EP1766246B1 - Method for controlling a lifting gear valve system - Google Patents

Abstract

The invention relates to a method for controlling the valve system for a double-acting lifting gear of a movable working machine or an add-on device comprising a hydraulic cylinder (6) connectable to a pump (38) through a control valve (44) and a pressure regulator (42) in such a way that it is liftable and lowerable. A pressure limiting valve (56) which is adjustable by a maximum bearing pressure is disposed in the pressure medium flow-path between the control valve (44) and the hydraulic cylinder (6). According to the invention, the lifting gear is lowerable in such a way that said maximum bearing pressure is attained and the lifting gear is stopped. When the lifting gear is stopped and a lowering signal is applied to the control valve (44), the motion monitoring is re-started in such a way that the bearing pressure is maintained substentially constant even in the case of an uneven ground or the like. The motion monitoring is over when a setting value returned to the initial value on the control unit.

Description

The invention relates to a method for controlling a Hubwerksventilanordnung according to the preamble of claim 1.

Such a method is known from EP 1 281 872 A known.

In modern medium and high-performance tractors, work-related hydraulics increasingly uses electrically controllable directional control valves for controlling the work functions of coupled devices. These hydraulic functions are controlled by means of a very compact control block, in which the control system with all the essential directional and control valves is combined into one unit. Such a control block is described for example in the catalog 1 987 760 507 (electronic-hydraulic hitch control for tractors) of the applicant.

FIG. 1 to which reference is already made, shows the basic structure of the working hydraulics of a tractor 1 or other mobile implement. The tractor 1 is according to FIG. 1 executed with a Heckhubwerk 2 and a front lifting 4, the lifting cylinder 6, 8 via a control block 10 with pressure medium of a hydraulic pump 12 can be supplied. In the illustrated prior art, the two hoists 2, 4 single-acting (ew) running - but there are also known solutions in which both the front lift 4 and the rear lift 2 double acting (dw) are running. The control block 10 contains each of the consumers 6, 8, etc. associated electro-hydraulically actuated directional control valves 14, which are controlled by an electrical control unit 16. The Setpoint values are set, for example, via a front control unit 18 or a rear control panel 20, which are arranged in the interior of the tractor cabin 22 or via a rear pushbutton 22 or a front pushbutton (not shown) arranged on the rear side of the tractor.

For detecting the occurring forces, pressures and speeds, a plurality of sensors, for example pressure sensors 26, rotational speed sensors 28, position sensors 30, force sensors 32 or speed sensors 34 are provided on the tractor 1, the signals of which can be processed by the control unit 16.

As already mentioned, the Heckhubwerk 2 is executed single-acting in most known solutions, wherein the lifting cylinder 6 by supplying pressure medium over the. Pump 12 is extended and the lowering by the weight of the Heckhubwerks 2 and possibly attached thereto device such as a plow 36 takes place.

For example, for sowing with a seed drill, the Heckhubwerk 2 is brought into a floating position, so that the attachment rests on the ground due to its own weight and overflows any bumps.

However, with the conventional single-acting rear elevators, the contact pressure can not be actively changed, since these hoists can not be operated in the "pressure" work area. For this purpose, double-acting Heckhubwerke are required, the basic structure corresponds to that used in the usual way double-acting front lift. The double-acting Heckhubwerke 2 make it possible to control the lifting cylinder 6 in the "push" direction, so that, for example, an active plowing is possible. This operating condition can also be used, for example, to rear the tractor to change the rear, large wheels so that it stands on the pendulum front axle and on the rear lift-operated attachment or directly on the lower links.

The previously used pressure sensor, for example, in the front lift is arranged on the wear side, there is a relief pressure control - the contact pressure remains unknown or is not used for control.

The position or pressure control of such hoists requires a considerable technical control effort and thus adversely affects the price of the working hydraulics.

The invention has for its object to provide a method for controlling a Hubwerksventilanordnung that allows a simplified control of the lowering movement in the working area "pressing".

This object is achieved by a method for controlling a Hubwerksventilanordnung with the features of claim 1.

The control concept of the invention requires that a Hubwerksventilanordnung is used, in which in the pressure fluid flow path between a continuously variable directional control valve, which is associated with a pressure compensator, and a working port, a continuously adjustable pressure limiting valve is provided via which the pressure at the working port, with a in Direction "lowering" effective pressure chamber of a lifting cylinder is connected to a maximum pressure - hereinafter called contact pressure - is limited.

