Patent Application
20100212308
The invention relates to a hydraulic control arrangement for a mobile machine comprising at least two hydraulic loads, one of them having a lifting function.
In U.S. Pat. No. 6,293,099 B1 a control arrangement is described which is provided for controlling the loads of a forklift. A forklift usually has a boom along which a fork is movable to lift or lower a load. The boom can moreover be tilted and laterally displaced, each of such functions being actuated via hydraulic cylinders. For controlling the pressure fluid volume flow to the respective hydraulic cylinder, in the known solution proportional valves are provided through which the pressure fluid volume flow to the respective hydraulic cylinder can be adjusted. Pressure fluid is usually supplied via an LS variable displacement pump or a constant displacement pump including a bypass pressure regulator. The variable displacement pump or the bypass pressure regulator can be controlled, in response to the maximum load pressure of all loads, so that the pump pressure is above the maximum load pressure by a predetermined Δp.
In such control arrangements a problem may arise when, for example, the empty unloaded fork is to be lifted and simultaneously the boom tilt is to be varied. In this case, the load pressure at the tilting cylinder is higher than the load pressure of the lifting cylinder so that the latter is preferably supplied with pressure fluid and the fork is lifted comparatively quickly, while the tilting motion is performed very slowly or is even stopped. This problem arises practically with all conventional forklifts.
It could be attempted to arrange in the pressure fluid flow path to the tilting cylinder an LS valve including metering orifice and pressure regulator to which the pressure upstream and downstream of the metering orifice is applied. In this case, lifting of the fork and tilting of the boom could be simultaneously performed, unless the maximum possible pump delivery is exceeded. In the case of undersupply, i.e. in case that the pump cannot deliver sufficient pressure fluid, the load having a higher load pressure slows down because the pump pressure prevailing upstream of the metering orifice thereof is dropped and thus the pressure difference above said metering orifice is reduced—the same problem as with the control arrangement including proportional valves is arising.
Compared to this, it is the object of the invention to provide a hydraulic control arrangement for a mobile machine in which plural loads can be simultaneously controlled.
In accordance with the invention, the at least two loads of the mobile machine are supplied with pressure fluid via a pump in response to the maximum load pressure. The pressure fluid volume flow to a load active in the lifting direction and the pressure fluid volume flow to another load are controlled via a respective LUDV valve including an inflow metering orifice and a pressure regulator connected downstream to which in the closing direction pressure corresponding approximately to the maximum load pressure of the loads and in the opening direction the pressure prevailing downstream of the inflow metering orifice is applied.
In such LUDV controls (load-pressure independent flow distribution) the LUDV pressure regulators arranged downstream of the metering orifice throttle the pressure fluid volume flow so strongly that the pressure downstream of all metering orifices is equal, preferably equal to the maximum load pressure, or slightly exceeds the latter. In the case of under-saturation, the pressure does not change downstream of the metering orifice. The pump pressure is applied upstream of all metering orifices in the same way so that the pressure difference changes at all metering orifices in the same way when the pump pressure is reduced in the case of under-saturation—in this way a proportional flow distribution of the delivery rate to the loads is ensured so that, for instance, also an unloaded fork of a forklift can be lifted and simultaneously a boom of the forklift can be tilted.
In a solution with a simple structure it may suffice when a further load is controlled by a proportional valve.
In an especially simply structured embodiment two loads which are provided, for instance, for tilting and for displacing a boom of a forklift are allocated to a metering orifice and an LUDV pressure regulator.
The flow direction of the pressure fluid to and from the load is controlled via a respective directional valve. That is to say, in this solution the metering orifices of the LUDV valves have a very simple design and are continuously adjustable in one direction so that the circuit can be realized in a very inexpensive manner.
In the event that the operating pressure of the loads controlled by a joint LUDV valve is lower than the operating pressure of the other loads, a pressure relief valve may be allocated to the pressure regulator of the joint LUDV valve.
The hydraulic actuation of a steering of the mobile machine is preferably performed via an LS valve including an inflow metering orifice and a steering pressure regulator.
