Patent Application
20100186401
The invention relates to a method for actuating a hydraulic consumer as recited in the preamble to claim 1 and a hydraulic control system for supplying pressure medium to the consumer, as recited in the other independent claim 7.
U.S. Pat. No. 5,138,883 A has disclosed a hydraulic control system in which a consumer such as a differential cylinder can be supplied via a valve device—which is equipped with two continuously adjustable directional control valves—with pressure fluid that is furnished by a pump. The supply to the consumer and the return from it each contain a respective continuously adjustable directional control valve. In their neutral positions, the directional control valves are prestressed into a closed position and, by means of pressure reduction valves, can each be moved in one direction in which the pump is connected to the associated pressure chamber and in another direction in which the respective associated pressure chamber is connected to the tank. In this known control system, through suitable triggering of the two directional control valves, the consumer can be operated with a so-called regeneration circuit. For example, when a cylinder travels outward, the contracting annular chamber is connected via the associated directional control valve to the pressure fluid inlet of the expanding annular chamber so that the cylinder is extended in a rapid movement. A disadvantage of the regeneration/differential circuit, however, is that due to the restraining of the consumer (effective area corresponds approximately to the piston rod area), the consumer cannot be operated with the maximum output.
If a control system of this kind is used in a mobile piece of equipment such as a backhoe loader, a mini- or compact excavator, or a telehandler, then the available digging power in the regeneration mode is too low due to the restraining of the consumer. Preferably, the regeneration mode is correspondingly used when lowering the machine component of the mobile piece of equipment. In order to operate the consumer with a high power, for example when digging or when lifting a load, a switch into the normal mode is executed, in which the expanding pressure chamber is connected to the pump and the contracting pressure chamber is connected to the tank.
In order to prevent the occurrence of cavitation in the pressure fluid supply with a pulling load, a load lowering valve can be provided in the return from the consumer, as is known, for example, from DE 196 08 801 C2 or from the data sheet VPSO-SEC-42; 04.52.12-X-99-Z from the company Oil Control, a subsidiary of the applicant.
The directional control valves are moved by means of a piloting device, which is equipped with pressure reduction valves and is actuated by a joystick; the operator decides when to switch from regeneration mode into normal mode.
In this case, it is often difficult to determine the correct moment to make the switch, as a result of which the consumer remains too long in the regeneration mode with reduced power or the switch to the normal mode is made prematurely even though it would be advantageous to operate the consumer at a high speed.
By contrast, the object underlying the present invention is to optimize the switching from regeneration mode to normal mode with regard to the energy savings entailed by the regeneration mode and the power available at the consumer.
This object is attained by means of a method with the combination of defining characteristics of claim 1 and by means of a hydraulic control system with the combination of defining characteristics of the other independent claim 7.
According to the invention, in order to actuate the consumer, a pressure chamber on the supply side and a pressure chamber on the return side of a hydraulic consumer are connected to a pump or a tank via a valve device that can be actuated by means of a control unit. To move the consumer rapidly, the valve device is moved into a regeneration mode in which the pressure fluid emerging from the return-side pressure chamber is added to the delivery rate of the pump so that the pump can be set to a lower delivery rate or the consumer executes its extending movement at a higher speed. The pressure fluid requirement is set by means of an actuator such as a joystick. According to the invention, the pump is set in accordance with a pressure regulation. In this case, a switch to the normal mode is automatically executed when the pump regulation reduces the pump delivery rate with no change in the set pressure fluid requirement (setting of the actuator), so that the consumer slows down or remains immobile. In other words, the pressure of the variable displacement pump is monitored. If it reaches its maximum pressure in the regeneration mode because of a rise in the resistance working against the consumer, then the swivel angle of the pump is reset in accordance with the characteristic curves of the pump control so that the volumetric flow of pressure fluid supplied by the pump no longer corresponds to the pressure fluid requirement preset for the actuator. According to the invention, a comparison of the pump flow rate to the pressure fluid requirement set by means of the actuator is used to decide when to switch to the normal mode. As a result, the optimum switching time is no longer decided based on the subjective assessment of the operator, thus permitting the consumer to be operated with greater operational reliability and improved effectiveness.
For example, the actual pump flow rate can be determined based on the swivel angle of the pump, which is embodied in the form of a variable displacement pump, and on the pump speed at a predetermined pump pressure.
The variable displacement pump is preferably embodied with an electroproportional swivel angle control; preferably, an actuating signal of a pressure control loop is then proportional to the swivel angle of the pump.
For this purpose, the actual pump pressure can be detected and compared to a setpoint pump pressure preset by means of the actuator. The pressure difference is then transmitted as an input signal to a controller, for example a PI controller or a PID controller, whose output signal is a measure for the swivel angle and constitutes the input signal of the pump controller.