According to the control concept according to the invention, this contact pressure is set automatically or manually by appropriately setting the pressure relief valve as a function of an operating range (for example normal lowering function, rear-door actuation, quick-action switch operation, tire change, use as a single-acting hoist) or an attached attachment. The driver is then via an operating device, which may also be a button or the like, a target value for adjusting the directional control valve in the direction of lowering, so that the hoist is lowered accordingly. When the preset maximum contact pressure is reached, the hoist stops - this operating state is detected by the control electronics and its monitoring cycle is started as long as there is a system deviation in the direction of lowering and the operating state "Stall" is present. This motion monitoring cycle is only ended when the setpoint is reset on the HMI device.

The desired contact pressure is thus adjusted by suitable adjustment of the continuously adjustable pressure relief valve and kept largely constant by suitable design of the motion monitoring of the hoist. The pressure relief valve thus acts practically as a pressure adjusting device, wherein it allows the electronic movement monitoring to set the contact pressure without the use of pressure sensors. It was found that this type of contact pressure adjustment for agricultural practice can be performed sufficiently accurately and quickly.

In a particularly preferred embodiment, the stopping of the hoist is detected when the Hoist speed falls below a predetermined limit. This hoist speed is usually required in the context of electrohydraulic hoist control anyway and is available as a signal.

Alternatively, from the set lowering signal, the expected hoist speed can first be determined with the help of a map stored in the control. Depending on this hoist speed, a monitoring path interval is then determined from a further characteristic field and a monitoring time interval is determined from the quotient of the monitoring path interval and the hoisting gear speed.

The control system detects that the hoist stops if the actual hoisting gear travel is significantly smaller than the monitoring path interval during the specified monitoring time interval.

This is the case, for example, when the guard path interval is about 1/30 of the total stroke and the actual stroke is less than 10% of this guard path interval, i. 1/300 of the total lift is. The monitoring time interval is usually between 0.05 and 5 seconds, preferably between 0.1 and 3 seconds.

In a particularly preferred control concept, the directional control valve is placed periodically in its neutral position and after a predetermined time interval back to sinks during motion monitoring, so that the contact pressure is adjusted again even with uneven ground and thus remains substantially constant.

In the event that the hoist is raised due to external forces, such as uneven ground during movement monitoring, the directional control valve is immediately placed from the neutral position to sinks, so that the bearing pressure is reset immediately.

The system is basically double-acting, but it can be operated single-acting by setting the pressure relief valve to a minimum value, so that the effective in the direction of lowering pressure chamber of the lift cylinder is practically always connected to the tank - it performs the same function as in a single-acting system.

In the event that the setting of the setpoint takes place via a fast pull-in button, the pressure relief valve remains set to the current bearing pressure, which ensures that the hoist is actuated double-acting. Upon reaching the contact pressure, i. when stopping the hoist, the directional control valve is not - as in the manner described above - adjusted to its neutral position, but remains in the position sinks, so that the hoist can follow any bumps. That There is a fastest lowering movement without consideration of the position setting.

For a longer operation of the quick-release switch is a shutdown for safety reasons - the directional control valve is switched to neutral, so that the pressure medium is not excessively heated.

When a back button is actuated, the maximum contact pressure is reduced to one via the pressure relief valve limited relatively low value. If, for example, the pressure is limited to approximately 50 bar during normal operation and when the quick-release switch is actuated, this pressure is reduced to 5 bar when the back button is actuated for safety reasons.

As explained above, the rear axle of a tractor can also be lifted by means of a double-acting rear lift. In order to prevent tilting of the tractor, according to the invention, the maximum contact pressure can be limited to a value such that an inadvertent lifting of the rear axle (danger of tipping over) is not possible. To change tires or the like, the driver must first, for example, at a terminal in the cab, a number of security queries work off before he can set the contact pressure on the pressure relief valve to a higher level, for example, 250 bar.

In the above-described control concepts, the use of a pressure sensor for determining the contact force is not required. In the case in which the system is designed in an expansion stage with pressure sensors for determining the contact pressure / relief pressure, etc., the setting of the pressure relief valve can be made automatically from the set target contact pressure. In the case in which the system is to be operated single-acting, the contact pressure is set to 0 bar and also set the pressure relief valve accordingly.

The term hoist is generally to be understood to mean a device by way of which a work implement, attachment or the like assigned to a mobile work implement can be moved relative to or against a reference plane.

Other advantageous developments of the invention are the subject of further subclaims.

• Figur 1 ein Grundschema der Arbeitshydraulik eines herkömmlichen Traktors;
• Figur 2 eine Schemadarstellung unterschiedlicher Betriebszustände eines doppeltwirkenden Heckhubwerks, das mit einer erfindungsgemäßen Hubwerksventilanordnung ausgeführt ist;
• Figur 3 einen Hydraulikschaltplan des Heckhubwerks, mit dem die Betriebszustände gemäß Figur 2 einstellbar sind;
• Figur 4 eine Detaildarstellung der Hubwerksventilanordnung aus Figur 3;
• Figur 5 eine Schnittdarstellung einer Hubwerksventilanordnung, die in der Schaltung gemäß Figur 3 verwendet ist und
• Figur 6 ein Diagramm zur Verdeutlichung der Steuerungsstruktur zur Ansteuerung der Hubwerksventilanordnung aus Figur 3.