In a variant, the pressure prevailing upstream of the allocated inflow metering orifice is applied to the steering pressure regulator in the closing direction and a spring and the pressure prevailing in the control line are applied in the opening direction. This control line is connected to a line portion guiding the load pressure of the steering.
It is preferred when a line portion located downstream of the steering pressure regulator is connected via a control passage and a check valve closing in the direction of the steering to an LS line conveying the maximum load pressure of the loads.
In an alternative solution, the control line (118) leads from a pressure fluid flow path upstream of the steering pressure regulator (112) to a line portion guiding the load pressure of the steering, two nozzles (120, 122) being arranged in the control line (118) and in the area between the two nozzles (120, 122) a control passage (124) leading to a control chamber active in the opening direction of the steering pressure regulator (112) branching off which is connected to an LS line (60) conveying the maximum load pressure via a check valve (126).
The control arrangement can be realized in an especially simple manner when the pressure fluid supply pump is a constant displacement pump with an allocated bypass pressure regulator which is pressurized by the pump pressure in the opening direction and by the maximum load pressure of the loads in the closing direction.
For pressure relief the LS line can be connected to a tank via a relief valve which is in the form of a flow control valve.
To protect the LS line an LS pressure relief valve may be provided in the same.
The control arrangement according to the invention is preferably used for controlling a forklift, wherein an LUDV valve for controlling the lifting function and an LUDV valve for controlling the tilting and lateral displacement of a boom of the forklift are provided.
Hereinafter preferred embodiments of the invention will be illustrated by way of schematic drawings, in which:
In
In the further load line 22 a lowering brake valve 24 is arranged which freely admits pressure fluid supply from the working port A to the two annular chambers and throttles the backflow from the two annular chambers to the working port A so that a controlled tilting of the boom is permitted. Such lowering brake valves or counter-balance valves are known from prior art so that any further explanations can be dispensed with.
The displacement cylinder 14 is a double rod cylinder, the two annular chambers being connected via an operating line 26 and/or another operating line 28 to the two working ports A, B of the directional valve section 6.
In both directional valve sections 4, 6 a 4/3 directional valve 34 and 32, respectively, is provided which are biased into the shown locked position and by which the pressure fluid flow direction to and from the cylinders 12, 14 can be adjusted—as will be illustrated hereinafter—.
The LUDV section 2 includes an LUDV valve 34 allocated to the two cylinders 12, 14 consisting of a metering orifice 36 and an LUDV pressure regulator 38 arranged downstream thereof. In such LUDV valves 34 the LUDV pressure regulator 38 is pressurized in the direction of its closing position by the maximum load pressure or a pressure approximately corresponding to the latter and in the opening direction by the pressure prevailing downstream of the respective metering orifice 36 connected upstream. In the shown embodiment the metering orifice 36 is in the form of a continuously variable 2/2 directional valve biased into its represented closing position. The metering orifice can be opened by supplying current to a proportional solenoid 40 for adjusting the pressure fluid volume flow to the loads 12, 14.
