DE2434840A1 - HYDRAULIC CONTROL SYSTEM - Google Patents

Description

european office case no. 10565 GFR

Hydraulic control system

The invention relates to a hydraulic control system with a depending on its flow rate Pressure in the crank chamber adjustable pump, a consumer connected to this via a pressure line and a pump control valve via which the pressure line can be connected to the crank chamber as a function of the pump outlet pressure is, also a connection of the pressure line with the crank chamber depending on the pressure at the consumer via a pilot line connected to an actuator and connected to the pressure line can be established.

In the known system (US Pat. No. 3,002,462), from which the invention is based, - as soon as a consumer is acted upon - the actuator is also acted upon, so that the pump outlet pressure is no longer passed into the crankcase, whereby immediately upon exposure to a consumer the Pump switches to maximum pressure. This pump only switches to minimum delivery when the pressure in the system is up Has reached maximum values.

The object to be solved with the invention is seen in the fact that the pump when a predetermined pressure is reached switches to their minimum funding at the consumer. This object has been achieved according to the invention in that a valve is provided in the pilot line which is in operative connection with the pressure line and as a function of

509807/0778

^{EUROPEANOFRCE} Case No. 10565 GFR

a predetermined pressure on the consumer into a closed one Position is movable. In this way, the flow of pressure to the actuator is then interrupted. The interruption is made possible primarily by installing the valve in the pilot line, then the pump outlet pressure is fed back into the crank chamber of the pump and the pump output is throttled. The interruption is secondary on the predeterminable pressure on the consumer. Because the interruption should take place at the latest when the Consumers, for example a lifting cylinder, fully extended is, but also when the maximum pump output is not sufficient, the full work, for example the full Extending the cylinder to perform. In such cases, the valve in shifted its closed position, in which the actuator is no longer pressurized.

The valve can expediently be actuatable via a solenoid which can be actuated via the pressure on the consumer Switch is excitable. The switch then expediently has a piston which carries a contact and a Line with the consumer can be pressurized against the action of a spring.

509807/0778

EUROPEAN OFFICE _{Case Nq # 1Q} 565 GFR

In the drawing are two embodiments explained in more detail below of the invention shown. It shows:

T- the hydraulic control system in a schematic representation;

FIG. 2 shows a hydraulic control system that is somewhat modified compared to FIG.

In Fig. 1 of the drawings is a hydraulic control system shown schematically that a pump 10, a hydraulic motor designed as a consumer, having a variable chamber or a retractable and extendable hydraulic cylinder 12 and a control slide valve 14. The pump 10 is provided with several in the drawing for simplicity for the sake of not shown reciprocating pistons are provided which extend at the end into a crank chamber and there rest against a drive cam, from which they are lifted depending on the pressure prevailing in the crank chamber can be.

The inlet of the pump 10 is connected to a collecting container 16 via a suction line 18, while the outlet of the pump 10 is connected to the first side of the control slide valve via a pressure line 20. The first side of the spool valve 14 is also connected to the collecting container via a line 22. The second side of the spool valve 14 is connected to the variable chamber of the hydraulic motor 12 via lines 24 and 25. Here, the line 24 is a supply line in which a check valve. is provided that prevents pressure medium from flowing back.

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DEERE & COMPANY

EUROPEAN OFRCE _{Case Nq # 1O} 565 GFR

The line 25 is a return line with an adjustable Throttle 27 is provided. When moving the spool valve 14 from its neutral position into a Direction, the supply line 24 is connected to the line 20 while the control slide valve 14 is displaced in the opposite direction with the return line 25 the collecting container 16 via the line 22 connects.

In the exemplary embodiment, the variable chamber of the hydraulic motor 12 is designed for actuating a conventional lifting shaft 28 with its lifting arm 30 of an agricultural tractor. The spool valve 14 is a servo valve which can be adjusted depending on the position of an optionally adjustable hand lever 32 via a linkage 34 and depending on the position of the lifting shaft 28 via a linkage 36. The linkages 34 and 36 correspond to those normally used in farm tractors and are designed so that the movement of the hand lever 32 moves the spool valve 14 out of its neutral position and holds it there until the lifting shaft has reached a position that corresponds to that which has been set by the lever 32. But then the linkage 36 will return the valve to its neutral position. Only if the linkage is set in such a way that the lifting shaft 28 assumes its maximum position and the lifting arm 30 extends to its maximum height, the linkage will not return the spool valve 14 to its neutral position and leave it in its open position.