In the following preferred embodiments of the invention will be explained in more detail with reference to schematic drawings. Show it:

• FIG. 1 a basic scheme of the working hydraulics of a conventional tractor;
• FIG. 2 a schematic representation of different operating conditions of a double-acting Heckhubwerks, which is designed with a Hubwerksventilanordnung invention;
• FIG. 3 a hydraulic circuit diagram of the Heckhubwerks, with the operating conditions according to FIG. 2 are adjustable;
• FIG. 4 a detailed view of the Hubwerksventilanordnung FIG. 3 ;
• FIG. 5 a sectional view of a Hubwerksventilanordnung, in the circuit according to FIG. 3 is used and
• FIG. 6 a diagram illustrating the control structure for controlling the Hubwerksventilanordnung FIG. 3 ,

It is assumed that the in FIG. 1 illustrated tractor 1 instead of a single-acting a double-acting Heckhubwerk 2, wherein the pressure medium supply of the two pressure chambers of the lifting cylinder 6 via a Hubwerksventilanordnung invention, which is composed with the directional control valves for controlling the other consumers of the tractor 1 to a control block 10.

A Heckhubwerk 2 according to FIG. 1 can be - as in FIG. 2 shown - use in different operating states. In the work area "carry" the Heckhubwerk and accordingly possibly actuated attachments 36 is either lifted off the ground or is worn in contact with the ground with a predetermined support force. This work area occurs, for example, when plowing or when cultivating.

In FIG. 2 left is the Hubkraftverlauf shown on the lifting height - this lifting force must be applied by the lifting cylinder 6 of the Heckhubwerks 2. For example, for sowing with a seed drill a load-free intermediate position is taken in the Heckhubwerk 2 is not acted upon by a force, so that the attachment rests on the ground due to its own weight. Such a load-free intermediate position is usually - as described below - adjusted by adjusting the directional control valve 14 in a floating position.

As mentioned above, the Heckhubwerk 2 can be controlled so that a force acting in the direction of the ground pressure force is applied to set the work area "pressing". Such an adjustment is required, for example, during active plowing or in a packer. In the working area "pressing" and the rear axle of the tractor 1 can be raised, so that a tire change is possible.

By means of the hoist valve arrangement 14 described in more detail below, it is possible in the working area "pressing" effective pressure force to different values are limited, this limit is varied depending on the operating conditions described in more detail below.

In FIG. 3 a circuit diagram of a Heckhubwerks 2 is shown, which is controlled via a Hubwerksventilanordnung 14 of the invention. This is accommodated in a disk-type housing and has a pressure port P, a tank port T and two working ports A, B. The pressure port P is connected via a pump line with a variable displacement pump 38, the discharge pressure in response to the highest, the consumers of the Tractors 1 applying load pressure is set. This load pressure is tapped at an LS connection. However, such a LS control is not a prerequisite for the system according to the invention.

The pressure port P is connected via an inlet channel 40 to an input port P 'of an individual pressure compensator 42 whose output port A' is connected to an input port P "of a continuously variable directional valve 44. Its return port R is connected to the tank port T of the hoist valve assembly 14 via a return channel 46 The directional control valve 44 has two working ports A "and B", which are connected via working channels 48, 50 with the two working ports A, B of the Hubwerksventilanordnung 14.

In each working channel 48, 50, a respective sink module 52, 54 is provided which serves in a basic position as a pilot-operated check valve for leak oil-free clamping of the lifting cylinder 6 of the Heckhubwerks 2 and in a control position flowing back from the lifting cylinder 6 Pressure medium volume flow in the sense of a flow control controls.

The working channel 50 can be connected to the tank connection T downstream of the sink module 54 via a pilot-controlled, proportionally adjustable pressure-limiting valve 56. The pressure in the other working channel 48 is limited by a secondary pressure relief valve 58. The lifting cylinder 6 is - as mentioned - executed double-acting, with an effective in the direction of "lowering" annular space 60 with the working port B and in the direction of "lifting" effective pressure chamber 62 is connected to the working port A of the Hubwerksventilanordnung 14. About the lifting cylinder 6 a pivotally mounted on a lifting shaft 64 arm 66 and other coupling elements are actuated, where, for example, an attachment, such as a seed drill or a plow 68 is grown.

Details of the Hubwerksventilanordnung 14 will be described with reference to the enlarged view in FIG FIG. 4 explained.