The pressure fluid volume flow to the lifting cylinder 10 is equally adjusted via an LUDV valve which hereinafter will be referred to as lifting LUDV valve 42. The basic structure thereof corresponds to that of the LUDV valve 34—thus it consists substantially of a lifting metering orifice 44 and a lifting LUDV pressure regulator 46 connected downstream thereof. The lifting metering orifice 44 equally is in the form of a continuously variable 2/2 directional valve the opening cross-section of which is in turn adjustable via a proportional solenoid 48. As will be explained in detail hereinafter, lifting of a load is performed by supplying pressure fluid to the bottom-side cylinder chamber 16 of the lifting cylinder 10. Lowering the load or the fork is solely performed by the weight force thereof, the lowering velocity being controlled by an LS valve 50. Such LS valve substantially consists of a continuously variable LS metering orifice 52 to which an LS pressure regulator 54 is allocated. The latter is arranged, in the shown embodiment, upstream of the LS metering orifice 52 and in the direction of its closing position the force of a spring is applied to it and in the direction of its closing position the force of a spring and the pressure downstream of the LS metering orifice and in the opening direction the pressure upstream of the LS metering orifice 52 is applied to it. In the shown embodiment the LS metering orifice 52 is a 2/2 directional seat valve permitting a leakage-free blocking of the operating line 18 in its shown blocking position. The LS metering orifice 52 can be adjusted manually or by means of a proportional solenoid 56. Further details of the described LS/LUDV valves are explained by way of
The pressure port P of the mobile control block 1 is provided at the output port of an LS pump which may be a constant displacement pump, for instance. The flow rate of said constant displacement pump, which is not shown, is then adjusted via a bypass pressure regulator 58 to which in the opening direction the pump pressure and in the closing direction the maximum load pressure of all loads and the force of a pressure regulator spring is applied. In the regulating position of the bypass pressure regulator 58 the pump pressure is constantly adjusted to a pump A corresponding to the force of the spring above the maximum load pressure which is tapped in an LS line 60. So as to be able to relieve the LS line 60, it is connected to a discharge line 64 connected to the tank port T of the mobile control block 1 via a relief valve 62 in the form of a flow control valve. A very low control oil flow constantly passes through said relief valve 62 to the tank not shown. An LS pressure relief valve 66 is provided in the LS line 60 to ensure the pressure.
Further details of the LUDV section 2 are illustrated by way of the enlarged representation in
The pressure fluid flows from the pressure port P via a feed passage 68 to the inlet port of the lifting metering orifice 44 and the LUDV metering orifice 36. The outlet port of the LUDV metering orifice 36 is connected to the inlet port of the LUDV pressure regulator 38 via a pressure regulator passage 70 so that the LUDV pressure regulator is pressurized in the opening direction by the pressure prevailing downstream of the LUDV metering orifice 36. As mentioned in the foregoing, said opening cross-section is adjusted by the proportional solenoid 40.
A rear control chamber 72 of the LUDV pressure regulator 38 is connected to the LS line 60 so that the pressure in the LS line 60 acts in the closing direction on the rear side of the pressure regulator piston. As there the maximum load pressure of all loads or at least a pressure corresponding thereto is applied, at the inlet of the LUDV pressure regulator 38 equally the maximum load pressure is adjusted in the regulating position. Said maximum load pressure is throttled via the LUDV pressure regulator 38 to the actual load pressure of the allocated load and is guided to the allocated load via the advance line 74 connected to the outlet port of the LUDV pressure regulator 38. In the advance line 76 a check valve 76 opening toward the two cylinders 12, 14 is disposed so that a pressure fluid backflow to the LUDV valve 34 is prevented. The pressure fluid displaced from the cylinders 12, 14 flows through the discharge passage 64 and the tank port T to the tank.
Basically, the lifting LUDV valve 42 has the same structure as the LUDV valve 34. The inlet of the lifting metering orifice 44 is connected to the feed passage 68 and the outlet is connected via a further pressure regulator passage 74 to the inlet of the lifting LUDV pressure regulator 46. The rear control chamber 76 thereof is equally connected to the LS line 60 so that the pressure regulator piston of the lifting LUDV pressure regulator 46 is pressurized in the closing direction by the maximum load pressure and in the opening direction by the pressure prevailing downstream of the lifting metering orifice 44. The latter is adjusted via the proportional solenoid 48. The outlet port of the lifting LUDV pressure regulator 46 is connected to the working port A via an advance passage 82 and a check valve 84 opening toward the working port A. In the area between the working port A and the check valve 84 a return passage 86, in which the LS valve 50 active in the lowering direction is arranged, branches off the advance passage 82.
The inlet of the LS feed metering orifice 52 is connected to the return passage 86. The outlet is connected, via a pressure regulator passage 88, to the inlet of the LS pressure regulator 54. The force of a spring 90 and the pressure at the outlet of the LS feed metering orifice 52 is applied in the closing direction to the pressure regulator piston thereof. This control pressure is tapped via a control passage 92 in the pressure regulator passage 88. In the opening direction the pressure upstream of the LS feed metering orifice 52 is active. This pressure is tapped via a control passage 94, wherein part of the control oil flow path, marked with 94a in
The pressure fluid volume flow being discharged from the lifting cylinder 10 is kept constant by the LS valve 50 independently of the load pressure. As already explained, the LS metering orifice 52 is a seat valve so that a leakage-free support of the lifting cylinder 10 is carried out in the shown closing position. For lowering the load the LS metering orifice 52 is opened, wherein the lowering velocity can be kept constant independently of the load pressure, as in the control position of the LS pressure regulator 54 a constant pressure difference corresponding to the force of the spring 90 is adjusted above the LS feed metering orifice 52.