The actuation of the consumer is further optimized if the regeneration mode is preset as a starting situation in certain movement directions of the consumer, for example when lowering an excavating component. In other words, as soon as the actuator (joystick) is moved in the lowering direction, a switch into the regeneration mode is automatically executed. This mode is maintained until the operator moves the joystick back into the zero position or beyond this zero position. The switch into the normal mode then occurs in the above-described fashion.
The switch between the regeneration mode and the normal mode preferably occurs by means of a ramp; the pressure fluid connection between the variable displacement pump and the expanding pressure chamber remains open and the pressure fluid connection of the contracting pressure chamber is opened in accordance with the curve of the ramp.
With a suitable embodiment, the swivel angle control of the variable displacement pump also permits a power control.
The apparatus complexity of the control system can be reduced if the supply and return of each consumer contains a continuously adjustable directional control valve, which has two switching positions, and a load lowering valve, thus permitting the supply and return to be actuated independently of each other.
The directional control valves, which are electrically or electrohydraulically adjustable, are preferably open to the tank in their neutral position.
The operational reliability of the control system is improved if the load lowering valves are embodied with a secondary pressure limiting function.
Other advantageous modifications of the invention are the subject of the remaining dependent claims.
In the following, a preferred exemplary embodiment of the invention will be explained in greater detail in conjunction with schematic drawings.
EFM system (electronic flow management) in which the valve elements that determine the volumetric flow of pressure fluid and the flow direction of the pressure fluid are electrically or electrohydraulically triggered as a function of characteristic curve families stored in a control unit 6. In this case, the setpoint values are input by means of a joystick 8 that is actuated by the operator in order to control the speed and position of the machine components (e.g. booms, shovels) of the piece of equipment.
In the exemplary embodiment shown, the two consumers 2, 4 are each embodied in the form of a differential cylinder with a pressure chamber 10 or 12 at the bottom and an annular chamber 14 or 16 around the piston rod. These pressure chambers 10, 14; 12, 16 can be respectively connected via a directional control valve section 18, 20 to a variable displacement pump 22 or a tank 24 in order to retract or extend the cylinder. The variable displacement pump 22 is pressure-controlled by means of a pump controller 26, which, once the predetermined pressure has been reached, adjusts the delivery rate of the pump so that the pressure in the system remains constant independent of the delivery rate. A change in the volumetric flow of the pressure fluid should result in practically no change in pressure.
The variable displacement pump 22 is moved by means of a pump controller 25, whose design is explained below in conjunction with the enlarged depiction in
A pump controller 25 of this kind has a pump control valve 26 that is embodied with three connections and is prestressed by a control spring 27 in the direction of a neutral position in which the three connections of the pump control valve 26 are closed. The control spring 27 is supported against the actuating piston 28 of an actuating cylinder 29 by means of which it is possible to swivel the swiveling swashplate of the variable displacement pump 22. The actuating piston 28 is prestressed by a spring into a home position in which the swivel angle of the variable displacement pump 22 is at a maximum. The valve slider of the pump control valve 26 is actuated by means of a proportional magnet 30 that can be supplied with current via a signal line 51 connected to the control unit 6.
This proportional magnet 30 is used to exert the control force on the control piston of the pump control valve 26; the movement occurs in proportion to the power of the current. An input connection of the pump control valve 26 is connected via a control line 31 to a pump line 38 connected to the pressure connection of the variable displacement pump 22. An output connection of the pump control valve 26 is connected via a conduit 32 to a control surface of the control piston that acts in the direction of the neutral position. This control surface delimits a spring chamber of the control spring 27. The pressure in the conduit 32 also impinges on a control surface that acts in the movement direction of the pump control valve 26 so that the pressure at the outlet of the pump control valve impinges on both sides of the control piston.
The conduit 32 is connected via a nozzle 33 to a connecting conduit 34 that contains two pressure limiting valves 35, 36 connected in series. The outlet of the downstream pressure limiting valve 36 in
The two pressure limiting valves 35, 36 are prestressed in the direction of their depicted home position in which the pressure fluid connection to the tank control conduit 37 is open.
The pressure in the control line 31, which is tapped via a pressure limiting line 39, acts on both of the pressure limiting valves 35, 36 in the switching direction. This pressure limiting line 39 also leads to the respective third connection of both pressure limiting valves 35, 36. The region of the connecting conduit 34 situated between the pressure limiting valve 35 and the nozzle 33 is connected to the spring chamber of the control spring 27 via a branch line 40 and a check valve that opens in the direction toward the pressure limiting valve 35. A connecting line also branches off from the pressure fluid flow path between the nozzle 33 and the pressure limiting valve 35 and is connected to the tank control conduit 37 via two additional nozzles 41, 42. An angle conduit 43 branches off between the two nozzles 41, 42 and feeds into the pressure fluid flow path between the two pressure balances 35, 36. Control surfaces that act in the direction of the spring-prestressed home position of the pressure limiting valves 35, 36 are also connected to the tank control conduit 37 via pilot lines 44, 45.