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DEERE & COMPANY

european office "Case No. 10565 GFR

The pressure within the crank chamber of the pump 10 is regulated via a pump control valve 38 which is connected to the pressure line or the pump outlet via line 40 and to the pump crank chamber via lines 42 and 44. The administration 42 is also connected to the pump inlet via a throttle. The pump control valve 38 is normally in his pressed closed position via a spring 48 and can via ■ a pilot line 50 depending on the pressure in the line 40 can be opened when the pressure in the line 40 is large enough to overcome the force of the spring 48.

A piston 52 is slidably disposed in a cylinder bore 54 and acts on the spring 48 and can be pressurized by the pressure in the cylinder bore 54 to the force that the spring exerts on the pump control valve 38 to enlarge. A pilot line 56 connects the cylinder bore 54 and the Feed line 24 between the spool valve 14 and the check valve 26, so that the liquid pressure that the hydraulic motor 12 is applied, likewise reaches the cylinder bore and acts on the piston 52 there.

A solenoid controlled valve 58 is provided in the pilot line 56 and is normally held in its open position by a spring 60. The valve 58 is in its closed position Slidable position in which it interrupts the connection between the supply line 24 and the cylinder bore 54. Likewise, the valve 58 in its closed position connects the cylinder bore 54 and the pilot line 56 the collecting container 16 via a return line 62. The electrical Circuit for the solenoid 64 of the valve 58 has

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european office case no. 10565 GFR

a voltage source 66 and a pushbutton switch 68 on. The latter has a fixed contact 70, which is attached to a suitable Carrier 72 is arranged via an insulator 74. The switch 68 is also provided with an adjustable contact 76, which is arranged at the end of a piston rod 78 via an insulator 80. The piston rod 78 in turn is on a piston 82 provided, which is guided displaceably in a cylinder bore 84. The piston 82 in turn is normally in its one Moved extreme end position in the cylinder bore 84 by a spring, in which normally the contacts 70 and 76 are not are in contact with each other.

A line 88 enables the connection between the hydraulic motor 12 and the cylinder bore 84, so that the fluid pressure of the hydraulic motor also acts on the piston 82. With such an arrangement, the switch 68 can be closed are to energize the solenoid 64, whereby the valve 58 is moved to its closed position, as soon as the pressure at the hydraulic motor 12 has a predetermined maximum value achieved in which the spring 86 is compressed and the piston rod 78 is extended. When the valve is 58 in shifting its closed position, the fluid pressure in the cylinder bore 54 and pilot line 56 will drop, and the pressure fluid can flow into the collecting container 16 via the return line 62.

Although it is not shown in detail, the hydraulic Control system have additional hydraulic consumers and associated control valves. Here the

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DEERE & COMPANY EUROPEAN OFFICE

Case No. 10565 GFR

additional hydraulic consumer also with the cylinder bore 54 be connected via pilot lines. This depends entirely depends on whether they have a greater pressure than the predictable one Minimum delivery pressure, which is held by the spring 48, need.

The following is to be carried out for the operation of the hydraulic system described above. Assuming that if the spool valve 14 is in its neutral position, the pump outlet pressure is up to the predetermined minimum delivery pressure, which is determined by the spring 48, ' increase. Then the pump control valve 38 is shifted to an open position so that the pump outlet pressure by the Pump control valve 38 and lines 42 and 44 enter the crank chamber of pump 10. The pressure in the crank chamber the pump 10 then holds the reciprocating pistons from their drive cams, so that the delivery of the pump 10 on the predetermined minimum delivery pressure, which is determined by the spring 48, is maintained. Now becomes the control spool valve 14 shifted out of its neutral position in order to connect the hydraulic motor 12 and the pump 10, the liquid pressure at the hydraulic motor 12 via the pilot line 56 in FIG transmit the cylinder bore 54 and act on the piston 52, to increase the pressure exerted on the pump control valve 38 via the spring 48. It will Pump control valve 38 moved to its closed position. The fluid pressure in the crank chamber of the pump 10 can be reduced via a throttle 46, the delivery rate of the pump 10 then increasing again.