A pressure compensator piston 69 of the pressure compensator 42 is acted upon by a pressure compensator spring 70 and the tapped in the opening direction and the pressure in a control channel 76 in the closing direction via a channel 72 from a connected to the LS port Lastmeldekanal 74 pressure between the pressure compensator 42 and the directional control valve 44 branches off from the inlet channel 40. The LS channel 74 leads to a control connection LS "of the directional control valve 44. This has two more control terminals X, which output side control terminals XA and XB are assigned.

The actuation of the directional control valve 44 via an in FIG. 5 illustrated pilot valve 78 and a pilot valve assembly, in the illustration according to FIG. 4 is formed by two electro-hydraulic pilot elements 75, 77. The triangle 79 indicates the pressure supply of these pilot control elements 77, 75. By way of the pilot valve 78 or the pilot control elements 77, 75, control oil can each be supplied to a control chamber of the directional control valve 44 until a valve slide 80 assumes a working position. This is detected by a position transducer 128. Once the position transducer 128, the desired position is reported, the pilot element 77, 75 is brought back into its neutral position. The position of the valve spool 80 is maintained in a controlled manner by the precontrol elements 77, 75 being driven in accordance with the signal of the displacement transducer 128. The pilot control elements 77, 75 are connected via control lines 82 and 84 to the pressure supply 79. The valve spool 80 is biased via a Zentrierfederanordnung 86 in its illustrated basic position (0), in which the LS channel 74 is connected to the tank channel 46 and all other aforementioned connections are shut off.

The valve body of the two sink modules 52, 54 are each by a spring 88 and the output at the A "and B" via pressure compensator channels. 90, 92 tapped individual load pressure downstream of the directional control valve 44 is acted upon in its basic position (a), in which the sink modules 52, 54 act as check valves, which allow a pressure fluid flow to the terminals A, B. In the opening direction, the valve bodies of the sink modules 52, 54 are each acted upon by the control pressure applied to the connection XA or XB, which is picked off via an unlocking channel 94, 96. This control pressure may correspond, for example, to the inlet pressure of the pilot valve arrangement 78.

The structure of the Hubwerksventilanordnung with the individual pressure compensator 42, the continuously variable directional control valve 44 and the two downstream sink modules 52, 54 substantially corresponds to the conventional solution of the valve SB23 LS, so that only the essential elements for understanding the invention are described in the following and in the In this regard, reference is made to the existing state of the art for the directional control valve SB23 LS.

For example, if the lifting cylinder 6 are moved to raise the plow 68, so the valve spool 80 of the directional control valve 44 is moved via the pilot valve assembly 78 in one of his (b) marked control positions. Depending on the position while a metering orifice is controlled, which is the individual pressure compensator 42 downstream. Depending on the orifice size, the pressure compensator 42 adjusts itself into a control position in which the pressure drop across the metering orifice is kept constant and thus a pressure-medium-independent pressure medium volume flow is set. This pressure medium volume flow is in the control positions indicated by (b) via the pressure compensator 42, the pressure port P "and the output port A" of the directional control valve 44 to the input port PDW of the sink module 52 and via its output port ADW to the working port A of the Hubwerksventilanordnung 14 and from there into the bottom-side pressure chamber 62 out - the lifting cylinder 6 extends. The displaced from the annular space 60 pressure fluid flows through the working port B of the Hubwerksventilanordnung 14, the working channel 50, the output terminal BDW and the input terminal PDW of the sink module 54 to port B "of the directional control valve 44 and from there via the return port R, the tank channel 46 and Tank connection T back to the tank This return flow is made possible by the fact that the inlet pressure applied to the pilot valve arrangement 78 via the control connection X and tapped off the output terminal XB of the directional control valve 44 and acted on the Entsperrkanal 96 the valve body in the opening direction, so that the sink module 54 unlocked and allows the backflow of the pressure medium to the tank T out. In these (b) marked positions of the sink module 54, this acts as a discharge pressure balance over which the running pressure medium volume flow is regulated to some extent.

For pressing an implement supported by the hoist, the directional control valve 44 is displaced into one of its control positions marked with (a), so that the pressure medium supply via the sink module 54 takes place in its return function to the annular space 60, while the pressure medium flowing out of the bottom pressure chamber 62 via the unlocked drain module 52 and the directional control valve 44 flows toward the tank. The unlocking takes place via the control pressure, which is guided via the control terminals X, XA of the directional control valve 44 and the Entsperrkanal 94 to the effective in the opening direction control surface of the sink module 52.

For load-free application, the directional control valve 44 is moved into its floating position (end position c) in which both sink modules 52, 54 are unlocked and moved into their through position marked with (b) and the working connections A, B and the control connection LS are connected to the tank connection T. and the input terminal P "is shut off.

In the working range "pressing" - as will be explained in detail below - the maximum pressure in the working channel 50 is limited by suitable adjustment of the proportionally adjustable pressure limiting valve 56 to a value of, for example, between 0 to 250 bar.