The two pressure limiting valves 35, 36 are set to different pressures. When the respective pressure is reached, the relevant pressure limiting valve 35, 36 is moved out of its depicted home position, thus opening a control oil flow path from the pump line 38 to the spring chamber of the control spring via the control line 31, the pressure limiting line 39, the relevant pressure limiting valve 35, 36, the connecting conduit 34, and the branch line 40 so that a pressure approximately equivalent to the pump pressure prevails in this spring chamber. Consequently, the actuating piston 28 is then moved toward the left in the depiction according to
In the normal mode of the variable displacement pump, the two pressure limiting valves 35, 36 are prestressed into their depicted home position. Adjusting the swivel angle of the pump requires a predetermined standby pressure of 20 bar, for example; only then is it possible to overcome the force of the return spring.
In the depicted home position—as mentioned above—the swivel angle of the variable displacement pump 22 is set to its maximum value. When the proportional magnet 30 is supplied with current, the control piston of the pump control valve 26 in the depiction according to
For further details relating to the design of the pump controller 26, the reader is referred to the above-mentioned data sheet RD 92 708.
As can also be inferred from the depiction in
The suction connection of the variable displacement pump 22 is connected to the tank 24 via a suction line 50 and a filter. The pressure fluid supplied by the variable displacement pump 22 flows to the consumers 2, 4 via the pump line 38 and the two directional control valve sections 18, 20, whose design is explained below in conjunction with
The temperature of the pressure fluid contained in the tank 24 is detected by a temperature sensor 54 and reported to the control unit 6 via a signal line. In order to prevent an overheating of the pressure fluid, a purge valve 57 is provided between the tank line 52 and the pump line 38. This purge valve 57 also has a pressure limiting function that makes it possible to limit the pressure in the pump line 38 to a maximum pressure. When the purge valve 57 is opened, the pressure fluid used to actuate the consumer, particularly in the regeneration circuit, can be exchanged for “fresh” pressure fluid from the tank 24. The opening of the purge valve 57 is likewise executed electrically as a function of a signal from the control unit 6.
According to
Each directional control valve 68, 70 is adjusted by means of a respective pilot valve 81, 83 with a proportional magnet 80, 82 that can be supplied with current by the central control unit 6 via signal lines in order, by adjusting the pilot valves 81, 83, for example of pressure reduction valves, to move the directional control valve 68, 70 independently of each other in the direction of their position shown in
The two load lowering valves 72, 74 have an intrinsically known design of the kind described, for example, in DE 196 08 801 C2, which was mentioned at the beginning, or in the above-mentioned publication from the company Oil Control. Load lowering valves of this kind permit the controlled lowering of a load and simultaneously function as a secondary pressure limiting valve. To that end, the load lowering valves are prestressed into a closed position by means of an adjustable prestressing spring 84, 86. As shown in
In the neutral positions—depicted in FIGS. 1 and 3—of the two directional control valves 68, 70, the two pressure chambers of each consumer 2, 4 are connected to the tank 24. The load F acting on the consumer 2 is supported in a leakage-free fashion by the load lowering valve 72, 74, which is embodied in the form of a seat valve. In this case, the load F can be in the form of a pulling or pushing load. The pressure limiting function of the two load lowering valves 72, 74 ensures that a maximum pressure cannot be exceeded in the lines 64, 66.
Several load situations will be explained below to better illustrate the invention.
Let us first assume that a pulling load F is acting on the cylinder 2 and that according to the depiction in
In the bottom pressure chamber 10, a pressure is present, which after the slider is set, lies between the maximum pump pressure (for example 250 bar) and 0 bar (slider in the neutral position). If one assumes that the pressure in the annular chamber 14 is approximately 250 bar (slider of the directional control valve 70 completely open, pump set to 250 bar) and that the pulling load corresponds to a pressure of 50 bar, then the bottom pressure chamber 10 must contain a pressure that equals the difference of the pressure in the annular chamber 14 minus the load, divided by the area ratio of the differential cylinder (for example 2) so that 250 bar in the annular chamber 14 and a load of 50 bar results in a pressure of approximately 100 bar in the pressure chamber 10.
With a pushing load, an equivalent function occurs in which the pressure in the supply-side supply line 64 is limited by the pressure limiting function of the load lowering valve 72.