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DEERE & COMPANY

european office case no. 10565 GFR

If the control spool valve 14 is already in its neutral position

ment, that is, it is back in his closed position, before the valve 58 has been closed by excessive pressure, then the fluid pressure in the pilot line 56 and the cylinder bore 54 is reduced via the throttle 90, so that the pressure on the pump control valve 38 acts, is reduced and the pump outlet capacity is also reduced to that predetermined by the spring 48 Minimum delivery pressure is reduced. The throttle 90 can also be omitted, since leakage oil can escape via the piston 52, and this leakage oil will reduce the pressure in cylinder bore 54 and pilot line 56.

If now the pressure at the hydraulic motor 12 reaches a value that is required to make the piston 82 and the piston rod 78 one sufficient value to shift, at which the contacts 72 and 76 before the control slide valve 14 again in the neutral position is returned, come into contact with each other, then the valve 58 is guided to its closed position, in of the cylinder bore 54 and the pilot line 56 with the sump 16 are in communication via the return line 62.

This immediately reduces the pump outlet pressure to its predetermined one Minimum delivery pressure. The system will maintain this setting until the pressure on the hydraulic motor 12 is through manual shifting of the spool valve 14 from the neutral position or when an additional consumer is switched on, which is not shown in the drawing falls off.

509807/0778

DEERE & COMPANY 2 A 3 A 8 A

_{Case No>}

Another hydraulic system according to the present invention is shown in Fig. 2 and has a pump 10 with a variable Delivery rate, a consumer in the form of a hydraulic motor 112 or having a variable chamber a retractable and extendable hydraulic cylinder 112 and a Control spool valve 114 on. Adjusting the pump is controlled by a pressure chamber formed from a piston 194 in a cylinder bore 192. The piston 194 is connected to the pump control part via a piston rod 198, for example a swash plate. A feather 196 rests against piston 194 in such a way as to bring piston 194 and its piston rod 198 into a position in which the pump has the greatest delivery rate. The delivery rate of the pump 110 or the inclination of the disc is reduced by applying pressure to the pressure space formed by the piston 194 and the cylinder bore 192 is, wherein the piston 194 and the piston rod 198 are displaced against the action of the spring 196.

The inlet of the pump 110 is connected to a sump 116 connected via an inlet line 118, and the outlet of the pump 110 is connected to the first side of a spool valve 114 via a pressure line 120 in connection. the The first side of the spool valve is also connected to the collecting container 116 via a return line 122. The second side of the spool valve 114 is connected to the variable chamber of the hydraulic motor 112 via lines 124 and 125 connected. Here, the line 124 is designed as a supply line and with a check valve 126 provided, which prevents the backflow, while the line 125 is designed as a return line, in the one Throttle 127 is provided with a variable cross section.

DEERE & COMPANY

european office case no. 10565 GFR

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The adjustment of the spool valve 114 from its Neutral position to one side connects the pressure line 124 with the pressure line 120, while when moving of the spool valve 114 from the neutral position in the opposite direction, the return line 125 is connected to the collecting container 116 via the line 122 will.

In the exemplary embodiment, a known lifting shaft 128 with lifting arm 130 of an agricultural tractor is actuated via the hydraulic motor 112 Position of the lifting shaft 128 can be adjusted via a linkage 136. The linkages 134 and are typical of those used in farm tractors and are designed in such a way that when the hand lever 132 is adjusted, the spool valve is moved from its neutral position into a The end position is adjusted and remains there until the lifting shaft has reached a position which is predetermined by the position of the hand lever. The linkage 136 will then return the spool valve to its neutral position. On the other hand, however, it should be noted that, when the hand lever 132 is in its maximum end position t, so that the lifting shaft 128 rotates into its extreme position and the lifting arm 130 can assume its highest position, the linkage 136 no longer returns the spool valve 114 to its neutral position, but leaves it in one of its end positions.