FIG. 5 shows a section through a valve disc, through which the Hubwerksventilanordnung 14 is realized. The valve disc has a disc-shaped housing 98, in which the pressure compensator 42, the directional control valve 44, the two sink modules 52, 54, the pilot valve 78, the secondary pressure relief valve 58 and the proportionally adjustable pressure relief valve 56 are integrated.

In the FIG. 5 illustrated valve disc 98 further includes a only schematically illustrated and manually operable emergency lowering valve 100 through which the working channels 48 and 50 are connected to the tank T.

At the in FIG. 5 The solution shown, the emergency lowering valve 100 is disposed in a connecting channel 102 between the working channels 48, 50. It has a ball 104, which is biased via an externally accessible grub screw 106 into a closed position in which a connection to the tank channel 46 and thus to the return port R is shut off. By loosening the grub screw 106, the previously clamped ball 104 is released and can therefore be brought by the higher pressure in the working channel 48 or 50 in an open position in which the connection to the tank channel 46 is open - the pressure medium can from the pressurized working channel 48 or 50 be drained.

Via the secondary pressure limiting valve 58, the pressure in the working channel 48 (port A) is limited to a maximum pressure set below the pump pressure. The construction of such secondary pressure relief valves is known, so that further explanations are unnecessary. The construction of the pilot operated proportionally adjustable pressure relief valve 56 is known per se - a piston 108 of the pressure relief valve 56 is a weak Compressive spring 110 and loaded by the pressure in the spring chamber against a valve seat in a closed position. The pressure in the spring chamber is limited by the force applied to a closing cone 114 by means of a proportional magnet 112.

The control of the proportional magnet 112 takes place in the manner described below via the control unit 16.

The lifting and lowering modules 52, 54 also have a conventional construction, wherein a modulatory piston 116 is biased by a closing spring 118 into a closed position. The spring chamber of the closing spring 118 is acted upon by the pressure in the working channel 48 or 50 in the closed position of the module piston 116. In the bottom of the module piston 116, a pilot valve body 120 is arranged, which is also biased by the closing spring 118 in its closed position, thereby closing a pilot port. The pilot valve body 120 has a projection engageable with a poppet 122. This topping piston can be acted upon at the rear by the pressure at the control connection XA (XB), which can be tapped off via the directional control valve 54 and its connection X. That upon application of the poppet piston 122 of the sink module 52 or 54, the pilot valve body 120 is raised against its force from the closing spring 118 from its pilot seat - the modul piston 116 is then pressure compensated and can be lifted off its seat by the poppet 122 against the force of the recoil spring 118 so that pressure fluid from the working port A or B to the tank T can flow out.

The reference numerals 124, 126, 130, 132, 134 pressure sensors are referred to, via which the pressures in the Working channels 48, 50, the pressure at the pressure port P, the load pressure and other pressures can be detected.

The pilot valve 78 according to FIG. 5 is designed as a 4/3-way valve, wherein the output terminals are connected to the control lines 82 and 84, which are guided to the frontal control chambers 136 and 138 of the directional control valve 44. At the in FIG. 5 left end face of the valve spool 80 of the directional control valve 44, a displacement transducer 128 is arranged, via which the valve spool stroke can be detected.

Since - as I said - the basic structure of the Hubwerksventilanordnung 14 according to FIG. 5 - Apart from the pressure relief valve 56, the emergency exhaust 106 and the positioning of the secondary pressure relief valve 58 and the pressure sensors 124, 126, 130, 132, 134 - are already known from the known valve SB23 LS, can be dispensed with the description of further constructive details of the above-described valve components ,

To set the operating range "pressing", the pilot valve 78 is controlled so that in the control chambers 136, 138, a control pressure difference acts through which the valve spool 80 from the in FIG. 5 shifted spring biased position to the left, so that pressure medium from the pressure port P, via the pressure compensator 42, the branching input port P "of the directional control valve 44, the output port B", which opens in its check valve function sink module 54 and the working channel 50 to the working port B and from there to the annular space 60 is promoted. The displaced from the bottom-side pressure chamber 62 pressure fluid is via the working port A, the unlocked in the manner described above sink module 52, the port A "of the directional control valve 44, the tank channel 46 and the return port R returned to tank T. The maximum contact pressure is limited by a suitable adjustment of the pressure relief valve 56 to a predetermined depending on the attachment used or depending on the task to the Heckhubwerk 2 value.

The pressure limiting valve 56 can according to FIG. 4 a switching valve 140 upstream or downstream, which can be moved via a magnet in a throttle position, so that the pressure medium can not flow through the pressure relief valve 56 to the tank. The switching valve 140 is actuated when the bearing pressure is to be set to a value that is above the adjustable pressure relief valve 56 value (for example, when changing tires).