As already mentioned, the force of a pressure regulator spring 98 and the pressure prevailing in the LS line are applied to the bypass pressure regulator 58 in the closing direction and the pressure prevailing in the feed passage 68 which is tapped via a passage 100 is applied in the opening direction. The relief valve 62 and the LS pressure limiting valve 66 each extend between the LS line 60 and the discharge passage 64.
The circuit shown in
As can be taken especially from
When changing the directional valve 30 to the shift position b, the two working ports A, B of the cylinder 12 are connected to the advance passage 64 and to the advance passage 74 so that, for instance, the boom is tilted via the tilt cylinder 12, the tilting rate being defined by the lowering brake valve 24 provided in the return path.
If the directional valve 32 is changed to the shift position b, the displacement cylinder 14 is displaced to the left in the representation according to
When simultaneously actuating the lifting cylinder 10 and the tilting cylinder 12, the pressure fluid volume flow is kept constant via the LUDV valves 34 and 42 in response to the adjusted opening cross-section of the metering orifices 44 and 36, wherein even in the case of under-saturation the distribution of the pressure fluid volume flow remains constant independently of the load so that even then both loads 16, 12 or 14 can still be controlled in parallel. As described in the beginning, this is not possible in conventional control arrangements for forklifts.
The steering pressure regulator 112 is pressurized in the closing direction by the pressure upstream, i.e. by the pressure prevailing in the area of the port C. This control pressure is tapped via a steering control line 114. In the opening direction an adjustable pressure regulator spring 116 as well as a steering control pressure tapped at a control line 118 act upon the steering pressure regulator 112. The steering line 118 extends from the steering unit 106 to a portion of the steering line 108 located upstream of the steering pressure regulator 112. The load pressure of the steering can be tapped via said control line 118. In the shown embodiment two nozzles 120, 122 jointly forming a pressure divider are disposed in the control line 118. In the area between the two nozzles 120, 122 a control passage 124 which is also connected to a spring-side control chamber of the steering pressure regulator 112 branches off so that the pressure prevailing in the control passage 124 in the opening direction acts upon the piston of the steering pressure regulator 112. In the shown embodiment the control passage 124 is connected to the LS line 60 via a further check valve 126.
The lower nozzle 122 in
It is another peculiarity of the embodiment shown in
In the variant shown in
In the case of under-saturation, i.e. when the pump is not adapted to convey sufficient pressure fluid, the pressure in the feed passage 68 drops and through the LUDV pressure regulators the respective load pressure of the LUDV loads is applied to the outlet of the inflow metering orifice so that accordingly the pressure difference above the LUDV metering orifices drops and less pressure fluid flows to the LUDV loads or the latter are no longer supplied with pressure fluid. The steering unit 106 is supplied with pressure fluid when the steering pressure regulator 112 is fully opened, however, so that the steering can continued to be actuated. Such integration of a steering in an LUDV control arrangement is known per se from DE 101 19 276 A1 so that further explanations can be dispensed with.
On principle, the afore-described control arrangements can also be employed in other mobile machines, such as wheel loaders, mini excavators etc.
The invention discloses a hydraulic control arrangement for a mobile machine, especially for a forklift, comprising at least two hydraulic loads, one of them having a lifting function. In accordance with the invention, the two loads are controlled each via an LUDV valve including inflow metering orifice and LUDV pressure regulator connected downstream.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 014 673.8 | Mar 2007 | DE | national |
| 10 2007 028 864.8 | Jun 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE08/00491 | 3/20/2008 | WO | 00 | 3/23/2010 |