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european OPBC _E CaseNo. 10565 GFR

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The pressure inside the pressure chamber, which comes from the piston 194 and the cylinder bore 192 is formed by a pump control valve 138 controlled, that with the pressure line 120 or the pump outlet via a line 140 and with the pump pressure chamber is connected via lines 142 and 144. The line 142 is connected to the pump inlet via a throttle 146 connected. The pump control valve 138 is normally in its closed position via a spring 148 hold and can be acted upon by the liquid pressure in the line 140 via a pilot line 150 to it in a Move open position in which the pressure in the liquid line 140 is large enough to overcome the force of the spring 148.

A piston 152 is slidably disposed in a cylinder bore 154 and acts on the spring 148 and is with the pressure acted upon, which prevails in the cylinder bore 154 to to increase the force that the spring exerts on the pump control valve 138. A pilot line 156 connects here the cylinder bore 154 with the pressure line 124 between the Check valve 126 and the hydraulic motor 112, so that the fluid pressure, which acts on the hydraulic motor 112, into the cylinder bore 154 is transmitted and act on the piston 152 can.

A solenoid operated valve 158 is provided in the pilot line 156 and is normally via a spring 160 in it Hold open position. The valve 158 can be in its closed Position in which there is the connection

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european office case no. 10565 GFR

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interrupts between the pressure line 124 and the cylinder bore 154. Likewise, the valve / if it is in its closed position, the cylinder bore 154 and the pilot line 156 to the sump 116 via a Connect return line 162. The electrical circuit for the solenoid 164 of the valve 158 has a voltage source 166 and a pressure-controlled switch 168. The desk 168 in turn is connected to a fixed contact 170 which is arranged on a suitable carrier 172 via an insulator 174, Mistake. This switch 168 is also equipped with a displaceable contact 176 which is on the end of a piston rod 178 is attached via an isolator 180. The piston rod 178 is received by a piston 182, which in turn is in a cylinder bore 184 is arranged displaceably. The piston 182 is normally pressed into an end position via a spring 186, in which the contacts 170 and 176 have no contact with one another.

A line 188 represents the connection between the hydraulic motor and the cylinder bore 184, so that the fluid pressure at the hydraulic motor also acts on the piston 182. In this construction, the switch 168 is closed to energize the solenoid 164 and to move the valve 158 to its closed position as soon as the pressure on the hydraulic motor 112 has reached a predetermined maximum value at which the spring 186 is compressed and the piston rod 178 is extended. When the valve 158 has now been moved into its closed position, the pressure fluid in the cylinder bore 154 and the pilot line 156 can flow off into the collecting container 116 via the return line 162.

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Although it is not shown in detail in the drawing, the hydraulic system can have additional hydraulic motors with control valves, these additional hydraulic motors connected to the cylinder bore 154 via pilot lines may or may not be, which depends solely on whether they have a greater need for pressure is than the predetermined minimum delivery pressure determined by the spring 148.

The following is to be said about the operation of the above hydraulic control system. When the control slide valve 114 is in its neutral position, the pump outlet pressure will rise up to a minimum delivery pressure which can be predetermined by the spring 148. The pump control valve 138 is then adjusted to an open position, the pump outlet pressure being conducted via the pump control valve 138 and the lines 14 and 144 into the pressure chamber formed by the piston 194 and the cylinder bore. The pressure in this pressure chamber will then move the piston 194 with piston rod 198 upwards, whereby the position of the swash plate is changed and the stroke of the pump piston can in turn be reduced so that the pump 110 has a minimum delivery pressure predetermined by the spring 148. If the spool valve 114 is now shifted from its neutral position in such a way that it connects the hydraulic motor 112 with the pump 110, the fluid pressure at the hydraulic motor 112 will reach the cylinder bore 154 via the pilot line 156 and act on the piston, whereby the force applied to the pump control valve via the spring 148 is increased so that the

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DEERE & COMPANY 2 4 O 4 b 4 U EUROPEAN OFRCE

_{Case Nq #} ^ _{565 GpR}

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Pump control valve 138 ultimately to its closed position is adjusted. The pressure fluid in the pressure chamber formed from the piston 194 and the cylinder bore 192 can flow through the throttle 146, after which the pump outlet pressure can rise again.