In the following, the control concept of the hoist drive is explained on the basis of different operating states.

As a rule, the rear linkage is operated double-acting. The pressure sensors 124, 126, 130, 132, 134 thereby enable a position / tension control, but the function is ensured even without this pressure detection, as a hedge in the working area "pressing" on the pressure relief valve 56 is possible. When using the in FIG. 5 shown expansion stage with pressure sensors 124, 126, 130, 132, 134, the pad pressure / relief pressure can be controlled via the pressure sensors. The hedge in the working area "pressing" then turn on the pressure relief valve 56, which is then automatically adjustable depending on the support / relief pressure. The basic concept of the control according to the invention is based on the in FIG. 3 illustrated expansion stage without pressure sensors - this basic concept is also in the in FIG. 5 shown Expansion stage applicable, the main difference to the solutions without pressure sensors is that the adjustment of the pressure relief valve 56 in response to the set contact pressure, which is to be controlled via the pressure control means of the pressure sensors. As will be explained below, both expansion stages make it possible to operate the rear lift both double-acting and single-acting.

1. Basic function

It is assumed that the rear lift 2 in the working area "pressing" (see FIG. 2 ) is to be operated, for example, to collect a plow. By setting on the rear operating device 20 or on another operating element, the driver generates an actuating signal via which the directional control valve 44 is moved to one of its lower positions (a) to the right (FIG. FIG. 4 ) is moved. At the same time, the maximum contact pressure in the working channel 50 is limited by suitable adjustment of the pressure limiting valve 56. This maximum pad pressure may vary depending on the attached implement - or as described below - depending on certain operating conditions. It is assumed that the pressure relief valve 56 is set to a pressure of 50 bar. The pressure fluid flow is conveyed via the working port B in the annular space 60 of the lifting cylinder 6 and returned from the bottom pressure chamber 62 via the open-drain module 52 and the directional control valve 44 to the tank T - the Heckhubwerk 2 is lowered and, for example, the plow fed. This lowering takes place according to the control system 16 predetermined regulation, such as a position control. Upon reaching a predetermined maximum contact pressure - ie when the set maximum pressure of, for example, 50 bar in the working channel 50 is exceeded, the pressure relief valve 56 opens and the pressure medium no longer flows via the working port B to the lifting cylinder 6 but to the tank T down - the Heckhubwerk 2 stops, the control unit 20 is still is set to "lower". From the "stopping" of the Heckhubwerks 2, the driver detects the achievement of the desired, preset contact pressure (50 bar) - the directional control valve 44 can also be switched neutral, so that this set, non-regulated pressure is maintained. Since this pressure can vary due to unevenness in the floor, etc. or due to external forces, a motion control is performed in the "Press" working area. This control concept is based on FIG. 6 explained.

The system is located according to FIG. 6 initially at rest, ie the driver has not yet switched to the work area "sinks". After switching to lowering, the path and time intervals for motion monitoring are calculated first. For this purpose, there are a variety of possibilities, with only two methods were selected by way of example. At the in FIG. 6 The solution initially shown on the basis of the output from the control unit 16 to the directional control valve 44 and the pilot valve 78 control signal, the expected normal Hubwerksgeschwindigkeit v determined via a stored in the memory of the controller 16 map. A further characteristic diagram is used to calculate a suitable path interval dw from this hoist speed v. From the quotient dw / v, a monitoring time interval dt is then determined. The aforementioned maps are tuned so that in the main work area "pressing" a possible constant path interval dw of about 1/30 of the total stroke results. As long as determined during the calculated time interval Travel carries at least about 90% of the aforementioned travel interval (1/30 of the total stroke), the controller recognizes that the Heckhubwerk 2 is still lowered. If this moves during the time interval by less than 10% of the calculated travel interval (1/30 of the total stroke), the controller recognizes that the rear lift 2 "stops" - the directional control valve 44 is set to its neutral position (0).

In the case in which continues from the electrohydraulic hoist control, a lowering target signal (target position has not yet reached) and - as described above - the lowering movement is switched off (directional control valve 44) in neutral position (0)) is switched to a motion monitoring mode. For this purpose, a "pressure measurement" is performed during a predetermined time interval, which does not have to be identical to the time interval described above for detecting the "stop" state. To do so, the directional control valve 44 is again moved to one of its "down" positions (a), i.e. a down movement is activated over a fixed ramp to make the "measure pressure". As a result, the Heckhubwerk 2 is lowered and can adapt to the current soil situation. After this lowering movement, the directional control valve 44 is returned to the neutral position (0) - the monitoring is carried out until the lowering signal is withdrawn via the operating device 20.