In regeneration mode, the consumer is moved at maximum speed; the force exerted by the consumer, however, is comparatively slight because the effective area of the consumer corresponds to the piston rod area. In order to trigger the maximum output of the consumer 2, the control system is switched from regeneration mode to the normal operating mode shown in
With a pushing load and an extending cylinder 2 (
With a retracting cylinder and a pulling or pushing load, the directional control valve section 18 is switched into the position shown in
According to the invention, it is preferable if the regeneration mode is activated by default in a certain movement direction of the consumer 2, 4. This can be the case, for example, when lowering the machine component of an excavator, for example a boom with a shovel. If the resistance to the movement of the working equipment subsequently rises, then the pump pressure of the variable displacement pump 22 is increased and is limited to a maximum value by the pump controller. As described at the beginning, when this maximum value is reached, the swivel angle of the variable displacement pump 22—and therefore also the actuating signal for the swivel angle—is limited so that the volumetric flow of pressure fluid supplied by the pump no longer corresponds to the pressure fluid requirement preset by means of the joystick 8. According to the invention, the relevant directional control valve section 18, 20 is switched into the above-described normal mode without intervention by the operator so that the maximum digging power is available, for example. The variable displacement pump 22 can be embodied with a swivel angle sensor for determining the swivel angle.
In the depicted home position (0) of the continuously adjustable directional control valve 104, the pressure fluid connection between the outlet line 60, the inlet line 56, and the return line 66 is closed. When the proportional magnet 106 is supplied with current, the pressure reducing valve 108 can be used to set a control pressure so that the valve slider of the directional control valve 104 is moved toward the right in the direction of the position labeled (a) in which the connection between the return line 66 and the outlet line 60 is opened. The pressure fluid connection to the inlet line 56 remains closed. When the pilot valve 83 is triggered, the valve slider of the directional control valve 104 is moved in the direction of position (b) so that the pressure fluid connection between the inlet line 56 and the return line 66, which is then functioning as a supply line, is correspondingly opened; the pressure fluid connection between the return line 66 and the outlet line 60 is closed.
The actuation of the load lowering valve 72 situated in the supply line 64 is carried out—as in the exemplary embodiment described at the beginning—by means of the pressure in the return line 66.
Naturally, the directional control valve 104 can also be integrated into the supply line 64 so that the load lowering valve 74 and the directional control valve 70 from
In order to retract the hydraulic cylinder (consumer 2), the directional control valve 104 is moved in the direction of its position of its positions (b) (sic) so that the variable displacement pump 22 conveys pressure fluid to the annular chamber 14 of the consumer via the pump line 38, the inlet line 56, the directional control valve 104, and the return line 66, which is then functioning as an inlet line. The directional control valve 104 is then used to correspondingly set the volumetric flow of pressure fluid and also the effective pressure in the annular chamber 14. The pressure in the return line 66 is used to move the load lowering valve 72 into its open position so that for example with a pushing load, cavitations are prevented since the consumer 2 remains restrained. With a pulling load, the load lowering valve 72 is completely or almost completely opened by the pressure in the supply, which pressure is tapped via the opening line 92, thus allowing the pressure fluid to flow out into the tank 24 via the load lowering valve 72 and the correspondingly set directional control valve 68.
During the extending movement of the consumer (hydraulic cylinder 2), the control system can also be operated once again in the regeneration mode; then the pilot valve 81 is used to switch the directional control valve 68 and the pilot valve 83 is used to move the directional control valve 104 toward its position (b) so that the pressure fluid flows out of the annular chamber 14 via the directional control valve 104, into the inlet line 58 and from there, via the directional control valve 68 and the check valve 100, the bypass conduit 96, and the supply line 64 to the pressure chamber 10 so that the consumer 2 is extended at a high speed. To exert a greater force, the directional control valve 104 is moved toward its position (a) so that the pressure fluid flows out of the annular chamber 14 into the tank 24. For further details about the various operating modes, please refer to the preceding explanations.
The present application has disclosed a hydraulic control system and a method for triggering a hydraulic consumer, which has a pressure chamber on the supply side and a pressure chamber on the return side that are connectable to a pump or a tank via a valve device. The valve device is actuated by means of a control unit that can move the valve device into a regeneration mode in which both of the pressure chambers are connected to the pump. According to the invention, the pump is pressure-regulated; in the regeneration mode, a switch to a normal mode—in which the inlet-side pressure chamber is connected to the pump and the return-side pressure chamber is connected to the tank—is automatically executed when the pump delivery rate falls below the pressure fluid requirement.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 029 358.7 | Jun 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/004990 | 6/20/2008 | WO | 00 | 12/18/2009 |