If the control slide valve 114 has already been returned to its neutral position before the valve 158 has been closed above the predeterminable pressure, then the valve 158 and the switch 168 will have no influence on the system, and the pilot line 156, the cylinder bore 154 and the piston 152 will ensure that sufficient pressure fluid is available in addition to delivery pressure for the actuation of the hydraulic motor 112. However, should the pressure at the hydraulic motor 112 reach or exceed the pressure required to close the switch 168 before the valve 114 has been returned to its neutral position, for example when an unusually large load is applied to the lifting arm 130 or because the hydraulic motor 112 has reached the end of its stroke, the valve 158 is then moved to its closed position in order to limit the pressure acting on the hydraulic motor 112. However, as soon as the valve 158 has now been moved into its closed position, the pressure fluid in the cylinder bore 154 and the pilot line 156 will flow into the collecting container 116 via the return line 162 so that the pump 110 can again return to its minimum delivery pressure. This system will remain in this position until the control slide valve 114 has again been shifted from the neutral position into one of its end positions, so that the pressure on the hydraulic motor 112 can be reduced.

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european office case no. 10565 GPR

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The hydraulic system shown in Fig. 2 differs from that shown in Fig. 1 not only in the particular one Training of the pump, but also in the mode of operation, namely when the system pressure does not reach or equal the pressure required to turn switch 168 close. In the embodiment shown in FIG. 1, the system repeatedly returns to its predetermined minimum delivery pressure back as soon as the spool valve 14 has been moved to its closed position. In the embodiment of FIG. 2, the pump has a greater outlet pressure at a predetermined value above the pressure at the hydraulic motor 112, as long as the pressure at the hydraulic motor 112 does not correspond to the pressure or exceeds that required to close switch 168. Thus, the hydraulic system shown in FIG can be used at higher pressures for a longer period of time than the system shown in FIG. However, experience has shown that the control of the hydraulic motor for a conventional lifting shaft with lifting arm of a tractor is only a small one Percentage of total hydraulic system usage claimed so that for most of the time the hydraulic system will be in his position for minimum funding. Thus, the system shown in Fig. 2 becomes a higher one Create pressure for the control of the lifting shaft 128 and limit the system pressure so that a still safe pressure level is not exceeded and the system will return to its minimum pressure as soon as the maximum pressure is reached or exceeded is, so that only the portion of the system between spool valve 114 and valve 158 for any Time needs to be kept at maximum system pressure.

Claims

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Claims (3)

EUROPEAN OFFICE ■;> Case No. 10565 GFR - 16 - claims 1.) Hydraulic control system with one in its flow rate depending on the pressure in the crank chamber adjustable pump, one with this via a pressure line connected consumer and a pump control valve, via which the pressure line depending on the pump outlet pressure can be connected to the crank chamber, a connection of the pressure line to the crank chamber also being dependent from the pressure at the consumer via an actuator connected to an actuator and connected to the pressure line Pilot line can be produced, characterized in that a valve (58 or 158) is provided, which is in operative connection with the pressure line (20, 24 or 120, 124) and is dependent can be displaced into a closed position by a predeterminable pressure on the consumer (12 or 112). 2. Hydraulic control system according to claim 1, characterized in that that the valve (58 or 158) via a solenoid (64 or 164) can be actuated, which is connected to a Pressure on the consumer (12 or 112) actuatable switch (68 or 168) can be excited. 3. Hydraulic system according to claim 2, characterized in that the switch (68 or 168) has a piston (82 or 182) which carries a contact and via a line (88) to the consumer (12 or 112) can be pressurized against the action of a spring (86). 609807/0778 Leeward