In the case where a hoist movement upwards due to external forces (for example, driving over a bump, the above-described renewed lowering movement is started immediately after the occurrence of this upward hoist movement, which can be independent of the set time interval (for example, 5 seconds). To Taking back the lowering signal, the system is back in its in FIG. 6 shown on the left.

In the above-described control concept, the time and distance intervals are determined from characteristic fields. In a simplified solution, instead of this relatively complicated method for determining the time / distance intervals from characteristic fields, it is also possible to use the hoist speed, which is detected anyway in the context of the electrohydraulic control (for example via the sensor 30). A "stop" of the Heckhubwerks 2 is then detected when the lowering speed during a predetermined time interval below a minimum speed. That instead of the travel interval, the hoist speed is evaluated directly.

2. Single-acting function of the rear lift

As mentioned, the Heckhubwerk can also be operated single acting. For this purpose, the pressure of the pressure limiting valve 56 is set to a minimum value, for example 5 to 8 bar, so that a minimum pressure is set at the working port B and thus in the annular space 60 of the lifting cylinder 6. If now a lowering signal is output via the electrohydraulic hoist control (EHR) and the above-described movement monitoring is activated, since the actual travel change of the hoisting gear (hoisting angle) is less than 10% of the expected path change per unit time (or the hoist speed is below the limit value), this becomes Directional control valve 44 is not moved to the neutral position (0) as in the double-acting function, but to the floating position (c) - the hoist can adapt to any unevenness in the floor. The set Behavior corresponds to that of conventional single-acting lifting gear valves.

3. Fast entry

To operate the fast access a quick-action switch is actuated, so that the Heckhubwerk is double-acting lowered at maximum speed until the set on the pressure relief valve 56 contact pressure is reached. When this contact pressure is reached, in contrast to the basic function described above, the directional control valve 44 is not switched to its neutral position (0), but remains in its lowering position 8b), so that the rear lifting mechanism 2 can immediately follow a further lowering movement.

In the event that the driver operates the quick-draw switch for a longer time (longer than, say, 10 seconds) and the rear lift 6 stops during this time, the directional control valve 44 is moved to its neutral position (0) to avoid unnecessary pressurization of the fluid.

During operation in the lowering direction, the pump of the working hydraulics may be in the saturation region, i. under certain circumstances, no other consumer can be operated.

4. Tailgate

Upon actuation of the tailgate 24 ( FIG. 1 ), the pressure relief valve - preferably automatically - to a relatively low pressure of example 5 bar set. The stroke of the Heckhubwerks 2 is carried out with a fixed load-compensated speed, depending on the way the speed can be increased after a ramp. In this operating mode, a sensitive coupling / uncoupling of the implements is possible. The empty hoist can be lowered quickly.

5. Lift the tractor

As explained in the introduction, it is desirable, for example, to change the tire, lift the tractor rear axle on the Heckhubwerk 2, so that the tractor 1 is on the oscillating front axle and a possibly not stable attachment, so that there is a significant risk of tipping. To reduce this, the maximum contact pressure is limited to a comparatively low pressure, for example 50 bar - a tire change is then not readily possible.

To change tires, the pressure of the pressure relief valve 56 must be increased, this mode can be adjusted only after a few queries, so there is deliberate operation restriction. Based on these safety queries can be checked, for example, whether the handbrake is tightened, the required pressure on the pressure relief valve (250 bar) is set or the switching valve 140 is moved to its blocking position, if the maximum pressure of the pressure limiting valve 56 is not sufficient (50 bar).

The above-described control concepts in cooperation with the Hubwerksventilanordnung can control the Heckhubwerk 2 in the working area "pressing" with high precision and reliability with very little control engineering and device complexity.

Instead of the above-described adjustable pressure limiting valve 56 and a fixed pressure relief valve can be used, which, however, a loss of comfort is associated.

Disclosed is a Hubwerksventilanordnung for controlling a double-acting hoist or an attachment with a continuously adjustable directional control valve and an individual pressure compensator, via which a pressure medium volume flow to and from a lifting cylinder of the hoist is controlled. In the pressure medium flow path between an output port of the directional control valve and a working port of the Hubwerksventilanordnung a proportionally adjustable pressure relief valve is provided, via which the pressure in this area can be limited to a maximum value. The adjustment of the pressure relief valve is preferably carried out depending on the operating conditions of the hoist or the type of attachment.

