can be briefly described as follows: During the work of the excavator, the control valves 12, 14, 16 and 18 divide the oil flow present between the function performed in each case and the excess outlet of the valve. For example, the. Share of the oil flow arriving at the support foot control valve 12 which is not required for the function to be performed. forwarded to the right and left travel control valve 16, 18 via the excess line 78. The proportion of this oil flow arriving at the control valves 16, 18, which is not required to actuate the driving functions, is passed on to the excess lines 80, 82. The Pressure selection valve 88 then operates as a function of the pressure increase in lines 80, 82 in order to pass on pressure drops in lines 80, 82 to control line 104 and thus to adjustment control 70 of adjustment pump 66. The adjustment control 70 operates in dependence on the pressure prevailing in the control line 104 in order to bring about a pump adjustment which only leads to a slightly larger amount of oil conveyed by the pump 66 than is necessary to actuate the support leg and / or driving functions.

Meanwhile, that portion of the Ulstromes arriving at the control valve 14 for pivoting the cabin, which is not required for the pivoting, is passed on to the upper weft line 108. The pressure selection valve 112 operates in dependence on the liquid pressure in the control line 104 and in the upper weft line 108 in order to connect the respectively lower pressure to the control line 118 and thereby to the adjusting device 72 of the variable pump 68. If the pressure in line 108 is greater than in line 118, the one-way valve 134 opens and thereby connects the oil flow of the excess line 108 with the amount of oil delivered by the variable displacement pump 66. As a result, the pump 68 can temporarily support the pump 66 in supplying the support leg and driving functions with unusually high amounts of oil. As a result, the pump 66 manages with a smaller adjustment than would otherwise be the case.

In those applications in which the adjustment of the pump 66 is sufficient under all operating conditions to supply the support leg and driving functions, the bypass circuit and the pressure selection valve 112 can be dispensed with; the excess line 108 is then connected directly to the adjusting device 72.

Claims (7)

1. Hydraulic system (10) with two variable pumps (66,68), each feeding a group of control valves (12, 14, 16, 18) with an excess outlet (30, 44, 58, 60), with an infeed of Pressure medium from one system to the other is possible, characterized in that a pressure selection valve (112) with its second and first inlet (114, 110) to a first pressure-dependent pump adjustment control (70) of the first variable displacement pump (66), to a downstream upper discharge outlet (58, 60) of a downstream control valve (16, 18) and the second privileged upper excess outlet (44) of a second privileged control valve (14) and with its outlet (116) to the second pressure-dependent pump adjustment control (72) of the second variable displacement pump (68 ) is connected and transmits a pressure drop at its first and second inlet (110, 114) to its outlet (116). 2. Hydraulic system according to claim 1, characterized by a bypass with a bypass line (132) which connects the first inlet (110) of the pressure selection valve (112) to the inlet (28) of the first preferred exercise function and has a one-way valve (134) which prevents flow of flow toward the pressure selection valve (112), wherein the flow in the second privileged excess outlet (44) is combined with the flow flow generated by the second variable pump (68) when the oil pressure in the second privileged excess outlet (44) is greater than the oil pressure in the downstream excess outlet (58, 60). 3. Hydraulic system according to claim 1 and 2, characterized by the following features: - The first pressure selection valve (88) is with its first and second inlet (84,86) to the first and second downstream upper outlet (58,60) and with its outlet (90) to the first pump adjustment control (70). connected and communicating an oil pressure drop at its first and second inlet to its outlet; - The second pressure selection valve (1.12) is with its first outlet (110) to the second privileged excess outlet (44) with its second outlet (114) to the outlet (90) of the first pressure selection valve (88) and with its outlet (116) the second pump adjustment control (72) is connected and transmits a pressure drop at its first and second inlet (110, 114) to its outlet (116). 4. Hydraulic system according to one of the preceding claims, characterized in that two line compensators (136; 138) are provided for faster adaptation of the variable displacement pump (66) to changes in demand of the functions operated by the privileged control valve (12), each of which has two cylindrical chambers (140 ; 142) of different diameters, in which a pair of pistons (150, 152; 160, 162) connected via a piston rod (154; 164) is slidably arranged, the pistons of larger diameter (152; 162) by spring elements (156, 158; 166, 168) in a balanced central position in the larger diameter cylindrical chambers are held, which are connected to each other and to the control line (104) via a line (148), while the one cylindrical chamber (140) of smaller diameter to the feed line (76) and the other cylindrical chamber (142). of smaller diameter are connected (144; 146) to the first upper line (78) of the privileged control valve (12). 5. Hydraulic system according to claim 4, characterized in that in the two chambers (140; 142) with each other and with the control line (104) connecting line (148) is the outlet (170) of a pressure relief valve (172), the inlet (174 ) is connected to the flow line (76). 6. Hydraulic system according to claim 5, characterized in that the pressure relief valve (172) is actuated by a solenoid. 7. Hydraulic system according to claim 2 and 5 or 6, characterized in that the inlet (174) of the pressure relief valve (172) via the bypass line (132) downstream of the one-way valve (134) is connected to the feed line (76).

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