LIST OF REFERENCE NUMBERS

1

tractor

2

Rear linkage

4

Front linkage

6

lifting cylinder

8th

lifting cylinder

10

control block

12

pump

14

lifting gear

16

control unit

18

control unit

20

control unit

22

cabin

24

Heck button

26

pressure sensor

28

Speed sensor

30

position sensor

32

force sensor

34

speed sensor

36

attachment

38

variable

40

inlet channel

42

pressure compensator

44

way valve

46

tank channel

48

working channel

50

working channel

52

lowering module

54

lowering module

56

Pressure relief valve

58

Secondary pressure relief valve

60

annulus

62

pressure chamber

64

Hubwelle

66

poor

68

attachment

69

Pressure regulator piston

70

Compensator spring

72

channel

74

LS-channel

75

pilot element

76

control channel

77

pilot element

78

Pilot valve assembly

79

Control oil supply

80

valve slide

82

control line

84

control line

86

Return spring arrangement

88

feather

90

Pressure balance channel

92

Pressure balance channel

94

Entsperrkanal

96

Entsperrkanal

98

valve disc

100

emergency discharge valve

102

connecting channel

104

Bullet

106

grub screw

108

piston

110

compression spring

112

proportional solenoid

114

closing cone

116

module piston

118

closing spring

120

Pilot valve body

122

topping

124

pressure sensor

126

pressure sensor

128

transducer

130

pressure sensor

132

pressure sensor

134

pressure sensor

136

control room

138

control room

140

switching valve

Claims (12)

1. A method for controlling a lifting gear valve arrangement of double-action lifting gear of mobile equipment or an add-on unit having a lifting cylinder (6), which for lifting or lowering is connectable to a pump (P) via a continuously adjustable directional control valve (44) and a pressure balance (42), characterised in that a preferably continuously adjustable pressure-limiting valve (56) is arranged in the pressure medium flow path between the directional control valve (44) and a pressure chamber (60) of the lifting cylinder (6) effective in the direction of lowering, and in that the method comprises the following steps:

   - adjustment of the pressure-limiting valve (56) to a maximum bearing pressure in dependence on an operating range or an add-on unit being used;

   - adjustment of a setpoint value by way of a control unit (18, 20, 24) for displacing the directional control valve (44) in the direction of lowering;

   - lowering of the lifting gear (2) until the maximum bearing pressure is reached and recognition of a "stop" state of the lifting gear (2), in which a control deviation in the direction of "lowering" exists;

   - commencement of motion monitoring of the lifting gear (2), as long as a lowering signal is still present at the directional control valve (44) and the lifting gear is in the "stop" state, and

   - termination of the motion monitoring when the setpoint value is reset at the control unit.
2. A method according to claim 1, in which "stopping" of the lifting gear (2) is recognised when a lifting gear speed falls below a predetermined limit value.
3. A method according to claim 1, comprising the steps:

   - reading out of an expected lifting gear speed in dependence on the preset lowering signal by means of stored performance characteristics;

   - reading out of a suitable monitoring path interval in dependence on the expected lifting gear speed by means of further performance characteristics;

   - calculation of a monitoring time interval from the quotient of the monitoring path interval and the lifting gear speed;

   - recognition of the "stop" state when the actual lifting gear path is substantially smaller than the monitoring path interval during the monitoring time interval.
4. A method according to claim 3, wherein the monitoring path interval is about 1/30 of the total lift and "stop" is recognised when the actual lifting gear path is less than 10% of the monitoring path interval.
5. A method according to one of claims 2 to 4, in which the monitoring time interval is between 0.05 and 5 seconds.
6. A method according to any one of the preceding claims, wherein, during the motion monitoring, the directional control valve (44) is periodically set into the neutral position (0) and after a predetermined time interval is set to lowering (a) again.
7. A method according to claim 6, wherein, during the motion monitoring, on lifting of the lifting gear as a result of external forces the directional control valve (44) is moved out of the neutral position (0) to lowering (a) again.
8. A method according to any one of the preceding claims, wherein the maximum bearing pressure is adjusted to about 0 bar, in order to operate the lifting gear in a single-action manner, the directional control valve (44) being moved into a floating position (c) when the maximum bearing pressure is reached.
9. A method according to any one of the preceding claims, wherein the control unit is a rapid motion switch, on operation of which the maximum bearing pressure is adjusted in such a way that the lifting gear (2) is actuated in a double-action manner, wherein the directional control valve (44) remains in the lowering position during the motion monitoring and after a predetermined switched-off time, during which the rapid motion switch is operated, is switched into the neutral position (0).
10. A method according to any one of the preceding claims, wherein the control unit is a pushbutton (24), on operation of which the maximum bearing pressure is limited to a comparatively low value (for example, 5 bar).
11. A method according to any one of the preceding claims, wherein the maximum bearing pressure is limited to a value that does not permit lifting of a rear axle of the mobile equipment and wherein a higher maximum bearing pressure suitable for lifting is adjustable only after a plurality of confirmation prompts.
12. A method according to any one of the preceding claims, wherein the bearing pressure is detected by way of pressure sensors (124, 126, 130, 132, 134) and regulated as a function of the measuring signals thereof and the adjustment of the maximum bearing pressure is effected as a function of the bearing pressure preset as setpoint value.

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